Ink-jet recording device having an ultrasonic generating element array

An ink-jet recording apparatus records an image onto a recording medium by flying an ink-droplet from an ink surface by a pressure of an ultrasonic beam. The apparatus including an ultrasonic generating element array having a plurality of ultrasonic elements arranged in an array for emitting ultrasonic beams, a driving device for applying a plurality of pulses having different phases from each other, and a converging device for converging the ultrasonic beams by interfering the ultrasonic beams with each other. The generating elements are simultaneously driven and sequentially shifted in an array direction, and the converging device converging the ultrasonic beams in a direction perpendicular to the array direction.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an ink-jet recording device which squirts 
droplets of liquid ink onto a recording medium to record an image, and 
more particularly to an ink-jet recording device which squirts droplets of 
liquid ink onto a recording medium by virtue of the pressure generated by 
ultrasonic beams emitted from piezoelectric elements. 
2. Description of the Related Art 
A so-called ink-jet printer has been put to practical use. This printer is 
a recording device which squirts droplets of liquid ink onto a recording 
medium, thereby to form ink dots thereon and recording an image thereon. 
It makes less noise than other recording devices. Nor does it require 
development or fixation of images recorded on the medium. The ink-jet 
printer is now popular as a device for recording data on ordinary paper. 
Many techniques for squirting ink-jet printer ink have been proposed to 
this date. Notable among them are: 
(a) To apply the pressure of vapor generated by a heating element to squirt 
a droplet of ink; and 
(b) To apply a mechanical pressure pulse generated by a piezoelectric 
element to squirt a droplet of ink. 
An ink-jet printer has a serial scanning head. The head is mounted on a 
carriage. It records data while moving in the direction (hereinafter 
referred to as "main-scanning direction") perpendicular to the direction 
in which recording paper is fed (hereinafter referred to as "sub-scanning 
direction"). Driven mechanically, the serial scanning head cannot move as 
fast as desired to accomplish high-speed recording. It is proposed that 
the serial scanning head be replaced by a line scanning head, because the 
line scanning head can record data faster since it is as long as a 
recording sheet is wide and need not move to record data on the recording 
sheet. However, it is difficult to use a line scanning head, for the 
following reasons. 
In an ink-jet recording system, ink is liable to concentrate locally as the 
solvent evaporates. The concentrated ink clogs up the fine nozzles 
arranged in a density which determines the resolution of an image the 
system can form. If the pressure of vapor is applied to form an ink jet, 
insoluble matter is likely to accumulate in each nozzle as it thermally or 
chemically reacts with the ink. If the pressure generated by an 
piezoelectric element is used to form an ink jet, each ink passage needs 
to be complex in structure and the ink is liable clog the passage. 
Nozzle clogging occurs at low frequency in a serial scanning head which has 
tens of nozzles to a hundred and odd nozzles. In a line scanning head 
having as many nozzles as several thousands, nozzle clogging takes place 
so frequently as to reduce the reliability of the head seriously. 
Furthermore, a conventional ink-jet recording device does not help to 
increase the resolution of images recorded. If vapor pressure is used, the 
device can hardly produce an ink droplet having a size of 20 .mu.m or less 
(which will form on recording paper a dot having a size of about 50 odd 
.mu.m). To use pressure generated by a piezoelectric element, the 
recording head needs to have a complex structure and cannot be made by the 
existing manufacturing technology so as to record high-resolution images. 
Various systems have been proposed which squirt ink droplets from a mass of 
ink, using the pressures of ultrasonic beams generated by an array of 
thin-film piezoelectric elements. Each is known as "nozzleless system" 
which has neither nozzles for forming dots on recording paper nor 
partitions for the ink passages. The nozzleless system can reliably 
prevent ink clogging and remedy nozzle clogging, if any. Moreover, the 
system can record high-resolution images since it form tiny ink droplets 
and squirts them stably. 
The nozzleless system, however, needs to comprise a plurality of 
piezoelectric element arrays arranged in a staggered fashion. Only one 
piezoelectric element array does not suffice to record high-resolution 
images. This is because ultrasonic beams are applied to ink, after 
converged by acoustic lenses larger than pixels (e.g., lenses having a 
size 30 times as large as the size of pixels). The nozzle system with 
piezoelectric element arrays arranged in a staggered fashion is, however, 
disadvantageous in that the ink periodically changes in concentration and 
that adjacent dots shift with respect to one another. 
The piezoelectric element arrays arranged in a staggered fashion may be 
replaced by a linear piezoelectric array which emits ultrasonic beams such 
that the beams interfere with one another in an ink reservoir and converge 
at a point, thereby achieving so-called phased array scanning. 
One of phased array scanning technique is known as "linear scanning," in 
which the ultrasonic beams from a piezoelectric element are converged at a 
point in an ink layer. Linear scanning cannot be performed without many 
drive-signal sources capable of generating element-driving signals which 
have accurately controlled different phases. The linear scanning is 
employed in ultrasonic diagnosis apparatus. When the linear scanning is 
utilized in an ink-jet recording device, there will arise a problem. 
The size of an ink droplet squirted when a pressure built up by ultrasonic 
beams is applied to liquid ink greatly depends on the frequency of the 
ultrasonic beams. For the ink-jet recording device to record images having 
a sufficient resolution, the ultrasonic elements must be driven by signals 
of a high frequency ranging from tens of magahertzes to hundreds of 
magahertzes, high frequency of the drive signals. To achieve phased array 
scanning by use of the such high-frequency signals, a drive circuit needs 
to delay the drive signals with high accuracy in the order of nanosecond 
(10.sup.-9 second), in view of the difference in length among the lines 
for supplying the signals from the drive circuit to the piezoelectric 
elements. 
In the case where a sector electronic scanning is performed by using the 
phased array, i.e., acoustic beams are applied into liquid ink to 
accomplish phased array scanning, an ink droplet may fail to fly 
perpendicular to a recording medium if the ultrasonic beams are converged 
at a point other than the desired point. If ink droplets fly slantwise to 
the medium, ink dots will be formed on the medium at different pitches. 
This has been proven by experiments in which acoustic beams were 
converged, forming a single beam whose axis was inclined at a few degrees 
to the perpendicular to the surface of liquid ink. 
To form ink dots at a regular pitch, the phases of the signals for driving 
piezoelectric elements must be controlled with high accuracy. In other 
words, the signal for driving a piezoelectric element needs to differ in 
phase very minutely from the signal for driving the immediately adjacent 
piezoelectric element. In order to control the phases of the drive signals 
so accurately, it is necessary to use a drive circuit complicated and thus 
expensive and a memory for storing a great amount of phase-correcting 
data. 
The piezoelectric elements used to perform phased array scanning are 
discrete members made by cutting a piezoelectric layer. When the layer 
with a limited length is divided into many discrete piezoelectric elements 
juxtaposed at a small pitch, in order to record images of high resolution, 
the elements will be narrow and will likely to be broken. Consequently, 
the piezoelectric element array cannot be manufactured at high yield. 
Assume that the piezoelectric elements are juxtaposed at a sufficiently 
small pitch to form ink dots in a high density. Then, noise will be 
generated due to the cross talk between the adjacent piezoelectric 
elements. The cross-talk noise greatly hinders the convergence of the 
ultrasonic beams emitted from the elements. 
The cross-talk noise between the elements forming either end portion of the 
piezoelectric element array differs in magnitude from the cross-talk noise 
between the elements forming a middle portion of the array. This is 
because no discrete electrodes are provided for the elements forming 
either end portion, or less discrete electrodes are provided for them than 
for the other elements. The cross-talk noise between the elements forming 
either end portion must be controlled differently from the cross-talk 
noise between the other elements. The method of controlling the cross-talk 
noise is unavoidably complicated. 
When phased array scanning is carried out to converge ultrasonic beams, 
forming a single beam which reach at a point in the surface of liquid ink, 
the axis of the single beam inevitably inclines to the ink surface, not 
extending perpendicular thereto. As a consequence, an ink droplet may fail 
to fly in a path perpendicular to the ink surface. To make matters worse, 
the ultrasonic beams are attenuated as they are reflected by the glass 
walls of the ink reservoir, decreasing the efficiency of squirting ink 
droplets. To prevent the reflection of beams, the piezoelectric element 
array may be processed to have a curved beam- emitting surface. If the 
array is so processed, the yield of the piezoelectric element array will 
lower. 
An ink-jet printer is known which has an acoustic lens for converging the 
ultrasonic beams from the piezoelectric element array, at a point in the 
surface of liquid ink. The lens is a bulk lens with a convex surface 
having a predetermined radius of curvature or a Fresnel lens (designed on 
the Fresnel diffraction theory) for shifting the phase of one beam with 
respect to another. When used in combination with an acoustic lens, the 
piezoelectric element array need not have a curved beam-emitting surface 
and can, therefore, be made easily. However, the ultrasonic beams are 
attenuated as they travel through the acoustic lens, and each beam is 
partly reflected at the interface between the lens and the liquid ink. The 
ultrasonic energy applied to the ink is less than required to squirt an 
ink droplet. The drive signals applied to the piezoelectric elements of 
the array must have an energy high enough to compensate for the inevitable 
energy loss of the ultrasonic beams. 
The piezoelectric element array may be formed into a curved beam-emitting 
surface so that the beams they emit may converge at a point in the surface 
of the ink, rendering it unnecessary to use an acoustic lens. In this 
case, the signals for driving the element need not have a high voltage, 
but the step of processing the array reduces the yield of the array. 
As described above, a piezoelectric element array having a curved 
beam-emitting surface is used, or a piezoelectric element array having a 
flat beam- emitting surface is used together with an acoustic lens, in 
order to achieve phased array scanning, thereby to converge the ultrasonic 
beams in a plane perpendicular to the axis of the array (i.e., the main 
scanning direction). If the a piezoelectric element array having a curved 
beam-emitting surface is used, the yield of the array will decrease. If a 
flat piezoelectric element array is used together with an acoustic lens, 
the signals for driving the piezoelectric elements must have a high 
energy. 
So-called sector electronic scanning is known which is one type of phased 
array scanning. In the sector electronic scanning, the piezoelectric 
elements juxtaposed and spaced in the main-scanning direction are driven 
by signals delayed with respect to one another. The elements emit 
ultrasonic beams which differ in phase. The beams are converged at a point 
is near the surface of liquid ink, whereby an ink droplet fly from that 
point. 
The sector electronic scanning is advantageous in that the point from which 
an ink droplet flies can be changed, regardless of the pitch at which the 
piezoelectric elements are juxtaposed. However, accurate delay times must 
be imparted to the drive signals so that the elements may emit ultrasonic 
beams which converge at a desired point. Accurate delay times can be 
imparted to the signals by nothing but a drive circuit which is 
complicated and which is hence very expensive. Without such a drive 
circuit, the sector electronic scanning cannot be accomplished. 
Furthermore, when the ultrasonic beams converge at a point other than the 
point located right above the midpoint of the array, forming a single 
ultrasonic beam, the axis of the single beam inclines to the ink surface. 
An ink droplet will fly a path inclined to the recording medium, forming 
an ink dot at a position off the desired position on the recording medium. 
(1) In the ink-jet recording technique, wherein piezoelectric element 
arrays arranged in staggered fashion are used to apply ultrasonic beams to 
ink to squirt an ink droplet, the ink periodically changes in 
concentration and that adjacent dots shift with respect to one another. 
Further, since the high-frequency signals for driving the piezoelectric 
elements must be phase-controlled accurately, phased array scanning cannot 
be effected without a drive circuit which is complicated and expensive. 
(2) In order to form ink dots at a desired pitch on a recording medium, the 
signal for driving a piezoelectric element needs to differ in phase very 
minutely from the signal for driving the immediately adjacent 
piezoelectric element. To control the phases of the drive signals so 
accurately, it is necessary to use a drive circuit complicated and thus 
expensive and a memory for storing a great amount of phase-correcting 
data. 
(3) With the ink-jet recording device which performs phased array scanning 
to apply ultrasonic beams at a point in liquid ink, squirting an ink 
droplet onto a recording medium, the piezoelectric elements can hardly 
arranged at a small pitch to record high-resolution images if each element 
comprises a discrete piezoelectric layer. If the elements are arranged at 
such a small pitch by all means, the yield of the device will lower. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide the following improved 
ink-jet recording devices: 
(1) An ink-jet recording device which comprises a linear array of 
ultrasonic generating elements and which can record images having a 
desired resolution. 
(2) An ink-jet recording device which comprises an array of ultrasonic 
generating elements, which can squirt ink droplets in parallel paths 
spaced apart at regular intervals in the direction in which the beam 
generating elements are juxtaposed. 
(3) An ink-jet recording device which operates in acoustic-wave mode and 
can squirt ink droplets in parallel paths spaced apart at regular 
intervals, by compensating periodical changes in ink concentration and 
preventing adjacent ink dots from shifting with respect to one another. 
(4) An ink-jet recording device which comprises an array of ultrasonic 
generating elements for emitting ultrasonic beams to liquid ink, thereby 
to squirt an ink droplet onto a recording medium, and which can easily 
record images having a high resolution. 
(5) An ink-jet recording device which comprises an array of ultrasonic 
generating elements for emitting ultrasonic beams to liquid ink, thereby 
to squirt an ink droplet onto a recording medium, and in which the 
cross-talk noise between the beam generating elements is small. 
(6) An ink-jet recording device which comprises an array of ultrasonic 
generating elements for emitting ultrasonic beams to liquid ink, thereby 
to squirt an ink droplet onto a recording medium, and in which the 
ultrasonic beams are efficiently converged at a point in the ink surface, 
thereby to squirt an ink droplet with high efficiency. 
(7) An ink-jet recording device which comprises an array of ultrasonic 
generating elements for emitting ultrasonic beams to liquid ink, thereby 
to squirt an ink droplet onto a recording medium, the elements having a 
flat beam-emitting surface and serving to converge the ultrasonic beams 
with high efficiency. 
(8) An ink-jet recording device which comprises an array of ultrasonic 
generating elements for emitting ultrasonic beams to liquid ink, thereby 
to squirt an ink droplet onto a recording medium, and in which the 
ultrasonic beams are efficiently converged at a point in the ink surface 
and a path in which the ink droplet flies can be controlled accurately. 
(9) An ink-jet recording device which comprises an array of ultrasonic 
generating elements for emitting ultrasonic beams to liquid ink, thereby 
to squirt an ink droplet onto a recording medium, and in which the array 
has a curved beam-emitting surface and discrete electrodes are provided on 
the curved beam-emitting surface, whereby the array functions like an 
acoustic lens to converge the ultrasonic beams with high efficiency. 
(10) An ink-jet recording device which comprises an array of ultrasonic 
generating elements for emitting ultrasonic beams to liquid ink, which can 
form ink droplets on a recording medium at a pitch less than the pitch at 
which the beam generating elements are juxtaposed, and which has a simple 
circuit for driving the beam generating elements. 
(11) An ink-jet recording device which comprises an array of ultrasonic 
generating elements for emitting ultrasonic beams to liquid ink, and in 
which the beam generating elements have a discrete electrode each, and the 
electric coupling and acoustic coupling between any two adjacent discrete 
electrodes are equal to those between any other two adjacent discrete 
electrodes, thus reducing the cross-talk noise between the between the 
beam generating elements and ultimately converging the ultrasonic beams 
with high efficiency. 
(12) An ink-jet recording device in which ultrasonic beams can be 
efficiently converged at a point near the surface of ink, first in a plane 
extending in the main-scanning direction and further in a plane extending 
perpendicular to the main-scanning direction, and which can easily record 
images having a high resolution. 
An ink-jet recording device according to a first aspect of the present 
invention comprises ultrasonic generating element array which has at least 
one ultrasonic element arranged in array for emitting ultrasonic beams; 
driving means for applying a plurality of pulses having different phases 
each other to converging ultrasonic beams by interfering the plurality of 
ultrasonic beams with each other emitted from the ultrasonic generating 
elements of a part of the ultrasonic generating element array, which are 
simultaneously driven, with sequentially shifting the ultrasonic 
generating elements simultaneously driven to an array direction; and 
converging means for converging each of the plurality of ultrasonic beams 
in a direction of perpendicular to the array direction. In this ink-jet 
recording device, the driving means includes a shift register for 
transferring an input image data, a latch for temporarily storing an image 
data parallel output from the shift register, and data selector/driver for 
selecting one of a plurality of pulse series, which have different phases, 
input from a plurality of common signal line corresponding to the image 
data temporarily stored in the latch and for driving the ultrasonic 
generating element according to the corresponding pulse series. The 
driving means has a first driving mode for simultaneously driving the 
ultrasonic generating elements to converge ultrasonic beams emitted from 
the ultrasonic generating element at a first point of a surface of the ink 
along center axis of the ultrasonic generating elements perpendicular to a 
ultrasonic generating surface of the ultrasonic generating elements, and a 
second driving mode for simultaneously driving the ultrasonic generating 
elements to converge ultrasonic beams emitted from regions divided into at 
least right region and left region of the ultrasonic generating element s 
at a second point different from the first point of center axis. 
An modification of the ink-jet recording device further comprising 
ultrasonic generating element array which has a plurality of ultrasonic 
elements arranged in array for emitting ultrasonic beams; driving means 
for applying a plurality of pulses having different phases each other to 
converging ultrasonic beams by interfering the plurality of ultrasonic 
beams with each other emitted from the at least one ultrasonic generating 
element; and converging means for converging the plurality of ultrasonic 
beams in a direction of perpendicular to an array direction, wherein the 
converging means includes Fresnel zone plate having a plurality of 
parallel sprite patterns extending in a same direction to the first 
direction and for converging the ultrasonic beams emitted from the 
ultrasonic generating elements into the ink. 
The drive circuit for driving the ultrasonic generating elements, thereby 
to perform linear electronic scanning is simple in structure. A compact 
ink-jet head can be manufactured by mounting the drive circuit on a head 
substrate. If provided with such a compact ink-jet heat, the ink-jet 
recording device can be modified into a line-scanning ink-jet recording 
device which can operate at high speed and which can record 
high-resolution images. 
The modification of the ink-jet recording device according to the first 
aspect of the invention has a linear Fresnel zone plate (also known as 
"Fresnel diffraction grating" or "Fresnel lens"), used in place of a 
cylindrical lens. The linear Fresnel zone plate is used as an acoustic 
lens which has no large depressions or projections and no curved surfaces 
and therefore involves but a small aberration. It has been made by 
in-surface process in which photolithography can be reliably performed in 
the sub-scanning direction (i.e., the direction at right angles to the 
main-scanning direction). 
The linear Fresnel zone plate consists of two types of strips which are 
alternately arranged side by side, symmetrically with respect to the 
midpoint of the plate. Each strip of the first type allows passage of 
waves, whereas each strip of the second type prohibits passage of waves or 
shift the waves by half the wavelength. Thus, the focal length of the 
linear Fresnel zone plate does not change as that of a bulky cylindrical 
lens, even if ultrasonic beams are applied slantwise with respect to the 
axes of the strips. 
Unlike a bulky cylindrical lens which has depressions and projections, each 
having a curved surface, the linear Fresnel zone plate can be flat. It can 
be manufactured by reliable process such as photolithography. It can 
converge ultrasonic beams with high accuracy. 
In the ink-jet recording device according to the first aspect of the 
invention, 
More specifically, an annular (or, disc-shaped) array may be used which 
consists of annular ultrasonic generating elements. The elements are 
concentric and divided into two groups. To impart a phase difference of 
180.degree. (i.e., .pi.) to the ultrasonic beam emitted from any annular 
element of the first group and the ultrasonic beam emitted from the 
adjacent annular element of the second group, it suffices to polarize the 
elements of the first group in one direction and those of the second group 
in the opposite direction, to provide one electrode on the entire annular 
array and to apply a drive voltage to this electrode. 
Instead, a linear array may be used which consists of strip-shaped 
ultrasonic generating elements. The elements are juxtaposed and divided 
into two groups. To impart a phase difference of 180.degree. to the 
ultrasonic beam emitted from any strip-shaped element of the first group 
and the ultrasonic beam emitted from the adjacent strip-shaped element of 
the second group, it suffices to polarize the elements of the first group 
in one direction and those of the second group in the opposite direction. 
According to the present invention it is possible to converge ultrasonic 
beams by imparting a phase difference of 180.degree. to the ultrasonic 
beam emitted from any strip-shaped element of the first group and the 
ultrasonic beam emitted from the adjacent strip-shaped element of the 
second group. In other words, the ultrasonic beams can efficiently be 
converged at a point in the ink surface, without using an acoustic lens or 
an ultrasonic generating element array which can perform the function of a 
lens. 
(1) The drive means supplies a first drive signal to the ultrasonic 
generating elements of the first group, and a second drive signal which is 
opposite in phase to the first drive signal, to the ultrasonic generating 
elements of the first group. 
When the array is driven in the first drive mode, the phases of the 
ultrasonic beams emitted from the first-group elements coincide with the 
phases of the ultrasonic beams emitted from the second-group elements 
coincide at the surface of the ink. As the elements of both groups are 
repeatedly driven, each time n elements, where n is less than the number 
of all elements, ink dots can be formed on a recording medium at the same 
pitch as the ultrasonic generating elements are juxtaposed, forming the 
array. 
When the array is driven in the second drive mode, the phases of the 
ultrasonic beams emitted from the first half of the simultaneously driven 
signals coincide at a point on a vertical line passing the midpoint of the 
group of the simultaneously driven elements, while the phases of the 
ultrasonic beams emitted from the second half of the simultaneously driven 
elements coincide at a different on the vertical line. An ink droplet can 
fly from a point off the vertical line. The distance between this point 
and the vertical line depends on the ratio of the distance between the two 
points on the vertical line to the thickness of the ink layer. Thus, the 
position at which an ink droplet may fly can be changed, regardless of the 
pitch at which the ultrasonic generating elements are juxtaposed. This 
makes it possible to record a high-resolution image. 
The drive means can be of simple structure since it needs only to supplies 
different signals, which are opposite in phase, to the array of ultrasonic 
generating elements. 
(2) Fresnel zone plate, which has a plurality of parallel sprite patterns 
extending in a same direction to the array direction of the ultrasonic 
generating elements and for converging the ultrasonic beams emitted from 
the ultrasonic generating elements into the ink, is provided. 
The ink-jet recording device according to the first aspect of the invention 
comprises may comprise a Fresnel zone plate and an ultrasonic-wave 
interference layer, as well as an array of ultrasonic generating elements. 
The elements are driven, emitting ultrasonic beams. The interference layer 
converges the ultrasonic beams in a first plane extending along the axis 
of the array. The Fresnel zone plate converges the beams in a second plane 
intersecting with the first plane at right angles. 
In the ink-jet recording devices according to the first aspect of the 
invention piezoelectric layer has at least one gap to cross the array 
direction of the ultrasonic generating element array. 
The piezoelectric layer may be completely divided by the gaps or may have 
notches extending thicknesswise or widthwise. The number K of gaps 
provided is preferably, N/2.gtoreq.K.gtoreq.N/n, where N is the number of 
all piezoelectric-beam generating elements and n is the number of the 
elements driven simultaneously. 
As mentioned above, the piezoelectric layer of the array is divided by a 
gaps or has notches, which are arranged in the lengthwise direction of the 
array. The gaps or notches shield the cross talk between the adjacent 
ultrasonic generating elements. Cross-talk noise is therefore reduced 
effectively. 
An ink-jet recording device according to a second aspect of the present 
invention comprises at least one ultrasonic generating element for 
emitting at least one ultrasonic beam; and matching means mounted on the 
ultrasonic generating element and including matching layer for 
acoustically matching between the ultrasonic generating element and the 
ink. The matching means further includes means for converging the 
ultrasonic beams in a direction perpendicular to an ultrasonic generating 
surface of the ultrasonic generating elements. Backing material arranged 
between the ultrasonic generating element and the electrode are further 
provided. 
This device is characterized by the converging/matching means having an 
acoustic matching member. The acoustic matching member has grooves formed 
based on the Fresnel ring theory for converging ultrasonic beams in a 
plane extending in the sub-scanning direction which intersects at right 
angles to the main-scanning direction. The converging/matching member has 
a thickness t, which is given as: 
EQU t=.lambda.m.times.(2n+1)/4 (1) 
where n is an integer greater than 0 and .lambda.m is the wavelength of the 
ultrasonic beams traveling in the member. The speed of the beams in the 
member is preferably an integral multiple of the speed of the beams in the 
liquid ink. 
Assume the converging/matching member has the following thickness t: 
EQU t=.lambda.m.times.n/2 (2) 
In this case, the ultrasonic beams are totally reflected at the interface 
between the lens and the ink. Consequently, virtually no beams are applied 
into the ink. 
The grooves made in the surface of the converging/matching member have a 
thickness d, which is given as: 
EQU d=1/{2.times.(1/.lambda.i-1/.lambda.m)}(3) 
where .lambda.i is the wavelength of the ultrasonic beams propagating in 
the liquid ink. If .lambda.m is substantially an integral multiple of 
.lambda.i, each thick portion and each thin portion of the member satisfy 
the equation (1), whereby acoustic matching is provided. As a result, the 
ultrasonic beams are effectively emitted into the ink from the thick and 
thin portions of the member, and an ink droplet flies onto a recording 
medium. 
To converge the ultrasonic beams, one of the methods described above may be 
combined with one of the methods described later. Among these methods are 
a method utilizing the delay of such as quadratic function, a method using 
a Fresnel zone plate and a method of driving elements in groups. 
The acoustic matching layer is provided directly on the array of ultrasonic 
generating elements. The grooves designed based on the Fresnel ring theory 
and arranged parallel to the main-scanning direction converge the 
ultrasonic beams in a plane extending in the sub-scanning direction. The 
beams are thereby emitted into the ink, without being reflected by the 
thick portions or thin portions of the converging/matching member. Thus, 
the beams are converged at the surface of the ink, whereby an ink droplet 
is effectively squirted from the ink surface. 
The ink-jet recording device according to the second aspect of the 
invention is characterized by the backing material which is provided on 
that surface of the ultrasonic generating elements array which faces away 
from the ink reservoir means. The backing material suppresses residual 
vibration of each ultrasonic generating element and helps to achieve 
efficient application of ultrasonic beams into the ink. An ink droplet can 
therefore be squirted in a correct path onto a recording medium. 
Preferably, the backing material is made of material whose acoustic 
impedance is 3.times.10.sup.6 kg/m.sup.2 s or more. It is desirable that 
the member have an attenuation coefficient a which satisfies the relation 
of a .times.2t.times.f&lt;-20 dB, where t is the thickness of the member and 
f is the frequency of the ultrasonic beams. 
The backing material can be dispensed with since the wiring board on which 
the ink-jet head and the drive circuit can suppress residual vibration of 
each ultrasonic generating element and helps to achieve efficient 
application of ultrasonic beams into the ink. Without the backing 
material, the ink-jet recording device will be more simple in structure. 
An ink-jet recording device according to a third aspect of the present 
invention comprises ultrasonic generating element array which has a 
plurality of ultrasonic elements arranged in array for emitting ultrasonic 
beams; driving means for selecting a predetermined number of continuous 
ultrasonic generating element group to be simultaneously driven from the 
ultrasonic generating element array, when a first ultrasonic generating 
element group has partial ultrasonic generating elements arranged at a 
center of array direction of the ultrasonic generating element group and a 
second ultrasonic generating element group has at least partial ultrasonic 
generating elements arranged at both side of the array direction of the 
first ultrasonic generating element group, for supplying two-phase driving 
signal of opposite phases to the first and second ultrasonic generating 
element groups with shifting a position of the ultrasonic generating 
element groups and repeating the driving signal supply operation. Another 
ink-jet recording apparatus according to the third aspect of the invention 
comprises ink holding means for holding a liquid ink to keep a 
predetermined surface; ultrasonic generating element array arranged in a 
predetermined pitch and for converging ultrasonic beams onto the liquid 
ink by a predetermined driving signal and for emitting ultrasonic beams 
moving along the liquid surface; and driving means for selecting a 
predetermined number of continuous ultrasonic generating element group to 
be simultaneously driven from the ultrasonic generating element array, for 
determining to assign each ultrasonic generating element of the ultrasonic 
generating element group one of a first region obtained by Fresnel 
diffraction equation in which ultrasonic should pass and a second region 
in which phase of the ultrasonic should shift in half wave length, and 
when a first group is assigned by the first region and a second group is 
assigned by the second region, for supplying two-phase driving signal of 
opposite phases to the first and second groups with shifting a position of 
the ultrasonic generating element groups and repeating the driving signal 
supply operation. Control means for controlling whether or not the driving 
means output the two-phase driving signal on the basis of an image signal 
to be recorded and/or means for controlling time period of output the 
two-phase driving signal by the driving means on the basis of an image 
signal of a pixel corresponding to the ultrasonic generating element group 
are further provided. The control means arranged corresponding to each 
ultrasonic generating element of the ultrasonic generating element array, 
and for inputting the two-phase driving signal and non-driving signal and 
controlling to provide corresponding ultrasonic element by selecting one 
of driving signal and non-driving signal of one of phases of the two-phase 
driving signal on the basis of select information of the ultrasonic 
generating element group according to the image signal to be recorded and 
a select information of two-phase driving signal. The driving means 
includes means for alternatively set a number of ultrasonic element in the 
ultrasonic generating element group to even-number or odd-number in array 
direction of a ultrasonic generating element of the ultrasonic generating 
element array. A total number of ultrasonic generating elements of the 
ultrasonic generating element array is a number which a number of 
ultrasonic generating elements in the ultrasonic generating element group 
is added to at least a number of pixels of a single line to be recorded. 
This third ink-jet recording device has an array of ultrasonic generating 
elements arranged in a row and spaced at equal intervals. Linear 
electronic scanning is accomplished by repeatedly driving the elements in 
groups, with drive signals of two types which differ in phase. The groups 
are defined by rounding the widths of individual elements and the pitch at 
which the elements are juxtaposed, based on the principle of a Fresnel 
zone plate. Due to the linear electronic scanning, the ultrasonic beams 
converge at a desired point in the surface of the ink, and the axis of the 
beam formed of the converged beams extends in a desired direction with 
respect to the ink surface. Ink droplets of the same size are therefore 
are squirted in parallel paths onto the recording medium. As a result, ink 
dots of the same size are formed on the medium, which are spaced at equal 
intervals along the axis of the ultrasonic generating element array. 
As described above, only two types of drive signals are used to achieve 
linear electronic scanning. The driving circuit, therefore, need not be so 
complicated as one required in the conventional ink-jet recording device 
wherein the signals for driving the ultrasonic generating elements must be 
accurately phase-controlled in order to effect phased array scanning. In 
accordance with the input image signals, the drive circuit supplies the 
first or second type of a drive signal to each ultrasonic generating 
element. 
An odd number of adjacent elements and an even number of adjacent elements 
may be alternately driven, the elements of each group driven 
simultaneously. In this case, there will be formed on the recording medium 
ink dots which are arranged at twice the pitch at which ink dots are 
arranged if the elements are repeatedly driven, each time an odd or even 
number of elements. 
The number of all ultrasonic generating elements constituting the array is 
the sum of the number of elements which are arranged over a distance equal 
to the maximum recording width and the number of elements which should be 
simultaneously driven to squirt an ink droplet. 
All ultrasonic generating elements of the array may be divided into a 
plurality of groups, and the groups may be driven at the same time to 
increase the recording speed. In this case, two sets of pixel signals are 
supplied to two control means controlling the two groups (first and second 
groups) of elements to be simultaneously driven, respectively, so that 
some of the ultrasonic beams emitted from the first group of elements 
overlap the some of the ultrasonic beams emitted from the second group of 
elements. 
The ink-jet recording device can record a 2-dimensional image on a 
recording medium by carrying out main scanning (i.e., linear electronic 
scanning) and sub-scanning. The sub-scanning is achieved by moving the 
recording medium in the direction at right angles to the main-scanning 
direction. The main scanning may be performed by driving groups of 
ultrasonic generating elements, one by one, while the sub-scanning is 
continuously carried out. In this case, data items representing as many 
lines as the element groups are stored in a memory, and are read and 
supplied to the control means, one by one, thereby recording one line 
extending in the main-scanning direction. 
As described above, the ink-jet recording device can perform linear 
electronic scanning. More precisely, drive signals of two type, i.e., 
0.degree.-phase signals and 180.degree.-phase signals, drive the 
ultrasonic generating elements, whereby ultrasonic beams are converged 
electronically. As phased array scanning is repeated, ink droplets 
sequentially fly onto the recording medium, forming a line of ink dots on 
the medium. Two or more arrays of elements need not be arranged in 
staggered fashion in order to record an image of high resolution. Without 
staggered arrays, the ink-jet recording device generates no image noise 
and hardly involves ink-clogging. Furthermore, since ink droplets fly in 
parallel paths when phased array scanning is carried out, they will form 
ink dots spaced apart at regular intervals. Having no lenses having a 
curved surface, the ink-jet recording device can be manufactured by a 
reliable and high-precision in-surface process such as photolithography, 
and can perform phased array scanning or linear array scanning accompanied 
by no aberration-related problems--unlike an ink-jet recording device 
which has a bulky acoustic lens with a curved surface. 
An ink-jet recording device according to a fourth aspect of the present 
invention comprises ultrasonic generating element array which has a 
plurality of ultrasonic elements arranged in array for emitting a 
plurality of ultrasonic beams; driving means for selecting a predetermined 
number of continuous ultrasonic generating element groups to be 
simultaneously driven from the ultrasonic generating element array, for 
supplying driving signal to each of the ultrasonic generating element 
groups with shifting a position of the ultrasonic generating element 
groups and repeating the driving signal supply operation; and a plurality 
of control means arranged corresponding to each of the ultrasonic 
generating element groups for controlling whether or not the driving means 
output the driving signal to the ultrasonic generating element groups on 
the basis of an corresponding image signals of pixels of the ultrasonic 
generating element groups, wherein the control means inputs an image 
signals corresponding to a plurality of ultrasonic generating elements 
overlapping two ultrasonic generating element groups, when the ultrasonic 
generating element group overlaps two ultrasonic generating element groups 
of the ultrasonic generating element array. Memory means for storing at 
least the image signal of the same number of line as a number of the 
ultrasonic generating element group and transfer means for transferring 
and shifting by single line image signals corresponding to each of the 
ultrasonic generating element group of the same line stored in the memory 
means are further provided. 
With the device according to the fourth aspect of the invention it is 
possible to perform linear electronic scanning by supplying drive signals 
of two types, which differ in phase, to the array of ultrasonic generating 
elements. In other words, signals for driving the ultrasonic generating 
elements need not be phase-controlled accurately. The drive circuit can be 
far simpler in structure. Moreover, the delay of the drive signals, 
occurring in the drive circuit or in wires connecting the circuit to the 
ultrasonic generating elements, does not affect the quality of images the 
device will record. It is unnecessary to take particular measures to 
eliminate such delay of drive signals. The device according to the fourth 
aspect can be provided as a line-scanning ink-jet recording device which 
operates at high speed, records high-resolution images and is yet 
inexpensive. 
An ink-jet recording device according to a fifth aspect of the present 
invention comprises ultrasonic generating element array having at least 
one ultrasonic generating element for generating ultrasonic from the 
plurality of ultrasonic generating elements and comprised of a plurality 
of ultrasonic generating means for emitting a plurality of ultrasonic 
beams; and driving means having a first driving mode for simultaneously 
driving an ultrasonic generating means comprised of even-numbered the 
ultrasonic generating means to converge an ultrasonic beams emitted from 
the ultrasonic generating means to a center of the ultrasonic generating 
means, and second driving mode for simultaneously driving an ultrasonic 
generating means comprised of odd-numbered the ultrasonic generating means 
to converge an ultrasonic beams emitted from the ultrasonic generating 
means to a center of the ultrasonic generating means. 
The device according to the fifth aspect can operate in two modes. In the 
first mode, an even number of ultrasonic generating elements, included in 
the array, are simultaneously driven. In the second mode, an odd number of 
ultrasonic generating elements, included in the array, are simultaneously 
driven. In either mode, the ultrasonic beams emitted from the elements 
simultaneously driven emit converge at a point located right above the 
midpoint of the group formed of the elements. Thus, the point at which the 
beams converge in the first mode is spaced from the point at which the 
beams converge in the second mode, by half the pitch at which the 
ultrasonic generating elements are juxtaposed. 
Hence, when the ultrasonic generating elements are driven, alternately in 
the first mode and the second mode, ink droplet fly from the ink surface 
in parallel paths which are spaced at half the pitch at which the elements 
are juxtaposed. The ink-jet recording device according to the fifth aspect 
can record images in a resolution twice as high as the conventional device 
wherein the ultrasonic generating elements are repeatedly, each time a 
predetermined number of elements. 
The pattern of setting the phases of the signals for driving an even number 
of elements simultaneously can be made identical to the pattern of setting 
the phases of the signals for driving an odd number of elements 
simultaneously. If the phase-setting patterns are the same, it is easy for 
the drive circuit to delay the drive signals with respect to one another. 
Furthermore, ultrasonic generating elements of any group may be 
simultaneously driven by signals in alternately opposite phases, thereby 
to emit ultrasonic beams whose phases comply with the Fresnel diffraction 
theory. In this case, the drive circuit can be more simple than otherwise. 
An ink-jet recording device according to a sixth aspect of the present 
invention comprises ultrasonic generating element array arranged in a 
predetermined pitch and for converging ultrasonic beams onto the liquid 
ink by a predetermined driving signal and for emitting ultrasonic beams 
moving along the liquid surface; driving means for simultaneously driving 
adjacent plurality of ultrasonic generating elements in the ultrasonic 
generating elements with a predetermined delay time and shifting a 
position of the ultrasonic generating element groups; and acoustic lens or 
Fresnel zone plate for converging ultrasonic beams emitted from the 
ultrasonic generating means to a surface of the liquid ink in a direction 
perpendicular to the array direction. 
The acoustic lens incorporated in the device according to the seventh 
embodiment is made of material in which sound speed is faster than in ink, 
such as glass or resin. The lens has a concave surface so as to converge 
the beams emitted from the ultrasonic generating elements at a point in 
the surface of the ink. Alternatively, the lens may have a Fresnel 
diffraction pattern consisting of strips arranged along the axis of the 
array of ultrasonic generating elements. The lens is designed such that 
its thickest portion has a thickness t which is given as: 
EQU t&lt;D.sup.2 /.lambda. 
where D is the aperture of the lens and .lambda. is the wavelength of the 
ultrasonic beams passing through the lens. 
The ultrasonic beams are converged in a first plane extending along the 
beam generating element array by imparting appropriate delay times to the 
signals for driving the adjacent elements at the same time. The beams are 
further converged in a second plane intersecting with the first plane by 
means of the acoustic lens. The inventors hereof have found that an ink 
droplet flies most efficiently when the single beam formed of the beams 
thus converged has substantially the same width in both the first plane 
and the second plane. To attain this desirable condition in the device 
according to the sixth aspect, the aperture of the acoustic lens is less 
than the length of the group of the ultrasonic generating elements which 
are driven simultaneously. 
More precisely, the delay times for the signals to drive the adjacent 
elements simultaneously are set in accordance with the ratio of the sound 
speed in the lens to the sound speed in the ink and also with the 
refraction angle (Snell laws) of the beams traveling from the lens into 
the ink, so that the simultaneously driven elements emit ultrasonic beams 
which converge in the first plane at a point in the ink surface. Further, 
the thickest portion of the acoustic lens has a thickness t which is less 
than D.sup.2 /.lambda. so that the ultrasonic beams travel straight 
through the lens. The beams emanating from the acoustic lens are refracted 
at the interface between the lens and the ink at an angle determined by 
the sound speed in the lens and the sound speed in the ink. Finally, the 
ultrasonic beams converge at a point near the surface of the ink. 
The width the beam formed on the converged beams has at the convergence 
point depends on the aperture and focal length of the acoustic lens if the 
frequency of the beams remains unchanged and the properties of the 
beam-transmitting media remain constant. As described above, the 
ultrasonic beams travel straight through the acoustic lens. Hence, the 
width the beams formed of these beams has in the second plane at the ink 
surface is determined by the thickness of the ink layer and the aperture 
of the lens. On the other hand, the width the beam has in the first plane 
at the ink surface is determined by the sum of the thickness of the lens 
and the that of the ink layer and also by the length of the group formed 
of the simultaneously driven elements. It is therefore possible to reduce 
the width the beams formed of these beams has in the second plane. 
It is more desirable that the beam formed of the converged ultrasonic beams 
have the same width in both the first plane and the second plane, so that 
an ink droplet may fly from the surface of the ink with the highest 
efficiency. This results in the secondary advantage that the ink droplet 
is virtually spherical and forms a circular ink dot on a recording medium. 
To make an effective use of the directivity the acoustic beams have, it is 
important to take some measures. First, the sound-wave sources (i.e., 
oscillators or wave-generating elements) and the ink reservoir are so 
arranged that the sound-wave beams may converge of themselves at the 
surface of the ink. Second, n sound-wave sources (n.gtoreq.4) are 
juxtaposed, forming an array. Third, the n sound-wave sources are 
repeatedly driven in groups, each time m adjacent ones (3.ltoreq.m&lt;n), 
whereby the m sound-wave sources emit sound-wave beams which converge at 
one point in the ink surface. Fourth, the grouping of the sound-wave 
sources is changed, thereby shifting the point in the ink surface, where 
the sound-wave beams converge. 
In the ink-jet head according to this invention, the sound-wave sources 
arranged in the form of an array are repeatedly driven in groups by a 
control unit or by signals, emitting sound waves. The sound waves converge 
propagate in specific directions with respect to the ink surface and 
converge at a specific point in the ink surface. As the sound-wave sources 
are repeatedly driven in groups, ink droplets of the same size fly 
sequentially from the ink surface onto a recording medium in parallel 
paths. As a result, ink dots uniform in ink concentration and spaced apart 
at regular intervals are formed on the medium, recording a high-quality 
image. Capable of effecting electronic focusing, the ink-jet head 
according to the invention can easily be modified into a linear-array 
head. Not requiring a plurality of arrays located in staggered fashion to 
form ink dots in high density, the ink-jet head generates but very little 
image noise. 
The ink droplets squirted through slit-like nozzles also have the same size 
and fly in parallel paths. The ink dots uniform in ink concentration and 
spaced apart at regular intervals will therefore be formed on the medium, 
recording a sharp and clear-cut image. Now will the nozzles be clogged 
with ink. In addition, when the ink-jet head effects phased array 
scanning, ink droplets fly in parallel paths spaced at regular intervals, 
rendering it unnecessary to correct or control the paths of ink droplets. 
In view of this, the head can well perform the function of a linear nozzle 
head. The ink-jet recording device according to the present invention is 
simple and compact and is easy to maintain. 
The array of ultrasonic generating elements comprises a piezoelectric layer 
having a uniform thickness, a common electrode provided on one surface of 
the piezoelectric layer, and discrete electrodes provided on the opposite 
surface of the piezoelectric layer. Although the piezoelectric layer is 
not divided into strips, its portions contacting the discrete electrodes 
can be driven independently. To manufacture the array, it suffices to 
perform dry or wet etching to provide the discrete electrodes. Dicing 
process need not be carried out to form the discrete electrodes. The 
etching, dry or wet, does not develop cracks in the piezoelectric layer, 
making it possible for the layer to be much broader than it is thick. 
Broader than it is thick, the piezoelectric layer can vibrate in its 
thickness direction, without resonating in the width direction. Therefore, 
the array can be manufactured at high yield and can squirt ink droplets 
inform in size. Since the piezoelectric layer is thin, the individual 
piezoelectric elements can be driven with high-frequency drive signals to 
squirt very tiny ink droplets so that a high-resolution image may be 
recorded on a recording medium. 
To converge ultrasonic beams in a plane extending to the array, it is 
better to divide an electrode layer into discrete electrodes than to 
divide not only the electrode layer but also a piezoelectric layer into 
strips, in order to reduce the pitch at which the piezoelectric elements 
are juxtaposed, constituting the array. Since the pitch is reduced, the 
grating lobes have far less amplitudes than the main lobe or are prevented 
to occur, and would not cause unnecessary ink droplets to fly from the ink 
surface. The ink-jet recording device can therefore record high-quality 
images. 
Another ink-jet recording device according to the present invention 
comprises a substrate and a piezoelectric element array. The substrate has 
a curved surface, on which the array is provided. To be more precise, the 
array comprises discrete electrodes mounted on the curved surface of the 
substrate, a piezoelectric layer provided on the discrete electrodes, and 
a common electrode provided on the piezoelectric layer. 
The method of manufacturing the array will be described. First, a 
trough-like groove is made in the supper surface of a block-shaped 
substrate. The curved bottom of the groove has a prescribed curvature. 
Next, strip-shaped discrete electrodes are juxtaposed in the trough-like 
groove at a predetermined pitch. A piezoelectric layer having a prescribed 
thickness is formed on the discrete electrodes by sputtering or the like. 
Finally, a common electrode is formed on the piezoelectric layer, also by 
sputtering or the like. 
The discrete electrodes may be formed in two alternative methods. In the 
first method, a patterned metal foil is bonded to the trough-like groove 
by means of anode bonding. The patterned foil is a high-precision one, 
which can be prepared by performing photolithography on a metal foil. 
During the anode bonding, heat and an electric field is applied to the 
substrate made of glass and the patterned metal foil, and the patterned 
foil is bonded to the glass due to an electrostatic force, without being 
deformed. In the second method, a metal foil, not patterned, is bonded to 
the trough-like groove by hot-pressing or the like, a patterned resin mask 
is formed on the foil, and the foil is patterned by photolithography using 
the resin mask. 
Since the discrete electrodes are curved and formed with a high precision 
in the order of microns, the array of piezoelectric elements can perform 
the function of a lens. Hence, the array emits ultrasonic beams which 
efficiently converge at a point in the ink surface. 
Still another ink-jet recording device according to the invention has a 
piezoelectric element array. The array comprises discrete electrode, a 
piezoelectric layer and a common electrode. The array is formed in the 
following steps. First, plate-shaped conductors and plate-shaped 
insulators are alternately combined, forming a rectangular block. Then, a 
trough-like groove is made in the upper surface of the block. Next, the 
piezoelectric layer is mounted in the groove. Finally, the common 
electrode is placed on the piezoelectric layer. In this case, too, the 
discrete electrodes are curved and formed with a high precision in the 
order of microns, the array of piezoelectric elements can perform the 
function of a lens. The array therefore emits ultrasonic beams which 
efficiently converge at a point in the ink surface. 
Another ink-jet recording device according to the invention has a 
piezoelectric element array. The array comprises discrete electrode, a 
piezoelectric layer and a common electrode and is characterized in that at 
least one piezoelectric element at either end is not driven at all to emit 
an ultrasonic beam. That is, the array has more piezoelectric elements 
than necessary to squirt ink droplets. Thus, the average capacitive load 
of the elements driven and the acoustic coupling between any two adjacent 
elements driven are less than otherwise. More precisely, the electric 
coupling and acoustic coupling between any two adjacent discrete 
electrodes are equal to those between any other two adjacent discrete 
electrodes. This minimizes the cross-talk noise between the beam 
generating elements. 
Since all piezoelectric elements but those located at the ends of the array 
are driven, emitting ultrasonic beams. Since the elements driven are 
located relatively remote from the walls of the ink reservoir unlike the 
elements at the ends of the array, the ultrasonic beams they emit are not 
reflected by the walls of the reservoir. The convergence of the beams is 
not hindered at all. 
Additional objects and advantages of the present invention will be set 
forth in the description which follows, and in part will be obvious from 
the description, or may be learned by practice of the present invention. 
The objects and advantages of the present invention may be realized and 
obtained by means of the instrumentalities and combinations particularly 
pointed out in the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Hereinafter, referring to the accompanying drawings, embodiments of the 
present invention will be explained in detail. 
FIG. 1 is a pictorial view of part of a recording head section in an 
ink-jet recording device according to an Embodiment 1-1 of the present 
invention. In the Embodiment 1-1, piezoelectric elements are used as 
ultrasonic generating elements. The piezoelectric elements are arranged in 
a one-dimensional array. 
The features of the Embodiment 1-1 is that a plurality of adjacent 
ultrasonic beams emitted from the piezoelectric element array are forced 
to interfere with each other within an ultrasonic interference layer 
formed of such material as glass, which is also used as an acoustic 
matching layer, and then are allowed to converge in the main-scanning 
direction, and that a one-dimensional Fresnel zone plate is used as means 
for forcing ultrasonic beams emitted from the piezoelectric element array 
to converge in the sub-scanning direction. 
The recording head section comprises an ultrasonic interference layer 11, a 
common electrode 12, a piezoelectric layer 13, a discrete electrode 14, a 
nozzle substrate (hereinafter, sometimes referred to as an ink pod), a 
Fresnel zone plate 16, and a driving circuit 21. 
The ultrasonic interference layer 11 also serves as an acoustic matching 
layer between the piezoelectric element support of the recording head 
section and piezoelectric element array 10 and ink 18, and is formed of, 
for example, glass. On the bottom surface of the ultrasonic interference 
layer 11, the piezoelectric layer 13 is formed via the common electrode 12 
made up of a thin metal film. 
The piezoelectric layer 13 is such that a layer of such a material as ZnO 
or PZT is formed all over (or in stripes on) the bottom surface of the 
ultrasonic interference layer 11 by a film forming method capable of 
controlling the film thickness arbitrarily, such as sputtering. On the top 
surface of the ultrasonic interference layer 11, a plurality of discrete 
electrodes 14 are formed with a pitch corresponding recording dots. The 
thickness of the piezoelectric layer 13 is determined by the wavelength of 
the ultrasonic wave used and designed so that the total of its thickness 
and the equivalent thickness of the metal common electrode 12 and the 
discrete electrode 14 sandwiching the piezoelectric layer 13 between them 
is half the wavelength of the ultrasonic wave. 
The common electrode 12, piezoelectric layer 13, and discrete electrode 14 
constitute the piezoelectric element array 10 or the ultrasonic generating 
element array. In FIG. 1, the piezoelectric element array 10 has only 
eight elements. In the case of an actual ink-jet head, for example, a line 
head as long as the length of the A4 size sheet with a resolution of 600 
dpi, about 5,000 piezoelectric elements are arranged in a line. In this 
case, the individual piezoelectric elements in the piezoelectric element 
array 10 are arranged in a line at regular intervals determined by the 
required recording density. A magnetostrictive transducer array may be 
used instead of the piezoelectric element array 10. In that case, a 
magnetostrictive transducer is used as the piezoelectric layer 13 and a 
discrete exciting coil (magnetization coil) 14 is used as the discrete 
electrode 14. Such an arrangement will be explained in Embodiment 3-3 and 
Embodiment 3-4. 
On the top surface of the ultrasonic interference layer 11, a nozzle 
substrate 15 in which a slit-like nozzle-cum-ink chamber with a 
trapezoidal cross section is formed is laminated so that the 
nozzle-cum-ink chamber may be positioned directly above the piezoelectric 
element array 10. The nozzle-cum-ink chamber is filled with liquid ink 18. 
At the boundary of the piezoelectric element array 10 and the ink 18, the 
one-dimensional Fresnel zone plate 16 is formed. The Fresnel zone plate 16 
is formed in such a manner that if the distance from the center of 
diffraction is x, first regions that pass ultrasonic waves with no phase 
shift are arranged at the positions of x=0 to 1K, .sqroot. 3.times.K to 
.sqroot. 5.times.K, .sqroot. 7.times.K to .sqroot. 9.times.K, .sqroot. 
11.times.K to .sqroot. 13.times.K, . . . and second regions that shift the 
phase of ultrasonic waves by a half-wave length are arranged at the 
positions of x=1 to .sqroot. 3.times.K, .sqroot. 5.times.K to .sqroot. 
7.times.K, .sqroot. 9.times.K to .sqroot. 11.times.K, .sqroot. 13.times.K 
. . . Here, P is the focal length or the thickness of the nozzle substrate 
15, .lambda. is the wavelength of the ultrasonic wave used, and 
K=(.lambda.p/2).sup.1/2. Since the first and second regions have only to 
differ relatively from each other by a half-wave length, only either the 
first or the second region is formed of a metal evaporation film by 
photolithography. Its thickness is determined to be about several .mu.m to 
several tens .mu.m that allow a half-wave length phase shift to take place 
due to the difference from a low sound speed in the ink. 
The operation of Embodiment 1-1 will be explained with reference to FIGS. 
2A and 2B. 
One typical phased array scanning technique is to group a specific number 
of adjacent piezoelectric elements in the piezoelectric element array into 
one unit and drive these units shifting the phase suitably so that the 
ultrasonic beams emitted from them may interfere with each other, by 
shifting the piezoelectric element to be driven one by one. Here, a case 
where linear scanning is effected using four piezoelectric elements as one 
unit. 
As shown in FIGS. 2A and 2B, a voltage of burst wave made up of an 
alternating current of a specific frequency and a pulse train is applied 
to the discrete electrodes 14.sub.1 to 14.sub.4 of four piezoelectric 
elements. 
Under these conditions, when a voltage of burst wave of a specific phase is 
applied to the two inner ones 14.sub.2, 14.sub.3 of the four piezoelectric 
elements, and a voltage of burst wave leading the voltage of burst wave 
applied to the discrete electrodes 14.sub.2, 14.sub.3 of the two inner 
piezoelectric elements is applied to the discrete electrodes 14.sub.1, 
14.sub.4 of the two outer piezoelectric elements, the ultrasonic beams 
emitted from the respective piezoelectric elements interfere with one 
another, producing a lens effect in the direction in which the 
piezoelectric elements are arranged in the piezoelectric element array 10 
(hereinafter, referred to as the array direction), or in the main-scanning 
direction. In the ultrasonic interference layer 11, the beams never 
converge in the direction perpendicular to the piezoelectric element array 
10 (in the sub-scanning direction). 
The ultrasonic beams arriving at the boundary with the ink chamber 
experience a lens effect by means of the Fresnel zone plate 16 in such a 
manner that they converge centripetally in the direction perpendicular to 
the piezoelectric element array 10 (i.e., the sub-scanning direction). 
Specifically, the convergence of the ultrasonic beams in the main-scanning 
direction starts at the inside of the ultrasonic interference layer 11 
also serving as an acoustic matching layer and extents to the ink 18 in 
the nozzle substrate 15, whereas the convergence in the sub-scanning 
direction takes place only within the ink 18 in the nozzle substrate 15. 
The ultrasonic beams are focused on the surface of the ink remaining still 
at the opening of the slit at the top surface of the nozzle substrate 15 
in both of the main-scanning and sub-scanning directions. 
In this way, the pressure of the converged ultrasonic beams forces an ink 
droplet to fly from the ink surface to record an image on a recording 
medium such as recording paper (not shown). With this recording method, 
when the ultrasonic beams are forced to converge on a dot using four 
piezoelectric elements as shown in FIGS. 3A to 3E, divisional driving is 
effected where one line is divided into four or more pieces, which are 
each driven with one fourth of the original timing. Namely, shifting in 
the main-scanning direction must be done by linear scanning using four 
piezoelectric elements as one unit. 
The operation of FIGS. 3A to 3E will be explained briefly. 
FIG. 3A pictorially shows a case where a voltage of burst wave is applied 
to the two inner ones 14.sub.3, 14.sub.4 of the grouped discrete 
electrodes 14.sub.2 to 14.sub.5, and a voltage of burst wave leading the 
voltage of burst wave applied to the two inner discrete electrodes 
14.sub.3, 14.sub.4 is applied to the two outer discrete electrodes 
14.sub.2, 14.sub.5. 
FIG. 3B pictorially shows a case where a voltage of burst wave is applied 
to the two inner ones 14.sub.4, 14.sub.5 of the next grouped discrete 
electrodes 14.sub.3 to 14.sub.6, and a voltage of burst wave leading the 
voltage of burst wave applied to the two inner discrete electrodes 
14.sub.4, 14.sub.5 is applied to the two outer discrete electrodes 
14.sub.3, 14.sub.6. 
FIG. 3C pictorially shows a case where a voltage of burst wave is applied 
to the two inner ones 14.sub.5, 14.sub.6 of the grouped discrete 
electrodes 14.sub.4 to 14.sub.7, and a voltage of burst wave leading the 
voltage of burst wave applied to the two inner discrete electrodes 
14.sub.5, 14.sub.6 is applied to the two outer discrete electrodes 
14.sub.4, 14.sub.7. 
FIG. 3D pictorially shows a case where the discrete electrodes 14.sub.1 to 
14.sub.8 divided into a group of discrete electrodes 14.sub.1 to 14.sub.4 
and a group of discrete electrodes 14.sub.5 to 14.sub.8, and the two 
groups are driven at the same time to squirt two droplets of ink with a 
specific pitch. 
FIG. 3E shows the same state as in FIG. 3A. 
Practically, it is desirable that the number of piezoelectric elements 
constituting one group is 20 or more. 
As described above, by grouping the piezoelectric elements in the 
piezoelectric element array 10, rearranging the grouping sequentially, and 
changing and applying the voltage of burst wave according to the positions 
of the piezoelectric elements 13 in the grouping, an ink droplet of a 
constant size is always forced to fly straight in a constant direction, 
which eliminates a mechanism for controlling the flying direction of an 
ink droplet, contributing greatly to the simplification of the recording 
device. 
Furthermore, by sequentially changing the grouping in the piezoelectric 
element array 10 and selectively applying a specific alternating-current 
voltage or a voltage of burst wave to the piezoelectric elements 13 
according to the positions of the elements in the grouping, the energy 
density of ultrasonic beam can be improved, variations in the size of ink 
droplet be alleviated, and high-quality recording be effected. 
In Embodiment 1-1, linear scanning in units of four piezoelectric elements 
has been explained. The number of elements for one unit to drive the 
piezoelectric element array in linear scanning, that is, the number of 
piezoelectric elements used to record one pixel, is not restricted to one 
unit of four piezoelectric elements. By using more piezoelectric elements, 
side lobe of the ultrasonic beams converging centripetally is reduced and 
the energy density is raised, thereby reducing variations in the ink 
droplet and lowering the driving voltage of the piezoelectric element 
array 10. 
A feature of Embodiment 1-1 is that the one-dimensional Fresnel zone plate 
16 is used as means for forcing the ultrasonic beams emitted from the 
piezoelectric element array 10 to converge in the sub-scanning direction. 
The effect of using the one-dimensional Fresnel zone plate 16 to force the 
ultrasonic beams to converge in the sub-scanning direction is as follows. 
An acoustic cylindrical lens using a bulk material that has the same cross 
section along the piezoelectric element array in the sub-scanning 
direction is used as ultrasonic beam converging means in the sub-scanning 
direction. Of the ultrasonic beams forced by phased array scanning to 
converge with a centripetal wave surface, however, those near the center 
strike the lens face or the lens surface at right angles, whereas those at 
both ends of the ultrasonic beams hit the lens surface obliquely. When F 
number (=focal length/lens aperture) is reduced to about 1 to increase the 
energy efficiency, the incidence angle to the vertical axis at both ends 
increases to about 30.degree.. When the incidence angle becomes larger 
with respect to the vertical axis, the curvature of the lens surface in 
the incident beam advancing direction becomes greater, thus shortening the 
focal length of the ultrasonic beams incident on that portion. As a 
result, the ultrasonic beams cannot focus on a single point. This makes 
the efficiency very low. Because the size of ink droplet is irregular and 
unstable, the picture quality is low. Additionally, it is difficult for 
the ink-jet printer to operate properly. 
In contrast, when the one-dimensional zone plate 16 is used to force 
ultrasonic beams to converge in the sub-scanning direction as in 
Embodiment 1-1, the focal length will not change even if the incidence 
angle of the ultrasonic beams changes with respect to the direction in 
which the beams extend in a belt. Therefore, the problem in using an 
acoustic cylindrical lens using a bulk material is solved. 
Furthermore, the Fresnel zone plate 16 with such a straight pattern is 
helpful in the manufacturing process. Specifically, in Embodiment 1-1, as 
shown in FIG. 4, on the top surface of the glass substrate, the ultrasonic 
interference layer 11 also serving as an acoustic matching layer, the 
Fresnel zone plate 16 with a straight pattern extending in the 
main-scanning direction. On the bottom surface of the glass substrate, the 
discrete electrode 14 with a straight pattern extending in the 
sub-scanning direction is formed on a lamination of the common electrode 
12 and the piezoelectric layer 13. Since each pattern is composed of 
straight lines without corners, they can be produced finely, precisely, 
and independently. The accuracy of positioning the top and bottom patterns 
of the glass substrate to combine them may be must less strict than the 
accuracy of forming each pattern. Therefore, a pattern suitable for high 
resolution can be produced using an easy-to-handle manufacturing process. 
Furthermore, another advantage of using the one-dimensional Fresnel zone 
plate 16 is that unlike a cylindrical lens using a curved surface bulk 
material, the Fresnel zone plate prevents the focus from moving according 
to the incidence angle of the ultrasonic beam and the aberration from 
occurring. 
Embodiment 1-2 
FIG. 5 shows the structure of a recording head according to an Embodiment 
1-2 of the present invention. In the Embodiment 1-2, means for forcing 
ultrasonic beams to converge in the main-scanning direction uses phased 
array scanning as in Embodiment 1-1, whereas a cylindrical lens 20 using a 
curved surface bulk material is used as means for forcing ultrasonic beams 
to converge in the sub-scanning direction. 
In this embodiment, as shown in FIG. 6, since the focal length (fa) of the 
beams in the central portion (7A-7A') striking the lens 20 at right angles 
differs from the focal length (fb) of the beams at the end portions 
(7B-7B') striking the lens 20 obliquely, the convergence characteristic is 
poorer than that in Embodiment 1-1. In addition, because the beams from 
both ends are diffracted in a complicated three-dimensional plane, an 
aberration takes place. 
Therefore, the recording head of Embodiment 1-2 is inferior to that of 
Embodiment 1-1 in the energy efficiency in generating squirted ink 
droplets and the uniformity of ink droplets. Since the recessed side of 
the cylindrical lens 20 serves as an ink chamber as it is, the former has 
the advantage of providing an ink passage with a large cross section. 
Thus, in the case of high-speed recording, the recording head of 
embodiment of 1-2 has the advantages that it can supply a sufficient 
amount of ink to deal with the speed, the change of ink concentration due 
to the evaporation of the ink solvent at the nozzle is slow, and the 
clogging of the nozzle is less liable to occur. 
Hereinafter, Embodiment 1-3 to Embodiment 1-8 featuring the structure of 
the piezoelectric element will be explained. 
Embodiment 1-3 
FIG. 7 is a perspective view of the recording head section in an ink-jet 
recording device according to an Embodiment 1-3 of the present invention. 
Embodiment 1-3 is characterized in that a single piezoelectric element is 
provided with a plurality of discrete electrodes and a plurality of 
ultrasonic waves are generated from the single piezoelectric element. 
In FIG. 7, a piezoelectric element array 10 is composed of a piezoelectric 
layer 13 of a long plate with a constant thickness, a common electrode 12 
formed on one side of the layer and a plurality of discrete electrodes 14 
formed on the other side of the layer. Namely, the piezoelectric layer 13, 
common electrode 12, and discrete electrodes 14 constitute a plurality of 
piezoelectric elements arranged one-dimensionally. 
On the surface of the common electrode opposite to the piezoelectric layer 
13, an acoustic lens 11 is formed. The acoustic lens 11 is formed of, for 
example, a glass plate, has a recessed surface on the opposite side to the 
piezoelectric element array 10, and functions as an acoustic concave lens. 
On the acoustic lens 11, an ink pod 15 is placed. In the ink pod 15, an 
ink chamber getting narrower gradually so as to wrap the passage of 
ultrasonic beams from the piezoelectric element array is formed on the 
recessed surface of the acoustic lens 11. The ink chamber is filled with 
liquid ink 18. 
On the bottom surface of the glass plate, a component member of the 
acoustic lens 11, an integrated driving circuit (hereinafter, referred to 
as a driving IC) 21 is mounted. The driving IC 21 is connected to the 
common electrode 12 and discrete electrodes 14 via a wiring pattern on the 
glass plate. 
The driving IC 21 performs linear electronic scanning by driving the 
piezoelectric element array 10 according to the image data to be recorded 
in such a manner that blocks of n adjacent piezoelectric elements in the 
array direction (the arrangement direction of piezoelectric elements, the 
main-scanning direction) are driven one after another. Specifically, 
high-frequency driving signals with a specific phase difference are 
supplied to the n piezoelectric elements in the selected block and these 
piezoelectric elements are driven simultaneously, thereby causing the 
ultrasonic beams emitted from the piezoelectric element array 10 to 
converge in the main-scanning direction. More specifically, as shown in 
FIG. 8, if the total number of elements in the piezoelectric element array 
10 is N and the number of piezoelectric elements driven at the same time 
is n, the first to n-th piezoelectric elements are driven simultaneously 
with a specific phase difference between them. Then, the second to (n+1)th 
piezoelectric elements are driven simultaneously with a specific phase 
difference between them. Similarly, the positions of piezoelectric 
elements simultaneously driven are shifted by one element each time the 
piezoelectric elements have been driven, thereby causing the direction of 
ultrasonic beams forced to converge to move linearly in the main-scanning 
direction. The waveform of the driving signal may be a rectangular burst 
as shown in FIG. 9 or a sinusoidal burst. Changing the phase difference 
for driving n piezoelectric elements means changing the timing that the 
driving signal of FIG. 9 starts to be applied. 
The ultrasonic beam emitted from the piezoelectric element array 10 and 
forced to converge in the main-scanning direction is further forced by the 
acoustic lens 11 to converge in the direction (the sub-scanning direction) 
perpendicular to the main-scanning direction, and finally converges on the 
liquid surface of ink 18 in the form of a dot. The pressure (radiation 
pressure) generated by the ultrasonic beams converged at the ink liquid 
surface grows a conical ink meniscus at the ink liquid surface, and in a 
short time, a droplet of ink is squirted from the tip of the ink meniscus. 
The squirted ink droplet flies straight on a recording medium (not shown), 
adheres to it, and is dried and fixed, thereby effecting image recording. 
Here, one of the parameters determining the size of a flying ink droplet is 
the frequency of an ultrasonic wave. Since the piezoelectric element array 
10 radiates ultrasonic waves making use of the resonance along the 
thickness of the piezoelectric layer 13, the frequency is determined by 
the thickness of the piezoelectric layer 13. Since the thickness is in 
inverse proportion to the frequency, the thinner the piezoelectric layer, 
the higher the frequency. Therefore, a printer with a higher resolution 
needs ultrasonic waves of higher frequencies, and the type and formation 
of the piezoelectric layer 13 must be selected accordingly. 
In addition to the thickness determined by the resolution, chief conditions 
for selecting the type of piezoelectric layer are an electromechanical 
coupling coefficient indicating the efficiency of converting an electric 
input into an ultrasonic output and a dielectric constant having an effect 
on the electrical matching with the driving IC. Ceramic such as zirconium 
titanate (PZT) and zinc oxide, macromolecular material such as a copolymer 
of vinylidene fluoride and ethylene trifluoride, a single crystal such as 
lithium niobate are used for the piezoelectric layer. Practically, PZT is 
suitable for a printer with a resolution of 600 dpi (dots per inch) or 
below and ZnO is suitable for a printer with a resolution (frequency) 
higher than 600 dpi in terms of the formation of the piezoelectric layer 
13 and performance. When a bulk of PZT is ground for a piezoelectric 
layer, an adhesive layer intervenes between the common electrode 12 and 
the acoustic lens 11, which is not shown in FIG. 7. 
The electrode 12 and electrodes 14 are formed by a thin filming technique 
such as evaporation of Ti, Ni, Al, Cu, or Au or sputtering, or by a baking 
technique based on printing using a screen of glass frits mixed with 
silver paste. Furthermore, the acoustic lens 11 is formed of glass or 
resin. When PZT is caused to adhere to the acoustic lens 11, the 
workability of lens material and the acoustic matching with the ink 18 in 
the piezoelectric layer 13 are taken into account. When ZnO is deposited 
by sputtering, however, the temperature at the time of sputtering and the 
ease of orientation of the piezoelectric layer are taken into 
consideration, in addition to the above factors. 
Embodiment 1-4 
FIG. 10 is a sectional view of a major portion of the recording head 
section in an ink-jet recording device according to an Embodiment 1-4 of 
the present invention. This is an example of using a Fresnel lens with 
straight slits in specific positions as the acoustic lens 11 in place of 
the concave lens of FIG. 7. The distance ri between slits and the depth d 
are expressed by the following equations: 
##EQU1## 
where ri is the distance from the center of the aperture of the lens, 
.lambda.w is the wavelength of an ultrasonic wave in ink, and .lambda.l is 
the wavelength of an ultrasonic wave in lens. 
Embodiment 1-5 
FIG. 11 is a sectional view of a major portion of the recording head 
section in an ink-jet recording device according to an Embodiment 1-5 of 
the present invention. In this embodiment, by forming the piezoelectric 
element array 10 into a concave shape using part of a circular cylinder 
instead of using an acoustic lens, ultrasonic beams are forced to converge 
in the sub-scanning direction. In this case, the piezoelectric element 
array 10 is supported on the piezoelectric element support 17. 
Embodiment 1-6 
FIG. 12 is a sectional view of a major portion of the recording head 
section in an ink-jet recording device according to an Embodiment 1-6 of 
the present invention. In this embodiment, an acoustic matching layer 11' 
is formed on one side of the acoustic lens 11 opposite to the 
piezoelectric element array 10. 
Embodiment 1-7 
FIG. 13 is a sectional view of a major portion of the recording head 
section in an ink-jet recording device according to an Embodiment 1-7 of 
the present invention. While in Embodiment 1-4, the acoustic lens 11 of a 
Fresnel lens also serves as the support for the piezoelectric element 
array 10, in this embodiment, the piezoelectric element support 17 and the 
acoustic lens 11 are provided separately. 
A more concrete embodiment associated with Embodiment 1-3 to Embodiment 1-7 
will be explained taking the basic structure of FIG. 7 as an example. Five 
4.5-cm-long PZT piezoelectric ceramic plates with a relative permittivity 
of 2000 were used as the piezoelectric layer 13, whose resonance frequency 
was determined to be 50 MHz (for a thickness of 40 m). At the time of 
mounting, these five ceramic plates were arranged on the acoustic lens, 
and a Ti/Ni/Au electrode was formed on both sides by sputtering to a 
thickness of 0.05 .mu.m, 0.05 .mu.m, and 0.2 .mu.m in that order, followed 
by a polarizing process under an electric field of 2 kV/mm. Thereafter, by 
etching the electrode on one side of the piezoelectric layer 13, 3000 
60-.mu.m-wide discrete electrodes 14 were formed at intervals of 15 .mu.m 
(a piezoelectric element arranging pitch of 75 .mu.m). Then, the 
piezoelectric layer 13, the common electrode 12 on the other side, and 
these discrete electrodes 14 constituted a piezoelectric element array 10. 
A 1-mm-thick pyrex was used as the acoustic lens 11 and worked into a 
concave so as to provide a lens curvature of 2.3 mm and an aperture of 1.5 
mm. The acoustic lens 11 was bonded to the piezoelectric element array 10 
with an epoxy resin adhesive so that the opening (concave) of the acoustic 
lens 11 may align with the position of the electrode of the piezoelectric 
element array 10. Then, an ink pod 15 was provided and a driving IC 21 was 
connected as shown in FIG. 7, in which way an ink-jet head was formed. The 
depth of ink 18 was determined to be 3 mm and the distance from the common 
electrode 12 to the ink liquid surface was determined to be 4 mm. 
Next, as a comparison example, a piezoelectric element array was produced 
by cutting with a dicing saw according to the above-described 
specification. Specifically, electrodes were formed on both sides of a 
40-.mu.m-thick PZT piezoelectric layer in the same manner as the above 
embodiment, and the resulting layer was bonded to an acoustic lens 
material with an epoxy resin. Thereafter, by using a dicing saw with a 
15-.mu.m-thick blade, slits were made as far as part of the acoustic lens 
material so that the piezoelectric layer may be cut off completely. 
By measuring the impedance characteristic using Embodiment 1-3 to 1-7 and 
the first comparison example, a check was made to see if there was any 
faulty channel. As a result, while in Embodiment 1-3 to Embodiment 1-7, 
none out of 3000 piezoelectric elements was faulty, in the first 
comparison example, 467 out of 3000 piezoelectric elements presented 
higher impedance. When the high-impedance places were seen through a 
microscope, cracks were found in the array direction of the piezoelectric 
layer. Thereafter, the ink-jet head of the first comparison example was 
immersed in an epoxy stripping agent to separate from the acoustic lens. 
Then, the piezoelectric layer was examined, and it found that the layer 
was damaged clearly. 
As a second comparison example, an ink-jet head with a cutting-off pitch 
large enough to prevent damage to the piezoelectric layer was produced. 
The frequency was the same 50 Mhz and a 40-.mu.m-thick PZT piezoelectric 
layer was used. On both sides of the piezoelectric layer, electrodes ware 
formed as in the first comparison example, and the resulting layer was 
bonded to an acoustic lens material with an epoxy resin. Thereafter, by 
using a dicing saw with a 15-.mu.m-thick blade, slits were made as far as 
part of the acoustic lens material with a pitch of 150 .mu.m. The number 
of piezoelectric elements was 15000. When the impedance characteristic of 
the ink-jet head was determined, no faulty channel was found. 
Next, when a sound field in water was measured using the ink-jet heads of 
Embodiment 1-3 to Embodiment 1-7 and the second comparison example, and 
the beam widths and the grating grove levels of the ultrasonic beam were 
compared at the central axis of -10 dB, it was found that the beam width 
was 0.16 mm in the embodiments and 0.20 mm in the second comparison 
example, and the grating grove level was -17 dB and -6 dB in the second 
comparison example. Namely, the beam width at the central axis was 
narrower in the embodiments, enabling ultrasonic beams to converge better, 
but the difference was not distinctive. In contrast, the grating grove 
level in the embodiments was 11 dB lower. This means that while in the 
comparison examples, there is a possibility that ink will fly from 
irrelevant points, Embodiment 1-3 to Embodiment 1-7 are free from such a 
problem. 
Next, an ink-droplet flying test was carried out actually. The driving 
signal voltage waveform applied to the piezoelectric element array was a 
20-MHz rectangular burst, the number of waves was 500 (25 .mu.s), and the 
voltage was 100 V. In Embodiment 1-3 to Embodiment 1-7, when the 2000 
elements in the piezoelectric element array were grouped into blocks of 20 
elements and one block was driven simultaneously, a droplet of ink was 
squirted only from the central axis. In contrast, in the second comparison 
example, in addition to those from the central axis, droplets of ink were 
squirted from the places near one end of 1500 elements where a grating 
grove has occurred. Examination of the phenomenon showed that the flying 
of ink droplets from the places other than the central axis took place due 
to a subtle inclination of the head. It is found that it was very 
difficult to adjust the head. Therefore, it is not practical that when not 
only discrete electrodes but also the piezoelectric layer are cut off, the 
cutting-off pitch is widened to prevent damage to them. 
The above results apply not only to the case where the acoustic lens 11 is 
a concave lens, but also to the case where the acoustic lens is a Fresnel 
lens and the case where the piezoelectric element has a concave shape as 
shown in FIG. 11. In the case of a concave piezoelectric element, it is 
difficult to form a piezoelectric element into a concave and then to cut 
off the concave element into an array. Furthermore, when higher 
frequencies are used to make ink droplets smaller, the arranging pitch on 
piezoelectric element array must be made narrower to eliminate the effect 
of the grating grove. For this reason, dividing only discrete electrodes 
to form an array is much more effective in a piezoelectric element array 
as with the present invention. 
As described above, with Embodiment 1-3 to Embodiment 1-7, by 
array-dividing only discrete electrodes without cutting off the 
piezoelectric layer, the arranging pitch on the piezoelectric element 
array can be made smaller without reducing the manufacturing yield than 
when the piezoelectric layer as well as discrete electrodes are 
array-divided. Furthermore, these embodiments are effective in making 
ultrasonic waves higher, so that high-resolution recording can be effected 
easily. 
Embodiment 1-8 
FIG. 14 is a perspective view of the recording head section in an ink-jet 
recording device according to an Embodiment 1-8 of the present invention. 
Embodiment 1-8 is characterized in that in a piezoelectric element array, 
gaps or slits are made in at least one portion of the longitudinal side of 
the piezoelectric layer. 
In FIG. 14, a piezoelectric element array 10 is composed of a piezoelectric 
layer 13 of a long plate with a constant thickness, a common electrode 12 
formed on one side of the layer and discrete electrodes 14 formed on the 
other side of the layer. Namely, the piezoelectric layer 13, common 
electrode 12, and discrete electrodes 14 constitute a plurality of 
piezoelectric elements arranged one-dimensionally. 
The following materials are suitable for the piezoelectric layer 13. As one 
of typical piezoelectric layers with a large electromechanical coupling 
coefficient, PZT (Pb(Zr, Ti)O.sub.3) is given. Since its relative 
permittivity is as high as 500 to 2000, its impedance drops too much in 
high-frequency driving and therefore it cannot be used. It is suitable for 
low-frequency driving. ZnO among ceramic materials and PVD 
(Polyvinyl-Diphenylfluoride) among organic materials are desirable for a 
piezoelectric layer with a relative permittivity of only about 10 suitable 
for high-frequency driving. 
On the surface of the common electrode 12 opposite to the piezoelectric 
layer 13, an acoustic lens 11 is formed. The acoustic lens 11 is a Fresnel 
lens with straight slits in specific positions in Embodiment 1-8 and may 
be a lens produced by forming a concave on the surface a glass plate. On 
the acoustic lens 11, an ink pod 15 is placed. In the ink pod 15, an ink 
chamber getting narrower gradually so as to wrap the passage of ultrasonic 
beams from the piezoelectric element array 10 is formed on the recessed 
surface of the acoustic lens 11. The ink chamber is filled with liquid ink 
18. 
The head portion thus constructed is mounted together with a driving IC 21 
on a wiring substrate 21a. The driving IC 21 is connected to the common 
electrode 12 via a wiring pattern (not shown) on the wiring substrate 21a 
and further connected to the discrete electrodes 14 via bonding wires. 
The basic image recording operation in this embodiment is the same as in 
Embodiment 1-3. Specifically, the driving IC 21 performs linear electronic 
scanning by driving the piezoelectric element array 10 according to the 
image data to be recorded in such a manner that blocks of n adjacent 
piezoelectric elements in the array direction (the main-scanning 
direction) are driven one after another. Specifically, high-frequency 
driving signals with a specific phase difference are supplied to the n 
piezoelectric elements in the selected block and these piezoelectric 
elements are driven simultaneously, thereby causing the ultrasonic beams 
emitted from the piezoelectric element array 10 to converge in the 
main-scanning direction. Similarly, the positions of piezoelectric 
elements simultaneously driven are shifted by one element each time the 
piezoelectric elements have been driven, thereby causing the direction of 
ultrasonic beams forced to converge to move linearly in the main-scanning 
direction. 
The ultrasonic beam emitted from the piezoelectric element array 10 and 
forced to converge in the main-scanning direction is further forced by the 
acoustic lens 11 to converge in the direction (the sub-scanning direction) 
perpendicular to the main-scanning direction, and finally converges on the 
liquid surface of ink 18 in the form of a dot. The pressure (radiation 
pressure) generated by the ultrasonic beams converged at the ink liquid 
surface grows a conical ink meniscus at the ink liquid surface, and in a 
short time, a droplet of ink is squirted from the tip of the ink meniscus. 
The squirted ink droplet flies straight on a recording medium (not shown), 
adheres to it, and is dried and fixed, thereby effecting image recording. 
FIG. 15 is a perspective view of the piezoelectric element array 10 in the 
ink-jet head shown in FIG. 14, seen from the direction perpendicular to 
the array direction. As shown in the figure, a gap 22 is made in the 
piezoelectric layer 13 so as to go through at least a part of the 
longitudinal side (the array direction) of the layer across the thickness. 
It is desirable that the number K of gaps 22 made in the piezoelectric 
layer 13 should be in the range of N/2&gt;=K&gt;=N/n and they be provided at 
regular intervals, where N is the total number of piezoelectric elements 
constituting the piezoelectric element array 10 and n is the number of 
piezoelectric elements driven simultaneously. 
When the piezoelectric layer 13 is divided into N pieces according to N 
piezoelectric elements constituting the piezoelectric element array 10, 
crosstalk noise is the smallest. Dividing the piezoelectric layer 13 into 
individual elements leads to a significant drop in the mass productivity. 
If the number of gaps is set at N/2&gt;=K, the distance between gaps 22 will 
be 100 .mu.m or more. Thus, by cutting deep into the piezoelectric layer 
with a dicer, gaps 22 can be made easily. If the number of gaps is in the 
range of K&gt;=N/n at minimum, the effect of reducing crosstalk will never 
fail to appear in driving to squirt individual droplets. Since the width 
of the gap 22 may be very small, if piezoelectric layers of the size 
corresponding to n signal lines or as large as an integral multiple of 
that size, the effect will not change. Such gaps as made in part of the 
thickness or width of the piezoelectric layer produce a similar effect. 
A more concrete embodiment will be described. Using a piezoelectric layer 
that has a gap for every n piezoelectric elements (n=14 in FIG. 15) for 
K&gt;=N/n, the minimum number of gaps, as shown in FIG. 15, generated 
crosstalk was measured. The piezoelectric layer was produced by making 
slits in a 1.05-mm-wide ZnO sintered material with a dicer with ten blades 
arranged so as to move parallel to the material and carrying out an 
automatic cutting operation in which the dicer is moved in parallel. 
FIG. 16 diagrammatically shows the piezoelectric element 10, piezoelectric 
layer 13, and discrete electrodes 14 to explain how a signal is applied to 
the array to examine the effect of reducing crosstalk. While a driving 
signal voltage of a 100-MHz burst waveform shown in FIG. 17 was being 
applied to only the central portion and both end portions of the (n) 
piezoelectric elements in one block that squirts a single droplet of ink, 
noise generated on the lines near the gap 22 applied with no driving 
signal voltage, or crosstalk was measured. Although no output waveform 
should be found on the lines, noise was measured in the form of the output 
waveform shown by broken lines in FIG. 18. Its amplitude is 4% or less 
(FIG. 18 has an enlarged ordinate of FIG. 17) and there was no phase 
shift. Using the piezoelectric layer 13 with such gaps, an ink-jet head as 
shown in FIG. 14 was constructed. Then, when the ink-jet head was operated 
on a printer, a A4-size monochromatic print with a high resolution of 600 
dpi could be obtained in 30 seconds. 
As a comparison example, an ink-jet head was constructed using the 
piezoelectric layer 13 shown in FIG. 19. The piezoelectric layer 13 in 
FIG. 19 is the same as that in the embodiment except that no gap is made. 
Like FIG. 16, FIG. 20 diagrammatically shows the piezoelectric element 10, 
piezoelectric layer 13, and discrete electrodes 14 to explain how a signal 
is applied to the array. As in the embodiment, while a driving signal 
voltage of a 100-MHz burst waveform shown in FIG. 17 was being applied to 
only the central portion and both end portions, crosstalk noise generated 
on the lines near the gap applied with no driving signal voltage, was 
measured. Crosstalk noise was measured in the form of the output waveform 
shown by solid lines in FIG. 18. The amplitude of the crosstalk noise was 
8% or less, more than twice the amplitude measured in the embodiment. 
As described above, with Embodiment 1-8, crosstalk can be suppressed to a 
low level, so that it is possible to realize high-resolution ink-jet 
recording needing high-frequency driving. A relatively small number of 
caps have only to be formed on the piezoelectric layer to form an ink-jet 
head, maintaining the mass productivity. 
Embodiment 1-9 
FIG. 21 shows the structure of a recording head section according to an 
Embodiment 1-9 of the present invention. Embodiment 1-9 differs from 
Embodiment 1-1 in that ultrasonic beans are forced to converge without 
effecting phased array scanning by using only a one-dimensional Fresnel 
zone plate 16. 
In Embodiment 1-9, the wavelength of the ultrasonic beam emitted from the 
piezoelectric element array 10 is set at a sufficiently small value as 
compared with the pitch on the piezoelectric element array 10. The 
ultrasonic beams of such a short wavelength advance straight without 
diverging in the direction perpendicular to the surface of the 
piezoelectric layer 13, passes through the ink chamber, and strikes the 
surface of ink 18, thereby squirting an ink droplet 19 with a size close 
to the wavelength in the ink 18, that is, with a sufficiently small (or 
too a small) droplet size with respect to the necessary resolution. 
According to the experiment conducted by the inventors, even when the 
surface of ink 18 is hit by ultrasonic beams of a relatively long 
wavelength as compared with a flying ink droplet 19 corresponding to the 
wavelength of the ultrasonic beams as in Embodiment 1-9, the ink droplet 
19 flies from the central portion of the ultrasonic beams accurately and 
stably because the ultrasonic beams have an intensity distribution where 
the intensity attenuates radially outward. 
The problem that the flying ink droplet 19 is too small as compared with 
the resolution can be solved by performing multiple recording (or 
overwriting) where ink droplets are forced to fly straight on the same 
pixel consecutively, to make the dot thicker. The operation of making a 
pixel thicker by overwriting can be put to practical use only by a method 
of generating ink droplets at a high-speed repeating period that enables 
dots to merge one another in ink droplets by forcing a subsequent flying 
ink droplet to arrive before the preceding flying ink droplet has been 
absorbed by the recording sheet. Therefore, this is an effect unique to an 
ink-jet recording device featuring high-speed recording. 
Furthermore, with Embodiment 1-9, since grouping in a main-scanning 
direction is not necessary, many ink droplets can be squirted in a single 
operation and recording time can be reduced. 
Embodiment 1-10 
With an ink-jet recording device of the present invention, an 
alternating-current voltage of a constant frequency or a pulse voltage is 
applied in a burst to the piezoelectric element array 10, which then 
generates ultrasonic beams synchronized with the frequency. In this case, 
to effect phased array scanning in Embodiment 1-1 and Embodiment 1-3, the 
phase of the ultrasonic beams generated from adjacent piezoelectric 
elements must be set so that they may each focus on specific positions. 
In Embodiment 1-10, a configuration of the driving circuit for the 
recording head used in the ink-jet recording devices in Embodiment 1-1 and 
Embodiment 1-2 will be explained. 
A configuration where a driving circuit for phased array scanning is 
mounted integrally on a head substrate on which a piezoelectric element 
array generating ultrasonic beams is new and produce a unique effect. 
It is well known that in an ink-jet recording device using ultrasonic 
beams, flying ink droplets depend greatly on the frequency of ultrasonic 
waves. To obtain the necessary resolution for a printer, the frequency of 
driving voltage ranging from several tens MHz to several hundreds MHz is 
needed. To apply a voltage of such high frequencies to each piezoelectric 
element to drive the piezoelectric element array and control the driving 
phase at an accuracy necessary for phased array scanning, the magnitude of 
delay due to long wiring distances and variations in the delay in the 
scanning circuit must be taken into consideration on the order of 
nanoseconds (10.sup.-9 sec). On this subject, the inventors actually made 
the following circuit and conducted an experiment to compare the 
performance. Specifically, the following three types of oscillators to 
produce a using frequency are compared with each other in terms of 
performance: 
(A1) A CR oscillator composed of a delay circuit made up of a capacitor and 
a resistor in each IC chip and a buffer circuit. 
(A2) A ring oscillator composed of a plurality of buffer circuits connected 
in series 
(A3) A configuration where a signal from an external quartz-crystal 
oscillator is directed into an IC via printed wires on the head substrate. 
The following three types of delay circuits for delay control to provide a 
phase difference in driving each piezoelectric element necessary for 
phased array scanning are compared with each other in terms of 
performance: 
(B1) A delay circuit composed of a capacitor and a resistor in each IC 
chip. 
(B2) A delay circuit composed of a plurality of buffer circuits connected 
in series. 
(B3) A configuration where a plurality of signals delayed outside the 
circuit are directed into the IC via a plurality of printed wires on the 
head substrate. 
The comparison results showed that methods by which errors in each circuit 
and errors between adjacent circuits can be minimized and the necessary 
accuracy can be obtained are (A3) and (B3) 
The above results suggest that a circuit for driving separate piezoelectric 
elements needs a data selector circuit. Because the driving circuits 
arranged on the head substrate are required by the printed wires provided 
close to and in parallel with these circuits and each supplying pulse 
trains of different phases to select the pulse of the necessary phase 
according to the respective timing, they need a data selector circuit. 
With the present invention, by providing the data selector circuit, it is 
possible to realize a compact, simple driving circuit having the function 
of applying to the piezoelectric element array a burst pulse voltage with 
an accurate specific phase difference necessary for phased array scanning. 
One of the most typical examples of a compact driving circuit IC mounted on 
the head substrate is a thermal head driving IC. As shown in FIG. 22, the 
thermal head driving IC generally comprises an image data transfer shift 
register 31 also capable of input and output to another chip, a latch 32 
that takes in the image data transmitted via the shift register 31 in 
parallel, and a gate/driver 33 that controls the passing of a common pulse 
determining the timing and width according to the image data held in the 
latch 32. The heading dots (heating resistive elements) in the thermal 
head TPH are driven by the output pulse voltage from the gate/driver 33. 
To drive the piezoelectric element array in an ink-jet recording device 
using ultrasonic beams to effect phased array scanning, the gate/driver 33 
of FIG. 22 must be replaced with another circuit. As described above, to 
realize phased array scanning, it is desirable that the necessary pulse 
train should be selected from several consecutive pulse trains with 
different phases. Therefore, the final stage must be a data selector 
instead of a gate. Thus, the recording head driving IC in the ink-jet 
recording device using ultrasonic beams is composed of the shift register 
31, latch 32, and data selector/driver 34 as shown in FIG. 23. 
In FIG. 23, the shift register 31 transfers the serially inputted image 
data according to the clock pulse. The image data taken in the shift 
register 31 is transferred in parallel to the latch 32, which stores it 
temporarily. Data items corresponding to two adjacent piezoelectric 
elements in the image data temporarily stored in the latch 32 are supplied 
to the data selector/driver 34 as control codes S11, S21, S12, S22, S13, 
S23, S14, S24, . . . (where S14, S24 are not shown). A plurality of pulse 
trains 1, 2, 3, with different phases are inputted to the data 
selector/driver 34, which selects any one of the pulse trains 1, 2, 3, . . 
. according to the control signal code supplied from the latch 32. The 
pulse train is amplified to a suitable voltage level and applied to the 
discrete electrode of the corresponding piezoelectric element, thereby 
driving the piezoelectric element. By such an operation, phased array 
scanning can be effected. 
The operation of the recording head driving circuit will be explained 
concretely, taking an example of effecting linear scanning by using four 
adjacent piezoelectric elements as a unit as shown in FIGS. 2A to 3E in 
Embodiment 1-1 and driving them while shifting the phase. Explanation will 
be given as to a case where the control signal codes supplied from the 
latch 32 to the data selector/driver 34 are set at S11=0, S12=1, S21=1, 
S22=0, S13=1, S23=0, S14=0, and S24=1. 
For example, a voltage of burst wave with phase 1 leading 2 is applied to 
two outer ones of the four piezoelectric elements, and a voltage of burst 
wave with phase *2 is applied to the two inner piezoelectric elements, 
which forces the ultrasonic beams to converge in the main-scanning 
direction and strike the ink as shown in FIG. 2B. The data obtained by 
converting the original image data at an image data processing circuit 
(not shown) is inputted to the shift register 31 so that control codes 
S11, S21, S12, S22, S13, S23, S14, S24, . . . may take the above values in 
forming the recording pixels. When the original image data is 0, or when 
it is the data not forming a recording pixel, the image data inputted to 
the shift register 31 undergoes conversion at the image data processing 
circuit so that all of S11, S21, S12, S22, S13, S23, S14, S24, . . . may 
be 0. 
The driving circuit in Embodiment 1-10 is new in the following points: 
(1) The final stage is not a single gate, but a data selector (data 
selector/driver 34). 
(2) A plurality of signal wires for supplying pulse trains selected at the 
data selector/driver 34 are provided as common lines for the individual 
piezoelectric elements on the head substrate. 
(3) A multi-bit signal for controlling the data selector/driver 34 is 
inputted to the serial input line for inputting the image data to the 
shift register 31. 
As for the third feature, a parallel input may be used instead of the 
serial input of FIG. 23. The former has the advantage that the number of 
input/-output terminals on a driving IC is small, and the latter has the 
advantage that the transfer speed need not be reduced. 
With the recording head driving circuit, when the size of flying ink 
droplets must be controlled, use of a configuration of selecting the 
necessary pulse from consecutive pulse trains of different frequencies 
makes it easy to realize the control. 
The basic configuration of the present invention has been described. In 
embodiment 301 to Embodiment 3-3, the grouping of piezoelectric elements 
(vibrators) will be explained. 
Embodiment 2-1 
FIG. 24 is a perspective view of the recording head section in an ink-jet 
recording device according to an Embodiment 2-1 of the present invention. 
FIGS. 25A and 25B show the recording head of another ink-jet recording 
device in Embodiment 2-1. 
Embodiment 1-3 is characterized by an acoustic matching layer. 
In FIG. 24, a piezoelectric element array 10 is composed of a piezoelectric 
layer 13 of a long plate with a constant thickness, a common electrode 12 
formed on one side of the layer and a plurality of discrete electrodes 14 
formed on the other side of the layer. Namely, the piezoelectric layer 13, 
common electrode 12, and discrete electrodes 14 constitute a plurality of 
piezoelectric elements arranged one-dimensionally. One of ceramic such as 
zirconium titanate (PZT), macromolecular material such as a copolymer of 
vinylidene fluoride and ethylene trifluoride, a single crystal such as 
lithium niobate, and a piezoelectric semiconductor such as zinc oxide is 
selected and used for the piezoelectric layer 13 according to the 
frequency of ultrasonic beam and the size of element. The electrode 12 and 
electrodes 14 are formed on the piezoelectric layer by a thin filming 
technique such as evaporation of Ti, Ni, Al, Cu, or Au or sputtering, or 
by a baking technique based on printing using a screen of glass frits 
mixed with silver paste. 
The piezoelectric element array 10 is formed on a backing material 26. The 
piezoelectric element array 10 may be formed directly on the backing 
material by sputtering or CVD techniques and also may be formed via an 
adhesive layer 28 as shown in FIG. 25A. 
On the surface of the common electrode 12 opposite to the piezoelectric 
layer 13, an acoustic matching layer 27 is formed. The acoustic matching 
layer 27 matches the piezoelectric element array 10 with ink acoustically. 
The acoustic impedance of the matching layer is set at a value near the 
square root of the product of the acoustic impedance of the piezoelectric 
layer 13 and that of ink. Practically, epoxy resin, a mixture of epoxy 
resin and fiber, or a mixture of epoxy resin and aluminum or tungsten 
powder is used. 
Materials for an acoustic matching layer-cum-acoustic lens 11" include, in 
addition to epoxy resin, resin material such as ethylene resin, propylene 
resin, styrene resin, methyl methacrylate resin, polyvinyl chloride, 
polyvinylidene chloride, polyvinyl acetate, styrol resin, cellulosic 
resin, imide resin, amide resin, fluoride plastic, silicon resin, 
polyester, polycarbonate, polybutadiene-type resin, nylon, polyacetal, 
urethane resin, phenol resin, melamine resin, or urea resin, and their 
copolymer resin. They also include rubber material such as polybutadiene 
rubber, natural rubber, or olefin rubber, and an inorganic compound such 
as various types of glass material, silicon, or its compound. They further 
include metal material such as aluminum, tin, lead, titanium, zinc, brass, 
or zirconium. 
On the basis of the Fresnel zone theory, grooves are further made in the 
acoustic matching layer 27, which then also serves as an acoustic lens, 
means for forcing the ultrasonic beans from the piezoelectric element 
array 10 to converge in the direction (the sub-scanning direction) 
perpendicular to the array direction (the main-scanning direction) of the 
piezoelectric element array 10. The thickness t of the acoustic matching 
layer-cum-acoustic lens 11" is expressed as t=.lambda.m.times.(2n+1)/4 as 
shown in equation (1), where n is an integer and Am is the wavelength of 
ultrasonic wave in the acoustic matching material. 
In the case of a Fresnel lens, the thickness t of the acoustic matching 
layer-cum-acoustic lens 11"0 of FIG. 24 has two types: the thickness t1 of 
a portion without slits and the thickness t2 of a portion with slits. As 
shown in equation (3), the depth d of the slits in the Fresnel lens is 
expressed as d=1/{2(1/.lambda.i-1/.lambda.m)}. Therefore, it is preferable 
that each of the thickness t1 of a portion without slits and the thickness 
t2 (t2=t1-d) of a portion with slits should meet equation (1), or not meet 
equation (2). From equation (2) and equation (3), the ratio of the 
wavelength .lambda.m in the acoustic matching material to the wavelength 
.lambda.i of ultrasonic wave in ink, or the ratio Vm/Vi of the sound speed 
Vm in the acoustic matching material to the sound speed Vi in ink is in 
the range given by the following expression: 
EQU {(2n+3)/(2n+1)}&lt;(Vn/Vi)&lt;{(2n+1)/(2n-1)} (4) 
Under this condition, a Fresnel lens is realized which provides acoustic 
matching, prevents the total reflection of ultrasonic waves at the lens 
interface, and has a high transmission efficiency of ultrasonic waves. 
Furthermore, when the material for the acoustic matching layer-cum-acoustic 
lens where the sound speed Vm in the range given by equation (4) is 
nonresistant to the solvent contained in the ink, a protective film may be 
formed on the lens surface using a material resistant to the solvent. It 
is desirable that the protective film should have such a thickness as does 
not prevent ultrasonic waves from traveling and converging in ink and 
maintain the surface state that prevents air bubbles contained in ink from 
adhering to the surface. For example, material such as polyimide may be 
used for the protective film. 
In the ink pod 15, an ink chamber getting narrower gradually so as to wrap 
the passage of ultrasonic beams from the piezoelectric element array 10 is 
formed on the acoustic matching-cum-acoustic lens 11". The ink chamber is 
filled with liquid ink 18. The driving IC 21 is formed on the backing 
material 26 and connected to the common electrode 12 and discrete 
electrodes 14 via a wiring pattern (not shown). 
In the present embodiment, the piezoelectric element array 10 is driven by 
the driving IC 21 in such a manner that if the total number of 
piezoelectric elements constituting the piezoelectric element array 10 is 
N and the number of piezoelectric elements simultaneously driven is n, the 
first to n-th piezoelectric elements will be grouped with a specific phase 
difference or on the basis of the Fresnel diffraction theory so that the 
ultrasonic beams may focus on the liquid surface of the ink, and one end 
is shifted by a half-wave length and driven. Then, the positions of the 
piezoelectric elements simultaneously driven are moved by one element and 
the second to (n+1)th piezoelectric elements are driven. A similar 
operation is repeated until the (N-n+1)th to N-th piezoelectric elements 
are driven. In scanning, a shift of more than one element may be used in 
place of a shift of a single piezoelectric element. Furthermore, the 
piezoelectric elements simultaneously driven are not restricted to one 
group in the total elements and may belong to two or more groups. 
A more concrete example according to an Embodiment 2-1 of the present 
invention will be explained. 
A PZT piezoelectric ceramic plate with a relative permittivity of 2000 was 
used as the piezoelectric layer 13, whose resonance frequency was 
determined to be 20 MHz (for a thickness of 100 .mu.m). A Ti/Ni/Au 
electrode was formed on both sides of the piezoelectric ceramic plate by 
sputtering to a thickness of 0.05 .mu.m, 0.05 .mu.m, and 0.2 .mu.m in that 
order, followed by a polarizing process under an electric field of 2 
kV/mm. Thereafter, by etching the electrode on one side of the 
piezoelectric layer 13, discrete electrodes 14 were formed so that the 
width of a piezoelectric element might be 120 .mu.m and the distance 
between electrodes be 30 .mu.m (the arrangement pitch of discrete elements 
be 150 .mu.m). The length of the electrode in the sub-scanning direction 
was 5 mm. 
Then, The acoustic matching layer-cum-acoustic lens 11" was produced using 
a material whose acoustic impedance was 6.times.10.sup.6 Kg/m.sup.2 s by 
mixing epoxy resin with aluminum powder for acoustic matching material. 
The sound speed in the acoustic matching material is 3100 m/s, about twice 
the sound speed in ink. After the lens had been bonded to the resinous 
backing material 26 with epoxy resin, the ink pod 15 was positioned as 
shown in FIG. 24. Then, the driving IC 21 was connected, which completed 
an ink-jet head. 
As a comparison example, by working glass into a concave, an ink-jet head 
that forces ultrasonic beams to converge in the sub-scanning direction was 
produced without using an acoustic matching layer-cum-acoustic lens. 
With Embodiment 2-1, a resolution of about 200 dpi was achieved and ink was 
able to fly efficiently. With the comparison example, however, the 
resolution was about 150 dpi at most and an ink droplet sometimes did not 
fly even if a 1.5-fold driving signal voltage was applied. 
While in Embodiment 2-1, the acoustic matching layer-cum-acoustic lens 11" 
has a single layer, it may have more layers. 
As described above, with Embodiment 2-1, by forming an acoustic matching 
layer-cum-acoustic lens formed of the same material on the piezoelectric 
element array, the ultrasonic beams can be radiated without being 
reflected in the ink. Therefore, it is possible to force the ultrasonic 
beams to converge effectively on the liquid surface of the ink, thereby 
squirting an ink droplet efficiently. Furthermore, by the electronic 
focusing technique or a driving technique based on Fresnel-type grouping, 
an ink droplet can be forced to fly vertically, enabling high-resolution 
recording. 
Embodiment 2-2 
A method of manufacturing the acoustic matching layer-cum-acoustic lens 11" 
used in Embodiment 2-1 will be explained. 
The Fresnel lens provided on the piezoelectric element array has an 
irregular cross section. If the wavelength of ultrasonic wave is .lambda., 
ultrasonic beans can converge provided that, for example, the difference 
in height between the projected portion and the recessed portion is 
.lambda./2, the height of the projected portion is 5.lambda./4, and the 
height of the recessed portion is 3.lambda./4. For example, when PZT with 
a relative permittivity of 2000 is used for the piezoelectric layer and 
the ultrasonic wave frequency is determined to be 7.5 MHz and the height 
of the projected portion of the Fresnel lens is determined to be 
3.lambda./4 in a low driving frequency region, the height of the projected 
portion will be 300 .mu.m and the height of the recessed portion will be 
100 .mu.m. In this case, the accuracy of the height of the projected 
portion and that of the recessed portion required for the ultrasonic beams 
to converge sufficiently is within .+-.10%. 
The projected portion needs a work accuracy of .+-.30 .mu.m and the 
recessed portion requires a work accuracy of .+-.10 .mu.m. In this range, 
the necessary work accuracy can be achieved easily by, for example, 
cutting a molded piece of epoxy resin into a Fresnel lens and laminated 
the lens above the piezoelectric element array via an adhesive layer. 
At a higher driving frequency, for example, at an ultrasonic wave frequency 
of 200 MHz, when 
.lambda. is .lambda.=16 .mu.m and the height of the projected portion is 
5.lambda./4, the height of the projected portion will be 20 .mu.m, the 
height of the recessed portion will be 12 .mu.m, the work accuracy 
required at the projected portion will be .+-.2 .mu.m and the work 
accuracy required at the recessed portion will be .+-.1 .mu.m. Therefore, 
the cutting work of a molded piece cannot provide a sufficient accuracy. 
Furthermore, one of means for manufacturing resinous molded pieces with a 
work accuracy of a thickness difference of 1 .mu.m at the irregular 
portion is a method of molding thermoplastic resin using a nickel 
electroforming stamper used for compact discs as a mold. Although compact 
discs require a high accuracy for the difference between the projected and 
recessed portions, they need a thickness of 1 mm 10% at best. In constant, 
the Fresnel lens requires a high accuracy for the height of the irregular 
portion and sometimes has a 300-mm-long shape extending lengthwise. With a 
molding method used for compact discs, it is difficult to control the 
height of the irregular portion and molding cannot be effected at a high 
accuracy for the lengthwise thickness difference. 
With the present embodiment, in a method of manufacturing resinous molded 
pieces to which a pattern is transferred using a metal mold on whose inner 
mold an reversed-lens-shaped stamper having a transfer pattern with a 
plurality of projecting parallel tracks is mounted, by forming resin 
relief grooves parallel to the projecting tracks and causing resin to flow 
in the direction perpendicular to the projecting tracks to transfer a 
pattern, it is possible to provide a method of manufacturing a transfer 
resin sheet whose irregular thickness and lengthwise thickness area 
controlled at a high accuracy. Furthermore, this method provides a resin 
sheet having a highly accurate lens pattern. Additionally, by providing a 
piezoelectric element array on the outer mold of the metal mold, an 
acoustic matching layer-cum-acoustic lens is formed of resin integrally on 
the piezoelectric element array. 
FIGS. 26A and 26B are perspective views of the recording head section where 
an acoustic matching layer-cum-acoustic lens 11" associated with 
Embodiment 2-2 are formed of resin integrally on the piezoelectric element 
array 10. An enlarged view of the irregularity of the lens 11" is also 
shown in the figure. 
The ink-jet head comprises: a piezoelectric element array 10 where a common 
electrode 12 of a 1-.mu.m-thick tungsten film is formed on one side of a 
piezoelectric element layer 13 of a 30-.mu.m-thick sintered PZT for 
.lambda.=16 .mu.m and discrete electrodes 14 of a 1-.mu.m-thick aluminum 
film with a pattern of a width of 40 .mu.m and a spacing of 20 .mu.m is 
formed on the other side of the layer; an acoustic matching 
layer-cum-acoustic lens 11" of epoxy resin with a height of 20 .mu.m .+-.1 
.mu.m at the projected portion, a height of12 .mu.m*1 .mu.m at the 
recessed portion, a length of 300 mm.+-.10 .mu.m across the longitudinal 
side, and a 10-mm-thick rubber backing material 26. 
Explained next will be a method of integrally forming the piezoelectric 
element array 10 and the acoustic matching layer-cum-acoustic lens 11" in 
the ink-jet head. FIG. 27 diagrammatically shows a manufacturing apparatus 
for injecting resin at a reduced pressure into a mold for forming a 
resinous sheet serving as an acoustic matching layer-cum-acoustic lens 11" 
having a highly accurate transfer pattern (irregular pattern) on the 
piezoelectric element array 10 through injection of uncured epoxy resin. 
FIG. 28 is a sectional view of the metal mold. 
The mode of FIG. 28 will be explained. A nickel electroforming stamper 26a 
(not shown in detail) on whose surface a plurality of 8-.mu.m-high, 
350-mm-long projecting tracks are formed is installed on a movable support 
26c, the inner mold of the metal mold, by a stamper clamp. In the movable 
support 26c, a relief groove 26d is made along the longitudinal side of 
the projecting track. Pressure reducing and increasing holes 26e and resin 
injecting inlets (not shown) are made in several places in the relief 
groove 26d. On the fixed support 26, the outer mold of the metal mold, the 
piezoelectric element array 10 is secured to a projecting pedestal 26f and 
a stopper 26g is formed. 
After the movable support 26c is moved until it hits the stopper 26g and 
the inside of the mold is reduced in pressure by a pressure-reducing pump 
41 via a pressure-reducing tank 42, a pressure reducing/increasing valve 
is closed to a medium level, a resin valve 44 is opened, and then a 
constant amount of resin is poured from a resin tank 45. At this time, 
since resin flows in the direction perpendicular to the projecting pattern 
toward the relief groove 26d in FIG. 27, resin can be poured uniformly 
into the inside of the fine recessed pattern without variations in the 
thickness along the longitudinal side. 
Then, the resin valve 44 is closed and the resin valve 44 and pressure 
reducing/increasing valve 43 are leaked. In this state, after the epoxy 
resin is cured by raising the temperature of the mold to 250.degree. C., 
the pressure reducing/increasing valve 43 is switched and the pressure is 
raised to about 2 to 10 kg/cm.sup.2 by a compressor 46. Then, the mold is 
opened while the resin is being stripped from the movable support 26c, the 
inner mold. Then, the piezoelectric element array 10 and the resinous 
sheet formed on the array are taken out and cut off into a desired shape, 
thereby producing a piezoelectric element array with an acoustic matching 
layer-cum-acoustic lens shown in FIGS. 26A and 26B. 
Embodiment 2-3 
FIGS. 29A and 29B show another embodiment in which a piezoelectric element 
array with an acoustic matching-cum-acoustic lens is formed using a resin 
film for .lambda.=16 .mu.m. FIG. 29A is an enlarged view of the 
electroforming stamper 26a of FIG. 28 and part of the piezoelectric 
element array 10 coated with a resin film 29a. FIG. 29B is an enlarged 
view of an area where a resinous sheet 29b is formed by moving the movable 
support 26c of FIG. 28 and transferring the pattern of the electroforming 
stamper 26a to the resin film 29a. 
For the electroforming stamper 26a, a transfer pattern is prepared on whose 
surface a plurality of projecting parallel tracks that have a rectangular 
cross section and have a height in rectangle of .lambda./2=8 .mu.m from 
the main plane, are formed. The stamper is mounted on the movable support 
26c. To the projecting pedestal 26f of the fixed support 26, the 
piezoelectric element array 10 has been secured temporarily. On the array, 
a polycarbonate resin film 29a with a thickness of about 20 .mu.m is 
coated. 
Then, at the same time that the movable support 26c is moved to the 
position of the stopper 26g mounted on the fixed support 26 and adjusted 
so that the distance of w=3.lambda./4 between the projecting portion of 
the projecting stamper 26a and the piezoelectric element array 10 may be 
12 .mu.m, the temperature of the mold is raised to 180.degree. C. while 
the pressure in the mold is being decreased by the pressure reducing pump 
41, thereby melting the resin film 29a. Because the melted resin flows in 
the direction perpendicular to the projecting pattern toward the relief 
groove 26d, the resin can be poured thoroughly into the inside of the fine 
recessed pattern without variations in the thickness along the 
longitudinal side. The surplus resin is forced to flow in the direction 
perpendicular to the projecting pattern, thereby thoroughly filling the 
resin in the inside of the fine recessed pattern without variations in the 
thickness along the longitudinal side. In this state, the temperature of 
the mold is cooled down below the heat distortion temperature to cure the 
resin, thereby forming a resin sheet 29b. Thereafter, the pressure is 
applied from the compressor 46. While the resin sheet 29b is being 
stripped from the inner mold, the metal mold is opened and a piezoelectric 
element array with an acoustic matching layer-cum-acoustic lens is taken 
out. By cutting the array into a desired shape, a piezoelectric element 
array with an acoustic matching layer-cum-acoustic lens shown in FIGS. 26A 
and 26B are produced. 
Embodiment 2-4 
An embodiment where a piezoelectric element array with an acoustic matching 
layer-cum-acoustic lens is formed using application of resin, will be 
explained. 
An electroforming stamper 26a is prepared which has a transfer pattern on 
whose surface a plurality of projecting parallel tracks that have a 
rectangular cross section and have a height in rectangle of .lambda./2 8 
.mu.m from the main plane, are formed. The stamper is mounted on the 
movable support 26c. To the projecting pedestal 26f of the fixed support 
26, the piezoelectric element array 10 has been secured temporarily. On 
the array, an uncured polycarbonate resin film with a thickness of about 
10 .mu.m is applied to form a resin coating layer. 
Then, at the same time that the movable support 26c is moved to the 
position of the stopper 26g mounted on the fixed support 26 and adjusted 
so that the distance of w=.lambda./4 between the projecting portion of the 
projecting stamper 26a and the piezoelectric element array 10 may be 4 
.mu.m, the pressure in the mold is decreased by the pressure reducing pump 
41. This allows the melted resin to flow in the direction perpendicular to 
the projecting pattern toward the relief groove 26d, so that the resin is 
poured thoroughly into the inside of the fine recessed pattern without 
variations in the thickness along the longitudinal side. The surplus resin 
is forced to flow in the direction perpendicular to the projecting 
pattern, thereby thoroughly filling the resin in the inside of the fine 
recessed pattern without variations in the thickness along the 
longitudinal side. In this state, the temperature of the mold is raised to 
250.degree. C. to cure the epoxy resin. Thereafter, the pressure is 
applied from the compressor 46. While the resin sheet is being stripped 
from the inner mold, the metal mold is opened and a piezoelectric element 
array with an acoustic matching layer-cum-acoustic lens is taken out. By 
cutting the array into a desired shape, a piezoelectric element array with 
an acoustic matching layer-cum-acoustic lens shown in FIGS. 26A and 26B 
are produced. 
While in Embodiment 2-2 to Embodiment 2-4, the projecting pedestal 26f is 
provided on the fixed support 26, to which the piezoelectric element array 
10 is secured temporarily, the piezoelectric element array may be 
temporarily secured directly on the fixed support 26 without the 
projecting pedestal 26f, according to the dimensions and shape of the 
resin sheet. In these embodiments, the resin is mixed with filler such as 
metallic oxide or metallic nitride so that the thermal expansion 
coefficient of the resin may be closer to that of the mold. Taking into 
account the difference in thermal expansion coefficient between the resin 
and the mold according to the inclusion rate of filler, the recessed 
portion of the electroforming stamper 26a may be made a little larger so 
that the volume of uncured or melted resin poured in the recessed portion 
of the electroforming stamper 26a may be 101% to 106% of that of the size 
after shaping. 
The methods explained in Embodiment 2-2 to Embodiment 2-4 may be applied 
not only to the manufacture of piezoelectric element arrays with an 
acoustic matching layer-cum-acoustic lens, but also to a case where an 
acoustic lens composed of a Fresnel lens is provided separately from an 
acoustic matching layer. 
As described above, with Embodiment 2-2 to Embodiment 2-4, when a resinous 
molded piece on which a pattern is transferred is produced using a metal 
mold on whose inner mold a stamper having a transfer pattern on which a 
plurality of projecting parallel tracks reverse to the irregularity of the 
Fresnel lens acting as an acoustic lens are formed, is mounted, a transfer 
resin sheet whose irregularity thickness and the thickness along the 
lengthwise side are controlled at high accuracy can be obtained easily by 
forming resin relief grooves parallel to the projecting tracks and 
allowing the resin to flow in the direction perpendicular to the 
projecting tracks to transfer the pattern. Therefore, even when the shape 
and size of the acoustic lens get finer and strict size accuracy is 
required, the requirements can be met. In addition, the method may be 
applied to a case where the piezoelectric element array is driven at high 
frequencies. 
Furthermore, by providing an piezoelectric element array on the outer mold 
of the metal mold, it is easy to produce a piezoelectric element array 
with an acoustic lens where the acoustic lens composed of a Fresnel lens 
is formed of resin integrally on the piezoelectric element array, or a 
piezoelectric element array with an acoustic matching layer-cum-acoustic 
lens. In this case, since an adhesive layer between the piezoelectric 
element array and the acoustic lens is not necessary, it is possible to 
produce the size and shape of the resin region laminated on the 
piezoelectric element array at higher accuracy. 
Embodiment 3-1 
Since the primary configuration of Embodiment 3-1 is the same as that of 
Embodiment 1-1, the drawing and explanation of it will not be given. Using 
FIGS. 30A and 30B, the operation of Embodiment 3-1 will be described. 
Embodiment 3-1is characterized in that piezoelectric elements are divided 
into a first group and a second group and driving signals of opposite 
phases (e.g., 0 phase and .pi. phase) are applied to the first group and 
the second group. 
The operation of performing linear scanning in the main-scanning direction, 
the direction in which the piezoelectric elements are arranged in the 
piezoelectric element array 10, by phased array scanning. As in Embodiment 
1-1, for simplicity, it is assumed that four piezoelectric elements forms 
one group (a piezoelectric element group), which is driven simultaneously. 
The operation of effecting linear scanning by shifting the positions of 
the piezoelectric element groups one by one will be explained. 
A voltage of burst wave composed of an alternating-current voltage of 
specific frequency or a pulse train is applied to the discrete electrodes 
14.sub.1 to 14.sub.4 of the four piezoelectric elements as a driving 
signal. As in Embodiment 1-1, the frequency of the driving signal must be 
set so that at least the wavelength of ultrasonic wave in the ultrasonic 
interference layer 11 (also used as an acoustic matching layer) may be 
larger than the pitch on the piezoelectric element array. Furthermore, the 
thickness of the ultrasonic interference layer 11 must be less than a 
specified value. To obtain the necessary resolution for a printer, the 
frequency of driving signal must be in the range of several tens MHz to 
several hundreds MHz. 
Under such conditions, two inner ones of the four piezoelectric elements 
are determined to be a first group, and the two outer ones are determined 
to be a second group. Then, a 2-phase driving signal of opposite phases, 0 
phase and .pi. phase, (a voltage of burst wave composed of an 
alternating-current voltage of specific frequency or a pulse train) is 
applied to the piezoelectric elements of the first and second groups. 
The number of piezoelectric elements simultaneously driven (referred to as 
the number of elements simultaneously driven) required for ink to be 
forced to fly in the form of a droplet is practically 10 to 100. These 
piezoelectric element groups are grouped so as to correspond to the 
2-phase driving signal of 0 phase and .pi. phase. The grouping is 
determined by the width and pitch determined from the focal length and 
wavelength on the basis of the concept of the Fresnel zone plate. Then, 
the piezoelectric elements arranged at regular intervals are grouped 
according to the determined width and pitch. For example, when the 
piezoelectric elements 13 (or discrete electrodes 14) are arranged with a 
pitch of 50 .mu.m, grouping is effected at the maximum error of 25 .mu.m. 
The details of the grouping will be explained later. 
One know method is to arrange piezoelectric elements according to the width 
and pitch of piezoelectric elements. When piezoelectric element arrays are 
arranged at regular intervals, one know method is to closely set the 
driving delay time difference given to the piezoelectric element groups 
simultaneously driven, as in phased array scanning in an ultrasonic 
diagnostic apparatus. With the present invention, however, since whether 
an ink droplet is squirted or not has only to be determined, even if the 
piezoelectric elements arranged at regular intervals are divided into two 
groups and driven by a 2-phase driving signal of 0 phase and .pi. phase, 
the ultrasonic beams can be forced to converge on a single point to 
control the flying of an ink droplet. This has been confirmed as a result 
of the experiments conducted by the inventors. It goes without saying that 
the smaller the pitch of piezoelectric elements, the fewer errors and the 
higher the convergence efficiency. This enables the piezoelectric element 
array 10 arranged at regular intervals to produce a lens effect in the 
arranging direction (the main-scanning direction). Furthermore, electronic 
scanning of ultrasonic beams can be realized easily by changing grouping 
sequentially. In the ultrasonic interference layer 11, however, the 
ultrasonic beams do not converge in the direction (or the sub-scanning 
direction) perpendicular to the array direction. 
In this embodiment, the Fresnel zone plate 16 is provided and the 
ultrasonic beams arrived at the interface with the ink chamber undergo a 
lens effect that forces the beams to converge centripetally in the 
direction (or the sub-scanning direction) perpendicular to the array 
direction, by means of the Fresnel zone plate 16. Therefore, the 
convergence in the main-scanning direction starts from inside the 
ultrasonic interference layer 11 and the convergence in the sub-scanning 
direction takes place only in the ink 18 in the nozzle substrate 15. 
The ultrasonic beams are forced to focus on the surface of ink remaining 
still due to surface tension at the slit opening in the top surface of the 
nozzle substrate 15 in the main-scanning direction and the sub-scanning 
direction. The pressure of the ultrasonic beams thus converged causes an 
ink droplet 19 to fly from the liquid surface of the ink 18 as shown in 
FIGS. 3A to 3E, thereby recording an image on a recording medium such as 
recording paper (not shown). 
By dividing and driving the piezoelectric element array 10 as described 
above, the following problem can be solved. 
The phased array method is characterized in that the convergence position 
of ultrasonic beam on the liquid surface can be controlled arbitrarily by 
controlling the phases of a plurality of beams and a plurality of 
ultrasonic wave sources need not be changed with respect to the 
convergence position of ultrasonic beam. In an ink-droplet generating 
mechanism that forces ultrasonic beams to converge to generate an ink 
droplet, however, it is found that an ink droplet flies in the direction 
in which ultrasonic beams converge. For example, experiments showed that 
when an ultrasonic beam at an angle of several degrees to the direction 
perpendicular to the ink liquid surface was forced to converge on the 
liquid surface of ink, the droplet flied in the direction of the angle. 
Specifically, when the phased array method is used, the flying angle of an 
ink droplet changes depending on the position on which the ultrasonic beam 
is forced to converge, with the result that the flying direction of the 
ink droplet from the liquid surface is at a specific angle to the vertical 
direction. This means that pixels with a different pitch are formed on 
recording paper. Therefore, to maintain the pitch of pixels on recording 
paper, it is necessary to predict the angle at which an ink droplet flies 
and perform phase control of the ultrasonic generating elements. The 
control is required to control the phase continuously at high accuracy. 
Such a circuit has the disadvantages of being very complex in 
configuration and needing a very large memory capacity to store a large 
volume of data for correction. 
In Embodiment 3-1, however, since the size of ink droplet is always kept 
constant as described above and complex processes including control of the 
flying direction of ink droplet are not needed, the device can be realized 
using a simpler configuration. 
Now, grouping at the time of driving the piezoelectric element array 10 
will be explained in detail. 
As well known in the field of optics, the Fresnel zone plate is such that 
in the case of a two-dimensional example, rings consisting of concentric 
circles whose radius Rm is proportional to the square root of integer m 
are arrange in such a manner that first rings that allow light to pass 
through without a phase shift are alternated with second rings that shift 
the phase of light by a half-wave length, thereby causing the light from 
each ring to converge at a point with the same phase. The principle of the 
Fresnel zone plate can be applied to ultrasonic waves that present wave 
motion like light. Actually, the aforementioned Fresnel zone plate 16 is 
constructed as a one-dimensional Fresnel zone plate, making use of the 
principle. In this case, a first region that allows ultrasonic waves to 
pass through with no phase shift corresponds to the first ring and a 
second region that shifts the phase of ultrasonic wave by a half-wave 
length corresponds to the second ring. 
With the present invention, by determining a method of driving the 
piezoelectric element array 10 where elements are one-dimensionally 
arranged at regular intervals, the piezoelectric element array 10 is 
forced to function equivalently as one-dimensional Fresnel zone plate. 
FIGS. 31A and 31B show an example of rounding off the distance Rm from the 
center of the Fresnel zone plate with respect to the arranging pitch (50 
.mu.m) on the piezoelectric element array 10 (FIG. 36A) and determining 
the phase of a driving signal supplied to each element in the 
piezoelectric element array 10 on the basis of the rounded-off value Rr 
(FIG. 36B) in a case where the sound speed in ink (the same as the sound 
speed in water) is 1500 m/s, the frequency of driving signal is 100 MHz, 
the wavelength of ultrasonic wave in ink is 15 .mu.m, the focal length f 
of ultrasonic beam is 5 mm, the number N of elements simultaneously driven 
in the piezoelectric element array 10 is 32, and the arranging pitch P on 
the piezoelectric element array 10 is 50 .mu.m. 
When of 32 consecutive piezoelectric elements to be simultaneously driven, 
those in the central portion of the arrangement (in this example, ten 
elements marked with element numbers 12 to 21) are determined to be a 
first group, and those located on both sides of the first group (in this 
example, three elements marked with element numbers 9 to 11 and another 
three elements marked with element numbers 22 to 24) are determined to be 
a second group. A 0-phase driving signal is supplied to the first group of 
piezoelectric elements and a .pi.-phase driving signal is supplied to the 
second group. 
FIG. 32 shows how grouping is effected in FIGS. 31A and 31B and a cross 
section of an ideal Fresnel zone plate. From FIG. 32, it can be seen that 
by grouping the piezoelectric element array, application of a 0-phase and 
.pi.-phase driving signals produces almost the same effect as the Fresnel 
zone plate. FIG. 33 shows the relative beam intensity at the depth of the 
focus (the liquid surface of ink) at each distance from the center when 
grouping is effected as shown in FIG. 32. From FIG. 33, it is obvious that 
the relative beam intensity is by far the highest in the central portion 
of the piezoelectric element array. Therefore, by grouping the 
piezoelectric elements in Embodiment 3-1, ultrasonic waves can be forced 
to converge effectively. 
To effect phased array scanning, such grouping is a necessary and minimum 
condition. In Embodiment 3-1, grouping is effected in such a manner that 
of the piezoelectric elements outside the second group, those marked with 
element numbers 8 and 25 are determined to be a first group, those marked 
with element numbers 6 and 7 and element numbers 26 and 27 outside this 
first group are determined to be a second group, those marked with element 
numbers 5 and 28 outside this second group are determined to be the first 
group, those marked with element numbers 4 and 29 outside this first group 
are determined be the second group, . . . A 0-phase driving signal is 
applied to the piezoelectric elements of the first group and a .pi.-phase 
driving signal is applied to the piezoelectric elements of the second 
group. By doing this, the convergence efficiency of ultrasonic beam can be 
improved. 
By effecting grouping in a group of piezoelectric elements simultaneously 
driven in the piezoelectric element array 10, applying a 0-phase and 
.pi.-phase driving signals to the individual piezoelectric elements in the 
first and second groups, shifting the position of the group of 
piezoelectric elements simultaneously driven by, for example, one element 
at a time in the arranging direction of the piezoelectric element array 
10, and repeating the same driving operation, the ultrasonic beams can be 
forced to converge on the liquid surface of ink 18 and the converging 
point can be moved linearly in the arranging direction of the 
piezoelectric element array 10 (in the main-scanning direction). 
By doing as described above, the present invention only requires a 2-phase 
driving signal, which can be generated using an inversion amplifier, 
whereas conventional phased array scanning requires a driving signal 
having a phase difference phase-controlled accurately. 
Embodiment 3-2 
The configuration of the recording head section and the principle of 
squirting ink in Embodiment 3-2 are the same as those in FIG. 5 and FIG. 6 
in Embodiment 1-2, so that the drawing and explanation of them will not be 
given and what is the difference between Embodiment 1-2 and the present 
embodiment will be explained. 
As in Embodiment 1-2, in Embodiment 3-2, it is found that the energy 
efficiency for squirting an ink droplet is decreased and the uniformity of 
ink droplet is degraded. Embodiment 3-1 is characterized by improving 
these factors. 
Like Embodiment 1-2, Embodiment 3-2, however, has the advantage of forming 
an ink passage with a large cross section, because the concave lens 
surface becomes an ink chamber as it is. Therefore, only when high-speed 
recording is required, Embodiment 3-2 produces the effect of supplying a 
sufficient amount of ink to deal with the speed, slowing the change of ink 
density due to evaporation of ink solvent, and making the nozzle less 
liable to clog up. 
Embodiment 3-3 
A piezoelectric element does not need as the ultrasonic generating elements 
of the present invention. Such embodiments are shown in Embodiment 3-4 and 
Embodiment 3-5. 
In Embodiment 3-3, the major configuration of the recording head section is 
the same as that of FIG. 1, the drawing and explanation of it will not be 
given. Embodiment 3-1 differs from Embodiment 1-2 in that magnetostrictive 
transducers separated by electrodes are used as ultrasonic generating 
elements and the transducers are arranged one-dimensionally to form an 
array. As in Embodiment 3-1, in Embodiment 3-3, grouping is effected, 
producing the same effect as the Fresnel zone plate. 
The magnetostrictive transducers 13 are such that they are formed of 
material such as Te.sub.0.3 D.sub.0.7 Fe.sub.2 or Te.sub.0.3 D.sub.0.7 
(Fe.sub.0.9 Mn.sub.0.1).sub.2 on the entire bottom surface or into belts 
by a film forming method capable of controlling the film thickness such as 
sputtering. On both ends of the magnetostrictive transducer 13, magnetic 
field applying elements (not shown) are provided. A permanent magnet, free 
from a power consumption problem and a heating problem, is suitable for 
the magnetic field applying elements. On the surface of the 
magnetostrictive transducer 13, discrete exciting coils 14 pairing with 
common electrodes 12 are formed with a pitch corresponding to the 
recording dots. The magnetostrictive transducer array may be such that 
island-shaped magnetostrictive transducers are formed with a pitch 
corresponding to the recording bits. The thickness of the magnetostrictive 
transducer 13 is designed to match with the wavelength of an ultrasonic 
wave used. 
The common electrode 12, magnetostrictive transducers 13, magnetic field 
applying element and exciting coil 14 constitute a magnetostrictive 
transducer array 10 serving as an ultrasonic generating element array. In 
the case of an actual ink-jet head, for example, a line head as long as 
the length of the A4 size sheet with a resolution of 600 dpi, about 5000 
magnetostrictive transducers are arranged in a line. In this case, the 
individual magnetostrictive transducers in the magnetostrictive transducer 
array 10 are arranged in a line at regular intervals determined by the 
required recording density. The remaining configuration is the same as 
that of Embodiment 1-1, so that the explanation of it will not be given. 
Using FIGS. 34A and 34B, the operation of Embodiment 3-3 will be explained, 
although part of the explanation will overlap with that of Embodiment 1-1. 
The operation of performing linear scanning in the main-scanning 
direction, the direction in which the magnetostrictive transducers are 
arranged in the magnetostrictive transducer array 10, by phased array 
scanning. As in Embodiment 1-1, for simplicity, it is assumed that four 
magnetostrictive transducers forms one group (a magnetostrictive 
transducer group), which is driven simultaneously. The operation of 
effecting linear scanning by shifting the positions of the 
magnetostrictive transducer groups one by one will be explained. 
A burst current composed of an alternating current of specific frequency or 
a pulse train is applied to the discrete exciting coils 14.sub.1 to 
14.sub.4 connected to four magnetostrictive transducers 14 as a driving 
signal. The frequency of the driving signal must be set so that at least 
the wavelength of ultrasonic wave in the ultrasonic interference layer 11 
(also used as an acoustic matching layer) may be larger than the pitch on 
the piezoelectric element array. Furthermore, the thickness of the 
ultrasonic interference layer 11 must be less than a specified value. To 
obtain the necessary resolution for a printer, the frequency of driving 
signal must be in the range of several tens MHz to several hundreds MHz. 
Under such conditions, two inner ones of the four magnetostrictive 
transducers are determined to be a first group, and the two outer ones are 
determined to be a second group. Then, a 2-phase driving signal of 
opposite phases, 0 phase and .pi. phase, (a burst current composed of an 
alternating current of specific frequency or a pulse train) is applied to 
the magnetostrictive transducers of the first and second groups. 
The number of magnetostrictive transducers simultaneously driven (referred 
to as the number of elements simultaneously driven) required for ink to be 
forced to fly in the form of a droplet is practically 10 to 100. These 
magnetostrictive transducer groups are grouped so as to correspond to the 
2-phase driving signal of 0 phase and .pi. phase. The grouping is 
determined by the width and pitch determined from the focal length and 
wavelength on the basis of the concept of the Fresnel zone plate. Then, 
the magnetostrictive transducers arranged at regular intervals are grouped 
according to the determined width and pitch. For example, when the 
magnetostrictive transducers in the magnetostrictive transducer array 10 
are arranged with a pitch of 50 .mu.m, grouping is effected at the maximum 
error of 25 .mu.m. The grouping is the same as that of the piezoelectric 
element array 10 in Embodiment 3-1, so that its explanation will not be 
given. 
By grouping the magnetostrictive transducer array 10 as described above and 
driving them with a 2-phase driving signal, the piezoelectric element 
array 10 arranged at regular intervals can produce a lens effect in the 
arranging direction (the main-scanning direction). Furthermore, electronic 
scanning of ultrasonic beams can be realized easily by changing grouping 
sequentially. In the ultrasonic interference layer 11, however, the 
ultrasonic beams do not converge in the direction (or the sub-scanning 
direction) perpendicular to the array direction. 
The ultrasonic beams arrived at the interface with the ink chamber undergo 
a lens effect that forces the beams to converge centripetally in the 
direction (or the sub-scanning direction) perpendicular to the array 
direction, by means of the Fresnel zone plate 16. Namely, the convergence 
in the main-scanning direction starts from inside the ultrasonic 
interference layer 11 (also used as an acoustic matching layer) and the 
convergence in the sub-scanning direction takes place only in the ink 18 
in the nozzle substrate 15. 
The ultrasonic beams are forced to focus on the surface of ink remaining 
still due to surface tension at the slit opening in the top surface of the 
nozzle substrate 15 in the main-scanning direction and the sub-scanning 
direction. The pressure of the ultrasonic beams thus converged causes an 
ink droplet 19 to fly from the liquid surface of the ink 18, thereby 
recording an image on a recording medium such as recording paper (not 
shown). 
As for a recording method, when ultrasonic beams are forced to converge on 
a dot using four magnetostrictive transducers as shown in FIGS. 35A to 
35E, division driving is effected in such a manner that one line is 
divided into four or more pieces and each piece is driven with a 1/4 or 
less timing. Since the concrete operation has been described in FIGS. 3A 
to 3E in Embodiment 1-1, a detailed explanation will be omitted. For the 
sake of explanation, the cooperating operation of four elements has been 
explained, there is no need of limiting the number of elements. Use of 
more elements to record one pixel makes smoother the wave surface of the 
ultrasonic beams converging centripetally and raises the energy density of 
the ultrasonic beams at the liquid surface of ink 18, thereby reducing 
variations in the ink droplet and reducing the driving current supplied to 
the magnetostrictive transducer array 10. 
Embodiment 3-4 
Since the configuration of the recording head section in Embodiment 3-4 is 
the same as that of Embodiment 3-3, the drawing and explanation of it will 
not be given. 
Referring to FIGS. 36A and 36B, the operation of an ink-jet head associated 
with Embodiment 3-4 will be explained. FIG. 36A is a sectional view taken 
along in the direction perpendicular to a magnetostrictive transducer 
array. FIG. 36B is a sectional view taken along in the direction along the 
magnetostrictive transducer array. FIG. 36A shows magnetic field applying 
means 14a that are provided on both sides of the magnetostrictive 
transducer 13 and applies a bias magnetic field to the magnetostrictive 
transducer 13. 
A voltage of burst wave composed of an alternating current of specific 
frequency (or a pulse train) is applied to part of the magnetostrictive 
transducer array 10, for example, to the discrete exciting coils 14.sub.1 
to 14.sub.4. The frequency of the applied alternating current is such that 
at least the wavelength of ultrasonic wave in the ultrasonic interference 
layer (an acoustic matching layer) is larger than the pitch of the sound 
wave sources (magnetostrictive transducers 13) in the array. When of the 
discrete exciting coils 14.sub.1 to 14.sub.4, the two inner ones 14.sub.2, 
14.sub.3 are applied with an alternating-current voltage, and the two 
outer ones are applied with a voltage of burst wave leading the inner two 
discrete exciting coils 14.sub.2, 14.sub.3 in phase (by a 1/4 phase in 
this embodiment), the ultrasonic beams interfere with each other as in 
Embodiment 3-3, thus producing a lens effect in the array direction (the 
main-scanning direction) in which the elements in the piezoelectric 
element array 10 are arranged. In the glass plate 1, however, the 
ultrasonic beams do not converge in the direction (or the sub-scanning 
direction) perpendicular to the array direction of the piezoelectric 
element array 10. 
The ultrasonic beams arrived at the interface with the ink 18 undergo a 
lens effect that forces the beams to converge centripetally in the 
direction (or the sub-scanning direction) perpendicular to the array 
direction of the piezoelectric element array 10, by means of the Fresnel 
zone plate 7. Namely, the convergence in the main-scanning direction 
starts from inside the glass plate 1 functioning as an acoustic matching 
layer (a sound interference layer) and the convergence in the sub-scanning 
direction takes place only in the ink 18. At this time, since the nozzle 
substrate 15 has been selected and set so that its thickness may agree 
with the focus, the ultrasonic beams are forced to focus on the surface of 
ink remaining still due to surface tension at the slit opening forming a 
nozzle. The pressure of the ultrasonic beams thus converged in the 
main-scanning and sub-scanning directions causes an ink droplet to fly 
easily from the liquid surface of ink, thereby recording a clear image on 
a recording medium without variations in the density. 
As described above, like Embodiment 3-3, the gist of Embodiment 3-4 is that 
four ultrasonic generating elements (magnetostrictive transducers) form 
one group, one line is division-driven with a 1/4 timing at a time, and 
the discrete exciting coils 14 are shifted in the main-scanning direction 
by linear scanning. 
While in Embodiment 3-4, one group consists of four magnetostrictive 
transducers to record one pixel, one group may consist of more 
magnetostrictive transducers, which prevents side lobe of the ultrasonic 
beams converging centripetally and raises the energy density, thereby 
reducing variations in the ink droplet and reducing the driving current 
supplied to the magnetostrictive transducer array. 
Furthermore, while in Embodiment 3-3 and Embodiment 3-4, the convergence 
position of the ultrasonic beams is set at the liquid surface facing the 
center of the set of ultrasonic generating elements grouped and a droplet 
is forced to fly straight in the direction perpendicular to the sound wave 
generating element group, the squirting position may be shifted by 
changing the timing for applying a voltage of burst wave, as described 
later. 
Embodiment 4 
The recording head section explained in Embodiment 3-1 to Embodiment 3-4 is 
constructed as a line scanning recording head that records one line at a 
time. The configuration of a scanning control section that controls the 
line scanning recording head to record an image will be explained using 
FIG. 37. 
Embodiment 4 employs a division driving method where one main scanning line 
is divided into a plurality of groups and scanning recording is effected 
to realize higher recording speeds. In the division driving method, an 
ultrasonic generating element array is divided into a plurality of (N) 
groups, and these individual groups are driven simultaneously to record N 
pixels at a time. Its recording speed is N times as fast as the case where 
no division driving is effected. FIG. 37 shows a case where the number N 
of divisions is 4. 
The scanning control section comprises an ultrasonic generating element 
array 10 (a piezoelectric element array 10 explained in Embodiment 3-1 and 
Embodiment 3-2 or a magnetostrictive transducer array 10 explained in 
Embodiment 3-3), a buffer driver group 51, a driving signal selector group 
52, data selectors 53.sub.1 to 53.sub.4, pointer scanning registers 
54.sub.1 to 54.sub.4, driving pattern scanning registers 55.sub.1 to 
55.sub.4, a pointer register 56, a pattern register 57, a clock control 
section 58, and an initial setting section 59. 
The number of elements in the ultrasonic generating element array 10 will 
be explained. 
When a thermal head used in an ordinary thermal recording method is used as 
a line scanning recording head, the number of pixels obtained in one line 
is the same as the number of heating elements in the head. With the 
present invention, however, linear scanning is effected by phased array 
scanning that repeats the operation of selecting a specific number of 
ultrasonic generating element groups in the ultrasonic element array 10 
where elements are arranged in lines and driving them simultaneously, 
while shifting the ultrasonic generating groups one by one in the 
arranging direction. Therefore, the total number of ultrasonic generating 
elements must be at least the number of elements equal to the sum of the 
number of elements for the recording width and the number of elements 
simultaneously driven needed for phased array scanning (the number of 
ultrasonic generating elements in one ultrasonic generating element 
group). 
The reason for this is that in phased array scanning, since the converging 
point of the ultrasonic beans is located on a line perpendicular to the 
element in the center of the side along which elements are arranged in the 
group of ultrasonic generating elements driven simultaneously, to force an 
ink droplet to fly as far as the positions corresponding to the right and 
left ends of the recording width of the recording sheet, as many 
ultrasonic generating elements as half the number of ultrasonic generating 
elements simultaneously driven in the group must be provided outside both 
of the right and left ends. The number of ultrasonic wave elements may, of 
course, be greater. Concretely, in the present embodiment, the number of 
elements in the ultrasonic generating element array 10 is set at 4992, the 
sum of the number of recording pixels in one line of A4 size with 600 dpi, 
4960, and the number of elements simultaneously driven, 32. 
A 2-phase driving signal is applied from the buffer driver group 51 between 
the common electrodes facing the discrete electrodes (or the discrete 
exciting coils) corresponding to the 4992 ultrasonic generating elements 
in the ultrasonic generating element array 10. The buffer driver group 51 
is composed of 4992 buffer drivers one-to-one corresponding to the 
individual elements in the ultrasonic generating element array 10. In a 
case where the ultrasonic generating elements are piezoelectric elements, 
a voltage of several tens V and a frequency of several hundreds MHz 
provide a sufficient capability for driving the ultrasonic generating 
elements. The buffer driver group 51 is supplied with a driving signal 
selected from three types of signal at the driving signal selector group 
52. 
FIG. 38 shows the structure of the driving signal selector group 52 in FIG. 
37. The driving signal selector group 52 is composed of n unit selectors 
42.sub.1 to 42.sub.n (n is the number of ultrasonic generating elements in 
the ultrasonic generating element array 10). These unit selector are 
connected to the respective buffer drivers in the buffer driver group 51 
on a one-to-one basis. The individual unit selectors 42.sub.1 to 42.sub.n 
receive three types of input signals, a 0-phase driving signal, a 
.pi.-phase driving signal, and a non-driving signal (a reference potential 
in the figure) as inputs A, B, and C, and select one of these three input 
signals according to two types of select signals, a 0-phase .pi.-phase 
select signal and a driving on/off select signal. The driving on/off 
select signal is generated from a recording signal and a pointer signal 
indicating an object of phased array at the data selectors 53.sub.1 to 
53.sub.4. 
The ultrasonic generating element array 10, buffer driver group 51, and 
driving signal selector group 52 basically include no structure for 
division-driving the ultrasonic generating element array 10. They are only 
for electronic linear scanning based on phased array scanning. Division 
driving is effected during scanning control. 
Using FIG. 39, a method of dividing the ultrasonic generating element array 
10 will be described. As shown in FIG. 39, in the ultrasonic generating 
element array 10, to cover 16 pixels at the right and left ends of the 
recording width corresponding to 4960 pixels, that is, the first to 16th 
pixels and the 4944th to 4960th pixels, as many elements as the number of 
elements simultaneously driven in phased array scanning, or 32 elements 
are allocated to both sides and sets of 16 elements are provided as cover 
blocks. 
Then, the ultrasonic generating element array 10 is divided into a first to 
44th groups. In the division, 4960 elements corresponding to the recording 
width are quadrisected and 1240 elements are determined to be the basic 
number of elements forming one group. The first and fourth groups on both 
sides are made of 1256 elements, the sum of the basic number of elements 
and the number of elements, 16, in the respective cover blocks L and R. By 
doing this, the connection between groups can be made reliably. The basic 
operation in the connection process will be explained with reference to 
the division arrangement of FIG. 39. 
In FIG. 39, the connection process is carried out at portions of the 
individual connection blocks as follows: at connection 1 at the right end 
of a first group, at connection 2 and connection 3 at both ends of a 
second group, at connection 4 and connection 5 at both ends of a third 
group, and at connection 6 at the left end of a fourth group. The number 
of elements in each connection block is 16, the same as that in cover 
blocks L and R. A recording operation by phased array scanning starts at 
the first pixel in the individual groups into which one line of recording 
pixels=4960 pixels is quadrisected, that is, the first pixel, the 1241st 
pixel, the 2481st pixel, and the 3721st pixel. In line with this, the 
first driven ultrasonic generating element group in each quadrisected 
group in the ultrasonic generating element array 10 is determined. 
Specifically, the first one of the recording pixels in one line is recorded 
by the 16 elements in cover block L of the first group and the 16 adjacent 
elements, a total of 32 elements; the 1241st pixel is recorded by the 16 
elements in connection 1 of the first group and the 16 adjacent elements 
in connection 2 of the second group, a total of 32 elements; the 2481st 
pixel is recorded by the 16 elements in connection 3 of the second group 
and the 16 adjacent elements in connection 4 of the third group, a total 
of 32 elements; and the 3721st pixel is recorded by the 16 elements in 
connection 5 of the third group and the 16 adjacent elements in connection 
6 of the fourth group, a total of 32 elements. Then, the 32 elements 
simultaneously driven in the ultrasonic generating element array 30 are 
shifted one by one and driven, which shifts the pixel to be recorded by a 
pixel at a time, effecting recording by phased array scanning. Finally, 
each group of one fourth of one line of recording pixels is shifted by 
1240 pixels, which completes recording one line. 
At the final stage of recording one line, the last pixel in each group of 
one fourth of one line of recording pixels is recorded as follows: the 
1240th pixel is recorded by the 16 elements in an element of the first 
group and connection 1, and the 15 elements in a element of the second 
group and connection 2, a total of 31 elements; the 2480th pixel is 
recorded by the 16 elements in an element of the second group and 
connection 3, and the 15 elements in an element of the third group and 
connection 4, a total of 31 elements; the 3720th pixel is recorded by the 
16 elements in an element of the third group and connection 5, and the 15 
elements in an element of the fourth group and connection 6, a total of 31 
elements; and the 4960th pixel is recorded by the 17 elements of the 
fourth group and 15 elements in cover block R adjacent thereto, a total of 
32 elements. 
The ultrasonic generating elements in the connection block set in each 
group in the ultrasonic generating element array cooperate with the 
ultrasonic generating elements in the block set in the adjacent group to 
record a pixel covered by the present group. Therefore, the connection 
block is controlled by the control blocks corresponding to two groups 
during the record scanning of one line. This is the basic connection 
process. The connection process is carried out by the data selector 43, 
pointer scanning register 54, and driving pattern scanning register 45 
shown in FIG. 37. 
FIG. 40 shows the structure of one of the data selectors 53.sub.1 to 
53.sub.4. The data selectors 53.sub.1 to 53.sub.4 perform data control 
including the process of connecting recording data (the image signals to 
be recorded). They receive six kinds of input signals: a pointer signal 
indicating the ultrasonic generating element group to be simultaneously 
driven in the ultrasonic generating element array, recording data C as the 
image signal to be recorded in the present group, recording data L and R 
as the image signals to be recorded in the groups on both sides, and a 
prebit input and a postbit input for activating the recording data in the 
groups on both sides. They output a driving on/off select signal to the 
driving signal selector group 52. The output section of each of the data 
selectors 53.sub.1 to 53.sub.4 is divided into three selector circuits 
63a, 63b, 63c according to the recording data to be dealt with. The 
selector circuits 63a, 63b, 63c carry out the following operation. 
The selector circuit 63b corresponds to the ultrasonic generating elements 
other than those in the connection block in the present group, and deals 
with only recording data C. 
The selector circuit 63a deals with either recording data L corresponding 
to the ultrasonic generating elements in the group scanning the pixel area 
previous to the pixel area covered by the present group from the input 
selector circuit 61, in a line of pixels, or recording data C 
corresponding to the ultrasonic generating elements in the present group. 
Recording data L is selected only when the pointer signal indicating the 
bottom-end ultrasonic generating element in the group scanning the 
previous pixel area is active. 
The selector circuit 63c deals with either recording data R corresponding 
to the group scanning the pixel area after the pixel area covered by the 
present group from the input selector circuit 62, in a line of pixels, or 
recording data C corresponding to the ultrasonic generating elements in 
the present group. Recording data R is selected only when the pointer 
signal indicating the top-end ultrasonic generating element in the group 
scanning the following pixel area is active. The pointer signal indicating 
the bottom-end ultrasonic generating element in the group scanning the 
previous pixel area is outputted as a prebit output signal and the pointer 
signal indicating the top-end ultrasonic generating element in the group 
scanning the following pixel area is outputted as a postbit output signal. 
FIG. 41 shows how the data selectors 53.sub.1 to 53.sub.4 are connected to 
each other. 
To each of the data selectors 53.sub.1 to 53.sub.4, a prebit output and a 
prebit input are connected and further a postbit output and a postbit 
input are connected. As for recording data items L, C, R inputted to the 
data selectors 53.sub.1 to 53.sub.4, the corresponding three or two data 
items of the four recording data item 1 to 4 transferred in parallel for 
each group are inputted. As seen from FIG. 41, the data selectors 53.sub.1 
to 53.sub.4 have the structure base on the operation of the data selectors 
53.sub.2 to 53.sub.3 for the second and third groups in the ultrasonic 
generating element array 10. Even for the data selectors 53.sub.1 to 
53.sub.4 for the first and fourth groups having cover blocks L, R at both 
sides in the ultrasonic generating element array 10, the same structure as 
that of the data selectors 53.sub.2 to 53.sub.4 can be used by 
inactivating the postbit input and prebit input (e.g., by placing them at 
a reference potential). 
The pointer scanning registers 54.sub.1 to 54.sub.4 of FIG. 37 will be 
explained. The pointer scanning registers 54.sub.1 to 54.sub.4 may be 
composed of serial-in, parallel-out shift registers, parallel-in, 
parallel-out shift registers, or parallel-serial-in, parallel-out shift 
registers. The number of stages of shift registers is determined to agree 
with the number of elements in each group in the ultrasonic generating 
element array 10. The parallel outputs of the pointer scanning registers 
54.sub.1 to 54.sub.4 pass through the data selectors 53.sub.1 to 53.sub.4 
and become select signals to the driving signal selector group 52. 
The operation of a parallel-in, parallel-out shift register will be 
explained. The pointer scanning registers 54.sub.1 to 54.sub.4 are the 
registers that scan the pointers indicating the ultrasonic generating 
elements to be active in phased array scanning. With the first timing in a 
recording operation of one line, the driving start pattern for each group 
in the ultrasonic generating element array 10 stored in the pointer 
register 56 in FIG. 37 is set initially at the initial setting section 59, 
and thereafter shift scanning is effected according to the scanning clock 
supplied via the clock control section 58. The initially set pattern in 
the pointer register 56 is determined by the driving start element set in 
each group in the ultrasonic generating element array corresponding to the 
beginning recording pixels, the first pixel, the 1241st pixel, the 2481st 
pixel, and the 3721st pixel. 
Specifically, the pattern is such that for the first pixel, the 16 elements 
in the cover block L of the first group and the 16 adjacent elements, a 
total of 32 elements, are active; for the 1241st pixel, the 16 elements in 
connection 1 of the first group and the 16 elements in connection 2 of the 
second group, a total of 32 elements are active; for the 2481st pixel, the 
16 elements in connection 3 of the second group and the 16 elements in 
connection 4 of the third group, a total of 32 elements are active; and 
for the 3721st pixel, the 16 elements in connection 5 of the third group 
and the 16 elements in connection 6 of the fourth group, a total of 32 
elements are active. 
The driving pattern scanning registers 55.sub.1 to 55.sub.4 are the 
registers indicating a 0-phase and .pi.-phase driving patterns for driving 
the active ultrasonic generating elements by a 0-phase and .pi.-phase 
driving signals. Like the pointer scanning registers 54.sub.1 to 54.sub.4, 
the driving pattern scanning registers may be composed of serial-in, 
parallel-out shift registers, parallel-in, parallel-out shift registers, 
or parallel-serial-in, parallel-out shift registers. 
The driving pattern is such that with the first timing in a recording 
operation of one line, the driving start 0/.pi. phase select pattern for 
each group in the ultrasonic generating element array 10 stored in the 
pattern register 56 is set initially at the initial setting section 59, 
and thereafter shift scanning is effected according to the scanning clock 
supplied via the clock control section 58. The initially set pattern in 
the pattern register 57 is determined by the driving start element set in 
each group in the ultrasonic generating element array 10 corresponding to 
the beginning recording pixels for a line of pixels, the first pixel, the 
1241st pixel, the 2481st pixel, and the 3721st pixel. 
Specifically, the pattern is formed by grouping the pixels using the width 
and pitch rounded off on the basis of the concept of the Fresnel zone 
plate in such a manner that for the first pixel, the 16 elements in the 
cover block of the first group and the 16 adjacent elements, a total of 32 
elements, are grouped; for the 1241st pixel, the 16 elements in connection 
1 of the first group and the 16 elements in connection 2 of the second 
group, a total of 32 elements are grouped; for the 2481st pixel, the 16 
elements in connection 3 of the second group and the 16 elements in 
connection 4 of the third group, a total of 32 elements are grouped; and 
for the 3721st pixel, the 16 elements in connection 5 of the third group 
and the 16 elements in connection 6 of the fourth group, a total of 32 
elements are grouped. Here, the recording data supplied to four groups in 
units of 32 elements has only to be always determined. Thereafter, they 
are masked by the pointer signal from the pointer register 56. The pattern 
data for the whole single line is not needed. 
Such a series of operations are controlled by the clock control section 58 
and the initial setting section 59, which provide a recording operation of 
one line. The pointer register 56 and pattern register 47 may be either a 
ROM in which fixed data is written or a RAM or a shift register in which 
data can be written externally. 
As described above, in embodiment 4, because the ultrasonic generating 
element array 10 is divided into a plurality of groups (four groups in the 
example shown) and it is controlled on the basis of the recording data 
whether or not the driving signal selector group 52 supplies a driving 
signal to the corresponding ultrasonic generating element group via the 
buffer driver group 51, four control means composed of the data selectors 
53.sub.1 to 53.sub.4, pointer scanning registers 54.sub.1 to 54.sub.4, and 
driving pattern scanning registers 55.sub.1 to 54.sub.4 are provided for 
the respective groups in the ultrasonic generating element array 10. When 
an ultrasonic generating element group of 32 elements to be simultaneously 
driven in the ultrasonic generating element array 10 extends over two 
groups, the connection process is carried out by inputting an image signal 
for the pixels corresponding to the ultrasonic generating elements in 
connection 1 to connection 4 extending over the two groups, to the two 
control means corresponding to the two groups. 
By effecting the connection process, scanning recording can be effected 
with a continuity at the boundary between groups, even if the ultrasonic 
generating element array 10 is divided into a plurality of groups for a 
division driving method. 
A modification of embodiment 4 associated with a method of driving the 
ultrasonic generating element array 10 will be explained. 
(1) While in embodiment 4, the number of elements simultaneously driven in 
the ultrasonic generating element array 10, or the number of ultrasonic 
generating elements simultaneously driven in each group is constant (32), 
the number may be odd and even alternately the arranging direction. By 
doing this way, a double recording density can be achieved using the same 
ultrasonic generating element array. Specifically, when the number of 
elements simultaneously driven is even, a pixel is recorded at a position 
opposite to center of two ultrasonic generating elements. When the number 
of elements simultaneously driven is odd, a pixel is recorded at a 
position opposite to an ultrasonic generating element itself. Therefore, 
by alternating an odd number of elements simultaneously driven with an 
even number of elements simultaneously driven, the recording density is 
twice as high as that achieved in scanning with a fixed odd or even number 
of elements simultaneously driven. 
To achieve this, the pointer scanning registers 54.sub.1 to 544.sub.4, 
driving pattern scanning registers 45.sub.1 to 45.sub.4, point register 
46, and pattern register 57 in FIG. 37 are made of a two-layer structure, 
and the number of elements simultaneously driven is switched between an 
odd and even numbers alternately, thereby producing a select signal to the 
data selectors 53.sub.1 to 53.sub.4. In this case, as shown in FIG. 37, a 
mode change signal for switching between the normal mode and the 
high-definition mode is externally supplied to the clock control section 
58. In the normal mode, a scanning clock is supplied only to the first 
layers of the pointer scanning registers 54.sub.1 to 54.sub.4, driving 
pattern scanning registers 45.sub.1 to 45.sub.4, point register 46, and 
pattern register 57, and the number of elements simultaneously driven is 
odd or even only. In the high-definition mode, a scanning clock is 
supplied to both of the first layer and the second layer, and the number 
of elements simultaneously driven is switched between odd and even 
alternately. 
(2) A control method of correcting the shortcoming of the ink-droplet 
squirting mechanism to improve the recording speed will be explained. With 
an ink-jet recording device of the present invention, an ink droplet flies 
from a free flat surface filled with ink liquid. As a result, when an ink 
droplet flies, ripples appear on the ink surface and it takes a certain 
time for the ripples to disappear each time an ink droplet flies. If an 
ink droplet is forced to fly at the position corresponding to the pixel 
immediately next to the pixel just recorded by the previous ink droplet, 
that is, if an attempt is made to record the adjacent pixel continuously 
in time, the focus of the ink droplet will not be determined and an 
unstable flying of ink droplet will result. 
In the above embodiments, scanning control where after the ripples on the 
ink surface have disappeared to some extent, the immediately adjacent 
pixel is recorded consecutively, has been explained. To achieve 
higher-speed recording, an ink droplet is forced to fly to a pixel 
sufficiently away from the just recorded pixel, not to the immediately 
adjacent pixel. That is, by recording a pixel through skip scanning, the 
recording speed can be improved. 
The basic operation of the control realized on the configuration of FIG. 37 
will be explained. The ultrasonic generating element array 10 is divided 
into four groups, which are separated into odd-numbered groups and 
even-numbered groups. The odd-numbered groups and even-numbered groups 
effect recording alternately. In this case, recording is effected in such 
a manner that pixels in the odd-numbered groups (the first group and the 
third group), for example, the first pixel and the 2481st pixel, are 
recorded first; then, pixels in the even-numbered groups (the second group 
and the fourth group) away from the previous groups, for example, the 
1241st pixel and the 3721st pixel, are recorded; thereafter, the operation 
returns to the odd-numbered groups and the adjacent pixels, or the second 
pixel and the 2482nd pixel are recorded; then the operation goes to the 
even-numbered groups and the 1242nd pixel and the 3722nd pixel are 
recorded. This doubles the interval time in recording two adjacent pixels, 
enabling effective use of the time required for ripples to disappear. 
While in the previous explanation, the four groups in the ultrasonic 
generating element array 10 record four pixels simultaneously, the above 
technique enables two groups to record two pixel at a time, reducing the 
recording speed to half. To obtain the same effect without sacrificing the 
recording speed, the ultrasonic generating element array is divided into 
eight or more groups, and a division driving method is performed where 
four or more groups are used to record four or more pixels. 
(3) To record a two-dimensional image with an ink-jet recording device of 
the present invention, the device is combined with a sub-scanning 
mechanism that feeds recording paper in the main-scanning direction of the 
line scanning recording head and in the direction perpendicular to the 
main-scanning direction, as with conventional image recording devices. 
Generally, the sub-scanning paper feed mechanism has two types: one type 
of paper feed mechanism feeds recording paper intermittently in 
synchronization with the recording speed of one line on the line scanning 
recording head, and the other type of feed mechanism feeds recording paper 
continuously. When the division driving method explained in the above 
embodiments, or a method of dividing the ultrasonic generating element 
array 10 into, for example, four groups and driving them, is used, a 
provision for transferring recording data to the control circuit in the 
line scanning recording head is needed. 
(3-1) FIG. 42 shows the structure of the recording data buffer in the basic 
quadrisection driving with intermittent sub-scanning. The recording data 
buffer buffers the recording data to be supplied to the data selector 
53.sub.1 to 53.sub.4 shown in FIG. 37 and FIG. 41, and is composed of a 
read/write control section 71, a write counter 72, a read counter 73, an 
address selector 74, a buffer memory 75, and a data selector 76. 
Since in intermittent sub-scanning, recording paper remains still until the 
line scanning recording head has finished recording one line, the buffer 
memory 75 has a memory capacity for one line and stores one line of print 
data serially inputted at its end via the data selector 76. This is done 
in the write mode. Under the control of the read/write control section 71, 
the data selector 76 transfers the print data to the buffer memory 75. The 
address selector 74 is controlled by the output from the write counter 72 
and transfers the write address to the buffer memory 75. By controlling 
the addresses in groups divided corresponding to the number of pixels 
(1240 pixels) into which the number of effective recording pixels (4960 
pixels in the previous example) in the line scanning recording head of the 
invention is quadrisected, the print data stored in the buffer memory 75 
is read out as recording data 1 to 4. This is done in the read mode. Under 
the control of the read/write control section 71, the data selector 76 
transfers the data read from the buffer memory 75 to the data registers 
43.sub.1 to 43.sub.4 of FIG. 37. The address selector 74 is controlled by 
the output of the read counter 73 and transfers the read address to the 
buffer memory 75. The recording data 1 to 4 are read sequentially, 
starting at that corresponding to the head of each divided group. 
When one line of recording has been completed in this way, the recording 
sheet is advanced by one scanning line in the sub-scanning direction. In 
the meantime, the next one line of print data is transferred to the buffer 
memory 75, and the recording of the next line starts. The buffer memory 75 
may be of a double buffer structure. With this structure, by switching 
each buffer memory alternately between the read mode and the write mode, 
the waiting time for print data transfer can be made shorter. 
(3-2) Recording data transfer in quadrisection driving with continuous feed 
sub-scanning will be described. A problem with a simple combination of 
division driving and continuous sub-scanning is that the main-scanning 
line is not straight. Specifically, as shown in FIG. 43, when the 
main-scanning width W is divided into four groups and tun individual 
groups undergo record scanning simultaneously, starting from the left end, 
the scanning lines 1 to 4 corresponding the respective groups of the 
main-scanning line each have a slope, with the result that the entire 
main-scanning line does not make a straight line. The reason for this is 
that the recording sheet is advanced even during the main scanning. 
In this modification, a buffer memory with as many lines as the number of 
divided groups in the ultrasonic generating element array is provided, for 
example, when the ultrasonic generating element array is divided into four 
groups, a buffer memory with four lines is provided. By controlling the 
buffer memory, the main-scanning line is made straight. 
FIGS. 44A and 44B illustrate the concept. 
FIG. 44A shows how the print data from which the recording data is made is 
stored in a four line buffer memory. In FIG. 44A, A1, A2, A3, A4 indicate 
the print data for the first line, second line, third line, and fourth 
line, respectively. Each of them is divided into four elements in the 
main-scanning direction and controlled in the form of A1-1 to A1-4, A2-1 
to A2-4, A3-1 to A3-4, and A4-1 to A4-4. 
FIG. 44B diagrammatically shows the recording signals actually recorded. 
B1, B2, B3, B4, B5, B6 indicate the number of main-scanning lines on the 
line scanning recording head. As shown in FIG. 43, each main-scanning line 
is not straight. To overcome this problem, four main-scanning lines are 
treated as one set, and the print data items corresponding to the set are 
combined so as to obtain a single straight line. Concretely, quadrisected 
elements A1-1, A1-2, A1-3, A1-4 in print data Al for the first line of 
FIG. 44A are allocated to elements B1-1, B2-2, B3-3, B4-4 shifted 
sequentially in the main-scanning direction in the main-scanning direction 
of the first to fourth lines of FIG. 44B. 
By doing this, the main-scanning line tilts a little toward the direction 
perpendicular to the sub-scanning direction, as a whole, but a straight 
main-scanning line can be achieved. If the main-scanning width W is 210 
mm, the inclination of the main-scanning line will be converted into a 
distance of about 170 .mu.m between one end and the other end of the 
main-scanning width W in the sub-scanning direction, so that it is so 
small that it can be neglected practically. 
To make the main-scanning line straight by the above technique, print data 
transfer control is carried out as follows. A four-line buffer memory 70 
that can store the image signals (print data) for four lines, the same 
number as the number of divided groups in the ultrasonic generating 
element array 10 is provided. The print data, the image signal, is stored 
in the four-line buffer memory as shown in FIG. 44A. The four-line buffer 
memory 70 shifts the print data corresponding to each group in the same 
line by one line one after another, and transfers it to control means 
corresponding to each group, that is, the data selectors 53.sub.1 to 
53.sub.4 of FIG. 37 as recording data 1 to 4. 
Specifically, for B1 recording lines, only data on A1-1 is transferred to 
the first group B1-1; for B2 recording lines, data on A2-1 is transferred 
to the first group B2-1 and data on A1-2 is transferred to the second 
group B2-2; for B3 recording lines, data on A3-1 is transferred to the 
first group B3-1, data on A2-2 is transferred to the second group B3-2, 
and data on A1-3 is transferred to the third group B3-3; for B4 recording 
lines, data on A4-1 is transferred to the first group B4-1, data on A3-2 
is transferred to the second group B4-2, data on A2-3 is transferred to 
the third group B4-3, and data on A1-4 is transferred to the fourth group 
B4-4; for B5 recording lines, data on A5-1 is transferred to the first 
group B5-1, data on A4-2 is transferred to the second group B5-2, data on 
A3-3 is transferred to the third group B5-3, and data on A2-4 is 
transferred to the fourth group B5-4. 
As described above, the four-line buffer memory 70 shifts the print data 
corresponding to each of the four groups in the same line by one line in 
time one after another and repeatedly transfers it as recording data 1 to 
4 to the data selector 53.sub.1 to 53.sub.4, with the result that a 
straight main-scanning line can be obtained in continuous feed 
sub-scanning. To effect continuous feed sub-scanning smoothly, it is 
desirable that in the case of quadrisection driving, a line buffer memory 
for one line should be added to the four-line buffer memory to form a 
five-line buffer memory. The additional line buffer memory is needed for a 
subsequent one line. 
(4) Gradation recording will be explained. Gradation recording on an 
ink-jet recording device of the present invention can be realized by 
changing the driving time of the ultrasonic generating elements according 
to the gradation image signal. Concretely, gradation recording can be 
achieved by changing the on time duration of the driving on/off select 
signal supplied to the driving signal selector group 52 in FIG. 37. The 
recording data signals from the data selectors 53.sub.1 to 53.sub.4 are 
used as it is as the driving on/off select signal, so that the pulse width 
of each pixel for the recording data has only to be modulated according to 
the multi-level recording data, the gradation image signal. 
FIG. 45 shows a circuit for gradation recording. In the circuit, a 
parallel-serial conversion circuit 78, which operates using the pixel 
clock and master clock generated at a clock control section 77 in 
synchronization with a transfer clock, converts multi-level recording data 
into a pulse-width modulation signal. 
Embodiment 5-1 
FIG. 46 is a perspective view of the recording head section used in an 
ink-jet recording device according to Embodiment 5-1 of the invention. As 
shown in FIG. 46, the recording head section comprises a piezoelectric 
element array 10, an acoustic lens 11, an ink reservoir 15, and a drive 
circuit 21. 
The piezoelectric element array 10 is formed of a piezoelectric layer 13, a 
common electrode 12, and a plurality of discrete electrodes 14. The 
piezoelectric layer 13 is an elongated plate having a uniform thickness. 
The common electrode 12 is mounted on the upper surface of the layer 13. 
The discrete electrodes 14 are mounted on the lower surface of the layer 
13, spaced apart one from another. The common electrode 13, the 
piezoelectric layer 13, and the discrete electrodes 14 constitute a 
plurality of piezoelectric elements. The piezoelectric elements are 
juxtaposed in a straight line which extends in the main-scanning 
direction. 
The acoustic lens 11 is provided on the upper surface of the common 
electrode 12. The lens 11 is, for example, a glass plate. It has a concave 
in the surface which faces away from the piezoelectric element array 10 
and functions as an acoustic concave lens. The ink reservoir 15 is placed 
on the acoustic lens 11. The reservoir 15 has an ink chamber. The ink 
chamber has a sector-shaped cross section, gradually narrowing away from 
the acoustic lens 11 for guiding ultrasonic beams from the piezoelectric 
elements. The ink chamber is filled with liquid ink 18. 
The drive circuit 21 is mounted on the lower surface of the glass plate, 
i.e., the acoustic lens 11. More precisely, the drive circuit 21 is 
connected to the common electrode 12 and the discrete electrodes 14 by a 
patterned wiring (not shown) provided on the lower surface of the glass 
plate. 
In accordance with input image data (described later in detail), the drive 
circuit 21 drives the piezoelectric element array 10, performing linear 
electronic scanning. To be more specific, the circuit 21 first supplies 
high-frequency drive signals delayed from one another to the n consecutive 
elements T(1) to T(n) of the array 10 so that an ink droplet may fly from 
a point P0 on the surface of the ink 18. The circuit 21 then supplies 
similar high-frequency drive signals the n elements T(2) to T(n+1) so that 
an ink droplet may fly from a point P1 spaced from point P0 by the pitch 
at which the piezoelectric elements are juxtaposed in the main-scanning 
direction. Next, the circuit 21 supplies similar high-frequency drive 
signals the n elements T(3) to T(n+2) so that an ink droplet may fly from 
a point P2 spaced from point P0 by a two-pitch distance from point P0. The 
circuit 21 further drives the piezoelectric elements in similar way, n 
elements each time. As a result, the recording head section will squirt 
ink droplets, one after another, onto a recording medium (not shown), 
forming a line thereon. 
The ultrasonic beams emitted from any n piezoelectric elements of the array 
10 are applied to the acoustic lens 11. The acoustic lens 11 converges the 
ultrasonic beams in a plane extending in the direction (sub-scanning 
direction) at right angles to the main-scanning direction. As a result, 
the beams reach a point in the surface of the ink 18. The beams applies a 
pressure (emission pressure) to the ink 18. A conical ink meniscus grows, 
and an ink droplet fly from the meniscus. The ink droplet lands on the 
recording medium (not shown), adheres thereto and dries, forming a dot on 
the medium. An image is thereby formed on the recording medium. 
The method of driving the piezoelectric element array 10 will be explained 
in greater detail, with reference to FIG. 47. In FIG. 47 the acoustic lens 
11 is not illustrated for simplicity of explanation. As shown in FIG. 47, 
the drive circuit 21 comprises a drive signal source 81 and a delay 
circuit 82. The drive signal source 81 generates drive signals in 
accordance with the input image data. The delay circuit 82 delays the 
drive signals by the time preset by a control circuit (not shown). The 
drive signal the circuit 82 has delayed are supplied to the piezoelectric 
elements of the array 10. 
Assume that adjacent n piezoelectric elements T(1) to T(n) form a group. If 
the delay circuit 82 delays the drive signals such that the phases of the 
ultrasonic beams emitted from the elements T(1) to T(n) coincide at point 
A on the surface of the ink 18, which is located right above the midpoint 
of the first group of piezoelectric elements, an ink droplet will fly from 
point A. If the delay circuit 82 delays the drive signals such that the 
phases of the ultrasonic beams emitted from the elements T(2) to T(n+1) 
coincide at point C on the surface 18a of the ink 18, which is located 
right above the midpoint of the group consisting of the elements T(2) to 
T(n+1), an ink droplet will fly from point C. Obviously, point C is at a 
distance d from point A, the distance d being equal to the pitch at which 
the piezoelectric elements are juxtaposed in the main-scanning direction. 
Also assume that adjacent n+1 piezoelectric elements T(1) to T(n+1) form a 
group. If n is an even number, the circuit 82 delays the drive signals to 
be supplied to the elements T(1) to T(n/2) in the same way as is necessary 
to fly an ink droplet from point A, delays the drive signal to be supplied 
to the element T(n/2+1) in the same way it delays the drive signal to the 
element T(n/2) as is required to fly an ink droplet from point A, and 
delays the drive signals to be supplied to the elements T(T/2+2) to T(n+1) 
more by one unit delay time than the drive signals supplied to the 
elements T(n/2+1) to T(n) to fly an ink droplet from point A. 
In other words, if n is an even number, the pattern of delaying the signals 
for driving the elements T(1) to T(n) to squirt an ink droplet from point 
A is divided into two sub-patterns. The first sub-pattern is applied to 
the elements T(1) to T(n/2), while the second sub-pattern is applied to 
the remaining elements T(n/2+2) to T(n+1), and the same delayed drive 
signal as supplied to the element T(n/2) is supplied to the middle element 
T(n/2+1). 
If n is an odd number, the pattern of delaying the signals for driving the 
elements T(1) to T(n) to squirt an ink droplet from point A is divided 
into two sub-patterns. The first sub-pattern is applied to the elements 
T(1) to T(n/2+0.5), while the second sub-pattern is applied to the 
remaining elements T(n/2+1.5) to T(n), and the same delayed drive signal 
as supplied to an additional element located between the elements 
T(n/2+0.5) and T(n/2+1.5) is supplied to the middle element T(n/2+1). 
In this case, when the piezoelectric elements T(1) to T(n+1) are driven 
simultaneously, an ink droplet flies from point B which is at a distance 
d/2 from point A. The distance d/2 is equal to half the pitch at which the 
piezoelectric elements are juxtaposed in the main-scanning direction. 
As described above, the piezoelectric elements can be driven in a first 
mode wherein an even number of elements forming a group emits an 
ultrasonic beam having an axis extending through the midpoint of the 
group. Alternatively, the elements can be driven in a second mode wherein 
an odd number of elements forming a group emit an ultrasonic beam having 
an axis extending through the midpoint of the group. In either case, the 
recording head section squirts ink droplets at half the pitch at which the 
piezoelectric elements are juxtaposed. Further, the recording head section 
squirts each ink droplet along a straight path perpendicular to the 
surface 18a of the ink 18, since the pattern (i.e., the drive-signal phase 
pattern) in which the drive signals are delayed to apply ink droplets from 
points A, B and C is symmetrical with respect to the midpoint of the group 
of elements driven at the same time. Still further, it is easy to delay 
the drive signals since the drive-signal delay pattern for the group 
consisting of n elements differs the drive-signal delay pattern fro the 
group consisting of (n+1) elements, by only one item corresponding to one 
piezoelectric element. 
A piezoelectric element array according to Embodiment 5-1 was made, and was 
driven by the method described above. 
The piezoelectric elements were juxtaposed at a pitch of 50 .mu.m. 
Thirty-six (36) forming a group were driven simultaneously by drive 
signals having a frequency of 100 MHz. The focal length of the ultrasonic 
beam emitted from the elements of each group emitted was 3 mm. (Namely, 
the thickness of the ink layer was 3 mm.) The velocity of sound was 1.5 
km/sec in the liquid ink 18, as in water. It follows that the wavelength 
the ultrasonic beam had while traveling through the liquid ink 18 was 15 
.mu.m. 
The phase (delay time) for each of the ultrasonic beams emitted from the 36 
piezoelectric elements forming the group was set at one of two values 
based on Fresnel diffraction theory. More specifically, the radius of 
Fresnel zone ring was determined by Equation (1) or (2): 
##EQU2## 
(n=0, 1, 2, . . . , where when n=0, r(0)=0.) 
EQU r(n)=(n.lambda.iF).sup.1/2 (n=0, 1, 2, . . . ) (2) 
where n is an integer equal to or greater than 0 (namely, n=0, 1, 2, . . . 
), .lambda.i is the wavelength of the ultrasonic beam, and F is the focal 
length (the thickness of the ink layer). Table 1 presented below shows the 
radii r(n) (n=0 to 19) of Fresnel zone rings, thus determined. 
TABLE 1 
______________________________________ 
r(0) 0 mm 
r(1) 0.150 mm 
r(2) 0.260 mm 
r(3) 0.336 mm 
r(4) 0.398 mm 
r(5) 0.451 mm 
r(6) 0.499 mm 
r(7) 0.543 mm 
r(8) 0.584 mm 
r(9) 0.622 mm 
r(10) 0.658 mm 
r(11) 0.692 mm 
r(12) 0.725 mm 
r(13) 0.756 mm 
r(14) 0.786 mm 
r(15) 0.815 mm 
r(16) 0.843 mm 
r(17) 0.871 mm 
r(18) 0.897 mm 
r(19) 0.923 mm 
______________________________________ 
Next, the delay time for the ultrasonic beam emitted from each 
piezoelectric element was set at such value that the beams emitted from 
the elements at a distance D greater than r(2n) and less than r(2n+1) were 
out of phase by half the wavelength with respect to the beams emitted from 
the elements at a distance D greater than r(2n+1) and less than r(2n+3), 
where D is the distance between each piezoelectric element and the 
midpoint of the cement group. The delay times .tau.(n) (n=1 to 36), thus 
set, were as shown in the second column of Table 2 presented below. When 
all elements of the group (i.e., the thirty-six elements) were driven at 
the same time, an ink droplet flew from the ink surface 18a, at a point 
located right above the midpoint between the 18th and 19th piezoelectric 
elements. This point corresponds to point A shown in FIG. 47. 
TABLE 2 
______________________________________ 
Flying point of 
Flying point of 
First piezoelectric 
Second piezoelectric 
element group 
element group 
Point A Point B 
______________________________________ 
.tau.(1) 5 nsec 5 nsec 
.tau.(2) 5 nsec 5 nsec 
.tau.(3) 5 nsec 5 nsec 
.tau.(4) 0 sec 0 sec 
.tau.(5) 0 sec 0 sec 
.tau.(6) 5 nsec 5 nsec 
.tau.(7) 5 nsec 5 nsec 
.tau.(8) 0 sec 0 sec 
.tau.(9) 5 nsec 5 nsec 
.tau.(10) 0 sec 0 sec 
.tau.(11) 5 nsec 5 nsec 
.tau.(12) 0 sec 0 sec 
.tau.(13) 0 sec 0 sec 
.tau.(14) 5 nsec 5 nsec 
.tau.(15) 5 nsec 5 nsec 
.tau.(16) 0 sec 0 sec 
.tau.(17) 0 sec 0 sec 
.tau.(18) 0 sec 0 sec 
.tau.(19) 0 sec 0 sec 
.tau.(20) 0 sec 0 sec 
.tau.(21) 0 sec 0 sec 
.tau.(22) 5 nsec 0 sec 
.tau.(23) 5 nsec 5 nsec 
.tau.(24) 0 sec 5 nsec 
.tau.(25) 0 sec 0 sec 
.tau.(26) 5 nsec 0 sec 
.tau.(27) 0 sec 5 nsec 
.tau.(28) 5 nsec 0 sec 
.tau.(29) 0 sec 5 nsec 
.tau.(30) 5 nsec 0 sec 
.tau.(31) 5 nsec 5 nsec 
.tau.(32) 0 sec 5 nsec 
.tau.(33) 0 sec 0 sec 
.tau.(34) 5 nsec 0 sec 
.tau.(35) 5 nsec 5 nsec 
.tau.(36) 5 nsec 5 nsec 
.tau.(37) undriving 5 nsec 
______________________________________ 
The array was divided into groups, each consisting of thirty-seven 
piezoelectric elements to be driven simultaneously to squirt an ink 
droplet from point B spaced from point A by half the pitch at which the 
piezoelectric elements were juxtaposed in the main-scanning direction. In 
this case, the phases (delay times) for the ultrasonic beams emitted from 
the elements were set at the values shown in the second column of Table 2. 
As evident from Table 2, the delay times for the beams from the first to 
18th elements were respectively identical to those set for squirting an 
ink droplet from point A; the delay time for the beam from the 19th 
element was equal to the delay time set for squirting an ink droplet from 
point A; and the delay times for the beams from the 20th to 37th elements 
were respectively identical to the 19th to 36th elements for squirting an 
ink droplet from point A. When all piezoelectric elements of the group 
(i.e., the thirty-seven elements) were driven at the same time, an ink 
droplet flew from the ink surface 18a, at point B located right above the 
19th element, or the midpoint of the group. 
FIG. 48 represents the acoustic distribution which was observed on the ink 
surface when the thirty-six piezoelectric elements were driven 
simultaneously, and also the acoustic distribution which was observed on 
the ink surface when the thirty-seven piezoelectric elements were driven 
simultaneously. In FIG. 48, plotted on the abscissa is the distance from 
the midpoint of the group of the elements, and plotted on the ordinate is 
the relative intensity of the ultrasonic beam emitted from each 
piezoelectric element. As can be understood from FIG. 48, the main beam 
was emitted from a point at a distance of 25 .mu.m from the midpoint of 
either group of elements (36 or 37 elements). The side lobes emitted from 
the group of elements differed in intensity, but slightly. The main beam 
emitted when the thirty-seven elements were driven simultaneously had 
intensity about 3% higher than the intensity of the main beam emitted when 
the thirty-six elements were driven simultaneously. Nonetheless, is 
virtually no difference was resulted in the size of the ink droplet 
actually flew from the liquid ink. However, the less the piezoelectric 
elements of one group than those of the another group, the greater the 
difference in the intensity of the main beam, producing a considerable 
difference in the size of the ink droplet. To reduce the difference in the 
intensity of the main beam, it is desirable to decrease that the number of 
piezoelectric elements forming a larger group or to change either the 
drive voltage or the number of bursts. 
In the method of setting the delay times at the values shown in Table 2, 
the delay time for imparting a .pi. shift to the phases of the ultrasonic 
waves was 5 nsec. This delay time was half the one-cycle period of the 
drive signals. The delay time may be multiplied an odd number times to 
provide similar results. The phases of the ultrasonic waves may be shifted 
by .pi., not only by using the delay circuit 82 shown in FIG. 47. But also 
can the phases be shifted by driving the piezoelectric elements with a 
drive signal voltage inverted in phase. When the elements are driven with 
such a drive signal voltage, it suffices to use a simple changeover 
switch, and the drive circuit is relatively simple and, hence, can be 
manufactured at low cost. 
In the method of setting the delay times at the values shown in Table 2, 
the delay times were set such that the ultrasonic beam emitted from the 
19th of the thirty-seven elements had the same phase as the beams emitted 
from the 18th and 20th elements. Nonetheless, the 19th element need not 
necessarily be driven. An ink droplet will fly in the same way even if the 
pattern of delaying the drive signals is divided into two sub-patterns, 
the first sub-pattern applied to the first 18 of the thirty-six elements, 
and the second sub-pattern applied to the 20th to 35th or 37th elements. 
In Embodiment 5-1, one piezoelectric element is added to the group 
consisting of thirty-six elements, thereby providing a group consisting of 
thirty-six elements. Instead, any other odd number of elements may be 
added to the group consisting of thirty-six elements. Rather, an odd 
number of elements may be removed from the group consisting of thirty-six 
elements, providing a group consisting of less piezoelectric elements. It 
is desirable, however, that one element be inserted in the 36-element 
group at the midpoint of the group so as to attain acoustic distribution 
on the ink surface which is symmetrical with respect to the midpoint of 
the element group. 
Embodiment 5-2 
The recording head section incorporated in an ink-jet recording device 
which is Embodiment 5-1 of the invention will be described. In this 
embodiment, the recording head section is driven by electronic focusing 
method. To be more precise, the groups of piezoelectric elements are 
driven with delay times which are quadratic functions obtained from the 
distances between a focal point and the piezoelectric elements a focal 
point. A delay time .tau. (n) given by Equation (3) shown below, is set 
for the n-th of the m piezoelectric elements forming a group. 
##EQU3## 
where d is the pitch at which the piezoelectric elements are juxtaposed, F 
is the focal length (the thickness of the ink layer), and v is the 
velocity of sound in the liquid ink. 
TABLE 3 
______________________________________ 
Flying point of 
Second piezoelectric 
element group 
Flying point of Point B 
First piezoelectric 
Conventional 
Driving 
element group Electric of the 
Point A Focus Method 
Invention 
______________________________________ 
.tau.(1) 
0 sec 0 sec 0 sec 
.tau.(2) 
9 nsec 10 nsec 9 nsec 
.tau.(3) 
18 nsec 19 nsec 18 nsec 
.tau.(4) 
27 nsec 28 nsec 27 nsec 
.tau.(5) 
34 nsec 36 nsec 34 nsec 
.tau.(6) 
42 nsec 43 nsec 42 nsec 
.tau.(7) 
48 nsec 50 nsec 48 nsec 
.tau.(8) 
54 nsec 56 nsec 54 nsec 
.tau.(9) 
60 nsec 62 nsec 60 nsec 
.tau.(10) 
65 nsec 68 nsec 65 nsec 
.tau.(11) 
69 nsec 72 nsec 69 nsec 
.tau.(12) 
73 nsec 76 nsec 73 nsec 
.tau.(13) 
77 nsec 80 nsec 77 nsec 
.tau.(14) 
79 nsec 83 nsec 79 nsec 
.tau.(15) 
82 nsec 86 nsec 82 nsec 
.tau.(16) 
83 nsec 88 nsec 83 nsec 
.tau.(17) 
84 nsec 89 nsec 84 nsec 
.tau.(18) 
85 nsec 90 nsec 85 nsec 
.tau.(19) 
85 nsec 90 nsec 85 nsec 
.tau.(20) 
84 nsec 90 nsec 85 nsec 
.tau.(21) 
83 nsec 89 nsec 84 nsec 
.tau.(22) 
82 nsec 88 nsec 83 nsec 
.tau.(23) 
79 nsec 86 nsec 82 nsec 
.tau.(24) 
77 nsec 83 nsec 79 nsec 
.tau.(25) 
73 nsec 80 nsec 77 nsec 
.tau.(26) 
69 nsec 76 nsec 73 nsec 
.tau.(27) 
65 nsec 72 nsec 69 nsec 
.tau.(28) 
60 nsec 68 nsec 65 nsec 
.tau.(29) 
54 nsec 62 nsec 60 nsec 
.tau.(30) 
48 nsec 56 nsec 54 nsec 
.tau.(31) 
42 nsec 50 nsec 48 nsec 
.tau.(32) 
34 nsec 43 nsec 42 nsec 
.tau.(33) 
27 nsec 36 nsec 34 nsec 
.tau.(34) 
18 nsec 28 nsec 27 nsec 
.tau.(35) 
9 nsec 19 nsec 18 nsec 
.tau.(36) 
0 sec 10 nsec 9 nsec 
.tau.(37) 
undriving 0 sec 0 sec 
______________________________________ 
Shown in the first column of Table 3 presented below are the delay times 
.tau.(n) which are set for thirty-six piezoelectric elements forming a 
group, when the elements are juxtaposed at a pitch of 50 .mu.m and driven 
simultaneously by drive signals having a frequency of 100 MHz, and the 
focal length of the ultrasonic beam emitted from the elements of each 
group emitted is 3 mm (namely, the thickness of the ink layer is 3 mm.).In 
this case, the minimum unit of delay time, i.e., a quantized delay time, 
is 1 nsec. When the thirty-six elements are driven with these time delays, 
an ink droplet will fly from point A (FIG. 47). With the conventional 
electronic focusing method it is comparatively easy to change the focal 
point where ultrasonic beams converge. Hence, to squirt an ink droplet 
from point B (FIG. 47) spaced from point A (FIG. 47) by half the pitch of 
the piezoelectric elements, it suffices to drive thirty-seven elements 
with the delay times calculated by Equation (3) and shown in the second 
column of Table 3. As is apparent from Table 3, the pattern of delaying 
the drive signals for the thirty-seven elements is quite different from 
the pattern of delaying the drive signals for the thirty-six elements. 
In the electronic focusing method according to Embodiment 5-2, the drive 
signals for the thirty-seven elements are delayed in the pattern specified 
in the third column of Table 3. More precisely, the delay times for the 
first 18 elements are respectively identical to the delay times for the 
first 18 of the thirty-six elements, the delay time for the 19th element 
is the same as the delay time for the 18th of the thirty-six elements, and 
the delay times for the 20th to 37th elements are respectively identical 
to the remaining 18 of the thirty-six elements. When the thirty-seven 
piezoelectric elements are driven with the time delays shown in the third 
column of Table 3, an ink droplet will fly from point B on the ink 
surface, which is located right above the 19th element, i.e., the midpoint 
of the 37-element group. 
Thus, the electronic focusing method according to Embodiment 5-2 can set 
the delay times for the thirty-seven elements, using only about half the 
amount of data required in the conventional electronic focusing method. In 
this respect the method of driving the piezoelectric element array, 
according to Embodiment 5-2, is advantageous over the conventional 
electronic focusing method. 
As described above, both Embodiment 5-1 and Embodiment 5-2 can squirt ink 
droplets in paths perpendicular to the ink surface, at half the pitch at 
which the piezoelectric elements are juxtaposed in the main-scanning 
direction. Therefore, Embodiments 5-1 and 5-2 can record images which have 
a resolution twice as high as is possible with the conventional ink-jet 
recording device which performs linear electronic scanning. In addition, 
Embodiments 5-1 and 5-2 need only to have an element-driving circuit which 
is more simple in structure than its equivalent incorporated in the 
conventional ink-jet recording device. 
Embodiment 5-3 
An ink-jet recording device according to Embodiment 5-3 of the present 
invention has a recording head section which is similar in structure to 
the recording head section (FIG. 46) of Embodiment 5-1. 
It differs in the way the drive circuit 21 drives the piezoelectric element 
array 10. In the array-driving method, the piezoelectric elements can be 
driven in either a first mode or a second mode. The first mode and the 
second mode will be explained, with reference to FIG. 49 and FIG. 50. In 
the first mode, delay times are set for n piezoelectric elements T(1) to 
T(n) forming a group, such that the ultrasonic beams emitted from the 
elements match in phase at point P0 where the vertical line extending from 
the midpoint of the group formed by the elements T(1) to T(n) intersects 
with the surface of liquid ink 18 as shown in FIG. 49. When the circuit 21 
drives the elements T(1) to T(n) in the first mode, an ink droplet will 
fly from point P0. When the circuit 21 drives the elements T(2) to T(n+1) 
in the first mode, an ink droplet will fly from a point spaced from point 
P0 by the pitch of the piezoelectric elements; when the circuit 21 drives 
the elements T(3) to T(n+2) in the first mode, an ink droplet will fly 
from a point spaced from point P0 by a two-pitch distance; and so forth. 
As a result, the recording head section will squirt ink droplets, one 
after another, onto a recording medium, forming a line thereon. 
In the second mode, delay times are set for n piezoelectric elements T(1) 
to T(n) forming a group, such that the ultrasonic beams emitted from the 
first n/2 elements, i.e., the elements T(1) to T(n/2), match in phase at 
point P1 which is located right above the midpoint of the group and below 
the surface of the ink 18, as illustrated in FIG. 50, and that the 
remaining n/2 elements, i.e., the elements T(n/2+1) to T(n), match in 
phase at point P2 which is located right above the middle element T(n/2+1) 
and above the surface of the ink 18, as illustrated in FIG. 50. As a 
result, an ink droplet will fly from a point other than point P0 from 
which an ink droplet flies as shown in FIG. 49 when the drive circuit 21 
drives the piezoelectric element array 10 in the first mode. 
A piezoelectric element array according to Embodiment 5-3 was made and 
actually driven by the method explained with reference to FIG. 49 and FIG. 
50. 
More specifically, thirty-four piezoelectric elements forming a group were 
driven simultaneously by drive signals having a frequency of 7.5 MHz. (The 
ultrasonic beam each element emits had a wavelength of 0.2 mm in the 
liquid ink 18.) The thickness of the ink layer was 10 mm. The 
piezoelectric elements were juxtaposed at a pitch of 190 .mu.m. 
The delay time for each of the ultrasonic beams emitted from the 
thirty-four piezoelectric elements forming the group was set at one of two 
values based on Fresnel diffraction theory. More specifically, in the 
first mode, the focal length was set at 10 mm (hereinafter referred to as 
"reference focal point") so that the ultrasonic beams emitted from all 
elements of the group may match in phase at a point in the surface of the 
link 18, which is located right above the midpoint of the group. In the 
second mode, a focal length of 9 mm, 1 mm shorter than the reference focal 
length, was set for the first to 17th piezoelectric elements, and a focal 
length of 11 mm, 1 mm longer than the reference focal length, was set for 
the 18th to 34th elements. In order to set a delay time to control the 
phase of the ultrasonic beam emitted from each element, the radius of 
Fresnel zone ring was determined by Equation (4) or (5): 
##EQU4## 
EQU r(n)=(n.lambda.iF).sup.1/2 (n=0, 1, 2, . . . ) (5) 
where n is an integer equal to or greater than 0, .lambda.i is the 
wavelength of the ultrasonic beam traveling through the ink 18, and F is 
the focal length. Table 4 presented below shows the radii r(n) (n=0 to 7) 
of Fresnel zone rings, thus determined, for the focal length of 9 mm, the 
focal length of 10 mm and the focal length of 11 mm. 
TABLE 4 
______________________________________ 
F = 9 mm (F1) F = 10 mm (F0) 
F = 11 mm (F2) 
______________________________________ 
r(0) 0 mm 0 mm 0 mm 
r(1) 0.950 mm 1.001 mm 1.050 mm 
r(2) 1.650 mm 1.739 mm 1.823 mm 
r(3) 2.136 mm 2.250 mm 2.359 mm 
r(4) 2.534 mm 2.669 mm 2.797 mm 
r(5) 2.881 mm 3.034 mm 3.178 mm 
r(6) 3.194 mm 3.362 mm 3.522 mm 
r(7) 3.482 mm 3.664 mm 3.837 mm 
______________________________________ 
Next, the delay time for the ultrasonic beam emitted from each 
piezoelectric element was set at such value that the beams emitted from 
the elements at a distance D greater than r(2n) and less than r(2n+1) were 
out of phase by .pi. with respect to the beams emitted from the elements 
at a distance D greater than r(2n+1) and less than r(2n+3), where D is the 
distance between each piezoelectric element and the midpoint of the cement 
group. To be more precise, a delay time of 67 nsec, which is half the 
one-cycle period of the drive signals, was set for the elements located at 
a distance D greater than r(2n) and less than r(2n+1), and a delay time of 
0 nsec was set for the elements located at a distance D greater than 
r(2n+1) and less than r(2n+3). Instead, the delay time of 67 nsec may be 
set for the elements located at a distance D greater than r(2n+1) and less 
than r(2n+3), which the delay time of 0 nsec for the elements located at a 
distance D greater than r(2n) and less than r(2n+1). The delay time may be 
multiplied an odd number times, in which case, too, the beams emitted from 
the elements at a distance D greater than r(2n) and less than r(2n+1) can 
be out of phase by .pi. with respect to the beams emitted from the 
elements at a distance D greater than r(2n+1) and less than r(2n+3). 
Further, since it suffices to set only two alternative phases for the 
ultrasonic beam emitted from each piezoelectric element, the phase of the 
beam can be shifted by driving the piezoelectric elements with a drive 
signal voltage inverted in phase. If this is the case, the delay circuit 
may be replaced by a simple changeover switch, rendering the drive circuit 
relatively simple and inexpensive. 
The delay times .tau.(n) (n=1 to 34), thus set, were as shown in Table 5 
presented below. More precisely, the values the delay times .tau.(1) to 
.tau.(34) assume for the first mode are shown in the first column of Table 
5, whereas the values the delay times assume for the second mode are shown 
in the second column of Table 5. As can be seen from Table 5, the delay 
times .tau.(1) to .tau.(17) are not exactly identical to the delay times 
.tau.(34) to .tau.(18), respectively. 
TABLE 5 
______________________________________ 
Second Driving 
Mode 
Focal Length of 
First Driving 
first to 17th 
Mode Elements: 9 
Focal Length of 
Focal Length of 
all Elements: 
18th to 34th 
10 mm Elements: 11 mm 
______________________________________ 
.tau.(1) 67 nsec 67 nsec 
.tau.(2) 0 sec 67 nsec 
.tau.(3) 0 sec 0 sec 
.tau.(4) 67 nsec 0 sec 
.tau.(5) 67 nsec 67 nsec 
.tau.(6) 0 sec 67 nsec 
.tau.(7) 0 sec 0 sec 
.tau.(8) 0 sec 0 sec 
.tau.(9) 67 nsec 67 nsec 
.tau.(10) 67 nsec 67 nsec 
.tau.(11) 67 nsec 67 nsec 
.tau.(12) 67 nsec 67 nsec 
.tau.(13) 0 sec 0 sec 
.tau.(14) 0 sec 0 sec 
.tau.(15) 0 sec 0 sec 
.tau.(16) 0 sec 0 sec 
.tau.(17) 0 sec 0 sec 
.tau.(18) 0 sec 0 sec 
.tau.(19) 0 sec 0 sec 
.tau.(20) 0 sec 0 sec 
.tau.(21) 0 sec 0 sec 
.tau.(22) 0 sec 0 sec 
.tau.(23) 67 nsec 0 sec 
.tau.(24) 67 nsec 67 nsec 
.tau.(25) 67 nsec 67 nsec 
.tau.(26) 67 nsec 67 nsec 
.tau.(27) 0 sec 67 nsec 
.tau.(28) 0 sec 0 sec 
.tau.(29) 0 sec 0 sec 
.tau.(30) 67 nsec 67 nsec 
.tau.(31) 67 nsec 67 nsec 
.tau.(32) 0 sec 67 sec 
.tau.(33) 0 sec 0 sec 
.tau.(34) 67 nsec 0 sec 
______________________________________ 
FIG. 51 is a diagram representing the acoustic distribution which was 
observed on the ink surface when the thirty-four piezoelectric elements 
were driven in the first mode, and also the acoustic distribution which 
was observed on the ink surface when the piezoelectric elements were 
driven in the second mode. In FIG. 51, plotted on the abscissa is the 
distance from the midpoint of the group of the elements, and plotted on 
the ordinate is the relative intensity of the ultrasonic beam emitted from 
each piezoelectric element. As can be understood from FIG. 51, the main 
beam was emitted from the midpoint of the elements group when the elements 
were driven in the first mode, and the main beam was emitted from a point 
shifted to the right by about 110 .mu.m when the elements were driven in 
the second mode. The main beam and side lobes emitted from the group of 
elements when the elements were driven in the second mode did differ in 
intensity, but slightly, from the main beam and side robes emitted when 
the elements were driven in the first mode. When the elements were driven 
in the first mode, a ink droplet flew from the ink surface 18a, at a point 
located right above the midpoint of the element group. When the elements 
were driven in the second mode, a ink droplet flew from the ink surface 
18a, at a point shifted to the right by about 110 .mu.m and located at the 
focal length longer than the reference focal length of 10 mm. The position 
where the ink droplet flies can be changed by altering the ratio of the 
difference between the focal distances for the first 17 elements and the 
remaining 17 elements to the thickness of the ink layer. 
FIG. 52 illustrates how the position at which an ink-droplet flew changed 
when said ratio of the focal-distance difference to the ink-layer 
thickness was altered. Needless to say, thirty-four elements juxtaposed at 
the pitch of 190 .mu.m were simultaneously driven in the second mode, and 
the layer of the ink 18 was 10 mm thick. The two focal points were above 
and below the ink surface 18a, each at the same distance therefrom. 
The ratio of the of the focal-distance difference to the ink-layer 
thickness is preferably 0.4 or less. If the ratio is greater than 0.4, the 
ink droplet will fly in a path inclined to the ink surface 18a, making it 
difficult to control the landing position of the droplet on the recording 
medium, or the ultrasonic beams emitted from the piezoelectric elements 
will not be converged enough to squirt an ink droplet unless the drive 
voltage is increased or the number of bursts is increased. To converge the 
ultrasonic beams sufficiently, it is desirable that the difference between 
the two focal distances be an even number times the wavelength the beams 
have while traveling in the liquid ink 18. In Embodiment 5-3, the two 
focal points are located above and below the ink surface 18a, 
respectively, each at the same distance the ink surface 18a. Rather, they 
may be in the ink surface 18a, in which case an ink droplet flies from a 
point shifted from the point located right above the midpoint of the 
element group. 
Thus, the position where an ink droplet flies can be controlled, regardless 
of the pitch at which the piezoelectric elements are juxtaposed in the 
main-scanning direction, merely by adjusting the difference between the 
focal distances for the first 17 elements and the remaining 17 elements. 
When the piezoelectric elements are driven in the first mode, Embodiment 
5-3 can record a high-resolution image. On the other hand, when the 
piezoelectric elements are driven in the second mode, Embodiment 5-3 can 
form ink dots of two sizes on the recording medium, thereby recording a 
pseudo gray-level image thereon. 
It is most desirable that two focal distances be set for exactly the halves 
of the element group as in Embodiment 5-3. Nevertheless, the focal 
distances may be set for two groups consisting of different numbers of 
piezoelectric elements, respectively. 
As described above, Embodiment 5-3 can record images at a resolution higher 
than the value defined by the pitch at which the piezoelectric elements 
are juxtaposed, and can record a pseudo gray-level image on a recording 
medium. Furthermore, it requires but a simple circuit for driving the 
piezoelectric elements. This is because the phases of the ultrasonic beams 
emitted from the thirty-four piezoelectric elements are controlled based 
on Fresnel diffraction theory. 
Embodiment 6-1 
FIG. 53 is a sectional view of the recording head section incorporated in 
an ink-jet recording device according to Embodiment 6-1 of the present 
invention. As FIG. 53 shows, the recording head section comprises a 
piezoelectric array 10, an acoustic lens 11, an ink reservoir 15, and a 
backing layer 80. The piezoelectric array 10 is formed of a piezoelectric 
layer 13, a common electrode 12, and a plurality of discrete electrodes 
14.sub.1, to 14.sub.n The common electrode 12 is mounted on the upper 
surface of the layer 13. The discrete electrodes 14.sub.1 to .sup.14.sub.n 
are mounted on the lower surface of the layer 13, spaced apart one from 
another. The common electrode 13, the piezoelectric layer 13, the discrete 
electrodes 14.sub.1 to .sup.14.sub.n constitute a plurality of 
piezoelectric elements. The piezoelectric elements are juxtaposed in a 
straight line which extends in the main-scanning direction. The acoustic 
lens 11 is provided on the upper surface of the common electrode 12. The 
backing layer 80 is provided on the lower surfaces of the discrete 
electrode 14.sub.1 to 14.sub.n. The ink reservoir 15 is placed on the 
acoustic lens 11. The reservoir 15 has an ink chamber, opening in the top 
and forming a slit. The ink chamber is filled with liquid ink 18. 
The piezoelectric layer 13 is made of ceramics such as lead zirconate 
titanate (PZT) or lead titanate, semiconductor piezoelectric substance 
such as ZnO or AlN, or a high-molecular piezoelectric substance such as 
polyvinylidine fluoride (PVDF) or a copolymer (P(VDF-TrFE)) of 
polyvinylidine fluoride and ethylene trifluoride. The common electrode 12 
and the discrete electrodes 14.sub.1 to 14.sub.n are made of Ti, Ni, Al, 
Cu, Cr, Au or the like, are comprised each a plurality of vapor-deposited 
metal films, or have been formed by print-coating a film made of 
glass-flit containing silver paste and then backing the film. 
The acoustic lens 11 is made of plastics having a groove formed based on 
Fresnel diffraction theory. The lens 11 may be a convex lens. The acoustic 
lens 11 functions to adjust the distribution of acoustic energy in the 
case where the piezoelectric layer 13 is made of a substance having a 
higher acoustic impedance than the ink 18, such as lead zirconate titanate 
(PZT) or ZnO. That is, the lens 11 is made of material whose acoustic 
impedance is intermediate between those of the layer 13 and the ink 18, so 
that the ultrasonic beams emitted from the piezoelectric array 10 may be 
applied to the ink 18 with high efficiency. For the same purpose, the 
concave portions of the lens 11 have each a thickness which is an integral 
multiple of .lambda./4, where .lambda. is the wavelength the ultrasonic 
beam have while traveling through the liquid ink 18. 
The backing layer 80, which is located below the piezoelectric array 10 and 
characterizes Embodiment 6-1, performs two functions. First, the layer 80 
mechanically supports the piezoelectric array 10. Second, the layer 80 
prevents the piezoelectric array 10 from vibrating excessively so that the 
array 10 may no longer vibrate once the supply of the drive voltage has 
been stopped. To perform the second function the layer 80 needs to be made 
of material having acoustic impedance of at least 3.times.10.sup.6 
kg/m.sup.2 s. The material may be glass such as quartz or Pyrex, rubber 
such as ferrite rubber or silicone, resin such as epoxy, ceramics such as 
alumina, or metal such as copper or aluminum. If made of material whose 
acoustic impedance is less than 3.times.10.sup.6 kg/m.sup.2 s, such as 
porous material, the layer 80 could not prevents the array 10 from 
vibrating excessively. It is desirable that the layer 80 have acoustic 
impedance lower than that of the piezoelectric layer 13 so that the 
ultrasonic beam may not be reflected from the interface between the array 
10 and the backing layer 80. 
The backing layer 80 attenuates the ultrasonic beam traveling in it. The 
beam, if reflected from the lower surface of the layer 80, does not reach 
the piezoelectric array 10 to affect the vibration of the array 10. The 
layer 80 can attenuate the beam sufficiently if it is a few millimeters 
thick and is made of ferrite rubber, whose attenuation coefficient is as 
large as about 3.8 dB/MHz-mm. If the layer 80 is made of quartz glass or 
the like, whose attenuation coefficient is as small as about 
6.5.times.10.sup.-4 dB/MHz-mm, it must be made thick or its lower surface 
must be roughened as shown in FIG. 54 in the case where the piezoelectric 
array 10 generates ultrasonic waves having a low frequency of tens of 
magahertzes. 
FIG. 55 is a perspective view of the piezoelectric array 10. As shown in 
FIG. 55, the common electrode 12 is mounted on the upper surface of the 
piezoelectric layer 13 which is an elongated plate. The discrete 
electrodes 14.sub.1 to 14.sub.n shaped like strips are provided on the 
lower surface of the piezoelectric layer 13 and juxtaposed, forming an 
array. Although the piezoelectric layer 13 is not divided into strips, its 
portions which are mounted on the discrete electrodes 14.sub.1 to 14.sub.n 
can be vibrated when the drive voltage is applied between the common 
electrode 12 and the discrete electrodes .sup.14.sub.1 to 14.sub.n. 
Needless to say, the piezoelectric layer 13 may divided into discrete 
strips. To do so, however, two additional manufacturing steps must be 
carried out, inevitably increasing the manufacturing costs of the array 
10. First, parts of the layer 13 must be etched way isotropically to 
provide discrete piezoelectric strips. Second, the gaps between the strips 
must be filled with filler such as silicone resin to isolate the strips 
both electrically and mechanically. If the layer 13 is divided into 
discrete strips, the piezoelectric element array 10 will convert electric 
energy to mechanical energy with high efficiency (i.e., electromechanical 
coupling coefficient). Hence, whether or not the layer 13 should be 
divided into strips depends upon which is more important, the reduction of 
manufacturing cost or the increase in the operating efficiency of the 
array 10. 
As indicated above, the backing layer 80 is provided on the lower surfaces 
of the discrete electrodes 14.sub.1 to .sup.14.sub.n, and the acoustic 
lens 11 on the upper surface of the common electrode 12. The lens 11 is a 
Fresnel lens consisting of thin straight strips and thick straight strips. 
The thick strips have different widths and are spaced by different gaps, 
which are designed on the basis of Fresnel diffraction theory. 
In operation, drive signals which differ in phase are simultaneously 
applied to the discrete electrodes 14.sub.1 to .sup.14.sub.n, driving a 
specific number of adjacent piezoelectric elements. Driven with the drive 
signals, the piezoelectric elements emit ultrasonic beams to a point in 
the surface of liquid ink. In other words, the beams are converged in a 
plane extending along the axis of the array 10 (main-scanning direction). 
Further, the beams are converged by the acoustic lens 11 in a plane 
extending in the direction (sub-scanning direction) at right angles to the 
axis of the piezoelectric element array 10. As a result, the ultrasonic 
beams are converged to a point in the ink surface. The beams thus 
converged applies a pressure to the ink 18, developing an ink meniscus. 
Eventually, an ink droplet 19 flies from that point in the ink surface. An 
ink droplet 19 can be squirted from a different point in the ink surface 
by simultaneously driving a different combination of adjacent 
piezoelectric elements. 
Embodiment 6-2 
FIG. 56 is a sectional view of the recording head section incorporated in 
an ink-jet recording device according to Embodiment 6-2 of the invention. 
The recording head section is mounted on the same substrate as the drive 
IC 21. It comprises a piezoelectric element array 10 and a backing layer 
80. The layer 80 is fitted in a recess made in the upper surface of the 
substrate and located flush with the upper surface of the substrate. The 
array 10 comprises a common electrode 12, a piezoelectric layer 13 and 
discrete electrodes 14. The discrete electrodes 14 are provided partly on 
the backing layer 80 and partly on the upper surface of the substrate. The 
electrodes 14 therefore have no stepped portions. Each discrete electrode 
14 can easily be connected to the drive IC 21 by a metal wire 21b. The 
common electrode 12 can be connected at any desired portion to the drive 
IC 21. The common electrode 12 may be divided into discrete ones, forming 
an electrode array. If this is the case, the discrete electrode 12 are 
made longer as shown in FIG. 57 and connected to the drive IC 21 by metal 
wires 21b, while the discrete electrodes 14 are connected to the drive IC 
21 by metal wires 17b. 
Embodiment 6-3 
FIG. 58 is a sectional view of the recording head section incorporated in 
an ink-jet recording device according to Embodiment 6-3 of the invention. 
This recording head section is characterized by a backing layer 80a. Made 
of material such as alumina or epoxy resin, the layer 80a has sufficient 
mechanical strength and large dielectric constant, so that it can serve as 
a wiring substrate as well. Thus, not only the piezoelectric element array 
10, but also the drive IC 21 is directly mounted on the backing layer 80a. 
It is required that the following relationship be satisfied: 
EQU a.times.2t.times.f&lt;-20 dB 
where a is the attenuation coefficient of ultrasonic waves in the layer 
80a, t is the thickness of the layer 80a, and f is the frequency of the 
ultrasonic waves. The value of 2.times.2t.times.f should be less than -60 
dB for a ultrasonic probe for medical use. By contrast, the requirements 
for an ink-jet head is not so severe. However, the frequency f is far 
higher than in the medical ultrasonic probe, and appropriate values must 
be selected for the attenuation coefficient a and the thickness t of the 
layer 80a. The backing layer 80a should therefore be made of proper 
material and have an appropriate thickness, in order to satisfy the 
relationship of a.times.2t.times.f&lt;-20 dB. 
Provided at the back of the piezoelectric element array 10, the backing 
layer 80a serves to efficiently converge the ultrasonic beams emitted from 
the array 10 at a point in the ink surface and to control the path of a 
flying ink droplet 19. 
Embodiment 7 
FIG. 59 is a perspective view of the recording head section provided in an 
ink-jet recording device according to Embodiment 7 of the present 
invention. The recording head section is similar in structure to the 
recording head section (FIG. 46) of Embodiment 5-1. It differs only in 
that the acoustic lens 11 has a width D less than the length L of a group 
of piezoelectric elements which are driven at the same time. 
One of the parameters that determine the size of an ink droplet which the 
recording head section squirts is the frequency of the ultrasonic beams 
the piezoelectric elements emit. The frequency of the beams is inversely 
proportional to the thickness of the piezoelectric layer 13, because the 
piezoelectric element array 10 emits ultrasonic beams by virtue of 
resonance which develops vertically in the piezoelectric layer 13. Namely, 
the thinner the layer 12, the higher the beam frequency. Further, the 
higher the beam frequency, the higher the resolution of an image the head 
section can record. The piezoelectric layer 13 should, therefore, be made 
of such a material in such a method that it may be as thin as is possible. 
Material for the piezoelectric layer 13 is selected in accordance with not 
only its desired thickness, but also its electromechanical coupling 
coefficient (i.e., efficiency of converting electric energy to mechanical 
energy) and its dielectric coefficient influencing the electrical matching 
between the layer 13 and the drive IC. Desired material is ceramics much 
as lead zirconate titanate (PZT), a copolymer of polyvinylidine fluoride 
and ethylene trifluoride, single crystal such as lithium niobate, or a 
semiconductor piezoelectric substance such as zinc oxide (ZnO), or a 
high-molecular piezoelectric substance such a copolymer (P(VDF-TrFE)) of 
polyvinylidine fluoride and ethylene trifluoride. To be more specific, the 
layer 13 should be made of PZT for an ink-jet printer which records images 
of resolution of 600 dpi or less, and made of ZnO for an ink-jet printer 
which records images of resolution higher than 600 dpi. In the case where 
the layer 13 is prepared by polishing a bulk of PZT or the like, an 
adhesion layer is interposed between the acoustic lens 11 and the common 
electrode 12. The recording head section (FIG. 46) of Embodiment 5-1 does 
not have such an adhesion layer. 
The common electrode 12 and the discrete electrodes 14 are made of Ti, Ni, 
Al, Cu, Cr, Au or the like, are comprised each a plurality of metal films 
formed by either vapor deposition or sputtering, or have been formed by 
print-coating a film made of silver paste containing glass flits and then 
by backing the film. The acoustic lens 11 is made of glass, resin or the 
like. If a layer of PZT or the like is bonded to the acoustic lens 11 by 
an adhesive, the lens 11 must be made of material which is easy to 
process, and the piezoelectric layer 13 must be made of material which 
achieves acoustic matching with the ink 18. If a layer of ZnO or the like 
is formed by sputtering, the lens 11 must be made of materials which not 
only is easy to process but also can withstand the sputtering temperature, 
and the piezoelectric layer 13 must be made of material which not only 
achieves acoustic matching with the ink 18 but also is easy to orient its 
grains. 
In Embodiment 7, the driving IC 21 sequentially performs the linear 
electronic scanning by driving the piezoelectric element array 10 with 
unit block of which a single block consists of piezoelectric element group 
having n piezoelectric elements adjacent in the array direction (extending 
direction of piezoelectric elements, or main -scanning direction) 
according to the image data to be recorded. 
In operation, the drive circuit 21 drives the piezoelectric element array 
10 in accordance with the input image data, thereby performing liner 
electronic scanning. To be more specific, the circuit 17 simultaneously 
drives the first to n-th piezoelectric elements with high-frequency drive 
signals which differ in phase, as is illustrated in FIG. 60. Next, the 
circuit 17 simultaneously drives the second to (n+1)th piezoelectric 
elements with high-frequency drive signals which differ in phase. Then, 
the circuit 17 simultaneously drives the third to (n+2)th piezoelectric 
elements with high-frequency drive signals which differ in phase, and so 
forth. As a result, the point at which the ultrasonic beams emitted from 
the piezoelectric elements converge linearly moves in the main scanning 
direction. The drive signals are either rectangular bursts as shown in 
FIG. 61 or sine-wave bursts. As described above, the drive signals have 
differ in phase. This means that the signals have leading edges at 
different times. A piezoelectric element array 10 according to Embodiment 
7 (FIG. 46) was made. More precisely, a piezoelectric layer 13 was 
prepared, which had a thickness of 100 .mu.m, made of PZT-based ceramic 
having a dielectric coefficient of 2000 and a resonance frequency of 20 
MHz. Two electrodes were formed by sputtering on the surfaces of the 
piezoelectric layer 13, respectively. Each electrode was comprises of 
three metal layers formed one on another, i.e., an Ti layer having a 
thickness of 0.05 .mu.m, an Ni layer having a thickness of 0.05 .mu.m and 
an Au layer having a thickness of 0.2 .mu.m. An electric field of 2 kv/mm 
was applied to the electrodes, thereby polarizing the electrodes. 
Thereafter, the electrode on one surface of the piezoelectric layer 13 was 
divided by etching, into discrete electrodes 14. The discrete electrodes 
14 had a width of 120 .mu.m, with gaps of 30 .mu.m among them. The 
discrete electrodes 14 were juxtaposed at the pitch of 150 .mu.m. The 
piezoelectric element array 10 thus made comprised the piezoelectric layer 
13, a common electrode 12 provided on one surface of the layer 13, and 
discrete electrodes 14 provided on the opposite surface of the layer 13. 
An acoustic lens 11 was made of a Pyrex glass plate having a thickness of 2 
mm. The lens 11 had a straight groove having a width of 1.5 mm and a 
concave bottom. The curvature of the concave bottom was 2.3 mm. The 
acoustic lens 11 and the piezoelectric element array 10 were adhered 
together by an epoxy-resin adhesive, with the common electrode 12 set in 
axial alignment with the straight groove of the lens 11. Then, an ink 
reservoir 15 and a drive circuit 71 were mounted on the upper and lower 
surfaces of the acoustic lens 11, respectively. An ink-jet head was 
thereby manufactured. The ink reservoir 15 had a depth of 3 mm and was 
filled with liquid ink 18. The surface of the ink 18 was 5 mm above the 
common electrode 12 of the array 10. The acoustic lens 11 satisfied the 
relationship of t&lt;D1/.lambda., where t is the thickness (2 mm) of the lens 
11, D is the width (1.5 mm) of the groove and .lambda. is the wavelength 
of the ultrasonic waves traveling through the lens 11. 
The ink-jet head was driven repeatedly, each time by driving a different 
number n of piezoelectric elements simultaneously, thereby squirting an 
ink droplet onto a recording medium. The numbers n were 10 (10 elements 
driven simultaneously forming a group extending 1.5 mm in the main 
scanning direction) and 24 (24 elements driven simultaneously forming a 
group extending 3.6 mm in the main scanning direction). The ultrasonic 
beam pattern formed at the same distance as the ink surface were examined. 
A -10 dB beam had a width of 0.33 mm at that position in the sound field 
which is central in the sub-scanning direction. When n=24, the resultant 
beam had a width of 0.34 mm, almost equal to the width of the -10 dB beam. 
When n=10, the resultant beam had a width of 0.76 mm, much greater than 
the width of the -10 dB beam. When various combinations of elements, each 
consisting of 16 elements (n=16), were sequentially driven, ink droplets 
having a size of about 80 .mu.m flew from the ink surface, forming 
circular dots on the recording medium in the density of about 200 dpi. 
When various combinations of elements, each consisting of 10 elements 
(n=10), were driven with a drive voltage about 1.3 times higher, ink 
droplets shaped like a rugby ball flew from the ink surface, forming 
elliptical dots on the recording medium in the density of about 130 dpi. 
The acoustic lens 11 which is of the type shown in FIG. 46 may be replaced 
by a Fresnel lens of the type shown in FIG. 62, which has straight grooves 
made in the upper surface and located at specific positions. The distance 
r(n) of each groove from the center of the lens and the depth d of each 
groove are given as follows: 
##EQU5## 
where .lambda.w is the wavelength the ultrasonic beams have while 
traveling through the ink, F is the focal length, and .lambda.l is the 
wavelength the ultrasonic beams have while traveling through the lens 11. 
As shown in FIG. 46 and FIG. 62, the acoustic lens 11 functions as a 
support for the piezoelectric layer 13. Instead, as shown in FIG. 63, an 
acoustic matching layer 11' may be interposed between the lens 11 and the 
common electrode 12, to support the piezoelectric layer 13. 
As described above, the ink-jet head according to Embodiment 7 can 
effectively perform line scanning, due to the use of an piezoelectric 
element array and an acoustic lens. The acoustic lens 11 extends in the 
sub-scanning direction for a distance shorter than the group of 
simultaneously driven elements extends in the main-scanning direction. Ink 
droplets can, therefore, fly efficiently, forming a high-resolution image 
on a recording medium. 
Embodiment 8-1 
FIG. 65 is a perspective view of the recording section incorporated in an 
ink-jet recording device according to Embodiment 8-1 of the present 
invention. Embodiment 8-1 is characterized by discrete electrodes 14 which 
are concentric annular members located near the ink reservoir. Except for 
this feature, Embodiment 8-1 is identical to any other embodiment 
described above. The arrows shown in FIG. 65 indicate the directions in 
which piezoelectric elements are polarized. 
FIGS. 66A and 66B are diagrams showing a piezoelectric element 10 
incorporated in recording head section. Although shaped like a thin disc, 
the element 10 can emit a converged ultrasonic beam. The piezoelectric 
element 10 comprises a plurality of concentric annular members. Of these 
annular members, the odd-numbered ones form a first group, and the 
even-numbered ones form a second group. Two drive voltages in different 
phases are applied to the first group and the second group, respectively, 
through terminals 91 and 92. To be more specific, a 0-phase drive voltage 
is applied to the terminal 91, and a .pi.-phase drive voltage to the 
terminal 92. 
FIG. 67 is a sectional view showing the piezoelectric element 10 in detail. 
As FIG. 67 shows, the element 10 comprises a piezoelectric disc 13, a 
common electrode 12 mounted on one surface of the disc 13, and concentric 
annular discrete electrodes 14 provided on the other surface of the disc 
13. 
FIG. 68 is a plan view illustrating the discrete electrodes 14. As shown in 
FIG. 68, the odd-numbered electrodes 14.sub.1, 14.sub.3 and 14.sub.5 form 
a first group, while the even-numbered electrodes 14.sub.2, 14.sub.4 and 
14.sub.6 form a second group. The discrete electrodes of the first group 
are connected by a conductor 91a, which is connected to the terminal 91. 
Similarly, the discrete electrodes of the second group are connected by a 
conductor 92a, which is connected to the terminal 92. 
A drive circuit (not shown) applies two drive voltages, which differ in 
phase by .pi. as shown in FIG. 66A, to the terminals 91 and 92, 
respectively. As a result, the piezoelectric element 10 emits a converged 
ultrasonic beam. 
It will be explained how the piezoelectric element 10 is manufactured. 
First, the electrode pattern 14 shown in FIG. 68 is formed on a substrate 
(not shown). The annular elements of the pattern 14 are electrically 
isolated by angular insulating layers (not shown, either) between the 
conductor 91A and the electrodes of even number 14.sub.2, 14.sub.4 and 
14.sub.6 and between the conductor 92a and the electrodes 14.sub.1, 
14.sub.3 and 14.sub.5. Then, the piezoelectric disc 13 having a uniform 
thickness is formed on the electrode pattern 14, covering neither the 
terminal 91 nor the terminal 92, by means of thing-film forming process 
such as sputtering. The disc 13 is made of piezoelectric material such as 
ZnO (zinc oxide), PZT (lead zirconate titanate) or PT (lead titanate). The 
common electrode 12 is then formed on the piezoelectric disc 13. Next, the 
disc 13 is uniformly polarized. Thus completes the manufacture of the 
piezoelectric element 10 (i.e., ink-jet head). 
In Embodiment 8-1, only the electrode pattern 14 is Fresnel-divided, 
forming discrete electrodes 14.sub.1 to 14.sub.6. The piezoelectric disc 
13 may also be divided into concentric annular members, of which the 
odd-numbered ones form a first group and the even-numbered ones form a 
second group. 
The recording head section of Embodiment 8-1 may have a plurality of 
ink-jet heads each having a discrete electrode pattern 14 shown in FIG. 
68. In this case, a single piezoelectric layer may be provided, covering 
all discrete electrode patterns 14 and exposing the terminals 91 and 92 
which are integral with the patterns 14. 
Embodiment 8-2 
FIGS. 69A and 69B are diagrams showing the recording head section provided 
in an ink-jet recording device according to Embodiment 8-2 of the 
invention. Like its counterpart of Embodiment 8-1, the recording head 
section has a piezoelectric element 10 which is shaped like a thin disc 
and which can yet emit a converged ultrasonic beam. As shown in FIGS. 69A 
and 69B, the element 10 is divided into concentric annular regions. Of 
these annular regions, the odd-numbered ones form a first group, and the 
even-numbered ones form a second group. The regions of the first group are 
polarized in one direction, whereas the regions of the second group are 
polarized in the opposite direction as indicated by arrow. Thus, the 
ultrasonic beams emitted from the annular regions of the first group are 
out of phase with respect to the ultrasonic beams emitted from the annular 
regions of the second group. 
FIG. 70 is a sectional view of the piezoelectric element 10 shown in FIGS. 
69A and 69B. As illustrated in FIG. 70, the element 10 comprises a 
piezoelectric disc 13, a common electrode 12 mounted on one surface of the 
disc 13, and concentric annular discrete electrodes 14.sub.1 to 14.sub.6 
provided on the other surface of the disc 13. As may be understood from in 
FIG. 68, the discrete electrodes 14.sub.1 to 14.sub.6 have been formed by 
Fresnel-dividing a disc-shaped electrode pattern 14. Those annular regions 
of the disc 13 which contact the odd-numbered electrodes 14.sub.1, 
14.sub.3 and 14.sub.5 are polarized downwards, whereas the annular regions 
of the disc 13 which contact the even-numbered electrodes 14.sub.2, 
14.sub.4 and 14.sub.6 are polarized upwards. All discrete electrodes are 
connected by a conductor 91a, which is connected to a terminal 91. 
The terminal 91 is connected to a drive circuit (not shown). The drive 
circuit applies the same drive voltage to the discrete electrodes 14.sub.1 
to 14.sub.6 of the piezoelectric element 10. Nonetheless, the ultrasonic 
beams emitted from the odd-numbered annular regions of the piezoelectric 
disc 13 differ in phase by .pi. from the ultrasonic beams emitted from the 
even-numbered annular regions of the disc 13. This is because, as 
mentioned above, the odd-numbered annular regions are polarized downwards, 
whereas the even-numbered annular regions are polarized upwards. Thus, 
Embodiment 8-2 achieves the same result as Embodiment 8-1. Embodiment 8-2 
is more advantageous in that the drive circuit need not generate two drive 
voltages and can be more simple in structure. 
In Embodiment 8-2, only the electrode pattern 14 is Fresnel-divided, 
forming discrete electrodes 14.sub.1 to 14.sub.6. The piezoelectric disc 
13 may also be divided into concentric annular members, of which the 
odd-numbered ones form a first group and the even-numbered ones form a 
second group. Furthermore, the recording head section of Embodiment 8-2 
may be modified to have a plurality of ink-jet heads. 
It will be explained how the piezoelectric element 10 shown in FIG. 70 is 
manufactured. 
To manufacture the element 10 shown in FIG. 70 it is necessary to apply a 
high voltage to the odd-numbered annular regions of the piezoelectric disc 
13, and to apply a high voltage of the opposite polarity to the 
even-numbered annular regions of the disc 13. This step of applying high 
voltages is unnecessary to manufacture the piezoelectric element 10 shown 
in FIG. 67, since two drive voltages of different phases are applied to 
the two groups of annular electrodes through the terminals 91 and 92. 
It will now be explained how to manufacture the piezoelectric element 10 
shown in FIG. 70. First, the odd-numbered annular electrodes 14.sub.1, 
14.sub.3 and 14.sub.5 are connected by a conductor (not shown), and the 
even-numbered annular electrodes 14.sub.2, 14.sub.4 and 14.sub.6 are 
connected by a conductor (not shown) as FIG. 67 and FIG. 68. The 
conductors are connected to two terminals, respectively. This done, the 
common electrode 12 is formed on the piezoelectric disc 13. Next, a DC 
high voltage of one polarity is applied between the common electrode 12 
and the first electrode, thereby polarizing the odd-numbered annular 
regions of the disc 13. Further, a DC high voltage of the opposite 
polarity is applied between the common electrode 12 and the second 
electrode, thereby polarizing the even-numbered annular regions of the 
disc 13. Now that the annular regions of the disc 13 of two groups have 
been polarized, the first and second terminals are connected together to 
the terminal 91. 
The piezoelectric element 10 may be manufactured in another method. First, 
a disc-shaped electrode is be formed on the lower surface of the 
piezoelectric disc 13. Then, concentric annular electrodes are formed on 
the upper surface of the disk 13. Next, the odd-numbered annular 
electrodes are polarized in one direction, and the even-numbered annular 
electrodes are polarized in the opposite direction. This done, a 
disc-shaped common electrode is formed on the annular electrodes, by means 
of sputtering or the like. 
Embodiment 8-3 
FIG. 71 is a perspective view of an array-type ink-jet head used in an 
ink-jet recording device according to Embodiment 8-3 of the present 
invention. This ink-jet head is a modification of the recording heads of 
Embodiments 8-1 and 8-2. As shown in FIG. 71, the array-type ink-jet head 
comprises a piezoelectric layer 13, a common electrode 12 formed on the 
upper surface of the layer 13, and discrete electrodes 14 provided on the 
lower surface of the layer 13. The discrete electrodes 14 are juxtaposed 
at regular intervals in main-scanning direction, forming an array. The 
piezoelectric layer 13 is divided into strip-shaped regions in sub-canning 
direction, which is perpendicular to the main-scanning direction. Of these 
regions, the odd-numbered ones are polarized in one direction, and the 
even-numbered ones are polarized in the opposite direction, as indicated 
by the arrows shown in FIG. 71. The common electrode 12, the piezoelectric 
layer 13 and the discrete electrodes 14 form a plurality of piezoelectric 
elements. 
The common electrode 12 is connected to the ground. The discrete electrodes 
14 are connected to a lead 91a, which in turn is connected to a drive 
circuit (not shown). The drive circuit drives n adjacent ones of the 
piezoelectric elements in accordance with the input image data, thereby 
performing phased array scanning. More precisely, the circuit 
simultaneously drives the first to n-th piezoelectric elements with 
high-frequency drive signals which differ in phase. Thus driven, the first 
to n-th elements emit the elements emits ultrasonic beams, which are 
converged in a plane extending in the sub-scanning direction and further 
in a plane extending in the main-scanning direction. Next, the drive 
circuit simultaneously drives the second to (n+1)th piezoelectric elements 
with high-frequency drive signals which differ in phase. Then, the drive 
circuit simultaneously drives the third to (n+2)th piezoelectric elements 
with high-frequency drive signals which differ in phase, and so forth. As 
a result, the point at which the ultrasonic beams emitted from the 
piezoelectric elements converge linearly moves in the main scanning 
direction. 
Converted twice, in two planes perpendicular to each other, the ultrasonic 
beams emitted from the array 10 of piezoelectric elements reach one point 
in the surface of the liquid ink filled in an ink reservoir (not shown). 
As a result, an ink droplet flies from that point onto a recording medium. 
Since, the point linearly moves by virtue of phased array scanning, the 
array-type ink-jet head can serve to provide a line printer. In this case, 
ink droplets can form dots on the recording medium at a density higher 
than determined by the pitch at which the piezoelectric elements are 
juxtaposed in the main-scanning direction. 
It will be explained how the array-type ink-jet head is manufactured, with 
reference to FIG. 72 which is a perspective view showing, in more detail, 
the ink-jet head shown in FIG. 71. 
First, the discrete electrodes 14 are formed on a substrate 26. Then, the 
piezoelectric layer 13 is formed on the substrate 26, covering the 
discrete electrodes 14. Next, an electrode is formed on the piezoelectric 
layer 13 and Fresnel-divided into strips, as is indicated by the broken 
lines shown in FIG. 72. The discrete electrodes 14 are then connected 
together, and the piezoelectric layer 13 is polarized as indicated by the 
arrows shown in FIG. 72. Thereafter, the electrodes on the upper surface 
of the layer 13 are connected together, or an electrode is formed on these 
electrodes, thereby forming the common electrode 12. 
The array-type ink-jet head may be manufactured in another method. At 
first, Fresnel-divided, strip-shaped electrodes are formed on the 
substrate 26. Next, the piezoelectric layer 13 is formed on the substrate 
26, covering the strip-shaped electrodes. Then, an electrode is formed on 
the piezoelectric layer 13, and the layer 13 is polarized in the same way 
as described above. This done, the strip-shaped electrodes are connected 
together, forming the common electrode 12. Finally, the electrode on the 
upper surface of the piezoelectric layer 13 is partly etched, forming the 
discrete electrodes 14 spaced apart at regular intervals. 
Since the strip-shaped piezoelectric elements can emit converged ultrasonic 
beams, the array-type ink-jet head according to Embodiment 8-3 is 
energy-efficient, can be manufactured at low cost, and can yet record 
high-resolution images. 
Embodiment 9 
FIGS. 73A and 73B are a sectional view and a plan view of the ink-jet heat 
used in an ink-jet recording device according to Embodiment 9 of the 
present invention. As seen from FIGS. 73A and 73B, the ink-jet head 
comprises an insulating substrate 26 made of glass or the like and having 
a trough-like groove, and a piezoelectric element array 10 provided in the 
groove. The array 10 comprises a thin-film piezoelectric layer 13, a 
common electrode 12 mounted on one surface of the layer 13, and discrete 
electrodes 14 provided on the opposite surface of the layer 13. The 
discrete electrodes 14 extend onto the flat part of the substrate 26. 
The piezoelectric layer 13 is made of piezoelectric material such as ZnO 
(zinc oxide), PZT (lead zirconate titanate) or PT (lead titanate), formed 
by means of thin-film forming process such as sputtering. The common 
electrode 12 has been formed by sputtering metal on the piezoelectric 
layer 13. If necessary, an acoustic matching layer or an waterproof 
coating is provided on the common electrode 12. The end portions of the 
discrete electrodes 14, located on the flat part of the substrate 26, are 
connected to a drive IC (not shown) which is mounted on the substrate 26. 
How to form the discrete electrodes 14 in the groove of the substrate 26 
will be explained, with reference to FIGS. 74A to 74D. 
First, as shown in FIG. 74A, metal foil 14a is patterned, forming having 
parallel elongated slits. Meanwhile, a glass substrate 26 is prepared, 
which has a trough-like groove 26h as illustrated in FIG. 74B. An 
electrode (not shown) is provided on the lower surface of the substrate 
26. 
Next, as shown in FIG. 74C, the metal foil 14a is placed on the substrate 
26. An electric field from a DC power supply 93 is applied between the 
foil 14a and the substrate 26 at high temperature ranging from 300 to 
500.degree. C. The metal foil 14a is thereby pressed onto the substrate 26 
by virtue of electrostatic force. This press-bonding of a metal layer to a 
glass substrate is known as "anode bonding." The edge portions of the foil 
14a, which connect the strip-shaped portions, are then cut off. The 
discrete electrodes 14 are thereby provided partly in the trough-like 
groove 26h and partly on the flat portion of the substrate 26. 
If the case where the discrete electrodes 14 need to be thinner than can be 
formed from processing metal foil, they will be formed by forming a metal 
film by sputtering on a film of, for example, polyimide, and then by 
patterning the metal film thus formed. In this case, the metal film is 
fixed to the polyimide film. Hence, it be patterned, in its entirety, into 
strips, without necessity of leaving the edge portions. Despite this, the 
metal film is patterned, forming having parallel elongated slits, and its 
edge portions are cut off after the strip-shaped portions have been bonded 
to the glass substrate by bonding and the polyimide film has been etched 
away. 
Another method of forming the discrete electrodes 14 on the substrate 26 
will be explained with reference to FIGS. 75A to 75F. First, as shown in 
FIG. 75A, a light-shielding mask 101 is prepared. The mask 101 is made of 
resin film 102, designed to pattern a metal film into discrete electrodes 
14. Then, as shown in FIG. 75B, the mask 101 is bent, forming a bulging 
portion which will fit into the trough-like groove 26h of the substrate 
26. The light-shielding mask 101 is mounted on the substrate 26, with the 
bulging portion fitted in the groove 26h, as illustrated in FIG. 75C. 
Next, as shown in FIG. 75D, a metal film 103 is formed on the substrate 26 
by means of sputtering, and a resist 104 is spin-coated on the metal film 
102. 
Further, as shown in FIG. 75E, the mask 101 is mounted on the resist 104, 
with the bulging portion aligned with the groove 26h of the substrate 26. 
The resist is exposed to light, and selective etching is performed on the 
metal film 103. As a result, the discrete electrodes 14 are formed in the 
groove 26h and on the substrate 26 with high precision, as illustrated in 
FIG. 75F. 
With Embodiment 9 it is easy to form U-shaped piezoelectric elements, by 
forming a piezoelectric layer on the substrate 26 after the discrete 
electrodes have been formed partly in the trough-like groove 26h of the 
substrate 26. In addition, the discrete electrodes can be formed with high 
precision, either by bonding the patterned metal foil in the groove 27h 
through anode bonding, or by fitting the bulging portion of the patterned 
mask 101 into the trough-like groove 27h. Formed with high precision, the 
discrete electrodes serve to record images of resolution as high as 
hundreds of dots per inch. 
Embodiment 10 
FIGS. 76A and 76B are a sectional view and a plan view of an ink-jet heat 
used an ink-jet recording device according to Embodiment 10 of the 
invention. As shown in FIG. 76A, the ink-jet head comprises a flat 
substrate 26 and a piezoelectric element array 10 mounted on the substrate 
26. The array 10 comprises a piezoelectric layer 13, a common electrode 12 
provided on one surface of the layer 13, and discrete electrodes 14 
provided on the opposite surface of the layer 13. Each discrete electrode 
14 has a U-groove made in its upper surface. Located in the U-groove, the 
common electrode 12 and the piezoelectric layer 13 are U-shaped, too. 
The discrete electrodes 14 have been formed by alternately combining 
plate-shaped conductors 106 and plate-shaped insulators 107, forming a 
rectangular block 95, and by forming a trough-like groove 95a in the upper 
surface of the block 95 as shown in FIG. 77B. The piezoelectric layer 13 
is mounted in the groove 95a, and the common electrode 12 is placed on the 
layer 13, whereby the array 10 is provided. The block 95 is secured on the 
substrate 26. The piezoelectric layer 13 is made of piezoelectric material 
such as ZnO (zinc oxide), PZT (lead zirconate titanate) or PT (lead 
titanate), formed by means of thin-film forming process such as 
sputtering. The common electrode 12 has been formed by sputtering metal on 
the piezoelectric layer 13. If necessary, an acoustic matching layer or an 
waterproof coating is provided on the common electrode 12. 
As shown in FIG. 76A, the plate-shaped conductors 106 (i.e., discrete 
electrodes 14) have their ends connected by bonding wires 91a to 
electrodes 91 provided on the substrate 26. The electrodes 91 are 
connected to a drive IC (not shown) which is mounted on the substrate 26. 
A method of forming the block 95 having the groove 95a will be explained, 
with reference to FIGS. 77A and 77B. At first, as shown in FIG. 77A, the 
conductors 106 (e.g., 35 .mu.m thick) and the insulators 107 (e.g., 4 
.mu.m thick), each shaped like a plate, are alternately juxtaposed and 
bonded together with an adhesive, thus forming a block. Thus, the 
conductors 106 (i.e., discrete electrodes 14) are arranged at the pitch of 
40 .mu.m. The block is cut, into an elongated block 95 which is, for 
example, 10 mm wide and 1 mm thick. A trough-like groove 95a is formed in 
on surface of the block 95. The groove 95a extends in the same direction 
as the conductors 106 and the insulators 107 are juxtaposed. The bottom of 
the groove 95a has a radius of curvature of, for example, 4 mm. 
The block 95, thus formed, is placed on and secured to the substrate 26 as 
shown in FIGS. 76A and 76B. The piezoelectric layer 13 is formed in the 
trough-like groove of the substrate 26. If necessary, the upper surface of 
each conductor 106 is plated to orient the crystals of the layer 13 and to 
facilitate the wire-bonding of the conductor 106 to the electrode 91. 
Finally, the common electrode 12 is formed on the piezoelectric layer 13. 
The block 95 described above can be formed by anisotropic etching of 
silicon. More specifically, an electrically conductive silicon substrate 
directly bonded to a glass substrate is anisotropically etched, forming 
deep, narrow parallel grooves. Due to the grooves, the silicon substrate 
is divided into a plurality of plate-shaped conductors. These grooves are 
filled with insulating resin, thus forming plate-shaped insulators. The 
conductors and the insulator, which are alternately juxtaposed, constitute 
a block. The block is mechanically processed to have a trough-like groove 
in its the upper surface. 
As described above, the discrete electrodes of the ink-jet head used in 
Embodiment 10 are formed by alternately juxtaposing conductors and 
insulators, each shaped like a plate, by bonding them together, forming an 
elongated block, and by mechanically forming a trough-like groove in the 
upper surface of the block. The discrete electrodes are therefore formed 
with precision in the order of microns. Provided with high-precision 
discrete electrodes, the ink-jet head can record images of resolution as 
high as hundreds of dots per inch. 
Embodiment 11 
The recording head section incorporated in an ink-jet recording device 
according to Embodiment 11 of the invention will be described. The 
recording head section is similar in structure to the recording head 
section (FIG. 46) of Embodiment 5-1. It differs only in the piezoelectric 
element array and the connection between the array and the drive circuit. 
FIG. 78 shows the discrete electrodes 14 of the piezoelectric element array 
10. As seen from FIG. 78, all discrete electrodes, but the electrodes 
14.sub.1 and 14.sub.2 at either end, are connected to drive signal sources 
S1 to Si provided in the drive circuit 21. The drive circuit 21 has delay 
circuits, which are not shown in FIG. 78. In other words, the drive 
circuit 21 does not drive the electrode 14.sub.1 and 14.sub.2 at either 
end of the array 10. These discrete electrodes are set at the same 
potential as the common electrode (not shown), e.g., at the ground 
potential. 
Namely, Embodiment 11 is characterized in that at least two of the 
piezoelectric elements of the array 10, which are located at the ends of 
the array 10, do not emit ultrasonic beams, not serving to squirt ink 
droplets. These elements help to reduce the average capacitive load for 
the piezoelectric elements which serve to squirt ink droplets. In 
addition, the acoustic couplings of the elements driven by the drive 
circuit 21 are averaged since the associated discrete electrodes are 
juxtaposed at regular intervals. As a result of this, cross-talk noise is 
far less than in the recording head section of the conventional ink-jet 
recording device. 
This advantage will be described in more detail, with reference to FIGS. 
79A and 79B. 
As shown in FIG. 79A, not only capacitive load C1 between the common 
electrode 12 and each discrete electrodes 14, but also capacitive load C2 
between any two adjacent discrete electrodes 14 is present in the 
piezoelectric element array 10. A piezoelectric element array identical to 
the array 10 shown in FIG. 79A was made and driven. The element Ta located 
at one end of the array had capacitive load about 13% less than that of 
the element Tb located at either end. The capacitive load C2 is calculated 
to be about a fifth (1/5) of the capacitive load C1. The less the pitch of 
the discrete electrodes 14, the greater the difference between the 
capacitive loads C1 and C2 and the greater the difference between the 
capacitive loads of the elements Ta and Tb. Even if the elements Ta and Tb 
are driven by the same drive signal, they will generate different 
cross-talk noises. These noises will influence the ultrasonic waves the 
elements Ta and Tb emit. 
How much the piezoelectric member of each piezoelectric element is deformed 
depends on the drive voltage applied to the piezoelectric member and the 
strain in the piezoelectric member. As shown in FIG. 79B, the element Ta 
is deformed to one side, quite differently from the element Tb located at 
neither end of the piezoelectric element array. The acoustic coupling of 
the element Ta influences the ultrasonic beams emitted from the elements 
(including Tb) driven by the drive circuit 21. 
The ultrasonic beam emitted from any piezoelectric element located near the 
element Ta is reflected by the wall of the ink reservoir. This impairs the 
convergence of the ultrasonic beams emitted from the driven piezoelectric 
elements. 
An ink-jet head similar to the recording head section (FIG. 46) of 
Embodiment 5-1 and incorporating a piezoelectric element array 10 of the 
type shown in FIG. 78 was manufactured. All piezoelectric elements, except 
those located at the ends of the array 10, were driven repeatedly, each 
time n elements, as in the embodiments described above, thereby forming a 
line of dots on recording paper. The dots were uniform in size and ink 
concentration, even at the end portions of the line. 
A conventional ink-jet head shown in FIG. 80 was manufactured and driven, 
for comparison with the ink-jet head according to Embodiment 11. As can be 
understood from FIG. 80, all piezoelectric elements of the conventional 
ink-jet head, including those located at the ends of the array, were 
driven repeatedly, each time n elements, thereby forming a line of dots on 
recording paper. The dots forming the end portions of the line were 
neither uniform in ink concentration nor aligned with the middle portion 
of the line. This may be attributed to two facts. First, the piezoelectric 
elements at the ends of the array generated cross-talk noise different 
from the cross-talk noise the other elements generated, as has been 
explained with reference to FIG. 79A and 79B. Second, the ultrasonic beam 
emitted from the elements were reflected by the walls 15a and 15b of the 
ink reservoir, impairing the convergence of the ultrasonic beams emitted 
from the driven piezoelectric elements. 
In Embodiment 11, the number of piezoelectric elements located at either 
end of the array 10 and not driven is optional. Furthermore, the number of 
elements located at one end of the array 10 and not driven may either be 
the same or different from the number of elements located at the other end 
of the array 10 and not driven. Still further, wires may be connected to 
the elements located at either end of the array 10 and not driven, for a 
particular purpose. 
Moreover, as illustrated in FIG. 81, grooves 22 may be cut in one surface 
of the piezoelectric layer 13 in order to minimize the influence of the 
acoustic coupling of the piezoelectric elements. The drive signals 
generated by the drive signal sources S1 to Si can be of any type that can 
drive the piezoelectric elements such that the ultrasonic beams emitted 
from the elements may converge at a point. 
In Embodiment 11, the cross-talk noise and acoustic coupling of each 
piezoelectric element can be reduced easily since the piezoelectric 
elements driven simultaneously have the same cross-talk noise and the same 
acoustic coupling. The drive circuit can be one having a simple structure, 
and the convergence of the ultrasonic beams emitted from the 
simultaneously driven piezoelectric elements is influenced but very little 
by the ultrasonic beam emitted from the elements and reflected by the 
walls of the ink reservoir. 
Additional advantages and modifications will readily occur to those skilled 
in the art. Therefore, the present invention in its broader aspects is not 
limited to the specific details, representative devices, and illustrated 
examples shown and described herein. Accordingly, various modifications 
may be made without departing from the spirit or scope of the general 
inventive concept as defined by the appended claims and their equivalents.