Piezoelectric type liquid droplet ejecting device which compensates for residual pressure fluctuations

A piezoelectric-type liquid droplet ejecting device including a piezoelectric element. A predetermined voltage pulse is applied to the piezoelectric element, whereupon residual pressure fluctuations are generated in the pressure chamber of the liquid droplet ejecting device. The piezoelectric element or a separate piezoelectric element generates an electric signal corresponding to the residual pressure fluctuations. A detection circuit receives the electric signal and supplies a detection signal corresponding to the electric signal to a calculation circuit for calculating a voltage pulse. The calculation circuit supplies the voltage pulse to a drive circuit, which applies it to the piezoelectric element. The voltage pulse deforms the piezoelectric element upon application thereto in a manner sufficient to compensate for residual pressure fluctuation in the pressure chamber.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a piezoelectric-type liquid droplet 
ejecting device and more particularly to more precisely compensating for 
residual pressure in the pressure chamber of the piezoelectric-type liquid 
droplet ejecting device caused by ejecting a droplet. 
2. Description of the Related Art 
Piezoelectric-type liquid droplet ejecting devices are used for ejecting a 
variety of liquids. The printhead of ink-jet printers often include a 
plurality of piezoelectric-type liquid droplet ejecting devices aligned in 
a row. As shown in FIG. 1, a conventional piezoelectric-type liquid 
droplet ejecting device included in such an ink-jet printer head includes 
a pressure chamber 10 defined by a housing 12. An ejection liquid, ink in 
this example, fills the pressure chamber 10. An ink supply channel 24 for 
supplying ink to the pressure chamber 10 is formed in one side of the 
housing 12 and a nozzle 22 through which ink is ejected is formed in the 
other. To a resilient side wall 14 of the housing 12 is provided a 
piezoelectric element 16, for example, a PZT (lead zirconate titanate) 
piezoelectric transducer. A pair of electrodes (not shown) are formed to 
opposing surfaces of the piezoelectric element 16. A drive circuit 18 is 
electrically connected to the electrodes of the piezoelectric element 16 
for supplying a voltage thereto. 
To eject ink from the pressure chamber 10 through the nozzle 22, the drive 
circuit 18 applies a pulse of voltage, hereinafter referred to as the 
drive voltage pulse, to an electrode of the piezoelectric element 16. The 
piezoelectric element 16, and consequently the resilient side wall 14, 
deforms to the shape indicated by the one-dash chain line. The internal 
volume of the pressure chamber 10 reduces accordingly, which increases the 
pressure of the pressure chamber 10, ejecting an ink droplet 20 from the 
nozzle 22. When the drive voltage pulse is completed and voltage applied 
by the drive circuit 30 returns to zero volts, the piezoelectric element 
16 returns to its initial shape (shape before it deformed), the volume in 
the pressure chamber 10 increases, and the pressure in the pressure 
chamber 10 decreases so that ink is sucked from the ink supply channel 24 
into the pressure chamber 10. 
The change in volume which ejects ink also generates a pressure wave in the 
pressure chamber 10. The pressure wave propagates via the ink medium in 
all directions throughout the pressure chamber 10 and crosses the pressure 
chamber 10 several times by reflecting off the housing 12 attenuating as 
it progresses. This pressure wave causes residual pressure fluctuations in 
the pressure chamber 10. Such residual pressure fluctuations, especially 
those near the nozzle, affect successive ink ejections. As shown in FIG. 
2, as a result of the pressure wave, the pressure near the nozzle 22 
fluctuates at a set cycle, with positive and negative pressure peaks, even 
after the piezoelectric element 16 returns to its initial shape upon the 
lowering edge of the drive voltage pulse. The set cycle of the residual 
pressure fluctuation is determined by the form of the pressure chamber 10 
and the propagation speed of the pressure wave. 
If the drive voltage pulse to eject a successive droplet is applied at time 
A shown by the one-dash chain line in FIG. 2, although deformation of the 
piezoelectric element 16 will reduce the volume of the pressure chamber 
10, because the pressure near the nozzle 22 is negative due to pressure 
fluctuations caused by the pressure wave of the previous ink ejection, 
pressure may not increase sufficiently in the pressure chamber 10 to eject 
an ink droplet. Even if pressure is sufficient to eject an ink droplet, 
the actual speed and volume of the droplet may vary from the desired speed 
and volume, causing variations in the printed characters. When succeeding 
ink ejections are performed varies greatly with desired character 
patterns, print speeds, and the like. Residual pressure fluctuations cause 
considerable variations in the ejection speed and volume of ink droplets. 
There has been known a piezoelectric-type liquid droplet ejecting device, 
such as that described in Japanese Patent Application Kokai No. 
SHO-61-3752, which attempts to reduce residual pressure fluctuations in 
the pressure chamber 10. The concept behind this liquid droplet ejecting 
device is to attempt to negate the residual pressure fluctuation by 
applying a negative cancellation pressure to the pressure chamber 10 when 
the residual pressure fluctuation is thought to be at a positive pressure 
peak. The negative cancellation pressure is generated by applying a cancel 
voltage pulse to the piezoelectric element 16. The cancel voltage pulse is 
a voltage pulse applied to the piezoelectric element 16, but with current 
reverse to that applied during ink ejection. Upon application of the 
cancel voltage pulse, the piezoelectric element 16 deforms outwardly, that 
is, in the opposite direction as during ink ejection, increasing the 
volume in the pressure chamber 10 and consequently reducing the pressure 
therein. Ideally, when the residual pressure near the nozzle 22 becomes 
high, as at time B in FIG. 2, a cancel voltage pulse is applied to the 
piezoelectric element 16. The cancel voltage pulse applied at this time 
will cause the piezoelectric element 16 to deform, thereby increasing the 
volume within the pressure chamber 10, and negating the residual pressure 
as indicated by the broken line in FIG. 2. 
The cycle of the residual pressure fluctuation varies with the shape of the 
pressure chamber 10, that is, the distance from the ink supply channel 24 
to the nozzle 22, and the propagation speed of the pressure wave in the 
pressure chamber 10. Also, the strength of the residual pressure depends 
on the attenuation rate of the pressure wave. Therefore when and at what 
strength the cancel voltage pulse is to be applied in the device described 
in Japanese Patent Application Kokal No. SHO-61-3752 is predetermined by 
tests which take these variables into account. The time of application and 
strength of the cancel voltage pulse can also be manually adjusted in this 
device to take into account dimensional errors. Also reducing the volume 
in the pressure chamber 10 to increase pressure when the residual pressure 
is negative also negates the residual pressure. 
However, there has been known a problem with conventional 
piezoelectric-type liquid droplet ejecting devices in that fluctuations in 
residual pressure are affected by the qualities of the ink, the ambient 
environment (that is, where the device is used), and the like. For 
example, the propagation speed of the pressure wave is affected by changes 
in temperature. Also, the rate at which the pressure wave attenuates 
changes with the qualities of the ink and the abundance of air bubbles 
mixed in the ink. Changes brought about by causes such as these change the 
cycle and the amplitude of the residual pressure fluctuations, 
invalidating the effectiveness of predetermined cancel voltage pulses. 
When the time of application of the cancel voltage pulse is only slightly 
off, predetermined cancel voltage pulses will only partially reduce 
residual pressure. If time of application of the cancel voltage pulse is 
off by a half cycle, the pressure waves will actually be strengthened. 
Although some piezoelectric-type liquid droplet ejecting devices, as 
described above, can be readjusted to eliminate residual pressure 
fluctuations by compensating for changes in the ambient environment, these 
adjustments require troublesome operations and, moreover, a great deal of 
skill, so they are not always practical. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to overcome the 
above-described drawbacks, and to provide a piezoelectric-type liquid 
droplet ejecting device which compensates for residual pressure 
fluctuations regardless of changes in the ambient environment and 
qualities of the ink. The present invention compensates for residual 
pressure fluctuations in the pressure chamber by, for example, negating 
the residual pressure fluctuation by applying a cancel voltage pulse to 
the piezoelectric element, by timing the application of successive voltage 
pulses for ejecting droplets to when the residual pressure detected in the 
pressure chamber is at, for example, a maximum pressure value or at zero 
pressure, or by modifying successive voltage pulses for ejecting droplets 
to meet other parameters of the residual pressure detected in the pressure 
chamber so as to successfully eject successive liquid droplets. 
A piezoelectric-type liquid droplet ejecting device according to the 
present invention for ejecting a liquid from a pressure chamber, the 
pressure chamber having an internal volume for containing the liquid, may 
include a piezoelectric element for changing the internal volume of the 
pressure chamber in response to application of electric voltage; a 
residual pressure fluctuation detection means for detecting residual 
pressure fluctuation, the residual pressure fluctuation being generated in 
the pressure chamber by application of a predetermined voltage pulse with 
a predetermined parameter to the piezoelectric element, the piezoelectric 
element deforming upon application of the predetermined voltage pulse; and 
a residual pressure fluctuation compensating means, for determining a 
compensation voltage pulse based on the residual pressure fluctuation 
detected by the residual pressure fluctuation detection means and for 
applying the compensation voltage pulse to the piezoelectric element, the 
compensation voltage pulse deforming the piezoelectric element upon 
application thereto in a manner sufficient to compensate for residual 
pressure fluctuation in the pressure chamber. 
The residual pressure fluctuation detection means preferably includes a 
detection element for generating an electric signal corresponding to 
residual pressure fluctuations in the pressure chamber, and a detection 
circuit connected to the detection element for receiving the electric 
signal and supplying a detection signal corresponding to the electric 
signal to the residual pressure fluctuation compensating means, and the 
residual pressure fluctuation compensation means preferably includes a 
calculation circuit for calculating the compensation voltage pulse based 
on residual pressure fluctuations as detected by the detection means, and 
a drive circuit for applying the compensation voltage pulse to the 
piezoelectric element. 
The calculation circuit preferably determines voltage, duration, and time 
of application of the compensation voltage pulse as required for negating 
the residual pressure fluctuation in the pressure chamber. 
The drive circuit preferably applies the compensation voltage pulse 
calculated in the calculation circuit to the piezoelectric element before 
application of an ejection voltage pulse, the ejection voltage pulse being 
of sufficient voltage and duration for causing the piezoelectric element 
to deform sufficiently to eject a liquid droplet from the pressure 
chamber. 
The calculation circuit preferably includes a peak detection means for 
detecting a peak in the electric signal; a peak level detection means for 
detecting a level of the peak; a half cycle calculation means for 
calculating a half cycle of the electric signal: a phase calculation means 
for calculating a phase based on the predetermined voltage pulse and the 
peak electric signal; and a compensation voltage pulse calculation means 
for calculating the voltage of the compensation voltage pulse based on the 
level of the peak, the pulse width of the compensation voltage pulse based 
on the half cycle, and the application time of the compensation voltage 
pulse based on the phase. 
The detection element may include the piezoelectric element, the 
piezoelectric element being deformed by residual pressure fluctuations in 
the pressure chamber, the piezoelectric element generating the electric 
signal by the piezoelectric electric effect corresponding to the residual 
pressure fluctuations, the piezoelectric element supplying the electric 
signal to the detection circuit, and the drive circuit preferably 
selectively applying the compensation voltage pulse and the ejection 
voltage pulse to the piezoelectric element. 
The drive circuit may include an isolation means for electrically isolating 
the drive circuit from the piezoelectric element during detection of 
residual pressure fluctuation in the pressure chamber. 
The detection element may include another piezoelectric element, the 
another piezoelectric element being deformed by residual pressure 
fluctuations in the pressure chamber, the another piezoelectric element 
generating the electric signal by the piezoelectric electric effect 
corresponding to the residual pressure fluctuations, the another 
piezoelectric element supplying the electric signal to the detection 
circuit, and the drive circuit selectively applying the ejection voltage 
pulse and the compensation voltage pulse to the piezoelectric element. 
The predetermined voltage pulse may be of sufficient voltage and duration 
for causing the piezoelectric element to deform sufficiently to eject a 
liquid droplet from the pressure chamber. 
The piezoelectric-type liquid droplet ejecting device may further include a 
predetermined voltage pulse application means for applying the 
predetermined voltage pulse to the piezoelectric element; and a memory 
means for storing a waveform of the compensation voltage pulse calculated 
in the calculation circuit and for supplying the compensation voltage 
pulse to the drive circuit. 
The compensation voltage pulse may include a combination of an ejection 
voltage pulse being of sufficient voltage and duration for causing the 
piezoelectric element to deform sufficiently to eject a liquid droplet 
from the pressure chamber; and a cancel voltage pulse being of sufficient 
voltage and duration for negating residual pressure fluctuation upon being 
applied to the piezoelectric element, the residual pressure fluctuation 
being generated in the pressure chamber by application of the ejection 
voltage pulse to the piezoelectric element. 
The calculation circuit may include a peak detection means for detecting a 
peak and an ensuing peak In the electric signal; a peak level detection 
means for detecting the peak level of the peak, and the ensuing peak level 
of the ensuing peak; a half cycle calculation means for calculating a half 
cycle of the electric signal corresponding to the time duration between 
when the peak level is detected and when the ensuing peak level is 
detected; an attenuation calculation means for calculating an attenuation 
rate based on the ratio of the peak level and the ensuing peak level; and 
a compensation voltage pulse waveform calculation means for calculating 
the waveform of the compensation voltage pulse so that an amplitude of the 
ejection voltage pulse and an amplitude of the cancel voltage pulse are at 
a ratio substantially equal to the ratio of the peak level and the ensuing 
peak level, so that the ejection voltage pulse and the cancel voltage 
pulse are respectively applied at durations substantially equal to the 
half cycle, and so that the cancel voltage pulse is applied substantially 
one half cycle after completion of application of the ejection voltage 
pulse. 
The detection element may include the piezoelectric element, the 
piezoelectric element being deformed by residual pressure fluctuations in 
the pressure chamber, the piezoelectric element generating the electric 
signal by the piezoelectric electric effect corresponding to the residual 
pressure fluctuations, the piezoelectric element supplying the electric 
signal to the detection circuit, and the drive circuit may selectively 
apply the compensation voltage pulse and the ejection voltage pulse to the 
piezoelectric element. 
The drive circuit may include an isolation means for electrically isolating 
the drive circuit from the piezoelectric element during detection of the 
residual pressure fluctuation in the pressure chamber. 
The detection element may include second piezoelectric element, the second 
piezoelectric element being deformed by residual pressure fluctuations in 
the pressure chamber, the second piezoelectric element generating the 
electric signal by the piezoelectric electric effect corresponding to the 
residual pressure fluctuations, the second piezoelectric element supplying 
the electric signal to the detection circuit, and the drive circuit 
selectively may apply the ejection voltage pulse and the compensation 
voltage pulse to the piezoelectric element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A piezoelectric-type liquid droplet ejecting device according to preferred 
embodiments of the present invention will be described while referring to 
the accompanying drawings wherein like components and parts are provided 
with the same numbering to avoid duplicating description. The preferred 
embodiments describe liquid droplet ejecting devices provided to a 
printhead of an ink-jet printer. 
According to a first embodiment of the present invention, a 
piezoelectric-type liquid droplet ejecting device for ejecting a liquid 
from a pressure chamber through a nozzle by changing the internal volume 
of the pressure chamber using a piezoelectric transducer, includes a 
pressure fluctuation detection means, for detecting residual pressure 
fluctuation in the pressure chamber caused by ejection of a liquid 
droplet, and a pressure fluctuation negating means, for negating the 
residual pressure in the pressure chamber by applying a voltage pulse, the 
voltage and time of application based on the residual pressure fluctuation 
as determined by the pressure fluctuation detection means, to the 
piezoelectric transducer to change the internal volume of the pressure 
chamber. 
As shown in FIG. 3, a first example of a piezoelectric-type liquid droplet 
ejecting device according to the first embodiment of the present invention 
includes a drive circuit 30, a detection circuit 32, and a calculation 
circuit 34. The drive circuit 30 is connected to a printer control circuit 
(not shown), for receiving input of a print signal SP therefrom, and the 
calculation circuit 34, for receiving input of a cancel signal SC 
therefrom. The drive circuit 30 is connected to the piezoelectric element 
16 for selectively supplying a print voltage pulse PP and a cancel voltage 
pulse PC thereto. The detection circuit 32 is connected to the line 
between the drive circuit 30 and the piezoelectric element 16 for 
detecting an electric signal VS therefrom. The detection circuit 32 is 
connected to the calculation circuit 34 for supplying a detection signal 
SV thereto. 
As shown in FIG. 4, the drive circuit 30 includes a pulse generator 36, an 
amp 38, and an analog switch 40. The pulse generator 36 is connected to 
the printer control circuit (not shown), for receiving the print signal SP 
therefrom, the calculation circuit 34, for receiving the cancel signal SC 
therefrom, and the analog switch 40, for supplying a switch signal SS 
thereto. The pulse generator 36 is also connected to the analog switch 40 
via the amp 38. The analog switch 40 is connected to the piezoelectric 
element 16 for supplying the print voltage pulse PP and the cancel voltage 
pulse PC thereto. 
The drive circuit 30 applies to the piezoelectric element 16 either a print 
voltage pulse PP, in response to a print signal SP inputted from the print 
controller, or a cancel voltage pulse PC, in response to a cancel signal 
SC inputted from the calculation circuit 34. The waveform of the print 
voltage pulse PP is predetermined as required to sufficiently deform the 
piezoelectric element 16 for ejecting an ink droplet 20. The waveform of 
the cancel voltage pulse PC, however, is controlled according to the 
voltage and pulse width of the cancel signal SC. As will be described in 
more detail later, the waveform of the cancel voltage pulse PC is required 
to sufficiently deform the piezoelectric element 16 to negate residual 
pressure fluctuations generated in the pressure chamber 10 when an ink 
droplet is ejected. When residual pressure is to be detected, the pulse 
generator 36 outputs a switch signal SS to the analog switch 40. That is, 
when residual pressure fluctuation in the pressure chamber 10 is being 
detected as will be described below, the switch signal SS interrupts the 
analog switch 40, electrically disconnecting the drive circuit 30 from the 
piezoelectric element 16. 
Residual pressure fluctuations in the pressure chamber 10 generated after 
application of a print voltage pulse PP apply pressure to the 
piezoelectric element 16. The piezoelectric effect causes the 
piezoelectric element 16 to generate an electric signal VS in response to 
this pressure. The detection circuit 32 including, for example, a voltage 
follower op amp 42 as shown in FIG. 5 detects the electric signal VS and 
outputs a detection signal SV identical to the electric signal VS to the 
calculation circuit 34. The op amp 42 acts as a buffer, that is, prevents 
measurements performed on the detection signal SV (as will be described 
later when explaining the calculation circuit) from affecting the electric 
signal VS. Fluctuations in the electric signal VS and the detection signal 
SV correspond to fluctuations in the average pressure in the pressure 
chamber 10 as indicated in FIG. 7. Stated differently, the electric signal 
VS and the detection signal SV change in correspondence with residual 
pressure fluctuations in the pressure chamber 10. 
The calculation circuit 34 calculates, based on the detection signal SV, 
the cancel voltage pulse PC required for negating residual pressure 
fluctuations in the pressure chamber 10. The calculation circuit 34 
includes, for example, a microcomputer as shown in FIG. 6 that includes a 
shaping portion (filter) 44, a peak P detection portion 46, a peak level 
PL detection portion 48, a half cycle .tau. calculation portion 50, a 
phase .phi. calculation portion 52, and a cancel voltage pulse PC 
calculation portion 54, connected serially in the order listed. The 
shaping portion 44, connected to the detection circuit 32, filters out or 
otherwise eliminates noise included in the detection signal SV outputted 
from the detection circuit 32. The peak detection portion 46 detects a 
first peak P in the detection signal SV outputted from the shaping portion 
44. The first peak P corresponds to the first positive pressure peak in 
the residual pressure fluctuation in the pressure chamber 10. The peak 
level PL detection portion 48 detects a peak level PL in the detection 
signal SV. The peak level PL is the voltage value of the detection signal 
SV at the first peak P. The half cycle .tau. calculation portion 50 
calculates the duration of the half cycle .tau. of the detection signal 
SV. The duration of the half cycle .tau. corresponds to the duration of 
time between the first negative pressure peak and the second positive 
pressure peak in the residual pressure fluctuation. The phase .phi. 
calculation portion 52 calculates a phase .phi.. The phase .phi. 
corresponds to the time lag between the lowering edge of the print voltage 
pulse PP and the first peak P. The cancel voltage pulse PC calculation 
portion 54 calculates a cancel voltage pulse PC having a cancel voltage VC 
required to sufficiently deform the piezoelectric element 16 to negate the 
residual pressure corresponding to peak level PL. The cancel voltage VC is 
calculated based on the peak level P using a predetermined data map, 
calculation formula, or the like. The pulse width of the cancel voltage 
pulse PC is determined by the half cycle .tau.. At almost the same time 
that the second positive pressure peak appears in the pressure chamber 10, 
the cancel voltage pulse PC calculation portion 54 outputs a cancel signal 
SC, representing the cancel voltage pulse PC, to the drive circuit 30. 
Said differently, the cancel voltage pulse PC calculation portion 54 
outputs the cancel signal SC at a timing delayed by the phase .phi. after 
the print voltage pulse PP is completed, whereupon the drive circuit 30 
applies the cancel voltage pulse PC to the piezoelectric element 16 which 
deforms to increase the volume in the pressure chamber 10, thereby 
negating the residual pressure fluctuation within the pressure chamber 10. 
In a liquid droplet ejecting device according to the first example of the 
first preferred embodiment, the actual residual pressure fluctuation 
within the pressure chamber 10 is detected by the piezoelectric element 16 
and the detection circuit 32. The calculation circuit 34 calculates a 
cancel voltage pulse PC suitable for negating the residual pressure 
fluctuation according to the detected pressure fluctuation and the drive 
circuit 30 applies it to the piezoelectric element 16. In the first 
preferred embodiment, the cancel voltage pulse acts as a compensation 
voltage pulse. Therefore, even if amplitude, cycle, and the like of the 
residual pressure fluctuation change because of changes such as in 
temperature, etc, of the ambient environment or qualities of the ink, the 
residual pressure fluctuation can be precisely reduced. Therefore, even in 
situations when performing relatively high-speed ink ejection, the 
pressure in pressure chamber 10 is stable and ink droplets 20 are ejected 
unaffected by the influence of residual pressure. 
According to the first example of the first preferred embodiment, all 
liquid droplet ejecting devices provided to the ink-jet printer 
independently detect residual pressure fluctuations and output cancel 
voltage pulses PC accordingly. Therefore, the device appropriately 
controls residual pressure regardless of individual differences between 
the individual liquid droplet ejecting devices. Even if rapid changes in, 
for example, temperature or qualities of the ink during supply thereof 
cause the cycle, amplitude, or the like of the residual pressure 
fluctuation to rapidly change, the residual pressure can be sufficiently 
reduced because a cancel voltage pulse PC is calculated with each ejection 
of an ink droplet 20 according to detected residual pressure fluctuations. 
In the first example of the first preferred embodiment, the piezoelectric 
element 16 and the detection circuit 32 act as a residual pressure 
fluctuation detection means and the drive circuit 30 and the calculation 
circuit 34 act as a residual pressure fluctuation compensation means. 
The following text describes a piezoelectric-type liquid droplet ejecting 
device according to a second example of the first preferred embodiment 
which, as shown in FIG. 8, is generally the same as the piezoelectric-type 
liquid droplet ejecting device according to the first example, except for 
an additional pressure detection piezoelectric element 60. Because the 
drive circuit 30 and the detection circuit 32 are electrically isolated in 
this case, fluctuations in residual pressure can be more accurately 
detected and also the analog switch can be omitted. The pressure detection 
piezoelectric element 60 and the detection circuit 32 in the second 
example of the preferred embodiment act as a residual pressure fluctuation 
detection means. 
The following text describes a third example of the first preferred 
embodiment. As shown in FIG. 9, a printhead is formed from a piezoelectric 
material, such as PZT piezoelectric transducer, with a plurality of 
channels formed therein. The channels act as pressure chambers 10. 
Electrodes are formed to both sides of walls 62 separating the individual 
pressure chambers 10. The walls 62 function as piezoelectric elements for 
the pressure chambers 10. Because in this case fluctuations in residual 
pressure can be detected at both side walls in one pressure chamber 10, 
the residual pressure can be negated with greater precision. In the liquid 
droplet ejecting device according to the third example of the first 
preferred embodiment, the side wall 62 and the detection circuit 32 
comprise the residual pressure fluctuation detection means. 
In a liquid droplet ejecting device constructed as described in the first 
preferred embodiment, a residual pressure fluctuation detection means, for 
example, a piezoelectric element 16 and a detection circuit, detect actual 
residual pressure fluctuations. A pressure fluctuation compensation means, 
for example, a calculation circuit 34 and a drive circuit, determine a 
voltage required to negate the detected residual pressure fluctuations and 
apply the voltage to a piezoelectric element. Therefore, even if the cycle 
or the amplitude of residual pressure fluctuations changes by changes in, 
for example, temperature and other aspects of the ambient environment, or 
changes in qualities of the liquid to be ejected, residual pressure 
fluctuations can be accurately reduced. Because of this, even if liquid 
droplets are ejected at relatively high speeds, residual pressure produces 
no influence and liquid droplets can be ejected at stable ejection 
conditions. 
A piezoelectric-type liquid droplet ejecting device according to a second 
preferred embodiment of the present invention relates to liquid droplet 
ejecting devices for ejecting an ejection liquid from a pressure chamber 
through a nozzle by changing the internal volume of the pressure chamber 
by a piezoelectric element. The liquid droplet ejecting device according 
to the second preferred embodiment includes a measure voltage waveform 
application means for applying a predetermined voltage waveform to the 
piezoelectric element, a pressure fluctuation detection means for 
detecting a pressure wave in the ejection liquid filled pressure chamber 
caused by the measure voltage waveform application means, a drive waveform 
calculation means for calculating the special characteristics of the 
pressure chamber and for calculating the drive voltage waveform for 
ejecting liquid according to the calculated individual characteristics, a 
waveform memory means for remembering the drive voltage waveform, and a 
liquid droplet ejecting means for ejecting liquid droplets using the drive 
voltage waveform. 
The second preferred embodiment will be described in regards to the type of 
piezoelectric-type liquid droplet ejecting device as shown in FIG. 10. 
Before describing the second preferred embodiment, however, an explanation 
of this type of piezoelectric-type liquid droplet ejecting device is in 
order. When a drive voltage 421A in a simple rectangular voltage pulse is 
applied to the piezoelectric element 16B, the piezoelectric element 16B 
deforms with the rising edge of the voltage pulse 421A. Consequently, the 
wall 14 to which piezoelectric element 16A is provided also deforms as 
indicated by the one-dash chain line in FIG. 10. When the piezoelectric 
element 16B deforms in this way, the volume of the pressure chamber 10 
increases. The increase in volume lowers pressure in the pressure chamber 
10. The low pressure suctions ink from the ink supply channel 24 into the 
pressure chamber 10. 
To eject an ink droplet 20, after a predetermined amount of time passes 
that is sufficient to allow the pressure fluctuations to settle the 
voltage applied to the piezoelectric element 10 is returned to zero so the 
piezoelectric element 10 returns to its initial shape before deforming 
(indicated by the whole line in FIG. 10). The volume of the pressure 
chamber 10 decreases, causing a corresponding increase in pressure in the 
pressure chamber 10. The increase in pressure forces an ink droplet 20 
through the nozzle 22. This type of liquid droplet ejecting device is 
often used in ink-jet printers. 
With this type of piezoelectric-type liquid droplet ejecting device 
ejecting ink, as described above, both the decrease in volume of the 
pressure chamber 10 for suctioning ink into the pressure chamber 10 and 
the increase in the pressure chamber 10 for ejecting an ink droplet 
generate a pressure wave. The pressure wave propagates through the 
pressure chamber 10 via the medium of the ink, reflects off the wall 14, 
the ink supply channel 24, and the nozzle 22 several times at a reflection 
rate, attenuating as it proceeds. 
Even when ink is ejected using a rectangular drive voltage pulse as in this 
example, the pressure wave generated when ink is suctioned from the ink 
supply channel 24 still exists in the pressure chamber 10 when ink is 
ejected. Because of this, the lowing edge of the drive voltage pulse has 
to be timed correctly in order to obtain stable effective ink ejection. 
Also the width of the voltage pulse must be set taking the state of the 
pressure wave in the pressure chamber 10 into consideration. 
FIG. 11 is a timing chart showing details of pressure fluctuations in the 
pressure chamber 10 when the rectangular voltage pulse 421A is applied to 
the piezoelectric element 16A. The solid line in the middle level 
represents displacement of the piezoelectric element 16A when a voltage 
pulse is applied. That is, the timing chart simply and briefly shows 
displacement status of the piezoelectric element 16A, including when ink 
is suctioned from the ink supply channel 24, and changes in pressure near 
the nozzle 22. 
After the drive voltage has risen as shown by the solid line in FIG. 11, 
and after the piezoelectric element 16A and the wall 14 have stabilized at 
the position indicated by the one-dash chain line in FIG. 10, the pressure 
near the nozzle 22 fluctuates at a set cycle determined by the shape of 
the pressure chamber 10 and the propagation speed of the pressure wave. 
Ink is ejected by returning the drive voltage to zero so the piezoelectric 
element 16A reverts back to the shape it had before the voltage was 
applied so the pressure in the pressure chamber 10 increases. However, the 
fluctuation in pressure affects the amount of pressure produced by 
returning the drive voltage to zero. For example, if the drive voltage is 
returned to zero when, as shown by the broken line in the third level of 
FIG. 11, pressure near the nozzle 22 is high, the pressure produced by the 
piezoelectric element 16 added to the already existing high pressure will 
produce a very high ejecting pressure. 
Contrarily, if the drive voltage is returned to zero when, as shown by the 
single-dot chain line in the third level of FIG. 11, the pressure near the 
nozzle 22 is negative, the pressure produced by the piezoelectric element 
16A is negated by the existing low pressure near the nozzle. The resulting 
pressure will probably be insufficient to eject ink. Even if pressure is 
sufficient to eject ink, the speed and volume of the ink drop 20 will 
probably not be at the predetermined speed and volume desired, so that 
high quality printing is not possible. 
The waveform of the voltage drive pulse must be determined with knowledge 
of the characteristic of the pressure wave in the pressure chamber. The 
vibration cycle of the pressure is the most important aspect for 
determining the rectangular voltage pulse. However, when a more 
complicated wave-type voltage pulse is used, other aspects, such as the 
phase and the attenuation rate of the pressure vibration, must also be 
taken into consideration. 
The cycle of the pressure wave depends on the propagation speed of the 
pressure wave in the pressure chamber 10, the shape of the pressure 
chamber 10, that is, the dimension from the ink supply channel 24 to the 
nozzle 22, and the like. The attenuation rate of the pressure wave depends 
on the shape of the nozzle 22. Conventionally, the characteristic of the 
pressure wave has been determined by calculations or tests. 
However, as previously described, the characteristics of the cycle, phase, 
attenuation rate, and the like of the pressure wave changes according to 
the qualities of the ink, the ambient environment, and the like. For 
example, the propagation rate of the pressure wave can be changed by the 
temperature. Also, the attenuation rate of the pressure wave changes with 
the qualities of the ink and the amount of air bubbles mixed therein. 
These changes change the characteristics of the pressure wave. Because of 
this, it can not be certain that the predetermined drive voltage pulse 
matches the pressure wave in the pressure chamber 10. 
As shown in FIG. 12, a liquid droplet ejecting apparatus in an ink-jet 
printer according to a first example of the second preferred embodiment of 
the present invention includes a drive circuit 30B, a detection circuit 
32B, a calculation circuit 34B, and a memory circuit 35. The drive circuit 
30B, the detection circuit 32B, and the calculation circuit 34B in the 
first example of the second preferred embodiment are interconnected 
similarly to the drive circuit 30, the detection circuit 32, and the 
calculation circuit 34 in the first example of the first preferred 
embodiment except that in the first example of the second preferred 
embodiment the memory circuit is connected between the calculation circuit 
34B and the drive circuit 30B for receiving and storing a waveform WF from 
the calculation circuit 34B and supplying the same to the drive circuit 
30B. Also the drive circuit 30B is connected to, for example, a switch on 
the control panel, for receiving input of a calibration signal SC. 
The drive circuit 30B and the detection circuit 32B of the first example of 
the second preferred embodiment are substantially the same as that of the 
first preferred embodiment. 
When normally printing, as shown in FIG. 13, the drive circuit 30B applies 
a print drive voltage wave PP to the piezoelectric element 16C upon 
receiving input of a print signal SP. When measuring the special 
characteristic of the pressure wave, the drive circuit 30B applies a 
measure drive voltage wave PC to the piezoelectric element 16C upon 
receiving input of a measure signal SC. The pulse generator 36A outputs a 
switch signal SS during detection of the pressure wave, which controls the 
analog switch 40 to electrically disconnect the piezoelectric element 16C 
from the drive circuit 30B. 
The detection circuit 32B is for detecting pressure fluctuations produced 
after application of the measure drive wave PC by detecting the electric 
signal VS generated in the piezoelectric element 16C by the pressure 
fluctuations in the pressure chamber 10. The detection circuit 32B outputs 
a detection signal SV, to the calculation circuit 34B. The voltage signal 
VS and the detection signal SV correspond to the average pressure in the 
pressure chamber 10 during pressure wave measurement. 
The calculation circuit 34B calculates the characteristics, for example, 
the cycle and the attenuation rate, of the pressure wave in the pressure 
chamber 10 based on the detection signal SV. As shown in FIG. 16, the 
detection signal SV corresponds to the average pressure in the pressure 
chamber 10. The calculation circuit 34 includes, for example, a 
microcomputer including, as shown in FIG. 14, a shaping portion (filter) 
44, a peak detection portion 46, a peak level detection portion 48, a 
cycle calculation portion 150, an attenuation rate calculation portion 
152, and a drive waveform calculation portion 154. The shaping portion 44 
eliminates noise in the detection signal SV by filtering or other methods. 
The peak detection portion 46 detects peaks P1 and P2 in the detecting 
signal SV corresponding to pressure fluctuation peaks in the pressure 
chamber 10. The peak level detection portion 48 detects the voltage value 
of the detection signal SV in each peak. In this example, the peak level 
detection portion 48 detects two peak levels Q1 and Q2, wherein peak level 
Q2 is successive to peak level Q1. However, the peak levels detected could 
be any two different peak levels. The cycle calculation portion 150 
calculates the cycle T from detected peak to detected peak in the 
detection signal SV. The attenuation rate calculation portion 152 
calculates the attenuation rate Q1/Q2 of pressure fluctuation by the 
change occurring in detection signal SV during the cycle T between 
detected peaks P1 and P2. The drive waveform calculation portion 154 
calculates the voltage and timing of the drive wave using parameters 
necessary for determining the drive waveform such as the cycle and the 
attenuation rate of the calculated pressure fluctuation. 
The drive waveform calculated in the drive waveform calculation portion 154 
is stored in the memory circuit 35 as a waveform WF. The memory circuit 35 
stores the drive waveform WF using a memory element such as the RAM shown 
in FIG. 15. The memory circuit 35 outputs the drive waveform WF to the 
drive circuit 30 during printing operations. 
When a calibration signal SC is inputted to the drive circuit 30B, 
operations are carried out to calibrate the drive waveform WF. The drive 
waveform for measuring the pressure wave (hereinafter referred to as the 
measure drive waveform) is applied to the piezoelectric element 16C. In 
terms of time, as shown in FIG. 16, first, the average pressure in the 
pressure chamber 10 rapidly increases with the rising edge of the voltage 
from zero. Afterward, the drive voltage is maintained at a set value. The 
pressure in the pressure chamber 10 attenuates as it fluctuates. After the 
pressure fluctuation has sufficiently attenuated, the drive voltage is 
returned to zero, again generating pressure fluctuations in the pressure 
chamber 10. At this time, the analog switch 40 shown in FIG. 13 is turned 
OFF. At the same time, the detection circuit 32B and the calculation 
circuit 34B operate to determine the drive waveform WF. The drive waveform 
WF includes an ejection voltage pulse EP and a cancel voltage pulse CP 
applied as shown in FIG. 16. That is, the ratio between the amplitude VP 
of the ejection voltage pulse EP and the amplitude VV of the cancel 
voltage pulse CP is substantially equal to the ratio between the peak 
level Q1 and the peak level Q2, the ejection voltage pulse EP and the 
cancel voltage pulse CP are respectively applied for durations 
substantially equal to the half cycle, and the cancel voltage pulse CP is 
applied one half cycle of time after the ejection voltage pulse EP. 
In this way, in an ink-jet printer with liquid droplet ejecting devices 
according to the first example of the second embodiment, the actual 
pressure fluctuation in each pressure chamber 100 is detected using the 
piezoelectric element 16C and the detection circuit 32B. Because the drive 
voltage waveform required for actual printing is determined based on the 
detected pressure wave, even if the cycle or the attenuation rate of the 
pressure fluctuation in the pressure chamber 10 changes because of changes 
in the qualities of the ink or in the ambient environment such as 
temperature, a voltage pulse can be applied at time that meets the 
pressure fluctuation so that ink droplet 20 can be stably ejected. 
Because pressure fluctuation is detected and drive waveforms are calculated 
separately in all the liquid droplet ejecting devices forming the ink-jet 
printer in this embodiment, all the devices print at appropriate drive 
waveforms regardless of differences in each liquid droplet ejecting 
device. 
The following text describes an ink-jet printer with liquid droplet 
ejecting devices according to a second example of the second preferred 
embodiment of the present invention. As shown in FIG. 17, the liquid 
droplet ejecting devices in this example are similar to those in the first 
example except that a piezoelectric element 60 for detecting pressure in 
the pressure chamber 10 is provided in addition to the piezoelectric 
element 16C for driving the ejection operation. The detection 
piezoelectric element 60 is connected to the input side of the detection 
circuit 32B. In this example, because the drive circuit 30B and the 
detection circuit 32B are electrically isolated, pressure fluctuations can 
be more accurately detected. Also, the analog switch can be omitted. 
As shown in FIG. 18, a third example according to the second preferred 
embodiment relates to an ink-jet printer head made from a piezoelectric 
material. A plurality of ink channels are formed directly in the 
piezoelectric material. Each channel forms a pressure chamber 10. 
Electrodes are formed to both sides of separation walls 62B separating the 
pressure chambers 10. The separation walls 62B function as piezoelectric 
elements during droplet ejection operations. In this example, because 
pressure fluctuations can be detected from both separation walls 62B of 
one pressure chamber 10, the drive waveform can be calculated with greater 
precision. 
Even in situations where the cycle, attenuation rate, and the like of 
pressure waves in the pressure chamber change because of changes in the 
qualities of the liquid to be ejected, or in the ambient environment such 
as the temperature, the liquid droplet ejecting device according to the 
second preferred embodiment of the present invention efficiently and 
stably prints by ejecting a liquid droplet with a set volume and at a 
predetermined speed because ejection voltage pulses are applied to the 
piezoelectric element at a time which matches a suitable pressure level in 
the pressure fluctuation. 
Although, methods for compensating for residual pressure fluctuations in 
the pressure chamber were described in the first preferred embodiment for 
a liquid droplet ejecting device which ejects droplets when a voltage 
pulse is applied to the piezoelectric element and in the second preferred 
embodiment for a liquid droplet ejecting device which ejects droplets when 
a voltage pulse applied to the piezoelectric element is turned off, these 
calculation methods should not be interpreted as limited to the referred 
types of liquid droplet ejecting devices. The method of calculating a 
compensation voltage pulse described in the first preferred embodiment can 
be applied to the type of liquid droplet ejecting device described in the 
second preferred embodiment, and vice versa. 
The present invention has been described above for use in a liquid droplet 
ejecting device wherein, as shown in FIG. 19, the voltage applied by a 
drive circuit 30 to the piezoelectric element 16 for ejecting a single 
droplet 20B is in the simplest possible waveform 42, that is, with only a 
single drive voltage pulse 421. For an extremely brief time directly after 
the pressure increase in the pressure chamber 10 pushes the ink 20 through 
the nozzle 22, the ink 20A remains connected to the tip of the nozzle 22. 
However, as the inertia of the ejected ink 20 moves the ink 20 forward, 
the connection breaks and the ink 20 forms a droplet 20B. 
Tonal printing can be performed using a single voltage pulse driven by, for 
example, adjusting the level or the pulse width of the drive voltage to 
increase or decrease the volume of ink in each droplet. However, with this 
method ink drops with large volumes are inevitably slower than those with 
lower volumes. This method also tends to form satellites, that is, 
unwanted smaller droplets in addition to the desired droplet. In both 
cases quality of printed characters is adversely affected. Also, great 
changes in the volume of the ink droplets are actually impossible using 
the single voltage pulse drive method. 
As shown in FIG. 20, there has been known a multipulse drive method for 
ejecting ink droplets in a broad range of volumes. With this method, drive 
voltage output from the drive circuit 18 to the piezoelectric element 16 
is in a waveform 44 including a plurality, three in this example, of 
voltage pulses 441, 442, and 443. The second drive voltage pulse 442 is 
applied to the piezoelectric element 16 while the ink droplet 20A ejected 
by application of a leading first voltage pulse 441 is still connected to 
the nozzle 22. A third drive voltage pulse 443 and further drive voltage 
pulses can be similarly consecutively applied to the piezoelectric element 
16B while the ink droplet ejected by application of the proceeding drive 
voltage pulse is still connected to the nozzle to provide an ink droplet 
20B with a desired volume. 
However, with this multi-pulse drive method residual pressure fluctuations 
are also generated in the pressure chamber 10 after ink 20 is discharged 
by the lead drive voltage pulse 441. Therefore, when the second drive 
voltage pulse 442 is applied to the piezoelectric element 16, the amount 
and speed of the ink changes depending on the phase of the residual 
voltage fluctuation. In particular, when the phase of the residual 
pressure fluctuation and the phase of the drive voltage pulse are opposite 
or near opposite, sometimes no ink will be ejected by the second drive 
voltage pulse. In the same way, when a third drive voltage pulse 443 or 
ensuing drive voltage pulse is applied to the piezoelectric element 16, 
the ejected droplet 20B is affected by residual pressure fluctuation from 
both the first drive voltage pulse, the second drive voltage pulse, and 
other preceding drive voltage pulses. 
Conventionally the cycle, phase, and attenuation rate of residual pressure 
fluctuations generated by the first and successive voltage pulses in the 
multi-pulse drive method have been measured or calculated beforehand to 
determine the time of application of successive drive voltage pulses. 
However, the cycle, phase, and attenuation rate characteristics of 
residual pressure fluctuations vary with such factors as the dimensions of 
the pressure chamber, the qualities of the ink, and the ambient 
environment. Therefore, actual residual pressure fluctuations do not 
always match residual pressure fluctuations determined by calculations or 
tests. Because of this problem, ejection of ink in predetermined volumes 
has been impossible with the conventional multi-pulse drive method because 
the phases of the residual pressure fluctuations and the drive voltage 
pulses do not always match. 
A liquid droplet ejecting device according to a third preferred embodiment 
of the second invention relates to a multi-pulse type liquid droplet 
ejecting device wherein liquid is ejected successively in small quantities 
from a pressure chamber to form a single larger liquid droplet. This is 
accomplished by a drive means successively applying a plurality of drive 
voltage pulse signals to a piezoelectric element to deform the 
piezoelectric element the same number of times as the number of drive 
voltage pulse signals. The liquid droplet ejecting device according to the 
third preferred embodiment is improved over conventional liquid droplet 
ejecting devices of this type by the inclusion of a detection means for 
detecting pressure fluctuations in the ink within the pressure chamber 
caused by each predetermined voltage pulse of the drive voltage pulse 
signal and a control means for controlling the drive means to generate 
voltage pulses successive to the predetermined voltage pulse based on the 
actual pressure fluctuation detected by the detection means. 
While referring to FIG. 21, the following text describes a first example of 
a multi-pulse piezoelectric-type liquid droplet ejecting device according 
to the third preferred embodiment. The structure of this multi-pulse 
piezoelectric-type liquid droplet ejecting device is similar to 
conventional multi-pulse types but has added thereto a detection circuit 
32A and a calculation circuit 34A. The detection circuit 32A is 
substantially the same as described in the first preferred embodiment and 
detects residual pressure fluctuations in the pressure chamber 10 with 
every predetermined voltage pulse 441 of the multi-pulse drive signal 44 
generated by the drive circuit 30A. As shown in FIG. 22, the calculation 
circuit 34A is similar to that described in the first preferred 
embodiment, but with a successive voltage pulse calculation portion 254 
instead of the cancel voltage pulse PC calculation portion 54. The 
successive voltage pulse calculation portion 254 calculates the voltage 
and time of application of the successive voltage pulse based on the cycle 
and the phase of the calculated pressure fluctuation. The calculation 
circuit 34A calculates, based on the residual pressure fluctuations 
detected by the detection circuit 32A, an appropriate pulse width and time 
for applying successive drive voltage pulses 442 and 443 of the 
multi-pulse drive signal 44 from the drive circuit 30A and controls the 
drive circuit 30A based on the results of the calculations. 
The following is an explanation of operations in the ink ejection device 
according to a first example of the third preferred embodiment. When the 
drive circuit 30A applies a first drive voltage pulse 441 having a 
predetermined voltage and width to the piezoelectric element 16A, the 
piezoelectric element 16A deforms as shown by the dotted line in FIG. 21. 
This causes the pressure in the pressure chamber 10 to increase so that 
ink is ejected from the nozzle 22. Afterward, the piezoelectric element 
16A reverts to the shape it had before liquid droplet ejection and the 
pressure within the pressure chamber 10 also temporarily returns to the 
pressure of before liquid droplet ejection. However, residual pressure 
fluctuation, generated in the pressure chamber 10 by the pressure of the 
ejection operation, causes the pressure in the pressure chamber 10 to 
increase and decrease. The residual pressure fluctuation in the pressure 
chamber 10 deforms the piezoelectric element, which generates a voltage 
accordingly from the piezoelectric effect. Upon detecting the lowering 
edge of the first voltage pulse, the pulse generator 36 outputs the switch 
signal SS to the analog switch 40, thereby electrically isolating the 
piezoelectric element 16 from the drive circuit 30, the detection circuit 
32A detects the voltage generated by the piezoelectric element 16A in 
accordance with the pressure fluctuations in the pressure chamber 10 and 
transmits the detected pressure value to the calculation circuit 34A. The 
calculation circuit 34A calculates width, time of application, height, and 
the like of a second drive voltage pulse 442 according to the detected 
pressure fluctuations. The pulse width, time of application, and the like 
calculated by the calculation circuit 34A depends on the type of droplet 
desired to be produced by the second drive voltage pulse 442. For example, 
an extremely large droplet might be desirable, in which case the second 
drive voltage pulse 442 would be timed to be applied while pressure in the 
pressure chamber 10, caused by residual pressure fluctuations, is high as 
shown in FIG. 23. However, when the voltage pulse is applied and its width 
might also be adjusted according to the conditions in the pressure chamber 
10 so that droplets are of a uniform size at all ejections. The 
calculation circuit 34A outputs the calculated pulse width and time of 
application to the drive circuit 30A in the form of a second drive signal 
442 for ejecting the successive droplet. The drive circuit 30A applies the 
second drive voltage pulse 442 to the piezoelectric element 16A for 
ejecting the successive droplet. Afterward, the detection circuit 32A 
detects the pressure fluctuation in the pressure chamber 10 caused by 
ejection of the second droplet, the calculation circuit 34A calculates the 
width and time of application of the successive drive voltage pulse 443, 
and the drive circuit 30A applies drive voltage pulse 443 to the 
piezoelectric element 16A accordingly. As shown in FIG. 21, directly after 
being ejected, the three droplets 20A ejected from the pressure chamber 10 
by the first, second, and third drive voltage pulses 441, 442, and 443 are 
connected to each other and to the nozzle. Shortly thereafter, the three 
droplets separate from the nozzle 22 and form a single large droplet 20B. 
The first example of the third preferred embodiment describes the same 
piezoelectric element 16A employed as a pressure sensor and as a droplet 
ejection means. However, as shown in FIG. 24, in a second example of the 
third preferred embodiment two piezoelectric elements, a pressure 
fluctuation detection piezoelectric element 60 and an ejection 
piezoelectric element 16A, are provided on either side of the pressure 
chamber 10. In this case, because the detection circuit 32A and the drive 
circuit 30A are electrically isolated, the detection circuit 32A is 
unaffected by the drive circuit 30A and so more accurately measures 
residual pressure fluctuations. Also, the analog switch is unnecessary. 
As shown in FIG. 25, in a third example of the third preferred embodiment, 
a plurality of channels are formed in a piezoelectric ceramic material. 
The channels act as pressure chambers 10 and the walls 62A act as 
piezoelectric elements. Drive voltage pulses from the drive circuit 30A 
are applied directly to the walls 62A of the pressure chambers 10. Because 
two walls 62A of each pressure chamber 10 generate electric signals 
corresponding to residual pressure fluctuation in the pressure chamber 10, 
residual pressure fluctuation can be more accurately measured. 
A liquid droplet ejecting device constructed as described in the third 
preferred embodiment relates to a multi-pulse type liquid droplet ejecting 
device for ejecting liquid from a pressure chamber in small quantities at 
a time to form a single larger liquid droplet by successively applying 
from a drive means to a piezoelectric element a plurality of drive voltage 
pulse signals to deform the piezoelectric element the same number of times 
as the number of drive voltage pulse signals. The multi-pulse type liquid 
droplet ejecting device according to the third preferred embodiment 
includes a detection means for detecting pressure fluctuations in the 
liquid droplet ejecting device with every predetermined voltage pulse of 
the drive voltage pulse signal and a control means for controlling the 
drive means to generate successive voltage pulses (after the predetermined 
voltage pulse) based on the detected results of the detection means. 
Therefore, droplet ejection is unaffected by changes in qualities of the 
ink or changes in the ambient environment, thereby allowing optimum 
printing. 
While the invention has been described in detail with reference to specific 
embodiments thereof, it would be apparent to those skilled in the art that 
various changes and modifications may be made therein without departing 
from the spirit of the invention. 
For example, the preferred embodiments describe residual pressure 
fluctuations measured for each ejection operation and a successive 
compensation voltage pulse calculated accordingly. For example, in the 
first preferred embodiment, residual pressure fluctuations were measured 
after each ejection of an ink droplet and a cancel voltage pulse PC 
outputted accordingly; in the second preferred embodiment, one series of 
operations from detection of the residual pressure fluctuations caused by 
each initial predetermined voltage pulse to calculation of drive waveform 
were performed for each ejection operation; and in the third preferred 
embodiment, residual pressure fluctuations were measured after every 
droplet ejection. However, residual pressure fluctuations could be 
detected, for example, by a test measurement, only at a predetermined 
sampling time, such as when an optional switch is manipulated, after a 
predetermined period of time passes, or directly after the printer power 
is turned ON. Actual drive voltage pulses can be timed based on this test 
measurement until the following test measurement is taken. This allows 
high-speed printing even if the detection circuit and the calculation 
circuit are not high speed components. 
For example, in the first preferred embodiment the calculated cancel 
voltage pulse PC and the phase .phi. could be stored in a memory and used 
to create cancel voltage pulses for each successive ejection of a droplet 
until an ensuing sampling time when residual pressure fluctuations in the 
pressure chamber 10 are again detected and a new cancel voltage pulse PC 
and phase .phi. are calculated. If sampling is performed before actual 
printing begins, there is no necessity to rapidly produce the cancel 
voltage pulse PC and negate the residual pressure before a successive ink 
ejection. Therefore, there is extra time to more precisely calculate the 
cancel voltage pulse PC and the phase .phi., expensive high-speed 
circuitry need not be used, and the half cycle .tau. of the total 
amplitude characteristic of the residual pressure fluctuation can be 
detected with greater precision. 
Also, a test drive voltage applied to the piezoelectric element before 
actual printing begins can be at a voltage lower than actually needed to 
eject an ink droplet. This is because the strength of the drive voltage 
affects the peak level of the residual pressure fluctuation, but not other 
qualities thereof such as its phase or half cycle. For example, in the 
first preferred embodiment, by applying a test drive pulse voltage with a 
known voltage, and then detecting the peak level PL in the resultant 
residual pressure fluctuation, a cancel voltage VC sufficient for negating 
residual pressure fluctuations brought about by a print voltage pulse PP 
with a known drive voltage can be determined from the relationship between 
the test drive voltage and the peak level PL of the resultant residual 
pressure fluctuation. Also, in the second preferred embodiment, the 
attenuation rate of the pressure wave can be calculated even if the 
voltage creates pressure fluctuation with peaks lower than during actual 
ink ejection. 
Further, although the preferred embodiments describe each liquid droplet 
ejecting device formed in the ink-jet printer as including an individual 
detection circuit and calculation circuit, and, in the second preferred 
embodiment, a memory circuit, these circuits need only be supplied to one 
or one portion of the liquid droplet ejecting devices. That is, 
measurements need not be performed at every pressure chamber. Only the 
residual pressure fluctuation in one pressure chamber or one group of 
pressure chambers need be measured to provide information representative 
of the others. The pressure determined at the selected pressure chambers 
can be used for producing drive voltage pulses for driving all the 
pressure chambers. For example, in the first preferred embodiment, the 
required cancel voltage pulse PC, the phase .phi., or the like determined 
by the liquid droplet ejecting device or devices including circuits can be 
used as the cancel voltage pulse PC, the phase .phi., and the like of the 
other liquid droplet ejecting devices. 
Also, the representative pressure chamber or chambers can be dummy pressure 
chambers, not actually used for ejection but with the same physical 
properties as the real pressure chambers. The drive voltage and the like 
determined at the dummy liquid droplet ejecting devices can be used in the 
liquid droplet ejecting devices which actually print. 
Still further, pressure fluctuations in the pressure chambers are 
transmitted, although in a rather attenuated form, through the ink supply 
channel to an ink tank. Therefore, if the pressure propagation 
characteristic of the ink supply channel is known, the characteristic of 
the pressure chamber and the residual pressure fluctuations in the ink in 
pressure chambers can be calculated by measuring pressure fluctuations in 
the ink in the ink tank. 
All the preferred embodiments describe measuring specific portions of the 
residual fluctuation to determine the voltage of and application time of a 
compensation voltage pulse. However these are only examples. For example, 
although the first preferred embodiment describes detecting the first 
positive pressure peak PL of the residual pressure fluctuation and 
determining and outputting a cancel voltage pulse PC for negating the 
pressure at the first positive pressure peak PL, the cancel voltage pulse 
PC could be determined according to the second or ensuing positive peaks 
or according to the first, second or ensuing negative pressure peaks. 
Similarly, in the first preferred embodiment, when the cancel voltage 
pulse, the phase .phi., and the like are determined by a test drive 
voltage pulse, the cancel voltage pulse can be output by detection of the 
first negative pressure peak. However, the negative pressure peak can only 
be detected when the phase .phi. is less than the half cycle .tau.. 
Changes in temperature change the relative duration of the phase .phi. and 
the half cycle .tau. so that sometimes the phase .phi. is greater than the 
half cycle .tau.. 
The circuit structures and functions of the components shown in the 
diagrams are only examples which can be modified as appropriate to meet 
special requirements. For example, in the first preferred embodiment, when 
the half cycle .tau. and the phase .phi. are substantially the same 
because of the pulse width of the print voltage pulse PP, the phase .phi. 
calculation portion 52 can be eliminated by assuming the half cycle .tau. 
and the phase .phi. to be equal (.phi.=.tau.). In this case, methods for 
determining when the cancellation voltage pulse PC is applied and setting 
the pulse width can be modified. 
The preferred embodiments describe the calculation circuit determining a 
compensation voltage pulse. However, a compensation voltage pulse could be 
initially set with a predetermined amplitude, voltage, and time lag at 
which it is to be applied and then corrected by the calculation circuit 
according to the residual pressure fluctuations detected by the detection 
circuit. For example, in the first preferred embodiment, the cancel 
voltage pulse could be initially set with a predetermined amplitude, 
voltage, and time lag at which it is to be applied after application of 
the print voltage pulse PP stops. The predetermined cancel voltage pulse 
would then be corrected based on the actual phase, amplitude, cycle, and 
the like of the residual pressure fluctuation detected by the detection 
circuit. 
Also, droplet ejection devices described in the second example of each 
preferred embodiment, wherein a separate piezoelectric element is used for 
detecting residual pressure fluctuations, can be feedback controlled. In 
this case, the detection piezoelectric element detects residual pressure 
fluctuations while the compensation voltage pulse is sequentially 
calculated and outputted to the drive piezoelectric element. For example, 
in the second example of the first preferred embodiment, the detection 
piezoelectric element detects residual pressure fluctuations while the 
cancel voltage required for negating the detected residual pressure is 
sequentially calculated and outputted to the piezoelectric element, 
thereby reducing the residual pressure to zero. This type of feedback 
control can also be applied to the liquid droplet ejecting device 
described in the third example of the preferred embodiments. For example, 
in the second preferred embodiment, after a print voltage pulse PP is 
applied to both side walls of a pressure chamber, resultant residual 
pressure fluctuation is detected at one of the side walls and the cancel 
voltage determined using the detection residual pressure is applied to the 
other side wall, thereby negating the detected residual pressure.