Tone recording method using ink recording head

A liquid jet recording method of recording on a recording material with liquid droplets discharged trough plural scanning nozzles, in which: EQU n/(s/p).gtoreq.2 EQU n/(s/p).times.k=g-1 are satisfied, PA1 where n (n.gtoreq.2) is a number of the nozzles arranged at pitch P (.mu.m); s (.mu.m) is a distance of relative movement between the nozzles and the recording material between adjacent scans; k (k.gtoreq.1) is a maximum number of ink droplets per pixel and per scan; g (g.gtoreq.3) is a number of tone levels.

FIELD OF THE INVENTION AND RELATED ART 
The present invention relates to an ink jet recording method and apparatus 
using an ink jet recording head having a plurality of ejection outlets 
(nozzles), capable of tone recording. 
In an ink jet recording system using the recording head, the ink is ejected 
to a recording material in accordance with recording signals. The system 
is widely used because of the low running cost and the quietness. A great 
number of nozzles are arranged in a line extending perpendicular to the 
relative movement direction between the recording material and the 
recording head, and therefore, one scan of the recording head over the 
recording material can cover a recording width corresponding to the number 
of nozzles, so that the high speed recording is accomplished relatively 
easily. 
When a tone gradation is to be provided in the ink jet recording system, it 
will be considered to change the size of liquid droplet ejected. However, 
there is no practical method for accomplishing this. Usually, therefore, 
the number of ink droplets per unit area is controlled on the basis of 
pseudo-half-tone image processing. In another method called "multi-droplet 
system" , a smaller size ink droplet is used, and a plurality of such ink 
droplets; are deposited substantially at the same point on the recording 
material to provide one recorded dot, in which the number of ink droplets 
is changed to reproduce the tone. This system permits the tone recording 
without reduction of the image resolution, and is particularly effective 
for the ink jet recording system in which difficulties arise in 
significantly changing the size of one liquid droplet. 
However, in a conventional multi-droplet system, one picture element 
(pixel) is recorded by a plurality of ink droplets ejected from one and 
the same nozzle, and therefore, if there is a variation in the sizes of 
the ink droplets of the individual nozzles, a non-uniform image results 
which includes stripes and/or image density unevenness. 
This problem becomes more significant where the number of nozzles of a 
recording head is increased to expand the recording width covered by one 
scan in an attempt to accomplish the high speed recording. The increase of 
the nozzle number and therefore the recording width results in a greater 
no frequency component of the spatial frequency of the unevenness, and 
therefore, in more conspicuous unevenness. Thus, the image quality is 
degraded. In the case of the tone recording, the unevenness is so 
conspicuous that only a several % variation among the ejection quantities 
of the nozzles is enough for one to recognize stripes caused by the 
density unevenness. 
In order to avoid the problem, the conventional multi-droplet system 
requires accurate head manufacturing in order to reduce the variation in 
the ejection quantities through the individual nozzles. This brings about 
high cost and low yield. As a method for removing the density unevenness 
through software, it is effective to change the number of ink ejections to 
compensate for the variation among the nozzles with the aid of image 
processing of error diffusing method or the like. However, such an image 
processing system results in increase of the system cost. In addition, 
even if such a processing is used, the number of ink droplets has to be 
readjusted if the variation among nozzles in the ink volumes changes with 
time. This makes the maintenance operation difficult. Furthermore, this 
method does not work where there is a non-ejection nozzle. 
This system also involves the problem that the density unevenness is not 
sufficiently suppressed when the variation in the ink droplet volume is 
larger. 
In order to accomplish a high quality tone recording of not less than 16 
tone gradations in the above-described system, stabilized ink ejections 
with a very small droplets required. Therefore, the manufacturing accuracy 
of the recording head has to be very high, so that the manufacturing 
method is totally different from that for the bi-level recording heads. 
This results in high cost and low yield. 
In the case of multi-droplet system of 3-5 tone gradations, the droplet 
size, volume or quantity is permitted to be relatively large as compared 
with that in the case of the 16 or more tone gradations. Therefore, the 
manufacturing tolerance in the recording head is so large that the same 
manufacturing method as in the bi-level recording head can be used. The 
cost can be reduced. 
The image provided by the recording head having such a large number of tone 
gradations is better in the image quality than the image recorded by the 
bi-level recording head because the grains are not conspicuous. However, 
as compared with the image provided by the recording head having the 16 or 
the like tone levels, particularly in the grains in the high light 
portions. 
U.S. Pat. No. 4,746,935 proposes multi-tone ink jet printer capable of 
accomplishing the tone recording on the basis of combinations of 1 pl, 2 
pl and 4 pl, for one pixel. According to this proposal, 8 kinds of ink 
droplet volumes, i.e., 0, 1, 2, 1+2(=3), 4, 1+4(=5), 2+4(=6), 1+2+4(=7), 
can be provided by three kinds of ink droplets (volume ratio). Therefore, 
the printing speed is increased as compared with the case where one ink 
droplet is overlaid 7 times. However, as shown in FIG. 20 of the U.S. Pat. 
No. '935 , the curve representing the relationship between the reflection 
density and the total volume of the ink droplets for one pixel is steep 
and convex-up. For this reason, even if the differences between adjacent 
total volumes of the ink for one picture element are the same, the 
differences, in the reflection density, corresponding thereto, are not the 
same. Therefore, in the zone where the volume of the ink droplet for one 
pixel is small, the differences of the adjacent possible reflection 
densities is large. On the contrary, in the zone where the volume of the 
ink droplet for one pixel is large, the difference between the possible 
reflection densities is small. In other words, the volume of the ink 
droplet does not significantly influence the tone gradation in the zone 
where the volume-of the ink droplet for one pixel is large. In addition, 
since the number of combinations of different ink droplets for one picture 
element is large (8 combinations in the case of 1 pl, 2 pl and 4 pl), the 
image processing circuit becomes complicated with the result of high 
design and manufacturing cost. 
Another problem of the ink jet printer of the U.S. Patent is that one 
recording head has to be provided with the nozzles having different 
ejection volumes, the difference being as large as 4 times (4 pl/1 pl), or 
8 times in the case of 1 pl to 8 pl. In this case, the difficulties arise 
in the manufacturing of the recording head. Generally, the recording head 
parameters influential to the volume of the ink droplet ejected, a 
distance between the heater and the ejection outlet, a size of the heater, 
a configuration of the ink outlet or barrier and an ejection outlet area. 
In order to change the volume of the ink droplet from 1 to 4, the changes 
of the heater-outlet distance, the heater area and the ejection outlet 
area has to be changed. The manufacturing will be difficult only using the 
conventional practical method. Therefore, in order to accomplish such a 
recording head, a new process has to be addled, with the result of 
increase of the manufacturing cost. 
In the ink jet printer disclosed in the U.S. Pat. No. '935, the ink 
ejection outlets providing the different ejection volumes (1 pl, 2 pl, and 
4 pl) are arranged along a scanning direction of the recording head and 
closely with each other at the front side of the recording head, so that 
the plural ink droplet ejections for a given one pixel can be effected 
through one scan. Therefore, the ink droplets are sequentially overlaid 
before the previous ink droplet has not yet seeped into or fixed on the 
recording material. In the image region in which the number of overlying 
droplets is large, the adjacent pixels are in contact with the result of 
feathering. If this occurs, the characters or the like become less clear. 
In the case of color image, the edges of the image becomes blurred by the 
feathering and ink mixture adjacent the edge of the monochromatic region, 
with the result of significant problem of the unacceptable degradation of 
the record quality. 
In the case of color image in the ink jet recording head, there is a 
problem that the edges of the image is blurred due to the smear resulting 
from ink mixture before the fixing at the edge of the monochromatic 
region, particularly. In order to avoid this problem, in the pixel area 
modulating method such as dithering method, there are known methods in 
which special recording material having a coated layer of high 
ink-absorbing nature to prevent the color mixture for individual dots, or 
in which different color dots are arranged in a staggered fashion as a 
preventing method for individual picture elements. However, if such method 
as used as they are, the running cost for the image output is increased, 
or the image resolution is decreased due to the staggered arrangement. 
The feathering or expansion of the ink in the recording material can be 
reduced by providing a certain length of fixing period. As a method using 
this, Japanese Laid-Open Patent Application No. 4523/1990 proposes that 
the recording material is scanned on the same line plural times, while the 
recording material is at rest, the number of scans being larger than the 
number of required colors. However, with this method, when black, yellow, 
magenta and cyan ink materials are used, the required time is 4 times with 
the result of significant reduction of the output speed. 
On the other hand, in order to provide a wide tone gradation range with the 
multi-droplet system, the adjacent liquid droplets are not in contact with 
the result of less expansion of the liquid when the number of liquid 
droplets overlaid on the recording material is small, although a 
sufficiently small liquid droplet is required as compared with the 
bi-level recording. However, where the number of liquid droplets overlaid 
is large, the adjacent liquid dots are in contact with the result of the 
large expansion or feathering. 
SUMMARY OF THE INVENTION 
Accordingly, it is a principal object of the present invention to provide 
an ink jet recording method and apparatus in which the tone recording is 
improved. 
It is another object of the present invention to provide an ink jet 
recording method and apparatus in which the tone recording is improved 
even if the ink droplet volumes are varied among the nozzles. 
It is a further object of the present invention to provide an ink jet 
recording method and apparatus in which the tone recording is improved 
even if one or some nozzles failed. 
It is a yet further object of the present invention to provide an ink jet 
recording method and apparatus in which uniform tone gradation can be 
provided despite property change of the recording head with time. 
It is a yet further object of the present invention to provide an ink jet 
recording method and apparatus wherein the variations in the volumes of 
the ink droplets ejected through individual nozzles is reduced for any 
tone gradation to suppress the unevenness of the image. 
It is a yet further object of the present invention to provide an ink jet 
recording method and apparatus in which the high quality tone recording 
without conspicuous grains is possible without extremely reducing the ink 
droplet volume. 
It is a further object of the present invention to provide an ink jet 
recording method and apparatus in which a large number of tone gradation 
levels can be provided with a small number of droplets. 
It is a yet further object of the present invention to provide an ink jet 
recording method and apparatus in which the expansion or feathering of the 
image dot is suppressed to provide desired colors of the image. 
According to an aspect of the present invention, there is provided a liquid 
jet recording method of recording on a recording material with liquid 
droplets discharged through plural scanning nozzles, the improvements 
residing in: 
EQU n/(s/p).gtoreq.2 
EQU n/(s/p).times.k=g-1 
are satisfied, where n (n.gtoreq.2) is a number of the nozzles arranged at 
pitch P (.mu.m); s (.mu.m) is a distance of relative movement between the 
nozzles and the recording material between adjacent scans; k (k.gtoreq.1) 
is a maximum number of ink droplets per pixel and per scan; g (g.gtoreq.3) 
is a number of tone levels. 
Then, one pixel is recorded by m nozzles through m main scans, where 
m=n/(s/nozzle pitch). As a result, when the ink droplet volume variation 
among the nozzles is in the form of the normal distribution with a 
standard deviation .sigma., for example, the variation of the ink quantity 
per pixel is reduced to .sigma./.sqroot.m, since one pixel is recorded by 
different m nozzles. 
According to another aspect of the present invention, there is provided a 
liquid jet recording method of recording on a recording material with 
liquid droplets discharged through plural scanning nozzles, the 
improvements residing in: 
EQU n/(s/p).gtoreq.2 
EQU n/(s/p).times.k&gt;g-1 
are satisfied, where n (n.gtoreq.2) is a number of the nozzles arranged at 
pitch P (.mu.m); s (.mu.m) is a distance of relative movement between the 
nozzles and the recording material between adjacent scans; k (k.gtoreq.1) 
is a maximum number of ink droplets per pixel and per scan; g (g.gtoreq.3) 
is a number of tone levels. 
Then, s/(nozzle pitch)=t represents the relative movement distance between 
the recording head and the recording material by the sub-direction-scan 
(sheet feed amount in the case of a serial printer) on the basis of a 
distance between adjacent nozzles. The number of scans for one picture 
element is m or m+1, where n/t=m (the decimal fraction is neglected, and 
in the case of no decimal fraction, the number of scans is m for one 
picture element). 
The maximum number of ink droplets for one pixel is (m+1).times.k, or 
m.times.k (where n/t includes no decimal fraction), but the number of 
droplets per one pixel is 0-g-1. Therefore, according to this aspect of 
this invention, the capacity of the number of ink droplets is larger than 
the number of ink droplets to be supplied to one pixel, and therefore, 
even if one or some of the ejection nozzles failed, they can be 
compensated for by other nozzles, so that the image is maintained uniform. 
According to a further aspect of the present invention, there is provided a 
liquid jet recording method in which plural liquid droplets are deposited 
at substantially the same portion to record a tone image, the improvement 
residing in that a plurality of nozzles for discharging the droplets are 
prepared, and the nozzles are operated to discharge the droplets in 
accordance with a scheme determined to operate the nozzles at 
substantially even frequencies. 
Then, the actuation frequencies of the individual nozzles are more uniform, 
and therefore, the limited number of nozzles actuation does not occur. 
These and other objects, features and advantages of the present invention 
will become more apparent upon a consideration of the following 
description of the preferred embodiments of the present invention taken in 
conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the accompanying drawings, the preferred embodiments of the 
present invention will be described in detail. 
Embodiment 1 
FIG. 1 shows an ink jet recording apparatus according to this invention. It 
comprises a recording head 1 having 128 nozzles (ink ejection or 
discharging outlets) at the density of 16 nozzles/mm (400 dpi). Each of 
the nozzles is provided with a heater (heat generating element) in the 
liquid passage communicating with the associated nozzle to produce ink 
ejection energy. The heater generates heat in response to electric pulse 
signal applied thereto. Upon the electric pulse supply thereto, the film 
boiling occurs in the ink. With the expansion of the bubble created by the 
film boiling, the ink is ejected. In this example, the ejection frequency 
of each of the nozzles is 2 kHz, and therefore, the driving frequency for 
the heater is 2 kHz. 
The recording apparatus further comprises a carriage 4 for carrying the 
recording head 1. The carriage 4 moves along the guiding shafts 5A and 5B. 
An ink supply tube 6 functions to supply the ink to the recording head 1 
from an unshown ink container. A flexible cable 7 functions to supply 
driving signals and controlling signals from an unshown controller to a 
head driving circuit mounted on the recording head 1 in accordance with 
record data (image information). The ink supply tube 6 and the flexible 
cable 7 are made of flexible material capable of following the movement of 
the carriage 4. 
To the carriage 4, an unshown belt extending in parallel with the guiding 
shafts 5A and 5B, is connected. The belt is driven by an unshown carriage 
motor, so that the carriage 4 is moved. 
A platen 3 extends also in parallel with the guiding shafts 5A and 5B. 
Designated by a reference numeral 2 is a recording material. While the 
carriage 4 is moved, the recording head 1 eject the ink to the recording 
material 2 at the portion faced thereto to effect the recording operation. 
The description will be made as to the method for 17 tone gradation 
recording, in which the number of liquid droplets per pixel is variable in 
the range of 0-16 inclusive. FIGS. 2 and 3 illustrate the concept of the 
recording method of this embodiment. The recording head 1 has vertically 
arranged 128 nozzles. For the convenience of explanation, the nozzles are 
identified by the numerals 1, 2, . . . , 128 from the top in this Figure. 
In operation, while the carriage is moved at the speed of 31.75 mm/sec in 
the main scan direction, the recording operation is carried out using only 
nozzles Nos. 121-128. Then, as shown in FIG. 3 at portion (a), the pixels 
1-8 (from the top of the recording material) are recorded 0 or 1 ink 
droplet. Subsequently, the recording material is fed upwardly (sub-scan 
direction) by a distance corresponding to 8 pixels (for the convenience of 
explanation, the recording head is shown as moving downwardly relative to 
the recording material in the Figure). Then, the recording operation is 
carried out using the nozzles Nos. 113-128. Then, as shown in FIG. 3 at 
portion (b), the nozzles Nos. 113-120 effect the recording on the picture 
elements 1-8 which have already been recorded by the nozzles Nos. 121-128 
in the previous scan, and the nozzles Nos. 121-128 effect the recording on 
new picture elements 9-16. Thus, the picture elements 1-8 are recorded by 
0-2 ink droplet per pixel. 
Thereafter, the recording material (sheet) is fed upwardly by the distance 
corresponding to the 8 pixels, and then, the recording operation is 
carried out using the nozzles Nos. 105-128. By repeating sequentially such 
recording operations, the pixels 1-8 are recorded by 0-16 ink droplets per 
pixel, after 16 scanning operations are completed, as shown in FIG. 3 at 
portions (c) and (d). In this manner, 17 tone gradation recording is 
effected. The similar operations are repeated thereafter so that the 
17-tone-graduation image is formed on the entire surface of the recording 
material. At the bottom of the image, each 8 nozzles is sequentially 
stopped from the bottom each time the scanning operation is completed. 
Noting one pixel, No. 1 pixel, for example in the resultant image, the 
pixel receives the liquid, 0 or 1 from 16 nozzles, i.e., Nos. 1, 9, 17, 
25, 33, 41, 49, 57, 65, 73, 81, 89, 97, 105, 113, 121 (the order of nozzle 
actuations is the opposite). Therefore, the variation of the ink ejection 
volume from the nozzles is averaged, so that the resultant image does not 
have any conspicuous stripe or unevenness, as contrasted to the image 
recorded through a conventional method in which one pixel is recorded by 
plural ink droplets from the same nozzle. 
Embodiment 2 
FIG. 4 is a perspective view of an ink jet recording apparatus of the 
second embodiment. A recording head 11 is a thermal energy ink jet 
recording head having 512 nozzles at the density of 16 nozzles/mm. The 
nozzles are arranged in the horizontal direction on the Figure. The 
recording head is movable along the rail 14. The recording material 12 is 
wrapped on a drum 13, which is rotated by an unshown motor. 
Referring to FIG. 5, the image formation process will be described in this 
method to provide 9 tone gradation recording. First, the recording head 11 
is moved to the leftmost position in FIG. 4. The recording operation is 
carried out using only 64 nozzles, i.e., nozzles Nos. 449-512, while the 
drum 13 is rotated one full turn (main scan) (FIG. 5, portion (a)). Then, 
the recording head 11 is moved to the right by a distance corresponding to 
64 pixels (sub-scan direction). Then, the recording operation is carried 
out using nozzles Nos. 385-512, while rotating the drum 13 through one 
turn (FIG. 5, portion(b)). The rightward movement of the recording head 11 
and the rotation of the drum 13, are repeated to effect the recording on 
the recording material. 
As a result, the first pixel, for example, is recorded by 8 nozzles, i.e., 
nozzles Nos. 1, 65, 129, 193, 257, 321, 385 and 449. The 9 level tone 
recording is effected by 0-8 droplets of the ink. 
Various images have been recorded with this method, and it has been 
confirmed that uniform and sharp images are provided without stripe. 
Embodiment 3 
In this embodiment, 17 tone gradation recording is possible. The structures 
of the apparatus are the same as that of the second embodiment except for 
the recording head. The recording head 11 has 256 nozzles, each of which 
ejects a smaller volume of ink droplet than in the second embodiment. 
FIG. 6 shows the concept of the recording in this embodiment. In this 
Figure, the recording material 12 is removed from the drum 13, and is 
expanded vertically. The position of the recording head 11 is designated 
by a reference numeral 11a. In this embodiment, the recording head 11 
moves to the right (sub-scan direction) when the drum 13 rotates (main 
scan direction). The movement speed is such that the recording head 11 
moves to the right by the distance corresponding to 16 pixels when the 
drum 1 rotates one full turn. In other words, the continuous motion is 
used such that the recording head 11 is at a position 1b at the start of 
the second rotation of the drum 13 and at a position 1c at the start of 
the third rotation. As a result, the recording operation is effected along 
a helical line on the drum. Similarly to the first and second embodiment, 
any one pixel is recorded by plural different nozzles. The image formation 
process is shown in FIG. 7. Various images have been recorded, and it has 
been confirmed that the images are substantially free from stripe and 
unevenness. 
In this embodiment, the image is slightly oblique, but the inclination is 
16 (pixels)/image size, and therefore, when, for example, the image size 
is 200 mm, the inclination is as small as 0.3 degrees which is not 
noticeable by human eyes. If the recording material 12 is inclined in the 
opposite direction when it is mounted on the drum 13, the deviation is 
compensated for, and therefore, the image is free from inclination. 
Embodiment 4 
The same recording apparatus and recording head 1 as in Embodiment 1 (FIG. 
1) was used, but the recording method was different. The number of toner 
gradation levels was 17 in this embodiment. 
FIG. 8 shows the image formation process in this embodiment. 
In operation for recording on the recording material 2, the carriage 4 is 
moved (main scan) using nozzles Nos. 113-128 (16 nozzles). Each of the 
nozzles ejects 0, 1 or 2 ink droplets per pixel in accordance with the 
image density (FIG. 8, portion (a)). Then, the recording medium 2 is fed 
upwardly (sub-scan) through a distance corresponding to 16 pixels. 
Subsequently, the recording operation is carried out using nozzles Nos. 
97-128. At this time, the nozzles Nos. 97-112 effect additional recording 
on the pixels 1-16 which have been subjected to the recording operation by 
the nozzles 113-128 during the previous scan, whereas the nozzles Nos. 
113-128 effect recording on the new pixels 17-32 (FIG. 8, portion (b)). 
Therefore, each of the pixels 1-16 is recorded by 0-4 droplets of the ink. 
Then, the recording material 2 is fed upwardly through the distance of 16 
pixels, and the recording operation is carried out using the nozzles Nos. 
81-128 (FIG. 8, portion (c)). By repeating this printing operation, each 
of the pixels 1-16 is recorded by 0-16 droplets of the ink after 
completion of the eighth scan. Thus, 17 tone gradation record is provided. 
The same operation is repeated from the ninth scan so as to provide the 17 
tone level image is provided on the entire surface. 
Various images have been recorded through this recording method, and it has 
been confirmed that the sharp and uniform images can be provided without 
stripe. 
In this embodiment, the selectable number of ink droplets is 3 (0, 1, 2) 
per picture element during one scan, but it may be larger. 
Embodiment 5 
In this embodiment, only the recording head 11 is different from Embodiment 
3 apparatus. The number of tone gradations is 4. The recording head 11 has 
129 nozzles and ejects large volume droplets. 
FIG. 9 illustrates the image formation process of this embodiment. In this 
embodiment, the movement speed of the drum 13 (main scan) is such that the 
recording head 11 moves rightwardly (sub-scan) through the distance 
corresponding to 43 pixels per one full turn of the drum 1. As a result, 
similarly to Embodiment 3, the image is recorded along a helical line on 
the drum 13. The same pixel is recorded by different 3 nozzles. 
Various images have been recorded, and it-has been confirmed that sharp 
images can be provided without stripe and unevenness. 
In this embodiment, the image is oblique as in Embodiment 3. However, the 
inclination is 43 pixels/image size, and therefore, the inclination is not 
noticeable with human eyes. Further if the recording material 12 is 
mounted on the drum 13 with the opposite inclination, the image is without 
the inclination. 
FIG. 10 summarizes the above-described embodiments. Here, n is the number 
of nozzles, s is the number of nozzles corresponding to the feed distance 
in the sub-scan direction; k is the maximum number of the ink droplets per 
pixel and per scan; g is the number of capable tone gradations or levels; 
and m=n/s. In the foregoing embodiments, m.gtoreq.3, and therefore one 
pixel is recorded by m main scans and by different m nozzles. When, 
therefore, the variation of the ink droplet volumes among the nozzles is 
in the form of the normal distribution with a standard deviation .sigma., 
for example, the variation of the ink volumes for the respective picture 
elements each recorded by different m nozzles is reduced to 
.sigma./.sqroot.m. The ink volume variation among the pixels, is 
recognized as the variation in the image density, but the image density 
variation is not necessarily required to be 0 for the purpose of clear 
image. Rather, it will suffice if it is small enough. Accordingly, as 
compared with the conventional apparatus, the clearer images can be 
provided with a simple structure. As for the value of m, it is desirably 
large in order to reduce the variations among the picture elements. If it 
is not less than 3 (m.gtoreq.3), very clear record of the pixel can be 
provided. The inventors' investigations have revealed that the image is 
sufficiently clearer when m=2 than the conventional record. 
Embodiment 6 
In this embodiment, the same apparatus as in Embodiment 1 was used. A 
different recording method is used to provide 17 tone gradation recording. 
Here, the maximum number of ink droplets per pixel and per scan (k) is 4, 
and the number of scans required for forming one pixel is 4 (FIG. 10). 
In this embodiment, when the maximum ink droplet number (k) per pixel and 
per scan is not less than 2, the ink droplet ejections are uniformly 
allotted to the individual nozzles so as to avoid concentration of 
ejecting actions on limited number of working nozzles. 
In operation, the recording operation is carried out using nozzles Nos. 
97-128 (s=32) out of 128 nozzles (n=128) in the first scan, while the 
carriage 4 is moved at a speed of 31.75 mm/sec in the main scan direction. 
During the recording, A1 (number) droplets (Kx, y/n/s: decimal fraction is 
rounded up to an integer) are ejected at a pixel (x, y) on the recording 
material 2 in accordance with the tone level information Kx,y (0-16) given 
for each pixels. Thereafter, the tone level information Kx,y is replaced 
by K1x,y (K1x,y=Kx,y-A1). Assuming that the tone level information Kx,y is 
13, A1 is 4, and K1x,y is 9. 
In the second scan, the recording sheet 2 is fed in the upward direction by 
a distance corresponding to s nozzles (sub-scan direction). Then, the 
recording operation is carried out using 2.times.s nozzles, i.e., nozzles 
Nos. 65-128, while the carriage 4 is moved at the speed of 31.75 mm. At 
this time, the nozzles Nos. 97-128 effect the similar recording operation 
in accordance with new tone level information Kx,y, whereas the s nozzles 
Nos. 65-96 ejects A2 ink droplets (K1x,yln/s-1), the decimal fraction is 
rounded up to an integer. At the pixel position (x, y) on the recording 
material 2 in accordance with the tone level information K1x,y produced 
after the first scan. Then, the tone level information K1x,y is replaced 
with K2x,y (K2x,y= K1x,y=A2). In the same example, A1 is 4, K2x,y is 5. 
In the third scan, the recording material is fed up through a distance 
corresponding to s nozzles. The recording operation is carried out using 
3.times.s nozzles, i.e., the nozzles Nos. 33-128, while the carriage is 
moved at a speed of 31.75 mm. During this operation, the nozzles Nos. 
97-128 effects the similar recording operation in accordance with new tone 
level information Kx,y. The s nozzles, that is, the nozzles Nos. 65-96 
effects the similar recording operation in accordance with the tone level 
information K1x,y produced after the previous main scan. The s nozzles 
Nos. 33-64 eject A3 ink droplets (K2x,y/(n/s-2), the decimal fraction is 
rounded up to an integer) at the pixel position (x, y) on the recording 
material. Then, the tone level information K2x,y is replaced with K3x,y 
(K3x,y=K2x,y-A3). In the same example, A3 is 4, K3x,y is 1. 
Before the fourth scan, the recording material 2 is fed up through a 
distance of s nozzles. Then, the recording operation is carried out using 
all the nozzles, i.e., the nozzles Nos. 1-128, while the carriage 4 is 
moved at the speed of 31.75 mm/sec. During the recording, the nozzles Nos. 
97-128 effect the similar recording operation in accordance with new tone 
level information Kx,y. The s nozzles, i.e., the nozzles Nos. 65-96 effect 
the similar recording in accordance with the tone level information K1x,y 
produced after the previous main scan. The s nozzles Nos. 33-64 effect the 
similar recording operation in accordance with the tone level information 
K2x,y produced after the previous scan. The s nozzles Nos. 1-32 eject A4 
ink droplets (K3x,y/(n/s-3)=K3x,y) on the pixel (x, y) on the recording 
material in accordance with the tone level information K3x,y produced 
after the previous main scan. The operations in the fourth scan are 
sequentially repeated to effect the recording on the entire surface of the 
recording material 2. As a result, a pixel at a position (x, y) on the 
recording material 2 has received Kx,y (number) ink droplets, the number 
being equal to the tone level information Kx,y. 
A pixel having the tone level information Kx,y which is not less than 2 in 
the image, is recorded by not less than 2 nozzles (the maximum number is 
n/s, here it is 4), and therefore, the variation in the ink volumes from 
the nozzles is reduced, so that the unevenness stripes is not recognized 
or less conspicuous. 
FIG. 11 shows the number of ink droplets A1 -A4 ejected in a scan in 
response to 0-16 tone level information K. 
Referring to FIG. 12, the description will be made as to the structure of 
the control system usable with the present invention. The image 
information supplied from a host computer 101 is once stored in a frame 
memory 103 by a main controller 102. The main controller 102 processes the 
image information to convert it to tone gradation or level signals 
suitable for the system (recording apparatus) used therewith. For example, 
the image information having 0-255 levels is converted to 17 tone signals 
(0-16) in the foregoing Embodiment 1. The tone signal is supplied to a 
driver controller 104 which divide the tone signal into plural scans, and 
the divided signals are supplied to the head driver 105 as the recording 
signals. The head driver 105 drives the recording head 106 in accordance 
with the supplied recording signal, thus ejecting droplets of the ink. 
Motor drivers 107 and 108 are effective to control a carriage moving motor 
109 and a sheet feeding motor 110. 
Embodiment 7 
In this embodiment, the same apparatus of Embodiment 1 is used except for 
the recording head. In this embodiment, the recording is effected with 7 
tone gradations. The recording head 1 has 129 nozzles which are capable of 
ejecting the droplets at the frequency of 12 kHz, in other words, the 
heater driving frequency is 12 kHz. The carriage 4 is moved at a speed of 
0.25 m/sec. The recording material 2 is fed up by 268.75 microns which 
corresponds to 43 nozzles, after each scan. 
The 7 tone gradation recording using the apparatus of this embodiment will 
be described. The number of ink droplets per pixel (square of 1/16 
mm.times.1/16 mm (62.5.times.62.5 microns)) is changed within the range of 
0-6 inclusive. 
FIGS. 13 and 14 illustrate the recording method in this embodiment. The 
recording head 1 which is schematically shown in provided with 129 nozzles 
arranged in the vertical direction. For the convenience of explanation, 
the nozzles are numbered 1, 2 . . . . . 128 and 129 from the top of the 
Figure. 
In operation, the recording operation is carried out using only the nozzles 
Nos. 87-129, while the carriage is moved in the main scan direction. At 
this time, in this embodiment, 3, at the maximum, ink droplets can be 
ejected per pixel because of the relation among the size of the pixel 
(62.5 microns), the carriage movement speed (0.25 m/sec) and the nozzle 
actuating frequency (12 kHz), as will be understood from the following 
equation. However, the recording operation is carried out using only two 
droplets. 
EQU [time required for the carriage to pass one pixel] =[size of 
pixel]/[carriage speed] 
EQU [maximum number of droplets in one pixel]=[carriage passing 
time].times.[ejection frequency] 
As a result, as shown in FIG. 14, at portion (a), the pixels 1-43 from the 
top of the recording material is recorded by 0-2 droplets of the ink. 
then, the recording material is fed up in the sub-scan direction through a 
distance corresponding to 43 pixels (in the Figure, the recording head is 
shown as being moved down, for the simplicity of explanation). Then, the 
recording operation is carried out using the nozzles Nos. 44-129. As a 
result, as shown in FIG. 14 at portion (b), the nozzles Nos. 44-86 record 
the 1-43 pixels having been recorded by the nozzles Nos. 87-129 in the 
previous scan. The nozzles Nos. 87-129 carry out the recording operation 
for the fresh pixel (44-86). Therefore, each of the pixels 1-43 are now 
recorded by 0-4 droplets of the ink. 
Then, the recording material is again fed up through the distance of 43 
pixels. The recording operation is carried out using the nozzles Nos. 
1-129. Thereafter, the recording material is fed up through the distance 
of 48 pixels. As shown in FIG. 14 at portions (c) and (d), the recording 
operation is repeated using all the nozzles Nos. 1-129. Then, the pixel 1, 
for example, receives 0-6 droplets of the ink supplied from 3 nozzles, 
i.e., the nozzles Nos. 1, 44 and 87 (the order of the ejecting operation 
is opposite), so that 7 tone gradation record is provided. Each of all the 
other pixels has uniform volume of ink droplets, and therefore, the image 
has less conspicuous unevenness. 
If there is a failed nozzle, that is, a nozzle incapable of ejecting the 
ink droplet, in this embodiment, for example, the nozzle No. 44 is failed, 
then the pixel to receive 2 droplets (at the maximum) from the nozzles 
Nos. 1, 44 and 87, is recorded by ejecting 3 ink droplets (at the maximum) 
from the remaining two nozzles, i.e., the nozzles Nos. 1 and 87. If the 
existence of the failed nozzle is known during the recording apparatus 
manufacturing process, the information to that event is stored in the 
memory (ROM or RAM) in the recording apparatus, and the controller 
properly selects the ejecting nozzles. If one or more nozzles become 
failed during use of the apparatus after the manufacturing thereof, a 
service man or user can write the information in the RAM of the recording 
apparatus, so that the other working nozzles can compensate for the failed 
nozzle or nozzles. 
Embodiment 8 
In this embodiment, the recording head has 288 nozzles which are operable 
at the ejecting frequency of 4 kHz, and the carriage moving distance per 
scan is 4500 microns (72 nozzles). The number of recordable tone 
gradations per pixel is 4. In the other respects, the apparatus is the 
same as in Embodiment 7. 
FIG. 15 illustrates concept of the recording method of this embodiment. In 
this embodiment, the number of droplets per pixel and per scan is 0-1, and 
one pixel is recorded by 4 scans, and therefore, the maximum number of 
droplets capable of being supplied to one pixel 4 as a total. 0n the other 
hand, the number of ink droplets to be supplied to one pixel is 0-3, and 
therefore, when all of the nozzles are in order, 3 scanning operations are 
enough. One or more nozzles can fail. If this occurs, during 3 scans other 
than the scan using the nozzle, the other 3 nozzles are used, so that the 
resultant image is free from stripes. 
For example, pixel 1 is to be recorded by 0-3 ink droplets ejected through 
4 nozzles, i.e., the nozzles Nos. 1, 73, 145 and 217 (the order of 
ejecting operation is the opposite). If the nozzle No. 73 fails, the pixel 
is recorded by 3 (at the maximum) ink droplets through the nozzles Nos. 1, 
145 and 217. Similarly to the foregoing embodiment, if the existence of 
the non-ejecting nozzle is known during the recording apparatus 
manufacturing process, the information to that event may be stored in 
memory of the recording apparatus (ROM or RAM), and the nozzles are 
properly selected through the control system. 
Embodiment 9 
In this embodiment, the recording head has 36 nozzles which are capable of 
being operated at frequency of 4 kHz. The carriage feeding distance per 
scan is 687.5 microns (11 nozzles). The number of tone gradations per 
pixel is 4. In the other respects, the apparatus of this embodiment is the 
same as Embodiment 7. 
FIG. 16 illustrates the conception of the recording method of this 
embodiment. In this embodiment, the carriage feeding distance per scan in 
the unit of nozzle number is not a reciprocal of an integer multiplied by 
the number of the nozzles of the head. Therefore, the number of scans for 
recording one pixel is either 3 or 4. In this embodiment, the number of 
ink droplets capable of being ejected per pixel per scan is 0-1, and 
therefore, the number of droplets capable of being ejected to one pixel is 
3 at the minimum (FIG. 16, at portion B) or 4 (FIG. 16 at portion A). 
Since the number of droplets to be supplied to one pixel is 0-3, the 
portion A has a margin of one drop. Therefore, as regards the nozzles Nos. 
1, 2, 3, 12, 13, 14, 23, 24, 25, 34, 35 and 36, even if they fail, the 
other nozzles can compensate for them similarly to Embodiments 7 and 8, so 
that the resultant image is free from stripes. 
FIG. 17 is a block diagram of an ink jet recording apparatus usable with 
the present invention. It comprises a host computer 201 for supplying the 
image data to be recorded, a memory (RAM) 202 storing the data concerning 
the failed nozzles, a controller processor 203 for determining the number 
of ink droplets to be ejected in accordance with the image data and for 
selecting the nozzles to be actuated in accordance with the failed nozzle 
data in the RAM 202. Designated by a reference numeral 204 is an ink jet 
recording head. 
Embodiment 10 
In this embodiment, the operational frequency of each of the nozzles is 
made more uniform. In this embodiment, the ejection or non-ejection of the 
ink f (m, n) is determined in accordance with the density or tone 
gradation for each pixel, as shown in FIG. 18. 
In FIG. 18, the n-th ink droplet is the droplet ejected through 16 nozzles 
for the same pixel. When the first pixel in FIG. 3 is noted, for example 
(FIG. 3), No. 121 nozzle ejects the first ink. No. 113 nozzle ejects the 
second ink droplet; No. 105 nozzle, the third droplet; No. 97 nozzle, the 
fourth droplet; No. 89 nozzle, the fifth droplet; No. 81 nozzle, the sixth 
droplet; No. 73 nozzle, the seventh droplet; No. 65 nozzle, the eighth 
droplet; No. 57 nozzle, the ninth droplet; No. 49 nozzle, the tenth 
droplet; No. 41 nozzle, the eleventh droplet; No. 33 nozzle, the twelfth 
droplet; No. 25 nozzle, the thirteenth droplet; No. 17 nozzle, the 
fourteenth droplet; No. 9 nozzle, the fifteenth droplet; and No. 1 nozzle, 
the sixteenth droplet. 
In FIG. 18, the ink droplet is ejected when f (m, n)=1, while the ink 
droplet is not ejected when f (m, n)=0. Therefore, when the tone m=1, for 
example, the first ink droplet is ejected, but when the tone m=2, the 
first ink droplet is not ejected (the nozzle is not used for the 
recording), the desired image density is provided by the second and third 
ink droplets. 
Therefore, the following represent the nozzle actuation frequency: 
##EQU1## 
At the bottom of FIG. 18 represents the operational frequency of the 
nozzle. 
By determining the ejection and non-ejection of the nozzles f (m, n), no 
particular order of ink droplets is frequently used, and therefore, the 
frequent drivings of particular nozzle or nozzles can be avoided, as long 
as the image to be recorded includes one or more particular tone levels. 
In the example of FIG. 18, 
##EQU2## 
is 8 or 9. In this embodiment, the maximum number of droplets N is 16, and 
therefore: 
##EQU3## 
This inequality accomplishes most uniform operation of the nozzles when the 
tone levels appear uniformly. 
If the following inequality is satisfied, it is sufficiently effective to 
extend the service life of the frequently used nozzle or nozzles. 
Embodiment 11 
In this embodiment, the used apparatus is the same as in Embodiment 2 of 
FIG. 4 except that the recording head has 256 nozzles and that the tone 
gradation number per pixel is 5. 
First, the recording head 11 is moved to the leftmost position in FIG. 4, 
and the recording operation is carried out using only nozzles Nos. 193-256 
(64 nozzles), while the drum 13 is rotated through one full turn. 
Then, the recording head 11 is moved to the right through a distance 
corresponding to 64 pixels. Then, the recording operation is carried out 
using 128 nozzles, i.e., the nozzles Nos. 129-256, while the drum is 
rotated through one full turn. In this manner, the recording head is moved 
to the right through the distance corresponding to 64 pixels, while the 
drum 13 is rotated one turn. This is repeated, so that the whole surface 
is recorded. 
As a result, the first pixel, for example, is recorded by nozzles Nos. 1, 
65, 129 and 193. (4 nozzles). Therefore, 5 tone gradation recording is 
accomplished with 0-4 ink droplets. 
In this embodiment, the ejection and non-ejection of the nozzle f (m, n) is 
determined in accordance with the tone or density level of a pixel, as 
shown in FIG. 19. In this embodiment, 
##EQU4## 
is satisfied, too. Here, the image density (OD) for each of the tone 
levels was as shown in FIG. 20. 
In the practical full-color image recording, the use of 5 tone levels is 
not enough, and therefore, it will be preferable to use also the known 
tone processing method such as dither method or error diffusing method or 
the like. 
In the combination with the known method, one droplet per pixel or zero 
droplet per pixel where the image density OD is not more than 0.55, and 
therefore, the operational frequency of the nozzle corresponding to the 
tone level 1 tends to increase in order to decrease the operational 
frequency of the nozzle corresponding to the tone level m=1 (the nozzle 
corresponding to the first ink droplet in this case) in view of the above, 
##EQU5## 
at n=1 is set to be 2 which is lower than the average. 
Thus, the tendency of significant increase of the operational frequency for 
1 droplet per pixel, is particularly significant when the maximum number 
of ink droplets n is not more than 10. 
Embodiment 12 
In this embodiment, the use is made with the recording head which is the 
same as in Embodiment 4, and the operational frequencies of the nozzles 
are made more uniform. 
The ejection or non-ejection of the ink may be determined in accordance 
with the tone level for each of picture elements in the same manner as in 
Embodiment 10. Since, however, the first and second ink droplets, the 
third and fourth ink droplets, and the fifteenth and sixteenth ink 
droplets, are ejected through the same nozzles, respectively, the 
uniformity between the ink droplets ejected through the same nozzle is 
achieved. 
It is preferable that one pixel is recorded by as large a number of 
different nozzles as possible from the standpoint of less unevenness. In 
view of this, the ejection and non-ejection is determined as shown in FIG. 
21. 
In FIG. 21, the values given in "SUM" are sums of 
##EQU6## 
With respect to the liquid droplets ejected from the same nozzle. By 
determining the ejection and non-ejection in accordance with FIG. 21, the 
nozzles can be operated at more even frequencies. 
The timing of one droplet ejection for the case of one droplet per pixel, 
is determined so that the ink is ejected at the earlier timing for all 
cases. Therefore, even if the density or tone levels are different in the 
adjacent pixels, two droplets are not ejected continuously except for the 
high density cases (m.ltoreq.8), and therefore, the ejections are 
stabilized. This is effective to improve the uniformity. The structure of 
the control system is the same as in FIG. 12. 
As described in the foregoing, according to Embodiments 10-12, the nozzles 
are operated at more even frequencies. Thus, the reduction of the 
recording head service life attributable to the particular nozzle or 
nozzles operated at higher frequencies, can be avoided. 
Embodiment 13 
FIG. 22 is a block diagram of a control system for an ink jet recording 
apparatus according to Embodiment 13. It comprises a host computer 201 for 
supplying the image data to be recorded, a memory (RAM) 202 for storing 
ejection nozzle data corresponding to the number of ink ejections, a 
processor controller 203. A recording head 204 has 128 nozzles arranged at 
the density of 16 nozzles/mm. A memory (ROM) 205 stores the ejection 
volume data for each nozzle. 
Using this apparatus, one pixel is recorded by 4 scans, wherein the number 
of droplets per pixel ranges between 0-4, inclusive so that 5 tone 
gradation image can be recorded. In FIGS. 23 and 24, the recording method 
is illustrated. In this Figure, the 128 nozzles are arranged vertically. 
For the convenience of explanation, the nozzle is numbered 1, 2 . . . . . 
128 from the top. 
The volume of the liquid droplet ejected by each nozzle is determined 
through a known method. The data are stored in the ROM. In this 
embodiment, the volume is determined in the following manner. The ejected 
in the droplet is photographed using optical microscope and TV camera, and 
the volume is calculated on the basis of the image thereof. 
In operation, the recording operation is carried out using only nozzles 
Nos. 97-128, while the carriage is moved at a speed of 31.75 mm/sec in the 
main scan direction. Then, pixels 1-32 from the top of the recording 
material is recorded by 0 or 1 ink droplet, as shown in FIG. 24 at portion 
(a). Then, the recording material is fed upwardly (sub-scan direction) 
through a distance corresponding to 32 pixels (in the Figure, the 
recording head is moved downwardly relative to the recording material, for 
the convenience of explanation). Then, the recording operation is carried 
out using the nozzles numbers 65 -96. As shown in FIG. 24, portion (b), 
the nozzles Nos. 65-96 effect further recording on the pixels 1 -32 having 
been subjected to the recording operation of the nozzles Nos. 97-128 in 
the previous scan. The nozzles Nos. 97-128 effect the recording for the 
new 33-64 pixels. Therefore, the pixels 1-32 are recorded by 0-2 droplets 
per pixel. 
Subsequently, the recording material is fed upwardly through a distance 
corresponding to 32 pixels, and the recording operation is carried out 
using nozzles Nos. 33-128 (FIG. 24, portion (c)). Further, the sheet is 
fed upwardly through the same distance, and the recording operation is 
carried out using all of the nozzles, i.e., Nos. 1-128 (FIG. 24, portion 
(d)). The above operations are repeated to cover the entire surface. Then, 
the first pixel, for example, is recorded by the ink droplets ejected 
through 4 nozzles, i.e., nozzles Nos. 1, 33, 65 and 97 (the order of 
ejections is the opposite). 
The number of ink droplets to be shot to one pixel is determined on the 
basis of the image data. In this embodiment, the number is 0, 1, 2, 3 and 
4 (5 kinds) since 5 tone gradation recording is effected. Which nozzles 
are to be used for ejecting the number of droplets, is determined by the 
processor using the data stored in the ROM, so that as many different 
nozzle combinations as possible are used and so that the sum of the ink 
volumes through the used nozzles is as close as possible to the average of 
the ejection volume of the entire recording head. 
Assuming, for example, that the ejection volumes of nozzles Nos. 1, 33, 65 
and 97 are 8 pl, 10 pl, 10 pl and 12 pl and that the average ejection 
volume of 128 nozzles of the recording head is 10 pl. When the number of 
droplets to be shot is 1, No. 33 or No. 65 nozzle is used. When it is 2, 
No. 1 nozzle and No. 97 nozzle, or No. 33 nozzle and No. 65 nozzle, are 
used. When it is 3, No. 1 nozzle, No. 33 nozzle and No. 97 nozzle, or No. 
1 nozzle, No. 65 nozzle and No. 97 nozzles, are used. If it is 4, all of 
these nozzles, i.e., 4 nozzles are used. 
The above calculations are effected for all pixels, and the recording 
operation is carried out while determining the nozzles to be used. 
FIG. 25 is a flow chart of the operations for the above. In FIG. 25, when 
the recording operation starts, the image data for 32 lines is received by 
the host computer 11 at step S1. At step S2, the number of ink droplets 
(m) to be shot to one pixel is determined from the image data. Here, m is 
0 -4. At step S3, if m=4, the operation proceeds to step S4 where 4 
nozzles are selected. On the other hand, if m.times.3 at step S3, the 
operation proceeds to step S5 where the ejection volume data is read out 
of the ROM 15. At step S6, average ejection volume xm=V is calculated. At 
step S7, the total ejection volume is calculated as the combination of the 
nozzles to be used, as shown in FIG. 26. On the basis of the calculation, 
the combination closest to V is selected. The result of selection is 
written in the RAM 12 at step S8. 
The operations in steps S2-S8 are repeated until all of the pixels in 32 
lines are finished (step S9). All the pixels are dealt with, the ink 
droplets are ejected at step S10, referring to the RAM 12, thus effecting 
record. The operations in steps. S1-S10 are repeated until all the lines 
are covered (step S11). 
The recording operations have been carried out through the recording 
method, and it has been confirmed that the variation in the ink volumes 
from the nozzles are compensated for all tone levels, and that the stripes 
and unevenness are less conspicuous. 
In this embodiment, the ejection volume data of the nozzles are stored in 
the ROM, and-the nozzles to be used are determined by the processor. 
However, the relations between the image signals and the nozzles to be 
used are determined beforehand, and the results are stored in a ROM. In 
this embodiment, the number of ink droplets ejected for one pixel from one 
nozzle per scan is either 0 or 1, but plural number may be used. 
Embodiment 14 
FIG. 27 is a block diagram of a control system of an ink jet recording 
apparatus of Embodiment 14. It comprises a host computer 201 for supplying 
the image data to be recorded, a memory (RAM) for storing the density or 
tone level data for the respective nozzles and a controller and processor 
203. Designated by a reference numeral 204 is an ink jet recording head 
having 128 nozzles arranged at the density of 16 nozzles/mm. 
Using all the nozzles to be used, the gray scales corresponding to various 
signal levels are recorded. The gray scales are read by a known density 
measuring device. Thus, the density-signal data are determined for the 
nozzles. This is stored in the RAM 202. When the recording operation is 
carried out for the recording medium, the operations are the same as 
Embodiment 13, but the nozzles to be used are determined, referring to the 
density data stored in the RAM 202. 
In this embodiment, the density data is stored in the RAM 202, and 
therefore, even if the density data for the nozzles changes for some 
reason or another after the recording apparatus is sold, it is possible 
for the user or the service man to change the data in the RAM 202. Even if 
one or more nozzles failed, the data in the RAM 202 may be changed so as 
to use another working nozzle in place of the failed nozzle, thus 
expanding the service life of the recording head. 
Embodiment 15 
FIG. 28 is a block diagram of a control system for an ink jet recording 
apparatus according to Embodiment 15. It comprises a host computer 201 for 
supplying the image data to be recorded, a memory (RAM) 202 for storing 
density level data for each nozzles and a processor and controller 203. 
Designated by a reference numeral 204 is an ink jet recording head having 
128 nozzles at the density of 16 nozzles/mm. The control system also 
comprises a CCD scanner. 
In this embodiment, the gray scales corresponding to various signal levels 
are recorded using all nozzles to be used. Then, the gray scales are read 
by the CCD scanner 206 to determine density-signal data for respective 
nozzles. The delta are stored in the RAM 202. The recording operation is 
carried out in the similar manner as in Embodiment 13, but the nozzles to 
be used are selected, referring to the density data stored in the RAM 202. 
In this embodiment, the apparatus has a built-in data reading device (CCD 
scanner). Therefore, even if the density data for the nozzles change for 
one reason or another after the apparatus is sold, the user can easily 
correct the data, and therefore, the maintenance is easier. 
In this embodiment, the record density of the nozzles are determined on the 
basis of OD level when one nozzle is operated, or the ejection volume 
which is substantially one-to-one correspondence with the OD level. 
However, the ejection speed or the like which is closely related with the 
ejection volume. 
According to Embodiments 13-15, the density variation among the picture 
elements can be minimized, and therefore, the clear images can be provided 
with simple system structure as compared with the conventional apparatus. 
Embodiment 16 
FIG. 29 shows the OD level when the recording liquid shown in FIG. 30 is 
shot on a coated sheet. The used multi-nozzle recording head has 48 
nozzles arranged at a nozzle pitch of 63.5 microns. The ejection liquid 
volume per nozzle is 0.008 nl. The pixel pitch in the main scan direction 
is 63.5 microns which is equal to the nozzle pitch. In FIG. 29, designated 
by 31 is the OD levels when the recording liquid is ejected in one scan, 
where as reference numeral 32 designate the OD levels when the recording 
liquid is shot by plural scans. In the latter case, the recording liquid 
is shot at the same position, but in the former case, the centers of the 
dots are deviated with the increase of the number of dots (multi-droplet 
recording). This is the cause of the difference of the curves. As will be 
understood from this Figure, the OD level becomes different by 0.2 at the 
maximum although the total volume of the shot liquid is the same. 
The present invention positively uses this, namely when one recording 
liquid is used, the reflection density (OD) of the dot provided by one 
scan is different from the reflection density of the dot provided by 
plural scans, even if the total amount per unit area is the same. The 
apparatus of this embodiment is the same as the apparatus in Embodiment 1 
except for the number of nozzles is 12. The structure of the control 
system is the same as shown in FIG. 12. 
The description will be made as to the method of 5 tone gradation record. 
FIG. 31 shows the concept of the recording method of this embodiment. The 
recording head 1 has 12 nozzles arranged vertically. For the convenience 
of explanation, the nozzles are numbered 1, 2 . . . . , 12 from the top. 
In operation, the recording operation is carried out using only nozzles 
Nos. 7-12, while the carriage is moved in the main scan direction. As a 
result, as show in FIG. 31 at portion (a), pixels 1 -6 from the top on the 
recording material are recorded by 0, 1 or 2 ink droplets. Then, the 
recording material is fed upwardly (sub-scan direction) through a distance 
corresponding to 6 pixels (in the Figure, the recording head is shown as 
moving downwardly, for the convenience of explanation). Then, the 
recording operation is carried out using nozzles Nos. 1-12. As a result, 
as shown in FIG. 31 at portion (b), the nozzles Nos. 1-6 effect the 
recording with 0 or 1 droplet on pixels 1-6 which have been subjected to 
the recording operation of the nozzles Nos. 7-12 in the previous scan, The 
nozzles Nos. 7-12 record new pixels 7-12 with 0, 1 or 2 droplets. 
Therefore, the pixels 1-6 are recorded by 0-3 droplets per pixel. 
The sheet is fed upwardly through a distance of 6 pixels, and the recording 
operation is carried out using the nozzles Nos. 1-12. As shown in FIG. 31 
at portion (c), the repetition of the above-described operations produces 
the record on the whole surface with 0-3 droplets. 
FIG. 32 illustrates the recording operation in more detail. In this 
embodiment, one pixel is recorded by 3 droplets at the maximum. 
Conventionally, the multi-droplet tone recording using 3 droplets at the 
maximum per one pixel can produce 4 tone levels, but in the present 
embodiment, 5 tone levels can be provided. 
Portion (a) of FIG. 32 shows the recorded image according to this 
embodiment. .smallcircle. or .circleincircle. indicates the droplet or 
droplets. The used multi-nozzle head had 12 nozzles each capable of 0.031 
nl per ejection. The recording density is 16 pixels per 1 mm. The image 
was provided by two scans (p) and (c). 
Dots 14, 15, 16 and 17 are provided by 1 droplet, 2 droplets, 2 droplets 
and 3 droplets per pixel, respectively. The image density increases in the 
order named. Reference numerals 14', 15', 16' and 17' indicate pixels for 
the dots 14, 15, 16 and 17, respectively. The pixel 14' is recorded by one 
droplet only through the first scan. The pixel 15' is recorded by one 
droplet in the first scan and one droplet in the second scan, in which the 
droplets are shot at the same point in the pixel. The pixel 16' is 
recorded by two droplets in the first scan, and therefore, the shot 
position of the droplets are deviated by a distance determined from the 
scanning speed and the ejection frequency. The pixel 17' is recorded by 
the same droplets as in the pixel 16' plus one droplet in the second scan 
(3 droplets in total), in which the third droplets provided by the second 
scan is deviated to the right from the second droplets in the first scan. 
The droplet ejection timing is controlled so that the three droplets are 
disposed at the regular intervals. The density in this pixel is the same 
as a pixel shot by one scan at the regular intervals. 
The pixels 15' and 16' are each recorded by two droplets per pixel. 
However, the dot record 16 of the pixel 16' has a higher image density 
than the dot record 15 of the pixel 15'. For this reason, 5 tone 
gradations (including no ejection) can be provided. In this embodiment, 
similarly to the case of FIG. 29, the coated sheet and water ink is used. 
The reason why the dot 16 has a higher density than the dot image 15 is the 
same as with FIG. 29. FIG. 33 shows the results of image density 
measurements. In this Figure, reference numerals 24, 25, 26 and 27 
indicate the image densities of the dots 14, 15, 16 and 17 of FIG. 32. In 
FIG. 33, ".DELTA." is the image densities when plural droplets are shot 
with 20 microns deviation for one pixel; ".smallcircle." indicates the 
image densities when the droplets are shot at the same position for one 
pixel. The image densities 25 and 26 (OD levels) are different by 
approximately 0.2 due to the difference of the shot positions despite they 
are provided by 2 droplets per pixel. As will be understood, this 
embodiment positively uses the difference. 
According to this embodiment, the number of tone gradations is increased in 
effect by 1 without changing the recording head structure. The better 
quality images can be provided. When the image having the image density of 
approximately 1.0 OD, the two droplet ejection per one pixel can be 
selected from 15 and 16 levels in FIG. 32 in accordance with the image 
signal, and therefore, the halftone level can be expressed more finely. 
In this embodiment, the two scanning operations are carried out with the 
deviation of the distance corresponding to 6 nozzles in the sub-scan 
direction. However, it is possible to effect the recording without 
deviation in the sub-scan direction between the two scans. In this case, 
the image processing software is simplified. 
Embodiment 17 
FIG. 17 illustrates Embodiment 17, in which the use is made with a 
recording head having 15 nozzles each capable of ejecting 0.023 nl 
recording liquid per ejection. The Figure shows schematically the recorded 
image, in which ".smallcircle." indicates a dot provided by one droplet; 
"502 " indicates a dot provided by two droplets shot on the same point; 
and " " indicates a dot provided by three droplets shot at the same point. 
The partly overlapped" " indicates a dot or one pixel provided by plural 
droplets through one scan. The used recording liquid and the sheet are the 
same as in the previous embodiment. The recording density is the same, 
that is, 16 pixels/mm in this embodiment, 4 droplets per pixel per scan at 
the maximum is capable. One pixel is scanned three times, and 8 tone 
gradations are possible. 
In FIG. 34, reference numerals 41-47 indicate recorded patterns for the 
respective tone levels. Reference numerals 41'-47' indicate single pixels 
in the respective patterns. Reference numerals 41, 43, 44, 46 and 47 are 
dot images recorded by one scan. The number of droplets per pixel is 1, 2, 
2, 3 and 4, respectively. Reference numeral 42 indicates a dot image 
recorded by 2 scans. Reference numeral 45 designates a dot image provided 
by 3 scans. Reference numerals 43 and 44 indicate dot images provided by 
two droplets per pixel, and the dot 43 is recorded by the first and second 
shots among the four shots, and the latter is recorded by the first and 
third shots. In the pixel 43', the two dot are partly overlaid, but in the 
pixel 44', the two dots are separate from each other. 
FIG. 35 shows the OD levels for the respective patterns of FIG. 34. In this 
Figure, reference numerals 51-57 indicate the density of the dots 41-47. 
As described with respect to the foregoing embodiment, the image density 
decreases with the degree of overlapping of the dots if the number of 
droplets per pixel is the same. Therefore, 
the density 52 of the dot 42&lt;the density 53 of the dot 43&lt;the density 54 of 
dot 44. 
Similarly, 
the density 55 of the dot 45&lt;the density 56 of the dot 46. 
In both of the droplets 43 and 44, the number of droplets m.sub.1 through 
the first scan is 2, the number of droplets through second or third scan 
is 0 (m.sub.2 =m.sub.3 =0). However, in this embodiment, the timings of 
the two droplet shots for one pixel in one scan, are selected in 
accordance with the image signal. In this Example, the time interval 
between the two droplets is changed. This embodiment is the same as the 
previous embodiment in that whether the same number of droplets is shot in 
one scan or in plural scans, is determined in accordance with the image 
signal. 
Similarly to Embodiment 16, the recording head or the sheet is moved in the 
sub-scan direction by the distance corresponding to 5 nozzles, for each 
scanning operation. Thus, one pixel is scanned three times. By doing so, 
the variation in the ink volumes of the nozzles is flatten, and therefore 
the image involves less conspicuous stripes and unevenness. 
The three scans may be carried out without deviation the recording head in 
the sub-scan direction. In this case, the image processing software is 
simplified. 
In accordance with Embodiments 16,and 17, a larger number of tone 
gradations can be provided even if the total number of droplets for one 
pixel is the same. This is because the number of droplets per scan is 
changed so that the shot positions of the droplets are changed. 
Embodiment 18 
The apparatus of this embodiment is the same as Embodiment 1 (FIG. 1) 
except for that the recording head has groups of nozzles, which groups 
provide different ink ejection volumes. FIG. 36 schematically shows the 
structure of the recording head in this embodiment. For the sake of 
simplicity of explanation, the recording head comprises three groups of 
ejection outlets 301, 302 and 303, each group having four successive 
ejection outlets. Each of the ejection outlets in the first group 301 are 
designed to eject 5 pl in the volume (ejection outlets Nos. 1-4). Each of 
the ejection outlets in the second group 302 is designed to eject a 
droplet of 8 pl (ejection outlet Nos. 5-8). Each of the ejection outlets 
in the third group 303 is designed to eject a droplet of 11 pl (ejection 
outlet Nos. 9-12). The ejection outlet groups 301-303 are arranged 
vertically in the Figure, in other words, the groups are arranged along 
one line in the sub-scan direction which is substantially perpendicular to 
the main scan direction along which the recording head is moved. 
The recording head 1 comprises base members 62 and 63, and the ejection 
outlets are opened at the surface of the base plate 62 faced to the 
recording material 2. In order to produce the recording head 1 at low 
cost, the conventional manufacturing process can be used substantially as 
it is. However, in order to permit the use, the volume ratio between the 
maximum ink droplet and the minimum ink droplet is desirably not more than 
3.0. The maximum ink droplet in this embodiment is 11 pl, and the minimum 
ink droplet is 5 pl. The volume ratio is 2.2, and therefore, the 
above-described desirable condition is satisfied, so that the recording 
head can be produced at relatively low cost. 
FIG. 37 shows the printing operation. The large outer square frame defines 
the entire record area of the recording material 2 to be covered by plural 
scans of the carriage 4. Five recording region (A, B, C, D and E) 
correspond to the ejection outlet grooves ejecting different volumes of 
droplet (3 volumes). The width of each of the regions measured in the 
vertical direction corresponds to the distance of one feed of the 
recording material 11. In the first scan, ink droplets of 5 pl is ejected 
using the ejection outlets Nos. 1-4 (301) to the top region A in 
accordance with the tone level of the image data (tone data), thus 
effecting dot-printing. Subsequently, the recording material 2 is fed 
upwardly in the Figure by 63.5 microns (ejection outlet pitch) .times.4 
(the number of ejection outlets)=254 microns. Thereafter, the second scan 
is started. 
In the second scan, the ejection outlets Nos. 1-4 (group 301) now at the 
region B eject ink droplets of each 5 pl in accordance with the tone of 
the image data as in the first scan, thus effecting the dot printing. 
Simultaneously, the ejection outlets Nos. 5-8 (group 302) now at the 
region A eject the droplets of the ink on the region A having been scanned 
by the first scan, in accordance with the tone of the image data. The 
ejection outlets here each eject 8 pl of the ink. In this recording, the 
droplet of 8 pl is not shot at the position where the 5 pl ink droplet is 
not shot in the first scan. After the second scan is completed, the 
recording material 2 is fed by the same distance, 245 microns, in the 
upward direction. Thereafter, the third scanning operation is started. 
In the third scan, the ejection outlets Nos. 1-4 (301) now in the third 
region C and ejection outlets Nos. 5-8 (302) now in the region B eject the 
ink droplets to effect the similar printing as in the second scan. 
Simultaneously, the ejection outlets Nos. 9-12 (303) now in the region A 
eject 11 pl ink droplets in accordance with the image data. Similarly, the 
11 pl ink droplets are not shot to the positions where the 5 pl and 8 pl 
droplets are not shot in the first and second scans. 
When the third scan is completed, the region C includes two states having 0 
pl ink droplet (no ink) per pixel and having 5 pl ink droplet per pixel, 
respectively. The region B includes three states having 0 pl droplet, 5 pl 
droplets and 13 pl droplets (=5 pl +8 pl). The region A includes four 
states having 0 pl droplet, 5 pl droplets, 13 pl droplets (=5 pl +8 pl) 
and 24 pl (=5 pl +8 pl +11 pl) per pixel, respectively. 
Similarly a fourth scan and fifth scan are carried out so that dots are 
printed on the recording material 11 in accordance with the tone levels of 
the image data. When the record in the region A expands all over the 
record area of the recording material 2, and the ejection outlets Nos. 
8-12 of the recording head (103) reaches the region E, and the printing 
operation is carried out. Then, the recording operation is completed. 
In this embodiment, the same volume ejection outlets constitute a block, 
and a plurality of such blocks are provided. However, it is a possible 
alternative that the ejection outlets providing different volumes of ink 
droplets may be alternately arranged, with the same advantageous recording 
effect. 
FIG. 37 shows a relation between the reflection image density and the ink 
volume per pixel of the recorded image on the recording material 2 as 
described in conjunction with FIG. 37. In the embodiment of FIGS. 36 and 
37, level 0 (no ink) provides the reflection density of 0.05 (the 
reflection density of the recording sheet 2 itself); the first level (I) 
of 5 pl provides 0.47; the second level (II) of 13 pl provides 1.02; and 
the third level (III) of 24 pl provides 1.38. 
As will be understood, as compared with the method proposed in U.S. Pat. 
No. 4,746,935, the intervals between adjacent reflection densities are 
more even, and therefore, the tone property is better. The reflection 
density at the first level (I) is 0.47 which is equivalent to the 
reflection density provided by 5 ink droplets (maximum) per pixel in the 
conventional multi-droplet method, when the maximum levels of the 
reflection densities in the images are the same. Accordingly, the density 
levels of the image formed through this embodiment is comparable to the 
image provided by 5 ink droplet per pixel through the conventional 
multi-droplet method. As regards the printing speed, this embodiment 
requires only three overlaying shots per pixel, and the printing speed can 
be increased by approx. 20%. 
The image data (tone level data) in this embodiment are produced by 
logarithmic correction .gamma. correction and subsequent 4 level error 
diffusion treatment to the data read from an original image by a 
monochromatic scanner, for example. 
Embodiment 19 
FIG. 39 shows the structure of the recording head 1 in Embodiment 19. In 
this embodiment, the ejection outlets are divided into two groups 311 and 
312. The ejection outlets of the group 311 provides 5 pl ink droplets, and 
the ejection outlets of the group 312 provides 14 pl ink droplets. The 
number of ejection outlets in the group 311 providing 5 pl ink droplets is 
8; and the number of ejection outlets in the group 312 providing 14 pl ink 
droplets, is 4. Similarly to the Embodiment 18 in FIG. 36, the recording 
head 1 is mounted on a carriage 4 of the serial type printer. The scanning 
operation is carried out as shown in FIG. 37, and the halftone image is 
recorded on the recording material 2 corresponding to the image data. 
Referring to FIG. 37, the operation of this embodiment will be described. 
In the first scan, only the ejection outlets Nos. 4-8 (311) are used to 
eject the ink droplets of 5 pl each to the pixels which are to receive 24 
pl/pixel ink and 10 pl/pixel ink in the region A, and simultaneously, the 
5 pl droplets are ejected to approx. 50% of the pixels which are to 
receive 5 pl/pixel. Then, the recording material is fed upwardly by 254 
microns in FIG. 37. Then, the second scan is started. 
In the second scan, the ejection outlets Nos. 1-4 (311) in the region B 
eject the ink droplets as in the first scan. Simultaneously, the ejection 
outlets Nos. 5-8 (311) now in the region A eject the ink droplets to the 
pixels which are to receive 5 pl/pixel droplet and which have not received 
the droplet from the ejection outlets Nos. 1-4 in the first scan. In 
addition, the ejection outlets Nos. 5 -8 eject 5 pl ink droplets to the 
pixels which are to receive 24 pl/pixel ink and 10 pl/pixel ink. 
Subsequently, the recording material 2 is fed upwardly by a distance of 
254 microns in FIG. 37. Then, the third scan is started. 
In the third scan, the ejection outlets Nos. 1-4 and ejection outlets Nos. 
5-8 now in the regions C and B, respectively eject the ink droplet of 5 pl 
as in the second scan. Simultaneously, the ejection outlets Nos. 9-12 
(312) now in the region A eject the ink droplets of 14 pl to only such 
pixels as are to receive 24 pl/pixel ink. 
When the third scan is completed, the recording operation is completed in 
the region A by four volumes of ink droplets, namely 0 pl (no ink), 5 pl, 
10 pl and 24 pl droplets. In the region B at this time, 0 pl, 5 pl and 10 
pl ink droplets are overlaid per pixel, and in the region C, 0 pl and 5 pl 
droplets are overlaid per pixel. 
In the fourth and fifth scans, the similar printing operations are carried 
out. When the record state of the region A expands all over the record 
area, the printing operation is completed. In this embodiment, the ink 
volumes per pixel is 0 pl, 5 pl, 10 pl and 24 pl, and therefore, 
substantially the same print quality as in Embodiment 1 can be provided, 
as will be understood from FIG. 38. 
Particularly in this embodiment, the pixels which are to receive 5 pl ink 
per pixel receives the ink selectively (at random, for example) from first 
group (ejection outlets Nos. 1-4) and second group (ejection outlets Nos. 
5-8). This is done in order to reduce the density variation in the 
direction of the array of the ejection outlets attributable to the 
manufacturing variation of the recording head. A pixel which is to receive 
5 pl/pixel ink is recorded with the ink ejected through a single ejection 
outlet per pixel. Therefore, if all of 5 pl/pixel pixels are printed by 
first ink droplets only, the non-uniformity may be conspicuous depending 
on the nature of the image. In this embodiment, the 5 pl/pixel pixels are 
recorded by both of the first and second ink droplets to flatten the 
variation. Therefore, according to this embodiment, the tone record is 
good without density unevenness. 
In both of the Embodiments 18 and 19, a group of ejection outlets providing 
smaller volumes, is disposed at a lower position, and therefore, when a 
large volume droplet and a small volume droplet are overlaid with each 
other, the small volume droplet is first shot. However, the order of 
record is not limited to this. The opposite arrangement having the large 
volume ejection outlets are disposed at the lower position, is possible. 
In Embodiments 18 and 19, the ejection outlets are arranged in the 
direction of sub-scan, and one pixel is recorded by overlaying ink 
droplets from ejection outlets in the different groups providing different 
volumes of droplet, and therefore, the number of scans for recording one 
pixel is reduced. The image quality in the high density region and the 
high light region can be increased substantially without reduction of the 
recording speed. 
In the foregoing embodiment, the volume ratio of the ejected ink droplets 
are so selected that the tone levels of the pixels overlayingly recorded 
are different at regular intervals. The large volume ink droplet is always 
overlaid on the small volume droplet, and therefore, the volume ratio 
between the maximum droplet and the minimum droplet can be made smaller, 
and the number of combinations of the different ink droplets is reduced 
substantially to one half. This makes easier the image signal processing 
for the selection of the ejection outlets. As a result, the halftone image 
can be produced relatively at low cost and without increase of the 
manufacturing cost of the main assembly and the recording head of the 
apparatus. 
In this embodiment, the ejection outlets providing the minimum volume ink 
droplets may be grouped into plural groups (two, in this embodiment), a 
pixel to receive one droplet of the minimum volume is recorded selectively 
by one group is ejection outlet or another, for example, alternately for 
the adjacent pixels. By doing so, the density variation along the line of 
the ejection outlets due to the manufacturing variation or the like, can 
be flattened. 
The volume of the ink droplet used in the low density region can be made 
smaller than the average of n ink volume ejected through n different 
ejection outlets. Therefore, the high density tone level or levels which 
are less influential to the tone reproduction can be omitted, and the 
number of tone levels in the low image density portion which are more 
important in the tone reproduction can be properly selected. Therefore, 
the good image can be provided at low cost even if the number of tone 
levels per pixel is small. 
Embodiment 20 
The apparatus of this embodiment is the same as with Embodiment 1 except 
for the recording head has 42 nozzles. The 4 tone gradation recording will 
be described using the apparatus of this embodiment. One pixel is recorded 
selectively by 0-3 ink droplets. 
FIG. 40 illustrates the concept of the recording method in this embodiment. 
The recording head 1 schematically shown, has 42 nozzles arranged 
vertically in the Figure. For the convenience of explanation, the nozzles 
are numbered 1, 20, 3, . . . , 42, from the top. The 42 nozzles are 
grouped into 14 blocks each having 3 nozzles. The blocks are named A, B, . 
. . , N. The nozzles in each block are designated by a-c. In this 
embodiment, the nozzles a in all of the blocks eject the droplet for a 
pixel where the image datum is not lower than 1; the nozzles b eject the 
droplets for a pixel where the image datum is not lower than 2; and the 
nozzles c eject the droplets where the image datum is at level 3. The 
recording operation is carried out using only nozzles Nos. 3-42 while the 
carriage is being moved (A in FIG. 40). As a result, pixels 1-40 from the 
top of the recording sheet (sub-scan direction) are recorded by 0 or 1 ink 
droplet. 
Then, the recording sheet is fed upwardly by a distance corresponding to 
one pixel (in the Figure the recording head is shown as being moved 
relative to the sheet, for the easy understanding, in addition, it is 
shown by the position deviated in the main scan direction). Then, the 
recording operation is effected using nozzles Nos. 2-42 (B in FIG. 40). As 
a result, the nozzles Nos. 2-41, effect the recording for the pixels 1-40. 
The nozzle No. 42 (nozzle c) effects the recording for the pixels at the 
position of pixel 41. Subsequently, the recording sheet is further fed 
upwardly by the distance corresponding to one pixel, and the recording 
operation is carried out using the nozzles Nos. 1-42 (C in FIG. 40), the 
nozzle No. 41 (nozzle b) effects the recording for the pixel at the 
position 41, and the nozzle No. 42 (nozzle c) effects the recording at the 
position 42. As a result, the nozzles Nos. 1-40 record the pixels 1-40 
having been subjected to the previous and further previous recording 
operations, thus the image is produced by 0-3 dots. For example, the pixel 
at position 40 is recorded by No. 42 nozzle (nozzle c), No. 41 nozzle 
(nozzle b) and No. 40 nozzle (nozzle a) in the order named. 
Then, the recording sheet is fed upwardly through a distance corresponding 
to 40 pixels, and the recording operation is carried out by the nozzles 
Nos. 1-42 (FIG. 3, D, the No. 1 nozzle (nozzle a) effects the recording 
for the position 41, and No. 2 nozzle (nozzle b) effects the recording for 
a position 42). Subsequently, the recording sheet is fed upwardly through 
a distance corresponding to one pixel (FIG. 40, E), and the recording 
operation is carried out using the nozzles Nos. 2-42. Further, the 
recording sheet is fed upwardly through a distance corresponding to one 
pixel, and the recording operation is carried out using the nozzles Nos. 
1-42. Then, the recording sheet is fed upwardly through a distance 
corresponding to 40 pixels, and the similar operations are repeated. By 
repeating such operations, all of the pixels are recorded by nozzles c, b 
and a, and the image is formed over the entire surface by 4 tone levels. 
At the bottom of the image, the nozzles Nos. 42, No. 41, No. 40, . . . are 
sequentially stopped for each scanning operation. 
Noting particular pixels, the first pixel (position 1) is recorded by the 
nozzles Nos. 1, 2 and 3; the second pixel is recorded by the nozzles Nos. 
2, 3 and 4. In this manner, each pixel is recorded by successive different 
3 nozzles, and therefore, the variation in the ink volumes of the nozzles 
is flattened in the image. As shown in FIG. 40, the pixels at positions 2, 
3 and 4, is recorded only by the nozzle No. 4 as regards the image data 1. 
Therefore, even if No. 5 nozzle ejection is oblique, it is not influential 
to the resultant image. As regards image datas 2 and 3, if the nozzle No. 
5 ejection is deviated, the deviation is influential to the pixels at 3, 4 
and 5 in the main scan direction. However, whenever the nozzle No. 5 is 
used, the No. 4 nozzle is also used, and the influence is reduced as a 
result. 
Various images have been formed through the recording method, and it has 
been confirmed that clear images without stripes and unevenness can be 
provided as compared with the conventional recording method in which one 
pixel is recorded by plural ink droplets ejected by the same nozzle. 
Embodiment 21 
FIG. 41 shows Embodiment 21. The recording head 1 of this embodiment is 
similar to that of Embodiment 20 in that it comprises 42 ink ejection 
outlets at the density of 16 nozzles/mm. However, No. 4 nozzle ejects the 
ink in a deviated direction. In such a case, the nozzle allotment a, b and 
c in each of the blocks is changed to b, c and a. Then, the nozzles a deal 
with the image data having a level not lower than 2; the nozzles b deal 
with the image data having the level 3; and the nozzles c deal with the 
image data having a level not lower than 1. The feeding in the sub-scan 
direction is the same as in Embodiment 1. In this embodiment, the stripes 
appearing in the image at the boundary between block A recording and block 
B recording, are removed, and a good image was produced. 
Embodiment 22 
In this embodiment, the recording head 1 is provided with 128 nozzles, and 
17 tone gradation recording is effected. That is, the number of droplets 
per pixel ranges between 0-16, inclusive. 
FIG. 42 illustrates the concept of the recording method of Embodiment 22. 
The schematically shown recording head 1 has 128 nozzles arranged 
vertically in the Figure. For the convenience of explanation, the nozzles 
are numbers 1, 2, 3, . . . . , 128 from the top. 
In operation, the recording operation is carried out using only the nozzles 
Nos. 123-128 (6 nozzles) while the carriage is being moved. As a result, 
the pixels at positions 1-6 from the top are recorded by 0 or 1 ink 
droplet. 
Subsequently, the sheet is fed upwardly by a distance corresponding to 10 
pixels (in the Figure, the recording head is shown as being moved 
downwardly relative to the recording sheet, for the convenience of 
illustration). Then, the recording operation is carried out using the 
nozzles Nos. 113-128. In this operation, the nozzles Nos. 113-120 effect 
the recording for the pixels at positions 1-6 having been subjected to the 
recording operation of the nozzles Nos. 123-128 in the previous scan. The 
nozzles Nos. 119-128 effect the recording at new positions 7-16. 
Therefore, the pixels 1-6 are recorded by 0, 1 or 2 ink droplets per 
pixel. 
Thereafter, the recording sheet is fed upwardly through a distance 
corresponding to 6 pixels. Then, the recording operation is carried out 
using the nozzles Nos. 107-128. By repeating such recording operations, 
the pixels at positions 1-8 are recorded by 0-16 droplets, when the 16th 
record is completed, so that an image having 17 tone gradations or levels 
can be provided. The same operations are repeated for 17th and subsequent 
scans, the 17 tone level image can be provided all over the surface. At 
the bottom of the image, the 6 nozzles and 10 nozzles from the bottom are 
stopped successively after scan. 
Noting the pixel at position 1, for example, the pixel is recorded by ink 
droplets ejected through 16 different nozzles, namely nozzles Nos. 1, 11, 
17, 27, 33, 43, 49, 59, 65, 75, 81, 91, 97, 107, 113 and 123 (the order of 
the recording actions is the opposite). Therefore, the ink volume 
variation among the nozzles is flattened on the image, and therefore, the 
resultant image has less conspicuous stripes and unevenness. 
Using the above recording method, various images have been recorded, and it 
has been confirmed that the images are clear without stripe and 
unevenness, as compared with the conventional recording method in which a 
pixel is recorded by plural ink droplets ejected through the same nozzle. 
Embodiment 23 
FIG. 43 shows Embodiment 23. The apparatus comprises a recording head 1 
having 512 ink ejection outlets arranged at the density of 16 nozzles/mm. 
The feed amount in the sub-scan direction corresponds to 64 pixels, 48 
pixels or 16 pixels. The feeding of these amounts are repeated to effect 
13 tone gradation recording. 
Embodiment 24 
FIG. 44 shows Embodiment 24. The apparatus of this embodiment has a 
recording head 1 provided with 48 ink ejection outlets arranged at the 
density of 16 nozzles/mm. 4 tone gradation recording is effected using 
this head. The recording head 1 is provided with 48 nozzles arranged in 
the vertical direction on the Figure. For the convenience of explanation, 
the nozzles are numbered 1, 2, 3, . . . , 48 from the top. 
The first recording operation is carried out using only the nozzles Nos. 
21-48, while the carriage is moved in the main scan direction (A in the 
Figure). At this time, the pixels at positions 1-20 (nozzles Nos. 21-40) 
from the top of the recording sheet, namely the positions where x=2 (x: 
number of overlaid droplets) are recorded by 2/pixel droplets (maximum), 
whereas pixels 20-28 from the top of the recording sheet (nozzle Nos. 
41-48), namely the positions where the number of overlaid droplets is 3, 
is recorded by 1/pixel droplet (maximum). 
Subsequently, the recording sheet is fed upwardly through a distance 
corresponding to 20 pixels (in the Figure, the recording head is shown as 
being downwardly relative to the recording sheets, for the convenience of 
illustration). Then, the recording operation is carried out using all of 
the nozzles (B). At this time, the nozzles Nos. 1-28 eject the ink droplet 
1/pixel (maximum). The nozzles Nos. 29-40 ejects 2/pixel droplets 
(maximum). In the rest of the portion (nozzles Nos. 41-48) is recorded by 
1/pixel droplet (maximum). 
The recording sheet is fed upwardly again through a distance corresponding 
to 20 pixels. The nozzles Nos. 1-28 eject the droplets at 1 droplet/pixel 
at the maximum; and the nozzles Nos. 29 -40 eject 2 droplets/pixel; and 
the nozzles Nos. 41-48 eject 1 droplet/pixel (C). 
The operations (upward feeding of the recording sheet through the distance 
of 20 pixels, 1/pixel recording by nozzles Nos. 1-28 and 41-48, and 
2/pixel recording by nozzles Nos. 29-40) are repeated. As a result, each 
of the pixels is recorded by 0, 1, 2 or 3 ink droplets, and therefore, 4 
tone gradation image can be provided. At the bottom of the image, the 
nozzles Nos. 1-20 effect the recording at 1 droplet/pixel at the maximum. 
In brief, the maximum number of droplets per pixel is 3, the pixel which is 
to receive two overlaid droplets receives 0-2 droplets during the first 
scan and receives 0-1 droplets in the second scan. The pixel which is to 
receive three overlaid droplets receives 0-1 ink droplets in each scan. 
Using the recording method of this embodiment, various images have been 
formed, and it has been confirmed that the clear images can be provided 
without stripes and unevenness as compared with the conventional recording 
method in which plural ink droplets are ejected through 1 nozzle/pixel. 
An additional advantage is that it is not required to the sub-scan feed 
distance is not necessarily constant, and therefore, it is not influenced 
by the number of nozzles or the nozzle pitch or the like. 
Embodiment 25 
FIG. 45 shows the structure of the apparatus of Embodiment 25. It comprises 
an ink jet recording head 7 for selectively ejecting black (Bk), cyan (C), 
magenta (M) and yellow (Y) ink droplets. The recording head includes a 
black head unit 71Bk, cyan head unit 71C, magenta head unit 71M and yellow 
head unit 71Y. The recording head 71 is mounted on a carriage 74, and is 
movable in the main scan directions along guide rails 75A and 75B by a 
carriage feeding motor (FIG. 47) which will be described hereinafter. 
Through ink ejection outlets or nozzles (FIG. 46), black, cyan, magenta or 
yellow ink droplets are selectively ejected to the recording material (a 
sheet of paper) 72, so that an image is formed on the recording material 
72 in accordance with the input signal. The recording material 72 is 
wrapped on a platen roller 73, which is rotated by a sheet feeding motor 
(FIG. 47), so that it is fed in the sub-scan direction crossing with the 
main scan direction at a predetermined pitch. 
As show in FIG. 46, the recording head 71 comprises black, cyan, magenta 
and yellow head units 71Bk, 71C, 71M and 71Y. In each of the head units, 1 
-N nozzles 76 are arranged in the sub-scan direction from the carriage 74 
side at a predetermined regular intervals P.sub.0. In the Figure, "Bi" 
indicates i-th nozzle for the black color. Similarly, "Ci" , "Mi" and "Yi" 
indicates the i-th nozzles for the cyan color, the magenta color and the 
yellow color, respectively. 
FIG. 47 shows the control circuit for the apparatus of this embodiment. It 
corresponds to FIG. 12. In FIG. 47, the recording head 406 includes four 
color head units 406Y, 406M, 406C and 406BK. Correspondingly, the driver 
controller 404 and the head driver 405 are provided for the four colors. 
In this embodiment, high quality color images can be recorded. 
FIGS. 48 and 49, similarly to Embodiment 20 in conjunction with FIG. 40, 
illustrate the head 71 drive timing and picture element recording process 
through the multi-scan system in which four droplets are overlaid 
substantially at the same position at the maximum. The multi-scan system 
is such that a plurality of droplets are shot substantially at the same 
position to provide one pixel having a tone gradation. However, depending 
on the level of the tone gradation, one pixel is provided by one droplet. 
When a nozzle Bi scans (scan 1) a selected position 503 on the recording 
material 72, an ejection signal P41 is selectively applied to the ejection 
means in the nozzle Bi (heat generating element, for example) so that the 
liquid droplet Di is ejected through the nozzle Bi (FIG. 49 at portion 
(a)). After the scan 1 operation, the recording material is fed by one 
pitch P.sub.0 which is the same as the nozzle interval in the sub-scan 
direction. Subsequently, the nozzle Bi+1 scans the scanning line along 
which the liquid droplet Di has been ejected (scan 2), during which the 
nozzle Bi+1 ejects the liquid droplet Di+1 by application of a selective 
ejection signal P42 so as to overlay the droplet Di+1 on the pixel 504 
already having the droplet Di on the recording material 72 (FIG. 49 at 
portion (b)). After the second scan, the recording material 72 is fed in 
the sub-scan direction at the pitch P.sub.0 equal to the nozzle interval. 
Then, the nozzle Bi+2 scans the scanning line along which the liquid 
droplets Di have been ejected (scan 3), during which an ejection signals 
P43 is selectively applied to eject the liquid droplet Di+2 through the 
nozzle Bi+2 (FIG. 49 at portion (c)). Similarly, the recording material 72 
is fed through the pitch P.sub.0. Then, during the scanning by the nozzle 
Bi+3 (scan 4), an ejection signal P44 is applied so that the liquid 
droplet Di+3 is ejected through the nozzle Bi+3 (FIG. 49 at portion (d)). 
Thus, the recording of the pixel 505 is completed (FIG. 49 at portion 
(e)). 
After the completion of scan 4, the recording material 72 is fed through 
the distance (N-3).times.P.sub.0 (N: the number of nozzles). Then, the 
pixel formation is started by the liquid droplet through the nozzle Bi. In 
the above process, the size of the dot in the pixel on the recording 
material (size of the recorded dot of the ink) can be changed by 
application or non-application of the ejection signal P41, P42, P43 and 
P44, so that plural tone gradations can be expressed. 
FIGS. 50 and 51 show a comparison example in which the drive timing and the 
image forming process are illustrated when the black and cyan pixels are 
formed adjacent to each other by 3 droplets respectively on the recording 
material 72 using the same timing as in FIG. 48. In scan 1, the black 
liquid droplet is ejected through nozzle Bi in response to ejection signal 
P61, so that a pixel 711 is recorded. After elapse of predetermined time 
period tc, a cyan liquid droplet is ejected through a nozzle Ci in 
response to an ejection signal. P64 so that a pixel 721 is recorded 
adjacent to the pixel 711. Similarly, in scan 2, the ejection signals P62 
and P65 are applied, and the liquid droplets ejected through nozzles Bi+1 
and Ci+2 are overlaid on the pixels 711 and 721. At this time, each of the 
black and cyan droplets on the recording material 72 have such sizes out 
of contact from each other, and therefore, the black pixel and cyan pixel 
are formed without color mixture. When, however, the ejected droplets are 
deposited by ejection signals P63 and P66 in the scan 3, the black color 
and the cyan color inks which have not yet completed seeping in contact 
with each other as a result of expansions of the dots, so that partly 
mixed pixel 721 results. This occurs in the wide part of the image. 
FIGS. 52 and 53 show the drive timing and the image formation process when 
the black and cyan pixels are formed by respectively three droplets on the 
recording material 72 through the multi-scan recording method of this 
embodiment. In this embodiment, both of the black and cyan droplets are 
not ejected in the scan 3, but only the black droplet is ejected in 
response to ejection signal P83 (FIG. 52) and is overlaid on the pixel 912 
recorded by the first and second scan to provide a pixel 913 (FIG. 53). At 
this time, the cyan color does not expand on the recording material 72, 
and therefore, the ink is not mixed. Subsequently, in the scan 4, the cyan 
droplet is ejected by the application of the ejection signal P86 in the 
scan 4 (FIG. 52). At this time, the cyan dot at the pixel 923 expands to 
such an extent that it becomes in contact with the black dot at the pixel 
913 (FIG. 53). However, the black ink on the pixel 913 ejected in the scan 
3, has already sufficiently seeped into the recording material, and 
therefore, the mixture as shown in FIG. 51 does not occur. Through the 
above process, the recording of the adjacent pixels 913 and 912 is 
completed. Thus, the color mixture can be reduced, and therefore, the 
image quality is improved. 
In this embodiment, it is a possible alternative that the cyan droplet is 
ejected in the scan 3, and the black droplet is ejected in the scan 4. It 
is also a possible alternative that the scan in which the different color 
ink ejections are prevented from being carried out simultaneously, is not 
limited to the scans 3 and 4, but may be applied to the other scan or 
scans. Generally, the color mixture tends to occur with increase of the 
number of liquid droplet shots for the same pixel, and therefore, it is 
preferable that the scan in which the different color ink droplets are not 
simultaneously ejected, is applied to the latter part of the scans for the 
same pixel recording. 
When adjacent black and cyan color pixels are recorded by four droplets, 
respectively on the recording material 72 through the multi-scan recording 
method, it is possible that a fifth scan may be added without feeding the 
recording material 72 in addition to the scans of FIG. 52. By doing so, 
the expansion timing of the different color ink dots which are adjacent on 
the recording material 72 may be deviated, thus reducing the color 
mixture. 
Embodiment 26 
FIG. 54 shows the drive timing according to Embodiment 26. In this 
embodiment, a black dot by three droplets and a yellow dot by four 
droplets are formed at adjacent pixels on the recording material 72. In 
this embodiment, in the scans 1, 2 and 3, the ejecting means in the black 
nozzles Bi, Bi+1 and Bi+2 are supplied with ejection signals P101, P102 
and P103, respectively, by which the nozzles eject the black liquid 
droplet to record the black pixel. The yellow pixel is recorded in the 
different manner. In scans 1 and 2, the ejection means in the yellow 
nozzles Yi and Yi+1 are supplied with ejection signals P104 and P105, by 
which the liquid droplets are ejected through the nozzles to record the 
yellow pixel. At this stage, because of the balance of the size of the 
dots of these colors, the black dot and the yellow dot are not merged or 
mixed, as shown in FIG. 53. In the scan 3, the droplets to be overlaid on 
the yellow pixel by the ejection signals P104 and P105 are not ejected, 
and therefore, the yellow dot does not expand. 
Subsequently, the ejection means in the yellow nozzle Yi+3 is supplied with 
ejection signals P106 and P107 in the scan 4, continuously but with a time 
interval Tb not resulting the conspicuous image disturbance. By doing so, 
two yellow liquid droplets are continuously ejected through the nozzle 
Yi+3, and they are overlaid on the pixel recorded in response to the 
ejection signals P104 and P105. By the shots of the two droplets, the 
yellow pixel is recorded by 4 droplets. At this time, the yellow pixel 
expands to such an extent as to be in contact with the adjacent black dot. 
However, the black ink seeps into the recording material or it is fixed 
before the scan 4, and therefore, they are not mixed on the recording 
material 72. Therefore, the mixture shown in FIG. 51 can be avoided. 
From the standpoint of stabilized ejection, it is preferable that the 
record interval tb between the ejection signals P106 and P107 is 
preferably not less than refilling time of the nozzle Yi+3 and 
sufficiently shorter than the recording head movement period between 
adjacent yellow pixels to be recorded by the nozzle Yi+3 in the scanning 
direction. The configuration of the ejection signals continuously applied 
to the ejection means in the same nozzle in a single scan for recording 
one pixel, the number of the groups, the profile of the ejection signal, 
the applicating timing or the like are properly determined by one skilled 
in the art in consideration of the ink seeping properly, ink fixing 
property, the nature of the image, the ejection property of the recording 
head or the like. 
For example, where a black dot with four droplets and a yellow dot with 
four droplets are formed at adjacent pixels, the ejection signals are 
applied in the scans 1 and 2 to eject four black droplets in total, and 
thereafter, in the scans 3 and 4, four yellow droplets in total are 
ejected onto the recording material. 
Embodiment 27 
FIGS. 55 and 58 show the drive timing and the image forming process in 
Embodiment 27. In this embodiment, three yellow droplets dot is formed 
adjacent, in the sub-scan direction, to a black pixel at which three black 
droplets are already received but do not seep into the recording material 
at high speed. The recording method is multi-scan type. 
In this embodiment, the yellow droplet ejection timing only is modified 
when the yellow pixel is recorded after the scanning operation for the 
black recording for the pixel 1211 is completed and after the sheet is fed 
by (N-3).times.P.sub.0 is carried out. More particularly, the liquid 
droplet is not ejected through the nozzle Yi in the scan 1. Next, in the 
scans 2, 3 and 4, the ejection means in the nozzles Yi+1, Yi+2 and Yi+3 
are supplied with ejection signals P1101, P1102 and P1103, so that a pixel 
1223 is recorded by yellow liquid. In this manner, the yellow dot 
recording and expansion thereof at a pixel adjacent to the black pixel 
1211 is deviated in the timing to permit or promote the fixing of the 
black dot in the pixel 1211, and therefore, the color mixture can be 
effectively prevented. 
In the Embodiments 25-27, the combination of the colors, and the scanning 
numbers of the like are not limiting. Also, the direction of the recording 
material feed is not limiting. The recording method of these embodiments 
may be used selectively only when the color mixture occurs due to the 
liquid overlaying nature of color inks at one pixel. According to these 
embodiments, the desired effects can be obtained without particular 
limitation to the pattern of the pixels on the recording material. In the 
foregoing descriptions of the embodiments, the adjacent pixels are to be 
formed one ink color, respectively, but the present invention is effective 
when at least one of the pixels is to be recorded by plural color inks 
(mixture of color). 
In Embodiments 25-27, one pixel is recorded by plural scans and plural 
droplets using a recording head having plural nozzles. In this case, the 
method comprises a first scanning step in which the liquid droplets are 
ejected selectively through the ejection outlets and a second scanning 
step in which the liquid is not ejected through the ejection outlets, in 
which when different color pixels are adjacent to each other on the 
recording material, the first scanning step is executed after the second 
scanning step at the time of at least one of the two color dots. 
Therefore, after the liquid is sufficiently seeped in the recording 
material or fixed on the recording material, the liquid droplet is 
deposited on the adjacent pixel, so that the color mixture can be 
prevented, and the good color images can be provided. 
The present invention is particularly suitably usable in an ink jet 
recording head and recording apparatus wherein thermal energy by an 
electrothermal transducer, laser beam or the like is used to cause a 
change of state of the ink to eject or discharge the ink. This is because 
the high density of the picture elements and the high resolution of the 
recording are possible. 
The typical structure and the operational principle are preferably the ones 
disclosed in U.S. Pat. Nos. 4,723,129 and 4,740,796. The principle and 
structure are applicable to a so-called on-demand type recording system 
and a continuous type recording system. Particularly, however, it is 
suitable for the on-demand type because the principle is such that at 
least one driving signal is applied to an electrothermal transducer 
disposed on a liquid (ink) retaining sheet or liquid passage, the driving 
signal being enough to provide such a quick temperature rise beyond a 
departure from nucleation boiling point, by which the thermal energy is 
provided by the electrothermal transducer to produce film boiling on the 
heating portion of the recording head, whereby a bubble can be formed in 
the liquid (ink) corresponding to each of the driving signals. By the 
production, development and contraction of the bubble, the liquid (ink) is 
ejected through an ejection outlet to produce at least one droplet. The 
driving signal is preferably in the form of a pulse, because the 
development and contraction of the bubble can be effected instantaneously, 
and therefore, the liquid (ink) is ejected with quick response. The 
driving signal in the form of the pulse is preferably such as disclosed in 
U.S. Pat. Nos. 4,463,359 and 4,345,262. In addition, the temperature 
increasing rate of the heating surface is preferably such as disclosed in 
U.S. Pat. No. 4,313,124. 
The structure of the recording head may be as shown in U.S. Pat. Nos. 
4,558,333 and 4,459,600 wherein the heating portion is disposed at a bent 
portion, as well as the structure of the combination of the ejection 
outlet, liquid passage and the electrothermal transducer as disclosed in 
the above-mentioned patents. In addition, the present invention is 
applicable to the structure disclosed in Japanese Laid-Open Patent 
Application No. 3123670/1984 wherein a common slit is used as the ejection 
outlet for plural electrothermal transducers, and to the structure 
disclosed in Japanese Laid-Open Patent Application No. 138461/1984 wherein 
an opening for absorbing pressure wave of the thermal energy is formed 
corresponding to the ejecting portion. This is because the present 
invention is effective to perform the recording operation with certainty 
and at high efficiency irrespective of the type of the recording head. 
The present invention is effectively applicable to a so-called full-line 
type recording head having a length corresponding to the maximum recording 
width. Such a recording head may comprise a single recording head and 
plural recording head combined to cover the maximum width. 
In addition, the present invention is applicable to a serial type recording 
head wherein the recording head is fixed on the main assembly, to a 
replaceable chip type recording head which is connected electrically with 
the main apparatus and can be supplied with the ink when it is mounted in 
the main assembly, or to a cartridge type recording head having an 
integral ink container. 
The provisions of the recovery means and/or the auxiliary means for the 
preliminary operation are preferable, because they can further stabilize 
the effects of the present invention. As for such means, there are capping 
means for the recording head, cleaning means therefor, pressing or sucking 
means, preliminary heating means which may be the electrothermal 
transducer, an additional bleating element or a combination thereof. Also, 
means for effecting preliminary ejection (not for the recording operation) 
can stabilize the recording operation. 
As regards the variation of the recording head mountable, it may be a 
single corresponding to a single color ink, or may be plural corresponding 
to the plurality of ink materials having different recording color or 
density. The present invention is effectively applicable to an apparatus 
having at least one of a monochromatic mode mainly with black, a 
multi-color mode with different color ink materials and/or a full-color 
mode using the mixture of the colors, which may be an integrally formed 
recording unit or a combination of plural recording heads. 
Furthermore, in the foregoing embodiment, the ink has been liquid. It may 
be, however, an ink material which is solidified below the room 
temperature but liquefied at the room temperature. Since the ink is 
controlled within the temperature not lower than 30.degree. C. and not 
higher than 70.degree. C. to stabilize the viscosity of the ink to provide 
the stabilized ejection in usual recording apparatus of this type, the ink 
may be such that it is liquid within the temperature range when the 
recording signal is the present invention is applicable to other types of 
ink. In one of them, the temperature rise due to the thermal energy is 
positively prevented by consuming it for the state change of the ink from 
the solid state to the liquid state. Another ink material is solidified 
when it is left, to prevent the evaporation of the ink. In either of the 
cases, the application of the recording signal producing thermal energy, 
the ink is liquefied, and the liquefied ink may be ejected. Another ink 
material may start to be solidified at the time when it reaches the 
recording material. The present invention is also applicable to such an 
ink material as is liquefied by the application of the thermal energy. 
Such an ink material may be retained as a liquid or solid material in 
through holes or recesses formed in a porous sheet as disclosed in 
Japanese Laid-Open Patent Application No. 56847/1979 and Japanese 
Laid-Open Patent Application No. 71260/1985. The sheet is faced to the 
electrothermal transducers. The most effective one for the ink materials 
described above is the film boiling system. 
The ink jet recording apparatus may be used as an output terminal of an 
information processing apparatus such as computer or the like, as a 
copying apparatus combined with an image reader or the like, or as a 
facsimile machine having information sending and receiving functions. 
The present invention is not limited to the thermal type ink jet system but 
is applicable to the other type system such as piezoelectric ink jet 
system. 
The recording material is not limited to the paper but is applicable to 
cloth such as the one for necktie. 
While the invention has been described with reference to the structures 
disclosed herein, it is not confined to the details set forth and this 
application is intended to cover such modifications or changes as may come 
within the purposes of the improvements or the scope of the following 
claims.