TONE RECORDING METHOD USING INK JET RECORDING HEAD

METHODE D'ENREGISTREMENT DE TONS UTILISANT UNE TETE A JET D'ENCRE

English Abstract

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

Claims

-92-

CLAIMS:

1. A liquid jet recording method of recording on a
recording material with liquid droplets of substantially
the same amount discharged through n(n~2) scanning
nozzles arranged at pitch p in a width measured in a
direction of a sub scan, comprising the steps of:
performing a first main scan by relative
movement between the nozzles and the recording material
in which each of a plurality of pixels are recorded with
at least one of the liquid droplets through a nozzle,
wherein a number of liquid droplets used to record each
pixel corresponds to respective tone signals and is not
more than k where k~1;
performing a sub-scan by relative movement
between the nozzles and the recording material in a
direction substantially transverse to a direction of the
first main scan, in which the distance of the relative
movement in the sub-scan direction is less than the
width; and
performing a second main scan in which each of
the plurality of pixels are recorded with at least one of
the liquid droplets through a different nozzle, a number
of liquid droplets used to record each of the plurality
of pixels in the second main scan corresponding to the
tone level signals and not more than k;
wherein g is a number of tone levels and g~3,
and wherein the steps of performing the sub-scan and the
second main scan are repeated for (g-1)/k-1 times so as
to record g tone images by discharging substantially the
same volume of droplets for each of the plurality of
pixels.

2. A liquid jet recording method according to claim
1, the improvements residing in:
n/(s/p)~2



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n/(s/p)xk=g-1
are satisfied,
where n(n~2) is a number of the nozzles arranged
at pitch P(microns); s(microns) is a distance of relative
movement between the nozzles and the recording material
between adjacent scans; k(k~1) is a maximum number of ink
droplets per pixel and per scan; g(g~3) is a number of
tone levels.

3. A liquid jet recording method according to claim
1,
wherein g-1 droplets are capable of being
discharged by different m nozzles by changing relative
position between the nozzles and the recording material
by a distance s(µm) in a direction of the nozzle
arrangement for each relative scan, where m is an integer
obtained by n/(s/p) with fraction rounded down, where p
is a pitch of the nozzles;
when a pixel is recorded with t(t~g-1) droplets
in accordance with tone level information for the pixel,
if t~m, the pixel is recorded by m different
nozzles, and
if t~m, the pixel is recorded by t different
nozzles.

4. A liquid jet recording method according to claim
1, the improvements residing in:
n/(s/p)>_2
n/(s/p)xk>g-1
are satisfied,
where n(n~2) is a number of the nozzles arranged
at pitch P(microns); s(microns) is a distance of relative
movement between the nozzles and the recording material
between adjacent scans; k(k~1) is a maximum number of ink
droplets per pixel and per scan; g(g~3) is a number of
tone levels.




-94-

5. A method according to claim 4, wherein among
n/(s/p) nozzles scanning one pixel, at least one of them
does not discharge the liquid.

6. A liquid jet recording method according to claim
1, the improvement residing in that 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.

7. A liquid jet recording method according to claim
1, the improvement residing in that a plurality of
nozzles for discharging the droplets are prepared; when
N, at maximum, nozzles are operated to discharge the
droplets, it is predetermined whether M-th(M=1-N) droplet
is to be discharged to maintain operation frequencies of
the nozzles to be lower than a predetermined level.

8. A liquid jet recording method according to claim
1, the improvement residing in that a plurality of
nozzles for discharging the droplets are prepared;
N+1
.SIGMA.f(G,M)~N-1
G=1
is satisfied,
where G is a tone level of each of pixels
(1~G~N+1); f(G,M)=1 when M-th droplet is discharged, and
f(G,M)=0 when the M-th droplet is not discharged.

9. A method according to claim 8, wherein the
following is satisfied:
N+1
.SIGMA.f (G, M)~(N/2)+1
G=1



-95-

10. A liquid jet recording method according to claim
1, the improvement residing in that a pixel is recorded
with plural droplets discharged through different nozzles
in plural scans, and that the nozzles to discharge the
droplets in the scans are selected in accordance with
record densities of the nozzles.

11. A method according to claim 10, wherein numbers
of the droplets to be discharged by the selected nozzles
are also determined in accordance with the record
densities of the nozzles.

12. A method according to claim 11, wherein in each
of the nozzles, thermal energy is used to cause a state
change in the liquid to discharge the liquid through the
nozzle.

13. A liquid jet recording method in which a pixel
is recorded by k droplets (k~2) per pixel and per scan,
and the pixel is recorded by m scans (m~2), the
improvement residing in that a total number M of droplets
to be discharged to a pixel is determined in accordance
with an image signal, where Mi is the number of droplets
discharged to the pixel in i-th scan (1~i~m) is changed.

m

where 1 ~Mi~k, and .SIGMA.Mi=M,

i=1

14. A method according to claim 13, wherein timings
of Mi droplet discharges is selected from k operable
timings in accordance with the image signal, when the
pixel is recorded in the i-th scan.

15. A method according to claim 13, wherein a
plurality (n) of nozzles are used to discharge the
droplets (n~2), a relative feeding movement between the



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nozzles and a recording material on which the droplets
are discharged is n/m per scan.

16. A liquid jet recording method according to claim
1, the improvement residing in that plural main scan
movements are effected between the nozzles and a
recording material in a main scan direction with plural
different amounts of scan movements therebetween in a
sub-scan direction which is different from the main scan
direction, and that a pixel is recorded by different
nozzles in at least two scan movements in the main scan
direction.

17. A method according to claim 16, wherein (k-1)
sub-scan movements of the amount which is the same as a
pitch at which the nozzles are disposed and one sub-scan
movement of the amount which is (n-k+1)x(the pitch), are
alternately effected to provide a tone image with (k+1)
tone levels,
where n is a number of the nozzles, and k(k~2)
is a maximum number of the droplets for a pixel.

18. A method according to claim 16, wherein the
amounts of the sub-scan movements are N1xP, N2xP, ...
N k xP,
where n is a number of the nozzles, P is the
pitch of the nozzles, k(k~2) is a maximum number of the
droplet for a pixel , and n=N1+N2+ ..N k.

19. A liquid jet recording method according to claim
1, the improvement residing in that a tone image is
formed by droplets discharged through different nozzles
for a pixel by plural main scans, and that an amount of
sub-scan movement is constant to provide different number
x of overlaid droplets.




-97-

20. A liquid jet recording method according to claim
1, wherein a toner color image is recorded using
different number, color and/or material of the liquid,
the improvement residing in that a first pixel on the
recording material is recorded by a plurality of main
scans, that a second pixel adjacent to the first pixel is
recorded by a plurality of main scans, and that when the
first and second pixels are recorded in different colors,
the main scans for at least one of the first and second
pixels are carried out before or after a main scan not
discharging the droplet.

21. A method according to claim 20, wherein the main
scan not discharging the droplet is the last or
subsequent main scan of the main scans for the other
pixel.

22. A method according to claim 1, wherein the
liquid is not discharged at least one of said first main
scan steps.

23. A method according to claim 1, wherein the
nozzles are operated in accordance with a scheme so
determined that the nozzles are operated at substantially
even frequencies among the nozzles.

24. A method according to claim 1, wherein the
nozzles to be operated are selected at each main scan
step in accordance with second densities of the nozzles.

25. A method according to claim 1, wherein plural
droplets are deposited for a pixel by one or more main
scan steps.

26. A method according to claim 1, wherein in at
least one of main scan steps, a different volume of the
droplet is discharged.




-98-

27. A method according to claim 1, wherein in at
least one of the sub-scan steps, the sub-scan amount is
different.

28. A method according to any one of the preceding
claims, wherein in each of the nozzles, thermal energy is
used to cause a state change in the liquid to discharge
the liquid through the nozzle.

29. A liquid jet recording apparatus for recording
on a recording material with liquid droplets discharged
through n(n~2) scanning nozzles arranged at pitch p in a
width measured in a direction of sub scan, comprising
main scan means for causing relative movement
between the nozzles and the recording material;
sub-scan means for causing relative movement
between the nozzles and the recording material in a
direction crossing with a movement direction of the first
main scan; and
control means for controlling said nozzles, main
scan means and sub-scan means, characterized in that said
control means performing the steps of:
performing a first main scan by relative
movement between the nozzles and the recording material
in which each of a plurality of pixels are recorded with
at least one of the liquid droplets through a nozzle,
wherein a number of liquid droplets used to record each
pixel corresponds to respective tone signals and is not
more than k where k~1;
performing a sub-scan by relative movement
between the nozzles and the recording material in a
direction substantially transverse to a direction of the
first main scan, in which the distance of the relative
movement in the sub-scan direction is less than the
width; and
performing a second main scan in which each of
the plurality of pixels are recorded with at least one of



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the liquid droplets through a different nozzle, a number
of liquid droplets used to record each of the plurality
of pixels in the second main scan corresponding to the
tone level signals and not more than k;
wherein g is a number of tone levels and g~3,
and wherein the steps of performing the sub-scan and the
second main scan are repeated for (g-1)/k-1 times so as
to record g tone images by discharging substantially the
same volume of droplets for each of the plurality of
pixels.

30. A liquid jet recording apparatus according to
claim 29, the improvements residing in:
n/(s/p)~2
n/(s/p)xk=g-1
are satisfied,
where n(n~2) is a number of the nozzles arranged
at pitch P(microns); s(microns) is a distance of relative
movement between the nozzles and the recording material
between adjacent scans; k(k~1) is a maximum number of ink
droplets per pixel and per scan; g(g~3) is a number of
tone levels.

31. A liquid jet recording apparatus according to
claim 29,
wherein g-1 droplets are capable of being
discharged by different m nozzles by changing relative
position between the nozzles and the recording material
by a distance s(µm) in a direction of the nozzle
arrangement for each relative scan, where m is an integer
obtained by n/(s/p) with fraction rounded down, where p
is a pitch of the nozzles;
when a pixel is recorded with t(t~g-1) droplets
in accordance with tone level information for the pixel,
if t~m, the pixel is recorded by m different
nozzles, and



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if t<m, the pixel is recorded by t different
nozzles.

32. A liquid jet recording apparatus according to
claim 29, wherein among n/(s/p) nozzles scanning one
pixel, at least one of them does not discharge the
liquid.

33. A liquid jet recording apparatus according to
claim 29, the improvement residing in that a plurality of
nozzles for discharging the droplets are prepared;
N+1
.SIGMA.f(G,M)~N-1
G=1
is satisfied,
where G is a tone level of each of pixels
(1~G~N+1); f(G,M)=1 when M-th droplet is discharged, and
f(G,M)=0 when the m-th droplet is not discharged.

34. A liquid jet recording apparatus according to
claim 29, wherein the following is satisfied:
N+1
.SIGMA.f(G, M)~(N/2)+1
G=1

35. A liquid jet recording apparatus according to
claim 29, the improvement residing in that a pixel is
recorded with plural droplets discharged through
different nozzles in plural scans, and that the nozzles
to discharge the droplets in the scans are selected in
accordance with record densities of the nozzles.

36. A liquid jet recording apparatus according to
claim 29, wherein a pixel is recorded by k droplets (k~2)
per pixel and per scan, and the pixel is recorded by m
scans (m~2), the improvement residing in that a total
number M of droplets to be discharged to a pixel is



-101-

determined in accordance with an image signal, where Mi
is the number of droplets discharged to the pixel in i-th
scan (1~i~m), and
m
where 1 ~Mi~k, and .SIGMA.Mi=M.
i=1

37. A liquid jet recording apparatus according to
claim 29, the improvement residing in that plural main
scan movements are effected between the nozzles and a
recording material in a main scan direction with plural
different amounts of scan movements therebetween in a
sub-scan direction which is different from the main scan
direction, and that a pixel is recorded by different
nozzles in at least two scan movements in the main scan
direction.

38. A liquid jet recording apparatus according to
claim 29, wherein the nozzles are operated in accordance
with a scheme so determined that the nozzles are operated
at substantially even frequencies among the nozzles.

39. A liquid jet recording apparatus according to
claim 29, wherein in at least one of the main scan steps,
a different volume of the droplet is discharged.

40. A liquid jet recording apparatus according to
claim 29, wherein in each of the nozzles, thermal energy
is used to cause a state change in the liquid to
discharge the liquid through the nozzle.

41. An apparatus according to any one of the
preceding claims 39-40, wherein thermal energy is used to
cause a state change in the ink to discharge the ink
droplets through the nozzle.

Description

2070355
-1-
TONE RECORDING METHOD USING INK JET RECORDING HEAD
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




2070355
-2-
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.
lp 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 the 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 g variation among the ejection




20'0355
-3-
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 the very
accurate head manufacturing in order to reduce the
variation in the ejection quantities through the
individual nozzles. This brings about the 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, the stabilized ink ejections


CA 02070355 1999-03-12
-4-
with a very small droplets is 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 host can be suppressed.
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 of grains are not
conspicuous. However, as compared with the image
provided by the recording head having the 16 or the
like tone levels, the grains are remarkable particularly
in the grains in high light portions.
U.S. Patent 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




2070355
-5-
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 Figure 5, 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), and therefore, the image processing circuit
becomes complicated with the result of high design and
manufacturing cost.
Another problem of the ink jet printer of the




2070355
-6-
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 added, with
the result of increase of the manufacturing cost.
In the ink jet printer disclosed in the U.S.
Patent, the ink ejection outlets providing the
different ejection volumes (1 pl, 2 pl, 3 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



2070355
ink droplet has not yet been seeped or fixed on the
recording material. In the image region in which the
number of overlying droplets is large, the adjacent
pixels are contacted 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
lp 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




20~03~~
_8_
certain length of fixing period. As a method using
this, Japanese Laid-Open Patent Application No.
4523/1990 proposes 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.



20?0355
_g_
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




207035
-lo-
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 trough plural scanning
nozzles, the improvements residing in:
n/(s/p) 2 2
n/ ( s/p ) x k = g - 1
are satisfied, where n (n 2 2) is a number of the
nozzles arranged at pitch P (um); s (pn) is a distance
of relative movement between the nozzles and the
recording material between adjacent scans; k (k z 1)
is a maximum number of ink droplets per pixel and per
scan; g (g 2 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 a, for example,
the variation of the ink quantity per pixel is reduced
to a/~, since one pixel is recorded by different m




20?0355
-11-
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 trough plural scanning
nozzles, the improvements residing in:
n/(s/p) z 2
n/(s/p) x k > g - 1
are satisfied, where n (n z 2) is a number of the
nozzles arranged at pitch P (um); s (um) is a distance
of relative movement between the nozzles and the
recording material between adjacent scans; k (k z 1)
is a maximum number of ink droplets per pixel and per
scan; g (g 2 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) x k, or m x 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




2070355
-12-
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.




2070355
-13-
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective view of an ink jet
recording apparatus according to an embodiment of the
present invention.
Figure 2 illustrates a recording operation in
the first embodiment.
Figure 3 illustrates the image formation
process in the first embodiment.
Figure 4 is a perspective view of an ink jet
recording apparatus according to a second embodiment
of the present invention.
Figure 5 represents the image formation
process in the second embodiment.
Figure 6 illustrates a recording operation in
the third embodiment.
Figures 7 - 9 illustrate image formation
process in the third, fourth and fifth embodiments.
Figure 10 illustrates the recording method in
the first - sixth embodiments.
Figure 11 is a table of ink droplet numbers
for respective scans in the sixth embodiment.
Figure 12 is a block diagram of a control
system with which the present invention is usable.
Figure 13 illustrates the recording operation
in the seventh embodiment of the present invention.
Figures 14, 15 and 16 show the image
formation process in the seventh, eighth and ninth




207035
-14-
embodiments.
Figure 17 is a block diagram of a control
system usable with the present invention.
Figures 18, 19 and 21 show tables of ink
ejections capable of providing the tone gradation in
the tenth, eleventh and twelfth embodiment.
Figure 20 is a table of image densities
corresponding to the tone gradation in the eleventh
embodiment.
Figure 22 is a block diagram of a control
system usable with the thirteenth embodiment.
Figure 23 illustrates the recording operation
in the thirteenth embodiment.
Figure 24 illustrates the image forming
process in the thirteenth embodiment.
Figure 25 is a flow chart of an image forming
operation in the thirteenth embodiment.
Figure 26 is a table for nozzle selection in
the thirteenth embodiment.
Figures 27 and 28 are block diagrams of the
control systems usable with the fourteenth and
fifteenth embodiment.
Figure 29 illustrates the difference in the
tone gradation due to the picture element formation
difference.
Figure 30 is a table showing the components
of the recording liquid.




20?0355
-15-
Figure 3i illustrates the image formation
process in the sixteenth embodiment.
Figure 32 shows the detail of the image
formation in the sixteenth embodiment.
Figure 33 illustrates the tone gradation in
the sixteenth embodiment.
Figure 34 shows the detail of the image
formation in the seventeenth embodiment.
Figure 35 illustrates the tone gradation in
the seventeenth embodiment.
Figure 36 is a perspective view of a
recording head according to the eighteenth embodiment.
Figure 37 illustrates the recording operation
using the recording head of the eighteenth embodiment.
Figure 38 is a graph of reflection density
vs. ink volume per pixel in the eighteenth embodiment.
Figure 39 is a perspective view of a
recording head according to a nineteenth embodiment.
Figures 40 - 44 illustrates the recording
methods in the twentieth - twenty fourth embodiments.
Figure 45 is a perspective view of an major
part of an ink jet recording apparatus according to an
embodiment of the present invention.
Figure 46 is a perspective view of a nozzle
arrangement of the ink jet recording head of Figure
45.
Figure 47 is a block diagram of a control




200355
-16-
system for an ink jet recording apparatus.
Figure 48 is.a~timing chart of ejection
signals.
Figure 49 is a side view illustrating image
forming process.
Figure 50 is a timing chart of ejection
signals in a comparison example.
Figure 51 is a top plan view showing image
formation process with the ejection signals applied in
accordance with the timing of Figure 50.
Figure 52 is a timing chart of ejection
signals according to the twenty fifth embodiment of
the present invention.
Figure 53 is a top plan view illustrating
image formation with the ejection signals applied with
the timing of Figure 52.
Figures 54 and 55 are timing charts of
ejection signals in twenty sixth and twenty seventh
embodiments of the present invention.
Figure 56 is a top plan view illustrating
image formation with the ejection signals at the
timing of Figure 55.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the accompanying drawings, the
preferred embodiments of the present invention will be
described in detail.



20703~~
-17-
Embodiment 1
Figure 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




zo7o3~~
-18-
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. Figures 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 Figure 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




2070355
-19-
(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 Figure 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
:i, 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
Figure 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-gradation 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.




2070355
-20-
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
Figure 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 Figure 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 Figure 4. The
recording operation is carried out using only 64
nozzles, i.e., nozzles Nos. 449 - 512, while the drum




20'0355
-21-
13 is rotated one full turn (main scan) (Figure 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 (Figure 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.
Figure 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




2070355
-zz-
expanded vertically. The position of the recording
head 11 is designated by a reference numeral lla. 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 lb at the start of the second rotation of the
drum 13 and at a position lc 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 Figure 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




2070355
-23-
is free from inclination.
Embodiment 4
The same recording apparatus and recording
head 1 as in Embodiment 1 (Figure 1) was used, but the
recording method was different. The number of toner
gradation levels was I7 in this embodiment.
Figure 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 (Figure 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 (Figure 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




2070355
-24-
recording operation is carried out using the nozzles
Nos. 81 - 128 (Figure 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 toner gradations is 4. The recording head
11 has 129 nozzles and ejects large volume droplets.
Figure 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




200355
-25-
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. However, if the
recording material 12 is mounted on the drum 13 with
the opposite inclination, so that the image is without
the inclination.
Figure 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 2 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 6, for example, the variation of the ink
volumes for the respective picture elements each
recorded by different m nozzles is reduced to a/~.
The ink volume variation among the pixels, is




2070355
-26-
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 2 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 (Figure 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




207355
-27-
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 Klx,y (Klx,y = Kx,y-A1). Assuming that
the tone level information Kx,y is 13, Al is 4, and
Klx,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 x
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 (Klx,y/(n/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 Klx,y
produced after the first scan. Then, the tone level
information Klx,y is replaced with K2x,y (K2x,y =




2070355
-28-
Klx,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 x 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 Klx,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




2070355
-29-
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 Klx,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
lq 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.
Figure 11 shows the number of ink droplets A1
- A4 ejected in a scan in response to 0 - 16 tone
level information K.




20703~~
-30-
Referring to Figure 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




2070355
-31-
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 x
1/16 mm (62.5 x 62.5 microns)) is changed within the
range of 0 - 6 inclusive.
Figures 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.
r', [time required for the carriage to pass one pixel]


CA 02070355 1999-03-12
-32-
- [size of pixel]/[carriage speed] and
[maximum number of droplets in one pixel] -
[carriage passing time] x [ejection frequency]
As a result, as shown in Figure 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 Figure 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 refed 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 Figure
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




20'0355
-33-
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




2070355
-34-
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.
Figure 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. On
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




2070355
-35-
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.
Figure 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 - l, and therefore, the number of
droplets capable of being ejected to one pixel is 3 at
the maximum (Figure 16, at portion A) or 4 (Figure 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




2070355
-36-
they fail, the other nozzles can compensate for them
similarly to Embodiments 7 and 8, so that the
resultant image is free from stripes.
Figure 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 Figure 18.
In Figure 18, the n-th ink droplet is the
droplet ejected through 16 nozzles for the same pixel.
When the first pixel in Figure 3 is noted, for example
(Figure 3), No. 121 nozzle ejects the first ink. No.
113 nozzle ejects the second ink droplet; No. 105
nozzle, the third droplet; No. No. 97 nozzle, the
fourth droplet; No. 89 nozzle, the fifth droplet; No.




207035a
-37-
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 Figure 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:
N
E f(m,n)
m=0
At the bottom of Figure 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


CA 02070355 1999-03-12
-38-
includes one or more particular tone levels.
In the example of Figure 18,
N
E f(rn,n)
m=0
is 8 or 9. In this embodiment, the maximum number of
droplets N is 16, and therefore:
N
E f(m,n) S_ (N/2) + 1
m=0
This inequation accomplishes most uniform
operation of the nozzles when the tone levels appear
uniformly.
If the following inequation is satisfied, it
is sufficiently effective to extend the service life
of the frequently used nozzle or nozzles. ~ f(m, n) ' rr~l,
m=0
Embodiment 11
In this embodiment, the used apparatus is the
same as in Embodiment 2 of Figure 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 Figure 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




2070355
-39-
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 Figure 19. In this embodiment,
N
E f(m,n) S_ (N/2) + 1
m=0
is satisfied, too. Here, the image density (OD) for
each of the tone levels was as shown in Figure 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




20'0355
-40-
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,
N
E f(m,n)
m=0
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 droplet n is not more than I0.
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 rnay
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
uniformization between the ink droplets ejected
through the same nozzle.




2070355
-41-
It is preferable that one pixel is recorded
by as large 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 Figure 21.
In Figure 21, the values given in "SUM" are
sums of
N
E f(m,n)
m=0
With respect to the liquid droplets ejected
from the same nozzle. By determining the ejection and
non-ejection in accordance with Figure 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 s 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 Figure 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



2070355
-42-
particular nozzle or nozzles operated at higher
frequencies, can be avoided.
Embodiment 13
Figure 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 Figures 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




2070355
-43-
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 Figure 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 Figure 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 (Figure 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 (Figure




2070355
-44-
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 much different
nozzle combination as possible is 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.
93 nozzles, are used. If it is 4, all of these
nozzles, i.e., 4 nozzles are used.




2070355
-45-
The above calculations are effected for all
pixels, and the recording operation is carried out
while determining the nozzles to be used.
Figure 25 is a flow chart of the operations
for the above. In Figure 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 S 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 x m =
V is calculated. At step S7, the total ejection
volume is calculated as the combination of the nozzles
to be used, as shown in Figure 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 510, referring to the RAM 12, thus
effecting record. The operations in steps S1 - S10
are repeated until all the lines are covered (step
S11).




2070355
-46-
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
Figure 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




207035
-47-
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
Figure 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




2070355
-48-
.:~
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 data 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.




207035
-49-
Embodiment 16
Figure 29 shows the OD level when the
recording liquid shown in Figure 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 Figure 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




2070355
-50-
1 except for the number of nozzles is 12. The
structure of the control system is the same as shown
in Figure 12.
The description will be made as to the method
of 5 tone gradation record.
Figure 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
f rom 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 Figure 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 Figure 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




2070355
-51-
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 Figure
31 at portion (c), the repetition of the above-
described operations produces the record on the whole
surface with 0 - 3 droplets.
Figure 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 Figure 32 shows the recorded
image according to this embodiment. O or O
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,




2070355
-52-
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 Figure
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




200355
-53-
Figure 29. Figure 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 Figure 32.
In Figure 33, "D" is the image densities when plural
droplets are shot with 20 microns deviation for one
pixel; "O" 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 i 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 Figure 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




2070355
-54-
between the two scans. In this case, the image
processing software is simplified.
Embodiment 17
Figure 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 " O " indicates a dot
provided by one droplet; "~O " 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 "C3D" 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 Figure 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




2070355
-55-
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.
Figure 35 shows the OD levels for the
respective patterns of Figure 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 < the density 53 of
the dot 43 < the density 54 of dot 44.
Similarly,
the density 55 of the dot 45 < the density 56 of
the dot 46.
In both of the droplets 43 and 44, the number
of droplets ml through the first scan is 2, the number
of droplets through second or third scan is 0 (m2 = m3
- 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




2070355
-56-
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 (Figure 1) except for that the
recording head has groups of nozzles, which groups
provide different ink ejection volumes. Figure 36
schematically shows the structure of the recording




2070355
-57-
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 3Ø 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




2070355
-58-
therefore, the above-described desirable condition is
satisfied, so that the recording head can be produced
at relatively low cost.
Figure 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)
x 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




20'0355
-59-
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 H 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




200355
-60-
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.
Figure 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 Figure 37. In the
embodiment of Figures 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




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method proposed in U.S. Patent 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 Y
correction and subsequent 4 level error diffusion
treatment to the data read from an original image by a
monochromatic scanner, for example.
Embodiment 19
Figure 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.




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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
Figure 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 Figure 37, and
the halftone image is recorded on the recording
material 2 corresponding to the image data.
Referring to Figure 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 Figure 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 receive the
droplet from the ejection outlets Nos. 1 - 4 in the
first scan. In addition, the ejection outlets Nos. 5




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- 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 Figure 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 i can be provided, as
will be understood from Figure 38.




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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 po$ition, is possible.




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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),




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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.
Figure 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




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explanation, the nozzles are numbered 1, 2, 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 Figure 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 Figure 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




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one pixel, and the recording operation is carried out
using the nozzles Nos. 1 - 42 (C in Figure 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 (Figure 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
(Figure 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




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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 Figure 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




2070355
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as compared with the conventional recording method in
which one pixel is recorded by plural ink droplets
ejected by the same nozzle.
Embodiment 21
Figure 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
v' 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.
Figure 42 illustrates the concept of the
recording method of Embodiment 22. The schematically




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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 NO. 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



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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
Figure 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




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64 pixels, 48 pixels or 16 pixels. The feeding of
these amounts are repeated to effect 13 tone gradation
recording.
Embodiment 24
Figure 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




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downwardly relative to the recording sheet, 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




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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
Figure 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 7lBk,
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 reciprocable in the main scan
directions along guide rails 75A and 75B by a carriage
feeding motor (Figure 47) which will be described
hereinafter. Through ink ejection outlets or nozzles
(Figure 46), black, cyan, magenta or yellow ink
droplets are selectively ejected to the recording




200355
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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 (Figure 47), so that it is fed in
the sub-scan direction crossing with the main scan
direction at a predetermined pitch.
As show in Figure 46, the recording head 71
comprises black, cyan, magenta and yellow head units
7lBk, 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 p0. 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.
Figure 47 shows the control circuit for the
apparatus of this embodiment. It corresponds to
Figure 12. In Figure 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.
Figures 48 and 49, similarly to Embodiment 20
in conjunction with Figure 40, illustrate the head 71
drive timing and picture element recording process




20703~~
_77_
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 (Figure 49 at portion (a)).
After the scan 1 operation, the recording material is
fed by one pitch p0 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 (Figure 49 at portion (b)). After the
second scan, the recording material 72 is fed in the
sub-scan direction at the pitch p0 equal to the nozzle
interval. Then, the nozzle Bi+2 scans the scanning
line along which the liquid droplets Di have been




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ejected (scan 3), during which an ejection signals P43
is selectively applied to eject the liquid droplet
Di+2 through the nozzle Bi+2 (Figure 49 at portion
(c)). Similarly, the recording material 72 is fed
through the pitch p0. 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 (Figure 49 at portion (d)).
Thus, the recording of the pixel 505 is completed
(Figure 49 at portion (e)).
After the completion of scan 4, the
recording material 72 is fed through the distance
~?~ (N-3) x p0 (N: the umber 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.
Figures 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 Figure 48. In scan 1, the black
liquid droplet is ejected through nozzle Bi in




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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 the seeping become 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.
Figures 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 (Figure




20'0355
-80-
52) and is overlaid on the pixel 912 recorded by the
first and second scan to provide a pixel 913 (Figure
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 (Figure 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 (Figure 53). However, the black ink
on the pixel 913 ejected in the scan 3, has already
been sufficiently seeped into the recording material,
and therefore, the mixture as shown in Figure 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




2070355
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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 Figure 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
Figure 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




20?0355
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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
Figure 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 Figure
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




2070355
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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
Figures 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.




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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) x p0 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




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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
e' 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




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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.
Patent 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 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




-87_ 207035 5
disclosed in U.S. Patents 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. Patent No. 4,313,124.
The structure of the recording head may be
as shown in U.S. Patent 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. 123670/1984
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.
A




-88-
207035 5
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, on 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 heating
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
A




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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 zoom temperature.
Since the ink is controlled within the temperature
not lower than 30 °C and not higher than 70 °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




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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




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or changes as may come within the purposes of the
improvements or the scope of the following claims.
10
20

Representative Drawing