Recording method for gradation recording with light-and dark-colored inks and apparatus therefor

In forming an image with plural recording heads corresponding to plural inks of different densities, the image data are so distributed that the image is formed with the ink of low density until the image density reaches a predetermined density level, but is formed with the inks of low and high densities when the image density exceeds the predetermined density level, and the distributed data are corrected according to the detection of temperature relating to the recording heads, whereby a desired recorded image can be obtained even in the presence of a variation in the head temperature. Also the image data are distributed in such a manner that, when the remaining amount of one of the plural inks becomes low, the recording is conducted with the remaining ink, whereby a desired image can be obtained even when the remaining amount of one of the plural inks with different densities becomes low.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an ink jet recording method for recording 
on a recording medium, by discharging ink from discharge openings of a 
recording head, utilizing plural inks of a same color with different 
densities, and an apparatus therefor. 
2. Related Background Art 
In the conventional ink jet recording method, the record is formed by 
depositing ink droplets onto a recording material such as paper, by 
discharging ink from plural ink discharge openings formed on a recording 
head, based on data signals. Such recording method is utilized for example 
in a printer, a facsimile apparatus or a copying apparatus. 
In such an apparatus there are known a method of utilizing an 
electric-thermal energy converting member in which a heat-generating 
element (electric-thermal energy converting member) is given an electric 
signal to locally heat the ink thereby inducing a variation in the 
pressure thereof and discharging the ink from the discharge opening, and a 
method utilizing an electric-mechanical converting member such as a 
piezoelectric element. 
In such recording methods, a half tone recording is achieved by the dot 
density control in which the half tone is represented by the control of 
the number of recording dots per unit area, while the recording dots are 
maintained at a constant size, or by the dot diameter control in which the 
half tone is represented by the control of the size of the recording dots. 
In general, the former dot density control is more popularly utilized, 
since the latter dot diameter control requires and is limited by the 
complex control method for delicately varying the recording dot size. 
Also in case the ink discharge means consists of the electric-thermal 
energy converting member which can achieve a high resolving power because 
it enables easier manufacture and can be arranged with a high density, the 
above-mentioned dot density control is generally employed since the amount 
of variation in pressure is difficult to control, so that the diameter of 
the recording dot is difficult to modulate over a wide range. 
One of the representative binarization methods employed in said dot density 
control for the continuous tone representation is the systematic dither 
method, but said method is associated with a drawback that the number of 
gradation levels is limited by the matrix size. More specifically, a 
larger number of gradation levels requires a larger matrix size, which 
leads to a larger pixel composed of said matrix in the recorded image, 
whereby the resolving power becomes deteriorated. 
Another representative binarization method is the conditionally determined 
dither method, such as the error diffusion method, in which the threshold 
value is varied in consideration of the pixels surrounding the input 
pixel, in contrast to the above-mentioned systematic dither method, which 
is an independently determined dither method wherein the threshold value 
for binarization is determined independently from the input pixel. Said 
conditionally determined dither methods, represented by the error 
diffusion method, have certain advantages such as the compatibility of the 
gradation and the resolving power, and extremely little generation of the 
moire pattern in the recorded image in case the original image is a 
printed image, but is also associated with a drawback of granularity in 
the lighter area of the image, leading to a tendency that the image 
quality is evaluated as low. This drawback is particularly conspicuous in 
a recording apparatus with a low recording density. 
For overcoming such granularity, there has been proposed a recording 
method, in an ink jet recording apparatus, of providing two recording 
heads for respectively discharging lighter-colored ink and darker-colored 
ink, and forming the recording dots with the light-colored ink from the 
low-density (light) level to the intermediate density level of the image, 
and with the dark-colored ink from the intermediate density level to the 
high-density (dark) level of the image. 
FIG. 4 shows a principal part of a conventional color ink Jet recording 
apparatus of the serial printing type, employing such light and dark inks. 
On a carriage 401 there are provided, with a predetermined mutual distance, 
a recording head Bkk for discharging dark black-colored ink, a head Bku 
for discharging light black-colored ink, a head Ck for discharging dark 
cyan-colored ink, a head Cu for discharging light cyan-colored ink, a head 
Mk for discharging dark magenta-colored ink, a head Mu for discharging 
light magenta-colored ink, a head Yk for discharging dark yellow-colored 
ink, and a head Yu for discharging light yellow-colored ink. 
A recording material, consisting for example of paper of a thin plastic 
sheet, is supplied through transport rollers (not shown) and is pinched 
between discharge rollers 402, and is advanced in the illustrated 
direction by an unrepresented transport motor. 
The carriage is guided and supported by a guide shaft 403 and an encoder. 
Said carriage reciprocates along said guide shaft, by means of a driving 
belt 404, driven by a carriage motor 405. 
In the interior (liquid path) of each ink discharge opening of the 
above-mentioned recording heads, there is provided a heat-generating 
element (electric-thermal converting member) for generating the thermal 
energy for ink discharge. 
An image can be formed by driving said heat-generating elements based on 
the recording signals, according to the timings read by said encoder, and 
discharging and depositing the ink droplets onto the recording material, 
in the order of dark black, light black, dark cyan, light cyan, dark 
magenta, light magenta, dark yellow and light yellow. 
In a home position of the carriage, selected outside the recording area, 
there is provided a recovery unit having a capping portion 406, for 
maintaining stability of the ink discharge. 
The above-explained light-dark multi-density recording method employing 
plural inks of different densities for a same color can improve the 
gradation particularly in the highlight area, and can reduce the 
granularity by the dots, thereby attaining higher image quality even by a 
simple increase of the density levels from two to three. This is because 
the noises felt by the single dots in the highlight area can be reduced by 
the deposition of lighter ink (with lower density) in such highlight area. 
However, in the ink jet recording apparatus employing such light and dark 
inks, the stable ink discharge may become difficult, depending on the 
situation of use. If, among plural inks of different densities of a same 
color, at least an ink cannot be discharged in stable manner, the desired 
image can no longer be obtained. 
In such ink jet recording apparatus utilizing such dark and light inks, the 
multi-value luminance signals of R, G and B colors supplied from a host 
equipment are converted in a color processing unit into multi-value 
density signals of Y, M, C and Bk colors, which are then divided, by a 
distribution table of a dot developing unit, into those to be recorded 
with the dark inks and those to be recorded with the light inks, and thus 
divided signals are binarized for recording by the recording heads. 
Consequently, if either of the dark and light inks is exhausted or becomes 
low in the remaining amount, the desired image can no longer be obtained 
even though the colors required for image formation are still present. 
Also the stability of the ink discharge amount is significantly influenced 
by the temperature of ink or recording head and that of the atmosphere. In 
general the discharge amount is low when the ink temperature is low, and 
becomes larger as the ink is heated. As a result there has been 
encountered a drawback that the density of the recorded image varies 
depending on the temperature of the recording inks. 
SUMMARY OF THE INVENTION 
In consideration of the foregoing, the present invention is to provide an 
ink jet recording method capable of providing a desired image even when 
the stable ink discharge becomes difficult in at least one among plural 
inks of different densities of a same color, and an apparatus therefor. 
The above-mentioned object can be attained, according to the present 
invention, by an ink jet recording method for recording on a recording 
medium by discharging ink from discharge openings of a recording head, 
utilizing plural inks of different densities of a same color, wherein if 
the stable ink discharge becomes difficult in at least one among said 
plural inks, the recording is conducted with the ink of remaining kind. 
Said recording head is preferably a head for discharging the ink utilizing 
thermal energy, provided with a thermal energy converting member for 
generating thermal energy to be given to the ink and adapted to induce a 
state change in the ink by the thermal energy applied by said thermal 
energy conversion member, thereby discharging the ink from the discharge 
opening based on said state change. 
The present invention also provides an ink jet recording apparatus for 
recording on a recording medium by discharging ink from discharge openings 
of a recording head, utilizing plural inks of different densities of a 
same color, comprising distribution means for determining, according to 
the image signal, the proportion of use of each of said plural inks for 
forming pixels corresponding to said image signal; discrimination means 
for discriminating that the stable discharge of at least one of said 
plural inks has become difficult; and variation means for varying the 
proportion determined by said distribution means, based on the result of 
discrimination by said discrimination means, in order to effect recording 
with ink other than the ink of which stable discharge has become 
difficult. 
According to the present invention, there are provided plural distribution 
tables for the inks of different densities, and, when the stable discharge 
of at least one of said plural inks has become difficult, said 
distribution tables are selectively used to effect the recording with the 
remaining inks thereby enabling to continue stable recording. 
Also the present invention, reached in consideration of the aforementioned 
drawback in the prior art, is to provide an ink jet recording apparatus 
capable of providing a desired image recording density even when the 
temperature of the recording head varies, thereby enabling recording with 
excellent gradation. 
The above-mentioned object can be attained, according to the present 
invention, by an ink jet recording apparatus for forming an image with 
plural recording heads corresponding to plural inks of different 
densities, comprising temperature detection means for detecting the 
temperature relative to said recording heads; distribution means for 
distributing the image data into data respectively corresponding to said 
plural inks; and correction means for correcting the data distributed by 
said distribution means, based on the temperature data detected by said 
temperature detection means. 
The present invention also provides a recording apparatus for forming an 
image with plural recording heads corresponding to plural inks of 
different densities, comprising temperature detection means for detecting 
the temperature relative to said recording heads; and distribution means 
for distributing the image data into plural data respectively 
corresponding to said plural inks and also according to the temperature 
data detected by said temperature detection means. 
The present invention furthermore provides a recording method for forming 
an image with plural recording heads corresponding to plural inks of 
different densities, comprising steps of detecting the temperature 
relative to said recording heads, distributing the image data into plural 
data respectively corresponding to said plural inks and also corresponding 
to said detected temperature data, and forming an image on a recording 
medium with said recording heads, based on said distributed data. 
According to the present invention, the temperature relative to the 
recording heads is detected, then the image data are distributed into 
plural data respectively corresponding to the plural inks and also 
corresponding to the detected temperature data, and an image is formed on 
a recording medium with said recording heads, based on said distributed 
data. Thus a desired image recording density can be obtained even when the 
temperature of the recording heads varies, and the tonal reproducing 
ability can be significantly improved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 5 is a perspective view showing the principal part of a color ink jet 
recording apparatus embodying the present invention. 
On a carriage 501 there are provided, with a predetermined distance, ink 
jet units respectively having an array of discharge openings for 
discharging light black-colored ink, an array for light cyan-colored ink, 
an array for light magenta-colored ink, and an array for light 
yellow-colored ink, and ink jet units respectively having an array of 
discharge openings for discharging dark black-colored ink, an array for 
dark cyan-colored ink, an array for dark magenta-colored ink and an array 
for dark yellow-colored ink. 
A recording material, such as paper or a thin plastic sheet, is supplied by 
transport rollers (not shown), and is pinched by discharge rollers 502 for 
advancement in the direction of an arrow, by means of an unrepresented 
transport motor. Said carriage is guided and supported by a guide shaft 
503 and an encoder. Said carriage reciprocates along said guide shaft, by 
means of a driving belt 504 driven by a carriage motor 505. In the 
interior (liquid path) of each ink discharge opening of the 
above-mentioned ink jet unit, there is provided a heat-generating element 
(electric-thermal energy converting member) for generating the thermal 
energy for ink discharge. 
An image can be formed by driving said heat-generating elements based on 
the recording signal and according to the timings read by said encoder, 
and discharging and depositing ink droplets onto said recording material 
in the order of the dark-colored inks and then the light-colored inks. In 
a home position of the carriage, selected outside the recording area, 
there is provided a recovery unit having a capping unit. When the 
recording operation is not conducted, the carriage is moved to said home 
position and the caps of said capping unit tightly cover the faces, having 
the ink discharge openings, of the corresponding ink jet units, thereby 
preventing the clogging of the discharge openings, resulting from the ink 
adhesion caused by evaporation of the ink solvent or from the deposition 
of dusts. 
The capping function of said capping unit is also utilized for the idle 
discharge mode in which the ink is discharged from the discharge openings 
to said cap in a spaced state, in order to resolve discharge deficiency or 
clogging in the ink discharge openings of lower recording frequency, and 
utilized also for the recovery of the ink discharge openings showing 
deficient discharge, by activating an unrepresented motor in the capped 
state of said discharge openings thereby sucking ink forcedly from said 
discharge openings. Also adjacent to said capping unit, there may be 
provided a blade or a wiping member, for cleaning the faces, having the 
ink discharge openings, of the ink jet units. 
FIG. 6 is an exploded perspective view showing the structure of the ink jet 
unit to be employed in the present embodiment, wherein a wiring board 200 
is connected, at an end thereof, with the wirings of a heater board 100, 
and is provided, at the other end, with plural pads for receiving 
electrical signals from the main body of the apparatus, corresponding 
respectively to the electric-thermal energy conversion members. 
Consequently the electrical signals from said main body can be supplied to 
the respective electrothermal energy conversion members. 
A metal support member 300, for supporting the rear surface of the wiring 
board 200 by planar contact, constitutes a bottom plate of the ink jet 
unit. A pressure spring 500 is provided, for applying an elastic pressure 
on a linear area in the vicinity of the ink discharge openings of a 
grooved ceiling plate 1300, with a portion formed in a substantially 
U-shaped cross section, claws for engaging with holes formed in the base 
plate, and a pair of rear legs for receiving the force, applied to the 
spring, by the base plate. 
The force of said spring maintains the wiring board 200 and the grooved 
ceiling plate 1300 in pressurized contact. The wiring board 200 is adhered 
to the support member for example by adhesive material. At an end of an 
ink supply tube 2200, there is provided a filter 700. An ink supply member 
600 is prepared by molding, and the grooved ceiling plate 1300 is provided 
with liquid paths communicating with the respective ink discharge 
openings. The ink supply member 600 is fixed to the support member 300 in 
simple manner by inserting two rear pins (not shown) of the ink supply 
member 600 into holes 1901, 1902 of the support member and thermally 
fusing the protruding ends of said pins. 
In this state, there is formed a uniform gap between an orifice plate 410 
and the ink supply member 600. Sealing agent is poured from an inlet 
formed on the upper part of said ink supply member, thereby sealing the 
bonding wires and the above-mentioned gap between the orifice plate 410 
and the ink supply member 600, and is further guided through a groove 310 
formed on the support member 300 thereby completely sealing the gap 
between the orifice plate 410 and the front end of the support member 300. 
FIG. 7 is a perspective view of the grooved ceiling plate 1300 to be 
employed in the present embodiment, seen from the side of the heater board 
100. There are provided plural liquid chambers, which are mutually 
separated by partition walls 10a-10c and are respectively provided with 
ink supply openings 20a-20d. 
Said partition walls 10a-10c are provided, on contact faces with the heater 
board 100, with grooves 30a-30c, which communicate with the external 
peripheral part of the grooved ceiling plate 1300. After said plate 1300 
is maintained in contact with the heater board, said external peripheral 
part is sealed with the sealing agent as explained above. In this 
operation, the sealing agent enters along said grooves, thereby filling 
the gap between said board and the heater board. In this manner, the 
liquid chambers can be completely separated by the steps known in the 
conventional head. The structure of said grooves varies according to the 
physical properties of the sealing agent and has to be shaped 
corresponding to the sealing agent to be employed. 
The above-explained structure of separate plural liquid chambers allows to 
supply different inks to the ink discharge openings. 
In the following there will be explained the detection of the remaining ink 
amount. FIG. 8 shows an example of the control system in the present 
embodiment, wherein a control unit 200 in the form of a microcomputer 
incorporating an A/D converter determines the proportion of use of each of 
plural inks in the present invention, and varies the determined 
proportion. There are also shown a recording head unit 10, a voltage 
conversion circuit 300, an alarm device 400 composed of a display unit 
such as an LED, or an acoustic alarm device such as a buzzer, or a 
combination thereof, a main scanning mechanism 500 including a motor etc. 
for causing a scanning motion of the carriage HC in the recording 
operation, and a sub scanning mechanism 600 including a motor for 
transporting the recording medium etc. There is also shown a remaining 
amount detection signal V from a tank. 
In the present embodiment, a constant current is given between two 
electrodes provided in an ink chamber b, and the remaining ink amount 
therein is detected by the resistance between said two electrodes. The 
remaining ink amount and the resistance between the electrodes are 
correlated as shown in FIG. 9. 
When the remaining ink amount reaches a predetermined amount or less, said 
resistance becomes higher to indicate that the remaining ink amount has 
reached said predetermined amount. 
FIG. 10 illustrates an ink cartridge employed in the present embodiment, 
and shows the detecting operation for the remaining ink amount. The 
interior of the ink cartridge body 1, defined by the tank walls 101, is 
divided by a wall 102 into two ink chambers a, b which mutually 
communicate at the bottom. An ink chamber a is filled with a compressed 
absorbent member 103 with regulated capillary force. The ink cartridge is 
further provided with an ink supply part 2 for connection with the ink jet 
recording head, an air communicating part 3, pins (electrodes) 4 for 
detecting the remaining ink amount, and an ink filling aperture 5, which 
is closed with a stopper 51 made for example of rubber. The ink chamber b 
is maintained at a reduced pressure. 
The positional relationship of the air communicating part 3, the ink supply 
part 2, the remaining amount detecting pins 4 and the ink filling aperture 
5 is not limited to the illustrated one. When the ink surface in the ink 
chamber b becomes lower than the upper one of two electrodes 4, the 
resistance therebetween is abruptly elevated as shown in FIG. 10, whereby 
a corresponding voltage is generated therebetween. Said voltage is 
supplied either directly or through a voltage conversion circuit 300 to an 
A/D converter of the control unit for A/D conversion. When thus obtained 
detection value becomes larger than a predetermined value Rth, a signal 
for switching the distribution table is sent to a table selection circuit 
in the control unit 200. 
In the present embodiment, the remaining ink amount is detected by the 
resistance between the electrodes provided in the ink tank, but such 
detection is not limited to the above-mentioned method and may also be 
achieved for example by a mechanical method or an optical method. 
FIG. 15 is a cross-sectional view of a state in which the cartridge for 
dark ink and that for light ink are mutually connected, wherein the ink 
filling apertures 5 and the stoppers 51 are omitted. The upper and lower 
ink chambers b are both maintained at a reduced pressure. 
Embodiment 1 
FIG. 1 is a view best representing the feature of the present invention, 
showing the process flow in case of image printing with dark and light 
inks by table selection and also in case either of the dark and light inks 
of a same color is exhausted. In FIG. 1, a color processing unit converts 
the red image luminance signal R, the green image luminance signal G and 
the blue image luminance signal B, by an input correction circuit into a 
cyan image density signal C, a magenta image density signal M and a yellow 
image density signal Y. These signals are subjected to color processing 
and conversion into new image density signals C, M, Y, Bk of cyan, 
magenta, yellow and black colors in a color correction (masking) circuit 
and a UCR (undercolor removal)/black generation circuit, and is then 
subjected to gamma conversion into image density signals C, M, Y, Bk of 
cyan, magenta, yellow and black colors by an output correction circuit. 
A dot developing unit positioned next selects the distribution table for 
distributing said density signals C, M, Y, Bk into those for recording 
heads for printing the inks of higher density and those for recording 
heads for printing the inks of lower density. According to thus selected 
distribution table, the density signals C, M, Y, Bk generated in the color 
processing unit are distributed into image density signals Ck, Mk, Yk, Bkk 
of dark cyan, dark magenta, dark yellow and dark black colors with higher 
dye densities and image density signals Cu, Mu, Yu, Bku of light cyan, 
light magenta, light yellow and light black colors of lower dye densities. 
Thus distributed signals are respectively binarized, and inks are 
discharged from the arrays of ink discharge openings of the ink jet units, 
according to said signals, thereby forming a color image. 
In FIG. 1, a distribution table A is used for distributing the printing 
data into those for dark inks and those for light inks so as to attain 
characteristics as shown in FIG. 2. A distribution table B is used in case 
of printing with the inks of dark colors only, without using those of 
light colors. A distribution table C is used in case of printing with the 
inks of light colors only, without using those of dark colors. In this 
case there is shown a printing operation of two images by two main 
scannings with the light-colored ink. In practice, an image density 
comparable to that printed with the dark-colored ink may be obtained with 
the light-colored ink only, by recording plural images in superposed 
manner in plural main scanning operations. The contents of the 
distribution tables shown in FIG. 1 are shown in FIGS. 3A to 3C. The 
distribution table A shown in FIG. 3A is used for distributing the 
printing data of each color, generated in the color processing unit, to 
the data for the dark-colored ink and those for the light-colored ink, and 
there are given the output data for the light cyan ink and the dark cyan 
ink, respectively by a solid line and a chain line, as a function of the 
input data. As will be apparent from the chart, the light-colored ink only 
is used until the input data reach a level a, and the light-colored ink 
and the dark-colored ink are combinedly used beyond said level a. The 
distribution table B, shown in FIG. 3B, distributes the data of each 
color, generated in the color processing unit, to the dark-colored ink 
only, wherein shown are the output data for the dark-cyan ink, by a chain 
line, as a function of the input data. The distribution table C, shown in 
FIG. 3C, distributes the data of each color, generated by the color 
processing unit, only to the light-colored ink, wherein shown are the 
output data for the dark-cyan ink for a first image, by a solid line, and 
the output data for the dark-cyan ink for a second image, by a 
double-dotted chain line, both as a function of the input data. As will be 
apparent from this chart, the first image alone is printed until the input 
data reach a level a, and the first and second images are superposedly 
printed beyond said level a to form the image of the high density area. 
The table selection shown in FIG. 1 automatically selects the tables A to C 
by a sequence shown in FIG. 2, to be executed by a control unit 200 shown 
in FIG. 8. In the sequence shown in FIG. 2, the detection of the remaining 
ink amount is executed for all the colors, for example at the completion 
of printing of a page. For example, if the light-cyan ink is less than a 
predetermined remaining amount, there is selected, only for the cyan 
color, a distribution table for printing with the dark-colored ink only 
without the light-colored ink, thereby preventing the lack of printing in 
low cyan density areas and thus obtaining a satisfactory image. Also if 
the dark-cyan ink is less than the predetermined remaining amount, there 
is selected, only for the cyan color, the distribution table for printing 
with the light-colored ink only without the dark-colored ink and there is 
also adopted the superposed recording methods by plural main scannings, 
thereby preventing the failure of printing of the high density areas and 
thus obtaining a satisfactory image. 
In the above-explained example, in case either of the dark and light cyan 
inks is exhausted, the distribution table for using the other remaining 
ink only is selected for the cyan color only, but there is preferably 
selected the same distribution table for all the colors. 
Also each of the distribution tables A to C may be composed of a single 
table for distributing the dark- and light-colored inks in the same manner 
for all the colors, or may be composed of plural different tables 
respectively corresponding to the colors and providing optimum 
distributions thereto. 
Also in the present embodiment the distribution tables are automatically 
selected according to the detection of the ink remaining amounts, but 
there may be provided a switch for selecting the distribution tables for 
arbitrary selection by the user. 
Also the selection of the distribution tables may be changed not 
necessarily at the completion of printing of a page but at any 
predetermined timing such as at the completion of printing of a line. 
Furthermore, the distribution table explained above is designed for 
printing with two inks of higher and lower densities for each color, but 
it may also be designed for printing with three inks of high, medium and 
low densities or with an even larger number of kinds of ink. 
Also in the present embodiment, the failure in the stable ink discharge in 
at least one among plural inks is judged from the low remaining ink 
amount, but it may also be detected by another factor not related to the 
low remaining amount, such as the failure in the ink discharge resulting 
from the clogging of the ink discharge openings. 
As explained in the foregoing, the ink jet recording apparatus of the 
present invention for printing with inks of higher and lower densities for 
each color comprises, in addition to the distribution table for 
distributing the density signals of C, M, Y, Bk colors to the density 
signals for printing with the inks of higher density and those for 
printing with the inks of lower density, a distribution table for 
distributing said density signals only to the inks of higher density, a 
distribution table for distributing said density signals only to the inks 
of lower density, and means for selecting said distribution tables, 
thereby enabling to obtain a normal image even when the ink of higher or 
lower density is exhausted or becomes not discharged properly. 
Embodiment 2 
In the following there will be explained an embodiment 2 of the present 
invention, in which the distribution tables are selected not by the 
stability of ink discharge but according to the density distribution of 
the image. 
The output image of a page is scanned in advance for detecting the density 
distribution of the image data, and, if the density distribution is 
concentrated in a high density region, the aforementioned distribution 
table B (FIG. 3B) is selected to effect the printing with the dark-colored 
inks only. On the other hand, if the density distribution is concentrated 
in a low density region, the aforementioned distribution table C (FIG. 3C) 
is selected to effect the printing with the light-colored inks only. 
The density distribution may be detected among the developed image data of 
a predetermined amount, or, in case of a copying apparatus or the like, by 
scanning of the original image. 
This embodiment, utilizing the detection of the density distribution of the 
image data, allows to obtain a uniform image without the granularity 
resulting from the printing with the dark-colored ink in the vicinity of a 
density level where the dark- and light-colored inks are switched. 
Embodiment 3 
In the following there will be explained an embodiment 3 of the present 
invention, in which, as shown in FIGS. 11A and 11B, the tank walls 101 are 
composed of a transparent or semitransparent material whereby optical 
detection of the remaining ink amount is rendered possible. In this case, 
there are provided, on a wall in the ink chamber b, a reflecting plate 42 
such as a mirror, and, outside the tank, a photosensor consisting of a 
light-emitting element 43 and a photosensor 44. Said light-emitting 
element 43 and photosensor 44 may be provided on the carriage or in the 
home position where the recovery system is provided. 
In the configuration shown in FIGS. 11A and 11B, the light-emitting element 
43 emits the light at a certain angle, and the photosensor 44 receives the 
light reflected by the reflecting plate. For example, the light-emitting 
element 43 is composed of an LED, and the photosensor 44 is composed of a 
phototransistor. FIG. 11A shows a state in which the ink is fully present, 
and the light from the light-emitting element 43 is intercepted by the ink 
and scarcely reaches the photosensor 44 so that the detection output 
thereof is small. However, when the ink is consumed to a state shown in 
FIG. 11B, the light from the light-emitting element 43 is scarcely 
intercepted so that the detection output of the photosensor becomes 
higher. 
FIG. 12 shows a variation in which the light-emitting element and the 
photosensor are positioned mutually opposite across the ink tank. Also in 
this case the ink chamber b is composed of a transparent or 
semitransparent material. This configuration can dispense with the 
reflecting plate, and also can improve the detection sensitivity since the 
light is directly received. 
The above-mentioned configurations of the detection means for the remaining 
ink amount allow to obtain the detection output from the photosensor 44 in 
the form of an analog signal. Consequently, in a color ink jet recording 
apparatus employing two inks of higher and lower densities for each of C, 
M, Y and Bk colors, it is rendered possible to use up the inks of higher 
and lower densities almost at the same time, by providing plural 
distribution tables corresponding to the differences between the detection 
outputs of the inks of higher and lower densities of each color and 
suitably selecting said distribution tables. 
In the structures shown in FIG. 11A, 11B and 12, the ink chamber b is 
maintained at a reduced pressure. 
Embodiment 4 
In the following there will be explained an embodiment 4 of the present 
invention. 
FIG. 13 shows the variation in the internal pressure in the ink supply 
unit, according to the ink supply amount in an ink tank as shown in FIG. 
1. In an initial state of recording, a small amount of ink is present in 
the ink chamber a, and a negative pressure is generated by the capillary 
force of the compressed ink absorbent member. As the ink amount in the ink 
chamber a becomes less by the ink supply, the negative pressure in said 
ink chamber a, generated by the capillary force determined by the 
compression rate (pore size distribution) of the compressed absorbent 
member, gradually increases. 
As the ink is consumed more, the ink distribution in the ink chamber a 
becomes stabilized, and the internal pressure remains thereafter 
substantially constant, by the introduction of air into the ink chamber b 
(stable ink supply period). 
When the ink in the ink chamber b is exhausted by further ink consumption, 
the ink in the chamber a starts to be consumed again, so that the negative 
pressure in the chamber a is changed. The stable ink discharge becomes no 
longer obtained when the negative pressure in the ink chamber a exceeds a 
certain value. It is therefore possible to detect the remaining ink amount 
by the negative pressure in the ink chamber, and to switch the 
distribution table upon detection of a state where the stable ink 
discharge becomes no longer possible, thereby preventing the deterioration 
of the image resulting from the unstable ink discharge. 
The present invention is not limited to the foregoing first to fourth 
embodiments, but is widely applicable to the ink jet recording apparatus 
for recording with plural inks of different densities. 
In the following there will be explained an embodiment in which the density 
is regulated by employing high-density ink and clear ink. 
FIG. 14 is a schematic exploded perspective view of an ink tank with 
improved efficiency of ink use, wherein the ink tank is divided by a 
partition 13c into an ink chamber 13a for dark ink and an ink chamber 13b 
for clear ink (dye-free ink consisting solely of solvent), and the color 
density is regulated according to the area ratio of ink supply apertures 
15a, 15b. Said ink chambers 13a, 13b for the dark ink and the clear ink 
are used as negative pressure generating chambers, and there are further 
provided ink containers 13e, 13f which are separated from said negative 
pressure generating chambers by partitions 13g, 13h having apertures 13i 
at the bottom. After the inks in negative pressure generating members 14a, 
14b are used, the inks are supplied from the ink containers 13e, 13f, 
whereby the ink supply pressure is maintained at a constant head pressure, 
and uniform ink supply thus made possible. The ink chambers are provided 
with air communicating holes 13d. 
In the ink tank explained above, the area ratio of the supply apertures of 
the ink tank is regulated respectively according to the darker and lighter 
colors of the recording heads by the partition provided in the tank, and 
the divided chambers are respectively filled with the dense-colored ink 
and the clear ink. When said ink tank is connected to the recording head, 
said inks flow into said recording head with a ratio determined by said 
area ratio of the apertures and are mixed in the recording head, thereby 
providing the ink of an intermediate density. When the clear ink is 
exhausted, the ink of the lower density becomes no longer discharged, so 
that the proper image can no longer be obtained. Consequently the 
remaining amount of the clear ink is detected, and the ink distribution 
table is switched when the clear ink is exhausted, whereby a proper image 
can be obtained until the ink of each color is used up. 
In the foregoing explanation, the two chambers are respectively filled with 
the ink of each color and the clear ink, but they may be replaced by the 
inks of different densities of a same color. In such case the remaining 
ink amount is detected for both inks, and the ink distribution table is 
switched according to the result of said detection, whereby all the inks 
in the ink tank can be used up while the proper image recording is 
maintained all the time. 
As detailedly explained in the foregoing, the present invention, in 
recording on a recording medium by ink discharge from the discharge 
openings of a recording head employing plural inks of different densities 
of a same color, allows to obtain a proper image even when the stable ink 
discharge becomes difficult in-at least one of said plural inks, by 
effecting the recording operation by the remaining ink. 
Embodiment 5 
In the following there will be explained an embodiment 5 of the present 
invention, with reference to the attached drawings. 
FIG. 16 is a perspective view of the principal part of a color ink jet 
recording apparatus embodying the present invention. 
On a carriage 623, there are provided, in parallel manner, an ink jet unit 
611A having an array of discharge openings for the ink of dark color, and 
an ink jet unit 611B having an array of discharge openings for the ink of 
light color. 
A recording material P such as paper or a thin plastic sheet, advanced by 
transport rollers (not shown), is pinched by discharge rollers 621 and is 
advanced as indicated by an arrow, by means of an unrepresented transport 
motor. 
The carriage 623 is guided and supported by a guide shaft 622 and an 
encoder (not shown). 
The carriage 623 reciprocates along the guide shaft 622, by means of a 
driving belt 624 driven by a carriage motor 625. 
In the interior (liquid path) of each ink discharge opening of said ink jet 
unit, there is provided a heat-generating element (electrothermal energy 
converting member) for generating thermal energy for ink discharge. 
An image is formed by driving said heat-generating elements based on the 
recording signal, according to the timings read by the encoder (not 
shown), thereby discharging and depositing ink droplets onto said 
recording material P in the order of the dark-colored ink and the 
light-colored ink. 
In a home position (HP) of the carriage selected outside the recording 
area, there is provided a recovery unit having a capping unit 626. When 
the recording operation is not executed, the carriage 623 is moved to the 
home position (HP) and the caps of the capping unit 626 tightly close the 
faces, having the discharge openings, of the corresponding ink Jet units, 
thereby preventing the clogging of the ink discharge openings, resulting 
from the ink deposition caused by evaporation of the ink solvent or from 
the dust deposition. 
The capping function of said capping unit 626 is also utilized in the 
preliminary discharge mode, in which the ink discharge is executed from 
the ink discharge openings to the capping unit 626 in a separated state, 
in order to resolve the discharge failure or clogging in the discharge 
openings of lower frequency of recording, and in the ink discharge 
recovery operation in which an unrepresented pump is activated in the 
capped state to suck the ink forcedly from the ink discharge openings 
thereby restoring the discharge openings with discharge failure. Also 
adjacent to the capping unit 626, there may be provided a blade or a 
wiping member for cleaning the face, having the ink discharge openings, of 
the ink jet unit. 
FIG. 17 is a schematic perspective view of the arrays of the ink discharge 
openings of the recording heads 612, seen from the side of the recording 
material, and FIG. 18 is a partial perspective view, schematically showing 
the structure of the ink discharge part. Referring to FIGS. 17 and 18, a 
head 612A for the dark-colored ink and a head 612B for the light-colored 
ink are provided in parallel manner, and each head is provided with an 
orifice face 601 containing plural discharge openings 602. In a liquid 
path 602 communicating with each discharge opening 602, there is provided 
a discharge energy generating element 604 for generating energy required 
for the ink discharge. An arrow y in FIG. 17 indicates the scanning 
direction of the carriage 623. In FIG. 18, there is provided a sensor 605 
for detecting the temperature of the recording head. In the present 
embodiment, said sensor 605 is composed of a diode sensor, and is provided 
at each end of the array of the discharge openings. The kind of the 
temperature detecting means is not limitative. The temperature may be 
detected by other sensors such as thermistor, or may be estimated by 
calculation, based on the duty ratio of the printed dots, in the counting 
of the number of the printed dots. 
FIG. 19 is a block diagram showing the basic configuration of the color ink 
Jet recording apparatus of the present embodiment. 
In FIG. 19, there are shown an image input unit 641 for optically reading 
the original image for example with a CCD, or for entering image luminance 
signals (R, G, B signals) for example from a host computer or a video 
equipment; an operation unit 642 provided with various keys for setting 
various parameters and for instructing the start of printing operation; 
and a CPU 643 for controlling the entire recording apparatus according to 
various programs stored in a ROM. 
A ROM 644 stores various programs for operating this recording apparatus, 
such as a control program and an error process program. More detailedly, 
said ROM includes an input gamma conversion table 644a to be referred to 
in the process of an input gamma conversion circuit; masking coefficients 
644b to be referred to in the process of a color correction (masking) 
circuit; a black generation/UCR table 644c to be referred to in the 
process of a black generation/UCR circuit; a density distribution table 
644d to be referred to in the process of a density distribution circuit to 
be explained later; and programs 644e mentioned above. 
There are further shown a RAM 645 to be used as a work area for the 
programs stored in the ROM and a temporary diversion area in the error 
processing; a processing unit 646 for the image signal processing to be 
explained later; a printer unit 647 for forming a dot image, in the 
recording operation, based on the image signal processed by said signal 
processing unit; and a bus line 648 for transmitting the address signals, 
data, control signals etc. within the present apparatus. 
In the following there will be given an explanation on the image signal 
processing unit. FIG. 20 shows the block diagram of the image signal 
processing system. An image processing circuit 651 effects masking, UCR 
(undercolor removal) etc., and any general image processing flow is 
applicable therein. 
The single-color data after color processing are fetched by a density 
distribution unit 652, which distributes the input data to the data for 
light-colored ink and those for dark-colored ink, according to the density 
distribution table 644d in the ROM 644 shown in FIG. 19. 
FIG. 21 shows an example of the conversion graph of the density 
distribution table, wherein a solid line and a chain line respectively 
correspond to the data for light-colored ink and those for dark-colored 
ink. If the 8-bit single-color data are within a range from 0 to 128, 
there are released the data for dark-colored ink at "0", and those for 
light-colored ink within a range from "0" to "255". If the single-color 
data are within a range from 128 to 255, the released data for 
dark-colored ink is varied from "0" to "255" while those for light-colored 
ink is varied from "255" to "0". 
In short, the recording operation of the present embodiment is conducted 
principally with the ink of lower dye concentration (light-colored ink) if 
the input data are low (highlight side), and principally with the ink of 
higher dye concentration (dark-colored ink) if the input data are high. 
However, as explained before, the ink discharge amount in the ink jet 
recording apparatus is significantly influenced by the temperature of the 
recording head. The ink discharge amount becomes larger as the ink 
temperature becomes higher, so that the density of the recorded image 
varies depending on the temperature of the recording head. 
Consequently, a data correction circuit 653 corrects the data for 
light-colored ink and those for dark-colored ink distributed by the 
density distribution table, based on the temperature data obtained from 
the temperature sensor 656 of the light-colored ink head and the 
temperature sensor 657 of the dark-colored ink head. FIG. 22 shows an 
example of the conversion graph for data correction, to be executed by 
said data correction circuit 653. If the head temperature is low, the 
graph is shifted to a side A to increase the output data, thereby 
increasing the density. Also if the heat temperature is high, the graph is 
shifted to a side B to decrease the output data, thereby reducing the 
density. The data for the dark- and light-colored inks, thus corrected 
according to the head temperature, are respectively binarized in the 
binarizing circuits 654, 655 shown in FIG. 20, and are supplied in the 
form of on/off data (1-bit signal) to the respective heads. 
The foregoing embodiment has been explained by single-colored ink, but the 
present invention is not limited to such embodiment and is applicable also 
to a color recording apparatus utilizing inks of higher and lower 
densities in plural colors such as cyan, magenta, yellow and black. Also 
the dye concentration of the ink is not limited to two levels of high and 
low, but may also be selected at three or more levels. This is because, if 
the dot density is different significantly between the inks of high and 
lower densities, the tonal rendition does not become linear in a portion 
where said inks of higher and lower densities are switched and a pseudo 
contour tends to appear in such portion. Also in such ink switching 
portion, there may result a variation in the granurality or the hue of the 
recorded image, thereby giving unnatural impression. For this reason it is 
preferable to conduct the recording operation with an increased number of 
ink densities, such as inks of higher, medium and lower densities. 
The configuration explained above allows to obtain desired density in the 
recorded image even when the temperature of the recording head varies, 
thereby significantly improving the tonal reproducibility. 
Embodiment 6 
In the following there will be explained an embodiment of the ink jet 
recording apparatus of the present invention, wherein the ink jet 
recording head is provided with plural liquid chambers in which the inks 
of different densities of a same color are supplied for improving the 
tonal reproducibility. 
FIG. 23 is a perspective view of the principal part of the color ink jet 
recording apparatus of an embodiment 6, wherein the functions are 
basically same as those of the embodiment 5. 
FIG. 24 is a schematic perspective view of the arrays of the ink discharge 
openings on the recording heads in said recording apparatus, seen from the 
side of the recording material. 
The ink jet recording apparatus illustrated in FIG. 23 has the recording 
heads for the inks of four colors of C (cyan), M (magenta), Y (yellow) and 
K (black), wherein each of the recording heads, arranged in parallel 
manner on a carriage 623, is provided with an array of the discharge 
openings for discharging the ink of dark color, and an array of the 
discharge openings for discharging the ink of light color. 
In the recording operation with the inks of dark and light colores, the 
aberration in the deposited positions of the dots of the dark and light 
colors is also important, and the density may vary by such aberration in 
the dot position. In the present embodiment, the arrays of the discharge 
openings for the inks of different densities are provided on a single 
recording head, so that said arrays are relieved from the vertical and 
horizontal positional aberrations, encountered in case said arrays are 
provided on different recording heads and the aberration in density scale, 
resulting from the deposited position can therefore be reduced. 
FIG. 25 is an exploded perspective view of the ink jet recording head to be 
employed in the present embodiment. 
A wiring board 200 is connected, at an end thereof, with the wirings of a 
heater board 100, and is provided, at the other end, with unrepresented 
plural pads serving to receive the electrical signals from the main body 
of the apparatus and respectively corresponding to the electrothermal 
converting members, whereby said electrical signals from said main body 
are transmitted to the respective electrothermal converting members. 
A metal support member 300, for supporting the rear surface of the wiring 
board 200 by planar contact, constitutes a base plate of the ink jet unit. 
A pressure spring 500 is provided, for applying an elastic pressure on a 
linear area in the vicinity of the ink discharge openings of a grooved 
ceiling plate 1300, with a portion formed in a substantially U-shaped 
cross section, claws for engaging with holes formed in the base plate, and 
a pair of rear legs for receiving the force, applied to the spring, by the 
base plate. The wiring board 200 and the grooved ceiling plate 1300 are 
maintained in pressure contact by the force of said spring. The wiring 
board 200 is adhered to the support member for example by adhesive 
material. 
At an end of an ink supply tube 2200, there is provided a filter 700. An 
ink supply member 600 is prepared by molding, and the grooved ceiling 
plate 1300 is integrally provided with an orifice plate 1201 and liquid 
path 1500 leading to respective ink supply apertures. The ink supply 
member 600 is fixed to the support member 300 in simple manner by 
inserting two rear pins (not shown) of the ink supply member 600 into 
holes 1901, 1902 of the support member and thermally fusing the protruding 
ends of said pins. 
In this state, there is formed a uniform gap between the orifice plate 1201 
and the ink supply member 600. A sealing agent is poured from an inlet 
formed on the upper part of said ink supply member, thereby sealing the 
bonding wires and the above-mentioned gap between the orifice plate 1201 
and the ink supply member 600, and also sealing the gap to the front end 
of the support member 300. 
FIG. 26 is a perspective view of the grooved ceiling plate 1300 of the 
recording head to be employed in the present embodiment, seen from the 
side of the heater board 100. There are provided plural liquid chambers, 
which are mutually separated by partition walls 10, and are respectively 
provided with ink supply openings 20a, 20b. 
Said partition walls 10 are provided, on contact faces with the heater 
board 100, with grooves 30, which communicate with the external peripheral 
part of the grooved ceiling plate 1300. After said plate 1300 is 
maintained in contact with the heater board, said external peripheral part 
is sealed with the sealing agent as explained above. In this operation, 
the sealing agent enters along said grooves, thereby filling the gap 
between said board and the heater board. In this manner, the liquid 
chambers can be completely separated by the steps known in the 
conventional head. The structure of said grooves varies according to the 
physical properties of the sealing agent and has to be shaped 
corresponding to the sealing agent to be employed. The above-explained 
structure of separate plural liquid chambers allow to supply different 
inks to the ink discharge openings. 
FIG. 27 shows the structure of an integral 4-head ink jet cartridge (IJC) 
in which the recording heads of four colors C, M, Y, K are integrally 
assembled by a frame 3000. Inside said frame 3000, the four recording 
heads are mounted with a predetermined mutual distance, and are fixed with 
the arrays of the ink discharge openings adjusted in the vertical and 
horizontal positions. There are also shown a frame cover 3100, and a 
connector 3200 for supplying the pads, provided on the wiring boards 200 
of the four recording heads with the electrical signals from the main body 
of the apparatus. 
FIG. 28 shows the state of the integral 4-head ink jet cartridge mounted on 
the carriage 623. Each ink tank is divided into upper and lower chambers, 
which are respectively filled with the inks of higher and lower densities. 
On said carriage, the ink jet cartridge (IJC) and the four ink tanks (IT) 
of C, M, Y and K colors are coupled by pressurized contact, whereby each 
ink is supplied from the corresponding ink tank to the recording head. 
Also in this embodiment, a diode sensor is provided on the heater board 100 
as temperature detection means for the recording heads. As explained in 
the foregoing, the temperature detection means is not particularly limited 
to such form, and the temperature may be detected by other detectors such 
as a thermistor, or may be estimated by calculation from the duty ratio of 
the printed dots. 
FIG. 29 is a block diagram of the image signal processing system, wherein 
an image processing circuit 651 includes masking and UCR (undercolor 
removal), and any commonly used image processing flow is applicable 
thereto. 
The C, M, Y and K data after image processing are fetched by a succeeding 
density distribution unit 652. In the present embodiment, according to the 
temperature data from the temperature sensor 658 of the recording head, an 
optimum one is selected from the plural density distribution tables 
prepared in advance, and the input data are distributed to the data for 
the light-colored ink and those for the dark-colored ink, according to 
thus selected distribution table. 
FIG. 30A shows an example of the distribution table for a low head 
temperature, while FIG. 30B shows an example of the distribution table for 
a high head temperature. 
These examples will be explained in the following, in comparison with the 
distribution table shown in FIG. 21. 
As the discharge amount is low for a low head temperature, the output data 
for the dark- and light-colored inks are increased for a given input data 
as shown in FIG. 30A thereby elevating the image density. Since the output 
data for the dark-colored ink are already saturated in a high level area 
(around 255) of the input data, the data for the light-colored ink are 
further added for elevating the image density. 
As the discharge amount becomes higher at a high head temperature, the 
output data are made lower, than in the standard state shown in FIG. 21, 
for a given input level in order to suppress the image density as shown in 
FIG. 30B. The switching of the distribution table in this manner according 
to the temperature of the recording head allows to always obtain a 
constant image density even in the presence of a temperature-dependent 
variation in the ink discharge amount, thereby enabling to realize an ink 
jet recording apparatus with satisfactory tonal rendition. 
The method of distribution of the input data into the data of the 
light-colored ink and those of the dark-colored ink based on the 
distribution table is same as in the embodiment 5. Based on the 
distribution table selected according to the temperature of the recording 
head, the input C, M, Y, K data are distributed into the data for the 
light-colored inks (C', M', Y', K') and those for the dark-colored inks 
(C", M", Y", K"), which are respectively binarized by binarizing circuits 
654, 655 shown in FIG. 29 and are supplied, in the form of on/off data 
(1-bit signals) to the respective recording heads. 
The present embodiment also enables to always reproduce a constant tonal 
density rendition regardless of the temperature of the recording heads, 
and can simplify the process by averaging the temperatures of the 
recording heads for the light- and dark-colored inks. 
However, in case the inks of different densities are dividedly used within 
a recording head, as in the present embodiment, the temperatures of the 
heads for the light- and dark-colored inks may become not considerable as 
an average when the number of the discharge openings increases. In such 
case, the distributed data for each ink may be corrected according to the 
temperature detected independently in each ink area. Also the recording 
head, which is internally divided into plural ink areas as in the present 
embodiment, may be combined with the image signal processing system 
employed in the embodiment 5, in which the data for the dark- and 
light-colored inks distributed by a distribution table are corrected 
according to the head temperature. 
The configuration containing the arrays of the discharge openings for the 
inks of different densities within a single head enables to limit the 
number of recording heads, thereby achieving compactization of the 
apparatus. 
The foregoing embodiment has been explained by a 4-color ink Jet recording 
apparatus employing cyan, magenta, yellow and black colors, but the number 
of colors is not limited to such embodiment and the present invention is 
likewise applicable to a recording apparatus employing the inks of 
different densities of a single color or plural colors of a different 
number. Also the dye concentration of the ink is not limited to two levels 
of high and low, but may be selected in three or more levels. If the dot 
density is significantly different between the inks of high and low 
densities, the tonal reproduction does not become linear in a portion 
where the inks of high and low densities are switched, and there may 
easily result a pseudo contour. Also in such ink switching portion, there 
may result a variation in the granularity or in the hue of the recorded 
image, thus giving an unnatural impression. It is therefore preferable to 
effect the recording operation with an increased number of densities of 
the ink, for example low, medium and high densities. 
Other Embodiments 
For controlling the ink discharge amount of the ink jet recording head, 
there has been proposed the PWM (pulse width modulation) control. Said PWM 
control method will be explained in detail in the following, with 
reference to the attached drawings. FIG. 31 is a view for explaining the 
divided pulses, wherein Vop indicates a driving voltage; P1 indicates the 
pulse width of an initial pulse (hereinafter called pre-pulse) of divided 
plural heating pulses; P2 is an interval time; and P3 is the pulse width 
of a second pulse (hereinafter called main pulse). T1, T2 or T3 indicates 
the time for defining P1, P2 or P3. The driving voltage Vop is a factor 
determining the electric energy required for generating the thermal energy 
by the electrothermal converting element provided in the ink path, and is 
determined by the area, resistance and film structure of said 
electrothermal converting element and by the structure of the ink flow 
path. There stand relationships P1=T1, P2=T2-T1 and P3=T3-T2. 
The PWM control of the present embodiment may also be named as pre-pulse 
width modulation control, in which, for the discharge of an ink droplet, 
the pulses are given in succession with widths P1, P2 and P3, and the 
width of the pre-pulse is modulated according to the temperature of the 
recording head or of the ink. Said pre-pulse is used principally for 
controlling the ink temperature in the liquid path, and has an important 
role in the discharge amount control. The width of said pre-pulse is 
preferably selected at such level as not to form a bubble in the ink,, by 
the energy generated by the electrothermal converting element in response 
to said pre-pulse. The interval time is to secure a time for transmission 
of the energy, generated by said pre-pulse, to the ink in the liquid path. 
The main pulse serves to generate a bubble in the ink present in the 
liquid path, thereby discharging the ink from the discharge opening, and 
its width is preferably determined according to the area, resistance and 
film structure of the electrothermal converting member and the structure 
of the liquid path. 
FIG. 32 is a chart showing the dependence of the discharge amount on the 
width of the pre-pulse, wherein V0 indicates the discharge amount at P1=0, 
which is determined by the head structure. 
As indicated by a curve a in FIG. 32, in response to the increase of the 
width P1 of the pre-pulse, the discharge amount Vd increases linearly 
within a range of said width P1 from 0 to P1LMT. Beyond said level P1LMT, 
the discharge amount loses linearity in the increase, and becomes 
saturated at a pulse width P1MAX. 
The range up to the pulse width P1LMT, in which the discharge amount Vd 
varies linearly in response to the variation of the pulse width P1, is 
effective for the discharge amount control by the variation of the pulse 
width P1. 
If the pulse width becomes larger than P1MAX, the discharge amount Vd 
becomes smaller than the maximum value VMA. This is due to a phenomenon 
that, by the application of a pre-pulse of a width in the above-mentioned 
range, small bubbles are formed on the electrothermal converting member 
and, the next main pulse being applied before said small bubbles vanish, 
said small bubbles disturb the bubble generation by said main pulse, 
thereby suppressing the discharge amount. Such range is called 
pre-bubbling range, in which the discharge amount control by the pre-pulse 
width becomes difficult. In the range P1-0 to P1LMT in FIG. 32, the slope 
of the linear portion is defined as the pre-pulse dependence coefficient 
which is represented by: 
EQU Kp=.DELTA.Vop/.DELTA.P1 
which is not dependent on the temperature but is determined by the head 
structure, driving conditions, physical properties of the ink etc. In FIG. 
32, curves b, c show the variations in other recording heads, indicating 
that the discharge characteristics are specific to the recording head. 
On the other hand, another factor determining the discharge amount of the 
ink jet recording head is the ink temperature of the discharge part (said 
temperature being sometimes replaceable by the temperature of the 
recording head). FIG. 33 shows the temperature dependence of the discharge 
amount. As indicated by a curve a therein, the discharge amount Vd 
linearly increases as a function of the temperature TH of the recording 
head. The slope of said line is defined as the temperature dependence 
coefficient, which is given by: 
EQU KT=.DELTA.Vdt/.DELTA.TH. 
This coefficient is independent from the driving conditions but is 
determined by the head structure, physical properties of the ink etc. Also 
in FIG. 33, curves b, c indicate the behaviors of other recording heads. 
FIG. 34 shows an actual control chart, incorporating the relations shown in 
FIGS. 32 and 33. In FIG. 34, T0 indicates the maintained temperature of 
the recording head. If the ink temperature at the discharge portion is 
lower than T0, the recording head is heated with a sub heater (not shown). 
Consequently the discharge amount control according to the ink temperature 
is conducted above said temperature T0. In FIG. 34, the discharge amount 
can be stabilized within a temperature range indicated as the PWM control 
range, and there is shown the relation between the discharge amount and 
the ink temperature at the discharge portion when the pre-pulse width is 
varied in 11 steps. Even in the presence of a variation in the ink 
temperature at the discharge portion, the discharge amount can be 
controlled within a width .DELTA.V around the target discharge amount Vd0, 
by varying the width of the pre-pulse for each temperature step of AT of 
the ink temperature. However, even with this PWM control, the discharge 
amount cannot be stabilized in a temperature range beyond the upper limit 
temperature TL of the PWM control. 
In the present embodiment, therefore, the discharge amount is regulated by 
heating with the sub heater, if the temperature of the recording head is 
lower than T0. Then, within a temperature range from T0 to T1, the 
discharge amount is regulated by the PWM control. In a temperature range 
beyond TL wherein the discharge control by such PWM control becomes 
impossible, the distributed data for the inks of different densities are 
corrected as explained in the foregoing embodiments 1 and 2. In this 
manner the tonal reproduction of the recorded image is improved, whereby 
an image without unevenness in the density can be obtained. 
As explained in the foregoing, the present invention, through the 
combination with the PWM discharge amount control, can improve the tonal 
rendition over a wider temperature range. 
Also in case of preparing plural distribution tables, the present 
embodiment can reduce the number thereof in comparison with the embodiment 
1 or 2, because a situation of low temperature need not be considered. 
As detailedly explained in the foregoing, the present invention is to 
detect the temperature relative to the recording head, to distribute the 
image data to plural sets of data respectively corresponding to plural 
kinds of inks, according to the detected temperature data, and to form an 
image on a recording medium by means of said recording head, based on thus 
distributed data, thereby being capable of providing the desired recorded 
image density even in the presence of a variation in the temperature of 
the recording head, and significantly improving the tonal reproducibility. 
The foregoing embodiments employ the ink jet recording head for recording, 
but such embodiments are not limitative and the present invention is 
applicable also, for example, to a thermal head or a thermal transfer 
head. 
Among various ink jet recording methods, the present invention brings about 
a particular effect when applied to a recording head of a system utilizing 
thermal energy for forming a flying liquid droplet for recording, and a 
recording apparatus utilizing such recording head. 
The principle and representative configuration of said system are 
disclosed, for example, in the U.S. Pat. Nos. 4,723,129 and 4,740,796. 
This system Is applicable to so-called on-demand recording or continuous 
recording, but is particularly effective in the on-demand recording 
because, in response to the application of at least a drive signal 
representing the recording information to an electrothermal converter 
element positions corresponding to a liquid channel or a sheet containing 
liquid (ink) therein, said element generates thermal energy capable of 
causing a rapid temperature increase exceeding the nucleate boiling point, 
thereby inducing film boiling on a heat action surface of the recording 
head and thus forming a bubble in said liquid (ink), in one-to-one 
correspondence wit h said drive signal. Said liquid (ink) is discharged 
through a discharge opening by the growth and contraction of said bubble, 
thereby forming at least a liquid droplet. Said drive signal is preferably 
formed as a pulse, as it realizes instantaneous growth and contraction of 
the bubble, thereby attaining highly responsive discharge of the liquid 
(ink). 
Such pulse-shaped drive signal is preferably that disclosed in the U.S. 
Pat. Nos. 4,463,359 and 4,345,262. Also the conditions described in the 
U.S. Pat. No. 4,313,124 relative to the temperature increase rate of said 
heat action surface allows to obtain further improved recording. 
The configuration of the recording head is given by the combinations of the 
liquid discharge openings, liquid channels and electrothermal converter 
elements with linear or rectangular liquid channels, disclosed in the 
above-mentioned patents, but a configuration disclosed in the U.S. Pat. 
No. 4,558,333 in which the heat action part is positioned in a flexed 
area, and a configuration disclosed in the U.S. Pat. No. 4,459,600 also 
belong to the present invention. 
Furthermore the present invention is effective in a structure disclosed in 
the Japanese Patent Laid-open Application No. 59-123670, having a slit 
common to plural electrothermal converter elements as a discharge opening 
therefor, or in a structure disclosed in the Japanese Patent Laid-open 
Application No. 59-138461, having an aperture for absorbing the pressure 
wave of thermal energy, in correspondence with each discharge opening. 
A full-line type recording head, capable of simultaneous recording over the 
entire width of the recording sheet, may be obtained by plural recording 
heads so combined as to provide the required length as disclosed in the 
above-mentioned patents, or may be constructed as a single integrated 
recording head, and the present invention can more effectively exhibit its 
advantages in such recording head. 
The present invention is furthermore effective in a recording head of 
interchangeable chip type, which can receive ink supply from the main 
apparatus and can be electrically connected therewith upon mounting on 
said main apparatus, or a recording head of cartridge type in which an ink 
cartridge is integrally constructed with the recording head. 
Also the recording apparatus is preferably provided with the discharge 
recovery means and other auxiliary means for the recording head, since the 
effects of the recording head of the present invention can be stabilized 
further. Examples of such means for the recording head include capping 
means, cleaning means, pressurizing or suction means, preliminary heating 
means composed of electrothermal converter element and/or another heating 
device, and means for effecting an idle ink discharge independent from the 
recording operation, all of which are effective for achieving stable 
recording operation. 
Furthermore, the present invention is not limited to a recording mode for 
recording a single main color such as black, but is extremely effective 
also to the recording head for recording plural different colors or full 
color by color mixing, wherein the recording head is either integrally 
constructed or is composed of plural units. 
In the foregoing embodiments of the present invention, the ink is assumed 
to be liquid, but the present invention is also applicable to the ink 
which is solid below room temperature but softens or liquefies at room 
temperature, or which softens or liquefies within a temperature control 
range from 30.degree. C. to 70.degree. C., which is ordinarily adopted in 
the ink jet recording. Thus the ink only needs to be liquid when the 
recording signal is given. 
Furthermore, the present invention is applicable to ink liquefied by 
thermal energy provided corresponding to the recording signal, such as the 
ink in which the temperature increase by thermal energy is intentionally 
absorbed by the state change from solid to liquid, or the ink which 
remains solid in the unused state for the purpose of prevention of ink 
evaporation, or the ink which starts to solidify upon reaching the 
recording sheet. In these cases the ink may be supported as solid or 
liquid in recesses or holes of a porous sheet, as described in the 
Japanese Patent Laid-open Application Nos. 54-56847 and 60-71260, and 
placed in an opposed state to the electrothermal converter element. The 
present invention is most effective when the above-mentioned film boiling 
is induced in the ink of the above-mentioned forms. 
Furthermore, the recording apparatus of the present invention may be 
constructed, not only as an integral or separate image output terminal for 
an information processing equipment such as a word processor or a 
computer, but also as a copying apparatus combined with an image reader or 
a facsimile apparatus having the function of transmission and reception. 
FIG. 35 is a block diagram showing the schematic configuration, when the 
ink jet recording apparatus of the present invention is applied to an 
information processing apparatus having the functions of word processor, 
personal computer, facsimile apparatus and copying apparatus, wherein 
provided are a control unit 1201 for controlling the entire apparatus, 
provided with a CPU such as a microprocessor and various I/O ports and 
effecting the control by sending control signals and data signals to 
various units and receiving control signals and data signals therefrom; a 
display unit 1202 for displaying various menus, document information and 
image data read by an image reader 1207; and a transparent 
pressure-sensitive touch panel 1203 provided on said display unit 1202 and 
serving for the input of an item displayed on the display unit 1202 or the 
input of coordinates, by a finger pressure applied thereon. 
An FM (frequency modulation) sound source unit 1204 reads the sound 
information, prepared for example by a music editor and stored in a memory 
1210 or an external memory 1212 in the form of digital data, and effects 
frequency modulation. The electrical signal from said FM sound source is 
converted into audible sound by a loudspeaker 1205. A printer unit 1206 
embodies the recording apparatus of the present invention, as an output 
terminal for the word processor, personal computer, facsimile and copying 
apparatus. 
An image reader 1207, for photoelectrically reading the original data, is 
positioned in the transport path of the originals, and reads the originals 
for facsimile transmission, for copying and for other purposes. A 
facsimile transmission/reception unit 1208 for effecting facsimile 
transmission of the original data read by the image reader 1207, and 
reception and decoding of the received facsimile signal, has the function 
of interfacing with the external line. A telephone unit 1209 has various 
telephone functions including the ordinary telephone functions and the 
message telephone function. A memory unit 1210 includes a ROM for storing 
a system program, a managing program and other application programs, a 
character font and a dictionary, a RAM for storing application programs 
loaded from the external memory 1212 and character information, and a 
video RAM. 
A keyboard unit 1211 serves for entering document information and various 
commands. An external memory 121, employing a floppy disk or a rigid disk 
as the memory medium, is used for storing character information, music or 
sound information, application programs of the user etc. 
FIG. 36 is an external view of the information processing apparatus shown 
in FIG. 35. A flat panel display 1301 is used for displaying various 
menus, pattern information and document information. On said display 1301 
there is provided a touch panel, for entering the coordinates or various 
items, by pressing for example with a finger. A handset 1302 is used when 
the apparatus functions as a telephone set. 
A keyboard 1303, provided with various function keys 1304, is detachably 
connected to the main body through a cord, and serves for entering various 
character information and various data. An insertion slot 1305 for the 
floppy disk is provided. 
A sheet stacker 1307 is used for stacking the originals to be read by the 
image reader 1207, and the originals after image reading are discharged 
from the rear part of the apparatus. An ink Jet printer 1306 is provided 
for image recording for example in the facsimile reception. 
The above-mentioned display 1301 may be composed of a cathode ray tube, but 
is preferably composed of a flat panel display such as liquid crystal 
display utilizing ferroelectric liquid crystal, because such flat panel 
display can achieve compactization, a smaller thickness and a lighter 
weight. In the use of the above-explained information processing apparatus 
as a personal computer or a word processor, the information entered from 
the keyboard 1211 shown in FIG. 35 is processed in the control unit 1201 
according to a predetermined program, and the result is released as an 
image from the printer unit 1206. Also in the function as a facsimile 
reception unit, the facsimile information supplied through a communication 
channel to the facsimile transmission/reception unit 1208 is processed in 
the control unit 1201 according to a predetermined program, and the result 
is released as a received image from the printer unit 1206. 
Also in the function as a copying apparatus, the original is read by the 
image reader 1207, and the read original data are supplied through the 
control unit 1201 and released as a copy image from the printer unit 1206. 
Also in the function as a facsimile transmitter, the original data read by 
the image reader 1207 are subjected to a transmission process by the 
control unit 1201 according to a predetermined program, and the result is 
transmitted to the communication channel through the facsimile 
transmission/reception unit 1208. The above-explained information 
processing apparatus may also be constructed as an integral unit 
incorporating the ink jet printer as shown in FIG. 37, for achieving 
improved portability. In FIG. 37, components equivalent to those in FIG. 
36 are represented by same numbers. 
The application of the recording apparatus of the present invention to the 
multi-function information processing apparatus explained above allows to 
obtain a recorded image of higher quality, whereby the functions of said 
information processing apparatus can be further improved. 
As detailedly explained in the foregoing, the present invention, in 
recording on a recording medium by discharging ink from discharge openings 
of a recording head utilizing plural inks of different densities of a same 
color, if stable discharge becomes difficult in at least one of said 
plural inks, switches a distribution table so as to effect the recording 
operation with the ink of the remaining kind, thereby providing a proper 
image. 
Also the present invention detects the temperature relative to a recording 
head, distributes the image data to plural sets of data, respectively 
corresponding to the plural inks and also corresponding to the detected 
temperature data, and forms an image on a recording medium with said 
recording head, based on thus distributed data. It is therefore rendered 
possible to obtain a desired recorded image density even in the presence 
of a variation in the temperature of the recording head, thereby 
significantly improving the total reproducibility.