Recording apparatus and method for correction of discharge failure and density unevenness

A recording apparatus records an image by scanning a first recording head relative to a recording medium of a particular type. The apparatus includes the first recording head, a pattern recording controller, a reader, a restoring device, a second recording head, a discriminator and a control unit. The pattern recording controller controls recording of a predetermined pattern with the first recording head at a predetermined timing either on the recording medium or on a pattern recording medium different from the recording medium. The reader reads the predetermined pattern and the restoring device performs a discharge restoring operation of the recording head. The discriminator discriminates a recording state of the first recording head, based on the predetermined pattern read by the reader. The control unit enables the second recording head to record the image to be recorded by the first recording head, in a case that after the discriminator discriminates the recording state as being poor and thereafter the discharge restoring operation performed by the restoring device and a pattern recording operation by the pattern recording controller have been executed a predetermined number of times, the discriminator has discriminated the recording state as being still poor.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a recording apparatus for forming an image 
according to an image signal or an original image, and more particularly 
to an ink jet recording apparatus. 
2. Related Background Art 
Among various recording apparatuses already known, the ink jet recording 
apparatus is attracting particular attention for full color image 
formation, because such apparatus, which forms dot records by discharging 
ink droplets from nozzles of a recording head, is advantageous in it's 
configuration and in the running cost. In this recording method, the 
recording is generally achieved by scanning motions of the recording head, 
having a nozzle array of a certain width (for example about 16 mm) in 
longitudinal and transversal directions relative to a recording material. 
However, because of eventual fluctuations in the amount and direction of 
ink discharge among the nozzles of the ink jet recording head, there are 
formed streaks on the recorded image. For this reason, the recorded image 
shows cyclic streaking unevenness with a pitch corresponding to the width 
of the recording head, thus deteriorating the image quality. Also 
variation of such unevenness in time is another drawback. 
Also eventual deposition of dusts or solidified ink on the nozzles of the 
recording head hinders proper ink discharge from the nozzles (hereinafter 
called discharge failure), thus causing a line-shaped defect on the 
recorded image and deteriorating the image quality. 
In order to prevent such unevenness of the recording head, so-called head 
shading, there is already commercialized a recording apparatus in which a 
predetermined pattern is printed and said unevenness is corrected by 
reading the printed pattern visually or by a reader. 
However, in such apparatus, since said correction is manually conducted by 
the operator, the correcting operation depends on the discretion of the 
operation and may not be executed properly. Also no sufficient measures 
are provided for the discharge failures. 
It is desired to constantly detect such phenomena deteriorating the image 
quality and to effect suitable correction. Particularly in case of 
employing a long web-shaped recording material, the recording operation 
may be conducted continuously on a very long recording material of 100 
meters or longer, so that the unevenness resulting from discharge failure 
during such recording operation poses a serious problem. In case said 
web-shaped recording material is composed of woven fabric, the probability 
of such discharge failure is significantly higher than in the ordinary 
recording paper, particularly coated paper, because fine fiber dusts tend 
to deposit on or in the vicinity of the nozzles of the recording head. 
SUMMARY OF THE INVENTION 
In consideration of the foregoing, an object of the present invention is to 
provide a recording apparatus capable of constantly providing stable 
recorded images with a simple structure. 
Another object of the present invention is to provide a recording apparatus 
capable of stable recording on a web-shaped recording medium. 
Still another object of the present invention is to provide a recording 
apparatus capable of stable recording on a recording medium with a rough 
surface such as woven fabric. 
The above-mentioned objects can be attained, according to the present 
invention, by a recording apparatus capable of forming an image by 
scanning motions of a recording head relative to a recording medium, 
comprising pattern recording means for recording a predetermined pattern 
by said recording head at a predetermined interval, reader means for 
reading said predetermined pattern recorded by said pattern recording 
means, discrimination means for discriminating the recording state of said 
recording head, based on the predetermined pattern read by said reader 
means, and control means for controlling said recording head according to 
the result of discrimination by said discrimination means. 
The recording apparatus of the present invention, having the 
above-explained configuration, is capable of preventing the deterioration 
of image quality by suitably checking the unevenness or discharge failure 
of the recording head and effecting unevenness correction or discharge 
recovery operation, or requesting the operator to replace the recording 
head.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Now the present invention will be clarified in detail by preferred 
embodiments thereof shown in the attached drawings. 
FIG. 1 is a cross-sectional view of a recording apparatus of the present 
invention, wherein shown are a main body 1; a roll 2 of web-shaped 
recording material (medium); a cutter 4 for cutting the recording material 
into a predetermined length; paired transport rollers 3, 5 for 
transporting the recording material in a predetermined direction; and a 
sub scanning roller 6 for positioning the recording material by precisely 
transporting the same by an amount corresponding to the recording width of 
a recording head to be explained later. The above-mentioned components 
constitute a transport path for the recording material supplied from the 
roll 2. 
There are further provided a cassette 7 for storing sheet-shaped recording 
materials; guide members 8 for guiding the recording material from the 
cassette 7 into the transport path from said roll 2, immediately in front 
of the transport rollers 5; a carriage 9 bearing a recording head (not 
shown) and movably supported by a pair of main scanning rails 9a in a 
direction perpendicular to the plane of the drawing; and a platen member 
10 positioned opposite to said carriage 9 across the recording material 
and provided with suction means that operates for example, by air suction 
or electrostatic suction, in order to maintain the recording material in 
flat state and to prevent the recording material from contacting the 
recording head during the recording operation. 
In the following there will be explained related mechanisms, with reference 
to FIG. 2. 
The carriage 9 is provided with recording heads 9C, 9M, 9Y, 9Bk 
respectively corresponding to cyan, magenta, yellow and black colors. An 
ink supply system 11 for supplying said recording heads with inks is 
provided with ink cartridges 11C, 11M, 11Y, 11Bk respectively 
corresponding to said colors. Inks are supplied to said recording heads, 
by means of unrepresented pumps, through tubes 12C, 12M, 12Y, 12Bk. A 
motor 13 drives the carriage 9 in the main scanning direction (lateral 
direction in the drawing), by means of a pulley 14 fixed to said motor 13, 
another pulley 15 and a belt 16. A motor 17 drives the ink supply system 
11 in the main scanning direction, in synchronization with the carriage 9, 
by means of a pulley 18 fixed to said motor 17, another pulley 19 and a 
belt 20. 
A recording material 22, composed for example of paper in the rolled or cut 
state as explained above, is transported upwards by the transport rollers 
5 and the sub scanning roller 6. A cap member 23 is provided at a position 
for effecting an operation for eliminating the causes of image quality 
deterioration (hereinafter called discharge recovery operation). Said cap 
member 23 serves to cover the nozzle faces of the recording heads 9C, 9M, 
9Y, 9Bk, and the ink is discharged or pushed out from the nozzles in such 
capped state, by activation or pressurization of the recording heads. At 
the same time high-speed air flow is directed toward the nozzle faces of 
the recording heads in the cap member 23, thus blowing off thus expelled 
ink and dusts from the nozzle faces, and eliminating the discharge failure 
and unevenness. 
A monitor 31, for monitoring the recording state of the recording heads, 
reads a predetermined pattern (of uniform density), printed at a 
predetermined interval on the right-end margin of the recording material 
22. 
FIG. 3 shows the details of said monitor 31. A calibration pattern 32, 
containing each of cyan, magenta, yellow and black colors in uniform 
density and by a scanning line, is printed at a predetermined interval at 
an end margin of the recording material 22. There are also provided a pair 
of lamps 33 for illuminating said calibration pattern 32; a projection 
lens 34 for projecting the image of said pattern 32 illuminated by the 
lamps 33; and a sensor 35, such as a CCD, for photoelectrically converting 
the image of the calibration pattern 32 projected by said lens 34. The 
number of elements in said sensor is preferably at least equal to that of 
the recording elements in the recording head. The output of said sensor 35 
is used for detecting the presence of discharge failure in the recording 
head and whether the unevenness of printing exceeds a predetermined level, 
and the aforementioned discharge recovery operation is conducted if 
necessary. 
Now the normal recording sequence will be explained with reference to FIGS. 
1 and 2. Referring to FIG. 1, when a recording material sensor (not shown) 
positioned in front of the transport rollers 5 detects a recording 
material fed from the roll 2 or the cassette 7, the transport rollers 5 
and the sub scanning roller 6 advances the recording material by a 
predetermined amount, until the leading end thereof reaches the sub 
scanning roller 6. 
When the leading end of the recording material 22 reaches the sub scanning 
roller 6 in FIG. 2, the carriage 9 and the ink supply system 11 are 
respectively driven by the motors 13, 17 in the scanning direction (to the 
right in FIG. 2). At the same time, the recording heads 9C, 9M, 9Y, 9Bk 
effect recording with a width I, according to image signals. 
After recording of a line, the carriage 9 and the ink supply system 11 are 
returned to a predetermined position at the left side in FIG. 2, and the 
recording material 22 is simultaneously advanced by the motor 21, by an 
amount precisely corresponding to said printing width I. 
After the above-explained sequence of recording and recording material 
transportation by a predetermined number of cycles, the recording material 
22 is discharged from the apparatus. 
In the following an explanation will be given on the monitor 31. FIG. 4 
shows the output signal of the sensor 35 of said monitor 31, wherein the 
abscissa corresponds to the pixels of said sensor 35, while the ordinate 
indicates the output of each pixel. The output of the sensor 35 is 
subjected to so-called shading correction, utilizing the recording 
material before printing as the white level. Since each pixel output 
corresponds to each nozzle of the recording head, the amount of ink 
discharge from each nozzle can be determined. 
A discharge failure is identified if the output signal becomes larger, even 
in one position, than a slice level b which is larger by a predetermined 
amount than the average pixel output a. Also large unevenness is 
identified if the output signal becomes larger than a slice level c which 
is larger by a predetermined amount than said average a or becomes smaller 
than a slice level d which is smaller by a predetermined amount than said 
average a. Empirically, the slice level b for detecting the discharge 
failure is preferably larger, by about 50%, than the average a, while the 
slice levels c, d for unevenness detection are preferably different, by 5 
to 10%, from the average a. 
However, the detection of level of unevenness is not limited to such 
method. There may instead be employed, for example, a method of 
calculating the standard deviation of the pixel outputs of the sensor and 
evaluating the level of unevenness from the magnitude of said standard 
deviation, or a method of calculating the sum A of absolute difference of 
adjacent pixels (A=.SIGMA..vertline.a.sub.i -a.sub.i+1 .vertline.) and 
evaluating said level by the magnitude of said sum A. 
For the purpose of unevenness correction, the pixel output values of the 
sensor 35, corresponding to the nozzles of the recording head, may be 
employed. However, in order to reduce the influence of noises etc., it is 
also possible to employ the average value of mutually adjacent pixels, for 
example three adjacent pixels of the sensor. 
Now reference is made to FIG. 5 for explaining a calibration sequence for 
detecting the discharge failure and unevenness and effecting the discharge 
recovery operation. As explained in the foregoing, in a series of 
recording sequences, the calibration patterns are printed at a 
predetermined interval (step S1). Said calibration pattern is read by the 
monitor 31 (step S2), and the presence of discharge failure is 
discriminated by the algorithm explained above (step S3). 
If a discharge failure is identified, there is discriminated whether or not 
to effect the recovery operation (step S4). The discrimination in the step 
S4 depends on whether the recovery operation is already conducted in this 
sequence. This is based on an empirical fact that most discharge failures 
are resolved if the aforementioned discharge recovery operation is 
properly conducted. After said discharge recovery operation (step S5), the 
sequence returns to the step S1 for calibration pattern printing, step S2 
for pattern reading and step S3 for discrimination of the discharge 
failure. If the step S4 again identifies the discharge failure, the 
recovery operation is not conducted, but an alarm for a head trouble is 
given and the operation of the apparatus is interrupted (step S6). 
On the other hand, if the step S3 identifies the absence of discharge 
failure, there is discriminated the absence of unevenness, according to 
the unevenness discriminating algorithm explained before (step S7). If the 
unevenness is identified absent, the recording operation is continued 
(step S12). On the other hand, if the step S7 identifies that the 
unevenness is equal to or larger than a predetermined level, there is 
discriminated whether to effect the unevenness correction operation (step 
S8), and there is conducted the unevenness correction (step S9). The 
unevenness correction in the step S9 is conducted, based on the output 
signal of the pattern read in the step S2, by correcting the drive signal 
(signal duration or voltage) of the required nozzles of the recording 
head. Then a pattern of uniform density, same as printed in the step S1, 
is printed (step S10), and the printed pattern is read by the monitor 31 
(step S11). 
The above-mentioned steps S7, S8, S9, S10 and S11 are repeated by a 
predetermined number of cycles (three times in the present embodiment), 
and, if the level of unevenness is still high, an alarm for a head trouble 
is given and the operation of the apparatus is interrupted (step S6). This 
is based on an empirical fact that this unevenness correcting sequence 
generally provides a practically sufficient effect after three cycles 
though the effect becomes still enhanced with a further increased number 
of cycles, while a significant unevenness after three correcting cycles is 
mostly caused by a trouble based in the recording head, such as the 
expired service life thereof. 
The discharge state of the recording heads can be maintained in 
satisfactory manner, by conducting the above-explained calibration 
sequence for each of the cyan, magenta, yellow and black colors. 
Consequently the working rate of the apparatus can be improved even in the 
unmanned state, and such measure is particularly effective in case of 
using continuous web-shaped recording medium. 
In the present embodiment, the recording material is assumed to be ordinary 
paper, but similar effects can also be obtained for other recording 
materials such as woven fabric. 
In the following there will be explained a second embodiment of the present 
invention shown in FIG. 6, wherein components equivalent to those in the 
first embodiment shown in FIG. 2 are represented by same numbers. 
This embodiment is featured by the presence of a recording material 
exclusive for calibration pattern printing. At an end of the platen 10, 
there is provided a recording material 41 exclusive for monitoring, 
supplied from a roll 42 and taken up, after printing, on a roll 43. The 
sequences of printing and calibration in the present embodiment will not 
be explained further, as they are same as in the first embodiment. 
This embodiment, enabling recording on the entire area of the recording 
material without any margin therein, avoids waste of the recording 
material and is particularly effective for long continuous recording. 
In the following there will be explained a third embodiment of the present 
invention. The cross-sectional structure of the apparatus of this 
embodiment will not be explained as it is basically the same as that of 
the first embodiment shown in FIG. 1. FIG. 7 is a perspective view of a 
recording head and related mechanisms of the present embodiment, wherein 
components equivalent to those in FIG. 2 are represented by same numbers. 
The carriage 9 is provided with the recording heads 9C, 9M, 9Y, 9Bk 
respectively corresponding to cyan, magenta, yellow and black colors. The 
ink supply system 11, for ink supply to said recording heads, is provided 
with ink cartridges 11C, 11M, 11Y, 11Bk respectively corresponding to said 
colors. The ink supply is conducted, when the carriage is in a chain-lined 
position 26 (hereinafter called ink supply position), from said system 11 
to sub tanks (not shown) of the carriage 9 by unrepresented pumps, as will 
be explained later in more detail. 
A reserve carriage 25, same in structure as the carriage 9, also receives 
the ink supply from the ink supply system 11 at the ink supply position 
26. A motor 13 drives the carriage 9 in the main scanning direction 
(lateral direction in the drawing) by means of a drive pulley 14 fixed to 
said motor, a pulley 15 and a belt 16. A motor 27 drives the reserve 
carriage 25 in said main scanning direction by a drive pulley 28 fixed to 
said motor 27, another pulley 29 and a belt 30. 
Caps 24a, 24b are provided for respectively covering the nozzles of the 
recording heads of the carriage 9 and the reserve carriage 25 at the home 
positions thereof, thereby preventing viscosity increase of the inks. 
Now reference is made to FIG. 8 for explaining the ink supply process. 
There are shown a main tank 45 receiving ink supply from the ink cartridge 
11C; a pump 46 for effecting ink pressurization for discharge recovery for 
the recording head 9C and ink supply to a sub tank 53 provided on the 
carriage; a support member 47 supporting a connector of an ink supply tube 
and moveable laterally by a motor 48 and a feed screw 49; a tube 50 
connecting the pump 46 with the support member 47 and having a connector 
member 50a at an end; a tube 51 provided at an end with a connector member 
51a engageable with said connector member 50a and supplying ink to the 
recording head 9C, said connector member 51a being provided with a valve 
(not shown) which is normally closed and opened only when coupled with the 
connector member 50a; a tube 52 connecting the recording head 9C with a 
sub tank 53 provided on the carriage; a tube 54 for returning the ink, 
overflowing at the ink supply, from the sub tank, having a connector 
member 54a at an end; a tube 55 connecting the support member 47 with the 
main tank 45 and provided at an end with a connector member 55a engageable 
with said connector member 54a; and a valve 56 provided in the tube 55, to 
be closed at the discharge recovery operation for ink pressurization. 
The ink is supplied, with said connector members mutually coupled at said 
ink supply position, by the pump 46 to the tubes 50, 51, recording head 
9C, tube 52, and sub tank 53, and, when the sub tank 53 is filled, the 
overflowing ink is returned to the main tank 55 through the tubes 54, 55. 
In this operation the valve 56 is in the open state. On the other hand, 
the ink pressurization at the discharge recovery operation is conducted, 
also at said ink supply position, with the connector members being 
mutually coupled, by activating the pump 46 with the valve 56 closed, 
whereby the ink pressure in the supply path is elevated to expel the ink 
from the nozzles of the recording head. The ink supply to the recording 
head in the course of actual recording operation is conducted from the sub 
tank 53 through the tube 52. 
The foregoing explanation has been limited to the system for cyan color, 
but a similar system is provided for each of magenta, yellow and black 
colors. Also the reserve carriage 25 has a same structure, and the ink 
supply and discharge recovery are conducted in the ink supply position 
shown in FIG. 7. 
In the following there will be explained the recording sequence of the 
above-explained third embodiment. 
Referring to FIG. 7, when the leading end of the recording material 22 is 
transported to the sub scanning roller, the carriage 9 is driven in the 
scanning direction (to the right in FIG. 7) by the motor 13. At the same 
time the recording heads 9C, 9M, 9Y, 9Bk effect recording with a width I, 
according to image signal. 
After recording of a line, the carriage 9 is returned to a predetermined 
position at the left side, and the recording material 22 is advanced by a 
distance precisely corresponding to the printing width I. The 
above-explained sequence of recording and transportation of recording 
material is repeated for a predetermined number of cycles, and then the 
recording material 22 is discharged from the apparatus. 
Now reference is made to FIG. 9 for explaining the calibration sequence for 
detecting the discharge failure or unevenness and effecting the discharge 
recovery operation in this third embodiment. This sequence is different 
from that of the first embodiment in FIG. 5, in the process when a trouble 
in the recording head is identified. When a trouble in the recording head 
is identified, the step S6 in FIG. 5 provides an alarm display and 
terminates the function of the apparatus. In the present embodiment having 
a reserve recording head as explained above, a step S16 provides the alarm 
for the trouble in the recording head and replaces the recording head by 
activating the reserve carriage 25. 
Thus the present embodiment monitors the unevenness and discharge failure 
in the recording heads, effects correction for unevenness and discharge 
recovery operation when required, and automatically replaces the recording 
heads when recovery is identified as not being possible, thereby 
preventing the deterioration in image quality and avoiding the 
interruption of recording. Thus the working rate of the apparatus can 
further be improved. 
In the present embodiment, the calibration pattern is printed in the margin 
of the recording material 22, but as an alternative it is also possible, 
as in the second embodiment, to provide a small-sized recording material 
41 for said calibration pattern, as shown in FIG. 10, and to print the 
calibration pattern at a predetermined interval. 
Also in the present embodiment, the recording material is assumed to be 
composed of ordinary paper, but similar effects can be obtained on other 
recording materials such as woven fabric. 
Also in the foregoing embodiments, the interval of detection of unevenness 
and discharge failure, or the timing of printing of the calibration 
pattern, is not particularly defined, but such calibrating operation may 
be conducted every line or every certain number of lines. The abnormality 
can be detected on real time basis if the calibration is conducted every 
line. On the other hand, a loss in the recording speed can be prevented by 
conducting the calibration at every certain number of lines. 
Said interval is preferably varied according to the kind of the recording 
material. More specifically, said interval is preferably made shorter for 
a recording material with a rougher surface, such as woven cloth, since 
short fibers tend to adhere around the nozzles of the recording head. 
As explained in the foregoing, the present invention always monitors the 
unevenness and discharge failure of the recording heads, whereby the 
correction for unevenness and the discharge recovery operation can be 
realized in an unmanned state and the deterioration in image quality can 
be prevented. 
Among various ink jet recording systems, the present invention brings about 
a particular effect when applied to a recording head and an ink jet 
recording system utilizing thermal energy for ink discharge. 
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 positioned 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 with 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 a 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 are 
also useable in 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 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 further more 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 emission 
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 an 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.