JPH05124221A - Image forming device and method for adjusting the device - Google Patents

Abstract

PURPOSE:To easily and accurately conduct a registration adjustment and a density unevenness correction in an image forming device performing recording using two or more recording heads each formed by arranging a plurality of recording elements. CONSTITUTION:Predetermined recording elements on recording heads (201C, 201M, 201Y, 201BK) formed by arranging a plurality of recording elements are selected so as to be positionally different per head in an element arrangement direction to form a registration adjusting pattern (TB) in a line form. A density unevenness correcting pattern (TA) is provided for every head. These patterns are read by sensors (217C, 217M, 217Y, 217BK), whereby a registration adjustment and a density unevenness correction are conducted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus and an adjusting method thereof, and more particularly to an image forming apparatus for forming an image using a recording head having a plurality of recording elements arranged therein and an adjusting method thereof. ..

In particular, the present invention relates to an apparatus provided with a mechanism for automatically adjusting the printing characteristics of a recording head of an ink jet recording apparatus, and is particularly effective for an apparatus for forming a color image in high gradation by superposing ink drops.

[0003]

2. Description of the Related Art With the spread of copiers, word processors, computers, and other information processing devices, and communication devices, digital images are recorded using recording heads such as ink jet systems and thermal transfer systems as image forming (recording) devices for these devices. Recorders are rapidly spreading. In such a recording apparatus, a recording head (hereinafter referred to as a multi-head in this section) in which a plurality of recording elements are integrated and arranged is generally used in order to improve the recording speed.

For example, in an ink jet recording head, a so-called multi-nozzle head in which a plurality of ink ejection ports and liquid paths are integrated is generally used, and a plurality of heaters are also integrated in a thermal transfer type or thermal type thermal head. It is normal.

However, due to variations in characteristics due to manufacturing processes, variations in characteristics of head constituent materials, and the like,
It is difficult to uniformly manufacture multi-head recording elements, and the characteristics of each recording element vary to some extent.
For example, in the multi-nozzle head, the shape of the ejection port, the liquid path, and the like vary, and also in the thermal head, the shape and resistance of the heater also vary. Such non-uniformity of characteristics among recording elements appears as non-uniformity in dot size and density recorded by each recording element, which eventually causes uneven density in a recorded image.

To solve this problem, various methods have been proposed in which density unevenness is visually detected, or the adjusted image is visually inspected, and the signal applied to each recording element is manually corrected to obtain a uniform image. Has been done.

For example, in the multi-head 330 in which the recording elements 31 are arranged as shown in FIG. 21 (a), when the input signals to each recording element are made uniform as shown in FIG. When density unevenness such as is visually detected, the input signal is corrected and a large input signal is applied to the recording element in the low density area and a large input signal is applied to the recording element in the high density area as shown in (d). Providing a small input signal is commonly known as manual correction.

In the case of a recording method capable of modulating the dot diameter or the dot density, it is known that gradation recording is achieved by modulating the dot diameter recorded by each recording element according to the input. For example, in an inkjet recording head using a piezo method or a bubble jet method, the drive voltage or pulse width applied to each ejection energy generating element such as a piezo element or an electrothermal conversion element, or the drive voltage or pulse width applied to each heater in a thermal head is used. It is considered that it is possible to make the dot diameters or dot densities of the respective recording elements uniform and the density distribution uniform as shown in FIG. If it is impossible or difficult to modulate the drive voltage or pulse width,
Alternatively, when it is difficult to adjust the density in a wide range even if they are modulated, for example, when one pixel is composed of a plurality of dots, the number of dots to be recorded is modulated according to the input signal, and the low density part On the other hand, a large number of dots can be recorded, and a small number of dots can be recorded in a high density portion. Further, in the case where one pixel is composed of one dot, the dot diameter can be changed by modulating the number of ink ejections (the number of times of ejection) for one pixel in the inkjet recording apparatus. As a result, the concentration distribution can be made uniform as shown in Fig. 21 (e).

Japanese Patent Laid-Open No. 57-41965 filed by the applicant of the present application discloses that a color image is automatically read by an optical sensor and a desired color image is formed by applying a correction signal to each color ink jet recording head. It is disclosed. This gazette discloses basic automatic adjustment, which is an important technical disclosure. However, although various problems become apparent in order to apply it to various device configurations in the course of practical application, no recognition of the technical problem of the present invention is found in this publication.

On the other hand, a method other than the density detection method is disclosed in JP-A-60-
No. 206660, U.S. Pat.No. 4,328,504, JP-A-50-147241 and JP-A-54-27728, the droplet landing positions are automatically read and corrected. It is known that the ball is landed at a precise position. Although these methods are also common as the technique of automatic adjustment, no recognition of the technical problem of the present invention is seen.

[0011]

In order to deal with such a problem, an uneven density reading unit is provided in the image forming apparatus,
It is effective to periodically read the density unevenness distribution in the printing element array range and recreate the density unevenness correction data. According to this, even if the density unevenness distribution of the head changes, the correction data is recreated accordingly, so that it is possible to always maintain a uniform image without unevenness.

However, even if the density unevenness correction data is stored in the memory, it may not be enough to obtain a high-quality image in an apparatus having a plurality of heads. For example, when the heads are replaced, the output characteristics of the recording heads are likely to change immediately after the replacement due to changes in environmental conditions. Therefore, in an apparatus having a plurality of heads, the landing positions of ink droplets with other heads should be adjusted ( The unevenness correction must be performed after the registration adjustment, which is referred to as "registration adjustment" below), which is very time-consuming, and an error occurs depending on the person who makes the adjustment. Even without such replacement, registration adjustment may be necessary for some reason. Therefore, making uneven correction including registration adjustment easy will improve the operability of the apparatus. Is highly desirable.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of performing registration adjustment and unevenness correction easily and accurately and capable of obtaining a high quality image.

[0014]

To this end, the present invention provides
In an image forming apparatus that forms an image using a recording head in which a plurality of recording elements are arranged, a unit that causes the recording head to record a predetermined test pattern, and a reading unit that reads the test pattern formed by the recording head. Means for adjusting registration of the recording head and correcting density unevenness on the basis of the result of the reading.

Further, according to the present invention, in an adjusting method of an image forming apparatus for forming an image using a recording head in which a plurality of recording elements are arranged, the recording head is caused to record a predetermined test pattern, and the recording head is recorded. The test pattern formed by the method is read, and the registration of the recording head is adjusted and the density unevenness is corrected based on the result of the reading.

[0016]

According to the present invention, in an image forming apparatus for recording an image by using two or more recording heads in which a plurality of recording elements are arranged, a test pattern is output separately from a normal image output operation, and the test pattern is output. By performing registration adjustment and density unevenness correction of each head according to the read signal of, it is possible to automate the operation that was previously performed by human eyes for registration adjustment and uneven density adjustment. The correction work can be performed easily and accurately, and a high-quality image can be formed.

[0017]

Embodiments of the present invention will be described in detail below with reference to the drawings in the following procedure.

(1) Mechanical configuration of the apparatus (Figs. 1 to 5) (2) Control system (Figs. 6 to 8) (3) Sequence of unevenness correction (Figs. 9 to 12) (4) Other Embodiments (FIGS. 13 to 20) (5) Others (1) Mechanical configuration of apparatus, etc. FIG. 1 shows an outline of an ink jet recording apparatus in the form of a serial printer according to an embodiment of the present invention. 201C, 201M, 201Y and 201BK are supplied with inks of cyan, magenta, yellow and black from an ink tank (not shown) via ink tubes. Then, the ink supplied to the print heads 201C, 201M, 201Y, and 201BK is driven by a print head driver or the like in response to a print signal according to print information from the main control unit, and ink drops are ejected from each print head. Is ejected and recording is performed on the recording medium 202.

A transport motor 208 is a drive source for intermittently feeding the recording medium 202, and includes a feed roller 204 and a transport roller 20.
The main scanning motor 206 that drives 5 is the main scanning carriage 203.
Is a drive source for scanning in the directions of arrows A and B via the main scanning belt 210. In this embodiment, pulse motors are used for the paper feed motor 208 and the main scanning motor 206 because accurate paper feed control is required.

When the recording medium 202 reaches the feeding roller 205, the feeding roller clutch 211 and the conveying motor 208 are turned on, and the recording medium 202 reaches the conveying roller 204 by the platen.
207 is conveyed. The recording medium 202 is detected by the detection sensor 212 provided on the platen 207, and the sensor information is used for position control, jam control, and the like. Recording medium 202
Reaches the transport roller 204, the feed roller clutch 21
1, the conveyance motor 208 is turned off, and the suction operation is performed from the inside of the platen 207 by a suction motor (not shown) to bring the recording medium 202 into close contact with the platen 207 which is the image recording area. Prior to the image recording operation on the recording medium 202,
Scan carriage 20 at the position of home position sensor 209
3 is moved, then forward scan is performed in the direction of arrow A, and cyan, magenta, yellow, and black inks are ejected from the predetermined positions from the recording heads 201C to 201BK to perform image recording. When the image recording for the predetermined length is completed, the scanning carriage 203 is stopped, and conversely, the backward scanning is started in the direction of arrow B, and the scanning carriage 203 is returned to the position of the home position sensor 209. Recording heads 201C to 201B during the backward scan
The paper feed for the length recorded by K is performed in the direction of arrow C by driving the carry roller 204 by the carry motor 208.

In this embodiment, the recording heads 201C to 201BK are ink jet recording heads of the type in which bubbles are formed by heat and ink droplets are ejected by the pressure of the bubbles.
It uses 4 units, each of which has 256 or more discharge ports assembled with an inch density.

When the scanning carriage 203 stops at the home position detected by the home position sensor 209,
The recovery device 220 recovers the recording head 1. This is a process for performing a stable recording operation, and in order to prevent unevenness at the start of ejection, which is caused by a change in the viscosity of the ink remaining in the ejection port of the recording head 201, the rest time, the temperature in the apparatus, and the ejection The recovery device 220 for the recording head 201 is set according to pre-programmed conditions such as time.
Is a process of performing a suction operation, a preliminary ejection operation of ink, and the like.

In the present embodiment, a case where a density unevenness correction / registration adjustment unit 237 including a test pattern recording unit for recording a test pattern by the recording head and a test pattern reading unit is provided outside the image recording area is shown. ing.

Then, by a control circuit not shown,
When the density unevenness correction command signal of the recording heads is issued, the carriage 203 equipped with each recording head is
After being conveyed to the outside of the recording area to 202 and passing through the part of the sensor 243, each recording head receives a signal from a control circuit (not shown) from the density unevenness correction / registration adjusting unit 237 on the test pattern recording sheet 213. A predetermined test pattern is recorded at a predetermined timing. After recording on the test pattern recording sheet by each recording head,
On the contrary, the carriage 203 carrying the recording head starts backward scanning in the direction of arrow B and is returned to the position of the home position sensor 209.

On the other hand, after a predetermined test pattern for unevenness correction and registration adjustment is recorded on the test pattern recording sheet 213 of the test pattern recording unit, the motor 216 is set after the state of the test pattern stabilizes. Is driven to convey the test pattern recording sheet 213 to the reading section in the D direction.

In this example, the recording density of the test pattern recorded on the sheet 213 by each recording head is read by the reading sensors 217C, 217M, 217Y, 217BK, and the recording heads read by each reading sensor are read. After the read signal of the test pattern recording is converted into a digital signal by the A / D converter 236, the read signal is temporarily stored in the RAM 219.

FIG. 2 is a schematic diagram for explaining the reading unit of the present embodiment. In order to improve the reading accuracy of the density unevenness of the test pattern by the recording head recorded on the recording medium 202, the recording of the illumination light source 218 is performed. Color filter 220 on the medium side
R, 220G and 220BL are provided so that the C, M and Y test patterns recorded on the recording sheet 215 are irradiated with R, G and BL lights. And, like this, C, M,
By irradiating the test pattern of each color of Y with the light of its complementary color, each reading sensor 217C, 217M, 217Y, 217
It is not necessary to make the spectral sensitivity of BK different for each color of the test pattern, and it becomes possible to read the density unevenness of each color while using the sensor of the same spectral sensitivity for each sensor.

In the figure, TA is a pattern formed by applying a uniform signal to eject ink from 256 or more ejection ports in order to correct the density unevenness of each color, and TB is the head of each color. It is a pattern for resist adjustment formed by ejecting ink from one ejection port, and at intervals of 64 ejection ports (4.064 mm), C, M, Y, and BK are the 32nd from the bottom in FIG. Th, 96th, 160th,
Recording is performed at the 224th discharge port.

The image signal read in this way is sent to the image forming section and is used for the correction of the drive condition of the recording head as described later.

In the present invention, the meaning of adjusting the density so that density unevenness does not occur at the time of image formation means to make the image density of the liquid droplets from a plurality of liquid discharge ports of the recording head uniform in the recording head itself, or To make the image density uniform among a plurality of heads, or to make a desired color by mixing a plurality of liquids to obtain a desired color or to obtain a desired density. It includes at least one, and preferably includes satisfying a plurality of these.

As the density uniformization correction means for that purpose,
It is preferable that the reference print giving the correction condition is automatically read and the correction condition is automatically determined, and it is not a matter of adding a manual adjustment device for fine adjustment and user adjustment to this.

The correction purpose determined by the correction condition is
Not only optimum printing conditions, but also adjustment within a predetermined range including an allowable range and reference densities that change according to a desired image may be used, and all that are included in the purpose of correction can be applied.

As an example, a case will be described in which density unevenness correction of a multi-head with the number N of recording elements is performed in which the print output of each element is converged to the average density value for the purpose of correction.

It is assumed that the density distribution when each element (1 to N) is driven by a certain uniform image signal S and printing is performed is as shown in FIG. First, the density of the part corresponding to each recording element OD ₁ ~
OD _N is measured and

[0035]

[Outer 1]

Find The average density is not limited to each element, and may be a method of integrating the reflected light amount to obtain an average value or a known method.

If the relationship between the value of the image signal and the output density of a certain element or a certain element group is as shown in FIG. 4, the signal actually given to this element or this element group is obtained by correcting the signal S to obtain the target density. It suffices to determine the correction coefficient α that brings the bar OD. That is, the correction signal S obtained by correcting the signal S to α × S = (bar OD / OD _n ) × S may be given to this element or group according to the input signal S. Specifically, it is executed by subjecting the input image signal to table conversion as shown in FIG.
In FIG. 5, a straight line A is a straight line having a slope of 1.0 and is a table which outputs an input signal without conversion, but a straight line B is a straight line having a slope α = bar OD / OD _n and the input signal S
Is a table for converting the output signal into α · S.
Therefore, if the head is driven after the table conversion for determining the correction coefficient α _n for each table as shown by the straight line B in FIG. 5 is performed on the image signal corresponding to the n-th recording element, N recordings are performed. Each density of the part recorded by the device is equal to OD. If such a process is performed on all recording elements, the uneven density is corrected and a uniform image is obtained. That is, the unevenness can be corrected by previously obtaining data as to which table conversion should be performed on the image signal corresponding to which printing element.

It is needless to say that this objective correction may be performed by comparing the densities of the respective nozzle groups (3 to 5 units) to perform an approximate uniformization process.

The density unevenness can be corrected by such a method. However, the density unevenness can be corrected thereafter depending on the usage state of the apparatus or environmental changes, or due to changes in the density unevenness before correction or changes in the correction circuit over time. Therefore, it is necessary to change the correction amount of the input signal in order to cope with such a situation. The cause is
In the case of an inkjet recording head, as it is used, deposits from the ink adhere to the vicinity of the ink ejection port,
It is conceivable that the concentration distribution may change due to foreign matter from the outside. This is also predicted from the fact that the density distribution may change due to deterioration or deterioration of each heater in the thermal head. In such a case, for example, since the density unevenness correction cannot be sufficiently performed with the input correction amount initially set at the time of manufacturing or the like, the problem that the density unevenness gradually becomes noticeable with use is also a problem in long-term use. It becomes a problem to be solved.

(2) Configuration of Control System Next, the control system of the apparatus of this example constructed by connecting the above-mentioned respective parts will be described.

FIG. 6 shows an example of the configuration of the control system. Here, H is a host device that supplies image data and various commands for recording to the device of this example, and has a computer, an image reader, and other forms. Reference numeral 101 denotes a CPU which is a main control unit of the apparatus of this example, and has a form of a microcomputer, and controls each unit according to a processing procedure described later.
102 is a ROM that stores programs and other fixed data corresponding to the processing procedure, and 219 is a RA that has a temporary storage area for image data and an area used for work in various control processes.
It is M.

Reference numeral 106 denotes an online switch with the host device, a command input for recording start, a command input for recording a test pattern for density unevenness correction, and an instruction input unit for giving information on the type of recording medium. Is. Reference numeral 108 denotes sensors that detect the presence / absence of a recording medium, the transport state, the presence / absence of remaining ink, and other operating states. Reference numeral 110 denotes a display unit, which is used to notify the operating state and setting state of the device and the presence / absence of an abnormality. An image processing unit 111 performs logarithmic conversion, masking, UCR, and color balance adjustment on image data related to recording.

Reference numeral 112 denotes the recording head 201 (the above-mentioned heads 201Y and 201).
M, 201C and 201BK are collectively shown) for driving the ink ejection energy generating element.
Reference numeral 113 denotes a temperature adjusting unit for adjusting the temperature of the recording head 201, and specifically, it may include, for example, a heating heater and a cooling fan provided for the head 1. 111 is a drive mechanism of the recovery device, 115 is a mechanism including a motor 206 for scanning the recording head, 116
Is a drive unit of a motor 208 that drives the recording medium transport system.

FIG. 7 shows in detail the system for correcting density unevenness in the above-mentioned configuration. Where 121C, 121
M, 121Y, and 121BK are cyan, magenta, yellow, and black image signals processed by the image processing unit 111, respectively. 122C, 122M, 122Y and 122BK are unevenness correction tables for the respective colors, and can be provided in the area of the ROM 102. 123C, 123M, 123Y and 123BK are the image signals after the correction. 130C to 130BK are gradation correction tables for each color, 131C to 131BK are binarization circuits using a dither method, an error diffusion method, etc., and the binarized signal is a driver 112 (not shown in FIG. 7). Through each color head 201C ~
Supplied to 201BK.

126C, 126M, 126Y and 126BK are color signals read by the sensor 217 through the color filters shown in FIGS. 1 and 2, and are input to the A / D converter 236.
A RAM area 119 temporarily stores the digital output signal, and the area of the RAM 219 can be used. 128C, 1
28M, 128Y and 128BK are based on the stored signal
This is the correction data calculated by the CPU 101. Reference numerals 129C to 129BK are unevenness correction RAMs for the respective colors, and the area of the RAM 219 can be used. The output unevenness correction signals 130C to 130BK for each color are supplied to the unevenness correction tables 122C to 122BK, respectively, and the image signals 121C to 121BK are converted so as to correct the unevenness of the heads 201C to 201BK.

FIG. 8 shows an example of the unevenness correction table. In this example, there are 61 correction straight lines having different slopes of 0.01 from Y = 0.70X to Y = 1.30X, and the unevenness correction signals 130C to 130C.
Change the correction straight line according to 130BK. For example, when a signal of a pixel to be recorded by an ejection port having a large dot diameter is input, a correction straight line having a small inclination is selected, and conversely, when a ejection port having a small dot diameter is selected, a correction straight line having a large inclination is selected to output an image signal to correct.

The unevenness correction RAMs 129C to 129BK store selection signals of correction straight lines necessary for correcting unevenness of each head. That is, the unevenness correction signals having 61 kinds of values of 0 to 60 are stored for the number of ejection ports, and the unevenness correction signals 130C to 130BK are output in synchronization with the input image signal. Then, the signals 123C to 123BK in which the unevenness is corrected by the γ straight line selected by the unevenness correction signal are the gradation correction table.
It is input to 130C to 130BK, where the gradation characteristics of each head are corrected and output. The signal is then binarized 131C ~
It is binarized by 131BK, and a color image is formed by driving the heads 201C to 201BK via the head driver.

On the other hand, regarding the registration adjustment, it is recognized how many pixels the line of another color (the ejection port on which the line is recorded) is separated from the black line (that is, the ejection port on which the line is recorded). Adjust the cash register. As shown in FIG. 2, C, M, and Y color reading sensors 217C and 217
For M and 217Y, R, G, and B filters 220 are used as light sources.
Since R, 220G, 220B are provided, each sensor 217C, 217
Two-color line patterns C and BK, M and BK, and Y and BK are input to M and 217Y at substantially the same level. Therefore, the signal input to BK sensor 217BK and 217C, 217M, 21
The signals input to 7Y are compared to identify the colors C, M, Y and BK. Each interval has a predetermined length, that is, 192 bits for the C pattern recorded using the 32nd ejection port from the bottom and the BK pattern recorded using the 224th ejection port from the bottom in FIG. 128 bits for the M pattern recorded using the 96th ejection port and the BK pattern recorded using the 224th ejection port
The Y pattern recorded using the 0th ejection port and the 224th pattern
The BK pattern recorded using the second ejection port is inspected to see if it has a length of 64 bits, and if the interval is not the prescribed length, use that ejection port for an ink head of an appropriate color. Change the range. For example, 64 ± α for Y and BK
If the length is one bit, the height of the Y head on the carriage is offset by ± α bits. Therefore, if the BK head is used as a reference, the range of ejection port usage for the Y head May be shifted upward or downward in FIG. 1 by ± α bits. In order to adjust the usage range of the ejection openings in this way, it is preferable that the number of ejection openings of each head is set to be larger than the ejection openings of the recording width in advance. It should be noted that fine adjustment of one bit or less can be dealt with by adjusting the ejection timing of the head and the amount of ejection energy to be applied according to the viscosity of ink, the ejection speed, and the like.

(3) Nonuniformity correction sequence With the above configuration, in the present example, the following processing is performed so that the nonuniformity correction can be performed more accurately.

By performing the unevenness correction process, the ejection energy generating element corresponding to the ejection port of the high density portion of the head lowers the driving energy (for example, drive duty), and conversely, the ejection energy corresponding to the ejection port of the thin portion. The generating element raises driving energy. As a result, the printhead density unevenness is corrected and a uniform image is obtained. However, if the density unevenness pattern of the head changes with use,
The unevenness correction signal used becomes improper, and unevenness occurs on the image. In such a case, the instruction input unit 106
The following procedure is started by operating the uneven correction signal rewriting mode instructing switch arranged in step 1 to instruct to rewrite the uneven correction data.

FIG. 9 shows an example of the unevenness correction processing procedure according to this embodiment.

First, in step S7, temperature adjustment is performed. This is due to the following reasons.

In the ink jet recording apparatus, in order to suppress fluctuations in image density, stabilize ejection, and the like, the recording head is normally moved to a predetermined temperature range (for example, a first temperature adjustment reference 40
The temperature is maintained at about ℃). Therefore, for example, when this procedure is activated to record a test pattern, as shown in the area a of FIG. 10, recording is performed in a state where the recording head temperature is 40 ° C. which is the first temperature adjustment reference.
On the other hand, in the case of actually continuously recording images, the head temperature rises as shown in the area b of FIG. 10, and the recording may be performed at a temperature of up to 50 ° C. which is the second temperature adjustment reference. is there.

From the experimental results, it is known that the unevenness of the density (OD value) also changes according to the temperature of the recording head, as shown in FIG. 11 (a). Therefore, in this case, as shown in FIG. 11 (b), when the unevenness correction for 40 ° C. is performed, it is possible to obtain a uniform image with no unevenness at the head temperature of 40 ° C. The image at ° C may still be uneven.

Therefore, in the apparatus of this example, the temperature control unit 113 (heater and fan) is appropriately turned on / off in accordance with the temperature of the recording head 1 during normal recording or during recording standby, and as shown in FIG. Keep the temperature of the recording head within the specified temperature range (about 40 ℃). On the other hand, in the density unevenness correction process, the set temperature is raised to 45 ° C, that is, the temperature adjustment reference is raised when printing the test pattern compared to the temperature adjustment reference for normal recording, and the heater and fan are set appropriately. By turning on / off, the head temperature is raised to about 45 ° C., a test pattern for density unevenness check is recorded, and density unevenness correction is performed based on this. As described above, by stabilizing the recording operation of the recording head by adjusting the temperature, that is, by forming a test pattern with the head temperature of 45 ° C. and performing density unevenness correction based on this, FIG. 11 (c) As shown in
It becomes possible to perform the uniform density unevenness correction over the entire temperature control range.

In this example, the head temperature is 40 ° C., which is the first temperature adjustment reference in this example, and 50 ° C., which is the maximum temperature rise during recording (second temperature adjustment reference). It is also possible to print the test patterns respectively, detect the density unevenness of these two types of test patterns, and perform the correction based on the average value of the density unevenness (first and second density data).

In addition, in order to shorten the overall time required for correcting the density unevenness, the head temperature is set to 40 ° C., for example.
To a temperature adjustment heater, an electric pulse is applied to the recording element (electrothermal conversion element) to the extent that ink does not eject to shorten the head temperature rise time and correct density unevenness. It is also possible to shorten the time required.

In order to reduce the head temperature to the normal recording state (45 ° C. → 40 ° C.) after recording and correcting the density unevenness correction test pattern as described below, the fan is driven and By performing the ink refresh using the recovery device 220, it is possible to shorten the time until the recording becomes possible.

Further, it is needless to say that the adjusted temperature at the time of recording the test pattern can be appropriately determined in relation to the temperature adjustment range at the time of normal recording.

Referring again to FIG. 9, in this example, the steps
A discharge stabilizing operation is executed in S9. This is because if the recording head does not have a normal ejection characteristic due to thickening of ink, mixing of dust or air bubbles, etc. This is because there is a risk that it will not be possible to recognize the deviation of the resist.

In the ejection stabilizing process, the recording head 20
It is possible to face the 1C to 201BK and the recovery device 220 and perform the suction process described above to forcibly discharge the ink from the ejection port. Further, the ejection port forming surface may be cleaned by abutting the ejection port forming surface of the ink absorber that can be arranged on the cap unit, or by blowing air or wiping. It is also possible to drive the recording head in the same manner as during normal recording to perform preliminary ejection. However, the drive energy at the time of preliminary ejection does not necessarily have to be the same as that at the time of recording. That is, the same processing as the so-called ejection recovery operation performed in the inkjet recording apparatus may be performed.

Instead of or after the above-described processing, a pattern for stabilizing the ejection can be printed on the printing medium. Then, after that, a test pattern or the like for density unevenness correction may be recorded.

By the way, in the present example, when the recordable width of the recording head 201 is set to be slightly larger than the image recording width to prepare for the registration adjustment between the heads, the recording width during the test pattern recording is the normal image recording width. It is preferably larger. Therefore, in such a case, the inspection over the width of the ejection port arrangement range is strongly desirable, and the test pattern recording of that width is performed.

FIG. 12 shows a configuration example of a circuit for performing such an operation. 141 is a selector for selecting a discharge port range used by the print head, and 143 and 145 are image data and a test pattern to be printed, respectively. A memory for storing 145 is a counter used for causing the selector 141 to select the range of ejection openings used in the actual printing operation.

When the ejection stabilizing process as described above is completed, a predetermined test pattern, that is, the pattern TB in FIG. 2, is printed by the recording heads 201C to 201BK in step S11.
And TA are recorded, and the misregistration and uneven density are read from this.

If the fixing stability on the sheet 213 before the reading is a problem, the reading processing of the registration deviation and the unevenness is performed in step S15 after the fixing stabilization such as waiting for the reading. You can

Then, in step S17, the discharge port use range is adjusted according to the distance of each color pattern from the black pattern of the pattern TB in FIG.

Next, in the unevenness correction in step S19, first, signals for the number of ejection ports are sampled from the signals obtained by reading the density irregularity, and these are set as data corresponding to each ejection port. These _{R 1, R 2, ... R} N (N is number of ejection ports) When,
After temporarily storing these in the RAM 119, the CPU 101 performs the following calculation.

These data are converted into concentration signals by performing an operation such that C _n = −log (R _n / R ₀ ) (R ₀ is a constant that satisfies R ₀ ≧ R _n ; 1 ≦ n ≦ N). ..

Next,

[0071]

[Outside 2]

Is calculated.

Next, how much the density corresponding to each ejection port deviates from the average density is calculated as follows.

ΔC _n = Bar C / C _n Next, the signal correction amount (ΔS) _n according to (ΔC) _n is calculated by ΔS _n = A × ΔC _n .

Here, A is a coefficient determined by the gradation characteristics of the head.

Subsequently, a selection signal of the correction straight line to be selected according to ΔS _n is obtained, and the unevenness correction signals having 61 kinds of values of “0” to “60” are stored in the unevenness correction RAMs 129C to 129BK for the number of ejection ports. Let Different γ straight lines are selected for each ejection port according to the unevenness correction data created in this way, density unevenness is corrected, and the unevenness correction data is rewritten.

The test pattern is recorded again by each recording head according to the correction data obtained in step S19, the test pattern of each recording head is read again, density unevenness correction data is calculated, and this operation is repeated several times. After that, the density unevenness correction operation may be terminated.

In the above-described embodiment of the present invention, when at least the density inspection printing of a test pattern or the like constitutes one pixel with a plurality of dots, the print duty, that is, the print setting is the number of constituent dots. It can be performed by modulating the number of recording dots in the inside. The print duty in this case is not 100%, preferably 75% or less 25
% Or more, and optimally it is preferable to form a test pattern with a print duty of 50%. This is because it is optimal for the method of optically obtaining the reflection density, and even a minute density change can be obtained as suitable for the printing characteristics of the recording head.

However, the print ratio can also be set by modulating the drive voltage and / or the drive pulse width or the number of ink drops per dot, and these can be set when one pixel is composed of one dot. It can also correspond to. That is, it goes without saying that the present invention can be applied even if the print ratio is set by performing modulation.

Further, the above-described embodiment of the present invention is an optimum embodiment in which the obtained correction processing is performed for each ejection energy generating element, but practically the convergence state and processing time of the density uniformization processing are taken into consideration. Then, it is preferable to perform correction so as to give a common correction to predetermined adjacent plural ejection energy generating elements. From this point of view, the optimum configuration is preferably configured such that the multiple ejection energy generating elements of the print head provide common correction for each block drive group including a plurality of elements. The block driving itself may be any known or publicly known method or a specific block driving method, but a driving condition that can carry out the corrected uniform density after determining the density unevenness of the present invention is given. It goes without saying that this is a prerequisite.

Further, the data relating to the test pattern may be provided from the host device for the configuration of FIG. 6, or may be provided by the test pattern data generating means integrated with the configuration of FIG. 6 or the recording head 201. Good.

Further, since the recording medium in the printed state can be read without being discharged to the outside of the machine, there are few error factors in density detection at the time of reading, and high-accuracy density detection is possible in combination with high-accuracy reading position accuracy. realizable.

If uniform density can be obtained over the discharge port array range by the density unevenness correction processing, this may be performed prior to the registration adjustment processing.

(4) Other Embodiments FIG. 13 is a schematic view of another embodiment, in which each recording head 201C, 2
As in the above example, a uniform image signal is given to 01M, 201Y, and 201BK to read a test pattern for density unevenness correction and registration adjustment recorded on the sheet 213, and a read signal is output. In this example, the density unevenness reading unit 237
Is composed of a linear reading sensor 232 and a light source 233. In the present embodiment, the line sensor is used as the reading sensor 232 for reading the test pattern recorded on the test pattern recording sheet 213 formed in a roll sheet shape, so that the sheet 213 and the reading sensor 232 are connected to each other. It is easy to keep the distance constant, and since only one reading sensor is required, the device structure can be downsized.

Further, as shown in FIG. 14, on the reading surface side of the reading line sensor 232, R, R is set in accordance with the position of the test pattern recorded by each recording head on the sheet 213.
By providing the color filters 234R, 234G, and 234BL for the respective colors G and BL, the reading accuracy of the reading sensor 232 for each color of the print pattern can be improved.

However, in this example, the unevenness reading sensor 23
2 is a single one, but generally the reading output of the sensor is
It changes depending on the color. For example, when using a sensor with spectral sensitivity close to visual sensitivity, which is commonly used,
The read output density is highest in BK, and decreases in the order of C, M, and Y. For example, the output ratio of BK: C: M: Y is 1: 0.
It looks like 8: 0.75: 0.25.

When the density unevenness correction amount is obtained from the ratio between the average density in the head and the density of the target ejection port, this difference in output does not matter. For example, assume that the output for C is K ₁ times the output for BK. Head 1BK
It is assumed that the average density inside the bar is OD _BK , the density at the _target outlet is OD _BKn , the average density inside the head 1C is OD _C , and the density at the target outlet of the head 1C is OD _Cn . Assuming that the unevenness of the target ejection port of the head 1BK is the same as that of the head 1C, the sensor output is bar OD _C = K ₁ × bar OD _BK , _DCn = K ₁ × OD _BKn . At this time, the correction value of _C is bar OD _C = (K ₁ × bar OD _BK ) / (K ₁ × OD _BKn ) = bar OD _BK / O
It becomes D _BKn and matches BK. Therefore, the output difference between the colors does not matter.

However, when the density unevenness correction amount is obtained from the absolute value of the density of the target ejection port or the difference between the average density and the target ejection port density, the difference in the sensor output between the colors becomes a problem.

[0089] For example, when obtaining the correction value from the difference between the average density and the target discharge port density, Bar OD _C -OD _Cn = K ₁ (bar OD _BK -OD _BKn), and this value is towards the C is BK It becomes K ₁ times. Although the correction data for the target ejection port is obtained based on this value, there is a problem that the final correction amount is different between BK and C even though the density unevenness of the head is equal. Occur.

Therefore, in the present embodiment, the ratio of the sensor output between the respective colors is obtained in advance, and the CPU 101 multiplies the sensor output by the reciprocal of this ratio during the unevenness reading process, and the unevenness correction is performed based on this. Solve a problem.

For example, the output ratio of BK, C, M and Y is 1:
K _1: K _2: When the K _3, multiplied by the "1" to the output of when I read the BK, when the C multiplied by ₁ / K 1, when the M 1 / K ₂
If Y, multiply by 1 / K ₃ .

By doing so, for example, in the above-mentioned example, 1 / K ₁ × (bar OD _C −OD _Cn ) = 1 / K ₁ {K ₁ × (bar OD _BK −OD _BKn )} = OD _BK −OD _BKn Therefore, the optimum correction can be performed without being affected by the sensor output ratio between the colors.

It should be noted that such correction of the sensor output is performed by the CPU1.
Instead of the calculation by 01, it can also be performed in the previous stage.

For example, when the A / D converter 236 is configured with 8 bits, the output value of each color is 8 bits of the dynamic range.
This is effective in reducing the resolution of the read data of each color because it has to be converted into digital data within the width.

That is, for example, as shown in FIG. 14, amplifiers 235C, 235M, 235Y, and 235BK for amplifying the read signals of the respective colors are provided, and the sensor output values of the read signals of the respective colors as shown in FIG. By adjusting so as to be almost equal as shown in 15 (b), it becomes possible to set the read signal width when the read signal is A / D converted to be narrow as a whole. Therefore, the resolution of the read data in 8 bits can be increased, and the reading accuracy can be further improved.

Even when register adjustment is performed with this system,
As in the above-described embodiment, it is possible to perform registration adjustment in the ejection port array direction of the head by performing reading with the line pattern as shown in FIG. 13, but since the pattern recording operation is for two scans. ,take time. Therefore, in this example, the line sensor 232 is effectively used. That is, the signal for density unevenness correction measures the density unevenness from the leading edge to the trailing edge of the recording in the paper feeding direction of the test pattern recording sheet 213, but at the same time, it measures the density unevenness of each test pattern for density unevenness measurement. By measuring the displacement, registration adjustment in the ejection port array direction can be performed. Also,
The registration adjustment in the head scanning direction can be performed by recognizing the blank distance between the color patterns (TA). For the registration adjustment, the recording start level of each color in the head scanning direction may be read, but here the threshold level for the density signal at the time of density unevenness correction (used when distinguishing the blank part and the printed part) is used as it is. For example, even if a gentle reaction is caused by the reaction characteristics of the sensor, edge recognition can be performed with high accuracy.

In the above embodiments, the unevenness correction and registration adjustment patterns are formed outside the area of the recording medium 202. However, in consideration of the possibility that various recording media are used in the inkjet recording apparatus, a test pattern is formed on the reference sheet 213, and by reading this, various recording media can be recorded. It is also for the purpose of being applicable, and it goes without saying that the test pattern may be directly recorded on the recording medium 202 and read to perform the correction and adjustment. Further, although the position of the reading sensor 232 is arranged as shown in FIG. 13 in the embodiment, the line sensor 332 slightly longer than the recording width can be made to scan together with the head as shown in FIG. However, in this case, if four sensors are not stacked and a filter is not mounted, the sensor sensitivity decreases in the order of C, M, and Y compared to BK, and the unevenness correction of Y may be insufficient. Just add it.

17 and 18 show the recording head 1 (C, M,
(Y, BK) has a long recording width and the recording head does not move for scanning, that is, a partial oblique view and a sectional view of an image forming apparatus using a so-called full line type recording head. Is A4 width (about 297 mm). As shown in FIG. 18, the recording head 1 (C, M, Y, BK) is used for recording paper 2
When normal image recording is performed upward, the recording sheet 2 stored in the cassette 38 is moved together with the sheet conveying belt 40 by the pickup roller 39 being rotated in the arrow F direction by a control circuit (not shown). The recording head 1 (C, M, Y, BK) conveys the image in the direction of the arrow F and discharges it onto the discharge tray 308 by the discharge roller 42.

When a density unevenness correction command signal for the recording head is issued by a control circuit (not shown), an unevenness correction pattern is formed on the recording medium 2 and the sensor 13 reads it. In this apparatus, the recording head 1 (C, M, Y, B
K) has not only the recording area of 4608 pixels but also the recording area of about 4700 pixels, and the registration adjustment in the ejection port array direction (main scanning direction) is performed by controlling the unused portion. So, the figure
When a uniform pattern for unevenness correction is read as shown in FIG. 19, the edge detection is performed by the threshold level as in the previous embodiment, and the unevenness correction is performed again in the pixel area where the positions of the respective colors are the edge portions. This means that the unevenness correction is repeated twice. However, in practice, when the unevenness correction is performed only once, a better quality image can be obtained. On the other hand, regarding the registration in the paper transport direction (sub-scanning direction), the edge of the recording start portion in each color pattern is detected, and the ejection timing is corrected from that position, as in the above embodiment. That is, for example, using BK as a reference, the ejection timing of that color is adjusted according to the interval with another color. For example, if there is a deviation of 0.064 mm between Y-BK and the transport speed is 133 mm / sec, the ejection timing is adjusted to 0.48 msec.

In the above embodiment, unless a filter is used to read each color pattern, the density level of each color is different and the correction level is different for each color. In addition, it is almost difficult to correct yellow. Therefore, for the sensor 13 of FIG. 18, as shown in FIG.
A filter frame 344 with G and BL filters 534R, 534G, and 534BL incorporated (there is an unfiltered portion 534BK for black) is provided, and this is rotated in synchronization with the paper conveyance speed. A method can be considered. According to this method, it is possible to prevent insufficient correction due to the low density level of yellow.

(5) Others The present invention can be applied to an image forming apparatus by various recording methods in which density unevenness and registration adjustment can be a problem (for example, a thermal printer), but when applied to an inkjet recording method. Above all, it brings an excellent effect in a recording apparatus of a system that uses thermal energy as energy used for ejecting ink. According to such a method, it is possible to achieve high density and high definition of recording, and it is more effective to prevent the occurrence of density unevenness.

With regard to its typical structure and principle, it is preferable to use the basic principle disclosed in, for example, US Pat. Nos. 4,723,129 and 4740796. This method can be applied to both the so-called on-demand type and the continuous type. In particular, in the case of the on-demand type, it is arranged corresponding to the sheet or liquid path holding the liquid (ink). In the electrothermal converter that is
By applying at least one drive signal corresponding to the recording information and giving a rapid temperature rise exceeding nucleate boiling, heat energy is generated in the electrothermal converter, and film boiling occurs on the heat acting surface of the recording head. This is effective because bubbles can be formed in the liquid (ink) corresponding to the drive signal one-to-one as a result. Due to the growth and contraction of the bubbles, liquid (ink) is ejected through the ejection openings to form at least one droplet. If this drive signal is made into a pulse shape, the growth and contraction of the bubbles will be performed immediately and appropriately.
In particular, it is possible to achieve ejection of liquid (ink) with excellent responsiveness,
More preferable. As the pulse-shaped drive signal, those described in US Pat. Nos. 4,463,359 and 4,345,262 are suitable. If the conditions described in US Pat. No. 4,313,124, which is an invention relating to the rate of temperature rise of the heat acting surface, are adopted, more excellent recording can be performed.

As the constitution of the recording head, in addition to the combination constitution of the discharge port, the liquid passage, and the electrothermal converter (the linear liquid passage or the right-angled liquid passage) as disclosed in the above-mentioned specifications, The present invention also includes configurations using US Pat. No. 4,558,333 and US Pat. No. 4,459,600, which disclose configurations in which the heat-acting portion is arranged in a bending region. In addition, a configuration is disclosed in which a common slit is used as a discharge portion of the electrothermal converter for a plurality of electrothermal converters.
The effect of the present invention is effective even if it is based on Japanese Patent Application Laid-Open No. 23670/1993 or Japanese Patent Application Laid-Open No. 59-138461, which discloses a structure in which an opening for absorbing a pressure wave of thermal energy is made to correspond to a discharge part.
That is, according to the present invention, recording can be surely and efficiently performed regardless of the form of the recording head.

Further, in a serial type apparatus, a recording head fixed to the apparatus main body, or a replacement that can be electrically connected to the apparatus main body and can be supplied with ink by being attached to the apparatus main body The present invention is also effective when a flexible chip type recording head or a cartridge type recording head in which an ink tank is integrally provided in the recording head itself is used.

Further, in addition to the recovery means for the recording head, which is provided in the present invention as a configuration of the recording apparatus, a preliminary auxiliary means or the like is added because the effect of the present invention can be further stabilized, which is preferable. Is. Specific examples of these include capping means, cleaning means, electrothermal converter or other heating element or preheating means by a combination thereof for the recording head, and ejection different from recording. Performing the preliminary ejection mode is also effective for stable recording.

Regarding the type and number of recording heads to be mounted, for example, only one is provided corresponding to a single color ink, and a plurality of inks having different recording colors and densities are supported. A plurality of pieces may be provided. That is, for example, the recording mode of the recording apparatus is not limited to the recording mode of only the mainstream color such as black, but may be either integrally formed of the recording heads or a combination of a plurality of them. Alternatively, the present invention is extremely effective for an apparatus provided with at least one of full colors by color mixing.

In addition, in the above-described embodiments of the present invention, the ink is described as a liquid, but it is an ink that solidifies at room temperature or lower and that softens or liquefies at room temperature, or an ink jet system. In general, the temperature of the ink itself is adjusted within the range of 30 ° C or more and 70 ° C or less to control the temperature of the ink so that the viscosity of the ink is within the stable ejection range. Anything can be used. In addition, the temperature rise due to thermal energy is positively prevented by using it as the energy for the state change of the ink from the solid state to the liquid state, or the ink that solidifies in the standing state is used for the purpose of preventing the evaporation of the ink. In any case, the ink is liquefied by applying heat energy according to the recording signal,
The present invention is also applicable to the case of using an ink that has a property of being liquefied only by thermal energy, such as one that is ejected to a liquid-in or one that has already started to solidify when it reaches a recording medium. In this case, the ink is
As described in JP-A-54-56847 or JP-A-60-71260, the electrothermal converter is held in a state of being held as a liquid or solid in the recesses or through holes of the porous sheet. It may be configured to face each other. In the present invention, the most effective one for the above-mentioned nuclear ink is to execute the above-mentioned film boiling method.

Further, as the form of the image forming apparatus, other than the one used as an image output terminal of information processing equipment such as a computer, a copying apparatus combined with a reader or the like,
Further, it may be a facsimile device having a transmission / reception function. In particular, in a device such as a copying machine or a facsimile equipped with an image reading means (reader) as a document reading system, it can also serve as a reading means for reading the density unevenness of a recorded image.

Although the above-mentioned embodiments show the respective constitutions in which a number of technical problems are taken up, all of the respective constitutions are not essential to the present invention, and the designed constitution of the device and the desired concentration uniformity can be obtained. It is shown that it is more preferable to use one or more of the above-mentioned configurations for a configuration arbitrarily required by setting the level.

[0110]

As described above, according to the present invention, in the image forming apparatus for performing image recording by using two or more recording heads in which a plurality of recording elements are arranged, aside from the normal image output operation. By outputting a test pattern and performing registration adjustment and density unevenness correction of each head according to the read signal of the test pattern, it is possible to automate operations that were previously performed by human eyes for registration adjustment. This makes it possible to perform registration adjustment and unevenness correction work easily and accurately, and to form a high-quality image.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of an inkjet recording apparatus as an example of an image forming apparatus of the present invention.

FIG. 2 is a schematic view showing the reading unit.

FIG. 3 is an explanatory diagram for explaining a mode of density unevenness correction in a multi-nozzle head.

FIG. 4 is an explanatory diagram of the same.

FIG. 5 is an explanatory diagram of the same.

FIG. 6 is a block diagram showing a configuration example of a control system of the inkjet recording apparatus according to the present embodiment.

FIG. 7 is a block diagram showing in detail a system for correcting density unevenness.

FIG. 8 is an explanatory diagram illustrating an unevenness correction table used in this example.

FIG. 9 is a flowchart showing an example of the unevenness correction processing procedure according to the present example.

FIG. 10 is an explanatory diagram for explaining a temperature change of a recording head.

11A to 11C are explanatory views for explaining a mode of performing stable density unevenness correction regardless of temperature.

FIG. 12 is a block diagram showing an example of a circuit configuration for selecting a discharge port use range.

FIG. 13 is a schematic perspective view of an inkjet recording apparatus according to another embodiment of the present invention.

FIG. 14 is a block diagram showing a configuration example for correcting a difference in output magnitude depending on colors of the reading sensor in the embodiment.

15 (a) and 15 (b) are explanatory views of the correction mode.

FIG. 16 is a schematic perspective view showing an inkjet recording apparatus according to still another embodiment of the present invention.

FIG. 17 is a schematic perspective view showing a main part of an inkjet recording apparatus according to a further embodiment of the present invention.

FIG. 18 is a schematic sectional view of the whole thereof.

FIG. 19 is an explanatory diagram of a test pattern and a read signal in the embodiment.

FIG. 20 is a schematic perspective view around the sensor unit in the embodiment.

21A to 21E are explanatory diagrams for explaining general density unevenness correction in a multi-nozzle head.

[Explanation of symbols]

 101 CPU 102 ROM 106 Instruction input unit 113 Head temperature adjustment unit 219 RAM 122C, 122M, 122Y, 122Bk uneven correction table 236 A / D converter 129C, 129M, 129Y, 129Bk uneven correction RAM 235C, 235M, 235Y, 235C amplifier 201,201 C, 201M, 201Y, 201Bk Recording head 202 Recording medium 203 Carriage 206 Motor 210 Main scanning belt 213 Test pattern recording sheet 214 Reading unit 217C, 217M, 217Y, 217Bk sensor 218 Light source 220 Recovery device TA Density unevenness correction test pattern TB Register adjustment test pattern

Claims (8)

[Claims] 1. An image forming apparatus for forming an image using a recording head in which a plurality of recording elements are arranged, a unit for causing the recording head to record a predetermined test pattern, and a test pattern formed by the recording head. An image forming apparatus comprising: a reading unit for reading the image forming unit and a unit for adjusting registration of the recording head and correcting uneven density based on the result of the reading. 2. The image forming apparatus according to claim 1, wherein the test pattern includes the registration adjustment test pattern and the density unevenness correction pattern. 3. The image forming apparatus according to claim 1, wherein the test pattern is used for both the registration adjustment and the density unevenness correction. 4. The image according to claim 1, wherein a plurality of the recording heads are provided corresponding to recording agents having different colors for performing multicolor recording. Forming equipment. 5. The recording head has the form of an ink jet recording head, and the ink jet recording head has an electrothermal conversion element used for causing film boiling of ink to eject the ink as the recording element. The image forming apparatus according to any one of claims 1 to 4, characterized in that: 6. An adjusting method of an image forming apparatus for forming an image using a recording head in which a plurality of recording elements are arranged, wherein a test formed by the recording head is performed by recording the test pattern on the recording head. A method for adjusting an image forming apparatus, comprising: reading a pattern; and adjusting registration of the recording head and correcting density unevenness based on a result of the reading. 7. The adjusting method of an image forming apparatus according to claim 6, wherein the test pattern includes a registration adjusting test pattern and a density unevenness correcting pattern. 8. The adjusting method of an image forming apparatus according to claim 6, wherein the test pattern is used for both the registration adjustment and the density unevenness correction.