JPH0428549A - Image formation device - Google Patents

Abstract

PURPOSE:To make it possible to read data at relatively high accuracy and perform any appropriate correction, if a comparatively low resolution reader is used by printing a test pattern image of a pattern where the number of stacked dots is smaller than in a routine recorded image, and performing corrective procedures to be take when a routine image is recorded according to the results of reading the test pattern image. CONSTITUTION:A test pattern image signal generation device 1007 generates a signal so that a pattern where the umber of separated or stacked print dots is small is previously printed. A test pattern image printed on a medium for recording is transported by a transport roller 1040, setting itself against a reading device 1014. During this period, the density of the test pattern image is read. A density signal from this reading device 1014 is sent to a correction factor calculation device 1014 to calculate a correction factor. the correction factor is converted to a correction factor for a routine image using a correction factor conversion device 1052.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that forms an image using a recording head having a plurality of recording elements arranged.

In particular, the present invention relates to an apparatus equipped with a mechanism for automatically adjusting the printing characteristics of a recording head of an inkjet recording apparatus, and is particularly effective for an apparatus that forms a color image with high gradation by overlapping ink droplets.

[Background Art 1] With the spread of information processing equipment such as copying machines, word processors, and computers, as well as communication equipment, digital images are being produced using recording heads based on inkjet methods, thermal transfer methods, etc. as image forming (recording) devices for these devices. Things that record are rapidly becoming popular. In such a recording apparatus, in order to improve the recording speed, it is common to use a recording head (hereinafter referred to as a multihead in this section) formed by an integrated arrangement of a plurality of recording elements.

For example, inkjet recording heads are generally so-called multi-nozzle heads in which multiple ink ejection openings and liquid channels are integrated, and thermal transfer type and thermal type thermal heads also generally have multiple heaters integrated in them. .

However, it is difficult to uniformly manufacture multi-head recording elements due to variations in characteristics due to the manufacturing process, variations in characteristics of head constituent materials, etc., and a certain degree of variation occurs in the characteristics of each recording element. For example, in the multi-nozzle head described above, variations occur in the shapes of ejection ports, liquid paths, etc., and in thermal heads, variations occur in the shapes, resistances, etc. of heaters. Such non-uniformity in characteristics between printing elements manifests itself as non-uniformity in the size and density of dots printed by each printing element, resulting in uneven density in the printed image.

To solve this problem, various methods have been proposed to obtain a uniform image by visually detecting density unevenness or visually inspecting the adjusted image and manually correcting the signals given to each recording element. .

For example, in a multi-head 330 in which recording elements 31 are lined up as shown in FIG. 32A, input signals to each recording element are input to a third
If density unevenness as shown in Fig. 32C is visually detected when the density is made uniform as shown in Fig. 2B, the input signal is corrected as shown in Fig. 32D, and a large input signal is applied to the recording element in the low density area. It is known as a general manual correction to apply a small input signal to the recording element in a high density area.

In the case of a recording system capable of modulating the dot diameter or dot density, it is known to achieve gradation recording by modulating the dot diameter recorded by each recording element in accordance with 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 piezo element or an ejection energy generating element such as an electrothermal conversion element is determined, and in the case of a thermal head, the drive voltage or pulse width is applied to each heater. It is considered possible to make the dot diameter or dot density uniform by each recording element and to make the density distribution uniform as shown in FIG. 32E by utilizing modulation of the dots according to the input signal. Also, if it is impossible or difficult to modulate the driving voltage or pulse width, or if it is difficult to adjust the concentration over a wide range even if they are modulated,
For example, when one pixel is composed of multiple dots,
The number of dots to be recorded can be modulated according to the human input signal, and a large number of dots can be recorded for low density areas, and a small number of dots can be recorded for high density areas. In addition, when one pixel is composed of one dot, an inkjet recording device also calculates the number of ink ejections per pixel (
The dot diameter can also be changed by modulating the number of implantations. With these, the concentration distribution can be made uniform as shown in FIG. 32E.

Japanese Unexamined Patent Application Publication No. 57-41965 filed by the applicant of the present application states that a color image is automatically read by an optical sensor,
It is disclosed that a correction signal is applied to each color inkjet recording head to form a desired color image. This publication discloses basic automatic adjustment and provides important technical disclosures. However, as the practical application progresses, various problems will become apparent in order to apply it to various device configurations, but this publication does not recognize the technical problems of the present invention.

On the other hand, for methods other than the concentration detection method, JP-A-60-20666
Publication No. 0, U.S. Pat.
There is known a device that automatically reads the landing position of a droplet and corrects it so that the droplet lands at an accurate position, as disclosed in Japanese Patent No. 27728. Although these methods are common as automatic adjustment techniques, there is no recognition of the technical problem of the present invention.

As mentioned above, it has been conventional practice to provide an image reading section in an image forming apparatus and periodically read the density unevenness distribution in the recording element array range to create density unevenness correction data. Even if the uneven density distribution of the head changes, the correction data can be regenerated accordingly, making it possible to always maintain a uniform image without unevenness.

FIG. 36 shows an example of a density unevenness reading unit that can be used in such a method, in which 501 is a recording medium on which a test pattern for measuring unevenness is formed, 502 is a light source that irradiates the surface of the recording medium, and 503 is its light source. A sensor for reading reflected light, 504 and 505 are lenses, and 506 is a reading unit equipped with these.

Then, by scanning the recording medium on which the test pattern is printed with the reading unit 506 having such a configuration and reading the unevenness distribution, it is possible to recreate the unevenness correction data.

[Problem to be solved by the invention]

A reading device such as the conventional example described above needs to have a resolution capable of faithfully reading density unevenness. Strictly speaking, a resolution of twice the spatial frequency of density unevenness is required, but empirically, it is about the same as the printing density (i.e., in the case of a printing density of 400 dots/inch, it is about 400 dots/inch). ) is known to require resolution.

For example, if the resolving power of the reading device is lower than the print density, density unevenness with a high spatial frequency or large density variation tends to be read as having a smaller frequency or variation than the actual density. For this reason, even if correction is performed based on this read data, the unevenness may not be completely eliminated by a single correction process, or in the worst case, the unevenness may not be eliminated even if repeated correction processing is performed. There is also. Therefore,
As printing density increases, high-resolution reading devices are required, but such high-resolution reading devices require high-sensitivity light-receiving elements, high-intensity illumination, minute signal processing circuits, maintenance, etc. It will be very expensive.

In other words, when correction is performed using the general reading device and unevenness correction method shown in the conventional example above without using such an expensive reading device, the resolution of density unevenness reading cannot be made that high, and the correction of unevenness is not stable. There was a problem that it could not be performed with high accuracy.

The causes of the above-mentioned density unevenness that have been clarified through studies of the present invention will be briefly explained.

Images recorded by a multihead having a plurality of recording elements are usually formed by independent dots for each recording element. In such a dot image, the density (density of the image viewed macroscopically to such an extent that individual dots cannot be recognized) is: A, area of the dot S B, density of the dot Dl C, positional deviation of the dot (from the set position) D, the density of the overlapping part of the dots D2E, and the density of the base D6. Among these, the density Dx of the overlapping part of the dots
, the density D6 of the base is uniquely determined by the printing method (for example, inkjet method, thermal transfer method, etc.) and the manner in which density unevenness occurs once the recording medium is determined. When discussing density unevenness, this is not a factor. Therefore, the main causes of density unevenness are dot area S, dot density D1, etc. in the direction in which the multi-heads are lined up. It is presumed that this is due to misalignment of the dots. Among these, the cause of density unevenness caused by dot misalignment is usually obvious (for example, the arrangement of recording elements is not uniform), so it is relatively easy to correct density unevenness by purely hardware correction. Can be made smaller.

Therefore, among the factors contributing to density unevenness, those that are subject to the correction method as in the previous example are mainly the density unevenness caused by the dot area S and dot density D1, and other factors such as those mentioned above are When excluded by the configuration, measuring density unevenness is equivalent to measuring unevenness in dot area and dot density. Therefore, in order to measure density unevenness with high precision, the reading device and printed matter must have a dot area S.

It is necessary to be in a state where the unevenness of the dot density D+ can be read accurately.

According to experiments conducted by the inventors of the present invention, when the printing ratio of dots is equal, the density unevenness becomes less noticeable as the ratio of the dot overlapping portion increases. In other words, it has been found that unevenness in dot area and unevenness in dot density are less likely to appear as unevenness in image density. Figures 37A and 37B show two printing patterns A and B with different dot overlapping ratios used in experiments by the inventors (pattern B has a larger dot overlapping ratio than pattern A). ). Further, a print pattern which is the same as print pattern B but has a smaller dot area than pattern B is shown in FIG. 37C. These patterns represent dot patterns developed based on the error diffusion method, etc., and their overlap (
The degree of separation) can be controlled by the placement of the dots in the pattern and/or the size of the dots.

Specifically, the arrangement can be controlled by data for each recording element, and the size can be controlled, for example, by controlling the energy of applied pulses in the case of an inkjet system.

FIG. 38 shows the results of printing such a printing pattern using a multi-head and measuring the density of the image. As can be seen from FIG. 38, the smaller the overlapping ratio of dots, the greater the density unevenness in the direction in which the multi-heads are arranged. From this, it can be seen that when configuring a recording apparatus, it is desirable to perform image processing to create a print pattern with large overlapping dots so that density unevenness is less noticeable.

However, from the perspective of correcting density unevenness,
It is preferable to measure the density using a print pattern in which density unevenness is easily noticeable. This is because, as described above, even if a conventional low-resolution reading device reads small density changes, the larger the density changes in the printed pattern, the easier it is to detect density unevenness.

From the above, it is possible to print a pattern with a high dot overlap ratio when recording an image, and print a pattern with a low dot overlap ratio as a density measurement pattern (also called a test pattern) for density unevenness correction. It can be seen that accurate unevenness correction can be performed.

By the way, when the test pattern image and the normal image have different patterns in this way, if a correction coefficient is calculated based on the density data obtained by reading the test pattern image and the normal image is corrected using the correction coefficient, It is expected that the correction will not be performed satisfactorily. This is because, as is clear from FIG. 38, the manner in which the density changes is different between each pattern. However, according to experiments conducted by the present inventors, it has been confirmed that there is a definite relationship between the density of the test pattern image and the density of the normal image, and the patterns of the test pattern image and the normal image are determined. If so, the relationship can be found in advance and the density or correction coefficient of the normal image can be found from the density or correction coefficient of the test pattern image.

That is, for example, the normal image is converted into pattern B in FIG. 37B.
, when a test pattern image is printed using each pixel of pattern A in FIG. 37A, the density between them is as follows: B/Bo-1=(A/A.-1) Xn
The relationship (1) was experimentally confirmed.

Here, A and B represent the densities of patterns A and B, respectively, and Ao and Bo are the respective densities when all dots have the same dot area and dot density (actually, an image printed by a multi-head can be substituted by the average concentration of Further, n is a conversion coefficient, and it has been confirmed that n=0.5 in the case of patterns A and B used here. This relational expression regarding density can be regarded as the relationship between the density correction coefficient for pattern A and the density correction coefficient for pattern B. Therefore, the density unevenness of the normal image is corrected using the density data obtained by reading the test pattern image. It becomes possible to do this.

The present invention has been made based on the above-mentioned consideration regarding density unevenness correction, and its purpose is to read test patterns with relatively high accuracy even when using a relatively inexpensive and low-resolution reading device. An object of the present invention is to provide an image forming apparatus capable of performing highly accurate non-uniformity correction based on the above.

[Means for Solving the Problems] To this end, the present invention provides a recording head in which a plurality of recording elements are arranged in order to form an image on a recording medium, and a recording head that performs recording with each of the plurality of recording elements by the recording head. a test pattern image formation control means for controlling image formation by the recording head; a reading means for reading the density of the test pattern image formed by the recording head based on the control of the test pattern image formation control means; A density correction means for performing density correction.

[Function] According to the above configuration, a test pattern image is printed with no overlapping dots, or at least a pattern with fewer overlapping dots than a normally recorded image, and the test pattern image is printed according to the result of reading this test pattern image. By performing correction when recording a normal image, relatively high-precision reading and corresponding correction can be made even if a relatively low-resolution reading device is used. As a result, an inexpensive image recording apparatus having highly accurate unevenness correction means is provided.

(The following is a margin) [Example] Hereinafter, with reference to the drawings, an example of the present invention will be described in detail in the following steps.

l) Overview (Figure 1) 2) Mechanical configuration of the device (Figure 2) 3) Reading system (Figures 3 to 12) 4) Control system (Figures 13 to 15) 5) Nonuniformity correction Sequence (Figures 16 to 25) 6)
Other Embodiments (FIGS. 26 to 31) [7) Others (1) Overview FIG. 1A is a block diagram showing the structural concept of an image forming apparatus according to Kitoma's first embodiment. The specific device configuration and its operation will be explained with reference to FIG. 2 and subsequent figures. In FIG. 1A, 1 is a multi-recording head consisting of a plurality of recording elements, 1014 is a reading head that reads the density of a recorded image, 10o2 is a recording medium such as recording paper, and 1040 is a recording medium 1002 facing the recording head 1. A conveyance roller 1051 for conveyance is a correction coefficient calculation device for calculating a correction coefficient for performing correction as described later in FIGS. 33 to 35 based on the density signal from the reading head 1014; Reference numeral 1052 is a correction coefficient conversion device that converts a correction coefficient based on the relational expression shown in the above-mentioned equation (1).
05 is configured. 1006 is an image signal from a host device (scanner, etc., not shown) and a correction coefficient creation device 10;
1007 is a test pattern image signal generation device that generates a test pattern image signal to be output during density unevenness correction processing, and 1008 is a correction start device (not shown). This is an image signal switching device that selects an image signal and a test pattern image signal based on a signal from an instruction device and sends the signal to the recording head. The operations during normal printing and unevenness correction printing will be described in detail below with reference to the flowcharts shown in FIGS. 39A and 39B.

(i) Normal image printing mode When image printing is instructed from a device (not shown) in step S31, the image signal for driving the recording head is changed to an image signal based on a signal from a host device (not shown) in step S32. Generated by generator 1006. This image signal is selected (as is) by the image signal switching device 1008 and input to the recording head 1, and the recording head 1 prints on the recording medium 1002 based on this signal, thereby obtaining a normal printed image (step 533).

(if) Density unevenness correction printing mode When a signal indicating the start of density unevenness correction is sent from a correction start instruction device (not shown) (step 541), the image signal switching device 1008 generates a test pattern image signal by changing the signal to be sent to the recording head 1. Switch to the signal from device 1007. The recording head 1 prints an image for density unevenness correction on the recording medium 1002 in accordance with the test pattern image signal (step 542). At this time, the test pattern image signal generating device 1007 is set in advance to generate a signal so as to print a pattern in which the printed dots in the pattern are separated or have little overlap, as described above, and the resulting image has no overlap. Otherwise, the image consists of fewer dots (hereinafter referred to as separated dots). As an example of a non-overlapping pattern, a printed pattern as shown in FIG. 37C can be considered.

The test pattern image printed on the recording medium is conveyed by the conveyance roller 1040 while facing the reading device 1014, and during this time, the density of the test pattern image is read (step 543).
The density signal from No. 4 is sent to the correction coefficient calculation device 1051, where correction coefficients as described later in FIGS. 33 to 35 are calculated (step 544). However, although the correction coefficient calculated at this time is suitable for correcting the test pattern image itself as described above, it is suitable for correcting the test pattern image itself;
This is different from the one that corrects the image (not necessarily an image of separated dots) depending on the image processing method, so this correction coefficient is converted into the correction coefficient converter 1052 as described above (
1) Convert to a correction coefficient for a normal image based on the relationship in the equation (step 545).

The correction coefficients converted as described above are input to the image signal generation device 1006. Image signal generator 100
In step 6, the correction coefficients input to the signal from the external host device are used to perform correction with reference to the correction table described later in FIG. 15, and an image signal is generated (step 846).
, printing is performed based on this signal (step 547).

By performing unevenness correction in this manner, an image with no or small density unevenness can be obtained.

When the above-described unevenness correction method is applied to an image forming apparatus having, for example, a 400 dot/inch multi-nozzle recording head and a reading device with an aperture of 100 μm, as shown in FIG. It took 3 to 4 correction processes (test pattern printing, reading, correction) to make the unevenness visible, but with this method, 1
Similar results were obtained with ~2 correction processes. In addition, when the aperture of the reading device was widened to 200 μm under the same conditions, density unevenness could be eliminated after 3 to 4 correction processes. Therefore, according to the method of this example, The same results as the conventional method can be obtained even if the resolution of the reading device is lowered, so it is possible to reduce the load on the reading device by reducing the number of correction processes (if it does not cause any problems). , it is possible to reduce the cost of the reading device.

FIG. 1B is a block diagram showing the structural concept of an image forming apparatus according to a second embodiment of the present invention.

In the figure, elements similar to those shown in FIG. 1A are given the same reference numerals, and their explanations will be omitted. In the figure, 1022
1025 is a correction recording medium, and 1025 is a density data converter 1.
251 and a correction coefficient calculation device 1252; 1027 is a correction recording medium supply control device for controlling the supply of the correction recording medium 1022;

The operations during normal printing and unevenness correction printing will be described in detail below.

(i) Normal image printing mode Based on a signal from a host device (not shown), an image signal for driving the recording head is generated by the image signal generator 1006, this is input to the recording head, and the recording head 1 is sent to the correction recording medium. Printing is performed on a normal recording medium different from 1022,
This results in an image.

(if) Density unevenness correction printing mode When a signal indicating the start of density unevenness correction processing is input from a correction start instruction device (not shown) to the correction recording medium supply control device 1027, the recording medium supply control device 1027 The correction recording medium supply device is operated, and the correction recording medium 1 is
022 is conveyed to the printing section. The correction recording medium 1022 is preset so that the dot area is smaller than usual (for example, in the inkjet recording method, the recording medium 1022 is set to have a layered code layer to suppress ink bleeding more than a normal recording material). ).This correction recording medium 102
2, the recording head 1 performs printing in response to a signal from the image signal generator 1006. As a result, the dots formed on this recording medium have less overlapping parts due to less bleeding, etc., and a separated dot image is obtained. This separated dot image is transferred to a reading device 2.10 by a conveying roller 1040.
14, where its concentration is read and converted into an electrical signal.

This signal is input to the correction coefficient creation device 1025.

The density data input to the correction coefficient creation device 1025 is
Since this is the density data of the test pattern image (separated dot image), if the correction coefficient is calculated as is, the correction coefficient will not be used to correct the normal image. Therefore, the input density data is converted into the density of a normal image by a density data conversion device 1251, and then inputted to a correction coefficient calculation device 1252, where a correction coefficient for normal image correction is calculated. Using the correction coefficients thus obtained and the image signal from the host device, the image signal generating device 1006 generates a head driving image signal, which is input to the recording head 1 and an image is printed.

According to this embodiment, since the patterns of the test pattern image and the normal image are common, the circuit for printing the test pattern image (for example, the image memory can be omitted, so even when correction is performed on multiple types of images, the cost is reduced). avoid close-ups,
An inexpensive image forming apparatus can be provided.

FIG. 1C is a block diagram showing the structural concept of an image forming apparatus according to a third embodiment of the present invention.

In the figure, elements similar to those shown in FIG. 1B are given the same reference numerals, and their explanations will be omitted. Also, 1002 is the first
A recording medium similar to that shown in Figure A is shown. 1st C
In the figure, 1037 is a recording head drive condition control device.

The operations during normal printing and unevenness correction printing will be described in detail below.

(i) Normal image printing mode Based on a signal from a host device (not shown), an image signal for driving the recording head is generated by the image signal generator 1006, and this is input to the recording head. The recording head performs recording while being controlled by a head drive condition control device 1037 so as to perform printing under preset drive conditions, thereby obtaining an image.

(ii) Density unevenness correction printing mode When a signal indicating the start of density unevenness correction is input from a correction start instruction device (not shown) to the head drive condition control device 1037, the head drive condition control device 1037 prints the head drive conditions. In order to reduce the dot area in the pattern, for example, in the case of a thermal method, the pulse width of the driving electric pulse is controlled to be short.

Since the subsequent processing is the same as that of the second embodiment shown in FIG. 1B, the explanation thereof will be omitted.

According to this embodiment, the separation dot control means is electrical, and the printing pattern data for the normal image and the correction image are common, so even when correction is performed on multiple types of images, the cost does not increase. An inexpensive image forming apparatus can be provided.

(2) Overview of Mechanical Structure of Apparatus FIG. 2A shows a schematic structure of an inkjet recording apparatus as an example of an apparatus for carrying out the embodiment of the present invention shown in FIG.

Here, IC, IM, IY, and IBK are print heads corresponding to cyan, magenta, yellow, and black inks, respectively, and the width in the printing medium conveyance direction, in this example, the short side of an A3 size printing medium. The length of (
400dpi over a range corresponding to 297mm
This is a full-line head with discharge ports arranged at a density of (dots/inch). 3 are these recording heads Ic-
This is a head holder that holds the IBK integrally, and can be moved by a head holder moving mechanism 5 in the direction A toward the recording position and in the direction B away from the recording position in the figure. The head holder moving mechanism 5 includes a drive source such as a motor,
It has a transmission mechanism that transmits the driving force to the head holder 3, a guide member that guides the movement of the head holder 3, etc., and by moving the head holder 3 in directions A and B appropriately, the recording heads Ic-IBK can be moved. The head holder 3 is set at a recording position where the ejection port faces the recording medium at a predetermined distance, a retracted position to receive the intrusion of the cap unit described below, and a position for capping each head. It is possible.

Reference numeral 7 denotes an ink supply/circulation system unit, which includes a supply path for supplying each color ink to each recording head, a circulation path for refreshing the ink, and an appropriate pump. Furthermore, by driving the pump during the ejection recovery process described below, it is possible to pressurize the ink supply path and forcibly discharge ink from each recording head.

9 is a cap unit, which is a recording head IC.

Caps 9C, 9M, 9Y, and 98 are made of an elastic material such as rubber and can be opposed to or joined to IM, IY, and IBK, respectively, and are made of an elastic material such as rubber to improve adhesion during joining.
Ink received from the print head during ejection recovery processing (
The printer has an absorber for absorbing waste ink (waste ink), and a waste ink path for introducing the waste ink into a waste ink tank (not shown). 11 is a cap unit moving mechanism, which includes a motor,
By having a transmission mechanism, a guide member, etc., and moving the cap unit 9 appropriately in the C direction and D direction in the figure,
The cap unit 9 can be set at a position directly below the head holder 3 in the retracted position and at a position where it does not obstruct the descent of the head holder 3 during recording.

During the ejection recovery process, the head unit 3 is raised in the direction B to a position where the cap unit 9 is not blocked from entering, and the cap unit 9 is placed in the space created by this.
The cap unit 9 is set at a position where the corresponding head and cap face each other. In this state, or in a state in which the head holder 3 is lowered and the ejection port forming portion of the recording head and the cap face each other at a predetermined interval or are joined, the pump etc. of the ink supply/circulation system unit 7 is driven. As a result, the ink can be forcibly discharged and causes of ejection failure such as dust, air bubbles, and thickened ink can be removed, thereby stabilizing the ink ejection condition during recording. Furthermore, in the above state, the print head may be driven in the same manner as during printing to perform ink ejection (preliminary ejection), thereby eliminating the cause of ejection failure. Note that when recording ends or is interrupted, the head may be capped to protect the ejection ports from drying.

Reference numeral 38 denotes a cassette containing recording media 2 such as paper, OHP film, etc. The recording media 2 accommodated here are separated and fed one by one by a pickup roller 39 rotating in the F direction. 4o is the fed recording medium 2
This is a conveyor belt that conveys the image in the E direction with respect to the recording positions of the recording heads IC to IBK, and is wound between the rollers 41. In addition, in order to increase the adhesion of the recording medium 2 to the belt 40 to ensure smooth conveyance and to obtain an appropriate distance between the head and the recording medium (head gap),
A member such as means for performing electrostatic adsorption or air adsorption, or a recording medium holding roller may be provided.

42 is a discharge roller for discharging the recording medium 2 on which recording has been completed, and 43 is a tray for stacking the discharged recording medium.

14 is a density unevenness reading unit, and a recording head IC
- It is arranged between the recording position by IBK and the ejection roller 42, facing the recording surface of the recording medium 2, and reads a test pattern formed on the recording medium 2 during processing for density uniformity correction, etc. 15 is a mechanism for scanning the reading unit, which will be described later with reference to FIG. Reference numeral 16 denotes a drive unit for driving each unit related to conveyance of the recording medium 2, that is, the feeding roller 39, the roller 41, and the ejection roller 42.

When correcting density unevenness, a recording medium housed in the cassette 38 is used as in the embodiment shown in FIG. 1B (a dedicated special paper may be used as the recording medium 1022, but this will be described later). is fed onto the conveyor belt 40 by rotating the pickup roller 39 in the direction of arrow F in the same way as during normal recording. and roller 4
1 rotates, the recording medium 2 is transferred to the conveyor belt 40.
At the same time, the recording medium 2 is conveyed in the direction of arrow E, and at this time, each recording head is driven and a test pattern is recorded on the recording medium 2.

Thereafter, the recording medium 2 on which this test pattern has been recorded is conveyed to the density unevenness reading unit 14.
After the recorded test pattern is read by a reading sensor or the like, it is discharged onto the tray 43.

Note that in this example, since a specific paper is used as the recording medium for forming the test pattern, a configuration may be adopted in which feeding other than the cassette 38 (so-called manual paper feeding) is performed in consideration of operability.

FIG. 2B shows the recording head 1 (recording head Ic, IM.

An ink system consisting of an ink supply/circulation system unit 7 is schematically shown.

In the recording head, 1a is a common liquid chamber to which an ink tube from an ink supply source is connected, and also communicates with an ink discharge port 1b via a liquid path. An ejection energy generating element such as an electrothermal conversion element is disposed in each liquid path, and ink is ejected from the corresponding ejection port in response to energization of the element.

An ink tank 701 serves as an ink supply source, and is connected to the common liquid chamber 1a of the recording head 1 via ink paths 703 and 705. 707 is a pump provided in the middle of the ink path 703, and 710 is a valve provided in the middle of the ink path 705.

By configuring the ink system in this way, the pump 70
By appropriately switching the operating state of 7 and the opening/closing state of the valve 710, the ink system can be set to each of the following modes.

(2) Print mode Ink necessary for recording is supplied to the head 1 from the ink tank 701 side. Note that since this embodiment is applied to an on-demand type inkjet printer, no pressure is applied to the ink during recording, and therefore the pump 56 is not driven. Also, assume that the valve 710 is opened.

In this mode, ink is supplied to the head 1 via the ink path 705 in response to ink ejection from the head 1 .

■Circulation mode This mode is used to circulate ink to supply ink to each head during the initial use of the device, or to remove air bubbles in the heads or supply channels and refresh the ink inside them at the same time. This is set when the inkjet printer is left unused for a long time.

In this mode, the valve 710 is opened and the pump 56 is operated, so that ink flows back into the ink tank 701 via the ink tank 701, the ink path 703, the head 1, and the ink path 705.

■Pressure mode If the ink inside the ejection port of the head l becomes thickened, or if the ejection port or liquid path becomes clogged, pressure is applied to the ink and the ink is pushed out from the ejection port 1b to remove the ink. This is the removal mode.

In this mode, the valve 710 is closed, the pump 707 is operated, and ink is supplied from the ink tank 701 to the print head 1 via the ink path 703.

(3) Reading system FIG. 3 shows an example of the configuration of the reading unit and its scanning mechanism in this embodiment.

A flat recording medium guide section (indicated by reference numeral 17 in FIG. 2A) serving as a platen is placed below the scanning section of the reading head 60, and the recording medium 2 is conveyed onto this guide section, and the recording medium 2 is conveyed onto this guide section. The image formed on the recording medium is read by the reading head 60 at the position. Note that the position of the reading head 60 shown in FIG.
This is the home position of 0. This home position is desirably located at a position laterally away from the recording medium transport range. This is because each reading device is away from dangers such as water droplets adhering to it due to ink evaporation.

In FIG. 3, 60 is a reading head, which slides on a pair of guide rails 61.61° to read images. The reading head 60 includes a light source 62 for illuminating the original, and a lens 63 for forming an image of the original onto a group of photoelectric conversion elements such as a CCD.
It is composed of etc. 64 is a flexible conducting wire bundle that supplies power to the light source 62 and the photoelectric conversion element and transmits image signals and the like from the photoelectric conversion element.

The reading head 60 is fixed to a driving force transmitting section 65 such as a wire for main scanning (G, H directions) in a direction intersecting the recording medium conveyance direction. Main scanning direction driving force transmission section 6
5 is stretched between pulleys 66 and 66 degrees, and is moved by the rotation of a main scanning pulse motor 67. By rotating the pulse motor 67 in the direction of the arrow, the reading head 6
0 reads the row information of the image perpendicular to the main scanning direction G with the number of bits corresponding to the photoelectric conversion element group while moving in the direction of arrow G.

After a predetermined width of the image has been read, the main scanning pulse motor 67 rotates in the direction opposite to the arrow I. As a result, the reading head 60 moves in the H direction and returns to the initial position. Note that 68 and 68' are supporting members.

If only one main scan is performed to read the density unevenness, the reading operation is completed above, but if the density unevenness is read for each of multiple colors, or if one color is read multiple times and averaged. When taking a value, for a certain color or after one main scan G,
The recording medium 2 is conveyed in the E direction by the conveyor belt 40 or the ejection roller 42, moves a predetermined distance (distance d equal to the pitch between each color pattern or the read image width in one main scan in the G direction), and then stops. do. Here, main scanning G is started again. Then, by repeating the main scanning G, the return H1 in the main scanning direction, and the movement of the recording medium (sub-scanning), it is possible to read the density unevenness of each color pattern or a plurality of times for one color. Note that in this process, instead of conveying the recording medium 2, the reading unit may perform sub-scanning. Further, if the sensor is a full-line sensor, a mechanism related to main scanning becomes unnecessary.

The image signal read in this way is sent to the image forming section,
This will be used to correct the driving conditions of the recording head, as will be described later.

In the present invention, the meaning of adjusting to prevent density unevenness during image formation is to equalize the image density of droplets from the plurality of liquid ejection ports of the printhead within the printhead itself, or to make adjustments for each of the printheads. At least one of: uniformizing the image density of the image, or performing uniformization so that a desired color can be obtained by mixing multiple liquids, or a desired density can be obtained. Preferably, satisfying more than one of these is included.

As for the density uniformity correction means for this purpose, it is preferable that the reference print giving the correction conditions is automatically read and the correction conditions are automatically determined, and a manual adjustment device for fine adjustment and user adjustment is applied to this. It's not something I refuse to do.

The purpose of correction determined by the correction conditions may be not only optimal printing conditions, but also adjustments to a predetermined range including tolerance ranges, or standard density that changes depending on the desired image, and all of the purposes included in the purpose of correction are applicable. It is possible.

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

Assume that the density distribution when printing is performed by driving each element (1-N) with a certain uniform image signal S is as shown in FIG. 33. First, the density QD of the portion corresponding to each recording element, ~ODs
The correction is not limited to measuring and correcting the average value for each beam, but may also be performed by a method of integrating the amount of reflected light to obtain an average value, or by a known method.

If the relationship between the value of the image signal and the output density of a certain element or a certain group of elements is as shown in FIG. What is necessary is to determine the correction coefficient α that brings about this. That is, a correction signal S obtained by correcting the signal S to αxS=(00100,)XS may be applied to this element or group in accordance with the input signal S. Specifically, the 35th
This is executed by performing table conversion as shown in the figure. Third
In Figure 5, straight line A is a straight line with a slope of 1.0, and is a table that outputs the input signal without converting it at all.
Straight line B is a straight line with a slope of α=00100n, and is a table for converting an input signal S into an output signal of α·S. Therefore, the correction coefficient α for each table as shown by the straight line B in FIG. 35 for the image signal corresponding to the n-th recording element. If the head is driven after table conversion is performed, each density of the portion recorded by N recording elements becomes equal to OD. If such processing is performed on all recording elements, density unevenness will be corrected and a uniform image will be obtained. That is, by obtaining data in advance about what kind of table conversion should be performed on the image signal corresponding to which recording element, it is possible to correct unevenness.

It goes without saying that this objective correction may be performed by comparing the densities of each nozzle group (in units of 3 to 5 nozzles) and may be used as an approximate uniformization process.

Although it is possible to correct density unevenness using this method, density unevenness may occur later depending on the usage conditions of the device or changes in the environment, or due to changes in the density unevenness situation before correction or changes over time in the correction circuit. Therefore, in order to deal with such a situation, it is necessary to change the amount of correction of the input signal. The possible cause of this is that as the inkjet recording head is used, the density distribution may change due to deposits from the ink adhering to the vicinity of the ink ejection ports or foreign matter from the outside adhering to the inkjet recording head. . This can also be predicted from the fact that in a thermal head, each heater may deteriorate or change in quality, resulting in a change in the concentration distribution. In such a case, for example, the initial input correction amount set at the time of manufacturing will no longer be sufficient to correct the density unevenness, so the problem with long-term use is that the density unevenness will gradually become more noticeable as the product is used. This becomes an issue that needs to be solved.

Incidentally, the distance between the reading unit and the recording medium on which the test pattern is recorded varies depending on the reading accuracy, but is preferably kept constant. Therefore, in order to maintain this spacing, configurations as shown in FIGS. 4 to 6 can be adopted.

FIG. 4 schematically shows an example of this, in which a housing 76 in which the reading unit 14 and its scanning mechanism 15 are housed includes a presser roller 78a that engages with the recording medium 2.

78b is provided. These rollers 78a, 7
Since 8b rotates in the recording medium conveyance direction,
There is no problem in transporting the recording medium. As a result, the recording medium 2 is prevented from floating, and the housing 76 is displaced according to the thickness of the recording medium 2, so that the above-mentioned interval is kept constant.

In FIG. 4, 74 is a lens for converting the emitted light from the light source 62 into parallel light, 73 is a sensor having a photoelectric conversion element group, 63 is a lens for converging reflected light, and 77 is an aperture with an aperture of d0. It is a filter with

Then, by a scanning mechanism as shown in Fig. 3, these lenses,
The sensor, light source, filter, etc. are scanned within the housing 76 in the G and H directions (directions perpendicular to the drawing in FIG. 4).

The reflected light from the recording medium passes through the lens 63 and the aperture d. The light enters the sensor 73 via a filter 77 having a filter 77.

This incident light is within a range of dl on the test pattern, and therefore the average of the unevenness within that range is detected. According to experiments by the inventors, the opening diameter is 0.
A thickness of about 2 to 1 mm was good. Then, by performing unevenness correction according to the detection results, it becomes possible to obtain a uniform image.

Note that if the reading unit itself including the lens, sensor, light source, etc. can be displaced in the vertical direction in FIG. 3 with respect to the scanning mechanism 15, a roller as a holding member may be provided on the reading unit itself. In this case, if the rollers have a caster structure, conveyance of the recording medium and movement of the reading unit can be carried out smoothly. Furthermore, in the case of a configuration in which the recording medium is read while being moved, reading can be performed while reducing the load on the rollers by making the scanning direction diagonal.

FIG. 5 shows another configuration example for maintaining a constant distance between the reading unit and the recording medium. In this example, a holding member 80 made of transparent plastic or the like is provided at the bottom of the housing.

In this example, the casing 76 that houses the reading unit and the scanning mechanism is initially separated from the platen 17 by about 10 mm, and when the recording medium 2 on which the test pattern is recorded comes under the reading unit, the casing 76 is lowered, and the recording medium 2 is held down by the transparent plastic 80. Then, by scanning the reading head 60, density unevenness is detected in the process. However, in this case, it is preferable that the image is completely fixed.

Such a configuration also prevents paper from floating and allows accurate reading. Furthermore, the transparent plastic 80 covering the lower part of the casing has the effect of preventing the light source 62, sensor 73, etc. from becoming dirty.

FIG. 6 shows yet another configuration example for maintaining the distance between the reading unit and the recording medium. In FIG. 6, the housing 76 is fixed in the vertical direction, but a cylindrical roller 81 made of transparent plastic or the like is rotatable about a shaft 82.

The recording medium 2 is held by the transparent roller 81, and density unevenness can be read from inside the transparent roller 81 while paper floating is prevented. According to this example as well, density unevenness can be accurately detected.

In addition to the embodiments described above, the main body of the apparatus has recording medium holding means on each of the upstream side and the downstream side.

The above-described high-precision reading is also possible with a device configured to read the recording medium between the downstream clamping means.

By the way, in order to rewrite the unevenness correction data when recording a color image with a head of three colors: cyan (C), magenta (M), and yellow (Y), or four colors including black (Bkl). In this case, it is highly desirable to record a test pattern for correction with each head, read the unevenness, and rewrite the unevenness correction data for each head.

At that time, when reading the unevenness of C, M, Y, especially Y, when white light is irradiated onto the Y test pattern and the reflected light is received without a filter, the amount of light received by the sensor 73 is as shown in Fig. 78. As shown in curve A, the dynamic range is narrow and uneven (the difference in optical density is small, 0.02 to 0.15
degree) is difficult to accurately read. So the 7th B
When using light that has passed through a blue filter as shown in the figure, the amount of received light is small overall (although the dynamic range is widened and the accuracy of reading unevenness is reduced), as shown by curve B in Figure 78. The same goes for C and M if R (red) and G (green) filters are used, respectively.

FIG. 8 shows an example of a configuration for switching such color filters. Here, 79 is a color filter switching section, and the shaft 7
Rotating around 9A, an R filter 77R, a G filter 77G, and a BL filter 77 are placed on the optical path to the sensor 73.
Aperture (no filter) 778K for BL or BK,
When reading the test pattern of each color, it is possible to selectively position it as appropriate. Note that the diameter of each filter or opening is d as described above. It is.

By doing so, it becomes possible to accurately correct unevenness for each color using a single unevenness reading sensor 73 and light source 62.

Note that the filter is located at a distance from the light source 62 to the sensor 73.
It can be anywhere on the optical path. Furthermore, in order to correct the amount of received light that decreases by the amount that passes through the filter, the amount of emitted light from the lamp light source is increased by the amount of the decrease, thereby widening the dynamic range as shown in FIG. 7C. Further, as will be described later, multiplication by an appropriate constant or signal amplification may be performed depending on the color.

Furthermore, instead of switching the color filters as described above, it is also possible to switch the light sources.

Figure 9 shows an example of its configuration, with R, G, and B
Four light sources 62R, 6 with L and white spectral characteristics
The configuration is such that 2G, 62BL, and 62W can be switched in the same way as the upper side. This also provides the same effect as above.

By the way, it is also possible to integrate the above-described mechanism for preventing floating of the recording medium 2 and the structure for expanding the dynamic range according to the color.

FIG. 1O shows an example of a configuration for this purpose. Here, 85 is a transparent presser roller divided into four parts in the circumferential direction, of which 85A is a colorless and transparent part, 85R is a part forming a red filter, 85G is a part forming a green filter,
5BL is a part forming a blue filter. 848 on the recording medium 2 is a test pattern by the black head IBK, 84G is a test pattern by the cyan head IC, 84M is a test pattern by the magenta head IM, and 84Y is a test pattern by the yellow head IY.

The reading unit 14, which can enter inside the transparent roller 85, is supported by a support rod 15', and the support rod 15' is movable in the direction of the arrow.

Test pattern 84BX by Blackhead IBK
When reading unevenness, rotate the roller 85 and
The unit 14 enters and moves while holding down the recording medium at the portion . Similarly, when reading the test pattern 84C of the cyan head IC, read the test pattern 84C at the position 85R, the test pattern 84M of the magenta head IM at the position 85G, and the test pattern 84Y of the yellow head IY at the position 85BL. Set to press the recording medium with .

As described above, according to this example, density unevenness of each color head can be read with high accuracy through the filter, and paper floating can be prevented, so that accurate reading is possible.

Next, scanning of the reading head in the configuration shown in FIG. 3 will be described.

As described above, the recording medium on which the test pattern has been recorded is conveyed to the reading unit 14, which is disposed on the recording surface side of the recording medium 2 downstream of the recording head in the conveyance direction. Thereafter, the pulse motor 67 in FIG. 3 is driven, and the reading unit 14, that is, the reading head 60 fixed to the driving force transmission part 65, such as a wire or a timing belt, connected to the pulse motor moves in the G direction in FIG. The test pattern recorded on the recording medium 2 is read by the reading sensor 73 while being main scanned.

In this embodiment, when the pulse motor 67 is driven by a control circuit to be described later to transport the reading unit 14, the pulse motor 67 is driven at a frequency different from the resonant frequency of the reading unit transport system. ing.

That is, when the pulse motor 67 is driven to transport the reading unit transport system, the resonance frequencies fω+, fω2, . At fω8..., the vibration of the reading unit conveyance system becomes extremely large. Therefore, when the reading unit 14 is conveyed at a resonant frequency where such a system vibrates, as shown in FIG. 12A, even if the recording density of the test pattern recorded on the recording medium 2 is uniform, Also, as shown in FIG. 12B, the reading unit 1
In some cases, the transport speed ■ω of No. 4 changes. In such a case, as a result, the read output from the reading unit 14 has an output characteristic with pitch unevenness as shown by ω in FIG. 12C, and the recording density of the test pattern recorded on the recording medium 2 cannot be read correctly.

Therefore, in this embodiment, in order to cope with such a case, the reading unit 14 is driven at a frequency f1 other than the resonance frequency of the reading unit transport system, and the test pattern is read at a constant reading speed. It becomes possible to accurately read the recorded density of the test pattern without being affected by the vibrations of the transport system.

(4) Configuration of control system Next, the control system of the device of this example, which is constructed by combining the above-mentioned parts, will be explained. The control configuration, signal processing configuration, etc. shown in FIG. 1 are specifically configured by the control system explained in FIGS. 13 onwards.

FIG. 13 shows an example of the configuration of the control system. Here, I]
is a host device that supplies image data and various commands related to recording to the apparatus of this example, and has a computer, an image reader, or other form. Reference numeral 101 denotes a CPU that constitutes the main control section of the apparatus of this example, and has the form of a microcomputer, and controls each section according to processing procedures etc. to be described later. 1
02 is a ROM that stores programs and other fixed data corresponding to the processing procedure; 104 is a RAM that has a temporary storage area for image data and an area used for work in various control processes.

Reference numeral 106 denotes an instruction input unit for inputting an online switch with the host device, inputting a command to start recording, inputting a command to record a test pattern for correcting density unevenness, and inputting information on the type of recording medium. Sensors 108 detect the presence or absence of a recording medium, its conveyance state, the presence or absence of a remaining amount of ink, and other operating states. Reference numeral 110 denotes a display unit, which is used to notify the operating status and setting status of the device, and whether or not an abnormality has occurred. 111 is for image data related to recording,
This is an image processing unit that performs logarithmic conversion, masking, tJcR, and color balance adjustment.

112 is the recording head 1 (the above heads IY, IM,
This is a head driver for driving the ink ejection energy generating elements of the IC and IBK.

Reference numeral 113 denotes a temperature adjustment section for adjusting the temperature of the recording head 1, and specifically, it can include, for example, a heating heater and a cooling fan provided for the head 1. Reference numeral 114 designates a drive unit for the color filter switching unit 79 described in connection with FIG. 8, and reference numeral 116 designates a drive unit for each motor that drives the recording medium transport system.

FIG. 14 shows in detail the system for correcting density unevenness among the above configurations. Here, 121c.

121M, 121Y and 1218 have image processing units 11
These are cyan, magenta, yellow, and black image signals processed in step 1, respectively. 122C, 122M
, 122Y and 1228 are unevenness correction tables for each hue, which can be provided in the ROM 102 area. 123G, 123M, 123Y and 1238 are image signals after the correction. 130
0 to 1308 are gradation correction tables for each hue, 131C
-1318 are binarization circuits using the dither method, error diffusion method, etc., and the binarized signals are sent to the driver 112 (14th
(not shown in the figure) to the respective color heads IC to IBK.

126C, 126M, 126Y and 1268,
These are the color signals read by the reading unit 14 through the color filters and apertures shown in FIG. 8, and are input to the A/D converter 127. 119 is a RAM area for temporarily storing the digital output signal, and the area of RAM 104 can be used. 128G, 128M,
128Y and 1288 are correction data calculated by CPUl0I based on the stored signals. 129
C-1298 has unevenness correction RAM for each hue, and RA
A region M104 can be used. The output unevenness correction signals 130G-1308 of each hue are supplied to unevenness correction tables 122C-1228K, and the image signals 121C-1218 are supplied to the head IC.
~ Converted to correct IBK unevenness.

FIG. 15 shows an example of an unevenness correction table, and in this example, Y
The slope from =0.70X to Y = 1.30X is 0.
There are 61 corrected straight lines that differ by O1, and the corrected straight lines are switched according to the unevenness correction signals 130c to 1308K. For example, when a pixel signal to be recorded by an ejection port with a large dot diameter is input, a correction straight line with a small slope is selected, and conversely, when an ejection port with a small dot diameter is used, a correction straight line with a large slope is selected to correct the image signal. to correct.

The unevenness correction RAMs 129C to 1298 store correction straight line selection signals necessary for correcting unevenness of each head. That is, it stores unevenness correction signals having 61 types of values from 0 to 60 for the number of ejection ports, and outputs unevenness correction signals 130C to 1308K in synchronization with the input image signal. Then, the signals 123C to 1238 whose unevenness has been corrected by the γ straight line selected by the unevenness correction signal are input to the gradation correction tables 130C to 1308K,
Here, the gradation characteristics of each head are corrected and output. The signals are then binarized by binarization circuits 131C to 1318K, and a color image is formed by driving heads IC to IBK via a head driver.

(5) Sequence of unevenness correction With the above configuration, in this example, the following processing is performed to perform unevenness correction more accurately and obtain a value of 1.

By performing unevenness correction processing, the drive energy (for example, drive duty) of the ejection energy generating element corresponding to the ejection port in the high density part of the head is reduced, and conversely, the ejection energy generating element corresponding to the ejection port in the light part of the head is reduced. Increase drive energy. As a result, the density unevenness of the recording head is corrected and a uniform image is obtained, but if the density unevenness pattern of the front and back sides changes with use, the unevenness correction signal used may become inappropriate, and the image Unevenness occurs on the top. In such a case, the next procedure is started by operating the unevenness correction signal rewriting mode instruction switch provided in the instruction input section 106 to instruct to rewrite the unevenness correction data.

FIG. 16 shows an example of the unevenness correction processing procedure according to this example.

When this procedure is started, first, input of the type of recording medium is accepted at the step Sl. To do this, a message "Please input the type of recording paper currently being used" is displayed on the display unit 110, such as a liquid crystal panel. Seeing this, the operator specifies the type of recording medium currently being used using a switch or the like provided in the instruction input section 106. A determination is made based on this in step S3, and if the type of recording paper input is not optimal for detecting density unevenness, such as an OHP sheet or trace coated paper, a message is displayed on the display unit 110 in step S5. , for example, displays a message such as "Please use specified paper." As a result,
If the paper is replaced with the designated paper and the designated paper type is input, or if the input recording medium type is the designated one from the beginning, proceed to the following procedure.

In this embodiment, the type of recording medium is input again each time the mode is entered into the unevenness correction data rewriting mode, and based on the input, it is determined whether or not to rewrite the unevenness correction data. However, information about the type of recording medium being used is usually already specified at the time of recording. For example, since the color tone of the printed output often differs depending on the type of recording medium, it is known that image processing such as masking coefficients is changed depending on the type of recording medium used.

Therefore, in a modified example of this embodiment, the type of recording medium used during normal recording is input, the optimal image processing is performed according to this, and when the unevenness correction data rewriting mode is entered, manual input is required in advance. It is determined whether or not to rewrite the unevenness correction data depending on the type of recording medium being used. Therefore, there is an advantage that there is no need to input the type of recording medium again.

Further, in the present embodiment, it was necessary to specify the recording medium by pressing a switch, but this is not necessary in yet another modification of the present embodiment.

FIG. 17 shows a recording medium 2' used in this example. Here, 20 is a recorded unevenness correction pattern, 25 is a recording medium identification mark, and the identification mark is provided at the leading end margin of the recording medium with a density corresponding to the type of the recording medium. and,
When reading the density unevenness, the density is read by the density unevenness reading unit 14 before reading the unevenness correction pattern.

Then, if it is determined that the paper is the designated paper, rewriting of the unevenness correction data will begin. If not, a display will be displayed to prompt the user to change the recording medium to the designated paper, and the work of rewriting the unevenness correction data will be prohibited. .

By doing so, it is possible to save the effort of inputting the type of recording medium.

In yet another modification of this embodiment, similar effects are obtained without using identification marks. For this purpose, a sensor unit for detecting the type of recording medium can be provided separately from the density unevenness reading unit 14.The configuration of this sensor is almost the same as that shown in FIG. 8, but the lamp is an ultraviolet lamp, and the sensor is Use one that is sensitive to ultraviolet light. Then, the type of recording medium is determined from the amount of light reflected from the margin itself of the recording medium. Generally, coated paper for inkjet recording often has a fluorescent agent added to it to make it look whiter. Therefore, if an ultraviolet lamp is used as the lamp, the type of recording medium can be determined from the reflected light. That is, when the amount of reflected light is large, it can be determined that the paper has a thick coating layer, when the amount of reflected light is medium, it is determined that the paper has a thin coating layer, and when it is rare, it can be determined that the paper is an OHP film. Only when it is determined that the paper has a lot of reflected light and is suitable for detecting density unevenness,
It is possible to read the density unevenness and rewrite the unevenness correction data, and otherwise display the same display as above and prohibit this. As a result, the same effect as described above can be obtained without requiring the operator to input the type of recording medium or providing an identification mark.

Referring again to FIG. 16, if the recording medium is suitable for unevenness correction processing, the process advances to step S7 and temperature adjustment is performed. This is due to the following reasons.

In an inkjet recording apparatus, the recording head is usually maintained within a predetermined temperature range (for example, about 40° C., which is the first temperature adjustment standard) in order to suppress fluctuations in image density, stabilize ejection, and the like. Therefore, for example, when this procedure is started and a test pattern is recorded, recording will be performed with the recording head temperature at 40°C, which is the first temperature adjustment standard, as shown in area a of Fig. 18. . On the other hand, when actually recording images continuously, the temperature of the head increases as shown in area b in Figure 18, and recording is performed at a maximum temperature of 50°C, which is the second temperature adjustment standard. There is also.

By the way, from the experimental results, as shown in Figure 19A,
It is known that the magnitude of density (00 value) unevenness changes depending on the temperature of the recording head. Therefore, in this case, as shown in FIG. 19B, if unevenness correction is performed for 40°C, a uniform image without unevenness can be obtained when the head temperature is 40°C.
Images at 50° C. may still be uneven.

Therefore, in the apparatus of this example, during normal recording or during recording standby, the temperature control section 1 adjusts the temperature of the recording head 1.
13 (heater and fan) as appropriate.
As shown in FIG. 8, the temperature of the recording head is maintained within a predetermined temperature range (approximately 40° C.). On the other hand, in the density unevenness correction process, the set temperature is raised to 45°C, that is, the temperature adjustment standard is raised when printing a test pattern compared to the temperature adjustment standard for normal recording, and the heater and fan are adjusted appropriately. After the head temperature is raised to around 45° C. by turning on/off, a test pattern for checking density unevenness is recorded, and density unevenness correction is performed based on this. As shown in FIG. 19C, by stabilizing the recording operation of the recording head by adjusting the temperature, for example, by forming a test pattern at a head temperature of 45° C. and correcting density unevenness based on this. Thus, it becomes possible to perform density unevenness correction more or less uniformly over the entire temperature control range.

In addition, in this example, test patterns are created when the head temperature is 40°C, which is the first temperature adjustment standard in this example, and when the head temperature is 50°C, which is the maximum temperature increase during recording (second temperature adjustment standard). is printed, the density unevenness of these two types of test patterns is detected, and the density unevenness (first and second
The correction may be performed based on the average value of the density data (density data).

In addition, in order to shorten the overall time required to correct density unevenness, the head temperature is adjusted from 40°C to 45°C, for example.
In order to increase the temperature, in addition to the temperature adjustment heater, electric pulses are applied to the recording element (electrothermal conversion element) to the extent that no ink is ejected, thereby shortening the time required to raise the head temperature and correcting density unevenness. can also be shortened.

Note that in order to lower the head temperature to the normal recording state (45°C - 40°C) after printing a test pattern for density unevenness correction as described below and performing correction, the fan must be driven and the above-mentioned ink By performing circulation, the time required to reach a recordable state can be shortened.

Furthermore, it goes without saying that the temperature adjustment during test pattern recording can be appropriately determined in relation to the temperature adjustment range during normal recording.

Referring again to FIG. 16, in this example, a discharge stabilization operation is executed in step s9. This increases the viscosity of the ink,
If the recording head does not have normal ejection characteristics due to the incorporation of dust or air bubbles, if density unevenness correction processing is performed as is, it may not be possible to accurately recognize the head characteristics (density unevenness). This is because there is.

In the ejection stabilization process, the recording heads 16 to IBK and the cap unit 9 can be placed opposite each other, and the above-mentioned pressurization mode can be set to forcibly eject ink from the ejection ports. Further, the ejection orifice forming surface may be cleaned by contacting the ejection orifice forming surface with an ink absorber that can be disposed in the cap unit, or by blowing air, wiping, or the like. It is also possible to perform preliminary ejection by driving the print head in the same way as during normal printing. However, the driving energy during preliminary ejection is not necessarily the same as that during recording (or may be). In other words, the same process as the so-called ejection recovery operation performed in an inkjet recording apparatus may be performed.

In addition, instead of or after the above processing,
A pattern for ejection stabilization can also be recorded on the recording medium. After that, a test pattern or the like for correcting density unevenness may be recorded.

Figure 20 shows examples of recording of these patterns. In the figure, ■ is a pattern for stabilizing ejection, and ■ is an inspection image pattern for inspecting the presence or absence of ejection failure (in the figure, while conveying the recording medium, The pattern is formed by sequentially driving from the ejection ports of 1) and 2) is a test pattern for detecting density unevenness. The pattern used here for ejection stabilization was one with a printing ratio of 100% duty, which was performed by driving all ejection ports of all print heads.

By recording this stable ejection pattern, the temperature of the head is stabilized, and the ink supply system is also in a steady state, creating conditions for normal printing, and whether there is any ejection failure during actual printing. It becomes possible to accurately grasp the density unevenness.

By the way, in an apparatus such as this example in which the recording head l is of the full multi-type and the recordable width is slightly larger than the image recording width in preparation for registration adjustment, the recording width when recording the test pattern is normally For example, the maximum recording paper size is A3, and the normal image recording width is the length of the short side of A3 or the long edge of A4. 297 mm, considering the left and right margins, and the printable width of the print head is 295 mm. This is for correcting errors in the relative positional relationship between each head and between the recording medium.

Therefore, in this case, it is important to inspect the width of 295 mm, which is the ejection port arrangement range (preferably, a test pattern with a length of 295 mm is recorded).

FIG. 21 shows an example of the configuration of a circuit for performing such an operation, in which 141 is a selector for selecting the range of ejection ports to be used in the recording head, and 143 and 145 store image data and test patterns to be recorded, respectively. memory,
A counter 145 is used to cause the selector 141 to select the ejection port range to be used during actual recording operation.

When the discharge stabilization process as described above is completed, step S
At 11, a predetermined test pattern is recorded by the recording head Ic-IBH, and density unevenness is read from this. The operation when recording a test pattern or reading density unevenness in this example will be explained using the timing chart of FIG. 22.

FIG. 22 is a timing chart showing the operation of the apparatus of this embodiment. At timing a in the figure, the density unevenness correction processing procedure is started, and after the above-mentioned processing, the recording medium 2 is moved to the image recording area at timing b. After being transported, timing C
The main scanning motor is driven at timings d, e, f, g.
cyan, magenta, yellow, and black recording head ICs.

The IM, IY, and IBK drivers are driven to record a test pattern onto the recording medium 2. This test pattern is used for reading density unevenness. At this time, the unevenness correction table is all straight lines with an inclination of 1.0, and all unevenness correction is not performed. Halftone is fine, printing ratio is 30~
It may be about 75%.

By the way, when a test pattern is recorded on the recording medium 2 by each recording head in this way, depending on the type of recording medium, the ink recorded from each recording head may not be absorbed instantly and may not be recorded on the recording medium 2. The density unevenness of the test pattern may not stabilize immediately.

Therefore, in this embodiment, the density unevenness of the test pattern is not read by the density unevenness reading unit 14 until the state of the density unevenness of the test pattern recorded by each recording head has stabilized. After the recording head finishes recording the test pattern, the recording paper is stopped without being conveyed for a predetermined time t (step 513 in FIG. 16), and the condition of the density unevenness of the test pattern is checked. After stabilization, the recording medium is transported at timing i, and stopped when the pattern C reaches the reading device, and at timing j, the reading sensor 17 is driven, and the reading unit 14 detects the density of the 0-color test pattern. I try to read unevenly. After that, the timing is the same, I2. M at m, Y
, The density unevenness of each BK color is read.

According to experiments by the inventors, a printing head with a resolution of 400 dpi has a printing ratio of 5 on coated paper for inkjet recording.
When a test pattern was recorded at 0%, the above-mentioned recording paper stop time of approximately 3 to 10 seconds was sufficient.

FIG. 23 is a timing chart showing another example of the operation of the device of this example. In this operation example, with respect to the conveying speed Vl when conveying the recording medium 2 to the recording position, the recording of the test pattern by the recording head is not completed at time g'), and the recording medium is conveyed to the density unevenness reading unit 14. By reducing the actual paper conveyance speed ■2, v+>v
z, and by this, the 22nd
The same effect as shown in the figure can be obtained.

After fixing stabilization as described above, step S1 in FIG.
In step 5, uneven reading processing is performed. That is, each unevenness is read from the test pattern recorded for each color, and the unevenness correction data for each head is rewritten.

However, in this example, although the unevenness reading sensor 73 is a single sensor, the reading output of the sensor generally changes depending on the color. For example, when using a sensor whose spectral sensitivity is close to the visual sensitivity, as is often used for -M, the read output density is the thickest for BK and decreases in the order of C, M, and Y. For example, if BK:C:M:Y(7) output ratio is 1
: 0.8 : 0.75 : 0.25.

If the density unevenness correction amount is determined from the ratio between the in-head average density and the density of the ejection port of interest, this difference in output does not pose a problem. For example, suppose the output for C is three times the output for BH. The average density in head IBK is 0Dax, the density at the target ejection port is 0DIIK, etc.
, the average density in the head IC is ODc, and the density at the target ejection port of the head IC is 0Dcn.

If the unevenness of the ejection port of interest in head IBK is the same as that in head LC, the sensor output will be 0Dc=+
X ODs+t, Dcn = K+ X 0DaKn
It is. At this time, the correction value of C becomes equal to BK. Therefore, the output difference between each color is not a problem.

However, when determining the density unevenness correction amount from the absolute value of the density of the ejection port of interest or the difference between the average density and the density of the ejection port of interest, the difference in sensor output between each color becomes a problem.

For example, when calculating the correction value from the difference between the average density and the target ejection port density, 0Dc-ODoo=1(ODllK-〇DIIKrl
), and this value for C is three times that for BK. Based on this value, correction data for the target ejection port is calculated, but even though the density unevenness of the heads is the same,
A problem arises in that the final correction amount is different for BK and C.

Therefore, in this embodiment, the ratio of sensor outputs between each color is determined in advance, and cpulo is used in the unevenness reading process.
This problem is solved by multiplying the sensor output by the reciprocal of this ratio by i and performing unevenness correction based on it.

For example, the output ratio of BK, C, M, and Y is 1:, :
When : becomes 3, the output when reading BK is "1"
For C, multiply 1/ by 2; for M, multiply 1/ by 2; for Y, multiply 17 by 3.

In this way, for example, in the above example, +X to 1/
(ODc 0Dcn) = l/to + (K, X (OD
BK - 0Daxn)1=OD, K - 0DBXn, and optimal correction can be performed without being affected by the sensor output ratio between each color.

Note that such correction of the sensor output may not be performed by calculation by CPUl0I, but may be performed at a previous stage thereof.

For example, if the A/D converter 127 is configured with 8 bits, the output value of each color is divided into 8 bits of the dynamic range.
It must be converted into digital data within the width (
This is effective in preventing the resolution of read data of each color from decreasing.

That is, for example, as shown in FIG. 24, amplifiers 135G, 135M, 135 amplify the read signal of each color.
Y, 1358K are provided, and the sensor output values of the read signals of each color as shown in Fig. 25A are adjusted to be almost equal as shown in Fig. 25B, so that the read signal when the read signal is A/D converted. The overall width can be set narrower. Therefore, the resolution of the read data within 8 bits can be increased, and the reading accuracy can be further improved.

Based on the above, unevenness correction is performed in step S17 in FIG. That is, from the signals obtained by reading the density unevenness, signals corresponding to the number of ejection ports are sampled, and these are used as data corresponding to each ejection port.

Assuming that these are R1, R2,...R, (N is the number of discharge ports), once these are stored in the RAM 119, the CP
The following calculation is performed in Ul0I.

These data are converted into a density signal by performing an operation such that C,=-log(R,1/Ro) (L is a constant such that R, ≧R, , 15n≦N).

Then the average concentration C=Σ　G, /N Calculate by calculation.

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

△C,=C/Cn Next, the signal correction amount (△S)n according to (△C)1 is △S
Determine by n=A XΔCl+.

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

Next, a selection signal for a correction straight line to be selected according to ΔSn is obtained, and unevenness correction signals having 61 types of values from "0" to "60" are stored in unevenness correction RAMs 129C to 1298 for the number of ejection ports.
Let K memorize it. Using the unevenness correction data created in this manner, a different γ straight line is selected for each ejection port, density unevenness is corrected, and the unevenness correction data is rewritten.

Then, through the determination step S19 in FIG. 16, a test pattern is recorded by each recording head again using this correction data, and the test pattern of each recording head is read again by the density unevenness reading unit 14 to calculate density unevenness correction data. After repeating this operation several times,
The density unevenness correction operation is ended.

In this way, test pattern recording of each recording head, reading by the density unevenness reading unit 14, and calculation of density unevenness correction data can be repeatedly performed multiple times or more automatically in one process for one recording medium. As a result, it is possible to improve the density unevenness correction accuracy of each recording head and shorten the correction time as a whole, even for recording heads whose density unevenness cannot be sufficiently corrected even with a single density unevenness correction operation. become able to.

In the embodiment of the present invention described above, in the case where one pixel is composed of a plurality of dots (when printing a small number of dots for density inspection such as a test pattern), the printing duty, that is, the setting of printing, is set within the number of constituent dots. This can be done by modulating the number of recorded dots.In this case, the printing duty is not 100%, but is preferably 75% or less and 25% or more, and optimally it is preferable to form the test pattern with a printing duty of 50%. This is because it is optimal for a method of optically obtaining reflection density, and allows minute changes in density to be obtained that are suitable for the print characteristics of the recording head.

However, the above printing ratio can also be set by modulating the drive voltage and/or drive pulse width, or the number of ink strikes per dot, and these also apply when one pixel is composed of one dot. It is possible. That is, it goes without saying that the present invention can be applied to any type of modulation in which the printing ratio is set.

In addition, although the above embodiment of the present invention is an optimal embodiment in which the obtained correction processing is performed for each ejection energy generating element, in practice, considering the convergence state of the density uniformization processing and the processing time, it is necessary to It is preferable to perform a process to apply a common correction to a plurality of adjacent ejection energy generating elements. The optimal configuration from this point of view is preferably such that the multiple ejection energy generating elements of the print head apply a common correction to each block drive group including a plurality of elements.

This block drive itself may be a well-known or publicly known method or a unique block drive method, but it is important to provide drive conditions that can implement the corrected uniform density after determining density unevenness according to the present invention. Needless to say, this is a prerequisite.

Furthermore, the data related to the test pattern may be provided from the host device for the configuration shown in FIG.
4. The test pattern data may be provided by the configuration shown in FIG. 4 or by a test pattern data generation means integrated with the recording head I.

(The following is a blank space) (6) Other Embodiments The present invention is not limited to the embodiments described above, and various modifications can be made without departing from the scope of the present invention. In the following, embodiments in which the present invention is applied to a serial printer will be mainly described. It goes without saying that the same control system and processing procedure as described above can be employed in the following examples as well.

FIG. 26 shows a schematic diagram of an embodiment of an inkjet recording device in the form of a serial printer, in which the recording head 2
01G, 201M, 201Y, 2018 from an ink tank (not shown) via an ink tube.
Inks of cyan, magenta, yellow, and black colors are supplied. And a recording head 201G.

The ink supplied to 201M, 201Y, and 2018 is driven by a print head driver or the like in response to a print signal corresponding to print information from the main control unit, which is similar to that shown in FIG. Ink droplets are ejected and recorded onto the recording medium 202.

The conveyance motor 208 is a drive source for intermittently feeding the recording medium 202, and includes a feed roller 204 and a conveyance roller 205.
The main scanning motor 206 that drives the main scanning carriage 20
3 in the directions of arrows A and H through the main scanning belt 210.

In this embodiment, since accurate paper feeding control is required, pulse motors are used for the paper feeding motor 208 and the main scanning motor 206.

When the recording medium 202 reaches the feeding roller 205, the feeding roller clutch 211 and the conveyance motor 208 are turned on.
The recording medium 202 is conveyed on a platen 207 until it reaches a conveyance roller 204 . The recording medium 202 is a platen 207
It is detected by a detection sensor 212 provided above, and the sensor information is used for position control, jam control, etc. When the recording medium 202 reaches the conveying roller 204, the feeding roller clutch 211. The conveyance motor 208 is turned off, and a suction operation (not shown) is performed from inside the platen 207 to bring the recording medium 202 into close contact with the platen 207 on the image recording area. Prior to the image recording operation on the recording medium 202, the home position sensor 2
The scanning carriage 203 is moved to position 09, and then forward scanning is performed in the direction of arrow A, and cyan, cyan, and
Magenta, yellow, and black ink is printed on the recording head z
Image recording is performed by ejecting from oic~201BK.

After recording the image for a predetermined length, the scanning carriage 20
3, and conversely, start a return scan in the direction of arrow B.
The scanning carriage 203 is returned to the position of the home position sensor 209. During the backward scan, the recording head 201C~
The transport motor 20 feeds the paper by the length recorded in 2018.
8 by driving the conveyance roller 204 to move the arrow C.
Do it in the direction of.

In this embodiment, the recording heads 2010 to 2018 are inkjet recording heads of the type that form bubbles using heat and eject ink droplets with the pressure of the bubbles, and each has 256 ejection openings assembled into four inkjet recording heads. I am using it.

The scanning carriage 203 is the home position sensor 209
When the recording head 1 is stopped at the home position detected by , the recovery device 220 performs a recovery operation of the recording head 1 . This is a process for stable recording operation, and the recording head 2
It remains in the discharge port of 01. In order to prevent unevenness at the start of ejection caused by changes in ink viscosity, etc., the pause time and internal temperature of the device must be adjusted.

Depending on pre-programmed conditions such as dispensing time,
This is a process in which the recovery device 220 performs a suction operation for the recording head 201, a preliminary ink ejection operation, and the like.

By repeating the operations described above, an image is recorded on the entire surface of the recording medium. In the figure, reference numeral 214 denotes a density unevenness reading unit that outputs a reading signal by giving a uniform image signal to each of the recording heads 201C to 2018K by the control circuit 215, reading a test pattern printed on the recording medium 202, and outputting a reading signal. It is provided outside the recording area. In this embodiment, it is arranged so as to face the recording surface side of the recording medium in the paper ejection side direction below the recording head with respect to the conveyance direction of the recording medium 202 (direction of arrow C). Then, as described above, the recording medium 202 on which the test pattern has been recorded is illuminated by the light source 218, and the recording density of the test pattern recorded on the recording paper by each recording head is read by the sensors 217G, 217M, 217Y, and 2178K. After the reading signal of the test pattern recording by each recording head read by each reading sensor is converted into a digital signal by the A/D converter 236, the read signal is temporarily stored in the RAM 219.

FIG. 27 is a schematic diagram for explaining the reading section of this example.
In order to improve the accuracy of reading the density unevenness of the test pattern recorded on the recording medium 202 by the recording head,
A color filter 220R is provided on the recording medium side of the illumination light source 18.
220G and 220BL are provided, and R, G, and B are used for the C, M, and Y test patterns recorded on the recording medium 202.
, L light is irradiated. Then, by irradiating the test patterns of each color of C, M, and Y with light of the complementary color, each reading sensor 217G
, 217M, 217Y, and 2178, there is no need to make the spectral sensitivities different for each color of the test pattern,
It becomes possible to read the density unevenness of each color while using sensors with the same spectral sensitivity for each sensor.

Note that a holding member as described above may be provided to this configuration to prevent the paper from floating during reading.

FIG. 28 shows a schematic diagram of another embodiment in which the present invention is applied to a device in the form of a serial printer, in which each recording head 2
Similar to the above, a test pattern recorded on the recording medium 202 by applying uniform image signals to 01C, 201M, 201Y, and 2018K is read and a read signal is output. In this example, the uneven density reading unit 214 provided outside the image recording area is composed of a linear reading sensor 232 and a light source 233.

In other words, as in this example, the density unevenness reading unit 214 is arranged so as to face the recording surface side of the recording medium in the paper ejection direction below the recording head with respect to the conveyance direction of the recording medium 202 (direction of arrow C). If a holding member similar to that described above is provided, it becomes easy to maintain a constant distance between the recording medium 202 and the reading sensor 232 when reading a test pattern recorded on the recording medium 202, and Since only one reading sensor is sufficient, the device configuration can also be downsized.

In addition, as shown in FIG. 29, the reading line sensor 232
On the reading surface side of the recording medium 202, R, G,
Color filters 234R, 234G, 2 for each color of B and L
34B, the reading accuracy of the reading sensor 232 for each color of the print pattern can be improved. Then, as described in FIGS. 24 and 25, the read signals of each color from the read sensor 232 are sent to the amplifier 235C.
By amplifying by ~2358K, the resolution of the read data can be increased and the reading accuracy can be further improved.

FIG. 30 shows still another embodiment in which the present invention is applied to a serial printer type device. In this example,
Each recording head 201C, 201M, 201Y.

20], when recording a test pattern on the recording medium 20 by scanning the carriage carrying BK in the A and B directions, the test pattern is recorded by the recording head of one color each time the carriage 203 is scanned once. After the reading line sensor 232 reads the test pattern recorded on the recording medium 202, the carriage 20
3 is scanned, and the test pattern is recorded on the recording medium 202 by the next recording head.

In other words, by reading the test pattern recorded on the recording medium by each recording head for each color as in this embodiment, the capacity of the RAM 219 that stores the read data of the test pattern can be reduced to , the device configuration can be made smaller.

FIG. 31 schematically shows another embodiment in which the present invention is applied to a serial printer type device. This shows a case where the density unevenness correction section 237 consisting of the following is provided outside the image recording area.

Also in this embodiment, after the test pattern is recorded by each recording head on the test pattern recording sheet 231 of the test pattern recording section, the test pattern recording is performed after the density unevenness of the test pattern has stabilized. The sheet 213 is conveyed to the uneven density reading section.

(7) Others The present invention can be applied to image forming apparatuses using various recording methods in which density unevenness is a problem (for example, thermal printers, etc.), but when applied to inkjet recording methods, it is proposed by Canon This brings about excellent effects in bubble jet type recording devices. According to this method, recording density can be increased,
This is because since high definition can be achieved, prevention of density unevenness becomes more effective.

As for typical configurations and principles thereof, it is preferable to use the basic principles disclosed in, for example, US Pat. No. 4,723,129 and US Pat. No. 4,740,796. This method can be applied to both the so-called on-demand type and continuous type, but especially in the case of the on-demand type, it is necessary to arrange the liquid (ink) in accordance with the sheet and liquid path that hold it. The electrothermal converter that is
Generating thermal energy in the electrothermal transducer and producing film boiling on the thermally active surface of the recording head by applying at least one drive signal that corresponds to recorded information and provides a rapid temperature rise above nucleate boiling. As a result, bubbles in the liquid (ink) can be formed in a one-to-one correspondence with this drive signal, which is effective. The growth and contraction of the bubble causes liquid (ink) to be ejected through the ejection opening to form at least one droplet. If this drive signal is in the form of a pulse, bubble growth and contraction will occur immediately and appropriately.
Particularly responsive liquid (ink) ejection can be achieved,
More preferred. This pulse-shaped drive signal is described in U.S. Pat. Nos. 4,463,359 and 4,345,262.
Those described in the specification are suitable. Furthermore, if the conditions described in US Pat. No. 4,313,124 concerning the invention regarding the temperature increase rate of the heat acting surface are adopted, even more excellent recording can be performed.

The configuration of the recording head includes, in addition to the combination configuration of ejection ports, liquid paths, and electrothermal converters (straight liquid flow path or right-angled liquid flow path) as disclosed in the above-mentioned specifications, a heat acting section. 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 wafer is placed in a bending region. In addition, Japanese Patent Application Laid-Open No. 1989-5 discloses a configuration in which a common slit is used as a discharge part of a plurality of electrothermal converters.
No. 9-23670 and Japanese Patent Application Laid-Open No. 1987-59 which discloses a configuration in which an opening for absorbing pressure waves of thermal energy corresponds to a discharge part.
The effects of the present invention are also effective even with a configuration based on the publication of No. 138461. That is, regardless of the form of the recording head, according to the present invention, recording can be performed reliably and efficiently.

Furthermore, in a full-line type (full multi-type) recording head whose length corresponds to the maximum width of the recording medium that can be recorded by the recording device, it is possible to have a configuration that satisfies the length by combining multiple recording heads, or to form them integrally. The recording head may be configured as a single recording head.

In addition, even for serial types, there are recording heads that are fixed to the device body, or replaceable recording heads that are installed on the device body to enable electrical connection with the device body and supply of ink from the device body. chip type recording head,
Alternatively, the present invention is also effective when using a cartridge type recording head in which an ink tank is integrally provided in the recording head itself.

Further, it is preferable to add recovery means for the recording head, preliminary auxiliary means, etc., which are provided as a configuration of the recording apparatus, to the present invention, because the effects of the present invention can be further stabilized. Specifically, these include capping means for the recording head, cleaning means, pressure or suction means, preheating means using an electrothermal transducer or another heating element, or a combination thereof; It is also effective to perform a preliminary ejection mode in which ejection is performed separately from printing in order to perform stable printing.

In addition, regarding the type and number of recording heads installed, for example, in addition to one type that corresponds to single-color ink, there is also a plurality of recording heads that correspond to multiple inks with different recording colors and densities. It may be something that can be done. In other words, for example, the recording mode of the recording device is not only a recording mode for only the mainstream color such as black (although the recording head may be configured integrally or by a combination of multiple heads, it can also be used for multiple colors of different colors). The present invention is also extremely effective for devices equipped with at least one of full colors, or mixed colors.

Additionally, in the embodiments of the present invention described above,
Although ink is described as a liquid, it is an ink that solidifies at room temperature or below, but softens or liquefies at room temperature, or in an inkjet method, the ink itself is
Generally speaking, the temperature is adjusted within the range of 0°C or more and 70°C or less so that the viscosity of the ink is within the stable ejection range, so the ink is in a liquid state when the recording signal is applied. Good to have. In addition, the temperature increase caused by thermal energy can be actively prevented by using it as energy for changing the state of the ink from a solid state to a liquid state, or
Or, in order to prevent ink evaporation, ink that solidifies when left unused is used, and in either case, the ink is liquefied by applying thermal energy according to the recording signal, and the liquid ink is ejected, or the recording medium The present invention is also applicable to the case where an ink that is liquefied only by thermal energy is used, such as an ink that begins to solidify by the time it reaches . The ink for such cases is disclosed in Japanese Patent Application Laid-Open No. 54-56847 or Japanese Patent Application Laid-Open No. 60-7126.
As described in Japanese Patent No. 0, the porous sheet may be held as a liquid or solid in the recesses or through-holes of the porous sheet, facing the electrothermal converter. In the present invention, the most effective method for the above-mentioned nuclear ink is the one that implements the above-mentioned film boiling method.

In addition, image forming apparatuses may take the form of image output terminals for information processing equipment such as computers, copying machines combined with leagues, etc., and even facsimile machines with transmitting and receiving functions. It may be. In particular, in devices such as copying machines and facsimile machines that are equipped with an image reading means (reader) as a document reading system, it can also be used as a reading means for reading density unevenness in a recorded image.

Although the above embodiments show various configurations that address a number of technical issues, all of the above configurations are not essential to the present invention (i.e., depending on the designed device configuration and the desired density uniformity level). This indicates that it is more preferable to use one or more of the above configurations to perform any configuration required depending on the settings.

[Effects of the Invention] As is clear from the above description, according to the present invention, a test pattern image with a pattern in which there is no overlapping dots or at least an overlapping portion of dots is smaller than that of a normally recorded image is printed, and this By making corrections when recording normal images according to the results of reading the test pattern image, even if a relatively low resolution reading device is used,
Relatively highly accurate reading and corresponding correction are possible. As a result, an inexpensive image recording apparatus having highly accurate unevenness correction means is provided.

[Brief explanation of the drawing]

1A to 1c are block diagrams for explaining the outline of each embodiment of the present invention, and FIG. 2A is a schematic diagram of an inkjet recording device in the form of a line printer according to an embodiment of the image forming apparatus of the present invention. 2B is a schematic diagram for explaining the ink system; FIG. 3 is a perspective view showing a configuration example of the reading unit and its scanning mechanism in FIG. 2A; FIGS. 4, 5 and 6 are 7A, 7B, and 7C are schematic side views showing an example of the word structure of the part for maintaining the distance between the reading unit and the recording medium, which expands the dynamic range of the amount of light received by the sensor according to the color. FIGS. 8, 9 and 10 are schematic diagrams showing an example of the word structure of a part for reading the density unevenness of a test pattern according to its color. FIG. FIGS. 12A, 12B, and 12C are explanatory diagrams for explaining the mode of scanning drive of the reading unit according to the example. Figure 13 is a block diagram showing an example of the configuration of the control system of the inkjet recording apparatus according to this example, Figure 14 is a block diagram showing details of the system for correcting density unevenness, and Figure 15 is An explanatory diagram for explaining the unevenness correction table to be used. FIG. 16 is a flowchart showing an example of the unevenness correction processing procedure according to this example. FIG. FIG. 18 is an explanatory diagram for explaining the temperature change of the recording head. FIGS. 19A, 1qB, and 19C show stable density unevenness correction regardless of temperature. FIG. 20 is an explanatory diagram showing an example in which a pattern for ejection stabilization, a pattern for detecting ejection failure, and a test pattern for density unevenness correction are recorded on a recording medium; FIG. 21 is a block diagram showing an example of the main configuration of a control system for correcting density unevenness across all ejection ports in a fully multi-type recording head according to this example. FIGS. 22 and 23 are test pattern recordings. 24 is a block diagram showing a configuration example for correcting the difference in the output size depending on the color of the unevenness reading sensor; FIG. 25A; FIG. 25B is an explanatory diagram of the mode of correction, FIG. 26 is a schematic diagram showing an embodiment in which the present invention is applied to a serial blink type device, FIG. 27 is a schematic diagram showing the reading system unit, and FIG. 28 is a serial A schematic diagram showing another embodiment in which the present invention is applied to a device in the form of a printer, FIG. 29 is a schematic diagram of the reading system unit, and FIGS. 30 and 31 are diagrams in which the present invention is applied to a device in the form of a serial printer. 32A to 32E, FIG. 33, FIG. 34, and FIG. 35 are schematic diagrams showing two other embodiments. The figure is an explanatory diagram for explaining the reading unit for correcting density unevenness, Figures 37A to 37C are conceptual diagrams showing the print pattern in the test pattern image according to the embodiment of the present invention, and Figure 38 is the above 39A and 39B are flowcharts showing processing procedures in density unevenness correction printing mode and normal printing mode using the above printing patterns. 1, IC, IM, IY, lBk, 201G,
201M, 201Y, 2018k... Recording head, 2.202... Recording medium, 3... Head holder, 5... Head holder moving mechanism, 7... Ink supply/circulation system unit, 9...・Cap unit, 11... Cap unit moving mechanism, 14, 214・
...reading unit, 15...reading unit scanning mechanism, 16...recording medium conveyance system drive section, 17...platen, 40...conveyance belt, 41...roller, 42...discharge roller , 60... Reading head, 62... Light source, 63, 74... Lens, 73, 217... Reading sensor, 76... Housing, 77R, 77G, 77BL... Color filter, 78a
, 78b - Pressing roller, 80... Pressing member, 81.85... Transparent roller, 101... CPU. 102...ROM. 104...RAM. 106... Instruction input section, 113... Head temperature adjustment section, 114... Color filter switching drive section, 119.219
...RAM. 122C, 122M, 122Y, 1228k...
Unevenness correction table, 127.236... A/D converter, 129c, 129M, 129Y, 1298k...
・Unevenness correction RAM, 135c, 135M, 135Y, 1
358, 235C, 235M, 235Y, 235C・
...Amplifier, 220...Recovery device. Fig. 1C Fig. 2B Fig. 7A Fig. 7B Fig. 0.5 +, OL 5 gradation level (Y) light J:8 1 person figure 12A figure 128 figure 12C figure ＼Q 16 figure 17 figure 18 figure 1 OA figure oj-erotic position! Fig. 198 Fig. 19c. To the record in Figure 25A, on the FD, top 1 entry No. Fig. 25B Fig. 27 Fig. 33 Fig. 34 Fig. 35 Fig. 36 Fig. 37A Fig. 37B Fig. 37C Figure 38 - 1 print a 1 code - Figure 39A (7 codes printed when wearing a hakama) Figure a98

Claims (1)

[Claims] 1) A recording head in which a plurality of recording elements are arranged to form an image on a recording medium, and an overlap of dots in a dot pattern recorded by each of the plurality of recording elements by the recording head. a test pattern image formation control means for controlling image formation by the recording head in order to form a test pattern image with a dot pattern having less overlap than that in normal image formation; reading means for reading the density of a test pattern image formed by the recording head based on control; and density correction for performing density correction when the recording head performs the normal image formation based on the density read by the reading means. An image forming apparatus comprising: means; 2) The test pattern image formation control means includes a test pattern image signal generation means for supplying a driving signal for the recording head corresponding to the test pattern image to the recording head, and the density correction means includes a 2. The image forming apparatus according to claim 1, further comprising calculation means for calculating a density correction coefficient for the normal image formation based on the read density. 3) The test pattern image formation control means has a recording medium for forming the test pattern image, controls the image formation according to the dot recording properties of the recording medium, and the density correction means includes: 2. The image forming apparatus according to claim 1, further comprising calculation means for calculating a density correction coefficient for the normal image formation based on the read density. 4) The test pattern image formation control means includes a drive condition control means for controlling the drive conditions of the recording head related to the test pattern image, and the density correction means controls the normal driving condition based on the read density. 2. The image forming apparatus according to claim 1, further comprising calculation means for calculating a density correction coefficient for image formation. 5) Image formation according to any one of claims 1 to 4, characterized in that a plurality of recording heads are provided corresponding to recording materials of different colors in order to perform multicolor recording. Device. 6) The recording head has the form of an inkjet recording head, and the inkjet recording head is characterized in that the recording element includes an electrothermal conversion element that is used to cause film boiling in the ink to eject the ink. The image forming apparatus according to any one of claims 1 to 5. 7) In an image forming apparatus that forms an image on a recording medium using a recording head in which a plurality of recording elements are arranged, dots in a dot pattern recorded by each of the plurality of recording elements by the recording head usually overlap. A test pattern image formation control means for controlling image formation by the recording head, in order to form a test pattern image with a dot pattern having less overlap than the dot overlap when performing image formation, and a test pattern image formation control means for controlling the test pattern image formation control means. reading means for reading the density of the test pattern image formed by the recording head based on the density; and density correction means for performing density correction when the recording head performs the normal image formation based on the density read by the reading means. An image forming apparatus characterized by comprising the following. 8) The recording head has the form of an inkjet recording head, and the inkjet recording head is characterized in that the recording element includes an electrothermal conversion element used for causing film boiling in the ink to eject the ink. The image forming apparatus according to claim 7.