JP2938968B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-uniformity correction data generating apparatus and an image forming apparatus, and more particularly to image forming in which an image is formed using a recording head having a plurality of recording elements arranged. It is suitable for application to an apparatus.

In particular, the present invention relates to an apparatus having a mechanism for automatically adjusting the print characteristics of a recording head of an ink jet recording apparatus, and is particularly effective for an apparatus for forming a color image at a high gradation by overlapping ink droplets.

[Background Art] With the spread of information processing devices such as copying machines, word processors and computers, and communication devices, digital images are formed by using a recording head of an ink jet system or a thermal transfer system as an image forming (recording) device of these devices. Recorders are rapidly becoming popular. In such a printing apparatus, in order to improve the printing speed, it is common to use a printing head in which a plurality of printing elements are integrated and arranged (hereinafter, referred to as a multi-head in this section).

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

However, it is difficult to uniformly manufacture the recording elements of the multi-head due to the characteristic variation due to the manufacturing process, the characteristic variation of the head constituent material, and the like, and a certain degree of variation occurs in the characteristic of each recording element. For example, in the above-described multi-nozzle head, variations occur in the shape of the ejection ports and liquid paths, and in the thermal head, variations also occur in the shape, resistance, and the like of the heater. Such non-uniformity of characteristics among the recording elements appears as non-uniformity in the size and density of dots recorded by each recording element,
Eventually, density unevenness occurs in the recorded image.

To cope with this problem, various methods have been proposed for visually detecting the density unevenness or visually inspecting the adjusted image and manually correcting the signal applied to each recording element to obtain a uniform image. .

For example, in a multi-head 330 in which the recording elements 31 are arranged as shown in FIG. 19A, when the input signal to each recording element is made uniform as shown in FIG. 19B, density unevenness as shown in FIG. 19C is visually found. In this case, as shown in Fig. 19D, it is general manual correction to correct the input signal and apply a large input signal to the recording element in the low density part and a small input signal to the recording element in the high density part. Also known as

It is known that in the case of a recording method capable of modulating a dot diameter or a dot density, gradation recording is achieved by modulating a dot diameter to be recorded by each recording element according to an input.
For example, in the case of an inkjet recording head using a piezo method or a bubble jet method, the driving voltage or pulse width applied to each ejection energy generating element such as a piezo element or an electrothermal conversion element is used. In the thermal head, the driving voltage or pulse width applied to each heater is used. Is modulated according to an input signal, it is considered that the dot diameter or dot density of each recording element can be made uniform, and the density distribution can be made uniform as shown in FIG. 19E. Also, when it is difficult or difficult to modulate the drive voltage or pulse width, or when it is difficult to adjust the concentration over a wide range even if they are modulated,
For example, when one pixel is composed of a plurality of dots,
The number of dots to be recorded is modulated according to the input signal, so that a large number of dots can be recorded in a low density portion and a small number of dots can be recorded in a high density portion. In the case where one pixel is composed of one dot, the dot diameter can be changed by modulating the number of ink ejections (the number of ejections) for one pixel in the ink jet recording apparatus. As a result, the concentration distribution can be made uniform as shown in FIG. 19E.

Japanese Patent Application Laid-Open No. 57-41965 filed by the present applicant discloses that a color image is automatically read by an optical sensor and a correction signal is given to each color ink jet recording head to form a desired color image. I have. This publication discloses basic automatic adjustment, and discloses important technical disclosures. However, various problems become evident in application to various device configurations in the course of practical application, but the technical problem of the present invention is not recognized in this publication.

On the other hand, other than the concentration detection method, JP-A-60-206660, U.S. Patent No. 4,328,604, JP-A-50-147
As disclosed in JP-A-241-241 and JP-A-54-27728, there is known an apparatus in which a landing position of a droplet is automatically read and corrected so that the droplet lands at an accurate position. These methods are also common as automatic adjustment techniques, but do not recognize the technical problem of the present invention.

[Problem to be Solved by the Invention] In order to cope with such a problem, a density unevenness reading unit is provided in the image forming apparatus, and the density unevenness distribution in the printing element array range is periodically read to obtain density unevenness correction data. It is effective to recreate it.

According to this, even if the density unevenness distribution of the head changes,
Since the correction data is re-created accordingly, it is possible to always maintain an even and uniform image.

FIG. 20 is an explanatory diagram of a mode of reading a test pattern. Here, 503A is a reading element such as a CCD arranged in the X direction on the reading sensor 503, and 520 is a recording head in which the recording elements 521 are arranged over a range 1 in the sub-scanning direction (Y direction) of the recording medium. 524 is a recording medium 501 and a recording head 52
This is a test pattern recorded by appropriately driving the recording element 521 in the process of relative movement with 0 (for example, conveyance of the recording medium 501 in the X direction).

The number of read elements such as a CCD is appropriately determined. For example, the number of read elements can be matched with the number of print elements of a print head. A read unit including such a read element group, a light source, and an optical system is illustrated. The density of the test pattern 524 can be read while scanning in the middle Y direction. Since reading is performed in the arrangement range of the reading elements, a plurality of pieces of density data corresponding to the number of reading elements are obtained for one printing element. The average of the density data is defined as the density of the printing element.

As described above, even if the input signals to all the recording elements of the multi-head are the same, if the read density is uneven, the input signal is corrected, and the image recording elements of the low density portion are corrected. Is given a large input, and a small input is given to an image recording element in a high density portion. In this way, the density of the entire multi-head is made uniform. When density unevenness appears in the correction value with subsequent use, the correction value is further corrected so that a uniform density can be always maintained.

By the way, the density distribution read by the configuration as shown in FIG. 20 is generally as shown in FIG. Here, the horizontal axis represents the arrangement direction of the image recording elements, and the vertical axis represents the density corresponding to each image recording element. The problem at this time is that the printing portion of the image recording element near the end of the multi-head has a different state than the printing portions of the other recording elements. That is, a portion printed by another image recording element has a printed portion by an adjacent recording element on both sides thereof, but the one side of the end element shows the ground color (for example, white) of the recording medium. Therefore, as shown in FIG. 21, the density at the end draws a smooth curve, and the density is read lower than the actual value. If the correction is performed in such a state, the density at the joint portion of the multi-head print area may be unnecessarily high.

SUMMARY OF THE INVENTION It is an object of the present invention to solve such a problem and to provide a density unevenness correction data creating apparatus capable of accurately correcting uneven density, and an image forming apparatus.

[Means for Solving the Problems] The present invention aims to solve such problems,
For this purpose, the present invention relates to an image forming apparatus for forming an image by moving a recording head in which a plurality of recording elements are arranged relative to a recording medium in a direction different from the direction of the arrangement of the plurality of recording elements. A test having a portion formed by driving the printing elements over the range of the arrangement of the plurality of printing elements and a portion provided in contact with both side portions thereof and formed by driving some of the printing elements. Pattern forming means for forming a pattern on the recording head; reading means for reading a test pattern formed by the pattern forming means; and a recording head formed by the recording head based on a result of reading by the reading means. Generating means for generating correction data for correcting an image.

According to the present invention, a test pattern is formed by moving a recording head in which a plurality of recording elements are arranged and a recording medium in a direction different from the direction of arrangement of the plurality of recording elements. An image forming apparatus comprising: a pattern forming unit configured to correct a density unevenness of an image recorded by the recording head using density unevenness correction data created based on a test pattern formed by the pattern forming unit; In the apparatus, the pattern forming unit is configured to drive a part of the recording elements provided by driving the recording elements over a range of the arrangement of the plurality of recording elements, and to drive a part of the recording elements provided in contact with both side parts thereof. A test pattern having a portion to be formed is formed on the recording head.

[Operation] According to the present invention, uneven data obtained by reading a test pattern is accurately associated with all the recording elements including the end recording element, and correction data for correcting an image is accurately obtained. Can be created. Further, since the portions on both sides are not formed by driving all the recording elements, no waste of the recording material occurs.

[Example] Hereinafter, an example of the present invention will be described in detail by the following procedure with reference to the drawings.

(1) Overview (Fig. 1) (2) Mechanical configuration of device (Fig. 2) (3) Reading system (Figs. 3 to 5) (4) Control system (Figs. 6 and 7) (5) Unevenness correction processing (FIGS. 8 to 12) (6) Second embodiment (FIGS. 13 and 14) (7) Third embodiment (FIGS. 15 to 18) 8) Others (1) Outline FIG. 1 is a schematic view of a main part of the present embodiment.

Here, reference numeral 1001 denotes a recording head provided with one or a plurality of recording heads according to the form of the image forming apparatus, and in a more specific embodiment described below, an ink jet for a so-called serial printer in which a plurality of ejection ports are aligned. It is a recording head. A scanning unit 1003 scans the recording medium (material to be recorded) 1002 with the recording head 1001, and a transport unit 1040 conveys the recording medium 1002 with respect to the recording position of the recording head 1001.

Reference numeral 1014 denotes a unit for reading a test pattern used for unevenness correction. In the first embodiment, the unit also serves as a reading unit for reading a document and outputting a signal used for recording.
This means includes a light source for irradiating the surface of the recording medium with light, a sensor for receiving the reflected light, and the like. Reference numeral 1020 denotes a density unevenness correction unit that corrects a driving condition of a print head during printing according to the density unevenness read from the test pattern.

Reference numeral 1015 denotes a control unit that rewrites unevenness correction data, drives the recording head, and executes irregular three-line printing, which will be described later, based on the read data.

(2) Configuration of Image Forming Unit FIG. 2 is a perspective view of one embodiment of the image forming unit equipped with the ink jet recording head of the drop-on-demand type in FIG.

In FIG. 2, the recording material 40 wound in a roll shape is conveyed in the 44 direction by being sandwiched and rotated by the feeding roller 43 via the conveying rollers 41 and 42. Guide rails 46 and 47 are placed in parallel across the recording material 45, and a recording head unit 49 mounted on a carriage 48 scans left and right. One guide rail 47 is provided with a slit,
By detecting this slit with a photo sensor provided on the carriage 48, the position of the carriage and the like can be recognized. The carriage 48 yellow, magenta, cyan, black four color heads 49Y, 49M, 49C, 49B _K is mounted, is this four-color ink tanks are arranged. Each head is 12
This is a so-called multi-nosl head having eight discharge ports. The recording material 45 is intermittently fed by the print width of the recording head 49, but when the recording material 45 is stopped, the recording head 49 scans in the P direction and ejects ink droplets according to the image signal.

(3) Reading System FIG. 3 shows a configuration example of a reading unit and its scanning mechanism in the present embodiment.

A transparent glass plate or the like is placed on the scanning portion of the read head 60, and the original 2 is placed downward on this plate so that the image on the original is read by the read head 60 from below. ing. The read head 60 shown in FIG.
Is the home position of the read head 60.

In FIG. 3, reference numeral 60 denotes a reading head, which reads an image by sliding on a pair of guide rails 61, 61 '.
The reading head 60 includes a light source 62 for illuminating the original and the original image CC.
It is composed of a lens 63 for forming an image on a photoelectric conversion element group such as D. Reference numeral 64 denotes a flexible bundle of conducting wires for supplying power to the light source 62 and the photoelectric conversion element and transmitting image signals and the like from the photoelectric conversion element.

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

After reading the image for a predetermined width, the main scanning pulse motor 67 rotates in the direction opposite to the arrow I. As a result, the read head 60 moves in the H direction and returns to the initial position.

Reference numerals 68, 68 'denote carriages, and guide rails 69, 6 for the sub-scanning (F) direction substantially orthogonal to the main scanning direction G.
Slide on 9 '. The carriage 68 'is fixed by a fixing member 70 to a driving force transmission unit 72 for the sub-scanning (F) direction such as a wire stretched on the pulleys 71, 71'.

After the end of the main scanning G, the pulley 71 is rotated in the direction of arrow H by a sub-scanning drive source (not shown) such as a pulse motor or a servomotor to a predetermined distance (the same width as the read image width in the main scanning G direction). Move the distance d) and move the carriages 68, 68 '.
Is sub-scanned in the direction of arrow F and stopped. Here, the main scanning G is started again. This main scanning G, return J in the main scanning direction,
By repeating the sub-scanning F, the entire original image area can be read.

Note that, instead of performing the sub-scanning of the reading unit, the sub-scanning may be performed on the document.

The image signal read from the test pattern is sent to the image forming unit, and is used for correcting the recording head driving conditions as described later.

In the present invention, the meaning of adjusting so that density unevenness does not occur at the time of image formation means that the image density due to droplets from a plurality of liquid ejection ports of the recording head is made uniform by the recording head itself, or for each of the plurality of heads. At least one of the following: uniforming the image density of the image, or performing homogenization in order to obtain a desired color or a desired density by mixing a plurality of liquids.
And preferably satisfies a plurality of these.

As a means for correcting the density uniformity, it is preferable to automatically read a reference print giving the correction conditions and automatically determine the correction conditions, and add a manual adjustment device for fine adjustment and user adjustment to this. I do not deny that.

The purpose of correction determined by the correction conditions may be not only the optimum printing conditions, but also adjustment within a predetermined range including an allowable range, or a reference density that changes according to a desired image, and all of the purposes included in the purpose of correction are applied. You can do it.

As an example, a description will be given of a case of correcting density unevenness of a multi-head with a recording element number N in which the print output of each element is made to converge to an average density value for the purpose of correction.

It is assumed that a density distribution occurs when each element (1 to N) is driven and printed by a certain uniform image signal S. First measuring the concentration 0D ₁ ~0D _N in the portion corresponding to each recording element an average density as the correction object Ask for. The average density is not limited to each element, and may be obtained by a method of integrating the amount of reflected light to obtain an average value or a known method.

If the relationship between the value of the image signal and the output density of a certain element or a certain group of elements is as shown in FIG. 4, the signal actually given to this element or this group of elements is obtained by correcting the signal S to obtain the target density May be determined.
That is, the correction signal S obtained by correcting the signal S to α × S = (（/ 0D _n ) × S may be given to this element or group according to the input signal S. Specifically, it is executed by performing a table conversion as shown in FIG. 5 on the input image signal.

In FIG. 5, a straight line A is a straight line having a slope of 1.0,
Although the table is a table that outputs the input signal without any conversion, the straight line B is a table that has a slope of α = ▼ / 0D _n and converts the output signal of the input signal S into α · S. Therefore, if the head is driven after performing a table conversion on the image signal corresponding to the n-th recording element and determining the correction coefficient α _n for each table as shown by the straight line B in FIG. Each density of the portion recorded by the recording element is equal to ▲. If such processing is performed on all recording elements, density unevenness is corrected, and a uniform image is obtained. That is, unevenness can be corrected by previously obtaining data indicating what table conversion should be performed on an image signal corresponding to which recording element.

Needless to say, this objective correction may be performed by comparing the densities of the nozzle groups (in units of 3 to 5 nozzles) to perform an approximate uniform processing.

Although it is possible to correct the density unevenness by such a method, the density unevenness occurs afterwards depending on the use state of the apparatus or environmental change, or a change in the density unevenness situation before correction or a temporal change of the correction circuit. It is expected that
To cope with such a situation, it is necessary to change the correction amount of the input signal. As a cause of this, it is conceivable that, as the ink jet recording head is used, a precipitate from the ink adheres to the vicinity of the ink ejection port or a foreign substance adheres to the vicinity of the ink ejection port, and the concentration distribution changes. . This is also predicted from the fact that the density distribution may change due to deterioration or deterioration of each heater in the thermal head. In such a case, for example, since the density unevenness correction is not sufficiently performed with the input correction amount set at the beginning of manufacturing or the like, the problem that the density unevenness gradually becomes conspicuous with use is also a problem in long-term use. This is a problem to be solved.

(4) Configuration of Control System FIG. 6 shows a configuration example of a control system having the above configuration. Here, 701 is a reading unit having the reading head 60, 702 is image data output by the reading head 60, 7
03 is an image processing unit that performs processing such as logarithmic conversion, masking, UCR, color balance adjustment, etc., 704 is an image signal after image processing, 705
A ROM in which an unevenness correction table is stored, 706 is an image signal after unevenness correction, 707 is a binarization circuit, 708 is an image signal after binarization, 709 is a head drive circuit, and 710 is a head drive signal. Reference numeral 711 denotes a recording head, which is representative of the heads 1Y to 1BK in FIG.

Reference numeral 712 denotes an unevenness read signal, 713 denotes a RAM for holding the readout signal, 715 denotes a CPU for controlling each unit, 716 and 718 denote an unevenness correction signal, and 717 denotes an unevenness correction RAM. Also, 720 is an ejection recovery means for improving the ejection state of the recording head 711 by performing suction or the like, 721 is a ROM storing a program described later with reference to FIG. 8, and 723 is for transporting the recording material 45. Means 725 means for causing the print head to scan the recording material.

The image-processed signal 704 is output to the unevenness correction table ROM 705.
Is converted to correct the unevenness of the recording head. This unevenness correction table has 64 correction straight lines, and switches the correction straight line (or curve) according to the unevenness correction signal 718.

FIG. 7 shows an example of the unevenness correction table.
There are 64 correction straight lines whose inclinations from = 0.68X to Y = 1.31X are different from each other by 0.01, and the correction straight lines are switched according to the unevenness correction signal 718. For example, when a signal of a pixel to be recorded at an ejection port having a large dot diameter is input, a correction straight line having a small inclination is selected, and when an ejection port having a small dot diameter is selected, a correction straight line having a large inclination is selected. to correct.

The unevenness correction RAM 717 stores a correction straight line selection signal required for correcting unevenness of each head. That is, the unevenness correction signals having 64 types of values from 0 to 63 are stored for the number of ejection ports, and the unevenness correction signal 718 is output in synchronization with the input image signal. The signal 706 corrected for unevenness by the straight line selected by the unevenness correction signal is binarized by a binarization circuit 707 using a dither method, an error diffusion method, or the like. By driving, a color image is formed.

By performing the above-described non-uniformity correction processing, the ejection energy generating element corresponding to the ejection port in the portion where the density of the head is high reduces the driving energy (for example, the driving duty),
Conversely, the discharge energy generating element corresponding to the discharge port in the thin portion increases the drive energy. As a result, density unevenness of the recording head is corrected and a uniform image is obtained.However, if the density unevenness pattern of the head changes during use, the unevenness correction signal used becomes improper and unevenness appears on the image. Occurs. In such a case, the unevenness correction data is rewritten.

(5) Unevenness Correction Processing FIG. 8 shows an example of an unevenness correction processing procedure according to this example.

When this procedure is started, first, in step S1, an ejection stabilizing operation by head recovery / initialization is executed. this is,
If the density unevenness correction processing is performed as it is when the recording head does not have a normal ejection characteristic due to thickening of ink, mixing of dust or air bubbles, etc., faithful characteristics of the head (density unevenness) are recognized. This is because there is a possibility that the operation cannot be performed.

In the ejection stabilization processing, the recording heads 49C to 49BK and the cap which is a component of the ejection recovery means 720 are opposed to and joined to each other, and the ink is forcibly ejected from the ejection ports by performing suction through the cap. Can be Further, it is also possible to clean the discharge port forming surface by abutting the ink absorber disposed on the cap unit with the discharge port forming surface, or by blowing air or wiping. Further, it is also possible to drive the recording head in the same manner as during normal recording to perform preliminary ejection.
However, the driving energy at the time of preliminary ejection does not necessarily have to be the same as at the time of printing. That is, the same processing as the so-called ejection recovery operation performed in the inkjet recording apparatus may be performed.

Note that, instead of or after the above-described processing, a pattern for stabilizing ejection can be recorded on a recording medium. Then, a test pattern or the like for density unevenness correction may be recorded thereafter. Such a pattern for stabilizing the ejection may be a warm-up area as described later.

Next, in steps S3 and S5, printing and reading of the test pattern are performed, respectively. The printing and reading modes performed in this example will be described.

As described above, the result of reading density unevenness by the method shown in FIG. 20 is as shown in FIG. Here, the horizontal axis is the Y direction, that is, the ejection port arrangement direction, and the vertical axis is the read density in the X direction averaged over the read element array range. As described above, the obtained density distribution does not show a sharp rise in density at both ends of the print area as described in the description of the conventional example.

As a countermeasure for this, as shown in FIG. 9, it is conceivable to adopt a method of printing three lines and performing correction using only the data of the center line. If three lines are printed, the recording pixels at both ends on the recording head will be adjacent to each other, and the problem of reading will be solved.

However, in this case, the following problems occur because printing is performed for three lines in which the width of the recording head is full. That is, (1) As shown in FIG. 10, since there are many read data, the memory cost increases.

(2) The calculation speed is reduced due to the large amount of read data.

(3) The consumption of the image recording agent (ink, toner, etc.) is large.

And other problems. Also, if the reading area is not properly secured in the scanning direction of the multi-head, the printing stability of the multi-head itself is uncertain. Low reliability.

And other problems.

Therefore, in the present embodiment, as shown in FIG.
Prints a test image by the line method. X is the printing direction of the ink jet head, and Y is the direction in which 128 ink ejection ports as image recording elements are arranged. As a printing method, first, the ejection openings from the 121st to the last end perform ink ejection on the first line. In the next second line, all the ejection ports perform ejection. In the last line, the eighth discharge port from the top discharges. An area surrounded by a dotted line is an area for reading a test image, and a warm-up section for printing is held on the left side of the area. The value of eight discharge ports is a value that can be regarded as the same printing state as the central part of the multi-head at the joint portion where the end nozzles have performed printing, and if this is satisfied, it will be an appropriate number be able to.

For example, if the number is set to two or more and 以下 or less of the total number of the ejection ports, it is possible to eliminate the adverse effect on the ejection due to the local temperature rise of the head. In the case of this example, if two or more discharge ports are used from the end, there is no problem in detecting the edge at the time of uneven reading, and in the print head of this example, the heat transfer from the surroundings is smaller as the end discharge port. Since it is difficult to raise the temperature, it is preferable to use this part positively because it is possible to achieve a uniform temperature over all the discharge ports. That is, since a normal recording operation state can be promptly obtained, the recording operation can be performed immediately after the correction processing.

When so-called block drive is performed (for example, in the present example, 128 discharge ports are divided into 16 blocks with eight blocks as one block, and drive is performed in block units), blocks are used as units. Can be. For example, one to three blocks at the end can be used, and within three blocks, the problem at the time of edge detection and the problem of local temperature rise can be solved, and the temperature uniformity can be achieved.

It is sufficient that the warm-up area printed before the reading area is longer than the section from the start of printing to the stable ejection. That is, as described above, when the recording head is left unattended, there is a possibility that the state of the vicinity of the discharge port may change due to evaporation of the ink liquid, and immediately after the start of the discharge, the printing state changes remarkably with time. Can be dealt with. If ejection is performed continuously from the start of printing, by taking this area, the test pattern area used as a test sample can be brought closer to the normal temporary printing state.

For the test sample printing, a 50% halftone print duty binarized using an error diffusion method, an average density storage method, or the like is used. There is no particular problem regarding reading and correction of the density with other values in the printing duty, but performing with 50% duty has the highest reliability of the density of the correction value for high duty and low duty. This is effective because unevenness is most likely to be noticeable to human eyes.

As a read head for reading the density of a sample, the read head shown in FIG. 20 can be used. In other words, the CCD element or BASIS camera element
The reading can be performed while moving the camera body 503 in which the 503A is arranged in the X direction. At this time, what is actually read as the density data is the area width after passing through the warm-up area (d in FIG. 11).

Referring again to FIG. 8, in steps S7 and S9,
In each case, averaging of the density in the X direction and assignment of density corresponding to the ejection port are performed. Each concentration is N
Therefore, in the present example, both sides 8
This is the reason why printing for each nozzle is required. By the way, each concentration obtained in this way is used as 128 lines (in this example, 128 lines).
The following method can be adopted as a method of assigning the number of discharge ports. First, a threshold value is determined with respect to the entire density distribution so that a printed portion and a blank portion can be clearly distinguished (broken line in FIG. 12). Next, a center value of coordinates having a density equal to or higher than the threshold value is obtained. The coordinates returned 64 times therefrom are sequentially applied to the 128 discharge ports as the first discharge ports. In this way, the printed density characteristics of each ejection port can be obtained. In FIGS. 9 and 10,
In performing the above process, data of 128 × 3 or more must always be processed. Therefore, although the density characteristics of the end ejection port can be obtained, the printing area and the reading area are considerably large, so that a considerable cost is required in the ink memory and time. On the other hand, in the present embodiment, these costs are reduced to less than half. Further, as compared with the case where the warm-up area is placed in the reading area, density information in a state where the ejection ports are stable is obtained, and the reliability of the density characteristics of each ejection port is increased. This increases the reliability of the correction operation.

Based on the above, an unevenness correction calculation is performed in step S11 in FIG. That is, the signals corresponding to the number of the ejection ports are sampled from the signal obtained by reading the density unevenness, and these are used as data corresponding to the respective ejection ports. These are denoted by R ₁ , R ₂ , ... R _N
Assuming that (N = 128), these are temporarily stored in the RAM 713, and then the CPU 715 performs the following calculation.

These data are converted into density signals by performing an operation of C _n = −1og (R _n / R _o ) (R _o is a constant satisfying R _o ≧ R _n ; 1 ≦ n ≦ N). Incidentally, when the threshold which the density value is preset is 1/2 of the constant read density of the test pattern, the position of the reading unit scanning direction becomes the threshold value is assumed to be P _1, P _N . This point corresponds to the position where the dot formed by the ejection port at the end is read only half by the reading sensor. Therefore, the read data at a point deviated inward of the test pattern by 1/2 dot from this point is set as read data corresponding to the end ejection port, and the values are adopted for C ₁ and C _N.

Next, average density Is calculated.

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

ΔC _n = / C _n Next, a signal correction amount (ΔS) _n corresponding to (ΔC) _n is obtained by ΔS _n = A × ΔC _n .

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

Subsequently, a selection signal of a correction straight line to be selected according to ΔS _n is obtained, and an unevenness correction signal having 64 types of values “0” to “63” is stored in the unevenness correction RAM 717 for the number of ejection ports (step S1).
3, S15). A different γ straight line is selected for each ejection port based on the unevenness correction data created in this way, density unevenness is corrected, and the unevenness correction data is rewritten.

The above processing can be performed once for each color recording head, or repeated a plurality of times until desired correction is performed. In addition to performing the test independently for each color, the test can be performed for a mixed color test pattern.

Further, it may be changed by the print duty of the test pattern. That is, when it is desired to perform appropriate correction in various density ranges, it is conceivable to print a test pattern at a print duty at which the density can be obtained and use the read result (for example, 30%, 50%). , 75%
, Or the average after printing at each duty).

Further, the formation or correction of the test pattern can be performed only when the recording medium is a predetermined one, and this may be performed regardless of the type. In this case,
For example, while forming, reading or correcting a test pattern with an appropriate duty according to the type of recording medium,
The threshold value can be changed according to the type of the recording medium.

In the above-described embodiment of the present invention, at least when performing density inspection printing of a test pattern or the like, one dot is used for a plurality of dots.
In the case of forming pixels, the print duty, that is, the print setting can be performed by modulating the number of recording dots within the number of constituent dots.

However, the printing ratio can be set by modulating the driving voltage and / or the driving pulse width, or by modulating the number of ink ejections per dot. These also correspond to the case where one pixel is composed of one dot. You can do it. In other words, it goes without saying that the present invention can be applied to whatever printing ratio is set by performing any kind of modulation.

Although the above embodiment of the present invention is an optimum embodiment in which the obtained correction processing is performed for each of the ejection energy generating elements, practically, in consideration of the convergence state and the processing time of the density uniformization processing, a predetermined value is obtained. It is preferable to perform correction so as to apply a common correction to a plurality of adjacent ejection energy generating elements.
From this point of view, it is preferable that the optimal configuration is such that the multiple ejection energy generating elements of the print head apply a common correction to each block drive group in which a plurality of elements are grouped. The block drive itself may be any of a well-known or known one, or a specific block drive method. However, a drive condition capable of implementing a corrected uniform density after determining the density unevenness of the present invention is given. Needless to say, this is a premise.

(6) Second Embodiment FIG. 13 shows a second embodiment of the present invention.

Here, apart from the image reading means in FIG.
A reading head for uneven density was provided independently in the image forming section.
Although the image reading section of this embodiment can be configured in the same manner as in FIG. 3, a mechanism for performing sub-scanning of the reading unit may not be required. In FIG. 13, the same reference numerals as those in FIG. 2 denote the same components.

The image forming section of this embodiment is provided with a density unevenness reading head as indicated by reference numeral 121 in FIG. The density unevenness reading head 121 is a line BASIS camera or the like having a reading density equal to the recording density of the head, and reads density unevenness of a print sample (test pattern) in the same manner as described above. However, at this time, the read head 121 remains fixed, the recording error 45 is delayed in the direction of 44 by the rotation of the paper feed roller, and the unevenness correction pattern passes under the unevenness read head. , Spot read head
121 reads density unevenness.

The image signal obtained here is processed in the same manner as in the first embodiment. FIG. 14 shows a control system according to this embodiment. Here, 701 to 718 indicate the same functions as those described in FIG. In this figure, each part 720, 721, 723, 72 in FIG.
5 is abbreviated. In the present embodiment, the density unevenness reading head 121 is completely separate from the image reading unit 701, and the unevenness correction RAM can be rewritten at any time in the same manner as in the first embodiment based on the image signal 712 obtained thereby, so that a uniform image can always be obtained. It becomes possible.

(7) Third Embodiment Next, a third embodiment will be described. In the first and second embodiments, an image forming apparatus having a reading system and a printing system has been described as an example. However, here, a dedicated area CCD sensor is separately prepared for a dot printer that performs printing by using a multi-level signal and reading is performed. Show the case.

FIG. 15 shows the arrangement. T is a test sample, and 605 is the body of a CCD area camera. The second embodiment is characterized in that the density is read without relatively moving the camera and the original.

CCD from the test sample in Fig. 15 in the direction of the arrow
FIG. 16 is a view of the camera, and 606 is a reading element. The reading elements are arranged uniformly on the XY plane, for a total of 38
There are 10,000 pixels. In addition, one dot of the print sample is set so as to be approximately 9 pixels as shown in FIG. With such a large number of pixels, the test sample area can be read at a time, and the readout at three times higher resolution increases the density assignment to the ejection ports by three times. In addition, according to this method, even if there is a limitation in the Y direction of the CCD camera 605, it is possible to cope with a considerable range by adjusting one and three lines of irregular three-line printing.

The density data obtained in this way is subjected to the same data processing as in the previous embodiment to obtain correction data.
In this case, since the image forming apparatus and the image reading apparatus are completely separate, the data processing path is slightly different from that of the above-described embodiment.

FIG. 18 shows a processing block of the data signal for the image forming apparatus and the reading apparatus. Reference numerals 702 to 718 denote the same operations in the image forming apparatus as those in FIG. 6 of the first embodiment. 901 is an area CCD density unevenness reading head, 902 and 904 are signal values thereof, 903 is RAM, 905 is CPU, 906 is RAM corresponding to the first and second embodiments, and is replaced every time density correction is performed. Things. Dedicated read head
The image signal 902 sent from the 901 is stored in the RAM 903,
Thereafter, the processing is performed by the CPU. The processing here is the same as in the first and second embodiments, but finally the unevenness correction data is written to the ROM. The written unevenness correction ROM 906 is
The ROM is used to select an unevenness correction table from the ROM. By performing such a process as needed, a stable and uniform image can always be obtained.

(8) Others The present invention can be applied to an image forming apparatus using various recording methods in which density unevenness may cause a problem (for example, a thermal printer), but when applied to an ink jet recording method, among them, Canon Inc. The present invention brings about an excellent effect in the bubble jet type recording apparatus proposed by the US Pat. According to such a method, it is possible to achieve a higher density and a higher definition of the recording, and it is more effective to prevent the occurrence of the density unevenness.

Regarding the typical configuration and principle, it is preferable to use the basic principle disclosed in, for example, US Pat. Nos. 4,723,129 and 4,740,796. This method can be applied to both the so-called on-demand type and the continuous type. In particular, in the case of the on-demand type, it is arranged corresponding to a sheet or a liquid path holding a liquid (ink). Applying at least one drive signal corresponding to the recording information and providing a rapid temperature rise exceeding nucleate boiling to the electrothermal exchanger, thereby causing the electrothermal transducer to generate thermal energy, and This is effective because a film in the liquid (ink) corresponding to the driving signal can be formed one by one by causing film boiling on the heat acting surface. The liquid (ink) is ejected through the ejection opening by the growth and contraction of the bubble to form at least one droplet. When the drive signal is formed into a pulse shape, the growth and shrinkage of the bubble are performed immediately and appropriately, so that the ejection of a liquid (ink) having particularly excellent responsiveness can be achieved, which is more preferable. U.S. Pat. No. 44
Those described in JP-A-63359 and JP-A-4345262 are suitable. Further, if the conditions described in US Pat. No. 4,313,124 relating to the invention relating to the temperature rise rate of the heat acting surface are employed, more excellent recording can be performed.

As a configuration of the recording head, in addition to a combination configuration (a linear liquid flow path or a right-angled liquid flow path) of a discharge port, a liquid path, and an electrothermal converter as disclosed in the above-mentioned specifications, A configuration using U.S. Pat. No. 4,558,333 and U.S. Pat. No. 4,459,600, which disclose a configuration in which is disposed in a bending region, is also included in the present invention. In addition, Japanese Unexamined Patent Publication No. 59-23670 discloses a configuration in which a common slit is used as a discharge section of an electrothermal converter for a plurality of electrothermal converters, and an aperture for absorbing a pressure wave of thermal energy is provided. The effect of the present invention is effective even if the configuration is based on JP-A-59-138461, which discloses a configuration corresponding to a discharge unit. That is, according to the present invention, recording can be reliably and efficiently performed regardless of the form of the recording head.

In addition, in the case of a serial type head as in the above example, a recording head fixed to the apparatus main body, or an electric connection with the apparatus main body or supply of ink from the apparatus main body by being attached to the apparatus main body. The present invention is also effective when a replaceable chip-type recording head which enables the recording or a cartridge-type recording head in which an ink tank is provided integrally with the recording head itself is used.

Further, it is preferable to add recovery means for the print head, preliminary auxiliary means, and the like provided as a configuration of the printing apparatus in the present invention since the effects of the present invention can be further stabilized. If these are specifically mentioned, capping means for the recording head, cleaning means, pressure or suction means, preliminary heating means by an electrothermal transducer or another heating element or a combination thereof, Performing a preliminary ejection mode in which ejection is performed separately from printing is also effective for performing stable printing.

Regarding the type or number of print heads to be mounted, for example, in addition to one provided for single color ink, a plurality of print heads are provided corresponding to a plurality of inks having different print colors and densities. May be used. That is, for example, the printing mode of the printing apparatus is not limited to the printing mode of only the mainstream color such as black, but may be any of integrally forming the printing head or a combination of a plurality of printing heads. The present invention is also extremely effective for an apparatus provided with at least one of full colors by color mixture.

In addition, in the embodiments of the present invention described above, the ink is described as a liquid. However, an ink that solidifies at or below room temperature and softens or liquefies at room temperature, or the ink itself in an inkjet method. In general, the temperature is controlled within a range of 30 ° C. or more and 70 ° C. or less to control the temperature so that the viscosity of the ink is in a stable ejection range. I just need. In addition, the temperature rise due to thermal energy can be positively prevented by using it as energy for changing the state of the ink from a solid state to a liquid state, or ink that solidifies in a standing state to prevent evaporation of the ink can be used. In any case, the ink is liquefied by the application of the thermal energy according to the recording signal, and the ink is liquefied, and the liquid ink is discharged. The present invention is also applicable to a case where an ink that liquefies for the first time by energy is used. The ink in such a case is disclosed in
No. -56847 or JP-A-60-71260, while being held as a liquid or solid substance in a porous sheet recess or through hole, facing the electric heat exchanger. It is good also as a form. In the present invention,
The most effective one for the above-described nuclear ink is to execute the above-described film boiling method.

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

Although the above-described embodiments show various configurations taking up a number of technical problems, all of the above-described configurations are not essential to the present invention, and the designed device configuration and setting of a desired concentration uniformization level are not necessary. This indicates that it is more preferable to arbitrarily require a configuration by using one or more of the above configurations.

[Effects of the Invention] As described above, according to the present invention, the uneven data obtained by reading the test pattern and the end recording element are included without wasting the recording agent or enlarging the memory or the like. There is an effect that it is possible to accurately correspond to all the recording elements and to accurately create correction data for correcting an image.

Thus, the image forming apparatus can form a high quality and high quality image.

[Brief description of the drawings]

FIG. 1 is a schematic view for explaining the outline of a first embodiment of the present invention, FIG. 2 is a schematic perspective view of a serial printer type inkjet recording apparatus according to an embodiment of the image forming apparatus of the present invention, FIG. 3 is a perspective view showing a configuration example of a reading unit and its scanning mechanism in the present embodiment, FIGS. 4 and 5 are explanatory views of a mode of correcting unevenness of a recording head, and FIG. 6 is a control system according to the first embodiment. FIG. 7 is an explanatory diagram for explaining an unevenness correction table used in the present example, FIG. 8 is a flowchart showing an example of an unevenness correction processing procedure according to the first embodiment, FIG. FIG. 10 is an explanatory diagram for explaining three-line printing of a test pattern on which the present invention is based, FIG. 10 is an explanatory diagram of density data obtained from the test pattern, and FIG. 11 is an irregularity 3 according to the first embodiment. By line printing FIG. 12 is an explanatory view of a test pattern, FIG. 12 is an explanatory view of density data obtained from the test pattern, and FIG. 13 and FIG. 14 are perspective views of an image forming apparatus according to a second embodiment of the present invention and FIG. FIG. 15, FIG. 16, and FIG. 17 are explanatory diagrams of reading means according to the third embodiment of the present invention, and FIG. 18 is an example of the configuration of the control system of the present embodiment. 19A to 19E are explanatory diagrams for explaining an aspect of density unevenness correction in a multi-nozzle head, FIG. 20 is an explanatory diagram for explaining conventional test pattern formation and reading thereof, FIG. 21 is an explanatory diagram of density data obtained by the reading. 45,1002… Recording medium (recording material), 48… Carriage, 49Y, 49M, 49C, 49BK, 711,1001… Recording (printing) head, 60,121,901… Read head, 701… Image reading unit, 703: Image processing unit, 705: Uneven correction table ROM, 707: Binarization circuit, 709: Driving circuit, 715,905: CPU, 717,906: Uneven correction RAM, 720: Discharge recovery means, 723: … Recording medium conveying means, 725, 1003… head scanning means, 1014… reading means, 1015… control means, 1020… unevenness correcting means.

(72) Inventor Hiromitsu Hirabayashi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Atsushi Arai 3-30-2, Shimomaruko 3-chome, Ota-ku, Tokyo Canon Inc. (58) Field surveyed (Int. Cl. ⁶ , DB name) B41J 2/01 B41J 2/13 B41J 29/46

Claims (7)

(57) [Claims] 1. An image forming apparatus for forming an image by moving a recording head on which a plurality of recording elements are arranged relative to a recording medium in a direction different from the arrangement direction of the plurality of recording elements, A test pattern having a portion formed by driving the printing elements over the range of the arrangement of the plurality of printing elements and a portion provided in contact with both sides thereof and formed by driving some of the printing elements is used. Pattern forming means to be formed on the recording head; reading means for reading a test pattern formed by the pattern forming means; and an image formed by the recording head based on a result of reading by the reading means. An image forming apparatus comprising: a creation unit that creates correction data for correction. 2. An image forming apparatus according to claim 1, wherein said pattern forming means forms said test pattern in the course of said movement of said recording head three times. 3. The image forming apparatus according to claim 1, wherein the reading unit reads the test pattern by scanning an optical sensor in an arrangement direction of the plurality of recording elements. 4. The correction means using only a portion of the test pattern read by the reading means formed by driving a printing element over a range of the arrangement of the plurality of printing elements. 4. The image forming apparatus according to claim 1, wherein data is created. 5. An image according to claim 1, wherein a plurality of said recording heads are provided corresponding to recording agents having different colors in order to perform multicolor color recording. Forming equipment. 6. The recording head according to claim 1, wherein the recording head is of an ink-jet type, and has an electrothermal conversion element used for causing ink to eject the ink by causing film boiling. An image forming apparatus according to any one of the above. 7. A test pattern is formed by moving a recording head having a plurality of recording elements arranged thereon and a recording medium in a direction different from the direction of arrangement of the plurality of recording elements. An image forming apparatus comprising: a pattern forming unit; and a correcting unit that corrects density unevenness of an image recorded by the recording head using density unevenness correction data created based on a test pattern formed by the pattern forming unit. In the above, the pattern forming means may be formed by driving a printing element over a range of the arrangement of the plurality of printing elements and driving a part of the printing elements provided in contact with both sides thereof. An image forming apparatus for forming a test pattern having a portion to be formed on the recording head.