JPH0428555A - Density variation correction data preparation device and image formation device - Google Patents

Abstract

PURPOSE:To detect a reference position for reading an end recording element always correctly, if a different color is detected and enable variation data to match a recording element accurately by making a threshold value for detecting the end recording element variable depending on the color of a test pattern. CONSTITUTION:To correct the density variation of data recorded by a recording head 1001, a density variation reading device 1014 is used which reads a test pattern formed on a medium for recording using the recording head 1001 and detects a density variation over a range where discharge orifices are arranged. This device consists of a matching device 1101A which matches one at the end of arranged discharge orifices with a density at a point where a specified threshold value is reached and allows preparation of correction data for a discharge energy generation element located in the discharge orifice based on the matched density, and a device 1101B to change the threshold value according to the color of a test pattern.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application 1] The present invention relates to an unevenness correction data creation device and an image forming device, and particularly to an image forming device that forms an image using a recording head formed by arranging a plurality of recording elements. This is suitable for application to devices.

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 a plurality of ink ejection openings and wave channels are integrated, and thermal transfer type and thermal type thermal heads also generally have a plurality of heaters integrated.

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. 34A, input signals to each recording element are input to a third
If density unevenness as shown in Fig. 34C is visually detected when the density is made uniform as shown in Fig. 4B, the input signal is corrected as shown in Fig. 34D, 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, for inkjet recording using a piezo system or a bubble jet system, the drive voltage or pulse width applied to each piezo element or electrothermal conversion element or other ejection energy generating element is changed, and the drive voltage or pulse width applied to each heater is changed for a thermal head. It is thought that by utilizing modulation of the pulse width according to the input signal, it is 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. 34E. In addition, when it is impossible or difficult to modulate the driving voltage or pulse width, or when it is difficult to adjust the density over a wide range even if modulated, for example when one pixel is composed of multiple dots, the input signal The number of dots to be recorded can be modulated accordingly, 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.

Furthermore, when one pixel is composed of one dot, the dot diameter can be changed by modulating the number of ink ejections (the number of dots) for one pixel in an inkjet recording apparatus. By these, the concentration distribution can be adjusted to the 34th E.
As shown in the figure, uniformity can be achieved.

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.

[Problems to be Solved by the Invention] In order to deal with this problem, a density unevenness reading unit is provided in the image forming apparatus, and the density unevenness reading section is periodically read in the recording element arrangement range and density unevenness correction data is generated. It is effective to recreate it.

According to this, even if the density unevenness distribution of the head changes, the correction data is re-created accordingly, making it possible to always maintain a uniform image without unevenness.

FIG. 38 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. Reflected light reading sensors 504 and 505 are lenses, and 506 is a reading unit equipped with these.

Then, by scanning the reading unit 506 having such a configuration and reading the unevenness distribution, it is possible to recreate the unevenness correction data.

FIG. 39 is an explanatory diagram of a mode of reading a test pattern. Here, 500 is a reading unit shown in FIG. 38, and 520 is a recording head in which recording elements 521 are arranged over a range β in the width direction (X direction) of the recording medium. 5
24 is a test pattern recorded by a predetermined width W by appropriately driving the recording element 521 during the relative movement between the recording medium 501 and the recording head 520 (for example, conveyance of the recording medium 501 in the X direction). . This test pattern 524 is then read by scanning the reading unit 500 in the X direction.

FIG. 40 shows the reading unit 500 in FIG.
The relationship between the scanning position and the read density of the test pattern when scanning in the direction is shown. As is clear from the figure, the beginning and end of this data are skewed, making it difficult to judge which point should be adopted as data for the recording element at the end of the recording head. For this reason, it is conceivable to set a threshold value of several tens of percent of the maximum output in advance, and use the point P at which the threshold value is reached as the reference point for the position of the edge recording element. Then, based on this reference point, the read data and the recording element are associated with each other to create unevenness correction data.

However, when an image forming apparatus has recording heads for two or more colors and unevenness correction is performed for each head, the following problems occur.

For example, if the spectral sensitivity of the uneven reading head shown in FIG. "l, 44" for cyan head, "1.46" for black head, °
A read density of '1.55'' was obtained. Since the read density differs for each color, if the same threshold value is used, the position of the detected edge will differ depending on the color.

For example, in FIG. 40, when the color of the head whose unevenness distribution is A is changed and an unevenness distribution like B is obtained, if the threshold value T remains unchanged, the detected reference point will be at the position of Po, The correspondence between the unevenness data and the recording elements becomes inaccurate, and as a result, there is a possibility that accurate correction cannot be performed.

SUMMARY OF THE INVENTION An object of the present invention is to solve such problems and provide a density unevenness correction data creation device and an image forming apparatus that can accurately correct density unevenness.

[Means for Solving the Problems] To this end, the unevenness correction data creation device of the present invention includes means for reading a test pattern formed by a recording head in which a plurality of recording elements are arranged, and detecting the density distribution within the range of the array. , a correction data creation means for obtaining correction data of driving conditions for uniformizing the density during image formation based on the reading result corresponding to the plurality of recording elements; The recording element at the end of the test pattern is provided with means for associating the density at a reference point where the density at the end of the density distribution reaches a predetermined threshold, and means for changing the threshold in accordance with the color of the test pattern. It is characterized by:

Further, the image forming apparatus of the present invention includes the unevenness correction data creation device described above, and a plurality of recording elements arranged in order to form an image on a recording medium, and the plurality of recording elements are arranged corresponding to recording agents of plural colors. The present invention is characterized in that it comprises a recording head, and a correction means for correcting the driving conditions of the plurality of recording elements for each recording head based on the created correction data when forming an image.

Furthermore, the present invention provides an image forming apparatus that forms an image on a recording medium using a plurality of recording heads in which a plurality of recording elements are arranged and are provided corresponding to recording agents of a plurality of colors. The present invention is characterized by comprising a data creation bag device and a correction means for correcting the driving conditions of the plurality of recording elements for each recording head based on the created correction data when forming an image.

[Function] According to the present invention, by making the threshold value for detecting the edge recording element variable according to the color of the test pattern, the reading standard for the edge recording element is always correctly determined even if the colors are different. By detecting the position where , it becomes possible to accurately associate the uneven data with the recording element.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail in the following steps with reference to the drawings.

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) Sequence of unevenness correction (Figure 15) Figures 16 to 25)6
Other Embodiments (FIGS. 28 to 33) 7 Others (1) Overview FIG. 1 is a schematic diagram of the main parts of this embodiment.

Here, 1001 is a print head provided one or more depending on the form of the image forming apparatus, and in a more specific embodiment described below, a plurality of ejection ports are provided over a range corresponding to the width of the print medium 1002. This is a so-called full multi-type inkjet recording head in which the inkjet recording heads are aligned.

1040 is a conveying means for the recording medium 1002, and the recording medium 1002 is
transport.

Density unevenness reading means 1014 reads a test pattern formed on the recording medium 1002 by the recording head 1001 and detects the density distribution over the ejection port arrangement range in order to correct the density unevenness printed by the print head 1001. It has a light source that irradiates light onto the surface of the recording medium, a sensor that receives the reflected light, and an appropriate conversion circuit. Reference numeral 1020 denotes a density unevenness correcting means, which corrects the driving conditions of the recording head according to the density unevenness read from the test pattern. Reference numeral 1017 is a platen that flattens the recording medium at the test pattern reading position.

1101A associates the density of the point at which a predetermined threshold has been reached for the discharge ports located at the end of the array of discharge ports, and based on this, corrects data for the discharge energy generating element located inside the discharge port. The corresponding means to be created, ll0IB, is means for changing the threshold value according to the color of the test pattern.

In this embodiment, the correction data creation function including these means is built into the image forming apparatus itself, but this may be a separate apparatus.

(2) Overview of Mechanical Configuration of Apparatus FIG. 2A shows a schematic configuration of an inkjet recording apparatus according to an embodiment of the present invention.

Here, Ic, LM, LY, and IBK are recording heads corresponding to cyan, magenta, yellow, and black inks, respectively, and the width in the recording medium conveyance direction, in this example, the short side of an A3 size recording medium. over a range corresponding to the length (297+am) of 400d
This is a full-line head with discharge ports arranged at a density of pi (dots/inch). 3 are these recording heads
This is a head holder that holds C to IBK together, 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, 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, and the like.
By appropriately moving the head holder 3 in directions A and B, the ejection ports of the print head IC-IBK are placed at a printing position facing the print medium at a predetermined distance, in order to receive the intrusion of the cap unit described below. The head holder 3 can be set at a retracted position, a position for capping each head, and the like.

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 9G, 9M, 9Y, and 98, which can face or be joined to IM, IY, and IBK, respectively, and are formed of an elastic material such as rubber to improve adhesion during joining, are used to store ink received from the recording 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). Reference numeral 11 denotes a cap unit moving mechanism, which includes a motor, a transmission mechanism, a guide member, etc., and moves the cap unit 9 in directions C and D in the figure as appropriate to move the cap unit 9 directly below the head holder 3 in the retracted position. The cap unit 9 can be set at a position that does not obstruct the lowering 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. 40 is the fed recording medium 2
This is a conveyor belt that conveys the image in the E direction with respect to the recording position by the recording head IC-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 placed between the recording position by the IB and the ejection roller 42, facing the recording surface of the recording medium 2, and reads the test pattern formed on the recording medium 2 during processing for density uniformity correction, etc. . IB is a mechanism for scanning the reading unit, which will be described below with respect 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, the recording medium stored in the cassette 38 (in this example, special paper is used, but this will be described later) moves the pickup roller 39 in the direction of arrow F as in normal recording. The paper is fed onto the conveyor belt 40 by rotating it. Then, as the roller 41 rotates, the recording medium 2 is transferred to the conveyor belt 4.
0 in the direction of arrow E, each recording head is driven at this time, 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, la is a common liquid chamber to which an ink pipe from an ink supply source is connected and also communicates with the ink ejection 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 When the ink inside the ejection port of the head 1 thickens, or when 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 the image. The reading head 60 includes a light source 62 for illuminating the original, a lens 63 for forming an image of the original on the light receiving surface of the sensor, and the like. 64 is a flexible conductive wire bundle that supplies power to the light source 62 and the sensor and transmits image signals and the like from the sensor. Note that the sensor may be a monocular sensor that reads reflected light in a predetermined range, or may be a sensor that is formed by arraying reading elements such as a CCD. In the latter case, 1
It is preferable to associate a plurality of reading elements with each ejection port, and to associate the average value of the read values with one ejection port.

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 unit 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 1, the reading head 6
0 reads line information of an image perpendicular to the main scanning direction G 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 68.68° is a support member.

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 added 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 a standard density that changes depending on the desired image (anything that is included in the purpose of correction is acceptable). It is applicable.

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 to N) with a certain uniform image signal S is as shown in FIG. 35. First, the density of the portion corresponding to each recording element is 00. ~00.
Measure and correct the average density OD = ΣOD, /N
seek. This average density is not limited to each element, and may be determined 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. 36, then the signal actually given to this element or this group of elements will correct the signal S to achieve the target density OD. 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 αX5=COD10Dn) x S may be applied to this element or group in accordance with the input signal S. Specifically, this is executed by performing table conversion as shown in FIG. 37 on the input image signal.

In FIG. 37, 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, whereas straight line B is a straight line with a slope of α=OD10D+, and is a table that outputs the input signal without converting it at all. This is a table for converting the output signal to α·S. Therefore, if the image signal corresponding to the n-th recording element is subjected to table conversion in which the correction coefficient α is determined for each table, as shown by the straight line B in FIG. 37, and then the head is driven, N Each density of the portion recorded by the recording element is 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 group of photoelectric conversion elements, 63 is a lens for converging reflected light, and 77 is an aperture with an aperture of do. 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 enters the sensor 73 via the lens 63 and the filter 77 having an aperture d0.

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. Further, in the case of a configuration in which reading is performed while moving the recording medium, 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, and 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 housing 76 housing the reading unit and scanning mechanism is initially spaced 10 mm away from the platen 17, and when the recording medium 2 on which the test pattern is recorded comes under the reading unit, the housing is lowered. and press the recording medium 2 with 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, when recording a color image using a head for three colors: cyan (C), magenta (M) 8, and yellow (Y), or four colors including black (Bk), it is necessary to rewrite the unevenness correction data. In order to do this, 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 unevenness in C, M, and Y, especially Y, when a white light Y test pattern is irradiated 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 an L (blue) filter as shown in the figure, as shown by curve B in Figure 78, the amount of received light will be smaller overall, but the dynamic range will be expanded and the accuracy of reading unevenness will be improved. It turns out. If R (red) and G (green) filters are used for C and M, respectively,
The same is true.

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, there is an R filter on the optical path to the sensor 73? ? R%G filter 77G, BL filter 77
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 do as described above.

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 l4, 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.

When reading unevenness in the test pattern 848 using the black head IBK, 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 84G of the cyan head IC, read it at the position 85H, for the test pattern 84M of the magenta head IM at the position 85G, and for 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 precision 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 frequency fωl+fω2. At fω, . . . , 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
4 may change. 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 fl other than the resonant 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.

FIG. 13 shows an example of the configuration of the control system. Here, H is a host device that supplies image data and various commands related to recording to the apparatus of this embodiment, and has a form such as a computer, an image reader, or the like. 1 is a CPU that forms the main control unit of the device of this example, and has the form of a microcomputer;
Each part is controlled according to the processing procedure described later. 102 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 indicates an online switch with the host device, input of commands to start recording, input of commands such as test pattern recording for density unevenness correction, and input of information on the type of recording medium.
This is an instruction input unit for inputting an instruction for a head to be corrected (it is also possible to specify a color to be intensively corrected), etc. 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. An image processing unit 111 performs logarithmic conversion, masking, OCR, and color balance adjustment on image data related to recording.

112 is the recording head 1 (the above heads IY, LM,
This is a head driver for driving the ink ejection energy generating elements of the ink ejection energy generating elements (IG and IBK shown collectively).

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 denotes a drive unit for the color filter switching unit 79 described in connection with FIG.

Reference numeral 116 denotes a drive unit for each motor that drives the recording medium conveyance 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 unit I.
These are cyan, magenta, yellow, and black image signals processed by Ill. 122C, 122
M, 122Y and 1228 are unevenness correction tables for each credit, which can be provided in the ROM 102 area.123G, 123M, 123Y
and 1238 is the image signal after the correction. 13
0G-1308 has a gradation correction table for each credit, 131
The G-1318 is a binarization circuit that uses a dither method, an error diffusion method, etc., and the binarized signal is sent to the driver 112 (first
4 (not shown in the figure) to the respective color heads IC to IBK.

12fiC, 126M, 126Y and! 268 represents each color signal read by the reading unit 14 through each color filter and aperture shown in FIG. 8, and is 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. 128C, 128M,
128Y and 1288 are correction data calculated by CPtJlol based on the stored signals. 1
29C to 1298 are each credit unevenness correction RAM,
An area of RAM 104 can be used. And the unevenness correction signal 130G-1308 of each credit which is the output
, respectively, unevenness correction table 122C-1228
K, and is converted into an image signal 121G-1218 so as to correct the unevenness of the heads IC to IBK.

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 0.01, and the corrected straight lines are switched according to the unevenness correction signals 130C to 130tlK. 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 RAM 129G-1298 stores correction straight line selection signals necessary to correct 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 signal 123C-1238 whose unevenness has been corrected by the γ straight line selected by the unevenness correction signal is 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 head drivers.

(The following is a blank space) (5) Sequence of non-uniformity correction With the above configuration, in this example, the following processing is performed to enable more accurate non-uniformity correction.

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 recording head density unevenness is corrected and a uniform image is obtained, but if the density unevenness pattern of the head changes as it is used, the unevenness correction signal used becomes inappropriate and unevenness appears on the image. occurs. 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, in step Sl, input of the type of recording medium is accepted. 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, the process proceeds 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 modification of this embodiment, the type of recording medium used during normal recording is manually determined, the optimal image processing is performed accordingly, and when entering the unevenness correction data rewriting mode, input 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 S6, and input for designating the recording head to be corrected is accepted.

This accepts information on the colors to be primarily corrected (cyan, magenta, yellow, and black can be specified).

Next, the process advances to step S7 to perform temperature adjustment. 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 (OD 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 with no 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 Turn on/off (heater and fan) as appropriate,
As shown in FIG. 18, 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 this example, tests were conducted when the head temperature was 40°C, which is the first temperature adjustment standard in this example, and 50°C, which is the maximum temperature increase during recording (second temperature adjustment standard). It is also possible to print a pattern, detect density unevenness in these two types of test patterns, and perform correction based on the average value of the density unevenness (first and second density data).

In addition, in order to shorten the overall time required 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 record the tested pattern for density unevenness correction as described below and lower the head temperature to the normal recording state (from 45°C to 40°C) after correction, the fan must be driven and the By circulating the ink, the time required to reach a printable 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.

During the ejection stabilization process, the recording heads Ic to IBK and the cap unit 9 can be placed facing 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 does not necessarily have to be the same as that during recording. That is, a process similar to 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 recording heads.

By recording this stable ejection pattern, the temperature of the head is stabilized, and the ink merging system is also in a steady state, creating conditions for normal printing, and whether or not there is ejection failure during actual printing. It becomes possible to accurately grasp the density unevenness.

By the way, in an apparatus in which the recording head 1 is of the full multi-type as in this example and the recordable width is slightly larger than the image recording width for registration adjustment, the recording width when recording the test pattern is It is preferable to make the image recording width larger than the normal image recording width. For example, the maximum recording paper size is A3, and the normal image recording width is 297 mm, which is the length of the short side of A3 or the long side of A4, and is approximately 293 mm, taking into account left and right margins. Further, consider a case where the recordable width of the recording head is 295 mm. This is to electrically adjust the range of the ejection ports to be used and to correct errors in the relative positional relationship between the mechanical heads and the recording medium.

Therefore, in this case, it is highly desirable to inspect a width of 295 mm, which is the ejection port array range, and 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
In accordance with the color information set in the IO, a threshold value is set for setting a reading reference position of the ejection opening at the end of the recording head 1.

For example, when the read density of a uniform halftone with a duty of 50% is approximately 0.78 for black, 0.73 for cyan, 0.72 for magenta, and 0.50 for yellow, the threshold value is set to, for example, 1/2 of each. be able to. That is, 0.39 for black and 0.39 for cyan and magenta.
36, yellow can be set to 0.25. However, the setting conditions for the threshold value can be set not only to 1/2 of the read density but also to other appropriate conditions. For example, if the reflection density of the recording medium itself is relatively high, it is preferable to set it to 1/2 of the sum of that density and the color reading density.

Next, in step Sll, a predetermined test pattern (described later with reference to FIG. 26) is generated by the recording heads IC to IBK.
will be recorded and the density unevenness will be 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, and at this time, all unevenness correction tables are set as straight lines with an inclination of 1.0, and no unevenness correction is performed.

The pattern may be a uniform halftone, and the printing ratio may be about 30 to 75%.

Here, when a test pattern is recorded on the recording medium 2 by each recording head in this way, the ink recorded from each recording head may not be absorbed instantly depending on the type of recording medium, and the ink may not be absorbed onto the recording medium 2. The density unevenness of the recorded 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. In order to do this, 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).Then, the density unevenness of the test pattern is checked. After the condition stabilizes, 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 reads the 0-color test pattern. After that, at the same timing, M, Y, and M at !2.m are read.
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 V when conveying the recording medium 2 with respect to the recording position, the recording medium is conveyed to the density unevenness reading unit 14 at a time point g') when the test pattern recording by the recording head is completed. By decelerating the paper conveyance speed v2 when
, and this also led to 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 commonly used sensor whose spectral sensitivity is close to the visual sensitivity, the read output density is highest for BK and decreases in the order of C, M, and Y.

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, assume that the output for C is twice the output for BK. The average density in head IBK is 0DBII, the density at the target ejection port is 0DBK, etc.
, the average density in the head IC is ODc, and the density at the target ejection port of the head IC is 0Den.

If the unevenness of the ejection port of interest in the head IBK is the same as that of the head IC, the sensor output will be 0Dc=+
X 0DIX, Den = KI X 0DIIKI
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-UUcll = KI (υυ8X
LllJII is n), and this value is higher for C than for B
It becomes 1 times that of K. Based on this value, correction data for the target ejection port is obtained, but there is a problem that the final correction amount is different for BK and C, even though the density unevenness of the head is the same. Occur.

Therefore, in this embodiment, the ratio of sensor outputs between each color is determined in advance, and the CPU 10 is used for unevenness reading processing.
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 l: to +:Ka.
: When it becomes Ks, the output when reading BK is "
Multiply by 1”, for C, multiply by l/, for M, multiply by 1
Multiply 7 by 2, and if it is Y, multiply by 1/Kl.

This way, for example in the example above, 1/KI
(ODC-0Dcn)”1/ni+ (KI X (o
os, -0DBK, ))”0Dax 0Dsxl.

Therefore, 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 the CPU 101, but may be performed at a previous stage.

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.
This is effective against the problem that the resolution of the read data of each color deteriorates because it has to be converted into digital data within the width.

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

FIG. 26 is an explanatory diagram for explaining the test pattern and its reading according to this example. Here, Wl is the formation range of the test pattern T in the recording medium transport direction E, and R
is the reading range in the direction E by the reading unit 14 (length R = dI in FIG. 4), and this R1
Density unevenness correction data is created based on the read data obtained from the. As shown in the figure, in this example, the length of R1 is smaller than the length of W, and R is within the range of Wl with a margin on both sides in the conveyance direction.

If the relationship between the two is not determined in this way, that is, if the length of R1 is greater than or equal to the length of Wl, then R1 is
In cases where the density is not within the range of However, according to this example, such inconvenience can be prevented.

In addition, especially providing a margin on the Tf side outside the range of R1,
That is, it is preferable to drive the recording head from before the part where reading is actually performed, also from the viewpoint of stabilizing its operation. From this point of view, by performing this drive, all or part of the above-mentioned stabilization processing (the processing of steps S7 and S9 in FIG. 16 and the processing for forming pattern 2 in FIG. 20) can be omitted. It also becomes possible.

In addition, in order to read within the range of wl with a margin on both sides of R1, for example, take into account the distance between the recording position and the reading position + the length of R1 and W, etc. after recording the test pattern. This can be done by determining the amount of transport.

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 R+, R*,...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 concentration signal by performing an operation such that Cn=log(R11/Re) (R is a constant such that R6≧R; 1≦n≦N). It is assumed that when the preset threshold value of the density value is 172, which is the constant reading density of the test pattern, the position in the scanning direction of the reading unit that becomes the threshold value is p, , p. This point corresponds to the position where only half of the dot formed by the outlet at the end is read by the read sensor. Therefore, the read data at a point shifted inward from this point by 1/2 dot of the test pattern is taken as the read data corresponding to the end discharge port, and that value is adopted for C, , C,.

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.

ΔC, = C/C.

Next, the signal correction amount (ΔS) according to (ΔC)n. ΔS
, =AX ΔCn.

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

Next, a selection signal for the correction straight line to be selected according to ΔSo is obtained, and unevenness correction signals having 61 types of values from "0" to "60" are stored in the 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.

Note that in this embodiment, the recording head to be corrected is
However, when performing full-color recording using a device such as the one according to this embodiment, two
In many cases, it is better to create unevenness correction data for heads of more than one color. In such a case, it is troublesome to set the duty every time. Therefore, as a modification of the present example, even in such a case, it is possible to perform unevenness correction by setting a plurality of colors at once in advance.

In this example, the same control system as described above can be adopted, but the 16th
At step S6 in the figure, a plurality of colors, such as cyan+black, cyan+magenta+black, etc., can be selected. Further, a single instruction input section for specifying the gold color may be provided. For example, when cyan and black are selected, a cyan pattern T and a black pattern T2 are printed on the recording medium 2, as shown in FIG. 27A. The threshold value is first set for the cyan pattern, and the cyan pattern T is read using this threshold value. When the reading is completed, a threshold value for the black pattern T2 is set, and the black pattern T2 is set.
2 will be read. Switching of the threshold value is done on recording medium 2.
Various methods may be used, such as monitoring the conveyance of the material and taking action accordingly.

This has the advantage that even if there are a plurality of heads involved in creating unevenness correction data, there is no need for the trouble of resetting the threshold every time.

Another modification is to print a mark in front of the test pattern that indicates which color head the test pattern is from, read it to determine which color head it is, and then set the optimal threshold. be able to.

FIG. 27B shows the test pattern of this example, where Ml is a mark indicating cyan and M2 is a mark indicating black.

Before printing the cyan test pattern, mark island is printed, and before printing the black test pattern, mark M is printed.
Print 2. The reading head first reads the mark M1, determines the color of the uneven density head, sets an optimal threshold value, and reads the test pattern T1.

Next, the mark M2 is read, the color is judged again, an optimal threshold is set, and the test pattern T2 is read using this.

By doing so, it becomes possible to automatically set the threshold value.

The above also applies when adjusting the amount of light emitted by the light source for reading, multiplying the reading output by an appropriate constant according to the color, or amplifying the signal as in this example. This method is effective because it may not always be possible to obtain a uniform density at the edges regardless of the color due to reflection, but it can be applied even more effectively if such adjustment is not performed.

Note that in the word examples described above, the threshold value is changed only according to the color, but it may be changed depending on the printing duty of the test pattern. In other words, if you want to make appropriate corrections in various density ranges, it is conceivable to print a test pattern at a printing duty that provides the density and use the reading results (for example, 30%, 50%, etc.). %, 75%, or when printing at each duty and then taking the average), the reading density differs depending on the duty, and therefore, when the threshold value is set to be constant regardless of the duty, there is an edge. Since there is a risk that the reading reference position of the partial ejection port may not be detected correctly, the threshold value may be changed depending on the print duty.

The above also applies when adjusting the amount of light emitted by the light source for reading, multiplying the reading output by an appropriate constant according to the color, or amplifying the signal as in this example. This method is effective because it may not always be possible to obtain a uniform density at the edges regardless of the color due to reflection, but it can be applied even more effectively when such adjustment is not performed.

Furthermore, in the above example, the test pattern was formed or corrected only when the recording medium was a specified one.
This may be done regardless of the type. In this case, for example, it is possible to form, read, or correct a test pattern with an appropriate duty according to the type of recording medium, and to change the threshold value according to the type of recording medium.

Further, in the above example, a test pattern of primary colors was printed to perform correction, but a test pattern of mixed colors may also be used.

In the embodiment of the present invention described above, at least when printing for density inspection such as a test pattern, if one pixel is composed of a plurality of dots, the printing duty, that is, the printing setting, is determined by recording within the number of constituent dots. This can be done by modulating the number of dots.

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 generating means integrated with the recording head 1.

(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. 28 shows a schematic diagram of an embodiment of an inkjet recording device of the serial plink type, 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 201C.

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 transport roller 204, the transport roller clutch 211. The wl feed 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, which is the image recording area. Recording medium 202
Prior to the image recording operation, the scanning carriage 203 is moved to the position of the home position sensor 209, and then,
Outward scanning is performed in the direction of arrow 1, and cyan, magenta, yellow, and black inks are ejected from predetermined positions by the recording heads 2010 to 2018 to record an image.

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 201C to 2018 are inkjet recording heads that form bubbles using heat and eject ink droplets using 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
In order to prevent unevenness at the start of ejection caused by changes in the viscosity of the ink remaining in the ejection port of 01, the pause time,
Temperature inside the device.

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 21g, and the recording Ha degree 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 read signal of the test pattern recorded by each recording head read by each read sensor is converted into a digital signal by the A/D converter 236, the read signal is temporarily stored in the RAM 219.

FIG. 29 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. By irradiating the test patterns of each color of C, M, and Y with light of the complementary color in this way, each reading sensor 217C
, 217M, 217Y, and 2178 for each color of the test pattern, and density unevenness of each color can be read while using a sensor 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. Further, for each color test pattern, as described in connection with FIG. 26, a margin is provided outside the area where reading is actually performed for use in correction. Such a test pattern can be formed by scanning the recording head three times, and the pattern formed by the second scan can be used for correction.

FIG. 30 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. 31, 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 2350.
By amplifying the data by ~2358K, the resolution of the read data can be increased and the reading accuracy can be further improved.

FIG. 32 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.

When the carriage carrying 2018K is scanned in the A and B directions to record a test pattern on the recording medium 20, 1 is printed every time the carriage 203 is scanned once.
After the color recording head records a test pattern and the read line sensor 232 reads the test pattern recorded on the recording medium 202, the carriage 203
is scanned, and a 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. 33 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 this bubble causes the liquid (ink) to be ejected through the ejection opening to form a small droplet (at least one droplet).If this drive signal is in the form of a pulse, the growth and contraction of the bubble will occur immediately and appropriately. Because you will be exposed to
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. That is, for example, the recording mode of the recording apparatus is not limited to a recording mode for only a mainstream color such as black, but may also be a recording mode in which the recording head is configured integrally or in a combination of multiple colors, The present invention is also extremely effective for devices equipped with at least one full color by color mixture.

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, 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 even if the ink is in a liquid state when the recording signal is applied. Bye. In addition, the temperature increase caused by thermal energy can be actively prevented by using the energy to change the state of the ink from a solid state to a liquid state, or ink that solidifies when left standing is used to prevent ink evaporation. In any case, the ink is liquefied by applying thermal energy in accordance with the recording signal, and the liquid ink is ejected, or the ink has already begun to solidify by the time it reaches the recording medium. The present invention is also applicable when using ink that is liquefied only by energy. The ink used in this case is
Publication No. 4-56847 or JP-A-60-71260
As described in the above publication, the porous sheet may be held in a liquid or solid state 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. Particularly in devices such as copying machines and facsimile machines that are equipped with image reading means (league) as a document reading system, it can also be used as a reading means for reading density unevenness in recorded images.

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, and the designed device configuration and the setting of the desired concentration uniformity level are This indicates that it is more preferable to perform any required configuration using one or more of the above configurations.

In addition, in the above description, an example has been described in which the present invention is implemented in a case where an unevenness correction data creation device is integrated into an image forming apparatus and unevenness correction data is created within the image forming apparatus as necessary. However, the unevenness correction data creation device according to the present invention is not limited to such a case, and may be provided separately from the image forming device. In this case, create head unevenness correction data with another device outside the image forming apparatus and perform R.
The head and the ROM may be installed as a pair in the image forming apparatus.

[Effects of the Invention] As explained above, according to the present invention, by varying the threshold value according to the color of the recording agent of the head related to unevenness correction, the correspondence between unevenness data and the recording element is accurately taken, and accurate This has the effect that unevenness correction data can be created.

Furthermore, this allows the image forming apparatus to form high quality and high quality images.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram for explaining the present invention in detail; FIG. 2A is a schematic side view 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; and FIG. 2B is a diagram showing the ink system thereof. A schematic diagram for explaining FIG. 3 is a perspective view showing an example of the structure of the reading unit and its scanning mechanism in FIG. 2A, and FIGS. 4, 5, and 6 maintain the distance between the reading unit and the recording medium. FIG. 7A, FIG. 7B, and FIG. 7C are explanatory diagrams for explaining the mode of expanding the dynamic range of the amount of light received by the sensor according to the color. 9 and 10 are schematic diagrams showing an example of the word structure of a part for reading density unevenness of a test pattern according to its color, and FIG. 11 shows an aspect of scanning drive of the reading unit according to this example. 12A, 12B, and 12C are explanatory diagrams for explaining fluctuations in read values according to fluctuations in the scanning speed of the reading unit. FIG. 13 is an inkjet according to this example. A block diagram showing an example of the configuration of a control system of a recording apparatus, FIG. 14 is a block diagram showing details of a system for correcting density unevenness, and FIG. 15 is an explanatory diagram for explaining an unevenness correction table used in this example. , FIG. 16 is a flowchart showing an example of the unevenness correction processing procedure according to the present example, FIG. 17 is a schematic diagram showing a state in which an identification mark is attached to a recording medium to perform density unevenness correction according to the type of recording medium, FIG. 18 is an explanatory diagram for explaining the temperature change of the recording head; FIGS. 19A, 19B, and 19c are explanatory diagrams for explaining the manner in which stable density unevenness correction is performed regardless of temperature; Fig. 20 is an explanatory diagram showing an example in which a pattern for stabilizing ejection, a pattern for detecting ejection failure, and a test pattern for correcting density unevenness are recorded on a recording medium, and Fig. 21 is a full multi-type according to this example. 22 and 23 are block diagrams illustrating an example of the configuration of main parts of a control system for correcting density unevenness over all ejection ports in a recording head of the present invention. FIG. 24 is a block diagram showing a configuration example for correcting the difference in output size depending on the color of the unevenness reading sensor; FIGS. 25A and 25B are explanatory diagrams of the mode of correction. , FIG. 26 is an explanatory diagram for explaining the test pattern and reading area according to this example, FIGS. 27A and 27B are explanatory diagrams for explaining two modified examples of this example, and FIG. A schematic diagram showing an embodiment in which the present invention is applied to a device in the form of a serial printer. FIG. 29 is a schematic diagram showing the reading system unit thereof. FIG. 30 is a schematic diagram showing another embodiment in which the present invention is applied to a device in the form of a serial printer. FIG. 31 is a schematic diagram of the reading system unit, FIGS. 32 and 33 are schematic diagrams showing two other embodiments in which the present invention is applied to a serial printer type device, and FIGS. 34A to 34 are schematic diagrams. 34E, 35, 36, and 37 are explanatory diagrams for explaining the mode of density unevenness correction in a multi-nozzle head, and FIG. 38 explains two examples of reading units for performing density unevenness correction. FIG. 39 is an explanatory diagram of the test pattern reading mode, and FIG. 40 is an explanatory diagram of the relationship between the scanning position of the reading unit and the density. 1, ]C, IM, IY, lBk, 201C, 201M
, 201Y, 2018k...Recording spatula 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, ]7...platen, 40...conveyance belt, 4I...roller, 42...discharge Roller, 60... Reading head, 62... Light source, 63.74... Lens, 73, 217... Reading sensor, 76... Housing, 77R, 77G, 77BL... Color filter, 711
1a, 7111b - Press roller, 80... Press 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,
1358, 235G, 235M, 235Y,
235C...Amplifier, 220...Recovery device. Fig. 2B Fig. 7A Fig. 7B Fig. 0.5 1.0 +, 5 agog i around Kuhn (Y)'s light valley cliff - Fig. C fcL)l f+ fω2 fω3 f(HzI Palace 7-7 Drive position Figure 12A Figure 12B Figure 12C Figure Figure Figure 12B Figure 12C Figure Figure Figure 19A Figure O1 Erotic position Figure 19c Fig. 25A Fig. 26 Fig. 27A Fig. 27B Fig. 29 Sect. Figure 38 yL. Figure 39

Claims (1)

[Claims] 1) means for reading a test pattern formed by a recording head in which a plurality of recording elements are arranged, and detecting the density distribution in the range of the array, and determining the density at the time of image formation based on the result of the reading. a correction data creation means for obtaining correction data of driving conditions for uniformizing the density distribution corresponding to the plurality of recording elements; 2) Claim for creating unevenness correction data, characterized by comprising means for making the density of a reference point corresponding to a density at an end portion reach a predetermined threshold value, and means for changing the threshold value according to the color of the test pattern. The unevenness correction data creation device according to item 1, a plurality of recording elements arranged in order to form an image on a recording medium, and a plurality of recording heads provided corresponding to recording agents of a plurality of colors; An image forming apparatus comprising: a correction means for correcting driving conditions of the plurality of printing elements for each printing head based on the created correction data. 3) The image forming apparatus according to claim 2, wherein a plurality of recording heads are provided corresponding to recording materials of different colors in order to perform multicolor recording. 4) 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 to cause film boiling in the ink to eject the ink. The image forming apparatus according to claim 2 or 3. 5) In an image forming apparatus that forms an image on a recording medium using a plurality of recording heads arranged in a plurality of recording elements and corresponding to recording agents of a plurality of colors, the unevenness correction data creation according to claim 1 is provided. An image forming apparatus comprising: an apparatus; and a correction means for correcting driving conditions of the plurality of printing elements for each printing head based on the created correction data when forming an image. 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 claim 5.