JPH0418362A - Image formation device - Google Patents

Abstract

PURPOSE:To execute a reading action correctively and stably by reading density variations in a state that a recording medium does not become afloat. CONSTITUTION:A reading unit 14 which makes its way into the inside of a transparent roller 85 for holding which is divided in four segments in a peripheral direction is movable. If a test pattern 84BK is read using a black head 1BK, a roller 85 is rotated to allow the unit 14 to enter and move in a state that a recording medium is held at a pat 85A. Similarly, if a test pattern 84C is read using a cyan head IC, the reading medium is held at a position 85R and if a test pattern 84M is read using a magenta head 1M, the recording medium is held at a position 85G. In addition, if a test pattern 84Y is read using a yellow head 1Y, the recording medium is held at a position 85BL. Subsequently, it is possible to read the density variations of various color heads accurately through a filter and at the same time, prevent a sheet from becoming afloat. Thus correct data reading is ensured.

Description

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

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

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

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

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

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

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

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

Japanese Unexamined Patent Publication No. 57-41965, for which the applicant filed eight applications, 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. Re-creating it is a move.

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. 36 shows an example of a density unevenness reading unit that can be used in such a method, in which 501 is a recording medium on which a test pattern for measuring unevenness is formed, 502 is a light source that irradiates the surface of the recording medium, and 503 is its light source. 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.

Further, FIG. 37 shows another example of the density unevenness reading unit, in which 520 is a line sensor made of a CCD or the like, 521 is a reading pixel of the line sensor 520, and 524 is an unevenness correction in which a recording element is formed with a width of d in the X direction. This is a test pattern for Then, while scanning the line sensor 520 in the X direction, the density of the test pattern formed by the print head is read. Therefore, the data read by each pixel 521 of the line sensor 520 corresponds to the density of data formed by each print element of the print head.

However, even in these configurations, there are points that need to be improved.

When reading density unevenness, it is necessary to maintain a constant distance between the density unevenness reading unit and the recording medium on which a test pattern for measuring unevenness is formed. This is because if this distance changes, the detection result will also change.

However, recording media such as paper curl under high or low humidity conditions, often lifting up and changing the distance from the uneven density reading unit.

In such a state, the detection result cannot be said to accurately reflect the density unevenness of the recording head, and it becomes difficult to perform accurate unevenness correction.

SUMMARY OF THE INVENTION It is an object of the present invention to solve these problems and to be able to perform accurate and stable reading operations, thereby improving the accuracy of density unevenness correction.

[Means for Solving the Problems] To this end, the image forming apparatus of the present invention includes a print head in which a plurality of print elements are arranged to form an image on a print medium, and a density control of a test pattern formed by the print head. density reading means for reading the image; density unevenness correcting means for correcting driving conditions of the plurality of recording elements in order to equalize the density during image formation based on the reading result; The present invention is characterized by comprising means for regulating floating of the recording medium on which the test pattern is formed in the vicinity.

The present invention also provides an image forming apparatus that forms an image on a recording medium using a recording head in which a plurality of recording elements are arranged, including a density reading means for reading the density of a test pattern formed by the recording head, and a density reading means for reading the density of a test pattern formed by the recording head; a density unevenness correcting means for correcting driving conditions of the plurality of recording elements in order to equalize the density during image formation based on the results of the above, and the test pattern is formed in the vicinity of the reading position by the density unevenness reading means. The recording medium is characterized by comprising means for regulating floating of the recording medium.

[Function] According to the present invention, since density unevenness is read in a state where the recording medium does not float, an accurate and stable reading operation can be performed, thereby improving the accuracy of density unevenness correction.

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

(1 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 (Figures 16 to 25) (
6) Other embodiments (FIGS. 26 to 31) (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.

Reference numeral 1014 denotes density unevenness reading means for reading a test pattern formed on the recording medium 1002 by the recording head 1001 in order to correct density unevenness recorded by the recording head 1001, and includes a light source that irradiates light onto the surface of the recording medium; It has a sensor that receives reflected light, an appropriate conversion circuit, and the like. 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.

Reference numeral 1078 denotes a holding member related to the main part holding means of this example, which is provided near the reading position by the density unevenness reading means 1014, and prevents the recording medium 1002 from floating by pressing the recording medium 1002 against the platen 1017. To perform accurate and stable reading operations by preventing This pressing member 1078 can have an appropriate shape such as a roller shape or a plate shape. Also, platen 10
There is a general conveyance technique in which the recording area is conveyed by performing air suction or electrostatic suction on the recording area 17, but these are usually only applied to the recording area and do not extend to the downstream side in the conveyance direction.

Therefore, the holding means in the present invention includes one in which the air suction conveyance area is extended to the reading area, and one in which electrostatic suction is performed again to equalize the suction state in the reading area.

In particular, by providing a pressing member such as a roller or a plate near the reading position, it is possible to reliably prevent floating with a simple configuration.

Depending on the form of this member, it may also be used as a color filter for reading according to the color of the test pattern.

Further, it is provided integrally with the density unevenness reading means 1014, and can be displaced according to the thickness of the recording medium 1002, so that the distance between the recording medium 1002 and the reading means 1014 can be kept constant regardless of the thickness of the recording medium with a simple configuration. It may be possible to do so. In addition, if the two are separated, and there is no need to take the above-mentioned interval into consideration, the density unevenness reading means 1014 is fixed in the vertical direction in the figure, and if it is necessary to take the interval into consideration, only the reading means 1014 is fixed in the vertical direction in the figure. It may also be possible to displace it.

(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, IM, IY, and IBK are print heads corresponding to cyan, magenta, yellow, and black inks, respectively, and the width in the printing medium conveyance direction, in this example, the short side of an A3 size printing medium. The length of (
400dpi over a range corresponding to 297mm
This is a full-line head with discharge ports arranged at a density of (dots/inch). 3 are these recording head ICs~
This is a head holder that holds the IBK integrally, and can be moved by a head holder moving mechanism 5 in the direction A toward the recording position and in the direction B away from the recording position in the figure. The head holder moving machine Wt5 includes a drive source such as a motor, a transmission mechanism that transmits the drive force to the head holder 3, and a drive source such as a motor.
It has a guide member etc. that guides the movement of the head holder 3, and by appropriately moving the head holder 3 in directions A and B, the ejection ports of the recording head IC-IBK face the recording medium at a predetermined distance. The head holder 3 can be set at a recording position, a retracted position for receiving the intrusion of a cap unit, which will be described next, 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. Further, during the ejection recovery process described below, by driving the pump, it is possible to pressurize the ink supply path and forcibly discharge ink from each recording head.

9 is a cap unit, which includes recording heads IC1LM,
Caps 9C, 9M, 9Y and 98, which can face or be joined to IY and IBK, respectively, and are made of an elastic material such as rubber to improve adhesion during joining, are used to store ink (waste) received from the recording head during ejection recovery processing. The printer has an absorber for absorbing ink (ink), and a waste ink path for introducing waste ink into a waste ink tank (not shown). 1
1 is a cap unit moving mechanism, which includes a motor, a transmission mechanism, a guide member, etc., and moves the cap unit 9 to C in the figure.
By appropriately moving the cap unit 9 in the direction and the direction D, the cap unit 9 can be set at a position directly below the head holder 3 in the retracted position and at a position where it does not obstruct the descent of the head holder 3 during recording.

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

Reference numeral 38 denotes a cassette containing recording media 2 such as paper, OHP film, etc. The recording media 2 accommodated here are separated and fed one by one by a pickup roller 39 rotating in the F direction. , 40, the fed recording medium 2 is E with respect to the recording position by the recording heads IC to IBK.
It is a conveyor belt that conveys in the direction, and is wound between rollers 41. In addition, in order to increase the adhesion of the recording medium 2 to the belt 40, ensure smooth conveyance, and obtain an appropriate distance between the head and the recording medium (head gap), electrostatic adsorption or air adsorption is performed. means, or
A member such as 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, which is a recording head IC.
- It is arranged between the recording position by IBK and the discharge roller 42, facing the recording surface of the recording medium 2, and reads a test pattern formed on the recording medium 2 during processing for density uniformity correction, etc. 15 is a mechanism for scanning the reading unit, which will be described later with reference to FIG. Reference numeral 16 indicates various parts related to conveyance of the recording medium 2, that is, a feeding roller 39, a roller 41, and a discharge roller 42.
This is a drive unit for driving.

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.

(Margin below) 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 and 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 l, 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 part (the part indicated by a line return 17 in FIG. 2A) forming a platen is placed below the scanning part of the reading head 60, and the recording medium 2 is conveyed onto this guide part. The image formed on the recording medium is read by the reading head 60 at that 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, and a lens 63 for forming an image of the original onto a group of photoelectric conversion elements such as a CCD.
It is composed of etc. 64 is a flexible conducting wire bundle that supplies power to the light source 62 and the photoelectric conversion element and transmits image signals and the like from the photoelectric conversion element.

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

After a predetermined width of the image has been read, the main scanning pulse motor 67 rotates in the direction opposite to the arrow I. As a result, the reading head 60 moves in the H direction and returns to the initial position. Note that 68.68'' 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. By repeating this main scanning G, return H in the main scanning direction, and movement of the recording medium (sub-scanning), density unevenness in each color pattern or density unevenness in one color can be read a plurality of times. 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 a density uniformity correction means for this purpose, it is possible to automatically read and automatically read the reference print that provides the correction conditions.

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

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

Assume that the density distribution when printing is performed by driving each element (1 to N) with a certain uniform image signal S is as shown in FIG. 33. First, the density of the portion corresponding to each recording element is 00. ~ODN
Measure and correct the average 1 degree OD = ΣODn/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. What is necessary is to determine the correction coefficient a that brings about this. That is, a correction signal S obtained by correcting the signal S to αX5=(ODloD,)XS may be applied to this element or group in accordance with the input signal S. Specifically, the 35th
This is executed by performing table conversion as shown in the figure. Third
In Figure 5, straight line A is a straight line with a slope of 1.0, and is a table that outputs the input signal without converting it at all.
Straight line B is a straight line with a slope of α=0D10D, l, and is a table for converting an input signal S into an output signal α·S. Therefore, the correction coefficient α for each table as shown by the straight line B in FIG. 35 for the image signal corresponding to the n-th recording element. If the head is driven after table conversion is performed, each density of the portion recorded by N recording elements becomes equal to that of the surface. 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 may not be sufficient to correct density unevenness, which may cause the long-term problem that density unevenness gradually becomes noticeable as the product is used. This poses a problem to be solved in use.

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 presser roller 78a that engages with the recording medium 2 is provided in a housing 76 in which the reading unit 14 and its scanning mechanism 15 are housed.

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

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

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

The reflected light from the recording medium 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, if unevenness correction is performed according to the detection result, a uniform image can be obtained.

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 mrn 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 8a. 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 above-mentioned embodiments, the above-mentioned high-accuracy reading is also possible with an apparatus in which the main body has recording medium holding means on each of the upstream and downstream sides, and is configured to read the recording medium between the upstream and downstream holding means. It is.

By the way, when recording a color image using a head for three colors: cyan (C), magenta (M), and yellow (Y), or four colors including black (Bk), the unevenness correction data must be rewritten. In order to achieve 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 the unevenness of C, M, Y, especially Y, when white light is irradiated onto the Y test pattern and the reflected light is received without a filter, the amount of light received by the sensor 73 is as shown in Fig. 78. As shown in curve A, the dynamic range is narrow and uneven (the difference in optical density is small (0.02 to 0.15
degree) is difficult to accurately read. So the 7th B
As shown in the figure, when using light that has passed through an L (blue) filter, the overall amount of received light decreases, but the dynamic range expands and the accuracy of reading unevenness increases, as shown by curve B in Figure 7A. become. 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, an R filter 77R, a G filter 77G, and a BL filter 77 are placed on the optical path to the sensor 73.
Aperture (no filter) 778K for BL or BK,
When reading the test pattern of each color, it is possible to selectively position it as appropriate. Note that the diameter of each filter or aperture is dD 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. 10 shows an example of a configuration for this purpose. Here, 85 is a transparent presser roller divided into four parts in the circumferential direction, of which 85A is a colorless and transparent part, 85R is a part forming a red filter, 85G is a part forming a green filter,
5BL is a part forming a blue filter. 848 on the recording medium 2 is a test pattern by the black head IBK, 84G is a test pattern by the cyan head IC, 84M is a test pattern by the magenta head IM, and 84Y is a test pattern by the yellow head IY.

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

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 85R, 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 accuracy through the filter, and paper floating can be prevented, so that accurate reading is possible.

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

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

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

In other words, when the pulse motor 67 is driven to convey the reading unit conveyance system, the vibration of the reading unit conveyance system becomes very thick (becomes) at the resonance frequency fωl + fω2 + fω3 . . . as shown in FIG. 11. When the reading unit 14 is conveyed at a resonant frequency where the vibration of such a system is large, as shown in FIG. 12A, even if the recording density of the test pattern recorded on the recording medium 2 is uniform, As shown in Fig. 12B, the conveyance speed ■ω of the reading unit 14 may change.In such a case, the read output from the reading unit 14 will change as shown in Fig. 12c. This results in output characteristics with pitch unevenness, making it impossible to correctly read the recording density of the test pattern recorded on the recording medium 2.

Therefore, in this embodiment, in order to cope with such a case, the reading unit 14 is driven at a frequency f1 other than the resonance frequency of the reading unit transport system, and the test pattern is read at a constant reading speed V. 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 example, and has the form of a computer, image league, or other form. 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, and 104 is an R having a temporary storage area for image data and an area used for work in various control processes.
It is AM.

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

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

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

FIG. 14 specifically shows in detail the system for correcting density unevenness among the above configurations. Here, 121C121M,
121Y and 1218 are cyan, magenta, yellow, and black image signals processed by the image processing unit 111, respectively. 122c, 122M, 1
22Y and 1228 are unevenness correction tables for each hue, which can be provided in the area of the ROM 102. 123G, 123M, 123Y and 1
238 is the image signal after the correction. 130c~1
308 is a gradation correction table for each hue, 131C to 13
18 is a binarization circuit using a dither method, an error diffusion method, etc., and the binarized signal is supplied to each color head IC-IBK via a driver 112 (not shown in FIG. 14). .

126C, 126M, 126Y and 126BK are
These are the color signals read by the reading unit 14 through the color filters and apertures shown in FIG. 8, and are input to the A/D converter 127. 119 is a RAM area for temporarily storing the digital output signal, and the area of RAM 104 can be used. 128C, 128M, 1
28Y and 1288 are correction data calculated by the CPUI (II) based on the stored signal. 129
C~1298 is unevenness correction RAM for each machine, and RA
A region M104 can be used. The output unevenness correction signals 130G to 130BK for each unit are supplied to unevenness correction tables 122C to 1228K, respectively, and the image signals 121C to 1218 are supplied to the head IC.
~ Converted to correct IBK unevenness.

FIG. 15 shows an example of an unevenness correction table, and in this example, Y
= o, 70X to Y = 1.3 (It has 61 correction straight lines whose slopes differ by 0.01 from
The correction straight line is switched according to the unevenness correction signals 130C to 1308K. For example, when a pixel signal to be recorded by an ejection port with a large dot diameter is input, a correction straight line with a small slope is selected, and conversely, when an ejection port with a small dot diameter is used, a correction straight line with a large slope is selected to correct the image signal. to correct.

The unevenness correction RAM 129C-1298 stores correction straight line selection signals necessary for correcting unevenness of each head. That is, unevenness correction signals having 61 types of values from 0 to 60 are stored for the number of ejection ports, and unevenness correction signals 130C to 13 (IBK) are output in synchronization with the input image signal. selected γ
The signals 123C to 1238 whose unevenness has been corrected by straight lines are input to gradation correction tables 130C to 1308K, where the gradation characteristics of each head are corrected and output.

The signal is then converted to 2 by the binarization circuits 131C to 1318K.
It is converted into a value and sent to the head IC to IBK via the head driver.
A color image is formed by driving the .

(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 S1, 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. In step S3, a judgment is made based on this, and if the manually input type of recording paper is not optimal for detecting density unevenness, such as OHP sheet or trace coated paper, the display unit 110 is displayed 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 recording pressure 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 input, the optimal image processing is performed accordingly, and when entering the unevenness correction data rewriting mode, the type of recording medium used during normal recording is 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 effect that there is no need to manually select the type of recording medium.

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 I4.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 it is medium, it can be determined that the paper has a thin coating layer, and when it is rare, it can be determined that the paper is a 01 (P film). And there is a lot of reflected light,
Only when it is determined that the specified paper is suitable for density unevenness detection, the density unevenness is read and the unevenness correction data is rewritten, and in other cases, the same display as above is displayed and this can be prohibited. As a result, the operator does not have to input the type of recording medium or provide an identification mark.
The same effect as above can be obtained.

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

In an inkjet recording apparatus, the recording head is usually maintained within a predetermined temperature range (for example, about 40° C., which is the first temperature adjustment standard) in order to suppress fluctuations in image density, stabilize ejection, and the like. Therefore, for example, when this procedure is started and a test pattern is recorded, recording will be performed with the recording head temperature at 40°C, which is the first temperature adjustment standard, as shown in area a of Fig. 18. . On the other hand, when actually recording images continuously, the temperature of the head increases as shown in area b in Figure 18, and recording is performed at a maximum 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 without unevenness can be obtained when the head temperature is 40°C.
Images at 50° C. may still be patchy.

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

In this example, the head temperature is 40°C, which is the first temperature adjustment standard in this example, and 50°C, which is the maximum temperature increase temperature (second temperature adjustment standard 1) during recording. It is also possible to print test patterns, 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 for soil where density unevenness correction is to be performed, the head temperature may be adjusted from 40°C to 45°C, for example.
In order to increase the temperature, in addition to the temperature adjustment heater, electric pulses are applied to the recording element (electrothermal conversion element) to the extent that no ink is ejected, thereby shortening the time required to raise the head temperature and correcting density unevenness. can also be shortened.

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

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

Referring again to FIG. 16, in this example, a discharge stabilization operation is executed in step S9. This increases the viscosity of the ink,
If the recording head does not have normal ejection characteristics due to the incorporation of dust or air bubbles, if density unevenness correction processing is performed as is, it may not be possible to accurately recognize the head characteristics (density unevenness). This is because there is.

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, ◎ is a test pattern for detecting density unevenness. The pattern used here for ejection stabilization was one with a printing ratio of 100% duty, which was performed by driving all ejection ports of all print heads.

By recording this stable ejection pattern, the temperature of the head is stabilized, and the ink supply system is also in a steady state, and the conditions for printing in the royal palace are established, and there is no ejection failure in the actual printing condition. It becomes possible to accurately grasp the density unevenness.

By the way, in an apparatus such as this example in which the recording head l is of the full multi-type and the recordable width is slightly larger than the image recording width in preparation for registration adjustment, the recording width when recording the test pattern is normally For example, if the maximum recording paper size is 43 plates, and the normal image recording width is the length of the short side of 43 plates or the long side of A4 plates. Consider a case where the width is approximately 293 mm considering the left and right margins for 297+nm, and the printable width of the print 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 preferable to perform an inspection over a width of 295 non, which is the ejection port arrangement range (preferably, to record a test pattern with a length of 295 mo+).

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

When the discharge stabilization process as described above is completed, step S
At 11, a predetermined test pattern is recorded by the recording head IC-IBK, and density unevenness is read from this. The operation at the time of 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 morph is driven at timings d, e, f, g.
cyan, magenta, yellow, and black recording head ICs.

The LM, 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 can be a uniform halftone, and the printing ratio is 30~30.
It may be about 75%.

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

Therefore, in this embodiment, the density unevenness of the test pattern is not read by the density unevenness reading unit 14 until the state of the density unevenness of the test pattern recorded by each recording head has stabilized. 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 Figure 1). After the state of is stabilized, the recording medium is transported at timing i, and stopped when the pattern C reaches the reading device, and the reading sensor 17 is driven at timing j, and the reading unit 14 tests the 0 color. The density unevenness of the pattern is read.After that, M, Y,
The density unevenness of each BK color is read.

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

FIG. 23 is a timing chart showing another example of the operation of the device of this example. In this operation example, when the recording head finishes recording the test pattern with respect to the conveying speed v1 when conveying the recording medium 2 to the recording position, the recording medium reaches the density unevenness reading unit 14. By reducing the paper conveyance speed v2 when conveying Vl>
V2, and this also allows the second
The same effect as in Figure 2 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 the thickest for BK and decreases in the order of C, M, and Y. For example, the output ratio of BK:C:M:Y is 1:0.8
: 0.75: 0.25.

If the one-degree unevenness correction amount is determined from the ratio between the in-head average density and the density at the ejection port of interest, this difference in output does not pose a problem. For example, assume that the output for C is one times the output for BK. Assume that the average density in the head IBK is 0Dax, the density at the target ejection port is OD, X, the average density in the head IC is ODc, and the density at the target ejection port in the head IC is ODo.

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 +
To X OD8, Dcll= K+ X 0Dllxn
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 usage, ODC0DCn = K1(ooix -OD++Kn
), and this value is 1 times larger for C than for BK. Based on this value, correction data for the target ejection port is calculated, but even though the density unevenness of the heads is the same,
A problem arises in that the final correction amount is different for BK and C.

Therefore, in this embodiment, the ratio of sensor outputs between each color is determined in advance, and 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 2 to IK, :
: When it becomes K3, the output when reading BK is “1”.
”, for C, multiply by 17Kl, for M, multiply by l/
Multiply by 2, and in the case of Y, multiply l/ by .

In this way, for example, in the above example, 1/x
(00cm 00.,,)=1/+(K+X(plane a
−0Dax−))”(IDBX ODm*,l), and optimal correction can be performed without being affected by the sensor output ratio between each color.

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

For example, if the A/D converter 127 is configured with 8 bits, the 8 values of each color are converted 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 135G, 135M, 135 amplify the read signal of each color.
Y, 1358K are provided, and the sensor output values of the read signals of each color as shown in Fig. 25A are adjusted to be almost equal as shown in Fig. 25B, so that the read signal when the read signal is A/D converted. The overall width can be set narrower. Therefore, the resolution of the read data in 8 bits can be increased, and the reading accuracy can be further improved.

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

If these are R3, Rz,...R, (N is the number of discharge ports), after storing these 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 Co=Log(Rn/Ro) (R is a constant such that R8≧R; 1≦n≦N).

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

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

ΔCn=C/Cr.

Next, (ΔC). The signal correction amount (△S)n according to △5
Determine by n=AXΔCn.

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

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

In the embodiment of the present invention described above, in the case where one pixel is composed of a plurality of dots (when printing a small number of dots for density inspection such as a test pattern), the printing duty, that is, the setting of printing, is set within the number of constituent dots. This can be done by modulating the number of recorded dots.The printing duty in this case is not 100%, but is preferably 75% or less and 25% or more.

Optimally, it is preferable to form a test pattern with a printing duty of 50%. This is because it is most suitable for a method of optically obtaining reflection density, and allows minute changes in density to be obtained as appropriate to the print characteristics of the recording head.

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

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

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

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

(Space below) (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. The following description will focus on an embodiment applied to a printer.It goes without saying that the same control system and processing procedure as described above can be employed in the following examples as well.

FIG. 26 shows a schematic diagram of an embodiment of an inkjet recording device in the form of a serial printer, in which the recording head 2
Inks of cyan, magenta, yellow, and black are supplied to inks 01C, 201M, 201Y, and 2018 from ink tanks (not shown) via ink tubes. And a recording head 20IC.

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.

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

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

When the recording medium 202 reaches the feeding roller 205, the feeding roller clutch 211 and the conveyance motor 208 are turned on.
The recording medium 202 is conveyed on a platen 207 until it reaches a conveyance roller 204 . The recording medium 202 is a platen 207
It is detected by a detection sensor 212 provided above, and the sensor information is used for position control, jam control, etc. When the recording medium 202 reaches the conveying roller 204, the feeding roller clutch 211. The conveyance motor 208 is turned off, and a suction operation (not shown) is performed from inside the platen 207 to bring the recording medium 202 into close contact with the platen 207 on the image recording area. Prior to the image recording operation on the recording medium 202, the home position sensor 2
The scanning carriage 203 is moved to position 09, and first, forward scanning is performed in the direction of arrow EIIA, 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 conveyance motor 20 feeds the paper by the length recorded in 201BK.
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 discharge ink droplets using the pressure of the bubbles, and eject 256 80
Four pieces are used, each assembled individually.

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,
This is a process in which the recovery device 220 performs a suction operation for the recording head 201, a preliminary ink ejection operation, etc. based on preprogrammed conditions such as the internal temperature of the device and the ejection time.

By repeating the operations described above, image recording is performed on the entire surface of the recording medium. In the figure, reference numeral 214 denotes a density unevenness reading unit that reads a test pattern printed on the recording medium 202 by applying a uniform image signal to each of the recording heads 2010 to 2018K by the control circuit 215 and outputs a read 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, in the same manner 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 density of the test pattern recorded on the recording paper by each recording head is read by the sensors 217C, 217M, 217Y, and 2178K. After the reading signal of the test pattern recording by each recording head read by each reading sensor is converted into a digital signal by the A/D converter 236, the read signal is temporarily stored in the RAM 219.

FIG. 27 is a schematic diagram for explaining the reading section of this example.
In order to improve the accuracy of reading the density unevenness of the test pattern recorded on the recording medium 202 by the recording head,
A color filter 220R is provided on the recording medium side of the illumination light source 18.
220G and 220BL are provided, and R, G, and B are used for the C, M, and Y test patterns recorded on the recording medium 202.
, L light is irradiated. 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.

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

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

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

FIG. 30 shows still another embodiment in which the present invention is applied to a serial printer type device. In this example,
Each recording head 201C, 201M, 2QIY.

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

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

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

As for typical configurations and principles thereof, it is preferable to use the basic principles disclosed in, for example, US Pat. No. 4,723,129 and US Pat. No. 4,740,796. This method can be applied to both the so-called on-demand type and continuous type, but especially in the case of the on-demand type, it is necessary to arrange the liquid (ink) in accordance with the sheet and liquid path that hold it. The electrothermal converter that is
Generating thermal energy in the electrothermal transducer and producing film boiling on the thermally active surface of the recording head by applying at least one drive signal that corresponds to recorded information and provides a rapid temperature rise above nucleate boiling. This is effective because, as a result, bubbles in the liquid (ink) can be formed in pairs corresponding to the drive signals. The growth and contraction of these bubbles causes the liquid (ink) to be ejected through the ejection opening, forming at least one droplet.If this drive signal is in the form of a pulse, the growth and contraction of the bubbles can be carried out 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 the case of a full-line type (multi-type) recording head whose length corresponds to the maximum width of the recording medium that can be recorded by the recording device, there are configurations in which multiple recording heads can be combined to meet the length, or they can be formed into a single body. The recording head may be configured as a single recording head.

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

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

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

Additionally, in the embodiments of the present invention described above,
Although ink is described as a liquid, it is an ink that solidifies at room temperature or below, but softens or liquefies at room temperature, or in an inkjet method, the ink itself is
Generally, 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, the image forming apparatus may take the form of an image output terminal for information processing equipment such as a computer, a copying device combined with a reader, etc., or a facsimile device with transmitting and receiving functions. It may be. Particularly in devices such as copying machines and facsimile machines that have long been equipped with an image reading means (reader) as a document reading system, it can also be used as a reading means for reading density unevenness in 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 implement any required configuration using one or more of the above configurations.

〔Effect of the invention〕

As described above, according to the present invention, density unevenness is read in a state where the recording medium does not float, so that an accurate and stable reading operation can be performed, thereby improving the accuracy of density unevenness correction.

[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. 1I 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. FIG. 2 is a block diagram showing an example of the configuration of a control system of a recording apparatus. FIG. 14 is a block diagram showing the system for density unevenness correction in detail, FIG. 15 is an explanatory diagram for explaining the unevenness correction table used in this example, and FIG. 16 is a diagram showing the unevenness correction processing procedure according to this example. A flowchart showing an example; FIG. 17 is a schematic diagram showing a state in which identification marks are attached to a recording medium in order to correct density unevenness depending on the type of recording medium; FIG. 18 is a diagram for explaining temperature changes in the recording head.・ FIG. 19A, FIG. 19B, and FIG. 19C are explanatory diagrams for explaining the mode of stably correcting density unevenness regardless of temperature. FIG. 20 is a pattern for stabilizing ejection; An explanatory diagram showing an example in which an ejection failure detection pattern and a test pattern for density unevenness correction are recorded on a recording medium. 22 and 23 are timing charts showing two examples of the operation of this example device from recording a test pattern to reading density unevenness. FIG. A block diagram showing a configuration example for correcting the difference in output size depending on the color of the reading sensor, FIGS. 25A and 25B are explanatory diagrams of the mode of correction, and FIG. FIG. 27 is a schematic diagram showing a reading system unit thereof; FIG. 28 is a schematic diagram showing another embodiment in which the present invention is applied to a serial printer-type device; FIG. 29 is a schematic diagram showing an embodiment in which the invention is applied. A schematic diagram of the reading system unit, FIGS. 30 and 31 are schematic diagrams showing two further embodiments in which the present invention is applied to a serial printer type device, FIGS. 32A to 32E, and FIG. 33. 34 and 35 are explanatory diagrams for explaining the mode of density unevenness correction in a multi-nozzle head, and FIGS. 36 and 37 are explanatory diagrams for explaining two examples of reading units for performing density unevenness correction. It is an explanatory diagram. L, IC, IM, IY, lBk, 201G, 201M,
201Y, 2018k...Recording head, 2.202...Recording medium, 3...Head holder, 5...Head holder moving mechanism, 7...Ink supply/circulation system unit, 9...Cap Unit, 11... Cap unit moving mechanism, 14, 214.
...reading unit, 15...reading unit scanning mechanism, 16...recording medium conveyance system drive section, 17...platen, 40...conveyance belt, 41...roller, 42...discharge roller , 60... Reading head, 62... Light source, 63, 74... Lens, 73, 217... Reading sensor, 76... Housing, 77R, 77G, 77BL... Color filter, 78a
, 78b - Pressing roller, 80... Pressing member, 81.85... Transparent roller, 101... CPU, 102... ROM, 104... RAM, 106... Instruction input section, 113. ...Head temperature adjustment section, 114...Color filter switching drive section, 119, 219
...RAM. 122G, 122M, 122Y, 1228k...
・Unevenness correction table, 127, 236...A/D converter, 129G, 129M, 129Y, 1298k...
・Unevenness correction RAM, 135G, 135M, 135Y
, 1358, 235C, 235M, 235Y,
235C...Amplifier, 220...Recovery device. Fig. 2B Fig. 7A Fig. 7B Fig. 7C Fig. Fig. Fig. fω1f-fω2 Pulse 7-7 driving property command fω3 f (H2I Fig. 12A Fig. 12B Fig. 12C Fig. 16 Fig. 18 Fig. 19A Figure Ot Ascending position Figure 19a I Rise W [Figure 19c Figure 24 - l do discharge ff1t] No. tC - Record 1. To earth [ ] No, Figure 258 Figure 34 Figure 35 No. 37 Figure 901z-ZU B 41

Claims (1)

[Scope of Claims] 1) A recording head in which a plurality of recording elements are arranged to form an image on a recording medium, a density reading means for reading the density of a test pattern formed by the recording head, and a result of the reading. density unevenness correction means for correcting driving conditions of the plurality of recording elements in order to equalize the density during image formation based on the density unevenness correction means; and a recording medium on which the test pattern is formed in the vicinity of a reading position by the density unevenness reading means. An image forming apparatus characterized by comprising means for regulating floating of the image forming apparatus. 2) The image forming apparatus according to claim 1, wherein a plurality of recording heads are provided corresponding to recording materials of different colors in order to perform multicolor recording. 3) 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 1 or 2. 4) In an image forming apparatus that forms an image on a recording medium using a recording head in which a plurality of recording elements are arranged, a density reading means for reading the density of a test pattern formed by the recording head, and a density reading means based on the result of the reading. density unevenness correction means for correcting driving conditions of the plurality of recording elements in order to make the density uniform during image formation; An image forming apparatus characterized by comprising: means for regulating. 5) 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 4.