JPH0439042A - Image forming device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] 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 formed by arranging a plurality of recording elements.

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

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

For example, inkjet recording heads are generally so-called multi-nozzle heads that have multiple integrated ink ejection ports and liquid channels, and thermal transfer and thermal heads also typically have multiple heaters integrated. .

However, it is difficult to uniformly manufacture multi-head recording elements due to variations in characteristics due to the manufacturing process and variations in characteristics of head constituent materials, etc., resulting in a certain degree of variation in the characteristics of each recording element6. In the multi-nozzle head described above, variations occur in the shapes of ejection ports, liquid paths, etc., and variations occur in the shapes and resistances of heaters in the thermal head as well. 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. 24A, the input signal to each recording element is
If density unevenness as shown in Fig. 24C is visually detected when the density is made uniform as shown in Fig. 4B, the input signal is corrected and a large input signal is applied to the recording element in the low density area as shown in Fig. 24D. 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. 24E by using 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. 24E.

Japanese Unexamined Patent Application Publication No. 57-41965 filed by the applicant of the present application states that a color image is automatically read by an optical sensor,
It is disclosed that a correction signal is applied to each color inkjet recording head to form a desired color image. This publication discloses basic automatic adjustment and provides important technical disclosures. However, as the technology is being put into practical use, various problems have become apparent in order to apply it to various device configurations, but there is no recognition of the technical problems of the present invention in this publication.

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

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

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

FIG. 28 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 unevenness measurement has been 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. 29 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 a reading unit as described above is provided in the main body of the image forming apparatus, it is preferable to place it on the downstream side in the recording medium conveyance direction from the recording position by the recording head in order to improve the efficiency of unevenness correction processing. .

That is, after forming a predetermined test pattern on the recording medium using the recording head, the recording medium may be conveyed to the reading position by the reading unit using the conveyance system. However, if the reading unit described above is one that reads the recording medium while moving (scanning) in a predetermined direction, for example, the recording medium must be stopped at the reading position to perform the reading in order to perform accurate reading. is preferable.

However, if the inertia of the recording medium transport system is large, it becomes difficult to accurately stop the recording medium after transporting it at a predetermined position where the test pattern directly faces the reading unit. This means, for example, that a plurality of recording heads are provided corresponding to the recording colors, and
When recording a test pattern for each color and reading each one to correct density unevenness for each color head, this becomes more noticeable as the feeding and stopping will be intermittent depending on the formation position of the test pattern for each color. becomes. In order to avoid this, it is conceivable to increase the pitch or pattern size of each color test pattern to a certain extent, that is, to increase the transport distance between test patterns to a certain extent to make it easier to control the transport amount. This results in an increase in the amount of recording media consumed as a whole.

SUMMARY OF THE INVENTION An object of the present invention is to solve such problems and provide an image forming apparatus that can perform accurate reading or correction.

In addition, the present invention does not require a complicated structure (,
Another object of the present invention is to propose an invention that can improve test pattern reading results.

[Means for Solving the Problem] To this end, the image forming apparatus of the present invention includes a recording head in which a plurality of recording elements are arranged in order to form an image on a recording medium, and a test pattern formed by the recording head is read. a reading means, a correction means for correcting the recording head driving conditions based on the reading result, a first conveying means involved in conveying the recording medium with respect to a recording position by the recording head, and a first conveying means from the first conveying means. Inertia is small,
a second conveying means involved in conveying the recording medium to a reading position by the reading means, and when reading the test pattern, the second conveying means carries out the conveyance after exiting the conveying state by the first conveying means. It is characterized by the following.

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 reading means for reading a test pattern formed by the recording head, and a reading means for reading a test pattern formed by the recording head; a correction means for correcting the recording head drive conditions based on the results; a first conveyance means involved in conveyance of the recording medium with respect to the recording position by the recording head; and a reading means having a smaller inertia than the first conveyance means. a second conveying means involved in conveying the recording medium with respect to a reading position according to the present invention, and when reading the test pattern, the second conveying means carries out conveyance after exiting the conveying state by the first conveying means. It is characterized by

In these, preferably the second conveying means is the first conveying means.
a recording medium ejecting means disposed adjacent to the conveying means, and after the test pattern is formed, the recording medium is conveyed until its rear end reaches the ejecting means, and then the first
Stop the transport means.

A control means is provided for controlling the ejection means to reverse the direction and set the test pattern at the reading position.

This preferred configuration, as an independent invention, has the effect of improving reading accuracy after stabilizing the inkjet fixing state, so that the recording area, the test pattern reading area, and the reading area are sequentially arranged from the upstream side to the downstream side with respect to the recording medium conveyance direction. In an inkjet image forming apparatus, the inkjet image forming apparatus is provided with an area for ejecting a recording medium from the recording medium, reads a test pattern formed on the recording medium, and corrects the recording means based on the reading result. It has a means capable of switching the conveyance direction of the recording medium on which the test pattern is formed, and the conveyance direction switchable means conveys at least the test pattern area of the recording medium on which the test pattern is formed from the reading area to the downstream side in the conveyance direction. The present invention also provides for changing the direction after reading the test pattern of the recording medium passing through the reading area.

[Function] According to the present invention, after exiting the conveyance state by the conveyance system with large inertia, which is mainly involved in conveyance related to the recording position, the conveyance related to the reading position is performed by the conveyance system with small inertia. Since accurate conveyance and stopping for reading can be performed, density unevenness can be read or corrected based on this.

Further, according to a preferred embodiment of the present invention, the separation area between the conveyance system (belt, etc.) mainly involved in conveyance related to the recording position and the conveyance system (ejection roller etc.) involved in conveyance related to the reading position is enlarged. Furthermore, there is no need to perform delicate control of both conveyance systems in order to convey the recording medium without any abnormality in setting the recording medium to the reading position.

The above-mentioned invention from another perspective of this preferred example is that the test pattern printing itself in inkjet recording can be in a good fixing state without any other requirements, and that the reading accuracy after forming a stable test pattern can be improved. I was able to achieve improvement. In this invention, the reading after switching the transport direction can also be performed at the time of the first switching by the transport direction switching means,
Preferably, it is also good to read in the normal conveyance direction at the second switching. With this invention, it is not necessary to stop the recording medium during reading (although it is also possible to read a recording medium that is continuously conveyed due to the effect of improving fixing performance).

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

1) Mechanical configuration of the device (Figure 2) 2) Reading system (Figures 3 to 12) 3) Control system (Figures 13 to 15) 4) Sequence of unevenness correction (Figures 16 to 15) Figure 25) 5)
In addition, the conveyance system related to the recording device and the conveyance system related to the reading position are separated, that is, a reading platen of a size that allows the recording medium to be placed near the reading position is provided, and when reading, the recording is performed on this platen. It is conceivable to stop the medium and then use a conveyance system with low inertia, for example, a discharge roller, to convey and stop the medium.

However, with such a configuration, there is a risk that the apparatus will become larger due to the provision of the reading platen opening, or that control regarding the conveyance system and ejection roller of the recording apparatus may become complicated.

(1) Overview of Mechanical Structure of Apparatus FIG. 1 shows a schematic structure 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 IBM in one piece, and can be moved by a head holder moving mechanism 5 in the direction A toward the recording position and in the direction B away from the recording position in the figure. The head holder moving mechanism 5 includes a drive source such as a motor,
It has a transmission mechanism that transmits the driving force to the head holder 3, a guide member that guides the movement of the head holder 3, etc., and moves the head holder 3 in directions A and B as appropriate to move the recording head IC-IBK. The head holder 3 is set at a recording position where the ejection port faces the recording medium at a predetermined distance, a retracted position to receive the intrusion of the cap unit described below, and a position for capping each head. It is possible.

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

9 is a cap unit, which includes a recording head ICIM,
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). 11
is a cap unit moving mechanism, which includes a motor, a transmission mechanism, a guide member, etc., and moves the cap unit 9 appropriately in directions C and D in the figure to a position directly below the head holder 3 in the retracted position. The cap unit 9 can be set at a position that does not obstruct the lowering of the head holder 3 during recording.

During the ejection recovery process, the head unit 3 is raised in the direction B to a position where the entry of the cap unit 9 is not revealed, 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. 44 is a conveyance roller, 45 is a registration roller, and the recording medium 2 fed by the pickup roller 39 is tilted (conveyed). This is a conveyor belt that conveys in the E direction with respect to the recording position according to the present invention, and is wound between rollers 41.

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. Further, 46 is a separation claw for separating the recording medium 2 from the belt 40 and guiding it to the ejection roller 42 side, and 47 and 48 are recording medium detection sensors provided before and after the ejection roller 42. Reference numeral 53 denotes a charger for charging the conveyor belt 40 to attract the recording medium 2, and is provided near the reading position by the reading unit I4. 5
Reference numeral 4 denotes a static elimination brush that eliminates static electricity from the conveyor belt 40, and connects to/disconnects from the conveyor belt 40 via a link 57 in response to turning on/off of a solenoid 55. Note that the ejection roller 42 is driven by a stepping motor (not shown) that is a component of the recording medium conveyance system drive unit, and is capable of forward and reverse rotation and arbitrary rotation.

14 is a density unevenness reading unit, which includes a writing head IC.
- It is arranged between the recording attachment 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 denotes a drive unit for driving each unit related to conveyance of the recording medium 2, that is, the feeding roller 39, the roller 4I, and the ejection roller 42.

When correcting density unevenness, the recording medium stored in the cassette 38 is fed onto the conveyor belt 40 by rotating the pickup roller 39 and rollers 44 and 45 in the same way as during normal recording. As the roller 41 rotates, the recording medium 2 is conveyed together with the conveyor belt 40 in the direction of arrow E, and at this time, each recording head is driven and a test pattern is recorded on the recording medium 2.

Thereafter, the recording medium 2 on which this test pattern has been recorded is conveyed to the density unevenness reading unit 14 as described later, and a reading operation as described later is performed.

FIG. 2 shows the recording head 1 (recording head IC, IM.

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

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

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

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

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

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

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

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

■Pressure mode 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, valve 71 (l is closed and pump 707
is operated, and ink is supplied from the ink tank 701 to the print head 1 via the ink path 703.

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

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

In FIG. 3, 60 is a reading head, which slides on a pair of guide rails 61.61° to read images. The reading head 60 includes a light source 62 for illuminating the original, a lens 63 for forming an image of the original onto a sensor, and the like. Reference numeral 64 denotes a flexible conductive wire bundle that supplies power to the light source 62 and the sensor and transmits image signals and the like from the photoelectric conversion element. Note that the sensor may be a monocular sensor that reads reflected light in a predetermined range (or may be one that is made up of an array of reading elements such as a CCD).In the latter case, a plurality of reading elements may be arranged in one discharge port. It is preferable that the average value of the read values is associated with one ejection port.

The reading head 60 is fixed to a driving force transmitting unit 65 such as a wire for main scanning (CG, H directions) in a direction intersecting the recording medium conveyance direction. Main scanning direction driving force transmission unit 6
5 is stretched between pulleys 66 and 66'', and is moved by the rotation of a pulse motor 67 for main scanning.The reading head 6 is moved by rotation of the pulse motor 67 in the direction of the arrow
0 reads line information of an image perpendicular to the main scanning direction G while moving in the direction of arrow G.

After a predetermined width of the image has been read, the main scanning pulse motor 67 rotates in the direction opposite to the arrow I. As a result, the reading head 60 moves in the H direction and returns to the initial position. Note that 68.68" is a support member.

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

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

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

The purpose of correction determined by the correction conditions may be not only optimal printing conditions, but also adjustments to a predetermined range including tolerance ranges, or 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. 25. First, the density OD of the portion corresponding to each recording element, ~ODN
Measure and correct the average density 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. 26, then the signal actually given to this element or this group of elements will correct the signal S to achieve the target density OD. What is necessary is to determine the correction coefficient α that brings about this. That is, the signal S is αxs=(o.

100, )xS, which is a correction signal S, may be applied to this element or group in accordance with the input signal S. Specifically, this is executed by performing table conversion as shown in FIG. 27 on the input image signal. In Figure 27, straight line A is a straight line with a slope of 1.0, and is a table that outputs the input signal without converting it at all, whereas straight line B has a slope of α = 0.
0100. This is a table that converts 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. 27 for the image signal corresponding to the n-th recording element. If the head is driven after table conversion is performed, each density of the portion recorded by N recording elements becomes equal to OD. If such processing is performed on all recording elements, density unevenness will be corrected and a uniform image will be obtained. That is,
If data indicating what kind of table conversion should be performed on the image signal corresponding to which recording element is obtained in advance, it is possible to correct unevenness.

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

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

Incidentally, the distance between the reading unit and the recording medium on which the test pattern is recorded varies depending on the reading accuracy, but is preferably kept constant. Therefore, in order to maintain this distance, in this example, the belt 40 is charged to bring the recording medium 2 into close contact with the belt to maintain the above distance, but configurations as shown in FIGS. 4 to 6 are also adopted. can.

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

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

In FIG. 4, 74 is a lens for converting the emitted light from the light source 62 into parallel light, 73 is a sensor having a photoelectric conversion element group, 63 is a lens for converging reflected light, and 77 is an aperture with an aperture of d0. This 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 light in the d+ range on the test pattern, and therefore, the average of the unevenness in that range is detected. According to experiments by the inventors, the opening diameter is 0.
A thickness of about 2 to 1 mm was good. Then, by performing unevenness correction according to the detection results, it becomes possible to obtain a uniform image. This fact is shown in FIGS. 1 and 5.

The same applies to the configurations shown in FIG. 6 and FIG. 1O.

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.

Further, the housing 76 is connected to the rotating member 501 via the support portion 503.
This member 501 can be rotated by a motor 502.

In this example, when conveying the recording medium 2, the member 501 is rotated to set the support portion 503 at the position shown by the broken line 503', and the housing 7 housing the reading unit and scanning mechanism is moved.
The lower surface of the presser member 80 of No. 6 is initially separated from the belt 40 by a height H, and when the recording medium 2 on which the test pattern is recorded comes under the reading unit, the housing is lowered,
The recording medium 2 is held down with transparent plastic 80. In other words, when the test pattern comes under the reading unit,
Even if the recording medium 2 is not in close contact due to curling or the like, the presser member will ensure that the recording medium 2 is in close contact. 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. However, if such contamination is not a problem, the member 80 may have an opening in the optical path (in this case, the member 80 does not have to be transparent).

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

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

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

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

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

At that time, when reading the unevenness of C, M, Y, especially Y, when white light is irradiated onto the Y test pattern and the reflected light is received without a filter, the amount of light received by the sensor 73 is as shown in Fig. 78. As shown in song 11A, the dynamic range is narrow and uneven (the difference in optical density is small, 0.02 to 0.1
5) is difficult to read accurately. Therefore, the seventh
If you use light that has passed through an L (blue) filter as shown in Figure B, the amount of light received will be smaller overall, but the dynamic range will be expanded and the accuracy of reading unevenness will increase, as shown by curve B in Figure 7A. It turns out. The same applies to C and M if R (red) and G (green) filters are used, respectively.

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

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

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

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

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

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

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

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

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

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

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

That is, when the pulse motor 67 is driven to transport the reading unit transport system, the resonance frequency fω1. fω2. At fω3..., the vibration of the reading unit conveyance system becomes extremely large. Therefore, when the reading unit 14 is conveyed at the resonance frequency where such a system vibrates, as shown in FIG. 22A, even if the recording density of the test pattern recorded on the recording medium 2 is uniform, Also, as shown in FIG. 12B, the reading unit 1
4 may change. In such a case, as a result, the read output from the reading unit 14 has an output characteristic with pitch unevenness as shown in ω in FIG. 120, and the recording density of the test pattern recorded on the recording medium 2 cannot be read correctly.

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

(3) Configuration of control system Next, the control system of the apparatus of this example, which is configured 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 inputting an online switch with the host device, inputting a command to start recording, inputting a command to record a test pattern for correcting density unevenness, and inputting information on the type of recording medium. In addition to the sensors 47.4g provided before and after the discharge roller, 108 is a sensor for detecting the presence or absence of a recording medium, the 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, UCR, and color balance adjustment.

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

113 is a 72 degree adjustment unit for adjusting the temperature of the recording head 1; specifically, 6114 is a 72 degree adjustment unit that may include, for example, a heating heater and a cooling fan disposed for the head 1; The drive section 116 of the color filter switching section 79 described with reference to FIG. 8 is a drive section of each motor that drives the recording medium conveyance system. 153 is charger 5
3, a driver 155 turns on/off the solenoid 55 and connects the static elimination brush 54 to the belt 40;
This is a driver for bringing the device into contact with/separating from the device.

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

121M, 121Y and 121BK are image processing unit 1
These are cyan, magenta, yellow, and black image signals processed in step 11, respectively. 122C, 122
123C, 123M, 123Y and 1238 are image signals after the correction. 130
0 to 130111 are gradation correction tables for each color layer, 13
1C to 1318 are 2 using dither method, error diffusion method, etc.
This is a digitization circuit, and the binary signal is sent to each color head IC to IBK via a driver 112 (not shown in FIG. 14).
supplied to

126C, 126M, 126Y and 1268,
These are the color signals read by the reading unit 14 through the color filters and apertures shown in FIG. 8, and are input to the A/D converter 127. 119 is a RAM area for temporarily storing the digital output signal, and the area of RAM 104 can be used. 128C, 128M, 1
28Y8 and 12gBK are correction data calculated by CPUl0I based on the stored signals. 129C
~1298 is a non-uniformity correction RAM for each color layer;
104 areas can be used. The output unevenness correction signals 130C to 130BK of each color layer are as follows:
The image signals 1210 to 1218 are supplied to the unevenness correction tables 1220 to 12213K, respectively, and the head IC
~ Converted to correct IBK unevenness.

FIG. 15 shows an example of an unevenness correction table, and in this example, Y
= 0.70X to Y = 1.30X, the teno slope is 0.
It has 61 correction straight lines that differ by 01, and the correction straight lines are switched according to the unevenness correction signals 130C to 1308K. For example, when a pixel signal to be recorded by an ejection port with a large dot diameter is input, a correction straight line with a small slope is selected, and conversely, when an ejection port with a small dot diameter is used, a correction straight line with a large slope is selected to correct the image signal. to correct.

The unevenness correction RAMs 129C to 1298 store correction straight line selection signals necessary to correct unevenness of each head. That is, it stores unevenness correction signals having 61 types of values from 0 to 60 for the number of ejection ports, and outputs unevenness correction signals 130C to 1308K in synchronization with the input image signal. Then, the signals 1230 to 1238, whose unevenness has been corrected by the γ straight line selected by the unevenness correction signal, are input to the gradation correction tables 1300 to 1308K,
Here, the gradation characteristics of each head are corrected and output. The signals are then binarized by binarization circuits 131C to 1318K, and a color image is formed by driving heads IC to IBK via a head driver.

(The following is a blank space) (4) Sequence of unevenness correction With the above configuration, in this example, the following processing is performed to perform unevenness correction more accurately.

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, the recording medium is fed, and in step S3, the driving of the conveyance belt 40 and the discharge roller 42 is started.

Next, the process advances to step S7 to perform temperature adjustment. This is due to the following reasons.

In an inkjet recording apparatus, the recording head is usually maintained within a predetermined temperature range (for example, about 40° C., which is the first temperature adjustment standard) in order to suppress fluctuations in image density, stabilize ejection, and the like. Therefore, for example, when this procedure is activated to record a test pattern, 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. . On the other hand, when actually recording images continuously, the temperature of the head increases as shown in area b in Figure 17, 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 18A,
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. 18B, if unevenness correction is performed for 40°C, a uniform image without unevenness can be obtained when the head temperature is 40°C.
Images at 50° C. may still be uneven.

Therefore, in the apparatus of this example, during normal recording or during recording standby, the temperature control section 1 adjusts the temperature of the recording head 1.
13 (heater and fan) as appropriate.
As shown in FIG. 7, 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. 18C, by stabilizing the recording operation of the recording head by adjusting the temperature, for example, by forming a test pattern at a head temperature of 45° C. and correcting density unevenness based on this. Thus, it becomes possible to perform density unevenness correction more or less uniformly over the entire temperature control range.

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

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

Note that in order to lower the head temperature to the normal recording state (45°C - 440°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 If you do the 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 you perform density unevenness correction processing as is, it will not be possible to accurately recognize the head characteristics (density unevenness). This is because there is a risk that

During the ejection stabilization process, the recording heads IC to IBM and the cap unit 9 can be placed opposite each other, and the above-mentioned pressurization mode can be set to forcibly eject ink from the ejection ports. Further, the ejection orifice forming surface may be cleaned by contacting the ejection orifice forming surface with an ink absorber that can be disposed in the cap unit, or by blowing air, wiping, or the like. It is also possible to perform preliminary ejection by driving the print head in the same way as during normal printing. However, the driving energy during preliminary ejection 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.

By the way, in an apparatus as in this example where the recording head 1 is of the full multi-type and the recordable width is slightly larger than the image recording width for registration adjustment, the recording width when recording the test pattern is normally For example, if the maximum recording paper size is 33-plate, and the normal image recording width is 297 mm, which is the length of the short side of 33-plate or the long piece of A4 paper. On the other hand, consider the case where the width is approximately 293+u+ considering the left and right margins, and the recordable width of the recording head is 295 mm.

This is to electrically adjust the range of the ejection ports to be used and to correct errors in the relative positional relationship between the mechanical heads and the recording medium.

Therefore, in this case, the discharge port arrangement range is 295m++m
It is highly desirable to test over a width of 295 mm, so that a test pattern recording with a length of 295 cm is performed.

FIG. 19 shows an example of the configuration of a circuit for performing such an operation, in which 141 is a selector for selecting the ejection opening range 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 heads 1C to IBK. Note that in this example, the test pattern forming apparatus uses the ejection roller 42 for conveyance during reading, so the position is shifted from the leading edge of the recording medium by a distance equal to or greater than the distance between the ejection roller and the reading position. At this time, the recording medium 2 becomes as shown in FIG. In other words,
When using this switchback method, please refer to the above 20th
It is preferable to provide means for determining printing timing as shown in the figure.

After printing the uneven pattern, the recording medium 2 is conveyed to the discharge roller 42 side and begins to be discharged. Here, in step S13, when the detection signal of the pre-ejection sensor 47 is in a state of no detection, that is, the recording medium 2 has moved away from the conveyor belt 40 (the recording medium is not affected by the belt with large inertia).
If this is detected, the drive of the discharge roller 42 is stopped in step S15. At this time, the recording medium 2
As shown in FIG. 1A, the recording medium stops with the end portion of the recording medium sandwiched between the discharge rollers 42. Note that the recording medium position at this time serves as a reference for controlling the amount of reverse feed to return to the reading position.

Next, in step S17, as shown in FIG. 21B,
The adsorption charger 53 is turned off and the static elimination brush nod 55 is turned on so that the static elimination brush 54 comes into contact with the conveyor belt 40. At this time, the conveyor belt 40 is rotating, so
If the conveyor belt 40 is made to rotate once in this state, static electricity will be removed from the conveyor belt 40. After the conveyor belt 40 has made one revolution, the drive of the conveyor belt 40 is stopped (step S19.521), and the discharge roller 42 is reversed as shown in FIG. The discharge roller 42 is rotated by a predetermined amount so that it comes down (step 523).
).

At this time, the printed recording medium may not be in close contact with the conveyor belt 40 due to paper curls or the like, and even if unevenness is read as it is, accurate reading cannot be performed. Therefore, as shown in FIG. 21D, the attraction charger 53 is turned on to bring the recording medium 2 into close contact with the conveyor belt 40 (step 525). In this example, the attraction charger 53 is provided at the position of the reading unit 14. Therefore, the recording medium is in close contact with the belt 40 at the reading position, and unevenness can be read accurately (step 527). According to this charging means exclusively for the reading position, it is possible to use a completely non-contact reading means, and the conveyance belt on the upstream side can be transported in addition to suction transport by the charging means.
This makes it possible to use various methods such as air suction conveyance.

After reading the unevenness and correcting the unevenness in this manner (step 529), the ejection roller 42 is rotated in the normal direction to eject the recording medium 2 (steps S31-335).

Here, when reading a single recording medium 2 with a pattern printed in multiple colors as shown in FIG. 20, if the distance from the ejection port 42 to the reading unit 14 is i, then Cyan test pattern 84 at the position shown in FIG. 21D.
After reading the magenta test pattern 84, the discharge roller 42 is rotated by a distance of dβ and then stopped.
M can be read. By continuing in the same manner, yellow and black test patterns 84Y and 848 can also be read.

As described above, the recording medium 2 is transferred to the conveyor belt 4 with large inertia.
After ejecting to the reference position (the position where the rear end is held between the ejection rollers) that is not affected by the conveyance caused by zero, the conveyor belt is stopped, and the charging state for holding the recording medium is released, the inertia is small. By reversing the rollers and stopping the reverse feed when they reach the reading position, they are again charged, so the transport system (belt, etc.) mainly involved in transport related to the recording position and the transport system related to the reading position are There is no need to increase the separation area from the conveyance system (discharge rollers, etc.) involved in this process. In addition, delicate control of both transport systems to ensure that the recording medium is set to the reading position and transported without any abnormalities is no longer required.Other advantages are that the completely non-contact reading mechanism of this example can be used reliably. There is.

Note that the test pattern used for reading density unevenness can be formed with all unevenness correction tables as straight lines with an inclination of 1.0, and unevenness correction is not performed at all.The pattern may be a uniform halftone. The printing ratio may be about 30 to 75%.

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

In such a case, the density unevenness of the test pattern recorded by each recording head may stabilize.
In order to prevent the density unevenness reading unit 14 from reading the density unevenness of the test pattern until the 210th
It is sufficient to provide a predetermined time t before reading as shown in the figure.

According to experiments, when a test pattern was recorded on coated paper for inkjet recording with a printing ratio of 50% using a recording head with a resolution of 400 dpi, the above-mentioned time t was approximately 3 to 1.
About 0 seconds was sufficient.

Incidentally, in this example, the unevenness reading sensor 73 is a single sensor, but 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, if the output ratio of BK:C:M:Y is 1:0.
8:0.75:0.25.

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

If the unevenness of the discharge port of interest in the head 113 is the same as that of the head Ic, the sensor output is ODc "K"
IXODBK, DCII=KIXODllK11. At this time, the correction value of C becomes equal to BK. Therefore, the output difference between each color is not a problem.

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

For example, when calculating the correction value from the difference between the average density and the target ejection port density, 0De-ODc,l=(OD,, -0DIXn)
This value is 1 times larger for C than for BK. Based on this value, correction data for the target ejection port is obtained, but there is a problem that the final correction amount is different for BK and C, even though the density unevenness of the head is the same. Occur.

Therefore, in this embodiment, the ratio of sensor outputs between each color is determined in advance, and the CPU 10 is used for unevenness reading processing.
This problem is solved by multiplying the sensor output by the reciprocal of this ratio by I and performing unevenness correction based on it.

For example, the output ratio of BK, C, M, and Y is 1:, :
: When , the output when reading BK is "1"
For C, multiply by 1/K +, for M, multiply by l/! If Y, multiply l/ by.

This way, for example in the example above, 1/KIX
(ODe-ODeJ=1/Kl (KIX (ODIK
-OD@+tn))"ODoODmKll, and it is possible to perform optimal correction without being affected by the sensor output ratio between each color.

Note that such correction of the sensor output is not performed by calculation by CPUl0I (it can also be performed in the previous stage).

For example, if the A/D converter 127 is configured with 8 bits, the output value of each color is divided into 8 bits of the dynamic range.
This is effective against the problem that the resolution of the read data of each color deteriorates because it has to be converted into digital data within the width.

That is, for example, as shown in FIG. 22, amplifiers 135C, 135M, and 135Y amplify the read signals of each color.
.
It becomes possible to set the read signal width at the time of /D conversion to be narrow as a whole. Therefore, the resolution of the read data in 8 bits can be increased, and the reading accuracy can be further improved.

Based on the above, the unevenness correction performed in step S29 in FIG. 16 is, for example, as follows. 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. These are R,,R,...R, (N is the number of discharge ports)
Then, after temporarily storing these in RAM 119,
The following calculations are performed on CPUl0I.

These data are converted into a concentration signal by performing an operation such that C,,=-log(R,,/Ro) (Ro is a constant such that R8≧RI; 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.

ΔC11=C/CゎNext, (ΔC). The signal correction amount (ΔS) according to Δ5
It is determined by ll=AXΔCll.

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

Next, a selection signal for the correction straight line to be selected according to ΔSo is obtained, and the unevenness correction signal having 61 types of values from "0" to "60" is applied to the unevenness correction RAMI 29C to 129 for the number of ejection ports.
Store it on 8K. 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.

In the embodiment of the present invention described above, at least when printing for density inspection such as a test pattern, if one pixel is composed of a plurality of dots, the printing duty, that is, the printing setting, is determined by recording within the number of constituent dots. This can be done by modulating the number of dots. In this case, the printing duty is not 100%, but preferably 75% or less and 25% or more, and optimally it is preferable to form a test pattern with a printing duty of 50%.This is a method for optically obtaining reflection density. This is because it is optimal for this purpose, and even minute density changes can be obtained that are suitable for the printing 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 generating means integrated with the recording head 1.

Further, 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.

For example, although the case where the present invention is applied to a line printer type device is described above, even in a serial printer type device, there is a problem with the reading position due to the inertia of the conveyance system that conveys the recording medium with respect to the recording position. If accurate position control becomes difficult, the same control as described above can be performed using a discharge roller with smaller inertia.

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

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

The configuration of the recording head includes, in addition to the combination configuration of ejection ports, liquid paths, and electrothermal converters (straight liquid flow path or right-angled liquid flow path) as disclosed in the above-mentioned specifications, a heat acting section. The present invention also includes configurations using US Pat. No. 4,558,333 and US Pat. No. 4,459,600, which disclose configurations in which the wafer is placed in a bending region. In addition, Japanese Patent Application Laid-Open No. 1989-5 discloses a configuration in which a common slit is used as a discharge part of a plurality of electrothermal converters.
No. 9-23670 and Japanese Patent Application Laid-Open No. 1987-59 which discloses a configuration in which an opening for absorbing pressure waves of thermal energy corresponds to a discharge part.
The effects of the present invention are also effective even with a configuration based on the publication of No. 138461. That is, regardless of the form of the recording head, according to the present invention, recording can be performed reliably and efficiently.

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

In addition, even if it is a serial type, it is a replacement head that is fixed to the device body, or is attached to the device body so that it can be electrically connected to the device body and can supply ink from the device body. The present invention is also effective when using a flexible chip-type recording head or a cartridge-type recording head in which an ink tank is integrally provided in the recording head itself.

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

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

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

In addition, image forming apparatuses may take the form of image output terminals for information processing equipment such as computers, copying machines combined with leagues, etc., and even facsimile machines with transmitting and receiving functions. It may be.

Although the above embodiments show various configurations that address a number of technical issues, all of the above configurations are not essential to the present invention, and the designed device configuration and the setting of the desired concentration uniformity level are This indicates that it is more preferable to perform any required configuration using one or more of the above configurations.

[Effects of the Invention] As explained above, according to the present invention, after exiting the conveyance state by the conveyance system with large inertia, which is mainly involved in conveyance related to the recording position, the conveyance related to the reading position is carried out by the conveyance system with small inertia. As a result, it is possible to accurately transport and stop the image for reading, so that the density unevenness can be accurately read or corrected based on this.

[Brief explanation of the drawing]

FIG. 1 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. FIG. 2 is a schematic diagram for explaining the ink system thereof. FIG. A perspective view showing a configuration example of the unit and its scanning mechanism; FIGS. 4, 5, and 6 are schematic side views showing other configuration examples of a part for maintaining the distance between the reading unit and the recording medium. Figures 7A, 7B, and 7C are explanatory diagrams for explaining how the dynamic range of the amount of light received by the sensor is expanded according to color. Figures 8, 9, and 10 are test patterns. FIG. 11 is an explanatory diagram for explaining the mode of scanning drive of the reading unit according to the present example; FIG. 12B and 12C are explanatory diagrams for explaining fluctuations in read values according to fluctuations in the scanning speed of the reading unit, and FIG. 13 is a block diagram showing an example of the configuration of the control system of the inkjet recording apparatus according to this example. , FIG. 14 is a block diagram showing in detail the system for correcting density unevenness, FIG. 15 is an explanatory diagram for explaining the unevenness correction table used in this example, and FIG. 16 is an unevenness correction processing procedure according to this example. A flowchart showing an example, FIG. 17 is an explanatory diagram for explaining temperature changes in the recording head, and FIGS. 18A, 18B, and 18C are diagrams illustrating a method for stably correcting density unevenness regardless of temperature. FIG. 19 is a block diagram showing an example of the main part configuration of a control system for correcting density unevenness over all ejection ports in the fully multi-type recording head according to this example; FIG. 20 is an explanatory diagram for correcting density unevenness An explanatory diagram showing an example in which a correction test pattern is recorded on a recording medium, FIGS. 21A to 21D are explanatory diagrams for explaining the operation of the apparatus shown in FIG. 1, and FIG. 23A and 23B are explanatory diagrams of the correction mode; FIGS. 24A to 24E, 25, and 26. 27 is an explanatory diagram for explaining the mode of density unevenness correction in a multi-nozzle head, and FIGS. 28 and 29 are explanatory diagrams for explaining two examples of reading units for performing density unevenness correction. be. 1. IC, IM, IY, IBk... Recording head, 2... 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 unit, 40...conveyance belt, 41...roller, 42...discharge roller, 47, 48... - Recording medium detection sensor, 53... Charger, 54... Static elimination brush, 55... Solenoid, 60... Reading head, 62... Light source, 63, 74... Lens, 73, 217 ...reading sensor, 76...casing, ? 7R, 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, 1358k...
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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 reading means for reading a test pattern formed by the recording head, and a method based on the result of the reading. a correction means for correcting the recording head driving conditions; a first conveyance means involved in conveying the recording medium with respect to the recording position by the recording head; and a first conveyance means having a smaller inertia than the first conveyance means and related to the reading position by the reading means. and a second conveying means involved in conveying the recording medium, and when reading the test pattern, the recording medium is conveyed by the second conveying means after exiting the conveying state by the first conveying means. image forming device. 2) The second conveying means is a recording medium ejecting means disposed adjacent to the first conveying means, and after the test pattern is formed, the recording medium is conveyed until the rear end reaches the ejecting means. 2. The image forming apparatus according to claim 1, further comprising a control means for controlling the first conveyance means to be subsequently stopped, the ejection means to be reversed, and the test pattern to be set at the reading position. Device. 3) The image forming apparatus according to claim 1 or 2, wherein a plurality of recording heads are provided corresponding to recording materials of different colors in order to perform multicolor recording. 4) The recording head has the form of an inkjet recording head, and the inkjet recording head is characterized in that the recording element includes an electrothermal conversion element used to cause film boiling in the ink to eject the ink. The image forming apparatus according to any one of claims 1 to 3. 5) 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, comprising: a reading means for reading a test pattern formed by the recording head; and a reading means for reading the test pattern formed by the recording head; a correction means for correcting head drive conditions; a first conveyance means involved in conveying the recording medium with respect to the recording position by the recording head; and a recording medium having a smaller inertia than the first conveyance means and with respect to the reading position by the reading means. and a second conveyance means involved in the conveyance of the image, and when reading the test pattern, the image is conveyed by the second conveyance means after exiting the conveyance state by the first conveyance means. Forming device. 6) The second conveying means is a recording medium ejecting means disposed adjacent to the first conveying means, and after the test pattern is formed, the recording medium is conveyed until the rear end reaches the ejecting means. 6. The image forming apparatus according to claim 5, further comprising a control means for controlling the first conveyance means to be subsequently stopped, the ejection means to be reversed, and the test pattern to be set at the reading position. Device. 7) 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 transducer used to cause film boiling in the ink to eject the ink. The image forming apparatus according to claim 5 or 6. 8) A recording area, a test pattern reading area, and an area for carrying out the recording medium from the reading area in order from the upstream side to the downstream side with respect to the recording medium conveyance direction, and reading the test pattern formed on the recording medium, and reading the test pattern. An inkjet image forming apparatus that corrects the recording means based on the result, comprising a means that operates in the discharge area and is capable of switching the conveyance direction of the recording medium on which the test pattern is formed, the conveyance direction switchable means. After conveying at least the test pattern area of the recording medium on which the test pattern is formed from the reading area to the downstream side in the conveying direction, the direction is switched, and then the test pattern of the recording medium passing through the reading area is read. An inkjet image forming apparatus characterized by: 9) 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 inkjet image forming apparatus according to claim 8.