JP2022039545A - Image forming apparatus, method for controlling image forming apparatus, and program - Google Patents

Abstract

To maintain image density quality of an image forming apparatus while preventing reduction in productivity.SOLUTION: An image forming apparatus comprises: an image carrier; image forming means that forms toner images in a plurality of colors on the image carrier; and a detection unit that irradiates the image carrier with light to detect a first detection value corresponding to a quantity of regularly reflected light and a second detection value corresponding to a quantity of irregularly reflected light. The image forming apparatus has control means that controls to acquire, from the detection unit, the first detection value and the second detection value of a pattern for correction in which different colors are arranged respectively for a plurality of patches formed on the image carrier, and correct density of the toner images formed by the image forming means by switching a first mode using the first detection value and a second mode using the second detection value for each of the colors. When there is an abnormality in a surface state of the image carrier, the control means changes arrangement of the colors in the pattern for correction so that the patch in the color using the first mode is not formed at a position of the abnormality.SELECTED DRAWING: Figure 10

Description

The present invention relates to an image forming apparatus, a control method for the image forming apparatus, and a program.

In recent years, in an electrophotographic color image forming apparatus, a reference image called "toner mark", "toner patch", "reference pattern", etc. is formed on an intermediate transfer belt, and the toner concentration of this reference image is detected. The image density is adjusted. However, the toner concentration of the detected reference image is easily affected by the surface shape of the intermediate transfer belt. Therefore, if the location where the surface shape changes coincides with the formation position of the reference image, various correction accuracy may decrease, and color shift or density variation may occur.

In Patent Document 1, a reference pattern is formed at a position on the transfer belt avoiding a region where the surface state changes significantly, the density of the reference pattern is detected, and the reference pattern density detection value and the surface state detection value are used. It is disclosed that the image density is automatically adjusted. Further, Patent Document 2 discloses that when a toner patch is formed at the position of a curl, the toner patch is not used for image quality adjustment control such as image density adjustment control and color shift adjustment control. Has been done.

Japanese Unexamined Patent Publication No. 11-249349 Japanese Unexamined Patent Publication No. 2010-217996

However, in the above-mentioned Patent Document 1, by forming the reference image in a portion different from the normal position, as a result, the formation timing of the reference image is later than usual, and the productivity is lowered. Further, in the above-mentioned Patent Document 2, although the reference image is formed, the read result is not reflected in the image forming conditions, so that the correction is not performed when the output density characteristic of the apparatus, which is the original purpose, fluctuates, and the image quality is deteriorated. Will be invited.

The present invention has been made to solve such a problem, and an object of the present invention is to maintain the image density quality of an image forming apparatus while suppressing a decrease in productivity.

The image forming apparatus of the present invention comprises an image carrier, an image forming means for forming toner images of a plurality of colors on the image carrier, and a first image carrier that irradiates the image carrier with light to correspond to the amount of forward reflected light. An image forming apparatus having a detection unit for detecting a detected value and a second detected value corresponding to the amount of diffusely reflected light, for correction in which different colors are arranged for each of a plurality of patches formed on the image carrier. The first detection value and the second detection value of the pattern are acquired from the detection unit, and the first mode using the first detection value and the second mode using the second detection value are switched for each color to obtain the image. It has a control means for controlling to correct the density of the toner image formed by the forming means, and the control means is at an abnormal position on the image carrier when there is an abnormality in the surface state of the image carrier. It is characterized in that the color arrangement of the correction pattern is changed so that the patch of the color using the first mode is not formed.

According to the present invention, it is possible to maintain the image density quality of the image forming apparatus while suppressing the decrease in productivity.

It is a schematic diagram which shows the structural example of the image forming apparatus. It is a schematic diagram which shows the structural example of a concentration detection sensor. It is a block diagram which shows the functional structure example of an image forming apparatus. It is a figure which shows an example of a black patch pattern. It is a figure which shows the toner pattern for correction. It is a figure which showed the relationship between the black toner density and the amount of reflected light. It is a figure which showed the relationship between the yellow toner density, and the amount of reflected light. It is a schematic diagram which shows the winding habit of an intermediate transfer belt. It is a figure which shows an example of the reflected light amount of the intermediate transfer belt at the time of the curl occurrence. It is a flow chart which shows the density | concentration correction processing which concerns on 1st Embodiment. It is a figure which shows the reference seal provided in the intermediate transfer belt. It is a figure which shows the relationship between the winding habit position of an intermediate transfer belt, and a patch arrangement. It is a flow chart which shows the density | concentration correction processing which concerns on 2nd Embodiment.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

<First Embodiment>
[Hardware configuration of image forming apparatus]
FIG. 1 is a configuration diagram of an image forming apparatus 200 according to the present embodiment. The image forming apparatus 200 can be realized by a printer, a copying machine, a multifunction device, a facsimile, or the like that forms a color image by an electrophotographic method. The image forming apparatus 200 is a so-called intermediate transfer tandem type image forming apparatus in which four image forming portions Pa to Pd are arranged side by side on the intermediate transfer belt 7. This method is a method in which the primary transfer image of each color is transferred onto the intermediate transfer belt 7, and then the primary transfer image is transferred from the intermediate transfer belt 7 to the recording material S, and the secondary transfer image is highly productive. It is a method.

The recording material S such as a sheet on which an image is formed is loaded in the paper feed cassette 60, and the paper feed roller pair 61 adopts a friction separation method according to the timing of image formation by the image forming units Pa to Pd. Is fed by. The paper feed roller pair 61 conveys the recording material S to the resist roller 62 via the transfer path. The resist roller 62 corrects the skew of the recording material S, adjusts the timing, and conveys the recording material S to the secondary transfer unit T2.

The image forming apparatus 200 forms an image by the image forming units Pa to Pd. The image forming units Pa to Pd as the image forming means are the photoconductors 1a to 1d, the chargers 2a to 2d, the laser scanner units 3a to 3d, the developing units 100a to 100d, the primary transfer units T1a to T1d, and the photoconductor cleaner, respectively. 6a to 6d are provided. The chargers 2a to 2d uniformly charge the surface of the photoconductors 1a to 1d. The photoconductors 1a to 1d are rotationally driveable photoconductor drums, and the laser scanner units 3a to 3d irradiate the photoconductors with a laser. The laser scanner units 3a to 3d irradiate the photoconductors 1a to 1d with a laser modulated according to the image information of the image formed by the control of the control unit 50. As a result, electrostatic latent images corresponding to the images are formed on the photoconductors 1a to 1d.

The developing units 100a to 100d as the developing means develop the electrostatic latent image formed on the photoconductors 1a to 1d with a developing agent. In this embodiment, toner is used as the developer. The developing units 100a to 100d develop the toner image by adhering the toner to the photoconductors 1a to 1d on which the electrostatic latent image is formed. The primary transfer units T1a to T1d are given a predetermined pressure amount and an electrostatic load bias, and the toner image is transferred from the photoconductors 1a to 1d to the intermediate transfer belt 7. At this time, the toner images formed on each of the photoconductors 1a to 1d are transferred so as to be superimposed on the intermediate transfer belt 7. The intermediate transfer belt 7 is an example of an image carrier.

The intermediate transfer belt 7 is, for example, a polyimide single-layer resin belt having a circumference of 800 mm, and an appropriate amount of carbon fine particles are dispersed in the resin to adjust the resistance of the belt and is black. The surface has high smoothness and glossiness, and the glossiness is about 100% (measured by a gloss meter IG-320 manufactured by HORIBA, Ltd.).

The image forming unit Pa forms a yellow toner image. The image forming unit Pb forms a magenta toner image. The image forming unit Pc forms a cyan toner image. The image forming unit Pd forms a black toner image. However, the number of colors of the formed toner image is not limited to four. The developers 100a to 100d of the present embodiment contain a two-component developer in which a non-magnetic toner and a magnetic carrier are mixed, but may contain a magnetic toner or a one-component developer of a non-magnetic toner.

A full-color toner image is formed by superimposing and transferring a toner image of each color of yellow, magenta, cyan, and black on the intermediate transfer belt 7. The toner remaining on the photoconductors 1a to 1d after the transfer is recovered by the photoconductor cleaners 6a to 6d. When the amount of toner contained in the developing units 100a to 100d is lower than a predetermined amount, toner is replenished from the toner bottles Ta to Td, which are replenishment containers for the developer, through a replenishment route (not shown).

The intermediate transfer belt 7 is provided on an intermediate transfer belt frame (not shown) and is an endless belt stretched by a secondary transfer inner roller 8, a first tension roller 10, a second tension roller 17, and a secondary transfer upstream roller 18. Is. Specifically, the intermediate transfer belt 7 includes a secondary transfer inner roller 8 having an outer diameter of φ12 mm, a first tension roller 10 having an outer diameter of φ8 mm, a second tension roller 17 having an outer diameter of φ12 mm, and a secondary transfer having an outer diameter of φ8 mm. It is stretched by a total of four upstream rollers 18, and is rotationally driven in the direction of arrow R7. The intermediate transfer belt 7 on which the full-color toner image is formed transfers the toner image to the secondary transfer unit T2 by rotating. Hereinafter, the four rollers for tensioning the intermediate transfer belt 7 are collectively referred to as a tension roller. However, the number of rollers constituting the tension roller is not limited to four.

The toner image formed on the intermediate transfer belt 7 is conveyed by the secondary transfer unit T2 at a timing that matches the recording material S. The secondary transfer unit T2 is a transfer nip unit formed by the secondary transfer inner roller 8 and the secondary transfer outer roller 9 arranged to face each other, and by applying a predetermined pressing force and electrostatic load bias. The toner image is adsorbed on the recording material S. In this way, the secondary transfer unit T2 transfers the toner image on the intermediate transfer belt 7 to the recording material S. The toner remaining on the intermediate transfer belt 7 after transfer is recovered by the transfer cleaner 11.

The recording material S on which the toner image is transferred is conveyed from the secondary transfer unit T2 to the fixing device 13 by the secondary transfer outer roller 9. The fuser 13 applies a predetermined pressure and heat to the recording material S in the fixing nip formed by the opposing rollers to melt and fix the toner image on the recording material S. The fuser 13 includes a heater that serves as a heat source, and is controlled so that the optimum temperature is always maintained. The recording material S on which the toner image is fixed is discharged onto the paper ejection tray 63. In the case of double-sided image formation, the recording material S is inverted by the inversion transport mechanism and conveyed to the resist roller 62.

The operation unit 51 can not only issue an image formation start command but also set an image image quality and input information of the recording material S to be set in the paper cassette 60 by the user using the display panel and the operation keys. The control unit 50 determines the image formation conditions based on the information input by the operation unit 51 and controls the image formation to be performed under the predetermined conditions.
A density detection sensor 70 for detecting the toner density is provided in the vicinity of the intermediate transfer belt 7. The density detection sensor 70 is arranged between the photoconductor 1d and the secondary transfer outer roller 9 in order to detect the density correction toner pattern (correction pattern) of each color formed on the intermediate transfer belt 7. The concentration detection sensor 70 is an example of a detection unit.

[Concentration detection sensor configuration]
FIG. 2 is a diagram showing a schematic configuration of the concentration detection sensor 70. The density detection sensor 70 is arranged opposite to the intermediate transfer belt 7 and detects a toner pattern formed on the intermediate transfer belt 7. The concentration detection sensor 70 is composed of an LED 71 as a light emitting element that emits infrared rays, PDs (photodiodes) 72 and PD73 as light receiving elements that receive infrared rays, and an electric substrate (not shown) on which they are mounted. The LED 71 is arranged so as to irradiate the intermediate transfer belt 7 with infrared rays at an incident angle of 20 °, and the PD 72 reflects the specular reflected light of the light applied to the intermediate transfer belt 7 and the toner pattern at a position of a reflection angle of -20 °. Arranged to receive light. Further, the PD 73 is arranged so that the LED 71 receives the diffuse reflected light of the light irradiated to the intermediate transfer belt 7 and the toner pattern at a position of a reflection angle of 50 °. Along with these optical elements, a drive circuit that supplies a current to the LED 71 and a light receiving circuit having an IV conversion function that converts the current flowing according to the amount of light received by the PD 72 and PD 73 into a voltage are mounted on the electronic substrate. The above drive circuit is an example of the concentration detection sensor drive unit 305 of FIG. 3, and the above light receiving circuit is an example of the concentration detection sensor detection unit 306 of FIG.

[Functional configuration of image forming apparatus]
FIG. 3 is a block diagram showing a schematic functional configuration of the image forming apparatus 200. The control unit 50 of FIG. 1 has a function of generating various instruction signals and executing arithmetic processing in order to operate various sensors and motors of the image forming apparatus 200 along the electrophotographic process. FIG. 3 shows a configuration in which the density of the toner image is corrected by the control unit 50 among various functional configurations of the image forming apparatus 200. The control unit 50 includes a CPU 81, a memory 82, an image data generation unit 89, an image processing unit 84, an I / F unit 85, and a controller 87. The CPU (Central Processing Unit) 81 executes a control program stored in a memory 82 or the like to control various operations of the image forming apparatus 200. The memory 82 stores various data other than the control program executed in the CPU 81. The CPU 81 is an example of the control means. The memory 82 is an example of a storage means.

The image data generation unit 89 has a function of converting various image data into laser control signals under the control of the CPU 81 and sending control signals to the laser drive units 303a to 303d. The image data generation unit 89 also includes a function of generating a toner pattern for density correction under the control of the CPU 81. The laser drive units 303a to 303d have a function of driving the laser elements of the laser scanner units 3a to 3d based on the signal sent from the image data generation unit 89 to control the lighting and the amount of light of the laser. The concentration detection sensor drive unit 305 has a function of controlling ON / OFF and drive current of the LED 71 inside the concentration detection sensor 70 according to a command signal of the CPU 81. The density detection sensor detection unit 306 has a function of voltage-amplifying the received light voltage signal corresponding to the received light amount detected by the PD 72 and PD 73 inside the density detection sensor 70 and sending the signal to the CPU 81.

Further, the CPU 81 exchanges data with the paper cassette 60. The CPU 81 can control the image forming process and the conveying process of the recording material S to form an image on the recording material S stored in the paper cassette 60. Further, the CPU 81 is connected to the UI panel unit as the operation unit 51 through the I / F unit 85. Further, the operation unit 51 accepts operations by the user, and is configured by, for example, a liquid crystal touch panel having the functions of the input unit 93 and the display unit 94. The operation unit 51 may be an external terminal such as a personal computer connected to the image forming apparatus 200.
Further, the CPU 81 is also electrically connected to the controller 87 and the image processing unit 84. The image information 88 is sent to the CPU 81 through the controller 87. The CPU 81 can form image data by processing the received image information 88 by the image processing unit 84.

[Measurement of toner concentration by density detection sensor]
Next, the toner pattern for density correction will be described. The toner pattern for density correction includes a patch pattern of each color. 4 (a) and 4 (b) show a cross-sectional view and a top view of the black toner pattern 501 as an example of the black patch pattern. As shown in FIG. 4A, the black toner pattern 501 is formed on the intermediate transfer belt 7. As shown in FIG. 4B, five patches having different densities are arranged in the black toner pattern 501 along the rotation direction of the intermediate transfer belt 7. The patch size of each patch is, for example, 16 mm in the main scanning direction (direction orthogonal to the rotation direction of the intermediate transfer belt 7) and 16.3 mm in the sub-scanning direction. The density signal values of each patch are, for example, 20%, 40%, 60%, 80%, and 100%. By acquiring the data in a wide density range by the image forming apparatus 200 in this way, it becomes possible to guarantee the gradation property for various output images. Of course, the number of patches is not limited to five, and may be small from the viewpoint of toner consumption, and a plurality of density signal values may be set in the vicinity of the density signal value which is particularly important. In this embodiment, the same patch size and density signal value pattern patch pattern is used for yellow, magenta, and cyan, which are colors other than black.

FIG. 5 is a diagram illustrating a toner pattern for density correction. As shown in FIG. 5, in the toner pattern for density correction, patch patterns of each color are arranged in a predetermined order. Further, a patchless portion is provided between the patch patterns of each color. FIG. 5 shows four arrangement patterns in which the arrangement order of each color is different. The memory 82 stores such a plurality of arrangement patterns in advance, and the CPU 81 determines which arrangement pattern to use when correcting the toner density. In pattern 1, patch patterns of each color are arranged in the order of yellow, magenta, cyan, and black from the upstream side in the rotation direction. In patterns 2 to 4, the order of yellow, magenta, and cyan remains the same, and the order of black is moved to the upstream side one by one. The proper use of these patterns 1 to 4 will be described in detail in the control flow described later.

The image forming apparatus 200 switches the mode between black and a color other than black to detect the density of the toner pattern. First, as the first mode, a detection mode for black (first mode) will be described. In the black detection mode, the CPU 81 calculates each patch density based on the detection value of each patch of the black toner pattern 501 acquired from the PD 72 that mainly receives specular reflected light via the density detection sensor detection unit 306. .. Since the LEDs 71, PD72, and PD73 are arranged as shown in FIG. 2 above, the PD72 detects the amount of reflected light contained in both the specular reflected light component and the diffusely reflected light component, and the PD73 contains only the diffusely reflected light component. Detects the amount of reflected light. Therefore, the CPU 81 uses the reflected light amount detected by the PD 73 to remove the diffusely reflected light component from the reflected light amount detected by the PD 72, and calculates the specular reflected light component by performing a correction calculation. When the color to be detected is black, the reflected light from the intermediate transfer belt 7 is large and there is almost no reflected light from the toner. Therefore, when the toner image density is high, the specular reflected light component detected by the PD 72 is greatly reduced. Therefore, the CPU 81 calculates each patch density from the detected specular reflected light component by using the relationship between the toner image density stored in advance in the memory 82 and the amount of specular reflected light. After that, the CPU 81 performs density correction using each patch density calculated.

FIG. 6 is a graph showing the relationship between the toner image density, the specular reflected light amount, and the diffusely reflected light amount when the black toner image is detected by the PD72. The horizontal axis of the graph shows the toner image density, and the vertical axis shows the amount of received light. The solid line data of the graph shows the amount of specular reflected light, and the alternate long and short dash line data shows the amount of diffusely reflected light. The image forming apparatus 200 calculates the toner image density from the sensor detection value by utilizing this relationship that has been clarified in advance. The portion of density 0 is the value of the amount of specularly reflected light on the surface of the intermediate transfer belt 7 itself, and it can be seen that the amount of specularly reflected light decreases significantly as the density of black toner (toner adhesion amount) increases.

Next, as a second mode for detecting the density of the toner pattern, a detection mode (second mode) for colors other than black will be described. In the detection mode for colors other than black, the CPU 81 calculates each patch density based on the detection value for each patch of the toner pattern received from the PD 73 via the density detection sensor detection unit 306. As described above, the reflected light amount of PD73 includes only the diffusely reflected light component. Toners of colors other than black have the characteristic that the irradiation light to the density detection sensor 70 is difficult to be absorbed and diffusely reflected. Therefore, the CPU 81 calculates each patch density from the detected diffusely reflected light component by using the relationship between the toner image density stored in advance in the memory 82 and the diffusely reflected light amount. After that, the CPU 81 performs density correction using each patch density calculated.

FIG. 7 is a graph showing the relationship between the toner image density and the amount of reflected light when a color other than black, for example, yellow toner is detected by PD73. The horizontal axis of the graph shows the toner image density, and the vertical axis shows the amount of received light. The alternate long and short dash data in the graph shows the amount of diffusely reflected light. The portion of density 0 is the value of the diffusely reflected light amount on the surface of the intermediate transfer belt 7, and it can be seen that the diffusely reflected light amount increases greatly as the density of the yellow toner (toner adhesion amount) increases.

When performing density detection in the full color mode, the CPU 81 controls to switch between the above two detection modes for each color. Further, in the present embodiment, the light amount setting of the LED 71 is different in the above two detection modes. Since the accuracy of the density correction increases as the dynamic range of the density detection sensor 70 increases, the CPU 81 adjusts the LED 71 to the optimum amount of light for each detection mode. Therefore, when the toner color to be detected changes between black and other colors, the CPU 81 switches the amount of light of the LED 71 in the patchless portion of each color. Of course, the same conditions may be used as long as the density correction accuracy can be maintained for each detection mode with the same amount of light.

[Method for determining abnormalities in the surface condition of the intermediate transfer belt 7]
Subsequently, a method for determining an abnormality in the surface state of the intermediate transfer belt 7 will be described.
When the intermediate transfer belt 7 having an endless belt shape shown in FIG. 1 is left in a relatively high temperature state for a long time, the outer shape of the tension rollers 8, 10, 17, and 18 is tensioned and stretched. It deforms into a shape that follows it (hereinafter, such a deformed part is referred to as a "curly part"). FIG. 8 is a schematic view showing a curl portion 40 generated at four locations on the intermediate transfer belt 7. In FIG. 8, for the sake of clarity, only the intermediate transfer belt 7 and the tension rollers 8, 10, 17, and 18 are shown among the constituent parts of the image forming apparatus 200, and the other parts are omitted. This deformation will eventually disappear when the image forming apparatus 200 outputs an image and the intermediate transfer belt 7 is left in a state where the phase at the time of stopping is changed (an external force does not act on the same portion). However, it takes a certain amount of time to resolve the problem.

FIG. 9 shows the rotation of the amount of specularly reflected light and the amount of diffusely reflected light detected by the concentration detection sensor 70 on the surface of the intermediate transfer belt 7 acquired after being left in a high temperature and high humidity environment (temperature 30 ° C., humidity 80%) for 3 days. The data for one lap in the direction is shown. The horizontal axis indicates the position (phase) of the intermediate transfer belt 7 in the rotation direction, and the vertical axis indicates the amount of reflected light. The data at the top of the graph shows the amount of specular reflected light, and the data at the bottom of the graph shows the amount of diffusely reflected light. It can be seen that there are two fluctuations in the left end and the center of the specular reflected light amount data. The part of the runout corresponds to the position of the curly part. In this way, the curly portion causes a large change in the amount of specularly reflected light even though the toner is not placed on it. This causes an erroneous detection when a black patch pattern is detected, which is a major factor in reducing the density correction accuracy. On the other hand, it can be seen that the curly part does not affect the amount of diffusely reflected light. That is, even if a patch pattern of a color other than black is arranged in the curl portion, the density correction accuracy is not affected. Therefore, when there is a curl portion, the CPU 81 controls to change the color arrangement of the toner pattern for density correction according to the position of the curl portion so that the black patch pattern is not formed on the curl portion. do. That is, the CPU 81 makes it possible to form a patch pattern of a color other than black on the curl portion. In the present embodiment, the CPU 81 changes to the surface state of the intermediate transfer belt 7 when there is a change of + -20% or more with respect to the average value of the reflected light amount of the PD 72 with respect to the surface of one round of the intermediate transfer belt 7. It is determined that there is a curly part. That is, the CPU 81 determines that there is an abnormality in the surface state of the intermediate transfer belt 7.

[Control flow of image forming apparatus 200]
Next, a control flow in which the image forming apparatus 200 according to the present embodiment performs density correction using the density detection sensor 70 will be described with reference to the flowchart of FIG. The processing of this flowchart is realized by the CPU 81 executing the control program stored in the memory 82.

First, in step S1, the CPU 81 starts the processing of this flowchart according to the instruction to start the control execution. In the present embodiment, the total number of output sheets of the recording material S is counted, and when the number of output sheets reaches a predetermined number (for example, 1000 sheets), the instruction to start control execution is set to be output to the CPU 81. There is.
Next, in step S2, the CPU 81 reads the data of the amount of reflected light for one round of the intermediate transfer belt 7 acquired in advance from the memory 82. This data is acquired by the CPU 81 from the concentration detection sensor 70 and stored in the memory 82 at the time of startup control when the main body main power supply (not shown) is turned on by the user. As described above, since it takes time to recover the curl that has been deformed by leaving it unattended, the surface state when the main power of the main body is turned on is often maintained even at the time of image output. It should be noted that the timing for acquiring the data of the amount of reflected light for one round of the intermediate transfer belt 7 is after the timing when the main body main power is turned on, and before the start of this flowchart, the main body main power is turned on. It doesn't have to be the timing that was done.

In the present embodiment, as shown in FIG. 11, a reference sticker 80 for grasping the phase information in the rotation direction of the intermediate transfer belt 7 is attached to the inside of the intermediate transfer belt 7. Further, the intermediate transfer belt frame (not shown) is provided with a reference seal sensor (not shown) for detecting the reference seal 80, and the data acquired from the concentration detection sensor 70 and the reference seal sensor during various engine operations are provided. It is possible to make a temporal association with the data acquired from. Therefore, the CPU 81 reads out the data acquired from the density detection sensor 70 and the data acquired from the reference sticker sensor and associates them in time to specify the position of the fluctuation portion of the reflected light amount as the curl portion.

Next, in step S3, the CPU 81 uses the data of the reflected light amount read in S2 to determine whether or not the amount of fluctuation of the reflected light amount with respect to the surface of the intermediate transfer belt 7 is equal to or greater than a predetermined value. For example, it is determined whether or not there is a change of + -20% or more with respect to the average value of the reflected light amount of PD72 for one round of the intermediate transfer belt 7. When the CPU 81 determines that the amount of fluctuation of the reflected light amount is equal to or more than a predetermined value, it is assumed that the surface state of the intermediate transfer belt 7 is abnormal, and the process proceeds to S4. When the CPU 81 determines that the amount of reflected light is less than a predetermined value, it is assumed that there is no abnormality in the surface state of the intermediate transfer belt 7 and the black patch pattern formation position has little influence on the correction accuracy, and the process proceeds to S5. move on.
In step S5, the CPU 81 selects a normal toner pattern (pattern 1 in FIG. 5), instructs the image data generation unit 89 to generate the selected toner pattern, and forms the selected toner pattern on the intermediate transfer belt 7. do.
Next, in step S6, the CPU 81 acquires the detection values for the patch patterns of each color formed on the intermediate transfer belt 7 by using the LEDs 71 and PD72, 73. Then, the CPU 81 acquires the density information of each patch for each color by using the acquired detection value, the amount of reflected light stored in advance in the memory 82, and the relationship between the toner image density.

Next, in step S7, the CPU 81 calculates the difference between the density information of each patch acquired in step S6 and the density of each patch stored in the memory 82 as a target value in advance. The CPU 81 corrects various conditions and parameters based on the difference. In this embodiment, the correction is performed using a LUT (LookUpTable). However, the correction method is not limited to this, and any method may be used as long as the concentration can be arbitrarily controlled, such as charging high voltage conditions and developing high voltage conditions. Next, in step S8, the CPU 81 initializes the count value of the number of output sheets and ends the processing of the series of flowcharts.

On the other hand, when it is determined in step S3 that there is an abnormality in the surface state of the intermediate transfer belt 7, in step S4, the CPU 81 has a position where the black patch pattern of the normal toner pattern (pattern 1 in FIG. 5) is formed. It is determined whether or not the intermediate transfer belt 7 overlaps with the winding habit portion. If it is determined that the CPU 81 overlaps the curl portion, the process proceeds to step S9. If it is determined that the CPU 81 does not overlap the curl portion, the process proceeds to step S5, and the CPU 81 controls to form a normal toner pattern.
In step S9, the CPU 81 reads out a plurality of arrangement patterns of the toner pattern for correction (FIG. 5) from the memory 82, and sequentially determines the positional relationship between the black patch pattern and the curly portion in the pattern 2, the pattern 3, and the pattern 4. judge. Then, select an arrangement pattern in which the black patch pattern and the curly part do not overlap. After that, the process proceeds to S10.

In the present embodiment, the peripheral length of the intermediate transfer belt 7 is 800 mm, and the length of all colors of the patch pattern is 400 mm. FIG. 12 is a schematic diagram showing the positional relationship between the curly portion of the intermediate transfer belt 7 and the toner pattern for density correction including each patch pattern of four colors. When the toner pattern is formed from the position A of the intermediate transfer belt 7, it is determined that the black patch pattern overlaps the curl portion in the setting of pattern 1 in FIG. Similarly, even in the setting of pattern 2, it is determined that the black patch pattern overlaps the curl portion. As a result, it is determined that the setting of the pattern 3 is appropriate, and the pattern 3 is selected.
Next, in step S10, the CPU 81 instructs the image data generation unit 89 to generate the toner pattern selected in step S9, and forms the selected toner pattern on the intermediate transfer belt 7. After that, the process proceeds to step S6.

According to the image forming apparatus 200 of the first embodiment as described above, even if the surface of the intermediate transfer belt 7 is deformed, the density is corrected by using the patch pattern and the diffuse reflection component that correct the density by using the specular reflection component. Optimize and control the placement of the patch pattern to be corrected. This makes it possible to maintain the density stability of the image without reducing the productivity.

<Second embodiment>
In the first embodiment, it is necessary to provide a reference seal 80 and a reference seal sensor in order to specify the position of the curly portion. In this embodiment, a method of specifying the position of the curly portion without using the reference seal 80 or the reference seal sensor will be described. Since the functional configuration of the image forming apparatus 200 in this embodiment is the same as that in the first embodiment, the description thereof will be omitted again.

[Control flow of image forming apparatus 200]
A control flow in which the image forming apparatus 200 according to the present embodiment performs density correction using the density detection sensor 70 will be described with reference to the flowchart of FIG. The processing of this flowchart is realized by the CPU 81 executing the control program stored in the memory 82, as in the first embodiment. The processing of S11 and S13 to 20 in the flowchart of FIG. 13 is the same as the processing of S1 and S3 to 10 of the flowchart of FIG. Hereinafter, the processing of S12, which is different from the flowchart of FIG. 10, will be described.

In step S12, the CPU 81 detects the amount of reflected light on the surface of one round of the intermediate transfer belt 7 with the PD 72 in the preset LED light amount. At this time, the CPU 81 synchronizes the time information of the reflected light amount of the rotated intermediate transfer belt 7 with the time information from the start of rotation of the intermediate transfer belt 7 and uses the transfer speed and the peripheral length of the intermediate transfer belt 7. The phase of the intermediate transfer belt 7 and the amount of reflected light are associated with each other. For example, the rotation direction in phase of the intermediate transfer belt 7 comes every time (4 sec) obtained by dividing the peripheral length (800 mm) of the intermediate transfer belt 7 by the transfer speed (200 mm / sec). As described above, the CPU 81 specifies the position of the curl portion of the intermediate transfer belt 7.

According to the image forming apparatus 200 of the second embodiment as described above, even if the surface of the intermediate transfer belt 7 is deformed, the density is corrected by using the patch pattern and the diffuse reflection component that correct the density by using the specular reflection component. Optimize and control the placement of the patch pattern to be corrected. This makes it possible to maintain the density stability of the image without reducing the productivity.

Although the present invention has been described above with the embodiments, the above embodiments are merely examples of embodiment of the present invention, and the technical scope of the present invention is limitedly interpreted by these. It shouldn't be. That is, the present invention can be implemented in various forms without departing from the technical idea or its main features.

(Other embodiments)
The present invention supplies a program that realizes one or more functions of the above-described embodiment to a system or device via a network or storage medium, and one or more processors in the computer of the system or device reads and executes the program. It can also be realized by the processing to be performed. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

7: Intermediate transfer belt, 70: Density detection sensor, 81: CPU, 82: Memory, 200: Image forming apparatus

Claims (13)

An image carrier, an image forming means for forming toner images of a plurality of colors on the image carrier, and a first detection value corresponding to a specular reflected light amount and a diffusely reflected light amount by irradiating the image carrier with light. An image forming apparatus having a detection unit for detecting a second detection value.
A first detection value and a second detection value of a correction pattern in which different colors are arranged for each of a plurality of patches formed on the image carrier are acquired from the detection unit, and the first detection value is used. It has a control means for controlling to correct the density of the toner image formed by the image forming means by switching between the mode and the second mode using the second detection value for each color.
When the surface state of the image carrier is abnormal, the control means changes the color of the correction pattern so that the patch of the color using the first mode is not formed at the abnormal position on the image carrier. An image forming apparatus characterized by changing the arrangement. 1. The control means is characterized in that the color arrangement of the correction pattern is changed so that the patch of the color using the second mode is formed at an abnormal position on the image carrier. The image forming apparatus according to. Further having a storage means for storing a plurality of the correction patterns having different color arrangements,
The control means is characterized in that the correction pattern is selected from the plurality of correction patterns so that the patch of the color using the first mode does not overlap with the abnormal position on the image carrier. Or the image forming apparatus according to 2. In the correction pattern, the patches are arranged along the rotation direction of the image carrier.
The image forming apparatus according to any one of claims 1 to 3, wherein the control means changes the arrangement order of colors of the correction pattern. The control means acquires the first detection value of the image carrier from the detection unit before forming the correction pattern on the image carrier, and the control means obtains the first detection value based on the acquired first detection value. The image forming apparatus according to any one of claims 1 to 4, wherein it is determined whether or not there is an abnormality in the surface state of the image carrier. The control means detects the abnormal size of the surface state of the image carrier based on the first detection value acquired from the detection unit, and when the abnormal size is equal to or larger than a predetermined value, the control means said. The fifth aspect of claim 5, wherein the color arrangement of the correction pattern is changed, and when the size of the abnormality is less than a predetermined value, the color arrangement of the correction pattern is controlled so as not to be changed. Image forming device. The image carrier is provided with a reference seal for detecting the phase of the image carrier.
The control means identifies an abnormal position on the image carrier based on the first detection value acquired from the detection unit and the result detected by the reference seal sensor that detects the reference seal. The image forming apparatus according to claim 5 or 6. The control means is characterized in that it identifies an abnormal position on the image carrier based on the first detection value acquired from the detection unit and the time from the start of rotation of the carrier. The image forming apparatus according to 5 or 6. The first aspect of claim 5 to 8, wherein the control means acquires the first detection value of the image carrier from the detection unit at the timing when the power of the image forming apparatus is turned on. Image forming device. The image forming apparatus according to any one of claims 1 to 9, wherein the color using the first mode is black, and the color using the second mode is a color other than black. The carrier is an endless belt,
The image forming apparatus according to any one of claims 1 to 10, wherein the abnormality in the surface state of the carrier is a winding habit attached by a roller that stretches the image carrier. An image carrier, an image forming means for forming toner images of a plurality of colors on the image carrier, and a first detection value corresponding to a specular reflected light amount and a diffusely reflected light amount by irradiating the image carrier with light. A control method for an image forming apparatus having a detection unit for detecting a second detection value.
A first detection value and a second detection value of a correction pattern in which different colors are arranged for each of a plurality of patches formed on the image carrier are acquired from the detection unit, and the first detection value is used. A control step of switching between a mode and a second mode using the second detection value for each color to correct the density of the toner image formed by the image forming means is included.
In the control step, when the surface state of the image carrier is abnormal, the color of the correction pattern is changed so that the patch of the color using the first mode is not formed at the abnormal position on the image carrier. A control method for an image forming apparatus, which comprises changing the arrangement. A program for making a computer function as each means of the image forming apparatus according to any one of claims 1 to 11.

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