JP6789702B2 - Image forming device - Google Patents

Description

The present invention relates to color shift correction control for correcting the amount of color shift of an image for each color formed by a plurality of image forming portions.

The electrophotographic image forming apparatus includes a plurality of image forming units for forming images of different colors. Then, the images formed by the plurality of image forming portions are superimposed and transferred to form a full-color image. In such an image forming apparatus, if the relative positions of the images of each color are deviated when the images of different colors are superimposed and transferred, the tint of the image formed on the sheet changes. Therefore, there is known an image forming apparatus that forms a color pattern on an intermediate transfer body by a plurality of image forming portions and corrects the writing timing of the plurality of image forming portions based on the result of detecting the color pattern by a sensor (. Patent Document 1).

The image forming apparatus described in Patent Document 1 is on top of a pattern image of a reference color and a pattern image of another color different from the reference color in order to detect the amount of color shift of an image having a low reflectance such as black. A superposed pattern image is formed by superimposing a black pattern image on the image.

Japanese Unexamined Patent Publication No. 2012-3234

However, when the superimposed pattern image is used to detect the amount of color shift, the output waveform corresponding to the detection result of the pattern image of the reference color and the output waveform corresponding to the detection result of the superimposed pattern image are different, and the colors are different. It may not be possible to detect the amount of deviation with high accuracy. This is because the amount of distortion of the output waveform of the pattern image other than the superimposed pattern is larger than the amount of distortion of the output waveform of the superimposed pattern image.

The amount of distortion of the output waveform is considered to be caused by the unevenness of the intermediate transfer body. In the superimposed pattern image, when the superimposed pattern passes through the measurement position of the sensor, an image of another color different from the reference color covers the intermediate transfer body, so that distortion of the output waveform of the sensor is suppressed.

Therefore, an object of the present invention is to correct the amount of color shift with high accuracy even when the output waveform corresponding to the detection result of the color pattern for detecting the amount of color shift is distorted.

In order to solve the above problems, the image forming apparatus of the present invention includes a plurality of image forming means for forming images of different colors, an intermediate transfer body to which the images are transferred and conveys the images, and a pattern image of a reference color. And the pattern image of another color different from the reference color, and the color pattern for detecting the amount of color shift related to the relative positional deviation between the image of the reference color and the image of the other color is intermediate. The detection means for detecting in the transfer body and the plurality of image forming means are made to form the first color pattern in the intermediate transfer body, the detection means is made to detect the first color pattern, and the detection result of the first color pattern. And the correction means for determining the amount of color shift based on the correction data and correcting the writing timing of the images of different colors formed by the plurality of image forming means based on the amount of color shift, and the plurality of correction means. The image forming means is made to form the second color pattern, the detecting means is made to detect the second color pattern, the plurality of image forming means are made to form the third color pattern, and the detecting means is made to form the third color pattern. It has a generation means for detecting and generating the correction data based on the detection result of the second color pattern and the detection result of the third color pattern, and the first color pattern is of the first color. The second color pattern includes a first pattern image and a first superimposed pattern image, and the second color pattern includes a second pattern image of the first color and a second superimposed pattern image formed on an image of a predetermined color. The third color pattern includes a third pattern image of the first color and a third superimposed pattern image, and the first superimposed pattern image is on top of the other first pattern image of the first color. wherein and the first color and overlap second color different first pattern image, the second superimposed pattern images, the second color of the second pattern image on the other of the second pattern image of the first color In the third superimposed pattern image , the third pattern image of the second color is superimposed on the other third pattern image of the first color, and the predetermined color is the first color. It is characterized in that it is different from the second color and is different from the second color.

According to the present invention, even when the output waveform corresponding to the detection result of the color pattern for detecting the color shift amount is distorted, the color shift amount can be corrected with high accuracy.

Schematic cross-sectional view of the image forming apparatus Schematic diagram illustrating the configuration of the sensor Schematic diagram of color pattern A formed on the intermediate transfer belt Schematic diagram of the detection result of the pattern image included in the color pattern Schematic diagram of the detection result of the magenta pattern image and the superimposed pattern image Experimental results of measuring the amount of color shift caused by distortion of the output waveform Schematic diagram of color patterns B and C formed to detect correction data Control block diagram of image forming apparatus Flow chart diagram including image forming operation of image forming apparatus Flow chart of color shift correction Flow chart of correction amount determination process for generating correction data Schematic diagram showing the size of the spot diameter of the sensor and the size of the color pattern B

(Image forming device)
FIG. 1 is a cross-sectional view showing the overall configuration of the color image forming apparatus 100 (hereinafter referred to as the image forming apparatus 100) according to the present embodiment, and shows the schematic configuration of an electrophotographic full-color printer. The image forming apparatus 100 shown in FIG. 1 has a document reading unit 101 and an image forming unit 102. The document reading unit 101 reads the document image, and the image forming unit 102 forms an image on the sheet based on the scanned image data.

The image forming unit 102 includes an image forming unit Y for forming a yellow image, an image forming unit M for forming a magenta image, an image forming unit C for forming a cyan image, and a black image. An image forming unit Bk for forming is provided. The image forming unit Y includes a photosensitive drum 103a, a charging device 104a for charging the photosensitive drum 103a, and an optical scanning device that emits a light beam (laser light) for forming an electrostatic latent image on the charged photosensitive drum 103a. 105a is provided. A photosensitive layer that functions as a photoconductor is formed on the surface of the photosensitive drum 103a. The image forming unit Y is provided with a developing device 106a for developing an electrostatic latent image with a developer and a cleaning device 107a for cleaning residual toner on the photosensitive drum 103a. Since the image forming units M, C, and Bk have the same configuration as the image forming unit Y, the description thereof is omitted here.

The image forming process performed by the image forming unit 102 will be described. Since the image forming processes of the image forming portions Y, M, C, and Bk are the same process, the yellow image forming portion Y will be described as an example. When the image forming process is started, the photosensitive drum 103a is rotated in the direction of arrow A by a motor (not shown). Then, the photosensitive drum 103a is charged by the charging device 104a. An electrostatic latent image is formed on the charged photosensitive drum 103a by a laser beam (light beam) emitted from the optical scanning device 105a, and the electrostatic latent image is developed by the developing device 106a using yellow toner. Toner.

Then, the yellow image developed on the photosensitive drum 103a is transferred to the intermediate transfer belt 109 by the transfer bias applied to the primary transfer roller 108a. The intermediate transfer belt 109 functions as an intermediate transfer body on which an image is transferred.

The images formed by the image forming portions Y, M, C, and Bk are transferred so as to overlap on the intermediate transfer belt 109. As a result, a full-color image is formed on the intermediate transfer belt 109. The arrow B direction indicates the transport direction in which the intermediate transfer belt 109 transports the image. The image supported on the intermediate transfer belt 109 is conveyed to the transfer unit T for transferring the image of the intermediate transfer belt 109 to the sheet. The secondary transfer unit T is a nip portion between the intermediate transfer belt 109 and the secondary transfer roller 111. The secondary transfer roller 111 presses the intermediate transfer belt 109 against the roller 110 to form a nip portion. The timing at which the image reaches the secondary transfer unit T and the timing at which the sheet reaches the secondary transfer unit T are controlled. A transfer bias is applied to the secondary transfer roller 111 when the sheet passes through the secondary transfer unit T. As a result, the image on the intermediate transfer belt 109 is transferred to the sheet. After that, the sheet on which the image is transferred is conveyed to the fixing device 112. The fuser 112 has a heater and two rollers, and the image is fixed to the sheet by the heat of the heater and the pressure of the rollers. Then, the sheet that has passed through the fixing device 112 is discharged to the outside of the device by the paper ejection roller.

The black image forming portion Bk is provided on the secondary transfer portion side of the other chromatic image forming portions Y, M, and C in the rotation direction of the intermediate transfer belt 109. By arranging in this way, when a monochrome image is formed, it is possible to suppress the time from the instruction of image formation by the user to the output of the image.

A sensor 113 is provided in the vicinity of the intermediate transfer belt 109 in order to detect a pattern image described later. As shown in FIG. 1, the optical sensor 113 is provided between the image forming unit Bk and the secondary transfer roller 111 in the transport direction of the intermediate transfer belt 109.

Further, the image forming apparatus 100 includes an operation unit 114. By operating the operation unit 114, the user can instruct the image forming apparatus 100 to start image formation, or instruct the image forming apparatus 100 to execute the color shift correction described later.

FIG. 2 is a cross-sectional view of a main part of the sensor 113 that detects a pattern image and a top view of the intermediate transfer belt 109. The sensor 113 is an optical sensor that detects the reflected light from the pattern image formed on the intermediate transfer belt 109. The sensor 113 detects, for example, diffusely reflected light from a pattern image. The sensor 113 includes a light emitting unit 601 that irradiates (projects) light toward the intermediate transfer belt 109, and a light receiving unit 602 that receives the reflected light from the intermediate transfer belt 109 or the pattern image. The light receiving unit 602 is arranged at a position where the incident angle and the reflected angle are not equal so that the diffusely reflected light of the light emitted from the light emitting unit 601 to the intermediate transfer belt 109 can be received. The light receiving unit 602 is arranged at a position where the light mirror-reflected from the pattern image is not received.

The sensor 113 outputs a signal at a level corresponding to the intensity of the light received by the light receiving unit 602 (the amount of received light). The sensor 113 has a lens 603 that collects the reflected light from the detection area 604 in the region 605 that is irradiated with the light from the light emitting unit 601. That is, the light receiving unit 602 selectively receives the diffuse reflected light from the detection area 604.

Subsequently, the color shift correction control will be described. The color shift correction control is a calibration for correcting the shift of the writing position of the image due to the manufacturing variation of the image forming apparatus and the shifting of the writing position due to the change of the internal temperature.

The image forming apparatus 100 executes color shift correction control when the number of images formed reaches a predetermined number or when the internal temperature of the image forming apparatus 100 changes by a predetermined temperature or more. Further, the image forming apparatus 100 executes color shift correction control, for example, when the main power supply of the image forming apparatus 100 is turned on. Further, the image forming apparatus 100 executes color shift correction control, for example, when the internal temperature of the image forming apparatus 100 changes by a predetermined temperature or more. Further, in the image forming apparatus 100, for example, when the user instructs the operation unit 114 to execute the color shift correction control, the color shift correction is executed.

FIG. 3 is a schematic view of the color pattern A formed on the intermediate transfer belt 109. The color pattern A includes a magenta pattern image 302, a yellow pattern image 301, a cyan pattern image 303, and a superposed pattern image 304 in which the magenta pattern image is exposed from a gap between the black pattern images. Since the reflected light from the black pattern image is small, the superimposed pattern image 304 is formed to detect the position of the black pattern image. Here, the magenta pattern image 302 corresponds to the first color pattern image, and the black pattern image corresponds to the second color pattern image.

The pattern image of the reference color is a magenta pattern image. The pattern image of the reference color may be a pattern image of another color other than black, for example, yellow. Since a known method is used for correcting the writing position of the image of each color based on the time when each pattern image is detected by the sensor 113, the description thereof is omitted here.

(Waveform distortion)
FIG. 4 shows an analog signal output from the sensor 113 when a pattern image is detected, and a digital signal obtained by binarizing the analog signal with the comparator 403 (FIG. 8). In FIG. 4, the solid line analog signal is an analog signal of the sensor 113 when the pattern image formed on the intermediate transfer belt 109 is detected by the sensor 113 after forming images for a plurality of pages. In FIG. 4, the broken line analog signal is an analog signal of the sensor 113 when the pattern image is detected by the sensor 113 in a state where the surface state of the intermediate transfer belt 109 is ideal.

As shown in FIG. 4, the output waveform (solid line) of the analog signal of the sensor 113 is distorted. In FIG. 4, the position of the center of gravity of the output waveform (broken line) of the analog signal of the sensor 113 corresponds to the timing when the period a / 2 elapses in the period a in which the sensor output value is equal to or higher than the threshold value. On the other hand, in FIG. 4, the position of the center of gravity of the output value (solid line) of the analog signal of the sensor 113 corresponds to the timing when the period b / 2 elapses in the period b in which the sensor output value is equal to or higher than the threshold value. That is, as shown in FIG. 4, the timing δ deviates between the position of the center of gravity when the output waveform is distorted and the position of the center of gravity when the output waveform is not distorted.

FIG. 5 is a diagram showing an analog signal and a digital signal output from the sensor 113 when the sensor 113 detects the pattern images 302, 304, 302 of the color pattern A.

In the state where the surface of the intermediate transfer belt 109 is rough after the images for a plurality of pages are formed, the output waveform of the pattern image 302 is distorted, but the output waveform of the superimposed pattern image 304 is not distorted. The reason why the output waveform of the superimposed pattern image 304 is not distorted is that the black pattern image covers the surface of the intermediate transfer belt 109. The output waveform of the yellow pattern image 301 and the output waveform of the cyan pattern image 303 are distorted in the same manner as the output waveform of the magenta pattern image 302. That is, the output waveforms of the pattern images 301, 302, and 303 have a timing δ shift, and the output waveform of the superimposed pattern image 304 does not have a timing δ shift.

If the positions of the centers of gravity of the pattern images 301 and 302 differ from the theoretical values by the amount of deviation δ due to the distortion of the output waveform, the relative positions of the magenta image and the yellow image in the transport direction of the intermediate transfer belt 109. The color shift amount Dy related to the shift is calculated by the equation (1). The center of gravity position Pm of the magenta pattern image 302, the center of gravity position Py of the yellow pattern image 301, and the true color shift amount Δy are set.
Dy = (Pm + δ)-(Py + δ)
= Pm-Py
= Δy ・ ・ ・ Equation (1)
That is, when the output waveform is similarly distorted, the deviation amount δ is canceled and the actual correction amount does not change.

On the other hand, since the output waveform of the superimposed pattern image 304 is not distorted like the output waveforms of the pattern images 301, 302, and 303, an error occurs in the amount of color shift of black. The color shift amount Dk relating to the relative positional shift between the magenta image and the black image in the transport direction of the intermediate transfer belt 109 is calculated by the equation (2). The center of gravity position Pm of the magenta pattern image 302, the center of gravity position Pk of the black pattern image 304, and the true color shift amount Δk are used.
Dk = Pk- (Pm + δ)
= Pk-Pm-δ
= Δk−δ ・ ・ ・ Equation (2)
That is, an error corresponding to the amount of deviation δ remains in the amount of color shift.

Therefore, the image forming apparatus 100 of the present invention generates a shift amount δ of the color shift amount from the detection results of the two color patterns B and C, and shifts to the color shift amount Dk calculated from the detection result of the color pattern A. The ideal color shift amount Δk is calculated by adding the amount δ. FIG. 7A is a schematic diagram of the color pattern B, and FIG. 7B is a schematic diagram of the color pattern C.

In the color pattern B, the yellow band image 305 is laid under the magenta pattern image 302 and the superimposed pattern image 304, and the band image 305 covers the surface of the intermediate transfer belt 109. As a result, the output waveform of the magenta pattern image 302 is not distorted, so the true color shift amount Δk of the black pattern image 304 is calculated based on the detection result of the color pattern B. The amount of toner adhered to the band image 305 is smaller than the amount of toner adhered to the magenta pattern image. This is because when the amount of toner adhering to the color pattern B exceeds the permissible range, the difference between the intensity of the reflected light from the band image 305 and the intensity of the reflected light from the pattern image 302 decreases, and the color This is because the amount of deviation cannot be detected with high accuracy. Further, the time spent cleaning the intermediate transfer belt 109 may increase.

On the other hand, the color pattern C is the same color pattern as the color pattern A. Unlike the color pattern B, the yellow band image 305 is not formed. The color pattern C may be only the magenta pattern image 302 and the superimposed pattern image 304. In the color pattern C, the color shift amount Dk of the black pattern image 304 is calculated based on the detection result of the color pattern B.

Then, the shift amount δ can be calculated by subtracting the color shift amount Dk calculated from the detection result of the color pattern C from the true color shift amount Δk calculated from the detection result of the color pattern B. If the yellow band image 305 is formed each time the color shift correction is executed, the consumption of the yellow developer increases. Therefore, the color pattern A is formed in the color shift correction control that is executed frequently. The amount of color shift of yellow and cyan is calculated from the detection result of the color pattern A by the sensor 113, and the amount of color shift of black is calculated based on the detection result of the color pattern A by the sensor 113 and the amount of shift δ. To. As a result, even if the distortion of the output waveform of the yellow, magenta, and cyan pattern images and the distortion of the output waveform of the black pattern image are different, the amount of color shift can be corrected with high accuracy for each color.

(Transition of waveform distortion)
Next, the transition of the waveform distortion when the surface state of the intermediate transfer belt 109 changes will be described. FIG. 6 shows the experimental results of investigating the relationship between the number of images formed and the amount of black color shift caused by the distortion of the output waveform. The horizontal axis shows the cumulative number of images formed, and the vertical axis shows the amount of color shift caused by distortion of the output waveform. From the experimental results of FIG. 6, it is considered that the amount of distortion increases as the number of images formed increases.

When the color shift correction is performed, for example, every time the cumulative number of image formations reaches 1000, the shift amount δ of the color shift amount due to the distortion of the output waveform does not change much. That is, it is not necessary to form the color pattern B every time the color shift correction is executed. Therefore, for example, the image forming apparatus 100 updates the deviation amount δ when an image for 50,000 pages is formed, and in the color shift correction executed every time the cumulative number of image formations reaches 1000, the image forming apparatus 100 performs. The color pattern A is detected.

(Control flow of image forming apparatus)
Next, a control block diagram of the image forming apparatus 100 will be described with reference to FIG. The CPU 400 is a control circuit that controls each part of the image forming apparatus 100. The ROM 401 stores a control program that is executed by the CPU 400 and is necessary for executing various processes of the flowchart described later. The RAM 402 is a system work memory for operating the CPU 400. The description of the image forming unit 102, the operating unit 114, and the sensor 113 will be omitted.

The temperature sensor 1005 detects the internal temperature of the image forming apparatus 100. The CPU 400 stores the internal temperature detected by the temperature sensor 1005 when the color shift correction is performed last time in the RAM 402, and performs the color shift correction when the stored temperature and the current temperature are different by a predetermined temperature or more. Execute and update the amount of color shift.

The comparator 403 converts the analog signal of the sensor 113 into a binary digital signal based on the threshold value set by the CPU 400. The converted digital signal is output to the color shift amount correction unit 200.

The color shift correction unit 200 determines the position of the center of gravity of each pattern image based on the output signal of the sensor 113 input via the comparator 403, and determines the position of the center of gravity of the magenta pattern image and the pattern image of another color. The amount of color shift is determined based on the difference from the position of the center of gravity. The color shift correction unit 200 calculates the color shift amount of yellow and cyan based on the color pattern detection result of the sensor 113, and the black color shift amount is calculated by the color pattern detection result of the sensor 113 and the RAM 402. Calculated based on the stored deviation amount δ.

Then, the color shift correction unit 200 colors the image writing position in the direction orthogonal to the transport direction of the intermediate transfer belt 109 with reference to the reference position in the direction in which the laser light emitted from the optical scanning device 105 is scanned. The distance is shifted by the distance corresponding to the amount of deviation. As a result, the writing timing in the main scanning direction in which the laser beam of the optical scanning device 105 scans the photosensitive drum 103 is corrected. Further, the color shift correction unit 200 sets the image writing position in the transport direction of the intermediate transfer belt 109 by a distance corresponding to the color shift amount with reference to the reference position in the direction in which the surface of the photosensitive drum 103 moves. shift. As a result, the writing timing in the sub-scanning direction parallel to the transport direction of the intermediate transfer belt 109 is corrected.

Next, an image forming operation in which the image forming apparatus 100 forms an image based on the image data will be described with reference to the flowchart of FIG. When the main power of the image forming apparatus 100 is turned on, the CPU 400 reads out the program stored in the ROM 401 and executes each process of the flowchart of FIG.

The CPU 400 executes color shift correction after the main power of the image forming apparatus 100 is turned on (S1). The color shift correction in step S1 will be described later using the flowchart of FIG. The CPU 400 stores the detection result of the amount of color shift and the temperature detected by the temperature sensor 1005 in the RAM 402. Then, the CPU 400 determines whether or not the image data has been transferred from the document reading unit 101 or a PC (not shown) (S2).

When the image data is transferred in step S2, the CPU 400 determines whether or not the execution condition of the color shift correction is satisfied (S3). In step S3, the execution condition of the color shift correction is, for example, the number of sheets on which the image forming apparatus 100 has formed an image since the previous color shift correction was executed. When the cumulative value of the number of image formations described above reaches a predetermined number, the CPU 400 determines that the execution condition is satisfied. When the execution condition of the color shift correction is satisfied in step S3, the CPU 400 executes the color shift correction (S4). The color shift correction in step S4 is the same as the color shift correction in step S1, and will be described later using the flowchart of FIG. Then, after the color shift correction is executed in step S4, the CPU 400 shifts the process to step S5.

On the other hand, if the execution condition of the color shift correction is not satisfied in step S3, the CPU 400 causes the image forming unit 102 to form an image based on the image data (S5). In step S5, the image writing position of the image forming unit 102 is shifted based on the color shift amount determined by the color shift amount correction unit 200. That is, the color shift amount correction unit 200 functions as a correction means for correcting the color shift amount based on the color shift amount.

When the image for one page is formed in step S5, the CPU 400 determines whether or not all the images included in the image data are formed (S6). If all the images included in the image data are not formed in step S6, the CPU 400 shifts the process to step S3. On the other hand, if all the images included in the image data are formed in step S6, the CPU 400 determines whether or not the execution condition of the correction amount determination process for generating the deviation amount δ is satisfied (S7).

In step S7, the execution condition of the correction amount determination process is, for example, the number of sheets on which the image forming apparatus 100 has formed an image since the previous correction amount determination process was executed. When the cumulative value of the number of image formations described above reaches, for example, 50,000, the CPU 400 determines that the execution condition is satisfied. When the execution condition of the correction amount determination process is satisfied in step S7, the CPU 400 executes the correction amount determination process (S8). The correction amount determination process in step S8 will be described later using the flowchart of FIG. Then, after the correction amount determination process is executed, the CPU 400 shifts the process to step S9.

On the other hand, if the execution condition of the correction amount determination process is not satisfied in step S7, the CPU 400 determines whether or not the main power supply of the image forming apparatus is turned off (S9). In step S9, when the main power supply is turned off, the CPU 400 ends the image forming operation of the image forming apparatus 100.

On the other hand, if the main power supply is not turned off in step S9, the CPU 400 shifts the process to step S2. If the image data has not been transferred in step S2, the CPU 400 shifts the process to step S9. That is, the CPU 400 repeatedly executes the processes of steps S2 and S9 until the image data is transferred or the main power is turned off.

Next, the color shift correction executed in steps S1 and S4 of FIG. 9 will be described with reference to the flowchart of FIG. In the color shift correction, the image forming unit 102 forms the color pattern A (FIG. 3), and the color shift amount correction unit 200 performs the color shift of each color based on the detection result of the color pattern A by the sensor 113 and the shift amount δ. Adjust the amount. The deviation amount δ is set to 0, for example, until the correction amount determination process is executed for the first time.

When the color shift correction is executed, the CPU 400 first determines the threshold value Th1 to be set in the comparator 403 (S101). In step S101, the CPU 400 causes the sensor 113 to detect the intermediate transfer belt 109, and acquires a sensor output value corresponding to the reflected light from the intermediate transfer belt 109. Next, the CPU 400 causes the image forming unit 102 to form the color pattern A, causes the sensor 113 to detect the color pattern A, and acquires the sensor output value corresponding to the reflected light from each pattern image of the color pattern A. Then, the CPU 400 determines a threshold value Th1 that is larger than the sensor output value corresponding to the reflected light from the intermediate transfer belt 109 and smaller than the sensor output value corresponding to the reflected light from each pattern image of the color pattern A.

Next, the CPU 400 causes the image forming unit 102 to form the color pattern A (described as the pattern image A in FIG. 10) (S102), and causes the sensor 113 to detect the color pattern A (S103). In step S103, the CPU 400 sets the threshold Th1 determined in step S101 in the comparator 403 and acquires the output value of the sensor 113. The color shift correction unit 200 determines the position of the center of gravity of each pattern image based on the digital signal of the sensor 113, and calculates the amount of color shift for each color.

Next, the CPU 400 reads out the deviation amount δ stored in the RAM 402 (S104) and transfers it to the color deviation correction unit 200. The color shift correction unit 200 determines the amount of color shift of each color (S105). In step S105, the amount of color shift between yellow and cyan is calculated from the detection result of the color pattern A. On the other hand, the color shift amount of black is calculated based on the detection result of the color pattern A and the shift amount δ input from the CPU 400. When the color shift amount is determined in step S105, the color shift amount correction unit 200 adjusts the writing position of the image forming unit 102. Then, the CPU 400 ends the color shift correction process.

Next, the correction amount determination process executed in step S8 of FIG. 9 will be described with reference to the flowchart of FIG. In the correction amount determination process, the image forming unit 102 forms the color patterns B and C (FIG. 7), and the CPU 400 generates the deviation amount δ based on the detection results of the color patterns B and C by the sensor 113. The deviation amount δ is stored in the RAM 402.

When the correction amount determination process is executed, the CPU 400 first determines the threshold value Th2 to be set in the comparator 403 (S201). In step S201, the CPU 400 causes the image forming unit 102 to form the color pattern B, causes the sensor 113 to detect the color pattern B, and acquires the sensor output value corresponding to the reflected light from the yellow band image 305 of the color pattern B. To do. Further, the CPU 400 acquires the sensor output value corresponding to the reflected light from the magenta pattern image 302 of the color pattern B and the superimposed pattern image 304. Then, the CPU 400 determines a threshold value Th2 that is larger than the sensor output value corresponding to the reflected light from the yellow band image 305 and smaller than the sensor output value corresponding to the reflected light from the pattern image 302 and the superimposed pattern image 304. To do.

Next, the CPU 400 causes the image forming unit 102 to form the color pattern B (described as the pattern image B in FIG. 11) (S202), and causes the sensor 113 to detect the color pattern B (S203). In step S203, the CPU 400 sets the threshold Th2 determined in step S201 in the comparator 403 and acquires the output value of the sensor 113. The color shift correction unit 200 determines the position of the center of gravity of each pattern image based on the digital signal of the sensor 113, and calculates the true amount of color shift of the black image with respect to the magenta image.

Next, the CPU 400 causes the image forming unit 102 to form the color pattern C (described as the pattern image C in FIG. 11) (S204), and causes the sensor 113 to detect the color pattern C (S205). In step S205, the CPU 400 sets the threshold value Th1 determined in step S101 in the comparator 403 and acquires the output value of the sensor 113. The color shift correction unit 200 determines the position of the center of gravity of each pattern image based on the digital signal of the sensor 113, and calculates the amount of color shift for each color.

Then, the CPU 400 calculates the deviation amount δ by subtracting the color deviation amount Dk calculated from the detection result of the color pattern C from the true color deviation amount Δk calculated from the detection result of the color pattern B (S207). The deviation amount δ calculated in step S207 corresponds to the correction data for correcting the color deviation amount of the black image. The deviation amount δ is stored in the RAM 402.

Further, the color shift correction unit 200 determines the amount of color shift of each color based on the detection result of the color pattern C acquired in step S205 (S207). In step S207, the amount of color shift between yellow and cyan is calculated from the detection result of the color pattern C. On the other hand, the color shift amount of black is calculated based on the detection result of the color pattern C and the shift amount δ calculated in step S206. When the color shift amount is determined in step S207, the color shift amount correction unit 200 adjusts the writing position of the image forming unit 102. Then, the CPU 400 ends the correction amount determination process.

(Dimension of color pattern B)
Next, the relationship between the color pattern B and the detection area 604 of the sensor 113 will be described with reference to FIG. The length L1 corresponds to the length of the detection area 604 of the sensor 113 in the transport direction of the intermediate transfer belt 109. The length L2 corresponds to the distance from the front end of the band image 305 to the front end of the magenta pattern image 302 in the transport direction of the intermediate transfer belt. The length L3 corresponds to the distance between the magenta pattern image and the superimposed pattern image 304 in the transport direction of the intermediate transfer belt.

In order to detect the deviation amount δ with high accuracy, it is desirable that the length L2 is longer than the length L1. If the length L2 is shorter than the length L1, the light receiving unit 602 simultaneously receives the reflected light from the intermediate transfer belt 109 and the pattern image 302 at the sensor output value (analog signal) of the pattern image 302. Therefore, the output waveform of the sensor 113 is distorted. Therefore, the length of the band image 305 in the transport direction is longer than that of the pattern image 302 by the length of the detection area 604 of the sensor 113.

Further, it is desirable that the length L3 is longer than the length L1. When the length L3 is smaller than the length L1, the light receiving unit 602 simultaneously receives the reflected light of the pattern image 302, the band image 305, and the superimposed pattern image 304 at the sensor output value (analog signal) of the pattern image 302. In this case as well, the output waveform of the sensor 113 is similarly distorted. Therefore, the distance between the pattern image 302 and the superimposed pattern image 304 in the transport direction is longer than the length of the detection area 604.

Further, in the above description, the correction amount determination process is executed when the number of images formed reaches 50,000. For example, the CPU 400 performs the correction amount determination process based on the update instruction from the operation unit 114. May be configured to execute. In this case, the operation unit 114 functions as an input means capable of inputting an update instruction for correction data.

As described above, according to the present invention, in the configuration in which the amount of color shift is corrected using the superimposed pattern image, the correction data is corrected even when the distortion of the sensor output waveform between the superimposed pattern image and the other pattern image is different. The amount of color shift can be obtained with high accuracy based on the above. Further, even when the distortion of the output waveform of the sensor 113 changes with the wear of the intermediate transfer belt 109, the correction data is updated, so that the amount of color shift can be corrected with high accuracy.

102 Image forming unit 109 Intermediate transfer belt 113 Sensor 200 Color shift correction unit 400 CPU

Claims (10)

Multiple image forming means for forming images of different colors,
An intermediate transfer body to which the image is transferred and conveys the image,
For detecting the amount of color shift related to the relative positional deviation between the reference color image and the other color image, including the reference color pattern image and the pattern image of another color different from the reference color. A detection means for detecting a color pattern in the intermediate transfer body, and
The plurality of image forming means are made to form a first color pattern on the intermediate transfer body, the detecting means is made to detect the first color pattern, and the color is based on the detection result of the first color pattern and correction data. A correction means for determining the amount of deviation and correcting the writing timing of the images of different colors formed by the plurality of image forming means based on the amount of color deviation.
The plurality of image forming means are made to form a second color pattern, the detecting means is made to detect the second color pattern, the plurality of image forming means are made to form a third color pattern, and the detecting means is made to form the third color pattern. It has a generation means for detecting a color pattern and generating the correction data based on the detection result of the second color pattern and the detection result of the third color pattern.
The first color pattern includes a first pattern image of the first color and a first superimposed pattern image.
The second color pattern includes a second pattern image of the first color and a second superimposed pattern image formed on an image of a predetermined color.
The third color pattern includes a third pattern image of the first color and a third superimposed pattern image.
In the first superimposed pattern image , a first pattern image of a second color different from the first color is superimposed on another first pattern image of the first color.
In the second superimposed pattern image , the second pattern image of the second color is superimposed on the other second pattern image of the first color.
In the third superimposed pattern image , the third pattern image of the second color is superimposed on the other third pattern image of the first color.
An image forming apparatus characterized in that the predetermined color is different from the first color and is different from the second color. When the first condition is satisfied, the correction means causes the plurality of image forming means to form the first color pattern.
The claim is characterized in that the generation means causes the plurality of image forming means to form the second color pattern and the third color pattern when a second condition different from the first condition is satisfied. The image forming apparatus according to 1. Further comprising a transfer means for transferring the image on the intermediate transfer body to a sheet.
When the number of images formed by the plurality of image forming means exceeds the first threshold value, the first condition is satisfied.
The image forming apparatus according to claim 2, wherein the second condition is satisfied when the number of images formed exceeds a second threshold value larger than the first threshold value. Further having an input means capable of inputting the update instruction of the correction data,
Claims 1 to 1, wherein the generation means causes the plurality of image forming means to form the second pattern image and the third pattern image when the update instruction is input from the input means. The image forming apparatus according to any one of 3. The image forming apparatus according to any one of claims 1 to 4, wherein the third color pattern further includes another pattern image of the first color. When the generation means generates the correction data, the correction means determines the color shift amount based on the detection result of the third color pattern and the correction data, and the plurality of correction means based on the color shift amount. The image forming apparatus according to claim 5, wherein the writing timing of the images of different colors formed by the image forming means of the above is corrected. The image forming apparatus according to any one of claims 1 to 6, wherein the second color is black. The detection means
A light emitting unit that irradiates the intermediate transfer body with light,
Any of claims 1 to 7, further comprising a light receiving unit that receives diffusely reflected light from the pattern image at a position where light emitted from the light emitting unit and mirror-reflected from the pattern image is not received. The image forming apparatus according to one item. The length from the front end of the image of the predetermined color to the front end of the second pattern image of the first color in the transport direction in which the intermediate transfer body transports the second color pattern is the length of the detection means in the transport direction. The image forming apparatus according to claim 8, wherein the image forming apparatus is longer than the length of the detection area of the above. The ninth aspect of claim 9, wherein the distance between the second pattern image of the first color and the second superimposed pattern image in the transport direction is longer than the length of the detection area of the detection means in the transport direction. Image forming device.

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