JP2018010154A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which: when a period during which an image forming operation is executed and a period during which an image forming apparatus is left standing are alternately repeated, the difference between the amount of color shift corresponding to the amount of increase in temperature and the amount of color shift corresponding to the amount of decrease in temperature is accumulated to cause a prediction error.SOLUTION: An image forming apparatus comprises: image forming parts 101 that each include a photoreceptor drum 101, an optical scanner 104, and a developer 105; temperature sensors 450 that each detect the temperature of the optical scanner 104; a timing correction part 507 that corrects a writing timing on the basis of the amount of color shift; and a color shift amount determination part 506 that acquires the amount of change in temperature detected by the temperature sensors 450 and converts the amount of change into the amount of color shift on the basis of a conversion condition. When the temperature detected by the temperature sensor 450 is not decreased by a predetermined temperature or more, the color shift amount determination part 506 converts the amount of change in detected temperature into the amount of color shift on the basis of a first conversion condition, and when the temperature detected by the temperature sensor 450 is decreased by the predetermined temperature or more, the color shift amount determination part 506 converts the amount of change in detected temperature into the amount of color shift on the basis of a second conversion condition.SELECTED DRAWING: Figure 7

Description

  The present invention relates to color misregistration correction that predicts the amount of color misregistration based on the temperature of an image forming apparatus.

  An electrophotographic image forming apparatus forms an image by forming an electrostatic latent image on a photoconductor using light from an optical scanning device and developing the electrostatic latent image using a developer. For example, an image forming apparatus that forms a full-color image has a plurality of image forming units that form images of different colors, and forms a full-color image by superimposing images formed by the plurality of image forming units. There is. In this image forming apparatus, when the temperature of the optical scanning device rises, an optical member such as a lens or a mirror in the optical scanning device is deformed, or the position of the optical member changes due to thermal deformation of the optical scanning device. As a result, the position at which the light from the optical scanning device scans the photoreceptor changes, and when the images of the respective colors are superimposed, the position of the image for each color does not match, and the color of the image changes. Therefore, the image forming apparatus forms a pattern image for detecting the color misregistration amount on the image carrier, detects the pattern by the sensor, detects the color misregistration amount, and outputs the image according to the detected color misregistration amount. Color misregistration correction that controls the above is executed.

  However, the correction technique as described above has a problem that a downtime occurs because a pattern image is formed and the amount of color misregistration is detected. For this reason, an image forming apparatus that stores in advance a correspondence relationship between the internal temperature of the image forming apparatus and the color misregistration amount and corrects the color misregistration amount in real time based on the amount of change in the internal temperature of the image forming apparatus is known. (Patent Document 1). Patent Document 1 discloses that the correspondence between the detected temperature change amount and the color shift amount is hysteresis. That is, the color shift amount corresponding to the temperature change amount when the detected temperature rises does not necessarily match the color shift amount corresponding to the temperature change amount when the detected temperature falls. For this reason, the image forming apparatus described in Patent Document 1 switches the prediction formula for predicting the color misregistration amount when the temperature rises and when the temperature falls.

JP 2010-91925 A

  Incidentally, the internal temperature of the image forming apparatus rises during a period in which the image forming operation is being performed, and falls during a period in which the image forming operation is not being performed. For example, the internal temperature of the image forming apparatus decreases during the period in which the image forming apparatus is left unattended. For this reason, when the image forming operation is performed after the image forming apparatus is left unattended, the image forming apparatus may predict the color misregistration amount based on the temperature drop during the leaving time. For example, in an image forming apparatus installed in an office, the execution period and the leaving period of the image forming operation are alternately repeated.

  However, when the detection temperature repeatedly rises and falls in the hysteresis region of the characteristics of the detection temperature and the color shift amount, there is a problem that the prediction accuracy for predicting the color shift amount from the change amount of the detection temperature is lowered. . This is because the difference between the color shift amount corresponding to the temperature increase amount and the color shift amount corresponding to the temperature decrease amount in the hysteresis region where the color shift amount corresponding to the temperature increase amount and the color shift amount corresponding to the temperature decrease amount are different. This is because a prediction error occurs due to accumulation.

  Therefore, an object of the present invention is to correct the color misregistration amount with high accuracy even when the execution period and the leaving period of the image forming operation are alternately repeated.

  In order to solve the above problems, an image forming apparatus according to the present invention includes a plurality of photoconductors, an optical scanning device that scans a laser beam to form an electrostatic latent image on each of the plurality of photoconductors, and the plurality of photoconductors. A plurality of image forming means for forming an image for each of a plurality of colors, and a developing unit that develops the electrostatic latent image formed on each of the photosensitive members using a developer of a different color; A temperature detection unit for detecting a temperature of the predetermined optical scanning device provided in a predetermined optical scanning device included in the predetermined image forming unit of the image forming units, and an image formed by the plurality of image forming units. A correction unit that corrects the writing timing of the predetermined image forming unit based on a color shift amount relating to a relative positional shift of an image formed by the predetermined image forming unit with respect to an image of the reference color; By temperature detection means Conversion means for acquiring a change amount of the temperature of the predetermined optical scanning device and converting the change amount of the temperature of the predetermined optical scanning device into the color misregistration amount based on a conversion condition. If the decrease in the temperature of the predetermined optical scanning device acquired by the detection unit is not equal to or higher than the predetermined temperature, the conversion unit converts the change amount of the temperature of the predetermined optical scanning device based on the first conversion condition to the color. If the decrease in the temperature of the predetermined optical scanning device obtained by the temperature detection means is equal to or higher than the predetermined temperature, the conversion means converts the amount of change in the temperature of the predetermined optical scanning device. The color shift amount is converted based on a second conversion condition.

  According to the present invention, the color misregistration amount can be corrected with high accuracy even when the execution period and the leaving period of the image forming operation are alternately repeated.

Schematic sectional view of the image forming apparatus Cross section of the main part of the image forming unit Cross section of optical scanning device Schematic diagram of pattern image Characteristic chart showing correspondence between temperature change and color shift Control block diagram of image forming apparatus Flowchart diagram showing image forming processing Characteristic chart showing correspondence between temperature change and color shift

(Image forming device)
FIG. 1 is a schematic cross-sectional view of an image forming apparatus 100 that forms a full-color image using a plurality of color toners (developers). FIG. 2 is an enlarged cross-sectional view of the image forming unit 101bk of the image forming apparatus 100 of FIG. The image forming apparatus 100 includes a reader unit 1R that reads a document, and a printer unit 1P that forms an image based on image data transferred from the reader unit 1R or an external PC. Furthermore, the image forming apparatus 100 includes an operation unit 90 that is operated by a user to perform print settings such as the number of prints.

  The printer unit 1P includes image forming units 101Y, 101M, 101C, and 101Bk, an intermediate transfer belt 107, a manual feed cassette 114, a paper feed cassette 115, a fixing device 113, and a paper discharge unit 116. The image forming unit 101Y forms a yellow image, the image forming unit 101M forms a magenta image, the image forming unit 101C forms a cyan image, and the image forming unit 101Bk forms a black image. The intermediate transfer belt 107 is a belt-like intermediate transfer body onto which an image for each color formed by the image forming units 101Y, 101M, 101C, and 101Bk is transferred. The intermediate transfer belt 107 is stretched around a driving roller 108 and driven rollers 109 and 110. The drive roller 108 rotates and the intermediate transfer belt 107 conveys the image in the direction of arrow B.

  The transfer roller 112 forms a nip portion (second nip portion) for transferring the image on the intermediate transfer belt 107 to the sheet S. A transfer bias is supplied to the transfer roller 112 from a high voltage power supply (not shown). Accordingly, the image on the intermediate transfer belt 107 is transferred to the sheet S at the nip portion (second nip portion) between the transfer roller 112 and the intermediate transfer belt 107. A sheet S for transferring an image is supplied from a manual feed cassette 114 or a paper feed cassette 115. The fixing device 113 has a heater and fixes an image on the sheet S by the pressure of two rollers and the heat of the heater. The sheet S on which the image is fixed in the fixing device 113 is conveyed to the paper discharge unit 116.

  The pattern detection sensor 45 is an optical sensor that detects a pattern image formed on the intermediate transfer belt 107. The pattern detection sensor 45 is disposed in the vicinity of the intermediate transfer belt 107. A plurality of pattern detection sensors 45 are arranged at different positions in the direction orthogonal to the conveyance direction of the intermediate transfer belt 107. For example, the first pattern detection sensor and the second pattern detection sensor are arranged at the same position in the conveyance direction of the intermediate transfer belt 107 and at different positions in the direction orthogonal to the conveyance direction. For example, the image forming apparatus 100 causes the first and second pattern detection sensors to detect the pattern images formed at different positions in the direction orthogonal to the conveyance direction of the intermediate transfer belt 107, and thereby the first and second pattern detection sensors. The amount of tilt of the image can be measured based on the detection result.

  Next, the configuration of the image forming unit 101Bk will be described with reference to FIG. The image forming unit 101Bk includes a photosensitive drum 102. A photosensitive layer that functions as a photoreceptor is formed on the surface of the photosensitive drum 102. Around the photosensitive drum 102, a charging device 103, an optical scanning device 104, a developing device (developing unit) 105, and a drum cleaning device 106 are arranged. A transfer roller 111 is provided at a position facing the photosensitive drum 102 via the intermediate transfer belt 107. Further, the developing device 105 is provided with a temperature sensor 118 for detecting the ambient temperature of the image forming unit 101Bk. The amount of change in the ambient temperature detected by the temperature sensor 118 is used to calculate the color misregistration amount. The temperature sensor 118 functions as a temperature detection unit that detects the ambient temperature of the image forming unit 101.

  The image forming units 101Y, 101M, and 101C have the same configuration except that the colors of the developers are different. On the other hand, the image forming unit 101Bk has a different structure from the other image forming units 101Y, 101M, and 101C. Specifically, the diameter of the photosensitive drum 102 of the image forming unit 101Bk is larger than the diameter of the photosensitive drums 102 of the other image forming units 101Y, 101M, and 101C. Further, the size of the optical scanning device 104 of the image forming unit 101Bk is larger than the size of the optical scanning devices 104 of the other image forming units 101Y, 101M, and 101C. The material of the optical scanning device 104 of the image forming unit 101Bk is different from the material of the optical scanning devices of the other image forming units 101Y, 101M, and 101C. However, since the configuration is the same except for the diameter, size, and material, description of the image forming units 101Y, 101M, and 101C is omitted.

  Next, an image forming process of the image forming apparatus 100 will be described. Since the image forming process in each of the image forming units 101Y, 101M, 101C, and 101Bk is the same, the image forming process will be described by taking the image forming unit 101Bk as an example, and the image formation in the other image forming units 101Y, 101M, and 101C is performed. A description of the process is omitted.

  First, the photosensitive drum 102 is rotated in the arrow A direction by a motor (not shown). The charging device 103 uniformly charges the surface of the photosensitive drum 102. The charged photosensitive drum 102 is exposed by laser light emitted from the optical scanning device 104Y. As a result, an electrostatic latent image is formed on the photosensitive drum 102. The developing device 105 develops the electrostatic latent image on the photosensitive drum 102 as a black toner image. When a full-color image is formed, an image is formed for each color in each of the image forming units 101Y, 101M, 101C, and 101Bk, and the image for each color is transferred onto the intermediate transfer belt 107 so as to overlap.

  Subsequently, the toner image on the photosensitive drum 102 is conveyed to a nip portion (first nip portion) between the photosensitive drum 102 and the intermediate transfer belt 107. A transfer bias is applied to the transfer roller 111, and the black toner image on the photosensitive drum 102 is transferred to the intermediate transfer belt 107. When forming a full-color image, images for each color component formed by the image forming units 101Y, 101M, 101C, and 101Bk are sequentially superimposed and transferred to the intermediate transfer belt 107. The toner remaining without being transferred from the photosensitive drum 102 to the intermediate transfer belt 107 is removed by the drum cleaning device 106.

  The toner image on the intermediate transfer belt 107 is conveyed to the nip portion (second nip portion) between the transfer roller 112 and the intermediate transfer belt 107 as the intermediate transfer belt 107 rotates in the direction of arrow B. At the nip portion (second nip portion) between the transfer roller 112 and the intermediate transfer belt 107, the toner image on the intermediate transfer belt 107 is transferred to the sheet S conveyed from the manual feed cassette 114 or the paper feed cassette 115. When the toner image on the sheet S is conveyed to the fixing device 113, the fixing device 113 fixes the toner image on the sheet S and discharges it to the paper discharge unit 116.

  FIG. 3A is a top view of the optical scanning device 104, and FIG. 3B is a cross-sectional view taken along the line AA ′ in FIG. A control board 203 for controlling a light source 202 that emits laser light is attached to the outside of the optical box 401. The optical box 401 includes a rotating polygon mirror 402 that deflects the laser light emitted from the light source 202 so that the laser light scans the photosensitive drum 102 in a predetermined direction. The rotary polygon mirror 402 is driven to rotate by a motor 403.

  The laser light deflected by the rotary polygon mirror 402 enters the fθ lens 404. The laser light that has passed through the fθ lens 404 is reflected by the reflection mirror 405 and the reflection mirror 406 and enters the fθ lens 407. The laser light that has passed through the fθ lens 407 is reflected by the reflection mirror 408, passes through the dustproof glass 409, and is emitted to the photosensitive drum 102. The laser beam scanned at a constant angular velocity by the rotary polygon mirror 402 passes through the fθ lens 404 and 407 and forms an image on the photosensitive drum 102, and scans the photosensitive drum 102 at a constant velocity.

  The optical scanning device 104 also includes a beam detector 412 (hereinafter referred to as BD 412) that generates a synchronization signal for determining the emission timing of the laser light based on the image data. The laser beam deflected by the rotating polygon mirror 402 passes through the fθ lens 404, is reflected by the reflection mirror 405 and the BD mirror (not shown), and enters the BD 412.

  A temperature sensor 450 that detects the temperature of the optical scanning device 104 is mounted on the control board 203. The amount of change in temperature of the optical scanning device 104 detected by the temperature sensor 450 is used to calculate the amount of color misregistration. The temperature sensor 450 functions as a temperature detection unit that detects the temperature of the optical scanning device 104.

  FIG. 5 is a graph showing the relationship between the amount of change in temperature detected by the temperature sensor 450 and the amount of color shift variation. The relationship between the detected temperature change amount of the temperature sensor 450 and the color shift variation amount when the detected temperature is rising, and the detected temperature change amount and color shift variation amount of the temperature sensor 450 when the detected temperature is decreased. It can be seen that the relationship is different. Therefore, it is necessary to determine whether the temperature of the optical scanning device 104 is rising or falling, and to predict the color misregistration amount from the detection temperature of the temperature sensor 450.

  In a conventional image forming apparatus, for example, an arithmetic expression (or table) for predicting a color misregistration amount when the temperature rises and an arithmetic expression (or table) for predicting a color misregistration amount when the temperature decreases. The calculation formula (or table) is switched based on the change in the detected temperature. However, when a conventional image forming apparatus repeatedly prints an image on a small number of sheets with a short time interval, the temperature change is small, and the difference between the predicted value when the temperature rises and the predicted value when the temperature falls As a result, the color misregistration amount cannot be predicted with high accuracy.

  Therefore, in the present invention, the conversion condition for converting the change amount of the detected temperature into the color misregistration amount is switched according to whether or not the previous detected temperature is higher than the current detected temperature by a predetermined temperature or more. Specifically, if the previous detected temperature is higher than the current detected temperature and the difference between the previous detected temperature and the current detected temperature is less than a predetermined temperature, the conversion condition (first The color misregistration amount is predicted based on the conversion condition. If the previous detected temperature is higher than the current detected temperature and the difference between the previous detected temperature and the current detected temperature is equal to or higher than a predetermined temperature, the conversion condition (second conversion condition) used when the temperature drops The amount of color misregistration is predicted based on the above. Accordingly, even when the image forming operation is executed after the image forming apparatus 100 is left unattended, the color misregistration amount can be predicted with high accuracy.

  Further, the image forming apparatus 100 not only predicts the color misregistration amount but also actually measures the color misregistration amount at a predetermined timing. As a method of actually measuring the color misregistration amount, the image forming apparatus 100 forms a pattern image on the intermediate transfer belt 107, measures the pattern image by the pattern detection sensor 45, and calculates an actual value of the color misregistration amount based on the measurement result. Generate.

  A pattern image formed on the intermediate transfer belt 107 will be described. As shown in FIG. 4, the pattern images 901 to 914 include a pattern inclined by 45 degrees with respect to the conveyance direction of the intermediate transfer belt 107 and a pattern inclined by −45 degrees with respect to the conveyance direction. Further, the magenta pattern images 901, 903, 905, 907, 908, 910, 912, and 914 that are reference images are formed so as to sandwich the yellow, cyan, and black pattern images.

  FIG. 4 shows a schematic diagram of the analog signal 301 output when the pattern detection sensor 45 detects the pattern images 901 to 914 and the binarized digital signal 302 output by the comparator (not shown). . The analog signal 301 and the digital signal 302 correspond to the measurement result of the pattern detection sensor 45.

The color misregistration amount determination unit 506 (FIG. 6) acquires the timing at which the digital signal 302 output from the comparator is switched from the high level to the low level and the timing at which the digital signal 302 is switched from the low level to the high level. In the color misregistration amount determination unit 506, the pattern detection sensor 45 detects the pattern images 901 to 914 based on the timing when the digital signal 302 is switched from the high level to the low level and the timing when the digital signal 302 is switched from the low level to the high level. Determine timing. For example, the color misregistration amount determination unit 506 determines the timing T at which the pattern detection sensor 45 detects the pattern images 901 to 914 based on Expression (1).
T = (Ta + Tb) + Ta (1)
Ta is a timing when the digital signal 302 is switched from the high level to the low level, and Tb is a timing when the digital signal 302 is switched from the low level to the high level.

  That is, the timing T is an intermediate timing between the timing Ta when the digital signal 302 is switched from the high level to the low level and the timing Tb when the digital signal 302 is switched from the low level to the high level.

  The image forming apparatus 100 determines intervals Y1, Y2, C1, C2, K1, K2, Y3, Y4,... At which the pattern images 901 to 914 are detected, and stores these intervals in the RAM 504. . Based on the stored detection data, the image forming apparatus 100 calculates a difference (color misregistration amount) between positions where images of colors other than magenta (yellow, cyan, black) are formed with respect to positions where magenta images are formed. To do.

For example, in the direction orthogonal to the conveyance direction of the intermediate transfer belt 107, the color misregistration amount ΔHy of the yellow image with respect to the magenta image is calculated based on Expression (2).
ΔHy = {(Y4−Y3) / 2− (Y2−Y1) / 2} / 2 Formula (2)
For example, in the conveyance direction of the intermediate transfer belt 107, the color misregistration amount ΔVy of the yellow image with respect to the magenta image is calculated based on the equation (3).
ΔVy = {(Y4-Y3) / 2 + (Y2-Y1) / 2} / 2 Formula (3)
Similarly, ΔHc, ΔVc, ΔHbk, and ΔVbk are also calculated using arithmetic expressions.

  Then, the image forming apparatus 100 corrects the writing timing of the optical scanning device of each image forming unit 101 based on the color misregistration amount regarding the relative positional deviation of the other color image with respect to the magenta image as the reference color. To do.

  The predetermined timing for forming the pattern image in order to acquire the actual measurement value of the color misregistration amount may be determined based on the temperature change amount of the image forming apparatus 100 or may be determined based on the number of image formations. Good. For example, if the difference between the detected temperature of the temperature sensor 450 when the image forming apparatus 100 previously formed the pattern image and the detected temperature of the current temperature sensor 450 is larger than the threshold value, the image forming apparatus 100 forms the pattern image. Update the measured value of the color misregistration amount. Alternatively, for example, when the number of images formed on the sheet S by the image forming apparatus 100 has reached a predetermined number since the image forming apparatus 100 previously formed the pattern image, the image forming apparatus 100 forms the pattern image. Thus, the actual measurement value of the color misregistration amount is updated.

  In the image forming apparatus 100, downtime occurs in order to update the actual measurement value of the color misregistration amount. Therefore, if the image forming apparatus 100 frequently updates the actual measurement value of the color misregistration amount, the productivity of the image forming apparatus 100 is lowered. Therefore, the image forming apparatus 100 calculates the color misregistration amount based on the temperature detected by the temperature sensor 450 between the timing when the actual measurement value of the color misregistration amount is updated and the timing when the actual measurement value of the color misregistration amount is updated next time. Predict.

  Note that the color misregistration amount with respect to the temperature change of the image forming units 101Y, 101M, and 101C is different from the color misregistration amount with respect to the temperature change of the image forming unit 101Bk. This is because the structure of the image forming unit 101Bk is different from the structure of the image forming units 101Y, 101M, and 101C. In particular, it has been experimentally found that the color misregistration amount with respect to the temperature change of the image forming unit 101Bk is larger than the color misregistration amounts with respect to the temperature change of the image forming units 101Y, 101M, and 101C. Therefore, the color misregistration amount of the image forming unit 101Bk is calculated based on the temperature change amount detected by the temperature sensor 118 and the temperature change amount detected by the temperature sensor 118 in addition to the color misregistration amount actually measured using the pattern image. Predict the amount of color shift. That is, the color misregistration amounts of the image forming units 101Y, 101M, and 101C are corrected based only on the actual measurement values of the color misregistration amounts. However, the present invention is not limited to the above configuration. A temperature sensor may be mounted on each of the optical scanning devices of all the image forming units 101Y, 101M, 101C, and 101Bk, and the color misregistration amount may be predicted for each color based on the temperature detected by each temperature sensor.

  Next, a control block diagram of the image forming apparatus 100 will be described with reference to FIG. A CPU 501 is a control circuit that controls each unit of the image forming apparatus 100. The ROM 502 stores a control program necessary for executing various processes in the flowcharts described later, which are executed by the CPU 501. A RAM 504 is a system work memory for the CPU 501 to operate. Description of printer unit 1P, operation unit 90, image forming units 101Y, 101M, 101C, and 101Bk (image forming unit 101 in FIG. 6), light source 202, control board 203, pattern detection sensor 45, and temperature sensors 450 and 118 Is omitted.

  The color misregistration amount determination unit 506 determines the color misregistration amount based on the change amount of the temperature detected by the temperature sensor 450 and the change amount of the temperature detected by the temperature sensor 118. Then, the color misregistration amount determination unit 506 adds the actual color misregistration amount acquired using the pattern image to the color misregistration amount determined based on the detected temperature to determine the color misregistration amounts ΔH and ΔV. . The color misregistration amount ΔH of the image forming unit 101Bk in the direction orthogonal to the conveyance direction of the intermediate transfer belt 107 is an amount obtained by adding the predicted value of the color misregistration amount to the actual color misregistration amount ΔHbk. On the other hand, only the actually measured values ΔHy and ΔHc of the color misregistration amounts are used as the color misregistration amounts ΔH of the image forming units 101Y and 101C in the direction orthogonal to the conveyance direction of the intermediate transfer belt 107. Similarly, in the color misregistration amount determination unit 506, the color misregistration amount ΔVbk of the image forming unit 101Bk in the conveyance direction of the intermediate transfer belt 107 is a value obtained by adding the predicted value of the color misregistration amount to the actual color misregistration amount ΔVbk. . On the other hand, only the color shift amounts ΔVy, Δ, and ΔVc of the color shift amounts of the image forming units 101Y and 101C in the conveyance direction of the intermediate transfer belt 107 are used.

  The timing correction unit 507 sets the image writing position in the direction orthogonal to the conveyance direction of the intermediate transfer belt 107 to the color shift amount ΔH with reference to the reference position in the direction in which the laser beam emitted from the optical scanning device 104 is scanned. Shift by the distance of the corresponding pixel. For example, the color misregistration amount determination unit 506 determines the timing at which light is emitted from the optical scanning device 104 to the BD 412 based on the reference signal (BD signal) output from the BD 412. The scanning speed of the laser light emitted from the optical scanning device 104 corresponds to the rotational speed of the rotary polygon mirror 402 of the optical scanning device 104 and is thus determined in advance. Therefore, the timing correction unit 507 calculates a time from when the laser beam is irradiated to the BD 412 to when the laser beam reaches a position shifted by a pixel corresponding to the color shift amount ΔH with respect to the image formation reference position. . The timing correction unit 507 corrects the writing timing in the main scanning direction by adding the calculated time to the time when the BD 412 outputs the reference signal.

  Further, the timing correction unit 507 is a distance corresponding to the color shift amount ΔV when the image writing position in the conveyance direction of the intermediate transfer belt 107 is based on the image formation reference position in the direction in which the surface of the photosensitive drum 102 moves. Just shift. The rotational speed of the photosensitive drum 102 is determined in advance. For example, the timing correction unit 507 calculates the time for the laser beam of the optical scanning device 104 to reach a position where the photosensitive drum 102 has moved by a distance corresponding to the color misregistration amount ΔV with reference to a predetermined image formation timing. . The timing correction unit 507 calculates the writing timing in the sub-scanning direction by adding the above-described calculated time to a predetermined image forming timing.

  As a result, the position on the intermediate transfer belt 107 where the image other than the reference image is formed relative to the position where the reference image is formed can be corrected. The color shift amounts ΔHy, ΔVy, ΔHc, ΔVc, ΔHbk, and ΔVbk calculated from the detection results of the pattern images 901 to 914 are stored in the RAM 504.

  An image forming operation in which the image forming apparatus 100 forms an image based on image data will be described with reference to the flowchart of FIG. Note that when the main power supply of the image forming apparatus 100 is turned on, the CPU 501 reads a program stored in the ROM 502 and first executes color misregistration correction. Then, the CPU 501 stores the actually measured value of the color misregistration amount and the temperature detected by each of the temperature sensors 450 and 118 in the RAM 504.

  When image data is transferred from the reader unit 1R or a PC (not shown), the CPU 501 executes the processing of the flowchart of FIG. In the following description, the detected temperature of the temperature sensor 450 is referred to as a temperature Tscn, the detected temperature of the temperature sensor 118 is referred to as a temperature Tdev, and the predicted value of the color misregistration amount is referred to as a predicted value X. Further, the subscript (NOW) represents the current value, and the subscript (PREV) represents the previous value stored in the RAM 504. The coefficients α, β, and γ and the predetermined temperature Tth may be determined in advance by experiments.

  First, the CPU 501 detects the temperature Tscn (NOW) of the optical scanning device 104 by the temperature sensor 450 and detects the ambient temperature Tdev (NOW) by the temperature sensor 118 (S100). Subsequently, the CPU 501 determines whether or not the temperature of the optical scanning device 104 has decreased by a predetermined temperature Tth (S101). In step S101, the CPU 501 determines whether or not the detected temperature Tscn (NOW) of the temperature sensor 450 is lower than the previous detected temperature Tscn (PREV) of the temperature sensor 450 and the difference in detected temperature is equal to or higher than a predetermined temperature Tth. judge.

When the detected temperature Tscn (NOW) of the temperature sensor 450 is lower than the previous detected temperature Tscn (PREV) of the temperature sensor 450 and the difference between the detected temperatures is equal to or higher than the predetermined temperature Tth, the color shift amount determination unit 506 performs the color shift. The amount is calculated based on equation (4) (S102).
X (NOW) = X (PREV) + α × ΔTscn + β × ΔTdev + γ × ΔTscn Equation (4)
However,
ΔTscn = Tscn (NOW) −Tscn (PREV)
ΔTdev = Tdev (NOW) −Tdev (PREV)
And

  Next, the color misregistration amount determination unit 506 adds the actual color misregistration amount stored in the RAM 504 in advance to the color misregistration amount predicted value X (NOW) (S103) to determine the color misregistration amounts ΔHbk and ΔVbk. . The timing correction unit 507 corrects the image writing timing based on the color misregistration amounts ΔHbk and ΔVbk determined in step S103 (S104), and the image forming unit 101 forms an image (S105). At this time, the timing correction unit 507 corrects the image writing timing of the image forming units 101Y and 101C based on the actually measured value of the color misregistration amount stored in the RAM 504.

  Furthermore, when the detected temperature Tscn (NOW) of the temperature sensor 450 is lower than the previous detected temperature Tscn (PREV) of the temperature sensor 450 and the difference between the detected temperatures is equal to or higher than the predetermined temperature Tth, the CPU 501 performs actual measurement of color misregistration correction. The value is updated (S106). In step S106, the CPU 501 causes the image forming unit 101 to form a pattern image, causes the pattern detection sensor 45 to detect the pattern image, and updates the actual measurement value of the color misregistration amount for each color.

  When the pattern image is formed and the actual color misregistration value is updated, the CPU 501 stores the temperature information acquired in step S100 and the current color misregistration amount predicted value X (NOW) in the RAM 504 (S107). Then, the execution of the image forming operation is terminated. In the temperature information stored in the RAM 504 in step S107, the current detected temperature Tscn (NOW) is stored as Tscn (PREV), and the current detected temperature Tdev (NOW) is stored as Tdev (PREV). In step S107, the predicted value X (NOW) of the current color misregistration amount is stored in the RAM 504 as the predicted value X (PREV).

In step S101, if the detected temperature Tscn (NOW) is equal to or higher than the previous detected temperature Tscn (PREV), or if the detected temperature difference is less than a predetermined temperature, the CPU 501 determines that the color misregistration amount determination unit 506 is the color. The amount of deviation is calculated based on equation (5) (S108).
X (NOW) = X (PREV) + α × ΔTscn + β × ΔTdev Equation (5)
However,
ΔTscn = Tscn (NOW) −Tscn (PREV)
ΔTdev = Tdev (NOW) −Tdev (PREV)
And The difference between Equation (4) and Equation (5) is the third term (γ × ΔTscn).

  Next, the color misregistration amount determination unit 506 adds the actual color misregistration amount stored in the RAM 504 in advance to the color misregistration amount predicted value X (NOW) (S109) to determine the color misregistration amounts ΔHbk and ΔVbk. . The timing correction unit 507 corrects the image writing timing based on the color misregistration amounts ΔHbk and ΔVbk determined in step S109 (S110), and the image forming unit 101 forms an image (S111). Then, the CPU 501 moves the process to step S107 and ends the execution of the image forming operation.

  The present invention does not intentionally suppress the influence of hysteresis in a region where the influence of hysteresis of temperature change can be tolerated. FIG. 8 is a graph in which equations (4) and (5) are entered in a graph (FIG. 6) in which the temperature change amount and the color misregistration amount data of the optical scanning device are plotted. The color misregistration amount determination unit 506 predicts the color misregistration amount based on Expression (5) except for a range where the temperature decrease is equal to or higher than the predetermined temperature Tth. Thereby, it is possible to compensate for the prediction accuracy of the color misregistration amount particularly in the period when the detection temperature is rising. On the other hand, the color misregistration amount determination unit 506 predicts the color misregistration amount based on Expression (4) in a range where the temperature decrease is equal to or higher than the predetermined temperature Tth. As a result, it is possible to suppress a decrease in prediction accuracy even when the temperature drop is significant.

  When the increase and decrease of the detected temperature are repeated in a short time, it is desirable to suppress the number of times that the expressions (4) and (5) are switched as much as possible. Therefore, even if the color misregistration amount with respect to the temperature change is hysteresis, the color misregistration amount may be predicted based on Expression (5) in a region where the influence can be allowed.

(Modification)
In the above description, the configuration in which the CPU 501 selects an arithmetic expression from Expression (4) and Expression (5) based on the temperature change amount of the optical scanning device 104 has been described. However, for example, the CPU 501 may select a table to be used for prediction from a plurality of tables based on the amount of change in temperature of the optical scanning device 104.

In the above description, equation (4) is configured to add the calculation result of γ × ΔTscn to equation (5). For example, instead of equation (4), the color misregistration amount is predicted by equation (6). May be.
X (NOW) = X (PREV) + θ × ΔTscn + β × ΔTdev (6)

DESCRIPTION OF SYMBOLS 101 Image formation part 102 Photosensitive drum 104 Optical scanning device 105 Developing device 118 Temperature sensor 506 Color shift amount determination part 507 Timing correction part

Claims (9)

A plurality of photoconductors, an optical scanning device that scans a laser beam to form an electrostatic latent image on each of the plurality of photoconductors, and an electrostatic latent image formed on each of the plurality of photoconductors are different. A plurality of image forming means for forming an image for each of a plurality of colors, and a developing unit that develops using a color developer;
A temperature detecting unit provided in a predetermined optical scanning device included in a predetermined image forming unit of the plurality of image forming units, and detecting a temperature of the predetermined optical scanning unit;
The predetermined image formation based on a color shift amount related to a relative positional shift of an image formed by the predetermined image forming unit with respect to a reference color image among images formed by the plurality of image forming units. Correction means for correcting the writing timing of the means;
Conversion means for acquiring a change amount of the temperature of the predetermined optical scanning device by the temperature detection means, and converting the change amount of the temperature of the predetermined optical scanning device into the color misregistration amount based on a conversion condition; Have
If the decrease in the temperature of the predetermined optical scanning device acquired by the temperature detection unit is not equal to or higher than the predetermined temperature, the conversion unit determines the amount of change in the temperature of the predetermined optical scanning device based on the first conversion condition. Converted into the color misregistration amount,
If the decrease in the temperature of the predetermined optical scanning device acquired by the temperature detection unit is equal to or higher than the predetermined temperature, the conversion unit uses the change amount of the temperature of the predetermined optical scanning device based on a second conversion condition. An image forming apparatus that converts the color misregistration amount into the color misregistration amount. An intermediate transfer body to which the plurality of images formed by the plurality of image forming means are transferred;
Detecting means for detecting a pattern image formed on the intermediate transfer member;
Control means for causing the plurality of image forming means to form the pattern image and causing the detection means to detect the pattern image;
Generating means for generating another color misregistration amount based on the detection result of the detection means,
The correction unit corrects the writing timing based on the other color misregistration amount generated by the generation unit and the color misregistration amount converted by the conversion unit. Image forming apparatus.   If the temperature drop of the predetermined optical scanning device acquired by the temperature detection unit is equal to or higher than the predetermined temperature, the control unit may detect the color misregistration amount after the plurality of image forming units have finished forming images. 3. The image forming apparatus according to claim 2, wherein the pattern image is formed by the plurality of image forming units and the pattern image is detected by the detecting unit.   The control means further has a difference between a detected temperature of the temperature detecting means when the plurality of image forming means previously formed the pattern image and a current detected temperature detected by the temperature detecting means larger than a threshold value. 4. The image forming apparatus according to claim 2, wherein the pattern image is formed on the plurality of image forming units in order to update the color misregistration amount.   The control means further controls, based on the number of image formations, whether or not to cause the plurality of image forming means to form the pattern image in order to update the color misregistration amount. The image forming apparatus according to any one of claims 1 to 4.   The number of images formed corresponds to the number of images formed by the plurality of image forming units since the plurality of image forming units formed the pattern image last time. Image forming apparatus. The predetermined optical scanning device includes a control board that controls a light source that emits the laser light to the outside of the predetermined optical scanning device,
The image forming apparatus according to claim 1, wherein the temperature detection unit is provided on the control board. Another temperature detection means provided at a position different from the temperature detection means, for detecting the ambient temperature of the predetermined image forming means,
The converting means further acquires the amount of change in the ambient temperature of the predetermined image forming means by the other temperature detecting means,
8. The conversion unit according to claim 1, wherein the conversion unit converts the change amount of the temperature of the predetermined optical scanning device and the change amount of the ambient temperature into the color misregistration amount based on the conversion condition. The image forming apparatus according to claim 1.   9. The image forming apparatus according to claim 8, wherein the other temperature detecting unit is provided in a developing unit of the predetermined image forming unit.

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