JP2006039092A - Color image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To construct a color misregistration stabilization control system and to optimize an optimum color misregistration.
A color shift over time until the next color detection is predicted, and the color shift over time is performed instead of performing control for correcting the color shift only once for the color shift value detected by the registration detection sensor. Control is performed to perform a plurality of color misregistration corrections in a stepwise manner with respect to the color misregistration value predicted to minimize the misregistration.
[Selection] Figure 1

Description

  The present invention relates to a color image forming apparatus that forms a color image on a recording material based on image information.

  Various types of electrophotographic color image forming apparatuses have been proposed which have a plurality of image forming units for speeding up and sequentially transfer images of different colors onto a recording material held on a conveying belt. Yes.

  By the way, problems with the apparatus having a plurality of image forming units include uneven movement of a plurality of photosensitive drums and conveyor belts due to machine accuracy and the like, and conveyance with the outer peripheral surface of the photosensitive drum at the transfer position of each image forming unit. For example, the relationship of the amount of movement of the belt is different for each color and does not match when the images are overlapped, resulting in color misregistration. In particular, in an apparatus having a plurality of image forming units having a laser scanner and a photosensitive drum, there is an error in the distance between the laser scanner and the photosensitive drum in each image forming unit. A difference occurs in the scanning width of the laser on the drum, and color misregistration occurs.

  An example of color misregistration is shown in FIG. 7 indicates the original image position, and 8 indicates the image position when color misregistration occurs. Also, (b) and (c) are cases where there is a color shift in the main scanning direction, but for the sake of explanation, two lines are drawn apart in the transport direction. (A) shows an inclination deviation of the main scanning line, and occurs when there is an inclination between the optical unit and the photosensitive drum. For example, the position is corrected in the direction of the arrow by adjusting the position of the optical unit or the photosensitive drum or the position of the lens. (B) shows a color shift due to variations in the main scanning line width, which occurs due to a difference in distance between the optical unit and the photosensitive drum. It tends to occur when the optical unit is a laser scanner. For example, the image frequency is finely adjusted (if the scanning width is long, the frequency is increased), and the length of the scanning line is changed to correct in the arrow direction. (C) shows a writing position error in the main scanning direction. For example, if the optical unit is a laser scanner, it is corrected in the direction of the arrow by adjusting the writing start timing from the beam detection position. (D) shows the writing position error in the paper transport direction. For example, the correction is made in the direction of the arrow by adjusting the writing start timing of each color from the detection of the leading edge of the paper.

  In order to correct these color misregistrations, a color misregistration detection pattern is formed for each color on the conveyor belt 3 and detected by a pair of photosensors provided on both sides of the downstream side of the conveyor belt. Various adjustments as described above are performed in accordance with the deviation value.

FIG. 3 shows an example of a color shift detection pattern. 9 and 10 are patterns for detecting a color misregistration value in the paper conveyance direction, and 11 and 12 are patterns for detecting a color misregistration value in the main scanning direction orthogonal to the paper conveyance direction. In terms of inclination, a to d represent black (hereinafter referred to as Bk), yellow (hereinafter referred to as Y), magenta (hereinafter referred to as M), and cyan (hereinafter referred to as C). Reference numerals tsf1 to 4, tmf1 to 4, tsr1 to 4, and tmr1 to 4 indicate detection timings of the respective patterns, and arrows indicate the moving direction of the conveyor belt 3. The moving speed of the conveying belt 3 is vmm / s, Bk is a reference color, the theoretical distance between each color of the paper conveying direction pattern and the Bk pattern is dsYmm, dsMmm, dsCmm, the patterns for the paper conveying direction of each color and the main scanning direction The measured distances between the patterns are dmfBkmm, dmfYmm, dmfMmm, dmfCmm, dmrBkmm, dmrYmm, dmrMmm, and dmrCmm, respectively. With Bk as a reference color, the color misregistration value δes of each color in the transport direction is
δesY = v * {(tsf2−tsf1) + (tsr2−tsr1)} / 2−dsY (formula 1)
δesM = v * {(tsf3−tsf1) + (tsr3−tsr1)} / 2−dsM (Expression 2)
δesC = v * {(tsf4-tsf1) + (tsr4-tsr1)} / 2-dsC (Formula 3)
It becomes. Regarding the main scanning direction, the color misregistration values δemf and δemr of the respective colors on the left and right are
dmfBk = v * (tmf1-tsf1) (Formula 4)
dmfY = v * (tmf2-tsf2) (Formula 5)
dmfM = v * (tmf3-tsf3) (Formula 6)
dmfC = v * (tmf4-tsf4) (Formula 7)
When
dmrBk = v * (tmr1-tsr1) (Formula 8)
dmrY = v * (tmr2-tsr2) (Formula 9)
dmrM = v * (tmr3-tsr3) (Formula 10)
dmrC = v * (tmr4-tsr4) (Formula 11)
From
δemfY = dmfY−dmfBk (Formula 12)
δemfM = dmfM−dmfBk (Formula 13)
δemfC = dmfC−dmfBk (Formula 14)
When
δemrY = dmrY−dmrBk (Formula 15)
δemrM = dmrM−dmrBk (Formula 16)
δemrC = dmrC−dmrBk (Formula 17)
Thus, the deviation direction can be determined from the sign of the calculation result, the writing position is corrected from δemf, and the main scanning width is corrected from δemr−δemf.
JP 2001-312116 A

  However, the conventional example has the following problems.

  Even if the color misregistration correction is performed to reduce the color misregistration amount, the color misregistration amount usually increases with time or as the number of printed sheets increases. As a result, if an appropriate time interval, print interval, etc. are available, it is necessary to detect the color misregistration value and correct the color misregistration.

FIG. 12 is a graph showing color misregistration values with respect to the number of prints or print time. When the color misregistration correction (t1) is performed with a correction value for setting the color misregistration value to 0 with respect to the color misregistration value obtained by detection, as shown in the figure until the next color misregistration correction (t2). If the behavior of color misregistration with time (f (t)) is assumed, the maximum value or the integrated value (time) of the number of prints (time) with respect to the absolute value of the color misregistration value (the area of the painted area in the figure) stabilizes the color misregistration. The index of

  As a result, if the color misregistration increases monotonously as shown in FIG. 12 with respect to the number of prints, the control for correcting the color misregistration with a correction value that makes the color misregistration value 0 becomes (Equation 18). For this reason, it is not always the optimal color shift stabilization control.

  The present invention has been made in view of the above-described problems, and it is an object of the present invention to construct a color shift stabilization control system and to achieve optimum color shift stabilization.

  In order to achieve the above object, a color image forming apparatus of the present invention has the following configuration.

(1) A plurality of image forming units each having an optical unit and a latent image forming medium, and the formed image is held on the endless belt passing through the plurality of image forming units or on the endless belt. A plurality of transfer means for transferring onto the recording material being conveyed, means for forming a color shift pattern for detection on the endless belt, and detecting a color shift pattern formed on the endless belt A color image forming apparatus comprising: means; a means for calculating a color deviation value of a detected color with respect to a reference color from a detection result of the color deviation pattern; and a means for correcting an image forming condition from the calculated color deviation value.
The timing for correcting the image forming condition is gradual from the detection of the color misregistration pattern to the next detection of the color misregistration pattern.

  (2) In the color image forming apparatus according to (1), the color misregistration correction performed at the stepwise timing is a color misregistration value from the calculated color misregistration value until a next color misregistration pattern is detected. The image forming conditions are corrected in accordance with the predicted color misregistration value that predicts.

  (3) In the color image forming apparatus according to (2), the prediction predicts that a color shift value in a next pattern detection is a value corresponding to the calculated color shift value. .

  (4) In the color image forming apparatus according to (2), the prediction is performed by calculating the color shift value in the next pattern detection from the calculated color shift value and the predicted color shift value when the previous color shift correction is performed. It is predicted to be a value corresponding to the sum of.

  (5) In the color image forming apparatus according to (3) or (4), the predicted color shift value is calculated by predicting a color shift value over time from the prediction to the next pattern detection with a polynomial expression. It is the value which was made.

  (6) The color image forming apparatus described in (5) is characterized in that the polynomial is in a linear form with environmental values such as time, the number of printed sheets, or temperature as variables.

  (7) The color image forming apparatus according to any one of (1) to (6), further comprising means for selecting the number of stages of color misregistration correction.

  According to the present invention, a color misregistration stabilization control system can be constructed, and a highly accurate color misregistration stabilization control system can be constructed, and more accurate color misregistration stabilization can be achieved. A control system can be constructed.

  Hereinafter, the best mode for carrying out the present invention will be described in detail based on the embodiments shown in the drawings.

  FIG. 1 is a schematic configuration diagram of an image forming apparatus to which the present invention is applied.

  FIG. 1 is a diagram illustrating the entire image forming apparatus according to an embodiment of the present invention.

  An embodiment of the present invention shows a color image forming apparatus having image forming means for four colors, that is, yellow Y, magenta M, cyan C, and black K. In FIG. 1, 1 forms an electrostatic latent image. Photosensitive drums (a, b, c, and d are for K, C, M, and Y, respectively), 2 is a laser scanner that forms an electrostatic latent image on the photosensitive drum 1 by performing exposure according to an image signal; Reference numeral 3 denotes an endless transport belt that also serves as a transfer belt for sequentially transporting paper to each color image forming unit. Reference numeral 4 denotes a driving roller that drives the transport belt 3 by being connected to a driving means including a motor and a gear (not shown). 5 is a driven roller that rotates according to the movement of the conveyor belt 3 and applies a constant tension to the conveyor belt 3, and 6 is a color misalignment detection pattern formed on the conveyor belt 3. A pair of optical sensors provided It is.

  When data to be printed is sent from the PC to the printer and image formation according to the system of the printer engine is completed and the printer is ready, the paper is supplied from the paper cassette and reaches the conveyance belt 3. Each color is sequentially conveyed to the image forming unit. The image signals of the respective colors are sent to the respective laser scanners 2 in synchronization with the conveyance of the paper by the conveying belt 3, and an electrostatic latent image is formed on the photosensitive drum 1, and the toner is developed by a developing device (not shown). It is transferred onto the paper at the transfer section. In FIG. 1, images are sequentially formed in the order of Y, M, C, and K. Thereafter, the sheet is separated from the conveying belt, and the toner image is fixed on the sheet by heat with a fixing device (not shown) and discharged to the outside.

  The operation of the embodiment of the present invention will be described below.

  FIG. 15 is a flowchart for explaining the color misregistration correction operation according to the embodiment of the present invention. First, it is determined whether the cartridge has been replaced (step 110). When the cartridge is replaced, the color misregistration correction control described below is performed.

  A color misregistration detection pattern as shown in FIG. 3 is formed on the conveyor belt 3 and read by a pair of color misregistration detection sensors 6 provided on both sides of the conveyor belt, and the difference from a predetermined reference color is detected. A color shift value between the taken colors is detected (step 111). Then, in order to perform color misregistration stabilization control, which will be described later, the detected color misregistration value between each color is stored in a nonvolatile memory such as an EEPROM (step 112). Next, the color shift of each color excluding the reference color for each item, such as the inclination in the sub-scanning direction to be corrected in the next step, the writing position, the writing position in the main scanning direction, and the overall magnification from the detected color shift value between each color. A correction value is calculated (step 113). Next, correction is performed for each item and each color according to the color misregistration correction value calculated in step 113 (step 114).

  Hereinafter, detailed color misregistration correction operations in steps 113 and 114 will be described.

  7 and 8 are diagrams for explaining operations related to correction of the inclination in the sub-scanning direction according to the embodiment of the present invention.

  Reference numeral 1 denotes a photosensitive drum, 2 denotes a laser scanner, 13 denotes a polygon mirror, 14 denotes a tilt correction lens, 16 denotes a motor, and 15 denotes a cam. One of the tilt correction lenses 14 is held by a cam 15 attached to the motor 16 shaft. When the motor 16 operates and the cam 15 rotates, one end of the tilt correction lens 14 moves in the rotation direction of the drum 1, and the incident position of the laser beam deflected by the polygon mirror 13 on the drum 1 changes. . The motor 16 is operated according to the detected color misregistration value to correct the inclination in the sub-scanning direction. At this time, since the tilt correction lens 14 moves only on the other end with reference to one end, for example, the left end side is fixed on the image, and only the right end side moves up and down, so the writing position in the sub-scanning direction also changes at the same time. To do. Therefore, the writing position in the sub-scanning direction is also corrected according to the amount of movement of the tilt correction lens 14 by the tilt correction operation.

  4, 5, and 6 are diagrams for explaining operations related to correction of the writing position in the sub-scanning direction according to the embodiment of the present invention.

  For example, when the detected color misregistration value has an error of 2 and 1/4 lines of the detected color with respect to the reference color, the correction is performed as follows. However, at this time, when the inclination correction described above is performed, a correction value is calculated in consideration of the change in the writing position due to the inclination correction, and the correction operation is performed. In a system using a laser scanner, in order to align the writing position for each line, the horizontal synchronization signal generator generates each polygon mirror surface in synchronization with the rotation of the polygon mirror driven by the polygon motor driver. A horizontal sync signal is used. The controller transmits image data in synchronization with a horizontal synchronization signal transmitted from the engine for each line in the image forming area. The amount of color misregistration for each line is performed by increasing or decreasing the timing of the horizontal synchronization signal transmitted to the controller in units of lines. When the line is delayed by two lines, the count number of the horizontal synchronization signal in the engine from the vertical synchronization signal indicating the reference position in the sub-scanning direction shown in FIG. 6 to the start of transmission of the horizontal synchronization signal to the controller is set to +2. . Correction within one line is performed by controlling the surface phase of the polygon. Four reference horizontal synchronization signals are generated at equal intervals during one line period by an internal timer of the engine. The surface phase of the polygon is controlled so that the horizontal synchronizing signal of each color is synchronized with a desired phase among the four phases of the reference horizontal synchronizing signal. Therefore, when delaying 1/4 line, the reference phase is switched from 1/4 phase to 2/4 phase.

  FIG. 9 is a diagram for explaining an operation related to correction of the main scanning width (overall magnification) according to the embodiment of the present invention.

A so-called PLL circuit is used. X'tal, a 1 / NR divider that divides the output of X'tal, a 1 / NF divider that divides the video clock output, a 1 / NR divider, and a 1 / NF divider. A phase comparator that outputs pulses with different polarities and widths depending on the phase difference of the output, a low-pass filter that smoothes the output of the phase comparator, and a VCO (voltage controlled oscillator) that varies in output frequency depending on the input voltage Consists of. The video clock frequency fV is X'tal, where fX is
fV = (NR / NF) * fX (Formula 19)
Thus, fV can be finely adjusted by finely adjusting NR (integer) and NF (integer). The set values of NR and NF are changed according to the detected color misregistration value, and the main scanning width is corrected. For example, when a color misregistration value is detected in a direction where the width is narrow, the ratio of NR and NF is decreased to decrease fV (the period is increased). At this time, since the video frequency changes, the writing position in the main scanning direction also changes (details of the writing position in the main scanning direction will be described later). Therefore, the writing position in the main scanning direction is also corrected in accordance with the change amount of the video clock due to the correction of the main scanning width. Also, the set values of NR and NF differ depending on the circuit configuration of the controller even for the same color shift value. Furthermore, the jitter of the video clock frequency may be deteriorated depending on the relationship between the controller circuit configuration and the set values of NR and NF. In such a case, the correction values for all colors including other colors are very small. There is a method of avoiding a setting in which jitter is deteriorated by adding or subtracting an amount (a range that does not affect the overall size of the image visually).

  10 and 11 are diagrams for explaining an operation related to correction of the writing position in the main scanning direction according to the embodiment of the present invention.

  For example, when the detected color misregistration value has an error of 2 and 1/4 dots of the detected color with respect to the reference color, the correction is performed as follows. However, at this time, if the above-described correction of the main scanning width is performed, a correction value including the variation amount of the writing position due to the main scanning width correction is calculated and the correction operation is performed. In a system using a laser scanner, in order to align the writing position for each line, as described above, the controller generates a horizontal synchronization signal generated by the horizontal synchronization signal generation unit of the engine and transmitted for each line in the image forming area. The video clock generation unit generates a video clock in synchronization with the video data, and the video data (image data) generated by the video data generation unit is directly transmitted to the engine laser drive unit in synchronization with the generated video clock. .

  The amount of color misregistration in units of one dot is performed by changing the count number of the video clock from the horizontal synchronization signal to the position where video data transmission is started (position where image formation is started). To delay 2 dots, the count number is set to +2. Correction within one dot is performed by controlling the synchronizing phase of the horizontal synchronizing signal. The sampling clock has a frequency four times that of the video clock in order to control the synchronizing phase of the horizontal synchronizing signal. The output of the video clock (four sampling clocks) is started in synchronization with a desired rising edge among the four clocks from the rising edge of the horizontal synchronizing signal, and the phase of the video clock with respect to the horizontal synchronizing signal is controlled. Therefore, when delaying by 1/4 dot, the sampling phase is switched from 1/4 phase to 2/4 phase.

  The above is the color misregistration correction control when the cartridge is replaced. FIG. 12 is a graph showing a color shift value for a certain item and a certain detected color with respect to the number of printed sheets. When the color misregistration correction control is performed (t1), the temporal behavior (200) of the color misregistration as shown in the figure until the next color misregistration correction control or the color misregistration stabilization control which will be described later is performed by a study experiment or the like. Assuming that the color misregistration value is small immediately after the color misregistration correction control at time t1, the color monotonously increases thereafter and becomes the maximum at the next color misregistration correction control t2.

  Next, the case where the cartridge has not been replaced in step 110 will be described. It is determined whether or not the specified number of sheets N has been printed since the previous color misregistration detection pattern was detected (step 115). The prescribed number at this time is an appropriate number that is likely to require color misregistration correction control due to the deterioration of color misregistration due to a temperature rise in the printer, for example, N = 900. When the specified number N of sheets have been printed, the color misregistration correction control from step 111 to step 114 is performed.

  Next, in step 116, it is determined whether or not the specified number of sheets M has been printed since the previous color misregistration detection pattern was detected. The prescribed number at this time is a number obtained by dividing the prescribed number N in step 115 into an appropriate number of steps m, M = 1 × N / (m + 1), 2 × N / (m + 1),. / (M + 1) sheets. FIG. 13 illustrates that the prescribed number M is applied to the case of FIG. 12 described above. However, M1 and M2 in the drawing are the number of printed sheets in each stage where the number of stages is m = 2. For example, M = M1, M2 = 300, and 600 sheets. When the specified number M of sheets has been printed, the color shift stabilization control described below is performed.

The color shift value at the current stage is predicted using the color shift value (step 112) held in the previous color shift correction control (step 117). Next, the prediction method will be described. As described in the color misregistration correction control, when the color misregistration correction control is performed by detecting the color misregistration value Δ, the behavior as shown in FIG. 12 is performed. Therefore, when the next color misregistration is detected, the same color misregistration value as the previous time is detected. It is expected to be Δ. Therefore, the predicted color misregistration value Δ ′ until the next color misregistration detection can be predicted by a linear approximation such as the following equation using the number of prints t as a variable.

  Predicted by using (Equation 20) is 201 in FIG. Therefore, the predicted color misregistration values at each stage are Δ ′ (M1) and Δ ′ (M2).

Next, in step 118, a color misregistration correction value is calculated from the predicted color misregistration value Δ 'by the same method as in step 113 described above. However, since the predicted color misregistration value obtained by (Equation 20) is a fluctuating value from the previous color misregistration correction control t1, the color misregistration correction value must also be calculated based on the color misregistration correction value at t1. It is necessary to note that. In step 119, color misregistration correction is performed in the same manner as in step 114 described above.
The above is the color misregistration stabilization control in this embodiment.

  FIG. 14 shows a color misregistration value (203) with respect to the number of prints when the color misregistration correction control is performed at t1 and t2, and the color misregistration stabilization control (M1, M2) is performed in two stages during that time. At each stage, although the correction is made by the predicted color shift value Δ ′, there is a shift between the predicted Δ ′ (201) and the actual color shift value (202) (FIG. 13). Remaining. However, the color misregistration state is stabilized as compared with FIG. 12 in which the color misregistration stabilization control is not performed.

  Therefore, if the color misregistration value in this embodiment is predicted and color misregistration correction is performed in stages, the color misregistration can be stabilized with a simple configuration.

  The color misregistration detection pattern formed on the transfer material is not limited to the pattern used in this embodiment.

  In this embodiment, the color misregistration correction is performed in two stages. However, the number of steps is not limited to two and may be a continuous correction that corrects color misregistration for each number of printed sheets.

  Further, in this embodiment, the color misalignment value until the next color misalignment detection is predicted by linear approximation. However, the prediction method is not limited to linear approximation, and may be a polynomial or various interpolation formulas, and it is possible to predict the same change in color misregistration value by a study experiment or the like. Good.

  Further, in the present embodiment, a prediction formula is established with the number of prints as a variable to predict the color misregistration value. However, the variables in the prediction formula may be environmental variables such as printing time and temperature, and may be predicted by not only one variable but also multiple variables.

  Further, in this embodiment, the color misregistration value is predicted in order to perform the color misregistration stabilization control. However, the prediction is not limited to the color misregistration value, and may be a color misregistration correction value or other correction values for correcting the color misregistration of the image forming conditions.

  In the first embodiment, the predicted color misregistration value in the color misregistration stabilization control is determined by prediction from the color misregistration value Δ detected in the previous color misregistration control. However, in this embodiment, the predicted color shift value in the color shift stabilization control is predicted from the sum of the color shift value Δ detected in the previous color shift control and the predicted color shift value Δ '' when the previous color shift correction is performed. It is characterized by determining. This will be described with reference to FIG. 16. In order to predict the color shift value at the next detection (t3) from the color shift value Δ detected at t2, it is predicted from the color shift change value from t1 to t2. Although the accuracy is good, this is not the case in the first embodiment, and the color misregistration correction is performed by the color misregistration stabilization control at M2, so the detected color misregistration value Δ at t2 is the color misregistration value from M2. The reason why the prediction (203) is made only with the detected color deviation value Δ is that the accuracy is poor. Therefore, if the predicted color shift value Δ ″ used in the color shift correction at M2 is taken into account, the color shift change value from t1 to t2 can be obtained, so that the prediction accuracy can be improved (204).

  Differences from the first embodiment will be described. Flow chart of color misregistration correction operation The color misregistration stabilization control in FIG. 15 is replaced with the flowchart of color misregistration stabilization control in the present embodiment shown in FIG. In step 120, when color misregistration occurs at the next detection by a value obtained by summing the previously detected color misregistration value Δ held in the memory and a predicted color misregistration value Δ ″ retained in the memory described later. Prediction is performed, and a predicted color shift value at each stage is calculated using (Expression 21) shown below.

The predicted color misregistration value Δ ′ until the next color misregistration detection can be predicted by linear approximation as shown in the following equation using the number of prints t as a variable.

  Next, in step 121 and step 122, when the color misregistration correction is the final stage in the color misregistration stabilization control, for example, at M2 in FIG. 16, color misregistration value prediction is performed at the next color misregistration stabilization control. Therefore, the predicted color shift value Δ ′ (M2) calculated in step 120 is held in the memory.

  Therefore, if the color misregistration stabilization control in this embodiment is performed, the color misregistration value until the next color misregistration detection can be predicted with higher accuracy, and as a result, highly accurate color misregistration stabilization can be achieved.

  The present embodiment is characterized by comprising means for selecting the number of steps for correcting color misregistration by color misregistration stabilization control. This is because when the environment at the time of color drift stabilization control is significantly different from the environment at the time of previous color drift detection, for example, when the temperature is too high, it is difficult to predict using the color drift value at the previous detection. For this reason, the number of steps is reduced to reduce the number of times of color misregistration stabilization control, or the number of steps is set to 0 and color misregistration stabilization control is not performed.

  Therefore, if the selection means in the present embodiment is provided, it is possible to achieve more accurate color misregistration stabilization by determining a case where the prediction is likely to deviate greatly.

1 is a configuration diagram illustrating an entire image forming apparatus according to an embodiment of the present invention. Diagram explaining various color shifts The figure explaining the pattern for color shift detection FIG. 6 is a diagram for explaining an operation related to correction of the writing position in the sub-scanning direction according to the embodiment of the present invention. FIG. 6 is a diagram for explaining an operation related to correction of the writing position in the sub-scanning direction according to the embodiment of the present invention. FIG. 6 is a diagram for explaining an operation related to correction of the writing position in the sub-scanning direction according to the embodiment of the present invention. The figure explaining the operation | movement regarding correction | amendment of the inclination of the subscanning direction which concerns on the Example of this invention. The figure explaining the operation | movement regarding correction | amendment of the inclination of the subscanning direction which concerns on the Example of this invention. The figure explaining the operation | movement regarding correction | amendment of the main scanning width which concerns on the Example of this invention. FIG. 6 is a diagram for explaining an operation related to correction of the writing position in the main scanning direction according to the embodiment of the present invention. FIG. 6 is a diagram for explaining an operation related to correction of the writing position in the main scanning direction according to the embodiment of the present invention. The figure explaining the color shift stabilization which concerns on a prior art example The figure explaining the timing of the color shift correction in the color shift stabilization control according to the embodiment of the present invention. The figure which shows color misregistration stabilization in 1st Example of this invention. 6 is a flowchart showing a control operation of color misregistration correction in the first embodiment of the present invention. The figure explaining the color shift stabilization control in 2nd Example of this invention. Flowchart showing color misregistration stabilization control in the second embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Laser scanner 3 Conveying belt 4 Drive roller 5 Driven roller 6 Optical sensor 13 Polygon mirror 14 Inclination correction lens 15 Cam 16 Motor

Claims (7)

A plurality of image forming units each having an optical unit and a latent image forming medium, and the formed image is conveyed while being held on the endless belt passing through the plurality of image forming units or on the endless belt. A plurality of transfer means for transferring onto the recording material, means for forming a color shift pattern for detection on the endless belt, means for detecting the color shift pattern formed on the endless belt, In a color image forming apparatus comprising: means for calculating a color shift value of a detected color with respect to a reference color from a detection result of the color shift pattern; and means for correcting an image forming condition from the calculated color shift value.
2. The color image forming apparatus according to claim 1, wherein the timing for correcting the image forming condition is stepwise from the detection of the color misregistration pattern to the next detection of the color misregistration pattern.   The color misregistration correction performed at the stepwise timing corrects the image forming condition according to a predicted color misregistration value obtained by predicting a color misregistration value from the calculated color misregistration value until a next color misregistration pattern is detected. The color image forming apparatus according to claim 1.   The color image forming apparatus according to claim 2, wherein the prediction predicts that a color misregistration value in a next pattern detection is a value corresponding to the calculated color misregistration value.   In the prediction, it is predicted that the color misregistration value in the next pattern detection is a value corresponding to the sum of the calculated color misregistration value and the predicted color misregistration value when the previous color misregistration correction is performed. The color image forming apparatus according to claim 2.   5. The color image according to claim 3, wherein the predicted color misregistration value is a value calculated by predicting a color misregistration value over time from the prediction to the next pattern detection with a polynomial expression. Forming equipment.   6. The color image forming apparatus according to claim 5, wherein the polynomial is in a linear form with environmental values such as time, number of printed sheets, or temperature as variables.   7. The color image forming apparatus according to claim 1, further comprising means for selecting the number of stages of color misregistration correction.