JPH10213940A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the color slippage of a formed color image to the minimum without deteriorating the processing efficiency of image forming processing. SOLUTION: At a first time, the color slippage is set to a value near the final value (64+7/8) only by changing the counted number of LS signals. The means, (63+1/8) is changed to (65+1/8). Thereafter, the left color slippage (65+1/8)-(64+7/8)=1/4 dot is changed extending over plural times by controlled variable (1/16 dot) which can be changed in interpaper timing each. Thus, the color slippage is changed to (65+1/16) at a second time and changed 1/16 by 1/16 on and after it. Then, it arrives at the final value (64+7/8) by the change of five steps as a whole and the correction of the color slippage is finished. In such a way, the color slippage is almost corrected at the first time and the left color slippage is corrected extending over the plural times on and after the second time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to a method in which latent images based on respective color components of a color image are formed on separate photosensitive members by a plurality of image writing means. A color toner image is formed on each photoconductor by developing a latent image of each color component with a color toner, and the color toner image formed on each photoconductor is transferred onto a recording medium by superimposing and transferring the color toner image on the recording medium. The present invention relates to an image forming apparatus that forms a color image.

[0002]

2. Description of the Related Art FIG. 1 is a schematic configuration diagram of an optical scanning device (a so-called ROS unit) of a general laser printer. A laser beam emitted from a laser light source 1 is collimated by a collimator lens 2 and then deflected and scanned by a rotating polygon mirror (polygon mirror) 3. The scanning speed is corrected by an fθ lens 4, and the surface of the photoconductor 5 is moved at a constant speed. It scans and forms a latent image according to the image signal. Further, an image signal writing timing signal (SOS) in the main scanning direction with respect to the photoconductor 5
Signal), a position detection sensor 6 is provided in a laser beam scanning area outside the photosensitive body area.

In general, in a color image forming apparatus,
To form latent images of four color components of cyan (C), magenta (M), yellow (Y), and black (K) and form a color image from these four latent images at high speed, as shown in FIG. A color image forming apparatus 110 provided with four optical scanning devices (ROS units) has been proposed. In the color image forming apparatus 110, each of the optical scanning devices 110a to 110d includes:
Triggered by an image writing start signal, each of the photoconductors 5a to 5a
5d, a latent image is formed on each sheet, and the developed toner images are sequentially transferred to the sheet 1 conveyed by the transfer belt 100.
01. Finally, after the four colors have been transferred, the fixing process is performed by a fixing device (not shown) to
1 to form a color image.

However, in a color image forming apparatus having a plurality of optical scanning devices as described above, a shift in a transfer position between colors, that is, a color shift, due to a shift in optical scanning position in each optical scanning device or the like. This may cause a significant reduction in image quality. Therefore, a method of detecting and correcting such a color shift has been proposed.

FIG. 3 shows a toner image pattern (hereinafter abbreviated as a registration control pattern) for detecting color misregistration of each color (K: black, Y: yellow, M: magenta, C: cyan) formed on the transfer belt 100. (Referred to as a registration control pattern) 109 as viewed from above. This registration pattern is formed at regular intervals on the transfer belt 100 as shown in FIG. 4, and the toner image patterns corresponding to the registration pattern are read by the sensors 102a and 102b. And
The arithmetic processing unit 103 calculates the position of each toner image pattern, detects the positional difference between each color, that is, the amount of color misregistration, and changes the image writing timing of the ROS according to the amount of color misregistration. Is corrected.

However, in the technique of forming the registration pattern on the entire surface of the transfer belt, it is necessary to stop the normal image forming process during the formation of the registration pattern. That is, since a dedicated processing cycle for correcting color misregistration is required, there is a problem that productivity of image forming processing is reduced.

In order to solve this problem, Japanese Patent Laid-Open No. 7-2
No. 34612 discloses that when a temperature change or the like that causes color misregistration occurs during a copy cycle with a large number of sheets, FIG.
It is described that the registration control pattern 90 for detecting the color shift is formed on the transfer belt 92 at the timing between the sheets to detect the amount of the color shift and correct the color shift.

However, in the above-mentioned publication, the content of forming a registration control pattern for detecting a color shift at the timing between sheets is described. However, a means for detecting and correcting the amount of color shift in a short period of time between sheets is described. It is not disclosed, and specific means for correcting the amount of color misregistration is unclear.

On the other hand, Japanese Patent Publication No. Hei 6-100862 discloses an electrostatic image recording apparatus 80 for obtaining a color image by repeatedly reciprocating a recording medium 82 to a recording section 84 as shown in FIG. An image line 86 for detecting a color shift in a direction perpendicular to the transport direction of the recording medium 82 is formed on the recording medium 82 before image formation, and the vertical position of the recording medium 82 is detected and corrected based on the pattern. A technique for performing this is disclosed. However, for the detected color shift amount,
A method is described in which the influence on the error of the correction amount due to a defect of an image line or the like is removed as much as possible by performing correction by a minimum control amount instead of adjusting at once.

However, when the correction is performed by the minimum control amount at a time, the time required for the correction may be long. Therefore, when a new large color shift suddenly occurs until the correction is completed,
It is difficult to respond quickly to the sudden color shift.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and minimizes color shift of a formed color image without deteriorating the processing efficiency of image forming processing. It is an object of the present invention to provide an image forming apparatus which can be suppressed to the limit.

[0012]

According to another aspect of the present invention, there is provided an image forming apparatus, comprising: a plurality of image writing means for forming latent images based on respective color components of a color image on different photosensitive members; The latent image of each color component is developed with a color toner to form a color toner image on each photoconductor, and the color toner image formed on each photoconductor is superimposed on a recording medium. An image forming apparatus for forming a color image on the recording medium by transferring, wherein at a time interval of an image forming process on the recording medium, a toner image pattern of each color component for detecting a position shift is formed on the photosensitive member. And a detecting means for detecting a shift amount of a writing position of each color component based on a position of a toner image pattern formed on each photoconductor by the pattern forming means. And the write position deviation of each color component is roughly corrected in the first interval based on the deviation amount of the write position of each color component detected by the detection means, and the remaining positional deviation amount is calculated in the second and subsequent intervals. Correction control means for performing correction a plurality of times.

Further, in the image forming apparatus according to the second aspect,
2. The image forming apparatus according to claim 1, wherein the image writing unit deflects and scans the laser beam based on each color component of the image to be formed on the photosensitive member by a rotary polygon mirror driven by a rotary polygon drive motor. Forming a latent image corresponding to each color component, and wherein the correction control unit corrects a writing position shift in the sub-scanning direction.

Further, in the image forming apparatus according to the third aspect,
3. The image forming apparatus according to claim 2, wherein the correction control unit corrects a writing position shift in the sub-scanning direction in units of one dot by changing a clock number of a line sync signal, and supplies the write polygon to the rotary polygon mirror driving motor. The correction of one dot or less is performed by changing the phase of the signal to be performed a plurality of times.

Further, in the image forming apparatus according to the fourth aspect,
4. The image forming apparatus according to claim 3, wherein a single control amount when the correction of one dot or less is performed is set based on a maximum control amount controllable by the correction control unit. I do.

According to a fifth aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the rotation polygon mirror driving motor corresponding to each color component is provided with a constant value for controlling the output timing of the main scanning start signal. A reference clock supply unit that supplies a reference clock having a frequency, wherein the correction control unit supplies the reference clock so as to switch the reference clock to a different phase at a predetermined timing based on a shift amount of a writing position of each color component. It is characterized by controlling the means.

Further, in the image forming apparatus according to the present invention,
6. The image forming apparatus according to claim 5, wherein the correction control unit switches a servo characteristic at the phase switching timing.

Further, in the image forming apparatus according to the present invention,
3. The image forming apparatus according to claim 2, wherein the line sync signal corresponding to each color component is a count reference signal for generating a write timing signal in the sub-scanning direction for each color, and the line sync signal for one color component is used as another. The switching of the count to the line sync signal of the color is performed after the phase of the reference clock supplied to the rotary polygon mirror drive motor for each color component is switched to stabilize the operation of the rotary polygon mirror drive motor.

Further, in the image forming apparatus according to the present invention,
2. The image forming apparatus according to claim 1, wherein the color misregistration correction cycle is executed before the first image formation after the power supply to the image forming apparatus is turned on or when the color misregistration correction cycle has not been executed for a predetermined time or more. Then, at intervals of the image forming process, the correction based on the variation of the writing position shift amount after the execution of the color shift correction cycle is performed.

In the image forming apparatus according to the first aspect, a plurality of image writing means form latent images based on respective color components of a color image on different photosensitive members. And
The formed latent image of each color component is developed with a color toner to form a color toner image on each photoconductor. Further, a color image is formed on the recording medium by superimposing and transferring the color toner image formed on each photoconductor onto the recording medium.

In the image forming apparatus according to the first aspect of the present invention, a pattern image forming unit forms a toner image pattern of each color component for detecting a position shift on a photosensitive member at intervals of an image forming process on a recording medium. I do. Then, based on the position of the toner image pattern formed on each photoconductor, the detection unit detects the amount of deviation of the writing position of each color component. Based on the detected shift amount of the write position of each color component, the correction control means
The writing position shift of each color component is roughly corrected in the first interval, and the remaining position shift amount is corrected a plurality of times in the second and subsequent intervals.

As described above, in the image forming apparatus according to the first aspect, the writing position deviation of each color component is corrected stepwise in the interval of the image forming process on the recording medium. That is, by performing the correction at intervals of the image forming process, there is no need to interrupt the image forming process and execute a special color shift correction cycle. For this reason, downtime due to the color misregistration correction cycle can be reduced, and deterioration of the processing efficiency of the image forming process can be avoided.

Further, since the writing position deviation amount of each color component is roughly corrected in the first interval, and the remaining position deviation amount is corrected a plurality of times in the second and subsequent intervals, it is possible to correct the writing position deviation more than once. The influence of the error of the writing position shift amount is reduced, and the time until the correction is completed is shorter than in the case where the correction is performed a plurality of times by a predetermined correction amount without performing the rough correction, so that sudden color shift is prevented. We can respond faster. Thereby, the color shift of the color image can be suppressed to the minimum.

As the image writing means, a laser beam based on each color component of an image to be formed is exposed by a rotating polygon mirror driven by a rotating polygon mirror driving motor. Means for forming a latent image corresponding to each color component by deflecting and scanning on the body can be used. In this case, the correction control unit can correct the writing position deviation in the sub-scanning direction.

In the case where the writing position shift in the sub-scanning direction is to be corrected, the correction control means changes the number of clocks of the line sync signal to correct the writing position shift in the sub-scanning direction. The correction of one dot or less may be performed by performing the correction in units of one dot and changing the phase of the signal supplied to the rotary polygon mirror driving motor a plurality of times.

Since the number of clocks of the line sync signal is changed only by changing the set value, it can be executed at one interval. However, the phase change (phase switching) of the signal supplied to the rotary polygon mirror driving motor is performed by the servo. The control is likely to be lost if a large change is made.

Therefore, as described in the fourth aspect, it is desirable to set a single control amount for performing correction of one dot or less based on the maximum control amount controllable by the correction control means. . By setting the controllable control amount as a reference, disturbance to the servo can be minimized, and the correction can be performed stably.

Incidentally, the phase change (phase switching) of the signal supplied to the rotary polygon mirror driving motor is realized by, for example, the image forming apparatus according to the fifth aspect. In the image forming apparatus according to the fifth aspect, a reference clock having a constant frequency for controlling the output timing of the main scanning start signal is supplied to the rotary polygon mirror driving motor corresponding to each color component by the reference clock supply unit. Then, under the control of the correction control unit, the reference clock supply unit performs a predetermined timing based on the shift amount of the writing position of each color component,
The supplied reference clock is switched to a different phase.

The timing of switching the phase of the reference clock will be described with reference to FIG. As shown in FIG. 13, the phase of the reference clock F is set to 0/4 (F in FIG. 13).
_Assuming that switching is performed from ( _0/4 ) to 1/4 delay (F _{1/4 in} FIG. 13), a case where switching is performed at the timing (X) and a case where switching is performed at the timing (Y) are considered. The output Co of the comparison circuit of the rotary polygon mirror drive motor is a signal obtained by comparing the input SOS signal with the rising edge of the reference clock F.

Here, when the switching is performed at the timing of (X), the comparison output Co becomes like the comparison output Cox0 / 4 → 1/4. It takes a long time for the control of the polygon mirror drive motor to stabilize. On the other hand, when the switching is performed at the timing of (Y), the comparison output Co becomes the comparison output Coy0 / 4 → 1/4, and the rotating polygon mirror driving motor speeds down smoothly. Mirror drive motor control is easily stabilized. The example shown in FIG. 13 is an example in which the phase is delayed. However, it is similarly possible to advance the phase. In this case, the phase is reversed at the timing when the speed of the rotary polygon mirror driving motor is smoothly increased. Can be switched.

When the phase is largely changed, a large phase comparison signal is output, and there is a possibility that a motor rotation fluctuation more than necessary occurs and the pull-in time becomes longer. As described above, it is desirable that the servo characteristics be switched at the above-described phase switching timing to suppress the motor rotation fluctuation and minimize the pull-in time.

The first example of switching the servo characteristics is a method of switching the servo gain. As shown in FIG. 13, the amplifier output is suppressed by lowering the amplifier gain. The second method is to input a reverse pulse as shown in FIG.

The third is a method for limiting the comparison output signal, in which the height of the pulse is suppressed as shown in FIG.
The fourth is a method of switching the offset voltage as shown in FIG.
As shown in FIG. 3, a DC offset is added so as to cancel the comparison output.

The line sync signal corresponding to each color component is often used as a count reference signal for generating a write timing signal in the sub-scanning direction for each color. In order to stabilize the reference clock supplied to the rotating polygon mirror driving motor for each component, after switching the phase of the reference clock supplied to the rotating polygon mirror driving motor for each color component and stabilizing the operation of the rotating polygon mirror driving motor, It is desirable to perform count switching from a line sync signal of one color component to a line sync signal of another color.

Although the execution of the color misregistration correction cycle lowers the efficiency of image forming processing, the color misregistration correction cycle must not be executed at all in order to maintain the image quality of the formed image at a predetermined level or more. I can't go.

Therefore, as described in claim 8, before the first image formation after the power supply to the image forming apparatus is turned on, or when the color misregistration correction cycle has not been executed for a predetermined time or more, the color misregistration correction is performed. Just execute the cycle. In this case, in the interval of the image forming process, the correction based on the variation of the writing position deviation amount after the execution of the color deviation correction cycle may be performed. Thus, the color misregistration correction cycle can be executed at an appropriate timing.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] First, claims 1-4 of the claims
A first embodiment corresponding to the invention described in (1) will be described.

[Overall Configuration of Image Forming Apparatus] FIG. 2 shows an overall configuration diagram of an image forming apparatus 210 for forming a multicolor image. In the image forming apparatus 210, as a normal image forming process, each of the optical scanning devices 210a to 210d triggers each of the photoconductors 15a to 15d by using an image writing start signal as a trigger.
A latent image of a corresponding color (one of cyan, magenta, yellow, and black) is formed on each. The latent image of each color is developed by a developing device (not shown) to form a color toner image.
Is transferred onto the sheet 201 conveyed in the direction of arrow Q. The paper 201 on which the four color toner images have been transferred is subjected to a fixing process by a fixing device (not shown), and a multicolor image is formed on the paper 201. Note that the configuration of the image forming apparatus 210 in FIG. 2 is substantially the same as the configuration of the above-described image forming apparatus 110 shown in FIGS. 4 and 7, and therefore a detailed description is omitted. However, in the image forming apparatus 210, the transfer belt 2
A toner image pattern (for example, a toner image pattern 240 formed at the timing between sheets shown in FIG.
And input to the arithmetic processing unit 203. The arithmetic processing unit 203 calculates the position of each toner image pattern, and detects the positional difference between the colors, that is, the color shift amount. Furthermore, the rotary polygon mirror driving motor control circuits 18a to 18a to
18d (see FIG. 9) to control the rotation of the rotary polygon mirror driving motors 17a to 17d, ie, the rotary polygon mirrors 13a to 13d.
3d rotation operation is controlled. Thus, the color shift is corrected by changing the image writing timing in each of the optical scanning devices 210a to 210d. The detection of the color misregistration amount from the registration pattern and the correction of the detected color misregistration amount are performed in separate cycles, and a correction cycle is inserted after the cycle of detecting the color misregistration.

[Color Misregistration Correction Operation in Image Forming Apparatus and Configuration Related to the Correction Operation] Hereinafter, the above-described image forming apparatus 2
The color misregistration correction operation in the sub-scanning direction (= the paper conveyance direction in FIG. 2) at 10 will be described. In the present embodiment, as the color shift correction in the sub-scanning direction, correction in units of one dot is performed by:
The correction is performed by changing the number of clocks of a line sync signal (hereinafter, referred to as an LS signal). One dot or less is corrected by a reference clock supplied to the rotary polygon mirror drive motor control circuits 18a to 18d (see FIG. 9) for each color. This is performed by changing the phase. The LS signal is an image writing timing signal for one line in the main scanning direction, and is output based on the SOS signal. In the LS signal, the H level indicates the timing of writing an image.

FIG. 11 is a block diagram of the image writing timing generation circuit 29 in the sub-scanning direction in the image forming apparatus 210. The image write start signal TR0 is
It is input to the fixed counter 23a for the first color. The fixed counter 23a counts the count value K for the pitch between prints of each color.
a, which is set in advance as the LS signal of the first color.
The count value Ka is counted using a as a reference clock.

The count end signal TR0a is input to a write start timing correction counter 20a, and after counting a predetermined count value Ca, generates a first color timing signal PSa. Since the first color is a reference, the count value Ca in the counter 20a is a fixed value. The count end signal TR0a for the first color is 2
The color is input to the fixed counter 23b.

The output signal from the fixed counter 23b for the second color is input to the delay 22b. Multiplexer 21
b selects the output of the delay 22b according to the time difference between the LSb signal and the LSa signal, and sets the write start timing correction counter 20b as the count end signal TR0b.
Output to For example, when the time difference between the LSa signal and the LSb signal is １ ／ cycle, a signal delayed by ８ + ／ (fixed) cycle is output to the counter 20b. Upon receiving the delayed signal, the counter 20b counts a count value based on the detected color misregistration data, and then generates the second color sub-scanning write timing signal PSb. Hereinafter, similarly, the third color write timing signal PSc and the fourth color write timing signal PSd are generated.

FIG. 9 shows a rotary polygon mirror driving motor 17 for each color.
FIG. 3 is a functional block diagram relating to control of the rotary polygon mirror drive motors 17a to 17d. FIG. 10 is an internal block diagram of the rotary polygon mirror drive motor control circuit 18 (general names of rotary polygon mirror drive motor control circuits 18a to 18d). As shown in FIG. 10, the rotary polygon mirror driving motor control circuit 18 includes a comparison circuit 72, a loop characteristic switching circuit 7,
4. It includes an amplifier 76 and a driver 78. The reference clock F is input to the comparison circuit 72, and the comparison circuit 72 compares the reference clock F with the SOS signal.
The comparison output Co based on the comparison result is input to the driver 78 via the amplifier 76, and the rotation operation of the rotary polygon mirror driving motor 17 is controlled based on the input signal Ao.

As shown in FIG. 17, each motor is controlled using the SOS signal as a comparison signal, and its rising edge (for example, edge E)
1 and the edge E3 or between the edge E2 and the edge E4).

Here, for example, the image on the belt is 1
To shift by / 4 dot, the phase should be 1/4 at the same frequency.
The timing of the SOS signal may be shifted by １ ／ period by supplying the reference clocks whose periods are shifted to the rotary polygon mirror driving motors of the respective colors.

As described above, the color misregistration correction in the sub-scanning direction can be performed by changing the values set in the variable counters 20a to 20d.
The correction is performed on a dot-by-dot basis, and correction of one dot or less is performed by inputting a reference clock having the same cycle and a different phase to the rotary polygon mirror driving motor.

The values set in the variable counters 20a to 20d can be changed at the timing between the sheets during the image forming process (corresponding to the color misregistration correction areas R1 and R2 shown in FIG. 5A). However, the switching of the phase of the input signal to the rotary polygon mirror driving motor causes disturbance to the servo, so that if it is largely changed, the control may be lost.
Therefore, in the present embodiment, the phase of the input signal is switched over a plurality of stages based on the maximum control amount in the controllable range. For example, when the maximum control amount that can be controlled when correcting 5/8 dot is 2/8 dot, 2
The correction is performed three times of / 8 dot + 2/8 dot + ／ dot.

[Explanation of Color Shift Correction Processing] The color shift correction processing in the sub-scanning direction at the timing between sheets according to the present embodiment will be described below with reference to FIG. Here, a description will be given by taking the color shift correction of the second color as an example. For example, if the set value of the variable counter 20b before color shift correction is 63
And the reference clock Fb of the rotary polygon mirror drive motor is 1/8
Delay. In addition, the variable counter 2 after detecting the color shift
It is assumed that the set value of 0b is 64 and the reference clock Fb is a 7/8 delay.

As a correction procedure, first, a value close to the final value (64 + 7/8) is set only by changing the count number of the LS signal. In this example, | (64 + 7/8)-(6
3 + ／) | = | 1 + 6/8 | = 2, so 63
To which 65 is added by adding 2. After that, the remaining color shift (65 + 1/8)-(64 + 7/8) = 1/4 dot is changed a plurality of times by a control amount that can be changed at the timing between sheets. In this example, if the control amount that can be changed at the sheet interval is 1/16 dot, the second time is 65+
It is changed to 1/16. Hereafter, it is changed by 1/16,
The final value (64 + 7 /
8) and the correction is completed.

When the change of the count number of the LS signal and the phase switching can be simultaneously performed, the count number of the LS signal is set to 65 in the first correction, and the phase of the rotary polygon mirror driving motor is set to 1 in the first correction. 1/1 from / 8 delay
Switch to 6 delay. Thereafter, the final value (64 + 7/8) is reached by a total of four steps in a similar procedure, and the correction is completed.

As described above, in the first embodiment, the writing position deviation of each color component is corrected stepwise at the timing between sheets. That is, by performing the correction at intervals of the image forming process, there is no need to interrupt the image forming process and execute a special color shift correction cycle. For this reason, downtime due to the color misregistration correction cycle can be reduced, and deterioration of the processing efficiency of the image forming process can be avoided.

The writing position deviation of each color component is set to 1
The correction is performed roughly at the first interval, and the remaining positional deviation is corrected a plurality of times at the second and subsequent intervals. Therefore, the influence of the error of the writing positional deviation is smaller than in the case of performing the correction once, and the general correction is performed. The time until the correction is completed is shorter than in the case where the correction is performed a plurality of times by a predetermined correction amount without performing the correction, and it is possible to respond more quickly to the occurrence of sudden color shift. Thereby, the color shift of the color image can be suppressed to the minimum.

[Second Embodiment] Next, a second embodiment corresponding to the invention described in claims 5 and 6 will be described.

Hereinafter, a method of switching the reference clock to a different phase in the rotary polygon mirror drive motor control circuit 18 shown in FIG. 10 will be described. Here, as shown in FIG. 13, when the phase of the rotary polygon mirror drive motor is switched from 0/4 to 1/4 delay, switching is performed at the timing of (X) and when switching at the timing of (Y). Is assumed.

The output Co from the comparison circuit 72 in FIG.
This is a signal comparing the input SOS signal with the rising edge of the reference clock F, and when switching is performed at the timing (X), the comparison output Co becomes the comparison output Cox0 / 4 → 1 /
As shown in FIG. 4, the speed is increased for a moment and then reduced, so that it takes a long time for the control of the rotary polygon mirror drive motor 17 to be stabilized.

On the other hand, when the switching is performed at the timing of (Y), the comparison output Co becomes like the comparison output Coy0 / 4 → 1/4, and the rotating polygon mirror driving motor 17 is reduced in speed smoothly. The rotary polygon mirror drive motor 17
Control is easy to stabilize. Although the example shown in FIG. 13 is an example in which the phase is delayed, it is similarly possible to advance the phase. In such a case, the timing at which the speed of the rotary polygon mirror driving motor 17 is smoothly increased is reversed. What is necessary is just to switch a phase.

Further, in the present embodiment, at the phase switching timing, for example, the servo characteristics are switched by one of the following methods to suppress the motor rotation fluctuation and minimize the pull-in time.

The first example of switching the servo characteristics is a method of switching the servo gain. As shown in FIG. 13A, a change in the amplifier output is suppressed by lowering the amplifier gain. The second method is to input a reverse pulse.
The reverse pulse as shown in (2) is input. Third, the method of limiting the comparison output signal suppresses the pulse height as shown in (3) of FIG. Fourth, a DC offset is added so as to cancel the comparison output as shown in (4) of FIG. 13 by a method of switching the offset voltage.

[Third Embodiment] Next, a third embodiment corresponding to the invention described in claim 7 will be described. FIG. 11 is a block diagram of a circuit for generating an image write timing in the sub-scanning direction. The basic operation has been described above.

In the third embodiment, as shown in FIG. 14, first, the phase of the reference clock F input to the rotary polygon mirror drive motor control circuit 18 (see FIG. 10) is switched in accordance with the color misregistration correction data (see FIG. 14). Arrow T1). After the switching of the phase, the control for the rotation operation of the rotary polygon mirror drive motor 17 is gradually stabilized. After the control is stabilized (after the arrow T2), the count is switched from the line sync signal LSa of one color component to the line sync signal LSb of another color (arrow T3). Thereby, the reference clock F can be stabilized.

FIG. 14 shows the second color as an example, and illustrates a case where a 7/8 delay is before the change and a 1/8 delay is after the change.

[Fourth Embodiment] Next, a fourth embodiment corresponding to the invention described in claim 8 will be described with reference to FIG.

When the power of the image forming apparatus 210 of FIG. 2 is turned on, the processing routine of FIG. 15 is started. When the copy is started in the image forming apparatus 210, the result of step S1 is affirmative, and the process proceeds to step S2, where it is determined whether or not the copy is the first copy after the power is turned on. Here, in the case of the first copy after the power is turned on, the internal temperature of the apparatus related to the color shift has changed from the time of the previous copy, and a large color shift may occur. Then, the normal registration control cycle is executed. After correcting the color misregistration, the process proceeds to a normal copy cycle.

On the other hand, if it is not the first copy in step S2, the flow advances to step S4 to determine whether or not a predetermined time has elapsed since the previous registration control cycle. here,
If a predetermined time or more has elapsed since the last registration control cycle, even if it is not the first time after turning on the power, the state such as the temperature inside the device has changed and color misregistration may have occurred. Also in this case, the process proceeds to step S3, and a normal registration control cycle is executed.

If the timing between the sheets is not the first copy after the power is turned on and the predetermined time has not elapsed since the previous registration cycle (when the affirmative determination is made in step S5), In step S6, the correction of the variation in the amount of color misregistration from the previous execution of the registration control cycle is performed.

Thus, at appropriate timing (=
A color misregistration correction cycle can be executed (immediately before the first copy after power-on and at a predetermined time interval thereafter).

In each of the above embodiments, the correction in the sub-scanning direction has been described. However, the correction can also be made in the main scanning direction in principle.

The above embodiments are also applicable to an image forming apparatus 210X using the intermediate transfer material 207 shown in FIG.
The same can be applied.

[0069]

According to the present invention, the writing position shift of each color component is corrected stepwise in the interval of the image forming process, so that the downtime due to the color shift correcting cycle can be reduced and the image forming process can be reduced. Can be avoided. In addition, since the writing position deviation of each color component is roughly corrected in the first interval, and the remaining position deviation amount is corrected a plurality of times in the second and subsequent intervals, a plurality of predetermined correction amounts can be obtained without performing the general correction. The time until the correction is completed is shorter than in the case of performing the correction over and over, so that it is possible to respond more quickly to the occurrence of sudden color shift, and it is possible to minimize the color shift of the color image.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical scanning device (ROS unit) incorporated in a general image forming apparatus.

FIG. 2 is an overall configuration diagram of an image forming apparatus according to an embodiment of the present invention.

FIG. 3 is a diagram showing an example of a resist pattern formed by a conventional technique.

FIG. 4 is a diagram showing a configuration for correcting a color shift from a registration control pattern.

5A is a diagram illustrating a color misregistration correction area, and FIG. 5B is a diagram illustrating an example of a registration control pattern.

FIG. 6 is a view showing the formation of a resist pattern in an embodiment of the prior patent.

FIG. 7 is an overall configuration diagram of an image forming apparatus that forms a multicolor image according to an embodiment of the prior patent.

FIG. 8 is a configuration diagram of an electrostatic image forming apparatus that forms a multicolor image in an embodiment of the prior patent.

FIG. 9 is an overall configuration diagram of a rotary polygon mirror drive motor control circuit in the embodiment according to the present invention.

FIG. 10 is an internal block diagram of a rotary polygon mirror driving motor.

FIG. 11 is a block diagram illustrating a configuration of a write timing signal generation circuit in a sub-scanning direction.

FIG. 12 is a diagram illustrating timings of various signals related to color misregistration correction in the sub-scanning direction.

FIG. 13 is a diagram illustrating a phase switching timing of a reference clock for controlling a rotary polygon mirror driving motor according to the second embodiment.

FIG. 14 is a diagram illustrating a relationship between a phase switching timing of a reference clock for controlling a rotary polygon mirror driving motor and an LS signal switching timing in a third embodiment.

FIG. 15 is a flowchart illustrating a processing routine according to a fourth embodiment.

FIG. 16 is an overall configuration diagram of another image forming apparatus to which the present invention can be applied.

FIG. 17 is a diagram showing a relationship between a reference clock for controlling a rotary polygon mirror driving motor and an SOS signal.

[Explanation of symbols]

13a, 13b, 13c, 13d Rotating polygon mirror 15a, 15b, 15c, 15d Photoconductor 17a, 17b, 17c, 17d Rotating polygon mirror driving motor 18a, 18b, 18c, 18d Rotating polygon mirror driving motor control circuit 29 Image writing timing generation Circuit 201 Paper (recording medium) 210 Image forming apparatus

Claims (8)

[Claims] A latent image based on each color component of a color image is formed on a different photosensitive member by a plurality of image writing means, and the formed latent image of each color component is developed with a color toner. An image forming apparatus that forms a color image on the recording medium by forming a color toner image on the recording medium and superimposing and transferring the color toner image formed on each of the photoconductors onto a recording medium; Pattern forming means for forming a toner image pattern of each color component for detecting a position shift on the photoconductor at intervals of image forming processing on a medium; and a toner image formed on each photoconductor by the pattern forming means. Detecting means for detecting the shift amount of the writing position of each color component based on the position of the pattern; and detecting the shift amount of the writing position of each color component detected by the detecting means. The writing position deviation of each color component,
An image forming apparatus comprising: a correction control unit that performs a general correction in a first interval and a plurality of corrections of a remaining displacement amount in a second and subsequent intervals. 2. The image writing means deflects and scans a laser beam based on each color component of an image to be formed on a photoreceptor by a rotary polygon mirror driven by a rotary polygon mirror drive motor to convert the laser beam into each color component. 2. The image forming apparatus according to claim 1, wherein the correction control unit corrects a writing position shift in a sub-scanning direction. 3. The correction control means corrects a writing position shift in the sub-scanning direction in units of one dot by changing the number of clocks of a line sync signal, and changes a phase of a signal supplied to the rotary polygon mirror driving motor. 3. The image forming apparatus according to claim 2, wherein the correction of one dot or less is performed by changing the number of times. 4. The method according to claim 1, wherein the correction is performed for one dot or less.
4. The image forming apparatus according to claim 3, wherein the control amount for each time is set based on a maximum control amount controllable by the correction control unit. 5. The correction control unit further comprising: a reference clock supply unit that supplies a reference clock having a constant frequency for controlling an output timing of a main scanning start signal to a rotary polygon mirror driving motor corresponding to each color component. 2. The image forming apparatus according to claim 1, wherein the control unit controls the reference clock supply unit to switch the reference clock to a different phase at a predetermined timing based on a shift amount of a writing position of each color component. 6. The image forming apparatus according to claim 5, wherein the correction control unit switches servo characteristics at the phase switching timing. 7. A line sync signal corresponding to each color component is used as a count reference signal for generating a write timing signal in the sub-scanning direction for each color, and a line sync signal of one color component is converted from a line sync signal of another color. 3. The image according to claim 2, wherein the switching to the signal is performed after the phase of a reference clock supplied to the rotary polygon mirror driving motor for each color component is switched to stabilize the operation of the rotary polygon mirror driving motor. Forming equipment. 8. A color misregistration correction cycle is executed before the first image formation after the power supply to the image forming apparatus is turned on or when the color misregistration correction cycle has not been executed for a predetermined time or more. 2. The image forming apparatus according to claim 1, wherein the correction based on the variation of the writing position shift amount after the execution of the color shift correction cycle is performed in the interval of.