JPH11237567A - Multi-color image formation device and method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the setting time until a motor is converged to an original rotation number per unit time and also to make controllable the rotation phase of a rotary polygon mirror in a short time by changing the frequency of a reference clock for plural times and turning the frequency of the reference clock to a normal rotation frequency in the interval of respective frequency change periods. SOLUTION: The frequency of a reference clock is changed twice or more times, and is turned to the normal rotation frequency in the interval of respective frequency change periods while the rotation phase of a rotary polygon mirror is controlled. In this device, the frequency of the generated reference clock is changed based on signals inputted from a registration control part 128 in a clock change control part 136. Based on a pattern image transferred to an intermediate transfer body and read by a sensor 124, the above change is outputted in an image interval to recording paper. body. When the frequency of the reference clock is changed, the rotation speed of the motor for driving the rotary polygon mirror is controlled in a PLL control part based on the changed frequency.

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 such as a laser beam printer or a digital copying machine which forms an image by an electrophotographic system by scanning a laser beam with an optical scanning device having a rotating polygon mirror. In particular, the present invention relates to an image forming apparatus and a method including a registration control for controlling a writing position in a sub-scanning direction.

[0002]

2. Description of the Related Art In a multicolor image forming apparatus employing an electrophotographic system, four color toners of black (K), cyan (C), magenta (M), and yellow (Y) are superposed on paper. Transfer and perform multi-color printing.

[0003] When performing multicolor printing, if the writing start positions of the respective colors are slightly shifted, they appear as color shifts when transferred onto recording paper in a superimposed manner, and the print quality is degraded.

In order to solve this problem and perform high-precision multi-color printing, a writing position control technique for correcting registration deviation is required.

[0005] Such a correction of registration misalignment, as two typical examples, includes, as one method, a method in which a toner image of a specific pattern is formed on an intermediate transfer member or the like and a light source and a photodetector are used. There is a method in which the pattern is detected by a sensor, the amount of registration deviation is calculated, and correction amount data is sent to each correction system to perform correction.

As another method, a specific pattern is prepared in advance outside an image forming area such as an intermediate transfer member, and the pattern is detected by a sensor, and the pattern detection timing and writing in the main scanning direction are performed. There is a method in which the amount of registration deviation is calculated based on the detection timing of a timing signal or the like, and correction amount data is sent to each correction system to perform correction.

[0007] In the writing position control technique, particularly with respect to registration deviation of one pixel or less in the sub-scanning direction, the rotation phase of the rotary polygon mirror disposed in the image forming apparatus is controlled with respect to a reference value. Conventionally, a technique for correcting a registration deviation by controlling a writing start position has been devised.

[0008] In brief, first, a PLL (Phase Locked Loop) is generated by a reference clock and a comparison clock so that a rotating polygon mirror driving motor for rotating the rotating polygon mirror is accurately rotated at a constant rotation speed. Perform control.

In this case, the comparison clock is a scanning light position by a photodetector arranged outside the scanning plane in the optical scanning device, which is an FG output in the rotary polygon mirror driving motor, a Hall element output, or a write timing signal in the main scanning direction. What is necessary is just to output from a detector.

If the reference clock is changed during such PLL control, a phase difference is generated between the reference clock and the reference clock. In the PLL control, the rotational speed of the rotary polygon mirror driving motor is reduced so as to eliminate the phase difference. To change. Thereafter, when the reference clock and the comparison clock have the same phase (or a predetermined phase difference), the rotation phase of the rotary polygon mirror changes, and the write timing signal in the main scanning direction changes the output timing accordingly. Can be done. Since the writing timing in the main scanning direction is kept constant in accordance with the writing timing signal in the main scanning direction, the writing timing in the sub-scanning direction can be controlled.

As a method for controlling a reference clock of a motor for rotating such a rotary polygon mirror to control a writing start timing in a sub-scanning direction, see Japanese Patent Application Laid-Open No. Hei 7-16008.
No. 4 and JP-A-7-281536 and JP-A-8-281536.
No. 152833.

Japanese Patent Application Laid-Open No. Hei 7-160084 discloses a multi-color image forming apparatus which has a plurality of image forming apparatuses, and in which a plurality of types of reference clocks having different phases are prepared in advance and the sub-scanning is performed. When a misregistration in the direction is detected, a reference clock having a phase corresponding to the correction amount is selected and used to control the writing start timing in the sub-scanning direction and correct the misregistration in the sub-scanning direction by one line or less. (See FIG. 9, details will be described later).

Japanese Patent Application Laid-Open No. 7-281536 discloses an apparatus for forming a multicolor image by superimposing a toner image on an intermediate transfer member a plurality of times with one image forming apparatus. Sometimes, a phase matching period for slightly increasing the frequency of the reference clock given to the motor is provided, and after returning to the original frequency after the phase matching period according to the control amount, the rotational phase of the rotary polygon mirror is gradually advanced to a desired value. Phase. In this way, the writing start timing in the sub-scanning direction is controlled, and the registration deviation in the sub-scanning direction is corrected (see FIG. 10, details will be described later).

Japanese Patent Application Laid-Open No. 8-152833 discloses an apparatus for forming a multicolor image by superimposing a toner image on an intermediate transfer body a plurality of times by using a single image forming apparatus. Sometimes, a phase matching period is set to slightly lower the frequency of the reference clock given to the motor, and after returning to the original frequency after the phase matching period according to the control amount, the phase of the mirror surface of the rotating polygon mirror is gradually delayed, and Phase. In this way, the writing start timing in the sub-scanning direction is controlled, and the registration shift in the sub-scanning direction is corrected (see FIG. 11, details will be described later).

In recent years, digital copiers, laser printers, and the like have been required to have high speed and high resolution. This is no exception for a multicolor image forming apparatus. In addition, the above-described registration control technique is indispensable to a multicolor image forming apparatus in order to maintain a high quality image.

In order to perform high-speed printing while maintaining a high-quality image, a technique for controlling registration without interrupting a print job during continuous printing is required. This technology forms a specific pattern of each color as a toner image on the primary transfer means such as an intermediate transfer body at the time between image formation of each color, detects the pattern with a sensor including a light source and a photodetector, and detects the amount of registration deviation. Calculate and correct the time between the image formation different from the pattern formation, or detect the specific pattern created beforehand outside the image forming area such as the intermediate transfer body during the time between each single color image formation The timing and the output timing such as a writing timing signal in the main scanning direction are detected, and the writing timing in the sub scanning direction is changed.

The shorter the time between these papers and the time between each monochrome image formation, the higher the printing performance of the apparatus.

Here, the conventional example (the technique described in the gazette)
Is performed during a print job in continuous printing, there are the following problems.

In Japanese Patent Application Laid-Open No. Hei 7-160084, when a correction operation is performed, reference clocks having different phases are switched as shown in FIG. Therefore, depending on the switching timing, the phase difference between the reference clock and the comparison clock increases, and the rotation fluctuation of the motor increases as shown in FIG. 9B. For this reason, the motor is deviated from the PLL control, which causes unstable rotation. FIG. 9B
As shown in (1), the time from the occurrence of rotation fluctuation to the return to the original rotation speed (settling time) is much longer than the frequency change time. If you print on the next recording paper without considering this time, that is, before the rotation of the motor is settled,
The effect of the rotation fluctuation appears on the image, resulting in color shift and impairing print quality. For this reason, the next sheet must be sent after a sufficient time has passed before the motor settles, resulting in a decrease in the output capability of the print image.

Next, in JP-A-7-281536 and JP-A-8-152833, as shown in FIGS. 10 and 11, the frequency is slightly increased or decreased to gradually change the phase. Although the occurrence of rapid rotation fluctuation is suppressed, the amount of change in frequency is very small, so that the larger the amount of rotation phase control of the rotary polygon mirror, the longer the phase matching period. Finally, overshoot and undershoot of rotation when returning the frequency to a considerable extent occur,
The settling time is longer than the phase matching period. For this reason, the output capability of the print image is reduced.

In order to solve this, as shown in FIG. 12, as a means for changing the rotation phase of the rotary polygon mirror, the reference clock of the motor for rotating the rotary polygon mirror is gradually increased (decreased) and then gradually decreased ( Increase).

However, in this method, overshoot and undershoot can be reduced, but cannot be almost completely eliminated.
As in Japanese Patent Application Laid-Open No. 536 and Japanese Patent Application Laid-Open No. 8-152833, overshoot and undershoot are inevitably generated, and the settling time becomes longer. Also, compared to the risk that the frequency profile of the reference clock to be changed becomes very complicated and the setting of the control amount becomes complicated, it is not effective countermeasures for overshoot and undershoot, and the device configuration becomes complicated. In addition, there is a problem that the cost of the apparatus increases.

[0023]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-mentioned facts, and has a simple structure to reduce the settling time required for a motor for driving a rotary polygon mirror to converge to an original rotation speed during rotation phase control. An image forming apparatus and method capable of performing rotation phase control of a rotary multi-face bell in a short time and performing registration correction without interrupting a print job even during continuous printing without impairing print image output capability. Is the purpose.

[0024]

According to a first aspect of the present invention, there is provided a comparison apparatus which is generated in accordance with a driving speed of a rotary polygon mirror driving motor for driving a rotary polygon mirror mounted on a multicolor image forming apparatus. When the driving speed is controlled by comparing a clock with a predetermined reference clock, the driving speed of the rotary polygon mirror driving motor is changed by changing the reference clock, and the driving speed of each color in the sub-scanning direction is changed. A multicolor image forming apparatus having a registration control for aligning a writing position and preventing a color shift of an output image,
A reference clock frequency changing means for changing a frequency of a reference clock supplied to the rotary polygon mirror driving motor; and controlling the reference clock frequency changing means to change the frequency of the reference clock two or more times and to change each frequency changing period. And a rotation phase control means for controlling the rotation phase of the rotary polygon mirror by using the frequency of the reference clock as a steady rotation frequency.

According to the first aspect of the present invention, the essential components required as a control system for registration control include a reference clock generating means for supplying a reference clock to be supplied to the rotary polygon mirror driving motor, and Position detection means for generating a writing start timing signal in the scanning direction;
Reference clock control means for controlling the frequency of the reference clock so as to have a predetermined frequency profile in accordance with the correction amount of the writing position in the sub-scanning direction, and a sub-clock from a toner image of a specific pattern formed on the intermediate transfer member or the like. A registration control means for calculating a write start position correction amount in the scanning direction and sending the correction amount to the reference clock control means.

Note that the registration control means determines the sub-scanning direction based on the time interval between the image formation start timing signal from a specific pattern formed outside the image forming area such as the intermediate transfer member and the writing timing signal in the main scanning direction. Means for calculating the write start position correction amount and sending the correction amount to the reference clock control means.

The reference clock control means changes the reference clock of the rotary polygon mirror driving motor in accordance with the frequency profile set by the correction amount data from the registration control means, and controls the rotation phase of the rotary polygon mirror.

That is, the position detecting means outputs a write start timing signal in the main scanning direction. The reference clock generator supplies a reference clock to the rotary polygon mirror drive motor. The rotary polygon mirror drive motor is controlled, for example, by a PLL based on a reference clock and a comparison clock (FG output, Hall element output, or write timing signal in the main scanning direction), and rotates accurately at a constant rotation speed. It is needless to say that the reference clock and the comparison clock are in a phase locked state with a predetermined phase difference (including the same phase) during the steady rotation because of the PLL control. The reference clock control means includes:
A frequency profile is set according to an instruction from the registration control means, and the frequency of the reference clock is changed for the rotary polygon mirror driving motor according to the set frequency profile.

Here, the rotation phase control means changes the reference clock twice or more. At this time, the frequency of the reference clock is set as a stationary rotation frequency at intervals of each frequency change period, and the rotation phase of the rotary polygon mirror is controlled. That is, overshoot and undershoot generated after the first control are suppressed by the second control.
If necessary, continue with the third and fourth rounds. As a result, overshoot and undershoot can be eliminated quickly. Further, since the control is not continuous control but is interrupted each time, a complicated frequency profile is not required.

More specifically, the frequency profile of claim 1 is composed of a plurality of frequencies based on the frequency of the steady rotation for performing printing. The frequency is set to return to a frequency for rotation or a frequency close to the frequency, and the frequency is changed again at a predetermined timing. The rotation settling time at the time of correction can be reduced by the two or more frequency changes.

According to a second aspect of the present invention, there is provided a comparison clock generated in accordance with the driving speed of a rotary polygon mirror driving motor for rotating a rotary polygon mirror mounted on a multicolor image forming apparatus, and a predetermined comparison clock. When the drive speed is controlled by comparing the drive speed with the reference clock, the drive speed of the rotary polygon mirror drive motor is changed by changing the reference clock, the write start position of each color in the sub-scanning direction is adjusted, and output is performed. In registration control for preventing color misregistration of an image, during the rotation phase control of the rotary polygon mirror, the frequency of a reference clock supplied to the rotary polygon mirror drive motor is changed to change the rotation speed of the rotary polygon mirror drive motor. After that, the frequency is once returned to the steady rotation frequency, and further changed at a predetermined timing in the same frequency increasing / decreasing direction as the first frequency change. Then back to the steady rotational frequency to control the rotation phase of the rotary polygonal mirror is characterized by.

According to a third aspect of the present invention, in the second aspect of the present invention, the predetermined timing is the first time that occurs when the rotation of the rotary polygon mirror returns to a steady rotation from a rotation change due to a first frequency change of the frequency. An overshoot or undershoot deviating from the steady rotation is the optimal timing for suppressing the overshoot or undershoot.

According to a fourth aspect of the present invention, in the second or third aspect of the invention, when the phase of the reference clock is increased or decreased, the motor is decelerated when the phase is advanced, and the phase is delayed. In this case, the motor is controlled so as to increase the speed.

According to a fifth aspect of the present invention, in the first aspect of the present invention, the reference clock supplied to the rotary polygon mirror driving motor during the rotation phase control of the polygon mirror is controlled. The frequency between each frequency change is characterized in that it is an increase / decrease range of less than the minimum value of the difference between the frequency to be changed and the steady rotation frequency with respect to the steady rotation frequency.

According to the second to fifth aspects of the present invention, when the frequency change of the reference clock is started based on the predetermined frequency profile as shown in FIG. 1, the rotating polygon mirror is driven by the first frequency change. The motor fluctuates once. This is because, for example, control is performed so as to follow a change in the reference clock by PLL control inside the motor.

Here, the motor follows the frequency change of the reference clock with a long delay due to the mechanical time constant of the motor itself, and overshoots (undershoots) the rotation speed corresponding to the frequency after the change. ). Further, when the reference clock returns to the frequency of the normal rotation, the reference clock similarly follows with a delay, causing an overshoot (undershoot) with respect to the normal rotation speed, and thereafter converging to the steady rotation while repeatedly generating overshoot and undershoot. I do.

At this time, the frequency is changed for the second time at an arbitrary timing at which the first overshoot (undershoot) occurs when returning to the normal rotation. This second frequency change suppresses the repetition of overshoot (undershoot) and quickly pulls back to the original number of revolutions, so that the settling time during the rotation phase control of the rotating polygon mirror is reduced.

[0038]

FIG. 2 is a schematic configuration diagram of an image forming apparatus 100 according to the present embodiment.

The image forming apparatus 100 includes a yellow image forming unit 101Y, a magenta image forming unit 10
1M, a cyan image forming unit 101C, and a black image forming unit 101K (hereinafter collectively referred to as the image forming unit 101) are arranged in one row, and have a so-called tandem configuration.

The image forming unit 101 includes an optical scanning device 102 and a developing unit 106 including a photosensitive member 104, respectively.
It has.

As shown in FIG. 3, the optical scanning device 102 is provided with a laser light source 108, and a collimator lens 112 is provided in the output direction of the laser beam 110 of the laser light source 108. After being collimated by the collimator lens 112, the light reaches a rotary polygon mirror 114. Rotating polygon mirror 11
Reference numeral 4 is adapted to rotate at high speed by the driving force of the rotary polygon mirror driving motor 115.

The laser beam 110 is applied to the rotating polygon mirror 11.
4 is deflected and scanned, and the photosensitive member 1 passes through the fθ lens 116.
04 is scanned at a constant speed to form an electrostatic latent image corresponding to the image signal.

Further, in the vicinity of the photoconductor 104, the photoconductor 10
A position detection sensor 118 is arranged in the laser beam scanning area and outside the area of the photoconductor 104 in order to detect a main scanning write timing signal for obtaining a write timing in the main scanning direction on the main scanning direction 4. The position detecting sensor 118 receives the light reflected by the mirror 117. The writing timing signal in the main scanning direction is also supplied to the rotary polygon mirror driving motor 115,
Used as a PLL comparison clock in the motor.

As shown in FIG. 2, an intermediate transfer member 120 is provided below each of the image forming units 101 arranged in tandem so as to be in contact with the respective photosensitive members 104. The intermediate transfer member 120 is an endless belt-shaped member that is supported by being wound around three rollers 119, and is driven in a loop at a constant speed in the direction of arrow A in FIG. 2 by the driving force of a driving unit (not shown). It has become.

The intermediate transfer member 120 transfers all the single-color images of yellow, magenta, cyan, and black developed by the respective photoconductors 10 in a single pass to form a multicolor toner image. Recording paper 122 conveyed one by one from a tray (not shown) in the direction of arrow B in FIG.
To form a multicolor image on the recording paper 122.

Here, a sensor 124 is provided on the downstream side of the black image forming unit 101K located at the most downstream side in the transport direction of the belt 120.

The sensor 124 includes a light source, a photodetector, and the like, reads a specific pattern formed on the intermediate transfer member 120, and sends an electrical output to a registration control unit 128 shown in FIG.

FIG. 4 is a control block diagram of the image forming apparatus 100 applied to the present embodiment.

The rotating polygon mirror driving motor 115 has an FG
The sensor 129 is provided, and the rotating polygon mirror driving motor 11 is provided.
A pulse signal (comparison clock) synchronized with the rotation speed of No. 5 is generated. This comparison clock is input to the selector 130.

The selector 130 is also supplied with a main scanning direction write timing signal detected from the position detection sensor 118.

The selector 130 is connected to the PLL control unit 132, and selectively sends out a main scanning direction write timing signal or a comparison clock to the PLL control unit 132.

The reference clock from the reference clock generator 126 is input to the PLL controller 132 via a clock change controller 136.
Further, the PLL control unit 132 is connected to the motor control circuit 134 and outputs a speed control signal for controlling the motor drive speed to the motor control circuit 134. As a result, the rotating polygon mirror driving motor 115
Control is always performed at an appropriate rotation speed and an appropriate phase.

That is, the reference clock supplied from the reference clock generating means 126 and the write timing signal in the main scanning direction detected from the position detection sensor 118 are used as P
The rotary polygon mirror 114 is accurately rotated at a constant speed by the LL control.

Here, in the clock change control unit 136,
It has the function of changing the frequency of the reference clock generated by the reference clock generator 126 based on the signal input from the registration controller 128.

This change is output at the image recording interval on the recording paper 122, transferred to the intermediate transfer member 120, and read by the sensor 124 (see FIG. 6).
It is made based on.

When the frequency of the reference clock is changed, P
The LL control unit 136 controls the rotation speed of the rotary polygon mirror driving motor 115 based on the changed frequency of the reference clock. Thereafter, when the frequency of the reference clock is returned to the original frequency, the rotating polygon mirror driving motor 11
5 returns to the original rotation speed, but its phase is shifted. By this phase shift, it becomes possible to control the write timing of each color to coincide.

The operation of this embodiment will be described below. As shown in FIG. 5, in the initial state, the phases of the reference clock supplied from the reference clock generating means 126 to the rotary polygon mirror driving motor 115 are the same for all four colors. The phases of the signals are also aligned. Therefore, the image writing timing in the sub-scanning direction is also a basic timing according to the distance between the photoconductors 104.

Here, as an example, it is assumed that a specific pattern formed on the intermediate transfer member 120 is as shown in FIG. The patterns of the respective colors should be superimposed originally, and the output of the respective colors is delayed for a predetermined time as a test pattern.

In this example, the timing for starting to write cyan is slightly earlier. That is, as shown in FIG. 6, the relationship between the widths KC (dimension c)> MC (dimension a)> YM (dimension b) is given in terms of the width of the sub-scan.

The sensor 124 detects this pattern, and sends the detection timing of each color toner image to the registration control unit 128.

Registration control section 128
Receives the output from the sensor 124, calculates the correction amount of one line or less of the write timing in the sub-scanning direction of cyan,
The correction amount data is output to the reference clock changing unit 136.

The reference clock changing section 136 receives the cyan correction amount data from the registration control section 128 and sets a frequency profile for controlling the reference clock of the rotary polygon mirror driving motor 115 of the cyan image forming unit 101C. After that, the reference clock of the rotary polygon mirror driving motor 115 is changed by the clock changing unit 136 according to the sub-scanning direction writing position correction frequency profile of the cyan image forming apparatus set by the correction execution command from the registration control unit 128, and the cyan image is changed. The writing position in the sub-scanning direction of the forming unit is corrected.

Next, the details of the correction frequency profile will be described with reference to FIG. In addition,
FIG. 7A shows a conventional example, and FIG. 7B shows this embodiment. In both cases, the vertical axis indicates frequency, and the horizontal axis indicates time.

When the frequency of the reference clock is changed once, when the correction execution command is received as shown in FIG. 7A, the frequency is first changed from time T1 to T2. Thereby, the rotating polygon mirror drive motor 18 decelerates to change its rotation speed to the rotation speed corresponding to the changed frequency. Next, at time T2, the frequency is returned to the steady rotation frequency for a period of ΔT. As a result, the rotating polygon mirror driving motor 115 accelerates to return to the steady rotation frequency.

However, the motor follows the change in frequency with a large delay due to its own large mechanical time constant, and further exceeds the control target value. The control amount of the rotation phase of the rotary polygon mirror 8 to be changed by the first frequency change is an area S surrounded by the changed frequency and the changed time.
However, in practice, a larger amount of phase moves than S1 due to the delay (S1a). This S1 and S1a
In order to return the difference ΔS1, the motor continues to accelerate even if it exceeds the steady rotation frequency, resulting in a large overshoot. S
The rotation overshoot for returning the difference ΔS1 between 1 and S1a returns the rotation phase to the difference ΔS1 or more due to the mechanical time constant (S1b). To return this again, an undershoot occurs this time. As described above, the number of revolutions gradually converges to the steady-state rotation frequency while repeating the overshoot and the undershoot, but it takes a long time to wait for this.

Therefore, as shown in FIG. 7B, the second frequency change is executed at the timing when the first overshoot occurs when returning to the normal rotation.

By executing the frequency change for the second time, the overshoot of the rotation can be suppressed, and the rotation can be settled to the steady rotation speed quickly. As shown in FIG. Is done.

At this time, the rotation phase change amount of the total to be changed is represented by S2 + S2b, and the actual phase change amount is S2a.
-S2c. It goes without saying that S2 + S2b = S2a-S2c.

The rotation polygon mirror drive motor 115 is driven by a variation in parts and a variation in assembly due to the assembly of the rotation polygon mirror drive motor 115.
The actual rotation frequency change of each rotary polygon mirror drive motor 1
15 may make a difference. Therefore, the time ΔT for determining the timing of the second frequency change may be changed by the rotary polygon mirror driving motor 18. However, the variation of the time ΔT is not large, and the rotation is performed by executing the timing of the second frequency change when the rotation frequency change of the rotary polygon mirror 114 reaches a predetermined frequency Fs as shown in FIG. The individual difference of the polygon mirror driving motor 115 can be absorbed.

Therefore, the rotation frequency of the rotary polygon mirror 8 is monitored by the timing signal for writing in the main scanning direction and the like.
Is desirably executed when the rotation frequency reaches the timing at which the second frequency change should be performed.

The first frequency change period (T1) shown in FIG.
The length of the second frequency change period (T3 → T4) and the length of the second frequency change period (T3 → T4) depend on the phase amount to be changed and the rotating polygon mirror driving motor 115.
An optimal time interval may be selected based on the mechanical time constant of the control and the amount of overshoot during control.

In the present embodiment, the description has been made on the basis of deceleration of the rotary polygon mirror driving motor, that is, the direction of delaying the rotation phase of the rotary polygon mirror. However, as in this embodiment, the phase is delayed over the entire control range. Control may be performed as described above, or control may be performed to advance the phase over the entire control range (when the phase is advanced, it is basically based on the fact that the rotating polygon mirror driving motor accelerates). Further, the leading direction control and the trailing direction control of the phase may be selectively used according to the control amount of the rotational phase.

Although the description has been made by limiting the frequency of the period ΔT between the first and second frequency changes to the steady rotation frequency, the frequency of the ΔT is a frequency close to the steady rotation (steady rotation frequency ± steady rotation frequency). If the difference is less than the minimum value of the difference between the change frequency and the change frequency), the setting does not change so much that the settling time can be shortened as in the embodiment.

By using the control method and the control frequency profile as described above, it is possible to shorten the rotation settling time of the rotary polygon mirror driving motor during the rotation phase control of the rotary polygon mirror with simple control. .

In this embodiment, a system having four image forming units has been described. However, the present invention is also applicable to a system having one, two or three image forming units.

[0076]

As described above, the multi-color image forming apparatus and method according to the present invention provide a rotary polygon mirror driving motor for driving a rotary polygon mirror with a simple configuration during rotation phase control without performing complicated control. Can reduce the settling time until the rotation speed converges to the steady rotation speed, and the rotation phase control of the rotating polygon mirror can be performed in a short time, so during continuous printing without impairing the output capability of the print image. Registration correction can be realized without interrupting the print job.

[Brief description of the drawings]

FIG. 1 is an example showing a reference clock frequency change profile for controlling a rotation phase of a rotating polygon mirror and a rotation fluctuation.

FIG. 2 is a schematic configuration diagram of a multicolor image forming apparatus to which the present invention is applied.

FIG. 3 is a schematic configuration diagram of an optical scanning device in a multicolor image forming apparatus to which the present invention is applied.

FIG. 4 is a schematic block diagram of a multicolor image forming apparatus to which the present invention is applied.

FIG. 5 is a timing chart showing a phase change of a main-scanning-direction writing timing signal due to rotation phase control of the rotary polygon mirror.

FIG. 6 is an example showing an example of a toner image for detecting a writing start timing in the sub-scanning direction.

FIG. 7 is a schematic diagram showing an example of a reference clock frequency change profile for controlling a rotation phase of a rotary polygon mirror, a schematic rotation variation, and a control amount;

FIG. 8 is a schematic diagram showing the timing of the second frequency change.

9A is a conventional example in which the rotation phase of a rotary polygon mirror is controlled to control the writing start position in the sub-scanning direction, and FIG. 9B is a schematic diagram illustrating the rotation fluctuation of the rotary polygon mirror in FIG. 9A. It is.

FIG. 10 shows another conventional example in which the rotation phase of a rotary polygon bell is controlled to change the writing start position in the sub-scanning direction.

FIG. 11 is another conventional example in which the rotation phase of a rotary polygon mirror is controlled to change the writing start position in the sub-scanning direction.

FIG. 12 shows another conventional example in which the rotation phase of a rotary polygon mirror is controlled to change the writing start position in the sub-scanning direction.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 Image forming unit 102 Optical scanning device 104 Photoconductor 108 Laser light source 110 Laser beam 112 Collimator lens 114 Rotating polygon mirror 115 Rotating polygon mirror driving motor 116 fθ lens 117 Mirror 118 Position detection sensor 120 Intermediate transfer body 122 Recording paper 124 Sensor 126 Reference Clock generation unit 128 Registration control unit 129 FG sensor 130 Selector 132 PLL control unit 134 Motor drive circuit 136 Clock change unit

Claims (5)

[Claims] 1. A comparison clock generated according to a driving speed of a rotary polygon mirror driving motor for driving a rotary polygon mirror mounted on a multicolor image forming apparatus is compared with a predetermined reference clock. When the driving speed is controlled by changing the reference clock, the driving speed of the rotary polygon mirror driving motor is changed by changing the reference clock, and the write start position of each color in the sub-scanning direction is adjusted to prevent color shift of the output image. A multicolor image forming apparatus having a registration control, wherein a reference clock frequency changing unit that changes a frequency of a reference clock supplied to the rotary polygon mirror driving motor; and The frequency of the reference clock is changed two or more times, and the frequency of the reference clock is changed to the steady rotation frequency at intervals of each frequency change period. And then, multi-color image forming apparatus having a rotation phase control means for controlling the rotational phase of said rotary polygonal mirror. 2. A comparison clock generated according to a driving speed of a rotary polygon mirror driving motor for driving a rotary polygon mirror mounted on a multicolor image forming apparatus is compared with a predetermined reference clock. When the driving speed is controlled by changing the reference clock, the driving speed of the rotary polygon mirror driving motor is changed by changing the reference clock, and the write start position of each color in the sub-scanning direction is adjusted to prevent color shift of the output image. In the registration control, during the rotation phase control of the rotating polygon mirror, the frequency of the reference clock supplied to the rotating polygon mirror driving motor is changed in order to change the rotation speed of the rotating polygon mirror driving motor, and then the rotation is once performed. At the predetermined timing, the frequency is further changed in the same frequency increasing / decreasing direction as that of the first frequency change, and thereafter the steady rotation frequency is changed. Controlling the rotation phase of the rotary polygon mirror back to a multicolor image forming method, wherein a. 3. The overshoot or undershoot that deviates from the first steady-state rotation that occurs when the predetermined timing returns to the steady-state rotation from the rotation fluctuation due to the first frequency change of the rotating polygon mirror is suppressed. 3. The multicolor image forming method according to claim 2, wherein the timing is optimal. 4. The control of increasing or decreasing the frequency of the reference clock so as to decelerate the motor when the phase is advanced and to increase the motor when the phase is delayed. Or the multicolor image forming method according to claim 3. 5. The frequency between each frequency change of the reference clock supplied to the rotary polygon mirror drive motor during the rotation phase control of the polygon mirror, wherein the frequency between the frequency change and the difference between the frequency to be changed and the normal rotational frequency is different from the steady rotational frequency. 5. An increase / decrease range that is less than the minimum value.
Item.