JPH07281536A - Color image forming device - Google Patents

Abstract

PURPOSE:To achieve highly accurate superimposition of monochromatic images in separate colors without causing exposure displacement in the direction of subscaning. CONSTITUTION:A color image forming device is equipped with an intermediate transfer body to which a developed monochromatic image on a photoreceptor is transferred; a detecting means by which a mark on the intermediate transfer body is detected in a prescribed position; and a control means which makes a latent image forming means start to form an electrostatic latent image in response to the timing of the mark detection by the detecting means. The color image forming device is provided with rotation phase control means 50 which controls the rotation phase of a rotary polygon mirror in response to the timing of the mark detection by the detecting means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus such as a color copying machine, a color printer or a color facsimile.

[0002]

2. Description of the Related Art Conventionally, as a color image forming apparatus, a belt-shaped photosensitive member is rotated and uniformly charged by a charging device, and a light beam corresponding to an image forming signal of one color plate is deflected and scanned by a rotating polygon mirror. While exposing, an electrostatic latent image corresponding to the image forming signal of one color plate is formed, and this electrostatic latent image is visualized by a developing unit with a developer of a color corresponding to that color plate, and an intermediate image is formed. An image forming operation of transferring to a transfer body is performed for each image forming signal of each color plate, and a visualized single color image of each color plate is superimposed and transferred onto an intermediate transfer belt to form a full color image and recorded. In a color image forming apparatus for collectively transferring onto paper, a triangular mark is provided on a belt-shaped photoconductor, and mark detection means for detecting the mark by a laser beam is provided at a predetermined position to obtain an image form for each color plate. An image with no color misregistration by controlling the rotation phase of the rotary polygon mirror with reference to the timing at which the mark detection means detects a mark for each exposure with the light beam corresponding to the signal, and controlling the exposure start timing in the sub-scanning direction. A method for obtaining the above is disclosed in JP-A-4-335665.

[0003]

In the color image forming apparatus described above, a single color image of a plurality of color plates is superposed and transferred onto the intermediate transfer belt, and then transferred collectively onto the recording paper. The superimposition of the single-color images for each of them always causes a deviation because the circumferential length of the intermediate transfer belt and the scanning interval of the rotary polygon mirror are not in an integral multiple relationship. For this reason, the superimposition of the monochromatic images of the respective color plates theoretically causes a shift amount of one line.

The present invention provides a color image forming apparatus which solves the above problems and is capable of superimposing a single color image of each color plate with high precision without causing an exposure position shift in the sub-scanning direction. With the goal.

[0005]

In order to achieve the above object, the invention according to claim 1 has a photosensitive member which is rotated and a rotary polygon mirror which is rotated by a rotary polygon mirror driving device. Latent image forming means for forming an electrostatic latent image corresponding to the image forming signal of each color on the body by deflecting and exposing a light beam corresponding to the image forming signal of each color by the rotating polygon mirror, and each color on the photoconductor. Developing means for developing an electrostatic latent image corresponding to each image forming signal with the developer of each color, and an intermediate transfer body for transferring the visualized single-color image on the photoconductor. And a detection means for detecting a mark provided on the intermediate transfer member at a predetermined position, and a control means for causing the latent image forming means to start forming an electrostatic latent image at the mark detection timing of the detection means. In the color image forming apparatus, the detection The mark detection timing of the stage in which with a rotational phase control means for controlling the rotational phase of said rotary polygonal mirror.

According to a second aspect of the present invention, in the color image forming apparatus according to the first aspect, formation of the electrostatic latent image is started after a certain period of time from the mark detection timing of the detection means.

According to a third aspect of the present invention, in the color image forming apparatus according to the first aspect, the detecting means is a reflection type photo sensor.

According to a fourth aspect of the present invention, in the color image forming apparatus according to the first aspect, the rotational phase control means controls the rotational phase of the rotary polygonal mirror to detect the mark of the rotary polygonal mirror when the mark is detected by the detection means. The rotational phase matching period of the rotary polygon mirror is changed according to the rotational phase shift amount.

According to a fifth aspect of the present invention, in the color image forming apparatus according to the first aspect, the rotation phase control means does not deviate from the phase control range of the rotary polygon mirror driving device by controlling the rotation phase of the rotary polygon mirror. The rotation phase of the rotary polygon mirror is changed within a range.

According to a sixth aspect of the present invention, in the color image forming apparatus according to the first aspect, the rotational phase control means controls the rotational phase of the rotary polygon mirror in a direction to follow a target phase.

According to a seventh aspect of the present invention, in the color image forming apparatus according to the second aspect, a reference serving as a rotation phase reference of the rotary polygon mirror driving device in which the control means starts oscillation by detecting a mark by the detection means. The number of signals is counted to manage the time from the mark detection timing of the detection means to the start of formation of the electrostatic latent image.

According to an eighth aspect of the present invention, in the color image forming apparatus according to the first aspect, the rotation phase control period of the rotary polygon mirror includes a phase difference detection period and a phase matching period.

According to a ninth aspect of the present invention, in the color image forming apparatus according to the first aspect, a reference signal serving as a rotation phase reference of the rotary polygon mirror is a divisor of the number of mirror surfaces of the rotary polygon mirror or a pulse for each rotation. It is a signal.

[0014]

According to the present invention, the photosensitive member rotates, and the latent image forming means deflects the light beam corresponding to the image forming signal of each color by the rotary polygon mirror rotated by the rotary polygon mirror driving device. The photoconductor is exposed to form an electrostatic latent image corresponding to the image forming signal of each color. The plurality of developing units visualize the electrostatic latent images corresponding to the image forming signals of the respective colors on the photoconductor with the developers of the respective colors, and the intermediate transfer member rotates to visualize the monochromatic image on the photoconductor. Is transcribed. The detection means detects the mark on the intermediate transfer body at a predetermined position, and the control means causes the latent image forming means to start forming an electrostatic latent image at the mark detection timing of the detection means. The rotation phase control means controls the rotation phase of the rotary polygon mirror according to the mark detection timing of the detection means.

According to a second aspect of the present invention, in the color image forming apparatus according to the first aspect, the electrostatic latent image formation is started after a certain period of time from the mark detection timing of the detection means.

According to a third aspect of the present invention, in the color image forming apparatus according to the first aspect, the detecting means including a reflection type photosensor detects the mark on the intermediate transfer member at a predetermined position.

According to a fourth aspect of the present invention, in the color image forming apparatus according to the first aspect, the rotary phase control means controls the rotary phase of the rotary polygon mirror to detect the mark of the detecting means. Changes the rotational phase matching period of the rotary polygon mirror.

According to a fifth aspect of the present invention, in the color image forming apparatus according to the first aspect, the rotation phase control means rotates within a range that does not deviate from the phase control range of the rotary polygon mirror driving device by the rotation phase control of the rotary polygon mirror. The rotation phase of the polygon mirror is changed.

According to a sixth aspect of the present invention, in the color image forming apparatus according to the first aspect, the rotation phase control means performs the rotation phase control of the rotary polygon mirror in a direction to follow the target phase.

According to a seventh aspect of the present invention, in the color image forming apparatus according to the second aspect, the control means counts a reference signal serving as a rotational phase reference of the rotary polygon mirror driving device which starts oscillation upon detection of a mark by the detection means. Then, the time management from the mark detection timing of the detection means to the start of the electrostatic latent image formation is performed.

According to an eighth aspect of the present invention, in the color image forming apparatus according to the first aspect, the rotation phase control period of the rotary polygon mirror includes a phase difference detection period and a phase matching period.

According to a ninth aspect of the present invention, in the color image forming apparatus according to the first aspect, the reference signal serving as a rotation phase reference of the rotary polygon mirror is a divisor of the number of mirror surfaces of the rotary polygon mirror or a pulse signal for each rotation. is there.

[0023]

FIG. 2 shows the outline of the first embodiment of the present invention. The first embodiment is an embodiment of the invention described in claims 1-9. In FIG. 2, reference numeral 1 denotes a flexible belt-shaped photosensitive member which is a belt-shaped image carrier, and the belt-shaped photosensitive member 1 is installed between rotating rollers 2 and 3 and driven by the rotating roller 2. Rotate in the sub-scanning direction (clockwise).

Reference numeral 4 is a charging member composed of a charging roller which is a charging means, and 5 is a laser writing system unit which is an image exposure means.
Denoted at 6 to 9 are developing units, which are provided in the rotary developing device and serve as a plurality of developing means respectively accommodating developers of different specific colors. The laser writing system unit 5 is incorporated in the main body of the apparatus by being housed in a holding housing having a slit-shaped exposure opening on the upper surface. The charging member 4 as a charging unit and the laser writing system unit 5 as an image exposure unit form a latent image forming unit.

For the laser writing system unit 5, an optical system in which a light emitting portion and a converging optical transmission body are integrated is used in addition to the optical system shown in the figure. The charging member 4, a portion of the laser writing system unit 5 that irradiates the belt-shaped photoconductor 1 with the laser writing light 5D, and the photoconductor cleaning device 15 include a plurality of rollers 2 and 3 that bridge the belt-shaped photoconductor 1. Is provided in the vicinity of one roller 2.

Each of the developing units 6, 7, 8 and 9 contains a developer having a yellow toner, a magenta toner, a cyan toner, and a black toner, respectively, and is close to the belt-shaped photoreceptor 1 at a predetermined position. Alternatively, it is provided with a developer carrying member composed of a developing sleeve which comes into contact with the developing roller, and has a function of visualizing an electrostatic latent image on the photosensitive belt 1 by non-contact development or a contact development method. Reference numeral 10 denotes an intermediate transfer member which is a transfer image carrier, and the intermediate transfer member 10 includes rotating rollers 11 and 12.
It is composed of an intermediate transfer belt which is installed between the two and is driven by one of the rotating rollers to rotate counterclockwise.

The belt-shaped photoreceptor 1 and the intermediate transfer belt 10 are in contact with each other at the rotating roller 3, and the intermediate transfer belt 10
A transfer bias is applied from a high-voltage power source to the bias roller 13 that is in contact with the inside of the sheet, and a single color image of one color plate formed on the belt-shaped photoreceptor 1 for the first time is transferred onto the intermediate transfer belt 10. It Similarly, the monochromatic images of the other color plates formed on the belt-shaped photoconductor 1 in the second to fourth times are superimposed on the monochromatic image of the one color plate formed in the first time on the intermediate transfer belt 10. It is transferred so as not to be displaced.

The transfer roller 14 constituting the transfer means is provided so as to come into contact with and separate from the intermediate transfer belt 10 by a contacting / separating mechanism. Reference numeral 15 is a photoconductor cleaning device that cleans the belt-shaped photoconductor 1, and 16 is an intermediate transfer belt cleaning device that cleans the intermediary transfer belt 10.
6A is an intermediate transfer belt 1 during image formation by a contact / separation mechanism.
The surface of the intermediate transfer belt 10 is kept apart from the surface of No. 0 and is pressed against the surface of the intermediate transfer belt 10 as shown in the figure only during cleaning after image transfer.

The color image forming process by the color image forming apparatus of the first embodiment is carried out as follows. First, the formation of a multicolor image according to this embodiment is performed according to the following image forming system. That is, the image reading device scans an original image and reads it with an image sensor, and the read color image data is arithmetically processed by an image data processing unit to obtain image data of each color, that is, image data of yellow, magenta, cyan, and black. Is created and is once stored in the image memory.

Next, the laser writing system unit 5 in the color image forming apparatus of the present embodiment, which is a recording portion, is formed by recording the image data of each color from the image memory at the time of recording.
Is input as an image forming signal of each color. That is, the image data of each color output from the image reading apparatus separate from the color image forming apparatus of this embodiment is sequentially input to the laser writing system unit 5.

In the laser writing system unit 5,
The rotary polygon mirror drive device 5A composed of a drive motor rotationally drives the rotary polygon mirror 5B, and the semiconductor laser 5E (see FIG. 7) is modulated and driven by the drive portion by the image data of each color sequentially input from the image reading device. A laser beam whose intensity changes according to the image data of each color is generated.
This laser beam is deflected and scanned by the rotary polygon mirror 5B, passes through the fθ lens 5C, the optical path is bent by the mirror 5G, and is irradiated onto the peripheral surface of the belt-shaped photoreceptor 1.

The belt-shaped photosensitive member 1 is discharged by the discharging lamp 21 and uniformly charged by the charging roller 4, and then exposed by the laser beam 5D from the mirror 5G to form an electrostatic latent image corresponding to the image signal of each color. Are sequentially formed. A bias is applied to the charging roller 4 from the power source to uniformly charge the belt-shaped photoreceptor 1, and the laser writing system unit 5 exposes the belt-shaped photoreceptor 1 with an image pattern of a desired full-color image of yellow. It is an image pattern of a single color when separated into magenta, cyan and black.

The electrostatic latent images corresponding to the image signals of the respective colors sequentially formed on the belt-shaped photoreceptor 1 are revealed by the development by the yellow, magenta, cyan and black developing units 6 to 9 in the rotary developing unit. The color is converted into a monochromatic image of each color. The developing unit 6 rotates to move to a developing position when an electrostatic latent image corresponding to a yellow image signal is formed on the belt-shaped photoconductor 1 to develop the electrostatic latent image into a yellow monochromatic image. Similarly, when the electrostatic latent images corresponding to the magenta, cyan, and black image signals are formed on the belt-shaped photosensitive member 1, the other developing units 7 to 9 are rotated to move to the developing position and the magenta, The cyan and black electrostatic latent images are developed to form magenta, cyan, and black single-color images, respectively.

A transfer bias is applied to the intermediate transfer belt 10 from a high voltage power supply through a bias roller 13, and yellow, magenta, and
The cyan and black monochromatic images are transferred one after another onto the intermediate transfer belt 10 rotating counterclockwise while contacting the belt-shaped photoreceptor 1. A yellow, magenta, cyan, and black single-color image is superimposed and transferred onto the intermediate transfer belt 10 to form a full-color image, which is fed from the paper feed table 17 by the paper feed roller 18 and registered by the registration roller 19. The image is transferred by the transfer roller 14 to the transfer sheet that has been conveyed to the transfer section through the.

The image of this transfer paper is fixed by the fixing device 20 to complete a full-color image, and is discharged to the tray 23. The intermediate transfer belt 10 and the belt-shaped photoreceptor 1 are seamless. The belt-shaped photoconductor 1 is cleaned by the photoconductor cleaning device 15 after the monochromatic images of yellow, magenta, cyan, and black are transferred to the intermediate transfer belt 10, and the intermediate transfer belt 10 is transferred after the image is transferred to the transfer paper. It is cleaned by the intermediate transfer belt cleaning device 16.

FIG. 3 is an enlarged view showing a part of this embodiment. Six marks 41 are provided on the end of the intermediate transfer belt 10.
A to 41F are provided at predetermined intervals, and the detection unit 40 including a mark detection sensor detects the marks 41A to 41F on the intermediate transfer belt 10 on the downstream side of the rotating roller 12 in the rotation direction of the intermediate transfer belt 10. The mark detection sensor 40 is composed of a reflective photo sensor composed of a reflective photo interrupt.

The mark detection sensor 40 has six marks 41.
Any mark of A to 41F, for example mark 41A
The laser writing system unit 5 starts writing the image of the first color on the belt-shaped photosensitive member 1 (exposure by the laser beam corresponding to the yellow image signal) by detecting the mark, and the mark 41A makes one round and the mark detection sensor is detected again. When 40 detects the mark 41A, writing of the image of the second color (exposure by the laser beam corresponding to the magenta image signal) is started.

At this time, the mark 4 of the mark detection sensor 40
The detection signals for 1B to 41F are the mark detection sensor 40.
By the management of the number of marks detected in step 3, a mask is applied so that the marks cannot be used as image writing timing. The density detecting means 22 composed of a P sensor is installed facing the upstream side in the rotation direction of the photoconductor belt 1 with respect to the portion of the photoconductor belt 1 in contact with the intermediate transfer belt 10, and optically detects the amount of toner on the photoconductor belt 1. To detect.

FIG. 8 shows the configuration of the position information detecting section of this embodiment. The mark detection signal from the mark detection sensor 40 is
The clock signal INP is input to the interrupt terminal of the control means 47 including a CPU (microcomputer having a central processing unit) that controls the sequence control, and is a down counter for counting the number of mark detection signals inside the CPU 47.

The CPU 47 causes the down counter to become 0 when the number of marks detected by the mark detection sensor 40 reaches the set value n (a certain period of time has elapsed after the mark detection sensor 40 detected the mark 41A). A write permission signal ENB for starting image writing by the laser writing system unit 5 is output to the NOR gate 48, and a mark detection signal from the mark detection sensor 40 to the laser writing system unit 5 is gated by the NOR gate 48, and an output signal of the NOR gate 48. Is a write start signal for the laser writing system unit 5.

FIG. 5 shows an operation flow relating to position information detection of this embodiment. When the present embodiment is in the print enable state, the CPU 47 determines in step 100 the input signal INP.
Mark detection sensor 40 is the first mark 41A from the state of
It is determined whether or not is detected. If the mark detection sensor 40 does not detect the mark 41A, the CPU 47 returns to step 100 and repeats step 100 until the mark detection sensor 40 detects the mark 41A.

It goes without saying that the CPU 47 sets the write enable signal ENB to the enable state "L (low level)" in the state where the mark detection sensor 40 does not detect the mark 41A. In the CPU, the mark detection sensor 40 has a mark 41A.
If it is detected, the process proceeds to the next step 101, 5 is set as the set value in the internal down counter, and at the same time, the write enable signal ENB is set to the mask state enable state "H (high level)", and the NOR gate 48 is set in step 102. From this, a write start signal is input to the laser writing system unit 5.

Next, the CPU 47 sets 1 in step 103.
It is determined whether or not the monochromatic image formation on the printing plate is completed, and if the monochromatic image formation on the one printing plate is not completed, step 103 is repeated. If the monochromatic image formation on the one printing plate is completed, the process proceeds to step 104. In step 104, the CPU 47 determines whether or not the monochromatic image formation of all printing plates is completed. When the monochromatic image formation of all printing plates is completed, the process relating to the position information detection is completed, and the monochromatic image formation of all printing plates is completed. If not, the routine proceeds to step 105, where it is judged whether or not the value of the down counter has become zero. If the value of the down counter is not 0, the CPU 47 repeats step 105, and when the value of the down counter becomes 0, the process returns to step 100. As a result, the mark detection sensor 40 becomes
The laser writing system unit 5 starts the exposure of each color plate every time the detection is performed.

The CPU 47 determines whether or not the monochromatic image formation on the first printing plate is completed, based on whether or not the down count value becomes 0 due to the countdown by the down counter in the interrupt routine shown in FIG. In this interrupt routine, the mark detection signal from the mark detection sensor 40 is "L" while the CPU 47 is executing the routine shown in FIG.
When the interrupt routine is completed, the CPU 47 returns to the place where the routine shown in FIG. 5 is exited and executes the continuation of the routine shown in FIG.

In this interrupt routine, the CPU 47 causes the mark detection sensor 40 to move the mark 4 to the mark 4 in step 106.
The mark 4 detected by the mark detection sensor 40 is decremented by 1 each time 1A to 41F is detected.
The number of 1A to 41F is counted, and in step 107 it is judged whether or not the value of the down counter has become 0. If the value of the down counter is not 0, the interrupt routine is ended. The CPU 47, when the value of the down counter becomes 0,
In step 108, the mask state is reset to set the write enable signal ENB to the enable state "L", and the interrupt routine is ended.

FIG. 4 shows the structures of the marks 41A to 41F and the mark detection sensor 40. White marks are printed as marks 41A to 41F near the ends of the intermediate transfer belt 10. The marks 41A to 41F are arranged at substantially equal intervals, but the accuracy may be rough. In the mark detection sensor 40, the intermediate transfer belt 10 has the rotating roller 1
The marks 41 </ b> A to 41 </ b> F are detected by being provided in the vicinity of the portion in contact with 2 and irradiating the intermediate transfer belt 10 with light and detecting the reflected light.

FIG. 7 shows a schematic structure from the laser writing system unit 5 to the mark detection sensor 40. When a color signal output from an image reading apparatus separate from the color image forming apparatus of this embodiment is input to the laser writing system unit 5, the semiconductor laser 5E in the laser writing system unit 5 is driven by the color signal. A laser beam having a strength corresponding to the color signal is generated by being modulated and driven by the section. This laser beam is rotationally scanned in the main scanning direction by a rotary polygon mirror (hereinafter referred to as a polygon mirror) 5B rotated by a rotary polygon mirror driving device including a polygon motor 5A, and an optical path is bent by a mirror 5G via an fθ lens 5C. The belt-shaped photoconductor 1 is irradiated with the light.

At this time, the laser beam scanned in the main scanning direction by the polygon mirror 5B is detected by the synchronization detecting sensor 5F before being irradiated on the photosensitive member 1 in one main scanning. The output signal of 5F is used as a synchronizing signal in the main scanning direction for image writing.
The polygon motor 5A rotates in synchronization with the motor synchronization signal, and the phase of this motor synchronization signal and the rotation phase of the polygon motor 5A are synchronized. The polygon mirror 5B has eight mirror surfaces, and the motor synchronization signal is two pulses per one rotation of the polygon mirror 5B.

FIG. 1 shows a part of this embodiment. The phase matching unit 50 receives the mark detection signal from the mark detection sensor 40 and the clock from the oscillator 51, divides the clock from the oscillator 51 as a source signal, and outputs it as a motor synchronization signal. The rotation speed and rotation phase of the polygon motor 5A are synchronously controlled by the PLL control unit in accordance with a motor synchronization signal from the phase matching unit 50.

In this embodiment, a signal obtained by dividing the clock from the oscillator 51 by 64 is the motor synchronizing signal. That is, when the clock cycle of the oscillator 51 is tc, the cycle tp of the motor synchronization signal is tp = 64 * tc. The phase matching unit 50 uses the rising edge of the mark detection signal from the mark detection sensor 40 as a rotation synchronization trigger and changes the phase of the motor synchronization signal in order to reset the rotation phase of the polygon motor 5A.

FIG. 9 shows the structure of the phase matching section 50. The mark detection signal from the mark detection sensor 40 is input to the flip-flop (F / F) 50A. F / F50A is
The output signal is set to "H" by the mark detection signal, and reset by the reset signal from the differentiating circuit 50B to become "L". Differentiating circuit 50B is 2
One pulse of the clock CK from the oscillator 51 is output in response to the rising edge of the motor synchronization signal from the frequency divider 50H. The output signal of the F / F 50A is the up counter 50C.
It is input to the clear terminal of.

The up counter 50C counts up the clock CK from the oscillator 51 when the output signal of the F / F 50A becomes L and the output signal becomes "0", and when the output signal of the F / F 50A becomes H. . That is, the up counter 50C starts the counting operation at the rising edge of the mark detection signal from the mark detection sensor 40, and the up counter 50C stops the counting operation at the subsequent rising edge of the motor synchronization signal to set the count value to "0". And

At this time, the final count value of the up counter 50C is latched in the down counter 50D at the falling edge of the output signal of the F / F 50A. The down counter 50D receives the motor synchronization signal from the frequency divider 50H as a clock and performs a countdown operation,
When the count value becomes "0", the counting is stopped and this state is held until the latch of the last count value of the next up counter 50C.

Up counter 50E, subtractor (SUB)
The 50G, the magnitude comparator (MC) 50F, and the divide-by-2 frequency divider 50H generate a motor synchronizing signal. Normally, the input signal b from the down counter 50D to the SUB 50G is "0", and the set value is SUB5 as another input signal a.
When input to 0G, the SUB 50G outputs the difference (ab) between both input signals a and b to the MC 50F. Up counter 5
0E counts up the clock from the oscillator 51.

The MC 50F compares the output signal of the SUB 50G with the count value of the up counter 50E, and when the count value of the up counter 50E becomes the same as the output signal of the SUB 50G, the output signal becomes "H". The up counter 50E is reset when the output signal of the MC 50F is input as a reset signal and the output signal of the MC 50F becomes "H". The output signal of the MC 50F is frequency-divided by 2 by the frequency divider 50H and output as a motor synchronization signal with a duty ratio of 50%. Down counter 50D
Latches the count value of the up counter 50C, the output signal b becomes "1", and the output signal b is output to the SUB 50G. Therefore, the SUB50G
"1" of the output signal b of the down counter 50D is subtracted from the set value a and the result is output to the MC 50F.

FIG. 10 shows a timing chart of this embodiment. In FIG. 10, the stationary period is a period during which normal image exposure is performed, and the phase difference detection period is the phase of the previous plate motor synchronization signal (phase of the polygon motor 5A) used for image formation of the previous color plate. The up-counter 50C counts the phase difference from the mark detection signal from the mark detection sensor 40, and the phase matching period is the phase of the motor synchronization signal according to the count value of the up-counter 50C in the count period. It is a period to shift to.

The counting period is from the rising edge c of the mark detection signal to the first rising edge d of the previous version motor synchronizing signal, and the up counter 50C is oscillated during the counting period by the output signal of the F / F 50A as described above. Count the clocks from 51. The final count value CNT in the counting period of the up counter 50C is latched in the down counter 50D at the falling edge of the output signal of the F / F 50A.

The count value CNT has a count period of time t.
Then, CNT = t / tc. During the phase matching period, the output signal b of the down counter 50D becomes "1" and 2
The motor synchronization signal from the frequency divider 50H is switched to a phase synchronization pulse signal which starts oscillation at timing d during the phase matching period. That is, the up counters 50E and SUB5
The cycle of the pulse signal generated by 0G and MC50F changes when the output signal b of the down counter 50D changes from "0" to "1", and the motor synchronization signal from the frequency divider 50H becomes a phase synchronization pulse signal. Switch. This phase synchronization pulse signal is a reference signal that serves as a rotation phase reference of the rotary polygon mirror driving device, and is provided every time the polygon mirror 5B rotates by a rotation angle corresponding to a divisor of the number of mirror surfaces, or every time it makes one rotation. It is a pulse signal that is generated. The period td of the phase-locked pulse signal has a relationship of td = tp-tc.

In the phase matching period, the motor synchronizing signal is output by the count value CNT of the counting period and the down counter 50D
Output signal b from "1" to "0" is reached, and after the phase matching period elapses, the phase of the phase synchronization pulse signal is the next-version motor synchronization signal used for image formation of the next color plate. (The mark detection sensor 40 is in a constant state in synchronization with the timing of detecting the mark 41A on the intermediate transfer belt 10). The cycle td of the phase synchronization pulse signal has a relationship of td <tp, and the phase of the motor synchronization signal from the frequency divider 50H is the target phase (synchronized with the mark 41A detection timing of the mark detection sensor 40 during the phase matching period). The control is performed in a direction to follow the constant phase state of the motor synchronization signal.

At timing e, the motor synchronizing signal from the frequency divider 50H switches to the next-version motor synchronizing signal when the output signal b of the down counter 50D changes from "1" to "0", and enters the steady period. Therefore, the phase matching period is the up counter 50 in the counting period.
It changes according to the count value CNT of C, that is, it changes depending on the phase shift amount between the phase of the predecessor motor synchronization signal (the phase of the polygon motor 5A) and the mark detection signal from the mark detection sensor 40.

The motor synchronization signal is switched as described above, and the polygon motor 5A is driven by the polygon motor drive circuit by the motor synchronization signal from the frequency divider 50H. The rotation phase of the polygon mirror 5B depends on the phase change of the motor synchronization signal from the frequency divider 50H.
The rotational phase control period of the polygon mirror 5B changes with the rotational phase change of A, and includes a counting period and a phase matching period. Since the output signal b of the down counter 50D is always "1" and the phase change of the motor synchronizing signal is small during the phase matching period, the phase control of the motor synchronizing signal does not deviate from the phase control range of the rotary polygon mirror driving device. Done in.

When the number of marks detected by the mark detection sensor 40 reaches the set value n, the CPU 47 operates the down counter 5
When 0D becomes 0, the write enable signal ENB is output to the NOR gate 48 to raise the write start signal from the NOR gate 48, and the laser writing system unit 5 synchronizes the image data of each color plate in synchronization with the rising of the write start signal. The image exposure is started. It goes without saying that the phase matching period ends within the period in which the CPU 47 counts the number of marks detected by the mark detection sensor 40 to the set value n.

In the first embodiment, the mark detecting sensor 4
By controlling the rotational phase of the polygon mirror 5B with the mark detection timing of 0, the exposure position shift in the sub-scanning direction is eliminated without depending on the variation of the peripheral length of the intermediate transfer belt 10 and the variation of the feed speed, and the image of each color plate is The overlapping position can be adjusted with high accuracy. Further, since the latent image formation is started after a certain period of time from the mark detection timing of the mark detection sensor 40, the next image formation can be started at the stage when the rotation of the polygon motor 5A is stable, and the sub-scanning direction of the image of each color plate. The initial stacking position deviation does not occur.

Further, since the reflection type photo sensor is used as the mark detecting sensor 40, the image forming position of the intermediate transfer belt 10 can be arbitrarily set. Also, the polygon mirror 5B
In the rotational phase control, since the phase matching period is changed depending on the phase shift amount at the time of mark detection by the mark detection sensor 40, it is possible to disperse the load on the phase convergence and as a result to perform reliable and stable phase convergence. Further, since the rotational phase control of the polygon mirror 5B is performed within a range that does not deviate from the phase control range of the rotary polygon mirror driving device, there is no dead time required for phase convergence from outside the phase control.

Further, since the rotational phase control of the polygon mirror 5B is performed in a direction to follow the target phase, the rotational phase of the polygon mirror 5B makes a stable phase transition. Also,
Since the time control from the mark detection timing of the mark detection sensor 40 to the start of latent image formation is performed by counting the reference signal of the rotary polygon mirror driving device that starts oscillation by the mark detection of the mark detection sensor 40, the phase of the polygon motor 5A It is possible to start the latent image formation that suits. Further, the rotational phase control of the polygon mirror 5B is performed in the phase difference detection period,
Since it consists of the phase matching period, it can be performed accurately.
Further, since the reference signal serving as the rotation phase reference of the polygon mirror 5B is a pulse signal for every rotation of the polygon mirror 5B or every rotation, the scanning phase of the polygon mirror 5B is controlled by controlling the phase of the reference signal. It can be performed.

Next, a second embodiment of the present invention will be described. The second embodiment is an embodiment of the invention described in claims 1 to 9, and FIG. 11 shows a part of the second embodiment in an enlarged manner. In the second embodiment, the mark is not provided on the intermediate transfer belt 10 in the first embodiment, and the laser light emitted from the semiconductor laser 5E of the laser writing system unit 5 is
It is rotated and scanned by the polygon mirror 5B, the optical path is changed by the reflecting plate 5G, and the belt-shaped photosensitive member 1 on the rotating roller 2 is irradiated with the light.

At this time, the belt-shaped photosensitive member 1 is exposed by the laser writing system unit 5 to form an electrostatic latent image 41A of a mark which serves as intermediate transfer position information.
A is visualized by the developing sleeve 6A of the developing unit 6 and transferred to the intermediate transfer belt 10 by applying a transfer bias by the bias roller 13. The mark 41B rotates counterclockwise by the rotation of the intermediate transfer belt 10 and is detected by the reflective photosensor 40 to become an intermediate transfer belt position information signal. The laser beam from the reflector 5G is detected by the synchronization detection sensor 5F, and the output signal of this synchronization detection sensor 5F is used as the synchronization signal in the main scanning direction for image writing.

FIG. 12 is an enlarged view of the mark detecting sensor 40. Light-emitting diode 4 of mark detection sensor 40
0A irradiates light through the lens 40C at an angle of 45 degrees with respect to the vertical line of the surface of the intermediate transfer belt 10 on which the mark 41B is formed, and the phototransistor 40B of the light receiving portion of the mark detection sensor 40 is The reflected light is taken in through the lens 40D at an angle of 0 degree with respect to the perpendicular of the surface of the intermediate transfer belt 10 on which the mark 41B is formed. The diameter Φ1 of the light emission beam emitted from the light emitting diode 40A to the intermediate transfer belt 10 is larger than the diameter Φ2 of the light reception beam introduced into the phototransistor 40B from the intermediate transfer belt 10 and is set to about Φ1 = Φ2 * 2.

The light emitting diode 40A and the phototransistor 40B have one end connected to the + 5V terminal of the power supply 42 through the resistors 40E and 40F, respectively, and the other end connected to the ground terminal. Mark 41 on the intermediate transfer belt 10
Depending on the presence or absence of B, the phototransistor 40B is turned on / off, and the detection signal 43 is obtained. The detection signal 43 is input to the timer 49 and the gate 48, and the timer 49 starts clock counting at the falling edge of the detection signal 43 when the phototransistor 40B is turned on.

The CPU 47 monitors the count value of the timer 49, and according to the count value of the timer 49, the mask signal 46
Is input to the gate 48. The gate 48 outputs the detection signal 43 according to the mask signal 46, and the output signal of the gate 48 is output to the laser writing system unit 5 as the writing start signal 45 to start the image exposure. The diameter of the laser light from the laser writing system unit 5 is 80 μm, and the light receiving spot diameter Φ2 of the mark detection sensor 40 is 2 m.
As m, the variation in image exposure and the variation in developer riding are averaged so that there is no influence.

FIG. 13 shows the operation timing of this embodiment. The mark detection sensor 40 detects the mark 41B and also detects an image in the image area on the intermediate transfer belt 10. Therefore, the CPU 47 outputs the mask signal after the first mark 41B is detected by the mark detection sensor 40 and the timer 49 starts the counting operation.
The mask signal is released when the intermediate transfer belt 10 rotates for one round and reaches a position 10 mm ahead of the mark 41B on the intermediate transfer belt 10 in the rotation direction of the intermediate transfer belt 10 to the detection position of the mark detection sensor 40.

The point 10 mm ahead of the mark 41B on the intermediate transfer belt 10 in the rotation direction of the intermediate transfer belt 10 is between the end of the image area on the intermediate transfer belt 10 where the image is formed and the tip of the mark 41B. From the mark 41B on the intermediate transfer belt 10.
A place 10 mm forward in the rotation direction may be another place as long as it satisfies the condition that it is located between the end of the image area on the intermediate transfer belt 10 and the tip of the mark 41B. When the CPU 47 generates the mask signal as described above, the writing start signal 45 detects only the mark 41B on the intermediate transfer belt 10, and the normal color superposition of the images of the respective color plates is possible.

FIG. 14 shows a flow of distance measurement for one round of the intermediate transfer belt when the power is turned on. The CPU 47 controls the driving device that drives the photoconductor 1 and the intermediate transfer belt 10 in step 10 after the power is turned on to start driving the photoconductor 1 and the intermediate transfer belt 10. Next, the CPU 47
In step 11, the power source of the charging roller 4 is turned on so that the photosensitive member 1 is uniformly charged by the charging roller 4.

Next, in step 12, the CPU 47 causes the laser writing system unit 5 to start writing by image exposure of the mark, and in step 13 in accordance with the movement of the mark 41A, the developing unit, for example, the black developing unit 6 develops. The developing roller 6A is used as a driving device for rotating the roller 6A and the like.
Etc. start rotating. Next, the CPU 47 turns on the developing bias to the developing roller 6A to apply the developing bias to the developing roller 6A in step 14, and turns on the developing bias to the developing roller 6A to apply the transfer bias to the bias roller 13 in step 15. Turn on the transfer bias to.

The CPU 47 determines whether or not the intermediate transfer belt 10 has rotated by the distance at which the mark 41B has been transferred onto the intermediate transfer belt 10 in step 16, and the intermediate distance by the distance at which the mark 41B has been transferred onto the intermediate transfer belt 10 has been reached. When the transfer belt 10 rotates, the power source of the charging roller is turned off in step 17, and the developing bias to the developing roller 6A is turned off by the high voltage power source for applying the developing bias to the developing roller 6A in step 18. Next, the CPU 47 executes step 1
At 9, the drive device for rotating the developing roller 6A and the like stops the rotation of the developing roller 6A and the like, and at step 20, the high-voltage power supply turns off the transfer bias to the bias roller 13.

After that, when the mark detection sensor 40 detects the mark 41B in step 21, the timer 49 starts the counting operation by the detection signal 43 in step 22. When the intermediate transfer belt 10 makes one round and the mark detection sensor 40 detects the mark 41B again in step 23, the timer 49 stops in step 24, and the distance of one round of the intermediate transfer belt 10 is measured by the timer and read by the CPU 47. . In this case, it is preferable that the motor used as a drive device for rotating the intermediate transfer belt 10 has little speed fluctuation. Next, in step 25, the intermediate transfer belt 10 is cleaned by the cleaning device 16 to remove the mark 41B, and the series of operations is completed.

FIG. 15 shows an operation flow from power-on in this embodiment. In step 30, the CPU 47 controls the rotary developing unit to set the black developing unit 6 at the developing position. Next, the CPU 47 creates the mark 41B according to the flow shown in FIG. 5 in step 31, measures the distance of one round of the intermediate transfer belt 10, and enters the standby state.

FIG. 16 shows the operation flow from the start of image data reception. In step 40, the CPU 47 controls the rotary developing unit to set the black developing unit 6 at the developing position. Next, the CPU 47 creates the mark 41B to be the writing start signal in the step 41 as described above, and the mark 41B is located 30 mm ahead of the mark detection position of the mark detection sensor 40 in the rotational direction of the intermediate transfer belt 10. And the intermediate transfer belt 10 is stopped.

When the image data from the image reading device is stored in the frame memory, the CPU 47 proceeds to step 4
The intermediate transfer belt 10 is rotated by a driving device that drives the intermediate transfer belt 10 at 3. In step 44, the mark detection sensor 40 detects the mark 41B, the timer 49 starts the counting operation, and a writing start signal is output from the gate 48 to the laser writing system unit 5 to start black image writing. Then, the end of the mark 41B reaches the detection position of the mark detection sensor 40, and the CPU 47 sets the mask signal to H to mask the detection signal 43, and in step 46, a black monochromatic image is formed on the photoconductor 1 as described above. It is formed and transferred onto the intermediate transfer belt 10. The CPU 47 is the intermediate transfer belt 10 described above.
From the result of the one-round distance measurement, in step 47, when the intermediate transfer belt 10 rotates for almost one round and the mark 41B reaches a position 10 mm ahead of the detection position of the mark detection sensor 40 in the rotation direction of the intermediate transfer belt 10, the mask signal is output. The detection signal 43 is unmasked by setting it to L.

Next, at step 48, the mark detection sensor 4
0 detects the mark 41B, the timer 49 starts the counting operation, and a writing start signal is output from the gate 48 to the laser writing system unit 5 to start the cyan image writing. When the end of the mark 41B reaches the detection position, the CPU
47 sets the mask signal to H to mask the detection signal 43, and in step 50, a cyan single color image is formed on the photoconductor 1 as described above and is transferred onto the intermediate transfer belt 10 so as to be superimposed on the black image. To be done. The CPU 47 performs step 51 based on the result of the one-round distance measurement result of the intermediate transfer belt 10 described above.
Then, the intermediate transfer belt 10 rotates for almost one turn and the mark 41B
Reaches a position 10 mm ahead of the detection position of the mark detection sensor 40 in the rotation direction of the intermediate transfer belt 10, the mask signal is set to L and the masking of the detection signal 43 is released.

Next, at step 52, the mark detection sensor 4
0 detects the mark 41B, the timer 49 starts the counting operation, and an image writing start signal is output from the gate 48 to the laser writing system unit 5 to start the image writing of magenta. When the end of the mark 41B reaches the detection position, the CPU 47 sets the mask signal to H to mask the detection signal 43, and in step 54, a magenta monochromatic image is formed on the photoconductor 1 and the intermediate transfer is performed. Belt 1
0 is transferred and superposed on the image. The CPU 47 determines that the intermediate transfer belt 10 has rotated nearly one full circle in step 55 based on the result of the one-round distance measurement of the intermediate transfer belt 10 described above, and the mark 4
When 1B reaches a position 10 mm ahead of the detection position of the mark detection sensor 40 in the rotation direction of the intermediate transfer belt 10, the mask signal is set to L and the detection signal 43 is unmasked.

Next, at step 56, the mark detecting sensor 4
0 detects the mark 41B, the timer 49 starts the counting operation, and a writing start signal is output from the gate 48 to the laser writing system unit 5 to start the yellow image writing. When the end of the mark 41B reaches the detection position and the CPU 47 sets the mask signal to H to mask the detection signal 43, the yellow monochromatic image is formed on the photoconductor 1 in step 58, and the intermediate transfer belt is formed. 1
A full-color image is obtained by transferring the image on the image above 0. Next, in step 59, the full-color image on the intermediate transfer belt 10 is transferred onto the transfer paper and fixed by the fixing device 20, and then discharged to the tray 23. In step 60, the cleaning device 16 operates to operate the intermediate transfer belt 10. The upper mark 41B is removed.

In the second embodiment, the same effect as in the first embodiment can be obtained. That is, the exposure phase shift in the sub-scanning direction is eliminated by controlling the rotational phase of the polygon mirror 5B by the mark detection timing of the mark detection sensor 40, regardless of the variation in the peripheral length of the intermediate transfer belt 10 and the variation in the feed speed. The overlapping positions of the images of the respective color plates can be adjusted with high accuracy. Further, since the latent image formation is started after a certain period of time from the mark detection timing of the mark detection sensor 40, the next image formation can be started at the stage when the rotation of the polygon motor 5A is stable, and the sub-scanning direction of the image of each color plate. The initial stacking position deviation does not occur.

Further, since the reflection type photo sensor is used as the mark detecting sensor 40, the image forming position of the intermediate transfer belt 10 can be arbitrarily set. Also, the polygon mirror 5B
In the rotational phase control, since the phase matching period is changed depending on the phase shift amount at the time of mark detection by the mark detection sensor 40, it is possible to disperse the load on the phase convergence and as a result to perform reliable and stable phase convergence. Further, since the rotational phase control of the polygon mirror 5B is performed within a range that does not deviate from the phase control range of the rotary polygon mirror driving device, there is no dead time required for phase convergence from outside the phase control.

Further, since the rotational phase control of the polygon mirror 5B is performed in a direction to follow the target phase, the rotational phase of the polygon mirror 5B makes a stable phase transition. Also,
Since the time control from the mark detection timing of the mark detection sensor 40 to the start of latent image formation is performed by counting the reference signal of the rotary polygon mirror driving device that starts oscillation by the mark detection of the mark detection sensor 40, the phase of the polygon motor 5A It is possible to start the latent image formation that suits. Further, the rotational phase control of the polygon mirror 5B is performed in the phase difference detection period,
Since it consists of the phase matching period, it can be performed accurately.

Further, since the reference signal serving as the reference for the rotational phase of the polygon mirror 5B is a pulse signal for every rotation of the polygon mirror 5B or for every rotation, the scanning of the polygon mirror 5B is controlled by controlling the phase of the reference signal. The phase can be controlled. In addition, the intermediate transfer belt 10
Is seamless, the mark 41B can be generated at any place, and can be used evenly. In addition,
The present invention is not limited to the above-described embodiments, but can be applied to other color image forming apparatuses such as color copying machines, color printers, color facsimiles, and drum-shaped photoconductors can be used instead of belt-shaped photoconductors. You may.

[0087]

As described above, according to the first aspect of the present invention, the photoconductor has a rotating photoconductor and a rotary polygon mirror rotated by a rotary polygon mirror driving device, and the image of each color is formed on the photoconductor. A latent image forming unit that forms an electrostatic latent image corresponding to each color image forming signal by exposing a light beam corresponding to the forming signal by the rotating polygonal mirror, and an image forming signal of each color on the photoconductor. A plurality of developing means for developing corresponding electrostatic latent images with developers of respective colors, an intermediate transfer member for rotating and transferring the visualized single color image on the photosensitive member, and the intermediate transfer member. In a color image forming apparatus having a detection means for detecting a mark provided on a body at a predetermined position, and a control means for causing the latent image forming means to start forming an electrostatic latent image at the mark detection timing of the detection means. , Mark detection tie of the detection means Since the rotation phase control means for controlling the rotation phase of the rotary polygonal mirror is provided by controlling the rotation phase of the rotary polygonal mirror by controlling the rotation phase of the rotary polygonal mirror according to the mark detection timing of the detection means, the variation in the circumferential length of the intermediate transfer member and the feed rate The exposure position shift in the sub-scanning direction can be eliminated and the overlapping position of the images of the respective color plates can be adjusted with high accuracy, regardless of the variation of.

According to the second aspect of the invention, in the color image forming apparatus according to the first aspect, since the electrostatic latent image is formed after a certain period of time from the mark detection timing of the detecting means, the rotary polygon mirror. The next image formation can be started when the rotation of the image is stabilized, and the initial overlay position deviation of the image of each color plate in the sub-scanning direction does not occur.

According to the third aspect of the present invention, in the color image forming apparatus according to the first aspect, since the detecting means is a reflection type photosensor, the image forming position of the intermediate transfer member can be arbitrarily set.

According to a fourth aspect of the present invention, in the color image forming apparatus according to the first aspect, the rotation phase control means controls the rotation phase of the rotary polygon mirror to detect the marks of the detection means. Since the rotational phase matching period of the rotary polygon mirror is changed according to the rotational phase shift amount of the mirror,
It is possible to disperse the load on the phase convergence and as a result to perform reliable and stable phase convergence.

According to a fifth aspect of the present invention, in the color image forming apparatus according to the first aspect, the rotational phase control means controls the rotational phase of the rotary polygon mirror to set the phase control range of the rotary polygon mirror driving device. Since the rotational phase of the rotary polygon mirror is changed within a range that does not deviate, no dead time is required for phase convergence outside the phase control.

According to the sixth aspect of the present invention, in the color image forming apparatus according to the first aspect, the rotation phase control means performs the rotation phase control of the rotary polygon mirror in a direction to follow the target phase. The rotation phase of the polygon mirror makes a stable phase transition.

According to a seventh aspect of the present invention, in the color image forming apparatus according to the second aspect, the control means is a rotational phase reference of the rotary polygon mirror driving device for starting oscillation by the mark detection of the detection means. Since the reference signal is counted to control the time from the mark detection timing of the detecting means to the start of the electrostatic latent image formation, the latent image formation can be started at the phase of the rotary polygon mirror.

According to the eighth aspect of the present invention, in the color image forming apparatus according to the first aspect, since the rotational phase control period of the rotary polygonal mirror includes the phase difference detection period and the phase matching period, the rotary polygonal mirror The rotation phase control can be performed accurately.

According to a ninth aspect of the present invention, in the color image forming apparatus according to the first aspect, a reference signal serving as a rotation phase reference of the rotary polygon mirror is a divisor of the number of mirror surfaces of the rotary polygon mirror or every rotation. Since this is a pulse signal of, the scanning phase of the rotary polygon mirror can be controlled by controlling the phase of the reference signal.

[Brief description of drawings]

FIG. 1 is a block diagram showing a part of a first embodiment of the present invention.

FIG. 2 is a sectional view showing the outline of the first embodiment.

FIG. 3 is a sectional view showing a part of the first embodiment.

FIG. 4 is a perspective view showing a part of the first embodiment.

FIG. 5 is a flowchart showing an operation flow of the first embodiment.

FIG. 6 is a flowchart showing an interrupt processing flow of the first embodiment.

FIG. 7 is a perspective view showing a part of the first embodiment.

FIG. 8 is a block diagram showing a part of the first embodiment.

FIG. 9 is a block diagram showing a phase matching unit in the first embodiment.

FIG. 10 is a timing chart showing the operation timing of the first embodiment.

FIG. 11 is a perspective view showing a part of a second embodiment of the present invention.

FIG. 12 is a schematic view showing a part of the second embodiment.

FIG. 13 is a timing chart showing the operation timing of the second embodiment.

FIG. 14 is a flowchart showing an operation flow of the second embodiment.

FIG. 15 is a flowchart showing an operation flow of the second embodiment.

FIG. 16 is a flowchart showing an operation flow of the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Photoconductor 4 ... Charging roller 5 ... Laser writing system unit 5A ... Polygon motor 5B ... Polygon mirror 6-9 ... Development unit 10 ... Intermediate transfer belt 40 Mark detection Sensors 41A to 41F Mark 47 CPU 50 ... Phase matching unit 51 Oscillator

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location G03G 15/01 114 A

Claims (9)

[Claims] 1. A photosensitive member which is rotated, and a rotating polygon mirror which is rotated by a rotating polygon mirror driving device, wherein a light beam corresponding to an image forming signal of each color is deflected by the rotating polygon mirror. And exposing to form an electrostatic latent image corresponding to the image forming signal of each color, and an electrostatic latent image corresponding to the image forming signal of each color on the photoconductor is developed by the developer of each color. A plurality of developing means for forming an image, an intermediate transfer body that is rotated to transfer the visualized monochromatic image on the photosensitive body, and a detection that detects a mark provided on the intermediate transfer body at a predetermined position. In a color image forming apparatus having a means and a control means for causing the latent image forming means to start forming an electrostatic latent image at the mark detection timing of the detecting means, the rotary polygon mirror of the rotating polygon mirror is detected at the mark detecting timing of the detecting means. Control rotation phase Color image forming apparatus comprising the rotational phase control means that. 2. The color image forming apparatus according to claim 1, wherein formation of the electrostatic latent image is started after a fixed period from the mark detection timing of the detecting means. 3. The color image forming apparatus according to claim 1, wherein the detecting means comprises a reflection type photo sensor. 4. The color image forming apparatus according to claim 1, wherein the rotational phase control means controls the rotational phase of the rotary polygonal mirror by the amount of rotational phase shift of the rotary polygonal mirror when the mark is detected by the detection means. A color image forming apparatus characterized by changing a rotational phase matching period of a rotary polygon mirror. 5. The color image forming apparatus according to claim 1, wherein the rotary phase control means controls the rotary phase of the rotary polygon mirror within a phase control range of the rotary polygon mirror driving device. A color image forming apparatus characterized by changing the rotation phase of the color image forming apparatus. 6. The color image forming apparatus according to claim 1, wherein the rotational phase control means controls the rotational phase of the rotary polygon mirror in a direction to follow a target phase. 7. A color image forming apparatus according to claim 2, wherein said control means counts a reference signal serving as a rotation phase reference of said rotary polygon mirror driving device which starts oscillation by detection of a mark by said detection means, and counts said reference signal. A color image forming apparatus, wherein time management is performed from the mark detection timing of the detection means to the start of formation of the electrostatic latent image. 8. The color image forming apparatus according to claim 1, wherein the rotation phase control period of the rotary polygon mirror includes a phase difference detection period and a phase matching period. 9. The color image forming apparatus according to claim 1, wherein the reference signal serving as a rotation phase reference of the rotary polygon mirror is a pulse signal for each rotation or a divisor of the number of mirror surfaces of the rotary polygon mirror. And a color image forming apparatus.