JPH08331334A - Image forming device - Google Patents

Abstract

PURPOSE: To facilitate a job such as adjustment of a beam power of each laser optical system and measurement of jitter of a motor driving a beam system and a rotary reflector. CONSTITUTION: A black printing station 26K of a reference printing station is provided with a PLL circuit 53K controlling the drive of a scanner motor 54K, a reference clock generating circuit 51K, and a frequency divider circuit 52K frequency-dividing a reference clock from the circuit 51K and applying the divided clock to a PLL circuit, and other print station 26Y (26M, 26C) is provided with a PLL circuit 53Y (53M, 53C) controlling drive of a scanner motor 54Y (54M, 54C), a reference clock generating circuit 51Y (51M, 51C), a frequency divider circuit 52Y (52M, 52C) frequency-dividing a reference clock from the circuit 51Y (51M, 51C), a frequency divider circuit 52Y (52M, 52C) frequency-dividing the reference clock and giving the divided clock to the PLL circuit, and a frequency division ratio adjustment circuit 57Y (57M, 57C) detecting a phase difference between a horizontal synchronizing signal from a write position sensor 50K and a horizontal synchronizing signal from its own write position sensor 50Y (50M, 50C) to adjust the frequency division ratio of the frequency divider.

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 color printer which forms images by sequentially superimposing images of a plurality of colors.

[0002]

2. Description of the Related Art As a laser printer for forming a color image, Japanese Patent Laid-Open No. 64-73369 is known. This is 20kHz from the crystal oscillator 1 as shown in Fig.6.
The reference frequency signal f0 of the counter 2 and the counter 9C,
It outputs to the clock inputs of 9Y and 9BK. The counter 2 divides the reference frequency signal f0 into 1/10 and outputs the divided 2 KHz reference frequency signals as reference frequency signals f1 to f10 having 10 different phases.
The selector circuit 3C uses the reference frequency signal f from the counter 2.
One of the reference frequency signals 1 to f10 is selected based on the select signal from the selector circuit 10C. The selector circuit 3Y selects one of the reference frequency signals f1 to f10 from the counter 2 based on the select signal from the selector circuit 10Y. The selector circuit 3BK selects one of the reference frequency signals f1 to f10 from the counter 2 based on the select signal from the selector circuit 10BK.

The PLL circuit 4M outputs a drive signal for driving the scanner motor 6M to the amplifier 5M based on the input reference frequency signal f1. Then, the rotation speed signal of the motor 6M is monitored by the FG sensor 7M, and the detected speed control signal is supplied to the PLL circuit 4M. PLL circuit 4M
Controls the drive current applied to the amplifier 5M so as to eliminate the phase difference between the frequency of the speed control signal and the reference frequency signal f1. The PLL circuit 4C outputs a drive signal for driving the scanner motor 6C based on the selected reference frequency signal to the amplifier 5C. Then, the rotation speed signal of the motor 6C is monitored by the FG sensor 7C, and the detected speed control signal is supplied to the PLL circuit 4C. The PLL circuit 4C controls the drive current applied to the amplifier 5C so as to eliminate the phase difference between the frequency of the speed control signal and the reference frequency signal.

The PLL circuit 4Y outputs a drive signal for driving the scanner motor 6Y to the amplifier 5Y based on the selected reference frequency signal. Then, the rotation speed signal of the motor 6Y is monitored by the FG sensor 7Y, and the detected speed control signal is supplied to the PLL circuit 4Y. PLL circuit 4Y
Controls the drive current applied to the amplifier 5Y so as to eliminate the phase difference between the frequency of the speed control signal and the reference frequency signal. The PLL circuit 4BK outputs a drive signal for driving the scanner motor 6BK to the amplifier 5BK based on the selected reference frequency signal. Then, the rotation speed signal of the motor 6BK is monitored by the FG sensor 7BK, and the detected speed control signal is supplied to the PLL circuit 4BK. PLL circuit 4
BK controls the drive current applied to the amplifier 5BK so as to eliminate the phase difference between the frequency of the speed control signal and the reference frequency signal.

The synchronizing sensor 8M receives the laser beam from the semiconductor laser 13M before image writing, and outputs a beam detect signal BDM which is a horizontal synchronizing signal to a counter 9C.
Input to the reset terminals R of 9Y and 9BK and the synchronization circuit 11M. The synchronization sensor 8C receives the laser beam from the semiconductor laser 13C before writing an image, and inputs a beam detect signal BDC which is a horizontal synchronization signal to the set terminal S of the counter 9C and the synchronization circuit 11C. Synchronous sensor 8
Y receives the laser beam from the semiconductor laser 13Y before image writing, and inputs the beam detect signal BDY which is a horizontal synchronizing signal to the set terminal S of the counter 9Y and the synchronizing circuit 11Y. The synchronous sensor 8BK receives the laser beam from the semiconductor laser 13BK before image writing,
The beam detect signal BDBK which is a horizontal synchronizing signal is input to the set terminal S of the counter 9BK and the synchronizing circuit 11BK.

The driver 12M determines the image writing position by the beam detect signal BDM output from the synchronizing circuit 11M, and on / off-modulates the semiconductor laser 13M based on the image signal M input from an external device. The driver 12C determines the image writing position by the beam detect signal BDC output from the synchronizing circuit 11C, and on / off modulates the semiconductor laser 13C based on the image signal C input from an external device. The driver 12Y uses the beam detect signal BD output from the synchronizing circuit 11Y.
The image writing position is determined by Y, and the semiconductor laser 13Y is turned on / off based on the image signal Y input from an external device.
Modulate off. The driver 12BK is a synchronous circuit 11BK
The image writing position is determined by the beam detect signal BDBK output from the semiconductor laser 13BK, and the semiconductor laser 13BK is ON / OFF-modulated based on the image signal BK input from the external device.

Selector circuits 10C, 10Y, 10BK
The counters 9C, 9Y and 9BK are the reference frequency signals f0.
The selector circuits 3C, 3Y, 3BK corresponding to the reference frequency signal for minimizing the BD phase shift amount counted based on the above, that is, the select signal for selecting any one of the reference frequency signals f1 to f10. Output to. Then, when adjusting the phase shift between the magenta printing station MS and the cyan printing station CS,
First, the semiconductor laser 1 of the magenta printing station MS
When the laser beam from 3Y is detected by the synchronous sensor 8Y, the beam detect signal BDY is output to the synchronous sensor 8Y.
Are output to the reset terminals R of the counters 9C, 9Y and 9BK, and the phase difference counting operation is started by the reference frequency signal f0.

Then, the laser beam from the semiconductor laser 13C of the magenta printing station CS is emitted by the synchronous sensor 8
When detected by C, the beam detect signal BDC is input to the set terminal S of the counter 9C by the synchronous sensor 8C. This stops the operation of the counter 9C and outputs the count data to the selector circuit 10C. In response to this, the selector circuit 10C refers to the ROM table and counts the beam detect signal B for the step.
A select signal for selecting any one of the reference frequency signals f1 to f10, which is an optimum reference frequency signal for returning the phase of DC, is input to the selector circuit 3C to match the phase.

[0009]

By the way, in such an image forming apparatus, at the time of assembly, in the laser optical system, the beam power is adjusted and the jitter of the motor rotating the beam system and the rotary reflector (polygon mirror) is reduced. Need to take measurements.

However, since the crystal oscillator for generating the reference frequency signal is common to each printing station as in the above-mentioned publication, the laser optical system of each printing station is individually assembled and operated. Therefore, when adjusting the beam power of each laser optical system or measuring the jitter of the motor that rotates the beam system and the rotary reflector, the reference frequency signal must be individually supplied to each printing station. It was necessary to prepare a device to be used as a reference frequency, and there was a problem that adjustment and measurement work was extremely troublesome.

Therefore, the invention according to claim 1 is such that, at the time of assembly, the adjustment of the beam power of each laser optical system constituting each printing station and the measurement of the jitter of the motor rotating the beam system and the rotary reflector are performed. (EN) Provided is an image forming apparatus which can be easily operated and which can prevent positional deviation in the sub-scanning direction as much as possible.

The invention according to claim 2 further provides an image forming apparatus capable of preventing color misregistration in the main scanning direction as much as possible.

[0013]

The invention according to claim 1 is
A photoconductor, a charging means for charging the photoconductor, a laser beam emitting means, and a rotary reflector for reflecting the laser beam from the emitting means and scanning the photoconductor charged by the charging means A laser optical system that writes an image as an electrostatic latent image on a photoconductor by an operation, a developing unit that develops an image written by this laser optical system to visualize it, and an image visualized by this developing unit. A plurality of printing stations provided with a transfer means for transferring to a transfer medium and a sync sensor for receiving a laser beam scanned by a laser optical system and generating a horizontal sync signal for determining a timing of writing an image on a photoconductor are arranged. In the image forming apparatus that forms images by sequentially superimposing and transferring images by the respective printing stations, one of the printing stations is used as a reference printing station. The rest is a subordinate printing station, and the reference printing station includes a PLL control means for controlling the rotation speed of the rotary reflector in a phase locked loop system, a reference frequency signal generation means for generating a reference frequency signal, and this reference. Reference frequency generating means for dividing the reference frequency signal from the frequency signal generating means and supplying it to the PLL control means as a reference frequency signal is provided, and the subordinate printing station controls the rotation speed of the rotary reflector by the phase locked loop method. PLL control means for controlling by, the reference frequency signal generating means for generating the reference frequency signal, and the reference frequency signal from the reference frequency signal generating means
The reference frequency generating means for supplying the reference frequency signal to the LL control means and the phase difference between the horizontal synchronizing signal from the synchronizing sensor of the reference printing station and the horizontal synchronizing signal from its own synchronizing sensor are detected. Frequency division ratio adjusting means for adjusting the frequency division ratio in the direction to make the phase difference zero is provided.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the frequency division ratio adjusting means of the subordinate printing station controls the frequency division ratio and the laser optical system controls the image formation on the photoconductor. This is done during a period other than the period in which writing is permitted.

[0015]

In the invention according to claim 1, the reference printing station divides the reference frequency signal from the reference frequency signal generating means by the reference frequency generating means and supplies it to the PLL control means as the reference frequency signal. The PLL control means controls the rotation speed of the rotary reflector in a phase locked loop system based on this reference frequency signal. On the other hand, the subordinate printing station divides the reference frequency signal from the reference frequency signal generating means by the reference frequency generating means and supplies it to the PLL control means as the reference frequency signal. The phase difference between the horizontal synchronizing signal from the synchronizing sensor and the horizontal synchronizing signal from its own synchronizing sensor is detected, and the frequency division ratio in the reference frequency generating means is adjusted in the direction to make the phase difference zero. Then, the PLL control means controls the rotation speed of the rotary reflector in a phase locked loop system based on the reference frequency signal. Also,
In the invention according to claim 2, the frequency division ratio adjusting means of the subordinate printing station performs the frequency division ratio adjustment control during a period other than the period in which the laser optical system is allowed to write an image on the photoconductor.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. In this embodiment, the invention is applied to a color laser printer. FIG. 1 schematically shows the configuration of a color laser printer, in which a sheet of transfer paper 21 that is a transfer medium is stored in a paper feed cassette 22 and the transfer paper 21 is transferred one by one onto a paper transport belt 23 at a predetermined timing. It is designed to be sent to.

The sheet conveying belt 23 is an endless belt belt wound between two belt driving rollers 24 and 25.
On the paper transport belt 23, the yellow images are sequentially transferred from the paper feed side.
Printing station 26Y, Magenta printing station 2
6M, a cyan printing station 26C and a black printing station 26K are arranged. That is, yellow
The printing station 26Y is located closest to the belt drive roller 24, and the black printing station 26K is located closest to the belt drive roller 25. The paper transport belt 23 has a two-layer structure in which the outer side is an insulating layer and the inner side is a conductive layer.

A belt charger 27 is arranged in front of the yellow-printing station 26Y.
Then, the paper transport belt 23 and the transfer paper 21 are charged to a surface potential of about 1 to 2 KV and the transfer paper 21 is attracted to the paper transport belt 23. Further, the transfer paper 2 is transferred from the paper feed cassette 22 to the paper transport belt 23.
A position sensor 28 is arranged at a position for sending out 1, and the position sensor 28 detects the leading end of the transfer paper 21 and outputs a print start signal PS.

Each of the printing stations 26Y, 26M,
26C and 26K have the same structure, and the photosensitive drums 29Y and 2Y
9M, 29C and 29K are provided, and the photosensitive drum 29
Chargers 30Y, 30M, 30C and 30K that charge the photosensitive surface substantially uniformly around Y, 29M, 29C and 29K, and the photosensitive surface is exposed by optical scanning, and an image is written as an electrostatic latent image by this exposure operation. Exposure device 31 constituting a laser optical system
Y, 31M, 31C, 31K, a developing device 3 for adhering toner to the electrostatic latent image written by this exposure device to develop it
2Y, 32M, 32C, 32K, and transfer rollers 33Y, 33M, 33C, 33K for transferring the toner image obtained by developing with this developing device to the transfer paper 21 are arranged.
The paper transport belt 23 is composed of the photosensitive drums 29Y and 29Y.
M, 29C, 29K and transfer rollers 33Y, 33M, 33
It passes between C and 33K.

A fixing device 34 is provided behind the black printing station 26K, and presses the transfer sheet 21 on which the image has been transferred, which is sent out through the sheet conveying belt 23,
It is designed to be heated and fixed. And this fixing device 3
The transfer paper 21 whose fixing is completed in 4 is discharged to the outside and stored in the paper storage unit 35.

The exposure devices 31Y, 31M, 31C, 3
A print pattern generation unit 36 that outputs print pattern signals Y, M, C, and K corresponding to respective color tones to 1K.
The Y, 36M, 36C, and 36K are connected to each other, and the write position specifying unit 3 that specifies the write position in the sub-scanning direction to the print pattern generating units 36Y, 36M, 36C, and 36K, respectively.
7Y, 37M, 37C and 37K are connected.

The write start position designating section 37Y uses the print start signal PS from the position sensor 28 as a reference.
A margin register 38Y storing a set value indicating a writing position in the sub-scanning direction, a timing counter 39Y counting up with activation of a print start signal PS from the position sensor 28, the margin register 38Y and a timing counter 39Y. It is composed of a comparator 40Y and the like for comparing the values of.

The write-out position designating section 37M, 37C, 3
7K is the write start position signals Y0 and M0 of the previous color.
, C0 as a reference, the pre-color dependent registers 38M, 38C, which store the set values indicating the writing position in the sub-scanning direction,
38K, pre-color dependent counters 39M, 39C, 39K, which count up with activation of the write start position signals Y0, M0, C0 of the previous color, and the previous-color dependent register 3
8M, 38C, 38K and pre-color dependent counters 39M, 3
Comparators 40M and 40 for comparing the values of 9C and 39K
It is composed of C, 40K, etc.

This color laser printer includes an exposure device 3
Photoconductor drum 29 by 1Y, 31M, 31C, 31K
The developing devices 32Y, 32M, 32C, 32K are applied to the electrostatic latent images formed on the Y, 29M, 29C, 29K photosensitive surfaces.
To develop with toners of yellow, magenta, cyan, and black, respectively, and the toner images are developed.
A color image is formed by sequentially superposing and printing on the transfer paper 21 conveyed above.

Each exposure device 31Y, 31M, 31C, 31
The writing start timing at which K starts image scanning on the photosensitive surfaces of the photosensitive drums 29Y, 29M, 29C, and 29K is controlled as follows. First, when the position sensor 28 detects the leading edge of the transfer paper 21, the print start signal PS is activated as shown in FIG. 2A, and the timing counter 39Y corresponding to the yellow printing station 26Y counts with this as a reference. Start up. That is, it becomes the active area of the timing counter 39Y as indicated by the diagonal lines in FIG. When the count value of the timing counter 39Y reaches the set value of the margin register 38Y, the writing start signal Y0 is output from the comparator 40Y as shown in FIG. Note that n shown in FIG. 2A indicates a page unit.

With the activation of the write start signal Y0 as a reference, the print pattern generation unit 36Y starts its operation to supply the yellow print pattern signal Y to the exposure device 31Y and the previous color corresponding to the magenta printing station 26M. The dependent counter 39M starts counting up. That is, the area becomes the active area of the front color dependent type counter 39M as indicated by the diagonal lines in FIG. Then, the count value of the front color dependent type counter 39M is the front color dependent type register 3
When the set value of 8M is reached, the writing start signal M0 is output from the comparator 40M as shown in FIG.

Similarly, with the activation of the write start signal M0 as a reference, the print pattern generation unit 36M starts its operation to supply the magenta print pattern signal M to the exposure device 31M and to the cyan print station 26C. The corresponding pre-color dependent counter 39C starts counting up. That is, it becomes the active area of the front color dependent type counter 39C as shown by the diagonal lines in FIG. And
When the count value of the previous color dependent type counter 39C reaches the set value of the previous color dependent type register 38C, the writing start signal C0 is output from the comparator 40C as shown in FIG.

Similarly, with the activation of the write start signal C0 as a reference, the print pattern generation section 36C starts its operation to supply the cyan print pattern signal C to the exposure device 31C and to the black print station 26K. The corresponding previous color dependent counter 39K starts counting up. That is, it becomes the active area of the front color dependent type counter 39K as shown by the slanted lines in FIG. And
When the count value of the previous color dependent type counter 39K reaches the set value of the previous color dependent type register 38K, the writing start signal K0 is output from the comparator 40K as shown in (h) of FIG. Then, based on the activation of the write start signal K0, the print pattern generation unit 36K starts its operation and supplies the black print pattern signal K to the exposure device 31K. The timing counter 39Y starts counting up based on the activation of PS, and outputs the write start signal Y0 from the comparator 40Y. Then, the previous color dependent type counter 39M counts based on the activation of the write start signal Y0. The start-up is started, and the write start signal M0 is output from the comparator 40M. Then, the pre-color dependent counter 39C starts counting up based on the activation of the write start signal M0, and the write start signal is output from the comparator 40C. C0 is output, and then the previous color sub-command is output based on the activation of the writing start signal C0. Type counter 39K begins counting up, and so has a configuration that outputs a start signal K0 writing from the comparator 40K, margin register 38Y and the previous color Dependent register 38M, 38
By properly adjusting the set values set to C and 38K, the image can be aligned on the transfer paper 21 at a desired position.

An exposure device 31Y, which constitutes a laser optical system,
As shown in FIG. 3, 31M, 31C, and 31K output a laser beam modulated by a print pattern signal from a laser light source 41 such as a semiconductor laser, and use this laser beam as a collimator lens 42, a cylindrical lens 43, and an imaging lens. After passing through 44, it is reflected by a reflection mirror 45 and then reflected by a reflection surface of a polygon mirror 46 which is a rotary reflector to be converted into scanning light. Then, after the scanning light is folded back by the folding mirror 47, it is irradiated onto the photosensitive surface of the photosensitive drum 29 via the aspherical correction lens 48. Therefore, the laser beam applied to the photosensitive surface of the photosensitive drum 29 is scanned in the main scanning direction which is the longitudinal direction of the photosensitive drum 29 by the rotation of the polygon mirror 46.

Another folding mirror 49 is arranged in front of the folding mirror 47 corresponding to the main scanning start position on the photosensitive drum 29, and the laser beam folded by the folding mirror 49 is a synchronous sensor in the main scanning direction. The writing position detecting sensor 50 is made incident. Then, the write-out position detecting sensor 50 outputs a horizontal synchronizing signal SOS which notifies the start of main scanning when the laser beam is detected. Therefore, the write-out position detection sensor 50 outputs the horizontal synchronization signal SOS once per scan.

In this apparatus, four exposure devices 31Y, 31
Since M, 31C and 31K are provided, a total of four horizontal synchronizing signals SOS will be output. If the phase of each horizontal synchronizing signal SOS is not fixed at a substantially constant position, a positional shift in the sub-scanning direction will occur. Therefore, it is necessary to fix the phases of the four horizontal synchronizing signals SOS at substantially constant positions.

Next, based on FIG. 4, four horizontal synchronizing signals S
A phase adjustment circuit that fixes the phase of the OS at a substantially constant position will be described. Each of the printing stations 26Y, 26M, 2
One of the 6C and 26K, that is, the black printing station 26K is used as a reference printing station, and the rest, that is, the yellow, magenta, and cyan printing stations 26, respectively.
Let Y, 26M, and 26C be subordinate printing stations.

The black printing station 26K is
A black optical system reference clock generation circuit 51K is provided as reference frequency signal generation means for generating a reference frequency signal.
Reference clock K from this reference clock generation circuit 51K
CLK is supplied to a frequency dividing circuit 52K which is a reference frequency generating means to divide the frequency, and a reference frequency signal KPL is supplied from the frequency dividing circuit 52K to a PLL (phase locked loop) circuit 5
We are supplying to 3K. The PLL circuit 53K instructs the motor driver 56K to match the frequency and phase of the reference frequency signal KPL and the rotation control signal KFG from the Hall element 55K that detects the rotation speed of the scanner motor 54K that rotationally drives the polygon mirror 46K. A control voltage is applied, and the rotation of the scanner motor 54K is controlled by the motor driver 56K.

Each of the yellow, magenta, and cyan printing stations 26Y, 26M, 26C serves as a reference frequency signal generating means for generating a reference frequency signal, and a yellow optical system reference clock generating circuit 51Y and a magenta optical system reference clock generating circuit 51M, respectively. , A cyan optical system reference clock generation circuit 51C is provided, and the reference clocks YCL from the respective reference clock generation circuits 51Y, 51M, 51C are provided.
K, MCLK, and CCLK are supplied to frequency dividing circuits 52Y, 52M, and 52C, which are reference frequency generating means, and frequency-divided, and the reference frequency signals YPL, MPL, and CPL are respectively output from the frequency dividing circuits 52Y, 52M, and 52C. It is supplied to the PLL circuits 53Y, 53M, and 53C. Each PLL
The circuits 53Y, 53M and 53C respectively include the reference frequency signals YPL, MPL and CPL and the polygon mirrors 46Y and 4Y.
Scanner motors 54Y and 5 that rotate 6M and 46C
Hall element 55Y that detects the rotational speed of 4M and 54C,
Rotation control signals YFG, MFG, C from 55M, 55C
A control voltage is applied to the motor drivers 56Y, 56M, 56C so as to match the frequency and phase with the FG, and the motor drivers 56Y, 56M, 56C control the rotations of the scanner motors 54Y, 54M, 54C, respectively. Has become.

The yellow, magenta, and cyan printing stations 26Y, 26M, and 26C have horizontal synchronizing signals KSOS from the writing position detecting sensor 50K of the black printing station 26K and their own writing position detecting sensors 50Y and 50M. A frequency division ratio adjusting circuit 57Y that detects a phase difference from the horizontal synchronizing signals YSOS, MSOS, and CSOS from 50C and adjusts the frequency division ratio of the frequency dividing circuits 52Y, 52M, and 52C in the direction to reduce the phase difference to zero. 57
M and 57C are provided respectively.

The frequency division ratio adjusting circuit 57Y detects the output timing of the horizontal synchronizing signal KSOS from the write-out position detecting sensor 50K and the horizontal synchronizing signal YSOS from the write-out position detecting sensor 50Y. When the synchronization signal YSOS is output earlier, the frequency division ratio of the frequency dividing circuit 52Y is increased to delay the output timing of the horizontal synchronization signal YSOS from the write-out position detection sensor 50Y, and the horizontal synchronization signal YSOS is output more than the horizontal synchronization signal KSOS. If the output is delayed, the frequency division ratio of the frequency dividing circuit 52Y is reduced to accelerate the output timing of the horizontal synchronizing signal YSOS from the write-out position detecting sensor 50Y. As a result, the phases of the horizontal synchronizing signal KSOS from the writing position detecting sensor 50K and the horizontal synchronizing signal YSOS from the writing position detecting sensor 50Y are fixed at a fixed position.

The frequency division ratio adjusting circuit 57M detects the output timings of the horizontal synchronizing signal KSOS from the writing position detecting sensor 50K and the horizontal synchronizing signal MSOS from the writing position detecting sensor 50M. When the synchronization signal MSOS is output earlier, the frequency division ratio of the frequency dividing circuit 52M is increased to delay the output timing of the horizontal synchronization signal MSOS from the write-out position detection sensor 50M, and the horizontal synchronization signal MSOS is output more than the horizontal synchronization signal MSOS. When the output is delayed, the frequency division ratio of the frequency dividing circuit 52M is decreased to accelerate the output timing of the horizontal synchronizing signal MSOS from the write position detecting sensor 50M. As a result, the phases of the horizontal synchronizing signal KSOS from the writing position detecting sensor 50K and the horizontal synchronizing signal MSOS from the writing position detecting sensor 50M are fixed at fixed positions.

The frequency division ratio adjusting circuit 57C detects the output timing of the horizontal synchronizing signal KSOS from the writing position detecting sensor 50K and the horizontal synchronizing signal CSOS from the writing position detecting sensor 50C. When the synchronization signal CSOS is output earlier, the frequency division ratio of the frequency divider circuit 52C is increased to delay the output timing of the horizontal synchronization signal CSOS from the write-out position detection sensor 50C, and the horizontal synchronization signal CSOS is output from the horizontal synchronization signal KSOS. When the output is delayed, the frequency division ratio of the frequency dividing circuit 52C is decreased to accelerate the output timing of the horizontal synchronizing signal CSOS from the writing position detecting sensor 50C. As a result, the phases of the horizontal synchronizing signal KSOS from the writing position detecting sensor 50K and the horizontal synchronizing signal CSOS from the writing position detecting sensor 50C are fixed to a fixed position.

Each of the frequency division ratio adjusting circuits 57Y, 57M, 5
7C adjusts the frequency division ratios of the frequency dividing circuits 52Y, 52M, and 52C, that is, the phase adjustment period has the timing shown in FIG. FIG. 5A shows the print start signal PS, and n indicates the page unit. Of FIG.
(b) is the exposure device 31 of the yellow printing station 26Y
The period during which the writing of the yellow electrostatic latent image by Y is permitted is shown. When the level is high, the yellow electrostatic latent image is written. FIG. 5D shows the magenta printing station 26.
A period during which the writing of the magenta electrostatic latent image by the M exposure device 31M is permitted is shown. When the magenta electrostatic latent image is high, the magenta electrostatic latent image is written. FIG. 5F shows a period during which the writing of the cyan electrostatic latent image by the exposure device 31C of the cyan printing station 26C is permitted, and the cyan electrostatic latent image is written at the high level. FIG. 5H shows a period during which the black electrostatic latent image writing by the exposure device 31K of the black printing station 26K is permitted.
At the high level, a black electrostatic latent image is written.

Then, as indicated by hatching in FIG. 5 (c),
The yellow frequency division ratio adjustment circuit 57Y adjusts the frequency division ratio of the frequency division circuit 52Y during a period other than the period during which the exposure device 31Y of the yellow printing station 26Y permits writing of the yellow electrostatic latent image. . Also,
As indicated by the diagonal lines in FIG. 5 (e), the magenta frequency division ratio adjusting circuit 57M is used in a period other than the period during which the exposure device 31M of the magenta printing station 26M permits the writing of the magenta electrostatic latent image. The frequency division ratio of 52M is adjusted. Further, as indicated by hatching in (g) of FIG. 5, the cyan frequency division ratio adjusting circuit 57C is divided into periods during the period other than the period during which the exposure device 31C of the cyan printing station 26C permits writing of the electrostatic latent image of cyan. The frequency division ratio of the frequency circuit 52C is adjusted.

In such a configuration, each printing station 26Y, 26M, 26C, 26K has its own reference clock generating circuit 51Y, 51M, 51C, 51.
Since K is provided, each exposure device (laser optical system) 31
When the Y, 31M, 31C and 31K are individually assembled, the reference clocks from the reference clock generating circuit are individually used to scan the motors 54Y, 54M, 54C and 54Y.
K can be driven, and the work of adjusting the laser beam power and measuring the jitter of the scanner motor that rotationally drives the beam system and polygon mirror can be facilitated.

Also, the horizontal synchronizing signal K from the writing position detecting sensor 50K is controlled by the yellow frequency division ratio adjusting circuit 57Y.
The phase of the horizontal synchronizing signal YSOS from the SOS and the writing position detecting sensor 50Y is fixed at a fixed position, and the writing position detecting sensor 5 is controlled by the magenta frequency division ratio adjusting circuit 57M.
The phase of the horizontal synchronizing signal KSOS from 0K and the horizontal synchronizing signal MSOS from the writing position detecting sensor 50M is fixed at a fixed position, and further, the horizontal synchronizing signal KS from the writing position detecting sensor 50K is adjusted by the cyan frequency division ratio adjusting circuit 57C.
Since the phase of the horizontal synchronizing signal CSOS from the OS and the writing position detection sensor 50C is fixed at a fixed position, it is possible to prevent positional deviation in the sub-scanning direction.

The yellow frequency division ratio adjusting circuit 57Y adjusts the frequency division ratio of the frequency dividing circuit 52Y during the period other than the period during which the writing of the yellow electrostatic latent image is permitted, and the magenta frequency division ratio adjustment. The circuit 57M controls the frequency dividing circuit 5 during the period other than the period during which the writing of the magenta electrostatic latent image is permitted.
The frequency division ratio of 2M is adjusted, and the frequency division ratio adjustment circuit 57C of cyan adjusts the frequency division ratio of the frequency division circuit 52C in a period other than the period in which writing of the electrostatic latent image of cyan is permitted. It is possible to prevent color deviation in the main scanning direction by adjusting the circumference ratio.

For example, the reference clock generation circuits 51Y, 5Y
When a standard crystal oscillator with an accuracy of ± 10 ppm is used for 1M, 51C, and 51K, it is possible to suppress color misregistration of up to ± 3 μm in the main scanning direction with A4 size printing.
It is possible to suppress the positional deviation of ± 2 μm at the maximum in the sub-scanning direction, and it is possible to suppress the color deviation and the positional deviation that can be ignored as a whole. In addition, although the embodiment has been described in which the present invention is applied to a color laser printer, the present invention is not necessarily limited to this, and the point is that it is applicable to an image forming apparatus having a plurality of printing stations.

[0045]

As described above, according to the first aspect of the invention, since the reference frequency signal generating means for generating the reference frequency signal is provided for each printing station, each printing station is assembled at the time of assembly. Since the work such as adjusting the beam power of the laser optical system and measuring the jitter of the motor rotating the beam system and the rotary reflector can be easily performed, and the phase of the horizontal synchronizing signal of each printing station can be fixed at a fixed position, Positional deviation in the sub-scanning direction can be prevented as much as possible.

According to the second aspect of the invention, the frequency division ratio adjustment control is performed during a period other than the period in which the laser optical system is allowed to write an image on the photosensitive member. The gap can be prevented as much as possible.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a color laser printer showing an embodiment of the present invention.

FIG. 2 is a timing chart showing an operation timing of a writing position designating unit of the embodiment.

FIG. 3 is a perspective view showing a configuration of an exposure apparatus of the same embodiment.

FIG. 4 is a block diagram showing a configuration of a phase adjustment circuit of the same embodiment.

FIG. 5 is a timing chart showing the timing of adjusting the frequency division ratio of the frequency division circuit by the frequency division ratio adjustment circuit of the embodiment.

FIG. 6 is a block diagram showing a configuration of a conventional phase adjustment circuit.

[Explanation of symbols]

21 ... Transfer paper 26Y, 26M, 26C, 26K ... Printing station 29, 29Y, 29M, 29C, 29K ... Photosensitive drum 31Y, 31M, 31C, 31K ... Exposure device (laser optical system) 46, 46Y, 46M, 46C, 46K ... Polygon mirror (rotary reflector) 50, 50Y, 50M, 50C, 50K ... Writing position detection sensor (synchronous sensor) 51Y, 51M, 51C, 51K ... Reference clock generation circuit (reference frequency signal generation means) 52Y, 52M, 52C, 52K ... Dividing circuit (reference frequency generating means) 53Y, 53M, 53C, 53K ... PLL circuit 57Y, 57M, 57C ... Dividing ratio adjusting circuit

Claims (2)

[Claims] 1. A rotary reflection device comprising a photoconductor, a charging unit for charging the photoconductor, and a laser beam emitting unit and reflecting the laser beam from the emitting unit to scan the photoconductor charged by the charging unit. A laser optical system having a body for writing an image as an electrostatic latent image on the photoconductor by an exposure operation, developing means for developing the image written by the laser optical system to visualize it, and this developing means. And a sync sensor for receiving a laser beam scanned by the laser optical system and generating a horizontal sync signal for determining an image writing timing on the photoconductor. In an image forming apparatus in which a plurality of printing stations are arranged and an image is formed by sequentially superposing and transferring images on a transfer medium by each printing station, One of the options is a reference printing station and the others are subordinate printing stations. The reference printing station generates a reference frequency signal and a PLL control means for controlling the rotation speed of the rotary reflector in a phase locked loop method. The reference frequency signal generating means and the reference frequency generating means for dividing the reference frequency signal from the reference frequency signal generating means and supplying it to the PLL control means as a reference frequency signal are provided. PLL control means for controlling the rotation speed of the body in a phase-locked loop system, reference frequency signal generation means for generating a reference frequency signal, and a reference frequency signal from the reference frequency signal generation means for frequency division. Reference frequency generating means for supplying a reference frequency signal to the control means, and the reference printing station. Frequency division of the reference frequency generating means by detecting the phase difference between the horizontal synchronization signal from the synchronization sensor and the horizontal synchronization signal from its own synchronization sensor An image forming apparatus comprising: a ratio adjusting unit. 2. The frequency division ratio adjusting means of the subordinate printing station performs the frequency division ratio adjustment control during a period other than the period during which the laser optical system is allowed to write an image on the photoconductor. The image forming apparatus according to item 1.