JP2003057910A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a position shift by making the shift less than a distance corresponding to resolution and to prevent gray coloring. SOLUTION: The image forming device which has a reference mark for positioning toner images of respective colors in image superposition and also has an intermediate transfer body where multi-color writing by a plurality of laser light sources and development are performed and visualized toner images are transferred one after another, is equipped with a synchronous detection and reference mark signal phase detection part 71 which detects the writing start position of the laser beam at the head among a plurality of laser beams and the reference mark and a clock generation and control part 72 which varies the driving clock frequency of a position control motor 70 driving and rotating an image formation medium and the intermediate transfer body according to the relative position relation between a detected synchronous signal and a detected reference mark detection signal.

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 copying machine, a color printer, and a color facsimile, which is provided with a plurality of writing devices and an intermediate transfer member, and more particularly to synchronization when images are transferred in superposition. The present invention relates to an image forming apparatus characterized by control.

[0002]

2. Description of the Related Art Many conventional color image forming apparatuses use a single laser light source to form a color image. In this color image forming apparatus, the photosensitive member is rotationally driven by the rotational driving unit in the sub-scanning direction to be uniformly charged by the charging unit, and one laser beam from a single laser light source is used as a polygon mirror or the like. By scanning with the scanning means and irradiating the charged surface of the photoconductor, images for a plurality of colors are sequentially written and electrostatic latent images for a plurality of colors are sequentially formed. The electrostatic latent images of a plurality of colors on the photoconductor are developed by a plurality of developing means to become a toner image of a plurality of colors, and the toner images of a plurality of colors on the photoreceptor are superposed on the intermediate transfer body by the transfer means. By being transferred, a full-color image is formed. The full-color image on the intermediate transfer body is transferred to a transfer material such as a recording paper or an OHP sheet fed from a paper feeding device by a transfer means and then discharged.

The scanning means is rotationally driven at a predetermined rotational speed by a polygon motor or the like. The line synchronization signal generating means detects the light beam from the scanning means at a predetermined position to generate a line synchronization signal, and the laser beam is modulated by the image signal in synchronization with the line synchronization signal so that the image of each line is imaged. Writing is done. The intermediate transfer reference signal generating means detects the mark on the intermediate transfer body at a predetermined position to generate an intermediate transfer reference signal, and the image forming operation of each color to form the toner image of each color on the photoconductor is performed by the intermediate transfer reference signal. It is done in synchronization with.

In such a color image forming apparatus, when high performance is required, it is necessary to increase the rotation speed of the scanning means or the frequency of the image signal. However, the number of rotations of the scanning means and the frequency of the image signal are limited, and the color image forming operation cannot always be performed at a desired speed. Therefore, a multi-laser type color image forming apparatus having a plurality of laser light sources has been proposed.

In this multi-laser type color image forming apparatus, a plurality of laser beams from a plurality of laser light sources are scanned by a scanning means such as a polygon mirror, and the charged surface of the photoconductor is irradiated with the laser beams. The image for the line is simultaneously written on the photoconductor. The line synchronization signal generation means detects the light beam from the scanning means at a predetermined position, generates one line synchronization signal for each of the plurality of light beams emitted from the plurality of laser light sources, and synchronizes with this line synchronization signal. Thus, a plurality of laser beams are modulated by the image signal, and image writing for a plurality of lines is simultaneously performed. Therefore, at the same time, the amount of information to be written on the photoconductor increases, so that the number of rotations of the scanning unit and the frequency of the image signal can be reduced, and a stable image can be formed at high speed.

[0006]

In a color copying apparatus having a plurality of beams, the rotation of the optical deflector and the photoconductor cannot be synchronized, so that when the toner image is transferred a plurality of times, the photoconductors corresponding to the number of beams are obtained. A positional deviation inevitably occurs in the sub-scanning direction by the above beam interval.

For example, the number of beams is 4 and the resolution is 60.
In the case of 0 dpi, since the beam pitch is 42.3 μm, there is a possibility that a positional deviation of 4 * 42.3 μm = about 170 μm will occur.

This deviation will increase in proportion as the number of beams increases.

Further, in order to avoid as much as possible the positional deviation (the larger the number of a plurality of beams, the greater the influence) caused by the asynchronous rotation of the polygon motor and the rotation of the photosensitive member, the beam writing order is set. An invention for switching is proposed in Japanese Patent Laid-Open No. 10-239939.

This is the phase difference between the belt mark (which consists of a photosensitive member or a position detecting member provided at one position on the transfer belt and a sensor for detecting this during rotation) and the polygon synchronization signal. The beam writing order is switched according to the.

More specifically, since the two-beam two-line correction is not synchronized with the rotation phase of the polygon mirror and the rotation of the primary transfer as shown in FIG. 7, when performing sub-scanning. A positional shift of up to 2 lines occurs. That is, as shown in FIG. 7, assuming that the time from the input of the first belt mark signal to the start of writing is Δt1 and the time from the input of the second belt mark signal to the start of writing is Δt2,
Since the time difference between Δt1 and Δt2 occurs randomly for each color, a maximum of two lines of positional deviation will occur in principle.

Therefore, as shown in FIG. 8, when the belt mark comes before the middle of the synchronization detection, the first LD
When the (laser diode) starts writing from the second image data, the maximum positional deviation of the second image data falls within one dot.

When such two-line correction is performed,
Two pieces of image data are written in the second LD or the first LD for each color. Which LD is used for writing is randomly determined by the belt mark and the timing of synchronization detection.

However, in principle, there is a power deviation between the first LD and the second LD. The breakdown of the deviation is, for example, as shown in FIG.
%, And the root mean square is 20.8%.

As described above, when the writing order of the beams is controlled so that the writing beams are randomly switched according to the phase difference between the belt mark and the synchronization detection signal, even if there is a slight power deviation among the plurality of beams, Even though the image data is the same, the light energy applied to the photoconductor has a deviation for each color, and there is a risk that the color balance is lost. In particular, when halftone gray is reproduced, it may have a significant adverse effect, and in the worst case, it is not inconceivable that the gray color will change to a gray color instead of becoming gray for each copy.

As a color misregistration state, the second LD is the first
If the power of the LD is 10% lower than that of the LD and the deviation between them is 10%, there are combinations as shown in FIG. 9, for example, and the state of color development changes depending on the combination pattern. It should be noted that this figure is shown in a state of being shifted in the main scanning direction for explanatory purposes. It should be noted that, experimentally, when the image is output with the power forcibly shifted, the color difference can be visually confirmed even with a deviation of 2%.

The present invention has been made in view of the circumstances of the prior art as described above, and the first purpose thereof is to reduce the positional deviation by setting the deviation to a resolution distance (42.3 μm in the case of 600 dpi) or less. To do.

A second object is to achieve a positional deviation of one line or less by synchronizing with the rotation of the polygon on the photosensitive member drive or transfer drive side without switching the beam writing order. Further, it is to prevent coloring of the gray.

Further, a third object is to use a driving means capable of accurately controlling the rotational position on the photosensitive member driving or transfer driving side without switching the beam writing order, thereby synchronizing the rotation and the polygon. By doing so, it is possible to achieve a positional deviation of one line or less, and also to prevent coloring of the gray.

[0020]

In order to achieve the above object, a first means is a plurality of laser light sources, an optical lens group for condensing them on an image forming medium, and light for scanning a laser beam on a photoconductor. An optical writing device having a deflector and a synchronization detection device for detecting the writing position of the laser beam, a plurality of developing devices for visualizing the latent image on the photoconductor, and a reference for aligning the toner images of the respective colors when the images are superposed. In an image forming apparatus having a reference mark and an intermediate transfer member for sequentially transferring a visualized toner image, a synchronization detection unit for detecting a writing start position of a head beam of the plurality of laser beams and the reference mark are provided. A reference mark detecting means for detecting, and a synchronization signal detected by the synchronization detecting means,
The image forming medium and the control unit that changes the drive clock frequency of the motor that rotationally drives the intermediate transfer member based on the relative phase relationship with the reference mark detection signal detected by the reference mark detecting unit. It is characterized by

According to a second aspect, in the first means, the control means changes the drive clock frequency between the end of writing the effective image area and the start of writing the next effective image area. And

A third means is the drive means according to the first means, wherein at least two kinds of drive clock frequencies of a motor for driving the image forming medium and the intermediate transfer member are a normal rotation clock frequency and a variable clock frequency. Having a clock frequency, the time to drive at a variable clock frequency or the number of clocks is determined by the phase relationship between the synchronization detection signal and the reference mark signal, and after the writing of the effective image area is completed, the next effective image area is written. It is characterized in that the normal rotation clock frequency is switched to the variable clock frequency before the start and is returned to the normal rotation clock frequency when a predetermined time or the number of clocks is completed.

A fourth means is the first or second means, wherein the control means keeps the time for changing the clock frequency constant and varies the phase depending on the phase relationship between the synchronization detection signal and the reference mark signal. It is characterized in that the clock frequency is determined and the clock frequency is switched.

A fifth means is the first, second, and fourth means, wherein the control means is the time (phase) from the detection of the reference mark signal to the first synchronization detection signal, It is characterized in that the rotational frequency of the intermediate transfer member is delayed by changing the clock frequency of the (stepping) motor by the distance that the surface of the photosensitive member moves.

A sixth means is characterized in that, in the fifth means, the amount by which the rotational position is delayed is equal to or less than the distance in the sub-scanning direction on the photoconductor by the number of laser light sources.

In the first, second and fifth means, a position control motor (stepping motor) or a traveling wave type ultrasonic motor is suitable as the motor.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment> The first embodiment is an embodiment of an electrophotographic digital color image forming apparatus including an electrophotographic digital color copying machine. This color copying machine includes a color printer as an electrophotographic image forming unit that forms an image on a transfer sheet as a transfer material by an electrophotographic process, and a plurality of colors, for example, red, by scanning an original and reading the image. It has a scanner as a document reading means for obtaining blue and green image signals and converting them into digital image signals.

FIG. 1 shows the main structure of the color printer. The color printer includes a photoconductor 11 and a rotating device 12.
And an intermediate transfer belt 13 as an intermediate transfer member, and a writing device 14 as an exposure unit. Photoconductor 11
Although the photoconductor drum was used for the above, a photoconductor belt or the like may be used. The intermediate transfer belt 13 may use an intermediate transfer body such as an intermediate transfer drum and an intermediate transfer roller.

A static elimination lamp (hereinafter referred to as QL) 1 as a static elimination means for eliminating static electricity around the photoconductor 11 is provided around the photoconductor 11.
5. Scorotron charger (hereinafter referred to as charging charger) as charging means for uniformly charging the photoconductor 11.
6, a potentiometer 17 for detecting the surface potential of the photoconductor 11, a photosensor (hereinafter referred to as P sensor) 18 as a density detection means for optically detecting the toner adhesion amount (density) of the photoconductor 11, the photoconductor 11 Pre-transfer charge eliminating lamp (hereinafter, referred to as PTL) 19 for eliminating charge before transferring toner image, photoconductor 1
A belt transfer charger 20 as a transfer unit for transferring the toner image on the image transfer belt 1 to the intermediate transfer belt 13 and a cleaning device 21 for cleaning the photoconductor 11 are arranged.

The rotating device 12 holds a plurality of developing devices for developing the electrostatic latent images of the respective colors on the photoconductor 11 into toner images of the respective colors, for example, developing the electrostatic latent images on the photoconductor 11. To develop a black toner image, the developing device 23 to develop the electrostatic latent image on the photoconductor 11 into a cyan toner image, and to develop the electrostatic latent image on the photoconductor 11 to develop a magenta image. A developing device 24 for forming a toner image and a developing device 25 for developing an electrostatic latent image on the photoconductor 11 to form a yellow toner image are held, and are rotationally driven by a revolver motor as a driving unit to thereby develop a plurality of developing devices 22. ~ 25 are selectively moved to the developing position.

Each of the plurality of developing devices 22 to 25 has a developing sleeve 22a to 25a at the developing position during the developing operation.
Is opposed to the photoconductor 11 and the developing sleeves 22a to 25a are rotationally driven by the developing motor to convey the developer in the developing devices 22 to 25 to the developing area between the photoconductor 11 and the developing sleeves 22a to 25a. The electrostatic latent image on the photoconductor 11 is developed. A revolver home position sensor (hereinafter referred to as a revolver HP sensor) 26 detects that the rotating device 12 is located at the stop reference position.

The intermediate transfer belt 13 has a plurality of rollers 27.
To 32, a predetermined roller among these rollers 27 to 32 is rotationally driven by the drum motor, and the intermediate transfer belt 13 is rotated. Inside the intermediate transfer belt 13, a reference mark serving as a reference for aligning the toner images of the respective colors when superimposing and transferring the toner images of the respective colors on the photoconductor 11 on the intermediate transfer belt 13 for each screen is transferred. One is provided.

In the vicinity of the intermediate transfer belt 13, a belt mark sensor (hereinafter referred to as a mark sensor) 33 as mark detecting means for detecting the reference mark on the intermediate transfer belt 13 along the rotation direction of the intermediate transfer belt 13. , A lubricant application device 34 that abuts the intermediate transfer belt 13 when the lubricant application solenoid is turned on to apply the lubricant on the intermediate transfer belt 13, and as a transfer unit that transfers the color image on the intermediate transfer belt 13 to a transfer sheet. The paper transfer device 35 and the belt cleaning device 36 as cleaning means for cleaning the intermediate transfer belt 13 to remove the toner on the intermediate transfer belt 13 are arranged.

The belt cleaning device 36 is composed of, for example, a cleaning member such as a cleaning blade. The belt cleaning device 36 is brought into contact with and separated from the intermediate transfer belt 13 by turning on / off a solenoid for contacting / separating the belt cleaning device, and contacts the intermediate transfer belt 13. When contacting, the toner on the intermediate transfer belt 13 is removed. The paper transfer device 35 is arranged to face the lowermost part of the intermediate transfer belt 13, and the belt cleaning device 36 is arranged between the paper transfer device 35 and the belt transfer charger 20. Belt cleaning device 3
The intermediate transfer belt cleaning solenoid 6 can be brought into contact with and separated from the intermediate transfer belt 13 by turning on / off the intermediate transfer belt cleaning solenoid, and the lubricant applying device 34 can apply the lubricant to the intermediate transfer belt 13 by turning on / off the lubricant applying solenoid. Yes or no is possible.

The peripheral length of the intermediate transfer belt 13 is the sum of the two A4 lateral sizes and the distance between the transfer materials (conveyance distance between the transfer materials). It is twice as long. One rotation of the photoconductor 11 forms one A4 lateral color image, and two rotations of the photoconductor 11 transfers two screens of the same color onto the intermediate transfer belt 13.

A registration roller 37 is arranged upstream of the paper transfer device 35 and a conveyance belt 38 is arranged downstream of the paper transfer device 35 in the conveyance path along which the transfer paper is conveyed. A fixing device having a fixing roller and a pressure roller pressed against the fixing roller is disposed on the downstream side. The conveyor belt 38 and the fixing roller of the fixing device are rotationally driven by the main motor, and the registration roller 3
Reference numeral 7 is rotationally driven by a main motor via a registration clutch. The registration sensor 39 is the registration roller 3
Detect the transfer paper before 7. The transfer paper is fed to the registration roller 37 from a paper feeding device selected from a plurality of paper feeding devices.

FIG. 2 shows a scanning optical system of the writing device 14. In the writing device 14, a plurality of beams emitted from a light source unit 41 that generates a light beam (hereinafter simply referred to as a beam) composed of a plurality of laser beams is incident on a rotary polygon mirror 43 as a scanning unit via a cylinder lens 42. To do. Each beam incident on the rotating polygon mirror 43 is
Scanning is performed by the rotation of the rotary polygon mirror 43, and the fθ lens 4
4. Through the scanning optical system including the toroidal lens 45 and the folding mirror 46, the photosensitive member 11 is simultaneously exposed and scanned in the main scanning direction at the beam pitch P in the sub scanning direction.

The rotary polygon mirror 43 is rotationally driven by a polygon motor, and a sync detector (not shown) as a line sync signal generating means detects the beam from the toroidal lens 45 at a predetermined position outside the writing area of the photoconductor 11. This synchronization detector includes a light source unit 41 to a cylinder lens 4
2. A plurality of beams incident through the rotary polygon mirror 43, the fθ lens 44, and the toroidal lens 45 are detected, and one output signal is output as a line synchronization signal for the plurality of beams.

Here, the light source unit 41 emits a plurality of beams modulated in accordance with the image signals by driving the light sources 41a and 41b, which are usually two semiconductor lasers, by the image signals. Further, the light source unit 41 is provided with a pitch adjusting mechanism for adjusting the beam pitch in the sub-scanning direction, and the light source unit 41 is rotated by this pitch adjusting mechanism to adjust the beam pitch in the sub-scanning direction. Light source unit 4
1, the light source 41 includes two semiconductor lasers.
The beams emitted from a and 41b are collimator lenses 4
The parallel light beams 1c and 41d are formed into parallel light beams, and are shaped into a predetermined light beam diameter by passing through a slit of an aperture member (not shown).

The beam from one of these aperture members has its polarization direction rotated by 90 degrees by the half-wave plate 41e, is incident on the beam synthesizing prism 41f as the beam synthesizing means, and is incident on the inclined surface of the beam synthesizing prism 41f. The light is reflected on the inner surface, reflected by the polarization beam splitter surface of the beam combining prism 41 f, and combined with the beam from the other aperture member serving as the reference and in the vicinity of its optical axis.

The two beams from the beam combining prism 41f are emitted at a predetermined angle .theta.m in the main scanning direction, and the collimating lens 41 in the semiconductor laser 41a.
By rotating the light source unit 41 around the optical axis by slightly decentering the optical axis with respect to c in the main scanning direction, a sub-scanning angle component of the emission angle between the two beams is obtained, and The beam pitch is adjusted. If the rotation angle of the light source unit 41 is α, then Δθs = θm · sin α. Although the number of light sources 41a and 41b is two, the number of light sources may be three or more.

FIG. 3 shows the control section of the color printer. The CPU 47 executes processing such as calculation according to the contents of the control program, and the ROM 48 contains the control program. RAM49 is used for storing and saving data,
The CPU 47, ROM 48 and RAM 49 are connected by a data bus and an address bus. The serial communication controller 50 includes the control unit of the scanner and the CPU 4
7, and sends and receives commands to and from the CPU 47, and is connected to the CPU 47 by a data bus and an address bus.

The write control IC 51 as a write control unit for controlling the exposure of the photoconductor 11 is connected to the CPU 47 by a data bus and an address bus, and has an exposure L.
It is connected to the D control unit 52 and the polygon motor 43a to control the exposure LD control unit 52 and the polygon motor 43a. The exposure LD control unit 52 controls the lighting of the LDs 41a and 41b in the writing device 14 according to an input signal from the writing control IC 51. I / O
The controller 53 controls the input / output of the CPU 47. C
The PU 47, the ROM 48, the RAM 49, the serial communication controller 50, the write control IC 51, and the I / O controller 53 constitute a control unit of the color printer.

The fixing device 54 has a fixing thermistor for detecting the surface temperature of the fixing roller and a fixing heater for heating the fixing roller, and the CPU 47 A / D converts the temperature detection signal of the fixing thermistor to A / D thereof. The surface temperature of the fixing roller is controlled to be constant by outputting a pulse width modulation (PWM) pulse for controlling the fixing heater based on the converted value to control the fixing heater on / off.

The CPU 47 outputs the output voltage fed back from the power pack unit 55 as a high voltage power source
The power pack unit 5 outputs the PWM signal to the power pack unit 55 based on the A / D conversion value based on the A / D conversion value.
5 to control the output voltage. Power pack unit 55
Applies a high voltage to the charging charger 16, the belt transfer charger 20, and the paper transfer device 35, and applies a grid voltage to the charging charger 16 to develop the developing devices 22 to 25.
A developing bias voltage is applied to each of the developing sleeves 22a to 25a.

An electrometer circuit 56 including the electrometer 17 detects the surface potential of the photoconductor 11 and the output signal of the electrometer 17 is CP.
It is input to the A / D input terminal of U47. P including a P sensor 18 including a light emitting diode and a phototransistor
The sensor circuit 57 optically detects the toner adhesion amount (density) of the photoconductor 11, and the phototransistor output signal of the P sensor 18 is input to the A / D input terminal of the CPU 47. C
The PU 47 connects the light emitting diode drive circuit of the P sensor 18 with P
The WM pulse is output to control the lighting of the light emitting diode.

The main motor 58 rotationally drives the transfer material transport system for transporting the transfer material, and the drum motor 59 rotationally drives the photoconductor 11 and the intermediate transfer belt 13. The developing motor 60 is used for the developing sleeve 22 of the developing devices 22 to 25.
a to 25a are rotationally driven, and these motors are ON signals from the CPU 47, a half speed signal for reducing the speed to half, and a lock for determining that the speed has reached the target speed. A signal is input.

The revolver motor 61 rotates the rotating device 12 equipped with the developing devices 22 to 25 in response to the four-phase output signal input from the CPU 47, and develops the developing device of the developing devices 22 to 25 that develops the designated color. Stop in position. The toner replenishment motor 62 is provided in each of the developing devices 22 to 25 from the toner cartridges such as black, cyan, magenta,
The toners of the respective colors of yellow are replenished, and the CPU 47 controls the on-time of the toner replenishment motor 62 according to the amounts of adhered toners of the colors of black, cyan, magenta, and yellow on the photoconductor 11 based on the input signal from the P sensor 18. To do.

The output signal of the mark sensor 33, which serves as an intermediate transfer reference signal that serves as a reference for aligning the toner images at the time of image superposition, is input to the interrupt terminal of the CPU 47 because strict accuracy in timing is required. It The output signal of the revolver HP sensor 26, which serves as a reference for the stop position of the rotating device 12, requires a strict timing accuracy to switch the output pulse (four-phase output signal) from the CPU 47 to the revolver motor 61 while the rotating device 12 is rotating. Therefore, it is input to the interrupt terminal of the CPU 47.

Next, in this embodiment, for example, A4
A basic sequence for continuously forming, for example, four screens of a full-color image of a lateral size (A4 size in a direction in which the transfer material conveying direction is shortened) will be described. In the color printer, in the stopped state, it is assumed that the rotating device 12 is stopped in the state where the developing device 22 whose developing color is black is located at the developing position. When a color image forming start (print start) command is received from the system control unit, the control unit of the color printer (hereinafter referred to as the printer control unit) turns on the QL 15 and the drum motor 59. For this reason, the drum motor 59 rotates to rotationally drive the photoconductor 11 and the intermediate transfer belt 13, and the photoconductor 11 is neutralized by the QL 15.

The printer control unit uses QL1 on the photoconductor 11.
When the charge removal start position by 5 reaches the position where the charge charger 16 is charged, the charge charger 16 is turned on. Next, when the position where charging by the charger 16 on the photoconductor 11 is started reaches the developing position, the printer control unit turns on the developing bias of the power pack unit 55 and simultaneously rotates the developing motor 60.

Further, in the printer control section, the position facing the developing position when the developing bias on the photoconductor 11 is turned on is the belt transfer position (the position where the toner image on the photoconductor 11 is transferred to the intermediate transfer belt 13). When it reaches, the belt transfer charger 20 is turned on. From the start of rotation of the photoconductor 11 to this point, the prerotation of the photoconductor 11 is performed.

At the same time, when the mark sensor 33 detects the reference mark on the intermediate transfer belt 13 by the rotation of the intermediate transfer belt 13, the mark detection signal of the mark sensor 33 is input to the interrupt terminal of the CPU 47 as the intermediate transfer reference signal, and the printer The control unit performs interrupt processing on the program. The printer control unit transmits a scan start command for the first color (black) of the first screen to the control unit of the scanner (hereinafter referred to as the scanner control unit) in the interrupt process.

When the scanner control unit receives the scan start command for the first color on the first screen from the printer control unit, the scanner control unit causes the scanner to read the original document to obtain the image signal for the first color on the first screen, and the read plural colors ( Red, blue,
The image signal of (green) is converted into the image signal of the first color on the first screen and transferred to the printer control unit.

The printer control section transfers the image signal transferred from the scanner control section to the writing control IC 51,
The writing control IC 51 converts the image signal into exposure data for the first color on the first screen (data for driving the semiconductor laser in the writing device 14 to perform the exposure for the first color) and outputs it to the exposure LD control unit 52. . The exposure LD control unit 52 uses the first screen 1 from the writing control IC 51.
LD41 in the writing device 14 according to the exposure data of the color
The first screen 1 is displayed on the photoconductor 11 by controlling the lighting of a and 41b.
By writing the image of the color, the electrostatic latent image of the first color on the first screen is formed.

The printer controller causes the developing motor 60 to start the rotation of the developing sleeve 22a of the developing device 22 for developing the first color of the first screen prior to the start of writing by the writing device 14. When the electrostatic latent image of the first color on the first screen on the photoconductor 11 reaches the developing position, the developing device 22 starts developing the electrostatic latent image to form a toner image of the first color on the first screen.

When the toner image of the first color of the first screen on the photoconductor 11 reaches the first transfer position (belt transfer position), it is transferred onto the intermediate transfer belt 13 by the belt transfer charger 20. When the scanner finishes reading the document to obtain the image signal of the first color on the first screen, it quickly returns to the home position and starts reading the document to obtain the image signal of the next color on the second screen (black). Wait at home position until.

Next, the printer controller sends a scan start command for the first color of the second screen to the scanner controller.
When the scanner control unit receives the scan start command for the first color on the second screen from the printer control unit, the scanner control unit displays the second
The original is read to obtain the image signal of the first color on the screen, the read image signals of a plurality of colors (for example, red, blue, and green) are converted into the image signal of the first color on the second screen and transferred to the printer controller. .

The printer controller transfers the image signal transferred from the scanner controller to the write control IC 51,
The writing control IC 51 converts the image signal into exposure data for the first color on the second screen and outputs the exposure data to the exposure LD control unit 52. The exposure LD control unit 52 writes the image of the first color of the second screen on the photoconductor 11 by controlling the lighting of the LDs 41a and 41b in the writing device 14 according to the exposure data of the first color of the second screen from the write control IC 51. Thus, the electrostatic latent image of the first color on the second screen is formed.

The developing sleeve 22a of the developing device 22 for developing the first color rotates without stopping even after the development of the electrostatic latent image of the first color on the first screen, and rotates during writing by the writing device 14. is doing. When the electrostatic latent image of the first color on the second screen on the photoconductor 11 reaches the developing position, the developing device 22 starts developing the electrostatic latent image to form a toner image of the first color on the second screen.

When the toner image of the first color of the second screen on the photoconductor 11 reaches the first transfer position (belt transfer position), it is transferred onto the intermediate transfer belt 13 by the belt transfer charger 20. When the scanner finishes reading the document for obtaining the image signal of the first color on the second screen, it quickly returns to the home position and starts reading the document for obtaining the image signal of the second color (cyan) on the first screen. Wait at home position until.

When the development of the electrostatic latent image for the first color on the second screen is completed, the printer control unit causes the revolver motor 61 to stop the developing device 23 for developing the second color (cyan) at the developing position. The rotating device 12 is rotated. Further, the printer control unit causes the belt cleaning device contact / separation solenoid 66 to separate the belt cleaning device 36 from the intermediate transfer belt 13 so that the image on the intermediate transfer belt 13 is not erased.

Thereafter, in the printer control section, the mark sensor 33 detects the reference mark on the intermediate transfer belt 13 and C
When the mark detection signal from the mark sensor 33 is input to the interrupt terminal of the PU 47 as the intermediate transfer reference signal, the interrupt process is started and a scan start command for the second color (cyan) of the first screen is transmitted to the scanner control unit.

When the scanner control unit receives the scan start command for the second color on the first screen from the printer control unit, it causes the scanner to read the original document to obtain the image signal for the second color on the first screen, and the read plural colors are read. The image signal is converted into the image signal of the second color on the first screen and transferred to the printer control unit.

The printer controller transfers the image signal transferred from the scanner controller to the writing control IC 51,
The writing control IC 51 converts the image signal into exposure data for the second color on the first screen and outputs it to the exposure LD control unit 52. The exposure LD control unit 52 controls the lighting of the LDs 41a and 41b in the writing device 14 according to the exposure data of the first screen second color from the writing control IC 51 to write the image of the second screen first color on the photoconductor 11. Thus, the electrostatic latent image of the second color on the first screen is formed.

The printer control unit controls the rotation of the developing sleeve 23a of the developing device 23 for developing the second color by the developing motor 6
0 is started prior to the start of writing by the writing device 14. When the electrostatic latent image of the second color on the first screen on the photoconductor 11 reaches the developing position, the developing device 23 starts developing the electrostatic latent image to form a toner image of the second color on the first screen.

When the toner image of the second color on the first screen on the photosensitive member 11 reaches the first transfer position, the belt transfer charger 20
Thus, the toner image of the first color of the first screen is transferred onto the intermediate transfer belt 13 at the same position as the toner image of the first color of the first screen. When the scanner finishes reading the original to obtain the image signal of the second color on the first screen, it quickly returns to the home position and starts reading the original to obtain the image signal of the second color on the second screen (cyan). Wait at home position until.

Next, the printer controller sends a scan start command for the second color of the second screen to the scanner controller.
When the scanner control unit receives a scan start command for the second color on the second screen from the printer control unit, the scanner control unit displays the second
The original is read to obtain the image signal of the second color of the screen, the read image signals of a plurality of colors are converted into the image signal of the second color of the second screen, and the image signals are transferred to the printer control unit.

The printer controller transfers the image signal transferred from the scanner controller to the write control IC 51,
The writing control IC 51 converts the image signal into exposure data for the second color of the second screen and outputs the exposure data to the exposure LD control unit 52. The exposure LD control unit 52 controls the lighting of the LDs 41a and 41b in the writing device 14 according to the exposure data of the second color of the second screen from the write control IC 51 to write the image of the second color of the second screen on the photoconductor 11. Thus, an electrostatic latent image of the second color on the second screen is formed.

The developing sleeve 23a of the developing device 23 for developing the second color rotates without stopping even after the development of the electrostatic latent image of the second color on the first screen, and rotates during writing by the writing device 14. is doing. When the electrostatic latent image of the second color on the second screen on the photoconductor 11 reaches the developing position, the developing device 23 starts developing the electrostatic latent image to form a toner image of the second color on the second screen.

When the toner image of the second color on the second screen on the photosensitive member 11 reaches the first transfer position, the belt transfer charger 20
As a result, the toner image of the first color of the second screen is transferred onto the intermediate transfer belt 13 at the same position as the toner image of the first color of the second screen. When the scanner finishes reading the original to obtain the image signal of the second color on the second screen, it quickly returns to the home position and starts reading the original to obtain the image signal of the next third color (magenta) on the first screen. Wait at home position until. When the development of the electrostatic latent image for the second color on the second screen is completed, the printer control unit causes the revolver motor 61 to rotate the rotation device 12 so that the developing device 24 for developing the third color (magenta) comes to the development position and stops. To rotate.

After that, in the printer controller, the mark sensor 33 detects the reference mark on the intermediate transfer belt 13 and C
When a mark detection signal is input from the mark sensor 33 to the interrupt terminal of the PU 47, the interrupt process is started and a scan start command for the third color (magenta) of the first screen is transmitted to the scanner control unit.

When the scanner control unit receives the scan start command for the third color of the first screen from the printer control unit, the scanner control unit causes the scanner to read the document for obtaining the image signal of the third color of the first screen, and the read plural colors are read. The image signal is converted into an image signal of the third color on the first screen and transferred to the printer control unit.

The printer control section transfers the image signal transferred from the scanner control section to the write control IC 51,
The writing control IC 51 converts the image signal into exposure data for the third color of the first screen and outputs it to the exposure LD control unit 52. The exposure LD control unit 52 controls the lighting of the LDs 41a and 41b in the writing device 14 according to the exposure data of the first screen and third color from the write control IC 51 to write the image of the first screen and third color on the photoconductor 11. Thus, an electrostatic latent image of the third color on the first screen is formed.

The printer control unit controls the rotation of the developing sleeve 24a of the developing device 24 for developing the third color to cause the developing motor 6 to rotate.
0 is started prior to the start of writing by the writing device 14. When the electrostatic latent image of the first screen and the third color on the photoconductor 11 reaches the developing position, the developing device 24 starts the development of the electrostatic latent image to form the toner image of the third color of the first screen.

When the toner image of the third color of the first screen on the photoconductor 11 reaches the first transfer position, the belt transfer charger 20
Thus, the first screen 1 is placed at the same position as the first screen first color toner image and the first screen second color toner image on the intermediate transfer belt 13.
The toner image of the first color and the toner image of the second color on the first screen are superimposed and transferred. When the scanner finishes reading the document for obtaining the image signal of the third color on the first screen, it quickly returns to the home position and starts reading the document for obtaining the image signal of the next third color (magenta) on the second screen. Wait at home position until.

Next, the printer controller sends a scan start command for the third color on the second screen to the scanner controller.
When the scanner control unit receives a scan start command for the third color of the second screen from the printer control unit, the scanner control unit displays the second
The original is read to obtain the image signal of the third color of the screen, the read image signals of a plurality of colors are converted into the image signal of the third color of the second screen, and the image signals are transferred to the printer control unit.

The printer controller transfers the image signal transferred from the scanner controller to the write control IC 51,
The writing control IC 51 converts the image signal into exposure data for the third color of the second screen and outputs the exposure data to the exposure LD control unit 52. The exposure LD control unit 52 controls the lighting of the LDs 41a and 41b in the writing device 14 according to the exposure data of the third color of the second screen from the writing control IC 51 to write the image of the third color of the second screen on the photoconductor 11. Thus, an electrostatic latent image of the third color on the second screen is formed.

The developing sleeve 24a of the developing device 24 for developing the third color rotates without stopping even after the development of the electrostatic latent image of the third color on the first screen, and rotates during writing by the writing device 14. is doing. When the electrostatic latent image of the second screen and the third color on the photoconductor 11 reaches the developing position, the developing device 24 starts the development of the electrostatic latent image to form the toner image of the third color of the second screen.

When the toner image of the third color of the second screen on the photoconductor 11 reaches the first transfer position, the belt transfer charger 20
The second screen 1 is placed at the same position as the second screen first color toner image and the second screen second color toner image on the intermediate transfer belt 13.
The toner image of the second color and the toner image of the second color on the second screen are superimposed and transferred.

When the scanner finishes reading the original document for obtaining the image data of the third color on the second screen, it quickly returns to the home position and obtains the original image data for the fourth color (yellow) of the next first screen. Wait at the home position until scanning starts. The printer controller is the second
When the development of the electrostatic latent image for the third color on the screen is completed, the revolver motor 61 rotates the rotating device 12 so that the developing device 25 for developing the fourth color (yellow) comes to the developing position and stops.

After that, in the printer controller, the mark sensor 33 detects the reference mark on the intermediate transfer belt 13 and C
When the mark detection signal from the mark sensor 33 is input to the interrupt terminal of the PU 47 as the intermediate transfer reference signal, the interrupt process is started and a scan start command for the fourth color of the first screen is transmitted to the scanner control unit.

When the scanner control section receives the scan start command for the fourth color of the first screen from the printer control section, the scanner control section causes the scanner to read the original document for obtaining the image data of the fourth color of the first screen, and the read plural colors are read. The image data is converted into image data of the fourth color on the first screen and transferred to the printer control unit.

The printer control unit transfers the image data transferred from the scanner control unit to the write control IC 51, and the write control IC 51 converts the image data into the exposure data of the fourth color of the first screen and the exposure LD control unit. Output to 52. The exposure LD control unit 52 controls the lighting of the LDs 41a and 41b in the writing device 14 according to the exposure data of the fourth color of the first screen from the write control IC 51 to write the image of the fourth color of the first screen on the photoconductor 11. Thus, the electrostatic latent image of the fourth color on the first screen is formed.

The printer control section controls the rotation of the developing sleeve 25a of the developing device 25 for developing the fourth color by the developing motor 6
0 is started prior to the start of writing by the writing device 14. When the electrostatic latent image of the fourth color on the first screen on the photoconductor 11 reaches the developing position, the developing device 25 starts developing the electrostatic latent image to form a toner image of the fourth color on the first screen.

When the toner image of the fourth color on the first screen on the photosensitive member 11 reaches the first transfer position, the belt transfer charger 20
As a result, the toner image of the first screen first color, the toner image of the second color of the first screen, and the toner image of the third color of the first screen are located at the same position on intermediate transfer belt 13 The full-color image of the first screen is formed by transferring the toner image of the first color and the toner image of the third color on the first screen in an overlapping manner.
When the scanner finishes reading the document for obtaining the image data of the fourth color on the first screen, it quickly returns to the home position and starts reading the document for obtaining the image data of the fourth color (yellow) of the next second screen. Wait at home position until.

Next, the printer controller sends a scan start command for the fourth color of the second screen to the scanner controller.
When the scanner control unit receives the scan start command for the fourth color on the second screen from the printer control unit, the scanner control unit displays the second
The original is read to obtain the image data of the fourth color of the screen, the read image data of a plurality of colors is converted into the image data of the fourth color of the second screen, and the image data is transferred to the printer control unit.

The printer control section transfers the image data transferred from the scanner control section to the write control IC 51, and the write control IC 51 converts the image data into the exposure data of the fourth color of the second screen and the exposure LD control unit. Output to 52. The exposure LD control unit 52 controls the lighting of the LDs 41a and 41b in the writing device 14 based on the exposure data of the fourth color of the second screen from the writing control IC 51 to write the image of the fourth color of the second screen on the photoconductor 11. Thus, the electrostatic latent image of the fourth color on the second screen is formed.

The developing sleeve 25a of the developing device 25 for developing the fourth color rotates without stopping even after the development of the electrostatic latent image of the fourth color on the first screen, and rotates during writing by the writing device 14. is doing. When the electrostatic latent image of the fourth color of the second screen on the photoconductor 11 reaches the developing position, the developing device 25 starts developing the electrostatic latent image to form a toner image of the fourth color of the second screen.

When the toner image of the fourth color on the second screen on the photoconductor 11 reaches the first transfer position, the belt transfer charger 20
The second screen first color toner image, the second screen second color toner image, the second screen second color toner image, and the second screen third color toner image on the intermediate transfer belt 13 The toner image of the second color and the toner image of the second color of the second screen are transferred together to form a full-color image of the second screen.
When the scanner finishes reading the document to obtain the image data of the fourth color on the second screen, it quickly returns to the home position and starts reading the document to obtain the image data of the next color on the third screen (black). Wait at home position until.

The printer controller completes the development of the electrostatic latent image of the fourth color on the second screen and transfers the toner image of the fourth color on the second screen to the belt (transfer from the photoconductor 11 to the intermediate transfer belt 13).
When the process is completed, the full-color image on the intermediate transfer belt 13 is transferred to the transfer material immediately before the full-color image on the intermediate transfer belt 13 reaches the paper transfer position between the intermediate transfer belt 13 and the paper transfer device 35. The transfer device 35 is turned on, and the paper transfer device 35 transfers the full-color image on the intermediate transfer belt 13 onto the transfer material.

When the secondary transfer of the full-color image of the first screen and the full-color image of the second screen (transfer of the full-color image from the intermediate transfer belt 13 to the transfer material) is completed, the printer control section sets the first color (black). The revolver motor 6 is arranged so that the developing device 22 for developing comes to the developing position and stops.
The rotating device 12 is rotated to 1.

Transfer of the full-color image of the first screen and the full-color image of the second screen from the intermediate transfer belt 13 to the transfer material for the first screen and the transfer material for the second screen is continued, and the first transfer is continued.
The transfer material for the first screen and the transfer material for the second screen to which the full-color image on the screen and the full-color image on the second screen are respectively transferred are conveyed to a fixing device by a conveyor belt 38, and the full-color image on the first screen is conveyed by the fixing device. Then, the full-color image on the second screen is fixed and discharged to the paper discharge tray.

When the mark sensor 33 detects the reference mark on the intermediate transfer belt 13 by the rotation of the intermediate transfer belt 13, the printer control unit inputs the mark detection signal from the mark sensor 33 to the interrupt terminal of the CPU 47 as the intermediate transfer reference signal. At that time, an interrupt process is entered on the program, and a scan start command for the first color (black) of the third screen is transmitted to the scanner controller.

When the scanner control section receives the scan start command for the first color of the third screen from the printer control section, it causes the scanner to read the original document for obtaining the image data of the first color of the third screen, and the read plural colors are read. The image data is converted into the image data of the first color on the third screen and transferred to the printer control unit.

The printer control section transfers the image data transferred from the scanner control section to the write control IC 51, and the write control IC 51 converts the image data into the exposure data of the first color of the third screen and the exposure LD control unit. Output to 52. The exposure LD control unit 52 writes the image of the first color of the third screen on the photoconductor 11 by controlling the lighting of the LDs 41a and 41b in the writing device 14 according to the exposure data of the first color of the third screen from the write control IC 51. Thus, an electrostatic latent image of the first color on the third screen is formed.

The steps from the development of the electrostatic latent image of the first color on the third screen to the belt transfer of the toner image of the fourth color on the fourth screen will be described below from the development of the electrostatic latent image of the first color on the first screen to the second screen. Four
It is performed in the same manner as the steps up to the belt transfer of the color toner image. After that, similarly to the formation of the full-color image of the first screen and the full-color image of the second screen, the full-color image of the third screen and the full-color image of the fourth screen are formed.

When the development of the electrostatic latent image of the fourth color on the fourth screen is completed and the belt transfer of the toner image of the fourth color on the fourth screen is completed, the printer control section transfers the full-color image on intermediate transfer belt 13 to the transfer material. The full-color image on the intermediate transfer belt 13 to be transferred to the intermediate transfer belt 13 and the paper transfer device 3
5 just before reaching the paper transfer position between
Is turned on, and the paper transfer device 35 transfers the full-color image on the intermediate transfer belt 13 onto the transfer material.

Thereafter, the printer controller turns on the belt cleaning device contact / separation solenoid 66 to bring the belt cleaning device 36 into contact with the intermediate transfer belt 13, thereby causing the belt cleaning device 36 to start cleaning the intermediate transfer belt 13.

When the secondary transfer of the full-color image of the third screen and the full-color image of the fourth screen is completed, the printer control section causes the developing device 22 for developing the first color (black) to come to the developing position and stop. Then, the revolver motor 61 rotates the rotating device 12. After that, the printer controller
The solenoid 66 for contacting / separating the belt cleaning device is turned off to set the belt cleaning device 36 to the intermediate transfer belt 13.
Away from. Further, the printer control unit controls the drum motor 59 to control the stop position of the intermediate transfer belt 13, and thereafter, this embodiment enters a standby state.

In this embodiment, two reference marks on the intermediate transfer belt 13 may be provided at predetermined intervals (for example, equal intervals) in the rotation direction of the intermediate transfer belt 13. In this case, the printer control unit sends a scan start command to the scanner control unit based on the detection time of the first reference mark on the intermediate transfer belt 13 by the mark sensor 33 for each color, so that one screen of the scanner is displayed. A second reference mark on the intermediate transfer belt 13 is formed by reading a document to obtain image data and forming one full-color image to be formed first among the two full-color images on the intermediate transfer belt 13. Of the two screens on the intermediate transfer belt 13 by sending a scan start command to the scanner control unit based on the detection time of the mark sensor 33 of the above, causing the scanner to read an original for obtaining image data of another one screen. The full color image is controlled so as to form one full-color image to be formed later.

FIG. 4 is a block diagram showing a schematic structure of a control circuit according to the clock control of the present invention. The position control motor, which serves as a motor for driving the photoconductor and the intermediate transfer drum, is integrated with a control circuit using a DC motor and an encoder, and tries to keep the absolute position with respect to the input clock to rotate. A description will be given by taking as an example what is constituted by a general servo motor.

This control circuit mainly includes a synchronization detection / reference mark signal phase detection unit (hereinafter referred to as a phase detection unit) 71, a clock generation / control unit 72, an arithmetic control circuit 68, and a phase comparison circuit 67. The control signal is output from the clock generation / control unit 72 to the position control motor 70.

The phase detecting section 71 comprises a counter 63 and a phase comparing circuit 64. The counter 63 is cleared by the line synchronization signal from the synchronization detector and counts up the clock from a clock generating section (not shown). The count value is output to the phase comparison circuit 64. The phase comparison circuit 64 compares the phase between the mark detection signal input as the intermediate transfer reference signal from the mark sensor 33 and the line synchronization signal from the synchronization detector. In FIG. 7, the first count value or the second count value is obtained. In the example of FIG. 1, the photosensitive member and the intermediate transfer member are mechanically connected by the timing belt by the timing belt 40, and are integrally driven by the position control motor 41, and the respective rotational relative positions do not shift. It may be provided on the photoreceptor 11 side. In addition to this, the photosensitive member 11 side rotates at a constant speed (independent motor), and the intermediate transfer belt 1
The position control motor 41 is installed on the 3 side, and the intermediate transfer belt 1
A mark sensor may be provided on the 3 side.

At this time, the phase comparison circuit 64 operates when the mark signal is input from the mark sensor 33,
The phase difference between the intermediate transfer reference signal and the line synchronization signal is obtained by taking in the count value of the counter 63 (the count value immediately before reset by the line synchronization signal of the counter 63) at the time when the first line synchronization signal is input from the synchronization detector. Is output to the arithmetic control circuit 68. Arithmetic control circuit 6
Reference numeral 8 may be a CPU or a hard-operated arithmetic unit. The arithmetic control circuit 68 calculates a phase shift amount from the count value, converts the phase shift amount into a distance, and sets the shift amount to the position control motor (position correction amount). The calculation process at this time is shown below.

Phase shift amount = total count value of synchronization interval (fixed value) / first count value (FIG. 7) Shift amount b = (1-phase shift amount) * (sub-value at synchronization interval time (ta)) Moving distance in scanning direction) = Δt1 / ta * (moving distance in sub-scanning direction at synchronization interval time (ta)) The clock generation / control unit 71 includes a clock generation unit 65, a counter 66, and a phase (count value). ) Comprising a comparison circuit 67 and the like. The clock generation unit 65 can generate a clock by dividing the internal clock by 7, and can generate at least two types of clocks, that is, a clock frequency (F0) during normal rotation and a clock frequency during variable rotation. . This clock frequency can be switched by HL of the GATE signal. During normal rotation of the position control motor (during writing of the latent image), the GATE signal is in the H state, and the clock having the frequency of F0 is output from the out output to rotate the position control motor 70 at a constant speed. When the detection of the phase detector 71 is completed, the phase measurement result is sent to the arithmetic control circuit 68. The arithmetic control circuit 68 calculates the shift amount as described above, and further calculates the time to switch to the variable clock frequency or the number of clocks.

The number of clocks n of the variable clock frequency is n = F1.b / a. (F0-F1), where a is the amount of movement of the photosensitive member surface per pulse of the position control motor and b is the amount of displacement. Given in. As an example, F0 = 2500 Hz, F1
= 1965 Hz, a = 98 μm, b = 80 μm, n = 3 pulses. The state of the clock in this case is shown in FIG.

The arithmetic control circuit 68 sets the number of clocks n of the variable clock in the phase (count value) comparison circuit 67. Next, the GATE signal is set to L for the clock generator 65. As a result, the clock frequency of the out output given to the position control motor 70 is switched from F0 to F1. In the example of FIG. 5, 2500 Hz to 1965 H
Switch to z. At the same time, the counter 66 starts counting the number of clocks output from the clock generator 65. That is, the number of clocks after the frequency is switched to F1 is counted.

The phase (count value) comparison circuit 67 compares the count value with the number of clocks of the variable clock set inside, and when the same value or the count value is exceeded, a signal is sent to the operation control circuit 68. In response to this, the GATE signal of the clock generator 65 is set to L, and the clock frequency is returned to the normal rotation frequency (F0). At this time,
The output of the phase (count value) comparison circuit 67 may directly control the GATE signal of the clock generator without passing through the arithmetic control circuit 68. In the example of FIG. 5, F for exactly 3 clocks is used.
The frequency of 1 (1965 Hz) is output, and then the normal clock frequency F0 (2500 Hz) is restored. Compared to the clock (waveform above Fig2) in which the normal rotation clock F0 (2500 Hz) is continuous, the frequency is F
Just at the third clock from the time of switching to 1 (1965 Hz), the clock phase is delayed by the shift amount b = 80 μm. As a result, the rotation position of the photoconductor 11 is delayed by the shift amount (position correction amount).

The mechanical position of the mark detector 33 is detected from the transfer position on the transfer belt 13 rather than the distance (L1) from the beam irradiation position on the photoconductor 11 to the transfer in FIG. The distance to the position is set to be long by L2, and in this embodiment, L2 = about 60 mm.
Is set to. That is, the mark detection signal is output,
Further, after the synchronization detection signal is input, the write operation is started after waiting a time of L2. In this example, assuming that the linear velocity of the transfer belt is about 200 mm / s, writing is started after this time t0 = 60/200 = 0.3 s.

As described above, since the belt mark signal is detected immediately after the transfer of the previous color is completed, the shift amount is calculated after detecting the belt mark signal, and the time until the writing of the next color is started (main If the amount of shift is corrected by changing the clock frequency of the position control motor to stabilize the rotation, the position correction is completed by the next color writing. If the time is 0.3 sec, the rotation can be stabilized with a sufficient margin.

That is, since this position correcting operation is performed every time (for each color) after the detection of the belt mark and before the start of the next image formation (writing start), the polygon mirror and the photoconductor are not synchronized. The random positional deviation that occurs due to this is corrected from the image front end, and the positional deviation can be minimized. The position-corrected transfer image on the transfer belt and the toner image on the photosensitive member of the next color are transferred at the same position without any positional deviation for one line during transfer. In the case of the present embodiment, since the example of two beams is used, the maximum value of the shift amount (position correction amount) is a maximum of two lines (42.3 μm * for 600 dpi *).
2 = 84.6 μm). If the number of beams increases, a shift amount (position correction amount) corresponding to the number of beams is required. However, by setting the shift amount to the maximum correction amount or less, the load on the motor when inputting the shift amount is increased. Can be minimized.

Although the position control motor 70 is used in this embodiment, an ultrasonic motor 75 as shown in FIG. 6 can be used instead of the position control motor 70. The ultrasonic motor 75 is driven by the motor driver 69 as shown in FIG. 6, and the clock from the clock generator 65 is input to the motor driver 69. The motor driver 69 operates the ultrasonic motor 7 according to this clock.
Drive 5 Since the ultrasonic motor rotates linearly in proportion to the input clock number, absolute rotational position control is possible.

Other parts, which are not particularly described, are constructed and function in the same manner as in the above-described embodiment shown in FIGS. 1 to 5.

As described above, according to the present embodiment, the writing start position of the head beam of a plurality of laser beams is detected by the synchronization detecting device, and the phase difference between this signal and the belt mark signal is fed to the transfer motor. -Since the position is corrected by performing the feedback, it is possible to prevent the positional deviation in a plurality of beams. Further, since the positional deviation can be prevented without switching the writing order of the two beams, it is possible to prevent gray coloring between the copies at the same time.

Further, since the timing of changing the target position ends between the end of transfer of the effective image area and the start of transfer of the next effective transfer area, a plurality of images in the effective image area are not detected, Positional deviation in the beam can be prevented.

Further, since the control clock of the position control motor is changed only by at least two kinds of frequencies, the clock generation circuit can be simplified and the cost can be reduced.

Since the time for changing the clock is constant, the stability of the system is improved.

Further, from the time (phase) of the reference mark signal and the synchronization signal, the rotational position of the photoconductor or the transfer belt is corrected by the amount of positional deviation randomly generated due to the non-synchronization of the polygon and the photoconductor or the transfer belt. Therefore, it is possible to prevent the positional deviation caused by the non-synchronization.

Furthermore, since the rotational position change amount is equal to or less than the distance in the sub-scanning direction on the photoconductor corresponding to the number of laser light sources, it is possible to minimize the load fluctuation on the photoconductor or the intermediate transfer motor, and The adverse effect of can be prevented.

[0122]

As described above, according to the present invention, the synchronization detecting means for detecting the writing start position of the first beam of the plurality of laser beams, the reference mark detecting means for detecting the reference mark, and the synchronization. A drive clock frequency of a motor that rotationally drives the image forming medium and the intermediate transfer member based on the relative phase relationship between the synchronization signal detected by the detection means and the reference mark detection signal detected by the reference mark detection means. And a control means for changing
The positional deviation can be reduced to 42.3 μm or less in the case of 0 dpi.

Further, even if the beam writing order is not switched, it is possible to suppress the positional deviation of one line or less by synchronizing with the rotation of the polygon on the side of the photosensitive member drive or the transfer drive, and it is possible to change the gray color. Can also be prevented.

[Brief description of drawings]

FIG. 1 is a diagram schematically illustrating a configuration of an image forming unit of an image forming apparatus according to an exemplary embodiment of the present invention.

FIG. 2 is a diagram schematically illustrating a configuration of an optical writing unit of the image forming apparatus according to the exemplary embodiment of the present invention.

FIG. 3 is a block diagram schematically showing an electrical configuration of the image forming apparatus according to the embodiment of the invention.

FIG. 4 is a block diagram showing a configuration of a motor control unit of the image forming apparatus according to the embodiment of the present invention.

5 is a timing chart showing a state of clock change for motor control of the motor control unit in FIG.

FIG. 6 is a block diagram showing a configuration of a motor control unit of an image forming apparatus according to another embodiment of the present invention.

FIG. 7 is a timing chart showing a conventional correction state.

FIG. 8 is a diagram showing a dot misalignment state in the correction of FIG.

9 is a diagram showing a state of color misregistration when there is a power deviation in the correction of FIG.

[Explanation of symbols]

11 photoconductor 13 Intermediate transfer belt 14 Writing device 20 Belt transfer charger 41 Light source 41a, 41b light source 47 CPU 51 Write control IC 52 LD control unit for exposure 63 counter 64 phase comparison circuit 65 clock generator 66 counter 67 Phase (count value) comparison circuit 68 Arithmetic control circuit 69 Motor driver 70 Phase control motor 71 Phase detector 72 Clock generation / control unit 75 ultrasonic motor

Continued front page    F-term (reference) 2H027 DA21 DE02 EB04 EC03 ED02                       ED24 EE04                 2H030 AA01 AD16 BB02 BB24 BB42                       BB56                 2H076 AB06 AB12 AB31 AB66 EA01                 2H200 FA04 GA23 GA34 GA50 GB12                       GB15 GB25 GB41 HA12 HB03                       JA02 JB10 JC03 JC09 JC19                       JC20 LA12 LA27 PA10 PA11                       PA20 PB13 PB39

Claims (6)

[Claims] 1. A plurality of laser light sources, an optical lens group for converging them on an image forming medium, an optical deflector for scanning a laser beam on a photoconductor, and a synchronization detection device for detecting a writing start position of a laser beam. An optical transfer device, a plurality of developing devices that visualize the latent image on the photoconductor, and a reference mark that serves as a reference for aligning the toner images of the respective colors when superimposing images, and an intermediate transfer body that sequentially transfers the visualized toner images. An image forming apparatus including: a synchronization detection unit that detects a writing start position of a head beam of the plurality of laser beams; a reference mark detection unit that detects the reference mark; and a synchronization detected by the synchronization detection unit. The image forming medium and the intermediate transfer member based on the relative phase relationship between the signal and the reference mark detection signal detected by the reference mark detecting means. An image forming apparatus characterized by comprising a control means for changing the driving clock frequency of a motor for rotation driving and. 2. The image forming apparatus according to claim 1, wherein the control unit changes the drive clock frequency between the end of writing the effective image area and the start of writing the next effective image area. . 3. A drive clock frequency of a motor for driving the image forming medium and the intermediate transfer member has at least two kinds of clock frequencies of a normal rotation clock frequency and a variable clock frequency, and the synchronization detection signal. The time to drive at the variable clock frequency or the number of clocks is determined by the phase relation between the reference mark signal and the standard mark signal, and the normal rotation clock is set between the end of writing the effective image area and the start of writing the next effective image area. 2. The image forming apparatus according to claim 1, wherein the frequency is switched to the variable clock frequency, and the clock frequency is returned to the normal rotation clock frequency when a predetermined time or the number of clocks is completed. 4. The control means sets the time for changing the clock frequency constant, determines a variable clock frequency according to the phase relationship between the synchronization detection signal and the reference mark signal, and switches the clock frequency. The image forming apparatus according to claim 1 or 2. 5. The clock of the (stepping) motor is controlled by the distance (phase) from the time when the reference mark signal is detected to the first synchronization detection signal when the photosensitive member surface is moved. 3. The rotation position of the intermediate transfer member is delayed by changing the frequency.
The image forming apparatus according to any one of 1 and 4. 6. The image forming apparatus according to claim 5, wherein the amount by which the rotational position is delayed is equal to or less than the distance in the sub-scanning direction on the photoconductor corresponding to the number of laser light sources.