JP2842209B2 - Multicolor image forming apparatus and image exposure control method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic multicolor image forming apparatus, and more particularly to a multicolor image forming apparatus provided with a plurality of image writing apparatuses for exposing and scanning a photosensitive member surface by reflecting a laser beam by a rotating mirror. The present invention relates to an image forming apparatus and an image exposure control method thereof.

[0002]

2. Description of the Related Art A conventionally known electrophotographic multicolor image forming apparatus obtains a multicolor image by sequentially superimposing toner images of a plurality of colors, and each time a toner image of each color is formed. Transfer to a recording paper and superimpose a toner image on the recording paper, or uniformly charge, image exposure,
In some cases, development is repeated, a plurality of color toner images are formed in an overlapping manner, and then transferred onto recording paper in a single transfer step. To form a color image in any of the above types, it is necessary to perform image exposure for three or four colors. As an apparatus for performing such image exposure, an apparatus for selectively exposing a photoconductor surface based on a digital signal has become widespread, and a laser beam that blinks based on a digital signal is reflected by a rotating mirror, and the photoconductor surface is exposed. Scanning devices are often used.

In order to reduce the time required for forming a multicolor image, an image forming apparatus having a plurality of scanning optical systems for performing image exposure as described above has been proposed, and a charger is provided around a photosensitive member. , A scanning optical system, a plurality of developing devices are arranged respectively, a device that obtains a multicolor image on a photoconductor, a device that carries and conveys recording paper and a plurality of photoconductors are arranged around the device, There is a type in which a plurality of toner images of a plurality of colors formed by a plurality of chargers, a scanning optical system, and a developing device provided in opposition to a photoreceptor are sequentially transferred onto recording paper. In such an image forming apparatus, the image exposure must be performed at exactly the right timing so that the toner images overlap exactly. This is because even a slight color misregistration significantly degrades the quality of a color image.

Techniques for accurately controlling the image writing timing are disclosed in Japanese Patent Application Laid-Open Nos. Sho 62-266575 and 62-295084.
The laser printer disclosed in Japanese Patent Application Laid-Open No. 62-266575 is set so as to irradiate a laser beam for each color when the clock signal is counted and the count value is set to the setting for each color. When the irradiation position deviates from the reference position, a deviation amount is detected and the set value is changed by an amount corresponding to the deviation amount. Also, Japanese Patent Application Laid-Open
The color copying machine disclosed in Japanese Patent Publication No. 295084 counts pulses of a predetermined cycle, and controls the timing of exposure start by a microprocessor. An interrupt of a relatively large cycle is applied until immediately before generation of a timing signal. C
In addition to reducing the load on the PU, an interrupt with a small timer setting value is performed once immediately before the timing signal is generated, and the timing signal is generated accurately.

[0005]

However, in an image writing apparatus that reflects a laser beam by a rotating mirror and exposes and scans a photoreceptor, one scanning is performed on one surface of a rotating mirror. Have a cycle. For this reason, as shown in FIG. 6, even when the scanning start signals B ₁ and B ₂ indicating the timing of starting image writing are correctly output, the laser beam must be irradiated in accordance with the cycle of the rotating mirror. After the scanning start signals B ₁ and B ₂ are output, control is performed so that the irradiation of the laser beam is started in accordance with the scanning timing signals A ₁ and A ₂ for synchronizing with the rotation of each of the plurality of rotating mirrors. . Therefore, if the rotating mirrors of a plurality of image writing apparatuses are rotating at different timings, the timing of the start of scanning varies within the time of one cycle of scanning by the rotating mirror (within Ta shown in FIG. 6). However, there is a problem that each color image is shifted in the sub-scanning direction by this amount.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has as its object to superimpose images formed by a plurality of image writing apparatuses to form each color when forming a multicolor image. It is an object of the present invention to provide a multicolor image forming apparatus capable of preventing the image from being shifted and obtaining high image quality, and an image exposure control method thereof.

[0007]

In order to solve the above-mentioned problems, the present invention is directed to an electrophotographic multi-color image forming apparatus which forms a multi-color image by superposing a plurality of color toner images. A laser generating device that generates a laser beam based on an image signal, a rotating mirror that reflects the laser beam while rotating, scans and exposes a photoconductor, and a reflecting surface of the rotating mirror is positioned at a predetermined position. And a plurality of image writing apparatuses each including a scanning timing sensor that detects that the scanning timing signal has been reached, and outputs a scanning timing signal, and a laser control unit that controls irradiation of a laser beam according to the scanning timing signal output by the scanning timing sensor. In the multi-color image forming apparatus, first, when the rotating mirror of the first image writing device that scans the laser beam is rotated, A motor drive control unit that synchronizes the rotation of a rotating mirror below the image writing device, a writing operation control device that outputs a writing start signal, and scanning from the first image writing device when the writing start signal is input. A scanning start control unit that synchronizes with the timing signal, or counts the scanning timing signal while synchronizing with the timing signal, and outputs a scanning start signal to the laser control unit of each image writing device, output from the scanning start control unit A delay circuit for delaying the scanning start signal to be performed by a predetermined time and then inputting the scanning start signal to the laser control unit of each image writing device.
It is assumed that after the N state, scanning is started in synchronization with the scanning timing signal of the image writing device.

According to a second aspect of the present invention, there is provided a laser generator for generating a laser beam based on an image signal, a rotating mirror for reflecting the laser beam while rotating, and scanning and exposing a photosensitive member. A scanning timing sensor that detects that the reflection surface of the rotating mirror has reached a predetermined position and outputs a scanning timing signal; and a laser control unit that controls irradiation of a laser beam according to the scanning timing signal output by the scanning timing sensor. An image exposure control method for a multi-color image forming apparatus including a plurality of image writing devices for each toner color,
First, the rotation of the rotating mirror of the first image writing device that scans the laser beam is synchronized with the rotation of the rotating mirrors of the second image writing device and below, and is synchronized with the scanning timing signal from the first image writing device. Or in synchronization with this, counts the scanning timing signal to generate a scanning start signal, and delays this scanning start signal within a period shorter than the cycle of the scanning timing signal.
Input to the laser control unit of each image writing device, the laser control unit of each image writing device synchronizes with the scanning timing signal output from the scanning timing sensor of the image writing device after this scanning start signal is input. Control to start laser beam irradiation.

In the multicolor image forming apparatus according to the first aspect of the present invention, the writing operation control device can also serve as a CPU that controls the operation of the entire device, and detects the position of the recording paper being conveyed. Alternatively, a write start signal is output so that an image is formed at a predetermined position according to the operation of the photoconductor. Further, after the writing start signal is input, the scanning start control unit sends a scanning start signal to the laser control unit of the first image writing device in synchronization with the scanning timing signal of the first image writing device. And outputs the scanning timing signal of the first image writing device to the laser control unit of the second or lower image writing device. When the counted value reaches a predetermined set value, the scanning timing signal is output. A scanning start signal is output to the laser control unit of each image writing device in synchronization with the signal.

[0010]

In the image forming apparatus according to the first aspect, the rotation of the rotating mirrors below the second image writing device is controlled by the motor drive control unit so that the rotation mirror of the first image writing device scans the laser beam first. Controlled to synchronize. Therefore, the scanning timing signal output from the first image writing device is counted, and if the scanning below the second image writing device is started according to the count value, there is a phase shift in the rotation cycle of the rotating mirror. It is possible to eliminate the deviation in the timing of the start of scanning.

However, as shown in FIG. 5A, the rotating mirror of the second image writing device (hereinafter referred to as the second rotating mirror) is used as the rotating mirror of the first image writing device (hereinafter referred to as the first rotating mirror). ), The scanning timing signal A ₂ (the position of the reflecting surface due to the rotation of the second rotating mirror is detected by the scanning timing signal A _{2 of} the second image writing device) due to the surface accuracy of the mirror surface and the rotation fluctuation of the drive motor. The signal output from the first image writing apparatus is slightly shifted in timing from the scanning timing signal A1 of the _first image writing apparatus.

For this reason, as shown in FIG. 4A, the scanning start control section counts the scanning timing signal A1 of the _first image writing device, and synchronizes with this to count the scanning timing signal A1 of the second image writing device. The start signal B ₂ is output, and after the scan start signal B ₂ is input, the second scan timing signal A
The timing of laser beam scanning started in accordance with ₂ may be shifted by one cycle of scanning. That is, when the second scan timing signal A ₂ is shifted after the first scan timing A ₁ signal, laser beam irradiation is started at the timing of the symbol a shown in FIG. 4 (a), the second scanning timing When the signal A ₂ is shifted before the first scanning timing signal A ₁ , the irradiation of the laser beam is started at the timing of the symbol “b” shown in FIG.

[0013] The delay circuit is intended to be used in order to eliminate the deviation of the timing of the start of laser scanning according to the second error of the scanning timing signal A ₂ as described above,
As shown in FIG. 4 (b), the scanning start signal B2 output from the scanning start control unit is delayed by a period indicated by a symbol Tb to be a _second signal.
To the laser control unit of the image writing device. Thus, even if there is some deviation in the scanning timing signal A _2, the scanning of the laser beam is started at all times a predetermined timing based on the scanning start signal B _2. The laser beam scanning is performed at a predetermined timing by the same operation in the third image writing device and the subsequent devices.

In the image exposure control method for an image forming apparatus according to the present invention, first, the rotation of the rotating mirror of the first image writing device that scans the laser beam is controlled by the rotation of the rotating mirrors below the second image writing device. The rotation is synchronized, and the laser control unit is controlled to start irradiation of the laser beam in synchronization with the scan timing signal output from the scan timing sensor of each image writing device after the scan start signal is input. Therefore, it is possible to eliminate the variation in the timing of the start of scanning within one cycle of the scanning.

The scanning start signal is generated by synchronizing with the scanning timing signal from the first image writing device or by synchronizing with the scanning timing signal and counting the scanning timing signal. After being delayed within a period shorter than the period of the scanning timing signal, the signals are input to the laser control units of the respective image writing devices, so that the first scanning start timing signal and the second or less scanning timing signals are transmitted to the rotating mirror. Even if there is a slight deviation due to accuracy or the like, the scanning start signal is input with a delay of a predetermined time, and the deviation due to the error is absorbed within this delay time, and the scanning of the laser beam is performed at an accurate timing according to the timing of the scanning start signal. Is started.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to an embodiment of the present invention. FIG. 2 shows FIG.
FIG. 3 is a block diagram showing a configuration of an image writing device and an image exposure control unit of the image forming apparatus shown in FIG. This image forming apparatus has a transfer belt 7 capable of electrostatically attaching and transporting a transfer sheet, and four photosensitive drums 1a, 1b, 1c, and 1d at positions opposed to the transfer belt 7. A charging device 6 is provided around each of the photosensitive drums 1 for uniformly charging the surface of the photosensitive drum, and a developing device for attaching toner to a latent image formed on the photosensitive drum to visualize the latent image. 3, a transfer device 4 for transferring the toner image formed on the photoreceptor to transfer paper, and a cleaning device 5 for removing and cleaning the toner remaining on the photoreceptor after the transfer of the toner image. .

The developing device 3 uses toners of different colors, and uses yellow, cyan, magenta, and black. Further, the photosensitive drum 1
Of four image writing devices 2a, 2b, 2c, 2 that scan a laser beam on each of them to form a latent image based on a difference in charging potential.
In the image writing device 2, the scanning timing is controlled by the image exposure control unit 8, and the toner image formed on each photosensitive drum is transferred onto the transfer paper conveyed by the transfer belt 7. It is designed to be transcribed exactly on the paper.

Each of the above image writing devices 2
As shown in FIG. 1, a laser generator 22 that generates a laser based on a digital image signal developed by dots, a rotating mirror 23 (polygon mirror) that reflects a laser beam while rotating and scans a photosensitive drum, and It has a scanning timing sensor 21 for detecting the position of the reflecting surface of the rotating mirror, and a laser control unit 24 for controlling the timing at which the laser generator 22 emits a laser beam. The rotating mirror 23 is provided with a reflecting surface on the peripheral surface of a regular octagon, and is driven to rotate around the central axis of the regular octagon. By rotating while reflecting the laser beam, the rotating mirror 23 rotates around the photosensitive drum 1. The surface is scanned in its axial direction. Such scanning of the laser beam is repeated for each reflection surface, and the photosensitive drum 1 rotates to sequentially scan in the sub-scanning direction.
A latent image is formed.

The scanning timing sensor 21 detects when each reflecting surface of the rotating mirror reaches a predetermined position and outputs a pulse signal. The scanning timing sensor 21 irradiates a laser beam based on this signal. In addition, it becomes possible to irradiate a predetermined position in the scanning direction with a laser beam. Therefore, after the scanning start signal is input, the laser control unit 24 controls the laser generator so as to irradiate a laser beam in synchronization with the scanning timing signal input from the scanning timing sensor.

The image exposure control section 8 includes a motor drive control section 10 for controlling a motor for driving the rotating mirrors of the respective image writing devices so as to rotate in synchronization with each other, and a transfer sheet conveyed on a transfer belt. CPU 11 that outputs a signal to start a write operation in accordance with the position of
A scan start control unit 12 that outputs a scan start signal to each image writing device based on a signal from U11, and a signal output from this scan start control unit is set to about 2 cycles of a scan cycle.
And a delay circuit 13 for delaying by a fraction of the time. The CPU 11 is also set so as to control the overall operation of the charging device 6, the developing device 3, the transfer device 4, the cleaning device 5, and the like, and inputs a dot-developed digital image signal to the laser control unit 24. It has become.

When a write start signal is input from the CPU 11, the scan start control unit 12 shifts the timing of the scan start signal to each image writing device so that the toner image is exactly overlapped on the transfer paper. It is set to output. That is, the arrow A shown in FIG.
The first photosensitive drum 1a on the transfer paper conveyed in the direction of
From the second photosensitive drum 1b, a magenta toner image from the third photosensitive drum 1c, and a black toner image from the fourth photosensitive drum 1d. The laser irradiation timing of the second, third, and fourth image writing devices is set so that the images are transferred to the same position.

Next, the operation of the image forming apparatus will be described.
An image exposure control method according to an embodiment of the present invention will be described. The rotating mirror 23a (polygon mirror) of the first image writing device 2a is rotationally driven at a constant speed by a driving motor (not shown). The scanning timing sensor 21a detects when each reflecting surface of the rotating mirror 23a has reached a predetermined position, and outputs a pulse signal (scanning timing signal A ₁ ). This scanning timing signal A ₁ is input to the scanning start control unit 12 and also to the motor drive control unit 10. The second, third, fourth image writing device 2b motor drive control unit 10 based on the scanning timing signals A _1, 2c, 2d
The motors that drive the rotating mirrors 23b, 23c, and 23d are synchronized with the drive motor of the first image writing device.

On the other hand, when a signal for starting the process of the image forming apparatus is inputted, the CPU 11 activates each photosensitive drum 1, the transfer belt 7, the charging device 6, the developing device 3 and the like, and is attracted to the transfer belt 7. The position of the conveyed transfer sheet is detected, and a write start signal is output to the scan start control unit 12 at a timing when an image is formed at a predetermined position. Upon receiving the write start signal, the scan start control unit 12 immediately outputs the scan start signal B ₁ to the first image writing device in synchronization with the _first scan timing signal A ₁ . (Timing shown in FIG. 3) This scanning start signal is delayed by the delay circuit 13a by the time indicated by the symbol Tc in FIG. 3, and is input to the laser control unit 24a of the first image writing device. (Timing shown in FIG. 3)

After the scanning start signal is turned on, the laser control section 24a starts irradiation of the laser beam in synchronization with the first pulse signal input from the first scanning timing sensor. (Timing shown in FIG. 3) The laser beam emitted from the laser generator 22a is reflected by the rotating mirror 23a and scans the peripheral surface of the photosensitive drum 1a. As a result, an electrostatic latent image is formed on the photosensitive drum 1a, and is formed into a toner image by the developing device 3a and then transferred onto a transfer sheet by the transfer device 4a.

Further, in the scanning start control unit 12, the first
After the scan start signal B ₁ is output, the number of pulses of the first scan timing signal A ₁ is counted, and when the count reaches a predetermined value (timing in FIG. 3), the first scan timing signal A ₁ is reset. scanning timing signal a ₁ in synchronization with the scanning start signal B ₂ second to an image writing device is output. The scanning start signal B ₂ is delayed by a delay circuit by a time indicated by reference symbol Tc in FIG. 3 and is input to the laser control unit 24b of the second image writing device 2b. Laser controller 24b (the timing Shown in FIG. 3) is, the scanning start signal B ₂ is ON
After the state, the second scanning timing sensor 21b
The laser beam irradiation is started in synchronization with the first pulse signal input from. (Timing shown in the figure) In this way, an electrostatic latent image is formed on the second photosensitive drum 1b, developed, and transferred to a sheet on a transfer belt.

At this time, a set value which determines the timing at which the second scan start signal B ₂ is outputted after the first scan start signal B ₁ is outputted in the scan start controller 12, ie, the first scan timing signal predetermined value to be compared with the number of counts a _1, based on the distance from the first photosensitive drum 1a to a position for transferring the position and the second photosensitive drum 1b for transferring the toner image, the transfer sheet is conveyed during this time Is set as time to be. Therefore, by setting this set value to an appropriate value, the toner image transferred from the second photosensitive drum 1b is accurately superimposed on the toner image transferred from the first photosensitive drum 1a.

The period of the rotating mirror 23 is synchronized in each image writing device, and the scanning start signal is inputted through the delay circuit 13. Therefore, a slight error in the scanning timing signal causes the laser beam irradiation start to start. Accurate superposition can be achieved without any variation in timing. The third image writing device and the fourth image writing device are similarly controlled, and the toner image formed on the photosensitive drum is transferred so as to be accurately overlapped with the toner image already transferred on the transfer paper. be able to.

The above embodiment is a multicolor image forming apparatus having a plurality of photosensitive drums and sequentially transferring toner images of a plurality of colors formed on the respective photosensitive drums to a sheet on a transfer belt. In the present invention, one photoconductor 5 as shown in FIG.
One and a plurality of image writing devices 52 are provided, and a latent image can be repeatedly formed and developed on the photoreceptor 51 to form a multi-color image. A multi-color image without toner can be formed on a photoreceptor and transferred onto paper in a single step. In the multicolor image forming apparatus, reference numeral 53 in FIG. 4 denotes a charging device, reference numeral 54 denotes a developing device, reference numeral 55 denotes a transfer device, and reference numeral 5 denotes a transfer device.
6 is a cleaning device, 57 is an exposure neutralization device, 58
Is a pre-transfer charging device.

[0029]

As described above, in the image forming apparatus according to the first aspect or the image exposure controlling method for the image forming apparatus according to the second aspect, the first image writing apparatus that first scans the laser beam. The rotation of the rotation mirror of the second image writing device and the rotation of the rotation mirror of the second image writing device are synchronized with each other. After the scanning start signal is input, the laser controller outputs the scanning output from the scanning timing sensor of each image writing device. Since the irradiation of the laser beam is controlled in synchronization with the timing signal, it is possible to eliminate the variation in the timing of the scanning start within one cycle of the scanning.

Further, the scanning timing signal of the first image writing device is counted and a scanning start signal for determining the timing of starting scanning of the second image writing device and the following is output, and the scanning start signal is turned on. After that, even if the irradiation of the laser beam is started in synchronization with the scanning timing signal of each image writing device, this scanning start signal is delayed before being input to the laser control unit.
Even if the scanning timing signal and the second or lower scanning timing signal slightly shift due to a mirror error or the like, laser beam scanning can always be started at a constant timing, and high-quality multi-color images without color shift and the like can be obtained. A color image can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a block diagram illustrating a configuration of an image writing device and an image exposure control unit of the image forming apparatus illustrated in FIG.

FIG. 3 is a timing chart showing an operation of the image forming apparatus shown in FIG.

FIG. 4 is a schematic configuration diagram showing another type of multicolor image forming apparatus to which the present invention can be applied.

FIG. 5 is a timing chart for explaining features of the image forming apparatus of the present invention.

FIG. 6 is a timing chart showing an operation of the conventional image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoreceptor 2 Image writing device 3 Developing device 4 Transfer device 5 Cleaning device 6 Charging device 7 Transfer belt 8 Image exposure control unit 10 Motor drive control unit 11 CPU (writing operation control device) 12 Scan start control unit 13 Delay circuit 21 Scan Timing sensor 22 Laser generator 23 Rotating mirror 24 Laser controller

Claims (2)

(57) [Claims] 1. An electrophotographic multicolor image forming apparatus for forming a multicolor image by superimposing toner images of a plurality of colors, comprising: a laser generator for generating a laser beam based on an image signal; A rotating mirror that reflects the laser beam while scanning and exposing the photoconductor, a scanning timing sensor that detects that the reflection surface of the rotating mirror has reached a predetermined position, and outputs a scanning timing signal;
A multi-color image forming apparatus including a plurality of image writing apparatuses each having a laser control unit for controlling irradiation of a laser beam in accordance with a scanning timing signal output by the scanning timing sensor; A motor drive control unit that synchronizes the rotation of the rotating mirrors below the second image writing device with the rotation of the rotating mirror of the device; a writing operation control device that outputs a writing start signal; and when the writing start signal is input. Scanning start control for synchronizing with or synchronizing with a scan timing signal from the first image writing device and counting the scan timing signal and outputting a scan start signal to the laser control unit of each image writing device. A scanning start signal output from the scanning start control unit is delayed by a predetermined time. And a delay circuit for inputting to the laser control unit of each image writing device, and the laser control unit is synchronized with a scanning timing signal of the image writing device after the scanning start signal is turned on. A multicolor image forming apparatus set to start scanning. 2. A laser generator for generating a laser beam based on an image signal, a rotating mirror that reflects the laser beam while rotating, scans and exposes a photoconductor, and a reflecting surface of the rotating mirror is positioned at a predetermined position. An image writing device having a scanning timing sensor that detects that the scanning timing signal has been reached, and outputs a scanning timing signal, and a laser control unit that controls irradiation of a laser beam according to the scanning timing signal output by the scanning timing sensor. What is claimed is: 1. An image exposure control method for a multicolor image forming apparatus comprising a plurality of toner colors, wherein a rotating mirror of a first image writing device that scans a laser beam is first rotated by a rotating mirror of a second image writing device or lower. In synchronization with the scanning timing signal from the first image writing device, or in synchronism therewith. At the same time, the scan timing signal is counted to generate a scan start signal. After the scan start signal is delayed within a period shorter than the cycle of the scan timing signal, the scan start signal is input to the laser control unit of each image writing device. After the scanning start signal is input, the laser control unit of each image writing device controls the laser beam irradiation to start in synchronization with the scanning timing signal output from the scanning timing sensor of the image writing device. An image exposure control method for a multicolor image forming apparatus.