JPH03179368A - Color image forming device - Google Patents

Abstract

PURPOSE:To eliminate the deviation of an exposure starting point where a latent image is formed and to prevent an image from being deviated by integrally providing a sensor which reads a reference pattern formed on an image forming body which forms an image by exposing the image with the aid of plural exposing means with the exposing means. CONSTITUTION:Plural image forming means consisting of electrostatic chargers 21 - 24, the exposing devices 110, 120, 130 and 140 and developing devices 31 - 34 are disposed on the circumferential edge of a turning photosensitive belt 1 at regular intervals and in parallel. Then, the sensor 112 which reads the reference pattern formed on the end part of the belt 1 or the like is integrally provided with the respective plural exposing means 110 or the like provided on the circumferential edge of the belt 1 in parallel so that intervals between the respective exposing devices 110 or the like and the sensor 112 or the like are kept constant every unit. Thus, the exposure starting point where the latent image is formed is prevented from being deviated and the image is prevented from being deviated.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a color image forming apparatus in which a toner image is formed on a belt-like image forming member using an electrophotographic method and is transferred onto a transfer material to obtain an image.

[Conventional technology]

As an image forming method for obtaining a color image using electrophotography, for example, Japanese Patent Application Laid-open Nos. 60-75850 and 60-767
No. 66, No. 60-95456, No. 60-95458, No. 60-158475, etc., latent image formation and development are performed on an image forming body according to the number of separated colors of an original image. There is a method of repeatedly overlapping color toner images on an image forming body and then transferring them to obtain a color image. As a first example, a color image forming apparatus employs an image forming method in which latent image formation and development are repeated in accordance with the number of separated colors of an original image read by a color scanner on an image forming body. A device with an exposure device and a developing device arranged around the periphery according to the number of separated colors (for example, three colors of yellow, magenta, and cyan, or four colors including black);
For example, there is one in which an exposure device and a developing device according to the number of separated colors are arranged around the periphery of a drum-shaped image forming body. Among these, a color image forming apparatus equipped with a belt-like image forming body will be described. A color image forming apparatus has a belt-like image forming body in which a photoconductor is coated or vapor-deposited on a flexible belt, and a tension roller is attached to the belt, and the tension roller is brought into sliding contact with a reference guide member by the tension generated by the pressure contact. By rotating the belt-shaped image-forming body while maintaining the same position, the surface of the belt-shaped image-forming body is always kept at a constant position during conveyance. An image forming means consisting of a plurality of developing units storing color (magenta, cyan, and black) is arranged, and these image forming means are arranged at regular intervals on a rotating belt-like image forming body. Further, in a color image forming apparatus, a reference pattern is formed on a belt-like image forming body, the reference pattern is detected by a sensor forming an exposure control circuit, and based on the detection, exposure is performed sequentially from a plurality of arrayed exposure devices. By starting, latent image formation is started from the same point on the belt-like image forming member.

[Problems to be solved by the invention]

However, in the color image forming apparatus described above, the timing for starting exposure from a plurality of exposure devices is determined by reading a reference pattern formed on a belt-like image forming body using a single sensor or a plurality of sensors. In this method, it is necessary to position the distance between the sensor and the exposure device and the array spacing of multiple exposure devices with strict mechanical precision. It was difficult to do so. When the exposure device is removed for maintenance or the like, it is extremely difficult to set it in the same position again. Further, in a color image forming apparatus that forms a color toner image by overlapping toner images on a belt-like image forming member as described above, the exposure start position on the belt-like image forming member from a plurality of exposure devices is If the deviation cannot be set per pixel, for example, about 80 μm or less, there is a problem that the image quality of the color toner image is degraded. Similar problems also exist in color image forming apparatuses that form color toner images by overlapping toner images on a drum image forming member. In view of the above-mentioned conventional problems, the present invention eliminates the possibility that the exposure start point for forming a latent image shifts when forming a latent image multiple times without positioning multiple exposure devices with strict mechanical precision. An object of the present invention is to provide a color image forming apparatus that aims to prevent image shift.

[Means to solve the problem]

The present invention achieves the above object by forming an image by exposing a belt-shaped image forming body that moves while being stretched between two rotating rollers, and a plurality of exposure means provided in parallel to the image forming body. The color image forming apparatus is characterized in that a sensor for reading a reference pattern formed on the image forming body and the exposure means are integrally provided. Further, the image forming body may be a belt-shaped image forming body that moves while being stretched between two rotating rollers.

【Example】

Next, embodiments of the present invention will be described based on the accompanying drawings. As shown in FIG. 1, the color image forming apparatus of this embodiment has a tension roller 5 attached to a belt-shaped image forming body (hereinafter referred to as a photoconductor belt) l in which a photoconductor is coated or mounted on a flexible belt. The photoreceptor bell l-1 surface is always maintained at a constant position when the photoreceptor bell l-1 is conveyed by rotating the photoreceptor bell while keeping it in sliding contact with the reference guide member 4 due to the tension generated by the pressure contact. . Here, the photoreceptor belt l
The photoreceptor on the outer circumferential surface of the photoreceptor is always maintained at a constant position relative to the surface of the guide member 4 during transportation, making it possible to form a stable image forming surface with a large curvature and a long width. Therefore, a large number of image forming means having the same shape as described above can be arranged in parallel. In FIG. 1, there are four chargers 21, 22, 23, 24, 4 exposure devices 110, 120, 130, 140, and a plurality of developing units 31, 2, 3, 4, and 4 that store toner of different colors. 32.
By arranging the image forming means consisting of 33 and 34 in parallel, the peripheral edges of the photoreceptor bell l-1 on which these image forming means rotate are arranged in parallel with a constant interval. Here, the guide member 4 except for the charger position, the exposure device position, the position where the sensor detects the reference pattern, and the position facing the developer
By forming the comb into a concave shape, the contact surface with the photoreceptor belt 1 is reduced, making it easier to move. In the color image forming apparatus of this embodiment, a sensor for reading a reference pattern formed at the end of the photoreceptor belt L is integrally provided in each of the plurality of exposure means arranged in parallel around the circumference of the photoreceptor belt L. There are certain characteristics. Thereby, the distance between each exposure device and the sensor is kept constant for each unit. Even if the exposure device is removed for maintenance, for example, the arrangement interval between the exposure device and the sensor is guaranteed. The exposure means of the color image forming apparatus of this embodiment will be explained below. FIG. 2 is a plan view showing an eleventh embodiment of the exposure device applied to the color image forming apparatus of this embodiment, and FIG. 3 is a sectional view taken along line AA of the exposure device shown in FIG. In the figure, the photoreceptor belt 1 is conveyed in the arrow direction X (here, the sub-scanning direction). The reference pattern at the end is formed by printing with ink or the like, for example. The exposure device 110 turns on the light source 114 to expose the photoreceptor bell)l.
The sensor 112 receives the reflected light from the reference pattern formed at the end of the sensor 112, and when the sensor 112 detects the reference pattern, the LED array 111 starts emitting light after a predetermined period of time has elapsed. This determines the exposure start point. Here, the LED array corresponds to exposure means. The exposure device 110 has an LE on the casing 115.
D array [1 and sensor 112 are arranged on the same straight line,
Further, the same light-converging lens array 113 is arranged on the LED array ill and the light-receiving portion of the sensor 112, for example, to form an image in a ratio of 1 to 1. The sensor 112 also uses the end of the light converging lens array 113 to detect a light image formed by imaging a reference pattern formed at the end of the photoreceptor belt l in a ratio of 1:1, and the LED array 111 Convergent lens array 1
13, spots are formed on the photoreceptor belt l in a ratio of l to l. Further, a light shielding plate 117 is provided to prevent light from the light source 114 from leaking into the light emitting portion of the LED array. FIG. 4 is a block diagram showing an exposure control circuit employed in the color image forming apparatus of this embodiment. The exposure control circuit A is a circuit that generates a timing to start exposure, and also corrects in the main scanning direction by detecting a deviation in the main scanning direction of the exposure means, here, the LED array 111, on the photoreceptor bell l-1. It consists of a reference pattern detection circuit B and an LED head control circuit C. The reference pattern detection circuit B generates the timing for starting exposure in the sub-scanning direction by detecting the reference pattern formed at the end of the photoreceptor belt I through the optical system as described above, and also detects the timing of starting exposure in the sub-scanning direction. It detects deviation in the main scanning direction, and the linear image sensor 11
2. Consists of an operational amplifier 151, a microprocessor 152, and a drive circuit 153. Linear image sensor 11
2 detects the reference pattern, and the drive circuit 153 sends charges from the light receiving section of the linear image sensor to the comparator 151 based on the reference clock from the microprocessor 152. The microprocessor 152 detects a reference pattern using the pulse signal output from the comparator 151, and also detects a deviation of the LED array Ill in the main scanning direction based on the edge position of the reference pattern. The reference pattern has a SN ratio (such as black on white or white on black).
It is preferable to use a material with a high difference in amount of reflected light. The LED drive circuit C drives, for example, 2974 LED elements corresponding to l life in the main scanning direction,
A frame memory 161 that stores one screen worth of image data corresponding to a specific color. A clock generation circuit 162 that generates a reference clock that is the operation timing of the LED drive 111 circuit counts the reference clock corresponding to the positional shift in the main scanning direction, and then calculates the l life in the main scanning direction based on the reference clock. a drive circuit 163 for transferring the image data of 20 minutes from the frame memory to the phase direction shift register group 164A to 164Z, and the phase direction shift register 1;
A latch circuit group 165A-1652 that holds the output from 64A-164Z, an LED driver group 166A-166Z that simultaneously drives 124 LED elements, and the LE
This is an LED array ill of approximately 2974 segments driven by D driver groups 166A-1662. The operation of the color image forming apparatus of this embodiment will be explained below. The photoreceptor belt l is conveyed in the sub-scanning direction by rotating two rotary rollers clockwise. The photoreceptor surface of the photoreceptor belt 1 is charged to a predetermined value by a charger 21 . Next, in a reference pattern detection unit provided together with the exposure device 110, a light source 114 illuminates the end of the photoreceptor belt, and the end of the photoreceptor is connected to a linear image sensor 112 via a light collection array 113. The image is formed on the light receiving section. When the light image from the reference pattern is not formed on the light receiving section, the linear image sensor 112 sequentially outputs a low-level analog voltage from the -c light receiving m based on the transfer lock from the drive circuit. As a result, the comparator 151 sends a low-level pulse signal to the microprocessor 152 using the reference voltage applied to the normal rotation terminal. In other words, since the microprocessor 152 does not detect the reference pattern, it does not calculate the amount of correction for the exposure start timing and the deviation in the main scanning direction. On the other hand, the reference pattern detection section I provided together with the exposure device
Here, when the reference pattern formed on the end I of the photoreceptor belt 1 is imaged on the light receiving part of the linear image sensor 112 via the light-collecting lens array 113, the linear image sensor 12 Drive circuit 153
It outputs an analog voltage that abruptly changes from low level to high level based on the transfer lock from the output. As a result, the comparator 152 sends a pulse signal changing from low level to high level to the microprocessor 152. The microprocessor 152 counts the reference clock that generates the transfer lock of the drive circuit 153 to count the continuous time of the high-level pulse signal, compares this count value with a set value, and calculates a value based on the set value. When the value is large, a flag indicating that the reference pattern has been detected is set, and the count number of the reference clock from low level to high level is calculated as the position of the edge of the reference pattern. As a result, the microprocessor 152 sends start data indicating the exposure start timing and correction data for the deviation in the main scanning direction to the drive circuit 163 of the LED drive circuit C. In the LED drive circuit C, after a predetermined period of time has elapsed based on the start data, that is, after the photoreceptor belt l has been conveyed a predetermined distance in the sub-scanning direction, the drive circuit 163 performs a process based on the correction data in the main-scanning direction. Based on this, the margin data is ziaded at the time of transfer from the frame memory. That is, by adjusting the image data sent from the frame memory 161 by adding margin data, the segment of the LED array 111 that emits light is shifted to the left or right based on the image data and starts emitting light. This process is performed for each screen. In this way, the exposure apparatus of this embodiment detects the deviation in the main scanning direction on the photoreceptor belt 1, corrects this, and sets the position in the sub-scanning direction in advance after detecting the reference pattern. By emitting light from the LED array 111 after a period of time has elapsed, image exposure is always started from a predetermined position on the photoreceptor belt 1. Thereafter, phase direction shift resist groups 164A-164Z and latch circuit groups 165A-165Z. The LED driver groups 166A to 166Z are driven to perform exposure scanning based on one screen's worth of yellow data. As a result, a latent image is formed at a predetermined position on the photoreceptor belt l. The latent image is developed with yellow toner by a developing device 31. Next, image formation based on magenta data, cyan data, and black data is performed by detecting the deviation of each exposure device on the photoreceptor belt l in the main scanning direction using a sensor that reads the reference pattern, and correcting this in the same manner as described above. , the position in the sub-scanning direction is controlled by controlling multiple exposure devices by emitting light from the LED array after a preset time elapses after detecting the reference pattern and always starting image exposure from a predetermined position on the photoreceptor belt l. Even without positioning with mechanical precision, it is possible to prevent the exposure start point for forming a latent image from shifting when repeatedly forming a latent image according to the number of separated colors of the original image, thereby preventing image shift. FIG. 5 is a plan view showing a second embodiment of the exposure device applied to the image forming apparatus of this embodiment, and FIG. 6 is a sectional view taken along line BB of the exposure device shown in FIG. In the figure, a photoreceptor belt 1 is conveyed in the sub-scanning direction X, and its end portion is made white and a reference pattern is formed with, for example, rectangular holes. In the exposure bag [110, similarly to the exposure apparatus shown in FIGS. 3 and 4, a light source 114A is turned on, and a sensor 1I2A receives changes in reflected light due to a reference pattern formed at the end of the photoreceptor belt l. When the sensor 112A detects the reference pattern, the LED array IIIA starts emitting light after a predetermined period of time, thereby determining the exposure start point in the sub-scanning direction X. The exposure device +10 has two parallel recesses formed in the block 115A, and the LED array Ill and the sensor 11 are placed in the recesses.
2 and 2 respectively, and the LED array 111 has the same light-converging lens array 1I3 that forms images in a ratio of 1 to 1, for example.
By arranging A, the LED array 111 forms spots on the photoreceptor belt l in a one-to-one manner. Sensor 11
2, a reference pattern formed at the end of the photoreceptor belt 1 is magnified and imaged by a lens 116 for image formation and detection. The light source 114A is arranged so as to be incident on the end of the photoreceptor directly below the sensor 112 in order to evenly irradiate the area directly below the sensor 112. In this example, the reference pattern was placed at the end of the photoreceptor belt, but when bonded photoreceptor belts are used, the reference pattern is formed near the bonded portion, and the sensor is placed near the bonded portion. It can also be used for detection. Further, the reference pattern at this time is not limited to being formed at the end of the photoreceptor belt, but may be provided near the center of the bonded portion. In this embodiment, an exposure device using an LED array is used as an exposure device, but the exposure device is not limited to this, and a laser exposure device that rotates and scans a laser beam with a polygon mirror may be used. The laser optical system is provided with a beam detector for detecting the polygon mirror surface. The writing timing in the main scanning direction is calculated in advance from the detection of the beam detector and the reference pattern to calculate the correction data, which is the writing timing in the main scanning direction. Margin data obtained by pattern detection and beam detector is added to the image data and sent. Similarly, the laser exposure device and the sensor for reading the reference pattern are provided integrally. In addition,
The sub-scanning is performed a certain period of time after the detection of the reference pattern. Moreover, these laser exposure apparatuses have an advantage in that maintenance and repair are easy because the sensor for reading the reference pattern is configured to be integrally attachable to and detachable from the main body. Further, similar effects can be obtained even when applied to a drum-shaped image forming body. Effects of the Invention As explained above, the present invention provides a color image forming apparatus that performs image formation by image exposure using an image forming body and a plurality of exposure means provided in parallel to the image forming body. By integrally providing the sensor that reads the reference pattern formed on the image forming body and the exposure means, it is possible to perform a process according to the number of separated colors of the original image without having to position multiple exposure devices with strict mechanical precision. It was possible to provide a color image forming apparatus that aims to prevent image shift by preventing the exposure start point for forming a latent image from shifting when forming a latent image repeatedly. Similar effects can be obtained even if the image forming body is a belt-shaped image forming body that moves while being stretched between two rotating rollers.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an image forming apparatus equipped with a belt-like image forming body, FIGS. 2 and 3 are lock diagrams of an exposure device applied to the image forming apparatus of the present invention,
FIGS. 5 and 6 are a plan view and a sectional view taken along line BB, showing a second embodiment of the exposure device applied to the image forming apparatus of the present invention. 1... Belt-shaped image forming body

Claims (2)

[Claims] (1) In a color image forming apparatus that forms an image by image exposure using an image forming body and a plurality of exposure means provided in parallel on the image forming body, a sensor for reading a reference pattern formed on the image forming body and a sensor for reading a reference pattern formed on the image forming body; A color image forming apparatus characterized in that an exposure means is integrally provided. (2) The color image forming apparatus according to claim 1, wherein the image forming member is a belt-shaped image forming member that moves while being stretched between two rotating rollers.