JPH04340563A - Color image forming device - Google Patents

Abstract

PURPOSE:To accurately eliminate the deviation of a writing position caused by the deviation of a belt-like photosensitive body in a subscanning direction and to obtain an image which has no color slurring and which is excellent in resolving power in a color image forming device where a latent image is formed on the belt-like photosensitive body by an optical writing device using a laser beam and a toner image obtained by development is superposed on the photosensitive body several times so as to obtain a multicolor image. CONSTITUTION:A mark 1A is put on the specified spot of the photosensitive belt 1, a mark sensor 23 for detecting the mark 1A is provided at the specified position of a device main body, and the time required for one rotation of the photosensitive belt 1 is measured according to a mark detection signal from the mark sensor 23, then the scanning speed of an exposing beam is adjusted so that the scanning time interval of the exposing beam of the optical writing device may be 1/n(n: integer) of the time required for one rotation, thereby accurately correcting the deviation of the writing position.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus that forms a latent image on a belt-shaped photoreceptor using an optical writing device using a laser beam.

0002

2. Description of the Related Art Many methods and devices have been proposed for obtaining color images using electrophotography. For example, JP-A-6
As disclosed in Japanese Patent No. 1-100770, a latent image is formed and developed in accordance with the number of separated colors of the original image on a photosensitive drum serving as an image forming member, and is transferred onto a transfer drum each time the development is performed. There is a method in which a multicolor image is formed on a drum and then transferred onto recording paper to obtain a color copy. A device using this method requires a transfer drum large enough to transfer one sheet of image onto its circumferential surface in addition to the photoreceptor drum, and the device does not have a large and complicated structure. Inevitable.

For example, as disclosed in Japanese Patent Laid-Open No. 61-149972, a latent image is formed and developed on a photosensitive drum according to the number of separated colors of an original image, and a latent image is formed on a transfer material each time the development is performed. There is a method to obtain multicolor copies by transferring. With this method, it is difficult to overlap multicolor images with high precision, and it is impossible to obtain a high-quality color image.

[0004] Also, by repeating the formation of a latent image on the photosensitive drum according to the number of separated colors of the original image and the development with color toner,
There is a method of superimposing color toner images on a photoreceptor drum and then transferring them to obtain a color image. The basic process of forming a multicolor image is described in Japanese Patent Application Laid-Open No. 60-75850 by the present applicant.
No. 60-76766, No. 60-95456, No. 60
This method is disclosed in Japanese Patent No. 95458, No. 60-158475, and the like.

[0005] In a multicolor image forming apparatus that obtains a color image by superimposing color images as described above, a plurality of developing units containing different color toners are arranged around the periphery of the photoreceptor drum. Generally, the photoreceptor drum is rotated multiple times to develop the latent image on the photoreceptor drum to obtain a color image.

Regarding image forming bodies, as described above, in addition to the photosensitive drum in which a photoconductor is coated or vapor-deposited on the circumferential surface of the drum, there is also a belt-like image forming body in which a photoconductor is coated or vapor-deposited on a flexible belt. Photoreceptors have also been proposed. The shape of the belt-shaped photoreceptor (hereinafter also referred to as photoreceptor belt) is determined by stretching it between rotating rollers including a drive roller, so space is effectively utilized to construct a compact color image forming device. It is effective if In addition, since the photoreceptor belt can run along a small curvature, it is possible to prevent poor separation of the transfer material by using a rotating roller with a small diameter and using this curvature to separate the transfer material. can.

[0007]

[Problems to be Solved by the Invention] As a result of further study by the inventor of the present invention regarding the technology using a belt-shaped photoreceptor, the following problems have become clear.

(1) When performing multiple writing using an optical writing device that uses a laser beam as an exposure beam to form a multicolor image (when writing images of each color superimposed on a photoreceptor), the belt Because it is driven by a separate roller, relative positional deviation occurs in the vertical direction due to slippage and changes in the effective diameter of the roller over time, and positional deviation occurs in the direction of movement of the belt-shaped photoreceptor (sub-scanning direction). There are problems in that color shift in the sub-scanning direction and a decrease in resolution occur. The present applicant has already made various proposals to solve this problem, but if the scanning time interval of the exposure beam is not an integer fraction of the time required for one rotation of the belt-shaped photoreceptor, However, there is a problem in that a deviation within one scanning interval (scanning pitch) inevitably remains in the alignment of the images of each color in the sub-scanning direction.

(2) In order to solve the above-mentioned problems, it is necessary to improve mechanical precision, but this alone is difficult to take as a sufficient countermeasure, so it is necessary to use high-precision parts. The resulting increase in costs is also a problem, and there are limits to mechanical measures alone.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to accurately control the displacement of the writing position without strictly regulating the displacement of the photoreceptor in the sub-scanning direction when performing multiple writing. The objective is to prevent color shift in the sub-scanning direction and a decrease in resolution, and to prevent unnecessary writing on the sensitive portion of the belt-shaped photoreceptor. Another object of the present invention is to provide a color image forming apparatus that achieves the above-mentioned objects while minimizing the complexity of the apparatus.

[0011]

[Means for Solving the Problem] The above object is to perform main scanning by an optical writing device that repeatedly scans an exposure beam on a belt-shaped photoreceptor using a rotating polygon mirror, and sub-scanning as the belt-shaped photoreceptor moves. A color image in which a latent image is formed on the belt-like photoreceptor, and toner images of different colors obtained by development are overlaid multiple times on the belt-like photoreceptor to obtain a multicolor image. In the forming apparatus, before writing by the optical writing device, the time required for one rotation of the belt-shaped photoreceptor is measured, and the scanning time interval of the exposure beam is an integral number of the time required for one rotation of the belt-shaped photoreceptor. This is achieved by a color image forming apparatus characterized in that the scanning speed of the exposure beam is adjusted so that the scanning speed of the exposure beam becomes 1.

The color image forming apparatus is characterized in that the time required for one rotation of the belt-shaped photoreceptor uses an average value obtained by rotating the belt-shaped photoreceptor two or more times.

Further, in the color image forming apparatus, the measurement of the time required for one revolution of the belt-shaped photoreceptor and the adjustment of the scanning speed of the exposure beam are performed when the power is turned on.

Furthermore, the color image forming apparatus is characterized in that the measurement of the time required for one rotation of the belt-shaped photoreceptor and the adjustment of the scanning speed of the exposure beam are performed every time a predetermined number of the color images are obtained.

Furthermore, the color image forming method is characterized in that the time required for one revolution of the belt-shaped photoreceptor is measured also during the optical writing, and the scanning speed of the exposure beam during the next exposure is readjusted. The device can also be mentioned as a preferred embodiment.

[0016]

[Embodiment] The present invention detects a vertical positional deviation of a belt-like photoreceptor, corrects the positional deviation based on the detection result, and corrects the optical writing position. In order to avoid unnecessary writing on areas (where toner can be attached), an optical writing device that uses a laser beam as the exposure beam is controlled, and the toner images are superimposed by multiple rotations of the belt-shaped photoreceptor. This is a color image forming apparatus.

FIG. 1 shows a color image forming apparatus which is an embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a photoreceptor belt which is a flexible belt-like image forming member coated or vapor-deposited with a photoconductor, and this photoreceptor belt 1 is installed between rotating rollers 2 and 3. The paper is transported clockwise by the rotation roller 2. 1A is a mark provided at a predetermined location on the photoreceptor belt 1 using a paint or material with high reflectance at least in a specific range. Reference numeral 4 denotes a guide member fixed to the main body of the apparatus so as to be inscribed in the photoreceptor belt 1. The photoreceptor belt 1 is brought into a tensioned state by the action of the tension roller 5, so that its inner peripheral surface slides on the guide member 4. Let it rub.

Reference numeral 6 denotes a scorotron-type charger as a charging means; 7 an optical writing device that performs writing (exposure) with a laser beam L as an exposure beam at an image exposure section between the charger 6 and the developing device; 8; 1 to 11 are a plurality of developing devices each containing a developer of a specific color, and these image forming devices are arranged at a portion of the photoreceptor belt 1 in contact with the guide member 4. Each of the developing units 8, 9, 10,
Reference numeral 11 denotes developer sleeves 8A, 9A, 10A, 1 which accommodate yellow, magenta, cyan, and black developers, respectively, and which maintain a predetermined gap from the photoreceptor belt 1.
1A, and has a function of visualizing the latent image on the photoreceptor belt 1 by a non-contact reversal development method. Unlike contact development, this non-contact development has the advantage of not interfering with the movement of the photoreceptor belt.

12 is a transfer device; 13 is a cleaning device; the blade 13A and toner conveying roller 13B of the cleaning device 13 are held at a position apart from the surface of the photoreceptor belt 1 during image formation; Only during cleaning, it is pressed against the surface of the photoreceptor belt 1 as shown.

Reference numeral 23 denotes a mark sensor which is an optical mark detection means using, for example, an LED as a light emitting element and a phototransistor as a light receiving element. The installation position of the mark sensor 23 is not limited to the position shown in FIG. 1, but may be installed anywhere as long as there is space. 35 is a belt drive motor which is a DC motor that drives the rotating roller 2.

The process of forming a color image using such a color image forming apparatus is carried out as follows.

That is, when color-specific image data output from an image reading device separate from the color image forming device is input to the optical writing device 7, the optical writing device 7 uses a writing light source (not shown). A laser beam L generated by a certain laser diode passes through a collimator lens and a cylindrical lens, and is driven by a drive motor 7 which is a DC motor.
The light beam is rotated and scanned by a rotating polygon mirror 74 rotated by a rotary polygon mirror 74, passed through an fθ lens 75 and a cylindrical lens 73, and the optical path is bent by a mirror 76 and a mirror 77.
The light is projected onto the circumferential surface of the photoreceptor belt 1, which has been uniformly charged by the charger 6 in advance, and is scanned in the main direction to form a bright line.

Exposure (writing) by scanning with the laser beam L is performed by control adjustment, which will be explained later, based on a mark detection signal obtained by the mark sensor 23. A laser beam L modulated by image data of the first color scans the circumferential surface of the photoreceptor belt 1. Therefore, a latent image corresponding to the first color is formed on the circumferential surface of the photoreceptor belt 1 by main scanning by the laser beam L and sub-scanning by the conveyance of the photoreceptor belt 1. This latent image is developed by a developing device 8 loaded with yellow (Y) toner (developing medium) of the developing means, and a toner image is formed on the circumferential surface of the photoreceptor belt 1. The obtained toner image, while being held on the circumferential surface of the belt, passes under a cleaning device 13, which is a cleaning means, which is separated from the circumferential surface of the photoreceptor belt 1, and enters the next image forming cycle.

That is, the photoreceptor belt 1 is connected to the charger 6.
The image data of the second color outputted from the image data processing section is then input to the optical writing device 7, and is applied to the circumferential surface of the photoreceptor belt 1 in the same manner as in the case of the first color described above. is written and a latent image is formed. The latent image is developed by a developer 9 loaded with magenta (M) toner as a second color.

This magenta (M) toner image is formed in the presence of the previously formed yellow (Y) toner image.

A developing device 10 has cyan (C) toner, and forms a cyan (C) toner image on the belt surface based on a control signal generated by an image data processing section.

Further, numeral 11 denotes a developing device containing black toner, which forms a black toner image superimposed on the belt surface by the same process. These developing devices 8, 9, 1
Direct current or even alternating current bias is applied to each sleeve 0 and 11, and non-contact development is performed using a two-component developer serving as a developing means, and non-contact development is performed on the photoreceptor belt 1 whose base is grounded. is now being carried out.

The color toner image thus formed on the circumferential surface of the photoreceptor belt 1 is sent from the paper feed cassette 14 via the paper feed guide 15 by applying a high voltage of opposite polarity to the toner in the transfer section. The image is transferred to the transferred transfer material.

That is, the top layer of the transfer material stored in the paper feed cassette 14 is conveyed out by the rotation of the paper feed roller 16, and is aligned with the timing of image formation on the photoreceptor belt 1 via the timing roller 17. and is supplied to the transfer device 12.

The transfer material to which the image has been transferred is reliably separated from the photoreceptor belt 1, which suddenly changes direction along the rotation roller 2, and heads upward, and after the image is fused by the fixing roller 18, The paper is discharged onto a tray 20 via a paper discharge roller 19.

On the other hand, the photoreceptor belt 1, which has completed the transfer to the transfer material, continues to be transported, and the remaining toner is removed by the cleaning device 13 in which the blade 13A and the toner transport roller 13B are brought into pressure contact with each other. Waiting for the end of the process, the blade 13A is pulled away again, and a little later, the toner conveying roller 13B is pulled away, and a new image forming process begins.

In the image forming apparatus shown in FIG.
The time required for one rotation of the photoreceptor belt 1 is measured from the timing detected by the sensor and the signal interval, and the scanning speed of the exposure beam of the optical writing device 7 is adjusted to accurately correct the writing position of the image data. This prevents color shift in the sub-scanning direction even if the photoreceptor belt 1 rotates and shifts in the sub-scanning direction during the process of forming a latent image.

FIG. 2 is a block diagram showing an example of a circuit for controlling the optical writing device 7. As shown in FIG.

Conventionally, in such an apparatus, correction of the deviation in the moving direction of the photoreceptor belt 1 is performed regardless of the scanning time interval determined by the rotation speed of the rotating polygon mirror 74 and the time required for one rotation of the photoreceptor belt 1. Therefore, an error close to the scanning pitch P (one pixel) of the maximum exposure beam occurs in the sub-scanning direction, and the amount of color shift in the sub-scanning direction can be quite large. In the case of controlling the circuit shown in FIG. 2, the photoreceptor belt 1 is
At the same time as calculating the exposure start position of the effective screen range of , color shift in the sub-scanning direction can be made extremely small.

In the circuit shown in FIG. 2, when color image formation is started, a reference clock pulse is sent from the reference clock generator 47 to the belt rotation time measuring section 44, frequency divider 45, It is supplied to the frequency generator 48. The frequency divider 45 and the frequency divider 48 divide the reference clock pulse by a set frequency division number and send pulse signals having a predetermined period to the DC motor driver 46 and the DC motor driver 49, respectively. And the DC motor driver 46,
49 is a polygon mirror drive motor 79 and a belt drive motor 35
to rotate the rotating polygon mirror 74 and the photoreceptor belt 1 at predetermined speeds. Each time the mark 1A on the photoreceptor belt 1 reaches the detection position of the mark sensor 23, the mark sensor 23 sends a mark detection signal to the exposure control section 41 and the belt rotation time measurement section 44. Based on this mark detection signal, the belt rotation time measuring section 44 detects one of the photoreceptor belts 1.
The required rotation time tb is measured, and the frequency division number is changed so that the scanning time interval ts of the laser beam L, which is the exposure beam, becomes an integer fraction of the time required for one rotation tb, and the frequency division number is sent to the frequency divider 45. The frequency divider 45 divides the reference clock pulse by a specified frequency division number and sends the pulse signal to the DC motor driver 46, so the polygon mirror drive motor 79 drives the rotating polygon mirror 74 at the scanning time interval ts. It is rotated at a rotation speed that is an integer fraction of the required rotation time tb. The exposure control unit 41 calculates the exposure (optical writing) start timing from the mark detection signal, and adjusts the timing to start the exposure (optical writing) in the image memory 42.
The image data, which is a color signal, stored in is read out, subjected to pulse width modulation in an exposure control section 41, and outputted to a laser diode 71 via a laser diode driver 43 to control its light emission.

[0037] Since the exposure of the second color and the subsequent colors is also performed by such control, the deviation of the photoreceptor belt 1 in the sub-scanning direction is corrected, and superimposition with almost no color deviation can be performed. Therefore, the error can be kept much smaller than the conventional error of one pixel (P) at maximum. In this way, a simple circuit can accurately and reliably prevent misalignment of a multicolor toner image.

The measurement of the time tb required for one rotation performed in the belt rotation time measuring section 44 may be performed by any one of the following methods, or by a combination of any of the following methods.

(a) The time required for one rotation of the photoreceptor belt 1 is measured and determined.

(b) Measure the time for N rotations of the photoreceptor belt, and divide by N to find the average value (N is an integer of 2 or more).

(c) This is performed when the color image forming apparatus is powered on, and the scanning speed of the laser beam L is also adjusted at the same time.

(d) The measurement of tb and the adjustment of the scanning speed of the laser beam L are performed every time a predetermined number of color images are formed.

(e) Measurement of tb is performed during exposure by scanning the laser beam L, and the scanning speed of the laser beam L during the next exposure is readjusted.

[0044]

[Effects of the Invention] As explained above, according to the present invention, the following effects can be obtained.

(1) Even in a color image forming apparatus using a belt-shaped photoreceptor, by providing an automatic exposure position correction mechanism, it is possible to prevent positional deviation of the photoreceptor in the sub-scanning direction when performing multiple writing of color images. It is possible to prevent deviations in the exposure (writing) position without strict regulation, and it is possible to reliably prevent color deviation in the sub-scanning direction and decrease in resolution.

(2) Since the scanning time interval of the exposure beam is adjusted to be an integer fraction of the time required for one rotation of the belt-shaped photoreceptor, the overlapping error of each color is calculated from the scanning pitch (one pixel) of the exposure beam. can also be made extremely small.

(3) Since unnecessary writing is not performed on the sensitive area (toner adherable area) of the photoreceptor, a means for preventing exposure and development outside the image range can be omitted.

(4) Since it is not necessary to extremely improve mechanical precision, an increase in device cost can be suppressed and the device can be downsized.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of a color image forming apparatus showing an embodiment of the present invention.

FIG. 2 is a block diagram showing an example of a circuit for controlling the optical writing device of the present invention.

[Explanation of symbols]

1...Photoreceptor belt
1A...Mark 2, 3...Rotating roller
6... Charger 7... Optical writing device
8...Developer 23...Mark sensor 35...Belt drive motor 41...Exposure control section
42... Image memory 43... Laser diode driver 44... Belt rotation time measuring section 45, 48... Frequency divider
46, 49...DC motor driver

Claims (5)

[Claims] [Claim 1] The belt-like photoreceptor is scanned by a main scan performed by an optical writing device that repeatedly scans an exposure beam on the belt-like photoreceptor using a rotating polygon mirror, and a sub-scan as the belt-like photoreceptor moves. In a color image forming apparatus, a latent image is formed on a photoreceptor, and toner images of different colors obtained by development are overlaid multiple times on the belt-shaped photoreceptor to obtain a multicolor image. Before writing with a writing device, measuring the time required for one rotation of the belt-shaped photoreceptor,
A color image forming apparatus, characterized in that the scanning speed of the exposure beam is adjusted so that the scanning time interval of the exposure beam is an integer fraction of the time required for one rotation of the belt-shaped photoreceptor. 2. The color image forming apparatus according to claim 1, wherein the time required for one rotation of the belt-shaped photoreceptor is determined by using an average value obtained by rotating the belt-shaped photoreceptor two or more times. 3. The color image forming apparatus according to claim 1, wherein the measurement of the time required for one rotation of the belt-shaped photoreceptor and the adjustment of the scanning speed of the exposure beam are performed when the power is turned on. 4. A color image according to claim 1, wherein the measurement of the time required for one rotation of the belt-shaped photoreceptor and the adjustment of the scanning speed of the exposure beam are performed every time a predetermined number of the color images are obtained. Forming device. 5. The measurement of the time required for one rotation of the belt-shaped photoreceptor is also performed during the optical writing, and the scanning speed of the exposure beam during the next exposure is readjusted.
color image forming device.