JPH09230661A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color image forming device which can set the write start timing in a position where deflection such as fluctuation of the line synchronous signal does not constitute a significant problem and which can make overlapping of different colors accurately. SOLUTION: Monochromic image of different colors are formed on a photo- sensitive element by a latent image forming means having a rotary multi-surface mirror and also a developing means and are transcribed on an intermediate transcibing member while they are overlapped one over another, and the image on the intermediate transcribing member is transcribed onto a transcribing material, followed by a fixation process so that a color image is produced. The arrangement further includes a sensing means to sense a mark furnished on the intermediate transcribing member in the specified position, a control means 52 to start forming an electrostatic latent image with the mark sensing timing given b the sensing means, and a means 59 to control the rotational phase of the rotary mirror at the mark sensing timing. This phase control means 59 makes phase control from the given mark sensing timing using the phase converging reference which is the phase where the period of line synch. signal is used as the unit.

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 such as a color copying machine, a color printer or a color facsimile.

[0002]

2. Description of the Related Art Conventionally, as a color image forming apparatus, a belt-shaped photosensitive member is rotated and uniformly charged by a charging device, and a light beam corresponding to an image forming signal of one color plate is deflected by a rotating polygon mirror. By exposing while scanning, an electrostatic latent image corresponding to an image forming signal of one color plate is formed, and this electrostatic latent image is visualized by a developing unit with a developer of a color corresponding to the color plate. An image forming operation of transferring to an intermediate transfer member is performed for image forming signals of each color plate, and a visualized single color image of each color plate is sequentially superimposed and transferred onto an intermediate transfer belt to form a full color image. In a color image forming apparatus for transferring all of the marks onto a recording sheet at a time, a triangular mark is provided on a belt-shaped photoconductor, and a mark detecting means for detecting the mark by a laser beam is provided at a predetermined position. The rotation phase of the rotary polygonal mirror is controlled with reference to the timing at which the mark detection means detects a mark for each exposure with the light beam corresponding to the image forming signal, and the exposure start timing in the sub-scanning direction is controlled to control the color misregistration. There are some which are designed to obtain a non-existent image (for example, Japanese Patent Laid-Open No. 4-3
No. 35665).

[0003]

In the color image forming apparatus described above, a single color image of a plurality of color plates is superposed and transferred onto the intermediate transfer belt and then transferred collectively onto the recording paper. When the single color images are superimposed on each plate, a deviation occurs because the peripheral length of the intermediate transfer belt and the scanning interval of the rotary polygon mirror are not in an integral multiple relationship. Therefore, the superposition of the monochromatic images of the respective color plates theoretically causes a deviation amount of one line at the maximum, which causes the color deviation. Furthermore, in the conventional method, the relationship between the write start timing and the fluctuation of the line synchronization signal is not taken into consideration, and even if the rotation phase of the rotary polygon mirror is controlled,
There was a possibility that the line would be misaligned. In addition, the rotation phase control requires a phase convergence period, and writing was started after the phase had converged, but this phase convergence period is a dead time from the overall sequence, so speed up It was becoming a problem.

The present invention has been made in view of the above circumstances, and it is possible to improve the above problems and set the write start timing to a position where fluctuations such as fluctuations of the line synchronization signal do not pose a problem, and exposure in the sub-scanning direction is performed. Positional deviation does not occur,
It is an object of the present invention to provide a color image forming apparatus capable of superposing each color with high accuracy.

[0005]

In order to achieve the above object, the invention according to claim 1 is provided with a rotating photoconductor and a rotary polygon mirror rotated by a rotary polygon mirror driving device, and each color is provided on the photoconductor. Latent image forming means for forming an electrostatic latent image corresponding to the image signal of each color by exposing a light beam corresponding to the image forming signal of the rotary polygonal mirror, and an image forming signal of each color on the photoconductor. And a plurality of developing means each having a developer carrying member for developing an electrostatic latent image corresponding to each of the developer with each color developer, and the visualized monochromatic image on the photoconductor is transferred. Intermediate transfer body, mark detection means for detecting a mark provided on the intermediate transfer body at a predetermined position, and formation of an electrostatic latent image on the latent image forming means by the mark detection timing of the mark detection means. Control means and the developing means After transferring the image that has been subjected to visible image processing and superimposed on the intermediate transfer member to the transfer material, the rotation phase of the rotary polygon mirror is controlled by the fixing means for fixing the image and the mark detection timing of the mark detecting means. In the color image forming apparatus provided with a phase control means, the phase control means controls the phase based on a phase in which the cycle of the line synchronization signal is a unit from the detection timing detected by the mark detecting means. There is.

According to a second aspect of the present invention, in the color image forming apparatus according to the first aspect, writing is started before the phase converges to the phase convergence reference.

According to a third aspect of the present invention, in the color image forming apparatus according to the first aspect, the phase correction amount is detected based on the time difference between the phase convergence reference and the line synchronization signal.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

First, a configuration example of a color image forming apparatus in which the present invention is carried out and a technique on which the present invention is based will be described with reference to FIG.
This will be described with reference to FIGS.

In FIG. 5, reference numeral 1 is a photoconductor belt which is a belt-shaped image carrier, and the photoconductor belt 1 is laid between rotary rollers 2 and 3.
3 is driven to rotate and convey in the sub-scanning direction (clockwise direction). In the vicinity of one of the rotating rollers 2 and 3, one of the rotating rollers 2 is provided with a photosensitive member cleaning device 15, a charge eliminating lamp 21, and a charging member 4 including a charging roller. Then, the charging member 4 uniformly charges the photoconductor belt 1. Further, reference numeral 5 is a laser writing system unit as an image exposing means, and 6 to 9 are developing units as a plurality of developing means which are provided in the rotary developing device and respectively store developers of specific colors different from each other.

The laser writing system unit 5 is incorporated in the main body of the apparatus by being housed in a holding case having a slit-shaped exposure opening on the upper surface. The portion of the laser writing system unit 5 that irradiates the photosensitive belt 1 with the laser writing light 5D is provided on the side of the rotating roller 2. The charging member 4 as a charging unit and the laser writing system unit 5 as an image exposing unit constitute a latent image forming unit.

Each developing unit 6, 7, of the rotary developing device
Reference numerals 8 and 9 respectively contain developers having toners of yellow, magenta, cyan, and black, respectively, and are developer bearings made of developing sleeves that come in close proximity or come into contact with the photosensitive belt 1 at predetermined positions. It is provided with a member and has a function of developing an electrostatic latent image on the photosensitive belt 1 by non-contact development or contact development.

Reference numeral 10 denotes an intermediate transfer member which is a transfer image carrier, and the intermediate transfer member 10 is provided between the rotating rollers 11 and 12 and is driven by one of the rotating rollers to rotate counterclockwise. It consists of an intermediate transfer belt that is conveyed. The photoconductor belt 1 and the intermediate transfer belt 10 are in contact with each other at the rotating roller 3, and a transfer bias is applied from a high-voltage power source to the bias roller 13 in contact with the inside of the intermediate transfer belt 10 so that the photoconductor belt 1 is exposed. The single color image of one color plate formed in the first time is transferred onto the intermediate transfer belt 10. Similarly, the monochromatic image of each of the other color plates formed on the photosensitive belt 1 for the second time to the fourth time is sequentially superimposed on the monochromatic image of the one color plate formed on the intermediate transfer belt 10 for the first time. It is transferred so as not to be displaced.

The transfer roller 14 constituting the transfer means is provided so as to contact and separate from the intermediate transfer belt 10 by a contact and separation mechanism. Reference numeral 16 is an intermediate transfer belt cleaning device for cleaning the intermediate transfer belt 10. A blade 16A of the cleaning device 16 is kept at a position separated from the surface of the intermediate transfer belt 10 during image formation by a contact / separation mechanism. Only during cleaning after image transfer, the surface is pressed against the surface of the intermediate transfer belt 10 as illustrated.

The process of forming a color image by the color image forming apparatus having such a structure is performed as follows. First, the formation of a multicolor image according to this example is performed according to the following image forming system. That is, an image reading device (not shown) scans an original color original image and reads it with an image sensor, and the read color image data is arithmetically processed by an image data processing unit to obtain image data of each color, that is, yellow. , Magenta, cyan, and black image data are created, and are temporarily stored in the image memory.

Next, the image data of each color is taken out from the image memory at the time of recording and is input as an image forming signal of each color to the laser writing system unit 5 in the color image forming apparatus of the present example which is a recording unit. That is, the image data of each color output from the image reading apparatus separate from the color image forming apparatus of this example is sequentially input to the laser writing system unit 5. Instead of the image reading device, image data of each color generated by a color-compatible personal computer, word processor, or the like can be used.

In the laser writing system unit 5,
As shown in FIG. 7, the rotary polygon mirror driving device 5A composed of a drive motor rotationally drives the rotary polygon mirror 5B, and the semiconductor laser 5E is modulated by a driving portion by image data of each color sequentially input from the image reading device. It is driven to generate a laser beam whose intensity changes according to the image data of each color. This laser beam is deflected and scanned by the rotary polygonal mirror 5B, passes through the fθ lens 5C, the optical path is bent by the mirror 5G, and is irradiated onto the peripheral surface of the photosensitive belt 1.

The photoconductor belt 1 is neutralized by the static elimination lamp 21, uniformly charged by the charging member 4, and then exposed by the laser beam 5D from the mirror 5G to form an electrostatic latent image corresponding to the image signal of each color. Are sequentially formed. Here, the charging member 4 is applied with a bias from a power source to uniformly charge the photoconductor belt 1, and the image pattern exposed on the photoconductor belt 1 by the laser writing system unit 5 is a desired full-color image of yellow, magenta, It is a monochrome image pattern when color separation is made into cyan and black.

The electrostatic latent images corresponding to the image signals of the respective colors sequentially formed on the photosensitive belt 1 are respectively produced by the yellow, magenta, cyan and black field developing units 6, 7, 8 and 9 in the rotary developing device. The color is developed by development to form a monochromatic image of each color. That is, when the electrostatic latent image corresponding to the yellow image signal of the first color is formed on the photoconductor belt 1, the yellow developing unit 6 is rotated to move to the developing position and the electrostatic latent image is formed by the toner. A yellow single color image is formed by development. Similarly, the other developing units 7, 8 and 9 are respectively rotated to the developing positions when the electrostatic latent images corresponding to the magenta, cyan and black image signals of the second and subsequent colors are formed on the photosensitive belt 1. The magenta, cyan, and black electrostatic latent images are moved and developed with toners of the respective colors, so that magenta, cyan, and black single-color images are formed.

A transfer bias is applied to the intermediate transfer belt 10 from a high-voltage power supply through a bias roller 13, and the yellow, magenta, cyan, and black monochromatic images sequentially formed on the photosensitive belt 1 are transferred to the photosensitive belt 1. While being in contact with each other, the images are sequentially superposed and transferred onto the intermediate transfer belt 10 which rotates counterclockwise. A yellow, magenta, cyan, and black single-color images are transferred onto the intermediate transfer belt 10 in a superimposed manner to form a full-color image. This full-color image is fed from the paper feed table 17 by the paper feed roller 18. Then, the image is transferred by the transfer roller 14 to the transfer sheet that has been conveyed to the transfer unit via the registration roller 19.

After the transfer is completed, the image on the transfer paper is fixed by the fixing device 20 to complete a full-color image, and the tray 23
Is discharged to Intermediate transfer belt 10 and photoconductor belt 1
Is seamless, and the photoreceptor belt 1 is cleaned by the photoreceptor cleaning device 15 after transferring the yellow, magenta, cyan, and black single-color images to the intermediate transfer belt 10, and the intermediate transfer belt 10 forms an image on the transfer paper. After the transfer, the blade 16A of the intermediate transfer belt cleaning device 16 is pressed against the belt surface,
Cleaning. The blade 16A of the intermediate transfer belt cleaning device 16 is placed at a position separated from the intermediate transfer belt 10 by a contacting / separating mechanism during image formation.

FIG. 6 is an enlarged view showing a part of the color image forming apparatus having the structure shown in FIG. In FIG. 6, six marks 41A to 41F are provided at predetermined intervals along the circumferential direction at the end of the intermediate transfer belt 10, and the detection means 40 including a mark detection sensor is the intermediate transfer belt 10.
The upper marks 41A to 41F are detected downstream of the rotary roller 12 in the rotation direction of the intermediate transfer belt 10. The mark detection sensor 40 is composed of a reflective photosensor in the illustrated example, but a transmissive photosensor may be used if only the mark portion of the intermediate transfer belt is made light transmissive.

The mark detection sensor 40 has six marks 41.
Any mark of A to 41F, for example mark 41A
The laser writing system unit 5 starts writing the image of the first color (exposure by the laser beam corresponding to the image signal of yellow) to the photoconductor belt 1 by detecting, and the mark 41A makes one round and the mark detection sensor 4 again.
When 0 detects the mark 41A, writing of the image of the second color (exposure by the laser beam corresponding to the magenta image signal) is started.

At this time, the mark 4 of the mark detection sensor 40
The detection signals for 1B to 41F are the mark detection sensor 4
By controlling the number of marks detected by 0, a mask is applied so that the marks cannot be used as image writing timing. The density detecting means 22 composed of a P sensor is installed to face the upstream side of the photosensitive belt 1 in the rotation direction of the photosensitive belt with respect to a portion of the photosensitive belt 1 which is in contact with the intermediate transfer belt 10. To detect.

FIG. 7 shows a schematic configuration from the laser writing system unit 5 to the mark detection sensor 40. In FIG. 7, when a color signal output from an image reading apparatus separate from the color image forming apparatus of this example is input to the laser writing system unit 5, the semiconductor laser 5E in the laser writing system unit 5 changes its color. The signal is modulated and driven by the driving unit to generate a laser beam having an intensity corresponding to the color signal. The laser beam is rotationally scanned in the main scanning direction by a rotary polygon mirror (hereinafter referred to as a polygon mirror) 5B rotated by a rotary polygon mirror driving device including a polygon motor 5A, and an optical path is formed by a mirror 5G via an fθ lens 5C. The photoconductor belt 1 is bent and irradiated.

At this time, the laser beam scanned in the main scanning direction by the polygon mirror 5B is detected by the synchronization detection sensor 5F before being irradiated on the photosensitive member 1 in one main scanning, and this synchronization detection sensor is detected. The output signal of 5F is used as a sync signal (line sync signal (Lsync)) in the main scanning direction for image writing. The polygon motor 5A rotates in synchronization with the motor synchronization signal, and the phase of this motor synchronization signal and the rotation phase of the polygon motor 5A are synchronized. The polygon mirror 5B has eight mirror surfaces, for example,
In this case, the motor synchronizing signal is 2 pulses per one rotation of the polygon mirror 5B.

Next, in the color image forming apparatus having the above structure,
The rotation phase of the rotary polygon mirror is controlled by the mark detection timing of the mark detection means. An example of this phase control means will be described.

FIG. 8 is a block diagram showing a configuration example of a phase matching circuit 51 which constitutes a phase control means of the polygon motor 5A and a motor control circuit 52 which is a motor drive control device.
FIG. 9 is a timing chart showing an example of the control operation of the configuration example shown in FIG. The motor control circuit 52 is PLL-controlled by the synchronization signal (PLS) output from the phase matching circuit 51, and controls the rotation speed and the rotation phase of the polygon mirror 5B. Phase matching circuit 51
Is a motor synchronization signal generation circuit 53 that generates a motor synchronization signal (PLS1), a minute pulse generation circuit 54 that generates a minute pulse signal (PLS2), and a synchronization signal (PLS1).
1) and a multiplexer 56 for selecting the minute pulse signal (PLS2) and a timing signal generation circuit 55 for generating timing signals to the circuits 53 and 54. Each circuit operates based on the clock signal (CLK) output from the oscillator 50.

The motor sync signal generation circuit 53 divides the clock pulse signal (CLK) to generate a sync pulse signal (PLS1) input to the motor control circuit 52. The motor control circuit 52 normally controls the rotation of the polygon motor 5A in synchronization with the synchronization pulse signal (PLS1). The mark detection signal (MARK) output from the mark detection sensor 40 is the timing signal generation circuit 5
5, the timing signal generating circuit 55 outputs a signal (MK1) to the motor synchronizing signal generating circuit 53. In the motor synchronization signal generation circuit 53, the multiplexer 5 outputs the motor synchronization signal (next version) (PLS1) for image formation of the next color plate at the timing (a) in FIG.
6 is output. The timing signal generation circuit 55 uses a motor synchronization signal (previous plate) (PLS) for forming an image of the previous color plate.
The signal (MK1) is output to the minute pulse generation circuit 54 at the rising timing (b) of 1), and the minute pulse generation circuit 54 generates a minute pulse (PLS2) having a pulse width shorter than the pulse width of the motor synchronization signal. ) To the multiplexer 56
Output to

The number of times the short pulse is generated is determined according to the time difference (t) between the timing (a) and the timing (b), and the timing signal generating circuit 55 causes the fine pulse generating circuit 54 to output the data (N). To send. This data (N)
If the pulse width of the motor synchronization signal is (tp) and the pulse width of the minute pulse is (td2), N = t / (tp
It is a numerical value determined by -td2).

When the minute pulse is generated N times in the minute pulse generation circuit 54, the motor synchronizing signal (PLS1) and the minute pulse (P) are generated at the timing (c) in FIG.
The phase will be the same as that of LS2). When the pulse generation ends, the short pulse generation circuit 54 outputs a signal (NEN
D2) is output. When the signal (NEND2) from the short pulse generation circuit 54 is input, the timing signal generation circuit 55 outputs a signal (SEL) to the multiplexer 56. During normal operation, the multiplexer 56 selects the motor synchronization signal (PLS1), selects the minute pulse (PLS2) during the phase matching period in which the minute pulse is generated, and controls the rotation phase of the polygon mirror 5B. It has become. In FIG. 9, the motor synchronization signal (PLS) indicates the selection result of the multiplexer 56.

In this way, by generating a minute pulse (PLS2) for the phase of the motor synchronizing signal (PLS),
The rotation phase of the motor can be controlled by gradually shifting. That is, the phase of the polygon mirror 5B is controlled so that the rotation phase is gradually advanced by the minute pulse (PLS). After the phase matching period, at timing (d),
Since the rotation of the polygon motor 5A is stabilized, laser writing is started at this point. Since the rotational phase control by this method is executed for each color, it is possible to perform high-precision image superposition with no exposure position deviation in the sub-scanning direction, and it is possible to obtain a color image without color deviation.

10 and 11 show another structural example of the phase control means for controlling the rotation phase of the rotary polygon mirror according to the mark detection timing of the mark detection means and the timing chart of its control operation. 10 and 11, the components and names shown in FIGS. 8 and 9 are denoted by the same reference numerals, and detailed description including the operation thereof will be omitted.

In FIG. 10, a phase matching circuit 58 includes a motor synchronizing signal generating circuit 53 for generating a motor synchronizing signal (PLS1), a minute pulse generating circuit 57 for generating a minute pulse (PLS3), and the synchronizing signal. Multiplexer 56 for selecting (PLS1) and minute pulse (PLS3)
And a timing signal generation circuit 55 for generating a timing signal in each of the circuits 53, 56 and 57.
Each of these circuits uses a clock signal (CL
K) as a reference. As shown in the timing chart of FIG. 11, the timing signal generation circuit 55 uses the motor synchronization signal (previous version) (PLS).
At the rising timing (b) of 1), the signal (M
K3) is output to the minute pulse generating circuit 57, and the minute pulse generating circuit 57 outputs the motor synchronizing signal (previous version) (PLS
A minute pulse (PLS3) longer than the pulse width of 1) is generated.

The number of generations of the minute pulse is determined according to the time difference (t) between the timing (a) and the timing (b). When the pulse width of the motor synchronization signal (PLS1) is (tp) and the pulse width of the minute pulse is (td3), the number of occurrences (N) is determined by N = (tp-t) / (td3-tp). It is a numerical value.

The minute pulse generation circuit 57 outputs N minute pulses.
When it occurs twice, at the timing (c), the phases of the motor synchronization signal (PLS1) and the minute pulse (PLS3) match. The minute pulse generation circuit 57 outputs a signal (NEND3) to the timing signal generation circuit 55 when the pulse generation is completed. The multiplexer 56 selects the motor synchronizing signal (PLS1) during normal operation, and selects the minute pulse (PLS3) during the phase matching period in which the minute pulse (PLS3) is generated to select the motor synchronizing signal (PLS3).
S) is output. The selection operation of the multiplexer 56 is performed by the timing signal generation circuit 55.
Is performed by the signal (SEL) output from. As a result, the phase of the motor synchronization signal (PLS1) is gradually shifted by the generation of the minute pulse (PLS3), and the rotation phase of the polygon motor 5A is controlled.
That is, the phase control of the polygon mirror 5B is performed so that the phase is gradually delayed by the minute pulse (PLS3). After the phase matching period, at timing (d), the rotation control of the polygon motor 5A becomes stable, so that laser writing is started at this point. Since such control is performed for each color, it is possible to superimpose images with high accuracy without exposure position deviation in the sub-scanning direction, and to obtain a color image without color deviation.

Next, FIGS. 12, 13 and 14 show still another configuration example of the phase control means for controlling the rotation phase of the rotary polygon mirror by the mark detection timing of the mark detection means and the timing chart of its control operation.

In FIG. 12, a phase matching circuit 59 includes a motor synchronizing signal generating circuit 53 for generating a motor synchronizing signal (PLS1), a minute short pulse generating circuit 54 for generating a minute pulse (PLS2), and a minute pulse. (PLS3) for generating the minute pulse generation circuit 57 and the synchronization signal (PLS3).
1), short pulse (PLS2), long pulse (PLS)
The multiplexer 56 for selecting 3) and each circuit 53, 5
4, 56, and 57, and a timing signal generation circuit 55 that generates timing signals. Each of these circuits operates based on the clock signal (CLK) from the oscillator 50. The basic operation of the circuit shown in FIG. 12 is the same as that of the circuit having the configuration shown in FIGS. 8 and 10, but a short pulse (PLS2) or a long pulse is used as a pulse used for phase control. (PLS3)
Whether or not to use is selectable by the mark detection signal (MARK).

FIG. 13A shows a mark detection signal (MAR).
When the rising timing of K) is at the HI level of the motor synchronizing signal (previous version) (PLS1), the circuit on the side having the configuration shown in FIG.
FIG. 13B is a timing chart when the phase matching is performed according to 2), and FIG. 13B illustrates the case where the phase matching is performed using the minute pulse (PLS3) using the circuit on the side having the configuration illustrated in FIG. It is a timing chart. In either case, the phase relationship between the mark detection signal (MARK) and the motor synchronization signal (previous version) (PLS1) is the same, but the phase matching is shorter in the case of using the minute pulse (PLS3). Can be terminated.

FIG. 14A shows a mark detection signal (M
When the rising timing of ARK) is at the LOW level of the motor synchronization signal (previous version) (PLS1), a phase is generated using the short pulse (PLS2) by using the circuit having the configuration shown in FIG. FIG. 14B is a timing chart when the matching is performed, and FIG. 14B is a timing chart when the phase matching is performed using the minute pulse (PLS3) by using the circuit having the configuration shown in FIG. Are shown respectively. In FIG. 14, the phase matching can be completed in a shorter time when the phase matching is performed using the minute pulse.

Thus, as is apparent from FIGS. 13 and 14, when the rising timing of the mark detection signal (MARK) is at the HI level of the motor synchronization signal (previous version) (PLS1), the minute pulse ( PLS3) is used to perform phase matching, and the motor synchronization signal (previous version) (PLS3)
When it is at the LOW level of 1), the short pulse (PLS)
By performing the phase matching using 2), the time required for the phase matching can be shortened.

In FIG. 12, the timing signal generation circuit 55 receives the motor synchronization signal (PLS1) and the mark detection signal (MARK), determines which pulse is used to perform the phase matching, and the short circuit is performed. When the pulse (PLS2) is used, the signal (MK2) is used, and the minute pulse (PK2) is used.
When LS3) is used, the signal (MK3) and the pulse number (N) are output to the pulse generation circuits 54 and 57. The minute pulse generation circuit 54 and the minute pulse generation circuit 57 generate minute pulses (PLS) according to the signals (MK2, MK3, N).
2) and the minute pulse (PLS3) are generated, and when the generation is completed, the signals (NEND2) and (NEND3) are output to the timing signal generation circuit 55.

The multiplexer 56 selects the motor synchronizing signal (PLS1) at the time of normal operation, and outputs the minute pulse (PLS1).
S2) is generated during the phase matching period, the short pulse (PL
S2) is selected, and the minute pulse (PLS3) is selected during the phase matching period in which the minute pulse (PLS3) is generated.
This selection is performed by the signal (SEL) output from the timing signal generation circuit 55, and finally the multiplexer 56 outputs the motor synchronization signal (PLS).

In this example, it is determined whether the phase matching is performed using the minute pulse (PLS2) or the minute pulse (PLS3) according to the timing of the mark detection signal (MARK). Therefore, the time required for phase matching can be shortened, the time from the mark detection to the writing start can be shortened, and the processing time of the whole process can be shortened.

Since the rotational phase control by the method described above is executed for each color, it is possible to superimpose images with high accuracy without deviation of the exposure position in the sub-scanning direction.
It is possible to obtain a color image without color shift. The basic idea of these techniques is disclosed in the specification of Japanese Patent Application No. 6-296632, which is a prior application of the present applicant.

By the way, in the method according to the above-mentioned prior application, the rotational phase of the rotary polygon mirror is controlled by the mark detection timing of the mark detection sensor 40, but as shown in FIG. 7, scanning is performed by the polygon mirror 5B. Laser light 5
In D, the laser beam is detected by the synchronization detection sensor 5F before the photosensitive belt 1 is irradiated in one scanning,
It is used as a synchronization signal (line synchronization signal (Lsync)) in the main scanning direction for image writing. That is, the writing timing of the laser is determined by the rise of the mark detection signal (MARK), but the writing is actually started from the rise of the line synchronization signal (Lsync) that appears thereafter.

However, the rising timing of the line synchronization signal may be shifted between the color plates due to the fluctuation of the polygon motor 5A and the accuracy of the polygon mirror 5B. Therefore, the writing determined by the mark detection signal (MARK) is performed. Depending on the relationship between the start timing and the fluctuation of the line sync signal, even if the rotation phase is controlled
The line may be misaligned. Further, in the method of the prior application, the phase matching period is required, and the writing is started after the phase matching, but the phase matching period is a dead time in terms of the entire sequence, which is a problem in speeding up. Becomes

Therefore, in the present invention, the mark detection sensor 40
The phase in which the period of the line synchronization signal is the unit from the detection timing detected by is used as the phase convergence reference, and the phase is controlled so that the phase of the line synchronization signal converges to this phase convergence reference. More specifically, the phase correction amount is detected by the time difference between the phase convergence reference and the rising time point of the line sync signal, and based on this correction amount, a short pulse or a long pulse is used by the phase matching circuit described above. Phase matching. In the present invention, since the phase matching is performed based on the line synchronization signal which is the writing start signal, writing is started before the phase converges to the phase convergence reference. Therefore, a slight shift may occur during the phase matching period immediately after the start of writing, but there is an advantage that the line shift over the entire one surface can be surely suppressed and the dead time used as the phase matching period is eliminated. .

[0049]

EXAMPLES Examples of the present invention will be described below, but the configuration of the color image forming apparatus is as shown in FIGS. 5 to 7, and the description thereof is omitted here.

FIG. 1 is a block diagram of a phase control means showing an embodiment of the present invention. The motor control circuit 52 is PLL-controlled by the motor synchronization signal (PLS) output from the phase matching circuit 59 as described above, and synchronously controls the rotation speed and rotation phase of the polygon motor 5A (polygon mirror 5B). . In this example, the phase matching circuit 59 has the same configuration as the phase matching circuit shown in FIG. 12, and the motor synchronizing signal generating circuit 53 for generating the motor synchronizing signal (PLS1) and the minute pulse (PLS2) are generated. The short pulse generation circuit 54, the fine pulse generation circuit 57 that generates a fine pulse (PLS3), and the synchronization signal (PLS).
1), short pulse (PLS2), long pulse (PLS)
The multiplexer 56 for selecting 3) and each circuit 53, 5
4, 56, and 57, and a timing signal generation circuit 55 that generates timing signals. Each of these circuits operates based on the clock signal (CLK) from the oscillator 50. Then, the phase matching circuit 59
Are a motor detection signal (PLS1) and a motor synchronization signal (PLS) based on a mark detection signal (MARK) input to the timing signal generation circuit 55 and a frame gate signal (FGATE) obtained from the line synchronization signal (Lsync).
1) Slightly shorter pulse signal, motor synchronization signal (P
Generates a very long pulse signal slightly longer than LS1). still,
The basic operation of the circuit shown in FIG. 1 is the same as that of the circuit having the configuration shown in FIG. 12, but a short pulse (PLS2) or a long pulse (PLS3) is used as a pulse for phase control. Mark detection signal (MAR
K) and the frame gate signal (FGATE).

The frame gate signal (FGATE) will be described with reference to FIG. Mark detection signal (MAR
Although the laser writing is started at the laser writing timing by the rising of K), the actual writing is started from the trailing edge of the line synchronization signal (Lsync) that appears after that, as described above. At this time, a frame gate signal (FGAT) is used as a frame gate signal.
E) changes from HI to LOW. Frame gate signal (F
GATE) becomes HI when the line synchronization signal (Lsync) is counted, the number of lines corresponding to the writing length of the recording in the sub-scanning direction is counted, and the last line synchronization signal (Lsync) is counted. That is, this frame gate signal (FGATE) represents the timing of actual writing. Therefore, the frame matching signal (FGATE) is input to the phase matching circuit 59. Therefore, in the following description, the frame gate signal (FGATE) will be used together with the description at the start of writing the first line.

FIG. 3 shows a line synchronization signal (Lsyn
The timing chart for explaining the detection method of the shift amount of the frame gate signal (FGATE) with respect to the phase convergence reference when there is phase fluctuation in c) is shown, and the detection of the phase shift amount is performed based on this timing chart. I will explain.

The writing timing of the laser comes at the rising edge of the mark detection signal (MARK), but writing is actually started at the trailing edge of the line synchronization signal (Lsync) that appears thereafter. This is as explained earlier. Also, from the rising edge of the mark detection signal (MARK) to the cycle (TLsync) of the line synchronization signal (Lsync).
The unit is set as a phase convergence reference, but here, the time point of TLsync / 2 which is half of the cycle (TLsync) is set as the phase convergence reference.

Therefore, in FIG. 3, the frame gate signal (FGATE) of the first plate is deviated from the phase convergence reference by t1. In this case, since the phase is advanced, if the phase matching circuit 59 adds a very long pulse signal to control the rotation phase, it will converge to the phase convergence reference after several pulses. Further, the frame gate signal (FGATE) of the second version is t2 displaced from the phase convergence reference. In this case, because the phase is delayed,
If the phase matching circuit 59 adds a very short pulse signal to control the rotation phase, it will converge to the phase convergence reference after several pulses. Similarly, the third and fourth editions are t3 and t, respectively.
Since the phase shift occurs for 4 hours, if the phase matching circuit 59 adds a long pulse signal and a short pulse to control the rotation phase, the phase is converged to the phase convergence reference after several pulses. By controlling the phase as described above,
The end position of the frame gate signal (FGATE) is 1 to 4
There will be no line misalignment because the versions will match.

The details of the rotational phase control operation with respect to the above deviation amount are the same as the method described in the description of the above-mentioned prior application. For example, in the timing charts of FIG. 13 and FIG.
The phase shift amount is detected from the shift amount t of the motor synchronization signal (previous version) (PLS1) with respect to the mark detection signal (MARK), as shown in FIG.
Frame gate signal (FGATE) of each plate for 2)
If replaced with the method of detecting as the deviation amounts t1 to t4, the subsequent phase matching using the short pulse and the long pulse becomes the same control.

Further, in the above description, the phase convergence criterion is the time point of TLsync / 2 which is half of the cycle (TLsync) of the cycle (TLsync) of the line synchronization signal (Lsync), but this is the phase matching. This is because the circuit 59 has a configuration capable of generating both a short pulse signal and a long pulse signal.
When the phase matching circuit shown in FIGS. 8 and 10 has only one of the short pulse signal and the long pulse signal, the period (Tls) of the line synchronization signal (Lsync) in FIG.
The phase may be converged based on the start or end position of (ync).

As a specific example, the control operation when the phase matching is performed by using the very long pulse signal will be described.
FIG. 4 is a timing chart showing an example of the control operation according to the present invention. When phase matching is performed using a very long pulse signal, the phase matching circuit of FIG. 1 (the configuration of FIG. 10 may be used)
Is a motor synchronization signal generation circuit 53 that generates a motor synchronization signal (PLS1), a minute pulse generation circuit 57 that generates a minute pulse (PLS3), and the synchronization signal (PLS).
1) and the multiplexer 56 for selecting the minute pulse (PLS3), and the timing signal generating circuit 55 for generating the timing signal to each of the circuits 53, 56, 57 are operated. Each of these circuits operates based on the clock signal (CLK) from the oscillator 50. The mark detection signal (MARK) and the frame gate signal (FGATE) obtained from the line synchronization signal (Lsync) are input to the timing signal generation circuit 55, and as shown in the timing chart of FIG. Signal (previous version) (PL
At the rising timing of S1), the signal (MK
3) is output to the minute pulse generation circuit 57, and the minute pulse generation circuit 57 outputs the motor synchronization signal (previous version) (PLS1).
A very long pulse (PLS3) longer than the pulse width of is generated.

In the case of the present invention, the number of occurrences of the minute pulse is determined by the amount of deviation of the frame gate signal (FGATE) with respect to the phase convergence reference (Tlsync / 2) in the case of the present invention. Shift time t in (b)
1 (= TLsync / 2-ta). This number of occurrences (N) depends on the motor synchronization signal (PLS
When the pulse width of 1) is tp and the pulse width of the minute pulse (PLS3) is td3, it is a numerical value determined by N = (tp-t1) / (td3-tp). During the phase matching period of the motor synchronization signal (PLS), timing (a) and timing (b)
Pulse (PLS3) from the first rising of the motor synchronization signal (PLS1) after detecting the deviation time t1
Is generated and converges at timing (c).

In the above description, the example of using the minute pulse is shown, but the case of using the minute pulse is the case where the timing (a) comes after the timing (b) as described above (see FIG. Frame gate signal (F
GATE)), in which case the start of the phase matching period is
First motor synchronization signal (PLS) after timing (a)
It is the rise of 1).

[0060]

As described above, according to the present invention,
From the detection timing detected by the mark detection means, the phase in units of the cycle of the line synchronization signal is used as the phase convergence reference, and control is performed so that the phase of the line synchronization signal converges to this phase convergence reference. Since it can be set at a position where the fluctuation of the signal is not a problem, reliable control is possible. Therefore, it is possible to perform highly accurate superposition between the monochromatic images of the respective color plates without causing the exposure position shift in the sub-scanning direction. Further, in the present invention, since the phase matching is performed based on the line synchronization signal which is the writing start signal, the writing is started before the phase converges to the phase convergence reference, and the dead time used as the phase matching period disappears. It is possible to achieve high throughput and to speed up color image formation.

[Brief description of drawings]

FIG. 1 is a block diagram of phase control means showing an embodiment of the present invention.

FIG. 2 is a timing chart showing the relationship among a mark detection signal, a line detection signal, and a frame gate signal.

FIG. 3 is a timing chart for explaining a method of detecting a shift amount of a frame gate signal with respect to a phase convergence reference when a line synchronization signal has a phase fluctuation between color plates.

FIG. 4 is a timing chart showing an example of a control operation by the phase control means shown in FIG.

FIG. 5 is a schematic configuration diagram showing an example of a color image forming apparatus in which the present invention is implemented.

6 is a cross-sectional view showing an enlarged part of the color image forming apparatus shown in FIG.

7 is a perspective view for explaining the configuration of a writing system used in the color image forming apparatus shown in FIG.

8 is a block diagram showing a configuration example of a phase control means used in the color image forming apparatus shown in FIG.

9 is a timing chart showing an example of a control operation by the phase control means shown in FIG.

10 is a block diagram showing another configuration example of the phase control unit used in the color image forming apparatus shown in FIG.

11 is a timing chart showing an example of a control operation by the phase control means shown in FIG.

12 is a block diagram showing still another configuration example of the phase control means used in the color image forming apparatus shown in FIG.

13 is a timing chart showing an example of a control operation by the phase control means shown in FIG.

FIG. 14 is a timing chart showing another example of the control operation by the phase control means shown in FIG.

[Explanation of symbols]

 1: Photosensitive belt 2, 3: Rotating roller 4: Charging member (charging roller) 5: Laser writing system unit 5A: Polygon motor 5B: Polygon mirror (rotating polygon mirror) 5C: fθ lens 5D: Laser writing light 5E: Semiconductor Laser 5F: Synchronous detection sensor 6-9: Developing unit 10: Intermediate transfer belt 11, 12: Rotating roller 13: Bias roller 14: Transfer roller 15: Cleaning device for photoconductor 16: Cleaning device for intermediate transfer belt 16A: Cleaning blade 16B: Cleaning blade support member 17: Paper feed table 18: Paper feed roller 19: Registration roller 20: Fixing device 21: Static elimination lamp 40: Mark detection sensor 41A to 41F: Mark 50: Oscillator 51, 58, 59: Phase matching circuit 52: Motor control circuit

Claims (3)

[Claims] 1. A photosensitive member which is rotated and a rotating polygon mirror which is rotated by a rotating polygon mirror driving device, and a light beam corresponding to an image forming signal of each color is deflected by the rotating polygon mirror to be exposed to the photosensitive member. And latent image forming means for forming electrostatic latent images corresponding to the image signals of the respective colors, and developing for developing the electrostatic latent images corresponding to the image forming signals of the respective colors on the photoconductor with the developers of the respective colors. A plurality of developing means each having an agent carrying member, an intermediate transfer member that is rotated to transfer the visualized monochromatic image on the photosensitive member, and a mark provided on the intermediate transfer member at predetermined positions. Mark detecting means for detecting the latent image, the control means for causing the latent image forming means to start forming an electrostatic latent image at the mark detecting timing of the mark detecting means, and the visible image processing by the developing means on the intermediate transfer member. Transfer the overlaid image to transfer material After that, in a color image forming apparatus including a fixing unit that fixes the image, and a phase control unit that controls the rotational phase of the rotary polygon mirror according to the mark detection timing of the mark detection unit, the phase control unit includes the mark A color image forming apparatus characterized in that phase control is performed based on a phase in which a cycle of a line synchronization signal is a unit from a detection timing detected by a detection means. 2. The color image forming apparatus according to claim 1, wherein writing is started before the phase converges to the phase convergence reference. 3. The color image forming apparatus according to claim 1, wherein the phase correction amount is detected based on the time difference between the phase convergence reference and the line synchronization signal.