JP3681808B2 - Color image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a color image forming apparatus such as a color copying machine, a color printer, and a color facsimile.
[0002]
[Prior art]
Conventionally, as a color image forming apparatus, a belt-shaped photoconductor is rotated and uniformly charged by a charging device, and exposure is performed while deflecting and scanning a light beam corresponding to an image forming signal of one color plate with a rotary polygon mirror. As a result, an electrostatic latent image corresponding to the image forming signal of one color plate is formed, and this electrostatic latent image is visualized with a developer corresponding to the color plate by the developing unit and transferred to the intermediate transfer member. A full-color image is formed by performing the image forming operation for each color plate on the image formation signal of each color plate and transferring the visualized single color image of each color plate on the intermediate transfer belt in sequence, which is then batch-recorded on the recording paper In the color image forming apparatus to be transferred, a triangular mark is provided on the belt-like photosensitive member, and mark detecting means for detecting the mark by a laser beam is provided at a predetermined position, and an image forming signal for each color plate is provided. The rotational phase of the rotary polygon mirror is controlled based on the timing at which the mark detecting means detects the mark for each exposure with the corresponding light beam, and the exposure start timing in the sub-scanning direction is controlled to obtain an image without color misalignment. For example, Japanese Patent Application Laid-Open No. 4-335665 discloses.
[0003]
[Problems to be solved by the invention]
In the above color image forming apparatus, since a plurality of color plate single-color images are superimposed and transferred onto the intermediate transfer belt and then transferred onto a recording sheet, the single-color image for each color plate is superimposed. 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. For this reason, the superposition of single color images for each color plate theoretically causes a shift amount of one line, which causes a color shift.
Furthermore, in the conventional method, the relationship between the write start timing and the fluctuation of the line synchronization signal is not taken into account, and there is a possibility that even if the rotational phase of the rotary polygon mirror is controlled, a deviation of one line may occur. .
In addition, a phase convergence period is required to control the rotational phase, and writing was started after the phase converged, but this phase convergence period is a dead time from the overall sequence, and speeding up It was becoming a problem.
[0004]
The present invention has been made in view of the above circumstances, and has improved the above-described problems, can set the write start timing at a position where fluctuations of the line synchronization signal do not cause a problem, and the exposure position deviation in the sub-scanning direction can be set. It is an object of the present invention to provide a color image forming apparatus that can superimpose colors with high accuracy without being generated.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 is provided with a rotating photoreceptor and a rotating polygon mirror rotated by a motor of a rotating polygon mirror driving device, and corresponding to the image forming signals of each color on the photoreceptor. A latent image forming means for forming an electrostatic latent image corresponding to an image signal of each color by deflecting and exposing a light beam with the rotary polygon mirror, and an electrostatic latent image corresponding to an image forming signal of each color on the photosensitive member A plurality of developing means each having a developer carrying member that visualizes each of the colors with a developer of each color, and a single color image of each color that has been rotated and visualized on the photoreceptor is sequentially superimposed and transferred. An intermediate transfer member, a mark detection unit that detects a mark provided on the intermediate transfer member at a predetermined position and outputs a mark detection signal, and an electrostatic latent image forming unit based on the mark detection timing of the mark detection unit. The system that initiates image formation Transfer means for transferring the image that has been subjected to visible image processing by the developing means and superimposed on the intermediate transfer member to a transfer material, fixing means for fixing the image transferred to the transfer material, and the rotary polygon mirror A synchronization detection sensor that detects a light beam scanned in the main scanning direction before being irradiated onto the photosensitive member and outputs a line synchronization signal that is a synchronization signal in the main scanning direction of image writing, and line synchronization of the synchronization detection sensor In a color image forming apparatus comprising phase control means for controlling the rotational phase of a motor that rotates the rotary polygon mirror based on a frame gate signal obtained from the signal and a mark detection signal of the mark detection means, the phase control means comprises a motor Motor synchronization signal generation circuit for generating a synchronization signal, and the motor synchronization signal Shorter than the pulse width of A fine pulse generation circuit that generates a short pulse and , The motor synchronization signal Pulse width longer than Fine pulse generation times to generate fine pulses Road and A timing signal generation circuit that generates a timing signal in each circuit, and a mark detection signal and a frame gate signal input to the timing signal generation circuit, Select whether to use a short pulse or a short pulse as a pulse to be used for phase control, A phase matching circuit that generates a motor synchronization signal, a minute pulse signal, or a minute pulse signal, and is controlled by the motor synchronization signal, minute pulse signal, or minute pulse signal output from the phase matching circuit, and the rotation A motor control circuit that synchronously controls the rotation speed and rotation phase of the motor that rotates the polygon mirror, and the phase control means detects the phase shift of the frame gate signal due to the phase fluctuation of the line synchronization signal between the color plates. As a reference for setting the phase convergence reference, a time point in units of the cycle of the line synchronization signal from the rising edge of the mark detection signal, which is the mark detection timing detected by the mark detection means, or a half time point of the cycle, The frame gate signal relative to the phase convergence criterion Phased Detect the amount of deviation, When the phase is advanced with respect to the phase convergence reference, a fine pulse is generated by the phase matching circuit according to the detected deviation amount to control the rotational phase of the motor, and the phase is delayed with respect to the phase convergence reference. The phase matching circuit generates a short pulse according to the detected deviation amount to control the rotational phase of the motor, The phase control is performed so that the phase of the frame gate signal converges on the phase convergence reference.
[0006]
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 on the phase convergence reference.
[0007]
According to a third aspect of the present invention, in the color image forming apparatus according to the first aspect, the phase convergence reference , Line synchronization signal Or frame gate signal The amount of phase correction is detected by the time difference between the two.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0009]
First, a configuration example of a color image forming apparatus in which the present invention is implemented and a technique that is a premise of the present invention will be described with reference to FIGS.
[0010]
In FIG. 5, reference numeral 1 denotes a photosensitive belt which is a belt-shaped image carrier, and this photosensitive belt 1 is installed between the rotating rollers 2 and 3, and is driven in the sub-scanning direction by driving the rotating rollers 2 and 3. It is rotated and conveyed (clockwise). A photosensitive member cleaning device 15, a charge eliminating lamp 21, and a charging member 4 made up of a charging roller are disposed in the vicinity of one of the rotating rollers 2 and 3. 1, the charging member 4 uniformly charges the photosensitive belt 1. Reference numeral 5 denotes a laser writing system unit as image exposure means, and reference numerals 6 to 9 denote development units as a plurality of development means provided in the rotary type developing device and respectively containing different color developers.
[0011]
The laser writing system unit 5 is housed in a holding housing having a slit-shaped exposure opening on the upper surface and is incorporated in the apparatus main body. 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 rotating roller 2 side. The charging member 4 as a charging means and the laser writing system unit 5 as an image exposure means constitute a latent image forming means.
[0012]
Each of the developing units 6, 7, 8, 9 of the rotary type developer contains a developer having toner of each color of yellow, magenta, cyan, and black, for example, and the photosensitive belt 1 at a predetermined position. And a developer carrying member composed of a developing sleeve that is close to or in contact with the toner, and has a function of developing the electrostatic latent image on the photoreceptor belt 1 by non-contact development or contact development.
[0013]
Reference numeral 10 denotes an intermediate transfer member which is a transfer image carrier. The intermediate transfer member 10 is provided between the rotation rollers 11 and 12 and is driven by one of the rotation rollers to rotate and be conveyed counterclockwise. It consists of an intermediate transfer belt. The photosensitive 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 a bias roller 13 that is in contact with the inner side of the intermediate transfer belt 10. The single color image of one color plate formed in the first time is transferred onto the intermediate transfer belt 10. Similarly, the single color images of the other color plates formed on the photosensitive belt 1 for the second time to the fourth time are sequentially overlapped with the single color image of the one color plate formed on the intermediate transfer belt 10 for the first time. And transferred so as not to cause a positional shift.
[0014]
The transfer roller 14 constituting the transfer unit is provided so as to be in contact with and separated from the intermediate transfer belt 10 by a contact and separation mechanism. Reference numeral 16 denotes an intermediate transfer belt cleaning device for cleaning the intermediate transfer belt 10, and the blade 16A of the cleaning device 16 is maintained at a position spaced from the surface of the intermediate transfer belt 10 during image formation by the contact / separation mechanism. Only during cleaning after image transfer, it is pressed against the surface of the intermediate transfer belt 10 as shown.
[0015]
The process of color image formation by the color image forming apparatus having such a configuration is performed as follows. First, the formation of a multicolor image according to this example is performed according to the following image forming system. In other words, an image reading device (not shown) scans an original color original image, reads it with an image sensor, and performs arithmetic processing on the read color image data in an image data processing unit, that is, image data for each color, that is, yellow. , Magenta, cyan, and black image data are created and temporarily stored in the image memory.
[0016]
Next, 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 this example which is a recording unit. That is, the image data of each color output from an image reading apparatus separate from the color image forming apparatus of this example is sequentially input to the laser writing system unit 5. Note that image data of each color generated by a color-compatible personal computer or a word press can be used instead of the image reading device.
[0017]
In the laser writing system unit 5, as shown in FIG. 7, the rotary polygon mirror 5B is rotationally driven by a rotary polygon mirror drive device 5A composed of a drive motor, and the semiconductor laser 5E receives each color sequentially input from the image reading device. A laser beam that is modulated and driven by the drive unit with the image data and changes in intensity corresponding to the image data of each color is generated. This laser beam is deflected and scanned by the rotating polygon mirror 5B, and the optical path is bent by the mirror 5G through the fθ lens 5C and irradiated onto the peripheral surface of the photosensitive belt 1.
[0018]
The photosensitive belt 1 is neutralized by the neutralizing lamp 21 and uniformly charged by the charging member 4, and then exposed to the laser beam 5D from the mirror 5G, and electrostatic latent images corresponding to the image signals of the respective colors are sequentially formed. It is formed. Here, the charging member 4 is applied with a bias from the power source to uniformly charge the photosensitive belt 1, and the image pattern exposed on the photosensitive belt 1 by the laser writing system unit 5 is a desired full-color image of yellow, magenta, This is a monochromatic image pattern when color separation is performed into cyan and black.
[0019]
The electrostatic latent images corresponding to the image signals of the respective colors sequentially formed on the photosensitive belt 1 are developed by the developing units 6, 7, 8, 9 of the yellow, magenta, cyan, and black field developing units, respectively. The color is changed to a single color image of each color. That is, when an electrostatic latent image corresponding to the yellow image signal of the first color is formed on the photosensitive belt 1, the yellow developing unit 6 moves to the developing position by rotation, and the electrostatic latent image is transferred with toner. Development is performed to form a yellow monochrome image. Similarly, the other developing units 7, 8, 9 are rotated to the developing position when electrostatic latent images corresponding to the second and subsequent magenta, cyan, and black image signals are formed on the photosensitive belt 1. The magenta, cyan, and black electrostatic latent images are developed with respective color toners, and magenta, cyan, and black single-color images are formed.
[0020]
The intermediate transfer belt 10 is applied with a transfer bias from a high-voltage power supply via a bias roller 13, and yellow, magenta, cyan, and black single-color images sequentially formed on the photosensitive belt 1 are in contact with the photosensitive belt 1. The images are sequentially superimposed and transferred onto the intermediate transfer belt 10 that rotates counterclockwise. A single color image of yellow, magenta, cyan, and black is superimposed and transferred onto the intermediate transfer belt 10 to form a full color image. The full color image is fed from the paper feed tray 17 by the paper feed roller 18. Then, the toner image is transferred by the transfer roller 14 to the transfer paper conveyed to the transfer portion via the registration roller 19.
[0021]
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 is discharged to the tray 23. The intermediate transfer belt 10 and the photoreceptor belt 1 are seamless, and the photoreceptor belt 1 is cleaned by the photoreceptor cleaning device 15 after each monochrome image of yellow, magenta, cyan, and black is transferred to the intermediate transfer belt 10. After the image is transferred onto the transfer sheet, the intermediate transfer belt 10 is cleaned by the blade 16A of the intermediate transfer belt cleaning device 16 in pressure contact with the belt surface. The blade 16A of the intermediate transfer belt cleaning device 16 is placed at a position separated from the intermediate transfer belt 10 by the contact / separation mechanism during image formation.
[0022]
6 is an enlarged view of a part of the color image forming apparatus having the configuration shown in FIG. In FIG. 6, six marks 41 </ b> A to 41 </ b> F 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 on the intermediate transfer belt 10. The marks 41 </ b> A to 41 </ b> F are detected downstream of the rotating roller 12 in the rotational direction of the intermediate transfer belt 10. The mark detection sensor 40 is constituted by a reflection type photosensor in the illustrated example, but a transmission type photosensor can also be used if only the mark portion of the intermediate transfer belt is made light transmissive.
[0023]
When the mark detection sensor 40 detects any of the six marks 41A to 41F, for example, the mark 41A, the laser writing system unit 5 writes the first color image on the photosensitive belt 1 (in the yellow image signal). When the mark 41A makes a round and the mark detection sensor 40 detects the mark 41A again, the second color image is written (exposure with the laser beam corresponding to the magenta image signal). Start.
[0024]
At this time, the detection signals for the marks 41B to 41F of the mark detection sensor 40 are masked so that they cannot be used as image writing timing by managing the number of marks detected by the mark detection sensor 40. The density detection means 22 composed of a P sensor is installed facing the upstream side of the photosensitive belt 1 in the rotational direction of the photosensitive belt 1 from the portion in contact with the intermediate transfer belt 10 on the photosensitive belt 1 to optically measure the toner amount on the photosensitive belt 1. To detect.
[0025]
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 5 E in the laser writing system unit 5 has its color. A laser beam having an intensity corresponding to the color signal is generated by being modulated and driven by the drive unit with the signal. This laser beam is rotationally scanned in the main scanning direction by a rotating polygon mirror (hereinafter referred to as a polygon mirror) 5B rotated by a rotating polygon mirror driving device including a polygon motor 5A, and an optical path is set by a mirror 5G via an fθ lens 5C. It is bent and irradiated onto the photosensitive belt 1.
[0026]
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 onto the photoconductor 1 within one main scanning, and the output of the synchronization detection sensor 5F. The signal is used as a synchronization signal (line synchronization signal (Lsync)) in the main scanning direction of image writing. The polygon motor 5A rotates in synchronization with the motor synchronization signal, and the phase of the motor synchronization signal and the rotation phase of the polygon motor 5A are synchronized. The number of mirror surfaces of the polygon mirror 5B is, for example, 8, and in this case, the motor synchronization signal is 2 pulses per rotation of the polygon mirror 5B.
[0027]
Next, in the color image forming apparatus configured as described above, the rotational 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.
[0028]
FIG. 8 is a block diagram showing a configuration example of a phase matching circuit 51 that forms phase control means of the polygon motor 5A and a motor control circuit 52 that is a motor drive control device, and FIG. 9 is a control of the configuration example shown in FIG. It is a timing chart which shows an example of operation.
The motor control circuit 52 is PLL-controlled by a synchronization signal (PLS) output from the phase matching circuit 51, and controls the rotation speed and rotation phase of the polygon mirror 5B. The phase matching circuit 51 includes 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), a synchronization signal (PLS1), and a minute pulse. It comprises a multiplexer 56 for selecting a signal (PLS2) and a timing signal generating circuit 55 for generating timing signals in the circuits 53 and 54. Each circuit operates based on a clock signal (CLK) output from the oscillator 50.
[0029]
The motor synchronization signal generation circuit 53 divides the clock pulse signal (CLK) to generate a synchronization pulse signal (PLS1) that is 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).
When the mark detection signal (MARK) output from the mark detection sensor 40 is input to the timing signal generation circuit 55, the signal (MK 1) is output from the timing signal generation circuit 55 to the motor synchronization signal generation circuit 53. The motor synchronization signal generation circuit 53 outputs a motor synchronization signal (next plate) (PLS1) for image formation of the next color plate to the multiplexer 56 at timing (a) in FIG.
The timing signal generation circuit 55 outputs the signal (MK1) to the fine pulse generation circuit 54 at the rising timing (b) of the motor synchronization signal (previous plate) (PLS1) for image formation of the previous color plate. The short pulse generation circuit 54 outputs a very short pulse (PLS 2) having a pulse width shorter than the pulse width of the motor synchronization signal to the multiplexer 56.
[0030]
The number of times the minute pulse is generated is determined according to the time difference (t) between the timing (a) and the timing (b), and the timing signal generation circuit 55 sends data (N) to the minute pulse generation circuit 54. This data (N) has a pulse width of the motor synchronization signal (tp) and a pulse width of the very short pulse (td2).
N = t / (tp−td2)
It is a numerical value determined by.
[0031]
When the minute pulse is generated N times in the minute pulse generation circuit 54, the phases of the motor synchronization signal (PLS1) and the minute pulse (PLS2) coincide with each other at the timing (c) in FIG. The minute pulse generation circuit 54 outputs a signal (NEND2) when the pulse generation is completed. The timing signal generation circuit 55 outputs a signal (SEL) to the multiplexer 56 when the signal (NEND2) from the minute pulse generation circuit 54 is input.
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 rotational 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.
[0032]
In this way, by generating the minute pulse (PLS2) of the phase of the motor synchronization signal (PLS), the rotational phase of the motor can be controlled by gradually shifting. That is, the phase of the polygon mirror 5B is controlled so that the rotational phase is gradually advanced by the short pulse (PLS).
After the phase matching period, at timing (d), the rotation of the polygon motor 5A is stabilized, and laser writing is started at this point.
Since the rotational phase control by this method is executed for each color, it is possible to superimpose images with high accuracy without exposure position deviation in the sub-scanning direction, and a color image without color deviation can be obtained.
[0033]
Next, another configuration example of the phase control means for controlling the rotation phase of the rotary polygon mirror based on the mark detection timing of the mark detection means and the timing chart of the control operation are shown in FIGS. 10 and 11, the same reference numerals are given to the components and names shown in FIGS. 8 and 9, and the detailed description including the operation will be omitted.
[0034]
In FIG. 10, a phase matching circuit 58 includes 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 (PLS1). And a multiplexer 56 for selecting a minute pulse (PLS3), and a timing signal generating circuit 55 for causing each of the circuits 53, 56, and 57 to generate a timing signal. Each of these circuits operates on the basis of a clock signal (CLK) from the oscillator 50.
As shown in the timing chart of FIG. 11, the timing signal generation circuit 55 outputs the signal (MK3) to the minute pulse generation circuit 57 at the rising timing (b) of the motor synchronization signal (previous version) (PLS1). The fine pulse generation circuit 57 generates a fine pulse (PLS3) longer than the pulse width of the motor synchronization signal (previous version) (PLS1).
[0035]
The number of occurrences of the minute pulse is determined according to the time difference (t) between the timing (a) and the timing (b). The number of occurrences (N) is, assuming that the pulse width of the motor synchronization signal (PLS1) is (tp) and the pulse width of the minute pulse is (td3).
N = (tp−t) / (td3−tp)
It is a numerical value determined by.
[0036]
When the minute pulse generation circuit 57 generates the minute pulse N times, the phase of the motor synchronization signal (PLS1) and the minute pulse (PLS3) coincide with each other at the timing (c). The fine 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 synchronization signal (PLS1) during normal operation and selects the minute pulse (PLS3) during the phase matching period in which the minute pulse (PLS3) is generated. Is output. Such a selection operation of the multiplexer 56 is performed by a signal (SEL) output from the timing signal generation circuit 55. As a result, the phase of the motor synchronization signal (PLS1) is gradually shifted by the generation of the minute pulse (PLS3), and the rotational 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 fine pulse (PLS3). After the phase matching period, rotation control of the polygon motor 5A is stabilized at timing (d), and 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 a color image without color deviation can be obtained.
[0037]
Next, still another example of the configuration of the phase control means for controlling the rotational phase of the rotary polygon mirror based on the mark detection timing of the mark detection means and the timing chart of the control operation are shown in FIGS.
[0038]
In FIG. 12, a phase matching circuit 59 includes 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 (PLS2), and a minute pulse (PLS3). A fine pulse generation circuit 57 for generating a signal, a multiplexer 56 for selecting the synchronization signal (PLS1), a fine pulse (PLS2), and a fine pulse (PLS3), and a timing signal to each of the circuits 53, 54, 56 and 57. And a timing signal generating circuit 55 for generating. Each of these circuits operates on the basis of a 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 the pulse used for phase control is either a short pulse (PLS2) or a fine pulse. Whether to use (PLS3) can be selected by a mark detection signal (MARK).
[0039]
FIG. 13A uses the circuit on the side having the configuration shown in FIG. 8 when the rising timing of the mark detection signal (MARK) is at the HI level of the motor synchronization signal (previous version) (PLS1). FIG. 13B is a timing chart when phase matching is performed with a short pulse (PLS2), and FIG. 13B is a phase matching with a long pulse (PLS3) using the circuit on the side having the configuration shown in FIG. It is a timing chart at the time of performing. In any 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 fine pulse (PLS3). Can be terminated.
[0040]
14A shows a circuit on the side having the configuration shown in FIG. 8 when the rise timing of the mark detection signal (MARK) is at the LOW level of the motor synchronization signal (previous version) (PLS1). FIG. 14B is a timing chart when phase matching is performed using a very short pulse (PLS2), and FIG. 14B shows a very long pulse (PLS3) using the circuit on the side having the configuration shown in FIG. The timing chart in the case of performing phase matching using is shown. In FIG. 14, phase matching can be completed in a shorter time by using the short pulse to perform phase matching.
[0041]
As can be seen 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 fine pulse (PLS3) is output. The phase matching is performed, and when the motor synchronization signal (previous version) (PLS1) is at the LOW level, the phase matching is performed using the short pulse (PLS2), thereby shortening the time required for the phase matching.
[0042]
In FIG. 12, a motor synchronization signal (PLS1) and a mark detection signal (MARK) are input to the timing signal generation circuit 55, which pulse is used to determine phase matching, and a short pulse (PLS2) is detected. ), The signal (MK2) is output to the pulse generation circuits 54 and 57, and when the fine pulse (PLS3) is used, the signal (MK3) and the number of pulses (N) are output. The minute pulse generation circuit 54 and the minute pulse generation circuit 57 generate a minute pulse (PLS2) and a minute pulse (PLS3) according to the signal (MK2, MK3, N). NEND2) and (NEND3) are output to the timing signal generation circuit 55.
[0043]
The multiplexer 56 selects the motor synchronization signal (PLS1) during normal operation, selects the short pulse (PLS2) during the phase matching period in which the fine pulse (PLS2) is generated, and the fine pulse (PLS3) A fine pulse (PLS3) is selected during the phase matching period to be generated. This selection is performed by a signal (SEL) output from the timing signal generation circuit 55, and finally the multiplexer 56 outputs a motor synchronization signal (PLS).
[0044]
In this example, it is determined whether to perform phase matching using the minute pulse (PLS2) or to perform phase matching using the minute pulse (PLS3) according to the timing of the mark detection signal (MARK). The time required for phase matching can be shortened, the time from mark detection to the start of writing can be shortened, and the processing time in the entire process can be increased.
[0045]
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 exposure position deviation in the sub-scanning direction, and a color image without color deviation can be obtained. .
The basic idea of these methods is disclosed in the specification of Japanese Patent Application No. 6-296632, which is a prior application of the present applicant.
[0046]
By the way, in the method according to the above 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, the laser beam 5D scanned by the polygon mirror 5B. The laser beam is detected by the synchronization detection sensor 5F before the photosensitive belt 1 is irradiated in one scan, and is used as a synchronization signal (line synchronization signal (Lsync)) in the main scanning direction of image writing. . That is, the laser write timing is determined by the rise of the mark detection signal (MARK), but actually the writing is started from the rise of the line synchronization signal (Lsync) that appears thereafter.
[0047]
However, the rising timing of the line synchronization signal may be shifted between the color plates depending on the fluctuation of the polygon motor 5A and the accuracy of the polygon mirror 5B. For this reason, the writing start timing determined by the mark detection signal (MARK) Depending on the relationship of fluctuations in the line synchronization signal, even if the rotational phase is controlled, there is a possibility that one line is shifted. In addition, in the method of the prior application, a phase matching period is required, and writing was started after phase matching. However, the phase matching period is a dead time from the whole sequence, and there is a problem in speeding up. It becomes.
[0048]
Therefore, in the present invention, the phase in units of the cycle of the line synchronization signal is used as a phase convergence reference from the detection timing detected by the mark detection sensor 40, and phase control is performed so that the phase of the line synchronization signal converges on this phase convergence reference. More specifically, the phase correction amount is detected based on the time difference between the phase convergence reference and the rise time of the line synchronization signal, and the short pulse or the long pulse is used by the above-described phase matching circuit based on the correction amount. Phase matching.
In the present invention, since phase matching is performed based on the line synchronization signal that is a write start signal, writing is started before the phase converges to the phase convergence reference. For this reason, a slight shift may occur during the phase matching period immediately after the start of writing. However, the line shift over the entire surface can be reliably suppressed, and the dead time used as the phase matching period is eliminated. .
[0049]
【Example】
Embodiments 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 a description thereof will be omitted here.
[0050]
FIG. 1 is a block diagram of phase control means showing an embodiment of the present invention.
As described above, the motor control circuit 52 is PLL-controlled by the motor synchronization signal (PLS) output from the phase matching circuit 59 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 generates a motor synchronization signal generation circuit 53 that generates a motor synchronization signal (PLS1) and a short pulse (PLS2). A very short pulse generating circuit 54, a very long pulse generating circuit 57 for generating a very long pulse (PLS3), and a multiplexer 56 for selecting the synchronizing signal (PLS1), the very short pulse (PLS2), and the very short pulse (PLS3). And a timing signal generating circuit 55 that causes each of the circuits 53, 54, 56, and 57 to generate timing signals. Each of these circuits operates on the basis of a clock signal (CLK) from the oscillator 50. Then, the phase matching circuit 59 uses 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) to generate a motor synchronization signal (PLS1), a motor A short pulse signal slightly shorter than the synchronization signal (PLS1) and a slightly long pulse signal slightly longer than the motor synchronization signal (PLS1) are generated.
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. However, as a pulse used for phase control, a fine pulse (PLS2) is used or a fine pulse ( Whether to use PLS3) can be selected by a mark detection signal (MARK) and a frame gate signal (FGATE).
[0051]
Here, the frame gate signal (FGATE) will be described with reference to FIG.
The laser writing timing is started by the rising edge of the mark detection signal (MARK), and the laser beam irradiation is started. However, as described above, the actual writing is started from the falling edge of the line synchronization signal (Lsync) that appears thereafter. .
At this time, the frame gate signal (FGATE) changes from HI to LOW as the frame gate signal. The frame gate signal (FGATE) counts the line synchronization signal (Lsync), counts the number of lines corresponding to the writing length in the sub-scanning direction of recording, and counts the HI when the last line synchronization signal (Lsync) is counted. It becomes. That is, this frame gate signal (FGATE) indicates the timing of actual writing. Therefore, a frame gate signal (FGATE) is input to the phase matching circuit 59. Therefore, in the following description, the frame gate signal (FGATE) will be described together with the description at the start of writing of the first line.
[0052]
FIG. 3 is a timing chart for explaining a method of detecting a shift amount of the frame gate signal (FGATE) with respect to the phase convergence reference when the line synchronization signal (Lsync) has a phase fluctuation between the color plates. The detection of the phase shift amount will be described based on the timing chart.
[0053]
The laser write timing is reached by the rise of the mark detection signal (MARK), but actually the writing is started from the fall of the line synchronization signal (Lsync) that appears thereafter. This is as explained earlier.
Further, the phase convergence reference is set in units of the cycle (TLsync) of the line synchronization signal (Lsync) from the rise of the mark detection signal (MARK). Convergence criteria.
[0054]
Therefore, in FIG. 3, the frame gate signal (FGATE) of the first version is shifted by t1 with respect to the phase convergence reference. In this case, since the phase is advanced, if the rotational phase is controlled by adding a very long pulse signal by the phase matching circuit 59, it will converge to the phase convergence reference after several pulses. Further, the second version of the frame gate signal (FGATE) is shifted by t2 with respect to the phase convergence reference. In this case, since the phase is delayed, if the rotational phase is controlled by adding a very short pulse signal by the phase matching circuit 59, it will converge to the phase convergence reference after several pulses.
Similarly, the third and fourth plates have t3 and t4 phase shifts, respectively. If the rotational phase is controlled by adding a fine pulse signal and a fine pulse by the phase matching circuit 59, respectively, after several pulses It will converge to the phase convergence criterion.
By performing the phase control as described above, the end positions of the frame gate signal (FGATE) coincide with each other in the first to fourth plates, and no line shift occurs.
[0055]
The details of the rotational phase control operation with respect to the shift amount are the same as the method described in the description of the previous application. For example, the phase shift amount is detected by the mark detection in the timing charts of FIGS. The frame gate signal (FGATE) of each plate with respect to the phase convergence reference (Tlsync / 2) as shown in FIG. 3 is detected from the shift amount t of the motor synchronization signal (previous version) (PLS1) with respect to the signal (MARK). If it is replaced with a method of detecting as the deviation amounts t1 to t4, the subsequent phase matching using the minute pulse or the minute pulse is the same control.
[0056]
In the above description, the phase convergence reference is the time point TLsync / 2 that is half the period (TLsync) in units of the period (TLsync) of the line synchronization signal (Lsync). This is because both the fine pulse signal and the fine pulse signal can be generated. As in the phase matching circuit shown in FIGS. 8 and 10, only one of the fine pulse signal and the fine pulse signal is configured. In this case, the phase convergence may be performed with reference to the start or end position of the period (Tlsync) of the line synchronization signal (Lsync) in FIG.
[0057]
Here, as a specific example, a control operation in the case of performing phase matching using a minute 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 minute pulse signal, the phase matching circuit of FIG. 1 (which may have the configuration of FIG. 10) includes a motor synchronization signal generation circuit 53 that generates a motor synchronization signal (PLS1), a minute pulse ( A fine pulse generating circuit 57 for generating PLS3), a multiplexer 56 for selecting the synchronizing signal (PLS1) and the fine pulse (PLS3), and a timing signal generating circuit for generating timing signals at the respective circuits 53, 56, 57 55 is activated. Each of these circuits operates based on the clock signal (CLK) from the oscillator 50.
The timing signal generation circuit 55 receives a mark detection signal (MARK) and a frame gate signal (FGATE) obtained from the line synchronization signal (Lsync). As shown in the timing chart of FIG. The signal (MK3) is output to the fine pulse generation circuit 57 at the rising timing of the signal (previous version) (PLS1). The fine pulse generation circuit 57 determines the pulse width of the motor synchronization signal (previous version) (PLS1). A long fine pulse (PLS3) is generated.
[0058]
In the present invention, the number of occurrences of the fine pulse is determined by the amount of deviation of the frame gate signal (FGATE) with respect to the phase convergence reference (Tlsync / 2) as described above, and the timing (a) and timing (b) in FIG. This time is determined according to the deviation time t1 (= TLsync / 2−ta). The number of occurrences (N) is as follows. When the pulse width of the motor synchronization signal (PLS1) is tp and the pulse width of the minute pulse (PLS3) is td3,
N = (tp−t1) / (td3−tp)
It is a numerical value determined by.
During the phase matching period of the motor synchronization signal (PLS), a fine pulse (PLS3) is generated from the rise of the first motor synchronization signal (PLS1) after detecting the time difference t1 between timing (a) and timing (b). And converge at timing (c).
[0059]
In the above description, an example in which a minute pulse is used has been shown. However, in the case of using a minute pulse, the timing (a) comes after the timing (b) as described above (2 in FIG. 3). In this case, the start of the phase matching period is the rise of the first motor synchronization signal (PLS1) after the timing (a).
[0060]
【The invention's effect】
As described above, according to the present invention, the phase control means uses the mark detection means as a reference for detecting the phase shift of the frame gate signal due to the fluctuation of the phase of the line synchronization signal between the color plates. A point in time that is the period of the line synchronization signal from the rising edge of the mark detection signal that is the detected mark detection timing or a point that is half the period is set as the phase convergence reference, and the frame gate signal relative to the phase convergence reference Phased Detect the amount of deviation, When the phase is advanced with respect to the phase convergence reference, a fine pulse is generated by the phase matching circuit according to the detected deviation amount to control the rotational phase of the motor, and the phase is delayed with respect to the phase convergence reference. The phase matching circuit generates a short pulse according to the detected deviation amount to control the rotational phase of the motor, Since the phase control is performed so that the phase of the frame gate signal converges on the phase convergence reference, the write start timing can be set at a position where the fluctuation of the line synchronization signal does not cause a problem, so that reliable control is possible. Therefore, it is possible to perform high-precision overlay between single color images of each color plate without causing an exposure position shift in the sub-scanning direction. Also, in the present invention, phase matching is performed based on the line synchronization signal or frame gate signal that is the write start signal, so that writing is started before the phase converges to the phase convergence reference, and the dead time that has been set as the phase matching period is reduced. This eliminates the need for high-speed throughput and speeds up color image formation.
[Brief description of the 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 between 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 there is a phase fluctuation in a line synchronization signal between color plates.
4 is a timing chart showing an example of a control operation by the phase control means shown in FIG. 1. FIG.
FIG. 5 is a schematic configuration diagram illustrating an example of a color image forming apparatus in which the present invention is implemented.
6 is an enlarged cross-sectional view showing a part of the color image forming apparatus shown in FIG.
7 is a perspective view for explaining a configuration of a writing system used in the color image forming apparatus shown in FIG. 5. FIG.
8 is a block diagram showing a configuration example of a phase control unit 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 a 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 unit shown in FIG.
12 is a block diagram showing still another configuration example of a phase control unit 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.
14 is a timing chart showing another example of the control operation by the phase control means shown in FIG. 12. FIG.
[Explanation of symbols]
1: Photoconductor belt
2, 3: Rotating roller
4: Charging member (charging roller)
5: Laser writing 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: Development unit
10: Intermediate transfer belt
11, 12: Rotating roller
13: Bias roller
14: Transfer roller
15: Photoconductor cleaning device
16: Intermediate transfer belt cleaning device
16A: Cleaning blade
16B: Cleaning blade support member
17: Paper feeder
18: Paper feed roller
19: Registration roller
20: Fixing device
21: Static elimination lamp
40: Mark detection sensor
41A-41F: Mark
50: Oscillator
51, 58, 59: phase matching circuit
52: Motor control circuit

Claims (3)

A rotating photoreceptor and a rotating polygon mirror rotated by a motor of a rotating polygon mirror drive device are provided, and the light beam corresponding to the image forming signal of each color is deflected by the rotating polygon mirror and exposed to each of the colors. A latent image forming unit that forms an electrostatic latent image corresponding to an image signal, and a developer carrying member that visualizes the electrostatic latent image corresponding to the image forming signal of each color on the photoreceptor with each color developer. A plurality of developing means each having an intermediate transfer body on which the monochrome images of the respective colors that have been rotated and visualized on the photosensitive body are sequentially superimposed and transferred, and marks provided on the intermediate transfer body. Mark detection means for detecting at a predetermined position and outputting a mark detection signal, control means for causing the latent image forming means to start forming an electrostatic latent image at the mark detection timing of the mark detection means, and development means Image processed and intermediate A transfer means for transferring the image superimposed on the transfer body to a transfer material; a fixing means for fixing the image transferred to the transfer material; and a light beam scanned in the main scanning direction by the rotary polygon mirror A synchronization detection sensor that outputs a line synchronization signal, which is a synchronization signal in the main scanning direction of image writing, and a frame gate signal obtained from the line synchronization signal of the synchronization detection sensor and the mark detection means In a color image forming apparatus provided with phase control means for controlling the rotational phase of a motor that rotates the rotary polygon mirror according to a mark detection signal,
The phase control means includes
A motor synchronizing signal generating circuit for generating a motor synchronization signal and a fine short pulse generation circuit for generating a fine short pulses having a shorter pulse width than the pulse width of the motor synchronizing signal, the pulse width longer than the pulse width of the motor synchronizing signal and fine long pulse generation circuits for generating a fine long pulse, and a timing signal generating circuit for generating a timing signal to each circuit, the mark detection signal and the frame gate signal inputted to the timing signal generating circuit, A phase matching circuit that selects whether to use a minute pulse or a minute pulse as a pulse used for phase control and generates a motor synchronization signal, a minute pulse signal, or a minute pulse signal,
A motor control circuit that is controlled by a motor synchronization signal, a minute pulse signal, or a minute pulse signal output from the phase matching circuit, and that synchronously controls the rotation speed and the rotation phase of the motor that rotates the rotary polygon mirror;
The phase control means uses a mark detection signal that is a mark detection timing detected by the mark detection means as a reference for detecting a phase shift of the frame gate signal due to a phase fluctuation of the line synchronization signal between the color plates. Set the point of time of the line synchronization signal from the rising edge as a unit or half of the cycle as the phase convergence reference, detect the amount of phase shift of the frame gate signal with respect to the phase convergence reference, When the phase is advanced, a fine pulse is generated by the phase matching circuit according to the detected deviation amount to control the rotational phase of the motor, and when the phase is delayed with respect to the phase convergence reference, the detected deviation is detected. the generated fine short pulses by the phase matching circuit to control the rotational phase of the motor depending on the amount, Furemuge to the phase convergence criterion Color image forming apparatus in which the phase of the bets signals, characterized in that the phase control so as to converge.   2. The color image forming apparatus according to claim 1, wherein writing is started before the phase converges on the phase convergence reference.   2. The color image forming apparatus according to claim 1, wherein a phase correction amount is detected based on a time difference between the phase convergence reference and a line synchronization signal or a frame gate signal.

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