JP2008260240A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: A conventional image clock control technique cannot form an image with an accurate recording position and high quality because an operation position in a sub-scanning direction cannot follow a resonance frequency fluctuation.
A reference frequency is set from a resonance frequency of a resonance scanner, and resonance scanner / image formation control is performed based on the reference frequency. An optical scanning detection unit is provided for detecting the vibration operation of the resonance scanner, and controls the vibration operation of the resonance scanner. The pixel clock for driving the light emitting element for image formation is controlled from the signal of the optical scanning detection means.
[Selection] Figure 1

Description

  The present invention relates to an apparatus for forming an image by electrophotography, and more particularly to an image forming apparatus using a resonance type optical deflector for a method of manipulating a light quantity based on image information on a photoconductor.

  Conventionally, various optical deflectors in which a mirror is driven to resonate have been proposed. The resonance type optical deflector has the following characteristics as compared with an optical scanning optical system using a rotating polygon mirror such as a polygon mirror. That is, it is possible to greatly reduce the size of the optical deflector, the power consumption is small, and there is theoretically no tilting of the mirror surface.

  On the other hand, since the resonance type deflector has a characteristic of repeatedly moving the mirror by vibration operation, the following proposals have been made as an image forming apparatus and control method using the resonance type deflector.

  In the image forming apparatus and the control method disclosed in Patent Document 1, the resonance type optical deflector is driven by separate excitation, and the frequency is driven at a limited reference frequency in the vicinity of the resonance frequency. In addition, only a resonant optical deflector that can be driven at the limited reference frequency is configured, and the yield is improved.

  In the image forming apparatus and control method disclosed in Patent Document 2, the resonance type optical deflector is driven at a reference frequency in the vicinity of the resonance frequency, and the phase control of the motor drive of the photosensitive drum is performed at this frequency. The resonance type optical deflector is oscillated without detecting whether the phase of the resonant optical deflector matches the phase.

In Patent Document 3, an image clock control technique for a resonant optical deflector disclosed as a correction method for a beam scanned at a sinusoidal angular velocity is a pixel clock control technique that determines pixel clock control from the operation of the resonant optical deflector. The purpose is to form a pattern with uniform spacing and no distortion, and refers to a clock generation method for that purpose.
JP-A-63-65766 Japanese Patent Laid-Open No. 01-302366 JP 05-136948 A

  However, the image clock control technique disclosed in Patent Document 3 determines the writing position and the period of the recording pixel clock and supplies the clock stably on the assumption that the resonance oscillation operation is always performed at the resonance frequency of the resonance type optical deflector. However, since the operation position in the sub-scanning direction cannot follow the resonance frequency fluctuation, the recording position is not accurate and high-quality image formation is not possible.

  As described in Patent Document 2, when the rotational driving of the photosensitive drum is controlled in accordance with the scanning of the resonance type optical deflector, the rotational operation response of the photosensitive drum cannot actually follow instantaneously. Since the recording position in the scanning direction cannot follow the frequency in the horizontal direction, the recording position lacks accuracy, and finally, unevenness occurs in image reproduction.

  The image forming apparatus and the control method disclosed in Patent Document 1 provide a device for separately driving the resonance type optical deflector. However, the phase control of the photosensitive drum and the resonance type light can be performed only by the separately excited drive. Since the phase control of the deflector is not performed and the relationship between the two becomes a free run, the recording position accuracy in the sub-scanning direction cannot be obtained, and unevenness occurs in the sub-scanning direction.

In an image forming apparatus having a resonant optical deflector as an optical scanning unit for image formation,
A reference frequency is set from the resonance frequency of the resonance type optical deflector, and the resonance type optical deflector / image formation control is performed based on the reference frequency.
In the image forming apparatus,
An optical scanning detection unit is provided for detecting the vibration operation of the resonant optical deflector, and the recording position is accurately determined by providing control of the vibration operation of the resonant optical deflector according to a signal from the optical scanning detection unit. Therefore, high-quality image formation can be performed also in the resonance type optical deflector.

  According to the present invention, the phase difference from the reference is detected, the resonant optical deflector is controlled, and the writing position and the pixel clock cycle are determined from the phase difference, so that a more accurate recording position is possible. As a result, an image forming apparatus using a resonant optical deflector that reproduces a high-quality image with a small apparatus is provided.

(First embodiment)
FIG. 5 shows a cross-sectional view of an image forming apparatus for carrying out the present invention.

  The image forming apparatus 5 corresponds to, for example, a 4-drum type color laser beam printer. In this color image forming apparatus, a transfer material cassette 503 is mounted at the lower right side of the main body apparatus. The transfer material set in the transfer material cassette 503 is taken out one by one by a paper feed roller 504 and fed to an image forming unit by a pair of conveying rollers 505-a and 505-b. In the image forming unit, a transfer conveyance belt 90 for conveying a transfer material is stretched flat in a transfer material conveyance direction (from right to left in FIG. 5) by a plurality of rotating rollers. It is electrostatically attracted to the conveyor belt 510. Further, four photosensitive drums 511 serving as image bearing members in the form of drums are arranged in a straight line so as to face the belt conveying surface to constitute an image forming unit.

  The developing unit 502 serving as an image forming unit includes the photosensitive drums 511C (CYAN), Y (YELLOW), M (MAGENTA), and K (BLACK) toners, a charger, and a developer. A predetermined gap is provided between the charger and the developer in the housing of each developing unit 502 described above, and the peripheral surface of the photosensitive drum 511 is charged with a predetermined charge from the exposure unit 501 formed of a laser scanner through the gap. Charge uniformly. The exposure units 501C, M, Y, and K are provided with a two-dimensional mirror as shown in FIG. The exposure unit 501 reflects the laser beam with an internal two-dimensional mirror and exposes the peripheral surface of the charged photosensitive drum 511 according to image information to form an electrostatic latent image. The developer transfers toner to the blackout portion of the formed electrostatic latent image to form (develop) the toner image. A transfer member 507 is disposed across the conveyance surface of the transfer conveyance belt 510. The toner images formed (developed) on the peripheral surfaces of the respective photosensitive drums 511 are absorbed and transferred by the charge generated on the transferred transfer material by the transfer electric field formed by the transfer member 507 corresponding to the toner images. It is transferred to the material surface. The transfer material onto which the toner image has been transferred is discharged out of the apparatus by a pair of discharge rollers 509-a and 509-b. The transfer / conveying belt 510 may be an intermediate transfer belt configured to temporarily transfer C (CYAN), Y (YELLOW), M (MAGENTA), and K (BLACK) toners, and then secondarily transfer the toner onto a transfer material. Absent.

  The control operation of the exposure unit 501 in the present invention will be described with reference to the block diagram of FIG. 1 and the flowchart of FIG.

  The resonance type optical deflector drive control unit 103 generates a signal for driving the resonance type optical deflector 101. Further, information such as a current flowing into the resonant optical deflector 101 is notified to the reference frequency determination processing 106 as an operating state.

  In the reference frequency determination processing 106, the natural frequency (S 2) of the resonant optical deflector 101 stored in a storage device (not shown), the resonant optical deflector 101 from the resonant optical deflector drive controller 103. The reference frequency fb is determined from the operating state and the frequency of the system clock according to an instruction from the formation control management means (not shown), and is given to the reference frequency generation unit 104 as the divided value 123 (S3).

  The reference frequency generation unit 104 generates a signal corresponding to the reference frequency fb determined by the reference frequency determination processing 106 by frequency division of the system clock, and passes it to the phase detection 108 as the reference signal 124.

Under the control of the laser control unit 102, the laser light emitted by the laser emission 111 is scanned in the main scanning direction by the resonance type optical deflector 101 via an optical system not shown in FIG. The position detection signal 121 is detected at 107. (S5, S8)
Using the position detection signal 121 and the reference signal 124, the phase detection 108 calculates phase difference information 120 between the scanning period of the resonant optical deflector 101 and the reference frequency fb from the reference frequency generator.

From the scanning period and phase difference information 120, the control amount of the resonant optical deflector 101 is supplied to the optical deflector drive controller 103, and the optical deflector drive controller 103 drives the resonant optical deflector 101. Further, the pixel clock generation unit 109 uses the scanning cycle / phase difference information 120 to generate the pixel clock 125. (S9)
The pixel clock 125 serves as a reference for generating image data to be supplied to the laser control unit 102 by the data generation unit 110.

  FIG. 4 shows an arrangement of the light deflector 401, the light receiving elements 402a and 402b, which are detectors, and the light source 404. The light beam 405 output from the light source 404 is deflected by the optical deflector 401. The light receiving elements 402a and 402b are arranged at angles θ1 and θ2 smaller than the maximum deflection angle 406 of the optical deflector. Θ1 and θ2 are target angles from the scanning center of the optical deflector. The light receiving elements 402a and 402b receive the deflected light beam 405 when the optical deflector 401 reaches θ1 and θ2, and generate an electrical signal.

  In the present embodiment, one or more times of t1, t2, t12, and t21 in FIG. 7 are detected based on this electrical signal. The phase detector 108 calculates phase difference information of the amplitude A1 of the frequency ω1, the amplitude A2 of the frequency ω2, and the phase difference φ of the frequency ω1 and the frequency ω2 from one or more of the times t1, t2, t12, and t21. To do. The resonance type optical deflector drive control unit 103 generates a drive signal to the optical deflector based on the phase difference information of A1, A2, and φ, and drives the movable reflecting mirror through the driver of the optical deflector.

  FIG. 6 shows a schematic configuration example of an exposure unit using the deflector portion of FIG. A light receiving element 605b is disposed at a deflection angle of the optical deflector 606 outside the range that defines the effective area of the photosensitive drum 604. Reference numeral 603 denotes an optical correction lens.

  FIG. 8 shows the angular velocity of the beam scanned on the photosensitive member in the above-described resonant optical deflector driven. The solid line shows the angular velocity characteristics when the control in FIG. 7 is performed. If this angular velocity characteristic is a straight line in the image forming region, it is easy to form pixels uniformly in the horizontal direction. However, in the characteristic shown by the solid line, the pixel density becomes non-uniform due to the difference in angular velocity, and image quality deterioration such as density unevenness occurs. The pixel clock generation unit 109 performs the density unevenness correction process by modulating the frequency of the pixel clock according to the angular velocity fluctuation.

  In the present invention, since it is possible to accurately correspond to the sub-scanning direction, high-quality image formation can be achieved by adopting the method described in Japanese Patent Laid-Open No. 5-136948 as the pixel clock modulation method. Is possible.

  The resonance-type optical deflector drive control unit 103 generates a drive waveform for driving the resonance-type optical deflector 101 based on the phase difference information 120 as described above, and from feedback information from the resonance-type optical deflector 101 for the drive waveform. The operating state of the resonance type optical deflector 101 is detected. Since a large change in the operating state indicates that a change has occurred in the resonance frequency, an instruction to change the reference frequency fb is sent to the reference frequency determination process 106.

  The reference frequency fb is changed at intervals of image forming units by a control MPU of the system (not shown) (S7), and a new frequency division value 123 is supplied to the reference frequency generating unit (S14) to form an image. I do.

(Second embodiment)
Examples of different deflector configurations are shown in FIGS.

  FIG. 2 shows an arrangement of an optical deflector 201, a light receiving element 202a as a detector, and a light source 204 for an example of detecting the position of laser light in a deflector of a resonant optical deflector. The light beam 205 output from the light source 204 is deflected by the optical deflector 201. The light receiving element 202a is disposed at angles θ1 and θ2 smaller than the maximum deflection angle 206 of the optical deflector, and θ1 is a target angle from the scanning center of the optical deflector. The light receiving element 202a receives the deflected light beam 205 when the light deflector 201 reaches θ1, and generates an electrical signal.

  Based on this electrical signal, one or more times of t1, t2 + t12 + t21 in FIG. 7 are detected. The phase detector 108 calculates phase difference information of the amplitude A1 of the frequency ω1, the amplitude A2 of the frequency ω2, and the phase difference φ of the frequency ω1 and the frequency ω2 from one or more of the times t1, t2, t12, and t21. To do. The resonance type optical deflector drive control unit 103 generates a drive signal to the optical deflector based on the phase difference information of A1, A2, and φ, and drives the movable reflecting mirror through the driver of the optical deflector.

  FIG. 3 shows a schematic configuration example of an exposure unit using the deflector portion of FIG. The light receiving element 305b is disposed at the deflection angle of the optical deflector 306 outside the range that defines the effective area of the photosensitive drum 304. Reference numeral 303 denotes an optical correction lens.

Configuration diagram of the first embodiment of the present invention The block diagram of the optical deflector in the 2nd Example of this invention Configuration diagram of a scanning system using an optical deflector in a second embodiment of the present invention 1 is a configuration diagram of an optical deflector according to a first embodiment of the present invention. 1 is a cross-sectional view of an image forming apparatus according to a first embodiment of the present invention. 1 is a configuration diagram of a scanning system using an optical deflector in a first embodiment of the present invention. Time-scan angle characteristics in the first embodiment of the present invention Example of scanning angular velocity in the first embodiment of the present invention Flowchart in the first embodiment of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Resonant type optical deflector 102 Laser control part 103 Resonant type optical deflector drive control part 104 Reference frequency generation part 105 System clock 106 Reference frequency determination 107 Optical scanning detection part 108 Phase detection 109 Pixel clock generation part 110 Data generation part 111 Laser Light emitting unit 201, 401 Resonant mirror 202a, 402a Optical detection 402b Optical detection 204, 404 Laser light source (light emitting unit)
205, 405 Laser light 206, 406 Scanning light 301, 601 Laser diode 302, 602 Collimator lens 303, 603 f-θ correction lens group 304, 604 Photosensitive drum 305, 605 Beam detector 306, 606 Resonant mirror 607 Other Beam detector

Claims (5)

In an image forming apparatus having a resonant optical deflector as an optical scanning unit for image formation,
An image forming apparatus, wherein a reference frequency is set from a resonance frequency of a resonance type optical deflector, and the resonance type optical deflector and image formation control are performed based on the reference frequency. The image forming apparatus according to claim 1,
The image forming apparatus, wherein the reference frequency is calculated by dividing a system clock of the image forming apparatus.   2. The image forming apparatus according to claim 1, wherein a pixel clock for driving a light emitting element for image formation is controlled from a signal of the light detection means. The image forming apparatus according to claim 2.
2. The image forming apparatus according to claim 1, wherein the reference frequency is determined by a driving state of the resonant optical deflector before starting image formation, and is not changed during image formation. The image forming apparatus according to claim 1,
An image forming apparatus comprising: an optical scanning detection unit for detecting a vibration operation of the resonance type optical deflector; and controlling a vibration operation of the resonance type optical deflector according to a signal from the optical scanning detection unit.

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