JP2005066934A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent reflected light during a transit time in a change of an angle of each mirror device of DMDs (digital mirror devices) from forming a latent image on a photosensitive drum, in a light scanning system composed of a light-emitting device, the DMDs and a polygon. <P>SOLUTION: In an image forming apparatus, the light-emitting device is turned off during the transit time when each mirror device of the DMDs changes the angle, and the mirror device makes the light-emitting device turned on only with timing at a proper reflection angle to the photosensitive drum. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrophotographic apparatus such as a copying machine, a printer, and a fax machine that performs image exposure with a plurality of laser beams.

  Conventionally, a polygon scanner has been used as an exposure scanning means for image formation.

  However, as the speed of image formation increases, the number of rotations of the polygon motor has reached its limit, and multiple line simultaneous writing with multiple beams has been proposed. However, it is difficult to match the amount of individual beams with multi-beams, leading to increased costs.

Therefore, a scanning system using DMD (digital mirror device) has been proposed (see Patent Document 1).
Japanese Patent Laid-Open No. 06-138403

  However, since the digital mirror device switches whether the light is reflected in a desired direction by changing the angle of each micromirror, it takes time to physically move the mirror. If the laser is kept on during the movement time of the mirror, beam spot exposure that is longer than the laser beam spot originally desired by the movement is performed.

  The present invention has been made paying attention to the above points. In the light scanning system of a light emitting element, DMD (digital mirror device) + polygon, reflection during movement time when each mirror device of DMD changes an angle. An object of the present invention is to provide an image forming apparatus that prevents light from forming a latent image on a photosensitive drum.

Therefore, the present invention
(1) A light beam emitted from a light emitting element, a mirror device in which a plurality of mirrors with variable individual angles are arranged in an array, and a light beam is irradiated onto a polygon mirror by changing the angle of each mirror of the mirror device In an image exposure scanning apparatus having dot forming means for forming a dot pattern on a photosensitive drum by changing the state of whether or not to perform, the angle of the mirror device is changed from an angle irradiated to the polygon mirror to an angle not irradiated The light emitting element is turned off at the timing when the state starts to be changed, and the light emitting element is turned on so that the light emitting element is turned on at the timing when the return to the angle to irradiate the polygon mirror is completed.

  (2) DMD in which a plurality of micromirror devices are arranged in the main scanning direction in (1) above, a multi-pixel simultaneous exposure means for simultaneously exposing a plurality of pixels in the main scanning direction by simultaneously exposing the DMD, and a polygon motor In the image forming means for forming an image, the light emitting element is turned on only at the simultaneous exposure timing, is turned off until the next simultaneous exposure timing, and the mirror angle of the DMD is turned off during the turn-off. The above-mentioned problems are solved by changing.

  An image forming device that performs multiple line simultaneous writing or multiple pixel simultaneous writing using a laser emitting unit, digital mirror device and polygon mirror, and realizes an image forming device that prevents image degradation due to tailing of the exposure spot without increasing the cost. To do.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a cross-sectional view for explaining the configuration of an image forming apparatus equipped with the sheet processing method of the present invention.

  Reference numeral 101 denotes an original platen glass on which originals fed from the automatic document feeder 160 are sequentially placed at predetermined positions. Reference numeral 102 denotes a document illumination lamp composed of, for example, a fluorescent lamp, which exposes a document placed on the document table glass 101. Reference numerals 103, 104, and 105 denote scanning mirrors, which are accommodated in an optical scanning unit (not shown), and guide reflected light from the document to the CCD unit 106 while reciprocating. The CCD unit 106 includes an imaging lens 107 that forms an image of reflected light from an original on the CCD, for example, an image sensor 108 composed of a CCD, a CCD driver 109 that drives the image sensor 108, and the like. An image signal output from the image sensor 108 is converted into, for example, 8-bit digital data and then input to the controller unit 150.

  Reference numeral 110 denotes a photosensitive drum, which is discharged by a pre-exposure lamp 112 in preparation for image formation. A primary charger 113 uniformly charges the photosensitive drum 110. Reference numeral 117 denotes an exposure unit, which is composed of, for example, a semiconductor laser and exposes the photosensitive drum 110 based on image data processed by the controller unit 150 that performs image processing and overall control of the apparatus, thereby forming an electrostatic latent image. . Reference numeral 118 denotes a developing device that contains a black developer (toner). Reference numeral 119 denotes a buffer unit that stores toner, and the toner is supplied from a detachable toner storage container (hereinafter referred to as a cartridge) set at 120. The toner supplied to the buffer unit 119 is supplied to the developing device according to the amount of toner in the developing device. A pre-transfer charger 121 applies a high voltage before transferring the toner image developed on the photosensitive drum 110 onto a sheet.

  Reference numerals 122, 124, 126, 128, and 130 denote paper feed units, and each paper feed roller 123, 125, 127, 129, 131 drives the transfer paper into the apparatus, and the registration roller 132 is disposed. Is temporarily stopped, the writing timing with the image formed on the photosensitive drum 110 is taken, and the sheet is fed again. Reference numeral 133 denotes a transfer charger, which transfers the toner image developed on the photosensitive drum 110 onto a transfer sheet to be fed. A separation charger 134 separates the transfer sheet on which the transfer operation has been completed from the photosensitive drum 110.

  The toner remaining on the photosensitive drum 110 without being transferred is collected by the cleaner 111. Reference numeral 135 denotes a conveyance belt which conveys the transfer sheet on which the transfer process has been completed to the fixing device 136 and is fixed by heat, for example. Reference numeral 137 denotes a flapper which controls the transfer sheet transport path after the fixing process in either the staple sorter 145 direction or the reverse path 139 direction. The sheets discharged to the staple sorter 145 are sorted into bins, and the staple unit 146 performs stapling according to instructions from the controller unit 150. The reverse path 139 is used when face-down paper discharge and double-sided copy are performed, and when face-down paper discharge is performed, the paper is reversed by the reversing unit 139 before being discharged. When performing double-sided copying, the paper is conveyed from the reverse path 139 to the double-sided path 144. Reference numerals 140 to 142 denote paper feed rollers that convey the retransfer paper on the duplex path 144 to the refeed roller 143. The retransfer sheet is conveyed by the sheet feeding rollers 140 to 142 and 143 while being timed with the transfer sheet fed from the sheet feeding unit, and is again conveyed to the position where the registration roller 132 is disposed.

  The controller unit 150 includes a microcomputer, an image processing unit, and the like, which will be described later, and performs the above-described image forming operation in accordance with instructions from the operation panel 151. Reference numeral 152 denotes a print data controller unit. This is to permit use of the copy machine by inserting a card as a control card when using a copy, and the copying machine main body stores the number of copies for each user ID having the control card.

  In this example, the control in which the user ID is written is inserted into the copying machine main body, the copying machine main body discriminates the ID, and the count number is managed. However, a configuration may be adopted in which the card itself is stored. For example, a non-contact memory such as a ferroelectric memory may be built in the card, and a count signal may be written from the print data controller side.

  FIG. 2 is a block diagram of the controller unit 150 in the image forming apparatus of the present invention.

  A CPU 201 controls the entire image processing apparatus, and sequentially reads and executes a program from a read-only memory 203 (ROM) that stores a control procedure (control program) of the apparatus main body. The address bus and data bus of the CPU 201 are connected to each load through 202 bus driver circuits and address decoder circuits. Reference numeral 204 denotes a random access memory (RAM) which is a main storage device used for storing input data, a working storage area, and the like.

  Reference numeral 205 denotes an image data hard disk which stores data input from the CCD unit and subjected to image processing. The image data is also stored when connected to a network or the like.

  Reference numeral 206 denotes an I / O interface, which is used by an operator to input keys and displays operation states of the apparatus 151 using liquid crystal and LEDs, and motors for driving a paper feed system, a transport system, and an optical system. 207, clutches 208, solenoids 209, and paper detection sensors 210 for detecting the paper to be conveyed are connected to each load of the apparatus. The developing device 118 is provided with a 211 residual toner detection sensor that detects the amount of toner in the developing device, and its output signal is input to the I / O port 206. In addition, signals from switches 212 for detecting the home position of each load, the open / closed state of the door, and the like are also input to the I / O port 206. A high voltage unit 213 outputs a high voltage to the above-described primary charger 113, developing device 118, pre-transfer charger 121, transfer charger 133, and separation charger 134 in accordance with instructions from the CPU.

  Further, an output from a temperature / humidity sensor (not shown) for detecting the temperature and humidity in the copying machine main body is directly connected to an analog port of the CPU 201, and is A / D converted and calculated as a digital value. From the temperature / humidity sensor, a voltage value representing temperature and a voltage value representing humidity are input to the analog port of the CPU.

  An image processing unit 215 receives an image signal output from the CCD unit 106, performs image processing to be described later, and outputs a control signal for the laser unit 117 according to the image data. Laser light output from the laser unit 117 irradiates and exposes the photosensitive drum 110, and a light emission state is detected by a 214 beam detection sensor which is a light receiving sensor in a non-image area, and an output signal thereof is an I / O port. 206 is input.

  FIG. 3 is a block diagram of the image processing unit 215 in the controller unit 150 in the image forming apparatus of the present invention.

  The image signal converted into an electrical signal by the CCD 106 is first corrected for variation between pixels by the shading circuit 301, and then subjected to data thinning processing at the zooming circuit 302 at the time of reduced copy and at the time of enlarged copy. Interpolate data. Next, in the edge enhancement circuit 303, for example, secondary differentiation is performed in a 5 × 5 window to enhance the edge of the image. Since this image data is luminance data, data conversion is performed by table search in the γ conversion circuit 304 in order to convert it into density data for output to the printer. The image data converted into the density data is input to the binarization processing unit 305. Here, for example, multi-value data is converted into binary data by the ED method. The image data converted into binary data is input to the combining circuit 307. The combining circuit 307 selectively outputs the input image data and the image data in the image memory 310 constituted by the hard disk 309, for example, or outputs the result of OR. The read / write control for the image memory 310 is performed by the memory controller 306, and when the image is rotated, the read address of the image data in the memory is controlled. These image data are input to the PWM circuit 308 for conversion into a signal of laser emission intensity, and a pulse width corresponding to the image density is output to the laser unit.

  Next, the rotation speed control and phase control of a general laser scanner motor will be described with reference to the block diagram of FIG.

  A brushless motor is used as the laser scanner motor, and the inside of the broken line shows the equivalent circuit. The inductance 705 is star-connected and excited by the bridge circuit 700 to generate a rotating magnetic field. A magnetic pattern is magnetized on the rotor 704, and the rotor 704 is rotated by a rotating magnetic field having an inductance 705 to rotate the rotary polygon mirror 802. The Hall elements 701 to 703 detect the magnetic field magnetized in the rotor 704, and the detected magnetic field is input to the rotating magnetic field control circuit 706. The rotating magnetic field control circuit 706 detects the rotational position of the rotor 704 based on the output signals of the Hall elements 701 to 703, and controls the bridge circuit 700 so as to always generate a magnetic field in which the rotor 704 performs rotational motion. The rotating magnetic field control circuit 706 receives an acceleration signal and a deceleration signal from the acceleration / deceleration control unit 707, and performs speed control and phase control by controlling the rotation of the motor based on the signals.

  The acceleration / deceleration control unit 707 includes a first acceleration / deceleration control unit (speed control unit) 708, a second acceleration / deceleration control unit (phase control unit) 709, and an acceleration / deceleration signal combining unit that combines signals from the control unit, a reference It consists of a signal generator 711.

  First, the control of the first acceleration / deceleration control unit 708 will be described with reference to the timing chart of FIG. FIG. 4-a shows the timing when the deceleration signal is output. The signal interval of the BD sensor 52 is alternately counted using two counters. When this counter reaches the set value X, it stops counting. If the next BD sensor signal is not input when the counter stops, that is, if the motor speed has not reached the set value, a deceleration signal is output until the next BD sensor signal is input. FIG. 4-b shows the timing when the acceleration signal is output. This is when the BD sensor signal is input before reaching the set value X, that is, when the motor speed exceeds the set value, and after the BD sensor signal is input, the acceleration signal is output until the set value X is reached. Is done. These controls are performed each time a BD sensor signal is input, and the speed is controlled so as to rotate at the target speed X.

  Next, the control of the second acceleration / deceleration control unit 709 will be described using the timing chart of FIG. FIG. 5-a shows the timing when the deceleration signal is output. When the phase ON signal is input to the second acceleration / deceleration control unit, the counter 1 that counts the BD sensor signal and the counter 2 that counts the reference signal generated by the reference signal generation unit start counting. A difference when the count value becomes a value set by the CPU or the like is detected. FIG. 5A shows a case where the set value is 3. When the BD signal first reaches the set count value, a deceleration signal calculated from the difference is output. For example, as shown in the figure, a pulse width that is 1/4 of the difference is output. Actually, the ratio of the output pulse width to the detected difference is determined by the motor characteristics or the like (shown in FIG. 5-a is merely an example). FIG. 5B shows a case where an acceleration signal is output. In this case, when the counter value for counting the reference signal reaches the set count value earlier than the BD signal, an acceleration signal calculated from the difference is output. FIG. 5B shows a case where the setting value is set to 3 and a pulse width of 1/4 of the difference is output as in the case of deceleration. This is only an example, and the ratio of the pulse width is determined by the characteristics of the motor as in the case of deceleration. In the above example, the case where the count value for difference comparison is set to 3 has been described, but if this value is also determined in consideration of the motor characteristics and the signal output from the first acceleration / deceleration control unit, more accurate control can be performed. it can.

  The acceleration / deceleration signals generated by the first and second acceleration / deceleration control units are combined by the acceleration / deceleration signal combining unit 710 and output to the control circuit 706 to control the rotation of the motor.

  In particular, the output timing of the acceleration signal and the deceleration signal is not particularly specified this time, but the image quality is not deteriorated by accelerating or decelerating the non-image area. When the above configuration is used, since the input timing of the BD sensor is known, it is naturally possible to know the image area. Therefore, it is desired to detect a non-image area and output a signal in other areas.

  Next, the phase control and speed control sequence will be described with reference to the flowchart of FIG. First, it waits for the laser scanner motor to be turned on at f1. When the motor is turned on, the process proceeds to f2 to determine whether or not the phase control (second acceleration / deceleration control) is turned on. In the case of the single color mode, it is not necessary to turn on the phase control, and the phase control is turned on only in the full color mode. That is, when the phase control is not turned on (monochromatic mode), only the first acceleration / deceleration control (speed control) operates. In this case, the process proceeds to f4, and the acceleration or deceleration signal is generated so that the control (first acceleration / deceleration control) described in FIG. 4, that is, the interval between the BD sensor signals becomes constant. Proceeding to f6, these signals are given to the control circuit 706 to control the rotation of the motor. When the phase control (second acceleration / deceleration control) is ON at f2 (full color mode), the process proceeds to f3, and not only the rotation control (first acceleration / deceleration control) but also the second acceleration / deceleration control (phase Control) also works. This is the control described with reference to FIG. 5, and generates a control signal for adjusting the phase of the BD sensor signal to the reference signal. Proceeding to f5, the signals generated by the first and second acceleration / deceleration controls are combined and supplied to the control circuit 706 to control the rotational speed and phase of the motor. Next, the process proceeds to f7, and if the motor is not turned off, the process returns to f2 again to determine whether the phase control is turned on, and the control is repeated. If the motor is turned off at f7, the control is terminated.

  FIG. 8 is a diagram showing the configuration of a conventional polygon scanner. This figure shows a case where the laser beam path is L-shaped. Reference numeral 802 denotes a rotary polygon mirror, and 803 denotes a laser scanner motor that rotationally drives the rotary polygon mirror 802. The number of surfaces of the rotary polygon mirror 802 is determined by parameters such as print speed and resolution. Reference numeral 801 denotes a laser diode which is a recording light source. The laser diode 801 is turned on or off according to an image signal or a control signal by a drive circuit (not shown), and the light modulation laser light emitted from the laser diode 801 is irradiated toward the rotary polygon mirror 802.

  The rotating polygon mirror 802 is rotated in the direction of the arrow, and the laser light emitted from the laser diode 801 is reflected as a modified beam that continuously changes its angle on its reflecting surface as the rotating polygon mirror 802 rotates. The reflected light is subjected to distortion correction and the like by a lens group (not shown), and scans in the main scanning direction of the photosensitive drum 11 via the reflecting mirror 805. One surface of the rotary polygon mirror 802 corresponds to one line scanning, and the laser light emitted from the laser diode 801 by the rotation of the rotary polygon mirror 802 scans the photosensitive drum 11 in the main scanning direction line by line.

  Further, a BD sensor 52 is arranged to generate a scanning start position reference signal in the main scanning direction. Actually, it is ideally installed near the scanning start position (near the photosensitive drum 11), but by using the folding mirror 807, the BD sensor 52 is arranged in the laser scanner unit. That is, the laser light reflected by each reflecting surface of the rotary polygon mirror 802 is detected by the BD sensor 52 prior to scanning one line. The detected BD signal is used as a scanning start reference signal in the main scanning direction, and the writing start position of each line in the main scanning direction is synchronized based on this signal.

  FIG. 9 is a block diagram of a laser scanner when the digital mirror device (DMD) of the present invention is used. DMD is an array of 16 μm × 16 μm square micromirrors arranged in an array by a semiconductor manufacturing process, and the angles of individual micromirrors can be changed independently. In this embodiment, description will be made using DMDs arranged in a line in the sub-scanning direction of an image.

  By arranging DMD 811 in the sub-scanning direction and performing polygon scanning by individually changing the angle of each micromirror, it becomes possible to simultaneously write a plurality of lines. This is shown in FIG.

  By changing the angle of each individual micromirror, whether the polygon mirror 802 is irradiated with laser light or not is switched. Here, when the angle of each mirror of the DMD is changed while the light source laser 801 is kept on, as shown in FIG. 11, the laser spot remains on the polygonal surface even while the angle of the mirror is changed. Irradiation results in a spot that extends longer than the spot originally intended to be exposed.

  Therefore, as shown in FIG. 12, a method is employed in which the laser 801 is turned on for a time during which it is determined that the individual micromirrors of the DMD 811 are in the reflection position with respect to the polygon surface.

  In FIG. 12, for example, when one micromirror is repeatedly turned on and off for each pixel, the mirror position is determined after the mirror movement times t1 and t3 as shown in the figure.

  Therefore, the laser 801 is configured to turn on after t1 after the mirror drive signal starts moving in the reflection direction, and to turn off within the time t2 when the next pixel is in the mirror off state.

  These t1, t2, and t3 may be determined as fixed values from the response speed specifications of the mirror device.

  Next, the case where the pixel arrangement of the DMD 811 is in the main scanning direction will be described with reference to FIG. When a plurality of DMDs 811 are used in the main scanning direction, a plurality of main scanning pixels can be exposed by a single laser exposure. The next exposure timing is a timing at which the polygon mirror moves by a plurality of pixels and connects to the previous plurality of pixels. After the exposure once, the polygon mirror rotates to change the angle until the next plurality of pixels are exposed, and the reflection angle of each micromirror of the DMD 811 is switched during that time. At that time, the laser 801 is turned off.

  The timing is shown in FIG. Here, the mirror-on state represents the timing at which a plurality of pixels are simultaneously exposed in the main scanning direction. The laser 801 is turned on for that time. The mirror-off state is the time until the position where the polygon motor rotates to expose the next plurality of pixels.

  During this time, the laser 801 is turned off. The longer the number of mirrors in the main scanning direction, the longer the turn-off time and mirror switching time.

  The above is the description of the embodiment of the present invention.

  In the present invention, the laser beam spot is prevented from extending by turning on / off the laser, but the same effect can be obtained by using a polarizing filter or slit that allows only incident light at a specific angle to pass.

Cross-sectional view of the image forming apparatus of the present invention 1 is a block diagram illustrating a configuration of an image forming apparatus of the present invention. Block diagram of the image processing unit Timing chart for speed control (first acceleration / deceleration control unit) Timing chart for phase control (second acceleration / deceleration control unit) Flow chart explaining phase control and speed control sequence Control block diagram of laser scanner motor of the present invention Configuration of conventional laser scanner unit Configuration diagram of laser scanner unit using DMD of the present invention The figure which showed the mode of exposure with the laser scanner unit using DMD of this invention The figure which showed the timing of exposure in the laser scanner unit using DMD of this invention The figure which showed a mode that the laser exposure spot extended by DMD angle change The figure which showed the mode of exposure when DMD was arranged in the main scanning direction with the laser scanner unit using DMD of this invention The figure which showed the timing of exposure at the time of arranging DMD in the main scanning direction with the laser scanner unit using DMD of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Document glass 102 Document illumination lamps 103, 104, 105 Scanning mirror 106 CCD unit 107 Imaging lens 108 Imaging element 109 CCD driver 110 Photosensitive drum 111 Cleaner 112 Pre-exposure lamp 113 Primary charger 117 Exposure means (laser unit)
118 Developer 119 Buffer 120 Removable Toner Storage Container (Cartridge)
121 Pre-transfer charger 122, 124, 126, 128, 130 Paper feed unit 123, 125, 127, 129, 131 Paper feed roller 132 Registration roller 133 Transfer charger 134 Separation charger 135 Transport belt 136 Fixing device 137 Flapper 139 Reverse Path (reversing part)
140 to 142 Paper feed roller 143 Refeed roller 144 Double-sided path 145 Staple sorter 146 Staple unit 150 Controller unit 151 Operation panel 152 Print data controller unit 160 Automatic document feeder 801 Laser diode (laser)
802 Rotating polygon mirror
805 Reflective mirror 807 Folding mirror

Claims (2)

  A light beam emitted from the light emitting element, a mirror device in which a plurality of mirrors with variable individual angles are arranged in an array, and whether to irradiate a polygon mirror with a light beam by changing the angle of each mirror of the mirror device In an image exposure scanning apparatus having dot forming means for forming a dot pattern on a photosensitive drum by changing the state, the angle of the mirror device is changed from an angle at which the polygon mirror is irradiated to an angle at which the polygon mirror is not irradiated. An image forming apparatus, wherein the light emitting element is turned off at a timing when the light emitting element is started, and the light emitting element is turned on at a timing when the light emitting element is returned to the angle irradiated to the polygon mirror.   2. The image forming apparatus according to claim 1, wherein a DMD in which a plurality of micromirror devices are arranged in the main scanning direction, and a multi-pixel simultaneous exposure unit that exposes a plurality of pixels in the main scanning direction at the same time by simultaneously exposing the DMD. In the image forming means for forming an image by rotating the polygon motor and repeating the plural pixel simultaneous exposure means, the light emitting element is turned on only at the simultaneous exposure timing, and is turned off until the next simultaneous exposure timing. An image forming apparatus characterized by changing a mirror angle.

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