JP2007185787A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress jitter based on the phase difference between the output from a sensor for sensing the laser writing start position of an image forming apparatus performing image exposure with laser light and the output from the rotation sensing element of a laser scanner motor when both outputs are switched. <P>SOLUTION: The image forming apparatus comprises: a first rotation clock generated based on the output from a sensor 19 for sensing laser light, a second rotation clock generated based on the output from a Hall element 32 for detecting the rotating magnetic field of a motor, and a clock regulation means 29 for outputting a regulation clock from the phase difference between the two clocks; a first control means for controlling the rotation speed of a laser scanner motor 16 based on the phase difference between the first rotation clock and a reference clock during image formation; and a second control means for controlling the rotation speed of the laser scanner motor 16 based on the phase difference between the second rotation clock and the regulation clock during non-image formation. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine that performs image exposure with a laser beam.

  In an image forming apparatus that forms an image by an electrophotographic method, a charging device that uniformly charges a photosensitive surface of a photoreceptor (hereinafter referred to as a photosensitive drum), and an electrostatic latent image corresponding to image information on the charged photosensitive surface. A latent image forming apparatus for forming an image and a developing device for developing the electrostatic latent image are provided. Further, a transfer device for transferring the developed latent image onto the recording paper is provided, and image forming processing is sequentially performed while rotating the photosensitive surface of the photosensitive drum.

  In such a latent image forming apparatus in an electrophotographic image forming apparatus, a rotating polygon mirror is used to scan laser light on a photosensitive drum, and image exposure is performed to form an electrostatic latent image. The rotary polygon mirror is rotationally driven by a laser scanner motor, and the laser scanner motor rotates at high speed to repeatedly scan the photosensitive drum. For this reason, when a phenomenon (jitter phenomenon) in which the start and end of the recorded image are deviated occurs, the image quality is deteriorated, and thus high-precision rotation speed control is required (in this specification, jitter is the main scanning direction of the photosensitive drum). This is a deviation in the scanning time of the scanning width in FIG. In particular, high speed machines, color machines, and the like are required to have performances of tens of thousands of rpm and jitter of 0.01% or less. For this reason, a PLL circuit is used to control the rotational speed of the motor, and the magnetic field of the rotating rotor is detected by a Hall element or inductor, and the phase of the rotational frequency signal obtained by frequency-converting this and the clock signal from the high-precision crystal oscillator The rotation speed is controlled to be constant.

  By the way, a semiconductor laser oscillator that emits laser light used in an electrophotographic image forming apparatus has a life of a lighting time, and those used for electrophotography are generally 400 to 600 hours, and long ones are 1000 hours. It has become. Due to the recent improvement in image quality and printing speed, the demand for laser oscillators has been increasing. For example, in a color electrophotographic apparatus, a one-drum machine that forms an electrostatic latent image of a plurality of colors with one semiconductor laser oscillator has a longer turn-on time of the semiconductor laser oscillator than a four-drum machine that has a semiconductor laser oscillator for each color. become longer. Furthermore, if it becomes a high-speed machine, the lighting control of the semiconductor laser oscillator will be fast, and the load will be even higher. Thus, some conventional electrophotographic apparatuses have a configuration in which laser lighting is not performed during non-image formation in order to extend the life of the semiconductor laser oscillator by reducing the lighting time as much as possible (see, for example, Patent Document 1).

The electrophotographic image forming apparatus described in Patent Document 1 includes a laser light source, a laser scanner motor, a rotary polygon mirror, and a sensor that detects a writing start position in the main scanning direction of the laser light irradiated onto the photosensitive drum. The first control means for controlling the rotation of the laser scanner motor based on the phase difference between the sensor output and the reference signal, the element for detecting the rotation of the laser scanner motor, and the phase difference between the output of the element and the reference signal Based on this, there is a second control means for controlling the rotation of the laser scanner motor. The first control means is switched during image formation, and the second control means is switched during non-image formation. As a result, the semiconductor laser oscillator can be turned off during non-image formation, and the lifetime of the semiconductor laser oscillator is extended by suppressing unnecessary lighting.
JP 2000-289247 A

  However, there is a phase difference between the output of the sensor that detects the write start position of the laser and the output of the element that detects the rotation of the laser scanner motor, and jitter that occurs before the rotation of the laser scanner motor stabilizes when switching. There was a problem that could not be suppressed.

  The present invention provides both outputs based on the phase difference between the sensor output for detecting the writing position in the main scanning direction of the laser and the output of the element for detecting the rotation of the laser scanner motor in an image forming apparatus that performs image exposure with laser light. The purpose is to perform stable rotation control while suppressing jitter at the time of switching.

  In order to achieve the above-mentioned object, the present invention comprises the following configurations (1) to (5).

(1) An image forming apparatus having a sensor for detecting laser light reflected by a reflecting surface of a rotary polygon mirror, a Hall element for detecting a rotating magnetic field of a rotor of a laser scanner motor, and a reference clock generating means for generating a reference clock In
Phase difference detection means for detecting a phase difference between the first rotation clock generated based on the output of the sensor and the second rotation clock generated based on the output of the Hall element;
Clock adjustment means for outputting an adjustment clock based on the reference clock from the detection result of the phase difference detection means;
First control means for controlling a rotation speed of a laser scanner motor based on a phase difference between the first rotation clock and the reference clock;
Second control means for controlling a rotation speed of a laser scanner motor based on a phase difference between the second rotation clock and the adjustment clock;
An image forming apparatus comprising control means for controlling the scanner motor by the first control means during image formation and by the second control means during non-image formation.

(2) An image forming apparatus having a sensor for detecting laser light reflected by a reflecting surface of a rotary polygon mirror, a Hall element for detecting a rotating magnetic field of a rotor of a laser scanner motor, and a reference clock generating means for generating a reference clock In
A phase difference detection means for detecting a phase difference between a first rotation clock generated based on the output of the sensor and a second rotation clock generated based on the output of the Hall element; and Rotation clock adjustment means for outputting an adjustment rotation clock based on the second rotation clock from the detection result;
First control means for controlling the rotational speed of the laser scanner motor based on the phase difference between the first rotational clock and the reference clock; and the rotational speed of the laser scanner motor based on the phase difference between the adjusted rotational clock and the reference clock. Second control means for controlling
An image forming apparatus comprising control means for controlling the scanner motor by the first control means during image formation and by the second control means during non-image formation.

(3) The first rotation clock generation means generates a rotation clock corresponding to the rotation speed of the laser scanner motor by dividing the output signal of the sensor by the number of reflection surfaces of the rotary polygon mirror. (1) The image forming apparatus according to (1) or (2), wherein the second rotation clock generation unit divides the output signal of the Hall element by the number of magnetic pole sets of the laser scanner motor. Thus, the rotation clock according to the rotation speed of the laser scanner motor is generated.

  (5) The image forming apparatus according to (1) or (2), wherein the non-image forming time is a standby time or a pre-rotation time period other than the image forming time.

  According to the present invention, there is provided an image forming apparatus capable of suppressing jitter at the time of switching between laser scanner motor rotation control performed by turning on a laser during image formation and laser scanner motor rotation control performed without turning on a laser during non-image formation. can do.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Embodiment 1]
FIG. 2 is a schematic configuration diagram illustrating the overall configuration of the image forming apparatus according to the embodiment of the present invention. 2A is a plan view and FIG. 2B is a side view. In FIG. 2, first, reference numeral 15 denotes a rotary polygon mirror, and 16 denotes a laser scanner motor for driving the rotary polygon mirror 15 to rotate. Here, a 12-sided rotary polygon mirror 15 is used. In the present embodiment, the rotary polygon mirror 15 having such a multifaceted structure is used, but the accompanying deterioration of jitter is prevented by improving the control method of the motor 16. This will be described in detail later. Reference numeral 17 denotes a laser diode which is a semiconductor laser oscillator which is a recording light source. The laser diode 17 is turned on or off according to an image signal by a drive circuit (not shown), and the light-modulated laser light emitted from the laser diode 17 is emitted toward the rotary polygon mirror 15.

  The rotating polygon mirror 15 is rotated in the direction of the arrow, and the laser light emitted from the laser diode 17 is reflected as a deflected beam whose angle is continuously changed on the reflecting surface as the rotating polygon mirror 15 rotates. The reflected light is subjected to distortion correction and the like by a lens group (not shown), and is scanned in the main scanning direction of the photosensitive drum 10 through the reflecting mirror 18. One surface of the rotary polygon mirror 15 corresponds to one line scanning, and laser light emitted from the laser diode 17 by the rotation of the rotary polygon mirror 15 scans the photosensitive drum 10 in the main scanning direction line by line. The photosensitive drum 10 is charged in advance by a charger 11, and is sequentially exposed by scanning with a laser beam to form an electrostatic latent image. Further, the photosensitive drum 10 is rotated in the direction of the arrow, and the formed electrostatic latent image is developed by the developing device 12, and the developed visible image is transferred to a transfer paper (not shown) by the transfer charger 13. . The transfer paper on which the visible image has been transferred is conveyed to the fixing device 14 and is discharged out of the apparatus after fixing.

  Here, a BD (BEAM DETECT) sensor 19 is disposed in the vicinity of the scanning start position in the main scanning direction on the side portion of the photosensitive drum 10. The laser light reflected by each reflecting surface of the rotary polygon mirror 15 is detected by the BD sensor 19 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. 1 is a block diagram showing a control circuit for controlling the rotation speed of the laser scanner motor 16. In FIG. 1, first, a brushless motor is used as the laser scanner motor 16, and the inside of the broken line shows an equivalent circuit thereof. The inductor 34 is star-connected and excited by the bridge circuit 20 to generate a rotating magnetic field. The rotor 30 is magnetized with a magnetic pattern, and is rotated by the rotating magnetic field of the inductor 34 to drive the rotary polygon mirror 15 to rotate. The Hall elements 31 to 33 detect a magnetic field magnetized in the rotor 30, and the detected magnetic field is input to the rotating magnetic field control circuit 23. The rotating magnetic field control circuit 23 detects the rotational position of the rotor 30 based on the output signals of the Hall elements 31 to 33, and controls the bridge circuit 20 so as to always generate a magnetic field in which the rotor 30 rotates.

  Further, the output signal of the Hall element 32 is input to the second rotation clock generator 25. The hall element 32 outputs a pulse signal having a frequency corresponding to the rotation speed of the motor 16, and outputs two pulses per rotation because the rotor 30 has two sets of magnetic patterns magnetized per rotation. The second rotation clock generator 25 divides the pulse signal of the Hall element 32 by 2 and outputs one pulse for one rotation of the motor 16 (frequency-divided Hall element signal of FIG. 3). Therefore, this pulse signal becomes a rotation clock corresponding to the rotation speed of the motor 16.

  On the other hand, the BD signal of the BD sensor 19 is input to the first rotation clock generator 26. Since the rotary polygon mirror 15 has 12 reflecting surfaces, twelve BD signals are output while the rotary polygon mirror 15 makes one rotation. The first rotation clock generator 26 divides the output signal of the BD sensor 19 by 12 and outputs one pulse for one rotation of the motor 16 (divided BD signal in FIG. 3). This pulse signal also becomes a rotation clock corresponding to the rotation speed of the motor 16. The switching circuit 24 selects one of the output signals of the rotation clock generators 25 and 26 by the switching signal from the switching unit 38 of the main control circuit (not shown), and outputs the selected signal to the PLL circuit 22. Regardless of which signal is selected, one pulse is output per rotation of the motor 16, but in this embodiment, when the laser beam during image formation scans the photosensitive drum 10, the output of the BD sensor 19 is output. The output signal of the first rotation clock generator 26 is selected according to the signal. When the laser beam other than the time of image formation is not scanned, the output of the second rotation clock generator 25 based on the output signal of the Hall element 32 is selected and output to the PLL circuit 22. This will be described in detail later.

  The output signals of the second rotation clock generator 25 and the first rotation clock generator 26 are input to the phase difference detector 28, and the phase difference detector 28 measures the phase difference between the two input signals. For example, if the phase difference is t, the data is output to the clock adjustment unit 29, and the clock adjusted in accordance with the phase difference data (correction reference clock in FIG. 3) is output to the clock selection unit 35. The clock selection unit 35 selects and outputs either the input reference clock or the adjusted clock according to the switching signal. In the present embodiment, the reference clock is output to the PLL circuit 22 when the laser beam at the time of image formation is scanning the photosensitive drum 10, and the clock adjustment unit 29 when the laser beam other than at the time of image formation is not being scanned. Is output to the PLL circuit 22.

  In any case, the PLL circuit 22 compares the phase of the rotation clock selected by the switching circuit 24 with the phase of the reference clock, and outputs the comparison result to the PWM circuit 21. The combination is [the output of the first rotation clock generator 26 and the reference clock] or [the output of the second rotation clock generator 25 and the adjustment clock of the clock adjustment unit output]. The reference clock is a highly accurate clock signal generated using a crystal oscillator (not shown) and corresponds to the target rotational speed of the motor 16. The PWM circuit 21 controls the output voltage of the bridge circuit 20 by pulse width modulation according to the output signal from the PLL circuit 22. If the rotation speed of the motor 16 increases, the frequency of the output pulse of the Hall element 32 and the frequency of the BD signal of the BD sensor 19 increase, and the phase of the rotation clock from the switching circuit 24 changes. As a result, the PLL circuit 22 controls the PWM circuit 21 so that the phase difference between the rotation clock and the reference clock is constant. As a result, the control works so that the output voltage of the bridge circuit 20 decreases, and the rotation speed of the motor 16 is controlled to a target speed corresponding to the reference clock.

  Further, when the rotation speed of the motor 16 decreases, the frequency of the output pulse of the Hall element 32 and the frequency of the BD signal of the BD sensor 19 decrease, and the phase of the circuit clock from the switching circuit 24 changes. At this time, since the control works so that the output voltage of the bridge circuit 20 is increased by the PLL circuit 22, the rotational speed of the motor 16 is controlled to the target speed. In this way, the rotation speed of the motor 16 is controlled to be constant, and the rotary polygon mirror 15 rotates at a constant rotation speed in the direction of the arrow shown in FIG.

  On the other hand, an image signal read by an image scanner (not shown) or an image signal transferred from an external device such as a computer (not shown) is supplied to the write timing control circuit 27. The BD signal from the BD sensor 19 is also supplied to the write timing control circuit 27. The writing timing control circuit 27 determines the writing start position timing in the main scanning direction of the photosensitive drum 10 based on the BD signal, and then drives the laser diode 17 according to the image signal. The laser light from the laser diode 17 is irradiated onto the photosensitive drum 10 by the rotary polygon mirror 15 as described above, and an image is formed.

  Here, since the output of the Hall element is generally about several hundred millivolts and is vulnerable to noise or the like, it may be considered that the detection accuracy is lower than the rotation speed detection method using the BD sensor 19. In the present embodiment, since the rotational speed of the motor 16 is controlled using a signal from the BD sensor 19 during laser beam scanning during image formation, the deterioration of jitter is prevented and the rotational speed of the motor 16 is controlled with high accuracy. can do.

  Further, since the laser diode 17 has a lifetime, the light emission of the laser diode 17 may be stopped at the time of standby or during the pre-rotation period other than the time of image formation. However, when the rotation speed of the motor 16 is controlled using the output of the BD sensor 19, a BD signal cannot be obtained unless the laser diode 17 is turned on.

  In the present embodiment, the rotation speed of the motor 16 is controlled using the output signal of the Hall element during standby or pre-rotation, which is a period other than image formation, and therefore the laser diode 17 is controlled to be turned off. This can prevent the life of the laser diode 17 from being reduced. In addition, the angle of the reflecting surface of the rotary polygon mirror 15 (the angle between adjacent reflecting surfaces) is formed with high accuracy, but since there is always a slight error, the output signal of the BD sensor 19 has an error of this angle. Including signals with different phases for each reflecting surface. In the present embodiment, the first rotation clock generator 26 divides the output signal of the BD sensor 19 by the number of reflection surfaces, and makes one pulse for one rotation of the rotary polygon mirror 15. Therefore, a rotation clock is always obtained based on the BD signal obtained from any one of the reflecting surfaces, and a stable rotation clock that does not include an angle error can be obtained.

  Switching of control during image formation and non-image formation will be described with reference to the timing chart of FIG. Image formation is performed in section a, and the laser scanner motor is controlled by synchronizing the frequency-divided BD signal (first rotation clock) with the reference clock by turning on the laser. The section b is in a non-image forming state, the laser is turned off, and the laser scanner motor is controlled by synchronizing the divided Hall element signal (second rotation clock) with the adjustment clock. Since image formation is performed again in section c, the laser is turned on, and the laser scanner motor is controlled by the divided BD signal and the reference clock. Since each of the divided BD signal and the divided Hall element signal has a reference clock and an adjustment clock as a reference, it is not necessary to lose sight of the synchronization target when switching the control, and the jitter of the laser scanner motor generated at the time of switching. Therefore, stable rotation control is possible.

[Embodiment 2]
FIG. 5 is a block diagram showing a second embodiment of the present invention. In the present embodiment, the divided Hall element signal is corrected by the rotation clock adjustment unit 37 from the phase difference between the divided BD signal (first rotation clock) and the Hall element signal (second rotation clock) (correction in FIG. 6). Divided Hall element signal). Then, the switching circuit 36 switches and outputs the divided BD signal (first rotation clock) and the corrected divided hall signal (adjusted rotation clock) to the PLL circuit 22.

  Switching of control during image formation and non-image formation according to the present embodiment will be described with reference to the timing chart of FIG. In section a, an image is formed, and the laser scanner motor is controlled by synchronizing the frequency-divided BD signal with the reference clock by turning on the laser. The section b is in a non-image forming state, the laser is turned off, and the laser scanner motor is controlled by synchronizing the corrected frequency dividing Hall element signal (adjusted rotation clock) with the reference clock. Since image formation is performed again in section c, the laser is turned on, and the laser scanner motor is controlled by the divided BD signal and the reference clock. The frequency-dividing Hall element signal and the corrected frequency-dividing Hall element signal are controlled in synchronization with the reference clock, and the laser scanner motor jitter generated when switching the control is suppressed, thereby enabling stable rotation control.

It is a block diagram which shows the speed control circuit of the laser scanner motor in 1st Example. 1 is a diagram illustrating a configuration of an image forming apparatus according to the present invention. 4 is a timing chart showing the relationship between a reference clock, a divided signal, and a corrected reference clock in the first embodiment. 3 is a timing chart for switching control during image formation and non-image formation in the first embodiment. It is a block diagram which shows the speed control circuit of the laser scanner motor in 2nd Example. It is a timing chart which shows the relationship between the reference | standard clock in 2nd Example, the frequency-divided signal, and a correction | amendment frequency division Hall element signal. It is a timing chart about the change of control at the time of image formation in the 2nd example, and non-image formation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Photosensitive drum 11 Charging device 12 Developing device 13 Transfer charging device 14 Fixing device 15 Rotating polygon mirror 16 Laser scanner motor 17 Laser diode 19 BD sensor 20 Bridge circuit 21 PWM circuit 22 PLL circuit 24 Switching circuit 25 Second rotation clock generator 26 First rotation clock generation unit 27 Write timing control circuit 28 Phase difference detection unit (corresponding to phase difference detection means)
29 Clock adjustment unit (corresponding to clock adjustment means)
30 Rotors 31 to 33 Hall element 34 Inductor 35 Clock selection unit 37 Rotation clock adjustment unit (corresponding to rotation clock adjustment means)
38, 39 switching unit (corresponding to the control means for controlling the scanner motor)
40 Reference clock generator

Claims (5)

In an image forming apparatus having a sensor for detecting laser light reflected by a reflecting surface of a rotary polygon mirror, a Hall element for detecting a rotating magnetic field of a rotor of a laser scanner motor, and a reference clock generating means for generating a reference clock,
Phase difference detection means for detecting a phase difference between the first rotation clock generated based on the output of the sensor and the second rotation clock generated based on the output of the Hall element;
Clock adjustment means for outputting an adjustment clock based on the reference clock from the detection result of the phase difference detection means;
First control means for controlling a rotation speed of a laser scanner motor based on a phase difference between the first rotation clock and the reference clock;
Second control means for controlling a rotation speed of a laser scanner motor based on a phase difference between the second rotation clock and the adjustment clock;
An image forming apparatus comprising control means for controlling the scanner motor by the first control means during image formation and by the second control means during non-image formation. In an image forming apparatus having a sensor for detecting laser light reflected by a reflecting surface of a rotary polygon mirror, a Hall element for detecting a rotating magnetic field of a rotor of a laser scanner motor, and a reference clock generating means for generating a reference clock,
A phase difference detection means for detecting a phase difference between a first rotation clock generated based on the output of the sensor and a second rotation clock generated based on the output of the Hall element; and Rotation clock adjustment means for outputting an adjustment rotation clock based on the second rotation clock from the detection result;
First control means for controlling the rotational speed of the laser scanner motor based on the phase difference between the first rotational clock and the reference clock; and the rotational speed of the laser scanner motor based on the phase difference between the adjusted rotational clock and the reference clock. Second control means for controlling
An image forming apparatus comprising control means for controlling the scanner motor by the first control means during image formation and by the second control means during non-image formation.   The first rotation clock generation means generates a rotation clock corresponding to the rotation speed of the laser scanner motor by dividing the output signal of the sensor by the number of reflection surfaces of the rotary polygon mirror. The image forming apparatus according to claim 1 or 2.   The second rotation clock generation means generates a rotation clock corresponding to the rotation speed of the laser scanner motor by dividing the output signal of the Hall element by the number of magnetic pole sets of the laser scanner motor. The image forming apparatus according to claim 1 or 2.   3. The image forming apparatus according to claim 1, wherein the non-image forming time is a standby time or a pre-rotation time which is a period other than the image forming time.

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