JP2016090757A - Optical scanner and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to identify a scanning direction and accurately control a range of scanning movement of a scanning body in either case of using an MEMS having an electromagnetic form or an electrostatic form.SOLUTION: An optical scanner includes an MEMS mirror 11, BD sensors 13 and 14, scanning direction identification part 24, BD signal output parts 22 and 23, and drive control part 25. The BD sensors 13 and 14 each have two photodiodes. The scanning direction identification part 24 identifies scanning directions when the respective BD sensors 13 and 14 are scanned on the basis of order of detection by the BD sensors 13 and 14. The BD signal output parts 22 and 23 output BD signals on the basis of detection values of the two photodiodes and the scanning directions identified by the scanning direction identification part 24. The drive control part 25 controls scanning movement on the basis of a timing at which the BD signals are output.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an optical scanning device that reciprocally scans an object to be scanned with a light beam and an image forming apparatus including the same.

  Among optical scanning devices provided in image forming apparatuses such as copying machines, printers, facsimiles, and multi-function machines, there are those that reciprocately scan a scanned object such as a photosensitive drum. In the optical scanning device, the light beam emitted from the light source is reflected by the scanning body that performs scanning motion, so that the scanning target is reciprocated. In such an optical scanning device, the drive characteristics of the scanning behavior of the scanning body may change due to changes in ambient temperature, and the range of scanning motion may change. If the range of scanning motion is changed, there arises a problem that the writing position of the latent image is shifted and the image quality is deteriorated.

  For this reason, a technique is known in which a BD (Beam Detect) sensor is provided at both ends of the scanning range, and the scanning motion of the scanning body is controlled based on the timing at which the BD sensor detects the light beam.

  However, in an optical scanning device equipped with such a BD sensor, the light that scans the scanning range depends on the temperature dependence of the light emission characteristics of the light source, the change in the reflectance of the reflecting surface of the scanning body, the temperature dependence of the lens characteristics, and the like. Spot changes in which the shape and diameter of the beam spot change may occur. When the spot change of the light beam occurs, the detection timing of the light beam by the BD sensor may be shifted, and the range of the scanning motion of the scanning body cannot be accurately controlled.

  Accordingly, there is known an optical scanning device in which each of the BD sensors has two light detection elements and controls the range of scanning motion of the scanning body based on the detection values of the two light detection elements (for example, (See Patent Document 1). According to the optical scanning device of this technique, even if a spot change of the light beam occurs, a shift in the detection timing of the light beam by the BD sensor is suppressed. In addition, in this conventional optical scanning device, in order to reduce the size of the optical scanning device, reduce costs, reduce power consumption / heat generation / noise, and shorten the time required for forming the first image, A MEMS (Micro Electro Mechanical System) is used as a driving device. This conventional optical scanning device is of an electromagnetic type, and the MEMS is bipolar driven in which a current is bidirectionally supplied to one winding. For this reason, in this conventional optical scanning device, the scanning direction is identified based on the polarity of the MEMS drive voltage.

JP 2011-7840 A

  However, when an electrostatic MEMS is used in the optical scanning device, the MEMS is unipolarly driven to always apply a voltage in a certain direction to the electrodes, and the polarity of the MEMS driving voltage is constant, so that the conventional optical scanning is performed. The identification method in the apparatus cannot identify the scanning direction. If the scanning direction when the BD sensor is scanned cannot be identified, the range of scanning motion of the scanning body cannot be accurately controlled. For this reason, the conventional optical scanning device cannot use an electrostatic MEMS, and further downsizing, cost reduction, power consumption / heat generation / noise reduction, and time required for image formation of the first sheet are reduced. It was an obstacle to shortening.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical scanning device capable of identifying the scanning direction and accurately controlling the scanning motion range of the scanning body, regardless of whether the electromagnetic type or electrostatic type MEMS is used, and an image forming apparatus having the optical scanning device. Is to provide.

  The optical scanning device of the present invention reciprocally scans a scanning range including a latent image forming region of a scanning object with a light beam. The optical scanning device includes a light source, a scanning body, a first BD sensor and a second BD sensor, a scanning direction identification unit, a first BD signal output unit and a second BD signal output unit, and a control unit. The light source emits a light beam. The scanning body scans and moves so as to scan the scanning range by reflecting the light beam emitted from the light source. The first BD sensor and the second BD sensor are arranged at the first end and the second end outside the latent image forming area and within the scanning range. The first BD sensor and the second BD sensor each have a first light detection element and a second light detection element. The first light detection element and the second light detection element are arranged adjacent to each other along the scanning direction, and output a detection value corresponding to the light amount of the detected light beam. The scanning direction identification unit identifies the scanning direction when each of the first BD sensor and the second BD sensor is scanned. The first BD signal output unit and the second BD signal output unit are identified by the detection value of the first light detection element, the detection value of the second light detection element, and the scanning direction identification unit for each of the first BD sensor and the second BD sensor. Based on the scanning direction, a BD signal is output. The control unit controls the scanning motion based on the timing when the BD signal is output. The scanning direction identification unit identifies the scanning direction based on the timing when the first BD sensor is scanned and the timing when the second BD sensor is scanned.

  In this configuration, when the first BD sensor is scanned by the light beam, the output value of the first light detection element and the first light detection element are scanned during scanning between the first light detection element and the second light detection element. The magnitude relationship with the output value is switched. The timing at which the magnitude relationship between the two output values interchanges hardly changes even if a spot change of the light beam occurs. For this reason, by outputting the BD signal based on the detection value of the first light detection element, the detection value of the second light detection element, and the scanning direction identified by the scanning direction identification unit, the influence of the spot change of the light beam Is suppressed, and a BD signal is output at an accurate timing.

  Further, since the scanning direction is identified based on the timing when the first BD sensor is scanned and the timing when the second BD sensor is scanned, the scanning direction can be identified without using the polarity of the driving voltage of the scanning body. Further, complicated processing is not required, and the configuration can be simplified. For example, the identification of the scanning direction is performed based on the order of the timing at which the first BD sensor is scanned and the timing at which the second BD sensor is scanned, or the time interval of each scanning timing.

  In the configuration described above, the scanning direction identification unit can identify the scanning direction based on the detection order of the first BD sensor and the second BD sensor.

  In this configuration, since the scanning direction is identified based on the detection order of the first BD sensor and the second BD sensor, the scanning direction can be identified without using the polarity of the driving voltage of the scanning body. Further, complicated processing is not required, and the configuration can be simplified.

  In addition, each of the first BD signal output unit and the second BD signal output unit can be configured to include a first signal generation unit, a second signal generation unit, and a selection unit. The first signal generation unit includes a first voltage conversion unit that converts the detection value of the first light detection element into a voltage value, a second voltage conversion unit that converts the detection value of the second light detection element into a voltage value, and a first voltage. The first bias unit that applies a predetermined bias voltage to the voltage value output from the conversion unit, the voltage value output from the first bias unit and the voltage value output from the second voltage conversion unit are compared, and the comparison result is determined. A first comparison unit that outputs a signal is included. The second signal generation unit includes a third voltage conversion unit that converts the detection value of the first light detection element into a voltage value, a fourth voltage conversion unit that converts the detection value of the second light detection element into a voltage value, and a fourth voltage. The second bias unit that applies a predetermined bias voltage to the voltage value output from the conversion unit, and the voltage value output from the third voltage conversion unit and the voltage value output from the second bias unit are compared, and the comparison result is obtained. A second comparator for outputting a signal; The selection unit selects either the output signal of the first signal generation unit or the output signal of the second signal generation unit based on the scanning direction identified by the scanning direction identification unit, and the BD based on the selected output signal Output a signal.

  In this configuration, even when noise is mixed in the output value of the first photodetecting element or the output value of the second photodetecting element, a bias voltage is added to the voltage value related to the output value of one photodetecting element. A shift in timing at which the magnitude relationship between the output value of the first photodetecting element and the output value of the second photodetecting element is switched is further suppressed. In addition, even when there are a plurality of timings at which the magnitude relationship between the output value of the first photodetecting element and the output value of the second photodetecting element is switched, the timing shift can be further reduced in consideration of the scanning direction.

  The scanning direction identification unit performs the first scanning from the first BD sensor toward the second BD sensor when the first signal based on the detection value of the second BD sensor is input after the signal based on the detection value of the first BD sensor is input. When the second signal based on the detection value of the second BD sensor is input, it is identified that the scanning is performed in the second scanning direction from the second BD sensor toward the first BD sensor. it can.

  In this configuration, the first BD sensor is disposed at the first end in the scanning range, the second BD sensor is disposed at the second end, and the scanning range is reciprocated, so that the light beam is detected by the first BD sensor. And the detection of the light beam by the second BD sensor are alternately repeated twice. From this, the scanning direction is identified according to the number of times of input of the signal based on the detection value of the second BD sensor, starting from the input of the signal based on the detection value of the first BD sensor.

  Further, the scanning direction identification unit performs the second scanning from the second BD sensor toward the first BD sensor when the first signal based on the detection value of the first BD sensor is input after the signal based on the detection value of the second BD sensor is input. When the second signal based on the detection value of the first BD sensor is input, it is identified that the scanning is performed in the first scanning direction from the first BD sensor toward the second BD sensor. it can.

  In this configuration, the first BD sensor is disposed at the first end in the scanning range, the second BD sensor is disposed at the second end, and the scanning range is reciprocated, so that the light beam is detected by the first BD sensor. And the detection of the light beam by the second BD sensor are alternately repeated twice. From this, the scanning direction is identified according to the number of times of input of the signal based on the detection value of the first BD sensor, starting from the input of the signal based on the detection value of the second BD sensor.

  In addition, the scanning direction identification unit is preferably configured by a counter circuit.

  In this configuration, one of the signal based on the detection value of the first BD sensor and the signal based on the detection value of the second BD sensor is connected to the reset terminal, and the other is connected to the input terminal, so that the first BD sensor and the second BD sensor are connected. The scanning direction can be identified by a simple process based on the detection order.

  An image forming apparatus according to the present invention includes an object to be scanned and an optical scanning device having any one of the above-described configurations.

  In this configuration, when the first BD sensor is scanned by the light beam, the output value of the first light detection element and the first light detection element are scanned during scanning between the first light detection element and the second light detection element. The magnitude relationship with the output value is switched. The timing at which the magnitude relationship between the two output values interchanges hardly changes even if a spot change of the light beam occurs. For this reason, by outputting the BD signal based on the detection value of the first light detection element, the detection value of the second light detection element, and the scanning direction identified by the scanning direction identification unit, the influence of the spot change of the light beam Is suppressed, and a BD signal is output at an accurate timing.

  Further, since the scanning direction is identified based on the detection order of the first BD sensor and the second BD sensor, the scanning direction can be identified without using the polarity of the driving voltage of the scanning body. Further, complicated processing is not required, and the configuration can be simplified.

  According to the present invention, the scanning direction can be identified and the scanning motion range of the scanning body can be accurately controlled regardless of whether electromagnetic or electrostatic MEMS is used.

1 is a diagram illustrating a schematic configuration of an image forming apparatus including an optical scanning device according to a first embodiment of the present invention. It is a figure which shows the transfer sequence to steady APC (Automatic Power Control) of a light source. It is a block diagram which shows schematic structure of an optical scanning device. (A) is a circuit diagram of the first signal generation unit and the second signal generation unit of the first BD signal output unit, (B) is a circuit of the first signal generation unit and the second signal generation unit of the second BD signal output unit FIG. (A) is a figure which shows the waveform of the input voltage and output signal of the 1st comparator at the time of A direction scanning, (B) is a figure which shows the waveform of the input voltage and output signal of the 2nd comparator at the time of A direction scanning. FIG. 6C is a diagram showing waveforms of the input voltage / output signal of the first comparator when scanning in the B direction, and FIG. 9D is a diagram showing waveforms of the input voltage / output signal of the second comparator when scanning in the B direction. FIG. It is a figure which shows the relationship between the scanning position by the scanning motion of a MEMS mirror, and time. (A) is a circuit diagram of a scanning direction identification unit for identifying that the scanning direction is the B direction, and (B) is a circuit diagram of a scanning direction identification unit for identifying that the scanning direction is the A direction. (A) (B) is a circuit diagram of the scanning direction identification part with which the optical scanning device concerning a 2nd embodiment is equipped.

  As shown in FIG. 1, the image forming apparatus 1 including the optical scanning device 10 according to the first embodiment includes, in addition to the optical scanning device 10, a photosensitive drum 2, and a charging device, a developing device, and a transfer (not shown). And a fixing device. The photosensitive drum 2 is an example of a scanning target scanned by the optical scanning device 10.

  The charging device charges the peripheral surface of the photosensitive drum 2 to a predetermined potential. The photosensitive drum 2 rotates in a predetermined direction. The optical scanning device 10 forms an electrostatic latent image in a latent image forming region on the peripheral surface of the photosensitive drum 2 by exposing the peripheral surface of the photosensitive drum 2 with laser light. The developing device visualizes the electrostatic latent image into a toner image by supplying toner to the peripheral surface of the photosensitive drum 2. The transfer device transfers the toner image on the circumferential surface of the photosensitive drum 2 to a sheet. The fixing device fixes the toner image to the sheet. Laser light is an example of a light beam.

  The optical scanning device 10 includes a MEMS mirror 11, a light source 12, BD sensors 13 and 14, a MEMS driving unit 15, and a scanning control unit 16.

  The light source 12 emits laser light toward the MEMS mirror 11.

  The MEMS mirror 11 reflects the laser light emitted from the light source 12 toward the photosensitive drum 2 while performing a scanning motion that oscillates in a direction away from and in contact with the photosensitive drum 2.

  As the MEMS mirror 11 performs scanning movement, the reflection direction of the laser light emitted from the light source 12 is changed, and the scanning range E2 including the latent image forming region E1 of the photosensitive drum 2 is changed by the laser light emitted from the light source 12. Are reciprocally scanned. The MEMS mirror 11 is a scanning body of the present invention.

  The BD sensors 13 and 14 are disposed outside the latent image forming area E1 of the photosensitive drum 2 and within the scanning range E2. The left BD sensor 13 in the direction of viewing the photosensitive drum 2 from the MEMS mirror 11 is disposed at the first end of the scanning range E2, and the right BD sensor 14 is disposed at the second end of the scanning range E2. Yes.

  A first scanning direction from the BD sensor 13 toward the BD sensor 14 is defined as an A direction. A second scanning direction from the BD sensor 14 toward the BD sensor 13 is a B direction.

  The BD sensor 13 includes photodiodes 131 and 132, and the BD sensor 14 includes photodiodes 141 and 142. The photodiode 131 and the photodiode 132 are disposed adjacent to each other along the A direction, and the photodiode 131 is disposed on the upstream side of the photodiode 132 in the A direction. Similarly, the photodiode 141 and the photodiode 142 are disposed adjacent to each other along the A direction, and the photodiode 141 is disposed on the upstream side of the photodiode 142 in the A direction. Each of the photodiodes 131, 132, 141, and 142 is a light detection element that outputs a detection value corresponding to the detected amount of laser light.

  The MEMS drive unit 15 controls the scanning motion of the MEMS mirror 11. The scanning control unit 16 comprehensively controls each unit device of the optical scanning device 10 including the MEMS driving unit 15.

  The MEMS drive unit 15 is an electrostatic type, is unipolarly driven, and the polarity of the drive voltage that vibrates the MEMS mirror 11 is constant. For this reason, the scanning direction cannot be identified from the polarity of the drive voltage that vibrates the MEMS mirror 11.

  The scanning control unit 16 generates a PWM signal based on the signals input from the BD sensors 13 and 14 and outputs the PWM signal to the MEMS driving unit 15. The MEMS drive unit 15 switches the direction of the scanning motion of the MEMS mirror 11 based on the PWM signal. The scanning control unit 16 outputs a PWM signal so that the scanning angle of the scanning range E2 is constant at a predetermined angle.

  As shown in FIG. 2, when the optical scanning device 10 is driven, the light source 12 emits light in the transition sequence to steady APC, and the BD sensor 13 and the BD sensor 14 emit light four times in total until laser light is detected. Keep doing.

  When the left BD sensor 13 detects twice and the right BD sensor 14 detects two times, the routine proceeds to steady APC and immediately before the timing when the BD sensors 13 and 14 will detect the laser beam. The light source 12 emits light. When laser light is detected by the BD sensors 13 and 14, the light source 12 is turned off.

  As shown in FIG. 3, the scanning control unit 16 includes a first BD signal output unit 22, a second BD signal output unit 23, a scanning direction identification unit 24, and a drive control unit 25. The drive control unit 25 includes a timer unit 26, a comparison unit 27, a storage unit 28, and a PMW control unit 29. The PMW control unit 29 has a memory 29M.

  The scanning direction identification unit 24 identifies the scanning direction when each of the BD sensors 13 and 14 is scanned.

  The first BD signal output unit 22 outputs a BD signal for the BD sensor 13 based on the detection value of the photodiode 131, the detection value of the photodiode 132, and the scanning direction identified by the scanning direction identification unit 24. Similarly, the second BD signal output unit 23 outputs a BD signal for the BD sensor 14 based on the detection value of the photodiode 141, the detection value of the photodiode 142, and the scanning direction identified by the scanning direction identification unit 24. .

  The drive control unit 25 controls the scanning motion of the MEMS mirror 11 based on the timing at which the BD signal is output from each of the first BD signal output unit 22 and the second BD signal output unit 23.

  The first BD signal output unit 22 includes a first signal generation unit 31, a second signal generation unit 32, and a selection unit 33. The second BD signal output unit 23 includes a first signal generation unit 34, a second signal generation unit 35, and a selection unit 36.

  As illustrated in FIG. 4A, the first signal generation unit 31 of the first BD signal output unit 22 includes an amplifier 311, an amplifier 312, a clamp circuit 313, and a first comparator 314.

  The amplifier 311 performs rectification of the output current of the photodiode 131 and current-voltage conversion, and converts a detection value, that is, a current value into a voltage value. The amplifier 312 performs rectification of the output current of the photodiode 132 and current-voltage conversion, and converts a detection value, that is, a current value into a voltage value. The clamp circuit 313 adds a predetermined reference bias voltage VS to the voltage output from the amplifier 311.

  The first comparator 314 compares the voltage value after the reference bias voltage VS is applied by the clamp circuit 313 with the voltage value output by the amplifier 312 and outputs a signal corresponding to the comparison result. That is, the first comparator 314 outputs a High signal when the voltage value after the reference bias voltage VS is applied by the clamp circuit 313 is larger than the voltage value output by the amplifier 312. The first comparator 314 outputs a Low signal when the voltage value output from the amplifier 312 is larger than the voltage value after the reference bias voltage VS is applied by the clamp circuit 313. The amplifier 311 corresponds to the first voltage conversion unit of the present invention. The amplifier 312 corresponds to the second voltage converter of the present invention. The first comparator 314 corresponds to the first comparison unit of the present invention. The clamp circuit 313 corresponds to the first bias unit of the present invention.

  The second signal generation unit 32 of the first BD signal output unit 22 includes an amplifier 321, an amplifier 322, a clamp circuit 323, and a second comparator 324.

  The amplifier 321 performs rectification of the output current of the photodiode 131 and current-voltage conversion, and converts a detection value, that is, a current value into a voltage value. The amplifier 322 performs rectification of the output current of the photodiode 132 and current-voltage conversion, and converts the detected value, that is, the current value into a voltage value. The clamp circuit 323 adds a predetermined reference bias voltage VS to the voltage output from the amplifier 322.

  The second comparator 324 compares the voltage value output from the amplifier 321 with the voltage value after the reference bias voltage VS is applied by the clamp circuit 323, and outputs a signal corresponding to the comparison result. That is, the second comparator 324 outputs a High signal when the voltage value after the reference bias voltage VS is applied by the clamp circuit 323 is larger than the voltage value output by the amplifier 321. The second comparator 324 outputs a Low signal when the voltage value output from the amplifier 321 is larger than the voltage value after the reference bias voltage VS is applied by the clamp circuit 323. The amplifier 321 corresponds to the third voltage converter of the present invention. The amplifier 322 corresponds to the fourth voltage converter of the present invention. The second comparator 324 corresponds to the second comparison unit of the present invention. The clamp circuit 323 corresponds to the second bias unit of the present invention.

  The output signal of the first comparator 314 and the output signal of the second comparator 324 are input to the selection unit 33.

  As illustrated in FIG. 4B, the first signal generation unit 34 of the second BD signal output unit 23 is configured in the same manner as the first signal generation unit 31 of the first BD signal output unit 22. The second signal generation unit 35 of the second BD signal output unit 23 is configured similarly to the second signal generation unit 32 of the first BD signal output unit 22. However, in the first signal generation unit 34 of the second BD signal output unit 23, the amplifier 311 performs rectification and current-voltage conversion of the output current of the photodiode 141 of the right BD sensor 14, and converts the detected value, that is, the current value into a voltage. The amplifier 312 performs rectification and current-voltage conversion of the output current of the photodiode 142 of the right BD sensor 14, and converts the detected value, that is, the current value into a voltage value. In the second signal generation unit 35 of the second BD signal output unit 23, the amplifier 321 performs rectification of the output current of the photodiode 141 of the right BD sensor 14 and current-voltage conversion, and converts the detected value, that is, the current value into a voltage. The amplifier 322 performs rectification and current-voltage conversion of the output current of the photodiode 142 of the right BD sensor 14, and converts the detected value, that is, the current value into a voltage value. Note that in FIG. 4B, for convenience of explanation, the same reference numerals are used for the same structures as in FIG.

  5A to 5D, the input voltage to the first comparator 314 and the second comparator 324 for each of the photodiodes 131 and 132 is shown on the vertical axis, and the time is shown on the horizontal axis. Yes. In addition, the detection value of the photodiode 131 arranged on the upstream side in the A direction is subjected to current-voltage conversion or the like, and the voltage value input to the first comparator 314 and the second comparator 324 is denoted by reference numeral V1, and in the A direction, A voltage value input to the first comparator 314 and the second comparator 324 after the detection value of the photodiode 132 arranged on the downstream side is subjected to current-voltage conversion or the like is indicated by a symbol V2. In FIGS. 5A to 5D, the detection value of the left BD sensor 13 is described, but the same applies to the detection value of the right BD sensor 14.

  As shown in FIGS. 5A and 5B, during the A-direction scanning, the voltage value V1 obtained by amplifying and converting the detection value of the upstream photodiode 131 is the detection value of the downstream photodiode 132. A waveform is drawn that is input prior to the voltage value V2 obtained by amplifying and converting the signal, and then increases and then decreases. For the voltage value V2, a similar waveform is drawn behind the voltage value V1. The first comparator 314 outputs a High signal when the voltage value V1 is higher than the voltage value V2, and outputs a Low signal when it is lower. The second comparator 324 outputs a High signal when the voltage value V2 is higher than the voltage value V1, and outputs a Low signal when it is lower.

  The timing to be detected by the first signal output unit 22 is a timing at which the magnitude relationship between the two input voltages is switched while both the input voltage of the first comparator 314 and the input voltage of the second comparator 324 are changed. This timing is a timing at which the laser beam scans any position between the photodiode 131 and the photodiode 132, and is indicated by the intersection C1 of the input voltage curve in FIG. 5A. Then, it is indicated by an intersection C2. In FIG. 5C, it is indicated by an intersection point C3, and in FIG. 5D, it is indicated by an intersection point C4.

  When there are a plurality of timings at which the magnitude relationship between the input voltage of the first comparator 314 and the input voltage of the second comparator 324 is switched, the reason for detecting the timing at which the magnitude relationship is switched while the two input voltages change together is as follows. Street. That is, any one of the voltage value V1 and the voltage value V2 such as the intersection point C5 in FIG. 5A, the intersection point C6 in FIG. 5B, the intersection point C7 in FIG. 5C, and the intersection point C8 in FIG. At the timing when the magnitude relationship is switched without changing, the waveform of the voltage value V1 and the dull waveform near the rising or falling edge of the voltage value V2 are compared with the reference bias voltage VS. For this reason, when the amount of light changes, the deviation of the intersection of both waveforms also becomes large, and when the output of the comparator is an open collector system, the rising angle of the waveform of the voltage value V1 and the waveform of the voltage value V2 becomes dull. This is because the jitter increases.

  As described above, since both the input voltage of the first comparator 314 and the input voltage of the second comparator 324 change, the timing at which the magnitude relationship between the two input voltages is interchanged is small. A BD signal is output at the timing.

  In addition, the reference bias voltage VS is added to the voltage value output from one photodiode by the clamp circuit, but only the output level when the laser beam is not incident is clamped, and the other level is kept unchanged. Therefore, even if there is a change in the amount of light, the shift in the timing of the intersection is further suppressed.

  The output signals of the comparators 314 and 324 are switched from High to Low or from Low to High when the magnitude relationship between the two input voltages is switched. For this reason, the output signals of the comparators 314 and 324 fall or rise at the intersections C1 to C4 described above. When the timing at which the output signals of the comparators 314 and 324 fall is the active edge of the BD signal, in FIGS. 5A to 5D, the intersection C1 in FIG. 5A and the line in FIG. The jitter is reduced at the timing when the output signal falls at the intersection C4.

  The selection units 33 and 36 select either the output signal of the first comparator 314 or the output signal of the second comparator 324 based on the scanning direction identified by the scanning direction identification unit 24, and based on the selected output signal To output a BD signal. That is, at the time of scanning in the A direction, the output signal of the first comparator 314 is selected, and the BD signal is output at the timing when the output signal of the first comparator 314 falls. Similarly, when scanning in the B direction, the output signal of the second comparator 324 is selected, and the BD signal is output at the timing when the output signal of the second comparator 324 falls.

  Next, a method for identifying the scanning direction of the BD sensors 13 and 14 will be described.

  The direction in which each of the BD sensors 13 and 14 is scanned can be identified based on the timing at which the BD sensor 13 is scanned and the timing at which the BD sensor 14 is scanned. As an example, the scanning direction can be identified based on the order of the timing when the BD sensor 13 is scanned and the timing when the BD sensor 14 is scanned.

  As shown in FIG. 6, the left BD sensor 13 is arranged at the first end in the scanning range E2, the right BD sensor 14 is arranged at the second end, and the scanning range E2 is reciprocally scanned. The detection of the laser beam by the left BD sensor 13 and the detection of the laser beam by the right BD sensor 14 are alternately repeated twice. From this, the scanning direction is identified according to the number of times of input of the signal based on the detection value of the right BD sensor 14 from the time of input of the signal based on the detection value of the left BD sensor 13. Further, the scanning direction is identified according to the number of times of input of the signal based on the detection value of the left BD sensor 13 from the time of input of the signal based on the detection value of the right BD sensor 14.

  As shown in FIGS. 7A and 7B, specifically, the scanning direction identification unit 24 is configured by two 1-bit counter circuits.

  As shown in FIG. 7A, in the 1-bit counter circuit, the BD signal output from the second BD signal output unit 23 is input to the reset terminal, and the BD signal output from the first BD signal output unit 22 is input to the input terminal. Is input. When identifying the scanning direction, the first BD signal output unit 22 and the second BD signal output unit 23 are output from any one of the first signal generation unit 31 and the second signal generation unit 32 set in advance. The selected signal is selected and output to the scanning direction identification unit 24.

  When the first signal based on the detection value of the left BD sensor 13 is input after the signal based on the detection value of the right BD sensor 14 is input, in the B direction from the right BD sensor 14 toward the left BD sensor 13 When the second signal based on the detection value of the left BD sensor 13 is input, it is identified that the scanning is performed in the A direction from the left BD sensor 13 toward the right BD sensor 14.

  As shown in FIG. 7B, in the other 1-bit counter circuit, the BD signal output from the first BD signal output unit 22 is input to the reset terminal, and the BD signal output from the second BD signal output unit 23 is Input to the input terminal. When the first signal based on the detection value of the right BD sensor 14 is input after the signal based on the detection value of the left BD sensor 13 is input, it is identified that scanning has been performed in the A direction, and the detection of the right BD sensor 14 is performed. When a second signal based on the value is input, it is identified that scanning was performed in the B direction.

  Thus, based on the detection order of the left BD sensor 13 and the right BD sensor 14, the identification of the scanning direction can be performed by a simple process.

  The scanning direction identified by the scanning direction identification unit 24 is output to the selection units 33 and 36. As described above, the selection unit 33 outputs a BD signal based on the detection value of the photodiode 131, the detection value of the photodiode 132, and the scanning direction identified by the scanning direction identification unit 24. The same applies to the selector 36. The BD signal output from the selectors 33 and 36 is input to the timer unit 26.

  The time measuring unit 26 measures the time interval of the input BD signal and outputs the measurement result to the comparison unit 27.

  The comparison unit 27 reads a preset reference time interval from the storage unit 28. The comparison unit 27 compares the time interval input from the time measuring unit 26 with a preset reference time interval, and calculates a correction value so that the range of the scanning movement of the MEMS mirror becomes a preset reference range. The correction value is output to the PWM control unit 29.

  The PWM control unit 29 refers to the lookup table stored in the storage unit 28 and acquires a PWM control value for adjusting the duty ratio of the PWM signal according to the correction value input from the comparison unit 27. The PWM control unit 29 temporarily stores the PWM control value in the memory 29M. When receiving a control signal from a main body control unit (not shown), the PWM control unit 29 reads a PWM control value from the memory 29M, adjusts the duty ratio, and outputs a PWM signal.

  Thereby, the scanning angle of the scanning range E2 is corrected so as to be fixed to a predetermined angle.

  According to the optical scanning device 10, since the polarity of the driving voltage of the MEMS mirror 11 is not used for identifying the scanning direction, it is possible to identify the scanning direction when using either an electromagnetic or electrostatic MEMS, The range of scanning motion of the MEMS mirror 11 can be accurately controlled.

  As shown in FIGS. 8A and 8B, in the optical scanning device 10A according to the second embodiment, the respective scanning directions of the BD signal of the left BD sensor 13 and the BD signal of the right BD sensor 14 are scanned. 2 n-bit counter circuits are used to identify the scanning direction based on the time interval at which each of the BD sensors 13 and 14 is scanned, that is, the time interval at which the BD signal is output. The n is a positive integer of 2 or more.

  For the BD signal of the left BD sensor 13, the BD sensor 13 is moved in the A direction from the timing when the BD sensor 13 is scanned in the B direction until the timing when the scanning direction is turned back and the BD sensor 13 is scanned in the A direction. The time from the scanning timing to the timing of scanning the BD sensor 13 in the B direction is much longer because there is a latent image forming area in between.

  For this reason, the combination of two BD signals with a short interval can be specified based on the timing interval when the BD signal of the BD sensor 13 is input. Thus, the timing of the BD signal detected earlier in the set of BD signals having a short interval is specified as the timing when the BD sensor 13 is scanned in the B direction, and the BD signal detected later is detected. The timing can be specified as the timing when the BD sensor 13 is scanned in the A direction. The same applies to the BD sensor 14. Specifically, the configuration is as follows.

  As shown in FIG. 8A, in the n-bit counter circuit, the BD signal of the left BD sensor 13 is input to the reset terminal, the clock signal is input to the input terminal, and the most significant bit is output. Next, the time interval until the BD signal of the left BD sensor 13 is input is measured. Thus, when the output is 0, the time interval is short and the BD signal is identified as a BD signal detected at the start position in the A direction. When the output is 1, the time interval is long and the BD signal is It is identified as a BD signal detected at the end position in the B direction.

  As shown in FIG. 8B, in another n-bit counter circuit, the BD signal of the right BD sensor 14 is input to the reset terminal, the clock signal is input to the input terminal, and the most significant bit is output. Then, the time interval until the BD signal of the right BD sensor 14 is input next is measured. Thus, when the output is 0, the time interval is short and the BD signal is identified as a BD signal detected at the start position in the B direction. When the output is 1, the time interval is long and the BD signal is It is identified as a detection signal detected at the end position in the A direction.

  Even with such a configuration, the scanning timing of the start position and end position in the A direction and the scanning timing of the start position and end position in the B direction are detected, and based on these timings, the driving voltage of the MEMS driving unit 15 is detected. Is controlled, and the range of the scanning motion of the MEMS mirror 11 is corrected.

  It is conceivable to construct a new embodiment by combining the technical features of the above-described embodiments.

  The above description of the embodiment is to be considered in all respects as illustrative and not restrictive. The scope of the present invention is shown not by the above embodiments but by the claims. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Photosensitive drum (to-be-scanned body)
10, 10A Optical scanning device 11 MEMS mirror (scanning body)
12 Light source 13, 14 BD sensor 131, 132, 141, 142 Photodiode (photodetection element)
DESCRIPTION OF SYMBOLS 15 MEMS drive part 16 Scan control part 22 1st BD signal output part 23 2nd BD signal output part 31, 34 1st signal generation part 32, 35 2nd signal generation part 33, 36 Selection part

Claims (8)

An optical scanning device that reciprocally scans a scanning range including a latent image forming region of a scanned object with a light beam,
A light source that emits a light beam;
A scanning body that scans and moves to reflect the light beam emitted from the light source and scan the scanning range;
A first BD sensor and a second BD sensor arranged at the first end and the second end outside the latent image forming area and within the scanning range, and are detected adjacent to each other along the scanning direction. A first BD sensor and a second BD sensor each having a first light detection element and a second light detection element that output a detection value corresponding to the amount of light;
A scanning direction identification unit for identifying a scanning direction when each of the first BD sensor and the second BD sensor is scanned;
For each of the first BD sensor and the second BD sensor, a BD signal based on the detection value of the first light detection element, the detection value of the second light detection element, and the scanning direction identified by the scanning direction identification unit. A first BD signal output unit and a second BD signal output unit for outputting
A control unit that controls the scanning motion based on the timing at which the BD signal is output,
The scanning direction identifying unit is an optical scanning device that identifies the scanning direction based on a timing at which the first BD sensor is scanned and a timing at which the second BD sensor is scanned.   The optical scanning device according to claim 1, wherein the scanning direction identification unit identifies the scanning direction based on a detection order of the first BD sensor and the second BD sensor.   2. The optical scanning device according to claim 1, wherein the scanning direction identification unit identifies the scanning direction based on a time interval at which each of the first BD sensor and the second BD sensor is scanned. Each of the first BD signal output unit and the second BD signal output unit is
The first voltage conversion unit that converts the detection value of the first photodetection element into a voltage value, the second voltage conversion unit that converts the detection value of the second photodetection element into a voltage value, and the first voltage conversion unit output A first bias unit for applying a predetermined bias voltage to the measured voltage value, and comparing the voltage value output from the first bias unit with the voltage value output from the second voltage conversion unit to generate a signal according to the comparison result A first signal generation unit including a first comparison unit to output;
The third voltage conversion unit that converts the detection value of the first light detection element into a voltage value, the fourth voltage conversion unit that converts the detection value of the second light detection element into a voltage value, and the fourth voltage conversion unit output A second bias unit for applying a predetermined bias voltage to the measured voltage value, a voltage value output from the third voltage conversion unit and a voltage value output from the second bias unit, and a signal corresponding to the comparison result A second signal generation unit including a second comparison unit to output;
Either the output signal of the first signal generation unit or the output signal of the second signal generation unit is selected based on the scanning direction identified by the scanning direction identification unit, and BD is selected based on the output signal of the selected one The optical scanning device according to claim 1, further comprising: a selection unit that outputs a signal. The scanning direction identification unit
When the first signal based on the detection value of the second BD sensor is input after the signal based on the detection value of the first BD sensor is input, scanning is performed in the first scanning direction from the first BD sensor to the second BD sensor. 5. When the second signal based on the detection value of the second BD sensor is input, it is identified that scanning has been performed in the second scanning direction from the second BD sensor toward the first BD sensor. The optical scanning device according to any one of the above. The scanning direction identification unit
When the first signal based on the detection value of the first BD sensor is input after the signal based on the detection value of the second BD sensor is input, scanning is performed in the second scanning direction from the second BD sensor to the first BD sensor. 6. When the second signal based on the detection value of the first BD sensor is input, it is identified that scanning has been performed in the first scanning direction from the first BD sensor toward the second BD sensor. The optical scanning device according to any one of the above.   The optical scanning device according to claim 1, wherein the scanning direction identification unit is configured by a counter circuit. A scanned object;
An image forming apparatus comprising the optical scanning device according to claim 1.

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