JP2013171228A - Optical scanning device and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively provide an optical scanning device and an image formation device that can correct a driving voltage of a MEMS mirror so as to compensate variation of a deflection angle of the MEMS mirror.SOLUTION: The optical scanning device comprises: a MEMS mirror 11; a driving unit 17 that oscillates the MEMS mirror 11 using a driving voltage varying at a basic cycle T; a light detection unit 43 that receives a laser beam LB deflected by the MEMS mirror 11 to output a detection signal; a correction value calculation unit 51 that calculates a correction voltage value to be used for correction of the driving voltage on the basis of a timing on which the detection signal is output; a direct current voltage generation unit 52 that generates a direct current voltage of a voltage value lower than the correction voltage value; a direct current voltage amplification unit 53 that amplifies the direct current voltage generated by the direct current voltage generation unit 52 so as to be equal to the correction voltage value; and a waveform shaping unit 54 that shapes a waveform of the amplified direct current voltage so as to vary at the basic cycle T and outputs a shaped waveform thereof to the driving unit 17 as the driving voltage.

Description

  The present invention relates to an optical scanning device including a MEMS mirror that deflects scanning laser light and an image forming apparatus including the optical scanning device.

  2. Description of the Related Art Conventionally, a MEMS (Micro Electro Mechanical Systems) mirror that reciprocally vibrates is known as a reflection mirror for deflecting a scanning laser beam toward a photosensitive member (see, for example, Patent Document 1). In FIG. 3 of Patent Document 1, reference numeral 8 indicates a MEMS mirror, and reference numerals a, b, c, and d indicate piezoelectric bodies as drive sources that vibrate the MEMS mirror 8. The MEMS mirror 8 causes torsional vibration by driving the driving sources a and b in the same phase and driving the driving sources c and d in the opposite phase to the driving sources a and b. As a result, the laser beam incident on the MEMS mirror 8 is deflected and scanned.

  FIG. 2 of Patent Document 1 describes a block diagram of a drive circuit for driving the drive sources a, b, c, and d. In FIG. 2 of Patent Document 1, a sine wave is generated by the oscillator 121a, and the sine wave is input to the phase inversion circuit 121b and the phase shifter 121c. In the phase shifter 121c, a signal adjusted so that the image signal and the phase of the MEMS mirror 8 correspond to each other is generated. The signal is amplified by the amplifier 121e and supplied to the drive sources a and b. The sine wave generated by the oscillator 121a is inverted in phase through the phase inversion circuit 121b and supplied to the driving sources c and d through the phase shifter 121d and the amplifier 121f.

  Patent Document 2 discloses a technique in which a mirror driving unit is configured as one electromagnetic actuator including a coil and a permanent magnet, and the mirror is vibrated by a torque acting on the permanent magnet when a current is passed through the coil. Is described. In this technique, similarly to Patent Document 1, a sine wave is generated by an arbitrary waveform generator, and then the sine wave is amplified by an amplifier.

  Further, in Patent Document 2, since the displacement angle (deflection angle) of the mirror changes due to an environmental change or a change over time, a light receiving element that receives the scanning light deflected by the mirror is disposed at a predetermined position. A technique is described in which an output is taken in and the phase and amplitude of a sine wave generated by an arbitrary waveform generator is adjusted so that scanning light passes through a light receiving element at a desired time.

JP 2004-177543 A JP 2008-40460 A

  However, the oscillators that can generate a sine wave and the amplifiers that can accurately amplify the sine wave described in Patent Document 1 and Patent Document 2 are expensive. In particular, an oscillator capable of generating a sine wave by changing the phase and amplitude as described in Patent Document 2 is more expensive. Therefore, in constructing an optical scanning device or an image forming apparatus that includes a MEMS mirror and can correct a drive voltage for driving the MEMS mirror so as to compensate for a change in the deflection angle of the MEMS mirror, There was room for improvement.

  Therefore, the present invention has been made in view of such circumstances, and an object of the present invention is to provide a MEMS mirror that deflects scanning laser light and compensate for a change in the deflection angle of the MEMS mirror. In addition, an optical scanning device capable of correcting a driving voltage for driving a MEMS mirror and an image forming apparatus including the same are provided at low cost.

  An optical scanning device according to the present invention includes a MEMS mirror that deflects laser light output from a light source, a drive unit that swings the MEMS mirror using a drive voltage that varies in a predetermined basic period, and the MEMS. Based on the timing at which the detection signal is output by the light detection unit that receives the laser beam deflected by the mirror at a predetermined position and outputs a detection signal indicating that the laser beam is received, A correction value calculation unit for calculating a correction voltage value that is a voltage value used when correcting the drive voltage so as to compensate for a change in the deflection angle of the MEMS mirror; and a DC voltage having a voltage value lower than the correction voltage value A DC voltage generating unit that generates the DC voltage generated by the DC voltage generating unit, a DC voltage amplifying unit that amplifies the DC voltage to be equal to the correction voltage value, The waveform of the DC voltage amplified by the DC voltage amplifier and shaped to vary the basic cycle, and a waveform shaping section for outputting to the drive unit as the drive voltage.

  According to this configuration, the DC voltage generation unit generates a DC voltage having a voltage value lower than the correction voltage value, and the generated DC voltage is set to a voltage value equal to the correction voltage value by the DC voltage amplification unit. Amplified. Then, the waveform of the amplified DC voltage is shaped by the waveform shaping unit so as to fluctuate in a predetermined basic cycle, and the AC voltage fluctuating in the basic cycle is output to the driving unit as a driving voltage.

  In other words, a MEMS mirror can be used by using a simple and inexpensive direct-current voltage generator and direct-current voltage amplifier without providing an oscillator capable of generating a sine wave by changing the phase and amplitude and an amplifier capable of accurately amplifying the sine wave. And the drive voltage when driving the MEMS mirror can be corrected to compensate for the change in the deflection angle of the MEMS mirror. As a result, an optical scanning device that includes a MEMS mirror that deflects the scanning laser beam and can correct the drive voltage for driving the MEMS mirror so as to compensate for the change in the deflection angle of the MEMS mirror is inexpensive. Can be provided.

  The driving unit includes a first driving unit and a second driving unit that drive the MEMS mirrors in opposite directions according to the driving voltage, and the waveform shaping unit is amplified by the DC voltage amplification unit. The drive output to the first drive unit and the second drive unit by alternately outputting the DC voltage to the first drive unit and the second drive unit every half of the basic cycle. It is preferable that the voltage waveform is shaped into a rectangular wave that fluctuates in the basic period.

  According to this configuration, the first drive unit and the second drive unit alternately output the output destination of the DC voltage amplified by the DC voltage amplification unit every half of the basic cycle. The waveform of the drive voltage output toward the one drive unit and the second drive unit can be shaped into a rectangular wave that fluctuates with a basic period.

  The waveform shaping unit is provided between the DC voltage amplification unit and the driving unit, and the output destination of the DC voltage amplified by the DC voltage amplification unit is the first driving unit and the second driving unit. It is preferable that the switching element includes a switching element that switches between the switching elements and a switching control unit that switches the switching element every half of the basic period.

  According to this configuration, the waveform shaping unit can be configured at low cost by using an inexpensive switching element that switches the supply path of the drive voltage in at least two directions.

  The correction value calculation unit further calculates a correction duty ratio, which is a duty ratio indicating a ratio of a period during which the DC voltage amplified by the DC voltage amplification unit is output to the drive unit in the basic period, The waveform shaping unit preferably sets the drive voltage to a high level during a period corresponding to the correction duty ratio calculated by the correction value calculation unit in the basic period.

  According to this configuration, since the drive voltage can be corrected not only using the correction voltage value but also using the correction duty ratio, the direct-current voltage output from the direct-current voltage amplification unit is supplied to the drive unit with the basic period. It is not necessary to accurately calculate the correction voltage value so as to compensate for the change in the deflection angle of the MEMS mirror when applied for a half period.

  The DC voltage amplifying unit includes an amplifier that amplifies the DC voltage generated by the DC voltage generating unit with a variable amplification factor, and the DC voltage generating unit is fixed in advance lower than the correction voltage value. It is preferable to further include an amplification factor setting unit that generates a DC voltage of a voltage value and sets a value obtained by dividing the correction voltage value by the previously fixed voltage value as the variable amplification factor.

  According to this configuration, a DC voltage having a fixed voltage value lower than the correction voltage value is generated by the DC voltage generator. That is, as compared with the case where the DC voltage generating unit is configured to generate DC voltages having various voltage values, the DC voltage generating unit can be simplified and inexpensively configured.

  Alternatively, the DC voltage amplifying unit includes an amplifier that amplifies the DC voltage generated by the DC voltage generating unit with a fixed amplification factor, and the DC voltage generating unit fixes the correction voltage value in advance. It is preferable to generate a DC voltage having a voltage value obtained by dividing by the amplification factor.

According to this configuration, the DC voltage amplifying unit can be configured at low cost by using an inexpensive amplifier that amplifies the DC voltage with a fixed amplification factor.

  An image forming apparatus according to the present invention includes: the optical scanning device; and an image forming unit that forms an image corresponding to the latent image on a sheet using a latent image formed on a photosensitive member by the optical scanning device. Is provided.

  According to the present invention, an optical scanning that includes a MEMS mirror that deflects scanning laser light and can correct a driving voltage for driving the MEMS mirror so as to compensate for a change in the deflection angle of the MEMS mirror. The apparatus and the image forming apparatus including the apparatus can be provided at low cost.

1 is a schematic cross-sectional view showing a multifunction machine as an example of an image forming apparatus to which an optical scanning device according to the present invention is applied. 1 is a block diagram illustrating an example of an electrical configuration of a multifunction machine. The figure which shows the arrangement | positioning relationship of the optical component which comprises an exposure part. The figure which shows the principle of an optical deflection | deviation part. Sectional drawing which cut | disconnected the optical deflection | deviation part shown in FIG. 4 along the AA line. The figure which shows the state which the PZT thin film of the mirror drive part of one side expanded, and the PZT thin film of the mirror drive part of the other side contracted in the same cross section as FIG. The block diagram which shows the structure of an exposure part. The figure which shows the time change of the deflection angle of a mirror part, and the detection signal output from a BD sensor. (A) The figure which shows the change of the voltage value of the direct-current voltage input into an amplifier and a waveform shaping part. (B) The figure which shows the change of the voltage value of the DC voltage input into a mirror drive part (1st drive part). (C) The figure which shows the change of the voltage value of the DC voltage input into a mirror drive part (2nd drive part). The figure which shows the change of the deflection angle of a mirror part according to the change of the voltage value of the DC voltage input into a mirror drive part. The block diagram which shows the structure of the exposure part different from FIG. (A) The figure which shows the change of the voltage value of the DC voltage input into a mirror drive part (1st drive part) according to the correction | amendment duty ratio calculated by the correction value calculation part. (B) The figure which shows the change of the voltage value of the DC voltage input into load according to the correction | amendment duty ratio calculated by the correction value calculation part. (C) The figure which shows the change of the voltage value of the direct-current voltage input into a mirror drive part (2nd drive part) according to the correction | amendment duty ratio calculated by the correction value calculation part.

  FIG. 1 is a schematic sectional view of a multifunction peripheral (image forming apparatus) to which an optical scanning device according to the present invention is applied. The multifunction device 1 has a plurality of functions such as a copy, a printer, and a scanner. The MFP 1 includes a main body unit 100, a document reading unit 200 disposed on the main body unit 100, a document feeding unit 300 disposed on the document reading unit 200, and an operation unit disposed on the upper front surface of the main body unit 100. 400.

  The document feeder 300 functions as an automatic document feeder, and can continuously send a plurality of documents placed on the document placing unit 301 to the document reading unit 200.

  The document reading unit 200 includes a carriage 201 equipped with a CCD (Charge Coupled Device) sensor and an LED (Light Emitting Diode), a document table 203 formed of a transparent member such as glass, and a document reading slit 205. When reading a document placed on the document table 203, the document is read by the CCD sensor while moving the carriage 201 in the longitudinal direction of the document table 203. On the other hand, when reading a document fed from the document feeding unit 300, the carriage 201 is moved to a position facing the document reading slit 205, and the document fed from the document feeding unit 300 is scanned. Reading is performed by the CCD sensor through the reading slit 205. The CCD sensor outputs the read original as image data.

  The main body 100 includes a paper storage unit 101, an image forming unit 103, and a fixing unit 105. The sheet storage unit 101 includes a sheet tray 107 that can store a bundle of sheets. In the stack of sheets stored in the sheet tray 107, the uppermost sheet is fed out toward the sheet transport unit 111 by driving the pickup roller 109. The sheet is conveyed to the image forming unit 103 through the sheet conveying unit 111.

  The image forming unit 103 forms a toner image on the conveyed paper based on the image data. The image forming unit 103 includes a photosensitive drum 113, an exposure unit (optical scanning device) 115, a developing unit 117, and a transfer unit 119. The exposure unit 115 generates light corresponding to image data (image data output from the document reading unit 200, image data transmitted from a personal computer, image data received by facsimile, etc.), and is uniformly charged photoconductor. Irradiate the peripheral surface of the drum 113. As a result, an electrostatic latent image corresponding to the image data is formed on the peripheral surface of the photosensitive drum 113. In this state, a toner image corresponding to image data is formed on the peripheral surface by supplying toner from the developing unit 117 to the peripheral surface of the photosensitive drum 113. This toner image is transferred to the paper conveyed from the paper storage unit 101 by the transfer unit 119.

  The sheet on which the toner image is transferred is sent to the fixing unit 105. The fixing unit 105 applies heat and pressure to the toner image and the paper to fix the toner image on the paper. The paper is discharged to the stack tray 121 or the paper discharge tray 123.

  The operation unit 400 includes a display unit 403 and an operation key unit 401. The display unit 403 has a touch panel function, and displays a screen including soft keys. The user performs an input operation such as setting input necessary for executing a function such as copying by operating a soft key while viewing the screen.

  The operation key unit 401 includes operation keys composed of hard keys. Specifically, a start key 405, a ten key 407, a stop key 409, a reset key 411, a function switching key for switching between a copy, a printer, a scanner, and a facsimile. 413 and the like.

  A start key 405 is a key for starting operations such as copying and facsimile transmission. A numeric keypad 407 is a key for inputting numbers such as the number of copies and a facsimile number. A stop key 409 is a key for stopping a copy operation or the like halfway. The reset key 411 is a key for returning the set contents to the initial setting state.

  The function switching key 413 includes a copy key, a transmission key, and the like, and is a key for switching between a copy function, a transmission function, and the like. When the copy key is operated, an initial copy screen is displayed on the display unit 403. When the transmission key is operated, an initial screen for facsimile transmission and mail transmission is displayed on the display unit 403.

  FIG. 2 is a block diagram illustrating an electrical configuration of the multifunction machine 1. The multifunction device 1 is connected so that the functional units such as the main unit 100, the document reading unit 200, the document feeding unit 300, the operation unit 400, the communication unit 600, and the control unit 500 can communicate with each other. It has been configured. Since the main body unit 100, the document reading unit 200, the document feeding unit 300, and the operation unit 400 have already been described, description thereof will be omitted.

  The communication unit 600 includes a facsimile communication unit 601 and a network I / F unit 603. The facsimile communication unit 601 includes an NCU (Network Control Unit) that controls connection of a telephone line with a destination facsimile and a modulation / demodulation circuit that modulates / demodulates a signal for facsimile communication. The facsimile communication unit 601 is connected to the telephone line 605.

  The network I / F unit 603 is connected to a LAN (Local Area Network) 607. A network I / F unit 603 is a communication interface circuit for executing communication with a terminal device such as a personal computer connected to the LAN 607.

  The control unit 500 includes, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an image memory, and the like. The CPU executes control necessary for operating the multifunction device 1 on the above-described components of the multifunction device 1 such as the main body 100. The ROM stores software and setting values necessary for controlling the operation of the multifunction device 1. The RAM is used for temporarily storing data generated during execution of software. The image memory temporarily stores image data (image data output from the document reading unit 200, image data transmitted from a personal computer, image data received by facsimile, etc.).

  FIG. 3 is a diagram showing an arrangement relationship of optical components that constitute the exposure unit 115. The exposure unit 115 includes a light source 31, a light deflection unit 10, two scanning lenses 33 and 35, and the like. The light source 31 is, for example, a laser diode, and irradiates a light beam (laser light) LB modulated in accordance with image data.

  A collimator lens 37 and a cylindrical lens 39 are disposed on the optical path between the light source 31 and the light deflection unit 10. The collimator lens 37 makes the light beam LB emitted from the light source 31 parallel light. The cylindrical lens 39 condenses the light beam LB converted into parallel light into a linear shape. The light beam LB condensed linearly is incident on the light deflection unit 10.

  A scanning lens 33 and a scanning lens 35 are disposed on the optical path between the light deflection unit 10 and the photosensitive drum 113. The light beam LB incident on the mirror unit 11 of the light deflection unit 10 is reflected and deflected by the mirror unit 11 and imaged on the photosensitive drum 113 by the scanning lenses 33 and 35. In other words, an electrostatic latent image is formed on the photosensitive drum 113 by scanning the photosensitive drum 113 with the light beam LB.

  The exposure unit 115 further includes a BD (Beam Detect) lens 41 and a BD sensor (light detection unit) 43. When the light beam LB scans the photosensitive drum 113 from one side 113a to the other side 113b of the photosensitive drum 113, the light beam LB exceeding the effective scanning range R is transmitted by the BD lens 41. The light is collected and received by the BD sensor 43. When receiving the light beam LB exceeding the effective scanning range R, the BD sensor 43 outputs a detection signal indicating that the light beam LB has been received. The detection signal output from the BD sensor 43 is used to synchronize the image signal representing the electrostatic latent image formed on the photosensitive drum 113 and the timing for scanning the effective scanning range R.

  The light deflection unit 10 will be described. FIG. 4 is a diagram illustrating the principle of the light deflecting unit 10. FIG. 5 is a cross-sectional view of the light deflection unit 10 shown in FIG. 4 taken along line AA.

  The light deflection unit 10 includes a mirror unit (MEMS mirror) 11, a frame 13, a torsion bar 15, and mirror drive units (drive units) 17a, 17b, 17c, and 17d.

  The shape of the frame 13 is a rectangle. The frame 13 includes a pair of side portions 13a and 13b extending in the longitudinal direction and a pair of side portions 13c and 13d extending in a direction orthogonal to the longitudinal direction. A mirror portion 11 is disposed at the center of the frame 13. The shape of the mirror part 11 is an ellipse. The major axis direction of the ellipse is the longitudinal direction of the frame 13. The light beam is incident on the mirror unit 11 and is reflected and deflected by the mirror unit 11.

  The torsion bar 15 extends in the minor axis direction of the ellipse of the mirror part 11, and the mirror part 11 is fixed to the torsion bar 15. One end of the torsion bar 15 is supported by the beam 19. The other end of the torsion bar 15 is supported by the beam 21. The beams 19 and 21 are supported by a pair of side portions 13c and 13d, respectively.

  On the beam 19, a mirror driving unit 17a is formed on the side 13c side of the torsion bar 15, and a mirror driving unit 17b is formed on the side 13d side of the torsion bar 15. On the beam 21, a mirror drive unit 17c is formed on the side 13c side of the torsion bar 15, and a mirror drive unit 17d is formed on the side 13d side of the torsion bar 15.

  As shown in FIG. 5, the mirror driving unit 17 a includes a lower electrode 23, a PZT thin film 25, and an upper electrode 27. The mirror driving units 17b, 17c, and 17d have the same configuration as the mirror driving unit 17a. Hereinafter, the mirror driving units 17a, 17b, 17c, and 17d will be referred to as the mirror driving unit 17 unless it is necessary to distinguish them. An alternating voltage that fluctuates at a predetermined fixed basic cycle is applied to the mirror drive unit 17 as a drive voltage. Thereby, the beams 19 and 21 bend, and the mirror part 11 inclines with the torsion bar 15 by that.

  6 has the same cross section as FIG. 5 so that the PZT thin film 25 of the mirror driving units 17a and 17c (first driving unit) extends and the PZT thin film 25 of the mirror driving units 17b and 17d (second driving unit) contracts. FIG. 6 is a diagram showing a state in which a driving voltage is applied to the mirror driving unit 17. The operation in which the torsion bar 15 tilts when the PZT thin film 25 of the mirror driving units 17a and 17c extends and the PZT thin film 25 of the mirror driving units 17b and 17d contracts is defined as a first operation. On the contrary, the operation in which the torsion bar 15 tilts as the PZT thin film 25 of the mirror driving units 17a and 17c contracts and the PZT thin film 25 of the mirror driving units 17b and 17d extends is referred to as a second operation.

  In the present optical deflection unit 10, the first operation and the second operation are performed by inverting the phase of the drive voltage applied to the mirror drive units 17a and 17c and the phase of the drive voltage applied to the mirror drive units 17b and 17d. And are performed alternately. As a result, as shown in FIG. 4, the mirror portion 11 swings around the torsion bar 15, and the deflection angle θ of the mirror portion 11 changes. In FIG. 4, reference numeral NL indicates a normal line of the mirror unit 11 when the mirror unit 11 is not swinging.

  FIG. 7 is a block diagram showing the configuration of the exposure unit 115. The exposure unit 115 includes a light source 31, a light deflection unit 10, a BD sensor 43, a correction value calculation unit 51, a DAC (DC voltage generation unit) 52, an amplifier (DC voltage amplification unit) 53, and a waveform shaping unit 54.

  The light beam LB output from the light source 31 is scanned by being reflected and deflected by the mirror unit 11 that is swung by the mirror driving units 17a, 17b, 17c, and 17d in the light deflecting unit 10. When receiving the light beam LB exceeding the effective scanning range R (FIG. 3), the BD sensor 43 outputs a detection signal indicating that the light beam LB has been received to the correction value calculation unit 51.

  The correction value calculation unit 51 corrects the drive voltage supplied to the mirror drive unit 17 to compensate for the change in the deflection angle θ of the mirror unit 11 due to environmental fluctuations such as ambient temperature and aging deterioration. A correction value such as a correction voltage value that is a voltage value at the time is calculated.

  Specifically, a method in which the correction value calculation unit 51 compensates for a change in the deflection angle θ of the mirror unit 11 will be described with reference to FIG. FIG. 8 is a diagram showing the change in the deflection angle θ of the mirror unit 11 and the detection signal output from the BD sensor 43 over time. When the environment changes, the deflection angle characteristic of the mirror unit 11 changes, for example, from a state where the maximum deflection angle indicated by a solid line is θm (hereinafter also referred to as an initial state) to a state where the maximum deflection angle indicated by a broken line is θm ′ (> θm). Change. Here, since the frequency of the drive voltage applied to the mirror drive unit 17 does not change even if the environment fluctuates, the frequency of the deflection angle characteristic of the mirror unit 11 does not change.

  On the other hand, the deflection angle θ0 of the mirror unit 11 when the BD sensor 43 detects the light beam LB is determined by the arrangement position of the BD sensor 43 and is not changed. For this reason, when the deflection angle characteristic of the mirror unit 11 is in the initial state, a detection signal indicating that the light beam LB is received from the BD sensor 43 is output at time t1. However, when the deflection angle characteristic of the mirror unit 11 changes as indicated by a broken line, a detection signal indicating that the light beam LB is received from the BD sensor 43 is output at time t2. Thus, there is a correlation between the change in timing at which the detection signal is output from the BD sensor 43 and the change in the maximum deflection angle of the mirror unit 11. This correlation is stored in advance in a ROM or the like as an experimental value from a test operation or the like.

  The correction value calculation unit 51 calculates the amount of change in the maximum deflection angle of the mirror unit 11 using the timing at which the detection signal is output from the BD sensor 43 and the above correlation stored in advance in the ROM or the like. Then, the voltage value of the drive voltage for compensating the calculated change amount is calculated as a correction voltage value. Then, the correction value calculation unit 51 outputs a digital signal indicating a voltage value smaller than the correction voltage value to the DAC 52 as a result of dividing the calculated correction voltage value by an amplification factor used in an amplifier 53 described later.

  Returning to FIG. 7, the DAC 52 is a so-called digital analog converter, which generates a DC voltage V <b> 1 indicated by the digital signal input from the correction value calculation unit 51 and outputs the DC voltage V <b> 1 to the amplifier 53.

  The amplifier 53 amplifies the DC voltage V <b> 1 input from the DAC 52 with a predetermined amplification factor, and outputs a voltage V <b> 2 equal to the correction voltage value to the waveform shaping unit 54.

  The waveform shaping unit 54 shapes the DC voltage V2 amplified by the amplifier 53 so as to fluctuate in a basic cycle that is a fluctuation cycle of the drive voltage supplied to the mirror drive unit 17.

  The waveform shaping unit 54 includes a switching element 541 and a switching control unit 542.

  The switching element 541 is an element that is provided between the amplifier 53 and the mirror driving unit 17 and switches the output destination of the DC voltage amplified by the amplifier 53 to the mirror driving units 17a and 17c or the mirror driving units 17b and 17d. The switching control unit 542 switches the switching element 541 every half of the basic period.

  FIG. 9A is a diagram illustrating a change in the voltage value of the DC voltage V <b> 1 input to the amplifier 53 and a change in the voltage value of the DC voltage V <b> 2 input to the waveform shaping unit 54. FIG. 9B is a diagram showing a change in the voltage value of the drive voltage V3 which is a DC voltage input to the mirror drive units 17a and 17c. FIG. 9C is a diagram showing a change in the voltage value of the drive voltage V4 that is a DC voltage input to the mirror drive units 17b and 17d. FIG. 10 is a diagram illustrating a change in the deflection angle θ of the mirror unit 11 according to a change in the voltage values of the drive voltages V3 and V4.

  As shown in FIG. 9A, when the DC voltage V1 input to the amplifier 53 rises at time t0 based on the correction voltage value calculated by the correction value calculation unit 51, it is input to the waveform shaping unit 54. The waveform of the DC voltage V2 amplified by the amplifier 53 rises smoothly. The reason why the waveform of the DC voltage V2 rises smoothly is that the response of the amplifier 53 is poor.

  Thereafter, in the waveform shaping unit 54, as shown in FIGS. 9B and 9C, the switching control unit 542 switches the switching element 541 every cycle T / 2 that is half the basic cycle T. The DC voltage V2 input to the waveform shaping unit 54 is alternately output between the mirror driving units 17b and 17d and the mirror driving units 17a and 17c every cycle T / 2 which is half the basic cycle T. As a result, the waveform shaping unit 54 shapes the waveform of the DC voltage V2 amplified by the amplifier 53 into a rectangular wave that fluctuates with the basic period T, and the drive voltage V3 of the mirror driving units 17b and 17d and the mirror driving units 17a and 17c. Is output as drive voltage V4. As a result, as shown in FIG. 10, the deflection angle θ of the mirror unit 11 is the maximum deflection when the period T / 2, for example, half of the basic period T elapses from time t0, according to the drive voltages V3 and V4. The magnitude of the angle increases to θm ′ and varies with the basic period T.

  According to the configuration of the above embodiment, the DAC 52 generates the DC voltage V 1 having a voltage value lower than the correction voltage value calculated by the correction value calculation unit 51, and the generated DC voltage V 1 is corrected by the amplifier 53. Amplified to a voltage value equal to the value. The waveform of the amplified DC voltage V2 is shaped so as to fluctuate with the basic period T by the waveform shaping unit 54, and the AC voltage fluctuating with the basic period T is output to the mirror driving unit 17 as the driving voltages V3 and V4. Will come to be.

  That is, in the present embodiment, a MEMS mirror can be used by using a simple and inexpensive DAC 52 and amplifier 53 without providing an oscillator capable of generating a sine wave by changing the phase and amplitude and an amplifier capable of accurately amplifying the sine wave. 11 can be driven, and the drive voltages V3 and V4 when the MEMS mirror 11 is driven can be corrected so as to compensate for the change in the deflection angle θ of the MEMS mirror 11. As a result, an optical scanning device that includes a MEMS mirror that deflects the scanning laser beam and can correct the drive voltage for driving the MEMS mirror so as to compensate for the change in the deflection angle of the MEMS mirror is inexpensive. Can be provided.

  The waveform shaping unit 54 includes a switching element 541 and a switching control unit 542. In other words, the output destination of the DC voltage V2 amplified by the amplifier 53 is simply output to the mirror driving units 17a and 17c and the mirror driving units 17b and 17d every half of the basic period T. The waveforms of the drive voltages V3 and V4 output toward the mirror drive units 17a and 17c and the mirror drive units 17b and 17d can be shaped into rectangular waves that vary with the basic period T.

  In addition, since the waveform shaping unit 54 can have a simple configuration using the switching element 541 that can switch the supply path of at least two drive voltages, the exposure unit 115 can be provided at low cost.

  Note that the configurations and settings shown in FIGS. 1 to 10 in the above embodiment are merely examples, and are not intended to limit the present invention.

  For example, the correction value calculation unit 51 further calculates a correction duty ratio that is a duty ratio indicating a ratio of a period during which the DC voltage V2 amplified by the amplifier 53 is output to the mirror drive unit 17 in the basic period T, and the waveform In the shaping part 54, you may comprise so that a drive voltage may be made into a high level during the period corresponding to the correction | amendment duty ratio calculated in the correction value calculation part 51 among the basic periods T. FIG. FIG. 11 shows a specific configuration.

  FIG. 11 is a block diagram showing the configuration of the exposure unit 115. As described above, the correction value calculation unit 51 calculates the amount of change in the maximum deflection angle of the mirror unit 11 using the timing at which the detection signal is output from the BD sensor 43 and the correlation stored in advance in the ROM or the like. calculate. The correction value calculation unit 51 calculates a correction voltage value for roughly compensating for the calculated change amount of the maximum deflection angle of the mirror unit 11 (for example, compensating for 95% of the change amount), and A correction duty ratio for compensating the remaining slight change amount (for example, compensating for 5% of the change amount) is calculated and output to the waveform shaping unit 54.

  Accordingly, the switching element 541 is configured so that the output destination of the DC voltage V2 amplified by the amplifier 53 can be switched to the load L in addition to the mirror driving units 17a and 17c and the mirror driving units 17b and 17d. ing.

  FIG. 12A is a diagram illustrating a change in the voltage value of the drive voltage V3 that is a DC voltage input to the mirror drive units 17a and 17c in accordance with the correction duty ratio calculated by the correction value calculation unit 51. . FIG. 12B is a diagram illustrating a change in the voltage value of the DC voltage VL input to the load L according to the correction duty ratio calculated by the correction value calculation unit 51. FIG. 12C is a diagram showing a change in the voltage value of the drive voltage V4, which is a DC voltage input to the mirror drive units 17b and 17d, according to the correction duty ratio calculated by the correction value calculation unit 51. .

  When the correction duty ratio calculated by the correction value calculation unit 51 is, for example, 40%, the switching control unit 542, as shown in FIG. 12A, the correction duty ratio calculated by the correction value calculation unit 51 is 40%. Accordingly, during the first 40% period of the basic period T, the switching element 541 is switched so that the output destination of the DC voltage V2 amplified by the amplifier 53 is the mirror driving units 17b and 17d.

  Subsequently, as illustrated in FIG. 12B, the switching control unit 542 performs a period of 10% of the basic period T, which is the remaining period until the half period T / 2 of the basic period T elapses, in the amplifier 53. The switching element 541 is switched so that the output destination of the DC voltage V <b> 2 amplified by the above is the load L.

  Subsequently, as shown in FIG. 12C, the switching control unit 542 sends the output destination of the DC voltage V2 amplified by the amplifier 53 to the mirror driving units 17a and 17c for a period of 40% of the basic period T. Thus, the switching element 541 is switched.

  Then, as shown in FIG. 12B, the switching control unit 542 performs the DC voltage V2 amplified by the amplifier 53 during a period of 10% of the basic period T that is the remaining period until the basic period T elapses. The switching element 541 is switched so that the output destination is the load L.

  According to this configuration, not only the correction voltage value but also the correction duty ratio is used to adjust the period during which the drive voltage is applied to the mirror drive unit 17, so that the drive voltage supplied to the mirror drive unit 17 Since the DC voltage V2 output from the amplifier 53 is applied to each mirror driving unit 17 for a period T / 2 that is half the basic period T, the maximum deflection angle of the mirror unit 11 becomes a predetermined value. It is not necessary to set the voltage value accurately.

  The waveform shaping unit 54 includes a switching element 541 and a switching control unit 542, and is not limited to a configuration that shapes the waveform of the DC voltage V2 input from the amplifier 53 into a rectangular wave that fluctuates in the basic period T. You may comprise using the cheap distributor etc. which can convert the waveform of DC voltage V2 input from 53 into the square wave, triangular wave, sawtooth wave, or sine wave etc. which fluctuate with the basic period T.

  However, in the case where the correction duty ratio is calculated by the correction value calculation unit 51, the waveform of the DC voltage V2 input from the amplifier 53 is shaped into a rectangular wave that fluctuates in the basic period T, and the duty of the rectangular wave is calculated. The waveform shaping unit 54 may be configured using an inexpensive distributor or the like whose ratio can be set to the correction duty ratio.

  In the configuration of the above embodiment, the waveform shaping unit 54 is configured to divide the output destination of the DC voltage V2 amplified by the amplifier 53 into two. As shown in the figure, there is only one mirror drive unit for driving the mirror unit, and the waveform shaping unit 54 adjusts the waveform of the DC voltage V2 amplified by the amplifier 53 in accordance with this. It may be configured to be shaped so as to fluctuate with the basic period T and output as a drive voltage to the mirror drive unit that exists only one.

  In this configuration, for example, the waveform shaping unit 54 is configured to include a switching element 541 and a switching control unit 542, and the switching control unit 542 is amplified by the amplifier 53, for example, every half of the basic period T. This can be realized by controlling the switching element 541 so as to alternately switch the output destination of the DC voltage V2 to the mirror drive unit and the load which are only one. Not limited to this, an inexpensive distributor or the like that can convert the waveform of the DC voltage V2 input from the amplifier 53 into a rectangular wave, a triangular wave, a sawtooth wave, a sine wave, or the like that fluctuates with the basic period T. It may be realized by configuring the waveform shaping unit 54 by using it.

  In the case where the correction duty ratio is calculated by the correction value calculation unit 51, the waveform of the DC voltage V2 input from the amplifier 53 is shaped into a rectangular wave that fluctuates in the basic period T, and the duty ratio of the rectangular wave is changed. The waveform shaping unit 54 may be configured using a distributor or the like that is variable in the correction duty ratio.

  In the above configuration, the amplifier 53 is configured to amplify the DC voltage V <b> 1 output from the DAC 52 with a predetermined amplification factor. Instead, the amplifier 53 is output from the DAC 52. You may comprise by the amplifier which can amplify DC voltage with a variable amplification factor.

  In accordance with this, the DAC 52 is configured to output a DC voltage having a fixed voltage value that is sufficiently smaller than the correction voltage value calculated by the correction value calculation unit 51 to the amplifier 53, and the correction value An amplification factor setting for calculating a value obtained by dividing the correction voltage value calculated by the calculation unit 51 by a voltage value fixed in advance of the DC voltage output from the DAC 52 and setting the calculated value as an amplification factor of the amplifier 53 The exposure unit 115 is further provided with a portion (not shown).

  According to this configuration, the DAC 52 generates a DC voltage having a fixed voltage value that is lower than the correction voltage value. That is, an image forming apparatus can be configured using a simplified and inexpensive DAC 52 as compared to the DAC 52 that generates DC voltages having various voltage values.

  In the above embodiment, a multifunction peripheral is described as an example of the image forming apparatus according to the present invention. However, the present invention is not limited to an image forming apparatus such as a printer, a copier, or a fax machine, a scanner, a projector, It can also be applied to an optical scanning device such as a barcode reader.

1 MFP (image forming device)
10 Light deflection part 11 Mirror part (MEMS mirror)
113 Photosensitive drum 115 Exposure unit (optical scanning device)
13 frame 13a, 13b, 13c, 13d side 15 torsion bar 17a, 17c mirror drive part (drive part, first drive part)
17b, 17d Mirror drive unit (drive unit, second drive unit)
19 Beam 23 Lower electrode 25 PZT thin film 27 Upper electrode 31 Light source 43 BD sensor (light detection unit)
51 Correction Value Calculation Unit 52 DAC (DC Voltage Generation Unit)
53 Amplifier (DC voltage amplifier)
54 Waveform Shaping Unit 541 Switching Element 542 Switching Control Unit L Load LB Light Beam (Laser Light)
R Effective scanning range T Basic period θ Deflection angle

Claims (7)

A MEMS mirror for deflecting the laser beam output from the light source;
A drive unit that swings the MEMS mirror using a drive voltage that fluctuates at a predetermined basic period;
A light detector that receives the laser beam deflected by the MEMS mirror at a predetermined position and outputs a detection signal indicating that the laser beam has been received;
Correction for calculating a correction voltage value that is a voltage value used when correcting the drive voltage so as to compensate for a change in the deflection angle of the MEMS mirror based on the timing at which the detection signal is output by the light detection unit. A value calculator,
A DC voltage generator that generates a DC voltage having a voltage value lower than the correction voltage value;
A DC voltage amplifier that amplifies the DC voltage generated by the DC voltage generator so as to have a voltage value equal to the correction voltage value;
A waveform shaping unit that shapes the waveform of the DC voltage amplified by the DC voltage amplification unit so as to fluctuate in the basic period, and outputs the waveform to the driving unit as the driving voltage;
An optical scanning device comprising: The driving unit includes a first driving unit and a second driving unit that drive the MEMS mirrors in opposite directions according to the driving voltage,
The waveform shaping unit alternately outputs the DC voltage amplified by the DC voltage amplification unit to the first driving unit and the second driving unit every half of the basic period. The optical scanning device according to claim 1, wherein the waveform of the drive voltage output to the one drive unit and the second drive unit is shaped into a rectangular wave that fluctuates in the basic period.   The waveform shaping unit is provided between the DC voltage amplifying unit and the driving unit, and outputs an output destination of the DC voltage amplified by the DC voltage amplifying unit to the first driving unit and the second driving unit. The optical scanning device according to claim 2, further comprising: a switching element that switches between the switching elements, and a switching control unit that switches the switching element every half of the basic period. The correction value calculation unit further calculates a correction duty ratio that is a duty ratio indicating a ratio of a period during which the DC voltage amplified by the DC voltage amplification unit is output to the drive unit in the basic period,
4. The waveform shaping unit according to claim 1, wherein the drive voltage is set to a high level during a period corresponding to the correction duty ratio calculated by the correction value calculation unit in the basic period. Optical scanning device. The DC voltage amplification unit includes an amplifier that amplifies the DC voltage generated by the DC voltage generation unit with a variable amplification factor,
The DC voltage generator generates a DC voltage having a fixed voltage value lower than the correction voltage value,
5. The optical scanning according to claim 1, further comprising: an amplification factor setting unit configured to set a value obtained by dividing the correction voltage value by the previously fixed voltage value as the variable amplification factor. apparatus. The DC voltage amplifying unit comprises an amplifier that amplifies the DC voltage generated by the DC voltage generating unit with a fixed amplification factor,
5. The optical scanning device according to claim 1, wherein the DC voltage generation unit generates a DC voltage having a voltage value obtained by dividing the correction voltage value by the amplification factor fixed in advance. 6. An optical scanning device according to any one of claims 1 to 6,
An image forming apparatus comprising: an image forming unit that forms an image corresponding to the latent image on a sheet using a latent image formed on a photosensitive member by the optical scanning device.

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