JP5849058B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to, for example, an optical scanning device used for forming an electrostatic latent image and an image forming apparatus including the same.

  In an electrophotographic image forming apparatus, a light beam modulated in accordance with image data is generated, the light beam is reflected and deflected, and the light beam deflected to an image carrier (for example, a photosensitive drum) is generated. An electrostatic latent image is formed by scanning. An optical deflector is a device that reflects and deflects a light beam. As an optical deflector, a technique using a MEMS (Micro Electro Mechanical Systems) mirror instead of a polygon mirror has been proposed. The MEMS mirror has advantages such as high-speed scanning and low power consumption.

  The optical deflector using the MEMS mirror causes the mirror unit fixed to the torsion bar to resonate with the mirror driving unit, thereby setting the variation range of the deflection angle of the mirror unit to a predetermined target variation range. In this state, the light beam incident on the mirror unit is reflected and deflected to scan the light beam. The displacement wave indicating the displacement of the deflection angle of the mirror part generated by the resonance of the mirror part is a sine wave, and while passing from the maximum amplitude value to 0 through the minimum amplitude value and from the minimum amplitude value to 0 through the amplitude. There is a period during which the mirror moves at a substantially constant speed while moving toward the maximum value. By making the scanning of the light beam during this period valid and invalidating the scanning of the light beam outside this period, an accurate image reproduction is realized.

  By the way, the variation range of the deflection angle of the mirror portion may change even if the driving voltage for resonating the mirror portion is the same due to a change in temperature of the environment where the MEMS mirror is installed, a change in air resistance to the mirror portion, and the like. is there. For example, even if the temperature inside the printer is room temperature at the start of the image forming operation, if the image forming operation is continuously performed, the temperature inside the printer rises. Due to this temperature rise, the MEMS mirror is thermally expanded and deformed, and the spring constant and moment of inertia of the components of the MEMS mirror change. As a result, the resonance frequency of the mirror portion changes, and as a result, the fluctuation range of the deflection angle of the mirror portion changes.

  Therefore, the drive signal is corrected in order to make the fluctuation range of the deflection angle of the mirror unit the target fluctuation range. However, this correction causes a transient response in the mirror portion, and it takes time to reach the target fluctuation range.

  As a technique capable of reducing the influence of the transient response, there has been proposed a technique in which a compensation signal is added to the drive signal when the drive signal for driving the mirror unit is corrected (for example, see Patent Document 1).

JP 2006-279888 A

  The technique described in Patent Document 1 is an apparatus used for optical space communication, and is not used by resonating a mirror unit. When the mirror unit is used by resonating like an optical scanning device, in addition to the change of the deflection angle, the deflection angle displacement wave (in other words, the change of the deflection angle of the mirror unit is represented in a waveform along the time axis). The change in the phase of the response waveform of the mirror part becomes a problem.

  If the phase of the deflection angle displacement wave changes, in the case of an optical scanning device applied to an image forming apparatus, a deviation occurs in the writing position of the main scanning line when the main scanning line is drawn on the photosensitive drum. This influence appears as color misregistration, for example, when a color image is formed by overlapping toner images of respective colors in a tandem type color printer.

  In general, the MEM mirror is driven at a driving frequency near the resonance frequency in order to obtain a large amplitude. As described above, when the difference between the resonance frequency and the drive frequency is small, the phase of the deflection angular displacement wave changes relatively large due to the change in the resonance frequency of the mirror portion. Therefore, it is necessary to correct the phase of the deflection angular displacement wave.

  By the way, in an electronic device (for example, an image forming apparatus such as a printer, a projector, a barcode reader, or the like) including an optical scanning device using a MEMS mirror, a MEMS mirror having a large Q value is used. Since the MEMS mirror having a large Q value has poor responsiveness, it takes time to reach the target value when correcting the phase of the deflection angular displacement wave.

  The present invention relates to an optical scanning device capable of shortening the time to reach the target value when correcting the phase of the deflection angle displacement wave in which the displacement of the deflection angle of the mirror portion is expressed in a wave shape along the time axis to the target value, and An object of the present invention is to provide an image forming apparatus including the same.

  An optical scanning device according to an aspect of the present invention that achieves the above object includes a mirror unit that deflects a light beam, a mirror driving unit that drives and vibrates the mirror unit with a driving force according to an input driving signal, A displacement wave computing unit that computes a deflection angle displacement wave in which a deflection angle displacement of the mirror unit that is vibrated by a mirror drive unit is expressed in a wave shape along a time axis; and a phase of the deflection angle displacement wave is determined in advance A determination unit that determines whether or not the target value is different from a predetermined target value; and a first signal that becomes the drive signal in order to set the phase to the target value when the phase is determined to be different from the target value. When the correction value is calculated by outputting the first pulse signal as the drive signal to the mirror drive unit at a predetermined cycle and calculating the correction value of the phase of the pulse signal , Of the first pulse signal A first pulse signal generation unit that corrects a phase and outputs the first pulse signal having a phase corrected by the correction value to the mirror drive unit as the drive signal at the predetermined period; A second pulse signal generation unit that temporarily generates a second pulse signal before the correction when the phase of the first pulse signal is corrected, and the second pulse signal generation unit includes: , Generating the second pulse signal at a timing at which the phase of the pulse center of the first pulse signal before the correction and the phase of the pulse center of the second pulse signal can be different from each other, A second pulse signal is output to the mirror driver.

  Here, “to output the second pulse signal to the mirror driving unit” not only outputs the second pulse signal to the mirror driving unit as a driving signal, but also the first pulse signal and the second pulse. This means that a case where a pulse signal obtained by synthesizing the signal is output to the mirror drive unit as a drive signal is included. Further, this means that not only the case where the pulse signal is directly output to the mirror driving unit but also the case where the pulse signal is output via a signal amplifier, for example.

  In order to set the phase of the deflection angular displacement wave to the target value, the phase of the first pulse signal, which is a drive signal for driving the mirror unit, is corrected. When this correction is performed, according to the optical scanning device according to one aspect of the present invention, the phase of the pulse center of the first pulse signal and the phase of the pulse center of the second pulse signal are not the same and are different. I am doing so. As a result, it is possible to cancel the component that causes the transient response included in the first pulse signal whose phase has been corrected. Therefore, it is possible to suppress the delay in the response of the mirror unit with respect to the first pulse signal whose phase has been corrected. As a result, it is possible to shorten the time for the phase of the deflection angular displacement wave to reach the target value.

  The pulse center is a coordinate of a position obtained by adding the coordinates of the position of the rising portion of the pulse signal and the coordinates of the position of the falling portion and dividing by two.

  As the phase of the deflection angular displacement wave, for example, the phase difference between the deflection angular displacement wave and the first pulse signal, the phase difference between the other signal serving as a reference and the deflection angular displacement wave, and the phase difference, not the deflection angular displacement wave Its own phase can be mentioned.

  In the above configuration, the apparatus further includes a signal synthesis unit that generates a signal obtained by synthesizing the first pulse signal before the correction and the second pulse signal, and outputs the signal as the drive signal to the mirror drive unit, The second pulse signal generation unit includes: a phase of a pulse center of a pulse synthesized with the second pulse signal in the first pulse signal; and a phase of a pulse center of the second pulse signal. The second pulse signal is generated at a timing that can be varied.

  This configuration is a mode in which a pulse signal obtained by synthesizing the first pulse signal and the second pulse signal is output as a drive signal to the mirror drive unit.

  In the above configuration, the second pulse signal generation unit includes a phase of a pulse center of a pulse synthesized with the second pulse signal in the first pulse signal, and a pulse center of the second pulse signal. The second pulse signal is generated at a timing at which the phase can be varied by 90 degrees.

  As described in the embodiment, according to the simulation performed by the present inventor, the phase of the pulse center of the pulse synthesized with the second pulse signal in the first pulse signal, and the second pulse It was confirmed that the time required for the phase of the deflection angular displacement wave to reach the target value can be shortened if the phase of the pulse center of the signal is different by 90 degrees.

  In the above configuration, the second pulse signal generation unit generates the second pulse signal configured by a rectangular wave.

  In the above configuration, the second pulse signal generation unit generates the second pulse signal at a timing that is combined with a pulse generated at the end of the pulse train composed of the first pulse signal before correction. To do.

  In the above configuration, the second pulse signal generation unit generates the second pulse signal having the same pulse width as the pulse width of the first pulse signal. The pulse width refers to the length from the position of the rising edge of the pulse signal to the position of the falling edge, or the length from the position of the falling edge of the pulse signal to the position of the rising edge.

  An image forming apparatus according to another aspect of the present invention provides a light source that irradiates a light beam modulated in accordance with image data, an image carrier, and the light beam emitted from the light source to the image carrier. The optical scanning device that scans to form an electrostatic latent image, and a developing unit that forms a toner image by supplying toner to the image carrier on which the electrostatic latent image is formed.

  The image forming apparatus according to another aspect of the present invention includes the optical scanning device according to one aspect of the present invention, and thus has the same effects as the optical scanning device.

  In the above configuration, the image carrier has one side and the other side, and the optical scanning device moves the image carrier from the one side toward the other side. The main scanning is performed in the main scanning direction with the light beam, and the one-side main scanning is performed in which the image carrier is not scanned from the other side toward the one side. When the phase of the pulse signal is corrected, the second pulse signal generation unit generates the second pulse signal after the main scan and before starting the next main scan, and The first pulse signal generation unit generates the corrected first pulse signal.

  When the phase of the first pulse signal is corrected during the main scanning period of the image carrier from one side to the other side, the phase of the deflection angular displacement wave changes during the main scanning period. This may affect the reproducibility of the image. According to this configuration, when the phase of the first pulse signal is corrected, after the main scan is finished, before the next main scan is started (in other words, after the main scan is finished, the next main scan is performed). In the period when the deflection angle of the mirror section is fluctuating), the second pulse signal is generated, and the first pulse signal with the phase corrected is generated. Therefore, when the image carrier is next subjected to main scanning from one side to the other side, the phase of the deflection angular displacement wave can reach the target value. It can be prevented from lowering.

  In the above configuration, the plurality of image carriers arranged in tandem, the plurality of developing units provided corresponding to the plurality of image carriers, and the plurality of image carriers, respectively. A plurality of optical scanning devices provided on the image carrier, and a transfer belt on which a color toner image is formed by transferring the toner images formed on the plurality of image carriers in a superimposed manner.

  In the tandem type, an optical scanning device is provided according to a plurality of colors (for example, yellow, cyan, magenta, and black) constituting a color. In these optical scanning devices, if the phases of the deflection angular displacement waves do not match, color deviation occurs in the color image. According to this configuration, since the optical scanning device according to one aspect of the present invention is applied to the tandem type image forming apparatus, the phase of the deflection angular displacement wave is corrected in each of the plurality of optical scanning devices. The time to reach the target value can be shortened.

  According to the present invention, when the phase of the deflection angle displacement wave in which the displacement of the deflection angle of the mirror portion is expressed in a wave shape along the time axis is corrected to the target value, the time to reach the target value can be shortened.

1 is a schematic diagram of an internal structure of an image forming apparatus to which an optical scanning device of the present invention is applied. FIG. 2 is a block diagram illustrating a configuration of the image forming apparatus illustrated in FIG. 1. It is a figure which shows the arrangement | positioning relationship of the optical component with which the exposure part which comprises the optical scanning device concerning this embodiment is equipped. It is a figure which shows the principle of an optical deflection | deviation part. It is sectional drawing which cut | disconnected the optical deflection | deviation part shown in FIG. 4 along the AA line. FIG. 6 is a diagram illustrating a state in which the PZT thin film of the mirror driving unit on one side is extended and the PZT thin film of the mirror driving unit on the other side is contracted in the same cross section as FIG. 5. It is a block diagram which shows the structure of the optical scanning device concerning this embodiment. It is a graph which shows an example of the 1st pulse signal. It is the graph which expanded the area of the time 0.00172 second-0.00178 second in FIG. It is a graph which shows an example of a deflection angle displacement wave. It is a graph which shows an example of the 2nd pulse signal. It is a graph which shows an example of the 1st pulse signal combined with the 2nd pulse signal. It is a graph which shows an example of the 1st pulse signal with which the 2nd pulse signal was synthesize | combined. It is a graph which compares the deflection angle displacement wave of this embodiment and a comparative example at the time of the correction | amendment of the phase of a 1st pulse signal. It is a graph which compares the deflection angle displacement wave of this embodiment and a comparative example after 0.05 second progress from the time of the correction | amendment of the phase of a 1st pulse signal. It is a graph which compares the deflection angle displacement wave of this embodiment and a comparative example after 0.15 second progress from the time of correction | amendment of the phase of a 1st pulse signal. 6 is a flowchart for explaining the operation of the image forming apparatus to which the optical scanning device according to the embodiment is applied.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of an internal structure of an image forming apparatus 1 to which an optical scanning device of the present invention is applied. The image forming apparatus 1 can be applied to, for example, a digital multifunction machine having functions of a copy, a printer, a scanner, and a facsimile. The image forming apparatus 1 includes an apparatus body 100, a document reading unit 200, and a document feeding unit 300.

  A document reading unit 200 is disposed on the apparatus main body 100, and a document feeding unit 300 is disposed on the document reading unit 200.

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

  The document reading unit 200 includes a carriage on which an exposure lamp or the like is mounted, a document table made of a transparent member such as glass, a CCD (Charge Coupled Device) sensor, and a document reading slit (all not shown). The CCD sensor outputs the read original as image data.

  The apparatus main body 100 includes a sheet storage unit 101, an image forming unit 103, and a fixing unit 105. The sheet storage unit 101 is disposed at the lowermost part of the apparatus main body 100 and includes two sheet cassettes 101a and 101b that can store a bundle of sheets.

  Among the paper cassettes 101a and 101b, in the bundle of paper stored in the selected cassette, the uppermost paper is sent out toward the paper conveyance path 107 of the apparatus main body 100 by driving a pickup roller (not shown). . The sheet is conveyed to the image forming unit 103 through the sheet conveyance path 107.

  The sheet conveyance path 107 extends in a substantially vertical direction from the lower side to the upper side along one side surface (right side surface in FIG. 1) of the apparatus main body 100, and the other side surface (left side surface in FIG. 1) above. And extends substantially horizontally along the lower side of the document reading unit 200. A discharge tray 131 is provided at the end.

  The image forming unit 103 forms a toner image on the conveyed paper. The image forming unit 103 includes a yellow image forming unit 111Y, a magenta image forming unit 111M, a cyan image forming unit 111C, and a black image forming unit 111BK, which are arranged in the order in which the toner images are transferred to the transfer belt 117. These units have the same configuration and will be described by taking the yellow image forming unit 111Y as an example.

  The yellow image forming unit 111Y includes a photosensitive drum 113 and an exposure unit 115. Around the photosensitive drum 113, a charging unit 119, a developing unit 121, and a cleaning unit 123 are arranged. The charging unit 119 uniformly charges the peripheral surface of the photosensitive drum 113. The exposure unit 115 generates a light beam modulated in accordance with image data (image data output from the document reading unit 200, image data transmitted from a personal computer, image data received by facsimile), and the like. Irradiate the circumferential surface of the charged photosensitive drum 113. As a result, an electrostatic latent image corresponding to yellow image data is formed on the peripheral surface of the photosensitive drum 113. In this state, by supplying yellow toner from the developing unit 121 to the peripheral surface of the photosensitive drum 113, a toner image corresponding to yellow image data is formed on the peripheral surface.

  The transfer belt 117 can move counterclockwise while being sandwiched between the photosensitive drum 113 and the primary transfer roller 125. The yellow toner image is transferred from the photosensitive drum 113 to the transfer belt 117. The yellow toner remaining on the peripheral surface of the photosensitive drum 113 is removed by the cleaning unit 123. The above is the description of the yellow image forming unit 111Y.

  Above the yellow image forming unit 111Y, the magenta image forming unit 111M, the cyan image forming unit 111C, and the black image forming unit 111BK, containers containing corresponding color toners, that is, a yellow toner container 127Y, a magenta toner container 127M, A cyan toner container 127C and a black toner container 127BK are arranged. Toner for each color is supplied with toner from the corresponding container.

  As described above, the yellow toner image is transferred to the transfer belt 117, and the magenta toner image is transferred onto the toner image. Similarly, the cyan toner image and the black toner image are transferred onto the transfer belt 117. As a result, a color toner image is formed on the transfer belt 117. In this way, a toner image of each color pattern is superimposed and transferred onto the transfer belt 117, whereby a color toner image is formed on the transfer belt 117. The color toner image is transferred by the secondary transfer roller 129 onto the sheet conveyed from the sheet storage unit 101 described above.

  The sheet on which the color toner image is transferred is sent to the fixing unit 105. The fixing unit 105 includes a heating roller and a fixing roller. The paper on which the color toner image is transferred is sandwiched between these rollers. As a result, heat and pressure are applied to the color toner image and the paper, and the color toner image is fixed to the paper. The sheet is discharged to a discharge tray 131.

  FIG. 2 is a block diagram showing a configuration of the image forming apparatus 1 shown in FIG. The image forming apparatus 1 has a configuration in which an apparatus main body 100, a document reading unit 200, a document feeding unit 300, an operation unit 400, a control unit 500, and a communication unit 600 are connected to each other by a bus. Since the apparatus main body 100, the document reading unit 200, and the document feeding unit 300 have already been described, description thereof will be omitted.

  The operation unit 400 includes an operation key unit 401 and a display unit 403. The display unit 403 has a touch panel function, and displays a screen including soft keys. The user operates the soft keys while viewing the screen to make settings necessary for executing functions such as copying.

  The operation key unit 401 is provided with operation keys including hard keys. Specifically, a function key for switching between a start key, a numeric keypad, a stop key, a reset key, a copy, a printer, a scanner, and a facsimile are provided.

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

  The function switching key 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.

  The control unit 500 includes 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 image forming apparatus 1 on the above-described components of the image forming apparatus 1 such as the apparatus main body 100. The ROM stores software necessary for controlling the operation of the image forming apparatus 1. The RAM is used for temporary storage of data generated during execution of software, storage of application software, and the like. 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.).

  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.

  A 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 optical scanning device 3 according to the present embodiment includes an exposure unit 115, a circuit (electric circuit, electronic circuit), a microcomputer, and the like. 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 a laser diode, for example, and emits a light beam 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 converts the light beam LB emitted from the light source 31 into parallel light. The cylindrical lens 39 condenses the light beam LB that has been 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 lens 41 and a BD sensor 43. The light beam LB scans the photosensitive drum 113 from one side 113a to the other side 113b of the photosensitive drum 113, and the light beam LB exceeding the effective scanning range R is condensed by the BD lens 41. The BD sensor 43 receives the light. A BD (Beam Detect) sensor 43 generates a BD signal as a reference for starting scanning (main scanning) on the photosensitive drum 113.

  The light deflection unit 10 is a piezoelectric drive type MEMS mirror. However, the MEMS mirror that can be used for the light deflection unit 10 is not limited to the piezoelectric drive type. FIG. 4 is a diagram showing the principle of the optical deflection unit 10, and FIG. 5 is a cross-sectional view of the optical deflection unit 10 shown in FIG. 4 cut along the line AA. The light deflection unit 10 includes a mirror unit 11, a frame 13, a torsion bar 15, and mirror 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 mirror unit 11 has an elliptical shape whose major axis direction matches 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 portion 11, and one end thereof is supported by the beam 19 and the other end is supported by the beam 21. The torsion bar 15 is integrally formed with the mirror part 11. 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. In the optical deflection unit 10, when a drive signal is input to the mirror drive unit 17, the mirror unit 11 is driven to vibrate with a drive force corresponding to the drive signal.

  6 shows a state in which a driving voltage is applied to the mirror driving unit 17 so that 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 in the same cross section as FIG. FIG. In FIG. 6, the beams 19 and 21 are bent, whereby the mirror portion 11 is inclined together with the torsion bar 15.

  Hereinafter, the operation in which 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 referred to as a first operation, and the PZT thin film 25 of the mirror driving units 17a and 17c contracts. An operation in which the PZT thin film 25 of the mirror driving units 17b and 17d extends will be described as a second operation. By applying a driving voltage to the mirror driving unit 17 to bend the beams 19 and 21 so that the first operation and the second operation are alternately repeated, the mirror unit 11 has the torsion bar 15 as an axis. Oscillates and the deflection angle θ varies. In addition, the code | symbol NL shown in FIG. 4 has shown the normal line of the mirror part 11 when the mirror part 11 is not vibrating.

  When the frequency of the drive voltage (hereinafter also referred to as drive frequency) is matched with the resonance frequency of the mirror unit 11, the mirror unit 11 resonates and the maximum value of the deflection angle θ can be increased. Accordingly, the mirror unit 11 is driven in a state where the drive frequency is substantially matched with the resonance frequency, and the light beam is reflected and deflected by the mirror unit 11, thereby scanning the photosensitive drum 113 with the light beam.

  FIG. 7 is a block diagram showing the configuration of the optical scanning device 3 according to this embodiment. The optical scanning device 3 includes a light source 31, a light deflection unit 10, a displacement wave calculation unit 51, a maximum deflection angle determination unit 53, a correction value calculation unit 55, a phase difference determination unit 57, a correction value calculation unit 59, and a first pulse signal generation. Unit 61, second pulse signal generation unit 63, signal synthesis unit 65, and amplification unit 67.

  In the optical deflecting unit 10, the mirror driving unit 17 drives and vibrates the mirror unit 11 with a driving force corresponding to the input driving signal.

  The displacement wave calculation unit 51 uses the BD signal output by the BD sensor 43 (FIG. 3) receiving the light beam LB to calculate the displacement of the deflection angle of the mirror unit 11 oscillated by the mirror drive unit 17 over time. A deflection angular displacement wave expressed in a wave shape along the axis is calculated.

  The maximum deflection angle determination unit 53 determines the maximum value of the deflection angle of the mirror unit 11 (in other words, the deflection angle fluctuation range) from the deflection angle displacement wave calculated by the displacement wave calculation unit 51.

  When the maximum value of the deflection angle determined by the maximum deflection angle determination unit 53 is different from a predetermined target value, the correction value calculation unit 55 uses the first pulse signal to set the maximum value of the deflection angle to the target value. The correction value of the maximum value of is calculated.

  The mirror drive unit 17 is driven by the mirror drive unit 17 by the first pulse signal which is a drive signal, and the mirror unit 11 is vibrated. There is a phase difference between the first pulse signal and the deflection angular displacement wave. This phase difference is determined by the resonance frequency of the MEMS mirror. The phase difference determination unit 57 (an example of a determination unit) determines whether or not the phase difference between the first pulse signal and the deflection angular displacement wave is different from a predetermined target value.

  When the phase difference determination unit 57 determines that the phase difference is different from the target value, the correction value calculation unit 59 calculates a correction value for the phase of the first pulse signal in order to set the phase difference to the target value.

  The first pulse signal generation unit 61 outputs a first pulse signal serving as a drive signal to the mirror drive unit 17 at a predetermined cycle. In the present embodiment, the first pulse signal is a rectangular wave. However, the first pulse signal may be pulsed and is not limited to a rectangular wave. When the correction value calculating unit 55 calculates the correction value of the maximum value of the first pulse signal, the first pulse signal generating unit 61 corrects the maximum value of the first pulse signal, and the correction value is corrected by the correction value. The first pulse signal having the maximum value is output to the mirror drive unit 17 as a drive signal at a predetermined cycle. Further, when the correction value calculation unit 59 calculates the correction value of the phase of the first pulse signal, the first pulse signal generation unit 61 corrects the phase of the first pulse signal, and the correction value is corrected by the correction value. The first pulse signal having the same phase is output to the mirror drive unit 17 as a drive signal at a predetermined cycle.

  When the phase of the first pulse signal is corrected, the second pulse signal generation unit 63 temporarily generates the second pulse signal before this correction is performed. Specifically, the second pulse signal generation unit 63 includes a pulse center phase of a pulse synthesized with the second pulse signal in the first pulse signal, a phase of the pulse center of the second pulse signal, Are generated at different timings (for example, 90 degrees different). This will be described later.

  In the present embodiment, the second pulse signal is constituted by one rectangular wave, and the pulse width of the second pulse signal is the same as the pulse width of the first pulse signal. However, the second pulse signal may be pulsed and is not limited to a rectangular wave. The number of pulses of the second pulse signal is not limited to one. The pulse width of the second pulse signal may be different from the pulse width of the first pulse signal.

  When the mirror driving unit 17 operates with voltage, the first pulse signal and the second pulse signal are voltage signals, and when the mirror driving unit 17 operates with current, the first pulse signal and the second pulse signal are operated. The pulse signal becomes a current signal.

  The signal synthesizer 65 receives the first pulse signal and the second pulse signal. When the second pulse signal generator 63 generates the second pulse signal (that is, when the phase of the first pulse signal is corrected), the signal synthesizer 65 receives the first pulse signal and the second pulse signal. A signal synthesized with the pulse signal is generated and output as a drive signal. The signal synthesis unit 65 outputs the first pulse signal as a drive signal when the second pulse signal generation unit 63 does not generate the second pulse signal (that is, when the phase of the first pulse signal is not corrected). .

  The amplification unit 67 amplifies the drive signal output from the signal synthesis unit 65. The amplified drive signal is input to the mirror drive unit 17.

  A description will be given of correction of the phase of the first pulse signal when the phase difference determination unit 57 determines that the phase difference between the first pulse signal and the deflection angular displacement wave is different from a predetermined target value. FIG. 8 is a graph showing an example of the first pulse signal. The vertical axis represents the value (V) of the first pulse signal, and the horizontal axis represents time (seconds). The first pulse signal is a rectangular wave generated continuously, and has a maximum value of 1.0 V, a minimum value of -1.0 V, and a cycle of 0.001 seconds.

  In this example, at time 0.0015 seconds, correction is started to delay the phase of the first pulse signal by 2 μs. The phase change of the first pulse signal due to this is shown in FIG. FIG. 9 is a graph obtained by enlarging a section from time 0.00172 seconds to 0.00178 seconds in FIG. The vertical axis represents the value (V) of the first pulse signal, and the horizontal axis represents time (seconds). When the phase of the first pulse signal is corrected, the rise of the first pulse signal is delayed by 2 μs around the time of 0.00175 seconds compared to the case where the phase of the first pulse signal is not corrected.

  The deflection angle displacement wave will be described. FIG. 10 is a graph showing an example of the deflection angle displacement wave. The vertical axis indicates the deflection angle (rad) of the mirror unit 11, and the horizontal axis indicates time (seconds). The deflection angle displacement wave is a sine wave, the maximum value is about 1 rad, the minimum value is about -1 rad, and the period is 0.001 second.

  Next, the synthesis of the first pulse signal and the second pulse signal will be described. FIG. 11 is a graph illustrating an example of the second pulse signal. FIG. 12 is a graph showing an example of the first pulse signal combined with the second pulse signal. FIG. 13 is a graph showing an example of the first pulse signal obtained by synthesizing the second pulse signal. The vertical axis and horizontal axis in FIGS. 11 to 13 are the same as the vertical axis and horizontal axis in FIG. 8.

  Referring to FIG. 11, the second pulse signal is one isolated pulse, the maximum value is 0.1V, and the minimum value is 0V. The second pulse signal is generated in a period from 0.0010 seconds before the correction of the phase of the first pulse signal to 0.0015 seconds of the correction start.

  Referring to FIG. 11 and FIG. 12, the second pulse signal generation unit 63 generates a pulse generated at the end of the pulse train composed of the first pulse signal before the phase of the first pulse signal is corrected. The second pulse signal is generated at the timing of combining the two. The pulse combined with the second pulse signal may be a pulse of the first pulse signal before phase correction, and is not limited to the last generated pulse. The second pulse signal generation unit 63 generates a second pulse signal having the same pulse width as that of the first pulse signal. The pulse width refers to the length from the position of the rising edge of the pulse signal to the position of the falling edge, or the length from the position of the falling edge of the pulse signal to the position of the rising edge.

  The second pulse signal generation unit 63 determines that the phase of the pulse center of the pulse generated at the end of the pulse train constituting the first pulse signal before phase correction and the phase of the pulse center of the second pulse signal are 90. The second pulse signal is generated at different timings. The pulse center is a coordinate of a position obtained by adding the coordinates of the position of the rising portion of the pulse signal and the coordinates of the position of the falling portion and dividing by two. In the case of the second pulse signal, the coordinates of the location at time 0.00125 seconds are the pulse center. In the case of the last pulse of the first pulse signal, the coordinates of the location at time 0.0010 seconds are the pulse center.

  Referring to FIG. 13, the maximum value of the portion of the first pulse signal synthesized with the second pulse signal increases from 1.0 V to 1.1 V, and the minimum value decreases from −1.0 V to −0. It has risen to 9V.

  In this embodiment, in order to correct the phase of the first pulse signal in order to set the phase of the deflection angular displacement wave of the mirror unit 11 to the target value, the second pulse signal is generated before this correction, A signal obtained by synthesizing the first pulse signal and the second pulse signal before correction is output to the mirror drive unit 17 as a drive signal. As a result, the time required for the phase of the deflection angular displacement wave to reach the target value can be shortened. This will be described.

  At time 0.001500 seconds, correction for delaying the phase of the first pulse signal by 2 μs is started. The deflection angle displacement wave by this is shown in FIGS. FIG. 14 is a graph showing the deflection angular displacement wave at the correction time (0.001500 seconds). FIG. 15 is a graph showing the deflection angular displacement wave after 0.05 seconds have elapsed from the correction time. FIG. 16 is a graph showing the deflection angular displacement wave after 0.15 seconds from the correction time.

  14 to 16, the vertical axis indicates the deflection angle (rad) of the mirror unit 11, and the horizontal axis indicates time (seconds). FIG. 14 shows a section from time 0.001480 seconds to 0.001520 seconds. FIG. 15 shows a section from 0.051480 seconds to 0.051520 seconds after 0.05 seconds have elapsed. In FIG. 16, a section from time 0.151480 seconds to 0.151520 seconds after the lapse of 0.15 seconds is shown.

  The solid line in the graph shows the case of this embodiment, that is, the case where the phase of the first pulse signal is corrected after the second pulse signal is generated. The dotted line in the graph shows the case of the comparative example, that is, the case where the phase of the first pulse signal is corrected without generating the second pulse signal. A one-dot chain line in the graph indicates a case where the phase of the first pulse signal is not corrected.

  Referring to FIG. 14, in the case of the present embodiment, immediately after the start of correction of the phase of the first pulse signal, the phase of the deflection angular displacement wave can be delayed by 2 μs. On the other hand, referring to FIGS. 14 to 16, in the case of the comparative example, the phase of the deflection angular displacement wave is 2 μm even after 0.15 seconds have elapsed after the start of the correction of the phase of the first pulse signal. Can't delay seconds. That is, in the comparative example, even when the first pulse signal whose phase is corrected is input to the mirror driving unit 17, the mirror unit 11 does not respond immediately but responds with a delay.

  As described above, according to the present embodiment, when the phase of the first pulse signal that is the drive signal for driving the mirror unit 11 is corrected, it is combined with the second pulse signal in the first pulse signal. The phase of the pulse center of the second pulse signal and the phase of the pulse center of the second pulse signal are not the same but different. As a result, it is possible to cancel the component that causes the transient response included in the first pulse signal whose phase has been corrected, thereby suppressing a delay in the response of the mirror unit 11 with respect to the first pulse signal whose phase has been corrected. As a result, it is possible to shorten the time required for the phase of the deflection angular displacement wave to reach the target value. As described in the embodiment, according to the simulation performed by the present inventor, the phase of the pulse center of the pulse synthesized with the second pulse signal in the first pulse signal, and the second pulse signal It was confirmed that the time for reaching the target value of the phase of the deflection angular displacement wave could be shortened if the phase at the pulse center was different by 90 degrees.

  In the present embodiment, the phase difference between the deflection angular displacement wave and the first pulse signal has been described as an example of the phase of the deflection angular displacement wave. However, the present invention is not limited to this. For example, the phase difference between another reference signal and the deflection angular displacement wave may be used, or the phase of the deflection angular displacement wave itself may be used instead of the phase difference.

  In the present embodiment, the first pulse signal and the second pulse signal before correction are combined. However, the present invention is not limited to this. For example, the second pulse signal generation unit is configured as described above. The optical scanning device 3 may be configured to generate a corresponding pulse signal later and switch the second pulse signal generation unit and the first pulse signal generation unit 61. Then, immediately before the correction, the signal switching unit may switch the first pulse signal generation unit to the second pulse signal generation unit to generate a pulse signal as shown in FIG.

  Next, the image forming apparatus 1 to which the optical scanning device 3 according to the present embodiment is applied will be described. Referring to FIG. 3, a light beam LB emitted from light source 31 is scanned on photosensitive drum 113 (an example of an image carrier) to form an electrostatic latent image. The optical scanning device 3 (FIG. 7) according to the present embodiment performs one-side main scanning to form an electrostatic latent image. In one-side main scanning, main scanning is performed in which the photosensitive drum 113 is scanned in the main scanning direction with the light beam LB from one side 113a to the other side 113b. This means that the photosensitive drum 113 is not scanned toward the side portion 113a. According to one-side main scanning, the image forming speed is inferior to that of both-side main scanning, but the image reproducibility can be improved.

  When the phase of the first pulse signal is corrected, after the main scan is finished, before the next main scan is started (in other words, after the main scan is finished, the deflection of the mirror unit 11 is performed to perform the next main scan). The second pulse signal generator 63 generates a second pulse signal during a period in which the angle fluctuates, and the first pulse signal generator 61 generates a first pulse signal whose phase has been corrected. Is generated.

  The operation of the image forming apparatus 1 to which the optical scanning device 3 according to the present embodiment is applied will be mainly described with reference to FIG. 3, FIG. 7, and FIG. FIG. 17 is a flowchart for explaining the operation. The image forming apparatus 1 starts an image forming operation (step S1). The image forming operation is an operation for executing a copy job, a printer job, or the like. This operation includes the following operation of scanning the photosensitive drum 113 with the light beam LB. The first pulse signal generation unit 61 generates a first pulse signal, and the first pulse signal is input to the mirror driving unit 17. Thereby, the mirror drive part 17 drives the mirror part 11, and makes the mirror part 11 resonate. In a state where the mirror unit 11 resonates, the light source 31 emits a light beam LB modulated corresponding to the image data. The light beam LB is reflected and deflected by the mirror unit 11 to scan the rotating photosensitive drum 113.

  The phase difference determination unit 57 determines whether or not the phase difference between the first pulse signal and the deflection angular displacement wave is different from the target value (step S2). When the phase difference determination unit 57 determines that the phase difference is different from the target value (Yes in step S2), the correction value calculation unit 59 corrects the phase of the first pulse signal in order to set the phase difference to the target value. Calculate the value. Then, after the main scanning ends (that is, after the output of the light beam LB corresponding to the image data), the control unit 500 starts the next main scanning (that is, outputs the light beam LB corresponding to the next image data). It is determined whether or not it is a period before starting (step S3).

  When the control unit 500 does not determine the period before the start of the next main scan after the end of the main scan (No in step S3), in other words, when it is determined that the period is during the main scan, step S3 is repeated.

  When the control unit 500 determines that the period before the start of the next main scan after the end of the main scan (Yes in step S3), the second pulse signal generation unit 63 outputs the second pulse signal of one pulse. First, the first pulse signal generator 61 starts outputting the first pulse signal whose phase has been corrected (step S4). Thereby, the phase difference is adjusted to the target value.

  The controller 500 determines whether the printing of the image has been completed (step S5). When the control unit 500 determines that the image printing is finished (Yes in step S5), the control unit 500 finishes the image forming operation. If the controller 500 does not determine that printing of the image has been completed (No in step S5), the process returns to step S2.

  When the phase difference determination unit 57 does not determine that the phase difference is different from the target value (No in step S2), in other words, when the phase difference matches the target value, the process proceeds to step S5.

  The image forming apparatus 1 to which the optical scanning device 3 according to the present embodiment is applied has the following effects. The phase of the first pulse signal is corrected during a period of main scanning of the photosensitive drum 113 from one side 113a to the other side 113b (that is, a period during which the light beam LB corresponding to image data is output). As a result, the phase of the deflection angular displacement wave changes during the main scanning period, which may reduce the reproducibility of the image. According to the image forming apparatus 1, when the phase of the first pulse signal is corrected, after the main scan is finished, before the next main scan is started (in other words, after the main scan is finished, the next main scan is performed). Therefore, during the period when the deflection angle of the mirror unit 11 is fluctuating, a second pulse signal is generated, and a first pulse signal whose phase is corrected is generated. Therefore, the next time when the photosensitive drum 113 is main-scanned from one side 113a to the other side 113b, the phase difference can be adjusted to the target value, so that the reproducibility of the image is lowered. Can be prevented.

  In particular, this embodiment is effective for a tandem type image forming apparatus. The tandem type refers to an image forming apparatus 1 as shown in FIG. The image forming apparatus 1 includes four photosensitive drums 113 arranged in tandem. The four photosensitive drums 113 are the photosensitive drum 113 of the yellow image forming unit 111Y, the photosensitive drum 113 of the magenta image forming unit 111M, the photosensitive drum 113 of the cyan image forming unit 111C, and the photosensitive drum of the black image forming unit 111BK. 113. The image forming apparatus 1 further includes four developing units 121 provided corresponding to the four photosensitive drums 113 and four exposure units 115 provided corresponding to the four photosensitive drums 113, respectively. (Optical scanning device 3) and a transfer belt 117 on which a color toner image is formed by transferring toner images formed on the four photosensitive drums 113 in a superimposed manner.

  In the tandem type, the optical scanning device 3 is provided according to a plurality of colors (for example, yellow, cyan, magenta, and black) constituting the color. In these optical scanning devices 3, if the phases of the deflection angular displacement waves do not match, color deviation occurs in the color image. Since the optical scanning device 3 according to this embodiment is applied to the tandem-type image forming apparatus 1, the target value is reached when the phase of the deflection angular displacement wave is corrected in each of the four optical scanning devices 3. The time to do can be shortened.

  In the above embodiment, the case where the present invention is applied to the image forming apparatus has been described. However, the present invention is not limited to the image forming apparatus, and may be applied to an optical scanning apparatus such as a projector, a barcode reader, or a laser microscope. You can also.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 3 Optical scanning device 10 Optical deflection part 11 Mirror part 17 (17a, 17b, 17c, 17d) Mirror drive part 31 Light source 57 Phase difference determination part (an example of determination part)
113 Photosensitive drum (an example of an image carrier)
115 Exposure unit 117 Transfer belt LB Light beam

Claims (9)

A mirror for deflecting the light beam;
A mirror drive unit for driving and vibrating the mirror unit with a driving force according to an input drive signal;
A displacement wave computing unit that computes a deflection angle displacement wave in which the displacement of the deflection angle of the mirror unit that is vibrated by the mirror drive unit is represented in a wave shape along the time axis;
A determination unit for determining whether or not the phase of the deflection angle displacement wave is different from a predetermined target value;
When it is determined that the phase is different from the target value, a correction value calculation unit that calculates a correction value of the phase of the first pulse signal serving as the drive signal in order to set the phase to the target value;
When the first pulse signal is output to the mirror drive unit as the drive signal at a predetermined cycle and the correction value is calculated, the phase of the first pulse signal is corrected, and the correction value A first pulse signal generation unit that outputs the first pulse signal having a phase corrected by the above-described period as the drive signal to the mirror drive unit at the predetermined period;
A second pulse signal generator that temporarily generates a second pulse signal before the correction when the phase of the first pulse signal is corrected;
The second pulse signal generation unit may change the phase of the pulse center of the first pulse signal before the correction and the phase of the pulse center of the second pulse signal at different timings. An optical scanning device that generates two pulse signals and outputs the second pulse signal to the mirror driving unit. The optical scanning device according to claim 1,
A signal synthesizing unit that generates a signal obtained by synthesizing the first pulse signal and the second pulse signal before the correction, and outputs the signal as the driving signal to the mirror driving unit;
The second pulse signal generation unit includes a phase of a pulse center of a pulse synthesized with the second pulse signal in the first pulse signal, a phase of a pulse center of the second pulse signal, An optical scanning device that generates the second pulse signal at a timing that can be varied.   The second pulse signal generation unit includes a phase of a pulse center of a pulse synthesized with the second pulse signal in the first pulse signal, a phase of a pulse center of the second pulse signal, The optical scanning device according to claim 2, wherein the second pulse signal is generated at a timing at which the second pulse signal can be varied by 90 degrees.   The optical scanning device according to claim 1, wherein the second pulse signal generation unit generates the second pulse signal configured by a rectangular wave.   2. The second pulse signal generation unit generates the second pulse signal at a timing that is combined with a pulse generated at the end of a pulse train composed of the first pulse signal before correction. The optical scanning apparatus as described in any one of -4.   6. The optical scanning device according to claim 1, wherein the second pulse signal generation unit generates the second pulse signal having the same pulse width as the pulse width of the first pulse signal. 7. . A light source that emits a light beam modulated in accordance with image data;
An image carrier;
The optical scanning device according to any one of claims 1 to 6, wherein the image bearing member is scanned with the light beam emitted from the light source to form an electrostatic latent image;
An image forming apparatus comprising: a developing unit that supplies toner to the image carrier on which the electrostatic latent image is formed to form a toner image. The image carrier has one side and the other side,
The optical scanning device performs main scanning for scanning the image carrier in the main scanning direction with the light beam from the one side to the other side, and from the other side Performing a one-side main scan not scanning the image carrier toward one side,
When the phase of the first pulse signal is corrected, the second pulse signal generation unit generates the second pulse signal after the main scan ends and before the next main scan starts. The image forming apparatus according to claim 7, wherein the first pulse signal generation unit generates the corrected first pulse signal. A plurality of the image carriers arranged in tandem;
A plurality of the developing units provided corresponding to each of the plurality of image carriers;
A plurality of the optical scanning devices provided corresponding to each of the plurality of image carriers;
The image forming apparatus according to claim 7, further comprising: a transfer belt on which a color toner image is formed by superimposing and transferring the toner images formed on the plurality of image carriers.

Images