JP2009186778A - Optical scanning device and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanning device in which the amplitude of the oscillation of a scanning mirror which scans a photoreceptor drum with light by oscillating at a mechanical resonance frequency can be corrected, and to provide an image forming apparatus using the optical scanning device. <P>SOLUTION: The optical scanning device includes: a time lag measurement part 211 and a mean processing part 212 which detect the time lag of the timing detected by light beams at optical sensors BD1 and BD2 in either one direction when a photoreceptor drum 43 is reciprocally scanned with an MEMS mirror 420, and obtain the actual scanning time on the basis of the time lag; and a bias voltage calculation part 213 which increases the amplitude of oscillation of the MEMS mirror 420 when the actual scanning time obtained by the mean processing part 212 is longer than a predetermined target scanning time, and reduces the amplitude of oscillation of the MEMS mirror 420 when the actual scanning time is shorter than the target scanning time. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical scanning apparatus that exposes a photosensitive drum used for image formation, and an image forming apparatus using the same.

  Conventionally, in an image forming apparatus such as a printer, a facsimile, or a copying machine, laser light emitted from a semiconductor laser is incident on a polygon mirror that rotates at high speed, and the photosensitive drum is scanned by the laser light reflected by the polygon mirror. An optical scanning device that forms an electrostatic latent image on the surface of a photosensitive drum is known (for example, see Patent Document 1).

An optical scanning device using a micro electro mechanical system (MEMS) mirror in which a mirror surface is formed on a substrate surface by a semiconductor process instead of the polygon mirror as described above is also known (for example, see Patent Document 2). . The MEMS mirror is superior to the polygon mirror in performance such as jitter and surface tilt. The MEMS mirror vibrates at a mechanical vibration frequency, thereby changing the swing angle and scanning the laser beam.
Japanese Patent Application Laid-Open No. 2002-166592 JP 2005-308820 A

  However, since the mechanical vibration frequency of the MEMS mirror greatly depends on the temperature of the device, the resonance frequency changes when the temperature of the MEMS mirror changes, thereby causing a disadvantage that the amplitude (swing angle) changes greatly. there were.

  The present invention has been made in view of such circumstances, and an optical scanning device capable of correcting the amplitude of a scanning mirror that scans a photosensitive drum with a light beam by vibrating at a mechanical resonance frequency, and An object of the present invention is to provide an image forming apparatus using the same.

  An optical scanning device according to the present invention outputs a light beam for exposing a photosensitive drum that forms an electrostatic latent image by being exposed with a light beam representing a scanning line of an image, and is output from the light source. A scanning mirror that reflects the light beam and vibrates at a mechanical resonance frequency to scan the photosensitive drum with the light beam, a drive unit that vibrates the scanning mirror, and an image of the image scanned on the photosensitive drum. A first optical sensor disposed at a predetermined position on the start side of the scanning line; a second optical sensor disposed at a predetermined position on the end side of the scanning line of the image scanned by the photosensitive drum; One of the case where the light beam is scanned by the scanning mirror in the image scanning direction which is the scanning direction of the scanning line of the image and the case where the light beam is scanned in the direction opposite to the image scanning direction. Only in this case, an actual scan is performed in which a time difference between the timing at which the light beam is detected by the first optical sensor and the timing at which the light beam is detected by the second optical sensor is detected, and an actual scanning time is obtained based on the time difference. When the actual scanning time acquired by the time acquisition unit and the actual scanning time acquisition unit is longer than a preset target scanning time, the amplitude of the scanning mirror is increased and the actual scanning time acquired by the actual scanning time acquisition unit is increased. And an amplitude adjustment unit that performs amplitude adjustment to reduce the amplitude of the scanning mirror when the scanning time is shorter than the target scanning time.

  According to this configuration, the first optical sensor is disposed at a predetermined position on the start side of the scanning line of the image scanned on the photosensitive drum. The second optical sensor is disposed at a predetermined position on the end side of the scanning line of the image scanned on the photosensitive drum. Then, when the light beam is scanned by the actual scanning time acquisition unit in the image scanning direction that is the scanning direction of the scanning line of the image, or when the light beam is scanned in the direction opposite to the image scanning direction, Only in this case, the time difference between the timing when the light beam is detected by the first optical sensor and the timing when the light beam is detected by the second optical sensor is detected, and the actual scanning time is obtained based on the time difference.

  The scanning mirror that reflects the light beam by vibrating at the mechanical resonance frequency reciprocates the light beam when scanning the photosensitive drum. For this reason, when the light beam is detected by the first and second photosensors after passing through the light receiving unit of the first and second photosensors in the image scanning direction, the light receiving unit of the first and second photosensors is scanned. In some cases, the light beam is detected by the first and second optical sensors after passing in the opposite direction. On the other hand, the optical sensor may have a difference in the detection timing of the light depending on the direction in which the light passes through the light receiving unit. Therefore, if a light beam is scanned in the image scanning direction, which is the scanning direction of the scanning line of the image, and a light beam is scanned in a direction opposite to the image scanning direction, a time difference is detected in both cases. May cause variations in the detected time difference.

  Therefore, the actual scanning time acquisition unit only includes the first optical sensor in either one of the case where the light beam is scanned in the image scanning direction and the case where the light beam is scanned in the direction opposite to the image scanning direction. The time difference between the timing at which the light beam is detected in step 2 and the timing at which the second light sensor detects the light beam is detected, and the actual scanning time is acquired based on this time difference. As a result, it is possible to improve the accuracy in obtaining the actual scanning time.

  The amplitude adjustment unit is configured to reduce the scanning speed of the light beam when the actual scanning time acquired by the actual scanning time acquisition unit is longer than the preset target scanning time, that is, the scanning mirror amplitude is smaller than a specified value. If this is considered, the amplitude of the scanning mirror is corrected so as to approach the specified value by increasing the amplitude of the scanning mirror. On the other hand, when the actual scanning time acquired by the actual scanning time acquisition unit is shorter than the target scanning time, that is, when it is considered that the scanning mirror amplitude is larger than the specified value and the scanning speed of the light beam is increased, the amplitude adjustment is performed. The unit corrects the amplitude of the scanning mirror so as to approach a specified value by decreasing the amplitude of the scanning mirror. Thereby, the amplitude of the scanning mirror that scans the photosensitive drum with the light beam can be corrected by oscillating at the mechanical resonance frequency.

  Further, it is preferable that the actual scanning time acquisition unit acquires the actual scanning time only when the light beam is scanned in the image scanning direction by the scanning mirror.

  According to this configuration, only when the light beam is scanned in the image scanning direction by the scanning mirror, the actual scanning time is acquired by the actual scanning time acquisition unit. Therefore, in the same direction as when image formation is actually performed. The time difference when the light beam is scanned is directly measured, and the difference between the time difference when the image is formed and the time difference when the amplitude of the scanning mirror is reduced is reduced. It becomes possible to improve.

  The first photosensor includes a plurality of photodetecting elements, and performs temperature compensation based on detection signals from the plurality of photodetecting elements. The second photosensor includes a plurality of photodetecting elements. It is preferable that temperature compensation is performed based on detection signals from the plurality of light detection elements.

  According to this configuration, the first light sensor includes a plurality of light detection elements, performs temperature compensation based on detection signals from the plurality of light detection elements, and the second light sensor includes a plurality of light detection elements. Since the temperature compensation is performed based on the detection signals from the plurality of photodetecting elements, the possibility that the detection accuracy of the light beam in the first and second photosensors decreases due to the temperature change is reduced. The possibility that the detection accuracy of the time difference by the acquisition unit is reduced is reduced.

  Further, it is preferable that the actual scanning time acquisition unit detects the time difference a plurality of times and acquires an average value of the plurality of time differences as the actual scanning time.

  According to this configuration, the actual scanning time acquisition unit detects the time difference a plurality of times, and an average value of the plurality of time differences is acquired as the actual scanning time. It is possible to reduce the error due to the variation in the time difference and improve the acquisition accuracy of the actual scanning time than when using it as the scanning time.

  Further, the drive unit superimposes a periodic signal, the frequency of which is set to coincide with the mechanical resonance frequency of the scanning mirror, on a predetermined DC voltage, and supplies the scanning mirror to the scanning mirror. The amplitude adjustment unit adjusts the amplitude by increasing the amplitude of the scanning mirror by increasing the DC voltage and decreasing the amplitude of the scanning mirror by decreasing the DC voltage. It is preferable.

  According to this configuration, a periodic signal whose frequency is set to match the mechanical resonance frequency of the scanning mirror by the drive unit is superimposed on the predetermined DC voltage and supplied to the scanning mirror, thereby causing the scanning mirror to Vibrates. Then, when the DC voltage component supplied to the scanning mirror increases, the amplitude of the scanning mirror increases, and when the DC voltage component decreases, the amplitude of the scanning mirror decreases. Therefore, the amplitude adjusting unit can increase the amplitude of the scanning mirror by increasing the DC voltage, and can decrease the amplitude of the scanning mirror by decreasing the DC voltage.

  An image forming apparatus according to the present invention includes the above-described optical scanning device, the photosensitive drum, a paper transport unit that supplies paper to the photosensitive drum, and an electrostatic latent image formed on the photosensitive drum. And an image forming unit that forms an image on the sheet supplied by the sheet conveying unit.

  According to this configuration, the amplitude of the scanning mirror that scans the photosensitive drum with the light beam can be corrected by oscillating at the mechanical resonance frequency by the above-described optical scanning device. Then, the photosensitive drum is exposed by the scanning mirror whose amplitude is corrected, whereby an electrostatic latent image is formed on the photosensitive drum, and an image is formed on the sheet based on the electrostatic latent image. The risk that the amplitude of the scanning mirror changes due to the change and the image quality deteriorates is reduced.

  In the optical scanning device, execution of amplitude adjustment by the amplitude adjustment unit is prohibited during a period in which exposure of the photosensitive drum related to image formation on one sheet of paper conveyed by the paper conveyance unit is executed. It is preferable to further include an amplitude adjustment prohibition unit.

  According to this configuration, execution of amplitude adjustment by the amplitude adjustment unit is prohibited during a period in which exposure of the photosensitive drum related to image formation on one sheet of paper conveyed by the paper conveyance unit in the optical scanning device is performed. Therefore, the possibility that the amplitude of the scanning mirror changes in the middle of the image formed on one sheet and the image is displaced is reduced.

  The optical scanning device having such a configuration can correct the amplitude of the scanning mirror that scans the photosensitive drum with the light beam by vibrating at the mechanical resonance frequency.

  Further, in the image forming apparatus having such a configuration, an electrostatic latent image is formed on the photosensitive drum by exposing the photosensitive drum by the scanning mirror whose amplitude is corrected by the optical scanning device. Since the image is formed on the paper based on the image, the possibility that the amplitude of the scanning mirror changes due to the temperature change and the image quality deteriorates is reduced.

  Embodiments according to the present invention will be described below with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted. FIG. 1 is a structural diagram schematically showing an internal configuration of a copying machine as an example of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram showing an example of the electrical configuration of the copying machine 1 shown in FIG. The image forming apparatus is not limited to a copying machine, but may be a printer, a facsimile, or a multifunction machine having these functions.

  The copying machine 1 includes a main unit 2, a stack tray 3 disposed on the left side of the main unit 2, a document reading unit 5 disposed on the top of the main unit 2, and an upper side of the document reading unit 5. A document feeding unit 6 disposed and a control unit 100 disposed inside the main body unit 2 are provided.

  A substantially rectangular operation panel 47 is provided at the front of the copying machine 1. The operation panel unit 47 includes a display unit 473 and an operation key unit 476. The display unit 473 is configured by, for example, a liquid crystal display having a touch panel function. The operation key unit 476 includes various key switches such as a start key for the user to input a print execution instruction and a numeric keypad for inputting the number of copies to be printed.

  The document reading unit 5 includes a scanner unit 51 including a CCD (Charge Coupled Device) 512, an exposure lamp 511, and the like, and a document table 52 and a document reading slit 53 made of a transparent member such as glass. The scanner unit 51 is configured to be movable by a drive unit (not shown). When reading a document placed on the document table 52, the scanner unit 51 is moved along the document surface at a position facing the document table 52, and the document image is scanned. The image data acquired while scanning is output to the control unit 100. Further, when reading a document fed by the document feeding unit 6, the document is moved to a position facing the document reading slit 53 and synchronized with the document feeding operation by the document feeding unit 6 via the document reading slit 53. The image of the original is acquired and the image data is output to the control unit 100.

  The document feeding unit 6 includes a document placing unit 61 for placing a document, a document discharge unit 62 for discharging a document whose image has been read, and a document placed on the document placing unit 61. A document transport mechanism 63 is provided that feeds the sheets one by one to transport them to a position facing the document reading slit 53 and discharges them to the document discharge section 62.

  The main body 2 includes a plurality of paper feed cassettes 461, a paper feed roller 462 that feeds the paper from the paper feed cassette 461 one by one and transports it to the image forming unit 40, and an image on the paper carried out from the paper feed cassette 461. And an image forming unit 40 that controls the operation of the entire apparatus.

  The image forming unit 40 includes a paper transport unit 411, an optical scanning device 42, a photosensitive drum 43, a developing unit 44, a transfer unit 41, and a fixing unit 45. The paper transport unit 411 is provided in the paper transport path in the image forming unit 40, and includes a transport roller 412 that supplies the paper transported by the paper feed roller 462 to the photosensitive drum 43, and a paper sheet that is discharged from the stack tray 3. Conveying rollers 463 and 464 that convey to the tray 48 are provided.

  The optical scanning device 42 forms an electrostatic latent image on the photosensitive drum 43 by outputting laser light or the like based on the image data output from the control unit 100 and exposing the photosensitive drum 43. The developing unit 44 develops the electrostatic latent image on the photosensitive drum 43 with toner to form a toner image. The transfer unit 41 transfers the toner image on the photosensitive drum 43 to a sheet. The fixing unit 45 heats the sheet on which the toner image is transferred to fix the toner image on the sheet.

  In this case, the developing unit 44, the transfer unit 41, and the fixing unit 45 correspond to an example of an image forming unit in claims.

  The control unit 100 includes, for example, a CPU (Central Processing Unit) that executes predetermined arithmetic processing, a ROM (Read Only Memory) that stores a predetermined control program, and a RAM (Random Access Memory) that temporarily stores data. And these peripheral circuits and the like. The control unit 100 is connected to the document reading unit 5, the image forming unit 40, the operation panel unit 47, and an HDD (Hard Disk Drive) 150. The control unit 100 functions as a copy control unit 101 and an amplitude adjustment control unit 111 (amplitude adjustment prohibition unit) by executing a control program stored in the ROM, the HDD 150, or the like.

  A copy control unit 101 controls the operation of each unit in the apparatus to execute copying of a document image. Specifically, the copy control unit 101 transmits image data read from the document by the document reading unit 5 to the image forming unit 40, and causes the image forming unit 40 to perform image formation of the image.

  The amplitude adjustment control unit 111 performs amplitude adjustment in the optical scanning device 42 during a period in which exposure of the photosensitive drum 43 related to image formation on one sheet of paper conveyed by the paper conveyance unit 411 in the optical scanning device 42 is executed. Is prohibited.

  FIG. 3 is an explanatory diagram for explaining an example of the configuration of the optical scanning device 42 according to an embodiment of the present invention. The optical scanning device 42 shown in FIG. 3 includes an optical sensor BD1 (first optical sensor), an optical sensor BD2 (second optical sensor), a laser diode LD (light source), and a MEMS mirror 420 (scanning mirror). The optical sensor BD1 is disposed in the vicinity of the end of the photosensitive drum 43 on the start side in the image scanning line. The optical sensor BD2 is disposed in the vicinity of the end of the photosensitive drum 43 on the end side in the scanning line of the image.

  Each of the optical sensors BD1 and BD2 includes a plurality of light detection elements, and performs temperature compensation based on detection signals from the plurality of light detection elements. As the optical sensors BD1 and BD2, for example, model S-9684 manufactured by Hamamatsu Photonics Co., Ltd. can be used. The optical sensors BD1 and BD2 having such a configuration can accurately detect the detection timing of the laser light with temperature compensation.

  The optical scanning device 42 scans the photosensitive drum 43 by reflecting the laser beam output from the laser diode LD by oscillating at a mechanical resonance frequency in accordance with a drive signal output from a driver circuit 224 described later. It is like that. When the scanned laser beams are applied to the optical sensors BD1 and BD2, detection signals indicating the detection timing of the laser beams are output from the optical sensors BD1 and BD2 to the time difference measuring unit 211 described later.

  FIG. 4 is a block diagram showing an example of the electrical configuration of the optical scanning device 42 shown in FIG. The optical scanning device 42 shown in FIG. 4 includes optical sensors BD1 and BD2, a laser diode LD, a MEMS mirror 420, a scanning control unit 421, a driving unit 422, and a switching element 423. The optical sensors BD 1 and BD 2 and the laser diode LD are connected to the scanning control unit 421, and the MEMS mirror 420 is connected to the driving unit 422.

  The scanning control unit 421 includes, for example, a CPU that executes predetermined arithmetic processing, a ROM that stores a predetermined control program, a RAM that temporarily stores data, a timer circuit that measures time, peripheral circuits thereof, and the like. Configured. The scan control unit 421 functions as an LD control unit 210, a time difference measurement unit 211, an average processing unit 212, and a bias voltage calculation unit 213 by executing a control program stored in the ROM or the like.

  For example, the control unit 100 may function as the scanning control unit 421 by executing a predetermined control program. The optical scanning device 42 may include the amplitude adjustment control unit 111.

  When executing image formation, the LD control unit 210 generates a signal representing a scanning line from the image data transmitted from the copy control unit 101 and outputs the signal to the laser diode LD. Thereby, the LD control unit 210 irradiates the MEMS mirror 420 with laser light representing the scanning line of the image data from the laser diode LD.

  The operation of the LD control unit 210 when adjusting the amplitude (swing angle) of the MEMS mirror 420 and the operations of the time difference measurement unit 211, the average processing unit 212, and the bias voltage calculation unit 213 will be described later.

  The drive unit 422 includes a drive clock generation unit 221, a DA converter 222, a superimposing circuit 223, and a driver circuit 224 configured using, for example, an oscillation circuit. The DA converter 222 is connected to the bias voltage calculation unit 213 via the switching element 423. The drive unit 422 causes the MEMS mirror 420 to vibrate at the mechanical resonance frequency fc. Further, the drive unit 422 adjusts the amplitude (swing angle) of the MEMS mirror 420 according to the voltage value set in the DA converter 222 by the bias voltage calculation unit 213.

  FIG. 5 is an explanatory diagram for explaining the operation of the drive clock generator 221 shown in FIG. The drive clock generation unit 221 is an oscillation circuit that generates a clock signal CLK (periodic signal) having a frequency set in advance so as to match the mechanical resonance frequency fc of the MEMS mirror 420. The cycle of the clock signal CLK is set to tcyc = 1 / fc.

  FIG. 6 is an explanatory diagram for explaining the operation of the DA converter 222 shown in FIG. The DA converter 222 outputs the DC voltage of the voltage Vb set by the bias voltage calculation unit 213 to the superposition circuit 223 as the bias voltage Vbias.

  FIG. 7 is an explanatory diagram for explaining the operation of the superposition circuit 223 shown in FIG. The superimposing circuit 223 outputs the driving voltage Vm obtained by superimposing the clock signal CLK generated by the driving clock generation unit 221 on the bias voltage Vbias output from the DA converter 222 to the driver circuit 224.

  The driver circuit 224 outputs the drive voltage Vm output from the superimposing circuit 223 to the MEMS mirror 420 to vibrate the MEMS mirror 420. In this case, the amplitude of the MEMS mirror 420, that is, the swing angle A shown in FIG. 3, increases as the bias voltage Vbias, which is a DC voltage component included in the drive voltage Vm, increases, and decreases as the bias voltage Vbias decreases. Accordingly, the drive unit 422 can adjust the swing angle A of the MEMS mirror 420 according to the set value of the bias voltage Vbias set by the bias voltage calculation unit 213.

  Next, an example of the operation of the copying machine 1 configured as described above will be described. FIG. 8 is a flowchart showing an example of the operation of the copying machine 1 shown in FIG. First, for example, when the power of the copying machine 1 is turned on, or during continuous printing on a plurality of sheets, between the sheets (for example, every time image formation is performed for one sheet), the optical scanning device 42 performs photosensitivity. When the exposure of the body drum 43 is not executed (NO in step S1), the amplitude adjustment control unit 111 outputs a control signal instructing the amplitude adjustment of the MEMS mirror 420 to the optical scanning device 42.

  Then, the switching element 423 is turned on according to the control signal from the amplitude adjustment control unit 111 (step S2). Then, amplitude adjustment processing by the scanning control unit 421 and the drive unit 422 is executed as follows.

  First, when adjusting the amplitude (swing angle) of the MEMS mirror 420, the LD control unit 210 continues the light emission of the laser diode LD, for example, for a preset period.

  Next, the time difference measuring unit 211 receives a laser beam detection signal from the optical sensors BD1 and BD2. Then, the time difference measuring unit 211 measures a time difference Δt from when the laser light is detected by the optical sensor BD1 until the laser light is detected by the optical sensor BD2, for example, using a timer circuit (step S3).

  By the way, the MEMS mirror 420 scans the laser beam by oscillating at the swing angle A shown in FIG. 3, so that the laser beam reciprocates on the photosensitive drum 43. At this time, if an optical sensor provided with a plurality of photodetecting elements for temperature compensation is used like the photosensors BD1 and BD2, in the image scanning direction due to the arrangement position of the plurality of photodetecting elements in each photosensor. There is a possibility that the timing at which the laser light is detected by the optical sensors BD1 and BD2 may be different between when the laser light is scanned and when the laser light is scanned in the direction opposite to the image scanning direction.

  Therefore, the time difference measuring unit 211 uses the optical sensor BD1 only in one of the case where the laser beam is scanned in the image scanning direction and the case where the laser beam is scanned in the opposite direction to the image scanning direction. It is preferable to detect a time difference Δt between the timing when the laser beam is detected and the timing when the laser beam is detected by the optical sensor BD2. Thereby, variation in the laser light detection timing in the optical sensors BD1 and BD2 due to the difference in the scanning direction of the laser light is reduced, so that the detection accuracy of the time difference Δt can be improved.

  In addition, since it is possible to improve the detection accuracy of the time difference Δt while using an optical sensor having a plurality of light detection elements for temperature compensation as the optical sensors BD1 and BD2, a detection error of the time difference Δt due to the influence of temperature. Can be easily reduced.

  Note that the phenomenon in which the detection timing of the light beam varies depending on the direction in which the light beam is scanned is significant in a photosensor having a plurality of photodetection elements for temperature compensation, but the same phenomenon also occurs in other photosensors. The photosensors BD1 and BD2 are not limited to those having a plurality of photodetecting elements for temperature compensation.

  Further, when the image formation is actually performed, the laser beam is scanned in the image scanning direction. Therefore, only when the laser beam is scanned in the same image scanning direction as the image formation is performed, the time difference Δt More preferably, the time difference from when the laser beam is detected by the optical sensor BD1 until the laser beam is detected by the optical sensor BD2 is measured as the time difference Δt.

  In this case, since the time difference Δt when the laser beam is scanned in the same direction as when the image is actually formed can be directly measured, the time difference Δt when the image is formed and the amplitude adjustment of the MEMS mirror 420 are adjusted. As a result of the reduction in deviation from the time difference Δt when performing, it is possible to improve the accuracy of amplitude adjustment.

  Next, the average processing unit 212 performs a scan within a preset time, for example, about 1 to 10 seconds, or a preset number of scan lines, for example, 100 lines or one sheet of scan lines. An average time Δtave is calculated by averaging the time differences Δt measured a plurality of times by the time difference measuring unit 211 (step S4). Thereby, the variation in the time difference Δt is absorbed as the average time Δtave, and the detection accuracy of the scanning time from the optical sensor BD1 to the optical sensor BD2 can be improved.

  Thereafter, since the amplitude of the MEMS mirror 420 is adjusted based on the average time Δtave thus obtained, the MEMS mirror 420 is improved by improving the detection accuracy of the scanning time from the optical sensor BD1 to the optical sensor BD2. The accuracy of the amplitude adjustment can be improved.

  Next, the bias voltage calculator 213 compares the average time Δtave calculated by the average processor 212 with the target scan time ts set in advance as the actual scan time (step S5). If the average time Δtave is equal to the target scanning time ts (“=” in step S5), the amplitude of the MEMS mirror 420 is equal to the target value. Therefore, it is not necessary to change the amplitude of the MEMS mirror 420. The amplitude adjustment process of the MEMS mirror 420 is terminated.

  When the average time Δtave is longer than the preset target scanning time ts (“>” in step S5), the amplitude of the MEMS mirror 420 becomes smaller than the target value, and the scanning speed of the laser light is slow. Therefore, the bias voltage calculation unit 213 increases the amplitude of the MEMS mirror 420 by changing the set value of the DA converter 222 and increasing the bias voltage Vbias (step S6).

  On the other hand, when the average time Δtave is shorter than the target scanning time ts (“<” in step S5), the bias voltage calculation unit 213 makes the amplitude of the MEMS mirror 420 larger than the target value, and the scanning speed of the laser light is high. Therefore, the bias voltage calculation unit 213 changes the setting value of the DA converter 222 to reduce the bias voltage Vbias, thereby reducing the amplitude of the MEMS mirror 420 (step S7).

  As a result, the bias voltage calculation unit 213 adjusts the output voltage Vb of the DA converter 222 so that the average time Δtave and the target scanning time ts coincide with each other. As a result, the amplitude of the MEMS mirror 420 is set to a predetermined specified value. It is adjusted to be constant in amplitude. In this case, the time difference measurement unit 211 and the average processing unit 212 correspond to an example of an actual scanning time acquisition unit, and the bias voltage calculation unit 213 corresponds to an example of an amplitude adjustment unit.

  Next, a period during which the image forming operation by the copy control unit 101 is being executed, more specifically, a period during which the photosensitive drum 43 is exposed for one sheet in the optical scanning device 42 (step S1). YES), the amplitude adjustment control unit 111 outputs a control signal for prohibiting the amplitude adjustment of the MEMS mirror 420 to the optical scanning device 42. Then, the switching element 423 is turned off according to the control signal from the amplitude adjustment control unit 111 (step S8).

  When the switching element 423 is turned off, the transmission path of the control signal from the bias voltage calculation unit 213 to the DA converter 222 is interrupted, so that the bias voltage calculation unit 213 outputs the voltage of the bias voltage Vbias output from the DA converter 222. As a result of the inability to change Vb, amplitude adjustment of the MEMS mirror 420 is prohibited.

  If the amplitude of the MEMS mirror 420 is adjusted and changed during the formation of an image on a single sheet, the width of the image in the main scanning direction changes midway, and the image is shifted. However, in the copying machine 1, the amplitude adjustment of the MEMS mirror 420 is prohibited by the amplitude adjustment control unit 111 during the period when the exposure of the photosensitive drum 43 for one sheet is executed in the optical scanning device 42. , It is possible to prevent the image from shifting due to the amplitude adjustment.

  As described above, according to the optical scanning device 42 and the copying machine 1 using the same according to the embodiment of the present invention, the scanning mirror that scans the photosensitive drum with the light beam by vibrating at the mechanical resonance frequency. The amplitude can be corrected.

1 is a structural diagram schematically illustrating an internal configuration of a copying machine that is an example of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating an example of an electrical configuration of the copier illustrated in FIG. 1. It is explanatory drawing for demonstrating an example of a structure of the optical scanning device concerning one Embodiment of this invention. FIG. 4 is a block diagram illustrating an example of an electrical configuration of the optical scanning device illustrated in FIG. 3. FIG. 5 is an explanatory diagram for describing an operation of a drive clock generation unit illustrated in FIG. 4. FIG. 5 is an explanatory diagram for explaining an operation of the DA converter shown in FIG. 4. FIG. 5 is an explanatory diagram for explaining the operation of the superposition circuit shown in FIG. 4. 3 is a flowchart showing an example of the operation of the copying machine shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Copy machine 2 Main body part 3 Stack tray 5 Document reading part 40 Image formation part 41 Transfer part 42 Optical scanning device 43 Photosensitive drum 44 Developing part 45 Fixing part 51 Scanner part 100 Control part 101 Copying control part 111 Amplitude adjustment part 210 LD Control unit 211 Time difference measurement unit 212 Average processing unit 213 Bias voltage calculation unit 221 Drive clock generation unit 222 DA converter 223 Superimposition circuit 224 Driver circuit 411 Paper transport unit 412 Transport roller 420 MEMS mirror 421 Scan control unit 422 Drive unit 423 Switching element 461 Paper cassette 462 Paper feed roller 463 Transport roller 473 Display unit 476 Operation key unit 511 Exposure lamp

Claims (7)

A light source that outputs a light beam for exposing a photosensitive drum that forms an electrostatic latent image by being exposed with a light beam that represents a scanning line of an image;
A scanning mirror that reflects the light beam output from the light source and scans the photosensitive drum with the light beam by vibrating at a mechanical resonance frequency;
A drive unit for vibrating the scanning mirror;
A first optical sensor disposed at a predetermined position on a start side of a scanning line of the image scanned on the photosensitive drum;
A second photosensor disposed at a predetermined position on the end side of the scanning line of the image scanned on the photosensitive drum;
One of the case where the light beam is scanned by the scanning mirror in the image scanning direction which is the scanning direction of the scanning line of the image and the case where the light beam is scanned in the direction opposite to the image scanning direction. Only in this case, an actual scan is performed in which a time difference between the timing at which the light beam is detected by the first optical sensor and the timing at which the light beam is detected by the second optical sensor is detected, and an actual scanning time is obtained based on the time difference. A time acquisition unit;
When the actual scanning time acquired by the actual scanning time acquisition unit is longer than a preset target scanning time, the amplitude of the scanning mirror is increased, and the actual scanning time acquired by the actual scanning time acquisition unit is the target. An optical scanning device comprising: an amplitude adjustment unit that performs amplitude adjustment to reduce the amplitude of the scanning mirror when the scanning time is shorter than the scanning time. The actual scanning time acquisition unit
The optical scanning device according to claim 1, wherein the actual scanning time is acquired only when the light beam is scanned in the image scanning direction by the scanning mirror. The first photosensor includes a plurality of light detection elements, and performs temperature compensation based on detection signals from the plurality of light detection elements,
The optical scanning device according to claim 1, wherein the second optical sensor includes a plurality of light detection elements, and performs temperature compensation based on detection signals from the plurality of light detection elements. The actual scanning time acquisition unit
The optical scanning device according to claim 1, wherein the time difference is detected a plurality of times, and an average value of the plurality of time differences is acquired as the actual scanning time. The drive unit is
A periodic signal whose frequency is set to coincide with the mechanical resonance frequency of the scanning mirror is superimposed on a predetermined DC voltage and supplied to the scanning mirror to vibrate the scanning mirror,
The amplitude adjuster is
The amplitude adjustment is performed by increasing the amplitude of the scanning mirror by increasing the DC voltage and decreasing the amplitude of the scanning mirror by decreasing the DC voltage. 5. The optical scanning device according to claim 1. The optical scanning device according to any one of claims 1 to 5,
The photosensitive drum;
A paper transport unit for supplying paper to the photosensitive drum;
An image forming apparatus comprising: an image forming unit configured to form an image on a sheet supplied by the sheet conveying unit based on an electrostatic latent image formed on the photosensitive drum. In the optical scanning device, amplitude adjustment for prohibiting the amplitude adjustment unit from performing amplitude adjustment during a period in which exposure of the photosensitive drum related to image formation on one sheet of paper conveyed by the paper conveyance unit is performed. The image forming apparatus according to claim 6, further comprising a prohibition unit.

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