JP2010160491A - Method of adjusting optical scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner in which the whole region of an effective scanning area on a face to be scanned is stably and accurately scanned with a light beam with a uniform spot diameter, and to provide an image forming apparatus using the optical scanner. <P>SOLUTION: A mirror driving means adjusts a scanning time in which the effective scanning area PA is scanned with a light beam which varies by a resonant frequency-following control by adjusting the oscillation amplitude of a deflector 65 so that the scanning time falls within a predetermined error range of a preliminarily determined scanning time. Further, a light beam is focused on the whole effective scanning region PA with a substantially uniform spot diameter with a scanning lens 66 of which the F-value is kept constant over the whole region of the effective scanning region PA. Thus, the scanning time in which the effective scanning region PA is scanned with the light beam is kept substantially constant and the effective scanning region PA is scanned stably and accurately with the light beam which is focused with a substantially uniform spot diameter. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical scanning apparatus that scans a light beam on a surface to be scanned in a main scanning direction, and an image forming apparatus that forms an electrostatic latent image using the apparatus.

  Examples of apparatuses using this type of optical scanning apparatus include image forming apparatuses such as laser printers, copiers, and facsimile machines. For example, in Patent Document 1, a laser beam modulated according to image data is incident on a deflector via a collimator lens, a cylindrical lens, and a reflection mirror and deflected. More specifically, the optical scanning device provided in this conventional apparatus is configured as follows.

  In this optical scanning device, a laser beam emitted from a semiconductor laser is passed through a collimator lens and a cylindrical lens, thereby shaping the laser beam into a horizontally long elliptical shape whose cross-sectional shape extends in the main scanning direction. Then, the laser beam is incident on the reflecting mirror of the deflector along the main scanning plane.

  In this apparatus, a deflector manufactured using a micromachining technique is used in order to solve various problems that occur particularly when a polygon mirror or a galvanometer mirror is used as a deflector. That is, a mirror vibrator in which a drive coil, a reflection mirror, and a ligament are integrally formed on a frame is processed using a photolithographic technique and an etching technique on a substrate such as quartz or silicon. Then, by applying a drive signal to the drive coil, the reflection mirror is swung about a swing axis that is substantially orthogonal to the main scanning direction, and the laser beam incident on the reflection mirror is deflected.

  The laser beam deflected in this way forms an image on a photosensitive member (corresponding to the “latent image carrier” of the present invention) through an arc · sin lens (scanning lens) and a cylindrical lens. Thus, an electrostatic latent image corresponding to the image data is formed.

JP-A-1-302317 (second page, FIGS. 2-4)

  By the way, in the said conventional apparatus, the resonance frequency of a mirror vibrator may vary depending on the processing method when manufacturing a mirror vibrator. Therefore, in order to solve this problem, by adjusting the frequency of the drive signal applied to the drive coil, the drive frequency of the mirror vibrator and the resonance frequency of the mirror vibrator are substantially matched, and the reflection mirror is always resonantly oscillated. ing. In addition, an arc / sin lens is used as the scanning lens, and the light beam is scanned at a constant scanning width at a constant speed by controlling the amplitude of the driving signal applied to the driving coil.

  However, when an arc / sin lens is used as the scanning lens, there is a characteristic that the Fno (F value) in the main scanning direction of the scanning end changes with respect to the scanning center. There is a problem that the spot diameter on the surface to be scanned at the end becomes non-uniform. That is, while a predetermined spot diameter is obtained in the central area of the effective scanning area of the surface to be scanned, the spot diameter changes as it goes to the end side. As a result, the scanning accuracy is degraded. Further, in an image forming apparatus equipped with an optical scanning device having such characteristics, a good latent image cannot be obtained, leading to a decrease in image quality.

  In addition, in the conventional device, there is a problem of variations in the resonance frequency due to the manufacturing method of the mirror vibrator. However, even when the same mirror vibrator is used, the resonance frequency fluctuates as the usage environment changes. May end up. Therefore, there is a demand for a technique that can scan the light beam stably against fluctuations in the resonance frequency.

  The present invention has been made in view of the above problems, and provides an optical scanning device capable of stably and highly accurately scanning a light beam with a uniform spot diameter over the entire effective scanning region on the surface to be scanned. An object of the present invention is to provide an image forming apparatus used.

  In order to achieve the above object, an optical scanning device according to the present invention is a light scanning device that scans a light beam in a main scanning direction on a surface to be scanned, and a light source that emits the light beam and substantially orthogonal to the main scanning direction. A deflector having a deflecting mirror surface, which is provided so as to be swingable about a swinging shaft and which reflects a light beam emitted from the light source and deflects the light beam in the main scanning direction, and provides a drive signal to the deflector. Mirror driving means for resonantly oscillating the deflection mirror surface about the oscillation axis, and a scanning optical system for forming an image of the light beam deflected by the deflector on the surface to be scanned. The means changes the driving frequency of the deflecting mirror surface by the mirror driving means so as to coincide with or become a value close to the resonance frequency according to the change in the resonance frequency of the deflector, and The swinging amplitude of the deflection mirror surface is adjusted according to the amount of fluctuation, and the scanning optical system is configured so that the F values are substantially the same over the entire effective scanning region on the surface to be scanned. It is characterized by that.

  In the invention configured as described above, the deflection mirror surface is driven to swing so that the drive frequency of the deflection mirror surface is equal to or close to the resonance frequency, and the deflection is performed according to the fluctuation amount of the frequency of the drive signal. The oscillation amplitude of the mirror surface is adjusted. Further, since the F values are substantially the same over the entire effective scanning area on the surface to be scanned, the light beam is imaged in the effective scanning area with a substantially uniform spot diameter. Therefore, even when the driving frequency of the deflecting mirror surface fluctuates due to fluctuations in the resonance frequency and the use environment such as temperature, the scanning time during which the light beam scans the effective scanning area can be kept substantially constant. In addition, the effective scanning area can be scanned with a light beam imaged with a substantially uniform spot diameter. Therefore, the effective scanning area can be stably scanned with high accuracy.

  In addition, the apparatus further includes a scanning time measuring unit that calculates a scanning time during which the light beam scans the effective scanning region and has at least one light beam detecting element, and the mirror driving unit is configured to output the scanning time by the output from the scanning time measuring unit. The scanning time may be made substantially constant by adjusting the swing amplitude of the deflecting mirror surface. With such a configuration, it is possible to automatically set the swing amplitude of the deflecting mirror surface to the optimum swing amplitude by using the output from the scanning time measuring means. Therefore, not only the individual difference of the resonance frequency caused by the manufacturing error of the deflection mirror surface but also the change of the resonance frequency due to the change of the use environment can be dealt with in real time. Therefore, the scanning time during which the light beam scans the effective scanning region can be made constant with higher accuracy.

  The light beam detecting element may be arranged outside a sweep surface formed by sweeping the light beam when scanning the effective scanning region. With such a configuration, the light beam detection element does not become an obstacle when the light beam scans the effective scanning region, so that it is not necessary to add a beam splitter or the like, and a simple configuration can be realized.

  Further, the scanning time measuring means has two light beam detection elements, and each of the light beam detection elements has an optical axis when the light beam scans substantially the center of the effective scanning area. It is good also as a structure arrange | positioned substantially symmetrically. With such a configuration, it is possible to easily calculate the scanning time for scanning the effective scanning region by using the time for the light beam to pass through the light beam detecting element.

  Further, the output of the light beam detecting element may be used as a horizontal synchronization signal when the light beam scans the effective scanning area. By adopting such a configuration, it is not necessary to add a light beam detection element for acquiring a horizontal synchronization signal, and the device configuration can be simplified.

  The image forming apparatus according to the present invention has the same configuration as the latent image carrier and the optical scanning device described above, and scans a light beam with a predetermined area on the surface of the latent image carrier as the effective scanning area. The image forming apparatus includes an exposure unit that forms an electrostatic latent image on the latent image carrier, and a developing unit that develops the electrostatic latent image with toner to form a toner image.

  In the invention configured as described above, an electrostatic latent image is stably and accurately formed on the latent image carrier by the optical scanning device described above, and the electrostatic latent image is developed with toner. Therefore, a highly accurate image can be obtained stably.

It is a figure which shows a mode that the amplitude of a drive signal is adjusted with the fluctuation | variation of a drive frequency. 1 is a diagram illustrating an image forming apparatus equipped with an exposure unit according to a first embodiment of an optical scanning device according to the present invention. FIG. 3 is a block diagram illustrating an electrical configuration of the image forming apparatus in FIG. 2. FIG. 3 is a main scanning sectional view showing a configuration of an exposure unit (optical scanning device) provided in the image forming apparatus of FIG. 2. It is a block diagram which shows the structure of the exposure unit and exposure control part of FIG. It is a figure which shows the deflector which is one component of an exposure unit. It is a figure which shows the deflector which is one component of an exposure unit. It is a schematic diagram for calculating the scanning time of the light beam. It is a flowchart which shows the control procedure of rocking | fluctuation amplitude. It is a figure which shows the deflector which is one component of the exposure unit which is 2nd Embodiment of the optical scanning device concerning this invention. It is a main scanning sectional view showing a third embodiment of the optical scanning device according to the present invention.

<Basic Operation of Optical Scanning Device According to the Present Invention>
First, the basic operation of the optical scanning device according to the present invention will be described in detail with reference to FIG. FIG. 1 is a diagram showing how the swing amplitude of the deflection mirror surface is adjusted by adjusting the amplitude of the drive signal as the frequency of the drive signal for driving the deflection mirror surface is adjusted.

  In FIG. 1, the vertical axis is the oscillation amplitude (Θ) of the deflecting mirror surface of the deflector, and the horizontal axis is time (t), the oscillation amplitude waveform F1 of the deflection mirror surface before the resonance frequency tracking control, and the resonance frequency tracking control. The swing amplitude waveform F2 of the subsequent deflection mirror surface and the swing amplitude waveform F3 of the deflection mirror surface after the swing amplitude adjustment are shown. In order to facilitate the understanding of the explanation, the drawing is such that the points at which the swinging amplitudes of the deflection mirror surfaces are zero overlap at time t0. The resonance frequency tracking control will be described later.

  When the deflection mirror surface is driven with the swing amplitude waveform F1, the light beam deflected by the deflection mirror surface at time t11 passes through the light beam detection position A and is detected by the light beam detection sensor. Further, the light beam deflected by the deflecting mirror surface at time t12 passes through the light beam detection position B and is detected by the light beam detection sensor. In this case, the time during which the light beam scans from the light beam detection position A to the light beam detection position B is PT1.

  Here, when the resonance frequency of the deflecting mirror surface changes due to a change in the operating environment temperature or the like, control is performed to adjust the frequency of the drive signal on the deflecting mirror surface according to the change of the resonance frequency (resonance frequency tracking control). ). That is, in the resonance frequency tracking control, control is performed so that the drive frequency of the deflection mirror surface substantially matches the resonance frequency in accordance with the fluctuation of the resonance frequency of the deflection mirror surface. In the resonance frequency tracking control, the resonance frequency of the deflecting mirror surface and the drive frequency are not necessarily substantially the same, and a sufficient effect can be obtained only by adjusting the drive frequency to the vicinity of the resonance frequency. .

  In the case of FIG. 1, the drive frequency of the deflecting mirror surface is adjusted to the high frequency side in accordance with the resonance frequency of the deflecting mirror surface that has fluctuated to the high frequency side, and the oscillation amplitude waveform of the deflecting mirror surface becomes F2. In this case, the light beam deflected by the deflection mirror surface passes through the light beam detection position A at time t21 and is detected by the light beam detection sensor, and passes through the light beam detection position B at time t22 to detect the light beam. It is detected by a sensor. Therefore, the time during which the light beam scans from the light beam detection position A to the light beam detection position B is PT2.

  Here, when the scanning time during which the light beam scans from the light beam detection position A to the light beam detection position B varies from PT1 to PT2, the scanning time is adjusted by adjusting the swing amplitude of the deflection mirror surface. (See waveform F3). In FIG. 1, the light beam deflected by the deflecting mirror surface passes through the light beam detection position A at time t11 by decreasing the oscillation amplitude of the deflecting mirror surface as shown by the waveform F3, and at time t12. It passes through the light beam detection position B. Therefore, the time that the light beam scans from the light beam detection position A to the light beam detection position B is PT1, and the time that the light beam scans from the light beam detection position A to the light beam detection position B before and after the resonance frequency tracking control. Can be adjusted to be substantially constant.

  Further, in FIG. 1, control is performed so that the oscillation amplitude of the deflecting mirror surface is decreased when the resonance frequency changes to the high frequency side. However, when the resonance frequency changes to the low frequency side, the same concept is used. Thus, adjustment may be made to increase the swinging amplitude of the deflection mirror surface. In all of the embodiments described below, the above-described resonance frequency tracking control and adjustment of the swing amplitude of the deflection mirror surface are performed.

<First Embodiment>
FIG. 2 is a view showing an image forming apparatus equipped with an exposure unit according to the first embodiment of the optical scanning apparatus of the present invention. FIG. 3 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. This image forming apparatus is a so-called four-cycle color printer. In this image forming apparatus, when a print command is given to the main controller 11 from an external device such as a host computer in response to an image formation request from the user, the engine controller 10 responds to the print command from the CPU 111 of the main controller 11. The engine unit EG is controlled to form an image corresponding to the print command on a sheet such as copy paper, transfer paper, paper, and OHP transparent sheet.

  In this engine unit EG, a photosensitive member 2 (corresponding to a “latent image carrier” of the present invention) is provided so as to be rotatable in the arrow direction (sub-scanning direction) in FIG. Further, a charging unit 3, a rotary developing unit 4, and a cleaning unit (not shown) are arranged around the photoconductor 2 along the rotation direction. A charging controller 103 is electrically connected to the charging unit 3 and applies a predetermined charging bias. By applying this bias, the outer peripheral surface of the photoreceptor 2 is uniformly charged to a predetermined surface potential. Further, the photosensitive member 2, the charging unit 3, and the cleaning unit integrally constitute a photosensitive member cartridge, and the photosensitive member cartridge is integrally detachable from the apparatus main body 5.

  Then, the light beam L is irradiated from the exposure unit 6 corresponding to the optical scanning device (exposure means) of the present invention toward the outer peripheral surface of the photoreceptor 2 charged by the charging unit 3. The exposure unit 6 exposes a light beam L on the surface of the photosensitive member 2 (corresponding to the “scanned surface” of the present invention) in accordance with an image signal given from an external device, and outputs electrostatic light corresponding to the image signal. A latent image is formed. The configuration and operation of the exposure unit 6 will be described in detail later.

  The electrostatic latent image thus formed is developed with toner by the developing unit 4 (corresponding to the “developing means” of the present invention). That is, in this embodiment, the developing unit 4 is configured as a support frame 40 that is rotatably provided around the axis, and a cartridge that is detachable with respect to the support frame 40, and for yellow that contains toner of each color. A developing unit 4Y, a magenta developing unit 4M, a cyan developing unit 4C, and a black developing unit 4K are provided. Then, based on a control command from the developing device controller 104 of the engine controller 10, the developing unit 4 is rotationally driven and these developing devices 4Y, 4M, 4C, 4K are selectively brought into contact with the photosensitive member 2. Alternatively, when positioned at a predetermined developing position facing each other with a predetermined gap, toner is applied to the surface of the photoreceptor 2 from a developing roller provided in the developing unit and carrying toner of a selected color. As a result, the electrostatic latent image on the photoreceptor 2 is visualized with the selected toner color.

  The toner image developed by the developing unit 4 as described above is primarily transferred onto the intermediate transfer belt 71 of the transfer unit 7 in the primary transfer region TR1. The transfer unit 7 includes an intermediate transfer belt 71 that is stretched over a plurality of rollers 72, 73, and the like, and a drive unit (not shown) that rotates the intermediate transfer belt 71 in a predetermined rotation direction by rotationally driving the roller 73. It has.

  In the vicinity of the roller 72, a transfer belt cleaner (not shown), a density sensor 76 (FIG. 3), and a vertical synchronization sensor 77 (FIG. 3) are arranged. Among these, the density sensor 76 is provided facing the surface of the intermediate transfer belt 71 and measures the optical density of the patch image formed on the outer peripheral surface of the intermediate transfer belt 71. The vertical synchronization sensor 77 is a sensor for detecting the reference position of the intermediate transfer belt 71, and is a synchronization signal output in association with the rotational drive of the intermediate transfer belt 71 in the sub-scanning direction, that is, a vertical synchronization signal. It functions as a vertical sync sensor for obtaining Vsync. In this apparatus, the operation of each part of the apparatus is controlled based on the vertical synchronization signal Vsync in order to align the operation timing of each part and to superimpose toner images of each color accurately.

  When transferring a color image to a sheet, each color toner image formed on the photoreceptor 2 is superimposed on the intermediate transfer belt 71 to form a color image and taken out from the cassette 8 one by one. The color image is secondarily transferred onto the sheet conveyed along the conveyance path F to the secondary transfer region TR2.

  At this time, in order to correctly transfer the image on the intermediate transfer belt 71 to a predetermined position on the sheet, the timing of feeding the sheet to the secondary transfer region TR2 is managed. Specifically, a gate roller 81 is provided on the transport path F on the front side of the secondary transfer region TR2, and the gate roller 81 rotates in accordance with the timing of the circumferential movement of the intermediate transfer belt 71. Are sent to the secondary transfer region TR2 at a predetermined timing.

  Further, the sheet on which the color image is formed in this way is conveyed to the discharge tray portion 51 provided on the upper surface portion of the apparatus main body 5 via the fixing unit 9 and the discharge roller 82. Further, when images are formed on both sides of the sheet, the sheet on which the image is formed on one side as described above is switched back by the discharge roller 82. As a result, the sheet is conveyed along the reverse conveyance path FR. Then, it is put again on the transport path F before the gate roller 81. At this time, the image is transferred to the surface of the sheet that is in contact with the intermediate transfer belt 71 and transfers the image in the secondary transfer region TR2. The surface is the opposite of the surface. In this way, images can be formed on both sides of the sheet.

  In FIG. 3, reference numeral 113 denotes an image memory provided in the main controller 11 for storing image data given from an external device such as a host computer via the interface 112, and reference numeral 106 is executed by the CPU 101. A ROM for storing calculation data, control data for controlling the engine unit EG, and the like, and a reference numeral 107 are RAMs for temporarily storing calculation results in the CPU 101 and other data.

  4 is a main scanning sectional view showing a configuration of an exposure unit (optical scanning device) provided in the image forming apparatus of FIG. 2, and FIG. 5 is a diagram showing a configuration of an exposure unit and an exposure control unit of the image forming apparatus of FIG. 6 and 7 are diagrams showing a deflector as one component of the exposure unit, FIG. 8 is a schematic diagram for calculating the scanning time of the light beam in the present embodiment, and FIG. 9 is the swing amplitude in the present embodiment. It is a flowchart which shows the control procedure of. Hereinafter, the configuration and operation of the exposure unit will be described in detail with reference to these drawings.

  The exposure unit 6 has an exposure housing 61. A single laser light source 62 is fixed to the exposure housing 61, and a light beam can be emitted from the laser light source 62. The laser light source 62 is electrically connected to the light source driving unit 102a of the exposure control unit 102. For this reason, the light source driving unit 102a controls the laser light source 62 on / off according to the image data, and the laser light source 62 emits a light beam modulated according to the image data.

  Further, in the exposure housing 61, a collimator lens 631, a cylindrical lens 632, a deflector 65, a scanning lens are used to scan and expose the light beam from the laser light source 62 onto the surface (not shown) of the photoreceptor 2. 66 (corresponding to the “scanning optical system” of the present invention) is provided. That is, the light beam from the laser light source 62 is shaped into collimated light of an appropriate size by the collimator lens 631 and then incident on the cylindrical lens 632 having power only in the sub-scanning direction Y. Then, by adjusting the cylindrical lens 632, the collimated light is imaged in the vicinity of the deflection mirror surface 651 of the deflector 65 in the sub-scanning direction Y. Thus, in this embodiment, the collimator lens 631 and the cylindrical lens 632 function as the beam shaping system 63 that shapes the light beam from the laser light source 62.

  The deflector 65 is formed by using a micromachining technique in which a micromachine is integrally formed on a semiconductor substrate by applying a semiconductor manufacturing technique. The deflector 65 reflects the light beam reflected by the deflection mirror surface 651 in the main scanning direction X. Deflection is possible. More specifically, the deflector 65 is configured as follows.

  As shown in FIG. 6, in this deflector 65, a silicon substrate 652 functions as a support member, and a movable plate 656 is provided by processing a part of the silicon substrate 652. The movable plate 656 is formed in a flat plate shape, is elastically supported on the silicon substrate 652 by a torsion spring 657, and is swingable about a swing axis AX1 extending substantially parallel to the sub-scanning direction Y. Further, a planar coil 655 that is electrically connected to a pair of outer electrode terminals (not shown) formed on the upper surface of the silicon substrate 652 via a torsion spring 657 is coated on the upper surface of the movable plate 656 with an insulating layer. It has been. In addition, an aluminum film or the like is formed as a deflection mirror surface 651 at the center of the upper surface of the movable plate 656.

  Further, as shown in FIG. 7, a recess 652a is provided at a substantially central portion of the silicon substrate 652 so that the movable plate 656 can swing around the swing axis AX1. Then, permanent magnets 659a and 659b are fixed to the inner bottom surface of the recess 652a in positions different from each other at both ends of the movable plate 656 in different orientations. Further, the planar coil 655 is electrically connected to the drive unit 102b of the exposure control unit 102, and the Lorentz depends on the direction of the current flowing through the planar coil 655 by the energization of the coil 655 and the direction of the magnetic flux by the permanent magnets 659a and 659b. A force acts and a moment for rotating the movable plate 656 is generated. As a result, the movable plate 656 (deflection mirror surface 651) swings with the torsion spring 657 as the swing axis AX1. Here, if the current flowing through the planar coil 655 is an alternating current and is continuously repeated, the deflection mirror surface 651 can be reciprocally oscillated with the torsion spring 657 as the swing axis AX1.

  As described above, in the deflector 65, the driving unit 102b of the exposure control unit 102 functions as the “mirror driving unit” of the present invention, and controls the driving unit 102b, thereby “the basic operation of the optical scanning device according to the present invention”. As described in the section, the drive frequency and oscillation amplitude of the deflecting mirror surface 651 are adjusted in accordance with the change in the resonance frequency of the deflector 65 due to the change in the use environment. In this manner, the light beam is deflected and scanned in the main scanning direction X by swinging the deflection mirror surface 651 about the swing axis AX. That is, the swing axis AX1 functions as the swing axis in the present invention.

  The light beam deflected by the deflecting mirror surface of the deflector 65 configured as described above is deflected toward the scanning lens 66. In this embodiment, the scanning lens 66 is configured so that the F values are substantially the same over the entire effective scanning area PA (see FIG. 8) on the surface of the photoreceptor 2. Therefore, the light beam deflected toward the scanning lens 66 is focused on the effective scanning area PA on the surface of the photoreceptor 2 with the substantially same spot diameter via the scanning lens. As a result, a light beam is scanned in parallel with the main scanning direction X, and a line-like latent image extending in the main scanning direction X is formed on the surface of the photoreceptor 2.

  Further, in this embodiment, as shown in FIG. 4, the start or end of the scanning light beam from the deflector 65 is turned back by mirrors 69a and 69b to synchronize sensors 60A and 60B (corresponding to the “beam detecting element” in the present invention). Leading to. These folding mirrors 69a and 69b and the synchronization sensors 60A and 60B are disposed outside the sweep surface formed by sweeping the light beam when scanning the effective scanning area PA. The folding mirrors 69a and 69b are disposed substantially symmetrically with respect to the optical axis L0 when the light beam scans the substantial center of the effective scanning area PA. Therefore, as schematically shown in FIG. 8, it can be considered that the synchronization sensors 60A and 60B are arranged substantially symmetrically with respect to the optical axis L0.

  The detection signals of the light beams from the synchronization sensors 60A and 60B are transmitted to the measuring unit 102c of the exposure control unit 102, and the scanning time for scanning the effective scanning area PA with the light beam is calculated in the measuring unit. The scanning time calculated in the measuring unit 102c is transmitted to the driving unit 102b (mirror driving means), and the driving unit 102b determines the swing amplitude of the deflection mirror surface 651 in accordance with the transmitted scanning time. . That is, the folding mirrors 69a and 69b, the synchronization sensors 60A and 60B, and the measuring unit 102c function as the scanning time measuring unit of the present invention. Further, in this embodiment, the synchronization sensors 60A and 60B function as a horizontal synchronization read sensor for obtaining a synchronization signal when the light beam scans the effective scanning area PA in the main scanning direction X, that is, the horizontal synchronization signal Hsync. I am letting.

  Next, the operation of the exposure unit 6 (optical scanning device) configured as described above will be described with reference to FIG. FIG. 9 is a flowchart showing the operation of the exposure unit 6 of FIG. In the exposure unit 6, resonance frequency tracking control (step S <b> 1) is performed in which the driving frequency of the deflector 65 is adjusted to a frequency corresponding to the resonance frequency of the deflector 65.

  Next, the laser light source 62 is turned on (step S2), and optical scanning of the surface (scanned surface) of the photosensitive member 2 is started. Then, the time Δts during which the light beams pass through the two synchronization sensors 60A, 60B is measured from the time when the light beams are incident on the synchronization sensors 60A, 60B (step S3), and then the measured value Δts in step 3 is used. Then, a scanning time Δtp during which the light beam scans the effective scanning area PA on the surface of the photosensitive member 2 is calculated (step S4).

  In step 4, first, the maximum swing amplitude Θm of the deflector 65 (deflection mirror surface 651) is calculated using the measured value Δts in step 3 (Equation 1).

そして、数１によって算出された偏向器６５（偏向ミラー面６５１）の最大揺動振幅Θmより、光ビームが感光体２の表面の有効走査領域ＰＡを走査する走査時間Δtpを算出する（数２）。

Then, from the maximum swing amplitude Θm of the deflector 65 (deflection mirror surface 651) calculated by Equation 1, a scanning time Δtp for scanning the effective scanning area PA on the surface of the photoreceptor 2 is calculated (Equation 2). ).

なお、数１、数２中における各記号は以下の通りである（図８参照）。

In addition, each symbol in Formula 1 and Formula 2 is as follows (refer FIG. 8).

Θs: rotation angle of the deflection mirror surface when the synchronous sensor detects the light beam (a known value from the arrangement relationship of the components constituting the exposure unit)
Θp: rotation angle of the deflecting mirror surface when the light beam scans the end of the effective scanning area (a known value from the arrangement relationship of the components constituting the exposure unit)
f: Deflector drive frequency Θm: Maximum swing amplitude of deflector (deflection mirror surface) Δts: Time for light beam to pass through two synchronous sensors Δtp: Scanning time for light beam to scan effective scanning area PA Δts is a time measured by the synchronous sensors 60A and 60B, and Δtp is a time calculated by the measuring unit 102c of the exposure control unit 102.

  The scanning time Δtp calculated in step S4 is transmitted to the drive unit 102b of the exposure control unit 102, and an error e with respect to the set value Δtp0 of the scan time of the effective scanning area PA set in advance in the drive unit 102b is calculated. (Step S5). If the error e is smaller than the preset allowable error value e0, the optical scanning of the surface of the photoreceptor 2 is continued with the same swinging amplitude Θm.

  However, if the error e calculated in step S5 is larger than the allowable error value e0, a new oscillation amplitude value Θm0 is calculated by equation 3 (step S7).

そして、ステップＳ７で算出した揺動振幅値Θm0にしたがって、駆動部１０２ｂ（ミラー駆動手段）は偏向器６５（偏向ミラー面６５１）の揺動振幅を調整する（ステップＳ８）。その後、誤差ｅが誤差許容値ｅ0よりも小さくなるまで上記したステップＳ３からの動作を繰返し行う。

Then, the drive unit 102b (mirror drive means) adjusts the swing amplitude of the deflector 65 (deflection mirror surface 651) according to the swing amplitude value Θm0 calculated in step S7 (step S8). Thereafter, the operation from step S3 is repeated until the error e becomes smaller than the allowable error value e0.

  As described above, according to this embodiment, the drive unit 102b (mirror drive unit) of the exposure control unit 102 changes the drive frequency of the deflector 65 according to the change in the resonance frequency of the deflector 65, and the resonance after change. The frequency is adjusted to be substantially the same as or close to the frequency. Then, the scanning time Δtp for scanning the effective scanning area PA with the light beam changed by adjusting the driving frequency is set in advance by adjusting the swing amplitude Θm of the deflector 65 (deflection mirror surface 651). It is adjusted so as to be within a predetermined error range e0 of the scanning time Δtp0. Further, the light beam is imaged on the effective scanning area PA with a substantially uniform spot diameter by the scanning lens 66 having substantially the same F value over the entire effective scanning area PA. Therefore, even when the driving frequency of the deflector 65 is adjusted by changing the resonance frequency of the deflector 65 in accordance with changes in the usage environment such as temperature, the scanning time for the light beam to scan the effective scanning area PA is substantially reduced. While being able to keep constant, the effective scanning area PA can be scanned with a light beam imaged with a substantially uniform spot diameter. Therefore, the effective scanning area PA can be stably scanned with high accuracy.

  In this embodiment, the time Δtp during which the light beam scans the effective scanning area PA is calculated from the outputs of the synchronization sensors 60A and 60B, and Δtp is set within a predetermined error range e0 of Δtp0 set in advance. The swing amplitude Θm of the deflector 65 (deflection mirror surface 651) is adjusted. Therefore, not only the individual difference of the resonance frequency caused by the manufacturing error of the deflector but also the change of the resonance frequency due to the change of the use environment can be dealt with in real time. Therefore, the scanning time during which the light beam scans the effective scanning area PA can be made constant with higher accuracy.

  In this embodiment, the folding mirrors 69a and 69b and the synchronization sensors 60A and 60B are arranged outside the sweep surface formed by sweeping the light beam when scanning the effective scanning area PA. Accordingly, the folding mirrors 69a and 69b and the synchronization sensors 60A and 60B do not become obstacles when the light beam scans the effective scanning area PA, so that it is not necessary to add a beam splitter or the like, and a simple configuration can be realized.

  In this embodiment, the two synchronization sensors 60A and 60B are disposed substantially symmetrically with respect to the optical axis when the light beam scans the substantial center of the effective scanning area PA (see FIG. 8). . Therefore, it is easy to calculate the scanning time Δtp during which the light beam scans the effective scanning area PA using the time Δts that is measured by the two synchronization sensors and passes through the two synchronization sensors 60A and 60B. It can be carried out.

  In this embodiment, the synchronization sensors 60A and 60B function as a horizontal synchronization reading sensor for obtaining a synchronization signal when the light beam scans the effective scanning area PA in the main scanning direction X, that is, the horizontal synchronization signal Hsync. I am letting. Therefore, it is not necessary to add a new sensor to obtain Hsync, and the apparatus configuration can be simplified.

  Further, according to this embodiment, the electrostatic latent image formed stably and with high accuracy by the exposure unit described above is developed with toner. Therefore, a highly accurate image can be obtained stably.

<Second Embodiment>
FIG. 10 is a diagram showing a second embodiment of the optical scanning device according to the present invention. The second embodiment is greatly different from the first embodiment in that the deflection mirror surface 651 is driven to swing using electrostatic force, and other configurations are the same as those in the first embodiment. is there. In addition, the same code | symbol is attached | subjected to the structure same as 1st Embodiment.

  In the deflector 65, a movable plate 656 is provided by processing a part of the silicon substrate 652, as shown in FIG. The movable plate 656 is formed in a flat plate shape, is elastically supported on the silicon substrate 652 by a torsion spring 657, and is swingable about a swing axis AX1 extending substantially parallel to the sub-scanning direction Y. In addition, an aluminum film or the like is formed as a deflection mirror surface 651 at the center of the upper surface of the movable plate 656.

  Further, as shown in FIG. 10, a concave portion 652a is provided at a substantially central portion of the silicon substrate 652 so that the movable plate 656 can swing around the swing axis AX1. Electrodes 658a and 658b are respectively fixed to positions on the inner bottom surface of the recess 652a that face both ends of the movable plate 656. These two electrodes 658a and 658b function as electrodes for driving the movable plate 656 to swing around the swing axis AX1. That is, these electrodes 658 a and 658 b are electrically connected to a drive unit (not shown) of the exposure control unit 102, and electrostatic adsorption force is applied between the electrode and the deflecting mirror surface 651 by applying a voltage to the electrode. Acts to draw one end of the deflecting mirror surface 651 toward the electrode. Therefore, when a predetermined voltage is alternately applied to the electrodes 658a and 658b from the driving unit, the deflection mirror surface 651 (movable plate 656) can be reciprocally oscillated using the torsion spring 657 as the swing axis AX1. In this embodiment, the deflection mirror surface 651 (movable plate 656) is driven to swing as described in the section "Basic operation of the optical scanning device according to the invention". Therefore, it has the same effect as the first embodiment.

  In order to swing the deflecting mirror surface 651 in this way, electromagnetic force, electrostatic force or the like is used, but it goes without saying that any of them may be used. However, since each driving method has the following characteristics, it is desirable to adopt them appropriately in consideration of them. That is, when an electromagnetic force is used as a driving force for driving the deflection mirror surface 651 to swing, the deflection mirror surface 651 can be driven to swing with a lower driving voltage than when an electrostatic attraction force is generated. Thus, voltage control is facilitated, and the positional accuracy of the scanning light beam can be increased. On the other hand, when the electrostatic attraction force is used as the driving force, there is no need to form a coil pattern, the deflector 65 can be further miniaturized, and the deflection scanning can be further speeded up.

<Third Embodiment>
FIG. 11 is a diagram showing a third embodiment of the optical scanning device according to the present invention. The third embodiment is greatly different from the first and second embodiments in that the scanning time of the light beam is measured by one synchronization sensor 60C and folding mirrors 69c to 69e. Other configurations are the same as those in the first and second embodiments.

  Also in this case, since the deflector 65 is controlled as in the first and second embodiments, the same operation and effect are obtained.

<Others>
The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, the relationship between the drive frequency f, the oscillation amplitude Θm, and the scanning time Δtp is stored in advance in the ROM 106 or the like, and based on these stored values, the deflector 65 (deflection mirror surface 651) in step S1 of FIG. ) Swinging amplitude may be substantially adjusted. Such a configuration also has the same effects as the above embodiment.

  In this case, the synchronization sensors 60A to 60C may not be provided. Even with this configuration, it is possible to realize an optical scanning device having the same effect as the above embodiment and having a simple configuration in which no synchronization sensor is provided.

  In the above embodiment, the optical scanning device according to the present invention is used as the exposure unit of the color image forming apparatus, but the application target of the present invention is not limited to this. That is, as an exposure unit of an image forming apparatus that scans a light beam on a latent image carrier such as a photoconductor to form an electrostatic latent image and develops the electrostatic latent image with toner to form a toner image. Can be used. Of course, the application target of the optical scanning device is not limited to the exposure means provided in the image forming apparatus, but can be applied to all optical scanning devices that scan the surface to be scanned with the light beam.

  2 ... photosensitive body (latent image carrier), 4 ... developing unit (developing means), 6 ... exposure unit (optical scanning device), 60A, 60B, 60C ... synchronous sensor (scanning time measuring means), 69a, 69b, 69c , 69d, 69e ... folding mirror (scanning time measuring means), 65 ... deflector, 651 ... deflection mirror surface, 66 ... scanning lens (scanning optical system), 102b ... driving unit (mirror driving means), 102c ... measuring unit ( (Scanning time measuring means), AX1 ... oscillating axis, PA ... effective scanning area, X ... main scanning direction, Y ... sub-scanning direction

Claims (6)

In an optical scanning device that scans a light beam in a main scanning direction on a surface to be scanned,
A light source that emits a light beam;
A deflector having a deflecting mirror surface provided so as to be swingable about a swing axis substantially orthogonal to the main scanning direction and reflecting a light beam emitted from the light source to deflect the light beam in the main scanning direction;
Mirror driving means for applying a drive signal to the deflector to resonate and swing the deflection mirror surface about the swing axis;
A scanning optical system that images the light beam deflected by the deflector onto the scanned surface;
The mirror driving means varies the driving frequency of the deflecting mirror surface by the mirror driving means so as to coincide with or become a value close to the resonance frequency according to the fluctuation of the resonance frequency of the deflector. Adjust the swing amplitude of the deflection mirror surface according to the amount of variation,
The optical scanning device is characterized in that the scanning optical system is configured so that F values are substantially the same in the entire effective scanning region on the surface to be scanned.   The apparatus further comprises a scanning time measuring means for calculating a scanning time for the light beam to scan the effective scanning area and having at least one light beam detecting element, and the mirror driving means is configured to deflect the deflection by an output from the scanning time measuring means. The optical scanning device according to claim 1, wherein the scanning time is made substantially constant by adjusting a swinging amplitude of a mirror surface.   The optical scanning device according to claim 2, wherein the light beam detecting element is disposed outside a sweep surface formed by sweeping the light beam when scanning the effective scanning region.   The scanning time measuring means has two light beam detection elements, and each of the light beam detection elements is substantially symmetric with respect to an optical axis when the light beam scans a substantial center of the effective scanning region. The optical scanning device according to claim 2 or 3, wherein   5. The optical scanning device according to claim 2, wherein an output of the light beam detection element is used as a horizontal synchronization signal when the light beam scans the effective scanning region. 6. A latent image carrier;
6. The optical scanning device according to claim 1, wherein the optical scanning device is configured to scan a light beam with a predetermined region on the surface of the latent image carrier as the effective scanning region. Exposure means for forming an electrostatic latent image on
An image forming apparatus comprising: developing means for developing the electrostatic latent image with toner to form a toner image.

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