JP2005070479A - Optical scanner and and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner in which the imaging position of a light beam with respect to a plane to be scanned and a scanning position with light beam on the plane to be scanned in a subscanning direction are simultaneously and excellently corrected, and to provide an image forming apparatus with the scanner. <P>SOLUTION: A parallel light beam emitted from a collimator lens 63 is directly made incident on the deflection mirror face 651 of a deflection device. The deflection device not only deflects the light beam in a main scanning direction X and scans with the light beam, but also adjusts the position of the scanning light beam on a photoreceptor 2 in a subscanning direction Y by deflecting the light beam in a subscanning direction Y simultaneously with the deflection and scanning. Further, a scanning lens 66 is formed of an optical element which is rotationally symmetrical with respect to an optical axis OA in order to focusing the parallel light beam on the surface 2a of the photoreceptor 2. Thus, the optical characteristic is nearly identical both in the main scanning direction X and the subscanning direction Y. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical scanning device used in an image forming apparatus such as a laser beam printer, and more particularly to an optical scanning device that simultaneously corrects an imaging position of a light beam on a surface to be scanned and a scanning position on the surface to be scanned. The present invention relates to an image forming apparatus equipped with the apparatus.

  2. Description of the Related Art Conventionally, in an optical scanning device used in an image forming apparatus such as a laser beam printer, a copying machine, or a facsimile machine, a light beam emitted from a light source such as a semiconductor laser is irradiated on the surface of a latent image carrier such as a photoconductor (scanned surface). ) The image is formed in a spot shape on the top and scanned in a predetermined direction. For example, in the apparatus described in Patent Document 1, a light beam emitted from a light source is collimated into a parallel light beam by a collimator lens, and further shaped into a beam focused in one direction by a cylindrical lens. The shaped light beam is deflected by a deflector such as a polygon mirror or a galvanometer mirror. The deflected light beam is imaged as a spot on the surface to be scanned via the scanning lens. In order to increase the resolution of the optical scanning device, the optical scanning device is optically designed so that the image formation point substantially coincides with the beam waist of the Gaussian beam.

JP-A-8-234125 (page 4, FIGS. 1 and 2)

  By the way, in the conventional apparatus, a surface tilt correction optical system is formed in order to correct the surface tilt. That is, on the front side of the deflector, a cylindrical lens having power only in the sub-scanning direction substantially orthogonal to the main scanning direction is arranged to form a line image parallel to the main scanning direction on the deflection mirror surface of the deflector, This line image is formed into a fixed spot on the surface to be scanned by the scanning lens. Therefore, when the optical scanning device is viewed in the sub-scan section, the deflecting mirror surface of the deflector and the surface to be scanned are optically conjugate. As a result, even if the deflection mirror surface is inclined, the scanning position on the surface to be scanned does not change in the sub-scanning direction.

  However, the addition of a cylindrical lens increases the number of parts and increases the device cost. In addition, an increase in the size of the optical scanning optical system is unavoidable due to an increase in optical components, and this is one of the major obstacles to downsizing the optical scanning device. There is also a problem that optical adjustment becomes complicated.

  Further, even if the above-described surface tilt correction is performed, component errors and assembly errors are inevitable. Therefore, there is an urgent need to match the scanning position of the light beam in the sub-scanning direction to the reference scanning position with a simple response without reassembling and adjusting the optical scanning device in the final adjustment stage after product assembly.

  Furthermore, in an optical scanning device that requires high resolution, the imaging position of the light beam is shifted in the direction of the optical axis due to environmental fluctuations such as a temperature change, even if it initially has a desired imaging performance. Defocusing may degrade imaging performance. In view of this, various techniques have been proposed in the past in order to correct the deviation of the imaging position. However, the above-described surface tilt correction optical system is a so-called anamorphic optical system, and has different optical characteristics in the main scanning direction and the sub-scanning direction. For this reason, as a matter of course, the rate of change in imaging characteristics due to temperature differs between the main scanning direction and the sub-scanning direction. Therefore, it is difficult to correct the shift of the imaging position due to the temperature variation in both the main scanning direction and the sub-scanning direction.

  For example, in the apparatus described in Patent Document 1, the main scanning section and the sub-scanning section of the optical scanning apparatus have a cross section with a larger amount of movement of the image plane due to a change in optical characteristics due to temperature variation, and a light source to a collimator. The cross section with the larger change in the amount of movement of the image plane due to the change in the distance to the lens is made the same, and the distance between the light source and the collimator lens is set to change appropriately depending on the temperature. As a result, the imaging position can be corrected to suppress the deviation of the imaging position. However, there is still much room for improvement.

  The present invention has been made in view of the above problems, and can appropriately correct the image forming position of the light beam with respect to the surface to be scanned and the light beam scanning position on the surface to be scanned in the sub-scanning direction. An object is to provide an optical scanning device and an image forming apparatus equipped with the device.

  In order to achieve the above object, an optical scanning device according to the present invention includes a light source that generates a light beam, a beam shaping unit that shapes the light beam from the light source into a parallel light beam, and a parallel beam emitted from the beam shaping unit. Deflection means for deflecting the light beam in the main scanning direction, imaging means for forming an image of the parallel light beam deflected by the deflection means on the surface to be scanned, having an optical element rotationally symmetric with respect to the optical axis, and a light source And a temperature correction unit that corrects the movement of the imaging position in the optical axis direction due to a temperature change by changing the distance between the beam shaping unit and the deflection unit. It has a deflection mechanism that deflects in the scanning direction and a fine adjustment mechanism that finely adjusts the scanning position of the light beam on the surface to be scanned in the sub-scanning direction that is deflected in a direction different from the main scanning direction. Doing things It is characterized.

  In the invention thus configured, the light beam from the light source is shaped into a parallel light beam and then deflected in the main scanning direction by the deflection mechanism of the deflection means. The parallel light beam deflected in this way is imaged on the surface to be scanned by the imaging means. Thus, the light beam incident on the image forming means is parallel light, and the optical elements constituting the image forming means corresponding to this are rotationally symmetric with respect to the optical axis. That is, in the optical scanning device according to the present invention, the optical characteristics are substantially the same in the main scanning direction and in the sub-scanning direction substantially orthogonal to the main scanning direction. Therefore, even if the refractive index of the optical element changes due to temperature fluctuation, the temperature correction means changes the distance between the light source and the beam shaping means, so that the light beam is connected in both the main scanning direction and the sub-scanning direction. The image position can be positioned on the surface to be scanned.

  In the present invention, the deflection means includes a fine adjustment mechanism in addition to the deflection mechanism described above. For this reason, the following functions are further provided. That is, this deflecting means not only simply deflects and scans the parallel light beam in the main scanning direction, but also has a function of deflecting the parallel light beam in a direction different from the main scanning direction before or after the deflection scanning, that is, a fine adjustment function. Have. The fine adjustment mechanism adjusts the scanning position of the light beam on the surface to be scanned in the sub-scanning direction. Thus, the fine adjustment mechanism can easily and precisely adjust the scanning position of the light beam on the surface to be scanned in the sub-scanning direction. As a result, not only the correction of the imaging position of the light beam but also the scanning position of the light beam can be corrected simultaneously.

  Here, as the deflection means, (1) a biaxial oscillating mirror type, (2) a combination of a polygon mirror (deflection mechanism) and a fine adjustment oscillating mirror (fine adjustment mechanism), (3) 2 A combination of two oscillating mirrors (one is a deflection mechanism and the other is a fine adjustment mechanism) can be used. Among these aspects, in particular, (1) the biaxial oscillating mirror type deflecting means can downsize the deflecting means compared to the deflecting means (2) and (3), and the apparatus can be further miniaturized. it can.

  The biaxially driven mirror type deflecting means includes an inner movable member having a deflection mirror surface that reflects a light beam from a light source, an outer movable member that supports the inner movable member so as to be swingable about a first axis, A support member for swingably supporting the movable member around a second axis different from the first shaft, an inner movable member swingably driven around the first axis, and an outer movable member swinged around the second axis And a mirror driving unit for driving. The mirror driving unit swings the deflection mirror surface with one of the first axis and the second axis as the main scanning deflection axis to scan the parallel light beam in the main scanning direction (deflection mechanism), while the other is The deflection mirror surface is driven to swing as a fine adjustment axis to change the scanning position of the light beam on the surface to be scanned (fine adjustment mechanism). As described above, the deflection mirror surface is configured to be swingable about two axes of the first axis and the second axis, so that the apparatus can be reduced in size.

  Further, the inner movable member, the outer movable member, and the support member can be made of silicon single crystal. For example, a silicon single crystal substrate can be used as a support member, and an inner movable member and an outer movable member can be formed by applying a micromachining technique to the substrate. When the inner movable member, the outer movable member, and the support member of the optical scanning unit are configured using the silicon single crystal as described above, the inner movable member and the outer movable member can be manufactured with high accuracy. Further, the inner movable member and the outer movable member can be swingably supported with the same spring characteristics as stainless steel, and the deflection mirror surface can be swung stably and at high speed.

  Further, when the deflection mirror surface is driven to swing by the mirror driving unit, the deflection mirror surface may be driven to swing around the main scanning deflection axis in the resonance mode. With this configuration, the deflection mirror surface can be driven to swing around the main scanning deflection axis with less energy. In addition, the main scanning period of the light beam on the surface to be scanned can be stabilized. On the other hand, in order to swing and position the deflection mirror surface around the fine adjustment axis, it is desirable to drive the deflection mirror surface in a non-resonant mode. This is because the oscillation driving of the deflection mirror surface around the fine adjustment axis requires stopping the oscillation of the deflection mirror surface around the fine adjustment axis after changing the scanning position of the light beam on the surface to be scanned. It is. Therefore, in order to perform the swing drive and swing stop with high accuracy, it is desirable to drive the swing in the non-resonant mode.

  In addition, as a driving force for swinging the deflection mirror surface, an electrostatic adsorption force, an electromagnetic force, or the like can be used. In particular, a static force is used to swing the deflection mirror surface around the main scanning deflection axis. It is desirable to use an electroadsorption force, and it is desirable to use an electromagnetic force to drive the deflection mirror surface to swing around the fine adjustment axis. The reason for the former is that it is not necessary to form a coil pattern, the deflection means can be miniaturized, and the deflection scanning can be further speeded up. On the other hand, the latter reason is that the deflection mirror surface can be oscillated and driven with a lower driving voltage than when electrostatic attraction force is generated, voltage control becomes easy, and the position accuracy of the light beam on the scanned surface It is because it can raise.

  FIG. 1 is a view showing an image forming apparatus equipped with an exposure unit as an embodiment of an optical scanning apparatus according to the present invention. FIG. 2 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 the engine unit EG, the photosensitive member 2 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.

  The light beam L is irradiated from the exposure unit 6 corresponding to the optical scanning device of the present invention toward the outer peripheral surface of the photosensitive member 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. 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 driven to rotate, and the developing devices 4Y, 4C, 4M, and 4K are selectively brought into contact with the photoreceptor 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. 2), and a vertical synchronization sensor 77 (FIG. 2) 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. 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. 2, 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.

  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. FIG. 4 is a sub-scan sectional view showing a configuration of an exposure unit (optical scanning device) provided in the image forming apparatus of FIG. 5 to 7 are diagrams showing a deflecting element (deflecting means) which is one component of the exposure unit. Further, FIG. 8 is a block diagram showing the configuration of the exposure unit and the exposure control unit. 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 so that a light beam can be emitted from the laser light source 62. As shown in FIG. 8, 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. Thus, in this embodiment, the laser light source 62 corresponds to the “light source” of the present invention.

  In addition, a collimator lens 63, a deflecting element 65, a scanning lens 66, and a folding mirror 67 are provided inside the exposure housing 61 in order to scan and expose the light beam from the laser light source 62 onto the surface of the photoreceptor 2. ing. That is, the light beam from the laser light source 62 is shaped into a parallel light beam by the collimator lens 63, and then the parallel light beam is incident on the deflection mirror surface 651 of the deflection element 65. In this embodiment, as shown in FIGS. 3 and 4, the laser light source 62 and the collimator lens 63 are held by the housing H in a state of being separated by a preset reference distance, and are collimated by the collimator lens 63. The beam diameter of the parallel light beam is a value corresponding to the reference distance. However, in this embodiment, as will be described later, the housing H is formed of a material having a linear expansion coefficient corresponding to the deviation caused by the temperature fluctuation in order to correct the deviation of the imaging position in the optical axis direction caused by the temperature fluctuation. Has been. For this reason, the said separation distance changes according to a temperature fluctuation | variation with a temperature fluctuation | variation, and a light beam changes. Then, the fluctuation of the separation distance displaces the imaging position of the light beam by the scanning lens 66 in the direction of the optical axis.

  Thus, the light beam corresponding to the temperature is emitted from the collimator lens 63 and deflected and scanned in the main scanning direction X by the deflection mirror surface 651 of the deflection element 65. The deflecting element 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, and the parallel light beams reflected by the deflecting mirror surface 651 are orthogonal to each other. The light beam can be deflected in the direction, that is, the main scanning direction X and the sub-scanning direction Y. More specifically, the deflection element 65 is configured as follows.

  In this deflecting element 65, as shown in FIG. 5, a silicon single crystal substrate (hereinafter referred to as “silicon substrate”) 652 functions as a “support member” of the present invention, and a part of the silicon substrate 652 is further processed. Thus, the outer movable plate 653 is provided. The outer movable plate 653 is formed in a frame shape, is elastically supported on the silicon substrate 652 by a torsion spring 654, and can swing around a second axis AX2 extending substantially parallel to the main scanning direction X. Further, a planar coil 655 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 654 is provided on the upper surface of the outer movable plate 653 as a “second axis driving coil. "Is provided by being coated with an insulating layer.

  A flat inner movable plate 656 is pivotally supported inside the outer movable plate 653. That is, the inner movable plate 656 is elastically supported on the inner side of the outer movable plate 653 by a torsion spring 657 whose axial direction is orthogonal to the torsion spring 654, and swings about a first axis AX1 extending substantially parallel to the sub-scanning direction Y. It is free. An aluminum film or the like is formed as a deflection mirror surface 651 at the center of the inner movable plate 656.

  Further, as shown in FIGS. 6 and 7, the outer movable plate 653 and the inner movable plate 656 can swing around the second axis AX2 and the first axis AX1, respectively, in the substantially central portion of the silicon substrate 652. In addition, a recess 652a is provided. Electrodes 658a and 658b are fixed to the inner bottom surface of the recess 652a at positions facing both ends of the inner movable plate 656 (see FIG. 6). These two electrodes 658a and 658b function as “first axis electrodes” for swinging and driving the inner movable plate 656 around the first axis AX1. That is, these first-axis electrodes 658 a and 658 b are electrically connected to the first drive unit 102 b of the exposure control unit 102, and static electricity is applied between the electrodes and the deflection mirror surface 651 by applying a voltage to the electrodes. The electroadsorption force acts to pull one end of the deflecting mirror surface 651 toward the electrode. Therefore, when a predetermined voltage is alternately applied from the first drive unit 102b to the first axis electrodes 658a and 658b, the deflection mirror surface 651 can be reciprocally oscillated with the torsion spring 657 as the first axis AX1. When the driving frequency of this reciprocating vibration is set to the resonance frequency of the deflecting mirror surface 651, the deflection width of the deflecting mirror surface 651 increases, and the end of the deflecting mirror surface 651 is displaced to a position close to the electrodes 658a and 658b. be able to. Further, when the end portion of the deflecting mirror surface 651 reaches a position close to the electrodes 658a and 658b by resonance, the electrodes 658a and 658b also contribute to driving the deflecting mirror surface 651, and vibration is maintained by both the end portion and the planar portion electrodes. Can be made more stable.

  As shown in FIG. 7, permanent magnets 659a and 659b are fixed to both ends of the outer movable plate 653 at outer positions on the inner bottom surface of the recess 652a in different orientations. Further, the second axis driving coil 655 is electrically connected to the second driving unit 102c of the exposure control unit 102, and the direction of the current flowing through the second axis driving coil 655 by the energization of the coil 655 is permanent. Lorentz force acts depending on the direction of magnetic flux generated by the magnets 659a and 659b, and a moment for rotating the outer movable plate 653 is generated. At this time, the inner movable plate 656 (deflection mirror surface 651) also swings around the torsion spring 654 as the second axis AX2 integrally with the outer movable plate 653. Here, if the current flowing through the second axis driving coil 655 is an alternating current and is continuously repeated, the deflection mirror surface 651 can be reciprocally oscillated with the torsion spring 654 as the second axis AX2.

  Thus, in the deflection element 65, the deflection mirror surface 651 can be driven to swing around the first axis AX1 and the second axis AX2 orthogonal to each other. Therefore, in this embodiment, the light beam is generated by swinging the deflecting mirror surface 651 about the first axis AX1 by controlling the mirror driving unit including the first axis driving unit 102b and the second axis driving unit 102c. The beam is deflected and scanned in the main scanning direction X. On the other hand, the position of the scanning light beam on the photosensitive member 2 in the sub-scanning direction Y is adjusted by swinging the deflection mirror surface 651 about the second axis AX2. As described above, in this embodiment, the first axis AX1 functions as the main scanning deflection axis, and the second axis AX2 functions as the fine adjustment axis. Functions as an adjustment mechanism. Of course, it is needless to say that the first axis AX1 may function as a fine adjustment axis and the second axis AX2 may function as a main scanning deflection axis.

  Returning to FIGS. 3 and 4, the description of the exposure unit 6 will be continued. The parallel light beam scanned by the deflecting element 65 as described above is finely adjusted in the sub-scanning direction Y and then emitted from the deflecting element 65 toward the surface (scanned surface) 2a of the photosensitive member 2. The parallel light beam is imaged on the surface 2 a of the photoreceptor 2 by the scanning lens 66. As a result, as shown in FIG. 9, the light beam scans 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 photoconductor 2.

  In this embodiment, as shown in FIG. 3, the start or end of the scanning light beam from the deflection element 65 is imaged on the synchronization sensor 60 by the horizontal synchronization imaging lens 69. That is, in this embodiment, the synchronization sensor 60 functions as a horizontal synchronization reading sensor for obtaining a synchronization signal in the main scanning direction X, that is, a horizontal synchronization signal HSYNC.

  As described above, according to this embodiment, the deflection element 65 not only deflects and scans the light beam in the main scanning direction X, but also deflects the light beam from the laser light source 62 in the sub-scanning direction Y simultaneously with the deflection scanning. By doing so, the position SL of the scanning light beam on the photosensitive member 2 can be adjusted in the sub-scanning direction Y. For this reason, the scanning position of the light beam in the sub-scanning direction Y on the photosensitive member 2 can be easily adjusted with high accuracy. As a result, even if the scanning light beam is deviated from the reference scanning position SL0 in the sub-scanning direction Y due to component error or assembly error, the deviation can be corrected and a high quality image can be formed. The “reference scanning position” is a planned position where the light beam is to be scanned, and is determined in advance at the design stage of the apparatus, and product assembly is performed so that the scanning light beam matches the reference scanning position.

  Here, an example of the fine adjustment process will be described with reference to FIG. For example, in the final adjustment stage after product assembly, when it is found that the scanning position SL of the scanning light beam is shifted by the shift amount Δy in the sub-scanning direction Y from the reference scanning position SL0 indicated by the broken line in FIG. Adjustments can be made as follows. That is, if the deviation amount Δy is obtained and stored in the RAM 107 as the storage means, the CPU 101 reads the deviation amount from the RAM 107 and swings the deflection mirror surface 651 around the second axis AX2 in accordance with the value. As a result, the position of the scanning light beam on the photosensitive member 2 in the sub-scanning direction Y is adjusted, and the scanning position SL of the scanning light beam coincides with the reference scanning position SL0. As described above, the scanning position SL of the light beam L in the sub-scanning direction Y can be easily matched with the reference scanning position SL0 with high accuracy, and as a result, a high-quality image can be formed.

  In this embodiment, the deviation amount is stored in the RAM 107 as “deviation information” of the present invention. Instead of storing the deviation amount itself, a value or data related to the deviation amount is stored as “deviation information”. You may make it make it. In addition, it is desirable to employ a non-volatile memory in order to store deviation amounts and related values even when the power is turned off. Further, the shift information may be stored on the controller 11 side.

  In addition, since the deflection element 65 includes not only the deflection mechanism that deflects the light beam in the main scanning direction X as described above but also the fine adjustment mechanism, it is not necessary to form a surface tilt correction optical system. Therefore, it is not necessary to provide a cylindrical lens before and after the deflection element 65. As a result, the number of parts of the exposure unit (optical scanning device) 6 is reduced, and the apparatus cost and the apparatus size can be reduced. Further, since the scanning lens 66 forms an image of the parallel light beam on the surface 2a of the photosensitive member 2, the scanning lens 66 is composed of an optical element that is rotationally symmetric with respect to the optical axis OA. That is, in the exposure unit (optical scanning device) 6 according to this embodiment, the optical characteristics are almost the same in the main scanning direction X and the sub-scanning direction Y. Therefore, even if the refractive index of the scanning lens 66 changes due to temperature fluctuation, the inconvenience due to temperature fluctuation can be eliminated as follows by appropriately selecting the linear expansion coefficient of the housing H.

  When temperature variation occurs, the optical characteristics of the scanning lens (optical element) 66 change, and the imaging position of the light beam shifts in the optical axis direction. At the same time, the housing H expands and contracts and the distance between the laser light source 62 and the collimator lens 63 changes. For this reason, the light beam emitted from the collimator lens 63 changes, and the imaging position of the light beam also changes in the optical axis direction. Therefore, by appropriately selecting the linear expansion coefficient of the housing H, it is possible to cancel the shift of the imaging position due to temperature fluctuation. Further, in the present embodiment, the optical characteristics are almost the same in the main scanning direction X and the sub-scanning direction Y, and the shift of the imaging position due to temperature fluctuation is the same in both directions X and Y. Therefore, the image forming position of the light beam can be positioned on the surface (scanned surface) 2a of the photosensitive member 2 in both the main scanning direction X and the sub-scanning direction Y by the expansion and contraction of the housing H accompanying the temperature fluctuation. In this way, the light beam imaging position on the surface 2a of the photoreceptor 2 and the light beam scanning position SL on the surface 2a can be corrected simultaneously and satisfactorily.

  In recent years, as the scanning lens 66, an injection-molded product of a resin material such as plastic is frequently used from the viewpoint of the degree of freedom of shape by molding and the cost. In such a resin lens, the refractive index fluctuation due to temperature fluctuation is larger than that of the glass lens, and the shift of the imaging position due to temperature fluctuation becomes a serious problem. Therefore, the present invention is very useful for the exposure unit (optical scanning device) 6 that uses a resin lens as the “imaging means” of the present invention.

  Furthermore, since the deflection element 65 is configured and operated as described above, the following functions and effects can be obtained in addition to the functions and effects described above.

  (A) Since the deflecting element 65 configured to swing the deflecting mirror surface 651 about two axes of the first axis AX1 and the second axis AX2 is used, deflecting means (polygon mirror + swinging mirror, Compared to the case where two oscillating mirrors are employed, the exposure unit 6 can be downsized, which is advantageous in terms of downsizing the apparatus.

  (B) In addition, since the outer movable plate 653 and the inner movable plate 656 of the deflection element 65 are formed by applying a micromachining technique to the single crystal substrate 652 of silicon, the deflection element 65 is highly accurate. Can be manufactured. Further, the inner movable plate 656 and the outer movable plate 653 can be swingably supported with the same spring characteristics as stainless steel, and the deflection mirror surface 651 can be swung stably and at high speed.

  (C) Further, when the deflection mirror surface 651 is driven to swing by the mirror drive unit including the drive units 102b and 102c, the deflection mirror surface 651 is swung around the first axis (main scanning deflection axis) AX1 in the resonance mode. Since it is configured to drive, the deflection mirror surface 651 can be driven to swing around the first axis AX1 with less energy. In addition, the main scanning period of the scanning light beam can be stabilized.

  (D) On the other hand, since the deflection mirror surface 651 is oscillated and driven in the non-resonance mode in order to oscillate and position the deflection mirror surface 651 about the second axis (fine adjustment axis) AX2, the following operation is performed. effective. That is, the swing drive of the deflection mirror surface 651 about the second axis AX2 changes and adjusts the scanning position SL of the scanning light beam in the sub-scanning direction Y. Therefore, after the change adjustment, the deflection mirror surface 651 swings about the second axis AX2. It is necessary to stop the movement. Therefore, in order to perform the swing drive and swing stop with high accuracy, it is desirable to drive the swing in the non-resonant mode.

  (E) Further, as a driving force for swinging and driving the deflection mirror surface 651, an electrostatic adsorption force, an electromagnetic force, or the like can be used. In particular, the deflection mirror surface 651 has a first axis (main scanning deflection axis). ) Since electrostatic attraction force is used to swing and drive around AX1, there is no need to form a coil pattern on the inner movable plate 656, and the deflection element 65 can be made smaller, and the deflection scan speeded up. can do.

  (F) Since the electromagnetic force is used to swing the deflection mirror surface 651 around the second axis (fine adjustment axis) AX2, the driving voltage is lower than that in the case where the electrostatic attraction force is generated. The deflection mirror surface 651 can be driven to swing, voltage control is facilitated, and the positional accuracy of the scanning light beam can be increased.

  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, in the above embodiment, the “imaging unit” of the present invention is configured by one scanning lens 66, but the lens configuration of the imaging unit is not limited to this, and the optical axis OA is not limited to this. The imaging means may be constituted by an imaging optical system having at least one rotationally symmetric lens (optical element). For example, as shown in FIG. 10, the image forming means may be constituted by two resin lenses 66A and 66B. In addition, all of the optical elements constituting the imaging means are not necessarily formed of a resin material, and a part or all of them may be formed of a glass material. However, particularly when part or all of the optical element is formed of a resin material, the usefulness of the present invention becomes remarkable as described in the above embodiment.

  Further, in the above embodiment, the deflection element 65 configured to swing the deflection mirror surface 651 about the two axes AX1 and AX2 is used as the “deflection means” of the present invention. For example, as shown in FIG. A deflection unit 650 in which two oscillating mirrors 65A and 65B are combined may be used. That is, in this embodiment, the light beam from the collimator lens 63 is deflected by the oscillating mirror 65A in the sub-scanning direction Y so that the scanning position in the sub-scanning direction Y on the surface (scanned surface) 2a of the photoreceptor 2 is fine. It is adjustable. That is, in the deflection unit 650 corresponding to the “deflection means” of the present invention, the oscillating mirror 65A functions as the “fine adjustment mechanism” of the present invention. The light beam from the oscillating mirror 65A is deflected in the main scanning direction X by the oscillating mirror 65B, and the light beam is scanned on the surface (scanned surface) 2a of the photosensitive member 2. That is, the oscillating mirror 65B functions as the “deflection mechanism” of the present invention. As these oscillating mirrors 65A and 65B, oscillating mirrors that are oscillated and driven by electromagnetic force or electrostatic attraction force as in the deflection element of FIG. 5, or galvanometer mirrors that are conventionally known can be used. . Further, as the “deflection mechanism” of the present invention, a polygon mirror or the like may be used instead of the oscillating mirror. Further, when the deflection mechanism and the fine adjustment mechanism are separately arranged in this way, the deflection mechanism is arranged on the collimator lens side, while the fine adjustment mechanism is arranged on the scanning lens (imaging means) side. Good.

  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.

1 is a diagram showing an image forming apparatus equipped with an exposure unit as an embodiment of an optical scanning device according to the present invention. FIG. 2 is a block diagram illustrating an electrical configuration of the image forming apparatus in FIG. 1. FIG. 2 is a main scanning sectional view showing a configuration of an exposure unit (optical scanning device) equipped in the image forming apparatus of FIG. 1. FIG. 2 is a sub-scan sectional view showing a configuration of an exposure unit (optical scanning device) provided in the image forming apparatus of FIG. 1. It is a figure which shows the deflection | deviation element which is one component of an exposure unit. It is a figure which shows the deflection | deviation element which is one component of an exposure unit. It is a figure which shows the deflection | deviation element which is one component of an exposure unit. It is a block diagram which shows the structure of an exposure unit and an exposure control part. It is a figure which shows typically the relationship between the scanning position of the scanning light beam on a photoreceptor, and a reference | standard scanning position. It is a figure which shows other embodiment of the optical scanning device concerning this invention. It is a figure which shows another embodiment of the optical scanning device concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 ... Photosensitive body (latent image carrier), 2a ... Photosensitive member surface (scanned surface), 4 ... Developing unit (developing means), 6 ... Exposure unit (exposure means, optical scanning device), 62 ... Laser light source, 63 ... Collimator lens (beam shaping means), 65 ... Deflection element (deflection means), 65A, 65B ... Oscillating mirror, 66 ... Scanning lens (optical element, imaging means), 66A, 66B ... Resin lens (optical element) 102b: first axis drive unit (mirror drive unit), 102c: second axis drive unit (mirror drive unit), 650 ... deflection unit (deflection means), 651 ... deflection mirror surface, 652 ... silicon substrate, 653 ... outside Movable plate, 656 ... inner movable plate, AX1 ... first axis (main scanning deflection axis), AX2 ... second axis (fine adjustment axis), OA ... optical axis, X ... main scanning direction, Y ... sub-scanning direction

Claims (9)

A light source that generates a light beam;
Beam shaping means for shaping the light beam from the light source into a parallel light beam;
Deflecting means for deflecting a parallel light beam emitted from the beam shaping means in a main scanning direction;
An imaging unit having an optical element rotationally symmetric with respect to the optical axis, and imaging a parallel light beam deflected by the deflection unit on a surface to be scanned;
Temperature correction means for correcting movement of the imaging position in the optical axis direction due to temperature change by changing the distance between the light source and the beam shaping means;
The deflection unit includes a deflection mechanism that deflects the parallel light beam from the beam shaping unit in the main scanning direction, and a deflection mechanism that deflects the parallel light beam in a direction different from the main scanning direction and in the sub-scanning direction substantially orthogonal to the main scanning direction. An optical scanning device comprising: a fine adjustment mechanism for finely adjusting a scanning position of the light beam on the surface to be scanned. The deflection means includes
An inner movable member having a deflection mirror surface for reflecting a parallel light beam from the light beam shaping means;
An outer movable member that supports the inner movable member so as to be swingable about a first axis;
A support member that swingably supports the outer movable member around a second axis different from the first axis;
A mirror drive unit that drives the inner movable member to swing around the first axis, and drives the outer movable member to swing around the second axis;
The mirror driving unit swings the deflection mirror surface with one of the first axis and the second axis as a main scanning deflection axis to deflect the parallel light beam in the main scanning direction, while The optical scanning device according to claim 1, wherein the deflection mirror surface is driven to swing as a fine adjustment axis to change the position of the light beam on the surface to be scanned in the sub-scanning direction.   The optical scanning device according to claim 2, wherein the inner movable member, the outer movable member, and the support member are made of silicon single crystal.   4. The optical scanning device according to claim 2, wherein the mirror driving unit swings and drives the deflection mirror surface about the main scanning deflection axis in a resonance mode.   5. The optical scanning device according to claim 2, wherein the mirror driving unit swings and drives the deflection mirror surface about the main scanning deflection axis by an electrostatic attraction force.   6. The optical scanning device according to claim 2, wherein the mirror driving unit swings and positions the deflecting mirror surface around the fine adjustment axis in a non-resonant mode.   The optical scanning device according to claim 2, wherein the mirror driving unit swings and positions the deflection mirror surface around the fine adjustment axis by electromagnetic force.   8. The optical scanning device according to claim 1, wherein at least one of the optical elements constituting the imaging means is a resin lens. A latent image carrier;
9. The optical scanning device according to claim 1, wherein the surface of the latent image carrier is the surface to be scanned and a light beam is scanned to form an electrostatic latent image on the latent image carrier. Exposure means for forming an image;
An image forming apparatus comprising: developing means for developing the electrostatic latent image with toner to form a toner image.

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