JP4576816B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

  The present invention provides an optical scanning device that scans a light beam using a plurality of deflecting mirror surfaces, for example, a deflecting light beam deflected by one deflecting mirror surface is further deflected by another deflecting mirror surface, and the deflection angle of the light beam is increased. The present invention relates to an optical scanning device to be increased and an image forming apparatus equipped with the device.

  Conventionally, an optical scanning device used in an image forming apparatus such as a laser beam printer, a copying machine, or a facsimile machine is provided with two deflection elements to increase the deflection angle of the light beam, and the deflection mirror surface of each deflection element. A configuration for deflecting a light beam may be employed (see, for example, Patent Document 1). In the optical scanning device described in Patent Document 1, the light beam deflected by the first deflection mirror surface is guided to the second deflection mirror surface by the transmission optical system, and the light from the first deflection mirror surface is guided by the second deflection mirror surface. The deflection angle of the light beam is increased by further deflecting the beam. Then, the light beam emitted from the second deflection mirror surface is guided onto the surface to be scanned through the scanning lens. Thus, by combining the first and second deflection mirror surfaces and the transmission optical system, the deflection angle of the light beam is increased.

JP-A-53-97447 (2nd page, Fig. 1)

  When a vibrating mirror such as a galvanometer mirror is used as the deflection element of the above optical scanning device, a drive signal having a frequency that matches the resonance frequency of the vibrating mirror is obtained so that vibration with the maximum amplitude can be obtained with the minimum power. It is generally performed to resonate the vibrating mirror. By resonating the vibration mirror in this way, the vibration amplitude of the vibration mirror is increased and the deflection angle of the light beam is increased.

  By the way, the resonance frequency of the oscillating mirror fluctuates with the temperature change of the environment in which the oscillating mirror is used. Therefore, the following problems may occur. That is, since the oscillating mirror is driven by a drive signal having a constant frequency, the vibration amplitude of the oscillating mirror increases when the resonance frequency matches the driving frequency. However, when the resonance frequency fluctuates with the temperature change as described above, a mismatch between the resonance frequency and the drive frequency occurs, and as a result, the vibration amplitude fluctuates. Therefore, when the temperature of the environment in which the oscillating mirror is used changes, the vibration amplitude of the oscillating mirror is not stable, and thus there is a problem that the light beam cannot be stably deflected.

  The present invention has been made in view of the above problems, and provides an optical scanning device capable of stably deflecting a light beam against a temperature change in an environment in which the optical scanning device is used, and an image forming apparatus including the device. The purpose is to provide.

In order to achieve the above object, an optical scanning device according to the present invention includes a light source that emits a light beam, first and second deflecting mirror surfaces that are swingable about independent main scanning deflection axes, A mirror driving unit that swings and drives the first and second deflection mirror surfaces about the main scanning deflection axis, deflects the light beam from the light source by the first deflection mirror surface, and further applies the deflection light beam. The first deflection mirror surface has a first resonance frequency band in which the deflection angle of the light beam is maximum at the first resonance frequency, and the second deflection mirror surface is deflected by the second deflection mirror surface. The mirror surface has a second resonance frequency band in which the deflection angle of the light beam is maximized at a second resonance frequency different from the first resonance frequency, and the first resonance frequency band and the second resonance frequency band are 1 resonance frequency and the above Overlap each other in the peak-to-peak band sandwiched by two resonance frequencies, the mirror drive unit, a common frequency of the peak-to-peak within the band, and wherein the driving oscillating the first and second deflection mirror surface To do.

In this way configured invention, a change in the deflection angle of the light beam by the two deflection mirror surface due to variations in the resonant characteristics, varying the deflection angle of the light beam so cancel each other. Therefore, even when there is a change in the resonance characteristic due to a temperature change in the use environment, the deflection angle of the light beam deflected by the first deflection mirror surface and further deflected by the second deflection mirror surface can be stabilized.

In particular, it is more preferable that the mirror drive unit swings and drives the first and second deflection mirror surfaces at a substantially central frequency between the first resonance frequency and the second resonance frequency . By oscillating and driving the first and second deflecting mirror surfaces in this manner, the light beam can be deflected with a stable deflection angle even when the first and second resonance frequencies are shifted to the high frequency side or the low frequency side. Can be deflected.

And a deflecting unit having the first and second deflecting mirror surfaces and the mirror driving unit, and an image forming unit for forming an image of the light beam on the surface to be scanned. A scanning optical system that scans in a main scanning direction substantially orthogonal to the main scanning deflection axis; and a transmission optical system that guides the light beam deflected by the first deflection mirror surface to the second deflection mirror surface. The optical system includes a concave mirror surface disposed so that a reflecting surface thereof faces the first and second deflecting mirror surfaces, and the optical beam deflected by the first deflecting mirror surface is the light beam deflected by the first deflecting mirror surface. The light beam may be emitted from the second deflection mirror surface toward the scanned surface by being reflected on the second deflection mirror surface. In this case, it is desirable that the first deflection mirror surface and the second deflection mirror surface are driven to swing in opposite phases.

  In this transmission optical system, the light beam deflected by the first deflection mirror surface is reflected by the concave mirror surface and guided to the second deflection mirror surface. By using a concave mirror as a transmission optical system in this way, a transmission optical system can be configured with a single concave mirror, and a plurality of optical components (two transmission lenses) are essential for configuring the transmission optical system. Compared with the conventional apparatus, the transmission optical system can be simple and configured with a small number of optical components. Further, since the transmission lens is not required, the influence of chromatic aberration can be eliminated, and the light beam can be deflected with excellent stability.

  In addition, any shape can be adopted as the shape of the concave mirror surface, and in particular, an ellipse whose focal point is the substantially center position of the first deflection mirror surface and the substantially center position of the second deflection mirror surface. When an elliptical surface formed by rotating an imaginary straight line passing through the two central positions as a rotation axis is used as the concave mirror surface, the following operational effects can be obtained. That is, since the first and second deflection mirror surfaces are located at the two focal points of the elliptical surface, the principal ray of the light beam deflected by the first deflection mirror surface is reflected by the concave mirror surface (elliptical reflection surface). Thereafter, the light enters the second deflection mirror surface. Therefore, the light beam deflected by the first deflection mirror surface can be reliably guided to the second deflection mirror surface, and the light beam can be stably deflected.

  Further, the arrangement relationship between the first and second deflection mirror surfaces is arbitrary, but a specific operational effect can be obtained by satisfying the following arrangement relationship. For example, when the first and second deflecting mirror surfaces are arranged side by side in a direction parallel to the main scanning direction, the light beam is incident on and emitted from the first and second deflecting mirror surfaces at an angle with respect to the main scanning plane. There is no need. That is, the optical components of the optical scanning device can be arranged in the same main scanning plane. As a result, it is possible to reduce the apparatus size in the sub-scanning direction substantially orthogonal to the main scanning direction, that is, to reduce the apparatus thickness. Further, when the first and second deflection mirror surfaces are arranged side by side in the sub-scanning direction substantially orthogonal to the main scanning direction, the area occupied by the deflecting means in the main scanning plane is minimized, and the apparatus size in the main scanning plane is reduced. Therefore, the apparatus can be reduced in size.

  Further, at least one of the first and second deflection mirror surfaces may be configured to be substantially conjugate with the surface to be scanned in a sub-scanning plane that is substantially orthogonal to the main scanning direction. By adopting such a configuration, it is possible to prevent the influence of the swing in the sub-scanning direction of the deflection mirror surface having a conjugate relationship with the surface to be scanned. Further, the size of the deflecting mirror surface in the sub-scanning direction can be reduced to reduce the size and weight of the deflecting means. As a result, the driving speed of the deflection mirror surface can be further improved to further increase the deflection speed of the light beam.

  Further, the optical scanning device includes a deflecting unit having the first and second deflecting mirror surfaces and the mirror driving unit, and an imaging unit for forming an image of a light beam on the scanned surface, and the scanned surface A scanning optical system that scans the light beam in a main scanning direction substantially orthogonal to the main scanning deflection axis, and a transmission optical system that transmits the light beam between the first and second deflection mirror surfaces, The transmission optical system includes a first transmission lens disposed so that a front focal point thereof substantially coincides with a substantially central position of the first deflection mirror surface, and a front focal point substantially coincident with a rear focal point of the first transmission lens. And a second transmission lens disposed so that the rear focal point substantially coincides with the substantially central position of the second deflection mirror surface, and deflected toward the first transmission lens by the first deflection mirror surface. A light beam is transmitted through the first and second transmissions. The first deflection mirror surface guides the light beam to the second transmission lens by the second deflection mirror surface, and deflects the light beam toward the second transmission lens through the second and first transmission lenses. The light beam may be deflected again by the first deflecting mirror surface by being guided to the deflecting mirror surface, and emitted toward the scanned surface. In this case, it is desirable that the first deflection mirror surface and the second deflection mirror surface are driven to swing with the same phase. With such a configuration, it is possible to always deflect the light beam with a stable deflection angle regardless of fluctuations in the resonance frequencies of the first and second deflection mirror surfaces due to temperature changes in the usage environment. Furthermore, since the reflection position of the light beam on the first deflection mirror surface and the reflection position of the light beam on the second deflection mirror surface are in a conjugate relationship, the light beam can be reliably transferred from the first deflection mirror surface. The light beam can be stably deflected by guiding the second deflection mirror surface from the second deflection mirror surface to the second deflection mirror surface.

  Of course, the first deflection mirror surface may be substantially conjugate with the surface to be scanned in a sub-scanning plane that is substantially orthogonal to the main scanning direction. By adopting such a configuration, it is possible to prevent the influence of the swing in the sub-scanning direction of the deflection mirror surface having a conjugate relationship with the surface to be scanned. Further, the size of the deflecting mirror surface in the sub-scanning direction can be reduced to reduce the size and weight of the deflecting means. As a result, the driving speed of the deflection mirror surface can be further improved to further increase the deflection speed of the light beam.

  In addition, as a deflecting unit in the case where the transmission optical system is configured by a concave mirror, one in which two deflecting elements (for example, galvanometer mirrors) having a single deflecting mirror surface are arranged in parallel can be used. A deflecting unit configured as described above may be used. That is, the deflection means includes a first movable member having the first deflection mirror surface, a second movable member having the second deflection mirror surface, and the first and second movable members substantially in the main scanning direction. A support member that swingably supports the main scanning deflection axis extending in a direction orthogonal to the main scanning deflection axis; and the mirror driving unit, wherein the mirror driving unit includes the first and second deflections around the main scanning deflection axis. The mirror surface is swung to deflect the light beam. Here, for the first movable member, the second movable member, and the support member, the first movable member, the second movable member, and the support member are integrally formed by processing one substrate. Also good. By integrally forming in this way, the first and second deflection mirror surfaces having the optimum resonance characteristics for the present invention can be easily created, and the light beam can be stably deflected. The deflecting means also supports a movable member having a deflecting mirror surface for deflecting the light beam on one surface, and the movable member swingably around the main scanning deflection axis extending in a direction substantially perpendicular to the main scanning direction. The deflecting mirror surface of the one of the two deflecting elements is the first deflecting mirror surface and the deflecting mirror of the other deflecting element. A surface whose surface is the second deflection mirror surface can be used. Note that a micromachining technique can be applied to the substrate processing method. By using the processing technique, a deflecting unit can be created with high accuracy, which is advantageous in stabilizing the deflection angle of the light beam.

  Moreover, a silicon single crystal can be used as the substrate, the movable member, and the support member. For example, a movable member can be formed by using a silicon single crystal substrate as a support member and applying a micromachining technique to the substrate. When the movable member and the support member of the deflection element are configured using the silicon single crystal in this way, the first and second deflection mirror surfaces can be manufactured with high accuracy. Further, the movable member can be supported in a swingable manner with the same spring characteristics as stainless steel, and the first and second deflection mirror surfaces can be swung stably and at high speed.

  Further, as a driving force for swinging and driving the first and second deflecting mirror surfaces, an electrostatic adsorption force, an electromagnetic force, or the like can be used, and each has the following characteristics. When the electrostatic attraction force is used, it is not necessary to form a coil pattern, the deflection element can be miniaturized, and the deflection operation of the light beam can be further accelerated. On the other hand, when the electromagnetic force is used, the first and second deflection mirror surfaces can be driven to oscillate with a lower driving voltage than when the electrostatic attraction force is generated, and the voltage control is facilitated. Can improve the position system. Thus, since it has a mutually different characteristic, what is necessary is just to employ | adopt the driving force according to the intended purpose.

<First Embodiment>
FIG. 1 is a view showing an image forming apparatus equipped with an exposure unit according to a first 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 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.

  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 (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. 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, the color toner images formed on the photoreceptor 2 are superimposed on the intermediate transfer belt 71 to form a color image, and the color images are 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.

  3 and 4 are main scanning sectional views showing the configuration of the exposure unit (optical scanning device) installed in the image forming apparatus of FIG. 1, and FIG. 5 is the exposure unit (optical scanning) installed in the image forming apparatus of FIG. FIG. 6 and FIG. 7 are diagrams showing a deflecting element (deflecting means) as a constituent element of the exposure unit, and FIG. 8 is a driving of a light beam by the deflecting element shown in FIGS. FIG. 9 is a schematic diagram showing the change in the deflection angle of the light beam when the resonance characteristic shown in FIG. 8 is changed. 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 a light source driving unit (not shown) of the exposure control unit 102. For this reason, the light source driving unit controls ON / OFF of the laser light source 62 according to the image data, and a light beam modulated in accordance with the image data is emitted from the laser light source 62.

  Further, in this exposure casing 61, a collimator lens 631, a cylindrical lens 632, and “deflecting means” of the present invention are used to scan and expose the light beam from the laser light source 62 onto the surface (not shown) of the photosensitive member 2. , A scanning lens 66 corresponding to the “imaging means” of the present invention, a transmission optical system 67, and a folding mirror 68 are 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 as shown in FIG. The Further, the light beam that has passed through the cylindrical lens 632 is folded back by the folding mirror 641 and then incident on the focusing lens 64 having power only in the main scanning direction X as shown in FIG. Then, by adjusting the cylindrical lens 632, the collimated light is imaged in the vicinity of the deflection mirror surface 651a of the deflection element 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. On the other hand, the focal length of the focusing lens 64 is longer than the distance between the lens 64 and the first deflection mirror surface 651a. Therefore, a line image extending in the main scanning direction X is formed in the vicinity of the deflecting mirror surface 651a of the deflecting 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 light beam reflected by the deflecting mirror surfaces 651a and 651b is in the main scanning direction. The light beam can be deflected to X. More specifically, the deflection element 65 is configured as follows.

  In this deflecting element 65, as shown in FIG. 6, 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, two movable plates (corresponding to “first and second movable members” of the present invention) 656a and 656b are provided in the main scanning direction X with a predetermined distance therebetween. The movable plate 656a is formed in a flat plate shape, is elastically supported on the silicon substrate 652 by a torsion spring 657, and can swing around a first axis AX1a extending substantially parallel to the sub-scanning direction Y. In addition, an aluminum film or the like is formed as a first deflection mirror surface 651a at the center of the upper surface of the movable plate 656a. The movable plate 656b is configured in the same manner as the movable plate 656a. That is, the movable plate 656b formed in a flat plate shape is provided to be swingable with respect to the silicon substrate 652 around the first axis AX1b, and an aluminum film or the like is provided at the center of the upper surface of the movable plate 656a as the second deflection mirror. A film is formed as the surface 651b.

  In addition, electrodes 658a and 658b are respectively fixed to the movable plates 656a and 656b on the inner bottom surface of the recess 652a of the silicon substrate 652 at positions facing both ends of the movable plate. These two electrodes 658a and 658b function as electrodes for swinging and driving the movable plates 656a and 656b around the first axes AX1a and AX1b. That is, these electrodes 658a and 658b are electrically connected to a drive unit (not shown) of the exposure control unit 102, and electrostatic application is performed between the electrodes and the deflecting mirror surfaces 651a and 651b by applying a voltage to the electrodes. The attraction force acts to draw one end of the deflecting mirror surfaces 651a and 651b toward the electrode. Therefore, when a predetermined voltage is alternately applied to the electrodes 658a and 658b from the drive unit, the deflection mirror surfaces 651a and 651b can be reciprocally oscillated using the torsion spring 657 as the first axes AX1a and AX1b, respectively. When the driving frequency of the reciprocating vibration is set to the resonance frequency bands B1 and B2 of the deflecting mirror surfaces 651a and 651b, the deflection widths of the deflecting mirror surfaces 651a and 651b are increased, and light from the deflecting mirror surfaces 651a and 651b is increased. The deflection angle of the beam can be increased (see FIG. 8). FIG. 8 is a diagram schematically showing the resonance characteristics A and B of the deflection angle of the light beam by the deflecting mirror surfaces 651a and 651b. The horizontal axis represents the driving frequency of the deflecting mirror surfaces 651a and 651b, and the vertical axis. Indicates the deflection angle of the light beam by the deflecting mirror surfaces 651a and 651b. In this embodiment, the electrodes 658a and 658b are arranged in a symmetrical relationship with the deflecting mirror surfaces 651a and 651b, and are configured to swing in opposite phases.

  Thus, in the deflecting element (deflecting means) 65, the drive unit of the exposure control unit 102 functions as the “mirror drive unit” of the present invention, and the deflection mirror surfaces 651a and 651b are moved to the first axis by controlling the drive unit. The light beam is deflected and swung in the main scanning direction X by swinging around AX1a and AX1b in opposite phases. That is, the first axes AX1a and AX1b are caused to function as main scanning deflection axes.

  The light beam reflected by the first deflection mirror surface 651a of the deflecting element 65 configured as described above is incident on the transmission optical system 67, and then is transmitted by the transmission optical system 67 to the second deflection mirror surface 651b of the deflection element 65. Returned to Therefore, for example, the light beam deflected to the first deflection angle by the deflection element 65 is emitted toward the scanning lens 66 at a second deflection angle larger than the first deflection angle. In this embodiment, the transmission optical system 67 is configured as follows.

  As shown in FIG. 4, the transmission optical system 67 is composed of a single concave mirror 671, and the reflection surface 671a of the concave mirror 671 and the first and second deflection mirror surfaces 651a and 651b are opposed to each other. Are arranged to be. The light beam deflected by the first deflecting mirror surface 651a is reflected by the reflecting surface 671a of the concave mirror 671 and guided to the second deflecting mirror surface 651b. In this embodiment, an ellipsoidal mirror in which the reflecting surface 671a is formed into an ellipsoid is used as the concave mirror 671. More specifically, an ellipse having a focus at approximately the center position P1a of the first deflection mirror surface 651a and approximately the center position P1b of the second deflection mirror surface 651b is represented by an imaginary straight line VL passing through the two center positions P1a and P1b. A part of an ellipsoid formed by rotating as a rotation axis is used as the reflection surface 671a. Therefore, the following effects can be obtained. That is, since the first and second deflection mirror surfaces 651a and 651b are positioned at two focal points, the principal ray of the light beam deflected by the first deflection mirror surface 651a is reflected by the concave mirror surface (elliptical reflection surface) 671a. Then, the light enters the second deflection mirror surface 651b. Therefore, the light beam deflected by the first deflection mirror surface 651a can be reliably guided to the second deflection mirror surface 651b. Then, this light beam is deflected by the second deflection mirror surface 651 b and emitted toward the scanning lens 66. As a result, the light beam can be scanned stably.

  The light beam deflected by the deflecting element 65 in this manner is applied to the surface (scanned surface) of the photosensitive member 2 through the scanning lens 66 and the folding mirror 68. 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.

  Thus, in this embodiment, the light beam deflected to the first deflection angle, for example, by the first deflection mirror surface 651a is reflected toward the second deflection mirror surface 651b by the concave mirror surface (elliptical reflection surface) 671a. Thus, the second deflection mirror surface 651b deflects the scanning lens 66 at a second deflection angle larger than the first deflection angle. The magnitude of the second deflection angle can be schematically represented as a resonance characteristic C obtained by adding the resonance characteristics A and B (see FIG. 8). Since the high frequency side of the resonance characteristic A and the low frequency side of the resonance characteristic B partially overlap each other, the resonance characteristic C has a band with a substantially constant deflection angle. In this embodiment, the first and second deflecting mirror surfaces 651a and 651b include the first driving frequency band DB1 in which the first and second resonance frequency bands B1 and B2 partially overlap each other, and the first and second deflecting mirrors. The light beam is deflected by being oscillated and driven at a frequency fD substantially at the center of the second drive frequency band DB2 where the inter-peak band PB sandwiched between the first and second resonance frequencies f1 and f2 of the surfaces 651a and 651b overlap each other. ing.

  In this embodiment, as shown in FIG. 3, the start or end of the scanning light beam from the deflection element 65 is guided to the synchronization sensor 60 by the folding mirrors 69a to 69c. 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 swings around the first axes AX1a and AX1b (main scanning deflection axes) parallel to the sub-scanning direction Y substantially orthogonal to the main scanning direction X. The first and second deflecting mirror surfaces 651a and 651b for deflecting the light beam are provided. The light beam deflected toward the transmission optical system 67 by the first deflection mirror surface 651a is guided to the second deflection mirror surface 651b by the transmission optical system 67, and is deflected again by the second deflection mirror surface 651b to be photosensitive. It is emitted toward the surface (scanned surface) of the body 2. In this way, the deflection angle of the light beam emitted toward the photosensitive member surface is made larger than the deflection angle of the light beam incident on the transmission optical system 67.

  Further, the first deflection mirror surface 651a is configured so as to be able to deflect the light beam more largely by the resonance phenomenon when driven to oscillate at the frequency of the first resonance frequency B1, and the second deflection mirror surface 651b includes the first deflection mirror surface 651b. When driven to oscillate at the frequency of the second resonance frequency band B2 that partially overlaps the resonance frequency band B1, the optical beam can be deflected more greatly by the resonance phenomenon (see FIG. 8).

  Further, the first and second deflection mirror surfaces 651a and 651b are portions where the first and second resonance frequency bands B1 and B2 partially overlap each other, that is, the high frequency side of the first resonance frequency band B1 and the second resonance frequency. The light beam is deflected by being oscillated by the mirror drive unit at the frequency fD of the first drive frequency band DB1 where the low frequency side of the band B2 overlaps each other. For this reason, as the resonance characteristics A and B of the deflection mirror surfaces 651a and 651b shift to the low frequency side, the deflection angle of the light beam by the first deflection mirror surface 651a driven at the frequency fD decreases, and the same frequency fD. The deflection angle of the light beam by the second deflecting mirror surface 651b driven by increases. Further, when shifted to the high frequency side, the reverse behavior is exhibited. In this way, the deflection angle of the light beam fluctuates so that the changes in the deflection angle of the light beam caused by the two deflecting mirror surfaces 651a and 651b due to fluctuations in the resonance characteristics A and B cancel each other. Therefore, even when there are fluctuations in the resonance characteristics A and B due to temperature changes in the use environment, the deflection angle of the light beam deflected by the first deflection mirror surface 651a and further deflected by the second deflection mirror surface 651b is stabilized. Can do.

  Here, even when the resonance characteristics A and B vary, the state in which the deflection angle of the light beam by the first and second deflection mirror surfaces 651a and 651b is stable will be described in more detail with reference to FIG. explain. In FIG. 9, the horizontal axis represents the driving frequency of the deflecting mirror surfaces 651a and 651b, and the vertical axis represents the second deflected by the transmission optical system 67 after being deflected by the first deflecting mirror surface 651a. The magnitude of the deflection angle of the light beam deflected by the deflection mirror surface 651b is shown. In this embodiment, the deflecting mirror surfaces 651a and 651b are oscillated and driven at the above-described frequency fD, and deflect the light beam at a deflection angle of the magnitude indicated by the one-dot chain line of the resonance characteristic C indicated by the broken line. ing. When the resonance characteristics A and B shift to the high frequency side due to the temperature change of the use environment, the deflection angle of the light beam deflected toward the scanning lens 66 by the second deflection mirror surface 651b is also shown as the resonance characteristic C1. Shift to the high frequency side (see FIG. 9A). However, as described above, since the deflection angle of the light beam by the first deflection mirror surface 651a increases and the deflection angle of the light beam by the second deflection mirror surface 651b decreases, the final deflected toward the scanning lens 66 is achieved. The deflection angle of a typical light beam does not vary as shown in FIG. Even when the resonance characteristics A and B are shifted to the low frequency side, the deflection angle of the final light beam deflected toward the scanning lens 66 does not vary as shown in FIG. 9B for the same reason. As described above, even when the resonance characteristics A and B are fluctuated due to the temperature change of the use environment, the deflection angle of the light beam deflected by the first deflection mirror surface 651a and further deflected by the second deflection mirror surface 651b is stabilized. Can be made.

  In this embodiment, the first resonance frequency f1 at which the deflection angle of the light beam by the first deflection mirror surface 651a is the maximum in the first resonance frequency band B1 and the second deflection mirror in the second resonance frequency band B2. The second resonance frequency f2 that maximizes the deflection angle of the light beam by the surface is different from each other, and both the first and second resonance frequencies f1 and f2 are included in the first drive frequency band DB1. ing. Therefore, the first drive frequency bandwidth DB1 that can stabilize the deflection angle of the light beam can be widened.

  In this embodiment, the mirror driving unit has a second driving frequency band DB2 in which the peak-to-peak band PB sandwiched between the first and second resonance frequencies f1 and f2 and the first driving frequency band DB1 overlap each other. The first and second deflection mirror surfaces 651a and 651b are driven to swing at a frequency. Accordingly, the first and second deflection mirror surfaces 651a and 651b are driven to swing at a frequency in the vicinity of the first and second resonance frequencies f1 and f2, so that the light beam can be deflected with a larger deflection angle. At the same time, the deflection angle of the light beam can be stabilized. Further, the first and second deflecting mirror surfaces 651a and 651b are driven to swing at a frequency fD substantially at the center of the second driving frequency band DB2. Therefore, it is possible to deflect the light beam with a stable deflection angle even when the first and second resonance characteristics A and B have a larger fluctuation toward the high frequency side or the low frequency side (see FIG. 9).

  In this embodiment, the magnitude of the deflection angle of the light beam deflected by the first deflection mirror surface 651a when the first deflection mirror surface 651a is driven to oscillate in the first resonance frequency band B1 is The second deflecting mirror surface 651b is configured to monotonously increase as the frequency increases in a range lower than the first resonance frequency f1, and monotonously decrease as the frequency increases in a range higher than the first resonance frequency f1. However, the magnitude of the deflection angle of the light beam deflected by the second deflection mirror surface 651b when driven to oscillate in the second resonance frequency band B2 is a frequency in the range lower than the second resonance frequency f2. It is configured to monotonously increase with increasing and monotonously decrease with increasing frequency in the range of higher frequencies than the second resonance frequency f2. Accordingly, the change in the deflection angle of the light beam caused by the two deflecting mirror surfaces 651a and 651b due to the change in both resonance characteristics A and B cancels each other more reliably, so that the deflection angle of the light beam can be further stabilized. .

  Further, in this embodiment, the transmission optical system includes a concave mirror 671 disposed so that the reflection surface 671a thereof faces the first and second deflection mirror surfaces 651a and 651b, and the concave mirror surface 671a is the first deflection. By reflecting the light beam deflected by the mirror surface 651a to the second deflection mirror surface 651b, the light beam is emitted from the second deflection mirror surface 651b toward the surface (scanned surface) of the photoreceptor 2. It is configured. Further, the first deflecting mirror surface 651a and the second deflecting mirror surface 651b are oscillated and driven in opposite phases to deflect the light beam. In this way, by using the concave mirror 671 as the transmission optical system 67, the transmission optical system 67 can be configured by a single concave mirror 671, and a plurality of optical components (two transmission lenses are used in configuring the transmission optical system). The transmission optical system is simpler and can be configured with a smaller number of optical components than the conventional apparatus that has required the above). Further, since the transmission lens is not required, the influence of chromatic aberration can be eliminated, and the light beam can be deflected with excellent stability.

  In this embodiment, the first and second deflecting mirror surfaces 651a and 651b are arranged side by side in a direction parallel to the main scanning direction X. Therefore, it is not necessary to make the light beam enter and exit the first and second deflecting mirror surfaces 651a and 651b at an angle with respect to the main scanning plane. That is, the optical components of the optical scanning device can be arranged in the same main scanning plane. As a result, the apparatus size in the sub-scanning direction Y can be reduced, that is, the apparatus can be thinned.

  In this embodiment, both the first and second deflection mirror surfaces 651a and 651b are substantially conjugate with the surface (scanned surface) of the photoreceptor 2 in the sub-scanning plane that is substantially orthogonal to the main scanning direction X. It is composed. By adopting such a configuration, it is possible to prevent the influence of the swinging of both deflection mirror surfaces 651a and 651b in the sub-scanning direction Y. Further, the size of the deflection mirror surfaces 651a and 651b in the sub-scanning direction Y can be reduced to reduce the size and weight of the deflection element (deflecting means). As a result, the driving speed of the deflection mirror surfaces 651a and 651b can be further improved to further increase the scanning speed of the light beam.

  Furthermore, in this embodiment, since the first deflection mirror surfaces 651a and 651b and the support member are integrally formed on one silicon substrate 652 using a micromachining technique, a deflection element (deflection means) is highly accurately formed. 65 can be created, which is advantageous in improving the scanning performance of the light beam. In addition, the movable plates 656a and 656b can be swingably supported with the same spring characteristics as stainless steel, and the first and second deflection mirror surfaces 651a and 651b can be swung stably and at high speed. Can do.

<Second Embodiment>
10 and 11 are main scanning sectional views showing a second embodiment of the optical scanning device according to the present invention. 12 is a sub-scan sectional view of the optical scanning device of FIG. The difference between the exposure unit 6 as the optical scanning device according to the second embodiment and the first embodiment is the configuration of the deflection element 65. That is, the second embodiment is that the first and second deflection mirror surfaces 651a and 651b are arranged in the sub-scanning direction Y as shown in FIG. In the exposure unit 6 configured in this manner, 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 only in the sub-scanning direction Y as shown in FIG. The light enters a cylindrical lens 632 having power. Further, as shown in FIG. 11, the light beam that has passed through the cylindrical lens 632 is incident on the focusing lens 64 having power only in the main scanning direction X, and is then folded back toward the first deflection mirror surface 651a by the folding mirror 641. . Then, by adjusting the cylindrical lens 632, the collimated light is imaged near the deflection mirror surface 651a at the lower position in the sub-scanning direction Y. The light beam deflected by the deflecting mirror surface 651a is reflected by the concave mirror surface 671a of the transmission optical system 67 and guided to the deflecting mirror surface 651b at the upper position, and directed toward the scanning lens 66 by the deflecting mirror surface 651b. Is deflected.

  Also in the second embodiment, the first and second deflecting mirror surfaces 651a and 651b are oscillated and driven by the mirror driving unit with the frequency fD of the second driving frequency band DB2 as the driving frequency to deflect the light beam. The same effects as the first embodiment are achieved. In addition, since the light beam is configured to be folded back by the concave mirror 671 of the transmission optical system 67, the same effect as the first embodiment is obtained. Further, since the first and second deflection mirror surfaces 651a and 651b are arranged side by side in the sub-scanning direction Y, the area occupied by the deflection element (deflection means) 65 in the main scanning plane is as shown in FIGS. This minimizes the size of the apparatus in the main scanning plane, and enables downsizing of the apparatus.

  In the first and second embodiments, both the first and second deflection mirror surfaces 651a and 651b are substantially conjugate with the surface of the photoconductor 2 (scanned surface) in the sub-scanning plane. Only one of the first and second deflecting mirror surfaces 651a and 651b may be substantially conjugate with the surface (scanned surface) of the photosensitive member 2, and by adopting such a configuration, the conjugate relationship with the scanned surface is obtained. The influence of the swinging of the deflection mirror surface in the sub-scanning direction can be prevented.

  In the first and second embodiments, the deflecting element 65 in which the first and second deflecting mirror surfaces 651a and 651b are integrated is used as the deflecting means. However, like the galvanometer mirror having one deflecting mirror surface. It goes without saying that two oscillating mirrors may be used in parallel.

<Third Embodiment>
FIG. 13 is a diagram showing a third embodiment of the optical scanning device according to the present invention. 13 is a main scanning sectional view showing a configuration of an exposure unit (optical scanning device) provided in the image forming apparatus of FIG. 1, FIG. 14 is a diagram showing a transmission optical system as one component of the exposure unit, FIG. 15 and FIG. 16 is a view showing a deflecting element as one component of the exposure unit. The difference between this embodiment and the first and second embodiments is that, as shown in FIG. 13, transfer optics for transmitting a light beam between the first deflection mirror surface 851a and the second deflection mirror surface 851b. The configuration of the system 87 and the configuration of the deflecting means 85 are different. Hereinafter, the configuration and operation of the exposure unit will be described in detail with a focus on differences from the first and second embodiments with reference to these drawings.

  The deflecting means 85 is composed of two deflecting elements 85a and 85b. Since the deflection elements 85a and 85b have the same structure, the configuration of one deflection element 85a will be described here, and the configuration of the other deflection element 85b will be denoted by a corresponding reference numeral, and description thereof will be omitted. The deflection element 85a 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 deflects the light beam reflected by the deflection mirror surface 851a in the main scanning direction X. It is possible. More specifically, the deflection element 85a is configured as follows.

  In this deflecting element 85a, as shown in FIG. 15, the silicon substrate 852a functions as a “supporting member” of the present invention, and a part of the silicon substrate 852a is further processed to move the movable plate 856a (“movable in the present invention” Member ") is provided. The movable plate 856a is formed in a flat plate shape, is elastically supported on the silicon substrate 852a by a torsion spring 857a, and is swingable about a first axis BX1a extending substantially parallel to the sub-scanning direction Y. In addition, an aluminum film or the like is formed as a deflection mirror surface 851a at the center of the upper surface of the movable plate 856a.

  Further, as shown in FIG. 16, a concave portion 8521a is provided at a substantially central portion of the silicon substrate 852a so that the movable plate 856a can swing around the first axis BX1a. Electrodes 8581a and 8582a are fixed to positions on the inner bottom surface of the recess 8521a that face both ends of the movable plate 856a. These two electrodes 8581a and 8582a function as electrodes for swinging and driving the movable plate 856a around the first axis BX1a. That is, these electrodes 8581a and 8582a are electrically connected to a drive unit (not shown) of the exposure control unit 102, and electrostatic application between the electrodes and the first deflection mirror surface 851a is caused by applying a voltage to the electrodes. The attracting force acts to draw one end portion of the first deflection mirror surface 851a toward the electrode side. Therefore, when a predetermined voltage is alternately applied to the electrodes 8581a and 8582a from the drive unit, the first deflection mirror surface 851a can be reciprocally oscillated using the torsion spring 857a as the first axis BX1a. When the driving frequency of the reciprocating vibration is set to a frequency in the resonance frequency band of the deflecting mirror surface 851a, the deflection width of the deflecting mirror surface 851a increases, and the deflection angle of the light beam by the deflecting mirror surface 851a can be increased. . In this embodiment, the first deflection mirror surface 851a and the second deflection mirror surface 851b are configured to swing with the same phase.

  As described above, in the deflecting unit 85, the drive unit of the exposure control unit 102 functions as the “mirror drive unit” of the present invention, and the deflection mirror surfaces 851a and 851b are moved around the first axis by controlling the drive unit. The light beam is deflected and swung in the main scanning direction X by swinging as in the first and second embodiments. That is, the first axis functions as the main scanning deflection axis.

  The light beam deflected by the first deflection mirror surface 851a of the deflecting element 85a configured as described above is incident on the transmission optical system 87, and then is transmitted by the transmission optical system 87 to the second deflection mirror surface 851b of the deflection element 85b. And then re-deflected by the transmission optical system 87. Then, the light is again returned to the first deflection mirror surface 851a of the deflection element 85a. Therefore, for example, the light beam deflected to the first deflection angle by the deflection element 85a is deflected toward the transmission optical system 87 by the deflection element 85b at a second deflection angle larger than the first deflection angle, and returned to the deflection element 85a. It is. Then, the light is deflected toward the scanning lens 66 at a third deflection angle larger than the second deflection angle. In this embodiment, the transmission optical system 87 is configured as follows.

  FIG. 14 is a diagram showing the configuration of the transmission optical system. The transmission optical system 87 includes a first transmission lens 871 disposed so that its front focal point substantially coincides with the substantially central position of the first deflection mirror surface 851a, and its front focal point is a rear focal point of the first transmission lens 871. And a second transfer lens 872 disposed so that the rear focal point substantially coincides with the substantially central position of the second deflection mirror surface 851b. Then, the light beam deflected at the first deflection angle toward the first transmission lens 871 by the first deflection mirror surface 851a is guided to the second deflection mirror surface 851b via the first and second transmission lenses 871 and 872. The light beam is guided to the first deflection mirror surface 851a by deflecting the light beam toward the second transmission lens 872 at the second deflection angle by the second deflection mirror surface 851b. As a result, the light beam is deflected again by the first deflection mirror surface 851a, and the light beam is emitted toward the scanning lens 66 at a third deflection angle larger than the first deflection angle.

  As a specific configuration of the transmission optical system 87 having such characteristics, those having the optical specifications shown in Table 1 can be adopted.

なお、本設計例においては伝達光学系８７を構成する第１伝達レンズ８７１の２面Ｓ1，Ｓ2および第２伝達レンズ８７２の2面Ｓ3，Ｓ4は軸対称非球面である。また、表中における各記号は以下の通りである。

In this design example, the two surfaces S1, S2 of the first transmission lens 871 and the two surfaces S3, S4 of the second transmission lens 872 constituting the transmission optical system 87 are axisymmetric aspheric surfaces. Moreover, each symbol in the table is as follows.

Si: surface number (where S0 is the first deflection mirror surface 851a and S5 is the second deflection mirror surface 851b)
ri: radius of curvature of surface number i di: axial distance from surface number i to (i + 1) surface ni: refractive index of surface number i Ki: when surface number i is an axisymmetric aspherical surface Aspheric coefficient of axisymmetric aspheric surface

ただし、ｚは光軸からの高さｙにおける非球面の点の非球面頂点の接平面からの距離である。

However, z is the distance from the tangent plane of the aspherical vertex of the aspherical point at the height y from the optical axis.

  In this embodiment, the reflection position of the light beam on the first deflection mirror surface 851a and the reflection position of the light beam on the second deflection mirror surface 851b have a conjugate relationship, so that the light beam can be reliably transmitted. The light beam can be stably deflected by guiding from the first deflection mirror surface 851a to the second deflection mirror surface 851b and from the second deflection mirror surface 851b to the second deflection mirror surface 851a.

  The light beam that has been incident and deflected twice in this manner on the deflecting element 85 a is applied to the surface (scanned surface) of the photosensitive member 2 via the scanning lens 66 and the folding mirror 68. 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.

  Also in this embodiment, since the first and second deflecting mirror surfaces 851a and 851b are driven to swing in the same manner as in the first and second embodiments, the same function and effect as in the first and second embodiments. Have

  Further, since the first deflection mirror surface 851a is configured to be substantially conjugate with the surface (scanned surface) of the photosensitive member 2 in the sub-scanning plane that is substantially orthogonal to the main scanning direction X (not shown), It is possible to prevent the influence of the swing in the sub-scanning direction Y of the first deflection mirror surface 851a having a conjugate relationship with the surface. Further, the size of the first deflection mirror surface 851a in the sub-scanning direction Y can be reduced, and the deflection element 85a can be reduced in size and weight.

  In the first to third embodiments, the deflecting mirror surfaces 651a, 651b, 851a, and 851b are swung using electrostatic force, but may be swung using other driving force. . Here, for example, an electromagnetic force can be used as another driving force.

<Fourth embodiment>
17 and 18 are views showing a fourth embodiment of the optical scanning device according to the present invention. The fourth embodiment is greatly different from the third embodiment in that the deflecting mirror surfaces 851a and 851b are driven to swing using electromagnetic force, and other configurations are different from those of the third embodiment. It is the same. Also in the deflecting element 65 of the first and second embodiments, the deflecting mirror surfaces 651a and 651b can be driven to swing using electromagnetic force by adopting the same configuration as that of the present embodiment. Here, description will be made by taking the deflection element 85a shown in FIGS. 17 and 18 as an example. Also, the same reference numerals are used for parts having the same configuration as in the third embodiment.

  In the deflection element 85a, as shown in FIG. 17, a movable plate 856a is provided by processing a part of the silicon substrate 852a. The movable plate 856a is formed in a flat plate shape, is elastically supported on the silicon substrate 852a by a torsion spring 857a, and is swingable about a first axis BX1a extending substantially parallel to the sub-scanning direction Y. Further, on the upper surface of the movable plate 856a, a planar coil 855a electrically connected to a pair of outer electrode terminals (not shown) formed on the upper surface of the silicon substrate 852a via a torsion spring 857a is coated with an insulating layer. ing. In addition, an aluminum film or the like is formed as a deflection mirror surface 851a at the center of the upper surface of the movable plate 856a.

  Further, as shown in FIG. 18, a concave portion 8521a is provided at a substantially central portion of the silicon substrate 852a so that the movable plate 856a can swing around the first axis BX1a. Then, permanent magnets 8591a and 8592a are fixed to the inner bottom surface of the recess 8521a at the outer positions of both ends of the movable plate 856a in different orientations. The planar coil 855a is electrically connected to a drive unit (not shown) of the exposure control unit 102, and the direction of the current flowing through the planar coil 855a by energization of the coil 855a and the magnetic flux generated by the permanent magnets 8591a and 8592a. Lorentz force acts depending on the direction, and a moment for rotating the movable plate 856a is generated. As a result, the movable plate 856a (deflection mirror surface 851a) swings with the torsion spring 857a as the first axis BX1a. Here, if the current flowing through the planar coil 855a is an alternating current and is continuously repeated, the deflection mirror surface 851a can be reciprocally oscillated with the torsion spring 857a serving as the first axis BX1a. When the driving frequency of the reciprocating vibration is set to a frequency in the resonance frequency band of the deflecting mirror surface 851a, the deflection width of the deflecting mirror surface 851a is increased, and the deflection angle of the light beam by the deflecting mirror surface 851a can be increased. .

  In order to swing the first deflection mirror surface 851a in this way, an electromagnetic force, an 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 swinging and driving the first deflection mirror surface 851a, the first deflection mirror surface 851a is driven to swing at 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, it is not necessary to form a coil pattern, the deflection element 85a can be further miniaturized, and the deflection scanning can be further speeded up.

  In the first and second embodiments, the deflection element 65 in which the first and second deflection mirror surfaces 651a and 651b are integrated is used. However, the deflection elements 85a and 85b in the third and fourth embodiments. Needless to say, these may be used in parallel.

  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 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. 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 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 schematic diagram which shows the resonance characteristic of the deflection | deviation element which is one component of an exposure unit. It is a schematic diagram which shows the fluctuation | variation of the resonance characteristic of the deflection | deviation element which is one component of an exposure unit. It is a main scanning sectional view showing a second embodiment of the optical scanning device according to the present invention. It is a main scanning sectional view showing a second embodiment of the optical scanning device according to the present invention. FIG. 12 is a sub-scan sectional view of the optical scanning device of FIGS. 10 and 11. It is a main scanning sectional view showing a third embodiment of the optical scanning device according to the present invention. It is a figure which shows the transmission optical system which is one component of the exposure unit which is 3rd Embodiment of the optical scanning device concerning this invention. It is a figure which shows the deflection | deviation element of the exposure unit which is 3rd Embodiment of the optical scanning device concerning this invention. It is a figure which shows the deflection | deviation element of the exposure unit which is 3rd Embodiment of the optical scanning device concerning this invention. It is a figure which shows the deflection | deviation element of the exposure unit which is 4th Embodiment of the optical scanning device concerning this invention. It is a figure which shows the deflection | deviation element of the exposure unit which is 4th Embodiment of the optical scanning device concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 ... Photosensitive body (latent image carrier), 4 ... Development unit (developing means), 6 ... Exposure unit (optical scanning device), 65 ... Deflection element (deflection means), 85a, 85b ... Deflection element (deflection means), 66 ... Scanning lens (imaging means), 67, 87 ... Transmission optical system, 651a, 651b, 851a, 851b ... Deflection mirror surface, 652, 852a ... Silicon substrate (support member), 656a, 656b, 856a ... Movable plate ( Movable member), 671 ... concave mirror (transmission optical system), 671a ... concave mirror surface, 871, 872 ... transmission lens, L ... light beam, P1a, P1b ... reflection position, AX1a, AX1b, BX1a ... main scanning deflection Axis, B1, B2 ... resonant frequency band, DB1, DB2 ... drive frequency band, PB ... peak-to-peak band, X ... main scanning direction, Y ... sub-scanning direction

Claims (18)

A light source that emits a light beam, first and second deflection mirror surfaces that are swingable about independent main scanning deflection axes, and the first and second deflection mirror surfaces around the main scanning deflection axis. An optical scanning device comprising: a mirror drive unit that oscillates and deflecting the light beam from the light source by the first deflection mirror surface; and deflecting the deflection light beam by the second deflection mirror surface;
The first deflection mirror surface has a first resonance frequency band in which the deflection angle of the light beam is maximum at the first resonance frequency ,
The second deflection mirror surface has a second resonance frequency band in which the deflection angle of the light beam is maximized at a second resonance frequency different from the first resonance frequency,
The first resonance frequency band and the second resonance frequency band overlap each other in a peak-to-peak band sandwiched between the first resonance frequency and the second resonance frequency,
The optical scanning device, wherein the mirror driving unit swings and drives the first and second deflection mirror surfaces at a common frequency within the peak-to-peak band .   2. The optical scanning device according to claim 1, wherein the mirror driving unit swings and drives the first and second deflection mirror surfaces at a frequency substantially in the center between the first resonance frequency and the second resonance frequency. A deflecting unit having the first and second deflecting mirror surfaces and the mirror driving unit; and an image forming unit configured to form an image of a light beam on the surface to be scanned; A scanning optical system that scans in a main scanning direction substantially orthogonal to the scanning deflection axis;
A transmission optical system for guiding the light beam deflected by the first deflection mirror surface to the second deflection mirror surface;
The transmission optical system includes a concave mirror surface disposed such that a reflection surface thereof faces the first and second deflection mirror surfaces, and the concave mirror surface is deflected by the first deflection mirror surface. 3. The optical scanning device according to claim 1, wherein the light beam is emitted from the second deflection mirror surface toward the scanned surface by reflecting the light beam onto the second deflection mirror surface.   4. The optical scanning device according to claim 3, wherein the mirror driving unit swings and drives the first deflection mirror surface and the second deflection mirror surface in opposite phases. 5.   The concave mirror surface is an ellipse having a focal point at approximately the center position of the first deflection mirror surface and approximately the center position of the second deflection mirror surface, and a virtual straight line passing through the two center positions as a rotation axis. The optical scanning device according to claim 3, wherein the optical scanning device has an elliptical surface formed by rotation.   6. The optical scanning device according to claim 3, wherein the first and second deflection mirror surfaces are arranged side by side in a direction parallel to the main scanning direction. 7.   6. The optical scanning device according to claim 3, wherein the first and second deflection mirror surfaces are arranged side by side in a sub-scanning direction substantially orthogonal to the main scanning direction.   8. The light according to claim 3, wherein at least one of the first and second deflection mirror surfaces is substantially conjugate with the surface to be scanned in a sub-scanning plane that is substantially orthogonal to the main scanning direction. Scanning device. A deflecting unit having the first and second deflecting mirror surfaces and the mirror driving unit; and an image forming unit configured to form an image of a light beam on the surface to be scanned; A scanning optical system that scans in a main scanning direction substantially orthogonal to the scanning deflection axis;
A transmission optical system for transmitting a light beam between the first and second deflecting mirror surfaces;
The transmission optical system includes a first transmission lens disposed so that a front focal point thereof substantially coincides with a substantially central position of the first deflection mirror surface, and a front focal point substantially equal to a rear focal point of the first transmission lens. And a second transmission lens arranged so that the rear focal point substantially coincides with the substantially central position of the second deflection mirror surface,
The light beam deflected toward the first transmission lens by the first deflection mirror surface is guided to the second deflection mirror surface through the first and second transmission lenses, and the second deflection mirror surface By deflecting the light beam toward the second transfer lens and guiding it to the first deflection mirror surface via the second and first transfer lenses, the light beam is deflected again by the first deflection mirror surface. The optical scanning device according to claim 1, wherein the optical scanning device emits light toward the scanned surface.   The optical scanning device according to claim 9, wherein the mirror driving unit swings and drives the first deflection mirror surface and the second deflection mirror surface in the same phase.   The optical scanning device according to claim 9 or 10, wherein the first deflection mirror surface is substantially conjugate with the surface to be scanned in a sub-scanning plane that is substantially orthogonal to the main scanning direction. The deflection means includes
A first movable member having the first deflection mirror surface;
A second movable member having the second deflection mirror surface;
A support member that swingably supports the first and second movable members about the main scanning deflection axis extending in a direction substantially orthogonal to the main scanning direction;
The mirror drive unit,
9. The optical scanning device according to claim 3, wherein the mirror driving unit swings the first and second deflection mirror surfaces around the main scanning deflection axis to deflect the light beam. The deflecting means supports a movable member having a deflection mirror surface for deflecting a light beam on one surface, and the movable member swingably around the main scanning deflection axis extending in a direction substantially perpendicular to the main scanning direction. It consists of two deflection elements comprising a support member and the mirror drive unit,
The deflection mirror surface of the one of the two deflection elements is the first deflection mirror surface, and the deflection mirror surface of the other deflection element is the second deflection mirror surface. The optical scanning device described.   The optical scanning device according to claim 12 or 13, wherein the movable member and the support member are integrally formed by processing one substrate.   The optical scanning device according to claim 14, wherein the substrate, the movable member, and the support member are made of silicon single crystal.   16. The optical scanning device according to claim 12, wherein the mirror driving unit swings and drives the first and second deflection mirror surfaces around the main scanning deflection axis by an electrostatic attraction force.   The optical scanning device according to claim 12, wherein the mirror driving unit swings and drives the first and second deflection mirror surfaces around the main scanning deflection axis by an electromagnetic force. A latent image carrier;
18. The same configuration as that of the optical scanning device according to claim 1, wherein an electrostatic latent image is formed on the latent image carrier by scanning the surface of the latent image carrier with a light beam. Exposure means to perform,
An image forming apparatus comprising: developing means for developing the electrostatic latent image with toner to form a toner image.

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