JP4701593B2 - Optical scanning apparatus and image forming apparatus - Google Patents

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 increases a deflection angle by making a light beam incident on a deflecting unit a plurality of times.

  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 configuration in which a light beam is deflected a plurality of times by a deflecting element has been employed in order to increase a deflection angle. (For example, refer to Patent Document 1). In the optical scanning device described in Patent Document 1, a deflection element having at least two deflection surfaces is used, and a light beam deflected by the first deflection surface is connected to the first deflection surface via an afocal transmission optical system. Leads to a different second deflection surface and performs the second deflection, thereby increasing the deflection angle of the light beam. The light beam emitted from the deflecting element is guided onto the surface to be scanned through the scanning lens (imaging means). As described above, the light beam is incident on the deflecting element a plurality of times to increase the deflection angle of the light beam and improve the scanning speed.

Japanese Patent Laid-Open No. 53-97448 (FIG. 2)

  In the apparatus described in Patent Document 1, a galvanometer mirror having a deflecting surface on each of both main surfaces is provided as a deflecting element (deflecting means). Further, the transmission optical system constitutes an afocal optical system by combining a plurality of transmission lenses and a plurality of reflection mirrors. More specifically, the following conditions are satisfied: (1) the front focal point of the first transmission lens substantially coincides with one main surface (first deflection surface) of the galvanometer mirror, and (2) the second transmission lens. The condition that the rear focal point substantially coincides with the other main surface (second deflection surface) of the galvanometer mirror, and (3) the condition that the rear focal point of the first transmission lens substantially coincides with the front focal point of the second transmission lens. The first and second transfer lenses are arranged so as to be satisfied. Further, four reflecting mirrors are arranged on the optical path of the light beam so that the light beam deflected by the first deflecting surface is incident on the second deflecting surface via the first and second transfer lenses. .

  As described above, the conventional optical scanning device uses a plurality of transmission lenses and a plurality of reflection mirrors, so that the transmission optical system is complicated and the number of optical components is increased. Therefore, a large space is required to configure the transmission optical system as described above, and the size of the optical scanning device (self-amplifying deflection scanning optical system) that increases the deflection angle by multiple incidences of the light beam on the deflection element is increased. Is invited. In addition, since a plurality of transfer lenses are used, the following problems also occur. That is, the wavelength of the light beam changes when the surrounding environment of the apparatus, particularly the environmental temperature, changes, and the apparatus provided with a plurality of transfer lenses is greatly affected by the chromatic aberration of the lens. In other words, the optical characteristics of the transmission optical system change greatly with changes in the surrounding environment of the apparatus. As a result, the scanning characteristics of the light beam become unstable, and the quality of the image formed on the scanned surface may deteriorate.

  The present invention has been made in view of the above problems, and an object thereof is to provide a compact optical scanning device capable of stably scanning a light beam and a compact optical scanning device and an image forming apparatus including the device. And

In order to achieve the above object, an optical scanning apparatus according to the present invention includes a deflecting unit that deflects a light beam using the first and second deflecting mirror surfaces, and an imaging unit that forms an image on the scanned surface. A scanning optical system that scans the light beam on the surface to be scanned in the main scanning direction, and each deflecting mirror surface of the deflecting means are directed to opposite sides, and is substantially orthogonal to the scanning direction of the light beam. A mirror drive unit that swings around a main scanning deflection axis extending in a direction, and a transmission optical system that guides the light beam deflected by the deflection unit to the deflection unit. The transmission optical system includes first and second concave surfaces A light beam deflected by the first deflecting mirror surface is reflected by the first concave mirror toward the second concave mirror, and the reflected light beam is guided to the second deflecting mirror by the second concave mirror; Again by the deflecting means. Together is larger than the deflection angle of the light beam incident to the deflection angle of the light beams emitted toward the surface to be scanned in the transfer optical system is, the reflecting surface of the first and second concave mirror is an paraboloid The first and second concave mirrors are arranged so that both focal points of the first and second concave mirrors are substantially coincident with each other.

In the invention configured as described above, a transmission optical system including first and second concave mirrors is provided in order to guide the light beam deflected by the deflecting unit to the deflecting unit again. In this transfer optical system, the light beam deflected by the deflecting means, for example, at the first deflection angle is reflected by the first concave mirror toward the second concave mirror, and the reflected light beam is deflected by the second concave mirror. Leading to means. This light beam is deflected again by the deflecting means and emitted toward the surface to be scanned at a second deflection angle larger than the first deflection angle. In this way, the deflection angle of the light beam deflected again by the deflecting means and emitted toward the surface to be scanned is configured to be larger than the deflection angle of the light beam incident on the transmission optical system. In the present invention, the transmission optical system is constituted by the first and second concave mirrors in order to increase the deflection angle. Accordingly, the transmission optical system can be configured with a simpler and fewer number of optical components than the conventional apparatus that requires a plurality of transmission lenses and reflection mirrors to configure the transmission optical system. Further, the transmission optical system can be reduced in size, and the optical scanning device equipped with the transmission optical system can be reduced in size. Furthermore, by not using a transfer lens, the influence of chromatic aberration can be removed, and the light beam can be scanned with excellent stability.

According to the present invention, the deflecting means includes first and second deflecting mirror surfaces for deflecting the light beam, and the second deflecting light beam deflected by the first deflecting mirror surface by the first concave mirror surface. While reflecting toward the mirror surface, the reflected light beam is guided to the second deflecting mirror by the second concave mirror surface. With this configuration, the light beam reflection directions of the first deflection mirror surface and the second deflection mirror surface can be set to be different from each other. Therefore, the scanning region of the light beam when the light beam incident toward the first deflecting mirror surface is deflected toward the first concave mirror surface, and the light beam from the second concave mirror surface are the second deflecting mirror surface. Thus, it is possible to prevent the light beam scanning area from being overlapped when deflected toward the surface to be scanned, so that the interference of the light beam can be eliminated.

Further, in the deflecting means, the movable plate on which the first deflection mirror surface is formed and the movable plate on which the second deflection mirror surface is formed are such that the first and second deflection mirror surfaces face each other. Each of the two movable plates is provided with a support member that swingably supports the movable plate around the main scanning deflection axis, and the mirror driving unit swings the movable plates. It may be configured to be driven dynamically. The deflection means includes a movable plate having the first deflection mirror surface formed on one main surface and the second deflection mirror surface formed on the other main surface, and the movable plate around the main scanning deflection axis. The mirror driving unit may be configured to swing and drive the movable plate. In particular, the deflecting means having a latter deflection mirror surface on one main surface and the other main surface of the movable plate, in comparison with the deflection means formed by combining the two movable plates, it is possible to reduce the number of optical components. Therefore, a simpler and more compact optical scanning device can be provided.

Further, the movable plate and the support member can be made of silicon single crystal. For example, a movable plate can be formed by using a silicon single crystal substrate as a support member and applying a micromachining technique to the substrate. This configuration of the movable plate and the support member deflection means using a silicon single crystal, it is possible to produce a movable plate with high accuracy. In addition, the movable plate can be swingably supported with the same spring characteristics as stainless steel, and the deflecting mirror surface can be swung stably and at high speed.

  The mirror driving unit may drive the deflection mirror surface to swing around the main scanning change axis in a 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 can be stabilized.

  Moreover, as a driving force for swinging and driving the deflecting mirror surface, an electrostatic attracting 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 scanning can be further speeded up. On the other hand, when an electromagnetic force is used, the deflection mirror surface can be driven to swing with a lower drive voltage than when an electrostatic attraction force is generated, voltage control is facilitated, and the position system of the deflection element is enhanced. Can do. Thus, since it has a mutually different characteristic, what is necessary is just to employ | adopt the driving force according to the intended purpose.

  The deflecting means is composed of a galvanometer mirror having a deflecting mirror surface for deflecting a light beam on both main surfaces, one of the two deflecting mirror surfaces being the first deflecting mirror surface, and the other being the second deflecting surface. It may be a deflecting mirror surface. By doing so, the first deflection mirror surface and the second deflection mirror surface are integrated, so that the number of optical components can be reduced. Therefore, a more simplified optical scanning device can be provided.

The reflecting surfaces of the first and second concave mirrors are paraboloids, and the first and second concave mirrors are arranged so that both focal points of the first and second concave mirrors are substantially coincident with each other. Therefore, the above invention is suitable . By doing so, the transmission optical system has an afocal configuration, and when a parallel light beam is incident on the transmission optical system, the light beam is emitted from the transmission optical system while being kept parallel. Furthermore, the following effects can be obtained. That is, the reflecting surface of the concave mirror can be a spherical surface, for example, but in this case, spherical aberration occurs. On the other hand, since the spherical aberration of the concave mirror can be eliminated by making the reflecting surface of the concave mirror a parabolic surface, the second light beam reflected by the second concave mirror toward the second deflecting mirror surface is obtained. The reflection position on the two-deflecting mirror surface is always constant. Therefore, a more accurate optical scanning device can be provided.

  Further, it is desirable that the transmission optical system is disposed outside a scanning region of a light beam scanned by the scanning optical system. With such a configuration, interference between the light beam and the transmission optical system can be prevented. In addition, the light beam can be easily incident on and emitted from the transmission optical system, and the apparatus can be thinned.

  Further, at least one of a reflection position for deflecting the light beam by the deflecting means for the first time and a reflection position for deflecting the light beam for the second time is sub-scanning which is substantially orthogonal to the scanning direction of the light beam scanned by the scanning optical system. A plane may be configured to be substantially conjugate with the surface to be scanned. By adopting such a configuration, it is possible to prevent the influence of the swinging of the deflecting means in the sub-scanning direction. In addition, the size of the deflecting unit in the sub-scanning direction can be reduced to reduce the size and weight of the deflecting unit. As a result, the driving speed of the deflecting means can be further improved to further increase the scanning speed of the light beam.

  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, 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.

  3 and 4 are main scanning sectional views showing the structure of an exposure unit (optical scanning device) provided in the image forming apparatus of FIG. FIG. 5 is a sub-scan sectional view showing a configuration of an exposure unit (optical scanning device) provided in the image forming apparatus of FIG. FIG. 6 and FIG. 7 are diagrams showing a deflecting means as one component of the exposure unit. FIG. 8 is a view showing a transmission optical system as one component of the exposure 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, 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 housing 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 a 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 as shown in FIG. . The collimated light is focused only in the sub-scanning direction Y, and forms a linear image in the vicinity of the first deflection mirror surface 651a of the deflection element 65. Thus, in this embodiment, the collimator lens 631 and the cylindrical lens 632 function as the beam shaping system 63 that shapes the light beam from the laser light source 62. The transmission optical system 67 is arranged so as to be different from the scanning angle region of the light beam scanned by the scanning optical system (deflection element 65 and scanning lens 66) in the sub-scanning section.

  The deflecting element 65 is formed using a micromachining technique in which a micromachine is integrally formed on a semiconductor substrate by applying a semiconductor manufacturing technique, and a light beam reflected by the first deflecting mirror surface 651a is applied in the main scanning direction X. The light beam can be deflected. 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, the movable plate 656 (the “movable member” in the present invention) is provided. The movable plate 656 is formed in a flat plate shape, is elastically supported on the silicon substrate 652 by a torsion spring 657, and can swing around a first axis AX1 extending substantially parallel to the sub-scanning direction Y. Further, on the upper surface of the movable plate 656, a planar coil 655 that is electrically connected to a pair of outer electrode terminals (not shown) formed on the upper surface of the silicon substrate 652 via a torsion spring 657 is coated with an insulating layer. ing. In addition, an aluminum film or the like is formed as a first deflection mirror surface 651a and a second deflection mirror surface 651b on the upper surface central portion and the lower surface central portion of the movable plate 656, respectively.

  Further, as shown in FIG. 7, a hole 652a is provided in a substantially central portion of the silicon substrate 652 so that the light beam can be reflected by both main surfaces of the movable plate 656. The permanent magnets 659a and 659b are fixed to the flange portion 652b that forms the outer periphery of the hole 652a in different orientations so as to correspond to the (+ X) side end and the (−X) side end of the movable member 656, respectively. ing. The planar coil 655 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 655 by energization of the coil 655 and the magnetic flux generated by the permanent magnets 659a and 659b. Lorentz force acts depending on the direction, and a moment for rotating the movable plate 656 is generated. As a result, the movable plate 656 (the first deflection mirror surface 651a and the second deflection mirror surface 652b) swings about the torsion spring 657 as the first axis AX1. Here, if the current flowing through the planar coil 655 is an alternating current and is continuously repeated, the movable plate 656 (the first deflection mirror surface 651a and the second deflection mirror surface 652b) is reciprocally oscillated with the torsion spring 657 as the first axis AX1. Can be made. When the driving frequency of the reciprocating vibration is set to the resonance frequency of the movable plate 656 (the first deflection mirror surface 651a and the second deflection mirror surface 652b) (“resonance mode” in the present invention), the swing width of the movable plate 656 is set. And the vibration maintenance can be further stabilized.

  Thus, in the deflection element 65, the drive unit of the exposure control unit 102 functions as the “mirror drive unit” of the present invention, and the first deflection mirror surface 651a and the second deflection mirror surface 651b are controlled by controlling the drive unit. By swinging around the first axis AX1, the light beam is deflected and scanned in the main scanning direction X. That is, the first axis AX1 is caused to function as a main scanning deflection axis.

  The light beam reflected by the first deflection mirror surface 651a of the deflection element 65 configured as described above is once incident on the transmission optical system 67, and then again transmitted by the transmission optical system 67 to the second deflection mirror of the deflection element 65. Returned to the surface 651b. 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.

  FIG. 8 is a diagram showing the configuration of the transmission optical system. The transmission optical system 67 includes a first concave mirror 671 having its reflecting surface 671a facing the first deflection mirror surface 651a and a second concave surface having its reflecting surface 672a facing the second deflection mirror surface 651b. And a concave mirror 672. 4 and FIG. 5, the light beam deflected to the first deflection angle by the first deflection mirror surface 651a of the deflection element 65 is reflected by the first concave mirror 671 and guided to the second concave mirror 672. At the same time, the light beam reflected by the second concave mirror 672 is guided to the second deflection mirror surface 651b. As a result, the light beam is deflected again by the deflecting element 65, and the light beam is emitted toward the scanning lens 66 at a second deflection angle larger than the first deflection angle.

  As a specific configuration of the transmission optical system 67 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６７を構成する第１凹面ミラー６７１および第２凹面ミラー６７２の反射面Ｓ1、Ｓ2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 the present design example, the reflecting surfaces S1 and S2 of the first concave mirror 671 and the second concave mirror 672 constituting the transmission optical system 67 are axisymmetric aspherical surfaces. Moreover, each symbol in the table is as follows.

Si: surface number (where S0 is the first deflection mirror surface 651a, and S3 is the second deflection mirror surface 651b)
ri: radius of curvature of surface number i di: axial distance from surface number i to (i + 1) surface Ki: aspherical coefficient of axisymmetric aspheric surface expressed by the following equation when surface number i is axisymmetric aspheric

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.

  Returning to FIGS. 3 and 4, the description of the exposure unit 6 will be continued. The light beam incident twice on the deflecting element 65 is emitted from the deflecting element 65 toward the photosensitive member 2, and the light beam passes through the scanning lens 66 and the folding mirror 68 corresponding to the “imaging means” of the present invention. The surface of the photoconductor 2 (scanned surface, not shown) is irradiated. 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.

  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 transmission optical system 67 includes the first concave mirror 671 and the second concave mirror 672 that are disposed with their reflecting surfaces facing the deflection elements. The transmission optical system 67 reflects the light beam deflected by the deflecting element 65 toward the second concave mirror 672 by the first concave mirror 671 and the reflected light beam by the second concave mirror 672. The incident angle is 65 to increase the deflection angle. Therefore, the transmission optical system 67 can be configured in a simpler manner and with a smaller number of optical components as compared with the conventional apparatus in which a plurality of transmission lenses and a plurality of reflection mirrors are indispensable in configuring the transmission optical system. Further, the transmission optical system 67 can be reduced in size, and the exposure unit 6 can be reduced in size. Furthermore, by not using a transfer lens, the influence of chromatic aberration can be removed, and the light beam can be scanned with excellent stability.

  In the above embodiment, the deflecting element 65 includes the first deflecting mirror surface 651a and the second deflecting mirror surface 651b for deflecting the light beam, and the reflecting surface of the first concave mirror 671 is the first deflecting mirror surface 651a. The light beam deflected by the first deflection mirror surface 651a is reflected toward the second concave mirror 672, while the reflection surface of the second concave mirror 672 is arranged opposite to the second deflection mirror surface 651b. The light beam from the first concave mirror 671 is reflected toward the second deflection mirror surface 651b. Therefore, the reflection directions of the light beams on the first deflection mirror surface 651a and the second deflection mirror surface 651b can be set differently. Therefore, the scanning region of the light beam when the light beam incident toward the first deflecting mirror surface 651a is deflected toward the first concave mirror 671 and the light beam from the second concave mirror surface 672 are second. Since it is possible to prevent the light beam scanning region from overlapping with the deflection mirror surface 651b toward the surface to be scanned, interference of the light beam can be eliminated.

  In this embodiment, the single deflecting element 65 having the first deflecting mirror surface 651a and the second deflecting mirror surface 652b on both main surfaces of the movable plate 656 is used as the “deflecting means”. An optical scanning device can be provided.

  In this embodiment, the deflecting element 65 includes a silicon substrate 652 made of a silicon single crystal substrate and a movable plate 656 formed by applying a micromachining technique to the substrate. Accordingly, the movable plate 656 can be manufactured with high accuracy, and the movable plate 656 can be swingably supported with the same spring characteristics as stainless steel, so that both the deflection mirror surfaces 651a and 651b can be stabilized. Moreover, it can swing at high speed.

  In this embodiment, the mirror driving unit swings and drives the movable plate 656 about the first axis AX1 (main scanning deflection axis) in the resonance mode. It can be driven to swing around one axis AX1 (main scanning deflection axis). In addition, the main scanning period of the light beam can be stabilized.

  In the embodiment and the design example described above, the first and the second concave mirrors 671, 672, the first deflecting mirror surface 651a, and the second deflecting mirror surface 651b substantially coincide with each other. Since the two concave mirrors 671 and 672 and the deflection element 65 are arranged, the following operational effects can be obtained. That is, by adopting such a configuration, the transmission optical system 67 becomes an afocal configuration. Therefore, if a parallel light beam is incident on the transmission optical system 67, the light beam remains parallel and the transmission optical system 67 It is injected from 67. Furthermore, since the spherical mirror aberration of the concave mirror can be eliminated by making the reflecting surface of the concave mirror a parabolic surface, the second light beam reflected by the second concave mirror 672 toward the second deflecting mirror surface 651b. The reflection position on the two deflection mirror surface 651b is always constant. Therefore, a more accurate optical scanning device can be provided.

  In this embodiment, as shown in FIG. 5, the transmission optical system 67 is disposed outside the scanning region of the light beam scanned by the scanning optical system (deflection element 65 and scanning lens 66). For this reason, interference between the light beam and the transmission optical system 67 can be prevented. In addition, the light beam can be easily incident on and emitted from the transmission optical system 67, and the apparatus can be thinned.

  Further, as shown in FIG. 5, the reflection position P1 of the light beam on the first deflection mirror surface 651a, the reflection position P2 of the light beam on the second deflection mirror surface 651b, and the surface to be scanned (the surface of the photoreceptor 2 shown in the figure). Are substantially conjugate in a sub-scanning plane that is substantially orthogonal to the scanning direction X of the light beam scanned by the scanning optical system. For this reason, the influence of the swinging of the deflection element 65 in the sub-scanning direction Y can be prevented, and surface tilt can be effectively prevented. Further, the deflection element 65 can be reduced in size and weight by reducing the size of the deflection element 65 in the sub-scanning direction. As a result, the driving speed of the deflecting element 65 can be further improved to further increase the scanning speed of the light beam.

  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, a galvanometer mirror having deflection mirror surfaces for deflecting a light beam on both main surfaces can be used as the deflection means. In this case, since one of the two deflection mirror surfaces functions as one deflection mirror surface and the other functions as the second deflection mirror surface, a simplified optical scanning device is provided in the same manner as the deflection element 65 described above. be able to.

  9 and 10 are views showing a second embodiment of the optical scanning device according to the present invention. The second embodiment is greatly different from the first embodiment in that a deflector (deflecting means) is configured by combining two deflecting elements each having a single deflecting mirror surface. This is the same as in the first embodiment. Hereinafter, the second embodiment will be described in detail focusing on the differences from the first embodiment.

  Since the deflecting elements 85a and 85b constituting the deflector 85 have the same structure, the structure of one deflecting element 85a will be described here, and the structure of the other deflecting element 85b will be described with a corresponding reference numeral. 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. 9, 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 AX1a 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. 10, 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 AX1a. 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 AX1a. 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 AX1. When the driving frequency of this reciprocating vibration is set to the resonance frequency of the deflecting mirror surface 851a, the deflection width of the deflecting mirror surface 851a is increased, and vibration maintenance can be further stabilized.

  Thus, in the deflection element 85a, the drive unit of the exposure control unit 102 functions as the “mirror drive unit” of the present invention, and the deflection mirror surface 851a is swung around the first axis AX1a by controlling the drive unit. Thus, the light beam is deflected in the main scanning direction X. That is, the first axis AX1 is caused to function as a main scanning deflection axis.

  The deflector 85 is configured by closely fixing the deflecting elements 85a and 85b so that the first axes thereof are parallel to each other as shown in FIGS. In this embodiment, as will be described below, the deflection mirror surface 851a functions as the first deflection mirror surface, while the deflection mirror surface 851b functions as the second deflection mirror surface.

  The light beam reflected by the first deflection mirror surface 851a of the deflector 85 configured as described above is once incident on the transmission optical system 67 and then again transmitted by the transmission optical system 67 to the second deflection mirror of the deflector 85. Returned to the surface 851b. Therefore, for example, the light beam deflected to the first deflection angle by the deflector 85 is emitted toward the scanning lens 66 at a second deflection angle larger than the first deflection angle. The configurations of the transmission optical system 67 and the scanning optical system (deflection element 65 and scanning lens 66) in this embodiment are the same as those in the first embodiment, and the same effects can be obtained.

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

  FIG. 11 is a diagram showing a third embodiment of the optical scanning device according to the present invention. The third embodiment is greatly different from the second embodiment in that the deflecting mirror surfaces 851a and 851b are driven using electrostatic attraction force, and other configurations are different from those of the second embodiment. It is the same. Here, a description will be given taking the deflector 85 shown in FIG. 11 as an example. In addition, the same reference numerals are used for parts having the same configuration as the above embodiment.

  The deflector 85 is composed of deflecting elements 85a and 85b having the same configuration. Here, the configuration of one deflecting element 85a will be described, and the configuration of the other deflecting element 85b will be described with a corresponding reference numeral. Omitted. In the deflection element 85a, as shown in FIG. 11, 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 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 851a at the center of the upper surface of the movable plate 856a.

  In addition, electrodes 8581a and 8582a are fixed to positions on the inner bottom surface of the recess 8521a of the silicon substrate 852a 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 AX1a. 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 with the torsion spring 857a serving as the first axis AX1a. When the driving frequency of the reciprocating vibration is set to the resonance frequency of the first deflection mirror surface 851a, the swing width of the first deflection mirror surface 851a increases, and the first deflection mirror surface 851a reaches a position close to the electrodes 8581a and 8582a. Can be displaced. Further, when the end portion of the first deflection mirror surface 851a reaches a position close to the electrodes 8581a and 8582a by resonance, the electrodes 8581a and 8582a also contribute to driving the first deflection mirror surface 851a, and both the end portion and the flat surface portion are driven. Vibration maintenance can be further stabilized by the electrodes.

  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. Further, when the first deflection mirror surface 851a is driven to swing, the first deflection mirror surface 851a may be driven to swing around the main scanning deflection axis in the resonance mode. With this configuration, the first deflection mirror surface 851a can be driven to swing around the main scanning deflection axis with less energy. In addition, the main scanning period of the scanning light beam can be stabilized.

  12 and 13 are views showing a fourth embodiment of the optical scanning device according to the present invention. The difference of this embodiment from the first embodiment is that the transmission optical system 67A differs from the scanning angle region of the light beam scanned by the scanning optical system (deflection element 65 and scanning lens 66) in the main scanning section. The other configuration is the same as that of the first embodiment.

  In this embodiment, as shown in FIG. 13, when the transmission optical system 67A is viewed from the sub-scanning plane, the two concave mirrors 671 and 672 are scanned by the scanning optical system (deflection element 65 and scanning lens 66). Although intersecting with the beam, both concave mirrors 671 and 672 are arranged so as to be out of the scanning area in the main scanning section as shown in FIG. For this reason, interference between the light beam and the transfer optical system 67A can be prevented. In addition, the light beam can be easily incident on and emitted from the transmission optical system 67A, and the apparatus can be thinned. Further, the exposure unit 6 can be made thin in the sub-scanning direction.

  The image forming apparatus of FIG. 1 may of course be equipped with the exposure unit of the fourth embodiment instead of the exposure unit of the first embodiment. Needless to say, in the fourth embodiment, the deflecting means of the second and third embodiments may be used.

  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 figure which shows the transmission optical system 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 figure which shows the deflection | deviation element which is one component of an exposure unit. It is a main scanning sectional view showing the composition of one embodiment of an exposure unit (optical scanning device). It is a sub-scanning sectional view showing the configuration of an embodiment of an exposure unit (optical scanning device).

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), 85 ... Deflector (deflection means) 66 ... Scanning Lens (imaging means), 67, 67A ... Transmission optical system, 651a, 651b, 851a, 851b ... Deflection mirror surface, 652, 852a, 852b ... Silicon substrate (support member), 656, 856a, 856b ... Movable plate (movable) Member), 671, 672 ... concave mirror, L ... light beam, P1, P2 ... reflection position, 671a, 672a ... reflection surface, AX1, AX1a ... main scanning deflection axis, X ... main scanning direction, Y ... sub-scanning direction.

Claims (10)

A deflecting unit configured to deflect the light beam by using the first and second deflecting mirror surfaces; and an imaging unit configured to form an image of the light beam on the surface to be scanned. A scanning optical system for scanning
A mirror drive unit that swings and drives around a main scanning deflection axis extending in a direction substantially orthogonal to the scanning direction of the light beam in a state where the respective deflection mirror surfaces of the deflection means are directed to opposite sides;
A transmission optical system for guiding the light beam deflected by the deflecting means to the deflecting means;
With
The transmission optical system includes first and second concave mirrors, and reflects the light beam deflected by the first deflection mirror surface toward the second concave mirror by the first concave mirror and the reflected light. The light that is deflected again by the deflecting unit and guided toward the scanned surface by guiding the beam to the second deflecting mirror by the second concave mirror is incident on the transmission optical system. While making it larger than the deflection angle of the beam ,
The reflecting surfaces of the first and second concave mirrors are paraboloids;
The optical scanning device , wherein the first and second concave mirrors are arranged so that both focal points of the first and second concave mirrors are substantially coincident with each other . In the deflecting means, the movable plate on which the first deflection mirror surface is formed and the movable plate on which the second deflection mirror surface is formed so that the first and second deflection mirror surfaces face each other. Arranged,
Each of the two movable plates is provided with a support member that supports the movable plate in a swingable manner around the main scanning deflection axis,
The optical scanning device according to claim 1, wherein the mirror driving unit drives the movable plates to swing. The deflection means includes a movable plate having the first deflection mirror surface formed on one main surface and the second deflection mirror surface formed on the other main surface, and swinging the movable plate about the main scanning deflection axis. A support member that is movably supported;
The optical scanning device according to claim 1, wherein the mirror driving unit drives the movable plate to swing.   The optical scanning device according to claim 2, wherein the movable plate and the support member are made of silicon single crystal.   5. The optical scanning device according to claim 2, wherein the mirror driving unit swings and drives the deflection mirror surface around the main scanning deflection axis in a resonance mode.   6. 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 electromagnetic force.   6. 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. The transmission optical system, an optical scanning apparatus according to any one of claims 1 is arranged outside the scanning area of the light beam scanned by the scanning optical system 7. At least one of the reflection position for deflecting the light beam at the deflecting means for the first time and the reflection position for deflecting the light beam for the second time is in a sub-scanning plane that is substantially orthogonal to the scanning direction of the light beam scanned by the scanning optical system the optical scanning device according to any one of claims 1 and has a substantially conjugate with the surface to be scanned 8. A latent image carrier;
Has an optical scanning apparatus having the same configuration as claimed in any one of claims 1 to 9, an electrostatic latent on the latent image bearing member the surface of the latent image carrier by scanning a light beam as said surface to be scanned 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.

Images