JP4453317B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device that deflects and scans a light beam from a light source, and more particularly to an optical scanning device that increases the deflection angle by causing a light beam to enter a deflection element a plurality of times and an image forming apparatus equipped with the device. It is.

  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, the deflected light beam deflected by the deflecting mirror surface of the deflecting element is again guided to the deflecting mirror surface to increase the deflection angle of the deflected deflected light beam for the second time. The light beam emitted from the deflecting element is guided onto the surface to be scanned through the scanning lens. In this way, the scanning speed of the light beam is improved by making the light beam incident on the deflecting element a plurality of times.

US Pat. No. 3,771,850

  In the conventional apparatus described above, a transmission optical system is provided to guide the light beam deflected by the deflection mirror surface of the deflection element to the deflection mirror surface again. The transmission optical system is composed of two transmission lenses and a plane mirror. It is configured. That is, the plane mirror is arranged at a distance (2f1 + 2f2) from the deflection element. Here, reference numerals f1 and f2 respectively denote focal lengths of two transfer lenses, that is, the first and second transfer lenses. A first transfer lens is disposed between the deflection element and the plane mirror at a distance f1 from the deflection element toward the plane mirror, and is further separated from the first transmission lens by a distance (f1 + f2). A second transfer lens is disposed. By adopting such a lens arrangement, the transmission optical system is a so-called afocal optical system.

  By the way, as this type of optical scanning device, a so-called pre-objective scanning type in which beam deflection is performed on the front side of the scanning lens (imaging means), that is, the light source side, and the rear side of the condenser lens (imaging means), that is, There is a so-called post-objective scanning type in which beam deflection is performed on the surface to be scanned.

  Among these, in the pre-objective scanning type optical scanning device, after shaping the light beam from the light source into a parallel beam, the parallel light beam is incident twice on the deflecting element, and the parallel light beam is scanned from the deflecting element. It is configured to inject toward the surface. The parallel light beam is condensed on the surface to be scanned by a scanning lens (imaging means) to form a spot-like image. When the light beam deflected by the deflecting element is imaged on the surface to be scanned by the scanning lens, how to suppress the curvature of field of the scanning lens becomes a big problem. Conventionally, as an approach for solving such a problem, a scanning lens system (imaging means) is configured using a plurality of lenses. However, the conventional apparatus has a problem that the entire apparatus is easily increased in size, optical adjustment between lenses is difficult, and the number of parts increases, so that it is difficult to reduce the cost.

  On the other hand, in a post-objective type optical scanning device, a light beam from a light source is incident on a deflection element via a condenser lens (imaging means). Then, after the light beam deflected by the deflecting element is incident again on the deflecting element using the transmission optical system, the light beam reflected and deflected by the deflecting element is directly guided onto the surface to be scanned, and the scanned object is scanned. Optical scanning is performed on the surface. Even in such an apparatus, it is necessary to configure a condensing lens system (imaging means) using a plurality of lenses in order to obtain excellent scanning performance by suppressing the curvature of field of the condensing lens. . As a result, as with the pre-objective scanning type apparatus, there are problems in that it is difficult to optically adjust between the lenses and it is difficult to reduce the cost because the number of parts increases.

  The present invention has been made in view of the above problems, and deflects a light beam from a light source by a deflecting element and guides the deflected light beam to the deflecting element by a transmission optical system so that the deflected light beam is deflected again by the deflecting element. An object of the present invention is to scan a light beam satisfactorily with a simple configuration in a so-called multiple-incidence type optical scanning apparatus that emits light toward a surface and an image forming apparatus equipped with the apparatus.

  In order to achieve the above object, an optical scanning device according to the present invention mainly shifts a light beam by oscillating a light source that emits a light beam and a deflection mirror surface that reflects the light beam around a predetermined main scanning deflection axis. A deflection element that deflects in the main scanning direction substantially orthogonal to the scanning deflection axis, a transmission optical system that guides the light beam deflected by the deflection element to the deflection element, and deflects the light beam from the light source by the deflection element. The transmission optical system includes an image forming unit configured to form an image on the scanned surface of the light beam which is deflected again by the deflecting element by guiding the beam to the deflecting element by the transmission optical system and is emitted toward the scanned surface. It has an imaging characteristic that corrects the field curvature of the imaging means.

  In the optical scanning apparatus configured as described above, after the light beam is deflected by the deflecting element on the front side (light source side) of the imaging unit, the deflected light beam is imaged on the surface to be scanned by the imaging unit. In order to suppress the curvature of the image plane formed on the surface to be scanned in this way, it is possible to reduce the curvature of field by devising only the configuration of the imaging means, for example, as in the prior art. In this case, the load required for reducing the curvature of field is applied only to the imaging means, and the above-described various problems occur. On the other hand, in the present invention, the transmission optical system has an imaging characteristic that corrects the curvature of field of the imaging unit, and the transmission optical system bears a part of the load. In order to bear a part of the role of correcting the curvature of field with respect to the transmission optical system provided to increase the deflection angle in this way, an optical element such as a lens is provided to the multiple-scanning optical scanning device. Without additional addition, the load on the image forming means is reduced, and the above-mentioned problems can be solved and a good light beam can be scanned.

Optical scanning device described above is a so-called pre-objective scanning is configured to further include a beam shaping means for guiding the deflecting element is shaped into a parallel light beam in the main scanning direction the light beam from the light source. Further, constitute a transfer optical system so as to diverge the light beam guided to the deflection element in accordance with the deflection angle thereof becomes larger. The transmission optical system may be configured to increase the divergence angle of the light beam guided to the deflection element in accordance with the deflection angle of the light beam.

  An optical scanning device according to the present invention includes a light source that emits a light beam, an imaging unit that focuses the light beam from the light source and forms an image on a surface to be scanned, and a deflection mirror surface that reflects the light beam. A deflection element that deflects a light beam in a main scanning direction substantially orthogonal to the main scanning deflection axis by swinging around a predetermined main scanning deflection axis, and a transmission optical system that guides the light beam deflected by the deflection element to the deflection element And condensing the light beam from the light source by the imaging means, entering the deflecting element, deflecting the light beam, and deflecting the deflected light beam again by the deflecting element by guiding the deflected light beam to the deflecting element by the transmission optical system. An optical scanning apparatus that emits a light beam toward a surface to be scanned, wherein the transmission optical system has an imaging characteristic that corrects a curvature of field of an imaging means in order to achieve the above-described object. Yes.

In the invention configured as described above, beam deflection is performed on the rear side of the imaging means, that is, on the scanned surface side. That is, the light beam from the light source is collected before being deflected by the deflecting element, and is imaged on the surface to be scanned through the deflecting mirror surface, the transmission optical system, and the deflecting mirror surface. Also in this post-objective scanning type device, in the same way as in the pre-objective scanning type device, a part of the role of correcting the curvature of field is imposed on the transmission optical system provided to increase the deflection angle. Without adding an optical element such as a lens separately to the optical scanning device of the double-incidence method, the load on the image forming means is reduced, the above-mentioned problems are solved, and a good light beam can be scanned. In this invention, the transmission optical system is adopted one having imaging properties that reduces the converging angle of the light beam in accordance with the deflection angle of the light beam guided to the deflection element.

  Further, as the deflection element, a polygon mirror or a galvano mirror that has been widely used conventionally can be used, but a deflection element configured as follows may be used. That is, the deflection element includes a movable member having a deflection mirror surface that reflects a light beam, and a support member that swingably supports the movable member about a main scanning deflection axis extending in a direction substantially orthogonal to the scanning direction of the light beam. And a mirror driving unit that drives the movable member to swing around the main scanning deflection axis. The mirror driving unit swings the deflection mirror surface around the main scanning deflection axis to scan the light beam in the main scanning direction. It is configured as follows. Further, the movable member and the support member can be made of silicon single crystal. 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 as described above, the movable member can be manufactured with high accuracy. In addition, the movable member can be swingably supported with the same spring characteristics as stainless steel, and the deflection mirror surface can be swung stably and at high speed.

  Further, when the deflection mirror surface is driven to swing by the mirror driving unit, the deflection mirror surface may be driven to swing around the main scanning deflection axis in the resonance mode. With this configuration, the deflection mirror surface can be driven to swing around the main scanning deflection axis with less energy. In addition, the main scanning period of the light beam 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 the electromagnetic force is used, the deflection mirror surface can be driven to swing with a lower drive voltage than when the electrostatic attraction force is generated, voltage control is facilitated, and the positional accuracy of the deflection element is increased. 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.

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

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

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

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

  In the vicinity of the roller 72, a transfer belt cleaner (not shown), a density sensor 76 (FIG. 2), and a vertical synchronization sensor 77 (FIG. 2) are arranged. Among these, the density sensor 76 is provided facing the surface of the intermediate transfer belt 71 and measures the optical density of the patch image formed on the outer peripheral surface of the intermediate transfer belt 71. The vertical synchronization sensor 77 is a sensor for detecting the reference position of the intermediate transfer belt 71, and is a synchronization signal output in association with the rotational drive of the intermediate transfer belt 71 in the sub-scanning direction, that is, a vertical synchronization signal. It functions as a vertical sync sensor for obtaining Vsync. In this apparatus, the operation of each part of the apparatus is controlled based on the vertical synchronization signal Vsync in order to align the operation timing of each part and to superimpose toner images of each color accurately.

  When transferring a color image to a sheet, 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.

  FIG. 3 is a main scanning sectional view showing a configuration of an exposure unit (optical scanning device) provided in the image forming apparatus of FIG. 4 and 5 are diagrams showing a deflecting element as one component of the exposure unit. FIG. 6 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 the exposure housing 61, a collimator lens 631, a cylindrical lens 632, a deflection element 65, a scanning lens 66, and a transmission light are transmitted in order to scan and expose the light beam from the laser light source 62 onto the surface 2a of the photoreceptor 2. An 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. The collimated light is focused only in the sub-scanning direction Y, and forms a linear image near the deflection mirror surface 651 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 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. The light beam reflected by the deflecting mirror surface 651 is moved 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. 4, 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, a movable plate 656 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 deflection mirror surface 651 at the center of the upper surface of the movable plate 656.

  Further, as shown in FIG. 5, a concave portion 652a is provided at a substantially central portion of the silicon substrate 652 so that the movable plate 656 can swing around the first axis AX1. Then, permanent magnets 659a and 659b are fixed to the inner bottom surface of the recess 652a at both ends of the movable plate 656 at different positions in different orientations. 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 (deflection mirror surface 651) swings with the torsion spring 657 as the first axis AX1. Here, if the current flowing through the planar coil 655 is alternating and continuously operated, the deflection mirror surface 651 can be reciprocally oscillated with the torsion spring 657 as the first axis AX1. When the driving frequency of the reciprocating vibration is set to the resonance frequency of the deflecting mirror surface 651, the deflection width of the deflecting mirror surface 651 is increased, and 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 deflection mirror surface 651 is swung around the first axis AX1 by controlling the drive unit. Thus, 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 deflection element 65 configured as described above is once incident on the transmission optical system 67 and then returned to the deflection mirror surface 651 of the deflection element 65 by the transmission optical system 67 again. 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. 6 is a diagram showing the configuration of the transmission optical system. The transmission optical system 67 includes a reflection mirror 673 arranged with the reflection surface 673a facing the deflection mirror surface 651, and two transmission lenses 674 and 675 arranged between the reflection mirror 673 and the deflection mirror surface 651. And. As shown in FIG. 3, the light beam deflected to the first deflection angle by the deflecting element 65 is guided to the reflection mirror 673 via the transmission lenses 674 and 675, and the light beam folded by the reflection mirror 673 is transmitted to the transmission lens. Guided to the deflecting element 65 via 675 and 674. As a result, the light beam is reflected 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.

  In this embodiment, in order to make the transmission optical system 67 an afocal system in the vicinity of the optical axis OA, both the transmission lenses 674 and 675 are composed of aspherical lenses having the same configuration and are symmetrical with respect to the intermediate image position P3. It is arranged. More specifically, the deflecting element 65 and the reflecting mirror 673 are arranged apart by a distance (4f). Here, the symbol f is the focal length of each transfer lens 674,675. Further, a transmission lens 674 is arranged at a distance f from the deflecting element 65 to the reflection mirror 673 side, and a transmission lens 675 is further arranged at a distance 2f from the transmission lens 674.

  On the other hand, at a position away from the optical axis OA, in order to correct the curvature of field of the scanning lens 66, the image planes I4 and I5 formed by the transmission lenses 674 and 675 are concave toward the optical axis direction. It is composed. On the optical axis OA, the two image planes I4 and I5 coincide with each other at the intermediate image position P3, but the two image planes I4 and I5 are separated from each other as the distance from the optical axis OA increases. With this configuration, the light beam guided from the transmission optical system 67 to the deflecting element 65 diverges according to the deflection angle. That is, in the main scanning direction, a parallel light beam is incident on the deflecting element 65 from the beam shaping system 63, but the light beam returned to the deflecting mirror surface 651 via the transmission optical system 67 depends on the deflection angle. The spread angle changes. More specifically, when the light beam travels along the optical axis OA (the deflection angle is zero), the parallel light beam is returned to the deflection mirror surface 651, while the deflection mirror surface increases as the absolute value of the deflection angle increases. The light beam returned to 651 becomes a divergent light beam, and its divergence angle increases in accordance with the deflection angle.

  As a specific configuration of the transmission optical system 67 having such characteristics, for example, one 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を構成する伝達レンズ６７４，６７５の４面Ｓ1〜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 four surfaces S1 to S4 of the transmission lenses 674 and 675 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 a deflecting mirror surface 651, S5 is a reflecting mirror surface 673a)
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, Ai, Bi: next when surface number i is axisymmetric aspheric surface Aspherical coefficient of the axisymmetric aspherical surface expressed by the equation

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 FIG. 3, the description of the exposure unit 6 will be continued. The light beam that has entered the deflecting element 65 twice is emitted from the deflecting element 65 toward the photosensitive member 2, and the light beam passes through a scanning lens 66 that functions as an “imaging unit” and a folding mirror 68. 2 is irradiated on the surface (scanned surface) 2a. 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, after the light beam is deflected twice by the deflecting element 65 on the light source side of the scanning lens 66 that is an imaging means, the deflected light beam is deflected by the scanning lens 66 on the surface of the photoreceptor 2. The image is formed on the (scanned surface). In this transmission optical system 67, the light beam deflected by the deflecting mirror surface 651 is guided again to the deflecting mirror surface 651 and incident twice to increase the deflection angle. Since it plays a part of the role of correcting the curvature of field on the surface 2a, the following effects are produced. This point will be described with reference to FIG.

  The parallel light beam from the beam shaping system 63 is deflected by the deflection mirror surface 651 and then incident again on the deflection mirror surface 651 as the parallel light beam by the transfer optical system 67. A light beam is emitted from the deflection mirror surface 651 toward the scanning lens 66. Here, when correction by the transmission optical system 67 is not performed (the apparatus described in Patent Document 1), the light beam LB from the deflection mirror surface 651 remains parallel at any deflection angle. Therefore, the image plane I formed by the scanning lens 66 has a concave shape toward the optical axis direction as indicated by a broken line in FIG. That is, the curvature of field of the scanning lens 66 is reflected as it is. As a result, the diameter of the spot imaged on the surface 2a of the photoreceptor 2 increases as the deflection angle increases, leading to a decrease in image quality.

  On the other hand, according to the present embodiment, since the transmission optical system 67 is configured such that the light beam guided from the transmission optical system 67 to the deflection element 65 diverges according to the deflection angle, from the deflection mirror surface 651. The light beam LB emitted toward the scanning lens 66 becomes a substantially parallel light beam when the deflection angle is zero (travels along the optical axis) as shown in FIG. As it increases, it becomes a divergent light beam. Accordingly, as the deflection angle increases, the image forming position of the light beam also moves to the surface 2a (scanned surface) side of the photosensitive member 2, and the image surface I formed by the scanning lens 66 is substantially coincident with the photosensitive member surface 2a. To do. For this reason, the light beam can be scanned satisfactorily.

  In this embodiment, the transfer optical system 67 has an imaging characteristic that corrects the curvature of field of the scanning lens 66, and the curvature of the image plane I formed by imaging the light beam is reduced. The load required for reduction is distributed to the scanning lens 66 and the transmission optical system 67. As described above, since the transmission optical system 67 bears a part of the load, it is easy to use a complicated lens system as the scanning lens 66 or to add an optical element such as a lens to the optical scanning device. A good light beam can be scanned with this configuration.

<Second Embodiment>
FIG. 8 is a diagram showing a second embodiment of the optical scanning device according to the present invention. The second embodiment is greatly different from the first embodiment in that the deflecting mirror surface 651 is driven using an electrostatic attraction force, and other configurations are the same as those in the first embodiment. . In this embodiment, in this deflection element 65, a movable plate 656 is provided by processing a part of a silicon substrate 652, as shown in FIG. The movable plate 656 is formed in a flat plate shape, is elastically supported on the silicon substrate 652 by a torsion spring 657, and can swing around a first axis AX1 extending substantially parallel to the sub-scanning direction Y. In addition, an aluminum film or the like is formed as a deflection mirror surface 651 at the center of the upper surface of the movable plate 656.

  In addition, electrodes 658 a and 658 b are respectively fixed to positions on the inner bottom surface of the recess 652 a of the silicon substrate 652 facing both ends of the movable plate 656. These two electrodes 658a and 658b function as electrodes for swinging and driving the movable plate 656 around the first axis AX1. That is, these electrodes 658 a and 658 b are electrically connected to a drive unit (not shown) of the exposure control unit 102, and electrostatic adsorption force is generated between the electrode and the deflecting mirror surface 651 by applying a voltage to the electrodes. Acts to draw one end of the deflecting mirror surface 651 toward the electrode. Therefore, when a predetermined voltage is alternately applied to the electrodes 658a and 658b from the driving unit, the deflection mirror surface 651 can be reciprocally oscillated with the torsion spring 657 as the first axis AX1. When the driving frequency of this reciprocating vibration is set to the resonance frequency of the deflecting mirror surface 651, the deflection width of the deflecting mirror surface 651 increases, and the end of the deflecting mirror surface 651 is displaced to a position close to the electrodes 658a and 658b. be able to. Further, when the end portion of the deflecting mirror surface 651 reaches a position close to the electrodes 658a and 658b by resonance, the electrodes 658a and 658b also contribute to driving the deflecting mirror surface 651, and vibration is maintained by both the end portion and the planar portion electrodes. Can be made more stable.

  In the present invention, electromagnetic force or electrostatic force is used to swing the deflecting mirror surface 651, but it goes without saying that any of them may be used. However, since each driving method has the following characteristics, it is desirable to adopt them appropriately in consideration of them. That is, when an electromagnetic force is used as a driving force for driving the deflection mirror surface 651 to swing, the deflection mirror surface 651 can be driven to swing with a lower driving voltage than when an electrostatic attraction force is generated. Thus, voltage control is facilitated, and the positional accuracy of the scanning light beam can be increased. On the other hand, when the electrostatic attraction force is used as the driving force, it is not necessary to form a coil pattern, the deflection element 65 can be further miniaturized, and the deflection scanning can be further speeded up. . Further, when the deflection mirror surface 651 is driven to swing, the deflection mirror surface 651 may be driven to swing around the main scanning deflection axis in the resonance mode. With this configuration, the deflection mirror surface 651 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.

  In the first and second embodiments, the deflecting element 65 processed by using the micromachining technique is used as the deflecting element that reflects the light beam and deflects the light beam. A deflection element such as a galvanometer mirror may also be used.

<Third Embodiment>
FIG. 9 is a diagram showing a third embodiment of the optical scanning device according to the present invention. The third embodiment is greatly different from the first embodiment in that the reflection mirror 673 is swingable about an axis substantially parallel to the main scanning deflection axis (first axis) AX1 of the deflection element 65. The driving portion (not shown) of the exposure control unit 102 is driven to swing in relation to the swinging operation of the deflecting mirror surface 651, and the other configurations are the same as in the first embodiment. Here, as the reflection mirror 673, a mirror having the same configuration as that of the deflector such as the deflecting element 65 or the galvanometer mirror can be employed. By adopting such a configuration, the deflection angle of the light beam can be further increased.

<Fourth embodiment>
FIG. 10 is a diagram showing a fourth embodiment of the optical scanning device according to the present invention. FIG. 11 is a main scanning sectional view showing the structure of the exposure unit (optical scanning device) in FIG. Further, FIG. 12 is a view showing a transmission optical system as one component of the exposure unit. The fourth embodiment is greatly different from the first embodiment in the configuration of the transmission optical system 67. Therefore, in the following, the same components are denoted by the same reference numerals and description thereof will be omitted, while differences will be described in detail with reference to the drawings.

  In the fourth embodiment, the transmission optical system 67 includes a concave mirror 671 arranged with its reflecting surface 671a facing the deflection mirror surface 651, and a transmission lens arranged between the concave mirror 671 and the deflection mirror surface 651. 672. Then, as shown in FIGS. 10 and 11, the light beam deflected to the first deflection angle by the deflecting element 65 is guided to the concave mirror 671 through the transmission lens 672, and the light beam folded by the concave mirror 671 is transmitted. The light is guided to the deflection element 65 through the transmission lens 672. As a result, the light beam is reflected again by the deflecting element 65, and the light beam is emitted toward the surface (scanned surface) 2a of the photosensitive member 2 at a second deflection angle larger than the first deflection angle.

  In this embodiment, in order to make the transmission optical system 67 an afocal system, one of the optical elements constituting the transmission optical system 67 is configured by a concave mirror 671 and the other is a transmission lens 672. The transmission lens 672 is composed of an aspheric lens, and the image surface formed by the transmission lens 672 is concave toward the optical axis direction. As a result, as in the first embodiment, the curvature of field of the scanning lens 66 is corrected, and the image surface I formed by the scanning lens 66 is substantially coincident with the photoreceptor surface 2a. For this reason, the light beam can be favorably scanned with the same effect as the first embodiment, that is, with a simple configuration.

<Fifth Embodiment>
The first to fourth embodiments are so-called pre-objective scanning optical scanning devices, but the object of application of the present invention is not limited to this, and the present invention can also be applied to so-called post-objective scanning devices. Hereinafter, this will be described in detail with reference to FIGS.

  FIG. 12 is a diagram showing a fifth embodiment of the optical scanning device according to the present invention. The fifth embodiment is greatly different from the first embodiment in the following two points, and other configurations are the same as those in the first embodiment. Therefore, in the following description, while focusing on the differences, the same components will be denoted by the same reference numerals and description thereof will be omitted.

  First, the first difference is that a condenser lens 660 is provided on the light source side of the deflecting element 65 instead of the scanning lens. In this apparatus, the light beam is condensed by the condenser lens 660 before being deflected by the deflecting element 65, and the surface of the photosensitive member 2 (scanned object) is passed through the deflecting mirror surface 651, the transmission optical system 67 and the deflecting mirror surface 651. Image).

  The second point is that the transfer optical system 67 has an imaging characteristic that corrects the curvature of field of the condenser lens 660 that functions as the “imaging unit” of the present invention. More specifically, the transmission optical system 67 has an imaging characteristic that reduces the condensing angle of the light beam guided to the deflecting element 65 in accordance with the deflection angle of the light beam. As described above, according to the present embodiment, the transmission optical system 67 guides the light beam deflected by the deflecting mirror surface 651 to the deflecting mirror surface 651 again and makes it incident twice, thereby increasing the deflection angle. Since the transmission optical system 67 plays a part of the role of correcting the curvature of field on the surface 2a of the photosensitive member 2, the following effects are produced. This point will be described with reference to FIG.

  In the post-objective scanning type apparatus, since the focused light beam is incident on the deflecting element 65, the focused light beam is guided to the surface (scanned surface) 2a of the photoreceptor 2 as it is. Therefore, when the correction by the transmission optical system 67 is not performed (the apparatus described in Patent Document 1), the light beam LB is condensed at a constant condensing angle at any deflection angle and imaged. Therefore, the image plane I formed by the scanning lens 66 has a concave shape toward the optical axis direction as indicated by a broken line in FIG. That is, the curvature of field of the condenser lens 660 is reflected as it is. As a result, the diameter of the spot imaged on the surface 2a of the photoreceptor 2 increases as the deflection angle increases, leading to a reduction in image quality.

  On the other hand, according to the present embodiment, the converging angle of the light beam guided from the transmission optical system 67 to the deflecting element 65 decreases according to the deflection angle, so that the deflecting mirror surface 651 is directed toward the photoreceptor surface 2a. The converging angle of the emitted light beam LB is the maximum value θo when the deflection angle is zero (moves along the optical axis) as shown in FIG. The maximum deflection angle becomes θ (+ a), θ (−a). Therefore, as the deflection angle increases, the imaging position of the light beam also moves to the surface 2a (scanned surface) side of the photoreceptor 2, and the image surface I formed by the condenser lens 660 is the photoreceptor surface 2a. Almost matches. For this reason, the light beam can be scanned satisfactorily.

  In this embodiment, the transfer optical system 67 has an imaging characteristic that corrects the curvature of field of the condensing lens 660, and the curvature of the image plane I formed by imaging the light beam. The load required for reducing the above is distributed to the condenser lens 660 and the transfer optical system 67. As described above, since the transmission optical system 67 bears a part of the load, a complicated lens system is used as the condenser lens 660, or an optical element such as a lens is not added to the optical scanning device. A simple light beam can be scanned with a simple configuration.

<Others>
The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, the multiple-incidence type optical scanning device having the configuration shown in the first to fifth embodiments has been illustrated, but the application target of the present invention is not limited to this, and a plurality of transmission optical systems are used. The present invention can be applied to all types of optical scanning devices that are incident once.

  In the first to fifth embodiments, 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. 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 explaining the correction | amendment operation | movement of a field curvature by the transmission optical system in 1st Embodiment. It is a figure which shows 2nd Embodiment of the optical scanning device concerning this invention. It is a figure which shows 3rd Embodiment of the optical scanning device concerning this invention. It is a figure which shows 4th Embodiment of the optical scanning device concerning this invention. FIG. 11 is a main scanning sectional view showing the configuration of the exposure unit (optical scanning device) in FIG. 10. It is a figure which shows 5th Embodiment of the optical scanning device concerning this invention. It is a figure explaining the correction | amendment operation | movement of a field curvature by the transmission optical system in 5th Embodiment.

Explanation of symbols

2 ... photosensitive member (latent image carrier), 2a ... surface (scanned surface), 4 ... developing unit (developing means), 6 ... exposure unit (optical scanning device), 63 ... beam shaping system (beam shaping means), 65 ... Deflection element, 67 ... Transmission optical system, 651 ... Deflection mirror surface, 652 ... Silicon substrate, 656 ... Movable plate, 660 ... Condensing lens (imaging means), L ... Light beam, OA ... Optical axis, P3. ..Intermediate image position, X: Main scanning direction, θo, θ (+ a), θ (-a): Condensing angle

Claims (9)

A light source that emits a light beam;
A deflection element that deflects the light beam in a main scanning direction substantially orthogonal to the main scanning deflection axis by swinging a deflection mirror surface that reflects the light beam about a predetermined main scanning deflection axis;
A transmission optical system for guiding the light beam deflected by the deflection element to the deflection element;
The light beam from the light source is deflected by the deflecting element, and the deflected light beam is guided to the deflecting element by the transmission optical system, thereby being deflected again by the deflecting element and emitted toward the scanning surface. Imaging means for imaging on the surface to be scanned ;
Beam shaping means for shaping the light beam from the light source into a parallel light beam in the main scanning direction and guiding it to the deflection element ;
The optical scanning apparatus according to claim 1 , wherein the transmission optical system has an imaging characteristic that diverges the light beam guided to the deflection element as the deflection angle increases . The transmission optical system optical scanning apparatus according to claim 1, wherein increasing the spread angle of the light beam guided to the deflection element in accordance with the deflection angle of the light beam. A light source that emits a light beam;
Imaging means for condensing the light beam from the light source and forming an image on the scanned surface;
A deflection element that deflects the light beam in a main scanning direction substantially orthogonal to the main scanning deflection axis by swinging a deflection mirror surface that reflects the light beam about a predetermined main scanning deflection axis;
A transmission optical system for guiding the light beam deflected by the deflection element to the deflection element,
The light beam from the light source is condensed by the imaging means, incident on the deflecting element, deflected, and deflected again by the deflecting element by guiding the deflected light beam to the deflecting element by the transmission optical system. In an optical scanning device that emits a light beam toward the surface to be scanned,
The optical scanning apparatus according to claim 1 , wherein the transmission optical system has an imaging characteristic that reduces a condensing angle of the light beam guided to the deflection element in accordance with a deflection angle of the light beam . The deflection element is
A movable member having the deflection mirror surface;
A support member for swingably supporting the movable member around the main scanning deflection axis;
A mirror drive unit that swings and drives the movable member around the main scanning deflection axis,
The mirror drive unit includes an optical scanning device according to any one of claims 1 to 3 is swung for scanning the light beam in the main scanning direction the deflection mirror surface in the main scanning deflection axis. The optical scanning device according to claim 4, wherein the movable member and the support member are made of silicon single crystal. The mirror drive unit includes an optical scanning apparatus according to claim 4 or 5, wherein swings drives the deflection mirror surface in the main scanning deflection axis in a resonant mode. The mirror drive unit includes an optical scanning apparatus according to any one of claims 4 to drive oscillating the deflection mirror surface in the main scanning deflection axis by an electromagnetic force 6. The optical scanning device according to any one of the mirror drive unit, to claims 4 to drive oscillating the deflection mirror surface in the main scanning deflection axis by an electrostatic attraction force 6. A latent image carrier;
Has an optical scanning apparatus having the same configuration as claimed in any one of claims 1 to 8, 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