JP2005106894A - Optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner, in which a deflection angle of a light beam is surely larger than the maximum deflection angle of the light beam given with a reference deflection mirror face, and to provide image forming apparatus furnished with the optical scanner. <P>SOLUTION: The reference deflection mirror face (third deflection mirror face 951c) deflects the light beam at a maximum deflection angle of 2×Θ3max, in a positive direction at a time t3max. In this case, all the deflection directions of light beams on other deflection mirror faces are aligned in the same direction as the deflection direction of the light beam deflected with the reference deflection mirror face (third deflection mirror face 951c), in order to give a a deflection angle Θs larger than 2×Θ3max to the light beam emitted from a N-th deflection mirror face 951n. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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

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

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

  In the above optical scanning device, the light beam deflected by the first deflection mirror surface is guided to the second deflection mirror surface by the transmission optical system, and the light beam from the first deflection mirror surface is further deflected by this second deflection mirror surface. This increases the deflection angle of the light beam. Therefore, when a vibrating mirror such as a galvanometer mirror is used as the deflection element of the optical scanning device, the deflection angle of the light beam emitted from the second deflection mirror surface toward the scanned surface is determined by the first deflection mirror surface. It is necessary to sufficiently adjust the vibration frequency and phase of each deflecting element so as to further increase the deflection angle of the deflected light beam.

  However, in the above optical scanning device, since sufficient measures have not been taken in this regard, the following problems may occur. That is, depending on the setting conditions of the vibration frequency and phase of each deflection element, the light beam may be deflected by the second deflection mirror surface so as to reduce the deflection angle of the light beam deflected by the first deflection mirror surface. is there. In other words, the deflection angle of the light beam emitted toward the scanned surface by the second deflection mirror surface may not be larger than the maximum deflection angle of the light beam by the first deflection mirror surface.

  The present invention has been made in view of the above problems, and includes an optical scanning device capable of reliably obtaining a deflection angle of a light beam that is surely larger than the maximum deflection angle of the light beam by a reference deflection mirror surface, and the device. Another object of the present invention is to provide an image forming apparatus.

  In order to achieve the above object, the optical scanning device according to the present invention includes a light source that emits a light beam and first to Nth deflection mirror surfaces that are swingable about independent main scanning deflection axes. N ≧ 2 natural number) and a mirror driving unit that drives the first to Nth deflection mirror surfaces to swing around the main scanning deflection axis, and the light beam from the light source is applied to the first deflection mirror surface. And is deflected at least once by the respective deflection mirror surfaces between the first to Nth deflection mirror surfaces, and then directed from one of the first to Nth mirror surfaces to the scanned surface. The mirror driving unit uses any one of the first to Nth deflection mirror surfaces as a reference deflection mirror surface, and the deflection angle of the light beam in the predetermined direction by the reference deflection mirror surface is the maximum. side The first to Nth deflecting mirror surfaces are driven to swing so that each of the deflecting mirror surfaces except the reference deflecting mirror surface deflects the light beam in the predetermined direction when it becomes a corner. .

  In the invention configured as described above, when the deflection angle of the light beam in the predetermined direction by the reference deflection mirror surface becomes the maximum deflection angle, the other deflection mirror surfaces also deflect the light beam in the same predetermined direction. It is configured. Therefore, when the deflection angle of the light beam in the predetermined direction by the reference deflection mirror surface becomes the maximum deflection angle, the other deflection mirror surface further deflects the light beam in the same direction as the deflection direction of the light beam by the reference deflection mirror surface. Thus, the deflection angle of the light beam emitted toward the surface to be scanned can be surely made larger than the maximum deflection angle of the light beam by the reference deflection mirror surface.

  Further, the mirror driving unit swings the first to Nth deflection mirror surfaces in a sine wave shape satisfying the following equations, with the Ath deflection mirror surface (where 1 ≦ A ≦ N is a natural number) as the reference deflection mirror surface. It may be configured to be driven dynamically.

このような構成にすることによって、交流電源を用いて偏向ミラー面の揺動周波数を容易に調整できる。さらに、基準偏向ミラー面による光ビームの偏向角が最大偏向角となる時に、他の偏向ミラー面により基準偏向ミラー面による光ビームの偏向方向と同じ方向にさらに光ビームを偏向することによって、被走査面へ向けて射出される光ビームの偏向角を確実に基準偏向ミラー面による光ビームの最大偏向角よりも大きくすることができる。

With such a configuration, the oscillation frequency of the deflection mirror surface can be easily adjusted using an AC power supply. Furthermore, when the deflection angle of the light beam by the reference deflection mirror surface reaches the maximum deflection angle, the light beam is further deflected by the other deflection mirror surface in the same direction as the deflection direction of the light beam by the reference deflection mirror surface. The deflection angle of the light beam emitted toward the scanning surface can be surely made larger than the maximum deflection angle of the light beam by the reference deflection mirror surface.

  The first and second deflection mirror surfaces and the mirror driving unit, and deflecting means for deflecting the light beam from the light source in a main scanning direction substantially orthogonal to the main scanning deflection axis, and the first A transmission optical system for guiding the light beam deflected by the deflection mirror surface to the second deflection mirror surface, and the transmission optical system is disposed such that a reflection surface thereof faces the first and second deflection mirror surfaces And the concave mirror surface reflects the light beam deflected by the first deflecting mirror surface to the second deflecting mirror surface, so that the light beam is reflected from the second deflecting mirror surface to the target object. You may comprise so that it may inject | emitted toward a scanning surface. In this case, it is desirable that the first deflecting mirror surface and the second deflecting mirror surface are driven to swing at opposite phases and the same frequency. In the transmission optical system configured as described above, the light beam deflected by the first deflection mirror surface is reflected by the concave mirror surface and guided to the second deflection mirror surface. By using a concave mirror as a transmission optical system in this way, a transmission optical system can be configured with a single concave mirror, and a plurality of optical components (two transmission lenses) are essential for configuring the transmission optical system. Compared with the conventional apparatus, the transmission optical system can be simple and configured with a small number of optical components. Further, since the transmission lens is not required, the influence of chromatic aberration can be eliminated, and the light beam can be deflected with excellent stability.

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

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

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

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

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

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

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

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

<Basic concept of invention>
First, the present invention will be described in detail with reference to FIGS. FIG. 1 is a schematic diagram of an optical scanning device that deflects a light beam by a plurality of deflecting mirror surfaces, and FIG. 2 is a schematic diagram showing conditions necessary for the optical scanning device of FIG. 1 to increase the deflection angle of the light beam. 3 is a schematic diagram showing the basis of the phase time difference that satisfies the conditions of FIG.

  FIG. 1 is a schematic diagram showing an optical scanning device that scans a light beam using N (where N ≧ 2 is a natural number) deflection mirror surfaces. In this apparatus, the light beam is deflected by the first to Nth deflection mirror surfaces 951a, 951b, 951c,..., 951m, 951n and then emitted from the Nth deflection mirror surface 951n at a deflection angle Θs. Two transmission lenses 971a, 972a, 971b, 972b,..., 971m, 972m each having the same power are arranged between the deflecting mirror surfaces to form transmission optical systems 97a, 97b,. The light beam is transmitted from the deflecting mirror surface to the deflecting mirror surface. When the rotation angle of the i-th deflection mirror surface is Θi, for example, the light beam is deflected by the i-th deflection mirror surface with a deflection angle of 2 · Θi. The broken line in the drawing indicates that the deflection mirror surface and the transmission optical system disposed between the third deflection mirror surface and the m-th deflection mirror surface are not shown.

  Since the transmission optical systems 97a to 97m have the same configuration, only the transmission optical system 97a will be described, and the other transmission optical systems will be denoted by the same reference numerals and description thereof will be omitted. The transmission optical system 97a includes a transmission lens 971a disposed so that its front focal point substantially coincides with the substantially central position of the first deflection mirror surface 951a, and the front focal point substantially coincides with the rear focal point of the transmission lens 971a. And a transmission lens 972a disposed so that the rear focal point substantially coincides with the substantially central position of the second deflection mirror surface 951b. Then, the light beam deflected by the first deflection mirror surface 951a toward the transmission lens 971a at the first deflection angle 2 · Θ1 is guided to the second deflection mirror surface 951b through the transmission lenses 971a and 972a, so that the second The deflecting mirror surface 951b deflects the light beam toward the transmission lens 971b at a deflection angle 2 · Θ1 + 2 · Θ2 which is further increased by the second deflection angle 2 · Θ2.

  The light beam deflected toward the transmission lens 971b is guided to the third deflection mirror surface 951c via the transmission lenses 971b and 972b. The light beam guided to the third deflection mirror surface 951c is further increased by the third deflection angle 2 · Θ3 toward the next transmission lens (not shown) by the third deflection mirror surface 951c, and the deflection angle 2 · Θ1 + 2・ Deflect by Θ2 + 2 ・ Θ3. Thereafter, the same operation is performed until the light beam is guided to the Nth deflection mirror surface 951n.

  The light beam guided to the Nth deflection mirror surface is emitted by the Nth deflection mirror surface 951n at a deflection angle Θs further increased by the Nth deflection angle 2 · ΘN. Therefore, the magnitude of the deflection angle Θs is an added value of the magnitudes of the deflection angles of the light beams by the respective deflection mirror surfaces.

  Here, each deflection mirror surface deflects the light beam while oscillating at a predetermined oscillation frequency. However, in such a case, depending on the setting conditions of the oscillation frequency and phase of each deflecting mirror surface, the deflecting mirror surfaces cancel each other out the deflection angles of the light beams, and a sufficient deflection angle may not be obtained. is there. Therefore, in the present invention, the configuration shown in FIG. 2 is used to ensure that the necessary deflection angle can be obtained. Hereinafter, the configuration will be described in detail.

  In FIG. 2, when the third deflection mirror surface 951c in FIG. 1 is used as a reference deflection mirror surface, the deflection angle Θs of the light beam emitted from the Nth deflection mirror surface 951n is a predetermined value of the light beam by the third deflection mirror surface 951c. The configuration is assured to be larger than the maximum deflection angle 2 · Θ3max of the light beam in the direction of. 2A shows the size of the rotation angle of the reference deflection mirror surface (third deflection mirror surface 951c) at time t, and FIG. 2B shows the size of the rotation angle of the first deflection mirror surface 951a at time t. FIG. 2C shows the magnitude of the rotation angle of the i-th deflection mirror surface (natural number 1 ≦ i ≦ N, except i = 1, 3) at time t.

  As shown in FIG. 2A, the reference deflection mirror surface (third deflection mirror surface 951c) has a maximum rotation angle Θ3max in the positive direction at time t3max, and deflects the light beam at the maximum deflection angle 2 · Θ3max. At this time, in order to make the deflection angle Θs of the light beam emitted from the Nth deflection mirror surface 951n larger than 2 · Θ3max, the deflection directions of the light beams by the other deflection mirror surfaces are all the reference deflection mirror surface ( The light beam may be deflected in the same direction as that of the third deflection mirror surface 951c). That is, the magnitudes of rotation angles Θ1a and Θia of the first and i-th deflection mirror surfaces shown in FIGS. 2B and 2C at the time t3max are in the same direction as Θ3max, that is, in the positive direction. The oscillation frequency and phase of each deflection mirror surface excluding the reference deflection mirror surface may be set. With such a configuration, the deflection angle Θs of the light beam emitted from the Nth deflection mirror surface 951n is reliably set to the maximum in the predetermined direction of the light beam by the reference deflection mirror surface (third deflection mirror surface 951c). The deflection angle can be made larger than 2 · Θ3max.

  Next, each deflecting mirror surface is configured to deflect the light beam while oscillating at a predetermined oscillating frequency in a sinusoidal shape as shown in Formula 2, and the Ath deflecting mirror surface (a natural number of 1 ≦ A ≦ N) is a reference. A deflection mirror surface. In this case, if the deflection mirror surface is swung as will be described in detail below, the deflection angle Θs of the light beam emitted from the Nth deflection mirror surface 951n is reliably set to a predetermined value of the light beam by the Ath deflection mirror surface. It can be made larger than the maximum deflection angle 2 · ΘAmax in the direction. FIG. 3A shows the magnitude of the rotation angle of the A-th deflection mirror surface at time t, and the A-th deflection mirror surface is oscillated at the reference oscillation frequency f. 3 (b) shows a state where the phase is delayed by αimin, and FIG. 3 (c) shows a rotation at time t of the i-th deflection mirror surface (1 ≦ i ≦ N, except A) where the phase is delayed by αimax. This indicates the size of the corner, and the i-th deflection mirror surface is oscillated at an oscillation frequency ki · f (ki: natural number).

  As shown in FIG. 3B, if the phase delay time of the i-th deflection mirror surface with respect to the A-th deflection mirror surface is made larger than αimin, the deflection angle of the light beam by the A-th deflection mirror surface (reference deflection mirror surface) can be increased. At the maximum time tAmax, the light beam is reliably deflected by the i-th deflection mirror surface in the same direction as the light beam deflection direction by the A-th deflection mirror surface (range indicated by PHB). Here, as shown in FIG. 3C, if the phase delay time of the i-th deflection mirror surface with respect to the A-th deflection mirror surface is made larger than αimax, the deflection direction of the light beam by the i-th deflection mirror surface is The phase delay time should not be larger than αimax because it is opposite to the deflection direction of the light beam by the deflection mirror surface.

  The i-th deflection mirror surface is configured to oscillate with ki · f as an oscillation frequency where ki is an arbitrary natural number. Here, by setting the phase delay time of the i-th deflection mirror surface to tAmax (= 1 / (4f)), the deflection angle of the light beam by the i-th deflection mirror surface at time tAmax becomes zero. From here, the light beam by the i-th deflection mirror surface is further delayed by delaying the phase of the i-th deflection mirror surface by a half period (= 1 / (2ki · f)) of the oscillation frequency of the i-th deflection mirror surface. Is the same as the deflection direction of the light beam by the A-th deflection mirror surface (range indicated by PHB). Therefore, the deflection angle Θs of the light beam emitted from the Nth deflection mirror surface 951n can be made larger than the maximum deflection angle 2 · ΘAmax in the predetermined direction of the light beam by the Ath deflection mirror surface.

  When the light beam is delayed by one period or more (= 1 / (ki · f)), the deflection direction of the light beam by the i-th deflection mirror surface is opposite to the deflection direction of the light beam by the A-th deflection mirror surface ( Outside the range indicated by PHB). Therefore, the deflection angle Θs of the light beam emitted from the Nth deflection mirror surface 951n is smaller than the maximum deflection angle 2 · ΘAmax in the predetermined direction of the light beam by the Ath deflection mirror surface.

  From the above, the phase difference time αi of the i-th deflection mirror surface is in the range represented by Equation 2. H / ki in Equation 2 is a generalized phase condition in each cycle because the i-th deflection mirror surface is swung in a sine wave.

  The number of times of deflection of the light beam by each deflecting mirror surface may be any number as long as it is one or more, and the deflection angle Θs in that case is expressed by the following equation.

また、光ビームが射出する偏向ミラー面は、第１ないし第Ｎ偏向ミラー面のいずれかからでもよいことは言うまでもない。この場合でも、数２で示す揺動周波数・位相条件で、各偏向ミラー面を揺動駆動すれば、光ビームの偏向角Θsを、確実に第Ａ偏向ミラー面（基準偏向ミラー面）による光ビームの所定の方向における最大偏向角２・ΘAmaxよりも大きくすることができる。

It goes without saying that the deflection mirror surface from which the light beam is emitted may be from any of the first to Nth deflection mirror surfaces. Even in this case, if each deflection mirror surface is driven to oscillate under the oscillation frequency and phase conditions shown in Equation 2, the deflection angle Θs of the light beam can be reliably determined by the light from the Ath deflection mirror surface (reference deflection mirror surface). The maximum deflection angle 2 · ΘAmax in a predetermined direction of the beam can be made larger.

  In FIG. 1, the transmission optical system is configured by a transmission lens, but various modifications other than those described above can be made without departing from the spirit of the transmission optical system. For example, various reflection elements may be used as the transmission optical system, or a combination of a transmission lens and a reflection element may be used. All of the embodiments described below have the above-described configuration.

<First Embodiment>
FIG. 4 is a view showing an image forming apparatus equipped with an exposure unit according to the first embodiment of the optical scanning device of the present invention. FIG. 5 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 (corresponding to the “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. 5), and a vertical synchronization sensor 77 (FIG. 5) 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. 5, 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.

  6 is a main scanning sectional view showing the configuration of an exposure unit (optical scanning device) provided in the image forming apparatus of FIG. 4, FIG. 7 is a diagram showing a transmission optical system as one component of the exposure unit, and FIG. FIG. 9 and FIG. 10 are diagrams showing a deflecting element 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 so that 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, a transmission optical system 87, and a folding mirror 68 are provided. That is, the light beam from the laser light source 62 is shaped into collimated light of an appropriate size by the collimator lens 631 and then incident on the cylindrical lens 632 having power only in the sub-scanning direction Y. The light beam that has passed through the cylindrical lens 632 is folded back by the folding mirror 641. By adjusting the cylindrical lens 632, the collimated light is imaged in the vicinity of the deflection mirror surface 851a of the deflection element 85a in the sub-scanning direction Y. Thus, in this embodiment, the collimator lens 631 and the cylindrical lens 632 function as the beam shaping system 63 that shapes the light beam from the laser light source 62.

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

  In this deflecting element 85a, as shown in FIG. 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 BX1a extending substantially parallel to the sub-scanning direction Y. In addition, an aluminum film or the like is formed as a deflection mirror surface 851a at the center of the upper surface of the movable plate 856a.

  Further, as shown in FIG. 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 BX1a. Electrodes 8581a and 8582a are fixed to positions on the inner bottom surface of the recess 8521a that face both ends of the movable plate 856a. These two electrodes 8581a and 8582a function as electrodes for swinging and driving the movable plate 856a around the first axis BX1a. That is, these electrodes 8581a and 8582a are electrically connected to a drive unit (not shown) of the exposure control unit 102, and electrostatic application between the electrodes and the first deflection mirror surface 851a is caused by applying a voltage to the electrodes. The attracting force acts to draw one end portion of the first deflection mirror surface 851a toward the electrode side. Therefore, when a predetermined voltage is alternately applied to the electrodes 8581a and 8582a from the drive unit, the first deflection mirror surface 851a can be reciprocally oscillated using the torsion spring 857a as the first axis BX1a. In this embodiment, the first deflection mirror surface 851a is used as a reference deflection mirror surface, and the first deflection mirror surface 851a and the second deflection mirror surface 851b are swung in the same phase and the same frequency as shown in Equation 2. It is configured to move.

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

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

  FIG. 7 is a diagram showing the configuration of the transmission optical system. The transmission optical system 87 includes a first transmission lens 871 disposed so that its front focal point substantially coincides with the substantially center position of the first deflection mirror surface 851a, and its front focal point is a rear focal point of the first transmission lens 871. And a second transfer lens 872 disposed so that the rear focal point substantially coincides with the substantially central position of the second deflection mirror surface 851b. Then, the light beam deflected by the first deflection mirror surface 851a toward the first transmission lens 871 at the first deflection angle 2 · Θ1 through the first and second transmission lenses 871 and 872 is used as the second deflection mirror surface 851b. And the second deflection mirror surface 851b guides the light beam toward the second transmission lens 872 at a deflection angle of 2 · Θ1 + 2 · Θ2 to guide it to the first deflection mirror surface 851a. As a result, the light beam is deflected again by the first deflection mirror surface 851a, and the light beam is emitted toward the scanning lens 66 at a deflection angle Θs larger than the first deflection angle 2 · Θ1 (see FIG. 8).

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

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

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

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

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

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

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

  The light beam that has been incident and deflected twice in this manner on the deflecting element 85 a is applied to the surface (scanned surface) of the photosensitive member 2 via the scanning lens 66 and the folding mirror 68. As a result, a light beam is scanned in parallel with the main scanning direction X, and a line-like latent image extending in the main scanning direction X is formed on the surface of the photoreceptor 2.

  Thus, in this embodiment, as shown in FIG. 8, the deflection angle Θs of the light beam emitted from the first deflection mirror surface 851a toward the scanning lens 66 is the deflection of the light beam by the first deflection mirror surface 851a. If the angle is the first deflection angle 2 · Θ1, and the deflection angle of the light beam by the second deflection mirror surface 851b is the second deflection angle 2 · Θ2, then 4 · Θ1 + 2 · Θ2. Here, since the first and second deflecting mirror surfaces 851a and 851b are swung in a sinusoidal form shown in Equation 2, Θs corresponds to the case where N = 2 in Equation 3.

  In this embodiment, as shown in FIG. 6, 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 deflecting unit 85 swings around the first axis (main scanning deflection axis) parallel to the sub-scanning direction Y substantially orthogonal to the main scanning direction X. First and second deflection mirror surfaces 851a and 851b for deflecting the beam are provided. Then, the light beam deflected toward the transmission optical system 87 by the first deflection mirror surface 851a is guided to the second deflection mirror surface 851b by the transmission optical system 87, so that the transmission optical system is transmitted by the second deflection mirror surface 851b. 87 and is guided to the first deflection mirror surface 851a by the transmission optical system 87. Then, the light is deflected again by the first deflecting mirror surface 851a and emitted toward the surface (scanned surface) of the photosensitive member 2. In this way, the deflection angle of the light beam emitted toward the photosensitive member surface is made larger than the deflection angle of the light beam incident on the transmission optical system 67. The mirror driving unit uses the first deflection mirror surface 851a as the reference deflection mirror surface, and the second deflection mirror when the magnitude of the deflection angle of the light beam in the predetermined direction by the first deflection mirror surface 851a becomes the maximum deflection angle. The surface swings and drives the first and second deflection mirror surfaces 851a and 851b so as to deflect the light beam in the same direction as the light beam deflection direction by the first deflection mirror surface 851a.

  Accordingly, when the deflection angle of the light beam in the predetermined direction by the reference deflection mirror surface (first deflection mirror surface 851a) becomes the maximum deflection angle, the second deflection mirror surface also deflects the light beam in the same predetermined direction. It is configured. Therefore, when the deflection angle of the light beam in the predetermined direction by the reference deflection mirror surface becomes the maximum deflection angle, the second deflection mirror surface further deflects the light beam in the same direction as the deflection direction of the light beam by the reference deflection mirror surface. Thus, the deflection angle of the light beam emitted toward the surface to be scanned can be surely made larger than the maximum deflection angle of the light beam by the reference deflection mirror surface.

  Further, in this embodiment, the first deflecting mirror surface 851a swings in a sine wave form expressed by i = 1, k1 = 1, α1 = 0, h = 0 in Equation 2 to deflect the light beam. . In addition, the second deflection mirror surface 851a swings in a sine wave shape expressed by i = 2, k2 = 1, α2 = 0, h = 0 in Equation 2, and deflects the light beam. Therefore, when the deflection angle of the light beam by the reference deflection mirror surface (first deflection mirror surface 851a) becomes the maximum deflection angle, the light beam is deflected by the second deflection mirror surface in the same direction as the deflection direction of the light beam by the reference deflection mirror surface. Is further deflected, the deflection angle of the light beam emitted toward the surface to be scanned can be surely made larger than the maximum deflection angle of the light beam by the reference deflection mirror surface.

  In this embodiment, the first deflection mirror surface 851a is configured to be substantially conjugate with the surface (scanned surface) of the photosensitive member 2 in the sub-scanning plane that is substantially orthogonal to the main scanning direction X (illustrated). (Omitted), it is possible to prevent the influence of the swing in the sub-scanning direction Y of the first deflection mirror surface 851a having a conjugate relationship with the surface to be scanned. Further, the size of the first deflection mirror surface 851a in the sub-scanning direction Y can be reduced, and the deflection element 85a can be reduced in size and weight.

Second Embodiment
FIG. 11 is a diagram showing a second embodiment of the optical scanning device according to the present invention. 11 and 12 are main scanning sectional views showing the configuration of an exposure unit (optical scanning device) equipped in the image forming apparatus of FIG. 4, and FIG. 13 is an exposure unit (optical scanning) equipped in the image forming apparatus of FIG. FIG. 14 and FIG. 15 are diagrams showing a deflecting element (deflecting means) as one component of the exposure unit. This embodiment differs greatly from the first embodiment in that a transmission optical system 67 that transmits a light beam between the first deflection mirror surface 651a and the second deflection mirror surface 651b as shown in FIG. The configuration differs from the configuration of the deflection element 65. Hereinafter, the configuration and operation of the exposure unit will be described in detail with a focus on differences from the first embodiment with reference to these drawings.

  In this embodiment, a folding mirror 641, a focusing lens 64, a deflection element 65 corresponding to the “deflection means” of the present invention, and a transmission optical system 67 are further provided. That is, the light beam from the laser light source 62 is shaped into collimated light of an appropriate size by the collimator lens 631 and then incident on the cylindrical lens 632 having power only in the sub-scanning direction Y as shown in FIG. The Further, the light beam that has passed through the cylindrical lens 632 is folded back by the folding mirror 641 and then incident on the focusing lens 64 having power only in the main scanning direction X as shown in FIG. Then, by adjusting the cylindrical lens 632, the collimated light is imaged in the vicinity of the deflection mirror surface 651a of the deflection element 65 in the sub-scanning direction Y. Thus, in this embodiment, the collimator lens 631 and the cylindrical lens 632 function as the beam shaping system 63 that shapes the light beam from the laser light source 62. On the other hand, the focal length of the focusing lens 64 is longer than the distance between the lens 64 and the first deflection mirror surface 651a. Therefore, a line image extending in the main scanning direction X is formed in the vicinity of the deflection mirror surface 651a of the deflection element 65.

  The deflecting element 65 is formed by using a micromachining technique in which a micromachine is integrally formed on a semiconductor substrate by applying a semiconductor manufacturing technique, and the light beam reflected by the deflecting mirror surfaces 651a and 651b is in the main scanning direction. The light beam can be deflected to X. More specifically, the deflection element 65 is configured as follows.

  In this deflecting element 65, as shown in FIG. 14, a silicon single crystal substrate (hereinafter referred to as “silicon substrate”) 652 functions as a “support member” of the present invention, and a part of the silicon substrate 652 is further processed. Thus, two movable plates (corresponding to “first and second movable members” of the present invention) 656a and 656b are provided in the main scanning direction X with a predetermined distance therebetween. The movable plate 656a is formed in a flat plate shape, is elastically supported on the silicon substrate 652 by a torsion spring 657, and can swing around a first axis AX1a extending substantially parallel to the sub-scanning direction Y. In addition, an aluminum film or the like is formed as a first deflection mirror surface 651a at the center of the upper surface of the movable plate 656a. The movable plate 656b is configured in the same manner as the movable plate 656a. That is, the movable plate 656b formed in a flat plate shape is provided to be swingable with respect to the silicon substrate 652 around the first axis AX1b, and an aluminum film or the like is provided at the center of the upper surface of the movable plate 656a as the second deflection mirror. A film is formed as the surface 651b.

In addition, electrodes 658a and 658b are respectively fixed to the movable plates 656a and 656b on the inner bottom surface of the recess 652a of the silicon substrate 652 at positions facing both ends of the movable plate. These two electrodes 658a and 658b function as electrodes for swinging and driving the movable plates 656a and 656b around the first axes AX1a and AX1b. That is, these electrodes 658a and 658b are electrically connected to a drive unit (not shown) of the exposure control unit 102, and electrostatic application is performed between the electrodes and the deflecting mirror surfaces 651a and 651b by applying a voltage to the electrodes. The attraction force acts to draw one end of the deflecting mirror surfaces 651a and 651b toward the electrode. Therefore, when a predetermined voltage is alternately applied to the electrodes 658a and 658b from the drive unit, the deflection mirror surfaces 651a and 651b can be reciprocally oscillated using the torsion spring 657 as the first axes AX1a and AX1b, respectively. In this embodiment, the first deflection mirror surface 651a is used as a reference deflection mirror surface, and the first deflection mirror surface 651a and the second deflection mirror surface 651b are swung in the sine wave form shown in Equation 2 with mutually opposite phase and same frequency. It is configured to move. That is, since the second deflection mirror surface 651b has an opposite phase,
Θ2 (t) = − Θ2max · sin {2π · k2 · f (t−α2) −π}
(However, k2 = 1, α2 = 0)
Is rocking. All other conditions are the same as in the first embodiment.

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

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

  As shown in FIG. 12, the transmission optical system 67 includes a single concave mirror 671, and the reflection surface 671a of the concave mirror 671 and the first and second deflection mirror surfaces 651a and 651b face each other. Are arranged to be. The light beam deflected by the first deflecting mirror surface 651a is reflected by the reflecting surface 671a of the concave mirror 671 and guided to the second deflecting mirror surface 651b. In this embodiment, an ellipsoidal mirror in which the reflecting surface 671a is formed into an ellipsoid is used as the concave mirror 671. More specifically, an ellipse having a focus at approximately the center position P1a of the first deflection mirror surface 651a and approximately the center position P1b of the second deflection mirror surface 651b is represented by an imaginary straight line VL passing through the two center positions P1a and P1b. A part of an ellipsoid formed by rotating as a rotation axis is used as the reflection surface 671a. Therefore, the following effects can be obtained. That is, since the first and second deflection mirror surfaces 651a and 651b are positioned at two focal points, the principal ray of the light beam deflected by the first deflection mirror surface 651a is reflected by the concave mirror surface (elliptical reflection surface) 671a. Then, the light enters the second deflection mirror surface 651b. Therefore, the light beam deflected by the first deflection mirror surface 651a can be reliably guided to the second deflection mirror surface 651b. Then, this light beam is deflected by the second deflection mirror surface 651 b and emitted toward the scanning lens 66. As a result, the light beam can be scanned stably.

  The light beam deflected by the deflecting element 65 in this manner is applied to the surface (scanned surface) of the photosensitive member 2 through the scanning lens 66 and the folding mirror 68. As a result, a light beam is scanned in parallel with the main scanning direction X, and a line-like latent image extending in the main scanning direction X is formed on the surface of the photoreceptor 2.

  Also in this embodiment, the first and second deflection mirror surfaces 651a and 651b are driven to swing in the same manner as in the first embodiment, and thus have the same operational effects as those in the first embodiment.

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

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

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

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

<Third Embodiment>
16 and 17 are main scanning sectional views showing a third embodiment of the optical scanning device according to the present invention. FIG. 18 is a sub-scan sectional view of the optical scanning device of FIG. The difference between the exposure unit 6 as the optical scanning device according to the third embodiment and the second embodiment is the configuration of the deflection element 65. That is, in the second embodiment, as shown in FIG. 18, the first and second deflection mirror surfaces 651a and 651b are arranged side by side in the sub-scanning direction Y. In the exposure unit 6 configured in this way, the light beam from the laser light source 62 is shaped into collimated light of an appropriate size by the collimator lens 631, and then only in the sub-scanning direction Y as shown in FIG. The light enters a cylindrical lens 632 having power. Further, as shown in FIG. 17, the light beam that has passed through the cylindrical lens 632 is incident on the focusing lens 64 having power only in the main scanning direction X, and is then folded back by the folding mirror 641 toward the first deflection mirror surface 651a. . Then, by adjusting the cylindrical lens 632, the collimated light is imaged near the deflection mirror surface 651a at the lower position in the sub-scanning direction Y. The light beam deflected by the deflecting mirror surface 651a is reflected by the concave mirror surface 671a of the transmission optical system 67 and guided to the deflecting mirror surface 651b at the upper position, and directed toward the scanning lens 66 by the deflecting mirror surface 651b. Is deflected.

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

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

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

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

<Fourth embodiment>
19 and 20 are views showing a fourth embodiment of the optical scanning device according to the present invention. The fourth embodiment is largely different from the first embodiment in that the deflection mirror surfaces 851a and 851b are driven to swing using electromagnetic force, and other configurations are different from those of the first embodiment. It is the same. Also in the deflecting element 65 of the second and third embodiments, the deflecting mirror surfaces 651a and 651b can be driven to swing using electromagnetic force by adopting the same configuration as that of the present embodiment. Here, description will be made by taking the deflection element 85a shown in FIGS. 19 and 20 as an example.

  In the deflection element 85a, as shown in FIG. 19, a movable plate 856a is provided by processing a part of the silicon substrate 852a. The movable plate 856a is formed in a flat plate shape, is elastically supported on the silicon substrate 852a by a torsion spring 857a, and is swingable about a first axis BX1a extending substantially parallel to the sub-scanning direction Y. Further, on the upper surface of the movable plate 856a, a planar coil 855a electrically connected to a pair of outer electrode terminals (not shown) formed on the upper surface of the silicon substrate 852a via a torsion spring 857a is coated with an insulating layer. ing. In addition, an aluminum film or the like is formed as a deflection mirror surface 851a at the center of the upper surface of the movable plate 856a.

  Further, as shown in FIG. 20, a concave portion 8521a is provided at a substantially central portion of the silicon substrate 852a so that the movable plate 856a can swing around the first axis BX1a. Then, permanent magnets 8591a and 8592a are fixed to the inner bottom surface of the recess 8521a at the outer positions of both ends of the movable plate 856a in different orientations. The planar coil 855a is electrically connected to a drive unit (not shown) of the exposure control unit 102, and the direction of the current flowing through the planar coil 855a by energization of the coil 855a and the magnetic flux generated by the permanent magnets 8591a and 8592a. Lorentz force acts depending on the direction, and a moment for rotating the movable plate 856a is generated. As a result, the movable plate 856a (deflection mirror surface 851a) swings with the torsion spring 857a as the first axis BX1a. Here, if the current flowing through the planar coil 855a is an alternating current and is continuously repeated, the deflection mirror surface 851a can be reciprocally oscillated with the torsion spring 857a serving as the first axis BX1a.

  In order to swing the first deflection mirror surface 851a in this way, an electromagnetic force, an electrostatic force, or the like is used, but it goes without saying that any of them may be used. However, since each driving method has the following characteristics, it is desirable to adopt them appropriately in consideration of them. That is, when an electromagnetic force is used as a driving force for swinging and driving the first deflection mirror surface 851a, the first deflection mirror surface 851a is driven to swing at a lower driving voltage than when an electrostatic attraction force is generated. Thus, voltage control is facilitated, and the positional accuracy of the scanning light beam can be increased. On the other hand, when the electrostatic attraction force is used as the driving force, it is not necessary to form a coil pattern, the deflection element 85a can be further miniaturized, and the deflection scanning can be further speeded up.

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

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

It is a schematic diagram of an optical scanning device that deflects a light beam by a plurality of deflection mirror surfaces. It is a schematic diagram which shows the conditions required in order for the optical scanning apparatus of FIG. 1 to increase the deflection angle of a light beam. It is a schematic diagram which shows the basis of the phase time difference which satisfy | fills the conditions of FIG. 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. 5 is a block diagram illustrating an electrical configuration of the image forming apparatus in FIG. 4. FIG. 5 is a main scanning sectional view showing a configuration of an exposure unit (optical scanning device) equipped in the image forming apparatus of FIG. 4. FIG. 5 is a view showing a transmission optical system as one component of an exposure unit (optical scanning device) provided in the image forming apparatus of FIG. 4. FIG. 5 is a schematic diagram showing a deflection angle of a light beam in an exposure unit (optical scanning device) equipped in the image forming apparatus of FIG. 4. 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 a second embodiment of the optical scanning device according to the present invention. It is a main scanning sectional view showing a second embodiment of the optical scanning device according to the present invention. FIG. 13 is a sub-scan sectional view of the optical scanning device of FIGS. 11 and 12. It is a figure which shows the deflection | deviation element of the exposure unit which is 2nd Embodiment of the optical scanning device concerning this invention. It is a figure which shows the deflection | deviation element of the exposure unit which is 2nd Embodiment of the optical scanning device concerning this invention. It is a main scanning sectional view showing a third embodiment of the optical scanning device according to the present invention. It is a main scanning sectional view showing a third embodiment of the optical scanning device according to the present invention. FIG. 13 is a sub-scan sectional view of the optical scanning device of FIGS. 11 and 12. It is a figure which shows the deflection | deviation element of the exposure unit which is 4th Embodiment of the optical scanning device concerning this invention. It is a figure which shows the deflection | deviation element of the exposure unit which is 4th Embodiment of the optical scanning device concerning this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 2 ... Photosensitive body (latent image carrier), 4 ... Development unit (developing means), 6 ... Exposure unit (optical scanning device), 65 ... Deflection element (deflection means), 85a, 85b ... Deflection element (deflection means), 67, 87 ... transmission optical system, 651a, 651b, 851a, 851b, 951a, 951b, 951c, 951m, 951n ... deflection mirror surface, 652, 852a ... silicon substrate (support member), 656a, 656b, 856a ... movable plate ( Movable member), 671 ... concave mirror (transmission optical system), 671a ... concave mirror surface, 871, 872 ... transmission lens, L ... light beam, P1a, P1b ... reflection position, AX1a, AX1b, BX1a ... main scanning deflection Axis, X ... main scanning direction, Y ... sub-scanning direction

Claims (18)

A light source that emits a light beam;
First to Nth deflection mirror surfaces provided so as to be swingable around independent main scanning deflection axes (where N ≧ 2 is a natural number);
A mirror driving unit that swings and drives the first to Nth deflection mirror surfaces around the main scanning deflection axis;
After the light beam from the light source is incident on the first deflection mirror surface and is deflected at least once by each deflection mirror surface between the first to Nth deflection mirror surfaces, the first Or emitted from any of the Nth mirror surfaces toward the scanned surface,
The mirror driving unit uses any one of the first to Nth deflection mirror surfaces as a reference deflection mirror surface, and the deflection angle of the light beam in a predetermined direction by the reference deflection mirror surface is a maximum deflection angle. In some cases, the first to Nth deflection mirror surfaces are driven to swing so that each of the deflection mirror surfaces excluding the reference deflection mirror surface deflects the light beam in the predetermined direction. . The mirror driving unit uses the A-th deflection mirror surface (where 1 ≦ A ≦ N is a natural number) as the reference deflection mirror surface, and each of the first to N-th deflection mirror surfaces is represented by the following rotation angle Θi (t) The optical scanning device according to claim 1, wherein the optical scanning device is driven to swing in a sinusoidal form as shown in FIG.

Deflection means having the first and second deflection mirror surfaces and the mirror driving section, for deflecting a light beam from the light source in a main scanning direction substantially orthogonal to the main scanning deflection axis;
A transmission optical system for guiding the light beam deflected by the first deflection mirror surface to the second deflection mirror surface;
The transmission optical system includes a concave mirror disposed so that a reflecting surface thereof faces the first and second deflecting mirror surfaces, and the concave mirror surface receives a light beam deflected by the first deflecting mirror surface. 3. The optical scanning device according to claim 1, wherein the light beam is emitted from the second deflection mirror surface toward the scanned surface by being reflected by the second deflection mirror surface. 4.   The optical scanning device according to claim 3, wherein the mirror driving unit swings and drives the first deflection mirror surface and the second deflection mirror surface at opposite phases and at the same frequency.   The concave mirror surface is an ellipse having a focal point at approximately the center position of the first deflection mirror surface and approximately the center position of the second deflection mirror surface, and a virtual straight line passing through the two center positions as a rotation axis. The optical scanning device according to claim 3, wherein the optical scanning device is an ellipsoid formed by rotation.   6. The optical scanning device according to claim 3, wherein the first and second deflection mirror surfaces are arranged side by side in a direction parallel to the main scanning direction.   6. The optical scanning device according to claim 3, wherein the first and second deflection mirror surfaces are arranged side by side in a sub-scanning direction substantially orthogonal to the main scanning direction.   8. The optical scanning device according to claim 3, wherein at least one of the first and second deflection mirror surfaces is substantially conjugate with the surface to be scanned in a sub-scanning plane substantially orthogonal to the main scanning direction. . Deflection means having the first and second deflection mirror surfaces and the mirror driving section, for deflecting a light beam from the light source in a main scanning direction substantially orthogonal to the main scanning deflection axis;
A transmission optical system for transmitting a light beam between the first and second deflecting mirror surfaces;
The transmission optical system includes a first transmission lens disposed so that a front focal point thereof substantially coincides with a substantially central position of the first deflection mirror surface, and a front focal point substantially equal to a rear focal point of the first transmission lens. And a second transmission lens arranged so that the rear focal point substantially coincides with the substantially central position of the second deflection mirror surface,
The light beam deflected toward the first transmission lens by the first deflection mirror surface is guided to the second deflection mirror surface through the first and second transmission lenses, and the second deflection mirror surface By deflecting the light beam toward the second transfer lens and guiding it to the first deflection mirror surface via the second and first transfer lenses, the light beam is deflected again by the first deflection mirror surface. The optical scanning device according to claim 1, wherein the optical scanning device emits light toward the scanned surface.   The optical scanning device according to claim 9, wherein the mirror driving unit swings and drives the first deflection mirror surface and the second deflection mirror surface with the same phase and the same frequency.   The optical scanning device according to claim 9 or 10, wherein the first deflection mirror surface is substantially conjugate with the surface to be scanned in a sub-scanning plane that is substantially orthogonal to the main scanning direction. The deflection means includes
A first movable member having the first deflection mirror surface;
A second movable member having the second deflection mirror surface;
A support member that swingably supports the first and second movable members about the main scanning deflection axis extending in a direction substantially orthogonal to the main scanning direction;
The mirror drive unit,
9. The optical scanning device according to claim 3, wherein the mirror driving unit swings the first and second deflection mirror surfaces around the main scanning deflection axis to deflect the light beam. The deflecting means supports a movable member having a deflection mirror surface for deflecting a light beam on one surface, and the movable member swingably around the main scanning deflection axis extending in a direction substantially perpendicular to the main scanning direction. It consists of two deflection elements comprising a support member and the mirror drive unit,
The deflection mirror surface of the one of the two deflection elements is the first deflection mirror surface, and the deflection mirror surface of the other deflection element is the second deflection mirror surface. Optical scanning device.   14. The optical scanning device according to claim 12, wherein the movable member and the support member are integrally formed by processing one substrate.   The optical scanning device according to claim 14, wherein the substrate, the movable member, and the support member are made of silicon single crystal.   16. The optical scanning device according to claim 12, wherein the mirror driving unit swings and drives the first and second deflecting mirror surfaces around the main scanning deflection axis by electrostatic attraction force.   16. The optical scanning device according to claim 12, wherein the mirror driving unit swings and drives the first and second deflection mirror surfaces around the main scanning deflection axis by electromagnetic force. A latent image carrier;
18. An exposure having the same configuration as that of the optical scanning device according to claim 1, wherein the latent image carrier is scanned with a light beam to form an electrostatic latent image on the latent image carrier. Means,
An image forming apparatus comprising: developing means for developing the electrostatic latent image with toner to form a toner image.

Images