JP2005250133A - Optical deflector and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical deflector which prevents stress generated between a substrate supporting a mirror and a base which fixes the substrate from being transferred to the mirror. <P>SOLUTION: The present invention is characterized by that the optical deflector has the mirror, a torsion bar elastically supporting the mirror, the substrate supporting the mirror by being connected with the torsion bar and the base on which the substrate is mounted, the mirror is fixed in the optical deflector rocking on the base, and the substrate and the base are fixed by that a permanent magnet and a magnetic thin film on the side of the substrate are pulled by each other. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical deflector created by using a MEMS (Micro Electro Mechanical Systems) technique. The present invention also relates to an image forming apparatus using this optical deflector.

  In recent years, development of an optical deflector using MEMS (Micro Electro Mechanical Systems) technology has been advanced. 6 and 7 are diagrams illustrating the optical deflector disclosed in Patent Document 1. FIG.

  Hereinafter, the optical deflector disclosed in Patent Document 1 will be described with reference to FIGS. 6 and 7. The optical deflector 1001 is formed by anodic bonding of upper and lower glass substrates 1003 and 1004 as upper and lower insulating substrates made of, for example, borosilicate glass, respectively, on the upper and lower surfaces of a silicon substrate 1002 that is a semiconductor substrate. It has a three-layer structure. The upper glass substrate 1003 is laminated on the left and right ends of the silicon substrate 1002 in FIG. 6 so as to open the upper part of the movable plate 1005 described later.

  The silicon substrate 1002 includes a flat movable plate 1005 and a torsion bar 1006 that pivotally supports the movable plate 1005 so as to be swingable in the vertical direction with respect to the silicon substrate 1002 at the center of the movable plate 1005. It is integrally formed by anisotropic etching in the manufacturing process. Therefore, the movable plate 1005 and the torsion bar 1006 are also made of the same material as the silicon substrate 1002. A flat coil 1007 made of a copper thin film for allowing a driving current for driving the movable plate 1005 to flow is provided on the periphery of the upper surface of the movable plate 1005 so as to be covered with an insulating film.

  Further, a total reflection mirror 1008 as a reflection mirror is formed by aluminum vapor deposition at the center of the upper surface surrounded by the planar coil 1007 of the movable plate 1005. Further, a pair of electrode terminals 1009 that are electrically connected via the portions of the planar coil 1007 and the torsion bar 6 are provided on the side upper surface of the torsion bar 1006 of the silicon substrate 1002. A planar coil 1007 is simultaneously formed on a silicon substrate 1002 by an electroforming coil method.

  On the left and right sides of the upper and lower glass substrates 1003 and 1004 in the drawing, a pair of circular permanents that make a magnetic field act on the planar coil 1007 portion on the opposite side of the movable plate 1005 parallel to the axial direction of the torsion bar 1006. Magnets 1010A and 1010B and 1011A and 1011B are provided. The three upper and lower permanent magnets 1010A and 1010B that are paired with each other are provided so that the upper and lower polarities are the same, for example, as shown in FIG. 2, the lower side is the N pole and the upper side is the S pole. The other three permanent magnets 1011A and 1011B are also provided so that the upper and lower polarities are the same, for example, as shown in FIG. Then, the permanent magnets 1010A and 1011A on the upper glass substrate 1003 side and the permanent magnets 1010B and 1011B on the lower glass substrate 1004 side are provided so that their upper and lower polarities are opposite to each other, as can be seen from FIG.

  Next, the operation of this optical deflector will be described. For example, a current is passed through the planar coil 1007 with one electrode terminal 1009 as a positive pole and the other electrode terminal 1009 as a negative pole. On both sides of the movable plate 1005, a magnetic field is formed by the permanent magnets 1010A and 1010B and the permanent magnets 1011A and 1011B in a direction crossing the planar coil 1007 along the plane of the movable plate 1005, and the planar coil in this magnetic field When a current flows through 1007, the magnetic force is applied to the planar coil 1007 according to the current density and magnetic flux density of the planar coil 7, in other words, to both ends of the movable plate 1005 in the direction according to the left hand rule of current / magnetic flux density / force framing. Force F acts.

  This magnetic force F is obtained by the following equation (1), where i is the current density flowing through the planar coil 1007 and B is the magnetic flux density of the upper and lower permanent magnets.

F = i × B (1)
On the other hand, when the movable plate 1005 rotates, the torsion bar 1006 is twisted, and a spring reaction force F ′ is generated.

Then, the movable plate 1005 rotates to a position where the magnetic force F and the spring reaction force F ′ are balanced. Therefore, the displacement angle φ of the movable plate 1005 can be controlled by controlling the current flowing through the planar coil 1007. For example, the incident light is incident on the total reflection mirror 1008 in a plane perpendicular to the axis of the torsion bar 1006. The reflection direction of the laser beam to be controlled can be freely controlled, and the laser beam can be scanned by repeatedly operating the total reflection mirror 1008 and continuously changing its displacement angle.
JP 07-218857 A

  The present inventor has noticed that the above-described optical deflector has the following problems. That is, it is difficult for the optical deflector to maintain the flatness of the reflecting surface because the silicon substrate 1002 and the glass substrates 1003 and 1004 are anodically bonded to each other.

  If a substrate with a movable plate (in this case, a silicon substrate 1002) is anodically bonded to a base (in this case, at least one of the glass substrates 1003 and 1004), it is bonded at a high temperature during bonding.

  In particular, when a mirror (movable plate) or a torsion bar made of silicon is joined to another type of member, the temperature drops to room temperature after joining, and thermal stress is generated due to the temperature difference at that time.

  As a result, the stress at the joint acts on the movable plate, and the flatness of the movable plate cannot be maintained.

  By the way, this inventor assumed joining by an adhesive agent as joining methods other than anodic joining. However, although bonding with adhesive does not generate stress as much as anodic bonding, no effort has been made to transmit stress to the movable plate, and even slight stress due to shrinkage of the adhesive is transmitted to the movable plate with high accuracy. There is still room for improvement in terms of maintaining flatness.

  Moreover, once it is joined by an adhesive, it is not easy to separate once it is joined.

  In particular, when considering this optical deflector as an application of a laser scanning display, the flatness of the mirror portion is required to be guaranteed at a very high level.

  Furthermore, not only at the time of joining, but the periphery of the movable plate may be exposed to high temperatures (for example, due to heat generated by driving) in the actual use environment, so it is necessary to prevent the stress generated from the joint from being transmitted to the movable plate each time. There is.

  It is an object of the present invention to provide an optical deflector that prevents stress generated between a substrate holding a mirror and a base for fixing the mirror from being transmitted to the mirror.

Therefore, the present invention
Mirror,
A torsion bar that elastically supports the mirror;
A substrate that supports the mirror by being coupled to the torsion bar;
A base on which the substrate is placed;
In the optical deflector that the mirror swings on the base,
The substrate and the base are fixed by adhering a permanent magnet and a magnetic thin film on the substrate side to each other.

  According to the present invention, it is possible to prevent the stress generated between the substrate and the base from being transmitted to the mirror.

  In the optical deflector of the present invention, a permanent magnet and a magnetic thin film are used when fixing the substrate supporting the mirror and the base supporting the substrate.

  More specifically, a magnetic thin film is provided on the substrate side, a permanent magnet is provided on the base, and the substrate and the base are fixed by adsorbing the magnetic thin film and the permanent magnet.

  An attractive force N acts between the permanent magnet adhered and fixed on the base side and the magnetic thin film provided on the substrate.

  In this embodiment, the substrate and the base have different linear expansion coefficients, but in this case, when the temperature changes, the attracting portion (contact portion between the magnetic thin film and the permanent magnet) has a force F in the in-plane direction of the substrate. Will work. When this force F exceeds the maximum static friction force μN (μ: static friction coefficient), the suction portion slips in the direction in which the horizontal force is relaxed.

  In this embodiment, the attracting portion between the magnetic thin film and the permanent magnet is designed so that the magnetic thin film and the permanent magnet slide relatively when a force exceeding the maximum static friction force is generated.

  Therefore, even if a large temperature change occurs during use, it is possible to prevent the flatness of the mirror from being damaged (deflected) by the force.

  Also, it is possible to easily replace the substrate and the base if necessary.

  The substrate of the optical deflector according to this embodiment may be a silicon substrate. In this case, the base may be a glass substrate or a resin substrate other than the silicon crystal substrate.

  A mirror is provided on the substrate. A torsion bar that elastically supports the mirror is provided between the mirror and the substrate. The torsion bar is connected to the mirror and the substrate. The torsion bar supports the mirror as it swings. The mirror can be called a movable plate. In this embodiment, a configuration in which a mirror of another member is arranged on the movable plate surface may be called a mirror, or a configuration in which the movable plate surface itself is a mirror may be called a mirror.

  In view of strength, the mirror, the torsion bar, and the substrate are preferably an integral mold having no joint surface. As the integral mold, a silicon substrate obtained by using a fine processing technique such as photolithography is preferable. Although the mirror and the substrate are separated from each other without being in direct contact with each other, it is preferable to form the separation region by using a technique such as etching in forming the separation region.

  In the optical deflector according to the present embodiment, the substrate is supported by the base, but the two are arranged apart from each other. A permanent magnet and a magnetic thin film are provided to form the separation region.

  Since the mirror has this separation region, it does not hit the base when swinging.

  It is preferable that the permanent magnet is disposed on the base side, the magnetic thin film is disposed on the substrate, and both are adsorbed in that state. The permanent magnet may be disposed on the base with an adhesive or the like, but the magnetic thin film in contact with the substrate preferably does not use an adhesive in order to contact the substrate. The magnetic thin film is preferably a thin film formed on a substrate (more specifically, vacuum film formation).

  As described above, in the present embodiment, it is not necessary to use an adhesive by using a permanent magnet and a magnetic thin film in order to adsorb the substrate and the base.

  In the optical deflector according to this embodiment, the mirror may be oscillated by at least one of electromagnetic drive, electrostatic drive, and piezoelectric drive.

  What is necessary is just to determine the number of the means, such as a magnet used by each drive, an electrode, and a coil, and the position suitably. The arrangement positions may be arranged on each of the substrate side (particularly the mirror opposite surface) and the base side, or may be arranged on either one.

The optical deflector according to this embodiment is a fine mirror having a mirror surface area of about several mm ² , but may be finer than that.
Further details will be described below.

  FIG. 1 is an exploded view of the electromagnetically driven optical deflector according to the first embodiment, and FIG. 2 is a cross-sectional view taken along line A-A ′ of FIG. 1. A movable mirror 103 is elastically supported by torsion bars 102A and B inside a fixed frame 101 which is a substrate. These are integrally formed by etching a silicon substrate. Aluminum is deposited on one surface of the movable mirror 103 to form a reflective surface. A bar magnet 104 is bonded to the side opposite to the reflecting surface. The magnetic thin films 105A and 105B, which are the features of the present invention, are formed by plating on the side opposite to the reflecting surface of the movable mirror 103 of the fixed frame 101. The material is preferably a material having a high magnetic permeability and a high saturation magnetic flux density, such as nickel or an alloy of nickel and iron.

  A coil substrate 112 and permanent magnets 115A and 115B, which are features of the present invention, are bonded onto a fixed base 111 that is a base. As shown in FIG. 1, the permanent magnets 115A and B are magnetized in a direction parallel to the substrate. On the coil substrate 112, a coil 113 is patterned by a photolithography technique, and both ends of the coil are connected to extraction electrodes 114A and 114B.

  The optical deflector of the present embodiment is assembled by attracting the magnetic thin films 105A and 105B and the permanent magnets 115A and 115B by magnetic force.

  When a current is passed from the extraction electrodes 114 </ b> A and B to the coil 113, a magnetic field is generated in a direction perpendicular to the coil substrate 112. By this magnetic field, a torque proportional to the magnetic field is generated for the bar magnet 104, and the movable mirror 103 elastically supported by the torsion bars 102A and 102B can be deflected. In addition, when the frequency of the alternating current flowing through the coil 113 is matched with the resonance frequency of the movable mirror 103, a large displacement angle can be obtained with low power consumption.

  In the optical deflector of the present embodiment, no adhesive is used to fix the silicon member, so that the movable mirror is not distorted in the initial state. Further, when the temperature change occurs, the joint is slipped and absorbs the thermal expansion difference, so that the mirror is not greatly distorted. Further, when the silicon member is damaged, it can be easily replaced.

  3 is an exploded view of the electrostatic drive type optical deflector according to the second embodiment, and FIG. 4 is a cross-sectional view taken along the line B-B ′ of FIG. 3. A movable mirror 203 is elastically supported by torsion bars 202A and B inside a fixed frame 201 which is a substrate. These are created by etching a silicon substrate. The magnetic thin films 205A and 205B, which are the features of the present invention, are formed by plating on the same side as the reflecting surface of the movable mirror 203 of the fixed frame 201. The material is preferably a material having a high magnetic permeability and a high saturation magnetic flux density, such as nickel or an alloy of nickel and iron.

  The mirror fixing member 208 has a movable mirror window 209 to which permanent magnets 215A and 215B, which are the features of the present invention, are bonded. As shown in FIG. 3, the permanent magnets 215A and 215B are magnetized in a direction parallel to the substrate. An electrode substrate 212 is bonded on the fixing table 211. On the electrode substrate 212, drive electrodes 213A and 213B are patterned by a photolithography technique, and are connected to extraction electrodes 214A and B, respectively.

  The optical deflector of this embodiment is assembled by attracting the magnetic thin films 205A and 205B and the permanent magnets 215A and B with magnetic force. In addition, the mirror fixing member 208 and the fixing base 211 as a base are coupled by an adhesive.

  When the potential of the extraction electrodes 214A and B is changed with respect to the movable mirror 203, the potential between the drive electrodes 213A and B changes, and electrostatic attraction is generated between the movable mirrors 203 according to the potential of the extraction electrodes 214A and B. Works. Due to this electrostatic attraction, torque is generated with respect to the movable mirror 203, and the movable mirror 203 elastically supported by the torsion bars 202A, B can be deflected. Further, when the frequency of the AC voltage applied to the extraction electrodes 214A and 214B is matched with the resonance frequency of the movable mirror 203, a large displacement angle can be obtained with low power consumption.

  In the optical deflector of the present embodiment, no adhesive is used to fix the silicon member, so that the movable mirror is not distorted in the initial state. Further, when the temperature change occurs, the joint is slipped and absorbs the thermal expansion difference, so that the mirror is not greatly distorted.

  Regarding the mirror driving method, it goes without saying that all methods generally used for optical deflectors, such as the piezoelectric effect and the shape memory effect, can be used in addition to those shown in these embodiments.

  FIG. 5 is a schematic view for explaining an optical scanning display (image forming apparatus) according to the present invention. The laser beam 310 emitted from the laser light source 303 is scanned in the horizontal direction by the optical deflector 301 of the present invention, and then scanned in the vertical direction by another optical deflector 302 to form an image on the screen 320. The optical deflectors 301 and 302 and the laser light source 303 are controlled by the control means 304. As the optical deflector 301, any one of the optical deflectors described in the embodiments and examples is used.

  In this embodiment, the screen may be provided in the optical scanning display of this embodiment or may be a separate body. Or if it is a projection surface, an indoor wall may be sufficient.

  By using the optical deflector of the present invention, the optical scanning display of the present invention can provide an optical scanning display in which image deterioration hardly occurs even when a temperature change occurs. Further, even if a site made of silicon is damaged, it can be easily replaced.

  The optical deflector according to this embodiment is provided in an electrophotographic image forming apparatus. The rest is the same as the optical deflector 301 described in the third embodiment. Light emitted from the light source is deflected and scanned by an optical deflector, and the surface of the photosensitive drum is irradiated with the deflected light to obtain a latent image. An image on the paper is formed from the obtained latent image. This configuration is particularly used for copying machines and laser beam printers.

FIG. 3 is an exploded view illustrating the electromagnetically driven optical deflector according to the first embodiment. It is sectional drawing explaining the electromagnetic drive type optical deflector of Example 1. FIG. It is an exploded view explaining the electrostatic drive type optical deflector of Example 1. FIG. It is sectional drawing explaining the electrostatic drive type optical deflector of Example 1. FIG. It is a figure explaining the optical scanning type display of Example 3. FIG. It is a top view explaining a general optical deflector. It is sectional drawing explaining a general optical deflector.

Explanation of symbols

101, 201 Fixed frame 102A, B, 202A, B Torsion bar 103, 203 Movable mirror 104 Bar magnet 105A, B, 205A, B Magnetic thin film 111, 211 Fixed base 112 Coil substrate 113 Coil 114A, B, 214A, B Electrodes 115A, B, 215A, B Permanent magnet 208 Mirror fixing member 212 Electrode substrate 213 Drive electrode 301, 302 Optical deflector 303 Laser light source 304 Control means 310 Laser light 320 Screen

Claims (3)

Mirror,
A torsion bar that elastically supports the mirror;
A substrate that supports the mirror by being coupled to the torsion bar;
A base on which the substrate is placed;
In the optical deflector that the mirror swings on the base,
The optical deflector, wherein the substrate and the base are fixed by adsorbing a permanent magnet and a magnetic thin film on the substrate side.   The optical deflector according to claim 1, wherein the mirror swings by at least one of electromagnetic driving, electrostatic driving, and piezoelectric driving. A light source and light source modulating means for modulating the light source;
An optical polarizer according to claim 1;
An image forming apparatus comprising control means for controlling the light source modulation means and the optical polarizer.

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