JP2007256557A - Mems actuator and scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an MEMS actuator capable of oscillating, at high speed and/or with a large amplitude, an oscillating member such as a micro mirror, and also to provide a scanner equipped with the MEMS actuator. <P>SOLUTION: The MEMS actuator includes a substrate 20a, a plurality of the oscillating members (micro mirrors A, B, and suspension beams 23A, 23B) which are held so that they can be oscillated around the oscillation axis with respect to the substrate, driving electrodes 30A, 30B, 31A and 31B which are provided to the oscillating members and the substrate, respectively, and an AC power source 60 for applying an AC voltage between the respective driving electrodes. The MEMS actuator is characterized in that the plurality of the oscillating members are provided side by side so that the respective oscillating axes are substantially parallel to each other and that the oscillating members are connected to each other through an elastic body 22. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a MEMS actuator configured to oscillate an oscillating member such as a micromirror using an electrostatic force generated by applying an alternating voltage, and a scanning device including the MEMS actuator.

  In recent years, there has been a demand for downsizing various apparatuses such as a laser beam scanning apparatus used in a printer, a copier, a projector, and the like using a laser beam. In response to the demand for downsizing of such devices, a micromirror scanner manufactured using MEMS (Micro Electro Mechanical Systems) technology that realizes miniaturization of various mechanical elements by applying technology in semiconductor manufacturing processes such as silicon Various MEMS actuators have been proposed (for example, see Patent Document 1).

A micromirror scanner used in a printer or the like is supported on a substrate or the like so as to be swingable via a hinge, reflects a laser beam, scans the laser beam, and swings and drives the micromirror A driving electrode to which the AC voltage is applied is formed using the MEMS technology. In such a micromirror scanner, a resonance phenomenon is caused by applying an AC voltage having a frequency such that the natural frequency (resonance frequency) of the micromirror and the oscillation frequency of the micromirror substantially coincide with each other. Thus, the micromirror can be swung with a relatively large swing angle (amplitude) even with a small driving force. In this way, the laser beam can be scanned by the micromirror by swinging the micromirror.
JP 2002-31376 A

  In recent years, high-speed printing has been demanded, and in order to realize high-speed printing, it is necessary to scan with laser light at high speed. In a printer or the like using a micromirror scanner, scanning of laser light is performed by swinging the micromirror. Therefore, in order to perform scanning of laser light at high speed, the micromirror must be swung at high speed. . As described above, since the resonance phenomenon is used to swing the micromirror, it is necessary to increase the resonance frequency of the micromirror in order to swing the micromirror at a high speed. Increasing the resonance frequency of the micromirror can be realized by supporting the micromirror in a swingable manner on a hinge having a high spring constant. However, if the micromirror is supported and swung by a hinge having a high spring constant, a large stress is generated in the hinge and the hinge may break, and therefore the micromirror cannot be swung with a large amplitude.

  Also, in order to make the optical unit compact, it is required to shorten the distance between the micromirror and the photosensitive drum provided in the printer or the like. When the distance between the micromirror and the photosensitive drum is shortened, the scanning range of the laser beam is narrowed. Therefore, in order to ensure a constant scanning range, it is necessary to swing the micromirror with a large amplitude. However, in order to swing the micromirror with a large amplitude, a large stress must be generated in the hinge, which may cause the hinge to break. When the hinge width is narrowed, the stress generated in the hinge can be reduced, but the torsional rigidity of the hinge is lowered, the resonance frequency of the micromirror supported by the hinge is lowered, and the micromirror swinging speed is increased. I can't speak.

  The present invention has been made to solve the problems of the prior art, and includes a MEMS actuator capable of swinging a swing member such as a micromirror at a high speed and / or a large amplitude, and the MEMS actuator. It is an object of the present invention to provide a scanning device.

  In order to solve the above-mentioned problems, the present invention provides a substrate and a plurality of swing members supported so as to be swingable about a swing axis with respect to the substrate, respectively. In order to drive each of the swinging members using electrostatic force, an AC voltage is applied between the driving electrodes provided on the respective swinging members and the substrate, and between the driving electrodes. An MEMS power supply is provided, and the plurality of oscillating members are arranged in parallel so that the respective oscillating shafts are substantially parallel to each other.

  A MEMS actuator according to the present invention includes a substrate, a plurality of oscillating members supported so as to be able to oscillate around the oscillating axis with respect to the substrate, and each oscillating member oscillatingly driven using electrostatic force. For this purpose, each of the oscillating members includes a driving electrode provided on each of the oscillating members and the substrate, and an AC power source for applying an AC voltage between the driving electrodes. They are juxtaposed so as to be substantially parallel to each other. As described above, the swing members arranged in parallel so that the respective swing shafts are substantially parallel to each other can swing around the swing shaft when an AC voltage is applied between the drive electrodes. It is configured.

  When these plural oscillating members are oscillated with the same phase and the same amplitude, for example, when light is emitted toward the plurality of oscillating members, the light is reflected in the same direction by any of the oscillating members. Therefore, when a plurality of rocking members rocks with the same phase and the same amplitude, the aggregate of the rocking members functions as one rocking member. The smaller the swing member, the smaller the moment of inertia. Therefore, if the small swing member is supported by the hinge, the resonance frequency of the swing member supported by the hinge increases, and the swing member can be swung faster. it can. Also, if the swing member is small, the stress generated in the hinge when swinging the swing member is small, and there is no fear that the hinge will break even if the swing member is greatly swung. Therefore, when the small swing member is supported by the hinge, the swing member can be swung at a high speed and / or with a large amplitude. As described above, the MEMS actuator according to the present invention can swing a plurality of small swinging members with the same phase, and the aggregate of the swinging members can function as one swinging member. By oscillating the moving member at a high speed and / or with a large amplitude, the same effect as when a large oscillating member is swung at a high speed and / or with a large amplitude can be exhibited.

  In addition, when a small swing member is supported on a hinge having low torsional rigidity, a hinge having low torsional rigidity generates less stress when the swinging member swings, and the moment of inertia of the supported swinging member is small. Since it is small, there is very little risk of the hinge breaking, and the swing member can be swung with a larger amplitude.

  As a configuration for oscillating the plurality of oscillating members in the same phase, as described in claim 2 of the claims, the plurality of oscillating members are connected to each other via an elastic body. Can be mentioned.

  A description will be given of the fact that each oscillating member can be oscillated in the same phase by connecting each oscillating member via an elastic body. When a plurality (n) of swing members are connected by an elastic body, the connected swing members swing together and the swing of each swing member is synchronized. When n rocking members are connected by an elastic body and rocked, (n−1) × 2 synchronized rocking modes can be generated.

  For example, as shown in FIGS. 5A and 5B, when two oscillating members (micromirrors A and B in FIG. 5) are connected, two oscillating modes occur, and FIG. As shown in c) to (f), when three swing members (micromirrors A, B, and C) are connected, four swing modes can occur. Such rocking modes include a rocking mode in which the phases of the rocking members are the same and a rocking mode that is not the same. Multiple rocking modes can occur, but each rocking mode has a different natural frequency. Therefore, an alternating voltage with a frequency corresponding to the natural frequency of the rocking mode in which each rocking member rocks in the same phase is driven. When applied between the electrodes, a swing mode in which each swing member swings in the same phase is generated, and each swing member swings in the same phase.

  In addition, as a result of intensive studies, the inventors according to the present invention, as in the MEMS actuator described above, when an oscillating member is oscillated by applying an alternating voltage between driving electrodes to generate an electrostatic force, It has been found that the swing amplitude of the swing member can be adjusted by adjusting the voltage value of the DC voltage applied to the substrate and the swing member that is swingably supported by the substrate.

  Therefore, as described in claim 3 of the claims, an amplitude adjusting electrode provided on each of the swing members and the substrate, respectively, for adjusting the swing amplitude of the swing members, It is preferable to further include a DC power source for applying a DC voltage between the amplitude adjusting electrodes.

  If the swinging amplitudes of the plurality of swinging members are different, light is not reflected in the same direction by the swinging members even if the swinging members are swung in the same phase. The swing amplitude of the swing member varies depending on, for example, the weight and shape of the swing member, the spring constant of the hinge that supports the swing member, and the like. As a method of aligning the swing amplitudes of a plurality of swing members, the swing member and hinge are processed by the laser ablation method or the like, and the weight and shape of the swing member, and the spring constant of the hinge that supports the swing member The method of adjusting is mentioned. However, according to the above preferred configuration, if the voltage value of the DC voltage applied between the amplitude adjusting electrodes is appropriately adjusted for each oscillating member, a plurality of oscillating members can be obtained without performing a laser ablation method or the like. The member can be swung with the same amplitude.

  Further, as a configuration for oscillating each of the plurality of oscillating members with the same amplitude, a DC power source for applying a DC voltage between the respective driving electrodes as described in claim 4, It is also possible to adopt a configuration in which the DC voltage and the AC voltage are applied in a superimposed manner between the driving electrodes.

  The DC voltage applied to the amplitude adjusting electrode according to claim 3 is superimposed on the AC voltage applied to the driving electrode, and the superimposed voltage is applied between the driving electrodes. The same effect as that of the configuration can be obtained. According to such a configuration, it is not necessary to provide an amplitude adjusting electrode, the configuration of the MEMS actuator can be simplified, and the manufacturing cost of the MEMS actuator can be suppressed.

  Further, according to the present invention, as claimed in claim 5, the substrate and the substrate are supported so as to be swingable around a swing shaft, and the swing shafts are substantially parallel to each other. A plurality of oscillating members arranged side by side, and driving electrodes provided at positions facing each other of the oscillating members in order to oscillate and drive the oscillating members using an electrostatic force. And an AC power source for applying an AC voltage between the driving electrodes.

  The MEMS actuator according to the present invention includes a substrate and a plurality of swing members that are supported so as to be swingable around the swing axis with respect to the substrate, and are arranged in parallel so that the swing shafts are substantially parallel to each other. Prepare. In order to oscillate and drive each oscillating member using electrostatic force, driving electrodes are provided at positions facing each other of each oscillating member, and by applying an AC voltage between each driving electrode, An electrostatic force is generated between the driving electrodes. The two oscillating members provided at positions where the driving electrodes are opposed to each other oscillate by being attracted or repelled by an electrostatic force generated between the driving electrodes.

  As described above, when the swing member is swung with the same phase and the same amplitude by the electrostatic force generated between the driving electrodes, the small swing member is similar to the MEMS actuator according to claim 1. The assembly can function as one swing member. Therefore, similarly to the MEMS actuator according to claim 1, the large rocking member can be moved at high speed and / or by swinging the small rocking member at high speed and / or large amplitude. The same effect as when rocking with a large amplitude can be exhibited.

  Furthermore, since the MEMS actuator of this invention can swing two swing members with two drive electrodes, it is not necessary to provide the drive electrodes on the substrate, and the configuration can be simplified accordingly. Manufacturing cost can be reduced.

  As a configuration for swinging the plurality of swinging members at the same phase, as described in claim 6 of the claims, the plurality of swinging members are connected to each other via an elastic body. be able to. The principle of rocking at the same phase by connecting a plurality of rocking members via an elastic body is the same as the configuration according to claim 2.

  Further, in the MEMS actuator according to claims 5 and 6, preferably, as described in claim 7 of the claims, each of the swinging members and the substrate are provided respectively. A configuration further comprising an amplitude adjusting electrode for adjusting the amplitude of oscillation and a DC power source for applying a DC voltage between the amplitude adjusting electrodes is preferable.

  In such a preferable configuration, similarly to the configuration described in claim 3 of the claims, by applying a DC voltage between the amplitude adjusting electrodes, a plurality of processing can be performed without performing a laser ablation method or the like. The swing member can be swung with the same amplitude.

  Further, as a configuration for oscillating each of the plurality of oscillating members with the same amplitude, a DC power source for applying a DC voltage between the driving electrodes as described in claim 8, It is also possible to adopt a configuration in which the DC voltage and the AC voltage are applied in a superimposed manner between the driving electrodes.

  Even if the DC voltage applied to the amplitude adjusting electrode according to claim 7 is superimposed on the AC voltage applied to the driving electrode, and the superimposed voltage is applied between the driving electrodes, The same effects as those described are obtained. According to such a configuration, it is not necessary to provide an amplitude adjusting electrode, the configuration of the MEMS actuator can be simplified, and the manufacturing cost of the MEMS actuator can be suppressed.

  Further, according to a ninth aspect of the present invention, the MEMS actuator according to any one of the first to eighth aspects, wherein each of the swinging members has a mirror surface, as recited in the ninth aspect of the present invention, A light source that emits light toward each mirror surface, a light detection element that outputs a detection signal when light reflected from the mirror surface of the light emitted from the light source enters, and an output from the light detection element Provided is a scanning device including light source control means for controlling the intensity of light emitted from the light source based on the detected signal.

  Each of the MEMS actuators according to claims 1 to 8 includes a plurality of swing members. For this reason, depending on the swing angle of the swing member, part of the reflected light reflected by one swing member may hit another swing member and not reach the photosensitive drum or the like to be scanned. If a part of the reflected light does not reach the scanning target, the intensity of the reflected light on the scanning target is lowered and the latent image cannot be formed accurately. In such a preferable configuration, based on the light detection element that outputs a detection signal when the reflected light of the light emitted toward the mirror surface of the oscillating member enters, and the detection signal output from the light detection element, Light source control means for controlling the intensity of light emitted from the light source. Since the light incident on the light detection element is reflected light reflected by the swing member, the light is incident on the light detection element when the swing angle of the swing member is a constant angle. A detection signal is output when the swing angle is a constant angle. Accordingly, the light source control means increases the intensity of the light emitted from the light source based on the timing at which the detection signal is output, so that the intensity of the light on the scanning target is reduced by the swing angle of the swing member. It is possible to prevent this. Therefore, according to this invention, it can prevent that the intensity | strength of the reflected light on a scanning object falls, and formation of a latent image can be performed exactly.

  In addition, as a configuration of a scanning device that controls the intensity of light emitted from a light source, the MEMS actuator according to any one of claims 1 to 8 and each of the swings according to claim 10 of the claims. A detection electrode provided on each of the moving member and the substrate; a detection power source for applying a voltage to the detection electrode; and a current generated between the detection electrodes based on a current generated between the detection electrodes. A configuration provided with a light control means for controlling the intensity can be employed.

  In such a configuration, since the detection voltage is applied to the detection electrode provided on the substrate and the detection electrode provided on the swinging member, these detection electrodes can be regarded as one capacitor. it can. The distance between the detection electrode provided on the substrate and the detection electrode provided on the swing member varies depending on the swing of the swing member. Therefore, a current corresponding to the swing of the swing member is generated between the detection electrodes. The light control means controls the intensity of light emitted from the light source based on the current. Therefore, the light control means increases the intensity of the light emitted from the light source based on the measured current, thereby preventing the light intensity on the scanning target from being lowered due to the swing angle of the swing member. Therefore, the latent image can be accurately formed.

  According to the present invention, it is possible to exhibit the same effect as when a swing member having a predetermined size is swung at a higher speed and / or with a larger amplitude without breaking the hinge. It is possible to provide a simple MEMS actuator and a scanning device including the MEMS actuator.

(Embodiment 1)
Hereinafter, an embodiment according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of a scanning device including a MEMS actuator according to an embodiment of the present invention. As illustrated in FIG. 1, the scanning device 100 according to the present embodiment includes a MEMS actuator 1 and a light source 2 that emits light L toward a micromirror included in the MEMS actuator 1 as described later. In addition, the scanning device 100 according to the present embodiment combines the collimator lens 3 for converting the light L emitted from the light source 2 into parallel light and the reflected light L ′ of the light L from the micromirror on the photosensitive member P. An fθ lens 4 and a cylindrical lens 5 for imaging are provided. In the scanning device 100 having the above configuration, the reflected light L ′ of the light L emitted from the light source 2 is scanned on the photosensitive member P by swinging the micromirror included in the MEMS actuator 1.

  The MEMS actuator 1 includes a MEMS device 10, an AC power supply 60, and a DC power supply 70.

  2A and 2B are schematic configuration diagrams of the MEMS device 10 according to the present embodiment, in which FIG. 2A shows a plan view, and FIG. 2B shows a cross-sectional view taken along the line CC in FIG. As shown in FIG. 2, the MEMS device 10 according to the present embodiment has a structure in which an upper layer substrate 20 formed of a silicon material and a lower layer substrate 50 formed of an insulating material (for example, a glass material) are vertically joined. Have. The MEMS device 10 according to the present embodiment can be easily manufactured by those skilled in the art by applying known MEMS techniques such as dry etching, anodic bonding, and film formation. A description of a simple manufacturing method is omitted.

  As shown in FIG. 2A, the upper substrate 20 includes a substrate body 20a and swing units 40A and 40B. The substrate main body 20a includes an outer peripheral portion 20b that forms both the left and right sides (Y axis shown in FIG. 2A) of the substrate main body 20a, and a central portion 20c that forms a central portion in the left-right direction of the substrate main body 20a. Yes. The central portion 20c is formed at two positions above and below the central portion in the left-right direction of the substrate body 20a. The region sandwiched between the outer peripheral portions 20b by the central portion 20c is partitioned into two regions on the left and right. A swing unit 40A is formed in the left region, and 40B is formed in the right region. Since the structure of the upper layer substrate 20 is bilaterally symmetric, the details of the left side of the upper layer substrate 20 will be described below, and the description of the details of the right side will be omitted as appropriate. For ease of explanation, a member formed on the left side of the central portion 20c is given a reference symbol “A”, and a member formed on the right side is given a reference symbol “B”.

  The swing unit 40A includes a swing member including the micro mirror A and the suspension beam 23A, adhesive pads 24A and 26A, hinges 25A and 27A, an amplitude adjusting electrode 28A, and a drive electrode 30A.

  The micromirror A is formed in an elliptical shape having a mirror surface A1 that reflects light on one surface, and is provided in the center of the swing unit 40A in the X-axis direction. Suspension beams 23A are formed at both ends of the micro mirror A in the direction of the swing axis (X axis shown in FIG. 2A). A hinge 25A and an adhesive pad 24A are formed at the end of the suspension beam 23A in the swing axis direction (the end opposite to the side connected to the micromirror A). The end of the suspension beam 23A in the swing axis direction is connected to the adhesive pad 24A via a hinge 25A. In addition, an opening is provided in an intermediate portion of the suspension beam 23A, and an adhesive pad 26A and a hinge 27A are formed in the opening. An intermediate portion of the suspension beam 23A is connected to the adhesive pad 26A via a hinge 27A.

  Further, an amplitude adjusting electrode (hereinafter referred to as a first electrode) 28 </ b> A extending to the outside of the MEMS device 10 is formed on a portion (the left side in FIG. 2) of the suspension beam 23 </ b> A outside the MEMS device 10. The first electrode 28A is paired with an amplitude adjusting electrode (hereinafter referred to as a second electrode) 29A extending inward from the outer peripheral portion 20b of the substrate body 20a, and is alternately arranged with the second electrode 29A in the X-axis direction. Has been. On the other hand, a driving electrode (hereinafter, referred to as a third electrode) 30A extending inside the MEMS device 10 is formed on a portion inside the MEMS device 10 of the suspension beam 23A (right side in FIG. 2). The third electrode 30A is paired with a driving electrode (hereinafter referred to as a fourth electrode) 31A extending from the central portion 20c of the substrate body 20a toward the suspension beam 23A, and alternately with the fourth electrode 31A in the X-axis direction. Has been placed.

  The swing unit 40B having the same configuration as the swing unit 40A formed as described above is formed in the right region, and the swing units 40A and 40B are oriented so that the swing members are parallel to the swing axis direction. Are installed side by side. Light L is emitted from the light source 2 toward the mirror surfaces A1 and B1 of the two micromirrors A and B provided in the swing unit 40A and the swing unit 40B, and the light L is emitted from the two micromirrors A. And B mirror surfaces A1 and B1.

  The micro mirror A of the swing unit 40A and the micro mirror B of the swing unit 40B are connected to each other via two elastic bodies 22 in a direction orthogonal to the swing axes of the swing units 40A and 40B. These elastic bodies 22 are supported at two locations of the outer edge portions of the micromirrors A and B that face the other micromirrors A and B. In this embodiment, the elastic body 22 is supported by the micromirrors A and B. However, the elastic body 22 is supported by the suspension beams 23A and 23B that swing together with the micromirrors A and B, so that the suspension beam is supported. The micromirrors A and B may be connected via 23A and 23B. In FIG. 2, the elastic body 22 is abstractly illustrated in the shape of a helical spring, but the shape of the elastic body 22 is not particularly limited and is actually easy to produce by dry etching. A meandering hinge shape, such as an S-shape, is suitable. Furthermore, the material of the elastic body 22 used for connecting the micromirrors A and B is not particularly limited, and for example, a polymer material such as PDMS can be used.

  On the other hand, as shown in FIG. 2B, the lower layer substrate 50 is formed in a concave shape at positions corresponding to the micromirrors A and B so that the micromirrors A and B can swing around the swing axis. Yes. In a state in which the upper layer substrate 20 and the lower layer substrate 50 are bonded, a peripheral wall 51 that forms the concave shape is formed at a position corresponding to the back surface of the bonding pads 24A and 24B of the lower layer substrate 50, and the bonding pad 26A, A fixing pad 52 formed in a convex shape from the bottom of the lower layer substrate 50 is formed at a position corresponding to the back surface of 26B and the central portion 20c. The bonding pads 24A and 24B are bonded to the peripheral wall 51, and the bonding pads 26A and 26B and the central portion 20c are bonded to the fixing pad 52.

  1 is connected to the third electrodes 30A and 30B and the fourth electrodes 31A and 31B, between the third electrode 30A and the fourth electrode 31A, and between the third electrode 30B and the fourth electrode. The same AC voltage can be applied between the electrode 31B and the electrode 31B.

  The DC power source 70 shown in FIG. 1 is connected to the first electrodes 28A and 28B and the second electrodes 29A and 29B, between the first electrode 28A and the second electrode 29A, and between the first electrode 28B and the second electrode 29B. A DC voltage having a different voltage value can be applied between the electrode 29B.

  When scanning the photosensitive drum P using the scanning device 100 having the above-described configuration, the AC power supply 60 is used between the third electrode 30A and the fourth electrode 31A and between the third electrode 30B and the fourth electrode 31B. The same AC voltage is applied to the first electrode 28A and the second electrode 29A, and the DC voltage is applied between the first electrode 28B and the second electrode 29B.

  When an AC voltage is applied between the third electrode 30A and the fourth electrode 31A and between the third electrode 30B and the fourth electrode 31B, an electrostatic force is generated between these electrodes. When the oscillating units 40A and 40B are manufactured in perfect shapes, the torque for generating the oscillating motion is 0 in the initial state and theoretically does not start, but it is actually inevitable. The swing units 40A and 40B start to swing when the electrostatic force is generated due to a process shape error or the like. With this electrostatic force, the micromirror A swings around the swing axis while resisting the elastic force of the hinges 25A and 27A, with the adhesive pads 24A and 26A being fixed ends, and the micromirror B is bonded to the adhesive pads 24B and 26B. As a fixed end, it swings around the swing axis while resisting the elastic force of the hinges 25B and 27B. Thus, when an alternating voltage is applied between the third electrode 30A and the fourth electrode 31A and between the third electrode 30B and the fourth electrode 31B, the micromirrors A and B are Swings at a frequency or 1/2 frequency. In the present embodiment, the resonance phenomenon is used to swing the micromirrors A and B, and the microphone mirrors A and B are swung with a large amplitude with a small driving force. The frequency of the alternating voltage applied between 31A and between the third electrode 30B and the fourth electrode 31B is close to the resonance frequency of the micromirrors A and B or approximately twice the resonance frequency, The micromirrors A and B oscillate at a frequency close to the resonance frequency.

  Between the first electrode 28A and the second electrode 29A and between the first electrode 28B and the second electrode 29B, the reflected light L ′ reflected by the mirror surfaces A1 and B1 of the micromirrors A and B is A DC voltage having a magnitude required for swinging the micromirrors A and B with a certain amplitude is applied so as to scan the photosensitive drum P only within a predetermined range. The amplitudes of the micromirrors A and B vary depending on the weight and shape of the micromirrors used for the micromirrors A and B, the spring constants of the hinges 25A, 25B, 27A, and 27B. However, it is used for the micromirrors A and B by adjusting the magnitude of the DC voltage applied between the first electrode 28A and the second electrode 29A and between the first electrode 28B and the second electrode 29B. The micromirrors A and B can be oscillated with a constant amplitude regardless of the weight and shape of the micromirrors and the spring constants of the hinges 25A, 25B, 27A, and 27B.

  More specifically, for example, if the magnitude of the DC voltage applied is varied between the first electrode 28A and the second electrode 29A, the resonance frequency characteristic curve of the micromirror A (the oscillation of the micromirror A) The curve showing the relationship between the frequency and the maximum amplitude) changes. FIG. 3 is an explanatory diagram showing the change. As shown in FIG. 3, when the DC voltage applied between the first electrode 28A and the second electrode 29A is increased from V0 to V1, the resonance frequency characteristic curve shifts in the direction of higher frequency, and conversely, the DC voltage is changed. When the voltage is lowered from V1 to V0, the resonance frequency characteristic curve shifts in the direction of lower frequency. This resonance frequency characteristic curve differs depending on the weight and shape of the micromirror used in the micromirror A, the spring constants of the hinges 25A and 27A, and the like. Therefore, if a DC voltage having a magnitude corresponding to the resonance frequency characteristic curve of the micromirror A is applied between the first electrode 28A and the second electrode 29A, the resonance frequency characteristic curve is shifted, and as a result, the reflected light L ′ is changed. The micromirror A can be swung with an amplitude large enough to scan the photosensitive drum P by a predetermined width. Similarly, with respect to the micromirror B, if a DC voltage having a magnitude corresponding to the resonance frequency characteristic curve of the micromirror B is applied between the first electrode 28B and the second electrode 29B, the reflected light L ′ is predetermined. The micromirror B can be swung with an amplitude large enough to scan on the photosensitive drum P by the width of.

  Further, as described above, the micromirrors A and B are connected by the elastic body 22, and the micromirrors A and B are restricted from swinging by being connected by the elastic body 22. And B swing at the same phase.

  If the micromirrors A and B are not connected by the elastic body 22, the phase of the micromirrors A and B swings with respect to the phase of the AC voltage of the micromirrors used for the micromirrors A and B. Based on the amount of phase delay in motion. The amount of delay in the oscillation phase with respect to the phase of the AC voltage of the micromirror varies from one micromirror to another due to processing errors and the like. FIG. 4 is a graph showing the amount of delay in the phase of oscillation of the micromirrors used in the micromirrors A and B with respect to the phase of the AC voltage. The vertical axis in FIG. 4 represents the phase difference between the phase of the AC voltage and the phase of oscillation of the micromirrors used in the micromirrors A and B, and the horizontal axis represents the frequency of the AC voltage applied by the AC power supply 60. ing. For example, when an AC voltage having a frequency f0 is applied to oscillate the micromirrors A and B, as shown in FIG. 4, the oscillation phase of the micromirror a used in the micromirror A is the phase of the AC voltage. It can be seen that the phase of oscillation of the micromirror b used in the micromirror B is delayed by θ2 (| θ1 | <| θ2 |) with respect to the phase of the AC voltage. As described above, since the amount of delay of the oscillation phase with respect to the phase of the AC voltage of the micromirror differs for each micromirror, when the micromirrors A and B are not connected by the elastic body 22, the micromirrors A and B Do not swing at the same phase.

  On the other hand, when the micromirrors A and B are connected by the elastic body 22, the micromirrors A and B swing with the same phase as described below.

  More specifically, when the micromirrors A and B are connected by an elastic body, the micromirrors A and B swing together and the swings of the micromirrors A and B are synchronized. Here, when the two micromirrors A and B are rocked by being connected by the elastic body 22, as shown in FIG. 5A, the rocking mode in which the micromirrors A and B rock in the same phase, As shown in FIG. 5B, a swing mode in which the micromirrors A and B swing at a phase different by 180 ° may occur. Since the natural frequency of each oscillation mode is different, the micromirrors A and B are in the same phase between the third electrode 30A and the fourth electrode 31A and between the third electrode 30B and the fourth electrode 31B. When an AC voltage having a frequency corresponding to the natural frequency of the swing mode that swings (the swing mode shown in FIG. 5A) is applied, the micromirrors A and B swing at the same phase.

  As described above, the MEMS actuator 1 according to the present embodiment can swing the two micromirrors A and B with the same amplitude and phase. Therefore, since the light L emitted from the light source 2 is always reflected in the same direction regardless of which micromirror A and B is reflected, the two micromirrors A and B function as one large micromirror. To do.

  The smaller the micromirrors A and B, the smaller the moment of inertia. Therefore, when the small micromirrors are supported by the hinges 25A, 25B, 27A, 27B, the resonances of the micromirrors A and B supported by the hinges 25A, 25B, 27A, 27B. The frequency is increased, and the micromirrors A and B can be swung at a higher speed. Therefore, since the MEMS actuator 1 according to the present embodiment uses the small micromirrors A and B that function as one large micromirror, each of the two MEMS actuators 1 is compared with the case where one large micromirror is used. The micromirrors A and B can be swung at high speed. The MEMS actuator 1 according to this embodiment can thus function two micromirrors A and B capable of high-speed oscillation as one large micromirror, so that one large micromirror can be swung at high speed. The same effect as when moved can be exhibited. Therefore, if the scanning device 100 including the MEMS actuator 1 according to this embodiment is used, the photosensitive drum P can be scanned at high speed, and high-speed printing can be realized.

  In addition, if the micromirrors supported by the hinges 25A, 25B, 27A, and 27B are small, the resonance frequency of the micromirror is high. Therefore, even if the small micromirror is supported by a hinge having a small spring constant, the micromirror The resonance frequency of is relatively high. A hinge having a low spring constant has a small stress generated when the micromirror is swung, and therefore, it is difficult to break even if the micromirror has a large amplitude. Therefore, when a small micromirror is supported by a hinge having a low spring constant, the micromirror can be swung with a large amplitude at a relatively high resonance frequency. Therefore, if the hinges 25A, 25B, 27A, 27B of the MEMS actuator 1 of the present embodiment having a low spring constant are used, the laser beam can be scanned in a large range at a relatively high speed.

  Since the distance from the light source 2 to the photosensitive drum P via the micromirror A is different from the distance from the light source 2 to the photosensitive drum P via the micromirror B, the reflected light reflected by the micromirror A is different. There is a possibility that L ′ and the reflected light L ′ reflected by the micromirror B interfere with each other on the photosensitive drum P and an accurate latent image cannot be formed. In order to avoid this interference, the light source 2 preferably emits incoherent light that is difficult to interfere. As the light source 2 that emits incoherent light, for example, a xenon lamp or a halogen lamp can be used. In addition, since interference fringes generated when using a coherent light source are regular, when using coherent light, the intensity of light emitted from the light source is changed and corrected. An accurate latent image can be formed.

  In the MEMS actuator 1 according to this embodiment, as shown in FIG. 2, two micromirrors A and B are arranged in parallel, but three or more micromirrors may be arranged in parallel. Further, when three or more are arranged in parallel, the influence of the light interference can be reduced by arranging them at different intervals instead of at equal intervals.

  In the present embodiment, the amplitude adjustment electrode (first electrode) 28A and the amplitude adjustment electrode (second electrode) 29A and the amplitude adjustment electrode (first electrode) 28B and the amplitude adjustment electrode ( The amplitude of the micromirrors A and B is adjusted by applying a DC voltage between the second electrode 29B and the method of adjusting the amplitude of the micromirrors A and B is limited to this method. Not. As another method, for example, an AC power source 60 and a DC power source 70 are connected to driving electrodes (third electrodes) 30A and 30B and driving electrodes (fourth electrodes) 31A and 31B, and the third electrode 30A. The DC voltage applied by the DC power supply 70 and the AC voltage applied by the AC power supply 60 are superimposed between the first electrode 31A and the fourth electrode 31A and between the third electrode 30B and the fourth electrode 31B. The method of applying by is mentioned. As described above, when the DC voltage and the AC voltage are superimposed and applied, the same effect as that obtained when the DC voltage and the AC voltage are applied to different electrodes (the driving electrode and the amplitude adjusting electrode) can be obtained. In the configuration in which the DC voltage and the AC voltage are superimposed, the amplitude adjusting electrode is applied between the third electrode 30A and the fourth electrode 31A and between the third electrode 30B and the fourth electrode 31B. Since 28A, 28B, 29A, and 29B are unnecessary, the structure of the MEMS actuator 1 can be simplified, and the manufacturing cost of the MEMS actuator can be suppressed. On the contrary, if an AC voltage is superimposed on the amplitude adjusting electrodes 28A, 28B, 29A, and 29B and the function of the driving electrode is given, the driving force is increased, so that the voltage can be reduced without changing the structure.

(Embodiment 2)
In addition to the configuration of the scanning device 100 according to the first embodiment, the scanning device 100 according to the present embodiment includes a light detection element 6 and a light source control unit 7 as shown in FIG. The light detection element 6 is configured to output a detection signal when the reflected light L ′ of the light L emitted toward the mirror surfaces A1 and B1 of the micromirrors A and B is incident. The light detection element 6 is disposed outside the effective scanning range S1 so as not to block the reflected light L ′ and prevent the latent image from being formed on the photosensitive drum P. This effective scanning range S1 is a scanning range scanned to form a latent image.

  Since the light incident on the light detection element 6 is reflected light L ′ reflected by the micromirrors A and B, the light detection element 6 receives light when the oscillation angle of the micromirrors A and B is a certain angle. A detection signal is output when the reflected light L ′ is incident and the swing angle of the micromirrors A and B is a certain angle.

  The light source control means 7 controls the intensity of light emitted from the light source 2 based on the detection signal output from the light detection element 6. Specific control of the intensity of light emitted from the light source 2 is performed by controlling the current value supplied to the light source 2, for example. As shown by the dotted line in FIG. 7, the light source control means 7 stores in advance the relationship between the elapsed time after the detection signal is output and the intensity of the light emitted from the light source 2. 7 controls the intensity of light emitted from the light source 2 based on this relationship. This relationship is determined in order to make the intensity of the reflected light L 'on the photosensitive drum P constant regardless of the swing angles of the micromirrors A and B.

  More specifically, as shown in FIG. 6, when the swing angle R of the micromirrors A and B is large, a part of the reflected light L ′ reflected by the micromirror A or B is converted to another micromirror A. Alternatively, when it hits B and does not reach the photosensitive drum P, and the swing angle R of the micromirrors A and B increases as shown by the solid line in FIG. 7, the intensity of the reflected light L ′ decreases on the photosensitive drum P. Therefore, by controlling the intensity of the light emitted from the light source 2 based on the swing angle R, it is possible to prevent the intensity of the reflected light L ′ on the photosensitive drum P from being lowered. The swing angle R of the micromirrors A and B varies with time due to the swing of the micromirrors A and B, and has a one-to-one relationship with the elapsed time after the detection signal is output. Therefore, if the intensity of the light L emitted from the light source 2 is controlled with respect to the elapsed time after the detection signal is output, it is possible to prevent the intensity of the reflected light L ′ on the photosensitive drum P from being lowered. The relationship indicated by the dotted line in FIG. 7 is obtained from this viewpoint by experiments or the like.

  As described above, the MEMS actuator 1 according to the present embodiment can prevent a decrease in illuminance on the photosensitive drum P by controlling the intensity of light emitted from the light source 2 by the light source control unit 7. Therefore, the latent image can be accurately formed.

  Control of the intensity of light emitted from the light source 20 as described above is performed by using the detection electrode provided on the substrate body 20a and the detection provided on the swing member instead of using the above-described method using the light detection element 6. This can be performed by applying a DC voltage (detection voltage) to the electrode. As the detection electrode provided on the substrate body 20a, for example, an electrode provided on the substrate body 20a is used separately from the fourth electrodes 31A and 31B, and the detection electrode provided on the swing member is provided on the substrate body 20a. Separately from the third electrodes 30A and 30B, electrodes provided on the swing member can be used so as to face the detection electrodes provided.

  The two detection electrodes face each other, and these detection electrode pairs can be regarded as one capacitor. The distance between the electrodes of the capacitor composed of two electrodes varies depending on the oscillation of the micromirrors A and B. Then, when this electrode pair is regarded as a capacitor, the capacitance of the capacitor composed of the electrode pair varies with the swing angle R. When a detection voltage is applied to the capacitor, a current corresponding to a change in the capacitance of the capacitor is generated.

  In this case, the light control means 7 controls the intensity of the light emitted from the light source 2 based on the current generated according to the capacitance of the capacitor, so that the swing angle R of the micromirrors A and B It is possible to prevent the light intensity on the photosensitive drum P from being lowered.

(Embodiment 3)
The scanning apparatus 100 of the third embodiment has the same configuration as that of the scanning apparatus 100 of the first embodiment except for the configuration of the MEMS device 10. Hereinafter, the MEMS device 1 of the scanning apparatus 100 according to the third embodiment will be described.

  8A and 8B are schematic configuration diagrams of the MEMS device 10 according to the present embodiment, in which FIG. 8A shows a plan view, and FIG. 8B shows a DD cross-sectional view of FIG. 8A. As shown in FIG. 8, the MEMS device 10 according to the present embodiment is similar to the MEMS device 10 of the first embodiment in that the upper layer substrate 20 formed of a silicon material and the lower layer formed of an insulating material (for example, a glass material). It has a structure in which the substrate 50 is stacked vertically.

  As shown in FIG. 8A, the upper layer substrate 20 is arranged in parallel on the left and right sides of the substrate body 20a constituting the left and right sides (in the Y axis shown in FIG. 8A) and the inner region of the substrate body 20a. Two swinging units 40A and 40B. Since the structures of the left and right swing units 40A and 40B are the same, the structure of the left swing unit 40A will be described below, and the description of the structure of the right swing unit 40B will be omitted as appropriate. For ease of explanation, the reference symbol “A” is attached to the member formed on the left swing unit 40A, and the reference symbol “B” is attached to the member formed on the right swing unit 40B. And

  The swing unit 40A includes a swing member including the micro mirror A and the suspension beam 23A, an adhesive pad 24A, a first electrode 28A, and a drive electrode 32A.

  The micromirror A is formed in an elliptical shape having a mirror surface A1 that reflects light on one surface, and is provided in the center of the swing unit 40A in the X-axis direction. Suspension beams 23A are formed at both ends of the micromirror A in the direction of the swing axis (X axis shown in FIG. 8A). The suspension beam 23A includes three elongated members extending in the X-axis direction shown in FIG. 8A from the micromirror A side. One of the three elongated members functions as a hinge 25A. An adhesive pad 24A is formed at the end of the central elongated member functioning as the hinge 25A in the swing axis direction (the end opposite to the side connected to the micromirror A). Of the three elongated members, the elongated member on the inner side of the MEMS device 10 (the side facing the swinging unit 40B) has a driving electrode (hereinafter referred to as a fifth electrode) extending inside the MEMS device 10. ) 32A is provided. The fifth electrodes 32A are alternately arranged in the X-axis direction with the fifth electrodes 32A formed in the drive unit 40B. Further, among the three elongated members, the elongated member outside the MEMS device 10 is provided with a first electrode 28 </ b> A extending outside the MEMS device 10. The first electrodes 28A are alternately arranged in the X-axis direction with the second electrodes 29A provided on the substrate body 20a. Further, the two micromirrors A and B are connected by two elastic bodies 22 as in the first embodiment.

  A swing unit 40B having the same configuration as the swing unit 40A formed as described above is formed in the right region. The oscillating unit 40A and the oscillating unit 40B are arranged side by side so that their oscillating members are parallel to the oscillating shaft.

  On the other hand, as shown in FIG. 8B, the lower layer substrate 50 is formed in a concave shape at positions corresponding to the micromirrors A and B so that the micromirrors A and B can swing around the swing axis. Yes. In the state where the upper layer substrate 20 and the lower layer substrate 50 are joined, a peripheral wall 51 forming the concave shape is formed at a position corresponding to the back surface of the adhesive pad 24A of the lower layer substrate 50. The adhesive pad 24A is a peripheral wall 51. It is glued to.

  The AC power supply 60 constituting the MEMS actuator 1 according to the present embodiment is connected to fifth electrodes 32A and 32B (hereinafter referred to as a pair of fifth electrodes) integrally formed with the micromirrors A and B, and An AC voltage can be applied between the fifth electrodes. Further, the DC power source 70 constituting the MEMS actuator 1 according to the present embodiment is connected to the first electrodes 28A and 28B and the second electrodes 29A and 29B, similarly to the MEMS actuator 1 of the first embodiment. DC voltages having different voltage values can be applied between the first electrode 28A and the second electrode 29A and between the first electrode 28B and the second electrode 29B.

  When the photosensitive drum P is scanned using the scanning device 100 having the above configuration, an AC voltage is applied to the pair of fifth electrodes by the AC power source 60, and the first power 28A and the second electrode 29A are applied by the DC power source 70. A DC voltage is applied between the first electrode 28B and the second electrode 29B. When an AC voltage is applied between the pair of fifth electrodes, an electrostatic force is generated between the pair of fifth electrodes. Due to this electrostatic force, the fifth electrodes 32A and 32B attract each other or repel each other, so that the micromirror A has a bonding pad 24A as a fixed end and a swing shaft while resisting the elastic force of the hinge 25A. The micro mirror B swings around the swing axis while resisting the elastic force of the hinge 25B with the adhesive pad 24B as a fixed end.

  As in the first embodiment, the DC voltage applied by the DC power supply 70 is such that the reflected light L ′ reflected by the mirror surfaces A1 and B1 of the micromirrors A and B scans the photosensitive drum P only within a predetermined range. In addition, the size is required to swing the micromirrors A and B with a certain amplitude. Accordingly, the micromirrors A and B swing with a constant amplitude. Further, since the micromirrors A and B are connected by the elastic body 22, they swing at the same phase as in the first embodiment.

  As described above, the MEMS actuator 1 according to the present embodiment can swing the micromirrors A and B with the same amplitude and phase as the MEMS actuator of the first embodiment. Therefore, since the light L emitted from the light source 2 is always reflected in the same direction regardless of which micromirror A and B is reflected, the two micromirrors A and B function as one large micromirror. And, it has the same effect as the MEMS actuator of the first embodiment.

  Further, since the actuator 1 of the MEMS according to the present embodiment swings due to an electrostatic force generated between the drive electrodes (fifth electrodes 32A and 32B) provided between the two micromirrors A and B, the micromirror A and The number of driving electrodes for swinging B is only two, and further, since there is no need to provide the driving electrode on the substrate body 20a, the configuration can be simplified and the manufacturing cost can be reduced.

  As shown in FIG. 8, the MEMS actuator 1 according to the present embodiment includes two micromirrors, but may include three or more.

  Further, since the MEMS actuator 1 according to the present embodiment includes two micromirrors, as shown in FIG. 6, a part of the reflected light L ′ reflected by the micromirror A or B is changed to other micromirrors. When hitting the mirror A or B, it does not reach the photosensitive drum P, and there is a problem that the intensity of the reflected light L ′ decreases on the photosensitive drum P. In order to solve this problem, the scanning device 100 according to the present embodiment includes the light detection element 6 and the light source control unit 7 described in the second embodiment, or the capacitance of the pair of fifth drive electrodes. Based on this, the intensity of the light emitted from the light source 2 may be controlled.

FIG. 1 is a schematic configuration diagram of a scanning device according to an embodiment of the present invention. 2 is a schematic configuration diagram of a MEMS device according to an embodiment of the present invention, FIG. 2 (a) is a plan view, and FIG. 2 (b) is a cross-sectional view taken along the line CC in FIG. 2 (a). Indicates. FIG. 3 is a graph for explaining that the resonance frequency characteristic curve shifts depending on the voltage value of the DC voltage. FIG. 4 is a graph showing the phase delay of the micromirror oscillation relative to the AC voltage phase. FIG. 5 is a diagram showing a swing mode of the micromirror. FIG. 6 is a diagram for explaining that part of the reflected light reflected by the micromirror is blocked by another micromirror. FIG. 7 is a graph showing the relationship between the swing angle of the micromirror and the intensity of light emitted from the light source, and the relationship between the swing angle of the micromirror and the intensity of reflected light. FIG. 8 is a schematic configuration diagram of a MEMS device according to another embodiment of the present invention. FIG. 8A is a plan view, and FIG. 8B is a cross-sectional view taken along the line DD in FIG. Indicates.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 MEMS actuator 10 MEMS device 100 Scanning device 2 Light source 28A, 28B, 29A, 29B Amplitude adjustment electrode 30A, 30B, 31A, 31B, 32A, 32B Drive electrode 40A, B Oscillation unit 6 Photodetection element 60 AC power supply 7 Light source control means 70 DC power supply A, B Micromirror L Light L ′ Reflected light

Claims (10)

A substrate,
A plurality of swinging members supported so as to be swingable about a swinging axis with respect to the substrate,
In order to drive each of the swinging members using electrostatic force, driving electrodes provided on each of the swinging members and the substrate,
An AC power source for applying an AC voltage between the drive electrodes,
The MEMS actuator according to claim 1, wherein the plurality of swing members are arranged in parallel so that swing axes thereof are substantially parallel to each other.   The MEMS actuator according to claim 1, wherein the plurality of swing members are connected to each other via an elastic body. An amplitude adjusting electrode provided on each of the swing members and the substrate, for adjusting the swing amplitude of the swing members;
The MEMS actuator according to claim 1, further comprising a DC power supply that applies a DC voltage between the amplitude adjusting electrodes. A DC power supply for applying a DC voltage between the drive electrodes;
4. The MEMS actuator according to claim 1, wherein the DC voltage and the AC voltage are applied in a superimposed manner between the driving electrodes. 5. A substrate,
A plurality of oscillating members that are supported so as to be able to oscillate around the oscillating axis with respect to the substrate, and are arranged in parallel so that the oscillating axes are substantially parallel to each other;
Driving electrodes provided at positions facing each other of the swing members in order to drive the swing members using an electrostatic force;
A MEMS actuator comprising: an AC power source that applies an AC voltage between the driving electrodes.   The MEMS actuator according to claim 5, wherein the plurality of swing members are connected to each other via an elastic body. An amplitude adjusting electrode provided on each of the swing members and the substrate, for adjusting the swing amplitude of the swing members;
The MEMS actuator according to claim 5, further comprising a DC power source that applies a DC voltage between the amplitude adjusting electrodes. A DC power supply for applying a DC voltage between the drive electrodes;
The MEMS actuator according to any one of claims 5 to 7, wherein the DC voltage and the AC voltage are applied in a superimposed manner between the driving electrodes. The MEMS actuator according to any one of claims 1 to 8, wherein each of the swinging members has a mirror surface.
A light source that emits light toward each of the mirror surfaces;
A light detection element that outputs a detection signal when light reflected from the mirror surface of the light emitted from the light source enters;
A scanning apparatus comprising: a light source control unit that controls intensity of light emitted from a light source based on a detection signal output from the light detection element. A MEMS actuator according to any one of claims 1 to 8,
Detection electrodes provided on each of the swing members and the substrate,
A detection power source for applying a voltage to the detection electrode;
And a light control means for controlling the intensity of light emitted from the light source based on a current generated between the detection electrodes.

Images