JP5223508B2 - Actuator and image forming apparatus - Google Patents

Description

  The present invention relates to an actuator used in an optical scanner or the like that generates a scanning light beam, and more particularly to an improvement in an actuator portion of a movable mirror that reflects a light beam to form scanning light.

  Optical scanners that form scanning light are used in laser printers, barcode readers, projectors, and the like. This optical scanner includes a reflection mirror that reflects a light beam to form a scanning beam. The reflecting mirror uses a rotating polygon mirror that rotates at high speed, or a galvanometer mirror that rotates the reflecting mirror forward and backward within a range of a swing angle like a rotating pendulum (hereinafter referred to as “oscillating rotation”). There is a type. It has been studied to form this galvanomirror type actuator with a micro structure device (MEMS). A very small optical scanner can be realized by MEMS.

  The MEMS mirror device includes a torsion bar (twisting) that supports the reflecting mirror, a drive mechanism that swings and rotates the reflecting mirror by magnetic force or electrostatic force, and the like. If the mirror device is operated at a deflection angle smaller than the breaking stress of the torsion bar, it operates without breaking.

  However, there is a possibility that the torsion bar that gives the rotational force to return the shaken mirror to the original may be damaged due to an excessive impact applied from the outside for some reason, or due to a defect at the time of manufacturing the mirror device. At this time, in the system that controls the mirror device, it detects that the mirror is not performing the specified operation, but to determine whether the cause is due to the mirror device breakage or other failure. take time.

For example, Patent Document 1 discloses a technique related to an optical switch that can easily detect breakage of a flexure part in a manufacturing stage where the movable electrode plate is not movable.
JP 2004-240249 A

  However, even if the technique described in Patent Document 1 is applied to a product, conductor wires 23a and 24a are formed on the flexure portion (spring portion), and damage is detected based on the presence or absence of conduction of these wires. A separate wiring must be formed on the flexure portion, increasing the number of process steps.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an actuator having a structure that can easily detect a breakage of a mirror device and a breakage detection structure that does not require a complicated manufacturing process to obtain the structure. To do.

  The actuator according to the present invention includes a movable plate on which a coil is formed, a pair of torsion bars that support the movable plate on a support portion in a swingable manner, a magnetic field generating means for applying a magnetic field to the coil, and the pair of torsion First and second lead wirings formed on the bar and connected to both ends of the coil, respectively, and an inspection circuit connected between the first and second lead wirings.

  According to such a configuration, the torsion bar can be inspected for breakage by the above-described inspection circuit using the first and second lead wires formed for drawing out the coil.

  More preferably, the first and second lead wires are thinner than the coil. For example, the thickness of the first and second lead wirings is in the range of 1/100 to 1/50 of the thickness of the coil. By forming the lead wiring thinly in this way, the lead wiring can be broken corresponding to the breakage of the torsion bar. Further, the influence of the lead wiring on the spring characteristics of the torsion bar can be reduced.

  More preferably, the width of the first and second lead wires is larger than the width of the coil. Thus, by forming the width of the lead wiring in this way, the resistance of the wiring portion can be reduced, and the characteristics during driving (for example, when an alternating current is passed through the coil) can be improved.

  For example, a control circuit including an AC power supply is connected between the first and second lead wires, and the inspection circuit is incorporated in the control circuit. In this way, by using the first and second lead wires for flowing an alternating current through the coil, it is possible to easily inspect the torsion bar for breakage with a simple structure. In addition, if an inspection circuit is incorporated in a control circuit having a drive circuit necessary for driving, such as passing an alternating current through the coil, the inspection circuit can be easily incorporated without significant design changes or structural changes. it can.

  An image forming apparatus according to the present invention includes the actuator. According to this structure, it is possible to easily determine the breakage of the torsion bar in the image forming apparatus.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same or related code | symbol is attached | subjected to what has the same function, and the repeated description is abbreviate | omitted.

<Embodiment 1>
1 and 2 are diagrams showing the structure of the actuator according to the present embodiment. 1A is a perspective view, and FIG. 1B is a cross-sectional view in a direction orthogonal to the torsion bar. 2A is a plan view, and FIG. 2B is a cross-sectional view taken along line AA in FIG. 2A.

  As shown in FIG. 1, the actuator according to the present embodiment includes a base substrate 10 in which a recessed space is formed, a movable mirror substrate in which a movable plate (mass part) 21 and a mirror (reflecting part, movable mirror) 25 are formed. 20.

  The base substrate 10 is made of, for example, a glass substrate or a silicon substrate, and forms a recessed space in which the movable mirror 22 vibrates by etching or forming spacer portions at both ends. A pair of permanent magnets 13 are arranged on both the left and right sides of the base substrate 10 to form a static magnetic field.

  The movable mirror substrate 20 is formed of a silicon single crystal substrate (thin plate) using a MEMS microfabrication technique. For example, the movable mirror substrate 20 is energized by a coil 23, a mirror 25 formed on the movable plate 21, The movable plate 21 includes a pair of torsion bars (torsion springs) 27a and 27b provided at both ends, and support frame fixing portions 29a and 29b that support the movable plate 21 via the torsion bars.

  When the actuator having such a configuration supplies (turns on) a current from the alternating current source 41 in the control circuit 40 to the coil 23, it acts by an electromagnetic force action (Fleming's left-hand rule) with a static magnetic field formed by the permanent magnet 13. A biasing force is generated in the coil 23, and the movable plate 21 rotates at a certain deflection angle corresponding to the current value with the torsion bars 27a and 27b as rotation axes (see FIG. 1B). When the current supply is stopped (turned off), the movable plate 21 returns to the original state by the spring force of the torsion bars 27a and 27b. When this on / off operation is performed at a high speed, the movable plate 21 is most likely to shake at a certain switching frequency (driving frequency) (resonant state). The actuator is used in a resonance state where this vibration is stable. When the mirror 22 oscillating with the movable electrode plate is irradiated with a light beam such as a laser beam in this way, the reflected light becomes a scanning light beam.

  Furthermore, by using an alternating current instead of the on / off operation of the current, the direction of force according to Fleming's left-hand rule is alternately changed, and a deflection angle in both directions can be obtained. Thereby, the scanning area can be further increased, which is preferable.

  Here, in the present embodiment, as shown in FIG. 2, lead wires 30a and 30b extending from both ends of the coil 23 onto the torsion bars 27a and 27b are formed. An inspection circuit (detection circuit) 43 is connected between the lead wires 30a and 30b (see FIG. 1A), and these wires (30a and 30b) are terminals for detecting breakage of the torsion bars 27a and 27b. It becomes.

  The lead wires 30a and 30b and the coil 23 are made of a conductive material, and for example, metal materials such as Ag (silver), Au (gold), Al (aluminum), and Cu (copper) can be used.

  The thickness of the lead-out wirings 30a and 30b is smaller than the thickness of the coil 23, and is, for example, in the range of 1/100 to 1/50 of the thickness of the coil 23. Further, when the silicon single crystal substrate constituting the movable mirror substrate 20 is about 50 μm, the thickness of the lead-out wirings 30a and 30b is, for example, 1 μm or less (1 μm to the limit of film formation).

  Thus, by forming the lead wires 30a and 30b thin, the lead wires 30a and 30b can be broken corresponding to the breakage of the torsion bars 27a and 27b. Further, the influence of the lead wires 30a and 30b on the spring characteristics of the torsion bars 27a and 27b can be reduced.

  The above-described inspection circuit 43 performs measurement by flowing a weak current for detecting breakage between the lead wires 30a and 30b at all times or in the detection mode. If breakage occurs in any of the torsion bars 27a and 27b, the lead-out wirings 30a and 30b on the torsion bars 27a and 27b are formed of a thin film, and therefore break together with the torsion bar. At this time, the inspection circuit 43 cannot measure a predetermined weak current, and can determine whether the torsion bars 27a and 27b are broken (broken). FIG. 3 shows how the torsion bar of the actuator of the present embodiment is broken.

  Based on the above determination, it is possible to perform abnormality occurrence handling processing such as stopping the generation of light beams. In addition, as an inspection method in the inspection circuit 43, the increase / decrease of the resistance value in addition to the current value may be measured and judged.

  The inspection circuit 43 may be incorporated in the control circuit 40 that controls the driving of the actuator (see FIG. 1A). The control circuit 40 includes a drive circuit configured using semiconductor elements such as MISFETs and wiring, and the torsion bars 27a and 27b can be easily broken (damaged) by adding a few circuits for inspection circuits. ) Can be determined. In this manner, the inspection circuit can be easily incorporated without making a significant design change or structural change.

  Next, the manufacturing process of the actuator according to the present embodiment will be described and the configuration will be clarified.

  FIG. 4 is a process cross-sectional view illustrating the manufacturing process of the actuator of the present embodiment.

  First, as shown in FIG. 4A, silicon oxide films 103 are formed as protective films on both surfaces of the silicon substrate 101. In addition to the silicon oxide film 103, another insulating film such as a silicon nitride film may be used.

  Next, as shown in FIG. 4B, the spiral coil 23 is formed on the silicon substrate 101 (the region to be the movable plate 21), and then the silicon substrate 101 is patterned to obtain the movable plate 21 and the torsion bar. 27a, 27b, etc. are formed. At this time, the support frame fixing portions 29a and 29b are also patterned simultaneously (see FIG. 1A). The patterning of the silicon substrate 101 is not limited to this process, and may be performed after patterning of an insulating film 24 and lead wirings 30a and 30b, which will be described later, for example.

  Next, as shown in FIG. 4C, a silicon oxide film, for example, is formed as an insulating film 24 on the silicon substrate 101 including the coil 23, and one end of this torsion bar (this In the case 27b), patterning is performed so that the insulating film 24 remains above, that is, in a region where the lead wiring 30b intersects with the coil 23 is formed. At this time, a contact hole C is formed on the end of the innermost coil 23.

  Next, as shown in FIG. 4D, for example, a Cu film is formed as a conductive film on the silicon substrate 101 including the insulating film 24 by a sputtering method and patterned, so that the torsion is started from the end of the coil 23. Lead wires 30a and 30b extending on the bars 27a and 27b are formed. At this time, as described above, the lead wires 30a and 30b are formed thinner than the coil 23 and thicker than the coil 23.

  Here, the coil 23 and the lead-out wirings 30a and 30b are formed of the same material, but different materials may be used. For example, since the lead wires 30a and 30b are preferably formed thin as described above, by using a material having a lower resistance than that of the coil 23, an increase in resistance can be reduced even if the lead wires 30a and 30b are formed thin.

  Next, as shown in FIG. 4E, the silicon oxide film 103 in the inner region of the coil 23 is removed and the silicon substrate 101 is exposed to form a mirror (reflecting part) 25. In the present embodiment, the mirror 25 is configured using the silicon substrate surface, but the mirror 25 may be formed by forming a metal film in the region. Further, as shown in FIG. 5, the mirror (reflecting portion) 25 may be formed by removing the silicon oxide film 103 on the surface opposite to the surface on which the coil 23 is formed and exposing the silicon substrate 101. In this case, the mirror area is improved. Further, the mirror 25 may be formed by forming a metal film on the surface. FIG. 5 is a cross-sectional view showing another configuration of the actuator of the present embodiment.

<Embodiment 2>
In the first embodiment, the lead wires 30 a and 30 b are formed in the upper layer of the coil 23, but may be formed in the lower layer of the coil 23.

  FIG. 6 is a diagram showing the structure of the actuator according to the present embodiment. 6A is a plan view, and FIG. 6B is a cross-sectional view taken along the line AA in FIG. 6A. In addition, the same code | symbol is attached | subjected to the location which is common in Embodiment 1 (FIG. 2 etc.), and a different part is demonstrated in detail.

  As shown in FIG. 6, in the actuator of the present embodiment, the coil 23 is disposed on the lead wires 30a and 30b extending on the torsion bars 27a and 27b. Specifically, the coil 23 is arranged on the lead-out wiring 30a via the insulating film 24 so that the outermost periphery of the coil 23 is located on the lead-out wiring 30b. It is configured to be connected to the lead-out wiring 30b.

  In this case, in the manufacturing process, after a metal thin film is deposited on the silicon oxide film 103 on the silicon substrate 101 and patterned to form the lead wires 30a and 30b, the insulating film 24 is formed on the lead wire 30b. Pattern. At this time, the contact hole C is formed simultaneously. Next, the coil 23 is formed so as to pass over the contact hole C and the lead wiring 30a. Thereafter, the silicon oxide film 103 is removed, and the mirror 25 is formed. In addition, since the material of each site | part and a specific manufacturing process are the same as that of Embodiment 1, the detailed description is abbreviate | omitted.

  Also in this embodiment, the same effects as those of the first embodiment are obtained. Furthermore, by forming the lead wirings 30a and 30b, which are thin films, in a lower layer with higher flatness, the film formability of the lead wirings 30a and 30b is improved.

  FIG. 7 is a diagram illustrating an example of an image forming apparatus using an actuator. FIG. 7A illustrates an example of an image projection apparatus. In the image projection apparatus, light emitted from the laser light source 1 is modulated with an image information signal by a modulator 2 and converted into a primary (left-right direction) scanning beam by an actuator 3. The primary scanning beam is further converted into a secondary (left / right / up / down) scanning beam by an actuator 4 and projected onto a screen or a wall 5 to display an image. The actuators 3 and 4 are operated in synchronization with the image information signal by a control unit (not shown). The actuators of the above embodiments can be incorporated as the actuators 3 and 4.

  FIG. 7B shows an example of a laser printer as an image forming apparatus. The light emitted from the laser light source 1 is modulated by a modulator 2 to which an image information signal is supplied. The modulated emitted light is converted into a primary (horizontal direction) scanning beam by the actuator 3 and scanned on the rotating charged photosensitive drum. An image based on an electrostatic latent image is formed on the surface of the photosensitive drum. The electrostatic latent image is developed by attaching a toner in a developing unit (not shown), and the toner image is transferred to the paper 6 and fixed to obtain an image. The actuator of the above embodiment can be incorporated as the actuator 3.

  In the above embodiment, the description has been given of the actuator in which the reflection mirror scans in the one-dimensional direction as an example. However, the present invention can also be applied to an actuator that scans in the two-dimensional direction. That is, it is possible to detect the same breakage by forming a conductive thin film integrally with the reflection mirror as an electrical wiring on each of the torsion bars corresponding to the scanning direction and measuring between any two terminals. .

  In addition, the examples and application examples described through the embodiments of the invention can be used in combination as appropriate according to the application, or can be used with modifications or improvements. The present invention is described in the description of the embodiments described above. It is not limited.

FIG. 2 is a perspective view and a sectional view showing the structure of the actuator according to the first embodiment. FIG. 2 is a plan view and a cross-sectional view showing the structure of the actuator according to the first embodiment. FIG. 3 is a diagram illustrating a state of fracture of the torsion bar of the actuator according to the first embodiment. FIG. 6 is a process cross-sectional view illustrating the manufacturing process of the actuator according to the first embodiment. FIG. 6 is a cross-sectional view showing another configuration of the actuator according to the first embodiment. FIG. 6 is a plan view and a cross-sectional view showing a structure of an actuator according to a second embodiment. It is a figure which shows the example of the image forming apparatus which uses an actuator.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Laser light source, 2 ... Modulator, 3, 4 ... Actuator, 5 ... Screen (wall), 6 ... Paper, 10 ... Base substrate, 13 ... Permanent magnet, 20 ... Movable mirror substrate, 21 ... Movable plate, 23 ... Coil, 24 ... insulating film, 25 ... mirror, 27a, 27b ... torsion bar, 29a, 29b ... support frame fixing part, 30a, 30b ... lead-out wiring, 40 ... control circuit, 41 ... alternating current source, 43 ... inspection circuit, 101 ... Silicon substrate, 103 ... Silicon oxide film, C ... Contact hole

Claims (4)

A movable plate on which a coil is formed;
A pair of torsion bars that swingably support the movable plate on a support;
Magnetic field generating means for applying a magnetic field to the coil;
First and second lead wires formed on the pair of torsion bars and respectively connected to both ends of the coil;
An inspection circuit connected between the first and second lead wires,
The actuator is characterized in that the thicknesses of the first and second lead wires are in the range of 1/100 or more and 1/50 or less of the thickness of the coil. The width of the first and second lead wires, actuator according to claim 1, wherein a greater than a width of the coil. A control circuit connected between the first and second lead wires and including an AC power supply;
The test circuit, actuator according to claim 1 or 2, characterized in that it is incorporated in the control circuit. An image forming apparatus, comprising an actuator according to any one of claims 1 to 3.

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