Patent Application
20130250384
The present application claims priority from Japanese application serial no. 2012-65766, filed on Mar. 22, 2012, the content of which is hereby incorporated by reference into this application.
The present invention relates to a light scanning mirror device for scanning an optical beam, in particular, to a light scanning mirror device which is suitable to be mounted in an image drawing device such as a portable projector, and furthermore, to a control method of the light scanning mirror device and an image drawing device which employs the light scanning mirror device.
As disclosed by Japanese Patent No. 4490019 cited below and in the same manner as in a cathode-ray tube television which draws an image by scanning an electron beam horizontally and vertically in accordance with a picture signal, a light scanning mirror device draws an image by scanning a laser light horizontally and vertically in accordance with a picture signal. In particular, the light scanning mirror device has attracted attention as a key device of the image drawing device, such as a head mounted display, a micro projector, etc., which can display an image regardless of location.
The image drawing device comprises an optical system with the combination of a laser light and a light scanning mirror device, and an image signal processing circuit. Owing to the utilization of a laser light, it has the features such as (1) reduction in size of the optical system and (2) no necessity of focusing. The image drawing device has an advantage that image drawing on a curved surface is also possible. Therefore, it is possible to consider various applications combined with the portable information device, such as an enlarged projection of information which is illegible on a small liquid crystal display of a mobile device, and employment for a presentation in a place away from the office.
As disclosed by Japanese Patent No. 4515029 cited below, the light scanning mirror device is required to support the scanning frequency of 10 kHz or higher for horizontal scanning and several tens of Hz for vertical scanning, from the viewpoint of the number of the scanning lines which form a screen. In particular, in the latter vertical scanning, velocity control is performed in order to draw the horizontal scanning lines at a constant interval. In general, the drive of a light scanning mirror device is performed by rotating a reflective mirror through the use of the Lorentz force induced to a current in a magnetic field. Accordingly, resonant drive is applied to the horizontal scanning driven at a high frequency of 10 kHz or higher. On the other hand, nonresonant drive is applied to the vertical scanning which needs to be controlled to keep a uniform velocity during the drawing of horizontal scanning lines.
As described above, the image drawing device has the merit that it is possible to perform enlarged drawing of an image, regardless of location. Accordingly, the application as a portable device is considered in particular, requiring low power consumption and small size. For example, in an image drawing device of the electromagnetic drive type which develops large heat loss, it is required to attain reduction of the power consumption (low power consumption) and reduction of the implementation size including a magnet.
On the other hand, from the trend of the product, improvement in the magnifying power of an image (ratio of the distance to a projection plane to a screen size), prevention of deterioration in the image quality of an enlarged screen, etc. are required. Therefore, it becomes necessary to realize a high frequency of the scanning speed and the enlargement of the scanning angle. This will lead to increase of the power consumption, or enlargement of the size of a magnet.
Therefore, for example, Published Japanese Translation of PCT International Publication No. 2011-517626 cited below examines a light scanning mirror device of an electrostatic driving type as a means to reduce the power consumption of the light scanning mirror device, and discloses a resonant drive in vacuum, as a method for obtaining a large scanning angle at a low voltage. In the light scanning mirror device disclosed by Published Japanese Translation of PCT International Publication No. 2011-517626, there is no issue in particular concerning the horizontal scanning. However, the resonant drive disclosed herein cannot support the constant velocity control required for the vertical scanning during the drawing of horizontal scanning lines. Therefore, it becomes necessary to adopt the nonresonant drive.
In addition, in the electrostatic driving for rotating a reflective mirror by the nonresonant drive, a method for enlarging the scanning angle at a low voltage is already disclosed by Published Japanese Unexamined Patent Application No. 2008-172902 cited below, for example. The light scanning mirror device disclosed by Published Japanese Unexamined Patent Application No. 2008-172902 comprises a movable electrode substrate which can move only in the up-and-down direction in which a large number of vertical holes are open, and a fixed electrode which stands straight in parallel to the wall surface of each vertical hole of the movable electrode substrate and has a height lower than the height of the vertical hole. In the present configuration, the movable electrode substrate is translated downward by the power developed to reduce the difference in the height direction when a voltage difference is applied between the electrodes.
The rotation of the reflective mirror is attained by a torque given to the reflective mirror when the position connecting the movable electrode substrate and the reflective mirror is shifted from the axis of rotation of the reflective mirror. However, in the present system, the torque is given only in one direction to the reflective mirror; accordingly, distortion developed in the torsion beam supporting the reflective mirror becomes twice, compared with the reflective mirror of the electromagnetic drive type which rotates in both directions. When the scanning angle is enlarged, it is necessary to enlarge the area of the movable electrode substrate.
The present invention has been made in view of the subject in the related art technology described above, and realizes a light scanning mirror device which has improved the performance, without sacrificing any required properties described above, such as reduced power consumption, low voltage driving, reduction in size, and an enlarged scanning angle. That is, the present invention aims at providing an excellent light scanning mirror device and its control method, and also providing an image drawing device which utilizes the light scanning mirror device concerned.
In order to solve the subject, the present invention adopts the configuration described in the scope of the following claims. That is, the present invention provides a reflective mirror device which comprises at least a reflective mirror and a torsion beam which is connected to a frame structure and enables the reflective mirror to rotate around at least one axis. In the reflective mirror device, there are at least a couple of cantilevers arranged in the horizontal plane of the reflective mirror and in axial symmetry centering on the axis of rotation, in the perpendicular direction to the axis of rotation, and a fixed electrode which stands in parallel facing the cantilever at rest, in the movement direction of the cantilever rotating around the axis of rotation. The fixed electrode has, to one cantilever, at least an adsorptive electrode on the side of the free end of the cantilever and a controlling electrode on the side of the fixed end of the cantilever, respectively. The cantilever, the adsorptive electrode, and the controlling electrode are electrically separated mutually. According to the present configuration, in the first process, a voltage is applied between the cantilever and the adsorptive electrode, and the free end side of the cantilever is accordingly fixed to the adsorptive electrode by use of a static electricity power; in the second process, a voltage is applied to the controlling electrode in the state where the free end of the cantilever is in contact with the adsorptive electrode and where the space between the controlling electrode and the cantilever changes from a narrow area on the side of the free end of the cantilever to a broad area on the side of the fixed end of the cantilever, and the cantilever is accordingly adsorbed to the controlling electrode from the area where the space between the controlling electrode and the cantilever is narrow, as the voltage applied to the controlling electrode is gradually increased from zero. Accordingly, a torque is generated around the axis of rotation by the adsorption power to rotate the reflective mirror device, and the scanning speed of the light scanning mirror device is controlled arbitrarily.
Specifically, in order to attain the purpose described above, the present invention provides a light scanning mirror device which comprises a movable electrode substrate and a fixed electrode substrate arranged oppositely to the movable electrode substrate in a laminated manner. The movable electrode substrate comprises in one substrate at least a reflective mirror, a frame unit enclosing the outer circumference of the reflective mirror, a torsion beam formed in a body connecting the reflective mirror and the frame unit so as to enable the reflective mirror to rotate around at least one axis, and a movable electrode attached to a part of the reflective mirror. The fixed electrode substrate comprises in one substrate a fixed electrode arranged oppositely to the movable electrode. In the light scanning mirror device, the movable electrode of the movable electrode substrate is a cantilever movable electrode provided with at least a couple of cantilevers arranged in axial symmetry centering on the one axis. The fixed electrode of the fixed electrode substrate comprises an adsorptive fixed electrode which adsorbs and fixes an electrode on the side of a free end of the cantilever movable electrode, and a rotation controlling fixed electrode which adsorbs the cantilever movable electrode and controls rotation of the reflective mirror. The adsorptive fixed electrode and the rotation controlling fixed electrode are separated electrically with each other.
According to the present invention, in the light scanning mirror device described above, it is preferable that the adsorptive fixed electrode of the fixed electrode substrate is arranged in the position distant from the rotation controlling fixed electrode with respect to the one axis. It is also preferable that a substrate which is transparent at least at a part corresponding to the reflective mirror is further laminated over a surface of the movable electrode substrate different from the surface facing the fixed electrode substrate laminated, so as to accomplish hermetic sealing of the reflective mirror. In addition, it is preferable that a through-hole electrode is formed in a part of the fixed electrode substrate, in order to electrically couple the movable electrode of the movable electrode substrate, and the adsorptive fixed electrode and the rotation controlling fixed electrode of the fixed electrode substrate, to the exterior of the light scanning mirror device.
According to the present invention, in the light scanning mirror device described above, it is preferable that the movable electrode substrate further comprises a second movable electrode different from the movable electrode, provided in axial symmetry centering on the one axis, and that the fixed electrode substrate further comprises a second rotation controlling fixed electrode arranged oppositely to the second movable electrode. It is also preferable that an insulating film with protrusions is provided over at least one of the contacting surfaces of the cantilever movable electrode and the fixed electrode. It is further preferable that an element for measuring a rotation angle of the reflective mirror is built in a part of the reflective mirror.
In order to attain the purpose described above as well, the present invention provides a control method of the light scanning mirror device described above, as follows. A voltage is applied between the cantilever movable electrode and the adsorptive fixed electrode to generate a static electricity power. By use of the static electricity power, the free end of the cantilever movable electrode is adsorbed and fixed to the adsorptive fixed electrode, and the cantilever movable electrode is kept in a state of being changeable from a narrow area on the side of the free end to a broad area on the side of the rotation controlling fixed electrode. The cantilever movable electrode is adsorbed to the rotation controlling fixed electrode, by changing gradually the voltage applied to the rotation controlling fixed electrode to generate an adsorption power. Accordingly, by use of the adsorption power, a torque to rotate the reflective mirror around the one axis is generated, and the reflective mirror is rotated.
Furthermore, the present invention provides an image drawing device which comprises at least a light source for emitting a beam-shaped light and a reflective mirror for reflecting the beam-shaped light emitted from the light source, and which draws an image by reflecting and scanning the beam-shaped light, by means of the reflective mirror. The image drawing device employs one of the light scanning mirror devices described above, for use as the reflective mirror.
According to the present invention, the configuration described above can provide, as the excellent effect, the light scanning mirror device which is an electrostatic driving type of low power consumption and which can rotate the reflective mirror at a low voltage, even for a large scanning angle, and also can provide the control method of the light scanning mirror device and the image drawing device which utilizes the light scanning mirror device.
Hereinafter, with reference to the accompanying drawings, the embodiments of the present invention are explained in detail.
First, with reference to
On the other hand, the fixed electrode substrate 102 is provided with a frame unit 102-5 for assembling by bonding to the frame unit 101-2 of the movable electrode substrate 101. In addition, an adsorptive fixed electrode 102-1 and a rotation controlling fixed electrode 102-2 are arranged, in a position horizontally opposing the cantilever movable electrode 101-4 on one side when assembled with the movable electrode substrate 101, and an adsorptive fixed electrode 102-3 and a rotation controlling fixed electrode 102-4 are arranged, in a position horizontally opposing the cantilever movable electrode 101-5 on the other side. The adsorptive fixed electrode 102-1, the rotation controlling fixed electrode 102-2, the adsorptive fixed electrode 102-3, and the rotation controlling fixed electrode 102-4 are separated electrically with each other. Here, wirings to each of the electrodes described above are not shown.
Next, operation of the light scanning mirror device 100, of which the detailed structure is explained in the above, is explained in detail with reference to
First, in an initial state (A), a voltage is applied between the cantilever movable electrodes 101-4 and 101-5 and the adsorptive fixed electrodes 102-1 and 102-3, then by the static electricity power developed between these electrodes, the tips on the free end side of the cantilever movable electrodes 101-4 and 101-5 are moved to the state (B) where the tips are adsorbed and fixed to the adsorptive fixed electrodes 102-1 and 102-3, respectively. It is so configured that, in the state (B), the electrode spacing between the rotation controlling fixed electrodes 102-2 and 102-4 and the cantilever movable electrodes 101-4 and 101-5 becomes wider gradually from the narrow area on the side of the free end of the cantilever movable electrodes 101-4 and 101-5 to the broad area on the side of the fixed end. An insulating film is formed on either of the surfaces of the movable electrode and the fixed electrode so that the electrodes may not be short-circuited. However, when electrons accumulate in the insulating film, the dynamic characteristics as the electrostatic actuator will be affected. Accordingly, it is preferable to adopt the structure of suppressing the influence due to electrification, by arranging the insulating film in the shape of small protrusions, for example, thereby reducing the total amount of electrons accumulated.
From the state (B), when a voltage is further applied between the cantilever movable electrode 101-4 and the rotation controlling fixed electrode 102-2, the static electricity power, which is in inverse proportion to the square of the spacing between the electrodes, acts strongly in the area where the spacing between the electrodes is narrow. Accordingly, the cantilever movable electrode 101-4 adsorbs to the rotation controlling fixed electrode 102-2, gradually from the free end side. The position at which this adsorption stops is given by a position where the reaction force from the fixed end of the cantilever movable electrode 101-4 balances with the electrostatic attraction from the free end, by the intermediary of the cantilever movable electrode deformed in response to the electrostatic attraction. Consequently, when the voltage applied between the electrodes is increased, the adsorption position moves to the direction of the axis of rotation of the reflective mirror 101-1. The change of the absorption position applies a torque which rotates the reflective mirror 101-1 counter clockwise centering on the axis of rotation 101-3. Therefore, the state shifts from the state (C) to the state (D).
On the other hand, the clockwise rotation from the state (D) at which the rotation has reached the extreme in the counter clockwise direction (the rotation at the maximum angle) is started by reducing the voltage which has been applied between the cantilever movable electrode 101-2 and the rotation controlling fixed electrode 102-2 to zero, and applying a voltage between the cantilever movable electrode 101-5 and the rotation controlling fixed electrode 102-4. Accordingly, the state is shifted from the state (D) to the state (H), as is the case with the procedure in the counter clockwise rotation described above.
The shift from the state (H) to the state (J), and furthermore, the shift from the state (B), which is equivalent to the state (J), to the state (D) are the same repetition as the shift in the counter clockwise rotation described above. By repeating the procedure from the state (B) to the state (J) described above, the reflective mirror device makes the desired rotation, that is, the reflective mirror device functions as the light scanning mirror device.
Next,
Here, referring to
In the vertical scanning when drawing the horizontal scanning lines from the top to the bottom, the voltage applied to the rotation controlling fixed electrode 102-4 is gradually increased from the position of the state (D) (refer to the waveform of the voltage (B) illustrated in
The applied voltage here is determined by the balance of the static electricity power (increasing in proportion to the square of the applied voltage) which develops in the non-adsorption part of the cantilever movable electrode 101-5 and the free end side of the rotation controlling fixed electrode 102-4, with the distance from the adsorption position to the axis of rotation and the reaction force from the torsion beam. The manner in which the voltage applied to the rotation controlling fixed electrode 102-4 is increased is determined uniquely by the reaction force due to the torsional rigidity of the torsion beam 101-3 and the magnitude of the torque applied to the torsion beam 101-3 of the reflective mirror 101-1 from the cantilever movable electrode 101-4. However, it is also possible to set the inclined part, not as a straight line like the voltage applied to the rotation controlling fixed electrode 102-4 as illustrated in the voltage (B) of
As a method for performing the velocity control of the vertical scanning to high accuracy, there is a method in which a sensor for detecting the rotation angle of the reflective mirror is built in the light scanning mirror device, and a detected voltage corresponding to the rotation angle is applied to the rotation controlling fixed electrode 102-4, to control the scanning speed. For the detection of the rotation angle in such a case, it will be possible to adopt, for example, a method in which a piezoresistive element is built in the torsion beam 101-3 and the distortion of the torsion beam developed due to rotation is measured from a Wheatstone bridge circuit, thereby the rotation angle is estimated, a method in which an electrostatic capacity sensor is provided in the reflective mirror 101-1 and the tilting angle of the reflective mirror is measured directly, and others.
Next, the following explains an example of the processing method of the movable electrode substrate and the fixed electrode substrate of the light scanning mirror device described above.
The movable electrode substrate is manufactured using a single crystal silicone substrate or a SOI (Silicon On Insulator) substrate. The present embodiment exemplifies the case where the former single crystal silicone substrate is employed.
The shape of the processed cross section of
Next, the following explains the second embodiment (Embodiment 2) according to the present invention, with reference to
That is, in the so-called contact accompanying actuator, such as the inclined electrode type electrostatic actuator which is formed by adsorbing and fixing the cantilever movable electrodes 401-4 and 401-5 to the adsorptive fixed electrodes 402-1 and 402-3, the malfunction caused by peripheral environment occurs, such as sticking of a contact portion due to molecules floating in the atmosphere (such as humidity and volatile organic matter), and the stoppage of the proper operation caused by dust intruded into the spacing of the electrodes. Therefore, in the present embodiment, the cap substrate 403 is provided in the upper part of the movable electrode substrate 401, as clearly seen from
The drive method of the light scanning mirror device 400 according to the present embodiment is also the same as that of Embodiment 1, and the explanation thereof is omitted here.
The hermetic sealing described above is performed by controlling the internal airtight pressure, through the employment of inert gas, such as nitrogen and argon, in the vacuum equipment, for example. The concrete methods of performing the hermetic sealing include, for example, a method for performing the hermetic sealing when the cap substrate is bonded, and a method for performing the hermetic sealing by making a leak hole at the time of bonding the cap substrate and subsequently filling up the leak hole in vacuum film deposition equipment.
When it is necessary to keep constant the pressure in the hermetic sealing space for the long term, it is possible to adopt measures in which a gas adsorption film is formed at a portion of the cap substrate 403 where the light does not pass. However, when such measures are not required but the pressure below a certain value is sufficient, it is possible to adopt simple measures in which the pretreatment is performed for removing molecules which are sticking to the part of the wall surface in the hermetic sealing space, before the hermetic sealing is made.
In the present embodiment, antireflection treatment by an antireflection film coating for example is made on the surface of the cap substrate 403 through which a laser light passes, so that the laser light may not reflect. At the time of hermetic sealing, a low temperature process is applied so that the function of the surface of the cap substrate may not be impaired. As the bonding method of the cap substrate at a low temperature, various methods are known, such as a method in which a pretreatment such as a film formation is performed so as to make a bonding interface have the same properties of material, and in which the surface concerned is activated in a high vacuum and bonded at a normal temperature, a method of fused bonding at about 200° C. using a low-melting glass and a eutectic crystal, and a method of anodic bonding at about 280° C. using Pyrex (registered trademark) glass. However, it is preferable to select the suitable method comprehensively from the viewpoints of temperature, bonding strength, airtightness, cost, etc., which does not impair the function of the processing for antireflection and antistatic treatment treated to the cap substrate.
In this way, according to Embodiment 2 of the present invention, it is possible to realize a stable light scanning without variation with time, by providing the hermetic sealing with the cap substrate 403 and thereby eliminating the influence of humidity and dust which exist in the peripheral environment. In that case, however, it is necessary to supply a power source into the hermetic sealing space. As wiring technology for that, it is possible to adopt the so-called side extraction electrode in which wiring is buried under the bonded surface of the substrate and the so-called through-hole electrode 402-6 as illustrated in
As already described, the causes of the malfunction of the electrostatic driving actuator, except for the peripheral environment, arise from the electrification phenomena in which electrons accumulate in an insulating film. With regard to the present matter, when coating an insulating film over the surface of the cantilever movable electrodes 402-4 and 402-5 and the surface of the rotation controlling fixed electrodes 402-2 and 402-4 for the prevention from short-circuiting as described above, not only by forming the insulating film in the shape of a film, but by forming the insulating film in the shape of small protrusions, it is also possible to reduce the total amount of electrons which accumulate on the insulating film, and to suppress the influence on the operation of the electrostatic driving actuator to the minimum.
Next, the following explains the third embodiment (Embodiment 3) according to the present invention, with reference to
In
In the configuration according to Embodiment 3 described above, the procedure of rotating the reflective mirror is the same as that in Embodiment 1, and the explanation thereof is omitted. However, the following explains the reason why it is possible to enlarge the rotation angle in particular.
In Embodiment 3, the reflective mirror 501-1 is first rotated by use of the first cantilever movable electrode 501-6. Accordingly, the second cantilever movable electrode 501-7 formed in a body with the reflective mirror 501-1 tilts similarly, and the electrode spacing between the electrode concerned and the second adsorptive fixed electrode 502-8 becomes narrow. Accordingly, the second cantilever movable electrode 501-7 as well as the first cantilever movable electrode 501-6 described above can be adsorbed and fixed at the second adsorptive fixed electrode 502-5 at a low voltage. Therefore, it becomes possible to control the rotation angle by the second rotation controlling fixed electrode 502-8. Here, two kinds of the cantilever movable electrodes 501-6 and 501-7 are employed; however, if the number is further increased, it is also possible to enlarge the scanning angle furthermore.
Furthermore, the following explains the fourth embodiment (Embodiment 4) according to the present invention, with reference to
In the resonance-type light scanning mirror device, a reflective mirror 801 is fixed to a first scanning axis substrate 804 via a distortion isolating groove 805, and the first scanning axis substrate 804 is connected by use of a torsion beam 803 to a second scanning axis substrate 806. Then, the reflective mirror 801 is configured so as to be driven at a resonance frequency of a comb electrode 802 formed at an end of the first scanning axis substrate 804 in the direction of rotation. When the present resonance-type light scanning mirror device, i.e., the biaxial light scanning mirror device according to the present embodiment, is mounted in an image drawing device, such as a copy machine and a printer, for example, judging from each property, it will be preferable to apply the resonance-type light scanning mirror device to the horizontal scanning and to apply the light scanning mirror device by use of the cantilever movable electrode described above to the vertical scanning.
In
At this time, a desired image is drawn on the image projection plane 911 by synchronizing the scanning angle of the light scanning mirror device 910 and the picture signal. The feature of the image drawing device according to Embodiment 5 lies in the point that no optical system exists in the path of the light after the light scanning mirror device. Accordingly, it becomes possible to attain a focus-free drawing, and it becomes possible to project a well-focused image even on an image projection plane 911 with a curved surface. That is, owing to such features, various kinds of applications can be expected, for example, applications to an image drawing device of a portable projector, an image drawing device of a copy machine and a printer, and furthermore to a navigation system in which information is projected directly on a windshield of a vehicle, etc.
The light scanning mirror device according to the present invention can reduce the power consumption which used to be in the order of 100 mW in the electromagnetic drive in the related art to the order of several mW, owing to the structure described above. Therefore, even in the outdoors where a power source is not available, it becomes possible to project the information in an enlarged size for hours, by coupling to information equipment such as a mobile-phone, for example, and it is also possible to easily expand and display the detailed information which used to be difficult to be read on a small screen such as a liquid crystal display. Accordingly, it becomes possible to improve the level of convenience greatly.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-065766 | Mar 2012 | JP | national |
