Mirror scanner

Abstract

To provide a mirror scanner capable of sufficiently driving a mirror for optical scanning while minimizing the device size.SOLUTION: A mirror scanner is provided, comprising: a mirror provided with a first surface for reflecting light and configured to be swingable about a swing axis; a permanent magnet provided on a second surface of the mirror on a side opposite the first surface; and a yoke having a pair of magnetic field generating ends located at a position facing the permanent magnet on the second surface side of the mirror, and a pair of extending portions extending along the second surface of the mirror.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a mirror scanner. [Background technology]

[0002] A scanning device is known that emits deflected light toward a predetermined area and detects the light returning from the predetermined area to obtain various information about an object located within the predetermined area. In such a scanning device, a movable mirror such as a MEMS (Micro Electro Mechanical System) mirror is provided as a part that deflects the light. As an optical scanning device having a movable mirror, an optical scanning device has been proposed that has an electromagnet consisting of a yoke and a coil wound around the yoke, and that generates a magnetic field by passing an alternating current through the coil, and drives the mirror by interaction with the magnetic field of a permanent magnet (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-69676 Summary of the Invention [Problem to be solved by the invention]

[0004] In the optical scanning device of the above-mentioned conventional technology, the yoke has a C-shape (or U-shape), and the end of the yoke, which is the magnetic field generating end, is positioned so as to face a permanent magnet provided on the surface opposite the light reflecting surface of the mirror (i.e., the back surface). As a result, a space equivalent to the height of the C-shaped yoke when placed vertically with the magnetic field generating end facing up is required on the back surface of the mirror, which increases the size of the entire device. This has resulted in a problem of limiting the location where the optical scanning device can be placed.

[0005] The present invention has been made in consideration of the above points, and one of its objects is to provide a mirror scanner that can sufficiently drive a mirror to perform optical scanning while keeping the device size small. [Means for solving the problem]

[0006] The invention described in claim 1 is characterized by comprising a mirror having a first surface that reflects light and that is oscillating around an oscillation axis, a permanent magnet arranged on a second surface of the mirror that is the surface opposite to the first surface, a yoke having a pair of magnetic field generating end portions arranged on the second surface side of the mirror in a position facing the permanent magnet, and a pair of extension portions extending along the second surface of the mirror. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram illustrating the overall configuration of a mirror scanner according to an embodiment of the present invention. [Figure 2A] 4A and 4B are diagrams illustrating the positional relationship between a mirror body and a yoke. [Figure 2B] 10A and 10B are views showing a yoke and a jig for clamping the yoke; [Figure 3] FIG. 10 is a diagram illustrating a configuration of a mirror scanner of a comparative example. [Figure 4] 10A and 10B are diagrams illustrating the positional relationship between a mirror body and a yoke in a comparative example. [Figure 5] 10 is a diagram showing the relationship between the drive current and the mirror deflection angle for each of the present embodiment and the comparative example. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0008] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail. In the following description of the embodiments and the accompanying drawings, the same reference numerals are used to designate substantially the same or equivalent parts.

[0009] 1 is a perspective view showing the overall configuration of a mirror scanner 100 according to this embodiment. The mirror scanner 100 is an optical scanning device that deflects light by periodically oscillating a movable mirror.

[0010] The mirror scanner 100 has a mirror main body 10 (hereinafter simply referred to as the main body) that deflects light, a yoke 20 that is a magnetic field generation source, and a drive circuit 30. The mirror scanner 100 of this embodiment is a magnetically driven MEMS device that operates the main body 10 by applying a magnetic field generated by the yoke 20 and the drive circuit 30 to the main body 10.

[0011] The main body 10 includes a plate-shaped support plate 11 serving as a support portion, a pair of torsion bars 12 extending from the support plate 11 along an oscillation axis AX, and a mirror 13 supported so as to be able to oscillate by the support plate 11 and the torsion bars 12. One end of each of the torsion bars 12 is fixed to the support plate 11, and the other end is fixed to the mirror 13. The mirror 13 oscillates relative to the support plate 11 as the torsion bars twist around the oscillation axis.

[0012] For example, the support plate 11, the torsion bars 12, and the mirror 13 are made of a semiconductor material. The main body 10, which is made up of the support plate 11, the torsion bars 12, and the mirror 13, can be integrally formed by processing a semiconductor wafer, for example.

[0013] Mirror 13 is a flat plate-shaped member and has light-reflecting surface 13S that is reflective to predetermined light. Light-reflecting surface 13S may be formed, for example, by evaporating metal onto the surface of a plate-shaped material that forms mirror 13. A permanent magnet 14 is disposed in the center of the surface of mirror 13 opposite light-reflecting surface 13S. In the following description, light-reflecting surface 13S of mirror 13 will also be referred to as the first surface, and the surface opposite light-reflecting surface 13S will also be referred to as the second surface.

[0014] In the mirror scanner 100 of this embodiment, the magnetic field generated by the yoke 20 and the drive circuit 30 acts on the permanent magnet 14, causing the mirror 13 to swing around a reference position. For example, the mirror 13 swings around a reference position where the light reflecting surface 13S is parallel to the surface of the support plate 11. That is, the mirror 13 swings around the swing axis in positive and negative directions, with the reference position being the 0-degree position.

[0015] The angle of the light reflecting surface 13S as viewed from the reference position (i.e., the swing angle) changes in response to the oscillation of the mirror 13. Specifically, when a magnetic field is applied to the permanent magnet 14 so that the torsion bar 12 twists around the oscillation axis AX, the mirror 13 oscillates around the oscillation axis AX while being supported by the support plate 11. Light emitted from a light source (not shown) is reflected by the light reflecting surface 13S of the mirror 13, and the reflection direction changes as the mirror 13 oscillates, thereby performing optical scanning. Note that in this embodiment, since there is only one oscillation axis, the scanning direction changes one-dimensionally; however, two-dimensional scanning is possible, for example, by reflecting light emitted from multiple light sources (e.g., a multi-emitter) arranged in a line by the mirror 13.

[0016] The yoke 20 is made of a soft magnetic material. The yoke 20 includes a pair of core portions 21A and 21B that extend substantially parallel to each other in the same direction, and a connecting portion 22 that connects the core portions 21A and 21B. That is, in this embodiment, the yoke 20 has a C-shape (U-shape).

[0017] The first coil portion 23A is formed of a steel wire wound around the core portion 21A of the yoke 20. The second coil portion 23B is formed of a steel wire wound around the core portion 21B. In this embodiment, the first coil portion 23A and the second coil portion 23B are formed using a single common steel wire. That is, the first coil portion 23A and the second coil portion 23B are configured so that current flows through them simultaneously. Alternatively, the first coil portion 23A and the second coil portion 23B may be configured using separate steel wires, and the current flowing through each may be individually controllable.

[0018] The yoke 20 also has a pair of magnetic field generating ends, namely, magnetic field generating ends 24A and 24B. The magnetic field generating end 24A is provided near the end of the core portion 21A opposite to the connection portion with the coupling portion 23, and has a convex shape that protrudes in a direction perpendicular to the extension direction of the core portion 21A. Similarly, the magnetic field generating end 24B is provided near the end of the core portion 21B opposite to the connection portion with the coupling portion 23, and has a convex shape that protrudes in a direction perpendicular to the extension direction of the core portion 21B.

[0019] In other words, the magnetic field generating ends 24A and 24B have a shape that protrudes in a direction perpendicular to a plane that includes each of the straight lines along the extension direction of the core portions 21A and 21B (i.e., a single plane formed by the surfaces of the core portions 21A, 21B, and the connecting portion 22). For example, as shown in Fig. 1, the magnetic field generating ends 24A and 24B are formed by adding a metal material processed into the shape of a triangular prism to the vicinity of each end of the core portions 21A and 21B.

[0020] The drive circuit 30 is a circuit that applies a drive current to the first coil portion 23A and the second coil portion 23B. For example, the drive circuit 30 applies an AC current as a drive current to the first coil portion 23A and the second coil portion 23B for resonantly driving the mirror 13. This causes the yoke 20 to function as an electromagnet, and an AC magnetic field is generated from the magnetic field generating end 24A and the magnetic field generating end 24B.

[0021] In the mirror scanner 100 of this embodiment, on the second surface side of the mirror 13 (i.e., the surface opposite to the light reflecting surface 13S), the core portions 21A and 21B of the yoke 20 are arranged so as to extend along the plate surface of the support plate 11 and the second surface of the mirror 13 in the reference position. For example, the yoke 20 is arranged so that the extending direction of the core portions 21A and 21B is approximately parallel to the plate surface of the support plate 11 and the second surface of the mirror 13 in the reference position. Furthermore, the yoke 20 is arranged so that the magnetic field generating ends 24A and 24B are positioned opposite the permanent magnet 14 on the second surface side of the mirror 13.

[0022] 2A is a diagram showing the relative positions of the main body 10 and the yoke 20. Note that the drive circuit 30 is not shown here.

[0023] The yoke 20 is fixed onto the base 26 by a jig 25 as shown in Fig. 2B and is disposed at the position shown in Fig. 2A. The jig 25 clamps the connecting portion 22 of the yoke 20 in a direction perpendicular to the extension direction of the core portions 21A and 21B (i.e., a direction perpendicular to the plate surface of the support plate 11), thereby fixing the yoke 20 onto the base 26. The jig 25 is made of a non-magnetic material with high thermal conductivity, such as aluminum. In addition to the function of fixing the yoke 20, the jig 25 also has the function of dissipating heat generated in the yoke 20 by driving the mirror scanner 100 through thermal conduction.

[0024] 2A, in the mirror scanner 100 of this embodiment, the yoke 20 is arranged so that it extends along the main surface of the main body 10 (i.e., the plate surface of the support plate 11 and the second surface of the mirror 13 in the reference position) (i.e., so that the core portions 21A and 21B extend along the second surface of the mirror 13 in the reference position). Therefore, the width of the mirror scanner 100 in the direction perpendicular to the main surface of the main body 10 is small. In other words, the mirror scanner 100 of this embodiment has a small height length based on the mounting surface of the yoke 20.

[0025] 3 is a diagram showing the configuration of a comparative mirror scanner 200, which has a different yoke shape and arrangement from the mirror scanner 100 of this embodiment. The comparative mirror scanner 200 is composed of a main body 10, a yoke 40, and a drive circuit 30.

[0026] The yoke 40 has a C-shape made up of a core portion 41 and extension portions 42A and 42B extending parallel to each other from both ends of the core portion 41. A coil 43 is wound around the core portion 41.

[0027] The yoke 40 also has magnetic field generating ends 44A and 44B that extend continuously from the ends of the extension portions 42A and 42B on the opposite side from the connection portions with the core portion 41. Unlike the magnetic field generating ends 24A and 24B of the mirror scanner 100 of this embodiment (see FIG. 1), the magnetic field generating ends 44A and 44B do not protrude in a direction perpendicular to a plane that includes each of the straight lines along the extension direction of the extension portions 42A and 42B, but protrude in a direction that forms a C-shaped tip within the plane.

[0028] The yoke 40 is disposed so that the magnetic field generating ends 44A and 44B face the permanent magnet 14 on the second surface side of the mirror 13. Therefore, for example, when the mirror scanner 200 of the comparative example is placed horizontally, the yoke 40 is disposed so that the core portion 41 is the bottom surface and the extension direction of the extension portions 42A and 42B is the vertical direction (i.e., the height direction).

[0029] 4 is a diagram showing the positional relationship between the main body 10 and the yoke 40 in a mirror scanner 200 of a comparative example. Note that the drive circuit 30 is not shown here.

[0030] In the mirror scanner 200 of the comparative example, the yoke 20 is arranged so that the extensions 42A and 42B are perpendicular to the plate surface of the support plate 11 and the second surface of the mirror 13 in the reference position. In addition, the magnetic field generating ends 44A and 44B extend continuously from the ends of the extensions 42A and 42B, respectively. Therefore, the width of the mirror scanner 100 in the direction perpendicular to the plate surface of the support plate 11 (i.e., the combined height of the main body 10 and the yoke 20 when the surface of the yoke 20 opposite to the surface facing the main body 10 is taken as the bottom) is large.

[0031] In contrast, in the mirror scanner 100 of this embodiment, the magnetic field generating ends 24A and 24B have a shape that protrudes from a plane that includes each of the straight lines along the extension directions of the core portions 21A and 21B. Therefore, as shown in Fig. 2A, it is possible to arrange the yoke 20 so that the yoke 20 extends along the main surface of the main body portion 10 (for example, so that the extension directions of the core portions 21A and 21B are approximately parallel to the main surface of the main body portion 10).

[0032] Therefore, in the mirror scanner 100 of this embodiment, the width of the mirror scanner 100 in the direction perpendicular to the main surface of the main body 10 (i.e., the length in the height direction based on the mounting surface of the yoke 20) can be made shorter than that of the mirror scanner 200 of the comparative example. This makes it possible to keep the device scale of the entire mirror scanner 100 small.

[0033] Furthermore, in the mirror scanner 200 of the comparative example, the coil 43 is located directly below the permanent magnet 14. Therefore, in order to prevent the operation of the permanent magnet 14 from being directly affected by the coil 43, it is necessary to set the magnetic field generating ends 44A and 44B at a certain height or more to increase the distance between the permanent magnet 14 and the coil 43. In contrast, in the mirror scanner 100 of the present embodiment, the first coil section 23A and the second coil section 23B are located at positions away from directly below the permanent magnet 14, making it possible to keep the height of the magnetic field generating ends 24A and 24B low.

[0034] Furthermore, in the mirror scanner 100 of this embodiment, a coil is wound around a pair of core portions, core portions 21A and 21B. Core portions 21A and 21B are arranged to extend along (for example, substantially parallel to) the plate surface of support plate 11 and the second surface of mirror 13 in the reference position. With this configuration, the lengths of core portions 21A and 21B do not affect the height of mirror scanner 100, and therefore it is possible to increase the number of turns of the coil by extending the lengths of core portions 21A and 21B, which are the portions around which the coil is wound, without increasing the height of mirror scanner 100.

[0035] Furthermore, despite the mirror scanner 100 of this embodiment being shorter than the mirror scanner 200 of the comparative example, it is possible to increase the number of turns of the coil wound around the core portion. For example, if the widths of the mirror scanner 100 and the mirror scanner 200 are the same, i.e., if the lengths of the core portion 41 and the core portions 21A and 21B are the same, the amount of coil wire that can be wound around the core portion is approximately twice as large. In other words, the number of turns of the coil can be increased while suppressing the height and without changing the size in the width direction (i.e., the length in the extension direction of the core portions 21A and 21B), and the mirror 13 can be oscillated with a smaller drive current.

[0036] 5 is a graph showing the relationship between the drive current applied by the drive circuit 30 and the oscillation angle of the mirror 13 when it oscillates (i.e., the maximum value of the oscillation angle around the reference position). The horizontal axis represents the effective current value (mA) of the drive current, and the vertical axis represents the mirror oscillation angle. Note that here, the mirror scanner 100 of this embodiment is shown by a solid line, and the mirror scanner 200 of the comparative example is shown by a dashed line.

[0037] The mirror scanner 100 of this embodiment can obtain the same oscillation angle with a drive current that is half or less the current value of the comparative mirror scanner 200. For example, the comparative mirror scanner 200 requires a drive current with an effective value of 100 mA or more to obtain an oscillation angle of 75°, but the mirror scanner 100 of this embodiment can obtain an oscillation angle of 75° with a drive current with an effective value of less than 50 mA.

[0038] In this way, the mirror scanner 100 of this embodiment can obtain the same force with less power than the comparative example. Therefore, the mirror scanner 100 of this embodiment can perform optical scanning equivalent to that of the conventional one while reducing power consumption.

[0039] If it is desired to increase the number of coil turns in the mirror scanner 200 of the comparative example, it is conceivable to wind the coil around the extensions 42A and 42B shown in Fig. 3. However, since the extensions 42A and 42B extend in a direction perpendicular to the surface of the support plate 11 and the second surface of the mirror 13 and require a length according to the number of coil turns, the length in the direction perpendicular to the surface of the support plate 11 (i.e., the height of the mirror scanner 200) becomes large. Therefore, in the mirror scanner 200 of the comparative example, it is not possible to increase the number of coil turns while suppressing the height of the mirror scanner 200.

[0040] As described above, according to the mirror scanner 100 of this embodiment, it is possible to keep the height of the entire device low. Also, it is possible to increase the number of turns of the coil without increasing the height of the device. Therefore, by using the mirror scanner 100 of this embodiment, it is possible to sufficiently drive the mirror to perform optical scanning while suppressing the device size and power consumption.

[0041] Furthermore, when the temperature of the yoke rises, the resistance value of the coil's conductor wire rises, increasing power consumption. Therefore, heat dissipation from the yoke is effective in reducing power consumption. In the mirror scanner 100 of this embodiment, as shown in FIG. 2B, the yoke 20 is fixed to the base 26 by a jig 25. The jig 25 is made of a material with high thermal conductivity, such as aluminum, and fixes the yoke 20 so as to sandwich the entire connecting portion 22, thereby providing a large contact surface area with the yoke 20. Therefore, heat dissipation from the yoke 20 can be performed efficiently.

[0042] Furthermore, since the height of the mirror scanner 100 can be kept low as described above, there are fewer restrictions on the installation location. Therefore, when used as an in-vehicle optical scanning device, for example, the mirror scanner 100 can be installed in spaces such as the bumper or dashboard of the automobile.

[0043] The present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, the mirror 13 is oscillated around one oscillation axis AX. However, differently from this, the mirror 13 may be configured to oscillate around two oscillation axes. For example, by configuring the mirror to be oscillated around two oscillation axes that are perpendicular to each other and arranging two yokes having the same configuration as the yoke 20 in the above-described embodiment so that each pair of core portions extends along the plate surface of the support plate and the magnetic field generating end faces the permanent magnet, it becomes possible to oscillate the mirror 13 around the two oscillation axes.

[0044] In the above embodiment, the pair of core portions 21A and 21B extend substantially parallel to each other in the same direction. However, this is not limiting, and the extension directions of core portions 21A and 21B may be configured to form an angle of less than 180 degrees with respect to each other. Furthermore, the lengths of core portions 21A and 21B may be different from each other.

[0045] In the above embodiment, the first coil portion 23A is wound around the core portion 21A, and the second coil portion 23B is wound around the core portion 21B. However, a coil may be wound around only one of the core portions 21A and 21B. Also, a coil may be wound around the connecting portion 22. [Explanation of symbols]

[0046] 100 mirror scanner 10 Main body 11 Support plate 12 Torsion bar 13. Mirror 13S light reflective surface 14 Permanent magnets 20 York 21A Core 21B Core 22 Connecting part 23A First coil section 23B Second coil section 24A magnetic field generating end 24B Magnetic field generating end 30 Drive circuit

Claims

[Claim 1] a mirror having a first surface that reflects light and that is swingable around a swing axis; a permanent magnet disposed on a second surface of the mirror opposite to the first surface; a yoke having a pair of magnetic field generating end portions arranged at positions facing the permanent magnet on the second surface side of the mirror, and a pair of extension portions extending along the second surface of the mirror; A mirror scanner comprising:

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