Light deflector

Abstract

To provide a light deflector that has high stiffness and cannot be damaged easily even by miniaturization and thinning.SOLUTION: A light deflector 2 includes: a mirror part 9 for reflecting light; a movable frame 8 provided so as to surround the mirror part 9; a pair of torsion bars 13a, 13b in which each of one end sections on a Y axis is connected to the mirror part 9 and each of the other end sections is connected to the movable frame 8; and semi-annular piezoelectric actuators 10a, 10b that are provided on the movable frame 8 and reciprocatively rotate the torsion bars 13a, 13b around the Y axis. The torsion bars 13a, 13b are in a constricted shape in which the breadth of both the ends is the widest and becomes narrower gradually toward the center in the longitudinal direction.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an optical deflector that uses a torsion bar to rotate a mirror portion back and forth. [Background technology]

[0002] Conventionally, there are known optical deflectors manufactured using MEMS (Micro Electro Mechanical Systems) technology, and optical scanning devices equipped with such optical deflectors. The optical deflector has a mirror part that rotates back and forth around a rotation axis, and reflects light from a light source in a direction according to the deflection angle of the mirror part, thereby optically scanning a predetermined area.

[0003] In the optical scanning device of Patent Document 1, the movable plate part is provided with reinforcing ribs near each connection part between the movable plate and the torsion beam on the back side of the reflecting surface. According to this optical scanning device, the part close to the rotation center where distortion is large is reinforced, so that the increase in the weight and moment of inertia of the movable plate part can be suppressed (Patent Document 1 / paragraph 0026, Figure 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5168659 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in this optical scanning device, the provision of the rib may cause discontinuity in the rigidity of the base of the torsion beam, and if the stress generated when the movable plate is driven and the optical scanning speed is increased is concentrated in one part of the torsion beam, there is a risk of it being damaged.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical deflector which has high rigidity and is not easily damaged even when made small and thin. [Means for solving the problem]

[0007] The optical deflector of the present invention comprises a mirror section which reflects light, a frame body provided so as to surround the mirror section, a pair of torsion bars, one end of each of which is coupled to the mirror section and the other end of each of which is coupled to the frame body on an axis passing through the center of the mirror section, and a piezoelectric actuator provided on the frame body, which rotates the torsion bars back and forth around the axis, When the connection portion between the torsion bar and the mirror portion is defined as a first connection portion, and the connection portion between the torsion bar and the frame body is defined as a second connection portion, the torsion bar has a narrowed shape in which the width is widest at the first connection portion and the second connection portion and gradually narrows toward the center in the longitudinal direction.

[0008] In the optical deflector of the present invention, the piezoelectric actuator rotates the mirror section back and forth around the axis line by using a pair of torsion bars. One end of each of the torsion bars is connected to the mirror section at a first connection part, and the other end of each of the torsion bars is connected to a frame on which the piezoelectric actuator is provided at a second connection part.

[0009] In order to relieve the stress of the torsion bar caused by the torsional motion, the torsion bar is made to have a constricted shape in which the width is widest at the first and second connection parts and gradually narrows toward the center in the longitudinal direction. The optical deflector of the present invention has a narrower width at the center compared to a linear torsion bar (conventional structure), which has a wide width at the center, and the rotational torque is smaller. In exchange, the optical deflector of the present invention has less distortion and higher rigidity, making it possible to make an optical deflector that is less likely to break even when made smaller and thinner.

[0010] In the optical deflector of the present invention, when the width of the first connection portion or the second connection portion of the torsion bar is defined as W1, the width of the center portion of the torsion bar in the longitudinal direction is defined as W2, and (W1-W2) / 2=W3, it is preferable that the width W4 of the torsion bar at the intermediate portion between the first connection portion or the second connection portion and the center portion in the longitudinal direction is given by W2+0.30-0.35×W3.

[0011] The resonant frequency and the limit deflection angle when the mirror part is rotated back and forth depend on the shape of the torsion bar. By setting the width W4 of the torsion bar in the above range, the resonant frequency and the limit deflection angle of the mirror part can be improved.

[0012] Furthermore, in the optical deflector of the present invention, when the mirror portion has a circular or elliptical shape, it is preferable that the edge of the torsion bar on the first connection portion side is on a tangent to the circular or elliptical shape of the mirror portion, perpendicular to the axis.

[0013] When the mirror portion is circular or elliptical, the edge of the torsion bar on the first connection portion side (mirror portion side) is on the above-mentioned tangent line, which makes it possible to clarify the length of the torsion bar.

[0014] Furthermore, in the optical deflector of the present invention, when the frame body has a circular or elliptical shape, it is preferable that the edge of the torsion bar on the second connection portion side is on a straight line connecting the end points of the curves that constitute the circular or elliptical shape of the frame body.

[0015] When the frame is circular or elliptical, the edge of the torsion bar on the second connection side (frame side) is on the straight line, which makes it possible to clarify the length of the torsion bar.

[0016] In the optical deflector of the present invention, it is preferable that the torsion bar has a straight portion including a center portion in a longitudinal direction, and the straight portion is 25% or less of the entire length of the torsion bar.

[0017] The torsion bar may have a straight portion in the center in the longitudinal direction. If the length of the straight portion is 25% or less of the total length of the torsion bar, the torsion bar can have the same performance as a torsion bar having a waisted shape consisting of only curves. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing the configuration of an optical scanner module. [Diagram 2] 3A to 3C are diagrams illustrating details of an optical deflector according to the present invention. [Diagram 3] An enlarged view of region R in Figure 2. [Figure 4] An enlarged view of area S in FIG. [Diagram 5] (a) is an overall perspective view of a torsion bar, (b) is a cross-sectional view of the torsion bar along line II. [Figure 6] FIG. 13 is a diagram illustrating a torsion bar (modified form). [Figure 7] 1A is a diagram illustrating a torsion bar (Reference Example A), and FIG. 1B is a diagram illustrating a torsion bar (Reference Example B). [Figure 8] FIG. 13 is a diagram illustrating a comparison of performance between different shapes of torsion bars. [Figure 9] FIG. 1 is a diagram illustrating a comparison of the performance of a conventional torsion bar structure and a new structure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] (Overall composition) First, the configuration of an optical scanner module 1 will be described with reference to FIG.

[0020] The optical scanner module 1 is a component used in, for example, a picoprojector, smart glasses (wearable devices), a headlamp for ADB (Adaptive Driving Beam), and the like, and is composed of an optical deflector 2, a light source 3, a control device 5, and the like.

[0021] (light deflector) The optical deflector 2 is manufactured using semiconductor processes and MEMS technology. The optical deflector 2 is a device that reflects light incident from a certain direction with a micromirror (mirror unit 9) that rotates around an axis and emits the reflected light as scanning light.

[0022] A mirror section 9, a piezoelectric actuator 10, a torsion bar 13, etc. are provided on a movable frame 8 ("frame" of the present invention) which is an inner frame of the optical deflector 2. Laser light 4a emitted from the light source 3 is incident on the mirror section 9 and reflected, and the reflected light (laser light 4b) scans, for example, a projection surface of a picoprojector.

[0023] (light source) The light source 3 is a laser diode (LD) having a central wavelength of about 450 nm, and emits blue light (laser light 4a). Note that a light emitting diode (LED) or the like may also be used as the light source.

[0024] (Control device) The control device 5 transmits control signals to the movable frame 8 and the light source 3. The control signals drive the piezoelectric actuator 10 in the movable frame 8, and the torsion bar 13 twists, causing the mirror section 9 to rotate back and forth. In addition, the on / off and brightness of the laser light 4a from the light source 3 are controlled by the control signal.

[0025] Next, the optical deflector 2 of this embodiment will be described in detail with reference to FIG.

[0026] (Mirror part) In an initial state, the mirror unit 9 is disposed so that a normal line extending from its center O to the front side faces straight forward in the optical deflector 2. The mirror unit 9 is supported by torsion bars 13 (13a, 13b) in the Y-axis direction (the "axis" of the present invention) and is disposed approximately in the center of the movable frame 8.

[0027] The reflecting surface of the mirror section 9 is formed by forming a thin metal film of Au, Pt, Al, etc., by, for example, a sputtering method or an electron beam deposition method. The shape of the mirror section 9 is not limited to a circle, and may be an ellipse or another shape.

[0028] (movable frame) The movable frame 8 has a dual structure of an inner frame body 8a and an outer frame body 8b, and is provided so as to surround the mirror section 9. The piezoelectric actuator 10 is composed of a semi-annular piezoelectric actuator 10a on the left side as viewed from the front and a semi-annular piezoelectric actuator 10b on the right side as viewed from the front, and is provided on the upper surface of the inner frame body 8a. In other words, the inner frame body 8a is an annular drive section in which a plurality of piezoelectric sections are arranged in a ring shape.

[0029] (Torsion bar) The torsion bar 13 is composed of a torsion bar 13a on the upper side when viewed from the front and a torsion bar 13b on the lower side when viewed from the front. One end of each of the torsion bars 13a and 13b is connected to the mirror unit 9, and the other end of each of the torsion bars 13a and 13b is connected to the inner frame body 8a. By connecting the torsion bars 13a and 13b in this manner, the reciprocating rotation of the mirror unit 9 in the Y-axis direction is stabilized. The shape of the torsion bars will be described in detail later.

[0030] (Semi-annular piezoelectric actuator) Semi-annular piezoelectric actuators 10a and 10b ("piezoelectric actuators" of the present invention) are provided on an inner frame body 8a. The inner frame body 8a is connected to torsion bars 13a and 13b on the Y axis and to an outer frame body 8b on the X axis.

[0031] The semi-annular piezoelectric actuators 10a and 10b have a structure in which a piezoelectric film of lead zirconate titanate (PZT) is sandwiched between a lower electrode and an upper electrode by a semiconductor process. By applying a voltage to the piezoelectric film via the lower electrode and the upper electrode, the semi-annular piezoelectric actuators 10a and 10b are bent and deformed, and the torsion bars 13a and 13b are twisted.

[0032] (Bellwing-shaped piezoelectric actuator) In the optical deflector 2, a movable frame 8 is disposed in the center of an outer frame support 11, and bellows-shaped piezoelectric actuators 6a and 6b are disposed on both sides of the movable frame 8. The bellows-shaped piezoelectric actuators 6a and 6b are coupled to the outer frame body 8b and the end of the outer frame support 11 on the X-axis.

[0033] The bellows-shaped piezoelectric actuators 6a and 6b are configured by arranging multiple cantilevers in the longitudinal direction adjacent to each other and connecting them in series by folding back at the top and bottom ends. By driving the bellows-shaped piezoelectric actuators 6a and 6b, the movable frame 8 rotates back and forth around the X-axis.

[0034] As a result, when the laser light 4a is reflected by the mirror portion 9, the optical deflector 2 emits the light forward of the optical deflector 2, and can perform scanning in two directions, that is, the X-axis direction and the Y-axis direction.

[0035] (Electrode pads) Electrode pads 7a-1 to 7a-8 (hereinafter referred to as electrode pads 7a) are arranged on the left side of the outer frame support 11 when viewed from the front, and electrode pads b-1 to 7b-8 (hereinafter referred to as electrode pads 7b) are arranged on the right side of the outer frame support 11 when viewed from the front. The electrode pads 7a, 7b are electrically connected so as to apply a drive voltage to each electrode of the bellows-shaped piezoelectric actuators 6a, 6b and the semi-annular piezoelectric actuators 10a, 10b.

[0036] Next, the torsion bar of this embodiment will be described in detail with reference to FIGS.

[0037] (Torsion bar structure) First, Fig. 3 shows an enlarged view of region R in Fig. 2. The torsion bars 13a and 13b of this embodiment have a narrowed shape in which the width is widest at the ends and gradually narrows toward the center in the longitudinal direction of the torsion bars 13a and 13b. The following description will be given using the torsion bar 13b as an example.

[0038] As shown in the figure, when the mirror portion 9 has a circular shape, a tangent line s1 of the mirror portion 9 (circular shape) perpendicular to the Y-axis becomes the edge of the connection portion between the torsion bar 13b and the mirror portion 9 (the “first connection portion” of the present invention).

[0039] When the mirror portion 9 has an elliptical shape, the edge of the connection portion between the torsion bar 13b and the mirror portion 9 is on a tangent line of the mirror portion 9 (of the elliptical shape) that is perpendicular to the Y-axis.

[0040] Furthermore, as shown in the figure, when the movable frame 8 has an elliptical shape, a straight line s2 connecting the end points (points where the curvature changes) of the curves that make up the movable frame 8 (elliptical shape) becomes the edge of the connection part between the torsion bar 13b and the movable frame 8 (the "second connection part" of the present invention).

[0041] When the movable frame 8 has a circular shape, the edge of the connection between the torsion bar 13b and the movable frame 8 is similarly on a straight line connecting the end points of the curves that form the movable frame 8 (circular shape).

[0042] By defining the edge (tangent line s1) of the connection between the torsion bar 13b and the mirror portion 9 and the edge (straight line s2) of the connection between the torsion bar 13b and the movable frame 8 as described above, the length of the torsion bar 13b can be clearly determined.

[0043] Next, Fig. 4 shows an enlarged view of the area S in Fig. 3. Here, the size of each part of the torsion bar 13b (hereinafter referred to as the torsion bar 13) will be described.

[0044] In the above-described optical deflector 2, the edge of the torsion bar 13 on the mirror section 9 side is a tangent line s1, and the edge of the torsion bar 13 on the movable frame 8 side is a straight line s2. Therefore, the distance between the tangent line s1 and the straight line s2 is the length L of the torsion bar 13.

[0045] The torsion bar 13 of this embodiment has a width W1 of 320 [μm] at the edge, and a width W2 of 160 [μm] at the center in the length direction of the torsion bar 13 (distance from the edge is L / 2: on the straight line m). The torsion bar 13 is made up of only curves so that the width gradually increases from the edge toward the center in the length direction. The width (W1=W2) of a conventional straight torsion bar is 220 [μm] (not shown).

[0046] Moreover, the distance W3 in the figure is given by W3 = (W1 - W2) / 2. In this case, it is preferable that the width W4 of the torsion bar 13 at the intermediate portion (distance from the edge: L / 4 on the line n) between the edge of the torsion bar 13 (tangent line s1 or line s2) and the center of the torsion bar 13 in the longitudinal direction satisfies the condition W2 + N × W3 (N = 0.30 to 0.35).

[0047] For example, when the width W1 is 320 μm and the width W2 is 160 μm, the distance W3 is 80 μm and the width W4 is 186 μm, assuming N=0.325. Therefore, the curved shape of the torsion bar 13 can be designed to satisfy the widths W1, W2, and W4.

[0048] Here, the principle of how the torsion bar 13 of this embodiment has high performance will be described with reference to FIG.

[0049] 5(a) is a perspective view of the torsion bar 13. As shown in the figure, the torsion bar 13 has a narrowed shape in which the width W1 is widest at the end edges and the width gradually narrows toward the center in the longitudinal direction. Since both ends of the torsion bar 13 are fixed ends in the torsional motion, the center in the longitudinal direction is the farthest position from the fixed ends and is subjected to large stress.

[0050] Fig. 5(b) is a cross-sectional view of the torsion bar 13 of Fig. 5(a) taken along line II. As shown in the cross-sectional view (top), the cut edge is a rectangle with a width W2 (=160 μm) and a thickness T. This width W2 is narrower than the width (220 μm) of a conventional straight torsion bar. The reduction in width W2 shortens the length of the arm from the rotation axis (Y-axis) and reduces the moment of inertia, suppressing the rotational torque (= moment of inertia x angular acceleration) and reducing distortion.

[0051] The torsion bar 13 of this embodiment has a structure in which the center is more easily twisted than the two ends, but since the distortion can be suppressed compared to the conventional structure, it is less likely to break. Therefore, the torsion bar 13 can increase the limit deflection angle of the mirror part 9 while maintaining a high resonance frequency characteristic.

[0052] The thickness T of the torsion bar 13 is about 25% of the width W2 of the torsion bar 13. Since the width W2 of the torsion bar 13 in this embodiment is 160 μm, the thickness T can be reduced to 40 μm or less.

[0053] The torsion bar may have the same widths W1 and W2 as the torsion bar 13 shown in Fig. 5 and may have a straight portion in part. Fig. 6 shows a modified torsion bar 20 having a straight portion D.

[0054] Since the straight portion D includes the center portion in the longitudinal direction of the torsion bar 20, the width W2 is the narrowest portion of the width of the torsion bar 20. It is preferable that the straight portion D is 25% or less of the entire length L of the torsion bar 20. If this condition is satisfied, the torsion bar 20 has the same characteristics as the torsion bar 13 in FIG. 4 (details will be described later).

[0055] Next, with reference to FIG. 7, a torsion bar (reference example) that can be said to have a constricted shape but has deteriorated performance compared to this embodiment will be described.

[0056] The torsion bar 30 (reference example A) shown in Fig. 7(a) is a case where the width W4 is smaller than the ideal value (N<0.30) as described above. As shown in the figure, the torsion bar 30 has a shape in which the straight portion D is relatively long near the center (straight line m) in the longitudinal direction. With this shape (D>0.25 x L), a decrease in the resonance frequency was observed (details will be described later).

[0057] Moreover, the torsion bar 40 (reference example B) shown in Fig. 7(b) is a case where the width W4 is larger than the ideal value (N>0.35) described above. As shown in the figure, the torsion bar 40 has a portion that is wider than the width W2 near the center (straight line m) in the longitudinal direction. Therefore, there was a tendency for the rotation torque to increase and the limit swing angle to decrease (details will be described later).

[0058] Figure 8 shows the results of a simulation comparing the performance of various torsion bar shapes. This simulation used commercially available software (IntelliSuite) to measure the resonance frequency [Hz] and limit deflection angle [°] based on the conventional straight shape.

[0059] The torsion bar 13 in Fig. 4 ("New 1" in Fig. 8) has a shape (constricted shape) with a width W4 determined by N = 0.325, and has a resonance frequency of 102% and a limit swing angle of 134%, both of which are superior to the conventional (straight) shape. This proves that the shape of the torsion bar 13 in this embodiment leads to improved performance.

[0060] The torsion bar 20 in Fig. 6 ("New 2" in Fig. 8) has a shape including a straight portion D, with the width W4 determined as N = 0.325, and the resonance frequency was 99% and the limit swing angle was 147%, with the limit swing angle being better than the conventional one. As the resonance frequency was also almost the same as the conventional one, it can be said that the torsion bar may have a configuration including the straight portion D.

[0061] The torsion bar 30 in Fig. 7(a) ("Reference Example A" in Fig. 8) has a shape in which the width W4 is determined as N = 0.150, and the results obtained are a resonance frequency of 106% and a limit deflection angle of 98%. The torsion bar 40 in Fig. 7(b) ("Reference Example B" in Fig. 8) has a shape in which the width W4 is determined as N = 0.500, and the results obtained are a resonance frequency of 109% and a limit deflection angle of 89%. Since the scanning range of the mirror part 9 becomes narrower when the limit deflection angle decreases, it was determined that these reference examples are aspects in which the performance is degraded.

[0062] Finally, a comparison of the performance between the conventional and new torsion bar structures will be described with reference to FIG.

[0063] The conventional linear torsion bar had a width W2 of 220 μm at the center (linear m), a resonance frequency of 19,849 Hz, and a limit swing angle of 11.9°. Note that the rotational torque was compared in terms of a ratio, so the conventional structure was set to "1."

[0064] In contrast, the width W2 of the center (straight line m) of the new constricted torsion bar 13 is 160 [μm], which is 73% of the conventional width. The resonance frequency of the torsion bar 13 is 19,886 [Hz], which is almost the same as the conventional structure, and the limit swing angle is 13.8 [°], which is 116% of the conventional angle. In addition, the rotational torque was successfully reduced to 40% of the conventional torque.

[0065] As described above, the torsion bar 13 of the new structure is not only less susceptible to breakage than the conventional structure, but also has high device characteristics. The optical deflector of the present invention can be applied to products that are highly required to be small and thin.

[0066] The above-described embodiment is merely an example, and various modifications are possible. When the mirror portion 9 has a rectangular shape, the side of the mirror portion 9 adjacent to the torsion bar 13b becomes the edge of the connection portion. When the movable frame 8 has a rectangular shape, the side of the movable frame 8 adjacent to the torsion bar 13b becomes the edge of the connection portion. [Explanation of symbols]

[0067] 1...optical scanner module, 2...optical deflector, 3...light source, 4a, 4b...laser light, 5...control device, 6a, 6b...bellows-shaped piezoelectric actuator, 7a1-7a8, 7b1-7b8...electrode pads, 8...movable frame, 8a...inner frame body, 8b...outer frame body, 9...mirror portion, 10a, 10b...semi-annular piezoelectric actuator, 11...outer frame support, 13, 13a, 13b, 20, 30, 40...torsion bars.

Claims

1. a mirror portion that reflects light; a frame provided to surround the mirror portion; a pair of torsion bars, one end of each of which is connected to the mirror portion and the other end of each of which is connected to the frame body, on an axis passing through the center of the mirror portion; a piezoelectric actuator provided on the frame body and configured to rotate the torsion bar back and forth around the axis line, When a connection portion between the torsion bar and the mirror portion is defined as a first connection portion and a connection portion between the torsion bar and the frame body is defined as a second connection portion, the torsion bar has a narrowed shape in which the width is greatest at the first connection portion and the second connection portion and the width gradually narrows toward the center in the longitudinal direction, When the width of the first connecting portion or the second connecting portion of the torsion bar is W1, and the width of the center portion of the torsion bar in the longitudinal direction is W2, and it is defined as (W1 - W2) / 2 = W3, An optical deflector characterized in that the width W4 of the torsion bar at the center between the first connection portion or the second connection portion and the center portion in the longitudinal direction is given by W2 + 0.30 × W3 or more and W2 + 0.35 × W3 or less.

2. 2. The optical deflector according to claim 1, wherein when the mirror portion has a circular or elliptical shape, the end of the torsion bar on the first connection portion side is on a tangent to the circular or elliptical shape of the mirror portion, perpendicular to the axis.

3. An optical deflector as described in claim 1 or 2, characterized in that when the frame body has a circular or elliptical shape, the end of the torsion bar on the second connection portion side is on a straight line connecting the end points of the curves that constitute the circular or elliptical shape of the frame body.

4. The torsion bar has a straight portion including a center portion in a longitudinal direction, 4. The optical deflector according to claim 1, wherein the straight portion is 25% or less of the entire length of the torsion bar.

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