Light deflector

Abstract

To provide a light deflector with which it is possible to increase the maximum permissible rotation angle of a torsion bar when the aspect ratio of the torsion bar is smaller than 1.SOLUTION: A light deflector 10 comprises: a mirror unit 11; torsion bars 12a, 12b that extend from each side of the mirror unit 11 along a rotation axis Da; inside actuators 13a, 13b that bind to the outside coupling regions 36 of the torsion bars 12a, 12b and cause the torsion bars 12a, 12b to reciprocate around the rotation axis Da; and a slit 20a, a slit 20b that have a closed end, and that are formed in the torsion bars 12a, 12b, extending along the rotation axis Da over a length range reaching an inside coupling region 38 and the outside coupling region 36.SELECTED DRAWING: Figure 2A

Description

[Technical field]

[0001] The present invention relates to an optical deflector that is installed in a scanning device and emits scanning light. [Background technology]

[0002] An optical deflector manufactured as a MEMS (Micro Electro Mechanical Systems) device reflects an incoming laser beam onto a mirror portion that rotates back and forth around a rotation axis, and emits the reflected light from the mirror portion as scanning light (e.g., Patent Documents 1 to 3).

[0003] The optical deflector in Patent Document 1 comprises a mirror section, a pair of torsion bars, one on each side of the mirror section in the extension direction of the rotation axis of the mirror section, extending from the mirror section along the rotation axis, and a piezoelectric actuator coupled to the tip end of each torsion bar to rotate the torsion bar back and forth around the rotation axis.

[0004] The optical deflector in Patent Document 2 comprises a mirror section, a total of four torsion bars, two on each side of the mirror section in the extension direction of the rotation axis of the mirror section, extending parallel to the rotation axis with equal gaps between them, and a piezoelectric actuator connected to the tip end of each torsion bar to rotate the torsion bar back and forth around the rotation axis.

[0005] The optical deflector of Patent Document 3 comprises a mirror section, four torsion bars, two on each side of the mirror section in the direction of extension of the rotation axis, with holes drilled so that the distance between the two becomes narrower toward the tip (i.e., in a figure-eight shape), and an electrostatic actuator that rotates the mirror section back and forth around the rotation axis from both sides perpendicular to the rotation axis. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2009-169290 A [Patent Document 2] JP 2016-151681 A [Patent Document 3] Patent No. 3905539 Summary of the Invention [Problem to be solved by the invention]

[0007] It is desirable for an optical deflector to have a large scan angle corresponding to the reciprocating rotation angle of the mirror part about the rotation axis, but the maximum reciprocating rotation angle of the mirror part is limited by the maximum allowable stress of the torsion bar to prevent the torsion bar from being damaged as it rotates reciprocatingly.

[0008] When the view from the thickness direction of the mirror is taken as the front view, the ratio of the width of the torsion bar in the front view to the thickness of the torsion bar is defined as the aspect ratio (AR). The point where the maximum stress occurs in the torsion bar, i.e., the point most likely to break as the torsion bar rotates back and forth, is on the rotation axis of the torsion bar when viewed from the front, when AR>1. Also, when AR<1, it is the corner, which is the point farthest from the rotation axis in the cross section of the torsion bar.

[0009] In the optical deflector of Patent Document 1, AR<1, the points of maximum stress in the mirror are the four corners of the cross section of the mirror, and in order to increase the maximum reciprocating rotation angle of the mirror with this structure, the only way is to narrow the width or thickness of the torsion bar. Reducing the width or thickness of the torsion bar increases the harmonics generated in the mirror, inducing abnormal vibrations in the mirror (such as vibrations in the extension direction of the rotation axis or perpendicular to the rotation axis).

[0010] In Patent Document 2, the two torsion bars on each side of the mirror portion are completely open at the end opposite the mirror portion, with a gap extending in the width direction, reducing the transmission efficiency of the rotational force transmitted from the piezoelectric actuator to the torsion bars.

[0011] In the optical deflector of Patent Document 3, the connection points where the two torsion bars on each side of the mirror section are connected to the mirror section are two locations that are separated in a direction perpendicular to the rotation axis. Therefore, compared to when there is only one connection point, the rotational driving force of the torsion bars or the reversal driving force when the rotation is reversed is increased, and the load on the actuator is increased.

[0012] An object of the present invention is to provide an optical deflector capable of overcoming the above-mentioned problems of the prior art and increasing the maximum allowable rotation angle of the torsion bar when the aspect ratio AR of the torsion bar is AR<1. [Means for solving the problem]

[0013] The optical deflector of the present invention comprises: A mirror portion having a mirror surface on one side in a thickness direction and reciprocatingly rotating around a rotation axis (Da) perpendicular to the thickness direction; a pair of torsion bars extending along the rotation axis from inner joining positions at both ends of the mirror part in the extension direction of the rotation axis; an actuator that couples the torsion bar from both sides in a width direction at an outer coupling position separated from the inner coupling position in the extension direction, and rotates the torsion bar reciprocally around the rotation axis at the outer coupling position; a slit formed in the torsion bar such that, in a front view as a direction when the mirror surface is viewed from the one side in the thickness direction, both ends in the extension direction are closed and the both ends extend along the rotation axis within a range of lengths reaching the inner coupling position and the outer coupling position; Equipped with The torsion bar has a dimension between both ends of Wa and a thickness of Ta when viewed from the front, The slit has a width Wb in the front view, (Wa-Wb) / Ta<1. Effect of the Invention

[0014] According to the present invention, in an optical deflector in which the aspect ratio AR of the torsion bar is AR<1, the slits are formed in the torsion bar so that both ends in the extension direction are closed in a front view, and the slits extend along the rotation axis over a length range that reaches the inner coupling region and the outer coupling region at both ends. As a result, the stress acting on each torsion bar during reciprocal rotation around the rotation axis is distributed to four places, the side surfaces of the torsion bar and the inner surfaces of the slits, so that the reciprocal rotation angle when the maximum allowable stress is generated in the torsion bar can be increased. [Brief description of the drawings]

[0015] [Figure 1] FIG. 2 is a schematic diagram of the optical deflector as viewed obliquely from the front. [Figure 2A] FIG. 2 is an enlarged front view of a range including the torsion bar and its periphery in FIG. [Figure 2B] FIG. 2B is an enlarged view of the outer bond region area of ​​FIG. 2A. [Figure 2C] FIG. 2B is an enlarged view of the inner bond region area of ​​FIG. 2A. [Figure 3A] 2B is a front view showing an area having an inner extension portion having a shape different from that of the inner extension portion in FIG. 2A together with the inner ends of the torsion bars on both sides thereof. FIG. [Figure 3B] FIG. 3B is a close-up of the inner bond region of FIG. 3A. [Figure 4] 2 is a cross-sectional view of the optical deflector cut in the thickness direction along the axis Ax in FIG. 1 with the mirror portion in a stationary state. [Diagram 5] 5 is a cross-sectional view taken along a plane parallel to the cross section of FIG. 4 at the position of the equal-width extension portion of the torsion bar. [Figure 6] FIG. 2 is an explanatory diagram of the aspect ratio of a torsion bar. [Figure 7] FIG. 13 is a stress distribution diagram around a slit when the slit is composed only of an equal-width extension portion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described. The present invention includes configurations obtained by modifying the embodiment in various ways within the scope of design matters of those skilled in the art. Note that the same reference numerals are used throughout the drawings to refer to components common to multiple embodiments.

[0017] (Light deflector / whole) 1 is a schematic diagram of an optical deflector 10 as viewed obliquely from the front. The optical deflector 10 is manufactured as a MEMS (Micro Electro Mechanical Systems) device from an SOI substrate. For ease of explanation, a view in a thickness direction of the optical deflector 10 (which is also the thickness direction of the mirror section 11) from the incident side of the incident light La (the mirror surface side in the thickness direction of the mirror section 11) will be referred to as a "front view."

[0018] The overall configuration of the optical deflector 10 will be roughly described with reference to Fig. 1. Details of the overall configuration of the optical deflector 10 are as described in, for example, Japanese Patent Application Laid-Open No. 2012-201386 of the present applicant.

[0019] The optical deflector 10 is installed in any device equipped as an optical scanner, such as a projector (including a picoprojector), a head-up display, an automobile headlight, or eyewear.

[0020] The optical deflector 10 has a symmetrical structure when viewed from the front, and includes a mirror section 11, upper and lower torsion bars 12a, 12b, left and right inner actuators 13a, 13b, a movable frame 14, left and right outer actuators 15a, 15b, and a fixed frame 16. The inner actuators 13a, 13b and the outer actuators 15a, 15b are all piezoelectric actuators.

[0021] For the convenience of explaining the configuration of the optical deflector 10, orthogonal axes Ax and Ay are defined at the center O of the mirror section 11. The axes Ax and Ay are defined as coordinate axes parallel to the mirror surface (the reflective film 64 in FIG. 4) of the mirror section 11, and are also two orthogonal rotation axes of the mirror section 11. Moreover, in the optical deflector 10, the sides closer to and farther from the center O are referred to as the inside and the outside, respectively.

[0022] The circular mirror section 11 has a reflective film 64 (FIG. 4) acting as a mirror surface on its front surface (one side in the thickness direction of the mirror section 11). Incident light La is emitted from a laser light source (not shown), enters the mirror section 11, is reflected by the mirror section 11, and is emitted from the mirror section 11 as scanning light Lb.

[0023] The torsion bars 12a, 12b extend along the axis Ay and mutually connect the mirror unit 11 and the movable frame 14. The inner actuators 13a, 13b have a peripheral contour shape that is long in the vertical direction when viewed from the front and connected to each other from the left and right, and each has an elliptical arc shape that is a semi-ellipse on the left and right.

[0024] 1, the torsion bars 12a and 12b extend from the mirror portion 11, pass beyond the joints with the inner actuators 13a and 13b, reach the movable frame 14, and are joined to the inner periphery of the movable frame 14. However, the torsion bars 12a and 12b may also be structured so as to remain at the positions of the joints with the inner actuators 13a and 13b without reaching the inner periphery of the movable frame 14.

[0025] The movable frame 14 has a vertically elongated elliptical contour shape similar to the overall shape of the left and right inner actuators 13a, 13b connected to each other in a front view, and surrounds the mirror unit 11, the torsion bars 12a, 12b, and the inner actuators 13a, 13b from the outside. The inner actuators 13a, 13b are interposed between the movable frame 14 and the torsion bars 12a, 12b.

[0026] The inner actuators 13a and 13b are supplied with driving voltages of a sine wave of a resonance frequency Fy with mutually opposite phases from a driving device (not shown), and reciprocally rotate the torsion bars 12a and 12b around the axis Ay at the resonance frequency Fy.

[0027] The outer actuators 15a and 15b are disposed on the left and right sides of the movable frame 14 and are interposed between the outer periphery of the movable frame 14 and the inner periphery of the fixed frame 16. The outer actuators 15a and 15b are composed of a plurality of linear piezoelectric cantilevers connected in series in a meander pattern. When the outer actuators 15a and 15b are numbered in order from the outside to the inside in the lateral direction (the direction parallel to the long side of the rectangular fixed frame 16), the odd-numbered piezoelectric cantilevers and the even-numbered piezoelectric cantilevers are supplied with driving voltages of a sawtooth wave or a triangular wave of a non-resonance frequency Fx (Fx < Fy) with mutually opposite phases from a control device (not shown). Thereby, the outer actuators 15a and 15b reciprocally rotate the movable frame 14 around a lateral rotation axis (different from the axis Ax).

[0028] A general operation of the entire optical deflector 10 will be described.

[0029] During the operation of the optical deflector 10, driving voltages are supplied from a driving device (not shown) to the torsion bar 12 (a general term for the torsion bars 12a and 12b) and the outer actuator 15 (a general term for the outer actuators 15a and 15b). Thereby, the mirror unit 11 reciprocally rotates around the axes Ax and Ay at non-resonance frequencies Fx and resonance frequency Fy, respectively. Fx and Fy are, for example, 60 Hz and 25 kHz, respectively.

[0030] On the other hand, incident light La of a laser beam from a laser light source (not shown) is incident on the mirror unit 11 that is reciprocally rotating around the axes Ax and Ay. Thereby, scanning light Lb as reflected light of the incident light La is emitted as a two-dimensional scanning beam from the mirror unit 11.

[0031] The incident light La may be three laser beams of different colors, red, green, and blue, or may be a single predetermined color. A light source control device (not shown) is capable of controlling the luminance (intensity) of the incident light La emitted from the laser light source for each color.

[0032] (Configuration of slits in the embodiment) Fig. 2A is an enlarged front view of the range including the torsion bars 12a, 12b and their surroundings in Fig. 1. Da is the vertical rotation axis of the mirror part 11, which extends on the axis Ay in Fig. 1. Note that in Fig. 2A and subsequent figures, the outer ends (ends farther from the center O) of the torsion bars 12a, 12b do not reach the inner periphery of the movable frame 14, and remain at the coupling positions with the torsion bars 12a, 12b.

[0033] The torsion bars 12a and 12b are formed with slits 20a and 20b, respectively. In the range including the mirror portion 11, the torsion bars 12a and 12b, and the inner actuators 13a and 13b, the structure is vertically symmetrical with respect to the axis Ax (FIG. 1) in the front view. Therefore, the configuration and function of the upper torsion bar 12a and slit 20a will be described, and the configuration and function of the lower torsion bar 12b and slit 20b will be omitted.

[0034] 2A, the slit 20a is formed in the torsion bar 12a so as to extend along the rotation axis Da and penetrate in the thickness direction. The slit 20a has an equal-width extension portion 22 that extends along the rotation axis Da with an equal width, and an outer expanded end portion 24a and an inner expanded end portion 24b that are connected to the outer and inner ends of the equal-width extension portion 22, respectively.

[0035] The circumferential line of the mirror portion 11 disappears at the joint between the mirror portion 11 and the torsion bar 12a. If the boundary line between the mirror portion 11 and the torsion bar 12a is set on the disappeared circumferential line, the equal-width extension portion 22 of the slit 20 reaches at least the boundary line toward the inside, and typically crosses the boundary line and enters the mirror portion 11. Note that the boundary line means the joint position between the mirror portion 11 and the torsion bar 12a.

[0036] The torsion bar 12a and the inner actuators 13a, 13b are mutually bonded in an outer bonding region 36. The outer bonding region 36 is defined as a region that is inside the left and right ends of the left and right curved outer corners (first corners) 30a, 30b in the width direction, outside the ends of the left and right curved outer corners 30a, 30b on the center O side in the extension direction, and inside the outer peripheral contours of the inner actuators 13a, 13b in the extension direction. The outer bonding region 36 refers to the bonding position between the torsion bar 12a and the mirror section 11 as a whole.

[0037] The mirror section 11 and the torsion bar 12a are mutually bonded in an inner bonding region 38. The inner bonding region 38 is defined as a region located inside the left and right ends of the left and right curved inner corners (second corners) 32a, 32b in the width direction and toward the center O from the ends of the left and right curved inner corners 32a, 32b farther from the center O in the extension direction. Furthermore, the inner bonding region 38 is defined as a region in the mirror section 11 where a predetermined stress is generated when the mirror section 11 rotates back and forth around the rotation axis Da. The inner bonding region 38 as a whole refers to the bonding position between the torsion bar 12a and the mirror section 11.

[0038] The curved outer corners 30a, 30b are formed at the corners between the side edges of the torsion bar 12a and the inner peripheral edges of the inner actuators 13a, 13b as first curved lines that extend outward from the side edges of the mirror section 11 in the width direction of the torsion bar 12a (direction perpendicular to the extension direction of the rotation axis Da and the thickness direction) and are curved inwardly of the outer bonding region 36. The curved inner corners (second corners) 32a, 32b are formed at the corners between the peripheral edge of the mirror section 11 and the side edges of the torsion bar 12a as second curved lines that extend outward from the side edges of the mirror section 11 in the width direction and are curved inwardly of the inner bonding region 38.

[0039] 2B and 2C are enlarged views of the ranges of the outer bonded region 36 and the inner bonded region 38 in FIG. 2A, respectively. The outer expanded end 24a and the inner expanded end 24b of the slit 20a are formed in the outer bonded region 36 and the inner bonded region 38, respectively. The stress relaxation as an effect of the outer expanded end 24a and the inner expanded end 24b will be described in detail in FIG. 7 described later. Here, only the configurations of the outer expanded end 24a and the inner expanded end 24b will be described with reference to FIG. 2B and FIG. 2C.

[0040] 2B, in front view, the outer expansion end 24a is circular (an example of a first curved contour shape) except for the boundary portion between the outer expansion end 24a and the equal-width extension portion 22. Meanwhile, the contour line of the boundary portion is set to a contour line that extends parallel to the first curved line of the curved outer corners 30a, 30b with approximately equal width.

[0041] The diameter of the outer expanded end 24a is larger than the width (Wb in FIG. 6 described later) of the constant-width extension portion 22, and the outer expanded end 24a is wider in the width direction of the slit 20a than the constant-width extension portion 22. The curved outer corners 30a, 30b serve to reinforce the outer expanded end 24a against widthwise expansion.

[0042] In Fig. 2C, the inner extension end 24b is formed in a shape (an example of a second curved contour shape) that is symmetrical with respect to the rotation axis Da in a front view. The inner extension end 24b is formed as a through hole defined by the outer curved contour parts 44a, 44b closer to the periphery of the mirror part 11 and the inner curved contour part 46 closer to the center O. The outer curved contour parts 44a, 44b are set to contour lines that are parallel to the second curved lines of the curved inner corner parts 32a, 32b with approximately the same width. The significance of such a contour line of the inner extension end 24b will be described later in comparison with the inner extension end 24c of the cylindrical hole in Figs. 3A and 3C.

[0043] The inner curved contour portion 46 is set to the contour line of a circular arc concentric with the circle of the mirror portion 11. The width of the inner extension end 24b is greater than the width of the constant-width extension portion 22, and the inner extension end 24b is wider in the width direction of the slit 20a than the constant-width extension portion 22. The curved inner corners 32a, 32b serve to reinforce the outer extension end 24a against widthwise expansion.

[0044] Fig. 3A is a front view of a range including the mirror part 11 and the inner ends of the torsion bars 12a and 12b in the extending direction of the rotation axis Da. Fig. 3B is an enlarged view of the inner joint region 38. The inner extension end 24c has the same shape as the outer extension end 24a, that is, a cylindrical hole (another example of the second curved contour shape), and is formed in the inner joint region 38 symmetrically with respect to the rotation axis Da, penetrating the mirror part 11. The boundary between the equal-width extension part 22 and the inner extension end 24c is set to a contour line extending parallel to the second curved line.

[0045] The diameter of the inner expanded end 24c is larger than the width of the uniform-width extension 22, and the inner expanded end 24c is wider in the width direction of the slit 20a than the uniform-width extension 22. The curved outer corners 30a and 30b serve to reinforce the inner expanded end 24c against widthwise expansion.

[0046] (Cross-sectional structure) 4 is a cross-sectional view taken in the thickness direction of the optical deflector 10 along the axis Ax in FIG. 1 with the mirror portion 11 in a stationary state, and FIG. 5 is a cross-sectional view taken along a plane parallel to the cross section of FIG. 4 at the position of the equal-width extension portion 22 of the torsion bar 12a.

[0047] 4 and 5, the SOI substrate 50 has a five-layered structure of, from the top, an oxide layer 51, an active layer 52, an oxide layer 53, a handling layer 54, and an oxide layer 55. The oxide layer 51, the oxide layer 53, and the oxide layer 55 are made of SiO2. The active layer 52 and the handling layer 54 are made of Si. The piezoelectric element 58 has a three-layered structure of, from the top, an upper electrode layer 59, a PZT (lead zirconate titanate) film layer 60, and a lower electrode layer 61.

[0048] The mirror section 11, torsion bar 12a and fixed frame 16 are composed of all layers of the SOI substrate 50. In contrast, the inner actuator 13a and the outer actuators 15a and 15b are composed of a three-layer laminate consisting of two oxide film layers 51 and an active layer 52 from the top of the SOI substrate 50, and a piezoelectric element 58 laminated thereon. The surface of the mirror section 11 is covered with a reflective film 64 made of a metal component. The reflective film 64 acts as a mirror surface that reflects incident light La (FIG. 1).

[0049] 5, the uniform-width extending portion 22 of the slit 20a penetrates the torsion bar 12a in the thickness direction. Although not shown, the outer extended end 24a and the inner extended end 24b of the slit 20a also penetrate the outer extended end 24a of the torsion bar 12a and the inner extended end 24b of the mirror portion 11 in the thickness direction, similar to the uniform-width extending portion 22.

[0050] The slits 20a in the torsion bar 12a are manufactured by deep RIE. Typical deep RIE methods include a method in which a sample is cooled to a low temperature using high-density plasma, a method in which an etching technique called the Bosch process is used, or a method in which both methods are used.

[0051] Although not shown in the figure, the laminated structure of the cross section in the outer bonding region 36 will be described. In the outer bonding region 36, the upper electrode layer 59 and the PZT film layer 60 of the three-layer laminate of the piezoelectric element 58 are removed by etching, and only the lower electrode layer 61, which is the bottom layer, remains without being removed. The lower electrode layer 61 is a layer of earth voltage, and as a result of the lower electrode layer 61 remaining in the outer bonding region 36, the lower electrode layers 61 of the left and right inner actuators 13a, 13b are electrically connected to each other in the outer bonding region 36. On the other hand, the left and right inner actuators 13a, 13b are separated in the outer bonding region 36 by the upper electrode layer 59 and the PZT film layer 60, so that they are supplied with a driving voltage and can be driven individually.

[0052] (Aspect Ratio) 6 is an explanatory diagram of the aspect ratio AR of the torsion bar 12a. In FIG. 6, the definitions of the various symbols are as follows: Wa: Width of both ends of the torsion bar 12a as viewed from the front Wb: Width of the equal width extension 22 as viewed from the front Wc: Width of the left and right portions of the torsion bar 12a divided into left and right portions by the equal-width extension portion 22 as viewed from the front Ta: thickness of the torsion bar 12a

[0053] As is clear from FIG. 6, the following equation (1) holds: This relationship is essential in the present invention. (1) Formula: Wa=Wb+2·Wc

[0054] In the present invention, it is set as shown in the following formula (2). (2) Formula: (Wa-Wb) / Ta<1

[0055] In the optical deflector 10 of the embodiment, from the viewpoint of suppressing harmonics, it is preferable to set the dimensions as shown in the following expressions (3) to (6). (3) Formula: 0.1≦(Wa-Wb) (4) Formula: Wb=Wc (5) Equation: Wa / Ta<1 (6) Formula: Wb≦2·Wc

[0056] The significance of formula (5) is that although the slits 20a, 20b are formed to prevent damage from occurring at the corners of the cross sections of the torsion bars 12a, 12b, if Wa / Ta≧1, damage may occur first on the rotation axis of the torsion bars 12a, 12b, which may defeat the purpose of forming the slits 20a, 20b. The significance of formula (6) is that if Wb>2·Wc, the vibration (pumping) of the mirror part 11 in the extension direction of the rotation axis Da becomes dominant. Also, it is advantageous for Wb to be 25 μm or more.

[0057] The two torsion bars facing each other in the width direction in Patent Document 3 have figure-eight holes formed therein, and the torsion bars are too far apart from each other to be considered slits according to the present invention, but are mathematically included in Wb>2·Wc, which increases the rotational driving force of the torsion bars or the reversal driving force when the rotation is reversed, increasing the load on the actuator.

[0058] Furthermore, if the aspect ratio of the torsion bar before the formation of the slits 20a is Wa / Ta=(Wa+2·Wc) / Ta<1, stress is applied to the torsion bar when it rotates back and forth around the rotation axis, but by providing the slits of the present invention in the torsion bar, it is possible to relieve the stress.

[0059] (Function and effect of the equal width extension portion) The effects of the torsion bar 12 (general term for the torsion bars 12a and 12b) will be described. First, the effects of the slit 20 having only the equal-width extending portion 22 in the middle, omitting the outer expanded end portion 24a and the inner expanded end portion 24b at both ends, will be described.

[0060] Since the torsion bar 12 has slits 20 (a collective term for slits 20a and 20b) with equal-width extensions 22, the total area of ​​the side surfaces is the area of ​​the outer side surfaces in the width direction plus the area of ​​the inner side surfaces of the slits 20 as the inner side surfaces. As a result, the area of ​​the side surfaces is increased, and the stress acting on the side surfaces is dispersed. This leads to a reduction in the stress in the torsion bar 12, and the maximum allowable rotation angle of the torsion bar 12 around the rotation axis Da without breakage is increased. Thus, the lateral scanning angle of the scanning light Lb around the rotation axis Da is increased.

[0061] According to the calculations of the inventors, the unit rotation angle (unit deflection angle: Mpa / deg) of the torsion bar 12 around the rotation axis Da is reduced by 25% due to the stress dispersion effect of the inner surface of the slit 20. This means that the limit deflection angle of the torsion bar 12 around the rotation axis Da is increased by 1.33 times.

[0062] (Stress relief structure) Fig. 7 is a stress distribution diagram around the slit 20a when the slits 20a, 20b of the optical deflector 10 do not have the outer extended end portion 24a and the inner extended end portions 24b, 24c, but have only the equal-width extension portion 22. Fig. 7 is a diagram showing a screen display based on the analysis results of a simulation, and shows that the stress increases from the dark areas to the light areas.

[0063] In the case where the outer expansion end 24a and the inner expansion end 24b are omitted in the slits 20a and 20b and only the equal-width extension portion 22 is formed, the maximum stress points appear at both ends of the equal-width extension portion 22. The white dashed circles Ca and Cb are shown as circles centered on the outer end and the inner end of the equal-width extension portion 22 of the slit 20a. It can be seen that the areas of high stress spread outward and inward from the outer end and the inner end of the equal-width extension portion 22, respectively, in the extension direction of the equal-width extension portion 22.

[0064] The position of the inner bonding region 38 will be described with reference to Fig. 7. As described above, the circumferential line of the mirror portion 11 disappears at the bonding portion between the mirror portion 11 and the torsion bar 12a. When the boundary line between the mirror portion 11 and the torsion bar 12a is set on the disappeared circumferential line, the inner bonding region 38 is set as a region on the mirror portion 11 side of the boundary line where a stress of a predetermined value or more is generated in the mirror portion 11.

[0065] In the optical deflector 10, an outer extended end 24a and an inner extended end 24b or an inner extended end 24c are connected to both ends of the equal-width extension portion 22 so that the maximum stress in the torsion bars 12a, 12b is equal to or lower than a predetermined upper limit.

[0066] The stress transmitted from the mirror portion 11 to the torsion bars 12a, 12b in the outward direction along the rotation axis Da is divided into left and right portions of the torsion bars 12a, 12b on both sides of the slit 20 in the width direction and transmitted in parallel to the inner joint region 38. The circular shape of the outer extension end portion 24a in front view has the effect of appropriately dispersing the stress transmitted in parallel to the left and right, making the stress uniform in the inner joint region 38 and reducing the maximum stress. The reduction in the maximum stress leads to an increase in the maximum allowable reciprocating angle of the mirror portion 11 around the rotation axis Da.

[0067] The effect of the inner extension end 24c will be described before the effect of the inner extension end 24b. The effect of the inner extension end 24c is the same as that of the outer extension end 24a. That is, the stress transmitted inward from the torsion bars 12a, 12b along the rotation axis Da in the mirror part 11 is divided into the left and right parts of the torsion bars 12a, 12b on both sides of the slit 20 in the width direction and transmitted in parallel to the mirror part 11. The circular shape of the inner extension end 24c in front view, like the outer extension end 24a, appropriately distributes the stress transmitted in parallel to the left and right, uniformizing the stress in the inner joint region 38 and reducing the maximum stress. The inner extension end 24c has a simpler shape than the inner extension end 24b, and therefore has the advantage of being less expensive to manufacture.

[0068] In order to reduce the maximum stress in the outer bonding region 36 and the inner bonding region 38, it may be advantageous in some cases to move the outer end and / or the inner end of the slit 20 slightly outward and inward, respectively, along the rotation axis Da from that shown in Fig. 7 before connecting the outer expanded end 24a and the inner expanded end 24b, 24c. In such a case, the outer end and / or the inner end of the slit 20 are not fixed to that shown in Fig. 7, but are appropriately advanced deeply into the outer bonding region 36 and the inner bonding region 38, respectively, along the rotation axis Da, and then the positions of the outer expanded end 24a and the inner expanded end 24b, 24c are set.

[0069] Next, the advantage of the inner extension end 24b over the inner extension end 24c will be described. The inner end of the inner extension end 24b is located outward in the extension direction of the rotation axis Da from the inner end of the inner extension end 24c. This means that the beam cross section of the incident light La is irradiated onto the entire surface of the mirror section 11, which is approximately circular.

[0070] In the inner extension end 24c (FIGS. 3A and 3B), the closest point to the center O penetrates deeply into the mirror portion 11 toward the center O. This means that the effective diameter of the mirror portion 11 in the direction of extension of the rotation axis Da is reduced, which causes a decrease in the resolution of the image generated by the scanning light Lb in the irradiation area of ​​a screen or the like. In contrast, the inner extension end 24b is formed along the circumferential contour of the mirror portion 11, and the closest point to the center O can be sufficiently farther away than the inner extension end 24c. Therefore, the torsion bar 12a relieves the stress of the inner ends of the torsion bars 12a and 12b while minimizing the reduction in the effective diameter of the mirror portion 11. This makes it possible to increase the reciprocating rotation angle of the mirror portion 11 around the rotation axis Da while avoiding the reduction in the effective diameter of the mirror portion 11.

[0071] In the optical deflector of the above-mentioned Patent Document 2, two torsion bars are provided on each side of the mirror section, not one on each side. That is, a gap is formed between the two torsion bars, and this gap is closed on the inside, i.e., the mirror section side, but is not closed on the outside, i.e., the opposite side of the mirror section, and is open. This means that two torsion bars are provided on each side of the mirror section.

[0072] In contrast, in the optical deflector 10, the slits 20a, 20b are closed at both ends in the direction in which the rotation axis extends, so that the torsion bars 12a, 12b in which the slits 20a, 20b are formed on the inner periphery side do not separate into two, but maintain a single torsion bar, and the optical deflector 10 is configured to have only one torsion bar on each side of the mirror section 11. As a result, the efficiency of force transmission from the inner actuators 13a, 13b to the torsion bars 12a, 12b in the optical deflector 10 is increased compared to the configuration of two torsion bars on each side of the optical deflector in Patent Document 2, and according to calculations by the inventors, the drive efficiency of the mirror section 11 around the rotation axis Da is improved by 29%.

[0073] (Modification) The optical deflector 10 is a two-axis scanning type optical deflector, but the optical deflector of the present invention may be a one-axis scanning type optical deflector as long as it has a configuration in which an actuator rotates the mirror portion back and forth around a rotation axis via a torsion bar.

[0074] The outer expanded end 24a and the inner expanded end 24b of the slits 20a, 20b are substantially circular in front view. However, the outer end and the inner end of the slit of the present invention may be a through hole that is symmetrical with respect to the rotation axis Da and has a regular polygon shape (e.g., an equilateral triangle, a square, a regular pentagon, etc.) in front view.

[0075] In the optical deflector 10, the equal-width extending portion 22 has been described as having the same width, but in the present invention, the extending portion at the location where the equal-width extending portion 22 of the optical deflector 10 is formed does not have to have an equal width over the entire length when viewed from the front. For example, both ends of the extending portion may have the same width when viewed from the front, and the width of the middle portion may be wider or narrower, or the widths of both ends of the extending portion may be different from each other, to the extent that the driving force by the inner actuators 13a and 13b is not significantly increased. [Explanation of symbols]

[0076] 10···optical deflector, 11···mirror portion, 12a, 12b···torsion bars, 13a, 13b···inner actuator, 14···movable frame, 20a, 20b···slit, 22···equal-width extension portion, 24a···outer extension end portion (outer end portion), 24b, 24c···inner extension end portion (inner end portion), 30a, 30b···curved outer corner portion (first corner portion), 32a, 32b···curved inner corner portion (second corner portion), 36···outer coupling region, 38···inner coupling region, 44···outer curved contour portion, 46···inner curved contour portion, Da···rotation axis.

Claims

1. a mirror portion having a mirror surface on one side in a thickness direction and rotating back and forth around a rotation axis (Da) perpendicular to the thickness direction; a pair of torsion bars extending along the rotation axis from inner coupling positions on both ends of the mirror portion in the extension direction of the rotation axis; an actuator that couples the torsion bar from both sides in the width direction at an outer coupling position separated from the inner coupling position in the extension direction, and rotates the torsion bar reciprocally around the rotation axis at the outer coupling position; a slit formed in the torsion bar so that, in a front view as a direction when the mirror surface is viewed from the one side in the thickness direction, both ends in the extension direction are closed, and the slit extends along the rotation axis within a length range included between the inner coupling position and the outer coupling position in the extension direction; Equipped with The torsion bar has a dimension Wa between both ends when viewed from the front and a thickness Ta, The slit has a width Wb in the front view, (Wa-Wb) / Ta<1, In the front view, a side edge of a first corner portion between a side edge of the torsion bar and a side edge of the actuator is formed by a first curved line that extends outward from the side edge of the torsion bar in the width direction and is a curve that is convex toward the inside of the first corner portion, An optical deflector, wherein the slit has a first curved contour shape whose width in the width direction is wider than Wb, and has an outer end formed within an outer coupling region that is set as an area that includes the outer coupling position.

2. In the optical deflector according to claim 1, The optical deflector, wherein the first curved contour shape is circular in the front view.

3. a mirror portion having a mirror surface on one side in a thickness direction and rotating back and forth around a rotation axis (Da) perpendicular to the thickness direction; a pair of torsion bars extending along the rotation axis from inner coupling positions on both ends of the mirror portion in the extension direction of the rotation axis; an actuator that couples the torsion bar from both sides in the width direction at an outer coupling position separated from the inner coupling position in the extension direction, and rotates the torsion bar reciprocally around the rotation axis at the outer coupling position; a slit formed in the torsion bar so that, in a front view as a direction when the mirror surface is viewed from the one side in the thickness direction, both ends in the extension direction are closed, and the slit extends along the rotation axis within a length range included between the inner coupling position and the outer coupling position in the extension direction; Equipped with The torsion bar has a dimension Wa between both ends when viewed from the front and a thickness Ta, The slit has a width Wb in the front view, (Wa-Wb) / Ta<1, In the front view, a side edge of a second corner between a side edge of the mirror portion and a side edge of the torsion bar is formed by a second curved line that extends outward from the side edge of the torsion bar in the width direction and is a curve that is convex toward the inside of the second corner, An optical deflector, wherein the slit has a second curved contour shape whose width in the width direction is wider than Wb, and has an inner end formed within an inner bonding area that is set as an area that includes the inner bonding position.

4. 4. The optical deflector according to claim 3, the mirror portion is circular in the front view, an optical deflector, wherein, in the front view, the second curved contour shape includes an inner curved contour portion extending in an arc concentric with the circle, and an outer curved contour portion located closer to the peripheral edge of the mirror portion than the inner curved contour portion and extending from both ends of the inner curved contour portion parallel to the second curved line.

5. 5. The optical deflector according to claim 3, a side edge of a first corner portion between a side edge of the torsion bar and a side edge of the actuator is formed by a first curved line that extends outward from the side edge of the torsion bar in the width direction and is a curve that convexly extends inward from the first corner portion, when viewed from the front, An optical deflector, wherein the slit has a first curved contour shape whose width in the width direction is wider than Wb, and has an outer end formed within an outer coupling region that is set as an area that includes the outer coupling position.

6. 5. The optical deflector according to claim 1, An optical deflector, wherein the slit extends with a uniform width along the rotation axis when viewed from the front within a length range included between the inner coupling position and the outer coupling position in the extension direction.

7. 5. The optical deflector according to claim 1, An optical deflector, wherein Wa / Ta<1.

8. 5. The optical deflector according to claim 1, An optical deflector, wherein Wb≦2·Wc.

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