Optical deflector

Abstract

An optical deflector (10) is provided with: a mirror unit (11); torsion bars (12a, 12b) extending from each side of the mirror part (11) along the rotation axis (Da); inner actuators (13a, 13b) coupled from both sides in an outer coupling region (36) of the torsion bars (12a, 12b) to reciprocate the torsion bars (12a, 12b) about a rotation axis (Da); and slits (20a, 20b) which have both closed ends, extend along the rotation axis (Da) over the entire length to the inside coupling region (38) and the outside coupling region (36), and are formed in the torsion bars (12a, 12b).

Description

Technical Field

[0001] The present invention relates to an optical deflector that is mounted on a scanning device and emits scanning light. Background Art

[0002] An optical deflector manufactured as a MEMS (Micro Electro Mechanical Systems) device causes a mirror unit that reciprocally rotates about a rotation axis to reflect an incident laser beam, and emits the reflected light as scanning light from the mirror unit (for example, Patent Documents 1 to 3).

[0003] The optical deflector of Patent Document 1 includes: a mirror unit; a pair of torsion bars, each having one on each side of the mirror unit in the extending direction of the rotation axis of the mirror unit, and extending from the mirror unit along the rotation axis; and a piezoelectric actuator that is coupled to the front end side end portions of the respective torsion bars to cause the torsion bars to reciprocally rotate about the rotation axis.

[0004] The optical deflector of Patent Document 2 includes: a mirror unit; a total of four torsion bars, each having two on each side of the mirror unit in the extending direction of the rotation axis of the mirror unit, and extending in parallel along the rotation axis with equal-width gaps therebetween; and a piezoelectric actuator that is coupled to the front end side end portions of the respective torsion bars to cause the torsion bars to reciprocally rotate about the rotation axis.

[0005] The optical deflector of Patent Document 3 includes: a mirror unit; a total of four torsion bars, each having two on each side of the mirror unit in the extending direction of the rotation axis, and having holes formed therein such that the interval between two of them becomes narrower toward the front end side farther from the mirror unit (i.e., in a V shape); and an electrostatic actuator that causes the mirror unit to reciprocally rotate about the rotation axis from both sides in a direction perpendicular to the rotation axis.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2009-169290

[0009] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2016-151681

[0010] Patent Document 3: Japanese Patent No. 3905539 Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] The light deflector preferably has a relatively large scanning angle corresponding to the reciprocating rotation angle of the mirror unit about the rotation axis. On the other hand, in order to prevent the torsion bar from breaking due to the reciprocating rotation, the maximum reciprocating rotation angle of the mirror unit is limited by the maximum allowable stress of the torsion bar.

[0013] When observing from the thickness direction of the mirror unit as the front view, the ratio of the width of the torsion bar to the thickness of the torsion bar in the front view is defined as the aspect ratio A.R. (Aspect Ratio). When A.R. > 1, the position where the maximum stress in the torsion bar is generated, that is, the part that is most likely to break as the torsion bar reciprocates, is the part of the torsion bar on the rotation axis in the front view. In addition, when A.R. < 1, it is the corner part that is farthest from the rotation axis on the cross-section of the torsion bar.

[0014] In the light deflector of Patent Document 1, A.R. < 1, and the part with the maximum stress of the mirror unit is the four corners of the cross-section of the mirror unit. In this structure, in order to increase the maximum reciprocating rotation angle of the mirror unit, only the width or thickness of the torsion bar can be narrowed. The reduction of the width and thickness of the torsion bar increases the higher harmonics generated in the mirror unit, becoming the cause of abnormal vibration of the mirror unit (vibration in the extending direction of the rotation axis, vibration in the direction perpendicular to the rotation axis, etc.).

[0015] In Patent Document 2, the two torsion bars on each side of the mirror unit are completely opened by a gap extending in the width direction at the end on the side opposite to the mirror unit. Therefore, the transmission efficiency of the rotational force transmitted from the piezoelectric actuator to the torsion bar is reduced.

[0016] In the light deflector of Patent Document 3, the two binding points where the two torsion bars on each side of the mirror unit are combined with the mirror unit become two separated parts in the direction perpendicular to the rotation axis. Therefore, compared with the case of one part, the driving force for rotation of the torsion bar or the reverse driving force during rotation reversal increases, and the load on the actuator increases.

[0017] An object of the present invention is to provide a light deflector that can overcome the above problems of the prior art and increase the maximum allowable rotation angle of the torsion bar when the aspect ratio A.R. of the torsion bar is A.R. < 1.

[0018] Means for Solving the Problem

[0019] The light deflector of the present invention includes:

[0020] A mirror unit having a reflecting surface on one side in the thickness direction and reciprocatingly rotating about a rotation axis (Da) perpendicular to the thickness direction;

[0021] A pair of torsion bars extending along the rotation axis from the inner binding positions at both ends of the mirror unit in the extending direction of the rotation axis;

[0022] An actuator that couples to both sides in the width direction of the torsion bar at an outer coupling position away from the inner coupling position in the extension direction, and causes the torsion bar to reciprocally rotate about the rotation axis at the outer coupling position; and

[0023] A slit formed in the torsion bar in such a manner that, when viewed from the front as the front view when observing the reflection mirror surface from one side in the thickness direction, both ends in the extension direction are closed, and it extends along the rotation axis within a length range where the both ends reach the inner coupling position and the outer coupling position,

[0024] The size between both ends of the torsion bar is Wa and the thickness is Ta when viewed from the front,

[0025] The width of the slit is Wb when viewed from the front,

[0026] (Wa - Wb) / Ta < 1.

[0027] Advantages of the Invention

[0028] According to the present invention, in an optical deflector in which the aspect ratio A.R. of the torsion bar is A.R. < 1, a slit is formed in the torsion bar in such a manner that, when viewed from the front, both ends in the extension direction are closed, and it extends along the rotation axis within the entire length range where the both ends reach the inner coupling region and the outer coupling region. Thus, when reciprocally rotating about the rotation axis, the stress applied to each torsion bar is dispersed over four surfaces, namely the side surface of the torsion bar and the inner side surface of the slit, and therefore, the reciprocal rotation angle when the maximum allowable stress is generated in the torsion bar can be increased. Description of the Drawings

[0029] Figure 1 is a schematic view of the optical deflector observed obliquely from the front.

[0030] Figure 2A is Figure 1 a front view of an enlarged range including the torsion bar and its periphery in

[0031] Figure 2B is Figure 2A an enlarged view of the range of the outer coupling region of

[0032] Figure 2C is Figure 2A an enlarged view of the range of the inner coupling region of

[0033] Figure 3A is a front view showing a range including an inner expansion portion having a shape different from that of the inner expansion portion of Figure 2A and the inner ends of the torsion bars on both sides thereof.

[0034] Figure 3B is Figure 3A an enlarged view of the inner joint area of

[0035] Figure 4 is a cross-sectional view taken along the Figure 1 axis Ax of

[0036] Figure 5 in the thickness direction of the deflector when sliced in a plane parallel to the cross-section of Figure 4 at the position of the equal-width extension of the torsion bar.

[0037] Figure 6 is an explanatory diagram regarding the aspect ratio of the torsion bar.

[0038] Figure 7 is a stress distribution diagram around the slit when the slit is composed only of the equal-width extension. Detailed Embodiment

[0039] Hereinafter, embodiments of the present invention will be described. The present invention includes configurations in which various changes have been made to the embodiments within the scope of design matters of those skilled in the art. In addition, for constituent elements common to multiple embodiments, the same reference numerals are used in all the figures.

[0040] (Deflector / Overall)

[0041] Figure 1 is a schematic view of the deflector 10 observed obliquely from the front. The deflector 10 is a MEMS (MicroElectro Mechanical Systems) device and is fabricated from an SOI substrate. For ease of explanation, when observing along the thickness direction of the deflector 10 (which is also the thickness direction of the mirror section 11) from the incident side of the incident light La (on the mirror surface side in the thickness direction of the mirror section 11), it is referred to as "when observing from the front".

[0042] Referring to Figure 1 , the overall structure of the deflector 10 will be schematically described. The detailed content of the overall structure of the deflector 10 is described, for example, in Japanese Patent Application Laid-Open No. 2012-201386 of the present applicant.

[0043] The deflector 10 is mounted on any device installed as an optical scanner, such as a projector (including a micro-projector), a head-up display, an automotive headlamp, or glasses.

[0044] When viewed from the front, the optical deflector 10 has a bilaterally symmetric structure, and includes a mirror section 11, upper and lower torsion bars 12a and 12b, left and right inner actuators 13a and 13b, a movable frame 14, left and right outer actuators 15a and 15b, and a fixed frame 16. The inner actuators 13a and 13b and the outer actuators 15a and 15b are all piezoelectric actuators.

[0045] For the convenience of explaining the structure of the optical deflector 10, axes Ax and Ay orthogonal to the center O of the mirror section 11 are defined. The axis Ax and the axis Ay are defined as coordinate axes parallel to the reflecting surface of the mirror section 11 ( Figure 4 the reflective film 64), and on the other hand, are also two rotational axes orthogonal to the mirror section 11. In addition, in the optical deflector 10, the side closer to the center O and the side farther away are referred to as the inner side and the outer side, respectively.

[0046] The circular mirror section 11 has a reflective film 64 ( Figure 4 ) on the surface side (one side in the thickness direction of the mirror section 11) that functions as a reflecting surface. The incident light La is emitted from a laser light source (not shown), enters the mirror section 11, is reflected at the mirror section 11, and is emitted from the mirror section 11 as the scanning light Lb.

[0047] The torsion bars 12a and 12b extend along the axis Ay and connect the mirror section 11 and the movable frame 14 to each other. When viewed from the front, the inner actuators 13a and 13b have an overall shape with an elliptical peripheral contour that is longer in the vertical direction when combined with each other from the left and right, and each has a shape of an elliptical arc of a left and right semi-ellipse.

[0048] In Figure 1 the example, the torsion bars 12a and 12b extend from the mirror section 11, exceed the joint 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 to stop at the position of the joint with the inner actuators 13a and 13b without reaching the inner periphery of the movable frame 14.

[0049] When viewed from the front, the movable frame 14 has a longitudinally elongated elliptical contour shape similar to the overall shape of combining the left and right inner actuators 13a and 13b, and surrounds the mirror section 11, the torsion bars 12a and 12b, and the inner actuators 13a and 13b from the outside. The inner actuators 13a and 13b are interposed between the torsion bars 12a and 12b and the movable frame 14.

[0050] The inner actuators 13a and 13b are supplied with driving voltages having a sinusoidal waveform of a resonance frequency Fy with opposite phases from a driving device (not shown), and cause the torsion bars 12a and 12b to reciprocally rotate about the axis Ay at the resonance frequency Fy.

[0051] The outer actuators 15a and 15b are disposed on the left and right of the movable frame 14, 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 zigzag pattern. In the outer actuators 15a and 15b, when numbered in sequence from the outside to the inside in the lateral direction (the direction parallel to the long side of the rectangular fixed frame 16), the piezoelectric cantilevers with odd numbers and the piezoelectric cantilevers with even numbers are supplied with drive voltages of sawtooth waves and triangular waves with non-resonant frequencies Fx (Fx < Fy) whose phases are opposite to each other by a control device (not shown). Thereby, the outer actuators 15a and 15b cause the movable frame 14 to rotate reciprocally about a lateral rotation axis (a rotation axis different from the axis Ax).

[0052] An illustrative operation of the entire optical deflector 10 will be described.

[0053] In the operation of the optical deflector 10, drive voltages are supplied to the torsion bars 12 (collective term for the torsion bars 12a and 12b) and the outer actuators 15 (collective term for the outer actuators 15a and 15b) from a drive device (not shown). Thereby, the mirror unit 11 rotates reciprocally about the axes Ax and Ay at non-resonant frequency Fx and resonant frequency Fy, respectively. Fx and Fy are, for example, 60 Hz and 25 kHz, respectively.

[0054] On the other hand, the incident light La of a laser beam from a laser light source (not shown) is incident on the mirror unit 11 that rotates reciprocally about the axes Ax and Ay. Thereby, the scanning light Lb, which is the reflected light of the incident light La, is emitted from the mirror unit 11 as a two-dimensional scanning light beam.

[0055] The incident light La can be laser beams of three different colors, red, green, and blue, or a specified single color. A light source control device (not shown) can control the brightness (intensity) of the incident light La emitted from the laser light source by color.

[0056] (Structure of the slit in the embodiment)

[0057] Figure 2A is Figure 1 an enlarged front view of the range including the torsion bars 12a and 12b and their surroundings. Da is the longitudinal rotation axis of the mirror unit 11 and extends on the axis Ay in Figure 1 . Also, in the figures after Figure 2A , the outer ends (ends far from the center O) of the torsion bars 12a and 12b do not reach the inner periphery of the movable frame 14 and stop at the connection positions with the inner actuators 13a and 13b.

[0058] Slits 20a and 20b are respectively formed in the torsion bars 12a and 12b. In the range including the mirror portion 11, the torsion bars 12a and 12b, and the inner actuators 13a and 13b, when viewed from the front, it is symmetrically structured up and down with respect to the axis Ax( Figure 1 ). Therefore, the structure and function of the upper torsion bar 12a and the slit 20a will be described, and the description of the structure and function of the lower torsion bar 12b and the slit 20b will be omitted.

[0059] In Figure 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 a constant-width extension portion 22 that extends along the rotation axis Da with a constant width, and an outer expansion end portion 24a and an inner expansion end portion 24b that are continuously provided at the outer and inner ends of the constant-width extension portion 22, respectively.

[0060] At the joint portion between the mirror portion 11 and the torsion bar 12a, the circumferential line of the mirror portion 11 disappears. If the boundary line between the mirror portion 11 and the torsion bar 12a is set on this disappearing circumferential line, the constant-width extension portion 22 of the slit 20a reaches at least the boundary line inward, and typically crosses the boundary line and enters the mirror portion 11. In addition, this boundary line means the joint position between the mirror portion 11 and the torsion bar 12a.

[0061] The torsion bar 12a and the inner actuators 13a and 13b are joined to each other in the outer joint region 36. The outer joint region 36 is defined as the following region: it is inward of the left and right ends of the respective curved outer corner portions (first corner portions) 30a and 30b in the width direction, it is outward of the ends on the center O side of the left and right curved outer corner portions 30a and 30b in the extending direction, and it is inward of the outer peripheral contours of the inner actuators 13a and 13b in the extending direction. In addition, the entire outer joint region 36 means the joint position between the torsion bar 12a and the mirror portion 11.

[0062] The mirror portion 11 and the torsion bar 12a are joined to each other in the inner joint region 38. The inner joint region 38 is defined as the following region: it is inward of the left and right ends of the respective curved inner corner portions (second corner portions) 32a and 32b in the width direction, and it is on the center O side of the ends of the left and right curved inner corner portions 32a and 32b that are away from the center O in the extending direction. Moreover, the inner joint region 38 is defined as the region in the mirror portion 11 where a prescribed stress is generated when the mirror portion 11 reciprocally rotates about the rotation axis Da. In addition, the entire inner joint region 38 means the joint position between the torsion bar 12a and the mirror portion 11.

[0063] The curved outer corners 30a and 30b are formed as a first curved line at the corner between the side edge of the torsion bar 12a and the inner peripheral edge of the inner actuators 13a and 13b. This first curved line extends outward beyond the side edge of the torsion bar 12a in the width direction of the torsion bar 12a (a direction perpendicular to the extending direction of the rotation axis Da and the thickness direction) and bulges inward toward the outer joint region 36. The curved inner corners (second corners) 32a and 32b are formed as a second curved line at the corner between the peripheral edge of the mirror unit 11 and the side edge of the torsion bar 12a. This second curved line extends outward beyond the side edge of the torsion bar 12a in the width direction and bulges inward toward the inner joint region 38.

[0064] Figure 2B and Figure 2C are respectively Figure 2A enlarged views of the ranges of the outer joint region 36 and the inner joint region 38. The outer expansion end 24a and the inner expansion end 24b of the slit 20a are respectively formed in the outer joint region 36 and the inner joint region 38. For stress relaxation as an effect of the outer expansion end 24a and the inner expansion end 24b, it will be described in detail in Figure 7 hereinafter. Here, referring to Figure 2B and Figure 2C , only the structures of the outer expansion end 24a and the inner expansion end 24b will be described.

[0065] In Figure 2B , when viewed from the front, except for the boundary portion between the outer expansion end 24a and the equal-width extension portion 22, the outer expansion end 24a is circular (an example of the first curved profile shape). On the other hand, the contour line of this boundary portion is set to a contour line that extends approximately equi-width and parallel to the first curved line of the curved outer corners 30a and 30b.

[0066] The diameter of the outer expansion end 24a is larger than the width of the equal-width extension portion 22 (Wb in Figure 6 hereinafter). The outer expansion end 24a extends from the equal-width extension portion 22 in the width direction of the slit 20a. The curved outer corners 30a and 30b have the significance of strengthening the width-direction extension of the outer expansion end 24a.

[0067] In Figure 2CIn [description], the inner expanding end portion 24b is formed in a shape that is symmetrical about the rotation axis Da in a front view (an example of the second bending contour shape). The inner expanding end portion 24b is formed as a through-hole defined by outer bending contour portions 44a, 44b near the periphery of the mirror portion 11 and an inner bending contour portion 46 near the center O. The outer bending contour portions 44a, 44b are set as contour lines that are approximately equal in width and parallel to the second bending line from the curved inner corner portions 32a, 32b. The significance of such a contour line of the inner expanding end portion 24b will be described later in comparison with Figure 3A the inner expanding end portion 24c of the cylindrical hole in FIG. 3C.

[0068] The inner bending contour portion 46 is set as an arc contour line that is concentric with the circle of the mirror portion 11. The width of the inner expanding end portion 24b is larger than the width of the equal-width extension portion 22, and the inner expanding end portion 24b expands from the equal-width extension portion 22 in the width direction of the slit 20a. The curved inner corner portions 32a, 32b serve to strengthen the expansion in the width direction of the inner expanding end portion 24b.

[0069] Figure 3A is a front view of a range including the mirror portion 11 and the inner ends of the torsion bars 12a, 12b in the extending direction of the rotation axis Da. Figure 3B is a view showing an enlarged part of the inner joint region 38. The shape of the inner expanding end portion 24c is the same cylindrical hole as the outer expanding end portion 24a (another example of the second bending contour shape), which is formed symmetrically about the rotation axis Da in the inner joint region 38 and penetrates the mirror portion 11. The boundary portion between the equal-width extension portion 22 and the inner expanding end portion 24c is set as a contour line extending parallel to the second bending line.

[0070] The diameter of the inner expanding end portion 24c is larger than the width of the equal-width extension portion 22, and the inner expanding end portion 24c expands from the equal-width extension portion 22 in the width direction of the slit 20a. The curved outer corner portions 30a, 30b serve to strengthen the expansion in the width direction of the inner expanding end portion 24c.

[0071] (Cross-sectional structure)

[0072] Figure 4 is a cross-sectional view taken along the Figure 1 axis Ax in the thickness direction of the optical deflector 10 when the mirror portion 11 is in a stationary state, Figure 5 is a cross-sectional view taken in a plane parallel to the cross-section of Figure 4 at the position of the equal-width extension portion 22 of the torsion bar 12a.

[0073] In Figure 4 and Figure 5In this case, the SOI substrate 50 has a stacked structure including five layers, which are, from above, an oxide film layer 51, an active layer 52, an oxide film layer 53, a processing layer 54, and an oxide film layer 55. The oxide film layers 51, 53, and 55 are composed of SiO 2 as a component. The active layer 52 and the processing layer 54 are composed of Si. The piezoelectric element 58 has a stacked structure including three layers, which are, from above, an upper electrode layer 59, a PZT (lead zirconate titanate) film layer 60, and a lower electrode layer 61.

[0074] The mirror part 11, the torsion bar 12a, and the fixed frame 16 are composed of all the layers of the SOI substrate 50. In contrast, the inner actuators 13a and 13b and the outer actuators 15a and 15b are composed of a three-layer stack of the two upper oxide film layer 51 and the active layer 52 of the SOI substrate 50 and the piezoelectric element 58 stacked thereon. The mirror part 11 is covered with a reflective film 64 made of a metal component on the surface. The reflective film 64 serves as a reflecting surface for reflecting the incident light La( Figure 1 ).

[0075] In Figure 5 , the equal-width extension part 22 of the slit 20a penetrates the torsion bar 12a in the thickness direction. The outer expansion end part 24a and the inner expansion end part 24b of the slit 20a also penetrate the outer expansion end part 24a of the torsion bar 12a and the inner expansion end part 24b of the mirror part 11 in the thickness direction, and the illustration is omitted.

[0076] The slit 20a in the torsion bar 12a is fabricated by deep reactive ion etching (Deep RIE). As typical deep reactive ion etching methods, there are a method of cooling the sample to a low temperature using a high-density plasma, a method using an etching technique called the Bosch process, and a method using both of them.

[0077] The stacked structure of the cross section in the outer bonding region 36 will be described, and the illustration is omitted. In the outer bonding region 36, the upper electrode layer 59 and the PZT film layer 60 in the three-layer stack of the piezoelectric element 58 are removed by etching, and only the lowermost lower electrode layer 61 remains without being removed. The lower electrode layer 61 is a layer at the ground voltage. As a result of leaving the lower electrode layer 61 in the outer bonding region 36, the lower electrode layers 61 of the left and right inner actuators 13a and 13b are electrically connected to each other in the outer bonding region 36. On the other hand, the left and right inner actuators 13a and 13b are separated in the outer bonding region 36 in the upper electrode layer 59 and the PZT film layer 60, and thus are supplied with drive voltages separately and can be driven independently.

[0078] (Aspect ratio)

[0079] Figure 6It is an explanatory diagram of the aspect ratio A.R. of the torsion bar 12a. In Figure 6 the definitions of the respective reference numerals are as follows.

[0080] Wa: Width of both ends of the torsion bar 12a when viewed from the front

[0081] Wb: Width of the equal-width extension portion 22 when viewed from the front

[0082] Wc: Width of the left and right portions of the torsion bar 12a divided by the equal-width extension portion 22 on the left and right when viewed from the front

[0083] Ta: Thickness of the torsion bar 12a

[0084] According to Figure 6 it can be seen that the following formula (1) holds.

[0085] Formula (1): Wa = Wb + 2 × Wc

[0086] In the present invention, it is set as the following formula (2).

[0087] Formula (2): (Wa - Wb) / Ta < 1

[0088] In the optical deflector 10 of the embodiment, from the viewpoint of suppressing higher harmonics, it is preferable to set the dimensions as the following formulas (3) to (6).

[0089] Formula (3): 0.1 ≤ (Wa - Wb)

[0090] Formula (4): Wb = Wc

[0091] Formula (5): Wa / Ta < 1

[0092] Formula (6): Wb ≤ 2 × Wc

[0093] The significance of formula (5) is that although the slits 20a and 20b are originally formed to prevent damage from occurring at the corners of the cross-sections of the torsion bars 12a and 12b, if Wa / Ta ≥ 1, damage may first occur on the rotation axes of the torsion bars 12a and 12b, and the meaning of forming the slits 20a and 20b is lost. The significance of formula (6) is that if Wb > 2 × Wc, the swing (up and down rocking) of the mirror portion 11 in the extending direction of the rotation axis Da becomes dominant. In addition, it is advantageous that Wb is 25 μm or more.

[0094] In Patent Document 3, two torsion bars opposed in the width direction are formed with V-shaped holes, and the torsion bars are too separated from each other. Therefore, it cannot be said to be the slit in the present invention, but it is included in Wb > 2·Wc in terms of mathematical formula. Therefore, the rotational driving force of the torsion bar or the reverse driving force at the time of rotational reversal increases, and the load on the actuator increases.

[0095] In addition, when the aspect ratio of the torsion bar before forming the slit 20a is Wa / Ta = (Wa + 2·Wc) / Ta < 1, stress is applied to the torsion bar when it reciprocally rotates about the rotation axis. However, by providing the slit of the present invention in the torsion bar, the stress can be alleviated.

[0096] (Function and effect of the equal-width extension part)

[0097] The function and effect on the torsion bar 12 (a general term for the torsion bars 12a and 12b) will be described. First, the function and effect of a structure in which the slit 20 omits the outer expansion ends 24a and the inner expansion ends 24b at both ends and only has the middle equal-width extension part 22 will be described.

[0098] As a result of the torsion bar 12 having the slit 20 (a general term for the slits 20a and 20b) with the equal-width extension part 22, the total area of the side surfaces is obtained by adding the area of the side surfaces on the outer side in the width direction and the area of the inner side surfaces of the slit 20 as the inner side surfaces. As a result, the area of the side surfaces increases, and the stress applied to the side surfaces is dispersed. This leads to a reduction in the stress of the torsion bar 12 and an increase in the maximum allowable rotation angle of the torsion bar 12 against breakage about the rotation axis Da. In this way, the lateral scanning angle of the scanning light Lb about the rotation axis Da increases.

[0099] In the inventor's calculation, due to the stress dispersion effect of the inner side surfaces of the slit 20, the unit rotation angle (unit swing angle: Mpa / deg) of the torsion bar 12 about the rotation axis Da is reduced by 25%. This means that the limit swing angle of the torsion bar 12 about the rotation axis Da becomes 1.33 times.

[0100] (Stress alleviation structure)

[0101] Figure 7 It is a stress distribution diagram around the slit 20a when the slits 20a and 20b of the optical deflector 10 do not have the outer expansion ends 24a and the inner expansion ends 24b and 24c and only have the equal-width extension part 22. Figure 7 It is a diagram shown on the screen display presenting the analysis result based on the simulation, showing that the stress increases as it moves from the darker part to the lighter part.

[0102] When the outer expansion ends 24a and the inner expansion ends 24b are omitted from the slits 20a and 20b and only the equal-width extension part 22 is formed, the maximum stress points appear at both ends of the equal-width extension part 22. The black dashed circles Ca and Cb represent the circles centered on the outer end and the inner end of the equal-width extension part 22 of the slit 20a. It can be seen that the regions with high stress extend outward and inward from the outer end and the inner end of the equal-width extension part 22 in the extension direction of the equal-width extension part 22.

[0103] Refer to Figure 7, the position of the inner joint region 38 will be described. As described above, at the joint of the mirror part 11 and the torsion bar 12a, the circumferential line of the mirror part 11 disappears. If the boundary line between the mirror part 11 and the torsion bar 12a is set on this disappeared circumferential line, the inner joint region 38 is set as the region that is located on the mirror part 11 side with respect to this boundary line and generates a stress of a specified value or more at the mirror part 11.

[0104] In the optical deflector 10, an outer expansion end portion 24a and an inner expansion end portion 24b or an inner expansion end portion 24c are continuously provided at both ends of the equal-width extension portion 22, respectively, so that the maximum stress in the torsion bars 12a and 12b is below a specified upper limit.

[0105] In the torsion bars 12a and 12b, the stress transmitted from the mirror part 11 side along the rotation axis Da to the outer side direction is separated in the width direction to the left and right portions of the torsion bars 12a and 12b on both sides of the slit 20 and is transmitted in parallel to the outer joint region 36. The circular shape of the outer expansion end portion 24a when viewed from the front has the following effects: making the stress transmitted in parallel and separated left and right be appropriately dispersed left and right, making the stress in the outer joint region 36 uniform, and reducing the maximum stress. The reduction of the maximum stress causes an increase in the maximum allowable reciprocating rotation angle of the mirror part 11 around the rotation axis Da.

[0106] Regarding the effect of the inner expansion end portion 24c, it will be described before the inner expansion end portion 24b. The effect of the inner expansion end portion 24c is the same as that of the outer expansion end portion 24a. That is, in the mirror part 11, the stress transmitted from the torsion bars 12a and 12b side along the rotation axis Da to the inner side direction is separated in the width direction to the left and right portions of the torsion bars 12a and 12b on both sides of the slit 20 and is transmitted in parallel to the mirror part 11. When viewed from the front, the circular shape of the inner expansion end portion 24c, like the outer expansion end portion 24a, has the following effects: making the stress transmitted in parallel and separated left and right be appropriately dispersed left and right, making the stress in the inner joint region 38 uniform, and reducing the maximum stress. The shape of the inner expansion end portion 24c is simpler than that of the inner expansion end portion 24b, so it has the advantage of low manufacturing cost.

[0107] In addition, in order to reduce the maximum stress in the outer joint region 36 and the inner joint region 38, depending on the situation, sometimes the outer end and / or the inner end of the slit 20 and Figure 7 Compared with the illustrated situation, it is advantageous to continuously provide the outer expansion end portion 24a and the inner expansion end portions 24b and 24c after slightly moving the outer side and the inner side along the rotation axis Da, respectively. In such a case, the outer end and / or the inner end of the slit 20 is not fixed to Figure 7Rather than the situation shown in the figure, the positions of the outer expansion end 24a and the inner expansion ends 24b and 24c are set after appropriately entering the outer engagement region 36 and the inner engagement region 38 deeper along the rotation axis Da respectively.

[0108] Next, the advantages of the inner expansion end 24b relative to the inner expansion end 24c will be described. The inner end of the inner expansion end 24b is located on the outer side of the inner end of the inner expansion end 24c in the extending direction of the rotation axis Da. This means that the light beam cross-section of the incident light La can irradiate the entire surface of the substantially circular mirror portion 11.

[0109] In the inner expansion end 24c ( Figure 3A and Figure 3B ), the point closest to the center O intrudes deeper into the center O in the mirror portion 11. This means that the effective diameter of the mirror portion 11 in the extending direction of the rotation axis Da decreases, which is the reason for the reduction in the resolution of the image generated by the scanning light Lb in the irradiation region such as a screen. In contrast, the inner expansion end 24b is formed along the circumferential contour of the mirror portion 11, and the point closest to the center O can be sufficiently separated from the inner expansion end 24c. Therefore, the torsion bar 12a suppresses the reduction of the effective diameter of the mirror portion 11 to the minimum, and relieves the stress at the inner ends of the torsion bars 12a and 12b. As a result, the reduction of the effective diameter of the mirror portion 11 can be avoided, and the reciprocating rotation angle of the mirror portion 11 around the rotation axis Da can be increased.

[0110] In the light deflector of the above-mentioned Patent Document 2, two torsion bars are provided on each side of the mirror portion instead of one torsion bar. That is, a gap is formed between the two torsion bars, and this gap is closed on the inner side, that is, the mirror portion side, but is open and not closed on the outer side, that is, the side opposite to the mirror portion. This means that two torsion bars are provided on each side of the mirror portion.

[0111] In contrast, in the light deflector 10, the slits 20a and 20b are closed at both ends in the extending direction of the rotation axis. Therefore, the torsion bars 12a and 12b having the slits 20a and 20b formed on the inner peripheral side do not separate into two respectively, but maintain one torsion bar, and the light deflector 10 has a structure with only one torsion bar on each side of the mirror portion 11. As a result, the transmission efficiency of the force from the inner actuators 13a and 13b to the torsion bars 12a and 12b in the light deflector 10 is higher than that of the light deflector of Patent Document 2 having two torsion bars on each side. According to the inventor's calculation, the driving efficiency of the mirror portion 11 around the rotation axis Da is increased by 29%.

[0112] (Modification example)

[0113] The optical deflector 10 is a biaxial scanning optical deflector. However, the optical deflector of the present invention only needs to have a structure in which an actuator reciprocates a mirror unit around a rotation axis via a torsion bar, and it can also be a uniaxial scanning optical deflector.

[0114] The outer expansion ends 24a and the inner expansion ends 24c of the slits 20a, 20b are substantially circular when viewed from the front. However, the outer ends and the inner ends of the slit of the present invention can also be through holes that are symmetrical about the rotation axis Da when viewed from the front and are regular polygons (for example, equilateral triangles, squares, and regular pentagons) when viewed from the front.

[0115] In the optical deflector 10, the equal-width extension 22 is described as having a constant width. However, in the present invention, the extension at the formation site of the equal-width extension 22 of the optical deflector 10 does not have to be an extension that is of the same width across the entire length when viewed from the front. For example, to the extent that the driving force generated by the inner actuators 13a, 13b does not increase significantly, the widths of both ends of this extension can be the same when viewed from the front, and the width in the middle can be wider or narrower, or the widths of both ends of this extension can be different from each other.

[0116] Reference Signs

[0117] 10: Optical deflector; 11: Mirror unit; 12a, 12b: Torsion bars; 13a, 13b: Inner actuators; 14: Movable frame; 20a, 20b: Slits; 22: Equal-width extension; 24a: Outer expansion end (outer end); 24b, 24c: Inner expansion ends (inner ends); 30a, 30b: Curved outer corner portions (first corner portions); 32a, 32b: Curved inner corner portions (second corner portions); 36: Outer bonding region; 38: Inner bonding region; 44: Outer curved contour portion; 46: Inner curved contour portion; Da: Rotation axis.

Claims

1. An optical deflector, characterized in that, it comprises: a mirror part having a reflecting surface on one side in the thickness direction and reciprocally rotating about 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 part in the extending direction of the rotation axis; an actuator coupled to both sides in the width direction of the torsion bar at an outer coupling position away from the inner coupling position in the extending direction, and reciprocally rotating the torsion bar about the rotation axis at the outer coupling position; and a slit formed in the torsion bar in such a manner that when viewed from the front when observing the reflecting surface along the thickness direction from the one side, both ends in the extending direction are closed, and it extends along the rotation axis within a length range included between the inner coupling position and the outer coupling position in the extending direction, 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 when viewed from the front, (Wa - Wb) / Ta < 1.

2. The optical deflector according to claim 1, characterized in that, when viewed from the front, the side edge of the first corner between the side edge of the torsion bar and the side edge of the actuator is formed by a first curved line which is a curve that expands outward in the width direction more than the side edge of the torsion bar and protrudes inward to the first corner, the slit has an outer end portion which is a first curved profile shape with a width wider than the Wb in the width direction and is formed in an outer coupling region set to include the outer coupling position.

3. The optical deflector according to claim 1, characterized in that, when viewed from the front, the side edge of the second corner between the side edge of the mirror part and the side edge of the torsion bar is formed by a second curved line which is a curve that expands outward in the width direction more than the side edge of the torsion bar and protrudes inward to the second corner, the slit has an inner end portion which is a second curved profile shape with a width wider than the Wb in the width direction and is formed in an inner coupling region set to include the inner coupling position.

4. The optical deflector according to claim 3, characterized in that, the mirror part is circular when viewed from the front, when viewed from the front, the second curved profile shape includes: an inner curved profile part extending in an arc concentric with the circle; and an outer curved profile part located on the peripheral side of the mirror part closer than the inner curved profile part and extending in parallel with the second curved line from both ends of the inner curved profile part.

5. The optical deflector according to claim 3 or 4, characterized in that, When viewed from the front, the side edge of the first corner between the side edge of the torsion bar and the side edge of the actuator is formed by a first bending curve, which is a curve that extends outward from the side edge of the torsion bar in the width direction and protrudes inwardly toward the first corner. The slit has an outer end, which has a first bent profile shape with a width wider than Wb in the width direction and is formed in an outer bonding region that is set to include the outer bonding position.

6. The optical deflector according to any one of claims 1 to 4, characterized in that when viewed from the front, the slit extends equi - width along the rotation axis within the length range between the inner bonding position and the outer bonding position in the extending direction.

7. The optical deflector according to any one of claims 1 to 4, characterized in that Wa / Ta < 1.

8. The optical deflector according to any one of claims 1 to 4, characterized in that Wb ≤ 2×Wc.

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