Optical reflection element

Abstract

An optical reflection element (1) comprises: a movable part (40) that is provided with a reflection surface; and a pair of drive parts (20) that are disposed so as to sandwich the movable part (40) therebetween in parallel with a rotation axis (R10) and rotate the movable part (40) with respect to the rotation axis (R10). Each of the drive parts (20) comprises: a diaphragm (21) in which ends of a plurality of vibration parts (101) extending in a direction intersecting the rotation axis (R10) in planar view are connected in a meander shape by a plurality of connection parts (112); a first rib (122a) that is disposed in each connection part (112) and extends practically parallel to the rotation axis (R10); and a second rib (122b) that is disposed in each connection part (112) and extends from the first rib (122a) in a direction away from the rotation axis (R10).

Description

Optical Reflective Elements

[0001] The present invention relates to an optical reflecting element having a movable portion on which a reflecting surface is formed.

[0002] An optical reflecting element having a movable part on which a reflective surface is formed is known. In this type of optical reflecting element, for example, the reflective surface is disposed on a movable part that rotates about a rotation axis, and a beam incident on the reflective surface is scanned as the movable part rotates.

[0003] The following Patent Document 1 describes an optical deflector equipped with a meander-shaped actuator (drive unit). The actuator includes a plurality of piezoelectric cantilevers arranged in parallel at intervals, a connecting portion connecting the ends of adjacent piezoelectric cantilevers on the same side, and a rib provided on the inside (piezoelectric cantilever side) of the connecting portion. The rib is arranged over a range in the width direction of the two piezoelectric cantilevers connected by the connecting portion that is wider than the range of the gap between the two piezoelectric cantilevers. By providing the rib on the connecting portion, deformation of the connecting portion is reduced, and the swing angle of the mirror unit around the axis caused by the actuator is increased.

[0004] JP 2014-235298 A

[0005] In the optical deflector described in Patent Document 1, ribs are provided in the region inside the connecting portion (on the piezoelectric cantilever side), and no ribs are provided in the region outside the connecting portion. In this case, the connecting portion may have its own resonance frequency that is different from the resonance frequency of the entire element. The resonant motion of the connecting portion at its own resonance frequency acts as an unwanted vibration on the entire element, and there is a risk that the mirror will perform a rotational motion that is different from the desired rotational motion.

[0006] This problem can be reduced by widening the rib width to the outer region of the connecting portion. However, widening the rib width increases the mass of the rib, which increases the moment of inertia of the actuator (driving portion). This may reduce the driving efficiency of the moving portion.

[0007] In view of such problems, the present invention aims to provide an optical reflecting element that can suppress unnecessary vibrations generated in meander-shaped connecting portions while suppressing a decrease in the drive efficiency of the movable portion due to the arrangement of ribs.

[0008] According to a main aspect of the present invention, there is provided an optical reflecting element including a movable part having a reflective surface, and a pair of drive parts arranged parallel to a rotation axis to sandwich the movable part and rotate the movable part about the rotation axis. Each of the drive parts includes a vibration plate having a plurality of vibration parts extending in a direction intersecting the rotation axis in a plan view and connected in a meandering shape by a plurality of connecting parts, a first rib arranged on each of the connecting parts and extending substantially parallel to the rotation axis, and a second rib arranged on each of the connecting parts and extending from the first rib in a direction away from the rotation axis.

[0009] In the optical reflecting element according to this aspect, the first rib increases the rigidity of the connecting portion in a direction parallel to the rotation axis, and the second rib increases the rigidity of the connecting portion outside the first rib. This increases the rigidity of the entire connecting portion, and suppresses unnecessary vibrations from occurring in the connecting portion during rotation of the movable portion. Furthermore, by providing the second rib rather than widening the width of the first rib, the rigidity of the connecting portion outside the first rib is increased, thereby suppressing the increase in mass due to the rib compared to widening the width of the first rib. Therefore, it is possible to suppress a decrease in the drive efficiency of the movable portion due to the arrangement of the rib.

[0010] As described above, according to the present invention, it is possible to provide an optical reflecting element that can suppress unwanted vibrations generated in meander-shaped connecting portions while suppressing a decrease in drive efficiency of the movable portion due to the arrangement of ribs.

[0011] The effects and significance of the present invention will become more apparent from the following description of the embodiments, however, the embodiments shown below are merely examples of how the present invention can be implemented, and the present invention is not limited to the embodiments described below.

[0012] FIG. 1 is a schematic plan view of the configuration of an optical reflecting element according to the first embodiment, as viewed from the front surface side. FIG. 2 is a schematic bottom view of the configuration of an optical reflecting element according to the first embodiment, as viewed from the back surface side. FIG. 3 is a schematic side view of the C1-C2 cross section of FIG. 2, according to the first embodiment. FIG. 4 is a schematic graph of a drive waveform when a movable section actually rotates, according to the first embodiment. FIG. 5(a) is a schematic bottom view of the configuration of a connecting portion and a rib, according to a simulation of a comparative example. FIG. 5(b) is a schematic side view of the C3-C4 cross section of FIG. 5(a), according to a simulation of a comparative example. FIG. 6(a) is a schematic bottom view of the configuration of a connecting portion and a rib, according to a simulation of the first embodiment. FIG. 6(b) is a schematic side view of the C5-C6 cross section of FIG. 6(a), according to a simulation of the first embodiment. FIG. 7 is a graph showing simulation results according to the comparative example and the first embodiment. FIG. 8 is a bottom view schematically showing the configuration of an optical reflecting element according to Embodiment 2, as viewed from the back surface side. FIG. 9 is a bottom view schematically showing the configuration of connecting portions and ribs according to a simulation of Embodiment 2. FIG. 10 is a graph showing simulation results according to a comparative example and Embodiments 1 and 2. FIG. 11(a) is a bottom view schematically showing the configuration of connecting portions and ribs according to Modification Example 1. FIG. 11(b) is a bottom view schematically showing the configuration of connecting portions and ribs according to Modification Example 2. FIG. 12(a) is a bottom view schematically showing the configuration of connecting portions and ribs according to Modification Example 3. FIG. 12(b) is a bottom view schematically showing the configuration of connecting portions and ribs according to a modified example of Modification Example 3. FIG. 13(a) is a bottom view schematically showing the configuration of connecting portions and ribs according to Modification Example 4. FIG. 13(b) is a bottom view schematically showing the configuration of connecting portions and ribs according to a modified example of Modification Example 4. Fig. 14(a) is a bottom view schematically showing the configuration of a connecting portion and a rib according to Modification Example 5. Fig. 14(b) is a bottom view schematically showing the configuration of a connecting portion and a rib according to a modification of Modification Example 5.

[0013] However, the drawings are for illustrative purposes only and do not limit the scope of the present invention.

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. For convenience, each drawing is labeled with X, Y, and Z axes that are orthogonal to each other. The positive direction of the Z axis is the vertically upward direction.

[0015] First Embodiment FIG. 1 is a schematic plan view of the configuration of an optical reflecting element 1 according to a first embodiment, as viewed from the front surface side (in the negative Z-axis direction).

[0016] The optical reflecting element 1 includes a fixed portion 10, a pair of drive portions 20, a pair of connecting beams 30, and a movable portion 40. The optical reflecting element 1 is configured to be point-symmetrical with respect to a center C10 in a plan view. Hereinafter, "inside" refers to the side closer to the center C10, and "outside" refers to the side farther from the center C10. The optical reflecting element 1 is formed by processing an SOI wafer, and each portion of the optical reflecting element 1 is integrally connected by an active layer 201, which will be described later.

[0017] The fixed part 10 is configured in a frame shape. In a plan view, the pair of drive parts 20 and the pair of connecting beams 30 are located in an opening 11 that penetrates the fixed part 10 in the Z-axis direction at the center of the fixed part 10, and are disposed between the fixed part 10 and the movable part 40. A pair of drive parts 20 and connecting beams 30 is disposed on each of the positive and negative sides of the X-axis of the movable part 40.

[0018] Movable portion 40 has a circular outline in a plan view. Movable portion 40 is supported by fixed portion 10 so as to be rotatable about rotation axis R10 via a pair of drive portions 20 and a pair of connecting beams 30. The center of movable portion 40 coincides with the position of center C10 of optical reflecting element 1.

[0019] The upper surface of the movable part 40 (the upper surface of the active layer 201 described later) is a reflective surface 40a that reflects light. Typically, the upper surface of the active layer 201 has sufficient reflectivity due to the generation of an SOI wafer, so the upper surface of the active layer 201 can be used as the reflective surface 40a. The reflectivity of the reflective surface 40a may be increased by polishing the upper surface of the active layer 201 of the movable part 40. Alternatively, an optical reflective film may be separately formed on the upper surface of the active layer 201 of the movable part 40, and the upper surface of the optical reflective film may be used as the reflective surface 40a.

[0020] The driving section 20 includes a vibration plate 21 having a meandering shape in a plan view, and four piezoelectric elements 22 .

[0021] The diaphragm 21 includes four vibration parts 101, one connection part 111, three linking parts 112, and one connection part 113. All four vibration parts 101 extend in a direction perpendicular to the rotation axis R10 (Y-axis direction) and are arranged side by side with a predetermined gap between them. The connection part 111 connects the fixed part 10 and an end of the outermost vibration part 101. The linking part 112 connects the ends of two adjacent vibration parts 101. The connection part 113 connects the end of the innermost vibration part 101 and the connecting beam 30.

[0022] The linking portion 112 and the connecting portions 111, 113 have a rectangular shape extending in the direction of the rotation axis R10 (X-axis direction) in a plan view. This allows the linking portion 112 to firmly connect two adjacent vibrating portions 101, the connecting portion 111 to firmly connect the fixed portion 10 and the outermost vibrating portion 101, and the connecting portion 113 to firmly connect the innermost vibrating portion 101 and the connecting beam 30.

[0023] The position of the inner end of the connecting portion 111 in the X-axis direction coincides with the position of the inner end of the outermost vibrating portion 101 in the X-axis direction. The positions of both ends of the linking portion 112 in the X-axis direction coincide with the positions of the inner and outer ends in the X-axis direction of the two vibrating portions 101 connected by the linking portion 112. The position of the outer end of the connecting portion 113 in the X-axis direction coincides with the position of the outer end of the innermost vibrating portion 101 in the X-axis direction.

[0024] The piezoelectric bodies 22 are formed on the upper surfaces of the eight vibrating members 101 provided in the pair of driving units 20. The piezoelectric bodies 22 are so-called piezoelectric transducers. Piezoelectric transducers are also called piezoelectric actuators. The piezoelectric bodies 22 have a layer structure consisting of a lower electrode layer 211, a piezoelectric layer 212, and an upper electrode layer 213, which will be described later. When a driving voltage is applied to the piezoelectric bodies 22, the piezoelectric layer 212 within the piezoelectric bodies 22 deforms due to the inverse piezoelectric effect, causing the vibrating members 101 in which the piezoelectric bodies 22 are formed to vibrate so as to bend. The piezoelectric bodies 22 are connected to electrodes on the fixed unit 10 via wiring on the vibrating members 101, the connecting members 111, and the linking members 112. For example, a cable (external wiring) connected to an external device is connected to the electrodes on the fixed unit 10 by wire bonding.

[0025] Of the four vibration portions 101 of one vibration plate 21, a first drive voltage of the same phase is applied to the piezoelectric bodies 22 on the first and third vibration portions 101 from the outside, and a second drive voltage of the same phase is applied to the piezoelectric bodies 22 on the second and fourth vibration portions 101 from the outside. At this time, the first drive voltage and the second drive voltage are opposite in phase to each other. As a result, the meandering vibration plate 21 rotates about the rotation axis R10, and the movable portion 40 supported by the pair of vibration plates 21 rotates about the rotation axis R10.

[0026] FIG. 2 is a bottom view schematically showing the configuration of optical reflecting element 1 as viewed from the back surface side (positive direction of the Z axis) according to the first embodiment.

[0027] In Fig. 2, intermediate oxide film 202 and base layer 203 formed on the back surface side (negative side of the Z axis) of optical reflecting element 1 are shown by dots for convenience. As will be described later with reference to Fig. 3, optical reflecting element 1 is formed by processing an SOI wafer consisting of active layer 201, intermediate oxide film 202, and base layer 203. That is, in Fig. 2, optical reflecting element 1 is composed of active layer 201, intermediate oxide film 202, and base layer 203 in the dotted areas, and is composed of only active layer 201 in the areas other than the dotted areas. Piezoelectric body 22 shown in Fig. 1 is formed on the front surface side of vibrating section 101.

[0028] The fixed portion 10 is composed of an active layer 201, an intermediate oxide film 202, and a base layer 203. One rib 121, three ribs 122, and one rib 123 are formed on the back surface of one diaphragm 21 so as to protrude in the negative direction of the Z axis. The ribs 121, 122, and 123 are composed of the intermediate oxide film 202 and the base layer 203. The rib 121 is formed on the back surface of the connecting portion 111, the rib 122 is formed on the back surface of the linking portion 112, and the rib 123 is formed on the back surface of the connecting portion 113. The connecting beam 30 is composed of the active layer 201, the intermediate oxide film 202, and the base layer 203. A rib 41 is formed on the back surface of the movable portion 40 so as to protrude in the negative direction of the Z axis. The rib 41 has a circular ring shape in a plan view and is composed of the intermediate oxide film 202 and the base layer 203.

[0029] The intermediate oxide film 202 and base layer 203 of the fixed portion 10 are respectively integrally formed with the intermediate oxide film 202 and base layer 203 constituting the rib 121. The intermediate oxide film 202 and base layer 203 constituting the rib 123 are respectively integrally formed with the intermediate oxide film 202 and base layer 203 constituting the rib 41.

[0030] The rib 122 includes a first rib 122a and a second rib 122b. The first rib 122a extends from one end of the connecting portion 112 to the other end in a direction parallel to the rotation axis R10 (the X-axis direction). The first rib 122a is disposed at the end of the connecting portion 112 on the rotation axis R10 side. The second rib 122b extends from the center of the first rib 122a in the X-axis direction to the end of the connecting portion 112 in a direction away from the rotation axis R10. The second rib 122b located on the Y-axis positive side of the rotation axis R10 extends in the Y-axis positive direction, i.e., a direction away from the rotation axis R10, while the second rib 122b located on the Y-axis negative side of the rotation axis R10 extends in the Y-axis negative direction, i.e., a direction away from the rotation axis R10.

[0031] The provision of the rib 122 on the rear surface of the connecting portion 112 increases the rigidity of the connecting portion 112. This makes it possible to suppress unnecessary vibrations occurring in the connecting portion 112.

[0032] FIG. 3 is a side view schematically showing a cross section taken along the line C1-C2 of FIG.

[0033] The optical reflecting element 1 is formed by processing a single SOI wafer in which an active layer 201, an intermediate oxide film 202, and a base layer 203 are stacked in the negative direction of the Z axis. The active layer 201 and the base layer 203 are made of, for example, silicon (Si), and the intermediate oxide film 202 is made of, for example, silicon dioxide (SiO ２ ) is composed of

[0034] First, a lower electrode layer 211, a piezoelectric layer 212, and an upper electrode layer 213 are stacked in the positive direction of the Z axis on the upper surface of the SOI wafer. Then, the lower electrode layer 211, the piezoelectric layer 212, and the upper electrode layer 213 are processed by etching so that the piezoelectric body 22 is formed on the upper surface of the vibration section 101. After that, the active layer 201 is processed, and the intermediate oxide film 202 and the base layer 203 are processed in this order. The active layer 201 is processed by etching from the upper side (positive side of the Z axis), and the intermediate oxide film 202 and the base layer 203 are processed by etching from the lower side (negative side of the Z axis). The thickness of the rib (the sum of the thicknesses of the intermediate oxide film 202 and the base layer 203) is greater than the thickness of the active layer 201.

[0035] The fixed portion 10 is composed of an active layer 201, an intermediate oxide film 202, and a base layer 203, and the vibrating portion 101 and the connecting portion 112 are composed of the active layer 201. The rib 122 is composed of the intermediate oxide film 202 and the base layer 203.

[0036] Incidentally, when a rib is provided on connecting portion 112, connecting portion 112 may have its own resonance frequency that differs from the resonance frequency of the entire optical reflecting element 1. The resonant motion of connecting portion 112 at such a unique resonance frequency acts as an unnecessary vibration on the entire optical reflecting element 1, and there is a risk that movable portion 40 will perform a rotational movement that differs from the desired rotational movement.

[0037] For example, when the optical reflecting element 1 is used for vertical scanning in a raster scan for image display, the drive signal for driving the movable part 40 has a sawtooth drive waveform with a frequency of 60 Hz, as shown in Fig. 4. In this case, this drive waveform f(t) can be expressed by the following equation (1) with the frequency F being 60 Hz.

[0038]

[0039] As shown in the above formula (1), the drive waveform f(t) is a superposition of multiple sine waves with frequencies that are whole integer multiples of 60 Hz. In this case, the larger the value of k, the smaller the amplitude of the sine wave, i.e., 1 / k. In other words, the higher the frequency of the sine wave, the smaller the amplitude of the sine wave.

[0040] On the other hand, when the resonant frequency of the connecting portion 112 matches the frequency of one of these sine waves, the connecting portion 112 resonates at that frequency. At this time, the resonance of the connecting portion 112 corresponds to the amplitude of the corresponding sine wave. As described above, the amplitude of a sine wave decreases as its frequency increases. Therefore, the higher the resonant frequency of the connecting portion 112, the smaller the resonant vibration of the connecting portion 112. The smaller the resonant vibration of the connecting portion 112, the less likely this resonant vibration will affect the rotational movement of the movable portion 40. For this reason, it is preferable that the resonant frequency of the connecting portion 112 be as high as possible.

[0041] From the above, the problem of unwanted vibrations caused by the connecting portion 112 can be suppressed by increasing the resonant frequency of the connecting portion 112 using a rib. In this case, for example, the resonant frequency of the connecting portion 112 can be increased by widening the width of the first rib 122a in the Y-axis direction toward the outer region of the connecting portion 112 in the Y-axis direction without providing the second rib 122b described above on the connecting portion 112. However, if the width of the first rib 122a in the Y-axis direction is widened, the mass of the rib increases, and therefore the moment of inertia of the drive unit 20 increases. This may result in a decrease in the drive efficiency of the movable portion 40.

[0042] To address the above-described problems of unwanted vibrations caused by the connecting portion 112 and the problem of increased mass of the rib, in the first embodiment, the connecting portion 112 is provided with a rib 122 including a first rib 122a and a second rib 122b. According to the first embodiment, the rib 122 increases the rigidity of the connecting portion 112, thereby increasing the resonant frequency of the connecting portion 112. This suppresses unwanted vibrations of the connecting portion 112 and allows the movable portion 40 to perform a desired rotational movement. Furthermore, according to the first embodiment, the mass of the rib 122 can be reduced compared to when the width of the first rib 122a is increased without providing the second rib 122b as described above. This suppresses an increase in the moment of inertia caused by the rib, thereby suppressing a decrease in the drive efficiency of the movable portion 40.

[0043] <Simulation of First Embodiment> Next, a simulation of the shape of the rib of the first embodiment carried out by the inventors will be described.

[0044] The inventors performed a simulation using the configuration of the comparative example shown in Figures 5(a) and (b) and the configuration of embodiment 1 shown in Figures 6(a) and (b) to change the length of each part to change the mass of the connecting part 112 and the rib 122 and obtain the resonant frequencies of the connecting part 112 and the rib 122.

[0045] Fig. 5A is a bottom view schematically illustrating the configuration of the connecting portion 112 and the rib 122 according to a simulation of a comparative example, and Fig. 5B is a side view schematically illustrating the C3-C4 cross section of Fig. 5A.

[0046] In the comparative example, the second rib 122b is omitted, and the rib 122 is composed of only the first rib 122a, as compared with the first embodiment. Note that in Fig. 5(a) , for the sake of convenience, the two vibration parts 101 connected to the connection part 112 are shown by dotted lines so that the positional relationship between the connection part 112 and the vibration part 101 can be understood.

[0047] In the simulation of the comparative example, the width W11 of the connecting portion 112 and the rib 122 (122a) in the X-axis direction was set to 1000 μm. The width W21 of the connecting portion 112 in the Y-axis direction was set to 500 μm. The width W22 of the rib 122 in the Y-axis direction was set to 50 μm as an initial setting.

[0048] In the configurations shown in Figures 5(a) and (b), the lengths of each section were set as described above, and the mass of the rib 122 was varied in six stages. Specifically, the weight of the rib 122 when the width W22 of the rib 122 was initially set to 50 µm was taken as the reference (100%), and the relative mass of the rib 122 was varied to 100%, 145%, 190%, 235%, 280%, and 325% by varying the width W22. The resonant frequencies of the connecting section 112 and the rib 122 were then obtained for each mass level of the rib 122. Specifically, the resonant frequency when the width W22 of the rib 122 was initially set to 50 µm was taken as the reference (100%), and the relative resonant frequency was obtained in response to changes in the width W22 of the rib 122.

[0049] Fig. 6(a) is a bottom view schematically showing the configuration of the connecting portion 112 and the rib 122 in the simulation of embodiment 1. Fig. 6(b) is a side view schematically showing the C5-C6 cross section of Fig. 6(a).

[0050] In the first embodiment, as described with reference to Fig. 2, the rib 122 is composed of a first rib 122a and a second rib 122b. For convenience, the two vibrating parts 101 connected to the connecting part 112 are also shown by dotted lines in Fig. 6(a).

[0051] In the simulation of embodiment 1, the width W11 of the connecting portion 112 and the rib 122 in the X-axis direction was set to 1000 μm, the same as in the comparative example. The width W12 of the second rib 122b in the X-axis direction was set to 50 μm as an initial setting. The width W21 of the connecting portion 112 in the Y-axis direction was set to 500 μm, the same as in the comparative example. The width W22 of the first rib 122a in the Y-axis direction was set to 50 μm.

[0052] In the configurations shown in Figures 6(a) and 6(b), the lengths of each section were set as described above, and the mass of the rib 122 was varied in four stages. Specifically, the weight of the rib 122 when the width W22 of the rib 122 (122a) in the comparative example was set to the reference weight (100%), which was the initial setting of 50 µm. By varying the width W12 of the second rib 122b in the first embodiment, the relative mass of the rib 122 in the first embodiment was varied to 145%, 190%, 235%, and 280%. The resonant frequencies of the connecting section 112 and the rib 122 were then obtained for each mass level of the rib 122. Specifically, the resonant frequency when the width W22 of the rib 122 (122a) in the comparative example was set to the reference weight (100%), which was the initial setting of 50 µm. The relative resonant frequencies were obtained in response to the variation in the width W12 of the second rib 122b in the first embodiment.

[0053] FIG. 7 is a graph showing simulation results according to the comparative example and the first embodiment.

[0054] In the comparative example, when the relative mass of the rib 122 was changed to 100%, 145%, 190%, 235%, 280%, and 325% in accordance with the change in the width W22 of the rib 122, the relative resonant frequency of the connecting portion 112 and the rib 122 changed to 100%, 111%, 124%, 139%, 157%, and 179%, respectively. In the first embodiment, when the relative mass of the rib 122 was changed to 145%, 190%, 235%, and 280% in accordance with the change in the width W12 of the second rib 122b, the relative resonant frequency of the connecting portion 112 and the rib 122 changed to 181%, 192%, 203%, and 218%, respectively. In the graph of FIG. 7 , for convenience, the points in the comparative example are connected by a smooth line, and the points in the first embodiment are connected by a smooth line.

[0055] In both the comparative example and embodiment 1, it was found that increasing the mass of the rib 122 can increase the resonance frequency of the connecting portion 112. However, as described above, an increase in the mass of the rib 122 increases the moment of inertia of the drive unit 20, which may reduce the drive efficiency of the movable portion 40. On the other hand, it was found that, when the mass of the rib 122 is the same in the comparative example and embodiment 1, the resonance frequency is higher in embodiment 1 than in the comparative example.

[0056] As described above, according to the first embodiment, it has been found that the resonance frequency of the connecting portion 112 can be increased by increasing the rigidity of the connecting portion 112 in accordance with an increase in the mass of the rib 122. This suppresses unnecessary vibrations of the connecting portion 112, allowing the movable portion 40 to perform a desired rotational movement. Furthermore, according to the first embodiment, it has been found that the resonance frequency can be increased even with the same mass, compared to the comparative example in which the rib 122 is configured only with the first rib 122a. This suppresses the moment of inertia of the drive portion 20, and suppresses a decrease in the drive efficiency of the movable portion 40.

[0057] <Effects of First Embodiment> According to the first embodiment, the following effects are achieved.

[0058] As shown in FIG. 2, each connecting portion 112 is provided with a first rib 122a extending parallel to the rotation axis R10 and a second rib 122b extending from the first rib 122a in a direction away from the rotation axis R10.

[0059] According to this configuration, the first rib 122a increases the rigidity of the connecting portion 112 in a direction parallel to the rotation axis R10, and the second rib 122b increases the rigidity of the connecting portion 112 outside the first rib 122a. This increases the overall rigidity of the connecting portion 112 and suppresses unwanted vibrations in the connecting portion 112 during rotation of the movable portion 40. Furthermore, instead of widening the width of the first rib 122a in the Y-axis direction as in the comparative example of FIG. 5A , providing the second rib 122b as in the first embodiment of FIG. 6A increases the rigidity of the connecting portion 112 outside the first rib 122a. As a result, as shown in the simulation results of FIG. 7 , compared to widening the width of the first rib 122a, the increase in mass due to the rib 122 can be suppressed to achieve a similar resonance frequency in the connecting portion 112. Therefore, a decrease in the drive efficiency of the movable portion 40 due to the arrangement of the rib 122 can be suppressed.

[0060] As shown in FIG. 2, the first rib 122a extends from one end of the connecting portion 112 to the other end.

[0061] This configuration effectively increases the rigidity of the connecting portion 112 in the direction parallel to the rotation axis R10, thereby effectively preventing a decrease in the drive efficiency of the movable portion 40 due to the arrangement of the rib 122.

[0062] The first rib 122a is disposed near the boundary of the connecting portion 112 on the rotation axis R10 side.

[0063] This configuration effectively prevents an increase in the moment of inertia caused by the first rib 122a.

[0064] The second rib 122b extends to the end of the connecting portion 112 in the direction away from the rotation axis R10.

[0065] This configuration can further increase the rigidity of the connecting portion 112.

[0066] The second rib 122b extends in a direction perpendicular to the rotation axis R10.

[0067] According to this configuration, the connecting portion 112 is less likely to vibrate in the direction of the rotation axis R10, and therefore, unnecessary vibrations can be suppressed from occurring in the connecting portion 112 when the movable portion 40 rotates.

[0068] The driving section 20 has a piezoelectric body 22 (piezoelectric actuator) for vibrating the vibrating section 101 .

[0069] According to this configuration, the piezoelectric body 22 can vibrate the vibrating portion 101 smoothly with a simple configuration.

[0070] Second Embodiment In the first embodiment, one second rib 122b is arranged for each first rib 122a, but in the second embodiment, two second ribs 122b are arranged for each first rib 122a.

[0071] FIG. 8 is a bottom view schematically showing the configuration of optical reflecting element 1 as viewed from the back surface side (positive direction of the Z axis) according to the second embodiment.

[0072] In the second embodiment, compared to the first embodiment shown in FIG. 2 , two second ribs 122b are formed for one first rib 122a. The two second ribs 122b extend from both ends of the first rib 122a in the X-axis direction to the end of the connecting portion 112 in a direction away from the rotation axis R10. That is, one second rib 122b is connected to the outer end of the first rib 122a, and the other second rib 122b is connected to the inner end of the first rib 122a. Both of the two second ribs 122b extend in the Y-axis direction. Furthermore, the two second ribs 122b extend along the outer periphery of the connecting portion 112.

[0073] <Simulation of Second Embodiment> The inventors performed a simulation of the rib shape of the second embodiment, similar to the simulation of the rib shape of the first embodiment.

[0074] FIG. 9 is a bottom view schematically showing the configuration of the connecting portion 112 and the rib 122 in the simulation of the second embodiment.

[0075] In the second embodiment, as described with reference to FIG. 8, the rib 122 is composed of a first rib 122a and two second ribs 122b.

[0076] In the simulation of the second embodiment, the width W11 of the connecting portion 112 and the rib 122 in the X-axis direction was set to 1000 μm, the same as in the first embodiment shown in FIGS. 6( a) and 6(b). The width W13 of the second rib 122b in the X-axis direction was set to 50 μm as an initial setting. The width W21 of the connecting portion 112 in the Y-axis direction was set to 500 μm, the same as in the first embodiment shown in FIG. 6( a). The width W22 of the first rib 122a in the Y-axis direction was set to 50 μm, the same as in the first embodiment shown in FIGS. 6( a) and 6(b).

[0077] In the configuration shown in FIG. 9 , the lengths of each section were set as described above, and the mass of the rib 122 was varied in three stages. Specifically, the weight of the rib 122 when the width W22 of the rib 122 (122a) was set to the initial setting of 50 μm in the comparative example shown in FIGS. 5( a) and 5(b) was taken as the reference (100%). The width W13 of the second rib 122b of the second embodiment was varied to vary the relative mass of the rib 122 of the second embodiment to 190%, 235%, and 280%. The resonant frequencies of the connecting section 112 and the rib 122 were then obtained for each mass level of the rib 122. Specifically, the resonant frequency when the width W22 of the rib 122 (122a) was set to the initial setting of 50 μm in the comparative example shown in FIGS. 5( a) and 5(b) was taken as the reference (100%). The relative resonant frequencies were obtained in response to changes in the width W13 of the second rib 122b of the second embodiment.

[0078] FIG. 10 is a graph showing simulation results for the comparative example and the first and second embodiments.

[0079] According to the second embodiment, when the relative mass of the rib 122 was changed to 190%, 235%, and 280% in accordance with the change in the width W13 of the second rib 122b, the relative resonance frequencies of the connecting portion 112 and the rib 122 changed to 219%, 238%, and 262%, respectively. For convenience, the graph in Fig. 10 connects the points in the second embodiment with smooth lines. For convenience, the graph in Fig. 10 also shows the results of the comparative example shown in Fig. 7 and the first embodiment.

[0080] It was also found in the second embodiment that increasing the mass of the rib 122 can increase the resonance frequency of the connecting portion 112. However, as described above, an increase in the mass of the rib 122 increases the moment of inertia of the drive portion 20, which may reduce the drive efficiency of the movable portion 40. On the other hand, it was found that, when the mass of the rib 122 is the same in the comparative example and the first and second embodiments, the resonance frequency is higher in the second embodiment than in the comparative example and the first embodiment.

[0081] As described above, according to the second embodiment, it has been found that the resonance frequency of the connecting portion 112 can be increased by increasing the rigidity of the connecting portion 112 in accordance with an increase in the mass of the rib 122. This suppresses unnecessary vibrations of the connecting portion 112, allowing the movable portion 40 to perform a desired rotational movement. Furthermore, according to the second embodiment, it has been found that the resonance frequency can be increased even with the same mass, compared to the first embodiment in which the rib 122 is provided with one first rib 122a. This suppresses the moment of inertia of the drive portion 20, and suppresses a decrease in the drive efficiency of the movable portion 40.

[0082] <Effects of Second Embodiment> According to the second embodiment, the following effects are achieved.

[0083] Two second ribs 122b extend from both ends of the first rib 122a.

[0084] This configuration can increase the rigidity near both ends of the first rib 122a. Furthermore, as shown in the simulation results in Fig. 10, compared to the first embodiment in which one first rib 122a is provided on the rib 122, the increase in mass due to the rib 122 can be suppressed in order to achieve a similar resonance frequency at the connecting portion 112. Therefore, a decrease in the drive efficiency of the movable portion 40 due to the arrangement of the rib 122 can be suppressed.

[0085] The first rib 122 a extends from one end to the other end of the connecting portion 112 , and the two second ribs 122 b extend along the outer periphery of the connecting portion 112 .

[0086] This configuration maximizes the area sandwiched between the two second ribs 122 b, i.e., the area in which the rigidity can be increased by the two second ribs 122 b, thereby effectively increasing the rigidity of the connecting portion 112 and effectively suppressing unwanted vibrations of the connecting portion 112.

[0087] If the connecting portion 112 is long in the direction of the rotation axis R10, another rib may be provided between the two second ribs 122b in a direction away from the rotation axis R10. This increases the rigidity of the connecting portion 112 near its center.

[0088] Modification Example 1 In the first embodiment, the connecting portion 112 has a rectangular shape in a plan view, but the shape of the connecting portion 112 is not limited to this. For example, the connecting portion 112 may have a shape whose width in the X-axis direction narrows with increasing distance from the rotation axis R10.

[0089] FIG. 11A is a bottom view schematically showing the configuration of the connecting portion 112 and the rib 122 according to the first modification.

[0090] Modification Example 1 differs from Embodiment 1 shown in Fig. 2 in the shape of the connecting portion 112. The width of the connecting portion 112 in Modification Example 1 narrows in the X-axis direction as it moves away from the rotation axis R10. That is, the outline of the connecting portion 112 includes a shape S1 that extends from the end of the first rib 122a in the X-axis direction toward the outer end of the second rib 122b in the Y-axis direction, and a shape S2 that extends along the outer end of the second rib 122b in the Y-axis direction.

[0091] The shape S1 is not limited to a linear shape, but may be a curved shape. The shapes S1 and S2 may be parts of an ellipse.

[0092] According to the first modification, the width of the connecting portion 112 narrows with increasing distance from the rotation axis R10. This configuration allows the connecting portion 112 to be lightweight, thereby increasing the resonance frequency of the drive portion 20.

[0093] In the second embodiment, the connecting portion 112 has a rectangular shape in a plan view, and the two second ribs 122 b extend in the Y-axis direction, but the shape of the connecting portion 112 and the direction in which the two second ribs 122 b extend are not limited to this. For example, the outline of the connecting portion 112 may include an elliptical arc shape, and the two second ribs 122 b may extend along the elliptical arc shape in a direction away from the rotation axis R10.

[0094] FIG. 11B is a bottom view schematically illustrating the configuration of the connecting portion 112 and the rib 122 according to the second modification.

[0095] In modified example 2, compared to embodiment 2 shown in Figure 8, the outer contour of the connecting portion 112 in the Y-axis direction has an elliptical arc shape, and two second ribs 122b are formed along the elliptical arc-shaped contour of the connecting portion 112.

[0096] According to Modification Example 2, similar to Modification Example 1, the width of the connecting portion 112 narrows with increasing distance from the rotation axis R10, allowing the connecting portion 112 to be configured lighter. Furthermore, since the two second ribs 122b extend from both ends of the first rib 122a, the rigidity near both ends of the first rib 122a can be increased. Furthermore, since the two second ribs 122b extend along the outer periphery of the connecting portion 112, the rigidity of the area sandwiched between the two second ribs 122b can be effectively increased.

[0097] <Modification 3> In the second embodiment, two second ribs 122b extend from both ends of the first rib 122a, but one second rib 122c may be arranged along the outer periphery of the connecting portion 112 so as to connect both ends of the first rib 122a.

[0098] FIG. 12A is a bottom view schematically showing the configuration of the connecting portion 112 and the rib 122 according to the third modified example.

[0099] 8, in Modification Example 3, one second rib 122c is formed on the underside of the connecting portion 112 instead of the two second ribs 122b. The second rib 122c is arranged so as to connect both ends of the first rib 122a along the rectangular outer periphery of the connecting portion 112. In this case, the second rib 122c has two straight line portions extending in the Y-axis direction and one straight line portion extending in the X-axis direction.

[0100] 12(b), the outer contour of the connecting portion 112 in the Y-axis direction may have an elliptical arc shape, and the second rib 122c may be formed along the elliptical arc shape of the connecting portion 112. In addition, in the configurations of FIGS. 12(a) and 12(b), the connecting portion 112 does not have to be formed in the area surrounded by the second rib 122c. In other words, a hole penetrating in the Z-axis direction may be provided near the center of the connecting portion 112. This allows the mass of the connecting portion 112 to be reduced.

[0101] 12(a) and 12(b), in Modification Example 3, the first rib 122a extends from one end to the other end of the connecting portion 112, and the second rib 122c is arranged so as to connect both ends of the first rib 122a along the outer periphery of the connecting portion 112. With this configuration, the first rib 122a and the second rib 122c are arranged along the outer periphery of the connecting portion 112, which can increase the rigidity of the connecting portion 112.

[0102] In the second embodiment, the two linear second ribs 122 b extend in the Y-axis direction, but the direction in which the two linear second ribs 122 b extend is not limited to this. For example, the two linear second ribs 122 b may extend in a direction inclined with respect to the X-axis direction and the Y-axis direction.

[0103] FIG. 13A is a bottom view schematically showing the configuration of the connecting portion 112 and the rib 122 according to the fourth modified example.

[0104] In the fourth modification, compared to the second embodiment shown in FIG. 8, the two second ribs 122b are formed in a straight line from the center of the first rib 122a to the outer end of the connecting portion 112.

[0105] As shown in Figure 13(b), the two second ribs 122b may be formed in a straight line from the end of the first rib 122a to the end near the center of the outer side of the connecting portion 112. Also, in Figures 13(a) and 13(b), the two second ribs 122b may extend in a curved line. However, as shown in Figures 13(a) and 13(b), it is preferable that the two second ribs 122b are formed symmetrically with respect to the YZ plane that passes through the center of the connecting portion 112. This allows the ribs 122 to be balanced in the X-axis direction.

[0106] <Modification 5> In the first embodiment, the second rib 122b extends in the Y-axis direction, but this is not limiting, and the second rib 122b may extend at an angle relative to the Y-axis direction.

[0107] FIG. 14A is a bottom view schematically showing the configuration of the connecting portion 112 and the rib 122 according to the fifth modified example.

[0108] In the fifth modification, the second rib 122b extends at an angle relative to the X-axis direction and the Y-axis direction, as compared to the first embodiment shown in Fig. 2. In this case, it is preferable that the center of gravity of the second rib 122b in the X-axis direction coincides with the center of the connecting portion 112. This allows the rib 122 to be balanced in the X-axis direction.

[0109] In the fifth modified example as well, the first rib 122a increases the rigidity of the connecting portion 112 in the direction parallel to the rotation axis R10, and the second rib 122b increases the rigidity of the connecting portion 112 on the outer side of the first rib 122a. This increases the rigidity of the entire connecting portion 112 and suppresses unnecessary vibrations from occurring in the connecting portion 112 when the movable portion 40 rotates.

[0110] As shown in Fig. 14(b), the second rib 122b does not have to extend to the outer end in the Y-axis direction of the connecting portion 112. However, as shown in Fig. 14(a), if the second rib 122b extends to the outer end in the Y-axis direction of the connecting portion 112, the rigidity of the connecting portion 112 can be further increased.

[0111] <Other Modifications> In the first and second embodiments and the first to fifth modifications, the first rib 122a extends from one end to the other end of the connecting portion 112 in the X-axis direction, but this is not limiting, and the first rib 122a does not have to extend to both ends of the connecting portion 112. In other words, the length of the first rib 122a in the X-axis direction may be slightly shorter than the length of the connecting portion 112 in the X-axis direction. In this case as well, the rigidity of the connecting portion 112 in the X-axis direction can be increased compared to when the first rib 122a is not provided.

[0112] In the first and second embodiments and the first to fifth modifications, the first rib 122a is disposed near the boundary of the connecting portion 112 on the rotation axis R10 side, but this is not limiting, and the first rib 122a may be disposed at a position slightly away from the boundary of the connecting portion 112 on the rotation axis R10 side. However, disposing the first rib 122a at the end of the connecting portion 112 on the rotation axis R10 side can suppress an increase in the moment of inertia caused by the first rib 122a.

[0113] In the first and second embodiments and the first to fifth modifications, the first rib 122a extends parallel to the rotation axis R10, but the present invention is not limited to this and may extend substantially parallel to the rotation axis R10. For example, the first rib 122a may extend in a direction slightly tilted from a direction parallel to the rotation axis R10 (the X-axis direction).

[0114] In the first embodiment and the first and fifth modified examples, the second rib 122b is formed in a straight line, but is not limited to this and may be formed in a curved line.

[0115] In the second embodiment and the second modified example, the two second ribs 122b extend from both ends of the first rib 122a, but this is not limiting and the second ribs 122b may extend from positions offset from both ends of the first rib 122a.

[0116] In the first and second embodiments and the first to fifth modifications, the vibrating section 101 extends in a direction perpendicular to the rotation axis R10, but the invention is not limited to this and may extend in any direction intersecting with the rotation axis R10. For example, the vibrating section 101 may extend in a direction slightly tilted from the direction perpendicular to the rotation axis R10.

[0117] In addition, the embodiments of the present invention can be modified in various ways as appropriate within the scope of the technical ideas set forth in the claims.

[0118] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0119] (Technology 1) An optical reflecting element comprising: a movable part provided with a reflective surface; and a pair of drive parts arranged parallel to a rotation axis to sandwich the movable part and rotate the movable part about the rotation axis, wherein each of the drive parts comprises: a vibration plate in which ends of a plurality of vibration parts extending in a direction intersecting the rotation axis in a planar view are connected in a meandering shape by a plurality of connecting parts; a first rib arranged on each of the connecting parts and extending substantially parallel to the rotation axis; and a second rib arranged on each of the connecting parts and extending from the first rib in a direction away from the rotation axis.

[0120] According to this technology, the first rib increases the rigidity of the connecting portion in a direction parallel to the rotation axis, and the second rib increases the rigidity of the connecting portion outside the first rib. This increases the rigidity of the entire connecting portion, and suppresses unnecessary vibrations from occurring in the connecting portion during rotation of the movable portion. Furthermore, by providing the second rib rather than widening the width of the first rib, the rigidity of the connecting portion outside the first rib is increased, thereby suppressing the increase in mass caused by the rib compared to widening the width of the first rib. Therefore, it is possible to suppress a decrease in the drive efficiency of the movable portion due to the arrangement of the rib.

[0121] (Technology 2) The optical reflecting element according to Technology 1, wherein the first rib extends from one end of the connecting portion to the other end thereof.

[0122] This technique can effectively increase the rigidity of the connecting portion in the direction parallel to the rotation axis, thereby effectively preventing a decrease in the drive efficiency of the movable portion due to the arrangement of the rib.

[0123] (Technology 3) The optical reflecting element according to Technology 1 or 2, characterized in that the first rib is disposed near the boundary of the connecting portion on the side of the rotation axis.

[0124] This technique can effectively suppress an increase in the moment of inertia caused by the first rib.

[0125] (Technology 4) The optical reflecting element according to any one of Technologies 1 to 3, wherein the second rib extends to an end of the connecting portion in a direction away from the rotation axis.

[0126] This technique can further increase the rigidity of the connecting portion.

[0127] (Technology 5) The optical reflecting element according to any one of Technologies 1 to 4, wherein the second rib extends in a direction perpendicular to the rotation axis.

[0128] According to this technique, the connecting portion is less likely to vibrate in the direction of the rotation axis, so that unnecessary vibrations can be suppressed from occurring in the connecting portion when the movable portion rotates.

[0129] (Technology 6) The optical reflecting element according to any one of Techniques 1 to 5, wherein the two second ribs extend from both ends of the first rib, respectively.

[0130] This technique can increase the rigidity of the first rib near both ends.

[0131] (Technology 7) In the optical reflecting element described in Technology 6, the first rib extends from one end of the connecting portion to the other end, and the two second ribs extend along the outer periphery of the connecting portion.

[0132] This technique maximizes the area between the two second ribs, i.e., the area where the rigidity can be increased by the two second ribs, thereby effectively increasing the rigidity of the connecting portion and effectively suppressing unwanted vibrations at the connecting portion.

[0133] (Technology 8) An optical reflecting element described in any one of technologies 1 to 5, characterized in that the first rib extends from one end of the connecting portion to the other end, and the second rib is arranged along the outer periphery of the connecting portion so as to connect both ends of the first rib.

[0134] According to this technique, the first rib and the second rib are arranged around the outer periphery of the connecting portion, thereby increasing the rigidity of the connecting portion.

[0135] (Technology 9) The optical reflecting element according to any one of Techniques 1 to 8, wherein the width of the connecting portion narrows with increasing distance from the rotation axis.

[0136] According to this technology, the connecting portion can be made lighter, and therefore the resonance frequency of the drive portion can be increased.

[0137] (Technology 10) The optical reflecting element according to any one of Technologies 1 to 9, wherein the driving section has a piezoelectric actuator for vibrating the vibrating section.

[0138] According to this technique, the vibrating portion can be vibrated smoothly by the piezoelectric actuator with a simple configuration.

[0139] REFERENCE SIGNS LIST 1 Optical reflecting element 20 Driving section 21 Vibrating plate 22 Piezoelectric body (piezoelectric actuator) 40 Movable section 40a Reflecting surface 101 Vibrating section 112 Connecting section 122a First rib 122b, 122c Second rib R10 Rotation axis

Claims

1. An optical reflecting element comprising: a movable part provided with a reflective surface; and a pair of drive parts arranged parallel to a rotation axis to sandwich the movable part and rotate the movable part about the rotation axis, wherein each of the drive parts comprises: a vibration plate in which ends of multiple vibration parts extending in a direction intersecting the rotation axis in a planar view are connected in a meandering shape by multiple connecting parts; a first rib arranged on each of the connecting parts and extending substantially parallel to the rotation axis; and a second rib arranged on each of the connecting parts and extending from the first rib in a direction away from the rotation axis.

2. An optical reflecting element according to claim 1, characterized in that the first rib extends from one end of the connecting portion to the other end.

3. An optical reflecting element as described in claim 1, characterized in that the first rib is disposed near the boundary of the connecting portion on the side of the rotation axis.

4. An optical reflecting element as described in claim 1, characterized in that the second rib extends to an end of the connecting portion in a direction away from the rotation axis.

5. An optical reflecting element according to claim 1, characterized in that the second rib extends in a direction perpendicular to the rotation axis.

6. An optical reflecting element according to claim 1, characterized in that the two second ribs extend from both ends of the first rib, respectively.

7. An optical reflecting element as described in claim 6, characterized in that the first rib extends from one end of the connecting portion to the other end, and the two second ribs extend along the outer periphery of the connecting portion.

8. An optical reflecting element as described in claim 1, characterized in that the first rib extends from one end of the connecting portion to the other end, and the second rib is arranged along the outer periphery of the connecting portion so as to connect both ends of the first rib.

9. An optical reflecting element according to claim 1, wherein the width of said connecting portion narrows with increasing distance from said rotation axis.

10. An optical reflecting element according to any one of claims 1 to 9, characterized in that the driving section has a piezoelectric actuator for vibrating the vibration section.

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