Vibration module and light deflector

Abstract

The purpose of the present invention is to provide a vibration module and a light deflector which make it possible to suppress a change in a deflection angle of a movable part caused by a change in static displacement of a piezoelectric body due to temperature change.　A vibration module (3) according to the present invention comprises a drive element (1), and a substrate (2) that supports the drive element (1). The drive element (1) is provided with: a movable part (11); a drive part that includes a piezoelectric body as a drive source and that rotates the movable part (11) around the rotation axis; and a fixation part (15) that supports the movable part (11) and the drive part and that is fixed to the substrate (2). The fixation part (15) is fixed to, at a plurality of portions which are separated from each other, the substrate (2) via an adhesive in which the elastic modulus decreases as the temperature increases. The plurality of portions include a portion corresponding to an antinode of vibration generated at the fixation part (15) at the time of resonance driving of the movable part (11).

Description

Vibration module and optical deflector

[0001] The present disclosure relates to a vibration module that rotates a movable part about a rotation axis and an optical deflector that includes the vibration module.

[0002] In recent years, drive elements that rotate a movable part using MEMS (Micro Electro Mechanical System) technology have been developed. In this type of drive element, a reflective surface is disposed on the movable part, so that light incident on the reflective surface can be scanned at a predetermined deflection angle. This type of drive element is mounted, for example, on image display devices such as head-up displays and head-mounted displays. In addition, this type of drive element can also be used in laser radars that detect objects using laser light.

[0003] The following Patent Document 1 describes a driving element that rotates a movable part using a so-called tuning fork vibrator. In this driving element, a piezoelectric element is disposed on each of a pair of arms extending along a rotation axis. When AC voltages with a phase difference of 180° (opposite phases) are applied to the piezoelectric elements, the pair of arms expand and contract in opposite directions. This causes the movable part to rotate about the rotation axis, and accordingly, a reflecting surface disposed on the movable part rotates. The tuning fork vibrator is connected to a frame-shaped fixed part via a connecting part extending along the rotation axis.

[0004] Japanese Patent No. 5045470

[0005] In the driving element having the above configuration, the piezoelectric element is driven so that the movable part rotates repeatedly at a natural resonant frequency. However, the driving amount (static displacement) of the piezoelectric element when a constant voltage is applied changes with temperature. Therefore, even if the same driving voltage is applied to the piezoelectric element, the deflection angle of the movable part during resonant driving changes with temperature.

[0006] In view of the above problem, the present disclosure aims to provide a vibration module and an optical deflector that can suppress changes in the deflection angle of a movable part due to changes in the static displacement of a piezoelectric body caused by temperature changes.

[0007] A first aspect of the present disclosure relates to a vibration module. The vibration module according to this aspect includes a drive element and a substrate supporting the drive element. The drive element includes a movable part, a drive unit including a piezoelectric element as a drive source and rotating the movable part about a rotation axis, and a fixed part supporting the movable part and the drive unit and fixed to the substrate. The fixed part is fixed to the substrate in a plurality of mutually separated portions with an adhesive whose elastic modulus decreases with increasing temperature, and the plurality of portions include portions corresponding to antinodes of vibration generated in the fixed part when the movable part is resonantly driven.

[0008] In the vibration module according to this aspect, the elastic modulus of the adhesive decreases with increasing temperature, so that the portion of the fixed part fixed with the adhesive corresponding to the vibration antinode is more likely to vibrate with increasing temperature. Therefore, with increasing temperature, the loss of vibration energy at the vibration antinode increases, and the Q value of the vibration module decreases. As a result, the increase in static displacement and the decrease in Q value with increasing temperature act in opposite directions, thereby suppressing changes in the output of the vibration module with temperature changes. This suppresses changes in the deflection angle of the movable part due to temperature changes.

[0009] A second aspect of the present disclosure relates to an optical deflector, the optical deflector including the vibration module according to the first aspect and a reflective surface disposed on the movable part.

[0010] The optical deflector according to this aspect includes the vibration module according to the above aspect, and therefore can suppress changes in the deflection angle of the movable part and the reflecting surface due to temperature changes, thereby enabling the light incident on the reflecting surface to be stably deflected and scanned at a predetermined deflection angle.

[0011] As described above, the vibration module and optical deflector disclosed herein can provide a vibration module and optical deflector that can suppress changes in the deflection angle of the movable part due to changes in the static displacement of the piezoelectric element caused by temperature changes.

[0012] The effects and significance of the invention according to the present disclosure (hereinafter referred to as the present invention) will become clearer from the following description of the embodiments. However, the embodiment described below is merely an example of how the present invention can be put into practice, and the present invention is not limited to the embodiment described below.

[0013] FIG. 1 is a perspective view showing the configuration of a drive element according to an embodiment. FIG. 2 is a perspective view of a drive element according to an embodiment, as seen from the bottom side. FIG. 3 is a plan view showing the configuration of a vibration module according to an embodiment. FIG. 4 is a perspective view showing an example of a usage form of a vibration module (optical deflector) according to an embodiment. FIG. 5 is a graph showing measurement results of static displacement of a piezoelectric body at each temperature according to an embodiment. FIG. 6 is a diagram showing simulation results of vibrations generated in a fixed part when a movable part is resonantly driven according to an embodiment. FIG. 7A is a plan view showing a method of fixing a drive element to a substrate according to an embodiment. FIG. 7B is a plan view showing a method of fixing a drive element to a substrate according to an embodiment. FIG. 8A is a diagram showing measurement positions when a drive element fixed by the fixing method shown in FIGS. 7A and 7B according to an embodiment is actually resonantly driven. FIG. 8B is a diagram showing a verification example in which vibrations generated in a fixed part are measured when a drive element fixed by the fixing method shown in FIGS. 7A and 7B according to an embodiment is actually resonantly driven. 9A is a graph schematically showing an ideal relationship between a change in static displacement of a vibration module with a change in temperature and a change in the Q value of the vibration module with a change in temperature, according to an embodiment. 9B is a graph schematically showing the temperature characteristics of the deflection angle of a movable part and a reflecting surface during resonant driving when the static displacement and the Q value have the ideal relationship as shown in FIG. 9A , according to an embodiment. 10A is a plan view showing a method of fixing a driving element to a substrate according to a first modification. 10B is a plan view showing a method of fixing a driving element to a substrate according to the first modification. 11A is a plan view showing a method of fixing a driving element to a substrate according to a second modification. 11B is a plan view showing a method of fixing a driving element to a substrate according to the second modification.

[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 Y axis direction is parallel to the rotation axis of the drive element, and the Z axis direction is the thickness direction of the drive element.

[0015] FIG. 1 is a perspective view showing the configuration of a driving element 1, and FIG. 2 is a perspective view of the driving element 1 as viewed from the bottom side (Z-axis negative side).

[0016] The driving element 1 includes a movable portion 11, two driving portions 12, two torsion portions 13, two support portions 14, and a fixed portion 15. The driving element 1 has a rectangular outline in a plan view. The driving element 1 has a shape that is symmetrical in the Y-axis direction and a shape that is symmetrical in the X-axis direction.

[0017] The movable portion 11 is supported by the fixed portion 15 via two torsion portions 13 and two support portions 14 so as to be rotatable about a rotation axis R0. The rotation axis R0 extends parallel to the length direction (Y axis direction) of the drive element 1 at the midpoint in the width direction (X axis direction) of the drive element 1. A reflective surface 11a is formed on the upper surface (the surface on the positive side of the Z axis) of the movable portion 11. The reflective surface 11a is formed by laminating a highly reflective material (e.g., metals or metal compounds such as gold, silver, copper, or aluminum, or silicon dioxide or titanium dioxide) on the upper surface of the movable portion 11. The reflective surface 11a may be formed by a dielectric multilayer film. Alternatively, the reflective surface 11a may be formed by the upper surface of the movable portion 11. In this case, the reflective surface may be formed by mirror-finishing the upper surface of the movable portion 11.

[0018] The two torsion sections 13 have a beam-like shape extending along the rotation axis R0 and are arranged to sandwich the movable section 11 in the Y-axis direction. One end of the torsion section 13 on the Y-axis positive side is connected to the side surface of the movable section 11 on the Y-axis positive side, and the other end is connected to the support section 14 on the Y-axis positive side. One end of the torsion section 13 on the Y-axis negative side is connected to the side surface of the movable section 11 on the Y-axis negative side, and the other end is connected to the support section 14 on the Y-axis negative side.

[0019] The two support portions 14 have a plate-like shape extending along the rotation axis, and each connects the two torsion portions 13 to the fixed portion 15 .

[0020] The two driving units 12 each include a piezoelectric element 12b as a driving source and rotate the movable unit 11 about a rotation axis R0. Each of the two driving units 12 is formed by a tuning fork vibrator. That is, the two driving units 12 are formed by arranging the two tuning fork vibrators in opposite directions along the rotation axis R0.

[0021] Each drive unit 12 includes a pair of arms 12a extending in an L-shape from the support unit 14. A piezoelectric element 12b for driving the movable unit 11 is disposed on the upper surface of the portion of each arm 12a extending in the Y-axis direction. In addition, a piezoelectric element 12c for detecting the vibration state of the arm 12a is disposed near the base of each arm 12a.

[0022] The piezoelectric bodies 12b and 12c have a layered structure in which electrode layers are disposed above and below a piezoelectric thin film of a predetermined thickness. The piezoelectric thin film is made of a piezoelectric material with a high piezoelectric constant, such as lead zirconate titanate (PZT). The material of the piezoelectric thin film is not limited to PZT, and piezoelectric materials with other compositions may also be used. The electrodes are made of a material with low electrical resistance and high heat resistance, such as platinum (Pt). The piezoelectric bodies 12b and 12c are disposed on the upper surfaces of the arm portion 12a by forming a layered structure including the piezoelectric thin film and the upper and lower electrodes on the upper surface of each of these portions using a method such as sputtering.

[0023] The fixed portion 15 has a rectangular frame shape in a plan view. The outer contour of the fixed portion 15 forms the outer contour of the drive element 1. The fixed portion 15 supports the movable portion 11, the drive portion 12, and the torsion portion 13 via two support portions 14. The movable portion 11 is fixed to the substrate 2 (see FIG. 3 ), as described below.

[0024] Two terminals 16 are arranged on the upper surface of the fixed portion 15. The terminal 16 on the positive side of the Y axis is connected to the two piezoelectric bodies 12b and two piezoelectric bodies 12c on the positive side of the Y axis via wiring 16a. The terminal 16 on the negative side of the Y axis is connected to the two piezoelectric bodies 12b and two piezoelectric bodies 12c on the negative side of the Y axis via wiring 16a. The upper surface of the terminal 16 is arranged with a plurality of terminals (not shown) connected to the positive electrodes of the corresponding piezoelectric bodies and a terminal (not shown) for connecting the negative electrodes of these piezoelectric bodies to ground. These terminals are connected to a drive circuit on the substrate 2 (see FIG. 3) by wire bonding.

[0025] The driving element 1 is constructed by laminating a material layer 1b on the lower surface of a substrate 1a of a predetermined thickness. The material layer 1b is laminated only in an area corresponding to the fixed portion 15, thereby increasing the mechanical strength of the fixed portion 15. The material of the material layer 1b may be a different material from that of the substrate 1a, or may be the same material as that of the substrate 1a.

[0026] Alternatively, the driving element 1 is formed by removing the material layer 1b by etching or the like from an integral structure consisting of a substrate 1a of a predetermined thickness and a material layer 1b so as to leave a region corresponding to the fixed portion 15. This increases the mechanical strength of the fixed portion 15. The material of the material layer 1b may be different from that of the substrate 1a, or may be the same material as that of the substrate 1a.

[0027] The substrate 1a has the same contour as the drive element 1 in a plan view and a constant thickness. A reflecting surface 11a and piezoelectric elements 12b and 12c are arranged in corresponding regions on the top surface of the substrate 1a. The substrate 1a is also removed by etching or the like so as to leave the movable section 11, drive section 12, torsion section 13, and support section 14, thereby forming the movable section 11, drive section 12, torsion section 13, and support section 14 on the substrate 1a. The area of ​​the substrate 1a other than the movable section 11, drive section 12, torsion section 13, and support section 14 forms an opening 15a that penetrates vertically.

[0028] The base material 1a is integrally formed from, for example, silicon. However, the material constituting the base material 1a is not limited to silicon and may be other materials. The material constituting the base material 1a is preferably a material with high mechanical strength and Young's modulus. The same applies to the material of the material layer 1b.

[0029] When the drive element 1 is driven, an AC voltage is applied to the four piezoelectric bodies 12b to resonantly drive the movable part 11 at the natural frequency (resonance frequency) of the drive element 1. As a result, each of the four piezoelectric bodies 12b deforms due to the inverse piezoelectric effect. At this time, the AC voltage applied to two piezoelectric bodies 12b aligned in the Y-axis direction is set to the same phase, and the AC voltage applied to two piezoelectric bodies 12b aligned in the X-axis direction is set to the opposite phase. As a result, the deformation direction (amplitude direction) of the two piezoelectric bodies 12b on the positive side of the X-axis is opposite to the deformation direction (amplitude direction) of the piezoelectric body 12b on the negative side of the X-axis. In this way, the deformation of the four piezoelectric bodies 12b deforms the arm portion 12a, and the movable part 11 is resonantly driven around the rotation axis R0 at a predetermined resonant frequency via the two torsion portions 13.

[0030] The four piezoelectric elements 12c for vibration detection generate currents due to the piezoelectric effect in response to the deformation of the corresponding arms 12a. Therefore, the vibration state of the arms 12a can be monitored from these currents. The drive circuit on the substrate 2 uses these currents to control the AC voltages applied to the piezoelectric elements 12b so that the amplitude, frequency, and phase of each arm 12a converge to their respective target values. This causes the movable element 11 and the reflecting surface 11a to rotate at the target resonant frequency and deflection angle.

[0031] FIG. 3 is a plan view showing the configuration of the vibration module 3. As shown in FIG.

[0032] The vibration module 3 includes the above-described driving element 1 and a substrate 2 on which the driving element 1 is mounted. The substrate 2 has a rectangular shape in a plan view. The substrate 2 may be, for example, a glass epoxy substrate, a paper phenol substrate, a ceramic substrate, or a glass substrate.

[0033] The substrate 2 is formed with a bottomed recess 2a into which the drive element 1 is fitted. The recess 2a has a rectangular shape in a plan view and is slightly larger than the outline of the drive element 1. The depth of the recess 2a is constant and is approximately the same as the thickness of the drive element 1. As described above, a drive circuit for driving the drive element 1 is mounted on the substrate 2.

[0034] The driving element 1 is fitted into the recess 2a and attached to the substrate 2. Specifically, adhesive is applied between the back surface of the fixing portion 15 of the driving element 1 and the bottom surface of the recess 2a, and the fixing portion 15 is fixed to the recess 2a. In this way, the driving element 1 is attached to the substrate 2. Thereafter, as described above, the driving circuit on the substrate 2 and each terminal of the terminal portion 16 of the driving element 1 are connected by wire bonding. In this way, the assembly of the vibration module 3 is completed.

[0035] In this embodiment, a reflecting surface 11a is formed on the upper surface of the movable part 11. Therefore, the vibration module 3 constitutes an optical deflector 3a that deflects light incident on the reflecting surface 11a in response to the driving of the movable part 11.

[0036] FIG. 4 is a perspective view showing an example of a usage form of the vibration module 3 (optical deflector 3a) of FIG.

[0037] In the example of Fig. 4, the vibration module 3 (optical deflector 3a) is used in a head-mounted display. Examples of head-mounted displays include AR glasses, AR goggles, VR glasses, and VR goggles. The head-mounted display in Fig. 4 is AR glasses. However, the usage form in Fig. 4 is just one example, and the vibration module 3 (optical deflector) can also be used in an in-vehicle head-up display, etc.

[0038] The AR glasses 4 include a frame 41, a pair of image generating units 42, and a pair of mirrors 43. The AR glasses 4 are worn on the user's head, similar to ordinary eyeglasses.

[0039] The frame 41 holds a pair of image generating units 42 and a pair of mirrors 43. The frame 41 has a front portion 41a and a pair of support portions 41b. The pair of support portions 41b extend rearward from the right and left ends of the front portion 41a. When the frame 41 is worn by a user, the front portion 41a is positioned in front of the user's pair of eyes E1. The frame 41 is made of a transparent material. The frame 41 may also be made of an opaque material.

[0040] The pair of image generation units 42 are arranged symmetrically in the width direction of the AR glasses 4. The image generation units 42 generate an image in the eye E1 of a user wearing the AR glasses 4 on the head.

[0041] The mirror 43 has a concave reflective surface and is installed on the inner surface of the front surface 41a of the frame 41. The mirror 43 almost totally reflects the light projected from the corresponding projection unit 42a and guides it to the user's eye E1.

[0042] The image generating unit 42 includes a projection unit 42a and a detection unit 42b.

[0043] The projection unit 42a is installed on the inner surface of the support unit 41b. The projection unit 42a projects light modulated by a video signal onto the corresponding mirror 43. The light from the projection unit 42a reflected by the mirror 43 is irradiated onto the fovea centralis, which is located at the center of the retina in the eye E1. This allows the user to visually grasp the frame image generated by the image generation unit 42. The pair of detection units 42b are installed on the inner surface of the front surface 41a, between the pair of mirrors 43. The detection units 42b are used to detect the user's line of sight.

[0044] The projection unit 42a scans the light modulated by the video signal horizontally and vertically across the retina of the eye E1. This projects a frame image onto the retina. At this time, the projection unit 42a changes the scanning range of the light so that the frame image is positioned at a position corresponding to the line of sight detected by the detection unit 42b. Horizontal scanning is several times faster than vertical scanning.

[0045] The vibration module 3 (optical deflector 3a) shown in Figure 3 is used for horizontal scanning of light modulated by a video signal. Since vertical scanning is slow, a low-speed optical deflector is used for this scanning. For example, an optical deflector (vibration module) using a meander-type drive element can be used for vertical scanning.

[0046] For example, three light sources emitting red, green, and blue light, respectively, are used as light sources. The emission intensity of each light source is modulated by a video signal. The light from these light sources is collimated by a collimator lens and then combined by two dichroic mirrors. The combined light is incident on the reflecting surface 11a of the vibration module 3 (optical deflector 3a) shown in Figure 3. The movable part 11 is resonantly driven, causing the light to repeatedly scan in the horizontal direction. The light reflected by the reflecting surface 11a is scanned in the vertical direction by the optical deflector at the subsequent stage. In this way, a frame image is projected onto the retina in the eye E1.

[0047] In the driving element 1 having the above configuration, the four piezoelectric bodies 12b are driven so that the movable part 11 rotates repeatedly at a natural resonant frequency, as described above. However, the driving amount (static displacement) of the piezoelectric bodies 12b when a constant voltage is applied changes depending on the temperature. Therefore, even if the same driving voltage (AC voltage) is applied to the piezoelectric bodies 12b, the rotation amount of the movable part 11 during resonant driving changes depending on the temperature.

[0048] FIG. 5 is a graph showing the results of measuring the static displacement of the piezoelectric body 12b at each temperature.

[0049] Here, a MEMS mirror for static displacement measurement, formed using a piezoelectric element with the same configuration as piezoelectric element 12b, was driven at a low speed (static displacement) to measure the total optical angle of the movable part. The drive signal was a 60 Hz sine wave (AC voltage). The MEMS mirror was placed in a thermostatic chamber with a window, and laser light was incident on the mirror through the window, causing the laser light to scan the detection surface. The rotation angle (total optical angle) of the movable part was measured from the scanning length at this time. Note that "deg" in Figure 5 represents the angle in degrees (°). That is, 1 deg = 1°.

[0050] By this measurement method, the temperature in the thermostatic chamber was changed, and the optical angle at each temperature was measured as the static displacement of the piezoelectric element 12b. The temperature in the thermostatic chamber was increased from room temperature to 85°C and then decreased to around room temperature.

[0051] In Fig. 5, the solid line shows the measurement results of the static displacement amount when the temperature in the thermostatic chamber was increased from room temperature to 85°C, and the dashed line shows the measurement results when the temperature in the thermostatic chamber was decreased from 85°C to near room temperature. The black circles in Fig. 5 indicate the measurement points. The solid line connects the measurement results of adjacent measurement points when the temperature was increased, and the dashed line connects the measurement results of adjacent measurement points when the temperature was decreased.

[0052] As shown in Figure 5, the static displacement of the piezoelectric body 12b increased as the temperature increased and decreased as the temperature decreased. Furthermore, the static displacement changed in a similar manner when the temperature increased and decreased. This confirmed that the amount of static displacement was approximately the same when the temperature increased and decreased, as long as the environmental temperature of the piezoelectric body 12b was the same.

[0053] Due to such characteristics of the piezoelectric body 12b, the deflection angle (amplitude in the rotation direction) of the movable part 11 and the reflecting surface 11a when they are resonantly driven changes depending on the environmental temperature of the drive element 1. That is, even if the movable part 11 is resonated with the same AC voltage, the deflection angle of the movable part 11 and the reflecting surface 11a increases as the environmental temperature rises. For this reason, the vibration module 3 is required to have a robust configuration in which the deflection angle of the movable part 11 and the reflecting surface 11a is less likely to change even when the environmental temperature changes.

[0054] Therefore, in this embodiment, the method of fixing the driving element 1 to the substrate 2 is improved so as to suppress the influence of static displacement caused by temperature changes.

[0055] Generally, the output of the vibration module 3, i.e., the deflection angle of the movable part 11 during resonant driving, is determined by the value obtained by multiplying the static displacement by the Q value of the vibration module 3. Therefore, when the static displacement increases with increasing temperature as described above, fluctuations in the output of the vibration module 3 due to temperature changes can be suppressed by decreasing the Q value of the vibration module 3 with increasing temperature. Preferably, by changing the Q value so that the value obtained by multiplying the static displacement and the Q value remains constant even when the temperature of the vibration module 3 changes, the effects of changes in static displacement due to temperature changes can be substantially eliminated.

[0056] In this embodiment, the Q value of the vibration module 3 is reduced in response to an increase in temperature by the characteristics of the adhesive that bonds the fixing portion 15 of the driving element 1 to the substrate 2 and the method of arranging the adhesive.

[0057] That is, in the past, adhesive was applied uniformly to the entire lower surface of fixed portion 15, and fixed portion 15 was fixed to recess 2a of substrate 2. In contrast, in this embodiment, the lower surface of fixed portion 15 is fixed to recess 2a of substrate 2 with adhesive at multiple discrete portions. Here, the multiple portions to which adhesive is applied include portions that correspond to antinodes of vibration that occur in fixed portion 15 when movable portion 11 is resonantly driven. In addition, an adhesive whose elastic modulus decreases with increasing temperature is used as the adhesive.

[0058] In this way, if the portions corresponding to the antinodes of vibration generated in the fixed part 15 when the movable part 11 is resonantly driven are fixed with an adhesive whose elastic modulus decreases with increasing temperature, the adhesive in the antinode portions will soften with increasing temperature, increasing the vibration of the antinode portions. This causes a loss of vibration energy and reduces the Q value of the vibration module 3. In this way, the Q value of the vibration module 3 can be reduced with increasing temperature, and as a result, the effects of static displacement due to temperature changes can be suppressed as described above.

[0059] Here, the decrease in the adhesive's elastic modulus with increasing temperature only needs to occur within the temperature range expected in the environment in which the vibration module 3 is used. For example, adhesives whose main components are epoxy resin, silicone resin, acrylic resin, and urethane resin can be used as such adhesives. Preferably, adhesives whose main components are silicone resin, urethane resin, and modified silicone resin, such as silicone-modified epoxy resin, which have a small elastic modulus after curing and a large temperature change in elastic modulus, are used. The elastic modulus may also be adjusted by mixing a filler into the resin. An adhesive having properties that can further suppress the effects of the static displacement described above should be selected.

[0060] The thickness of the adhesive should be set to a thickness that allows the bonded vibration antinode to vibrate appropriately at each temperature. In the area of ​​the back surface of the fixed part 15 that is not fixed with adhesive, a gap corresponding to the thickness of the adhesive is generated.

[0061] FIG. 6 is a diagram showing the results of a simulation of vibrations in the Z-axis direction that occur in the fixed part 15 when the movable part 11 is resonantly driven.

[0062] For convenience, only the configuration of the fixing portion 15 is shown in FIG. 6. In FIG. 6, the closer to black the color, the greater the vibration, and the closer to white the color, the smaller the vibration. In FIG. 6, vibration is greater in the portions P11 to P13 and P21 to P23 circled by dashed lines. In other words, these portions P11 to P13 and P21 to P23 correspond to the antinodes of vibration. Therefore, by discretely fixing these portions P11 to P13 and P21 to P23 to the substrate 2 with the adhesive described above, the Q value of the vibration module 3 can be reduced as the temperature rises.

[0063] If the entire lower surface of the fixing portion 15 is uniformly fixed to the substrate 2 with adhesive, as in the past, the vibration of the antinode portion is limited by the adhesion of the portions other than the antinode portion, making it difficult for the antinode portion to vibrate smoothly. Therefore, even if the temperature of the vibration module 3 rises, the vibration of the antinode portion is unlikely to change significantly, and energy loss due to the vibration of the antinode portion is unlikely to occur. For this reason, it is difficult to reduce the Q value of the vibration module 3 as the temperature rises.

[0064] In contrast, in this embodiment, as described above, the portions P11 to P13 and P21 to P23 corresponding to the vibration antinodes are discretely fixed to the recess 2a of the substrate 2 with the adhesive, so that the vibration of the vibration antinodes can be increased as the temperature rises. Therefore, the Q value of the vibration module 3 can be effectively reduced as the temperature rises, and as a result, the effects of static displacement can be effectively suppressed.

[0065] 6 do not necessarily have to be fixed to the substrate 2 with the adhesive. For example, the intermediate portions P13 and P23 do not have to be applied with adhesive, and only the portions P11, P12, P21, and P22 near the four corners may be fixed to the substrate 2 with adhesive.

[0066] However, it is preferable that the parts that form a pair symmetrical about the rotation axis R0 (parts P11 and P21, parts P12 and P22, and parts P13 and P23) are either both fixed or neither fixed. In other words, if only one part of a pair is fixed with an adhesive, the support of the drive element 1 to the substrate 2 will be unbalanced across the rotation axis R0, which may cause unstable resonant driving of the movable part 11. Therefore, in order to stably resonantly drive the movable part 11, it is preferable that the parts that form a pair symmetrical about the rotation axis R0 are either both fixed to the substrate 2 or neither fixed to the substrate 2.

[0067] 7A and 7B are plan views showing a method for fixing the driving element 1 to the substrate 2. FIG.

[0068] In this fixing method, adhesive 20 is applied to portions P11, P12, P21, and P22 of the six antinode portions P11 to P13 and P21 to P23 shown in Figure 6, and the driving element 1 is fixed to the recess 2a of the substrate 2. That is, as shown in Figure 7A, adhesive 20 is applied to the four corners of the recess 2a corresponding to portions P11, P12, P21, and P22, and then, as shown in Figure 7B, the driving element 1 is placed in the recess 2a. In this way, the driving element 1 is fixed to the substrate 2, and the vibration module 3 is formed. Note that instead of applying adhesive 20 to the recess 2a, adhesive 20 may be applied to the fixing portion 15 side and fixed.

[0069] Fig. 8A is a diagram showing measurement positions when the drive element 1 fixed by the fixing method shown in Fig. 7A and Fig. 7B is actually driven to resonate. Fig. 8B is a diagram showing a verification example in which vibration in the Z-axis direction generated in the fixed portion 15 is measured when the drive element 1 fixed by the fixing method shown in Fig. 7A and Fig. 7B is actually driven to resonate. Note that in Fig. 8B, "deg" represents the angle in degrees (°). That is, 1 deg = 1°.

[0070] Here, the driving element 1 was resonantly driven at around 55 kHz. The AC voltage applied to the piezoelectric body 12b was set to about 5 V. The vibration was measured at six positions A to F in Figure 8A under room temperature conditions. The thickness of the adhesive 20 was set to about 1 μm.

[0071] FIG. 8B is a graph showing the measurement results.

[0072] In Figure 8B, the horizontal axis represents the phase of one vibration cycle, and the vertical axis represents the displacement of each part in the Z-axis direction. As shown in Figure 8B, vibrations of about 60 to 80 nm were measured at positions A, C, D, and F, which are close to the antinodes of the vibration. In contrast, almost no vibration occurred at positions B and E, which correspond to the nodes of the vibration.

[0073] In order to appropriately reduce the Q value of the vibration module 3 during resonant driving, it is necessary to appropriately vibrate the vibration antinode of the fixed part 15 fixed with the adhesive 20 within the temperature range expected in the usage environment of the vibration module 3. The measurement results in Fig. 8B show that in a room temperature environment, the Q value of the vibration module 3 can be appropriately reduced by vibrating the vibration antinode of the fixed part 15 fixed with the adhesive 20 with a vibration displacement (amplitude) of about 60 to 80 nm.

[0074] For example, if the expected temperature range in the usage environment is 0 to 50°C, the elastic modulus of the adhesive 20 is smaller at around 50°C than at room temperature, so the vibration at the antinode of the vibration of the fixed part 15 fixed with the adhesive 20 will be larger than in the case of Fig. 8B. Conversely, the elastic modulus of the adhesive 20 is larger at around 0°C than at room temperature, so the vibration at the antinode of the vibration of the fixed part 15 fixed with the adhesive 20 will be smaller than in the case of Fig. 8B.

[0075] 4 is mounted on the vibration module 3 (optical deflector), in order to obtain a larger swing angle, the voltage applied to the piezoelectric body 12b is increased to about 10 V. In this case, if the expected temperature range in the usage environment is 0° C. or higher and 50° C. or lower, the vibration displacement (amplitude) of the vibration antinode of the fixed part 15 fixed with the adhesive 20 will be about 50 nm even when the environmental temperature is 0° C.

[0076] Therefore, if the antinode of vibration of the fixed part 15 fixed with the adhesive 20 is 50 nm or more in this temperature range during resonant driving, the antinode can be vibrated appropriately, and the Q value of the vibration module 3 can be appropriately reduced. This makes it possible to appropriately suppress the influence of static displacement of the piezoelectric body 12 b during resonant driving.

[0077] The thickness of the adhesive 20 must be set to a thickness necessary to properly generate vibrations that may occur at the antinodes of vibration of the fixed part 15 fixed with the adhesive 20 within the expected temperature range. For example, the thickness of the adhesive 20 may be set to be approximately 100 times or more the maximum vibration displacement (maximum amplitude) that occurs at the antinodes of vibration of the fixed part 15 fixed with the adhesive 20 within the expected temperature range.

[0078] FIG. 9A is a graph that schematically shows the ideal relationship between the change in static displacement of the vibration module 3 due to a change in temperature and the change in the Q value of the vibration module 3 due to a change in temperature.

[0079] 9A, ideally, the Q value of the vibration module 3 should change so that the value obtained by multiplying the static displacement and the Q value at each temperature is approximately constant across the entire temperature range. This allows the output characteristics of the vibration module 3 to be maintained approximately constant regardless of temperature changes. As a result, as shown in FIG. 9B, the deflection angle of the movable part 11 and the reflecting surface 11a during resonant driving can be maintained approximately constant regardless of temperature changes.

[0080] In other words, the type (temperature characteristics) of the adhesive 20 and the thickness of the adhesive 20 can be adjusted so that such a change in the Q value is obtained in relation to the change in static displacement accompanying a change in temperature. This allows the effect of static displacement accompanying a change in temperature on the resonant driving of the movable part 11 to be offset by the change in the Q value caused by the adhesive 20 in response to the temperature of the vibration module 3. As a result, the deflection angle of the movable part 11 and the reflecting surface 11a during resonant driving can be kept approximately constant regardless of temperature changes.

[0081] <Effects of the embodiment> According to the above embodiment, the following effects can be achieved.

[0082] As shown in Figures 7A and 7B, the fixed portion 15 is fixed to the recess 2a of the substrate 2 at a plurality of mutually discrete portions P11, P12, P21, and P22 by an adhesive 20 whose elastic modulus decreases with increasing temperature, and the plurality of portions P11, P12, P21, and P22 are four of the portions P11 to P13 and P21 to P23 that correspond to the antinodes of vibration generated in the fixed portion 15 when the movable portion 11 is driven, as shown in Figure 6.

[0083] With this configuration, the elastic modulus of the adhesive 20 decreases with increasing temperature, so that the portion of the fixed portion 15 fixed with the adhesive 20 corresponding to the vibration antinode is more likely to vibrate with increasing temperature. Therefore, with increasing temperature, the loss of vibration energy at the vibration antinode increases, and the Q value of the vibration module 3 decreases. As a result, the increase in static displacement and the decrease in Q value with increasing temperature act in opposite directions, and as a result, changes in the output of the vibration module with changes in temperature are suppressed. Therefore, changes in the deflection angle of the movable portion due to temperature changes can be suppressed.

[0084] 7A and 7B , the multiple portions P11, P12, P21, and P22 of the fixed portion 15, which are discretely fixed to the substrate 2 with the adhesive 20, all correspond to antinodes of vibration generated in the fixed portion 15 during resonant driving. This allows the vibration antinode portions fixed with the adhesive 20 to vibrate smoothly without being restricted by other fixed portions. This allows vibration energy to be smoothly dissipated in the vibration antinode portions fixed with the adhesive 20, and the Q value of the vibration module 3 can be appropriately reduced with temperature changes. This allows the effect of static displacement due to temperature changes on resonant driving to be appropriately suppressed.

[0085] 7A and 7B, the multiple portions of the fixed portion 15 fixed with the adhesive 20 include portions P11, P12, P21, and P22 corresponding to an even number of vibration antinodes, and these portions P11, P12, P21, and P22 corresponding to the even number of vibration antinodes form symmetric pairs (portion P11 and portion P21, portion P12 and portion P22) with respect to the rotation axis R0. This allows the drive element 1 to be supported in a balanced manner relative to the substrate 2 in a direction perpendicular to the rotation axis R0. Therefore, the movable portion 11 can be resonantly driven in a stable manner.

[0086] 7A and 7B , fixing portion 15 has a rectangular (oblong) frame shape in a plan view, and the multiple portions fixed with adhesive 20 include portions P11, P12, P21, and P22 that correspond to the antinodes of vibration near the four corners of this frame shape. By fixing the four corners of the rectangle in this way, fixing portion 15 can be stably supported on substrate 2.

[0087] The vibration displacement during resonant driving at the vibration antinode portion fixed by the adhesive 20 is preferably set to 50 nm or more within a predetermined temperature range (0°C or higher and 50°C or lower). As a result, as described with reference to FIG. 8B , vibrations according to the elastic modulus of the adhesive 20 can be generated at the vibration antinode portion of the fixed portion 15 at a predetermined temperature within this temperature range. Therefore, the Q value of the vibration module 3 can be appropriately changed in accordance with temperature changes, and changes in the deflection angle of the movable portion 11 due to temperature changes can be appropriately suppressed.

[0088] Here, the predetermined temperature range can be set to between 0°C and 50°C. This allows the Q value of the vibration module 3 to be appropriately changed in accordance with temperature changes within the temperature range expected in the everyday use environment of, for example, AR glasses 4, and makes it possible to appropriately suppress changes in the deflection angle of the movable part due to temperature changes. This allows the vibration module 3 to perform operations suited to the everyday use environment.

[0089] 1, the driving unit 12 is a tuning fork vibrator, which allows the movable unit 11 to rotate smoothly and repeatedly about the rotation axis R0 (resonant driving).

[0090] 1, two tuning-fork vibrators (drive units 12) are arranged in opposite directions along the rotation axis R0, which allows the movable unit 11 to be driven stably with a larger torque.

[0091] <Modifications> The configuration examples of the present invention are not limited to the above-described embodiment, and various modifications are possible.

[0092] For example, in the above embodiment, of the multiple vibration antinode portions P11 to P13, P21 to P23 that occur in the fixed portion 15 when the movable portion 11 is resonantly driven, four portions P11, P12, P21, and P22 near the four corners of the fixed portion 15 are fixed to the substrate 2 with adhesive 20, but the portions to which the fixed portion 15 of the substrate 2 is adhered are not limited to these.

[0093] 10A and 10B show a first modification of the method of fixing the driving element 1 to the substrate 2. Also, the second modification of the method of fixing the driving element 1 to the substrate 2 is shown in the plan views of FIGS. 11A and 11B.

[0094] 10A and 10B, all of the vibration antinodes P11 to P13 and P21 to P23 may be fixed with adhesive 20. In this case, as shown in Fig. 10A, adhesive 20 is applied to the portions of recess 2a corresponding to the vibration antinodes P11 to P13 and P21 to P23, and then, as shown in Fig. 10B, drive element 1 is placed in recess 2a. In this way, drive element 1 is fixed to substrate 2, and vibration module 3 is formed.

[0095] 11A and 11B, vibration antinodes P11 to P13 and P21 to P23 as well as vibration node portions P31 and P32 may be further fixed with adhesive 20. In this case, as shown in Fig. 11A, adhesive 20 is applied to portions of recess 2a corresponding to vibration antinode portions P11 to P13 and P21 to P23 and vibration node portion P32, and then, as shown in Fig. 11B, drive element 1 is placed in recess 2a. In this way, drive element 1 is fixed to substrate 2, and vibration module 3 is formed.

[0096] In these cases, similarly to the cases of FIGS. 7A and 7B, instead of applying adhesive 20 to recess 2a, adhesive 20 may be applied to fixing portion 15 side for fixing.

[0097] 11A and 11B can increase the fixing strength of the drive element 1 compared to the case of Fig. 10A and 10B. However, because the node parts P31 and P32 near the vibration antinode parts P11, P12, P21, and P22 fixed with the adhesive 20 are fixed, the vibration of the vibration antinode parts P11, P12, P21, and P22 is likely to be restricted by the fixing of the node parts P31 and P32.

[0098] Therefore, in order to make the antinode portion vibrate more stably in response to temperature changes and to properly control the Q value of the vibration module 3, it is preferable to discretely fix only the antinode portion of the vibration of the fixed portion 15 to the substrate 2 with adhesive 20, as in the above embodiment and modified example.

[0099] In addition, in the above embodiment, the recess 2 a for installing the driving element 1 is provided in the substrate 2, but the recess 2 a does not necessarily have to be provided in the substrate 2. For example, the fixing portion 15 of the driving element 1 may be fixed to the upper surface of the flat substrate with the adhesive 20 by the above-mentioned method.

[0100] The substrate 2 is preferably made of a material whose elastic modulus decreases with increasing temperature, thereby enabling the Q value of the vibration module 3 to be reduced more effectively with increasing temperature. Examples of such materials include a glass epoxy substrate and a ceramic substrate.

[0101] Furthermore, in the above embodiment, the two drive units 12 are arranged in opposite directions along the rotation axis R0, but one of the two drive units 12 may be omitted.

[0102] In the above embodiment, the driving unit 12 is a tuning fork type vibrator, but the driving unit 12 may be a vibrator of another type that is resonantly driven. For example, the driving unit 12 may be a meandering type vibrator that is resonantly driven.

[0103] In addition, in the above embodiment, the shape of the movable part 11 is circular, but the shape of the movable part 11 may be other shapes such as square. The shape of the driving element 1 in a plan view and the dimensions of each part of the driving element 1 can also be changed as appropriate.

[0104] Furthermore, the driving element 1 may be used as an element other than an optical deflector. When the driving element 1 is used as an element other than an optical deflector, the movable part 11 does not need to have the reflecting surface 11 a, and may have another member other than the reflecting surface 11 a.

[0105] 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.

[0106] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0107] (Technology 1) A vibration module comprising: a driving element; and a substrate supporting the driving element, wherein the driving element comprises: a movable part; a driving part including a piezoelectric body as a driving source and rotating the movable part about a rotation axis; and a fixed part supporting the movable part and the driving part and fixed to the substrate, wherein the fixed part is fixed to the substrate in a plurality of mutually separated parts by an adhesive whose elastic modulus decreases with increasing temperature, and the plurality of parts include parts corresponding to antinodes of vibration generated in the fixed part when the movable part is driven at resonance.

[0108] According to this technology, the elastic modulus of the adhesive decreases with increasing temperature, so that the portion of the fixed part fixed with the adhesive corresponding to the antinode of vibration is more likely to vibrate with increasing temperature. Therefore, with increasing temperature, the loss of vibration energy at the antinode increases, reducing the Q value of the vibration module. As a result, the increase in static displacement and the decrease in Q value with increasing temperature act in opposite directions, thereby suppressing changes in the output of the vibration module with temperature changes. This makes it possible to suppress changes in the deflection angle of the movable part due to temperature changes.

[0109] (Technology 2) The vibration module according to Technology 1, wherein the plurality of portions are all portions corresponding to antinodes of the vibration.

[0110] This technology allows the vibration antinodes fixed with adhesive to vibrate smoothly without being restricted by other fixed parts. This allows vibration energy to be smoothly dissipated in the vibration antinodes fixed with adhesive, and the Q value of the vibration module can be appropriately reduced with temperature changes. This allows the effect of static displacement caused by temperature changes on resonant drive to be appropriately suppressed.

[0111] (Technology 3) In the vibration module described in Technology 1 or 2, the plurality of portions include portions corresponding to an even number of antinodes of the vibration, and the portions corresponding to the even number of antinodes of the vibration form pairs symmetrical with respect to the rotation axis.

[0112] According to this technique, the drive element is supported on the substrate in a well-balanced manner in the direction perpendicular to the rotation axis, thereby enabling the movable part to be resonantly driven in a stable manner.

[0113] (Technology 4) A vibration module according to any one of technologies 1 to 3, characterized in that the fixing portion has a rectangular frame shape in a planar view, and the plurality of portions include portions corresponding to antinodes of the vibration near the four corners of the frame shape.

[0114] According to this technique, the fixing portion can be stably supported on the substrate by fastening the vicinity of the four corners of the rectangle.

[0115] (Technology 5) A vibration module according to any one of technologies 1 to 4, characterized in that the vibration displacement of the antinode portion fixed with the adhesive during resonant driving is 50 nm or more in a predetermined temperature range.

[0116] This technology allows vibrations corresponding to the elastic modulus of the adhesive to be generated at the antinode of the vibration of the fixed part at a predetermined temperature within the temperature range, thereby allowing the Q value of the vibration module to be appropriately changed in accordance with temperature changes, and appropriately suppressing changes in the deflection angle of the movable part due to temperature changes.

[0117] (Technology 6) The vibration module according to Technology 5, wherein the temperature range is 0°C or more and 50°C or less.

[0118] This technology allows the Q value of the vibration module to be appropriately changed in accordance with temperature changes within the expected temperature range of everyday use environments, such as AR glasses, and appropriately suppresses changes in the deflection angle of the moving part due to temperature changes, thereby enabling the vibration module to perform operations suited to everyday use environments.

[0119] (Technology 7) The vibration module according to any one of technologies 1 to 6, wherein the driving unit is a tuning fork vibrator.

[0120] According to this technique, the movable part can be smoothly and repeatedly rotated (resonantly driven) about the rotation axis.

[0121] (Technology 8) In the vibration module according to Technology 7, the two tuning-fork vibrators are arranged in opposite directions along the rotation axis.

[0122] This technique allows the moving part to be driven stably with a larger torque.

[0123] (Technology 9) An optical deflector comprising: the vibration module according to any one of technologies 1 to 8; and a reflecting surface disposed on the movable part.

[0124] According to this technology, since the vibration module according to any one of technologies 1 to 8 is included, it is possible to suppress changes in the deflection angle of the movable part and the reflecting surface due to temperature changes, and therefore it is possible to stably deflect and scan the light incident on the reflecting surface at a predetermined deflection angle.

[0125] The vibration module and optical deflector of the present disclosure can suppress changes in the deflection angle of the movable part due to changes in the static displacement of the piezoelectric element caused by temperature changes, making the vibration module and optical deflector of the present disclosure industrially useful.

[0126] REFERENCE SIGNS LIST 1 drive element 2 substrate 3 vibration module 3a optical deflector 11 movable portion 11a reflecting surface 12 drive portion 12b, 12c piezoelectric body 15 fixed portion 20 adhesive P11 to P13, P22 to P23 portions (portions corresponding to vibration loops) R0 rotation axis

Claims

1. A vibration module comprising: a driving element; and a substrate supporting the driving element, wherein the driving element comprises: a movable part; a driving part including a piezoelectric body as a driving source and rotating the movable part about a rotation axis; and a fixed part supporting the movable part and the driving part and fixed to the substrate, wherein the fixed part is fixed to the substrate in a plurality of mutually discrete portions by an adhesive whose elastic modulus decreases with increasing temperature, and the plurality of portions include portions corresponding to antinodes of vibration generated in the fixed part when the movable part is driven at resonance.

2. A vibration module according to claim 1, wherein all of the plurality of portions correspond to antinodes of the vibration.

3. A vibration module as described in claim 1, wherein the plurality of portions include portions corresponding to an even number of antinodes of the vibration, and the portions corresponding to the even number of antinodes of the vibration form symmetric pairs with respect to the rotation axis.

4. A vibration module as described in claim 1, characterized in that the fixing portion has a rectangular frame shape in a planar view, and the multiple portions include portions corresponding to the antinodes of the vibration near the four corners of the frame shape.

5. A vibration module as claimed in claim 1, characterized in that the vibration displacement of the antinode portion fixed with the adhesive during resonant driving is 50 nm or more within a specified temperature range.

6. The vibration module according to claim 5, wherein the temperature range is from 0°C to 50°C.

7. The vibration module according to claim 1, wherein the driving section is a tuning fork type vibrator.

8. A vibration module according to claim 7, characterized in that the two tuning-fork type vibrators are arranged in opposite directions along the rotation axis.

9. An optical deflector comprising: a vibration module according to any one of claims 1 to 8; and a reflecting surface disposed on the movable part.

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