Mirror actuator

Abstract

This mirror actuator 1 includes: a mirror 2 that reflects a light beam emitted from a light source 110; a support 3 that supports the mirror 2 from a rear surface 22 side; an adhesive 4 that is provided between the rear surface 22 of the mirror 2 and the support 3 and fixes the mirror 2 to the support 3; a shaft 5 to which the support 3 is attached such that an axial direction is parallel to a reflection surface 21 of the mirror 2; and a motor 6 that rotates or reciprocally rotates the shaft 5 around the axial direction of the shaft 5 in order to scan the light beam in a scanning zone 200. The rear surface 22 of the mirror 2 faces the support 3 with a gap therebetween and is not in contact with the support 3.

Description

Mirror actuator Cross-references to related applications

[0001] This application claims priority under Japanese Patent Application No. 2024-220349 (title of invention "Mirror Actuator") filed on 16 December 2024 and Japanese Patent Application No. 2024-220350 (title of invention "Mirror Actuator") filed on 16 December 2024, the contents of which these Japanese patent applications are incorporated herein by reference in their entirety.

[0002] The present invention relates to a mirror actuator in general, and more specifically to a mirror actuator used in a LiDAR system to reflect laser light and scan a scanning zone.

[0003] LiDAR systems, an abbreviation for Light-Detection-and-Ranging systems, are remote sensing methods that measure the distance to an object within a scanning zone. They detect the attributes of the surrounding environment (e.g., the shape of the object, its contour, the distance to the object, etc.) by illuminating the object with a light beam and measuring the reflected light from the object with a sensor. Such LiDAR systems are used in various fields, including autonomous driving. LiDAR systems typically use a light source that emits a light beam, a sensor that acts as a light receiver, and a mirror to reflect the light beam emitted from the light source towards the scanning zone. Typically, the scanning zone is scanned by rotating the mirror to change the reflection angle of the light beam.

[0004] Patent Document 1 discloses a mirror actuator 500, as shown in Figure 1, used to rotate a mirror in the LiDAR system described above. Figure 1 is a longitudinal cross-sectional view passing through the axis of the mirror actuator 500. As shown in Figure 1, the mirror actuator 500 comprises a mirror 501 used to scan a light beam, a rotatable shaft (rotation axis) 503 to which the mirror 501 is attached, having a central axis parallel to the reflective surface 502 of the mirror 501, a support 504 attached to the shaft 503 and further supporting the mirror 501, and a motor 505 that performs scanning in a planar direction by rotating the shaft 503 to which the mirror 501 is attached via the support 504.

[0005] In the mirror actuator 500 shown in Figure 1, the mirror 501 reflects a light beam emitted from a light source (not shown) toward the scanning zone using the reflective surface 502 of the mirror 501. The rotatable shaft 503 has a rotation axis parallel to the reflective surface 502 of the mirror 501. The support 504 is connected to the back surface of the mirror 501, for example via an adhesive member, and supports the mirror 501 from the back side. In recent years, mainly in the field of autonomous driving technology, there has been an increasing demand for accurate and three-dimensional measurement of the distance from the vehicle body to an object and the shape of the object. The mirror actuator 500 shown in Figure 1 achieves scanning of an object by changing the reflection angle of the light beam at the mirror 501 by rotating or reciprocating the mirror 501.

[0006] In a LiDAR system, a light beam emitted from a light source and reflected by the mirror 501 strikes an object, and the reflected light from the object reaches a sensor (not shown). The detection of the distance from the LiDAR system to the object and the shape of the object is achieved by calculating the time difference between the time the light beam is emitted from the light source and the time the reflected light from the object is received by the sensor. Therefore, in order to accurately detect the distance to the object and the shape of the object, it is necessary to accurately control the reflection angle of the light beam by the mirror 501. More specifically, in order to accurately control the reflection angle of the light beam by the mirror 501, it is necessary to increase the flatness of the mirror 501. For example, if the mirror 501 is warped and its flatness is low, the warping of the mirror 501 makes it difficult to accurately control the reflection angle of the light beam, making it difficult to accurately detect the distance to the object and the shape of the object. Therefore, it is necessary to eliminate the warping that occurs in the mirror 501 and increase the flatness of the mirror 501.

[0007] Furthermore, the light beams used in LiDAR systems primarily consist of one of three laser wavelengths: 905 nm, 940 nm, or 1550 nm, taking into account the absorption wavelengths of atmospheric components. Generally, LiDAR systems used for vehicle safety checks and autonomous driving utilize a 905 nm laser beam. However, for the same output (power), the safety performance of a 1550 nm laser beam for the human eye is approximately 40 times greater than that of a 905 nm laser beam. Therefore, by using a 1550 nm laser beam, it is possible to realize a LiDAR system with higher output while maintaining safety for the human eye. In addition, a 1550 nm laser beam is less affected by atmospheric conditions (e.g., rain and fog), allowing for more reliable measurements in various environments. For this reason, LiDAR systems using a 1550 nm laser beam are considered promising for the future.

[0008] Typical dielectric multilayer films used in mirrors of such LiDAR systems include TiO ２ +SiO２ Stacked film, Ta ２ O ５ + SiO ２ Stacked films are included. However, TiO ２ + SiO ２ Stacked film or Ta ２ O ５ + SiO ２ To form the stacked film, a dielectric layer (TiO ２ + SiO ２ In the case of the stacked film, the TiO ２ layer and the SiO ２ layer. Ta ２ O ５ + SiO ２ In the case of the stacked film, Ta ２ O ５ layer and the SiO ２ layer) needs to be significantly increased. The increase in the film thickness of the dielectric layer causes an increase in the warping of the mirror during the formation of the dielectric multilayer film, that is, a decrease in the flatness of the mirror. Furthermore, the increase in the film thickness of the dielectric layer also leads to an increase in the cost of the mirror.

[0009] Also, each of the TiO ２ + SiO ２ stacked film and Ta ２ O ５ + SiO ２ stacked film has a problem that the reflectance has a high angular dependence of the incident angle with respect to the laser light of 1550 nm. For example, in the case of the TiO ２ + SiO<00--0027>stacked film, when the laser light of 1550 nm is incident on the TiO ２ + SiO ２ stacked film at an incident angle of 35°, the reflectance is different from when the laser light of 1550 nm is incident on the TiO ２ + SiO ２The reflectivity differs significantly from that when incident on a multilayer film. This dependence of the mirror's reflectivity on the incident angle destabilizes the intensity of the reflected light from the mirror when scanning the light beam, reducing the measurement accuracy of the LiDAR system. For these reasons, there has been a high demand for a mirror that has high reflectivity with low incident angle dependence for 1550 nm laser light, as well as a thin dielectric layer and high flatness.

[0010] Furthermore, in order to rotate or reciprocate a mirror at high speed, it is necessary to attach the mirror to the axis of rotation via a support member. As mentioned earlier, in order to accurately orient the light beam to a predetermined location in a LiDAR system, it is necessary to eliminate the warping of the mirror attached to the mirror actuator and increase its flatness. However, depending on the operating environment, situations may arise in which the mirror warps. For example, consider the case when operating a LiDAR system in a high-temperature environment. If the coefficient of linear expansion of the mirror (the rate at which the length or volume of an object expands per unit temperature due to a rise in temperature; also called the coefficient of thermal expansion) and the coefficient of linear expansion of the support body that supports the mirror differ significantly, a large difference will occur between the amount of expansion and contraction of the mirror and the amount of expansion and contraction of the support member in a high-temperature environment. Generally, since the mirror is directly bonded to the support body, the difference between the amount of expansion and contraction of the mirror and the amount of expansion and contraction of the support member generates strong bending stress on the mirror, causing it to warp. When the mirror warps, its flatness decreases, making it difficult to accurately control the reflection angle of the light beam. Thus, due to the difference in the coefficient of thermal expansion between the mirror and the support member, the flatness of the mirror decreases depending on the usage environment, making it difficult to accurately detect the distance to the object and the shape of the object.

[0011] Furthermore, in order to control the reflection angle of the light beam with high precision, it is necessary to adjust the parallelism of the mirror's reflective surface with respect to the axial direction of the rotation axis of the mirror actuator (for example, the left-right direction in Figure 1 for shaft 503 in Figure 1) with precision in units of mdeg. However, in general mirror actuator manufacturing methods, it is extremely difficult to adjust the parallelism of the mirror to within a few mdeg units, and adjusting the parallelism of the mirror has been a major challenge in improving the measurement accuracy of LiDAR systems.

[0012] Japanese Patent Publication No. 2024-11914

[0013] The present invention addresses the above-mentioned conventional problems, and its objective is to provide a mirror actuator equipped with a mirror that has a reflectivity that is high and low dependence on the incident angle for a 1550 nm light beam, as well as high flatness.

[0014] Such objectives are achieved by the present invention as defined in (1) below: (1) A mirror actuator used to scan a scanning zone by reflecting a light beam emitted from a light source, comprising: a mirror having a reflective surface that reflects the light beam emitted from the light source and a back surface opposite to the reflective surface; a support that supports the mirror from the back surface side; an adhesive provided between the back surface of the mirror and the support for fixing the mirror to the support; a shaft to which the support is attached such that its axial direction is parallel to the reflective surface of the mirror; and a motor that rotates or reciprocates the shaft around the axial direction of the shaft in order to scan the scanning zone with the light beam, wherein the back surface of the mirror faces the support with a gap between them and does not contact the support.

[0015] In the mirror actuator of the present invention, the mirror is fixed to the support by an adhesive provided between the back surface of the mirror and the support. Therefore, the back surface of the mirror faces the support with a gap in between and does not come into contact with the support. As a result, even if the amount of thermal expansion and contraction of the mirror and the support differ in high-temperature environments, the bending stress generated in the mirror is mitigated by the thickness and elasticity of the adhesive. Therefore, warping of the mirror is mitigated, and the decrease in the flatness of the mirror in high-temperature environments can be suppressed.

[0016] Figure 1 is a cross-sectional view of a conventional mirror actuator. Figure 2 is a schematic diagram of a LiDAR system including a mirror actuator according to an embodiment of the present invention. Figure 3 is a perspective view of a mirror actuator according to an embodiment of the present invention. Figure 4 is a perspective view of the mirror actuator shown in Figure 3 from a different angle. Figure 5 is an exploded perspective view of the mirror actuator shown in Figure 3. Figure 6 is a perspective view of the mirror, adhesive, support, and shaft shown in Figure 3. Figure 7 is a schematic cross-sectional view illustrating the configuration of the mirror shown in Figure 3. Figure 8 is a graph showing the reflectance of the mirror shown in Figure 3 for each wavelength of light at different incident angles. Figure 9 is a schematic diagram illustrating the configuration of a counter film formed on the back surface of the substrate. Figure 10 is a perspective view showing a modified example of the support according to the present invention. Figure 11 is a cross-sectional perspective view showing the operation of the attitude adjustment mechanism. Figure 12 is a schematic diagram showing how the attitude of the mirror changes due to the attitude adjustment by the attitude adjustment mechanism. Figure 13 is a perspective view showing a modified example of the adjustment screw of the attitude adjustment mechanism according to the present invention. Figure 14 is a top view illustrating that an adhesive is provided between the mirror and the support, and that the mirror and the support face each other with a gap between them. Figure 15 is a schematic diagram illustrating how the degree of mirror warping in a high-temperature environment changes when the mirror and support are bonded together using adhesive so that they face each other with a gap in between, and when the mirror is directly mounted on the support. Figure 16 is a top view showing the internal structure of the motor shown in Figure 3.

[0017] Hereinafter, a mirror actuator according to an embodiment of the present invention will be described based on a preferred embodiment shown in the accompanying drawings. The figures referred to below are schematic diagrams prepared for the purpose of explaining the present invention. The dimensions (length, width, thickness, etc.) of each component shown in the drawings do not necessarily reflect the actual dimensions. In addition, the same reference numeral is used for identical or corresponding elements in each figure. In the following description, the positive direction of the Z-axis in each figure may be referred to as "upward," and the negative direction of the Z-axis may be referred to as "downward."

[0018] <Mirror Actuator> First, a mirror actuator according to an embodiment of the present invention will be described in detail with reference to Figures 2 to 16. Figure 2 is a schematic diagram of a LiDAR system including a mirror actuator according to an embodiment of the present invention. Figure 3 is a perspective view of a mirror actuator according to an embodiment of the present invention. Figure 4 is a perspective view of the mirror actuator shown in Figure 3 from a different angle. Figure 5 is an exploded perspective view of the mirror actuator shown in Figure 3. Figure 6 is a perspective view of the mirror, adhesive, support, and shaft shown in Figure 3. Figure 7 is a schematic cross-sectional view illustrating the configuration of the mirror shown in Figure 3. Figure 8 is a graph showing the reflectance of the mirror shown in Figure 3 for each wavelength of light at different incident angles. Figure 9 is a schematic diagram illustrating the configuration of a counter film formed on the back surface of the substrate. Figure 10 is a perspective view showing a modified example of the support of the present invention. Figure 11 is a cross-sectional perspective view showing the operation of the attitude adjustment mechanism. Figure 12 is a schematic diagram showing how the attitude of the mirror changes due to the attitude adjustment by the attitude adjustment mechanism. Figure 13 is a perspective view showing a modified example of the adjustment screw of the attitude adjustment mechanism of the present invention. Figure 14 is a top view illustrating that an adhesive is provided between the mirror and the support, and that the mirror and the support face each other with a gap in between. Figure 15 is a schematic diagram illustrating how the degree of warping of the mirror in a high-temperature environment changes when the mirror and support are bonded together using an adhesive so that they face each other with a gap in between, and when the mirror is mounted directly on the support. Figure 16 is a top view illustrating the internal structure of the motor shown in Figure 3. Note that in Figure 5, the orientation of the mirror has been changed from that of the mirror in Figures 3 and 4 in order to show the structure of the back side of the mirror.

[0019] Figure 2 schematically shows a LiDAR system 100 including the mirror actuator 1 of the present invention. The LiDAR system 100 comprises a light source 110, the mirror actuator 1 of the present invention used to scan a scanning zone 200 by reflecting a light beam emitted from the light source 110 using a mirror 2, and a sensor 120 for detecting reflected light from an object within the scanning zone 200. The LiDAR system 100 can measure the distance to an object by measuring the time difference between the time when the light beam emitted from the light source 110 irradiates an object within the scanning zone 200 and the time when the reflected light from the object returns to the sensor 120. Furthermore, the LiDAR system 100 can scan within the scanning zone 200 and detect the shape of an object by rapidly rotating or reciprocating the mirror 2 attached to the mirror actuator 1 of the present invention. Typically, the LiDAR system 100 is used in autonomous driving technology to check the surrounding conditions of a vehicle and detect objects such as traffic signs, obstacles, and pedestrians. The light beam emitted from the light source 110 is far-infrared light, and more specifically, monochromatic laser light at 1550 nm. Hereinafter, the mirror actuator 1 of the present invention will be described assuming that the light beam emitted from the light source 110 is monochromatic laser light at 1550 nm.

[0020] The mirror actuator 1 is used to scan the scanning zone 200 by reflecting the light beam emitted from the light source 110. The light beam emitted from the light source 110 is directed by the mirror actuator 1 to scan the scanning zone 200, and the sensor 120 detects the reflected light from objects within the scanning zone 200.

[0021] As shown in Figures 3 and 4, the mirror actuator 1 has an overall shape that is roughly rectangular with an elongated length in the Z direction. The mirror actuator 1 is very small, for example, with dimensions of approximately 20 mm (total length in the X direction) x approximately 41 mm (total length in the Y direction) x 60 mm (total length in the Z direction).

[0022] As shown in Figures 3 to 5, the mirror actuator 1 includes a mirror 2 having a reflective surface 21 that reflects a light beam emitted from a light source 110 and a back surface 22 on the opposite side of the reflective surface 21; a support 3 that supports the mirror 2 from the back surface 22 side; an adhesive 4 (see Figure 6) provided between the back surface 22 of the mirror 2 and the support 3 to fix the mirror 2 to the support 3; a shaft 5 to which the support 3 is attached so that its axial direction (central axis CA) is parallel to the reflective surface 21 of the mirror 2; a motor 6 that rotates the shaft 5 around its axial direction in order to scan the scanning zone 200 with a light beam; and a base portion 7 that supports the shaft 5 so that it can rotate from above and below.

[0023] Figure 6 shows an exploded perspective view of the mirror 2, the support 3 that supports the mirror 2, the adhesive 4 for fixing the mirror 2 to the support 3, and the shaft 5. As shown in Figures 3 and 4, the mirror 2 is a plate-like member that is elongated in the Z direction, having a reflective surface 21 that reflects the light beam emitted from the light source 110 and a back surface 22 on the opposite side of the reflective surface 21. Figure 7 shows a schematic representation of the film structure of the mirror 2. As shown in Figure 7, the mirror 2 comprises a substrate 23 and a dielectric multilayer film 24 provided on the surface of the substrate 23.

[0024] The base material 23 is a sheet-like member and functions as a substrate for the mirror 2. Typically, the base material 23 is formed from a material comprising at least one selected from glass, glass ceramics, silicon, metal (aluminum, copper, etc.), and sapphire. In an example of the present invention, the base material 23 is formed from glass. In an embodiment of the present invention, the thickness of the base material 23 is preferably in the range of 1.0 to 2.0 mm, and in one preferred example, the thickness of the base material 23 is about 1.1 mm.

[0025] The dielectric multilayer film 24 is a sheet-like member provided on the surface of the substrate 23 and has the function of reflecting the light beam emitted from the light source 110. The dielectric multilayer film 24 has multiple SiO ２ The film 241 and multiple Si films 242 are formed by alternately stacking them.

[0026] The dielectric multilayer film 24 is formed on the surface of the substrate 23 by the following procedure. First, the front and back surfaces of the substrate 23 of the mirror 2 are polished. Specifically, a uniform plane is created by polishing the front and back surfaces of the substrate 23 with a high-speed rotating grinding wheel, making the thickness of the substrate 23 uniform and achieving the desired flatness. Next, multiple SiO2 film layers are formed on the surface of the substrate 23. ２ A dielectric multilayer film 24 is formed by alternately stacking film 241 and a plurality of Si films 242. On the surface of the substrate 23, SiO ２ The process of forming the film 241 and the formed SiO ２ By repeating the process of forming a Si film 242 on the surface of film 241, SiO ２ Film 241 and Si film 242 are alternately laminated on the surface of the substrate 23. For example, SiO ２ Film 241 and Si film 242 are in the chamber, SiO ２ Alternatively, by ionizing Si into gas particles using an ion gun device and then irradiating the surface of the substrate 23, Si particles or SiO2 will be released onto the surface of the substrate 23. ２ The film can be formed using an ion-assisted evaporation method that presses particles against the surface.

[0027] Multiple SiO ２ The thickness of each film 241 is preferably in the range of 0.1 to 0.5 μm, and in one preferred example, multiple SiO ２ The total thickness of film 241 is approximately 1.8 μm. The thickness of each of the multiple Si films 242 is preferably in the range of 0.05 to 0.2 μm, and in one preferred example, the total thickness of the multiple Si films 242 is approximately 0.6 μm. In one preferred example, the thickness of the dielectric multilayer film 24 is approximately 2.4 μm, the thickness of the substrate 23 is approximately 1.1 mm, and the thickness of the dielectric multilayer film 24 is 0.003 times or less the thickness of the substrate 23. The uppermost SiO of the dielectric multilayer film 24 ２ Film 241 or Si film 242 (in the example in Figure 7, SiO ２ The surface of the film 241) becomes the reflective surface 21 of the mirror 2.

[0028] Figure 8 is a graph showing the reflectance of the mirror 2 equipped with the dielectric multilayer film 24 described above, against wavelength at different incident angles. In the graph of Figure 8, the horizontal axis corresponds to the wavelength of the light beam emitted from the light source 110, and the vertical axis corresponds to the reflectance of the mirror 2 when the light beam is incident on the reflective surface 21 of the mirror 2 at incident angles of 35°, 55°, and 75°. As shown in Figure 8, the mirror 2 of the present invention has a high reflectance of 98% or more for light in the wavelength range of 1310 nm to 1730 nm, at all incident angles of 35°, 55°, and 75°. Thus, the mirror 2 has a high reflectance (98% or more) and low dependence on the incident angle for light with a very wide wavelength range of 1310 nm to 1730 nm. In particular, mirror 2 has a reflectivity of 98% or more for far-infrared light, including monochromatic laser light of 1550 nm emitted from the light source 110 of the LiDAR system 100, and exhibits very low dependence on the incident angle. By using such mirror 2 in the LiDAR system 100, the intensity of the reflected light from mirror 2 can be stabilized when scanning the light beam, enabling accurate scanning of the scanning zone 200 over a wide incident angle.

[0029] As mentioned in the section on conventional technology, a common dielectric multilayer film for mirrors is TiO ２ +SiO ２ Multilayer film, Ta ２ O ５ +SiO ２ Multilayer films are one example, but TiO ２ Ya Ta ２ O ５ Compared to Si, TiO has a lower refractive index for light in the far-infrared region (e.g., monochromatic laser light at 1550 nm). Therefore, in order to achieve a refractive index that is sufficiently high (e.g., 98%) and has low incident angle dependence for light in the far-infrared region, a dielectric layer (TiO ２ +SiO ２ If it is a multilayer film, TiO ２ Layer and SiO ２ Layer, Ta ２ O ５ +SiO ２ If it is a multilayer film, Ta ２ O５ Layer and SiO ２ The number of layers needs to be increased. As mentioned in the section on the prior art, increasing the number of layers and thickness of such dielectric multilayer films leads to mirror warping and increased costs.

[0030] The dielectric multilayer film 24 of the mirror 2 of the present invention is composed of multiple SiO ２ Since film 241 and multiple Si films 242 are formed by alternately stacking them, the dielectric layer (SiO ２ By reducing the number of layers of film 241 and Si film 242, it is possible to achieve a reflectivity that is high and low dependent on the incident angle for light in the far-infrared region. ２ O ５ +SiO ２ If a multilayer film is used to achieve reflection characteristics equivalent to those of the dielectric multilayer film 24 for far-infrared light, as shown in Figure 8, the thickness of the dielectric multilayer film 24 will typically be about 11.5 μm or more. Therefore, the dielectric multilayer film 24 is TiO ２ +SiO ２ Multilayer film or Ta ２ O ５ +SiO ２ Compared to conventional techniques using multilayer films, it is possible to achieve high reflectivity with low incident angle dependence for light in the far-infrared region with a film thickness that is an order of magnitude thinner. Thus, because the film thickness of the dielectric multilayer film 24 is extremely thin compared to conventional techniques, the bending stress generated in the mirror 2 during the deposition of the dielectric multilayer film 24 can be suppressed, and the flatness of the mirror 2 can be improved. Furthermore, the dielectric layer (SiO2) of the dielectric multilayer film 24 ２ Since the number of layers of film 241 and Si film 242 can be reduced, the cost of the dielectric multilayer film 24 can be reduced.

[0031] Furthermore, the mirror 2 may further include a counter film 25 provided on the back surface of the substrate 23. Typically, the counter film 25 is made of SiO ２It is composed of a single film. When the dielectric multilayer film 24 is deposited on the surface of the substrate 23, ion-assisted deposition is performed in a chamber. At this time, the temperature inside the chamber becomes high, around 300°C. Generally, the linear expansion coefficient (thermal expansion coefficient) of the substrate 23 and the SiO of the dielectric multilayer film 24 ２ The coefficients of linear expansion of film 241 and Si film 242 are significantly different. For example, glass, SiO ２ The average coefficient of linear expansion of Si is 10 × 10, respectively. -６ , 2.1 × 10 -６ , 2.6 × 10 -６ Therefore, when the dielectric multilayer film 24 is deposited and the environment returns from a high temperature to a room temperature environment, the difference in the coefficient of linear expansion of the substrate 23 and the dielectric multilayer film 24 causes the amount of expansion and contraction of the substrate 23 and the dielectric multilayer film 24 to differ significantly. As a result, bending stress is generated in both the substrate 23 and the dielectric multilayer film 24, causing warping of both the substrate 23 and the dielectric multilayer film 24. As shown in Figure 9, the film thickness of the substrate 23 is b [mm], and the Young's modulus of the substrate 23 is E s [GPa], Poisson's ratio of substrate 23 is ν s When the length (half value) of the substrate 23 is l [mm] and the thickness of the dielectric multilayer film 24 is d [mm], the amount of warpage after film formation is δ. c When calculated using Stoney's formula with the amount of warpage before film formation as δ0, it can be expressed as shown in equation (1) below.

[0032]

[0033] As shown in equation (1) above, the amount of warpage δ of the dielectric multilayer film 24 after film formation. c The amount of warping δ of the mirror 2 increases in proportion to the thickness d of the dielectric multilayer film 24. As mentioned above, the thickness d of the dielectric multilayer film 24 of the mirror 2 is very thin compared to the conventional technology, so the amount of warping δ of the mirror 2 that occurs when the dielectric multilayer film 24 is formed c From equation (1) above, it can be seen that this also becomes very small.

[0034] Furthermore, the coefficient of linear expansion of the base material 23 is α s The coefficient of linear expansion of the dielectric multilayer film 24 is α ｆ The Young's modulus E of the dielectric multilayer film 24 ｆ[GPa], the Poisson's ratio of the dielectric multilayer film 24 is ν ｆ , when the measurement room temperature is T [°C] and the film formation temperature is τT d [°C], the internal stress σ generated in the base material 23 and the dielectric multilayer film 24 can be expressed by the following formula (2).

[0035]

[0036] As shown in the above formula (2), the internal stress σ is the sum of the true stress σ ｉ of the dielectric multilayer film 24 and the thermal stress (the second term in formula (2)). In order to reduce or cancel the warp of the mirror 2, a counter film 25 is often formed on the back surface 22 of the mirror 2. As shown in formula (1), the warp amount δ c of the mirror 2 after the formation of the dielectric multilayer film 24 is inversely proportional to the square of the film thickness b [mm] of the base material 23. Furthermore, when there is a variation in the film thickness b of the base material 23 (that is, when the film thickness b is not constant but fluctuates), there is also a variation σ ０ in the warp amount of the mirror 2 after the formation of the dielectric multilayer film 24. The variation σ ０ in the warp amount of the mirror 2 can be expressed by the following formula (3).

[0037]

[0038] When a large number of mirrors 2 are manufactured, a plurality of base materials 23 are individually picked up, the film thickness b of each base material 23 is measured, and further, the warp amount δ c of the mirror 2 after the formation of the dielectric multilayer film 24 is measured. Then, according to the measured film thickness b of each base material 23 and the warp amount δ c of the mirror 2 after the formation of the dielectric multilayer film 24, the film thickness of the counter film 25 for canceling the warp amount of the mirror 2 is determined, and the counter film 25 with the determined film thickness is formed on the back surface of the base material 23 after the formation of the dielectric multilayer film 24. In this way, for each mirror 2, the film thickness b of the base material 23 and the warp amount δ cBy forming a counter film 25 having a film thickness determined based on this on the back surface of the base material 23, the warpage of the mirror 2 that occurs when forming the dielectric multilayer film 24 on the surface of the base material 23 can be canceled by the warpage of the mirror 2 that occurs when forming the counter film 25 on the back surface of the base material 23, and the flatness of the mirror 2 can be improved.

[0039] However, the film thickness b and the warpage amount δ of the base material 23 of each mirror 2 c measurement, and the film thickness b and the warpage amount δ c The determination of the film thickness of the counter film 25 based on is a high-cost operation that requires a lot of man-hours. In order to omit such a high-cost operation, as shown in FIG. 9, a counter film 25 formed of the same film material, film structure, and film thickness as the dielectric multilayer film 24 may be provided on the back surface of the base material 23. The warpage of the mirror 2 that occurs when forming the counter film 25 on the back surface of the base material 23 is affected by the film thickness b of the base material 23, similar to the warpage of the mirror 2 that occurs when forming the dielectric multilayer film 24 on the surface of the base material 23. Therefore, by forming the counter film 25 on the back surface of the base material 23 with the same film material, film structure, and film thickness as the dielectric multilayer film 24 formed on the surface of the base material 23, the warpage of the mirror 2 that occurs when forming the dielectric multilayer film 24 on the surface of the base material 23 can be canceled by the warpage of the mirror 2 that occurs when forming the counter film 25 on the back surface of the base material 23. With such a configuration, it is not necessary to measure the film thickness b of each base material 23 and the warpage amount δ of the mirror 2 after forming the dielectric multilayer film 24, and determine the film thickness of the counter film 25 according to the measured film thickness b and warpage amount δ. As a result, the warpage of the mirror 2 can be suppressed without performing the above-described high-cost operation, and the flatness of the mirror 2 can be improved.

[0040] ​​​​Returning to Figure 6, the support 3 is a member that is fixedly attached to the shaft 5 and supports the mirror 2 from the back surface 22 side of the mirror 2. The support 3 supports the mirror 2 such that the reflective surface 21 and the back surface 22 of the mirror 2 are parallel to the central axis CA of the shaft 5. Typically, the support 3 is made of a metal material such as aluminum. The support 3 comprises a flat central support portion 31 having a surface facing the back surface 22 of the mirror 2 and a back surface facing the shaft 5, a pair of extension portions 32 extending linearly outward from each of the two sides of the central support portion 31, an upper bush portion 33a formed on the back surface of the central support portion 31 and attached to the upper part of the shaft 5, a lower bush portion 33b attached to the lower part of the shaft 5, and an attitude adjustment mechanism 34 for adjusting the attitude of the mirror 2 relative to the shaft 5.

[0041] The central support portion 31 is a flat plate-shaped member having an elongated shape in the Z direction. The front and back surfaces of the central support portion 31 are flat surfaces parallel to the reflective surface 21 and back surface 22 of the mirror 2. The central support portion 31 includes a groove 311 formed in the upper part of the back surface of the central support portion 31, and an elongated opening 312 in the Z direction that penetrates the central part of the central support portion 31 in the thickness direction and separates the upper and lower parts of the back surface of the central support portion 31. The groove 311 is an arc-shaped groove formed to prevent the adjustment screw 342 of the attitude adjustment mechanism 34, which will be described later, from coming into contact with the back surface of the central support portion 31. The groove 311 is in the upper part of the back surface of the central support portion 31 and extends linearly outward from the region adjacent to the adjustment hole 341 formed in the upper bush portion 33a. The inner end of the groove 311 is continuous with the adjustment hole 341, and the outer end of the groove 311 is open outward.

[0042] The pair of extension portions 32 are plate-like portions that extend linearly outward from each of the longitudinal sides of the central support portion 31, spaced apart from each other. In the illustrated configuration, the support 3 has four extension portions 32, but all four extension portions 32 have the same configuration, so one extension portion 32 will be described in detail as a representative example. The surface of the extension portion 32 is continuous with the surface of the central support portion 31 in parallel, and the back surface of the extension portion 32 is continuous with the back surface of the central support portion 31 in parallel. Therefore, the surface and back surface of the extension portion 32 are flat surfaces parallel to the reflective surface 21 and back surface 22 of the mirror 2. In addition, the extension portion 32 extends linearly from the side surface of the central support portion 31 in a direction perpendicular to the longitudinal direction of the central support portion 31. As shown in Figures 6 and 14, adhesive 4 is discretely provided on the surface of the extended portion 32, and the surface of the extended portion 32 and the back surface 22 of the mirror 2 are bonded together by the adhesive 4. In the illustrated configuration, there are four extended portions 32, but the present invention is not limited to this. Depending on the support force required to support the mirror 2 of the extended portion 32, the support 3 may have five or more extended portions 32, or it may have three or fewer extended portions 32. Furthermore, depending on the support force required to support the mirror 2 of the extended portion 32, the extended portions 32 may be omitted. In this case, as shown in Figure 10, adhesive 4 is discretely provided between the surface of the central support portion 31 and the back surface 22 of the mirror 2, and the surface of the central support portion 31 and the back surface 22 of the mirror 2 are bonded together by the adhesive 4.

[0043] Returning to Figure 6, the upper bush portion 33a is a substantially cuboidal member provided on the upper part of the back surface of the central support portion 31. The upper bush portion 33a is located on the back surface of the central support portion 31 and is provided adjacent to the opening 312 from above. The upper bush portion 33a comprises a substantially rectangular parallelepiped body portion 331a, a through hole 332a that penetrates the body portion 331a in the Z direction and through which the shaft 5 is inserted, a set screw hole 333a that penetrates the body portion 331a from the back surface of the body portion 331a and communicates with the through hole 332a, and a set screw 334a for fixing the shaft 5 to the upper bush portion 33a. The body portion 331a has a substantially rectangular parallelepiped shape, and the surface of the body portion 331a is in contact with the back surface of the central support portion 31.

[0044] The through-hole 332a is a circular hole that runs linearly through the main body portion 331a from the top surface to the bottom surface. The shaft 5 is inserted through the through-hole 332a. As shown in Figure 11, the diameter φ1 of the shaft 5 is slightly smaller than the diameter φ2 of the through-hole 332a. Therefore, the upper portion of the shaft 5 is loosely fitted into the through-hole 332a. The set screw hole 333a is a screw hole formed on the back surface of the main body portion 331a and communicates with the through-hole 332a. The set screw 334a is screwed into the set screw hole 333a to fix the shaft 5 to the upper bush portion 33a. The direction in which the set screw 334a is tightened is perpendicular to the Z direction. After inserting the shaft 5 through the through hole 332a, the set screw 334a is screwed into the set screw hole 333a, and the shaft 5 is tightened inside the through hole 332a, thereby fixing the shaft 5 to the upper bush portion 33a, and thereby fixing the position of the mirror 2 relative to the shaft 5.

[0045] The lower bush portion 33b is a substantially cuboidal member provided on the lower part of the back surface of the central support portion 31. The lower bush portion 33b is located on the back surface of the central support portion 31 and is provided adjacent to the opening 312 from below. Similar to the upper bush portion 33a, the lower bush portion 33b comprises a substantially rectangular parallelepiped body portion 331b, a through hole 332b that penetrates the body portion 331b in the Z direction and through which the shaft 5 is inserted, a set screw hole 333b that communicates with the through hole 332b from the back surface of the body portion 331b, and a set screw 334b ​​for fixing the shaft 5 to the lower bush portion 33b. The body portion 331b, set screw hole 333b, and set screw 334b ​​of the lower bush portion 33b have the same configuration as the body portion 331a, set screw hole 333a, and set screw 334a of the upper bush portion 33a, so their description is omitted. On the other hand, the through hole 332b has a diameter approximately equal to the diameter φ1 of the shaft 5. Therefore, the lower portion of the shaft 5 is fitted tightly into the through hole 332b.

[0046] Returning to Figure 6, the attitude adjustment mechanism 34 consists of components for adjusting the attitude of the mirror 2 relative to the shaft 5 (the angle of the mirror 2 relative to the central axis CA of the shaft 5). As shown in Figure 12, the attitude adjustment mechanism 34 includes an adjustment hole 341 that penetrates the main body portion 331a of the upper bush portion 33a in a direction perpendicular to the Z direction, and an adjustment screw 342 that screws into the adjustment hole 341.

[0047] The adjustment hole 341 is a circular hole formed between the two sides of the main body portion 331a of the upper bush portion 33a, on the side closer to the central support portion 31 than the through hole 332a. Also, as shown in Figure 11, the portion of the inner circumferential surface of the adjustment hole 341 opposite to the central support portion 31 communicates with the through hole 332a of the upper bush portion 33a. Therefore, when the shaft 5 is inserted through the through hole 332a, the portion of the upper part of the shaft 5 on the central support portion 31 side is located inside the adjustment hole 341. The adjustment hole 341 includes a screw groove 3411 formed on the base end side of its inner circumferential surface, and a flat portion 3412 formed on the inner circumferential surface on the tip side of the screw groove 3411. The adjustment screw 342 is screwed into the screw groove 3411 to adjust the position of the mirror 2 relative to the shaft 5. The position of the mirror 2 relative to the shaft 5 is adjusted by adjusting the degree to which the adjustment screw 342 is threaded into the thread groove 3411 of the adjustment hole 341. The adjustment screw 342 has a thread groove formed on its outer circumference and comprises a threaded portion 3421 that screws into the thread groove 3411 of the adjustment hole 341, a shaft portion 3422 that extends linearly from the tip of the threaded portion 3421 toward the tip, and a tip portion 3423 provided at the tip of the shaft portion 3422 that fits into the flat portion 3412 of the adjustment hole 341. As described above, when the shaft 5 is inserted through the through hole 332a, the portion of the upper part of the shaft 5 on the central support portion 31 side is located inside the adjustment hole 341. In this state, the shaft portion 3422 contacts the portion of the upper part of the shaft 5 that is on the central support portion 31 side within the adjustment hole 341, and biases the upper part of the shaft 5 in a direction away from the adjustment screw 342 within the through hole 332a.

[0048] As shown in Figure 11, the shaft portion 3422 is concentric with the threaded portion 3421 and the tip portion 3423, and has a tapered shape in which the diameter gradually decreases from the base end to the tip end of the adjustment screw 342. Therefore, as shown by the arrow in Figure 11, when the adjustment screw 342 is tightened clockwise (in the direction of the arrow around the adjustment screw 342 in Figure 11) and screwed into the threaded groove 3411 of the adjustment hole 341, the diameter of the portion of the shaft portion 3422 that contacts the shaft 5 gradually increases. As a result, the pressing force applied from the shaft portion 3422 to the upper portion of the shaft 5 increases, and the position of the upper portion of the shaft 5 within the through hole 332a of the upper bush portion 33a is displaced in a direction away from the adjustment screw 342 (in the direction of the arrow that spans the shaft 5 and the set screw 334a in Figure 11). On the other hand, as shown in Figure 12, the lower portion of the shaft 5 is fitted tightly into the through hole 332b of the lower bush portion 33b. Therefore, as the position of the upper part of the shaft 5 shifts within the through-hole 332a, the angle of the support 3 with respect to the central axis CA of the shaft 5 changes. As a result, as shown in Figure 12, the upper part of the mirror 2 held by the support 3 tilts away from the shaft 5, and the posture of the mirror 2 with respect to the shaft 5 changes. This posture adjustment mechanism 34 makes it possible to fine-tune the posture of the mirror 2 with respect to the shaft 5 (the angle of the mirror 2 with respect to the central axis CA of the shaft 5) in mdeg units, thereby improving the parallelism of the mirror 2 with respect to the central axis CA of the shaft 5. By adjusting the degree of screwing of the adjustment screw 342 while measuring the parallelism of the mirror 2 with respect to the central axis CA of the shaft 5 and tightening the set screw 334a, the parallelism of the mirror 2 with respect to the central axis CA of the shaft 5 can be fine-tuned with mdeg units. As a result, the reflection angle of the light beam by the mirror 2 can be controlled with high precision, and the measurement accuracy of the LiDAR system 100 can be greatly improved.

[0049] In the illustrated configuration, the shaft portion 3422 has a tapered shape concentric with the threaded portion 3421 and the tip portion 3423, but the present invention is not limited thereto. As shown in Figure 13, the central axis of the shaft portion 3422 may not be located on the same line as the central axes of the threaded portion 3421 and the tip portion 3423, and the adjustment screw 342 may be configured to have a cylindrical shape with a constant diameter. Even with such a configuration, the position of the mirror 2 relative to the shaft 5 can be finely adjusted by the degree to which the adjustment screw 342 is screwed in.

[0050] Returning to Figure 6, the adhesive 4 has the function of bonding the back surface 22 of the mirror 2 to the surface of the stretched portion 32 of the support 3. The adhesive 4 is an elastic adhesive that hardens at room temperature. In the illustrated embodiment, the adhesive 4 is provided discretely in multiple locations between the back surface 22 of the mirror 2 and the surface of the stretched portion 32 of the support 3 so as to have a circular planar shape, but the present invention is not limited thereto. The planar shape of the adhesive 4, the position of the bonding locations, and the number of bonding locations may be changed within the range in which the mirror 2 and the support 3 can rotate or reciprocate as a single unit. Furthermore, the adhesive 4 is not particularly limited as long as it hardens at room temperature and is elastic after hardening. For example, an elastic adhesive can be used as the adhesive 4. Note that in the illustrated embodiment, the adhesive 4 is provided between the back surface 22 of the mirror 2 and the surface of the stretched portion 32 of the support 3.

[0051] As shown in Figure 14, the adhesive 4 is provided between the back surface 22 of the mirror 2 and the surface of the extended portion 32 of the support 3, fixing the mirror 2 to the support 3 while the mirror 2 is separated from the central support portion 31 and the extended portion 32 of the support 3. More specifically, the mirror 2 is fixed to the support 3 by the adhesive 4 through a gap formed by the thickness of the adhesive 4. Here, the back surface 22 of the mirror 2 faces the surfaces of the central support portion 31 and the extended portion 32 of the support 3 through a gap, and does not come into contact with the support 3. The separation distance D between the mirror 2 and the support 3 corresponds to the thickness of the adhesive 4 that has hardened between the back surface 22 of the mirror 2 and the support 3. In other words, the mirror 2 is supported by the support 3 via the adhesive 4 so as to be suspended from the support 3. In this way, by bonding the mirror 2 and the support 3 using adhesive 4 so that the mirror 2 and the support 3 face each other with a gap in between, when the mirror actuator 1 is used in a high-temperature environment, the bending stress generated in the mirror 2 due to the difference between the coefficient of thermal expansion of the mirror 2 and the coefficient of thermal expansion of the support 3 can be reduced, and warping of the mirror 2 can be prevented.

[0052] Figure 15 is a schematic diagram illustrating how the degree of warping of the mirror 2 in a high-temperature environment changes when the mirror 2 and the support 3 are bonded together using adhesive 4 so that they face each other with a gap in between, and when the mirror 2 is directly mounted on the support 3. Figure 15(a) shows the mirror 2 and support 3 in a normal temperature environment when the mirror 2 is directly bonded to the support 3. That is, in Figure 15(a), the mirror 2 is supported by the support 3 while in contact with it. Figure 15(b) shows the mirror 2 and support 3 in a high-temperature environment when the mirror 2 is directly bonded to the support 3. Figure 15(c) shows the mirror 2 and support 3 in a normal temperature environment when the mirror 2 and support 3 are bonded together so that they face each other with a gap in between. That is, in Figure 15(c), the mirror 2 is not in contact with the support 3. Figure 15(d) shows the mirror 2 and support 3 in a high-temperature environment when the mirror 2 and support 3 are bonded together so that they face each other with a gap in between.

[0053] As shown in Figure 15(a), it is assumed that there is no warping in the mirror 2 and support 3 under normal temperature conditions (e.g., ambient temperature of 20°C). Furthermore, due to the difference in materials between the mirror 2 and support 3, the linear expansion coefficient (thermal expansion coefficient) of the mirror 2 and the linear expansion coefficient of the support 3 are different. Therefore, as shown in Figure 15(b), under high temperature conditions (e.g., ambient temperature of 75°C), a difference occurs between the amount of elongation of the mirror 2 in the X direction in Figure 15 and the amount of elongation of the support 3. This difference causes warping in the mirror 2, reducing its flatness.

[0054] On the other hand, in the mirror 2 of the mirror actuator 1 of the present invention, as shown in Figure 14, the mirror 2 and the support 3 are bonded together using an adhesive 4 so that the mirror 2 and the support 3 face each other with a gap in between. In this case, as shown in the enlarged view in Figure 14, bonds are formed at the interface between the adhesive 4 and the back surface 22 of the mirror 2, and at the interface between the adhesive 4 and the surface of the stretched portion 32 of the support 3, as indicated by the arrows in the figure. As a result, by ensuring a certain thickness of the adhesive 4, a buffer area (dotted line portion in the figure) is created in the center of the adhesive 4. As a result, when the mirror 2 and the support 3 are stretched when the mirror 2 is placed in a high-temperature environment, the buffer area of ​​the adhesive 4 mitigates the bending stress generated in the mirror 2.

[0055] As shown in Figure 15(c), it is assumed that there is no warping in the mirror 2 and support 3 under normal temperature conditions. As shown in Figure 15(d), due to the difference in the coefficient of thermal expansion of the mirror 2 and the support 3, even if there is a difference in the amount of expansion and contraction of the mirror 2 and the support 3 under high temperature conditions, the bending stress generated in the mirror 2 is mitigated by the thickness and elasticity of the adhesive 4. Therefore, the warping generated in the mirror 2 is mitigated, and the decrease in the flatness of the mirror 2 under high temperature conditions can be suppressed.

[0056] To significantly suppress the decrease in flatness of the mirror 2 under high-temperature conditions, it is preferable to set the separation distance D between the back surface 22 of the mirror 2 and the surface of the extended portion 32 of the support 3 to 0.5 mm or more. By setting the separation distance D to 0.5 mm, a sufficient buffer area can be formed in the adhesive 4, thereby suppressing the decrease in flatness of the mirror 2 under high-temperature conditions. In this way, by bonding the mirror 2 and the support 3 using the adhesive 4 so that the mirror 2 and the support 3 face each other with a gap in between, the decrease in flatness of the mirror 2 under high-temperature conditions can be suppressed, and accurate control of the reflection angle of the light beam under high-temperature conditions becomes possible. As a result, even under high-temperature conditions, the mirror actuator 1 can accurately orient the light beam to a predetermined location.

[0057] Returning to Figure 6, the shaft 5 is a cylindrical member having a central axis CA that extends linearly in the Z direction. The shaft 5 is inserted through the through hole 332a of the upper bush portion 33a and the through hole 332b of the lower bush portion 33b of the support 3, and the support 3 that supports the mirror 2 is fixedly attached to the shaft 5 by tightening the set screws 334a and 334b. When the shaft 5 rotates around the central axis CA by the motor 6, the mirror 2 also rotates in accordance with the rotation of the shaft 5.

[0058] Returning to Figure 5, the motor 6 is a block-shaped member formed in the shape of a low-profile rectangular parallelepiped. The motor 6 has the function of rotating or reciprocating the shaft 5 that supports the mirror 2. The motor 6 comprises a bottom cover 61, a pair of coils 62 held on the bottom cover 61 and spaced apart from each other in the X direction, a movable magnet 63, a core portion 64 made up of a plurality of stacked plates and inserted into the coils 62, and electrodes 65 for connecting to an external device. Figure 16 shows the internal structure of the motor 6. Note that in order to show the internal structure of the motor 6, the plates of the core portion 64 located above the pair of coils 62 are omitted in Figure 16.

[0059] The bottom cover 61 is a plate-like member having a roughly rectangular parallelepiped planar shape and functions as a substrate for the mirror actuator 1. The bottom cover 61 has a rectangular planar shape and supports a pair of coils 62, a movable magnet 63, and a core portion 64 from below.

[0060] The pair of coils 62 are elongated cylindrical spiral coil members in the Y direction and are installed on the bottom cover 61. Each of the pair of coils 62 is spaced apart from each other on the bottom cover 61 and is installed parallel to each other in the X direction. In addition, each of the pair of coils 62 has a substantially square cross-sectional shape when viewed from the Y direction, and furthermore, the whole has a cylindrical shape with a hollow center. The pair of coils 62 are formed by processing a conductor into a spiral shape, and when an electric current is passed through the conductor, a magnetic field is generated around it, creating a magnetic field path that circulates through the core portion 64 through which the pair of coils 62 are inserted, causing the movable magnet 63 to rotate or reciprocate.

[0061] The movable magnet 63 is a permanent magnet that is rotatably mounted on the bottom cover 61. The movable magnet 63 rotates or reciprocates due to the adhesive and repulsive forces generated between it and the core portion 64, which is magnetized by the magnetic flux generated by the pair of coils 62. As will be described later, the lower end of the shaft 5 is integrated with the movable magnet 63, and the shaft 5 and the mirror 2 also rotate or reciprocate as the movable magnet 63 rotates or reciprocates.

[0062] The core portion 64 is a component composed of multiple stacked plates installed on the bottom cover 61. The core portion 64 is used as an electromagnet. The core portion 64 passes through the cavities of a pair of coils 62 and faces the movable magnet 63 with a gap between them. By controlling the strength and direction of the current flowing through the pair of coils 62, the movable magnet 63 can be rotated or reciprocated in any direction and angle.

[0063] Multiple electrodes 65 are metal members connected to an external device to conduct current through a pair of coils 62. Each of the multiple electrodes 65 is connected to the corresponding end of the pair of coils 62, and current flows through the pair of coils 62 through the electrodes 65. By controlling the direction and strength of the current flowing through the pair of coils 62, the adhesive or repulsive force between the portion of the core 64 that is in close proximity to and facing the movable magnet 63 and the movable magnet 63 can be controlled, thereby allowing the movable magnet 63 to rotate or reciprocate.

[0064] Returning to Figure 5, the base portion 7 is a member that supports the shaft 5 from both ends in the Z direction. The base portion 7 includes a plate-shaped bottom portion 71 that rotatably supports the lower end of the shaft 5, a plate-shaped cover portion 72 that rotatably supports the upper end of the shaft 5, and a side portion 73 that connects the bottom portion 71 and the cover portion 72 so that the bottom portion 71 and the cover portion 72 are spaced apart from each other and face each other in the Z direction.

[0065] The bottom portion 71 is a plate-like part with a substantially rectangular planar shape that supports the shaft 5 from below. The upper and lower surfaces of the bottom portion 71 are flat surfaces perpendicular to the Z direction, and the thickness (length in the Z direction) of the bottom portion 71 is constant. The bottom portion 71 is supported from below by the motor 6. As shown in Figure 4, the length of the bottom portion 71 in the X direction is longer than the length of the motor 6 in the X direction, and furthermore, the length of the bottom portion 71 in the Y direction is shorter than the length of the motor 6 in the Y direction. Returning to Figure 5, the bottom portion 71 also has a lower bearing 711 that rotatably receives the lower end of the shaft 5 from below. The lower bearing 711 is a donut-shaped member formed on the bottom portion 71, and by fitting the lower end of the shaft 5 into its inner ring, it stabilizes the posture of the shaft 5 and enables smooth rotation of the shaft 5.

[0066] The cover portion 72 is a plate-like portion with a substantially rectangular planar shape that supports the shaft 5 from above. The upper and lower surfaces of the cover portion 72 are flat surfaces perpendicular to the Z direction. The cover portion 72 has an upper bearing 721 that rotatably receives the upper end of the shaft 5 from above. The upper bearing 721 is a donut-shaped member formed on the cover portion 72, and by fitting the upper end of the shaft 5 into its inner ring, it stabilizes the axis of the shaft 5 and enables smooth rotation of the shaft 5.

[0067] The side portion 73 is the part that connects the bottom portion 71 and the lid portion 72 such that the bottom portion 71 and the lid portion 72 are spaced apart from each other and face each other in the Z direction. The side portion 73 connects the end of the bottom portion 71 on the +Y direction side and the end of the lid portion 72 on the +Y direction side. The side portion 73 comprises a main body portion 731 that extends linearly in the height direction and a base portion 732 that is provided so as to protrude outward from the lower end of the main body portion 731. A substrate 74 for connecting electrodes 65 for supplying current to a pair of coils 62 and an external device is provided on the base portion 732. The shaft 5 is rotatably supported by the lower bearing 711 and the upper bearing 721, and current is supplied to the pair of coils 62 via the substrate 74.

[0068] Thus, in the mirror actuator 1 of the present invention, the mirror 2 is provided on the surface of the substrate 23 and a plurality of SiO ２ It is composed of a dielectric multilayer film 24 in which film 241 and multiple Si films 242 are alternately stacked. ２ By using a dielectric multilayer film 24 formed by alternately stacking films 241 and Si films 242, a mirror 2 with high reflectivity to far-infrared light (especially monochromatic laser light at 1550 nm) can be obtained. Furthermore, conventional TiO ２ +SiO ２ Multilayer film and Ta ２ O ５ +SiO ２ Compared to multilayer films, the dielectric layer (SiO ２The number of layers of film 241 and Si film 242 can be reduced. As a result, warping of the mirror 2 during the deposition of the dielectric multilayer film 24 can be reduced, and a decrease in the flatness of the mirror 2 can be prevented. In addition, since the number of dielectric layers can be reduced, the mirror 2 can be made lighter, and as a result, the mirror 2 can be rotated or reciprocated at high speed. Therefore, this leads to an improvement in the measurement accuracy of the LiDAR system 100. Furthermore, SiO ２ Since film 241 and Si film 242 are inexpensive and allow for a reduction in the number of dielectric layers, the cost of mirror 2 can be reduced.

[0069] Furthermore, the mirror 2 of the mirror actuator 1 of the present invention is SiO ２ The dielectric multilayer film 24 is composed of alternating layers of film 241 and Si film 242. Such a dielectric multilayer film 24 has a reflectivity that is very high (e.g., 98% or more) and low dependence on the incident angle for light in the far-infrared region (e.g., monochromatic laser light at 1550 nm). ２ By using a mirror 2 having a dielectric multilayer film 24 constructed by alternately stacking films 241 and Si films 242, the intensity of reflected light from the mirror 2 when scanning the light beam can be stabilized, enabling accurate scanning of the scanning zone 200.

[0070] Furthermore, in the mirror actuator 1 of the present invention, the mirror 2 is fixed to the support 3 by an adhesive 4 provided between the back surface 22 of the mirror 2 and the support 3. Therefore, the back surface 22 of the mirror 2 faces the support 3 with a gap in between and does not come into contact with the support 3. As a result, even if the amount of thermal expansion and contraction of the mirror 2 and the amount of thermal expansion and contraction of the support 3 differ in a high-temperature environment, the bending stress generated in the mirror 2 is mitigated by the thickness and elasticity of the adhesive 4. Therefore, warping of the mirror 2 is mitigated, and the decrease in the flatness of the mirror 2 in a high-temperature environment can be suppressed.

[0071] Furthermore, the mirror actuator 1 of the present invention is equipped with a posture adjustment mechanism 34 for adjusting the orientation of the mirror 2 with respect to the shaft 5. By using such a posture adjustment mechanism 34, the parallelism of the reflective surface 21 of the mirror 2 with respect to the shaft 5 can be finely adjusted. By finely adjusting the parallelism of the mirror 2, the reflection angle of the light beam can be controlled with high precision, and the measurement accuracy of the LiDAR system 100 can be improved.

[0072] Although the mirror actuator of the present invention has been described above based on the illustrated embodiments, the present invention is not limited thereto. Each component of the present invention can be replaced with any other component that can perform a similar function, or any other component can be added to each component of the present invention.

[0073] Those skilled in the art and the field to which the present invention pertains will be able to modify the configuration of the mirror actuator of the present invention as described without significantly departing from the principles, concepts, and scope of the present invention, and the mirror actuator having the modified configuration will also be within the scope of the present invention.

[0074] Furthermore, the number and types of components of the mirror actuators in each embodiment shown in Figures 2 to 16 are merely illustrative examples for illustrative purposes, and the present invention is not necessarily limited thereto. Embodiments in which any components are added or combined, or any components are removed, are also within the scope of the present invention, without departing from the principles and intent of the present invention.

[0075] In the mirror actuator according to the present invention, the mirror is fixed to the support by an adhesive provided between the back surface of the mirror and the support. Therefore, the back surface of the mirror faces the support with a gap in between and does not come into contact with the support. As a result, even if the amount of thermal expansion and contraction of the mirror and the support differ in high-temperature environments, the bending stress generated in the mirror is mitigated by the thickness and elasticity of the adhesive. Therefore, warping of the mirror is mitigated, and the decrease in the flatness of the mirror in high-temperature environments can be suppressed. Thus, the present invention has industrial applicability.

Claims

1. A mirror actuator used to scan a scanning zone by reflecting a light beam emitted from a light source, comprising: a mirror having a reflective surface that reflects the light beam emitted from the light source and a back surface opposite to the reflective surface; a support that supports the mirror from the back surface side; an adhesive provided between the back surface of the mirror and the support for fixing the mirror to the support; a shaft to which the support is attached such that its axial direction is parallel to the reflective surface of the mirror; and a motor that rotates or reciprocates the shaft around the axial direction of the shaft in order to scan the scanning zone with the light beam, wherein the back surface of the mirror faces the support with a gap between them and does not contact the support.

2. The mirror actuator according to claim 1, wherein the gap between the back surface of the mirror and the support is 0.5 mm or more.

3. The mirror actuator according to claim 1, wherein the adhesive is discretely provided between the back surface of the mirror and the support.

4. The mirror actuator according to claim 1, wherein the support comprises a plate-shaped central support portion on which the mirror is fixed, a bush portion formed on the back surface of the central support portion through which the shaft is inserted, and a set screw for fixing the bush portion to the shaft.

5. The mirror actuator according to claim 4, wherein the adhesive is provided between the back surface of the mirror and the front surface of the central support portion of the support.

6. The mirror actuator according to claim 4, wherein the support further comprises extended portions that extend linearly outward from each of the two sides of the central support portion, and the adhesive is provided between the back surface of the mirror and the extended portion of the support.

7. The mirror actuator according to claim 1, wherein the support body is provided with a posture adjustment mechanism for adjusting the posture of the mirror relative to the shaft.

8. The mirror actuator according to claim 7, wherein the support further comprises a plate-shaped central support portion on which the mirror is fixed, and a bush portion formed on the back surface of the central support portion, through which the shaft is inserted and fixedly attached to the shaft, the bush portion comprising a block-shaped main body portion provided on the back surface of the central support portion and extending linearly in the axial direction of the shaft, a through hole that penetrates the main body portion in the axial direction of the shaft and through which the shaft is inserted, and a set screw for fixing the shaft to the bush portion.

9. The mirror actuator according to claim 8, wherein the attitude adjustment mechanism includes an adjustment hole that penetrates the main body of the bush portion in a direction perpendicular to the axial direction of the shaft and has a screw groove formed on the base end side of the inner circumferential surface and a flat portion formed on the inner circumferential surface on the tip side of the screw groove, and an adjustment screw that screws into the screw groove of the adjustment hole, wherein the attitude of the mirror with respect to the shaft is adjusted by adjusting the degree of screwing of the adjustment screw into the screw groove of the adjustment hole.

10. The mirror actuator according to claim 9, wherein the bushing portion further comprises a set screw hole that penetrates the main body portion and communicates with the through hole, and the position of the mirror with respect to the shaft is fixed by screwing the set screw into the set screw hole.

11. The mirror actuator according to claim 9, wherein the adjustment hole of the attitude adjustment mechanism is formed in a portion of the bush portion that is closer to the central support portion than the through hole.

12. The mirror actuator according to claim 9, wherein the adjustment screw comprises a screw portion having a screw groove formed on its outer surface and screwing into the screw groove of the adjustment hole, a shaft portion extending linearly from the tip of the screw portion toward the tip, and a tip portion provided at the tip of the shaft portion and fitting into the flat portion of the adjustment hole, the through hole of the bush portion is in communication with the adjustment hole of the attitude adjustment mechanism, and the shaft portion of the adjustment screw presses against the shaft that passes through the through hole of the bush portion.

13. The mirror actuator according to claim 12, wherein the diameter of the through hole of the bushing portion communicating with the adjustment hole of the attitude adjustment mechanism is greater than the diameter of the shaft, and the shaft portion of the adjustment screw presses against the shaft, thereby biasing the shaft in the direction opposite to that of the adjustment screw within the through hole of the bushing portion.

14. The mirror actuator according to claim 12, wherein the position of the shaft within the through hole of the bushing portion is changed by adjusting the degree of threading of the adjustment hole of the adjustment screw with respect to the screw groove.

15. The mirror actuator according to claim 12, wherein the shaft portion of the adjustment screw is concentric with the threaded portion and the tip portion, and has a tapered shape in which the diameter gradually decreases from the base end to the tip end.

16. The mirror actuator according to claim 12, wherein the central axis of the shaft portion of the adjustment screw is not located on the same line as the central axis of the screw portion and the tip portion.

17. The mirror actuator according to claim 8, wherein the bushing portion is attached to the upper portion of the shaft, and further comprises a second bushing portion attached to the lower portion of the shaft.

Images