JP2022140128A - mirror actuator - Google Patents

Abstract

To provide a mirror actuator that can be reduced in size while ensuring the rigidity of a mirror part.SOLUTION: A mirror actuator (1) comprises: a mirror part (10) that has a first surface (11) reflecting an electromagnetic wave and a second surface (12) on the opposite side of the first surface (11), and has a processing pattern formed on the second surface (12); and a holding part (40) that swingably holds the mirror part (10). The processing pattern is composed of a portion in which the members of the mirror part (10) are present and a portion in which the members are not present, and the density of a first area including the center (c) of the second surface (12) is larger than the density of a second area located closer to a peripheral part of the mirror part (10) than the first area.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to mirror actuators.

2. Description of the Related Art In recent years, devices have been developed that acquire information about surrounding objects and the like from the results of detecting electromagnetic waves. 2. Description of the Related Art As a scanning device that scans an electromagnetic wave, there is a device that reflects and deflects an electromagnetic wave emitted from an irradiation unit by a reflecting mirror. In order to increase the flatness during driving, there have been proposals for reducing weight while maintaining rigidity by processing the back surface, but it was difficult to achieve both rigidity and weight reduction (see, for example, Patent Document 1).

WO2014/122781

In scanning devices, movable mirror actuators with reflective mirrors are sometimes used. Mirror actuators include MEMS mirrors, which are small movable mirror devices manufactured by, for example, MEMS (Micro Electro Mechanical Systems) technology.

Here, the reflecting mirror of the mirror actuator becomes thicker and heavier if the rigidity is secured by increasing the flatness. On the other hand, in order to increase the resonance frequency that oscillates the reflecting mirror, it is desired to reduce the weight of the reflecting mirror.

An object of the present disclosure made in view of the above is to provide a mirror actuator capable of reducing the weight while ensuring the rigidity of the mirror section.

A mirror actuator according to one embodiment includes:
a mirror portion having a first surface that reflects electromagnetic waves and a second surface opposite to the first surface, the second surface having a processed pattern formed thereon;
a holding part that holds the mirror part so that it can swing,
The processing pattern consists of a portion where the member of the mirror portion exists and a portion where the member does not exist, and the density of the mirror portion in the first region including the center of the second surface is higher than that in the first region. The density is greater than that of the second region located on the peripheral side.

According to the present disclosure, it is possible to provide a mirror actuator capable of reducing the weight while ensuring the rigidity of the mirror section.

FIG. 1 is a plan view showing a schematic configuration of a mirror actuator according to one embodiment. FIG. 2 is a cross-sectional view of the mirror actuator of FIG. 1 taken along line AA. 3 is an exploded enlarged view of the mirror portion of the mirror actuator of FIG. 1, etc. FIG. FIG. 4 is an example of a processing pattern for cutting the second surface of the mirror section. FIG. 5 is an example of a processing pattern for cutting the second surface of the mirror section. FIG. 6 is an example of a processing pattern for cutting the second surface of the mirror section. FIG. 7 is an example of a processing pattern for cutting the second surface of the mirror section. FIG. 8 is an example of a processing pattern for cutting the second surface of the mirror section. FIG. 9 is an example of a processing pattern for cutting the second surface of the mirror section. FIG. 10 is an example of a processing pattern for cutting the second surface of the mirror section. FIG. 11 is an example of a processing pattern for cutting the second surface of the mirror section. FIG. 12 is an example of a processing pattern for cutting the second surface of the mirror section. FIG. 13 is an example of a processing pattern for cutting the second surface of the mirror section.

FIG. 1 is a plan view showing a schematic configuration of a mirror actuator 1 according to one embodiment. FIG. 2 is a cross-sectional view of the mirror actuator 1 of FIG. 1 taken along line AA. The mirror actuator 1 is an actuator provided with a movable reflecting mirror that is used for reflecting and deflecting electromagnetic waves with a reflecting mirror. The electromagnetic waves may be visible light, for example, or infrared light, for example. In this embodiment, the mirror actuator 1 is a MEMS mirror.

As an example, the mirror actuator 1 is used in an electromagnetic wave detection device that is mounted on a vehicle to assist safe driving. When the mirror actuator 1 is used in the electromagnetic wave irradiation of the electromagnetic wave detection device, the mirror actuator 1 deflects the electromagnetic waves input from, for example, a laser diode so that the electromagnetic waves are output to a predetermined range of space. At least part of the electromagnetic waves deflected by the mirror actuator 1 can be reflected by predetermined targets (persons, objects, etc.). The electromagnetic wave (reflected wave) reflected by the target is detected by the light receiving system of the electromagnetic wave detection device, and the target is specified and the distance to the target is calculated by the processor.

In particular, the mirror actuator 1 is required to have a high resonance frequency when used in an on-vehicle electromagnetic wave detection device. For example, the mirror actuator 1, which is a MEMS mirror, is driven at a resonance frequency in the main scanning direction (the direction of oscillation about a "first axis (a1)" to be described later). Low-frequency noise may occur while the vehicle is running, and if the resonance frequency is low, such noise may cause the mirror actuator 1 to malfunction. Therefore, by increasing the resonance frequency, the reliability of the operation of the mirror actuator 1 can be increased. Also, by increasing the resonance frequency, the mirror actuator 1 can oscillate the reflecting mirror at high speed. Here, the resonance frequency can be increased by reducing the weight of the reflecting mirror. With the configuration described below, the mirror actuator 1 according to this embodiment can reduce the weight while ensuring the rigidity of the reflecting mirror, and as a result, can increase the resonance frequency.

As shown in FIGS. 1 and 2, in this embodiment, the mirror actuator 1 includes a mirror section 10, a columnar member 41, a holding section 40, and a driving section 30. As shown in FIGS. The mirror actuator 1 also includes a rib portion 20 , a substrate 50 and a package 60 .

The mirror section 10 has a first surface 11 that reflects electromagnetic waves and a second surface 12 opposite to the first surface 11 . The first surface 11 is a reflective mirror. The second surface 12 is cut according to a processing pattern which will be described later. In this embodiment, the shape of the mirror section 10 is a circle (perfect circle), but the shape is not limited to this. As another example, the shape of the mirror portion 10 may be elliptical, square, rectangular, or the like. The diameter of the reflecting mirror is 6 mm as an example. The thickness of the portion where the second surface 12 of the mirror section 10 is not shaved is, for example, 150 μm. The thickness of the portion where the second surface 12 of the mirror section 10 is shaved is, for example, 50 μm. The depth to which the second surface 12 of the mirror section 10 is shaved is not particularly limited, but is preferably 50% or more of the thickness when not shaved in order to enhance the weight reduction effect. In addition, the depth of the second surface 12 of the mirror section 10 to be cut is preferably 80% or less of the thickness when it is not cut, in order to maintain rigidity. The second surface 12 is cut according to the processing pattern by a method such as etching of semiconductor manufacturing technology. For example, a technique such as Deep RIE (Reactive Ion Etching) may be used, but it is not limited to this. The reflective mirror may be a thin film of a metal material with high light reflectance, such as gold or aluminum.

The holding portion 40 swingably holds the mirror portion 10 via a columnar member 41 connected at the center c of the mirror portion 10 . In this embodiment, the columnar member 41 is connected so as to be perpendicular to the plane of the mirror section 10 (the plane parallel to the reflecting mirror). The mirror section 10 and the columnar member 41 may be adhered or integrally formed. Further, the columnar member 41 and the holding portion 40 may be adhered or integrally formed. The material of the mirror section 10 excluding the reflecting mirror, the columnar member 41 and the holding section 40 may be, for example, silicon. The materials of the mirror section 10, the columnar member 41, and the holding section 40 may be different materials, and may be formed of a plurality of materials. The holding part 40 is provided on the substrate 50 . The substrate 50 is insulating and may be a silicon substrate made of silicon oxide or the like.

Here, FIG. 3 is an exploded enlarged view of the mirror portion 10, the holding portion 40, etc. of the mirror actuator 1. As shown in FIG. In this embodiment, the holding section 40 includes a first holding section 42 that holds the mirror section 10 via a columnar member 41, a second holding section 44 that holds the first holding section 42 via a torsion bar 43, Prepare. A tip portion of the columnar member 41 on the side of the holding portion 40 is connected to the first holding portion 42 . As shown in FIG. 3 , a portion of the second surface 12 of the mirror section 10 that is connected to the columnar member 41 may be referred to as a connection region 13 of the second surface 12 .

The mirror section 10 swings about the first holding section 42 with the first axis (a1) and the second axis (a2) as rotation axes. The swing direction with the first axis (a1) as the rotation axis corresponds to the main scanning direction in which the mirror section 10 is driven by the resonance frequency. The swinging direction around the second axis (a2) orthogonal to the first axis (a1) corresponds to the sub-scanning direction in which the mirror section 10 is driven at a frequency lower than the resonance frequency. As described above, the mirror actuator 1 according to the present embodiment drives the mirror section 10 in two-dimensional directions, but it may be driven only in one-dimensional direction (main scanning direction).

The drive section 30 swings the mirror section 10 about the first axis (a1) by changing the drive voltage at the resonance frequency. Further, in the present embodiment, the drive section 30 swings the mirror section 10 around the second axis (a2) by changing the drive voltage at a frequency lower than the resonance frequency. The drive unit 30 includes, for example, electrodes that are arranged so as to mesh with each other. A driving voltage is applied to the electrodes. The drive unit 30 swings the mirror unit 10 by generating an electrostatic force corresponding to the potential difference between the electrodes. Here, the driving section 30 is not limited to one that swings the mirror section 10 by electrostatic force. As another example, the driving section 30 may have a magnet arranged to swing the mirror section 10 by the Lorentz force. The drive unit 30 is provided on the substrate 50 .

The rib portion 20 is provided on the substrate 50 to give strength to the substrate 50 . As shown in FIG. 2, in this embodiment, the substrate 50 is mounted to contact the package 60 only at its edges. Therefore, the rib portion 20 is provided in order to impart rigidity to the substrate 50 and prevent deformation. The substrate 50 and the rib portion 20 may be bonded with a known semiconductor material. The material of the rib portion 20 is, for example, silicon, but is not limited to this. Here, the package 60 may be sealed with a sealing member made of a material (glass as an example) that transmits electromagnetic waves reflected by the reflecting mirror, or may have an opening as shown in the example of FIG.

As described above, the second surface 12 of the mirror section 10 is cut according to the machining pattern for weight reduction. The machining pattern is to grind the mirror section 10 such that the density of the first region r1 including the center c of the mirror section 10 is higher than the density of the second region r2 not including the center c of the mirror section 10. Just do it. The second region r2 is a region located closer to the periphery of the mirror section 10 than the first region r1. The first region r1 and the second region r2 may be regions of concentric circles around the center c of the mirror section 10 . There may be a third region r3 with a lower pattern density than the second region r2. The change in pattern density from the center c of the mirror portion 10 toward the peripheral portion side of the mirror portion 10 may be a gentle change. Here, the density is indicated by the amount of members forming the mirror section 10 per unit volume. The member forming the processing pattern in the first region r1 may be formed thicker in the surface direction or thickness direction of the second surface 12 than the member forming the processing pattern in the second region r2.

The textured pattern may have a honeycomb structure, for example, as shown in FIG. A honeycomb structure is a structure in which regular hexagons are arranged without gaps, and is a structure that combines strength and lightness. Here, in FIG. 4 and FIGS. 5 to 13 described later, the colored portions of the machining pattern correspond to the portions to be cut on the second surface 12 . In other words, the portion of the processing pattern shown in white is the portion where the member of the mirror section 10 remains more than the portion of the processing pattern colored. That is, the processing pattern is formed by a portion where the member of the mirror section 10 exists and a portion where the member does not exist. For example, when the processed pattern has a honeycomb structure, the members of the mirror section 10 form the walls of the honeycomb structure. The wall is formed so as to surround a portion of the mirror section 10 where no member exists. The processing pattern in FIG. 4 combines a honeycomb structure pattern near the center c, which has a slightly larger white portion, and a honeycomb structure pattern in other portions. As shown in FIG. 4, comparing the first region r1 including the center c with the second region r2 not including the center c, the first region r1 includes more white portions. In other words, the density of the first region r1 is higher than the density of the second region r2 in the mirror section 10 having the second surface 12 cut according to the processing pattern of FIG. As a result, the portion distant from the center c to some extent can be cut to reduce the weight, and the shape and rigidity of the mirror portion 10 can be maintained by slightly reducing the amount of cutting in the portion near the center c. When attaching the mirror section 10 to the first holding section 42 via the columnar member 41, the two opposing walls forming the honeycomb structure may be parallel to the second axis (a2). The hexagons forming the honeycomb structure may not be regular hexagons, but may be, for example, elongated hexagons in which the sides parallel to the second axis (a2) are longer than the other sides.

Moreover, as shown in FIG. 4, the processing pattern may be such that the edge of the second surface 12 is not cut. The edge is the outer edge of the second surface 12, which is the circumferential portion in the example of FIG. If the processing pattern does not cut the edge of the second surface 12, the rigidity of the mirror section 10 can be further ensured. A wall-like member surrounding the second region r2 may be formed along the edge of the second surface 12 . The wall-like member surrounding the second region r2 may be formed thicker than the member forming the pattern formed in the second region r2. When the mirror section 10 swings greatly, the edge may collide with the substrate 50 and be damaged. A wall-like member surrounding the second region r2 may be formed of the member of the mirror section 10 .

Also, as shown in FIG. 4, the processing pattern may have symmetry. Symmetry is not limited to any particular symmetry and includes, for example, translational symmetry, rotational symmetry and mirror image symmetry. If the processing pattern has symmetry, the mirror section 10 can be easily processed (etched).

The working pattern may have a gradual decrease in density from the center c to the edges, as shown in FIGS. 5, 6 and 7, for example. 5, 6, and 7 do not cut the connection region 13 of the second surface 12 with the columnar member 41. As shown in FIG. In other words, the connection area 13 is formed by the member of the mirror section 10 , and the connection area 13 has no area without the member of the mirror section 10 . Also, the connection region 13 may be a region where the density of the processed patterns formed on the second surface 12 is the highest. Since the strength of the connection region 13 is maintained when the processing pattern does not cut the connection region 13, the rigidity of the mirror section 10 can be further secured. The connection area 13 may be larger than the area to which the columnar member 41 is connected. 5, 6 and 7 do not shave the edge of the second surface 12, and the rigidity of the mirror section 10 can be ensured. 5, 6 and 7 have symmetry, which facilitates the processing of the mirror section 10. FIG.

The processing pattern may be, for example, a spiral pattern in which the density gradually decreases from the center c toward the edges, as shown in FIG. Moreover, the processing pattern of FIG. 8 does not grind the edge of the second surface 12, and furthermore, the rigidity of the mirror section 10 can be ensured.

The machining pattern has, for example, a first straight line portion and a second straight line portion that intersects with the first straight line portion, as shown in FIG. The second surface 12 may not be cut. The first straight portion and the second straight portion may be formed like walls by the members of the mirror portion 10 . The pattern formed by the first linear portion and the second linear portion may be formed symmetrically about an axis parallel to the first axis (a1) or the second axis (a2). Here, the first linear portion and the second linear portion may be orthogonal as shown in FIG. 9, or may intersect at an angle other than 90°. For example, when the mirror section 10 is attached to the first holding section 42 via the columnar member 41, the angle formed by the first straight line section and the second straight line section in the direction of the second axis (a2) The opening angle may be larger than the opening angle in the direction of the first axis (a1). The processing pattern of FIG. 9 does not shave the connection area 13 and does not shave the edge of the second surface 12, and furthermore, the rigidity of the mirror section 10 can be ensured. Moreover, the processing pattern of FIG. 9 has symmetry, which facilitates processing of the mirror section 10 .

The processing pattern may be a pattern for cutting the second surface 12 except for a partial region including the center c, as shown in FIGS. 10, 11, 12 and 13, for example. The processing patterns shown in FIGS. 10, 11, 12 and 13 can enhance the effect of reducing the weight of the mirror section 10. FIG. Here, in the machining patterns of FIGS. 10, 11, 12 and 13, the second region r2 (see FIG. 4) that does not include the center c is the portion (colored part).

The partial area including the center c is, for example, a circle (perfect circle), a rhombus, a square, or an ellipse, but is not limited to these. When the partial area including the center c is square, when the mirror section 10 is attached to the first holding section 42 via the columnar member 41, the first axis (a1) and the second axis (a2) are square. It may be arranged so as to intersect the vertices. When the partial area including the center c is rhombus, when the mirror section 10 is attached to the first holding section 42 via the columnar member 41, the first axis (a1) is parallel to the long diagonal line of the rhombus. may be arranged as If the partial area including the center c is elliptical, when the mirror section 10 is attached to the first holding section 42 via the columnar member 41, the first axis (a1) is parallel to the major axis of the ellipse. may be placed in 10, 11, 12 and 13, the second surface 12 is not cut in a part of the region including the center c (shown in white), but this region is different from FIG. It may be the processing pattern (for example, honeycomb structure) of FIG. In this case, a first region r1 and a second region r2 having different densities may be formed in a partial region including the center c, as shown in FIGS. 10, 11, 12, and 13 do not cut the connection area 13, and furthermore, the rigidity of the mirror section 10 can be ensured. 10, 11, 12 and 13 have symmetry, which facilitates the processing of the mirror section 10. FIG.

Here, when the holding section 40 holds the mirror section 10 having the second surface 12 cut according to the machining patterns of FIGS. can be set arbitrarily). However, regarding the processing pattern of FIG. 9, the holding portion 40 is arranged so that the portions corresponding to the first straight portion and the second straight portion of the mirror portion 10 do not overlap in the direction of the first axis (a1). It is preferred to retain the portion 10 . Since the non-shaved portions corresponding to the first straight portion and the second straight portion exist obliquely to the swinging direction, they act like braces in an earthquake-resistant structure, further increasing the rigidity of the mirror portion 10. This is because it is possible to ensure

As described above, the mirror actuator 1 according to the present embodiment can be lightened while ensuring the rigidity of the mirror section 10 by the above configuration. Therefore, the mirror actuator 1 according to the present embodiment can increase the resonance frequency, and can be mounted on, for example, an in-vehicle device to achieve high operational reliability and high-speed oscillation of the reflecting mirror.

Although the present disclosure has been described with reference to figures and examples, it should be noted that various variations and modifications will be readily apparent to those skilled in the art based on the present disclosure. Therefore, it should be noted that these variations and modifications are included within the scope of this disclosure.

For example, the processing patterns shown in FIGS. 4 to 13 are representative examples, and the invention is not limited to these. For example, although regular hexagons are arranged in FIG. 4, a machining pattern in which other shapes such as equilateral triangles or squares are arranged may be used. Also, as long as the density of the first region r1 is higher than the density of the second region r2, a part of one processing pattern in FIGS. 4 to 13 is combined with a part of another processing pattern. you can

Reference Signs List 1 mirror actuator 10 mirror section 11 first surface 12 second surface 13 connection area 20 rib section 30 driving section 40 holding section 41 columnar member 42 first holding section 43 torsion bar 44 second holding section 50 substrate 60 package

Claims (9)

a mirror portion having a first surface that reflects electromagnetic waves and a second surface opposite to the first surface, the second surface having a processed pattern formed thereon;
a holding part that holds the mirror part so that it can swing,
The processing pattern consists of a portion where the member of the mirror portion exists and a portion where the member does not exist, and the density of the mirror portion in the first region including the center of the second surface is higher than that in the first region. A mirror actuator having a density greater than that of the second region located on the peripheral side. A columnar member that connects the first region and the holding portion,
2. The mirror actuator according to claim 1, wherein a connection region of said second surface with said columnar member has the highest density of said processed pattern. The processing pattern has a wall-shaped first linear portion and a second linear portion that intersects with the first linear portion, and the first linear portion and the second linear portion 3. A mirror actuator according to claim 2, wherein said second surface is not shaved at a portion. a drive unit that swings the mirror unit about a first axis by changing a drive voltage at a resonance frequency;
4. The holding portion holds the mirror portion so that portions of the mirror portion corresponding to the first straight portion and the second straight portion do not overlap in the direction of the first axis. the mirror actuator described in . The drive section also swings the mirror section in a direction of a second axis orthogonal to the first axis,
a resonance frequency for oscillation about the first axis is higher than a resonance frequency for oscillation about the second axis;
The mirror section is configured such that, of the angles formed by the first straight line portion and the second straight line portion, the angle that opens in the direction of the second axis is larger than the angle that opens in the direction of the first axis. 5. The mirror actuator according to claim 4, which is connected to said holding portion via said columnar member. The mirror actuator according to any one of claims 3 to 5, wherein said first straight portion and said second straight portion are perpendicular to each other. 7. The mirror actuator according to any one of claims 1 to 6, wherein said processed pattern includes a wall-like pattern surrounding said second region along an edge of said second surface. The processed pattern has a honeycomb structure formed of wall-shaped members, and the wall-shaped members in the first region are closer to the second surface than the wall-shaped members in the second region. 8. A mirror actuator according to claim 7, which is formed thick in the plane direction. 9. The mirror actuator according to claim 8, wherein the pattern surrounding said second area is formed thicker in the surface direction of said second surface than the wall-shaped member formed in said second area.

Images