Optical scanning device

Abstract

This optical scanning device is provided with: a micromirror device (2) having a mirror section (20) provided with a reflecting surface (20A) that reflects incident light, a first actuator that swings the mirror section (20) about a first axis (a1) parallel to the reflecting surface (20A) when the mirror section (20) is stationary, and a second actuator that swings the mirror section (20) about a second axis (a2) parallel to the reflecting surface (20A) and orthogonal to the first axis (a1); a light source (50) that emits a light beam (Lb); a first light detection element (51) and a second light detection element (52) that detect the position of the light beam (Lb) reflected by the mirror unit (20) in the one-dimensional direction; and a processor that calculates, on the basis of detection signals output from the first light detection element (51) and the second light detection element (52), the amplitude of the mirror section around the first axis (a1), the amplitude of the mirror section around the second axis (a2), and the phase difference between the oscillation of the mirror section (20) around the first axis (a1) and the oscillation of the mirror section around the second axis (a2).

Description

Technical Field

[0001] The technology of the present invention relates to an optical scanning device. Background Art

[0002] As one of the Micro Electro Mechanical Systems (MEMS) devices fabricated using fine processing technology of silicon (Si), a micromirror device (also referred to as a micro scanner) is known. The micromirror device is driven by a drive control unit provided in the optical scanning device. The drive control unit drives the mirror unit of the micromirror device to two-dimensionally scan an object with a light beam reflected by the mirror unit.

[0003] The optical scanning method performed by the micromirror device is superior in terms of being small, lightweight, and having low power consumption compared to the conventional optical scanning method using a polygonal mirror. Therefore, the application of the micromirror device to a LiDAR (Light Detection and Ranging) device or a scanning beam display, etc. has received attention.

[0004] In such an optical scanning device, the light beam is deflected by changing the angle of the mirror unit. Therefore, in order to grasp the scanning position of the light beam in the object, it is necessary to detect the motion of the mirror unit. As an example of a method for detecting the motion of the mirror unit, a method of setting a strain sensor near the mirror unit and calculating the angle of the mirror unit based on the output value of the strain sensor is known. However, since the strain sensor detects changes in the physical properties of the material, the detection sensitivity is temperature-dependent and changes due to material deterioration. Therefore, the detection accuracy of the motion of the mirror unit by the strain sensor is low.

[0005] As another method for detecting the motion of the mirror unit, a method of detecting the angle of the mirror unit by irradiating the back surface of the mirror unit with a light beam is known. In Japanese Patent Laid-Open No. 2021-025938, the following is proposed: a light source that emits a light beam parallel to the back surface of the mirror unit that has been subjected to antireflection processing is provided, a light detector is provided on the optical path of the light beam, and the angle of the mirror unit is detected based on the light reception result of the light detector. Based on the fact that the back surface of the mirror unit blocks the light beam when the mirror unit is tilted, and thus the amount of light received by the light detector changes, the angle of the mirror unit can be detected. And in Japanese Patent Laid-Open No. 2012-198511, the following is proposed: the angle of the mirror unit is detected by measuring the position of the light beam that is irradiated onto the back surface of the mirror unit and reflected by the back surface using a two-dimensional position detection element. Summary of the Invention

[0006] Technical Problem to be Solved by the Invention

[0007] However, in the method described in Japanese Unexamined Patent Application Publication No. 2021-025938, since the light beam is emitted parallel to the back surface of the mirror unit, the movement of the mirror unit cannot be detected with high precision. Further, in the method described in Japanese Unexamined Patent Application Publication No. 2021-025938, since it is necessary to perform antireflection processing on the back surface of the mirror unit, there are also problems that the manufacturing process for manufacturing the micromirror device increases and the manufacturing cost increases.

[0008] Further, in the method described in Japanese Unexamined Patent Application Publication No. 2012-198511, the position of the light beam reflected by the back surface of the mirror unit is detected using a two-dimensional position detection element, and thus the movement of the mirror unit can be detected with high precision. However, there is a problem that using the two-dimensional position detection element makes the optical scanning device very expensive.

[0009] An object of the technology of the present invention is to provide an optical scanning device capable of detecting the movement of a mirror unit at low cost and with high precision.

[0010] Means for Solving the Technical Problem

[0011] To achieve the above object, the optical scanning device of the present invention includes: a micromirror device having a mirror unit having a reflection surface for reflecting incident light, a first actuator for swinging the mirror unit about a first axis parallel to the reflection surface when the mirror unit is stationary, and a second actuator for swinging the mirror unit about a second axis parallel to the reflection surface and orthogonal to the first axis; a light source for emitting a light beam; a first light detection element and a second light detection element for detecting the position of the light beam reflected by the mirror unit in a one-dimensional direction; and a processor for calculating, based on detection signals output from the first light detection element and the second light detection element, the amplitude of the mirror unit about the first axis, the amplitude of the mirror unit about the second axis, and the phase difference between the swing of the mirror unit about the first axis and the swing about the second axis.

[0012] Preferably, the first light detection element and the second light detection element respectively detect the position of the light beam reflected by the reflection surface of the mirror unit or the back surface, which is the side opposite to the reflection surface, in a one-dimensional direction.

[0013] Preferably, the processor causes the mirror unit to perform precession motion or spiral motion by applying a first drive signal and a second drive signal having the same drive frequency to the first actuator and the second actuator, respectively.

[0014] Preferably, the position information detection directions of the first light detection element and the second light detection element are different from each other and are not linear.

[0015] Preferably, the position detection direction of the first light detection element is parallel to the first axis, and the position detection direction of the second light detection element is parallel to the second axis.

[0016] Preferably, the processor calculates a phase difference based on the time difference between the detection signal output from the first light detection element and the detection signal output from the second light detection element.

[0017] Preferably, the processor performs the following processing: calculates a correction amount for targeting the operation of the mirror unit based on the amplitude around the first axis, the amplitude around the second axis, and the phase difference; corrects the first drive signal and / or the second drive signal according to the calculated correction amount.

[0018] Preferably, the first light detection element and the second light detection element are each a one-dimensional position detection element having a strip-shaped light receiving surface extending in one direction.

[0019] The first light detection element and the second light detection element may each be a photodiode array in which a plurality of photodiodes are arranged in one direction.

[0020] Advantages of the Invention

[0021] According to the technology of the present invention, an optical scanning device capable of detecting the operation of a mirror unit at low cost and with high precision can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic diagram of the optical scanning device.

[0023] Figure 2 is a block diagram showing an example of the hardware configuration of the drive control unit.

[0024] Figure 3 is a perspective external view of the micromirror device.

[0025] Figure 4 is a top view of the micromirror device observed from the light incident side.

[0026] Figure 5 is a top view of the micromirror device observed from the back side.

[0027] Figure 6 is along Figure 4 sectional view taken along line A-A of.

[0028] Figure 7 is along Figure 4 sectional view taken along line B-B of.

[0029] Figure 8 is a diagram showing an example in which the first actuator is driven in an anti-phase resonance mode.

[0030] Figure 9 is a diagram showing an example in which the second actuator is driven in an anti-phase resonance mode.

[0031] Figure 10 This is a diagram showing an example of drive signals applied to the first actuator and the second actuator.

[0032] Figure 11 This is a diagram for explaining the temporal change of the maximum deflection angle.

[0033] Figure 12 This is a diagram for explaining the precession motion of the mirror unit.

[0034] Figure 13 This is a diagram showing an example of the structure of the motion detection unit.

[0035] Figure 14 This is a block diagram showing an example of functions implemented by the CPU of the control device.

[0036] Figure 15 This is a diagram showing an example of detection signals detected by the first light detection element and the second light detection element.

[0037] Figure 16 This is a graph showing the temporal changes of the amplitude and phase difference when the orbit is spiral.

[0038] Figure 17 This is a diagram showing another example of detection signals detected by the first light detection element and the second light detection element.

[0039] Figure 18 This is a graph showing the temporal changes of the amplitude and phase difference when the orbit is circular.

[0040] Figure 19 This is a diagram showing the motion detection unit according to the first modification example.

[0041] Figure 20 This is a diagram showing the motion detection unit according to the second modification example.

[0042] Figure 21 This is a diagram showing the motion detection unit according to the third modification example. Detailed Embodiment

[0043] An example of an embodiment related to the technology of the present invention will be described with reference to the accompanying drawings.

[0044] Figure 1 Roughly shows an optical scanning device 10 according to an embodiment. The optical scanning device 10 includes a micromirror device (hereinafter referred to as MMD (Micro Mirror Device).) 2, a light source 3, a control device 4, and a motion detection unit 5. The optical scanning device 10 optically scans a scanned surface 6 by reflecting a light beam La emitted from the light source 3 through the MMD 2 under the control of the control device 4. The scanned surface 6 is, for example, a screen.

[0045] MMD2 is a micromirror device with a piezoelectric biaxial drive method that enables the mirror unit 20 (refer to Figure 3 ) to swing around the first axis a1 and the second axis a2 orthogonal to the first axis a1. Hereinafter, the direction parallel to the first axis a1 is referred to as the X direction, the direction parallel to the second axis a2 is referred to as the Y direction, and the direction orthogonal to the first axis a1 and the second axis a2 is referred to as the Z direction.

[0046] The light source 3 is a laser device that emits a laser beam, for example, as the light beam La. The light source 3 preferably irradiates the reflecting surface 20A (refer to Figure 3 ) provided in the mirror unit 20 perpendicularly with the light beam La in a state where the mirror unit 20 of the MMD2 is stationary.

[0047] The control device 4 outputs drive signals to the light source 3 and the MMD2 according to the light scanning information. The light source 3 generates the light beam La according to the input drive signal and irradiates it onto the MMD2. The MMD2 swings the mirror unit 20 around the first axis a1 and the second axis a2 according to the input drive signal.

[0048] Details will be described later, but in the present embodiment, the control device 4 causes the mirror unit 20 to perform a precession motion or a helical motion. By performing the precession motion of the mirror unit 20, the light beam La reflected by the mirror unit 20 is scanned on the scanned surface 6 in a manner of depicting a circular orbit. And, by performing the helical motion of the mirror unit 20, the light beam La reflected by the mirror unit 20 is scanned on the scanned surface 6 in a manner of depicting a helical orbit, for example. The helical light beam La is used for a LiDAR device, for example.

[0049] In addition, the precession motion refers to a motion in which the normal line N orthogonal to the reflecting surface 20A of the mirror unit 20 to be described later depicts a circular orbit. And, the helical motion is a motion in which the normal line N depicts a helical orbit.

[0050] Details will be described later. The motion detection unit 5 detects the motion of the mirror unit 20 by irradiating the back side of the mirror unit 20 (that is, the side opposite to the surface irradiated with the light beam La) with the light beam Lb for detecting the motion of the mirror unit 20. The control device 4 performs feedback control according to the detection signal output from the motion detection unit 5 so that the motion of the mirror unit 20 is maintained at the target motion.

[0051] Figure 2An example of the hardware structure of the control device 4 is shown. The control device 4 includes a CPU (Central Processing Unit) 40, a ROM (Read Only Memory) 41, a RAM (Random Access Memory) 42, a light source driver 43, and an MMD driver 44. The CPU 40 reads programs and data from storage devices such as the ROM 41 into the RAM 42 to execute processing, thereby implementing the overall functions of the control device 4. The CPU 40 is an example of the processor related to the technology of the present invention.

[0052] The ROM 41 is a non-volatile storage device and stores programs for the CPU 40 to execute processing and data such as the aforementioned light scanning information. The RAM 42 is a non-volatile storage device that temporarily holds programs and data.

[0053] The light source driver 43 is a circuit that outputs a drive signal to the light source 3 according to the control of the CPU 40. In the light source driver 43, the drive signal is a drive voltage for controlling the irradiation timing and irradiation intensity of the light source 3.

[0054] The MMD driver 44 is a circuit that outputs a drive signal to the MMD 2 according to the control of the CPU 40. In the MMD driver 44, the drive signal is a drive voltage for controlling the timing, period, and deflection angle of the swinging of the mirror unit 20 of the MMD 2.

[0055] The CPU 40 controls the light source driver 43 and the MMD driver 44 according to the light scanning information. The light scanning information is information indicating how to scan the light beam La on the scanned surface 6. In the present embodiment, it is information indicating that the light beam La is scanned on the scanned surface 6 in a circular or spiral orbit. Additionally, for example, when the light scanning device 10 is assembled in a LiDAR device, the light scanning information includes the timing and scanning range for scanning the distance measurement light beam La.

[0056] Moreover, the CPU 40 controls the detection operation of the motion detection unit 5 and, according to the detection signal output from the motion detection unit 5, controls the MMD driver 44 to maintain the motion of the mirror unit 20 at the target motion.

[0057] Next, an example of the MMD 2 will be described. Figures 3 to 7 An example of the MMD 2 will be described. Figure 3 This is a perspective view of the exterior of the MMD 2. Figure 4 This is a top view of the MMD 2 observed from the light incident side. Figure 5 This is a top view of the MMD 2 observed from the back side. Figure 6 This is a cross-sectional view taken along the A-A line of Figure 4 This is a cross-sectional view taken along the A-A line ofFigure 7 is a cross-sectional view cut along line B-B of Figure 4 .

[0058] As Figure 3 and Figure 4 shown, MMD2 has a mirror section 20, a first actuator 21, a second actuator 22, a support frame 23, a first support section 24, a second support section 25, and a fixing section 26. MMD2 is a so-called MEMS device.

[0059] The mirror section 20 has a reflecting surface 20A for reflecting incident light. The reflecting surface 20A is formed of a metal thin film such as gold (Au) or aluminum (Al) provided on one surface of the mirror section 20. The reflecting surface 20A is, for example, circular.

[0060] The first actuator 21 is arranged to surround the mirror section 20. The support frame 23 is arranged to surround the mirror section 20 and the first actuator 21. The second actuator 22 is arranged to surround the mirror section 20, the first actuator 21, and the support frame 23. In addition, the support frame 23 is not an essential component in the technology of the present invention.

[0061] The first support section 24 connects the mirror section 20 and the first actuator 21 on the first axis a1, and supports the mirror section 20 so as to be swingable about the first axis a1. The first axis a1 is parallel to the reflecting surface 20A when the mirror section 20 is stationary. For example, the first support section 24 is a torsion bar extending along the first axis a1. And the first support section 24 is connected to the support frame 23 on the first axis a1.

[0062] The second support section 25 connects the first actuator 21 and the second actuator 22 on the second axis a2, and supports the mirror section 20 and the first actuator 21 so as to be swingable about the second axis a2. The second axis a2 is parallel to the reflecting surface 20A when the mirror section 20 is stationary and orthogonal to the first axis a1. And the second support section 25 is connected to the support frame 23 and the fixing section 26 on the second axis a2.

[0063] The fixing section 26 is connected to the second actuator 22 through the second support section 25. The outer shape of the fixing section 26 is rectangular, and surrounds the second actuator 22. The lengths of the fixing section 26 in the X direction and the Y direction are, for example, about 1 mm to 10 mm respectively. The thickness of the fixing section 26 in the Z direction is, for example, about 5 μm to 0.2 mm.

[0064] The first actuator 21 and the second actuator 22 are respectively piezoelectric actuators having piezoelectric elements. The first actuator 21 applies a torque about the first axis a1 to the mirror section 20. The second actuator 22 applies a torque about the second axis a2 to the mirror section 20 and the first actuator 21. Thereby, the mirror section 20 swings about the first axis a1 and the second axis a2.

[0065] The first actuator 21 is an annular thin plate member that surrounds the mirror unit 20 in the XY plane. The first actuator 21 is composed of a pair of first movable parts 21A and second movable parts 21B. The first movable part 21A and the second movable part 21B are each semi-annular. The first movable part 21A and the second movable part 21B are symmetric with respect to the first axis a1 and are connected on the first axis a1.

[0066] The support frame 23 is an annular thin plate member that surrounds the mirror unit 20 and the first actuator 21 in the XY plane.

[0067] The second actuator 22 is an annular thin plate member that surrounds the mirror unit 20, the first actuator 21, and the support frame 23 in the XY plane. The second actuator 22 is composed of a pair of first movable parts 22A and second movable parts 22B. The first movable part 22A and the second movable part 22B are each semi-annular. The first movable part 22A and the second movable part 22B are symmetric with respect to the second axis a2 and are connected on the second axis a2.

[0068] In the first actuator 21, a piezoelectric element 27A and a piezoelectric element 27B are respectively provided on the first movable part 21A and the second movable part 21B. Further, in the second actuator 22, a piezoelectric element 28A and a piezoelectric element 28B are respectively provided on the first movable part 22A and the second movable part 22B.

[0069] In addition, in Figure 3 and Figure 4 the illustration of the wiring and electrode pads for applying drive signals to the piezoelectric elements 27A, 27B, 28A, and 28B is omitted. A plurality of electrode pads are provided on the fixing part 26.

[0070] As Figure 5 shown, an elliptical structure 29 is provided on the back surface 20B of the mirror unit 20. The structure 29 is a so-called rib, and is arranged such that the center of the ellipse coincides with the center of the back surface 20B. The minor axis of the structure 29 is parallel to the X direction, and the major axis is parallel to the Y direction.

[0071] The resonance frequency of the mirror unit 20 around the first axis a1 and the resonance frequency around the second axis a2 change according to the shape of the structure 29. Therefore, the lengths of the structure 29 in the minor axis direction and the major axis direction are determined such that the resonance frequency of the mirror unit 20 around the first axis a1 coincides with the resonance frequency around the second axis a2. In addition, the shape of the structure 29 is not limited to an elliptical shape, and may be a circular shape or the like.

[0072] As Figure 6 and Figure 7As shown, the MMD2 is formed, for example, by etching an SOI (Silicon On Insulator) substrate 30. The SOI substrate 30 is a substrate in which a silicon oxide layer 32 is provided on a first silicon active layer 31 made of single crystal silicon, and a second silicon active layer 33 made of single crystal silicon is provided on the silicon oxide layer 32.

[0073] The mirror unit 20, the first actuator 21, the second actuator 22, the support frame 23, the first support portion 24, and the second support portion 25 are formed of the second silicon active layer 33 remaining after removing the first silicon active layer 31 and the silicon oxide layer 32 from the SOI substrate 30 by etching. The second silicon active layer 33 functions as an elastic portion having elasticity. The fixing portion 26 is formed of the three layers of the first silicon active layer 31, the silicon oxide layer 32, and the second silicon active layer 33.

[0074] The structure 29 is formed by etching the first silicon active layer 31 and the silicon oxide layer 32.

[0075] The piezoelectric elements 27A, 27B, 28A, and 28B have a stacked structure in which a lower electrode 71, a piezoelectric film 72, and an upper electrode 73 are stacked in this order on the second silicon active layer 33. In addition, an insulating film is provided on the upper electrode 73, but illustration thereof is omitted.

[0076] The upper electrode 73 and the lower electrode 71 are formed of, for example, gold (Au) or platinum (Pt). The piezoelectric film 72 is formed of, for example, a piezoelectric material, that is, PZT (lead zirconate titanate). The upper electrode 73 and the lower electrode 71 are electrically connected to the control device 4 via wirings and electrode pads.

[0077] A drive voltage is applied to the upper electrode 73 from the control device 4. The lower electrode 71 is connected to the control device 4 via wirings and electrode pads, and is given a reference potential (for example, ground potential).

[0078] When a positive or negative voltage is applied to the piezoelectric film 72 along the polarization direction, a deformation (for example, expansion and contraction) proportional to the applied voltage is generated. That is, the piezoelectric film 72 exhibits a so-called inverse piezoelectric effect. The piezoelectric film 72 exhibits the inverse piezoelectric effect by applying a drive voltage to the upper electrode 73 from the control device 4 to displace the first actuator 21 and the second actuator 22.

[0079] Figure 8 The case where the first actuator 21 is driven by elongating one piezoelectric film 72 and contracting the other piezoelectric film 72 in the first movable portion 21A and the second movable portion 21B is shown. In this way, the first movable portion 21A and the second movable portion 21B are displaced in opposite directions to each other, and thereby the mirror unit 20 rotates about the first axis a1.

[0080] And, Figure 8This is an example in which the first actuator 21 is driven in a resonance mode with an inverse phase where the displacement directions of the first movable part 21A and the second movable part 21B are opposite to the rotation direction of the mirror part 20. In Figure 8 the first movable part 21A is displaced in the -Z direction, and the second movable part 21B is displaced in the +Z direction, whereby the mirror part 20 rotates in the +Y direction. In addition, the first actuator 21 can be driven in a resonance mode with a same phase where the displacement directions of the first movable part 21A and the second movable part 21B are the same as the rotation direction of the mirror part 20.

[0081] The angle at which the normal N of the reflecting surface 20A of the mirror part 20 is inclined in the YZ plane is called the first deflection angle θ1. When the normal N of the reflecting surface 20A is inclined in the +Y direction, the first deflection angle θ1 takes a positive value, and when it is inclined in the -Y direction, the first deflection angle θ1 takes a negative value.

[0082] The first deflection angle θ1 is controlled by a drive signal (hereinafter referred to as the first drive signal) applied by the control device 4 to the first actuator 21. The first drive signal is, for example, an alternating voltage of a sine wave. The first drive signal includes a drive voltage waveform V 1A (t) applied to the first movable part 21A and a drive voltage waveform V 1B (t) applied to the second movable part 21B. The drive voltage waveform V 1A (t) and the drive voltage waveform V 1B (t) are in inverse phase with each other (i.e., the phase difference is 180°).

[0083] Figure 9 This shows an example in which the second actuator 22 is driven in a resonance mode with an inverse phase where the displacement directions of the first movable part 22A and the second movable part 22B are opposite to the rotation direction of the mirror part 20. In Figure 9 the first movable part 22A is displaced in the -Z direction, and the second movable part 22B is displaced in the +Z direction, whereby the mirror part 20 rotates in the +X direction. In addition, the second actuator 22 can be driven in a resonance mode with a same phase where the displacement directions of the first movable part 22A and the second movable part 22B are the same as the rotation direction of the mirror part 20.

[0084] The angle at which the normal N of the reflecting surface 20A of the mirror part 20 is inclined in the XZ plane is called the second deflection angle θ2. When the normal N of the reflecting surface 20A is inclined in the +X direction, the second deflection angle θ2 takes a positive value, and when it is inclined in the -X direction, the second deflection angle θ2 takes a negative value.

[0085] The second deflection angle θ2 is controlled by a drive signal (hereinafter referred to as the second drive signal) applied by the control device 4 to the second actuator 22. The second drive signal is, for example, an alternating voltage of a sine wave. The second drive signal includes a drive voltage waveform V 2A (t) applied to the first movable part 22A and a drive voltage waveform V 2B (t) applied to the second movable part 22B. The drive voltage waveforms V 2A (t) and V 2B (t) are in opposite phases (i.e., the phase difference is 180°).

[0086] Figure 10 An example of drive signals applied to the first actuator 21 and the second actuator 22 is shown. Figure 10 (A) of shows the drive voltage waveforms V 1A (t) and V 1B (t) included in the first drive signal. Figure 10 (B) of shows the drive voltage waveforms V 2A (t) and V 2B (t) included in the second drive signal.

[0087] The drive voltage waveforms V 1A (t) and V 1B (t) are respectively expressed as follows.

[0088] V 1A (t) = A1(t)sin(2πf d t)

[0089] V 1B (t) = A1(t)sin(2πf d t + π)

[0090] Here, t is time. f d is the drive frequency. A1(t) is the amplitude voltage and changes according to time t. The phase difference between the drive voltage waveform V 1A (t) and the drive voltage waveform V 1B (t) is π (i.e., 180°).

[0091] The drive voltage waveforms V 1A (t) and V 1B (t) are respectively applied to the first movable part 21A and the second movable part 21B, whereby the mirror part 20 swings around the first axis a1 (see Figure 8 ).

[0092] The drive voltage waveforms V 2A (t) and V 2B (t) are respectively expressed as follows.

[0093] V 2A V(t) = A2(t)sin(2πft d + φ)

[0094] V 2B V(t) = A2(t)sin(2πft d + π + φ)

[0095] Here, A2(t) is the amplitude voltage and varies according to the time t. The driving voltage waveforms V 2A (t) and V 2B (t) have a phase difference of π (i.e., 180°). Also, φ is the phase difference between the driving voltage waveforms V 1A (t) and V 1B (t), and between the driving voltage waveforms V 2A (t) and V 2B (t). In this embodiment, in order to cause the mirror unit 20 to perform a precessional motion or a helical motion, φ is set to π / 2 (i.e., 90°).

[0096] The driving voltage waveforms V 2A (t) and V 2B (t) are respectively applied to the first movable part 22A and the second movable part 22B, whereby the mirror unit 20 swings around the second axis a2 (refer to Figure 9 ).

[0097] As described above, the first driving signal and the second driving signal have the same driving frequency f d , and a phase difference of 90°. In order to cause the mirror unit 20 to perform a precessional motion, as Figure 11 shown, it is necessary to appropriately set the amplitude voltages A1(t) and A2(t) so that the maximum deflection angle θ of the first deflection angle θ1 m1 is consistent with the maximum deflection angle θ of the second deflection angle θ2 m2 . The maximum deflection angle θ m1 represents the amplitude of the mirror unit 20 around the first axis a1, and is hereinafter referred to as the amplitude θ m1 . Similarly, the maximum deflection angle θ m2 represents the amplitude of the mirror unit 20 around the second axis a2, and is hereinafter referred to as the amplitude θ m2 .

[0098] If the amplitude voltages A1(t) and A2(t) are set to prescribed values independent of the time t, then as Figure 12As shown, the reflector unit 20 performs precession motion in a manner that the normal line N of the reflective surface 20A describes a circular orbit centered on the rotation axis C parallel to the Z direction. Furthermore, if the amplitude voltages A1(t) and A2(t) are linearly changed with respect to time t, the reflector unit 20 performs spiral motion in a manner that the normal line N of the reflective surface 20A describes a spiral orbit centered on the rotation axis C. Alternatively, the amplitude voltages A1(t) and A2(t) may be changed in a manner that they alternately increase and decrease with respect to time t.

[0099] Figure 13 FIG. 5 shows an example of the structure of the motion detection unit 5. Figure 13 As shown in FIG. 1 , the motion detection unit 5 includes a light source 50, a first light detection element 51, and a second light detection element 52. The light source 50 emits a light beam Lb for motion detection. For example, the light source 50 is a laser diode that emits a laser beam with a wavelength of about 980 nm as the light beam Lb. In the present embodiment, the light source 50 is disposed on the back side of the reflector unit 20. When the reflector unit 20 is stationary, the light source 50 emits a light beam Lb to the back side 20B (reference Figure 5 ) irradiates the light beam Lb vertically. In addition, the light source 50 preferably irradiates the light beam Lb in the area surrounded by the structure 29 in the back side 20B.

[0100] The first light detecting element 51 is a one-dimensional position detecting element having a strip-shaped light receiving surface 51A extending in one direction and detecting the position of the light receiving position in the extending direction of the light receiving surface 51A. Similarly, the second light detecting element 52 is a one-dimensional position detecting element having a strip-shaped light receiving surface 52A extending in one direction and detecting the position of the light receiving position in the extending direction of the light receiving surface 52A.

[0101] The first photodetector 51 and the second photodetector 52 have sensitivity in a wavelength band including the wavelength of the light beam Lb. The first photodetector 51 and the second photodetector 52 are disposed so that the light receiving surfaces 51A and 52A are perpendicular to the Z direction and face the back surface 20B of the reflector 20 .

[0102] The light beam Lb emitted from the light source 50 and reflected by the back surface 20B of the reflector portion 20 performs precession motion or spiral motion through the reflector portion 20 to describe a circular or spiral track TR. The first light detection element 51 and the second light detection element 52 are respectively arranged at positions through which the track TR passes. The light receiving surface 51A of the first light detection element 51 passes through the center of the track TR and extends in the X direction (first direction). The light receiving surface 52A of the second light detection element 52 passes through the center of the track TR and extends in the Y direction (second direction). In the present embodiment, the first light detection element 51 and the second light detection element 52 are arranged on the XY plane at positions that are rotationally symmetrical at 90° relative to the center of the track TR.

[0103] In the present embodiment, the position detection direction of the first light detection element 51 is parallel to the first axis a1, and the position detection direction of the second light detection element 52 is parallel to the second axis a2. Thus, the position detection directions of the first light detection element 51 and the second light detection element 52 are different from each other and are not linear. This is because if the position detection directions of the first light detection element 51 and the second light detection element 52 are linear, the first light detection element 51 and the second light detection element 52 both detect the amplitude around the same axis. Assuming that the position detection direction of the first light detection element 51 is the +X direction and the position detection direction of the second light detection element 52 is the -X direction, then both the first light detection element 51 and the second light detection element 52 detect the amplitude around the first axis a1.

[0104] When the track TR passes through the light receiving surface 51A, the first light detection element 51 detects the position P1 where the light receiving surface 51A receives the light beam Lb, and outputs a detection signal S1 representing the position P1. When the track TR passes through the light receiving surface 52A, the second light detection element 52 detects the position P2 where the light receiving surface 52A receives the light beam Lb, and outputs a detection signal S2 representing the position P2. The position P1 corresponds to the amplitude θ m1 . The position P2 corresponds to the amplitude θ m2 . The time difference between the track TR passing through the position P1 and the position P2 corresponds to the phase difference φ between the swing of the mirror unit 20 around the first axis a1 and the swing around the second axis a2.

[0105] Alternatively, the light beam Lb emitted from the light source 50 can be made to be incident on the back surface 20B of the mirror unit 20 via an optical system including a mirror, a lens, etc.

[0106] Figure 14 An example of the functions implemented by the CPU 40 of the control device 4 is shown. The CPU 40 implements various functions by executing processes according to programs stored in storage devices such as the ROM 41. The CPU 40 functions as a drive control unit 60, an operation information calculation unit 61, a deviation amount calculation unit 62, a correction necessity determination unit 63, and a correction amount calculation unit 64. And, the operation information calculation unit 61 includes a frequency calculation unit 65, an amplitude calculation unit 66, and a phase difference calculation unit 67.

[0107] The drive control unit 60 controls the MMD driver 44, and outputs a first drive signal and a second drive signal for causing the mirror unit 20 to perform a target operation to the MMD 2. The operation information calculation unit 61 calculates information related to the operation of the mirror unit 20. Specifically, the frequency calculation unit 65 calculates the drive frequency f based on the first drive signal and the second drive signal output from the MMD driver 44 d。The amplitude calculation unit 66 calculates the amplitude θ based on the detection signals S1 and S2 output from the first light detection element 51 and the second light detection element 52. m1 、θ m2 。The phase difference calculation unit 67 calculates the phase difference φ based on the detection signals S1 and S2 output from the first light detection element 51 and the second light detection element 52.

[0108] In addition, the motion information calculation unit 61 only needs to calculate at least the amplitude θ m1 、θ m2 and the phase difference φ. Moreover, the phase difference calculation unit 67 can accurately obtain the phase difference φ by using not only the detection signals S1 and S2 but also the drive frequency f d .

[0109] The deviation calculation unit 62 calculates the deviation between the actual motion and the target motion of the mirror unit 20 based on the amplitude θ m1， θ m2 calculated by the motion information calculation unit 61 and the phase difference φ.

[0110] The correction necessity determination unit 63 determines whether it is necessary to correct the first drive signal and / or the second drive signal based on the deviation calculated by the deviation calculation unit 62.

[0111] When it is determined by the correction necessity determination unit 63 that correction is necessary, the correction amount calculation unit 64 calculates the correction amount for correcting the first drive signal and / or the second drive signal based on the amplitude θ m1， θ m2 calculated by the motion information calculation unit 61 and the phase difference φ.

[0112] The drive control unit 60 corrects the first drive signal and / or the second drive signal generated by the MMD driver 44 according to the correction amount calculated by the correction amount calculation unit 64, thereby setting the motion of the mirror unit 20 to the target motion.

[0113] Figure 15 FIG. shows an example of the detection signals S1 and S2 output from the first light detection element 51 and the second light detection element 52. In Figure 15 , the track TR is spiral. The first light detection element 51 outputs the detection signal S1 at the timing when the track TR passes through the first axis a1, that is, when the first deflection angle θ1 is maximum. The above position P1 is represented by the magnitude of the detection signal S1. Similarly, the second light detection element 52 outputs the detection signal S2 at the timing when the track TR passes through the second axis a2, that is, when the second deflection angle θ2 is maximum. The above position P2 is represented by the magnitude of the detection signal S2. The detection signals S1 and S2 are pulse-shaped signals.

[0114] The amplitude calculation unit 66 converts the position P1 represented by the magnitude of the detection signal S1 into the amplitude θ based on the geometric positional relationship among the light source 50, the first light detection element 51, and the mirror unit 20. m1 Moreover, the amplitude calculation unit 66 converts the position P2 represented by the magnitude of the detection signal S2 into the amplitude θ based on the geometric positional relationship among the light source 50, the second light detection element 52, and the mirror unit 20. m2 .

[0115] The phase difference calculation unit 67 obtains the time difference between the detection signal S1 and the detection signal, and converts this time difference into the phase difference φ. For example, the phase difference calculation unit 67 obtains the time difference between the rising time of the detection signal S1 and the rising time of the detection signal S2. Additionally, the phase difference calculation unit 67 can obtain the time difference between the falling time of the detection signal S1 and the falling time of the detection signal S2. Moreover, the phase difference calculation unit 67 can obtain the time difference between the central value of the detection signal S1 and the central value of the detection signal S2. The central value refers to the time at the center between the rising time and the falling time.

[0116] Figure 16 Represents the time variation of the amplitude θ m1 , θ m2 and the phase difference φ when the track TR is spiral. When the mirror unit 20 performs the target movement and the track TR is spiral, the amplitude θ m1 , θ m2 increases or decreases linearly with time, and the phase difference φ becomes π / 2.

[0117] The deviation calculation unit 62 calculates the deviation of the time variation of the amplitude θ m1 , θ m2 calculated by the amplitude calculation unit 66 from the target linear time variation. Moreover, the deviation calculation unit 62 calculates the deviation between the phase difference φ calculated by the phase difference calculation unit 67 and the target value π / 2.

[0118] The correction necessity determination unit 63 determines that correction of the first drive signal and / or the second drive signal is required when the deviation of the amplitude θ m1 or the amplitude θ m2 exceeds the threshold value or when the deviation of the phase difference φ exceeds the threshold value.

[0119] When the deviation of the amplitude θ m1 exceeds the threshold value, the correction amount calculation unit 64 calculates the correction amount of the amplitude voltage A1(t) required to make the temporal variation of the amplitude θ m1 a target linear temporal variation. Moreover, when the deviation of the amplitude θ m2 exceeds the threshold value, the correction amount calculation unit 64 calculates the correction amount of the amplitude voltage A1(t) required to make the temporal variation of the amplitude θ m2The correction amount of the amplitude voltage A2(t) required to set the temporal change as a target linear temporal change. Further, when the deviation amount of the phase difference φ exceeds the threshold value, the correction amount calculation unit 64 calculates the correction amount of the timings of the first drive signal and the second drive signal required to set the phase difference φ to the target value, that is, π / 2.

[0120] Figure 17 Another example of the detection signals S1 and S2 output from the first light detection element 51 and the second light detection element 52. In Figure 17 , the track TR is circular. Figure 18 Indicates the amplitude θ m1 , θ m2 and the temporal changes of the phase difference φ when the track TR is circular.

[0121] When the track TR is circular, the amplitudes θ m1 , θ m2 become prescribed values that do not change over time. The deviation amount calculation unit 62 calculates the deviation amounts of the amplitudes θ m1 , θ m2 calculated by the amplitude calculation unit 66 from the target values. Other processes based on the control device 4 are the same as in the case where the track TR is spiral.

[0122] As described above, according to the present embodiment, by using the first light detection element 51 and the second light detection element 52 that detect the position in the one-dimensional direction, it is possible to detect the amplitudes θ m1 , θ m2 and the phase difference φ of the mirror unit 20. Therefore, according to the present embodiment, it is possible to detect the operation of the mirror unit 20 inexpensively and with high precision.

[0123] Hereinafter, various modification examples of the above-described embodiment will be described.

[0124] [First Modification Example]

[0125] In the above-described embodiment, the first light detection element 51 and the second light detection element 52 detect the position of the light beam Lb emitted from the operation detection light source 50 and reflected by the back surface 20B of the mirror unit 20. Instead of this, the first light detection element 51 and the second light detection element 52 may detect the position of the light beam La emitted from the light source 3 and reflected by the reflection surface 20A of the mirror unit 20.

[0126] Figure 19 Shows the operation detection unit 5 according to the first modification example. In this modification example, the operation detection unit 5 includes the first light detection element 51 and the second light detection element 52 having the same structure as in the above-described embodiment. In this modification example, since the operation of the mirror unit 20 is detected using the light beam La emitted from the light source 3, the operation detection light source 50 is not required.

[0127] In this modified example, the first light detection element 51 and the second light detection element 52 are arranged on the surface side of the mirror unit 20 (i.e., the reflection surface 20A side). The first light detection element 51 and the second light detection element 52 are respectively arranged such that the light receiving surfaces 51A and 52A are orthogonal to the Z direction and face the reflection surface 20A of the mirror unit 20. The light receiving surface 51A of the first light detection element 51 passes through the center of the orbit TR of the light beam La and extends in the X direction. The light receiving surface 52A of the second light detection element 52 passes through the center of the orbit TR of the light beam La and extends in the Y direction.

[0128] Other structures and processes of the optical scanning device according to this modified example are the same as those in the above-described embodiment.

[0129] In addition, the light beam La emitted from the light source 3 can be made to enter the reflection surface 20A of the mirror unit 20 via an optical system including a mirror, a lens, etc.

[0130] [Second Modified Example]

[0131] Moreover, in the above-described embodiment, the first light detection element 51 and the second light detection element 52 are respectively one-dimensional position detection elements having strip-shaped light receiving surfaces extending in one direction. Instead of this, the first light detection element 51 and the second light detection element 52 can also be respectively photodiode arrays.

[0132] Figure 20 FIG. 5 shows the motion detection unit 5 according to the second modified example. In this modified example, the first light detection element 51 and the second light detection element 52 are respectively photodiode arrays in which a plurality of photodiodes PD are arranged in one direction. In this modified example, among the plurality of photodiodes PD constituting the first light detection element 51, the position of the photodiode PD that receives the light beam Lb corresponds to the above-described position P1. Similarly, among the plurality of photodiodes PD constituting the second light detection element 52, the position of the photodiode PD that receives the light beam Lb corresponds to the above-described position P2.

[0133] The first light detection element 51 outputs a detection signal S1 indicating the position of the photodiode PD that receives the light beam Lb. The second light detection element 52 outputs a detection signal S2 indicating the position of the photodiode PD that receives the light beam Lb.

[0134] Other structures and processes of the optical scanning device according to this modified example are the same as those in the above-described embodiment.

[0135] In addition, the first light detection element 51 and the second light detection element 52 included in the motion detection unit 5 according to the first modified example (refer to Figure 19 ) can be respectively photodiode arrays.

[0136] [Third Modified Example]

[0137] In addition, in the above-described embodiment, the motion detection unit 5 has two light detection elements, but it may also have three or more light detection elements that detect positions in a one-dimensional direction.

[0138] Figure 21 The motion detection unit 5 according to the third modified example is shown. In this modified example, in addition to the first light detection element 51 and the second light detection element 52, a third light detection element 53 is further provided. The first light detection element 51 and the second light detection element 52 have the same structure as that in the above-described embodiment.

[0139] The third light detection element 53 is a one-dimensional position detection element having a strip-shaped light receiving surface 53A extending in one direction and performing position detection of the light receiving position in the extending direction of the light receiving surface 53A. The light receiving surface 53A of the third light detection element 53 passes through the center of the track TR and extends in a direction (third direction) that is 45° in the X direction and the Y direction. When the track TR passes through the light receiving surface 53A, the third light detection element 53 detects the position P3 where the light receiving surface 53A receives the light beam Lb and outputs a detection signal S3 indicating the position P3.

[0140] In this modified example, the amplitude calculation unit 66 calculates the amplitude θ based on the detection signals S1, S2, and S3 output from the first light detection element 51, the second light detection element 52, and the third light detection element 53 m1 , θ m2 . The phase difference calculation unit 67 calculates the phase difference φ based on the detection signals S1, S2, and S3. In this way, in addition to using the detection signals S1 and S2, the detection signal S3 is also used, so that the amplitude θ m1、 θ m2 and the phase difference φ can be calculated with higher accuracy.

[0141] In addition, when three or more light detection elements are provided in the motion detection unit 5, it is preferable that the position detection directions of any two of the three or more light detection elements are not linear.

[0142] In addition, in the above-described embodiment, the position detection direction of the first light detection element 51 is set to the X direction and the position detection direction of the second light detection element 52 is set to the Y direction, but it is not limited thereto. As long as the position detection directions of the first light detection element 51 and the second light detection element 52 are different from each other and not linear, they are acceptable.

[0143] [Other Modified Examples]

[0144] The structure of the MMD2 shown in the above-described embodiment can be appropriately changed. For example, in the above-described embodiment, the first actuator 21 and the second actuator 22 are provided in a ring shape, but one or both of the first actuator 21 and the second actuator 22 can be provided in a bent structure. Further, as the first support portion 24 and the second support portion 25, support members having a structure other than a torsion bar can be used.

[0145] Further, the hardware structure of the control device 4 can be variously deformed. The processing unit of the control device 4 may be constituted by one processor, or may be constituted by a combination of two or more processors of the same type or different types (for example, a combination of a plurality of FPGAs (Field Programmable Gate Arrays), and / or a combination of a CPU and an FPGA). For example, the drive control unit 60, the motion information calculation unit 61, the deviation amount calculation unit 62, the correction necessity determination unit 63, and the correction amount calculation unit 64 in the above-described embodiment may be constituted by one or two or more processors.

[0146] As long as there is no contradiction, the above-described embodiment and each modification can be appropriately combined.

[0147] All documents, patent applications, and technical standards described in this specification are incorporated herein by reference to the same extent as if each was specifically and individually recited.

Claims

1. An optical scanning device, comprising: A micromirror device having a mirror portion with a reflecting surface for reflecting incident light, a first actuator for swinging the mirror portion about a first axis parallel to the reflecting surface when the mirror portion is stationary, and a second actuator for swinging the mirror portion about a second axis parallel to the reflecting surface and orthogonal to the first axis; A light source that emits a light beam; A first light detection element and a second light detection element that detect the position of the light beam reflected by the mirror portion in a one-dimensional direction; And A processor that calculates, based on detection signals output from the first light detection element and the second light detection element, the amplitude of the mirror portion about the first axis, the amplitude of the mirror portion about the second axis, and the phase difference between the swing of the mirror portion about the first axis and the swing of the mirror portion about the second axis.

2. The optical scanning device according to claim 1, wherein The first light detection element and the second light detection element respectively detect the position of the light beam reflected by the reflecting surface of the mirror portion or by the surface on the side opposite to the reflecting surface, i.e., the back surface, in a one-dimensional direction.

3. The optical scanning device according to claim 1, wherein The processor causes the mirror portion to perform a precession motion or a spiral motion by respectively applying a first drive signal and a second drive signal having the same drive frequency to the first actuator and the second actuator.

4. The optical scanning device according to claim 3, wherein The position detection directions of the first light detection element and the second light detection element are different from each other and are not linear.

5. The optical scanning device according to claim 4, wherein The position detection direction of the first light detection element is parallel to the first axis, and the position detection direction of the second light detection element is parallel to the second axis.

6. The optical scanning device according to claim 4, wherein The processor calculates the phase difference based on the time difference between the detection signal output from the first light detection element and the detection signal output from the second light detection element.

7. The optical scanning device according to claim 4, wherein The processor performs the following processing: Calculating a correction amount for making the operation of the mirror portion a target operation based on the amplitude about the first axis, the amplitude about the second axis, and the phase difference; and Correcting the first drive signal and / or the second drive signal based on the calculated correction amount.

8. The optical scanning device according to claim 1, wherein The first light detection element and the second light detection element are respectively one-dimensional position detection elements having a strip-shaped light receiving surface extending in one direction.

9. The optical scanning device according to claim 1, wherein The first light detection element and the second light detection element are respectively a photodiode array in which a plurality of photodiodes are arranged in one direction.

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