Optical scanning device and abnormality detection method

Abstract

To provide an optical scanner and an abnormality detection method allowing high-speed detection of an abnormal operation of a mirror during the operation.SOLUTION: An optical scanner of the present disclosure comprises: a micromirror device including a mirror that has a reflection surface reflecting light and can be swung around at least one axis, and an actuator that swings the mirror; a control unit that controls the operation of the actuator; a light irradiation device that irradiates a rear face on the opposite side of the reflection surface of the mirror with illumination light; a detection device that receives incident of reflected light of the illumination light reflected by the mirror and outputs a position signal representing the position of the incident light; and an abnormality detection device that detects an abnormal operation of the mirror based on the amount of variation over time of the position signal.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The technology of the present disclosure relates to an optical scanning device and an abnormality detection method. [Background technology]

[0002] A micromirror device (also called a microscanner) is known as one of the microelectromechanical systems (MEMS) devices fabricated using silicon (Si) microfabrication technology. A micromirror device is formed with a mirror and an actuator that oscillates the mirror. Because this micromirror device is small and consumes low power, it is used in laser scanners such as LiDAR (Light Detection and Ranging) and HUD (Head-Up Display).

[0003] With laser scanners such as LiDAR and HUD, it is important to ensure the safety of the user. For example, if the mirror stops moving while the laser light output from the light source is on, the laser light will be continuously emitted to the same position, which is dangerous. Therefore, it is necessary to detect abnormal mirror movement while the mirror is in operation. To detect abnormal mirror movement, it is necessary to accurately detect the mirror's deflection angle while the mirror is in operation.

[0004] Patent Document 1 describes a method of detecting the deflection angle of a mirror by irradiating the rear surface of the mirror with light, receiving the light reflected by the mirror with a light receiving element, and calculating the output signal of the light receiving element. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-170499 Summary of the Invention [Problem to be solved by the invention]

[0006] Although Patent Document 1 describes the detection of the mirror's deflection angle, it does not describe the detection of abnormal mirror behavior. One possible method for detecting abnormal mirror behavior is to monitor the mirror's amplitude and determine that abnormal behavior has occurred if the amplitude falls outside a predetermined range. However, detecting the mirror's amplitude requires acquiring and evaluating a waveform for one oscillation period, making it impossible to quickly detect abnormal mirror behavior.

[0007] The technique of the present disclosure aims to provide an optical scanning device and an abnormality detection method that enable abnormal operation of a mirror to be detected at high speed during operation. [Means for solving the problem]

[0008] In order to achieve the above object, the optical scanning device disclosed herein comprises a micromirror device including a mirror having a reflective surface that reflects light and that can oscillate around at least one axis, and an actuator that oscillates the mirror; a control device that controls the operation of the actuator; a light irradiation device that irradiates illumination light onto the back surface of the mirror opposite the reflective surface; a detection device that receives reflected light of the illumination light reflected by the mirror and outputs a position signal that represents the position of the incident light; and an abnormality detection device that detects abnormal operation of the mirror based on the amount of temporal variation in the position signal.

[0009] The detection device is a position detection element that can detect the position of the center of gravity of the amount of incident light, and the position signal preferably represents the position of the center of gravity of the amount of light.

[0010] It is preferable that the control device drives the actuator to resonate the mirror at a constant oscillation period.

[0011] The abnormality detection device preferably detects the amount of fluctuation of the position signal in a time interval that is less than 5% of the oscillation period as the amount of fluctuation.

[0012] The abnormality detection device preferably detects, as the amount of fluctuation, the amount of fluctuation in the position signal over a time interval that is smaller than 5% and larger than 0.05% of the oscillation period.

[0013] The abnormality detection device preferably includes a detection unit that detects the amount of fluctuation, and a determination unit that determines whether the amount of fluctuation is equal to or greater than a threshold value.

[0014] It is preferable that the detection unit be composed of a delay circuit that delays the position signal output from the detection device by a certain period of time, and a differential amplifier circuit that amplifies and outputs the difference between the position signal output from the detection device and the position signal delayed by the delay circuit.

[0015] The determining unit is preferably a comparator.

[0016] The detection device is a position detection element that can simultaneously detect the center of gravity position and light intensity of incident light, and it is preferable that the abnormality detection device detects abnormal operation based on an intensity signal representing the light intensity output from the detection device in addition to the position signal.

[0017] It is preferable that the mirror is oscillating about a first axis and a second axis that are orthogonal to each other, and the detection device detects the two-dimensional position of the incident light.

[0018] The abnormality detection method disclosed herein is a method for detecting an abnormality in an optical scanning device that includes a micromirror device including a mirror having a reflective surface that reflects light and that can oscillate around at least one axis, and an actuator that oscillates the mirror, and a control device that controls the operation of the actuator, and includes irradiating illumination light onto the back surface of the mirror opposite the reflective surface, and detecting abnormal operation of the mirror based on the amount of temporal variation in the position of the reflected light of the illumination light reflected by the mirror. [Effects of the Invention]

[0019] According to the technique of the present disclosure, it is possible to provide an optical scanning device and an abnormality detection method that enable abnormal operation of a mirror to be detected at high speed during operation. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 2 is a schematic diagram of an optical scanning device. [Figure 2] FIG. 1 is a schematic diagram of a micromirror device. [Figure 3] FIG. 2 is a diagram illustrating a first deflection angle of the movable mirror. [Figure 4] 10A and 10B are diagrams illustrating a second deflection angle of the movable mirror. [Figure 5] 5A and 5B are diagrams illustrating an example of drive signals to be applied to a first actuator and a second actuator. [Figure 6] FIG. 1 is a schematic diagram illustrating an example of the configuration of an angle detection device. [Figure 7] FIG. 1 is a block diagram illustrating an example of a configuration of an anomaly detection device. [Figure 8] 10A and 10B are diagrams illustrating an example of an output signal, a delay signal, and a fluctuation amount when the movable mirror is operating normally. [Figure 9] 10A and 10B are diagrams illustrating an example of an output signal, a delay signal, and a fluctuation amount when an abnormal operation occurs in the movable mirror. [Figure 10] 5A and 5B are diagrams illustrating an example of a position signal and an intensity signal output from a detection device. [Figure 11] FIG. 1 illustrates an example of an optical method. [Figure 12] FIG. 10 is a diagram showing evaluation results. [Figure 13] FIG. 10 is a diagram showing the waveform of the fluctuation amount when Δt / T=0.5%. [Figure 14] FIG. 10 is a diagram showing the waveform of the fluctuation amount when Δt / T=5%. [Figure 15] FIG. 10 is a diagram showing the waveform of the fluctuation amount when Δt / T=0.01%. [Figure 16] 10A and 10B are diagrams illustrating an example of determination by a conventional determination method based on a position signal. [Figure 17] 10A and 10B are diagrams illustrating an example of determination by a conventional determination method based on a position signal. [Figure 18]FIG. 10 is a block diagram showing the configuration of an anomaly detection device according to a modified example. [Figure 19] FIG. 10 is a diagram illustrating an example of a determination method based on an intensity signal. DETAILED DESCRIPTION OF THE INVENTION

[0021] An example of an embodiment of the technology of the present disclosure will be described with reference to the accompanying drawings.

[0022] FIG. 1 schematically illustrates an optical scanning system 10 according to one embodiment. The optical scanning system 10 includes an optical scanning device 2 and a light source 3. The optical scanning device 2 includes a micro mirror device (hereinafter referred to as an MMD) 4, a control device 5, an angle detection device 6, and an anomaly detection device 7. The optical scanning system 10 is used in laser scanners such as LiDAR and HUD.

[0023] The optical scanning device 2 performs optical scanning by reflecting the laser light La incident from the light source 3 by the MMD 4 under the control of the control device 5. When the optical scanning system 10 is used in LiDAR, the optical scanning device 2 scans the laser light La in a helical pattern, for example. In this embodiment, the optical scanning pattern is helical, but the optical scanning pattern is not limited to a helical pattern and may be a Lissajous pattern, a raster pattern, or the like.

[0024] The MMD 4 is a piezoelectric two-axis drive micromirror device that can oscillate a movable mirror 20 (see FIG. 2) around a first axis a1 and a second axis a2 that is perpendicular to the first axis a1. Hereinafter, the direction parallel to the first axis a1 will be referred to as the X direction, the direction parallel to the second axis a2 as the Y direction, and the direction perpendicular to the first axis a1 and the second axis a2 as the Z direction.

[0025] The light source 3 is a laser device that emits laser light La. When the movable mirror 20 of the MMD 4 is stationary, the light source 3 irradiates the laser light La perpendicularly to a reflecting surface 20A (see FIG. 2) of the movable mirror 20. The laser light La is an example of "light" according to the technology of the present disclosure.

[0026] The control device 5 inputs drive signals to the light source 3 and the MMD 4. The light source 3 generates laser light La based on the input drive signal and irradiates the MMD 4 with the laser light La. The MMD 4 oscillates the movable mirror 20 around the first axis a1 and the second axis a2 based on the input drive signal.

[0027] As will be described in detail later, the control device 5 causes the movable mirror 20 to resonate around the first axis a1 and the second axis a2, respectively. As a result, the laser light La reflected by the movable mirror 20 scans the plane so as to describe a circle.

[0028] As will be described in detail later, the angle detection device 6 detects the angle of the movable mirror 20 by irradiating the back side of the movable mirror 20 (i.e., the side opposite to the surface irradiated with the laser light La) with illumination light Lb for angle detection. The detection operation of the angle detection device 6 is controlled by the control device 5. For example, the control device 5 performs feedback control to correct the drive signal based on the signal output from the angle detection device 6.

[0029] Although details will be described later, the abnormality detection device 7 detects abnormal operation of the movable mirror 20 during operation based on the amount of temporal fluctuation in the signal output from the angle detection device 6.

[0030] Next, an example of the configuration of the MMD 4 will be described with reference to Fig. 2. Fig. 2 is a schematic diagram of the MMD 4.

[0031] The MMD 4 has a movable mirror 20, a first actuator 21, a second actuator 22, a support frame 23, a first support portion 24, a second support portion 25, a connection portion 26, and a fixing portion 27. The MMD 4 is formed, for example, by etching an SOI (Silicon On Insulator) substrate. The movable mirror 20 is an example of a "mirror" according to the technology of the present disclosure.

[0032] The movable mirror 20 has a reflecting surface 20A that reflects incident light. The reflecting surface 20A is formed of a thin metal film such as gold (Au) or aluminum (Al) provided on one surface of the movable mirror 20. The reflecting surface 20A is, for example, circular.

[0033] The support frame 23 is disposed so as to surround the movable mirror 20. The second actuator 22 is disposed so as to surround the movable mirror 20 and the support frame 23. The first actuator 21 is disposed so as to surround the movable mirror 20, the support frame 23, and the second actuator 22.

[0034] The first support portion 24 connects the movable mirror 20 and the support frame 23 on the first axis a1, and supports the movable mirror 20 so that it can swing around the first axis a1. The first axis a1 is in a plane that includes the reflecting surface 20A when the movable mirror 20 is stationary. For example, the first support portion 24 is a torsion bar that extends along the first axis a1.

[0035] The second support section 25 connects the support frame 23 and the second actuator 22 on the second axis a2, and supports the movable mirror 20 and the support frame 23 so that they can swing about the second axis a2. The second axis a2 is perpendicular to the first axis a1 in a plane including the reflecting surface 20A when the movable mirror 20 is stationary.

[0036] The connecting portion 26 connects the first actuator 21 and the second actuator 22 on the first axis a1. The connecting portion 26 also connects the first actuator 21 and the fixed portion 27 on the first axis a1.

[0037] The fixed portion 27 has a rectangular outer shape and surrounds the first actuator 21. The lengths of the fixed portion 27 in the X and Y directions are each, for example, about 1 mm to 10 mm. The thickness of the fixed portion 27 in the Z direction is, for example, about 5 μm to 0.2 mm.

[0038] The first actuator 21 and the second actuator 22 are piezoelectric actuators each equipped with a piezoelectric element. The first actuator 21 applies a rotational torque about a first axis a1 to the movable mirror 20. The second actuator 22 applies a rotational torque about a second axis a2 to the movable mirror 20. This causes the movable mirror 20 to oscillate about the first axis a1 and the second axis a2.

[0039] The first actuator 21 is an annular thin plate member that surrounds the movable mirror 20, the support frame 23, and the second actuator 22 in the XY plane. The first actuator 21 is composed of a pair of a first movable part 21A and a second movable part 21B. The first movable part 21A and the second movable part 21B are each approximately semi-annular. The first movable part 21A and the second movable part 21B have shapes that are line-symmetrical with respect to the first axis a1, and are connected on the first axis a1.

[0040] The support frame 23 is an annular thin plate member that surrounds the movable mirror 20 in the XY plane.

[0041] The second actuator 22 is an annular thin plate member that surrounds the movable mirror 20 and the support frame 23 in the XY plane. The second actuator 22 is composed of a pair of a first movable part 22A and a second movable part 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 shaped to be line-symmetric with respect to the second axis a2 and are connected on the second axis a2.

[0042] In the first actuator 21, a piezoelectric element is provided on each of the first movable portion 21A and the second movable portion 21B. In the second actuator 22, a piezoelectric element is provided on each of the first movable portion 22A and the second movable portion 22B.

[0043] 3 and 4 explain the deflection angle when the movable mirror 20 swings. Fig. 3 shows the deflection angle θ1 around the first axis a1 of the movable mirror 20 (hereinafter referred to as the first deflection angle). Fig. 4 shows the deflection angle θ2 around the second axis a2 of the movable mirror 20 (hereinafter referred to as the second deflection angle).

[0044] 3, the angle at which the normal N to the reflecting surface 20A of the movable mirror 20 is tilted in the YZ plane is referred to as the first deflection angle θ1. When the normal N to the reflecting surface 20A is tilted in the +Y direction, the first deflection angle θ1 takes a positive value, and when it is tilted in the -Y direction, the first deflection angle θ1 takes a negative value.

[0045] The first deflection angle θ1 is controlled by a drive signal (hereinafter referred to as the first drive signal) that the control device 5 provides to the first actuator 21. The first drive signal is, for example, a sinusoidal AC voltage. The first drive signal is a drive voltage waveform V applied to the first movable portion 21A. 1A (t) and the driving voltage waveform V applied to the second movable portion 21B 1B (t) and the driving voltage waveform V 1A (t) and the drive voltage waveform V 1B (t) are in opposite phase to each other (i.e., a phase difference of 180°).

[0046] 4, the angle at which the normal N to the reflecting surface 20A of the movable mirror 20 is tilted in the XZ plane is referred to as the second deflection angle θ2. When the normal N to the reflecting surface 20A is tilted in the +X direction, the second deflection angle θ2 takes a positive value, and when it is tilted in the -X direction, the second deflection angle θ2 takes a negative value.

[0047] The second deflection angle θ2 is controlled by a drive signal (hereinafter referred to as a second drive signal) that the control device 5 provides to the second actuator 22. The second drive signal is, for example, a sinusoidal AC voltage. The second drive signal is a drive voltage waveform V applied to the first movable portion 22A. 2A (t) and the driving voltage waveform V applied to the second movable portion 22B 2B (t) and the driving voltage waveform V 2A (t) and the drive voltage waveform V 2B (t) are in opposite phase to each other (i.e., a phase difference of 180°).

[0048] 5 shows an example of a drive signal applied to the first actuator 21 and the second actuator 22. FIG. 5(A) shows a drive voltage waveform V1A (t) and V 1B (t) shows the drive voltage waveform V included in the second drive signal. 2A (t) and V 2B (t) is shown.

[0049] Drive voltage waveform V 1A (t) and V 1B (t) are expressed by the following formulas (1A) and (1B), respectively. V 1A (t)=A1sin(2πf d t) (1A) V 1B (t)=A1sin(2πf d t+π) (1B)

[0050] where t is time. d is the driving frequency. A1 is the amplitude. Driving voltage waveform V 1A (t) and the drive voltage waveform V 1B The phase difference with (t) is π (i.e., 180°).

[0051] Drive voltage waveform V 2A (t) and V 2B (t) are expressed by the following formulas (2A) and (2B), respectively. V 2A (t)=A2sin(2πf d t+φ) (2A) V 2B (t)=A2sin(2πf d t+π+φ) (2B)

[0052] where A2 is the amplitude of the driving voltage waveform V 2A (t) and the drive voltage waveform V 2B The phase difference with (t) is π (i.e., 180°). φ is the driving voltage waveform V 1A (t) and the drive voltage waveform V 2A (t) is the phase difference between the amplitudes A1 and A2. In this embodiment, φ is set to 90° in order to make the optical scanning pattern helical by causing the movable mirror 20 to perform precession. The amplitudes A1 and A2 may be changed according to the time t.

[0053] In this embodiment, the driving frequency f d is the resonance frequency of the movable mirror 20. As a result, the movable mirror 20 resonates at a constant oscillation period T. The oscillation period T is expressed as T=1 / f d It is expressed as:

[0054] Fig. 6 shows an example of the configuration of the angle detection device 6. As shown in Fig. 6, the angle detection device 6 includes a light irradiation device 30, a light deflection member 31, a detection device 32, a collimator lens 33, and a condenser lens 34. The light irradiation device 30 emits illumination light Lb for angle detection. For example, the light irradiation device 30 is a laser diode that emits laser light with a wavelength of approximately 980 nm as the illumination light Lb.

[0055] The light deflection member 31 has a cut surface formed by cutting a cylindrical base material at an angle relative to the axis of rotational symmetry of the cylinder, and a reflecting surface 31A is formed on the cut surface. The light deflection member 31 is positioned so that the illumination light Lb emitted from the light irradiation device 30 is incident on the reflecting surface 31A at an incident angle of approximately 45°.

[0056] A collimator lens 33 is disposed between the light irradiation device 30 and the light deflection member 31. The illumination light Lb emitted from the light irradiation device 30 is incident on the reflecting surface 31A via the collimator lens 33. The traveling direction of the illumination light Lb emitted from the light irradiation device 30 is, for example, the Y direction. The illumination light Lb incident on the reflecting surface 31A is deflected by an angle of 90°, travels in the Z direction, and is incident on the back surface 20B of the movable mirror 20. The back surface 20B is the surface opposite to the surface on which the reflecting surface 20A of the movable mirror 20 is provided. Although not shown, a beam structure (also referred to as a rib) is provided on the back surface 20B to increase the strength of the movable mirror 20.

[0057] A condenser lens 34 is disposed between the light deflection member 31 and the movable mirror 20. The condenser lens 34 is, for example, a biconvex lens, and is disposed so that the illumination light Lb deflected by the light deflection member 31 travels along its optical axis AX. The illumination light Lb passes through the center of the condenser lens 34 and is incident on the rear surface 20B of the movable mirror 20.

[0058] The illumination light Lb incident on the rear surface 20B of the movable mirror 20 is reflected at a reflection angle according to the deflection angles (first deflection angle θ1 and second deflection angle θ2) of the movable mirror 20. The illumination light Lb reflected by the rear surface 20B of the movable mirror 20 is incident on the light receiving surface 32A of the detection device 32 via a condenser lens 34. An optical deflection member 31 is disposed in the center of the light receiving surface 32A.

[0059] The detector 32 is a position-sensitive element capable of detecting the position of the center of gravity of the incident light, and outputs a position signal representing the position of the center of gravity of the incident light. In this embodiment, a two-dimensional PSD (Position Sensitive Detector) that detects the two-dimensional position of the incident light is used as the detector 32. The detector 32 detects the position of the center of gravity of the incident light in the X direction and the Y direction on the light-receiving surface 32A. The detector 32 outputs a position signal Px(t) representing the position of the center of gravity of the light in the X direction and a position signal Py(t) representing the position of the center of gravity of the light in the Y direction. As shown in FIG. 6, the position signal Py(t) changes depending on the first deflection angle θ1. Although not shown, the position signal Px(t) changes depending on the second deflection angle θ2.

[0060] The detection device 32 of this embodiment can simultaneously detect the position of the center of gravity and the light intensity of the incident light, and outputs intensity signals Ix(t) and Iy(t) representing the light intensity of the incident light in addition to position signals Px(t) and Py(t). The intensity signal Ix(t) represents the light intensity in the X direction. The intensity signal Iy(t) represents the light intensity in the Y direction.

[0061] The control device 5 performs feedback control to correct the first drive signal and the second drive signal based on the position signals Px(t) and Py(t) output from the angle detection device 6.

[0062] 7 shows an example of the configuration of the anomaly detection device 7. The anomaly detection device 7 has a detection unit 40 and a determination unit 41. The detection unit 40 is configured with a delay circuit 42 and a differential amplifier circuit 43. In this embodiment, the anomaly detection device 7 performs anomaly detection using the position signal Py(t) of the position signals Px(t) and Py(t) output from the detection device 32.

[0063] The position signal Py(t) is input to the detection unit 40. Specifically, the position signal Py(t) is input to a delay circuit 42 and a differential amplifier circuit 43. The delay circuit 42 delays the input position signal Py(t) by a certain time Δt and outputs the delayed signal. Hereinafter, the signal output from the delay circuit 42 will be referred to as a delayed signal Py(t-Δt). Hereinafter, the time Δt will be referred to as a delay time Δt. The delay time Δt is shorter than the oscillation period T.

[0064] The delay signal Py(t-Δt) output from the delay circuit 42 is input to the differential amplifier circuit 43. The differential amplifier circuit 43 amplifies and outputs the difference between the position signal Py(t) and the delay signal Py(t-Δt). That is, the delay circuit 42 adjusts the phase of the position signal Py(t) to generate the delay signal Py(t-Δt). Hereinafter, the output signal output from the differential amplifier circuit 43 will be referred to as the fluctuation amount ΔPy(t). The fluctuation amount ΔPy(t) represents the amount of temporal fluctuation in the position signal Py(t). In other words, the fluctuation amount ΔPy(t) represents the amount by which ΔPy(t) fluctuates over a time interval shorter than the oscillation period T.

[0065] The fluctuation amount ΔPy(t) output from the differential amplifier circuit 43 is input to the determination unit 41. The determination unit 41 is configured with a comparator. The determination unit 41 determines whether the fluctuation amount ΔPy(t) is equal to or greater than a threshold value Vth, and outputs the determination result to the control device 5. Here, the fluctuation amount ΔPy(t) being equal to or greater than the threshold value Vth means that the absolute value of the fluctuation amount ΔPy(t) is equal to or greater than the threshold value Vth, in other words, ΔPy(t)≧Vth or ΔPy(t)≦−Vth.

[0066] The control device 5 stops the operation of the light source 3 and the MMD 4 in accordance with the determination result output from the determination unit 41. Specifically, the control device 5 stops the operation of the light source 3 and the MMD 4 when the determination unit 41 determines that the fluctuation amount ΔPy(t) is equal to or greater than the threshold value Vth.

[0067] 8A and 8B show examples of the position signal Py(t), the delay signal Py(t-Δt), and the fluctuation amount ΔPy(t) when the movable mirror 20 is operating normally. Fig. 8A shows an example of the position signal Py(t) and the delay signal Py(t-Δt). Fig. 8B shows an example of the fluctuation amount ΔPy(t).

[0068] When the movable mirror 20 resonates at a constant oscillation period T, the position signal Py(t) ideally forms an approximately sinusoidal wave, as shown in Fig. 8(A). In Fig. 8(A), the position signal Py(t) is shown by a solid line, and the delay signal Py(t-Δt) is shown by a dashed line. The fluctuation amount ΔPy(t) shown in Fig. 8(B) corresponds to the fluctuation voltage ΔV of the position signal Py(t) with respect to the delay time Δt. The fluctuation amount ΔPy(t) ideally forms an approximately sinusoidal wave.

[0069] 9A and 9B show examples of the position signal Py(t), the delay signal Py(t-Δt), and the fluctuation amount ΔPy(t) when an abnormal operation occurs in the movable mirror 20. Fig. 9A shows an example of the position signal Py(t) and the delay signal Py(t-Δt). Fig. 9B shows an example of the fluctuation amount ΔPy(t).

[0070] As shown in FIG. 9, when an abnormal operation occurs in the movable mirror 20, the amount of fluctuation ΔPy(t) changes significantly and becomes equal to or greater than the threshold value Vth, and the determining unit 41 determines that the operation of the movable mirror 20 is abnormal.

[0071] Even if the movable mirror 20 is operating normally, the position signal Py(t) may have noise in its waveform due to stray light or the like being included in the light reflected from the rear surface 20B of the movable mirror 20. Stray light is generated, for example, when the illumination light Lb is reflected by a beam structure or the like provided on the rear surface 20B. To accurately detect abnormal operation of the movable mirror 20 without being affected by noise, the delay time Δt must be set within an appropriate range. Specifically, it is preferable to set the ratio (Δt / T) of the delay time Δt to the oscillation period T within an appropriate range.

[0072] For example, it is preferable to specify the upper limit as Δt / T<5%. In this case, the detection unit 40 detects the amount of fluctuation in the position signal Py(t) over a time interval that is less than 5% of the oscillation period T as the fluctuation amount ΔPy(t). It is even more preferable to specify the upper and lower limits as 0.05%<Δt / T<5%. In this case, the detection unit 40 detects the amount of fluctuation in the position signal Py(t) over a time interval that is less than 5% and greater than 0.05% of the oscillation period T as the fluctuation amount ΔPy(t).

[0073] [Verification of effects through experiments] By using the abnormality detection device 7 configured as described above, it becomes possible to quickly detect abnormal operation of the movable mirror 20 during operation. In order to verify this effect, the applicant fabricated multiple MMDs 4 and conducted experiments.

[0074] The fabricated MMD4 was driven at a driving frequency of f dWith the movable mirror 20 undergoing precession at a frequency of approximately 1420 Hz, the signal output from the detector 32 was input to the anomaly detector 7 to evaluate the accuracy of anomaly detection. The oscillation period T was approximately 704 μs. FIG. 10 shows examples of the position signals Px(t), Py(t) and intensity signals Ix(t), Iy(t) output from the detector 32. In this experiment, the position signal Py(t) was input to the anomaly detector 7. The delay time Δt was changed in the anomaly detector 7 to evaluate the accuracy of anomaly detection for multiple ratios Δt / T.

[0075] Furthermore, because abnormal behavior is unlikely to occur under normal conditions, we generated abnormal behavior by operating the MMD4 under load conditions. The loads included operating the MMD4 in a high-temperature, high-humidity environment, applying external shocks to the MMD4, and operating the MMD4 at a high drive voltage.

[0076] The evaluation criteria were determined based on the results of determining abnormal operation based on measurement values ​​obtained by directly measuring the operation of the movable mirror 20 using an optical method. FIG. 11 shows an example of the optical method. As shown in FIG. 11, an evaluation laser beam LE is irradiated onto the reflecting surface 20A of the movable mirror 20 from an evaluation light source 50 via a collimating lens 51, and the light reflected by the reflecting surface 20A is imaged on a position sensitive detector (PSD) 54 via lenses 52 and 53. The image position obtained by the PSD is converted into the deflection angle of the movable mirror 20. Note that, to improve the accuracy of the deflection angle conversion, it is preferable to install a reference mirror with a known angle instead of the MMD 4 and perform calibration to calibrate the angle and position information.

[0077] The deflection angles (first deflection angle θ1 and second deflection angle θ2) of the movable mirror 20 were measured using the optical method described above, and a composite angle obtained by combining the first deflection angle θ1 and the second deflection angle θ2 was calculated. When the movable mirror 20 is performing precession, the composite angle is constant. When the composite angle exceeds a range of ±10% from the steady value, it is determined that an abnormal operation has occurred, and the time at which this determination is made is used as the reference time.

[0078] The accuracy of anomaly detection by the anomaly detection device 7 was evaluated based on multiple evaluation items. The evaluation items used in this experiment were "detection time," "missed detection," and "false detection." Detection time is an evaluation item related to the time it took to detect an abnormal operation (anomaly detection time). Missed detection is an evaluation item related to whether or not an abnormal operation was detected. False detection is an evaluation item related to whether or not an abnormal operation was falsely detected between the start of operation and the occurrence of the abnormal operation.

[0079] 12 shows the evaluation results. Examples 1 to 7 are experimental examples of anomaly detection using the anomaly detection device 7 of this embodiment, and the ratio Δt / T varies depending on the setting value of the delay time Δt. The comparative example is an experimental example of anomaly detection using a conventional determination method based on the position signal Py(t) without using the anomaly detection device 7 of this embodiment.

[0080] In the evaluation results of detection time, P indicates that the slowest anomaly detection time (worst detection time) in the experiment using 100 samples was less than 350 μs from the reference time. F1 indicates that the worst detection time was less than 700 μs from the reference time. F2 indicates that the worst detection time was 700 μs or more from the reference time.

[0081] In the evaluation results of false negatives, P indicates that the experiment was conducted using 100 samples and that abnormal behavior was detected in all samples, i.e., there were no false negatives. F indicates that abnormal behavior could not be detected in at least one sample, i.e., there was a false negative.

[0082] In the evaluation results of false positives, P indicates that the number of false positives divided by the total number of samples (false positive rate) was less than 10% in an experiment using 100 samples. F1 indicates that the false positive rate was less than 50%. F2 indicates that the false positive rate was 50% or more.

[0083] According to the evaluation results of the detection time, it is found that the worst detection time is less than 350 μs from the reference time when Δt / T<5%. In other words, it is preferable to set Δt / T<5% in order to quickly detect abnormal operation of the movable mirror 20 during operation.

[0084] The evaluation results of missed detection show that missed detection does not occur when 0.01%<Δt / T<10%. In other words, from the viewpoint of missed detection, it is preferable to set the lower limit of Δt / T to 0.01%.

[0085] The evaluation results of false detection show that false detection does not occur when Δt / T is 0.05% or less. False detection is mainly caused by noise due to stray light. In other words, from the viewpoint of noise resistance, it is preferable to set the lower limit of Δt / T to 0.05%.

[0086] Figures 13 to 15 show waveforms of the fluctuation amount ΔPy(t). Figure 13 shows the waveform of the fluctuation amount ΔPy(t) when Δt / T=0.5%. Figure 14 shows the waveform of the fluctuation amount ΔPy(t) when Δt / T=5%. Figure 15 shows the waveform of the fluctuation amount ΔPy(t) when Δt / T=0.01%.

[0087] Figure 13 shows an example of a waveform that enables fast and accurate anomaly detection when 0.05%<Δt / T<10%. The waveform shown in Figure 13 has a larger amplitude during abnormal operation than during normal operation, allowing for fast and accurate detection of abnormal operation. Figure 13 also shows that the above amplitude relationship is maintained even when noise due to stray light is mixed into the waveform, enabling stable detection of abnormal operation.

[0088] Figure 14 shows an example of a waveform that causes a detection miss when Δt / T≧5%. In the waveform shown in Figure 14, the amplitude during abnormal operation is smaller than the amplitude during normal operation, so the abnormal operation cannot be detected, resulting in a detection miss.

[0089] Fig. 15 shows an example of a waveform that causes false detection when Δt / T≦0.05%. The waveform shown in Fig. 15 has small amplitude during normal operation and abnormal operation, so it is susceptible to noise caused by stray light, etc., and false detection is likely to occur.

[0090] 16 and 17 show examples of determinations made by a conventional determination method based on the position signal Py(t). In the conventional determination method, abnormalities are detected by comparing the position signal Py(t) with a threshold value Vth2. In both of the waveforms shown in FIGS. 16 and 17, the amplitude decreases after an abnormal operation occurs, making it impossible to detect the abnormal operation and resulting in a missed detection. If the amplitude increases after the abnormal operation occurs, the abnormal operation would be detected even with the conventional determination method, but it would take time for the position signal Py(t) to exceed the threshold value Vth2 after the abnormal operation occurs. For this reason, high-speed abnormality detection is not possible.

[0091] [Various variations] In the above embodiment, the anomaly detection device 7 detects an anomaly based on the position signal Py(t), but it may also perform anomaly detection based on the position signal Px(t). Furthermore, the anomaly detection device 7 may perform anomaly detection based on each of the position signals Py(t) and Px(t). In this case, for example, the anomaly detection device 7 determines that an abnormal operation has occurred when the amount of temporal variation in either the position signal Py(t) or Px(t) is equal to or greater than a threshold value.

[0092] Furthermore, the anomaly detection device 7 may perform anomaly detection based on an intensity signal in addition to a position signal. FIG. 18 shows the configuration of an anomaly detection device 7A according to a modified example. The anomaly detection device 7A performs anomaly detection based on an intensity signal Iy(t) in addition to a position signal Py(t) output from the detection device 32. The anomaly detection device 7A includes a detection unit 40 and a determination unit 41A. The determination unit 41A performs the above-mentioned determination based on the amount of fluctuation ΔPy(t) of the position signal Py(t), and also performs a determination based on the intensity signal Iy(t).

[0093] 19 shows an example of a determination method based on the intensity signal Iy(t). The intensity signal Iy(t) fluctuates within a certain range D when the movable mirror 20 is operating normally, but falls outside the certain range D when abnormal operation of the movable mirror 20 occurs. For this reason, the determination unit 41A monitors the intensity signal Iy(t), and determines that abnormal operation has occurred when the intensity signal Iy(t) falls outside the certain range D. In this way, by performing abnormality detection based on the intensity signal in addition to the position signal, the accuracy of abnormality detection is further improved.

[0094] Anomaly detection may be performed based on all of the position signals Px(t), Py(t) and intensity signals Ix(t), Iy(t).

[0095] In the above embodiment, the detector 40 is configured with the delay circuit 42 and the differential amplifier circuit 43, but the detector 40 may also be configured with a differentiation circuit. The detector 40 may also be configured with a high-pass filter. In this case, the cutoff frequency of the high-pass filter may be set according to the upper limit value of Δt / T. The detector 40 may also be configured with a band-pass filter. In this case, the cutoff frequencies on the high-frequency side and low-frequency side of the band-pass filter may be set according to the lower and upper limits of Δt / T.

[0096] Furthermore, in the above embodiment, the anomaly detection device 7 is configured with an analog circuit, but the anomaly detection device 7 may be configured in part or entirely with a digital circuit. For example, the position signal Py(t) may be digitized by an ADC (Analog to Digital Converter) and the digitized signal may be processed by software (program). In this case, a general-purpose processor may be used as the anomaly detection device 7. This general-purpose processor may include a CPU (Central Processing Unit), a programmable logic device (PLD), a dedicated electric circuit, etc. The processor performs detection processing and determination processing.

[0097] Furthermore, while the above embodiment uses a micromirror device having a mirror that can oscillate around two axes, the micromirror device may also have a mirror that can oscillate around one axis. That is, the micromirror device may include a mirror that can oscillate around at least one axis and an actuator that oscillates the mirror. Furthermore, the detection device is not limited to one that detects the two-dimensional position of incident light, but may also be one that detects the one-dimensional position of incident light.

[0098] All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference. [Explanation of symbols]

[0099] 2 Optical scanning device 3 light source 4 Micromirror Device (MMD) 5. Control device 6 Angle detection device 7,7A Abnormality detection device 10 Optical scanning system 20 Movable mirror 20A reflective surface 20B back side 21 First actuator 21A 1st moving part 21B 2nd moving part 22 Second actuator 22A 1st moving part 22B 2nd moving part 23 Support Frame 24 1st support part 25 Second support part 26 Connection 27 Fixed part 30 Light irradiation device 31 Light deflection member 31A Reflective surface 32 Detection device 32A light receiving surface 33 Collimating Lens 34 Condenser Lens 40 Detector 41,41A Judgment part 42 Delay Circuit 43 Differential amplifier circuit 50 Evaluation light source 51 Collimating Lens 52,53 Lens 54 Position detection element AX optical axis LE evaluation laser light La laser light lb lighting light N normal

Claims

1. a micromirror device including a mirror having a reflective surface that reflects light and that is swingable around at least one axis, and an actuator that swings the mirror; a control device for controlling the operation of the actuator; a light irradiation device that irradiates illumination light onto a rear surface of the mirror opposite to the reflecting surface; a detection device onto which the reflected light of the illumination light reflected by the mirror is incident and which outputs a position signal representing the position of the incident light; an abnormality detection device that detects abnormal operation of the mirror based on a temporal fluctuation amount that is a difference between the position signal and a delayed signal obtained by delaying the position signal by a certain delay time; An optical scanning device comprising:

2. the detection device is a position detection element that can detect the position of the center of gravity of the amount of incident light, The position signal represents the light amount center position.

2. The optical scanning device according to claim 1.

3. the control device drives the actuator to resonate the mirror at a constant oscillation period; 2. The optical scanning device according to claim 1.

4. The ratio of the delay time to the oscillation period is less than 5%.

4. The optical scanning device according to claim 3.

5. The ratio of the delay time to the oscillation period is less than 5% and greater than 0.05%; 4. The optical scanning device according to claim 3.

6. The anomaly detection device includes a detection unit that detects the amount of fluctuation, and a determination unit that determines whether the amount of fluctuation is equal to or greater than a threshold value.

4. The optical scanning device according to claim 3.

7. The detection unit a delay circuit that delays the position signal output from the detection device by the delay time; a differential amplifier circuit that amplifies and outputs the difference between the position signal output from the detection device and the position signal delayed by the delay circuit; It is made up of 7. The optical scanning device according to claim 6.

8. The determination unit is a comparator.

8. The optical scanning device according to claim 7.

9. the detection device is a position detection element that can simultaneously detect the position of the center of gravity of the amount of light of the incident light and the light intensity, the abnormality detection device detects the abnormal operation based on an intensity signal representing the light intensity output from the detection device in addition to the position signal; 3. The optical scanning device according to claim 2.

10. the mirror is oscillating about a first axis and a second axis that are orthogonal to each other; the detection device detects the two-dimensional position of the incident light; 2. The optical scanning device according to claim 1.

11. a micromirror device including a mirror having a reflective surface that reflects light and that is swingable around at least one axis, and an actuator that swings the mirror; a control device for controlling the operation of the actuator; A method for detecting an abnormality in an optical scanning device, comprising: irradiating the rear surface of the mirror opposite to the reflecting surface with illumination light; detecting an abnormal operation of the mirror based on a temporal variation amount that is a difference between a position signal indicating a position of the reflected light of the illumination light reflected by the mirror and a delay signal obtained by delaying the position signal by a certain delay time; An anomaly detection method comprising:

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