Optical Scanning Device

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, an actuator that swings the mirror, and a piezoelectric element that generates and outputs an electromotive force through the swinging of the mirror; a control unit that controls the operation of the actuator; and an abnormality detection device that detects an abnormal operation of the mirror based on the amount of variation over time of an output signal from the piezoelectric element.SELECTED DRAWING: Figure 6

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] In laser scanners such as LiDAR and HUD, it is important to ensure the safety of users. 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 quickly detect abnormal mirror movement while the mirror is in operation.

[0004] Patent Document 1 describes detecting an abnormality based on a current flowing through a driving piezoelectric part as an actuator. Patent Document 1 also describes detecting an abnormality using a detecting piezoelectric part provided separately from the driving piezoelectric part.

[0005] Patent Documents 2 and 3 describe detecting an abnormality in a micromirror device based on the amplitude of a mirror detected by a piezoelectric element for detecting an abnormality.

[0006] Patent Document 4 describes that a sensor is provided to detect the state of the mirror, and detection is made based on the phase difference between the mirror scanning position and the drive voltage, or the maximum mirror scanning angle (that is, amplitude). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-134391 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-132762 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-080978 [Patent Document 4] Japanese Patent Application Publication No. 06-123845 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the detection method described in Patent Document 1 detects abnormalities based on the current flowing in the driving piezoelectric element or the detecting piezoelectric element, and is therefore thought to be unable to detect abnormalities other than short circuits in the piezoelectric element. Furthermore, the detection methods described in Patent Documents 2 and 3 require acquisition and evaluation of a waveform for one oscillation period in order to detect the mirror's amplitude, making it impossible to detect abnormal mirror operation at high speed. Similarly, the detection method described in Patent Document 4 requires acquisition and evaluation of a waveform for one oscillation period in order to detect the phase difference or amplitude, making it impossible to detect abnormal mirror operation at high speed.

[0009] 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]

[0010] 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, an actuator that oscillates the mirror, and a piezoelectric element that generates and outputs an electromotive force due to the oscillation of the mirror, a control device that controls the operation of the actuator, and an abnormality detection device that detects abnormal operation of the mirror based on the amount of temporal fluctuation in the output signal from the piezoelectric element.

[0011] It is preferable that the control device drives the actuator to resonate the mirror at a constant oscillation period.

[0012] The abnormality detection device preferably detects the amount of fluctuation of the output signal in a time interval that is less than 10% of the oscillation period as the amount of fluctuation.

[0013] The abnormality detection device preferably detects, as the amount of fluctuation, the amount of fluctuation in the output signal over a time interval that is smaller than 10% and larger than 0.05% of the oscillation period.

[0014] 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.

[0015] It is preferable that the detection unit is composed of a delay circuit that delays the output signal output from the piezoelectric element by a certain time, and a differential amplifier circuit that amplifies and outputs the difference between the output signal output from the piezoelectric element and the output signal delayed by the delay circuit.

[0016] The determining unit is preferably a comparator.

[0017] It is preferable that the mirror is capable of swinging around a first axis and a second axis that are perpendicular to each other, and the piezoelectric element generates an electromotive force when the mirror swings around the first axis or the second axis.

[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, an actuator that oscillates the mirror, and a piezoelectric element that generates and outputs an electromotive force due to the oscillation of the mirror, and a control device that controls the operation of the actuator, and includes detecting abnormal operation of the mirror based on the amount of temporal variation in the output signal from the piezoelectric element. [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 block diagram illustrating an example of a configuration of an anomaly detection device. [Figure 7] 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 8] 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 9] FIG. 1 shows four types of waveforms used in the experiment. [Figure 10] FIG. 1 illustrates an example of an optical method. [Figure 11] FIG. 10 is a diagram showing evaluation results. [Figure 12]FIG. 10 is a diagram showing the waveform of the fluctuation amount when Δt / T=0.5%. [Figure 13] FIG. 10 is a diagram showing the waveform of the fluctuation amount when Δt / T=15%. [Figure 14] FIG. 10 is a diagram showing the waveform of the fluctuation amount when Δt / T=0.01%. [Figure 15] 10A and 10B are diagrams illustrating examples of determination by a conventional determination method based on an output signal. [Figure 16] 10A and 10B are diagrams illustrating examples of determination by a conventional determination method based on an output 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] 1 is a schematic diagram of 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, and an anomaly detection device 6. 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 L 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, for example, scans the laser light L in a helical pattern. 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 L. When the movable mirror 20 of the MMD 4 is stationary, the light source 3 irradiates the laser light L perpendicularly to a reflecting surface 20A (see FIG. 2) of the movable mirror 20. The laser light L 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 L based on the input drive signal and irradiates the MMD 4 with the laser light L. 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] Although the details will be described 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 L reflected by the movable mirror 20 scans the plane so as to describe a circle.

[0028] Although details will be described later, the abnormality detection device 6 detects abnormal operation of the movable mirror 20 during operation based on the amount of temporal variation in the output signal output from a piezoelectric element provided in the MMD 4 as an angle sensor.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] The support frame 23 is an annular thin plate member that surrounds the movable mirror 20 in the XY plane.

[0040] 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.

[0041] 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.

[0042] The MMD 4 also has a first angle detection sensor 31 and a second angle detection sensor 32, each composed of a piezoelectric element. The first angle detection sensor 31 is provided, for example, on the first movable portion 21A and in the vicinity of the connection portion 26. The first angle detection sensor 31 generates and outputs an electromotive force due to the oscillation of the movable mirror 20 about the first axis a1. In other words, the first angle detection sensor 31 outputs a signal corresponding to the angle of the movable mirror 20 about the first axis a1.

[0043] The second angle detection sensor 32 is provided, for example, on the first movable portion 22A and in the vicinity of the second support portion 25. The second angle detection sensor 32 generates and outputs an electromotive force due to the oscillation of the movable mirror 20 about the second axis a2. In other words, the second angle detection sensor 32 outputs a signal corresponding to the angle of the movable mirror 20 about the second axis a2.

[0044] The control device 5 performs feedback control to correct the drive signals given to the first actuator 21 and the second actuator 22 based on the signals output from the first angle detection sensor 31 and the second angle detection sensor 32.

[0045] 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).

[0046] 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.

[0047] 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°).

[0048] 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.

[0049] 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°).

[0050] 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 V 1A (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.

[0051] 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 dt+π) (1B)

[0052] 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°).

[0053] 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)

[0054] 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.

[0055] 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:

[0056] 6 shows an example of the configuration of the anomaly detection device 6. The anomaly detection device 6 has a detection unit 40 and a determination unit 41. The detection unit 40 is composed of a delay circuit 42 and a differential amplifier circuit 43. In this embodiment, the anomaly detection device 6 performs anomaly detection using the output signal output from the first angle detection sensor 31 out of the output signals output from the first angle detection sensor 31 and the second angle detection sensor 32 to the control device 5. Hereinafter, the output signal output from the first angle detection sensor 31 will be represented as S(t).

[0057] The output signal S(t) from the first angle detection sensor 31 is input to the detection unit 40. Specifically, the output signal S(t) is input to a delay circuit 42 and a differential amplifier circuit 43. The delay circuit 42 delays the input output signal S(t) by a certain time Δt and outputs it. Hereinafter, the signal output from the delay circuit 42 will be referred to as a delayed signal S(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.

[0058] The delay signal S(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 output signal S(t) and the delay signal S(t-Δt). That is, the delay circuit 42 adjusts the phase of the output signal S(t) to generate the delay signal S(t-Δt). Hereinafter, the output signal output from the differential amplifier circuit 43 will be referred to as a fluctuation amount ΔS(t). The fluctuation amount ΔS(t) represents the amount of temporal fluctuation in the output signal S(t) from the first angle detection sensor 31. In other words, the fluctuation amount ΔS(t) represents the amount by which the output signal S(t) fluctuates over a time interval shorter than the oscillation period T.

[0059] The fluctuation amount ΔS(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 ΔS(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 ΔS(t) being equal to or greater than the threshold value Vth means that the absolute value of the fluctuation amount ΔS(t) is equal to or greater than the threshold value Vth, in other words, ΔS(t)≧Vth or ΔS(t)≦−Vth.

[0060] 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 amount of fluctuation ΔS(t) is equal to or greater than the threshold value Vth.

[0061] 7A and 7B show examples of the output signal S(t), the delay signal S(t-Δt), and the fluctuation amount ΔS(t) when the movable mirror 20 is operating normally. Fig. 7A shows an example of the output signal S(t) and the delay signal S(t-Δt). Fig. 7B shows an example of the fluctuation amount ΔS(t).

[0062] When the movable mirror 20 resonates at a constant oscillation period T, the output signal S(t) ideally forms an approximately sinusoidal wave, as shown in Fig. 7(A). In Fig. 7(A), the output signal S(t) is shown by a solid line, and the delayed signal S(t-Δt) is shown by a dashed line. The fluctuation amount ΔS(t) shown in Fig. 7(B) corresponds to the fluctuation voltage ΔV of the output signal S(t) with respect to the delay time Δt. The fluctuation amount ΔS(t) ideally forms an approximately sinusoidal wave.

[0063] 8A and 8B show examples of the output signal S(t), the delay signal S(t-Δt), and the fluctuation amount ΔS(t) when an abnormal operation occurs in the movable mirror 20. Fig. 8A shows an example of the output signal S(t) and the delay signal S(t-Δt). Fig. 8B shows an example of the fluctuation amount ΔS(t).

[0064] As shown in FIG. 8, when an abnormal operation occurs in the movable mirror 20, the amount of fluctuation ΔS(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.

[0065] Even if the movable mirror 20 is operating normally, the waveform of the output signal S(t) may be distorted due to noise, crosstalk, and the like. Crosstalk occurs when the drive signals given to the first actuator 21 and the second actuator 22 interfere with each other, or when the oscillation of the movable mirror 20 around one axis affects the oscillation of the movable mirror 20 around the other axis. To accurately detect abnormal operation of the movable mirror 20 regardless of the influence of noise, crosstalk, and the like, it is necessary to set the delay time Δt 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.

[0066] For example, it is preferable to specify the upper limit as Δt / T<10%. In this case, the detection unit 40 detects the amount of fluctuation in the output signal S(t) over a time interval that is less than 10% of the oscillation period T as the fluctuation amount ΔS(t). It is even more preferable to specify the upper and lower limits as 0.05%<Δt / T<10%. In this case, the detection unit 40 detects the amount of fluctuation in the output signal S(t) over a time interval that is less than 10% and greater than 0.05% of the oscillation period T as the fluctuation amount ΔS(t).

[0067] [Verification of effects through experiments] By using the abnormality detection device 6 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.

[0068] Specifically, experiments were conducted using four types of waveforms A to D to evaluate the accuracy of abnormality detection due to differences in the waveform of the output signal S(t) from the first angle detection sensor 31. The four types of waveforms A to D were achieved by changing the structure of the movable mirror 20, the arrangement of the first angle detection sensor 31, etc. FIG. 9 shows the four types of waveforms A to D used in the experiments. Waveform A is an ideal waveform (i.e., a sine wave). Waveform B is a waveform that includes noise. Waveform C is a waveform that includes crosstalk. Waveform D is a waveform that includes crosstalk and noise.

[0069] The fabricated MMD4 was driven at a driving frequency of f d With the movable mirror 20 undergoing precession at a frequency of approximately 1420 Hz, the output signal S(t) having the above four types of waveforms A to D was input to the anomaly detection device 6 to evaluate the accuracy of anomaly detection. The oscillation period T was approximately 704 μs. In the anomaly detection device 6, the delay time Δt was changed to evaluate the accuracy of anomaly detection for multiple ratios Δt / T.

[0070] 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.

[0071] 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. 10 shows an example of the optical method. As shown in FIG. 10, 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.

[0072] 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.

[0073] The accuracy of anomaly detection by the anomaly detection device 6 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.

[0074] 11 shows the evaluation results. Examples 1 to 7 are experimental examples of anomaly detection using the anomaly detection device 6 of this embodiment, and the ratio Δt / T varies depending on the setting value of the delay time Δt. Comparative Examples 1 and 2 are experimental examples of anomaly detection using a conventional determination method based on the output signal S(t) without using the anomaly detection device 6 of this embodiment.

[0075] In the evaluation results of detection time, P indicates that the latest anomaly detection time (worst detection time) in the experiment using 100 samples was before the reference time. F1 indicates that the worst detection time was later than the reference time and less than 500 μs from the reference time. F2 indicates that the worst detection time was later than the reference time and more than 500 μs from the reference time.

[0076] 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.

[0077] 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.

[0078] According to the evaluation results of the detection time, for all of waveforms A to D, when Δt / T<10%, the detection time is faster than the reference detection time by the optical method. In other words, it is clear that Δt / T<10% is preferable for quickly detecting abnormal operation of the movable mirror 20 during operation.

[0079] According to the evaluation results of missed detection, it is found that for all of waveforms A to D, when Δt / T<10%, there is no missed detection.

[0080] The evaluation results of false detection show that for waveforms A and C that do not contain noise, the false detection rate is less than 10% when Δt / T<10%. On the other hand, for waveforms B and D that contain noise, the false detection rate is 10% or more when Δt / T≦0.05%. In other words, from the perspective of noise resistance, it is preferable to set the lower limit of Δt / T to 0.05%.

[0081] Figures 12 to 14 show waveforms of the fluctuation amount ΔS(t). Figure 12 shows the waveform of the fluctuation amount ΔS(t) when Δt / T=0.5%. Figure 13 shows the waveform of the fluctuation amount ΔS(t) when Δt / T=15%. Figure 14 shows the waveform of the fluctuation amount ΔS(t) when Δt / T=0.01%.

[0082] The waveform shown in Fig. 12 has a large difference in amplitude before and after the occurrence of abnormal operation. In other words, Fig. 12 shows that when 0.05%<Δt / T<10%, abnormality detection can be performed quickly and accurately.

[0083] The waveform shown in Fig. 13 has a small difference in amplitude before and after the occurrence of abnormal operation. That is, Fig. 13 shows that when Δt / T≧10%, the accuracy of anomaly detection decreases compared to when 0.05%<Δt / T<10%.

[0084] The difference in amplitude between before and after the occurrence of abnormal operation in the waveform shown in Fig. 14 is larger than that in the waveform shown in Fig. 13, but smaller than that in the waveform shown in Fig. 12. Fig. 14 shows that noise resistance decreases when Δt / T≦0.05%.

[0085] 15 and 16 show examples of determination using a conventional determination method based on the output signal S(t). In the conventional determination method, abnormality detection is performed by comparing the output signal S(t) with a threshold value Vth2. FIG. 15 shows a case where the amplitude increases after an abnormal operation occurs. In this case, the conventional determination method can detect abnormal operation, but it takes time for the output signal S(t) to exceed the threshold value Vth2 after the abnormal operation occurs. For this reason, abnormality detection cannot be performed quickly. FIG. 16 shows a case where the amplitude decreases after the abnormal operation occurs. In this case, the conventional determination method does not detect the abnormal operation, resulting in a missed detection.

[0086] [Various variations] 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 limit value and upper limit value of Δt / T.

[0087] Furthermore, since the output signal S(t) from the first angle detection sensor 31 made up of a piezoelectric element is very small, an amplifier circuit, a buffer circuit, etc. may be added to the anomaly detection device 6. Furthermore, a filter circuit for the purpose of reducing noise may be added to the anomaly detection device 6.

[0088] Furthermore, in the above embodiment, the anomaly detection device 6 is configured with an analog circuit, but part or all of the anomaly detection device 6 may be configured with a digital circuit. For example, the output signal S(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 6. 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.

[0089] Furthermore, in the above embodiment, the abnormality detection device 6 detects an abnormality based on the output signal from the first angle detection sensor 31, but it may also detect an abnormality based on the output signal from the second angle detection sensor 32. Furthermore, the abnormality detection device 6 may detect an abnormality based on each of the two output signals from the first angle detection sensor 31 and the second angle detection sensor 32. In this case, for example, the abnormality detection device 6 determines that an abnormal operation has occurred when the amount of temporal variation in either of the two output signals is equal to or greater than a threshold value.

[0090] 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, an actuator that oscillates the mirror, and a piezoelectric element that generates and outputs an electromotive force due to the oscillation of the mirror.

[0091] 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]

[0092] 2 Optical scanning device 3 light source 4 Micromirror Device (MMD) 5. Control device 6. Anomaly detection device 10 Optical scanning system 20 Movable mirror 20A reflective surface 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 31 First angle detection sensor 32 Second angle detection sensor 40 Detector 41 Judgment section 42 Delay Circuit 43 Differential amplifier circuit 50 Evaluation light source 51 Collimating Lens 52,53 Lens 54 Position detection element A,B,C,D waveform L laser light LE evaluation laser light N normal

Claims

1. a micromirror device including: a mirror having a reflective surface that reflects light and that is oscillating around at least one axis; an actuator that oscillates the mirror; and a piezoelectric element that generates and outputs an electromotive force due to the oscillation of the mirror; a control device for controlling the operation of the actuator; an abnormality detection device that detects abnormal operation of the mirror based on the amount of temporal fluctuation of the output signal from the piezoelectric element; Equipped with The abnormality detection device 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, The detection unit a delay circuit that delays the output signal output from the piezoelectric element by a certain delay time; a differential amplifier circuit that amplifies the difference between the output signal output from the piezoelectric element and the output signal delayed by the delay circuit and outputs the amplified value as the fluctuation amount. Optical scanning device.

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

3. The ratio of the delay time to the oscillation period is less than 10%.

3. The optical scanning device according to claim 2.

4. The ratio of the delay time to the oscillation period is less than 10% and greater than 0.05%.

3. The optical scanning device according to claim 2.

5. The determination unit is a comparator.

2. The optical scanning device according to claim 1.

6. the mirror is oscillating about a first axis and a second axis that are orthogonal to each other; the piezoelectric element generates the electromotive force by the oscillation of the mirror around the first axis or the second axis; 3. The optical scanning device according to claim 2.

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