Optical scanning device, method of driving the same, and image drawing system

Abstract

An optical scanning device includes a mirror section having a reflecting surface that reflects incident light; a first actuator that causes the mirror section to oscillate around a first axis that lies in a plane that includes the reflecting surface when the mirror section is stationary; a second actuator that causes the mirror section to oscillate around a second axis that lies in the plane that includes the reflecting surface when the mirror section is stationary and is orthogonal to the first axis; a pair of first angle detection sensors that output signals corresponding to an angle of the mirror section around the first axis and are disposed at positions that face each other across the first axis or the second axis; and at least one processor that generates a first angle detection signal that indicates the angle of the mirror section around the first axis by adding or subtracting a pair of first output signals output from the pair of first angle detection sensors.

Description

TECHNICAL FIELD

[0001] The present application relates to an optical scanning device, a driving method thereof, and an image drawing system. BACKGROUND

[0002] As one of micro electro mechanical systems (MEMS) devices fabricated using a fine processing technology of silicon (Si), a micro mirror device (also referred to as a micro scanner) is known. An optical scanning device provided with the micro mirror device is small and low in power consumption, and thus application to an image drawing system such as a laser display or a laser projector is expected.

[0003] The mirror section of the micro mirror device is formed so as to be able to oscillate around a first axis and a second axis orthogonal to each other, and by the mirror section oscillating around each axis, light reflected by the mirror section is two-dimensionally scanned. Also, a micro mirror device capable of causing light to perform Lissajous scanning by causing the mirror section to resonate around each axis is known.

[0004] In such a micro mirror device, in order to control the deflection angle of the mirror section with high precision, an angle detection sensor that outputs a signal corresponding to the angle of the mirror section is known (for example, refer to Japanese Patent Application Publication No. 2019-082634 and Japanese Patent Application Publication No. 2018-063228).

[0005] In Japanese Patent Application Publication No. 2019-082634, it is described that “the amplitude of the rotation of the mirror section is obtained from the output signal of the detection signal acquisition section”. Specifically, in Japanese Patent Application Publication No. 2019-082634, it is described that “a P-P (Peak To Peak) value of the change in signal voltage corresponding to the rotation of the mirror section is obtained, and from data representing the relationship between the signal voltage and the amplitude of the rotation of the mirror section, the amplitude of the rotation of the mirror section is obtained”. The amplitude of the rotation of the mirror section corresponds to the maximum value of the deflection angle (hereinafter, referred to as the maximum deflection angle).

[0006] In Japanese Patent Application Publication No. 2018-063228, it is described that “the oscillation angle of the MEMS mirror is obtained from the amount of change in the angle of the MEMS mirror with respect to the resonance direction when the MEMS mirror is driven at the resonance frequency”. SUMMARY

[0007] Technical problem to be solved by the application

[0008] Japanese Patent Application Publication Nos. 2019-082634 and 2018-063228 disclose the provision of a first angle detection sensor for detecting the angle of the mirror portion around a first axis and a second angle detection sensor for detecting the angle of the mirror portion around a second axis. However, when the mirror portion oscillates simultaneously around both the first and second axes, the output signal of the first angle detection sensor contains a vibration component caused by the oscillation of the mirror portion around the second axis. Furthermore, the output signal of the second angle detection sensor also contains a vibration component caused by the oscillation of the mirror portion around the first axis. Thus, in a micromirror device with a dual-axis drive, the presence of vibration from an axis different from the axis of the object being detected superimposed on the output signal of the angle detection sensor becomes a problem as noise. Hereinafter, this noise will be referred to as vibration noise.

[0009] To maintain a constant maximum deflection angle of the reflector, the amplitude of the output signal from the angle detection sensor needs to be accurately detected. Furthermore, when the reflector is driven by resonance, to maintain its oscillation in a resonant state, the phase of the output signal from the angle detection sensor needs to be accurately detected.

[0010] However, when vibration noise is superimposed on the output signal of the angle detection sensor, it is impossible to accurately detect the amplitude and phase of the output signal of the angle detection sensor, making it difficult to control the oscillation of the reflector with high precision.

[0011] The technical objective of this invention is to provide a light scanning device, its driving method, and an image drawing system capable of controlling the oscillation of a reflector with high precision.

[0012] According to the technology of the present invention, a light scanning device, its driving method, and an image drawing system capable of controlling the deflection angle of a reflector with high precision can be provided.

[0013] means for solving technical problems

[0014] To achieve the above objectives, the optical scanning apparatus of the present invention comprises: a mirror portion having a reflective surface for reflecting incident light; a first actuator for oscillating the mirror portion about a first axis located in a plane including the reflective surface when the mirror portion is stationary; a second actuator for oscillating the mirror portion about a second axis located in a plane including the reflective surface when the mirror portion is stationary and orthogonal to the first axis; a pair of first angle detection sensors outputting signals corresponding to the angle of the mirror portion about the first axis and disposed at positions opposite each other across the first axis or the second axis; and at least one processor that generates a first angle detection signal representing the angle of the mirror portion about the first axis by adding or subtracting a pair of first output signals output from the pair of first angle detection sensors.

[0015] The preferred processor adjusts the amplitude level of at least one of the pair of first output signals to make the amplitude of the vibration noise contained in the pair of first output signals consistent, and then adds or subtracts the pair of first output signals.

[0016] Preferably, a pair of first angle detection sensors are positioned opposite each other across the first axis. The processor generates the first angle detection signal by subtracting one of the pair of first output signals after the amplitude level is adjusted.

[0017] Preferably, a pair of first angle detection sensors are positioned opposite each other across the second axis. The processor generates a first angle detection signal by adjusting the sum of the amplitude levels of the pair of first output signals.

[0018] The preferred processor has a first drive signal generation unit that generates a first drive signal applied to the first actuator and feeds back the first angle detection signal to the first drive signal generation unit.

[0019] Preferably, the first drive signal generation unit is a drive circuit with a phase synchronization circuit.

[0020] The first driving signal is preferably a sine wave.

[0021] The preferred first angle detection sensor is a piezoelectric element.

[0022] Preferably, the processor further comprises a pair of second angle detection sensors that output a signal corresponding to the angle of the reflector portion around the second axis and are disposed at a position opposite to the first axis or the second axis. The processor adjusts the amplitude level of at least one of the pair of second output signals output from the pair of second angle detection sensors and adds or subtracts the pair of second output signals after the amplitude level adjustment, thereby generating a second angle detection signal representing the angle of the reflector portion around the second axis.

[0023] The preferred processor adjusts the amplitude level of at least one of the pair of second output signals to make the amplitudes of the vibration noise contained in the pair of second output signals consistent, and then adds or subtracts the pair of second output signals.

[0024] Preferably, a pair of second angle detection sensors are positioned opposite each other across the second axis. The processor generates the second angle detection signal by subtracting one of the two second output signals from the other after the amplitude level is adjusted.

[0025] Preferably, a pair of second angle detection sensors are positioned opposite each other across the first axis. The processor generates a second angle detection signal by adjusting the sum of the amplitude levels of the pair of second output signals.

[0026] The preferred processor has a second drive signal generation unit that generates a second drive signal applied to the second actuator and feeds back the second angle detection signal to the second drive signal generation unit.

[0027] Preferably, the second drive signal generation unit is a drive circuit with a phase synchronization circuit.

[0028] The second driving signal is preferably a sine wave.

[0029] The second angle detection sensor is preferably a piezoelectric element.

[0030] The image rendering system of the present invention includes: any one of the above-mentioned light scanning devices; and a light source that illuminates a reflector portion. In the image rendering system, the processor controls the illumination timing of the light source based on a first angle detection signal and a second angle detection signal.

[0031] In the driving method of the optical scanning device of the present invention, the optical scanning device includes: a mirror section having a reflective surface for reflecting incident light; a first actuator for oscillating the mirror section about a first axis located in a plane including the reflective surface when the mirror section is stationary; a second actuator for oscillating the mirror section about a second axis located in a plane including the reflective surface when the mirror section is stationary and orthogonal to the first axis; and a pair of first angle detection sensors that output signals corresponding to the angle of the mirror section about the first axis and are disposed at positions opposite each other across the first axis or the second axis, and generate a first angle detection signal representing the angle of the mirror section about the first axis by adding or subtracting the pair of first output signals output from the pair of first angle detection sensors.

[0032] Invention Effects

[0033] According to the technology of the present invention, a light scanning device, its driving method, and an image drawing system capable of controlling the oscillation of a reflector with high precision can be provided. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of an optical scanning device.

[0035] Figure 2 This is a three-dimensional view of the micromirror device.

[0036] Figure 3 This is a top view of the micromirror device observed from the light incident side.

[0037] Figure 4 It is along Figure 3 A cross-sectional view of the AA wire cut.

[0038] Figure 5 It is along Figure 3 A sectional view of the BB wire cut.

[0039] Figure 6 It is along Figure 3 A cross-sectional view of a CC wire cut.

[0040] Figure 7 This is a diagram showing an example of driving the first actuator.

[0041] Figure 8 This is a diagram showing an example of driving the second actuator.

[0042] Figure 9 This is a graph representing an example of the first and second drive signals.

[0043] Figure 10 This is a block diagram illustrating an example of the structure of the drive control unit.

[0044] Figure 11 This is a diagram illustrating an example of the signal output from a pair of first-angle detection sensors.

[0045] Figure 12 This is a diagram illustrating an example of the signal output from a pair of second-angle detection sensors.

[0046] Figure 13 This is a circuit diagram showing the structure of the first signal processing unit.

[0047] Figure 14 This is a diagram showing the filtering characteristics of the first BPF circuit and the second BPF circuit included in the gain adjustment circuit of the first signal processing unit.

[0048] Figure 15 This is a diagram illustrating an example of the first signal processing.

[0049] Figure 16 This is a circuit diagram showing the structure of the second signal processing unit.

[0050] Figure 17 This is a diagram showing the filtering characteristics of the first BPF circuit and the second BPF circuit included in the gain adjustment circuit of the second signal processing unit.

[0051] Figure 18 This is a diagram illustrating an example of the second signal processing.

[0052] Figure 19 This is a block diagram illustrating an example of the structure of the first drive signal generation unit.

[0053] Figure 20 This is a block diagram illustrating an example of the structure of the second drive signal generation unit.

[0054] Figure 21 This diagram illustrates the generation process of the first zero-crossing pulse.

[0055] Figure 22 This diagram illustrates the generation process of the second zero-crossing pulse.

[0056] Figure 23 This is a top view of the micromirror device according to the second embodiment.

[0057] Figure 24 This is a diagram illustrating an example of the signal output from a pair of first angle detection sensors according to the second embodiment.

[0058] Figure 25 This is a diagram illustrating an example of the signal output from a pair of second angle detection sensors according to the second embodiment.

[0059] Figure 26 This is a block diagram showing the structure of the first drive signal generation unit according to the second embodiment.

[0060] Figure 27 This diagram illustrates an example of the first signal processing involved in the second embodiment.

[0061] Figure 28 This is a block diagram showing the structure of the second drive signal generation unit according to the second embodiment.

[0062] Figure 29 This diagram illustrates an example of the second signal processing involved in the second embodiment.

[0063] Figure 30 This is a diagram illustrating an example of the gain and phase characteristics of a bandpass filter circuit. Detailed Implementation

[0064] An example of an embodiment of the technology of the present invention will be described with reference to the accompanying drawings.

[0065] [First Implementation]

[0066] Figure 1 The image depiction system 10 according to one embodiment is schematically shown. The image depiction system 10 includes a light scanning device 2 and a light source 3. The light scanning device 2 is configured to include a micromirror device (hereinafter referred to as "MMD (Micro Mirror Device)") 4 and a drive control unit 5. The drive control unit 5 is an example of a processor according to the technology of the present invention.

[0067] The image drawing system 10, under the control of the drive control unit 5, performs optical scanning on the scanned surface 6 by reflecting the light beam L irradiated from the light source 3 through the MMD4, thereby drawing an image. The scanned surface 6 is, for example, a screen.

[0068] The image rendering system 10 is suitable, for example, for a Lissajous laser display. Specifically, the image rendering system 10 can be used with laser scanning displays such as AR (Augmented Reality) glasses or VR (Virtual Reality) glasses.

[0069] MMD4 enables the reflector section 20 (reference) Figure 2 A piezoelectric dual-axis driven micromirror device that oscillates around a first axis a1 and a second axis a2 orthogonal to the first axis a1. Hereinafter, the direction parallel to the second axis a2 is called the X direction, the direction parallel to the first axis a1 is called the Y direction, and the direction orthogonal to the first axis a1 and the second axis a2 is called the Z direction.

[0070] The light source 3 is a laser device that emits a laser beam, such as a laser beam, as a light beam L. Preferably, the light source 3 is positioned so that the reflective surface 20A (see reference) of the reflector section 20 of the MMD4 is stationary. Figure 2 The light beam L is vertically irradiated. However, when the light beam L is vertically irradiated from the light source 3 onto the reflecting surface 20A, there is a possibility that the light source 3 may become an obstacle when the beam L scans the surface 6 for mapping. Therefore, it is preferable to control the light beam L emitted from the light source 3 to vertically irradiate the reflecting surface 20A using an optical system. The optical system may or may not include lenses. Furthermore, the angle at which the light beam L emitted from the light source 3 irradiates the reflecting surface 20A is not limited to vertical; the light beam L can be irradiated obliquely onto the reflecting surface 20A.

[0071] The drive control unit 5 outputs drive signals to the light source 3 and MMD4 based on the light scanning information. The light source 3 generates a light beam L based on the input drive signal and illuminates the MMD4. The MMD4 causes the reflector unit 20 to oscillate around the first axis a1 and the second axis a2 based on the input drive signal.

[0072] Details will be described later, but the drive control unit 5 causes the reflector 20 to resonate around the first axis a1 and the second axis a2 respectively, so that the light beam L reflected by the reflector 20 scans in a way that depicts a Lissajous waveform on the scanned surface 6. This optical scanning method is called the Lissajous scanning method.

[0073] Next, using Figures 2-6 Here is an example of MMD4. Figure 2 This is a 3D rendering of the MMD4. Figure 3 This is a top view of MMD4 viewed from the light incident side. Figure 4 It is along Figure 3 A cross-sectional view of the AA wire cut. Figure 5 It is along Figure 3 A sectional view of the BB wire cut. Figure 6 It is alongFigure 3 A cross-sectional view of a CC wire cut.

[0074] like Figure 2 and Figure 3 As shown, the MMD4 has a mirror portion 20, a first support portion 21, a first movable frame 22, a second support portion 23, a second movable frame 24, a connecting portion 25, and a fixing frame 26. The MMD4 is a so-called MEMS scanner.

[0075] The mirror section 20 has a reflective surface 20A for reflecting incident light. The reflective surface 20A is disposed on one side of the mirror section 20 and is formed, for example, from a thin film of metal such as gold (Au), aluminum (Al), silver (Ag), or a silver alloy. The shape of the reflective surface 20A is, for example, a circle centered on the intersection of the first axis a1 and the second axis a2.

[0076] The first axis a1 and the second axis a2 exist in the plane containing the reflecting surface 20A when the reflector section 20 is stationary. The planar shape of MMD4 is rectangular, symmetrical about the first axis a1 and symmetrical about the second axis a2.

[0077] The first support portion 21 is disposed on the outer side of the reflector portion 20 at a position opposite each other across the second axis a2. The first support portion 21 is connected to the reflector portion 20 on the first axis a1 and supports the reflector portion 20 so that it can swing about the first axis a1. In this embodiment, the first support portion 21 is a torsion bar extending along the first axis a1.

[0078] The first movable frame 22 is a rectangular frame surrounding the reflector section 20, and is connected to the reflector section 20 via the first support section 21 on the first axis a1. Piezoelectric elements 30 are formed on the first movable frame 22 at positions opposite each other across the first axis a1. Thus, by forming two piezoelectric elements 30 on the first movable frame 22, a pair of first actuators 31 are constituted.

[0079] A pair of first actuators 31 are positioned opposite each other across the first axis a1. The first actuators 31 apply a rotational torque about the first axis a1 to the mirror section 20, causing the mirror section 20 to oscillate about the first axis a1.

[0080] The second support portion 23 is disposed on the outer side of the first movable frame 22 at a position opposite to it across the first axis a1. The second support portion 23 is connected to the first movable frame 22 on the second axis a2, and supports the first movable frame 22 and the reflector portion 20 so that they can swing about the second axis a2. In this embodiment, the second support portion 23 is a torsion bar extending along the second axis a2.

[0081] The second movable frame 24 is a rectangular frame surrounding the first movable frame 22, and is connected to the first movable frame 22 via the second support portion 23 on the second axis a2. Piezoelectric elements 30 are formed on the second movable frame 24 at positions opposite each other across the second axis a2. Thus, by forming two piezoelectric elements 30 on the second movable frame 24, a pair of second actuators 32 are constituted.

[0082] A pair of second actuators 32 are positioned opposite each other across the second axis a2. The second actuators 32 apply a rotational torque about the second axis a2 to the mirror section 20 and the first movable frame 22, causing the mirror section 20 to oscillate about the second axis a2.

[0083] The connecting part 25 is disposed on the outside of the second movable frame 24 at a position opposite each other across the first axis a1. The connecting part 25 is connected to the second movable frame 24 on the second axis a2.

[0084] The fixed frame 26 is a rectangular frame that surrounds the second movable frame 24, and is connected to the second movable frame 24 via the connecting part 25 on the second axis a2.

[0085] Furthermore, in the first movable frame 22, near the first support portion 21, a pair of first angle detection sensors 11A and 11B are provided at positions opposite each other across the first axis a1. The pair of first angle detection sensors 11A and 11B are each composed of a piezoelectric element. The first angle detection sensors 11A and 11B convert the force applied due to the deformation of the first support portion 21 accompanying the rotation of the reflector portion 20 around the first axis a1 into a voltage and output a signal. That is, the first angle detection sensors 11A and 11B output signals corresponding to the angle of the reflector portion 20 around the first axis a1.

[0086] Furthermore, in the second movable frame 24, near the second support portion 23, a pair of second angle detection sensors 12A and 12B are provided at positions opposite each other across the second axis a2. The pair of second angle detection sensors 12A and 12B are each composed of a piezoelectric element. The second angle detection sensors 12A and 12B convert the force applied due to the deformation of the second support portion 23 accompanying the rotation of the reflector portion 20 around the second axis a2 into a voltage and output a signal. That is, the second angle detection sensors 12A and 12B output signals corresponding to the angle of the reflector portion 20 around the second axis a2.

[0087] exist Figure 2 and Figure 3 In the diagram, the wiring and electrode pads used to apply drive signals to the first actuator 31 and the second actuator 32 are omitted. Furthermore, in Figure 2 and Figure 3The wiring and electrode pads used for detecting the output signals of sensors 11A and 11B at the first angle and sensors 12A and 12B at the second angle are also omitted from the illustration. Multiple electrode pads are provided on the mounting frame 26.

[0088] like Figure 4 and Figure 5 As shown, MMD4 is formed, for example, by etching an SOI (Silicon On Insulator) substrate 40. The SOI substrate 40 is a substrate in which a silicon oxide layer 42 is disposed on a first silicon active layer 41 made of monocrystalline silicon and a second silicon active layer 43 made of monocrystalline silicon is disposed on the silicon oxide layer 42.

[0089] The reflector portion 20, the first support portion 21, the first movable frame 22, the second support portion 23, the second movable frame 24, and the connecting portion 25 are formed from the second active silicon layer 43 remaining after the first silicon active layer 41 and the silicon oxide layer 42 have been removed from the SOI substrate 40 through an etching process. The second active silicon layer 43 functions as an elastic part with elasticity. The fixing frame 26 is formed from these three layers: the first active silicon layer 41, the silicon oxide layer 42, and the second active silicon layer 43.

[0090] The first actuator 31 and the second actuator 32 have piezoelectric elements 30 on the second silicon active layer 43. The piezoelectric element 30 has a stacked structure in which a lower electrode 51, a piezoelectric film 52 and an upper electrode 53 are sequentially stacked on the second silicon active layer 43. In addition, an insulating film is provided on the upper electrode 53, but it is not shown in the figure.

[0091] The upper electrode 53 and the lower electrode 51 are formed, for example, of gold (Au) or platinum (Pt). The piezoelectric film 52 is formed, for example, of a piezoelectric material, namely PZT (lead zirconate titanate). The upper electrode 53 and the lower electrode 51 are electrically connected to the aforementioned drive control unit 5 via wiring and electrode pads.

[0092] A driving voltage is applied to the upper electrode 53 by the drive control unit 5. The lower electrode 51 is connected to the drive control unit 5 via wiring and electrode pads, and a reference potential (e.g., ground potential) is applied to it.

[0093] When a positive or negative voltage is applied to the piezoelectric film 52 along the polarization direction, it undergoes deformation (e.g., expansion or contraction) proportional to the applied voltage. That is, the piezoelectric film 52 exhibits the so-called inverse piezoelectric effect. The piezoelectric film 52 exhibits the inverse piezoelectric effect by applying a driving voltage from the drive control unit 5 to the upper electrode 53, thereby displacing the first actuator 31 and the second actuator 32.

[0094] like Figure 6As shown, the first angle detection sensor 11A is also composed of a piezoelectric element 30, including a lower electrode 51, a piezoelectric film 52, and an upper electrode 53 stacked on the second silicon active layer 43. When a force (pressure) is applied to the piezoelectric film 52, polarization proportional to the pressure is generated. That is, the piezoelectric film 52 exhibits the piezoelectric effect. When a force is applied to the piezoelectric film 52 through the deformation of the first support portion 21 accompanying the rotation of the reflector portion 20 around the first axis a1, the piezoelectric film 52 exhibits the piezoelectric effect and generates a voltage.

[0095] The first angle detection sensor 11B has the same structure as the first angle detection sensor 11A, so it is omitted from the illustration. Similarly, the second angle detection sensors 12A and 12B have the same structure as the first angle detection sensor 11A, so they are also omitted from the illustration.

[0096] Figure 7 An example is shown whereby a rotational torque about a first axis a1 is generated in a pair of first actuators 31 by stretching one piezoelectric film 52 and contracting the other piezoelectric film 52. In this way, one and the other of the pair of first actuators 31 are displaced in opposite directions, thereby causing the mirror section 20 to rotate about the first axis a1.

[0097] and, Figure 7 This example demonstrates how the first actuator 31 is driven in an out-of-phase resonance mode where the displacement directions of the pair of first actuators 31 and the rotation direction of the reflector 20 are opposite to each other. Alternatively, the first actuator 31 can be driven in an in-phase resonance mode where the displacement directions of the pair of first actuators 31 and the rotation direction of the reflector 20 are the same.

[0098] The deflection angle (hereinafter referred to as the first deflection angle) θ1 of the reflector section 20 about the first axis a1 is controlled by a drive signal (hereinafter referred to as the first drive signal) applied to the first actuator 31 by the drive control unit 5. The first drive signal is, for example, a sinusoidal AC voltage. The first drive signal includes a drive voltage waveform V applied to one of the pair of first actuators 31. 1A (t) and the driving voltage waveform V applied to the other. 1B (t). Drive voltage waveform V 1A (t) and driving voltage waveform V 1B (t) are out of phase with each other (i.e., phase difference 180°).

[0099] In addition, the first deflection angle θ1 is the angle at which the normal of the reflecting surface 20A is tilted relative to the Z direction on the XZ plane.

[0100] Figure 8An example is shown whereby a rotational torque about a second axis a2 is generated in a pair of second actuators 32 by stretching one piezoelectric film 52 and contracting the other piezoelectric film 52. In this way, one and the other of the pair of second actuators 32 are displaced in opposite directions, thereby causing the mirror section 20 to rotate about the second axis a2.

[0101] and, Figure 8 This example demonstrates how the second actuator 32 is driven in an out-of-phase resonance mode where the displacement directions of the pair of second actuators 32 and the rotation direction of the reflector 20 are opposite to each other. Alternatively, the second actuator 32 can be driven in an in-phase resonance mode where the displacement directions of the pair of second actuators 32 and the rotation direction of the reflector 20 are the same.

[0102] The deflection angle (hereinafter referred to as the second deflection angle) θ2 of the reflector section 20 about the second axis a2 is controlled by a drive signal (hereinafter referred to as the second drive signal) applied to the second actuator 32 by the drive control unit 5. The second drive signal is, for example, a sinusoidal AC voltage. The second drive signal includes a drive voltage waveform V applied to one of the pair of second actuators 32. 2A (t) and the driving voltage waveform V applied to the other. 2B (t). Drive voltage waveform V 2A (t) and driving voltage waveform V 2B (t) are out of phase with each other (i.e., phase difference 180°).

[0103] In addition, the second deflection angle θ2 is the angle at which the normal of the reflecting surface 20A is tilted relative to the Z direction on the YZ plane.

[0104] Figure 9 This represents an example of the first drive signal and the second drive signal. Figure 9 (A) represents the driving voltage waveform V contained in the first driving signal. 1A (t) and V 1B (t). Figure 9 (B) indicates the driving voltage waveform V contained in the second driving signal. 2A (t) and V 2B (t).

[0105] Drive voltage waveform V 1A (t) and V 1B (t) are represented as follows.

[0106] V 1A (t)=V off1 +V1sin(2πf d1 t)

[0107] V 1B (t)=Voff1 +V1sin(2πf d1 t+α)

[0108] Here, V1 is the amplitude voltage. off1 This is the bias voltage. f d1 α is the driving frequency (hereinafter referred to as the first driving frequency). t is time. α is the driving voltage waveform V. 1A (t) and V 1B The phase difference of (t). In this embodiment, for example, it is set to α = 180°.

[0109] Drive voltage waveform V 1A (t) and V 1B (t) is applied to a pair of first actuators 31, thereby causing the mirror section 20 to operate at a first driving frequency f. d1 To oscillate around the first axis a1 (reference) Figure 7 ).

[0110] Drive voltage waveform V 2A (t) and V 2B (t) are represented as follows.

[0111] V 2A (t)=V off2 +V2sin(2πf d2 t+φ)

[0112] V 2B (t)=V off2 +V2sin(2πf d2 t+β+φ)

[0113] Here, V2 is the amplitude voltage. off2 This is the bias voltage. f d2 Hereinafter, β represents the driving frequency (hereinafter referred to as the second driving frequency). t represents time. β represents the driving voltage waveform V. 2A (t) and V 2B The phase difference (t). In this embodiment, for example, it is set to β = 180°. And, φ is the driving voltage waveform V. 1A (t) and V 1B (t) and driving voltage waveform V 2A (t) and V 2B The phase difference (t). Furthermore, in this embodiment, for example, it is set to V. off1 =V off2 =0V.

[0114] Drive voltage waveform V 2A (t) and V 2B (t) is applied to a pair of second actuators 32, thereby causing the mirror section 20 to operate at a second driving frequency f. d2To oscillate around the second axis a2 (reference) Figure 8 ).

[0115] First driving frequency f d1 The second driving frequency is set to be consistent with the resonant frequency of the reflector section 20 around the first axis a1. d2 It is set to be consistent with the resonant frequency of the reflector section 20 around the second axis a2. In this embodiment, it is set to f. d1 >f d2 That is, the oscillation frequency of the reflector section 20 around the first axis a1 is higher than the oscillation frequency around the second axis a2. Additionally, the first driving frequency f... d1 and the second driving frequency f d2 It doesn't necessarily have to match the resonant frequency. For example, the first driving frequency f d1 and the second driving frequency f d2 These can be frequencies within a frequency range near the resonant frequency (e.g., the range of half the width of a frequency distribution with the resonant frequency as its peak). This frequency range is, for example, within the range of the so-called Q value.

[0116] Figure 10 This illustrates an example of the structure of the drive control unit 5. The drive control unit 5 includes a mirror drive unit 4A and a light source drive unit 3A. The mirror drive unit 4A includes a first drive signal generation unit 60A, a first signal processing unit 61A, a first phase shifting unit 62A, a first zero-crossing pulse output unit 63A, a second drive signal generation unit 60B, a second signal processing unit 61B, a second phase shifting unit 62B, and a second zero-crossing pulse output unit 63B.

[0117] The first drive signal generation unit 60A, the first signal processing unit 61A, and the first phase shifting unit 62A can perform feedback control to maintain the oscillation of the reflector 20 around the first axis a1 in a resonant state. The second drive signal generation unit 60B, the second signal processing unit 61B, and the second phase shifting unit 62B can perform feedback control to maintain the oscillation of the reflector 20 around the second axis a2 at a specified frequency.

[0118] The first drive signal generation unit 60A generates a drive voltage waveform V based on a reference waveform. 1A (t) and V 1B The first drive signal (t) is applied to a pair of first actuators 31 via the first phase shifter 62A. As a result, the mirror section 20 oscillates around the first axis a1. The first angle detection sensors 11A and 11B output signals corresponding to the angle of the mirror section 20 around the first axis a1.

[0119] The second drive signal generation unit 60B generates a drive voltage waveform V based on the reference waveform. 2A(t) and V 2B The second drive signal (t) generates a second drive signal and applies it to a pair of second actuators 32 via the second phase shifter 62B. As a result, the mirror section 20 oscillates around the second axis a2. The second angle detection sensors 12A and 12B output signals corresponding to the angle of the mirror section 20 around the second axis a2.

[0120] The first drive signal generated by the first drive signal generation unit 60A and the second drive signal generated by the second drive signal generation unit 60B are set to be phase synchronized.

[0121] Figure 11 This illustrates an example of signals output from a pair of first-angle detection sensors 11A and 11B. Figure 11 In the diagram, S1a1 and S1a2 represent the signals output from a pair of first angle detection sensors 11A and 11B when the reflector 20 oscillates only around the first axis a1 and not around the second axis a2. Signals S1a1 and S1a2 have a first driving frequency f. d1 The waveform signals are approximately sinusoidal and are out of phase with each other.

[0122] When the reflector 20 is simultaneously oscillated around the first axis a1 and the second axis a2, vibration noise RN1 caused by the oscillation of the reflector 20 around the second axis a2 is superimposed on the output signals of the pair of first angle detection sensors 11A and 11B. S1b1 represents the signal in signal S1a1 superimposed with vibration noise RN1. S1b2 represents the signal in signal S1a2 superimposed with vibration noise RN1. In addition, vibration noise RN1 is highlighted for the purpose of explaining this embodiment.

[0123] Thus, in the case of dual-axis drive, the signals S1b1 and S1b2 output from the first angle detection sensors 11A and 11B are superimposed with vibration noise RN1, and the amplitudes of signals S1b1 and S1b2 change with each cycle. Therefore, it is difficult to directly determine the amplitude and phase from the signals S1b1 and S1b2 output from the first angle detection sensors 11A and 11B.

[0124] Figure 12 This illustrates an example of signals output from a pair of second-angle detection sensors 12A and 12B. Figure 12 In the diagram, S2a1 and S2a2 represent the signals output from a pair of second angle detection sensors 12A and 12B when the reflector 20 oscillates only around the second axis a2 and not around the first axis a1. Signals S2a1 and S2a2 have a second driving frequency f. d2 The waveform signals are approximately sinusoidal and are out of phase with each other.

[0125] When the reflector 20 is simultaneously oscillated around the first axis a1 and the second axis a2, vibration noise RN2 caused by the oscillation of the reflector 20 around the first axis a1 is superimposed on the output signals of the pair of second angle detection sensors 12A and 12B. S2b1 represents the signal in signal S2a1 superimposed with vibration noise RN2. S2b2 represents the signal in signal S2a2 superimposed with vibration noise RN2. In addition, vibration noise RN2 is highlighted for the purpose of explaining this embodiment.

[0126] Thus, in the case of dual-axis drive, the signals S2b1 and S2b2 output by the second angle detection sensors 12A and 12B are superimposed with vibration noise RN2, and the amplitudes of signals S2b1 and S2b2 change with each cycle. Therefore, it is difficult to directly determine the amplitude and phase based on the signals S2b1 and S2b2 output by the second angle detection sensors 12A and 12B.

[0127] The first signal processing unit 61A generates a signal (hereinafter referred to as the first angle detection signal) S1c after removing vibration noise RN1 based on S1a1 and S1a2 output from a pair of first angle detection sensors 11A and 11B. The second signal processing unit 61B generates a signal (hereinafter referred to as the second angle detection signal) S2c after removing vibration noise RN2 based on S2a1 and S2a2 output from a pair of second angle detection sensors 12A and 12B.

[0128] Figure 13 This illustrates the structure of the first signal processing unit 61A. The first signal processing unit 61A is composed of analog arithmetic circuits. For example... Figure 13 As shown, the first signal processing unit 61A consists of a buffer amplifier 71, a variable gain amplifier 72, a subtraction circuit 73, and a gain adjustment circuit 74. The gain adjustment circuit 74 consists of a first BPF (Band Pass Filter) circuit 75A, a second BPF circuit 75B, a first detector circuit 76A, a second detector circuit 76B, and a subtraction circuit 77. The subtraction circuit 73 and the subtraction circuit 77 are differential amplifier circuits composed of operational amplifiers.

[0129] The signal S1b1 output from the first angle detection sensor 11A is input to the positive input terminal (non-inverting input terminal) of the subtraction circuit 73 via the buffer amplifier 71. Furthermore, the signal output from the buffer amplifier 71 branches off midway before being input to the subtraction circuit 73 and is input to the first BPF circuit 75A within the gain adjustment circuit 74.

[0130] The signal S1b2 output from the first angle detection sensor 11B is input to the negative input terminal (inverting input terminal) of the subtraction circuit 73 via the variable gain amplifier 72. Furthermore, the signal output from the variable gain amplifier 72 branches off midway before being input to the subtraction circuit 73 and is input to the second BPF circuit 75B within the gain adjustment circuit 74.

[0131] like Figure 14 As shown, the first BPF circuit 75A and the second BPF circuit 75B respectively have a second driving frequency f d2 The passband B1 is the center frequency. For example, passband B1 is f. d2 The frequency band is ±5kHz. Vibration noise RN1 has a second driving frequency f. d2 Therefore, it passes through passband B1. Thus, the first BPF circuit 75A extracts and outputs the vibration noise RN1 (reference) from the signal input to buffer amplifier 71. Figure 11 The second BPF circuit 75B extracts and outputs vibration noise RN1 from the signal input to the variable gain amplifier 72 (reference). Figure 11 ).

[0132] The first detection circuit 76A and the second detection circuit 76B are each constructed, for example, by an RMS-DC converter (Root Mean Square value to Direct Current converter). The first detection circuit 76A converts the amplitude of the vibration noise RN1 input from the first BPF circuit 75A into a DC voltage signal and inputs it to the positive input terminal of the subtraction circuit 77. The second detection circuit 76B converts the amplitude of the vibration noise RN1 input from the second BPF circuit 75B into a DC voltage signal and inputs it to the negative input terminal of the subtraction circuit 77.

[0133] The subtraction circuit 77 outputs a value d1, which is the difference between the DC voltage signal input from the first detector circuit 76A and the DC voltage signal input from the second detector circuit 76B. This value d1 corresponds to the difference between the amplitude of the vibration noise RN1 contained in the signal S1b1 output from the first angle detection sensor 11A and the amplitude of the vibration noise RN1 contained in the signal S1b2 output from the first angle detection sensor 11B. The subtraction circuit 77 inputs this value d1 as a gain adjustment value to the gain adjustment terminal of the variable gain amplifier 72.

[0134] The variable gain amplifier 72 adjusts the amplitude level of signal S1b2 by multiplying the value d1, which is the gain adjustment input, by the signal S1b2 input from the first angle detection sensor 11B. Thus, feedback control is performed via the gain adjustment circuit 74, thereby adjusting the amplitude of the vibration noise RN1 contained in the signal S1b2 after the variable gain amplifier 72 to match the amplitude of the vibration noise RN1 contained in the signal S1b1 after the buffer amplifier 71.

[0135] The subtraction circuit 73 outputs the value obtained by subtracting the signal S1b2 input to the negative input terminal from the signal S1b1 input to the positive input terminal. Through the aforementioned feedback control, the amplitudes of the vibration noise RN1 contained in the two signals are identical. Therefore, through the subtraction processing based on the subtraction circuit 73, the vibration noise RN1 contained in the two signals cancels each other out. Thus, the signal output from the subtraction circuit 73 after removing the vibration noise RN1 is the first angle detection signal S1c (reference). Figure 15 ).

[0136] Figure 15 The diagram illustrates the generation of a first angle detection signal S1c based on the outputs S1b1 and S1b2 from a pair of first angle detection sensors 11A and 11B. The first angle detection signal S1c corresponds to a signal whose amplitude is doubled after removing the vibration noise RN1 from signal S1b1.

[0137] The first angle detection signal S1c generated by the first signal processing unit 61A is input to the first drive signal generation unit 60A and the first zero-crossing pulse output unit 63A. Furthermore, when the oscillation of the reflector unit 20 around the first axis a1 maintains a resonant state, such as... Figure 15 As shown, the first angle detection signal S1c output from the first signal processing unit 61A is relative to the drive voltage waveform V contained in the first drive signal. 1A (t) produces a 90° delay in phase.

[0138] like Figure 16 As shown, the second signal processing unit 61B consists of a buffer amplifier 81, a variable gain amplifier 82, a subtraction circuit 83, and a gain adjustment circuit 84. The gain adjustment circuit 84 consists of a first BPF circuit 85A, a second BPF circuit 85B, a first detector circuit 86A, a second detector circuit 86B, and a subtraction circuit 87. The subtraction circuit 83 and the subtraction circuit 87 are differential amplifier circuits composed of operational amplifiers.

[0139] The signal S2b1 output from the second angle detection sensor 12A is input to the positive input terminal of the subtraction circuit 83 via the buffer amplifier 81. Furthermore, the signal output from the buffer amplifier 81 branches off midway before being input to the subtraction circuit 83 and is input to the first BPF circuit 85A within the gain adjustment circuit 84.

[0140] The signal S2b2 output from the second angle detection sensor 12B is input to the negative input terminal of the subtraction circuit 83 via the variable gain amplifier 82. Furthermore, the signal output from the variable gain amplifier 82 branches off midway before being input to the subtraction circuit 83 and is input to the second BPF circuit 85B within the gain adjustment circuit 84.

[0141] like Figure 17 As shown, the first BPF circuit 85A and the second BPF circuit 85B respectively have a first driving frequency f d1 The passband B2 is the center frequency. For example, passband B2 is f. d1 The frequency band is ±5kHz. The vibration noise RN2 has a first driving frequency f. d1 Therefore, it passes through passband B2. Thus, the first BPF circuit 85A extracts and outputs the vibration noise RN2 (reference) from the signal input to buffer amplifier 81. Figure 12 The second BPF circuit 85B extracts and outputs vibration noise RN2 from the signal input to the variable gain amplifier 82 (reference). Figure 12 ).

[0142] The first detection circuit 86A and the second detection circuit 86B are, for example, composed of RMS-DC converters. The first detection circuit 86A converts the amplitude of the vibration noise RN2 input from the first BPF circuit 85A into a DC voltage signal and inputs it to the positive input terminal of the subtraction circuit 87. The second detection circuit 86B converts the amplitude of the vibration noise RN2 input from the second BPF circuit 85B into a DC voltage signal and inputs it to the negative input terminal of the subtraction circuit 87.

[0143] The subtraction circuit 87 outputs a value d2, which is the difference between the DC voltage signal input from the first detector circuit 86A and the DC voltage signal input from the second detector circuit 86B. This value d2 corresponds to the difference between the amplitude of the vibration noise RN2 contained in the signal S2b1 output from the second angle detection sensor 12A and the amplitude of the vibration noise RN2 contained in the signal S2b2 output from the second angle detection sensor 12B. The subtraction circuit 87 inputs this value d2 as a gain adjustment value to the gain adjustment terminal of the variable gain amplifier 82.

[0144] The variable gain amplifier 82 adjusts the amplitude level of signal S2b2 by multiplying the value d2, which is the gain adjustment input, by the signal S2b2 input from the second angle detection sensor 12B. Thus, feedback control is performed via the gain adjustment circuit 84, thereby adjusting the amplitude of the vibration noise RN2 contained in the signal S2b2 after passing through the variable gain amplifier 82 to match the amplitude of the vibration noise RN2 contained in the signal S2b1 after passing through the buffer amplifier 81.

[0145] The subtraction circuit 83 outputs the value obtained by subtracting the signal S2b2 input to the negative input terminal from the signal S2b1 input to the positive input terminal. Through the aforementioned feedback control, the amplitudes of the vibration noise RN2 contained in the two signals are identical. Therefore, through the subtraction processing based on the subtraction circuit 83, the vibration noise RN2 contained in the two signals cancels each other out. Thus, the signal output from the subtraction circuit 83 after removing the vibration noise RN2 is the second angle detection signal S2c (reference). Figure 18 ).

[0146] Figure 18 The diagram illustrates the generation of a second angle detection signal S2c based on the outputs S2b1 and S2b2 from a pair of second angle detection sensors 12A and 12B. The second angle detection signal S2c corresponds to a signal whose amplitude is doubled after removing the vibration noise RN2 from signal S2b1.

[0147] The second angle detection signal S2c generated by the second signal processing unit 61B is input to the second drive signal generation unit 60B and the second zero-crossing pulse output unit 63B. Furthermore, when the oscillation of the reflector unit 20 around the second axis a2 maintains a resonant state, such as... Figure 18 As shown, the second angle detection signal S2c output from the second signal processing unit 61B is relative to the drive voltage waveform V contained in the second drive signal. 2A (t) produces a 90° delay in phase.

[0148] Return to Figure 10 The first angle detection signal S1c, input from the first signal processing unit 61A, is fed back to the first drive signal generation unit 60A. The first phase shift unit 62A shifts the phase of the drive voltage waveform output from the first drive signal generation unit 60A. For example, the first phase shift unit 62A shifts the phase by 90°.

[0149] Figure 19 This is an example illustrating the structure of the first drive signal generation unit 60A. For example... Figure 19 As shown, the first drive signal generation unit 60A includes a signal generation circuit 91A and a phase synchronization circuit 92A. The first drive signal generation unit 60A is a drive circuit of the so-called PLL (Phase Locked Loop) type.

[0150] The phase synchronization circuit 92A receives a first driving frequency f from the signal generation circuit 91A. d1 The sampling reset signal is received from the first signal processing unit 61A (reference). Figure 10 Input the first angle detection signal S1c. The phase synchronization circuit 92A adjusts the phase of the sampling clock signal it generates based on the sampling reset signal and the first angle detection signal S1c.

[0151] The signal generation circuit 91A generates the driving voltage waveform V constituting the first driving signal based on the sampling clock signal input from the phase synchronization circuit 92A. 1A (t) and V 1B (t).

[0152] Thus, feedback control is performed by maintaining a 90° phase difference between the first drive signal and the first angle detection signal S1c through the first phase shifter 62A and the PLL-type first drive signal generation unit 60A. By maintaining a 90° phase difference between the first drive signal and the first angle detection signal S1c, the oscillation of the reflector 20 around the first axis a1 is maintained in a resonant state.

[0153] The second angle detection signal S2c, input from the second signal processing unit 61B, is fed back to the second drive signal generation unit 60B. The second phase shift unit 62B shifts the phase of the drive voltage waveform output from the second drive signal generation unit 60B. For example, the second phase shift unit 62B shifts the phase by 90°.

[0154] Figure 20 This is an example illustrating the structure of the second drive signal generation unit 60B. For example... Figure 20 As shown, the second drive signal generation unit 60B includes a signal generation circuit 91B and a phase synchronization circuit 92B. The second drive signal generation unit 60B is a so-called PLL-type drive circuit.

[0155] The phase synchronization circuit 92B receives a second driving frequency f from the signal generation circuit 91B. d2 The sampling reset signal, and from the second signal processing unit 61B (reference) Figure 10 Input the second angle detection signal S2c. The phase synchronization circuit 92B adjusts the phase of the sampling clock signal it generates based on the sampling reset signal and the second angle detection signal S2c.

[0156] The signal generation circuit 91B generates the drive voltage waveform V that constitutes the second drive signal based on the sampling clock signal input from the phase synchronization circuit 92B. 2A (t) and V 2B (t).

[0157] Thus, feedback control is performed by maintaining a 90° phase difference between the second drive signal and the second angle detection signal S2c through the second phase shifter 62B and the PLL-type second drive signal generation unit 60B. By maintaining a 90° phase difference between the second drive signal and the second angle detection signal S2c, the oscillation of the reflector 20 around the second axis a2 is maintained in a resonant state.

[0158] Return to Figure 10 The first zero-crossing pulse output unit 63A generates a zero-crossing pulse (hereinafter referred to as the first zero-crossing pulse) ZC1 based on the first angle detection signal S1c input from the first signal processing unit 61A. The first zero-crossing pulse output unit 63A is composed of a zero-crossing detection circuit.

[0159] like Figure 21 As shown, the first zero-crossing pulse output unit 63A generates the first zero-crossing pulse ZC1 by timing the AC signal, i.e., the first angle detection signal S1c, to cross zero volts. The first zero-crossing pulse output unit 63A inputs the generated first zero-crossing pulse ZC1 to the light source drive unit 3A.

[0160] The second zero-crossing pulse output unit 63B generates a zero-crossing pulse (hereinafter referred to as the second zero-crossing pulse) ZC2 based on the second angle detection signal S2c input from the second signal processing unit 61B. The second zero-crossing pulse output unit 63B is composed of a zero-crossing detection circuit.

[0161] like Figure 22 As shown, the second zero-crossing pulse output unit 63B generates the second zero-crossing pulse ZC2 by timing the AC signal, i.e., the second angle detection signal S2c, to cross zero volts. The second zero-crossing pulse output unit 63B inputs the generated second zero-crossing pulse ZC2 to the light source drive unit 3A.

[0162] The light source driving unit 3A drives the light source 3, for example, based on drawing data supplied from outside the image drawing system 10. Furthermore, the light source driving unit 3A controls the irradiation timing in a manner that synchronizes the irradiation timing of the laser beam with the first zero-crossing pulse ZC1 and the second zero-crossing pulse ZC2 input from the mirror driving unit 4A.

[0163] As described above, according to the technology of the present invention, vibration noise caused by the oscillation of the reflector portion around the second axis is removed by subtracting one of the pair of first output signals from a pair of first angle detection sensors. Thus, a first angle detection signal representing the angle of the reflector portion around the first axis is generated, and the vibration noise is removed, thereby enabling high-precision control of the oscillation of the reflector portion. Furthermore, by maintaining the oscillation of the reflector portion in a resonant state, the amplitude (maximum deflection angle) of the oscillation of the reflector portion remains constant.

[0164] [Second Implementation]

[0165] Next, the image depiction system according to the second embodiment will be described. The difference between the image depiction system of this embodiment and that of the first embodiment lies in the configuration of the pair of first angle detection sensors 11A and 11B and the pair of second angle detection sensors 12A and 12B in the MMD4. Regarding the pair of first angle detection sensors 11A and 11B, in the first embodiment, they were positioned opposite each other across the first axis a1; in contrast, in the second embodiment, they are positioned opposite each other across the second axis a2. Regarding the pair of second angle detection sensors 12A and 12B, in the first embodiment, they were positioned opposite each other across the second axis a2; in contrast, in the second embodiment, they are positioned opposite each other across the first axis a1.

[0166] Figure 23 This is a top view showing the structure of the MMD4 according to this embodiment. For example... Figure 23 As shown, a pair of first angle detection sensors 11A and 11B are respectively disposed on the first movable frame 22 near the first support portion 21. The first angle detection sensor 11A is disposed near the first support portion 21 connected to one side of the reflector portion 20. The first angle detection sensor 11B is disposed near the first support portion 21 connected to the other side of the reflector portion 20. Therefore, the pair of first angle detection sensors 11A and 11B are disposed opposite each other across the second axis a2 and across the reflector portion 20. Furthermore, the pair of first angle detection sensors 11A and 11B are disposed at a position offset from the first axis a1 in the same direction (the -X direction in this embodiment).

[0167] Furthermore, a pair of second angle detection sensors 12A and 12B are respectively disposed on the second movable frame 24 near the second support portion 23. The second angle detection sensor 12A is disposed near the second support portion 23 connected to one side of the first movable frame 22. The second angle detection sensor 12B is disposed near the second support portion 23 connected to the other side of the first movable frame 22. Therefore, the pair of second angle detection sensors 12A and 12B are disposed opposite each other across the first axis a1 and across the reflector portion 20 and the first movable frame 22. Furthermore, the pair of second angle detection sensors 12A and 12B are disposed at a position offset from the second axis a2 in the same direction (the +Y direction in this embodiment).

[0168] Figure 24 This illustrates an example of signals output from a pair of first angle detection sensors 11A and 11B in this embodiment. Figure 24In this context, S1a represents the signal output from a pair of first angle detection sensors 11A and 11B when the reflector 20 oscillates only around the first axis a1 and not around the second axis a2. In this embodiment, the first angle detection sensors 11A and 11B are positioned offset in the same direction relative to the first axis a1, thus outputting a signal with a first driving frequency f. d1 Waveform signals in phase with each other.

[0169] When the reflector 20 is simultaneously oscillating around the first axis a1 and the second axis a2, the output signal of the first angle detection sensor 11A is superimposed with vibration noise RN1a caused by the oscillation of the reflector 20 around the second axis a2. Similarly, when the reflector 20 is simultaneously oscillating around the first axis a1 and the second axis a2, the output signal of the first angle detection sensor 11B is superimposed with vibration noise RN1b caused by the oscillation of the reflector 20 around the second axis a2. The first angle detection sensors 11A and 11B are positioned opposite each other across the second axis a2, therefore the vibration noises RN1a and RN1b superimposed on them are out of phase.

[0170] Thus, in the case of dual-axis drive, the first angle detection sensor 11A outputs a signal S1b1 superimposed with vibration noise RN1a, and the first angle detection sensor 11B outputs a signal S1b2 superimposed with vibration noise RN1b.

[0171] Figure 25 This illustrates an example of signals output from a pair of second-angle detection sensors 12A and 12B in this embodiment. Figure 25 In this context, S2a represents the signal output from a pair of second angle detection sensors 12A and 12B when the reflector 20 oscillates only around the second axis a2 and not around the first axis a1. In this embodiment, the second angle detection sensors 12A and 12B are positioned offset in the same direction relative to the second axis a2, thus outputting a signal with a second driving frequency f. d2 Waveform signals in phase with each other.

[0172] When the reflector 20 is simultaneously oscillating around the first axis a1 and the second axis a2, the output signal of the second angle detection sensor 12A is superimposed with vibration noise RN2a caused by the oscillation of the reflector 20 around the first axis a1. Similarly, when the reflector 20 is simultaneously oscillating around the first axis a1 and the second axis a2, the output signal of the second angle detection sensor 12B is superimposed with vibration noise RN2b caused by the oscillation of the reflector 20 around the first axis a1. The second angle detection sensors 12A and 12B are positioned opposite each other across the first axis a1, therefore the vibration noises RN2a and RN2b superimposed on them are out of phase.

[0173] Thus, in the case of dual-axis drive, the second angle detection sensor 12A outputs a signal S2b1 superimposed with vibration noise RN2a, and the second angle detection sensor 12B outputs a signal S2b2 superimposed with vibration noise RN2b.

[0174] In this embodiment, the difference between the drive control unit 5 and the drive control unit 5 in the first embodiment lies only in the structure of the first signal processing unit 61A and the second signal processing unit 61B. For example... Figure 26 As shown, in this embodiment, the first signal processing unit 61A replaces the subtraction circuit 73 and has an addition circuit 73A. The addition circuit 73A outputs the sum of the values ​​of the signal S1b1 input from the first angle detection sensor 11A via the buffer amplifier 71 and the signal S1b2 input from the first angle detection sensor 11B via the variable gain amplifier 72.

[0175] In this embodiment, the amplitude level of the vibration noise RN1b contained in the signal S1b2 is adjusted by the gain adjustment circuit 74 to match the amplitude level of the vibration noise RN1a contained in the signal S1b1. Therefore, through the addition processing based on the adder circuit 73A, the vibration noises RN1a and RN1b cancel each other out. Therefore, the signal with the vibration noises RN1a and RN1b removed is output from the adder circuit 73A, which is the first angle detection signal S1c.

[0176] Figure 27 This embodiment illustrates the generation of a first angle detection signal S1c based on S1b1 and S1b2 output from a pair of first angle detection sensors 11A and 11B. In this embodiment, the same first angle detection signal S1c as in the first embodiment is also obtained (see reference). Figure 15 ).

[0177] like Figure 28 As shown, in this embodiment, the second signal processing unit 61B replaces the subtraction circuit 83 and has an addition circuit 83A. The addition circuit 83A outputs the sum of the values ​​of the signal S2b1 input from the second angle detection sensor 12A via the buffer amplifier 81 and the signal S2b2 input from the second angle detection sensor 12B via the variable gain amplifier 82.

[0178] In this embodiment, the amplitude level of the vibration noise RN2b contained in the signal S2b2 is adjusted by the gain adjustment circuit 84 to match the amplitude level of the vibration noise RN2a contained in the signal S2b1. Therefore, through the addition processing based on the adder circuit 83A, the vibration noises RN2a and RN2b cancel each other out. Therefore, the signal with the vibration noises RN2a and RN2b removed is output from the adder circuit 83A, which is the second angle detection signal S2c.

[0179] Figure 29 This embodiment illustrates the generation of a second angle detection signal S2c based on S2b1 and S2b2 output from a pair of second angle detection sensors 12A and 12B. In this embodiment, the same second angle detection signal S2c as in the first embodiment is also obtained (see reference). Figure 15 ).

[0180] As described above, a pair of first angle detection sensors 11A and 11B can be positioned opposite each other across the first axis a1 or the second axis a2. When the pair of first angle detection sensors 11A and 11B are positioned opposite each other across the first axis a1, vibration noise can be removed by subtracting one of their output signals from the other. When the pair of first angle detection sensors 11A and 11B are positioned opposite each other across the second axis a2, vibration noise can be removed by adding their output signals.

[0181] Similarly, a pair of second angle detection sensors 12A and 12B can be positioned opposite each other across the first axis a1 or the second axis a2. When the pair of second angle detection sensors 12A and 12B are positioned opposite each other across the second axis a2, vibration noise can be removed by subtracting one of their output signals from the other. When the pair of second angle detection sensors 12A and 12B are positioned opposite each other across the first axis a1, vibration noise can be removed by adding their output signals.

[0182] [Variation Example]

[0183] Next, variations of the above embodiments will be described. In each of the above embodiments, the gain adjustment circuit 74 extracts the signal with the second driving frequency f through the first BPF circuit 75A and the second BPF circuit 75B. d2 The vibration noise. Instead, it can be achieved at the first driving frequency f. d1 With the second driving frequency f d2 A low-pass filter circuit with a cutoff frequency between the two points extracts the signal with the second driving frequency f. d2 Vibration noise. Furthermore, in the above embodiments, the gain adjustment circuit 84 extracts the signal with the first driving frequency f through the first BPF circuit 85A and the second BPF circuit 85B. d1 The vibration noise. Instead, it can be achieved at the first driving frequency f. d1 With the second driving frequency f d2 A high-pass filter circuit with a cutoff frequency between the two points extracts the signal with the first driving frequency f. d1 Vibration noise.

[0184] The structure of the MMD4 shown in the above embodiment is an example. The structure of the MMD4 can be modified in various ways. For example, the first actuator 31 that causes the mirror part 20 to swing about the first axis a1 can be disposed in the second movable frame 24, and the second actuator 32 that causes the mirror part 20 to swing about the second axis a2 can be disposed in the first movable frame 22.

[0185] Furthermore, the hardware structure of the drive control unit 5 can be modified in various ways. In the above embodiments, the drive control unit 5 is composed of analog computing circuits, but it can also be composed of digital computing circuits. The drive control unit 5 can be composed of a single processor, or it can be composed of a combination of two or more processors of the same or different types. The processor includes a CPU (Central Processing Unit), a programmable logic device (PLD), and dedicated circuits, etc. As is well known, a CPU is a general-purpose processor that functions as a processing unit to execute software (programs). A PLD is a processor such as an FPGA (Field Programmable Gate Array) whose circuit structure can be modified after manufacturing. A dedicated circuit is a processor such as an ASIC (Application Specific Integrated Circuit) that has a circuit structure specifically designed to perform specific processing.

[0186] [Comparative Example]

[0187] Next, a comparative example with the technology of the present invention will be described. In the technology of the present invention, as described above, vibration noise is removed by adding or subtracting a pair of output signals from a pair of angle detection sensors. In contrast, vibration noise can be removed by performing frequency filtering on the output signals from the angle detection sensors. Hereinafter, as a comparative example, an example of removing vibration noise by frequency filtering will be described.

[0188] In this comparative example, at least one of the pair of first angle detection sensors 11A and 11B is sufficient. Similarly, at least one of the pair of second angle detection sensors 12A and 12B is sufficient.

[0189] Furthermore, in this comparative example, the first signal processing unit 61A is configured to have a first driving frequency f d1 This is a bandpass filter circuit for the passband of the center frequency. Similarly, the second signal processing unit 61B is configured to have a second driving frequency f. d2 This is a bandpass filter circuit with a center frequency passband. Therefore, the first signal processing unit 61A outputs a signal with a second driving frequency f. d2The signal has been cleaned up to remove vibration noise. The second signal processing unit 61B outputs a signal with the first driving frequency f. d1 The vibration noise signal has been removed.

[0190] Thus, vibration noise can be removed by configuring the first signal processing unit 61A and the second signal processing unit 61B as bandpass filter circuits. However, sometimes accurate phase information cannot be obtained from the signal after vibration noise has been removed. This is caused by the phase response of the bandpass filter circuit.

[0191] Figure 30 This is an example illustrating the gain and phase characteristics of a bandpass filter circuit. Figure 30 The bandpass filter circuit shown has a center frequency of 10kHz. The phase changes drastically near the center frequency; therefore, if the frequency of the signal input to the bandpass filter circuit deviates from the center frequency, it will cause a significant phase change in the output signal from the bandpass filter circuit. Thus, the output signal from the angle detection sensor passing through the bandpass filter circuit is likely to experience a significant phase change, making it difficult to use as timing information to maintain the resonant state of the output signal from the bandpass filter circuit.

[0192] If a zero-crossing pulse is generated based on the output signal from the bandpass filter circuit and input to the light source driver unit 3A, an image that is synchronously drawn with the scanning offset of the light based on MMD4 is drawn onto the scanned surface 6. In this case, a phaser that allows manual adjustment of the phase of the output signal from the bandpass filter circuit needs to be provided, and the user can manually adjust the phaser to eliminate the offset while observing the image drawn onto the scanned surface 6.

[0193] In contrast, the technology of this invention does not use a bandpass filter circuit but removes vibration noise by adding or subtracting a pair of output signals from a pair of angle detection sensors. Therefore, by removing vibration noise, the output signal can be used as timing information to maintain the resonant state without significant phase changes. Thus, manual adjustment of phasers by the user is unnecessary.

[0194] All documents, patent applications and technical standards described in this specification are incorporated herein by reference to the same extent as those specifically and individually described herein.

Claims

1. An optical scanning device, comprising: The reflecting mirror section has a reflecting surface that reflects incident light; A first actuator causes the mirror section to oscillate about a first axis, which lies in a plane including the reflective surface when the mirror section is stationary; A second actuator causes the mirror portion to oscillate about a second axis, which lies in a plane including the reflecting surface when the mirror portion is stationary and is orthogonal to the first axis. A pair of first angle detection sensors, each outputting a signal corresponding to the angle of the reflector portion about the first axis, are configured at opposing positions across the first axis and on the same side relative to the reflector portion; and At least one processor, In the optical scanning device, After the processor makes the amplitude of the vibration noise contained in each of the pair of first output signals consistent by adjusting the amplitude level of at least one of the pair of first output signals output from the pair of first angle detection sensors, it generates a first angle detection signal representing the angle of the reflector portion around the first axis by subtracting the pair of first output signals.

2. The optical scanning device according to claim 1, wherein, The processor has a first drive signal generation unit that generates a first drive signal applied to the first actuator and feeds back the first angle detection signal to the first drive signal generation unit.

3. The optical scanning device according to claim 2, wherein, The first drive signal generation unit is a drive circuit with a phase synchronization circuit.

4. The optical scanning device according to claim 2, wherein, The first driving signal is a sine wave.

5. The optical scanning device according to claim 1, wherein, The first angle detection sensor is a piezoelectric element.

6. The optical scanning device according to claim 1, further comprising: A pair of second angle detection sensors, each outputting a signal corresponding to the angle of the reflector portion around the second axis, are positioned opposite each other across the first axis or the second axis. The processor adjusts the amplitude level of at least one of the pair of second output signals output from the pair of second angle detection sensors, and adds or subtracts the pair of second output signals after the amplitude level adjustment, thereby generating a second angle detection signal representing the angle of the reflector portion about the second axis.

7. The optical scanning device according to claim 6, wherein, After the processor makes the amplitude of the vibration noise contained in each of the pair of second output signals consistent by adjusting the amplitude level of at least one of the pair of second output signals, it adds or subtracts the pair of second output signals.

8. The optical scanning device according to claim 6, wherein, The pair of second angle detection sensors are positioned opposite each other across the second axis. The processor generates the second angle detection signal by subtracting one of a pair of second output signals after the amplitude level has been adjusted.

9. The optical scanning device according to claim 6, wherein, The pair of second angle detection sensors are positioned opposite each other across the first axis. The processor generates the second angle detection signal by adding a pair of second output signals after the amplitude level has been adjusted.

10. The optical scanning device according to claim 6, wherein, The processor has a second drive signal generation unit that generates a second drive signal applied to the second actuator and feeds back the second angle detection signal to the second drive signal generation unit.

11. The optical scanning device according to claim 10, wherein, The second drive signal generation unit is a drive circuit with a phase synchronization circuit.

12. The optical scanning device according to claim 10, wherein, The second driving signal is a sine wave.

13. The optical scanning device according to claim 6, wherein, The second angle detection sensor is a piezoelectric element.

14. An image depiction system, comprising: The optical scanning apparatus according to any one of claims 6 to 13; and A light source that illuminates the reflector portion. In the image depiction system, The processor controls the timing of the light irradiation from the light source based on the first angle detection signal and the second angle detection signal.

15. A driving method for an optical scanning device, the optical scanning device comprising: The reflecting mirror section has a reflecting surface that reflects incident light; A first actuator causes the mirror section to oscillate about a first axis, which lies in a plane including the reflective surface when the mirror section is stationary; A second actuator causes the reflector to oscillate about a second axis, which lies in a plane including the reflecting surface when the reflector is stationary and is orthogonal to the first axis; and A pair of first angle detection sensors, each outputting a signal corresponding to the angle of the reflector portion around the first axis, are positioned opposite each other across the first axis and on the same side relative to the reflector portion. In the driving method of the optical scanning device, After adjusting the amplitude level of at least one of the pair of first output signals from the pair of first angle detection sensors to make the amplitude of the vibration noise contained in each of the pair of first output signals consistent, a first angle detection signal representing the angle of the reflector portion around the first axis is generated by subtracting the pair of first output signals.

Images