Optical scanning device, driving method for optical scanning device, and image drawing system

Abstract

To provide an optical scanning device, a method for driving the optical scanning device, and an image drawing system capable of suppressing deterioration in image quality of an image to be drawn.SOLUTION: A drive control part includes the steps of: applying a first drive signal having a first drive frequency to a first actuator; applying a second drive signal having a second drive frequency to a second actuator; deriving a first average phase delay time by averaging first phase delay times of output signals of a first angle detection sensor with respect to the first drive signal of a plurality of periods; deriving a second average phase delay time by averaging second phase delay times of output signals of a second angle detection sensor for the second drive signal of the plurality of periods; generating a first reference signal based on the first drive signal and the first average phase delay time; and generating a second reference signal based on the second drive signal and the second average phase delay time.SELECTED DRAWING: Figure 16

Description

[Technical field]

[0001] The present disclosure relates to an optical scanning device, a driving method for an optical scanning device, and an image drawing system. [Background technology]

[0002] A micromirror device (also called a microscanner) is known as one of the Micro Electro Mechanical Systems (MEMS) devices fabricated using silicon (Si) microfabrication technology. Optical scanning devices equipped with this micromirror device are small and consume low power, so they are expected to be applied to image drawing systems such as laser displays and laser projectors.

[0003] In a micromirror device, a mirror portion is formed so as to be able to swing around a first axis and a second axis that are perpendicular to each other, and the light reflected by the mirror portion is scanned two-dimensionally as the mirror portion swings around each axis. Also, a micromirror device is known that enables Lissajous scanning of light by resonating the mirror portion around each axis.

[0004] Patent document 1 discloses an optical scanning device having a sensor that detects the rotation angle of a mirror part, and a look-up table that stores correction amounts for correcting the amplitude and phase of the rotation angle of the mirror part obtained from the sensor, the correction amounts corresponding to each temperature.

[0005] Patent document 2 discloses an optical scanning device that detects a current generated by a change in the capacitance of an actuator that drives a mirror portion, outputs a current signal from which components above a predetermined frequency are cut off, and adjusts the drive signal applied to the actuator based on the time difference between the maximum and minimum values ​​of the current signal.

[0006] Patent document 3 discloses an optical scanning device in which first and second control frequencies are adjusted according to the phase of vibration of the mirror section so that the maximum amplitude of vibration remains within the resonance range of the mirror section, and the first and second control frequencies do not have a substantially fixed integer ratio. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2018-101040 A [Patent Document 2] JP 2017-181951 A [Patent Document 3] Special Publication No. 2013-513828 Summary of the Invention [Problem to be solved by the invention]

[0008] The optical scanning device uses a first angle detection sensor that detects the angle of the mirror unit around a first axis, and a second angle detection sensor that detects the angle of the mirror unit around a second axis. For example, the optical scanning device outputs a reference signal (e.g., a zero-cross signal) that indicates that the angle of the mirror unit has reached a reference angle based on the output signals of the first angle detection sensor and the second angle detection sensor. This reference signal is used to control the timing of light irradiation by a light source that irradiates light onto the mirror unit.

[0009] The output signal of the first angle detection sensor may have an unstable signal waveform due to the influence of the oscillation of the mirror unit around the second axis. Similarly, the output signal of the second angle detection sensor may have an unstable signal waveform due to the influence of the oscillation of the mirror unit around the first axis. In these cases, when a reference signal is output based on the output signals of the first angle detection sensor and the second angle detection sensor, the output timing of the reference signal shifts depending on the period. In this case, the image quality of the drawn image is reduced due to the timing of irradiation of light by the light source shifting for each period.

[0010] However, the techniques described in Patent Documents 1 to 3 do not take into consideration the deviation in the output timing of the reference signal.

[0011] The present disclosure has been made in consideration of the above circumstances, and aims to provide an optical scanning device, a driving method for an optical scanning device, and an image drawing system that can suppress deterioration in image quality of a drawn image. [Means for solving the problem]

[0012] The optical scanning device disclosed herein is an optical scanning device including: a mirror section having a reflective surface that reflects incident light; a first actuator that oscillates the mirror section around a first axis that is in a plane including the reflective surface of the mirror section when stationary; a second actuator that oscillates the mirror section around a second axis that is in the plane including the reflective surface of the mirror section when stationary and that intersects with the first axis; a first angle detection sensor that outputs a signal according to the angle of the mirror section about the first axis; a second angle detection sensor that outputs a signal according to the angle of the mirror section about the second axis; and at least one processor, wherein the processor applies a first drive signal having a first drive frequency to the first actuator. applying a second drive signal having a second drive frequency to a second actuator, deriving a first average phase delay time by averaging a first phase delay time of an output signal of a first angle detection sensor for multiple cycles of the first drive signal, deriving a second average phase delay time by averaging a second phase delay time of an output signal of a second angle detection sensor for multiple cycles of the second drive signal, generating a first reference signal indicating that the angle about the first axis has become a reference angle based on the first drive signal and the first average phase delay time, and generating a second reference signal indicating that the angle about the second axis has become a reference angle based on the second drive signal and the second average phase delay time.

[0013] In addition, in the optical scanning device disclosed herein, the first angle detection sensor may be a pair of angle detection sensors arranged at opposing positions across the first axis or the second axis, and the output signal of the first angle detection sensor may be an output signal obtained by adding or subtracting a pair of output signals output from the pair of angle detection sensors, and the second angle detection sensor may be a pair of angle detection sensors arranged at opposing positions across the first axis or the second axis, and the output signal of the second angle detection sensor may be an output signal obtained by adding or subtracting a pair of output signals output from the pair of angle detection sensors.

[0014] In addition, in the optical scanning device disclosed herein, the first reference signal may be a signal indicating that the angle around the first axis has become zero, and the second reference signal may be a signal indicating that the angle around the second axis has become zero.

[0015] In addition, in the optical scanning device disclosed herein, the processor may derive a first average phase delay time by averaging a first phase delay time at a time when the output signal of the first angle detection sensor is zero, and derive a second average phase delay time by averaging a second phase delay time at a time when the output signal of the second angle detection sensor is zero.

[0016] In addition, the optical scanning device disclosed herein may be configured such that the processor derives a first average phase delay time by averaging a first phase delay time from a time when the first drive signal in a corresponding period is zero to a time when the output signal of the first angle detection sensor is zero, and derives a second average phase delay time by averaging a second phase delay time from a time when the second drive signal in a corresponding period is zero to a time when the output signal of the second angle detection sensor is zero.

[0017] In addition, in the optical scanning device disclosed herein, the processor may generate the first reference signal and the second reference signal based on a time obtained by adding a shift time according to preset conditions to the first average phase delay time and the second average phase delay time, respectively.

[0018] In the optical scanning device of the present disclosure, the above conditions may include a first phase delay time and a second phase delay time.

[0019] In the optical scanning device of the present disclosure, the above conditions may further include a drive voltage of the first drive signal and a drive voltage of the second drive signal.

[0020] In the optical scanning device of the present disclosure, the above conditions may further include a first drive frequency and a second drive frequency.

[0021] In the optical scanning device according to the present disclosure, the above conditions may further include an environmental temperature.

[0022] In addition, the optical scanning device disclosed herein is provided with a delay time derivation mode that derives a delay time, and the processor executes the delay time derivation mode during calibration to obtain the delay time, and when generating the first reference signal and the second reference signal, the delay time previously obtained during calibration may be used.

[0023] In addition, the optical scanning device disclosed herein may have an average phase delay time derivation mode for deriving a first average phase delay time and a second average phase delay time, and the processor may execute the average phase delay time derivation mode during calibration to obtain the first average phase delay time and the second average phase delay time, and when generating the first reference signal and the second reference signal, the processor may use the first average phase delay time and the second average phase delay time obtained in advance during calibration.

[0024] In addition, the image drawing system of the present disclosure is an image drawing system including any of the optical scanning devices described above and a light source that irradiates light onto a mirror portion, and a processor controls the timing of the light source's irradiation based on a first reference signal and a second reference signal.

[0025] The present disclosure also provides a driving method for an optical scanning device including a mirror section having a reflective surface that reflects incident light, a first actuator that oscillates the mirror section about a first axis in a plane including the reflective surface of the mirror section when stationary, a second actuator that oscillates the mirror section about a second axis that is in the plane including the reflective surface of the mirror section when stationary and intersects with the first axis, a first angle detection sensor that outputs a signal according to the angle of the mirror section about the first axis, and a second angle detection sensor that outputs a signal according to the angle of the mirror section about the second axis, the driving method including providing a first driving signal having a first driving frequency to the first actuator, a second drive signal having a second drive frequency is applied to the etrator; a first average phase delay time is derived by averaging a first phase delay time of an output signal of the first angle detection sensor for multiple cycles of the first drive signal; a second average phase delay time is derived by averaging a second phase delay time of an output signal of the second angle detection sensor for multiple cycles of the second drive signal; a first reference signal indicating that the angle about the first axis has become a reference angle is generated based on the first drive signal and the first average phase delay time; and a second reference signal indicating that the angle about the second axis has become a reference angle is generated based on the second drive signal and the second average phase delay time. Effect of the Invention

[0026] According to the present disclosure, degradation in image quality of a drawn image can be suppressed. [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 is a schematic diagram of an image drawing system. [Diagram 2] FIG. 1 is a perspective view of the appearance of a micromirror device. [Diagram 3] 4 is a graph showing an example of a first drive signal. [Figure 4] 6 is a graph showing an example of a second drive signal. [Diagram 5] 3 is a block diagram showing an example of a functional configuration of a drive control unit. FIG. [Figure 6]4A to 4C are diagrams illustrating an example of signals output from a pair of first angle detection sensors. [Figure 7] 6A to 6C are diagrams illustrating an example of signals output from a pair of second angle detection sensors. [Figure 8] 4 is a circuit diagram showing an example of the configuration of a first signal processing unit. FIG. [Figure 9] FIG. 4 is a diagram illustrating an example of a first signal processing. [Figure 10] FIG. 11 is a diagram illustrating an example of a second signal processing. [Figure 11] 10 is a diagram for explaining deviations in timing at which the first angle detection signal crosses zero. FIG. [Figure 12] 11 is a diagram for explaining a process of deriving a first average phase delay time. FIG. [Figure 13] 11 is a diagram for explaining a process of deriving a second average phase delay time. FIG. [Figure 14] 11 is a diagram illustrating an example of a relationship between a first average phase delay time and a first deviation time. FIG. [Figure 15] 13 is a diagram illustrating an example of a relationship between a second average phase delay time and a second deviation time. FIG. [Figure 16] 4A to 4C are diagrams for explaining a generation process of a first zero cross pulse. [Figure 17] 10 is a diagram for explaining a generation process of a second zero cross pulse. FIG. [Figure 18] 13 is a flowchart showing an example of a first delay time derivation process. [Figure 19] 13 is a flowchart showing an example of a second delay time derivation process. [Figure 20] 10 is a flowchart showing an example of a first zero cross pulse generating process. [Figure 21] 10 is a flowchart showing an example of a second zero cross pulse generating process. [Figure 22] FIG. 2 is a schematic plan view of the image drawing system during calibration. [Figure 23] 10 is a flowchart showing an example of a first calibration process. [Figure 24]FIG. 11 is a diagram for explaining a first calibration process. [Diagram 25] FIG. 11 is a diagram for explaining a first calibration process. [Figure 26] 10 is a flowchart showing an example of a second calibration process. [Figure 27] FIG. 11 is a diagram for explaining a second calibration process. [Figure 28] FIG. 11 is a diagram for explaining a second calibration process. [Figure 29] FIG. 13 is a plan view of a micromirror device according to a modified example. [Diagram 30] FIG. 11 is a circuit diagram showing a configuration of a first signal processing unit according to a modified example. [Diagram 31] 6 is a diagram showing an example of a relationship between a first drive frequency and a first delay time. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Hereinafter, examples of embodiments for carrying out the technology of the present disclosure will be described in detail with reference to the drawings.

[0029] First, the configuration of an image drawing system 10 according to the present embodiment will be described with reference to Fig. 1. As shown in Fig. 1, the image drawing system 10 has an optical scanning device 2 and a light source 3. The optical scanning device 2 includes a micro mirror 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 disclosed technology.

[0030] The image drawing system 10 draws an image by reflecting a light beam L emitted from a light source 3 by an MMD 4 and optically scanning a scanned surface 6 under the control of a drive control unit 5. The scanned surface 6 is, for example, a screen for projecting an image, or the retina of a human eye.

[0031] The image rendering system 10 is applied to, for example, a Lissajous scanning laser display. Specifically, the image rendering system 10 is applicable to a laser scan display such as an Augmented Reality (AR) glass or a Virtual Reality (VR) glass.

[0032] The MMD4 is a piezoelectric two-axis drive type micromirror device that can oscillate the mirror section 20 (see FIG. 2) around a first axis a1 and a second axis a2 perpendicular to the first axis a1. Hereinafter, the direction parallel to the second axis a2 is referred to as the X direction, the direction parallel to the first axis a1 is referred to as the Y direction, and the direction perpendicular to the first axis a1 and the second axis a2 is referred to as the Z direction. In this embodiment, an example is shown in which the first axis a1 and the second axis a2 are perpendicular to each other (i.e., they intersect perpendicularly), but the first axis a1 and the second axis a2 may intersect at an angle other than 90°. The term "intersect" here means within a certain angle range including an allowable error with 90° as the center.

[0033] The light source 3 is a laser device that emits, for example, a laser beam as the light beam L. The light source 3 outputs, for example, three colors of laser beams, R (Red), G (Green), and B (Blue). When the mirror section 20 of the MMD 4 is stationary, the light source 3 preferably irradiates the light beam L perpendicularly to the reflecting surface 20A (see FIG. 2) of the mirror section 20. When the light beam L is irradiated perpendicularly from the light source 3 to the reflecting surface 20A, the light source 3 may become an obstacle when the light beam L is scanned and drawn on the scanned surface 6. For this reason, it is preferable to control the light beam L emitted from the light source 3 by an optical system and irradiate it perpendicularly to the reflecting surface 20A. The optical system may include a lens or may not include a lens. The angle at which the light beam L emitted from the light source 3 is irradiated to the reflecting surface 20A is not limited to perpendicular, and the light beam L may be irradiated obliquely to the reflecting surface 20A.

[0034] The drive control unit 5 outputs drive signals to the light source 3 and the MMD 4 based on the optical scanning information. The light source 3 generates a light beam L based on the input drive signal and irradiates the MMD 4 with the light beam L. The MMD 4 swings the mirror unit 20 around the first axis a1 and the second axis a2 based on the input drive signal.

[0035] The drive control unit 5 causes the mirror unit 20 to resonate around the first axis a1 and the second axis a2, so that the light beam L reflected by the mirror unit 20 scans the scanned surface 6 so as to draw a Lissajous waveform. This light scanning method is called a Lissajous scanning method.

[0036] Next, the configuration of the MMD 4 according to this embodiment will be described with reference to Fig. 2. As shown in Fig. 2, the MMD 4 has a mirror section 20, a first support section 21, a first movable frame 22, a second support section 23, a second movable frame 24, a connection section 25, and a fixed frame 26. The MMD 4 is a so-called MEMS scanner.

[0037] The mirror section 20 has a reflecting surface 20A that reflects incident light. The reflecting surface 20A is provided on one surface of the mirror section 20, and is formed of a metal thin film such as gold (Au), aluminum (Al), silver (Ag), or a silver alloy. The shape of the reflecting surface 20A is, for example, a circular shape centered on the intersection of the first axis a1 and the second axis a2.

[0038] The first axis a1 and the second axis a2 exist in a plane including the reflecting surface 20A when the mirror section 20 is stationary. The planar shape of the MMD 4 is rectangular and is line-symmetric with respect to the first axis a1 and line-symmetric with respect to the second axis a2.

[0039] The first support parts 21 are disposed on the outer sides of the mirror part 20 at positions facing each other across the second axis a2. The first support parts 21 are connected to the mirror part 20 on the first axis a1, and support the mirror part 20 so that it can swing around the first axis a1. In this embodiment, the first support parts 21 are torsion bars extending along the first axis a1.

[0040] The first movable frame 22 is a rectangular frame surrounding the mirror section 20, and is connected to the mirror 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 facing each other across the first axis a1. In this manner, the two piezoelectric elements 30 are formed on the first movable frame 22, thereby constituting a pair of first actuators 31.

[0041] The pair of first actuators 31 are disposed at positions facing 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, thereby causing the mirror section 20 to swing about the first axis a1.

[0042] The second support parts 23 are disposed on the outer sides of the first movable frame 22 at positions facing each other across the first axis a1. The second support parts 23 are connected to the first movable frame 22 on the second axis a2, and support the first movable frame 22 and the mirror part 20 so as to be swingable around the second axis a2. In this embodiment, the second support parts 23 are torsion bars extending along the second axis a2.

[0043] The second movable frame 24 is a rectangular frame surrounding the first movable frame 22, and is connected to the first movable frame 22 on the second axis a2 via the second support portion 23. Piezoelectric elements 30 are formed on the second movable frame 24 at positions facing each other across the second axis a2. In this manner, the two piezoelectric elements 30 are formed on the second movable frame 24, thereby constituting a pair of second actuators 32.

[0044] The pair of second actuators 32 are disposed at positions facing 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, thereby causing the mirror section 20 to swing about the second axis a2.

[0045] The connection portions 25 are disposed on the outer side of the second movable frame 24 at positions facing each other across the first axis a1. The connection portions 25 are connected to the second movable frame 24 on the second axis a2.

[0046] The fixed frame 26 is a rectangular frame body that surrounds the second movable frame 24, and is connected to the second movable frame 24 via a connection portion 25 on the second axis a2.

[0047] In addition, the first movable frame 22 is provided with a pair of first angle detection sensors 11A, 11B in positions facing each other across the first axis a1 near the first support portion 21. Each of the pair of first angle detection sensors 11A, 11B is composed of a piezoelectric element. Each of the first angle detection sensors 11A, 11B converts a force applied by deformation of the first support portion 21 accompanying rotation of the mirror portion 20 about the first axis a1 into a voltage and outputs a signal. That is, the first angle detection sensors 11A, 11B output a signal according to the angle of the mirror portion 20 about the first axis a1.

[0048] Further, the second movable frame 24 is provided with a pair of second angle detection sensors 12A, 12B in positions facing each other across the second axis a2 near the second support portion 23. Each of the pair of second angle detection sensors 12A, 12B is composed of a piezoelectric element. Each of the second angle detection sensors 12A, 12B converts a force applied by deformation of the second support portion 23 accompanying rotation of the mirror portion 20 about the second axis a2 into a voltage and outputs a signal. That is, the second angle detection sensors 12A, 12B output a signal according to the angle of the mirror portion 20 about the second axis a2.

[0049] 2, wiring and electrode pads for applying drive signals to the first actuator 31 and the second actuator 32 are omitted. Also, wiring and electrode pads for outputting signals from the first angle detection sensors 11A, 11B and the second angle detection sensors 12A, 12B are omitted. A plurality of electrode pads are provided on the fixed frame 26.

[0050] The deflection angle (hereinafter referred to as the "first deflection angle") θ1 of the mirror section 20 around the first axis a1 is controlled by a drive signal (hereinafter referred to as the "first drive signal") that the drive control section 5 provides to the first actuator 31. The first drive signal is, for example, a sinusoidal AC voltage. The first drive signal is a drive voltage waveform V 1A (t) and the driving voltage waveform V applied to the other 1B (t) and the driving voltage waveform V 1A (t) and the driving voltage waveform V 1B (t) are in opposite phase to each other (i.e., the phase difference is 180°).

[0051] The first deflection angle θ1 is an angle at which the normal to the reflecting surface 20A is inclined with respect to the Z direction on the XZ plane.

[0052] The deflection angle θ2 of the mirror section 20 around the second axis a2 (hereinafter referred to as the "second deflection angle") is controlled by a drive signal (hereinafter referred to as the "second drive signal") that the drive control section 5 provides to the second actuator 32. The second drive signal is, for example, a sinusoidal AC voltage. The second drive signal is a drive voltage waveform V 2A (t) and the driving voltage waveform V applied to the other 2B (t) and the driving voltage waveform V 2A (t) and the driving voltage waveform V 2B (t) are in opposite phase to each other (i.e., the phase difference is 180°).

[0053] The second deflection angle θ2 is an angle at which the normal to the reflecting surface 20A is inclined with respect to the Z direction in the YZ plane.

[0054] FIG. 3 shows an example of the first drive signal, and FIG. 4 shows an example of the second drive signal. FIG. 3 shows a drive voltage waveform V 1A (t) and V 1B FIG. 4 shows the drive voltage waveform V 2A (t) and V 2B (t) is shown.

[0055] Drive voltage waveform V 1A (t) and V 1B (t) is expressed as follows, respectively: V 1A (t)=V off1 +V1sin(2πf d1 t) V 1B (t)=V off1 +V1sin(2πf d1 t+α)

[0056] where V1 is the amplitude voltage. V off1 is the bias voltage. V off1 f may be zero. d1 is the drive frequency (hereinafter referred to as the "first drive frequency"); t is time; α is the drive voltage waveform V 1A (t) and V 1B In this embodiment, for example, α=180°.

[0057] Drive voltage waveform V 1A (t) and V 1B When the first actuator 31 is applied with the first drive frequency f d1 It oscillates around the first axis a1.

[0058] Drive voltage waveform V 2A (t) and V 2B (t) is expressed as follows, respectively: V 2A (t)=V off2 +V2sin(2πf d2 t+φ) V 2B (t)=V off2 +V2sin(2πf d2 t+β+φ)

[0059] where V2 is the amplitude voltage. V off2 is the bias voltage. V off2 f may be zero. d2 is the drive frequency (hereinafter referred to as the "second drive frequency"); t is time; β is the drive voltage waveform V 2A (t) and V2B In this embodiment, for example, β=180°. Also, φ is the phase difference of the driving voltage waveform V 1A (t) and V 1B (t) and the driving voltage waveform V 2A (t) and V 2B (t) is the phase difference.

[0060] Drive voltage waveform V 2A (t) and V 2B When the second actuator 32 is applied with the second drive frequency f d2 It oscillates around the second axis a2.

[0061] First drive frequency f d1 is set to coincide with the resonance frequency of the mirror portion 20 about the first axis a1. d2 is set to coincide with the resonance frequency around the second axis a2 of the mirror portion 20. In this embodiment, f d1 >f d2 That is, the mirror section 20 has a higher oscillation frequency around the first axis a1 than around the second axis a2. d1 and the second driving frequency f d2 does not necessarily have to coincide with the resonant frequency. For example, the first driving frequency f d1 and the second driving frequency f d2 and may be frequencies within a frequency range near the resonant frequency (for example, a half-width range of a frequency distribution having a peak value at the resonant frequency). This frequency range is, for example, within the range of a so-called Q value.

[0062] Next, the functional configuration of the drive control unit 5 will be described with reference to Fig. 5. As shown in Fig. 5, the drive control unit 5 has a first drive signal generation unit 60A, a second drive signal generation unit 60B, a first signal processing unit 61A, a second signal processing unit 61B, a first phase shift unit 62A, a second phase shift unit 62B, a first derivation unit 63A, a second derivation unit 63B, a third derivation unit 64, a first zero cross pulse output unit 65A, a second zero cross pulse output unit 65B, and a light source drive unit 66.

[0063] The first drive signal generating section 60A, the first signal processing section 61A, and the first phase shifting section 62A may perform feedback control so that the oscillation of the mirror section 20 about the first axis a1 maintains a vibration state of a designated frequency. The second drive signal generating section 60B, the second signal processing section 61B, and the second phase shifting section 62B may perform feedback control so that the oscillation of the mirror section 20 about the second axis a2 maintains a vibration state of a designated frequency.

[0064] The first drive signal generating section 60A generates the above-mentioned drive voltage waveform V 1A (t) and V 1B A first drive signal including (t) is generated, and the generated first drive signal is applied to the pair of first actuators 31 via the first phase shift section 62A. This causes the mirror section 20 to oscillate around the first axis a1.

[0065] The second drive signal generating section 60B generates the above-mentioned drive voltage waveform V 2A (t) and V 2B A second drive signal including (t) is generated, and the generated second drive signal is applied to the pair of second actuators 32 via the second phase shift section 62B. This causes the mirror section 20 to oscillate around the second axis a2.

[0066] The first drive signal generated by the first drive signal generating section 60A and the second drive signal generated by the second drive signal generating section 60B have a drive voltage waveform V 2A (t) and V 2B In the equation for (t), the phase is synchronized as indicated by φ.

[0067] The first angle detection sensors 11A and 11B output signals corresponding to the angle of the mirror section 20 about the first axis a1. The second angle detection sensors 12A and 12B output signals corresponding to the angle of the mirror section 20 about the second axis a2.

[0068] Fig. 6 shows an example of signals output from the pair of first angle detection sensors 11A and 11B. In Fig. 6, S1a1 and S1a2 represent signals output from the pair of first angle detection sensors 11A and 11B when the mirror unit 20 is not swung around the second axis a2 but is swung only around the first axis a1. The signals S1a1 and S1a2 are generated at a first drive frequency f d1 These are waveform signals that approximate sine waves having the same phase as each other.

[0069] When the mirror unit 20 is swung simultaneously around the first axis a1 and the second axis a2, vibration noise RN1 caused by the swinging of the mirror unit 20 around the second axis a2 is superimposed on the output signals of the pair of first angle detection sensors 11A, 11B. S1b1 represents a signal in which the vibration noise RN1 is superimposed on the signal S1a1. S1b2 represents a signal in which the vibration noise RN1 is superimposed on the signal S1a2. In the example of FIG. 6, the vibration noise RN1 is emphasized for the purpose of explaining this embodiment.

[0070] Fig. 7 shows an example of signals output from the pair of second angle detection sensors 12A and 12B. In Fig. 7, S2a1 and S2a2 represent signals output from the pair of second angle detection sensors 12A and 12B when the mirror unit 20 is not swung around the first axis a1 but is swung only around the second axis a2. The signals S2a1 and S2a2 are generated at a second drive frequency f d2 These are waveform signals that approximate sine waves having the same phase as each other.

[0071] When the mirror unit 20 is swung simultaneously around the first axis a1 and the second axis a2, vibration noise RN2 caused by the swinging of the mirror unit 20 around the first axis a1 is superimposed on the output signals of the pair of second angle detection sensors 12A, 12B. S2b1 represents a signal in which the vibration noise RN2 is superimposed on the signal S2a1. S2b2 represents a signal in which the vibration noise RN2 is superimposed on the signal S2a2. In the example of FIG. 7, the vibration noise RN2 is emphasized for the purpose of explaining this embodiment.

[0072] The first signal processing unit 61A generates a signal (hereinafter referred to as a "first angle detection signal") S1c from which the vibration noise RN1 has been removed, based on S1a1 and S1a2 output from the pair of first angle detection sensors 11A and 11B. The second signal processing unit 61B generates a signal (hereinafter referred to as a "second angle detection signal") S2c from which the vibration noise RN2 has been removed, based on S2a1 and S2a2 output from the pair of second angle detection sensors 12A and 12B.

[0073] The first signal processing unit 61A can be realized, for example, by a circuit having a configuration shown in Fig. 8. As shown in Fig. 8, the first signal processing unit 61A is composed 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 is composed of a first BPF (Band Pass Filter) circuit 75A, a second BPF circuit 75B, a first detection circuit 76A, a second detection circuit 76B, and a subtraction circuit 77. The subtraction circuit 73 and the subtraction circuit 77 are differential amplifier circuits composed of operational amplifiers.

[0074] The signal S1b1 output from the first angle detection sensor 11A is input to a positive input terminal (non-inverting input terminal) of a subtraction circuit 73 via a buffer amplifier 71. The signal output from the buffer amplifier 71 is branched on the way to be input to the subtraction circuit 73, and is input to a first BPF circuit 75A in a gain adjustment circuit 74.

[0075] The signal S1b2 output from the first angle detection sensor 11B is input to a negative input terminal (inverting input terminal) of a subtraction circuit 73 via a variable gain amplifier 72. The signal output from the variable gain amplifier 72 is branched on the way to be input to the subtraction circuit 73, and is input to a second BPF circuit 75B in a gain adjustment circuit 74.

[0076] The first BPF circuit 75A and the second BPF circuit 75B each have a second driving frequency f d2 The passband B1 has a center frequency of, for example, f d2The vibration noise RN1 is in the frequency band of ±5 kHz. d2 , the signal passes through the passband B1. Therefore, the first BPF circuit 75A extracts and outputs the vibration noise RN1 from the signal input from the buffer amplifier 71. The second BPF circuit 75B extracts and outputs the vibration noise RN1 from the signal input from the variable gain amplifier 72.

[0077] The first detection circuit 76A and the second detection circuit 76B are each formed of, for example, an RMS-DC converter (Root Mean Squared 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.

[0078] The subtraction circuit 77 outputs a value d1 obtained by subtracting the DC voltage signal input from the second detection circuit 76B from the DC voltage signal input from the first detection circuit 76A. The value d1 corresponds to the difference between the amplitude of the vibration noise RN1 included in the signal S1b1 output from the first angle detection sensor 11A and the amplitude of the vibration noise RN1 included in the signal S1b2 output from the first angle detection sensor 11B. The subtraction circuit 77 inputs the value d1 to a gain adjustment terminal of the variable gain amplifier 72 as a gain adjustment value.

[0079] The variable gain amplifier 72 adjusts the amplitude level of the signal S1b2 input from the first angle detection sensor 11B by multiplying the signal S1b2 input from the first angle detection sensor 11B by the value d1 input as a gain adjustment value. In this manner, feedback control is performed by the gain adjustment circuit 74, so that the amplitude of the vibration noise RN1 contained in the signal S1b2 after passing through the variable gain amplifier 72 is adjusted to match the amplitude of the vibration noise RN1 contained in the signal S1b1 after passing through the buffer amplifier 71.

[0080] The subtraction circuit 73 outputs a value obtained by subtracting the signal S1b2 input to the negative input terminal from the signal S1b1 input to the positive input terminal. Because the amplitudes of the vibration noise RN1 contained in both signals match due to the above feedback control, the vibration noise RN1 contained in both signals is cancelled out by the subtraction process by the subtraction circuit 73. Therefore, the subtraction circuit 73 outputs a first angle detection signal S1c (see FIG. 9), which is a signal from which the vibration noise RN1 has been removed.

[0081] 9 shows how the first angle detection signal S1c is generated based on the outputs S1b1 and S1b2 from the pair of first angle detection sensors 11A and 11B. The first angle detection signal S1c corresponds to a signal obtained by removing the vibration noise RN1 from the signal S1b1 and doubling its amplitude.

[0082] When the oscillation of the mirror section 20 around the first axis a1 is maintained in a resonant state, as shown in FIG. 9, the first angle detection signal S1c output from the first signal processing section 61A has a driving voltage waveform V 1A There is a phase lag of 90° relative to (t).

[0083] The second signal processing unit 61B can be realized by a configuration similar to that of the first signal processing unit 61A, and therefore a description thereof will be omitted.

[0084] 10 shows how the second angle detection signal S2c is generated based on the outputs S2b1 and S2b2 from the pair of second angle detection sensors 12A and 12B. The second angle detection signal S2c corresponds to a signal obtained by removing the vibration noise RN2 from the signal S2b1 and doubling its amplitude.

[0085] When the oscillation of the mirror section 20 around the second axis a2 is maintained in a resonant state, as shown in FIG. 10, the second angle detection signal S2c output from the second signal processing section 61B has a driving voltage waveform V 2A There is a phase lag of 90° relative to (t).

[0086] The first angle detection signal S1c generated by the first signal processing unit 61A is fed back to the first drive signal generating unit 60A. The first phase shifting unit 62A shifts the phase of the drive voltage waveform output from the first drive signal generating unit 60A. The first phase shifting unit 62A shifts the phase by, for example, 90°.

[0087] The second angle detection signal S2c generated by the second signal processing unit 61B is fed back to the second drive signal generating unit 60B. The second phase shifting unit 62B shifts the phase of the drive voltage waveform output from the second drive signal generating unit 60B. The second phase shifting unit 62B shifts the phase by, for example, 90°.

[0088] The first angle detection signal S1c generated by the first signal processing unit 61A is ideally a sine wave, but in many cases it is not a smooth sine wave. This is because the processing by the first signal processing unit 61A cannot completely remove the effects of the oscillation of the mirror unit 20 around the second axis a2. In this case, as shown in FIG. 11 as an example, the timing at which the first angle detection signal S1c crosses zero shifts slightly depending on the period. FIG. 11 shows an example in which waveforms of the timing at which the first angle detection signal S1c crosses zero for multiple periods are superimposed.

[0089] Therefore, the first derivation unit 63A reduces the influence of the deviation for each period by averaging the first angle detection signal S1c for a plurality of periods. The process by the first derivation unit 63A will be described below.

[0090] The first derivation unit 63A derives the first average phase delay time by averaging the phase delay time of the first angle detection signal S1c relative to the first drive signal over the most recent multiple cycles (hereinafter referred to as the "first phase delay time"). Specifically, as shown in FIG. 12 as an example, the first derivation unit 63A derives the first average phase delay time by averaging the first phase delay time t1 from the point in time when the first drive signal in the corresponding cycle is zero to the point in time when the first angle detection signal S1c is zero for the most recent multiple cycles of the first drive signal and the first angle detection signal S1c. In this embodiment, the first drive signal is a bias voltage Voff1 Therefore, the point when the first drive signal is zero is when the first drive signal is V off1 It means a point in time.

[0091] Similarly, the second angle detection signal S2c generated by the second signal processing unit 61B is also ideally a sine wave, but since the influence of the oscillation of the mirror unit 20 about the first axis a1 remains, it is often not a smooth sine wave. Therefore, the second derivation unit 63B reduces the influence of the above-mentioned deviation for each period by averaging the second angle detection signal S2c for multiple periods. The processing by the second derivation unit 63B will be described below.

[0092] The second derivation unit 63B derives the second average phase delay time by averaging the phase delay time of the second angle detection signal S2c relative to the second drive signal over the most recent multiple cycles (hereinafter referred to as the "second phase delay time"). Specifically, as shown in FIG. 13 as an example, the second derivation unit 63B derives the second average phase delay time by averaging the second phase delay time t2 from the point in time when the second drive signal in the corresponding cycle is zero to the point in time when the second angle detection signal S2c is zero for the most recent multiple cycles of the second drive signal and the second angle detection signal S2c. In this embodiment, the second drive signal is a bias voltage V off2 Therefore, the point when the second drive signal is zero is when the second drive signal is V off2 It means a point in time.

[0093] In the above processing by the first derivation unit 63A and the second derivation unit 63B, the time point at which the sine wave becomes zero from negative to positive is used, but is not limited to this. For example, the time point at which the sine wave becomes zero from positive to negative may be used, or both the time point at which the sine wave becomes zero from negative to positive and the time point at which the sine wave becomes zero from positive to negative may be used.

[0094] The above-described processing by the first derivation unit 63A and the second derivation unit 63B can reduce the influence of the difference in the timing at which the first angle detection signal S1c and the second angle detection signal S2c cross zero from one period to the next. However, a time lag t31 (hereinafter referred to as the "first time lag t31") may occur between the timing at which the first angle detection signal S1c becomes zero and the timing at which the first deflection angle θ1 actually becomes zero. Similarly, a time lag t32 (hereinafter referred to as the "second time lag t32") may occur between the timing at which the second angle detection signal S2c becomes zero and the timing at which the second deflection angle θ2 actually becomes zero.

[0095] Fig. 14 shows an example of the relationship between the first average phase delay time and the first delay time t31, and Fig. 15 shows an example of the relationship between the second average phase delay time and the second delay time t32. As shown in Fig. 14, as the first average phase delay time becomes longer, the first delay time t31 becomes longer. As shown in Fig. 15, as the second average phase delay time becomes longer, the second delay time t32 becomes shorter.

[0096] Therefore, the third derivation unit 64 derives the first delay time t31 and the second delay time t32 as delay times according to a preset condition. In this embodiment, an example in which the first average phase delay time and the second average phase delay time are applied as the conditions will be described. Note that, instead of the first average phase delay time, for example, the first phase delay time of the most recent period may be used. Also, instead of the second average phase delay time, for example, the second phase delay time of the most recent period may be used.

[0097] Specifically, the third derivation unit 64 calculates the first average phase delay time t1 according to the following function f1: avg A first deviation time t31 corresponding to the above is derived. t31=f1(t1 avg ) The third derivation unit 64 uses the first average phase delay time t1 instead of the function f1. avg The first average phase delay time t1 is calculated by using a lookup table in which the first average phase delay time t1 and the first deviation time t31 are associated with each other. avgA first deviation time t31 may be derived according to the above.

[0098] Moreover, the third derivation unit 64 calculates the second average phase delay time t2 according to the following function f2: avg A second delay time t32 corresponding to the above is derived. t32 = f2(t2 avg ) In addition, the third derivation unit 64 uses the second average phase delay time t2 instead of the function f2. avg The second average phase delay time t2 is calculated using a lookup table in which the second average phase delay time t32 is associated with the second average phase delay time t2 avg A second delay time t32 may be derived according to the above.

[0099] The function f1 is a function obtained by approximating the relationship between the first average phase delay time obtained by calibration and the first delay time t31. The function f2 is a function obtained by approximating the relationship between the second average phase delay time obtained by calibration and the second delay time t32. The calibration will be described later in detail.

[0100] The first zero-cross pulse output unit 65A generates a reference signal (hereinafter referred to as the "first reference signal") based on the first drive signal, the first average phase delay time derived by the first derivation unit 63A, and the first offset time t31 derived by the third derivation unit 64. The first reference signal is a signal indicating that the angle of the mirror unit 20 around the first axis a1 has become a reference angle. In this embodiment, an example in which zero is applied as this reference angle will be described. That is, the first zero-cross pulse output unit 65A generates a zero-cross pulse (hereinafter referred to as the "first zero-cross pulse") ZC1 as an example of the first reference signal based on the first drive signal, the first average phase delay time derived by the first derivation unit 63A, and the first offset time t31 derived by the third derivation unit 64. The first zero-cross pulse output unit 65A is configured by a zero-cross detection circuit. The first zero-cross pulse is a zero-cross signal indicating that the angle of the mirror unit 20 around the first axis a1 has become zero.

[0101] As shown in FIG. 16, the first zero-cross pulse output section 65A outputs a pulse when the first drive signal is zero (V off1 The first zero-cross pulse output unit 65A generates a first zero-cross pulse ZC1 at a timing when a time equal to the sum of the first average phase delay time and the first shift time t31 has elapsed from the timing when the light crosses the light-source polarity t1. The first zero-cross pulse output unit 65A outputs the generated first zero-cross pulse ZC1 to the light source driving unit 66.

[0102] The second zero-cross pulse output unit 65B generates a reference signal (hereinafter referred to as the "second reference signal") based on the second drive signal, the second average phase delay time derived by the second derivation unit 63B, and the second shift time t32 derived by the third derivation unit 64. The second reference signal is a signal indicating that the angle of the mirror unit 20 around the second axis a2 has become a reference angle. In this embodiment, an example in which zero is applied as this reference angle will be described. That is, the second zero-cross pulse output unit 65B generates a zero-cross pulse (hereinafter referred to as the "second zero-cross pulse") ZC2 as an example of the second reference signal based on the second drive signal, the second average phase delay time derived by the second derivation unit 63B, and the second shift time t32 derived by the third derivation unit 64. The second zero-cross pulse output unit 65B is configured by a zero-cross detection circuit. The second zero-cross pulse is a zero-cross signal indicating that the angle of the mirror unit 20 around the second axis a2 has become zero.

[0103] As shown in FIG. 17, the second zero-cross pulse output section 65B outputs a zero-cross pulse when the second drive signal is zero (V off2 The second zero-cross pulse output unit 65B generates a second zero-cross pulse ZC2 at a timing when a time equal to the second average phase delay time plus the second shift time t32 has elapsed from the timing when the light source crosses the light-source polarity reference line 101. The second zero-cross pulse output unit 65B outputs the generated second zero-cross pulse ZC2 to the light source driving unit 66.

[0104] Although the first zero-cross pulse output section 65A and the second zero-cross pulse output section 65B output zero-cross pulses using both the time when the sine wave becomes zero from negative to positive and the time when the sine wave becomes zero from positive to negative, the present invention is not limited to this. For example, the first zero-cross pulse output section 65A and the second zero-cross pulse output section 65B may output zero-cross pulses using either the time when the sine wave becomes zero from negative to positive and the time when the sine wave becomes zero from positive to negative.

[0105] The light source driving unit 66 drives the light source 3 based on, for example, drawing data supplied from outside the image drawing system 10. In addition, the light source driving unit 66 controls the irradiation timing of the laser light from the light source 3 so that the irradiation timing is synchronized with the first zero cross pulse ZC1 and the second zero cross pulse ZC2.

[0106] Next, the flow of the first delay time derivation process will be described with reference to Fig. 18. For example, the process is executed at a predetermined time interval while the image is being drawn by the image drawing system 10. This time interval may be, for example, a time interval corresponding to one period of the first drive signal, a time interval corresponding to multiple periods, or a time interval set in advance regardless of the period.

[0107] 18, the first derivation unit 63A acquires, for each period, a first phase delay time from a point in time when the first drive signal in the corresponding period is zero to a point in time when the first angle detection signal S1c is zero. In step S12, the first derivation unit 63A derives a first average phase delay time by averaging the first phase delay times of the most recent multiple periods acquired in step S10.

[0108] In step S14, the third derivation unit 64 derives the first delay time t31 according to the first average phase delay time derived in step S12, in accordance with the above-mentioned function f1. When the process of step S14 ends, the first delay time derivation process ends. The first average phase delay time and the first delay time t31 are updated by periodically executing the first delay time derivation process while the image is being drawn.

[0109] Next, the flow of the second delay time derivation process will be described with reference to Fig. 19. For example, the process is executed at a predetermined time interval while the image is being drawn by the image drawing system 10. This time interval may be, for example, a time interval corresponding to one period of the second drive signal, a time interval corresponding to multiple periods, or a time interval set in advance regardless of the period.

[0110] 19, the second derivation unit 63B acquires, for each period, a second phase delay time from a point in time when the second drive signal in the corresponding period is zero to a point in time when the second angle detection signal S2c is zero. In step S22, the second derivation unit 63B derives a second average phase delay time by averaging the second phase delay times of the most recent multiple periods acquired in step S20.

[0111] In step S24, the third derivation unit 64 derives the second delay time t32 according to the second average phase delay time derived in step S22, in accordance with the above-mentioned function f2. When the process of step S24 ends, the second delay time derivation process ends. By periodically executing the second delay time derivation process while the image is being drawn, the second average phase delay time and the second delay time t32 are updated.

[0112] Next, the flow of the first zero cross pulse generation process will be described with reference to Fig. 20. For example, while the image drawing system 10 is drawing an image, the first zero cross pulse generation process shown in Fig. 20 is executed.

[0113] In step S30 of Fig. 20, the first zero cross pulse output section 65A judges whether or not the first drive signal is zero. If this judgment is an affirmative judgment, the process proceeds to step S32, and if this judgment is a negative judgment, step S30 is executed again.

[0114] In step S32, the first zero cross pulse output section 65A waits until a time equal to the sum of the first average phase delay time and the first delay time t31 derived by the first delay time derivation process has elapsed from the time when the first drive signal became zero in step S30. When the time equal to the sum of the first average phase delay time and the first delay time t31 has elapsed from the time when the first drive signal became zero in step S30, the determination in step S32 becomes positive, and the process proceeds to step S34.

[0115] In step S34, the first zero cross pulse output unit 65A generates the first zero cross pulse ZC1 and outputs the generated first zero cross pulse ZC1 to the light source driving unit 66. When the process of step S34 ends, the process returns to step S30. When the image drawing process by the image drawing system 10 ends, the first zero cross pulse generation process ends.

[0116] Next, the flow of the second zero cross pulse generation process will be described with reference to Fig. 21. For example, while the image drawing system 10 is drawing an image, the second zero cross pulse generation process shown in Fig. 21 is executed.

[0117] 21, the second zero-cross pulse output section 65B determines whether or not the second drive signal is zero. If this determination is positive, the process proceeds to step S42, and if this determination is negative, step S40 is executed again.

[0118] In step S42, the second zero cross pulse output section 65B waits until the time equal to the sum of the second average phase delay time derived by the second delay time derivation process and the second delay time t32 has elapsed from the time when the second drive signal became zero in step S40. When the time equal to the sum of the second average phase delay time and the second delay time t32 has elapsed from the time when the second drive signal became zero in step S40, the determination in step S42 becomes positive, and the process proceeds to step S44.

[0119] In step S44, the second zero cross pulse output unit 65B generates the second zero cross pulse ZC2 and outputs the generated second zero cross pulse ZC2 to the light source driving unit 66. When the process of step S44 ends, the process returns to step S40. When the image drawing process by the image drawing system 10 ends, the second zero cross pulse generation process ends.

[0120] Next, a process for obtaining the above-mentioned functions f1 and f2 by calibration will be described. FIG. 22 is a schematic plan view of the image drawing system 10 during calibration. As shown in FIG. 22, during calibration, the image drawing system 10 further includes an imaging device 7. The imaging device 7 is provided at a position where it can image the surface 6 to be scanned. The imaging device 7 images the surface 6 to be scanned at a preset frame rate, and outputs image data obtained by imaging to the drive control unit 5. The frame rate of the imaging device 7 is set to, for example, the same frame rate as the frame rate when the image drawing system 10 draws an image. An example of the imaging device 7 is a digital camera.

[0121] The optical scanning device 2 according to this embodiment has a delay time derivation mode for deriving a first delay time t31 and a second delay time t32. By executing the delay time derivation mode during calibration, a first calibration process shown in FIG. 23 and a second calibration process shown in FIG. 26 are executed. Examples of the timing for executing the calibration include the timing of starting up the optical scanning device 2 and the timing when a user inputs an instruction to execute the calibration. The calibration may also be executed before the optical scanning device 2 is shipped from the factory. In this case, data obtained by the calibration is stored in, for example, a non-volatile storage unit provided in the drive control unit 5. In this case, the image drawing system 10 may not include the imaging device 7 at the user's base to which the optical scanning device 2 is shipped.

[0122] 23, as described above, the first drive signal generation unit 60A generates a first drive signal and applies the generated first drive signal to the pair of first actuators 31 via the first phase shift unit 62A. That is, in the first calibration process, the mirror unit 20 is swung only around the first axis a1 without swung around the second axis a2.

[0123] In step S52, the first derivation unit 63A acquires, for each period, a first phase delay time from the time when the first drive signal in the corresponding period is zero to the time when the first angle detection signal S1c is zero. In step S54, the first derivation unit 63A derives a first average phase delay time by averaging the first phase delay times of the most recent multiple periods acquired in step S52.

[0124] In step S56, the first zero cross pulse output section 65A generates a first zero cross pulse ZC1 at a timing when a time equal to the first average phase delay time plus the first offset time t31 has elapsed since the timing when the first drive signal crosses zero. The first zero cross pulse output section 65A outputs the generated first zero cross pulse ZC1 to the light source drive section 66. In the first calibration process, the light source drive section 66 causes the light source 3 to irradiate laser light in synchronization with the first zero cross pulse ZC1. The first offset time t31 at this time is a time set as a temporary value.

[0125] The above-mentioned processes from step S50 to step S56 are executed multiple times while changing the first drive frequency and the first delay time t31. When the first drive frequency is changed, the first average phase delay time also has a different value. That is, based on each of the multiple combinations of the first average phase delay time and the first delay time t31, the first zero cross pulse ZC1 is output from the first zero cross pulse output section 65A, and the laser light is irradiated from the light source 3.

[0126] In step S58, the third derivation unit 64 acquires image data captured by the imaging device 7. The drive control unit 5 and the imaging device 7 are time-synchronized. Therefore, based on the time information added to the image data, the third derivation unit 64 can identify which image data is image data when the laser light is irradiated based on which combination of the first average phase delay time and the first shift time t31.

[0127] When the first delay time t31 set as a provisional value for the first average phase delay time is different from the actual first delay time t31, an image represented by image data corresponding to the combination of the first average phase delay time and the first delay time t31 is as shown in Fig. 24 as an example. A bright spot P1 shown in Fig. 24 indicates a bright spot drawn on the scanned surface 6 by reflecting the laser light irradiated from the light source 3 based on the first zero cross pulse ZC1 based on the time point when the first drive signal becomes zero from negative to positive, by the mirror unit 20 of the MMD 4. A bright spot P2 shown in Fig. 24 indicates a bright spot drawn on the scanned surface 6 by reflecting the laser light irradiated from the light source 3 based on the first zero cross pulse ZC1 based on the time point when the first drive signal becomes zero from positive to negative, by the mirror unit 20 of the MMD 4.

[0128] That is, in this case, in the image represented by the image data, the bright spot P1 and the bright spot P2 are shifted on the axis corresponding to the second axis a2. In contrast, when the first delay time t31 set as a provisional value for the first average phase delay time coincides with the actual first delay time t31, the image represented by the image data corresponding to the combination of the first average phase delay time and the first delay time t31 is as shown in FIG. 25 as an example. That is, in this case, the bright spot P1 and the bright spot P2 overlap.

[0129] Therefore, in step S60, the third derivation unit 64 identifies a combination of the first average phase delay time and the first delay time t31 when image data in which the bright spot P1 and the bright spot P2 overlap is captured as a correct combination. Since a plurality of such correct combinations are obtained, the relationship between the first average phase delay time and the first delay time t31 shown in FIG. 14 is obtained as an example. The third derivation unit 64 derives a function f1 by approximating the obtained relationship between the first average phase delay time and the first delay time t31. This function f1 is used in step S14 of the first delay time derivation process (see FIG. 18) described above. The third derivation unit 64 may store the obtained relationship between the first average phase delay time and the first delay time t31 as a lookup table. When the process of step S60 ends, the first calibration process ends.

[0130] 26, as described above, the second drive signal generation unit 60B generates the second drive signal and applies the generated second drive signal to the pair of second actuators 32 via the second phase shift unit 62B. That is, in the second calibration process, the mirror unit 20 is not swung around the first axis a1, but is swung only around the second axis a2.

[0131] In step S72, the second derivation unit 63B acquires, for each period, a second phase delay time from the time when the second drive signal in the corresponding period is zero to the time when the second angle detection signal S2c is zero. In step S74, the second derivation unit 63B derives a second average phase delay time by averaging the second phase delay times of the most recent multiple periods acquired in step S72.

[0132] In step S76, the second zero cross pulse output section 65B generates a second zero cross pulse ZC2 at a timing when a time equal to the second average phase delay time plus the second delay time t32 has elapsed since the timing when the second drive signal crosses zero. The second zero cross pulse output section 65B outputs the generated second zero cross pulse ZC2 to the light source drive section 66. In the second calibration process, the light source drive section 66 causes the light source 3 to irradiate laser light in synchronization with the second zero cross pulse ZC2. The second delay time t32 at this time is a time set as a temporary value.

[0133] The above-mentioned processes from step S70 to step S76 are executed multiple times while changing the second driving frequency and the second delay time t32. When the second driving frequency is changed, the second average phase delay time also has a different value. That is, based on each of the multiple combinations of the second average phase delay time and the second delay time t32, the second zero cross pulse ZC2 is output from the second zero cross pulse output section 65B, and the laser light is irradiated from the light source 3.

[0134] In step S78, the third derivation unit 64 acquires image data captured by the imaging device 7. The drive control unit 5 and the imaging device 7 are time-synchronized. Therefore, based on the time information added to the image data, the third derivation unit 64 can identify which image data is image data when the laser light is irradiated based on which combination of the second average phase delay time and the second deviation time t32.

[0135] When the second delay time t32 set as a provisional value for the second average phase delay time is different from the actual second delay time t32, an image represented by image data corresponding to the combination of the second average phase delay time and the second delay time t32 is as shown in Fig. 27 as an example. A bright spot P3 shown in Fig. 27 indicates a bright spot drawn on the scanned surface 6 by reflecting the laser light irradiated from the light source 3 based on the second zero cross pulse ZC2 based on the time point when the second drive signal becomes zero from negative to positive, by the mirror unit 20 of the MMD4. A bright spot P4 shown in Fig. 27 indicates a bright spot drawn on the scanned surface 6 by reflecting the laser light irradiated from the light source 3 based on the second zero cross pulse ZC2 based on the time point when the second drive signal becomes zero from positive to negative, by the mirror unit 20 of the MMD4.

[0136] That is, in this case, in the image represented by the image data, the bright spot P3 and the bright spot P4 are shifted on the axis corresponding to the first axis a1. In contrast, when the second delay time t32 set as a provisional value for the second average phase delay time coincides with the actual second delay time t32, the image represented by the image data corresponding to the combination of the second average phase delay time and the second delay time t32 is as shown in FIG. 28, for example. That is, in this case, the bright spot P3 and the bright spot P4 overlap.

[0137] Therefore, in step S80, the third derivation unit 64 identifies a combination of the second average phase delay time and the second delay time t32 when image data in which the bright spot P3 and the bright spot P4 overlap is captured as a correct combination. Since a plurality of such correct combinations are obtained, the relationship between the second average phase delay time and the second delay time t32 shown in FIG. 15 is obtained as an example. The third derivation unit 64 derives a function f2 by approximating the obtained relationship between the second average phase delay time and the second delay time t32. This function f2 is used in step S24 of the above-mentioned second delay time derivation process (see FIG. 19). The third derivation unit 64 may store the obtained relationship between the second average phase delay time and the second delay time t32 as a lookup table. When the process of step S70 is completed, the second calibration process is completed.

[0138] As described above, according to this embodiment, the difference in output timing between the first zero cross pulse ZC1 and the second zero cross pulse ZC2 per period can be reduced, thereby suppressing deterioration in the image quality of the drawn image.

[0139] The configuration of the MMD 4 shown in the above embodiment is just an example. Various modifications are possible to the configuration of the MMD 4. For example, a first actuator 31 that swings the mirror section 20 around the first axis a1 may be disposed on the second movable frame 24, and a second actuator 32 that swings the mirror section 20 around the second axis a2 may be disposed on the first movable frame 22.

[0140] In the above embodiment, the pair of first angle detection sensors 11A and 11B are arranged at positions facing each other across the first axis a1, but the present invention is not limited to this. For example, as shown in FIG. 29, the pair of first angle detection sensors 11A and 11B may be arranged at positions facing each other across the second axis a2. In the example of FIG. 29, the pair of first angle detection sensors 11A and 11B are arranged near the first support portion 21 on the first movable frame 22. The first angle detection sensor 11A is arranged near the first support portion 21 connected to one side of the mirror portion 20. The first angle detection sensor 11B is arranged near the first support portion 21 connected to the other side of the mirror portion 20. Therefore, the pair of first angle detection sensors 11A and 11B are arranged at positions facing each other across the second axis a2 and across the mirror portion 20. Further, the pair of first angle detection sensors 11A, 11B are disposed at positions shifted in the same direction (the -X direction in the example of FIG. 29) from the first axis a1.

[0141] When the pair of first angle detection sensors 11A, 11B are disposed at positions facing each other across the first axis a1 as in the above embodiment, the vibration noise can be eliminated by subtracting one of the output signals from the other. On the other hand, when the pair of first angle detection sensors 11A, 11B are disposed at positions facing each other across the second axis a2 as in this embodiment, the vibration noise can be eliminated by adding up the output signals of the two.

[0142] An example of the configuration of the first signal processing unit 61A in this embodiment is shown in Fig. 30. As shown in Fig. 30, in this embodiment, the first signal processing unit 61A has an adder circuit 73A instead of the subtractor circuit 73. The adder circuit 73A outputs a value obtained by adding a signal S1b1 input from the first angle detection sensor 11A via the buffer amplifier 71 and a signal S1b2 input from the first angle detection sensor 11B via the variable gain amplifier 72.

[0143] In the above embodiment, the pair of second angle detection sensors 12A and 12B are arranged at positions facing each other across the second axis a2, but the present invention is not limited to this. For example, as shown in FIG. 29, the pair of second angle detection sensors 12A and 12B may be arranged at positions facing each other across the first axis a1. In the example of FIG. 29, the pair of second angle detection sensors 12A and 12B are arranged near the second support portion 23 on the second movable frame 24. The second angle detection sensor 12A is arranged near the second support portion 23 connected to one side of the first movable frame 22. The second angle detection sensor 12B is arranged 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 arranged at positions facing each other across the first axis a1 and across the mirror portion 20 and the first movable frame 22. Further, the pair of second angle detection sensors 12A, 12B are disposed at positions shifted in the same direction (the +Y direction in the example of FIG. 29) from the second axis a2.

[0144] In the case where the pair of second angle detection sensors 12A, 12B are arranged at positions facing each other across the second axis a2 as in the above embodiment, the vibration noise can be removed by subtracting one of the output signals from the other. In contrast, in the case where the pair of second angle detection sensors 12A, 12B are arranged at positions facing each other across the first axis a1 as in this embodiment, the vibration noise can be removed by adding the output signals of the two. The configuration of the second signal processing unit 61B in this embodiment can be realized by the same configuration as the first signal processing unit 61A shown in FIG. 30, so the description will be omitted.

[0145] In the above embodiment, any one of the pair of first angle detection sensors 11A, 11B may be provided on the MMD 4. Similarly, any one of the pair of second angle detection sensors 12A, 12B may be provided on the MMD 4.

[0146] In the above embodiment, the first average phase delay time and the second average phase delay time are derived when an image is drawn, but the present invention is not limited to this. The first average phase delay time and the second average phase delay time may be acquired by executing an average phase delay time derivation mode for deriving the first average phase delay time and the second average phase delay time during calibration. In this case, when the first zero cross pulse ZC1 and the second zero cross pulse ZC2 are generated, the first average phase delay time and the second average phase delay time acquired in advance during calibration are used. In this case, the timing of execution of the calibration may be, for example, when the MMD4 is started up or when an instruction to execute the calibration is input by the user.

[0147] In the above embodiment, the third derivation unit 64 derives the first delay time t31 according to the first average phase delay time according to the function f1, but the present invention is not limited to this. FIG. 31 shows an example of the relationship between the first drive frequency and the first delay time t31. FIG. 31 shows the relationship between the first drive frequency and the first delay time t31 when the mirror unit 20 is swung around the first axis a1 so as to obtain two different first deflection angles θ1. The solid line in FIG. 31 shows the relationship between the first drive frequency and the first delay time t31 when the mirror unit 20 is swung around the first axis a1 at an angle where the first deflection angle θ1 is larger than that shown by the broken line. As shown in FIG. 31, the higher the first drive frequency, the longer the first delay time t31. FIG. 31 shows the relationship between the first drive frequency and the first delay time t31, but the first delay time t31 changes depending on not only the first drive frequency but also the drive voltage of the first drive signal. The drive voltage of the first drive signal corresponds to, for example, the amplitude of the first drive signal.

[0148] Therefore, the third derivation section 64 may further derive a first delay time t31 according to the first drive frequency F1 and the drive voltage V1 of the first drive signal, according to the following function f3. t31=f3(t1 avg , F1, V1) Similarly, the third derivation section 64 may further derive a second delay time t32 according to the second drive frequency F2 and the drive voltage V2 of the second drive signal, according to the following function f4. t32=f4(t2 avg , F2, V2)

[0149] Furthermore, the third derivation unit 64 may further derive a first delay time t31 and a second delay time t32 according to the environmental temperature T, in accordance with the following functions f5 and f6. In this case, the MMD 4 is provided with a temperature sensor that measures the environmental temperature. t31=f5(t1 avg , T) t32=f6(t2 avg , T)

[0150] Furthermore, the third derivation section 64 may further derive a first delay time t31 according to the first drive frequency F1, the drive voltage V1 of the first drive signal, and the environmental temperature T, in accordance with the following function f7. t31=f7(t1 avg , F1, V1, T) Similarly, the third derivation section 64 may further derive a second delay time t32 according to the second drive frequency F2, the drive voltage V2 of the second drive signal, and the environmental temperature T, in accordance with the following function f8. t32=f8(t2 avg , F2, V2, T) In the above functions f3 and f7, only one of the first drive frequency F1 and the drive voltage V1 of the first drive signal may be used. In the above functions f4 and f8, only one of the second drive frequency F2 and the drive voltage V2 of the second drive signal may be used.

[0151] Moreover, the hardware configuration of the drive control unit 5 can be modified in various ways. The drive control unit 5 can be configured using at least one of an analog arithmetic circuit and a digital arithmetic circuit. The drive control unit 5 may be configured with one processor, or may be configured with a combination of two or more processors of the same type or different types. The processor includes a CPU (Central Processing Unit), a programmable logic device (PLD), a dedicated electric circuit, and the like. As is well known, a CPU is a general-purpose processor that executes software (programs) and functions as various processing units. A PLD is a processor such as an FPGA (Field Programmable Gate Array) whose circuit configuration can be changed after manufacture. A dedicated electric circuit is a processor having a circuit configuration designed specifically to execute a specific process such as an ASIC (Application Specific Integrated Circuit). [Explanation of symbols]

[0152] 2 Optical scanning device 3 light source 4. Micromirror Device (MMD) 5 Drive control section 6 Scanned surface 7. Imaging Equipment 10 Image drawing system 11A, 11B First angle detection sensor 12A, 12B Second angle detection sensor 20 Mirror section 20A reflective surface 21 1st support part 22 First movable frame 23 Second support part 24 Second movable frame 25 Connection 26 Fixed Frame 30 Piezoelectric element 31 First actuator 32 Second actuator 60A First drive signal generator 60B second drive signal generating unit 61A First signal processing section 61B Second signal processing section 62A 1st phase shift section 62B Second phase shift section 63A 1st derivation part 63B 2nd derived part 64 Third Derivation 65A 1st zero cross pulse output section 65B Second zero cross pulse output section 66 Light source driver 71 Buffer Amplifier 72 Variable Gain Amplifier 73, 77 Subtraction circuit 73A Adding circuit 74 Gain adjustment circuit 75A 1st BPF circuit 75B 2nd BPF circuit 76A 1st detection circuit 76B Second detection circuit L Light beam P1, P2, P3, P4 bright spots RN1, RN2 vibration noise S1c First angle detection signal S2c Second angle detection signal ZC1 1st zero cross pulse ZC2 Second zero cross pulse a1 First axis a2 2nd axis f d1 First Drive Frequency f d2 Second Drive Frequency

Claims

1. a mirror portion having a reflecting surface that reflects incident light; a first actuator that oscillates the mirror section around a first axis that is in a plane including the reflecting surface of the mirror section when the mirror section is stationary; a second actuator that oscillates the mirror section around a second axis that is within a plane that includes the reflecting surface of the mirror section when the mirror section is stationary and that intersects with the first axis; a first angle detection sensor that outputs a signal corresponding to an angle of the mirror portion about the first axis; a second angle detection sensor that outputs a signal corresponding to an angle of the mirror portion about the second axis; At least one processor; An optical scanning device comprising: The processor, applying a first drive signal having a first drive frequency to the first actuator; applying a second drive signal having a second drive frequency to the second actuator; deriving a first average phase delay time by averaging a first phase delay time of an output signal of the first angle detection sensor with respect to a plurality of periods of the first drive signal; deriving a second average phase delay time by averaging a second phase delay time of an output signal of the second angle detection sensor with respect to a plurality of periods of the second drive signal; generating a first reference signal indicating that the angle about the first axis has become a reference angle at a time when a time equal to the first average phase delay time plus a first deviation time according to a preset first condition has elapsed from a time when the first drive signal becomes a reference value; A second reference signal is generated at a time when a time equal to the sum of the second average phase delay time and a second deviation time according to a second preset condition has elapsed from the time when the second drive signal becomes a reference value, which indicates that the angle around the second axis has become a reference angle. Optical scanning device.

2. the first angle detection sensor is a pair of angle detection sensors arranged at positions facing each other across the first axis or the second axis, the output signal of the first angle detection sensor is an output signal obtained by adding or subtracting a pair of output signals output from a pair of angle detection sensors, the second angle detection sensor is a pair of angle detection sensors arranged at positions facing each other across the first axis or the second axis, The output signal of the second angle detection sensor is an output signal obtained by adding or subtracting a pair of output signals output from a pair of angle detection sensors.

2. The optical scanning device according to claim 1.

3. the first reference signal is a signal indicating that the angle around the first axis has become zero, The second reference signal is a signal that indicates that the angle around the second axis has become zero.

3. The optical scanning device according to claim 1 or 2.

4. The processor, deriving the first average phase delay time by averaging the first phase delay time at a time point when the output signal of the first angle detection sensor is zero; The second phase delay time is averaged at a time when the output signal of the second angle detection sensor is zero to derive the second average phase delay time.

4. The optical scanning device according to claim 3.

5. The processor, deriving the first average phase delay time by averaging the first phase delay time from a time when the first drive signal is zero to a time when the output signal of the first angle detection sensor is zero in a corresponding period; The second average phase delay time is derived by averaging the second phase delay time from a time when the second drive signal is zero to a time when the output signal of the second angle detection sensor is zero in a corresponding period.

5. The optical scanning device according to claim 4.

6. the first condition includes the first phase delay time, The second condition includes the second phase delay time. The optical scanning device according to claim 1 .

7. the first condition further includes a drive voltage of the first drive signal, The second condition further includes a drive voltage of the second drive signal.

7. The optical scanning device according to claim 6.

8. the first condition further includes the first drive frequency, The second condition further includes the second drive frequency.

8. The optical scanning device according to claim 6 or 7.

9. The first condition and the second condition further include an environmental temperature.

9. The optical scanning device according to claim 6, wherein the optical scanning device is a light source.

10. A delay time derivation mode for deriving the delay time is provided, The processor, Acquiring the delay time by executing the delay time derivation mode during calibration; When generating the first reference signal and the second reference signal, The first delay time and the second delay time obtained in advance are used in The optical scanning device according to claim 1 .

11. The first average phase delay time and the second average phase delay time are derived in an average phase delay time derivation mode, The processor, Executing the average phase delay time derivation mode during calibration to obtain the first average phase delay time and the second average phase delay time; When generating the first reference signal and the second reference signal, the first average phase delay time and the second average phase delay time obtained in advance in the calibration are used. The optical scanning device according to any one of claims 1 to 10.

12. An optical scanning device according to any one of claims 1 to 11; A light source that irradiates light onto the mirror portion; An image rendering system comprising: The processor controls a timing of emitting light from the light source based on the first reference signal and the second reference signal. Image drawing system.

13. a mirror portion having a reflecting surface that reflects incident light; a first actuator that oscillates the mirror section around a first axis that is in a plane including the reflecting surface of the mirror section when the mirror section is stationary; a second actuator that oscillates the mirror section around a second axis that is within a plane that includes the reflecting surface of the mirror section when the mirror section is stationary and that intersects with the first axis; a first angle detection sensor that outputs a signal corresponding to an angle of the mirror portion about the first axis; a second angle detection sensor that outputs a signal corresponding to an angle of the mirror portion about the second axis; A method for driving an optical scanning device comprising: applying a first drive signal having a first drive frequency to the first actuator; applying a second drive signal having a second drive frequency to the second actuator; deriving a first average phase delay time by averaging a first phase delay time of an output signal of the first angle detection sensor with respect to a plurality of periods of the first drive signal; deriving a second average phase delay time by averaging a second phase delay time of an output signal of the second angle detection sensor with respect to a plurality of periods of the second drive signal; generating a first reference signal indicating that the angle about the first axis has become a reference angle at a time when a time equal to the first average phase delay time plus a first deviation time according to a preset first condition has elapsed from a time when the first drive signal becomes a reference value; A second reference signal is generated at a time when a time equal to the sum of the second average phase delay time and a second deviation time according to a second preset condition has elapsed from the time when the second drive signal becomes a reference value, which indicates that the angle around the second axis has become a reference angle. A method for driving an optical scanning device.

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