Optical scanning device and method for driving optical scanning device

Abstract

This optical scanning device comprises a mirror part, a first actuator, a second actuator, a first angle sensor, and a processor. The processor performs processing for deriving a first phase difference between a first drive signal and an output signal of the first angle sensor on the basis of the output signal of the first angle sensor, and changing a first drive frequency and a second drive frequency while maintaining the ratio between the first drive frequency and the second drive frequency along a preset frequency ratio line so that the first phase difference falls within a first target range. The frequency ratio line is a line representing a frequency ratio corrected on the basis of the amount of change of the ratio between a first resonance frequency in a case where the mirror part is swung around a first axis and a second resonance frequency in a case where the mirror part is swung around a second axis.

Description

Optical scanning device and method for driving optical scanning device

[0001] The technology of the present disclosure relates to an optical scanning device and a method for driving an optical scanning device.

[0002] Micromirror devices (also called microscanners) are known as one type of microelectromechanical systems (MEMS) device fabricated using silicon (Si) microfabrication technology. Because these micromirror devices are small and consume little power, they are expected to be widely used in laser displays, laser projectors, optical coherence tomography, and other applications.

[0003] In a micromirror device, a mirror portion is formed so as to be able to oscillate around a first axis and a second axis that are orthogonal to each other, and the mirror portion oscillates around each axis to two-dimensionally scan the laser light reflected by the mirror portion. Also known is a micromirror device that enables Lissajous scanning of laser light by resonating the mirror portion around each axis. Lissajous scanning refers to forming a Lissajous pattern by scanning the trajectory of the laser light on the scanning surface.

[0004] The Lissajous pattern is determined by the frequency ratio and phase difference between a first drive signal for oscillating the mirror unit around a first axis and a second drive signal for oscillating the mirror unit around a second axis. For this reason, in optical scanning devices, the frequency ratio and phase difference are generally fixed to constant values ​​so that the Lissajous pattern does not change (see, for example, JP 2012-068349 A).

[0005] Furthermore, in order to draw large images in a drawing device using an optical scanning device, it is necessary to increase the scanning range of the laser light on the scanning surface. In order to increase the scanning range, it is common to perform resonant driving by setting the frequency of the first drive signal (hereinafter referred to as the first drive frequency) and the frequency of the second drive signal (hereinafter referred to as the second drive frequency) to values ​​close to the resonant frequency of the micromirror device so that the oscillation amplitude of the mirror portion increases.

[0006] Since the resonant frequency of a micromirror device varies due to individual differences such as manufacturing variations or changes in the external environment such as temperature changes, it is necessary to change the first drive frequency and the second drive frequency taking into account the variation in the resonant frequency. However, changing the first drive frequency and the second drive frequency changes the frequency ratio, which in turn changes the scanning trajectory. For this reason, Japanese Patent Application Laid-Open No. 2012-068349 proposes changing the first drive frequency and the second drive frequency while maintaining the frequency ratio so as not to change the scanning trajectory.

[0007] However, because the resonant frequencies of the micromirror device are different around the first axis and the second axis, the resonant frequencies around the first axis and the second axis vary independently due to differences between individual micromirror devices or changes in the external environment. Therefore, the optimal frequency ratio for achieving a desired scanning range size varies depending on differences between individual micromirror devices or changes in the external environment. For example, even if the first drive frequency and the second drive frequency are set to have the optimal frequency ratio for achieving a desired scanning range size, a subsequent change in the resonant frequencies due to external factors may cause a change in the optimal frequency ratio, resulting in a change in the size of the scanning range.

[0008] Therefore, if the resonant frequency fluctuates, even if the first drive frequency and the second drive frequency are changed while maintaining the frequency ratio as described in JP 2012-068349 A, it may not be possible to satisfy the required scanning range size.

[0009] The technology disclosed herein aims to provide an optical scanning device and a driving method for an optical scanning device that can satisfy the required scanning range size even when the resonant frequency fluctuates due to changes in the external environment, etc.

[0010] In order to achieve the above-mentioned object, the optical scanning device of the present disclosure includes a mirror unit having a reflective surface that reflects incident light, a first actuator that oscillates the mirror unit around a first axis, a second actuator that oscillates the mirror unit around a second axis that intersects the first axis, a first angle sensor that outputs a signal corresponding to the angle of the mirror unit about the first axis, and a processor that applies a first drive signal having a first drive frequency to the first actuator and applies a second drive signal having a second drive frequency to the second actuator, wherein the processor derives a first phase difference between the first drive signal and the output signal of the first angle sensor based on the output signal of the first angle sensor, and performs processing to change the first drive frequency and the second drive frequency along a predetermined frequency ratio line while maintaining the ratio between the first drive frequency and the second drive frequency so that the first phase difference falls within a first target range, and the frequency ratio line is a line that represents a frequency ratio corrected based on the amount of change in the ratio between the first resonant frequency when the mirror unit is oscillated around the first axis and the second resonant frequency when the mirror unit is oscillated around the second axis.

[0011] It is preferable that the first target range is a range determined based on the phase difference between the first drive signal and the output signal of the first angle sensor when the mirror portion is oscillated around the first axis with the first drive frequency as the resonant frequency.

[0012] The amplitude voltages of the first drive signal and the second drive signal are preferably set to predetermined values.

[0013] The amplitude voltages of the first drive signal and the second drive signal may be values ​​corrected in accordance with the amount of change in the Q value for each of the first axis and the second axis.

[0014] The amplitude voltages of the first drive signal and the second drive signal may be values ​​corrected in accordance with the amount of change in the amplitude voltages for the first axis and the second axis, respectively.

[0015] It is preferable that the processor derives a first accumulated value by accumulating the first phase delay time of the output signal of the first angle sensor relative to the first drive signal a first number of accumulations that is an integer multiple of the number of times corresponding to one frame period, and that the average value obtained by dividing the derived first accumulated value by the first number of accumulations is used as the first phase difference.

[0016] It is preferable that the optical system further includes a second angle sensor that outputs a signal corresponding to the angle of the mirror portion around the second axis, and the processor derives a second phase difference between the second drive signal and the output signal of the second angle sensor based on the output signal of the second angle sensor, and changes the first drive frequency and the second drive frequency so that the first phase difference is within a first target range and the second phase difference is within a second target range.

[0017] It is preferable that the second target range is a range determined based on the phase difference between the second drive signal and the output signal of the second angle sensor when the mirror portion is oscillated around the second axis with the second drive frequency as the resonant frequency.

[0018] It is preferable that the processor derives a second accumulated value by accumulating the second phase delay time of the output signal of the second angle sensor relative to the second drive signal a second number of accumulations that is an integer multiple of the number of accumulations corresponding to one frame period, and divides the derived second accumulated value by the second number of accumulations to obtain an average value as the second phase difference.

[0019] A driving method for an optical scanning device disclosed herein is a driving method for an optical scanning device including: a mirror unit having a reflective surface that reflects incident light; a first actuator that oscillates the mirror unit around a first axis; a second actuator that oscillates the mirror unit around a second axis that intersects the first axis; a first angle sensor that outputs a signal corresponding to the angle of the mirror unit about the first axis; and a processor that applies a first drive signal having a first drive frequency to the first actuator and applies a second drive signal having a second drive frequency to the second actuator, wherein the processor derives a first phase difference between the first drive signal and the output signal of the first angle sensor based on the output signal of the first angle sensor, and performs processing to change the first drive frequency and the second drive frequency along a predetermined frequency ratio line while maintaining the ratio between the first drive frequency and the second drive frequency so that the first phase difference falls within a first target range, wherein the frequency ratio line is a line that represents a frequency ratio corrected based on the amount of change in the ratio between the first resonant frequency when the mirror unit is oscillated around the first axis and the second resonant frequency when the mirror unit is oscillated around the second axis.

[0020] According to the technology disclosed herein, it is possible to provide an optical scanning device and a driving method for an optical scanning device that can satisfy the required scanning range size even when the resonant frequency fluctuates due to changes in the external environment, etc.

[0021] FIG. 1 is a schematic diagram of an optical scanning device. FIG. 2 is an external perspective view of a micromirror device. FIG. 3 is a graph showing an example of a first drive signal and a second drive signal. FIG. 4 is a block diagram showing an example of the configuration of a drive control unit. FIG. 5 is a diagram explaining the processing of a first signal processing unit. FIG. 6 is a diagram explaining the processing of a second signal processing unit. FIG. 7 is a diagram explaining the processing of a first phase difference derivation unit. FIG. 8 is a diagram explaining the processing of a second phase difference derivation unit. FIG. 9 is a diagram explaining correction of a frequency ratio line. FIG. 10 is a diagram explaining frequency change processing. FIG. 11 is a diagram explaining a method of determining a first target range. A flowchart showing the flow of frequency change processing. FIG. 12 is a block diagram showing an example of the configuration of a drive control unit according to a modified example. FIG. 13 is a flowchart showing the flow of frequency change processing according to a modified example.

[0022] An example of an embodiment of the technology of the present disclosure will be described with reference to the accompanying drawings.

[0023] 1 is a schematic diagram of an image drawing system 10 according to one embodiment. The image drawing system 10 includes an optical scanning device 2 and a light source 3. The optical scanning device 2 includes a micro mirror device (hereinafter referred to as an MMD) 4 and a drive control unit 5. The drive control unit 5 is an example of a processor according to the disclosed technology.

[0024] The image drawing system 10 draws an image by optically scanning a surface 6 to be scanned with a light beam LB emitted from a light source 3, which is reflected by an MMD 4 under the control of a drive control unit 5. The surface 6 to be scanned may be a screen, the retina of a human eye, or the like.

[0025] The image rendering system 10 is applicable 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.

[0026] MMD4 is the first axis a １ and the first axis a １ The second axis a intersecting ２ The micromirror device is a piezoelectric two-axis drive type that can oscillate the mirror portion 20 (see FIG. 2) around the second axis a. ２ The direction parallel to the axis a is the X direction. １ The direction parallel to the axis a is the Y direction. １ and the second axis a ２ The direction perpendicular to the X direction is called the Z direction. In this embodiment, the X direction and the Y direction are perpendicular to each other.

[0027] The light source 3 is a laser device that emits, for example, laser light as the light beam LB. For example, the light source 3 outputs laser light of three colors: R (Red), G (Green), and B (Blue). When the mirror unit 20 of the MMD 4 is stationary, the light source 3 preferably irradiates the light beam LB perpendicularly to a reflecting surface 20A (see FIG. 2 ) of the mirror unit 20. Note that if the light beam LB is irradiated perpendicularly to the reflecting surface 20A, the light source 3 may become an obstacle when the light beam LB scans and draws on the scanned surface 6. For this reason, it is preferable to control the light beam LB emitted from the light source 3 using an optical system to irradiate the reflecting surface 20A perpendicularly. The optical system may or may not include a lens. Furthermore, the angle at which the light beam LB emitted from the light source 3 is irradiated on the reflecting surface 20A is not limited to perpendicular, and the light beam LB may be irradiated obliquely with respect to the reflecting surface 20A.

[0028] 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 LB based on the input drive signal and irradiates the MMD 4 with the light beam LB. The MMD 4 rotates the mirror unit 20 along the first axis a based on the input drive signal. １ and the second axis a ２ Rock it around.

[0029] The drive control unit 5 rotates the mirror unit 20 along the first axis a １ and the second axis a ２ , the light beam LB reflected by the mirror portion 20 scans the surface to be scanned 6 so as to draw a Lissajous pattern. This optical scanning method is called a Lissajous scanning method.

[0030] Next, an example of the MMD 4 will be described with reference to Fig. 2. Fig. 2 is an external perspective view of the MMD 4. As shown in Fig. 2, the MMD 4 has a mirror unit 20, a first support unit 21, a first movable frame 22, a second support unit 23, a second movable frame 24, a connection unit 25, and a fixed frame 26. The MMD 4 is a so-called MEMS scanner.

[0031] The mirror section 20 has a reflecting surface 20A that reflects incident light. The reflecting surface 20A is formed of a metal thin film, such as gold (Au), aluminum (Al), silver (Ag), or a silver alloy, provided on one surface of the mirror section 20. The shape of the reflecting surface 20A is, for example, a first axis a １ and the second axis a ２ It is a circle with the intersection point of

[0032] 1st axis a １ and the second axis a ２ The plane shape of the MMD 4 is rectangular, and the first axis a １ and is symmetrical about the second axis a ２ It is symmetric with respect to .

[0033] The first support portion 21 is provided on the outer side of the mirror portion 20 with a second axis a ２ The first support portion 21 is disposed at a position facing each other with the first axis a １ The mirror section 20 is connected to the first axis a １ In this embodiment, the first support portion 21 supports the first axis a １ It is a torsion bar extending along the

[0034] The first movable frame 22 is a rectangular frame that surrounds the mirror unit 20 and is １ The first movable frame 22 is connected to the mirror unit 20 via the first support unit 21. １ The piezoelectric elements 30 are formed at positions facing each other with the first movable frame 22 therebetween. In this way, the two piezoelectric elements 30 formed on the first movable frame 22 constitute a first actuator 31.

[0035] The two piezoelectric elements 30 constituting the first actuator 31 are arranged along the first axis a １ The first actuator 31 is arranged at a position facing the mirror unit 20 with the first axis a １ By applying a rotational torque around the first axis a １ Swing it around.

[0036] The second support portion 23 is provided on the outside of the first movable frame 22 along the first axis a １ The second support portion 23 is disposed at a position facing each other with the second axis a ２ The first movable frame 22 and the mirror unit 20 are connected to the second axis a ２ In this embodiment, the second support portion 23 supports the second axis a ２ It is a torsion bar extending along the

[0037] The second movable frame 24 is a rectangular frame that surrounds the first movable frame 22 and is oriented along the second axis a ２ The second movable frame 24 is connected to the first movable frame 22 via the second support portion 23. The second movable frame 24 is connected to the second axis a ２ The piezoelectric elements 30 are formed at positions facing each other with the second movable frame 24 therebetween. In this way, the two piezoelectric elements 30 formed on the second movable frame 24 constitute a second actuator 32.

[0038] The two piezoelectric elements 30 constituting the second actuator 32 are arranged along the second axis a ２ The second actuator 32 is arranged at a position facing the mirror unit 20 and the first movable frame 22 with the second axis a ２ By applying a rotational torque around the second axis a ２ The mirror portion 20 is swung around the

[0039] The connecting portion 25 is provided on the outside of the second movable frame 24 with the first axis a １ The connecting portions 25 are arranged at positions facing each other with the second axis a ２ It is connected to the second movable frame 24 at the top.

[0040] The fixed frame 26 is a rectangular frame body that surrounds the second movable frame 24 and is oriented along the second axis a ２ The upper surface of the movable frame 22 is connected to the second movable frame 24 via a connecting portion 25 .

[0041] The first movable frame 22 is provided with a first angle sensor 11A in the vicinity of the first support portion 21. The first angle sensor 11A is １The mirror section 20 is configured with two piezoelectric elements 12 arranged at positions facing each other with the first axis a １ The first angle sensor 11A converts the force applied by the deformation of the first support part 21 due to the rotation around the first axis a of the mirror part 20 into a voltage and outputs a signal. １ It outputs a signal according to the surrounding angle.

[0042] The second movable frame 24 is provided with a second angle sensor 11B in the vicinity of the second support portion 23. The second angle sensor 11B is ２ The mirror section 20 is configured with two piezoelectric elements 13 arranged at positions facing each other with the second axis a ２ The second angle sensor 11B converts the force applied by the deformation of the second support part 23 due to the rotation around the second axis a of the mirror part 20 into a voltage and outputs a signal. ２ It outputs a signal according to the surrounding angle.

[0043] 2 does not show wiring and electrode pads for applying drive signals to the first actuator 31 and the second actuator 32. Also, in FIG. 2, wiring and electrode pads for outputting signals from the first angle sensor 11A and the second angle sensor 11B are not shown. A plurality of electrode pads are provided on the fixed frame 26.

[0044] The first axis a of the mirror section 20 １ The oscillation amplitude around the center (hereinafter referred to as the first oscillation amplitude) A １ is controlled by a drive signal (hereinafter referred to as a first drive signal) that is applied to the first actuator 31 by the drive control unit 5. 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., a phase difference of 180°).

[0045] The first oscillation amplitude A １is the maximum value of the angle at which the normal to the reflecting surface 20A is inclined with respect to the Z direction in the XZ plane.

[0046] The second axis a of the mirror portion 20 ２ The oscillation amplitude around the center (hereinafter referred to as the second oscillation amplitude) A ２ is controlled by a drive signal (hereinafter referred to as a second drive signal) that is applied to the second actuator 32 by the drive control unit 5. 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., a phase difference of 180°).

[0047] The second oscillation amplitude A ２ is the maximum value of the angle at which the normal to the reflecting surface 20A is inclined with respect to the Z direction in the YZ plane.

[0048] 3A and 3B show examples of the first and second drive signals. FIG. 3A shows a drive voltage waveform V １Ａ (t) and V １Ｂ (t) and offset voltage V ｏｆｆ１ FIG. 3B shows the drive voltage waveform V ２Ａ (t) and V ２Ｂ (t) and offset voltage V ｏｆｆ２ Indicates that.

[0049] Drive voltage waveform V １Ａ (t) and V １Ｂ (t) are expressed as follows: V １Ａ (t) = V ｏｆｆ１ +V １ sin(2πf ｄ１ t) V １Ｂ (t) = V ｏｆｆ１ +V １ sin(2πf ｄ１ t + α)

[0050] Here, V １ is the amplitude voltage. V ｏｆｆ１ is the bias voltage. ｏｆｆ１may be zero. ｄ１ is the drive frequency (hereinafter referred to as the first drive frequency), t is time, and α is the drive voltage waveform V １Ａ (t) and V １Ｂ In this embodiment, for example, α=180°.

[0051] The two piezoelectric elements 30 constituting the first actuator 31 are applied with a driving voltage waveform V １Ａ (t) and V １Ｂ By applying the first drive frequency f(t), the mirror section 20 ｄ１ The first axis a １ Swinging around.

[0052] Drive voltage waveform V ２Ａ (t) and V ２Ｂ (t) are expressed as follows: V ２Ａ (t) = V ｏｆｆ２ +V ２ sin(2πf ｄ２ t+φ) V ２Ｂ (t) = V ｏｆｆ２ +V ２ sin(2πf ｄ２ t + β + φ)

[0053] Here, V ２ is the amplitude voltage. V ｏｆｆ２ is the bias voltage. ｏｆｆ２ 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 V ２Ｂ In this embodiment, for example, β is set to 180°. 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 between the amplitude voltage V １ and amplitude voltage V ２ may be different from

[0054] The two piezoelectric elements 30 constituting the second actuator 32 are driven by a driving voltage waveform V ２Ａ (t) and V２Ｂ By applying the second drive frequency f ｄ２ and the second axis a ２ Swinging around.

[0055] First drive frequency f ｄ１ The mirror unit 20 is aligned with the first axis a １ The second drive frequency f is set to coincide with the resonance frequency (hereinafter referred to as the first resonance frequency) when the rotor is oscillated around the center of the rotor. ｄ２ The mirror part 20 is aligned with the second axis a ２ The frequency f is set to coincide with the resonance frequency (hereinafter referred to as the second resonance frequency) when the rotor is oscillated around the center of the rotor. ｄ１ >f ｄ２ That is, the mirror unit 20 is １ The oscillation frequency around the second axis a ２ The first driving frequency f ｄ１ does not necessarily coincide with the first resonance frequency, and the second drive frequency f ｄ２ does not necessarily have to coincide with the second resonance frequency. For example, the first drive frequency f ｄ１ may be a frequency within a frequency range near the first resonant frequency, and the second drive frequency f ｄ２ may be a frequency within a frequency range near the second resonant frequency, for example, a frequency range in which the oscillation amplitude is 1 / √2 times or more of the peak value (so-called Q value range).

[0056] 4 shows an example of the configuration of the drive control unit 5. The drive control unit 5 has a mirror drive unit 4A and a light source drive unit 3A. The mirror drive unit 4A has a first drive voltage waveform generation unit 60A, a first signal processing unit 61A, a first phase shift unit 62A, a first phase difference derivation unit 63A, a first zero-cross pulse output unit 64A, a second drive voltage waveform generation unit 60B, a second signal processing unit 61B, a second phase shift unit 62B, a second phase difference derivation unit 63B, a second zero-cross pulse output unit 64B, a frequency change unit 65, and a memory 66.

[0057] The first drive voltage waveform generating unit 60A, the first signal processing unit 61A, and the first phase shift unit 62A are１ The second drive voltage waveform generating unit 60B, the second signal processing unit 61B, and the second phase shift unit 62B perform feedback control so that the oscillations around the mirror unit 20 maintain a resonant state. ２ Feedback control is performed to maintain the surrounding oscillations in a resonant state.

[0058] The first drive voltage waveform generating section 60A generates the above-mentioned drive voltage waveform V １Ａ (t) and V １Ｂ (t) is generated, and the generated driving voltage waveform V １Ａ (t) and V １Ｂ (t) is applied to the two piezoelectric elements 30 constituting the first actuator 31 via the first phase shift unit 62A. As a result, the mirror unit 20 is rotated along the first axis a １ The first angle sensor 11A rotates around the first axis a of the mirror unit 20. １ It outputs a signal according to the surrounding angle.

[0059] The second drive voltage waveform generating section 60B generates the above-mentioned drive voltage waveform V ２Ａ (t) and V ２Ｂ (t) is generated, and the generated driving voltage waveform V ２Ａ (t) and V ２Ｂ (t) is applied to the two piezoelectric elements 30 constituting the second actuator 32 via the second phase shift section 62B. As a result, the mirror section 20 is rotated along the second axis a ２ The second angle sensor 11B rotates around the second axis a of the mirror unit 20. ２ It outputs a signal according to the surrounding angle.

[0060] The first signal processing unit 61A generates a first sensor signal S1 based on the signal output from the first angle sensor 11A. Specifically, as shown in FIG. 5, the first signal processing unit 61A subtracts one of two signals output from the two piezoelectric elements 12 constituting the first angle sensor 11A from the other, thereby obtaining a second axis a ２ The first sensor signal S1 is generated by removing vibration noise caused by surrounding vibrations. The first sensor signal S1 is an example of the "output signal of the first angle sensor" according to the technology of the present disclosure.

[0061] The second signal processing unit 61B generates a second sensor signal S2 based on the signal output from the second angle sensor 11B. Specifically, as shown in FIG. 6, the second signal processing unit 61B subtracts one of two signals output from the two piezoelectric elements 13 constituting the second angle sensor 11B from the other, thereby obtaining a second sensor signal S2 for the first axis a. １ The second sensor signal S2 is generated from which vibration noise caused by surrounding vibrations has been removed. The second sensor signal S2 is an example of the "output signal of the second angle sensor" according to the technology of the present disclosure.

[0062] The first phase difference derivation unit 63A derives an integrated value by integrating the phase delay time of the sensor signal S1 relative to the first drive signal a first integration count, which is n times the number N corresponding to one frame period TF, and derives an average value by dividing the derived integrated value by the first integration count to derive the first phase difference PD1. The first phase difference PD1 is the average phase delay time of the sensor signal S1 relative to the first drive signal. Here, n is an integer. In this embodiment, n=1. n may be an integer of 2 or more. Furthermore, one frame period TF is one period of optical scanning in which the light beam LB is scanned on the scanned surface 6, and specifically, it is the time it takes for a Lissajous pattern to be drawn once on the scanned surface 6. Furthermore, the number N corresponding to one frame period TF is determined by the number of times the first drive frequency f is applied to one frame period TF. ｄ１ is the value multiplied by

[0063] 7, the first phase difference deriving unit 63A binarizes the first drive signal and the sensor signal S1. Here, for example, the first drive signal has a drive voltage waveform V １Ａ The first phase difference deriving unit 63A uses the phase delay time δ of the sensor signal S1 with respect to the binarized first drive signal. １ ~δ Ｎ and calculate the phase delay time δ １ ~δ Ｎ The first phase difference derivation unit 63A divides the derived integrated value by the first number of integrations N to derive the first phase difference PD1.

[0064] The second phase difference derivation unit 63B derives an integrated value by integrating the phase delay time of the sensor signal S2 with respect to the second drive signal a second number of times obtained by multiplying the number M corresponding to one frame period TF by n, and derives an average value by dividing the derived integrated value by the second number of times of integration as the second phase difference PD2. The second phase difference PD2 is the average phase delay time of the sensor signal S2 with respect to the second drive signal. Here, the number M corresponding to one frame period TF is the number of times the second drive frequency f ｄ２ is the value multiplied by

[0065] Specifically, as shown in Fig. 8, the second phase difference deriving unit 63B binarizes the second drive signal and the sensor signal S2. Here, for example, as the second drive signal, ２Ａ The second phase difference deriving unit 63B uses the phase delay time δ of the sensor signal S2 with respect to the binarized second drive signal. １ ~δ Ｍ and calculate the phase delay time δ １ ~δ Ｍ The second phase difference derivation unit 63B divides the derived integrated value by the second number of integrations M to derive the second phase difference PD2.

[0066] The first zero-cross pulse output unit 64A generates a first zero-cross pulse ZC1 based on the first drive signal and the first phase difference PD1 derived by the first phase difference derivation unit 63A. １ This is a signal that indicates that the surrounding angle has reached zero.

[0067] The second zero-cross pulse output unit 64B generates a second zero-cross pulse ZC2 based on the second drive signal and the second phase difference PD2 derived by the second phase difference deriving unit 63B. ２ This is a signal that indicates that the surrounding angle has reached zero.

[0068] The light source driver 3A drives the light source 3 based on, for example, drawing data supplied from outside the image drawing system 10. The light source driver 3A also controls the irradiation timing of the laser light so that the irradiation timing is synchronized with the first zero-cross pulse ZC1 and the second zero-cross pulse ZC2 input from the mirror driver 4A. Note that when a drive frequency ratio, which will be described later, is changed, the scanning trajectory (i.e., the Lissajous pattern) of the light beam LB changes, and therefore the light emission pattern of the light source 3 is corrected in accordance with the change in the scanning trajectory.

[0069] When the optical scanning device 2 is started, the drive control unit 5 rotates the mirror unit 20 along the first axis a １ and the second axis a ２ , the first driving frequency f is set to increase the oscillation amplitude of the mirror section 20. ｄ１ and the second driving frequency f ｄ２ When the optical scanning device 2 is started up, the frequency changer 65 operates in addition to the above-mentioned components.

[0070] In this embodiment, the frequency changer 65 changes the first driving frequency f along a preset frequency ratio line so that the first phase difference PD1 derived by the first phase difference deriving unit 63A falls within a first target range. ｄ１ and the second driving frequency f ｄ２ The frequency change process is performed while maintaining a constant ratio (hereinafter referred to as the drive frequency ratio R) between the drive frequency R and the frequency V. The frequency ratio line is included in the start condition data stored in the memory 66.

[0071] The frequency ratio line represents the drive frequency ratio R corrected based on the amount of change in the ratio between the first resonant frequency and the second resonant frequency (hereinafter referred to as the resonant frequency ratio). The first resonant frequency and the second resonant frequency each fluctuate due to external factors applied to the MMD 4, and therefore the resonant frequency ratio also changes due to the external factors. Therefore, the frequency ratio line is corrected based on the amount of change in the resonant frequency ratio. For example, an external factor is a factor resulting from a mounting jig used to mount the MMD 4 on a substrate or the like. Even with the same MMD 4, the resonant frequency ratio changes when the mounting jig is changed.

[0072] FIG. 9 illustrates the correction of the frequency ratio line. In FIG. 9, L0 is a frequency ratio line representing the resonant frequency ratio before an external factor is applied to the MMD 4. L1 is a frequency ratio line representing the resonant frequency ratio after an external factor is applied to the MMD 4. The frequency ratio line L1 is a frequency ratio line obtained by correcting the frequency ratio line L0 based on the amount of change in the resonant frequency ratio due to the external factor. For example, the drive control unit 5 measures the resonant frequency ratio at a predetermined timing before the optical scanning device 2 is activated, and corrects the frequency ratio line L0 to generate the frequency ratio line L1. Here, the frequency ratio line L1 is an example of a "predetermined frequency ratio line" according to the technology disclosed herein.

[0073] 10 shows an example of the frequency change process. As shown in FIG. 10, the frequency changer 65 changes the first driving frequency f along the frequency ratio line L1 so that the first phase difference PD1 falls within the first target range. ｄ１ and the second driving frequency f ｄ２ The first driving frequency f ｄ１ and the second driving frequency f ｄ２ When changing the amplitude voltage V of the first drive signal and the second drive signal, １ , V ２ is not changed but remains at the preset value.

[0074] In principle, when PD1=90°, the first oscillation amplitude A １ Therefore, it is conceivable to set the first target range to a range centered on 90°. However, in reality, when PD1=90°, the first oscillation amplitude A １ Therefore, in this embodiment, the first driving frequency f ｄ１ is set as the first resonance frequency, and the mirror portion 20 is rotated along the first axis a １ The range is determined based on the first phase difference PD1 when the lens is swung around the center.

[0075] Specifically, as shown in FIG. 11, the first driving frequency f ｄ１ is set as the first resonance frequency, and the mirror portion 20 is rotated along the first axis a １ When the first oscillation amplitude A １The first phase difference PD1 at which f is maximized is calculated, and the first target range is determined with the calculated first phase difference PD1 as the center. ｃ１ is the first resonant frequency. １Ｐ is the first oscillation amplitude A １ The maximum value of A １Ｐ The first oscillation amplitude A is equal to or greater than a predetermined ratio of １ The first target range may be determined so that

[0076] 12 shows the flow of the frequency change process. In the frequency change process, first, the frequency changer 65 reads out the activation condition data from the memory 66 and obtains the corrected frequency ratio line L1 (step S10). Next, the frequency changer 65 obtains the first phase difference PD1 derived by the first phase difference deriving unit 63A (step S11).

[0077] The frequency changing unit 65 determines whether the acquired first phase difference PD1 is within the first target range (step S12). If the acquired first phase difference PD1 is not within the first target range (step S12: NO), the frequency changing unit 65 changes the first driving frequency f along the frequency ratio line L1. ｄ１ and the second driving frequency f ｄ２ and PD1 by a predetermined amount (step S13). After that, the frequency changer 65 returns the process to step S11 and again acquires the first phase difference PD1 derived by the first phase difference deriving unit 63A.

[0078] The frequency changer 65 repeatedly executes steps S11 to S13 until the first phase difference PD1 falls within the first target range. When the first phase difference PD1 falls within the first target range (step S12: YES), the frequency changer 65 ends the frequency change process.

[0079] As described above, in this embodiment, even if the resonant frequency ratio fluctuates due to a change in the external environment or the like, the first phase difference PD1 is set to be within the first target range by the frequency change process executed at startup, so that the first oscillation amplitude A １In this embodiment, the frequency change process is performed based on the drive frequency ratio R corrected based on the amount of change in the resonance frequency ratio due to an external environmental change or the like. Therefore, the first oscillation amplitude A １ As the second oscillation amplitude A ２ (That is, the scanning range of the light beam LB in the X and Y directions becomes larger.)

[0080] Conventionally, when the resonant frequency ratio fluctuates due to an external environmental change, the first oscillation amplitude A １ or second oscillation amplitude A ２ However, in this embodiment, the frequency change process described above is performed, so that the required scanning range size can be satisfied.

[0081] The applicant also intends to fix the mirror portion 20 to the first axis a １ and the second axis a ２ The amount of change in the resonance frequency ratio when the mirror section 20 is oscillated around the first axis a １ The first resonance frequency and the second axis a when oscillated around ２ It was found that the change in the ratio between the first and second resonance frequencies is equal to the change in the ratio between the first and second resonance frequencies when the mirror unit 20 is oscillated around the center of the mirror unit 20. Therefore, before starting the optical scanning device 2, the change in the resonance frequency ratio can be determined by driving the mirror unit 20 on a single axis and measuring the first and second resonance frequencies. When the mirror unit 20 is driven on a single axis, the first and second resonance frequencies can be determined easily and accurately, and the frequency ratio line can be easily corrected with high precision.

[0082] For example, the frequency ratio line L1 is a line that is formed by dividing the mirror section 20 into two equal parts along the first axis a １ A first driving frequency f is a frequency at which the amplitude (e.g., Vpp value) of the first sensor signal S1 reaches a preset value (e.g., a maximum value) when the sensor is driven in a single axis around the center. ｄ１ (i.e., the first resonance frequency), and the mirror portion 20 is rotated along the second axis a ２ A second driving frequency f is a frequency at which the amplitude (e.g., Vpp value) of the second sensor signal S2 reaches a predetermined value (e.g., a maximum value) when the second sensor signal S2 is driven in a single axis around the center of the sensor.ｄ２ (i.e., the second resonant frequency) and calculate the amount of change in the ratio between them. Specifically, the frequency ratio line L1 is obtained by correcting the frequency ratio line L0 as described above based on the amount of change in the ratio between them.

[0083] When measuring the first and second resonance frequencies for obtaining the frequency ratio line L1 (see FIG. 9) by driving the mirror unit 20 in a single axis, the drive control unit 5 １Ｓ , V ２Ｓ It is preferable to set the amplitude voltage V １Ｓ The mirror unit 20 is aligned with the first axis a １ The amplitude voltage V ２Ｓ The mirror part 20 is aligned with the second axis a ２ The predetermined value means the amplitude voltage of the second drive signal when driving a single axis around the center of the rotor. Also, the predetermined value is the amplitude voltage V set when measuring the first resonance frequency and the second resonance frequency to obtain the frequency ratio line L0 before correction. １Ｓ , V ２Ｓ This is because the MMD 4 has a nonlinearity in which the first and second resonance frequencies change depending on the deflection angle of the mirror portion 20, and the amplitude voltage V １Ｓ , V ２Ｓ This is because if the frequency is changed significantly, the influence of nonlinearity will appear, and the first and second resonant frequencies may change.

[0084] In addition, the first oscillation amplitude A １ and the second oscillation amplitude A ２ is the amplitude voltage V １ and amplitude voltage V ２ Therefore, the amplitude voltage V １ and amplitude voltage V ２ However, as in the present embodiment, the first drive frequency f is changed based on the first phase difference PD1. ｄ１ and the second driving frequency f ｄ２ By changing the value of the resonant frequency, the resonance state can be maintained, thereby reducing power consumption.

[0085] In the above embodiment, the frequency changer 65 changes the first driving frequency f so that the first phase difference PD1 derived by the first phase difference deriving unit 63A falls within the first target range. ｄ１ and the second driving frequency f ｄ２ Instead, the first driving frequency f is changed so that the second phase difference PD2 derived by the second phase difference deriving unit 63B falls within the second target range. ｄ１ and the second driving frequency f ｄ２ The second target range may be changed by changing the second drive frequency f ｄ２ is set as the second resonance frequency, and the mirror portion 20 is rotated along the second axis a ２ When the second oscillation amplitude A ２ The second phase difference PD2 at which the second oscillation amplitude A is maximized is calculated, and the second oscillation amplitude A is determined around the calculated second phase difference PD2. ２ The second oscillation amplitude A is equal to or greater than a predetermined percentage of the maximum value of ２ The second target range may be determined so that the following is obtained. A specific method for determining the second target range is the same as the method for determining the first target range (see FIG. 11).

[0086] In the above embodiment, f ｄ１ >f ｄ２ However, ｄ１ <f ｄ２ That is, the first resonant frequency may be lower than the second resonant frequency.

[0087] The amount of change in oscillation amplitude relative to a change in frequency is larger for a larger Q value. Therefore, the frequency changer 65 adjusts the phase difference (f ｄ１ <f ｄ２ In the case of ｄ１ >f ｄ２ In this case, it is also preferable to perform frequency change processing based on the second phase difference PD2).

[0088] 13 shows the configuration of the drive control unit 5 according to a modified example. In this modified example, the frequency changer 65 performs frequency change processing based on both the first phase difference PD1 and the second phase difference PD2. Specifically, the frequency changer 65 changes the first drive frequency f so that the first phase difference PD1 derived by the first phase difference deriving unit 63A falls within a first target range and the second phase difference PD2 derived by the second phase difference deriving unit 63B falls within a second target range. ｄ１ and the second driving frequency f ｄ２ Change the

[0089] 14 shows the flow of a frequency change process according to the modified example. In the frequency change process according to the modified example, first, the frequency changer 65 reads out the activation condition data from the memory 66 and obtains the corrected frequency ratio line L1 (step S20). Next, the frequency changer 65 obtains the first phase difference PD1 derived by the first phase difference deriving unit 63A and the second phase difference PD2 derived by the second phase difference deriving unit 63B (step S21).

[0090] The frequency changing unit 65 determines whether the acquired first phase difference PD1 is within the first target range (step S22). If the acquired first phase difference PD1 is within the first target range (step S22: YES), the frequency changing unit 65 determines whether the acquired second phase difference PD2 is within the second target range (step S23).

[0091] If the acquired first phase difference PD1 is not within the first target range (step S22: NO), or if the acquired second phase difference PD2 is not within the second target range (step S23: NO), the frequency change unit 65 changes the first driving frequency f along the frequency ratio line L1. ｄ１ and the second driving frequency f ｄ２ and PD1 and PD2 by a predetermined amount (step S24). After that, the frequency changer 65 returns the process to step S21 and acquires the first phase difference PD1 and the second phase difference PD2 again.

[0092] The frequency changer 65 repeatedly executes steps S21 to S24 until the first phase difference PD1 falls within the first target range and the second phase difference PD2 falls within the second target range. If the second phase difference PD2 falls within the second target range (step S23: YES), the frequency changer 65 ends the frequency change process.

[0093] In this modification, the frequency change process is performed based on both the first phase difference PD1 and the second phase difference PD2, so that it is possible to more accurately satisfy the required size of the scanning range.

[0094] In the above embodiment, the amplitude voltage V １ , V ２ is set to a preset value, but before the frequency change process, the amplitude voltage V １ , V ２ may be corrected based on the resonance characteristics of the MMD 4. For example, the drive control unit 5 may correct the amplitude voltage V １ the first axis a １ The amplitude voltage V ２ the second axis a ２ The Q value may be corrected in accordance with the amount of change in the Q value of the filter. Here, the amount of change in the Q value refers to the amount of change caused by changes in the external environment, etc.

[0095] In the above embodiment, the amplitude voltage V １ , V ２ is a preset value, but the amplitude voltage V is set to a value that keeps the area and shape of the image drawn on the surface 6 to be scanned by the light beam LB constant. １ , V ２ It is also preferable to correct the value from a preset value. １ and the second axis a ２ When the voltage swings around １ , V ２The correction amount of can be calculated based on the Q value obtained from the frequency characteristics when the mirror unit 20 is driven in a single axis. Therefore, before starting the optical scanning device 2, the mirror unit 20 is driven in a single axis to measure the first Q value and the second Q value, and the dissipated energy (energy leaking from the MMD 4 to the surrounding environment) is calculated from the amount of change in the first Q value and the second Q value. The amplitude voltage V １ , V ２ Here, the first Q value is the correction amount for the first axis a １ The second Q value is the Q value for the second axis a ２ Specifically, the Q value of the amplitude voltage V required to reduce the dissipated energy is １ , V ２ The correction amount of the amplitude voltage V １ , V ２ By correcting the above, the area and shape of the image can be made constant. When the mirror unit 20 is driven on a single axis, the first Q value and the second Q value can be easily and accurately calculated. １ , V ２ can be easily corrected with high accuracy.

[0096] When the mirror unit 20 is driven in a single axis to measure the first Q value and the second Q value, the drive control unit 5 controls the amplitude voltage V １Ｓ , V ２Ｓ It is preferable that the amplitude voltage V is set to a predetermined value. Here, the predetermined value is the amplitude voltage V that is set when measuring the first resonance frequency and the second resonance frequency to obtain the frequency ratio line L0 before correction. １Ｓ , V ２Ｓ is.

[0097] The drive control unit 5 also controls the amplitude voltage V １ , V ２ the first axis a １ and the second axis a ２ The amplitude voltage V during single-axis driving for each of １Ｓ , V ２Ｓ For example, the drive control unit 5 may correct the amplitude voltage V １Ｓ , V ２ＳThe change ratio is calculated for each of the amplitude voltages V １ , V ２ By multiplying by this, the amplitude voltage V １ , V ２ The change ratio is a value obtained by dividing the value after the change by the value before the change. Specifically, the drive control unit 5 corrects the mirror unit 20 along the first axis a １ When a single axis is driven around the sensor, the amplitude (for example, Vpp value) of the first sensor signal S1 becomes a preset value (for example, maximum value). １Ｓ The mirror part 20 is aligned with the second axis a ２ When a single axis is driven around the sensor, the amplitude (for example, Vpp value) of the second sensor signal S2 becomes a preset value (for example, maximum value). ２Ｓ The drive control unit 5 measures the amplitude voltage V when the uncorrected frequency ratio line L0 is obtained. １Ｓ , V ２Ｓ The measured value of and the newly measured amplitude voltage V １Ｓ , V ２Ｓ By comparing the measured value of the amplitude voltage V １Ｓ , V ２Ｓ In both cases before and after the change, the amplitude of the first sensor signal S1 becomes a preset value. １Ｓ When measuring the first driving frequency f ｄ１ is the first resonance frequency, and the amplitude of the second sensor signal S2 becomes a preset value. ２Ｓ When measuring the second driving frequency f ｄ２ is preferably set as the second resonant frequency.

[0098] Further, in order to obtain the frequency ratio line L0, the first drive frequency f when the mirror section 20 is driven in two directions is calculated based on the ratio between the first resonance frequency and the second resonance frequency measured by driving the mirror section 20 in a single direction. ｄ１ and the second driving frequency f ｄ２ The frequency ratio of

[0099] The configuration of the MMD 4 shown in the above embodiment is an example. The configuration of the MMD 4 can be modified in various ways. For example, １The first actuator 31 that swings the mirror unit 20 around the second axis a is disposed on the second movable frame 24. ２ A second actuator 32 for swinging the periphery may be disposed on the first movable frame 22 .

[0100] In the above embodiment, the first angle sensor 11A is １ The piezoelectric element 12 is configured by two piezoelectric elements 12 arranged at positions facing each other with the first axis a １ Similarly, in the above embodiment, the second angle sensor 11B may be configured by one piezoelectric element 12 arranged near the second axis a ２ The piezoelectric element 13 is configured by two piezoelectric elements 13 arranged at positions facing each other with the second axis a ２ Alternatively, the piezoelectric element 13 may be configured by a single piezoelectric element 13 disposed in the vicinity of the piezoelectric element 13 .

[0101] The hardware configuration of the drive control unit 5 can be modified in various ways. The drive control unit 5 may be configured with either an analog circuit or a digital circuit, or both. The drive control unit 5 may be configured with a single processor, or may be configured with a combination of two or more processors of the same or different types. Processors include a central processing unit (CPU), a programmable logic device (PLD), a dedicated electrical circuit, etc. 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 a field programmable gate array (FPGA), whose circuit configuration can be changed after manufacturing. A dedicated electrical circuit is a processor, such as an application specific integrated circuit (ASIC), having a circuit configuration designed specifically to execute specific processing.

[0102] All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

[0103] The following technology can be understood from the above description. [Supplementary Item 1] A device comprising: a mirror unit having a reflective surface that reflects incident light; a first actuator that swings the mirror unit around a first axis; a second actuator that swings the mirror unit around a second axis that intersects the first axis; a first angle sensor that outputs a signal according to the angle of the mirror unit about the first axis; and a processor that applies a first drive signal having a first drive frequency to the first actuator and applies a second drive signal having a second drive frequency to the second actuator, wherein the processor derives a first phase difference between the first drive signal and the output signal of the first angle sensor based on the output signal of the first angle sensor, and performs processing to change the first drive frequency and the second drive frequency along a predetermined frequency ratio line while maintaining the ratio between the first drive frequency and the second drive frequency so that the first phase difference falls within a first target range, An optical scanning device, wherein the frequency ratio line is a line representing a frequency ratio corrected based on an amount of change in the ratio between a first resonance frequency when the mirror unit is oscillated about the first axis and a second resonance frequency when the mirror unit is oscillated about the second axis. [Supplementary Item 2] The optical scanning device according to Supplementary Item 1, wherein the first target range is a range determined based on a phase difference between the first drive signal and the output signal of the first angle sensor when the mirror unit is oscillated about the first axis, with the first drive frequency as a resonance frequency. [Supplementary Item 3] The optical scanning device according to Supplementary Item 1 or Supplementary Item 2, wherein amplitude voltages of the first drive signal and the second drive signal are preset values. [Supplementary Item 4] The optical scanning device according to Supplementary Item 1, wherein the amplitude voltages of the first drive signal and the second drive signal are values ​​corrected according to an amount of change in the Q value for each of the first axis and the second axis. [Supplementary Item 5] The optical scanning device according to Supplementary Item 1, wherein the amplitude voltages of the first drive signal and the second drive signal are values ​​corrected according to the amount of change in the amplitude voltage for each of the first axis and the second axis.[Supplementary Item 6] The optical scanning device of any one of Supplementary Items 1 to 5, wherein the processor derives a first integrated value by integrating a first phase delay time of an output signal of the first angle sensor relative to the first drive signal a first integration count that is an integer multiple of a count corresponding to one frame period, and sets the first phase difference to an average value obtained by dividing the derived first integrated value by the first integration count. [Supplementary Item 7] The optical scanning device of any one of Supplementary Items 1 to 6, further comprising a second angle sensor that outputs a signal according to an angle of the mirror section about the second axis, and wherein the processor derives a second phase difference between the second drive signal and the output signal of the second angle sensor based on the output signal of the second angle sensor, and changes the first drive frequency and the second drive frequency so that the first phase difference is within the first target range and the second phase difference is within a second target range. [Supplementary Item 8] The optical scanning device according to Supplementary Item 7, wherein the second target range is a range determined based on a phase difference between the second drive signal and the output signal of the second angle sensor when the mirror unit is oscillated around the second axis with the second drive frequency as a resonance frequency. [Supplementary Item 9] The optical scanning device according to Supplementary Item 7 or Supplementary Item 8, wherein the processor derives a second integrated value by integrating a second phase delay time of the output signal of the second angle sensor relative to the second drive signal a second integration number that is an integer multiple of a number corresponding to one frame period, and divides the derived second integrated value by the second integration number to obtain an average value as the second phase difference.

Claims

a first actuator that swings the mirror unit around a first axis; a second actuator that swings the mirror unit around a second axis that intersects the first axis; a first angle sensor that outputs a signal according to the angle of the mirror unit around the first axis; and a processor that applies a first drive signal having a first drive frequency to the first actuator and applies a second drive signal having a second drive frequency to the second actuator, wherein the processor derives a first phase difference between the first drive signal and the output signal of the first angle sensor based on an output signal of the first angle sensor, and performs a process of changing the first drive frequency and the second drive frequency along a predetermined frequency ratio line while maintaining the ratio between the first drive frequency and the second drive frequency so that the first phase difference falls within a first target range, the frequency ratio line being a line that represents a frequency ratio corrected based on an amount of change in the ratio between a first resonance frequency when the mirror unit is swung around the first axis and a second resonance frequency when the mirror unit is swung around the second axis. Optical scanning device.

2. An optical scanning device as described in claim 1, wherein the first target range is a range determined based on a phase difference between the first drive signal and the output signal of the first angle sensor when the mirror portion is oscillated around the first axis with the first drive frequency as a resonant frequency.

3. The optical scanning device according to claim 1, wherein the amplitude voltages of the first drive signal and the second drive signal are preset values.

4. The optical scanning device according to claim 1, wherein the amplitude voltages of the first drive signal and the second drive signal are values ​​corrected according to the amount of change in Q value for each of the first axis and the second axis.

5. The optical scanning device according to claim 1, wherein the amplitude voltages of the first drive signal and the second drive signal are values ​​corrected according to the amount of change in the amplitude voltage for each of the first axis and the second axis.

6. The optical scanning device of claim 1, wherein the processor derives a first integrated value by integrating a first phase delay time of an output signal of the first angle sensor relative to the first drive signal a first integration count which is an integer multiple of a count corresponding to one frame period, and divides the derived first integrated value by the first integration count to obtain an average value which is the first phase difference.

7. An optical scanning device as described in claim 1, further comprising a second angle sensor that outputs a signal according to the angle of the mirror section about the second axis, wherein the processor derives a second phase difference between the second drive signal and the output signal of the second angle sensor based on the output signal of the second angle sensor, and changes the first drive frequency and the second drive frequency so that the first phase difference is within the first target range and the second phase difference is within a second target range.

8. An optical scanning device as described in claim 7, wherein the second target range is a range determined based on a phase difference between the second drive signal and an output signal of the second angle sensor when the mirror portion is oscillated around the second axis with the second drive frequency as a resonant frequency.

9. The optical scanning device of claim 8, wherein the processor derives a second integrated value by integrating a second phase delay time of the output signal of the second angle sensor relative to the second drive signal a second integration count that is an integer multiple of a count corresponding to one frame period, and divides the derived second integrated value by the second integration count to obtain an average value, which is the second phase difference.

10. A method for driving an optical scanning device comprising: a mirror section having a reflective surface that reflects incident light; a first actuator that oscillates the mirror section about a first axis; a second actuator that oscillates the mirror section about a second axis intersecting the first axis; a first angle sensor that outputs a signal according to an angle of the mirror section about the first axis; and a processor that applies a first drive signal having a first drive frequency to the first actuator and applies a second drive signal having a second drive frequency to the second actuator, the method comprising the steps of: the processor deriving a first phase difference between the first drive signal and an output signal of the first angle sensor based on an output signal of the first angle sensor; and performing a process of changing the first drive frequency and the second drive frequency while maintaining the ratio between the first drive frequency and the second drive frequency along a preset frequency ratio line so that the first phase difference falls within a first target range, a frequency ratio line that represents a frequency ratio corrected based on an amount of change in a ratio between a first resonance frequency when the mirror portion is oscillated around the first axis and a second resonance frequency when the mirror portion is oscillated around the second axis.

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