Mirror driving device and optical scanning device

Abstract

This mirror drive device comprises a first drive signal generation circuit that generates a first drive signal having a first frequency, a second drive signal generation circuit that generates a second drive signal having a second frequency, a first rectangular wave signal generation circuit that has a first phase accumulator that accumulates first phase amounts in synchronization with a clock signal and generates a first rectangular wave signal having a first frequency on the basis of the output of the first phase accumulator, a second rectangular wave signal generation circuit that has a second phase accumulator that accumulates second phase amounts in synchronization with the clock signal and generates a second rectangular wave signal having a second frequency on the basis of the output of the second phase accumulator, and a frame synchronization signal generation circuit that generates a frame synchronization signal in response to the coincidence of rising or falling of the first rectangular wave signal and the second rectangular wave signal.

Description

Mirror drive device and optical scanning device

[0001] The technology of the present disclosure relates to a mirror drive device and 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] A micromirror device has a mirror portion that is formed to be swingable around a first axis and a second axis that are orthogonal to each other, and the mirror portion swings around each axis to two-dimensionally scan a light beam reflected by the mirror portion. Also known is a micromirror device that enables Lissajous scanning of a light beam by resonating the mirror portion around each axis. Lissajous scanning refers to forming a Lissajous pattern by scanning a light beam on a surface to be scanned.

[0004] To draw an image in synchronization with the Lissajous scan, it is necessary to generate a synchronization signal (hereinafter referred to as a frame synchronization signal) for each cycle of the Lissajous scan. To generate such a synchronization signal, it is known to provide a micromirror device with a first angle sensor that detects the deflection angle of the mirror unit about a first axis and a second angle sensor that detects the deflection angle of the mirror unit about a second axis (see, for example, JP 2022-184514 A).

[0005] According to the technology described in Japanese Patent Laid-Open No. 2022-184514, it is possible to generate a frame synchronization signal based on the output signals of the first angle sensor and the second angle sensor.

[0006] However, when a frame synchronization signal is generated based on the output signals of the first angle sensor and the second angle sensor, jitter may occur in the frame synchronization signal, causing blurring in the image drawn for each frame. This is because the output signals of the first angle sensor and the second angle sensor are analog signals generated by the piezoelectric effect or the like in response to the oscillation of the mirror, and are not signals that accurately represent one cycle of Lissajous scanning (i.e., one frame period).

[0007] The technique of the present disclosure aims to provide a mirror drive device and an optical scanning device that are capable of generating a frame synchronization signal with reduced jitter.

[0008] In order to achieve the above object, the mirror drive device of the present disclosure is a mirror drive device that drives a mirror device having a mirror portion that oscillates around a first axis in response to a first drive signal and oscillates around a second axis in response to a second drive signal, and is equipped with: a first drive signal generation circuit that generates a first drive signal having a first frequency based on a clock signal; a second drive signal generation circuit that generates a second drive signal having a second frequency based on the clock signal; a first rectangular wave signal generation circuit that has a first phase accumulator that accumulates by a first phase amount corresponding to the first frequency in synchronization with the clock signal and generates a first rectangular wave signal having the first frequency based on the output of the first phase accumulator; a second rectangular wave signal generation circuit that has a second phase accumulator that accumulates by a second phase amount corresponding to the second frequency in synchronization with the clock signal and generates a second rectangular wave signal having the second frequency based on the output of the second phase accumulator; and a frame synchronization signal generation circuit that generates a frame synchronization signal in response to the matching of the rising or falling edges of the first rectangular wave signal and the second rectangular wave signal.

[0009] It is preferable that the mirror device has a first angle sensor that outputs a first angle signal corresponding to the angle of the mirror portion about the first axis, and a second angle sensor that outputs a second angle signal corresponding to the angle of the mirror portion about the second axis.

[0010] It is preferable to include a first cross signal generation circuit that generates a first cross signal indicating that the angle around the first axis has passed the reference angle based on the first angle signal, and a second cross signal generation circuit that generates a second cross signal indicating that the angle around the second axis has passed the reference angle based on the second angle signal.

[0011] It is preferable that the device is provided with a reset control circuit that performs reset control to simultaneously reset the accumulated values ​​of the first phase accumulator and the second phase accumulator when the time difference between the rise or fall of the first cross signal and the second cross signal becomes equal to or less than a threshold value, and that the first phase accumulator and the second phase accumulator start accumulating from the point at which they are reset.

[0012] The reference angle is preferably 0 degrees.

[0013] It is preferable that the reset control circuit performs reset control when a predetermined condition is satisfied.

[0014] The predetermined condition is preferably that a certain period of time has elapsed or that the environmental temperature has changed by a certain amount or more.

[0015] The optical scanning device disclosed herein is an optical scanning device comprising: a mirror device having a mirror portion that oscillates around a first axis in response to a first drive signal and oscillates around a second axis in response to a second drive signal; and a mirror drive device that drives the mirror device, wherein the mirror drive device comprises: a first drive signal generation circuit that generates a first drive signal having a first frequency based on a clock signal; a second drive signal generation circuit that generates a second drive signal having a second frequency based on the clock signal; a first rectangular wave signal generation circuit that has a first phase accumulator that accumulates by a first phase amount corresponding to the first frequency in synchronization with the clock signal, and generates a first rectangular wave signal having the first frequency based on the output of the first phase accumulator; a second rectangular wave signal generation circuit that has a second phase accumulator that accumulates by a second phase amount corresponding to the second frequency in synchronization with the clock signal, and generates a second rectangular wave signal having the second frequency based on the output of the second phase accumulator; and a frame synchronization signal generation circuit that generates a frame synchronization signal in response to the rising or falling edges of the first rectangular wave signal and the second rectangular wave signal coinciding.

[0016] According to the technique of the present disclosure, it is possible to provide a mirror driving device and an optical scanning device that are capable of generating a frame synchronization signal with reduced jitter.

[0017] 1 is a schematic diagram of an image drawing system; FIG. 1 is an external perspective view of a micromirror device; FIG. 2 is a graph showing an example of a first drive signal and a second drive signal; FIG. 3 is a block diagram showing an example of the configuration of a drive control device; FIG. 4 is a block diagram showing the configuration of a first drive signal generating section and a second drive signal generating section; FIG. 5 is a block diagram showing the configuration of a first rectangular wave signal generating section and a second rectangular wave signal generating section; FIG. 6 is a block diagram showing an example of the configuration of a frame synchronization signal generating section; FIG. 7 is a diagram showing an example of a Lissajous pattern; FIG. 8 is a diagram showing an example of a frame synchronization signal; FIG. 9 is a diagram showing an example of a first cross signal generating process; FIG. 10 is a flowchart showing an example of the flow of reset control; FIG. 11 is a diagram explaining a time difference; FIG. 12 is a flowchart showing an example of the execution timing of reset control; and FIG. 13 is a diagram explaining the effects of the embodiment.

[0018] An example of an embodiment of the technology of the present disclosure will be described with reference to the accompanying drawings.

[0019] 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 device 5. The MMD 4 is an example of a "mirror device" according to the technology of the present disclosure.

[0020] 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 device 5. The surface 6 to be scanned may be a screen, the retina of a human eye, or the like.

[0021] The image rendering system 10 is applicable to, for example, a Lissajous scanning laser display. Specifically, the image rendering system 10 is applicable to laser scan displays such as AR (Augmented Reality) glasses and VR (Virtual Reality) glasses.

[0022] MMD4 is the first axis a １ and the first axis a １ The second axis a intersects with ２ The micromirror device is a piezoelectric two-axis drive type that can oscillate the mirror portion 20 (see FIG. 2) around the first axis a. １ The direction parallel to this is the X direction, and the second axis a ２ 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.

[0023] 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). The light source 3 may irradiate the light beam LB perpendicularly to a reflecting surface 20A (see FIG. 2 ) of the mirror unit 20 of the MMD 4 when the mirror unit 20 is stationary. Note that if the light beam LB is irradiated perpendicularly to the reflecting surface 20A from the light source 3, the light source 3 may become an obstacle when the light beam LB is scanned and drawn on the scanned surface 6. For this reason, it is preferable to control the light beam LB emitted from the light source 3 to irradiate the reflecting surface 20A perpendicularly using an optical system. 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.

[0024] The drive control device 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.

[0025] The drive control device 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.

[0026] 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.

[0027] 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

[0028] 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 .

[0029] 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

[0030] 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.

[0031] 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.

[0032] 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

[0033] 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.

[0034] 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

[0035] 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.

[0036] 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 .

[0037] 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 A signal corresponding to the angle of the surroundings (hereinafter referred to as a first angle signal S1) is output.

[0038] 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 A signal corresponding to the angle of the surroundings (hereinafter referred to as a second angle signal S2) is output.

[0039] 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.

[0040] 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 device 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°).

[0041] The first oscillation amplitude A １ 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 XZ plane.

[0042] 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 device 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°).

[0043] 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.

[0044] 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 FIG. 3B shows the drive voltage waveform V ２Ａ (t) and V ２Ｂ (t) is shown.

[0045] 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)

[0046] Here, V １ is the amplitude voltage. V ｏｆｆ１ is the bias voltage. ｏｆｆ１ may be zero.ｄ１ is the first frequency; t is time; α is the driving voltage waveform V １Ａ (t) and V １Ｂ In this embodiment, for example, α=180°.

[0047] The two piezoelectric elements 30 constituting the first actuator 31 are applied with a driving voltage waveform V １Ａ (t) and V １Ｂ When the first frequency f(t) is applied to the mirror section 20, the mirror section 20 receives the first frequency f ｄ１ The first axis a １ Swinging around.

[0048] 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)

[0049] Here, V ２ is the amplitude voltage. V ｏｆｆ２ is the bias voltage. ｏｆｆ２ may be zero. ｄ２ is the second frequency; t is time; β is the driving voltage waveform V ２Ａ (t) and V ２Ｂ In this embodiment, for example, β=180°. Also, φ is the phase difference between the first drive signal and the second drive signal.

[0050] The two piezoelectric elements 30 constituting the second actuator 32 are driven by a driving voltage waveform V ２Ａ (t) and V ２Ｂ When the second frequency f(t) is applied to the mirror section 20, the mirror section 20 receives the second frequency f ｄ２ and the second axis a ２ Swinging around.

[0051] first frequency f ｄ１ The mirror unit 20 is aligned with the first axis a １The second 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 Higher than the surrounding oscillation frequency.

[0052] 4 shows an example of the configuration of the drive control device 5. The drive control device 5 has a mirror drive device 4A and a light source drive device 3A. The mirror drive device 4A has a first drive signal generation unit 40A, a second drive signal generation unit 40B, a frequency setting unit 41, a first reset control unit 42, a first rectangular wave signal generation unit 43A, a second rectangular wave signal generation unit 43B, a frame synchronization signal generation unit 44, a first cross signal generation unit 45A, a second cross signal generation unit 45B, a second reset control unit 46, and an oscillator 47. The oscillator 47 supplies a clock signal CLK to each unit.

[0053] The first drive signal generating unit 40A and the second drive signal generating unit 40B each include a DDS (Direct Digital Synthesizer). The first drive signal generating unit 40A generates the above-mentioned first drive signal based on a clock signal CLK. The second drive signal generating unit 40B generates the above-mentioned second drive signal based on the clock signal CLK. The first drive signal generating unit 40A corresponds to the "first drive signal generating circuit" according to the technology of the present disclosure. The second drive signal generating unit 40B corresponds to the "second drive signal generating circuit" according to the technology of the present disclosure.

[0054] The frequency setting unit 41 sets the first frequency f ｄ１ is set in the first drive signal generator 40A, and the second frequency f ｄ２The first reset control unit 42 controls the phase difference φ between the first and second drive signals by transmitting a first reset signal RS1 to the first drive signal generation unit 40A and a second reset signal RS2 to the second drive signal generation unit 40B at a predetermined timing.

[0055] The first rectangular wave signal generating unit 43A generates a first rectangular wave signal SQ1 based on the clock signal CLK. The second rectangular wave signal generating unit 43B generates a second rectangular wave signal SQ2 based on the clock signal CLK. The frequency setting unit 41 sets a first setting value M1 for the first rectangular wave signal generating unit 43A and a second setting value M2 for the second rectangular wave signal generating unit 43B. That is, the first rectangular wave signal SQ1 has the same frequency as the first drive signal, and the second rectangular wave signal SQ2 has the same frequency as the second drive signal.

[0056] The frame synchronization signal generation unit 44 generates a frame synchronization signal SYNC that indicates the start timing of one cycle of Lissajous scanning based on the first rectangular wave signal SQ1 and the second rectangular wave signal SQ2, and outputs the generated frame synchronization signal SYNC to the light-source driving device 3A. Specifically, the frame synchronization signal generation unit 44 generates the frame synchronization signal SYNC in response to the matching of the rising or falling edges of the first rectangular wave signal SQ1 and the second rectangular wave signal SQ2. In this embodiment, the frame synchronization signal generation unit 44 generates the frame synchronization signal SYNC in response to the matching of the rising edges of the first rectangular wave signal SQ1 and the second rectangular wave signal SQ2. The frame synchronization signal generation unit 44 corresponds to a "frame synchronization signal generation circuit" according to the technology disclosed herein.

[0057] The first cross signal generator 45A generates a first cross signal ZC1 based on the first angle signal S1 output from the first angle sensor 11A. Specifically, the first cross signal generator 45A subtracts one of the two signals output from the two piezoelectric elements 12 that make up the first angle sensor 11A from the other, thereby generating a first cross signal ZC1 for the second axis a. ２ After generating the first angle signal S1 from which vibration noise caused by surrounding vibrations has been removed, the first cross signal ZC1 is generated.１ This signal indicates that the angle around the reference angle has passed the reference angle. The first cross signal generating unit 45A corresponds to a "first cross signal generating circuit" according to the technology of the present disclosure.

[0058] The second cross signal generator 45B generates a second cross signal ZC2 based on the second angle signal S2 output from the second angle sensor 11B. Specifically, the second cross signal generator 45B subtracts one of the two signals output from the two piezoelectric elements 13 constituting the second angle sensor 11B from the other, thereby generating a second cross signal ZC2 for the first axis a. １ After generating the second angle signal S2 from which vibration noise caused by the surrounding vibration has been removed, the second cross signal ZC2 is generated. ２ This signal indicates that the angle around the reference angle has passed the reference angle. The second cross signal generating unit 45B corresponds to the "second cross signal generating circuit" according to the technology of the present disclosure.

[0059] In this embodiment, the reference angle is 0 degrees. That is, the first cross signal ZC1 and the second cross signal ZC2 are so-called zero cross signals.

[0060] When the time difference between the rise or fall of the first cross signal ZC1 and the second cross signal ZC2 becomes equal to or less than a threshold, the second reset control unit 46 simultaneously resets the first square wave signal generation unit 43A and the second square wave signal generation unit 43B by sending a reset signal (hereinafter referred to as a simultaneous reset signal RS0) to the first square wave signal generation unit 43A and the second square wave signal generation unit 43B. The second reset control unit 46 corresponds to the "reset control circuit" according to the technology of the present disclosure.

[0061] The first and second rectangular wave signal generating units 43A and 43B start generating the first and second rectangular wave signals SQ1 and SQ2 from the point when they are simultaneously reset, so that the cycle in which the frame synchronization signal SYNC is generated coincides with one frame cycle.

[0062] Next, the configuration of each section within the mirror driver 4A will be described. Fig. 5 shows the configuration of the first drive signal generator 40A and the second drive signal generator 40B. The first drive signal generator 40A includes a DDS 50A and a phase shift circuit 51A. The DDS 50A includes a phase accumulator 52A, a waveform read-only memory (ROM) 53A, and a digital-to-analog converter (DAC) 54A.

[0063] The phase accumulator 52A has 2 phases between 0 and 2π radians. Ｎ The phase accumulator 52A is an N-bit modulo-N counter having steps. For example, N=64. The phase accumulator 52A accumulates the first phase amount Δ1 corresponding to the first set value M1 in synchronization with the clock signal CLK, and outputs the accumulated values ​​sequentially to the waveform ROM 53A. The phase accumulator 52A starts accumulation from 0, and when the accumulated value reaches 2π, it resets the accumulated value to 0 and starts accumulation again. The first set value M1 is the first frequency f ｄ１ is the tuning word value corresponding to

[0064] The frequency of the clock signal CLK is f ｃ Then, the first set value M1 is set to satisfy the following formula: ｄ１ = f ｃ ×M1 / 2 Ｎ

[0065] The first phase amount Δ1 satisfies the following formula: Δ1=2π×M1 / 2 Ｎ

[0066] The waveform ROM 53A stores one cycle of sine wave data as reference wave data. The accumulated value from the phase accumulator 52A is input to the waveform ROM 53A as an address. One cycle of sine wave signal is output by reading data from the first address (corresponding to 0) to the last address (corresponding to 2π) of the waveform ROM 53A.

[0067] The DAC 54A converts the digital sine wave signal output from the waveform ROM 53A into an analog signal and outputs it from the DDS 50A. The sine wave signal output from the DDS 50A has a first frequency f ｄ１ It has.

[0068] The phase shift circuit 51A shifts the phase of the sine wave signal output from the DDS 50A to generate the drive voltage waveform V １Ａ (t) and V １Ｂ (t) is generated and output. １Ａ (t) and V １Ｂ (t) is applied to the two piezoelectric elements 30 that constitute the first actuator 31. As a result, the mirror section 20 rotates along the first axis a １ The first angle sensor 11A swings around the center axis, and outputs a first angle signal S1.

[0069] The second drive signal generating section 40B includes a DDS 50B and a phase shift circuit 51 B. The DDS 50B includes a phase accumulator 52B, a waveform ROM 53B, and a DAC 54B.

[0070] The phase accumulator 52B stores 2π between 0 and 2π radians. Ｎ The phase accumulator 52B is an N-bit modulo-N counter having steps. The phase accumulator 52B accumulates the second phase amount Δ2 corresponding to the second set value M2 in synchronization with the clock signal CLK, and outputs the accumulated values ​​sequentially to the waveform ROM 53B. The phase accumulator 52B starts accumulation from 0, and when the accumulated value reaches 2π, it resets the accumulated value to 0 and starts accumulation again. The second set value M2 is set to the second frequency f ｄ２ is the tuning word value corresponding to

[0071] The second set value M2 is set to satisfy the following formula: ｄ２ = f ｃ ×M2 / 2 Ｎ

[0072] The second phase amount Δ2 satisfies the following formula: Δ2=2π×M2 / 2 Ｎ

[0073] The waveform ROM 53B stores one cycle of sine wave data as reference wave data. The accumulated value from the phase accumulator 52B is input to the waveform ROM 53B as an address. One cycle of sine wave signal is output by reading data from the first address to the last address of the waveform ROM 53B.

[0074] The DAC 54B converts the digital sine wave signal output from the waveform ROM 53B into an analog signal and outputs it from the DDS 50B. The sine wave signal output from the DDS 50B has a second frequency f ｄ２ It has.

[0075] The phase shift circuit 51B shifts the phase of the sine wave signal output from the DDS 50B to generate the drive voltage waveform V ２Ａ (t) and V ２Ｂ (t) is generated and output. ２Ａ (t) and V ２Ｂ (t) is applied to the two piezoelectric elements 30 that constitute the second actuator 32. As a result, the mirror section 20 rotates along the second axis a ２ The second angle sensor 11B swings around the center axis, and outputs a second angle signal S2.

[0076] The first reset control unit 42 transmits a first reset signal RS1 to the phase accumulator 52A and transmits a second reset signal RS2 to the phase accumulator 52B. Upon receiving the first reset signal RS1, the phase accumulator 52A resets its accumulated value to 0 and starts accumulation. Upon receiving the second reset signal RS2, the phase accumulator 52B resets its accumulated value to 0 and starts accumulation. The time difference between when the first reset control unit 42 transmits the first reset signal RS1 and the second reset signal RS2 corresponds to the phase difference φ.

[0077] 6 shows the configuration of the first rectangular wave signal generating unit 43A and the second rectangular wave signal generating unit 43B. The first rectangular wave signal generating unit 43A is configured by a DDS 60A having a phase accumulator 61A and a waveform ROM 62A. The first rectangular wave signal generating unit 43A corresponds to the "first rectangular wave signal generating circuit" according to the technology of the present disclosure.

[0078] The phase accumulator 61A has the same configuration as the phase accumulator 52A of the DDS 50A, and accumulates a first phase amount Δ1 corresponding to a first set value M1 in synchronization with the clock signal CLK, and sequentially outputs the accumulated values ​​to the waveform ROM 62A. The phase accumulator 61A corresponds to the “first phase accumulator” according to the technology of the present disclosure.

[0079] The waveform ROM 62A stores one cycle of a rectangular wave as reference wave data. The accumulated value is input to the waveform ROM 62A from the phase accumulator 61A as an address. One cycle of a rectangular wave signal is output by reading data from the first address to the last address of the waveform ROM 62A. The rectangular wave signal output from the waveform ROM 62A has a first frequency f ｄ１ and corresponds to the first rectangular wave signal SQ1 described above.

[0080] It should be noted that it is not necessary to use the waveform ROM 62A to generate the square wave signal. Instead of the waveform ROM 62A, it is also possible to generate the first square wave signal SQ1 using a switching element or the like.

[0081] The phase accumulator 61B has the same configuration as the phase accumulator 52B of the DDS 50B, and accumulates a second phase amount Δ2 corresponding to the second set value M2 in synchronization with the clock signal CLK, and sequentially outputs the accumulated values ​​to the waveform ROM 62B. The phase accumulator 61B corresponds to the "second phase accumulator" according to the technology of the present disclosure.

[0082] The waveform ROM 62B stores one cycle of a rectangular wave as reference wave data. The accumulated value is input to the waveform ROM 62B from the phase accumulator 61B as an address. One cycle of a rectangular wave signal is output by reading data from the first address to the last address of the waveform ROM 62B. The rectangular wave signal output from the waveform ROM 62B has a second frequency f ｄ２ and corresponds to the second square wave signal SQ2 described above.

[0083] It should be noted that it is not necessary to use the waveform ROM 62B to generate the square wave signal. Instead of the waveform ROM 62B, it is also possible to generate the second square wave signal SQ2 using a switching element or the like.

[0084] The second reset control unit 46 simultaneously transmits a simultaneous reset signal RS0 to the phase accumulator 61A and the phase accumulator 61B. Upon receiving the simultaneous reset signal RS0, the phase accumulator 61A and the phase accumulator 61B simultaneously reset their accumulated values ​​to 0 and start accumulating.

[0085] 7 is a schematic diagram showing the process of generating the first rectangular wave signal SQ1 by the first rectangular wave signal generating unit 43A. FIG. 7 compares the case where M1=1 with the case where M1=3. The first phase amount Δ1 changes according to the first set value M1, so that the period T １ The period T １ is the first frequency f ｄ１ And, T １ = 1 / f ｄ１ The second rectangular wave signal SQ2 has the same relationship as the first rectangular wave signal SQ1.

[0086] 8 shows an example configuration of the frame synchronization signal generator 44. The frame synchronization signal generator 44 has a match determination unit 44A, a pulse signal generator 44B, and a pulse width expander 44C. The first rectangular wave signal SQ1 and the second rectangular wave signal SQ2 are input to the match determination unit 44A. The match determination unit 44A determines whether the rising edges of the first rectangular wave signal SQ1 and the second rectangular wave signal SQ2 match. Specifically, the match determination unit 44A performs a determination every clock cycle in synchronization with the clock signal CLK.

[0087] The pulse signal generating unit 44B generates a pulse signal PS having a pulse width of one clock period in response to the match determining unit 44A determining that the rising edges of the first rectangular wave signal SQ1 and the second rectangular wave signal SQ2 match.

[0088] The pulse width expander 44C is, for example, a latch circuit, and expands the pulse width of the pulse signal PS. The pulse signal PS with its pulse width expanded is the frame synchronization signal SYNC described above. Note that the pulse signal PS may be used as the frame synchronization signal SYNC without providing the pulse width expander 44C.

[0089] FIG. 9 shows an example of a Lissajous pattern. For the sake of simplicity, in FIG. 9,ｄ１ :f ｄ２ = 4:3, and φ = 0. Fig. 10 shows the first rectangular wave signal SQ1 and the second rectangular wave signal SQ2 generated in the case of the Lissajous pattern shown in Fig. 9 .

[0090] 10, a frame synchronization signal SYNC is generated for each frame period TF. One frame period TF is equal to the period T of the first rectangular wave signal SQ1. １ and the period T of the second rectangular wave signal SQ2 ２ In this example, TF=4×T １ is.

[0091] 11 shows an example of a process for generating the first cross signal ZC1 by the first cross signal generator 45 A. The first cross signal generator 45 A generates the first cross signal ZC1 so that the first cross signal ZC1 rises when the first angle signal S1 crosses zero from negative to positive and falls when the first angle signal S1 crosses zero from positive to negative.

[0092] 12 shows an example of the process of generating the second cross signal ZC2 by the second cross signal generator 45B. The second cross signal generator 45B generates the second cross signal ZC2 so that it rises when the second angle signal S2 crosses zero from negative to positive and falls when the second angle signal S2 crosses zero from positive to negative.

[0093] 13 shows an example of the flow of reset control by the second reset control unit 46. First, the second reset control unit 46 detects the rising edge of the first cross signal ZC1 (step S10). Next, the second reset control unit 46 detects the rising edge of the second cross signal ZC2 (step S11).

[0094] Next, the second reset control unit 46 determines whether the time difference Δt between the time when the rising edge of the first cross signal ZC1 is detected and the time when the rising edge of the second cross signal ZC2 is detected is equal to or less than a threshold value (step S12). If the time difference Δt is greater than the threshold value (step S12: NO), the second reset control unit 46 returns the process to step S10. The second reset control unit 46 repeats steps S10 to S12, and when the time difference Δt becomes equal to or less than the threshold value, transmits a simultaneous reset signal RS0 (step S13).

[0095] 14 illustrates the time difference Δt calculated by the second reset control unit 46. For example, the time difference Δt is the elapsed time from when the first cross signal ZC1 rises until the next time the second cross signal ZC2 rises. The smaller the threshold value, the more accurately the period of the Lissajous scan caused by the oscillation of the mirror unit 20 can be detected. However, since a deviation may occur between the first cross signal ZC1 and the second cross signal ZC2 due to deterioration over time, etc., it is preferable to determine the threshold value taking this deviation into consideration.

[0096] The reset control by the second reset control unit 46 is performed to compensate for the difference between the actual Lissajous scanning period due to the oscillation of the mirror unit 20 and the generation period of the frame synchronization signal SYNC. In principle, this difference is zero, but it can occur when the characteristics of the MMD 4 change due to changes in environmental temperature, changes over time, etc. For this reason, it is preferable that the reset control be performed when predetermined conditions are met.

[0097] 15 shows an example of the timing of executing reset control. After the MMD 4 starts operating, the second reset control unit 46 determines whether a predetermined condition is met (step S20). For example, the predetermined condition is that a certain amount of time has passed since the previous reset control was performed. Another predetermined condition is that the environmental temperature has changed by more than a certain amount. A temperature sensor may be provided in the MMD 4 to measure the environmental temperature.

[0098] If the predetermined condition is not satisfied (step S20: NO), the second reset control unit 46 executes the determination of step S20 again. If the predetermined condition is satisfied (step S20: YES), the second reset control unit 46 executes the reset control shown in Fig. 13 (step S21). When the reset control ends, the second reset control unit 46 returns the process to step S20.

[0099] FIG. 16 illustrates the effects of the above embodiment. First, as a comparative example, assume that the frame synchronization signal SYNC is generated based on the first cross signal ZC1 and the second cross signal ZC2. This corresponds to generating the frame synchronization signal based on the output signals of the first angle sensor 11A and the second angle sensor 11B. The output signals of the first angle sensor 11A and the second angle sensor 11B are analog signals generated by the piezoelectric effect in response to the oscillation of the mirror unit 20. Therefore, in the comparative example, the generation cycle of the frame synchronization signal SYNC is unstable, resulting in jitter. This causes blurring in the image drawn for each frame.

[0100] In contrast, in the above embodiment, the frame synchronization signal SYNC is generated based on the first rectangular wave signal SQ1 and the second rectangular wave signal SQ2 generated by the phase accumulators 61A and 61B in synchronization with the clock signal CLK, so that the generation cycle of the frame synchronization signal SYNC is stable and jitter can be suppressed, thereby suppressing blurring of the image drawn for each frame.

[0101] The phase accumulator 52A of the first drive signal generating unit 40A and the phase accumulator 52B of the second drive signal generating unit 40B are reset at different times unless φ=0. Furthermore, the phase difference φ changes depending on the type of Lissajous pattern. Therefore, the phase accumulators 52A and 52B cannot be used to generate the first rectangular wave signal SQ1 and the second rectangular wave signal SQ2.

[0102] Furthermore, by performing reset control when the predetermined conditions are satisfied as described above, it is possible to compensate for the difference between the actual Lissajous scanning period due to the oscillation of the mirror section 20 and the generation period of the frame synchronization signal SYNC.

[0103] 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, １ The 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 .

[0104] 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 .

[0105] The hardware configuration of the drive control device 5 can be modified in various ways. The drive control device 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, 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 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) that has a circuit configuration designed specifically to execute specific processing.

[0106] 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.

[0107] The above description allows the understanding of the following technology: [Supplementary Item 1] A mirror drive device for driving a mirror device having a mirror portion that oscillates about a first axis in response to a first drive signal and oscillates about a second axis in response to a second drive signal, comprising: a first drive signal generation circuit that generates the first drive signal having a first frequency based on a clock signal, a second drive signal generation circuit that generates the second drive signal having a second frequency based on the clock signal, a first rectangular wave signal generation circuit that has a first phase accumulator that accumulates in increments of a first phase amount corresponding to the first frequency in synchronization with the clock signal, and generates a first rectangular wave signal having the first frequency based on an output of the first phase accumulator, a second rectangular wave signal generation circuit that has a second phase accumulator that accumulates in increments of a second phase amount corresponding to the second frequency in synchronization with the clock signal, and generates a second rectangular wave signal having the second frequency based on the output of the second phase accumulator, and a frame synchronization signal generation circuit that generates a frame synchronization signal in response to a coincidence of rising or falling edges of the first rectangular wave signal and the second rectangular wave signal. [Supplementary Item 2] The mirror drive device according to Supplementary Item 1, wherein the mirror device comprises: a first angle sensor that outputs a first angle signal corresponding to the angle of the mirror section about the first axis; and a second angle sensor that outputs a second angle signal corresponding to the angle of the mirror section about the second axis. [Supplementary Item 3] The mirror drive device according to Supplementary Item 2, wherein the mirror drive device comprises: a first cross signal generation circuit that generates a first cross signal indicating that the angle about the first axis has passed a reference angle based on the first angle signal; and a second cross signal generation circuit that generates a second cross signal indicating that the angle about the second axis has passed the reference angle based on the second angle signal. [Supplementary Item 4] The mirror drive device according to Supplementary Item 3, further comprising: a reset control circuit that performs reset control to simultaneously reset the accumulated values ​​of the first phase accumulator and the second phase accumulator when a time difference between the rise or fall of the first cross signal and the second cross signal becomes equal to or less than a threshold, wherein the first phase accumulator and the second phase accumulator start accumulating from the point of reset.[Supplementary Item 5] The mirror drive device according to Supplementary Item 4, wherein the reference angle is 0 degrees. [Supplementary Item 6] The mirror drive device according to Supplementary Item 4 or Supplementary Item 5, wherein the reset control circuit performs the reset control when a predetermined condition is satisfied. [Supplementary Item 7] The mirror drive device according to Supplementary Item 6, wherein the predetermined condition is that a predetermined time has elapsed or that the environmental temperature has changed by a predetermined temperature or more.

Claims

1. A mirror drive device that drives a mirror device having a mirror portion that oscillates around a first axis in response to a first drive signal and oscillates around a second axis in response to a second drive signal, comprising: a first drive signal generation circuit that generates the first drive signal having a first frequency based on a clock signal; a second drive signal generation circuit that generates the second drive signal having a second frequency based on the clock signal; a first square wave signal generation circuit that has a first phase accumulator that accumulates in increments of a first phase amount corresponding to the first frequency in synchronization with the clock signal, and generates a first square wave signal having the first frequency based on the output of the first phase accumulator; a second square wave signal generation circuit that has a second phase accumulator that accumulates in increments of a second phase amount corresponding to the second frequency in synchronization with the clock signal, and generates a second square wave signal having the second frequency based on the output of the second phase accumulator; and a frame synchronization signal generation circuit that generates a frame synchronization signal in response to the first square wave signal and the second square wave signal matching in their rising or falling edges.

2. A mirror drive device according to claim 1, wherein the mirror device comprises: a first angle sensor that outputs a first angle signal corresponding to the angle of the mirror section about the first axis; and a second angle sensor that outputs a second angle signal corresponding to the angle of the mirror section about the second axis.

3. A mirror drive device as described in claim 2, comprising: a first cross signal generation circuit that generates a first cross signal indicating that the angle around the first axis has passed a reference angle based on the first angle signal; and a second cross signal generation circuit that generates a second cross signal that indicates that the angle around the second axis has passed the reference angle based on the second angle signal.

4. A mirror drive device as described in claim 3, further comprising a reset control circuit that performs reset control to simultaneously reset the accumulated values ​​of the first phase accumulator and the second phase accumulator when the time difference between the rise or fall of the first cross signal and the second cross signal becomes equal to or less than a threshold value, and the first phase accumulator and the second phase accumulator start accumulating from the point when they are reset.

5. The mirror drive device according to claim 4, wherein the reference angle is 0 degrees.

6. The mirror drive device according to claim 4, wherein the reset control circuit performs the reset control when a predetermined condition is satisfied.

7. The mirror drive device according to claim 6, wherein the predetermined condition is that a certain amount of time has passed or that the environmental temperature has changed by more than a certain amount.

8. An optical scanning device comprising: a mirror device having a mirror portion that oscillates around a first axis in response to a first drive signal and oscillates around a second axis in response to a second drive signal; and a mirror drive device that drives the mirror device, wherein the mirror drive device comprises: a first drive signal generation circuit that generates the first drive signal having a first frequency based on a clock signal; a second drive signal generation circuit that generates the second drive signal having a second frequency based on the clock signal; a first square wave signal generation circuit that has a first phase accumulator that accumulates by a first phase amount corresponding to the first frequency in synchronization with the clock signal, and generates a first square wave signal having the first frequency based on the output of the first phase accumulator; a second square wave signal generation circuit that has a second phase accumulator that accumulates by a second phase amount corresponding to the second frequency in synchronization with the clock signal, and generates a second square wave signal having the second frequency based on the output of the second phase accumulator; and a frame synchronization signal generation circuit that generates a frame synchronization signal in response to the first square wave signal and the second square wave signal matching in their rising or falling edges.

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