Driving circuit for optical deflector, and optical scanner

Abstract

The present invention increases sensor output corresponding to the deflection angle of a mirror of an optical deflector.　The purpose of this driving circuit is to drive an optical deflector equipped with a mirror and an actuator. The driving circuit includes: a control unit; a first voltage generation unit that is interposed between the control unit and a first piezoelectric cantilever group which constitutes part of the actuator, and that is configured so as to be able to supply a drive voltage to the first piezoelectric cantilever group; a second voltage generation unit that is interposed between the control unit and a second piezoelectric cantilever group which constitutes another part of the first actuator, and that is configured so as to be able to suppl a drive voltage to the second piezoelectric cantilever group; a first amplification unit that is interposed between the control unit and the first piezoelectric cantilever group and that is configured so as to be able to amplify a voltage generated by the displacement of the first piezoelectric cantilever group; and a first switch configured so as to be able to switch, under the control of the control unit, between connecting the first piezoelectric cantilever group to either the first voltage generation unit or the first amplification unit.

Description

Drive circuit for optical deflector, optical scanning device

[0001] The present disclosure relates to a drive circuit for an optical deflector and an optical scanning device.

[0002] An optical deflector having a rotatable mirror is known. Such an optical deflector can freely change the reflection direction of light by making light such as laser light incident on the mirror and rotating the mirror. That is, the light can be scanned in one or two directions. For example, Japanese Patent Application Laid-Open No. 2020-11692 (Patent Document 1) describes an optical irradiation device including the above-described optical deflector. The optical deflector includes an actuator provided symmetrically with the mirror interposed therebetween to rotate the mirror, and a sensor provided at each end of these actuators to detect the displacement amount of each actuator. Since the displacement amount of the actuator corresponds to the deflection angle of the mirror, the deflection angle of the mirror can be detected by detecting the displacement amount.

[0003] By the way, in the above-described optical deflector, since the sensor is provided in a smaller area than the actuator, it has been difficult to obtain a sensor output (for example, voltage) at a sufficient level when the deflection angle of the mirror is small.

[0004] Japanese Patent Application Laid-Open No. 2020-11692

[0005] One of the objects of the specific aspect according to the present disclosure is to provide a technique capable of increasing the sensor output corresponding to the deflection angle of the mirror of the optical deflector.

[0006] [1] A drive circuit according to one aspect of the present disclosure is a circuit for driving an optical deflector comprising at least a mirror and a first actuator having a plurality of piezoelectric cantilevers, the drive circuit comprising: a control unit; a first voltage generating unit interposed between a first piezoelectric cantilever group which is part of the first actuator and the control unit and configured to supply a drive voltage to the first piezoelectric cantilever group; a second voltage generating unit interposed between a second piezoelectric cantilever group which is another part of the first actuator and the control unit and configured to supply a drive voltage to the second piezoelectric cantilever group; a first amplification unit interposed between the first piezoelectric cantilever group and the control unit and configured to amplify the voltage generated by the displacement of the first piezoelectric cantilever group; and a first switch interposed between the first voltage generating unit and the first amplification unit and the first piezoelectric cantilever group and configured to switch, under the control of the control unit, whether to connect the first piezoelectric cantilever group to the first voltage generating unit or the first amplification unit. [2] One embodiment of the optical scanning apparatus relating to the present disclosure is an optical scanning apparatus comprising: a drive circuit as described in [1] above; and an optical deflector connected to the drive circuit.

[0007] According to the above configuration, a technique is obtained that makes it possible to increase the sensor output corresponding to the deflection angle of the mirror of the optical deflector.

[0008] Figure 1(A) is a diagram showing the schematic configuration of an optical scanning device according to one embodiment. Figure 1(B) is a schematic diagram illustrating an example of the use of the optical scanning device. Figure 2 is a schematic diagram showing an example of the configuration of an optical deflector. Figure 3 is a circuit diagram showing an example of the configuration of a drive circuit. Figure 4 is a diagram showing a table of the phase of the detection signal and the state of the image when any of the piezoelectric cantilevers from groups A to D are used as sensors, and when image display applications are assumed. Figure 5 is a diagram showing a specific example of the waveform diagram of the drive voltage and detection signal in the case of "Normal" shown in Figure 4. Figure 6(A) is a diagram schematically showing the movement (displacement) of each piezoelectric cantilever from groups A to D at time (1) shown in Figure 5. Figure 6(B) is a diagram schematically showing the movement (displacement) of each piezoelectric cantilever from groups A to D at time (2) shown in Figure 5. Figure 7 is a diagram showing a specific example of the waveform diagram of the drive voltage and detection signal in the case of "TYPE_A" shown in Figure 4. Figure 8(A) schematically shows the movement (displacement) of each piezoelectric cantilever in groups A to D during time (1) as shown in Figure 7. Figure 8(B) schematically shows the movement (displacement) of each piezoelectric cantilever in groups A to D during time (2) as shown in Figure 7. Figure 9 is a diagram showing a specific example of the waveform diagram of the drive voltage and detection signal in the case of "TYPE_C" shown in Figure 4. Figures 10(A) and 10(B) schematically show the movement (displacement) of each piezoelectric cantilever in groups A to D during time (1) and (2) as shown in Figure 9, respectively. Figure 11 is a diagram showing a specific example of the waveform diagram of the drive voltage and detection signal in the case of "TYPE_E" shown in Figure 4. Figures 12(A) and 12(B) schematically show the movement (displacement) of each piezoelectric cantilever in groups A to D during time (1) and (2) as shown in Figure 11, respectively. Figure 13 is a diagram showing an example of the relationship between the sensor detection signal and the deflection angle (mechanical half-angle) of the mirror for each driving method. Figure 14 is a flowchart showing the operation of the control unit of the drive circuit. Figure 15 is a timing chart of each drive voltage and detection signal. Figure 16 is a diagram illustrating the connection state of each switch 53, 54, 63, and 64 of the drive circuit 2 in normal mode. Figure 17 shows an example of the relationship between the detection signal (sensor output) and the deflection angle of the mirror (mechanical half-angle) when using the "Normal" and "TYPE_E" drive methods.Figure 18 is a circuit diagram showing an example of the configuration of a modified drive circuit.

[0009] Figure 1(A) is a diagram showing the schematic configuration of an optical scanning device according to one embodiment. The optical scanning device 100 of this embodiment is for scanning light such as laser light incident from a light source, and is composed of an optical deflector 1 and a drive circuit 2. The optical deflector 1 has a rotatable mirror, and the direction of light reflection can be freely changed by incidenting light such as laser light onto this mirror. The drive circuit 2 is connected to the optical deflector 1 and controls the operation of the optical deflector 1. In this specification, the input / output relationship between the optical deflector 1 and the drive circuit 2 is defined as "input" when the transmission of an electrical signal from the optical deflector 1 to the drive circuit 2, and as "output" when the transmission of an electrical signal from the drive circuit 2 to the optical deflector 1.

[0010] Figure 1(B) is a schematic diagram illustrating an example of the use of the optical scanning device. The optical scanning device 100 according to this embodiment can be used to configure an image projection device (projector) that forms an image on a screen SC by scanning laser light incident from a light source (not shown) in two directions (H direction and V direction). Although not shown or described here, when used for image display purposes, the image projection device is configured by appropriately adding the appropriate components (e.g., optical system) to the optical scanning device 100.

[0011] Figure 2 is a schematic diagram showing an example of the configuration of an optical deflector. The illustrated optical deflector 1 includes a mirror 20, a first support section 22 comprising a pair of torsion bars 21a and 21b, actuators 24 and 26, a second support section 28 supporting the first support section 22, actuators 30 and 32, two sensors 34, and two sensors 36a and 36b. In this specification, actuator 30 corresponds to the "first actuator" and actuator 32 corresponds to the "second actuator".

[0012] The mirror 20 has a reflective surface for reflecting incident light and is configured to be rotatable around two axes, the X-axis and the Y-axis, as shown in the figure. The first support part 22 supports the mirror 20 by a pair of torsion bars 21a and 21b.

[0013] Actuators 24 and 26 generate a driving force to rotate the mirror 20 around the Y-axis via a pair of torsion bars 21a and 21b. The second support portion 28 supports the first support portion 22. Actuators 30 and 32 generate a driving force to rotate the mirror 20 around the X-axis via the second support portion 28 and the first support portion 22.

[0014] Actuators 24, 26 and actuators 30, 32 can each be, for example, piezoelectric, electrostatic, or electromagnetic actuators. In this embodiment, piezoelectric actuators are used as actuators 24 and 26.

[0015] Actuators 30 and 32 each have a configuration in which five piezoelectric cantilevers are connected. Each of the piezoelectric cantilevers 30a, 30b, 30c, 30d, and 30e of actuator 30, and the piezoelectric cantilevers 32a, 32b, 32c, 32d, and 32e of actuator 32, is composed of a piezoelectric body, a lower electrode and an upper electrode positioned on either side of the piezoelectric body, and a support body that supports them. Actuator 32 is positioned on the opposite side of actuator 30 from actuator 30, with the mirror 20 in between.

[0016] Each sensor 34 is used to detect the movement (displacement) of the actuators 24 and 26, and is located adjacent to each torsion bar 21a and 21b. Each sensor 34 is positioned symmetrically with respect to the X-axis.

[0017] Each sensor 36a and 36b is for detecting the movement (displacement) of actuators 30 and 32, and is located adjacent to the ends of actuators 30 and 32 that are furthest from the mirror 20, specifically adjacent to the piezoelectric cantilevers 30e and 32e, respectively. Each sensor 36a and 36b is located symmetrically with respect to the Y-axis. In this specification, sensor 36a corresponds to the "first sensor" and sensor 36b corresponds to the "second sensor". Each sensor 36a and 36b is configured to move together (i.e., in conjunction) with the piezoelectric cantilevers 30e and 32e when they move.

[0018] As described above, the actuator 30 is composed of five piezoelectric cantilevers 30a to 30e. These piezoelectric cantilevers 30a to 30e are arranged in odd-numbered positions, starting from the one closest to the mirror 20, and the piezoelectric cantilevers 30a, 30c, and 30e are arranged in even-numbered positions, and wiring is provided to allow each to be supplied with an independent drive voltage. The details of each wiring are not shown in the illustration, but for example, they are provided on the surface of each piezoelectric cantilever 30a, etc.

[0019] Similarly, the actuator 32 is composed of five piezoelectric cantilevers 32a to 32e. These piezoelectric cantilevers 32a to 32e are wired to be able to independently supply a drive voltage to the odd-numbered cantilevers 32a, 32c, and 32e, and the even-numbered cantilevers 32b and 32d, starting from the one closest to the mirror 20. The details of each wire are not shown in the illustration, but they are provided on the surface of each piezoelectric cantilever, such as 32a.

[0020] In the following explanation, the odd-numbered piezoelectric cantilevers 30a, 30c, and 30e of actuator 30 may be collectively referred to as "group A piezoelectric cantilevers." The input / output terminals for electrical signals on these group A piezoelectric cantilevers are referred to as "terminal VA." Similarly, the even-numbered piezoelectric cantilevers 30b and 30d may be collectively referred to as "group B piezoelectric cantilevers." The input / output terminals for electrical signals on these group B piezoelectric cantilevers are referred to as "terminal VB." The group A piezoelectric cantilevers and the group B piezoelectric cantilevers are arranged alternately, with one of each group's piezoelectric cantilevers alternating.

[0021] Similarly, the odd-numbered piezoelectric cantilevers 32a, 32c, and 32e of actuator 32 are sometimes collectively referred to as "group C piezoelectric cantilevers." The input / output terminals for electrical signals on these group C piezoelectric cantilevers are referred to as "terminal VC." Similarly, the even-numbered piezoelectric cantilevers 32b and 32d are sometimes collectively referred to as "group D piezoelectric cantilevers." The input / output terminals for electrical signals on these group D piezoelectric cantilevers are referred to as "terminal VD." The piezoelectric cantilevers of group C and group D are arranged alternately, with one of each group's piezoelectric cantilevers alternating.

[0022] Sensor 36a is provided adjacent to the piezoelectric cantilever 30e of actuator 30. Sensor 36b is provided adjacent to the piezoelectric cantilever 32e of actuator 32. In the following description, the electrical signal input / output terminal of sensor 36a will be referred to as "terminal Vs1", and the electrical signal input / output terminal of sensor 36b will be referred to as "terminal Vs2".

[0023] Figure 3 is a circuit diagram showing an example of the configuration of a drive circuit. The illustrated drive circuit 2 includes a control unit 50, drive amplifiers 51 and 52, switches 53 and 54, a buffer amplifier 55, a sensor amplifier 56, drive amplifiers 61 and 62, switches 63 and 64, a buffer amplifier 65, and a sensor amplifier 66. Note that this shows the configuration for driving actuators 30 and 32, and the configuration for driving actuators 24 and 26 is not shown or described.

[0024] The control unit 50 controls the operation of each actuator 30 and 32 by supplying a drive voltage to each actuator 30 and 32. The control unit 50 also detects the displacement of each actuator 30 and 32 based on the detection signals from each sensor 36a and 36b. Furthermore, the control unit 50 controls the connection state of each switch 54 and 64 to make the piezoelectric cantilevers of groups A and D in each actuator 30 and 32 usable as sensors, and detects the displacement of each actuator 30 and 32 based on the detection signals from the piezoelectric cantilevers of groups A and D. The control unit 50 can be configured using, for example, a microcomputer.

[0025] The drive amplifier 51 is connected between the control unit 50 and terminal VB, and generates a drive voltage to operate the piezoelectric cantilevers of group B by amplifying the signal output from the control unit 50. The drive voltage output from the drive amplifier 51 is supplied to the piezoelectric cantilevers of group B via terminal VB. In this specification, the drive amplifier 51 corresponds to the "second voltage generation unit".

[0026] The drive amplifier 52 is connected between the control unit 50 and terminal VA via a switch 53, and generates a drive voltage to operate the piezoelectric cantilevers of group A by amplifying the signal output from the control unit 50. The drive voltage output from the drive amplifier 52 is supplied to the piezoelectric cantilevers of group A via terminal VA. In this specification, the drive amplifier 52 corresponds to the "first voltage generation unit".

[0027] Switch 53 is connected between the drive amplifier 52 and terminal VA. Switch 53 is also connected to the control unit 50, and its connection state is switched based on a control signal provided by the control unit 50. Switch 53 has terminal a which provides a connection between the drive amplifier 52 and VA, and terminal b which provides a connection between switch 54 and VA. High-voltage compatible switch ICs (for example, switches with a configuration combining a high-voltage gate driver IC and a power MOSFET) can be used as switch 53 and switches 54, 63, and 64, which will be described later. In this specification, switch 53 corresponds to the "first switch".

[0028] Switch 54 is connected between terminal Vs1 and the control unit 50. More specifically, switch 54 is connected to the control unit 50 via a buffer amplifier 55 and a sensor amplifier 56. Switch 54 is also connected to the control unit 50, and its connection state is switched based on a control signal provided by the control unit 50. Switch 54 has terminal a, which provides a state where Vs1 is connected to the buffer amplifier 55, and terminal b, which provides a state where Vs1 is connected to the reference potential terminal (GND terminal). Terminal a of switch 54 is connected to terminal b of switch 53. It is preferable that a resistive element is connected between Vs1 and the reference potential terminal. This is because it is possible to prevent charge accumulation in the second sensor 36a connected to Vs1 when it is not in use.

[0029] The buffer amplifier 55 and the sensor amplifier 56 are connected in series. The input side of the buffer amplifier 55 is connected to terminal a of the switch 54, and the output side is connected to the input side of the sensor amplifier 56. The output side of the sensor amplifier 56 is connected to the control unit 50. The buffer amplifier 55 is for adjusting the impedance of the signal detected by Vs1. The sensor amplifier 56 is for amplifying the output voltage of the buffer amplifier 55. In this specification, the buffer amplifier 55 and the sensor amplifier 56 correspond to the "first amplification unit".

[0030] The drive amplifier 61 is connected between the control unit 50 and terminal VC, and generates a drive voltage to operate the piezoelectric cantilevers of group C by amplifying the signal output from the control unit 50. The drive voltage output from the drive amplifier 61 is supplied to the piezoelectric cantilevers of group C via terminal VC. In this specification, the drive amplifier 61 corresponds to the "fourth voltage generation unit".

[0031] The drive amplifier 62 is connected to the control unit 50 and terminal VD via a switch 63, and generates a drive voltage to operate the piezoelectric cantilevers of group D by amplifying the signal output from the control unit 50. The drive voltage output from the drive amplifier 62 is supplied to the piezoelectric cantilevers of group D via terminal VD. In this specification, the drive amplifier 62 corresponds to the "third voltage generation unit".

[0032] Switch 63 is connected between the drive amplifier 62 and terminal VD. Switch 63 is also connected to the control unit 50, and its connection state is switched based on a control signal provided by the control unit 50. Switch 63 has terminal a, which provides a connection between the drive amplifier 62 and VD, and terminal b, which provides a connection between switch 64 and VD. In this specification, switch 63 corresponds to the "second switch".

[0033] Switch 64 is connected between terminal Vs2 and the control unit 50. More specifically, switch 64 is connected to the control unit 50 via a buffer amplifier 65 and a sensor amplifier 66. Switch 64 is also connected to the control unit 50, and its connection state is switched based on a control signal provided by the control unit 50. Switch 64 has terminal a, which provides a state where terminal Vs2 is connected to the buffer amplifier 65, and terminal b, which provides a state where Vs2 is connected to the reference potential terminal (GND terminal). Terminal a of switch 64 is connected to terminal b of switch 63. It is preferable that a resistive element is connected between Vs2 and the reference potential terminal. This is because it is possible to prevent charge accumulation in the second sensor 36b connected to Vs2 when it is not in use.

[0034] The buffer amplifier 65 and the sensor amplifier 66 are connected in series. The input side of the buffer amplifier 65 is connected to terminal a of the switch 64, and the output side is connected to the input side of the sensor amplifier 66. The output side of the sensor amplifier 66 is connected to the control unit 50. The buffer amplifier 65 is for adjusting the impedance of the signal detected by Vs2. The sensor amplifier 66 is for amplifying the output voltage of the buffer amplifier 65. In this specification, the buffer amplifier 65 and the sensor amplifier 66 correspond to the "second amplification section".

[0035] Here, the principle of using the actuator as a sensor in the optical scanning device 100 of this embodiment will be explained. Generally, when an external force is applied to a piezoelectric material, a voltage is generated due to the piezoelectric positive effect. This generated voltage can be used as a detection signal for the sensor. On the other hand, when a voltage is applied to a piezoelectric material, stress is generated in the piezoelectric material due to the piezoelectric inverse effect. This generated stress can be used as the driving force for the actuator. By utilizing these effects, the part that is normally used as an actuator to rotate the optical deflector 1 around the X axis can be used as a sensor, thereby increasing the effective area of ​​the sensor. As a result, the detection signal of the sensor can be increased even when the deflection angle is small. In the optical scanning device 100 of this embodiment, when the deflection angle is small, a specific piezoelectric cantilever is used as a sensor to detect the deflection angle, and when the deflection angle is large, sensors 36a and 36b are used to detect the deflection angle.

[0036] Figure 4 is a table showing the phase of the detection signal and the state of the image when any of the piezoelectric cantilevers from groups A to D are used as sensors, and when an image display application is assumed. In Figure 4, "act(1 / 2)" indicates use as an actuator, and "sen" indicates use as a sensor. Also, "A", "B", "C", and "D" represent the piezoelectric cantilevers from groups A, B, C, and D, respectively.

[0037] In Figure 4, "Normal" indicates the case where the piezoelectric cantilevers of groups B and D are driven with forward-phase drive voltages, and the piezoelectric cantilevers of groups A and C are driven with reverse-phase drive voltages, and sensors 36a and 36b are used as sensors. Since the detection signals from sensors 36a and 36b obtained from Vs1 and Vs2 have waveforms of the same phase, the control unit 50 can use the sum of the two detection signals as the sensor output corresponding to the displacement.

[0038] "TYPE_A" shows the case where the piezoelectric cantilevers of groups B and D are driven with the same phase drive voltage, and the piezoelectric cantilevers of groups A and C are used as sensors. Since the drive voltages of the piezoelectric cantilevers of groups B and D are in phase, the control unit 50 can use the sum of the detection signals from sensors 36a and 36b obtained from Vs1 and Vs2 as the sensor output corresponding to the displacement. "TYPE_B" is the case where TYPE_A is inverted symmetrically in the X-axis direction, and the sensor output is approximately the same as in the case of TYPE_A.

[0039] "TYPE_C" describes the case where the piezoelectric cantilevers of group B are driven with a forward-phase drive signal, the piezoelectric cantilevers of group A are driven with an out-of-phase drive voltage, and the piezoelectric cantilevers of groups C and D are used as sensors. Since the detection signals of the piezoelectric cantilevers of groups C and D are out of phase with each other, one of the detection signals from the sensors obtained from VC and VD (piezoelectric cantilevers 32a, 32c, 32e of group C and piezoelectric cantilevers 32b, 32d of group D) can be inverted and the value added by the control unit 50 can be used as the sensor output corresponding to the displacement. "TYPE_D" ​​is the case where TYPE_C is inverted symmetrically in the Y-axis direction, and the sensor output will be approximately the same as in the case of TYPE_C.

[0040] "TYPE_E" represents the case where the piezoelectric cantilevers of groups B and C are driven with opposite-phase drive voltages, and the piezoelectric cantilevers of groups A and D are used as sensors. Since the detection signals of the piezoelectric cantilevers of groups A and D are in opposite phases, one of the detection signals from the sensors obtained from VA and VD (piezoelectric cantilevers 30a, 30c, 30e of group A and piezoelectric cantilevers 32b, 32d of group D) is inverted and the value obtained by adding them together in the control unit 50 can be used as the sensor output corresponding to the displacement. "TYPE_F" is the case where TYPE_E is inverted symmetrically in the Y-axis direction, and the sensor output is approximately the same as in the case of TYPE_E.

[0041] Figure 5 shows specific examples of the waveform diagrams of the drive voltage and detection signal in the "Normal" case shown in Figure 4. "VactA" is an example of the waveform of the drive voltage applied to terminal VA, i.e., the drive voltage applied to the piezoelectric cantilever of group A, and "VactC" is an example of the waveform of the drive voltage applied to terminal VC, i.e., the drive voltage applied to the piezoelectric cantilever of group C. Since these drive voltages are in phase, they overlap and are represented as a single waveform.

[0042] "VactB" is an example waveform of the drive voltage applied to terminal VB, i.e., the drive voltage applied to the piezoelectric cantilever of group B, and "VactD" is an example waveform of the drive voltage applied to terminal VD, i.e., the drive voltage applied to the piezoelectric cantilever of group D. Since these drive voltages are in phase, they overlap and are represented as a single waveform. The drive voltages of "VactA" and "VactC" and the drive voltages of "VactB" and "VactD" are out of phase by half a period, i.e., they are in opposite phase.

[0043] "Vsen1" is an example waveform of the detection signal obtained from terminal Vs1, i.e., the detection signal of sensor 36a. "Vsen2" is an example waveform of the detection signal obtained from terminal Vs2, i.e., the detection signal of sensor 36b. Since these detection signals are in phase, they overlap and are represented as a single waveform. The detection signals of "Vsen1" and "Vsen2" and the drive waveforms of "VactA" and "VactC" are approximately in phase.

[0044] FIG. 6(A) is a diagram schematically showing the movement (displacement) of each piezoelectric cantilever in groups A to D at the time (1) shown in FIG. 5. Since the drive signals ("VactA" and "VactC" in FIG. 5) to each piezoelectric cantilever in groups A and C are in the same phase, at the time (1), each piezoelectric cantilever in groups A and C is displaced. In the schematic diagram in the figure, each piezoelectric cantilever in groups A and C is displaced such that the lower side of each deflects upward. Along with this, the sensor 36a disposed on the outermost A (piezoelectric cantilever 30e) in the figure is also displaced in the same direction as group A, and the detection signal of sensor 36b is similarly displaced in the same direction as group C. The detection signal is output in the same phase as the drive signals to the piezoelectric cantilevers in groups A and C.

[0045] FIG. 6(B) is a diagram schematically showing the movement (displacement) of each piezoelectric cantilever in groups A to D at the time (2) shown in FIG. 5. Since the drive signals ("VactB" and "VactD" in FIG. 5) to each piezoelectric cantilever in groups B and D are in the same phase, at the time (2), each piezoelectric cantilever in groups B and D is displaced. In the schematic diagram in the figure, each piezoelectric cantilever in groups B and D is displaced such that the upper side of each deflects upward. Along with the displacement of each piezoelectric cantilever 30 in groups A and C, the sensor 36a is similarly displaced, so the detection signal is output in the opposite phase to the drive signals to the piezoelectric cantilevers in groups B and D. The detection signal of sensor 36b is the same.

[0046] Thus, in the case of "Normal", since all the piezoelectric cantilevers in groups A to D are used for the rotation of the mirror 20, when an image is drawn on the screen, light can be scanned at a wide angle in the V direction (see FIG. 1(B)). On the other hand, the detection signals of the sensors 36a and 36b become relatively small. Hereinafter, this case of "Normal" is taken as a reference (represented as "REF" in FIG. 4).

[0047] FIG. 7 is a diagram showing a specific example of waveforms of a driving voltage and a detection signal in the case of "TYPE_A" shown in FIG. 4. In this case, detection signals "VsenA" and "VsenC", which are voltages generated by displacements of piezoelectric cantilevers in Group A and Group C used as sensors, are in the same phase with each other. Also, driving voltages "VactB" and "VactD" applied to piezoelectric cantilevers in Group B and Group D are in the same phase with each other. Further, detection signals "VsenA" and "VsenC" and driving voltages "VactB" and "VactD" are in the same phase.

[0048] FIG. 8(A) is a diagram schematically showing movements (displacements) of piezoelectric cantilevers in Groups A to D at time (1) shown in FIG. 7. At time (1), piezoelectric cantilevers in Group B and Group D are displaced. In the schematic diagram in the figure, piezoelectric cantilevers in Group B and Group D are displaced such that their upper sides are bent upward. Also, along with displacements of piezoelectric cantilevers in Group B and Group D, piezoelectric cantilevers in Group A and Group C are displaced such that their lower sides are bent upward.

[0049] FIG. 8(B) is a diagram schematically showing movements (displacements) of piezoelectric cantilevers in Groups A to D at time (2) shown in FIG. 7. At time (2), piezoelectric cantilevers in Group B and Group D return to their initial positions. Along with this, piezoelectric cantilevers in Group A and Group C also return to their initial positions.

[0050] As described above, in the case of "TYPE_A", piezoelectric cantilevers in Group B and Group D are used for rotation of mirror 20, but piezoelectric cantilevers in Group A and Group C are not used. Therefore, when an image is drawn on the screen, theoretically, the light scanning range is narrowed (offset) to 1 / 2 in the V direction (see FIG. 1(B)). On the other hand, detection signals from piezoelectric cantilevers in Group A and Group C used as sensors become relatively large. Although detailed description is omitted, the same applies to the case of "TYPE_B".

[0051] Figure 9 shows a specific example of the waveform diagrams of the drive voltage and detection signal in the case of "TYPE_C" shown in Figure 4. In this case, the detection signals "VsenC" and "VsenD", which are voltages generated by the displacement of each piezoelectric cantilever in groups C and D used as sensors, are in opposite phases to each other. Also, the drive voltages "VactA" and "VactB" applied to each piezoelectric cantilever in groups A and B are in opposite phases to each other. Furthermore, the drive voltage "VactA" and the detection signal "VsenD" are in phase, and the drive voltage "VactB" and the detection signal "VsenC" are in phase.

[0052] Figures 10(A) and 10(B) schematically show the movement (displacement) of each piezoelectric cantilever in groups A to D at times (1) and (2) shown in Figure 9, respectively. At time (1), the piezoelectric cantilever of group A is displaced. In the schematic diagram in the figure, the piezoelectric cantilever of group A is displaced so that its lower side is curved upward. At time (2), the piezoelectric cantilever of group B is displaced. In the schematic diagram in the figure, the piezoelectric cantilever of group B is displaced so that its upper side is curved upward. Furthermore, as the piezoelectric cantilevers of groups A and B are displaced alternately, the piezoelectric cantilevers of groups C and D are displaced in opposite phases as a result.

[0053] Thus, in the case of "TYPE_C", the piezoelectric cantilevers of groups A and B are used to rotate the mirror 20, but the piezoelectric cantilevers of groups C and D are not used. Therefore, when drawing an image on the screen, the scanning range of light in the V direction (see Figure 1(B)) is narrowed (offset). Also, because the sensors (piezoelectric cantilevers 32a, 32c, 32e of group C and piezoelectric cantilevers 32b, 32d of group D) are not driven, the image is distorted into a parallelogram shape. On the other hand, the detection signals from the piezoelectric cantilevers of groups C and D, which are used as sensors, become relatively larger. Noise can be canceled by combining each detection signal with a differential inverter circuit. The same applies to "TYPE_D", although a detailed explanation is omitted.

[0054] Figure 11 shows a specific example of the waveform diagrams of the drive voltage and detection signal in the case of "TYPE_E" shown in Figure 4. In this case, the detection signals "VsenA" and "VsenD" from the piezoelectric cantilevers of groups A and D, which are used as sensors, are in opposite phases to each other. Also, the drive voltages "VactB" and "VactC" applied to the piezoelectric cantilevers of groups B and C are in opposite phases to each other. Furthermore, the drive voltage "VactB" and the detection signal "VsenA" are in phase, and the drive voltage "VactC" and the detection signal "VsenD" are in phase.

[0055] Figures 12(A) and 12(B) schematically show the movement (displacement) of each piezoelectric cantilever in groups A to D at times (1) and (2) shown in Figure 11, respectively. At time (1), the piezoelectric cantilever of group C is displaced. In the schematic diagram in the figure, the piezoelectric cantilever of group C is displaced so that its lower side is curved upward. In conjunction with this, the piezoelectric cantilever of group D is displaced so that its upper side is curved upward. Similarly, at time (2), the piezoelectric cantilever of group B is displaced. In the schematic diagram in the figure, the piezoelectric cantilever of group B is displaced so that its upper side is curved upward. In conjunction with this, the piezoelectric cantilever of group A is displaced so that its upper side is curved upward.

[0056] Thus, in the case of "TYPE_E," the piezoelectric cantilevers of groups A and D are used as sensors, and the piezoelectric cantilevers of groups B and C are used to rotate the mirror 20. Since the piezoelectric cantilevers of groups B and C are arranged symmetrically on either side of the mirror 20, when drawing an image on the screen, the scanning range of light in the V direction (see Figure 1(B)) is narrowed, but the distortions on the left and right cancel each other out, so no distortion occurs in the image. On the other hand, the detection signals from the piezoelectric cantilevers of groups A and D, which are used as sensors, become relatively larger. Noise can also be canceled by combining each detection signal with a differential inverter circuit. The same applies to "TYPE_F," although a detailed explanation is omitted. The drive circuit 2 shown in Figure 3 above is configured to be suitable for the driving method of "TYPE_E," but by swapping terminals VA and VB, and terminals VC and VD, it can be configured to be suitable for the driving method of "TYPE_F."

[0057] As described above, in the case of "TYPE_E" or "TYPE_F", although the scanning range of light in the V direction is narrowed, distortion of the image (scanning range) is not produced, and the detection signal can be increased. Therefore, in the range where the deflection angle of the mirror 20 is relatively small, the detection signal can be increased by using the driving method of "TYPE_E" or "TYPE_F", so the deflection angle can be detected with high accuracy. Also, in the range where the deflection angle of the mirror 20 is relatively large, a wide-angle deflection can be obtained and a sufficiently large detection signal for the sensor can be secured by using the conventional "Normal" driving method. Figure 13 is a diagram showing an example of the relationship between the sensor detection signal and the deflection angle of the mirror (mechanical half-angle) for each driving method. It can be seen that the detection signal is lowest in the case of "Normal", followed by "TYPE_C", and the detection signals are highest for "TYPE_A" and "TYPE_E".

[0058] Figure 14 is a flowchart showing the operation of the control unit of the drive circuit. Figure 15 is a timing chart of each drive voltage and detection signal. Here, it is assumed that a higher-level device (not shown) instructs the control unit 50 of the drive circuit 2 to operate the drive circuit 2 in either a mode with a relatively small swing angle (low swing angle mode) or a mode with a relatively large swing angle (normal mode), and that the "TYPE_E" drive method described above is used in the low swing angle mode. Figure 16 is a diagram illustrating the connection state of each switch 53, 54, 63, and 64 of the drive circuit 2 in the normal mode. Note that the connection state of each switch 53, 54, 63, and 64 of the drive circuit 2 in the low swing angle mode is as shown in Figure 3 above.

[0059] In response to a trigger such as power-on, the control unit 50 starts driving the optical deflector 1 in normal mode (step S11). That is, the control unit 50 controls all switches 53, etc. to be connected to terminal a (see Figure 16). As the control signals given from the control unit 50 to each switch 53, etc., for example, as shown in (1) of Figure 15, a signal that is low level when controlling to terminal a and high level when controlling to terminal b can be used.

[0060] The control unit 50 inputs a drive voltage capable of driving the optical deflector 1 with a relatively large deflection angle (for example, ±4°) in forward phase to each piezoelectric cantilever of group A and group D, and inputs the same drive voltage in reverse phase to each piezoelectric cantilever of group B and group C (step S12). The respective drive voltages for each piezoelectric cantilever of group A to D are illustrated in Figures 15(2) to (5). In normal mode, the control unit 50 detects the deflection angle of the mirror 20 based on the detection signals (Vsen1, Vsen2) from sensors 36a and 36b.

[0061] As long as no command to change to low oscillation angle mode is not issued from the higher-level device (step S13; NO), the processing in step S12 continues. When a command to change to low oscillation angle mode is issued (step S13; YES), the control unit 50 sets the voltage input to each piezoelectric cantilever of group A and group D to 0 (step S14). Next, the control unit 50 controls each switch 53, etc. to be connected to terminal b (step S15, see Figure 3).

[0062] The control unit 50 inputs a drive voltage to each of the piezoelectric cantilevers in groups B and C that is capable of driving the optical deflector 1 with a relatively small deflection angle (for example, ±1.0°) (step S16). In this low deflection angle mode, the control unit 50 detects the deflection angle of the mirror 20 based on the detection signals (VsenA, VsenD) from each of the piezoelectric cantilevers in groups A and D. The detection signals from sensors 36a and 36b become 0 (GND level).

[0063] As long as no command to change to normal mode is not issued from the higher-level device (step S17; NO), the processing in step S16 continues. When a command to change to normal mode is issued (step S17; YES), the control unit 50 controls all switches 53, etc., to be connected to terminal a (see Figure 16). After that, the process returns to step S12.

[0064] Figure 17 shows an example of the relationship between the detection signal (sensor output) and the mirror's deflection angle (mechanical half-angle) when using the "Normal" and "TYPE_E" driving methods. When the deflection angle is small, the "TYPE_E" driving method can be used to increase the sensor output relative to the deflection angle. When the deflection angle is large, the "Normal" driving method can be used to secure the required deflection angle and obtain a sufficient sensor output.

[0065] Figure 18 is a circuit diagram showing an example configuration of a modified drive circuit. The drive circuit 2a shown in Figure 18 differs from the drive circuit 2 of the above-described embodiment in that two switches 71 and 72 and a differential inverting circuit 73 are added. In detail, switch 71 is connected between the buffer amplifier 55 and the sensor amplifier 56. Terminal a of switch 71 is connected to the input side of the sensor amplifier 56, and terminal b is connected to the differential amplifier circuit 73.

[0066] Switch 72 is connected between the buffer amplifier 65 and the sensor amplifier 66. Terminal a of switch 72 is connected to the input side of the sensor amplifier 66, and terminal b is connected to the differential amplifier circuit 73. Each switch 71 and 72 is configured to switch its connection state according to a control signal provided by the control unit 50. For each switch 71 and 72, a high-voltage compatible switch IC similar to the switch 53 described above can be used, for example.

[0067] The differential amplifier circuit 73 has two input terminals connected to the output terminals of buffer amplifiers 55 and 65 via switches 71 and 72, respectively, and one output terminal connected to the control unit 50. When switches 53, 54, 63, 64, 71, and 72 are switched to terminal b, the detection signals (VsenA and VsenD) from the piezoelectric cantilevers of groups A and D are input to each input terminal of the differential amplifier circuit 73, and the signal amplified by the difference between these detection signals is output to the control unit 50. Since detection signals VsenA and VsenD are in opposite phase, the detection signals can be made louder by amplifying them with the differential amplifier circuit 73.

[0068] As described above, according to this embodiment, even when the angle of deflection of the mirror is small, the sensor output (e.g., voltage) can be increased, that is, obtained at a sufficient level.

[0069] This disclosure is not limited to the embodiments described above, and can be implemented in various ways within the scope of the gist of this disclosure. For example, the optical deflector 1 is not limited to the configuration of the embodiments described above. In particular, the number of piezoelectric cantilevers is not limited to the five exemplified. Also, the use of the optical scanning device is not limited to image illumination devices. For example, the optical scanning device of this disclosure can be used when configuring a light fixture for illuminating the area around a vehicle, which can variably control the light illumination range and dimming range, or other light fixtures for drawing information on the road surface around a vehicle. Alternatively, the optical scanning device of this disclosure can be used to scan the distance measuring light in an optical distance measuring device (LiDAR).

[0070] The present disclosure has the following features: (Note 1) A drive circuit for driving an optical deflector comprising at least a mirror and a first actuator having a plurality of piezoelectric cantilevers, the drive circuit comprising: a control unit; a first voltage generating unit interposed between a first piezoelectric cantilever group which is part of the first actuator and the control unit and configured to supply a drive voltage to the first piezoelectric cantilever group; a second voltage generating unit interposed between a second piezoelectric cantilever group which is another part of the first actuator and the control unit and configured to supply a drive voltage to the second piezoelectric cantilever group; a first amplification unit interposed between the first piezoelectric cantilever group and the control unit and configured to amplify the voltage generated by the displacement of the first piezoelectric cantilever group; and a first switch interposed between the first voltage generating unit and the first amplification unit and the first piezoelectric cantilever group and configured to switch, under the control of the control unit, whether to connect the first piezoelectric cantilever group to the first voltage generating unit or the first amplification unit. (Note 2) The drive circuit according to Note 1, wherein the control unit controls the first switch to connect the first piezoelectric cantilever group and the first amplifier, and detects the amount of displacement of the first actuator based on the output voltage of the first amplifier. (Note 3) The drive circuit according to Note 1, wherein the optical deflector further includes a first sensor that generates a voltage corresponding to the amount of displacement of the first actuator, and the control unit detects the amount of displacement of the first actuator based on the output voltage of the first amplifier when the first switch is controlled to connect the first piezoelectric cantilever group and the first amplifier, and detects the amount of displacement of the first actuator based on the voltage output of the first sensor when the first switch is controlled to connect the first piezoelectric cantilever group and the first voltage generator.(Note 4) The drive circuit according to Note 1, wherein the optical deflector further includes a first sensor that generates a voltage corresponding to the displacement of the first actuator, and the control unit controls the first switch to connect the first piezoelectric cantilever group and the first amplifier when the mirror of the optical deflector is operated in an operating mode with a relatively small deflection angle, and detects the displacement of the first actuator based on the output voltage of the first amplifier, and controls the first switch to connect the first piezoelectric cantilever group and the first voltage generating unit when the mirror of the optical deflector is operated in an operating mode with a relatively large deflection angle, and detects the displacement of the first actuator based on the output voltage of the first sensor. (Note 5) The drive circuit according to any one of Notes 1 to 4, wherein the plurality of piezoelectric cantilevers of the first piezoelectric cantilever group and the second piezoelectric cantilever are arranged alternately one by one. (Note 6) The optical deflector further comprises a second actuator having a plurality of piezoelectric cantilevers and positioned on the opposite side of the mirror from the first actuator, the drive circuit further includes: a third voltage generating unit interposed between a third piezoelectric cantilever group, which is part of the second actuator, and the control unit, and configured to supply a drive voltage to the third piezoelectric cantilever group; a fourth voltage generating unit interposed between a fourth piezoelectric cantilever group, which is another part of the second actuator, and the control unit, and configured to supply a drive voltage to the fourth piezoelectric cantilever group; a second amplification unit interposed between the third piezoelectric cantilever group and the control unit, and configured to amplify the voltage generated by the displacement of the third piezoelectric cantilever group; and a second switch interposed between the third voltage generating unit and the second amplification unit and the third piezoelectric cantilever group, and configured to switch, under the control of the control unit, whether to connect the third piezoelectric cantilever group to the third voltage generating unit or the second amplification unit, the drive circuit according to any one of Notes 1 to 5. (Note 7) An optical scanning device comprising: a drive circuit described in any of Notes 1 to 6; and an optical deflector connected to the drive circuit.(Note 8) An optical scanning device comprising: an optical deflector; and a drive circuit connected to the optical deflector, wherein the optical deflector comprises: a mirror; a first actuator; and a second actuator provided symmetrically with respect to the first actuator across the mirror, the first actuator having a first piezoelectric cantilever group which is part and a second piezoelectric cantilever group which is another part, the second actuator having a third piezoelectric cantilever group which is part and a fourth piezoelectric cantilever group which is another part, and the drive circuit rotates the mirror by supplying a drive voltage to the first piezoelectric cantilever group and the fourth piezoelectric cantilever group to displace each of them. (Note 9) The optical scanning device according to Note 8, wherein the drive voltages supplied to the first piezoelectric cantilever group and the fourth piezoelectric cantilever group are in opposite phase to each other. (Note 10) The optical scanning device according to Note 8 or 9, wherein the first piezoelectric cantilever group and the third piezoelectric cantilever each include a plurality of piezoelectric cantilevers that are odd-numbered when counted from the mirror side, and the second piezoelectric cantilever group and the fourth piezoelectric cantilever each include a plurality of piezoelectric cantilevers that are even-numbered when counted from the mirror side. (Note 11) The optical scanning device according to Note 8 or 9, wherein the first piezoelectric cantilever group and the third piezoelectric cantilever each include a plurality of piezoelectric cantilevers that are even-numbered when counted from the mirror side, and the second piezoelectric cantilever group and the fourth piezoelectric cantilever each include a plurality of piezoelectric cantilevers that are odd-numbered when counted from the mirror side.

[0071] 1: Optical deflector, 2: Drive circuit, 20: Mirror, 21a, 21b: Torsion bar, 22: First support part, 24, 26: Actuator, 28: Second support part, 30, 32: Actuator, 30a-30e, 32a-32e: Piezoelectric cantilever, 34: Sensor, 36a, 36b: Sensor, 100: Optical scanning device

Claims

1. A drive circuit for driving an optical deflector comprising at least a mirror and a first actuator having a plurality of piezoelectric cantilevers, the drive circuit comprising: a control unit; a first voltage generating unit interposed between a first piezoelectric cantilever group, which is part of the first actuator, and the control unit, and configured to supply a drive voltage to the first piezoelectric cantilever group; a second voltage generating unit interposed between a second piezoelectric cantilever group, which is another part of the first actuator, and the control unit, and configured to supply a drive voltage to the second piezoelectric cantilever group; a first amplification unit interposed between the first piezoelectric cantilever group and the control unit, and configured to amplify the voltage generated by the displacement of the first piezoelectric cantilever group; and a first switch interposed between the first voltage generating unit and the first amplification unit and the first piezoelectric cantilever group, and configured to switch, under the control of the control unit, whether to connect the first piezoelectric cantilever group to the first voltage generating unit or the first amplification unit.

2. The drive circuit according to claim 1, wherein the control unit controls the first switch to connect the first piezoelectric cantilever group and the first amplifier, and detects the amount of displacement of the first actuator based on the output voltage of the first amplifier.

3. The drive circuit according to claim 1, wherein the optical deflector further includes a first sensor that generates a voltage corresponding to the displacement of the first actuator, and the control unit detects the displacement of the first actuator based on the output voltage of the first amplifier when the first switch is controlled to connect the first piezoelectric cantilever group and the first amplifier, and detects the displacement of the first actuator based on the voltage output of the first sensor when the first switch is controlled to connect the first piezoelectric cantilever group and the first voltage generator.

4. The drive circuit according to claim 1, wherein the optical deflector further includes a first sensor that generates a voltage corresponding to the displacement of the first actuator, and the control unit controls the first switch to connect the first piezoelectric cantilever group and the first amplifier when the mirror of the optical deflector is operated in an operating mode with a relatively small deflection angle, and detects the displacement of the first actuator based on the output voltage of the first amplifier, and controls the first switch to connect the first piezoelectric cantilever group and the first voltage generating unit when the mirror of the optical deflector is operated in an operating mode with a relatively large deflection angle, and detects the displacement of the first actuator based on the output voltage of the first sensor.

5. The drive circuit according to claim 1, wherein each of the plurality of piezoelectric cantilevers in the first piezoelectric cantilever group and the second piezoelectric cantilever is arranged alternately, one at a time.

6. The drive circuit according to claim 1, further comprising: a second actuator having a plurality of piezoelectric cantilevers and positioned on the opposite side of the mirror from the first actuator, wherein the optical deflector further comprises: a third voltage generating unit interposed between a third piezoelectric cantilever group, which is part of the second actuator, and the control unit, and configured to supply a drive voltage to the third piezoelectric cantilever group; a fourth voltage generating unit interposed between a fourth piezoelectric cantilever group, which is another part of the second actuator, and the control unit, and configured to supply a drive voltage to the fourth piezoelectric cantilever group; a second amplification unit interposed between the third piezoelectric cantilever group and the control unit, and configured to amplify the voltage generated by the displacement of the third piezoelectric cantilever group; and a second switch interposed between the third voltage generating unit and the second amplification unit and the third piezoelectric cantilever group, and configured to switch, under the control of the control unit, whether to connect the third piezoelectric cantilever group to the third voltage generating unit or the second amplification unit.

7. An optical scanning device comprising: a drive circuit according to claim 1; and an optical deflector connected to the drive circuit.

8. An optical scanning device comprising: an optical deflector; and a drive circuit connected to the optical deflector, wherein the optical deflector comprises: a mirror; a first actuator; and a second actuator provided symmetrically with respect to the first actuator across the mirror; the first actuator comprises a first piezoelectric cantilever group which is part of it and a second piezoelectric cantilever group which is another part of it; the second actuator comprises a third piezoelectric cantilever group which is part of it and a fourth piezoelectric cantilever group which is another part of it; and the drive circuit rotates the mirror by supplying a drive voltage to the first piezoelectric cantilever group and the fourth piezoelectric cantilever group to displace each of them.

9. The optical scanning apparatus according to claim 8, wherein the drive voltages supplied to the first piezoelectric cantilever group and the fourth piezoelectric cantilever group are in opposite phases to each other.

10. The optical scanning apparatus according to claim 8 or 9, wherein the first piezoelectric cantilever group and the third piezoelectric cantilever each include a plurality of piezoelectric cantilevers that are odd-numbered when counted from the mirror side, and the second piezoelectric cantilever group and the fourth piezoelectric cantilever each include a plurality of piezoelectric cantilevers that are even-numbered when counted from the mirror side.

11. The optical scanning apparatus according to claim 8 or 9, wherein the first piezoelectric cantilever group and the third piezoelectric cantilever each include a plurality of piezoelectric cantilevers that are even-numbered when counted from the mirror side, and the second piezoelectric cantilever group and the fourth piezoelectric cantilever each include a plurality of piezoelectric cantilevers that are odd-numbered when counted from the mirror side.

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