JP6789704B2 - Optical scanning device - Google Patents

Description

The present invention relates to an optical scanning device including an optical deflector.

MEMS (Micro Electro Mechanical Systems) optical deflectors are known. An optical scanning device including the MEMS optical deflector is also known.

A typical MEMS optical deflector has a mirror portion that can reciprocate around a predetermined axis and a rotation angle of a mirror portion that has a piezoelectric film and is around the axis according to the driving voltage of the piezoelectric film. It has a piezoelectric actuator to control. Further, in the typical piezoelectric actuator, the piezoelectric film is formed on only one side of the substrate layer (example: Patent Document 1), and a unipolar in which a predetermined offset bias voltage is superimposed on the periodic vibration voltage for reciprocating rotation of the mirror portion. It is driven by the driving voltage of.

Japanese Unexamined Patent Publication No. 2012-203079

The optical scanning device prevents uneven illuminance of the scanning light when it is installed in the irradiation device and used as the irradiation light, and ensures the quality of the generated image when it is installed in the image device and used as the image generation light. Therefore, it is advantageous to scan the irradiation area with scanning light at a constant velocity. Therefore, it is desired that the drive voltage of the piezoelectric actuator and the rotation angle of the mirror portion around the axis have a linear relationship.

In the unipolar drive voltage type optical deflector, the minimum value and the maximum value of the drive voltage of the piezoelectric film are set to the rotation angles at both ends of the reciprocating rotation angle range of the mirror portion around the axis. However, in this case, in the conventional optical deflector, the rotation angle of the mirror portion around the axis tends to be smaller than the rotation angle defined by the linear relationship at the intermediate value of the drive voltage of the piezoelectric film.

The linear relationship between the drive voltage of the piezoelectric actuator and the rotation angle of the mirror portion around the axis is improved as the offset bias voltage is increased. However, if the maximum value of the drive voltage is not within the withstand voltage of the piezoelectric film, the piezoelectric film will be damaged due to dielectric breakdown or the like. Therefore, when the offset bias voltage is increased, the amplitude of the periodic vibration voltage included in the drive voltage must be reduced by the increase. However, a decrease in the amplitude of the periodic vibration voltage is not preferable because it causes a decrease in the rotation angle range of the reciprocating rotation of the mirror portion.

An object of the present invention is a mirror around an axis with respect to a drive voltage of a piezoelectric actuator while sufficiently securing a reciprocating rotation angle range of a mirror portion in an optical scanning device that drives a piezoelectric film of an optical deflector by a unipolar drive method. This is to improve the linearity of the rotation angle of the portion.

The optical scanning apparatus of the present invention
Light source and
It has a mirror portion that can reciprocate around a predetermined axis, reflects incident light from the light source in a direction corresponding to the rotation angle around the axis, and emits as scanning light, and a piezoelectric film. An optical deflector having a piezoelectric actuator that controls the rotation angle of the mirror portion around the axis according to the driving voltage of the piezoelectric film, and
A control device that supplies the drive voltage to the piezoelectric actuator with the drive voltage of the unipolar is provided .
The drive voltage is a periodic vibration voltage that causes the mirror portion to reciprocate around the axis at a constant frequency by being applied to the piezoelectric film, and a component when the periodic vibration voltage is expanded by the Foulier series. The alignment of the drive voltage and the rotation angle based on the second-fold frequency component in which the phase of the first-fold frequency component whose frequency is twice and the amplitude is a predetermined ratio is changed with respect to the Fühlier series expansion frequency component. It is generated by superimposing a linear correction voltage, which is a correction voltage for improving the performance, and a predetermined bias voltage.
The phase of the linearity correction voltage is set so that the value of the drive voltage becomes a value that is maximum away from the withstand voltage of the piezoelectric film in accordance with the phase in which the absolute value of the periodic vibration voltage is minimized. and said that you are.

The inventor of the present invention uses a multiple frequency component having a frequency twice as high as a predetermined ratio of the amplitude with respect to the Fühlier series expansion frequency component, which is a component when the periodic vibration voltage is expanded into the Foulier series, as the first frequency component. If the frequency component whose phase is changed of the first frequency component is used as the second frequency component and the linearity correction voltage generated based on the second frequency component is included in the drive voltage, the offset bias voltage does not increase. However, it was found that the linearity of the rotation angle of the mirror portion around the axis with respect to the drive voltage of the piezoelectric actuator is improved.

According to the present invention, a linearity correction voltage is generated based on this finding, and the linearity correction voltage is included in the drive voltage. As a result, it is possible to improve the linearity of the rotation angle of the mirror portion around the axis with respect to the drive voltage of the piezoelectric actuator while sufficiently securing the reciprocating rotation angle range of the mirror portion.

In the optical scanning apparatus of the present invention, it is preferable that the Fourier series expansion frequency component is represented only by a sine wave component.

The periodic vibration voltage is either an odd function, an even function, or a function obtained by superimposing an odd function and an even function. On the other hand, all cosine waves can be replaced with sine waves of the same frequency by changing the phase by π / 2. With the above configuration, the Fourier series expansion frequency component is represented only by the sinusoidal component, and the linearity correction voltage is based on the second multiple frequency component consisting only of the multiple frequency sine wave component with respect to the Fourier series expansion sinusoidal component of the periodic vibration voltage. Even if the periodic vibration voltage is not an odd function but an even function or a function obtained by superimposing an odd function and an even function, the linearity correction voltage for the periodic vibration voltage can be set without any problem. Can be done.

In the optical scanning apparatus of the present invention, when the phase change from the first-fold frequency component to the second-fold frequency component is a change that advances the phase, the control device maintains the code of the second-fold frequency. When the component is generated as the linearity correction voltage and the phase change from the first-fold frequency component to the second-fold frequency component is a change that delays the phase, the second-fold frequency component whose sign is reversed is said. It is preferable to generate it as a linearity correction voltage.

The amount of change in the rotation angle of the mirror around the axis with respect to the amount of change in the drive voltage tends to be insufficient when the drive voltage is low, so the linearity is worse when the drive voltage is low than when it is high. Tend to do. According to the above configuration, depending on whether the phase change from the 1st frequency component to the 2nd frequency component is a change that advances or delays the phase, the periodic vibration voltage is adjusted to the phase in which the periodic vibration voltage decreases. The linearity correction voltage increases the amount of decrease in the drive voltage. As a result, the linearity correction voltage can be effectively used for improving the linearity of the rotation angle of the mirror portion around the axis with respect to the drive voltage of the piezoelectric actuator.

In the optical scanning apparatus of the present invention, it is preferable that the phase difference between the first-fold frequency component and the second-fold frequency component is set to π / 2.

According to this configuration, the phase change is set to π / 2. As a result, the absolute value of the second-fold frequency sine wave component becomes maximum in accordance with the phase in which the periodic vibration voltage drops maximum, and the amount of drop in the drive voltage is maximized. As a result, the linearity correction voltage for improving the linearity can be used more effectively.

In the optical scanning apparatus of the present invention, it is preferable that the linearity correction voltage is set based only on the second frequency component having a predetermined order or less.

According to this configuration, the linearity correction voltage has a small number of double frequency components, so that the process of generating the linearity correction voltage is simplified.

Schematic perspective view of the light deflector. 2 (a) is a diagram showing a flat state of the cantilever, and FIG. 2 (b) is a diagram showing a curved state of the cantilever. Block diagram of the optical scanning device. Explanatory drawing of unipolar drive voltage. The graph which shows the relationship between the drive voltage and the rotation angle of a mirror part when the drive voltage of an outer actuator does not include a linearity correction voltage. The waveform diagram of another drive voltage whose offset bias voltage is different from the offset bias voltage of FIG. The graph which showed the relationship between the drive voltage and the rotation angle of a mirror part with an offset bias voltage as a parameter. Graph showing the relationship between offset bias voltage and maximum linear error The waveform diagram of the unipolar drive voltage of FIG. 4 and its second harmonic voltage. A graph showing the relationship between the amplitude ratio of the second harmonic voltage and the total harmonic distortion when the piezoelectric film of the cantilever of the outer actuator is driven by the drive voltage including the second harmonic voltage. Explanatory drawing about the reason why the phase of the second harmonic voltage was delayed. The figure explaining the problem when the second harmonic voltage which does not change the phase is used as a linearity correction voltage. The figure which shows the sawtooth wave as an example of a periodic vibration voltage. The figure which shows the triangular wave as another example of a periodic vibration voltage.

FIG. 1 is a schematic perspective view of the light deflector 1. The light deflector 1 is a kind of MEMS. The optical deflector 1 includes a mirror portion 2 rotatably arranged in the center, a movable frame 3 that surrounds the mirror portion 2 from the outside, and a fixed frame 4 that surrounds the movable frame 3 from the outside.

For convenience of explanation of the structure, a three-axis coordinate system including an X-axis, a Y-axis, and a Z-axis is defined. The center O as the origin of the three-axis coordinate system is set at the center of the mirror surface 2a of the circular mirror portion 2. The X-axis, Y-axis and Z-axis are orthogonal to each other at the center O. The X-axis and the Y-axis are set parallel to the long side and the short side of the rectangular fixed frame 4, respectively. The Z axis is set parallel to the thickness direction of the fixed frame 4.

Further, for convenience of explanation, the side where the mirror surface 2a of the mirror portion 2 can be seen in the Z-axis direction is defined as the front side of the optical deflector 1, and the vertical and horizontal directions of the front view of the optical deflector 1 are the X-axis. The front view of the optical deflector 1 is defined so as to be aligned in the direction and the Y-axis direction.

The normal of the mirror surface 2a passes through the center O and is perpendicular to the mirror surface 2a. The mirror portion 2 can reciprocate around the first axis and the second axis, which will be described later. The normal of the mirror surface 2a fluctuates as the mirror portion 2 reciprocates. However, the center O as the center of the mirror surface 2a maintains immobility during the reciprocating rotation of the mirror portion 2. The mirror portion 2 of FIG. 1 is shown in a state where the normal line of the mirror surface 2a coincides with the Z axis.

The pair of torsion bars (elastic beams) 5a and 5b project from both sides of the mirror portion 2 along the diameter in the vertical direction in the circular mirror portion 2 when viewed from the front, and are connected to the inner peripheral circle of the movable frame 3 at the protruding ends. ing. The axes of the torsion bars 5a and 5b define the first axis on which the mirror portion 2 rotates. When the normal of the mirror surface 2a coincides with the Z axis, the first axis coincides with the Y axis. As the mirror portion 2 reciprocates around the first axis, the mirror portion 2 swings left and right in front view.

The inner actuators 6a and 6b are arranged on the left and right sides of the mirror portion 2 in the front view, and are individually formed in a semicircular shape and an overall circumferential shape in the front view. The inner actuators 6a and 6b are coupled to the intermediate portion of the torsion bars 5a and 5b at the upper and lower ends.

The handle portions 12a and 12b extend along the X-axis and connect the midpoint of the outer semicircle of the inner actuators 6a and 6b and the inner peripheral circle of the circular hole of the movable frame 3 at both ends. The inner actuators 6a and 6b are unipolar type piezoelectric actuators having a piezoelectric film formed on one side of the substrate layer and being curved and deformed by the driving voltage of the unipolar supplied to the piezoelectric film.

The axes of the handle portions 12a and 12b define the second axis. During the operation of the optical deflector 1, the mirror portion 2 reciprocates around the first axis that coincides with the axis of the torsion bar 5, and reciprocates around the second axis that coincides with the axes of the handle portions 12a and 12b. Rotate.

The outer actuators 7a and 7b are arranged on the left and right sides of the movable frame 3 in front view inside the fixed frame 4, and are coupled to the outer peripheral edge of the movable frame 3 and the inner peripheral edge of the fixed frame 4 at both ends. The coupling point where the outer actuators 7a and 7b are coupled to the outer peripheral edge of the movable frame 3 and the coupling point to which the outer actuators 7a and 7b are coupled to the inner peripheral edge of the fixed frame 4 are separated from the center O by an equal distance on the − side in the Y-axis direction. The outer actuators 7a and 7b are unipolar type piezoelectric actuators having a piezoelectric film formed on one side of the substrate layer and being curved and deformed by the driving voltage of the unipolar supplied to the piezoelectric film.

The outer actuators 7a and 7b reciprocate the movable frame 3 around the X-axis. As the movable frame 3 reciprocates around the X axis, the mirror portion 2 reciprocates around the second axis. Both the first axis and the second axis are set on a plane including the mirror surface 2a and are orthogonal to each other at the center O. The second axis coincides with the X axis when the normal of the mirror surface 2a coincides with the Z axis.

The intersection angle between the second axis and the X axis at the center O changes with the reciprocating rotation of the mirror portion 2 around the first axis. Since the first axis and the movable frame 3 reciprocate integrally around the X axis, the rotation angle of the movable frame 3 around the X axis is the rotation angle of the first axis around the second axis. In other words, it is equal to the rotation angle of the mirror portion 2 around the second axis.

Hereinafter, the torsion bars 5a and 5b are collectively referred to as "torsion bars 5" when not particularly distinguished. The inner actuators 6a and 6b are collectively referred to as "inner actuator 6" unless otherwise specified. The outer actuators 7a and 7b are collectively referred to as "outer actuator 7" unless otherwise specified. The handle portions 12a and 12b are collectively referred to as "handle portion 12" when not particularly distinguished.

The outer actuator 7 includes a plurality of cantilever 15s connected by a folded-back portion 16 so as to form a meander pattern, and the inner circumference of the fixed frame 4 is provided at both ends via the proximal end side coupling portion 18 and the distal end side coupling portion 19. And are connected to the outer circumference of the movable frame 3, respectively. The plurality of cantilever 15s are arranged in the X-axis direction with the longitudinal direction aligned in the Y-axis direction.

FIG. 2 is an operation explanatory view of the outer actuator 7. FIG. 2 shows the outer actuator 7a on the left side. The outer actuators 7a and 7b have a symmetrical structure when viewed from the front, and the operation is also symmetrical.

FIG. 2A is a diagram showing a flat state of the cantilever 15, and FIG. 2B is a diagram showing a curved state of the cantilever 15.

In FIG. 2, for convenience of explanation, the cantilever 15 is numbered No. 1 in the order of arrangement from the proximal end side coupling portion 18 side to the distal end side coupling portion 19 side. 1-No. Add 4. Then, the odd number No. The cantilever 15s 1 and 3 are indicated by the cantilever 15o (“o” means odd), and the even number No. The cantilever 15s 2 and 4 are indicated by the cantilever 15e (“e” means even).

In FIG. 2A, all the cantilever 15s are in a flat state, and the proximal end side coupling portion 18 and the distal end side coupling portion 19 are aligned in rotation positions in the X-axis direction.

In FIG. 2B, the cantilever 15o and 15e are respectively convexly curved in the opposite directions in the Z-axis direction. In order to bend the cantilever 15o and 15e convexly in the opposite direction in the Z-axis direction, a driving voltage is applied to the piezoelectric film of the cantilever 15o and 15e in opposite phases. As a result of the cantilever 15o and 15e being curved convexly in the opposite direction in the Z-axis direction, the tip end side end portion (the end portion on the movable frame 3 side in the path of the meander pattern) is the base end side end portion in all the cantilever 15s. It is displaced to the same side in the Z-axis direction with respect to (the end on the fixed frame 4 side in the path of the meander pattern). Then, this displacement amount is accumulated in the entire outer actuator 7, and the rotation amount of the tip side coupling portion 19 around the X axis increases. In this way, with the supply of the drive voltage of the opposite phase to the piezoelectric films of the cantilever 15o and 15e, the tip side coupling portion 19 reciprocates around the X axis, and the movable frame 3 has the tip side coupling portions on both the left and right sides. It reciprocates around the X-axis by the driving force of the outer actuator 7 via 19.

Returning to FIG. 1, the electrode pads 8a and 8b are formed on the surfaces of the short sides of the fixed frame 4, respectively, and have a laminated structure of the inner actuator 6 and the outer actuator 7 via predetermined wiring (not shown). Is connected to each electrode layer formed above and below the piezoelectric film. Typically, the electrode pads 8a and 8b connected to the lower electrode layer of the inner actuator 6 and the outer actuator 7 are maintained at the ground voltage.

The optical deflector 1 is loaded in a package (not shown), and each terminal of the package and each of the electrode pads 8a and 8b are connected by a bonding wire (not shown). The laser light source 14 emits the incident light La of the light deflector 1 from the outside of the package toward the center O of the mirror surface 2a of the mirror portion 2 of the light deflector 1.

The mirror unit 2 reflects the incident light La incident on the center O in a direction corresponding to each rotation angle around the first axis and the second axis, and emits it as scanning light Lb to a predetermined irradiation region. In FIG. 1, the incident light La is directly incident on the mirror portion 2 from the laser light source 14 and is directly directed to the irradiation region. In the actual product, the optical system is arranged on the outside of the package to change the optical path.

The operation of the light deflector 1 alone will be schematically described. In the optical deflector 1, the mirror portion 2 reciprocates around the axis (first axis) of the torsion bar 5 by the operation of the inner actuator 6. The mirror portion 2 is also included in the mirror surface 2a of the mirror portion 2 and is orthogonal to the first axis at the center O of the mirror surface 2a by the operation of the outer actuator 7, and the axes of the handle portions 12a and 12b (second axis). It reciprocates around.

In a typical optical scanning device 25, the scanning light Lb scans the irradiation region in the vertical direction by the reciprocating rotation of the mirror portion 2 around the first axis. Further, the scanning light Lb scans the irradiation region in the lateral direction by the reciprocating rotation of the mirror portion 2 around the second axis. The vertical and horizontal directions are typically aligned in the vertical and horizontal directions, respectively, when the optical scanning device 25 is equipped in an image generating device such as a projector.

For example, the frequency of the reciprocating rotation of the mirror portion 2 around the first axis is 18 kHz, and the frequency of the reciprocating rotation of the mirror portion 2 around the second axis is 60 Hz. Resonance is used for the reciprocating rotation of the mirror portion 2 around the first axis. Resonance is not used for the reciprocating rotation of the mirror portion 2 around the second axis, and only the acting force of the outer actuator 7 is used.

FIG. 3 is a block diagram of the optical scanning device 25. The optical scanning device 25 is installed in, for example, a video device, a projector, a vehicle headlight, or the like. The optical scanning device 25 includes an optical deflector 1, a laser light source 14, and a control device 27.

The laser light source 14 has a resonance runout angle sensor 30 and a non-resonance runout angle sensor 31 in addition to the inner actuators 6a and 6b and the cantilever 15o and 15e described above. The resonant runout angle sensor 30 and the non-resonant runout angle sensor 31 are not shown in FIG. Typically, the resonant runout sensor 30 is provided on one of the inner actuators 6a and 6b, and the non-resonant runout sensor 31 is one cantilever 15 of one of the plurality of cantilever 15s of the outer actuators 7a and 7b. It is provided in.

The specific structures of the resonance runout angle sensor 30 and the non-resonance runout angle sensor 31 are as follows. The piezoelectric film formed on the surface side (Z-axis direction + side) of the common substrate layer in the inner actuator 6 and the cantilever 15 is separated by a slit. One of the separated piezoelectric films acts as it is as the piezoelectric film of the piezoelectric actuator. On the other hand, the resonance runout angle sensor 30 or the non-resonance runout angle sensor 31 serves as a piezoelectric sensor for detecting distortion, and detects the amount of bending deformation of the substrate layer. As the amount of bending deformation of the substrate layer increases, the rotation angle of the mirror portion 2 around the first axis and the second axis increases.

The control device 27 controls the current flow of the laser light source 14 as well as turning on / off (turning on and off) the laser light source 14. The intensity of the incident light La (FIG. 1) is related to the current flow of the laser light source 14. The control device 27 generates a drive voltage to be supplied to the inner actuators 6a and 6b and the cantilever 15o and 15e. The drive voltages supplied from the control device 27 to the inner actuators 6a and 6b are in opposite phase to each other. The drive voltages supplied from the control device 27 to the cantilever 15o and 15e are also in opposite phase to each other.

The control device 27 detects the rotation angle and the reciprocating rotation frequency of the mirror unit 2 around the first axis based on the detection current from the resonance runout angle sensor 30. The control device 27 also detects the rotation angle and the reciprocating rotation frequency of the mirror portion 2 around the second axis based on the detection current from the non-resonant runout angle sensor 31. The control device 27 feedback-controls the drive voltages of the inner actuator 6 and the outer actuator 7 by using the detected rotation angle and the reciprocating rotation frequency of the mirror unit 2 around the first axis and the second axis as feedback signals. ..

FIG. 4 shows the unipolar drive voltage (hereinafter, simply referred to as “drive voltage”) of the cantilever 15 of the outer actuator 7. Hereinafter, in order to distinguish between the drive voltage of the inner actuator 6 and the drive voltage of the outer actuator 7, the drive voltage of the outer actuator 7 is indicated by "drive voltage Vin". In FIG. 4, the horizontal axis represents the phase of the drive voltage Vin, and the vertical axis represents the value of the drive voltage Vin.

The drive voltage Vin in FIG. 4 is obtained by superimposing the offset bias voltage Vb on the periodic vibration voltage Vpe, and the linearity correction voltage Vli described later (specifically, the secondary harmonic voltage Vks described later. However, Vli = It does not include (sometimes + Vks and some Vli = -Vks). That is, Vin = Vpe + Vb. In this embodiment, Vb = 0V is defined as an offset bias voltage that sets the minimum value of the drive voltage Vin to 0V regardless of whether Vin contains Vli or not.

In the example of FIG. 4, the periodic vibration voltage Vpe is set to a sine wave having an amplitude of 20 V and a frequency of 60 Hz. The offset bias voltage Vb is 0V.

FIG. 5 shows the relationship between the drive voltage Vin (= Vpe + Vb) when the drive voltage Vin of the outer actuator 7 does not include the drive voltage Vin of FIG. 4, that is, the linearity correction voltage Vli, and the rotation angle Aro of the mirror portion 2. It is a graph which shows. Since Vb = 0V, Vin = Vpe is substantially obtained. The "ideal response characteristic" is the relationship between the drive voltage Vin and the rotation angle Aro when the rotation angle Aro of the mirror portion 2 ideally changes when the drive voltage Vin of the outer actuator 7 is changed. By definition, the ideal response characteristic is linear.

Hereinafter, the rotation angle Aro = 0 ° is defined as the rotation angle of the mirror portion 2 around the second axis when the periodic vibration voltage Vpe becomes the minimum value regardless of the offset bias voltage Vb. Assuming that the mirror unit 2 changes from downward to upward in front view as the periodic vibration voltage Vpe increases, the mirror unit 2 is most downward in front view when the drive voltage Vin is the minimum value.

In the optical deflector 1 as an actual product, the minimum and maximum values of the drive voltage Vin are adjusted to the minimum and maximum values of the rotation angle Aro. Therefore, the rotation angles Aro at both ends of the control range of the drive voltage Vin exist on the ideal response characteristic. However, the actual rotation angle Aro in the middle of the control range of the drive voltage Vin deviates from the ideal value to the lower side. In the characteristics of FIG. 5, when the drive voltage Vin = 20V, that is, when the mirror unit 2 faces directly in front, the difference between the actual rotation angle Aro and the ideal rotation angle is the maximum value (hereinafter, "" It is called "maximum linear error".

FIG. 6 is a waveform diagram of another drive voltage Vin whose offset bias voltage Vb is different from that of the offset bias voltage Vb of FIG. The offset bias voltages Vb included in the two drive voltages Vin shown in FIG. 6 are 10 V and 20 V, respectively. Similar to the drive voltage Vin of FIG. 4, the two drive voltages Vin do not include the linearity correction voltage Vli, Vin = Vpe + Vb, and the periodic vibration voltage Vpe included in the drive voltage Vin has an amplitude. Is a sine wave with a frequency of 20 V and a frequency of 60 Hz.

In this way, the periodic vibration voltage Vpe included in the drive voltage Vin can be set to various drive voltages Vin by changing the offset bias voltage Vb while making the periodic vibration voltage Vpe common to a sine wave having an amplitude of 20 V and a frequency of 60 Hz. it can. In addition, regardless of the value of the offset bias voltage Vb, the mirror unit 2 is the center position of the reciprocating rotation angle around the second axis in front view, in other words, when the drive voltage Vin is at the average value. It is set at the center position of the swing rotation angle in the vertical direction.

FIG. 7 is a graph showing the relationship between the drive voltage Vin and the rotation angle Aro of the mirror portion with the offset bias voltage Vb as a parameter. Each drive voltage Vin in FIG. 7 does not include the linearity correction voltage Vli, and Vin = Vpe + Vb.

From the graph of FIG. 7, the linearity of the relationship between the drive voltage Vin and the rotation angle Aro is improved as the offset bias voltage Vb becomes 0V, 3.5V, 10V, 20V, 30V. It can be seen that the relationship between the drive voltage Vin and the rotation angle Aro approaches the ideal response characteristic.

FIG. 8 is a graph showing the relationship between the offset bias voltage Vb included in the drive voltage Vin and the maximum linear error. In FIG. 8, the relationship between the offset bias voltage Vb and the maximum linear error was investigated with Vin = Vpe + Vb. The periodic vibration voltage Vpe included in the drive voltage Vin is a sine wave having an amplitude of 20 V and a frequency of 60 Hz regardless of the offset bias voltage Vb.

From the graph of FIG. 8, it can be seen that the maximum linear error decreases as the offset bias voltage Vb increases. Further, from the graphs of FIGS. 7 and 8, it can be inferred that if the offset bias voltage Vb included in the drive voltage Vin is increased, the linear relationship between the drive voltage Vin and the rotation angle Aro is improved.

However, a problem arises here. It is necessary to consider the withstand voltage of the piezoelectric film formed on the cantilever 15 of the outer actuator 7. That is, when a driving voltage Vin equal to or higher than the withstand voltage is applied to the piezoelectric film, the piezoelectric film is damaged due to dielectric breakdown or the like. On the other hand, when the offset bias voltage Vb is increased while keeping the drive voltage Vin below the withstand voltage, it is necessary to reduce the amplitude of the periodic vibration voltage Vpe according to the increase in the offset bias voltage Vb. However, a decrease in the amplitude of the periodic vibration voltage Vpe leads to a decrease in the rotation angle range of the rotation angle Aro, which is not preferable.

The present inventor improves the linearity of the relationship between the drive voltage Vin and the rotation angle Aro without increasing the offset bias voltage Vb, that is, while sufficiently securing the rotation angle range of the rotation angle Aro. I got the knowledge. The findings will be described in detail below.

FIG. 9 is a diagram showing the relationship between the drive voltage Vin (= Vpe + Vb) of the unipolar of FIG. 4 and the second harmonic voltage Vks as the linearity correction voltage Vli. In FIG. 9, the horizontal axis represents the phase of the drive voltage Vin (= the phase of 1/2 of the phase of the second harmonic voltage Vks), and the vertical axis represents the drive voltage Vin and the second harmonic voltage Vks.

Here, the second harmonic voltage Vks, the Fourier series expansion frequency component, the first multiple frequency component, the second multiple frequency component, and the Fourier series expansion sinusoidal component will be described.

The periodic vibration voltage Vpe as a periodic function can be represented by the Fourier series expansion frequency component expanded by the Fourier series (example: (Equation 2) and (Equation 4a) described later). When the periodic vibration voltage Vpe is an odd function, the periodic vibration voltage Vpe can be expressed only by the Fourier series expansion sinusoidal component (example: (Equation 2) described later). Further, even if the periodic vibration voltage Vpe is an even function or a function obtained by superimposing an odd function and an even function, the cosine wave can be replaced with a sine wave having the same frequency by changing the phase of π / 2. .. Therefore, all periodic vibration voltages Vpe can be represented by the Fourier series expansion sinusoidal component.

Further, when the periodic vibration voltage Vpe is expressed by the Fourier series expansion frequency component expanded by the Fourier series, the first frequency component whose frequency is twice and the amplitude is a predetermined ratio with respect to the Fourier series expansion frequency component is defined. Can be done. Further, it is possible to define a second frequency component in which the phase is changed by the phase change constant θ with respect to the first frequency component.

Examples of the second frequency component are ζ * sin (2t−π / 2) of (Equation 1a), ζ * sin (2t + π / 2) of (Equation 1b), and ζ * [of (Equation 3a), which will be described later. ...]. An example of the first-fold frequency component is that ± π / 2 as the phase change constant θ is removed from each sine wave component as the second-fold frequency component in (Equation 1a), (Equation 1b) and (Equation 3a). It becomes.

In addition, t used in sin (t), sin (2t), etc. in this embodiment is not the time itself, but the time is t'(the unit of t'is seconds), and the frequency of the periodic vibration voltage Vpe is set. When it is set to 60 Hz, it means t = 120πt'. That is, t is defined as a simplified notation of 120πt'.

Further, ζ * sin (2t-π / 2) in (Equation 1a) is an example of θ (= −π / 2) <0, and is an example in which the phase of the second frequency component is delayed with respect to the first frequency component. Is. Ζ * sin (2t + π / 2) in (Equation 1b) is an example of θ (= π / 2)> 0, and is an example in which the phase of the second-fold frequency component is advanced with respect to the first-fold frequency component.

The linearity correction voltage Vli is set based on the second frequency component as a correction voltage for improving the linearity between the drive voltage Vin and the rotation angle Aro. Further, as is well known, the cosine wave can be replaced with a sine wave by changing the phase of π / 2. Therefore, the multiple frequency component of only the cosine wave component or the multiple frequency component in which the cosine wave component and the sine wave component are mixed can be represented only by the second multiple frequency sine wave component.

When the periodic vibration voltage Vpe consists of a single sine wave (= 20 sin (t)) as shown in FIG. 4, even if the periodic vibration voltage Vpe is expanded in Fourier series, the frequency component expanded in Fourier series is the same. Only a single sine wave (= 20 sin (t)). The second harmonic voltage Vks is the first-fold frequency for the first-fold frequency component whose frequency is double and the amplitude is a predetermined ratio for the single sine wave (= 20 sin (t)). It corresponds to the second harmonic component with the phase of the component delayed by π / 2. When the periodic vibration voltage Vpe is a single sine wave, there is only one second frequency component, and there is only one second harmonic voltage Vks as the second frequency component.

In the example of FIG. 9, the second harmonic voltage Vks is defined as Vks = 2sin (2t−π / 2), whereas the periodic vibration voltage Vpe is 20 sin (t) as a single sine wave. Generally speaking, the second harmonic voltage Vks is Vks = ζ * 20sin (2t + θ), and Vks = ζ * 20sin (2t−π / 2) is an example of θ = −π / 2. "*" Means multiplication. The amplitude ratio ζ is defined by the amplitude of ζ = Vks / the amplitude of Vpe, and in the example of FIG. 9, ζ = 0.1. Since the amplitude of the periodic vibration voltage Vpe is 20V, the amplitude of the second harmonic voltage Vks is 2V.

FIG. 10 shows the relationship between the amplitude ratio of the second harmonic voltage Vks and the total harmonic distortion when the piezoelectric film of the cantilever 15 of the outer actuator 7 is driven by the drive voltage Vin including the second harmonic voltage Vks. It is a graph shown. The periodic vibration voltage Vpe used in the example of FIG. 10 is a sine wave having Vpe = 20sin (t), an amplitude of 20V, and a frequency of 60Hz.

The total harmonic distortion factor on the vertical axis of FIG. 10 is defined when the cantilever 15 of the outer actuator 7 of the optical deflector 1 is driven by the drive voltage Vin (= Vpe-Vks + Vb). At this time, the actual reciprocating rotation of the mirror portion 2 around the second axis is expanded by the Fourier series, and the sine wave component (harmonic component) of the second order or higher is extracted from the expanded Fourier series, and the extracted harmonics are extracted. The ratio of the energy amount of the wave component to the energy of the entire actual reciprocating rotation is the total harmonic distortion factor. The first-order sine wave component included in the Fourier series expansion is an undistorted vibration component of the mirror portion 2 around the second axis.

In FIG. 10, the drive voltage Vin is Vin = Vpe-Vks + Vb, which is an example of Vli = -Vks in Vin = Vpe + Vli + Vb. The Vks is represented by Vks = ζ * 20sin (2t−π / 2), similarly to the Vks described in FIG. In FIG. 10, the phase change constant θ is uniformly set to θ = −π / 2 at any Vin Vks. θ = −π / 2 is Vli = −Vks because the phase change from the first-fold frequency component to the second-fold frequency component delays the phase. Note that Vin = Vpe + Vks + Vb is an example in which Vks is set to the linearity correction voltage Vli (= Vks) without inverting the sign thereof.

In FIG. 10, ζ = 0 means the amplitude = 0 of the second harmonic voltage Vks. Therefore, the drive voltage Vin when ζ = 0 is Vin = Vpe + Vb, which is the same as the conventional drive voltage Vin. It means that the ratio of the second harmonic voltage Vks (linearity correction voltage Vli) to the drive voltage Vin increases as ζ increases.

From FIG. 10, it can be seen that the total harmonic distortion decreases as the offset bias voltage Vb increases. Further, as the ζ of the second harmonic voltage Vks (= ζ * 20sin (2t−π / 2)) is gradually increased from ζ = 0, the total harmonic distortion gradually decreases, and the total harmonic distortion is increased. It can be seen that when the wave distortion factor reaches a predetermined value determined according to the offset bias voltage Vb, the total harmonic distortion factor switches from falling to rising for the subsequent increase. The decrease in the total harmonic distortion means that the linearity of the rotation angle Aro with respect to the drive voltage Vin is improved.

From FIG. 10, instead of increasing the offset bias voltage Vb, the secondary harmonic voltage Vks is superposed on the periodic vibration voltage Vpe by adjusting its amplitude ratio ζ, so that the rotation angle Aro is linear with respect to the drive voltage Vin. It turns out that the sex can be improved.

In the optical deflector 1 as a product, the maximum linear error needs to be 0.05 to 0.1 ° or less. The maximum linear error = 0.1 ° corresponds to the total harmonic distortion = 2% in the graph of FIG. From FIG. 10, it can be seen that if the offset bias voltage Vb ≧ 20V, the total harmonic distortion ≦ 2% is almost achieved. Further, it can be seen that even if the offset bias voltage Vb = 10V, if ζ = 4 to 9%, the total harmonic distortion rate ≦ 2% is almost achieved. However, when the offset bias voltage Vb = 3.5V or less, it can be seen that it is difficult to achieve the total harmonic distortion ≦ 2% no matter how much ζ is increased.

As described above, as the offset bias voltage Vb is increased, the linearity of the rotation angle Aro with respect to the drive voltage Vin is improved, but the drive voltage Vin exceeds the withstand voltage of the piezoelectric film of the cantilever 15 of the outer actuator 7. Is not allowed. Therefore, it is necessary to reduce the amplitude of the periodic vibration voltage Vpe by the amount of increasing the offset bias voltage Vb. Reducing the amplitude of the periodic vibration voltage Vpe is not preferable because it leads to a reduction in the control range of the rotation angle.

In the optical scanning apparatus 25 of the embodiment, the offset bias voltage Vb is set to Vb = 10V instead of Vb ≧ 20V, and ζ = 4 to 9%. As a result, the linearity of the rotation angle of the mirror portion 2 around the second axis with respect to the drive voltage Vin is improved while sufficiently securing the control range of the rotation angle of the mirror portion 2 around the second axis. Can be done.

FIG. 11 is an explanatory diagram of the reason why the phase change constant θ of the second harmonic voltage Vks (= ζ * 20sin (2t−π / 2)) is set to −π / 2. Note that θ = −π / 2 means that the phase change constant θ delays the phase of ζ * 20 sin (2t). At the second harmonic voltage Vks, ζ = 0.1. The broken line in FIG. 11 shows that when the driving voltage Vin (solid line) is applied to the piezoelectric film of the cantilever 15 and the mirror portion 2 is actually rotated around the second axis, the actual rotation is linearly related. It shows that it shifts. The broken line is shown by converting this deviation into a voltage and superimposing it on the drive voltage Vin.

As can be seen from the characteristics of FIG. 5 (actual characteristics that deviate downward from the ideal response characteristics), the unit change amount of the rotation angle Aro with respect to the unit change amount of the drive voltage Vin is when the drive voltage Vin is low. It is small and increases as the drive voltage Vin rises. Further, as described with reference to FIG. 10, the linearity is improved as the offset bias voltage Vb is increased. Therefore, the broken line in FIG. 11 appears as a characteristic that does not sufficiently decrease on the minimum value side of the drive voltage Vin, not on the maximum value side.

In order to deal with this, it is easy to superimpose the linearity correction voltage Vli on the periodic vibration voltage Vpe so that the drive voltage Vin drops sufficiently as the drive voltage Vin becomes the minimum value. Can be understood. In this way, when the phase change constant θ is −π / 2, that is, when the phase change constant θ delays the phase, the linearity correction voltage Vli is set based on the sign-inverted second harmonic voltage Vks. (Vli = -Vks).

FIG. 12 is a diagram illustrating a problem when the second harmonic voltage Vks whose phase is not changed with respect to the drive voltage Vin is set to the linearity correction voltage Vli. In FIG. 12, the drive voltage Vin = Vpe + Vb. However, Vpe = 20 sin (t). The second harmonic voltage Vksa is Vksa = ζ * 20sin (2t−π / 2), and the second harmonic voltage Vksb is Vksb = ζ * 20sin (2t). However, ζ = 0.1.

The drive voltage Vin has a minimum value when t = 3π / 2 + 2nπ (where n is a positive integer), whereas the second harmonic voltage Vksa has a maximum value of ζ when t = 3π / 2 + 2nπ. become. Therefore, if -Vksa, which is the sign-inverted second harmonic voltage Vksa, is set to the linearity correction voltage Vli, that is, if Vli = -Vksa, the drive voltage Vin can be pushed down when t = 3π / 2 + 2nπ. .. As a result, it is possible to prevent deterioration of the linearity of the rotation angle Aro with respect to the drive voltage Vin.

On the other hand, the second harmonic voltage Vksb becomes 0 when t = 3π / 2 + 2nπ, so the second harmonic voltage Vksb is superimposed on the periodic vibration voltage Vpe with or without sign inversion. However, the drive voltage Vin cannot be pushed down. Therefore, even if the second harmonic voltage Vksb is superimposed on the periodic vibration voltage Vpe, the linearity cannot be improved.

Next, the second harmonic voltage Vks (= ζ * 20 sin (2t + π / 2)) as the second harmonic component with the phase change constant θ set to π / 2 will be considered. Vks = ζ * 20sin (2t + π / 2) is the one in which the phase of ζ * 20sin (2t) as the first multiple frequency component is advanced. ζ * 20sin (2t + π / 2) becomes the minimum value −ζ when t = 3π / 2 + 2nπ. As a result, ζ * 20sin (2t + π / 2) does not invert the sign contrary to the above-mentioned ζ * 20sin (2t−π / 2), and if Vks that maintains the sign is defined as the linearity correction voltage Vli, That is, if Vli = + Vksa, the drive voltage Vin can be pushed down when t = 3π / 2 + 2nπ. As a result, it is possible to prevent deterioration of the linearity of the rotation angle Aro with respect to the drive voltage Vin.

The phase change constant θ is not limited to ± π / 2. The phase change constant θ may be in the range of −π <θ <π (where θ ≠ 0). In this range, when t = 3π / 2 + 2nπ (where n is a positive integer), | Vks |> 0 as the absolute value of the secondary harmonic voltage Vks, so the secondary harmonic voltage Vks is + This is because the drive voltage Vin can be pushed down by the secondary harmonic voltage Vks when t = 3π / 2 + 2nπ by superimposing it on the periodic vibration voltage Vpe by (addition) or − (subtraction).

In the optical scanning device 25, the drive voltage Vin can be expressed by a specific equation as follows (Equation 1a) to (Equation 1c). In addition, in (Equation 1a) to (Equation 1c) and other equations, the amplitude of the periodic vibration voltage Vpe is normalized and unified to 1. Actually, if the amplitude is 20 V, 20 or the like is added as a coefficient to (Equation 1a) or the like.

The second harmonic voltage Vks of (Equation 1a) is the first multiple frequency whose frequency is twice and the amplitude is a predetermined ratio with respect to the Fourier series expansion frequency component represented by expanding the periodic vibration voltage Vpe into the Fourier series. The phase of the component is −π / 2, which corresponds to the code-inverted second harmonic component that has been changed. In this case, since the periodic vibration voltage Vpe is a single sine wave, the Fourier series expansion frequency component represented by expanding the periodic vibration voltage Vpe to the Fourier series also becomes a single sine wave component. Further, the predetermined ratio of the amplitude is specifically 0.1.

The ζ * cos (2t) of (Equation 1c) can replace the ζ * sin (2t−π / 2) of (Equation 1a) with a cosine wave while maintaining the frequency and the amplitude ratio ζ. Shown. That is, the linearity correction voltage Vli is obtained by inverting the sign of the double frequency voltage whose phase is delayed by π / 2 with respect to the periodic vibration voltage Vpe as a single sine wave. It means the same as setting the double frequency sine wave component to the linearity correction voltage Vli without changing the phase with respect to the voltage Vpe. Therefore, both are the same as the constitution of the invention.

FIG. 13 shows a sawtooth wave voltage Vramp as an example of the periodic vibration voltage Vpe. The length of 2π in the phase on the horizontal axis corresponds to one cycle of the saw-wave voltage Vramp.

The ideal sawtooth voltage Vramp rises momentarily and then gradually falls at a predetermined falling speed. The optical scanning device 25 may be turned on when the sawtooth wave voltage Vram rises because the rise is momentary, but in principle, the laser light source 14 is turned off, and the laser light source is turned off during the period when the sawtooth wave voltage Vramp falls. 14 is turned on, and the brightness of the scanning point of the scanning light Lb is controlled by controlling the energizing current value of the laser light source 14. As a result, a monochrome image is generated in the irradiation region of the scanning light Lb. When it is desired to generate a color image, three types of laser light sources 14 are prepared according to the three primary colors of light, and the brightness is controlled for each laser light source 14.

The following (Equation 2) shows the frequency component when the Fourier series of the sawtooth voltage Vramp is expanded. (Equation 3a) expresses the drive voltage Vin by an equation using (Equation 2). In (Equation 3b), each double frequency sine wave component of the linearity correction voltage Vli of (Equation 3a) is replaced with a double frequency cosine wave component.

(Equation 2), (Equation 3a) and (Equation 3b) will be described in detail. On the right side of (Equation 3a), the linearity correction voltage Vli is arranged between the periodic vibration voltage Vpe and the offset bias voltage Vb. The Vli on the right side of (Equation 3a) is the range enclosed in parentheses after "ζ *", and the frequency is doubled for each frequency component when the Fourier series is expanded in (Equation 2). It consists of double frequency components. Since the sawtooth voltage Vram as the periodic vibration voltage Vpe is an odd function, when expanded into the Fourier transform series, each component becomes only a sinusoidal component as shown on the right side of (Equation 2). Therefore, the double frequency component in the corresponding range of the linearity correction voltage Vli on the right side of (Equation 3a) becomes the double frequency sine wave component.

(Equation 3b) is a modification of (Equation 3a), and replaces the double frequency sine wave component of the periodic vibration voltage Vpe of (Equation 3a) with the double frequency cosine wave component, and also drives the Vin and linearity correction voltage. The components of the same frequency of Vli are arranged so that they are next to each other. (Equation 3a) and (Equation 3b) mean that the constitution of the invention is the same.

FIG. 14 shows a triangular wave voltage Vtri as another example of the periodic vibration voltage Vpe. The length of 2π in the phase on the horizontal axis corresponds to one cycle of the triangular wave voltage Vtri.

Since the triangle wave voltage Vtri has the same rising speed and falling speed, the control device 27 keeps the laser light source 14 in the lit state during both the voltage rising period and the voltage falling period of the triangular wave voltage Vtri, and images in the irradiation region. Can be generated. However, since the scanning direction in the vertical direction is reversed between the voltage rise period and the voltage drop period, when the optical scanning device 25 is used as the image generator, the voltage rises in the brightness control of the irradiation region by the energization control of the laser light source 14. It is necessary to use it properly for the period control and the voltage drop period control.

The triangular wave Vtri as the drive voltage Vin can be expanded into a Fourier series by either an odd function or an even function. The following (Equation 4a) is a Fourier series expansion equation when the triangular wave Vtri is an odd function. (Equation 4b) is a Fourier series expansion equation when the triangular wave Vtri is an even function. (Equation 5) shows that the cosine wave in (Equation 4b) can be replaced with a sine wave by changing the phase of the cosine wave by π / 2.

(Equation 4a), (Equation 4b) and (Equation 5) will be described in detail. The right side of (Equation 4a) consists of only the sinusoidal component. Therefore, when the periodic vibration voltage Vpe is a triangular wave Vtri, the linearity correction voltage Vli can be generated by the same method as the sawtooth wave voltage Vramp. That is, a first-fold frequency component having a frequency twice that of the Fourier series expansion sine wave component of the triangular wave Vtri and an amplitude having a predetermined amplitude ratio ζ is obtained. The first multiple frequency component is composed of only a sinusoidal frequency component. Then, a second-fold frequency sine wave component to which a phase change constant θ for advancing or delaying the phase with respect to the first-fold frequency component is added is obtained. The second multiple frequency sinusoidal component is composed of only the sinusoidal frequency component. Finally, the linearity correction voltage Vli set based on the second-fold frequency sinusoidal component is generated.

In (Equation 4b), since the Fourier series expansion is performed using the triangular wave Vtri as an even function, all the Fourier series expansion frequency components on the right side are cosine wave components. However, as shown in (Equation 5), the cosine wave can be converted into a sine wave having the same frequency by changing the phase of π / 2. Therefore, the Fourier series expansion cosine wave component of the even function of (Equation 4b) is replaced with a sine wave component, and the multiple frequency wave component is composed only of the double frequency sine wave component in the same manner as in (Equation 4a). The linearity correction voltage Vli can be generated based on the double frequency sinusoidal component.

A general periodic function is expressed by superimposing an odd function Fourier series expansion sine wave component and an even function Fourier series expansion cosine wave component. The Fourier series expansion sine wave component of the even function can be replaced with the Fourier series expansion sine wave component by the replacement of the equation (5). Thus, any periodic function can be represented by the Fourier series expansion sinusoidal component.

The present invention has the following configuration as a modified example.

In the embodiment, the drive voltage of the unipolar supplied to the cantilever 15 of the outer actuator 7 of the optical deflector 1 is described as positive (example: FIGS. 5 to 14). In the present invention, the driving voltage of the unipolar of the piezoelectric film of the piezoelectric actuator of the optical deflector may be negative. In the embodiment, when the drive voltage of the unipolar is used negatively, the ground voltage is applied to the lower electrode layer of the piezoelectric film of the cantilever 15, and the negative drive voltage is supplied to the upper electrode layer of the piezoelectric film. To. When the drive voltage of the unipolar is used negatively, the action of the optical deflector 1 is to replace the absolute value of the drive voltage of the unipolar with the absolute value, and if the replaced absolute value is regarded as a positive drive voltage, the drive voltage of the unipolar is positive. The operation of the above-described embodiment described in the case of use can be applied as it is.

In the embodiment, a single sine wave, sawtooth voltage Vram or triangular wave Vtri is used as the drive voltage Vin, but the drive voltage Vin of the present invention can adopt other periodic vibration voltage.

In the embodiment, the frequency of the reciprocating rotation of the mirror portion 2 around the second axis is 60 Hz. In the present invention, the constant frequency for reciprocating the mirror portion around the axis may be a frequency other than 60 Hz.

In the embodiment (Equation 2), the sawtooth voltage Vramp as an example of the periodic vibration voltage Vpe is expanded to the Fourier series to an infinite order. However, in the present invention, the linearity correction voltage Vli can be set based only on the second frequency component of the predetermined order or less by limiting the second frequency component to the frequency component of the predetermined order or less. In that case, since the number of the second frequency components is reduced, the process of generating the linearity correction voltage Vli is simplified. Further, when synthesizing (adding) a plurality of second-fold frequency components having different frequencies by a synthesizer, it is possible to avoid complication and enlargement of the structure of the synthesizer.

In the embodiment, the linearity correction voltage Vli is added to the drive voltage Vin of the outer actuator 7 to improve the linearity of the outer actuator 7. However, in the present invention, in order to improve the linearity of the inner actuator 6, it is also possible to apply a linearity correction voltage to the drive voltage of the inner actuator 6.

1 ... Optical deflector, 2 ... Mirror part, 7 ... Outer actuator (piezoelectric actuator), 14 ... Laser light source (light source), 25 ... Optical scanning device, 27 ... Control device ..

Claims (5)

Light source and
It has a mirror portion that can reciprocate around a predetermined axis, reflects incident light from the light source in a direction corresponding to the rotation angle around the axis, and emits as scanning light, and a piezoelectric film. An optical deflector having a piezoelectric actuator that controls the rotation angle of the mirror portion around the axis according to the driving voltage of the piezoelectric film, and
A control device that supplies the drive voltage to the piezoelectric actuator with the drive voltage of the unipolar is provided .
The drive voltage is a periodic vibration voltage that causes the mirror portion to reciprocate around the axis at a constant frequency by being applied to the piezoelectric film, and a component when the periodic vibration voltage is expanded by the Foulier series. The alignment of the drive voltage and the rotation angle based on the second-fold frequency component in which the phase of the first-fold frequency component whose frequency is twice and the amplitude is a predetermined ratio is changed with respect to the Fühlier series expansion frequency component. It is generated by superimposing a linear correction voltage, which is a correction voltage for improving the performance, and a predetermined bias voltage.
The phase of the linearity correction voltage is set so that the value of the drive voltage becomes a value that is maximum away from the withstand voltage of the piezoelectric film in accordance with the phase in which the absolute value of the periodic vibration voltage is minimized. optical scanning apparatus characterized by there. In the optical scanning apparatus according to claim 1,
An optical scanning apparatus characterized in that the Fourier series expansion frequency component is represented only by a sine wave component. In the optical scanning apparatus according to claim 2,
The control device is
When the phase change from the first-fold frequency component to the second-fold frequency component is a change that advances the phase, the second-fold frequency component that maintains the sign is generated as the linearity correction voltage.
When the phase change from the first-fold frequency component to the second-fold frequency component is a change that delays the phase, the second-fold frequency component whose sign is reversed is generated as the linearity correction voltage. Optical scanning device. In the optical scanning apparatus according to claim 3,
An optical scanning apparatus, wherein the phase change is a π / 2 phase advance or lag. In the optical scanning apparatus according to any one of claims 1 to 4.
An optical scanning apparatus characterized in that the linearity correction voltage is set based only on a second frequency component having a predetermined order or less.