JP7027689B2 - Light deflector and image projection device - Google Patents

Description

The present invention relates to a light deflector and an image projection device.

In recent years, as a means for deflecting and scanning a light beam, a small size in which a movable part and an elastic beam part having a reflective surface provided on a substrate are integrally formed by micromachining technology for microfabrication of silicon or glass applying semiconductor manufacturing technology. Optical deflection elements (MEMS (Micro Electro Mechanical Systems) deflection elements) have been developed.

Patent Document 1 describes the scanning center of the optical beam of the optical deflection element by changing the offset voltage of the drive signal applied to the piezoelectric actuator as a method of adjusting the mechanical misalignment that occurs when the optical deflection element is assembled to the printer. We are proposing a method to correct.

However, in the conventional technique, there is a problem that the scanning line is distorted due to the influence of the natural vibration mode of the light deflection element, and the luminance unevenness occurs in the drawn image by beam scanning.

The present invention has been made in view of the above, and an object of the present invention is to provide a light deflection device and an image projection device capable of suppressing the occurrence of luminance unevenness.

In order to solve the above-mentioned problems and achieve the object, the present invention has a movable portion having a reflective surface and a plurality of beams that swingably support the movable portion around one axis so as to be continuous. A first drive signal is transmitted to one of a support portion including a meandering portion, a plurality of piezoelectric members individually provided on the plurality of beams, and two the piezoelectric members individually provided on two adjacent beams. A control unit for inputting and inputting a second drive signal to the other is provided, and the first drive signal and the second drive signal are signals having a periodic waveform, and the first drive signal is provided. The ratio of the rise time to the fall time in one cycle of the signal is larger than that of the second drive signal, and the control unit adjusts the offset voltage of the first drive signal to perform optical scanning by the reflecting surface. Correct the center of.

According to the present invention, it is possible to provide an optical deflection device and an image projection device capable of suppressing the occurrence of luminance unevenness.

FIG. 1 is a diagram showing a configuration example of the optical scanning system of the present embodiment. FIG. 2 is a diagram showing an example of a detailed configuration of the surface to be scanned. FIG. 3 is a diagram showing a configuration example of the light deflection element. FIG. 4 is a diagram illustrating a drive signal applied to scan the reflection mirror in a sawtooth shape. FIG. 5 is a diagram illustrating a drive signal applied to scan the reflection mirror in a sawtooth shape. FIG. 6 is a diagram showing the result of evaluating the mirror deflection angle when the drive signal is applied to the optical deflection element in the reference state. FIG. 7 is a diagram showing the result of evaluating the mirror deflection angle when the drive signal is applied to the optical deflection element in the reference state. FIG. 8 is a diagram showing an example of a mirror deflection angle after adjusting the phase difference. FIG. 9 is a diagram for explaining the relationship between the frequency component of the sawtooth signal and the frequency characteristic of the resonance mode. FIG. 10 is a diagram illustrating the relationship between the frequency component of the drive signal and the resonance frequency of the optical deflection element. FIG. 11 is a diagram showing the characteristics of the mirror deflection angle obtained when the drive signal is applied to the optical deflection element. FIG. 12 is a diagram showing the characteristics of the mirror deflection angle obtained when the drive signal is applied to the optical deflection element. FIG. 13 is a diagram showing a high frequency vibration component among the light deflection characteristics. FIG. 14 is a diagram showing a high frequency vibration component among the light deflection characteristics. FIG. 15 is a diagram qualitatively showing the characteristics of the phase change and the change in the vibration width with respect to the high frequency vibration generated when the symmetry of the drive signal is changed. FIG. 16 is a diagram showing the time change of the mirror deflection angle. FIG. 17 is a diagram showing the time change of the high frequency vibration component. FIG. 18 is a diagram showing an example of a drive waveform applied to the optical deflection element and a projected scan line image. FIG. 19 is a diagram showing an example of a waveform of a drive signal. FIG. 20 is a diagram showing an example of a waveform of a drive signal. FIG. 21 is a diagram showing an example of a waveform of a drive signal. FIG. 22 is a diagram showing an example of the amount of central fluctuation of the scanning line when the offset voltage is changed. FIG. 23 is a diagram showing an example of luminance unevenness when the offset voltage is changed. FIG. 24 is a diagram showing an example of an image having luminance unevenness in the vertical direction. FIG. 25 is a diagram showing an example of the filter transmittance of the low-pass filter. FIG. 26 is a diagram showing an example of a drive signal waveform when a low-pass filter is applied. FIG. 27 is a schematic view showing an example of an automobile equipped with a head-up display device. FIG. 28 is a schematic view showing an example of a head-up display device. FIG. 29 is a diagram showing an example of an image forming apparatus incorporating an optical writing apparatus. FIG. 30 is a schematic view showing an example of an optical writing device. FIG. 31 is a schematic view of an automobile equipped with a laser radar device, which is an example of an object recognition device. FIG. 32 is a schematic view showing an example of a laser radar device.

An embodiment of the light deflector and the image projection device according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a diagram showing a configuration example of the optical scanning system of the present embodiment. FIG. 1 is a conceptual diagram of the entire system including a light deflector used for performing a two-dimensional image display. As shown in FIG. 1, the optical scanning system of the present embodiment includes a light deflection element 11, a light source 12, a light source drive system 13, an optical system 14, a control device 19, a light detection unit 20, and a storage unit. It is equipped with 110.

The optical deflection device of this embodiment is configured to include, for example, an optical deflection element 11 and a control device 19. The configuration of the light deflection device is not limited to this, and includes a part or all of other components (light source 12, light source drive system 13, optical system 14, photodetection unit 20, storage unit 110). May be good.

The light source 12 emits a laser beam. The light source drive system 13 drives the light source 12 according to the signal from the control device 19. The optical system 14 is an optical system for incidenting the laser beam emitted from the light source 12 onto the light deflection element 11.

The photodetection unit 20 detects the light emitted from the light deflection element 11. The photodetector 20 can be realized by, for example, a photodiode. The photodetection unit 20 outputs a voltage (detection signal) according to the amount of received laser light.

The control device 19 controls the drive of the optical deflection element 11. The control device 19 includes an image signal calculation unit 18, a detection signal calculation unit 17, and a drive control unit 16.

The image signal calculation unit 18 calculates a signal (synchronous signal) for controlling the light source 12 based on the acquired optical scanning information. The detection signal calculation unit 17 acquires the detection signal detected by the photodetection unit 20, and calculates, for example, the timing (reference timing) at which light is received, based on the acquired detection signal. The drive control unit 16 outputs a drive signal of the optical deflection element 11 based on information such as optical scanning information and reference timing.

The control device 19 acquires optical scanning information from, for example, an external device or a network. The method of acquiring the optical scanning information is not limited to this, and the optical scanning information may be stored in the ROM or FPGA in the control device 19, or a storage device such as an SSD may be newly provided in the control device 19. , The storage device may be configured to store optical scanning information. Here, the optical scanning information is information indicating how the surface to be scanned 15 is optical-scanned. For example, when displaying an image by optical scanning, the optical scanning information is image data. Further, for example, when optical writing is performed by optical scanning, the optical scanning information is write data indicating the writing order and the writing location. In addition, for example, when object recognition is performed by optical scanning, the optical scanning information is irradiation data indicating the timing and irradiation range of irradiating the light for object recognition.

Each part of the control device 19 is realized by, for example, one or more processors. For example, each of the above parts may be realized by causing a processor such as a CPU (Central Processing Unit) to execute a program, that is, by software. Each of the above parts may be realized by a processor such as an IC (Integrated Circuit) and an FPGA (Field-Programmable Gate Array), that is, hardware. Each of the above parts may be realized by using software and hardware in combination. When a plurality of processors are used, each processor may realize one of each part, or may realize two or more of each part.

The storage unit 110 stores various information used in various processes. For example, the storage unit 110 stores control table data used by the control device 19. The storage unit 110 can be configured by any commonly used storage medium such as an HDD (Hard Disk Drive), an optical disk, a memory card, and a RAM (Random Access Memory).

The light deflection element 11 is, for example, a MEMS device having a reflection mirror 10 (reflection surface) and capable of moving (swinging) the reflection mirror 10. The light deflection element 11 deflects the irradiation light from the light source 12 and scans the light, so that an image corresponding to the light scanning signal (image signal or the like) can be projected on the scanned surface 15. The surface to be scanned 15 is, for example, a screen.

FIG. 2 is a diagram showing an example of a detailed configuration of the surface to be scanned 15. In FIG. 2, the timing of optical scanning is controlled by using two photodetectors 20. The optical scanning area 50 is divided into an image drawing area 50a and a non-image drawing area 50b. The photodetector 20 is installed in the non-image drawing area 50b. In the non-image drawing area 50b, the laser beam is turned on only in the portion of the photodetection unit 20 so that unnecessary light does not appear as image noise. The timing of optical scanning is equivalent to the deflection angle of the reflection mirror 10. By controlling the timing of laser emission with reference to the time input to the photodetector 20, a fine image is formed on the surface to be scanned 15. Further, the deviation of the center of the deflection angle of the optical deflection element 11 is detected based on the passing time of the optical detection unit 20. For example, the detection signal calculation unit 17 detects the deviation of the center of the deflection angle from the detection signal detected by the optical detection unit 20, that is, the deviation of the center of the optical scan.

Hereinafter, an example of a detailed configuration of the light deflection element 11 will be described. As a configuration example of the optical deflection device, there is a device using a thin film piezoelectric body made of a thinned piezoelectric material as an actuator. In an optical deflector using a piezoelectric actuator, a thin film piezoelectric material is formed by superimposing it on the surface of a cantilever. In this configuration, in-plane expansion and contraction caused by the piezoelectric characteristics of the piezoelectric body is transmitted to the support that becomes the cantilever, and if one end of the cantilever is fixed, the other end of the cantilever can be pressed according to the amount of voltage applied to the piezoelectric body. It can be vibrated up and down. By arranging a small reflection mirror near the cantilever and utilizing the shrinkage of the thin film caused by applying a voltage to the piezoelectric thin film as described above, the element size is about several mm square and the diameter is 1 mm provided in the element. It is possible to scan a minute mirror of about several mm at high speed.

FIG. 3 is a diagram showing a configuration example of an optical deflection element 11 that enables two-dimensional optical beam scanning using a cantilever.

As shown in FIG. 3, the reflection mirror 10 is connected to the mirror peripheral frame 312 via the torsion bars 311a and 311b to form the movable portion 320. The movable portion 320 is sandwiched between a pair of meandering beam portions 330a and 330b formed by meandering with a plurality of folded portions, respectively. The meandering beam portions 330a and 330b are examples of meandering portions that are continuous so that a plurality of beams meander.

One end of each of the meandering beam portions 330a and 330b is supported by the support substrate 301, and the multi-end is connected to the movable portion 320. The support substrate 301 is an example of a support portion that swingably supports the movable portion 320 around one axis (X-axis in FIG. 3).

Each of the meandering beam portions 330a and 330b is divided into a beam portion 340A and a beam portion 340B every other time. Piezoelectric members are individually provided for each adjacent beam portion. The piezoelectric member is, for example, PZT (lead zirconate titanate). Hereinafter, the piezoelectric members provided on the beam portion 340A and the beam portion 340B, respectively, are referred to as the Ath piezoelectric member and the Bth piezoelectric member. The actuator including the Ath piezoelectric member provided on the beam portion 340A and the beam portion 340A is referred to as Ach. Further, the actuator including the Bth piezoelectric member provided on the beam portion 340B and the beam portion 340B is referred to as Bch.

The drive control unit 16 applies different voltages to the A-th piezoelectric member and the B-th piezoelectric member to generate warpage in the meandering beam portions 330a and 330b. As a result, the adjacent beam portions 340A and 340B bend in different directions, the deflections are accumulated, and the movable portion 320 rotates around the X axis (= vertical direction) at a large angle. That is, by adopting separate signal waveforms for each of the voltage waveform applied to the Ath piezoelectric member (hereinafter referred to as A drive signal) and the voltage waveform applied to the Bth piezoelectric member (hereinafter referred to as B drive signal). , Optical scanning with the X-axis as the center of rotation becomes possible. The drive control unit 16 inputs a first drive signal (Ath drive signal) to one of two piezoelectric members individually provided on two adjacent beams (beam portions), and a second drive signal to the other. Corresponds to the control unit that inputs (the Bth drive signal). The A-th drive signal and the B-th drive signal are signals having a sawtooth-like periodic waveform as described later.

On the other hand, in the horizontal direction centered on the Y axis, optical scanning by resonance is performed using the torsion bars 311a and 311b connected to the reflection mirror 10. In the movable portion 320, the reflection mirror 10 is swingably supported around the Y-axis by the mirror peripheral frame 312 via the torsion bars 311a and 311b and the cantilever 313.

The following raster scanning method is generally used as a scanning method for two-dimensionally scanning an optical beam. That is, in the horizontal direction centered on the Y-axis, the mirror is scanned by a high-speed (several kHz to several tens of kHz) sine wave signal matching the excitation frequency of the horizontal resonance mode of the optical deflection element 11. On the other hand, in the vertical direction centered on the X-axis, the mirror is scanned by a drive signal having a sawtooth waveform at a lower speed (several Hz to several tens of Hz). For example, in an image drawing device using light beam scanning, an image can be drawn with an update time equal to the scanning frequency in the vertical direction by blinking the light emission timing of the light beam according to the scanning angle of the mirror.

When forming a serrated scanning line in the vertical direction, it is desired that the scanning angle of the light beam, that is, the mirror deflection angle of the light deflection element 11 changes linearly with the passage of time. In reality, due to the influence of the natural vibration mode of the light deflection element 11, a vibration component having a frequency higher than the scanning frequency is superimposed on the scanning line, and the scanning line may be distorted. In particular, it is the resonance mode caused by the meandering beam structure of the optical deflection element 11 that has a great influence on the distortion of the scanning line. The vibration direction is a vertical direction with the X axis as the rotation axis, and the resonance frequency thereof is about 100 to 1000 Hz.

The serrated waveform applied to the serpentine beam for vertical optical scanning is generated by the superposition of sinusoidal waves with a frequency that is an integral multiple of the scanning frequency. Therefore, the higher-order vibration signal excites the vibration component corresponding to the above-mentioned vertical resonance mode. As a result, this vibration is superimposed on the sawtooth-shaped scanning line, and the scanning line is distorted. Since this distortion of the scanning line occurs in the vertical direction, when a two-dimensional image is drawn, luminance unevenness occurs in the vertical direction of the image.

As described above, in the driving of the optical deflection element 11 by applying a normal sawtooth signal, the scanning line is distorted due to the influence of the natural vibration mode of the optical deflection element 11 when performing beam scanning in the vertical direction. Luminance unevenness may occur in the drawn image due to beam scanning. Further, when the optical deflection element 11 is mounted on an optical control device such as a head-up display or a laser radar, the center of the scanning line may be deviated due to a change in environmental temperature or a positional shift over time.

Therefore, in the present embodiment, the center shift of the scanning line can be corrected so as to suppress the occurrence of luminance unevenness in the light deflection element 11 utilizing the vibration of the cantilever due to the piezoelectric effect.

Specifically, the following configuration is adopted in this embodiment. First, as a sawtooth drive signal (sawtooth signal), a sawtooth waveform (Ach) including a rising period in which the voltage increases from the minimum value to the maximum value in one cycle, and conversely, the voltage is from the maximum value to the minimum value. A sawtooth waveform (Bch) including a fall time that decreases to is adopted. Then, regarding the null frequency (frequency at which the intensity becomes zero in theory) that appears when this serrated signal is decomposed into frequency components, the null frequency of the drive signal applied to the odd-th cantilever and the null frequency applied to the even-th cantilever are applied. The vertical resonance frequency of the optical deflection element 11 is set to be positioned between the null frequency of the drive signal to be driven.

Further, when the odd-numbered or even-numbered cantilever is driven independently when the optical deflection element 11 is driven, the high-frequency vibrations generated by the odd-numbered and even-numbered cantilever are in an opposite phase relationship with each other, respectively. Set the driving conditions so that the vibration widths of the high-frequency vibrations of are almost equal.

When the center of the deflection angle of the scanning line is shifted (when the center of the scanning line is deviated), for example, the drive control unit 16 eliminates the deviation of the center by changing the offset voltage of the drive signal of the Ach having a large rise period. The center of the runout angle is corrected as follows. Since the rising (Ach) has a higher displacement linearity with respect to the voltage of the piezoelectric material than the falling (Bch), the center of the scanning line is centered while suppressing the occurrence of luminance unevenness by changing the offset voltage of the Ach. It can be corrected.

4 and 5 are diagrams illustrating a general A-th drive signal and B-th drive signal applied to scan the reflection mirror 10 in a sawtooth pattern. The Ath drive signal 451 is a sawtooth signal having a frequency of fA. The repetition period TA (= 1 / fA) has a rising period (TrA) in which the applied voltage uniformly increases from the minimum value to the maximum value, and conversely, a falling period in which the applied voltage uniformly decreases from the maximum value to the minimum value. It is divided into periods (TfA).

The Bth drive signal 452 is a sawtooth signal having a frequency of fB. The repetition period TB (= 1 / fB) is a falling period (TfB) in which the applied voltage uniformly decreases from the maximum value to the minimum value and a rising period (TrB) in which the applied voltage uniformly increases from the minimum value to the maximum value. ) And.

When an image is drawn by optical scanning by the optical deflection element 11, the period of TrA and TfB is the image drawing time zone. Generally, the repetition frequency of the Ath drive signal and the Bth drive signal are equal. In the following description, it is assumed that fs = fA = fB for the repetition frequency fs of the drive signal. Further, in the following description, the applied voltage refers to the difference between the maximum voltage value and the minimum voltage value.

Further, as shown in FIG. 5, the time when the Ath drive signal becomes 0.5 times the applied voltage in the rising period (rising midpoint) and the time when the B driving signal becomes 0.5 times the applied voltage in the falling period. The state in which the doubled times (falling midpoint) match is defined as the reference state. In the reference state, it is assumed that the phase difference between the Ath drive signal and the Bth drive signal is 0 °. When a phase difference is given to both, a time lag occurs between the rising midpoint and the falling midpoint.

Here, for the following explanation, the parameters represented by the following equations (1) and (2) are defined as symmetry.
Symmetry A = TrA / TA ・ ・ ・ (1)
Symmetry B = TfB / TB ... (2)

Symmetry A means the ratio (ratio) of the time TrA (time for optical scanning) from the minimum value to the maximum value with respect to one cycle (TA) of the Ath drive signal. Symmetry B means the ratio (ratio) of the time TfB (time for optical scanning) from the maximum value to the minimum value with respect to one cycle (TB) of the B-th drive signal. Since the Bth drive signal has a shape (reverse sawtooth shape) in which the Ath drive signal is inverted, the ratio of the rise time to the fall time in one cycle is B for the A drive signal. It becomes larger than the drive signal.

For example, when the ratio of the rise time to the fall time of the Ath drive signal is 9: 1, symmetry A = 90%. If symmetry A = symmetry B, the rising start time of the Ath drive signal and the falling start time of the Bth drive signal are at the same timing in the reference state. On the other hand, when the symmetry A and the symmetry B are set to different values, the rise start time of the Ath drive signal and the fall start time of the B drive signal are different even in the reference state.

First, an example of the result of evaluating the mirror deflection angle when the optical deflection element 11 is driven by the conventional drive method will be described. 6 and 7 are the results of evaluating the mirror deflection angle when only the Ath drive signal and the Bth drive signal are applied to the optical deflection element 11 in the reference state, respectively.

As shown in FIGS. 6 and 7, periodic high-frequency vibration components 652 and 752 are superimposed on the linear deflection angles 651 and 751 on the mirror deflection angle. The vibration frequencies 661 and 761 of the high frequency vibration correspond to the frequency of the lowest order resonance mode among the resonance modes that vibrate with the X axis of the light deflection element 11 as the rotation axis. Further, the high frequency vibration is generated in substantially the same phase when only the Ath drive signal and only the Bth drive signal are applied.

In the conventional drive method, in order to suppress high frequency vibration components generated in the same phase in the reference state, a phase difference is added between the Ath drive signal and the Bth drive signal so that the high frequency signals overlap in opposite phases. Drive conditions are determined in advance. FIG. 8 is a diagram showing an example of a mirror deflection angle after adjusting the phase difference. As shown in FIG. 8, the high frequency component is removed from the phase difference imparted to the Ath drive signal 801 and the Bth drive signal 802, and the mirror deflection angle 803 changes substantially linearly. However, as will be described later, it was confirmed that even if the applied phase difference was slightly different from the optimum value, high-frequency vibration was expressed and sufficient linearity of the scanning line could not be obtained.

The generation of high-frequency vibration is caused by the resonance mode of the optical deflection element 11 being caused by the application of the Ath drive signal or the Bth drive signal. This resonance frequency fluctuates due to continuous driving of the optical deflection element 11 or a temperature change, and the optimum phase difference also changes accordingly. Therefore, it is difficult to continue driving the optical deflection element 11 while maintaining the optimum phase difference.

FIG. 9 is a diagram for explaining the relationship between the frequency component of the sawtooth signal in the conventional drive method and the frequency characteristic of the lowest-order resonance mode that vibrates with the X axis of the optical deflection element 11 as the rotation axis. .. The frequency component of the sawtooth waveform is obtained by Fourier transforming the ideal sawtooth waveform and decomposing the applied signal into frequency components. The frequency component of the sawtooth waveform is represented by the superposition of the applied voltage components generated at the drive frequency interval from direct current (0 Hz).

FIG. 9 also shows the spectral characteristic 901 of the lowest-order resonance mode that vibrates with the X-axis as the rotation axis, which is possessed by the optical deflection element 11. FIG. 9 shows an example in which the frequency of the drive signal is set to one half-integer of the resonance frequency of the optical deflection element 11. When set in this way, the signal component generated periodically and the resonance frequency of the optical deflection element 11 do not overlap, so that the magnitude of the vibration component is theoretically reduced as much as possible. However, as a result, when the Ath drive signal and the Bth drive signal are individually driven as shown in FIGS. 6 and 7, a large high frequency vibration is generated.

What should be noted in the frequency characteristics of the sawtooth waveform is that the frequency characteristics of the drive signal have a null frequency at which the signal strength is theoretically zero. The null frequency fn of the sawtooth waveform is given by the following equation (3) using the repetition frequency fs of the drive signal and the symmetry S.
fn = N × fs / (1-S) ・ ・ ・ (3)

N is an integer and the null frequency appears periodically. As is clear from the equation (3), the null frequency can be adjusted to a desired value by using the drive frequency of the sawtooth signal or the symmetry as a parameter.

Here, the "null frequency" will be described. For example, when the MEMS mirror is driven by a predetermined modulated signal (for example, a serrated signal), depending on the type of the modulated signal, the frequency spectrum (the modulated signal is Fourier transformed and decomposed into frequency components) is divided into frequency components at regular intervals. There is a "valley" (a point where the power density is theoretically zero). This valley is generally called a null point. Therefore, in this specification, the frequency that takes a null point is defined as "null frequency".

It was confirmed that a null frequency also existed in the drive signal of the sawtooth waveform, and it was inductively clarified that the frequency was given by the above equation (3).

In the drive signal spectrum (see FIG. 9), discrete frequency components appear corresponding to the drive frequency, but if only one serrated pulse is Fourier transformed, it will be continuously attenuated toward null. Such spectral characteristics can be obtained. In a periodic sawtooth signal, the continuous spectrum is used as an envelope and has discrete signal components at drive frequency intervals. That is, the signal component near the null frequency is also suppressed to be relatively low.

That is, in the frequency band including the null frequency and its vicinity (hereinafter, also referred to as “null frequency band”), the signal intensity of the high frequency component of the drive signal becomes the minimum (minimum at the null frequency) (see FIG. 9).

It is also known that a plurality of null frequency bands exist at predetermined frequency intervals (see FIG. 9).

Next, a method of driving the optical deflection element 11 of the present embodiment and the occurrence of luminance unevenness will be described.

FIG. 10 is a diagram illustrating the relationship between the frequency component of the drive signal and the resonance frequency peculiar to the optical deflection element 11 in the present embodiment. In the drive method of the optical deflection element 11 in the present embodiment, the null frequencies of the sawtooth waveforms of the Ath drive signal and the Bth drive signal are different from each other, and the optical deflection element 11 is located between the null frequencies. Set so that the resonance frequency is located. For example, in FIG. 10, it is shown that the resonance frequency is located between the null frequency 1001 of the Ath drive signal and the null frequency 1002 of the Bth drive signal.

As described above, the null frequency of the sawtooth signal can be controlled by the repetition frequency fs of the drive signal and the symmetry S. However, if the Ath drive signal and the Bth drive signal are different from each other, it is difficult to draw a periodically stable scanning line. Therefore, making the null frequencies different from each other means making symmetry A and symmetry B different from each other.

Further, it is preferable that the null frequencies of the Ath drive signal and the Bth drive signal are located in the vicinity of the resonance frequency of the optical deflection element 11. This is because there is almost no signal component in the vicinity of the null frequency, so even if the resonance mode of the optical deflection element 11 exists in the vicinity of this band, the high frequency vibration generated by the excitation of this vibration mode can be significantly suppressed. Is.

By setting the drive signal in this way, it is possible to obtain a scanning line in which the high frequency signal is suppressed when the Ath drive signal and the Bth drive signal are simultaneously applied in the reference state. Hereinafter, this operating principle will be described. FIG. 11 is a diagram showing the characteristics of the mirror deflection angle obtained when only the Ath drive signal is applied to the optical deflection element 11. FIG. 12 is a diagram showing the characteristics of the mirror deflection angle obtained when only the Bth drive signal is applied to the optical deflection element 11. As the applied voltage of the Ath drive signal increases, the mirror deflection angle of the optical deflection element 11 deflects from 0 ° in the positive angular direction. On the other hand, in the B-th drive signal, the mirror deflection angle of the optical deflection element 11 is deflected from the negative angular direction toward 0 ° as the applied voltage decreases.

From FIGS. 11 and 12, when only the Ath drive signal and the Bth drive signal are applied, the vibration width is suppressed as compared with the conventional drive method, but the high frequency vibration is superimposed on the scanning line by the optical deflection element 11. It can be confirmed that it has been done.

13 and 14 are diagrams showing high-frequency vibration components among the light deflection characteristics shown in FIGS. 11 and 12. The high-frequency vibration component is extracted, for example, by taking a difference from an ideal scanning line that is a linear approximation of the scanning line in the optical scanning range. The optical scanning range may be set to an arbitrary time region in the rise period of the A drive signal or the fall period of the B drive signal.

Here, the phase and vibration width will be further considered as parameters representing the characteristics of high-frequency vibration. Further, in the evaluation of the phase amount of the high frequency vibration, attention is paid to the phase of the maximum point for the vibration due to the Ath drive signal, and the phase of the minimum point for the vibration due to the Bth drive signal.

FIG. 15 is a diagram qualitatively showing the characteristics of the phase change and the vibration width change found by the inventor with respect to the high frequency vibration generated when the symmetry of the Ath drive signal and the Bth drive signal is changed.

The graph at the top of FIG. 15 shows the phase change. The vertical axis of this graph represents the phase of high frequency vibration. When the values on the vertical axis of the Ath drive signal and the Bth drive signal are the same, the phases of the high frequency vibrations generated by the respective drive signals are shifted by 180 °. That is, high frequency vibration occurs in the opposite phase. Further, it is shown in the upper part of FIG. 15 that there is a region (phase change region) in which the phase changes abruptly in both the Ath drive signal 1501 and the Bth drive signal 1502. The phase difference 1503 given before and after this phase change region is approximately 180 °. Further, when the phase change region is set so that the resonance frequency of the optical deflection element 11 and the null frequency of the drive signal match, that is, the resonance frequency of the optical deflection element 11 is substituted into the value of the null frequency fn in the equation (3). Appears in the vicinity of the symmetry obtained when

When the same symmetry is set for the Ath drive signal and the Bth drive signal as in the conventional drive method, the high frequency vibration generated by the application of each signal is generated in the same phase except in a special case. The special case is a case where the symmetry of the signal is determined so that the resonance frequency of the optical deflection element 11 and the null frequency of the drive signal substantially match.

On the other hand, in the drive method according to the present embodiment, the symmetry of the Ath drive signal and the Bth drive signal is made different from each other so that the resonance frequency of the optical deflection element 11 exists between the null frequencies of the respective signals. Set. By appropriately giving the symmetry of the Ath drive signal and the Bth drive signal, it becomes possible to express the high frequency vibration generated by the application of the Ath drive signal and the Bth drive signal in the opposite phase.

The graph at the bottom of FIG. 15 is a diagram showing changes in the vibration width of high-frequency vibration when the symmetry of the drive signals (A drive signal 1511 and B drive signal 1512) is changed. Arrows 1521, 1522 indicate the symmetry setting values of the Ath drive signal and the Bth drive signal, respectively. Arrow 1523 indicates a theoretical value of symmetry in which the resonance frequency and the null frequency match.

The high-frequency vibration width becomes extremely small at a specific symmetry, and the vibration width increases as the distance from the symmetry increases. The symmetry in which the high frequency vibration is minimized is theoretically a symmetry in which the resonance frequency of the optical deflection element 11 and the null frequency of the drive signal match. However, in an actual element, it may deviate slightly from this theoretical value. Further, it was confirmed that this deviation amount was different when the Ath drive signal and the Bth drive signal were applied, and the minimum value of the high frequency vibration width was also different.

In the drive method according to the present embodiment, the symmetry of the Ath drive signal and the Bth drive signal is set to be different from each other, and the resonance frequency of the optical deflection element 11 is set to exist between the null frequencies of the respective signals. .. Therefore, although the high-frequency vibration width is not a minimum value, it is possible to provide symmetry such that the respective vibration widths match each other.

As described above, according to the drive method according to the present embodiment, the vibration widths of the high frequency vibrations generated when the Ath drive signal and the Bth drive signal are independently applied are equal to each other, and the respective vibrations are in opposite phase to each other. The symmetry to be expressed can be set for each of the Ath drive signal and the Bth drive signal.

FIG. 16 is a diagram showing a time change of the mirror deflection angle when the optical deflection element 11 is driven by simultaneously applying the Ath drive signal and the Bth drive signal in the reference state by the drive method of the present embodiment. .. FIG. 17 is a diagram showing the time change of the high frequency vibration component in this case. In FIGS. 16 and 17, the broken line represents the mirror deflection angle, the thick line represents the Ath drive signal, and the thin line represents the Bth drive signal. By individually adjusting the symmetry of the Ath drive signal and the Bth drive signal as described above, the scanning line of the optical deflection element 11 is linearly displaced with respect to the sawtooth signal, and the high frequency vibration can be completely removed. It is possible.

In the results shown in FIGS. 16 and 17, a value larger than the symmetry of the Ath drive signal was set for the symmetry of the Bth drive signal. From the operating principle of the drive method of the present embodiment, there is no limitation on the magnitude of the symmetry of the Ath drive signal and the Bth drive signal. However, when the symmetry of the B-th drive signal, that is, the applied signal having a longer fall period in one cycle of the sawtooth wave is relatively increased, the scan line linearity is improved. It was found as a result of driving the deflection element 11. The index of scanning line linearity is an index for evaluating linearity, and is defined as the following equation (4).
Scanning line linearity index = (deviation of scanning line from straight line due to mirror deflection) / (total scanning width of scanning line that approximates the scanning range linearly) ... (4)

It should be noted that the smaller the value of the scan line linearity index, the more the high frequency component is removed from the scan line due to the mirror deflection, and the scan line closer to the straight line is drawn.

Next, a method of correcting the scanning center of the optical deflection element 11 will be described with reference to FIGS. 18 to 24.

FIG. 18 is a diagram showing an example of a drive waveform applied to the light deflection element 11 and a scanning line image projected on the screen. When the Ath drive signal 1801 and the Bth drive signal 1802 are input to the optical deflection element 11 to scan the laser beam one-dimensionally, a laser scanning line appears in the vertical direction in FIG. 18 on the screen. When the optical deflection element 11 is attached to an optical control device such as a head-up display or a laser radar, a displacement 1822 may occur at the center 1821 of the scanning line due to a change in the environmental temperature or a displacement over time (FIG. 18). lower left). On the other hand, the center 1823 of the swing width can be controlled by changing the offset voltage 1812 of the drive signal (the A drive signal 1811 in FIG. 18) (lower right of FIG. 18).

From FIG. 19, a correction method for the scanning center will be described based on actual numerical data. The numerical values shown below are examples and are not limited to these numerical values. 19 to 21 are diagrams showing examples of waveforms of the A-th drive signal (signals 1901, 2001, 2101) and the B-th drive signal (signals 1902, 2002, 2102).

In FIGS. 19 to 21, the Ath drive signal (Ach) generated a waveform with Tra / TA = 0.82 and TfA / TA = 0.18. The Bth drive signal (Bch) generated a waveform with TrA / TA = 0.136 and TfA / TA = 0.864.

The resonance frequency of the optical deflection element 11 was 375 Hz. Therefore, the drive frequency is set to 57.5 Hz, which is a value obtained by dividing the resonance frequency by a half-integer ratio, for example, 6.5. This is because uneven brightness can be suppressed.

As shown in the above equation (3), in the drive method in the present embodiment, the repetition frequency fs of any drive signal can be selected, and suitable symmetry is obtained from the relationship between the selected repetition frequency fs and the known resonance frequency f1. The value is calculated. More specifically, a driving condition in which f1 / fs = a half-integer is desirable. This is due to the following reasons.

Ideally, the sawtooth waveform has no signal strength at a null frequency, and has no signal strength other than a vibration component that is an integral multiple of the drive signal. On the other hand, when the drive vibration is set so that the null frequency of the signal and the resonance frequency of the optical deflection element 11 are slightly different as in the present embodiment, the signal strength of the drive signal is set in the vicinity of the resonance frequency of the optical deflection element 11. When present, it excites a large high-frequency vibration component. Therefore, it is effective to suppress the high frequency vibration component by matching the resonance frequency of the optical deflection element 11 with the frequency band corresponding to the gap of the signal component periodically generated for each drive signal frequency.

FIG. 20 is a diagram showing a drive signal waveform when the offset voltage of the Ath drive signal (Ach) is changed. FIG. 21 is a diagram showing a drive signal waveform when the offset voltage of the Bth drive signal (Bch) is changed. In FIGS. 20 and 21, the drive voltage value was set to 23 Vp-p, and the offset voltage was changed from 0 V to 4 V.

FIG. 22 is a diagram showing an example of the amount of central fluctuation of the scanning line when the offset voltage is changed. A scanning line was projected on the screen, and the projected scanning line was photographed with a camera to calculate the amount of central fluctuation of the runout angle. The amount of fluctuation in the center of the runout angle is linear with respect to the offset voltage. By increasing (or decreasing) the offset voltage value 2201 of Ach and the offset voltage value 2202 of Bch, respectively, or by increasing or decreasing the offset voltage value of either Ach or Bch, the center of the deflection angle is changed in both directions. Can be done.

FIG. 23 is a diagram showing an example of luminance unevenness when the offset voltage is changed. As described with reference to FIGS. 6, 7, and 8, the luminance unevenness is reduced by setting the phase difference and symmetry so as to cancel the vibration generated in Ach and Bch, and the optical deflection element 11 is driven. There is. However, it was found that if the offset voltage is changed when the scanning center is deviated, the driving force generated in the cantilever changes and deviates from the operating conditions that cancel the vibrations of Ach and Bch, and as a result, the uneven brightness worsens. There is.

FIG. 23 is a diagram showing the relationship between the Ach offset voltage 2301 and the Bch offset voltage 2302 and the luminance unevenness. FIG. 23 shows how the amount of luminance unevenness changes when the offset voltages of Ach and Bch are changed. Luminance unevenness is defined as the maximum amount of deviation from the mirror linearity / the amount of mirror amplitude × 100%. The smaller the maximum amount of deviation from the mirror linearity, the smaller the luminance unevenness.

FIG. 24 is a laser scan image when the light deflection element 11 is biaxially scanned, and is an image (left side) in which the luminance unevenness in the vertical direction is 1.7% and an image (right side) in which the luminance unevenness in the vertical direction is 3%. It is a figure which shows an example.

As shown in FIG. 23, it is obtained that the luminance unevenness of Ach is less likely to fluctuate with respect to the offset voltage. Therefore, when the center of the scanning line is deviated, it is possible to realize highly robust control for luminance unevenness by changing the offset voltage of Ach (rising). Therefore, in the present embodiment, for example, the drive control unit 16 corrects the center of the optical scan by the reflection mirror 10 by adjusting the offset voltage of the Ath drive signal (Ach).

One of the reasons why the luminance unevenness of Ach is less likely to fluctuate with respect to the offset voltage is the piezoelectric hysteresis described below. It is known that a general piezoelectric element such as PZT has a piezoelectric hysteresis in which a difference occurs between the displacement amount when the voltage is increased and the displacement amount when the voltage is decreased. Therefore, there is a difference between the displacement of the cantilever at the rising edge (Ach, when the voltage is increased) and the displacement of the cantilever at the falling edge (Bch, when the voltage is lowered). That is, the displacement at the falling edge (when the voltage is lowered) contributes more to the displacement with respect to the fluctuation of the offset voltage. As a result, even if the same offset voltage is fluctuated between the rising edge and the falling edge, the falling edge contributes more to the luminance unevenness.

In the present embodiment, the symmetries of the A-th drive signal and the B-th drive signal are made different from each other, so that the vibration widths of the high-frequency vibrations generated by the application of the respective signals are matched, and the vibration widths are further expressed in opposite phases in the reference state. The phase difference of high frequency vibration does not necessarily have to be completely 180 °. For example, a condition in which the phases overlap with each other may be set as an initial value, and a phase difference may be added between the Ath drive signal and the Bth drive signal in order to correct a slight phase shift from the completely opposite phase. For example, a phase difference within a predetermined range (for example, ± 10 °) may be imparted from the reference state (reference phase difference = 0 °). In this case, the difference in the design parameters of the optical deflection element 11 and the slight difference in the optimum symmetry condition generated by the manufacturing error or the like can be compensated by the phase difference correction.

Further, it is also effective to further reduce the high frequency vibration component by providing a difference between the applied voltages of the A drive signal and the B drive signal as needed. For example, the drive control unit 16 may be configured such that at least one of the maximum value and the minimum value of the Ath drive signal and the Bth drive signal is different from each other, and the applied voltages of both are different from each other.

As shown in the lower part of FIG. 15, the vibration width of the high frequency vibration generated by the application of the drive signal can be adjusted by changing the symmetry of the drive signal. Further, by finely adjusting the applied voltages of the Ath drive signal and the Bth drive signal, the vibration width of the high frequency vibration due to the application of each drive signal can be completely matched. This makes it possible to remarkably suppress the generation of high-frequency vibration when the Ath drive signal and the Bth drive signal are applied at the same time.

In particular, when the symmetry of the drive signal is brought close to the theoretical value of the symmetry in which the resonance frequency of the optical deflection element 11 and the null frequency of the drive signal match, the vibration width of the high frequency vibration due to the Bth drive signal depends on the A drive signal. It has been experimentally found that it is relatively smaller than the vibration width of high-frequency vibration. In this case, the vibration width of the high frequency vibration can be matched by setting the applied voltage of the Bth drive signal to be relatively high.

In the present embodiment, the resonance frequency of the optical deflection element 11 is positioned between the null frequency of the A drive signal and the null frequency of the B drive signal. As a result, with respect to the high-frequency vibration caused by the natural vibration mode of the optical deflection element 11 when the Ath drive signal or the Bth drive signal is driven independently, the vibration widths are matched and the vibrations are in reverse phase with each other. It can be expressed. Therefore, as a result, it is possible to suppress the generation of high frequency vibration when the Ath drive signal and the Bth drive signal are applied at the same time.

Here, as is clear from the lower part of FIG. 15, the closer the null frequency of the drive signal is to the resonance frequency of the optical deflection element 11, the higher the frequency vibration generated when the Ath drive signal or the Bth drive signal is applied alone. Vibration width becomes smaller. Therefore, even if a slight phase shift of the high frequency vibration occurs, the vibration width of the high frequency vibration generated when the Ath drive signal and the Bth drive signal are applied at the same time is small.

The generation of high-frequency vibration is caused by the high-frequency component included in the drive signal exciting the light deflection element 11 in the resonance mode. Therefore, for example, a notch filter may be used to remove signal components near the resonance frequency (a predetermined band including the resonance frequency) from the drive signal. This makes it possible to reduce the vibration width of the high-frequency vibration generated when the Ath dynamic signal or the Bth drive signal is driven independently.

In the present embodiment, among the vibration modes peculiar to the optical deflection element 11, the driving method for suppressing the excitation of the lowest-order vibration mode that has a great influence on the distortion of the scanning line has been described. On the other hand, the light deflection element 11 has various vibration modes, which may affect the deflection characteristics of the mirror. For example, a higher-order vibration mode having the X-axis of FIG. 3 as the rotation axis generates vibration having a shorter period than the high-frequency vibration component, which has been a problem in the present embodiment. In another frequency band, there is also a vibration mode with the Y axis as the rotation axis. When this vibration mode is excited, for example, a so-called wavy line that vibrates in the horizontal direction is drawn while it is intended to draw a straight line in the vertical direction.

When a sawtooth waveform is given as the drive signal, as shown in FIGS. 9 and 10, the signal components are generated up to the high frequency band at the drive frequency interval, so that the higher-order vibration mode as described above is unintentionally excited. However, the image drawn by the light deflection element 11 may be distorted.

In order to prevent such excitation in a higher-order vibration mode, it is effective to apply a low-pass filter to the applied signal to cut (suppress) high-frequency components. FIG. 25 is a diagram showing an example of the filter transmittance of the low-pass filter.

FIG. 26 is a diagram showing an example of a drive signal waveform when a low-pass filter is applied. FIG. 26 shows an example of a drive signal waveform when the transmission band is on the lower frequency side than the null frequency and the remaining components are cut. Since most of the vibration components that form the sawtooth shape are present on the lower frequency side than the null frequency, cutting the high frequency components has almost no effect on the applied signal waveform. More realistically, the resonance frequency of the lowest vibration mode and the vibration mode generated next may be known in advance, and the cutoff frequency of the filter may be set between the resonance frequencies of these two vibration modes. ..

By removing the high-frequency signal component from the sawtooth signal in this way, it is possible to prevent the natural vibration mode of the optical deflection element 11 from being excited, and to prevent distortion from occurring in the image drawn by optical scanning. Can be suppressed.

[Image projection device]
Next, the image projection device to which the light deflection device of the present embodiment is applied will be described in detail with reference to FIGS. 27 and 28. FIG. 27 is a schematic view showing an example of an automobile 400 equipped with a head-up display device 500, which is an example of an image projection device. Further, FIG. 28 is a schematic view showing an example of the head-up display device 500.

The image projection device is a device that projects an image by optical scanning, and is, for example, a head-up display device 500. As shown in FIG. 27, the head-up display device 500 is installed near, for example, a windshield (windshield 401, etc.) of an automobile 400. The projected light L emitted from the head-up display device 500 is reflected by the windshield 401 and heads toward the observer (driver 402) who is the user.

As a result, the driver 402 can visually recognize the image or the like projected by the head-up display device 500 as a virtual image. A combiner may be installed on the inner wall surface of the windshield so that the user can visually recognize the virtual image by the projected light reflected by the combiner.

As shown in FIG. 28, in the head-up display device 500, laser light is emitted from the red, green, and blue laser light sources 501R, 501G, and 501B. Each laser light source corresponds to the light source 12 in FIG. The emitted laser light passes through an incident optical system composed of collimator lenses 502, 503, 504 provided for each laser light source, two dichroic mirrors 505, 506, and a light amount adjusting unit 507. It is deflected by the light deflection element 11 having the reflection mirror 10.

Then, the deflected laser beam is projected onto the screen via a projection optical system including a free curved mirror 509, an intermediate screen 510, and a projection mirror 511.

In the head-up display device 500, the laser light sources 501R, 501G, 501B, the collimator lenses 502, 503, 504, and the dichroic mirrors 505 and 506 are unitized by an optical housing as a light source unit 530.

The head-up display device 500 projects the intermediate image displayed on the intermediate screen 510 onto the windshield 401 of the automobile 400, so that the intermediate image is visually recognized by the driver 402 as a virtual image.

The laser light of each color emitted from the laser light sources 501R, 501G, and 501B is regarded as substantially parallel light by the collimator lenses 502, 503, and 504, respectively, and is combined by two dichroic mirrors 505 and 506. The combined laser beam is two-dimensionally scanned by the light deflection element 11 having the reflection mirror 10 after the light amount is adjusted by the light amount adjusting unit 507. The projected light L two-dimensionally scanned by the light deflection element 11 is reflected by the free-form surface mirror 509, corrected for distortion, and then condensed on the intermediate screen 510 to display an intermediate image. The intermediate screen 510 is composed of a microlens array in which microlenses are two-dimensionally arranged, and magnifies the projected light L incident on the intermediate screen 510 in microlens units.

The light deflection element 11 reciprocates the reflection mirror 10 in the biaxial direction, and two-dimensionally scans the projected light L incident on the reflection mirror 10. The drive control of the light deflection element 11 is performed in synchronization with the light emission timing of the laser light sources 501R, 501G, and 501B.

The head-up display device 500 as an example of the image projection device has been described above, but the image projection device is a device that projects an image by performing optical scanning by a light deflection element 11 having a reflection mirror 10. good.

For example, it is mounted on a projector that is placed on a desk or the like and projects an image on a display screen, or is mounted on a mounting member mounted on an observer's head or the like, and is projected onto a reflection / transmission screen of the mounting member, or an eyeball is used as a screen. The same can be applied to a head-mounted display device or the like that projects an image.

Further, the image projection device includes not only vehicles and mounting members, but also moving objects such as aircraft, ships, and mobile robots, and work robots that operate drive targets such as manipulators without moving from the spot. It may be mounted on a non-moving body.

[Optical writing device]
Next, the optical writing device to which the optical deflection device of the present embodiment is applied will be described in detail with reference to FIGS. 29 and 30. FIG. 29 is an example of an image forming apparatus incorporating the optical writing apparatus 600. Further, FIG. 30 is a schematic view showing an example of the optical writing device 600.

As shown in FIG. 29, the optical writing device 600 is used as a constituent member of an image forming device represented by a laser printer 650 or the like having a printer function using a laser beam. In the image forming apparatus, the optical writing device 600 performs optical writing on the photoconductor drum by lightly scanning the photoconductor drum, which is the surface to be scanned 15, with one or a plurality of laser beams.

As shown in FIG. 30, in the optical writing device 600, the laser light from the light source 12 such as a laser element passes through an imaging optical system 601 such as a collimator lens, and then is 1 by an optical deflection element 11 having a reflection mirror 10. It is deflected axially or biaxially.

Then, the laser beam deflected by the light deflection element 11 passes through a scanning optical system 602 including a first lens 602a, a second lens 602b, and a reflection mirror unit 602c, and then passes through a surface to be scanned 15 (for example, a photoconductor drum or a photosensitive member). Irradiate the paper) and write with light. The scanning optical system 602 forms a spot-shaped light beam on the scanned surface 15.

Further, the light source 12 and the light deflection element 11 having the reflection mirror 10 are driven under the control of the control device 19.

As described above, the optical writing device 600 can be used as a component of an image forming device having a printer function by laser light. Further, by making the scanning optical system different so that optical scanning can be performed not only in the uniaxial direction but also in the biaxial direction, the laser beam is deflected to the thermal media to scan the light, and the laser label device for printing by heating and the like. It can be used as a constituent member of the image forming apparatus of.

Since the optical deflection element 11 having the reflection mirror 10 applied to the optical writing device consumes less power for driving than the rotating multi-sided mirror using a polygon mirror or the like, the power saving of the optical writing device can be achieved. It is advantageous. Further, since the wind noise at the time of vibration of the light deflection element 11 is smaller than that of the rotating polymorphic mirror, it is advantageous for improving the quietness of the optical writing device 600. The optical writing device 600 requires an overwhelmingly small installation space as compared with a rotating polymorphic mirror, and the amount of heat generated by the optical deflection element 11 is also small, so that it is easy to miniaturize the image forming apparatus. It is advantageous.

[Object recognition device]
Next, the object recognition device to which the light deflection device of the present embodiment is applied will be described in detail with reference to FIGS. 31 and 32. FIG. 31 is a schematic view of an automobile equipped with a laser radar device, which is an example of an object recognition device. Further, FIG. 32 is a schematic view showing an example of a laser radar device. The object recognition device is a device that recognizes an object in the target direction, and is, for example, a laser radar device.

As shown in FIG. 31, the laser radar device 700 is mounted on, for example, an automobile 701, and by lightly scanning the target direction and receiving the reflected light from the target object 702 existing in the target direction, the target object is received. Recognize 702.

As shown in FIG. 32, the laser light emitted from the light source 12 passes through an incident optical system composed of a collimating lens 703, which is an optical system in which divergent light is substantially parallel light, and a plane mirror 704, and a reflection mirror. The optical deflection element 11 having 10 scans in the uniaxial or biaxial direction.

Then, the laser beam is applied to the object 702 in front of the apparatus via the projection lens 705 or the like which is a projection optical system. The drive of the light source 12 and the light deflection element 11 is controlled by the control device 19. The reflected light reflected by the object 702 is photodetected by the photodetector 709. That is, the reflected light is received by the image pickup element 707 via the light receiving optical system such as the condenser lens 706, and the image pickup element 707 outputs the detection signal to the signal processing circuit 708. The signal processing circuit 708 performs predetermined processing such as binarization and noise processing on the input detection signal, and outputs the result to the distance measuring circuit 710.

In the distance measuring circuit 710, the object 702 is determined by the time difference between the timing at which the light source 12 emits the laser beam and the timing at which the laser beam is received by the photodetector 709, or the phase difference for each pixel of the image sensor 707 that receives the light. The presence or absence of the light source is recognized, and the distance information to the object 702 is calculated.

Since the light deflection element 11 having the reflection mirror 10 is less likely to be damaged and is smaller than the polymorphic mirror, it is possible to provide a compact radar device with high durability.

Such a laser radar device 700 is attached to, for example, a vehicle, an aircraft, a ship, a robot, or the like, and can lightly scan a predetermined range to recognize the presence or absence of an obstacle and the distance to the obstacle.

Although the laser radar device 700 has been described as an example of the object recognition device, the object recognition device performs light scanning by controlling the light deflection element 11 having the reflection mirror 10 by the control device 19, and the reflected light by the light detector. The device may be any device that recognizes the object 702 by receiving light, and is not limited to the above-mentioned example.

For example, a biometric authentication device that recognizes an object by calculating object information such as shape from distance information obtained by light scanning the hand or face and referring to it as a record, and recognizing an intruder by optical scanning into the target range. The same can be applied to the components of a security sensor, a three-dimensional scanner that calculates and recognizes object information such as a shape from distance information obtained by optical scanning, and outputs it as three-dimensional data.

10 Reflection mirror 11 Light deflection element 12 Light source 13 Light source drive system 14 Optical system 15 Scanned surface 16 Drive control unit 17 Detection signal calculation unit 18 Image signal calculation unit 19 Control device 20 Light detection unit 110 Storage unit

Japanese Patent No. 4830470

Claims (8)

A moving part with a reflective surface and
A support portion that includes a meandering portion that is continuous so that a plurality of beams meander, and a support portion that swingably supports the movable portion around one axis.
A plurality of piezoelectric members individually provided on the plurality of beams, and
A control unit that inputs a first drive signal to one of the two piezoelectric members individually provided on the two adjacent beams and a second drive signal to the other.
A photodetector that detects the light reflected by the reflecting surface and outputs a detection signal,
Equipped with
The first drive signal and the second drive signal are signals having a periodic waveform.
The ratio of the rise time to the fall time in one cycle of the first drive signal is larger than that of the second drive signal.
The control unit does not adjust the offset voltage of the second drive signal so that the center of the optical scan due to the reflective surface detected based on the detection signal is not displaced, and the control unit does not adjust the offset voltage of the first drive signal. Adjust the offset voltage,
Light deflector. As for the resonance frequency of the structure including the movable portion and the support portion, the frequency at which the signal intensity of the high frequency component of the first drive signal is minimized and the signal intensity of the high frequency component of the second drive signal are minimized. The frequency between the frequency and
The light deflector according to claim 1. The frequency of the first drive signal and the second drive signal is one half-integer of the resonance frequency of the structure including the movable portion and the support portion.
The light deflector according to claim 1. The first drive signal and the second drive signal have a phase difference within a predetermined range from the reference phase difference.
The light deflector according to claim 1. The first drive signal and the second drive signal differ from each other in at least one of a maximum value and a minimum value.
The light deflector according to claim 1. A notch filter that suppresses a high frequency component in a predetermined band including a resonance frequency of a structure including the reflection surface and the support portion among the frequency components of the first drive signal and the second drive signal is further provided. ,
The light deflector according to claim 1. A low-pass filter that suppresses a high frequency component in a band higher than the resonance frequency of the structure including the reflection surface and the support portion among the frequency components of the first drive signal and the second drive signal is further provided.
The light deflector according to claim 1. The light deflector according to any one of claims 1 to 7 , and the light deflector.
A light source that irradiates the light deflector with light,
An image projection device.

Images