JP6513962B2 - Optical scanner - Google Patents

Description

  BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an optical scanning device that scans a laser beam in a target area.

  2. Description of the Related Art Conventionally, there has been known an optical scanning device that performs Lissajous scanning of pulsed laser light (hereinafter simply referred to as "pulsed light") within a target area. As this type of optical scanning device, for example, a light source unit that emits pulse light at a preset emission timing, a light scanning unit configured with a two-dimensional galvano mirror, and a driving unit that drives the light scanning unit What is provided is disclosed (see, for example, Patent Document 1).

  Specifically, in the light scanning portion, movable portions having light reflecting surfaces are formed so as to be pivotable about first and second axes orthogonal to each other, and the movable portions are pivoted about the first axis and the second axis. The light incident on the light reflecting surface by movement is Lissajous scanned in the target area. The drive unit outputs a first drive signal for swinging the movable unit around the first axis and a second drive signal for swinging the movable unit around the second axis to the light scanning unit to make the movable unit the first axis. , Swing driving around the second axis. At this time, it is efficient to rock and drive around the first axis and the second axis at the resonance frequency of the movable portion.

  In the optical scanning device of the conventional example, when the resonant frequency fluctuates due to a temperature change of the movable portion, for example, when the frequency of each drive signal and the resonant frequency of the movable portion deviate, the frequency of one drive signal is shifted The frequency of the other drive signal is changed while maintaining the frequency ratio of the first drive signal and the second drive signal.

JP 2012-68349 A

  However, since the fluctuation of the resonance frequency does not necessarily maintain the above-mentioned frequency ratio around the first and second axes, according to the optical scanning device of the conventional example, one is oscillated at the resonance frequency. Can be driven, but the other case can not be driven by oscillating at the resonant frequency. Therefore, there is room for improvement from the viewpoint of efficient driving.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical scanning device capable of performing efficient driving even if the resonance frequency changes.

In the light scanning device according to one aspect of the present invention, the movable portion having the light reflecting surface is swung about first and second axes orthogonal to each other by the first and second driving frequencies, and the pulse light by the light source is subjected to Lissaur scanning An optical scanning device, wherein the first and second drive frequencies are changed according to the shift amount of the first resonance frequency around the first axis and the shift amount of the second resonance frequency around the second axis, The emission timing of the pulsed light is changed based on the timing table according to the combination of the shift directions of the resonance frequency .

The optical scanning device according to one aspect of the present invention is characterized in that the first and second drive frequencies are set according to the shift amount of the first resonance frequency around the first axis and the shift amount of the second resonance frequency around the second axis. It changes and the emission timing of the said pulsed light is changed based on the timing table according to the combination of the shift direction of both resonance frequency . Thus, the optical scanning device can be driven efficiently even if the resonance frequency changes.

FIG. 1 is a block diagram showing a schematic configuration example of an embodiment of a light ranging device including a light scanning device. It is a figure which shows the structural example of a two-dimensional galvanometer mirror. It is a figure which shows an example of the bridge circuit comprised with the piezo-resistance element for detecting the rocking angle of the movable part of a light scanning part. It is a figure which shows an example of the frequency characteristic of a two-dimensional galvanometer mirror. It is a figure which shows an example of the frequency characteristic of a two-dimensional galvanometer mirror. It is a figure explaining the timing table memorize | stored in the memory area. It is a figure explaining the field of the timing table defined based on phase difference information. It is a figure explaining the correspondence of the 1st gap quantity and the 2nd gap quantity, and the field of a timing table. It is a flow chart which shows an example of change processing of the 1st drive frequency and the 2nd drive frequency. It is a flowchart which shows an example of the subroutine in the measurement of resonant frequency.

Hereinafter, embodiments of the present invention will be described based on the drawings.
FIG. 1 is a block diagram showing an example of a schematic configuration of an embodiment of a light ranging device including a light scanning device. In the following description, for example, the light scanning apparatus 1 shown in FIG. 1 is a light measurement that measures the distance to an object (including a person) present in the target area by performing Lissajous scanning of pulsed light in the target area. The case where the distance measuring apparatus 100 is used as a light scanning unit will be described.

  As shown in FIG. 1, the optical distance measuring apparatus 100 according to the present embodiment includes an optical scanning device 1, a light receiving unit 6, a distance measuring unit 7, an image generation unit 8, and a display unit 9. The light scanning device 1 includes an electromagnetically driven light scanning unit 2, a driving unit 3 for driving the light scanning unit 2, a memory 4 for storing a timing table, and a light source unit 5 for emitting pulsed light. The drive unit 3 is an example of a control unit. The light receiving unit 6 reflects the pulse light emitted from the light source unit 5 on the object in the target area, and receives the reflected pulse light. The distance measuring unit 7 measures, for example, the distance from the light receiving unit 6 to the object by analyzing the reflected pulse light. The image generation unit 8 generates a distance image based on the measurement result of the distance measurement unit 7. The display unit 9 outputs (displays) the distance image generated by the image generation unit 8.

  The light scanning unit 2 includes a movable portion having a light reflection surface, and the movable portion swings around first and second axes orthogonal to each other according to the frequency of a first drive signal and the frequency of a second drive signal described later. Be done. That is, the light scanning unit 2 reflects pulse light incident on the light reflecting surface by swinging the movable portion about the first and second axes, and performs two-dimensional scanning such as Lissajous scanning in the target area It is possible. In the present embodiment, for example, the two-dimensional galvano mirror described in Japanese Patent No. 2722314 proposed by the present applicant can be applied to the light scanning unit 2.

  FIG. 2 is a view showing a configuration example of a two-dimensional galvano mirror. The two-dimensional galvano mirror 20 illustrated in FIG. 2 illustrates an example of the light scanning unit 2. The two-dimensional galvano mirror 20 includes a frame-shaped fixed portion 21, an outer movable portion 23a, and an inner movable portion 23b. The outer movable portion 23a is disposed inside the fixed portion 21 and is swingably supported by the pair of second torsion bars 22c and 22d. The inner movable portion 23b is disposed inside the outer movable portion 23a, and is swingably supported by a pair of first torsion bars 22a and 22b orthogonal to the axial direction of the second torsion bars 22c and 22d. In the present embodiment, the central axes of the first torsion bars 22a and 22b are x-axis (first axis), and the central axes of the second torsion bars 22c and 22d are y-axis (second axis).

A light reflecting surface 24 is formed at the center of the inner movable portion 23b. In addition, a first drive coil 25a is formed at the peripheral edge of the outer movable portion 23a, and a second drive coil 25b is formed at the peripheral edge of the inner movable portion 23b. The end of the first drive coil 25a is connected to the first electrode terminal 26a formed in the fixed portion 21, and the end of the second drive coil 25b is connected to the second electrode terminal 26b formed in the fixed portion 21. It is done.
Further, the pair of first permanent magnets 27 a and 27 b and the pair of second permanent magnets 27 c and 27 d are disposed to face each other with the fixing portion 21 interposed therebetween.

  In the two-dimensional galvano mirror 20, each movable portion 23a, 23b is driven by the current (for example, alternating current) flowing through each drive coil 25a, 25b and the magnetic field of the first permanent magnets 27a, 27b and the second permanent magnets 27c, 27d. Lorentz force acts. As a result, as the two-dimensional galvano mirror 20 swings in accordance with the Lorentz force, the pulse light incident on the light reflecting surface 24 is reflected by the light reflecting surface 24. Therefore, the optical scanning device 1 can scan the Lissajous within the target area using the pulse light reflected by the two-dimensional galvano mirror 20. The fixed portion 21, the first torsion bars 22a and 22b, the second torsion bars 22c and 22d, the outer movable portion 23a, and the inner movable portion 23b are integrally formed of, for example, a semiconductor substrate.

  FIG. 3 is a view showing an example of a bridge circuit formed of piezoresistive elements for detecting the swing angle of the movable portion of the light scanning unit. In the first torsion bars 22a and 22b shown in FIG. 2, a rocking operation about the x axis of the inner movable portion 23b, that is, a strain (stress) generated by a twist of the first torsion bars 22a and 22b is detected. The first to fourth piezoresistive elements R1 to R4 are provided.

  In addition, in the second torsion bars 22c and 22d shown in FIG. 2, in order to detect the swing (rotational movement) of the outer movable portion 23a about the y axis, that is, the distortion (stress) caused by the twisting of the second torsion bars 22c and 22d. The fifth to eighth piezoresistive elements R5 to R8 are provided.

  The first to fourth piezoresistive elements R1 to R4 and the fifth to eighth piezoresistive elements R5 to R8 are connected by wires not shown, respectively, to form a bridge circuit P (input voltage Vi as shown in FIG. 3). , Output voltage Vo).

  Here, the first to fourth piezoresistive elements R1 to R4 are formed of, for example, P-type diffusion resistors, and the resistance value increases when subjected to tensile stress, and the resistance value decreases when subjected to compressive stress. is there. Therefore, by monitoring the output voltage Vo of the bridge circuit (hereinafter, simply referred to as "first bridge circuit") formed of the first to fourth piezoresistive elements R1 to R4, the drive unit 3 is movable inward. It is possible to continuously detect a voltage according to the swing angle (deflection angle) of the portion 23b about the x axis.

  Similarly, the drive unit 3 monitors the output voltage Vo of a bridge circuit (hereinafter, simply referred to as a "second bridge circuit") configured of the fifth to eighth piezoresistive elements R5 to R8. It is possible to continuously detect the voltage according to the swing angle (deflection angle) around the y-axis of the outer movable portion 23a and the inner movable portion 23b.

  In the two-dimensional galvano mirror 20 shown in FIG. 2, a drive current (oscillation current) is supplied to the first drive coil 25 a and the second drive coil 25 b. Then, according to the Lorentz force, the inner movable portion 23b swings around the x axis by the first torsion bars 22a and 22b, and the outer movable portion 23a and the inner movable portion 23b are y by the second torsion bars 22c and 22d. Swing around the axis. That is, the inner movable portion 23b can swing around the x axis and the y axis.

  Therefore, when the inner movable portion 23 b swings around the x axis and the y axis, the Lissajous scan is performed in the target area by the pulse light reflected by the light reflecting surface 24. Here, the two-dimensional galvano mirror 20 has two natural vibration modes (resonance frequency) around the x axis and around the y axis. The resonance frequency is, for example, a frequency at which the current value required to swing the two-dimensional galvano mirror 20 is the smallest in each swing direction. Thus, the optical scanning device 1 can suppress, for example, power consumption and the like. The resonance frequency tends to shift (shift) when the temperature around the light scanning unit changes or the temperature of the light scanning unit itself changes. Also, the resonance frequency tends to fluctuate even with the change over time of the light scanning unit.

The drive current of the corresponding resonance frequency or the drive current of the frequency near that is supplied as a drive signal from the drive unit 3 to the first drive coil 25a and the second drive coil 25b.
In the following description, the resonant frequency around the x axis of the two-dimensional galvano mirror 20 is referred to as the “first resonant frequency”, and the resonant frequency around the y axis, that is, the movable frequency including the outer movable portion 23a and the inner movable portion 23b. The resonant frequency around the y-axis of the entire unit is referred to as "second resonant frequency".

  Also, for example, when the outer movable portion 23a and the inner movable portion 23b of the two-dimensional galvano mirror 20 incline to one around the y axis, the fifth piezoresistive element R5 and the eighth piezoresistive element R8 shown in FIG. When stress is applied, the sixth piezoresistor R6 and the seventh piezoresistor R7 receive compressive stress. Further, when the fifth piezoresistor R5 and the eighth piezoresistor R8 receive a compressive stress due to the outer movable portion 23a and the inner movable portion 23b being inclined to the other of the y-axis, the sixth piezoresistor The element R6 and the seventh piezoresistive element R7 receive tensile stress.

  Returning to FIG. 1, the drive unit 3 outputs a first drive signal (drive current) for swinging the inner movable portion 23 b around the x axis to the light scanning unit 2 to rotate the inner movable portion 23 b around the x axis. Swing drive. In addition, the drive unit 3 outputs a second drive signal (drive current) for swinging the outer movable unit 23a and the inner movable unit 23b shown in FIG. 2 around the y axis to the light scanning unit 2, thereby moving each movable unit 23a. , 23b are driven to swing around the y axis.

  More specifically, the drive unit 3 gives, for example, two drive signals having a frequency near a resonant frequency around two orthogonal axes (x-axis and y-axis) of the two-dimensional galvano mirror 20 while giving a predetermined phase difference. The two-dimensional galvanometer mirror 20 is supplied. That is, the drive unit 3 can rock and drive the two-dimensional galvano mirror 20 about the x axis and the y axis.

  Here, the frequency of the first drive signal (hereinafter sometimes simply referred to as “first drive frequency”) is a value corresponding to the first resonance frequency of the light scanning unit 2 (for example, manufacturing of the light ranging device 100 It is preset as a first initial set value set at the time. Similarly, the frequency of the second drive signal (hereinafter sometimes simply referred to as “second drive frequency”) is a value corresponding to the second resonance frequency of the light scanning unit 2 (for example, the light ranging device It is preset as the 2nd initial setting value set at the time of manufacture of 100). However, for example, the actual first resonance frequency and the second resonance frequency of the light scanning unit 2 may be changed to the first and second initial setting values, for example, due to manufacturing variations, temporal changes, or changes in the use environment (in particular, temperature). May actually be different (frequency characteristics shift).

  Therefore, the drive unit 3 of the optical scanning device 1 in the present embodiment matches the first drive frequency with the first resonance frequency around the x axis (first axis), and the second drive frequency as the y axis (second axis) The emission timing of the pulsed light by the light source 51 is set based on the first and second drive frequencies that are made to coincide with the surrounding second resonance frequency and are made to coincide. That is, if the first resonance frequency fluctuates, the drive unit 3 changes the first drive frequency to match the first resonance frequency after the fluctuation. In other words, the drive unit 3 causes the first drive frequency to follow the changed first resonance frequency. Here, the fluctuation indicates, for example, a state in which the first initial setting value or the second initial setting value is shifted by a predetermined value.

  In addition, when the second resonance frequency fluctuates, the drive unit 3 changes the second drive frequency to match the second resonance frequency after the fluctuation. In other words, the drive unit 3 makes the second drive frequency follow the second resonance frequency after the change.

  Therefore, when at least one of the first resonance frequency and the second resonance frequency fluctuates, the driving unit 3 sets the first driving frequency or the first resonance frequency or the second resonance frequency after fluctuation so as to match the first resonance frequency or the second resonance frequency. Change the second drive frequency.

  Here, in the present embodiment, as an example, the first drive frequency has a frequency value higher than the second drive frequency, and the inner movable portion 23b of the two-dimensional galvano mirror 20 has high speed around the x axis. It is rocked and driven at a low speed around the y-axis.

  The drive unit 3 also includes a first drive circuit 31, a second drive circuit 32, a first shift amount detection unit 33, a second shift amount detection unit 34, and a frequency change unit 35. The first drive circuit 31 generates a first drive signal and outputs the signal to the light scanning unit 2. The second drive circuit 32 generates a second drive signal and outputs the signal to the light scanning unit 2. The first shift amount detection unit 33 detects a first shift amount that is a shift amount between the frequency of the output first drive signal and the first resonance frequency of the light scanning unit 2. The second shift amount detection unit 34 detects a second shift amount that is a shift amount between the frequency of the output second drive signal and the second resonance frequency of the light scanning unit 2. The frequency changing unit 35 changes the first drive frequency based on the detection result of the first shift amount detection unit 33 and changes the second drive frequency based on the detection result of the second shift amount detection unit 34.

Hereinafter, the details of the first drive circuit 31, the second drive circuit 32, the first deviation amount detection unit 33, the second deviation amount detection unit 34, and the frequency change unit 35 will be continued.
The first drive circuit 31 and the second drive circuit 32 respectively generate the first drive signal and the second drive signal based on the newly changed frequency in the frequency changing unit 35 and output the same to the light scanning unit 2. The first drive circuit 31 and the second drive circuit 32 include, for example, frequency synthesizers of DDS (Direct Digital Synthesizer) type or PLL (Phase Locked Loop) type, and can freely generate a frequency from a reference clock signal. it can. That is, each of the first drive circuit 31 and the second drive circuit 32 can set the frequency of the drive signal with high resolution, and can change the frequency as needed.

  The first shift amount detection unit 33 detects a first shift amount based on the phase difference between the first drive signal output from the first drive circuit 31 and the output signal of the first bridge circuit. The second shift amount detection unit 34 detects a second shift amount based on the phase difference between the second drive signal output from the second drive circuit 32 and the output signal of the second bridge circuit. Here, a method of detecting the first shift amount by the first shift amount detection unit 33 and the second shift amount by the second shift amount detection unit 34 will be briefly described with reference to FIGS. 4 and 5.

  FIG.4 and FIG.5 is a figure which shows an example of the frequency characteristic of a two-dimensional galvano mirror. FIG. 4 shows the swing angle (vertical axis) of the two-dimensional galvano mirror 20 with respect to the drive frequency (horizontal axis), and FIG. 5 shows the drive frequency-phase difference characteristic, and the drive signal with respect to the drive frequency (horizontal axis) And the phase difference (vertical axis) between the signal (gain [dB]) (hereinafter simply referred to as "rocking angle signal") indicating the rocking angle of the two-dimensional galvano mirror 20. That is, the output signal of the first bridge circuit corresponds to the swing angle signal of the inner movable portion 23b about the x axis, and the output signal of the second bridge circuit is the swing angle signal of the inner movable portion 23b about the y axis It corresponds to

In FIG. 4 and FIG. 5, in order to make the explanation easy to understand, the horizontal axis is a scale (shift amount of the resonance frequency) shifted by predetermined hertz (for example, 2 [Hz]) in + and-directions with reference to the resonance frequency. Represents
In FIG. 4, among the drive frequencies, the resonance frequency is a peak value of the graph. FIG. 4 shows a case where the drive frequency is a first drive frequency and the resonance frequency is a first resonance frequency, and the first resonance frequency is 1400 [Hz] as an example of a first initial setting value. The second resonance frequency is also set to 420 [Hz] as an example of the second initial setting value (not shown) from the frequency characteristics of the two-dimensional galvano mirror. Here, the first resonant frequency is not limited to 1400 Hz, and may be 1300 Hz, for example. Also, the second resonance frequency is not limited to 420 Hz.

  In FIG. 5, when the two-dimensional galvano mirror 20 is driven by a drive signal having the same frequency as the resonance frequency (in this example, the first resonance frequency: 1400 Hz), the drive signal (in this example) The phase of the swing angle (signal) of the light reflecting surface 24 is delayed by 90 degrees with respect to the phase of the first drive signal). As a result, a phase difference of 90 degrees occurs between the drive signal and the swing angle signal. That is, when the phase difference between the drive signal and the swing angle signal of the light reflecting surface 24 is other than 90 degrees, the drive frequency and the resonant frequency of the two-dimensional galvano mirror 20 do not match. In other words, in FIGS. 4 and 5, for example, it can be considered that the frequency characteristic (resonance frequency) of the two-dimensional galvano mirror 20 is shifted due to temperature change.

  In the present embodiment, it is possible to obtain in advance the frequency characteristics of the two-dimensional galvano mirror 20. Therefore, in the present embodiment, by detecting the phase difference between the drive signal and the swing angle signal, the amount of shift between the drive frequency and the actual resonant frequency of the two-dimensional galvano mirror 20 can be grasped. The second resonance frequency (420 [Hz]) is also different from the value of the first resonance frequency, but the same tendency as in FIG. 4 and FIG.

  By using the first deviation amount and the second deviation amount detection method described above, the first deviation amount detection unit 33 performs the first deviation amount detection process based on the frequency characteristics of the inner movable portion 23b shown in FIG. The deviation amount (first deviation amount) between the drive frequency and the first resonance frequency is detected. In addition, the second deviation amount detection unit 34 calculates the deviation amount (second deviation amount) between the second drive frequency and the second resonance frequency based on the frequency characteristic around the y axis of the inner movable portion 23b shown in FIG. To detect.

  Specifically, the first shift amount detection unit 33 sets the first drive signal and the first drive signal on the basis of the drive frequency-phase difference characteristic for the x axis rotation shown in FIG. 5 about the x axis of the inner movable portion 23b. The first shift amount (shift amount of the first resonance frequency) is detected from the phase difference with the output signal of the bridge circuit. Further, the second shift amount detection unit 34 is configured to generate the second drive signal and the second bridge circuit based on the drive frequency-phase difference characteristic (not shown) for the y-axis rotation about the y axis of the inner movable portion 23b. The second shift amount (shift amount of the second resonance frequency) is detected from the phase difference with the output signal.

  The frequency changing unit 35 determines whether it is necessary to change the first drive frequency and the second drive frequency according to the detection results of the first shift amount detection unit 33 and the second shift amount detection unit 34, and it is necessary If it is determined that there is, the first drive frequency and the second drive frequency are changed. Alternatively, when it is determined that the frequency changer 35 needs to change at least one of the first drive frequency and the second drive frequency, the first drive frequency or the second drive frequency that requires the change is determined. Change

  In the present embodiment, for example, if the shift amount of the first resonance frequency and the second resonance frequency is within a predetermined hertz (for example, 2 [Hz]) from within the reference region, the frequency changing unit 35 determines that the reference region is within. Do not perform frequency change. Further, when the shift amount of at least one of the first resonance frequency and the second resonance frequency exceeds a predetermined hertz from the reference region, the frequency changing unit 35 sets a flag for changing the driving frequency to ON. . In the present embodiment, an area in which this flag is set to ON is called a flag set area.

  In FIG. 5, for example, when the first resonance frequency (first initial setting value) shifts to the negative side by exceeding a predetermined hertz, the phase difference exceeds the first threshold, so the frequency changer 35 changes the drive frequency. Run. Also, for example, when the first resonance frequency is shifted to the positive side by more than the predetermined hertz, the phase difference falls below the second threshold, so the frequency changer 35 changes the drive frequency. The first threshold and the second threshold indicate phase differences when shifting from the reference area to the flag set area. Details will be described in the process of the flowchart.

  Returning to FIG. 1, the memory 4 associates, for example, the measurement position in the target area, the emission time (the number of clocks) indicating the timing of emitting the pulse light, the value of the first drive frequency, the value of the second drive frequency, etc. A plurality of timing tables are stored. The measurement position is, for example, each area divided into grid-like blocks.

  FIG. 6 is a diagram for explaining the timing table stored in the memory area. In the present embodiment, for example, the timing table of the reference area and the first to eighth timing tables, which will be described later when manufacturing the optical distance measuring apparatus 100, are stored in the memory area 41 designated by a predetermined address number. Keep it. That is, in this embodiment, the timing table to be newly used can be arranged at another address with respect to the timing table currently in use. That is, in the present embodiment, by providing a plurality of timing tables in advance, it is possible to select the timing table and to cope with the temporal change and the temperature change.

  FIG. 7 is a diagram for explaining the area of the timing table determined based on the phase difference information. The horizontal axis indicates the value [Hz] of the first drive frequency, and the vertical axis indicates the value [Hz] of the second drive frequency. The center of the reference region corresponds to the first resonance frequency (first initial setting value) and the second resonance frequency (second initial setting value). In the present embodiment, even if the first resonance frequency or the second resonance frequency fluctuates due to a temperature change or the like, for example, within the reference area, the deviation of the scanning width at the measurement position in the target area at the time of Lissajous scanning is It means that the value falls within the allowable range without changing the first drive frequency or the second drive frequency. The data of the timing table of the reference area shown in FIG. 7 is stored in the timing table of the reference area in the memory area 41 shown in FIG.

  The first to eighth regions shown in FIG. 7 are regions determined according to the deviation of the phase difference between the first resonance frequency and the second resonance frequency. The frequency changing unit 35 determines any one of the reference area and the first to eighth areas according to the detection results of the first shift amount detection unit 33 and the second shift amount detection unit 34, and Make a selection.

  FIG. 8 is a diagram for explaining the correspondence between the first deviation amount and the second deviation amount and the area of the timing table. In FIG. 8, the shift (first shift amount and second shift amount) of the phase difference between the first resonance frequency (RF1) and the second resonance frequency (RF2) with reference to the reference region, and the first to first shown in FIG. An example of the correspondence of the 8th field is shown.

  For example, in the first region shown in FIG. 7, the first resonance frequency is shifted (varied) from the reference region to the minus (−) side by more than a predetermined hertz, and the second resonance frequency is from the reference region to the plus (+) side It represents that it has shifted above a predetermined hertz. The second region indicates that the first resonant frequency does not deviate from the reference region, and the second resonant frequency shifts from the reference region to the plus (+) side by more than a predetermined hertz. In the third region, the first resonance frequency is shifted from the reference region to the plus (+) side by more than a predetermined hertz, and the second resonance frequency is shifted from the reference region to the plus (+) side by more than the predetermined hertz It represents. Hereinafter, in the same manner, at least one of the first resonance frequency and the second resonance frequency in the fourth to eighth regions is also shifted beyond the predetermined hertz. The details of the process using FIGS. 7 and 8 will be described later using flowcharts (see FIGS. 9 and 10).

  Referring back to FIG. 1 again, the light source unit 5 emits pulse light toward the light reflecting surface 24 formed on the inner movable portion 23 b of the light scanning unit 2, and drives the light source 51 and the light source 51. It includes a light source control unit 52 to control and a light projecting optical system 53.

The light source 51 is, for example, a laser diode, emits light according to a drive (emission) signal from the light source control unit 52, and emits pulsed light.
The light source control unit 52 controls the emission timing of pulse light by the light source 51. The light source control unit 52 reads the timing table from the memory 4 and, for example, at a preset timing based on a predetermined swing angle (for example, a gain corresponding to 0 degree) of the inner movable portion 23b (light reflection surface 24). The light source 51 is made to emit light.
The light projecting optical system 53 converts the pulsed light emitted by the light source 51 into a preferable state (for example, parallel light), and includes, for example, a collimator lens.

  The pulse light emitted from the light source unit 5 is reflected by the light reflecting surface 24 of the light scanning unit 2. As a result, the light scanning unit 2 of the light scanning device 1 uses the reflected pulse light to scan the inside of the target area for Lissajous scanning. At this time, by causing the light source 51 to emit light based on the above-mentioned timing table, pulse light is emitted so as to draw a preset trajectory (Lissajous pattern) in the target area.

  The light receiving unit 6 receives and detects the reflected light of the pulse light emitted from the light source unit 5 and can use, for example, a photo sensor. As described above, the pulsed light from the light source unit 5 is emitted by the light scanning unit 2 to draw a Lissajous pattern to the inside of the target area. If an object is present at these positions, the pulsed light emitted from the light source unit 5 is reflected according to the existing object. The light receiving unit 6 receives pulse light reflected by an object present in the target area. The light receiving unit 6 may directly receive the reflected pulse light, or may receive light via the light reflecting surface 24 of the light scanning unit 2.

  The distance measuring unit 7 receives the emission timing of the pulse light by the light source unit 5 and the light reception timing of the pulse light reflected by the light receiving unit 6, and reflects the pulse light based on the time difference between them (light flight time) Measure the distance to an object or person. The measurement of the distance by the distance measuring unit 7 is performed at each measurement position in the target area for each emission of pulse light from the light source unit 5, and the measurement result is output to the image generation unit 8.

  The image generation unit 8 determines the pixel value of each measurement position based on the distance measured by the distance measurement unit 7, and generates a distance image for the target area, for example, for each period of Lissajous scanning by the light scanning unit 2. . The generated distance image can be an image that differs in color for each measured distance, that is, for an existing object in the target area, a three-dimensional image in which the distance and depth are reflected. The distance image generated by the image generation unit 8 is output to the display unit 9.

  The display unit 9 includes a display such as a liquid crystal screen, for example, and displays the distance image output from the image generation unit 8. The user can recognize from the distance image displayed on the display unit 9 whether or not an object is present in the target area. When an object is present, the user can also recognize the position of the object in the target area, the distance to the object, the shape of the object, and the like. In addition, since the distance image is updated for each Lissajous scanning cycle, the user can recognize the change in the posture of the object.

Next, the operation related to the process of changing the drive frequency in the light scanning device 1 of the present embodiment will be described.
FIG. 9 is a flowchart showing an example of the process of changing the first drive frequency and the second drive frequency. Note that, prior to the processing of this flowchart, the first drive circuit 31 and the second drive circuit 32 generate the first drive signal and the second drive signal based on the frequency determined by the frequency changer 35, respectively. Output to scanning unit 2. Here, the frequency of the output first drive signal and the frequency of the second drive signal are the frequencies updated in the previous change process. In the case where the frequency of the first drive signal is not updated at all, the frequency of the first drive signal is the first resonance frequency (the first initial setting value), and the frequency of the second drive signal is the second resonance frequency (the second initialization Value).

  In the present embodiment, it is assumed that the change of the drive frequency, the change of the laser emission timing, and the change of the control parameter are performed for each Lissajous scanning cycle as necessary. Therefore, in the process of the following flowchart, by repeating the processes of steps S1 to S5, for example, information relating to the latest change is overwritten and stored in a predetermined area of the memory 4. Then, at the next Lissajous scan, the drive unit 3 reads the information relating to the latest change from the memory 4, and if at least one of the first and second resonance frequencies is out of the reference area, the change of the drive frequency, laser After changing the timing of injection, changing the control parameters, etc., a Lissajous scan is performed. The details will be described below.

  In step S1, the drive unit 3 executes a subroutine of measurement of the resonance frequency. Details of this subroutine will be described later with reference to FIG. When this subroutine is executed, information on whether to change the drive frequency can be obtained.

  In step S2, the drive unit 3 determines whether the drive frequency needs to be changed. Specifically, the frequency changing unit 35 determines whether the flag is set to on based on the process of step S1. The flag being set on means that any one of the first flag to the eighth flag described later is set on. If the flag is set to ON, it is determined that the drive frequency needs to be changed, and the process proceeds to step S3. If the flag is set to OFF, the drive frequency needs to be changed. It is determined that there is no, and the process returns to the process of step S1, and the subroutine of measuring the resonance frequency is repeated again.

In step S3, the drive unit 3 changes the drive frequency. Specifically, the drive unit 3 reads out the information relating to the latest change from the memory 4 based on the subroutine of measurement of the resonance frequency, and at least one of the first and second resonance frequencies is out of the reference region. The values of the drive frequency to be changed are set based on the setting states of the first to eighth flags.
In step S4, the drive unit 3 changes the timing of laser emission. Specifically, the frequency changing unit 35 reads the selected timing table from the memory 4 and sets the timing of laser emission.
In step S5, the drive unit 3 changes the control parameter. Specifically, the frequency changing unit 35 changes control parameters such as the number of clocks based on the selected timing table.

  Here, when the first resonance frequency deviates (shifts) and thereby deviates from the reference region, the frequency changing unit 35 changes the first drive frequency according to the first amount of deviation. Further, when the second resonance frequency deviates (shifts) and thereby deviates from the reference region, the frequency changing unit 35 changes the second drive frequency in accordance with the second deviation amount. The first drive circuit 31 and the second drive circuit 32, for example, as described above, include frequency synthesizers of the DDS system or the PLL system, so that setting of frequencies with high resolution is possible. That is, the first and second drive signals of the changed frequency can be reliably output, and the light scanning unit 2 can be driven efficiently and stably.

Next, a subroutine for measuring the resonance frequency will be described.
FIG. 10 is a flowchart showing an example of a subroutine in measurement of the resonance frequency.
In step S10, the drive unit 3 measures the phase difference. Specifically, the first shift amount detection unit 33 detects a shift amount (first shift amount) between the first drive frequency and the first resonance frequency (resonance frequency around the x axis). The second shift amount detection unit 34 detects a shift amount (second shift amount) between the second drive frequency and the second resonance frequency (resonance frequency around the y axis).

  In step S11, the drive unit 3 determines whether at least one of the first resonant frequency and the second resonant frequency has deviated from the reference region. If it deviates from the reference area, the process proceeds to step S12, and if it is within the reference area, the subroutine of measuring the resonance frequency is ended, and the process returns to the process of step S2 shown in FIG.

  In step S12, the drive unit 3 performs a process of setting a flag to set on / off of the flag. Specifically, the drive unit 3 determines any one of the first to eighth regions determined by the combination of the first resonance frequency and the second resonance frequency, based on the measurement process of the phase difference in step S10. Here, in the present embodiment, the first to eighth areas shown in FIG. 7 are associated with flags (first to eighth flags). That is, the drive unit 3 sets the first flag on in the case of the first region, sets the second flag on in the case of the second region in the measurement process of the phase difference in step S10, and so on. In the case of the eighth region, the eighth flag is set to on. In addition, for example, when the fluctuation of the first resonant frequency and the second resonant frequency shifts from the first region to the second region, the drive unit 3 sets the first flag to OFF and turns the second flag to ON. Set

  That is, when the flag is set to on, it means that one of the first to eighth flags is set to on, while the flag (first to eighth flags) is set to off If present, it means that the first resonant frequency and the second resonant frequency are within the reference region. When the process of step S12 is finished, the subroutine of measuring the resonance frequency is finished, and the process returns to the process of step S2 shown in FIG.

  As described above, in the present embodiment, for example, since setting of the frequency with high resolution is possible, the first and second drive frequencies are made to follow and change according to the fluctuation of the first and second resonance frequencies. As a result, the deviation of the scanning locus by the light scanning unit 2 can be efficiently suppressed. Therefore, the light scanning device 1 can be driven efficiently and stably with respect to the light scanning unit 2.

  Further, in the present embodiment, as described above, the relationship between the drive frequency and the resonant frequency can be monitored by monitoring the phase difference and the output voltage Vo. Thus, in the present embodiment, even if the resonance frequency deviates from the reference area, the timing table is changed to any one of the first to eighth areas according to the set states of the first to eighth flags. Since the Lissajous scan can be performed, it is possible to provide a system that is resistant to changes with time and temperature.

  Further, in the present embodiment, even if at least one of the first resonance frequency and the second resonance frequency fluctuates due to a temperature change, a time-dependent change, etc., there is no need to generate the timing table in real time. It is possible to suppress an increase in the load on a central processing unit (CPU) in a unit.

  The process when one Lissajous scan is completed will be described in more detail as follows. In the processing of the above-mentioned flowchart, for example, when the flag is changed from the off setting to the on setting, the drive unit 3 sets the on at the stage when the pulse light of the last distance measuring point of a certain frame is finished. Change the reference destination to the address of the timing table corresponding to the flag. As for the drive frequency, the drive frequency is changed after the measurement of the last distance measurement point of a certain frame. However, if the drive frequency is changed, the phase difference is also changed, so that the irradiation of the pulsed light is stopped until the phase difference between the two axes becomes a predetermined phase relationship. Thereafter, the timing table can be changed by resuming emission of pulsed light.

Next, the overall operation of the light ranging device 100 including the light scanning device 1 having the above configuration will be described.
First, when the main switch or the like (not shown) is turned on and the light ranging apparatus 100 is activated, the drive unit 3 outputs the first drive signal and the second drive signal to the light scanning unit 2 to make the light reflection surface 24 It is driven to oscillate around x-axis and y-axis. The light source unit 5 emits pulse light based on the timing table. Subsequently, in the target area, pulse light is emitted to each measurement position set in advance on the Lissajous scanning trajectory by the light scanning unit 2, and distance measurement is performed by the distance measurement unit 6 for each measurement position. Then, when distance measurement at all measurement positions in the target area is completed, the image generation unit 8 generates a distance image for the target area, and the generated distance image is displayed on the display unit 9. That is, the distance image is generated for each cycle of Lissajous scanning by the light scanning unit 2.

  More specifically, the first shift amount detection unit 33 of the drive unit 3 detects the first shift amount when the first resonance frequency fluctuates, and the second shift amount detection unit 34 of the drive unit 3 When the resonance frequency fluctuates, a second deviation amount is detected. That is, the first shift amount detection unit 33 detects the first resonance frequency around the x axis in each Lissajous scan cycle, and the second shift amount detection unit 34 detects the second resonance frequency around the y axis in every Lissajous scan cycle To detect When the combination of the first resonant frequency and the second resonant frequency deviates from the reference region shown in FIG. 7, the frequency changing unit 35 of the drive unit 3 fluctuates the first drive frequency according to the first to eighth regions. The second drive frequency is made to coincide with the fluctuating second resonance frequency. As a result, the drive unit 3 can drive at the first resonance frequency and the second resonance frequency, so that efficient rocking drive can be performed on the two-dimensional galvano mirror 20.

Then, the drive unit 3 sets the emission timing of the pulsed light by the light source 51 with reference to the appropriate timing table based on the matched first and second drive frequencies.
Such processing is performed, for example, if the emission timing is not adjusted even if the first drive frequency is made to coincide with the varied first resonance frequency and the second drive frequency is made to coincide with the varied second resonance frequency. This is because a deviation may occur in the scanning width of pulsed light for Lissajous scanning at each measurement position. Therefore, the drive unit 3 sets the emission timing so that the deviation of the scanning width can be suppressed within the allowable range at each measurement position. However, the ratio of the first resonance frequency to the second resonance frequency is preferably maintained, for example, about 3: 1 from the viewpoint of efficient rocking drive.
Thus, the optical scanning device 1 can suppress the deviation of the scanning width by the optical scanning unit 2 within the allowable (error) range at each measurement position. Therefore, the optical distance measuring apparatus 100 can perform stable distance measurement at each measurement position in the target area.

  Although the optical distance measuring apparatus has been described above as one embodiment of the present invention, it can be configured as an optical scanning apparatus including the light scanning unit 2 and the driving unit 3 as another embodiment of the present invention Nor. In this case, light is input to the light reflecting surface 24 from a separately configured light source, and the light scanning device can scan the input light within the target area for Lissajous scanning.

  Next, modifications of the above embodiment will be described. In the above embodiment, the swing angle signal around the x axis and the y axis of the inner movable portion 23b is detected by the output voltage of the bridge circuit configured by the piezoresistive element.

  However, the present invention is not limited to this, and as a modification, for example, based on the description in JP-A-2004-78130 and JP-A-2004-242488, other than the output voltage of the bridge circuit formed of piezoresistive elements. The signal may be detected as a swing angle signal around the x axis and the y axis of the inner movable portion 23b. In this case, in the modification, the back electromotive force generated in the first drive coil 25a and the second drive coil 25b may be detected, and swing angle signals about the x axis and the y axis may be determined. However, when the light scanning unit 2 is driven by a drive signal having a frequency that matches the resonance frequency, the phase difference between the drive signal and the swing angle signal (counter electromotive force signal) of the inner movable unit 23b is 0 degrees. Become.

  In the modification, the first shift amount and the second shift amount may be detected based on the temperature of the light scanning unit 2 or in the vicinity thereof without using the swing angle signal of the inner movable portion 23b. For example, in a modification, a temperature sensor that detects the temperature of the light scanning unit 2 or in the vicinity thereof may be provided. That is, in the modification, the “temperature-first resonance frequency table” and the “temperature-second resonance” in which the temperature at or near the light scanning unit 2 is associated with the resonant frequency for each of the x-axis and y-axis. Reference to the frequency table is stored in the memory 4.

  In this way, the drive unit 3 refers to the temperature-first resonance frequency table based on the detection result of the temperature sensor, and thereby the first shift amount between the frequency of the first drive signal and the first resonance frequency. (In other words, the shift amount associated with the temperature change of the first resonance frequency) can be detected (calculated). Similarly, the drive unit 3 refers to the temperature-second resonance frequency table based on the detection result of the temperature sensor to determine the second deviation amount between the frequency of the second drive signal and the second resonance frequency (in other words, If it does, it is possible to detect (calculate) the shift amount accompanying the temperature change of the second resonance frequency.

  In the above embodiment, the first deviation amount between the frequency of the first drive signal and the first resonance frequency and the second deviation amount between the frequency of the second drive signal and the second resonance frequency are detected. Only one or the other may be detected. Preferably, only the amount of deviation about the x axis, which is driven to rock at high speed, that is, only the amount of deviation between the frequency of the first drive signal and the first resonance frequency is detected.

  In the above embodiment, an electromagnetic drive type two-dimensional galvano mirror is used as the light scanning unit, but the present invention is not limited to this, and an electromagnetic drive type, an electrostatic method, a piezoelectric method, a thermal method The present invention can also be applied to a light scanning unit configured to swing and drive a movable unit having a light reflecting surface by various driving methods such as, for example. In addition, the technology disclosed herein may be applied to a one-dimensional galvano mirror.

  Further, although a plurality of timing tables are set in the above embodiment, the present invention is not limited to this, and a table of the reference region is set, and the timing of the reference region is shifted when the resonance frequency deviates. A timing table corresponding to the amount of deviation may be generated based on the table.

  DESCRIPTION OF SYMBOLS 100 ... Light ranging apparatus, 2 ... Light scanning part, 3 ... Drive part, 4 ... Memory, 5 ... Light source part, 6 ... Light reception part, 7 ... Ranging part, 8 ... Image generation part, 9 ... Display part, 20 Two-dimensional galvano mirror (light scanning unit) 21 fixed portion 22a, 22b first torsion bar 22c 22d second torsion bar 23a outer movable portion 23b inner movable portion 25a first Drive coil, 25b: second drive coil, 31: first drive circuit, 32: second drive circuit, 33: first shift amount detector, 34: second shift amount detector, 35: frequency changer, 51: Light source, 52: light source control unit, 53: projection optical system

Claims (6)

The movable portion is first having a light reflecting surface, a first orthogonal to each other by a second driving frequency, is swung to the second axis, an optical scanning device for Lissajous scanning pulse light by the light source,
The first and second drive frequencies are changed according to the shift amount of the first resonance frequency around the first axis and the shift amount of the second resonance frequency around the second axis, and a combination of shift directions of both resonance frequencies Changing the emission timing of the pulsed light based on the timing table according to
Optical scanning device. A reference region including the first initial setting value of the first resonant frequency and the second initial setting value of the second resonant frequency, and a plurality of regions surrounding the reference region are set in advance.
Each of the reference area and the plurality of areas is associated with a timing table including information on the emission timing,
The shift amount of the first resonant frequency and the shift amount of the second resonant frequency are detected, and the reference region and one of the plurality of regions are determined according to the detection result to select a timing table. The optical scanning device according to claim 1, wherein the emission timing of the pulse light is set based on a selected timing table . The combination of the shift directions of the two resonant frequencies is that only the first resonant frequency is shifted in the positive or negative direction, that only the second resonant frequency is shifted in the positive or negative direction, and The resonant frequency and the second resonant frequency are shifted in the positive or negative direction, and one of the first resonant frequency and the second resonant frequency is shifted in the positive direction, and the other is shifted in the negative direction. The optical scanning device according to claim 1 , further comprising: At least one of the shift amount of the first resonance frequency in the positive direction, the shift amount of the first resonance frequency in the negative direction, the shift amount of the second resonance frequency in the positive direction, and the shift amount of the second resonance frequency in the negative direction The optical scanning device according to any one of claims 1 to 3, wherein the first and second drive frequencies are changed and the emission timing is changed when H exceeds a predetermined hertz . A reference area including the first initial setting value of the first resonant frequency and the second initial setting value of the second resonant frequency is set in advance, and the reference area includes a timing table including information on the emission timing. Are associated,
The shift amount of the first resonant frequency and the shift amount of the second resonant frequency are detected, and it is determined whether at least one of the first resonant frequency and the second resonant frequency is out of the reference region,
When the first resonance frequency and the second resonance frequency are within the reference area, the emission timing of the pulse light is set based on a timing table associated with the reference area,
When at least one of the first resonance frequency and the second resonance frequency deviates from the reference area, the information on the emission timing according to the shift amount is calculated based on the timing table associated with the reference area. The optical scanning device according to claim 1 , wherein a timing table including the timing information is generated, and the emission timing of the pulse light is set based on the generated timing table . A light source for emitting pulse light toward a movable portion having a light reflection surface;
An optical scanning unit in which the movable unit is swung about first and second axes orthogonal to each other by a first and second driving frequency, and the light source scans the pulsed light by the light source;
The first and second drive frequencies are changed according to the shift amount of the first resonance frequency around the first axis and the shift amount of the second resonance frequency around the second axis, and a combination of shift directions of both resonance frequencies A control unit that changes the emission timing of the pulsed light based on a timing table corresponding to
An optical scanning device comprising: