Measuring apparatus, method for controlling measuring apparatus, control program for measuring apparatus, and computer-readable recording medium storing computer program

Abstract

To suppress the problem that, when the speed of a measurement target changes, the accuracy of measuring relative positional relationships among a plurality of portions in the measurement target decreases.SOLUTION: The measuring apparatus includes a projector for emitting light, a photodetector for receiving reflected light as light reflected from a measurement target and returning after being emitted from the projector, and a controller. The controller causes the projector to sequentially emit light, at predetermined timings, toward a plurality of different portions of the measurement target, causes the photodetector to receive reflected light from the respective portions, obtains acceleration of the measurement target on the basis of a plurality of light receiving timings corresponding to the portions in the photodetector, respectively, and corrects relative positional relationships in measurement results of the plurality of portions on the basis of the plurality of light receiving timings and the acceleration.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a measurement device. [Background technology]

[0002] With the advancement of AD (Autonomous Driving) and ADAS (Advanced Driver-Assistance Systems), research and development is underway into LiDAR (Light Detection and Ranging) as a measurement device used to understand the surrounding environment and estimate the vehicle's position while driving. LiDAR is equipped with a reflective sensor. The reflective sensor projects (irradiates) a laser beam onto the object to be measured and receives the light that is reflected back from the object. LiDAR outputs information about the object by measuring the distance to the object based on the time difference between when the reflective sensor projects the laser beam and when it receives the reflected light.

[0003] Conventionally, there has been known a measuring device that measures multiple locations on a moving object over time while the moving object is moving relatively. In this measuring device, a light projector sequentially emits light toward multiple different locations on the moving object at predetermined timings, and a light receiver receives the light reflected from each of the multiple locations. The shape of the moving object is measured based on multiple light reception timings corresponding to the multiple locations on the light receiver. In such a measuring device, the relative distance between the moving object and the measuring device changes during the time difference between the light projection timing at one location on the moving object and the light projection timing at another location on the moving object. For this reason, conventional measuring devices employ a technique for correcting the relative positional relationship in the measurement results of multiple locations on the moving object based on the moving speed of the moving object to cancel out errors due to the relative distance (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2016 / 115260 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional measuring devices can measure the shape of a moving object with high accuracy when the speed of the moving object is constant. However, when the speed of the moving object is not constant, the shape of the moving object cannot be measured with high accuracy, so there is room for improvement.

[0006] This specification discloses a technique that can solve the above-mentioned problems. [Means for solving the problem]

[0007] The technology disclosed in this specification can be realized, for example, in the following forms.

[0008] (1) A measurement device disclosed in this specification includes a light projector that emits light, a light receiver that receives light reflected from a measurement object, and a controller. The controller controls the light projector to emit light sequentially at predetermined timings toward multiple different locations on the measurement object, controls the light receiver to receive the light reflected from each of the multiple locations, acquires the acceleration of the measurement object based on multiple light reception timings corresponding to each of the multiple locations on the light receiver, and corrects the relative positional relationship in the measurement results of the multiple locations based on the multiple light reception timings and the acceleration. This measurement device can prevent a decrease in measurement accuracy of the relative positional relationship between multiple locations on the measurement object when the speed of the measurement object changes.

[0009] (2) In the above-described measuring device, the measuring device may be configured to use an FMCW method, and the controller may be configured to acquire the acceleration of the object to be measured based on the velocity difference at each location between multiple frames. According to this measuring device, the measuring device uses an FMCW method and can acquire the velocity of the object to be measured from each frame, thereby efficiently and accurately acquiring the acceleration of the object to effectively prevent a decrease in the measurement accuracy of the relative positional relationship between multiple locations on the object to be measured.

[0010] The technology disclosed in this specification can be realized in various forms, such as a measuring device, a measuring method, a control program for the measuring device, and a computer-readable recording medium on which a computer program is recorded. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a block diagram showing the configuration of a measurement device 1 according to an embodiment. [Figure 2] Flowchart showing measurement processing [Figure 3] FIG. 10 is an explanatory diagram showing the results of shape measurement without correction. [Figure 4] An explanatory diagram showing the results of shape measurement when corrected by speed [Figure 5] An explanatory diagram showing the results of shape measurement when corrected with acceleration. DETAILED DESCRIPTION OF THE INVENTION

[0012] A. Implementation: A-1. Configuration of measuring device 1: FIG. 1 is a block diagram showing the configuration of a measurement device 1 according to this embodiment. The measurement device 1 is a device that measures the distance to an object 90. The measurement device 1 has a function as a LiDAR. The measurement device 1 measures the distance to the object 90 using the FMCW (Frequency Modulated Continuous Wave) method. That is, the measurement device 1 irradiates the object 90 with frequency-modulated measurement light (irradiation light L1), causes reflected light L2 from the object 90 to interfere with measurement light (reference light L4), and measures the distance to the object 90 based on the frequency (beat frequency) of a beat signal Sb, which is the detection result of the interference light L5. The measurement device 1 can measure not only the distance to the object 90 but also the relative speed of the object 90.

[0013] The measurement device 1 includes a generating device 10, an optical device 20, a detecting device 30, and a signal processing device 40. The optical device 20 is an example of a light projector and a light receiver.

[0014] The generating device 10 is a device that generates frequency-modulated light (frequency-modulated light L3). The generating device 10 outputs the frequency-modulated light L3 to the optical device 20. A part of the frequency-modulated light L3 (measurement light) output by the generating device 10 becomes the illumination light L1 that is irradiated onto the object 90, and another part becomes the reference light L4 that is made to interfere with the reflected light L2. The generating device 10 has a signal generator 11, a current source 12, a laser light source 13, and a temperature controller 14.

[0015] The signal generator 11 generates a voltage signal for controlling the current source 12. The signal generator 11 is, for example, a waveform generator, and generates, for example, a triangular wave voltage signal and outputs it to the current source 12. The current source 12 generates a current signal for controlling the laser light source 13. The current source 12 generates a current signal corresponding to the voltage signal of the signal generator 11. For example, the current source 12 generates a triangular wave current signal corresponding to the triangular wave voltage signal and outputs it to the laser light source 13.

[0016] The laser light source 13 emits light whose frequency is modulated (frequency-modulated light L3). For example, the laser light source 13 is configured using a distributed feedback (DFB) laser element. The laser light source 13 generates laser light whose frequency corresponds to the current signal of the current source 12. The laser light generated is frequency-modulated in the range of 193.4024 to 193.4266 THz (λ=1549.903 to 1550.097 nm). For example, the laser light source 13 generates laser light (frequency-modulated light L3) whose frequency gradually increases or decreases according to a triangular wave current signal. The laser light source 13 outputs the laser light to the optical device 20.

[0017] The temperature regulator 14 adjusts the temperature of the laser light source 13 (particularly the laser element) to a predetermined temperature. The temperature regulator 14 has, for example, a temperature sensor 14A and a thermoelectric element (for example, a Peltier element), and measures the temperature of the laser light source 13 with the temperature sensor 14A and adjusts the laser light source 13 to a predetermined temperature by feedback-controlling the thermoelectric element based on the measurement result of the temperature sensor 14A.

[0018] The optical device 20 is a device that irradiates the object 90 with frequency-modulated light (irradiation light L1) and causes reflected light L2 from the object 90 to interfere with reference light L4 (measurement light). The optical device 20 uses part of the measurement light (frequency-modulated light L3) input from the generation device 10 as irradiation light L1 to irradiate the object 90, and part of the measurement light input from the generation device 10 as reference light L4, and causes the reflected light L2 from the object 90 to interfere with the reference light L4 to generate interference light L5 (interference wave). The optical device 20 outputs the interference light L5 (interference wave) caused by interference between the reflected light L2 and the reference light L4 to the detection device 30.

[0019] The optical device 20 includes a branching device 21, a circulator 22, an optical system 23, an optical waveguide 24, and a coupler 25. The branching device 21 branches the frequency-modulated light L3 from the generation device 10. The branching device 21 is configured, for example, by an optical coupler. One of the branched light beams (frequency-modulated light L3) is output to the circulator 22 and becomes the illumination light L1 that is irradiated onto the object 90. The other branched light beam (frequency-modulated light L3) is output to the optical waveguide 24 and becomes the reference light L4 that interferes with the reflected light L2. The circulator 22 guides the light from the branching device 21 (illumination light L1) to the optical system 23, and guides the light from the optical system 23 (reflected light L2) to the coupler 25.

[0020] The optical system 23 irradiates light (irradiation light L1) toward the object 90 and collects and outputs reflected light L2. The optical system 23 is composed of optical elements such as lenses, mirrors, and prisms. The optical system 23 has, for example, a light-projecting optical system that irradiates the irradiation light L1 toward the object, and a light-receiving optical system that collects the reflected light L2. The optical system 23 may also have a function of scanning the irradiation light L1. The optical system 23 outputs the collected reflected light L2 to the circulator 22. The reflected light L2 is input to the coupler 25 via the circulator 22.

[0021] The optical waveguide 24 forms an optical path of a predetermined length from the splitter 21 to the coupler 25. The optical waveguide 24 guides the reference light from the splitter 21 to the coupler 25 over a predetermined optical path length. The optical waveguide 24 is made up of, for example, an optical fiber. The coupler 25 combines the reflected light L2 from the circulator 22 with the reference light L4 from the optical waveguide 24. The coupler 25 is made up of, for example, an optical coupler. The coupler 25 functions as an interferometer that causes interference between the reflected light L2 and the reference light L4, and generates interference light L5 (interference wave) by causing interference between the reflected light L2 and the reference light L4. The coupler 25 outputs the interference light L5 to the detection device 30.

[0022] The detection device 30 detects interference light L5 between the reflected light L2 and the reference light L4 and outputs a beat signal Sb. The detection device 30 has a photoelectric converter 31 and an amplifier 32. The photoelectric converter 31 outputs an electrical signal (current signal) corresponding to the intensity of the detected optical signal (here, interference light L5). The photoelectric converter 31 is, for example, a photodiode. The interference light L5 detected by the photoelectric converter 31 is a wave whose amplitude changes periodically due to interference between the reflected light L2 and the reference light L4, which have different frequencies.

[0023] The amplifier 32 converts the current signal of the photoelectric converter 31 into a voltage signal and outputs it. The amplifier 32 is configured, for example, by a transimpedance amplifier. The beat signal Sb output from the amplifier 32 is a signal that indicates the difference in frequency between the reflected light L2 and the reference light L4. The beat frequency of the beat signal Sb corresponds to the frequency of the beat component of the interference light L5. The beat frequency of the beat signal Sb also corresponds to the difference in frequency between the reflected light L2 and the reference light L4.

[0024] The signal processing device 40 is a device that calculates the distance to the object 90 based on the beat signal Sb. The signal processing device 40 has an A / D converter, an arithmetic unit, a storage device, etc. (not shown). The arithmetic unit is composed of an arithmetic processing device such as a CPU, a GPU, or an MPU. The storage device is composed of a main storage device and an auxiliary storage device, and is a device that stores programs and data. The arithmetic unit executes the programs stored in the storage device, thereby performing various processes for measuring the distance to the object 90. In FIG. 1, the various processes performed by the signal processing device 40 are shown as functional blocks. The signal processing device 40 is an example of a controller.

[0025] The signal processing device 40 has a signal acquiring unit 41, an analyzing unit 42, and an output unit 43. The signal acquiring unit 41 acquires the beat signal Sb of the detection device 30 as a digital signal. The signal acquiring unit 41 is configured by, for example, an A / D converter (such as an A / D conversion board). The analyzing unit 42 calculates the distance to the object 90 based on the beat signal Sb. The output unit 43 outputs the analysis result of the analyzing unit 42 to the outside. For example, the output unit 43 outputs distance data indicating the distance to the object 90 and speed data indicating the relative speed of the object 90 to a vehicle ECU, which is an external device.

[0026] A-2. Measurement process: The measurement device 1 executes a measurement process. The measurement process involves sequentially irradiating a plurality of different locations on the measurement target (object 90) with irradiation light L1 at predetermined timings, receiving reflected light L2 from each of the locations, and measuring the shape of the measurement target based on multiple light-receiving timings corresponding to each of the locations. The optical device 20, for example, has multiple light-emitting elements (laser elements) arranged in a predetermined direction. The optical device 20 causes each of the multiple light-emitting elements to emit light in a time-division manner, sequentially irradiating the plurality of locations on the object 90 with irradiation light L1, and receiving reflected light L2 from each of the locations (hereinafter, this series of operations is referred to as a "light-emitting and receiving operation"). In the following description, the multiple light-emitting elements are arranged vertically, and emit light in order from the lowest light-emitting element to the highest light-emitting element.

[0027] Fig. 2 is a flowchart showing the measurement process. When the signal processing device 40 receives an instruction to start measurement from, for example, an external device, it executes the measurement process shown in Fig. 2. The signal processing device 40 determines whether the measurement timing has arrived (S110). The measurement timing is the timing that triggers the start of the measurement process of the measurement device 1 in units of one frame (the process of performing the above-mentioned light emission and reception operation once to obtain the measurement result (point cloud data)). If the signal processing device 40 determines that the measurement timing has not arrived (S110: NO), it waits as is.

[0028] When the signal processing device 40 determines that the measurement timing has arrived (S110: YES), it causes the optical device 20 to perform a light projection and reception operation (S120). This allows the signal processing device 40 to acquire one frame of point cloud data. The point cloud data is data on a plurality of measurement points P corresponding to a plurality of different locations on the object 90. The measurement points P are arranged at equal intervals in the vertical direction (Z coordinate in FIGS. 3 to 5 described below). The positional relationship of the measurement points P in the horizontal direction (Y coordinate in FIGS. 3 to 5 described below) corresponds to the difference in TOF (Time of Flight) between the plurality of measurement points P. TOF is the time difference between the light projection timing at which the measurement device 1 emits the irradiated light L1 and the light reception timing at which the reflected light L2 is received. A measurement point P with a relatively short TOF is closer to the measurement device 1 than a measurement point P with a relatively long TOF.

[0029] Next, the signal processing device 40 acquires velocity data indicating the relative velocity (hereinafter simply referred to as "velocity v") of the object 90 (S130). As described above, the measuring device 1 of this embodiment employs the FMCW method, and therefore can acquire the relative velocity of the object 90 (each measurement point P) based on one frame of point cloud data.

[0030] Next, the signal processing device 40 acquires acceleration data indicating the relative acceleration (hereinafter simply referred to as "acceleration α") of the object 90 (S140). For example, the signal processing device 40 acquires the acceleration data based on changes in velocity v between multiple different frames for each measurement point P. Specifically, for each measurement point P, the signal processing device 40 calculates the acceleration α from the difference between velocity v0 in the frame at the immediately previous measurement timing and velocity v1 in the frame at the current measurement timing.

[0031] The signal processing device 40 corrects the relative positional relationship in the measurement results of the multiple locations based on multiple light receiving timings (point cloud data) corresponding to the multiple locations and the acceleration α (S150). Specifically, the signal processing device 40 calculates the measurement position Y1 of each measurement point P as the corrected position Y of the measurement point P based on the following equation 1: 1h Correct to. Y 1h =Y1-[(1 / 2)×(v1-v0)×Δt 2 ]-(v1×Δt)...Equation 1 Δt: Time difference between the previous measurement and the current measurement

[0032] Thereafter, the signal processing device 40 returns to S110. Note that the signal processing device 40 may return to S110 and execute the next light projection and reception operation before completing the processes of S130 to S150. In other words, the processes of S130 to S150 for one frame and the light projection and reception operation for the next frame may be executed simultaneously in parallel.

[0033] A-3. Advantages of this embodiment: FIG. 3 is an explanatory diagram showing the results of shape measurement without correction. FIG. 4 is an explanatory diagram showing the results of shape measurement when corrected with velocity v, and FIG. 5 is an explanatory diagram showing the results of shape measurement when corrected with acceleration α. ​​In each diagram, a vehicle is illustrated as the object 90. The object 90 is not traveling at a constant speed, but is decelerating by braking. The first measurement point Pb is a measurement point corresponding to the lowest point at the front end of the object 90. The final measurement points Pt1 to Pt3 are measurement points corresponding to the highest points at the front end of the object 90. Hereinafter, the horizontal distance between the lowest and highest points of the object 90 will be referred to as the vehicle position deviation E.

[0034] As described above, the measurement device 1 is configured to sequentially irradiate the irradiation light L1 toward a plurality of different locations on the measurement target (object 90) at predetermined timings. Therefore, in one light projection and reception operation, there is a time difference (hereinafter referred to as the "light projection time difference") between the light projection timing corresponding to the first measurement point Pb and the last measurement point Pt1. During this light projection time difference, the object 90 approaches the measurement device 1 at a speed v, and the relative distance between the object 90 and the measurement device 1 changes.

[0035] FIG. 3 shows point cloud data acquired by the light projecting and receiving operation without correction. If no correction process is performed on the point cloud data acquired by the light projecting and receiving operation of S120, the measurement result of the shape of the object 90 will deviate from the correct shape of the object 90 depending on the relative distance. For example, as shown in FIG. 3, in the horizontal direction, the position deviation ΔE1 of the position Dt1 of the last measurement point Pt1 relative to the position Db of the first measurement point Pb significantly deviates from the vehicle position deviation E on the object 90. The position Dt1 of the last measurement point Pt1 is located forward of the position Db of the first measurement point Pb by the position deviation ΔE1. ​​The error between the position Dt1 of the last measurement point Pt1 and the correct position Dt of the highest point of the object 90 is the sum of the vehicle position deviation E and the position deviation ΔE1.

[0036] FIG. 4 shows point cloud data corrected by the velocity v of the object 90. Even when correction processing is performed on the point cloud data acquired by the light projection and reception operation of S120 based on the velocity v (the velocity v is constant), the measurement result of the shape of the object 90 deviates from the correct shape of the object 90. This is because, as described above, the velocity v of the object 90 is not constant but changes (decelerates) during the light projection time difference. For example, as shown in FIG. 4, in the horizontal direction, the position deviation ΔE2 of the position Dt2 of the last measurement point Pt2 relative to the position Db of the first measurement point Pb deviates from the vehicle position deviation E on the object 90. The position Dt2 of the last measurement point Pt2 is located behind the position Db of the first measurement point Pb by the position deviation ΔE2. The error between the position Dt2 of the last measurement point Pt2 and the correct position Dt of the highest point of the object 90 is the position deviation ΔE2 minus the vehicle position deviation E.

[0037] 5 shows point cloud data corrected by the acceleration α of the object 90. When correction processing is performed on the point cloud data acquired by the light emitting and receiving operation of S120 based on the acceleration α, the measurement results of the shape of the object 90 approach the correct shape of the object 90. For example, as shown in FIG. 5, in the horizontal direction, the position deviation of the position Dt3 of the last measurement point Pt3 from the position Db of the first measurement point Pb matches the vehicle position deviation E on the object 90. The position Dt3 of the last measurement point Pt3 is located behind the position Db of the first measurement point Pb by the amount of the vehicle position deviation E.

[0038] B. Variations: The technology disclosed in this specification is not limited to the above-described embodiments, and can be modified into various forms without departing from the spirit thereof, for example, the following modifications are also possible.

[0039] The configuration of the measuring device 1 in the above embodiment is merely an example and can be modified in various ways. For example, the measuring device 1 is a flash type, but is not limited to this, and may be a scanning type equipped with a scanner. Furthermore, the measuring device 1 may be fixed at a predetermined position or may be placed on a mobile body.

[0040] In the above embodiment, the measurement device 1 employs the FMCW method. However, a measurement device other than the FMCW method may also be used. Such a measurement device can calculate the velocity of the measurement object based on the positional deviation of each measurement point between multiple frames and the light projection period. Then, the velocity between frames at different timings is acquired, and the acceleration of the measurement object can be acquired based on the difference between these velocities. For example, for a certain measurement point, a first velocity is calculated based on the positional deviation between the position in a first frame and the position in a subsequent second frame and the light projection period. Next, a second velocity is calculated based on the positional deviation between the position in the second frame and the position in a subsequent third frame and the light projection period. The acceleration of the measurement object is acquired from the difference between the first velocity and the second velocity.

[0041] In the above embodiment, measurement of the shape of the object in the vertical direction (up and down direction) has been exemplified, but the present invention is not limited to this and may also be applied to measurement of the shape in the horizontal direction. [Explanation of symbols]

[0042] 1: Measuring device 10: Generating device 11: Signal generator 12: Current source 13: Laser light source 14: Temperature controller 14A: Temperature sensor 20: Optical device 21: Branching device 22: Circulator 23: Optical system 24: Optical waveguide 25: Coupler 30: Detecting device 31: Photoelectric converter 32: Amplifier 40: Signal processing device 41: Signal acquisition unit 42: Analysis unit 43: Output unit 90: Object L1: Irradiated light L2: Reflected light L3: Frequency-modulated light L4: Reference light L5: Interference light

Claims

1. A projector that emits light; a light receiver that receives reflected light that is emitted by the light projector and reflected back from the object to be measured; a controller, The controller The light projector is caused to emit light toward a plurality of different locations on the measurement object at predetermined timings in sequence, and the light receiver is caused to receive reflected light from each of the plurality of locations; acquiring an acceleration of the object to be measured based on a plurality of light receiving timings corresponding to the plurality of locations on the light receiver; The measuring device corrects the relative positional relationship in the measurement results of the plurality of locations based on the plurality of light receiving timings and the acceleration.

2. 2. The measuring device according to claim 1, The measuring device is an FMCW type, The controller A measuring device that acquires the acceleration of the measurement object based on the velocity difference at each location between multiple frames.

3. A control method for a measurement device including a light projector that emits light and a light receiver that receives reflected light that is returned from a measurement target after being reflected by the light projector, the method comprising: The light projector is caused to emit light toward a plurality of different locations on the measurement object at predetermined timings in sequence, and the light receiver is caused to receive reflected light from each of the plurality of locations; acquiring an acceleration of the object to be measured based on a plurality of light receiving timings corresponding to the plurality of locations on the light receiver; A method for controlling a measurement device, which corrects a relative positional relationship in measurement results of the plurality of locations based on the plurality of light receiving timings and the acceleration.

4. A computer included in a measuring device including a light projector that emits light and a light receiver that receives reflected light that is returned from a measurement object after being emitted by the light projector, The light projector is caused to emit light toward a plurality of different locations on the measurement object at predetermined timings in sequence, and the light receiver is caused to receive reflected light from each of the plurality of locations; acquiring an acceleration of the object to be measured based on a plurality of light receiving timings corresponding to the plurality of locations on the light receiver; A control program for a measurement device that corrects the relative positional relationship in the measurement results of the plurality of locations based on the plurality of light receiving timings and the acceleration.

5. A computer-readable recording medium having recorded thereon a computer program for controlling a measuring device including a light projector that emits light and a light receiver that receives reflected light that is returned from a measurement object after being emitted by the light projector, The light projector is caused to emit light toward a plurality of different locations on the measurement object at predetermined timings in sequence, and the light receiver is caused to receive reflected light from each of the plurality of locations; acquiring an acceleration of the object to be measured based on a plurality of light receiving timings corresponding to the plurality of locations on the light receiver; A computer-readable recording medium having recorded thereon a computer program for correcting the relative positional relationship in the measurement results of the plurality of locations based on the plurality of light-receiving timings and the acceleration.

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