Apparatus and method for measuring distance and / or velocity of an object

Abstract

This measurement device comprises: a light source for emitting frequency-modulated light; an interference optical system for separating the light emitted from the light source into reference light and output light and generating interference light resulting from interference between the reference light and reflection light produced by the reflection of the output light by an object; a photodetector for receiving the interference light and outputting a detection signal corresponding to the intensity of the interference light; a storage device for storing a plurality of items of correction data that are to be used to correct the detection signal and are each associated with one corresponding operation state from among a plurality of different light source operation states; and a processing circuit for transmitting, to the light source, a control signal for sweeping the frequency of the light emitted from the light source, correcting the detection signal on the basis of one or more items of correction data selected from among the plurality of items of correction data according to the operation state of the light source, generating measurement data relating to the distance and / or speed of the object on the basis of the corrected detection signal, and outputting the measurement data.

Description

[Technical Field]

[0001] The present disclosure relates to an apparatus and method for measuring the distance and / or velocity of an object. [Background technology]

[0002] A ranging device using the FMCW (Frequency Modulated Continuous Wave) method sends out frequency-modulated electromagnetic waves and measures distance based on the difference in frequency between the transmitted and reflected waves. When the electromagnetic waves used are radio waves such as millimeter waves, the FMCW ranging device is called an FMCW radar. In FMCW radar, a voltage-controlled oscillator (VCO), for example, is used as the radio wave oscillation source. When the electromagnetic waves are light such as visible light or infrared light, the FMCW ranging device is called an FMCW lidar (LiDAR). In FMCW lidar, a laser light source, for example, is used as the light source.

[0003] FMCW LIDAR emits periodically frequency-modulated light from a light source toward a target. The reflected light from the target interferes with a reference light from the light source to produce an interference light. The interference light is detected by a photodetector and converted into an electrical signal. This electrical signal contains a signal component with a frequency corresponding to the difference between the frequency of the reflected light and the frequency of the reference light. This signal component is called the "beat signal." The frequency of the beat signal is called the "beat frequency." There is a correlation between the beat frequency and the distance to the target. Therefore, the distance to the target can be calculated based on the beat frequency. Furthermore, the Doppler shift of the reflected light from a moving target can be used to calculate the target's velocity. Unlike time-of-flight (ToF) LIDAR, FMCW LIDAR detects the frequency of the electrical signal output from the photodetector, making the ranging results less susceptible to ambient light disturbances. However, the accuracy of FMCW LIDAR ranging has been thought to depend on how linearly the light frequency can be modulated with respect to time.

[0004] Patent Document 1 describes that even if the voltage-controlled oscillator of an FMCW radar sweeps the voltage linearly with time, the frequency changes nonlinearly, resulting in a degradation of ranging performance. To solve this problem, Patent Document 1 discloses a method for dynamically changing the sampling timing of the interference signal based on the sweep signal obtained from an artificial target. It describes how this makes it possible to compensate for the nonlinearity of the frequency sweep.

[0005] Patent Document 2 discloses an FMCW radar device that corrects the frequency of an interference signal using correction data corresponding to a plurality of distances and a plurality of ambient temperatures, thereby improving detection accuracy.

[0006] Patent Document 3 discloses an example of an FMCW lidar device that continuously measures the frequency of a beat signal and calculates the distance to an object based on the average value of the measured frequency. It describes how this eliminates the effects of nonlinear laser chirp, enabling accurate distance measurement. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2006 / 035199 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-185973 [Patent Document 3] JP 2019-45200 A Summary of the Invention [Problem to be solved by the invention]

[0008] The present disclosure provides a novel technique for measuring distance and / or velocity more precisely in FMCW lidar, regardless of the operating state of the light source. [Means for solving the problem]

[0009] A measurement device according to one aspect of the present disclosure includes a light source that emits frequency-modulated light; an interference optical system that separates the light emitted from the light source into reference light and output light, and generates interference light between the reference light and reflected light resulting from the output light being reflected by an object; a photodetector that receives the interference light and outputs a detection signal corresponding to the intensity of the interference light; a memory device that stores a plurality of correction data used to correct the detection signal, each of the plurality of correction data being associated with a corresponding one of a plurality of different operating states of the light source; and a processing circuit that sends a control signal to the light source that sweeps the frequency of the light emitted from the light source, corrects the detection signal based on one or more correction data selected from the plurality of correction data depending on the operating state of the light source, and generates and outputs measurement data regarding the distance and / or speed of the object based on the corrected detection signal.

[0010] A general or specific aspect of the present disclosure may be realized by a system, an apparatus, a method, an integrated circuit, a computer program, or a recording medium such as a computer-readable recording disk, or by any combination of a system, an apparatus, a method, an integrated circuit, a computer program, and a recording medium. The computer-readable recording medium may include a volatile recording medium or a non-volatile recording medium such as a CD-ROM (Compact Disc-Read Only Memory). An apparatus may be composed of one or more devices. When an apparatus is composed of two or more devices, the two or more devices may be located in a single device or may be located separately in two or more separate devices. In this specification and claims, the term "apparatus" may refer not only to a single device but also to a system consisting of multiple devices. [Effects of the Invention]

[0011] According to an embodiment of the present disclosure, the detection signal output from the photodetector is corrected in accordance with the operating state of the light source, thereby mitigating the effects of nonlinear frequency modulation that occurs differently depending on the operating state, thereby enabling more accurate measurement of the distance and / or velocity of an object. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 shows data obtained from an experiment conducted by the present inventors. [Figure 2] FIG. 2 is a block diagram showing a schematic configuration of the measurement device according to the first embodiment. [Figure 3] FIG. 3 is a block diagram showing an example of the configuration of the light source and the interference optical system. [Figure 4] FIG. 4 is a diagram showing an example of a control signal output from a processing circuit and a drive current signal output from a drive circuit. [Figure 5] FIG. 5 is a block diagram showing an example of the configuration of a measurement device in which the interference optical system is a fiber optical system. [Figure 6] FIG. 6 is a block diagram showing an example of a measurement device equipped with an optical deflector. [Figure 7A] FIG. 7A is a diagram schematically illustrating an example of temporal changes in the frequencies of the reference light and the reflected light when the object is stationary. [Figure 7B] FIG. 7B is a diagram schematically showing the change over time in the frequencies of the reference light and the reflected light when the object approaches the measurement device. [Figure 8] FIG. 8 is a flowchart showing an example of the calibration operation. [Figure 9] FIG. 9 is a graph showing an example of the analysis results of the period of the detection signal. [Figure 10] FIG. 10 is a diagram showing an example of the relationship between the control signal voltage and the period. [Figure 11A] FIG. 11A shows an example of a correction table associated with a first operating state of the light source. [Figure 11B]FIG. 11B illustrates an example of a correction table associated with a second operating state of the light source. [Figure 12] FIG. 12 is a diagram showing an example of the waveform of the detection signal before and after correction. [Figure 13] FIG. 13 is a diagram showing an example of a conversion table that defines the relationship between the frequency of the beat signal and the distance. [Figure 14A] FIG. 14A is a diagram showing an example of a conversion table that defines the relationship between the frequency of a beat signal corresponding to the first operating state and the distance. [Figure 14B] FIG. 14B is a diagram showing an example of a conversion table that defines the relationship between the frequency of the beat signal corresponding to the second operating state and the distance. [Figure 15] FIG. 15 is a flowchart showing an example of a distance measurement operation. [Figure 16] FIG. 16 is a block diagram showing a schematic configuration of a measurement device according to the second embodiment. [Figure 17] FIG. 17 is a flowchart showing the calibration operation in the second embodiment. [Figure 18] FIG. 18 is a flowchart showing an example of a distance measurement operation in the second embodiment. [Figure 19A] FIG. 19A is a diagram showing an example of a correction table that defines the relationship between the voltage of the control signal and the sampling interval. [Figure 19B] FIG. 19B is a diagram showing an example of a correction table that defines the relationship between the phase of frequency modulation and the period ratio. [Figure 19C] FIG. 19C is a diagram showing an example of a correction table that defines the relationship between the phase of frequency modulation and the sampling interval. [Figure 20] FIG. 20 is a graph showing the results of creating a correction table when calibration is performed with two types of modulation voltage amplitude. [Figure 21A] FIG. 21A is a graph showing the results of applying a correction table corresponding to Vm=0.7V to the detection signal obtained when Vm=0.7V. [Figure 21B]FIG. 21B is a graph showing the results of applying a correction table corresponding to Vm=0.7V to the detection signal obtained when Vm=1.0V. [Figure 21C] FIG. 21C is a graph showing the results of applying the correction table corresponding to Vm=1.0V to the detection signal obtained when Vm=1.0V. [Figure 22] FIG. 22 is a graph showing an example of the results of creating a correction table when calibration is performed using two types of bias voltages. [Figure 23] FIG. 23 is a graph showing an example of the results of creating a correction table when calibration is performed at two different temperatures. [Figure 24] FIG. 24 is a diagram showing an example in which a new correction table is created from two existing correction tables. [Figure 25] FIG. 25 is a diagram showing an example in which a new table is created from two existing correction tables. [Figure 26] FIG. 26 is a block diagram showing the configuration of a measurement device in an experimental example for verifying the effects of an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013] (Findings that formed the basis of this disclosure) The inventors discovered the following phenomenon in the waveform of the detection signal obtained by detecting interference light in an FMCW lidar. Even if the control voltage of the light source is swept linearly to linearly modulate the light frequency, the frequency changes nonlinearly, and the nonlinearity differs depending on the operating state of the light source. This phenomenon will be explained below with reference to Figure 1.

[0014] FIG. 1 shows data obtained from an experiment conducted by the inventors. In the experiment, a semiconductor laser light source was used as the light source. The frequency of the laser light emitted from the light source is changed by changing the voltage of the control signal (hereinafter also referred to as "control voltage") input to the light source. The control signal is set within a predetermined voltage range V m(hereinafter, also referred to as "modulation voltage amplitude") is swept linearly at a predetermined period. As a result, laser light whose frequency is periodically modulated is emitted from the light source.

[0015] Graph (a) in FIG. 1 shows an example of the time variation of the voltage of the control signal input to the light source. In this example, the control signal is in the voltage range V m1 The voltage range is swept linearly with respect to time. The center of the voltage range (hereinafter also called the "bias voltage") is V b Graph (b) in Figure 1 shows an example of the time variation of the control voltage when the same laser light source is controlled under the same temperature conditions with different control signals. In this example, the bias voltage is V b However, the modulation voltage amplitude is V m2 V m2 is V m1 It is 1.5 times the

[0016] Graphs (c) and (d) in Fig. 1 show examples of the waveforms of electrical signals (hereinafter also referred to as "detection signals") obtained by detecting the interference light between the reflected light generated when a laser beam is emitted from a light source toward a stationary reference reflector and the reference light traveling from the light source toward the photodetector via an optical system. Graphs (c) and (d) respectively show waveforms of electrical signals (hereinafter also referred to as "detection signals") obtained by detecting the interference light between the reflected light generated when a laser beam is emitted from a light source toward a stationary reference reflector and the reference light traveling from the light source toward the photodetector via an optical system. m1 and V m2 The time axis in these graphs is the same as the time axis in graphs (a) and (b).

[0017] Graphs (e) and (f) in Figure 1 show the time variation of the instantaneous frequency of the beat signal, obtained by frequency analysis of the signal waveforms in graphs (c) and (d), respectively. The waveforms in graphs (e) and (f) were obtained based on the signal voltage in the range from time t1 to t2 in graphs (c) and (d), respectively.

[0018] Graph (g) in Figure 1 shows the relationship between the two modulation voltage amplitudes V m1 and V m21 plots the instantaneous frequency corresponding to the control signal voltage.

[0019] In this experiment, light was irradiated onto a stationary object. If the light frequency was swept linearly in response to the linear sweep of the control voltage, the frequency of the beat signal should be constant over time. However, as shown in graphs (e) and (f) in Figure 1, the frequency of the beat signal fluctuates over time. In addition, when the modulation voltage amplitude is V m1 In the case of V m2 The nonlinearity of the beat signal frequency with respect to time is different between the cases (1) and (2). This indicates that the nonlinearity of the light frequency change with respect to time varies depending on the magnitude of the modulation voltage amplitude.

[0020] Furthermore, as can be seen from graph (g) in Figure 1, even when the frequency of the beat signal is plotted against the voltage of the control signal, the nonlinearity of the fluctuation in the frequency of the beat signal is evident when the amplitude of the modulation current is V m1 In the case of V m2 For example, when the modulation current amplitude is V m1 In the example of Fig. 1, the frequency of the beat signal tends to increase relatively with increasing control voltage on the high voltage side, while the amplitude of the modulation current is V m2 In the example shown in Fig. 1, a tendency for saturation is observed at the same high-voltage control voltage. This indicates that even if a specific control voltage is applied to a laser light source at a given moment, the frequency of the light emitted from the laser light source does not necessarily remain constant, but fluctuates depending on the modulation voltage amplitude of the control signal. The reason for this phenomenon is thought to be as follows: The way in which the heat imparted to the laser element by the current driving the laser element changes over time varies depending on the magnitude of the modulation voltage amplitude. This difference in the way of change affects the temporal changes in the resonator length, gain curve, and oscillation mode of the laser element, and is thought to cause differences in the fluctuations in the laser oscillation frequency.

[0021] If the beat frequency fluctuates with respect to the control voltage or time in this way, the distance to the target cannot be uniquely determined. One possible approach to stabilizing the fluctuations in the beat frequency is to integrate (i.e., average) the spectrum obtained by frequency analysis with respect to the control voltage or time. However, such integration increases the spectral linewidth of the beat signal, making it difficult to determine the peak frequency of the beat signal and reducing the accuracy of distance measurement. Unlike FMCW radar, which uses radio waves, it is not possible to directly detect optical frequency signals, and therefore it is not possible to directly feedback-control the control voltage to linearly change the laser oscillation frequency.

[0022] As described above, it has been found that in an FMCW lidar, the above-mentioned problems arise when the operating state of the light source varies. In order to solve the above-mentioned problems, the inventors have devised the configurations of the embodiments of the present disclosure described below. Exemplary embodiments of the present disclosure will be described below.

[0023] A measurement device according to an embodiment of the present disclosure includes a light source, an interference optical system, a photodetector, a storage device, and a processing circuit. The light source emits frequency-modulated light. The interference optical system separates the light emitted from the light source into a reference light and an output light, and generates interference light between the reference light and reflected light resulting from reflection of the output light by an object. The photodetector receives the interference light and outputs a detection signal corresponding to the intensity of the interference light. The storage device stores a plurality of correction data used to correct the detection signal. Each of the plurality of correction data is associated with a corresponding one of a plurality of different operating states of the light source. The processing circuit sends a control signal to the light source to sweep the frequency of the light emitted from the light source. The processing circuit corrects the detection signal based on one or more correction data selected from the plurality of correction data depending on the operating state of the light source, and generates and outputs measurement data related to the distance and / or velocity of the object based on the corrected detection signal.

[0024] According to the above configuration, the processing circuit can appropriately correct the detection signal based on one or more correction data selected from a plurality of correction data according to the operating state of the light source, thereby mitigating the influence of nonlinear frequency modulation that occurs differently depending on the operating state, and enabling more accurate measurement of the distance and / or speed of the target object.

[0025] The measurement device may further include a temperature sensor that measures the temperature of the light source. The multiple correction data may include two or more first correction data, each of which may be associated with a corresponding one of two or more operating states in which the temperature of the light source differs. The processing circuit may correct the detection signal based on one or more first correction data selected from the two or more first correction data in accordance with the temperature of the light source measured by the temperature sensor. With this configuration, the processing circuit can appropriately correct the detection signal based on the one or more first correction data selected in accordance with the temperature of the light source. This makes it possible to mitigate the effect of nonlinear frequency modulation, which occurs differently depending on the temperature of the light source, and to more accurately measure the distance and / or velocity of an object.

[0026] The control signal may be a signal that inputs a periodically varying voltage or current to the light source. The plurality of correction data may include two or more second correction data, each of which may be associated with a corresponding one of two or more operating states in which the voltage or current of the control signal has a different amplitude. The processing circuit may correct the detection signal based on one or more second correction data selected from the two or more second correction data in accordance with the current amplitude of the voltage or current. This configuration allows the processing circuit to appropriately correct the detection signal based on one or more second correction data selected in accordance with the current amplitude of the voltage or current of the control signal. This reduces the effect of nonlinear frequency modulation, which occurs differently depending on the amplitude of the voltage or current of the control signal, thereby enabling more accurate measurement of the distance and / or velocity of an object.

[0027] The control signal may be a signal input to the light source, which may be a voltage that periodically fluctuates around a certain bias voltage or a current that periodically fluctuates around a certain bias current. The plurality of correction data may include two or more third correction data, each of which may be associated with a corresponding one of two or more operating states in which the bias voltage or the bias current of the control signal differs. The processing circuit may correct the detection signal based on one or more third correction data selected from the two or more third correction data in accordance with the current bias voltage or the current bias current. This configuration allows the processing circuit to appropriately correct the detection signal based on one or more third correction data selected in accordance with the current bias voltage or bias current of the control signal. This reduces the effect of nonlinear frequency modulation, which occurs differently depending on the bias voltage or bias current of the control signal, thereby enabling more accurate measurement of the distance and / or velocity of an object.

[0028] If the storage device does not store correction data corresponding to the current operating state of the light source, the processing circuit may generate correction data corresponding to the current operating state based on at least one of the plurality of correction data stored in the storage device, and correct the detection signal based on the generated correction data. For example, the processing circuit may select one or more correction data that are closest to the current operating state from the plurality of correction data, and correct the detection signal based on the selected correction data. By performing such an operation, the detection signal can be corrected even if the storage device does not store correction data corresponding to the current operating state, and the distance and / or velocity of the target object can be measured more accurately.

[0029] If the storage device does not store correction data corresponding to the current operating state of the light source, the processing circuit may select, from the plurality of correction data stored in the storage device, two correction data associated with two operating states closest to the current operating state, generate correction data corresponding to the current operating state by interpolation using the selected two correction data, and correct the detection signal based on the generated correction data. The two operating states closest to the current operating state refer to the operating state closest to the current operating state and the operating state second closest to the current operating state. By performing interpolation using the two correction data corresponding to the two operating states, appropriate correction data corresponding to the current operating state can be generated. By correcting the detection signal based on the generated correction data, the distance and / or velocity of an object can be measured more accurately even if the storage device does not store correction data corresponding to the current operating state.

[0030] Each of the plurality of correction data may include information on a correction value corresponding to each of a plurality of voltage values ​​or a plurality of current values ​​in the control signal. The correction value may be, for example, a coefficient for correcting the period of the detection signal. The processing circuit can correct the detection signal by determining the period from the detection signal and multiplying the period by the correction value.

[0031] Each of the plurality of correction data may include information on a correction value corresponding to each of a plurality of phases or a plurality of timings in the frequency modulation by the control signal, and the processing circuit can appropriately correct the detection signal based on the correction data including such correction value information.

[0032] Each of the plurality of correction data may include information on a correction value for changing a sampling timing when the processing circuit samples the detection signal, and the processing circuit can correct the detection signal by determining the sampling timing of the detection signal in accordance with the correction value.

[0033] Each of the plurality of correction data may be data indicating a correction table or a correction function for determining a correction value used to correct the detection signal. The processing circuit can appropriately correct the detection signal based on the correction value indicated by the correction data corresponding to the current operating state.

[0034] The processing circuit may create the plurality of correction data and store each of the plurality of correction data in the storage device in association with the operating state of the corresponding light source. By such an operation, the above-described operation of selecting correction data according to the operating state and correcting the detection signal during measurement can be realized.

[0035] According to another embodiment of the present disclosure, a method is executed by a computer in a system including a measurement device. The measurement device includes a light source that emits frequency-modulated light, an interference optical system that separates the light emitted from the light source into a reference light and an output light and generates interference light between the reference light and reflected light resulting from reflection of the output light by an object, a photodetector that receives the interference light and outputs a detection signal corresponding to the intensity of the interference light, and a storage device that stores a plurality of correction data used to correct the detection signal, each of the plurality of correction data being associated with a corresponding one of a plurality of different operating states of the light source. The method includes sending a control signal to the light source that sweeps the frequency of the light emitted from the light source, correcting the detection signal based on one or more correction data selected from the plurality of correction data depending on the operating state of the light source, and generating and outputting measurement data related to the distance and / or velocity of the object based on the corrected detection signal.

[0036] According to yet another embodiment of the present disclosure, there is provided a computer program executed by a computer in a system including a measurement apparatus. The measurement apparatus includes a light source that emits frequency-modulated light, an interference optical system that separates the light emitted from the light source into a reference light and an output light and generates interference light between the reference light and reflected light resulting from reflection of the output light by an object, a photodetector that receives the interference light and outputs a detection signal corresponding to the intensity of the interference light, and a storage device that stores a plurality of correction data used to correct the detection signal, each of the plurality of correction data being associated with a corresponding one of a plurality of different operating states of the light source. The computer program causes the computer to correct the detection signal based on one or more correction data selected from the plurality of correction data depending on the operating state of the light source, and to generate and output measurement data related to the distance and / or velocity of the object based on the corrected detection signal.

[0037] In this disclosure, all or part of a circuit, unit, device, component, or part, or all or part of a functional block in a block diagram, may be implemented by one or more electronic circuits, including, for example, a semiconductor device, a semiconductor integrated circuit (IC), or an LSI (large scale integration). An LSI or IC may be integrated on a single chip or may be configured by combining multiple chips. For example, functional blocks other than memory elements may be integrated on a single chip. While the terms LSI and IC are used here, the term may be changed depending on the degree of integration, and may be referred to as a system LSI, a VLSI (very large scale integration), or an ULSI (ultra large scale integration). A field programmable gate array (FPGA), which is programmable after LSI fabrication, or a reconfigurable logic device, which can reconfigure connections within an LSI or set up circuit partitions within an LSI, may also be used for the same purpose.

[0038] Furthermore, all or part of the functions or operations of a circuit, unit, device, component, or section can be implemented by software processing. In this case, the software is recorded on one or more non-transitory recording media such as ROMs, optical disks, hard disk drives, etc., and when the software is executed by a processor, the functions specified in the software are performed by the processor and peripheral devices. A system or device may include one or more non-transitory recording media on which software is recorded, a processor, and necessary hardware devices, such as interfaces.

[0039] The embodiments of the present disclosure will be described in more detail below. Note that the embodiments described below are all comprehensive or specific examples. The numerical values, shapes, components, component placement and connection configurations, steps, and step order shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, components that are not recited in the independent claims that represent the highest concepts are described as optional components. Furthermore, each figure is a schematic diagram and is not necessarily an exact illustration. Furthermore, in each figure, substantially identical or similar components are denoted by the same or similar reference numerals, and redundant explanations may be omitted or simplified.

[0040] (First embodiment) A measurement device according to a first exemplary embodiment of the present disclosure will be described. The measurement device of this embodiment is a distance measuring device that measures the distance to an object using FMCW-LiDAR technology. The measurement device may measure the speed of the object in addition to or instead of the distance. The measurement device may be mounted on a moving object such as an autonomous vehicle, an automated guided vehicle (AGV), an unmanned aerial vehicle (UAV), or a mobile robot. The measurement device may be mounted on any device and used, not limited to moving objects.

[0041] <Configuration> Fig. 2 is a block diagram showing a schematic configuration of the measurement device 100 according to this embodiment. In Fig. 2, thick arrows represent the flow of light, and thin arrows represent the flow of signals or data. Fig. 2 also shows an object 300, the object of which distance and / or speed is to be measured. The object 300 may be any object, such as an obstacle, a person, or a moving body (e.g., an automobile, a motorcycle, a mobile robot, or a drone).

[0042] The measurement device 100 shown in Fig. 2 includes a light source 110, an interference optical system 120, a photodetector 130, a processing circuit 140, and a storage device 150. The light source 110 can change the frequency of the emitted light in response to a control signal output from the processing circuit 140. The interference optical system 120 separates the light emitted from the light source 110 into reference light and output light, and generates interference light by causing the reference light to interfere with the reflected light generated when the output light is reflected by the object 300. The interference light is incident on the photodetector 130. The detailed configurations of the light source 110 and the interference optical system 120 will be described later.

[0043] The photodetector 130 receives the interference light and generates and outputs an electrical signal corresponding to the intensity of the interference light. This electrical signal will be referred to hereinafter as a "detection signal." The photodetector 130 includes one or more light-receiving elements. The light-receiving elements include photoelectric conversion elements such as photodiodes. The photodetector 130 may also be a sensor, such as an image sensor, that includes multiple light-receiving elements.

[0044] The processing circuit 140 is an electronic circuit that controls the light source 110 and performs processing based on the detection signal output from the photodetector 130. The processing circuit 140 may include a control circuit that controls the light source 110 and a signal processing circuit that performs signal processing based on the detection signal. The processing circuit 140 may be configured as a single circuit or may be a collection of multiple separate circuits. The processing circuit 140 sends a control signal to the light source 110. The control signal periodically changes the frequency of the light emitted from the light source 110 within a predetermined range. In other words, the control signal is a signal that sweeps the frequency of the light emitted from the light source 110. The control signal is a signal that inputs a voltage or current that periodically fluctuates with a certain amplitude to the light source 110. The processing circuit 140 acquires the detection signal output from the photodetector 130 while the light source 110 is emitting frequency-modulated light and corrects the detection signal according to the operating state of the light source 110. The processing circuit 140 corrects the detection signal based on correction data stored in the storage device 150. Based on the corrected detection signal, processing circuit 140 determines the distance to object 300 and / or the velocity of object 300. Processing circuit 140 generates and outputs data indicating the distance and / or velocity. This data will be referred to hereinafter as "measurement data."

[0045] The storage device 150 includes any storage medium, such as a semiconductor memory, a magnetic disk, or an optical disk. The storage device 150 stores correction data used in the correction process executed by the processing circuit 140. The correction data in this embodiment includes multiple correction tables. Each of the multiple correction tables is recorded in association with a corresponding one of multiple different operating states of the light source 110. FIG. 2 illustrates an example of a correction table corresponding to a first operating state of the light source 110 and a correction table corresponding to a second operating state of the light source 110. Details of these correction tables will be described later. Each correction table is an example of correction data. The correction data is not limited to correction tables and may be data in any format, such as a function that defines the correspondence between the operating state and the correction value of the detection signal. The storage device 150 also stores a computer program executed by the processing circuit 140.

[0046] The processing circuit 140 and the memory device 150 may be integrated on a single circuit board or may be provided on separate circuit boards. The functions of the processing circuit 140 may be distributed across multiple circuits. At least a portion of the functions of the processing circuit 140 may be realized by an external computer installed in a location remote from the other components. Such an external computer may control the operations of the light source 110 and the photodetector 130 and / or perform signal processing based on the detection signal output from the photodetector 130 via a wired or wireless communication network.

[0047] When measuring the distance to the object 300, the processing circuit 140 performs the following operations. A control signal is sent to the light source 110, causing the light source 110 to emit light whose frequency changes periodically within a predetermined range. From the plurality of correction tables stored in the storage device 150, one or more correction tables are selected according to the current operating state of the light source 110. Corrects the waveform of the detection signal based on the selected correction table. The frequency of the beat signal is calculated by frequency analysis based on the corrected waveform. The calculated frequency is converted into a distance value, and measurement data including that distance value is output externally.

[0048] The measurement data is output to, for example, a display device 210. When the measurement device 100 is mounted on a moving body, the measurement data may be output to a control device 220 that controls the operation (e.g., steering, speed, etc.) of the moving body. The measurement data may be recorded in the storage device 150 or an external storage device.

[0049] Next, a more detailed configuration example of the light source 110 and the interference optical system 120 will be described.

[0050] 3 is a block diagram showing an example configuration of the light source 110 and the interference optical system 120. In this example, the light source 110 includes a drive circuit 111 and a light-emitting element 112. The drive circuit 111 receives a control signal output from the processing circuit 140, generates a drive current signal corresponding to the control signal, and inputs the drive current signal to the light-emitting element 112. The light-emitting element 112 may be an element that emits laser light with high coherence, such as a semiconductor laser element. The light-emitting element 112 emits laser light whose frequency is modulated in response to the drive current signal.

[0051] The frequency of the laser light emitted from the light emitting element 112 is modulated at a constant period. The frequency modulation period may be, for example, 1 microsecond (μs) or more and 10 milliseconds (ms) or less. The frequency modulation amplitude may be, for example, 100 MHz or more and 1 THz or less. The wavelength of the laser light may be, for example, in the near-infrared wavelength range of 700 nm or more and 2000 nm or less. In sunlight, the amount of near-infrared light is less than the amount of visible light. Therefore, by using near-infrared light as the laser light, the influence of sunlight can be reduced. Depending on the application, the wavelength of the laser light may be in the visible light wavelength range of 400 nm or more and 700 nm or less, or in the ultraviolet light wavelength range.

[0052] FIG. 4 shows examples of a control signal output from the processing circuit 140 and a drive current signal output from the drive circuit 111. Parts (a) and (b) of FIG. 4 show examples of the waveforms of the control signal and the drive current signal, respectively. The control signal applies a voltage that fluctuates with a predetermined period and a predetermined amplitude to the drive circuit 111 of the light source 110. For example, as shown in part (a) of FIG. 4, the voltage of the control signal can be modulated into a sawtooth waveform. The voltage of the control signal is not limited to a sawtooth waveform, but may also be modulated into a triangular waveform. A control signal whose voltage repeatedly changes linearly, such as a sawtooth or triangular waveform, can sweep the frequency of the light emitted from the light-emitting element 112 in a manner that is close to linear. However, as mentioned above, the frequency sweep is not completely linear. The amplitude of the modulation waveform of such a control signal is called the modulation voltage amplitude, and the voltage at the center of the modulation range is called the bias voltage. The control signal applies a voltage that fluctuates around the bias voltage to the drive circuit 111 of the light source 110.

[0053] The drive circuit 111 converts the control signal into a drive current signal and drives the light-emitting element 112 with the drive current signal. As shown in part (b) of Figure 4, the drive current signal changes with a waveform corresponding to the control signal. The modulation range, i.e., amplitude, of the drive current signal is called the modulation current amplitude, and the current in the center of the modulation range is called the bias current. When the voltage of the control signal increases, the drive current signal increases, and the frequency of the laser light emitted from the light-emitting element 112 increases (i.e., the wavelength becomes shorter). Conversely, when the voltage of the control signal decreases, the drive current signal decreases, and the frequency of the laser light emitted from the light-emitting element 112 decreases (i.e., the wavelength becomes longer).

[0054] The interference optical system 120 in the example shown in FIG. 3 includes a splitter 121, a mirror 122, and a collimator 123. The splitter 121 splits the laser light emitted from the light emitting element 112 of the light source 110 into reference light and output light, and combines the light reflected from the object 300 with the reference light to generate interference light. The mirror 122 reflects the reference light back to the splitter 121. The collimator 123 includes a collimating lens and irradiates the output light with a nearly parallel divergence angle onto the object 300. Note that the interference optical system 120 is not limited to the configuration shown in FIG. 3 and may be, for example, a fiber optical system. In this case, a fiber coupler may be used as the splitter 121. The reference light does not necessarily need to be reflected by the mirror 122; for example, the reference light may be returned to the splitter 121 by routing an optical fiber.

[0055] 5 is a block diagram showing a configuration example of a measurement apparatus 100 in which the interference optical system 120 is a fiber optical system. In the example shown in FIG. 5, the interference optical system 120 includes a first fiber splitter 125, a second fiber splitter 126, and an optical circulator 127. The first fiber splitter 125 splits the laser light 20 emitted from the light source 110 into a reference light 21 and an output light 22. The first fiber splitter 125 inputs the reference light 21 to the second fiber splitter 126 and inputs the output light 22 to the optical circulator 127. The optical circulator 127 inputs the output light 22 to a collimator 123. The optical circulator 127 also inputs reflected light 23, which is generated when the output light 22 is irradiated onto the object 300, into the second fiber splitter 126. The second fiber splitter 126 causes the interference light 24 between the reference light 21 and the reflected light 23 to enter the photodetector 130. The collimator 123 shapes the beam shape of the output light 22 and outputs the output light 22 towards the object 300.

[0056] The measurement device 100 may further include an optical deflector that changes the direction of the emitted light. FIG. 6 is a block diagram showing an example of the measurement device 100 that includes an optical deflector 170. The optical deflector 170 may be, for example, a MEMS ( microelectromechanical system) mirror or galvanometer mirror. The optical deflector 170 can change the output direction of the output light 22 by changing the angle of the mirror according to a command from the processing circuit 140. This enables beam scanning. The optical deflector 170 is not limited to the above configuration and may be, for example, a beam scanning device using an optical phased array and a slow-light waveguide, as described in International Publication No. 2019 / 130720.

[0057] Next, the FMCW-LiDAR technology used in this embodiment will be briefly described with reference to FIGS. 7A and 7B.

[0058] FIG. 7A is a schematic diagram illustrating an example of the temporal change in the frequency of the reference light and the reflected light when the object 300 is stationary. Here, we will explain an example in which the frequency changes in a triangular waveform. In FIG. 7A, the solid line represents the reference light, and the dashed line represents the reflected light. The frequency of the reference light shown in FIG. 7A increases linearly over one period and then decreases linearly by the same amount. The frequency of the reflected light is shifted along the time axis compared to the frequency of the reference light by the amount of time it takes for the output light to be emitted from the measurement device 100, reflected by the object 300, and returned. Therefore, the interference light between the reference light and the reflected light has a frequency corresponding to the difference between the frequency of the reflected light and the frequency of the reference light. The double arrow in FIG. 7A represents the difference between the two frequencies. The photodetector 130 outputs a signal indicating the intensity of the interference light. This signal is called a beat signal. The frequency of the beat signal, i.e., the beat frequency, is equal to the above-mentioned frequency difference. The processing circuit 140 can calculate the distance from the measurement device 100 to the object 300 based on the beat frequency.

[0059] FIG. 7B is a diagram illustrating the temporal change in the frequency of the reference light and the reflected light when the object 300 approaches the measurement device 100. When the object 300 approaches, the frequency of the reflected light shifts in the increasing direction along the frequency axis due to Doppler shift compared to when the object 300 is stationary. The amount of frequency shift of the reflected light depends on the magnitude of the component of the velocity vector at a certain part of the object 300 projected onto the direction of the reflected light. The beat frequency differs when the frequencies of the reference light and the reflected light increase linearly and when they decrease linearly. In the example shown in FIG. 7B, the beat frequency when both frequencies decrease linearly is higher than the beat frequency when both frequencies increase linearly. The processing circuit 140 can calculate the velocity of the object 300 based on the difference between these beat frequencies. When the object 300 moves away from the measurement device 100, the frequency of the reflected light shifts in the decreasing direction along the frequency axis compared to when the object 300 is stationary. In this case as well, the velocity of the object 300 can be calculated based on the difference in beat frequency between when the frequencies of the reference light and the reflected light increase linearly and when they decrease linearly.

[0060] <Operation> The operation of the measurement device 100 of this embodiment will be described below.

[0061] The operation of the measurement device 100 of this embodiment can be roughly divided into two processes: (1) calibration and (2) distance measurement. Calibration is performed, for example, by a person in charge at the manufacturer (hereinafter referred to as the "operator") before shipping the measurement device 100. Distance measurement is mainly performed by the user of the measurement device 100.

[0062] <Calibration operation> Fig. 8 is a flowchart showing an example of the calibration operation. The calibration operation includes steps S401 to S409 shown in Fig. 8. The operation of each step will be described below. Here, an example will be described in which the operating state of the light source 110 is determined by the modulation voltage amplitude of the control signal.

[0063] (Step S401) While the measurement device 100 is stationary, the operator places a stationary reference object at a specific distance from the measurement device 100. The reference object may be, for example, a mirror, a diffuse reflector, or an actual object to be measured.

[0064] (Step S402) The processing circuit 140 determines the modulation voltage amplitude of the control signal. The value of this amplitude may be determined by an operator, and the processing circuit 140 may set it according to the operator's operation. The amplitude value may be determined, for example, by creating a list of multiple values ​​that may actually be used by the user of the measurement device 100 and selecting one value from the list. If the measurement device 100 can operate by switching between multiple distance ranges (i.e., measurable distance ranges), different modulation voltage amplitudes may be set according to the respective distance measurement ranges.

[0065] (Step S403) The processing circuit 140 sends a control signal to the light source 110, causing the light source 110 to emit frequency-modulated light. This operation is performed in accordance with an instruction from an operator.

[0066] (Step S404) The processing circuit 140 acquires a detection signal from the photodetector 130. While light is being emitted from the light source 110, the photodetector 130 outputs a detection signal corresponding to the intensity of the interference light. The time length of the detection signal acquired by the processing circuit 140 may be, for example, approximately 1 to 50 times the modulation period. When averaging the detection signal to improve the S / N ratio of the detection signal, the processing circuit 140 acquires the detection signal for a relatively long time and repeats the process of averaging the detection signal over a predetermined period of time that is sufficiently shorter than the modulation period. The processing circuit 140 includes, for example, an analog-to-digital (A / D) converter and a memory. The processing circuit 140 digitizes the detection signal waveform using, for example, the A / D converter and stores the digitized signal in memory.

[0067] (Step S405) The processing circuit 140 stops the emission of light from the light source 110 by stopping the transmission of the control signal. This step can be performed in accordance with an instruction from an operator. Alternatively, the processing circuit 140 may automatically stop the emission in accordance with a predetermined program. Note that, if the calibration operation is to be continuously repeated, the light may continue to be emitted.

[0068] (Step S406) The processing circuit 140 analyzes the period of the detection signal. The period analysis method may, for example, extract the maximum value of an upwardly convex portion or the minimum value of a downwardly convex portion in the waveform of the detection signal, and define one period as the period from the maximum value to the next maximum value, or the period from the minimum value to the next minimum value. Alternatively, the period analysis method may extract zero-crossing points (i.e., points where the value of the detection signal changes from positive to negative or negative to positive), and define one period as the period from a positive-to-negative zero-crossing point to the next positive-to-negative zero-crossing point, or from a negative-to-positive zero-crossing point to the next negative-to-positive zero-crossing point.

[0069] Figure 9 is a graph showing an example of the analysis results of the detection signal period. In this example, a waveform showing the relationship between the control signal voltage and the detection signal voltage is plotted. The control signal voltage V i , V i+1 , V i+2 , ... i , P i+1 , P i+2 ,... In this example, the control signal voltage is V i From the point of V i+1 The time length up to this point is the period P i It is defined as follows.

[0070] Next, the processing circuit 140 calculates the control signal voltage V i , V i+1 , V i+2 , and the period P at that voltage i , P i+1 , Pi+2 , , , and an approximate expression for the plotted points is obtained. The approximate expression is, for example, a polynomial of degree two or higher, and can be obtained using, for example, the least squares method.

[0071] (Step S407) The processing circuit 140 creates a correction table indicating the relationship between the voltage of the control signal and the period ratio based on the generated approximation formula, and writes the correction table to the storage device 150. FIGS. 11A and 11B are diagrams showing examples of the correction table. The correction table may be recorded in a format indicating the relationship between the control signal and the period ratio for each different operating state of the light source (in this example, the modulation voltage amplitude). FIGS. 11A and 11B show examples of correction tables associated with different first and second operating states of the light source, respectively. In this example, two correction tables are recorded, but three or more correction tables may be recorded. Furthermore, the correction data indicating the relationship between the control signal and a correction value such as the period ratio may be recorded in another format, such as a function, instead of the correction table format.

[0072] The period ratio may be, for example, a value obtained by normalizing the period by a predetermined constant so that the beat frequency after correcting the waveform of the detection signal is a value theoretically derived from the distance to the reference object, the modulation period, the modulation frequency range, and the speed of light. Figure 12 shows an example of the waveform of the detection signal before and after correction. The constant may be set to a value such that the beat frequency of the waveform of the detection signal after correction is a constant value 1 / Pm.

[0073] The relationship between the beat frequency and the distance can be stored in the memory of the processing circuit 140 or in the storage device 150 in the form of a conversion table such as that shown in Fig. 13. Such a conversion table is used when the processing circuit 140 calculates the distance value during the distance measurement operation.

[0074] The period ratio may be determined by normalizing the period ratio for each operating state using an appropriate constant. In this case, the relationship between the beat frequency and the distance for each operating state may be recorded in the memory of the processing circuit 140 as correction data such as a conversion table or a function, as shown in Figures 14A and 14B.

[0075] (Steps S408 and S409) The processing circuit 140 determines whether or not all calibrations have been performed for the modulation voltage amplitude values ​​required when the measuring device 100 is actually used. Because the modulation voltage amplitude value is a continuous quantity, it determines whether or not all calibrations have been performed for voltage values ​​at regular intervals (e.g., 0.1 V) within a predetermined amplitude value range. If all calibrations have been performed, the calibration process ends. If all calibrations have not been performed, the processing circuit 140 updates the modulation voltage amplitude and repeats steps S403 to S407.

[0076] By performing the above-described calibration operation, the processing circuit 140 can store in the storage device 150 correction tables corresponding to a plurality of different operating states.

[0077] It should be noted that the operating state of the light source 110 depends not only on the modulation voltage amplitude of the control signal but also on other parameters, such as the bias voltage of the control signal or the temperature of the light source 110. When the operating state of the light source 110 is determined based on a parameter other than the modulation voltage amplitude, steps S402 and S409 are performed for that parameter.

[0078] <Distance measurement operation> Next, an example of a distance measurement operation by the measurement device 100 will be described. Here, too, an example will be described in which the operating state of the light source 110 is determined by the modulated voltage amplitude of the control signal.

[0079] Fig. 15 is a flowchart showing an example of a distance measurement operation. When performing a distance measurement operation, the processing circuitry 140 in this embodiment executes the operations of steps S1001 to S1011 shown in Fig. 15. The operation of each step will be described below.

[0080] (Step S1001) Processing circuit 140 first determines the modulation voltage amplitude of the control signal. The value of this amplitude may be determined, for example, by a user of measurement device 100 and set by processing circuit 140 in accordance with the user's operation. Measurement device 100 may be configured to operate by switching between multiple distance measurement ranges (i.e., measurable distance ranges). In this case, the user sets an appropriate distance measurement range according to the environment in which the target object is present.

[0081] (Step S1002) The processing circuit 140 sends a control signal to the light source 110, causing the light source 110 to emit frequency-modulated light. This operation is performed in accordance with a user's instructions.

[0082] (Step S1003) The processing circuit 140 acquires the detection signal output from the photodetector 130. As in step S404 in the calibration operation shown in Fig. 8, when averaging the signal to improve the S / N ratio of the signal, the detection signal is acquired for a relatively long time, and the process of averaging the detection signal is repeated over a predetermined time that is sufficiently shorter than the modulation period.

[0083] (Step S1004) The processing circuit 140 stops the emission of light from the light source 110 by stopping the transmission of the control signal. This step can be performed in accordance with an instruction from the user. Alternatively, the processing circuit 140 may automatically stop the emission in accordance with a predetermined program. Note that if the distance measurement operation is to be continuously repeated, the light may continue to be emitted.

[0084] (Steps S1005 and S1006) Processing circuit 140 searches storage device 150 to determine whether a correction table corresponding to the determined modulation voltage amplitude exists. The correction table is data that defines the relationship between the control signal voltage and the period ratio (i.e., the correction value), as shown in, for example, Figures 11A and 11B. If a corresponding correction table exists in storage device 150, processing circuit 140 reads the correction table from storage device 150.

[0085] (Step S1007) If there is no correction table corresponding to the determined modulation voltage amplitude, the processing circuit 140 creates a correction table. The processing circuit 140 can create a correction table, for example, by the following method. First, the processing circuit 140 selects two correction tables from multiple correction tables stored in the storage device 150 that correspond to the two modulation voltage amplitudes closest to the determined modulation voltage amplitude. The processing circuit 140 can generate a correction table corresponding to the determined modulation voltage amplitude by performing interpolation based on these correction tables. For example, assume that the current modulation voltage amplitude is A0, the modulation voltage amplitudes corresponding to the two selected correction tables are A1 and A2, and the correction values ​​corresponding to the amplitudes A1 and A2 are R1 and R2, respectively. In this case, the correction value R0 corresponding to the current modulation voltage amplitude A0 can be calculated, for example, by R0 = R1 + (A0 - A1) × (R2 - R1) / (A2 - A1).

[0086] (Step S1008) The processing circuit 140 corrects the waveform of the detection signal based on the correction table. This correction suppresses fluctuations in the period of the beat signal, for example, as shown in FIG.

[0087] (Step S1009) The processing circuit 140 performs frequency analysis on the waveform of the corrected detection signal. In this step, for example, the processing circuit 140 performs a Fourier transform on the waveform of the detection signal to generate a frequency spectrum. Then, the frequency at which the maximum peak of the frequency spectrum is obtained is determined, and this frequency is set as the beat frequency.

[0088] (Step S1010) The processing circuit 140 converts the beat frequency into a distance value and calculates it. In this conversion process, the processing circuit 140 converts the beat frequency into a distance value as shown in FIG. 3、 A conversion table such as that shown in FIG. 14A or FIG. 14B is read from a memory in the processing circuit 140 and used.

[0089] (Step S1011) The processing circuitry 140 outputs measurement data including information on the calculated distance values ​​to an external device such as the display device 210.

[0090] Through the above operations, processing circuit 140 can generate distance data for object 300. When measuring distance continuously, the operations from steps S1001 to S1011 are repeated continuously. When measuring the speed of object 300 in addition to the distance, a triangular wave control signal is used instead of the sawtooth wave control signal shown in Fig. 4, and the speed can be calculated by the method described with reference to Figs. 7A and 7B.

[0091] As described above, in this embodiment, the processing circuit 140 corrects the detection signal using the correction table corresponding to the modulation voltage amplitude of the control signal as correction data, and then performs frequency analysis based on the corrected detection signal. This reduces the fluctuation in the frequency of the beat signal contained in the detection signal and makes it possible to calculate the distance value, thereby enabling more accurate measurement of the distance to the target object.

[0092] (Second embodiment) Next, a measurement device according to a second embodiment will be described.

[0093] <Configuration> 16 is a block diagram showing a schematic configuration of a measurement device 100 according to the second embodiment. The difference from the first embodiment is that the measurement device 100 further includes a temperature sensor 160. The temperature sensor 160 measures the temperature of the light source 110 and sends the temperature value data to the processing circuit 140.

[0094] The nonlinearity of the frequency modulation of the light emitted from the light source 110 when the voltage of the control signal is swept is affected by changes in the temperature of the light-emitting element 112. Therefore, the temperature sensor 160 can be positioned so that it can measure the temperature of the light-emitting element 112 as directly as possible. The temperature of the light-emitting element 112 may be estimated indirectly by attaching the temperature sensor 160 to the measurement device 100 and measuring the ambient temperature. However, to improve measurement accuracy and temporal tracking capability, the temperature sensor 160 may be positioned so that its temperature detection unit is fixed to the light-emitting element 112 itself or to a heat sink to which the light-emitting element 112 is fixed.

[0095] <Operation> Fig. 17 is a flowchart showing the calibration operation in the second embodiment. The difference from the calibration operation in the first embodiment shown in Fig. 8 is that steps S402, S408, and S409 are replaced with steps S1201, S1202, and S1203, respectively. The operations of these steps will be described below.

[0096] In step S1201, the temperature of the light source 110 is set. The temperature value can be set to any value within the temperature range in which the measurement device 100 is expected to operate. The temperature of the light source 110 can be controlled, for example, by driving a Peltier element affixed to the light emitting element 112.

[0097] In step S1202, it is determined whether or not all calibrations have been performed for the operating temperature range of the measurement device 100. Because the operating temperature is a continuous quantity, it is determined whether or not calibration has been completed for all temperatures at 10°C intervals within the operating temperature range. If calibration has not been completed for all temperatures, the process proceeds to step S1203, where the processing circuitry 140 updates the temperature setting of the light source 110 and repeats the operations from step S403 to step S407.

[0098] Fig. 18 is a flowchart showing an example of distance measurement operation in the second embodiment. The differences from the distance measurement operation in the first embodiment shown in Fig. 15 are that step S1001 is omitted, step S1301 is added between steps S1003 and S1004, and the correction table referenced in step S1302 is different. The operations of these steps will be described below.

[0099] In step S1301, the temperature sensor 160 measures the temperature of the light source 110, and the processing circuit 140 acquires the temperature value. The temperature is acquired at intervals of, for example, about 0.1 to 1 second. To reduce variations in the measurement value, the temperature values ​​measured multiple times may be averaged.

[0100] In step S1302, the processing circuit 140 searches whether a correction table corresponding to the measured temperature exists in the storage device 150. If a corresponding correction table exists in the storage device 150, that correction table is used (step S1006), and if a corresponding correction table does not exist, a correction table is created (step S1007). The processing in step S1007 is the same as in the first embodiment.

[0101] With the above-described configuration and operation, the processing circuit 140 in this embodiment corrects the detection signal using the correction table corresponding to the temperature of the light source 110 as correction data, and performs frequency analysis based on the corrected detection signal. This makes it possible to obtain a distance value by reducing fluctuations in the frequency of the beat signal contained in the detection signal, enabling more precise measurement of the distance to the object.

[0102] The correction table is not limited to the above format, and may be any correction table that corrects nonlinear variations in the period of the detection signal. For example, as shown in FIG. 19A, a correction table may be used that specifies the sampling time intervals for the control voltage (i.e., virtually non-uniform sampling intervals) for the A / D conversion sampling timing, which is normally equal time intervals. The detection signal reconstructed by changing the sampling timing in this way may be used as the corrected detection signal. Also, as shown in FIG. 19B, a correction table may be used that specifies the period ratio for the phase of frequency modulation. Alternatively, as shown in FIG. 19C, a correction table may be used that specifies the sampling time interval for the phase of frequency modulation. In each of the examples in FIGS. 19B and 19C, a correction table that specifies the relationship between the timing (i.e., time) of frequency modulation and a correction value such as the sampling interval or period ratio may be used instead of the phase. Furthermore, in each of the above examples, a correction table that specifies the relationship between the drive current and the period ratio or sampling interval may be used instead of the control voltage. Instead of the above-described correction table, the approximation formula itself may be stored as a correction function in a storage device such as a memory, and the processing circuit 140 may be configured to correct the detection signal based on the correction function corresponding to the operating state. Furthermore, the operating state of the light source 110 may be determined by any combination of two or more of the control voltage or drive current, the temperature, and the bias voltage or bias current. In this case, correction data may be created and recorded for each combination.

[0103] (Example) Next, the results of experiments conducted to verify the effects of the embodiments of the present disclosure will be described.

[0104] <Creating a correction table for different modulation voltage amplitudes> 20 is a graph showing the results of creating a correction table when calibration is performed with two types of modulation voltage amplitude based on the configuration and operation of the first embodiment. b The voltage is 1.7V, the light source temperature is 27°C, and the modulation voltage amplitude Vm were set to 0.7 V and 1.0 V. The approximate equation was created using a cubic function. The normalization constant for calculating the period ratio was determined to an appropriate value. In this example, the normalization constant was determined so that the sum of the period ratios over the analysis period for each operating state was equal. Therefore, the absolute value of the beat frequency was not the same for each operating state. As shown in Figure 20, it was confirmed that the shapes of the correction table graphs differed between the two operating states.

[0105] 21A to 21C are graphs showing the results of applying different correction tables to three detection signals corresponding to three operating states with different modulation voltage amplitudes, and determining frequency spectra through frequency analysis.

[0106] Figure 21A shows the V m The detection signal obtained when V = 0.7V m The figure shows the result of applying the correction table corresponding to =0.7 V. A beat signal appears in the area indicated by the arrow in the figure.

[0107] Figure 21B shows the V m The detection signal obtained when V = 1.0V is m = 0.7V (i.e., corresponding to a different operating state). The normalization constant was set to an appropriate value, so the absolute value of the beat signal frequency is shifted, but what is noteworthy is that the line width of the beat signal has become thicker. This is thought to be because, due to the application of a correction table corresponding to a different operating state, periodic fluctuations remained in the detection signal after correction. If the line width of the beat signal is thick, errors will occur when calculating the peak frequency, reducing the accuracy of the distance value. Simply correcting the absolute value of the beat signal frequency after frequency analysis will not narrow the line width of the beat signal, and therefore will not improve the accuracy of the distance value.

[0108] Figure 21C shows the V m The detection signal obtained when V = 1.0V is m= 1.0V. It can be seen that the line width of the beat signal is narrower than in the example of Figure 21B. In this state, the distance value can be determined with high accuracy simply by correcting the absolute value of the frequency of the beat signal after frequency analysis.

[0109] In this embodiment, the correction table is created using the modulation voltage amplitude as a parameter, but since the control signal and the drive current have a corresponding relationship as described above, the amplitude of the drive current may be used instead of the modulation voltage amplitude.

[0110] <Creating a correction table for different bias voltages> 22 is a graph showing an example of the results of creating a correction table when calibrating with two types of bias voltages. In this example, the modulation voltage amplitude V m The light source temperature is 27°C and the bias voltage V b were set to 1.3 V and 2.0 V. From the results in Fig. 22, it was confirmed that the shapes of the graphs in the correction table differed between the two operating states.

[0111] In this embodiment, the correction table is created using the bias voltage as a parameter, but since the control signal and the drive current have a corresponding relationship as described above, the bias current may be used instead of the bias voltage.

[0112] <Creating a correction table for different temperatures> 23 is a graph showing an example of the results of creating a correction table when calibration is performed at two different temperatures. m is 1.3V, bias voltage V b The voltage was set to 2.0 V in common, and the light source temperatures were set to 15° C. and 40° C. From the results in FIG. 23, it was confirmed that the shapes of the graphs in the correction table differed between the two operating states.

[0113] <Creating a correction table using interpolation> Figure 24 shows two already existing correction tables (V m=0.7V and V m =1.0V), and now V m 10 is a diagram showing an example of a correction table for V = 0.85V. m =0.7V and V m In the control voltage range where there are period ratio values ​​for both V = 1.0 V and V = 1.0 V, interpolate the period ratios from both tables. m The cycle ratio was calculated for V = 0.85 V. Outside this range, the trend of the plot inside the range was extrapolated to V m A cycle ratio of =0.85V was calculated.

[0114] Fig. 25 is a diagram showing an example in which a new correction table for a temperature of 25°C is created from two existing correction tables (in this example, for temperatures of 15°C and 40°C). For clarity, Fig. 25 is partially enlarged. The period ratio of the correction table for a temperature of 25°C was calculated by interpolation from the period ratios for temperatures of 15°C and 40°C.

[0115] Even if the operating state parameters are continuous in this way, it is possible to create a correction table with intermediate values ​​(i.e., corresponding to operating states not stored in the storage device) based on a correction table created discretely. Creating and using such a correction table with intermediate values ​​can further improve the accuracy of distance measurement.

[0116] <Other experimental examples> 26 is a diagram showing a measurement device 2601 in another experimental example for verifying the effects of an embodiment of the present disclosure. Unlike the configuration of the measurement device 100 shown in FIG. 2, the measurement device 2601 receives a dummy detection signal output from an external sine wave oscillator 2602 as input to the processing circuit 140 instead of the detection signal from the photodetector 130. Here, the dummy detection signal is a sine wave, and its amplitude and frequency are set to values ​​close to those of the original detection signal (e.g., 1 Vpp and 50 MHz). Similarly to the above-described embodiment, the storage device 150 in this experimental example also stores different correction tables depending on the operating state of the light source 110.

[0117] First, let us consider a case where the measurement operation of the measuring device 2601 is performed without applying the correction table. In this case, it is assumed that the display device 210 displays a constant distance value corresponding to the frequency of the dummy detection signal. It is also assumed that the variation in the value when the distance value is acquired multiple times is constant as long as the amount of frequency fluctuation of the dummy detection signal does not change.

[0118] Next, let us consider a case where the measurement device 2601 performs a measurement operation while applying different correction tables depending on the operating state of the light source 110. Here, let us consider a case where the modulation voltage amplitude of the light source 110 is V ma and V mb The modulation voltage amplitude is changed in two ways, and the measurement device 2601 performs measurement operations while applying the correction table corresponding to each modulation voltage amplitude. ma and V mb The values ​​of are, for example, 0.7 V and 1.0 V, respectively. ma When distance values ​​are acquired multiple times with the setting set to , the variance of the values ​​is σ a and the modulation voltage amplitude is V mb When distance values ​​are acquired multiple times with the setting set to , the variance of the values ​​is σ b Let's say.

[0119] When such an experiment is performed, the variance of the distance values ​​is σ a ≠σ b The reason is that when different correction tables are applied to the same dummy detection signal, the spectral linewidth of the corrected detection signal changes, and the variation in distance values ​​also changes according to the change in linewidth. On the other hand, in a conventional device that applies correction to the beat signal frequency after frequency analysis, the spectral linewidth of the original beat signal does not change even if different corrections are applied to different modulation voltage amplitudes, so the variation in distance values ​​is σ a =σ b This becomes:

[0120] From the above experiments, it can be seen that in the measurement device according to the embodiment of the present disclosure, the variation in distance values ​​is controlled by applying different correction tables to the detection signal before frequency analysis depending on the operating state of the light source 110.

[0121] In the above-described embodiment of the present disclosure, a correction is made to the detection signal before frequency analysis, thereby suppressing a decrease in measurement accuracy due to nonlinearity in the frequency modulation of laser light. A similar problem can be addressed by correcting the control signal itself for frequency modulation of laser light to eliminate nonlinearity. However, such a method requires nonlinear correction of the control signal to the light source. While generating a nonlinear control signal and controlling the current or voltage using that control signal are difficult, the correction of the detection signal before frequency analysis is performed at the signal processing level, making it simple and highly accurate. Therefore, the embodiment of the present disclosure enables measurements to be performed more easily and accurately than conventional methods. [Industrial Applicability]

[0122] The measurement device disclosed herein can be used in applications such as FMCW lidar systems mounted on mobile objects such as automated guided vehicles (AGVs), automobiles, unmanned aerial vehicles, or industrial robots, or on monitoring devices. [Explanation of symbols]

[0123] 100 Rangefinder 110 Light source 111 Drive circuit 112 Light-emitting element 120 Interference Optical System 121 Switch 122 Mirror 123 Collimator 124 Collimating Lens 125 1st Fiber Splitter 126 Second Fiber Splitter 127 Optical Circulator 130 Photodetector 140 Processing Circuit 150 Storage device 160 Temperature Sensor 170 Optical deflector 210 Display device 220 Control device 300 Objects

Claims

1. a light source that emits frequency-modulated light; an interference optical system that separates the light emitted from the light source into reference light and output light, and generates interference light between the reference light and reflected light generated when the output light is reflected by an object; a photodetector that receives the interference light and outputs a detection signal corresponding to the intensity of the interference light; a storage device that stores a plurality of correction data used to correct the detection signal, each of the plurality of correction data being associated with a corresponding one of a plurality of different operating states of the light source; a processing circuit that sends a control signal to the light source to sweep the frequency of the light emitted from the light source, corrects the detection signal based on one or more correction data selected from the plurality of correction data in accordance with an operating state of the light source, and generates and outputs measurement data related to the distance and / or speed of the object based on the corrected detection signal; A measuring device comprising:

2. Further comprising a temperature sensor that measures the temperature of the light source; the plurality of correction data include two or more first correction data, each of which is associated with a corresponding one of two or more operating states in which the temperature of the light source is different; the processing circuit corrects the detection signal based on one or more first correction data selected from the two or more first correction data in accordance with the temperature of the light source measured by the temperature sensor; The measurement device according to claim 1 .

3. the control signal is a signal that inputs a periodically varying voltage or current to the light source; the plurality of correction data include two or more second correction data, each of which is associated with a corresponding one of two or more operating states in which the amplitude of the voltage or the current of the control signal is different; the processing circuit corrects the detection signal based on one or more second correction data selected from the two or more second correction data in accordance with the current amplitude of the voltage or the current. The measurement device according to claim 1 .

4. the control signal is a signal that inputs a voltage that periodically fluctuates around a certain bias voltage or a current that periodically fluctuates around a certain bias current to the light source, the plurality of correction data include two or more third correction data, each of which is associated with a corresponding one of two or more operating states in which the bias voltage or the bias current of the control signal is different; the processing circuit corrects the detection signal based on one or more third correction data selected from the two or more third correction data in accordance with the current bias voltage or the current bias current. The measurement device according to claim 1 .

5. 5. A measurement device as described in any one of claims 1 to 4, wherein, when correction data corresponding to the current operating state of the light source is not stored in the storage device, the processing circuit generates correction data corresponding to the current operating state based on at least one of the plurality of correction data stored in the storage device, and corrects the detection signal based on the generated correction data.

6. 6. A measurement device as described in any one of claims 1 to 5, wherein, when correction data corresponding to the current operating state of the light source is not stored in the storage device, the processing circuit selects two correction data associated with two operating states that are closest to the current operating state from the plurality of correction data stored in the storage device, generates correction data corresponding to the current operating state by interpolation processing using the two selected correction data, and corrects the detection signal based on the generated correction data.

7. The measurement device according to claim 1 , wherein each of the plurality of correction data includes information on a correction value corresponding to each of a plurality of voltage values ​​or a plurality of current values ​​in the control signal.

8. The measurement device according to claim 1 , wherein each of the plurality of correction data includes information on a correction value corresponding to each of a plurality of phases or a plurality of timings in frequency modulation by the control signal.

9. 9. The measurement device according to claim 1, wherein each of the plurality of correction data includes information on a correction value for changing a sampling timing when the processing circuit samples the detection signal.

10. 10. The measurement device according to claim 1, wherein each of the plurality of correction data is data indicating a correction table or a correction function for determining a correction value used to correct the detection signal.

11. The measurement device according to claim 1 , wherein the processing circuitry creates the plurality of pieces of correction data and stores each of the plurality of pieces of correction data in the storage device in association with an operating state of the corresponding light source.

12. 1. A computer-implemented method in a system including a metrology device, comprising: The measuring device is a light source that emits frequency-modulated light; an interference optical system that separates the light emitted from the light source into reference light and output light, and generates interference light between the reference light and reflected light generated when the output light is reflected by an object; a photodetector that receives the interference light and outputs a detection signal corresponding to the intensity of the interference light; a storage device that stores a plurality of correction data used to correct the detection signal, each of the plurality of correction data being associated with a corresponding one of a plurality of different operating states of the light source; Equipped with The method comprises: sending a control signal to the light source to sweep the frequency of the light emitted from the light source; correcting the detection signal based on one or more correction data selected from the plurality of correction data in accordance with an operating state of the light source; generating and outputting measurement data relating to the distance and / or velocity of the object based on the corrected detection signal; A method comprising:

13. A computer program executed by a computer in a system including a measurement device, The measuring device is a light source that emits frequency-modulated light; an interference optical system that separates the light emitted from the light source into reference light and output light, and generates interference light between the reference light and reflected light generated when the output light is reflected by an object; a photodetector that receives the interference light and outputs a detection signal corresponding to the intensity of the interference light; a storage device that stores a plurality of correction data used to correct the detection signal, each of the plurality of correction data being associated with a corresponding one of a plurality of different operating states of the light source; Equipped with The computer program causes the computer to: correcting the detection signal based on one or more correction data selected from the plurality of correction data in accordance with an operating state of the light source; generating and outputting measurement data relating to the distance and / or velocity of the object based on the corrected detection signal; A computer program that executes

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