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

Abstract

This measurement device comprises a light source, correction optical system, interference optical system, light reception device, storage device, and processing circuit. The interference optical system separates the light emitted from the light source into reference light and output light and generates first interference light that is interference light between the reference light and reflected light that is produced by the reflection of the output light by an object and second interference light that is interference light between the reference light and reflected light that is produced by the reflection of the output light by the correction optical system. The light reception device outputs a first detection signal corresponding to the intensity of the first interference light and a second detection signal corresponding to the intensity of the second interference light. The processing device transmits, to the light source, a control signal for sweeping the frequency of the light emitted from the light source, updates correction data stored in the storage device on the basis of the second detection signal, and generates measurement data on the basis of the updated correction data and the first detection signal.

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 light reflected 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 light reflected from a moving target can be used to calculate the target's velocity. For example, the velocity of the target can be calculated based on the difference in the frequency of the beat signal during the up-chirp period, when the frequency of the light emitted from the light source increases, and during the down-chirp period, when the frequency decreases.

[0004] Unlike ToF (Time of Flight) lidars, FMCW lidars detect the frequency of the electrical signal output from a photodetector, which means that their ranging results are less susceptible to the effects of ambient light.However, it has been thought that the accuracy of FMCW lidar ranging depends on how linearly the optical frequency can be modulated with respect to time.

[0005] 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.

[0006] Patent Document 2 discloses an FMCW radar device that corrects the frequency of an interference signal using correction data corresponding to multiple distances and multiple ambient temperatures, thereby improving detection accuracy.

[0007] 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 and enables accurate distance measurement.

[0008] Patent Document 4 discloses an ophthalmic device used to identify the position of a measurement target site inside a human eye. This ophthalmic device includes a measurement optical system, a reference optical system, a calibration optical system, a light-receiving element, and a computing device. The measurement optical system irradiates light from a light source into the interior of the subject's eye and guides the reflected light. The reference optical system guides the light from the light source to generate reference light. The calibration optical system guides the light from the light source. The light-receiving element receives measurement interference light, which is a combination of the reflected light guided by the measurement optical system and the reference light guided by the reference optical system, and calibration interference light, which is a combination of the calibration light guided by the calibration optical system and the reference light guided by the reference optical system. The computing device identifies the position of the measurement target site inside the subject's eye from the measurement interference light and calibration interference light received by the light-receiving element. The document describes that this configuration allows the position of the measurement target site inside the subject's eye to be accurately identified even if the characteristics of the interference light change over time. [Prior art documents] [Patent documents]

[0009] [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 [Patent Document 4] Japanese Patent Application Laid-Open No. 2013-180111 Summary of the Invention [Problem to be solved by the invention]

[0010] The present disclosure provides a technology that can suppress a decrease in the accuracy of distance and / or speed measurements in a measurement device that uses FMCW technology, even if the output characteristics of the light source change due to the passage of time, changes in the usage environment, or changes in the operating state of the light source. [Means for solving the problem]

[0011] A measurement device according to one aspect of the present disclosure includes a light source, a calibration optical system, an interference optical system, a light-receiving device, a storage device, and a processing circuit. The light source emits frequency-modulated light. The calibration optical system has at least one reflecting surface. The interference optical system separates the light emitted from the light source into reference light and output light, and generates a first interference light, which is interference light between the reference light and the reflected light generated when the output light is reflected by an object, and a second interference light, which is interference light between the reference light and the reflected light generated when the output light is reflected by the calibration optical system. The light-receiving device includes at least one photodetector and outputs a first detection signal corresponding to the intensity of the first interference light and a second detection signal corresponding to the intensity of the second interference light. The storage device stores correction data used to correct the first detection signal. The processing circuit sends a control signal to the light source that sweeps the frequency of the light emitted from the light source, updates the correction data based on the second detection signal, corrects the first detection signal based on the updated correction data, and generates and outputs measurement data regarding the distance and / or speed of the object based on the corrected first detection signal.

[0012] 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]

[0013] According to an embodiment of the present disclosure, even if the output characteristics of the light source change due to the passage of time, changes in the usage environment, or changes in the operating state of the light source, it is possible to suppress a decrease in the accuracy of measuring distance and / or speed. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 shows data obtained from an experiment conducted by the present inventors. [Figure 2] FIG. 2 is a block diagram illustrating a schematic configuration of a measurement device according to an exemplary 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 5A] FIG. 5A is a diagram showing an example of a calibration optical system. [Figure 5B] FIG. 5B is a diagram showing another example of the calibration optical system. [Figure 5C] FIG. 5C is a diagram showing yet another example of the calibration optical system. [Figure 6] FIG. 6 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 7] FIG. 7 is a block diagram showing an example of a measurement device equipped with an optical deflector. [Figure 8A] FIG. 8A 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 8B] FIG. 8B 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 9] FIG. 9 is a flowchart showing an example of the calibration operation. [Figure 10A] FIG. 10A is a graph showing an example of the analysis results of the period of the detection signal. [Figure 10B] FIG. 10B 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 another embodiment. [Figure 17] FIG. 17 is a block diagram showing a schematic configuration of a measurement device according to still another embodiment. [Figure 18] FIG. 18 is a block diagram showing a schematic configuration of a measurement device according to still another 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 block diagram showing a schematic configuration of a measurement device according to another embodiment. [Figure 21] FIG. 21 is a block diagram showing a schematic configuration of a measurement device according to a first modified example of the embodiment of the present disclosure. [Figure 22] FIG. 22 is a block diagram showing a schematic configuration of a measurement device according to a second modified example of the embodiment of the present disclosure. [Figure 23] FIG. 23 is a flowchart showing a calibration operation of a measurement apparatus according to a third modified example of the embodiment of the present disclosure. [Figure 24] FIG. 24 is a flowchart showing the calibration operation of the measurement apparatus according to the fourth modified example of the embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0015] (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 this nonlinearity can change due to various factors, such as changes in the operating state of the light source, changes in the usage environment, and the passage of time. This phenomenon will be explained below with reference to Figure 1.

[0016] FIG. 1 shows an example of data obtained from an experiment conducted by the inventors. In this experiment, a semiconductor laser light source placed at a stationary point emitted laser light toward a stationary target, a reflector. The voltage of a control signal input to the light source (hereinafter also referred to as the "control voltage") was linearly swept over a predetermined voltage range Vm (hereinafter also referred to as the "modulation voltage amplitude") at a predetermined period, causing the light source to emit laser light whose frequency was periodically modulated. An interference optical system was used to cause interference between the reflected light from the reflector and the emitted light from the light source, and the interference light was detected by a photodetector, and the acquired signal was recorded.

[0017] 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 m1The 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

[0018] 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 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 obtained by detecting the interference light between the reflected light generated when a laser beam is emitted from a light source toward a stationary reflector and the reference light traveling from the light source toward the photodetector via an optical system. m1 and V m2 The time axes in these graphs are the same as those in graphs (a) and (b). Graphs (a) to (d) show the signal changes over one cycle of the control voltage. Hereinafter, the cycle of the control voltage may be referred to as the "modulation cycle."

[0019] 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.

[0020] Graph (g) in Figure 1 shows the relationship between the two modulation voltage amplitudes V m1 and V m2 1 plots the instantaneous frequency corresponding to the control signal voltage.

[0021] In this experiment, the 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 in the cases of (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.

[0022] 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.

[0023] When the beat frequency fluctuates with respect to the control voltage or time, the distance to the target cannot be uniquely determined. A similar phenomenon can occur when the characteristics of the light source change due to various factors, such as changes in the operating environment (e.g., temperature or humidity), the passage of time, or vibration. Even if the characteristics of the light source change, it is necessary to suppress any deterioration in measurement accuracy.

[0024] In order to solve the above 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.

[0025] A measurement apparatus according to an embodiment of the present disclosure includes a light source, a calibration optical system, an interference optical system, a light-receiving device, a storage device, and a processing circuit. The light source emits frequency-modulated light. The calibration optical system has at least one reflecting surface. The interference optical system separates the light emitted from the light source into reference light and output light, and generates a first interference light, which is interference light between the reference light and reflected light generated when the output light is reflected by an object, and a second interference light, which is interference light between the reference light and reflected light generated when the output light is reflected by the calibration optical system. The light-receiving device includes at least one photodetector and outputs a first detection signal corresponding to the intensity of the first interference light and a second detection signal corresponding to the intensity of the second interference light. The storage device stores correction data used to correct the first detection signal. The processing circuit sends a control signal to the light source that sweeps the frequency of the light emitted from the light source, updates the correction data based on the second detection signal, corrects the first detection signal based on the updated correction data, and generates and outputs measurement data regarding the distance and / or speed of the object based on the corrected first detection signal.

[0026] According to the above configuration, the processing circuit updates the correction data based on the measurement result of the second interference light using the calibration optical system, and can appropriately correct the first detection signal based on the updated correction data. This makes it possible to measure distance and / or velocity with high accuracy even if the output characteristics of the light source change due to, for example, aging, changes in the usage environment, or changes in the operating state of the light source.

[0027] The correction data may be created, for example, by a calibration performed by the manufacturer of the measurement device before shipment and recorded in the storage device. The operation of updating the correction data is performed by a user of the measurement device. The user can cause the measurement device to execute an operation to update the correction data before or at any timing during measurement. Updating the correction data may be an operation of modifying and overwriting existing correction data, an operation of rewriting existing correction data with new correction data, or an operation of recording new correction data while leaving the existing correction data. Furthermore, if no existing correction data exists in the storage device, the correction data may be updated by creating new correction data. The operation of creating new correction data may be performed during calibration performed by the manufacturer of the measurement device before shipment. In this disclosure, for convenience, the operation of creating new correction data is also referred to as "updating" the correction data.

[0028] The interference optical system may include an optical switch that switches between a first state in which the output light is emitted to the object and a second state in which the output light is emitted to the calibration optical system. The processing circuit may operate in a measurement mode in which the distance and / or velocity of the object is measured and a calibration mode in which the correction data is updated. In the measurement mode, the processing circuit may set the optical switch to the first state, correct the first detection signal based on the correction data, and generate the measurement data based on the corrected first detection signal. In the calibration mode, the processing circuit may set the optical switch to the second state, and update the correction data based on the second detection signal.

[0029] According to the above configuration, by switching between measurement mode and calibration mode, it is possible to update the correction data and measure distance and / or speed using a common optical system and a common photodetector, which makes it possible to reduce the size and manufacturing costs of the measurement device.

[0030] The measurement device may further include a time counter that measures the usage time of the light source. The processing circuit may switch between the measurement mode and the calibration mode based on the usage time of the light source. For example, the processing circuit may switch from the measurement mode to the calibration mode when the usage time of the light source since the last time the correction data was updated exceeds a certain threshold. This makes it possible to automatically switch to the calibration mode at an appropriate time and update the correction data when the usage time of the light source becomes longer. As a result, it is possible to suppress a decrease in measurement accuracy due to an increase in the usage time of the light source.

[0031] The measurement device may further include a temperature sensor that measures the temperature of the light source. The processing circuit may switch between the measurement mode and the calibration mode based on the temperature of the light source. For example, if the measured light source temperature is outside a predetermined range, the processing circuit may switch from the measurement mode to the calibration mode. The predetermined range may be set to, for example, a range that includes the temperature when the correction data was created or last updated. The processing circuit may switch from the measurement mode to the calibration mode if the measured light source temperature is below or exceeds a threshold. With this configuration, even if the characteristics of the light source change due to a change in the light source temperature, the correction data can be appropriately corrected to prevent a decrease in measurement accuracy.

[0032] The processing circuit may switch between the measurement mode and the calibration mode in response to a user input. For example, when a user uses an input device built into or connected to the measurement device to perform an operation to instruct the start of the calibration mode, the processing circuit may switch from the measurement mode to the calibration mode. This allows the user to update the correction data at any timing.

[0033] The processing circuit may switch to the calibration mode when, in the measurement mode, the operating state of the light source is changed by changing the control signal. For example, the processing circuit may switch to the calibration mode when the amplitude of the control voltage applied to the light source is changed to change the range of measurable distances. This makes it possible to mitigate the effect of nonlinear frequency modulation, which occurs differently depending on the operating state of the light source, and enables more accurate measurement of distance and / or velocity.

[0034] The storage device may further store a reference distance corresponding to the optical path length of the calibration optical system. The processing circuit may update the correction data based on the second detection signal and the reference distance. The reference distance may be, for example, the optical distance from a light source to a specific reflective surface of the calibration optical system. The processing circuit may generate, as updated correction data, correction data for correcting the second detection signal so that a distance theoretically derived from the frequency of the second detection signal coincides with the reference distance.

[0035] A measurable distance range may be set for the measurement device. The reference distance may be included in the distance range. For example, if the measurable distance range is from 0 m to 100 m, the reference distance may be set to a distance within that range, such as 50 m. In this way, by setting the reference distance to a distance close to the distance actually measured, the correction data can be more appropriately corrected.

[0036] The interference optical system may include an optical fiber, a mirror, or a multi-pass cell. By using an interference optical system including these optical elements, it becomes easier to ensure a relatively long optical path length, thereby improving the quality of the calibration.

[0037] The 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.

[0038] The correction data may include information on correction values ​​corresponding to 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.

[0039] The 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.

[0040] The correction data may be data representing a correction table or a correction function for determining a correction value used to correct the detection signal, and the processing circuit can appropriately correct the detection signal based on the correction value determined based on the correction table or the correction function.

[0041] 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 light whose frequency is periodically modulated; a calibration optical system having at least one reflecting surface; an interference optical system that separates the light emitted from the light source into reference light and output light and generates a first interference light that is an interference light between the reference light and the light reflected from an object when the output light is reflected; and a second interference light that is an interference light between the reference light and the light reflected from the calibration optical system when the output light is reflected; a light-receiving device that includes at least one photodetector and outputs a first detection signal corresponding to the intensity of the first interference light and a second detection signal corresponding to the intensity of the second interference light; and a storage device that stores correction data used to correct the first detection signal. The method includes updating the correction data based on the second detection signal, correcting the first detection signal based on the updated correction data, and generating and outputting measurement data related to the distance and / or velocity of the object based on the corrected first detection signal.

[0042] 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 computer program is stored on a non-transitory computer-readable recording medium. The measurement apparatus includes: a light source that emits light whose frequency is periodically modulated; a calibration optical system having at least one reflecting surface; an interference optical system that separates the light emitted from the light source into reference light and output light and generates first interference light, which is interference light between the reference light and the light reflected from the output light by an object; and second interference light, which is interference light between the reference light and the light reflected from the calibration optical system by the output light; a light-receiving device that includes at least one photodetector and outputs a first detection signal corresponding to the intensity of the first interference light and a second detection signal corresponding to the intensity of the second interference light; and a storage device that stores correction data used to correct the first detection signal. The computer program causes the computer to perform the following: updating the correction data based on the second detection signal; correcting the first detection signal based on the updated correction data; and generating and outputting measurement data regarding the distance and / or speed of the object based on the corrected first detection signal.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] (Embodiment) A measurement device according to an 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.

[0047] <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, and a display device 210 and a control device 220 connected to the measurement device 100. 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).

[0048] 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, a storage device 150, and a calibration optical system 180. 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 a reference light and an output light, and generates interference light by causing the reference light to interfere with the output light reflected by the object 300 or the calibration optical system 180. The interference light between the reference light and the reflected light reflected by the object 300 is referred to as "first interference light." The interference light between the reference light and the reflected light reflected by the calibration optical system 180 is referred to as "second interference light." These interference lights are incident on the photodetector 130. The calibration optical system 180 is used in a calibration operation to update the correction data stored in the storage device 150. The calibration optical system 180 includes one or more optical elements having at least one reflecting surface. Detailed configurations of the light source 110, the interference optical system 120, and the calibration optical system 180 will be described later.

[0049] 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 is referred to as a "detection signal." A detection signal based on the first interference light is referred to as a "first detection signal," and a detection signal based on the second interference light is referred to as a "second 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 be a sensor including multiple light-receiving elements, such as an image sensor. In this embodiment, one photodetector 130 detects both the first interference light and the second interference light. As in other embodiments described below, a photodetector that detects the first interference light and a photodetector that detects the second interference light may be provided separately. In this case, an interference optical system that generates the first interference light and an interference optical system that generates the second interference light may be provided separately. In this specification, a device including at least one photodetector is referred to as a "light-receiving device." The light-receiving device generates and outputs a first detection signal corresponding to the intensity of the first interference light and a second detection signal corresponding to the intensity of the second interference light.

[0050] 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 causes the light source 110 to periodically change the frequency of the light emitted 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 at a certain amplitude to the light source 110.

[0051] The processing circuit 140 in this embodiment operates by switching between a measurement mode in which the distance and / or velocity of the object 300 is measured and a calibration mode in which correction data is updated. In the measurement mode, the processing circuit 140 acquires a first detection signal output from the photodetector 130 while the light source 110 is emitting frequency-modulated light, and corrects the first detection signal based on correction data stored in the storage device 150. The correction data may be, for example, data that defines the correspondence between the voltage of the control signal and a correction value for correcting the period or frequency of the detection signal. Details of the correction data will be described later. The processing circuit 140 determines the distance to the object 300 and / or the velocity of the object 300 based on the first detection signal corrected using the correction data. The processing circuit 140 generates and outputs data indicating the distance and / or velocity. This data will be referred to as "measurement data" hereinafter. On the other hand, in the calibration mode, the processing circuit 140 acquires the second detection signal output from the photodetector 130 while the light source 110 is emitting frequency-modulated light, and corrects the correction data based on the second detection signal and a reference distance set according to the optical path length of the calibration optical system 180. The processing circuit 140 updates the existing correction data with the corrected correction data. In subsequent measurements, the processing circuit 140 corrects the first detection signal using the updated correction data to generate measurement data.

[0052] 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 performed by the processing circuit 140 and data on the reference distance corresponding to the optical path length of the calibration optical system 180. The correction data may include, for example, one or more correction tables. The correction data may also include multiple correction tables. Each of the multiple correction tables may be recorded in association with a corresponding one of multiple different operating states of the light source 110. Here, the operating state of the light source 110 may be a state characterized by, for example, the aforementioned modulation voltage amplitude, bias voltage, or temperature of the light source 110. The correction data is not limited to a correction table and may be data in any format, such as a function. The storage device 150 also stores a computer program executed by the processing circuit 140.

[0053] 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.

[0054] Next, examples of the configurations of the light source 110, the interference optical system 120, and the calibration optical system 180 will be described.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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).

[0059] The interference optical system 120 in the example shown in FIG. 3 includes a splitter 121, a mirror 122, an optical switch 128, 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 reference light with light reflected from the object 300 or the calibration optical system 180 to generate interference light. The mirror 122 reflects the reference light back to the splitter 121. The optical switch 128 switches the output destination of the output light between the collimator 123 and the calibration optical system 180. That is, the optical switch 128 can switch between a first state in which the output light is emitted to the object 300 and a second state in which the output light is emitted to the calibration optical system 180. The operation of the optical switch 128 is controlled by the processing circuit 140. In the measurement mode, the processing circuit 140 sets the optical switch 128 to the first state, causing the output light 22 to enter the collimator 123. In the calibration mode, the processing circuit 140 sets the optical switch 128 to the second state, causing the output light 22 to enter the calibration optical system 180. The collimator 123 includes a collimating lens, and irradiates the output light output from the optical switch 128 at a nearly parallel divergence angle onto the object 300. The calibration optical system 180 has at least one reflective surface. The calibration optical system 180 reflects the output light output from the optical switch 128 from the reflective surface and returns the reflected light to the optical switch 128.

[0060] 5A to 5C are diagrams schematically illustrating examples of the calibration optical system 180. FIG. 5A shows an example of the calibration optical system 180 including an optical fiber 180A. In this example, output light from the optical switch 128 is reflected by a reflecting surface 181 at the end of the optical fiber 180A and returns to the optical switch 128. FIG. 5B shows an example of the calibration optical system 180 including a mirror 180B. In this example, output light from the optical switch 128 is reflected by the reflecting surface of the mirror 180B and returns to the optical switch 128. FIG. 5C shows an example of the calibration optical system 180 including a multipass cell 180C. In this example, output light from the optical switch 128 is multiple-reflected by the reflecting surfaces of multiple mirrors included in the multipass cell and returns to the optical switch 128.

[0061] A measurable distance range (e.g., 0 m to 50 m) is set for the measurement apparatus 100. A reference distance determined according to the optical path length is set for the calibration optical system 180 and recorded in the storage device 150. The calibration optical system 180 can be designed so that the reference distance falls within the measurable distance range of the measurement apparatus 100. For example, in the example of FIG. 5A , the optical path length from the optical switch 128 to the reflecting surface 181 at the end of the optical fiber 180A can be set as the reference distance. In the example of FIG. 5B , the optical path length from the optical switch 128 to the reflecting surface of the mirror 180B can be set as the reference distance. In the example of FIG. 5C , half the optical path length from the optical switch 128 through the multipath cell 180C and back to the optical switch 128 can be set as the reference distance. The calibration optical system 180 can be designed so that these reference distances fall within the range of the distances measurable by the measurement apparatus 100. With this configuration, the optical path length of light traveling from optical switch 128 through calibration optical system 180 and back to optical switch 128 is closer to the optical path length expected during measurement. This reduces the effect of reflection noise over short distances within the device and avoids problems such as the beat frequency being too low to measure due to a distance that is too short. As an example, consider a case where the measurement distance range of measurement device 100 is 0 to 20 m. In this case, the length of optical fiber 180A in the example of FIG. 5A, the optical path length from optical switch 128 to mirror 180B in the example of FIG. 5B, and half of the optical path length from optical switch 128 through multipath cell 180C and back to optical switch 128 in the example of FIG. 5C can be designed to values ​​ranging from several tens of centimeters to several tens of meters. In the example of FIG. 5A, the optical path length may be increased by bending or rolling optical fiber 180A. In the example of FIG. 5B, the optical path length may be increased by combining not only mirror 180B but also other mirrors or other optical elements.

[0062] 3, the interference optical system 120 may include, for example, a fiber optical system. In that 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, and the reference light may be returned to the splitter 121 by, for example, routing an optical fiber.

[0063] FIG. 6 is a block diagram showing a configuration example of a measurement apparatus 100 in which the interference optical system 120 includes a fiber optical system. In the example shown in FIG. 6, the interference optical system 120 includes a first fiber splitter 125, a second fiber splitter 126, and an optical circulator 127 in addition to a collimator 123 and an optical switch 128. The first fiber splitter 125 splits the laser light 20 emitted from the light source 110 into reference light 21 and 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 the optical switch 128 and inputs reflected light 23 from the optical switch 128 to the second fiber splitter 126. The second fiber splitter 126 inputs interference light 24 between the reference light 21 and the reflected light 23 to the photodetector 130. The optical switch 128, in accordance with a command from the processing circuit 140, causes the output light 22 to be incident on one of the collimator 123 and the calibration optical system 180. The collimator 123 shapes the beam shape of the output light 22 and emits the output light 22 towards the target 300.

[0064] The measurement device 100 may further include an optical deflector that changes the direction of the emitted light. FIG. 7 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 a 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. The optical deflector 170 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.

[0065] Next, the FMCW-LiDAR technology used in this embodiment will be briefly described with reference to FIGS. 8A and 8B.

[0066] FIG. 8A 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 explain an example in which the frequency changes in a triangular waveform. In FIG. 8A, the solid line represents the reference light, and the dashed line represents the reflected light. The frequency of the reference light shown in FIG. 8A increases linearly during the modulation 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 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. 8A 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.

[0067] FIG. 8B is a diagram schematically illustrating an example of temporal changes in the frequencies 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 an 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 linearly increase and decrease. In the example shown in FIG. 8B, the beat frequency when both frequencies linearly decrease is higher than the beat frequency when both frequencies linearly increase. 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 a 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.

[0068] <Operation> The operation of the measurement device 100 of this embodiment will be described below.

[0069] The operation of the measuring device 100 of this embodiment can be broadly divided into two steps: (1) calibration and (2) measurement. Calibration is an operation performed by a user of the measuring device 100 to update the correction table. The correction table is generated in advance by the manufacturer before shipping the measuring device 100 and is recorded in the storage device 150. Measurement is an operation performed by a user of the measuring device 100 to measure the distance and / or speed to the target object 300.

[0070] <Calibration operation> Fig. 9 is a flowchart showing an example of the calibration operation. The calibration operation includes steps S310 to S350 shown in Fig. 9. The operation of each step will be described below. The calibration operation can be started in accordance with an instruction from the user, for example.

[0071] (Step S310) The processing circuit 140 switches the output destination of the optical switch 128 so that the output light is incident on the calibration optical system 180, and then sends a control signal to the light source 110. The modulation voltage amplitude, bias voltage, and modulation period of the control signal can be set to predetermined values ​​or values ​​specified by the user. In response to the control signal, the light source 110 begins emitting frequency-modulated light.

[0072] (Step S320) 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. The processing circuit 140 may average the detection signal to improve the S / N ratio of the detection signal. In this case, 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.

[0073] (Step S330) 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 according to an instruction from an operator. Alternatively, the processing circuit 140 may automatically stop the emission according to a predetermined program. Note that the light may continue to be emitted when repeating the calibration operation for a plurality of different operating conditions or when continuing to measure distance after updating the correction table.

[0074] (Step S340) The processing circuit 140 analyzes the period of the detection signal. For example, one method of analyzing the period is to identify the maximum point of the upwardly convex portion of the detection signal waveform or the minimum point of the downwardly convex portion, and define the period from the maximum point to the next maximum point or the period from the minimum point to the next minimum point as one period. Alternatively, if the detection signal values ​​are uniformly distributed between positive and negative values, the period may be determined based on zero-crossing points. A zero-crossing point is a point where the signal value changes from positive to negative or from negative to positive. The processing circuit 140 may extract zero-crossing points from the detection signal 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.

[0075] FIG. 10A is a graph showing an example of the analysis results of the period of the detection signal. In this graph, a waveform showing the relationship between the voltage of the control signal and the voltage of the detection signal 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.

[0076] Next, the processing circuit 140 adjusts the control signal voltage V i , V i+1 , V i+2 , and the period P at that voltage i , P i+1 , P i+2 , , , and find an approximate expression for the plotted points. The approximate expression is, for example, a polynomial of degree two or higher, and can be found using, for example, the least squares method.

[0077] (Step S350) Based on the generated approximation formula, the processing circuit 140 creates a correction table indicating the relationship between the voltage of the control signal and the period ratio, and updates the existing correction table recorded in the storage device 150 by overwriting the contents of the correction table. Note that instead of overwriting, the existing correction table may be left as it is and a new correction table may be recorded. At this time, the correction table may be recorded in association with a timestamp or information indicating the operating state at that time.

[0078] 11A and 11B are diagrams showing examples of correction tables. The correction tables may be recorded in a format showing 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 one, or three or more correction tables may be recorded. Furthermore, the format is not limited to a correction table, and correction data showing 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.

[0079] The period ratio may be a value obtained by normalizing the period by a predetermined constant so that the beat frequency calculated from the waveform of the corrected detection signal is a value theoretically derived from the optical path length, modulation period, modulation frequency range, and speed of light of the calibration optical system 180. 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 corrected detection signal is a constant value 1 / Pm.

[0080] 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.

[0081] The period ratio may be determined by normalizing the period ratio for each operating state with an appropriate constant. In this case, the relationship between the beat frequency and the distance for each operating state may be recorded as correction data such as a conversion table or function, as shown in Figures 14A and 14B.

[0082] By performing the above-described calibration operation, the processing circuit 140 can appropriately update the correction table according to the current state. When the correction table is first created before product shipment, the correction table can be created in the same manner as shown in FIG.

[0083] <Distance measurement operation> Next, an example of the measurement operation by the measurement device 100 will be described.

[0084] Fig. 15 is a flowchart showing an example of a measurement operation. When performing a measurement operation, the processing circuit 140 in this example executes the operations of steps S900 to S990 shown in Fig. 15. The operation of each step will be explained below. The measurement operation is started in accordance with an instruction from the user.

[0085] (Step S900) Processing circuit 140 first determines whether or not to perform a calibration operation to update the correction table. If a calibration operation is to be performed, the process proceeds to step S910. If a calibration operation is not to be performed, the process proceeds to step S920.

[0086] The calibration operation may be performed, for example, when there is a high possibility that a change has occurred in the characteristics of the light source 110. The characteristics of the light source 110 may change over time or depending on temperature, for example. Therefore, the processing circuit 140 may determine whether to perform the calibration operation based on the length of time the light source 110 has been used or the temperature of the light source 110. Alternatively, the processing circuit 140 may determine whether to perform the calibration operation in accordance with an instruction from a user.

[0087] FIG. 16 is a diagram illustrating an example configuration of a measurement device 100 that performs a calibration operation based on the usage time of the light source 110. In this example, the measurement device 100 includes a time counter 190 that measures the usage time of the light source 110. The usage time may be the time from when the light source 110 began to be used until the present, or the time from when the clock was last reset until the present. The time counter 190 outputs the measured time to the processing circuit 140. The processing circuit 140 may determine to perform calibration if the measured time exceeds a certain threshold (e.g., 10 days, 3 months, 1 year, etc.). In this way, the processing circuit 140 can switch between a measurement mode and a calibration mode based on the usage time of the light source 110.

[0088] FIG. 17 is a diagram illustrating an example configuration of a measurement device 100 that performs a calibration operation based on the temperature of the light source 110. In this example, the measurement device 100 includes a temperature sensor 160 that measures the temperature of the light source 110. The temperature sensor 160 may be positioned so as to measure the temperature of the light-emitting element 112 as directly as possible. For example, the temperature sensor 160 may be positioned so as to be fixed to the light-emitting element 112 itself or to a heat sink to which the light-emitting element 112 is fixed. The temperature sensor 160 outputs the measured temperature to the processing circuit 140. The processing circuit 140 may determine to perform calibration if the measured temperature exceeds a certain threshold value or if the measured temperature is below a certain threshold value. In this way, the processing circuit 140 can switch between a measurement mode and a calibration mode based on the temperature of the light source 110.

[0089] FIG. 18 is a diagram showing an example configuration of a measurement device 100 that performs a calibration operation in accordance with instructions from a user. In this example, the measurement device 100 is connected to an input device 200 that accepts input from a user. The input device 200 may be any input means, such as a button, a keyboard, or a touch screen. The input device 200 and the display device 210 may be configured as a single device. In this example, the processing circuit 140 performs the calibration operation in response to an input from the user using the input device 200. In this way, the processing circuit 140 can switch between a measurement mode and a calibration mode in response to an input from the user.

[0090] In addition to the above, the characteristics of the light source 110 may change due to various factors. For example, the characteristics of the light source 110 may change due to an impact. For this reason, the measurement device 100 may include a sensor such as a gyroscope that measures the magnitude of the impact. The processing circuit 140 may determine to perform a calibration operation when the measured magnitude of the impact or its cumulative value exceeds a threshold.

[0091] The characteristics of the light source 110 also depend on the modulation voltage amplitude, modulation current amplitude, bias voltage, bias current, or input power of the control signal. Therefore, the processing circuit 140 may determine to perform a calibration operation when the modulation voltage amplitude, modulation current amplitude, bias voltage, bias current, or input power of the control signal changes by a threshold value or more. Note that the modulation voltage amplitude, modulation current amplitude, bias voltage, bias current, and input power can be changed by user operation. In this way, the processing circuit 140 may switch to the calibration mode when the operating state of the light source 110 is changed by changing the control signal in the measurement mode.

[0092] (Step S910) Processing circuit 140 performs a calibration operation to correct the correction table. This calibration operation is the same as the operation shown in Fig. 9. Processing circuit 140 updates the correction table according to the current state by performing the operations from steps S310 to S350 shown in Fig. 9. After step S910, the process proceeds to step S920.

[0093] (Step S920) The processing circuit 140, with the output destination of the light from the optical switch 128 set to the collimator 123, sends a control signal to the light source 110, causing the light source 110 to emit frequency-modulated light. As a result, the target 300 is irradiated with the laser light.

[0094] (Step S930) The processing circuit 140 acquires the detection signal output from the photodetector 130. The photodetector 130 outputs a detection signal corresponding to the intensity of the interference light while light is being emitted from the light source 110. 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. The processing circuit 140 may average the detection signal to improve the S / N ratio of the detection signal. In this case, the processing circuit 140 acquires the detection signal for a relatively long period of time and repeats the process of averaging the detection signal over a predetermined period of time that is sufficiently shorter than the modulation period.

[0095] (Step S940) 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 distance measurement is to be continuously repeated, the light may continue to be emitted.

[0096] (Step S950) The processing circuit 140 acquires the correction table from the storage device 150. If the correction table is updated in step S910, the processing circuit 140 acquires the updated correction table. The correction table may be data that defines the relationship between the control signal voltage and the period ratio (i.e., the correction value), for example, as shown in FIG. 11A.

[0097] (Step S960) The processing circuit 140 corrects the period 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.

[0098] (Step S970) 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.

[0099] (Step S980) The processing circuit 140 converts the beat frequency into a distance value and calculates it. In this conversion process, the processing circuit 140 reads out and uses a conversion table such as that shown in Figure 13, 14A, or 14B from its internal memory.

[0100] (Step S990) The processing circuitry 140 outputs measurement data including information on the calculated distance values ​​to an external device such as the display device 210.

[0101] Through the above operations, processing circuit 140 can generate distance data of object 300. When measuring distance continuously, the operations shown in FIG. 15 may be repeated continuously. When measuring the speed of object 300 in addition to the distance, a triangular wave control signal may be used instead of the sawtooth wave control signal shown in FIG. 4. Processing circuit 140 can calculate the speed using the method described with reference to FIGS. 8A and 8B.

[0102] As described above, in this embodiment, the correction table can be appropriately updated even if the characteristics of the light source 110 change due to aging or changes in the operating environment. The processing circuit 140 corrects the detection signal based on the updated correction table and performs frequency analysis based on the corrected detection signal. This reduces the error in the frequency of the beat signal contained in the detection signal and enables the distance to be calculated, enabling more accurate measurement of the distance to the target object.

[0103] If the storage device 150 stores a plurality of correction tables according to the operating state or the use environment, the above calibration operation may be performed for each correction table.

[0104] The correction table is not limited to a format that defines the relationship between the control voltage and the period ratio. For example, as shown in FIG. 19A, a correction table that specifies the sampling time interval with respect to the control voltage may be used. In this case, the sampling timing of the A / D conversion, which is normally equal in time interval, is changed. The processing circuit 140 may use the detection signal reconstructed by changing the sampling timing in this way as the corrected detection signal. Also, as shown in FIG. 19B, a correction table that specifies the period ratio with respect to the phase of frequency modulation may be used. Alternatively, as shown in FIG. 19C, a correction table that specifies the sampling time interval with respect to the phase of frequency modulation may be used. In each of the examples of FIGS. 19B and 19C, a correction table that defines 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 defines the relationship between the drive current and the period ratio or sampling interval instead of the control voltage may be used. Instead of a correction table, an 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 at that time.

[0105] In the above embodiment, a common optical system and photodetector are used in both the measurement mode and the calibration mode. However, separate optical systems and photodetectors may be provided for each mode. FIG. 20 illustrates an example of such a configuration. The measurement device 100 shown in FIG. 20 includes a first photodetector 130A for measurement and a second photodetector 130B for calibration. The first photodetector 130A and the second photodetector 130B form a light receiving device. The interference optical system 120 includes an optical switch 129, a first optical system 120a for measurement, and a second optical system 120b for calibration. The optical switch 129 switches the output destination of the light output from the light source 110 between the first optical system 120a and the second optical system 120b in accordance with a command from the processing circuit 140. The first optical system 120a separates the light input from the optical switch 129 into output light and reference light, causes the output light to be incident on the object 300, and causes first interference light, which is interference light between the reflected light from the object 300 and the reference light, to be incident on the first photodetector 130A. The second optical system 120b separates the light input from the optical switch 129 into output light and reference light, causes the output light to be incident on the calibration optical system 180, and causes second interference light, which is interference light between the reflected light from the calibration optical system 180 and the reference light, to be incident on the second photodetector 130B.

[0106] 20, in measurement mode, processing circuit 140 directs the output of light from optical switch 129 to first optical system 120a, corrects the first detection signal output from first photodetector 130A based on the correction data, and generates measurement data based on the corrected first detection signal. Meanwhile, in calibration mode, processing circuit 140 directs the output of light from optical switch 129 to second optical system 120b, and updates the correction data based on the second detection signal output from second photodetector 130B. With this configuration and operation, it is possible to obtain the same effects as the above-described embodiments.

[0107] 20, since different photodetectors are used in the measurement mode and the calibration mode, an optical branching device such as a half mirror or a beam splitter may be used instead of the optical switch 129. In this case, the processing circuit 140 may update the correction data based on the detection signal output from the second photodetector 130B while performing the operation in the measurement mode. Such an operation allows the correction data to be updated while continuously measuring the distance or speed, thereby further improving the accuracy of the measurement.

[0108] (First Modification) A measurement device according to a first modified example of the embodiment of the present disclosure will be described. Fig. 21 is a block diagram showing the configuration of a measurement device 1001 according to this modified example. Below, differences between the measurement device 1001 of this modified example and the measurement device 100 shown in Fig. 7 will be described.

[0109] 7 uses reflected light 23 reflected by the calibration optical system 180 to generate or update correction data for detection signals. On the other hand, in the measurement device 1001 of this modified example, a calibration optical system 180 separate from the interference optical system 120 is not provided, and internally reflected light 231 generated in a part of the interference optical system 120 is used to generate or update correction data.

[0110] Internal reflection occurs on the path of the output light 22 in the interference optical system 120. Internal reflection can occur, for example, in optical elements constituting part of the interference optical system 120, in connections between optical elements and optical fibers, and in connections between optical fibers. For example, as shown in FIG. 21 , a portion of the output light 22 incident on the collimator 123 may return as internally reflected light 231 instead of being output toward the target 300. In this modification, the internally reflected light 231 in the collimator 123 is used to correct the detection signal described above. In this case, it can be said that the collimator 123 also serves as the calibration optical system 180. Because the optical path length of the path along which the internally reflected light 231 from the collimator 123 travels is known, a detection signal (i.e., a second detection signal) obtained by detecting interference light between the internally reflected light 231 and the reference light 21 can be used to perform processing similar to that of the above-described embodiment.

[0111] (Second Modification) A measurement apparatus according to a second modified example of the embodiment of the present disclosure will be described below. Fig. 22 is a block diagram showing the configuration of a measurement apparatus 1002 according to this modified example.

[0112] In the measurement device 1002 according to this modification, a portion of the output light 22 is branched by a portion of the interference optical system 120 and input into the path of the reflected light 23. For example, as shown in FIG. 22 , a portion of the output light 22 incident on the optical circulator 127 may not be output toward the collimator 123 but may leak into the path of the reflected light 23. Such leakage light 221 from the optical circulator 127 can be used to perform processing similar to that of the above-described embodiment and modifications. In this modification, the optical circulator 127 can be said to also serve as the calibration optical system 180.

[0113] (Third Modification) A measurement apparatus according to a third modified example of the embodiment of the present disclosure will be described. The configuration of the measurement apparatus of this modified example is the same as that of the measurement apparatus 100 of the above-described embodiment. However, the calibration operation of the measurement apparatus of this modified example is different from that of the above-described embodiment.

[0114] Fig. 23 is a flowchart showing the calibration operation of the measurement device according to this modification. The calibration operation of this modification differs from the operation shown in Fig. 9 in that, after step S340, in which period analysis is performed, step S360, in which the success or failure of the period analysis is determined, is executed. If it is determined in step S360 that the period analysis was successful ("Yes" in S360), the process proceeds to step S350, in which the correction table is updated.

[0115] On the other hand, if it is determined in step S360 that the period analysis has failed (if "No" in S360), the process proceeds to step S370. Specific examples of cases in which it is determined in step S360 that the period analysis has failed include, for example, (1) the period P detected during the period analysis performed in step S340 is too small, and i , P i+1 , P i+2 , ...exceeds a specified value, or (2) when the correlation between the period obtained by analyzing each detection signal and the detection signal falls below a specified value when period analysis of multiple detection signals is performed in step S340. In cases such as (1) and (2), the periods of the detection signals (i.e., peak intervals) vary greatly, making it difficult to analyze the trend of period changes. In step S370, a signal indicating the error content is output to an external device such as display device 210. Display device 210 displays, for example, "calibration error" or "analysis error."

[0116] According to the calibration operation of this modified example, it is possible to prevent the correction table from being updated with incorrect contents, and therefore it is possible to prevent a decrease in the measurement accuracy of the measurement device.

[0117] (Fourth Modification) A measurement device according to a fourth modified example of the embodiment of the present disclosure will be described. The configuration of the measurement device of this modified example is the same as that of the measurement device 100 of the above-described embodiment. However, the calibration operation of the measurement device of this modified example is different from that of the above-described embodiment.

[0118] 24 is a flowchart showing the calibration operation of the measurement device according to this modification. The calibration operation of this modification differs from the operation shown in FIG. 9 in that, after step S340, which performs period analysis, step S380 is added, in which an old correction table created based on the results of the previous period analysis is compared with a new correction table created based on the results of the current period analysis. Then, in step S390, a determination is made as to whether or not to select a new correction table based on the comparison result of the old and new correction tables in step S380. If a new correction table is selected ("Yes" in S390), the process proceeds to step S350, where the old correction table is updated to the new correction table. If a new correction table is not selected ("No" in S390), the process proceeds to end without updating the correction table.

[0119] The comparison of the new and old correction tables in step S380 is performed, for example, by performing correction processing on the detection signal using each of the new and old correction tables and comparing the full widths at half maximum of the frequency spectra obtained.

[0120] In step S390, for example, if the comparison result in step S380 shows that the full width at half maximum of the frequency spectrum of the detection signal corrected using the new correction table is smaller than the full width at half maximum of the frequency spectrum of the detection signal corrected using the old correction table, the new correction table is selected. Alternatively, the comparison result in step S380 may be displayed on display device 210, and the user may select the new correction table by inputting via the interface.

[0121] In the above-described embodiments and modifications of the present disclosure, correction is performed on 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, correction of the detection signal before frequency analysis is performed at the signal processing level, making it simple and highly accurate. Therefore, the embodiments of the present disclosure enable 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 128 Optical Switch 129 Switch 130 Photodetector 140 Processing Circuit 150 Storage device 160 Temperature Sensor 170 Optical deflector 180 Calibration optical system 180A optical fiber 180B Mirror 180C Multipass Cell 190 Time Counter 200 Input Device 210 Display device 220 Control device 300 Objects

Claims

1. a light source that emits frequency-modulated light; a calibration optical system having at least one reflective surface; an interference optical system that separates the light emitted from the light source into reference light and output light, and generates a first interference light that is an interference light between the reference light and reflected light generated when the output light is reflected by an object, and a second interference light that is an interference light between the reference light and reflected light generated when the output light is reflected by the calibration optical system; a light receiving device including at least one photodetector, and configured to output a first detection signal corresponding to the intensity of the first interference light and a second detection signal corresponding to the intensity of the second interference light; a storage device that stores correction data used to correct the first detection signal; a processing circuit that sends a control signal to the light source to sweep the frequency of the light emitted from the light source, updates the correction data based on the second detection signal, corrects the first detection signal based on the updated correction data, and generates and outputs measurement data related to the distance and / or speed of the object based on the corrected first detection signal; A measuring device comprising:

2. the interference optical system includes an optical switch that switches between a first state in which the output light is emitted to the object and a second state in which the output light is emitted to the calibration optical system, The processing circuitry The apparatus operates in a measurement mode for measuring the distance and / or velocity of the object and a calibration mode for updating the correction data; in the measurement mode, the optical switch is set to the first state, the first detection signal is corrected based on the correction data, and the measurement data is generated based on the corrected first detection signal; in the calibration mode, the optical switch is set to the second state, and the correction data is updated based on the second detection signal; The measurement device according to claim 1 .

3. a time counter for measuring the usage time of the light source; the processing circuit switches between the measurement mode and the calibration mode based on the usage time of the light source. The measurement device according to claim 2 .

4. Further comprising a temperature sensor that measures the temperature of the light source; The measurement device according to claim 2 or 3, wherein the processing circuit switches between the measurement mode and the calibration mode based on the temperature of the light source.

5. The measurement device according to claim 2 , wherein the processing circuit switches between the measurement mode and the calibration mode in response to an input from a user.

6. The measurement device according to claim 2 , wherein the processing circuit switches to the calibration mode when the operating state of the light source is changed by changing the control signal in the measurement mode.

7. the storage device further stores a reference distance corresponding to the optical path length of the calibration optical system; the processing circuit updates the correction data based on the second detection signal and the reference distance. The measuring device according to any one of claims 1 to 6.

8. a measurable distance range is set for the measurement device, The reference distance is included in the distance range. The measurement device according to claim 7.

9. The measurement apparatus according to claim 1 , wherein the calibration optical system includes an optical fiber, a mirror, or a multi-pass cell.

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

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

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

13. The measurement device according to claim 1 , wherein the correction data indicates a correction table or a correction function for determining a correction value used to correct the first detection signal.

14. The measurement apparatus according to claim 1 , wherein the calibration optical system is a part of the interference optical system.

15. 1. A computer-implemented method in a system including a metrology device, comprising: The measuring device is a light source that emits light whose frequency is periodically modulated; a calibration optical system having at least one reflective surface; an interference optical system that separates the light emitted from the light source into reference light and output light, and generates a first interference light that is an interference light between the reference light and reflected light generated when the output light is reflected by an object, and a second interference light that is an interference light between the reference light and reflected light generated when the output light is reflected by the calibration optical system; a light receiving device including at least one photodetector, and configured to output a first detection signal corresponding to the intensity of the first interference light and a second detection signal corresponding to the intensity of the second interference light; a storage device that stores correction data used to correct the first detection signal; Equipped with The method comprises: updating the correction data based on the second detection signal; correcting the first detection signal based on the updated correction data; generating and outputting measurement data relating to the distance and / or velocity of the object based on the corrected first detection signal; A method comprising:

16. A computer program executed by a computer in a system including a measurement device, The measuring device is a light source that emits light whose frequency is periodically modulated; a calibration optical system having at least one reflective surface; an interference optical system that separates the light emitted from the light source into reference light and output light, and generates a first interference light that is an interference light between the reference light and reflected light generated when the output light is reflected by an object, and a second interference light that is an interference light between the reference light and reflected light generated when the output light is reflected by the calibration optical system; a light receiving device including at least one photodetector, and configured to output a first detection signal corresponding to the intensity of the first interference light and a second detection signal corresponding to the intensity of the second interference light; a storage device that stores correction data used to correct the first detection signal; Equipped with The computer program causes the computer to: updating the correction data based on the second detection signal; correcting the first detection signal based on the updated correction data; generating and outputting measurement data relating to the distance and / or velocity of the object based on the corrected first detection signal; A computer program that executes

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