Measurement device

Abstract

This measurement device comprises: a light-emitting element that emits light for irradiating an object, periodically changes the frequency of the light, and can adjust the frequency range in which the frequency changes; a signal generation circuit that generates a digital periodic signal; a digital-analog conversion circuit that converts the digital periodic signal into an analog periodic signal, and outputs the analog periodic signal; an amplitude change circuit that adjusts the amplitude of the analog periodic signal by a gain to generate a drive signal; a drive circuit that changes the frequency on the basis of the drive signal; and a signal line that is electrically connected to the amplitude change circuit, and is for controlling the gain.

Description

Measuring equipment

[0001] The present disclosure relates to a measurement device.

[0002] Conventionally, LiDAR (Light Detection and Ranging) technology exists, which generates measurement data related to the distance and / or speed of an object by illuminating the object with light and detecting the light reflected from the object. A typical example of a measurement device using LiDAR technology includes a light source, a photodetector, and a processing circuit. The light source emits light to illuminate the object. The photodetector detects the reflected wave from the object and outputs a signal corresponding to the time delay of the reflected wave. The processing circuit acquires data related to the distance and speed of the object based on the signal output from the photodetector, for example, using FMCW (Frequency Modulated Continuous Wave) technology. Patent Document 1 discloses an example of a measurement device using FMCW technology.

[0003] Japanese Patent Application Laid-Open No. 2020-008475

[0004] Christopher V. Poulton, et al., “Frequency-modulated Continuous-wave LIDAR Module in Silicon Photonics”, OFC2016, W4E.3, (2016).

[0005] The present disclosure provides a measurement device that can acquire measurement data of an object more accurately.

[0006] A measurement device according to one aspect of the present disclosure includes a light-emitting element that emits light to illuminate an object, wherein the frequency of the light changes periodically and the frequency range within which the frequency changes is adjustable; a signal generation circuit that generates a digital periodic signal; a digital-to-analog conversion circuit that converts the digital periodic signal into an analog periodic signal and outputs the analog periodic signal; an amplitude change circuit that adjusts the amplitude of the analog periodic signal using a gain to generate a drive signal; a drive circuit that changes the frequency based on the drive signal; and a signal line electrically connected to the amplitude change circuit, the signal line being for controlling the gain.

[0007] A comprehensive or specific aspect of the present disclosure may be realized as a system, an apparatus, a method, an integrated circuit, a computer program, or a recording medium such as a computer-readable recording disk, or as 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, for example, a non-volatile recording medium such as a CD-ROM (Compact Disc-Read Only Memory). An apparatus may consist of one or more devices. When an apparatus consists 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. The multiple devices included in a "system" may include devices installed in remote locations away from other devices and connected via a communication network.

[0008] According to the technology of the present disclosure, it is possible to realize a measurement device that can acquire measurement data of an object more accurately.

[0009] FIG. 1 is a block diagram schematically illustrating the configuration of a measurement device according to an exemplary embodiment of the present disclosure. FIG. 2A is a diagram schematically illustrating the time changes in the frequencies of the reference light and the reflected light when the object is stationary. FIG. 2B is a diagram schematically illustrating the time changes in the frequencies of the reference light and the reflected light when the object approaches the measurement device. FIG. 3 is a graph illustrating the relationship between the distance from the measurement device to the object and the beat frequency. FIG. 4 is a diagram schematically illustrating the relationship between the injection current value and the frequency of the laser light in a distributed feedback laser diode. FIG. 5 is a diagram for explaining the correspondence relationship between the current value range and the frequency range in the graph shown in FIG. 4. FIG. 6A is a diagram schematically illustrating the relationship between the frequency of the laser light and time in the narrow range mode and the wide range mode. FIG. 6B is a diagram schematically illustrating the relationship between the intensity of the laser light and time in the narrow range mode and the wide range mode. FIG. 7A is a flowchart illustrating an example of a measurement operation performed by a processing circuit. FIG. 7B is a flowchart illustrating an example of a measurement operation performed by the processing circuit in step S101 shown in FIG. 7A. FIG. 7C is a flowchart showing an example of the measurement operation performed by the processing circuit in step S104 shown in FIG. 7A. FIG. 8 is a block diagram schematically showing a conventional configuration for emitting laser light based on Patent Document 1. FIG. 9 is a block diagram schematically showing a specific configuration of the light source and processing circuit in the measurement device according to this embodiment. FIG. 10 is a diagram schematically showing an example of an amplitude change circuit. FIG. 11 is a graph schematically showing the relationship between the amplitude of the drive signal and the S / N ratio in this embodiment. FIG. 12 is a flowchart showing an example of the light source drive operation performed by the processing circuit. FIG. 13 is a graph showing the relationship between time and voltage of the drive signal in the light source in the working example. FIG. 14A is a graph showing an enlarged portion of the relationship between drive voltage and time in a first example. FIG. 14B is a graph showing an enlarged portion of the relationship between drive voltage and time in a second example. FIG. 14C is a graph showing an enlarged portion of the relationship between drive voltage and time in a third example.

[0010] In the present 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). The 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 programmed after the LSI is manufactured, or a reconfigurable logic device, which can reconfigure the connection relationships within the LSI or set up circuit sections within the LSI, can also be used for the same purpose.

[0011] 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 executed by the processor and peripheral devices. A system or device may include one or more non-transitory recording media on which the software is recorded, a processor, and required hardware devices, such as interfaces.

[0012] In this disclosure, "light" refers to electromagnetic waves including not only visible light (wavelength of about 400 nm to about 700 nm), but also ultraviolet light (wavelength of about 10 nm to about 400 nm) and infrared light (wavelength of about 700 nm to about 1 mm). In this specification, ultraviolet light may be referred to as "ultraviolet light," and infrared light may be referred to as "infrared light."

[0013] Exemplary embodiments of the present disclosure will be described 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 will be described as optional components. Furthermore, each figure is a schematic diagram and is not necessarily an exact illustration. Furthermore, in each figure, substantially identical components are assigned the same reference numerals, and duplicated descriptions may be omitted or simplified.

[0014] First, the findings that form the basis of this disclosure will be described.

[0015] In recent years, FMCW-LiDAR technology has been developed, which combines a wide dynamic range and high resolution for distance, is less susceptible to disturbances, and can acquire measurement data on the distance and / or speed of fast-moving objects. By using light instead of millimeter waves, the diameter of the light spot illuminating the object can be made relatively small, enabling improved spatial resolution.

[0016] In a measurement device using FMCW-LiDAR technology, measurement data of an object is obtained using light whose frequency changes periodically. Patent Document 1 discloses a laser length measuring device as an example of such a measurement device. The laser length measuring device includes, in this order, a drive waveform signal generation unit, a digital-to-analog (DA) converter, a low-pass filter, a laser drive unit, and a laser element. The drive waveform signal generation unit generates a triangular wave digital signal. The DA converter converts the digital signal into an analog signal. The analog signal is a voltage signal. The low-pass filter removes high-frequency components from the analog signal to generate a drive signal. The laser drive unit converts the drive signal into a current signal and supplies it to the laser element. The laser element emits laser light whose frequency changes periodically in the shape of a triangular wave.

[0017] As a result of the inventors' investigation into the above laser length measuring device, they found that if the amplitude of the analog signal generated by the DA converter is small, the repeatability decreases when measurement data of an object is repeatedly acquired under the same conditions. This is because when the amplitude of the analog signal is small, the voltage fluctuation caused by noise generated by DA conversion becomes large relative to the amplitude.

[0018] The present inventors have found this problem and have come up with a measurement device according to an embodiment of the present disclosure that solves the problem. The measurement device according to this embodiment will be described below.

[0019] (Embodiment) The following first describes the configuration of a measurement device according to this embodiment, FMCW-LiDAR technology, frequency changes according to measurement distance, and measurement operation. Next, we will explain the issues with conventional configurations that emit laser light with periodically changing frequencies, the specific configurations of the light source and processing circuit included in the measurement device according to this embodiment, the relationship between the amplitude of the drive signal and the S / N ratio, the drive operation of the light source, and examples.

[0020] [Configuration of Measurement Apparatus] First, an example configuration of a measurement apparatus 100 according to an embodiment of the present disclosure will be described with reference to Fig. 1. Fig. 1 is a block diagram schematically illustrating the configuration of a measurement apparatus according to an exemplary embodiment of the present disclosure. Fig. 1 shows an object 10 to be measured. The measurement apparatus 100 shown in Fig. 1 acquires measurement data related to the distance and / or velocity of the object 10 using laser light whose frequency changes periodically. The frequency range over which the frequency changes is adjustable.

[0021] As shown in Fig. 1, the measurement apparatus 100 includes a light source 20, an interference optical system 30, a beam shaper 40, an optical deflector 50, a photodetector 60, a processing circuit 70, and a memory 72. The thick arrows in Fig. 1 represent the flow of light. The thin arrows in Fig. 1 represent the transmission and reception of signals.

[0022] Each component of the measurement device 100 will be described below.

[0023] The light source 20 emits a laser beam 20L whose frequency can be changed. ０The frequency may be changed over time in a constant time period, for example, in a triangular or sawtooth wave shape. The time period of the frequency change may vary. The time period of the frequency may be, for example, 1 μsec or more and 10 ms or less. The frequency width may be, for example, 100 MHz or more and 1 THz or less. The wavelength of the laser light may be included in the wavelength range of near-infrared light, for example, 700 nm or more and 2000 nm or less. Since the amount of near-infrared light in sunlight is less than the amount of visible light, the laser light 20L ０ If near-infrared light is used as the laser light 20L, the influence of sunlight as noise can be reduced. ０ The wavelength of the laser beam may be in the visible light wavelength range of 400 nm to 700 nm, or may be in the ultraviolet light wavelength range. The light source 20 may include, for example, a light emitting element such as a distributed feedback laser diode or an external cavity laser diode. These laser diodes are inexpensive and compact, capable of single-mode oscillation, and capable of changing the frequency of the laser beam depending on the amount of current applied. The detailed configuration of the light source 20 will be described later.

[0024] The interference optical system 30 includes a first fiber splitter 32, a second fiber splitter 34, and an optical circulator 36. The first fiber splitter 32 splits the laser light 20L emitted from the light source 20 into a first fiber splitter 32 and a second fiber splitter 34. ０ Reference light 20L １ and 20L of light ２ The first fiber splitter 32 splits the reference light 20L １ is input to the second fiber splitter 34, and the irradiation light 20L ２ is input to the optical circulator 36. The optical circulator 36 outputs the irradiation light 20L ２ is input to the beam shaper 40. The optical circulator 36 irradiates the object 10 with the irradiating light 20L. ２ Reflected light 20L generated by irradiation with ３ is input to the second fiber splitter 34. The second fiber splitter 34 splits the reference light 20L １ and reflected light 20L ３ Interfered light 20L obtained by superimposing and interfering ４ is input to the photodetector 60.

[0025] The beam shaper 40 shapes the irradiation light 20L emitted from the interference optical system 30. ２ Adjust the spot shape of the irradiated light 20L after beam shaping. ２ may be, for example, a flash of light, a line beam, or a point beam. The beam shaper 40 may include, for example, a collimating lens.

[0026] The optical deflector 50 deflects the irradiation light 20L emitted from the beam shaper 40. ２ The optical deflector 50 deflects the target scene including the object 10 with the illumination light 20L. ２ The optical deflector 50 can be scanned by, for example, a micromechanical electrosystem (MEMS) mirror or a galvanometer mirror. Alternatively, the optical deflector 50 may be a beam scanning device using an optical phased array and a slow-light waveguide, as described in International Publication No. WO 2019 / 130720.

[0027] The photodetector 60 detects the interference light 20L ４ The photodetector 60 includes one or more photodetection elements. ０ Interfered light 20L based on ４ The signal output corresponds to the intensity of the light.

[0028] In the measurement device 100, the irradiation light 20L ２ The optical path from the interference optical system 30 to the object 10 and the reflected light 20L ３ The optical paths from the object 10 to the interference optical system 30 overlap each other. By employing such a coaxial optical system, the configuration of the measurement device 100 can be simplified and stable measurements can be achieved. Note that the above two optical paths may be designed not to overlap each other.

[0029] The processing circuit 70 controls the operations of the light source 20, the beam shaper 40, the optical deflector 50, and the photodetector 60. The processing circuit 70 processes the signal output from the photodetector 60 using FMCW-LiDAR technology. The processing circuit 70 generates and outputs measurement data related to the distance and / or velocity of the object 10 based on the signal. The operation of the processing circuit 70 will be described in detail below.

[0030] The computer program executed by the processing circuit 70 is stored in memory 72, such as ROM or RAM (Random Access Memory). As such, the measurement device 100 includes a processing device including the processing circuit 70 and memory 72. The processing circuit 70 and memory 72 may be integrated on a single circuit board or provided on separate circuit boards. The control and signal processing functions of the processing circuit 70 may be distributed across multiple circuits. The processing device may be installed in a remote location away from the other components and control the operations of the light source 20, beam shaper 40, optical deflector 50, and photodetector 60 via a wired or wireless communication network.

[0031] [FMCW-LiDAR Technology] Next, the FMCW-LiDAR technology will be briefly described with reference to Figures 2A and 2B. Details of the FMCW-LiDAR technology are disclosed in, for example, Non-Patent Document 1.

[0032] FIG. 2A shows the reference beam 20L when the object 10 is stationary. １ and reflected light 20L ３ 2A is a diagram showing a time variation of the frequency of the reference light 20L shown in FIG. 2A. The solid line represents the reference light, and the dashed line represents the reflected light. １ The frequency of the reference light 20L repeats a triangular wave-like change over time. １ The frequency of the reflected light 20L alternates between up-chirp and down-chirp. The increase in frequency during the up-chirp is equal to the decrease in frequency during the down-chirp. ３ The frequency of the reference light 20L １ The frequency of the reflected light 20L is shifted along the time axis compared to the frequency of the reflected light 20L. ３ The amount of time shift is 20L of irradiation light. ２ is emitted from the measurement device 100, is reflected by the object 10, and is reflected light 20L ３ As a result, the reference light 20L １ and reflected light 20L ３ and interference light 20L ４ Reflected light 20L ３ Frequency and reference light 20L１ The double-headed arrow in FIG. 2A represents the difference between the two frequencies. ４ The signal is called a beat signal. The frequency of the beat signal, i.e., the beat frequency, is equal to the difference between the above frequencies. From the beat frequency, the processing circuitry 70 can generate data regarding the distance of the object 10.

[0033] FIG. 2B shows the reference beam 20L when the object 10 approaches the measurement device 100. １ and reflected light 20L ３ 1 is a diagram showing a time change in the frequency of the reflected light 20L due to the Doppler shift when the object 10 approaches. ３ The frequency of the reflected light 20L is shifted in the increasing direction along the frequency axis compared to when the object 10 is stationary. ３ The amount of frequency shift of the reflected light 20L is calculated by dividing the velocity vector of the object 10 by ３ The beat frequency depends on the component projected in the direction of the reference beam 20L. １ and reflected light 20L ３ The beat frequencies in the up-chirp and down-chirp periods are different. In the example shown in FIG. 2B , the beat frequencies in both down-chirp periods are higher than the beat frequencies in both up-chirp periods. Processing circuitry 70 can generate data related to the velocity of object 10 from the difference in beat frequency due to Doppler shift. Furthermore, processing circuitry 70 can generate data related to the distance of object 10 from the average value of the beat frequencies in the up-chirp and down-chirp periods.

[0034] Next, the relationship between the distance from the measurement device 100 to the object 10 and the beat frequency will be described with reference to Figure 3. If the frequency range during the up-chirp or down-chirp period is Δf, the time required for Δf to change is Δt, the speed of light is c, and the distance from the measurement device 100 to the object 10 is d, then the beat frequency f ｂｅａｔ is expressed by the following equation (1).

[0035] The beat frequency f in equation (1)ｂｅａｔ is obtained by multiplying the time rate of change of frequency Δf / Δt by the round trip time (2d / c) from the measuring device 100 to the object 10.

[0036] FIG. 3 shows the relationship between the distance d from the measurement device 100 to the object 10 and the beat frequency f ｂｅａｔ The thick solid line represents the relationship between Δf=12.5 GHz and Δt=10 μsec, i.e., the time rate of change of the frequency is Δf / Δt=1.25×10 １５ The thick dashed line represents a mode where Δf = 1.12 GHz and Δt = 10 μsec, i.e., the time rate of change of frequency is Δf / Δt = 1.12 × 10 １４ The thin dashed horizontal lines represent the beat frequencies f ｂｅａｔ This is an example of the maximum measurable frequency, which is 75 MHz.

[0037] According to equation (1), the measurement range d increases as the time rate of change of the frequency Δf / Δt decreases. ｂｅａｔ Considering the maximum measurable value of , the ranging range d is 9 m in the mode with a high time rate of change of frequency and 100 m in the mode with a low time rate of change of frequency. The mode with a high time rate of change of frequency is a mode with a narrow ranging range, i.e., a narrow range mode. The mode with a low time rate of change of frequency is a mode with a wide ranging range, i.e., a wide range mode.

[0038] The accuracy of distance measurement improves as the time rate of change of frequency increases. The higher the time rate of change of frequency Δf / Δt, the greater the accuracy of the beat frequency f relative to the amount of change in distance d. ｂｅａｔ This is because the amount of change in the beat frequency f ｂｅａｔ is obtained by Fourier transforming the beat signal in time. Compared with the frequency resolution of the Fourier transform, the beat frequency f ｂｅａｔ The greater the change in the frequency, the more accurate the distance measurement. In the example shown in Figure 3, when distance measurement is performed with a frequency resolution of 800 Hz, the distance measurement accuracy is about 0.1 mm in narrow range mode and about several mm in wide range mode. This distance measurement accuracy is the accuracy of 50 repetitions.

[0039] When measuring not only distance but also speed, the beat frequency f ｂｅａｔ is required to be equal to or less than the maximum measurable value. Taking into account the amount of change due to Doppler shift, in the wide range mode, Δf = 0.56 GHz and Δt = 10 μsec, that is, the time rate of change of frequency is Δf / Δt = 5.6 × 10 １３ When the frequency was Hz / sec, the distance measurement accuracy was on the order of several centimeters.

[0040] The narrow range mode can be applied, for example, when generating measurement data of an object 10 at a short distance with high accuracy. The short distance can be, for example, 0 m or more and 10 m or less. The wide range mode can be applied, for example, when generating measurement data of an object 10 at both a short distance and a long distance with a certain degree of accuracy. The long distance can be, for example, more than 10 m and 200 m or less. The time rate of change of frequency in the narrow range mode and the wide range mode is respectively expressed as the beat frequency f in equation (1). ｂｅａｔ is determined by the maximum measurable value of , and the near and far distances d.

[0041] [Frequency Change According to Measurement Distance] Next, an example of the relationship between the applied current value and the frequency of the laser light in a distributed feedback laser diode, which is an example of a light emitting element included in the light source 20, will be described with reference to Fig. 4. Fig. 4 shows the relationship between the applied current value in the distributed feedback laser diode and the frequency of the laser light 20L ０ When a current is applied to a distributed feedback laser diode, the active layer included in the laser diode is heated, causing a slight change in the cavity length of the active layer. As the cavity length changes, the laser light 20L ０ The larger the applied current value, the more the amount of heat in the active layer increases, and the more the frequency of the laser light 20L ０ The amount of change in frequency increases.

[0042] In the example shown in FIG. 4, when the DC component of the current value is 250 mA and the AC component is 266 mAp-p, the laser light 20L ０The frequency range of the laser beam of 250 mA is Δf = 12.5 GHz. If the DC component of the current value is 250 mA and the AC component is 10 mA p-p, the frequency range of the laser beam of 250 mA is Δf = 0.56 GHz. When the time period of the applied current is 2Δt = 20 μsec, the time rate of change of the frequency in the narrow range mode described above is Δf / Δt = 1.25 × 10 １５ Hz / sec, and the time rate of change of frequency in wide range mode Δf / Δt = 5.6 × 10 １３ Hz / sec can be achieved.

[0043] In the example shown in Figure 4, the portion where the frequency of the laser light changes nonlinearly with the current value is used in the narrow range mode and the wide range mode. Furthermore, the DC component of the current value is the same in the narrow range mode and the wide range mode. As a result, the frequency range in the narrow range mode includes the frequency range in the wide range mode.

[0044] Two different portions in which the frequency of the laser light changes nonlinearly with respect to the current value may be used for the narrow range mode and the wide range mode. Next, with reference to Fig. 5, the correspondence relationship between the current value range and the frequency range in the graph shown in Fig. 4 will be described. Fig. 5 is a diagram for explaining the correspondence relationship between the current value range and the frequency range in the graph shown in Fig. 4. As shown in Fig. 5, for the range of current values, ΔI １ , ΔI ２ , and ΔI ３ are arranged in this order in the direction of increasing current value. １ , Δf ２ , and Δf ３ are arranged in this order in the direction of decreasing frequency. １ , Δf ２ , and Δf ３ are the current values ​​ΔI １ , ΔI ２ , and ΔI ３ The graph shown in FIG. 5 shows the range of frequencies obtained when changing the range of ΔI １ and Δf １ The first correspondence relationship between ２ and Δf ２and ΔI ３ and Δf ３ Each correspondence is approximately linear. １ >ΔI ２ >ΔI ３ is satisfied, and Δf ２ >Δf ３ >Δf １ The ratio of the frequency range to the range of current values ​​is given by Δf ３ / ΔI ３ >Δf ２ / ΔI ２ >Δf １ / ΔI １ The relationship is satisfied.

[0045] In the first correspondence relationship, the range of current values ​​for which linearity can be achieved is the widest among the three correspondence relationships, but the frequency range is the narrowest among the three correspondence relationships. In the second correspondence relationship, the range of current values ​​for which linearity can be achieved is narrower than in the first correspondence relationship, but the frequency range is the widest among the three correspondence relationships. In the third correspondence relationship, the range of current values ​​for which linearity can be achieved is the narrowest among the three correspondence relationships, but the frequency range is wider than in the first correspondence relationship.

[0046] In the first to third correspondence relationships, when the applied current is changed over time in a triangular wave shape with the same period 2Δt, the second correspondence relationship can be applied to the narrow range mode, and the first and third correspondence relationships can be applied to the wide range mode. This is because the time rate of change of frequency in the second correspondence relationship is higher than the time rate of change of frequency in the first and third correspondence relationships. In the wide range mode, the irradiated light 20L ２ The higher the intensity of the reflected light 20L from the object 10 at a long distance, the more effective the reflected light 20L is. ３ The laser light 20L emitted from the light source 20 can be obtained. ０ The intensity of the irradiated light 20L increases with the applied current value. ２ In terms of obtaining the above, the third correspondence relationship is more suitable for the wide range mode than the first correspondence relationship.

[0047] However, from the viewpoint of eye safety, regardless of the wide range mode or narrow range mode, the irradiation light is 20L. ２ The intensity of the irradiated light 20L is below a predetermined intensity. This is because it is assumed that a person may suddenly enter the vicinity or that a person may observe with binoculars from a long distance. When the wavelength is 1550 nm and the period 2Δt of the triangular wave is sufficiently long, that is, 10 seconds or more in continuous emission, the irradiated light 20L ２ The intensity of the irradiated light 20L may be, for example, 10 mW or less. Even at a short distance, an object 10 with low reflectivity may exist. Therefore, regardless of the wide range mode or the narrow range mode, ２ It is advantageous that the intensity of the light is as high as possible within 10 mW.

[0048] Next, referring to FIGS. 6A and 6B, the laser beam 20L in the narrow range mode and the wide range mode is ０ 6A illustrates an example of how the frequency and intensity of the laser beam 20L changes over time in the narrow range mode and the wide range mode. ０ 6B is a diagram showing a relationship between the frequency and time of the laser beam 20L in the narrow range mode and the wide range mode. ０ 6A and 6B are diagrams schematically illustrating the relationship between the intensity and time of the narrow range mode shown in FIG. 6A and 6B are based on the second correspondence relationship shown in FIG. 5. The wide range mode shown in FIG. 6A and 6B is based on the third correspondence relationship shown in FIG. 5.

[0049] As shown in FIG. 6A, the laser beam 20L in the narrow range mode ０ The frequency of is in the frequency range Δf ２ The laser light 20L in the wide range mode changes periodically with time. ０ The frequency of is in the frequency range Δf ３ The laser light 20L in the narrow range mode and the wide range mode changes periodically with time. ０ The period 2Δt of the frequency change is equal to each other. By fixing the period regardless of whether it is the narrow range mode or the wide range mode, the change in the amount of heat generated by the active layer included in the laser diode due to an increase or decrease in the applied current value becomes constant, and it is possible to maintain a linear increase or decrease in frequency.

[0050] Each period of frequency change in the narrow range mode includes the following first up-chirp period and second up-chirp period: In the first up-chirp period, the frequency is within the frequency range Δf ２ In the first down-chirp period, the frequency increases monotonically from the lower limit to the upper limit of the frequency range Δf ２ Each period of frequency change in the wide range mode includes the following second up-chirp period and second down-chirp period. In the second up-chirp period, the frequency falls within the frequency range Δf ３ The frequency increases monotonically from the lower limit to the upper limit of the frequency range Δf ３ decreases monotonically from the upper limit to the lower limit.

[0051] In the narrow range mode, the signal output from the photodetector 60 includes a first signal component in the first up-chirp period and a second signal component in the first down-chirp period. The processing circuit 70 generates and outputs measurement data based on the first and second signal components. In the wide range mode, the signal output from the photodetector 60 includes a third signal component in the second up-chirp period and a fourth signal component in the second down-chirp period. The processing circuit 70 generates and outputs measurement data based on the third and fourth signal components. The generated measurement data in the narrow range mode and wide range mode includes not only data related to the distance to the object 10 but also data related to its velocity.

[0052] As shown in Figure 6B, the intensity in the wide range mode is greater than or equal to the intensity in the narrow range mode. Therefore, in the wide range mode, the effective reflected light 20L from the object 10 at a long distance is ３ If the intensity in the narrow range mode is also sufficiently high, effective reflected light 20L can be obtained from an object 10 with low reflectivity at a short distance. ３ The intensity in the narrow range mode can be, for example, 1 mW or more and 6 mW or less. The intensity in the wide range mode can be, for example, 6 mW or more and 10 mW or less.

[0053] As shown in Figures 6A and 6B, as the frequency increases, the intensity decreases, and as the frequency decreases, the intensity increases. This relationship of increase and decrease is due to the negative rate of change of frequency relative to the current value, as shown in Figure 5.

[0054] [Measurement Operation] Next, an example of the measurement operation performed by the processing circuit 70 will be described with reference to Figures 7A to 7C. Figure 7A is a flowchart showing an example of the measurement operation performed by the processing circuit 70. The processing circuit 70 performs the operations of steps S101 to S105 shown in Figure 7A. Figures 7B and 7C are flowcharts showing examples of the measurement operation performed by the processing circuit 70 in steps S101 and S104 shown in Figure 7A, respectively.

[0055] <Step S101> The processing circuit 70 measures the object 10 at a long distance or a short distance in the wide range mode. The details of this operation are as shown in Fig. 7B. The processing circuit 70 measures the laser light 20L having a time-varying frequency in the wide range mode. ０ The processing circuit 70 causes the light source 20 to emit the interference light 20L. ４ The processing circuit 70 generates and outputs measurement data relating to the distance and speed of the object 10 based on the signal output from the photodetector 60 (step S101C).

[0056] <Step S102> The processing circuit 70 determines whether the object 10 is in a short distance based on the measurement result in step S101. Measurement results from other measurement sensors may be used instead of the measurement result in step S101. If the determination is Yes, the processing circuit 70 executes the operation of step S103. If the determination is No, the processing circuit 70 executes the operation of step S101.

[0057] <Step S103> The processing circuitry 70 determines whether measurement can be performed in narrow range mode. If the beat frequency including the Doppler shift is equal to or lower than the upper limit of the measurable range, measurement can be performed in narrow range mode. If the determination is Yes, the processing circuitry 70 executes the operation of step S104. If the determination is No, the processing circuitry 70 executes the operation of step S101.

[0058] <Step S104> The processing circuit 70 measures the object 10 at a short distance in the narrow range mode. The details of this operation are as shown in Fig. 7C. The processing circuit 70 measures the laser light 20L having a time-varying frequency in the narrow range mode. ０ The processing circuit 70 causes the light source 20 to emit the interference light 20L. ４ (Step S104B). The processing circuit 70 generates and outputs measurement data relating to the distance and speed of the object 10 based on the signal output from the photodetector 60 (Step S104C). The distance measurement accuracy in the narrow range mode in Step S104 is improved compared to the distance measurement accuracy in the wide range mode in Step S101.

[0059] <Step S105> The processing circuit 70 determines whether to end the measurement. If the determination is Yes, the processing circuit 70 ends the measurement operation. If the determination is No, the processing circuit 70 executes the operation of step S102. However, in step S102, the processing circuit 70 determines whether the object 10 is in the close range based on the distance measurement result in step S104, rather than the measurement result in step S101.

[0060] The measurement device 100 according to this embodiment operates by switching between a wide range mode and a narrow range mode, thereby adjusting the range and accuracy of distance measurement and the irradiation light 20L. ２ The intensity of the beam can be appropriately changed to obtain measurement data of the object 10.

[0061] [Laser light 20L with periodically changing frequency ０ Next, referring to FIG. 8, a laser beam 20L having a periodically changing frequency is emitted. ０ The following describes the problems with the conventional configuration that emits the laser light 20L. ０ is the irradiation light 20L for irradiating the object 10. ２ Since the laser light 20L ０ It can be said that the laser beam 20L is the light that illuminates the object 10. ０8 is a block diagram showing a schematic configuration of a conventional configuration for emitting a light emitting element 24. The configuration shown in Fig. 8 includes a signal generating circuit 71, a DA conversion circuit 21, a low-pass filter 22, a drive circuit 23, and a light emitting element 24 in this order.

[0062] The signal generating circuit 71 receives the laser light 20L. ０ The signal generating circuit 71 generates a digital periodic signal of a triangular wave for periodically changing the frequency of the laser beam 20L emitted from the light emitting element 24. The signal generating circuit 71 may be, for example, an FPGA. The DA conversion circuit 21 converts the digital periodic signal into an analog periodic signal and outputs it. The analog periodic signal is a voltage signal. The low-pass filter 22 removes high-frequency components from the analog periodic signal output from the DA conversion circuit 21 to generate a drive signal. The drive circuit 23 controls the laser beam 20L emitted from the light emitting element 24 based on the drive signal. ０ Specifically, the drive circuit 23 converts the drive signal into a drive current and supplies the drive current to the light emitting element 24. The light emitting element 24 emits laser light 20L whose frequency changes periodically in a triangular wave shape. ０ The five bubbles shown in Fig. 8 represent examples of a digital periodic signal, an analog periodic signal, a drive signal, a drive current, and a frequency. These bubbles correspond to the behavior during the frequency down-chirp period.

[0063] The inventors of the present invention have studied conventional configurations and found that the smaller the amplitude of the analog periodic signal, the lower the repeatability. This is because the smaller the amplitude of the analog periodic signal, the larger the voltage fluctuations caused by noise generated by DA conversion become relative to the amplitude. As a result, the signal-to-noise ratio of the drive signal decreases. Examples of noise include quantization error, differential nonlinearity error, and integral nonlinearity error, which are described below.

[0064] Quantization error: In DA conversion, a digital signal is generated as a stepped voltage as an analog signal because it is composed of a finite number of levels and a clock. Quantization error refers to the difference between the linear voltage of an ideal analog signal and the stepped voltage of an actual analog signal.

[0065] Differential nonlinearity error: The step voltage generated by ideal DA conversion is expressed as an integer multiple of the LSB, which is the analog voltage value per digital signal level. However, slight fluctuations occur in actual step voltages. Differential nonlinearity error refers to these fluctuations.

[0066] Integral nonlinearity error: Integral nonlinearity error refers to the difference between the ideal voltage and the actual voltage in the entire signal waveform, and corresponds to the accumulation of differential nonlinearity error.

[0067] The present inventors have found the above-mentioned problem and have come up with a measurement device 100 according to the present embodiment that solves the problem. The measurement device 100 according to the present embodiment includes a light source 20 and a processing circuit 70 that can suppress a decrease in repeatability.

[0068] [Specific Configuration of Light Source 20 and Processing Circuit 70] Next, with reference to FIG. 9 , a specific configuration of the light source 20 and processing circuit 70 capable of suppressing a decrease in repeatability will be described. FIG. 9 is a block diagram schematically illustrating a specific configuration of the light source 20 and processing circuit 70 in the measurement device 100 according to this embodiment. The light source 20 illustrated in FIG. 9 includes a DA conversion circuit 21, an amplitude change circuit 25, a low-pass filter 22, a drive circuit 23, and a light-emitting element 24, in this order. The processing circuit 70 illustrated in FIG. 9 includes a signal generation circuit 71. The measurement device 100 includes a signal line 80 electrically connecting the processing circuit 70 and the amplitude change circuit 25. The DA conversion circuit 21, the low-pass filter 22, the drive circuit 23, the light-emitting element 24, and the signal generation circuit 71 are as described with reference to FIG. 8 . To further explain the drive circuit 23, the drive current generated by the drive circuit 23 includes a DC component and an AC component. The AC component is determined by the drive signal. The DC component may be constant regardless of the amplitude of the drive signal, or may vary depending on the amplitude of the drive signal.

[0069] 9 differs from the configuration shown in Fig. 8 in that an amplitude change circuit 25 is provided between the DA conversion circuit 21 and the drive circuit 23. In the example shown in Fig. 9, the amplitude change circuit 25 is provided between the DA conversion circuit 21 and the low-pass filter 22, but this is not limiting. The amplitude change circuit 25 may also be provided between the low-pass filter 22 and the drive circuit 23.

[0070] In the measurement device 100 according to this embodiment, with some exceptions described below, the amplitude of the analog periodic signal generated by the DA conversion circuit 21 is fixed so as to be close to the maximum value, regardless of whether the narrow range mode or wide range mode is selected. In this specification, unless otherwise specified, the amplitude of the analog periodic signal generated by the DA conversion circuit 21 is simply referred to as the "amplitude of the analog periodic signal." The amplitude of the analog periodic signal may be, for example, 0.8 times or more and 1.0 times or less of the maximum value. The closer the amplitude of the analog periodic signal is to the maximum value, the more the aforementioned noise effect on repeatability can be reduced. When the amplitude of the analog periodic signal is maximum, the noise effect is lowest.

[0071] In the measurement device 100 according to this embodiment, the amplitude change circuit 25 adjusts the amplitude of the analog periodic signal by a gain. The processing circuit 70 controls the gain via a signal line 80. Two balloons shown in FIG. 9 represent the analog periodic signal before adjustment input to the amplitude change circuit 25 and the analog periodic signal after adjustment output from the amplitude change circuit 25. By adjusting the amplitude of the analog periodic signal by a gain, the amplitude of the drive signal can be changed depending on the narrow range mode and the wide range mode, and the laser light 20L ０ The gain is adjusted to the frequency range of the laser light 20L. ０ The gain in the narrow range mode is greater than the gain in the wide range mode.

[0072] Fig. 10 is a diagram schematically illustrating an example of the amplitude change circuit 25. The amplitude change circuit 25 illustrated in Fig. 10 is a general amplifier circuit capable of adjusting gain. As illustrated in Fig. 10, the amplitude change circuit 25 includes an operational amplifier 25a and a digital potentiometer 25b. The operational amplifier 25a includes a positive terminal which is a grounded non-inverting input terminal and a negative terminal which is an inverting input terminal electrically connected to the digital potentiometer 25b.

[0073] The digital potentiometer 25b defines the gain as follows: The digital potentiometer 25b digitally controls the position of a wiper electrically connected to the negative terminal of the operational amplifier 25a based on a signal from the processing circuit 70 via a signal line 80. With the wiper position as a reference, the input voltage V ｉｎ The value of the resistor on the side is R １ and the output voltage V ｏｕｔ The value of the resistor on the side is R ２ These resistors are variable resistors. １ and R ２ varies depending on the wiper position.

[0074] The operational amplifier 25a operates so that the voltage difference between the positive terminal and the negative terminal becomes zero. ｉｎ / R １ +V ｏｕｔ / R ２ = 0, and V ｏｕｔ =-(R ２ / R １ ) V ｉｎ is obtained. ２ / R １ corresponds to the gain. The gain may be greater than, equal to, or less than 1. In this specification, the gain is defined as |V ｏｕｔ | / |V ｉｎ | and has a positive value.

[0075] As described above, in the measurement device 100 according to this embodiment, by fixing the amplitude of the analog periodic signal close to its maximum value, it is possible to reduce the voltage fluctuations caused by noise generated by DA conversion relative to the amplitude. As a result, the S / N ratio of the drive signal obtained by combining the amplitude and gain of the analog periodic signal is improved, and it is possible to suppress a decrease in repeatability.

[0076] Unlike the measurement device 100 according to this embodiment, when the narrow range mode and wide range mode are realized by the conventional configuration shown in FIG. 8 , the amplitude of the analog periodic signal is adjusted via the digital periodic signal by the signal generation circuit 71. Specifically, by increasing the amplitude of the analog periodic signal, the frequency range is widened, resulting in the narrow range mode. Conversely, by decreasing the amplitude of the analog periodic signal, the frequency range is narrowed, resulting in the wide range mode. However, as described above, when the amplitude of the analog periodic signal is small, the signal-to-noise ratio of the drive signal decreases, resulting in a decrease in repeatability.

[0077] In this specification, "changing the amplitude of the analog periodic signal via the digital periodic signal by the signal generation circuit 71" means that the amplitude of the analog periodic signal generated by the DA conversion circuit 21 is changed as a result of the signal generation circuit 71 changing the digital periodic signal.

[0078] [Relationship Between Amplitude of Drive Signal and S / N Ratio] Next, the relationship between the amplitude of the drive signal and the S / N ratio in the measurement device 100 according to this embodiment will be described with reference to Fig. 11. Fig. 11 is a graph schematically showing the relationship between the amplitude of the drive signal and the S / N ratio in this embodiment.

[0079] Point A in Figure 11 represents a state where the analog periodic signal has the maximum amplitude and the minimum gain. Point B in Figure 11 represents a state where the analog periodic signal has the maximum amplitude and the maximum gain. Point C in Figure 11 represents a state where the analog periodic signal has the minimum amplitude and the maximum gain. Point D in Figure 11 represents a state where the analog periodic signal has the minimum amplitude and the minimum gain. "Signal A" in Figure 11 represents the analog periodic signal. The ABCD rectangle in Figure 11 represents the range of amplitude and S / N of the drive signal that can be achieved by adjusting the amplitude and gain of the analog periodic signal.

[0080] In the measurement device 100 according to this embodiment, the desired amplitude of the drive signal is realized by changing the gain by the amplitude changing circuit 25 on the line segment AB represented by the thick solid line while keeping the amplitude of the analog periodic signal fixed at its maximum. In other words, when the frequency range is changed from the first frequency range to the second frequency range, the amplitude of the analog periodic signal is the same in the first frequency range and the second frequency range, but the gain is different in the first frequency range and the second frequency range. Unlike the measurement device 100 according to this embodiment, it is also possible to realize the desired amplitude of the drive signal by changing the amplitude of the analog periodic signal via a digital periodic signal by the signal generating circuit 71 on the line segment BC represented by the thin solid line while keeping the gain fixed at its maximum.

[0081] Comparing the two, as shown in Figure 11, the S / N ratio of the drive signal when the amplitude of the drive signal is adjusted along line segment AB is higher than the S / N ratio of the drive signal when the amplitude of the drive signal is adjusted along line segment BC. In the former case, the S / N ratio of the drive signal can be maintained at a high value even if the amplitude of the drive signal is small. This is because the S / N ratio of the drive signal depends on the amplitude of the analog periodic signal and not on the gain. In range α shown in Figure 11, the S / N ratio of the drive signal is highest on line segment AB. Range α is the range in which the amplitude of the drive signal is equal to or greater than the product of the maximum amplitude and minimum gain of the analog periodic signal and is equal to or less than the product of the maximum amplitude and minimum gain of the analog periodic signal.

[0082] However, if the amplitude of the desired drive signal is excessively small, it may not be possible to achieve the desired drive signal amplitude on the line segment AB. In this case, the measurement device 100 according to this embodiment achieves the desired drive signal amplitude by changing the amplitude of the analog periodic signal via the digital periodic signal using the signal generation circuit 71 while keeping the gain fixed at a minimum on the line segment AD represented by the thick dashed line. In other words, when the frequency range changes from the first frequency range to the second frequency range, and the second frequency range is narrower than the frequency range when the gain is set to a minimum value, the signal generation circuit 71 changes the digital periodic signal. Unlike the measurement device 100 according to this embodiment, it is also possible to achieve the desired drive signal amplitude on the line segment CD represented by the thin dashed line by changing the gain using the amplitude change circuit 25 while keeping the amplitude of the analog periodic signal fixed at a minimum.

[0083] Comparing the two, as shown in Figure 11, the S / N ratio of the drive signal when the amplitude of the drive signal is adjusted on line segment AD is higher than the S / N ratio of the drive signal when the amplitude of the drive signal is adjusted on line segment CD. In the former case, the S / N ratio of the drive signal increases the further away from point D. In range β shown in Figure 11, the S / N ratio of the drive signal is highest on line segment AD. Range β is the range in which the amplitude of the drive signal is equal to or greater than the product of the minimum amplitude value of the analog periodic signal and the minimum gain value, and is equal to or less than the product of the maximum amplitude value of the analog periodic signal and the minimum gain value.

[0084] As described above, in the measurement device 100 according to this embodiment, the amplitude of the drive signal is adjusted on the line segments AB and AD to realize the narrow range mode and the wide range mode. As a result, compared to when the amplitude of the drive signal is adjusted on the line segments BC and CD, the signal-to-noise ratio of the drive signal is improved, and it is possible to suppress a decrease in repeatability.

[0085] If both the narrow range mode and the wide range mode can be achieved by adjusting the amplitude of the drive signal on the line segment AB, then both modes can be achieved while maintaining a high S / N ratio for the drive signal. While the narrow range mode can be achieved by adjusting the amplitude of the drive signal on the line segment AB, there are cases where the wide range mode cannot be achieved by adjusting the amplitude of the drive signal on the line segment AB. Even in such cases, the wide range mode can be achieved by adjusting the amplitude of the drive signal on the line segment AD, so the wide range mode can be achieved while maintaining a relatively high S / N ratio for the drive signal.

[0086] When both modes are realized by adjusting the amplitude of the drive signal on line segment AB, the gain is different in both modes. Even when the narrow range mode is realized by adjusting the amplitude of the drive signal on line segment AB and the wide range mode is realized by adjusting the amplitude of the drive signal on line segment AD, the gain is different in both modes unless the narrow range mode coincides with point A. In either case, the frequency ranges are different in both modes, so it can be said that the gain differs depending on the frequency range of each mode.

[0087] At points A and B, the amplitude of the analog periodic signal does not need to be maximum, and may be, for example, 0.8 to 1.0 times its maximum value. At points C and D, the amplitude of the analog periodic signal does not need to be minimum, and may be, for example, 1.0 to 1.2 times its minimum value. At points B and C, the gain does not need to be maximum, and may be, for example, 0.8 to 1.0 times its maximum value. At points A and D, the gain does not need to be minimum, and may be, for example, 1.0 to 1.2 times its minimum value.

[0088] [Driving Operation of Light Source 20] Next, with reference to Fig. 12, an example of the driving operation of the light source 20 executed by the processing circuitry 70 in step S101A shown in Fig. 7B and step S104A shown in Fig. 7C will be described. Fig. 12 is a flowchart showing an example of the driving operation of the light source 20 executed by the processing circuitry 70. The processing circuitry 70 executes the operations of steps S201 to S206 shown in Fig. 12.

[0089] <Step S201> The processing circuit 70 determines the measurement mode, which is either the narrow range mode or the wide range mode.

[0090] <Step S202> The processing circuit 70 reads the set value of the amplitude of the drive signal corresponding to the measurement mode from the memory 72. The memory 72 stores the set values ​​of the amplitude of the drive signal in the narrow range mode and the wide range mode before the measurement operation.

[0091] <Step S203> The processing circuit 70 determines whether the set value of the amplitude of the drive signal is greater than the value obtained by multiplying the maximum value of the amplitude of the analog periodic signal by the minimum value of the gain. This value corresponds to the value on the horizontal axis of point A in Figure 11. If the determination is Yes, the processing circuit 70 performs the operation of step S204. If the determination is No, the processing circuit 70 performs the operation of step S205.

[0092] <Step S204> The processing circuit 70 determines the amplitude of the analog periodic signal to be the maximum value, and determines the gain by dividing the set value of the amplitude of the drive signal by the maximum amplitude of the analog periodic signal. The gain and the amplitude of the analog periodic signal determined in this way can realize the amplitude of the drive signal on the line segment AB shown in Figure 11.

[0093] <Step S205> The processing circuit 70 determines the gain to be the minimum value, and determines the amplitude of the analog periodic signal as the value obtained by dividing the set value of the amplitude of the drive signal by the minimum value of the gain. The gain and amplitude of the analog periodic signal determined in this way can realize the amplitude of the drive signal on the line segment AD shown in Figure 11.

[0094] <Step S206> More specifically, the signal generation circuit 71 included in the processing circuit 70 outputs a digital periodic signal corresponding to the analog periodic signal whose amplitude has been determined as described above to the DA conversion circuit 21 as shown in Fig. 9. The "D signal" shown in Fig. 12 represents the digital periodic signal. The processing circuit 70 further outputs a signal corresponding to the gain determined as described above to the amplitude change circuit 25 via a signal line 80 as shown in Fig. 9.

[0095] The above driving operation allows the light source 20 to be driven by a driving signal with a high S / N ratio. Therefore, the measurement device 100 according to this embodiment can suppress a decrease in repeatability compared to a measurement device having the conventional configuration shown in Fig. 8, and can acquire measurement data of the object 10 more accurately.

[0096] A portion of the above driving operation may be modified as follows: Before the measurement operation, the following table, created based on the processing in steps S203 to S205, is stored in the memory 72. The table includes correspondence relationships between the amplitudes of multiple driving signals, the amplitudes of multiple analog periodic signals, and multiple gains. Each of the amplitudes of the multiple driving signals corresponds to one of the amplitudes of the multiple analog periodic signals and one of the multiple gains. In the driving operation shown in FIG. 12 , the processing circuit 70 may read the table from the memory 72 instead of steps S203 to S205, and determine the amplitude and gain of the analog periodic signal corresponding to the set value of the amplitude of the driving signal based on the table.

[0097] [Example] Next, with reference to FIGS. 13 to 14C and Table 1, an example of the driving operation of the light source 20 included in the measurement device 100 according to this embodiment will be described. FIG. 13 is a graph showing the relationship between time and voltage of the driving signal within the light source 20 in this example. The horizontal axis represents time, and the vertical axis represents the voltage of the driving signal, i.e., the driving voltage. In the example shown in FIG. 13, the amplitude of the driving voltage is approximately ±250 mV. This driving voltage is achieved by combining the amplitude and gain of the analog periodic signal under the following conditions: the number of bits of the digital periodic signal is 14, the maximum amplitude of the analog periodic signal is ±1.0 V, and the gain adjustment range is 0.5 to 1.0.

[0098] Table 1 shows the repeatability for three example combinations of the analog periodic signal amplitude and gain. In the first example, the analog periodic signal amplitude is ±500 mV and the gain is 0.5. In the second example, the analog periodic signal amplitude is ±330 mV and the gain is 0.75. In the third example, the analog periodic signal amplitude is ±250 mV and the gain is 1.0.

[0099] The repeatability was evaluated by measuring the distance and velocity 50 times for a stationary object 10 located 1 m away from the measurement device 100. The drive voltage error shown in Table 1 represents the integral nonlinearity error evaluated by dividing the two cycles of the triangular waveform drive voltage shown in FIG. 13 into an up-chirp period and a down-chirp period. The up-chirp period of the drive voltage corresponds to regions 2 and 4 shown in FIG. 13, and the down-chirp period of the drive voltage corresponds to regions 1, 3, and 5.

[0100] As shown in Table 1, even though the actual drive voltage amplitude is almost the same in the first to third examples, the drive voltage error, the standard deviation of the distance, and the standard deviation of the velocity are smallest in the first example, second smallest in the second example, and largest in the third example.

[0101] 14A to 14C are graphs showing enlarged portions of the relationship between drive voltage and time for the first to third examples, respectively. As shown in FIGS. 14A and 14B, the drive voltage variations are approximately the same when the gain is 0.5 and 0.75. As shown in FIG. 14C, the drive voltage variations when the gain is 1.0 are greater than the drive voltage variations when the gain is 0.5 and 0.75. The drive voltage variations shown in FIGS. 14A to 14C correspond to the drive voltage errors shown in Table 1.

[0102] From the examples, it can be seen that the larger the amplitude of the analog periodic signal, the more the decrease in repeatability can be suppressed, and the more accurately measurement data of the object 10 can be acquired.

[0103] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0104] [Technology 1] A measurement device comprising: a light-emitting element that emits light to illuminate an object, wherein the frequency of the light changes periodically and the frequency range within which the frequency changes is adjustable; a signal generation circuit that generates a digital periodic signal; a digital-to-analog conversion circuit that converts the digital periodic signal into an analog periodic signal and outputs the analog periodic signal; an amplitude change circuit that adjusts the amplitude of the analog periodic signal using a gain to generate a drive signal; a drive circuit that changes the frequency based on the drive signal; and a signal line electrically connected to the amplitude change circuit, the signal line being for controlling the gain.

[0105] This measurement device makes it possible to obtain measurement data of an object more accurately.

[0106] [Technology 2] The measurement device according to Technology 1, wherein the gain varies depending on the frequency range.

[0107] This measurement device allows the gain to be adjusted to vary the frequency range of the light.

[0108] [Technology 3] The measurement device according to Technology 1 or 2, wherein the amplitude changing circuit includes a digital potentiometer that defines the gain.

[0109] This measurement device allows the gain to be adjusted using a variable resistor.

[0110] [Technology 4] The measurement device according to any one of Technologies 1 to 3, wherein, when the frequency range is changed, the amplitude change circuit changes the gain while keeping the amplitude of the analog periodic signal output from the digital-to-analog conversion circuit fixed.

[0111] In this measurement device, the amplitude of the analog periodic signal is fixed, so that the frequency range of the light can be changed while maintaining a high signal-to-noise ratio of the drive signal.

[0112] [Technology 5] The measurement device according to any one of Technologies 1 to 3, wherein when the frequency range is changed, if a desired frequency range cannot be achieved even if the amplitude changing circuit changes the gain while the amplitude of the analog periodic signal output from the digital-to-analog conversion circuit is fixed, the signal generation circuit changes the digital periodic signal.

[0113] This measurement device can achieve the desired narrow frequency range while still providing a relatively high signal-to-noise ratio for the drive signal.

[0114] [Technology 6] The measurement device according to any one of Technologies 1 to 3, wherein, when the frequency range is changed from a first frequency range to a second frequency range, the amplitude of the analog periodic signal is the same in the first frequency range and in the second frequency range, and the gain is different in the first frequency range and in the second frequency range.

[0115] In this measurement device, the amplitude of the analog periodic signal is fixed, so that the frequency range of the light can be changed while maintaining a high signal-to-noise ratio of the drive signal.

[0116] [Technology 7] The measurement device according to any one of Technologies 1 to 3, wherein when the frequency range is changed from a first frequency range to a second frequency range, and the second frequency range is narrower than the frequency range when the gain is set to a minimum value, the signal generation circuit changes the digital periodic signal.

[0117] This measurement device can achieve the desired narrow frequency range while still providing a relatively high signal-to-noise ratio for the drive signal.

[0118] The measurement device according to the embodiment of the present disclosure can be used, for example, in a ranging system mounted on a vehicle such as an automobile, an unmanned aerial vehicle (UAV), or an automated guided vehicle (AGV), or for vehicle detection purposes.

[0119] 10 Object 20 Light source 20L ０ Laser light 20L １ Reference light 20L２ Irradiation light 20L ３ Reflected light 20L ４ Interference light 21 DA conversion circuit 22 Low-pass filter 23 Driver circuit 24 Light-emitting element 25 Amplitude change circuit 30 Interference optical system 40 Beam shaper 50 Optical deflector 60 Photodetector 70 Processing circuit 72 Memory 80 Signal line 100 Measurement device

Claims

1. A measuring device comprising: a light-emitting element that emits light for irradiating an object, wherein the frequency of the light changes periodically and the frequency range in which the frequency changes is adjustable; a signal generation circuit that generates a digital periodic signal; a digital-to-analog conversion circuit that converts the digital periodic signal into an analog periodic signal and outputs the analog periodic signal; an amplitude change circuit that adjusts the amplitude of the analog periodic signal by a gain to generate a drive signal; a drive circuit that changes the frequency based on the drive signal; and a signal line electrically connected to the amplitude change circuit for controlling the gain.

2. The measuring device according to claim 1, wherein the gain varies according to the frequency range.

3. The measuring device according to claim 1 or 2, wherein the amplitude change circuit includes a digital potentiometer that defines the gain.

4. When changing the frequency range, the amplitude change circuit changes the gain while fixing the amplitude of the analog periodic signal output from the digital-to-analog conversion circuit. The measuring device according to claim 1 or 2.

5. When changing the frequency range and fixing the amplitude of the analog periodic signal output from the digital-to-analog conversion circuit, if the desired frequency range cannot be achieved even when the amplitude change circuit changes the gain, the signal generation circuit changes the digital periodic signal. The measuring device according to claim 1 or 2.

6. When changing the frequency range from a first frequency range to a second frequency range, the amplitude of the analog periodic signal is the same in the case of the first frequency range and the case of the second frequency range, and the gain is different in the case of the first frequency range and the case of the second frequency range. The measuring device according to claim 1 or 2.

7. When changing the frequency range from a first frequency range to a second frequency range, and the second frequency range is narrower than the frequency range when the gain is set to the minimum value, the signal generation circuit changes the digital periodic signal. The measuring device according to claim 1 or 2.

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