Measuring equipment

Abstract

To achieve distance measurement by an FMCW system using a laser light source having a response delay.SOLUTION: A measuring apparatus comprises: a generation device that generates frequency-modulated light; an optical device that irradiates an object with the light and causes reflected light from the object and reference light to interfere with each other; a detection device that detects an interference wave between the reflected light and the reference light and outputs a beat signal; and a signal processing device that obtains a distance to the object on the basis of a time change of beat frequency of the beat signal.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a measurement device. [Background technology]

[0002] There are known measurement devices such as LiDAR (Light Detection and Ranging, Laser Imaging Detection and Ranging) that acquire distance information to surrounding objects by measuring light (see, for example, Patent Document 1). FMCW (Frequency Modulated Continuous Wave) measurement devices irradiate the object with frequency-modulated irradiation light, and measure the distance to the object and the relative speed to the object based on the beat frequency of the interference wave generated by interference between the light reflected from the object and a reference light. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2020-502503 Summary of the Invention [Problem to be solved by the invention]

[0004] In FMCW measurement devices, the direct current of the laser light source is generally controlled to modulate the light so that the frequency increases or decreases linearly over time. However, due to a response delay of the laser light source, the frequency of the light actually output from the laser light source may not increase or decrease linearly over time.

[0005] An object of the present invention is to realize distance measurement by the FMCW method using a laser light source with a response delay. [Means for solving the problem]

[0006] One aspect of the present invention for achieving the above object is a measurement device including: a generating device that generates frequency-modulated light; an optical device that irradiates an object with the light and causes reflected light from the object to interfere with a reference light; a detecting device that detects an interference wave between the reflected light and the reference light and outputs a beat signal; and a signal processing device that determines the distance to the object based on a change over time in the beat frequency of the beat signal.

[0007] Other problems and solutions disclosed in the present application will be made clear in the detailed description and drawings. [Effects of the Invention]

[0008] According to the present invention, distance can be measured by the FMCW method using a laser light source with a response delay. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is an explanatory diagram of the overall configuration of a measurement device 1. As shown in FIG. [Figure 2] 2A and 2B are diagrams illustrating the time-dependent changes in the frequencies of the measurement light and the reflected light. [Figure 3] 3A and 3B are diagrams illustrating the outline of the change in beat frequency over time. [Figure 4] FIG. 4 is a flow diagram of the processing performed by the analysis unit 42. [Figure 5] FIG. 5 is an explanatory diagram of a method for measuring the beat frequency. [Figure 6] Fig. 6A is an explanatory diagram of a first table stored in advance in the analysis unit 42. Fig. 6B is an explanatory diagram of a second table stored in advance in the analysis unit 42. [Figure 7] FIG. 7 is a diagram illustrating the outline of the change in beat frequency fB over time when the object 90 is moving. [Figure 8] 8A to 8C are explanatory diagrams showing the change over time in the frequency of frequency-modulated light. [Figure 9]9A and 9B are explanatory diagrams of the case where light is modulated so that the frequency increases or decreases linearly with the passage of time. [Figure 10] FIG. 10 is a graph showing the time variation of the frequency of the measurement light and the reflected light when the object 90 is moving. [Figure 11] 11A and 11B are explanatory diagrams showing a case where the frequency increases or decreases non-linearly with the passage of time. DETAILED DESCRIPTION OF THE INVENTION

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, identical or similar components may be designated by common reference numerals, and redundant description may be omitted.

[0011] <Overall structure> FIG. 1 is an explanatory diagram of the overall configuration of a measurement device 1. As shown in FIG.

[0012] The measuring device 1 is a device that measures the distance to an object 90. The measuring device 1 has a function as what is called LiDAR (Light Detection and Ranging, Laser Imaging Detection and Ranging). The measuring device 1 measures the distance to the object 90 using the FMCW (Frequency Modulated Continuous Wave) method. That is, the measuring device 1 irradiates the object 90 with frequency-modulated measurement light (irradiation light), causes the reflected light from the object 90 to interfere with the measurement light (reference light), and measures the distance to the object 90 based on the frequency (beat frequency) of a beat signal that is a detection result of the interference light. Note that the measuring device 1 can measure not only the distance to the object 90 but also the relative speed with respect to the object 90.

[0013] The measurement device 1 includes a generating device 10, an optical device 20, a detecting device 30, and a signal processing device 40.

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

[0015] The signal generator 11 generates a voltage signal for controlling the current source 12. The signal generator 11 is, for example, a waveform generator, and generates a voltage signal, for example, a triangular wave, and outputs it to the current source 12. The current source 12 generates a current signal for controlling the light source. The current source 12 generates a current signal corresponding to the voltage signal of the signal generator 11. For example, the current source 12 generates a triangular wave current signal corresponding to the triangular wave voltage signal and outputs it to the laser light source 13. The laser light source 13 emits light whose frequency is modulated (frequency-modulated light). For example, the laser light source 13 is configured using a distributed feedback (DFB) laser element. The laser light source 13 generates laser light whose frequency corresponds to the current signal of the current source 12. The laser light generated is frequency-modulated in the range of 193.4024 to 193.4266 THz (λ=1549.903 to 1550.097 nm). For example, the laser light source 13 generates laser light whose frequency gradually increases or decreases according to a triangular wave current signal (frequency-modulated light). The laser light source 13 outputs the laser light to the optical device 20. The temperature regulator 14 adjusts the temperature of the laser light source 13 (particularly the laser element) to a predetermined temperature. The temperature regulator 14 has, for example, a temperature sensor 14A and a thermoelectric element (for example, a Peltier element), and measures the temperature of the laser light source 13 with the temperature sensor 14A and adjusts the laser light source 13 to a predetermined temperature by feedback-controlling the thermoelectric element based on the measurement result of the temperature sensor 14A.

[0016] The optical device 20 is a device that irradiates the object 90 with frequency-modulated light (measurement light) and causes the reflected light from the object 90 to interfere with the reference light (measurement light). The optical device 20 uses a portion of the measurement light input from the generation device 10 as irradiation light to irradiate the object 90, and a portion of the measurement light input from the generation device 10 as reference light, and causes the reflected light from the object 90 to interfere with the reference light to generate interference light (interference wave). The optical device 20 outputs the interference light (interference wave) caused by the interference of the reflected light and the reference light to the detection device 30. The optical device 20 has a branching device 21, a circulator 22, an optical system 23, an optical waveguide 24, and a coupler 25. The splitter 21 splits the frequency-modulated light from the generation device 10. The splitter 21 is configured, for example, by an optical coupler. One of the split lights is output to the circulator 22 and becomes the illumination light to be irradiated onto the object 90. The other of the split lights is output to the optical waveguide 24 and becomes the reference light to be interfered with the reflected wave. The circulator 22 guides the light (irradiated light) from the branching device 21 to the optical system 23 and also guides the light (reflected light) from the optical system 23 to the coupler 25 . The optical system 23 irradiates light toward the object 90 and collects and outputs the reflected light. The optical system 23 is composed of optical elements such as lenses, mirrors, and prisms. The optical system 23 has, for example, a light-projecting optical system that irradiates the irradiated light toward the object, and a light-receiving optical system that collects the reflected light. The optical system 23 may also have a function of scanning the irradiated light. The optical system 23 outputs the collected reflected light to the circulator 22. The reflected light is input to the coupler 25 via the circulator 22. The optical waveguide 24 forms an optical path of a predetermined length from the splitter 21 to the coupler 25. The optical waveguide 24 guides the reference light over a predetermined optical path length from the splitter 21 to the coupler 25. The optical waveguide 24 is formed of, for example, an optical fiber. The coupler 25 combines the reflected light from the circulator 22 with the reference light from the optical waveguide 24. The coupler 25 is configured by, for example, an optical coupler. The coupler 25 functions as an interferometer that causes interference between the reflected light and the reference light, and generates interference light (interference wave) by causing interference between the reflected light and the reference light. The coupler 25 outputs the interference light to the detection device 30.

[0017] The detector 30 detects the interference light between the reflected light and the reference light and outputs a beat signal. The detector 30 includes a photoelectric converter 31 and an amplifier 32. The photoelectric converter 31 outputs an electric signal (current signal) corresponding to the intensity of the detected optical signal (here, interference light). The photoelectric converter 31 is, for example, a photodiode. The interference light detected by the photoelectric converter 31 is a wave whose amplitude changes periodically due to interference between reflected light and reference light, which have different frequencies. The amplifier 32 converts the current signal of the photoelectric converter 31 into a voltage signal and outputs it. The amplifier 32 is configured, for example, by a transimpedance amplifier. The beat signal output from the amplifier 32 is a signal that indicates the difference in frequency between the reflected light and the reference light. The beat frequency of the beat signal corresponds to the frequency of the beat component of the interference light. The beat frequency of the beat signal also corresponds to the difference in frequency between the reflected light and the reference light.

[0018] The signal processing device 40 is a device that determines the distance to the object 90 based on the beat signal. The signal processing device 40 has an A / D converter, an arithmetic unit, a storage device, etc., which are not shown. The arithmetic unit is configured as an arithmetic processing device such as a CPU, a GPU, or an MPU. The storage device is configured as a main storage device and an auxiliary storage device, and is a device that stores programs and data. The arithmetic unit executes the programs stored in the storage device, thereby performing various processes for measuring the distance to the object 90. In FIG. 1, the various processes performed by the signal processing device 40 are shown as functional blocks.

[0019] The signal processing device 40 has a signal acquiring unit 41, an analyzing unit 42, and an output unit 43. The signal acquiring unit 41 acquires the beat signal of the detection device 30 as a digital signal. The signal acquiring unit 41 is configured by, for example, an A / D converter (such as an A / D conversion board). The analyzing unit 42 calculates the distance to the object 90 based on the beat signal. The processing of the analyzing unit 42 will be described later. The output unit 43 outputs the analysis result of the analyzing unit 42 to the outside. For example, the output unit 43 outputs distance data indicating the distance to the object 90 and speed data indicating the relative speed of the object 90 to a vehicle ECU, which is an external device.

[0020] <Reference Explanation 1> Before describing the processing of the analysis unit 42 of this embodiment, a general FMCW measurement method will be described.

[0021] 9A and 9B are explanatory diagrams illustrating the case where light is modulated so that the frequency linearly increases or decreases with the passage of time. FIG. 9A is a graph showing the temporal change in the frequency of the measurement light and the reflected light, with the horizontal axis representing time and the vertical axis representing frequency. Note that the period in which the frequency increases is sometimes referred to as the gradual increase period, and the period in which the frequency decreases is sometimes referred to as the gradual decrease period. FIG. 9B is a graph showing the frequency analysis results of the beat signal (analysis results obtained by fast Fourier transform (FFT)), with the horizontal axis representing frequency and the vertical axis representing amplitude (intensity). First, a case where the object 90 is stationary (when the relative velocity with respect to the object 90 is zero) will be described.

[0022] f in the figure B indicates the frequency difference between the measurement light (illumination light, reference light) and the reflected light. Δt indicates the time it takes for the light to travel to and from the object 90. T indicates the gradual increase period or gradual decrease period (the modulation time for modulating the frequency). F indicates the modulation frequency width (the width of increase or decrease in frequency).

[0023] Here, since the frequency increases linearly with the passage of time, the slope of the graph is constant, and Δt is given by the following equation (1). Δt=(T / F)·fB ···(1)

[0024] Here, if the speed of light is c and the distance to the object 90 is R, it takes time Δt for light to travel to and from the object 90, so the distance R is given by the following equation (2). 2R=c Δt R=(c T / 2F) f B ···(2)

[0025] In the above equation (2), the frequency f B can be obtained by FFT-analyzing the beat signal as shown in FIG. 9B. The speed of light c, modulation time T, and modulation frequency width F are known. Therefore, the frequency f B By calculating the distance R to the object 90, the distance R can be calculated.

[0026] 10 is a graph showing the time variation of the frequency of the measurement light and the reflected light when the object 90 is moving. Note that the light is modulated so that the frequency increases or decreases linearly with the passage of time. As shown in the graph of the reflected light, when the object 90 is moving, the frequency shifts due to the Doppler effect.

[0027] f in the figure dop f indicates the frequency shift due to the Doppler effect (Doppler shift frequency). up f indicates the frequency difference between the measurement light (illumination light, reference light) and the reflected light during the gradual increase period. dn indicates the difference in frequency between the measurement light (illumination light, reference light) and the reflected light during the gradual decrease period.

[0028] frequency f up can be obtained by FFT analysis of the beat signal during the increasing period. dn can be obtained by FFT analysis of the beat signal during the decreasing period. The frequency analysis of the beat signal is performed separately for the increasing period and the decreasing period. Then, the frequency f upand frequency f dn Based on this, the frequency f B can be calculated, and the distance R can be calculated based on the above-mentioned equation (2). f B =(f up +f dn ) / twenty three)

[0029] Also, the frequency f up and frequency f dn Based on this, the Doppler shift frequency f dop can be calculated, and the relative velocity V can be calculated based on the following equation (5). f dop =(f up -f dn ) / twenty four) V=(λ / 2) f dop ···(5) (λ is the wavelength of light)

[0030] <Reference explanation 2: Light source response delay> 11A and 11B are explanatory diagrams illustrating a case where the frequency increases or decreases nonlinearly with the passage of time. FIG. 11A is a graph showing the temporal change in the frequency of the measurement light (illumination light, reference light) and the reflected light, with the horizontal axis representing time and the vertical axis representing frequency. FIG. 11B is a graph showing the frequency analysis results (FFT analysis results) of the beat signal, with the horizontal axis representing frequency and the vertical axis representing amplitude (intensity). Here, for simplicity of explanation, it is assumed that the object 90 is stationary (the relative velocity with respect to the object 90 is zero).

[0031] In an actual laser light source 13, there is a response delay between when the input current changes and when the frequency of the output laser light changes. As a result, even if the current source 12 inputs a triangular wave current signal to the laser light source 13, the frequency of the laser light output from the laser light source 13 does not increase or decrease linearly over time.

[0032] When the frequency changes nonlinearly in this way, the frequency difference between the measurement light (illumination light, reference light) and the reflected light is not constant. As a result, as shown in FIG. 11B, even if frequency analysis (FFT analysis) is performed on the beat signal, it is difficult to find an intensity peak at a specific frequency (in contrast, when the frequency changes linearly, a peak appears at a specific frequency, as shown in FIG. 9B). Therefore, when the frequency changes nonlinearly, it is difficult to find the beat frequency f B As a result, it becomes difficult to calculate the distance R based on the above-mentioned equation (2).

[0033] <Processing of the analysis unit 42> 2A and 2B are schematic explanatory diagrams showing the temporal changes in the frequencies of the measurement light (irradiation light, reference light) and the reflected light. Fig. 2A is an explanatory diagram showing the case where the object 90 is close. Fig. 2B is an explanatory diagram showing the case where the object 90 is far. In each diagram, the horizontal axis represents time, and the vertical axis represents frequency.

[0034] As shown in FIGS. 2A and 2B, due to the effect of a response delay of the laser light source 13, the difference in frequency between the measurement light (irradiation light, reference light) and the reflected light during the gradual increase period gradually increases (f B1 <f B2 <f B3 When the object 90 is close, the change over time in the difference in frequency between the measurement light and the reflected light is relatively small, as shown in FIG. 2A. On the other hand, when the object 90 is far, the change over time in the difference in frequency between the measurement light and the reflected light is relatively large, as shown in FIG. 2B.

[0035] 3A and 3B are diagrams outlining the change in beat frequency over time. FIG. 3A is an explanatory diagram for the case where the object 90 is close. FIG. 3B is an explanatory diagram for the case where the object 90 is far away. In each diagram, the horizontal axis represents time, and the vertical axis represents beat frequency. The dotted lines in the diagrams correspond to linear approximations of the solid line graphs.

[0036] As shown in FIGS. 3A and 3B, the beat frequency of the beat signal changes over time due to the effect of the response delay of the laser light source 13. (In contrast, when the frequency increases or decreases linearly as shown in FIG. 9A, the beat frequency remains constant during the gradual increase period or the gradual decrease period and does not change over time.) When the object 90 is close, the change in the beat frequency over time is relatively small, as shown in FIG. 3A. For example, when the object 90 is close, the ratio of the change in the beat frequency to the change in time (corresponding to the slope of the graph) is relatively small, as shown in FIG. 3A. On the other hand, when the object 90 is far, the change in the difference in frequency between the measurement light (illumination light, reference light) and the reflected light over time, i.e., the change in the beat frequency over time, is relatively large, as shown in FIG. 3B. For example, when the object 90 is close, the ratio of the change in the beat frequency to the change in time is relatively large, as shown in FIG. 3B.

[0037] Therefore, the analysis unit 42 obtains the change in the beat frequency over time, and obtains the distance to the object 90 based on the change in the beat frequency over time. Specifically, the analysis unit 42 obtains the distance to the object 90 based on the ratio of the change in the beat frequency to the change in time (the rate of change in the beat frequency over time; equivalent to the slope of the graph).

[0038] 4 is a flow diagram of the processing performed by the analysis unit 42. Each process in the diagram is realized by the arithmetic processing unit constituting the signal processing device 40 executing an analysis program.

[0039] The analysis unit 42 first measures the beat frequency for each time period (S101). Fig. 5 is an explanatory diagram of a method for measuring the beat frequency. The graph in the figure shows the beat signal, with the horizontal axis representing time and the vertical axis representing voltage.

[0040] The analysis unit 42 first determines the time at which the beat signal reaches its peak (peak time). The black circles on the graph in the figure indicate the peaks (extreme values; maximum or minimum values) of the beat signal. For example, the analysis unit 42 sequentially measures the times at which the sign of the voltage gradient of the beat signal (the differential value of the beat signal) changes as peak times. Here, the analysis unit 42 measures the peak time at which the beat signal reaches its maximum value (the time at which the sign of the voltage gradient changes from positive to negative) and the peak time at which the beat signal reaches its minimum value (the time at which the sign of the voltage gradient changes from negative to positive). However, the analysis unit 42 may measure only the peak time of the maximum value of the beat signal or only the peak time of the minimum value of the beat signal. Instead of measuring the peak time of each peak of the beat signal, the analysis unit 42 may detect the peak time, for example, at predetermined intervals or at predetermined time intervals. The analysis unit 42 measures multiple peak times during the gradual increase period or during the gradual increase period.

[0041] Next, the analysis unit 42 calculates the beat frequency based on the interval between the two peak times. For example, the analysis unit 42 calculates the beat frequency at a time (timing) based on the interval between the peak time of a certain maximum value of the beat signal and the peak time of the next maximum value (the time of one cycle of the beat signal). The analysis unit 42 may also calculate the beat frequency at a time based on the interval between the peak time of a certain minimum value of the beat signal and the peak time of the next minimum value (the time of one cycle of the beat signal). The analysis unit 42 may also calculate the beat frequency at a time based on the interval between the peak time of a certain maximum value (or minimum value) of the beat signal and the peak time of the next minimum value (or maximum value) (the time of a half cycle of the beat signal). Alternatively, the analysis unit 42 may calculate the beat frequency at a time based on the interval between the peak time of a certain maximum value (or minimum value) of the beat signal and the peak time of a maximum value (or minimum value) several cycles later. The analysis section 42 measures the beat frequency at each of a plurality of times (a plurality of timings) during the gradual increase period or the gradual decrease period.

[0042] 5, the analysis unit 42 alternately calculates the beat frequency based on the peak times of the two maximum values ​​and the beat frequency based on the peak times of the two minimum values ​​every half period. This allows the beat frequency to be calculated every half period of the beat signal, making it possible to calculate the beat frequency with high time resolution.

[0043] Next, the analysis unit 42 obtains a time change in the beat frequency (S102). Here, the analysis unit 42 obtains the ratio of the amount of change in the beat frequency to the amount of change in time (time change rate of the beat frequency) as an index showing the time change in the beat frequency. In other words, the analysis unit 42 calculates the slope of the graph (straight line) shown in FIG. 3A or 3B. Specifically, the analysis unit 42 obtains the rate of change in the beat frequency f for each of the multiple times t obtained in S101. B Based on this, the linear approximation formula (f B =A·t+B), and the slope A of this approximation equation is taken as a value indicating the time change of the beat frequency. (As will be described later, the analysis unit 42 can also calculate the relative velocity of the object 90 based on the intercept B of this approximation equation.) Note that the method for calculating the ratio of the change in the beat frequency to the change in time (the time change rate of the beat frequency) is not limited to the least squares method, and other calculation methods may be used. For example, the analysis unit 42 may calculate the rate of increase in the beat frequency to the increase in time based on the beat frequency at each of two times, immediately after the start and immediately before the end of the gradual increase period (or gradual decrease period) (in other words, the slope of the line connecting the two points may be taken as the time change rate of the beat frequency).

[0044] Next, the analysis unit 42 derives the distance to the object 90 based on the change in the beat frequency over time (here, the ratio of the change in the beat frequency to the change in time; the time change rate of the beat frequency) (S103). FIG. 6A is an explanatory diagram of a first table stored in advance in the analysis unit 42. In the first table, a slope A indicating the change in the beat frequency over time is associated with a distance R. The analysis unit 42 determines the distance R by referring to the first table based on the change in the beat frequency over time (slope A) determined in S102. For example, if the slope indicating the change in the beat frequency over time is A4, the analysis unit 42 will derive the distance to the object 90 as R4 by referring to the first table. Note that the analysis unit 42 determines the distance R by referring to the first table based on the slope A determined in S102. i and A i+1 If the value is between i The distance R corresponding to i and slope A i+1 The distance R corresponding to i+1 Based on this, the distance R corresponding to the gradient A obtained in S102 may be interpolated.

[0045] The analysis unit 42 may derive the relative velocity with respect to the object 90 based on the time change of the beat frequency or the magnitude of the beat frequency. A method for deriving the relative velocity will be described below.

[0046] 6B is an explanatory diagram of a second table stored in advance in the analysis unit 42. In the second table, a slope A indicating a change in beat frequency over time is associated with a reference intercept B0. FIG. 7 shows the beat frequency f B As already explained, when the object 90 is moving, the frequency shifts due to the Doppler effect. dop indicates the frequency shift due to the Doppler effect (Doppler shift frequency). In the figure, the reference intercept B0 and the Doppler shift frequency f dop FIG.

[0047] As already explained, the analysis unit 42 calculates the beat frequencies f for the respective times t calculated in S101. B Based on this, the linear approximation formula (f B =A·t+B) to find the slope A, which indicates the time change in the beat frequency, and the intercept B. Intercept B is an index that indicates the magnitude of the multiple beat frequencies found in S101. Next, the analysis unit 42 determines the reference intercept B0 by referring to the second table based on the change over time (slope A) of the beat frequency determined in S102. The reference intercept B0 in the second table shown in Fig. 6B corresponds to the intercept value when the slope is a specific value A when the object 90 is stationary (see Fig. 7). The reference intercept B0 is an index that indicates the magnitude of the beat frequency when the object 90 is stationary. Then, the analysis unit 42 calculates the difference between the intercept B and the reference intercept B0. As shown in FIG. 7, the difference between the intercept B and the reference intercept B0 is calculated based on the Doppler shift frequency f dop For example, when the gradient indicating the time change of the beat frequency is A4, the analysis unit 42 calculates the intercept B and the reference intercept B 04 By calculating the difference between dop The analysis unit 42 calculates the Doppler shift frequency f dop Based on the above equation (5), the relative velocity V(=(λ / 2) f dop ) can be obtained.

[0048] 8A to 8C are explanatory diagrams showing changes in the frequency of frequency-modulated light over time, where the vertical axis represents time and the vertical axis represents frequency.

[0049] FIG. 8A shows how a gradual increase period in which the frequency gradually increases and a gradual decrease period in which the frequency gradually decreases are alternately repeated. When the signal generator 11 of the generating device 10 outputs a triangular wave voltage signal, the laser light source 13 outputs light whose frequency changes over time (frequency-modulated light) as shown in FIG. 8A. When frequency-modulating light as shown in FIG. 8A (when the frequency of the frequency-modulated light changes over time so that gradual increase periods and gradual decrease periods are alternately repeated), it is desirable that the analyzing unit 42 have a first table (and a second table) for the gradual increase period and a first table (and a second table) for the gradual decrease period, respectively. This makes it possible to determine the distance to the object 90 (and the relative velocity with respect to the object 90) during each of the gradual increase period and the gradual decrease period.

[0050] FIG. 8B shows a repeating pattern of a gradual increase in frequency followed by a sudden drop in frequency. FIG. 8C shows a repeating pattern of a gradual decrease in frequency followed by a sudden rise in frequency. When the signal generator 11 of the generating device 10 outputs a sawtooth voltage signal, the laser light source 13 outputs frequency-modulated light whose frequency changes over time, as shown in FIGS. 8B and 8C. When frequency-modulating light as shown in FIGS. 8B and 8C, the analyzing unit 42 only needs to have one type of first table (and second table). This eliminates the need for the analyzing unit 42 to have first tables for both the gradual increase period and the gradual decrease period, thereby reducing the amount of data in the tables.

[0051] Incidentally, the characteristics of the laser light source 13 (particularly the laser element) change with temperature, and therefore the response delay of the laser light source 13 also changes with temperature. Therefore, the time change in the frequency of the laser light output from the laser light source 13 changes according to the temperature. As a result, even if the distance to the object 90 remains the same, if the temperature changes, the time change (slope A) of the beat frequency calculated in S102 changes. Therefore, it is desirable that the analysis unit 42 has a first table that associates temperature, the change over time of the beat frequency (slope A), and the distance R. In other words, it is desirable that the first table that associates the change over time of the beat frequency (slope A) with the distance R also associates temperature. In this case, the analysis unit 42 detects the temperature using a temperature sensor, and determines the distance R by referring to the first table based on the temperature detected by the temperature sensor and the change over time of the beat frequency (slope A) determined in S102. This can improve the accuracy of distance measurement.

[0052] In the above description, the analysis unit 42 stores in advance a first table that associates the change in beat frequency over time (slope A) with the distance R, and determines the distance R by referring to the first table using the change in beat frequency over time (slope A) determined in S102 as a key. However, the analysis unit 42 may determine the distance R without using a table. For example, the analysis unit 42 may be provided with a function that converts the change in beat frequency over time (slope A) into the distance R, and may determine the distance to the object 90 by using this function to convert the change in beat frequency over time (slope A) determined in S102 into the distance R. In this manner, the analysis unit 42 can also determine the distance to the object 90 based on the change in beat frequency of the beat signal over time.

[0053] Similarly, the distance R may be calculated based on the temperature detected by the temperature sensor and the change over time of the beat frequency (slope A) without using a table. For example, the analysis unit 42 may use a function to calculate the distance R based on the temperature detected by the temperature sensor and the change over time of the beat frequency calculated in S102 (slope A). This also allows the analysis unit 42 to improve the accuracy of measuring the distance.

[0054] When the distance to the object 90 is determined using the temperature detected by the temperature sensor, it is desirable that the temperature sensor detect the temperature of the laser light source 13 (particularly the laser element) of the generation device 10. This allows the distance to the object 90 to be determined according to the temperature characteristics of the laser light source 13, thereby improving the accuracy of distance measurement. In this case, the analysis unit 42 should use the temperature detected by the temperature sensor 14A provided in the temperature adjustment device. This allows the temperature sensor 14A to be used for both purposes. However, the analysis unit 42 may also determine the distance to the object 90 using the temperature detected by a temperature sensor other than the temperature sensor 14A of the temperature adjustment device.

[0055] ===Summary=== The measurement device 1 described above includes a generating device 10, an optical device 20, a detecting device 30, and a signal processing device 40. As shown in FIG. 11A, when a laser light source with a response delay is used, the frequency increases or decreases nonlinearly over time. In such a case, as shown in FIGS. 3A and 3B, the beat frequency of the beat signal changes over time. Furthermore, as shown in FIGS. 3A and 3B, the change in the beat frequency over time differs depending on the distance to the target. Therefore, the signal processing device 40 of this embodiment calculates the distance to the target 90 based on the change in the beat frequency of the beat signal over time. This enables distance measurement using a laser light source with a response delay by the FMCW method. Furthermore, the use of an inexpensive laser light source reduces the cost of the measurement device 1.

[0056] The signal processing device 40 obtains the beat frequency at each of a plurality of times (a plurality of timings) in the gradual increase period or the gradual decrease period (see S101 in FIG. 4), and obtains the time change of the beat frequency based on the obtained plurality of beat frequencies (S102). For example, as shown in FIGS. 3A and 3B, the signal processing device 40 obtains the beat frequency f corresponding to each of three times in a certain gradual increase period. B1 ,f B2 ,f B3 The three beat frequencies f B1 ,f B2 ,f B3Based on this, the ratio of the amount of change in the beat frequency to the amount of change over time (corresponding to the time change in the beat frequency; corresponding to the slope of the graphs shown in FIGS. 3A and 3B) is calculated. As a result, in the process of S103, the distance to the target object can be measured based on the time change in the beat frequency. Note that instead of calculating multiple beat frequencies in the gradual increase period, the signal processing device 40 may also calculate multiple beat frequencies in the gradual decrease period and calculate the time change in the beat frequency (for example, the slope of the graph) based on the calculated multiple beat frequencies.

[0057] As shown in Fig. 5, the signal processing device 40 determines the peak time when the beat signal reaches its peak, and determines the beat frequency based on the interval between peak times. This makes it possible to determine the change in the beat frequency over time during the gradual increase period or gradual decrease period. Note that the method for measuring the beat frequency is not limited to this. For example, the signal processing device 40 may determine the time when the beat signal reaches a predetermined voltage (e.g., 0 V), and also determine the beat frequency based on the interval between times when the beat signal reaches a predetermined voltage (e.g., the center voltage (average voltage) of the beat signal).

[0058] As shown in FIG. 5 , the signal processing device 40 determines the peak time when the beat signal reaches its maximum value and the peak time when the beat signal reaches its minimum value, and calculates the beat frequency for each half cycle of the beat signal based on the interval between the peak times. This allows the beat frequency to be calculated with high time resolution. However, the timing for calculating the beat frequency is not limited to this. For example, the signal processing device 40 may calculate the peak time or the beat frequency for each predetermined cycle or each time a predetermined time has elapsed. Note that calculating the peak time or the beat frequency for each predetermined cycle or each time a predetermined time has elapsed can reduce the computational load on the signal processing device 40 compared to calculating the beat frequency for each half cycle of the beat signal.

[0059] The signal processing device 40 obtains the beat frequency at each of a plurality of times in the gradual increase period or the gradual decrease period (see S101 in FIG. 4), and obtains the relative velocity of the object based on the magnitude of the obtained beat frequencies (see FIGS. 6B and 7). For example, as shown in FIG. 7, the signal processing device 40 obtains a linear approximation formula (f B 6B, the signal processing device 40 calculates the Doppler shift frequency f from the difference between the intercept B and the reference intercept B0. dop This allows us to calculate the relative velocity of the object V(=(λ / 2) f dop ) can be obtained. Instead of obtaining the intercept B of the linear approximation equation by the least squares method, the signal processing device 40 can obtain the Doppler shift frequency f based on an index indicating the magnitude of another beat frequency. dop The relative velocity of the object may be calculated by calculating

[0060] The signal processing device 40 stores in advance a table that associates the change in beat frequency over time with the distance (see FIG. 6A), and determines the distance by referring to this table. This allows the distance to be determined based on the change in beat frequency over time. However, the signal processing device 40 may also determine the distance without using the table.

[0061] When determining distance by referencing a table, it is desirable that the table correlating distance with time-varying beat frequency also correlates temperature.Then, it is desirable that the signal processing device 40 determines distance by referencing the table based on the temperature detected by the temperature sensor and the time-varying beat frequency.This can improve the accuracy of distance measurement.

[0062] It is preferable to obtain the distance by looking up the table based on the temperature detected by the temperature sensor and the time change of the beat frequency, without using a table, thereby improving the accuracy of the distance measurement.

[0063] When the distance to the object 90 is determined using the temperature detected by the temperature sensor, it is desirable that the temperature sensor detects the temperature of the generation device 10 (laser light source 13). This allows the distance to the object 90 to be determined according to the temperature characteristics of the laser light source 13, thereby improving the accuracy of distance measurement.

[0064] The above measurement method involves (1) generating frequency-modulated light, (2) irradiating the light onto the object 90 and causing the reflected light from the object 90 to interfere with the reference light, (3) detecting the interference wave between the reflected light and the reference light with the detection device 30 and outputting a beat signal from the detection device 30, and (4) determining the distance to the object 90 based on the change over time in the beat frequency of the beat signal. This makes it possible to measure the distance by the FMCW method using a laser light source with a response delay.

[0065] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments and includes various modifications. Furthermore, the above embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, some of the configurations of the above embodiments can be added to, deleted from, or replaced with other configurations. [Explanation of symbols]

[0066] 1 measuring device, 10 Generating device, 11 Signal generator, 12 current source, 13 laser light source, 14 temperature controller, 14A temperature sensor, 20 Optical device, 21 Branching device, 22 Circulator, 23 Optical system, 24 optical waveguides, 25 couplers, 30 detection device, 31 photoelectric converter, 32 amplifier, 40 signal processing device, 41 signal acquisition unit, 42 analysis section, 43 output section, 90 Objects

Claims

1. a generator for generating frequency modulated light; an optical device that irradiates the light onto an object and causes reflected light from the object to interfere with a reference light; a detector that detects an interference wave between the reflected light and the reference light and outputs a beat signal; a signal processing device that determines the distance to the object based on a time change in the beat frequency of the beat signal; Equipped with The signal processing device includes: a table in which the change over time and the distance are associated with each other is stored in advance; determining the time change of the beat frequency based on the beat signal output from the detection device, and determining the distance by referring to the table; Measuring equipment.

2. 2. The measuring device according to claim 1, The signal processing device includes: determining the beat frequency at each of a plurality of times during a period in which the frequency of the light increases or decreases, and determining the change over time based on the determined plurality of beat frequencies; Measuring equipment.

3. 3. The measuring device according to claim 2, The signal processing device includes: A peak time at which the beat signal reaches a peak is determined; determining the beat frequency based on the interval between the peak times; Measuring equipment.

4. 4. The measuring device according to claim 3, The signal processing device includes: a peak time when the beat signal reaches a maximum value and a peak time when the beat signal reaches a minimum value are respectively determined; determining the beat frequency for each half period of the beat signal based on the interval between the peak times; Measuring equipment.

5. The measuring device according to any one of claims 1 to 4, The signal processing device includes: determining the beat frequency at each of a plurality of times during a period in which the frequency of the light increases or decreases, and determining the relative velocity of the object based on the magnitudes of the determined plurality of beat frequencies; Measuring device.

6. A measuring device according to any one of claims 1 to 5, A temperature sensor is provided to detect the temperature. The table associates the temperature and the change over time with the distance, the signal processing device determines the distance by referring to the table based on the temperature detected by the temperature sensor and the change over time; Measuring equipment.

7. A measuring device according to any one of claims 1 to 6, A temperature sensor is provided to detect the temperature. the signal processing device calculates the distance based on the temperature detected by the temperature sensor and the change over time. Measuring equipment.

8. The measuring device according to claim 7, The temperature sensor detects the temperature of the generating device.

9. generating frequency modulated light; irradiating the light onto an object and causing reflected light from the object to interfere with a reference light; detecting an interference wave between the reflected light and the reference light with a detection device, and outputting a beat signal from the detection device; and determining a distance to the object based on a time change in a beat frequency of the beat signal; In addition to carrying out the above, a table in which the change over time and the distance are associated with each other is stored in advance; determining the time change of the beat frequency based on the beat signal output from the detection device, and determining the distance by referring to the table; Measurement method.

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