JP7804493B2 - Measuring equipment - Google Patents

Description

The present invention relates to a measuring device.

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

Special Publication No. 2020-502503

In FMCW measurement devices, it is common to control the direct current of the laser light source to modulate the light so that the frequency increases or decreases linearly over time. However, due to response delays in the laser light source, the frequency of the light actually output from the laser light source may not increase or decrease linearly over time.

The present invention aims to achieve distance measurement using the FMCW method using a laser light source with a response delay.

One aspect of the present invention to achieve the above object is a measurement device that includes a generator that generates frequency-modulated light, an optical device that irradiates an object with the light and causes the reflected light from the object to interfere with a reference light, a detector that detects the interference wave between the reflected light and the reference light and outputs a beat signal, and a signal processor that determines the distance to the object based on the change over time in the beat frequency of the beat signal.

Furthermore, the problems disclosed in this application and the solutions thereto will be made clear in the detailed description and drawings.

According to the present invention, distance can be measured using the FMCW method with a laser light source that has a response delay.

FIG. 1 is an explanatory diagram of the overall configuration of a measurement device 1. 2A and 2B are diagrams illustrating the change over time in the frequencies of the measurement light and the reflected light. 3A and 3B are diagrams illustrating the outline of the change in beat frequency over time. FIG. 4 is a flow diagram of the processing performed by the analysis unit 42. FIG. 5 is an explanatory diagram of a method for measuring the beat frequency. 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. FIG. 7 is a diagram illustrating the outline of the change in beat frequency f _B over time when the object 90 is moving. 8A to 8C are explanatory diagrams showing the change over time in the frequency of frequency-modulated light. 9A and 9B are diagrams illustrating the case where light is modulated so that the frequency increases or decreases linearly with the passage of time. 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. 11A and 11B are diagrams illustrating a case where the frequency increases or decreases non-linearly with the passage of time.

The following describes embodiments of the present invention with reference to the drawings. Note that in the following description, identical or similar components may be designated by common reference numerals, and redundant explanations may be omitted.

<Overall structure>
FIG. 1 is an explanatory diagram of the overall configuration of a measurement device 1.

The measuring device 1 is a device that measures the distance to an object 90. The measuring device 1 functions as a so-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 interference between the reflected light from the object 90 and the measurement light (reference light), and measures the distance to the object 90 based on the frequency (beat frequency) of the beat signal that is the 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.

The measurement device 1 has a generating device 10, an optical device 20, a detecting device 30, and a signal processing device 40.

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.

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 13. The current source 12 generates a current signal corresponding to the voltage signal of the signal generator 11. For example, the current source 12 generates a triangular wave current signal corresponding to the triangular wave voltage signal and outputs the triangular wave current signal 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. 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 regulates 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 (e.g., 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.

The optical device 20 is a device that irradiates the object 90 with frequency-modulated light (measurement light) and causes interference between reflected light from the object 90 and 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 interference between 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 by, for example, an optical coupler. One of the split lights is output to the circulator 22 and becomes the irradiation 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 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 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.

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 electrical 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.

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, a calculation device, a storage device, etc. (not shown). The calculation device is composed of a calculation processing device such as a CPU, GPU, or MPU. The storage device is composed of a main storage device and an auxiliary storage device, and is a device that stores programs and data. The calculation device executes the programs stored in the storage device, thereby performing various processes for measuring the distance to the object 90. Figure 1 shows the various processes performed by the signal processing device 40 as functional blocks.

The signal processing device 40 has a signal acquisition unit 41, an analysis unit 42, and an output unit 43. The signal acquisition unit 41 acquires the beat signal from the detection device 30 as a digital signal. The signal acquisition unit 41 is configured, for example, by an A/D converter (such as an A/D conversion board). The analysis unit 42 calculates the distance to the object 90 based on the beat signal. The processing of the analysis unit 42 will be described later. The output unit 43 outputs the analysis results of the analysis 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 an external device, such as a vehicle ECU.

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

Figures 9A and 9B are explanatory diagrams of the case where light is modulated so that the frequency increases or decreases linearly over time. Figure 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 called the gradual increase period, and the period in which the frequency decreases is sometimes called the gradual decrease period. Figure 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, we will explain the case where the object 90 is stationary (when the relative velocity with respect to the object 90 is zero).

In the figure, _fB 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 back and forth to 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).

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)・f _B ...(1)

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)

In the above equation (2), the frequency _fB can be obtained by FFT analysis of the beat signal as shown in Fig. 9B. The speed of light c, modulation time T, and modulation frequency width F are known. Therefore, by performing FFT analysis of the beat signal to obtain the frequency _fB , the distance R to the target object 90 can be calculated.

Figure 10 is a graph showing the change in frequency of the measurement light and reflected light over time when the object 90 is moving. Note that the light is modulated so that the frequency increases or decreases linearly over time. As shown in the graph of reflected light, when the object 90 is moving, the frequency shifts due to the Doppler effect.

In the figure, f _dop indicates the amount of frequency shift due to the Doppler effect (Doppler shift frequency), f _up indicates the frequency difference between the measurement light (illumination light, reference light) and the reflected light during the gradual increase period, and f _dn indicates the frequency difference between the measurement light (illumination light, reference light) and the reflected light during the gradual decrease period.

The frequency f _up can be obtained by FFT analysis of the beat signal during the gradual increase period. The frequency f _dn can be obtained by FFT analysis of the beat signal during the gradual decrease period. Note that the frequency analysis of the beat signal is performed separately for each of the gradual increase period and the gradual decrease period. Then, based on the frequency f _up and the frequency f _dn , the frequency f _B can be obtained as shown in the following equation (3), and the distance R can be obtained based on the above-mentioned equation (2).
_fB = ( _fup + _fdn )/2...(3)

Furthermore, based on the frequency f _up and the frequency f _dn , the Doppler shift frequency f _dop can be calculated as in the following equation (4), and the relative velocity V can be calculated based on the following equation (5).
f _dop = (f _up - f _dn )/2 (4)
V=(λ/2)・f _dop ...(5)
(λ is the wavelength of light)

<Reference explanation 2: Light source response delay>
11A and 11B are explanatory diagrams illustrating a case where the frequency increases or decreases nonlinearly over 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).

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.

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, even when frequency analysis (FFT analysis) is performed on the beat signal, an intensity peak is unlikely to appear at a specific frequency, as shown in Fig. 11B (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 determine the beat frequency _fB by frequency analysis of the beat signal, and as a result, it is difficult to determine the distance R based on the above-mentioned equation (2).

<Processing of analysis unit 42>
2A and 2B are diagrams illustrating the time variation of the frequency of the measurement light (illumination light, reference light) and the reflected light. Fig. 2A is an explanatory diagram illustrating the case where the distance to the object 90 is close. Fig. 2B is an explanatory diagram illustrating the case where the distance to the object 90 is far. In each diagram, the horizontal axis represents time, and the vertical axis represents frequency.

2A and 2B, due to the effect of a response delay of the laser light source 13, the frequency difference between the measurement light (illumination light, reference light) and the reflected light during the gradual increase period gradually increases (f _B1 < f _B2 < f _B3 ). When the distance to the object 90 is close, as shown in FIG. 2A, the change over time in the frequency difference between the measurement light and the reflected light is relatively small. On the other hand, when the distance to the object 90 is far, as shown in FIG. 2B, the change over time in the frequency difference between the measurement light and the reflected light is relatively large.

Figures 3A and 3B are schematic explanatory diagrams of the change in beat frequency over time. Figure 3A is an explanatory diagram when the object 90 is close. Figure 3B is an explanatory diagram when 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.

As shown in Figures 3A and 3B, the beat frequency of the beat signal changes over time due to the response delay of the laser light source 13. (In contrast, when the frequency increases or decreases linearly as shown in Figure 9A, the beat frequency remains constant during the gradual increase and decrease periods and does not change over time.) When the object 90 is close, the change in beat frequency over time is relatively small, as shown in Figure 3A. For example, when the object 90 is close, the ratio of the change in beat frequency to the change in time (corresponding to the slope of the graph) is relatively small, as shown in Figure 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, i.e., the change in beat frequency over time, is relatively large, as shown in Figure 3B. For example, when the object 90 is close, the ratio of the change in beat frequency to the change in time is relatively large, as shown in Figure 3B.

The analysis unit 42 therefore determines the change in beat frequency over time and calculates the distance to the object 90 based on the change in beat frequency over time. Specifically, the analysis unit 42 calculates the distance to the object 90 based on the ratio of the change in beat frequency to the change in time (the rate of change in beat frequency over time; equivalent to the slope of the graph).

Figure 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 that constitutes the signal processing device 40 executing an analysis program.

The analysis unit 42 first measures the beat frequency over time (S101). Figure 5 is an explanatory diagram of the beat frequency measurement method. The graph in the figure shows the beat signal, with the horizontal axis representing time and the vertical axis representing voltage.

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; local 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 slope 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 slope 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 slope changes from negative to positive). However, the analysis unit 42 may measure only the peak time of the local maximum value of the beat signal, or only the peak time of the local 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 after a predetermined period of time has elapsed. The analysis unit 42 measures multiple peak times during the gradual increase period or during the gradual increase period.

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 that 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 that 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 that 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 half a cycle of the beat signal). Alternatively, the analysis unit 42 may calculate the beat frequency at that 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 unit 42 measures the beat frequency at each of multiple times (multiple timings) during the gradual increase period or gradual decrease period.

In the example shown in FIG. 5, the analysis unit 42 alternately calculates the beat frequency based on the peak times of two maximum values and the beat frequency based on the peak times of 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.

Next, the analysis unit 42 calculates the change in the beat frequency over time (S102). Here, the analysis unit 42 calculates the ratio of the change in the beat frequency to the change in time (the time rate of change of the beat frequency) as an index indicating the change in the beat frequency over time. In other words, the analysis unit 42 calculates the slope of the graph (straight line) shown in FIGS. 3A and 3B. Specifically, the analysis unit 42 calculates a linear approximation formula ( _fB = A·t + B) using the least squares method based on the beat frequencies _fB at each of the multiple times t calculated in S101, and sets the slope A of this approximation formula as a value indicating the change in the beat frequency over time. (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 formula.) Note that the method for calculating the ratio of the change in the beat frequency to the change in time (the time rate of change 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 with respect to the increase in time based on the beat frequencies at two times, immediately after the start and immediately before the end of the gradual increase period (or gradual decrease period) (that is, the slope of the line connecting the two points may be regarded as the rate of change of the beat frequency with time).

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 pre-stored in the analysis unit 42. The first table associates a slope A indicating the change in the beat frequency over time 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 A 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. In addition, if the slope A obtained in S102 is a value between the slopes A _i and A _i+1 in the first table, the analysis unit 42 may interpolate the distance R corresponding to the slope _A obtained in S102 based on the distance R _i corresponding to the slope A i and the distance R _{i+ 1 corresponding to the slope A i+1} .

The analysis unit 42 may derive the relative velocity with respect to the object 90 based on the change in the beat frequency over time or the magnitude of the beat frequency. The method for deriving the relative velocity is described below.

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 .
7 is a diagram illustrating the outline of the change in beat frequency _fB over time when the object 90 is moving. As already explained, when the object 90 is moving, the frequency shifts due to the Doppler effect. In the diagram, _fdop indicates the amount of frequency shift (Doppler shift frequency) due to the Doppler effect. The diagram also illustrates the relationship between the reference intercept _B0 and the Doppler shift frequency _fdop .

As already explained, the analysis unit 42 calculates a linear approximation formula ( _fB = A·t + B) by the least squares method based on the beat frequencies _fB at the respective times t calculated in S101, and calculates the slope A indicating the change in beat frequency over time, as well as the intercept B. The intercept B is an index indicating the magnitude of the beat frequencies calculated 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 corresponds to the Doppler shift frequency _fdop . For example, when the slope indicating the time change of the beat frequency is _A4 , the analysis unit 42 calculates the Doppler shift frequency _fdop by calculating the difference between the intercept B and the reference intercept _B04 . The analysis unit 42 can calculate the relative velocity V (=(λ/2)· _fdop ) based on the Doppler shift frequency _fdop and the above-mentioned equation (5).

Figures 8A to 8C are explanatory diagrams showing the change in frequency of frequency-modulated light over time. The vertical axis in the diagrams represents time, and the vertical axis represents frequency.

Figure 8A shows how a gradual increase period in which the frequency gradually increases and a gradual decrease period in which the frequency gradually decreases alternately. 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 Figure 8A. When frequency-modulating light as shown in Figure 8A (when the frequency of the frequency-modulated light changes over time so that gradual increase periods and gradual decrease periods alternate), it is desirable for the analysis unit 42 to have a first table (and second table) for the gradual increase period and a first table (and 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.

Figure 8B shows a gradual increase in frequency followed by a sudden drop, repeated. Figure 8C shows a gradual decrease in frequency followed by a sudden rise, repeated. 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 Figures 8B and 8C. When frequency-modulating light as shown in Figures 8B and 8C, the analysis unit 42 only needs to have one type of first table (and second table). This means that the analysis unit 42 does not need to have first tables for both the gradual increase period and the gradual decrease period, thereby reducing the amount of data in the tables.

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 with temperature. As a result, even if the distance to the target 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.

In the above explanation, the analysis unit 42 pre-stores a first table that associates the change in beat frequency over time (slope A) with the distance R, and determines the distance R by referencing 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 also 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 way, 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.

Similarly, the distance R may be calculated based on the temperature detected by the temperature sensor and the change over time in 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 in the beat frequency calculated in S102 (slope A). In this way, the analysis unit 42 can also improve the accuracy of distance measurement.

When determining the distance to the object 90 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.

===Summary===
The measurement device 1 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 object. Therefore, the signal processing device 40 of this embodiment calculates the distance to the object 90 based on the change in the beat frequency of the beat signal over time. This enables distance measurement using the FMCW method using a laser light source with a response delay. Furthermore, since an inexpensive laser light source can be used, the cost of the measurement device 1 can be reduced.

The signal processing device 40 calculates the beat frequency at each of multiple times (multiple timings) during the gradual increase period or the gradual decrease period (see S101 in FIG. 4 ), and calculates the change in the beat frequency over time based on the calculated multiple beat frequencies (S102). For example, as shown in FIGS. 3A and 3B , the signal processing device 40 calculates beat frequencies f _B1 , f _B2 , and f _B3 corresponding to three times during a certain gradual increase _period , _and calculates the ratio of the change in the beat frequency to the change in time (corresponding to the change in the beat frequency over time; corresponding to the slope of the graph shown in FIGS. 3A and _3B ) based on the calculated three beat frequencies f B1 , f B2 , and f B3. This allows the distance to the target to be measured based on the change in the beat frequency over time in the process of S103. Note that instead of calculating multiple beat frequencies during the gradual increase period, the signal processing device 40 may also calculate multiple beat frequencies during the gradual decrease period and calculate the change in the beat frequency over time (e.g., the slope of the graph) based on the calculated multiple beat frequencies.

As shown in FIG. 5, the signal processing device 40 determines the peak time at which the beat signal reaches its peak, and then 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 or decrease period. However, the method for measuring the beat frequency is not limited to this. For example, the signal processing device 40 may determine the time at which the beat signal reaches a predetermined voltage (e.g., 0 V), and also determine the beat frequency based on the interval at which the beat signal reaches a predetermined voltage (e.g., the center voltage (average voltage) of the beat signal).

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 beat frequency for each predetermined cycle or after a predetermined amount of time has elapsed. Note that when the peak time or beat frequency is calculated for each predetermined cycle or after a predetermined amount of time has elapsed, the computational load on the signal processing device 40 can be reduced compared to when the beat frequency is calculated for each half cycle of the beat signal.

The signal processing device 40 obtains the beat frequency at each of a plurality of times during 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 magnitudes 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 equation (f _B = A · t + B) by the least squares method based on the beat frequencies at each of a plurality of times during a certain gradual increase period, and obtains a slope A that indicates the time change of the beat frequency and an intercept B that serves as an index indicating the magnitudes of the plurality of beat frequencies. The signal processing device 40 then obtains the Doppler shift frequency f _dop from the difference between the intercept B and the reference intercept B ₀ by referring to the second table shown in FIG. 6B , and is thereby able to obtain the relative velocity V (= (λ/2) · f _dop ) of the object. Note that instead of obtaining the intercept B of the linear approximation equation by the least squares method, the signal processing device 40 may obtain the Doppler shift frequency f _dop based on another index indicating the magnitude of the beat frequency, thereby obtaining the relative velocity of the object.

The signal processing device 40 pre-stores a table that associates distance with changes in beat frequency over time (see Figure 6A), and determines distance by referencing this table. This allows distance to be determined based on changes in beat frequency over time. However, the signal processing device 40 may also determine distance without using a table.

When determining distance by referencing a table, it is desirable that the table correlating distance with time-dependent changes in beat frequency also correlates temperature. The signal processing device 40 then determines distance by referencing the table based on the temperature detected by the temperature sensor and the time-dependent changes in beat frequency. This can improve the accuracy of distance measurement.

It is desirable to determine the distance without using a table, but by referencing the table based on the temperature detected by the temperature sensor and the change in beat frequency over time. This can improve the accuracy of distance measurement.

When determining the distance to the object 90 using the temperature detected by the temperature sensor, it is desirable that the temperature sensor detect 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.

The above measurement method involves (1) generating frequency-modulated light, (2) irradiating the object 90 with the light 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 distance using the FMCW method using a laser light source with a response delay.

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 that include 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.

1. Measuring device,
10 Generating device, 11 Signal generator,
12 current source, 13 laser light source,
14 temperature controller, 14A temperature sensor,
20 Optical device, 21 Branching device,
22 circulator, 23 optical system,
24 optical waveguide, 25 coupler,
30 Detector, 31 Photoelectric converter, 32 Amplifier,
40 signal processing device, 41 signal acquisition unit,
42 analysis unit, 43 output unit,
90 Object

Claims (9)

a generator for generating frequency modulated light;
an optical device that irradiates the light onto an object and causes the 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 calculates the distance to the object based on a time change in the beat frequency of the beat signal ,
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 device. 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. 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. 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 device. 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. The 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. The 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. 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 the distance to the object based on a time change in the 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.