Measuring equipment

Abstract

To accurately calculate a distance to an object.SOLUTION: A measuring apparatus comprises: a generation device that generates measuring light frequency-modulated so as to repeat a gradual increase period in which a frequency increases, a gradual decrease period in which the frequency decreases, and a fixed period in which the frequency is fixed, in a predetermined order; an optical device that irradiates an object with the measuring light and causes reflected light from the object and the measuring light to interfere with each other; a detection device that detects an interference wave between the reflected light and the measuring light and outputs a beat signal; and a signal processing device that obtains a distance to the object on the basis of a first frequency indicating a beat frequency of the beat signal in the gradual increase period, a second frequency indicating a beat frequency of the beat signal in the gradual decrease period, and a third frequency indicating a beat frequency of the beat signal in the fixed period.SELECTED DRAWING: Figure 3

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, light is modulated so that periods of increasing frequency alternate with periods of decreasing frequency, and the distance to the target is calculated based on the beat frequency during the increasing period and the beat frequency during the decreasing period. However, if the relative velocity of the target increases, it may become difficult to accurately calculate the distance to the target (see below).

[0005] The present invention aims to accurately calculate the distance to an object. [Means for solving the problem]

[0006] One aspect of the present invention to achieve the above object is a measurement device including: a generating device that generates measurement light that is frequency-modulated so that a gradual increase period in which the frequency increases, a gradual decrease period in which the frequency decreases, and a fixed period in which the frequency remains constant are repeated in a predetermined order; an optical device that irradiates an object with the measurement light and causes reflected light from the object to interfere with the measurement light; a detecting device that detects an interference wave between the reflected light and the measurement light and outputs a beat signal; and a signal processing device that calculates a distance to the object based on a first frequency that indicates the beat frequency of the beat signal during the gradual increase period, a second frequency that indicates the beat frequency of the beat signal during the gradual decrease period, and a third frequency that indicates the beat frequency of the beat signal during the fixed period.

[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, the distance to the object can be calculated accurately. [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 explanatory diagrams showing the time change in the frequency of the frequency-modulated light and the time change in the frequency of the measurement light and the reflected light, respectively. [Figure 3] FIG. 3 is a flow diagram of the processing performed by the analysis unit 42. [Figure 4] FIG. 4 is an explanatory diagram showing various patterns of the magnitude relationship between the measurement light and the reflected light. [Figure 5] 5A and 5B are explanatory diagrams of the calculation frequency. [Figure 6] FIG. 6 is a flow diagram of a modified example. [Figure 7] FIG. 7 is an explanatory diagram of the frequencies of the measurement light and the reflected light in a modified example. [Figure 8]8A and 8B are explanatory diagrams of the case where light is modulated so that the frequency increases or decreases with the passage of time. [Figure 9] FIG. 9 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 10] FIG. 10 is a diagram illustrating the influence when the relative speed of the object 90 is high. 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] 8A and 8B are explanatory diagrams illustrating the case where light is modulated so that the frequency increases or decreases over time. FIG. 8A 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. 8B 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. 8B. 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] 9 is a graph showing the time variation of the frequency of the measurement light and the reflected light when the object 90 is moving. 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 up and frequency f dn Based on this, the frequency fB 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: When the relative velocity is high> FIG. 10 is a diagram illustrating the effect when the relative velocity of the object 90 is high. For the sake of explanation, the frequency f up and frequency f dn The magnitude of is the frequency f up and frequency f dn The size is the same as the

[0031] As shown in Figure 10, when the relative velocity of the object 90 increases, the frequency of the reflected light during the gradual increase period may become higher than the frequency of the measurement light. However, when the beat frequency is calculated by frequency analysis of the beat signal, the absolute value of the difference in frequency between the measurement light and the reflected light is calculated, and therefore it is not possible to determine the magnitude relationship between the frequency of the measurement light and the frequency of the reflected light. For this reason, the frequency f obtained by frequency analysis of the beat signal under the conditions shown in Figure 10 up and frequency f dn is the frequency f under the conditions shown in Figure 9. up and frequency f dn Therefore, the frequency f obtained under the conditions shown in Figure 10 is up and frequency f dnIf the distance R is calculated by applying the above equations (2) and (3), the distance to the object cannot be calculated correctly. In this way, if the relative velocity of the object 90 increases and the frequency of the reflected light during the gradual increase period becomes higher than the frequency of the measurement light, the distance to the object cannot be calculated correctly. Similarly, if the relative velocity of the object 90 increases and the frequency of the reflected light during the gradual decrease period becomes lower than the frequency of the measurement light, the distance to the object cannot be calculated correctly.

[0032] 2A is an explanatory diagram showing the change in frequency of frequency-modulated light over time, where the horizontal axis represents time and the vertical axis represents frequency.

[0033] As shown in FIG. 2A , the generator 10 generates a measurement light whose frequency is modulated so that a gradual increase period, a gradual decrease period, and a fixed period are repeated in a predetermined order. In other words, the generator 10 generates a measurement light whose frequency is modulated so that a period including a gradual increase period, a gradual decrease period, and a fixed period is repeated at a predetermined cycle. The fixed period is a period during which the frequency is constant. The signal generator 11 of the generator 10 outputs a voltage signal in which the voltage increases during the gradual increase period, decreases during the gradual decrease period, and maintains a constant voltage during the fixed period. In other words, the signal generator 11 outputs a voltage signal with a constant voltage between adjacent triangular waves. By outputting such a voltage signal from the signal generator 11, the current source 12 increases the current during the gradual increase period, decreases the current during the gradual decrease period, and maintains a constant current during the fixed period. As a result, the laser light source 13 outputs light whose frequency changes over time (frequency-modulated light) as shown in FIG. 2A .

[0034] 2B is an explanatory diagram of the time change in the frequency of the measurement light (illumination light, reference light) and the reflected light, in which the horizontal axis represents time and the vertical axis represents frequency.

[0035] The signal acquisition unit 41 of the signal processing device 40 acquires the beat signal of the detection device 30 as a digital signal, and the analysis unit 42 performs frequency analysis (e.g., FFT analysis) on the beat signal. The analysis unit 42 performs frequency analysis on the beat signal during the gradual increase period to obtain a frequency f up The analysis unit 42 performs frequency analysis on the beat signal during the gradual decrease period to obtain the frequency f dn The analysis unit 42 performs frequency analysis on the beat signal during a certain period to obtain the frequency f c (3rd frequency) f c indicates the difference in frequency between the measurement light (illumination light, reference light) and the reflected light during a certain period (more specifically, the absolute value of the difference in frequency between the measurement light and the reflected light). Therefore, the frequency f obtained by frequency analysis of the beat signal during a certain period is c indicates the amount of frequency shift due to the Doppler effect (Doppler shift frequency) (where frequency f c is the Doppler shift frequency f dop (equivalent to the absolute value of

[0036] The frequency f acquired by the analysis unit 42 up , f dn and f c The frequency f obtained in this way is the absolute value of the difference in frequency between the measurement light and the reflected light. up , f dn and f c Based on this, the analysis unit 42 calculates the distance (and relative speed) of the object 90 as follows:

[0037] FIG. 3 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. FIG. 4 is an explanatory diagram showing various patterns of the magnitude relationship between the measurement light and the reflected light. In the case of patterns B and C in the diagram, the frequency f up and frequency f dnIt is possible to calculate the distance R by applying these equations (2) and (3) to the above equations. However, in the cases of patterns A and D in the figure, the relative speed of the object 90 increases, and as a result, the distance R cannot be calculated correctly even if the above equations (2) and (3) are used.

[0038] S001~S005 The analysis unit 42 calculates the frequency f up and frequency f dn Compare the magnitude relationship with frequency f dn is the frequency f up Here, the analysis unit 42 determines whether the frequency f dn is the frequency f up Determine whether it is greater than (f up <f dn ) where frequency f up and frequency f dn If the same, the result of S001 is YES (f up ≦f dn ) However, the frequency f up and frequency f dn If the values ​​are the same, the result of S001 may be NO.

[0039] When the magnitude relationship between the measurement light and the reflected light corresponds to pattern A or pattern B in Figure 4, the frequency f dn is the frequency f up On the other hand, if the magnitude relationship between the measurement light and the reflected light corresponds to pattern C or pattern D in FIG. up is the frequency f dn Since it is larger, the analysis unit 42 will determine NO in S001.

[0040] frequency f dn is the frequency f up If it is greater (YES in S001), the analysis unit 42 determines whether the following two conditions (condition A) are satisfied (S002). Note that the determination in S002 corresponds to a determination of whether the frequency of the reflected light during the gradual increase period is greater than the frequency of the measurement light. [Condition A] TIFF0007804494000001.tif32170

[0041] In condition A, α is a predetermined threshold value. When pattern A applies, if there is no abnormality in the measurement result, the value of the right side of the first conditional expression will be almost zero. Therefore, in the second conditional expression of condition A, by determining whether the value of the right side of the first conditional expression is smaller than the threshold value α, the frequency f up , f dn and f c It is determined whether there are any abnormalities in the measurement results. If error determination is not necessary, the second of the two conditions in condition A may be omitted. This also applies to conditions B to D described below.

[0042] If the analysis unit 42 determines that condition A is satisfied (YES in S002), it determines that the pattern corresponds to pattern A (S011). On the other hand, if the analysis unit 42 determines that condition A is not satisfied (NO in S002), it determines whether the next two conditions (condition B) are satisfied (S003). The determination in S003 corresponds to a determination of whether the frequency of the reflected light during the gradual increase period is smaller than the frequency of the measurement light. [Condition B] TIFF0007804494000002.tif31170

[0043] In condition B, α is a predetermined threshold value, similar to condition A described above. When pattern B is met, if there is no abnormality in the measurement results, the value of the left side of the first conditional expression will be almost zero. Therefore, in the second conditional expression of condition B, by determining whether the value of the left side of the first conditional expression is smaller than the threshold value α, the frequency f up , f dn and f c It is judged whether there are any abnormalities in the measurement results.

[0044] When the analysis unit 42 determines that the condition B is satisfied (YES in S003), it determines that the pattern B applies (S012). On the other hand, when the analysis unit 42 determines that the condition B is not satisfied (NO in S003), it notifies an error (S015). up , f dn and f c If there is an abnormality in the measurement result, the value on the left side of the second conditional expression of condition A or condition B exceeds threshold α, so neither condition A nor condition B is satisfied, resulting in an error.

[0045] frequency f dn is the frequency f up If it is smaller (NO in S001), the analysis unit 42 determines whether the following two conditions (condition C) are satisfied (S004). The determination in S004 corresponds to a determination whether the frequency of the reflected light during the gradual decrease period is greater than the frequency of the measurement light. [Condition C] TIFF0007804494000003.tif31170

[0046] In condition C, α is a predetermined threshold value, similar to the above-mentioned conditions A and B. When pattern C applies, if there is no abnormality in the measurement results, the value of the left side of the first conditional expression will be almost zero. Therefore, in the second conditional expression of condition C, by determining whether the value of the left side of the first conditional expression is smaller than the threshold value α, the frequency f up , f dn and f c It is judged whether there are any abnormalities in the measurement results.

[0047] If the analysis unit 42 determines that condition C is satisfied (YES in S004), it determines that the pattern corresponds to pattern C (S013). On the other hand, if the analysis unit 42 determines that condition C is not satisfied (NO in S004), the analysis unit 42 determines whether the next two conditions (condition D) are satisfied (S005). The determination in S005 corresponds to a determination of whether the frequency of the reflected light during the gradual decrease period is smaller than the frequency of the measurement light. [Condition D] TIFF0007804494000004.tif31170

[0048] In condition D, α is a predetermined threshold value, similar to the above conditions A to C. When pattern D applies, if there is no abnormality in the measurement results, the value of the right-hand side of the first conditional expression will be almost zero. Therefore, in the second conditional expression of condition D, by determining whether the value of the right-hand side of the first conditional expression is smaller than the threshold value α, the frequency f up , f dn and f c It is judged whether there are any abnormalities in the measurement results.

[0049] When the analysis unit 42 determines that the condition D is satisfied (YES in S005), it determines that the pattern corresponds to pattern D (S014). On the other hand, when the analysis unit 42 determines that the condition D is not satisfied (NO in S005), it notifies an error (S016). up , f dn and f c If there is an abnormality in the measurement result, the value on the left side of the second conditional expression of condition C or condition D exceeds the threshold α, so neither condition C nor condition D is satisfied, resulting in an error.

[0050] As described above, the analysis unit 42 determines the magnitude relationship between the frequency of the measurement light and the frequency of the reflected light during the gradual increase period and the gradual decrease period by making the determinations in S001 to S005. For example, the analysis unit 42 determines the magnitude relationship between the frequency f up , f dn and f c The analysis unit 42 determines the magnitude relationship between the frequency of the measurement light and the frequency of the reflected light during the gradual increase period based on the above. up , f dn and f c In other words, the analyzing unit 42 determines the magnitude relationship between the frequency of the measurement light and the frequency of the reflected light during the gradual decrease period based on the frequency f up , f dn and f cBy making the determinations in S001 to S005 based on this, it is determined whether the distance R can be calculated using the above-mentioned formulas (2) and (3). Note that the order of the determinations in S001 to S005 is not limited to this. Furthermore, the method of determining whether the frequency of the reflected light in the gradual increase period is higher than the frequency of the measurement light (whether it corresponds to pattern A) or whether the frequency of the reflected light in the gradual decrease period is lower than the frequency of the measurement light (whether it corresponds to pattern D) is not limited to this (see modified examples).

[0051] S011 If the determination in S001 is YES and condition A is satisfied (YES in S002), the analysis unit 42 determines that the pattern corresponds to pattern A. In this case, the analysis unit 42 calculates the frequency f B , and the frequency f B The distance R is calculated based on the above (S011). f B =(-f up +f dn ) / 2 (6)

[0052] S012 If the determination in S001 is YES and the condition B is satisfied (YES in S003), the analysis unit 42 determines that the pattern B applies (S012). In this case, the analysis unit 42 calculates the frequency f B , and the frequency f B The distance R is calculated based on the above (S012). f B =(f up +f dn ) / 2 (7)

[0053] S013 If the determination in S001 is NO and condition C is satisfied (YES in S004), the analysis unit 42 determines that the pattern corresponds to pattern C (S013). In this case, the analysis unit 42 calculates the frequency f B, and the frequency f B The distance R is calculated based on the above (S013).

[0054] S014 If the determination in S001 is NO and the condition D is satisfied (YES in S005), the analysis unit 42 determines that the pattern corresponds to pattern D (S013). In this case, the analysis unit 42 calculates the frequency f B , and the frequency f B The distance R is calculated based on the above (S014). f B =(f up -f dn ) / 2 ···(8)

[0055] As described above, the analyzer 42 calculates the frequency f up , f dn and f c Based on this, the magnitude relationship between the frequency of the measurement light and the frequency of the reflected light during the gradual increase period and the gradual decrease period is determined (S001 to S005), and a function according to the determination result is used to calculate the frequency f up and f dn Based on the frequency f B and calculate the frequency f B Based on this, the distance R is calculated (S011 to S014). This makes it possible to accurately calculate the distance R to the object 90.

[0056] As shown in patterns B and C, when the frequency of the reflected light in the gradual increase period is lower than the frequency of the measurement light and the frequency of the reflected light in the gradual decrease period is higher than the frequency of the measurement light, the analysis unit 42 calculates the frequency f up and f dnOn the other hand, if the frequency of the reflected light in the gradually increasing period is higher than the frequency of the measurement light as shown in pattern A, or if the frequency of the reflected light in the gradually decreasing period is lower than the frequency of the measurement light as shown in pattern D, calculating the distance R using the above equations (3) and (7) will be inaccurate. For this reason, in such cases, a function other than the above equations (3) and (7) (the above equations (6) and (8)) is used to calculate the distance R based on the frequency f up and f dn The distance R is calculated based on the above (S011, S014).

[0057] As explained above, the frequency f obtained by frequency analysis of the beat signal over a certain period of time is c corresponds to the amount of frequency shift due to the Doppler effect (Doppler shift frequency). Therefore, the analysis unit 42 calculates the frequency f of the beat signal over a certain period of time. c The relative velocity V may be calculated using the following equation (9) based on the above. V=(λ / 2) f c ···(9)

[0058] When calculating the relative velocity V based on the above equation (9), the analysis unit 42 calculates the frequency f dn is the frequency f up If the frequency f is greater than the predetermined frequency (YES in S001), it is determined that the object 90 is moving in the approaching direction. dn is the frequency f up If it is smaller than the frequency f (NO in S001), it is determined that the object 90 is moving in the direction away. In this way, the analysis unit 42 can determine the relative velocity V of the object 90 and the direction in which the object 90 is moving (approaching or moving away). In other words, the analysis unit 42 can determine the frequency f dn is the frequency f up If it is greater than f dop =-f c as the Doppler shift frequency f dop The analysis unit 42 may calculate the relative velocity V by using the above-mentioned equation (5). dn is the frequency f upIf it is smaller than f dop =f c as the Doppler shift frequency f dop and then use the above-mentioned equation (5) to calculate the relative velocity V.

[0059] <Calculation frequency> 5A and 5B are explanatory diagrams of the calculation frequency.

[0060] As already explained, the generating device 10 generates a measurement light that is frequency-modulated so as to repeat a gradual increase period, a gradual decrease period, and a constant period in a predetermined order (see also FIG. 2A). FIGS. 5A and 5B show that a period including a gradual increase period, a gradual decrease period, and a constant period is repeated at a predetermined cycle T0. If each of the gradual increase period, the gradual decrease period, and the constant period is T, the cycle T0 (repeated cycle T0) is three times the cycle T0.

[0061] As already explained, the analysis unit 42 performs frequency analysis on the beat signal during the gradual increase period to obtain the frequency f up and frequency f dn and frequency f c By obtaining the frequency f up , f dn and f c In other words, to calculate the distance R and the relative velocity V, the frequency f up , f dn and f c 9, which requires a predetermined period T0 including a gradual increase period, a gradual decrease period, and a fixed period. In this embodiment, since a fixed period must be provided, the repetition period T0 shown in Figures 5A and 5B is longer than the repetition period shown in Figure 9 by the amount of the fixed period, and is 1.5 times the repetition period shown in Figure 9.

[0062] 5A, the analysis unit 42 may calculate the distance R and the relative velocity V for each repetition period T0. That is, as shown in FIG. 5A, the analysis unit 42 calculates the distance R and the relative velocity V for a certain period T1 at a frequency f up , f dn and f c The distance R and the relative velocity V are calculated based on the period T1, and the frequency f up , f dn and f c However, as shown in FIG. 5A, if the calculation of the distance R and the relative velocity V is repeated at a period T0, the temporal resolution will be lower than in the reference example.

[0063] Therefore, as shown in FIG. 5B, the analysis unit 42 calculates different combinations of frequencies f up , f dn and f c 5B, the analysis unit 42 repeatedly calculates the distance R and the relative velocity V based on the frequency f up , f dn and f c and calculating the distance R and the relative velocity V based on the frequency f up , f dn and f c and calculating the distance R and the relative velocity V based on the above, and calculating the frequency f in the period (for example, period T3) that precedes the gradual increase period and the gradual decrease period. up , f dn and f c The analysis unit 42 calculates the distance R and the relative velocity V based on the frequency f in a period T0 including a gradual increase period, a gradual decrease period, and a fixed period. up , f dn and f cand calculate the distance R and the relative velocity V, and this is repeated while shifting the period T by a period T shorter than the period T. In other words, the analysis unit 42 calculates the frequency f up , f dn and f c Then, in a period (for example, period T2) overlapping with the period (for example, period T1), the frequency f up , f dn and f c By repeatedly calculating the distance R and the relative velocity V based on the above, the distance R and the relative velocity V are calculated for each period T. This makes it possible to shorten the calculation period for the distance R and the relative velocity V, and improve the temporal resolution.

[0064] <Variation 1> The method of determining whether the frequency of the reflected light during the gradual increase period is greater than the frequency of the measurement light (whether it corresponds to pattern A) or whether the frequency of the reflected light during the gradual decrease period is smaller than the frequency of the measurement light (whether it corresponds to pattern D) is not limited to the determinations in S001 to S005 described above.

[0065] 6 is a flow diagram of a modified example, in which each process is realized by the arithmetic processing unit constituting the signal processing device 40 executing an analysis program.

[0066] S101~S103 The analysis unit 42 calculates the frequency f up and frequency f dn Compare the magnitude relationship with frequency f dn is the frequency f up It is determined whether it is greater than (S101). This process is the same as S001 described above.

[0067] frequency f dn is the frequency f up If it is greater than the frequency f dn is the frequency f cThe analysis unit 42 determines whether the frequency f is smaller than twice the frequency f (S102). dn is the frequency f c If the frequency f is smaller than twice the normal frequency (YES in S102), it is determined that the magnitude relationship between the measurement light and the reflected light corresponds to pattern A in FIG. 4 (S011). dn is the frequency f c If it is greater than twice the value (NO in S102), it is determined that the magnitude relationship between the measurement light and the reflected light corresponds to pattern B in FIG. 4 (S012).

[0068] Also, the frequency f dn is the frequency f up If it is smaller than the frequency f up is the frequency f c The analysis unit 42 determines whether the frequency f is smaller than twice the frequency f (S103). up is the frequency f c If the frequency f is greater than twice the normal frequency (NO in S103), the analyzer 42 determines that the magnitude relationship between the measurement light and the reflected light corresponds to pattern C in FIG. up is the frequency f c If it is smaller than twice the value (YES in S103), it is determined that the magnitude relationship between the measurement light and the reflected light corresponds to pattern D in FIG. 4 (S014).

[0069] As described above, the analysis unit 42 performs the determinations in S101 and S102 to determine the frequency f up , f dn and f c The analysis unit 42 determines whether the frequency of the measurement light and the frequency of the reflected light are higher or lower during the gradual increase period based on the above. up , f dn and f c In other words, the analyzing unit 42 determines the magnitude relationship between the frequency of the measurement light and the frequency of the reflected light during the gradual decrease period based on the frequency f up , f dn and f cBased on this, the determinations in S101, S102, and S103 are performed to determine whether the distance R can be calculated using the above-described equations (2) and (3).

[0070] The analysis unit 42 calculates the frequency f up and f dn Based on the frequency f B (S011 to S014) and calculate the frequency f B The distance R is calculated based on the above equation. Note that the processes in S011 to S014 in Fig. 6 are the same as the processes in S011 to S014 in Fig. 3. As a result, the distance R to the object 90 can be accurately calculated even in this modified example.

[0071] <Variation 2> In the above description, the fixed period is provided after the gradual decrease period, but the order of the gradual increase period, gradual decrease period, and fixed period is not limited to this.

[0072] 7 is an explanatory diagram of the frequencies of the measurement light and the reflected light in the modified example. The diagram shows the change in the frequency of the frequency-modulated light over time, with the horizontal axis representing time and the vertical axis representing frequency.

[0073] In the modified example, the fixed period is provided after the gradual increase period. As shown in Fig. 7, the generation device 10 of the modified example generates frequency-modulated measurement light so as to repeat the gradual increase period, the fixed period, and the gradual decrease period in order.

[0074] In the modified example, the analysis unit 42 also calculates the beat frequencies f up , f dn and f c The three beat frequencies f up , f dn and f c Based on this, it is possible to calculate the distance R and the relative velocity V.

[0075] Also in the modified example, as shown in FIG. 7, the analysis unit 42 calculates different combinations of frequencies f up , f dn and f c It is desirable to repeatedly calculate the distance R and the relative velocity V based on the above. This makes it possible to shorten the calculation cycle of the distance R and the relative velocity V, and to improve the temporal resolution. However, the analysis unit 42 may also calculate the distance R and the relative velocity V for each repetition cycle T0.

[0076] ===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. 9, the signal processing device 40 detects beat frequencies f corresponding to the increasing period and the decreasing period. up and f dn Calculate the beat frequency f up and f dn , and calculates the distance R based on the frequency of the reflected light. However, as shown in FIG. 10, when the relative speed of the object 90 increases, the frequency of the reflected light during the gradual increase period may become higher than the frequency of the measurement light, and if the distance R is calculated in the same manner as in FIG. 9, it may become impossible to accurately calculate the distance to the object. Therefore, the generation device 10 of this embodiment generates measurement light that is frequency-modulated so that a gradual increase period in which the frequency increases, a gradual decrease period in which the frequency decreases, and a fixed period in which the frequency remains constant are repeated in a predetermined order. Furthermore, the signal processing device 40 generates beat frequencies f corresponding to the gradual increase period, the gradual decrease period, and the fixed period, respectively. up (1st frequency), f dn (second frequency) and f c The distance R to the target is calculated based on the beat frequency f up (first frequency) and f dn (second frequency) as well as the beat frequency f c By also using the (third frequency) to find the distance R to the object, the distance to the object can be calculated accurately.

[0077] The signal processing device 40 described above receives a signal at a frequency f up, f dn and f c For example, the signal processing device 40 determines whether the frequency of the measurement light is greater than the frequency of the reflected light by processing steps S001 to S005 in FIG. 3 and steps S101 to S103 in FIG. 6. up , f dn and f c The signal processing device 40 then determines the magnitude relationship between the frequency of the measurement light and the frequency of the reflected light during the gradual increase period and the gradual decrease period based on the above equations (3), (7), (6), and (8). up (first frequency) and f dn The distance R to the object is calculated based on the second frequency. This makes it possible to accurately calculate the distance to the object.

[0078] Furthermore, when the frequency of the reflected light in the gradually increasing period is lower than the frequency of the measurement light and the frequency of the reflected light in the gradually decreasing period is higher than the frequency of the measurement light, as shown in patterns B and C in FIG. 4, the signal processing device 40 calculates the frequency f up and f dn On the other hand, if the frequency of the reflected light in the gradually increasing period is higher than the frequency of the measurement light as shown in pattern A, or if the frequency of the reflected light in the gradually decreasing period is lower than the frequency of the measurement light as shown in pattern D, a different function (the above-mentioned formulas (6) and (8)) is used to calculate the distance R based on the frequency f up and f dn Based on this, the distance R is calculated (S104, S107). This makes it possible to accurately calculate the distance to the object.

[0079] 5B and 7, the signal processing device 40 receives the signal at a frequency f up , f dn and f cIt is desirable to repeat the calculation of the distance R based on the above at a cycle (for example, cycle T) shorter than the repetition cycle T0 of the frequency-modulated light. This allows the calculation cycle of the distance R to be shortened even if the repetition cycle T0 is lengthened by providing a certain period.

[0080] 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]

[0081] 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 generating device that generates measurement light that is frequency-modulated so that a gradual increase period in which the frequency increases, a gradual decrease period in which the frequency decreases, and a fixed period in which the frequency is constant are repeated in a predetermined order; an optical device that irradiates the measurement light onto an object and causes reflected light from the object to interfere with the measurement light; a detector that detects an interference wave between the reflected light and the measurement light and outputs a beat signal; a signal processing device that calculates the distance to the object based on a first frequency that indicates the beat frequency of the beat signal during the gradual increase period, a second frequency that indicates the beat frequency of the beat signal during the gradual decrease period, and a third frequency that indicates the beat frequency of the beat signal during the fixed period; and Equipped with The signal processing device includes: determining a magnitude relationship between the frequency of the measurement light and the frequency of the reflected light based on the first frequency, the second frequency, and the third frequency; determining the distance based on the first frequency and the second frequency using a function according to the magnitude relationship; Measuring device.

2. A measuring device according to claim 1, The signal processing device includes: if the frequency of the reflected light during the gradual increase period is lower than the frequency of the measurement light and the frequency of the reflected light during the gradual decrease period is higher than the frequency of the measurement light, using a predetermined function to determine the distance based on the first frequency and the second frequency; When the frequency of the reflected light during the gradual increase period is higher than the frequency of the measurement light, or when the frequency of the reflected light during the gradual decrease period is lower than the frequency of the measurement light, the distance is calculated based on the first frequency and the second frequency using a function different from the predetermined function. Measuring device.

3. A measuring device according to claim 1 or 2, a period including the gradual increase period, the gradual decrease period, and the fixed period is repeated at a predetermined cycle, the signal processing device repeats determining the distance based on the first frequency, the second frequency, and the third frequency at a cycle shorter than the predetermined cycle. Measuring device.

4. A measuring device according to claim 3, The signal processing device includes: determining the distance based on the first frequency, the second frequency, and the third frequency during the certain period that comes after the gradually increasing period and the gradually decreasing period; determining the distance based on the first frequency, the second frequency, and the third frequency during the certain period between the gradually increasing period and the gradually decreasing period; and determining the distance based on the first frequency, the second frequency, and the third frequency during the certain period that precedes the gradually increasing period and the gradually decreasing period; Each of the following is performed: Measuring device.

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