Electromagnetic wave distance measuring device and electromagnetic wave distance measuring method

Abstract

The apparatus includes an electromagnetic wave generating unit (11) that generates electromagnetic waves whose frequency changes over time, an irradiating unit (12) that irradiates an object (M1) with a portion of the electromagnetic waves generated by the electromagnetic wave generating unit (11), a measurement interference signal generating unit (12) that generates a measurement interference signal which is an interference wave between a reflected wave of the electromagnetic wave that is irradiated to the object (M1) and reflected by the object (M1) and an electromagnetic wave that is not irradiated to the object (M1), a reference interference signal generating unit (20) that generates a reference interference signal having a higher frequency than the measurement interference signal based on a signal including the measurement interference signal from the measurement interference signal generating unit (12), a sampling unit (42) that samples the measurement interference signal based on the reference interference signal, and a distance calculating unit (43) that calculates the distance from the irradiating unit (12) to the object (M1) based on the result of sampling by the sampling unit (42).

Description

[Technical Field]

[0001] The present disclosure relates to an electromagnetic wave ranging device and an electromagnetic wave ranging method. [Background technology]

[0002] Distance measuring devices that measure the distance to an object by the FMCW (Frequency Modulated Continuous Wave) method have been disclosed (see, for example, Patent Document 1). This distance measuring device measures the distance to an object based on a measurement interference signal obtained by interfering light reflected by an object from one of two laser beams split from a laser light source with the other laser beam, and an auxiliary interference signal obtained by interfering the other two laser beams split from the laser light by applying different delay times to each of the other laser beams. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2024-007750 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the device described in Patent Document 1 has a problem in that the signal propagation paths tend to be long because the measurement interference signal and the auxiliary interference signal are propagated along different paths.

[0005] The present disclosure was made in recognition of the above-mentioned problems, and aims to provide an electromagnetic wave ranging device and an electromagnetic wave ranging method that can shorten the signal propagation path more than ever before. [Means for solving the problem]

[0006] The electromagnetic wave ranging device according to the present disclosure is characterized by comprising an electromagnetic wave generating unit that generates electromagnetic waves whose frequency changes over time; an irradiating unit that irradiates an object with a portion of the electromagnetic waves generated by the electromagnetic wave generating unit; a measurement interference signal generating unit that generates a measurement interference signal that is an interference wave between a reflected wave of the electromagnetic wave that is irradiated to the object and reflected by the object and an electromagnetic wave that is not irradiated to the object; a reference interference signal generating unit that generates a reference interference signal having a higher frequency than the measurement interference signal based on a signal including the measurement interference signal from the measurement interference signal generating unit; a sampling unit that samples the measurement interference signal based on the reference interference signal; and a distance calculating unit that calculates the distance from the irradiating unit to the object based on the result of sampling by the sampling unit. [Effects of the Invention]

[0007] The electromagnetic wave ranging device according to the present disclosure calculates the distance to an object based on a measurement interference signal, which is an interference wave between the reflected wave of an electromagnetic wave reflected by the object and the electromagnetic wave that was not irradiated to the object, and a reference interference signal generated based on the measurement interference signal. Therefore, since at least a portion of the path for propagating the measurement interference signal and the path for propagating the reference interference signal can be made common, the signal propagation path can be shortened. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a block diagram showing a schematic configuration of an electromagnetic wave distance measuring device according to a first embodiment. [Figure 2] FIG. 1 is a block diagram showing an example of a hardware configuration of an electromagnetic wave distance measuring device according to a first embodiment. [Figure 3] 1 is a block diagram showing an example of a hardware configuration of an electromagnetic wave distance measuring device according to a first embodiment. [Figure 4] 10 is a table showing signals included in input to a first signal converter in the electromagnetic wave distance measuring device according to the first embodiment. [Figure 5] 5A is a graph showing a change over time in the frequency of a measurement interference signal according to the first embodiment, and FIG. 5B is a graph showing a change over time in the frequency of a signal included in an input to a first signal converter according to the first embodiment. [Figure 6] 4 is a flowchart showing an example of processing performed by a signal processing unit according to the first embodiment. [Figure 7] 10 is a graph showing a change over time in frequency of a signal from a branching / combining unit including a reference interference signal according to the second embodiment. [Figure 8] 8A is a graph showing the change over time in the amplitude of a reference interference signal according to the second embodiment, FIG. 8B is a graph showing the change over time in the amplitude of a measurement interference signal according to the second embodiment, and FIG. 8C is a graph showing the results of sampling the reference interference signal according to the second embodiment. [Figure 9] 9A is a graph showing the time change in the frequency of a reference interference signal according to the second embodiment; FIG. 9B is a graph showing the time change in the frequency of a measurement interference signal according to the second embodiment; FIG. 9C is a graph showing the relationship between the distance to the object and the wavenumber in the results of sampling the reference interference signal according to the second embodiment; and FIG. 9D is a graph showing the spectrum obtained by Fourier transforming the results of sampling the reference interference signal according to the second embodiment. [Figure 10] FIG. 11 is a block diagram showing a schematic configuration of an electromagnetic wave distance measuring device according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Embodiment 1 First, a schematic configuration of an electromagnetic wave distance measuring device 1 according to the first embodiment will be described with reference to Fig. 1. Fig. 1 is a block diagram showing a schematic configuration of the electromagnetic wave distance measuring device 1 according to the first embodiment. The electromagnetic wave distance measuring device 1 irradiates a target with radar light whose frequency changes with time, and calculates a distance L to the target based on the frequency of the wave reflected from the target. airThe electromagnetic wave ranging device 1 is an FMCW-LiDAR (Frequency Modulated Continuous Wave-Light Detection and Ranging) type ranging device that measures electromagnetic waves. As shown in Fig. 1, the electromagnetic wave ranging device 1 includes a light source 11, an irradiation unit 12, a lens barrel 13, a branching unit 14, a branching / combining unit 15, a first signal conversion unit 20, a second signal conversion unit 30, and a signal processing unit 40. In Fig. 1, the dashed arrows indicate the propagation paths of optical signals (light waves), and the solid arrows indicate the propagation paths of electrical signals.

[0010] Light source 11 is a frequency sweep light source that generates laser light whose frequency changes over time. For example, light source 11 receives power from a power source (not shown) and generates continuous-wave laser light whose frequency changes linearly over time. In the first embodiment, light source 11 constitutes an electromagnetic wave generating unit that generates electromagnetic waves.

[0011] The irradiation unit 12 irradiates the laser light L1 generated by the light source 11 toward the object M1, which is the object to be measured for distance, and outputs light input from the side of the object M1 toward the branching unit 14. The irradiation unit 12 is configured to include, for example, an optical circulator and an optical fiber (not shown) that connects the optical circulator to the lens barrel 13, and irradiates the laser light L1 generated by the light source 11 from the optical fiber through the lens barrel 13 toward the object M1, and outputs light input to the optical fiber from the side of the object M1 toward the branching unit 14.

[0012] Lens barrel 13 is disposed between irradiation unit 12 and object M1, and collects a portion of the laser light from irradiation unit 12 and irradiates the object M1 with the collected light. For example, lens barrel 13 is configured with one or more lenses, is connected to the optical fiber of irradiation unit 12, and collects a portion of the laser light propagating from the optical fiber of irradiation unit 12 and irradiates the object M1 with the collected light. Of the laser light from irradiation unit 12, a portion of laser light L2 is irradiated onto object M1 via lens barrel 13, and a reflected wave reflected by object M1 is input to irradiation unit 12 again via lens barrel 13. Furthermore, a portion of laser light L3 from irradiation unit 12 is not irradiated onto object M1, but is Fresnel reflected on the propagation path of laser light L3 irradiated onto object M1 from irradiation unit 12, and a Fresnel reflected wave, which is a wave reflected by Fresnel reflection, is input to irradiation unit 12.

[0013] For example, a portion of the laser light L2 from the irradiation unit 12 is irradiated onto the object M1 via the optical fiber and the lens barrel 13, and a reflected wave reflected by the object M1 is input to the irradiation unit 12 via the lens barrel 13 and the optical fiber. Furthermore, a portion of the laser light L3 from the irradiation unit 12 is not irradiated onto the object M1 but is Fresnel reflected at the air interface at the connection between the optical fiber and the lens barrel 13, and the reflected wave is input to the irradiation unit 12. In other words, a portion of the laser light L3 from the irradiation unit 12 is not irradiated onto the object M1 but is Fresnel reflected at the air interface at the end of the optical fiber on the object M1 side, and the reflected wave is input to the irradiation unit 12. At this time, a measurement interference signal is generated, which is an interference wave between the reflected wave of the laser light L2 from the object and the reflected wave of the laser light L3 due to Fresnel reflection. In the first embodiment, the air interface where the laser light L3 is Fresnel reflected constitutes a measurement interference signal generation unit that generates the measurement interference signal.

[0014] The measurement interference signal is a difference between the optical path length of the laser light L2 irradiated from the irradiation unit 12, reflected by the object M1, and input to the irradiation unit 12, and the optical path length of the laser light L3 irradiated from the irradiation unit 12, reflected by the object M1, and input to the irradiation unit 12, which is a distance L air In the following description, the distance Lair Measure the distance L air The generated measurement interference signal is incident on the irradiating unit 12 and outputted toward the branching unit 14.

[0015] The branching unit 14 branches the measurement interference signal from the irradiation unit 12. The branching unit 14 is configured, for example, by an optical coupler or a beam splitter, and divides the measurement interference signal from the irradiation unit 12 into two. The branching unit 14 outputs one of the branched measurement interference signals, L4, to the branching / combining unit 15, and outputs the other branched measurement interference signal, L5, to the second signal converting unit 30. One of the measurement interference signals, L4, branched by the branching unit 14 is used as a reference light when calculating the distance to the object M1 based on the other measurement interference signal, L5, branched by the branching unit 14.

[0016] The branching / combining unit 15 branches the measurement interference signal at a branching point, has a loop path 15a which is a delay path for giving one of the branched signals a delay time relative to the other signal, and recombines the one signal propagated through the loop path 15a with the other signal at the branching point. In this way, the branching / combining unit 15 generates a signal having a beat frequency corresponding to the optical path length of the loop path 15a based on the measurement interference signal. Note that the branching / combining unit may be configured to branch the measurement interference signal, give one of the branched signals a delay time relative to the other signal, and then recombine the two signals. For example, the branching / combining unit may have a propagation path for propagating one of the branched signals from the measurement interference signal and a propagation path for propagating the other branched signal from the measurement interference signal, and recombine the one signal and the other signal propagated through the respective propagation paths. When the branching / combining unit is configured in this way, the branching / combining unit generates a signal having a beat frequency corresponding to the optical path length difference between the propagation path for propagating one signal and the propagation path for propagating the other signal, based on the measurement interference signal. The branching / combining unit 15 outputs the generated signal to the first signal conversion unit.

[0017] The first signal converter 20 generates a reference interference signal, which is a digital signal having a beat frequency higher than that of the measurement interference signal, based on the signal input from the branching / combining unit 15. In other words, the first signal converter 20 generates a reference interference signal, which is a digital signal having a beat frequency higher than that of the measurement interference signal, based on the measurement interference signal. The beat frequency of the reference interference signal generated by the first signal converter 20 needs to be at least twice that of the measurement interference signal, but is preferably four times or more that of the measurement interference signal. In the first embodiment, the first signal converter 20 constitutes a reference interference signal generator. The first signal converter 20 includes an optoelectric converter 21, a band-pass filter (hereinafter referred to as a BPF (Band-pass filter)) 22, a time gate 23, and an AD converter 24.

[0018] The photoelectric conversion unit 21 converts the optical signal, which is the measurement interference signal input from the branching / combining unit 15, into an electrical signal. For example, the photoelectric conversion unit 21 is configured with a photodiode and converts the optical signal into an electrical signal by generating a current corresponding to the input optical signal. The BPF 22 extracts a signal of a specific frequency from the electrical signal converted from the optical signal by the photoelectric conversion unit 21. The time gate 23 extracts a signal of a specific time from the signal extracted by the BPF 22. The AD conversion unit 24 converts the analog signal extracted by the time gate 23 into a digital signal by sampling it at a specific frequency. In this way, the first signal conversion unit 20 generates a reference interference signal based on the input measurement interference signal. The first signal conversion unit 20 outputs the generated reference interference signal, which is a digital signal, to the signal processing unit 40. Details of the first signal conversion unit 20 will be described later.

[0019] The second signal conversion unit 30 has a photoelectric conversion unit 31 and an AD conversion unit 32. The photoelectric conversion unit 31 converts the measurement interference signal L5, which is an optical signal branched by the branching unit 14, into an electrical signal by photoelectric conversion. The AD conversion unit 32 converts the measurement interference signal, which has been converted into an electrical signal by the photoelectric conversion unit 31, into a digital signal and outputs it to the signal processing unit 40. The details of the photoelectric conversion unit 31 and the AD conversion unit 32 are similar to those of the photoelectric conversion unit 21 and the AD conversion unit 24, and therefore will not be described in detail.

[0020] The signal processing unit 40 has a signal acquiring unit 41, a sampling unit 42, and a distance calculation unit 43. The signal acquiring unit 41 acquires a reference interference signal, which is a digital signal, from the first signal converting unit 20, and acquires a measurement interference signal, which is a digital signal, from the second signal converting unit 30.

[0021] The sampling unit 42 samples the measurement interference signal acquired by the signal acquiring unit 41 based on the reference interference signal acquired by the signal acquiring unit 41. For example, the sampling unit 42 samples the measurement interference signal at a timing related to the beat frequency of the reference interference signal. Specifically, the sampling unit 42 samples the measurement interference signal at a time corresponding to a zero-crossing point where the phase of the reference interference signal becomes 0°. For example, the sampling unit 42 samples the measurement interference signal sampled by a resampling method.

[0022] The sampling unit 42 may be configured to sample the measurement interference signal acquired by the signal acquiring unit 41 based on the reference interference signal acquired by the signal acquiring unit 41. For example, the sampling unit may be configured to sample the measurement interference signal at times corresponding to zero-crossing points where the phase of the reference interference signal is 180°, or at times corresponding to both zero-crossing points where the phase of the reference interference signal is 0° and 180°, or at times where the phase of the reference interference signal is 90°, or at times where the phase of the reference interference signal is 270°, or at times where the phase of the reference interference signal is 90° and 270°, or at times where a displacement of the reference interference signal exceeds a predetermined threshold, or at more than one of these times.

[0023] The distance calculation unit 43 calculates the distance L from the irradiation unit 12 to the object M1 based on the result of sampling by the sampling unit 42. air In other words, the distance calculation unit 43 calculates the distance L from the air interface of the irradiation unit 12 to the object M1 based on the result of sampling by the sampling unit 42. air For example, the distance calculation unit 43 extracts frequency components from the measurement interference signal by fast Fourier transform based on the sampling result by the sampling unit 42, and calculates the distance L from the irradiation unit 12 to the object M1 based on the spectrum of the beat frequency obtained by analyzing the extracted frequency components. air Calculate.

[0024] Next, the hardware configuration of the signal processing unit 40 will be described with reference to Figures 2 and 3. Figure 2 is a diagram showing an example of the hardware configuration of the signal processing unit 40, and Figure 3 is a diagram showing an example of the hardware configuration of the signal processing unit 40 that is different from that shown in Figure 2. For example, as shown in Figure 2, the signal processing unit 40 is a computer having a processor 40a, a memory 40b, and an I / O port 40c, and is configured so that the processor 40a reads and executes a program stored in the memory 40b.

[0025] 3, the signal processing unit 40 is a computer that has a processing circuit 40d, which is dedicated hardware, and an I / O port 40c, and executes a program. The processing circuit 40d is configured, for example, by a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof. Each function of the signal processing unit 40 is realized by the processor 40a or the processing circuit 40d, which is dedicated hardware, executing a program. Note that the signal processing unit 40 may have hardware other than that described above.

[0026] Next, the first signal converter 20, which is configured to generate a reference interference signal of the electromagnetic wave distance measuring device 1, will be described in detail with reference to Figures 1, 4 and 5. Figure 4 is a table showing signals included in the input to the first signal converter 20. As shown in Figure 4, the first signal converter 20 converts the beat frequency, which is the measurement interference signal, into the measurement distance L. air Twice as much as (2L) air ), the beat frequency is the delay length L loop The corresponding signal, the beat frequency of which is the delay length L loop and 2L air The total length (L loop +2L air ) and the beat frequency is the signal corresponding to the delay length L loop and 2L airThe difference in length (L loop -2L air ) and a signal corresponding to the loop path 15a. Note that a signal generated based on an optical signal that has looped through the loop path 15a multiple times is omitted.

[0027] 5A is a graph showing a time change in the frequency of the measurement interference signal according to the first embodiment, and FIG. 5B is a graph showing a time change in the frequency of the signal included in the input to the first signal converting unit 20 according to the first embodiment. As described above, the first signal converting unit 20 extracts a signal of a specific frequency and a specific time from the input signal including the measurement interference signal using the BPF 22 and the time gate 23. For example, as shown in FIG. 5B, the first signal converting unit 20 extracts a signal in a frequency band from frequency f1 to frequency f2 using the BPF 22, and extracts a signal from time t1 to time t2 using the time gate 23. As a result, the first signal converting unit 20 extracts a signal in a frequency band from frequency f1 to frequency f2 using the time gate 23. loop In other words, the first signal converter 20 extracts, from the signal input from the splitter / synthesizer 15, a signal that does not include the frequency of the reflected wave of the laser light that is irradiated onto the object M1 and reflected by the object M1, that is, a signal whose beat frequency is within the delay length L loop The signal corresponding to is extracted as the reference interference signal.

[0028] The first signal conversion unit 20 may be configured to extract a signal corresponding to at least one of a signal of a specific frequency and a signal of a specific time from a signal including the input measurement interference signal. For example, the first signal conversion unit 20 may have only one of the BPF 22 and the time gate 23 and be configured to extract a signal corresponding to either a signal of a specific frequency or a signal of a specific time.

[0029] Next, the processing performed by the signal processing unit 40 will be described with reference to Fig. 1 and Fig. 6. Fig. 6 is a flowchart showing an example of the processing performed by the signal processing unit 40. As shown in Fig. 6, when the signal processing unit 40 starts the processing, it first acquires a measurement interference signal and a reference interference signal generated based on the measurement interference signal (step ST01). In this processing, the signal processing unit 40 acquires the reference interference signal from the first signal conversion unit 20 and the measurement interference signal from the second signal conversion unit 30 using the signal acquisition unit 41.

[0030] After the process of step ST01, the signal processing unit 40 samples the measurement interference signal based on the acquired reference interference signal (step ST02). In this process, the signal processing unit 40 resamples the measurement interference signal, for example, at a timing related to the beat frequency of the reference interference signal.

[0031] After performing the process of step ST02, the signal processing unit 40 extracts frequency components from the measured interference signal by fast Fourier transform based on the result of sampling in the process of step ST02 (step ST03).

[0032] After performing the process of step ST03, the signal processing unit 40 calculates the measured distance L from the irradiation unit 12 to the object M1 based on the peak position of the extracted frequency component. air (step ST04). After performing the process of step ST04, the signal processing unit 40 ends the process.

[0033] As described above, the electromagnetic wave distance measuring device 1 according to the first embodiment includes a light source 11 that generates laser light whose frequency changes over time, an irradiation unit 12 that irradiates the object M1 with part of the laser light generated by the light source 11, a measurement interference signal generation unit that generates a measurement interference signal which is an interference wave between a reflected wave of the laser light that is irradiated to and reflected by the object M1 and the laser light that is not irradiated to the object M1, a branching and combining unit 15 that branches the measurement interference signal and combines it again by giving one of the branched signals a delay time relative to the other signal, a first signal conversion unit 20 that generates a reference interference signal having a higher frequency than the measurement interference signal based on the signal from the branching and combining unit 15, a sampling unit 42 that samples the measurement interference signal based on the reference interference signal, and a distance L from the irradiation unit 12 to the object M1 based on the result of sampling by the sampling unit 42. air and a distance calculation unit that calculates:

[0034] With this configuration, the electromagnetic wave distance measuring device 1 calculates the distance L to the object M1 based on a measurement interference signal, which is an interference wave between the reflected wave of the laser light reflected by the object M1 and the laser light that was not irradiated onto the object M1, and a reference interference signal generated based on the measurement interference signal. air Since the path for propagating the measurement interference signal and the path for propagating the reference interference signal can be at least partially common, the signal propagation path can be shortened.

[0035] Similarly, the signal processing unit 40 according to the first embodiment includes a signal acquiring unit 41 that acquires a measurement interference signal, which is an interference wave between a reflected wave of laser light that is reflected by the object M1 when a portion of the laser light, whose frequency changes over time, is irradiated onto the object M1 and the laser light that is not irradiated onto the object M1, and a reference interference signal that is a signal with a higher frequency than the measurement interference signal that is generated based on a signal including the measurement interference signal; a sampling unit 42 that samples the measurement interference signal based on the reference interference signal; and a distance calculating unit that calculates the distance to the object based on the sampling result by the sampling unit 42.

[0036] With this configuration, the signal processing unit 40 calculates the distance L to the object M1 based on a measurement interference signal, which is an interference wave between the reflected wave of the laser light reflected by the object M1 and the laser light that is not irradiated onto the object M1, and a reference interference signal generated based on the measurement interference signal. air Since the path for propagating the measurement interference signal and the path for propagating the reference interference signal in the electromagnetic distance measuring device can be at least partially common, the signal propagation path in the electromagnetic distance measuring device can be shortened.

[0037] The first signal converter 20 according to the first embodiment is configured to generate a reference interference signal by extracting, from the signal from the branching / combining unit 15, a signal that does not include a reflected wave of the laser light that is irradiated onto the object M1 and reflected by the object M1. air Since the signal that does not change depending on the measurement distance L is extracted as the reference interference signal, air This makes it possible to stabilize the measurement results.

[0038] In the first embodiment, the first signal converter 20 is configured to generate the reference interference signal by extracting, from the signal input from the branching / combining unit 15, a signal that does not include the frequency of the reflected wave of the laser light that is irradiated onto the object M1 and reflected by the object M1, but this is not limiting. The electromagnetic wave distance measuring device may be configured to generate a reference interference signal having a higher frequency than the measurement interference signal based on the signal from the branching / combining unit. For example, the electromagnetic wave distance measuring device may extract, from the four signals included in the signal from the branching / combining unit, a signal having a beat frequency that is equal to or greater than the delay length L, which is the optical path length related to the delay time of the branching / combining unit 15. loop The reference interference signal may be generated by extracting a signal other than the signal corresponding to the reference interference signal.

[0039] Embodiment 2 Next, an electromagnetic wave ranging device according to embodiment 2 will be described with reference to Figures 7 to 9. The electromagnetic wave ranging device according to embodiment 2 differs from the electromagnetic wave ranging device 1 according to embodiment 1 in the range of signals extracted by the first signal conversion unit, but the configuration of each unit is the same, and the same configuration as in embodiment 1 is given the same names and symbols as in embodiment 1, and description thereof will be omitted.

[0040] 7 is a graph showing a time change in the frequency of a signal from the branching and combining unit including a reference interference signal according to the second embodiment. Similar to the first signal conversion unit 20 according to the first embodiment, the first signal conversion unit according to the second embodiment extracts a signal of a specific frequency and a specific time from the input signal including the measurement interference signal by using a BPF and a time gate. For example, as shown in FIG. 7, the first signal conversion unit according to the second embodiment extracts a signal in a frequency band from frequency f3 to frequency f4 by using a BPF, and extracts a signal from time t1 to time t2 by using a time gate. As a result, the first signal conversion unit according to the second embodiment extracts a signal in a frequency band from frequency f3 to frequency f4 by using a BPF, and extracts a signal from time t1 to time t2 by using a time gate. In this way, the first signal conversion unit according to the second embodiment extracts a signal in a region where the beat frequency is within a delay length L, which is included in an area A2 shown in the graph of FIG. 7, from the signal from the branching and combining unit 15. loop and 2L air The difference in length (L loop -2L air ) as a reference interference signal. In other words, the first signal converter according to the second embodiment extracts, from the signal input from the branching / combining unit 15, a signal containing the frequency of the reflected wave of the laser light irradiated onto the object M1 and reflected by the object M1, where the beat frequency is equal to the delay length L loop and 2L air A signal corresponding to the difference in length between the reference interference signal and the reference interference signal is extracted.

[0041] Generally, in FMCW-LiDAR systems, the frequency of laser light from a light source is controlled so that it changes linearly over time. However, due to the effects of chromatic dispersion of laser light, it is difficult to achieve a completely linear change in frequency. However, if the frequency of the generated electromagnetic wave changes nonlinearly, the beat frequency spectrum deteriorates due to the effects of frequency nonlinearity, making it difficult to improve ranging accuracy. For example, since the measurement interference signal and the reference interference signal have different frequencies, depending on the structure of the electromagnetic wave ranging device, they will have different nonlinearities due to the effects of chromatic dispersion. Sampling the measurement interference signal based on such a reference interference signal will result in a mismatch in the chromatic dispersion of each signal, making it difficult to improve ranging accuracy.

[0042] In contrast, in the electromagnetic wave ranging device of embodiment 2, even if the frequency of the laser light from the light source 11 changes nonlinearly, the first signal conversion unit extracts a reference interference signal from the signal input from the branching and combining unit 15, which is a signal containing the frequency of the reflected wave of the laser light irradiated onto the object M1 and reflected by the object M1, i.e., a signal having nonlinearity similar to that of the measurement interference signal, and the signal processing unit 40 is configured to calculate the distance to the object M1 based on the reference interference signal and the measurement interference signal, so that nonlinearity caused by chromatic dispersion, etc. of the laser light from the light source 11 can be compensated for based on the reference interference signal.

[0043] Hereinafter, compensation of the nonlinearity of laser light using a reference interference signal will be described with reference to FIGS. 8 and 9. FIG. 8A is a graph showing a temporal change in the amplitude of a reference interference signal according to the second embodiment. FIG. 8B is a graph showing a temporal change in the amplitude of a measurement interference signal according to the second embodiment. FIG. 8C is a graph showing a result of sampling the reference interference signal according to the second embodiment. FIG. 9A is a graph showing a temporal change in the frequency of a reference interference signal according to the second embodiment. FIG. 9B is a graph showing a temporal change in the frequency of a measurement interference signal according to the second embodiment. FIG. 9C is a graph showing the relationship between the distance to an object and the wavenumber in the result of sampling the reference interference signal according to the second embodiment. FIG. 9D is a graph showing a spectrum obtained by Fourier transforming the result of sampling the reference interference signal according to the second embodiment. FIGS. 9A and 9B show that the reference interference signal generated by the first signal converter according to the second embodiment and the measurement interference signal have similar nonlinearities.

[0044] For example, consider a case in which, in the signal processing unit 40, the signal acquiring unit 41 acquires the signal shown in FIG. 8A from the first signal converting unit as the reference interference signal, acquires the signal shown in FIG. 8B from the second signal converting unit 30 as the measurement interference signal, and the sampling unit 42 samples the measurement interference signal at the time corresponding to the rising zero-cross point (circle shown in FIG. 8A) where the phase of the reference interference signal becomes 0°. In this case, the sampling unit 42 samples the measurement interference signal at a timing according to the nonlinearity of the laser beam. As a result, as shown in FIGS. 8C and 9C, the influence of the nonlinearity of the laser beam can be suppressed in the results of sampling by the sampling unit 42. The distance calculating unit 43 extracts frequency components from the measurement interference signal by fast Fourier transform based on the results of sampling by the sampling unit 42, thereby acquiring the spectrum of the beat frequency shown in FIG. 9D and calculating the distance L to the object M1. air Calculate.

[0045] As described above, the electromagnetic wave distance measuring device according to the second embodiment is configured to generate a reference interference signal by extracting a signal including the frequency of the reflected wave of the laser light irradiated to the object M1 and reflected by the object M1 from the signal from the branching / combining unit 15. With this configuration, even if the change in the frequency of the laser light irradiated to the object M1 is nonlinear, the electromagnetic wave distance measuring device according to the second embodiment can compensate for the nonlinearity of the laser light based on the reference interference signal, thereby obtaining a distance L to the object M1 that is shorter than conventionally possible. air The calculation accuracy can be improved.

[0046] In the second embodiment, the electromagnetic wave distance measuring device calculates the beat frequency from the signal from the branching / combining unit 15 by the delay length L loop and 2L air The difference in length (L loop -2L air ) as a reference interference signal, but is not limited to this. The electromagnetic wave distance measuring device may be configured to generate a reference interference signal by extracting, from the signal input from the branching and combining unit 15, a signal including the frequency of the reflected wave of the laser light irradiated to the object M1 and reflected by the object M1, and for example, the electromagnetic wave distance measuring device may extract, from the signal from the branching and combining unit 15, a signal including the frequency of the reflected wave of the laser light irradiated to the object M1 and reflected by the object M1, and generate a reference interference signal. loop and 2L air The total length (L loop +2L air ) as a reference interference signal, thereby generating the reference interference signal.

[0047] In addition, from the signal from the branching and combining unit 15, the beat frequency is loop and 2L air The difference in length (L loop -2L air ) signal, or beat frequency, corresponding to the delay length L loop and 2L air The total length (L loop +2L air ) as the reference interference signal, the measurement distance Lair , and the delay length L loop According to the Nyquist theorem, it is required to satisfy the following formula (1): In formula (1), R is the measurement distance L air is the measurement range, and n is the refractive index of the optical fiber. 2(2L air +R) <nL loop -2L air -R ∴6L air +3R <nL loop ·······(1)

[0048] For example, the measurement distance (length of the air layer) L air is 0.13 [m], the measurement range R is 0.01 [m], the refractive index n of the optical fiber is 1.44, and the delay length (length of the loop path 15a) is 0.63 [m], the left and right sides of the formula (1) are 0.81 [m] and 0.91 [m], respectively, which satisfies the formula (1). air Since the beat frequency changes depending on the frequency, it is necessary to set the frequency band to be extracted by the BPF 22 so as to satisfy the measurement range R in the band of each signal.

[0049] Embodiment 3 Next, an electromagnetic wave ranging device 3 according to a third embodiment will be described with reference to Fig. 10. The electromagnetic wave ranging device 3 according to the third embodiment differs from the electromagnetic wave ranging device 1 according to the first embodiment in the configuration for generating a reference interference signal based on a measurement interference signal from the irradiator 12, but the other configurations are the same. Therefore, the same configurations as those in the first embodiment are given the same names and symbols as those in the first embodiment, and the description thereof will be omitted.

[0050] As shown in FIG. 10 , the electromagnetic wave distance measuring device 3 according to the third embodiment includes a light source 11, an irradiation unit 12, a lens barrel 13, a photoelectric conversion unit 16, an AD conversion unit 32, a signal conversion unit 50, and a signal processing unit 40. In FIG. 10 , the dashed arrows indicate the propagation paths of optical signals (light waves), and the solid arrows indicate the propagation paths of electrical signals. As with the electromagnetic wave distance measuring device 1 according to the first embodiment, a portion of the laser light L3 from the irradiation unit 12 is not irradiated onto the target M1 but is Fresnel-reflected at the air interface at the end of the optical fiber on the target M1 side, and the reflected wave is input to the irradiation unit 12. At this time, a measurement interference signal is generated, which is an interference wave between the reflected wave of the laser light L2 from the target and the reflected wave of the laser light L3 due to Fresnel reflection. The irradiation unit 12 outputs the generated measurement interference signal to the photoelectric conversion unit 16.

[0051] The photoelectric conversion unit 16 converts the optical signal, which is the measurement interference signal input from the irradiation unit 12, into an electrical signal. Details of the photoelectric conversion unit 16 are similar to those of the photoelectric conversion unit 21 according to the first embodiment, and therefore will not be described again. The photoelectric conversion unit 16 outputs the measurement interference signals S1 and S2 converted into electrical signals to the signal conversion unit 50 and the AD conversion unit 32.

[0052] The signal converter 50 includes a frequency converter 51 and an AD converter 24. The frequency converter 51 converts the input measurement interference signal S1 into a signal having a higher beat frequency, thereby generating a reference interference signal. For example, the frequency converter 51 samples the input measurement interference signal S1 and, based on the sampling result, generates a reference interference signal having a new beat frequency obtained by multiplying the beat frequency of the input measurement interference signal S1. The beat frequency of the reference interference signal generated by the frequency converter 51 may be at least two real multiples of the measurement interference signal, but is preferably four or more times the measurement interference signal. The frequency converter 51 outputs the generated reference interference signal to the AD converter 24. The AD converter 24 converts the analog signal from the frequency converter 51 into a digital signal and outputs the digital signal to the signal processor 40. In the third embodiment, the signal converter 50 constitutes a reference interference signal generator that generates a reference interference signal having a higher frequency than the measurement interference signal, based on a signal including the measurement interference signal.

[0053] The AD conversion unit 32 converts the measurement interference signal from the photoelectric conversion unit 16, which is an analog signal, into a digital signal and outputs it to the signal processing unit .

[0054] As described above, in the electromagnetic wave distance measuring device 3 according to the third embodiment, the reference interference signal generating unit generates a reference interference signal having a higher frequency than the measurement interference signal by multiplying the frequency of the measurement interference signal from the measurement interference signal generating unit by a real number. With this configuration, even if the measurement interference signal has nonlinearity, the reference interference signal and the measurement interference signal have nonlinearities that are similar to each other, so that the electromagnetic wave distance measuring device 3 can compensate for the nonlinearity of the laser light based on the reference interference signal, and the distance L to the object M1 can be measured more accurately than in the past. air Furthermore, with this configuration, the electromagnetic wave distance measuring device 3 does not require the branching unit 14, the branching / combining unit 15, the BPF 22, the time gate 23, and the like in the first embodiment, and therefore the number of components can be reduced.

[0055] In the first to third embodiments described above, the electromagnetic wave ranging device is an FMCW-LiDAR ranging device equipped with light source 11, which is a frequency-swept light source that generates laser light whose frequency varies over time. However, the present invention is not limited to this. In any of the above-described embodiments, the electromagnetic wave ranging device may be an FMCW ranging device that irradiates an object with electromagnetic waves other than radar light whose frequency varies over time and measures the distance to the object based on the frequency of the waves reflected from the object. For example, the electromagnetic wave ranging device may be an FMCW radar device that includes a radio wave generator that generates radio waves whose frequency varies over time, irradiates the object with the radio waves from the radio wave generator, and measures the distance to the object based on the frequency of the waves reflected from the object. Even in such a device, at least a portion of the path for propagating the measurement interference signal and the path for propagating the reference interference signal can be shared, thereby achieving the effect of shortening the signal propagation path.

[0056] In addition, the present disclosure allows for free combination of the respective embodiments, modification of any of the components of the respective embodiments, or omission of any of the components of the respective embodiments. [Industrial Applicability]

[0057] The electromagnetic wave distance measuring device according to the present disclosure can be used, for example, to calculate the distance to an object based on a reflected wave when an electromagnetic wave is irradiated toward the object. [Explanation of symbols]

[0058] 1 Electromagnetic wave distance measuring device, 3 Electromagnetic wave distance measuring device, 11 Light source (electromagnetic wave generating unit), 12 Irradiation unit (measurement interference signal generating unit), 13 Optical tube, 14 Branching unit, 15 Branching and combining unit, 15a Loop path, 16 Photoelectric conversion unit, 20 First signal conversion unit (reference interference signal generating unit), 21 Photoelectric conversion unit, 22 BPF, 23 Time gate, 24 AD conversion unit, 30 Second signal conversion unit, 31 Photoelectric conversion unit, 32 AD conversion unit, 40 Signal processing unit, 41 Signal acquisition unit, 42 Sampling unit, 43 Distance calculation unit, 50 Signal conversion unit, 51 Frequency conversion unit, L airDistance (measurement distance), M1 object.

Claims

1. An electromagnetic wave generating unit that generates electromagnetic waves whose frequency changes over time, An irradiation unit that irradiates an object with a portion of the electromagnetic waves generated by the electromagnetic wave generating unit, A measurement interference signal generation unit generates a measurement interference signal which is an interference wave of the reflected wave of the electromagnetic wave that was irradiated onto the object and reflected by the object, and the electromagnetic wave that was not irradiated onto the object. A reference interference signal generation unit generates a reference interference signal with a higher frequency than the measurement interference signal based on a signal including the measurement interference signal from the measurement interference signal generation unit, A sampling unit that samples the measurement interference signal based on the reference interference signal, The system includes a distance calculation unit that calculates the distance from the irradiation unit to the object based on the sampling results from the sampling unit. An electromagnetic wave distance measuring device characterized by the following features.

2. The electromagnetic wave generating unit is a light source that generates laser light as the electromagnetic wave. The electromagnetic wave distance measuring device according to feature 1.

3. The measurement interference signal generation unit generates the measurement interference signal, which is an interference wave of the reflected wave of the laser light that is irradiated onto the object and reflected by the object, and the Fresnel reflected wave in the propagation path of the laser light that is irradiated onto the object by the irradiation unit. The electromagnetic wave distance measuring device according to claim 2, characterized in that it is as described above.

4. The unit includes a branching and combining unit that branches the measurement interference signal from the measurement interference signal generation unit, gives one of the branched signals a delay time relative to the other signal, and then recombines them. The reference interference signal generation unit generates a reference interference signal with a higher frequency than the measured interference signal, based on the signal from the branching and combining unit. The electromagnetic wave distance measuring device according to claim 2 or 3, characterized in that it is as described above.

5. The system includes a branching section for branching the aforementioned measurement interference signal, The branching and combining unit then newly branches one of the measurement interference signals that was branched by the branching unit and combines them again. The sampling unit samples the other measurement interference signal that has been branched by the branching unit, based on the reference interference signal. The electromagnetic wave distance measuring device according to feature 4.

6. The reference interference signal generation unit generates the reference interference signal by extracting a signal of a specific frequency from the signal from the branching and combining unit. The electromagnetic wave distance measuring device according to feature 4.

7. The reference interference signal generation unit generates the reference interference signal by extracting a signal at a specific time from the signal from the branching and combining unit. The electromagnetic wave distance measuring device according to feature 4.

8. The reference interference signal generation unit generates the reference interference signal by extracting a signal from the signal from the branching and combining unit that does not include the frequency of the reflected electromagnetic wave that was irradiated onto the object and reflected by the object. The electromagnetic wave distance measuring device according to feature 4.

9. The reference interference signal generation unit generates the reference interference signal by extracting a signal from the signal from the branching and combining unit that includes the frequency of the reflected wave of the electromagnetic wave that was irradiated onto the object and reflected by the object. The electromagnetic wave distance measuring device according to feature 4.

10. The branching and combining unit has a loop path that branches the measured interference signal, delays it, and then returns it to the branching point for recombination. The electromagnetic wave distance measuring device according to feature 4.

11. The reference interference signal generation unit generates a reference interference signal with a higher frequency than the measurement interference signal by multiplying the frequency of the measurement interference signal from the measurement interference signal generation unit by a real number. The electromagnetic wave distance measuring device according to any one of claims 1 to 3.

12. A signal acquisition unit acquires a measurement interference signal, which is an interference wave between the reflected wave of an electromagnetic wave whose frequency changes over time is irradiated onto an object and reflected by the object, and the electromagnetic wave that was not irradiated onto the object, and a reference interference signal, which is a signal with a higher frequency than the measurement interference signal, generated based on the signal including the measurement interference signal. A sampling unit that samples the measurement interference signal based on the reference interference signal, The system includes a distance calculation unit that calculates the distance to the object based on the sampling results from the sampling unit. An electromagnetic wave distance measuring device characterized by the following features.

13. An electromagnetic wave distance measurement method performed by an apparatus comprising an electromagnetic wave generation unit, an irradiation unit, a measurement interference signal generation unit, a reference interference signal generation unit, a sampling unit, and a distance calculation unit, The electromagnetic wave generating unit generates electromagnetic waves whose frequency changes with time, The irradiation unit irradiates an object with a portion of the electromagnetic waves generated by the electromagnetic wave generating unit, The measurement interference signal generation unit generates a measurement interference signal which is an interference wave of the reflected wave of the electromagnetic wave that was irradiated onto the object and reflected by the object, and the electromagnetic wave that was not irradiated onto the object. The steps include: The reference interference signal generation unit generates a reference interference signal with a higher frequency than the measurement interference signal based on a signal including the measurement interference signal from the measurement interference signal generation unit; The sampling unit performs the steps of sampling the measurement interference signal based on the reference interference signal, The distance calculation unit includes the step of calculating the distance from the irradiation unit to the object based on the sampling results from the sampling unit. An electromagnetic wave distance measurement method characterized by the following features.

14. An electromagnetic wave distance measurement method performed by an apparatus comprising a signal acquisition unit, a sampling unit, and a distance calculation unit, The signal acquisition unit acquires a measurement interference signal, which is an interference wave between the reflected wave of the electromagnetic wave reflected by the object when a portion of the electromagnetic wave whose frequency changes over time is irradiated onto the object, and the electromagnetic wave that was not irradiated onto the object, and a reference interference signal, which is a signal with a higher frequency than the measurement interference signal, generated based on the signal including the measurement interference signal. The sampling unit performs the steps of sampling the measurement interference signal based on the reference interference signal, The distance calculation unit includes the step of calculating the distance to the object based on the sampling results from the sampling unit. An electromagnetic wave distance measurement method characterized by the following features.

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