Electromagnetic distance measurement device and electromagnetic distance measurement method

Abstract

The present invention is provided with: an electromagnetic wave generation unit (11) that generates electromagnetic waves having a frequency that changes with time; an irradiation unit (12) that irradiates an object (M1) with a portion of the electromagnetic waves generated by the electromagnetic wave generation unit (11); a measurement interference signal generation unit (12) that generates a measurement interference signal, which is an interference wave of reflected waves of the electromagnetic waves radiated to the object (M1) and reflected by the object (M1), and the electromagnetic waves radiated to the object (M1); a reference interference signal generation unit (20) that generates a reference interference signal having a higher frequency than the measurement interference signal on the basis of a signal including the measurement interference signal from the measurement interference signal generation unit (12); a sampling unit (42) that samples the measurement interference signal on the basis of the reference interference signal; and a distance calculation unit (43) that calculates the distance from the irradiation unit (12) to the object (M1) on the basis of the result of the sampling by the sampling unit (42).

Description

Electromagnetic wave distance measuring device and electromagnetic wave distance measuring method

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

[0002] Distance measuring devices that measure the distance to an object using a frequency modulated continuous wave (FMCW) method have been disclosed (see, for example, Patent Document 1). This distance measuring device measures the distance to the 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 with different delay times.

[0003] JP 2024-007750 A

[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.

[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.

[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.

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

[0009] Hereinafter, embodiments according to 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 embodiment 1 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 embodiment 1. The electromagnetic wave distance measuring device 1 irradiates a target with radar light whose frequency changes over time, and calculates a distance L to the target based on the frequency of the wave reflected from the target. ａｉｒ The electromagnetic wave ranging device 1 is a frequency modulated continuous wave-light detection and ranging (FMCW-LiDAR) type ranging device that measures the distance between a target and an object. 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] The light source 11 is a frequency sweep light source that generates laser light whose frequency changes over time. For example, the 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, the 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] The lens barrel 13 is disposed between the irradiation unit 12 and the object M1 and focuses a portion of the laser light from the irradiation unit 12 and irradiates the object M1. For example, the lens barrel 13 is configured with one or more lenses and is connected to the optical fiber of the irradiation unit 12. The lens barrel 13 focuses a portion of the laser light propagating from the optical fiber of the irradiation unit 12 and irradiates the object M1. A portion of the laser light L2 from the irradiation unit 12 is irradiated onto the object M1 via the lens barrel 13, and a reflected wave reflected by the object M1 is input to the irradiation unit 12 again via the lens barrel 13. Furthermore, a portion of the laser light L3 from the irradiation unit 12 is Fresnel reflected on the propagation path of the laser light L3 irradiated onto the object M1 from the irradiation unit 12 without being irradiated onto the object M1, and a Fresnel reflected wave, which is a wave reflected by Fresnel reflection, is input to the 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 Fresnel reflected at the air interface at the connection between the optical fiber and the lens barrel 13 without being irradiated onto the object M1, 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 Fresnel reflected at the air interface at the end of the optical fiber on the object M1 side without being irradiated onto the object M1, 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 at which 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 L ａｉｒ The measurement distance Lａｉｒ The generated measurement interference signal is incident on the irradiation unit 12 and output 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 by, for example, 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. As a result, 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 of the branched signals 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 a photoelectric 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 converter 30 has a photoelectric converter 31 and an AD converter 32. The photoelectric converter 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 converter 32 converts the measurement interference signal, which has been converted into an electrical signal by the photoelectric converter 31, into a digital signal and outputs the digital signal to the signal processor 40. The details of the photoelectric converter 31 and the AD converter 32 are similar to those of the photoelectric converter 21 and the AD converter 24, and therefore will not be described in detail.

[0020] The signal processing unit 40 includes 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 a time corresponding to a zero-crossing point where the phase of the reference interference signal is 180°, or at both a zero-crossing point where the phase of the reference interference signal is 0° and a zero-crossing point where the phase of the reference interference signal is 180°, or at a time where the phase of the reference interference signal is 90°, or at a time where the phase of the reference interference signal is 270°, or at both a time where the phase of the reference interference signal is 90° and a time where the phase of the reference interference signal is 270°, or at a time where the displacement of the reference interference signal exceeds a predetermined threshold, or at a plurality 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 include hardware other than that described above.

[0026] Next, the first signal converter 20, which is a component for generating 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 (2L) ａｉｒ ), the beat frequency is the optical path length related to the delay time of the branching / combining unit 15, ｌｏｏｐ The signal corresponding to the beat frequency 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 ａｉｒ The 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 converter 20 according to the first embodiment. As described above, the first signal converter 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 converter 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 converter 20 extracts a signal whose beat frequency is within the delay length L, which is included in the area A1 in the graph of FIG. 5B . ｌｏｏｐ In other words, the first signal converter 20 extracts, from the signal input from the splitter / combiner 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 equal to or less than 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 may 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 measurement interference signal by fast Fourier transform based on the result of sampling in the process of step ST02 (step ST03).

[0032] When the process of step ST03 is performed, 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 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 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, which 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 result of sampling 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 wave ranging device can be at least partially common, the signal propagation path in the electromagnetic wave ranging 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 a 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 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] 7 to 9, an electromagnetic wave ranging device according to embodiment 2 will be described. 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 converter, but the configuration of each unit is the same, and the same components as those in embodiment 1 are given the same names and symbols as those in embodiment 1, and their description 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 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 using a BPF, and extracts a signal from time t1 to time t2 using a time gate. As a result, the first signal conversion unit according to the second embodiment extracts a signal from the branching and combining unit 15 including a beat frequency within a delay length L, which is included in an area A2 shown in the graph of FIG. 7 . ｌｏｏｐ and 2L ａｉｒ The difference in length (L ｌｏｏｐ -2L ａｉｒ 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, the beat frequency of which 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 laser light from the light source is controlled so that its frequency changes linearly over time. However, due to the effects of chromatic dispersion of the 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 different effects of chromatic dispersion. If the measurement interference signal is sampled based on such a reference interference signal, a mismatch in the chromatic dispersion of each signal will occur, 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 the temporal change in the amplitude of the reference interference signal according to the second embodiment. FIG. 8B is a graph showing the temporal change in the amplitude of the measurement interference signal according to the second embodiment. FIG. 8C is a graph showing the results of sampling the reference interference signal according to the second embodiment. FIG. 9A is a graph showing the temporal change in the frequency of the reference interference signal according to the second embodiment. FIG. 9B is a graph showing the temporal change in the frequency of the 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. FIG. 9D is a graph showing a spectrum obtained by Fourier transforming the results 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 acquisition unit 41 acquires the signal shown in FIG. 8A from the first signal conversion unit as a reference interference signal, acquires the signal shown in FIG. 8B from the second signal conversion unit 30 as a measurement interference signal, and the sampling unit 42 samples the measurement interference signal at a 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 calculation 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 target 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 compensates for the nonlinearity of the laser light based on the reference interference signal, thereby making it possible to obtain 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 However, the electromagnetic wave distance measuring device is not limited to this configuration as long as it is 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 extracts, 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 generates 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 / combining unit 15, the beat frequency is ｌｏｏｐ and 2L ａｉｒ The difference in length (L ｌｏｏｐ -2L ａｉｒ ) or the beat frequency is the signal corresponding to the delay length L ｌｏｏｐ and 2L ａｉｒ The total length (L ｌｏｏｐ +2L ａｉｒ ) is extracted as the reference interference signal, the measurement distance L ａｉｒ , and the delay length Lｌｏｏｐ According to the Nyquist theorem, it is required to satisfy the following formula (1): ａｉｒ The measurement range of 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] Third Embodiment 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 components 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 , dashed arrows indicate the propagation paths of optical signals (light waves), and 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 converter 32 converts the measurement interference signal from the photoelectric converter 16 , which is an analog signal, into a digital signal and outputs it to the signal processor 40 .

[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 it is possible to reduce the number of parts.

[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 changes over time. However, this 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 changes 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 changes 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.

[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.

[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 ａｉｒ Distance (measurement distance), M1 object.

Claims

1. An electromagnetic wave ranging device 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 which is an interference wave between a reflected wave of the electromagnetic wave that is irradiated to the object and reflected by the object, and the 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 sampling result by the sampling unit.

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

3. The electromagnetic wave ranging device of claim 2, characterized in that the measurement interference signal generating unit generates the measurement interference signal, which is an interference wave between the reflected wave of the laser light irradiated onto the object and reflected by the object, and the Fresnel reflected wave in the propagation path of the laser light irradiated onto the object by the irradiating unit.

4. An electromagnetic wave ranging device as described in claim 2 or 3, characterized in that it is provided with a branching and combining unit that branches the measurement interference signal from the measurement interference signal generating unit, gives one of the branched signals a delay time relative to the other signal, and combines them again, and the reference interference signal generating unit generates the reference interference signal having a higher frequency than the measurement interference signal based on the signal from the branching and combining unit.

5. An electromagnetic distance measuring device as described in claim 4, characterized in that it comprises a branching unit that branches the measurement interference signal, the branching and combining unit newly branches one of the measurement interference signals branched by the branching unit and then combines it again, and the sampling unit samples the other of the measurement interference signals branched by the branching unit based on the reference interference signal.

6. An electromagnetic wave ranging device as claimed in any one of claims 4 or 5, characterized in that the reference interference signal generating unit generates the reference interference signal by extracting a signal of a specific frequency from the signal from the branching and combining unit.

7. An electromagnetic wave ranging device according to any one of claims 4 to 6, characterized in that the reference interference signal generating unit generates the reference interference signal by extracting a signal at a specific time from the signal from the branching and combining unit.

8. An electromagnetic wave ranging device as described in any one of claims 4 to 7, characterized in that the reference interference signal generating unit generates the reference interference signal by extracting from the signal from the branching and combining unit a signal that does not contain the frequency of the reflected wave of the electromagnetic wave that is irradiated to the object and reflected by the object.

9. An electromagnetic wave ranging device as described in any one of claims 4 to 7, characterized in that the reference interference signal generating unit generates the reference interference signal by extracting a signal from the signal from the branching and combining unit that contains the frequency of the reflected wave of the electromagnetic wave that is irradiated to the object and reflected by the object.

10. An electromagnetic wave distance measuring device as claimed in any one of claims 4 to 9, characterized in that the branching and combining unit has a loop path that branches the measurement interference signal, gives a delay time, returns it to the branching point and combines it again.

11. An electromagnetic distance measuring device as described in any one of claims 1 to 3, characterized in that the reference interference signal generation unit generates the 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 generation unit by a real number.

12. An electromagnetic wave ranging device comprising: a signal acquisition unit that acquires a measurement interference signal, which is an interference wave between a portion of an electromagnetic wave whose frequency changes over time is irradiated onto an object and reflected by the object, and the electromagnetic wave that is not irradiated onto the object; and a reference interference signal, which is a signal with a higher frequency than the measurement interference signal and is generated based on a signal including the measurement interference signal; a sampling unit that samples the measurement interference signal based on the reference interference signal; and a distance calculation unit that calculates the distance to the object based on the sampling result by the sampling unit.

13. An electromagnetic wave ranging method performed by an apparatus comprising an electromagnetic wave generating unit, an irradiating unit, a measurement interference signal generating unit, a reference interference signal generating unit, a sampling unit, and a distance calculating unit, comprising: a step in which the electromagnetic wave generating unit generates electromagnetic waves whose frequency changes with time; a step in which the irradiating unit irradiates an object with part of the electromagnetic waves generated by the electromagnetic wave generating unit; a step in which the measurement interference signal generating unit generates a measurement interference signal which is an interference wave between a reflected wave of the electromagnetic wave irradiated to the object and reflected by the object, and the electromagnetic wave that was not irradiated to the object; a step in which the reference interference signal generating unit generates a reference interference signal having a frequency higher than that of the measurement interference signal, based on a signal including the measurement interference signal from the measurement interference signal generating unit; a step in which the sampling unit samples the measurement interference signal based on the reference interference signal; and a step in which the distance calculating unit calculates the distance from the irradiating unit to the object based on the sampling result by the sampling unit.

14. An electromagnetic wave ranging method performed by a device having a signal acquisition unit, a sampling unit, and a distance calculation unit, comprising the steps of: the signal acquisition unit acquiring a measurement interference signal, which is an interference wave between a portion of an electromagnetic wave whose frequency changes over time is irradiated onto an object and reflected by the object, and the electromagnetic wave that is not irradiated onto the object; and a reference interference signal, which is a signal having a higher frequency than the measurement interference signal and generated based on a signal including the measurement interference signal; the sampling unit sampling the measurement interference signal based on the reference interference signal; and the distance calculation unit calculating the distance to the object based on the result of sampling by the sampling unit.

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