Distance measuring device

Abstract

To provide a ranging apparatus that can adequately ensure both of a measurable distance range and a resolution.SOLUTION: A ranging apparatus 1 comprises: a signal generation part 2 that generates a first signal S1 having a first repetition frequency F1 and a second signal S2 having a second repetition frequency F2 higher than the first repetition frequency F1; a light source part 3 that generates and outputs light the wavelength of which is temporally modulated by internal modulation based on the first signal S1; a modulation part 4 that outputs light the wavelength of which outputted from the light source part 3 is further temporally modulated by the Doppler effect by an external modulation based on the second signal S2; a division part 5 that divides the light outputted from modulation part 4 into measurement light L1 and reference light L2; an irradiation part 6 that irradiates the measurement light L1 onto an object K; a detector 7 that detects the interference light L4 between the reflection light L3 from the object K and the reference light L2; and a calculation part 8 that calculates the distance to the object K, based on the output signal R from the detector 7.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a distance measuring device. [Background technology]

[0002] A conventional optical distance measuring device is disclosed in, for example, Patent Document 1. This conventional distance measuring device measures distance using multiple distance measuring signals, and generates transmitted light by performing quadrature modulation on an optical carrier. The distance measuring device receives the transmitted light reflected by the object to be measured, and calculates the distance to the object based on multiple signals obtained by performing quadrature demodulation on the reflected light. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 116980 Summary of the Invention [Problem to be solved by the invention]

[0004] One known optical distance measurement method is the frequency modulated continuous wave (FMCW) method. In the FMCW method, measurement light modulated so that the frequency shifts linearly over time is irradiated onto the object, and the distance to the object can be calculated by performing a Fourier transform on the signal based on the interference light between the measurement light and the reflected light. In the FMCW method, the measurable distance depends on the frequency period of the measurement light. On the other hand, the resolution of the distance to the object depends on the linearity of the frequency of the measurement light. Because this resolution is determined by a fixed ratio to the distance calculated by the reciprocal of the period of the measurement light, it can be said that there is a trade-off between the measurable distance and the resolution.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a distance measuring device that can sufficiently ensure both the range of measurable distances and resolution. [Means for solving the problem]

[0006] A distance measuring device according to one aspect of the present disclosure includes a signal generating unit that generates a first signal having a first repetition frequency and a second signal having a second repetition frequency higher than the first repetition frequency; a light source unit that generates and outputs light whose wavelength is modulated over time by internal modulation based on the first signal; a modulator that further modulates the wavelength of the light output from the light source unit over time by the Doppler effect using external modulation based on the second signal; a splitting unit that splits the light output from the modulator into measurement light and reference light; an irradiation unit that irradiates the measurement light toward an object; a detection unit that detects interference light between the reference light and reflected light of the measurement light reflected by the object; and a calculation unit that calculates the distance to the object based on the output signal from the detection unit.

[0007] This distance measuring device performs multi-phase modulation on the measurement light irradiated toward the object using long-period internal modulation based on a first signal and short-period external modulation based on a second signal. This distance measuring device can simultaneously obtain long-period data and short-period data related to the distance to the object by Fourier transforming the output signal from the detection unit. This distance measuring device can sufficiently ensure both the range of measurable distances and resolution by using long-period data suitable for long-distance measurement and short-period data suitable for high resolution.

[0008] The signal generator may generate the second repetition frequency to be an integer multiple of the first repetition frequency, which makes it possible to align the phase of the reference light and the phase of the reflected light, thereby simplifying the calculation for calculating the distance to the object.

[0009] The signal generator may synchronize one of the first signal and the second signal with the other, which makes it possible to align the phase of the reference light and the phase of the reflected light, thereby simplifying the calculation for calculating the distance to the object.

[0010] The signal generator may synchronize the first and second signals based on an external trigger signal, which allows the phase of the reference light and the phase of the reflected light to be aligned, simplifying the calculation for calculating the distance to the object.

[0011] The waveform modulated by the first signal and the waveform modulated by the second signal may have a triangular time waveform, which makes it easy to distinguish between the reference light component and the reflected light component in the interference light and simplifies the calculation for calculating the distance to the object.

[0012] The light source unit may have a variable optical path length resonator in which the optical path length between the resonators changes over time based on the first signal. In this case, internal modulation in the light source unit can be achieved with a simple configuration.

[0013] The calculation unit may calculate a first differential frequency of the reflected light with respect to the reference light and a second differential frequency of the reference light with respect to the reflected light, and calculate the distance to the object based on the first differential frequency and a first intensity of the interference light for the first differential frequency, and the second differential frequency and a second intensity of the interference light for the second differential frequency. In this case, the position of the object can be roughly calculated based on the long-cycle data, and then the position of the object can be calculated with high resolution based on the short-cycle data. [Effects of the Invention]

[0014] According to the present disclosure, both the range of measurable distances and resolution can be sufficiently ensured. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a block diagram illustrating a configuration of a distance measuring device according to an embodiment of the present disclosure. [Figure 2] FIG. 2(a) is a diagram showing an example of the waveform of a first signal, and FIG. 2(b) is a diagram showing a waveform modulated by the first signal. [Figure 3] FIG. 10(a) is a diagram showing an example of the waveform of a second signal, and FIG. 10(b) is a diagram showing the waveform modulated by the second signal. [Figure 4] 5A and 5B are diagrams illustrating examples of waveforms of measurement light and reference light. [Figure 5] 10A and 10B are diagrams illustrating an example of a waveform of interference light between reflected light and reference light. [Figure 6] FIG. 10 is a diagram illustrating the relationship between the difference frequency and the intensity of interference light. [Figure 7] FIG. 10 is a block diagram showing a modified example of the light source unit. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, preferred embodiments of a distance measuring device according to one aspect of the present disclosure will be described in detail with reference to the drawings.

[0017] Fig. 1 is a block diagram showing the configuration of a distance measuring device according to an embodiment of the present disclosure. The distance measuring device 1 shown in Fig. 1 is configured as a device that measures the distance to an object K based on a frequency modulated continuous wave (FMCW) method. The distance measuring device 1 irradiates the object K with measurement light L1 that has been modulated so that the frequency shifts linearly with time, and calculates the distance to the object K by Fourier transforming a signal based on interference light L4 between reference light L2 and reflected light L3.

[0018] 1, the distance measuring device 1 includes a signal generating unit 2, a light source unit 3, a modulating unit 4, a coupler (splitting unit) 5, a collimator (irradiating unit) 6, a detecting unit 7, and a calculating unit 8. The optical components from the light source unit 3 to the detecting unit 7 are optically connected by, for example, optical fibers.

[0019] The signal generating unit 2 is a part that generates a signal used to modulate the measurement light L1. The signal generating unit 2 is configured by, for example, an analog waveform shaper. In the example of FIG. 1, the signal generating unit 2 is configured by a first signal generating unit 2A that outputs a signal to the light source unit 3 and a second signal generating unit 2B that outputs a signal to the modulation unit 4. The first signal generating unit 2A and the second signal generating unit 2B are connected to each other so that they can communicate information with each other.

[0020] The first signal generating unit 2A generates a first signal S1 having a first repetition frequency F1 and outputs it to the light source unit 3 (see FIG. 2(a)). The second signal generating unit 2B generates a second signal S2 having a second repetition frequency F2 higher than the first repetition frequency F1 and outputs it to the modulator 4 (see FIG. 3(a)). In this embodiment, the signal generating unit 2 operates to synchronize one of the first signal S1 generated by the first signal generating unit 2A and the second signal S2 generated by the second signal generating unit 2B with the other.

[0021] The light source unit 3 is a part that generates and outputs a light beam L0 whose wavelength is modulated over time by internal modulation based on a first signal S1. The light source unit 3 is configured to include a laser light source 12 and a resonator 13. As the laser light source 12, for example, a stable light source such as a laser diode (LD) is used. The laser light source 12 generates and outputs continuous light such as CW (Continuous Wave) light. In this embodiment, the resonator 13 is a Fabry-Perot type variable optical path length resonator 13A.

[0022] The optical path length variable resonator 13A has an optical path length variable element 14 inside the resonators 13, 13. The optical path length variable element 14 is made of an electro-optic crystal such as a KTN crystal. A first signal S1 from the first signal generator 2A is input to the optical path length variable element 14. The optical path length variable resonator 13A temporally changes the optical path length between the resonators 13, 13 by internal modulation based on the first signal S1 input from the first signal generator 2A to the optical path length variable element 14. The light beam L0 output from the light source unit 3 becomes chirped light and is input to the modulator 4 via an attenuator 15 and the like.

[0023] The modulation unit 4 is a part that performs external modulation based on the second signal S2 to further temporally modulate the wavelength of the light beam L0 output from the light source unit 3 by the Doppler effect and outputs the modulated light. Also, The modulation unit 4 is configured by, for example, an electro-optic (EO) phase modulator. Good The EO phase modulator receives a second signal S2 from a second signal generator 2B. The optical beam L0 is further modulated in time by a modulator 4 and input to a coupler 5.

[0024] 2(a) is a diagram showing an example of the waveform of the first signal, and FIG. 2(b) is a diagram showing the modulated waveform by the first signal. As shown in FIG. 2(a), in this embodiment, a signal having a time waveform consisting of a succession of parabolas with a positive proportionality constant is generated as the first signal S1. As a result, as shown in FIG. 2(b), the modulated waveform W1 from the light source unit 3 becomes a triangular time waveform. More specifically, the modulated waveform W1 from the light source unit 3 becomes a sawtooth waveform, and in each period, a portion where the frequency increases linearly with time and a portion where the frequency instantaneously decreases are formed.

[0025] 3(a) is a diagram showing an example of the waveform of the second signal, and FIG. 3(b) is a diagram showing the modulated waveform by the second signal. As shown in FIG. 3(a), in this embodiment, the second signal S2 is generated as a signal having a time waveform consisting of a series of parabolas with a positive proportionality constant, similar to the first signal S1. As a result, as shown in FIG. 3(b), the modulated waveform W2 by the modulator 4 becomes a triangular time waveform. Like the modulated waveform W1 by the light source 3, the modulated waveform W2 by the light source 3 becomes a sawtooth waveform, and in each period, there are formed portions where the frequency increases linearly with time and portions where the frequency instantaneously decreases.

[0026] As described above, the second repetition frequency F2 of the second signal S2 is higher than the first repetition frequency F1 of the first signal S1. As a result, the period of the modulated waveform W2 in the modulator 4 is shorter than the period of the modulated waveform W1 in the light source 3. In the example of FIG. 3(a), the second repetition frequency F2 of the second signal S2 is an integer multiple (here, five times) of the first repetition frequency F1 of the first signal S1. Therefore, one period of the modulated waveform W1 in the light source 3 corresponds to five periods of the modulated waveform W2 in the modulator 4.

[0027] The coupler 5 is a part that splits the light beam L0 output from the modulator 4 into a measurement light L1 and a reference light L2. As shown in Fig. 4, the measurement light L1 and the reference light L2 are multi-phase modulated lights that are obtained by superimposing the internal modulation in the light source 3 and the external modulation in the modulator 4. That is, as shown in Fig. 4, the time waveforms W4 of the measurement light L1 and the reference light L2 have waveforms in which the long-period sawtooth waveform shown in Fig. 2(b) is superimposed on the short-period sawtooth waveform shown in Fig. 3(b).

[0028] The measurement light L1 output from the coupler 5 is input to the input port of a three-port circulator 16. The measurement light L1 is output from the input / output port of the circulator 16 and irradiated onto an object K outside the distance measuring device 1 via a collimator 6. Reflected light L3 of the measurement light L1 reflected by the object K returns to the distance measuring device 1 and passes through the input / output port of the circulator 16 and the output port to be input to a coupler 17 downstream of the coupler 5. The reference light L2 output from the coupler 5 is directly input to the downstream coupler 17. In the downstream coupler 17, interference light L4 is generated by interference between the reflected light L3 and the reference light L2. The interference light L4 is input to the detection unit 7.

[0029] The detection unit 7 is a part that detects the interference light L4 between the reflected light L3 and the reference light L2. The detection unit 7 is configured, for example, by a balance detector. The balance detector is a detector that receives two optical inputs and detects the difference between their photocurrents. The detection unit 7 outputs an output signal R indicating the detection result to the calculation unit 8.

[0030] The calculation unit 8 calculates the distance to the object K based on the output signal from the detection unit 7. The calculation unit 8 is physically configured by a computer system including, for example, a processor, a memory, etc. Examples of the computer system include a personal computer, a microcomputer, a cloud server, and a smart device (such as a smartphone or a tablet terminal). The calculation unit 8 may be configured by a programmable logic device (PLD) or an integrated circuit such as a field-programmable gate array (FPGA).

[0031] An example of calculation of the distance to the object K by the calculation unit 8 will be described below. FIG. 5 is a diagram showing an example of the waveform of interference light between reflected light and reference light. In the time waveform W4 of interference light L4 shown in the figure, the reflected light L3 is light that is returned after the measurement light L1 is reflected by the object K, and therefore is delayed in time relative to the reference light L2 according to the distance to the object K. As the reflected light L3 is delayed relative to the reference light L2, a frequency difference occurs between the reference light L2 and the reflected light L3.

[0032] The calculation unit 8 calculates a first difference frequency Δf1 of the reflected light L3 relative to the reference light L2, and a second difference frequency Δf2 of the reference light L2 relative to the reflected light L3. The calculation unit 8 calculates the distance to the object K based on the first difference frequency Δf1, a first intensity P1 of the interference light L4 relative to the first difference frequency Δf1, and a second intensity P2 of the interference light L4 relative to the second difference frequency Δf2. The relationship between the first difference frequency Δf1 and the first intensity P1, and the relationship between the second difference frequency Δf2 and the second intensity P2, can be determined by Fourier transform of the output signal R of the interference light L4, as shown in FIG.

[0033] The calculation unit 8 calculates long-cycle data based on the internal modulation (modulation waveform W1) in the light source unit 3 and short-cycle data based on the external modulation (modulation waveform W2) in the modulation unit 4 regarding the distance to the object K. If the chirp width of the modulation waveform W1 is B1 and the first repetition frequency is F1, the chirp speed of the modulation waveform W1 is expressed as B1 x F1. If the distance to the object K based on the long-cycle data is X1, X1 can be calculated using the following formula (1). In formula (1), c is the speed of light. X1=(c / (2F1))×{(P1×Δf1+P2×Δf2) / (P1+P2)} / B1 …(1)

[0034] If the chirp width of modulated waveform W2 is B2 and the second repetition frequency is F2, the chirp speed of modulated waveform W2 is expressed as B2 x F2. If the distance to object K based on the short cycle data is X2, X2 can be calculated using the following formula (2). In formula (2), m is an integer equal to or greater than 0. X2=(c / (2F2))×{Δf1-(P1×Δf1+P2×Δf2) / (P1+P2)} / B2+m(c / (2F2)) …(2)

[0035] The integer m in equation (2) is a parameter that determines how many periods of the modulated waveform W2 the delay of the reflected light L3 relative to the reference light L2 corresponds to. The calculation unit 8 first roughly calculates the position of the object K based on the long-period data. Then, the value of m is adjusted so that it is closest to the calculated value, and the position of the object K is calculated with high resolution based on the short-period data.

[0036] As described above, the distance measuring device 1 performs multiple phase modulation on the measurement light L1 irradiated toward the object K by long-period internal modulation based on the first signal S1 and short-period external modulation based on the second signal S2. The distance measuring device 1 can simultaneously obtain long-period data and short-period data regarding the distance to the object K by performing a Fourier transform on the output signal R from the detection unit 7. The distance measuring device 1 can sufficiently ensure both the range of measurable distances and resolution by using long-period data suitable for long-distance measurement and short-period data suitable for high resolution.

[0037] When attempting to increase the amount of frequency shift of the measurement light using a single phase modulation, it is conceivable that other parameters important for distance measurement, such as the laser linewidth, may actually be affected. Furthermore, there is a risk that distortion may occur in the waveform of the measurement light, reducing the linearity of the frequency shift. In contrast, as described above, the distance measuring device 1 applies multiple phase modulation to the measurement light L1, thereby suppressing the amount of shift of the measurement light L1 while ensuring sufficient resolution for the distance to the object K.

[0038] In the distance measuring device 1, the signal generating unit 2 generates the second repetition frequency F2 so that it is an integer multiple of the first repetition frequency F1. This makes it possible to align the phase of the reference light L2 and the phase of the reflected light L3, thereby simplifying the calculations required to calculate the distance to the object K. Also, in the distance measuring device 1, the signal generating unit 2 synchronizes one of the first signal S1 and the second signal S2 with the other. This makes it possible to align the phase of the reference light L2 and the phase of the reflected light L3, thereby simplifying the calculations required to calculate the distance to the object K.

[0039] In the distance measuring device 1, the modulated waveform W1 by the first signal S1 and the modulated waveform W2 by the second signal S2 have triangular time waveforms. In this embodiment, the modulated waveform W1 by the first signal S1 and the modulated waveform W2 by the second signal S2 also have sawtooth time waveforms. This makes it easy to distinguish between the component of the reference light L2 and the component of the reflected light L3 in the interference light L4, simplifying the calculation for calculating the distance to the object K.

[0040] In the distance measuring device 1, the light source unit 3 has an optical path length variable resonator 13A in which the optical path length between the resonators 13, 13 changes over time based on the first signal S1. This makes it possible to realize internal modulation in the light source unit 3 with a simple configuration.

[0041] In the distance measuring device 1, the calculation unit 8 calculates a first difference frequency Δf1 of the reflected light L3 relative to the reference light L2, and a second difference frequency Δf2 of the reference light L2 relative to the reflected light L3. Then, the calculation unit 8 calculates the distance to the object K based on the first difference frequency Δf1 and a first intensity P1 of the interference light L4 relative to the first difference frequency Δf1, and the second difference frequency Δf2 and a second intensity P2 of the interference light L4 relative to the second difference frequency Δf2. This makes it possible to roughly calculate the position of the object K based on the long-cycle data, and then calculate the position of the object K with high resolution based on the short-cycle data.

[0042] The present disclosure is not limited to the above-described embodiment. For example, in the above-described embodiment, the signal generating unit 2 synchronizes one of the first signal S1 and the second signal S2 with the other. However, other methods may be used to synchronize the first signal S1 and the second signal S2. For example, the signal generating unit 2 may synchronize the first signal S1 and the second signal S2 based on an external trigger signal. In this case, too, the phase of the reference light L2 and the phase of the reflected light L3 can be aligned, simplifying the calculation for calculating the distance to the object K.

[0043] In the above embodiment, the optical path length variable resonator 13A is used for internal modulation in the light source unit 3, but for example, as shown in Fig. 7, a heater 18 may be provided in the laser light source 12, and the heater 18 may be controlled based on a first signal S1 to temporally modulate the wavelength of the light beam L0 output from the light source unit 3. Even in this embodiment, the internal modulation in the light source unit 3 can be realized with a simple configuration. [Explanation of symbols]

[0044] 1...Range measuring device, 2 (2A, 2B)...Signal generating unit, 3...Light source unit, 4...Modulating unit, 5...Coupler (splitting unit), 6...Collimator (irradiating unit), 7...Detecting unit, 8...Calculating unit, 13A...Optical path length variable resonator, F1...First repetition frequency, F2...Second repetition frequency, Δf1...First differential frequency, Δf2...Second differential frequency, P1...First intensity, P2...Second intensity, S1...First signal, S2...Second signal, W1, W2...Modulated waveform, L0...Light beam, L1...Measurement light, L2...Reference light, L3...Reflected light, L4...Interference light, K...Object.

Claims

1. a signal generating unit that generates a first signal having a first repetition frequency and a second signal having a second repetition frequency higher than the first repetition frequency; a light source unit that generates and outputs light whose wavelength is modulated over time by internal modulation based on the first signal; a modulation unit that further temporally modulates the wavelength of the light output from the light source unit by external modulation based on the second signal using a Doppler effect or an electro-optic phase modulator, and outputs the modulated light; a splitter that splits the light output from the modulator into measurement light and reference light; an irradiation unit that irradiates the measurement light toward an object; a detection unit that detects interference light between the reference light and reflected light of the measurement light reflected by the object; a calculation unit that calculates the distance to the object based on the output signal from the detection unit.

2. The distance measuring device according to claim 1 , wherein the signal generating section generates the second repetition frequency to be an integer multiple of the first repetition frequency.

3. 3. The distance measuring device according to claim 1, wherein the signal generating section synchronizes one of the first signal and the second signal with the other.

4. 3. The distance measuring device according to claim 1, wherein the signal generating section synchronizes the first signal and the second signal based on an external trigger signal.

5. 3. The distance measuring device according to claim 1, wherein the waveform modulated by the first signal and the waveform modulated by the second signal have triangular time waveforms.

6. 3. The distance measuring device according to claim 1, wherein the light source unit has an optical path length variable resonator in which the optical path length between resonators changes over time based on the first signal.

7. A distance measuring device as described in claim 1 or 2, wherein the calculation unit calculates a first differential frequency of the reflected light relative to the reference light and a second differential frequency of the reference light relative to the reflected light, and calculates the distance to the object based on the first differential frequency and a first intensity of the interference light relative to the first differential frequency, and the second differential frequency and a second intensity of the interference light relative to the second differential frequency.

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