Long-range high-precision frequency modulation continuous wave distance measurement system with optical switch capable of rapidly switching optical path

Abstract

The invention provides a long-range high-precision frequency-modulated continuous wave ranging system with an optical switch capable of rapidly switching optical paths, and relates to the technical field of interference ranging. According to the system, a flight time infrared distance measurement module and a semiconductor optical switch switching module are added on the basis of an existing frequency modulation interference distance measurement system; the flight time infrared distance measurement module measures rough distances between different parts of the to-be-measured workpiece and the distance measurement module; the semiconductor optical switch switching module switches the optical path of a reference light beam to different optical path difference delay lines according to the distance measured by the flight time infrared distance measurement module when the interference distance measurement module measures a beat frequency signal, and matches the optical path of a measurement path and the optical path of a reference path, so that the measurement path and the reference path are kept at a coherence length. Therefore, the measurement precision is not deteriorated along with the increase of the distance; and finally, adding the interference distance and the optical path difference transmitted by the semiconductor optical switch switching module, and finally demodulating the distance of the to-be-measured workpiece according to the ratio of the optical path difference to the actual optical path, thereby completing distance measurement.

Description

Technical Field

[0001] The invention relates to the technical field of interference distance measurement, and in particular to a long-range high-precision frequency-modulated continuous wave distance measurement system with an optical switch that quickly switches the optical path. Background Art

[0002] The commonly used ranging products on the market include 3D cameras (ToF), and the ranging methods used mainly include direct pulse ranging, random pulse correlation ranging, phase ranging, etc.

[0003] Among them, the ranging principle of the direct pulse ranging method is to calculate the distance information by measuring the flight time between the pulse sent from the transmitter, passing through the target and returning to the detector. This method is generally used for long-range ranging, is not suitable for close-range ranging, and has low accuracy.

[0004] The ranging principle of the random pulse correlation ranging method is to calculate the distance information by calculating the cross-correlation function between the emitted random pulse signal and the returned random pulse signal. This method has strong anti-interference ability and is generally suitable for long-distance ranging. Its ranging accuracy is limited by the modulation frequency of the random signal and has low accuracy.

[0005] The ranging principle of the phase ranging method is to calculate the distance information by detecting the phase displacement between the periodic signal sent from the transmitter, passing through the target and returning to the detector. This method has high measurement accuracy, but because it is a periodic signal, its maximum measurement distance is limited by the maximum phase displacement of 2π. The multi-frequency phase ranging method proposed later uses periodic signals of 2 or more frequencies to expand the ranging range, but it is still limited by the period of the periodic signal. Therefore, the phase ranging method is generally used for short-distance, high-precision measurement occasions. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a long-range high-precision frequency-modulated continuous wave ranging system with optical switches that quickly switch the optical path in view of the above-mentioned deficiencies in the prior art, so as to solve or alleviate at least one of the problems existing in the prior art, namely, the large amount of collected data, the degradation of measurement accuracy with distance, and the large amount of data.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows: the present invention provides a long-range high-precision frequency-modulated continuous wave ranging system with an optical switch that quickly switches the optical path, comprising a frequency-modulated continuous wave laser emission module, an interference ranging module, a time-of-flight infrared ranging module, a semiconductor optical switch switching module, a beat frequency signal acquisition module, a signal processing module and a distance demodulation module;

[0008] The frequency modulated continuous wave laser emission module emits a large bandwidth linear frequency modulated laser and injects it into the interference ranging module;

[0009] The interference distance measurement module measures the beat frequency signals of different positions of the workpiece to be measured based on the large-bandwidth linear frequency-modulated laser emitted by the frequency-modulated continuous-wave laser emission module;

[0010] The time-of-flight infrared distance measurement module measures the distance between different parts of the workpiece to be measured and the distance measurement module, and feeds back to the semiconductor optical switch switching module;

[0011] The semiconductor optical switch switching module switches the reference beam optical path to a delay line with a different optical path difference according to the distance measured by the time-of-flight infrared ranging module when the interference ranging module measures the beat frequency signal, matches the optical path of the measurement path and the reference path, keeps the measurement path and the reference path at the coherent length, thereby ensuring that the measurement accuracy does not deteriorate with the increase of the distance, and transmits the optical path difference to the distance demodulation module;

[0012] The beat frequency signal acquisition module acquires the beat frequency signals of different positions of the workpiece to be measured by the interference ranging system and sends them to the signal processing module;

[0013] The signal processing module demodulates the interference distance based on the beat frequency signal collected by the beat frequency signal collection module;

[0014] The distance demodulation module adds the interference distance demodulated by the signal processing module to the optical path difference transmitted by the semiconductor optical switch switching module, and finally demodulates the distance of the workpiece to be measured through the ratio of the optical path difference and the actual optical path, thereby completing the distance measurement.

[0015] Preferably, the frequency modulated continuous wave laser emission module emits a large bandwidth linear frequency modulated laser with a frequency modulation range of 100nm and injects it into the interference ranging module.

[0016] Preferably, the semiconductor optical switch module includes a semiconductor package and a data feedback line encapsulated in the semiconductor package, an acquisition card fast switching switch and delay lines with different optical path differences; one end of the data feedback line is connected to the time-of-flight infrared ranging module to directly communicate through a data interface, and the other end is connected to a signal acquisition card to collect feedback results from the time-of-flight infrared ranging module; the acquisition card is connected to the fast switching switch as a signal generator; the fast switching switch is connected to delay lines with different optical path differences to achieve switching of different optical path differences according to the signal sent by the acquisition card.

[0017] Preferably, the beat frequency signal is a frequency shift generated when the reference light and the measurement light interfere with each other.

[0018] Preferably, the interference optical path structure in the interference ranging module includes a coupler 1, a circulator, a coupler 2, a detector 1, a detector 2, a flange, and a zoom lens; wherein the coupler 1 receives the large-bandwidth linear tuned laser emitted by the frequency-modulated continuous-wave laser emission module, and divides the tuned laser into a measuring beam and a reference beam; wherein the measuring beam passes through the circulator flange and the zoom lens connected in sequence, is emitted onto the workpiece to be measured, and then returns to the circulator and is transmitted to the coupler 2; the reference beam is switched to delay lines with different optical path differences by a semiconductor optical switch switching module and is then transmitted to the coupler 2; the coupler 2 recouples the two beams of light and then divides them into two beams, which are respectively transmitted to the detector 1 and the detector 2; the detector 1 and the detector 2 respectively collect the beat frequency signal and the optical path difference signal and transmit them to the signal processing module and the distance demodulation module.

[0019] The beneficial effects of the above technical solution are: the long-range high-precision frequency-modulated continuous wave ranging system with optical switch fast switching optical path provided by the present invention adopts the optical switch fast switching optical path method, which has the advantages of reducing long-range acquisition pressure, improving ranging precision stability and ranging accuracy. It can achieve fast micron-level high-precision ranging and improve measurement speed. It has simple structure, easy implementation, convenient adjustment and high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A structural block diagram of a long-range high-precision frequency-modulated continuous wave ranging system with an optical switch that quickly switches the optical path provided by an embodiment of the present invention;

[0021] Figure 2 A schematic diagram of a semiconductor optical switch that quickly switches optical paths according to an embodiment of the present invention;

[0022] Figure 3 A schematic diagram of the optical path structure of an interferometric ranging module provided in an embodiment of the present invention.

[0023] In the figure: 1. Time-of-flight infrared ranging module; 2. Semiconductor optical switch switching module; 3. Frequency-modulated continuous wave laser emission module; 4. Interference ranging module; 5. Beat frequency signal acquisition module; 6. Signal processing module; 7. Distance demodulation module; 22. Semiconductor packaging; 21. Data feedback line; 23. Fast switching switch; 24. Delay line with different optical path difference; 41. Coupler 1; 42. Circulator; 43. Coupler 2; 44. Detector 1; 45. Detector 2; 46. Flange; 47. Zoom lens. DETAILED DESCRIPTION

[0024] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0025] In this embodiment, a long-range high-precision frequency-modulated continuous wave ranging system with an optical switch that quickly switches the optical path is provided. Figure 1 As shown, it includes a frequency modulated continuous wave laser emission module 3, an interference ranging module 4, a time-of-flight infrared ranging module 1, a semiconductor optical switch switching module 2, a beat frequency signal acquisition module 5, a signal processing module 6 and a distance demodulation module 7;

[0026] The frequency modulated continuous wave laser emission module 3 emits a large bandwidth linear frequency modulated laser and injects it into the interference ranging module; in this embodiment, the frequency modulated continuous wave laser emission module 3 emits a large bandwidth linear frequency modulated laser with a frequency modulation range of 100nm and injects it into the interference ranging module 4.

[0027] The interference distance measurement module 4 measures the beat frequency signals at different positions of the workpiece to be measured based on the large-bandwidth linear frequency-modulated laser emitted by the frequency-modulated continuous-wave laser emission module 3; the beat frequency signal is the frequency offset generated when the reference light and the measurement light interfere.

[0028] The time-of-flight infrared distance measurement module 1 measures the distance between different parts of the workpiece to be measured and the distance measurement module, and feeds back to the semiconductor optical switch switching module 2;

[0029] In this embodiment, the time-of-flight infrared ranging module 1 uses the GYTOF10M ranging module to measure the rough distance of the distance measurement system of different parts of the workpiece to be measured; GYTOF10M is a low-cost infrared laser ranging sensor module; its operating voltage is 3.7v-5v, with low power consumption, small size and easy installation. Its working principle is that it is through the time phase difference between the emitted light and the reflected light of the object to be measured, and finally obtains direct distance data through a precise algorithm. This module has two ways to read data, namely serial port UART (TTL level) + IIC (2-wire) mode, the baud rate of the serial port is configurable from 2400bps to 230400bps, there are two modes of continuous and query output, and the settings can be saved when the power is off. Arduino, 51, stm32 single-chip communication programs are provided. GYTOF10M can set the module distance alarm value and switch output. If the set distance alarm value exceeds, the OUT pin directly outputs a high level. In IIC mode, if necessary, the internal IIC address can be set to be different so that multiple sensors can be directly connected to the same bus. GYTOF10M distance measurement uses dynamic time filtering, and the data will be more stable when the output frequency is lower.

[0030] The semiconductor optical switch switching module 2 switches the reference beam optical path to a delay line with a different optical path difference according to the distance measured by the time-of-flight infrared ranging module 1 when the interference ranging module 4 measures the beat frequency signal, matches the optical path of the measurement path and the reference path, keeps the measurement path and the reference path at the coherent length, thereby ensuring that the measurement accuracy does not deteriorate with the increase of the distance, and transmits the optical path difference to the distance demodulation module 7;

[0031] In this embodiment, the semiconductor optical switch module is as follows: Figure 2 The device shown includes a semiconductor package 22 and a data feedback line 21 encapsulated in the semiconductor package 22, a collection card fast switching switch 23 and delay lines 24 with different optical path differences; one end of the data feedback line 21 is connected to the time-of-flight infrared ranging module 1, and directly communicates through the 232 data interface, and the other end is connected to the signal acquisition card to collect the feedback result of the time-of-flight infrared ranging module 1; the acquisition card is connected to the fast switching switch 23 as a signal generator; the fast switching switch 23 is connected to the delay lines 24 with different optical path differences, and different optical path differences are switched according to the signal sent by the acquisition card; according to the feedback result of the time-of-flight infrared ranging module 1, the fast switching switch 23 can quickly switch the delay lines with different optical path differences to match the measurement optical path.

[0032] The beat signal acquisition module 5 acquires the beat signals of different positions of the workpiece to be measured by the interference ranging system and sends them to the signal processing module 6;

[0033] The signal processing module 6 obtains the optical path difference through Fourier transform based on the beat frequency signal collected by the beat frequency signal collection module 5, and then demodulates the interference distance;

[0034] The distance demodulation module 7 (GPU) adds the interference distance demodulated by the signal processing module 6 to the optical path difference transmitted by the semiconductor optical switch switching module 2, and finally demodulates the distance of the workpiece to be measured through the ratio of the optical path difference and the actual optical path, thereby completing the distance measurement.

[0035] In this embodiment, the interference optical path structure in the interference distance measurement module 4 is as follows: Figure 3 As shown, it includes a coupler 1 41, a circulator 42, a coupler 2 43, a detector 1 44, a detector 2 45, a flange 46, and a zoom lens 47; wherein the coupler 1 41 receives the large-bandwidth linear tuned laser emitted by the frequency-modulated continuous-wave laser emission module 3, and divides the tuned laser into a measuring beam and a reference beam; wherein the measuring beam passes through the circulator 42 flange 46 and the zoom lens 47 connected in sequence, and then is emitted to the workpiece to be measured, and then returns to the circulator 42 and is transmitted to the coupler 2 43; the reference beam is switched to different optical path difference delay lines by the semiconductor optical switch switching module 2 and is transmitted to the coupler 2 43; the coupler 2 43 recouples the two beams of light and then divides them into two beams and transmits them to the detector 1 44 and the detector 2 45 respectively; the detector 1 44 and the detector 2 45 respectively collect the beat frequency signal and the optical path difference signal and transmit them to the signal processing module 6 and the distance demodulation module 7.

[0036] The core idea of ​​FM laser ranging technology is to use the change of the frequency of the emitted light beam over time (linear modulation) to introduce the frequency offset between the reference light and the measurement light, and to calculate the distance of the measured object by measuring this offset. The following are the detailed working steps:

[0037] 1. Linear frequency modulated light source: The laser emits a beam whose frequency changes linearly with time. The frequency f(t) is expressed as:

[0038]

[0039] Among them, f0 is the initial frequency, Δf is the frequency modulation range (the difference between the maximum frequency and the minimum frequency), T is the linear frequency modulation period, and t is the current time (0 <t≤T);

[0040] 2. Interference between reference light and measurement light: The emitted light beam is split into two beams by a beam splitter: reference light and measurement light. The reference light returns through a fixed path, while the measurement light returns to the interferometer after being reflected by the surface of the object being measured. The two beams of light converge in the interferometer and form interference fringes. Due to the different distances of the measured object, there is a time delay τ when the measurement light returns to the interferometer, which is proportional to the distance d of the object:

[0041]

[0042] Where c is the speed of light (about 3×10 8 m / s), d is the distance of the object.

[0043] 3. Frequency shift (beat frequency): When the reference light and the measurement light are recombined in the interferometer, there is an optical path difference Δd when the measurement light beam returns, which causes the reference light and the measurement light to produce a frequency shift (beat frequency) when interfering. Due to the time delay τ of the measurement light, there is a frequency difference between the two beams when interfering. For a linear frequency modulation signal, the frequency difference Δf beat The relationship with the time delay τ is as follows:

[0044]

[0045] Where Δf beat is the interference fringe frequency offset (beat frequency), Δf is the frequency sweep range, T is the frequency sweep period, and τ is the time delay caused by the optical path difference;

[0046] 4. Distance calculation: by measuring the frequency shift Δf of the interference fringes beat , we can find the time delay τ and then get the distance d of the target:

[0047]

[0048] So the distance

[0049] The long-range high-precision frequency-modulated continuous wave ranging system of the present invention with optical switch that quickly switches the optical path is based on the above-mentioned frequency-modulated laser ranging technology. By switching the optical path of the reference beam to a delay line 24 with different optical path difference, the optical path of the measurement path and the reference path are matched, so that the measurement path and the reference path are kept at the coherent length, thereby ensuring that the measurement accuracy of the interference ranging does not deteriorate with the increase of distance.

[0050] In this embodiment, it is assumed that the frequency of the light beam emitted by the transmitting laser at time t=0 is f0, and its frequency increases linearly with time, and the frequency change form is:

[0051] f(t)=f(0)+k·t

[0052] Wherein, the modulation rate k is defined as:

[0053]

[0054] When the measuring beam hits the target and reflects back, the optical path delay is τ. At this time, the frequency of the returning beam is:

[0055] f(t-τ)=f 0+ +k·(t-τ)=f0+k·tk·τ

[0056] Therefore, the frequency difference between the return beam and the reference beam is:

[0057]

[0058] Substituting the time delay τ and distance relationship The relationship between the frequency shift of the interference fringes and the measured distance is obtained:

[0059]

[0060] Solve for the optical path distance d:

[0061]

[0062] Since the signals to be processed in actual measurements are often affected by noise and multipath effects, frequency domain analysis (such as fast Fourier transform, FFT) is usually used to extract the frequency components of the interference signal to accurately determine the frequency difference Δf beat The intensity of the interference signal can be expressed in the following form:

[0063]

[0064] in, is the initial phase of the laser;

[0065] By performing FFT analysis on the interference signal I(t), the main peak in the spectrum is obtained, and then Δf is determinedbeat , and finally the distance d is calculated.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

Claims

1. A long-range high-precision frequency-modulated continuous wave ranging system with fast optical switch switching, characterized in that: It includes a frequency modulated continuous wave laser emission module, an interference ranging module, a time-of-flight infrared ranging module, a semiconductor optical switch switching module, a beat frequency signal acquisition module, a signal processing module and a distance demodulation module; The frequency modulated continuous wave laser emission module emits a large bandwidth linear frequency modulated laser and injects it into the interference ranging module; The interference distance measurement module measures the beat frequency signals of different positions of the workpiece to be measured based on the large-bandwidth linear frequency-modulated laser emitted by the frequency-modulated continuous-wave laser emission module; The time-of-flight infrared distance measurement module measures the distance between different parts of the workpiece to be measured and the distance measurement module, and feeds back to the semiconductor optical switch switching module; The semiconductor optical switch switching module switches the reference beam optical path to a delay line with a different optical path difference according to the distance measured by the time-of-flight infrared ranging module when the interference ranging module measures the beat frequency signal, matches the optical path of the measurement path and the reference path, keeps the measurement path and the reference path at the coherent length, thereby ensuring that the measurement accuracy does not deteriorate with the increase of the distance, and transmits the optical path difference to the distance demodulation module; The beat frequency signal acquisition module acquires the beat frequency signals of different positions of the workpiece to be measured by the interference ranging system and sends them to the signal processing module; The signal processing module demodulates the interference distance based on the beat frequency signal collected by the beat frequency signal collection module; The distance demodulation module adds the interference distance demodulated by the signal processing module to the optical path difference transmitted by the semiconductor optical switch switching module, and finally demodulates the distance of the workpiece to be measured through the ratio of the optical path difference and the actual optical path, thereby completing the distance measurement.

2. The long-range high-precision frequency-modulated continuous wave ranging system for fast switching of optical paths by an optical switch according to claim 1, characterized in that: The frequency modulated continuous wave laser emission module emits a large bandwidth linear frequency modulated laser with a frequency modulation range of 100nm and injects it into the interference distance measurement module.

3. The long-range high-precision frequency-modulated continuous wave ranging system for fast optical switch switching according to claim 1, characterized in that: The semiconductor optical switch module includes a semiconductor package and a data feedback line encapsulated in the semiconductor package, an acquisition card fast switching switch and delay lines with different optical path differences; one end of the data feedback line is connected to the time-of-flight infrared ranging module to directly communicate through a data interface, and the other end is connected to the signal acquisition card to collect the feedback result of the time-of-flight infrared ranging module; the acquisition card is connected to the fast switching switch as a signal generator; the fast switching switch is connected to the delay lines with different optical path differences to achieve switching of different optical path differences according to the signal sent by the acquisition card.

4. The long-range high-precision frequency-modulated continuous wave ranging system for fast switching of optical paths by optical switches according to claim 1, characterized in that: The beat frequency signal is a frequency shift generated when the reference light and the measurement light interfere with each other.

5. The long-range high-precision frequency-modulated continuous wave ranging system for fast switching of optical paths by optical switches according to claim 3, characterized in that: The interference optical path structure in the interference ranging module includes a coupler 1, a circulator, a coupler 2, a detector 1, a detector 2, a flange, and a zoom lens; wherein the coupler 1 receives a large-bandwidth linear tuned laser emitted by a frequency-modulated continuous-wave laser emission module, and divides the tuned laser into a measurement beam and a reference beam; wherein the measurement beam passes through a circulator flange and a zoom lens connected in sequence, is emitted onto a workpiece to be measured, and then returns to the circulator and is transmitted to the coupler 2; the reference beam is switched to delay lines with different optical path differences by a semiconductor optical switch switching module and is then transmitted to the coupler 2; the coupler 2 recouples the two beams of light and then divides them into two beams and transmits them to the detector 1 and the detector 2 respectively; the detector 1 and the detector 2 respectively collect beat frequency signals and optical path difference signals and transmit them to the signal processing module and the distance demodulation module.

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