Co-path optical path laser ranging system and method for correcting absolute distance based on phase method

Abstract

The invention provides a co-path optical path laser ranging system and method for correcting an absolute distance based on a phase method. An arbitrary waveform generator is adopted to perform frequency modulation on a laser signal of a semiconductor laser; the object light and the reference light reflected by the optical fiber collimation unit are transmitted in a common-path manner, and are transmitted to the processor through the loop unit, the photoelectric detector and the data collector; the processor extracts a beat frequency signal of the interference light, obtains an absolute distance according to a frequency modulation continuous wave distance measurement principle, obtains an updated absolute distance after a target moves, and calculates a phase difference to obtain a relative distance measurement value based on an intensity signal of the interference light corresponding to a position before and after the target moves; and correcting the absolute distance measured twice by using the relative distance measurement value to obtain the corrected twice absolute distance. The advantages of a frequency difference method and a phase difference method are combined, a high-precision measurement result can be obtained, the problem of phase ambiguity can be avoided, and precision requirements and measurement requirements of different occasions can be met.

Description

Technical Field

[0001] The present invention relates to the field of laser radar technology, and more specifically to a common optical path laser ranging system and method for correcting absolute distance based on a phase method. Background Art

[0002] LiDAR uses laser as light source and photoelectric detection technology to realize active detection technology of target distance. It has the advantages of high precision, high speed and small size, and is widely used in fields such as autonomous driving, drones, intelligent robots, 3D modeling, and geographic mapping. For example, LiDAR can help robots accurately locate and navigate in complex environments and update environmental maps in real time; in the manufacturing process, LiDAR can be used to detect changes in the size and shape of mechanical parts, monitor the position and movement of objects on the production line in real time, and ensure accurate control of the production process. How to ensure the ranging accuracy of LiDAR has always been an important research topic in this field.

[0003] For relative distance measurement, Zhang Enyao et al. disclosed in the document "Improvement of the Performance of Fiber Heterodyne Interferometry Displacement Sensors" that a dual-path fiber Fizeau interferometer is composed of semiconductor lasers (LD), optical isolators, fiber directional couplers, self-focusing lenses, etc., and uses triangular wave current modulation and upper and lower edge beat frequency signal differential phase detection to improve the measurement sensitivity and displacement response speed. The phase drift of the system is detected by an auxiliary interferometer, and the LD emission wavelength is feedback controlled to improve the stability of the system. However, the optical path structure in this technology is complex, which affects the measurement efficiency, and it needs to be split by a coupler. The optical path difference between the reference light and the object light is large. External factors (such as air turbulence, mechanical vibration, etc.) will have different effects on the phase of the two beams, resulting in increased phase noise, thereby reducing the stability and accuracy of the measurement.

[0004] For absolute distance measurement, the frequency difference method is often used, and the absolute distance can be directly obtained by measuring the frequency difference. The accuracy of frequency measurement is usually not as high as that of phase difference method, especially in the case of short distance and high precision requirements; but the phase difference method can only measure the phase information to obtain relative distance information, but cannot obtain the absolute distance. In summary, when using frequency information for distance measurement, although the absolute distance can be obtained directly, the accuracy of frequency distance measurement is relatively low; when using phase information for distance measurement, information needs to be obtained through phase difference, and relative position information can only be obtained through two measurements. In addition, when the ranging distance is greater than the ranging wavelength, there will be a multi-value problem, that is, the phase difference is periodic within a cycle, so there is a phase ambiguity problem. The absolute ranging accuracy of frequency modulated continuous wave can reach the millimeter level, and the measurement accuracy is low. Compared with absolute ranging, relative ranging has higher measurement accuracy and can reach sub-nanometer. To achieve high-precision absolute ranging, optical frequency comb technology is currently mainly used. The equipment used is large and costly, and the general cost is more than one order of magnitude of frequency modulated continuous wave ranging. Therefore, how to combine relative ranging with absolute ranging to improve measurement accuracy and reduce costs has become an important research topic in this field. Summary of the invention

[0005] The purpose of the present invention is to provide a common optical path laser ranging system and method for correcting absolute distance based on the phase method, which combines the advantages of the frequency difference method and the phase difference method, can not only obtain high-precision measurement results, but also avoid phase ambiguity problems, while reducing the measurement cost, and can adapt to the accuracy requirements and measurement requirements of different occasions.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] A common optical path laser ranging system for correcting absolute distance based on a phase method, comprising an arbitrary waveform generator, a semiconductor laser, a loop unit, an optical fiber collimation unit, a photoelectric detector, a data collector and a processor;

[0008] The arbitrary waveform generator generates a frequency modulation signal, and performs frequency modulation on the laser signal of the semiconductor laser by controlling the driving current of the semiconductor laser;

[0009] The output end of the semiconductor laser is connected to the loop unit via an optical fiber;

[0010] The loop unit is connected to the optical fiber collimation unit via an optical fiber, and is used to transmit the laser signal to the optical fiber collimation unit;

[0011] The optical fiber collimation unit is used to transmit a part of the laser signal to the target, collect the object light reflected by the target, and reflect a part of the laser signal to form a reference light. The object light received by the optical fiber collimation unit and the reference light are transmitted in the same way.

[0012] The loop unit receives the object light and the reference light transmitted back by the optical fiber collimation unit, and transmits them to the photoelectric detector;

[0013] The photoelectric detector is used to convert the intensity signal of the interference light of the object light and the reference light into an electrical signal, and transmit it to the data acquisition device;

[0014] The data collector is used to receive the electrical signal converted by the photoelectric detector and transmit it to the processor;

[0015] The processor is used to receive the electrical signal, extract the beat frequency signal of the interference light based on the electrical signal, obtain the absolute distance according to the frequency modulated continuous wave ranging principle, and obtain the updated absolute distance after the target moves; calculate the phase difference based on the intensity signal of the interference light corresponding to the position before and after the target moves to obtain the relative distance measurement value, and use the relative distance measurement value to correct the absolute distances of the two measurements to obtain the corrected absolute distances of the two measurements.

[0016] Furthermore, the arbitrary waveform generator is also used to generate a synchronous electrical signal, which is transmitted to a data collector, and the synchronous electrical signal has the same frequency as the frequency modulation signal.

[0017] Furthermore, the signal transmission mode between the loop unit and the photodetector includes: one or more of optical fiber transmission, collimator conversion transmission, and free space optical transmission.

[0018] Furthermore, the loop unit is provided with three interfaces, namely, port a, port b and port c, wherein port a is used to receive a laser signal from a DFB laser, port b is used to output the laser signal to a fiber collimation unit and receive object light and reference light, and port c is used to transmit the object light and reference light to a photodetector.

[0019] Furthermore, the optical fiber collimation unit adopts an optical fiber collimator with a PC-type interface, a lens with transmission and reflection functions, or a combination structure of an optical fiber and a collimator.

[0020] Furthermore, the frequency modulation signal is a symmetrical triangle wave or a sawtooth wave, and the synchronous electrical signal is a square wave with a duty cycle of 50%.

[0021] The present invention also provides a common optical path laser ranging method based on phase method to correct absolute distance, which is applied to the above-mentioned common optical path laser ranging system based on phase method to correct absolute distance, and comprises the following steps:

[0022] The arbitrary waveform generator generates a frequency modulation signal, transmits it to the semiconductor laser, and performs frequency modulation on the laser signal of the semiconductor laser;

[0023] The frequency modulated laser signal is transmitted to the optical fiber collimation unit through the loop unit;

[0024] The fiber collimation unit transmits a part of the laser signal to the target, collects the object light reflected by the target, and reflects a part of the laser signal to form a reference light;

[0025] The object light received by the optical fiber collimation unit and the reference light reflected at the end face of the optical fiber collimation unit are transmitted together and transmitted to the photoelectric detector via the loop unit;

[0026] The photoelectric detector converts the intensity signal of the interference light of the object light and the reference light into an electrical signal and transmits it to the data collector;

[0027] The data collector receives the electrical signal converted by the photodetector and transmits it to the processor;

[0028] The processor receives the electrical signal, extracts the beat frequency signal of the interference light based on the electrical signal, obtains the absolute distance according to the frequency modulated continuous wave ranging principle, and obtains the updated absolute distance after the target moves; calculates the phase difference based on the intensity signal of the interference light corresponding to the position before and after the target moves to obtain the relative distance measurement value, and uses the relative distance measurement value to correct the absolute distances of the two measurements to obtain the corrected absolute distances, specifically including:

[0029] According to the frequency modulation ranging principle, the absolute distances before and after the target movement are obtained as l1 and l2 respectively. According to the absolute distances l1 and l2, the theoretical value of the relative distance Δl' is obtained:

[0030] Δl'=l2-l1

[0031] The relative distance measurement is calculated as follows:

[0032]

[0033] Wherein, Δl represents the relative distance measurement value of the position before and after the target moves; τ1 is the time difference corresponding to the optical path difference between the object light and the reference light when measuring the distance at the position before the target moves; τ2 is the time difference corresponding to the optical path difference between the object light and the reference light when measuring the distance at the position after the target moves; is the phase difference actually measured based on the intensity signal of the interference light corresponding to the position of the target before and after movement; f0 is the initial frequency of the laser signal; c is the speed of light;

[0034] Based on the error analysis method, the absolute error or relative error between the relative distance measurement value Δl and the relative distance theoretical value Δl' is obtained, and based on the absolute error or relative error, the absolute distances l1 and l2 are corrected respectively.

[0035] Further, based on the error analysis method, the absolute error or relative error between the relative distance measurement value Δl and the relative distance theoretical value Δl' is obtained, and the absolute distances l1 and l2 are respectively corrected based on the absolute error or relative error, which specifically includes:

[0036] Compare the relative distance measurement value Δl with the relative distance theoretical value Δl', and analyze the error distribution law;

[0037] According to the error distribution law, an error model is established by means of data fitting to obtain the absolute error correction parameter or relative error correction coefficient;

[0038] Based on the absolute error correction parameter or relative error correction coefficient, the absolute distances l1 and l2 are respectively corrected.

[0039] Further, according to the frequency modulation ranging principle, the absolute distances before and after the target moves are respectively l1 and l2, and the specific formula used is as follows:

[0040] l1 = n1λ + r1, n1 = 0, 1, 2, 3, 4……

[0041] l2 = n2λ + r2, n2 = 0, 1, 2, 3, 4……

[0042] Among them, λ is the wavelength of the laser signal, the meaning of n1 is the integer multiple part of the wavelength in the absolute distance l1, corresponding to the integer multiple of the phase periodicity in the interference light intensity I 上升 in, the meaning of r1 is the decimal part excluding the integer multiple of the wavelength in the absolute distance l1, 0 < r1 < λ, corresponding to the phase part in the interference light intensity I 上升 in The meaning of n2 is the integer multiple part of the wavelength in the absolute distance l2, corresponding to the integer multiple of the phase periodicity in the interference light intensity I' 上升 in, the meaning of r2 is the decimal part excluding the integer multiple of the wavelength in the absolute distance l2, 0 < r2 < λ, corresponding to the phase part in the interference light intensity I' 上升 in

[0043] When only phase ranging is used, Δl < λ, which means that even if the relative moving distance is greater than λ, the relative ranging method can only measure the decimal part excluding the integer multiple of the wavelength, which can be expressed as

[0044]

[0045] When the relative moving distance is greater than λ, at this time, the relative distance cannot be directly obtained from because The formula for the relative distance theoretical value Δl' is as follows:

[0046] Δl'=l2-l1=(n2-n1)λ-(r2-r1).

[0047] Furthermore, after obtaining the beat frequency interference signal phase corresponding to the absolute distance l1, The distance corresponding to the phase part The accuracy of r'1 is higher than that of r1, and the corrected absolute distance l'1 = n1λ + r'1 is obtained;

[0048] The phase of the beat frequency interference signal corresponding to the absolute distance l2 is obtained. The distance corresponding to the phase part The accuracy of r'2 is higher than that of r2, and the corrected absolute distance l'2=n2λ+r'2 is obtained.

[0049] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects: the common optical path laser ranging system and method for correcting absolute distance based on the phase method provided by the present invention adopts the phase method to measure the distance to obtain the relative distance measurement value, adopts the frequency modulated continuous wave (FMCW) to measure the distance to obtain the absolute distance, and adopts the phase method to measure the distance to correct the frequency modulated continuous wave (FMCW) ranging. In particular, when the ranging accuracy of the frequency modulation method is poor and there is a system error, the high-precision characteristics of the phase method can be used to correct it.

[0050] Among them, the present invention combines the characteristics of the optical path, the object light received by the optical fiber collimation unit and the reference light reflected at the end face of the optical fiber collimation unit are transmitted together to form interference light, which is transmitted to the photodetector through the loop unit. When measuring the distance, the phase difference is calculated based on the intensity signal of the interference light corresponding to the position before and after the target moves. Since the object light and the reference light are transmitted together, the interference of the external environment (such as temperature, pressure, vibration, etc.) on the object light and the reference light is consistent. When calculating the phase difference, the external interference can be offset by phase subtraction, which maximizes the measurement accuracy. The present invention is based on the intensity signal of the interference light corresponding to the position before and after the target moves, and the phase difference is calculated to obtain the relative distance measurement value to obtain the ranging result. Compared with the traditional frequency difference method ranging method, higher measurement accuracy can be achieved. The key to combining frequency modulated continuous wave ranging and phase ranging is to use their respective advantages: frequency modulated continuous wave is suitable for long-distance and large-scale measurements, while phase ranging provides higher accuracy, which can reach sub-nanometers.

[0051] Phase ranging can effectively correct the error of frequency modulated continuous wave (FMCW) ranging by providing high-precision short-range measurement data. By establishing an error model, correction factor, or real-time correction strategy, the FMCW ranging result can be accurately corrected, thereby obtaining higher accuracy over the entire ranging range. This combined method can utilize both the long-range range of FMCW ranging and the high-precision characteristics of phase ranging to achieve a more ideal ranging effect. At the same time, it does not require the use of large equipment, is low-cost, and has high universal applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0053] Figure 1 It is a structural schematic diagram of a common optical path laser ranging system for correcting absolute distance based on a phase method according to the present invention;

[0054] Figure 2 This is a schematic diagram of a triangular wave frequency modulation signal according to an embodiment of the present invention;

[0055] Figure 3 It is a schematic diagram of the structure of a typical FMCW laser radar ranging system in the prior art;

[0056] Figure 4 This is a beat frequency signal diagram obtained by a typical FMCW laser radar ranging system in the prior art;

[0057] Figure 5 A beat frequency signal diagram obtained after improving the optical path of the common optical path laser ranging system for correcting absolute distance based on the phase method of the present invention;

[0058] Figure 6 A schematic diagram of the structure of a fiber collimation unit formed by a combination of an optical fiber and a collimating lens;

[0059] Description of reference numerals:

[0060] Figure 1 1. Arbitrary waveform generator; 2. Semiconductor laser; 3. Loop unit (divided into three ports a, b, and c, port a input and port b output, port b input and port c output); 4. Fiber collimation unit; 5. Photoelectric detector; 6. Data acquisition device (two inputs); 7. Processor; 8. The position of the target before moving; 8', the position of the target after moving;

[0061] Figure 3Among them, 3-1, tunable laser; 3-2, isolator; 3-3, coupler 1; 3-4, circulator; 3-5, lens; 3-6, target; 3-7, coupler 2; 3-8, balanced detector;

[0062] Figure 6 In the figure, 6-1, optical fiber; 6-2, collimating lens. DETAILED DESCRIPTION

[0063] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0064] The purpose of the present invention is to provide a common optical path laser ranging system and method for correcting absolute distance based on the phase method, which combines the advantages of the frequency difference method and the phase difference method, can not only obtain high-precision measurement results, but also avoid the phase ambiguity problem, and can adapt to the accuracy requirements and measurement requirements of different occasions.

[0065] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0066] like Figure 1 As shown, the common optical path laser ranging system for correcting absolute distance based on the phase method provided by the present invention includes an arbitrary waveform generator 1, a semiconductor laser 2, a loop unit 3, a fiber collimation unit 4, a photodetector 5, a data collector 6 and a processor 7;

[0067] The arbitrary waveform generator 1 generates a frequency modulation signal, and performs frequency modulation on the laser signal of the semiconductor laser 2 by controlling the driving current of the semiconductor laser 2;

[0068] The output end of the semiconductor laser 2 is connected to the loop unit 3 via an optical fiber;

[0069] The loop unit 3 is connected to the optical fiber collimation unit 4 via an optical fiber, and is used to transmit the laser signal to the optical fiber collimation unit 4;

[0070] The optical fiber collimation unit 4 is used to transmit a part of the laser signal to the target, collect the object light reflected by the target, and reflect a part of the laser signal to form a reference light. The object light received by the optical fiber collimation unit 4 and the reference light are transmitted together.

[0071] The loop unit 3 receives the object light and the reference light sent back by the optical fiber collimation unit 4, and transmits them to the photodetector 5;

[0072] The photoelectric detector 5 is used to convert the intensity signal of the interference light of the object light and the reference light into an electrical signal, and transmit it to the data acquisition device 6;

[0073] The data collector 6 is used to receive the electrical signal converted by the photodetector 5 and transmit it to the processor 7;

[0074] The processor 7 is used to receive the electrical signal, and extract the beat frequency signal of the interference light based on the electrical signal, obtain the absolute distance according to the frequency modulated continuous wave ranging principle, and obtain the updated absolute distance after the target moves; based on the intensity signal of the interference light corresponding to the position before and after the target moves, calculate the phase difference to obtain the relative distance measurement value, and use the relative distance measurement value to correct the absolute distances of the two measurements to obtain the corrected absolute distances of the two measurements.

[0075] The relative distance measurement value described in the present invention refers to the difference between the positions of the target before and after the target moves, that is, the distance the target moves, that is, the relative displacement of the target can be measured when the optical fiber collimation unit 4 is fixed. Figure 1 Where l1 and l2 represent the distances from the position 8 before the target moves and the position 8' after the target moves to the optical fiber collimation unit 4, respectively, and Δl represents the distance the target moves.

[0076] The arbitrary waveform generator 1 is also used to generate a synchronous electrical signal and transmit it to the data collector 6. The synchronous electrical signal has the same frequency as the frequency modulation signal, for example, 1 kHz. For example, the frequency modulation signal is a symmetrical triangle wave or a sawtooth wave, and other waveforms can also be used. The synchronous electrical signal is a square wave with a duty cycle of 50%. The embodiment of the present invention takes a triangle wave frequency modulation signal as an example.

[0077] For example, the semiconductor laser 2 may be a narrow line width semiconductor laser, such as a DFB (Distributed Feedback Laser) laser; the loop unit (3) may be an optical fiber circulator.

[0078] For example, the signal transmission mode between the loop unit 3 and the photodetector 5 includes: one or more of optical fiber transmission, collimator conversion transmission, and free space optical transmission.

[0079] Specifically, the loop unit 3 is provided with three interfaces, namely, port a, port b and port c, wherein port a is used to receive the laser signal from the DFB laser 2, port b is used to output the laser signal to the fiber collimation unit 4 and receive the object light and the reference light, and port c is used to transmit the object light and the reference light to the photodetector 5.

[0080] For example, the optical fiber collimation unit 4 may be a fiber collimator with a PC-type interface, a lens with transmission and reflection functions, or a combination structure of an optical fiber and a collimator. Figure 6 As shown. The present invention does not limit the selection of the optical fiber collimation unit 4, and only requires that the optical fiber collimation unit 4 can realize the transmission and reflection functions of the laser signal, and the laser signal is reflected at the end face of the optical fiber collimation unit 4 to form a reference light. After the object light passes through the optical fiber collimation unit 4, it is transmitted to the photodetector 5 through the loop unit 3 with the reference light, so that the optical path difference between the measured reference light and the object light is closer to the distance to be measured, reducing the measurement error.

[0081] In FMCW laser ranging, a triangle wave is generally used as the modulation waveform to linearly modulate the frequency of the laser, such as Figure 2 As shown in the figure, the variation of laser frequency over time under the modulation of periodic triangle wave, the solid line trace represents the optical frequency of reference light, and the dotted line trace represents the optical frequency of object light. Because there is a time delay between them, there is a difference in the frequency of the two when mixing occurs. In one frequency modulation cycle, the frequency difference will jump, but because the change time is extremely short, the impact can be ignored, so the difference frequency signal obtained by mixing can be regarded as a sine wave with a fixed frequency.

[0082] After the frequency modulation signal modulates the laser signal, the photodetector 5 receives a sine wave with a phase mutation within the T / 2 period, which is an AC signal. The AC signal processing method can be used for filtering and signal amplification. If there is no frequency modulation signal, at a measurement position, the photodetector 5 obtains a DC signal.

[0083] Under the rising edge modulation of the triangle wave, the instantaneous frequency of the reference light is expressed as:

[0084]

[0085] Among them, f0 represents the initial frequency of the laser, α=2B / T is the frequency modulation rate, that is, the slope of the rising edge of the triangle wave, and B is the frequency modulation bandwidth.

[0086] In one frequency modulation period T, the expression of the reference optical signal is:

[0087]

[0088] The object light signal expression is:

[0089] in, is the initial phase of the reference light, E1 is the amplitude of the reference light, and E2 is the amplitude of the object light.

[0090] After mixing interference, the time domain expression of the difference frequency signal intensity can be obtained as follows:

[0091]

[0092] Since the quadratic term is much smaller than the phase term, ignoring the quadratic term yields:

[0093]

[0094] When the falling edge occurs, the instantaneous frequency of the reference signal is expressed as Similarly, we can get:

[0095]

[0096] According to the odd function property of cosine function, we can get:

[0097]

[0098] The synchronized square wave generated at the arbitrary waveform generator can be used to separate the rising and falling edge signals of the triangle wave at the data acquisition device. From the expression, it can be seen that the phase difference between the rising and falling edges is 4πf0τ.

[0099] Where τ represents E r (t)Relative E e (t) time delay.

[0100] The distance measurement result of the present invention can only be used for relative distance measurement, because when the phase difference is greater than 2π, phase winding will occur and the specific phase value cannot be determined. In addition, when performing relative distance measurement, the phase corresponding to the change in distance between two measurements also needs to be less than 2π.

[0101] FMCW (Frequency Modulated Continuous Wave) radar achieves ranging by transmitting a continuous wave signal whose frequency changes linearly with time. There is a frequency difference between the signal received by the receiver and the transmitted signal, and this frequency difference is proportional to the target distance. Therefore, according to the principle of frequency modulated continuous wave ranging, the calculation formula for obtaining the absolute distance is as follows:

[0102]

[0103] Where, l represents the absolute distance of the distance to be measured in a single measurement;

[0104] τ is the time difference corresponding to the optical path difference between the object light and the reference light when measuring the distance to be measured;

[0105] α is the frequency modulation rate, α = 2B / T, where B is the frequency modulation bandwidth and T is the frequency modulation period;

[0106] f is the frequency difference obtained based on the beat frequency signal of the interference light obtained by a single measurement.

[0107] Based on the above principle, the present invention provides a common optical path laser ranging method based on phase method to correct absolute distance, which is applied to the above common optical path laser ranging system based on phase method to correct absolute distance, and includes the following steps:

[0108] The arbitrary waveform generator 1 generates a frequency modulation signal, transmits it to the semiconductor laser 2, and performs frequency modulation on the laser signal of the semiconductor laser 2;

[0109] The frequency modulated laser signal is transmitted to the optical fiber collimation unit 4 through the loop unit 3;

[0110] The optical fiber collimation unit 4 transmits a part of the laser signal to the target, collects the object light reflected by the target, and reflects a part of the laser signal to form a reference light;

[0111] The object light received by the optical fiber collimation unit 4 is transmitted together with the reference light and transmitted to the photodetector 5 via the loop unit 3;

[0112] The photodetector 5 converts the intensity signal of the interference light of the object light and the reference light into an electrical signal and transmits it to the data collector 6;

[0113] The data collector 6 receives the electrical signal converted by the photodetector 5 and transmits it to the processor 7;

[0114] The processor 7 receives the electrical signal, extracts the beat frequency signal of the interference light based on the electrical signal, obtains the absolute distance according to the frequency modulated continuous wave ranging principle, and obtains the updated absolute distance after the target moves; calculates the phase difference based on the intensity signal of the interference light corresponding to the position before and after the target moves to obtain the relative distance measurement value, and uses the relative distance measurement value to correct the absolute distances of the two measurements to obtain the corrected two absolute distances, which specifically includes:

[0115] According to the frequency modulation ranging principle, the absolute distances before and after the target movement are obtained as l1 and l2 respectively. The theoretical value of the relative distance Δl' is obtained based on the absolute distances l1 and l2:

[0116] Δl'=l2-l1

[0117] The relative distance measurement is calculated as follows:

[0118]

[0119] Wherein, Δl represents the relative distance measurement value of the position before and after the target moves; τ1 is the time difference corresponding to the optical path difference between the object light and the reference light when measuring the distance at the position before the target moves; τ2 is the time difference corresponding to the optical path difference between the object light and the reference light when measuring the distance at the position after the target moves; is the phase difference actually measured based on the intensity signal of the interference light corresponding to the position of the target before and after movement; f0 is the initial frequency of the laser signal; c is the speed of light;

[0120] Based on the error analysis method, the absolute error or relative error between the relative distance measurement value Δl and the relative distance theoretical value Δl' is obtained, and based on the absolute error or relative error, the absolute distances l1 and l2 are corrected respectively.

[0121] Specifically, the common optical path laser ranging method for correcting absolute distance based on the phase method according to an embodiment of the present invention is introduced as follows:

[0122] 1. About relative distance measurement using phase ranging:

[0123] Specifically, based on the intensity signal of the interference light corresponding to the position of the target before and after movement, the phase difference is calculated to obtain the relative distance measurement value, which specifically includes:

[0124] When measuring the distance at the position where the target moves before, the time domain expression of the difference frequency signal intensity obtained after the interference of the object light and the reference light is:

[0125]

[0126] In the formula, I 上升 ,I 下降 are the light intensities of the rising and falling edges of the difference frequency signal obtained after the interference of the object light and the reference light when measuring the distance at the position where the target was before moving; I1 and I2 are the light intensities of the reference light and the object light respectively; τ1 is the time difference corresponding to the optical path difference between the object light and the reference light when measuring the distance at the position where the target was before moving; α=2B / T is the frequency modulation rate, that is, the slope of the rising edge of the triangular wave, B is the frequency modulation bandwidth, and T is the frequency modulation period;

[0127] When measuring the distance at the position where the target was before it moved, the phase difference between the light intensity at the rising edge and the falling edge is 4πf0τ1;

[0128] Similarly, when measuring the distance at the position where the target moves, the time difference corresponding to the optical path difference between the object light and the reference light is τ2. The time domain expression of the intensity of the difference frequency signal obtained after the interference between the object light and the reference light is:

[0129]

[0130] In the formula, I′ 上升 , I′ 下降They are the light intensity at the rising and falling edges of the difference frequency signal obtained after the interference of the object light and the reference light when measuring the distance to the position of the target after it moves;

[0131] When measuring the distance at the position where the target moves, the phase difference between the rising and falling edges is 4πf0τ2;

[0132] The combined phase difference is calculated based on the intensity signal of the interference light at the position before and after the target moves:

[0133] 4πf0τ1-4πf0τ2=4πf0(τ1-τ2);

[0134] Depend on Conclusion

[0135] Among them, because the phase difference of the light intensity at the rising edge and the falling edge is doubled, the corresponding measured phase difference also needs to be doubled, which is

[0136] but,

[0137] The range is 0-2π, when hour,

[0138]

[0139] Then the value range of Δl is 0-λ, where λ is the wavelength of the laser signal.

[0140] For phase difference ranging, the maximum ranging distance depends on the wavelength of the laser signal, and the ranging accuracy depends on the resolution of the phase difference.

[0141] The present invention further calculates the combined phase difference of the intensity signals of the interference light at the position before and after the target moves based on the phase difference of the light intensity at the rising edge and the falling edge, and uses the combined phase difference of the rising edge and the falling edge to obtain the distance difference. Compared with measuring the distance by comparing the phase difference of the two rising edges, the distance accuracy is doubled at the same phase difference resolution.

[0142] In the above, the phase difference actually measured is based on the intensity signal of the interference light at the position before and after the target moves. Specifically, it can be calculated by using the existing technologies in the field, such as the cross-correlation method, the fast Fourier transform method, the Hilbert transform method, the zero-crossing method (interpolation method), etc. The cross-correlation method: perform cross-correlation on two discrete signals, find the position of the correlation peak, calculate the time offset, and then convert it into a phase difference in combination with the sampling frequency. It is suitable for processing periodic signals and non-periodic signals; the fast Fourier transform (FFT) method: perform FFT on the signal to obtain the phase information in the spectrum, and then calculate the phase difference between the two signals at the same frequency point. This method is suitable for sinusoidal signals with stable frequency; the Hilbert transform method: perform Hilbert transform on the signal to obtain the analytical signal (including amplitude and phase information), and then calculate the phase difference; the zero-crossing method (interpolation method): find the zero-crossing point in the sampled data, accurately locate the time difference of the zero-crossing point by interpolation, and calculate the phase difference accordingly. It is suitable for data with high sampling rate.

[0143] In addition, the following embodiments may also be used for calculating the phase difference:

[0144] When performing signal processing, the phase difference can also be directly obtained by referring to only the rising edge part when measuring the positions of the front and rear targets before and after they move, that is:

[0145] 2πf0τ1-2πf0τ2=2πf0(τ1-τ2)

[0146] Depend on Conclusion

[0147] Similarly, we get the above,

[0148] like Figure 3 It is a typical FMCW laser radar ranging system in the prior art. Two couplers are set. The reference light and the object light are not transmitted in the fiber collimation unit. The beat frequency signal obtained by the system during ranging is as follows: Figure 4 As shown, it can be seen that before the optical path is improved in the present invention, the beat frequency signal does not have obvious sinusoidal characteristics, it is difficult to observe an obvious sinusoidal signal from the signal, and its phase cannot be determined.

[0149] Figure 5 The beat frequency signal obtained by improving the optical path of the high-precision laser phase ranging system of the common optical path of the present invention is shown. Figure 4 By comparison, it can be seen that the present invention can observe the part with obvious sinusoidal signal characteristics, which can be used to obtain phase information after fitting, and the waveform integrity is significantly improved compared with the signal before the optical path is improved. It can be seen that the present invention has better technical effects than the traditional FMCW laser radar ranging system and achieves technical improvement.

[0150] In addition, compared with the typical FMCW lidar ranging system in the prior art, the present invention forms a reference light by reflecting through an optical fiber collimation unit, which can reduce the use of couplers, reduce the energy loss generated by the couplers, and improve the overall efficiency of the system. At the same time, various errors introduced by the couplers are reduced. Meanwhile, the object light and the reference light received by the optical fiber collimation unit are transmitted in a common path, reducing the non-common path error, further improving the ranging accuracy of the relative distance measurement, and providing a reliable data basis and technical support for correcting the absolute distance.

[0151] 2. Regarding the absolute distance measurement using FMCW ranging:

[0152] The length l of the absolute distance can be expressed as

[0153] l = 2nλ + r n = 0, 1, 2, 3, 4...

[0154] Where r > 0. Therefore, for a determined l, the displacement-determined n and r can be obtained. Numerically, n is equal to the integer part of l divided by 2λ, and r is equal to the remainder.

[0155] Then there is

[0156] l1 = 2n1λ + r1 n1 = 0, 1, 2, 3, 4...

[0157] l2 = 2n2λ + r2 n2 = 0, 1, 2, 3, 4...

[0158] Among them, λ is the wavelength of the laser signal. The meaning of n1 is the integer multiple part of the wavelength in the absolute distance l1, corresponding to the integer multiple of the phase periodicity in the interference light intensity I 上升 (i.e., corresponding to n12π), and the meaning of r1 is the decimal part of the absolute distance l1 excluding the integer multiple of the wavelength, 0 < r1 < λ, corresponding to the phase part in the interference light intensity I 上升 (i.e., 2πf0τ1); similarly, the meaning of is the integer multiple part of the wavelength in the absolute distance l2, corresponding to the integer multiple of the phase periodicity in the interference light intensity I' 上升 上升 上升 上升 上升

[0159] When only phase ranging is used, Δl < λ, which means that even if the relative moving distance is greater than λ, the relative ranging method can only measure the decimal part excluding the integer multiple of the wavelength, which can be expressed as

[0160]

[0161] When the relative moving distance is greater than λ, at this time, it cannot be obtained from The relative distance is obtained directly from The formula for the theoretical value of relative distance Δl' is as follows:

[0162] Δl'=l2-l1=(n2-n1)λ-(r2-r1).

[0163] For the absolute distance, the phase of the beat frequency interference signal corresponding to l1 is obtained. The distance corresponding to the phase part Since the phase has a higher accuracy than the frequency, the accuracy of r'1 is higher than that of r1, and the corrected l'1 = 2n1λ + r'1 can be obtained. Similarly, the corrected l'2 = 2n2λ + r'2 can be obtained. This part is the correction of the absolute distance by the phase method, and the starting point is that the phase part has a higher accuracy.

[0164] As mentioned above, when measuring relative distance, if there is only relative distance measurement data, the following conditions must be met: This is actually due to the periodicity of the cosine function. When combined with absolute distance measurement, we have

[0165]

[0166] Therefore, the difference in absolute distance can be used to demodulate the phase period ambiguity problem of relative distance; this part is a correction of absolute distance to relative ranging, which solves the problem that the phase period of relative ranging cannot be measured.

[0167] 3. Correction of frequency modulated continuous wave (FMCW) ranging by phase ranging

[0168] 3.1 Correction principle

[0169] Frequency modulated continuous wave (FMCW) ranging method usually relies on frequency modulation and signal time delay to estimate the target distance, which can achieve a larger ranging range, but it may have certain errors due to the influence of factors such as signal propagation conditions, nonlinear errors, and system deviations. In contrast, the phase ranging method has higher accuracy and is suitable for shorter ranging ranges, but it is also affected by problems such as multipath effects and phase ambiguity.

[0170] By taking advantage of the high precision of phase ranging, we can correct the FMCW ranging results. The basic idea of ​​the correction is to use phase ranging to accurately measure short distances, and then correct the system error of FMCW ranging based on this accurate result.

[0171] 3.2 Calibration steps

[0172] (1) Measure and compare the results of the two methods

[0173] Use the FMCW ranging method to measure the distance of the target and get a rough distance value (there may be a certain error).

[0174] At the same target distance, the phase ranging method is used for accurate measurement to obtain an accurate distance value.

[0175] By comparing the FMCW ranging value with the phase ranging value, the difference between the two can be found. These differences mainly come from the errors in the FMCW ranging method (such as nonlinear error, system deviation, etc.).

[0176] (2) Establish error model

[0177] The measured values ​​of FMCW ranging are compared with those of phase ranging, and the error distribution law is analyzed.

[0178] Through data fitting methods (such as linear regression, nonlinear fitting, etc.), an error model is established to find out the system deviation in FMCW ranging (including sensor calibration error, frequency response error, etc.). For example, if the difference between FMCW ranging and phase ranging within a certain distance range is a linear relationship, then an error correction coefficient can be obtained through linear fitting.

[0179] (3) Correction of FMCW ranging results

[0180] According to the error model or correction coefficient, the FMCW ranging result is corrected. For example, if the FMCW ranging and phase ranging are linearly related, the FMCW result can be directly corrected by the correction factor (such as the error compensation coefficient): the phase ranging result is multiplied by the correction factor to obtain the FMCW ranging result; if the difference between the FMCW ranging and the phase ranging can be calculated using the error model, the error value calculated by the error model can be used for correction: the phase ranging result minus the error value can obtain the FMCW ranging result.

[0181] (4) Considering corrections for different ranging ranges

[0182] In practical applications, the error models of FMCW and phase ranging may not be globally consistent, that is, the error characteristics of the two may be different in different ranging ranges. Therefore, the error model can be subdivided into multiple different ranging intervals, and different correction factors can be used for different intervals.

[0183] For example, within a short distance (the effective range of phase ranging), the phase ranging result can be used to directly correct the FMCW ranging; within a long distance range (the advantageous range of FMCW ranging), more complex nonlinear error correction needs to be considered.

[0184] (5) Real-time calibration and dynamic correction

[0185] In practical applications, the measurement data of FMCW ranging and phase ranging can be collected in real time, and the FMCW ranging result can be adjusted according to the error compared in real time.

[0186] The FMCW ranging results are continuously corrected through a dynamic error compensation algorithm (such as Kalman filtering or other adaptive filtering methods).

[0187] The FMCW method is suitable for long-distance measurement, while the phase method is suitable for short-distance measurement. Therefore, the range must be reasonably selected and corrected to ensure that the advantages of the two methods complement each other in practical applications.

[0188] Phase ranging can effectively correct the error of frequency modulated continuous wave (FMCW) ranging by providing high-precision short-range measurement data. By establishing an error model, correction factor, or real-time correction strategy, the FMCW ranging result can be accurately corrected, thereby obtaining higher accuracy over the entire ranging range. This combined method can utilize both the long-distance range of FMCW ranging and the high-precision characteristics of phase ranging to achieve a more ideal ranging effect.

[0189] In addition, to combine the two methods of frequency modulated continuous wave (FMCW) ranging and phase ranging to achieve both a wide ranging range and high accuracy, the following strategies can also be considered:

[0190] 1. Multi-stage ranging (multi-segment measurement)

[0191] By utilizing the different advantages of frequency modulated continuous wave (FMCW) and phase ranging, the measurement method is switched within different ranging ranges. Specifically:

[0192] Short-range high-precision phase: For closer targets, phase ranging can be used because of its higher accuracy and is suitable for accurate measurement of close distances.

[0193] Long distance and wide range stage: For long-distance targets, frequency modulated continuous wave (FMCW) can be used. Due to its large dynamic range, it is suitable for measuring long-distance targets.

[0194] In this method, certain algorithms and circuit designs are used to switch between different distance segments, so that the overall system can maintain good accuracy and dynamic range throughout the entire distance measurement range.

[0195] 2. Composite measurement (fusion ranging method)

[0196] Another method is to fuse the results of the two ranging methods. Phase ranging and FMCW ranging methods can be combined by multi-sensor fusion or data processing fusion:

[0197] Using the rough distance information provided by FMCW, the approximate position of the target and the rough distance measurement result are obtained.

[0198] Phase ranging is then used to make fine measurements of close ranges and accurately calculate the distance to the target.

[0199] This approach can use the wide ranging range of FMCW to make a rough measurement, and then accurately calculate it through phase ranging methods, so that the system can provide high-precision measurements over different distance ranges.

[0200] 3. Dynamic Gain Switching

[0201] In one system, the performance of both methods is optimized at different distances by dynamically switching the gain:

[0202] When the target is far away, the FMCW method can handle the problem of large signal attenuation while maintaining low noise due to its large dynamic range.

[0203] When the target is close, using phase ranging can improve accuracy and reduce measurement errors.

[0204] By dynamically adjusting the signal gain, the best measurement method can be selected based on the distance to the target.

[0205] 4. Mixed signal processing and calibration

[0206] By performing signal processing on the measurement results of the two ranging methods, the advantages of the two can be complemented. For example:

[0207] The errors in phase ranging caused by multipath effects can be calibrated by utilizing the reliability of the FMCW method at a longer distance.

[0208] The low precision of the FMCW method at close distances can be compensated by the high precision of phase ranging.

[0209] In this way, through signal processing and data fusion, the system's ranging range and accuracy are improved.

[0210] 5. Dual-frequency or multi-frequency technology

[0211] If the hardware allows, higher ranging accuracy and range can be achieved through dual-frequency or multi-frequency ranging. The frequency modulated continuous wave method can use different frequencies for multiple measurements and improve accuracy through difference frequency technology; phase ranging can also perform phase measurements at multiple frequencies and decode through multi-frequency information to reduce errors.

[0212] In summary, the key to combining FMCW ranging and phase ranging is to take advantage of their respective advantages: FMCW is suitable for long-distance and large-range measurements, while phase ranging provides higher accuracy. By dynamically switching measurement methods at different distances or through data fusion technology, a ranging system with both high accuracy and a large ranging range can be achieved.

[0213] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A common optical path laser ranging system based on phase method to correct absolute distance, characterized in that: It comprises an arbitrary waveform generator (1), a semiconductor laser (2), a loop unit (3), an optical fiber collimation unit (4), a photodetector (5), a data acquisition device (6) and a processor (7); The arbitrary waveform generator (1) generates a frequency modulation signal, and performs frequency modulation on the laser signal of the semiconductor laser (2) by controlling the driving current of the semiconductor laser (2); The output end of the semiconductor laser (2) is connected to the loop unit (3) via an optical fiber; The loop unit (3) is connected to the optical fiber collimation unit (4) via an optical fiber, and is used to transmit the laser signal to the optical fiber collimation unit (4); The optical fiber collimation unit (4) is used to transmit a part of the laser signal to the target, collect the object light reflected by the target, and reflect a part of the laser signal to form reference light. The object light received by the optical fiber collimation unit (4) and the reference light are transmitted together. The loop unit (3) receives the object light and the reference light transmitted back by the optical fiber collimation unit (4), and transmits them to the photoelectric detector (5); The photoelectric detector (5) is used to convert the intensity signal of the interference light of the object light and the reference light into an electrical signal and transmit it to the data acquisition device (6); The data collector (6) is used to receive the electrical signal converted by the photoelectric detector (5) and transmit it to the processor (7); The processor (7) is used to receive the electrical signal, extract the beat frequency signal of the interference light based on the electrical signal, obtain the absolute distance according to the frequency modulated continuous wave ranging principle, and obtain the updated absolute distance after the target moves; Based on the intensity signal of the interference light corresponding to the position of the target before and after movement, the phase difference is calculated to obtain the relative distance measurement value, and the absolute distances of the two measurements are corrected using the relative distance measurement value to obtain the two corrected absolute distances.

2. The common optical path laser ranging system based on phase method to correct absolute distance according to claim 1, characterized in that: The arbitrary waveform generator (1) is also used to generate a synchronous electrical signal, which is transmitted to a data collector (6), wherein the synchronous electrical signal has the same frequency as the frequency modulation signal.

3. The common optical path laser ranging system based on phase method to correct absolute distance according to claim 1, characterized in that: The signal transmission mode between the loop unit (3) and the photoelectric detector (5) includes: one or more of optical fiber transmission, collimator conversion transmission, and free space optical transmission.

4. The common optical path laser ranging system based on phase method to correct absolute distance according to claim 1, characterized in that: The loop unit (3) is provided with three interfaces, namely, port a, port b and port c, wherein port a is used to receive a laser signal from a DFB laser (2), port b is used to output the laser signal to a fiber collimation unit (4) and receive object light and reference light, and port c is used to transmit the object light and reference light to a photoelectric detector (5).

5. The common optical path laser ranging system based on phase method to correct absolute distance according to claim 1, characterized in that: The optical fiber collimation unit (4) adopts an optical fiber collimator with a PC-type interface, a lens with transmission and reflection functions, or a combined structure of an optical fiber and a collimator.

6. The common optical path laser ranging system based on phase method to correct absolute distance according to claim 2, characterized in that: The frequency modulation signal is a symmetrical triangle wave or a sawtooth wave, and the synchronous electrical signal is a square wave with a duty cycle of 50%.

7. A common optical path laser ranging method based on phase method to correct absolute distance, applied to the common optical path laser ranging system based on phase method to correct absolute distance according to any one of claims 1 to 6, characterized in that: The steps include: The arbitrary waveform generator (1) generates a frequency modulation signal and transmits it to the semiconductor laser (2), thereby frequency modulating the laser signal of the semiconductor laser (2); The frequency modulated laser signal is transmitted to the optical fiber collimation unit (4) through the loop unit (3); The optical fiber collimation unit (4) transmits a part of the laser signal to the target, collects the object light reflected by the target, and reflects a part of the laser signal to form a reference light; The object light received by the optical fiber collimation unit (4) and the reference light reflected at the end face of the optical fiber collimation unit (4) are transmitted together and transmitted to the photoelectric detector (5) via the loop unit (3); The photoelectric detector (5) converts the intensity signal of the interference light of the object light and the reference light into an electrical signal and transmits it to the data acquisition device (6); The data collector (6) receives the electrical signal converted by the photodetector (5) and transmits it to the processor (7); The processor (7) receives the electrical signal, extracts the beat frequency signal of the interference light based on the electrical signal, obtains the absolute distance according to the frequency modulated continuous wave ranging principle, and obtains the updated absolute distance after the target moves; Based on the intensity signal of the interference light corresponding to the position of the target before and after movement, the phase difference is calculated to obtain the relative distance measurement value, and the absolute distances of the two measurements are corrected using the relative distance measurement value to obtain the corrected absolute distances, specifically including: According to the frequency modulation ranging principle, the absolute distances before and after the target movement are obtained as l1 and l2 respectively. The theoretical value of the relative distance Δl' is obtained based on the absolute distances l1 and l2: Δl'=l2-l1 The relative distance measurement is calculated as follows: Wherein, Δl represents the relative distance measurement value of the position before and after the target moves; τ1 is the time difference corresponding to the optical path difference between the object light and the reference light when measuring the distance at the position before the target moves; τ2 is the time difference corresponding to the optical path difference between the object light and the reference light when measuring the distance at the position after the target moves; is the phase difference actually measured based on the intensity signal of the interference light corresponding to the position of the target before and after movement; f0 is the initial frequency of the laser signal; c is the speed of light; Based on the error analysis method, the absolute error or relative error between the relative distance measurement value Δl and the relative distance theoretical value Δl' is obtained, and based on the absolute error or relative error, the absolute distances l1 and l2 are corrected respectively.

8. The high-precision laser phase ranging method for a common optical path according to claim 7, characterized in that: The error analysis method is used to obtain the absolute error or relative error between the relative distance measurement value Δl and the relative distance theoretical value Δl', and based on the absolute error or relative error, the absolute distances l1 and l2 are respectively corrected, specifically including: Compare the relative distance measurement value Δl with the relative distance theoretical value Δl', and analyze the error distribution law; According to the error distribution law, the error model is established through data fitting method to obtain the absolute error correction parameter or relative error correction coefficient; Based on the absolute error correction parameter or the relative error correction coefficient, the absolute distances l1 and l2 are corrected respectively.

9. The high-precision laser phase ranging method for a common optical path according to claim 7, characterized in that: According to the frequency modulation ranging principle, the absolute distances before and after the target moves are obtained as l1 and l2 respectively. The specific formula used is as follows: l1=n1λ+r1n1=0,1,2,3,4…… l2=n2λ+r2n2=0,1,2,3,4…… Among them, λ is the wavelength of the laser signal, the meaning of n1 is the integer multiple part of the wavelength in the absolute distance l1, corresponding to the periodic integer multiple of the phase in the interference light intensity I before the target moves, and the meaning of r1 is the decimal part excluding the integer multiple of the wavelength in the absolute distance l1, 0 < r1 < λ, corresponding to the phase part in the interference light intensity I 上升 Among them, the meaning of r1 is the decimal part excluding the integer multiple of the wavelength in the absolute distance l1, 0 < r1 < λ, corresponding to the phase part in the interference light intensity I 上升 in the phase part The meaning of n2 is the integer multiple part of the wavelength in the absolute distance l2, corresponding to the periodic integer multiple of the phase in the interference light intensity I' after the target moves, and the meaning of r2 is the decimal part excluding the integer multiple of the wavelength in the absolute distance l2, 0 < r2 < λ, corresponding to the phase part in the interference light intensity Y' 上升 Among them, the meaning of r2 is the decimal part excluding the integer multiple of the wavelength in the absolute distance l2, 0 < r2 < λ, corresponding to the phase part in the interference light intensity Y' 上升 in the phase part When only phase ranging is used, Δl<λ, which means that even if the relative moving distance is greater than λ, the relative ranging method can only measure the fractional part excluding the integer multiples of the wavelength, which can be expressed as When the relative moving distance is greater than λ, it is impossible to The relative distance is obtained directly from The formula for the theoretical value of relative distance Δl' is as follows: Δl'=l2-l1=(n2-n1)λ-(r2-r1).

10. The high-precision laser phase ranging method for a common optical path according to claim 9, characterized in that: The phase of the beat frequency interference signal corresponding to the absolute distance l1 is obtained. The distance corresponding to the phase part The accuracy of r'1 is higher than that of r1, and the corrected absolute distance l'1 = n1λ + r'1 is obtained; The phase of the beat frequency interference signal corresponding to the absolute distance l2 is obtained. The distance corresponding to the phase part The accuracy of r'2 is higher than that of r2, and the corrected absolute distance l'2=n2λ+r'2 is obtained.

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