A multi-frequency fusion I-TOF ranging method and system

Abstract

This invention relates to a multi-frequency fusion I-TOF ranging method and system, belonging to the field of laser ranging. The optical signal output from the light source is modulated by an intensity modulator and split into two paths: a measurement light and a reference light. The modulation signal is composed of n (n>2) sinusoidal signals of different frequencies with specific relationships superimposed. After the measurement light is emitted, it is reflected by the target object. The reference light and the return light from the measurement path are received by photodetectors and processed into digital signals by circuitry. The phase difference between the multi-frequency signals in the reference light and the return light is extracted to obtain the ranging results of the multi-frequency signals. Finally, an algorithm is used to fuse them to obtain an accurate ranging result. This invention, by reasonably selecting the frequencies of multiple modulation signals and combining them with a fusion algorithm, can achieve a large range, high precision, and high robustness in distance measurement.

Description

Technical Field

[0001] This invention relates to the field of laser ranging, specifically to a multi-frequency fusion I-TOF ranging method and system. Background Technology

[0002] Indirect Time-of-Flight (I-TOF) technology uses phase detection to achieve laser ranging. It has the advantages of fast measurement speed and high measurement accuracy, and is widely used in systems such as laser 3D scanning and lidar. It also has wide applications in military and civilian fields such as intelligent construction, reverse engineering, digital cities, and battlefield mapping.

[0003] According to the principle of phase-based ranging, there is a trade-off between the measurement accuracy of a single frequency and the unambiguous measurement range; both cannot be simultaneously achieved. Therefore, multiple modulation frequencies are usually superimposed for measurement. That is, a large measurement range is achieved using low-frequency signals, while high-precision measurement is achieved using high-frequency signals. In this process, selecting the optimal combination of signal frequencies and completing the fusion of multi-frequency measurement information becomes particularly important. Summary of the Invention

[0004] To achieve optimal selection of signal frequency combinations and efficient, high-precision multi-frequency measurement information fusion in a multi-frequency I-TOF ranging system, this invention proposes a multi-frequency fusion I-TOF ranging method. Through quantitative analysis, it proposes selection criteria for different signal frequencies, enabling the simplest frequency combinations. It also proposes an algorithm for progressive fusion of multi-frequency measurement results through multi-level threshold determination, achieving efficient and high-precision multi-frequency information fusion and effectively improving the measurement performance of the I-TOF system.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] In a first aspect, the present invention provides a multi-frequency fusion I-TOF ranging method, comprising the following steps:

[0007] (1) Integrating continuous optical signals and multi-frequency f i The superimposed modulation signals, i = 1, 2, ..., n, are modulated by an intensity modulator and then split into reference light and measurement light; where n represents the number of frequency signals in the multi-frequency signal, f i Let f1 represent the frequency of the i-th frequency signal, satisfying f1 > f2 > ... > f n ;

[0008] (2) The reference light is directly incident on the reference path light detector, and the measurement light is incident on the measurement path light detector after being reflected by the target object. The two signals received by the reference path light detector and the measurement path light detector are converted into digital signals, and the phase difference of each frequency signal in the reference light and the measurement return light is extracted respectively.

[0009] (3) Calculate the independent ranging results of the multi-frequency signals based on the phase difference of each frequency signal;

[0010] (4) The independent ranging results of the multi-frequency signals are fused together to calculate the final ranging result D, as shown in the following formula:

[0011] D = N n-1 m n-1 +N n-2 m n-2 +…+N2m2+N1m1+d1

[0012] Where, m n-1 N represents the measurement distance corresponding to a 2π phase difference generated by the (n-1)th frequency signal. n-1 m n-1 The coefficients to be determined are (i = n-1, n-2, ..., 1), and d1 represents the independent ranging result of the first frequency signal.

[0013] Furthermore, in step (3), the calculation formula for the independent ranging results of the multi-frequency signals is as follows:

[0014]

[0015]

[0016] Where, d i This represents the independent ranging result for the i-th frequency signal. m represents the phase difference between the reference light and the i-th frequency signal in the measured return light. i Let represent the measured distance when the i-th frequency signal generates a 2π phase difference, and c represent the speed of light.

[0017] Furthermore, in the formula for calculating the final ranging result D, the coefficient N to be determined... i The solution method for (i = n-1, n-2, ..., 1) is as follows:

[0018] Set the threshold parameter a = u1m i b = u2m i c = u3m i Where u1, u2, and u3 represent threshold coefficients, satisfying 0≤u1≤0.5, 0≤u2≤0.5, and 0.5≤u3≤1;

[0019] When d i <a and hour,

[0020] When d i >c and hour,

[0021] In other cases, N i =floor(d i+1 / m i ), where floor(.) represents rounding down.

[0022] Furthermore, in a multi-frequency superimposed modulation signal, the selection of each frequency signal should meet the following conditions:

[0023] e i+1 <m i <e i+2 i = 1, 2, ..., n-2

[0024]

[0025] Among them, e1, e i+1 e i+2 Let m represent the independent ranging noise of the 1st, (i+1th), and (i+2th)th frequency signals, respectively. n-1 m n D represents the measurement distance corresponding to the (i+1)th and (i+2)th frequency signals generating a 2π phase difference, respectively. k 'r' represents the measurement range, and 'r' represents the measurement accuracy.

[0026] Furthermore, in a multi-frequency superimposed modulated signal, the formula for calculating the independent ranging noise of each frequency signal is as follows:

[0027]

[0028] Among them, e i p represents the independent ranging noise of the i-th frequency signal. i This represents the independent phase detection noise of the i-th frequency signal.

[0029] Secondly, the present invention provides a multi-frequency fusion I-TOF ranging system for implementing the above ranging method, comprising:

[0030] Modulated optical signal transmitting module, which is used to transmit optical signals based on continuous optical signals and multi-frequency f i The superimposed modulation signals i = 1, 2, ..., n generate a multi-frequency signal and transmit it, where n represents the number of frequency signals in the multi-frequency signal, and f i Let f1 represent the frequency of the i-th frequency signal, satisfying f1 > f2 > ... > f n ;

[0031] A beam splitter is used to split a multi-frequency signal into a reference beam and a measurement beam.

[0032] The photodetector includes a reference optical path detector and a measurement optical path detector. The reference optical path detector is used to directly detect the incident reference light signal, and the measurement optical path detector is used to detect the measurement return light signal reflected by the target object.

[0033] The signal processing module is used to convert the two signals received by the reference path optical detector and the measurement path optical detector into digital signals;

[0034] The phase detection module is used to extract the phase difference between the reference light and the measurement return light at various frequencies.

[0035] The fusion algorithm module is used to calculate the independent ranging results of multi-frequency signals based on the phase difference of each frequency signal; and to fuse the independent ranging results of multi-frequency signals to calculate the final ranging result D, as shown in the following formula:

[0036] D = N n-1 m n-1 +N n-2 m n-2 +…+N2m2+N1m1+d1

[0037] Where, m n-1 N represents the measurement distance corresponding to a 2π phase difference generated by the (n-1)th frequency signal. n-1 m n-1 The coefficients to be determined are d1, where d1 represents the independent ranging result of the first frequency signal.

[0038] Furthermore, the modulated optical signal transmitting module includes a light source, a modulator, and a frequency generator. Both the light source and the frequency generator are connected to the modulator. The continuous optical signal emitted by the light source and the multi-frequency signal generated by the frequency generator... i The superimposed modulation signals i = 1, 2, ..., n are input to the modulator and modulated to generate a multi-frequency signal. Where I0 is the emitted light power of the light source. For frequency f i The phase of the corresponding sinusoidal signal, where t represents time.

[0039] The beneficial effects of this invention are as follows: The multi-frequency fusion I-TOF ranging method provided by this invention can achieve large range, high precision, and high robustness ranging of the I-TOF system. Specifically, by reasonably setting the modulation frequency interval in a gradient, the optimal balance between system performance and complexity is achieved, that is, the contradiction between large range and high precision is resolved with the simplest frequency combination; at the same time, an algorithm for progressive fusion of multi-frequency measurement results is implemented through multi-level threshold judgment to achieve high robustness measurement across the entire range. Attached Figure Description

[0040] Figure 1This is a schematic diagram of the I-TOF ranging system in this invention;

[0041] Figure 2 This is a flowchart of the multi-frequency signal measurement result fusion algorithm in this invention;

[0042] Figure 3 A schematic diagram of the experimental results of multi-frequency fusion I-TOF ranging in an embodiment of the present invention. Detailed Implementation

[0043] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0044] like Figure 1 As shown, this invention discloses a multi-frequency fusion I-TOF ranging system, including a light source, modulator, beam splitter, photodetectors (reference optical path detector and measurement optical path detector), signal processing module, phase detection module, and fusion algorithm module. The light signal output by the light source is modulated by the intensity modulator and split into two paths: a measurement light and a reference light. The modulation signal is composed of n (n>2) sinusoidal signals of different frequencies with specific relationships superimposed. The measurement light is reflected by the target object after being emitted. The reference path light and the measurement path return light are received by the photodetectors and processed into digital signals by the signal processing module. The phase detection module extracts the phase difference between the multi-frequency signals in the reference light and the measurement return light to obtain the ranging results of the multi-frequency signals respectively. Finally, the fusion algorithm module fuses the signals to obtain an accurate ranging result.

[0045] The method for implementing I-TOF ranging based on this system includes the following steps:

[0046] a. The light source is continuous light with power I0; the frequency of the sinusoidal signal constituting the modulation signal is f. i (i = 1, 2, 3), then the intensity of the modulated optical signal can be expressed as (i = 1, 2, 3), where I0 is the emitted light power of the light source. For frequency f i The phase of the corresponding sinusoidal signal, f i The expression satisfies f1 > f2 > f3.

[0047] b. The multi-frequency superimposed modulation signal is modulated by an intensity modulator and then split into reference light and measurement light by a beam splitter. The reference light is directly incident on the reference path photodetector, while the measurement light is reflected from the target object and then incident on the measurement path photodetector. Both signals are converted into digital signals by the signal processing module, and then the phase difference between the multi-frequency signals in the reference light and the measurement return light is extracted by the phase detection module. (i = 1, 2, 3).

[0048] c. The measured distances corresponding to the 2π phase differences generated by each frequency signal can be expressed as:

[0049]

[0050] where c is the speed of light;

[0051] The independent ranging results of each frequency signal can be expressed as:

[0052]

[0053] Define the signal noise as the difference between the maximum and minimum values of the signal, and the independent phase discrimination noise of each frequency signal is p i (i = 1, 2, 3), and the independent ranging noise of each frequency signal is:

[0054]

[0055] There is usually e i <e i+1 .

[0056] d. Assume that the required measurement range is D k , and the required measurement accuracy is r. Then, when selecting each frequency signal, it should meet e2 < m1 < e3, and the upper limit of the selected frequency should meet m n-1 < D k < m n , and the lower limit of the selected frequency should meet e1 < r; in this embodiment, it is required that D m = 50m, r = 1mm. Therefore, f1 = 500 MHz, f2 = 20 MHz, and f3 = 2.5 MHz are selected.

[0057] e. After fusing the multi-frequency measurement results, the final ranging result D is calculated.

[0058] In a specific implementation of the present invention, as Figure 2 shown, the final ranging result D obtained by fusing in step e can be expressed as:

[0059] D = N2m2 + N1m1 + d1

[0060] where N1 and N2 represent coefficients; since f i has been determined, m i is determined. Then, d i+1 and d i are used to obtain N i (i = 2, 1) in sequence, and then D can be obtained.

[0061] In this embodiment, the process of obtaining N i includes the following steps:

[0062] a. Set the threshold parameter a = u1m i 、b = u2m i 、c = u3m i , where 0 ≤ u1 ≤ 0.5, 0 < u2 ≤ 0.5, 0.5 ≤ u3 ≤ 1 are three threshold coefficients; in this embodiment, u1 = 0.4, u2 = 0.5, and u3 = 0.6 are selected.

[0063] b. When d i < a and when

[0064] When d i > c and when

[0065] In other cases, there is always N i = floor(d i+1 / m i );

[0066] where the function floor(x) represents rounding down x.

[0067] As Figure 3 shown is a schematic diagram of the multi - frequency fusion I - TOF ranging result of a specific embodiment of the present invention. The target board moves linearly within the range of 0.5m to 35m and pauses briefly at multiple positions, while performing multi - frequency fusion ranging. The measurement speed is 10,000 points per second, the measurement time is about 5 minutes, there are no singular points during the measurement, and the measurement accuracy at a fixed position is less than 1mm. It can be seen that the method proposed by the present invention has the characteristics of high precision and high robustness in the full range.

[0068] The above - described embodiments are only a preferred solution of the present invention, but they are not intended to limit the present invention. Those of ordinary skill in the relevant technical field can still make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all technical solutions obtained by means of equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A multi-frequency fusion I-TOF ranging method, characterized in that, Includes the following steps: (1) Integrating continuous optical signals and multi-frequency f i The superimposed modulation signals, i = 1, 2, ..., n, are modulated by an intensity modulator and then split into reference light and measurement light; where n represents the number of frequency signals in the multi-frequency signal, f i Let f1 represent the frequency of the i-th frequency signal, satisfying f1 > f2 > ... > f n The selection of each frequency signal should meet the following conditions: e i+1 <m i <e i+2 ,i=1,2,…n-2 m n-1 <D k <m n e1<r Among them, e1, e i+1 e i+2 Let m represent the independent ranging noise of the 1st, (i+1th), and (i+2th)th frequency signals, respectively. n-1 m n D represents the measurement distance corresponding to the (i+1)th and (i+2)th frequency signals generating a 2π phase difference, respectively. k 'r' represents the measurement range, and 'r' represents the measurement accuracy. (2) The reference light is directly incident on the reference path light detector, and the measurement light is incident on the measurement path light detector after being reflected by the target object. The two signals received by the reference path light detector and the measurement path light detector are converted into digital signals, and the phase difference of each frequency signal in the reference light and the measurement return light is extracted respectively. (3) Calculate the independent ranging results of the multi-frequency signals based on the phase difference of each frequency signal, using the following formula: Where, d i This represents the independent ranging result for the i-th frequency signal. m represents the phase difference between the reference light and the i-th frequency signal in the measured return light. i represents the measured distance when the i-th frequency signal generates a 2π phase difference, and c represents the speed of light; (4) The independent ranging results of the multi-frequency signals are fused together to calculate the final ranging result D, as shown in the following formula: D=N n-1 m n-1 +N n-2 m n-2 +…+N2m2+N1m1+d1 Where, m n-1 N represents the measurement distance corresponding to a 2π phase difference generated by the (n-1)th frequency signal. n-1 m n-1 The coefficients to be determined are d1, where d1 represents the independent ranging result of the first frequency signal. The method for solving for the coefficients to be determined is as follows: Set the threshold parameter a = u1m i b = u2m i c = u3m i Where u1, u2, and u3 represent threshold coefficients, satisfying 0≤u1≤0.5, 0≤u2≤0.5, and 0.5≤u3≤1; When d i <a and hour, When d i >c and hour, In other cases, N i =floor(d i+1 / m i ), where floor(.) represents rounding down.

2. The multi-frequency fusion I-TOF ranging method according to claim 1, characterized in that, In a multi-frequency superimposed modulated signal, the formula for calculating the independent ranging noise of each frequency signal is as follows: Among them, e i p represents the independent ranging noise of the i-th frequency signal. i This represents the independent phase detection noise of the i-th frequency signal.

3. A multi-frequency fusion I-TOF ranging system for implementing the ranging method of claim 1, characterized in that, include: Modulated optical signal transmitting module, which is used to transmit optical signals based on continuous optical signals and multi-frequency f i The superimposed modulation signals i = 1, 2, ..., n generate a multi-frequency signal and transmit it, where n represents the number of frequency signals in the multi-frequency signal, and f i Let f1 represent the frequency of the i-th frequency signal, satisfying f1 > f2 > ... > f n ; A beam splitter is used to split a multi-frequency signal into a reference beam and a measurement beam. The photodetector includes a reference optical path detector and a measurement optical path detector. The reference optical path detector is used to directly detect the incident reference light signal, and the measurement optical path detector is used to detect the measurement return light signal reflected by the target object. The signal processing module is used to convert the two signals received by the reference path optical detector and the measurement path optical detector into digital signals; The phase detection module is used to extract the phase difference between the reference light and the measurement return light at various frequencies. The fusion algorithm module is used to calculate the independent ranging results of multi-frequency signals based on the phase difference of each frequency signal; and to fuse the independent ranging results of multi-frequency signals to calculate the final ranging result D, as shown in the following formula: D=N n-1 m n-1 +N n-2 m n-2 +…+N2m2+N1m1+d1 Where, m n-1 N represents the measurement distance corresponding to a 2π phase difference generated by the (n-1)th frequency signal. n-1 m n-1 The coefficients to be determined are d1, where d1 represents the independent ranging result of the first frequency signal.

4. The multi-frequency fusion I-TOF ranging system according to claim 3, characterized in that, The modulated optical signal transmitting module includes a light source, a modulator, and a frequency generator. Both the light source and the frequency generator are connected to the modulator. The continuous optical signal emitted by the light source and the multi-frequency signal generated by the frequency generator... i The superimposed modulation signals i = 1, 2, ..., n are input to the modulator and modulated to generate a multi-frequency signal. Where I0 is the emitted light power of the light source. For frequency f i The phase of the corresponding sinusoidal signal, where t represents time.

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