High-frame-rate multi-frequency i-ToF ranging method and system

Abstract

The invention provides a high-frame-rate multi-frequency i-ToF ranging method and system, and belongs to the field of laser measurement. The measuring light and the reference light are multi-frequency signals, and the phase difference of the multi-frequency signals in the reference light digital signal and the measuring return light digital signal is extracted; calculating a measurement result of a single frequency according to the phase difference of each frequency signal, and obtaining a real distance corresponding to the frequency combination through a table look-up method according to a difference value of the measurement results of every two frequencies; and averaging the real distances corresponding to all the frequency combinations as a final distance measurement result. The look-up table refers to a difference value between every two frequency measurement results under different positive integer combinations and a difference value between the real distance and one of the frequency measurement results. During table look-up, a positive integer combination is determined according to a difference value of measurement results of every two frequencies, and then a real distance is obtained through further table look-up. According to the invention, by selecting a plurality of similar modulation signal frequencies and combining an algorithm, wide-range, high-frame-rate and low-ambiguity distance measurement can be realized.

Description

Technical Field

[0001] The present invention relates to the field of laser measurement, and in particular to a high-frame-rate multi-frequency i-ToF ranging method and system. Background Art

[0002] Indirect time-of-flight (i-ToF) technology uses the proportional relationship between the energy values collected by the sensor in different time windows to analyze the signal phase, indirectly measuring the phase difference between the transmitted and received signals, and thus determining the distance. It has a wide range of applications in consumer electronics, robotics, security monitoring, rail transportation, and other fields.

[0003] During the measurement process, in order not to reduce the frame rate, the measurement accuracy of the two frames in the measurement image should be relatively close. However, in order to prevent the difference between the measured values of the two frequencies from being submerged by the measurement noise, the two measurement frequencies need to have a certain difference, that is, the selected measurement frequencies should be similar within a certain numerical range. Summary of the Invention

[0004] In order to achieve the requirements of high frame rate and high measurement accuracy in the i-ToF ranging system, the present invention proposes a high frame rate multi-frequency i-ToF ranging method and system to achieve high frame rate and efficient multi-frequency distance fusion, 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 high frame rate multi-frequency i-ToF ranging method, wherein the measurement light and the reference light are multi-frequency signals, and the method comprises:

[0007] Extract the phase difference between the reference light digital signal and the multi-frequency signal in the measurement return light digital signal; calculate the measurement result of a single frequency based on the phase difference of each frequency signal, and use the table lookup method to obtain the true distance corresponding to the frequency combination based on the difference between the measurement results of each two frequencies; take the average of the true distances corresponding to all frequency combinations as the final ranging result;

[0008] The query table establishment process in the table lookup method is as follows:

[0009] Calculate the distance period interval d of each frequency signal mi , establish the theoretical distance relationship:

[0010]

[0011] Among them, d represents the theoretical distance, n1, n2, n3, n n are all positive integers, indicating the number of complete measurement interval cycles; d n Indicates the measurement result of the nth frequency, d mnIndicates the distance cycle interval corresponding to the nth frequency;

[0012] According to the theoretical distance relationship, a lookup table of pairwise frequencies is established. The lookup table refers to the frequency of the pairwise frequencies in different positive integer combinations n. k1 、n k2 The difference Δd between the two frequency measurement results, and the difference D between the true distance and one of the frequency measurement results h -d i , D h represents the true distance of the hth pairwise frequency lookup table;

[0013] When looking up the table, the positive integer combination n is determined based on the difference Δd between the measurement results of the two frequencies. k1 、n k2 , then look up the table to get D h -d i , and finally calculate D h .

[0014] Furthermore, the reference light digital signal and the measurement return light digital signal are obtained as follows:

[0015] The multi-frequency superimposed modulation signal is modulated by an intensity modulator and then divided into reference light and measurement light;

[0016] After being emitted, the measurement light is reflected by the target object. The reference path light and the measurement path return light are received by the reference light detector and the measurement light detector respectively. The measurement light detector is regulated by the square wave signal. The light detector converts the optical signal into an electrical signal, which is then processed into a digital signal by the signal processing module to obtain the reference light digital signal and the measurement return light digital signal respectively.

[0017] Furthermore, the multi-frequency superposition modulation signal is obtained by randomly superposing multiple coprime frequencies in a given frequency interval, which can be expressed as:

[0018]

[0019] Where I0 is the light source output power, ψ i is the frequency f i The phase of the corresponding cosine signal, t is time, and n is the number of different frequencies.

[0020] Furthermore, the given frequency range is estimated by the following formula:

[0021]

[0022] Among them, d min d max are the minimum and maximum values of the estimated measurement distance range, respectively, and f min 、f maxare the minimum and maximum values of a given frequency interval, respectively.

[0023] Furthermore, the formula for calculating the measurement result of a single frequency based on the phase difference of each frequency signal is:

[0024]

[0025] in, represents the phase difference between the reference light and the i-th frequency signal in the measurement return light, f i is the frequency of the i-th frequency signal, d i represents the measurement result of the i-th frequency, and c represents the speed of light.

[0026] Furthermore, the phase difference between the reference light and the i-th frequency signal in the measurement return light is The calculation formula is:

[0027]

[0028] Where A is the signal amplitude, Represents the phase difference of the i-th frequency signal at four different phase sampling points.

[0029] Furthermore, when establishing the lookup table, Δd and D h -d i The calculation formula is as follows:

[0030] Δd=(n k1 -1)·d mi -(n k2 -1)·d mj

[0031] D h -d i =(n k1 -1)·d mi

[0032] Given a positive integer combination n k1 、n k2 Under the condition that the distance period interval d between two selected frequency signals is known mi d mj , we can get Δd and D by substituting into the above formula. h -d i .

[0033] Furthermore, the distance period interval d of each frequency signal is mi The calculation formula is as follows:

[0034]

[0035] Among them, f iis the frequency of the i-th frequency signal, and c represents the speed of light.

[0036] Furthermore, the number of frequencies in the multi-frequency signal is four.

[0037] In a second aspect, the present invention provides a high frame rate multi-frequency i-ToF ranging system for implementing the above-mentioned high frame rate multi-frequency i-ToF ranging method.

[0038] The present invention has the following beneficial effects: It provides a high-frame-rate multi-i-ToF ranging method that can achieve long-range, high-frame-rate, and low-ambiguity distance measurement in an i-ToF system. By properly setting the measurement frequency, the effective measurement range is maximized while maintaining a high frame rate for the effective depth image. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of a high frame rate multi-frequency i-ToF ranging system in the present invention. DETAILED DESCRIPTION

[0040] 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.

[0041] like Figure 1 As shown, the present invention discloses a high frame rate multi-frequency i-ToF ranging system, including a light source, a modulator, a beam splitter, a light detector (a reference light detector and a measurement light detector), a rectangular wave signal generator, a signal processing module, a distance fusion algorithm module, etc. The light signal output by the light source is modulated by an intensity modulator and then divided into two paths, measurement light and reference light, by a beam splitter. The modulation signal of the intensity modulator is composed of n (n>3) cosine signals of different frequencies that satisfy a specific relationship. After the measurement light is emitted, it is reflected by the target object. The reference path light and the measurement path return light are received by the reference light detector and the measurement light detector respectively. The square wave signal is used to control the measurement light detector so that it is selected according to the phase of the reference light. The two light detectors convert the received light signal into an electrical signal, which is then processed into a digital signal by the signal processing module and the phase difference of the multi-frequency signals in the reference light and the measurement return light is extracted. Finally, the ranging result of a single frequency in the multi-frequency signal is obtained by the fusion algorithm module, and then the accurate ranging result is obtained by fusion.

[0042] In a specific implementation of the present invention, a method for implementing i-ToF ranging based on the above system includes the following steps:

[0043] a. The light source is continuous light with a power of I0; the frequency of the cosine signal constituting the modulation signal is f i(i=1, 2, 3, 4), the intensity of the modulated optical signal can be expressed as:

[0044]

[0045] Where I0 is the light source output power, ψ i is the frequency f i The phase of the corresponding cosine signal, t is time, and n is the number of different frequencies.

[0046] Here, f i The frequencies are similar within a certain frequency range. Each frame measurement uses the method of taking random numbers within the selected range to select n coprime frequencies. The formula for selecting the measurement frequency is as follows:

[0047]

[0048] Among them, d min d max are the minimum and maximum values of the estimated measurement distance range, respectively, and f min 、f max are the minimum and maximum values of a given frequency interval, respectively.

[0049] In this embodiment, in each measurement frame, four coprime numbers are randomly selected within the range of 20-35 MHz as measurement frequency values, that is, f1=25 MHz, f2=32 MHz, f3=21 MHz, and f4=29 MHz are selected.

[0050] b. The modulated cosine wave signal light is split into two paths: measurement light and reference light through a beam splitter. The reference light is incident on the reference light detector, and the measurement light is incident on the target object. After being reflected by the target object, it is incident on the measurement light detector. The measurement light detector is modulated by the square wave signal. The multi-frequency light signals received by the reference and measurement light detectors are converted into digital signals. The phase difference between the reference light and the measurement return light is calculated respectively, and the ranging result of a single frequency is calculated from this.

[0051] The measurement results of a single frequency can be expressed as:

[0052]

[0053] in, represents the phase difference between the reference light and the i-th frequency signal in the measurement return light, f i is the frequency of the i-th frequency signal, d i represents the measurement result of the i-th frequency, and c represents the speed of light.

[0054] Here, phase sampling is performed based on the phase of the reference light, and multiple square wave pulse exposure sampling is performed within one cosine cycle. Taking the phase sampling points 0°, 90°, 180°, and 270° as an example, the integrated energy value of the i-th frequency signal at each phase sampling point is calculated:

[0055]

[0056] Combine the integrated energy values of the four phase sampling points to calculate the phase difference:

[0057]

[0058] Where A is the signal amplitude, Represents the phase difference of the i-th frequency signal at four different phase sampling points, Represents the phase difference of the i-th frequency signal.

[0059] c. According to the difference between the two frequency measurement results, the actual distance D corresponding to the frequency combination is obtained by table lookup method. h , take the average of the actual distances corresponding to all frequency combinations as the final distance measurement result D. Among them, D h Represents the true distance of the h-th pairwise frequency lookup table, The true distance D h Take the mean as the final ranging result, n represents the number of frequencies in the multi-frequency signal, Indicates the number of permutations and combinations.

[0060] The final distance measurement result D obtained by fusion can be expressed as:

[0061]

[0062] Among them, D1, D2, D3, D4, D5, and D6 are the distance measurement results of a single measurement frequency and two by two fusion. The present invention can achieve a large range, high frame rate, and low ambiguity distance measurement by selecting multiple similar modulation signal frequencies and combining them with an algorithm.

[0063] When looking up the table, determine the positive integer combination n based on the difference between the measurement results of the two frequencies k1 、n k2 , then look up the table to get D h -d i , and finally calculate D h Taking the frequency combination of f1 = 25MHz and f2 = 32MHz as an example, the corresponding lookup table is shown in Table 1:

[0064] Table 1

[0065]

[0066] As shown in Table 1, the query table refers to the k1 、n k2 The difference Δd between the two frequency measurement results, and the difference D between the true distance and one of the frequency measurement results h -d i , D h The actual distance of the h-th pairwise frequency lookup table. Therefore, the closest positive integer combination n can be found by Δd. k1 、n k2 , and then get D h -d1; Since d1 is known, the ranging result under the frequency combination of f1 = 25 MHz and f2 = 32 MHz can be obtained.

[0067] The process of establishing the query table is as follows:

[0068] Calculate the distance period interval d of each frequency signal mi , establish the theoretical distance relationship:

[0069]

[0070] Among them, f i is the frequency of the ith frequency signal, c represents the speed of light, n1, n2, n3, n n are all positive integers, indicating the number of complete measurement interval cycles; d N Indicates the measurement result of the nth frequency, d MN Indicates the distance cycle interval corresponding to the nth frequency; d represents the theoretical distance. If a suitable measurement modulation frequency is selected, according to d i and d j The difference Δd, combined with the table lookup, can be used to know the corresponding n i and n j , a true distance can be calculated for every two similar frequencies

[0071] The range of positive integers in the lookup table can be set according to the measurement distance range, for example, 1-10. In the theoretical distance relationship, d is considered equal, and the measurement results of two different frequencies are considered equal, that is:

[0072] Δd=(n k1 -1)·d mi -(n K2 -1)·d mj

[0073] D h -d i =(n k1 -1)·d mi

[0074] Given a positive integer combination n k1 、b K2 Under the condition that the distance period interval d between two selected frequency signals is known mi d mj , we can get Δd and D by substituting into the above formula. h -d i All lookup tables corresponding to any two frequencies can be established using this method.

[0075] This embodiment also provides a high frame rate multi-frequency i-ToF ranging system for implementing the above method, including:

[0076] A signal transmitting and receiving module, which is used to transmit a multi-frequency signal and receive a reference light digital signal and a measurement return light digital signal;

[0077] A signal processing module, which is used to extract the phase difference between the reference light digital signal and the multi-frequency signal in the measurement return light digital signal;

[0078] The multi-frequency table lookup calculation module is used to calculate the measurement results of a single frequency based on the phase difference of each frequency signal. The true distance corresponding to the frequency combination is obtained by table lookup based on the difference between the measurement results of two frequencies. The average of the true distances corresponding to all frequency combinations is taken as the final ranging result.

[0079] The lookup table module stores a lookup table of pairwise frequencies. The lookup table establishment process is as follows:

[0080] Calculate the distance period interval d of each frequency signal mi , establish the theoretical distance relationship:

[0081]

[0082] Among them, d represents the theoretical distance, n1, n2, n3, n n are all positive integers, indicating the number of complete measurement interval cycles; d n Indicates the measurement result of the nth frequency, d mn Indicates the distance cycle interval corresponding to the nth frequency;

[0083] According to the theoretical distance relationship, a lookup table of pairwise frequencies is established. The lookup table refers to the frequency of the pairwise frequencies in different positive integer combinations n. k1 、n k2 The difference Δd between the two frequency measurement results, and the difference D between the true distance and one of the frequency measurement results h -d i , D h represents the true distance of the hth pairwise frequency lookup table;

[0084] When looking up the table, determine the positive integer combination n based on the difference between the measurement results of the two frequencies k1 、n k2 , then look up the table to get D h -d i , and finally calculate D h .

[0085] In a specific implementation of the present invention, the signal transmission-receiving module includes:

[0086] Modulated optical signal transmission module, used to generate multiple cosine wave signals of similar frequencies and transmit them, f i , i=1, 2, ...n, n is the number of multi-frequency signals; the modulated optical signal transmission module includes a light source, a modulator, a frequency generator, and a waveform generator. The light source, frequency generator, and waveform modulator are all connected to the modulator. The continuous optical signal emitted by the light source generates a multi-frequency superimposed modulation signal under the generation of the frequency generator and the waveform generator, which is input into the modulator and modulated by the modulator to generate a multi-frequency signal.

[0087] The square wave signal transmitting module is used to generate a gate signal for controlling the exposure of the measuring light detector. The width of the gate signal should be as small as possible.

[0088] A beam splitter is used to split the multi-frequency signal into reference light and measurement light.

[0089] The optical detector includes a reference optical detector and a measuring optical detector. The reference optical detector is used to directly detect the incident reference optical signal, and the measuring optical path is used to detect the measuring return optical signal reflected by the object under test.

[0090] As for the system embodiment, since it basically corresponds to the method embodiment, the relevant parts can be referred to the partial description of the method embodiment, and the implementation methods of the remaining modules will not be repeated here. The system embodiment described above is only illustrative, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of the present invention. Ordinary technicians in this field can understand and implement it without paying any creative work.

[0091] Embodiments of the system of the present invention can be applied to any device with data processing capabilities, such as a computer or other device. System embodiments can be implemented through software, hardware, or a combination of software and hardware. For example, a software implementation, as a logical device, is implemented by a processor of any device with data processing capabilities, reading corresponding computer program instructions from non-volatile memory into internal memory and executing them.

[0092] The above-described embodiments merely illustrate several implementations of the present invention, and while the descriptions are relatively specific and detailed, they are not to be construed as limiting the scope of the present invention. Persons skilled in the art will readily appreciate that variations and modifications may be made without departing from the spirit of the present invention, and all such variations and modifications fall within the scope of protection of the present invention.

Claims

1. A high frame rate multi-frequency i-ToF ranging method, wherein the measurement light and reference light are multi-frequency signals, characterized in that: The method comprises: Extract the phase difference between the reference light digital signal and the multi-frequency signal in the measurement return light digital signal; calculate the measurement result of a single frequency based on the phase difference of each frequency signal, and use the table lookup method to obtain the true distance corresponding to the frequency combination based on the difference between the measurement results of each two frequencies; take the average of the true distances corresponding to all frequency combinations as the final ranging result; The query table establishment process in the table lookup method is as follows: Calculate the distance period interval d of each frequency signal MI , establish the theoretical distance relationship: Among them, d represents the theoretical distance, n1, n2, n3, n N are all positive integers, indicating the number of complete measurement interval cycles; d n Indicates the measurement result of the nth frequency, d MN Indicates the distance cycle interval corresponding to the nth frequency; According to the theoretical distance relationship, a lookup table of pairwise frequencies is established. The lookup table refers to the frequency of the pairwise frequencies in different positive integer combinations n. K1 、n K2 The difference Δd between the two frequency measurement results, and the difference D between the true distance and one of the frequency measurement results h -d i , D h represents the true distance of the hth pairwise frequency lookup table; When looking up the table, the positive integer combination n is determined based on the difference Δd between the measurement results of the two frequencies. k1 、n k2 , then look up the table to get D h -d i , and finally calculate D h .

2. The high frame rate multi-frequency i-ToF ranging method according to claim 1, characterized in that: The reference light digital signal and the measurement return light digital signal are obtained as follows: The multi-frequency superimposed modulation signal is modulated by an intensity modulator and then divided into reference light and measurement light; After being emitted, the measurement light is reflected by the target object. The reference path light and the measurement path return light are received by the reference light detector and the measurement light detector respectively. The measurement light detector is regulated by the square wave signal. The light detector converts the optical signal into an electrical signal, which is then processed into a digital signal by the signal processing module to obtain the reference light digital signal and the measurement return light digital signal respectively.

3. The high frame rate multi-frequency i-ToF ranging method according to claim 2, characterized in that: The multi-frequency superposition modulation signal is obtained by randomly superimposing multiple mutually prime frequencies in a given frequency range, which can be expressed as: Where I0 is the light source output power, ψ i is the frequency f i The phase of the corresponding cosine signal, t is time, and n is the number of different frequencies.

4. The high frame rate multi-frequency i-ToF ranging method according to claim 3, characterized in that: The given frequency range is estimated by the following formula: Among them, d min d max are the minimum and maximum values of the estimated measurement distance range, respectively, and f min 、f max are the minimum and maximum values of a given frequency interval, respectively.

5. The high frame rate multi-frequency i-ToF ranging method according to claim 1, characterized in that: The formula for calculating the measurement result of a single frequency based on the phase difference of each frequency signal is: in, represents the phase difference between the reference light and the i-th frequency signal in the measurement return light, f i is the frequency of the i-th frequency signal, d i represents the measurement result of the i-th frequency, and c represents the speed of light.

6. The high frame rate multi-frequency i-ToF ranging method according to claim 5, characterized in that: Phase difference between the reference light and the i-th frequency signal in the measurement return light The calculation formula is: Where A is the signal amplitude, Represents the phase difference of the i-th frequency signal at four different phase sampling points.

7. The high frame rate multi-frequency i-ToF ranging method according to claim 1, characterized in that: When creating a lookup table, Δd and D h -d i The calculation formula is as follows: Δd=(n k1 -1)·d mi -(n k2 -1)·d mj D h -d i =(n k1 -1)·d mi Given a positive integer combination n k1 、n k2 Under the condition that the distance period interval d between two selected frequency signals is known mi d mj , we can get Δd and D by substituting into the above formula. h -d i .

8. The high frame rate multi-frequency i-ToF ranging method according to claim 1, characterized in that: The distance period interval d of each frequency signal mi The calculation formula is as follows: Among them, f i is the frequency of the i-th frequency signal, and c represents the speed of light.

9. The high frame rate multi-frequency i-ToF ranging method according to claim 1, characterized in that: The number of frequencies in the multi-frequency signal is 4.

10. A high frame rate multi-frequency i-ToF ranging system, used to implement the method of claim 1, characterized in that: The system comprises: A signal transmitting and receiving module, which is used to transmit a multi-frequency signal and receive a reference light digital signal and a measurement return light digital signal; A signal processing module, which is used to extract the phase difference between the reference light digital signal and the multi-frequency signal in the measurement return light digital signal; The multi-frequency table lookup calculation module is used to calculate the measurement results of a single frequency based on the phase difference of each frequency signal. The true distance corresponding to the frequency combination is obtained by table lookup based on the difference between the measurement results of two frequencies. The average of the true distances corresponding to all frequency combinations is taken as the final ranging result. The lookup table module stores a lookup table of pairwise frequencies. The lookup table establishment process is as follows: Calculate the distance period interval d of each frequency signal mi , establish the theoretical distance relationship: Among them, d represents the theoretical distance, n1, n2, n3, n N are all positive integers, indicating the number of complete measurement interval cycles; d N Indicates the measurement result of the nth frequency, d MN Indicates the distance cycle interval corresponding to the nth frequency; According to the theoretical distance relationship, a lookup table of pairwise frequencies is established. The lookup table refers to the frequency of the pairwise frequencies in different positive integer combinations n. K1 、n k2 The difference Δd between the two frequency measurement results, and the difference D between the true distance and one of the frequency measurement results h -d i , D h represents the true distance of the hth pairwise frequency lookup table; When looking up the table, determine the positive integer combination n based on the difference between the measurement results of the two frequencies k1 、n k2 , then look up the table to get D h -d i , and finally calculate D h .

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