A high frame rate multi-frequency i-tof ranging method and system

Abstract

The application provides a high frame rate multi-frequency i-ToF ranging method and system, and belongs to the field of laser measurement. Measurement light and reference light are multi-frequency signals, and the phase difference of the multi-frequency signals in the reference light digital signal and the measurement return light digital signal is extracted; the measurement result of a single frequency is calculated according to the phase difference of each frequency signal, the real distance corresponding to the frequency combination is obtained through a table lookup method according to the difference value of the measurement results of two frequencies; and the real distances corresponding to all frequency combinations are averaged to obtain the final ranging result. The query table refers to the difference value of the measurement results of two frequencies under different positive integer combinations, and the difference value of the real distance and the measurement result of one frequency. When the table is looked up, the positive integer combination is determined according to the difference value of the measurement results of two frequencies, and the real distance is further obtained through the table lookup. Through the selection of multiple similar modulation signal frequencies and the combination of algorithms, the application can realize long-range, high frame rate and low ambiguity distance measurement.

Description

Technical Field

[0001] This invention relates to the field of laser measurement, and specifically to a high frame rate multi-frequency i-ToF ranging method and system. Background Technology

[0002] Indirect Time-of-Flight (i-ToF) technology analyzes the proportional relationship between energy values ​​collected by sensors at different time windows to determine the signal phase, indirectly measuring the phase difference between the transmitted and received signals to obtain the distance. It has wide applications in consumer electronics, robotics, security monitoring, and rail transportation.

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

[0004] To achieve the requirements of high frame rate and high measurement accuracy in i-ToF ranging systems, this invention proposes a high frame rate multi-frequency i-ToF ranging method and system, which realizes high frame rate and efficient multi-frequency distance fusion, effectively improving the measurement performance of i-ToF systems.

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

[0006] In a first aspect, the present invention provides a high frame rate multi-frequency i-ToF ranging method, wherein the measuring light and the reference light are multi-frequency signals, and the method includes:

[0007] Extract the phase difference between the reference light digital signal and the multi-frequency signals in the measured return light digital signal; calculate the measurement result of a single frequency based on the phase difference of each frequency signal; obtain the true distance corresponding to the frequency combination by looking up a table based on the difference between the measurement results of each pair of frequencies; take the average of the true distances corresponding to all frequency combinations as the final ranging result.

[0008] The process of creating the lookup table in the table lookup method is as follows:

[0009] Calculate the distance period interval d for each frequency signal. mi Establish the theoretical distance relationship:

[0010]

[0011] Where d represents the theoretical distance, and n1, n2, n3, n n All are positive integers, representing the number of complete measurement distance intervals; d n d represents the measurement result of the nth frequency. mnThis represents the distance period interval corresponding to the nth frequency;

[0012] Based on the theoretical distance relationship, a lookup table of pairwise frequencies is established. This lookup table refers to the frequency of different positive integer combinations n. k1 n k2 The difference Δd between each pair of frequency measurements, and the difference D between the actual distance and one of the frequency measurements. h -d i D h This represents the true distance between the h-th pairwise frequency lookup tables;

[0013] When looking up a table, the positive integer combination n is determined based on the difference Δd between the measured values ​​of each pair of frequencies. k1 n k2 Then look up the table to get D. h -d i Finally, D was calculated. h .

[0014] Furthermore, the reference light digital signal and the measurement return light digital signal are obtained in the following ways:

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

[0016] 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 photodetector and the measurement photodetector, respectively. The measurement photodetector is controlled by a square wave signal. The photodetector 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, a multi-frequency superimposed modulation signal refers to a signal obtained by randomly selecting multiple coprime frequencies within a given frequency range and superimposing them, expressed as:

[0018]

[0019] Where I0 is the emitted light power of the light source, and ψ i For frequency f i The phase of the corresponding cosine signal, where 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] Where, d min d max These are the minimum and maximum values ​​of the estimated measurement distance range, respectively, f. min f maxThese are the minimum and maximum values ​​for a given frequency range, respectively.

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

[0024]

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

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

[0027]

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

[0029] Furthermore, when creating 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 combination of positive integers n k1 n k2 Given that the distance period interval d between two selected frequency signals is known... mi d mj Substituting these values ​​into the above equation yields Δd and D. h -d i .

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

[0034]

[0035] Among them, f iLet be the frequency of the i-th frequency signal, and c represent the speed of light.

[0036] Furthermore, the number of frequencies in the multi-frequency signal is 4.

[0037] Secondly, 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 beneficial effects of this invention are as follows: This invention provides a high frame rate multi-i-ToF ranging method, which enables distance measurement with a large range, high frame rate, and low ambiguity using an i-ToF system. By rationally setting the measurement frequency, the effective measurement range is maximized while maintaining a high frame rate for the effective depth image. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of a high frame rate multi-frequency i-ToF ranging system according to the present invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the 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 merely illustrative and not intended to limit the invention.

[0041] like Figure 1 As shown, this invention discloses a high frame rate multi-frequency i-ToF ranging system, including a light source, modulator, beam splitter, photodetectors (reference photodetector and measurement photodetector), rectangular wave signal generator, signal processing module, distance fusion algorithm module, etc. The light signal output by the light source is modulated by the intensity modulator and then split into two paths, measurement light and reference light, by the beam splitter. The modulation signal of the intensity modulator is composed of n (n>3) different frequency cosine signals 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 photodetector and the measurement photodetector, respectively. The measurement photodetector is controlled by the square wave signal to select according to the phase of the reference light. The two photodetectors convert the received light signals into electrical signals, which are then processed into digital signals 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 fused to obtain an accurate ranging result.

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

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

[0044]

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

[0046] Here, f i The frequencies are similar within a certain frequency range. For each frame measurement, n coprime frequencies are selected by randomly generating numbers within a selected range. The formula for selecting the measurement frequency is as follows:

[0047]

[0048] Where, d min d max These are the minimum and maximum values ​​of the estimated measurement distance range, respectively, f. min f max These are the minimum and maximum values ​​for a given frequency range, respectively.

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

[0050] b. The modulated cosine wave signal light is split into two paths, measurement light and reference light, by a beam splitter. The reference light is incident on the reference photodetector, and the measurement light is incident on the target object. After being reflected by the target object, it is incident on the measurement photodetector. The measurement photodetector is modulated by a square wave signal to convert the multi-frequency optical signals received by the reference photodetector and the measurement photodetector into digital signals. The phase difference of each frequency signal in 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 result of a single frequency can be expressed as:

[0052]

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

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

[0055]

[0056] Calculate the phase difference by combining the integrated energy values ​​from the four phase sampling points:

[0057]

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

[0059] c. Based on the difference between the pairwise frequency measurements, the true distance D corresponding to the frequency combination is obtained by looking up a table. h The average of the actual distances corresponding to all frequency combinations is taken as the final ranging result D. Where D... h This represents the true distance between the h-th pairwise frequency lookup tables. The true distance D h The average value is taken as the final ranging result, where n represents the number of frequencies in the multi-frequency signal. This represents the number of permutations and combinations.

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

[0061]

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

[0063] When looking up a table, the positive integer combination n is determined based on the difference between the measured values ​​of each pair of frequencies. k1 n k2 Then look up the table to get D. h -d i Finally, D was calculated. 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, a lookup table refers to a table that matches different combinations of positive integers n. k1 n k2 The difference Δd between each pair of frequency measurements, and the difference D between the actual distance and one of the frequency measurements. h -d i D h Let Δd represent the true distance of the h-th pairwise frequency lookup table. Therefore, the closest positive integer combination n can be found using Δd. k1 n k2 Thus, we obtain D. h -d1; Since d1 is known, the ranging result under the frequency combination of f1 = 25MHz and f2 = 32MHz can be obtained.

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

[0068] Calculate the distance period interval d for each frequency signal. mi Establish the theoretical distance relationship:

[0069]

[0070] Among them, f i Let n1, n2, n3, n be the frequency of the i-th frequency signal, c represent the speed of light, and n be the frequency of the i-th frequency signal. n All are positive integers, representing the number of complete measurement distance intervals; d N d represents the measurement result of the nth frequency. MN This represents the distance period interval corresponding to the nth frequency; d represents the theoretical distance, which, if a suitable measurement modulation frequency is selected, is determined based on d. i and d j The difference Δd, combined with a table lookup, can be used to determine the corresponding n. i and n j The 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 measured distance range, for example, 1-10; in the theoretical distance relationship formula, 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 combination of positive integers n k1 b K2 Given that the distance period interval d between two selected frequency signals is known... mi d mj Substituting these values ​​into the above equation yields Δd and D. h -d i This method can be used to create all lookup tables that correspond to each pair of frequencies.

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

[0076] The signal transmitting-receiving module is used to transmit multi-frequency signals and receive reference optical digital signals and measurement return optical digital signals;

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

[0078] The multi-frequency lookup table calculation module is used to calculate the measurement result of a single frequency based on the phase difference of each frequency signal, and obtain the true distance corresponding to the frequency combination by looking up the difference between the measurement results of each pair of 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 lookup tables with pairwise frequencies. The lookup table creation process is as follows:

[0080] Calculate the distance period interval d for each frequency signal. mi Establish the theoretical distance relationship:

[0081]

[0082] Where d represents the theoretical distance, and n1, n2, n3, n n All are positive integers, representing the number of complete measurement distance intervals; d n d represents the measurement result of the nth frequency. mn This represents the distance period interval corresponding to the nth frequency;

[0083] Based on the theoretical distance relationship, a lookup table of pairwise frequencies is established. This lookup table refers to the lookup table for different positive integer combinations n. k1 n k2 The difference Δd between each pair of frequency measurements, and the difference D between the actual distance and one of the frequency measurements. h -d i D h This represents the true distance between the h-th pairwise frequency lookup tables;

[0084] When looking up a table, the positive integer combination n is determined based on the difference between the measured values ​​of each pair of frequencies. k1 n k2 Then look up the table to get D. h -d i Finally, D was calculated. h .

[0085] In one specific embodiment of the present invention, the signal transmitting-receiving module includes:

[0086] The modulated optical signal transmitting module is used to generate and transmit multiple cosine wave signals of similar frequencies. i i = 1, 2, ..., n, where n is the number of multi-frequency signals; the modulated optical signal transmitting module includes a light source, a modulator, a frequency generator, and a waveform generator. The light source, the frequency generator, and the waveform modulator are all connected to the modulator. The continuous optical signal emitted by the light source generates a multi-frequency superimposed modulated signal under the generation of the frequency generator and the waveform generator. The signal is then 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 gating signal that controls the exposure of the photodetector. The width of the gating signal should be as small as possible.

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

[0089] A photodetector includes a reference photodetector and a measurement photodetector. The reference photodetector is used to directly detect the incident reference light signal, while the measurement photodetector is used to detect the measurement return light signal reflected by the object being measured.

[0090] For the system embodiments, since they basically correspond to the method embodiments, relevant details can be found in the descriptions of the method embodiments; the implementation methods of the remaining modules will not be repeated here. The system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of the present invention according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0091] The system embodiments of the present invention can be applied to any device with data processing capabilities, such as a computer or other similar device. The system embodiments can be implemented in software, hardware, or a combination of both. Taking software implementation as an example, as a logical device, it is formed by the processor of any data processing device loading the corresponding computer program instructions from non-volatile memory into memory for execution.

[0092] The above-described embodiments are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. Those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all 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, and the measurement light is reflected back from the target object to obtain the measurement return light; characterized in that, The method includes: Extract the phase difference between the reference light digital signal and the multi-frequency signals in the measured return light digital signal; calculate the measurement result of a single frequency based on the phase difference of each frequency signal; obtain the true distance corresponding to the frequency combination by looking up a table based on the difference between the measurement results of each pair of frequencies; take the average of the true distances corresponding to all frequency combinations as the final ranging result. The process of creating the lookup table in the table lookup method is as follows: Calculate the distance period interval for each frequency signal. Establish the theoretical distance relationship: ； in, Indicates the theoretical distance. All are positive integers, representing the number of complete measurement distance intervals; This represents the measurement result for the nth frequency. This represents the distance period interval corresponding to the nth frequency; Based on the theoretical distance relationship, a lookup table of pairwise frequencies is established. This lookup table refers to different combinations of positive integers... The difference between the pairwise frequency measurement results and the difference between the actual distance and one of the frequency measurement results. , This represents the true distance between the h-th pairwise frequency lookup tables; and The calculation formula is as follows: ； ； Given a combination of positive integers Given the distance period interval of two selected frequency signals. Substituting into the above formula, we can obtain... and ; When looking up a table, the difference between the measured values ​​of each pair of frequencies is used. Determine the combination of positive integers Then look up the table to get Finally, the calculation yielded .

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 the measurement light is emitted, it is reflected by the target object to obtain the measurement return light. The reference light and the measurement return light are received by the reference photodetector and the measurement photodetector, respectively. The measurement photodetector is controlled by a square wave signal. The photodetector 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, A multi-frequency superposition modulated signal is obtained by randomly selecting multiple coprime frequencies within a given frequency range and superimposing them, as follows: ； in, The emitted light power of the light source. For frequency f i The phase of the corresponding cosine signal, where t is time and n is the number of different frequencies. Let i be the frequency of the i-th frequency signal. It is a modulated signal with multiple frequencies superimposed.

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: ； ； in, These are the minimum and maximum values ​​of the estimated measurement distance range, respectively. These are the minimum and maximum values ​​for a given frequency range, respectively. It represents the speed of light.

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 as follows: ； in, This represents the phase difference between the reference light and the i-th frequency signal in the measured return light. Let i be the frequency of the i-th frequency signal. This represents the measurement result for the i-th frequency. It 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: ； in, For signal amplitude, This 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, Distance period interval of each frequency signal The calculation formula is as follows: ； in, Let i be the frequency of the i-th frequency signal. It represents the speed of light.

8. 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.

9. A high frame rate multi-frequency i-ToF ranging system, used to implement the method of claim 1, characterized in that, The system includes: The signal transmitting-receiving module is used to transmit multi-frequency signals and receive reference optical digital signals and measurement return optical digital signals; The signal processing module is used to extract the phase difference between the reference light digital signal and the multi-frequency signal in the measured return light digital signal; The multi-frequency lookup table calculation module is used to calculate the measurement result of a single frequency based on the phase difference of each frequency signal, and obtain the true distance corresponding to the frequency combination by looking up the difference between the measurement results of each pair of frequencies; the average of the true distances corresponding to all frequency combinations is taken as the final ranging result. The lookup table module stores lookup tables with pairwise frequencies. The lookup table creation process is as follows: Calculate the distance period interval for each frequency signal. Establish the theoretical distance relationship: ； in, Indicates the theoretical distance. All are positive integers, representing the number of complete measurement distance intervals; This represents the measurement result for the nth frequency. This represents the distance period interval corresponding to the nth frequency; Based on the theoretical distance relationship, a lookup table of pairwise frequencies is established. This lookup table refers to different combinations of positive integers... The difference between the pairwise frequency measurement results and the difference between the actual distance and one of the frequency measurement results. , This represents the true distance between the h-th pairwise frequency lookup tables; When looking up a table, the positive integer combination is determined based on the difference between the measured values ​​of each pair of frequencies. Then look up the table to get Finally, the calculation yielded .

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