A FMCW laser radar system and its distance calibration method and device

Abstract

The invention relates to the technical field of FMCW radar ranging, and discloses an FMCW laser radar system and a distance calibration method and device thereof. In the invention, a signal processing module uses a calibration path time domain signal after frequency shift to perform real-time calibration on a measurement path time domain signal, and can partially calibrate factors affecting ranging accuracy such as laser drive current noise, triangle wave linearity, time domain white noise, etc., thereby effectively improving the ranging accuracy of the FMCW laser radar. In addition, in view of the problem that a too short calibration path length corresponds to a lower calibration path frequency found in actual use, a frequency jump is easily generated when demodulating the lower frequency, resulting in a loss of calibration effect, by frequency shifting the calibration path time domain signal, the problem of calibration effect failure caused by the calibration path itself can be solved without changing the physical length of the calibration coil, thereby further improving the ranging accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of FMCW radar ranging, and in particular to an FMCW laser radar system and a distance calibration method and device thereof. Background Art

[0002] FMCW (Frequency-modulated continuous-wave) radar achieves ranging based on an optical FMCW interferometer system. However, due to the deterioration of ranging accuracy caused by factors such as noise in the FMCW lidar system, a calibration path is usually added to the FMCW lidar system to calibrate the ranging results, so as to reduce the impact of system noise on ranging accuracy to a certain extent. The length of the calibration path affects its calibration effect. A too short calibration path length corresponds to a lower calibration path angular frequency. Frequency jumps are likely to occur when demodulating a lower frequency, resulting in a deterioration in the calibration effect. At the same time, when the calibration path length is consistent with the distance to the target, the calibration effect is best (the ranging accuracy after calibration is used as the evaluation standard).

[0003] However, for FMCW lidar, the length of the calibration path that can be increased is limited, and increasing the calibration path length places high requirements on the equipment, resulting in a high cost for FMCW lidar ranging and an inability to improve the ranging accuracy of FMCW lidar. Summary of the invention

[0004] In view of this, the present invention provides an FMCW laser radar system and a distance calibration method and device thereof to solve the problem that increasing the calibration path length leads to a high cost of FMCW laser radar ranging and cannot improve the FMCW laser radar ranging accuracy.

[0005] In a first aspect, the present invention provides a FMCW laser radar system, which includes: a laser, a spectrometer, a calibration coil, a first mixer, a second mixer, a signal processing module and a lens; the laser is connected to the spectrometer, and the spectrometer is respectively connected to the calibration coil, the second mixer and the lens; the first mixer is respectively connected to the calibration coil and the signal processing module; the second mixer is respectively connected to the signal processing module and the lens;

[0006] A spectrometer is used to obtain the modulated signal wave output by the laser, split the modulated signal wave into a reference wave, a calibration signal and a measurement signal, transmit the reference wave to the first mixer and the second mixer, transmit the calibration signal to the first mixer via the calibration coil, and emit the measurement signal to the target object through the lens;

[0007] The first mixer is used to mix the reference wave and the calibration signal to obtain a calibration path time domain signal;

[0008] The second mixer is used to receive the measurement wave sent by the lens, and mix the reference wave with the measurement wave to obtain a measurement path time domain signal; wherein the measurement wave is a signal wave generated by the measurement signal after being reflected by the target object to the lens;

[0009] The signal processing module is used to perform frequency shift on the calibration path time domain signal, and use the frequency shifted calibration path time domain signal to perform real-time calibration on the measurement path time domain signal to obtain the distance value of the calibrated target object.

[0010] The present embodiment provides an FMCW laser radar system, which realizes mixing processing of a reference wave and a calibration signal through a first mixer, and realizes mixing processing of a reference wave and a measurement wave through a second mixer, and then the signal processing module uses the calibration path time domain signal after frequency shift to perform real-time calibration on the measurement path time domain signal, and can partially calibrate factors affecting the ranging accuracy such as laser drive current noise, triangle wave linearity, time domain white noise, etc., thereby effectively improving the ranging accuracy of the FMCW laser radar. In addition, in actual use, it is found that a too short calibration path length corresponds to a lower calibration path frequency, and frequency hopping is easily generated when demodulating the lower frequency, resulting in loss of calibration effect. By frequency shifting the calibration path time domain signal, the problem of calibration effect failure caused by the calibration path itself can be solved without changing the physical length of the calibration coil, thereby further improving the ranging accuracy.

[0011] In a second aspect, the present invention provides a distance calibration method for an FMCW laser radar system, which is applied to a signal processing module in the FMCW laser radar system; the method comprises:

[0012] Acquire a calibration path time domain signal, perform frequency shift processing and signal processing on the calibration path time domain signal, and obtain a calibration path angle frequency;

[0013] Acquire a measurement path time domain signal, perform signal processing on the measurement path time domain signal, and obtain a measurement path angle frequency;

[0014] The distance calibration is performed based on the calibration road angle frequency and the measurement road angle frequency to obtain the distance value of the target object after calibration.

[0015] The present embodiment provides a distance calibration method for an FMCW laser radar system, which performs frequency shift processing and signal processing on the calibration path time domain signal, and performs signal processing on the measurement path time domain signal, and then performs distance calibration based on the calibration path angular frequency and the measurement path angular frequency. Since the calibration path time domain signal and the measurement path time domain signal are synchronized, factors affecting the ranging accuracy, such as laser drive current noise, triangle wave linearity, time domain white noise, etc., can be partially calibrated. Since the length of the calibration coil is known, the ranging accuracy of the FMCW laser radar system can be further improved without changing the physical length of the calibration coil.

[0016] In an optional implementation, the calibration path time domain signal is subjected to frequency shift processing and signal processing respectively to obtain the calibration path angle frequency, including:

[0017] Perform A / D conversion on the time domain signal of the calibration path to obtain a digital signal of the calibration path;

[0018] Perform FFT transformation on the digital signal of the calibration path to obtain the frequency domain signal of the calibration path;

[0019] Performing frequency shift on the calibration path frequency domain signal to obtain a frequency shifted calibration path signal;

[0020] Performing Hilbert transformation on the frequency-shifted calibration path signal to obtain a calibration path analytical signal;

[0021] The calibration path analysis signal is demodulated to obtain the calibration path angle frequency.

[0022] The present embodiment provides a distance calibration method for an FMCW laser radar system. In the FMCW laser radar system, the longer the distance a signal light wave travels in space, the greater the instantaneous frequency of the light signal obtained after mixing it with a reference wave. Furthermore, since the calibration path has limited effect on improving the ranging accuracy, an FFT transformation and frequency shift are performed on the digital signal of the calibration path before the Hilbert transform to increase the instantaneous frequency of the signal after mixing the calibration path and the reference wave. This does not require increasing the actual length of the calibration path, thereby improving the calibration effect of the calibration path without changing the physical length of the calibration path.

[0023] In an optional implementation, frequency shifting the calibration path frequency domain signal to obtain a frequency-shifted calibration path signal includes:

[0024] Determine an amplitude peak value and a frequency corresponding to the amplitude peak value based on the calibration path frequency domain signal;

[0025] Determine the peak spread based on the amplitude peak, and select frequency domain data within the peak spread using the frequency corresponding to the amplitude peak as a reference point;

[0026] The amplitude peak and the frequency domain data are shifted rightward to a preset frequency shift range to obtain a frequency-shifted calibration path signal; wherein the maximum value of the preset frequency shift range is less than half of the sampling frequency.

[0027] The present embodiment provides a distance calibration method for an FMCW laser radar system, which obtains a frequency-shifted calibration path signal by shifting the amplitude peak and frequency domain data to the right to a preset frequency shift range, thereby increasing the calibration path distance value, improving the calibration effect of the calibration path, and further improving the ranging accuracy of the FMCW laser radar system.

[0028] In an optional implementation, signal processing is performed on the measurement path time domain signal to obtain the measurement path angle frequency, including:

[0029] Perform A / D conversion on the time domain signal of the measurement path to obtain a digital signal of the measurement path;

[0030] Perform Hilbert transformation on the digital signal of the measurement path to obtain the analytical signal of the measurement path;

[0031] The measurement path analysis signal is demodulated to obtain the measurement path angular frequency.

[0032] The present embodiment provides a distance calibration method for an FMCW laser radar system, which obtains a measurement path analysis signal by performing A / D conversion and Hilbert transform on a measurement path time domain signal, and then performs signal demodulation on the measurement path analysis signal to obtain a measurement path angular frequency, thereby laying a foundation for subsequent calculation of a distance value of a target object and improving the calibration accuracy of the distance value of the target object.

[0033] In an optional implementation, distance calibration is performed based on the calibration road angle frequency and the measurement road angle frequency to obtain a distance value of the target object after calibration; wherein the calculation formula of the distance value of the target object after calibration is as follows:

[0034]

[0035] in, Indicates the distance value of the target after calibration, Indicates the measured road angle frequency, Indicates the calibration road angle frequency, represents the physical length of the calibration coil, Indicates the distance value increased after the frequency shift processing of the time domain signal of the calibration path.

[0036] In a third aspect, the present invention provides a distance calibration device for an FMCW laser radar system, which is used to perform the distance calibration method for an FMCW laser radar system according to the second aspect or any corresponding embodiment thereof, the device comprising:

[0037] A first signal processing unit is used to obtain a calibration path time domain signal, and perform frequency shift processing and signal processing on the calibration path time domain signal to obtain a calibration path angle frequency;

[0038] The second signal processing unit is used to obtain a measurement path time domain signal, perform signal processing on the measurement path time domain signal, and obtain a measurement path angle frequency;

[0039] The distance calibration unit is used to perform distance calibration based on the calibration road angle frequency and the measurement road angle frequency to obtain the distance value of the target object after calibration.

[0040] In a fourth aspect, the present invention provides a computer device, comprising: a memory and a processor, the memory and the processor being communicatively connected to each other, the memory storing computer instructions, and the processor executing the distance calibration method of the FMCW lidar system of the second aspect or any corresponding embodiment thereof by executing the computer instructions.

[0041] In a fifth aspect, the present invention provides a computer-readable storage medium having computer instructions stored thereon, the computer instructions being used to enable a computer to execute the distance calibration method for an FMCW lidar system of the first aspect or any two of its corresponding embodiments.

[0042] In a sixth aspect, the present invention provides a computer program product, comprising computer instructions, wherein the computer instructions are used to enable a computer to execute the distance calibration method of the FMCW lidar system of the above-mentioned second aspect or any corresponding embodiment thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0044] Figure 1 is a schematic structural diagram of a FMCW laser radar system according to an embodiment of the present invention;

[0045] Figure 2 is a schematic diagram of triangular wave modulation according to an embodiment of the present invention;

[0046] Figure 3 is a flow chart of a distance calibration method for an FMCW laser radar system according to an embodiment of the present invention;

[0047] Figure 4 is a flow chart of another distance calibration method for an FMCW laser radar system according to an embodiment of the present invention;

[0048] Figure 5 is a flow chart of another distance calibration method for an FMCW laser radar system according to an embodiment of the present invention;

[0049] Figure 6 is a schematic diagram of a flow chart of a signal processing module according to an embodiment of the present invention performing real-time calibration on a measurement path time domain signal using a calibration path time domain signal;

[0050] Figure 7is a schematic diagram of a time domain signal of a calibration path according to an embodiment of the present invention;

[0051] Figure 8 is a schematic diagram for comparing time domain signals of the calibration path before and after frequency shift according to an embodiment of the present invention;

[0052] Fig. 9 is a schematic diagram of a time domain signal of a calibration path after frequency shift according to an embodiment of the present invention;

[0053] Fig.10 is a schematic diagram of the instantaneous frequency of the calibration path after frequency shift according to an embodiment of the present invention;

[0054] Fig.11 is a schematic diagram of a measurement path time domain signal according to an embodiment of the present invention;

[0055] Fig.12 is a schematic diagram of measuring the instantaneous frequency of a path according to an embodiment of the present invention;

[0056] Fig.13 is a schematic diagram of a distance standard deviation according to an embodiment of the present invention;

[0057] Fig.14 is a structural block diagram of a distance calibration device for an FMCW laser radar system according to an embodiment of the present invention;

[0058] Fig.15 It is a schematic diagram of the hardware structure of a computer device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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 those skilled in the art without creative work are within the scope of protection of the present invention.

[0060] The ranging principle of FMCW (Frequency-modulated continuous-wave) radar is that a narrow bandwidth radio wave generated by a signal generator is modulated with an appropriate waveform (such as a triangle wave); a small part of the radio wave is introduced into the mixer as a reference wave; and most of the radio waves are emitted from the transmitting antenna toward the target; the returning signal wave (i.e., echo) is received by the receiving antenna, and is mixed with the reference wave in the mixer to generate a time domain signal (i.e., beat signal), whose frequency is related to the propagation time of the echo and the frequency modulated wave; by demodulating the frequency of the beat signal, the distance of the target relative to the radar can be determined. The radar system using light waves is called FMCW lidar, and its ranging principle is based on the optical FMCW interference system. Since the optical FMCW interferometry method can not only send and receive signals more simply, but also can use various functional optical FMCW interferometers to realize optical FMCW interference, it is more flexible than FMCW radar; and with the continuous development of optical fiber as a waveguide, the development of FMCW lidar based on optical fiber system has been further promoted.

[0061] Due to the deterioration of ranging accuracy caused by noise and other reasons in the FMCW laser radar system, a calibration path is usually added to the system to calibrate the ranging results. The calibration path refers to the introduction of a part of the signal into one end of a waveguide of known length inside the system. The signal output from the other end of the waveguide enters the mixer and mixes with the reference wave to generate a calibration path signal. Using the calibration path signal, the measurement path signal transmitted to the space target and received at the same time can be calibrated, which reduces the impact of system noise on ranging accuracy to a certain extent. In theory, the length of the calibration path affects its calibration effect. A too short calibration path length corresponds to a lower calibration path angular frequency. When demodulating a lower frequency, frequency jumps are easily generated, resulting in a deterioration of the calibration effect; at the same time, when the calibration path length is consistent with the distance to the target, the calibration effect is best (with the ranging accuracy after calibration as the evaluation standard). In summary, the calibration path length should not be too short, and the ranging range of the system should be taken into account.

[0062] For FMCW LiDAR based on optical fiber system, a certain length of calibration path means that a certain length of calibration path optical fiber needs to be added to the device, which will make the overall device larger and place higher requirements on optical path design and structural design. For chip-based FMCW LiDAR that integrates the optical path system on-chip, the length of the calibration path that can be increased is limited, and there are higher requirements for coupling and packaging processes. In summary, the method of increasing the length of the calibration path to optimize the calibration effect and thus improve the ranging accuracy is not applicable to current FMCW LiDAR.

[0063] The embodiment of the present invention provides an FMCW laser radar system and a distance calibration method thereof, for FMCW laser radar (including an optical fiber system-based or chip-based FMCW laser radar), the calibration effect of the calibration path is improved by improving the demodulation algorithm without changing the physical length of the calibration path.

[0064] This embodiment provides a FMCW laser radar system, such as Figure 1 As shown, it includes: a laser 101, a beam splitter 102, a calibration coil 103, a first mixer 104, a second mixer 105, a signal processing module 106 and a lens 107; the laser 101 is connected to the beam splitter 102, and the beam splitter 102 is respectively connected to the calibration coil 103, the second mixer 105 and the lens 107; the first mixer 104 is respectively connected to the calibration coil 103 and the signal processing module 106; the second mixer 105 is respectively connected to the signal processing module 106 and the lens 107;

[0065] The spectrometer 102 is used to obtain the modulated signal wave output by the laser 101, divide the modulated signal wave into a reference wave, a calibration signal and a measurement signal, and transmit the reference wave to the first mixer 104 and the second mixer 105, transmit the calibration signal to the first mixer 104 via the calibration coil 103, and emit the measurement signal to the target object through the lens 107.

[0066] Specifically, the spectrometer 102 divides the modulated signal wave into various waveguides according to different intensity ratios. For example, according to the maximum optical power that each component in the FMCW lidar system can withstand, the spectrometer 102 divides the modulated signal wave into a reference wave, a calibration signal and a measurement signal according to an intensity ratio of 1:9:9.

[0067] The first mixer 104 is used to mix the reference wave and the calibration signal to obtain a calibration time domain signal.

[0068] The second mixer 105 is used to receive the measurement wave sent by the lens 107 and mix the reference wave with the measurement wave to obtain a measurement path time domain signal; wherein the measurement wave is a signal wave generated by the measurement signal after being reflected by the target object to the lens 107.

[0069] Specifically, the measurement signal is transmitted to the target object in space through the lens 107, and returns to the lens 107 after being reflected by the target object, and is introduced into the second mixer 105 to be mixed with the reference wave to obtain a measurement path time domain signal.

[0070] Furthermore, if Figure 2 As shown, taking triangle wave modulation as an example, a complete modulation cycle on the rising edge of the triangle wave [ ], the calculation formula of the vibration electric field of the reference wave and the signal wave (ie, the calibration signal or the measurement signal) before entering the mixer (ie, the first mixer 104 or the second mixer 105) is as follows:

[0071] (1)

[0072] (2)

[0073] in, represents the vibrating electric field of the reference wave, represents the vibrating electric field of the signal wave, represents the vibration amplitude of the reference wave, represents the vibration amplitude of the signal wave, Indicates the delay time of the signal wave relative to the reference wave. Indicates phase, phase The calculation formula is as follows:

[0074] (3)

[0075] in, represents the angular frequency modulation rate, represents the angular frequency at the center of the modulation period, Indicates the initial phase, angular frequency modulation rate The calculation formula is as follows:

[0076] (4)

[0077] in, B Represents the bandwidth, which is the maximum value of the triangle wave.

[0078] Furthermore, the reference wave and the signal wave (i.e., the calibration signal or the measurement signal) enter the mixer (i.e., the first mixer 104 or the second mixer 105). Since the two beams of light come from the same light source, the light signal (beat frequency signal) after the interference between the two is:

[0079] (5)

[0080] in, is the light intensity of the synthetic field (i.e., the beat frequency signal), is the angular frequency of the beat signal, is the initial phase of the beat signal, For time.

[0081] It should be noted that although the square-law detection of the photodetector is used to achieve mixing in actual use, that is, the reference wave and the signal wave are mixed to obtain the sum frequency and the difference frequency, due to the limitation of the bandwidth of the photodetector, only the difference frequency is obtained after filtering out the high frequency, so it is actually a beat frequency signal (that is, the time domain signal of the calibration path or the time domain signal of the measurement path).

[0082] The signal processing module 106 is used to perform frequency shift on the calibration path time domain signal, and use the frequency shifted calibration path time domain signal to perform real-time calibration on the measurement path time domain signal to obtain a distance value of the target object after calibration.

[0083] Specifically, in order to obtain the relative distance of the target object, the delay time of the signal wave relative to the reference wave must be known. That is, the angular frequency of the beat signal must be known. Therefore, it is necessary to demodulate the beat signal and obtain its instantaneous angular frequency. The measurement path time domain signal is calibrated in real time through the calibration path time domain signal to improve the accuracy of the required distance.

[0084] The present embodiment provides an FMCW laser radar system, which realizes mixing processing of a reference wave and a calibration signal through a first mixer, and realizes mixing processing of a reference wave and a measurement wave through a second mixer, and then the signal processing module uses the calibration path time domain signal after frequency shift to perform real-time calibration on the measurement path time domain signal, and can partially calibrate factors affecting the ranging accuracy such as laser drive current noise, triangle wave linearity, time domain white noise, etc., thereby effectively improving the ranging accuracy of the FMCW laser radar. In addition, in actual use, it is found that a too short calibration path length corresponds to a lower calibration path frequency, and frequency hopping is easily generated when demodulating the lower frequency, resulting in loss of calibration effect. By frequency shifting the calibration path time domain signal, the problem of calibration effect failure caused by the calibration path itself can be solved without changing the physical length of the calibration coil, thereby further improving the ranging accuracy.

[0085] According to an embodiment of the present invention, an embodiment of a distance calibration method for an FMCW lidar system is provided. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0086] In this embodiment, a distance calibration method for an FMCW laser radar system is provided, which can be used in the signal processing module 106 in the above-mentioned FMCW laser radar system. Figure 3 is a flow chart of a distance calibration method for an FMCW laser radar system according to an embodiment of the present invention. Figure 3 As shown, the process includes the following steps:

[0087] Step S301, obtaining a calibration path time domain signal, performing frequency shift processing and signal processing on the calibration path time domain signal, and obtaining a calibration path angle frequency.

[0088] Step S302: Acquire a measurement path time domain signal, perform signal processing on the measurement path time domain signal, and obtain a measurement path angle frequency.

[0089] Step S303, performing distance calibration based on the calibration road angle frequency and the measured road angle frequency to obtain a distance value of the target object after calibration.

[0090] Specifically, the calculation formula for the distance value of the target object after calibration is as follows:

[0091] (6)

[0092] in, Indicates the distance value of the target after calibration, Indicates the measured road angle frequency, Indicates the calibration road angle frequency, represents the physical length of the calibration coil, Indicates the distance value increased after the frequency shift processing of the time domain signal of the calibration path.

[0093] The present embodiment provides a distance calibration method for an FMCW laser radar system, which performs frequency shift processing and signal processing on the calibration path time domain signal, and performs signal processing on the measurement path time domain signal, and then performs distance calibration based on the calibration path angular frequency and the measurement path angular frequency. Since the calibration path time domain signal and the measurement path time domain signal are synchronized, factors affecting the ranging accuracy, such as laser drive current noise, triangle wave linearity, time domain white noise, etc., can be partially calibrated. Since the length of the calibration coil is known, the ranging accuracy of the FMCW laser radar system can be further improved without changing the physical length of the calibration coil.

[0094] In this embodiment, a distance calibration method for an FMCW laser radar system is provided, which can be used in the signal processing module 106 in the above-mentioned FMCW laser radar system. Figure 4 is a flow chart of a distance calibration method for an FMCW laser radar system according to an embodiment of the present invention. Figure 4 As shown, the process includes the following steps:

[0095] Step S401, obtaining a calibration path time domain signal, performing frequency shift processing and signal processing on the calibration path time domain signal, and obtaining a calibration path angle frequency.

[0096] Specifically, the above step S401 includes:

[0097] Step S4011, performing A / D conversion (Analog to Digital Converter, conversion of analog signal to digital signal) on the calibration path time domain signal to obtain a calibration path digital signal.

[0098] Step S4012, performing FFT transformation (Fast Fourier Transform) on the calibration path digital signal to obtain a calibration path frequency domain signal.

[0099] Step S4013: frequency-shift the calibration path frequency domain signal to obtain a frequency-shifted calibration path signal.

[0100] Specifically, the calibration path digital signal needs to be transformed into the frequency domain by FFT before Hilbert transformation, and the amplitude peak and the spectrum near it are shifted to the right by a known frequency range to obtain the calibration path signal after frequency shift.

[0101] In some optional implementations, the above step S4013 includes:

[0102] Step a1: determining an amplitude peak and a frequency corresponding to the amplitude peak based on the calibration path frequency domain signal.

[0103] Specifically, after the calibration path digital signal is transformed by FFT, the frequency corresponding to the amplitude peak value in the calibration path frequency domain signal is found by peak finding.

[0104] Step a2, determining the peak spread based on the amplitude peak, and taking the frequency corresponding to the amplitude peak as a reference point, selecting frequency domain data within the peak spread.

[0105] Specifically, frequency domain data within a range of about 1 / 4 times the sampling frequency around the frequency corresponding to the amplitude peak is selected, wherein all frequency domain data within the peak width is selected.

[0106] Step a3, shifting the amplitude peak and frequency domain data to the right to a preset frequency shift range to obtain a frequency-shifted calibration path signal; wherein the maximum value of the preset frequency shift range is less than half of the sampling frequency.

[0107] Specifically, the preset frequency shift range is determined according to the ranging range and the sampling frequency, that is, the preset frequency shift range ensures that the peak broadening after the frequency shift is generally located near the frequency value corresponding to the maximum ranging range and is not greater than 1 / 2 times the sampling frequency.

[0108] Step S4014, performing Hilbert transform (Hilbert transform is a linear operator that generates functions with the same definition domain as functions) on the frequency-shifted calibration path signal to obtain a calibration path analytical signal.

[0109] Specifically, the calibration path resolves the signal The calculation formula is as follows:

[0110] (7)

[0111] in, is the signal after Hilbert transformation of the calibration signal after frequency shift, is the calibration signal after frequency shift, To calibrate the road angle frequency, is the initial phase of the calibration signal after frequency shift, is a pure imaginary number, that is .

[0112] Step S4015, the calibration path analysis signal is demodulated to obtain the calibration path angle frequency.

[0113] Specifically, after demodulating the calibration path analysis signal, its instantaneous angular frequency is obtained, that is, the calibration path angular frequency , and its calculation formula is as follows:

[0114] (8)

[0115] in, is the calibration angle frequency before frequency shift, is the instantaneous angular frequency difference before and after the frequency shift.

[0116] Step S402, obtain the measurement path time domain signal, perform signal processing on the measurement path time domain signal, and obtain the measurement path angle frequency. Figure 3 Step S302 of the illustrated embodiment will not be described in detail here.

[0117] Step S403: perform distance calibration based on the calibration road angle frequency and the measured road angle frequency to obtain the distance value of the target object after calibration. Figure 3 Step S303 of the illustrated embodiment will not be described in detail here.

[0118] The present embodiment provides a distance calibration method for an FMCW laser radar system. In the FMCW laser radar system, the longer the distance a signal light wave travels in space, the greater the instantaneous frequency of the light signal obtained after mixing it with a reference wave. Furthermore, since the calibration path has limited effect on improving the ranging accuracy, an FFT transformation and frequency shift are performed on the digital signal of the calibration path before the Hilbert transform to increase the instantaneous frequency of the signal after mixing the calibration path and the reference wave. This does not require increasing the actual length of the calibration path, thereby improving the calibration effect of the calibration path without changing the physical length of the calibration path.

[0119] In this embodiment, a distance calibration method for an FMCW laser radar system is provided, which can be used in the signal processing module 106 in the above-mentioned FMCW laser radar system. Figure 5 is a flow chart of a distance calibration method for an FMCW laser radar system according to an embodiment of the present invention. Figure 5 As shown, the process includes the following steps:

[0120] Step S501, obtain the calibration path time domain signal, perform frequency shift processing and signal processing on the calibration path time domain signal, and obtain the calibration path angle frequency. Figure 4 Step S401 of the illustrated embodiment will not be described in detail here.

[0121] Step S502: Acquire a measurement path time domain signal, perform signal processing on the measurement path time domain signal, and obtain a measurement path angle frequency.

[0122] Specifically, the above step S502 includes:

[0123] Step S5021, performing A / D conversion on the measurement path time domain signal to obtain a measurement path digital signal.

[0124] Step S5022: Perform Hilbert transform on the measurement path digital signal to obtain a measurement path analytical signal.

[0125] Specifically, the measurement path resolution signal The calculation formula is as follows:

[0126] (9)

[0127] in, To measure the digital signal after Hilbert transformation, To measure the digital signal, To measure the road angle frequency, To measure the initial phase of the digital signal, is a pure imaginary number, that is .

[0128] Step S5023: demodulate the measurement path analysis signal to obtain the measurement path angle frequency.

[0129] Specifically, the road angle frequency is measured The calculation formula of (i.e. the instantaneous angular frequency of the measurement path signal) is as follows:

[0130] (10)

[0131] (11)

[0132] Step S503: perform distance calibration based on the calibration road angle frequency and the measured road angle frequency to obtain the distance value of the target object after calibration. Figure 4Step S403 of the illustrated embodiment will not be described in detail here.

[0133] The present embodiment provides a distance calibration method for an FMCW laser radar system, which obtains a measurement path analysis signal by performing A / D conversion and Hilbert transform on a measurement path time domain signal, and then performs signal demodulation on the measurement path analysis signal to obtain a measurement path angular frequency, thereby laying a foundation for subsequent calculation of a distance value of a target object and improving the calibration accuracy of the distance value of the target object.

[0134] The following is a specific example to illustrate the specific steps of a distance calibration method for an FMCW laser radar system.

[0135] Embodiment 1:

[0136] like Figure 6 As shown, the specific steps of a distance calibration method for an FMCW laser radar system include:

[0137] The mixed calibration path time domain signal is converted into a calibration path digital signal through A / D conversion, such as Figure 7 As shown, the physical length of the calibration coil is 0.8m, the sampling frequency of the calibration digital signal is 250MHz, and the modulation frequency of the triangle wave (i.e. ) is 61035Hz, and the calibration digital signal is superimposed with noise that causes the linearity of the triangle wave to deteriorate, laser drive current noise, time domain random white noise and random sampling noise.

[0138] The calibration digital signal is converted to the frequency domain by FFT, and the peak value of the calibration frequency domain amplitude and its nearby spectrum are shifted to the right. Here, the right frequency shift is set to 1 / 4 of the sampling frequency. The single-sided spectrum of the calibration before and after the frequency shift is shown as follows: Figure 8 As shown; after frequency shift, the time domain signal of the calibration path becomes Fig. 9 As shown; obviously, Figure 7 In comparison, the frequency of the calibration path signal after frequency shift has increased, which means that the corresponding calibration path distance value has increased.

[0139] The calibration path signal after frequency shift is Hilbert transformed to obtain the calibration path analysis signal. The calibration path analysis signal is demodulated to obtain the instantaneous frequency of the calibration path as shown in Fig.10 As shown, all frequencies in the figure are averaged to obtain a frequency of the calibration path after frequency shift.

[0140] While the calibration path signal is being processed, the mixed measurement path time domain signal is converted into a measurement path digital signal through A / D conversion, such as Fig.11As shown in the figure, this measurement path receives the signal of a target object 45m away from the laser radar. The sampling frequency of the measurement path signal is 250MHz, and the modulation frequency of the triangle wave is 61035Hz. In addition to the noise that causes the linearity of the triangle wave to deteriorate, the laser drive current noise, the time domain random white noise and the random sampling noise, there are also random phases and random amplitudes superimposed on the spatial measurement on the digital signal of the measurement path.

[0141] Perform Hilbert transform on the digital signal of the measurement path to obtain the measurement path analysis signal, demodulate the measurement path analysis signal to obtain the instantaneous frequency of the measurement path, such as Fig.12 As shown, all frequencies in the figure are averaged to obtain a measurement path frequency.

[0142] Distance calibration is performed based on the calibration road angle frequency and the measured road angle frequency. The distance value corresponding to 1 / 4 of the sampling frequency is collected and calculated 1000 times for the calibration path and the measurement path frequency. After calibration, 1000 distance values ​​are obtained and the distance standard deviation is calculated. The signals at multiple distances are collected and the distance standard deviation is calculated. Fig.13 The distance accuracy after frequency shift, the distance accuracy before frequency shift, and the distance accuracy of the uncalibrated measurement path are plotted at each distance. Since the smaller the standard deviation, the higher the accuracy, Fig.13 It can be seen that the calibration effect of the calibration road can effectively improve the accuracy of the measurement road distance; after increasing the frequency of the calibration road through frequency shift, the calibration effect of the calibration road is more obvious, and the effect of improving the distance accuracy is more obvious.

[0143] In this embodiment, a distance calibration device for an FMCW laser radar system is also provided, which is used to implement the above-mentioned embodiments and preferred implementation modes, and will not be repeated hereafter. As used below, the term "unit" may be a combination of software and / or hardware that implements a predetermined function. Although the devices described in the following embodiments are preferably implemented in software, the implementation of hardware, or a combination of software and hardware, is also possible and conceivable.

[0144] This embodiment provides a distance calibration device for an FMCW laser radar system. Fig.14 As shown, including:

[0145] The first signal processing unit 1401 is used to obtain a calibration path time domain signal, and perform frequency shift processing and signal processing on the calibration path time domain signal to obtain a calibration path angle frequency;

[0146] The second signal processing unit 1402 is used to obtain a measurement path time domain signal, perform signal processing on the measurement path time domain signal, and obtain a measurement path angle frequency;

[0147] The distance calibration unit 1403 is used to perform distance calibration based on the calibration road angle frequency and the measurement road angle frequency to obtain the distance value of the target object after calibration.

[0148] In some optional implementations, the first signal processing unit 1401 includes:

[0149] The first conversion subunit is used to perform A / D conversion on the calibration path time domain signal to obtain a calibration path digital signal;

[0150] The first transformation subunit is used to perform FFT transformation on the calibration path digital signal to obtain a calibration path frequency domain signal;

[0151] The frequency shift subunit is used to perform frequency shift on the calibration path frequency domain signal to obtain a frequency shifted calibration path signal;

[0152] The second transformation subunit is used to perform Hilbert transformation on the calibration path signal after frequency shift to obtain a calibration path analysis signal;

[0153] The first demodulation subunit is used to perform signal demodulation on the calibration path analysis signal to obtain a calibration path angle frequency.

[0154] In some optional embodiments, the frequency shift subunit is specifically used to determine the amplitude peak and the frequency corresponding to the amplitude peak based on the calibration path frequency domain signal; determine the peak width based on the amplitude peak, and select frequency domain data within the peak width with the frequency corresponding to the amplitude peak as a reference point; move the amplitude peak and the frequency domain data to the right to a preset frequency shift range to obtain a calibration path signal after frequency shift; wherein the maximum value of the preset frequency shift range is less than half of the sampling frequency.

[0155] In some optional implementations, the second signal processing unit 1402 includes:

[0156] The second conversion subunit is used to perform A / D conversion on the measurement path time domain signal to obtain the measurement path digital signal;

[0157] The third transformation subunit is used to perform Hilbert transformation on the measurement path digital signal to obtain a measurement path analytical signal;

[0158] The second demodulation subunit is used to demodulate the measurement path analysis signal to obtain the measurement path angle frequency.

[0159] In some optional implementations, the calculation formula of the distance value of the calibrated target object in the distance calibration unit 1403 is as follows:

[0160]

[0161] in, Indicates the distance value of the target after calibration, Indicates the measured road angle frequency, Indicates the calibration road angle frequency, represents the physical length of the calibration coil, Indicates the distance value increased after the frequency shift processing of the time domain signal of the calibration path.

[0162] The further functional description of each of the above modules and units is the same as that of the above corresponding embodiments and will not be repeated here.

[0163] In this embodiment, a distance calibration device of an FMCW lidar system is presented in the form of a functional unit, where the unit refers to an ASIC (Application Specific Integrated Circuit) circuit, a processor and memory that executes one or more software or fixed programs, and / or other devices that can provide the above functions.

[0164] The embodiment of the present invention also provides a computer device having the above Fig.14 A distance calibration device for an FMCW laser radar system is shown.

[0165] See also Fig.15 , Fig.15 is a schematic diagram of the structure of a computer device provided by an optional embodiment of the present invention, such as Fig.15 As shown, the computer device includes: one or more processors 10, a memory 20, and interfaces for connecting various components, including high-speed interfaces and low-speed interfaces. Various components are connected to each other using different buses for communication, and can be installed on a common mainboard or installed in other ways as needed. The processor can process the instructions executed in the computer device, including instructions stored in or on the memory to display the graphical information of the GUI on an external input / output device (such as, a display device coupled to the interface). In some optional embodiments, if necessary, multiple processors and / or multiple buses can be used together with multiple memories and multiple memories. Similarly, multiple computer devices can be connected, and each device provides some necessary operations (for example, as a server array, a group of blade servers, or a multi-processor system). Fig.15 A processor 10 is taken as an example.

[0166] The processor 10 may be a central processing unit, a network processor or a combination thereof. The processor 10 may further include a hardware chip. The hardware chip may be a dedicated integrated circuit, a programmable logic device or a combination thereof. The programmable logic device may be a complex programmable logic device, a field programmable gate array, a general purpose array logic or any combination thereof.

[0167] The memory 20 stores instructions executable by at least one processor 10, so that the at least one processor 10 executes the method shown in the above embodiment.

[0168] The memory 20 may include a program storage area and a data storage area, wherein the program storage area may store an operating system, an application required for at least one function; the data storage area may store data created according to the use of the computer device, etc. In addition, the memory 20 may include a high-speed random access memory, and may also include a non-transient memory, such as at least one disk storage device, a flash memory device, or other non-transient solid-state storage device. In some optional embodiments, the memory 20 may optionally include a memory remotely arranged relative to the processor 10, and these remote memories may be connected to the computer device via a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0169] The memory 20 may include a volatile memory, such as a random access memory; the memory may also include a non-volatile memory, such as a flash memory, a hard disk or a solid state drive; the memory 20 may also include a combination of the above types of memory.

[0170] The computer device also includes an input device 30 and an output device 40. The processor 10, the memory 20, the input device 30 and the output device 40 may be connected via a bus or other means. Fig.15 The example of connecting through bus is taken in the following.

[0171] The input device 30 can receive input digital or character information, and generate key signal input related to the user settings and function control of the computer device, such as a touch screen, a keypad, a mouse, a track pad, a touch pad, an indicator bar, one or more mouse buttons, a trackball, a joystick, etc. The output device 40 may include a display device, an auxiliary lighting device (e.g., an LED) and a tactile feedback device (e.g., a vibration motor), etc. The above-mentioned display device includes but is not limited to a liquid crystal display, a light emitting diode, a display and a plasma display. In some optional embodiments, the display device may be a touch screen.

[0172] The embodiment of the present invention also provides a computer-readable storage medium. The method according to the embodiment of the present invention can be implemented in hardware, firmware, or can be implemented as a computer code that can be recorded in a storage medium, or can be implemented as a computer code that is originally stored in a remote storage medium or a non-temporary machine-readable storage medium and will be stored in a local storage medium through a network download, so that the method described herein can be stored in such software processing on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. Among them, the storage medium can be a magnetic disk, an optical disk, a read-only storage memory, a random access memory, a flash memory, a hard disk or a solid-state hard disk, etc.; further, the storage medium can also include a combination of the above types of memories. It can be understood that a computer, a processor, a microprocessor controller, or programmable hardware includes a storage component that can store or receive software or computer code. When the software or computer code is accessed and executed by a computer, a processor, or hardware, the method shown in the above embodiment is implemented.

[0173] A part of the present invention may be applied as a computer program product, such as a computer program instruction, which, when executed by a computer, can call or provide the method and / or technical solution according to the present invention through the operation of the computer. Those skilled in the art should understand that the existence of the computer program instruction in a computer-readable medium includes, but is not limited to, a source file, an executable file, an installation package file, etc., and accordingly, the way in which the computer program instruction is executed by the computer includes, but is not limited to: the computer directly executes the instruction, or the computer compiles the instruction and then executes the corresponding compiled program, or the computer reads and executes the instruction, or the computer reads and installs the instruction and then executes the corresponding installed program. Here, the computer-readable medium may be any available computer-readable storage medium or communication medium accessible to the computer.

[0174] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A FMCW laser radar system, characterized in that: The system comprises: a laser, a spectrometer, a calibration coil, a first mixer, a second mixer, a signal processing module and a lens; the laser is connected to the spectrometer, and the spectrometer is respectively connected to the calibration coil, the second mixer and the lens; the first mixer is respectively connected to the calibration coil and the signal processing module; the second mixer is respectively connected to the signal processing module and the lens; The spectrometer is used to obtain the modulated signal wave output by the laser, split the modulated signal wave into a reference wave, a calibration signal and a measurement signal, transmit the reference wave to the first mixer and the second mixer, transmit the calibration signal to the first mixer via the calibration coil, and emit the measurement signal to the target object via the lens; The first mixer is used to mix the reference wave and the calibration signal to obtain a calibration time domain signal; The second mixer is used to receive the measurement wave sent by the lens, and mix the reference wave with the measurement wave to obtain a measurement path time domain signal; wherein the measurement wave is a signal wave generated by the measurement signal being reflected from the target object to the lens; The signal processing module is used to perform frequency shift on the calibration path time domain signal, and use the frequency shifted calibration path time domain signal to perform real-time calibration on the measurement path time domain signal to obtain a distance value of the target object after calibration.

2. A distance calibration method for an FMCW laser radar system, characterized in that: A signal processing module applied to the FMCW laser radar system as claimed in claim 1; the method comprising: Acquire a calibration path time domain signal, and perform frequency shift processing and signal processing on the calibration path time domain signal to obtain a calibration path angle frequency; Acquire a measurement path time domain signal, perform signal processing on the measurement path time domain signal, and obtain a measurement path angle frequency; A distance calibration is performed based on the calibration road angle frequency and the measurement road angle frequency to obtain a distance value of the calibrated target object.

3. The method according to claim 2, characterized in that The calibration path time domain signal is subjected to frequency shift processing and signal processing respectively to obtain the calibration path angle frequency, including: Performing A / D conversion on the calibration path time domain signal to obtain a calibration path digital signal; Performing FFT transformation on the calibration path digital signal to obtain a calibration path frequency domain signal; Performing frequency shift on the calibration path frequency domain signal to obtain a frequency shifted calibration path signal; Performing Hilbert transformation on the frequency-shifted calibration path signal to obtain a calibration path analysis signal; The calibration path analysis signal is demodulated to obtain the calibration path angle frequency.

4. The method according to claim 3, characterized in that The step of frequency-shifting the calibration path frequency domain signal to obtain a frequency-shifted calibration path signal includes: Determine an amplitude peak value and a frequency corresponding to the amplitude peak value based on the calibration path frequency domain signal; Determine a peak spread based on the amplitude peak, and select frequency domain data within the peak spread with the frequency corresponding to the amplitude peak as a reference point; The amplitude peak value and the frequency domain data are shifted rightward to a preset frequency shift range to obtain the calibration path signal after the frequency shift; wherein the maximum value of the preset frequency shift range is less than half of the sampling frequency.

5. The method according to claim 2, characterized in that: The measuring path time domain signal is processed to obtain the measuring path angle frequency, including: Performing A / D conversion on the measurement path time domain signal to obtain a measurement path digital signal; Perform Hilbert transformation on the digital signal of the measurement path to obtain the analytical signal of the measurement path; The measurement path analysis signal is demodulated to obtain the measurement path angular frequency.

6. The method according to claim 2, characterized in that The distance calibration is performed based on the calibration road angle frequency and the measurement road angle frequency to obtain the distance value of the calibrated target object; wherein the calculation formula of the distance value of the calibrated target object is as follows: in, Indicates the distance value of the target after calibration, Indicates the measured road angle frequency, Indicates the calibration road angle frequency, represents the physical length of the calibration coil, Indicates the distance value increased after the frequency shift processing of the time domain signal of the calibration path.

7. A distance calibration device for an FMCW laser radar system, characterized in that: The device is used to perform the distance calibration method of the FMCW laser radar system according to any one of claims 2 to 6, comprising: A first signal processing unit is used to obtain a calibration path time domain signal, and perform frequency shift processing and signal processing on the calibration path time domain signal to obtain a calibration path angle frequency; A second signal processing unit is used to obtain a measurement path time domain signal, and perform signal processing on the measurement path time domain signal to obtain a measurement path angle frequency; The distance calibration unit is used to perform distance calibration based on the calibration road angle frequency and the measurement road angle frequency to obtain the distance value of the calibrated target object.

8. A computer device, characterized in that: include: A memory and a processor, wherein the memory and the processor are communicatively connected to each other, the memory stores computer instructions, and the processor executes the distance calibration method of the FMCW laser radar system according to any one of claims 2 to 6 by executing the computer instructions.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer instructions, and the computer instructions are used to enable a computer to execute the distance calibration method of the FMCW laser radar system according to any one of claims 2 to 6.

10. A computer program product, characterized in that The method comprises computer instructions for causing a computer to execute the distance calibration method for the FMCW laser radar system according to any one of claims 2 to 6.

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