Millimeter wave radar measurement precision compensation method

Abstract

The invention relates to the technical field of millimeter-wave radars, in particular to a millimeter-wave radar measurement precision compensation method, which comprises a radar information acquisition module, a radar correction parameter extraction module and a radar in-service measurement and verification module, and is characterized in that the radar information acquisition module transmits and receives a fixed-frequency electromagnetic wave signal; the radar correction parameter extraction module takes the linear displacement echo signal as input to obtain a signal correction parameter; in the radar in-service measurement and verification, parameterization compensation is carried out on the dynamic echo signal, arc tangent demodulation is carried out, and finally displacement information in the echo signal is obtained. The method has the advantages that the problem of fluctuation of measurement results of the millimeter-wave radar under attenuation modulation and multiple reflection backgrounds is solved, an I / Q consistency orthogonalization compensation method is provided, relative average errors are 3.2 micrometers and 2.4 micrometers respectively compared with measurement results of a laser displacement sensor, and micron-order precision compensation and verification of millimeter-wave radar measurement are achieved.

Description

Technical Field

[0001] This application relates to the technical field of radar ranging, and particularly to a method for compensating the measurement accuracy of a millimeter-wave radar. Background Art

[0002] Millimeter-wave radar is a highly sensitive measurement system that has attracted wide attention in recent years. Due to its advantages such as low manufacturing cost, small size, high sensitivity, and non-contact measurement, millimeter-wave radar is widely used in various fields such as earthquake and avalanche monitoring, vehicle identification, workpiece micro-motion measurement, and human vital sign monitoring. According to the difference in measurement principles, millimeter-wave radar can be divided into two categories: Frequency-Modulated Continuous Wave (FMCW) and Phase-Modulated Continuous Wave (PMCW). Compared with PMCW radar, FMCW radar is sensitive to narrowband noise, often requires complex spectrum analysis techniques, and has a higher cost. The measurement process of PMCW radar is based on the micro-Doppler effect, providing higher micro-distance and micro-velocity measurement accuracy

[12] . At the same time, because the phase change measurement is more sensitive to targets with acceleration or non-linear motion trends, PMCW radar has better application prospects in identifying complex moving targets.

[0003] However, the measurement accuracy of millimeter-wave radar is often affected by many factors. There is a quadrature homodyne structure in the front-end configuration of millimeter-wave radar to extract the echo phase information by outputting two orthogonal signals (I / Q signals). However, the congenital / acquired defects of the electronic hardware path will cause the quadrature homodyne structure of the radar to be damaged, resulting in obvious amplitude-phase imbalance (i.e., I / Q imbalance) and DC offset in the I / Q signals, leading to fluctuations in the radar measurement results and even large deviations from the true values. In addition, the atmospheric attenuation and multiple reflections of electromagnetic waves will affect the performance of correction / compensation methods (such as piecewise elliptical fitting, Schmidt orthogonalization process, singular value decomposition, etc.). The atmospheric attenuation of electromagnetic waves will cause the echo energy to decrease non-linearly with the increase of the distance between the radar and the target, resulting in an attenuation modulation phenomenon in the I / Q signals, aggravating the spectrum leakage and affecting the signal quality. At the same time, the multiple reflections of electromagnetic waves between the radar and the target will cause the echo to be repeatedly delayed and received by the receiving end, resulting in multiple harmonic coupling phenomena in the I / Q signals, increasing the complexity and accuracy of I / Q imbalance correction / compensation. Therefore, compensating for and suppressing the I / Q imbalance and DC offset in the I / Q signals is of great significance for improving the measurement accuracy of millimeter-wave radar under the background of attenuation modulation and multiple reflections.

[0004] Static parameter compensation for dynamic signals is a practical parametric compensation strategy. Since I / Q imbalance and DC offset are only related to the inherent / acquired defects of the hardware channels in the millimeter-wave radar quadrature homodyne structure, the I / Q signals in different displacement scenarios will have the same I / Q imbalance and DC offset. Therefore, extracting the I / Q imbalance and DC offset parameters using the I / Q signals generated by linear displacement and applying them to dynamic signal compensation will greatly reduce the signal processing complexity and improve the compensation efficiency and feasibility. However, the atmospheric attenuation and multiple reflections of electromagnetic waves also affect the quality of the I / Q signals generated by linear displacement, and the spectral leakage, multiple harmonics, and noise in the signals still affect the compensation and suppression of I / Q imbalance and DC offset. Therefore, accurately extracting the I / Q imbalance and DC offset parameters in the I / Q signals generated by the linear displacement between the radar and the target under the coupling action of attenuation modulation and multiple harmonics is the core issue for improving the measurement accuracy of millimeter-wave radars.

[0005] Based on this, a method for compensating static I / Q signals and extracting parameters of millimeter-wave radars has been developed, and a verification device for compensating millimeter-wave radar measurements with micron-level accuracy has been designed, which has important engineering significance and good application prospects for realizing micron-level measurements of millimeter-wave radars. Summary of the Invention

[0006] The present invention provides a micron-level accuracy compensation method for millimeter-wave radar measurements to solve the technical problems existing in the above-mentioned background technology. To achieve the above object, the micron-level accuracy compensation method and verification device for millimeter-wave radar measurements provided by the present invention include:

[0007] Radar information acquisition module: Transmit and receive electromagnetic waves with a fixed frequency through a 120 GHz millimeter-wave radar, output I / Q signals through the quadrature homodyne structure of the radar, and finally transmit them to the signal acquisition control processing platform;

[0008] Radar correction parameter extraction module: Take the I / Q signals generated by the linear displacement echo as the input of the amplitude-phase correction model to obtain the correction parameters;

[0009] In-service measurement and verification module of the radar: Perform parametric compensation on the I / Q signals generated by the dynamic echo and perform arctangent demodulation to finally obtain the displacement information in the echo signal;

[0010] The radar information acquisition module includes the following:

[0011] Millimeter-wave radar module: Used to transmit and receive electromagnetic wave signals with a frequency of 120 GHz, and output a two-way orthogonal signal according to the echo. The two-way orthogonal signal specifically includes: an in-phase I channel and a quadrature-phase Q channel, that is, I / Q signals. And a programmable logic operational amplifier is used to apply a controllable gain to the I / Q signals.

[0012] Precision 3D Displacement Platform: A fine-tuning platform used to install and adjust the spatial position of a millimeter-wave radar, capable of achieving fine-tuning of positions in three degrees of freedom in the Cartesian coordinate system in space.

[0013] Electrically Controlled Slide and Its Controller: While serving as a platform for installing and adjusting the spatial position of the precision 3D displacement platform, the electrically controlled slide also functions as a device for generating and controlling linear displacement. The precision 3D displacement platform is installed on the electrically controlled slide, enabling position changes with a single degree of freedom and a constant moving speed, driving a linear displacement between the precision 3D displacement platform and the millimeter-wave radar and the target object. The slide controller is used to quantitatively control the moving speed and direction of the electrically controlled slide.

[0014] Target Object to be Measured: The measurement target of the millimeter-wave radar and its system, including but not limited to metal objects such as aero-engine turbine blades, rectangular blades, and rotary cutters.

[0015] Motor Module: Includes a servo motor and a servo motor controller. The motor shaft is connected to the target object to be measured through connecting devices such as a flange to quantitatively control the rotation speed and direction of the target object to be measured.

[0016] DAQ Signal Acquisition Module: Includes a DAQ acquisition card, a PC-side oscilloscope, and a signal acquisition platform. The DAQ acquisition card converts the dual-channel quadrature analog signal after the logic operation amplification module into a digital signal and transmits it to the PC-side oscilloscope for visualization. The signal acquisition platform can control the sampling frequency of the digital signal and perform directional address storage.

[0017] The radar correction parameter extraction module includes the following:

[0018] The radar correction parameter extraction module takes the I / Q signal output by the radar after a linear displacement with the target object as the input of the amplitude-phase correction model and outputs the I / Q imbalance parameters and DC offset of the I / Q signal; the amplitude-phase model is specifically the I / Q consistency orthogonalization compensation method; the correction parameters specifically include: amplitude correction parameter A a , phase correction parameter A p , I / Q dual-channel DC offset parameters I0 and Q0;

[0019] For the I / Q channel signals I[n] and Q[n] in the I / Q consistency orthogonalization compensation method in the radar correction parameter extraction module, where n = 1,…,N and N is the total data length, it is specifically as follows:

[0020] Step S11, eliminate the DC offset and high-frequency noise in the I / Q signal through a differential-filter combination operation, and preliminarily suppress multiple harmonic interferences, and output signals and can be expressed as:

[0021]

[0022] where m = 1, …, N - 1 represents a single discrete data point, A b represents the gain of the logic operational amplifier, J represents the number of multiple reflections of the electromagnetic wave between the radar and the target, λ represents the frequency of the electromagnetic wave, v represents the relative velocity between the radar and the target, f s represents the sampling frequency, and x0 represents the initial distance between the radar and the target. K e and respectively represent the attenuation modulation term, amplitude imbalance term, and phase imbalance term in the signal and . The DC offsets I0 and Q0 of the I / Q channel signals can be estimated as:

[0023]

[0024] where n = 1, …, N - 2.

[0025] Step S12: Utilize the all-pass property of the Hilbert transform to construct an amplitude-phase correction factor in the frequency domain to obtain the initial value of the correction parameter, and construct an I / Q consistency orthogonality objective function to optimize the correction parameter. The amplitude-phase correction factor constructed in the frequency domain can be expressed as:

[0026]

[0027] where exp(·) represents the exponential function, A a represents the initial value of the amplitude imbalance, A p represents the initial value of the phase imbalance, k represents the discrete points uniformly distributed on the frequency axis, N represents the total data length of the signal, and i represents the imaginary unit; then, transform the signal to the frequency domain through Fourier transform and couple it with the amplitude-phase correction factor. The coupled signal can be expressed as:

[0028]

[0029] where and respectively represent the amplitude responses on the negative frequency axis and the positive frequency after the signal is coupled with the amplitude-phase correction factor C O . Then, recombine and and transform them back to the time-domain signal

[0030]

[0031] To further optimize the amplitude-phase imbalance parameter A a and A p , the I / Q consistency orthogonality objective function is constructed as follows:

[0032]

[0033] where α is the adjustment factor, and M IQ is the combined constraint term for consistency and orthogonality, and its expanded mathematical structure is:

[0034]

[0035] where represents the initial phase angles of each harmonic of the signals and . When is satisfied, the combined constraint term M IQ will approach 1, and the objective function converges, thus realizing the optimization of A a and A p . Then, the optimized values of the amplitude-phase imbalance parameters and are coupled into the signal , and the inverse Hilbert transform is performed to restore the phase of the signal :

[0036]

[0037] where H -1 {·} represents the inverse Hilbert operator. Further, considering the additional amplitude-phase imbalance error caused by the inverse Hilbert transform, the Schmidt orthogonalization process is introduced to suppress it. The Schmidt orthogonalization process can be expressed as:

[0038]

[0039] where E{·} represents the averaging operator.

[0040] After correcting the I / Q signals, to solve the problem that the evaluation range of the arctangent algorithm is limited, i.e., in , a phase unwrapping operation is added to obtain the long-range displacement change, and the calculation formula is as follows:

[0041]

[0042] where unwrap[·] is the phase unwrapping operator.

[0043] In summary, in step S1, according to the I / Q consistency orthogonalization compensation method, the correction parameter A a , A p , I0 and Q0 are obtained, and the long-range displacement change is obtained by using the arctangent and phase unwrapping algorithms.

[0044] The in-service measurement and verification module of the radar includes the following:

[0045] The relative position of the millimeter-wave radar and the target to be measured is adjusted by using an electric control slide table and a precision 3D displacement platform. The target to be measured is driven by a servo motor to rotate at a fixed speed and direction. The DAQ acquisition module is used to collect and store the dynamic I / Q signals output by the radar. The correction parameters obtained by the radar correction parameter extraction module are used to compensate the dynamic I / Q signals. For the data characteristics of the echoes of the rotating blade and the rotating tool, the tip clearance and the radial displacement of the tool are obtained by using the power positioning method and the direct demodulation method respectively. Finally, the measurement results will be compared and analyzed with the measurement results of the laser rangefinder.

[0046] Furthermore, the compensation of the dynamic I / Q signals includes the following:

[0047] Step S21, for the dynamic I / Q signals I D [m] and Q D [m] output by the radar, the correction parameters I0 and Q0 obtained by the radar correction parameter extraction module are used to compensate the DC offset. This process can be described as:

[0048]

[0049] Using the amplitude-phase correction factor, the correction parameters A a and A p obtained by the radar correction parameter extraction module are coupled into the signal . The specific steps are the same as those in formulas (3) to (5). The inverse Hilbert transform is performed on the obtained signal to obtain the signal To further suppress the inverse Hilbert error, the Schmidt orthogonalization process is used for processing:

[0050]

[0051] Among them,

[0052] Furthermore, the power positioning method includes the following:

[0053] For the periodic mutation response property of the phase of the rotating blade echo, using the signals and Calculate the enhanced power of the echo signal to determine the time when the blade tip reaches the lower end of the millimeter-wave radar. The calculation method of the enhanced power can be described as follows:

[0054]

[0055] By using the maximum point of the enhanced power of the echo signal in the time domain, the arrival time of the blade tip can be located to determine the time range when the blade sweeps across the lower end of the radar, and finally the extraction of the blade tip clearance information is completed.

[0056] Furthermore, the direct demodulation method includes the following content:

[0057] Regarding the property that the echo phase of the rotating tool is continuous, use the signal and to directly calculate the phase change of the echo signal and demodulate it into the radial displacement. This process can be described as follows:

[0058]

[0059] After obtaining the blade tip clearance of the rotating blade and the radial displacement of the rotating tool by using the power positioning method and the direct demodulation method, use a laser rangefinder to measure the same target object respectively. The measurement results will be compared with the measurement results after compensation by the millimeter-wave radar, and error analysis will be carried out.

[0060] The beneficial effects of the present invention compared with the prior art are as follows:

[0061] The present invention provides a new method and process for millimeter-wave radar micron-level measurement compensation, namely the I / Q consistency orthogonalization parameter compensation method, and systematically elaborates the corresponding measurement mechanism and steps. For the process of extracting correction parameters, first, perform differential-filtering preprocessing on the signal to eliminate and initially suppress the DC offset and multiple harmonic couplings in the radar I / Q signals. Then, construct an amplitude-phase correction factor in the frequency domain and couple it into the Q-channel signal to obtain the initial value of the I / Q imbalance parameters. Then, construct an I / Q consistency orthogonalization objective function to optimize the I / Q imbalance parameters. Finally, use the Schmidt orthogonalization process to suppress the additional amplitude-phase errors caused by the inverse Hilbert transform. For the dynamic measurement signal compensation process, first use the obtained correction parameters to suppress and compensate the DC offset and I / Q imbalance of the dynamic I / Q signals respectively. Then, regarding the characteristics of the echo signal of the rotating blade, use the power positioning method to determine the time range when the blade sweeps across the lower end of the radar and complete the extraction of the blade tip clearance information. At the same time, regarding the characteristics of the echo signal of the rotating tool, use the direct demodulation method to obtain the radial displacement information of the tool. Finally, the accuracy and feasibility of the I / Q consistency orthogonalization parameter compensation method in millimeter-wave radar micron-level measurement are verified through simulation and experiments. Description of the Drawings

[0062] Figure 1 System framework flowchart of the present invention

[0063] Figure 2 Flowchart of the radar information acquisition module of the present invention

[0064] Figure 3 Principle diagram of millimeter-wave radar measurement of the present invention

[0065] Figure 4 Example model diagram of the millimeter-wave radar measurement and verification device of the present invention

[0066] Figure 5 Interface diagram of the signal control processing platform of the present invention

[0067] Figure 6 Flowchart of the extraction of radar I / Q imbalance parameters of the present invention

[0068] Figure 7 Analysis diagram of the simulation I / Q signal and compensation error of the present invention: (a) Simulation waveform of the I / Q channel; (b) Simulation I / Q constellation diagram; (c) Frequency-domain response of the simulation I / Q signal; (d) Frequency-domain response of the simulation I / Q after compensation; (e) Measurement results of the simulation linear displacement before and after compensation; (f) Measurement error of the simulation linear displacement before and after compensation;

[0069] Figure 8 Example of the tip clearance measurement of the present invention (parameter extraction): (a) I / Q waveform of the linear displacement based on the tip; (b) I / Q constellation diagram; (c) I / Q constellation diagram after compensation; (d) Measurement results of the linear displacement before and after compensation;

[0070] Figure 9 Example of the tip clearance measurement of the present invention (dynamic measurement compensation): (a) I / Q waveform of the dynamic tip clearance measurement; (b) I / Q waveform after compensation; (c) I / Q enhanced power; (d) Comparison of the measurement results with the laser measurement results;

[0071] Figure 10 Example of the tool radial displacement measurement of the present invention (parameter extraction): (a) I / Q waveform of the linear displacement based on the tool axis; (b) I / Q constellation diagram; (c) I / Q constellation diagram after compensation; (d) Measurement results of the linear displacement before and after compensation;

[0072] Figure 11 Example of the tool radial displacement measurement of the present invention (dynamic measurement compensation): (a) I / Q waveform of the dynamic tool radial measurement; (b) I / Q waveform after compensation; (c) Comparison of the measurement results with the laser measurement results; (d) Comparison of the maximum radial displacement between the laser and radar measurements;

[0073] Reference signs

[0074] ForFigure 4 The reference numerals in the exemplary model of the millimeter-wave radar measurement and verification device are explained in detail as follows:

[0075] 1. Electrically controlled slide table; 2. Precision 3D displacement platform; 3. Millimeter-wave radar; 4. Servo motor; 5. Object to be measured; 6. Laser displacement sensor; 7. Servo motor controller; 8. Electrically controlled slide table controller; 9. DAQ signal acquisition module; 10. Signal control and processing module. Specific implementation manners

[0076] The embodiments of the present invention are described in detail below. The examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the present invention, and should not be construed as a limitation to the present invention.

[0077] The micron-level accuracy compensation method for millimeter-wave radar measurement is as Figure 1 shown and specifically includes the following contents:

[0078] Radar information acquisition module: Transmit and receive fixed-frequency electromagnetic waves through a 120 GHz millimeter-wave radar, output I / Q signals through the quadrature homodyne structure of the radar, and finally transmit them to the signal acquisition control and processing platform;

[0079] Radar correction parameter extraction module: Take the I / Q signals generated by the linear displacement echo as the input amplitude and phase correction model input to obtain the correction parameters;

[0080] In-service measurement and verification module of the radar: Perform parametric compensation on the I / Q signals generated by the dynamic echo and perform arctangent demodulation to finally obtain the displacement information in the echo signal;

[0081] The radar information acquisition module specifically includes:

[0082] Millimeter-wave radar module: Used to transmit and receive electromagnetic wave signals with a frequency of 120 GHz and output dual-channel orthogonal signals according to the echo. The dual-channel orthogonal signals specifically include: in-phase I channel and quadrature-phase Q channel, that is, I / Q signals. And use a programmable logic operational amplifier to apply a controllable gain to the I / Q signals.

[0083] Precision 3D displacement platform: A fine-tuning platform for installing and adjusting the spatial position of the millimeter-wave radar, which can perform fine-tuning of the position in three degrees of freedom of the Cartesian coordinate system in space.

[0084] Electrically Controlled Slide and Its Controller: While the electrically controlled slide serves as a platform for installing and adjusting the spatial position of a precision 3D displacement platform, it also functions as a device for generating and controlling linear displacement. The precision 3D displacement platform is installed on the electrically controlled slide, enabling position changes with a single degree of freedom and a constant moving speed, driving a linear displacement between the precision 3D displacement platform, the millimeter-wave radar, and the target object. The slide controller is used to quantitatively control the moving speed and direction of the electrically controlled slide.

[0085] Target Object to be Measured: The measurement target of the millimeter-wave radar and its system, including but not limited to metal objects such as aeroengine turbine blades, rectangular blades, and rotary cutters.

[0086] Motor Module: Comprising a servo motor and a servo motor controller, the motor shaft is connected to the target object to be measured through connecting devices such as a flange, achieving quantitative control of the rotation speed and direction of the target object to be measured.

[0087] DAQ Signal Acquisition Module: Comprising a DAQ acquisition card, a PC-side oscilloscope, and a signal acquisition platform. The DAQ acquisition card converts the dual-channel quadrature analog signal after the logic operation amplification module into a digital signal and transmits it to the PC-side oscilloscope for visualization. The signal acquisition platform can control the sampling frequency of the digital signal and perform directional address storage.

[0088] Furthermore, the working process of the radar information acquisition module includes the following steps:

[0089] Regarding the radar signal acquisition process as Figure 2 shown, the measurement principle of the millimeter-wave radar module is as Figure 3 , the example model of the millimeter-wave radar measurement and verification device is as Figure 4 shown, and the signal acquisition control processing platform is as Figure 5 shown in.

[0090] Regarding the parameter extraction process, the target object and the radar will be in a relatively stationary state. By adjusting the precision 3D displacement platform and the electrically controlled slide, the radar and the target object are on the same horizontal line. By controlling the electrically controlled slide, the millimeter-wave radar is driven to move directionally at a fixed moving speed, and at the same time, the DAQ acquisition module is used to acquire and store the radar I / Q signals for transmission to the radar correction parameter extraction module.

[0091] Regarding the dynamic signal acquisition process, the relative position between the target object and the radar will change. The electrically controlled slide and the moving precision 3D displacement platform are used to adjust the initial position of the millimeter-wave radar and make it on the same horizontal plane as the target object. The motor module is in the working state, driving the target object to rotate at a fixed speed. At the same time, the DAQ acquisition module is used to acquire and store the radar I / Q signals for transmission to the radar in-service measurement and verification module.

[0092] Specifically, it includes the following content:

[0093] Step S21, using the correction parameter A a ,A p ,I0, Q0, to obtain the compensated dynamic I / Q signals;

[0094] Step S22, adopting the power positioning method to extract the position where the peak value of the I / Q signal is located;

[0095] Step S23, adopting the direct demodulation method to obtain the displacement information in the phase of the I / Q signal;

[0096] Based on the peak position determined in step S22, locate the position with the largest displacement change to achieve single-point distance measurement. Based on the displacement information calculated in step S23, achieve continuous displacement measurement.

[0097] The introduction of the parameters of each module is shown in Table 1:

[0098] Table 1 Introduction of module parameters

[0099]

[0100] The radar correction parameter extraction module specifically includes the construction and coupling of the frequency-domain amplitude-phase correction factor, the construction of the I / Q consistency orthogonalization objective function, and the suppression of the inverse Hilbert amplitude-phase error.

[0101] The in-service measurement and verification module of the radar specifically includes the compensation of the I / Q signals of the tip clearance of the rotating blade, the positioning of the tip clearance, and the comparison with the laser measurement results; the compensation of the I / Q signals of the radial displacement of the rotating tool, the calculation of the tool radial displacement, and the comparison with the laser measurement results.

[0102] To verify the effectiveness of the radar correction parameter extraction module, a compensation model including DC offset, amplitude-phase imbalance, attenuation modulation, and multiple harmonic coupling is constructed as follows:

[0103]

[0104] where n = 1, …, N is the data point identifier of the discrete I / Q signals, x0 is the initial distance between the radar and the target, Δφ is the phase imbalance parameter, K e is the attenuation index, D I is the DC offset of the I-channel number, D Q is the DC offset of the Q-channel number, A b is the amplitude gain, v is the relative velocity between the radar and the target, f s is the sampling frequency, λ is the electromagnetic wave wavelength, and J is the number of multiple reflections of the electromagnetic wave between the radar and the target.

[0105] Set the parameter K in the simulation model e = 1.5, Ab = 1, D I = 0.25V, D Q = 0.3V, f s = 4000, v = 1.17mm / s. The time-domain waveforms of the simulated I / Q signals are as Figure 7 (a) shown; the I-Q locus diagram is as Figure 7 (b), and its correction process is as follows:

[0106] Step S11, eliminate the DC offset and high-frequency noise in the I / Q signal through differential-filter combination operation, and preliminarily suppress the multiple harmonic interference, and output the signals and can be expressed as:

[0107]

[0108] where m = 1,..., N-1 represents a single discrete data point. The DC offset of the I / Q channel signal can be estimated as:

[0109]

[0110] Step S12, utilize the all-pass property of the Hilbert transform to construct the amplitude-phase correction factor in the frequency domain to obtain the initial value of the correction parameter, and construct the I / Q consistency orthogonality objective function to realize the optimization of the correction parameter. The amplitude-phase correction factor constructed in the frequency domain can be expressed as:

[0111]

[0112] where exp(·) represents the exponential function, A a represents the initial value of the amplitude imbalance, A p represents the initial value of the phase imbalance, k represents the discrete points uniformly distributed on the frequency axis, N represents the total data length of the signal, and i represents the imaginary unit; then, transform the signal to the frequency domain through Fourier transform, and couple it with the amplitude-phase correction factor. The coupled signal can be expressed as:

[0113]

[0114] where, and respectively represent the amplitude responses on the negative frequency axis and the positive frequency after the signal is coupled with the amplitude-phase correction factor C O . Then, recombine and and transform them to the time-domain signal

[0115]

[0116] To further optimize the amplitude-phase imbalance parameter A a and A p , the I / Q consistency orthogonality objective function is constructed as follows:

[0117]

[0118] where α is the adjustment factor, and M IQ is the combined constraint term for consistency and orthogonality, and its expanded mathematical structure is:

[0119]

[0120] where represents the initial phase angle of each harmonic of the signals and . When is satisfied, the combined constraint term M IQ will approach 1, and the objective function converges, thereby realizing the optimization of A a and A p . Then, the optimized values of the amplitude-phase imbalance parameters and are coupled into the signal , and the inverse Hilbert transform is performed to restore the phase of the signal :

[0121]

[0122] where H -1 {·} represents the inverse Hilbert operator. Further, considering the additional amplitude-phase imbalance error caused by the inverse Hilbert transform, the Schmidt orthogonalization process is introduced to suppress it. The Schmidt orthogonalization process can be expressed as:

[0123]

[0124] where E{·} represents the averaging operator.

[0125] After correcting the I / Q signals, to solve the problem that the evaluation range of the arctangent algorithm is limited, i.e., within , a phase unwrapping operation is added to obtain the long-range displacement change, and the calculation formula is as follows:

[0126]

[0127] where unwrap[·] is the phase unwrapping operator.

[0128] In summary, in step S1, according to the I / Q consistency orthogonality compensation method, the correction parameter A a , A p , I0 and Q0 are obtained, and the long-range displacement change is obtained by using the arctangent and phase unwrapping algorithms.

[0129] To verify the effectiveness of the radar in-service measurement and verification module, the radar I / Q imbalance parameter extraction and dynamic measurement of the rotating blade tip clearance and the rotating tool radial displacement are carried out respectively.

[0130] For the I / Q imbalance parameter extraction process in the rotating blade tip clearance measurement example, the initial distance between the blade tip and the millimeter-wave radar is set to 2.5 mm, the sampling frequency f s = 2 kHz, and the moving speed of the electric control slide table is 1.17 mm / s, driving a linear displacement between the millimeter-wave radar and the blade tip. The I / Q signal constellation diagram output by the radar is as shown in Figure 8 (a), and the compensated I / Q signal constellation diagram is as shown in Figure 8 (b). The comparison of the linear displacement measurement results is as shown in Figure 8 (c), and the error between the compensated result and the ideal displacement is as shown in Figure 8 (d). After compensation, the absolute error of the linear displacement measurement result is 12.4 μm.

[0131] For the dynamic measurement process in the rotating blade tip clearance measurement example, the fixed distance between the blade tip and the millimeter-wave radar is set to 4.5 mm, the sampling frequency f s = 100 kHz, and the blade rotation speed is 40 RPM. During this process, the time-domain waveform of the I / Q dynamic signal output by the radar is as shown in Figure 9 (a), and the compensated time-domain waveform of the I / Q dynamic signal is as shown in Figure 9 (b). The position of the blade tip clearance located by the power positioning method is as shown in Figure 9 (c), and the comparison between the compensated blade tip clearance measurement result and the laser measurement result is as shown in Figure 9 (d). Compared with the laser rangefinder, the relative measurement error within three circles is 3.2 μm.

[0132] For the I / Q imbalance parameter extraction process in the rotating tool radial displacement measurement example, the initial distance between the tool shaft body and the millimeter-wave radar is set to 3.0 mm, the sampling frequency f s = 4 kHz, and the moving speed of the electric control slide table is 2.34 mm / s, driving a linear displacement between the millimeter-wave radar and the blade tip. The I / Q signal constellation diagram output by the radar is as shown in Figure 10 (a), and the compensated I / Q signal constellation diagram is as shown in Figure 10 (b). The comparison of the linear displacement measurement results is as shown in Figure 10As shown in (c), the error between the compensated result and the ideal displacement is as Figure 10 shown in (d). After compensation, the absolute error of the linear displacement measurement result is 5.4 μm.

[0133] For the dynamic measurement process in the example of measuring the radial displacement of a rotating tool, set the fixed distance between the tool shaft body and the millimeter-wave radar (Radar) to 2.5 mm, and the sampling frequency f s = 100 kHz, and the blade rotation speed is 80 RPM. During this process, the time-domain waveform of the I / Q dynamic signal output by the radar is as Figure 11 shown in (a), and the time-domain waveform of the compensated I / Q dynamic signal is as Figure 11 shown in (b), and the tip clearance position located by the power positioning method is as Figure 11 shown in (c), and the comparison between the compensated tip clearance measurement result and the laser (Laser) measurement result is as Figure 11 shown in (d). Compared with the laser rangefinder, the average relative measurement error within three circles is 2.4 μm.

[0134] In summary, the present invention provides a millimeter-wave radar micron-level measurement compensation method, namely the I / Q consistency orthogonalization compensation method, and systematically elaborates the corresponding measurement and verification mechanisms and steps. For the two measurement examples of the tip clearance of a rotating blade and the radial displacement of a rotating tool, in the process of extracting the I / Q imbalance parameters, the proposed method respectively achieves absolute mean errors of 12.4 μm and 5.4 μm. For the two measurement examples of the tip clearance of a rotating blade and the radial displacement of a rotating tool, in the dynamic measurement process, compared with the laser rangefinder, the proposed method respectively achieves relative mean errors of 3.2 μm and 2.4 μm at the measurement distances of 2.5 mm and 4.5 mm. Therefore, the experimental results prove the application ability of the proposed method in terms of accuracy improvement. In summary, the proposed method can be applied in the micron-level measurement of millimeter-wave radar.

[0135] The above has introduced in detail the micron-level precision compensation method for millimeter-wave radar measurement provided by the present invention. In this article, specific embodiments are used to simply elaborate the basic principles and implementation manners of the present invention, but the protection scope of the present invention is not limited thereto. For those of ordinary skill in the art, it can be understood that without departing from the principles and spirits of the present invention, various changes, modifications, substitutions, and variations can be made to the embodiments herein, and the scope of the present invention is defined by the appended claims and their equivalents.

[0136] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0137] The series of detailed descriptions listed above are only specific descriptions of the feasible embodiments of the present invention, and they are not intended to limit the protection scope of the present invention. Any equivalent embodiments or changes made without departing from the technical spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A millimeter wave radar measurement accuracy compensation method, characterized in that: The following steps are involved: Step S1, radar information acquisition module: transmit and receive fixed frequency electromagnetic waves through millimeter wave radar, and output I / Q signals through orthogonal homodyne structure, and finally transmit them to the signal acquisition control processing platform; Step S2, radar correction parameter extraction module: the I / Q signal generated by the linear displacement echo is used as the input amplitude phase correction model input to obtain the correction parameter; Step S3, radar in-service measurement and verification module: perform parameterized compensation on the I / Q signal generated by the dynamic echo, and perform inverse tangent demodulation to finally obtain the displacement information in the echo signal; Step S4: The radar information acquisition module collects the signals required by the radar correction parameter extraction module and the radar in-service measurement and verification module respectively, completes the correction parameter extraction and dynamic signal compensation, and finally realizes the millimeter wave measurement accuracy compensation.

2. The method according to claim 1, characterized in that The amplitude phase correction model specifically includes the following contents: Step S11, eliminating DC offset and high-frequency noise in the I / Q signal through a differential-filtering combination operation, and preliminarily suppressing multiple harmonic interference; Step S12, using the all-pass property of the Hilbert transform, constructing an amplitude and phase correction factor in the frequency domain to obtain an initial value of the correction parameter, and constructing an I / Q consistency orthogonalization objective function to optimize the correction parameter; Step S13, using the Schmidt orthogonalization process to suppress the amplitude-phase imbalance error caused by the inverse Hilbert transform.

3. The method according to claim 2, characterized in that: After the amplitude-phase correction factor is coupled with the signal in the frequency domain, the phase and amplitude level of the signal itself can be finely adjusted.

4. The method according to claim 2, characterized in that: The I / Q consistency orthogonalization objective function includes the processed I / Q signal and the consistency and orthogonality constraints, and can optimize the correction parameter value.

5. The method according to claim 1, characterized in that The radar in-service measurement and verification module specifically includes the following contents: Step S21, using correction parameter A a ,A p ,I0,Q0, obtain the compensated dynamic I / Q signal; Step S22, using a power location method to extract the location of the I / Q signal peak; Step S23, using a direct demodulation method to obtain the displacement information in the I / Q signal phase; According to step S22, the peak position is determined and the position with the maximum displacement change is located to achieve single-point distance measurement. According to the displacement information calculated in step S23, continuous displacement measurement is achieved.

6. The method according to claim 5, characterized in that: The power location method utilizes the orthogonal characteristics of I / Q signals and adopts a square accumulation method to obtain the power of the radar baseband signal and its maximum value point.

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