Close-range millimeter wave radar displacement measurement system

Abstract

The invention relates to the technical field of millimeter-wave radars, in particular to a short-distance millimeter-wave radar displacement measurement system, which is characterized in that an echo signal acquisition module is used for acquiring a first static echo signal and a dynamic echo signal; and the correction parameter calculation module constructs a second static echo signal according to the first static echo signal and a direct current offset component in the first static echo signal, and obtains an amplitude imbalance parameter and a phase imbalance parameter according to the second static echo signal, thereby realizing high-precision imbalance parameter estimation under any amplitude modulation condition. Meanwhile, the dynamic echo signal is corrected through the signal correction module according to the amplitude imbalance parameter, the phase imbalance parameter and the direct current offset component, the corrected dynamic echo signal is obtained, and the correction precision of the dynamic echo signal reflected by the measured object is remarkably improved; and a displacement measurement result is obtained through the displacement measurement module according to the corrected dynamic echo signal, so that the accuracy and the reliability of the displacement measurement result are further improved.

Description

Technical Field

[0001] The present application relates to the technical field of millimeter wave radar, and in particular to a short-range millimeter wave radar displacement measurement system. Background Art

[0002] Millimeter wave radar displacement measurement technology is a high-precision, non-contact measurement method that uses electromagnetic wave signals in the millimeter wave frequency band to detect the displacement changes of target objects. In practical applications, millimeter wave radar systems usually use orthogonal radio transceivers to obtain the orthogonal amplitude components In-phase (I) and Quadrature (Q) of the echo signal, and then the displacement information of the target object can be solved by demodulating the I / Q signal.

[0003] However, due to the limitation of hardware circuit performance, the I / Q signal may be unbalanced in amplitude and phase. This imbalance will reduce the signal quality, cause signal distortion, and seriously affect the measurement accuracy of the millimeter-wave radar. Therefore, it is necessary to correct the imbalance of the I / Q signal of the echo signal. The existing patent application with publication number CN113520344A provides a radar-based vital sign estimation, which generates compensated I and Q signals associated with the detected target by performing ellipse fitting on the in-phase signal and the orthogonal signal associated with the detected target, and determines the displacement signal based on the compensated I and Q signals. Although the patent application adopts an ellipse correction method to correct the imbalance of the I / Q signal, in the close-range static measurement of the millimeter-wave radar, the echo signal is prone to show a strong amplitude modulation phenomenon, and its I / Q trajectory changes from an ellipse to a tapered ellipse, which causes the ellipse correction method to fail, thereby reducing the accuracy of the displacement measurement. Summary of the invention

[0004] Based on this, it is necessary to provide a short-range millimeter-wave radar displacement measurement system to address the problem that the existing I / Q signal imbalance correction method is not ideal, resulting in inaccurate displacement measurement results.

[0005] The present application provides a short-range millimeter wave radar displacement measurement system. The system includes an echo signal acquisition module, a correction parameter calculation module, a signal correction module and a displacement measurement module, wherein the first end of the echo signal acquisition module is connected to the first end of the correction parameter calculation module, the second end of the correction parameter calculation module is connected to the second end of the signal correction module, the second end of the echo signal acquisition module is connected to the first end of the signal correction module, and the third end of the signal correction module is connected to the displacement measurement module;

[0006] The echo signal acquisition module is used to acquire a first static echo signal and a dynamic echo signal;

[0007] The correction parameter calculation module is used to construct a second static echo signal according to the first static echo signal and a DC offset component in the first static echo signal, and obtain an amplitude imbalance parameter and a phase imbalance parameter according to the second static echo signal; wherein the second static echo signal includes a second static echo I signal and a second static echo Q signal, and the expression of the second static echo I signal is:

[0008]

[0009] In the formula, I n (t) is the second static echo I signal, I(t) is the first static echo I signal, Q(t) is the first static echo Q signal, D Q is the DC offset component of the first static echo Q signal, D I is the DC offset component of the first static echo I signal, [·]' represents the derivative;

[0010] The expression of the second static echo Q signal is:

[0011]

[0012] In the formula, Q n (t) is the second static echo Q signal;

[0013] The signal correction module is used to correct the dynamic echo signal according to the amplitude imbalance parameter, the phase imbalance parameter and the DC offset component to obtain a corrected dynamic echo signal;

[0014] The displacement measurement module is used to obtain a displacement measurement result according to the corrected dynamic echo signal.

[0015] Furthermore, the correction parameter calculation module includes a formula solving unbalanced parameter unit; the formula solving unbalanced parameter unit is based on the formula

[0016]

[0017] Calculate the amplitude imbalance parameter A e ; In the formula, represents the mean value within the second static echo I signal period, represents the mean value within the period of the second static echo Q signal;

[0018] According to the formula

[0019]

[0020] Calculate the phase imbalance parameter P e; In the formula, w0 = 4πv / λ, v is the fixed rate of change of the distance between the millimeter-wave radar and the object being measured, and λ is the wavelength of the millimeter-wave radar.

[0021] Further, the correction parameter calculation module includes an ellipse parameter estimation unit and a first unbalance parameter calculation unit connected to the ellipse parameter estimation unit;

[0022] The ellipse parameter estimation unit is used to obtain the ellipse parameters according to the oblique ellipse implicit equation and the second static echo signal; the oblique ellipse implicit equation is:

[0023]

[0024] Wherein, a, b, c, d, e are unknown parameters of the oblique elliptic implicit equation; the matrix expression of the oblique elliptic implicit equation is:

[0025]

[0026] In the formula, m is the number of sample points, I m =I n (m), Q m =Q n (m);

[0027] The expression of the ellipse parameter X is:

[0028] X=(A H A) - A H G

[0029] Where X = [abcde] T , A H is the symmetric matrix of matrix A;

[0030] The first imbalance parameter calculation unit is used to calculate the amplitude imbalance parameter and the phase imbalance parameter according to the ellipse parameter; wherein the expression of the amplitude imbalance parameter is:

[0031]

[0032] In the formula, A e is the amplitude imbalance parameter;

[0033] The expression of the phase imbalance parameter is:

[0034]

[0035] Where P e is the phase imbalance parameter.

[0036] Furthermore, the direction of the phase imbalance parameter is positive when the determination coefficient is greater than 1, and negative when it is less than 1; wherein, when the phase imbalance parameter P e ∈(-π / 2,π / 2) and P e ≠0, the expression of the determination coefficient L is:

[0037]

[0038] In the formula, I c (t)=I(t)-D I , Q c (t) = Q(t) - D Q , I c (t) = A e I c (t), T is the signal period of the first static echo signal, I(t) is the first static echo I signal, and Q(t) is the first static echo Q signal.

[0039] Further, the correction parameter calculation module includes a complex signal construction unit and a second unbalance parameter calculation unit;

[0040] The complex signal construction unit is used to construct a complex signal according to the second static echo signal, and perform Euler transformation on the complex signal; the expression of the complex signal is:

[0041] F n (t) = I n (t)+jQ n (t)

[0042] The expression of the complex signal after Euler transformation is:

[0043]

[0044] Where, Δθ=π / 2+2P e , K = 2w0cosP e , w0=2πf, f is the frequency of the first static echo signal;

[0045] The second unbalance parameter calculation unit is used to calculate the complex signal after Euler transformation in the spectrum 0, 2f IF and -2f IF The amplitude information at the position and the amplitude imbalance parameter and the phase imbalance parameter are mathematically related to each other to obtain the amplitude imbalance parameter and the phase imbalance parameter; the mathematical relationship is expressed as follows:

[0046]

[0047] In the formula, Re[·] represents the real part of the signal, Im[·] represents the imaginary part of the signal, and A[-2f IF ] indicates that the complex signal after Euler transformation is at -2f IF The amplitude at A * [2f IF ] represents the conjugate signal of the complex signal after Euler transformation at 2f IF The amplitude at f IF represents the intermediate frequency signal;

[0048] The amplitude imbalance parameter A e The expression is:

[0049]

[0050] The phase imbalance parameter P e The expression is:

[0051]

[0052] In the formula, tan2 -1 [·] is the four-quadrant inverse tangent.

[0053] Furthermore, the expression of the corrected dynamic echo signal is:

[0054]

[0055] In the formula, I' a (t) is the corrected dynamic echo I signal, I a (t) is the dynamic echo I signal before correction, Q' a (t) is the corrected dynamic echo Q signal, Q a (t) is the dynamic echo Q signal before correction, A e is the amplitude imbalance parameter, P e is the phase imbalance parameter.

[0056] Further, the echo signal acquisition module includes a signal preprocessing unit, and the signal preprocessing unit is connected to the signal correction module;

[0057] The signal preprocessing unit is used to denoise the dynamic echo signal; wherein the denoising method includes at least one of a finite length unit impulse response low-pass filter, wavelet decomposition denoising, and a low-frequency component of a maximum discrete wavelet transform.

[0058] Further, the displacement measurement module includes an inverse tangent demodulation unit, and the inverse tangent demodulation unit is connected to the signal correction module;

[0059] The inverse tangent demodulation unit is used to perform inverse tangent demodulation on the corrected dynamic echo signal to obtain the displacement measurement result; the expression of the displacement measurement result is:

[0060]

[0061] Where d(t) represents the displacement measurement result at time t, I' a (t) is the corrected dynamic echo I signal, Q' a (t) is the corrected dynamic echo Q signal.

[0062] Further, the displacement measurement module includes a long displacement measurement unit, and the long displacement measurement unit is connected to the signal correction module;

[0063] The long displacement measurement unit is used to obtain the displacement measurement result by using a translation phase angle algorithm when the displacement information changes more than a half-wavelength measurement range; the expression of the displacement measurement result is:

[0064]

[0065] Where d(t) represents the displacement measurement result at time t, I' a (t) is the corrected dynamic echo I signal, Q' a (t) is the corrected dynamic echo Q signal.

[0066] Further, the period T of the first static echo signal is:

[0067]

[0068] Wherein, v is the fixed rate of change of the distance between the millimeter wave radar and the object to be measured, λ is the wavelength of the millimeter wave radar, and f is the frequency of the first static echo signal.

[0069] The above-mentioned short-range millimeter-wave radar displacement measurement system collects the first static echo signal and the dynamic echo signal through the echo signal acquisition module, and the correction parameter calculation module constructs the second static echo signal according to the first static echo signal and the DC offset component in the first static echo signal, and obtains the amplitude imbalance parameter and the phase imbalance parameter according to the second static echo signal, thereby realizing high-precision imbalance parameter estimation under arbitrary amplitude modulation conditions. At the same time, the dynamic echo signal is corrected according to the amplitude imbalance parameter, the phase imbalance parameter and the DC offset component through the signal correction module to obtain the corrected dynamic echo signal, which significantly improves the correction accuracy of the dynamic echo signal reflected by the object to be measured. Then, the displacement measurement result is obtained according to the corrected dynamic echo signal through the displacement measurement module, thereby further improving the accuracy and reliability of the displacement measurement result. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 A schematic diagram of the structure of a short-range millimeter-wave radar displacement measurement system in one embodiment;

[0071] Figure 2 It is a schematic structural diagram of a short-range millimeter-wave radar displacement measurement system in another embodiment;

[0072] Figure 3 (a) is a schematic diagram of the ideal displacement change of a millimeter wave radar in one embodiment;

[0073] Figure 3 (b) is a time domain waveform diagram of a dynamic echo signal in one embodiment;

[0074] Figure 4 (a) is a time domain waveform diagram of a first static echo signal in one embodiment;

[0075] Figure 4 (b) is a trajectory diagram of a first static echo signal in one embodiment;

[0076] Figure 5 (a) is a trajectory diagram of a second static echo signal in one embodiment;

[0077] Figure 5 (b) is a spectrum diagram of a complex signal in one embodiment;

[0078] Figure 6 (a) is a time domain waveform diagram of a corrected dynamic echo signal in one embodiment;

[0079] Figure 6 (b) is a schematic diagram of displacement measurement results obtained by using an inverse tangent demodulation method in one embodiment;

[0080] Figure 6 (c) is a schematic diagram of displacement measurement results obtained by using a translation phase angle algorithm in one embodiment;

[0081] Figure 6 (d) is a schematic diagram of displacement measurement error obtained by using a translation phase angle algorithm in one embodiment;

[0082] Figure 7 is a time domain waveform diagram of a dynamic echo signal in another embodiment;

[0083] Figure 8 (a) is a time domain waveform diagram of a first static echo signal in another embodiment;

[0084] Figure 8 (b) is a trajectory diagram of the first static echo signal in another embodiment;

[0085] Fig. 9 (a) is a time domain waveform diagram of a second static echo signal in another embodiment;

[0086] Fig. 9 (b) is a spectrum diagram of a complex signal in another embodiment;

[0087] Fig.10 is a time domain waveform diagram of a corrected dynamic echo signal in another embodiment;

[0088] Fig.11 A schematic diagram of a displacement measurement result obtained by using an inverse tangent demodulation method in another embodiment;

[0089] Fig.12 (a) is a schematic diagram of displacement measurement results of blade tip clearance measurement using millimeter wave radar sensing in one embodiment;

[0090] Fig.12 (b) is a schematic diagram of the displacement measurement results of blade tip clearance measurement using a laser displacement sensor in one embodiment.

[0091] Description of the accompanying drawings: 100 echo signal acquisition module; 200 correction parameter calculation module; 300 signal correction module; 400 displacement measurement module. DETAILED DESCRIPTION

[0092] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0093] Example 1

[0094] like Figure 1 As shown, this embodiment provides a short-range millimeter-wave radar displacement measurement system, including an echo signal acquisition module, a correction parameter calculation module, a signal correction module and a displacement measurement module, wherein the first end of the echo signal acquisition module is connected to the first end of the correction parameter calculation module, the second end of the correction parameter calculation module is connected to the second end of the signal correction module, the second end of the echo signal acquisition module is connected to the first end of the signal correction module, and the third end of the signal correction module is connected to the displacement measurement module.

[0095] The echo signal acquisition module is used to acquire a first static echo signal and a dynamic echo signal.

[0096] Among them, the first static echo signal refers to the echo signal generated when the distance between the millimeter-wave radar sensor and the object under test changes at a fixed rate. There are two situations for this distance change: one is that the object under test is in a stationary state, and the millimeter-wave radar sensor moves away from or close to the object under test at a fixed moving speed; the other is that the millimeter-wave radar sensor is in a stationary state, and the object under test moves away from or close to the millimeter-wave radar sensor at a fixed moving speed. Further, the first static echo signal includes a first static echo I signal I(t) and a first static echo Q signal I(t). The first static echo I signal is the orthogonal amplitude component I channel signal of the first static echo signal, and the first static echo Q signal is the orthogonal amplitude component Q channel signal of the first static echo signal.

[0097] The dynamic echo signal is the orthogonal amplitude component I and Q signals of the echo signal of the object under test measured by the millimeter wave radar at the initial position and located in the short-range range. The frequency of the millimeter wave radar is 24GHz to 240GHz, and the short-range range is (0,10λ], where λ is the wavelength of the millimeter wave radar. For example, when the frequency of the millimeter wave radar is 120GHz, the short-range range is (0,25]mm. The object under test is an object whose surface can reflect millimeter waves, such as metal.

[0098] Specifically, Figure 2 As shown, the echo signal acquisition module may include a static echo signal acquisition unit for acquiring a first static echo signal and a dynamic echo signal acquisition unit for acquiring a dynamic echo signal. Further, the echo signal acquisition module may also include a signal preprocessing unit, a first end of the signal preprocessing unit is connected to the dynamic echo signal acquisition unit, and a second end is connected to the first end of the signal correction module. The signal preprocessing unit is used to denoise the dynamic echo signal. Among them, the denoising method may include but is not limited to using a finite impulse response (FIR) low-pass filter, wavelet decomposition denoising, and low-frequency components in the maximum discrete wavelet transform.

[0099] The correction parameter calculation module is used to construct a second static echo signal according to the first static echo signal and the DC offset component in the first static echo signal. The second static echo signal includes a second static echo I signal I n (t) and the second static echo Q signal Q n (t). The second static echo I signal is the orthogonal amplitude component I signal of the second static echo signal, and the second static echo Q signal is the orthogonal amplitude component Q signal of the second static echo signal. The expression of the second static echo I signal is:

[0100]

[0101] In the formula, I n(t) is the second static echo I signal, I(t) is the first static echo I signal, Q(t) is the first static echo Q signal, D Q is the DC offset component of the first static echo Q signal, D I is the DC offset component of the first static echo I signal, and [·]' represents the derivative.

[0102] The expression of the second static echo Q signal is:

[0103]

[0104] In the formula, Q n (t) is the second static echo Q signal.

[0105] Specifically, Figure 2 As shown, the correction parameter calculation module may include a DC offset component calculation unit and a ratio differential signal construction unit, a first end of the static echo signal acquisition unit is connected to the first end of the DC offset component calculation unit, a second end of the DC offset component calculation unit is connected to the first end of the ratio differential signal construction unit, a second end of the static echo signal acquisition unit is connected to the second end of the ratio differential signal construction unit, and a third end of the DC offset component calculation unit is connected to the third end of the signal correction module.

[0106] The DC offset component calculation unit is used to obtain the DC offset component in the first static echo signal. The DC offset component in the first static echo signal includes the DC offset component D of the first static echo I signal. I and the DC offset component D of the first static echo Q signal Q . Specifically, the method of obtaining the DC offset component may include but is not limited to calculating the average value of the first static echo signal within a complete cycle to directly obtain the DC offset component; using signal difference technology to estimate and remove the AC component through the difference between adjacent data points, thereby indirectly obtaining the DC offset component; directly extracting the component with a frequency of 0 in the spectrum of the first static echo signal; using an FIR ultra-low-pass filter to pre-process the first static echo signal to remove high-frequency noise and then calculating the average value within the signal cycle to obtain a more accurate DC offset component. Among them, the signal period of the first static echo signal is shown in formula (3):

[0107]

[0108] Where v is the fixed rate of change of the distance between the millimeter wave radar and the object being measured, λ is the wavelength of the millimeter wave radar, and f is the frequency of the first static echo signal. In particular, when the first static echo signal is denoised using an FIR ultra-low pass filter, its cutoff frequency is between (0, f] Hz.

[0109] The ratio difference signal construction unit is used to construct a second static echo signal by ratio, difference and reciprocal according to the first static echo I signal and the first static echo Q signal after the DC offset component is removed. It can be understood that the second static echo signal includes the second static echo I signal as shown in formula (1) and the second static echo Q signal as shown in formula (2).

[0110] The correction parameter calculation module is also used to obtain an amplitude imbalance parameter and a phase imbalance parameter according to the second static echo signal. Figure 2 As shown, the correction parameter calculation module also includes a formula solving unbalanced parameter unit, the first end of the formula solving unbalanced parameter is connected to the third end of the ratio differential signal construction unit, and the second end is connected to the third end of the signal correction module. The formula solving unbalanced parameter unit calculates the amplitude unbalanced parameter A according to the formula shown in formula (4): e , calculate the unbalance parameter P according to the formula shown in formula (5) e :

[0111]

[0112] In the formula, represents the mean value of the second static echo I signal within one cycle, Represents the average value of the second static echo Q signal within one cycle.

[0113]

[0114] Where w0 = 4πv / λ, v is the fixed rate of change of the distance between the millimeter-wave radar and the object being measured, and λ is the wavelength of the millimeter-wave radar.

[0115] Further, such as Figure 2 As shown, the correction parameter calculation module may also include an ellipse parameter estimation unit and a first unbalanced parameter calculation unit, the first end of the ellipse parameter estimation unit is connected to the third end of the ratio differential signal construction unit, the second end is connected to the first end of the first unbalanced parameter calculation unit, and the second end of the first unbalanced parameter calculation unit is connected to the third end of the signal correction module.

[0116] The ellipse parameter estimation unit is used to obtain the ellipse parameters according to the oblique ellipse implicit equation and the second static echo signal. Specifically, the ellipse parameter estimation unit fits the ellipse center to the second static echo signal based on the oblique ellipse implicit equation to estimate the ellipse parameters. Wherein, the oblique ellipse implicit equation is:

[0117]

[0118] In the formula, a, b, c, d, e are the unknown parameters of the oblique elliptic implicit equation. From formula (6), we can see that the number of unknowns in the oblique elliptic implicit equation is 5, and the number of independent equations is n.

[0119] The matrix expression of the oblique elliptic implicit equation is:

[0120]

[0121] In the formula, m is the number of sample points, I m =I n (m), Q m =Q n (m).

[0122] When the number of independent equations is greater than the number of unknowns of the oblique elliptic implicit equation, the optimal solution of equation (7) is:

[0123] X=A + G (8)

[0124] In the formula, A + represents the MP generalized inverse of matrix A. Where is a full column rank matrix, and the generalized inverse calculation formula of the full column rank matrix A + =(A H A) - A H , the expression of the ellipse parameter X is:

[0125] X=(A H A) - A H G (9)

[0126] Where X = [abcde] T , A H is a symmetric matrix of matrix A.

[0127] The first imbalance parameter calculation unit is used to calculate the amplitude imbalance parameter and the phase imbalance parameter according to the ellipse parameter. Specifically, based on the ellipse parameter shown in formula (9), the amplitude imbalance parameter shown in formula (10) and the phase imbalance parameter shown in formula (11) can be calculated:

[0128]

[0129] In the formula, A e is the amplitude imbalance parameter.

[0130]

[0131] Where P e is the phase imbalance parameter.

[0132] Furthermore, the directions of the phase imbalance parameter as shown in formula (5) calculated by the imbalance parameter calculation unit and the phase imbalance parameter as shown in formula (11) calculated by the first imbalance parameter calculation unit can be determined according to the determination coefficient as shown in formula (12).

[0133] When the phase imbalance parameter P e ∈(-π / 2,π / 2) and P e When ≠0, the expression of the determination coefficient L is:

[0134]

[0135] In the formula, I c (t)=I(t)-D I , Q c (t(=Q(t)-D Q , I c (t) = A e I c (t), T is the signal period of the first static echo signal, I(t) is the first static echo I signal, and Q(t) is the first static echo Q signal.

[0136] Specifically, the formula for solving the imbalance parameter unit substitutes the amplitude imbalance parameter shown in formula (4) and the first static echo signal into formula (12) to calculate the determination coefficient. When the determination coefficient is greater than or equal to 1, the direction of the phase imbalance parameter shown in formula (5) is positive, that is, P e =|P e |, when the determination coefficient is less than 1, the direction of the phase imbalance parameter shown in formula (5) is negative, that is, P e =-|P e |; Similarly, the first imbalance parameter calculation unit brings the amplitude imbalance parameter shown in formula (10) and the first static echo signal into formula (12) to calculate the determination coefficient. When the determination coefficient is greater than or equal to 1, the direction of the phase imbalance parameter shown in formula (11) is positive, that is, P e =|P e |, when the determination coefficient is less than 1, the direction of the phase imbalance parameter shown in formula (11) is negative, that is, P e =-|P e |.

[0137] The validity of judging the positive or negative phase imbalance parameter based on the positive or negative determination coefficient L is demonstrated as follows:

[0138] When P e When >0, the expression of the determination coefficient L is shown in formula (13):

[0139]

[0140] Due to 4cos(w0t) 2 tan(P e ) 2 >0, therefore L>0.

[0141] When P e <0, the expression of the determination coefficient L is shown in formula (14):

[0142]

[0143] Due to 4cos(w0t) 2 tan(P e ) 2 >0, therefore L<0.

[0144] In addition, if Figure 2 As shown, the correction parameter calculation module may also include a complex signal construction unit and a second unbalanced parameter calculation unit, wherein the first end of the complex signal construction unit is connected to the third end of the ratio differential signal construction unit, the second end is connected to the first end of the second unbalanced parameter calculation unit, and the second end of the second unbalanced parameter calculation unit is connected to the third end of the signal correction module.

[0145] The complex signal construction unit is used to construct a complex signal according to the second static echo signal, and perform Euler transformation on the complex signal. The expression of the constructed complex signal is:

[0146] F n (t) = I n (t)+jQ n (t) (15)

[0147] The expression of the complex signal after Euler transformation is:

[0148]

[0149] Where, Δθ=π / 2+2P e , K = 2w0cosP e , w0=2πf, f is the first static echo signal (I n (t) and Q n (t)). From formula (18), we can see that the complex signal F n (t) There is also a DC component at and Frequency and mirror frequency Element.

[0150] The second unbalance parameter calculation unit is used to calculate the complex signal F n (t)0,2f in the spectrum IFand -2f IF The amplitude information at 0, 2f and the mathematical relationship between the amplitude imbalance parameter and the phase imbalance parameter are used to obtain the amplitude imbalance parameter and the phase imbalance parameter. IF and -2f IF The mathematical relationship between the amplitude information at and the amplitude imbalance parameter and the phase imbalance parameter is:

[0151]

[0152] In the formula, Re[·] represents the real part of the signal, Im[·] represents the imaginary part of the signal, and A[-2f IF ] indicates that the complex signal after Euler transformation is at -2f IF The amplitude at A * [2f IF ] indicates the conjugate signal of the complex signal after Euler transformation at 2f IF The amplitude at f IF It represents intermediate frequency (IF). In a preferred embodiment, the intermediate frequency is equal to the frequency f of the first static echo signal.

[0153] Then, the amplitude imbalance parameter A can be obtained by the mathematical relationship shown in formula (17): e The expression is:

[0154]

[0155] Phase imbalance parameter P e The expression is:

[0156]

[0157] In the formula, tan2 -1 [·] is the four-quadrant inverse tangent.

[0158] Compared with the phase imbalance parameter calculated by the imbalance parameter unit and the first imbalance parameter calculation unit, the phase imbalance parameter obtained by the second imbalance parameter calculation unit can directly obtain the phase direction without calculating the determination coefficient, further improving the efficiency of signal correction.

[0159] The signal correction module is used to correct the dynamic echo signal according to the amplitude imbalance parameter, the phase imbalance parameter and the DC offset component to obtain a corrected dynamic echo signal. Optionally, the signal correction module can choose to obtain the amplitude imbalance parameter and the phase imbalance parameter from the formula solving imbalance parameter unit, the first imbalance parameter calculation unit or the second imbalance parameter calculation unit. In order to improve the accuracy and reliability of the parameters, the signal correction module can also integrate the amplitude imbalance parameter and the phase imbalance parameter calculated by the formula solving imbalance parameter unit, the first imbalance parameter calculation unit and the second imbalance parameter calculation unit. For example, the final amplitude imbalance parameter and phase imbalance parameter are determined by performing average value calculation or other statistical processing on the amplitude imbalance parameters and phase imbalance parameters provided by these units. The calculation formula for the corrected dynamic echo signal is:

[0160]

[0161] In the formula, I' a (t) is the corrected dynamic echo I signal, I a (t) is the dynamic echo I signal before correction, Q' a (t) is the corrected dynamic echo Q signal, Q a (t) is the dynamic echo Q signal before correction. Further, the dynamic echo I signal I before correction a (t) and the dynamic echo Q signal Q before correction a (t) can be signals denoised by the signal preprocessing unit to further improve the reliability of the correction result.

[0162] The displacement measurement module is used to obtain the displacement measurement result according to the corrected dynamic echo signal. The corrected dynamic echo signal includes a corrected dynamic echo I signal and a corrected dynamic echo Q signal. Specifically, Figure 2 As shown, the displacement measurement module may include an inverse tangent demodulation unit, which is connected to the signal correction module. The inverse tangent demodulation unit is used to perform inverse tangent demodulation on the corrected dynamic echo signal to obtain a displacement measurement result. The expression of the displacement measurement result is:

[0163]

[0164] Where d(t) represents the displacement measurement result at time t.

[0165] Furthermore, when the displacement of the measured object is large and exceeds half a wavelength, in order to improve the accuracy of the displacement measurement result, in some embodiments, such as Figure 2As shown, the displacement measurement module may also include a long displacement measurement unit, which is connected to the signal correction module. The long displacement measurement unit is used to obtain the displacement measurement result by using the translation phase angle algorithm when the displacement information changes more than the half-wavelength measurement range. The translation phase angle algorithm calculates the displacement by measuring the change of the phase angle, and can maintain a high measurement accuracy within a large displacement range. The expression of the displacement measurement result d(t) is:

[0166]

[0167] Finally, the short-range millimeter-wave radar displacement measurement system provided in this embodiment can be used in the field of industrial automation for product quality control on production lines and position monitoring of equipment such as robotic arms and conveyor belts to ensure high efficiency and quality of production; at the same time, in the field of aerospace, it can be widely used in blade tip clearance measurement, online vibration monitoring, and position detection of key components such as landing gear, providing solid technical support for flight safety and efficiency.

[0168] Exemplarily, the echo signal acquisition module in this embodiment can be a 24GHz millimeter wave radar module (such as HLK-LD112, HLK-LD303, etc.), which can receive the reflected echo signal, including the first static echo signal and the dynamic echo signal in this embodiment, and has the characteristics of high sensitivity, low power consumption, and strong anti-interference, and is suitable for close-range displacement measurement. For applications that require higher frequencies and more precise measurements, millimeter wave radar modules with higher frequency bands can also be selected. The correction parameter calculation module can be an embedded processor or a microcontroller (such as STM32, etc.), which includes a memory and a processor, and a computer program is stored in the memory. When the processor executes these programs, it is realized that the second static echo signal is constructed according to the first static echo signal and the DC offset component in the first static echo signal, and the amplitude imbalance parameter and the phase imbalance parameter are obtained according to the second static echo signal. The signal correction module and the displacement measurement module can be a digital signal processing chip (such as a DSP chip) or an FPGA (field programmable gate array), which includes a memory and a processor. The memory stores computer programs. When the processor executes these programs, the dynamic echo signal is corrected according to the amplitude imbalance parameter, the phase imbalance parameter and the DC offset component to obtain a corrected dynamic echo signal, and the displacement measurement result is obtained according to the corrected dynamic echo signal.

[0169] The short-range millimeter-wave radar displacement measurement system of this embodiment collects the first static echo signal and the dynamic echo signal through the echo signal acquisition module, and the correction parameter calculation module constructs the second static echo signal according to the first static echo signal and the DC offset component in the first static echo signal, and obtains the amplitude imbalance parameter and the phase imbalance parameter according to the second static echo signal, thereby realizing high-precision imbalance parameter estimation under arbitrary amplitude modulation conditions. At the same time, the signal correction module corrects the dynamic echo signal according to the amplitude imbalance parameter, the phase imbalance parameter and the DC offset component to obtain a corrected dynamic echo signal, which significantly improves the correction accuracy of the dynamic echo signal reflected by the object to be measured. Then, the displacement measurement module obtains the displacement measurement result according to the corrected dynamic echo signal, thereby further improving the accuracy and reliability of the displacement measurement result.

[0170] Example 2

[0171] In order to better understand the short-range millimeter-wave radar displacement measurement system in Example 1, the following explanation is combined with specific simulation experiments. It should be noted that in this embodiment, the method of combining formulas to solve and calculate amplitude imbalance parameters and phase imbalance parameters in the short-range millimeter-wave radar displacement measurement system is called RD-EQ, the method of combining elliptic equation fitting to calculate amplitude imbalance parameters and phase imbalance parameters is called RD-EC, and the method of combining complex signal spectrum to calculate amplitude imbalance parameters and phase imbalance parameters is called RD-S. The specific process is as follows:

[0172] 1. Record the dynamic echo signal I collected by the dynamic echo signal acquisition unit a (t) and dynamic echo Q signal Q a The simulation signal models of (t) are:

[0173]

[0174] In the formula, A T is the I / Q signal amplitude factor, represents the phase change, d(t) is the displacement change to be obtained, awgn{·,S NR} indicates that the signal-to-noise ratio is increased to S NR White Gaussian noise, A e is the amplitude imbalance parameter, P e is the phase imbalance parameter, D I is the DC offset component of the dynamic echo I signal, D Q is the DC offset component of the dynamic echo Q signal. Specifically, in this embodiment, S NR =50dB, A e=1.1, A T =1,P e =-0.2rad, D I =1.5V, D Q =2.1V. At this time, the displacement change d(t) to be obtained is as follows: Figure 3 (a) As shown. Further, the 5-layer maximum discrete wavelet packet transform is used to take the first wavelet packet component in the 5th layer decomposition to denoise the dynamic echo I signal and the dynamic echo Q signal respectively. The time domain waveforms of the denoised dynamic echo I signal and the dynamic echo Q signal are shown in Figure 3 (b) As shown. It can be understood that Figure 3 The I signal in (b) is the dynamic echo I signal after denoising. Figure 3 The Q signal in (b) is the dynamic echo Q signal after denoising.

[0175] 2. The simulation signal models of the first static echo I signal I(t) and the first static echo Q signal Q(t) collected by the static echo signal collection unit are respectively:

[0176]

[0177] Wherein, η(t) can be any amplitude modulation term. In this embodiment, d0 is the initial distance between the millimeter wave radar sensor and the object being measured. When the moving speed v = 1.25 mm / s, d0 = 10 mm, S NR =50dB, A T =50 condition, A e =1.1,P e =-0.2rad, D I =1.5V, D Q =2.1V,

[0178] At this time, the time domain waveforms of the first static echo I signal and the first static echo Q signal are as follows: Figure 4 As shown in (a), the trajectory diagram is Figure 4 (b) As shown. It can be understood that Figure 4 (a) and Figure 4 The I signal in (b) is the first static echo I signal, Figure 4 (a) and Figure 4 The Q signal in (b) is the first static echo Q signal. Further, in this embodiment, after filtering the first static echo I signal and the first static echo Q signal using an FIR ultra-low pass filter with a cutoff frequency of 0.2f, the signal mean within one cycle is calculated to obtain the DC offset component in equations (25) and (26). Specifically, at the sampling frequency f s=2000Hz, the DC offset component is calculated as D I =1.500064,D Q =2.100095.

[0179] 3. Remove the DC offset component in the first static echo I signal and the first static echo Q signal, and then construct the second static echo I signal as shown in formula (27) and the second static echo Q signal as shown in formula (28) by ratio, difference and reciprocal:

[0180]

[0181] Where [·]' is the derivative process, and the corresponding discrete I / Q signal is a differential process. Figure 5 (a) is a signal trajectory diagram of the second static echo I signal and the second static echo Q signal, Figure 5 (b) is a complex signal spectrum diagram of the second static echo I signal and the second static echo Q signal. It can be understood that Figure 5 The In-signal in (a) is the second static echo I signal, and the Qn-signal is the second static echo Q signal. Further, after a simple arrangement of equations (27) and (28), the second static echo I signal shown in equation (29) and the second static echo Q signal shown in equation (30) can be obtained:

[0182]

[0183] Where w0 = 4πv / λ, v is the fixed rate of change of the distance between the millimeter-wave radar and the object being measured, and λ is the wavelength of the millimeter-wave radar.

[0184] 4. According to the first static echo I signal and the first static echo Q signal, the amplitude imbalance parameter and the phase imbalance parameter are solved by the RD-EQ, RD-EC and RD-S methods respectively. In order to reflect the accuracy of the displacement measurement of the present application, this embodiment is compared with the existing I / Q signal imbalance correction method by simulation experiments, including the Gram-Schmidt orthogonalization procedure (GSOP) method, ellipse correction (EC) and spectrum correction method. Table 1 shows the imbalance parameter estimation errors of the existing I / Q signal imbalance correction method and the RD-EQ, RD-EC and RD-S methods. It can be seen from Table 1 that the imbalance parameter estimation error of the RD-series in this embodiment is smaller than the imbalance parameter estimation error obtained by the existing I / Q signal imbalance correction method, and can provide more accurate imbalance parameters for the subsequent correction of dynamic echo signals.

[0185] Table 1

[0186]

[0187] 5. Perform correction according to the amplitude imbalance parameter and phase imbalance parameter obtained in step 4, as well as the denoised dynamic echo I signal and dynamic echo Q signal. This embodiment takes the correction of the amplitude imbalance parameter and phase imbalance parameter calculated by the RD-EC method as an example, and obtains the following: Figure 6 (a) is a time domain waveform diagram of the corrected dynamic echo I signal and dynamic echo Q signal. It can be understood that Figure 6 The I signal in (a) is the corrected dynamic echo I signal, and the Q signal is the corrected dynamic echo Q signal.

[0188] 6. Perform arc tangent demodulation on the corrected dynamic echo I signal and dynamic echo Q signal obtained in step 5 to obtain Figure 6 (b) shows the displacement measurement result. Further, when the displacement information changes more than the half-wavelength measurement range, the long displacement measurement can be achieved by using the translation phase angle algorithm. Figure 6 The corrected dynamic echo I signal and dynamic echo Q signal shown in (a) are obtained by using the phase angle translation algorithm as follows: Figure 6 (c) shows the displacement measurement results and compares them with the true displacement. Figure 6 (c) It can be seen that after mean alignment, the average measurement error of the ideal displacement change is 0.0966μm, the root mean square error is 0.1044μm, and the maximum error is 0.3810μm. The specific demodulation displacement measurement error is as follows Figure 6 (d) as shown.

[0189] Example 3

[0190] This embodiment uses millimeter-wave radar to measure blade tip clearance as an application scenario to further verify the effectiveness and practicality of the present application.

[0191] The object to be measured in this embodiment is a rectangular metal blade with a diameter of 140 mm and a thickness of 3 mm. The motor speed of the rectangular metal blade is 100 RPM, and the sampling frequency of the millimeter wave radar sensor is up to 100 kHz. In particular, in this embodiment, the dynamic echo signal generated by the rectangular metal blade is recorded as the blade tip clearance echo signal. Figure 7 This is the time domain waveform of the blade tip gap echo signal collected by the echo signal acquisition module after denoising. Figure 7 The I signal in is the blade tip clearance echo I signal. Figure 7The Q signal in is the blade tip gap echo Q signal. In this example, the 5-layer maximum discrete wavelet packet transform is also used to remove noise from the blade tip gap echo signal by taking the first wavelet packet component in the 5th layer of decomposition. Specifically, the object to be measured in this embodiment is in a stationary state, the initial position d0 of the millimeter wave radar sensing distance from the blade end face is 5mm, and the sampling frequency is f s =4kHz, the millimeter wave radar sensor moves away from the object at a fixed speed v=2.34mm / s. After the millimeter wave radar sensor moves continuously for 20mm, the time domain waveforms of the first static echo I signal and the first static echo Q signal collected by the echo signal collection module are as follows: Figure 8 (a) shows the signal trajectory. Figure 8 (b) is shown. Afterwards, this embodiment uses an FIR ultra-low pass filter with a cutoff frequency of 0.3744 Hz to filter the first static echo I signal and the first static echo Q signal, and at a sampling frequency f s =4000Hz, the DC offset component of the static echo signal is calculated as D I =1.3428V, D Q =2.2210V.

[0192] Afterwards, a second static echo I signal is constructed according to equation (1), and a second static echo Q signal is constructed according to equation (2). Fig. 9 (a) shows the time domain waveform diagram of the second static echo I signal and the second static echo Q signal, Fig. 9 (b) shows a complex signal spectrum diagram constructed based on formula (17). Then, the amplitude imbalance parameter and the phase imbalance parameter are calculated using the same method as in Example 2. Table 2 shows the calculation results of the DC offset component and the imbalance parameter estimation error of the existing I / Q signal imbalance correction method and the RD-EQ, RD-EC and RD-S methods.

[0193] Table 2

[0194]

[0195]

[0196] Next, the denoised blade tip gap echo signal is corrected based on the DC offset component, amplitude imbalance parameter and phase imbalance parameter calculated in Table 2. Table 2 also shows the demodulation displacement root mean square error corresponding to each correction method. By observing Table 2, it can be intuitively seen that the RD-series correction method proposed in this application is superior to the existing correction method in terms of imbalance parameter estimation error and demodulation displacement root mean square error, and shows a lower error value.

[0197] The time domain waveform of the corrected blade tip gap echo signal is as follows: Fig.10 Finally, the corrected blade tip clearance echo signal is subjected to arc tangent demodulation, and the displacement measurement result is as follows: Fig.11 This figure also intuitively shows the corresponding relationship between the arc tangent demodulation area and the blade tip clearance area. Fig.11 It can be found that the blade tip clearance area in the dynamic echo signal is interfered by the non-blade tip part, which makes the direct application of the translation phase angle algorithm ineffective. In view of this, this embodiment combines the existing signal amplitude positioning technology to accurately locate the blade tip clearance area and extract the clearance information through the mutation of phase information. The extracted blade tip clearance area is as follows Fig.12 (a) shows the measurement results of the laser displacement sensor. Fig.12 (b) As shown. Within the 300 μm blade tip clearance relative change measurement range, this embodiment is as follows Fig.12 The laser displacement sensor measurement results shown in (b) are used as the benchmark for comparison, and the average measurement error of the millimeter-wave radar sensor is 2.23μm, and the maximum error is 4.92μm. This data fully verifies the effectiveness and high precision of the RD-series correction method proposed in this application.

[0198] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0199] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A short-range millimeter wave radar displacement measurement system, characterized in that: The system comprises an echo signal acquisition module, a correction parameter calculation module, a signal correction module and a displacement measurement module, wherein a first end of the echo signal acquisition module is connected to a first end of the correction parameter calculation module, a second end of the correction parameter calculation module is connected to a second end of the signal correction module, a second end of the echo signal acquisition module is connected to a first end of the signal correction module, and a terminal of the signal correction module is connected to the displacement measurement module; The echo signal acquisition module is used to acquire a first static echo signal and a dynamic echo signal; The correction parameter calculation module is used to construct a second static echo signal according to the first static echo signal and a DC offset component in the first static echo signal, and obtain an amplitude imbalance parameter and a phase imbalance parameter according to the second static echo signal; wherein the second static echo signal includes a second static echo I signal and a second static echo Q signal, and the expression of the second static echo I signal is: In the formula, I n (t) is the second static echo I signal, I(t) is the first static echo I signal, Q(t) is the first static echo Q signal, D Q is the DC offset component of the first static echo Q signal, D I is the DC offset component of the first static echo I signal, [·]' represents the derivative; The expression of the second static echo Q signal is: In the formula, Q n (t) is the second static echo Q signal; The signal correction module is used to correct the dynamic echo signal according to the amplitude imbalance parameter, the phase imbalance parameter and the DC offset component to obtain a corrected dynamic echo signal; The displacement measurement module is used to obtain a displacement measurement result according to the corrected dynamic echo signal.

2. The short-range millimeter wave radar displacement measurement system according to claim 1, characterized in that: The correction parameter calculation module includes a formula solving unbalanced parameter unit; the formula solving unbalanced parameter unit is based on the formula Calculate the amplitude imbalance parameter A e ; In the formula, represents the mean value within the second static echo I signal period, represents the mean value within the period of the second static echo Q signal; According to the formula Calculate the phase imbalance parameter P e ; In the formula, w0 = 4πv / λ, v is the fixed rate of change of the distance between the millimeter-wave radar and the object being measured, and λ is the wavelength of the millimeter-wave radar.

3. The short-range millimeter wave radar displacement measurement system according to claim 1, characterized in that: The correction parameter calculation module includes an ellipse parameter estimation unit and a first unbalance parameter calculation unit connected to the ellipse parameter estimation unit; The ellipse parameter estimation unit is used to obtain the ellipse parameters according to the oblique ellipse implicit equation and the second static echo signal; the oblique ellipse implicit equation is: Wherein, a, b, c, d, e are unknown parameters of the oblique elliptic implicit equation; the matrix expression of the oblique elliptic implicit equation is: In the formula, m is the number of sample points, I m =I n (m), Q m =Q n (m); The expression of the ellipse parameter X is: X=(A H A) - A H G Where X = [abcde] T , A H is the symmetric matrix of matrix A; The first imbalance parameter calculation unit is used to calculate the amplitude imbalance parameter and the phase imbalance parameter according to the ellipse parameter; wherein the expression of the amplitude imbalance parameter is: In the formula, A e is the amplitude imbalance parameter; The expression of the phase imbalance parameter is: Where P e is the phase imbalance parameter.

4. The short-range millimeter wave radar displacement measurement system according to any one of claims 2-3, characterized in that: The direction of the phase imbalance parameter is positive when the determination coefficient is greater than 1, and negative when it is less than 1; wherein, when the phase imbalance parameter P e ∈(-π / 2,π / 2) and P e ≠0, the expression of the determination coefficient L is: In the formula, I c (t)=I(t)-D I , Q c (t) = Q(t) - D Q , I c (t) = A e I c (t), T is the signal period of the first static echo signal, I(t) is the first static echo I signal, and Q(t) is the first static echo Q signal.

5. The short-range millimeter wave radar displacement measurement system according to claim 1, characterized in that: The correction parameter calculation module includes a complex signal construction unit and a second unbalance parameter calculation unit; The complex signal construction unit is used to construct a complex signal according to the second static echo signal, and perform Euler transformation on the complex signal; the expression of the complex signal is: F n (t)=I n (t)+jQ n (t) The expression of the complex signal after Euler transformation is: Where, Δθ=π / 2+2P e , K = 2w0cosP e , w0=2πf, f is the frequency of the first static echo signal; The second unbalance parameter calculation unit is used to calculate the complex signal after Euler transformation in the spectrum 0, 2f IF and -2f IF The amplitude information at the position and the amplitude imbalance parameter and the phase imbalance parameter are mathematically related to obtain the amplitude imbalance parameter and the phase imbalance parameter; the mathematical relationship is expressed as: In the formula, Re[·] represents the real part of the signal, Im[·] represents the imaginary part of the signal, and A[-2f IF ] indicates that the complex signal after Euler transformation is at -2f IF The amplitude at A*[2f IF ] represents the conjugate signal of the complex signal after Euler transformation at 2f IF The amplitude at f IF represents the intermediate frequency signal; The amplitude imbalance parameter A e The expression is: The phase imbalance parameter P e The expression is: In the formula, tan2 -1 [·] is the four-quadrant inverse tangent.

6. The short-range millimeter wave radar displacement measurement system according to claim 1, characterized in that: The expression of the corrected dynamic echo signal is: In the formula, I' a (t) is the corrected dynamic echo I signal, I a (t) is the dynamic echo I signal before correction, Q' a (t) is the corrected dynamic echo Q signal, Q a (t) is the dynamic echo Q signal before correction, A e is the amplitude imbalance parameter, P e is the phase imbalance parameter.

7. The short-range millimeter wave radar displacement measurement system according to claim 1, characterized in that: The echo signal acquisition module includes a signal preprocessing unit, and the signal preprocessing unit is connected to the signal correction module; The signal preprocessing unit is used to denoise the dynamic echo signal; wherein the denoising method includes at least one of a finite length unit impulse response low-pass filter, wavelet decomposition denoising, and a low-frequency component of a maximum discrete wavelet transform.

8. The short-range millimeter wave radar displacement measurement system according to claim 1, characterized in that: The displacement measurement module includes an inverse tangent demodulation unit, and the inverse tangent demodulation unit is connected to the signal correction module; The inverse tangent demodulation unit is used to perform inverse tangent demodulation on the corrected dynamic echo signal to obtain the displacement measurement result; the expression of the displacement measurement result is: Where d(t) represents the displacement measurement result at time t, I' a (t) is the corrected dynamic echo I signal, Q' a (t) is the corrected dynamic echo Q signal.

9. The short-range millimeter wave radar displacement measurement system according to claim 1, characterized in that: The displacement measurement module includes a long displacement measurement unit, and the long displacement measurement unit is connected to the signal correction module; The long displacement measurement unit is used to obtain the displacement measurement result by using a translation phase angle algorithm when the displacement information changes more than a half-wavelength measurement range; the expression of the displacement measurement result is: Where d(t) represents the displacement measurement result at time t, I' I (t) is the corrected dynamic echo I signal, Q' a (t) is the corrected dynamic echo Q signal.

10. The short-range millimeter wave radar displacement measurement system according to claim 1, characterized in that: The period T of the first static echo signal is: Wherein, v is the fixed rate of change of the distance between the millimeter wave radar and the object to be measured, λ is the wavelength of the millimeter wave radar, and f is the frequency of the first static echo signal.

Images