A homodyne laser interferometer signal phase discrimination method and apparatus

Abstract

The application discloses a homodyne laser interferometer signal phase demodulation method and device, and the method comprises the following steps: obtaining redundant measurement information of the homodyne laser interferometer; calibrating model parameters of an interference signal model based on the redundant measurement information; obtaining an integer part of a real-time phase to be solved, and calculating a decimal part of the real-time phase by using the calibrated interference signal model, and obtaining the real-time phase based on the integer part and the decimal part. Compared with an ellipse correction method suitable for a homodyne quadrature interferometer, the method uses three-phase and more than three-phase signals, increases measurement redundant information, reduces accidental errors of displacement measurement caused by noise, and makes the displacement measurement result have higher precision. Moreover, the method does not need to seek a linear conversion relationship between multiple-phase signals and quadrature signals, and because the redundant measurement information is fully utilized, the displacement measurement result can stably approach a theoretical upper limit of precision when any number of detection signals.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of signal processing of precision measurement, and in particular to a method for phase demodulation of a homodyne laser interferometer. BACKGROUND

[0002] The increasingly developed ultra-precision machining industry puts forward higher requirements on the precision, resolution and other indicators of displacement measuring instruments. The homodyne laser interferometer is based on the single-frequency laser interference principle, takes the laser wavelength as the reference, and can realize nanometer-level precision displacement measurement, with the advantages of high precision, large range, non-contact, etc. Since the displacement to be measured is indirectly represented by the phase of the interferometer photoelectric detector signal, the accuracy of the phase demodulation algorithm directly determines the accuracy of the displacement measurement. How to eliminate nonlinear errors and reduce accidental errors to improve the accuracy and precision of displacement measurement has always been the focus of research on the signal processing module of the homodyne laser interferometer.

[0003] There are three factors that cause nonlinear errors in the traditional homodyne quadrature interferometer during signal phase demodulation: (1) the photoelectric detection signal contains unknown DC bias; (2) the amplitudes of the two photoelectric detection signals are not strictly equal; (3) the phases of the two photoelectric detection signals are not strictly orthogonal. The classical nonlinear error correction method uses an ellipse model to fit the two photoelectric detection signals to calibrate the DC bias error, amplitude inequality error and non-orthogonal error of the signals, as described in Heydemann P. Determination and correction of quadrature fringe measurement errors in interferometers. Applied Optics, 1981, 20(19): 3382-3384. In addition, patents CN109539976 and CN109539975 use a spiral phase plate and a liquid crystal phase retarder, respectively, to generate phase changes in the interference light to obtain data for error correction, and then perform ellipse fitting on the data to correct the errors. Due to the lack of quantitative analysis of the fitting process, the fitting accuracy of the ellipse correction is greatly affected by the number and distribution of the data points. When the data points are few and unevenly distributed within the ellipse, the fitting accuracy is difficult to guarantee, and increasing the number of data points will increase the time spent on calibration and reduce the calibration and measurement efficiency of the interferometer. Patent CN101839686 further considers the harmonic components of the interference signal on the basis of the ellipse correction, and supplements the nonlinear error correction method for harmonics. However, the first-order approximation of the harmonic model is used for phase calculation, so the accuracy still needs to be improved. Patent CN106225667 compensates for nonlinear errors by adjusting the optical layout and adjusting the gain, which requires high performance of optical elements such as polarizing plates and polarization beam splitters, and increases the complexity of the system.

[0004] In addition, increasing the number of detection signals, i.e., multiphase homodyne interferometry technology, can further reduce accidental errors caused by noise, see Greco V, Iemmi C, Ledesma S, et al. Multiphase homodyne interferometry: analysis of some error sources. Applied Optics, 1995, 34(13): 2207-2213. However, the existing multiphase interferometer signal phase demodulation method mostly linearly combines three-phase signals or four-phase signals into two-phase new orthogonal signals, and still uses ellipse correction to compensate for nonlinear errors, see Greco V, Iemmi C, Ledesma S, et al. Three-channel Homodyne Interferometer. Applied Optics, 1994. It can be seen that, in addition to being affected by the number and distribution of fitting data points, there is no general criterion for how to select a reasonable signal linear combination relationship. An inappropriate transformation relationship will not be able to fully utilize the redundant detection information and obtain a theoretical accuracy better than that of the quadrature interferometer.

[0005] In summary, the ellipse correction method widely used for nonlinear error compensation of homodyne quadrature interferometers has a precision limited by the number and distribution of fitting data points, and cannot avoid the contradiction between high precision and high calculation speed. Increasing the number of detection signals can further improve the precision, but the existing homodyne multiphase interferometer signal processing method only applies to three-phase signals or four-phase signals with two special numbers, and cannot introduce more signals with more numbers to reduce random errors and improve precision. In addition to three-phase signals or four-phase signals, other signals with other numbers cannot stably provide the highest precision approaching the theoretical upper limit when using signal linear combination for phase demodulation. SUMMARY

[0006] The technical problem to be solved by the present application is that the ellipse correction method in the prior art has a precision limited by the number and distribution of fitting data points, and the existing homodyne multiphase interferometer signal processing method only applies to three-phase signals or four-phase signals with two special numbers, and cannot introduce more signals with more numbers to reduce random errors and improve precision. In addition to three-phase signals or four-phase signals, other signals with other numbers cannot stably provide the highest precision approaching the theoretical upper limit when using signal linear combination for phase demodulation.

[0007] To solve the above technical problems, the present application provides a homodyne laser interferometer signal phase demodulation method, comprising:

[0008] Obtaining redundant measurement information of a homodyne laser interferometer;

[0009] calibrate model parameters of the interference signal model based on the redundant measurement information;

[0010] obtain an integer part of a real-time phase to be solved, and obtain a decimal part of the real-time phase by using the calibrated interference signal model, and obtain the real-time phase based on the integer part and the decimal part.

[0011] Optionally, the step of obtaining the redundant measurement information of the homodyne laser interferometer comprises

[0012] At least three photodetectors are installed on an interference light path of the homodyne laser interferometer, and after being converted by an analog-to-digital converter, multi-channel photodetector signals become redundant digital quantities used for phase discrimination.

[0013] Optionally, the step of calibrating the model parameters of the interference signal model based on the redundant measurement information comprises:

[0014] The positions of the reference mirror or the moving mirror are moved multiple times, the corresponding interference signals of the photodetectors are recorded, and a corresponding interference signal model equation set is established.

[0015] A nonlinear equation set solving algorithm based on a least square method is used to solve the interference signal model equation set, and the model parameters of the interference signal model are calculated.

[0016] Optionally, the step of obtaining the integer part of the real-time phase to be solved, and obtaining the decimal part of the real-time phase by using the calibrated interference signal model, and obtaining the real-time phase based on the integer part and the decimal part comprises:

[0017] A phase integer part of the real-time phase is obtained by performing cycle counting on the signal;

[0018] A real-time phase decimal part is calculated by establishing a signal model equation set to be discriminated, substituting the calibrated model parameters, and using a nonlinear equation set solving algorithm based on a least square method to solve the equation set.

[0019] The phase integer part and the phase decimal part are added to obtain the real-time phase.

[0020] Optionally, the step of using the nonlinear equation set solving algorithm based on the least square method to solve the equation set comprises:

[0021] An iteration initial value X0 of a variable X is calculated by using a preset parameter nominal value for a nonlinear equation set Y=F(X)+e of an interference signal;

[0022] Y is a detection signal, X is a quantity to be solved, and e is a signal noise.

[0023] A minimum target function is selected The variable X is solved iteratively according to the following iterative formula:

[0024] X k+1 =X k +[J T (X k )J(X k )] -1 J T (X k )[Y-F(X k )]

[0025] Wherein, is the Jacobian matrix of the signal model function;

[0026] Based on the given error preset value ε and the maximum number of iterations k max , if ||X k+1 -X k ||≥ε and k<k max , the minimum target function is selected According to the iterative formula, the variable X is iteratively solved, and the iteration is continued, otherwise the iteration is ended and the solution result X close to the true value is obtained k+1 .

[0027] To solve the above technical problems, the application provides a zero difference laser interferometer signal phase discrimination device, comprising:

[0028] A redundant information acquisition module is configured to acquire redundant measurement information of the zero difference laser interferometer;

[0029] A model parameter calibration module is configured to calibrate model parameters of the interference signal model based on the redundant measurement information;

[0030] A phase solution module is configured to acquire an integer part of a real-time phase to be solved, calculate a decimal part of the real-time phase by using the calibrated interference signal model, and obtain the real-time phase based on the integer part and the decimal part.

[0031] Optionally, the redundant information acquisition module is specifically configured to:

[0032] At least three photoelectric detectors are installed on an interference light path of the zero difference laser interferometer, and multi-channel photoelectric signals are converted into redundant digital quantities for phase discrimination after being converted by an analog-to-digital converter.

[0033] Optionally, the model parameter calibration module is specifically configured to:

[0034] The position of a reference mirror or a moving mirror is moved for multiple times, the interference signals of the detectors are recorded, and a corresponding interference signal model equation set is established;

[0035] Solving the interference signal model equation set by using a nonlinear equation set solving algorithm based on the least square method to calculate the model parameters of the interference signal model.

[0036] Optionally, the phase calculation module is specifically configured to:

[0037] The phase integer part of the real-time phase is obtained by performing cycle counting on the signal.

[0038] The real-time phase decimal part is calculated by establishing a signal model equation set to be phased, substituting the calibrated model parameters, and solving the equation set by using a nonlinear equation set solving algorithm based on the least square method.

[0039] The real-time phase is obtained by adding the phase integer part and the decimal part.

[0040] Optionally, the model parameter calibration module is specifically configured to:

[0041] S1: Using a preset parameter nominal value to calculate an iteration initial value X0 of a variable X for a nonlinear equation set Y = F(X) + e of an interference signal;

[0042] Wherein, Y is a detection signal, X is a to-be-calculated quantity, and e is a signal noise.

[0043] S2: Selecting a minimization objective function The variable X is iteratively solved according to the following iteration formula:

[0044] X k+1 =X k +[J T (X k )J(X k )] -1 J T (X k )[Y-F(X k )]

[0045] Wherein, is a Jacobian matrix of a signal model function.

[0046] S3: Based on a given error preset value ε and a maximum iteration number k max , if ||X k+1 -X k ||≥ε and k < k max , then returning to S2 to continue iteration, otherwise ending iteration and obtaining a solution result X k+1 close to the true value.

[0047] To solve the above technical problems, the present application provides a computer device, comprising a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor implements the above method when executing the computer program.

[0048] To solve the above technical problems, the present application provides a computer readable storage medium, which stores a computer program, wherein the program is executed by a processor to implement the above method.

[0049] Compared with the prior art, one or more embodiments of the above scheme can have the following advantages or beneficial effects:

[0050] The zero difference laser interferometer signal phase discrimination method and device of the present application use three-phase and more than three-phase signals, increase the measurement redundancy information, reduce the accidental error of displacement measurement caused by noise, and make the displacement measurement result have higher precision. Moreover, the method does not need to seek the linear conversion relationship between the multiple-phase signal and the quadrature signal, and can make the displacement measurement result stably approach the theoretical upper limit of precision at any number of detection signals by fully utilizing the redundant measurement information. BRIEF DESCRIPTION OF DRAWINGS

[0051] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0052] Figure 1 A flow chart of the zero difference laser interferometer signal phase discrimination method provided by the embodiment of the present application;

[0053] Figure 2 A distribution diagram of the decimal part of the phase of each detector signal in the zero difference laser interferometer signal phase discrimination method provided by the embodiment of the present application;

[0054] Figure 3 A structure diagram of the zero difference laser interferometer signal phase discrimination device provided by the embodiment of the present application;

[0055] Figure 4 A structure diagram of the experimental system used in the zero difference laser interferometer signal phase discrimination method provided by the embodiment of the present application;

[0056] Figure 5a The displacement measurement error obtained by the elliptical correction method provided by the embodiment of the present application;

[0057] Figure 5b The displacement measurement error obtained by performing interferometer displacement measurement in the case of four probe signals provided by the embodiment of the present application;

[0058] Figure 5c The displacement measurement error obtained by performing interferometer displacement measurement in the case of four probe signals provided by the embodiment of the present application;

[0059] Figure 6 The displacement root mean square error comparison chart of the zero difference laser interferometer signal phase detection method using the ellipse correction method and the zero difference laser interferometer signal phase detection method provided by the embodiment of the present application;

[0060] Figure 7 The structural diagram of a computer device provided by the present application.

[0061] Explanation of the figure numbers in the drawings :

[0062] Photoelectric detector 301, gain controller 302, low pass filter 303, field programmable logic gate array 304, analog-to-digital converter 305, host computer 306, fiber coupler 307, non-polarization beamsplitter 308, single frequency laser 309, polarization beamsplitter A 310, 1 / 4 waveplate A 311, reference mirror 312, retroreflector 313, polarization beamsplitter B 314, piezoelectric ceramic motion stage 315, motion mirror 316, 1 / 4 waveplate B 317;

[0063] Single frequency laser 401, fiber coupler 402, non-polarization beamsplitter 403, polarization beamsplitter A 404, 1 / 4 waveplate A 405, reference mirror 406, retroreflector 407, polarization beamsplitter B 408, motion mirror 409, 1 / 4 waveplate B 410, piezoelectric ceramic motion stage 411. DETAILED DESCRIPTION

[0064] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0065] The ellipse correction method widely used for compensating nonlinear errors of a homodyne quadrature interferometer has the problems of precision limited by the number and distribution of fitting data points, and the contradiction between high precision and high calculation speed. Increasing the number of detection signals can further improve the precision, but the existing homodyne multi-coherence interferometer signal processing method can only introduce signals in two special number cases of three-phase signals or four-phase signals to reduce random errors and improve precision, and cannot introduce signals in more number cases. When the signals in the number cases other than three-phase signals or four-phase signals are used for phase demodulation in a linear combination manner, they cannot stably provide the highest precision approaching the theoretical upper limit.

[0066] To solve the problems of the ellipse correction method in the prior art, the precision of which is limited by the number and distribution of fitting data points, and the existing homodyne multi-coherence interferometer signal processing method which can only introduce signals in two special number cases of three-phase signals or four-phase signals to reduce random errors and improve precision, and cannot introduce signals in more number cases, and when the signals in the number cases other than three-phase signals or four-phase signals are used for phase demodulation in a linear combination manner, they cannot stably provide the highest precision approaching the theoretical upper limit, the present application provides a homodyne laser interferometer signal phase demodulation method and device.

[0067] The homodyne laser interferometer signal phase demodulation method provided by the present application will be described below.

[0068] Example 1

[0069] As shown in Figure 1 , the present application provides a homodyne laser interferometer signal phase demodulation method, which comprises:

[0070] Step S101: Obtain redundant measurement information of a homodyne laser interferometer.

[0071] In an implementation manner, at least three photoelectric detectors can be installed on an interference light path of the homodyne laser interferometer, and the multi-channel photoelectric signals are converted into redundant digital quantities for phase demodulation after passing through an analog-to-digital converter. It should be noted that when the redundant measurement information is obtained by installing at least three photoelectric detectors, the phases of the signals do not need to be orthogonal.

[0072] Specifically, the redundant measurement information is obtained as follows: in a single-frequency laser interferometric measurement system, laser generated by a single-frequency laser passes through a beam splitter to divide into one measurement light and one reference light, the two lights return through a mirror to interfere, and N (N≥3) photoelectric detectors are arranged on the interference light path, the signal sizes of the detectors are in a sinusoidal function relationship with the displacement change amount of a moving mirror, and the signals are used as input signals of a phase demodulation method. One of the detector signals is taken as a reference signal, and the phase change thereof includes an integer period part ( The integer part of the real-time phase is obtained by counting the periods of the signal The remaining detector signals are spaced apart from the reference detector signal by a fractional part of the phase of the reference detector signal The distribution of the fractional part of the phase of each detector signal is shown in the diagram Figure 2 .

[0073] Step S102: based on the redundant measurement information, calibrate the model parameters of the interference signal model.

[0074] In an implementation, the position of the reference mirror or the moving mirror can be moved multiple times, the corresponding interference signals of the detectors are recorded, and a corresponding interference signal model equation set is established; and a nonlinear equation set solving algorithm based on the least square method is used to solve the interference signal model equation set, and the model parameters of the interference signal model are calculated.

[0075] Step S103: obtain the integer part of the real-time phase to be solved, calculate the fractional part of the real-time phase by using the calibrated interference signal model, and obtain the real-time phase based on the integer part and the fractional part.

[0076] In an implementation, the phase integer part of the real-time phase is obtained by counting the periods of the signal; the fractional part of the real-time phase is calculated by establishing a signal model equation set to be evaluated, substituting the calibrated model parameters, and using a nonlinear equation set solving algorithm based on the least square method to solve the equation set; and the real-time phase is obtained by adding the phase integer part and the fractional part. Specifically, the phase integer part of the real-time phase can be obtained by counting the periods of the detection signal The integer part of the phase to be measured is calculated The fractional part of the phase to be measured can be calculated by using the calibrated interference signal model to calculate the fractional part of the real-time phase.

[0077] Specifically, the step of calculating the fractional part of the real-time phase includes S1 to S3:

[0078] S1: using a preset parameter nominal value, calculate the iteration initial value X0 of the variable X for the nonlinear equation set Y=F(X)+e of the interference signal;

[0079] Wherein, Y is the detection signal, X is the quantity to be solved, and e is the signal noise;

[0080] S2: select the minimization objective function According to the following iteration formula, the variable X is iteratively solved:

[0081] X k+1 = X k +[J T (X k )J(Xk ) -1 J T (X k )[Y-F(X k )

[0082] where, is the Jacobian matrix of the signal model function;

[0083] S3: if the given error preset value ε and the maximum iteration number k max , return S2 to continue iteration, otherwise end iteration and get the solution close to the true value X k+1 k ||≥ε and k max k+1 .

[0084] Specifically, the interference signal model parameter self-calibration: the model of each detector signal is as follows

[0085]

[0086] where, is the signal phase decimal part of the reference detector, is the phase interval between the remaining N-1 detectors and the reference detector, A k ,p k ,ε k (k=0,1,2,...,N-1) is the AC amplitude, DC offset and measurement noise of each detector.

[0087] It should be noted that the signal phase decimal part of the reference detector is the real-time phase decimal part to be solved. And the phase interval between the remaining N-1 detectors and the reference detector characterizes the relative position between the detectors.

[0088] After completing the interference signal model parameter self-calibration, when the moving mirror is at the position to be measured, the phase calculation is carried out based on the detector signal model shown by the following formula.

[0089]

[0090] where, the model parameters are all substituted with the calibrated values.

[0091] The unknown quantities in the above signal equation set only include the reference detector phase and the signal noise ε0,ε1,...,ε N-1 , and similarly to the self-calibration, the equation set is recorded as

[0092] Y=F(X)+e​​

[0093] where Y = [y0, y1,..., yN-1]T N-1 ] T is the detected signal, is the phase to be measured, e = [e0, e1,..., eN-1]T N-1 ] T is the signal random noise.

[0094] The above equation set is solved by using a least square based nonlinear equation set solving method, and the decimal part of the phase to be measured is obtained

[0095] The integer part and the decimal part are added to obtain the phase to be measured as shown in the following formula

[0096] In one implementation, the least square based nonlinear equation set solving method in the method has the following specific steps:

[0097] 1) For the nonlinear equation set Y = F(X) + e, first calculate the initial value X0 of the algorithm for iteratively solving the variable X.

[0098] For the self-calibration of the interference signal model parameters, since the signal has been normalized in advance, in the variable X to be solved, the iteration initial value of the signal amplitude A0,..., A N-1 is 1, the iteration initial value of the direct current bias p0,..., p N-1 is 0, the initial value of the phase interval is the design nominal value, and the iteration initial value of the reference detector signal phase is determined by the following formula

[0099]

[0100] Since the is not an integer multiple of π when the detectors are arranged, because in this case the signal phases y0, y k are consistent or exactly opposite, no additional effective measurement information is added in the equation set, and this is also true when k = 1. Therefore, the above formula always makes sense.

[0101] For real-time phase calculation, the iteration initial value of the reference detector signal phase is determined by the following formula

[0102]

[0103] The displacement of the M times moving mirror is changed to obtain M signal model equation sets, which contain M × N equations, as shown in the following formula

[0104]

[0105] ...

[0107]

[0108] where, are the decimal part of the reference detector signal phase under different displacement of M mirrors, respectively.

[0109] The above nonlinear equations contain MxN equations, and contain the reference detector signal phase System parameters A k ,p k (k=0, 1, 2,..., N-1), There are 3N+M-1 variables to be solved in total, and ε k (k=1, 2,..., MN-1) are MxN random variables. According to the above equation set, it is recorded as:

[0110] Y=F(X)+e

[0111] where, is the 3N+M-1 variables to be solved, Y=[y0, y1,..., y MN-1 ] T is the detection signal, e=[ε0, ε1,..., ε MN-1 ] T is the signal random noise.

[0112] The above equation set is solved by using the nonlinear equation solving method based on the least square method, and the model parameters in the variable X are calculated which is the calibration value, and the model parameter self-calibration is completed.

[0113] 2) Select the minimization objective function The variable X is iteratively solved according to the following iterative formula:

[0114] X k+1 =X k +[J T (X k )J(X k )] -1 J T (X k )[Y-F(X k )]

[0115] where, is the Jacobian matrix of the signal model function.

[0116] 3) Given error preset value ε and maximum iteration number k max , if ||Xk+1 -X k ||≥ε and k <k max Then return to S2 and continue the iteration; otherwise, end the iteration to obtain a solution X that is close to the true value. k+1 .

[0117] As can be seen from the above, the zero-difference laser interferometer signal phase detection method provided by the present invention divides the signal phase measurement into integer and fractional part measurements, obtains redundant measurement information by increasing the number of detection signals, solves the nonlinear equations of the interference signal model using an iterative algorithm, and simultaneously calculates the phase interval between multiple detectors, the AC amplitude of each signal, the DC bias and the measured phase, thereby realizing the self-calibration of the interference signal model parameters and high-precision phase calculation.

[0118] Compared to the ellipse correction method applicable to zero-difference orthogonal interferometers, this method uses three-phase or higher signals, increasing measurement redundancy and thus reducing random errors in displacement measurement caused by noise, resulting in higher precision. Furthermore, this method does not require seeking a linear transformation relationship between multiphase and orthogonal signals, and by fully utilizing redundant measurement information, it can stably approach the theoretical upper limit of accuracy with any number of probe signals.

[0119] The following describes the zero-difference laser interferometer signal phase detection device provided in the embodiments of the present invention.

[0120] Example 2

[0121] like Figure 3 As shown, the present invention provides a phase detection device for a zero-difference laser interferometer signal, comprising:

[0122] Redundancy information acquisition module 210 is used to acquire redundant measurement information of the zero-difference laser interferometer;

[0123] The model parameter calibration module 220 is used to calibrate the model parameters of the interference signal model based on the redundant measurement information.

[0124] The phase calculation module 230 is used to perform real-time phase calculation using the calibrated interference signal model.

[0125] In one scenario, the redundant information acquisition module 210 is specifically used to install at least three photodetectors on the interference optical path of the zero-difference laser interferometer, and the multiple photoelectric signals are converted into redundant digital quantities for phase detection after passing through an analog-to-digital converter.

[0126] In one scenario, the model parameter calibration module 220 is specifically configured to record the corresponding interference signals of the detector by moving the position of the reference mirror or the moving mirror multiple times, and to establish a corresponding interference signal model equation set; and to solve the interference signal model equation set by using a nonlinear equation set solving algorithm based on the least square method to calculate the model parameters of the interference signal model.

[0127] In one scenario, the phase calculation module is specifically configured to obtain the integer part of the real-time phase by performing period counting on the signal; to obtain the decimal part of the real-time phase by establishing a signal model equation set to be evaluated, substituting the calibrated model parameters, and solving the equation set by using a nonlinear equation set solving algorithm based on the least square method to calculate the real-time phase decimal part; and to obtain the real-time phase by adding the integer part and the decimal part of the phase.

[0128] Further, the model parameter calibration module 220 is specifically configured to:

[0129] S1: Using the preset parameter nominal value to calculate the initial value X0 of the variable X for the nonlinear equation set Y = F(X) + e of the interference signal;

[0130] wherein Y is the detection signal, X is the quantity to be calculated, and e is the signal noise;

[0131] S2: Selecting a minimization objective function According to the following iteration formula, the variable X is iteratively solved:

[0132] X k+1 =X k +[J T (X k )J(X k )] -1 J T (X k )[Y-F(X k )]

[0133] wherein, is the Jacobian matrix of the signal model function;

[0134] S3: Based on the given error preset value ε and the maximum number of iterations k max , if ||X k+1 -X k ||≥ε and k < k max , then return to S2 to continue iteration, otherwise end the iteration and obtain the solution result X k+1 close to the true value.

[0135] From the above, the signal phase discrimination device of the homodyne laser interferometer provided by the application divides the signal phase measurement into integer part and decimal part measurement, acquires redundant measurement information by increasing the number of detection signals, solves the nonlinear equation set of the interference signal model by using an iterative algorithm, and simultaneously calculates the mutual interval phase between multiple detectors, the AC amplitude of each signal, the DC bias and the measured phase, so that the interference signal model parameters are self-calibrated and high-precision phase calculation is realized.

[0136] Compared with the elliptical correction scheme suitable for the homodyne quadrature interferometer, the device uses three-phase and more than three-phase signals, increases the measurement redundancy information, reduces the accidental error of displacement measurement caused by noise, and makes the displacement measurement result have higher precision. Moreover, the device does not need to seek the linear conversion relationship between multiple signals and quadrature signals, and because the redundant measurement information is fully utilized, the displacement measurement result can stably approach the theoretical upper limit of precision when the number of detection signals is arbitrary.

[0137] The signal phase discrimination method of the homodyne laser interferometer provided by the application will be described below in combination with specific examples. Figure 4 As shown in the single-frequency laser interferometer, the laser generated by the single-frequency laser 309 is divided into a reference light and a measurement light after passing through the polarization beam splitter 310; the reference light passes through the 1 / 4 wave plate 311, is reflected by the reference mirror 312, returns to the original path, passes through the polarization beam splitter A 310, and reaches the non-polarization beam splitter 308, and the reference light is deflected by 90° by passing through the 1 / 4 wave plate A 311 twice; the measurement light passes through the polarization beam splitter B 314 and the 1 / 4 wave plate B 317 in turn, is reflected by the moving mirror 316, returns to the original path, is reflected by the polarization beam splitter B 314, the reflector 313, and the polarization beam splitter B 314 in turn, passes through the 1 / 4 wave plate B 317, is reflected by the moving mirror 316, returns, and reaches the non-polarization beam splitter 308 after passing through the polarization beam splitter B 314, and the measurement light is deflected by 180° by passing through the 1 / 4 wave plate B 317 four times; the piezoelectric ceramic motion table 315 can cause the moving mirror 316 fixed thereon to have a corresponding displacement; the reference light and the measurement light interfere with each other at the non-polarization beam splitter 308 to form interference light; the interference light is transmitted through the optical fiber after entering the optical fiber coupler 307, is received by the photodetector 301 in the signal processing board, is converted into an analog voltage signal, is subjected to gain control by the gain controller 302 and low-pass filtering by the low-pass filter 303 in turn, is converted into a signal digital quantity by the analog-to-digital converter 305, is received by the field programmable gate array (FPGA) 304, and the interference signal phase is obtained by processing the algorithm in the FPGA according to the application, and the phase discrimination result is output by the host computer 306.

[0138] As shown in the single-frequency laser interferometer, Figure 4The zero difference interferometer displacement measurement system shown applies the signal phase discrimination method of the present application, which is encoded and run in the FPGA of the signal processing board card. In an embodiment, the single frequency laser source has a wavelength of 780 nm, the motion mirror is driven by a piezoelectric ceramic with a displacement resolution of 0.1 nm, and the measured signal-to-noise ratio of the photoelectric signal in the experiment is 37.6 dB. Under the experimental conditions of an interference signal-to-noise ratio of 37.6 dB, the phase discrimination method proposed in the present application is used to measure the displacement of the interferometer in the case of three probe signals and four probe signals, and the displacement measurement errors obtained are as shown in Figure 5b 、 Figure 5c On the contrary, the displacement measurement error obtained by using the ellipse correction method is as shown in Figure 5a The average displacement measurement error of the two phase discrimination methods is zero, and the phase discrimination method proposed in the present application has smaller displacement measurement error variance. The root mean square error of displacement of the two methods is as shown in Figure 6 The root mean square error of displacement of the phase discrimination method proposed in the present application is 1.11 nm and 0.85 nm in the case of three probe signals and four probe signals, respectively, which is reduced by 26% and 44% compared with the ellipse correction method; the phase discrimination method in the FPGA spends less than 50us every time, which meets the real-time measurement requirements of most current precision measurement equipment.

[0139] Example 3

[0140] To solve the above technical problems, the present application provides a computer device, as shown in Figure 7 It includes a memory 510, a processor 520, and a computer program stored in the memory and executable on the processor, and the processor implements the method as described above when executing the computer program.

[0141] The computer device can be a desktop computer, a notebook computer, a palm computer, a cloud server and the like. The computer device can include, but is not limited to, a processor 520 and a memory 510. Those skilled in the art can understand that Figure 7 It is only an example of a computer device and does not constitute a limitation on the computer device, and can include more or fewer components than the illustration, or combine certain components, or different components, for example, the computer device can also include an input / output device, a network access device, a bus, etc.

[0142] The processor 520 can be a central processing unit (CPU), and can also be other general-purpose processors, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or the processor can also be any conventional processor.

[0143] The memory 510 can be an internal storage unit of the computer device, such as a hard disk or a memory of the computer device. The memory 510 can also be an external storage device of the computer device, such as a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, etc. Further, the memory 510 can include both an internal storage unit and an external storage device of the computer device. The memory 510 is used to store the computer program and other programs and data required by the computer device. The memory 510 can also be used to temporarily store data that has been output or will be output.

[0144] Example 4

[0145] The embodiments of the present application further provide a computer readable storage medium, which can be the computer readable storage medium included in the memory in the above-mentioned embodiments, or can be a computer readable storage medium that exists separately and is not assembled into the computer device. The computer readable storage medium stores one or more computer programs, and the programs are executed by the processor to implement the above-mentioned method.

[0146] The integrated modules / units, if implemented in the form of software functional units and sold or used as independent products, can be stored in a computer readable storage medium. Based on such understanding, all or part of the processes in the above-mentioned embodiment methods can also be completed by a computer program instructing related hardware, and the computer program can be stored in a computer readable storage medium. The computer program can implement the steps of each method embodiment when executed by a processor. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or some intermediate forms. The computer readable medium can include any entity or device, recording medium, U disk, mobile hard disk, magnetic disk, optical disk, computer memory 510, read-only memory (ROM), random access memory (RAM), electrical carrier signal, telecommunication signal, and software distribution medium, etc. that can carry the computer program code. It should be noted that the computer readable medium can include or exclude contents according to the requirements of legislation and patent practice in the jurisdiction, for example, in some jurisdictions, according to legislation and patent practice, the computer readable medium does not include electrical carrier signals and telecommunication signals.

[0147] For system or device embodiments, since they are basically similar to method embodiments, they are described more simply, and the relevant parts can refer to the part of the description of the method embodiments.

[0148] Those skilled in the art can clearly understand that, for the convenience and brevity of description, only the division of the above functional units and modules is taken as an example, and in actual application, the above functions can be completed by different functional units and modules according to needs, that is, the internal structure of the device is divided into different functional units or modules to complete all or part of the functions described above. Each functional unit or module in the embodiment can be integrated in one processing unit, or each unit can exist physically, or two or more units can be integrated in one unit. The integrated unit can be realized in the form of hardware or software functional unit. In addition, the specific names of each functional unit or module are only for easy distinction, and do not limit the protection scope of the present application. The specific working process of the units and modules in the system can refer to the corresponding process in the foregoing method embodiments, which will not be repeated here.

[0149] It should be noted that, as used in this document, the terms "apparatus," "device," "system," or the like are intended to refer to a functional operation, and can be implemented in turn by software, hardware, firmware, digital signal processing, and / or combinations of them. It should be noted that, as used in this document, the terms "first," "second," "third," etc., are intended to distinguish between similar objects only, and are not intended to, nor should be construed to, imply that a specific order or sequence is implied. Similarly, use of the terms "top," "bottom," "front," "back," and / or the like are not intended to denote a specific orientation in space, but are used for the purpose of illustration only. Furthermore, the use of the terms "including," "containing," or "comprising" or the like, are intended to be non- exclusive and are used conjunctively to describe components, features, objects, and / or the like that can or can not be present. Additionally, the use of the term "in accordance with" is intended to be non-exclusive and is used conjunctively to describe components, features, objects, and / or the like that can or can not be present.

[0150] It should be understood that the terms used in the specification and the following claims are merely used to describe particular embodiments and do not intend to limit the present application. As used in the specification and the appended claims, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0151] It should also be understood that the term "and / or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items, as well as to the lack of combinations when interpreted in the alternative.

[0152] As used in this specification and claims, the terms "if" and "when" can be interpreted to mean "upon determination" or "in response to a determination" or "in response to detecting," depending on the context. Similarly, the phrase "if it is determined" or "if a described condition or event occurs" can be interpreted to mean "upon determining," or "in response to determining" or "upon detecting," or "in response to detecting," depending on the context.

[0153] The preferred embodiments of the present application have been described above with the intent to enable those skilled in the art to make and use it. Various modifications to these embodiments will occur to those skilled in the art and are intended to be encompassed by the appended claims. The modifications are intended to be as broad as those modifications as would be protected by the prior art and are intended to be within the scope of the present application.

Claims

1. A phase detection method for a homodyne laser interferometer signal, characterized in that, include: Obtain redundant measurement information from a zero-difference laser interferometer; Based on the redundant measurement information, the model parameters of the interference signal model are calibrated; Obtain the integer part of the real-time phase to be solved, and calculate the fractional part of the real-time phase using the calibrated interference signal model, and obtain the real-time phase based on the integer part and the fractional part; The step of acquiring the redundant measurement information of the zero-difference laser interferometer includes: At least three photodetectors are installed in the interference optical path of the zero-difference laser interferometer, and the multiple photoelectric signals are converted into redundant digital quantities for phase detection after being converted by an analog-to-digital converter. The phases of the multiple photoelectric signals are not orthogonal. The step of calibrating the model parameters of the interferometric signal model based on the redundant measurement information includes: The position of the reference mirror or the moving mirror is moved multiple times, the corresponding interference signals of the detector are recorded, and the corresponding interference signal model equations are established. The equations of the interference signal model are solved using a nonlinear equation-solving algorithm based on the least squares method, and the model parameters of the interference signal model are calculated.

2. The phase detection method for a homodyne laser interferometer signal according to claim 1, characterized in that, The steps of obtaining the integer part of the real-time phase to be solved, calculating the fractional part of the real-time phase using the calibrated interference signal model, and obtaining the real-time phase based on the integer part and the fractional part include: The integer part of the real-time phase is obtained by counting the cycles of the signal. By establishing a set of equations for the signal model to be phased, substituting the calibrated model parameters, and using a nonlinear equation-solving algorithm based on the least squares method to solve the above set of equations, the fractional part of the real-time phase is calculated. The real-time phase is obtained by adding the integer part and the fractional part of the phase.

3. The phase detection method for a homodyne laser interferometer signal according to claim 2, characterized in that, The method for solving the above system of equations using a nonlinear equation-solving algorithm based on the least squares method includes: For the nonlinear equation system Y=F(X)+e of the interference signal, the initial iterative value X0 of variable X is calculated using the preset nominal parameter values; Where Y is the detection signal, X is the quantity to be solved, and e is the signal noise; Select the minimum objective function The variable X is solved iteratively using the following iterative formula: X k+1 =X k +[J T (X k )J(X k )] -1 J T (X k )[Y-F(X k )] in, Let be the Jacobian matrix of the signal model function; Based on a given error preset value ε and the maximum number of iterations k max If ||X k+1 -X k ||≥ε and k <k max Then execute the selection of the minimum objective function. The iteration process is repeated according to the given formula to solve for variable X. Otherwise, the iteration ends and a solution close to the true value is obtained. k+1 .

4. A phase detector for a zero-difference laser interferometer signal, characterized in that, include: The redundancy information acquisition module is used to acquire the redundancy measurement information of the zero-difference laser interferometer. The model parameter calibration module is used to calibrate the model parameters of the interference signal model based on the redundant measurement information. The phase calculation module is used to obtain the integer part of the real-time phase to be calculated, and to calculate the fractional part of the real-time phase using the calibrated interference signal model, and to obtain the real-time phase based on the integer part and the fractional part. The redundant information acquisition module is specifically used for: At least three photodetectors are installed in the interference optical path of the zero-difference laser interferometer, and the multiple photoelectric signals are converted into redundant digital quantities for phase detection after being converted by an analog-to-digital converter. The phases of the multiple photoelectric signals are not orthogonal. The model parameter calibration module is specifically used for: The position of the reference mirror or the moving mirror is moved multiple times, the corresponding interference signals of the detector are recorded, and the corresponding interference signal model equations are established. The equations of the interference signal model are solved using a nonlinear equation-solving algorithm based on the least squares method, and the model parameters of the interference signal model are calculated.

5. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the method as described in any one of claims 1 to 3.

6. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the method as described in any one of claims 1 to 3.

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