Device and method for measuring non-linear errors of a dual-frequency interferometer

Abstract

This application relates to a measurement device and method for dual-frequency interferometric nonlinear error. The measurement device includes: a laser output module, an interferometric module, a photoelectric conversion module, and an error calculation module. The laser output module emits a measurement laser to the interferometric module. The interferometric module splits the measurement laser beam and projects the split light signal onto a target object; it also generates an interference signal based on the light signal reflected from the target object. The photoelectric conversion module performs photoelectric conversion on the interference signal to generate an electrical signal. The error calculation module enhances the electrical signal to obtain an enhanced electrical signal, and performs nonlinear error calculation based on the enhanced electrical signal and the parameters of the laser output module and the interferometric module to obtain the calculation result. The enhancement processing is either square operation processing or orthogonal demodulation processing. By enhancing the measurement signal itself, the accuracy of the error measurement result is improved.

Description

Technical Field

[0001] This application relates to the field of laser measurement technology, and in particular to a measuring device and method for measuring dual-frequency interferometric nonlinear error. Background Technology

[0002] With the rapid development of laser technology, dual-frequency (heterodyne) laser interferometers have achieved significant improvements over single-frequency (zero-difference) laser interferometers. They overcome the susceptibility to environmental interference inherent in single-frequency laser interferometers and have been widely used in large-scale equipment such as lithography machines and CNC machine tools. Heterodyne laser interferometers, with their high resolution, large measurement range, and strong traceability, are hailed as the "standard ruler" in the field of precision measurement. However, their ultimate measurement accuracy is not limited by theoretical resolution, but primarily constrained by nonlinear errors caused by factors such as frequency aliasing, polarization aliasing, and ellipticization. These errors are periodic and do not decay with increasing measurement distance. In ultra-precision measurements at the sub-nanometer or even picometer level, they have become a non-negligible systematic error source, severely restricting the application of interferometers in high-end equipment manufacturing and cutting-edge scientific research. Therefore, accurate measurement of nonlinear errors is of great significance for evaluating and improving the accuracy of heterodyne laser interferometers.

[0003] However, in traditional nonlinear error measurement techniques, the optical paths for generating the reference signal and the measurement signal are not completely shared. Therefore, environmental disturbances have inconsistent effects on the two, resulting in measurement errors that are easily affected by the environment, leading to low accuracy in nonlinear error measurement. Summary of the Invention

[0004] Therefore, it is necessary to provide a dual-frequency interferometric nonlinear error measurement device and method that can improve the accuracy of nonlinear error measurement results, addressing the aforementioned technical problems.

[0005] In a first aspect, this application provides a device for measuring dual-frequency interferometric nonlinear error, the device comprising: a laser output module, an interferometric module, a photoelectric conversion module, and an error calculation module;

[0006] The laser output module is used to emit a measurement laser to the interference module;

[0007] The interference module is used to split the measurement laser beam and project the split light signal onto the target object; it is also used to generate an interference signal based on the light signal reflected by the target object.

[0008] The photoelectric conversion module is used to perform photoelectric conversion on the interference signal to generate an electrical signal;

[0009] The error calculation module is used to enhance the electrical signal to obtain an enhanced electrical signal, and to perform nonlinear error calculation based on the enhanced electrical signal, the parameters of the laser output module and the interference module to obtain the calculation result. The enhancement processing is either square operation processing or orthogonal demodulation processing.

[0010] In one embodiment, the error calculation module includes a signal processing module and an error calculation unit;

[0011] The signal processing module is used to enhance the electrical signal to obtain the enhanced electrical signal;

[0012] The error calculation unit is used to perform nonlinear error calculation based on the parameters of the laser output module and the interference module, as well as the enhanced electrical signal, to obtain the calculation result.

[0013] In one embodiment, the signal processing module includes a high-pass filter unit and a signal processing unit;

[0014] The high-pass filter unit is used to perform high-pass filtering on the electrical signal to obtain a filtered first electrical signal;

[0015] The signal processing unit is used to enhance the filtered first electrical signal to obtain an enhanced first electrical signal.

[0016] The error calculation unit is used to perform nonlinear error calculation based on the parameters of the laser output module and the interference module, as well as the enhanced first electrical signal, to obtain the calculation result.

[0017] In one embodiment, the signal processing unit includes: a square operator and a low-pass filter;

[0018] The square operator is used to perform a square operation on the filtered first electrical signal to obtain the square signal of the filtered first electrical signal;

[0019] The low-pass filter is used to perform low-pass filtering on the squared signal to obtain the enhanced first electrical signal.

[0020] In one embodiment, the signal processing unit includes: a phase-locked loop and an amplitude output unit;

[0021] The phase-locked loop is used to output a second electrical signal based on the filtered first electrical signal; the second electrical signal and the filtered first electrical signal have the same frequency, and the phase difference between the second electrical signal and the filtered first electrical signal is constant;

[0022] The amplitude output device is used to perform quadrature demodulation processing on the filtered first electrical signal and the second electrical signal, and then calculate the enhanced first electrical signal.

[0023] In one embodiment, the amplitude output unit includes a first mixer, a phase shifter, a second mixer, a first low-pass filter, a second low-pass filter, and a demodulator;

[0024] The first mixer is used to perform mixing processing on the filtered first electrical signal and the second electrical signal, and output a first mixed signal;

[0025] The first low-pass filter is used to perform low-pass filtering on the first mixing signal to obtain the first branch processed signal;

[0026] The phase shifter is used to shift the second electrical signal by a preset angle to obtain a phase-shifted electrical signal;

[0027] The second mixer is used to perform mixing processing on the phase-shifted electrical signal and the filtered first electrical signal, and output a second mixed signal;

[0028] The second low-pass filter is used to perform low-pass filtering on the second mixing signal to obtain the second branch processed signal;

[0029] The demodulator is used to perform quadrature demodulation on the first branch processed signal and the first branch processed signal to obtain the enhanced first electrical signal.

[0030] In one embodiment, the error calculation unit includes: an error initialization subunit, a coefficient calculator, and an error calculation subunit;

[0031] The coefficient calculator is used to calculate coefficients based on the parameters of the laser output module and the interference module; the parameters include the laser wavelength and the optical subdivision number.

[0032] The error initialization subunit is used to perform mean processing on the enhanced first electrical signal to obtain a third electrical signal, and to perform nonlinear error calculation based on the enhanced first electrical signal and the third electrical signal to obtain the nonlinear error under phase unit.

[0033] The error calculation subunit is used to perform phase displacement conversion on the nonlinear error in the phase unit according to the coefficient, so as to obtain the nonlinear error in the displacement unit.

[0034] Secondly, this application provides a method for measuring dual-frequency interferometric nonlinear error, the method comprising:

[0035] Acquire the electrical signal output by the photoelectric conversion module in the dual-frequency interferometric nonlinear error measurement device;

[0036] The electrical signal is enhanced to obtain an enhanced electrical signal. Based on the enhanced electrical signal and the parameters of the laser output module and the interference module, nonlinear error is calculated to obtain the calculation result. The enhancement process is either square operation processing or orthogonal demodulation processing.

[0037] In one embodiment, the calculation of nonlinear error based on the enhanced electrical signal and the parameters of the laser output module and the interference module to obtain the calculation result includes:

[0038] The coefficients are calculated based on the parameters of the laser output module and the interference module; the parameters include the laser wavelength and the optical subdivision number.

[0039] The enhanced first electrical signal is averaged to obtain a third electrical signal, and the nonlinear error is calculated based on the enhanced first electrical signal and the third electrical signal to obtain the nonlinear error under phase unit.

[0040] The phase shift transformation is performed on the nonlinear error in the phase unit based on the coefficient to obtain the nonlinear error in the phase unit.

[0041] In one embodiment, the step of performing nonlinear error estimation based on the enhanced first electrical signal and the third electrical signal to obtain the nonlinear error in phase unit includes:

[0042] Perform a difference operation on the enhanced first electrical signal and the third electrical signal to obtain a difference signal;

[0043] The nonlinear error under the phase unit is obtained based on the ratio of the difference signal to the third electrical signal.

[0044] The aforementioned dual-frequency interferometric nonlinear error measurement device and method include: a laser output module, an interferometric module, a photoelectric conversion module, and an error calculation module; the laser output module is used to output a measurement laser to the interferometric module; the interferometric module is used to split the measurement laser and project the split light signal onto the target object; it is also used to generate an interference signal based on the light signal reflected from the target object; the photoelectric conversion module is used to perform photoelectric conversion on the interference signal to generate an electrical signal; the error calculation module is used to enhance the electrical signal to obtain an enhanced electrical signal, and to perform nonlinear error calculation based on the enhanced electrical signal and the parameters of the laser output module and the interferometric module to obtain the calculation result. By using the measured laser signal itself as a reference to enhance the signal (i.e., demodulating the amplitude of the measured laser signal), and then calculating the nonlinear error based on the enhanced electrical signal and the parameters of the laser output module and the interferometer module, the accuracy of the nonlinear error calculation results is avoided by using other signals as reference signals. The error measurement process only needs to process the measured laser signal's own data and is not affected by other signals. It has strong anti-interference capabilities, achieves high precision in dual-frequency interferometric nonlinear error calculation results, is simple and easy to implement, and can meet the requirements for nonlinear error testing at the pm level. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the drawings used in the description of the embodiments of this application or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a structural block diagram of a dual-frequency interferometric nonlinear error measurement device in one embodiment;

[0047] Figure 2 This is a structural block diagram of the error calculation module in a dual-frequency interferometric nonlinear error measurement device in one embodiment;

[0048] Figure 3 This is a block diagram of the signal processing module in a dual-frequency interferometric nonlinear error measurement device in one embodiment;

[0049] Figure 4 This is a block diagram of the signal processing unit in a dual-frequency interferometric nonlinear error measurement device in one embodiment;

[0050] Figure 5 This is a block diagram of the signal processing unit in the dual-frequency interferometric nonlinear error measurement device in another embodiment;

[0051] Figure 6 This is a schematic diagram of the amplitude output device in a dual-frequency interferometric nonlinear error measurement device in one embodiment;

[0052] Figure 7 This is a structural block diagram of the error calculation unit in a dual-frequency interferometric nonlinear error measurement device in one embodiment;

[0053] Figure 8 This is a flowchart illustrating a method for measuring dual-frequency interferometric nonlinear error in one embodiment;

[0054] Figure 9 This is a flowchart illustrating the method for measuring dual-frequency interferometric nonlinear error in another embodiment;

[0055] Figure 10 This is a flowchart illustrating the method for measuring the nonlinear error of dual-frequency interferometry in yet another embodiment. Detailed Implementation

[0056] To facilitate understanding of this application, a more complete description of the application will be provided below with reference to the accompanying drawings. Embodiments of the application are shown in the drawings. However, the application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0057] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0058] It is understood that the terms "first," "second," etc., used herein may be used to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of this application, a first resistor may be referred to as a second resistor, and similarly, a second resistor may be referred to as a first resistor. Both the first resistor and the second resistor are resistors, but they are not the same resistor.

[0059] It is understood that the term "connection" in the following embodiments should be understood as "electrical connection," "communication connection," etc., if the connected circuits, modules, units, etc., have electrical signal or data transmission with each other.

[0060] It is understandable that "at least one" refers to one or more, and "multiple" refers to two or more. "At least a part of an element" refers to part or all of an element.

[0061] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising / including” or “having,” etc., specify the presence of the stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. Meanwhile, the term “and / or” as used in this specification includes any and all combinations of the associated listed items.

[0062] With the rapid development of laser technology, dual-frequency (heterodyne) laser interferometers have achieved significant improvements over single-frequency (zero-difference) laser interferometers. They overcome the susceptibility to environmental interference inherent in single-frequency laser interferometers and have been widely used in large-scale equipment such as lithography machines and CNC machine tools. Heterodyne laser interferometers, with their high resolution, large measurement range, and strong traceability, are hailed as the "standard ruler" in the field of precision measurement. However, their ultimate measurement accuracy is not limited by theoretical resolution, but primarily constrained by nonlinear errors caused by factors such as frequency aliasing, polarization aliasing, and ellipticization. These errors are periodic and do not decay with increasing measurement distance. In ultra-precision measurements at the sub-nanometer or even picometer level, they have become a non-negligible systematic error source, severely restricting the application of interferometers in high-end equipment manufacturing and cutting-edge scientific research. Therefore, accurate measurement of nonlinear errors is of great significance for evaluating and improving the accuracy of heterodyne laser interferometers. However, in traditional nonlinear error measurement techniques, the optical paths for generating the reference signal and the measurement signal are not completely shared. Therefore, environmental disturbances have inconsistent effects on the two, resulting in measurement errors that are easily affected by the environment, leading to low accuracy in nonlinear error measurement.

[0063] In view of the above-mentioned technical problems, this application provides a dual-frequency interferometric nonlinear error measuring device that can improve the accuracy of nonlinear error measurement results. The following embodiments will specifically describe the dual-frequency interferometric nonlinear error measuring device.

[0064] In one exemplary embodiment, such as Figure 1 As shown, the dual-frequency interferometric nonlinear error measurement device includes: a laser output module, an interferometric module, a photoelectric conversion module, and an error calculation module;

[0065] Laser output module, used to output measurement laser to the interferometer module;

[0066] The interference module is used to split the measurement laser beam and project the split light signal onto the target object; it is also used to generate an interference signal based on the light signal reflected by the target object.

[0067] The photoelectric conversion module is used to convert interference signals into electrical signals through photoelectric conversion.

[0068] The error calculation module is used to enhance the electrical signal to obtain the enhanced electrical signal. Based on the enhanced electrical signal and the parameters of the laser output module and the interference module, it performs nonlinear error calculation to obtain the calculation result. The enhancement processing is either square operation processing or orthogonal demodulation processing.

[0069] Optionally, the laser output module can be any type of laser, such as a semiconductor laser, solid-state laser, fiber laser, or gas laser. A laser with a specific frequency difference can be selected based on the actual application requirements; no restrictions are imposed here. Methods for generating light of different frequencies include, but are not limited to, incorporating any of the following principles in the laser output module: the Zeeman principle, the acousto-optic frequency shift principle, the birefringence-Zeeeman principle, or the dual-longitudinal-mode principle. The dual-frequency light emitted by the laser output module based on the above principles can be co-path or non-co-path, i.e., spatially separated.

[0070] Optionally, the interference module can be any type of interferometer, such as a dual-frequency laser interferometer, Mach-Zehnder interferometer, Fabry-Perot interferometer, Michelson interferometer, single-axis interferometer, multi-axis interferometer, discrete / integrated interferometer, plane mirror interferometer, pyramidal interferometer, etc., including interferometers with shared dual-frequency optical paths and interferometers with separate dual-frequency optical paths. The photoelectric conversion module can be any type of photodiode, phototransistor, fiber optic converter, photodetector, photoemitter, or photoelectric sensor. The error calculation module can include any type of processor, such as amplifiers and / or filters, digital signal processors, microprocessors, field-programmable gate arrays, application-specific integrated circuits, or system-on-a-chip.

[0071] Optionally, the target object is in motion and can be positioned on the signal output side of the interferometer module. The motion mode of the target object is not limited; it can move at a constant speed, change speed, or in a straight line or curve. It can move towards or away from the interferometer module. The light signal reflected by the target object can contain its displacement information. For example, the initial phase angle of the light signal after beam splitting by the interferometer module is... The light signal reflected by the target object is Where d is the displacement of the target object, n is the refractive index, and N is the optical subdivision number of the interferometer module. To measure the laser wavelength.

[0072] Optionally, the parameters of the laser output module can be the laser wavelength, and the parameters of the interference module can be the optical subdivision number, which can be set according to the actual needs of the scenario.

[0073] Optionally, the enhanced electrical signal can be the amplitude signal of the electrical signal or the square signal of the amplitude of the electrical signal.

[0074] In the embodiments of this application, the laser output module is activated to emit a measurement laser beam. The laser output module emits a measurement laser with a fixed frequency difference to the interference module according to a pre-existing frequency difference. After receiving the measurement laser, the interference module splits the measurement laser according to its frequency and projects the split light signal onto the target object. The target object reflects the projected light signal, which is then transmitted back to the interference module. The interference module combines the reflected light signal from the target object to generate an interference signal, which is then output to the photoelectric conversion module. It should be noted that after splitting the measurement laser, the interference module obtains two beams of different frequencies. Optionally, the two beams of different frequencies can be simultaneously projected onto the target object for reflection, and the two beams reflected from the target object can be combined to generate an interference signal, which is then output to the photoelectric conversion module. Alternatively, one frequency beam can be reflected by the reflective surface of the interference module itself, and the other frequency beam can be projected onto the target object for reflection. The beam reflected from the target object and the signal reflected from the reflective surface of the interference module can be combined to generate an interference signal, which is then output to the photoelectric conversion module. The beams projected onto the reflecting surface of the interference module and the beams projected onto the target object can be configured according to the actual scene requirements of the interference module. The photoelectric conversion module performs photoelectric conversion on the interference signal, generating an electrical signal, which is then transmitted to the error calculation module for processing. The error calculation module performs enhancement processing on the electrical signal. Optionally, in the first method, it performs high-pass filtering on the electrical signal, then squares and performs low-pass filtering on the filtered signal to obtain an enhanced first electrical signal. Based on the first electrical signal, the parameters of the laser output module, and the interference module, it performs nonlinear error calculation to obtain the result. Optionally, in the second method, it performs high-pass filtering on the electrical signal, inputs the filtered signal to a phase-locked loop (PLL), and performs quadrature demodulation on the filtered signal and the PLL output information to obtain an enhanced first electrical signal. Based on the first electrical signal, the parameters of the laser output module, and the interference module, it performs nonlinear error calculation to obtain the result. It should be noted that the high-pass filtering and phase-locked loop in the above two enhancement processing operations can also be omitted. That is, the electrical signal output by the photoelectric conversion module can be directly squared and low-pass filtered to obtain the first enhanced electrical signal; or the electrical signal output by the photoelectric conversion module can be quadrature demodulated to obtain the first enhanced electrical signal.

[0075] The aforementioned dual-frequency interferometric nonlinear error measurement device includes a laser output module, an interferometric module, a photoelectric conversion module, and an error calculation module. The laser output module emits a measurement laser to the interferometric module. The interferometric module splits the measurement laser beam and projects the split light signal onto the target object; it also generates an interference signal based on the light signal reflected from the target object. The photoelectric conversion module performs photoelectric conversion on the interference signal to generate an electrical signal. The error calculation module enhances the electrical signal to obtain an enhanced electrical signal, and calculates the nonlinear error based on the enhanced electrical signal and the parameters of the laser output module and the interferometric module to obtain the calculation result. By using the laser signal itself as a reference to enhance the signal (i.e., demodulating the signal amplitude), and then calculating the nonlinear error based on the enhanced electrical signal and the parameters of the laser output module and the interferometer module, the accuracy of the nonlinear error measurement results is avoided by using other signals as reference signals. The error calculation process only needs to process the laser signal itself and is not affected by other signals. It has strong anti-interference capabilities, achieves high precision in dual-frequency interferometric nonlinear error calculation results, is simple and easy to implement, and can meet the requirements for nonlinear error testing at the pm level.

[0076] In one exemplary embodiment, such as Figure 2 As shown, the error calculation module includes a signal processing module and an error calculation unit;

[0077] The signal processing module is used to enhance electrical signals to obtain enhanced electrical signals.

[0078] The error calculation unit is used to perform nonlinear error calculation based on the parameters of the laser output module and the interference module, as well as the enhanced electrical signal, and obtain the calculation results.

[0079] The signal enhancement processing operations can include amplification and / or high-pass filtering, squaring, and low-pass filtering; they can also include amplification and / or high-pass filtering, phase locking, low-pass filtering, and quadrature demodulation. Furthermore, other modules capable of calculating amplitude signal correlation data can also be used for signal enhancement processing, and there are no restrictions here. It should be noted that the amplification and / or high-pass filtering and phase locking in the above enhancement processing operations can be set according to actual application requirements; they can be set or not, and there are no restrictions here.

[0080] In the embodiments of this application, when performing enhancement processing on the electrical signal, the first optional approach is to perform high-pass filtering on the electrical signal based on the signal processing module, and then perform squaring and low-pass filtering on the high-pass filtered signal based on the error calculation unit to obtain the enhanced first electrical signal. The error calculation unit then performs nonlinear error calculation on the enhanced first electrical signal, the parameters of the laser output module, and the interference module to obtain the calculation result. The second optional approach is to perform high-pass filtering on the electrical signal, input the high-pass filtered signal to a phase-locked loop (PLL), and perform quadrature demodulation on the high-pass filtered signal and the PLL output information to obtain the enhanced first electrical signal. Finally, nonlinear error calculation is performed on the enhanced first electrical signal, the parameters of the laser output module, and the interference module to obtain the calculation result.

[0081] By using the laser signal itself as a reference to enhance the signal, i.e. demodulating the amplitude of the laser signal, an enhanced electrical signal is obtained. Nonlinear error is then calculated based on the enhanced electrical signal and the parameters of the laser output module and the interference module. This avoids the influence of other signals as reference signals on the accuracy of the nonlinear error measurement results. The error measurement process only needs to process the measurement signal's own data and is not affected by other signals, thus exhibiting strong anti-interference capabilities.

[0082] In one exemplary embodiment, such as Figure 3 As shown, the signal processing module includes a high-pass filter unit and a signal processing unit;

[0083] The high-pass filter unit is used to perform high-pass filtering on the electrical signal to obtain the first filtered electrical signal.

[0084] The signal processing unit is used to enhance the filtered first electrical signal to obtain the enhanced first electrical signal.

[0085] The error calculation unit is used to perform nonlinear error calculation based on the parameters of the laser output module and the interference module, as well as the enhanced first electrical signal, to obtain the calculation result.

[0086] The high-pass filter unit may also include amplification processing. High-pass filtering can remove the DC component from an electrical signal to obtain a filtered first electrical signal. Optionally, the electrical signal transmitted from the photoelectric conversion module to the high-pass filter unit is represented by the following expression (1):

[0087] (1);

[0088] In the formula, A is the DC component of the interference signal, and B is the amplitude of the ideal interference signal. The angular frequency difference between the two-frequency lasers Let C be the phase change caused by the motion of the object, D be the amplitude of the first-order nonlinear error, and D be the amplitude of the second-order nonlinear error. In actual optical systems, there are also higher-order nonlinear errors, which are omitted here.

[0089] In practical scenarios, the second-order nonlinear error is smaller than the first-order nonlinear error. Therefore, for example, only the first-order nonlinear error is considered. This example does not limit the application scope of this application. The dual-frequency interferometric nonlinear error of this application can be used to measure nonlinear errors of any order. Based on the above analysis, the electrical signal transmitted from the photoelectric conversion module to the high-pass filter unit is represented by the following equation (2):

[0090] (2);

[0091] In the formula, A is the DC component of the interference signal, and B is the amplitude of the ideal interference signal. The angular frequency difference between the two-frequency lasers Let C be the phase change caused by the motion of the object, and let C be the amplitude of the first-order nonlinear error.

[0092] After processing by the high-pass filter unit, the filtered first electrical signal can be represented by the following relationship (3):

[0093] (3);

[0094] In the formula, B is the amplitude of the ideal interference signal. The angular frequency difference between the two-frequency lasers Let C be the phase change caused by the motion of the object, and let C be the amplitude of the first-order nonlinear error.

[0095] In the embodiments of this application, for the electrical signal output by the photoelectric conversion module, the DC component of the electrical signal is filtered out by a high-pass filter unit to obtain a filtered first electrical signal. The filtered first electrical signal is then transmitted to an error calculation unit. Optionally, the error calculation unit performs a squaring operation and a low-pass filtering process on the filtered first electrical signal to obtain an enhanced first electrical signal. Nonlinear error calculation is then performed based on the enhanced first electrical signal, the parameters of the laser output module, and the interference module to obtain the calculation result. Optionally, the filtered first electrical signal is input to a phase-locked loop (PLL), and quadrature demodulation is performed on the filtered first electrical signal and the PLL output signal to obtain an enhanced first electrical signal. Nonlinear error calculation is then performed based on the enhanced first electrical signal, the parameters of the laser output module, and the interference module to obtain the calculation result. It should be noted that the high-pass filtering and PLL in the above two enhancement operations can also be omitted; that is, the electrical signal output by the photoelectric conversion module can be directly squared and low-pass filtered to obtain the enhanced first electrical signal; or quadrature demodulation can be performed on the electrical signal output by the photoelectric conversion module to obtain the enhanced first electrical signal.

[0096] By using the measured signal itself as a reference to enhance the signal (i.e. demodulate the signal amplitude), and then calculating the nonlinear error based on the enhanced signal and the parameters of the laser output module and the interferometer module, the accuracy of the nonlinear error calculation results is avoided by using other signals as reference signals. The error calculation process only needs to process the measured signal's own data and is not affected by other signals, thus exhibiting strong anti-interference capabilities.

[0097] In one exemplary embodiment, such as Figure 4 As shown, the signal processing unit includes: a square operator and a low-pass filter;

[0098] The squaring unit is used to perform a squaring operation on the filtered first electrical signal to obtain the square signal of the filtered first electrical signal;

[0099] A low-pass filter is used to perform low-pass filtering on a squared signal to obtain the first electrical signal after enhancement.

[0100] The squaring unit can be any type of processor, such as a digital signal processor, microprocessor, field-programmable gate array, application-specific integrated circuit, or system-on-a-chip. The low-pass filter may also include amplification and other enhancement operations; there are no restrictions on this.

[0101] In the embodiments of this application, the squaring unit performs a squaring operation on the filtered first electrical signal to obtain the square signal of the filtered first electrical signal, that is, the square signal of the amplitude, which is represented by the following expression (4):

[0102] (4);

[0103] In the formula, B is the amplitude of the ideal interference signal. The angular frequency difference between the two-frequency lasers Let C be the phase change caused by the motion of the object, and let C be the amplitude of the first-order nonlinear error.

[0104] The squared signal is filtered by a low-pass filter to obtain the first enhanced electrical signal, which is represented by the following expression (5):

[0105] (5);

[0106] In the formula, B is the amplitude of the ideal interference signal. Let C be the phase change caused by the motion of the object, and let C be the amplitude of the first-order nonlinear error.

[0107] It should be noted that the above steps are for the case where the signal processing unit is connected to the high-pass filter unit. When the signal processing unit is connected to the photoelectric conversion module, i.e. there is no high-pass filter unit, the square operator performs a square operation on the electrical signal output by the photoelectric conversion module to obtain the square signal of the electrical signal, i.e. the square signal of the amplitude.

[0108] By using the measured signal itself as a reference to enhance the signal, the square signal of the electrical signal is obtained. The amplitude of the signal is then demodulated using the square signal of the electrical signal. Based on the enhanced signal and the parameters of the laser output module and the interferometer module, nonlinear error is calculated. Since the square signal of the electrical signal is essentially the square of the amplitude, the nonlinear error calculation always revolves around the parameters of the measured signal itself, avoiding the influence of other signals as reference signals on the accuracy of the nonlinear error measurement results. This method has strong anti-interference capabilities.

[0109] In one exemplary embodiment, such as Figure 5 As shown, the signal processing unit includes: a phase-locked loop and an amplitude output unit;

[0110] A phase-locked loop (PLL) is used to output a second electrical signal based on a filtered first electrical signal. The second electrical signal and the filtered first electrical signal have the same frequency, and the phase difference between the second electrical signal and the filtered first electrical signal is constant.

[0111] The amplitude output unit is used to perform quadrature demodulation processing on the filtered first and second electrical signals, and then calculate the enhanced first electrical signal.

[0112] The phase-locked loop (PLL) includes a phase detector (PD), a proportional-integral-derivative (PID) controller, and a voltage-controlled oscillator (VCO). The PLL is used to synchronize the frequency of the output second electrical signal with the frequency of the filtered first electrical signal, and to lock the phase difference between the second and filtered first electrical signals to a constant. The amplitude output unit includes a first mixer, a phase shifter, a second mixer, a first low-pass filter, a second low-pass filter, and a demodulator. It should be noted that the PLL in the signal processing unit can be configured according to actual application requirements; it can be included or omitted. That is, without a PLL, the electrical signal output from the photoelectric conversion module or the high-pass filter unit is directly transmitted to the amplitude output unit for quadrature demodulation processing to obtain the enhanced first electrical signal.

[0113] In this embodiment, a high-pass filter unit and a phase-locked loop are provided as an example of a device for measuring the nonlinear error of dual-frequency interferometry. This example does not limit the scope of protection of this application. Optionally, the first electrical signal output by the high-pass filter unit can be represented by the following expression (6):

[0114] (6);

[0115] The first electrical signal output from the high-pass filter unit is input into the phase-locked loop for synchronization processing to obtain the second electrical signal, which is represented by the following expression (7):

[0116] (7);

[0117] In the formula, , , This represents the amplitude of the phase-locked loop output signal.

[0118] In the embodiments of this application, the phase-locked loop performs synchronous processing on the first electrical signal output by the high-pass filter unit to obtain the second electrical signal. The amplitude output unit performs phase shifting, frequency mixing, and low-pass filtering on the filtered first and second electrical signals to obtain the enhanced first electrical signal.

[0119] It should be noted that the above steps apply to the case where the signal processing unit is connected to the high-pass filter unit and the high-pass filter unit is connected to the phase-locked loop. When the amplitude output unit is connected to the photoelectric conversion module, there is no high-pass filter unit and phase-locked loop. The amplitude output unit performs quadrature demodulation processing on the electrical signal output by the photoelectric conversion module to obtain the first electrical signal after enhancement processing.

[0120] By using the measured signal itself as a reference to enhance the signal (i.e. demodulate the signal amplitude), and then calculating the nonlinear error based on the enhanced first electrical signal and the parameters of the laser output module and the interferometer module, the accuracy of the nonlinear error calculation results is avoided by using other signals as reference signals. The error calculation process only needs to process the measured signal's own data and is not affected by other signals, thus exhibiting strong anti-interference capabilities.

[0121] In one exemplary embodiment, such as Figure 6 As shown, the amplitude output unit includes a first mixer, a phase shifter, a second mixer, a first low-pass filter, a second low-pass filter, and a demodulator; the input terminal of the first mixer is connected to the output terminal of the phase-locked loop and the output terminal of the high-pass filter unit, respectively.

[0122] The first mixer is used to perform frequency mixing processing on the filtered first electrical signal and the second electrical signal, and output the first mixed signal.

[0123] The first low-pass filter is used to perform low-pass filtering on the first mixing signal to obtain the first branch processed signal;

[0124] A phase shifter is used to shift the second electrical signal by a preset angle to obtain a phase-shifted electrical signal;

[0125] The second mixer is used to mix the phase-shifted electrical signal and the filtered first electrical signal to output the second mixed signal.

[0126] The second low-pass filter is used to perform low-pass filtering on the second mixing signal to obtain the second branch processed signal.

[0127] The demodulator is used to perform quadrature demodulation on the first branch processed signal and the second branch processed signal to obtain the enhanced first electrical signal.

[0128] The preset angle can be 90 degrees.

[0129] In the embodiments of this application, for the first electrical signal output by the high-pass filter unit and the second electrical signal output by the phase-locked loop, the first electrical signal after high-pass filtering is divided into two branch signals, which are transmitted to the first mixer and the second mixer respectively; the second electrical signal is divided into two branch signals, and one branch signal is transmitted to the first mixer, while the other branch signal is phase-shifted, for example, by 90 degrees, and the phase-shifted branch signal is input to the second mixer for processing; the first mixer and the second mixer respectively perform mixing processing on the received branch signals to obtain a first mixed signal and a second mixed signal; the first mixed signal is transmitted to the first low-pass filter for processing to obtain a first branch processed signal; the second mixed signal is transmitted to the second low-pass filter for processing to obtain a second branch processed signal; the demodulator performs quadrature demodulation on the first branch signal and the second branch processed signal to obtain an enhanced first electrical signal, where the enhanced first electrical signal is an amplitude signal.

[0130] In one exemplary embodiment, such as Figure 7 As shown, the error calculation unit includes: an error initialization subunit, a coefficient calculator, and an error calculation subunit;

[0131] The coefficient calculator is used to calculate coefficients based on the parameters of the laser output module and the interference module; the parameters include the laser wavelength and the optical subdivision number.

[0132] The initial error subunit is used to perform mean processing on the enhanced first electrical signal to obtain the third electrical signal, and to perform nonlinear error calculation based on the enhanced first electrical signal and the third electrical signal to obtain the nonlinear error under the phase unit.

[0133] The error calculation subunit is used to perform phase displacement conversion on the nonlinear error in phase units based on the coefficients, so as to obtain the nonlinear error in displacement units.

[0134] In the embodiments of this application, the coefficient calculator performs corresponding division operations on the parameters of the laser output module and the interference module to obtain coefficients. Optionally, the coefficients can be obtained through... To represent, where, For measuring laser wavelength, N is the optical subdivision number.

[0135] In the embodiments of this application, the error initialization subunit obtains a third electrical signal by performing mean processing on the enhanced first electrical signal. Optionally, if the enhanced first electrical signal is a squared amplitude signal, that is, after squaring, the third electrical signal can be obtained through... This is represented as follows: where B is the amplitude of the ideal interference signal, and C is the amplitude of the first-order nonlinear error. If the first electrical signal after enhancement is an amplitude signal, i.e., after quadrature demodulation, the third electrical signal can be... Let B be the amplitude of the ideal interference signal and C be the amplitude of the first-order nonlinear error.

[0136] In the embodiments of this application, when the error initialization subunit performs nonlinear error calculation based on the enhanced first electrical signal and the third electrical signal, optionally, if the enhanced first electrical signal is a squared amplitude signal, the nonlinear error under the phase unit can be calculated by... This is represented; if the first electrical signal after enhancement is an amplitude signal, the nonlinear error under phase unit can be expressed as follows: This is represented. It should be noted that the nonlinear error in phase units can also be directly output. That is, in this case, the nonlinear error in phase units is the final calculation result, and there is no need to perform subsequent phase shift transformation operations.

[0137] In the embodiments of this application, when the error calculation subunit performs phase displacement conversion on the nonlinear error in phase unit according to the coefficient, it multiplies the coefficient and the nonlinear error in phase unit to obtain the nonlinear error in displacement unit. Optionally, if the first electrical signal after enhancement processing is a squared amplitude signal, the nonlinear error in displacement unit is represented by the following expression (8):

[0138] (8);

[0139] In the formula, B is the amplitude of the ideal interference signal. Let C be the phase change caused by the motion of the object, and let C be the amplitude of the first-order nonlinear error. Where λ is the laser wavelength and N is the optical subdivision number.

[0140] If the first electrical signal after enhancement is an amplitude signal, the nonlinear error under the displacement unit is expressed by the following expression (9):

[0141] (9);

[0142] In the formula, B is the amplitude of the ideal interference signal. Let C be the phase change caused by the motion of the object, and let C be the amplitude of the first-order nonlinear error. Where λ is the laser wavelength and N is the optical subdivision number.

[0143] By using the measured signal itself as a reference to enhance the signal (i.e. demodulate the signal amplitude), and then estimating the nonlinear error based on the enhanced signal and the parameters of the laser output module and the interferometer module, the accuracy of the nonlinear error estimation result is avoided by using other signals as reference signals. The error calculation process only needs to process the measured signal's own data and is not affected by other signals, thus exhibiting strong anti-interference capabilities.

[0144] In one exemplary embodiment, such as Figure 8 As shown, based on any of the dual-frequency interferometric nonlinear error measurement devices in the above embodiments, this application also provides a method for measuring dual-frequency interferometric nonlinear error, such as... Figure 8 As shown, the method for measuring dual-frequency interferometric nonlinear error is applied to the error calculation module in a dual-frequency interferometric nonlinear error measurement device. The method includes:

[0145] S801, acquire the electrical signal output by the photoelectric conversion module in the dual-frequency interferometric nonlinear error measurement device;

[0146] S802 enhances the electrical signal to obtain an enhanced electrical signal, and calculates the nonlinear error based on the enhanced electrical signal and the parameters of the laser output module and the interference module to obtain the calculation result.

[0147] The enhancement processing is either square operation processing or quadrature demodulation processing. The enhanced electrical signal can be an amplitude signal or a squared amplitude signal.

[0148] In the embodiments of this application, the electrical signal output by the photoelectric conversion module is enhanced to obtain an enhanced electrical signal. Optionally, a first approach involves filtering or amplifying the DC component of the electrical signal to obtain a filtered electrical signal; then, the filtered signal is squared and low-pass filtered to obtain an enhanced first electrical signal, which is a squared amplitude signal. Optionally, a second approach involves filtering or amplifying the DC component of the electrical signal to obtain a filtered electrical signal; the filtered electrical signal is then input to a phase-locked loop (PLL), and the filtered signal and the PLL output signal are quadratured to obtain the enhanced first electrical signal, which is an amplitude signal. Finally, nonlinear error calculations are performed based on the enhanced first electrical signal, the parameters of the laser output module, and the interference module to obtain the calculation result.

[0149] In one exemplary embodiment, such as Figure 9 As shown, based on the enhanced electrical signal and the parameters of the laser output module and the interferometer module, nonlinear error calculations are performed to obtain the calculation results, including:

[0150] S901, the coefficients are calculated based on the parameters of the laser output module and the interference module;

[0151] The parameters include the laser wavelength and the optical subdivision number.

[0152] In the embodiments of this application, a division operation is performed on the parameters of the laser output module and the interference module to obtain coefficients. Optionally, the coefficients are... ,in, For measuring laser wavelength, N is the optical subdivision number.

[0153] S902, the first electrical signal after enhancement is averaged to obtain the third electrical signal, and the nonlinear error is calculated based on the first and third electrical signals after enhancement to obtain the nonlinear error under the phase unit.

[0154] In the embodiments of this application, when the enhanced first electrical signal is averaged, a third electrical signal is obtained. Optionally, if the enhanced first electrical signal is a squared amplitude signal, that is, after squaring, the third electrical signal can be obtained through... This is represented as follows: where B is the amplitude of the ideal interference signal, and C is the amplitude of the first-order nonlinear error. If the first electrical signal after enhancement is an amplitude signal, i.e., after quadrature demodulation, the third electrical signal can be... The expression is shown, where B is the amplitude of the ideal interference signal and C is the amplitude of the first-order nonlinear error. Nonlinear errors are calculated on the enhanced first and third electrical signals to obtain the nonlinear error in phase units. It should be noted that the nonlinear error in phase units can also be directly output; that is, in this case, the nonlinear error in phase units is the final calculation result, and no subsequent phase shift conversion operation is required.

[0155] S903, based on the coefficient, performs a phase displacement transformation on the nonlinear error in phase units to obtain the nonlinear error in displacement units.

[0156] In the embodiments of this application, when performing phase displacement conversion on the nonlinear error under phase unit according to the coefficient, the coefficient and the nonlinear error under phase unit are multiplied to obtain the nonlinear error under displacement unit. Optionally, if the first electrical signal after enhancement is a squared amplitude signal, the nonlinear error under displacement unit is represented by the above expression (8). If the first electrical signal after enhancement is an amplitude signal, the nonlinear error under displacement unit is represented by the above expression (9).

[0157] In one exemplary embodiment, such as Figure 10 As shown, nonlinear error is calculated based on the enhanced first and third electrical signals to obtain the nonlinear error per phase unit, including:

[0158] S1001, Perform a difference operation on the enhanced first electrical signal and the third electrical signal to obtain the difference signal;

[0159] S1002, based on the ratio of the difference signal and the third electrical signal, obtain the nonlinear error under the phase unit.

[0160] In the embodiments of this application, the difference between the enhanced first electrical signal and the third electrical signal is divided by the third electrical signal to obtain the nonlinear error in phase units. Optionally, if the enhanced first electrical signal is a squared amplitude signal, the nonlinear error in phase units can be obtained by... This is represented; if the first electrical signal after enhancement is an amplitude signal, the nonlinear error under phase unit can be expressed as follows: To express.

[0161] In the description of this specification, references to terms such as "some embodiments," "other embodiments," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative descriptions of the above terms do not necessarily refer to the same embodiments or examples.

[0162] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above 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.

[0163] The above embodiments are merely illustrative of several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A device for measuring dual-frequency interferometric nonlinear error, characterized in that, The measuring device includes: a laser output module, an interference module, a photoelectric conversion module, and an error calculation module; The laser output module is used to emit a measurement laser to the interference module; The interference module is used to split the measurement laser beam and project the split light signal onto the target object; it is also used to generate an interference signal based on the light signal reflected by the target object. The photoelectric conversion module is used to perform photoelectric conversion on the interference signal to generate a single electrical signal; The error calculation module is used to perform high-pass filtering on the electrical signal to obtain a filtered first electrical signal; to perform enhancement processing on the filtered first electrical signal to obtain an enhanced first electrical signal; and to perform nonlinear error calculation based on the parameters of the laser output module and the interference module, as well as the enhanced first electrical signal, to obtain the calculation result. The error calculation module only receives and processes a single electrical signal output from the photoelectric conversion module, and does not receive or process any independent reference optical path or reference electrical signal. The enhancement processing is either square operation processing or orthogonal demodulation processing. The error calculation module includes a high-pass filtering unit, a signal processing unit, and an error calculation unit; the error calculation unit includes an error initialization subunit, a coefficient calculator, and an error calculation subunit. The coefficient calculator is used to calculate coefficients based on the parameters of the laser output module and the interference module; the parameters include the laser wavelength and the optical subdivision number. The error initialization subunit is used to perform mean processing on the enhanced first electrical signal to obtain a third electrical signal, and to perform nonlinear error calculation based on the enhanced first electrical signal and the third electrical signal to obtain the nonlinear error under phase unit. The error calculation subunit is used to perform phase displacement conversion on the nonlinear error in the phase unit according to the coefficient, so as to obtain the nonlinear error in the displacement unit.

2. The measuring device according to claim 1, characterized in that, The signal processing unit includes: a square operator and a low-pass filter; The square operator is used to perform a square operation on the filtered first electrical signal to obtain the square signal of the filtered first electrical signal; The low-pass filter is used to perform low-pass filtering on the squared signal to obtain the enhanced first electrical signal.

3. The measuring device according to claim 1, characterized in that, The signal processing unit includes: a phase-locked loop and an amplitude output unit; The phase-locked loop is used to output a second electrical signal based on the filtered first electrical signal; the second electrical signal and the filtered first electrical signal have the same frequency, and the phase difference between the second electrical signal and the filtered first electrical signal is constant; The amplitude output device is used to perform quadrature demodulation processing on the filtered first electrical signal and the second electrical signal, and then calculate the enhanced first electrical signal.

4. The measuring device according to claim 3, characterized in that, The amplitude output unit includes a first mixer, a phase shifter, a second mixer, a first low-pass filter, a second low-pass filter, and a demodulator; The first mixer is used to perform mixing processing on the filtered first electrical signal and the second electrical signal, and output a first mixed signal; The first low-pass filter is used to perform low-pass filtering on the first mixing signal to obtain the first branch processed signal; The phase shifter is used to shift the second electrical signal by a preset angle to obtain a phase-shifted electrical signal; The second mixer is used to perform mixing processing on the phase-shifted electrical signal and the filtered first electrical signal, and output a second mixed signal; The second low-pass filter is used to perform low-pass filtering on the second mixing signal to obtain the second branch processed signal; The demodulator is used to perform quadrature demodulation on the first branch processed signal and the second branch processed signal to obtain the enhanced first electrical signal.

5. A method for measuring dual-frequency interferometric nonlinear error, characterized in that, An error calculation module applied in the measuring device for dual-frequency interferometric nonlinear error as described in any one of claims 1-4, the method comprising: Obtain the single electrical signal output by the photoelectric conversion module in the dual-frequency interferometric nonlinear error measurement device; The electrical signal is high-pass filtered to obtain a filtered first electrical signal; the filtered first electrical signal is enhanced to obtain an enhanced first electrical signal; nonlinear error is calculated based on the parameters of the laser output module and the interference module, as well as the enhanced first electrical signal, to obtain the calculation result; the enhancement processing is either square operation processing or orthogonal demodulation processing. The calculation of nonlinear error based on the parameters of the laser output module and the interference module, as well as the enhanced first electrical signal, yields the following results: The coefficients are calculated based on the parameters of the laser output module and the interference module; the parameters include the laser wavelength and the optical subdivision number. The enhanced first electrical signal is averaged to obtain a third electrical signal, and the nonlinear error is calculated based on the enhanced first electrical signal and the third electrical signal to obtain the nonlinear error under phase unit. The phase displacement transformation is performed on the nonlinear error in the phase unit based on the coefficient to obtain the nonlinear error in the displacement unit.

6. The measurement method according to claim 5, characterized in that, The step of calculating the nonlinear error based on the enhanced first electrical signal and the third electrical signal to obtain the nonlinear error in phase units includes: Perform a difference operation on the enhanced first electrical signal and the third electrical signal to obtain a difference signal; The nonlinear error under the phase unit is obtained based on the ratio of the difference signal to the third electrical signal.

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