System and method for correcting nonlinear error in F-P (Fabry-Perot) sensor

Abstract

The invention discloses a system and a method for correcting non-linear errors in an F-P (Fabry-Perot) sensor, which are used for carrying out non-linear correction, including phase compensation and angle compensation, on output signals of the F-P sensor so as to improve the measurement accuracy of the F-P sensor, and can be flexibly adjusted and optimized to adapt to different measurement environments and requirements.

Description

Technical Field

[0001] The present invention belongs to the technical field of sensors, and in particular relates to a system and method for correcting nonlinear errors in FP sensors. Background Art

[0002] Length, as one of the most basic geometric parameters, its precise measurement is of great significance to the promotion of scientific research and development in various fields. Micro-displacement measurement technology plays a vital role in many scenarios such as precision machinery assembly, high-precision and ultra-precision processing, target aiming and space positioning, and plays an immeasurable role in many fields such as machinery, aerospace, and military. With the continuous advancement of modern industrial manufacturing, the demand for precision positioning technology is increasing, which has prompted micro-displacement measurement technology to meet higher accuracy standards. Some application scenarios even require an error range of nanometers, which poses more stringent challenges to measurement technology.

[0003] Among many micro-displacement sensors, Fabry-Perot (FP) sensors have attracted widespread attention due to their significant advantages such as simple structure, low price, high precision and high sensitivity. In addition to the field of micro-displacement sensing, FP sensors also have higher practical application value in the fields of medical testing, hydroacoustic detection, bridge construction, power monitoring, etc. However, there are nonlinear errors in existing FP sensors, which mainly come from: (1) There will be multiple reflections and transmissions between two parallel reflection surfaces, resulting in the generation of nonlinear errors. (2) The reflectivity of the reflector changes with the change of the incident angle, causing the output signal of the FP sensor to be distorted, thereby generating nonlinear errors. (3) In the data processing process, the nonlinear characteristics of the analog-to-digital converter, nonlinear filtering, and nonlinear fitting will also generate nonlinear errors.

[0004] The existing nonlinear error compensation methods in FP sensors mainly include the following: (1) Frequency locking technology, which converts displacement changes into frequency changes by locking the frequency of the adjustable laser to a certain resonant mode of the interferometer, but requires high-precision frequency-stabilized lasers and frequency measurement equipment, which is expensive. (2) Interference spectroscopy technology, which simulates the relative distance change of the optical path by calculating interference fringes and determining the phase at a fixed wavelength, but requires rapid scanning and changing of the laser wavelength, and has high requirements on the response speed and stability of the equipment. (3) Hardware improvement, by improving the hardware structure of the FP sensor, such as using higher-precision components, optimizing the design of the interference cavity, etc., although the generation of nonlinear errors can be reduced from the source, hardware improvement requires a lot of R&D and production costs. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a system and method for correcting nonlinear errors in FP sensors.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] The present invention also provides a system for correcting nonlinear errors in an FP sensor, which performs nonlinear correction on an output signal of the FP sensor through phase compensation and angle compensation.

[0008] The present invention also provides a system for correcting nonlinear errors in an FP sensor, comprising: a laser, a circulator, a laser collimator, a laser interferometer, a plane reflector, a photoelectric detector, and an acquisition card; wherein the output end of the laser is connected to the first port of the circulator; the second port of the circulator is connected to the input end of the laser collimator; the output end of the laser collimator 3 is used as a transmitting end to make the laser vertically incident on the surface of the plane reflector of the target to be measured; the probe of the laser interferometer is vertically aligned with the surface of the plane reflector of the target to be measured; the third port of the circulator is connected to the input end of the photoelectric detector; the output end of the photoelectric detector is connected to the input end of the data acquisition card; and the output end of the acquisition card is connected to the input end of the processor.

[0009] The present invention also provides a method for correcting nonlinear errors in a FP sensor, and performs nonlinear correction on an output signal of the FP sensor through phase compensation and angle compensation.

[0010] The present invention also provides a method for correcting nonlinear errors in a FP sensor, comprising:

[0011] According to the phase value of the plane reflector movement collected by the laser interference and the FP sensor, the micro displacement value of the plane reflector movement is obtained;

[0012] The vertical coordinate of the phase curve output by the FP sensor is divided into equal step values ​​from 0 to 360°, with a step value of 0.01°. The vertical coordinate after division is marked as 0.01°×n, (n=0,1,2,3,…,36000), and a phase sliding window sequence is established, which is recorded as A;

[0013] The phase sliding window sequence A is taken as a known parameter and the corresponding time points (t1, t2, t3, ... t i ), and obtain the time sliding window sequence, denoted as B;

[0014] Taking the time sliding window sequence B as a known parameter, the corresponding ordinate values ​​on the FP sensor output phase curve are found by solving the function value method, which are recorded as (φ1, φ2, φ3, …φ j );

[0015] The j groups of ordinate phase values ​​are averaged as the phase experimental value of the FP sensor, and the corresponding phase change measured by the laser interferometer is 0.01°×n. The two groups of data are subtracted to obtain the phase error value, which will be used as the pre-compensation value for phase nonlinear error compensation.

[0016] The phase pre-compensation value is interpolated and iteratively compensated for the phase curve output by the FP sensor;

[0017] The two compensated phase curves are subtracted to obtain the phase error curve between the FP sensor and the laser interferometer;

[0018] The measurement results are compensated for the angular nonlinear error, and the data measured by the laser interferometer is used as the abscissa and the data measured by the FP sensor is used as the ordinate to obtain the displacement curve graph;

[0019] Perform linear fitting on the displacement curve to obtain the slope k, and obtain the angle θ of the angle error through the slope k;

[0020] Substituting the angle of the angular error into the phase error curve, we can obtain the error curve after compensating for the two nonlinear errors of phase and angle.

[0021] Preferably, the plane mirror moves in a sinusoidal manner with a peak-to-peak value of 4 μm.

[0022] Preferably, the calculation formula for obtaining the micro displacement value ΔL of the plane reflector is:

[0023]

[0024] Wherein, λ0 is the central wavelength of the laser output.

[0025] The present invention performs nonlinear correction on the output signal of the FP sensor, including phase compensation and angle compensation, to improve the measurement accuracy of the FP sensor, and can be flexibly adjusted and optimized to adapt to different measurement environments and requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0027] Figure 1 is a schematic diagram of a device in an embodiment of the present invention;

[0028] Figure 2The data collected by the FP sensor and the laser interferometer; (a) is the 0-360° phase curve, (b) is the micro-displacement curve, and (c) is the local magnified view of the micro-displacement curve;

[0029] Figure 3 is the nonlinear phase error curve of the FP sensor;

[0030] Figure 4 The data are collected by the laser interferometer after the nonlinear phase error of the FP sensor is compensated; (a) is the 0-360° phase curve after compensation, (b) is the displacement curve after compensation, and (c) is the enlarged view of the local displacement curve after compensation;

[0031] Figure 5 The micro displacement error curve with and without nonlinear phase error compensation algorithm;

[0032] Figure 6 Schematic diagram of FP sensor measuring optical axis cosine error;

[0033] Figure 7 is the error curve after optical axis angle compensation;

[0034] Figure 8 4 is a flow chart of a method in an embodiment of the present invention. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] like Figure 1 As shown, the present invention provides a system for correcting nonlinear errors in FP sensors, including: a laser 1, a circulator 2, a laser collimator 3, a laser interferometer 4, a plane reflector 5, a photodetector 6, and an acquisition card 7.

[0038] The output end of the laser 1 is connected to the first port of the circulator 2; the second port of the circulator 2 is connected to the input end of the laser collimator 3; the output end of the laser collimator 3 is used as the transmitting end to make the laser vertically incident on the surface of the plane reflector 5 of the target to be measured; the probe of the laser interferometer 4 is vertically aligned with the surface of the plane reflector 5 of the target to be measured; the third port of the circulator 2 is connected to the input end of the photodetector 6; the output end of the photodetector 6 is connected to the input end of the data acquisition card 7; the output end of the acquisition card 7 is connected to the input end of the processor.

[0039] like Figure 8 As shown, the present invention also provides a method for correcting nonlinear errors in FP sensors, comprising:

[0040] Step 1: The output end of laser 1 is connected to the first port of circulator 2;

[0041] Step 2: The second port of the circulator 2 is connected to the input end of the laser collimator 3;

[0042] Step 3: The output end of the laser collimator 3 is used as the transmitting end to make the laser vertically incident on the surface of the plane reflector 5 of the target to be measured;

[0043] Step 4: The probe of the laser interferometer 4 is vertically aligned with the surface of the plane reflector 5 of the target to be measured;

[0044] Step 5: The third port of the circulator 2 is connected to the input end of the photodetector 6;

[0045] Step 6: The output end of the photodetector 6 is connected to the input end of the acquisition card 7;

[0046] Step 7: The output end of the acquisition card 7 is connected to the input end of the processor, and nonlinear error compensation is performed from the software algorithm;

[0047] Step 8: Turn on laser 1, and the central wavelength of the output laser is λ0;

[0048] Step 9: Move the plane reflector 5 in a sinusoidal form with a peak-to-peak value of 4 μm.

[0049] Step 10: The laser interferometer 4 collects the phase information of the movement of the plane reflector 5, such as Figure 2 As shown by the red dashed line in (a);

[0050] Step 11: The FP sensor collects the phase information of the movement of the plane reflector (5), such as Figure 2 (a) is shown by the blue solid line;

[0051] Step 12: Perform phase nonlinear error compensation, and substitute the phase value of the movement of the plane reflector 5 collected by the laser interference and the FP sensor into the following formula: Among them, Δφ is Figure 2 (a) The ordinate values ​​of the two phase curves of the FP sensor and the laser interferometer, ΔL is the micro-displacement value of the plane reflector 5, and the obtained micro-displacement curve is shown in Figure 2 (b) and Figure 2 (c) as shown.

[0052] Step 13: The vertical coordinate of the phase curve output by the FP sensor is divided into equal step values ​​from 0 to 360°, with a step value of 0.01°. The vertical coordinate after division is marked as 0.01°×n, (n=0, 1, 2, 3, ..., 36000), and a phase sliding window sequence is established, which is recorded as A;

[0053] Step 14: Take the obtained phase sliding window sequence A as a known parameter and find the corresponding time points (t1, t2, t3, ... t i ), and obtain the time sliding window sequence, denoted as B;

[0054] Step 15: Take the time sliding window sequence B as a known parameter and find the corresponding ordinate value on the FP sensor output phase curve by solving the function value method, which are recorded as (φ1, φ2, φ3, …φ j );

[0055] Step 16: Take the average of the j groups of ordinate phase values ​​as the phase experimental value of the FP sensor. The corresponding phase change measured by the laser interferometer is 0.01°×n. Subtract the two groups of data to obtain the phase error value, such as Figure 3 As shown, under different phase sliding windows, the error values ​​corresponding to different phase values ​​within 0-360° are obtained, and this value will be used as the pre-compensation value when compensating for the phase nonlinear error;

[0056] Step 17: The phase pre-compensation value obtained in step 13 is interpolated and iteratively compensated for the phase curve output by the FP sensor. The compensated phase curve is as follows: Figure 4 (a) shows the displacement curve. Figure 4 (b) and Figure 4 (c)

[0057] Step 18: Figure 4 The difference between the two compensated phase curves in (b) is used to obtain the phase error curve between the FP sensor and the laser interferometer, as shown in Figure 5 As shown, the red curve represents the measurement error without the phase nonlinear error compensation algorithm, and the blue solid line represents the measurement error curve obtained after the compensation algorithm is used, which proves that the phase nonlinear error compensation algorithm of the present application can effectively reduce the measurement error of the system;

[0058] Step 19: Compensate the angle nonlinear error of the measurement results. The compensation diagram is as follows: Figure 6 As shown, the data measured by the laser interferometer is used as the horizontal axis, and the data measured by the FP sensor is used as the vertical axis to draw a displacement curve;

[0059] Step 20: Perform a linear fit on the displacement curve obtained in step 16 to obtain the slope k, and substitute k into the following expression: Among them, θ is the angle of the angular error, that is, the angle of the angular error θ can be obtained by the slope k;

[0060] Step 21: Substitute the angle of the angle error into the phase error curve obtained in step 18 through an iterative algorithm, and finally obtain the error curve after the two nonlinear errors of phase and angle are compensated, as shown in Figure 7 As shown, the results show that the present application can effectively reduce the displacement error from -100nm to 300nm to -40nm to 100nm.

[0061] The present invention has the following technical effects:

[0062] (1) The nonlinear error compensation of the experimental results is performed using the laser interferometer measurement results, and the compensation accuracy is better than the traditional method;

[0063] (2) Parameters can be flexibly adjusted and optimized to adapt to different measurement environments;

[0064] (3) After the nonlinear error is compensated once, there is no need for recalibration, which can effectively solve the problem of high-precision measurement within a long working distance;

[0065] (4) The output of FP sensors can be processed in real time, which is easy to implement and integrate;

[0066] The present invention can solve the problem in the prior art that the reflectivity of the two reflection surfaces of the FP cavity is too high, resulting in multi-beam interference and causing measurement errors; at the same time, the technical solution provided by the present invention can meet the high-precision nanometer-level micro-displacement measurement within a large working range.

[0067] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A system for correcting nonlinear errors in FP sensors, characterized in that: The nonlinearity of the output signal of the FP sensor is corrected by phase compensation and angle compensation.

2. A system for correcting nonlinear errors in FP sensors, characterized in that: include: A laser, a circulator, a laser collimator, a laser interferometer, a plane reflector, a photoelectric detector, and an acquisition card; wherein the output end of the laser is connected to the first port of the circulator; the second port of the circulator is connected to the input end of the laser collimator; the output end of the laser collimator 3 is used as a transmitting end to make the laser vertically incident on the surface of the plane reflector of the target to be measured; the probe of the laser interferometer is vertically aligned with the surface of the plane reflector of the target to be measured; the third port of the circulator is connected to the input end of the photoelectric detector; the output end of the photoelectric detector is connected to the input end of the data acquisition card; the output end of the acquisition card is connected to the input end of the processor.

3. A method for correcting nonlinear errors in FP sensors, characterized in that: The nonlinearity of the output signal of the FP sensor is corrected by phase compensation and angle compensation.

4. A method for correcting nonlinear errors in FP sensors, characterized in that: include: According to the phase value of the plane reflector movement collected by the laser interference and the FP sensor, the micro displacement value of the plane reflector movement is obtained; The vertical coordinate of the phase curve output by the FP sensor is divided into equal step values ​​from 0 to 360°, with a step value of 0.01°. The vertical coordinate after division is marked as 0.01°×n, (n=0,1,2,3,…,36000), and a phase sliding window sequence is established, which is recorded as A; The phase sliding window sequence A is taken as a known parameter and the corresponding time points (t1, t2, t3, ... t i ), and obtain the time sliding window sequence, denoted as B; Taking the time sliding window sequence B as a known parameter, the corresponding ordinate values ​​on the FP sensor output phase curve are found by solving the function value method, which are recorded as (φ1, φ2, φ3, …φ j ); The j groups of ordinate phase values ​​are averaged as the phase experimental value of the FP sensor, and the corresponding phase change measured by the laser interferometer is 0.01°×n. The two groups of data are subtracted to obtain the phase error value, which will be used as the pre-compensation value for phase nonlinear error compensation. The phase pre-compensation value is interpolated and iteratively compensated for the phase curve output by the FP sensor; The two compensated phase curves are subtracted to obtain the phase error curve between the FP sensor and the laser interferometer; The measurement results are compensated for the angular nonlinear error, and the data measured by the laser interferometer is used as the abscissa and the data measured by the FP sensor is used as the ordinate to obtain the displacement curve graph; Perform linear fitting on the displacement curve to obtain the slope k, and obtain the angle θ of the angle error through the slope k; Substituting the angle of the angular error into the phase error curve, we can obtain the error curve after compensating for the two nonlinear errors of phase and angle.

5. The method for correcting nonlinear errors in FP sensors according to claim 4, characterized in that: The plane mirror moves in a sinusoidal pattern with a peak-to-peak value of 4 μm.

6. The method for correcting nonlinear errors in a FP sensor according to claim 5, characterized in that: The calculation formula for the micro displacement value ΔL of the plane reflector is: Wherein, λ0 is the central wavelength of the laser output.

Images