A system and method for correcting non-linear error in an F-P sensor

Abstract

The present invention discloses a system and method for correcting the non-linear error in an F-P sensor, which performs non-linear correction on the output signal of the F-P sensor, including phase compensation and angle compensation, 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 particularly relates to a system and method for correcting the non-linear error in an F-P sensor. Background Art

[0002] Length, as one of the most basic geometric parameters, its accurate measurement is of crucial significance for promoting scientific research and the development of various fields. The micro-displacement measurement technology plays a vital role in multiple scenarios such as precision mechanical assembly, high-precision and ultra-precision machining, target aiming and spatial positioning, and has an inestimable impact on multiple fields such as machinery, aerospace, and military. With the continuous progress of modern industrial manufacturing, the demand for precision positioning technology is increasing day by day, which prompts the micro-displacement measurement technology to reach higher precision standards. Some application scenarios even require an error range of nanometers, which poses a more stringent challenge to the measurement technology.

[0003] Among many micro-displacement sensors, the Fabry-Perot (F-P) sensor has attracted widespread attention due to its significant advantages such as simple structure, low cost, high precision, and high sensitivity. In addition, besides the micro-displacement sensing field, the F-P sensor also has higher practical application value in fields such as medical detection, underwater acoustic detection, bridge construction, and power monitoring. However, there are non-linear errors in existing F-P sensors, which mainly come from: (1) There will be multiple reflections and transmissions between two parallel reflecting surfaces, resulting in the generation of non-linear errors. (2) The reflectivity of the mirror changes with the change of the incident angle, resulting in the distortion of the output signal of the F-P sensor, thereby generating non-linear errors. (3) In the data processing process, the non-linear characteristics of the analog-to-digital converter, non-linear filtering, and non-linear fitting will also generate non-linear errors.

[0004] The existing non-linear error compensation methods in F-P sensors mainly include the following several kinds: (1) The frequency locking technology, by locking the frequency of the tunable laser on a certain resonant mode of the interferometer, converting the displacement change into a frequency change, but it requires high-precision frequency stabilization lasers and frequency measurement equipment, and the cost is relatively high. (2) The interference spectroscopy technology, by calculating the interference fringes and determining the phase at a fixed wavelength to simulate and determine the relative distance change of the optical path, but it requires a rapid scan to change the laser wavelength, and has high requirements for the response speed and stability of the equipment. (3) Hardware improvement, by improving the hardware structure of the F-P sensor, such as using higher-precision components and optimizing the design of the interference cavity. Although it can reduce the generation of non-linear errors from the source, the hardware improvement requires more 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 the non-linear error in an F-P sensor.

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

[0007] The present invention also provides a system for correcting the non-linear error in an F-P sensor, which performs non-linear correction on the output signal of the F-P sensor through phase compensation and angle compensation.

[0008] The present invention also provides a system for correcting the non-linear error in an F-P sensor, comprising: a laser, a circulator, a laser collimator, a laser interferometer, a plane mirror, a photodetector, and a data 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 serves as the transmitting end, making the laser vertically incident on the surface of the measured target plane mirror; the probe of the laser interferometer is vertically aligned with the surface of the measured target plane mirror; the third port of the circulator is connected to the input end of the photodetector; the output end of the photodetector is connected to the input end of the data acquisition card; the output end of the data acquisition card is connected to the input end of the processor.

[0009] The present invention also provides a method for correcting the non-linear error in an F-P sensor, which performs non-linear correction on the output signal of the F-P sensor through phase compensation and angle compensation.

[0010] The present invention also provides a method for correcting the non-linear error in an F-P sensor, comprising:

[0011] According to the phase value of the movement of the plane mirror collected by laser interference and the F-P sensor, the micro-displacement value of the movement of the plane mirror is obtained;

[0012] The ordinate of the phase curve output by the F-P sensor is equally divided with a step value from 0 to 360°, the step value is 0.01°, and the divided ordinate is denoted as 0.01°×n, (n = 0, 1, 2, 3,..., 36000), and a phase sliding window sequence is established, denoted as A;

[0013] Taking the phase sliding window sequence A as a known parameter, the corresponding time points (t1, t2, t3,...t i ) in the phase curve of the laser interferometer are found by the method of solving function values, and a time sliding window sequence is obtained, denoted as B;

[0014] Taking the time sliding window sequence B as a known parameter, the corresponding ordinate values on the output phase curve of the F-P sensor are found by the method of solving function values, denoted as (φ1, φ2, φ3,...φ j );

[0015] The phase values of j groups of vertical coordinates are averaged as the phase experimental value of the F-P sensor. The corresponding phase change measured by the laser interferometer is 0.01°×n. The difference between the two sets of data is used to obtain the phase error value, which will be used as the pre-compensation value for phase non-linear error compensation.

[0016] The phase pre-compensation value is used to compensate the phase curve output by the F-P sensor through interpolation iteration.

[0017] The difference between the two compensated phase curves is taken to obtain the phase error curve of the F-P sensor and the laser interferometer.

[0018] Angle non-linear error compensation is performed on the measurement results. The data measured by the laser interferometer is used as the abscissa, and the data measured by the F-P sensor is used as the ordinate to obtain a displacement curve graph.

[0019] The displacement curve is linearly fitted to obtain the slope k, and the included angle θ of the angular error is obtained through the slope k.

[0020] The included angle of the angular error is substituted into the phase error curve to obtain the error curve after phase and angle non-linear error compensation.

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

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

[0023]

[0024] Where λ0 is the central wavelength of the laser output by the laser.

[0025] The present invention performs non-linear correction on the output signal of the F-P sensor, including phase compensation and angle compensation, 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. Brief Description of the Drawings

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

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

[0028] Figure 2Data collected by the F-P sensor and the laser interferometer; among them, (a) is the 0-360° phase curve, (b) is the micro-displacement curve, and (c) is the enlarged view of the local micro-displacement curve;

[0029] Figure 3 Is the non-linear phase error curve of the F-P sensor;

[0030] Figure 4 Data collected by the F-P sensor after non-linear phase error compensation and the laser interferometer; among them, (a) is the compensated 0-360° phase curve, (b) is the compensated displacement curve, and (c) is the enlarged view of the compensated local displacement curve;

[0031] Figure 5 Is the micro-displacement error curve with / without the non-linear phase error compensation algorithm;

[0032] Figure 6 Is the schematic diagram of the cosine error of the measurement optical axis of the F-P sensor;

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

[0034] Figure 8 Is the flowchart of the method in the embodiment of the present invention. Specific implementation manner

[0035] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0036] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation manners.

[0037] As Figure 1 shown, the present invention provides a system for correcting non-linear errors in an F-P sensor, including: a laser 1, a circulator 2, a laser collimator 3, a laser interferometer 4, a plane mirror 5, a photodetector 6, and a data 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 serves as the transmitting end, enabling the laser to be perpendicularly incident on the surface of the measured target plane mirror 5; the probe of the laser interferometer 4 is perpendicularly aligned with the surface of the measured target plane mirror 5; 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] As Figure 8 shown, the present invention also provides a method for correcting the non-linear error in an F-P sensor, including:

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

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

[0042] Step 3: Use the output end of the laser collimator 3 as the transmitting end, enabling the laser to be perpendicularly incident on the surface of the measured target plane mirror 5;

[0043] Step 4: Vertically align the probe of the laser interferometer 4 with the surface of the measured target plane mirror 5;

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

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

[0046] Step 7: Connect the output end of the acquisition card 7 to the input end of the processor, and perform non-linear error compensation from the software algorithm;

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

[0048] Step 9: Move the plane mirror 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 mirror 5, as shown by the red dashed line in Figure 2 (a);

[0050] Step 11: The F-P sensor collects the phase information of the movement of the plane mirror (5), as shown by the blue solid line in Figure 2 (a);

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

[0052] Step Thirteen: Divide the ordinate of the phase curve output by the F-P sensor from 0 to 360° with an equal step value of 0.01°, and record the divided ordinate as 0.01°×n, (n = 0, 1, 2, 3, …, 36000), and establish a phase sliding window sequence, denoted as A;

[0053] Step Fourteen: Take the obtained phase sliding window sequence A as a known parameter, and find the corresponding time points (t1, t2, t3, … t i ) in the phase curve of the laser interferometer by solving the function value method, and obtain a time sliding window sequence, denoted as B;

[0054] Step Fifteen: Take the time sliding window sequence B as a known parameter, and find the corresponding ordinate values on the phase curve output by the F-P sensor by solving the function value method, denoted as (φ1, φ2, φ3, … φ j );

[0055] Step Sixteen: Take the average of the j groups of ordinate phase values as the phase experimental value of the F-P sensor. The corresponding phase change measured by the laser interferometer is 0.01°×n. Subtract the two groups of data to obtain a phase error value, as Figure 3 shown, that is, under different phase sliding windows, the error values corresponding to different phase values within 0 - 360° are obtained. This value will be used as the pre-compensation value during phase non-linearity error compensation;

[0056] Step Seventeen: Use the phase pre-compensation value obtained in Step Thirteen to compensate the phase curve output by the F-P sensor through interpolation iteration. The compensated phase curve is as Figure 4 (a) shown, and the displacement curve is as Figure 4 (b) and Figure 4 (c) shown;

[0057] Step Eighteen: Subtract the two compensated phase curves in Figure 4 (b) to obtain the phase error curve between the F-P sensor and the laser interferometer, as Figure 5 shown, where the red curve represents the measurement error without the phase non-linearity error compensation algorithm, and the blue solid line represents the measurement error curve obtained after the compensation algorithm, proving that the phase non-linearity error compensation algorithm of the present application can effectively reduce the measurement error of the system;

[0058] Step Nineteen: Perform angular non - linear error compensation on the measurement results. The compensation schematic diagram is as shown in Figure 6 . Take the data measured by the laser interferometer as the abscissa and the data measured by the F - P sensor as the ordinate to draw a displacement curve graph;

[0059] Step Twenty: Perform linear fitting on the displacement curve obtained in Step Sixteen to obtain the slope k, and substitute k into the following expression: where θ is the included angle of the angular error, that is, the included angle θ of the angular error can be obtained through the slope k;

[0060] Step Twenty - One: Substitute the included angle of the angular error into the phase error curve obtained in Step Eighteen through the iterative algorithm, and finally obtain the error curve after compensating for both phase and angular non - linear errors, as shown in Figure 7 . The results show that this application can effectively reduce the displacement error from - 100 nm to 300 nm to - 40 nm to 100 nm.

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

[0062] (1) Use the measurement results of the laser interferometer to perform non - linear error compensation on the experimental results, and the compensation accuracy is better than that of traditional methods;

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

[0064] (3) After one - time compensation for non - linear errors, there is no need for re - calibration, which can effectively solve the problem of high - precision measurement within a long working distance;

[0065] (4) The results output by the F - P sensor 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 high reflectivity of the two reflecting surfaces of the F - P cavity leads to multi - beam interference, 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 above - described embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solution of the present invention should fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for correcting the non-linear error in an F-P sensor, characterized in that, Including: Obtain the micro-displacement value of the moving plane mirror according to the phase values of the plane mirror movement collected by the laser interferometer and the F-P sensor; Perform equal-step value segmentation on the ordinate of the phase curve output by the F-P sensor from 0 to 360°, with the step value being 0.01°. Denote the segmented ordinate as 0.01°×n, where n = 0, 1, 2, 3, ···, 36000, and establish a phase sliding window sequence, denoted as A; Taking the phase sliding window sequence A as a known parameter, the corresponding time points (t1, t2, t3, ··· t i ) in the phase curve of the laser interferometer are found by solving the function value method, and the time sliding window sequence is obtained, denoted as B; Taking the time sliding window sequence B as a known parameter, find the corresponding ordinate values on the output phase curve of the F-P sensor by solving the function value method, which are respectively denoted as (φ1, φ2, φ3, ··· φ j ); Take the average of the j groups of ordinate phase values as the phase experimental value of the F-P sensor. The corresponding phase change measured by the laser interferometer is 0.01°×n. Calculate the difference between the two sets of data to obtain the phase error value, which will be used as the pre-compensation value during phase non-linear error compensation; Compensate the phase curve output by the F-P sensor through interpolation iteration using the phase pre-compensation value; Calculate the difference between the two compensated phase curves to obtain the phase error curve between the F-P sensor and the laser interferometer; Perform angle non-linear error compensation on the measurement results. Use the data measured by the laser interferometer as the abscissa and the data measured by the F-P sensor as the ordinate to obtain a displacement curve graph; Perform linear fitting on the displacement curve to obtain the slope k, and obtain the included angle θ of the angle error through the slope k; Substitute the included angle of the angle error into the phase error curve to obtain the error curve after compensating for both phase and angle non-linear errors.

2. The method for correcting the non-linear error in the F-P sensor according to claim 1, characterized in that, The plane mirror moves in a sinusoidal form with a peak-to-peak value of 4 μm.

3. The method for correcting the non-linear error in the F-P sensor according to claim 2, characterized in that The calculation formula for obtaining the micro-displacement value ΔL of the moving plane mirror is: where λ0 is the central wavelength of the laser output by the laser.

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