A method for displacement calculation of a single-frequency laser interferometer

Abstract

The present invention discloses a method for displacement calculation of a single-frequency laser interferometer. The feature of this method is that it uses the method of sub-packet normalization to divide the sampling points of the interference signal into multiple groups of data. Each group of data is separately normalized, and each group of data after sub-packeting is further divided into multiple data segments for identifying the intersection points of the quadrature interference signals. The displacement calculation of the data group is separately calculated through the data segments before the first intersection point, the data segments after the last intersection point, and the data segments between the intersection points, so as to obtain the displacement corresponding to a single group of data. The displacements obtained by calculating all data groups are summarized to achieve the measurement of the total displacement of the target object. Compared with the prior art, the present invention has a strong anti-interference ability, high accuracy in target displacement measurement, better meets the application requirements of precision measurement, has a simple method, low detection cost, and further broadens the application scenario of the laser interferometer in the industrial environment.

Description

Technical Field

[0001] The present invention relates to the technical field of laser interferometer measurement, and specifically to a method for calculating the displacement of a single-frequency laser interferometer. Background Art

[0002] As a technology with the highest displacement measurement accuracy, laser interferometry plays an important role in the field of industrial precision machining. Existing laser interferometers for high-precision displacement measurement can be divided into dual-frequency laser interferometers and single-frequency laser interferometers.

[0003] The dual-frequency laser interferometer calculates the displacement of the target object by collecting the change in the frequency of the interferometer signal, and has the advantage of strong anti-interference ability. However, the measurement speed of the dual-frequency laser interferometer is determined by the frequency difference between the two light sources, which limits the sampling speed of the dual-frequency laser interferometer. The single-frequency laser interferometer measures the displacement by accumulating the phase change period of the interference signal. This method's measurement speed is related to the level acquisition speed. In theory, as long as the sampling rate is increased, the measurement speed can be continuously improved. However, the single-frequency laser interferometer is a DC system and has poor anti-interference ability. Changes in laser light intensity and environment will affect the measurement accuracy. Summary of the Invention

[0004] The purpose of the present invention is to design a method for calculating the displacement of a single-frequency laser interferometer in view of the deficiencies of the prior art. The method uses sub-packet normalization processing to divide the sampling points of the interference signal into multiple groups of data. Each group of data is separately normalized, and the maximum and minimum values of the interference signal are updated in real time. Each group of data after sub-packeting is further divided into multiple data segments to identify the intersection points of the quadrature interference signals. By separately calculating the data segments before the first intersection point, the data segments after the last intersection point, and the data segments between the intersection points, the displacement corresponding to a single group of data is obtained. The displacements calculated from all data groups are summarized to achieve the measurement of the total displacement of the target object. The method is simple and greatly improves the anti-interference ability of the single-frequency laser interferometer and the accuracy of target displacement detection.

[0005] The purpose of the present invention is achieved as follows: A method for calculating the displacement of a single-frequency laser interferometer, characterized in that the method specifically includes the following steps:

[0006] Step 1: Perform sub-packet processing on two groups of quadrature interference signals obtained by acquisition. Every m sampling points are packed as a group of data, and the two interference signals in this group of data are normalized by the maximum interference voltage and the minimum interference voltage of this group of data.

[0007] Step 2: Find all the intersection points of the two interference signals in this group of data, and determine whether this group of data is the first group of data. If it is the first group of data, calculate the displacement L corresponding to the data points before the first intersection point start and the displacement L corresponding to the data points after the last intersection pointstop ; If it is not the first set of data, let L start = 0, calculate the displacement L corresponding to the data point after the last intersection stop , and the displacement L start is calculated by the following formula (a):

[0008]

[0009] The displacement L stop is calculated by the following formula (b):

[0010]

[0011] where λ is the laser wavelength; and are respectively the phase change amounts generated by the data points before the first intersection of the two interference signals; and are respectively the phase change amounts generated by the data points after the last intersection of the two interference signals.

[0012] Step 3: Take the data points between every two intersections of this set of data as a data segment. Within this data segment, if interference signal 1 is in front of interference signal 2, the half - period count value is increased by 1; if interference signal 2 is in front of interference signal 1, the half - period count value is decreased by 2; if neither of the above two situations is met, the half - period count value remains unchanged. Judge all data segments within this set of data in turn to obtain the half - period count value N corresponding to this set of data. Then, the displacement L corresponding to this set of data seg is calculated by the following formula (c):

[0013]

[0014] Step 4: Judge whether this set of data is the last set of data. If it is not the last set of data, add the displacements L start and L seg calculated in steps 2 and 3 to the displacement temporary value L', extract the data after the last intersection of this set of data and merge it with the next set of data, perform a normalization operation, and repeat steps 2 and 3; if it is the last set of data, calculate the final displacement L (i.e., the total displacement L of the target object). The displacement L is calculated by the following formula (d):

[0015] L = L′ + L seg + L start + L stop (d).

[0016] Compared with the prior art, the present invention has a strong anti-interference ability, high target displacement measurement accuracy, better meets the application requirements of precision measurement, has a simple method, low detection cost, and further broadens the application scenario of the laser interferometer in the industrial environment. Description of the Drawings

[0017] Figure 1 It is a schematic flow chart of the present invention;

[0018] Figure 2 It is a diagram of two orthogonal interference signals;

[0019] Figure 3 It is a diagram of the interference signal after normalization. Detailed Embodiments

[0020] Refer to Figure 1 , the present invention calculates the displacement of the single-frequency laser interferometer according to the following steps:

[0021] Step 1: Perform sub-packaging processing on two groups of orthogonal interference signals obtained by acquisition. Every m sampling points are packed as a group of data, and the two interference signals in this group of data are normalized through the maximum interference voltage and the minimum interference voltage of this group of data.

[0022] Step 2: Find all the intersection points of the two interference signals in this group of data, and determine whether this group of data is the first group of data. If it is the first group of data, calculate the displacement L corresponding to the data points before the first intersection point start and the displacement L corresponding to the data points after the last intersection point stop ; if it is not the first group of data, then let L start =0, calculate the displacement L corresponding to the data points after the last intersection point stop , the displacement L start is calculated by the following formula (a):

[0023]

[0024] The displacement L stop is calculated by the following formula (b):

[0025]

[0026] where λ is the laser wavelength; and are respectively the phase change amounts generated by the data points before the first intersection point of the two interference signals; and are respectively the phase change amounts generated by the data points after the last intersection point of the two interference signals.

[0027] Step 3: Take the data points between every two intersection points of this group of data as a data segment. Within this data segment, if several interference signals 1 are in front of interference signal 2, the half-cycle count value is incremented by 1; if interference signal 2 is in front of interference signal 1, the half-cycle count value is decremented by 2; if neither of the above two cases is satisfied, the half-cycle count value remains unchanged. After sequentially judging all the data segments within this group of data, obtain the half-cycle count value N corresponding to this group of data, then this group of data consists of the displacement amounts L corresponding to all the data segments seg is calculated by the following formula (c):

[0028]

[0029] Step 4: Determine whether this group of data is the last group of data. If it is not the last group of data, add the displacement amounts L start and L seg obtained in Steps 2 and 3 to the displacement temporary value L', extract the data after the last intersection point of this group of data and merge it with the next group of data, perform a normalization operation, and repeat Steps 2 and 3; if it is the last group of data, calculate the final displacement amount L (i.e., the total displacement amount L of the target object), and the displacement amount L is calculated by the following formula (d):

[0030] L = L′ + L seg +L start +L stop (d).

[0031] The features of the present invention and other related features are further described in detail below with reference to a group of data through the accompanying drawings for the understanding of those skilled in the same industry:

[0032] Example 1

[0033] Refer to Figure 2 , in this example, the data graph of two orthogonally interfering signals obtained by sampling. This group of data contains 3000 sampling points, and the wavelength of the laser light source used is 780.246 nanometers. These 3000 sampling points are used as a group of data for data processing.

[0034] Refer to Figure 3 , perform a normalization process on the two interfering signals within this group of data. The normalized interfering signals are as shown in Figure 2 .

[0035] In this embodiment, the phase change corresponding to the data point before the first intersection point of interference signal 1 is 0.243π; the phase change corresponding to the data point before the first intersection point of interference signal 2 is 0.282π. According to the following formula (a):

[0036]

[0037] Calculate the displacement L corresponding to the data points before the first intersection point start is 51 nanometers.

[0038] In this embodiment, the phase change corresponding to the data points after the last intersection point of interference signal 1 is 0.308π, and the phase change corresponding to the data points after the last intersection point of interference signal 2 is 0.350π. According to the following formula (b):

[0039]

[0040] Calculate the displacement L corresponding to the data points after the last intersection point stop is 64 nanometers.

[0041] In this embodiment, there are 6 data segments between the intersection points, and interference signal 1 is in front of interference signal 2 in all data segments, N = 6. According to the following formula (c):

[0042]

[0043] Calculate the displacement L corresponding to all data segments seg is 1170 nanometers.

[0044] In this embodiment, there is only one set of data, and the displacement temporary value L' is 0. Substitute the L start 、L stop and L seg obtained by the above calculation process into the following formula (d), and the total displacement L of the target object can be calculated as 1285 nanometers.

[0045] L = L′ + L seg + L start + L stop (d).

[0046] The above embodiments are only for further illustration of the present invention, and are not intended to limit the patent of the present invention. All equivalent implementations of the present invention should be included within the scope of the claims of the patent of the present invention.

Claims

1. A method for displacement calculation of a single-frequency laser interferometer, characterized in that The method specifically includes the following steps: Step 1: Perform sub-packet processing on two sets of orthogonal interference signals obtained by acquisition, and perform normalization operations; Step 2: Find the intersection points in the data set and calculate the displacement L corresponding to the data points before the first intersection point start and the displacement L corresponding to the data points after the last intersection point stop , where the displacement L start and the displacement L stop are calculated by the following equations (a) and (b) respectively: where λ is the laser wavelength; and are the phase change amounts generated by the data points before the first intersection of the two interference signals respectively; and are the phase change amounts generated by the data points after the last intersection of the two interference signals respectively; Step 3: Take the data points between every two intersection points of this group of data as a data segment. Within this data segment, if a number of interference signals 1 are in front of interference signal 2, the half-cycle count value is incremented by 1; if a number of interference signals 2 are in front of interference signal 1, the half-cycle count value is decremented by 2; if neither of the above two cases is satisfied, the half-cycle count value remains unchanged. After sequentially judging all data segments within this group of data, the half-cycle count value N corresponding to this group of data is obtained, and the displacement L corresponding to all data segments of this group of data seg is calculated by the following formula (c): Step 4: Determine whether this group of data is the last group of data. If it is not the last group of data, add the displacement amounts L start and L seg calculated in Steps 2 and 3 to the displacement temporary value L', extract the data after the last intersection point of this group of data and merge it with the next group of data, perform a normalization operation, and repeat Steps 2 and 3; if it is the last group of data, calculate according to the following formula (d) to obtain the total displacement amount L of the target object: L = L′ + L seg + L start + L stop (d).

2. The method for displacement calculation of a single-frequency laser interferometer according to claim 1, characterized in that The sub-packet processing and normalization in Step 1 are to pack every m sampling points as a group of data, and through the maximum interference voltage and minimum interference voltage of this group of data, perform normalization operations on the two interference signals in this group of data, and the maximum interference voltage and minimum interference voltage of the interference signals can be updated in real time to enhance the anti-interference ability.

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