CN-121977451-A - Ultra-high precision measuring method, device and system for grating distance of grating ruler

CN121977451ACN 121977451 ACN121977451 ACN 121977451ACN-121977451-A

Abstract

The application provides a method, a device and a system for ultra-high precision measurement of grating pitch of a grating ruler, and relates to the technical field of precision optical measurement, wherein the method comprises the steps of obtaining three-dimensional morphology data of the surface of the grating ruler collected by an optical profiler; and carrying out rotation and multi-line signal superposition averaging on the corrected data based on the accurate period direction to obtain a one-dimensional mean value signal, processing the obtained one-dimensional mean value signal by adopting a weighted spectrum analysis algorithm, and calculating to obtain the grating pitch of the grating ruler. The ultra-high precision measuring method, the device and the system for the grating pitch of the grating ruler can take the grating pitch of the grating ruler as an independent parameter to carry out the measuring method of quick, automatic and ultra-high precision calibration, thereby fundamentally solving the bottlenecks of low efficiency, difficult decoupling and dependence on manpower in the prior art.

Inventors

WANG LEIJIE
XIN YANG
ZHU YU
YE WEINAN
ZHANG MING
ZENG HONGJIAN
CHENG RONG
LI XIN

Assignees

清华大学

Dates

Publication Date: 20260505
Application Date: 20260225

Claims (10)

1. The ultra-high precision measurement method for the grating pitch of the grating ruler is characterized by comprising the following steps of: acquiring three-dimensional morphology data of the surface of a grating ruler acquired by an optical profiler; Performing inclination correction on the three-dimensional morphology data to obtain corrected data, and performing grid line direction identification on the corrected data based on rotation searching and a spectrum amplitude maximization principle to obtain an accurate period direction of a grating ruler; and based on the accurate period direction, rotating the corrected data and overlapping and averaging the corrected data with a plurality of lines of signals to obtain a one-dimensional average value signal, processing the obtained one-dimensional average value signal by adopting a weighted spectrum analysis algorithm, and calculating to obtain the grating pitch of the grating ruler.
2. The method of claim 1, wherein said tilt correcting said three-dimensional topography data to obtain corrected data comprises: performing first-order plane fitting on the three-dimensional morphology data by adopting a least square method to obtain a fitting plane; and correcting the Z-direction inclination of the three-dimensional morphology data based on the fitting plane to obtain corrected data.
3. The method according to claim 1, wherein the performing the raster direction recognition on the corrected data based on the rotation search and the spectrum amplitude maximization principle to obtain the accurate period direction of the raster scale includes: And searching a rotation angle which enables the multi-line signals to present the optimal periodicity in the superposition average direction by rotating the corrected data, and taking the found rotation angle as the accurate periodicity direction of the grating ruler.
4. A method according to claim 3, wherein said finding a rotation angle that causes the multi-line signal to exhibit the best periodicity in the superimposed average direction by rotating the corrected data, and taking the found rotation angle as the exact periodicity direction of the grating scale, comprises: setting an angle searching range and a searching step; In the angle search range, sequentially rotating a data matrix corresponding to the corrected data by taking the search steps as intervals, and carrying out superposition average on the data under each rotation angle along the column direction to obtain a corresponding one-dimensional average signal; Performing fast Fourier transform on each one-dimensional mean signal, and recording corresponding spectrum main frequency amplitude values until all rotation angles are traversed, wherein the target rotation angle is used as the accurate periodic direction of the grating ruler; The target rotation angle is a rotation angle corresponding to the maximum frequency spectrum main frequency amplitude.
5. The method of claim 4, wherein the rotating the corrected data based on the precise cycle direction and superposition-averaging the plurality of lines of signals to obtain a one-dimensional average signal comprises: And rotating the corrected data to the target rotation angle, and performing multi-row signal superposition averaging to obtain a one-dimensional mean value signal with optimal signal-to-noise ratio.
6. The method according to claim 1 or 5, wherein the processing the obtained one-dimensional mean signal by using a weighted spectrum analysis algorithm, and precisely calculating the grating pitch of the grating ruler, comprises: Performing fast Fourier transform on the one-dimensional mean value signal to obtain a discrete spectrum, and identifying a peak spectral line and an adjacent spectral line in the discrete spectrum, wherein the adjacent spectral line comprises a left adjacent spectral line and a right adjacent spectral line; calculating a positive frequency deviation based on the peak spectral line and the right adjacent spectral line, and calculating a negative frequency deviation based on the peak spectral line and the left adjacent spectral line; carrying out weighted fusion on the positive frequency deviation and the negative frequency deviation according to the amplitude values of the adjacent spectral lines to obtain a weighted spectrum interpolation coefficient; and calculating the normalized digital frequency of the one-dimensional mean value signal based on the weighted spectrum interpolation coefficient, and calculating according to the normalized digital frequency to obtain the grating pitch of the grating ruler.
7. The method of claim 6, wherein said weighting the positive frequency deviation and the negative frequency deviation based on the magnitudes of the neighboring spectral lines to obtain weighted spectral interpolation coefficients, comprising: calculating the ratio of the amplitudes of two spectral lines in the adjacent spectral lines, and determining the weight corresponding to the left adjacent spectral line and the weight corresponding to the right adjacent spectral line based on the ratio; and determining the weight corresponding to the left adjacent spectral line and the weight corresponding to the right adjacent spectral line based on the ratio, and carrying out weighted average on the positive frequency deviation and the negative frequency deviation to obtain the weighted spectrum interpolation coefficient.
8. The method of claim 1, wherein the optical profiler is a white light scanning interferometer profiler and the grating pitch is the pitch of a one-dimensional grating scale or a two-dimensional planar grating scale.
9. An ultra-high precision measuring device for the grating pitch of a grating ruler, which is characterized by comprising: the data acquisition module is used for acquiring three-dimensional morphology data of the surface of the grating ruler acquired by the optical profiler; the inclination correction module is used for carrying out inclination correction on the three-dimensional morphology data to obtain corrected data; The grating line direction recognition module is used for recognizing the grating line direction of the corrected data based on the rotation search and spectrum amplitude maximization principle to obtain the accurate period direction of the grating ruler; and the grid distance calculation module is used for carrying out rotation and multi-line signal superposition and average on the corrected data based on the accurate period direction to obtain a one-dimensional mean value signal, processing the obtained one-dimensional mean value signal by adopting a weighted spectrum analysis algorithm, and calculating to obtain the grid distance of the grating ruler.
10. The ultra-high precision measuring system for the grating pitch of the grating ruler is characterized by comprising an optical profiler and a processing unit, wherein the optical profiler is used for acquiring three-dimensional morphology data of the surface of the grating ruler, and the processing unit is used for executing the steps of the ultra-high precision measuring method for the grating pitch of the grating ruler according to any one of claims 1 to 8.

Description

Ultra-high precision measuring method, device and system for grating distance of grating ruler Technical Field The application relates to the technical field of precise optical measurement, in particular to a method, a device and a system for ultra-high precision measurement of grating pitch of a grating ruler. Background The grating ruler is used as a core sensor for modern ultra-precise displacement measurement, and the accuracy of the grating distance (namely the nominal distance between grating lines) directly determines the reference of displacement measurement. The tiny deviation of the grid distance can be amplified through a measuring system, and finally, a non-negligible proportional error is introduced, so that the positioning accuracy of high-end equipment such as a photoetching machine, a coordinate measuring machine and the like is seriously affected. In the related art, for the precision test technology of the two-dimensional plane grating line direction, a perfect and efficient measurement method is still lacking up to now. The direction error of the grid line and the mechanical reference, especially the non-orthogonality between the two grid line directions, can directly lead to abbe error and cosine error in displacement measurement, and severely restricts the further improvement of the positioning precision of the ultra-precise workbench. Based on the method, the independent, accurate and efficient measurement and calibration of the grating pitch of the grating ruler are key preconditions for ensuring the metering performance and traceability of the grating ruler. Disclosure of Invention The application aims to provide a method, a device and a system for measuring the grating pitch of a grating ruler with ultra-high precision, which can take the grating pitch of the grating ruler as an independent parameter to carry out quick, automatic and ultra-high precision calibration, thereby fundamentally solving the bottleneck that the prior art has low efficiency and is difficult to decouple and relies on manpower. In a first aspect, the application provides a method for measuring ultra-high precision of a grating pitch of a grating ruler, comprising the following steps: The method comprises the steps of acquiring three-dimensional morphology data of the surface of a grating ruler, acquiring the three-dimensional morphology data of the surface of the grating ruler, performing inclination correction on the three-dimensional morphology data to obtain corrected data, performing grating line direction identification on the corrected data based on rotation searching and spectrum amplitude maximization principles to obtain the accurate period direction of the grating ruler, performing rotation and multi-line signal superposition averaging on the corrected data based on the accurate period direction to obtain a one-dimensional mean value signal, processing the obtained one-dimensional mean value signal by adopting a weighted spectrum analysis algorithm, and calculating to obtain the grating pitch of the grating ruler. Optionally, the inclination correction is carried out on the three-dimensional morphology data to obtain corrected data, wherein the method comprises the steps of carrying out first-order plane fitting on the three-dimensional morphology data by adopting a least square method to obtain a fitting plane, and carrying out Z-direction inclination correction on the three-dimensional morphology data based on the fitting plane to obtain corrected data. Optionally, based on the rotation search and spectrum amplitude maximization principle, carrying out raster line direction identification on the corrected data to obtain the accurate periodic direction of the raster scale, wherein the method comprises the steps of searching a rotation angle which enables a plurality of lines of signals to present the optimal periodicity in the superposition average direction by rotating the corrected data, and taking the found rotation angle as the accurate periodic direction of the raster scale. Optionally, the method comprises the steps of rotating the corrected data, finding out the rotation angle enabling the multi-line signals to show the optimal periodicity in the superposition average direction, taking the found rotation angle as the accurate periodicity direction of the grating ruler, setting an angle searching range and a searching step, sequentially rotating a data matrix corresponding to the corrected data in the angle searching range at intervals of the searching step, superposing and averaging the data under each rotation angle along the column direction to obtain a corresponding one-dimensional average value signal, carrying out fast Fourier transform on each one-dimensional average value signal, recording the corresponding spectrum dominant frequency amplitude, and taking the target rotation angle as the accurate periodicity direction of the grating ruler until all rotation angles are traversed, where