Circular grating self-calibration angle measurement method and system based on common aperture bimodal

Abstract

The invention discloses a circular grating self-calibration angle measurement method and system based on common aperture bimodal. The method comprises the following steps: synchronously acquiring a heterodyne interference signal from narrow linewidth laser and a low-coherence interference signal from a broadband light source through a common-aperture optical probe; the local scribed line manufacturing error of the inverted circular grating and the installation geometric error of the system are processed respectively; and finally, outputting a calibrated high-precision angle value through an error decoupling and compensation model. The system integrates double light sources, a beam combining and splitting device and a signal processing unit, and realizes synchronous acquisition of angle and morphology information under the same probe. Full error compensation can be completed on line without an external reference, the problem that the scribing error and the installation error are difficult to separate is fundamentally solved, and the precision, the reliability and the environmental adaptability of circular grating angle measurement are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of precision optical measurement, and in particular to a circular grating self-calibration angle measurement method and system based on a common-aperture dual-mode. BACKGROUND

[0002] In the field of high-precision angle measurement, circular grating encoders are widely used in key scenarios such as precision rotary tables, astronomical telescopes, semiconductor lithography equipment, and aerospace inertial reference systems due to their high resolution, good repeatability, and compact structure. However, their actual angle measurement accuracy is often restricted by two main errors: one is the low-frequency geometric error caused by the installation eccentricity and tilt between the grating disc and the rotating main shaft; the other is the periodic non-uniformity or local defects in the grating line manufacturing process, which leads to mid-high frequency harmonic errors. To improve accuracy, traditional methods usually rely on offline calibration or introduce external high-precision standards such as laser interferometers for periodic calibration, but such methods not only interrupt the normal workflow, but also are difficult to reflect the dynamic error characteristics of the device in the real running environment, and cannot meet the needs of modern high-end equipment for "online, external reference-free, long-term stable" self-calibration capabilities.

[0003] To address the above challenges, some existing technologies propose self-calibration schemes. Among them, Chinese invention patent CN107560589B "Circular grating error separation and compensation method based on multiple reading heads" represents a mainstream approach: this scheme arranges three or more photoelectric reading heads on the circumference, uses their spatial phase difference to collect multiple moire signals, and combines Fourier analysis or least squares fitting to separate the harmonic components in the grating lines, thereby achieving full-band error compensation. This method can effectively improve the angle measurement accuracy under ideal laboratory conditions, but its effectiveness is highly dependent on a key premise - all reading heads must maintain consistent output performance over a long period. In actual engineering applications, due to factors such as optical window contamination, temperature drift, mechanical vibration, or electronic device aging, any reading head may experience unpredictable performance degradation (such as decreased sensitivity, DC offset, or nonlinear distortion). Once such a situation occurs, the system cannot identify abnormal signals, but instead will include incorrect data into the error reconstruction model without distinction, leading to distorted calibration results and even worse overall accuracy than the uncalibrated state. More seriously, this scheme belongs to an open-loop redundant architecture, lacking the ability to perceive the health status of sensors and fault tolerance mechanisms, and has significant reliability risks in long-term unattended or harsh environment applications.

[0004] In addition, other single-channel self-calibration methods (such as phase modulation or spectrum analysis-based techniques) are structurally simple, but only rely on a single sensing path to extract error information, and cannot distinguish between real angle changes and sensor itself drift or local defects of the grating, and also lack an internal verification mechanism. Therefore, the current technology generally has a fundamental contradiction of "fragile multi-sensor scheme and blind single-sensor scheme", which is difficult to balance the integrity of error compensation and the robustness of system operation at the same time, and urgently needs a new self-calibration architecture that can realize full-band error decoupling and has internal reliability.

[0005] Although the existing circular grating self-calibration technology improves the angle measurement accuracy to some extent, it still faces the contradiction that cannot be reconciled in practical application: the multi-reading head redundant scheme can cover a wide error frequency band, but it highly depends on the consistency of multiple sensor outputs; while the single-channel modulation or signal processing method is simple in structure, but lacks the ability to explain the separability of error sources, and cannot perceive its own state. The multi-reading head scheme represented by CN107560589B essentially builds on the ideal assumption that "all reading heads are normal and stable in performance". However, under long-term operation or complex working conditions, the performance degradation of any reading head due to pollution, aging, temperature drift or mechanical looseness will destroy this premise, and the system cannot identify abnormal signals or suppress their pollution to the overall calibration results, which may eventually lead to compensation failure or even accuracy deterioration. More importantly, such methods belong to an open-loop architecture, lack an internal verification mechanism, and cannot determine whether the calibration result is reliable.

[0006] On the other hand, single-channel self-calibration methods (such as phase modulation techniques) avoid the complexity of multi-sensor arrangement, but only extract error information through a single signal path, making it difficult to distinguish whether the angle change is caused by real rotation or by sensor itself drift or local defects of the grating. Due to the lack of independent reference, its error model is easily affected by common mode interference, and the reliability of the calibration result is difficult to guarantee.

[0007] In summary, the existing technology generally has a fundamental defect of "integrity and robustness cannot be achieved": either relying on fragile multi-point consistency or falling into blind single-channel inference, both of which cannot meet the stringent requirements of high-end equipment for "external reference-free, full-band compensation, and long-term reliable operation". SUMMARY

[0008] The technical solution of the present application to solve the above technical problems is to provide a circular grating self-calibration angle measurement method based on a common-aperture dual-mode, comprising the following steps:

[0009] S1, synchronously collecting original signals: synchronously collecting first modal signals and second modal signals through a common-aperture optical probe during rotation of a circular grating; the first modal signals are heterodyne beat frequency signals derived from a narrow-linewidth laser, used for angle sensing; the second modal signals are low-coherence interference signals derived from a broadband light source, used for measuring local topography of the grating;

[0010] S2, demodulating an original angle sequence: processing the first modal signals to demodulate phase changes thereof, to obtain an original angle sequence containing errors;

[0011] S3, inverting local ruling error: processing the second modal signals to invert local ruling pitch deviation of a current measurement position of the grating through interference envelope peak positioning or spectral analysis, and to convert the local ruling pitch deviation into ruling manufacturing error related to angles by integration;

[0012] S4, fitting installation geometry error: calculating a residual sequence according to the original angle sequence and the ruling manufacturing error; and separating installation geometry error based on a rigid body kinematics model to fit the residual sequence;

[0013] S5, outputting calibrated angles: compensating for errors of the original angle sequence by using a calibration model, and outputting calibrated angle values.

[0014] Further, in step S2, demodulating the original angle sequence specifically includes:

[0015] performing digital phase-locked or fast Fourier transform on the first modal signals to extract instantaneous phases thereof:

[0016] ;

[0017] wherein, R is a grating radius, and ε inst (θ) is installation geometry error;

[0018] a continuous phase ΦA(t) is obtained through phase unwrapping, and the original angle sequence is calculated:

[0019] .

[0020] Further, in step S3, inverting the local ruling error specifically includes:

[0021] performing Fourier transform on the second modal signals to obtain an axial depth scanning signal AB(z):

[0022] ;

[0023] wherein, w(k) is a window function used for suppressing sidelobes;

[0024] Locate the envelope peak position of AB(z) to determine the actual depth of the grating scribe line reflective surface;

[0025] The local scribe line pitch deviation δΛ is calculated by comparing the actual depth with the ideal equidistant scribe line position.

[0026] ;

[0027] Based on the mapping relationship between angle and engraving index, the discrete δΛ sequence is integrated to generate continuous engraving manufacturing errors.

[0028] Further, in step S4, the rigid body kinematic model is... .

[0029] Furthermore, it also includes the downgrade operation steps:

[0030] Monitor the signal-to-noise ratio of the second mode signal;

[0031] When the signal-to-noise ratio is lower than a preset threshold, the system switches to historical map mode and calls up pre-stored scribing manufacturing error data. ;

[0032] Combined with the above Based on the currently acquired first modal signal, execute steps S4 and S5 to output the calibration angle.

[0033] This invention also proposes a circular grating self-calibration angle measurement system based on a common aperture dual-mode for implementing the method described above, comprising:

[0034] Rotating reflective circular grating;

[0035] A common aperture dual-mode optical probe is fixedly positioned and points towards the working surface of the circular grating; the common aperture dual-mode optical probe includes:

[0036] A narrow linewidth laser source is used to provide the first measurement beam;

[0037] A broadband light source is used to provide a second measurement beam;

[0038] A beam combiner is used to combine the first measurement beam and the second measurement beam into a composite beam.

[0039] A focusing objective lens is used to focus the composite light onto the same micro-area on the surface of the rotating reflective circular grating;

[0040] A beam splitter is used to receive and separate the information-carrying optical signal returned from the rotating reflective circular grating.

[0041] The first detection module is used to receive the optical signal corresponding to the first measurement beam after being separated by the beam splitter, and convert it into a first electrical signal;

[0042] The second detection module is used to receive the optical signal corresponding to the second measurement beam after being separated by the beam splitter, and convert it into a second electrical signal;

[0043] The signal processing unit, connected to the first detection module and the second detection module, is configured to synchronously acquire the first electrical signal and the second electrical signal, and execute the self-calibration angle measurement method as described in any one of claims 1-5, and output calibrated angle information.

[0044] Furthermore, an acousto-optic modulator is provided in the output optical path of the narrow linewidth laser source to frequency shift the laser to generate the frequency difference required for heterodyne interference.

[0045] Furthermore, the beam combining device is an optical fiber coupler; the narrow linewidth laser source and the broadband source are connected to the input end of the optical fiber coupler via optical fiber; the output end of the optical fiber coupler is connected to the focusing objective lens via optical fiber.

[0046] Furthermore, the second detection module is a spectral analysis module, specifically a spectral domain optical coherence tomography configuration, including a spectrometer and a linear array detector, used to analyze the low coherence interference spectrum of the second measurement beam.

[0047] The circular grating self-calibration angle measurement method and system based on common aperture dual-mode provided by this invention have the following significant advantages:

[0048] 1. Achieve in-situ decoupling and compensation for errors across the entire frequency band, significantly improving the final angle measurement accuracy:

[0049] This invention utilizes dual-mode signals with different physical principles to directly and independently observe and inversely deduce the grating manufacturing error during measurement, thereby accurately separating it from the mixed error. The remaining residual is then used to fit the installation geometric error, fundamentally avoiding the mutual "contamination" of the two types of errors. This decoupling mechanism based on physical perception allows for targeted compensation for both high-frequency grating local defects and low-frequency installation eccentricity and tilt, thus improving the system accuracy to near the theoretical limit of the inherent resolution of the grating grating.

[0050] 2. Eliminate reliance on high-precision benchmarks and achieve true "self-calibration":

[0051] This invention innovatively utilizes low-coherence interference to directly measure the micro-area morphology of the grating itself as a built-in "ruler," providing a real-time reference standard derived from the object being measured for angle measurement. The system requires no external benchmarks or prior calibration data, and can complete online identification and compensation of the entire error chain on-site, achieving "self-sufficient" high-precision measurement and greatly improving the portability and field applicability of the equipment.

[0052] 3. Adopting a common aperture integrated design ensures measurement consistency and long-term stability.

[0053] This invention focuses two measurement beams onto the same micro-area on the grating surface through the same optical aperture and objective lens, ensuring strict consistency in the physical positions of the two modes. This common-path design ensures high synchronization of common-mode interference such as mechanical vibration, air disturbance, and thermal drift experienced by the two modes, which can be effectively suppressed in subsequent differential processing. Simultaneously, the single-probe design simplifies the system structure, reduces assembly and adjustment difficulty, and improves the system's mechanical stability and reliability. Attached Figure Description

[0054] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0055] Figure 1 This is a flowchart illustrating the steps of the circular grating self-calibration angle measurement method based on common aperture dual-mode described in this invention.

[0056] Figure 2 This is a schematic diagram of the system structure of the present invention;

[0057] Figure 3 This is a schematic diagram comparing the dual-modal error characteristics of the present invention.

[0058] Explanation of icon numbers:

[0059] 11. Narrow linewidth laser source; 12. Broadband light source; 13. Beam combiner; 14. Focusing objective; 15. Beam splitter; 16. First detection module; 17. Second detection module; 18. Signal processing unit; 2. Rotary reflective circular grating. Detailed Implementation

[0060] This invention proposes a circular grating self-calibration angle measurement method and system based on common aperture dual-mode, aiming to construct a self-reference mechanism inherent in the measurement process, and realize online decoupling and compensation of full-band errors without external reference or multi-sensor consistency.

[0061] The following will describe the circular grating self-calibration angle measurement method and system based on common aperture dual-mode proposed in this invention through specific embodiments:

[0062] Example 1:

[0063] In the technical solution of this embodiment, such as Figure 1 As shown, a self-calibration angle measurement method for circular gratings based on common aperture dual-mode includes the following steps:

[0064] S1. Synchronous acquisition of raw signals: During the rotation of the circular grating, the first mode signal I is synchronously acquired through a common aperture optical probe. A (t) and the second mode signal S B (k); The first mode signal is a heterodyne interference beat frequency signal originating from a narrow linewidth laser, used for angle sensing; the second mode signal is a low coherence interference signal originating from a broadband light source, used for measuring the local morphology of the grating;

[0065] S2. Demodulate the original angle sequence: Process the first mode signal, demodulate its phase change, and obtain the original angle sequence containing the error;

[0066] S3. Inverting Local Grating Error: Process the second mode signal, and through interference envelope peak positioning or spectral analysis, invert the local grating pitch deviation at the current measurement position, and integrate it to convert it into an angle-related grating manufacturing error;

[0067] S4. Fitting Installation Geometric Errors: Calculate the residual sequence based on the original angle sequence and the engraving manufacturing error; perform harmonic fitting on the residual sequence based on the rigid body kinematics model to separate and obtain the installation geometric errors;

[0068] S5. Output calibration angle: Using the calibration model, perform error compensation on the original angle sequence and output the calibrated angle value.

[0069] Furthermore, in step S2, demodulating the original angle sequence specifically includes:

[0070] Perform digital phase-locked loop or fast Fourier transform on the first mode signal to extract its instantaneous phase:

[0071] ;

[0072] in, R is the grating radius, ε inst (θ) represents the installation geometric error;

[0073] The continuous phase ΦA(t) is obtained by unwrapping the phase, and then the original angle sequence is calculated:

[0074] .

[0075] Furthermore, in step S3, the inversion of local scribing errors specifically includes:

[0076] Performing a Fourier transform on the second modal signal yields the axial depth scan signal:

[0077] ;

[0078] Where w(k) is a window function used to suppress sidelobes;

[0079] Locate the peak position z of the envelope of AB(z). peak [n], this position corresponds to the actual depth of the reflective surface of the current grating line, and determines the actual depth of the reflective surface of the grating line;

[0080] The local scribe line pitch deviation δΛ is calculated by comparing the actual depth with the ideal equidistant scribe line position.

[0081] ;

[0082] Based on the mapping relationship between angle and engraving index, the discrete δΛ sequence is integrated to generate continuous engraving manufacturing errors.

[0083] The mapping relationship between angle and scale line index is as follows: in This represents the angle increment between adjacent sampling points.

[0084] Further, in step S4, the rigid body kinematic model is... .

[0085] Specifically, the residual sequence is defined as follows:

[0086] ;

[0087] The residual theoretically contains only the true rotation angle θtrue[n] and the installation error εinst(θ).

[0088] Based on the rigid body kinematics model, the installation error can be expressed as:

[0089]

[0090] Typically, the first 2-3 harmonics are sufficient to cover the main eccentricity and tilt effects. The least squares method is used to fit the coefficients. ;

[0091] ;

[0092] Since θtrue[n] is a monotonically increasing unknown, it can be modeled as a first-order polynomial. , and optimize in conjunction with harmonic coefficients.

[0093] Substitute the fitted εinst(θA[n]) and εB[n] into the calibration model to calculate the final angle output:

[0094] ;

[0095] This result is a high-precision angle value that has eliminated installation geometric errors and scribing manufacturing errors, and can be directly used for servo control or data recording.

[0096] Furthermore, it also includes the downgrade operation steps:

[0097] Monitor the signal-to-noise ratio of the second mode signal;

[0098] When the signal-to-noise ratio is lower than a preset threshold, the system switches to historical map mode and calls up pre-stored scribing manufacturing error data. ;

[0099] Combined with the above Based on the currently acquired first modal signal, execute steps S4 and S5 to output the calibration angle.

[0100] The key difference between the technical solution of this application and traditional harmonic fitting methods lies in:

[0101] ① The engraving error is not obtained through mathematical assumptions, but is directly observed and inverted by low-coherence interferometry, and has physical interpretability;

[0102] ② The installation error fitting is based on the "residual sequence after removing the scribing error", which avoids the mutual contamination of the two types of errors;

[0103] ③ The entire process does not rely on any prior calibration data or external benchmarks, forming a closed-loop self-verification logic.

[0104] The above steps together constitute a complete, hardware-implementable self-calibration algorithm, which is one of the key technical solutions that this invention aims to protect.

[0105] Example 2:

[0106] This invention also proposes a circular grating self-calibration angle measurement system based on a common aperture dual-mode for implementing the method described above, such as... Figure 2 , Figure 3 As shown, it includes:

[0107] Rotating reflective circular grating;

[0108] A common aperture dual-mode optical probe is fixedly positioned and points towards the working surface of the circular grating; the common aperture dual-mode optical probe includes:

[0109] Narrow linewidth laser source 11 is used to provide the first measurement beam;

[0110] Broadband light source 12 is used to provide a second measurement beam;

[0111] The beam combiner 13 is used to combine the first measurement beam and the second measurement beam into a composite beam.

[0112] Focusing objective 14 is used to focus the composite light onto the same micro-area on the surface of the rotating reflective circular grating 2;

[0113] Beam splitter 15 is used to receive and separate the information-carrying optical signal returned from the rotating reflective circular grating 2.

[0114] The first detection module 16 is used to receive the optical signal corresponding to the first measurement beam after being separated by the beam splitter 15, and convert it into a first electrical signal;

[0115] The second detection module 17 is used to receive the optical signal corresponding to the second measurement beam after being separated by the beam splitter 15, and convert it into a second electrical signal;

[0116] The signal processing unit 18 is connected to the first detection module 16 and the second detection module 17, and is configured to synchronously acquire the first electrical signal and the second electrical signal, and execute the self-calibration angle measurement method as described in any one of claims 1-5, and output the calibrated angle information.

[0117] Furthermore, an acousto-optic modulator is provided in the output optical path of the narrow linewidth laser source 11 to frequency shift the laser to generate the frequency difference required for heterodyne interference.

[0118] Furthermore, the beam combiner 13 is an optical fiber coupler; the narrow linewidth laser source 11 and the broadband light source 12 are connected to the input end of the optical fiber coupler via optical fibers; the output end of the optical fiber coupler is connected to the focusing objective lens 14 via optical fibers.

[0119] Furthermore, the second detection module 17 is a spectral analysis module, specifically a spectral domain optical coherence tomography configuration, including a spectrometer and a linear array detector, used to analyze the low coherence interference spectrum of the second measurement beam.

[0120] (1) Rotating reflective circular grating 2:

[0121] Diameter: 100 mm;

[0122] Radius: R: 50 mm;

[0123] Nominal scribe line pitch: Λ0: 20 μm (corresponding to 50,000 lines per revolution);

[0124] Materials: Fused silica substrate, coated with a high-reflectivity aluminum film;

[0125] (2) Narrow linewidth laser source 11 (for heterodyne interference):

[0126] Type: Helium-neon (He-Ne) laser or single-frequency semiconductor laser;

[0127] Wavelength λ: 632.8 nm;

[0128] Linewidth: < 1 MHz;

[0129] Output power: ≥ 5 mW;

[0130] (3) Acousto-optic modulator (AOM):

[0131] Modulation frequency difference Δf: 80 MHz;

[0132] Diffraction efficiency: > 80%;

[0133] Drive power: 1.5 W;

[0134] (4) Broadband light source 12 (for low-coherence interference):

[0135] Type: Superluminescent diode (SLD);

[0136] Center wavelength λc: 830 nm;

[0137] Full width at half maximum (FWHM) of the spectrum: ≈ 50 nm;

[0138] Coherence length Lc: ≈ 10–12 μm (calculated from Lc≈2ln2 / π⋅λc2 / Δλ);

[0139] Output power: ≥ 10 mW;

[0140] (5) Fiber optic coupler of bundle combiner 13:

[0141] Type: Single-mode fiber (SMF-28e) 50:50 coupler;

[0142] Operating wavelength range: 600–900 nm (compatible with dual light sources);

[0143] Insertion loss: < 0.2 dB;

[0144] (6) Focusing objective lens:

[0145] Type: Infinity-corrected microscope objective;

[0146] Numerical aperture (NA): 0.25;

[0147] Working distance: Approximately 10 mm;

[0148] Focused spot diameter: ≤ 20 μm (on the grating surface);

[0149] (7) Beam splitter 15:

[0150] Type: Cubic polarization-independent beam splitter;

[0151] Spectrophotometric ratio: 50:50;

[0152] Wavelength range: 600–900 nm;

[0153] (7) High-speed photodetector (PD1, used for heterodyne signal) of the first detection module 16:

[0154] Bandwidth: ≥ 200 MHz;

[0155] Responsivity: 0.5 A / W @ 632.8 nm;

[0156] Rise time: < 2 ns;

[0157] (8) The spectral analysis module (PD2, for low coherence signals) of the second detection module 17:

[0158] Type: Spectral domain OCT (SD-OCT) configuration;

[0159] Spectrometer core: 830 nm center wavelength, linear CCD array;

[0160] Spectral resolution: 0.1 nm;

[0161] A-scan rate: ≥ 20 kHz;

[0162] (9) Signal processing unit 18:

[0163] High-speed ADC sampling rate (PD1 channel): ≥ 500 MS / s;

[0164] FPGA model: Xilinx Kintex-7 or equivalent;

[0165] DSP clock speed: ≥ 1 GHz;

[0166] Angle calculation update rate: ≥ 10 kHz.

[0167] During operation, a narrow-linewidth laser is modulated by an acousto-optic modulator to generate an 80 MHz frequency shift, forming two coherent beams required for heterodyne interference; an 830 nm SLD broadband light source12 is used for low-coherence interferometry. The two optical signals are combined via a 50:50 fiber coupler and focused onto the same micro-area (spot diameter approximately 18 μm) on the circular grating surface using the same NA=0.25 objective lens, ensuring complete overlap of the two detection modes. The reflected light returns along the original optical path, is separated by a beam splitter, and then sent to a high-speed photodetector with a bandwidth of 200 MHz and a spectral analysis module for synchronous acquisition. All signals are ultimately input to an FPGA+DSP processing unit to execute real-time phase demodulation, topography inversion, and error decoupling algorithms, outputting calibrated angle values.

[0168] Dual-modal working principle and mathematical model:

[0169] (1) Mode A: Heterodyne laser interferometry (high-precision angle sensing);

[0170] A narrow-linewidth laser (e.g., wavelength 632.8 nm) generates a frequency difference Δf (e.g., 80 MHz) via an acousto-optic modulator, which, after illuminating a grating, forms a beat frequency signal.

[0171] ;

[0172] Where: λ is the laser wavelength (e.g., 632.8nm); The optical path length is the change, and R is the grating radius; This refers to installation geometric errors caused by eccentricity δ, tilt α, etc. The original angle output can be calculated by extracting the phase ϕA(t) using digital phase-locked loop or FFT.

[0173] ;

[0174] (2) Mode B: Low-coherence interference morphology perception (local structure observation):

[0175] Light emitted from broadband light source 12 (center wavelength λc = 830 nm, coherence length Lc ≈ 10 μm, Lc ≈ 10 μm) is focused onto the grating surface by the same objective lens. Due to the short coherence length, interference fringes only occur when the optical path difference between the reference arm and the sample arm is less than the coherence length. By scanning the reference arm or using spectral domain detection, the position of the local interference envelope peak can be obtained, and thus the actual local pitch Λlocal(θ) of the grating lines in the current field of view can be inverted.

[0176] Define local pitch deviation:

[0177] ;

[0178] Where Λ0 is the nominal pitch (e.g., 20 μm).

[0179] Convert it to an equivalent angular error (by accumulating phase):

[0180] ;

[0181] This is the high-order harmonic error caused by defects in the engraving process.

[0182] The core of this invention lies in constructing a self-reference mechanism inherent in the measurement process through a common-aperture dual-modal interferometry architecture, thereby achieving online decoupling and self-calibration of errors across the entire frequency band without the need for external standards or multi-sensor consistency assumptions. The following is combined with... Figure 3 The flowchart shown details the specific implementation steps of the algorithm.

[0183] The installation error εinst only modulates the heterodyne interference phase and does not affect the measurement of micro-area morphology by low coherence interferometry;

[0184] The scribe line error εB is sensed by both modes, but low-coherence interference can directly provide its local form.

[0185] Construct the calibration equation:

[0186] .

[0187] This system requires only one physical probe, fundamentally avoiding the reliance on cross-sensor consistency inherent in multi-readhead solutions. Even if slow drift occurs within the probe's internal components, differential processing can effectively suppress errors as long as both modes are affected by a common mode. Furthermore, when the low-coherence interferometry module fails to provide effective topographic information due to a decrease in signal-to-noise ratio, the system can automatically switch to "historical scribe pattern mode," utilizing the previously stored data to continue compensating for scribe errors, thereby ensuring basic angle measurement performance and achieving task continuity.

[0188] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A self-calibrated angle measurement method for circular gratings based on a common aperture dual-mode, characterized in that, Includes the following steps: S1. Synchronous acquisition of raw signals: During the rotation of the circular grating, the first mode signal and the second mode signal are acquired synchronously through a common aperture optical probe; the first mode signal is a heterodyne interference beat frequency signal from a narrow linewidth laser, used for angle sensing; the second mode signal is a low coherence interference signal from a broadband light source, used for measuring the local morphology of the grating. S2. Demodulate the original angle sequence: Process the first mode signal, demodulate its phase change, and obtain the original angle sequence containing the error; S3. Inverting Local Grating Error: Process the second mode signal, and through interference envelope peak positioning or spectral analysis, invert the local grating pitch deviation at the current measurement position, and integrate it to convert it into an angle-related grating manufacturing error; S4. Fitting Installation Geometric Errors: Calculate the residual sequence based on the original angle sequence and the engraving manufacturing error; perform harmonic fitting on the residual sequence based on the rigid body kinematics model to separate and obtain the installation geometric errors; S5. Output calibration angle: Using the calibration model, perform error compensation on the original angle sequence and output the calibrated angle value.

2. The method according to claim 1, characterized in that, In step S2, demodulating the original angle sequence specifically includes: Perform digital phase-locked loop or fast Fourier transform on the first mode signal to extract its instantaneous phase: ； in, R is the grating radius, ε inst (θ) represents the installation geometric error; IA(t) is the instantaneous light intensity of the first mode signal, I0 is the DC bias light intensity, V is the modulation depth, Δf is the heterodyne beat frequency, t is the time variable, λ is the laser wavelength, d(θ(t)) is the dynamic optical path difference, and θ(t) is the real-time rotation angle of the circular grating. The continuous phase ΦA(t) is obtained by unwrapping the phase, and then the original angle sequence is calculated: 。 3. The method according to claim 1, characterized in that, In step S3, the inversion of local scribing errors specifically includes: Performing a Fourier transform on the second modal signal yields the axial depth scan signal AB(z): ； Where w(k) is a window function used to suppress sidelobes; Locate the peak position z of the envelope of AB(z). peak [n] determines the actual depth of the reflective surface of the grating; The local scribe line pitch deviation δΛ is calculated by comparing the actual depth with the ideal equidistant scribe line position. ； Based on the mapping relationship between angle and engraving index, the discrete δΛ sequence is integrated to generate continuous engraving manufacturing errors.

4. The method according to claim 1, characterized in that, In step S4, the rigid body kinematic model is: ; εinst(θ) represents the installation geometric error, θ represents the rotation angle, a0 represents the DC component, a1, b1 represent the first-order harmonic coefficients, a2, b2 represent the second-order harmonic coefficients, and ... represent higher-order harmonic terms.

5. The method according to claim 1, characterized in that, It also includes the downgrade operation steps: Monitor the signal-to-noise ratio of the second mode signal; When the signal-to-noise ratio is lower than a preset threshold, the system switches to historical map mode and calls up pre-stored scribing manufacturing error data. ; In conjunction with the above Based on the currently acquired first modal signal, execute steps S4 and S5 to output the calibration angle.

6. A circular grating self-calibration angle measurement system based on a common aperture dual-mode for implementing the method of any one of claims 1-5, characterized in that, include: Rotating reflective circular grating; A common aperture dual-mode optical probe is fixedly positioned and points towards the working surface of the circular grating; The common aperture dual-mode optical probe includes: A narrow linewidth laser source is used to provide the first measurement beam; A broadband light source is used to provide a second measurement beam; A beam combiner is used to combine the first measurement beam and the second measurement beam into a composite beam. A focusing objective lens is used to focus the composite light onto the same micro-area on the surface of the rotating reflective circular grating; A beam splitter is used to receive and separate the information-carrying optical signal returned from the rotating reflective circular grating. The first detection module is used to receive the optical signal corresponding to the first measurement beam after being separated by the beam splitter, and convert it into a first electrical signal; The second detection module is used to receive the optical signal corresponding to the second measurement beam after being separated by the beam splitter, and convert it into a second electrical signal; The signal processing unit, connected to the first detection module and the second detection module, is configured to synchronously acquire the first electrical signal and the second electrical signal, and execute the self-calibration angle measurement method as described in any one of claims 1-5, and output calibrated angle information.

7. The system according to claim 6, characterized in that, An acousto-optic modulator is provided in the output optical path of the narrow linewidth laser source to frequency shift the laser and generate the frequency difference required for heterodyne interference.

8. The system according to claim 6, characterized in that, The beam combining device is an optical fiber coupler; the narrow linewidth laser source and the broadband light source are connected to the input end of the optical fiber coupler via optical fiber; the output end of the optical fiber coupler is connected to the focusing objective lens via optical fiber.

9. The system according to claim 6, characterized in that, The second detection module is a spectral analysis module, specifically a spectral domain optical coherence tomography configuration, including a spectrometer and a linear array detector, used to analyze the low coherence interference spectrum of the second measurement beam.

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