Circular grating high-precision dynamic angle measurement method and system based on correlated imaging

Abstract

The invention discloses a circular grating high-precision dynamic angle measurement method and system based on correlated imaging, and the method comprises the following steps: a light source emits correlated light beams, and the correlated light beams are collected and split into reference light and object light; calculating a second-order correlation function for the N-time pulse sampling data; the light intensity distribution of an object light path is modulated through rotation of the circular grating, so that # imgabs0 # changes along with the angle; calculating a second-order correlation function between the light intensity distribution # imgabs 1 # of the reference light path and the light intensity # imgabs 2 # of the object light path, and extracting the non-local correlation between the light intensity distribution and the angle; establishing a grating angle-correlation peak value mapping database; and outputting an angle value in real time through peak value matching. According to the technical scheme, the non-local correlation characteristic of correlated imaging is applied to dynamic angle measurement for the first time, the correlated imaging technology is combined with a circular grating angle measurement system, angle information is extracted through a correlation function, and the defects of a traditional grating angle measurement system in the aspects of dynamic measurement and interference resistance are overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of optical measurement, and particularly to a high-precision dynamic angle measurement method and system for circular gratings based on correlated imaging. Background Art

[0002] The circular grating angle measurement technology is a high-precision angle measurement method widely used in industrial automation, robot navigation, aerospace and other fields. Its core principle is to convert the angle information into an optical intensity signal through the interaction between the grating lines and the photodetector, and then calculate the rotation angle.

[0003] The existing circular grating angle measurement technologies mainly include the Moiré fringe-based angle measurement technology that calculates the angle through the change in the optical intensity of the Moiré fringe generated by the grating lines, the multi-reading head redundancy technology that uses multiple reading heads to improve the measurement accuracy and reliability, and the optoelectronic encoder technology that combines the grating lines and the photodetector to achieve high-resolution angle measurement.

[0004] Chinese Patent Publication No. "CN102353347A", titled "A High-Precision Circular Grating Angle Measurement System", discloses a circular grating angle measurement method based on Moiré fringes, which adopts a multi-reading head redundancy design and Moiré fringe signal processing to improve the angle measurement accuracy and anti-interference ability, but does not solve the problems of dynamic measurement and anti-interference.

[0005] Although the existing technologies meet the requirements of high-precision angle measurement to a certain extent, there are still some problems. The anti-interference ability is poor, and factors such as environmental vibration and temperature change are likely to cause the optical path to shift, affecting the measurement accuracy; the dynamic measurement is limited. At high speeds of rotation, the sampling rate of the photodetector is insufficient, resulting in dynamic errors; the signal calculation is complex, and it relies on high-density grating lines or multi-reading head redundancy design, with high costs.

[0006] In the existing circular grating angle measurement system based on Moiré fringes, first, the light source emits a parallel light beam and irradiates the rotating circular grating. Then, the Moiré fringe generated by the grating lines is received by the photodetector. Finally, the rotation angle is calculated by demodulating the change in the optical intensity of the Moiré fringe. However, this method requires high accuracy in the alignment of the optical path and has poor anti-vibration ability. At high speeds of rotation, the Moiré fringe signal is prone to distortion, and the dynamic measurement accuracy is low.

[0007] In the existing circular grating angle measurement system based on optoelectronic encoders, first, the light source emits a light beam and irradiates the rotating circular grating. Then, the photodetector receives the transmitted or reflected optical intensity signal. Finally, the rotation angle is calculated by resolving the phase change of the optical intensity signal. However, this method requires high stability of the light source and high accuracy in the alignment of the optical path. At high speeds of rotation, the signal sampling rate is insufficient, and the dynamic error is significant.

[0008] Although the prior art has achieved high precision in static angle measurement, there are still significant deficiencies in dynamic measurement and anti-interference ability. Summary of the Invention

[0009] The technical solution of the present invention to solve the above technical problems is to provide a high-precision dynamic angle measurement method for circular gratings based on correlated imaging, including the following steps:

[0010] The light source emits correlated light beams, and after beam splitting, the light is divided into a reference light and an object light;

[0011] Calculate the second-order correlation function for N pulse sampling data, and the formula is:

[0012]

[0013] Where: is the light intensity distribution recorded by the spatially resolved detector in the reference optical path during the i-th sampling; is the total light intensity recorded by the bucket detector in the object optical path during the i-th sampling; N is the number of samplings; θ is the rotation angle of the circular grating;

[0014] Modulate the light intensity distribution of the object optical path by rotating the circular grating, so that varies with the angle;

[0015] Calculate the light intensity distribution of the reference optical path and the light intensity of the object optical path The second-order correlation function between them is calculated, and the non-local correlation between the light intensity distribution and the angle is extracted;

[0016] Establish a mapping database of grating angle - correlation peak;

[0017] Output the angle value in real time through peak matching.

[0018] Further, the steps of establishing the mapping database of grating angle - correlation peak and outputting the angle value in real time through peak matching include:

[0019] Rotate the circular grating to a known angle θ k (k = 1, 2,..., M), and record the corresponding light intensity distribution I of the reference optical path ref (x, y) and the total light intensity I of the object optical path obj (θ k );

[0020] For each angle θ k , repeat sampling N times, and calculate the second-order correlation function G (2) (x, y, θ k );

[0021] For each G (2) (x, y, θk ), extract its peak position (x k , y k ) through the peak detection algorithm. The peak position (x k , y k ) and the angle θ k are related as follows:

[0022] Database = {(θ 1 , x 1 , y 1 ), (θ 2 , x 2 , y 2 ),..., (θ M , x M , y M )};

[0023] Store the angle θ k and the corresponding peak position (x k , y k ) as a mapping database;

[0024] Extract the peak position (x real , y real ) of the real-time correlation function, search in the mapping database for the peak position (x real , y real ) closest to (x k , y k ); according to the matching result, output the corresponding angle value θ k .

[0025] Further, the high-precision dynamic angle measurement method for circular gratings based on correlation imaging further includes the following steps:

[0026] According to the state estimation at the previous moment and the state transition matrix F k , predict the state at the current moment and the error covariance

[0027] Obtain the actual measurement value z k ;

[0028] Calculate the measurement residual: Among them, for angle measurement, the observation matrix can be expressed as: H k = [1 0];

[0029] Use the Kalman gain K k to correct the predicted state to obtain the optimal state estimation

[0030] Furthermore, the high-precision dynamic angle measurement method for circular gratings based on correlated imaging further includes the following steps:

[0031] According to the peak offset (Δx k , Δy k ) and the current angle Δθ k , calculate the estimated eccentricity error. The calculation formula is:

[0032] Adjust the rotation center position of the grating according to the calculated eccentricity error (Δx, Δy).

[0033] Furthermore, the adjustment method for adjusting the rotation center position of the grating according to the calculated eccentricity error (Δx, Δy) includes:

[0034] By finely adjusting the grating installation position, reduce the eccentricity error; or

[0035] Introduce an eccentricity error compensation algorithm in the signal processing unit to correct the result of angle calculation.

[0036] To solve the above technical problems, the present invention also proposes a circular grating rotation angle measurement system based on correlated imaging for performing the high-precision dynamic angle measurement method for circular gratings based on correlated imaging as described above, including:

[0037] Light source module: A pulsed quantum correlated light source emits a beam with spatio-temporal correlation characteristics;

[0038] Beam splitting unit: Splits the light source into a reference optical path and an object optical path;

[0039] Rotating circular grating: The object optical path irradiates a rotating disk engraved with a radial grating, and the grating period matches the correlated imaging sampling frequency;

[0040] Bucket detector: Placed behind the grating transmission / reflection optical path, only collects the total light intensity signal;

[0041] Spatial resolution detector: A high-speed CMOS camera is set in the reference optical path to record the spatial distribution of the light field;

[0042] Signal processing unit: Real-time calculates the correlation function of the reference light and the bucket detector signal, and inversely calculates the instantaneous rotation angle of the grating.

[0043] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0044] (1) The combination of correlated imaging and circular grating angle measurement: For the first time, the non-local correlation characteristics of correlated imaging are applied to dynamic angle measurement. The correlated imaging technology is combined with the circular grating angle measurement system, and the correlation function is used to extract angle information, solving the deficiencies of traditional grating angle measurement systems in dynamic measurement and anti-interference.

[0045] (2) Dynamic error suppression and super-resolution measurement: By leveraging the noise suppression characteristics of correlated imaging and compressive sensing algorithms, high-precision dynamic angle measurement is achieved. Under high-speed rotation conditions, sub-pixel level angle resolution is realized, significantly improving the dynamic measurement accuracy.

[0046] (3) Application of Kalman filter: The Kalman filter is used to predict and correct the dynamic angle sequence, suppressing noise and dynamic errors. Combining Kalman filtering with correlated imaging enables real-time high-precision angle tracking.

[0047] (4) Adaptive calibration: The eccentricity error of the grating is adjusted in real-time through the peak shift of the correlation function, eliminating the need for mechanical calibration structures. Reducing the system's dependence on mechanical precision improves the system's reliability and adaptability. Description of the Drawings

[0048] To more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0049] Figure 1 It is a flowchart of the steps of the high-precision dynamic angle measurement method for circular gratings based on correlated imaging according to the present invention;

[0050] Figure 2 It is a structural block diagram of the high-precision dynamic angle measurement method for circular gratings based on correlated imaging according to the present invention.

[0051] Figure 3 It is a schematic structural diagram of the high-precision dynamic angle measurement system for circular gratings based on correlated imaging according to the present invention.

[0052] Explanation of the reference numerals in the drawings:

[0053] Label Name Label Name 1 Light source module 4 Barrel detector 2 Spectral splitting unit 5 Spatially-resolved detector 3 Rotating circular grating 6 Signal processing unit Detailed Embodiments

[0054] The present invention proposes a high-precision dynamic angle measurement method and system for circular gratings based on correlated imaging, aiming to propose a new high-precision dynamic angle measurement scheme by combining correlated imaging technology and Kalman filtering, effectively solving the limitations of the prior art.

[0055] The following will illustrate the high-precision dynamic angle measurement method for circular gratings based on correlated imaging proposed by the present invention in specific embodiments:

[0056] In the technical solution of this embodiment, as Figure 1 、 Figure 2As shown in the figure, a high-precision dynamic angle measurement method for circular gratings based on correlated imaging includes the following steps:

[0057] Step 1: The light source emits correlated light beams, which are collected and split into a reference light beam and an object light beam; (The spatio-temporal distribution of the reference light beam is recorded by a CMOS camera; the total light intensity of the object light beam after passing through the rotating circular grating is collected by a bucket detector.)

[0058] Step 2: Calculate the second-order correlation function for the N - pulse sampling data. The formula is:

[0059]

[0060] Where: is the light intensity distribution recorded by the spatially resolved detector (such as a CMOS camera) in the reference optical path at the i - th sampling; is the total light intensity recorded by the bucket detector in the object optical path at the i - th sampling; N is the number of samplings; θ is the rotation angle of the circular grating;

[0061] Step 3: Modulate the light intensity distribution of the object optical path by the rotation of the circular grating so that varies with the angle;

[0062] Step 4: Calculate the second - order correlation function between the light intensity distribution of the reference optical path and the light intensity of the object optical path, and extract the non - local correlation between the light intensity distribution and the angle;

[0063] Step 5: Establish a mapping database of grating angle - correlation peak, and output the angle value in real - time through peak matching.

[0064] Specifically, after the step of calculating the second - order correlation function between the light intensity distribution of the reference optical path and the light intensity of the object optical path and extracting the non - local correlation between the light intensity distribution and the angle, a compressive sensing algorithm is adopted to improve the measurement speed. The specific steps are as follows:

[0065] (1) Signal sparse representation:

[0066] Represent the grating signal x as a sparse signal in the Fourier domain or wavelet domain. For example, the grating signal usually has only a few non - zero frequency components in the Fourier domain.

[0067] (2) Random sampling:

[0068] In the object optical path, the bucket detector randomly samples the light intensity signal y at a frequency lower than the Nyquist sampling rate.

[0069] The sampling process can be expressed as: y = Φx;

[0070] where Φ is a random measurement matrix.

[0071] (3) Sparse reconstruction:

[0072] Solve the following optimization problem through the compressive sensing algorithm to reconstruct the original signal x:

[0073] min||x|| 1 subject to y = Φx;

[0074] The reconstructed signal x contains high-resolution angle information.

[0075] (4) Angle calculation:

[0076] Convert the reconstructed signal x into angle information, and combine with the Kalman filter for dynamic tracking and correction.

[0077] The compressive sensing algorithm can reduce the sampling rate: Under high-speed rotation conditions, traditional methods require a high sampling rate to capture the dynamic changes of the grating, while compressive sensing can achieve high-precision measurement at a low sampling rate. Sparse signal reconstruction: Represent the grating signal as a sparse signal in a specific transform domain (such as the Fourier domain or the wavelet domain), and reconstruct high-resolution angle information through the compressive sensing algorithm.

[0078] Furthermore, the step of establishing the mapping database of the grating angle-correlation peak and real-time outputting the angle value through peak matching includes:

[0079] Rotate the circular grating to a known angle θ k (k = 1, 2,..., M), and record the corresponding reference optical path light intensity distribution I ref (x, y) and the total light intensity I of the object optical path obj (θ k );

[0080] For each angle θ k , repeat sampling N times, and calculate the second-order correlation function G (2) (x, y, θ k );

[0081] For each G (2) (x, y, θ k ), extract its peak position (x k , y k ) through the peak detection algorithm. The relationship between the peak position (x k , y k ) and the angle θ k is:

[0082] Database = {(θ 1 , x 1 , y 1),(θ 2 ,x 2 ,y 2 ),...,(θ M ,x M ,y M )};

[0083] Store the angle θ k and the corresponding peak position (x k , y k ) in a mapping database;

[0084] Extract the peak position (x real , y real ) of the real-time correlation function, and search in the mapping database for the peak position (x real , y real ) closest to (x k , y k ); According to the matching result, output the corresponding angle value θ k ;

[0085] Specifically, if the peak position is between two known angles, the accuracy can be further improved through an interpolation algorithm (such as linear interpolation).

[0086] Furthermore, the high-precision dynamic angle measurement method for circular gratings based on correlation imaging further includes the following steps:

[0087] According to the state estimate at the previous moment and the state transition matrix F k , predict the state at the current moment and the error covariance

[0088] Obtain the actual measurement value (i.e., the angle solved by correlation imaging) z k .

[0089] Calculate the measurement residual (i.e., the difference between the actual measurement value and the predicted value):

[0090] Among them, for angle measurement, the observation matrix can be expressed as: H k = [1 0].

[0091] Use the Kalman gain K k to correct the predicted state and obtain the optimal state estimate

[0092] Specifically, introduce a Kalman filter to predict and correct the dynamic angle sequence to improve the tracking accuracy under high-speed rotation;

[0093] The state variables of the Kalman filter include the angle θ kand angular velocity ω k , the purpose of which is to estimate the rotation angle of the circular grating in real time.

[0094] 1) Prediction stage

[0095] Based on the state estimate at the previous moment and the state transition matrix F k , predict the state at the current moment and the error covariance For a circular grating with uniform rotation, the state transition matrix can be expressed as: where Δt is the sampling time interval.

[0096] For example, if the angle at the previous moment is θ k-1 , and the angular velocity is ω k-1 , then the predicted angle at the current moment is:

[0097] 2) Correction stage

[0098] Obtain the actual measurement value (i.e., the angle obtained by correlated imaging resolution) z k .

[0099] Calculate the measurement residual (i.e., the difference between the actual measurement value and the predicted value):

[0100] where, for angle measurement, the observation matrix can be expressed as: H k = [1 0].

[0101] Use the Kalman gain K k to correct the predicted state and obtain the optimal state estimate

[0102] For example, if the measurement residual is y k , then the corrected angle is:

[0103] Furthermore, the high-precision dynamic angle measurement method for a circular grating based on correlated imaging further includes the following steps:

[0104] According to the peak offset (Δx k , Δy k ) and the current angle Δθ k , calculate the estimated eccentricity error, and the calculation formula is:

[0105] Adjust the rotation center position of the grating according to the calculated eccentricity error (Δx, Δy).

[0106] Furthermore, the adjustment method for adjusting the rotation center position of the grating according to the calculated eccentricity error (Δx, Δy) includes:

[0107] By fine-tuning the installation position of the grating, the eccentricity error is reduced; or

[0108] An eccentricity error compensation algorithm is introduced into the signal processing unit to correct the result of angle calculation.

[0109] The present invention also proposes a circular grating rotation angle measurement system based on correlated imaging, as Figure 3 shown, including:

[0110] Light source module: A pulsed quantum correlated light source (such as a pseudo-thermal light source) emits a beam with spatio-temporal correlation characteristics;

[0111] Beam splitting unit: Splits the light source into a reference optical path and an object optical path;

[0112] Rotating circular grating: The object optical path irradiates a rotating disk engraved with a radial grating, and the grating period matches the correlated imaging sampling frequency;

[0113] Bucket detector: Placed behind the grating transmission / reflection optical path, only collects the total light intensity signal;

[0114] Spatially resolved detector: A high-speed CMOS camera is set in the reference optical path to record the spatial distribution of the light field;

[0115] Signal processing unit: Calculates the correlation function of the reference light and the bucket detector signal in real time, and inversely calculates the instantaneous rotation angle of the grating.

[0116] As mentioned above, the above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A circular grating high-precision dynamic angle measurement method based on correlation imaging, characterized in that: The following steps are involved: The light source emits a correlation light beam, which is collected and divided into reference light and object light after beam splitting; The second-order correlation function is calculated for N pulse sampling data, and the formula is: in: is the light intensity distribution recorded by the spatially resolved detector in the reference light path at the i-th sampling; is the total light intensity recorded by the bucket detector in the object light path at the i-th sampling; N is the number of samplings; θ is the rotation angle of the circular grating; The light intensity distribution of the object light path is modulated by rotating the circular grating, so that Varies with angle; Calculate the light intensity distribution of the reference light path Light intensity along the light path of the object The second-order correlation function between the intensity distribution and the angle is extracted; Establishing a grating angle-correlation peak mapping database; Output angle value in real time through peak matching.

2. The circular grating high-precision dynamic angle measurement method based on correlation imaging according to claim 1 is characterized in that: The step of establishing a mapping database of grating angles and associated peak values ​​and outputting angle values ​​in real time through peak matching comprises: Rotate the circular grating to a known angle θ k (k=1,2,...,M), record the corresponding reference light path intensity distribution I ref (x, y) and the total light intensity I of the object light path obj (θ k ); For each angle θ k , repeat sampling N times, calculate the second-order correlation function G (2) (x,y,θ k ); For each G (2) (x,y,θ k ), and extract its peak position (x k ,y k ), peak position (x k ,y k ) and angle θ k The relationship between them is: Database={(θ1,x1,y1),(θ2,x2,y2),...,(θ M ,x M ,y M )}; The angle θ k The corresponding peak position (x k ,y k ) is stored as a mapping database; Extract the peak position of the real-time correlation function (x real ,y real ), search the mapping database for (x real ,y real ) is the closest peak position (x k ,y k );According to the matching result, output the corresponding angle value θ k .

3. The circular grating high-precision dynamic angle measurement method based on correlation imaging according to claim 1 is characterized in that: The following steps are also included: According to the state estimation at the last moment And the state transfer matrix F k , predict the current state and error covariance Get the actual measured value z k ; Calculate the measurement residuals: Among them, for angle measurement, the observation matrix can be expressed as: H k =[10]; Using the Kalman gain K k Correct the predicted state to obtain the optimal state estimate 4. The circular grating high-precision dynamic angle measurement method based on correlation imaging according to claim 3 is characterized in that: The following steps are also included: According to the peak shift (Δx k ,Δy k ) and the current angle Δθ k , calculate the estimated eccentricity error, the calculation formula is: Adjust the rotation center position of the grating according to the calculated eccentricity error (Δx, Δy).

5. The circular grating high-precision dynamic angle measurement method based on correlation imaging according to claim 4 is characterized in that: The method for adjusting the rotation center position of the grating according to the calculated eccentricity error (Δx, Δy) comprises: Reduce the eccentricity error by fine-tuning the grating installation position; or An eccentricity error compensation algorithm is introduced into the signal processing unit to correct the result of angle solution.

6. A circular grating rotation angle measurement system based on correlation imaging, used to perform the circular grating high-precision dynamic angle measurement method based on correlation imaging as claimed in any one of claims 1 to 5, characterized in that: include: Light source module: The pulsed quantum correlation light source emits a light beam with space-time correlation characteristics; Splitting unit: used to divide the light source into a reference light path and an object light path; Rotating circular grating: The object light path illuminates a rotating disk engraved with a radial grating, and the grating period matches the associated imaging sampling frequency; Bucket detector: placed after the grating transmission / reflection light path, only collects the total light intensity signal; Spatially resolved detector: A high-speed CMOS camera is set in the reference light path to record the spatial distribution of the light field; Signal processing unit: used to calculate the correlation function between the reference light and the bucket detector signal in real time and invert the instantaneous rotation angle of the grating.

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