A high-precision dynamic angle measurement method and system for circular grating based on correlation imaging

Abstract

The present invention discloses a high-precision dynamic angle measurement method and system using a circular grating based on correlation imaging. The method comprises the following steps: a light source emits a correlated light beam, which is collected and split into reference light and object light after beam splitting; a second-order correlation function is calculated for N pulse sampling data; the light intensity distribution of the object light path is modulated by rotating the circular grating so that #imgabs0# varies with angle; a second-order correlation function is calculated between the light intensity distribution #imgabs1# of the reference light path and the light intensity #imgabs2# of the object light path, extracting the non-local correlation between the light intensity distribution and angle; a mapping database of grating angle-correlation peaks is established; and angle values are output in real time through peak matching. The present invention's technical solution is the first to apply the non-local correlation characteristics of correlation imaging to dynamic angle measurement. It combines correlation imaging technology with a circular grating angle measurement system, extracting angle information using correlation functions, and addressing the shortcomings of traditional grating angle measurement systems in terms of dynamic measurement and interference resistance.

Description

Technical Field

[0001] The present invention relates to the field of optical measurement technology, and in particular to a circular grating high-precision dynamic angle measurement method and system based on correlation imaging. Background Art

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

[0003] Existing circular grating angle measurement technologies mainly include moiré-based angle measurement technology that calculates angles through the changes in the light intensity of the moiré fringes generated by the grating lines, multi-reader redundancy technology that uses multiple read heads to improve measurement accuracy and reliability, and photoelectric encoder technology that combines grating lines with photoelectric detectors to achieve high-resolution angle measurement.

[0004] The Chinese patent publication number is "CN102353347A", and the name is "A High-Precision Circular Grating Angle Measurement System". It discloses a circular grating angle measurement method based on Moiré fringes. It adopts a multi-reader redundant 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] While existing technologies have met the need for high-precision angle measurement to a certain extent, some challenges remain. They suffer from poor anti-interference capabilities, and factors like environmental vibration and temperature fluctuations can easily cause optical path deviations, impacting measurement accuracy. Dynamic measurement is limited, and at high speeds, the photodetector's sampling rate is insufficient, leading to dynamic errors. Signal processing is complex, requiring high-density grating lines or redundant multiple readhead designs, which are costly.

[0006] Existing circular grating angle measurement systems based on moiré fringes first emit a parallel beam of light to illuminate a rotating circular grating. The moiré fringes generated by the grating lines are then detected by a photodetector. Finally, the rotation angle is calculated by demodulating the intensity variations of the moiré fringes. However, this method requires high optical path alignment accuracy and has poor vibration resistance. At high rotation speeds, the moiré fringe signal is easily distorted, resulting in low dynamic measurement accuracy.

[0007] Existing circular grating angle measurement systems based on photoelectric encoders first emit a light beam onto a rotating circular grating. A photodetector then receives the transmitted or reflected light intensity signal. Finally, the rotation angle is calculated by calculating the phase change of the intensity signal. However, this method places high demands on light source stability and optical path alignment accuracy. At high rotation speeds, the signal sampling rate is insufficient, resulting in significant dynamic errors.

[0008] Although existing technologies have achieved high accuracy in static angle measurement, they still have significant deficiencies in dynamic measurement and anti-interference capabilities. Summary of the Invention

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

[0010] The light source emits a correlated light beam, which is collected and split into reference light and object light after beam splitting;

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

[0012]

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

[0014] The light intensity distribution of the object light path is modulated by rotating the circular grating, so that Changes with angle;

[0015] 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 two is used to extract the non-local correlation between the light intensity distribution and the angle;

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

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

[0018] Furthermore, the step of establishing a mapping database of grating angles and associated peak values and outputting angle values in real time through peak matching includes:

[0019] 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 );

[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 ), and extract its peak position (x k ,y k ), peak position (x k ,y k ) and angle θ k The relationship between them is:

[0022] Database={(θ1,x1,y1),(θ2,x2,y2),...,(θ M ,x M ,y M )};

[0023] The angle θ k The corresponding peak position (x k ,y k ) is stored as a mapping database;

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

[0025] Furthermore, the circular grating high-precision dynamic angle measurement method based on correlation imaging also includes the following steps:

[0026] Estimated based on the state at the previous moment and the state transition matrix F k , predict the current state and error covariance

[0027] Get the actual measurement value z k ;

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

[10] ;

[0029] Using the Kalman gain K k Correct the predicted state to obtain the optimal state estimate

[0030] Furthermore, the circular grating high-precision dynamic angle measurement method based on correlation imaging also includes the following steps:

[0031] According to the peak shift (Δx k ,Δyk ) 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 method for adjusting the rotation center position of the grating according to the calculated eccentricity error (Δx, Δy) includes:

[0034] By fine-tuning the grating installation position, reduce the eccentricity error; or

[0035] An eccentricity error compensation algorithm is introduced into the signal processing unit to correct the angle solution result.

[0036] To solve the above technical problems, the present invention further proposes a circular grating rotation angle measurement system based on correlation imaging, which is used to implement the above-mentioned circular grating high-precision dynamic angle measurement method based on correlation imaging, comprising:

[0037] Light source module: The pulsed quantum correlation light source emits a beam with space-time correlation characteristics;

[0038] Splitting unit: divides the light source into reference light path and object light path;

[0039] 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;

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

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

[0042] Signal processing unit: calculates the correlation function between the reference light and the bucket detector signal in real time, and inverts 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) Combination of correlation imaging and circular grating angle measurement: For the first time, the non-local correlation characteristics of correlation imaging are applied to dynamic angle measurement. The correlation imaging technology is combined with the circular grating angle measurement system, and the angle information is extracted using the correlation function, which solves the shortcomings of the traditional grating angle measurement system in dynamic measurement and anti-interference.

[0045] (2) Dynamic error suppression and super-resolution measurement: High-precision dynamic angle measurement is achieved through the noise suppression characteristics of correlation imaging and compressed sensing algorithms. Under high-speed rotation conditions, sub-pixel angle resolution is achieved, significantly improving dynamic measurement accuracy.

[0046] (3) Application of Kalman filter: Kalman filter is used to predict and correct dynamic angle sequences, suppressing noise and dynamic errors. Kalman filter is combined with correlation imaging to achieve real-time high-precision angle tracking.

[0047] (4) Adaptive calibration: The grating eccentricity error is adjusted through real-time feedback of the correlation function peak offset, without the need for a mechanical calibration structure. This reduces the system's dependence on mechanical accuracy and improves the system's reliability and adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0049] Figure 1 This is a flowchart of the steps of the circular grating high-precision dynamic angle measurement method based on correlation imaging according to the present invention;

[0050] Figure 2 This is a structural block diagram of the circular grating high-precision dynamic angle measurement method based on correlated imaging described in the present invention.

[0051] Figure 3 This is a schematic structural diagram of the circular grating high-precision dynamic angle measurement system based on correlated imaging described in the present invention.

[0052] Description of Figure Numbers:

[0053] Label name Label name 1 Light source module 4 Bucket detector 2 Spectroscopic unit 5 Spatially resolved detectors 3 Rotating ring grating 6 Signal processing unit DETAILED DESCRIPTION

[0054] The present invention proposes a high-precision dynamic angle measurement method and system for circular grating based on correlation imaging. By combining correlation imaging technology and Kalman filtering, a new high-precision dynamic angle measurement solution is proposed, which effectively solves the limitations of existing technologies.

[0055] The following is an explanation of the circular grating high-precision dynamic angle measurement method based on correlation imaging proposed by the present invention in a specific embodiment:

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

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

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

[0059]

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

[0061] Step 3: Rotate the circular grating to modulate the light intensity distribution of the object light path so that Changes with angle;

[0062] Step 4: 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 two is used to extract the non-local correlation between the light intensity distribution and the angle;

[0063] Step 5: Establish a mapping database of grating angles and associated peaks, and output angle values in real time through peak matching.

[0064] Specifically, when calculating the light intensity distribution of the reference light path Light intensity along the light path of the object After extracting the second-order correlation function between the light intensity distribution and the angle, the compressed sensing algorithm is used to improve the measurement speed. The specific steps are as follows:

[0065] (1) Signal sparse representation:

[0066] The grating signal x is represented as a sparse signal in the Fourier domain or the 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 light 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 the random measurement matrix.

[0071] (3) Sparse reconstruction:

[0072] The compressed sensing algorithm is used to solve the following optimization problem and reconstruct the original signal x:

[0073] min||x||1subject to y=Φx;

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

[0075] (4) Angle calculation:

[0076] The reconstructed signal x is converted into angle information and combined with the Kalman filter for dynamic tracking and correction.

[0077] Compressed sensing algorithms can reduce sampling rates: Under high-speed rotation conditions, traditional methods require high sampling rates to capture the dynamic changes of the grating, while compressed sensing can achieve high-precision measurements at low sampling rates. Sparse signal reconstruction: The grating signal is represented as a sparse signal in a specific transform domain (such as the Fourier domain or wavelet domain), and high-resolution angular information is reconstructed using compressed sensing algorithms.

[0078] Furthermore, the step of establishing a mapping database of grating angles and associated peak values and outputting angle values in real time through peak matching includes:

[0079] 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 );

[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 ), and extract its peak position (x k ,y k ), peak position (x k ,y k ) and angle θ k The relationship between them is:

[0082] Database={(θ1,x1,y1),(θ2,x2,y2),...,(θ M ,x M ,yM )};

[0083] The angle θ k The corresponding peak position (x k ,y k ) is stored as a mapping database;

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

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

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

[0087] Estimated based on the state at the previous moment and the state transition matrix F k , predict the current state and error covariance

[0088] Get the actual measurement value (i.e. the angle of the associated imaging solution) z k .

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

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

[0091] Using the Kalman gain K k Correct the predicted state to obtain the optimal state estimate

[0092] Specifically, a Kalman filter is introduced 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 k and angular velocity ω k , whose purpose is to estimate the rotation angle of the circular grating in real time.

[0094] 1) Prediction stage

[0095] Estimated based on the state at the previous moment and the state transition matrix F k , predict the current state and error covariance For a circular grating rotating at a constant speed, the state transfer 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 , the angular velocity is ω k-1 , then the predicted angle at the current moment is:

[0097] 2) Correction stage

[0098] Get the actual measurement value (i.e. the angle of the associated imaging solution) z k .

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

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

[0101] Using the Kalman gain K k Correct the predicted state to obtain the optimal state estimate

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

[0103] Furthermore, the circular grating high-precision dynamic angle measurement method based on correlation imaging also includes the following steps:

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

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

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

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

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

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

[0110] Light source module: A pulsed quantum correlation light source (such as a pseudothermal light source) emits a beam with space-time correlation characteristics;

[0111] Splitting unit: divides the light source into reference light path and object light path;

[0112] 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;

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

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

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

[0116] 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 changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A high-precision dynamic angle measurement method of circular grating based on correlation imaging, characterized in that: The following steps are involved: The light source emits a correlated light beam, which is collected and split 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 time; is the total light intensity recorded by the bucket detector in the object light path at the i-th sampling time; N is the number of sampling times; 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 Changes 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 two is used to extract the non-local correlation between the light intensity distribution and the angle; Establishing a mapping database of grating angle-correlation peak; Output angle values 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 the real ,y real ) is closest to the peak position (x k ,y k ); According to the matching results, 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: The Kalman filter is introduced to predict and correct the dynamic angle sequence to improve the tracking accuracy under high-speed rotation; The state variables of the Kalman filter include the angle θ k and angular velocity ω k ; Prediction stage: estimate based on the state of the previous moment and the state transition matrix F k , predict the current state and error covariance For a circular grating rotating at a constant speed, the state transfer matrix can be expressed as: Where Δt is the sampling time interval; If the angle at the previous moment is θ k-1 , the angular velocity is ω k-1 , then the predicted angle at the current moment is: Calibration phase: Get the actual measured value z k ; Calculate the measurement residuals: For angle measurement, the observation matrix can be expressed as: H k =[1 0]; 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 θ 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) includes: By fine-tuning the grating installation position, reduce the eccentricity error; or An eccentricity error compensation algorithm is introduced into the signal processing unit to correct the angle solution result.

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 according to any one of claims 1 to 5, characterized in that: include: Light source module: The pulsed quantum correlation light source emits a beam with space-time correlation characteristics; Splitting unit: used to divide the light source into reference light path and 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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