A method for localizing a biased spot based on a laser triangulation system

Abstract

This invention discloses a method for skewed spot localization based on a laser triangulation system. The method comprises: 1. Setting reference points within the working distance of the ranging system, acquiring spot waveforms at each reference point, and performing mean fusion processing to construct a standard template set; 2. Performing dual filtering processing combining temporal and spatial domains on the spot waveforms acquired during the measurement process; 3. Performing coarse localization on the spot waveforms processed in step 2, and matching the nearest standard template from the standard template set; 4. Performing cross-correlation calculations on the filtered spot waveforms and the standard template waveforms to obtain a correlation coefficient sequence; 5. Performing cubic spline interpolation on the correlation coefficient sequence obtained in step 4, and finding the coordinates corresponding to the maximum value of the interpolation result as the relative pixel displacement between the two waveforms; 6. Using the coordinates of the reference points, converting the relative pixel displacement into the absolute pixel position, i.e., the spot localization result. This invention has the advantages of low error, high measurement repeatability, and ease of embedding into a system.

Description

Technical Field

[0001] This invention relates to the field of laser triangulation technology, and in particular to a method for locating skewed light spots based on a laser triangulation system. Background Technology

[0002] Laser triangulation systems offer advantages such as simple principle, fast response speed, and non-contact measurement, making them widely used in military, aerospace, intelligent manufacturing, and the Internet of Things (IoT) fields. A laser triangulation system primarily consists of a laser triangulation optical path, a signal acquisition circuit, and a microcontroller chip. Its working principle involves a laser source projecting a laser beam onto the target object. This beam forms a point spot on the object's surface and is reflected. The reflected beam is then converged by a receiving lens group and finally imaged onto an image detection device. The waveform of the point spot is transmitted to the microcontroller chip via the data acquisition circuit for positioning processing. Based on the triangulation relationship formed by the geometric optical path, the final displacement of the target object is obtained.

[0003] In practical applications, the accuracy of laser triangulation systems is affected by factors such as optical path structure, measurement environment, object surface characteristics, and positioning algorithms. Among these, the spot positioning algorithm, as the final step in obtaining displacement results from the sensor, is crucial for improving accuracy and has profound research significance and broad potential for improvement.

[0004] A laser source forms a point spot on the surface of the object being measured, and its energy follows a Gaussian normal distribution. Due to modulation by the asymmetric optical path in the ranging system, the point spot inevitably exhibits a skewed phenomenon. Currently, the more mature spot center localization algorithms mainly fall into two categories based on their implementation: the gray-scale centroid method and function fitting. However, current traditional localization methods are based on the assumption that the spot energy follows a Gaussian distribution, ignoring the impact of the spot skewed characteristics on the localization error, and thus cannot meet the requirements for high accuracy.

[0005] Therefore, those skilled in the art are dedicated to developing a method for locating biased light spots based on a laser triangulation system to solve the above problems. Summary of the Invention

[0006] In view of the above-mentioned deficiencies of the prior art, the technical problem to be solved by the present invention is how to correct the error caused by the spot skewness characteristics in positioning.

[0007] To achieve the above objectives, this invention provides a method for locating a biased spot based on a laser triangulation system, characterized by the following steps:

[0008] Step 1: Set up reference points within the working distance of the ranging system, collect the light spot waveforms of each reference point and perform mean fusion processing to construct a standard template set;

[0009] Step 2: Perform dual filtering processing on the light spot waveform acquired during the measurement process, combining time and spatial domains;

[0010] Step 3: Perform coarse positioning on the light spot waveform after processing in Step 2, and match the nearest standard template in the set of standard templates;

[0011] Step 4: Perform cross-correlation calculation on the filtered spot waveform and the standard template waveform to obtain a correlation coefficient sequence;

[0012] Step 5: Perform cubic spline interpolation on the correlation coefficient sequence obtained in Step 4, and find the coordinates corresponding to the maximum value of the interpolation result, which will be used as the relative pixel displacement between the two waveforms;

[0013] Step 6: Use the coordinates of the reference point to convert the relative pixel displacement into the absolute pixel position, i.e., the spot positioning result.

[0014] Furthermore, the specific steps for constructing the standard template set in step 1 are as follows:

[0015] Step 1.1: Set n reference points at equal intervals within the sensor's measurement range;

[0016] Step 1.2: Using the Lambertian standard plate as the target object, continuously acquire multiple image point waveforms at each of the aforementioned reference points;

[0017] Step 1.3: Average and fuse multiple light spot waveforms of a single reference point to obtain a standard light spot waveform, i.e., the standard template;

[0018] Step 1.4: Record the photosensitive element position q where the peak of the standard spot waveform is located, and use its coordinates as the template number q. i , (i = 1, 2, ..., n);

[0019] Step 1.5: Repeat steps 1.3 and 1.4 for each of the reference points across the full range to form the standard template set;

[0020] Step 1.6: Store the positions of each reference point, the standard spot template and its corresponding number in the processor memory, in the format of number + spot waveform + reference point position.

[0021] Furthermore, the sensor is a one-dimensional laser triangulation displacement sensor with a range of 10 mm and a linear array image detector with a size of 974 pixels.

[0022] Furthermore, the specific steps of the waveform filtering process in step 2 are as follows:

[0023] Step 2.1: Set a time sliding window. After storing nine waveforms in the window, perform an averaging operation to complete the time-domain filtering operation.

[0024] Step 2.2: Perform bilateral filtering on the waveform of the time domain filtering, calculate the spatial domain weight based on the distance between the neighboring pixels and the center pixel, and calculate the value domain weight based on the difference between the gray value of the neighboring pixels and the gray value of the center pixel.

[0025] Step 2.3: Use the waveform obtained after the above steps as the effective spot waveform f(x) i The waveform length is m, and i = 1, 2, ..., m.

[0026] Further, in step 2.2, the expression for the bilateral filtering process is:

[0027]

[0028] Among them, Ω i This represents a sliding window region of size 2n+1 centered at pixel i; i, j∈Ω i w d (i,j) represents the geometric proximity between neighboring pixel j and the center pixel i, w r (h(i),h(j)) represents the gray-level similarity between neighboring pixel j and center pixel i;

[0029] Proximity function w d (i,j) can be represented as:

[0030]

[0031] Similarity function w r (h(i),h(j)) can be represented as:

[0032]

[0033] Furthermore, the size of the sliding window area is 5.

[0034] Furthermore, the specific steps for standard template matching in step 3 are as follows:

[0035] Step 3.1: Based on the effective spot waveform f(x) i The peak value of the image spot is used for coarse localization to preliminarily determine the pixel coordinate position p where the center of the image spot is located;

[0036] Step 3.2: To match the valid waveform with a standard template, iterate through the standard template set in the processor's memory and find the standard template closest to the valid waveform, denoted as g(x). iThe distance is defined as the difference between the pixel coordinates of the peaks of two waveforms, and the relationship they satisfy is:

[0037] pq = min(pq) i ), i∈(1,n).

[0038] Furthermore, the specific steps for cross-correlation calculation of the two waveforms in step 4 are as follows:

[0039] Step 4.1: Calculate the average light intensity grayscale value of each effective waveform. The average light intensity and grayscale value of the matching standard template

[0040] Step 4.2: Calculate using the zero-normalized cross-correlation function, as shown in the following formula:

[0041]

[0042] Cross-correlation is performed on the effective waveform and the matched standard template. The displacement is determined by the similarity constraints of the intensity distribution of the light spot waveforms at similar positions in terms of gray level and position, and the correlation coefficient sequence C(u) is obtained.

[0043] Furthermore, the specific steps for determining the relative pixel displacement in step 5 are as follows:

[0044] Step 5.1: Perform cubic spline interpolation on the obtained correlation coefficient sequence C(u), with an interpolation interval of one-hundredth of a pixel;

[0045] Step 5.2: Traverse and sort the cubic spline interpolation results to determine the sub-pixel position x corresponding to the maximum value of the interpolation result. u ;

[0046] Step 5.3: Process to obtain the effective waveform and the relative pixel displacement Δ of the matching standard template, where Δ = x u -m+1.

[0047] Furthermore, the specific steps for converting relative displacement into absolute position in step 6 are as follows:

[0048] Step 6.1: Add the relative pixel distance Δ to the coordinates of the reference point corresponding to the standard template to obtain the absolute pixel position x of the center of the measured spot waveform across the entire range. s The expression is: x s =Δ+q;

[0049] Step 6.2: Use the calibration function built into the ranging system to convert the absolute pixel position into the actual displacement in the world coordinate system.

[0050] Compared with traditional methods and devices, the present invention improves the repeatability and positioning accuracy of the system while ensuring the basic signal distribution characteristics, and has the following beneficial effects:

[0051] 1. The correlation method is a relative displacement calculation method. Setting a benchmark template provides reference coordinates for converting relative displacement into absolute position.

[0052] 2. The light spot skewness varies in different reference point standard templates. The measured light spot can be cross-correlated with the template with the closest shape to reduce positioning error.

[0053] 3. In the same ranging system, the template at the reference point is easy to obtain during calibration, is not affected by optical path parameters, and does not require mathematical formulas to describe the spot shape. This also makes the template establishment method easy to extend to ranging systems of different specifications.

[0054] This method is no longer limited by the image spot shape constraints caused by the principles and object surface characteristics, significantly improving measurement repeatability. For cross-correlation interpolation, the computational cost is low, making it easy to embed and implement in the system.

[0055] The following will further explain the concept, specific structure, and technical effects of the present invention in conjunction with the accompanying drawings, so as to fully understand the purpose, features, and effects of the present invention. Attached Figure Description

[0056] Figure 1 This is a schematic diagram of the system structure of a preferred embodiment of the present invention;

[0057] Figure 2 This is a schematic diagram of a biased light spot signal according to a preferred embodiment of the present invention;

[0058] Figure 3 This is a schematic flowchart of a preferred embodiment of the positioning method of the present invention;

[0059] Figure 4 This is a schematic diagram of a standard light spot template according to a preferred embodiment of the present invention;

[0060] Figure 5 This is a schematic diagram showing the details of correlation coefficient sequence interpolation in a preferred embodiment of the present invention;

[0061] Figure 6 This is a schematic diagram of the positioning result of a preferred embodiment of the present invention. Detailed Implementation

[0062] The following description, with reference to the accompanying drawings, illustrates several preferred embodiments of the present invention to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0063] In the accompanying drawings, components with the same structure are indicated by the same numerical designation, and components with similar structures or functions are indicated by similar numerical designations. The dimensions and thicknesses of each component shown in the drawings are arbitrary, and the present invention does not limit the dimensions and thicknesses of each component. To make the illustrations clearer, the thickness of some components has been appropriately exaggerated in the drawings.

[0064] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0065] In the description of this invention, it should be noted that the terms "middle", "upper", "lower", "left", "right", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0066] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0067] A method for locating a biased spot based on a laser triangulation system, the principle of which is as follows: Figure 1 As shown, the specific steps include:

[0068] S1: Set up reference points within the working distance of the ranging system, collect the light spot waveforms of each reference point and perform mean fusion processing to construct a set of standard templates;

[0069] S2: Perform dual filtering processing on the light spot waveform acquired during the measurement process, combining time and spatial domains;

[0070] S3: Perform coarse positioning on the light spot waveform after processing in S2, and match the nearest standard template in the standard template set;

[0071] S4: Perform cross-correlation calculation on the filtered measurement waveform and the standard template waveform to obtain the correlation coefficient sequence;

[0072] S5: Perform cubic spline interpolation on the correlation coefficient sequence obtained in S4, and find the coordinates corresponding to the maximum value of the interpolation result as the relative pixel displacement between the two waveforms;

[0073] S6: Use the coordinates of the reference point to convert the relative pixel displacement into the absolute pixel position, i.e., the spot positioning result. The overall process is as follows: Figure 2 As shown.

[0074] In this embodiment, the biased spot positioning method based on the laser triangulation system is used to realize the spot center positioning of the one-dimensional laser triangulation displacement sensor. The positioning result is used to calculate the displacement of the measured object. By establishing a standard spot template and performing cross-correlation calculation on the filtered measurement waveform, the present invention achieves displacement measurement with high repeatability accuracy.

[0075] In this embodiment, the one-dimensional laser triangulation displacement sensor used has a range of 10mm, the linear array image detector has a size of 974 pixels, and the received light spot signal is a one-dimensional waveform signal with a skewed Gaussian distribution, such as... Figure 3 As shown.

[0076] Optionally, a standard template set is constructed according to step S1, including:

[0077] S1.1: Within the sensor's measurement range, n reference points are set at equal intervals, including the zero point;

[0078] S1.2: Using the Lambertian standard plate as the target object, multiple image spot waveforms are continuously acquired at each reference point position;

[0079] S1.3: Average and fuse multiple light spot waveforms at a single reference point to obtain a standard light spot waveform, i.e., a standard template;

[0080] S1.4: Record the location of the peak of the standard spot waveform in the photosensitive element and use its coordinates as the template number;

[0081] S1.5: Repeat the operations of S1.3 and S1.4 for each reference point of the full range to form a standard template set;

[0082] S1.6: Store the positions of each reference point, the standard spot template, and its corresponding number in the processor memory. The format is: number + spot waveform + reference point position.

[0083] In this embodiment, the standard light spot template stored in the displacement sensor is as follows: Figure 4 As shown.

[0084] Optionally, the measurement waveform is processed according to the filtering method in step S2, including:

[0085] S2.1: Whenever the sensor measures the distance to the object being measured, a time sliding window is set for the real-time measurement waveform. After storing nine waveforms in the window, an averaging operation is performed to complete the time-domain filtering operation.

[0086] S2.2: Perform bilateral filtering on the waveform after time-domain filtering. Calculate the spatial domain weight by the distance between neighboring pixels and the center pixel. Calculate the value domain weight by using the difference between the gray value of the neighboring pixels and the gray value of the center pixel.

[0087] In this embodiment, the expression for the bilateral filtering operation is:

[0088]

[0089] Among them, Ω i This represents a sliding window region of size 2n+1 centered at pixel i; i, j∈Ω i w d (i,j) represents the geometric proximity between neighboring pixel j and the center pixel i, w r (h(i),h(j)) represents the gray-level similarity between neighboring pixel j and center pixel i.

[0090] Proximity function w d (i,j) can be represented as:

[0091] Similarity function w r (h(i),h(j)) can be represented as:

[0092] In this embodiment, the sliding window size used in the bilateral filtering process is 5, and the waveform obtained after the above steps is taken as the effective spot waveform f(x). i The waveform length is 974, and i = 1, 2, ..., 974.

[0093] Optionally, according to step S3, a standard template is matched, including:

[0094] Step 3.1: Based on the effective waveform f(x) i The peak value of the image spot is used for coarse localization to preliminarily determine the pixel coordinate position p where the center of the image spot is located;

[0095] Step 3.2: To match the valid waveform with a standard template, iterate through the standard template set in the processor's memory and find the standard template closest to the valid waveform, denoted as g(x). i The distance is defined as the difference between the pixel coordinates of the peaks of two waveforms, and the relationship they satisfy is:

[0096] pq = min(pq) i), i∈(1,n).

[0097] In this embodiment, the coordinates of the center of the image spot of the measured waveform are pixel number 516. The template number closest to 516 in the standard spot template set is traversed, and the template number 532 is selected. This template is used as the cross-correlation template in the positioning algorithm for subsequent calculations.

[0098] Optionally, perform cross-correlation calculation on the two waveforms according to step S4, including:

[0099] Step 4.1: Calculate the average light intensity grayscale value of each effective waveform. The average light intensity and grayscale value of the matching standard template

[0100] Step 4.2: Calculate using the zero-normalized cross-correlation function, as shown in the following formula:

[0101]

[0102] Cross-correlation is performed on the effective waveform and the matching standard template. The displacement is determined by the similarity constraints of the intensity distribution of the light spot waveforms at similar positions in terms of gray level and position, and the correlation coefficient sequence C(u) is obtained.

[0103] Optionally, the relative pixel displacement is determined according to step S5, including:

[0104] Step 5.1: Perform cubic spline interpolation on the obtained correlation coefficient sequence C(u), with an interpolation interval of one-hundredth of a pixel;

[0105] Step 5.2: Traverse and sort the cubic spline interpolation results to determine the sub-pixel position x corresponding to the maximum value of the interpolation result. u ;

[0106] Step 5.3: Process to obtain the effective waveform and the relative pixel displacement Δ of the matching standard template, where Δ = x u -m+1.

[0107] In this embodiment, the details of the correlation coefficient sequence interpolation results are as follows: Figure 5 As shown, the relative pixel displacement of the processed effective waveform and the matching standard template is x. u = -19.5.

[0108] Optionally, the absolute position is converted according to the relative displacement in step S6, including:

[0109] Adding the relative pixel distance Δ to the coordinates of the reference point corresponding to the standard template, we obtain the absolute pixel position of the measured spot waveform center across the entire range, expressed as: x s =Δ+q;

[0110] By utilizing the calibration function built into the laser triangulation displacement sensor, the absolute pixel position is converted into the actual displacement in the world coordinate system, thus obtaining the displacement result of the measured object.

[0111] In this embodiment, a laser triangulation displacement sensor is used to repeatedly measure the displacement of the object under test. To evaluate the repeatability accuracy of the method of the present invention, the measurement data are processed using traditional gray-scale centroid method, Gaussian localization method, Gaussian template cross-correlation method, and the method of the present invention. The results are as follows: Figure 6 As shown in the figure, the results indicate that the method of the present invention not only conforms to the characteristics of the skewed distribution of light spot in principle, but also exhibits high measurement repeatability and stability in the final positioning results, providing a new approach for high-precision positioning technology.

[0112] This invention is not limited to the above-described embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of this invention shall be considered equivalent substitutions, including but not limited to changes in name, changes in part model and size, adjustments to the installation position or angle of the mechanism, overall or partial enlargement or reduction, and adjustments to the relative positions of parts. All of these are included within the scope of protection of this invention.

[0113] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for locating a biased light spot based on a laser triangulation system, characterized in that, Includes the following steps: Step 1: Set up reference points within the working distance of the ranging system, collect the light spot waveforms of each reference point and perform mean fusion processing to construct a standard template set; Step 2: Perform dual filtering processing on the light spot waveform acquired during the measurement process, combining time and spatial domains; Step 3: Perform coarse positioning on the light spot waveform after processing in Step 2, and match the nearest standard template in the set of standard templates; Step 4: Perform cross-correlation calculation on the filtered spot waveform and the standard template waveform to obtain a correlation coefficient sequence; Step 5: Perform cubic spline interpolation on the correlation coefficient sequence obtained in Step 4, and find the coordinates corresponding to the maximum value of the interpolation result, which will be used as the relative pixel displacement between the two waveforms; Step 6: Use the peak position of the matching standard template to convert the relative pixel displacement into the absolute pixel position, i.e., the spot positioning result.

2. The method for locating a biased spot based on a laser triangulation system as described in claim 1, characterized in that, The specific steps for constructing the standard template set in step 1 are as follows: Step 1.1: Set equal intervals within the sensor's measurement range The aforementioned reference points; Step 1.2: Using the Lambertian standard plate as the target object, continuously acquire multiple light spot waveforms at each of the aforementioned reference points; Step 1.3: Average and fuse multiple light spot waveforms of a single reference point to obtain a standard light spot waveform, i.e., the standard template; Step 1.4: Record the location of the peak value of the standard spot waveform at the photosensitive element. Use its coordinates as template number k , k=1,2,…,n ; Step 1.5: Repeat steps 1.3 and 1.4 for each of the reference points across the full range to form the standard template set; Step 1.6: Store the positions of each reference point, the standard template and its corresponding number in the processor memory, in the format of number + standard spot waveform + reference point position.

3. The method for locating a biased spot based on a laser triangulation system as described in claim 2, characterized in that, The sensor is a one-dimensional laser triangulation sensor with a range of 10 mm and a linear array image detector with a size of 974 pixels.

4. The method for locating a biased spot based on a laser triangulation system as described in claim 2, characterized in that, The specific steps of the waveform filtering process in step 2 are as follows: Step 2.1: Set a time sliding window. After storing nine waveforms in the window, perform an averaging operation to complete the time-domain filtering operation. Step 2.2: Perform bilateral filtering on the waveform of the time domain filtering, calculate the spatial domain weight based on the distance between the neighboring pixels and the center pixel, and calculate the value domain weight based on the difference between the gray value of the neighboring pixels and the gray value of the center pixel. Step 2.3: Use the waveform obtained after the above steps as the effective spot waveform. The waveform length is m , .

5. The method for locating a biased spot based on a laser triangulation system as described in claim 4, characterized in that, In step 2.2, the expression for the bilateral filtering process is: ； in, Represented by pixels a Centered on, 2 l A sliding window area of ​​size +1; a,b ; Represented as neighboring pixels b With the center pixel a Geometric proximity between them Represented as neighboring pixels b With the center pixel a Gray-scale similarity between them; Proximity function Represented as: ； Similarity function Represented as: 。 6. The method for locating a biased spot based on a laser triangulation system as described in claim 5, characterized in that, The size of the sliding window area is 5.

7. The method for locating a biased spot based on a laser triangulation system as described in claim 4, characterized in that, The specific steps for standard template matching in step 3 are as follows: Step 3.1: Based on the effective light spot waveform The peak value is used for coarse localization to preliminarily determine the pixel coordinates of the center of the image spot. ; Step 3.2: Match a standard template to the effective light spot waveform. Iterate through the standard template set in the processor memory and find the standard template closest to the effective light spot waveform, denoted as... The distance is defined as the difference between the pixel coordinates of two waveform peaks, and they satisfy the following relationship: 。 8. The method for locating a biased spot based on a laser triangulation system as described in claim 7, characterized in that, The specific steps for cross-correlation calculation of the two waveforms in step 4 are as follows: Step 4.1: Calculate the average intensity grayscale value of the effective light spot waveform. The average light intensity and grayscale value of the matching standard template ; Step 4.2: Calculate using the zero-normalized cross-correlation function, as shown in the following formula: ； Cross-correlation is performed on the effective spot waveform and the matched standard template. The displacement is determined by the similarity of the intensity distribution of spot waveforms at similar positions in terms of gray level and position, resulting in a correlation coefficient sequence. C(u) .

9. The method for locating a biased spot based on a laser triangulation system as described in claim 8, characterized in that, The specific steps for determining the relative pixel displacement in step 5 are as follows: Step 5.1: Process the obtained correlation coefficient sequence C(u) Perform cubic spline interpolation calculations with an interpolation interval of one-hundredth of a pixel. Step 5.2: Traverse and sort the cubic spline interpolation results to determine the sub-pixel position corresponding to the maximum value of the interpolation result. ; Step 5.3: Process to obtain the effective spot waveform and the relative pixel displacement of the matching standard template. Δ ,and .

10. The method for locating a biased spot based on a laser triangulation system as described in claim 9, characterized in that, The specific steps for converting relative pixel displacement to absolute pixel position in step 6 are as follows: Step 6.1: Relative pixel displacement Δ By adding the peak position of the matching standard template to the photosensitive element position, the absolute pixel position of the measured spot waveform center across the entire range is obtained. The expression is: ; Step 6.2: Use the calibration function built into the ranging system to convert the absolute pixel position into the actual displacement in the world coordinate system.

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