A tread contour registration method based on double-circle-center constraint

Abstract

The application discloses a kind of tread contour registration methods based on double circle center constraint, comprising: laser projects line laser to the surface of wheel, camera sampling picture;Extraction light strip center line in image, each three-dimensional coordinate on light strip center line is projected to light plane, and the tread contour of actual measurement is obtained;The closest and the second closest two arc regions of distance with inner side surface are looked up on the profile and are recorded as arc region I, arc region II;Realize circle using it respectively, and the real measurement circle center coordinates I, II are obtained;Realize rotation angle and translation amount using real measurement circle center coordinates I, II and reference circle center coordinates I, II;Again, using the rotation angle and translation amount solved to light strip center line rotation translation, it is aligned with reference tread contour, and registration is completed.This method aims at accurately obtaining the rotation translation parameter between real measurement tread contour and reference tread contour, so that real measurement tread contour can be quickly and accurately aligned, and the detection precision and speed of subsequent wheel geometric parameter are improved.

Description

Technical Field

[0001] This invention relates to the field of wheelset measurement, and more specifically to a tread profile registration method based on dual-center constraints. Background Technology

[0002] In recent years, structured light measurement technology has been widely used in the field of wheelset geometric parameter detection. For example, patent document CN115326812A proposes an on-board wheelset measurement sensor and measurement method. This method uses a laser to project laser light onto the surface of the wheel, a camera to collect laser images, and then analyzes the geometric dimensions of the wheel based on the laser images.

[0003] In the structured light wheelset measurement scheme, the laser beam plane passes through the axle (coinciding with the wheelset's cross-section), and the camera is positioned around the laser, forming a certain angle with the beam plane. Therefore, in the acquired images, the laser stripe contour line is rotated and translated compared to the wheel's reference design contour (the contour line on the wheel's cross-section). To facilitate the evaluation of wheel geometry and comparative analysis of tread wear, the acquired laser stripe contour (tread contour) needs to be aligned with the wheel's reference design contour (the tread contour on the wheel's cross-section), i.e., contour registration needs to be performed.

[0004] Patent document CN112937633A proposes a portable wheelset parameter measuring instrument. When aligning the measured profile to a standard profile, the translation amount is obtained by fitting the center of the arc where the rim apex is located using a radius-constrained circular arc fitting method; the rotation amount is obtained by fitting the outer inclined segment of the rim using a least-squares curve fitting method. However, for wheels in actual service, the central angle of the arc segment where the rim apex is located is usually small and contains noise, easily leading to light scattering and unclear boundaries, causing the fitted arc to contain outliers. Conventional least-squares fitting methods cannot guarantee the accuracy and effectiveness of locating the center, thus affecting the measurement accuracy of the rim dimensions. Furthermore, the inclined segment of the outer rim is relatively short, making it difficult to guarantee its fitting accuracy. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a tread profile registration method based on dual-center constraints. This method aims to accurately obtain the rotation and translation parameters between the measured tread profile and the reference tread profile, enabling the measured tread profile to be quickly and accurately aligned, thereby improving the accuracy and speed of subsequent wheel geometry parameter (rim height, rim thickness, rim vertical wear, QR value, etc.) detection.

[0006] Therefore, the technical solution of the present invention is as follows:

[0007] A tread profile registration method based on dual-center constraints includes the following steps:

[0008] 1) A laser projects a linear laser beam onto the surface of the wheel to be tested, and a camera captures the image of the laser beam. The light plane of the laser passes through the wheel axle.

[0009] Extract the center line of the laser stripe from the laser stripe image, obtain the three-dimensional coordinates of each pixel on the center line of the laser stripe in the camera coordinate system, and then project each three-dimensional coordinate onto the light plane of the laser to obtain the two-dimensional coordinates of each point. The two-dimensional coordinates form the measured tread profile.

[0010] Find the two arc regions that are closest to and second closest to the inner side surface on the measured tread profile. The two arc regions have different radii and are respectively denoted as arc region I and arc region II.

[0011] By fitting circles to circular arc regions I and II respectively, the measured center coordinates I and II of the circle are obtained.

[0012] 2) Rotate and translate the measured center coordinates I and II respectively, and make the rotated and translated measured center coordinates I and II overlap with the reference center coordinates I and II. Establish a system of equations and solve for the rotation angle and translation. Among them, the reference center coordinates I and II are pre-stored reference data, representing the center coordinates of the arc regions I and II on the reference tread profile. The reference tread profile is the tread profile intercepted by the positive section, and the positive section passes through the wheel axle.

[0013] The center line of the light stripe is rotated and translated by the obtained rotation angle and translation amount, and then aligned with the reference tread profile to complete the tread profile registration.

[0014] Furthermore, by fitting circles to arc regions I and II respectively, the measured center coordinates I and II are obtained; the method is as follows:

[0015] Construct the objective function minf(o x ,o y ):

[0016]

[0017] Among them, (x i ,y i Let be the i-th two-dimensional coordinate point within the arc region I, and m represent the total number of points within the arc region I. x ,o y (x′) represents the measured coordinates of the center of the circle I. j ,y′ j) represents the j-th two-dimensional coordinate point within arc region II, n represents the total number of points within arc region II, L represents the distance between reference center coordinate I and reference center coordinate II, α represents the angle between the line connecting reference center coordinate I and reference center coordinate II and the horizontal line, and r and r' represent the reference radius values ​​corresponding to arc region I and arc region II, respectively, which are obtained through the standard design documents of the wheel;

[0018] The objective function is solved using optimization methods to minimize its value, thus obtaining the measured coordinates of the circle center I(o). x ,o y );

[0019] Based on: Solve for the measured coordinates of the center of the circle II(o′) x ,o′ y ).

[0020] Preferably, the optimization method includes the LM method, the Nelder-Mead method, the least squares method, the Gauss-Newton method, and the Levenberg-Marquardt method.

[0021] Further, in step 1), find the two arc regions closest to and second closest to the inner surface on the measured tread profile. The two arc regions have different radii and are denoted as arc region I and arc region II, respectively. The method is as follows:

[0022] Find the two-dimensional coordinate points on the inner side profile of the measured tread profile, and fit the straight line S using the found two-dimensional coordinate points.

[0023] Calculate the distances between other two-dimensional coordinate points on the center line of the light stripe and the fitted straight line S respectively. Store the two-dimensional coordinate points whose distance values ​​are in distance interval I into the point set corresponding to the arc region I, and store the two-dimensional coordinate points whose distance values ​​are in distance interval II into the point set corresponding to the arc region II.

[0024] The distance intervals I and II are obtained based on the standard design documents or wheel design models.

[0025] Furthermore, the two-dimensional coordinate points on the inner surface contour line are located on the measured tread contour as follows:

[0026] Method 1:

[0027] The inner surface contour line is located on the left / right side of the laser strip image in advance. Multiple pixels are found on the corresponding side of the center line of the light strip, and the two-dimensional coordinates corresponding to these pixels are marked as two-dimensional coordinate points on the inner surface contour line.

[0028] Alternatively, method two:

[0029] ① Calculate the centroid of the measured tread profile. On the measured tread profile, take the point farthest from the centroid as the previous point; take the two-dimensional coordinate point closest to the previous point as the current point, and take the two-dimensional coordinate point closest to the current point as the next point.

[0030] The following judgments are made on the two-dimensional coordinate points on the measured tread profile in sequence:

[0031] Determine whether the directions of the direction vector formed by the previous point and the current point, and the direction vector formed by the current point and the next point, are consistent.

[0032] If they match, the subsequent point is recorded as the tread profile point, and the current point is updated to the previous point and the subsequent point is updated to the current point. The two-dimensional coordinate point closest to the current point is recorded as the subsequent point; continue to the next judgment; until all two-dimensional coordinate points on the measured tread profile have been traversed;

[0033] If there is a discrepancy, skip the subsequent point and record the other two-dimensional coordinate point that is closest to the current point as the new subsequent point; perform the next judgment again; until all two-dimensional coordinate points on the measured tread profile have been traversed;

[0034] Based on the order in which the two-dimensional coordinate points are judged, number each tread profile point sequentially; remove 3% to 10% of the tread profile points, and use the other tread profile points to perform step ②;

[0035] ② Obtain the direction vector P between the first numbered tread profile point and the middle numbered tread profile point, and the direction vector Q between the middle numbered tread profile point and the last numbered tread profile point.

[0036] When it is known in advance that the arrangement of the two-dimensional coordinate points in the measured tread profile from left to right is the inner surface, tread surface, and outer surface:

[0037] If the cross product of direction vectors P and Q is less than 0, the tread profile point with the last number is marked as a point on the inner side profile line, and a straight line is fitted with the tread profile point with the next last number.

[0038] If the cross product of direction vectors P and Q is greater than 0, the first numbered tread profile point is marked as a point on the inner side profile line, and a straight line is fitted between it and the second numbered tread profile point.

[0039] When it is known in advance that the arrangement of the two-dimensional coordinate points in the measured tread profile from left to right is the outer surface, tread surface, and inner surface:

[0040] If the cross product of direction vectors P and Q is greater than 0, the tread profile point with the last number is marked as a point on the inner side profile line, and a straight line is fitted with the tread profile point with the next last number.

[0041] If the cross product of direction vectors P and Q is less than 0, the first numbered tread profile point is marked as a point on the inner side profile line, and a straight line is fitted using it and the second numbered tread profile point.

[0042] ③ Calculate the distance between other tread profile points and the straight line fitted in step ②. If the distance value is less than the threshold A, mark it as a point on the inner side profile line.

[0043] Preferably, the threshold A is 1 / 4 to 2 / 3 times the average tread profile point spacing.

[0044] Furthermore, the methods for obtaining distance interval I and distance interval II are as follows:

[0045] Method 1:

[0046] In the wheel design digital model, the distance d1 between the end point of the arc region I and the inner side profile line is directly measured; the distance d2 between the end point of the arc region II and the inner side profile line is measured.

[0047] Then the distance interval I is [0, d1] and the distance interval II is [d1, d2].

[0048] Alternatively, method two:

[0049] Calculations are performed in the standard design documents for wheels:

[0050] d1 = r(1-cosα)

[0051] d2=r'(1-cosα)+r'(cosα+cosβ)

[0052] α represents the angle between the line connecting the reference center coordinates I and II and the horizontal line, and β represents the angle between the line connecting the reference center coordinates II and III and the horizontal line. Reference center coordinates III is the center coordinates of the third arc closest to the inner surface contour line.

[0053] Then the distance interval I is [0, d1] and the distance interval II is [d1, d2].

[0054] Further, in step 2), the measured center coordinates I and II are rotated and translated respectively, and the measured center coordinates I and II after rotation and translation are set to be equal to the reference center coordinates I and II respectively. A system of equations is established, and the rotation angle θ and translation t are solved simultaneously. x t y The method is as follows:

[0055]

[0056]

[0057] Among them, (a x ,a y (a′) represents the coordinates of the reference circle center I, (a′) x ,a′ y ) represents the coordinates of the reference circle center II, (o x ,o y (o′) represents the measured coordinates of the center of the circle I, (o′) x ,o′ y ) represents the measured coordinates of the center of the circle II.

[0058] Furthermore, the reference center coordinates I and II are obtained based on the standard design documents of the wheel or based on the wheel design model.

[0059] Compared with existing technologies, the method provided in this application has the following advantages:

[0060] (1) During actual train operation, the wear area of ​​the wheel is mainly concentrated on the inner side of the wheel flange and the tread, while the area from the top of the wheel flange to the inner side and the outer side (circular area I and circular area II in this scheme) hardly wears. Therefore, this method uses the non-wearable area (circular area I and circular area II) to fit the double center, and uses the double center as the positioning reference to jointly constrain the registration matrix (rotation and translation). Compared with calculating the registration matrix in the wearable area, the matrix solution result is more accurate and can improve the accuracy of the registration result.

[0061] Furthermore, the registration matrix (rotation and translation) obtained by this scheme can be used as prior information. In subsequent applications of visual sensors (lasers, cameras), after each image acquisition, the camera can convert the pixels to the light plane to obtain the measured tread profile. Then, the pre-stored registration matrix can be directly retrieved to rotate and translate each two-dimensional element in the measured tread profile to obtain the registered tread profile. Based on this profile, relevant wear indicators such as rim height, rim thickness, and QR can be calculated. Since the tread profile has been converted to the positive cross section, the calculated indicators can be used to analyze the degree of wheel wear more clearly and intuitively, improving the convenience of wear detection.

[0062] (2) Fitting the rim center is easily affected by outliers, leading to low measurement accuracy. Therefore, when solving for the double center, this method establishes a common constraint on the two arc regions to form an objective function. Compared with fitting the center coordinates of the two arc regions separately, the constraint is stronger, and the calculated center coordinates are more accurate. This scheme can maintain effective measurement accuracy in complex environments such as light scattering, edge effects, boundary blurring, local deformation, and oil contamination.

[0063] (3) By constraining whether each point on the center line of the light strip is in the same direction, noise and abrupt change points can be effectively eliminated, thereby ensuring the accuracy of the contour and further improving the accuracy of finding the arc area and the accuracy of fitting the center. Attached Figure Description

[0064] Figure 1 This is a schematic diagram of the reference tread surface profile;

[0065] Figure 2 This is a schematic diagram of the measured tread profile;

[0066] Figure 3 These are schematic diagrams of arc region I and arc region II;

[0067] Figure 4 This is a schematic diagram showing the sorting of the tread contour points in a specific implementation method;

[0068] Figure 5 This is a schematic diagram of the wheelset structure in a specific implementation method;

[0069] Figure 6 For LM A Standard design documents for wheel tread profile;

[0070] Figure 7 The inner side profile of the tread surface and the three arc regions closest to the inner side profile;

[0071] Figure 8 This is a schematic diagram showing the arrangement of two-dimensional coordinate points from left to right in the measured tread profile during step ②. Detailed Implementation

[0072] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0073] A tread profile registration method based on dual-center constraints includes the following steps:

[0074] 1) A laser projects a linear laser beam onto the surface of the wheel to be tested, and a camera captures the image of the laser beam. The laser beam passes through the wheel axle (e.g., ...). Figure 5 If there are multiple line lasers projected onto the surface of the wheel, registration is performed on only one laser line at a time.

[0075] Extract the center line of the laser stripe from the laser stripe image, obtain the three-dimensional coordinates of each pixel on the center line of the laser stripe in the camera coordinate system, and then project each three-dimensional coordinate onto the light plane of the laser to obtain the two-dimensional coordinates of each point. The two-dimensional coordinates form the measured tread profile.

[0076] In specific implementation, the preferred method for projecting each three-dimensional coordinate onto the light plane of the laser is the Rodrigues transform method.

[0077] In the actual measured tread profile (such as...) Figure 2 Find the two arc regions that are closest to and second closest to the inner surface on the surface. The two arc regions have different radii and are denoted as arc region I and arc region II, respectively.

[0078] By fitting circles to circular arc regions I and II respectively, the measured center coordinates I and II of the circle are obtained.

[0079] 2) Rotate and translate the measured center coordinates I and II respectively, and then overlap the rotated and translated measured center coordinates I and II with the reference center coordinates I and II. Establish a system of equations and solve for the rotation angle and translation. Reference center coordinates I and II are pre-stored reference data, representing the reference tread profile (e.g., ...). Figure 1 The coordinates of the center of the circular arc regions I and II on the ) are given. The reference tread profile is the tread profile cut by the positive section, which passes through the wheel axle.

[0080] The center line of the light stripe is rotated and translated by the obtained rotation angle and translation amount, and then aligned with the reference tread profile to complete the tread profile registration.

[0081] Among them, the rotation angle θ and translation t are solved simultaneously. x t y The solution formula is as follows:

[0082]

[0083]

[0084] Among them, (a x ,a y (a′) represents the coordinates of the reference circle center I, (a′) x ,a′ y ) represents the coordinates of the reference circle center II, (o x ,o y (o′) represents the measured coordinates of the center of the circle I, (o′) x ,o′ y ) represents the measured coordinates of the center of the circle II.

[0085] The reference center coordinates I and II are obtained from the standard wheel design documents (TB / T 449-2016 "Roller Wheel Flange Tread Shape") or from the wheel design model. Figure 6 For LM AAccording to the standard design drawing of the wheel tread profile, the radius of each arc on the wheel has a standard value. In this scheme, the two arc regions that are closest to and second closest to the inner side: arc region I and arc region II correspond to arc segments of R25 and R12, respectively.

[0086] In practice, a planar coordinate system is established on the frontal section of the wheel, where the frontal section is the section passing through the axle (e.g., ...). Figure 5 The plane shown is used to cut out the wheel profile from the cross section and record it as the reference tread profile. On the reference tread profile, find the arc region I and the second closest to the inner side surface. Record the center coordinates of the two arcs as reference center coordinates I and reference center coordinates II, respectively.

[0087] Fitting the rim center is easily affected by outliers, leading to low measurement accuracy. Therefore, in this embodiment, when solving for the dual center, a common constraint is established for the two arc regions to form the objective function minf(o x ,o y );

[0088] Specifically, circles are fitted using arc region I and arc region II respectively to obtain the measured center coordinates I and II; the method is as follows:

[0089] Construct the objective function minf(o x ,o y ):

[0090]

[0091] Among them, (x i ,y i Let be the i-th two-dimensional coordinate point within the arc region I, and m represent the total number of points within the arc region I. x ,o y (x′) represents the measured coordinates of the center of the circle I. j ,y′ j Let ) represent the j-th two-dimensional coordinate point within arc region II, n represent the total number of points within arc region II, L represent the distance between reference center coordinates I and reference center coordinates II, α represent the angle between the line connecting reference center coordinates I and reference center coordinates II and the horizontal line, and r and r' represent the reference radius values ​​corresponding to arc regions I and II, respectively. These values ​​are determined using the standard wheel design documents (such as...). Figure 6 )get;

[0092] The objective function is solved using optimization methods to minimize its value, thus obtaining the measured coordinates of the circle center I(o). x ,o y );

[0093] Based on: Solve for the measured coordinates of the center of the circle II(o′) x ,o′ y ).

[0094] The optimization methods include the LM method, the Nelder-Mead method, the least squares method, the Gauss-Newton method, and the Levenberg-Marquardt method.

[0095] More specifically, such as Figure 3 As shown, in step 1), the two arc regions closest to and second closest to the inner side surface are found on the measured tread profile. The two arc regions have different radii and are denoted as arc region I and arc region II, respectively. The method is as follows:

[0096] Find the two-dimensional coordinate points on the inner side profile of the measured tread profile, and fit the straight line S using the found two-dimensional coordinate points.

[0097] like Figure 3 As shown, the distances between other two-dimensional coordinate points on the center line of the light stripe and the fitted straight line S are calculated respectively. Two-dimensional coordinate points with distance values ​​in distance interval I are stored in the point set corresponding to the arc region I, and two-dimensional coordinate points with distance values ​​in distance interval II are stored in the point set corresponding to the arc region II.

[0098] The distance intervals I and II are obtained based on the standard design documents or wheel design models.

[0099] The method for finding the two-dimensional coordinate points on the inner surface contour line on the measured tread profile is as follows:

[0100] Method 1:

[0101] The inner surface contour line is located on the left / right side of the laser strip image in advance. Multiple pixels are found on the corresponding side of the center line of the light strip, and the two-dimensional coordinates corresponding to these pixels are marked as two-dimensional coordinate points on the inner surface contour line.

[0102] For example: if it is known in advance that the inner surface contour line is on the left side of the laser stripe image, then multiple pixels are searched to the left of the center line of the light stripe; if it is known in advance that the inner surface contour line is on the right side of the laser stripe image, then multiple pixels are searched to the right of the center line of the light stripe.

[0103] Alternatively, method two:

[0104] ① Calculate the centroid of the measured tread profile, and take the point on the measured tread profile that is farthest from the centroid as the preceding point; for example... Figure 4 As shown, the two-dimensional coordinate point closest to the previous point is denoted as the current point, and the two-dimensional coordinate point closest to the current point is denoted as the subsequent point;

[0105] The following judgments are made on the two-dimensional coordinate points on the measured tread profile in sequence:

[0106] Determine whether the directions of the direction vector formed by the previous point and the current point, and the direction vector formed by the current point and the next point, are consistent.

[0107] If they match, the subsequent point is recorded as the tread profile point, and the current point is updated to the previous point and the subsequent point is updated to the current point. The two-dimensional coordinate point closest to the current point is recorded as the subsequent point; continue to the next judgment; until all two-dimensional coordinate points on the measured tread profile have been traversed;

[0108] If there is a discrepancy, skip the subsequent point and record the other two-dimensional coordinate point that is closest to the current point as the new subsequent point; perform the next judgment again; until all two-dimensional coordinate points on the measured tread profile have been traversed;

[0109] Based on the order in which the two-dimensional coordinate points are judged, each tread profile point is numbered sequentially. This step adopts a method of traversing and sorting the two-dimensional coordinate points one by one. If a subsequent point meets the condition, it is marked as a tread profile point; otherwise, it is skipped first, and then traversed again. Therefore, the tread profile points that are sorted to the end are likely to be noisy or miscellaneous points that do not meet the condition. Therefore, in order to delete these points, in specific implementation, the last 3% to 10% of the tread profile points are removed, and other tread profile points are used to execute step ②.

[0110] ② Obtain the direction vector P between the first numbered tread profile point and the middle numbered tread profile point, and the direction vector Q between the middle numbered tread profile point and the last numbered tread profile point.

[0111] When it is known in advance that the arrangement of the two-dimensional coordinate points in the measured tread profile from left to right is the inner surface, tread surface, and outer surface:

[0112] If the cross product of direction vectors P and Q is less than 0, then the tread profile point with the last number is marked as a point on the inner surface profile line, and a straight line is fitted using this point and the tread profile point with the next last number (e.g.) Figure 8 (b));

[0113] If the cross product of direction vectors P and Q is greater than 0, then the first numbered tread profile point is marked as a point on the inner surface profile line, and a straight line is fitted using it and the second numbered tread profile point (e.g., ...). Figure 8 (a));

[0114] When it is known in advance that the arrangement of the two-dimensional coordinate points in the measured tread profile from left to right is the outer surface, tread surface, and inner surface:

[0115] If the cross product of direction vectors P and Q is greater than 0, then the tread profile point with the last number is marked as a point on the inner surface profile line, and a straight line is fitted using it and the tread profile point with the next last number (e.g.) Figure 8 (c));

[0116] If the cross product of direction vectors P and Q is less than 0, then the first numbered tread profile point is marked as a point on the inner surface profile line, and a straight line is fitted using it and the second numbered tread profile point (e.g., ...). Figure 8 (d));

[0117] ③ Calculate the distance between other tread profile points and the straight line fitted in step ②. If the distance value is less than the threshold A, mark it as a point on the inner side profile line.

[0118] In practice, the threshold A is 1 / 4 to 2 / 3 times the average tread profile point spacing.

[0119] The methods for obtaining distance interval I and distance interval II are as follows:

[0120] Method 1:

[0121] In the wheel design digital model, the distance d1 between the end point of the arc region I and the inner side profile line is directly measured; the distance d2 between the end point of the arc region II and the inner side profile line is measured.

[0122] Then the distance interval I is [0, d1] and the distance interval II is [d1, d2].

[0123] Alternatively, method two:

[0124] In the standard design documents of the wheel (such as...) Figure 6 Calculated in )

[0125] d1 = r(1-cosα)

[0126] d2=r'(1-cosα)+r'(cosα+cosβ)

[0127] like Figure 7 As shown, α represents the angle between the line connecting the reference center coordinates I and II and the horizontal line, and β represents the angle between the line connecting the reference center coordinates II and III and the horizontal line. Reference center coordinates III are the center coordinates of the third arc closest to the inner surface contour line.

[0128] Then the distance interval I is [0, d1] and the distance interval II is [d1, d2].

[0129] As a subsequent application of the present invention, the center line of the laser strip after rotation and translation is used to calculate the rim height, thickness, and QR value. Since the center line of the laser strip after conversion is aligned with the reference contour, the relevant wear indicators such as rim height, rim thickness, and QR can be obtained more intuitively.

[0130] The foregoing description of specific exemplary embodiments of the present invention is for illustrative and descriptive purposes. It is not intended to be exhaustive, nor to limit the invention to the precise forms disclosed; obviously, many changes and variations are possible in accordance with the foregoing teachings. The exemplary embodiments were chosen and described to explain the specific principles of the invention and its practical application, thereby enabling others skilled in the art to implement and utilize various exemplary embodiments of the invention, as well as their different alternatives and modifications. The scope of the invention is intended to be defined by the appended claims and their equivalents.

Claims

1. A tread profile registration method based on double-center constraints, characterized in that, Includes the following steps: 1) A laser projects a linear laser beam onto the surface of the wheel to be tested, and a camera captures the image of the laser beam. The light plane of the laser passes through the wheel axle. Extract the center line of the laser stripe from the laser stripe image, obtain the three-dimensional coordinates of each pixel on the center line of the laser stripe in the camera coordinate system, and then project each three-dimensional coordinate onto the light plane of the laser to obtain the two-dimensional coordinates of each point. The two-dimensional coordinates form the measured tread profile. Find the two arc regions that are closest to and second closest to the inner side surface on the measured tread profile. The two arc regions have different radii and are respectively denoted as arc region I and arc region II. By fitting circles to circular arc regions I and II respectively, the measured center coordinates I and II of the circle are obtained; the method is as follows: Construct the objective function : in, Let be the i-th two-dimensional coordinate point within the circular arc region I, and m represent the total number of points within the circular arc region I. Indicates the measured coordinates of the center of the circle, I. Let be the j-th two-dimensional coordinate point within the arc region II, n represent the total number of points within the arc region II, and L represent the distance between the reference center coordinates I and the reference center coordinates II. This represents the angle between the line connecting the coordinates of the reference center I and the coordinates of the reference center II and the horizontal line. r' and r' represent the reference radius values ​​corresponding to arc region I and arc region II, respectively, which are obtained through the standard design documents of the wheel; The objective function is solved using optimization methods to minimize its value, thus obtaining the measured coordinates I of the circle center. ; Based on: Solve for the measured coordinates of the center of the circle II ; 2) Rotate and translate the measured center coordinates I and II respectively, and make the rotated and translated measured center coordinates I and II overlap with the reference center coordinates I and II. Establish a system of equations and solve for the rotation angle and translation. Among them, the reference center coordinates I and II are pre-stored reference data, representing the center coordinates of the arc regions I and II on the reference tread profile. The reference tread profile is the tread profile intercepted by the front section, and the front section passes through the wheel axle. The center line of the light stripe is rotated and translated by the obtained rotation angle and translation amount, and then aligned with the reference tread profile to complete the tread profile registration.

2. The tread profile registration method based on double-center constraints as described in claim 1, characterized in that: The optimization methods include the LM method, the Nelder-Mead method, the least squares method, the Gauss-Newton method, and the Levenberg-Marquardt method.

3. The tread profile registration method based on double-center constraints as described in claim 1, characterized in that: In step 1), find the two arc regions closest to and second closest to the inner side surface on the measured tread profile. The two arc regions have different radii and are denoted as arc region I and arc region II, respectively. The method is as follows: Find the two-dimensional coordinate points on the inner side profile of the measured tread profile, and fit the straight line S using the found two-dimensional coordinate points. Calculate the distances between other two-dimensional coordinate points on the center line of the light stripe and the fitted straight line S respectively. Store the two-dimensional coordinate points whose distance values ​​are in distance interval I into the point set corresponding to the arc region I, and store the two-dimensional coordinate points whose distance values ​​are in distance interval II into the point set corresponding to the arc region II. The distance intervals I and II are obtained based on the standard design documents or wheel design models.

4. The tread profile registration method based on double-center constraints as described in claim 3, characterized in that: The method for finding the two-dimensional coordinate points on the inner surface contour line on the measured tread profile is as follows: Method 1: The inner surface contour line is located on the left / right side of the laser strip image in advance. Multiple pixels are found on the corresponding side of the center line of the light strip, and the two-dimensional coordinates corresponding to these pixels are marked as two-dimensional coordinate points on the inner surface contour line. Alternatively, method two: ① Calculate the centroid of the measured tread profile. On the measured tread profile, take the point farthest from the centroid as the previous point; take the two-dimensional coordinate point closest to the previous point as the current point, and take the two-dimensional coordinate point closest to the current point as the next point. The following judgments are made on the two-dimensional coordinate points on the measured tread profile in sequence: Determine whether the directions of the direction vector formed by the previous point and the current point, and the direction vector formed by the current point and the next point, are consistent. If they match, the subsequent point is recorded as the tread profile point, and the current point is updated to the previous point and the subsequent point is updated to the current point. The two-dimensional coordinate point closest to the current point is recorded as the subsequent point; continue to the next judgment; until all two-dimensional coordinate points on the measured tread profile have been traversed; If there is a discrepancy, skip the subsequent point and record the other two-dimensional coordinate point that is closest to the current point as the new subsequent point; perform the next judgment again; until all two-dimensional coordinate points on the measured tread profile have been traversed; Based on the order in which the two-dimensional coordinate points are judged, number each tread profile point sequentially; remove 3% to 10% of the tread profile points, and use the other tread profile points to perform step ②; ② Obtain the direction vector P between the first numbered tread profile point and the middle numbered tread profile point, and the direction vector Q between the middle numbered tread profile point and the last numbered tread profile point. When it is known in advance that the arrangement of the two-dimensional coordinate points in the measured tread profile from left to right is the inner surface, tread surface, and outer surface: If the cross product of direction vectors P and Q is less than 0, the tread profile point with the last number is marked as a point on the inner side profile line, and a straight line is fitted with the tread profile point with the next last number. If the cross product of direction vectors P and Q is greater than 0, the first numbered tread profile point is marked as a point on the inner side profile line, and a straight line is fitted between it and the second numbered tread profile point. When it is known in advance that the arrangement of the two-dimensional coordinate points in the measured tread profile from left to right is the outer surface, tread surface, and inner surface: If the cross product of direction vectors P and Q is greater than 0, the tread profile point with the last number is marked as a point on the inner side profile line, and a straight line is fitted with the tread profile point with the next last number. If the cross product of direction vectors P and Q is less than 0, the first numbered tread profile point is marked as a point on the inner side profile line, and a straight line is fitted using it and the second numbered tread profile point. ③ Calculate the distance between other tread profile points and the straight line fitted in step ②. If the distance value is less than the threshold A, mark it as a point on the inner side profile line.

5. The tread profile registration method based on double-center constraints as described in claim 4, characterized in that: The threshold A is 1 / 4 to 2 / 3 times the average tread profile point spacing.

6. The tread profile registration method based on double-center constraints as described in claim 3, characterized in that: The methods for obtaining distance interval I and distance interval II are as follows: Method 1: In the wheel design digital model, the distance d1 between the end point of the arc region I and the inner side profile line is directly measured; the distance d2 between the end point of the arc region II and the inner side profile line is measured. Then the distance interval I is [0, d1] and the distance interval II is [d1, d2]. Alternatively, method two: Calculations are performed in the standard design documents for wheels: β represents the angle between the line connecting the reference center coordinates I and II and the horizontal line, and β represents the angle between the line connecting the reference center coordinates II and III and the horizontal line, where reference center coordinates III is the center coordinates corresponding to the third arc closest to the inner surface contour line; Then the distance interval I is [0, d1] and the distance interval II is [d1, d2].

7. The tread profile registration method based on double-center constraints as described in claim 1, characterized in that: In step 2), the measured center coordinates I and II are rotated and translated respectively, and the measured center coordinates I and II after rotation and translation are set to be equal to the reference center coordinates I and II respectively. A system of equations is established, and the rotation angle θ and translation amount are solved simultaneously. , The method is as follows: in,( , ) represents the coordinates of the reference circle center I, ( , () indicates the coordinates of the reference circle center II. Indicates the measured coordinates of the circle center, I. Indicates the measured coordinates of the center of the circle, II.

8. The tread profile registration method based on double-center constraints as described in claim 1, characterized in that: The reference center coordinates I and II are obtained from the standard design documents of the wheel or from the wheel design model.

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