Smooth obstacle avoidance path planning method for three-dimensional weaving process

Abstract

The invention discloses a smooth obstacle avoidance path planning method for a three-dimensional weaving process, and the method achieves the planning of a non-linear path of three-dimensional weaving through the steps: building a coordinate transformation model, detecting the position of a weaving array, guiding the weaving array to catalog, planning a global path, and outputting path points. When part of the guide rods in the guide rod array deviate in a certain row or a certain column, all the guide rods can be avoided through the weaving global path planned by the method, collision is avoided, and the weaving efficiency and safety are effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of three-dimensional weaving, and particularly to a three-dimensional weaving path planning method. Background Art

[0002] Compared with traditional composite materials, three-dimensional woven composite materials not only have the advantages of high specific strength and high specific modulus, but also have the characteristics of anti-delamination, high damage tolerance against cracking, and strong designability, and have been widely used in the fields of aerospace, transportation, and civil thermal engineering.

[0003] At present, the forming process of composite material preforms mainly focuses on equal-thickness components and straight-line paths. Among them, the weaving path takes the straight-line paths in rows or columns in the guide rod array arranged in rows and columns as the planned path. This path planning method is difficult to realize the planning of non-straight-line paths, thus unable to meet the needs of weaving complex fabric structures. Moreover, if some guide rods in the guide rod array are offset in a certain row or column, still taking the straight-line path as the planned path will cause the weaving needle to interfere with the offset guide rod with a certain probability, posing a safety hazard.

[0004] Therefore, a new technical solution needs to be proposed to solve the above technical problems. Summary of the Invention

[0005] In view of the above problems, the present invention provides a smooth obstacle avoidance path planning method for three-dimensional weaving process, which can realize the planning of non-straight-line paths for three-dimensional weaving.

[0006] In order to achieve the above object, the technical solution that the present invention can adopt is as follows:

[0007] A smooth obstacle avoidance path planning method for three-dimensional weaving process, comprising the following steps:

[0008] (1) Photograph the weaving table through a camera, and obtain the top view images of all guide rods on the weaving table from the captured images;

[0009] (2) Control the weaving needle to move to nine points on the weaving table in sequence, and calculate the transformation matrix H by the least square method according to the images corresponding to the nine points and the coordinates of the weaving needle, so as to obtain the transformation model between the image coordinate system and the weaving needle coordinate system;

[0010] (3) Catalog each guide rod;

[0011] (4) The weaving path successively passes through the spaces between the guide rods. For all points located between two adjacent guide rods along the weaving path, they are taken as intermediate path points. After the selection of the intermediate path points is completed, all the intermediate path points are connected using cubic spline interpolation, and the curve of the obtained weaving path is represented by a cubic spline interpolation polynomial; and the velocity of the curve is obtained by solving the first derivative of the cubic spline interpolation polynomial, and the acceleration of the curve is obtained by solving the second derivative of the cubic spline interpolation polynomial.

[0012] (5) The output curve is used as the obstacle avoidance path after planning. The obstacle avoidance path is sampled at equal intervals, and discrete weaving needle position points are output.

[0013] Furthermore, in step (2), the transformation matrix H is:

[0014]

[0015] The transformation model between the image coordinate system and the weaving needle coordinate system is: [x, y, 1] T = H[u, v, 1] T ;

[0016] where x and y are the true coordinates of the point in the weaving needle coordinate system, u and v are the coordinates of the point in the image coordinate system, S x , S y are the scaling factors between these two coordinate systems, T x , T y are the translation factors, and θ is the rotation angle.

[0017] Furthermore, in step (1), all the guide rods are set as cylinders. The heights of all the guide rods are the same and the diameters are known. The position of the guide rod is characterized by the circular center of the guide rod.

[0018] Furthermore, in step (1), the top-down image is denoised. After denoising, the top-down image is binarized, and then the Hough gradient circle center detection method is used to detect the target circle center coordinates as the circular center.

[0019] Furthermore, in step (3), the method for cataloging the guide rods is: the guide rod in the x-th row and y-th column is marked as (x, y).

[0020] Furthermore, in step (4), when a certain section of the weaving path is surrounded by at least three guide rods, the points between the two adjacent guide rods with the shortest distance are taken as intermediate path points.

[0021] Furthermore, in step (4), the polynomial of cubic spline interpolation is as follows:

[0022]

[0023] Where \(t\) represents the movement time, \(i = 1,\cdots,n\) represents the \(i\)-th segment, and there is one segment between every two intermediate path points; \(j = 1,2\), where 1 represents the abscissa of the path and 2 represents the ordinate of the path; \(a\), \(b\), \(c\), and \(d\) are the four coefficients of the cubic spline interpolation polynomial.

[0024] Further, in step (5), check whether there are collision points on the planned obstacle avoidance path. If there are collision points, adjust the path points near the collision points and re-plan the obstacle avoidance path; if there are no collision points, perform equidistant sampling on the planned obstacle avoidance path and output discrete weaving needle position points.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: It can realize the planning of non-linear paths for three-dimensional weaving. When some guide rods in the guide rod array are offset in a certain row or a certain column, all guide rods can also be avoided without collision through the global weaving path planned by this method, effectively improving the weaving efficiency and safety.

[0026] The design method provided by the present invention can be stored on a storage medium as a computer program at the same time, including the following technical solutions:

[0027] An electronic device includes: one or more processors; and a storage device for storing one or more programs, and when the one or more programs are executed by the one or more processors, the one or more processors are caused to implement the above prediction method.

[0028] And:

[0029] A computer-readable medium has a computer program stored thereon, and when the program is executed by a processor, the above prediction method is implemented. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram for cataloging guide rods.

[0031] Figure 2 It is a schematic diagram for obtaining the final weaving path from intermediate path points for linear weaving.

[0032] Figure 3 It is a schematic diagram for obtaining the final weaving path from intermediate path points for oblique weaving.

[0033] Figure 4 It is a schematic diagram for obtaining the final weaving path from intermediate path points for curved weaving.

[0034] Figure 5 It is a schematic diagram for comparing the paths before and after the offset of the guide rod. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] To make the objectives, design process, technical methods, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0036] The present invention provides a method for planning a smooth obstacle-avoiding path in a three-dimensional weaving process, including the following steps:

[0037] (1) Calibrate the camera through the prior art to eliminate distortion, and obtain the internal and external parameters of the camera. For example, the camera calibration work can be carried out through the OpenCV software, and the calibration plate is photographed by the camera at 10 different positions and angles, and then the cv.calibrateCamera calibration function is used for calibration to obtain the camera internal parameters, distortion coefficients, translation matrix, and rotation matrix. When the RMS reprojection error is between 0.1 and 1.0, it indicates that a good calibration effect has been achieved.

[0038] After camera calibration, photograph the weaving table through the camera, and obtain the top-down images of all the guide rods on the weaving table from the photographed images.

[0039] (2) Control the weaving needles to move sequentially to nine points on the weaving table. According to the images corresponding to the nine points and the coordinates of the weaving needles, based on the principle of simulation change, and calculate the transformation matrix H by the least squares method to obtain the transformation model between the image coordinate system and the weaving needle coordinate system. Among them, the principle of affine transformation is:

[0040]

[0041] Among them, x and y are the true coordinates of the point in the weaving needle coordinate system, u and v are the coordinates of the point in the image coordinate system, S x , S y is the scaling coefficient between these two coordinate systems, T x , T y is the translation coefficient, and θ is the rotation angle. Thus, the rotation matrix is defined as:

[0042]

[0043] The transformation model between the image coordinate system and the weaving needle coordinate system [x, y, 1] T = H [u, v, 1] T . After obtaining the matrix H by the least squares method, the position of any point in the image coordinate system in the robot coordinate system can be obtained.

[0044] (3) Catalog each guide rod.

[0045] Before cataloging, first detect the positions of the weaving array. Since the guide rods are cylinders, with the same height and known diameter for each guide rod, the position of the guide rod can be characterized by the center of the circle. During the image acquisition process, problems such as uneven illumination or unstable image information transmission may lead to poor quality of the acquired guide array images, with image noise present. It is necessary to denoise the images.

[0046] Use the Non-Local Means denoising algorithm for image smoothing. The Non-Local Means denoising algorithm uses the redundant information commonly present in natural images to remove noise. It utilizes the entire image to remove noise, searches for similar regions in the image in units of image blocks, and then averages these regions, which can relatively well remove the Gaussian noise present in the image. The specific implementation is to set two fixed-size windows: the search window and the neighborhood window. The neighborhood window slides within the search window, and the weight of the pixel is determined according to the similarity between neighborhoods. The estimated value of the current pixel is obtained by weighted averaging of the pixels in the image that have a similar neighborhood structure to it.

[0047] After image denoising, perform binarization on the image, and then use the Hough gradient circle center detection method to detect the coordinates of the target circle center. The principle is to calculate the modulus vectors of all non-zero pixel points in the image. These modulus vectors intersect with each other, accumulate the number of intersections of the modulus vectors of all points in the two-dimensional space, and set a corresponding threshold. When the number of intersections of the modulus vectors of the calculated points is greater than this threshold, that point is considered to be the center of a certain circle.

[0048] After denoising, binarization, and circle center detection, the coordinates of each guide rod in the image coordinate system can be obtained, and then its coordinates in the robot coordinate system (i.e., the weaving needle coordinate system) can be obtained through the rotation matrix.

[0049] The cataloging of the guide rods is as Figure 1 shown. The guide rod in the x-th row and y-th column is marked as (x, y). Since the guide rods may be bent, offset, etc., the coordinates of the guide rods in the same row will not be the same but may vary within a certain range. Therefore, by setting an error range, the guide rods with coordinates within the error range are judged to be in the same row or the same column, and then the cataloging of the guide rods is completed.

[0050] (4) Global path planning.

[0051] The weaving path passes through the spaces between the guide rods in sequence. All the points located between two adjacent guide rods through which the weaving path passes are used as intermediate path points. When a certain section through which the weaving path passes is surrounded by at least three guide rods, the point between the two adjacent guide rods with the shortest distance is used as the intermediate path point.

[0052] For linear weaving, there are four cases: in the x direction, in the y direction, and at ±45°. As Figure 2As shown in the figure, for the x-direction weaving, the final weaving path is obtained from the intermediate path points. The intermediate path points are defined as the midpoints of the centers of the adjacent guide rods in the y-direction. For example, the intermediate points in the figure are {(1,1),(2,1)}, {(1,2),(2,2)}, ······, {(1,5),(2,5)}. The same applies to the y-direction.

[0053] As Figure 3 shown in the figure, for the -45° oblique weaving, the intermediate points are {(1,4),(1,5)}, {(1,4),(2,4)}, {(2,3),(2,4)}, {(2,3),(3,3)}, ······, {(4,1),(5,1)}. The same applies to the +45° oblique weaving.

[0054] For the curved weaving, there are also three cases: x-direction, y-direction, and ±45° oblique direction.

[0055] The figure shows the x-direction weaving, and the intermediate points are {(3,1),(4,1)}, {(4,1),(4,2)}, {(4,2),(5,2)}, {(4,2),(4,3)}, ······, {(4,4),(4,5)}, {(3,5),(4,5)}. The same applies to the y-direction and the ±45° oblique direction.

[0056] The coordinates of each intermediate path point are obtained by taking the average of the horizontal and vertical coordinates of the two adjacent guide rods. For example, {(3,1),(4,1)} represents the midpoint between the two guide rods with coordinates (3,1) and (4,1), and the coordinates of the intermediate path point can be obtained by taking the average of their horizontal and vertical coordinates as (3.5,1).

[0057] After the selection of the intermediate path points is completed, cubic spline interpolation is used to connect all the intermediate points. The resulting curve has the advantages of third-order differentiability and smoothness, and its analytical expression can be obtained. The polynomial of cubic spline interpolation is as follows:

[0058]

[0059] where t represents the motion time, i = 1,..., n, representing the i-th segment (each segment is between two intermediate points); j = 1, 2, representing the horizontal and vertical coordinates of the path (1 for the horizontal coordinate, 2 for the vertical coordinate); a, b, c, d are the four coefficients of the interpolation polynomial. The above curve has a total of n + 1 known data points, and the cubic function has a total of 8n unknown coefficients to be solved. The boundary conditions provide 2(n + 1) equations:

[0060]

[0061] where i = 1,..., n, p i,jDenote known data points. These two equations ensure that the initial and end points of each segment are the same as the known data points, for a total of 2(n + 1) equation equations.

[0062] All intermediate points need to ensure continuity of the 0th, 1st, and 2nd derivatives, providing 6(n - 1) equations:

[0063]

[0064] Among them, the continuity conditions of the 0th, 1st, and 2nd derivatives each provide 2(n - 1) equation equations. These equations respectively ensure the continuity of the curve and the first- and second-order smoothness.

[0065] So far, there are 8n - 4 equations. Since the velocities at the starting and ending points of the planned path are both zero, the remaining four equations can be supplemented using fixed boundary conditions:

[0066]

[0067] Therefore, these 8n unknown coefficients can be obtained from the following system of equations:

[0068]

[0069] Substitute the coordinates of all the above intermediate path points into Equation (7) to solve the equation, where is the expression of the interpolated path, represents the moment t i corresponding to the horizontal and vertical coordinates of the intermediate path point, such as represents the abscissa of the first intermediate path point at time t1, then represents the ordinate of the first intermediate path point at time t1; p represents the horizontal and vertical coordinates of the intermediate point, such as p 1,1 represents the abscissa of the first intermediate path point, p 1,2 is the ordinate of the first intermediate path point. By substituting all intermediate points, the 8n unknowns in Equation (3) can be solved; so far, after obtaining all unknown coefficients, Equation (3) becomes a known expression, that is, the avoidance path can be obtained by cubic spline interpolation from Equation (3). At the same time, since this path is analytic, the velocity and acceleration

[0070]

[0071]

[0072] After completing the global path planning, it is necessary to first check whether there are collision points. If there are collision points, it is necessary to adjust the path points near the collision points and re-plan the obstacle avoidance path. If there are no collision points, the final path is sampled at equal intervals to output discrete weaving needle position points.

[0073] The global path planning completed by the above method can avoid all guide rods without collision, effectively improving the weaving efficiency and safety. As Figure 5 shown, in the case where the actual guide rod is offset, the global path planning of the weaving operation can still be completed by the above method and achieve the above technical effects of improving the weaving efficiency and safety. When this planning method is applied to actual three-dimensional weaving, the robotic arm of the weaving robot can complete the weaving by tracking the weaving needle position points output by the above method according to the set weaving speed.

[0074] In addition, there are many specific implementation methods and ways for the present invention, and the above description is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for planning a smooth obstacle avoidance path in a three-dimensional weaving process, characterized in that, including the following steps (1) Photograph the weaving table with a camera, and obtain the top-down images of all the guide rods on the weaving table from the captured images; (2) Control the weaving needles to move sequentially to nine points on the weaving table. According to the images corresponding to the nine points and the coordinates of the weaving needles, calculate the transformation matrix H by the least squares method to obtain the transformation model between the image coordinate system and the weaving needle coordinate system; (3) Catalog each guide rod; (4) The weaving path passes through the spaces between the guide rods in sequence. All the points located between two adjacent guide rods passed by the weaving path are used as intermediate path points. After the selection of the intermediate path points is completed, use cubic spline interpolation to connect all the intermediate path points. The curve of the obtained weaving path is represented by a cubic spline interpolation polynomial; and the velocity of the curve is obtained by solving the first derivative of the cubic spline interpolation polynomial, and the acceleration of the curve is obtained by solving the second derivative of the cubic spline interpolation polynomial; (5) Output the curve as the planned obstacle avoidance path, sample the obstacle avoidance path at equal intervals, and output discrete weaving needle position points.

2. The method for smooth obstacle avoidance path planning of a three-dimensional weaving process according to claim 1, wherein: In step (2), the transformation matrix H is: The transformation model between the image coordinate system and the knitting needle coordinate system is: [x, y, 1] T = H[u, v, 1] T ; where x and y are the true coordinates of a point in the coordinate system of the knitting needles, u and v are the coordinates of the point in the image coordinate system, S x , S y is the scaling factor between these two coordinate systems, T x , T y is the translation factor, and θ is the rotation angle.

3. The method for smooth obstacle avoidance path planning in a three-dimensional weaving process according to claim 2, wherein: In step (1), it is assumed that all the guide rods are cylinders, and the heights of the guide rods are the same and the diameters are known. The position of the guide rod is characterized by the circular center of the guide rod.

4. The three-dimensional weaving process smooth obstacle avoidance path planning method according to claim 3, wherein: In step (1), denoise the top-down image. After denoising, perform binary processing on the top-down image, and then use the Hough gradient circle center detection method to detect the target circle center coordinates as the circular center.

5. The three-dimensional weaving process smooth obstacle avoidance path planning method according to claim 4, characterized in that: In step (3), the method for cataloging the guide rods is: mark the guide rod in the x-th row and y-th column as (x, y).

6. The three-dimensional weaving process smooth obstacle avoidance path planning method according to claim 5, characterized in that: In step (4), when a certain section passed by the weaving path is surrounded by at least three guide rods, the points between the two adjacent guide rods with the shortest distance are used as intermediate path points.

7. The method for smooth obstacle avoidance path planning of the three-dimensional weaving process according to claim 5, characterized in that: In step (4), the polynomial of cubic spline interpolation is as follows: where t represents the movement time, i = 1,..., n, represents the i-th segment, and there is one segment between every two intermediate path points; j = 1, 2, 1 represents the abscissa of the path, 2 represents the ordinate of the path; a, b, c, d are the four coefficients of the cubic spline interpolation polynomial.

8. The method for planning a smooth obstacle avoidance path in a three-dimensional weaving process according to claim 7, characterized in that: In step (5), check whether there are collision points on the planned obstacle avoidance path. If there are collision points, adjust the path points near the collision points and re-plan the obstacle avoidance path; if there are no collision points, sample the planned obstacle avoidance path at equal intervals and output discrete weaving needle position points.

9. An electronic device, comprising: one or more processors; and a storage device for storing one or more programs, which when executed by the one or more processors, cause the one or more processors to implement the design method according to any one of claims 1 to 8.

10. A computer-readable medium having a computer program stored thereon, characterized in that, The program, when executed by the processor, implements the design method according to any one of claims 1 to 8.

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