Curved surface variable-ratio automatic extension method in three-dimensional CAD (Computer Aided Design) environment

Abstract

The invention discloses a curved surface variable-ratio automatic extension method in a three-dimensional CAD environment, and the method comprises the steps: building a section bisector through writing a program based on the element selection and parameter input of a to-be-extended curved surface by a user, and building a tangent extension curve and a curvature extension curve of the section bisector at the same time through combining the advantages and disadvantages of the tangent extension and curvature extension of the curved surface; the variable-ratio extension curve is constructed between the tangent extension curve and the curvature extension curve according to different ratio values, curved surface variable-ratio automatic extension modeling is completed, the problems of poor curvature retentivity, insufficient curvature extension and curved surface distortion of original tangent extension are effectively solved, the design difficulty is reduced, and the design efficiency is improved. Standardized design of software and dominant expression of design experience are achieved, and a new thought is provided for multi-state rapid, efficient and automatic extension design of the curved surface in the three-dimensional CAD environment.

Description

Technical Field

[0001] This invention relates to, but is not limited to, the field of digital manufacturing, and to a method for automatic extension of curved surfaces with varying ratios in a three-dimensional CAD environment. Background Technology

[0002] Curved surface design is an important engineering technique in modern design, capable of significantly improving product performance. It not only creates unique aesthetic effects in industrial products and architecture, but also optimizes product functionality and structural performance, providing higher levels of functional performance and user experience, and enhancing product competitiveness. Furthermore, curved surface design supports sustainable design principles and has wide applications in aircraft manufacturing, automotive design, mold making, and architectural design.

[0003] Surface extension is a technique used in surface design that involves continuously extending an existing surface to create a new surface shape. Existing 3D CAD software primarily uses tangent extension and curvature extension. Tangent extension is a linear extension along the surface boundary. For surfaces with gentle curvature, it maintains the original geometric features well, achieving a smooth transition and exhibiting good extensibility. However, for surfaces with large curvature, the extended surface fails to maintain the original curvature trend, resulting in severe surface distortion. Curvature extension extends the surface based on the original curvature along the boundary direction, consistently maintaining the original curvature trend, but its extension performance is poor. Furthermore, due to the complexity of surface configurations in 3D CAD environments, surfaces often fail to extend or have insufficient extension dimensions. Manual surface reconstruction is complex, inefficient, and results in poor surface extension quality. Summary of the Invention

[0004] The purpose of this invention is to solve the above problems by proposing an automatic variable ratio extension method for curved surfaces in a 3D CAD environment. By writing a program to establish the bisectors of the cross section, and combining the advantages and disadvantages of tangent extension and curvature extension of the curved surface, the tangent extension curve and curvature extension curve of the bisectors of the cross section are established at the same time. According to different ratio values, a variable ratio extension curve is constructed between the tangent extension curve and the curvature extension curve to complete the automatic variable ratio extension modeling of the curved surface.

[0005] The technical solution of this invention is as follows: This invention provides an automatic extension method for curved surfaces with varying ratios in a three-dimensional CAD environment, comprising: Step 1. Open the surface model to be extended in 3D CAD software; Step 2. In the 3D CAD software, manually select the surface to be extended, the edge line of the surface to be extended, the left edge line adjacent to the extended edge, the left edge plane, the right edge line, and the right edge plane in the model of the surface to be extended; Step 3. Enter the number of extended surface sections CN, the surface extension ratio CR, and the surface extension length CL in the user interface; Where CN is an integer, CN≥1; CR is a decimal, 0 ≤ CR ≤ 1; CL is a positive number, 0 <CL; Step 4. By writing a program to read the elements input in Step 2 and the parameters input in Step 3, the variable ratio automatic extension of the surface to be extended is completed in the 3D CAD software. In the above-described method for automatic extension of curved surfaces with varying ratios in a 3D CAD environment, the method of automatically extending the curved surface with varying ratios by writing a program in the 3D CAD software is as follows: modeling the cross-section of the curved surface to be extended using equal-division planes, modeling the cross-section group of the curved surface to be extended, modeling the variable-ratio extension curve, and finally completing the automatic extension of the curved surface with varying ratios based on the modeling of the variable-ratio extension curve. The design method includes the following steps: 1-1. Using the left and right edge planes of the elements input in step 2 and the number of sections CN in step 3, establish the planes that divide the sections equally; 1-1-1. Measure the angle plna between the left edge plane and the right edge plane using a measurement function; 1-1-2. Determine the value of the included angle plna between the planes, and classify and establish planes that equally divide the cross-section; 1-1-2-1. When plna=0, establish a plane for dividing the cross-section equally from the left edge plane according to the number of cross-sections CN to the right edge plane at equal distances; 1-1-2-1-1. Measure the distance plndis between the left and right edge planes using a measurement function; 1-1-2-1-2. Start from the left edge plane and offset by a distance plndis to establish an offset trial plane; 1-1-2-1-3. Measure the distance trydis between the offset trial plane and the right edge plane using a measurement function; 1-1-2-1-4. When trydis=0, the correction parameter disk=1; when trydis<>0, the correction parameter disk=-1; 1-1-2-1-5. Establish a loop variable disi, where disi is a positive integer, initially 1, with a step size of 1, and a value range of (1, CN). 1-1-2-1-6. Establish the disi-th equally divided plane by offsetting a distance of disk*disi*plndis / (CN+1) from the left edge plane; 1-1-2-1-7. Repeat steps 1-1-2-1-5 to 1-1-2-1-6 to complete the creation of the cross-section dividing plane by equal distances; 1-1-2-2. When plna<>0, establish a plane for dividing the cross-section equally from the left edge plane according to the number of cross-sections CN to the right edge plane by equal angles; 1-1-2-2-1. Measure the angle plnangle between the left and right edge planes using a measurement function; 1-1-2-2-2. Establish the intersection line of the two end faces by intersecting the left edge plane and the right edge plane; 1-1-2-2-3. Rotate the left edge plane by a factor of plnangle about the intersection of the two end faces as the axis of rotation to create a rotational trial-and-error plane; 1-1-2-2-4. Measure the angle tryangle between the rotated trial plane and the right edge plane using a measurement function; 1-1-2-2-5. When tryangle=0, adjust parameter anglek=1; when tryangle<>0, adjust parameter anglek=-1. 1-1-2-2-6. Establish a loop variable anglei, where anglei is a positive integer, initially 1, with a step size of 1, and a value range of (1, CN). 1-1-2-2-7. Rotate the left edge plane by anglek* anglei,*plnangle / (CN+1) degrees about the intersection of the two end faces to create the i-th equally divided plane; 1-1-2-2-8. Repeat steps 1-1-2-2-6 to 1-1-2-2-7 to complete the creation of the cross-section dividing plane by angle; 1-2. Intersect the established cross-section dividing plane with the surface to be extended (input element from step 2) to create CN equally dividing cross-section lines; 1-3. Use the left edge line, right edge line, and equally divided section line of the input element in step 2 to create a section group of the surface to be extended; 1-4. Establish a loop variable i, where i is a positive integer, with an initial value of 1, a step size of 1, and a value range of (1, CN+2). 1-5. Establish an extension point by intersecting the i-th curve in the section group of the surface to be extended with the edge line of the surface to be extended, which is the input element in step 2; 1-6. Extend the i-th curve in the section group of the surface to be extended by taking the extension point established in step 1-5 as the boundary, and extend the curve by tangent. The extension length is the parameter CL input in step 3, and establish the i-th tangent extension curve. 1-7. Extend the curvature of the i-th curve in the section group of the surface to be extended, taking the extension point established in step 1-5 as the boundary, and extend the curve with the extension length of the parameter CL input in step 3, and establish the i-th curvature extension curve. 1-8. Take the i-th tangent extension curve and the i-th curvature extension curve, and input the surface extension ratio CR according to step 3 to establish the i-th variable ratio extension curve; 1-8-1. The extension curve of the i-th tangent line contains m points evenly distributed at its endpoints, where m is a positive integer and m>2; 1-8-2. The i-th curvature extension curve contains m points with endpoints evenly distributed; 1-8-3. Establish a loop variable j, where j is a positive integer, initially set to 1, with a step size of 1, and a value range of (1, m). 1-8-4. Connect the j-th point on the i-th tangent extension curve with the j-th point on the i-th curvature extension curve to establish a straight line, and establish the j-th variable ratio control point on the straight line starting from the j-th point on the i-th tangent extension curve according to the surface extension ratio CR. 1-8-5. Repeat steps 1-8-3 to 1-8-4 to connect the variable ratio control points in the order of variable j to establish the i-th variable ratio extension curve; 1-9. Repeat steps 1-4 to 1-8 to complete the establishment of variable ratio extension curves for all curves in the section group of the surface to be extended; 1-10. Using the variable ratio extension curve of the curve established in steps 1-9 as the cross-section line, and the edge line of the surface to be extended (input element in step 2) as the guide line, construct the surface to complete the variable ratio automatic extension modeling of the surface to be extended.

[0006] The beneficial effects of this invention are as follows: It proposes an automatic surface extension method with variable ratio in a 3D CAD environment. Based on the user's element selection and parameter input of the surface to be extended, it utilizes software programming to automatically determine and model the equally divided sections in 3D CAD software, calculate and model the variable ratio extension curve of the section's equally divided lines, and automatically extend the surface with variable ratio. This solves the problems of extension errors and insufficient extension dimensions during the surface extension process. Furthermore, this automatic surface extension method with variable ratio in a 3D CAD environment proposes an intermediate state between tangent extension and curvature extension through the calculation and modeling of the variable ratio extension curve. This method effectively solves the problems of poor curvature preservation, insufficient curvature extension, and distortion in tangent extensions, significantly reducing design complexity and enabling standardized software design and explicit expression of design experience. Furthermore, based on adjustments to the extension ratio data, it allows for the creation of multi-state surface extensions in tangent and curvature extensions. This method has broad applicability, suitable for surface extension designs of any complexity, and its clear approach and rigorous logic provide a new and effective way to achieve high-quality, efficient, and standardized surface configuration design. Attached Figure Description

[0007] Figure 1This is a schematic diagram of the surface model to be extended; Figure 2 This is a schematic diagram of a model with equally divided cross-section lines; Figure 3 This is a schematic diagram of a variable ratio extension curve model; Figure 4 This is a schematic diagram of an automatic extension model for curved surfaces with varying ratios. The numbers in the figure are explained as follows: 1-Surface to be extended, 2-Edge line of surface to be extended, 3-Left edge line, 4-Right edge line, 5-Left edge plane, 6-Right edge plane, 7-Sectional plane, 8-Sectional line, 9-Extension point, 10-Tangent extension curve, 11-Curvature extension curve, 12-Variable ratio control point, 13-Variable ratio extension curve, 14-Automatic variable ratio extension of surface. Detailed Implementation

[0008] according to Figures 1-4 An automatic surface extension method with varying ratios in a 3D CAD environment includes the following steps: Step 1. Open the model of the surface to be extended (1) in the 3D CAD software; Step 2. In the 3D CAD software, manually select the following elements from the model of the surface to be extended: 1. Surface to be extended; 2. Edge line of the surface to be extended; 3. Left edge line adjacent to the extended edge; 5. Left edge plane; 4. Right edge line; 6. Right edge plane. Step 3. Enter the number of extended surface sections CN, the surface extension ratio CR, and the surface extension length CL in the user interface; Where CN is an integer, CN≥1; CR is a decimal, 0 ≤ CR ≤ 1; CL is a positive number, 0 <CL; In this embodiment, CN=2, CR=0.6, and CL=300mm are respectively set; Step 4. By writing a program to read the elements input in Step 2 and the parameters input in Step 3, the variable ratio automatic extension of the surface to be extended is completed in the 3D CAD software. As described above, a method for automatically extending a surface to be extended at a variable ratio in 3D CAD software by writing a program includes: establishing a cross-sectional dividing plane of the surface to be extended, a cross-sectional group of the surface to be extended, a variable ratio extension curve, and finally completing the automatic extension of the surface to be extended at a variable ratio. The design method includes the following steps: 1-1. Using the left edge plane 5, the right edge plane 6, and the number of cross sections CN=2, establish the cross section dividing plane 7; 1-1-1. Measure the angle plna between the left edge plane 5 and the right edge plane 6 using a measurement function. In this embodiment, plna = 0°. 1-1-2. Determine the value of the plane angle plna, and classify and establish the planes that equally divide the cross-section 7; 1-1-2-1. When plna=0, establish a cross-section dividing plane 7 from the left edge plane 5 according to the cross-section number CN=2 to the right edge plane at equal distances; 1-1-2-1-1. The distance plndis between the left and right edge planes is measured using a measurement function. In this embodiment, plndis = 2217 mm. 1-1-2-1-2. Starting from the left edge plane 5, offset by a distance plndis to establish an offset trial plane; 1-1-2-1-3. Measure the distance trydis between the offset trial plane and the right edge plane 6 using a measurement function. In this embodiment, trydis = 0 mm. 1-1-2-1-4. When trydis=0, establish the correction parameter disk=1; 1-1-2-1-5. Establish a loop variable disi, where disi is a positive integer, initially 1, with a step size of 1, and a value range of (1, CN=2). 1-1-2-1-6. Offset the left edge plane 5 by disk*disi*plndis / (CN+1)=1*disi*2217 / (2+1)= disi*739 distance to establish the disi-th equally divided plane; 1-1-2-1-7. Repeat steps 1-1-2-1-5 to 1-1-2-1-6. Complete the process of creating the cross-section dividing plane by equal distances. 7; 1-2. Create two equally divided section lines 8 by intersecting the established cross-section plane 7 with the input element to be extended surface 1; 1-3. Create a section group for the surface to be extended by combining the left edge line 3, the right edge line 4, and the equally divided section line 8 of the input element; 1-4. Establish a loop variable i, where i is a positive integer, with an initial value of 1, a step size of 1, and a value range of (1, CN+2=4). 1-5. Establish extension point 9 by intersecting the i-th curve in the section group of the surface to be extended with the edge line 2 of the input element surface to be extended; 1-6. Using the extension point 9 established in step 1-5 as the boundary, extend the i-th curve in the section group of the surface to be extended by tangent. The extension length is the input parameter CL=300mm, and the i-th tangent extension curve 10 is established. 1-7. Using the extension point 9 established in step 1-5 as the boundary, extend the curve of the i-th curve in the section group of the surface to be extended. The extension length is the parameter CL=300mm input in the middle, and the i-th curvature extension curve 11 is established. 1-8. Extend the i-th tangent curve 10 and the i-th curvature curve 11, and input the surface extension ratio CR=0.6 in step 3 to establish the i-th variable ratio extension curve 13; 1-8-1. The i-th tangent extension curve 10 contains m points evenly distributed at its endpoints, where m is a positive integer and m>2. In this embodiment, m=4. 1-8-2. The i-th curvature extension curve 11 contains m=4 points with endpoints evenly distributed; 1-8-3. Establish a loop variable j, where j is a positive integer, initially set to 1, with a step size of 1, and a range of values ​​of (1, m=4). 1-8-4. Connect the j-th point on the i-th tangent extension curve 10 with the j-th point on the i-th curvature extension curve 11 to establish a straight line, and establish the j-th variable ratio control point 12 on the straight line starting from the j-th point on the i-th tangent extension curve 10 according to the surface extension ratio CR=0.6; 1-8-5. Repeat steps 1-8-3 to 1-8-4 to connect the variable ratio control points 12 in the order of variable j to establish the i-th variable ratio extension curve 13; 1-9. Repeat steps 1-4 to 1-8 to complete the establishment of variable ratio extension curve 13 for all curves in the section group of the surface to be extended; 1-10. Using the variable ratio extension curve 13 of the curve established in steps 1-9 as the cross-section line, and the edge line 2 of the input element to be extended surface as the guide line, construct the surface and complete the automatic construction of the variable ratio extension surface 14 of the surface to be extended.

[0009] This invention proposes an automatic surface extension method with variable ratio in a 3D CAD environment. Based on the user's element selection and parameter input for the surface to be extended, it utilizes software programming to automatically determine and model the equally divided sections in 3D CAD software, calculate and model the variable ratio extension curve of the section dividing line, and automatically extend the surface with variable ratio. This solves the problems of extension errors and insufficient extension dimensions during the surface extension process. This method, through the calculation and modeling of the variable ratio extension curve, proposes an intermediate state between tangent extension and curvature extension, effectively solving the problems of poor curvature retention and insufficient curvature extension and distortion in tangent extension. This effectively reduces the design difficulty and realizes standardized software design and explicit expression of design experience. Furthermore, based on the adjustment of the extension ratio data, it can realize the creation of multi-state surface extension surfaces in tangent extension and curvature extension. This method has wide applicability and is suitable for surface extension designs of any complex form. Its approach is clear and logically rigorous, providing a new and effective way to achieve high-quality, efficient, and standardized surface configuration design.

Claims

1. A method for automatic extension of curved surfaces with varying ratios in a 3D CAD environment, characterized in that, include: Step 1: Open the surface model to be extended in 3D CAD software; Step 2: In the 3D CAD software, select the surface to be extended, the edge line of the surface to be extended, the left edge line adjacent to the extended edge, the left edge plane, the right edge line, and the right edge plane in the surface model to be extended; Step 3: Input the number of extended surface sections CN, the surface extension ratio CR, and the surface extension length CL in the user interface. Where CN is an integer, CN≥1; CR is a decimal, 0 ≤ CR ≤ 1; CL is a positive number, 0 <CL; Step 4: Read the elements input in Step 2 and the parameters input in Step 3, and complete the automatic extension of the surface to be extended by a variable ratio in the 3D CAD software.

2. The automatic extension method for curved surfaces with varying ratios in a three-dimensional CAD environment according to claim 1, characterized in that, The automatic extension of the surface to be extended by variable ratio in 3D CAD software is achieved by: modeling the cross-section of the surface to be extended in equal planes, modeling the cross-section group of the surface to be extended, modeling the variable ratio extension curve, and finally completing the automatic extension of the surface to be extended by variable ratio based on the modeling of the variable ratio extension curve.

3. The automatic extension method for curved surfaces with varying ratios in a three-dimensional CAD environment according to claim 2, characterized in that, Step 11. Using the left edge plane, the right edge plane, and the number of sections CN, establish the planes that divide the sections equally; Step 12. Intersect the established cross-section dividing plane with the surface to be extended to create CN equally divided cross-section lines; Step 13. Create a section group for the surface to be extended by using the left edge line, right edge line, and equally divided section lines; Step 14. Create a loop variable i, where i is a positive integer, with an initial value of 1, a step size of 1, and a value range of (1, CN+2). Step 15. Establish an extension point by intersecting the i-th curve in the section group of the surface to be extended with the edge line of the surface to be extended; Step 16. Extend the i-th curve in the section group of the surface to be extended by taking the extension point established in Step 15 as the boundary, and extend the curve by tangent with the extension length as parameter CL, and establish the i-th tangent extension curve. Step 17. Extend the curvature of the i-th curve in the section group of the surface to be extended, with the extension point established in Step 15 as the boundary, and the extension length is parameter CL, to establish the i-th curvature extension curve. Step 18. Combine the i-th tangent extension curve and the i-th curvature extension curve with the surface extension ratio CR to create the i-th variable ratio extension curve; Step 19. Repeat steps 14 to 18 to complete the establishment of variable ratio extension curves for all curves in the section group of the surface to be extended; Step 20. Using the variable ratio extension curve of the curve established in Step 19 as the cross-section line, and the edge line of the surface to be extended (input element in Step 2) as the guide line, construct the surface to complete the variable ratio automatic extension modeling of the surface to be extended.

4. The automatic extension method for curved surfaces with varying ratios in a three-dimensional CAD environment according to claim 3, characterized in that, The method of establishing cross-sectional dividing planes using the left edge plane, right edge plane, and cross-section quantity CN involves the following steps: By measuring the angle between the left edge plane and the right edge plane, cross-sectional dividing planes are established according to their classification. Step 21. Measure the angle plna between the left edge plane and the right edge plane using the measurement function; Step 22. Determine the value of the plane angle plna, and classify and establish the planes that divide the cross section equally; Step 22-1. When plna=0, establish a cross-section dividing plane from the left edge plane to the right edge plane according to the number of cross-sections CN, dividing the cross-sections equally by distance; Step 22-2. When plna≠0, establish a plane for dividing the cross-section equally from the left edge plane according to the number of cross-sections CN to the right edge plane by equal angles.

5. The automatic extension method for curved surfaces with varying ratios in a three-dimensional CAD environment according to claim 4, characterized in that, When plna=0, the process of establishing a cross-section dividing plane from the left edge plane according to the cross-section number CN to the right edge plane by equal distances, and establishing the cross-section dividing plane by equal distances through the trial and error plane, includes the following steps: Step 31. Measure the distance plndis between the left edge plane and the right edge plane using the measurement function; Step 32. Start from the left edge plane and offset by a distance plndis to establish an offset trial plane; Step 33. Measure the distance trydis between the offset trial plane and the right edge plane using the measurement function; Step 34. When trydis=0, set the correction parameter disk=1; when trydis≠0, set the correction parameter disk=-1. Step 35. Create a loop variable disi, where disi is a positive integer, initially 1, with a step size of 1, and a value range of (1, CN). Step 36. Offset the left edge plane by a distance of disk*disi*plndis / (CN+1) to establish the disi-th equally divided plane; Step 37. Repeat steps 35 to 36 to complete the creation of the cross-section dividing plane by equal distance.

6. The automatic extension method for curved surfaces with varying ratios in a three-dimensional CAD environment according to claim 4, characterized in that, When plna≠0, the process of establishing a cross-section dividing plane by dividing the cross-section from the left edge plane to the right edge plane by equal angles according to the number of cross-sections CN, and establishing the cross-section dividing plane by equal angles through a trial-and-error plane, includes the following steps: Step 41. Measure the angle plnangle between the left edge plane and the right edge plane using the measurement function; Step 42. Establish the intersection line of the two end faces by intersecting the left edge plane and the right edge plane; Step 43. Rotate the left edge plane by a factor of plnangle about the intersection of the two end faces to create a rotational trial-and-error plane; Step 44. Measure the angle tryangle between the rotated trial plane and the right edge plane using the measurement function; Step 45. When tryangle=0, adjust parameter anglek=1; when tryangle≠0, adjust parameter anglek=-1. Step 46. Create a loop variable anglei, where anglei is a positive integer, initially 1, with a step size of 1, and a value range of (1, CN). Step 47. Rotate the left edge plane around the intersection of the two end faces as the axis of rotation. Anglek*anglei*plnangle / (CN+1) degrees are used to establish the i-th equally divided plane; Step 48. Repeat steps 46 to 47 to complete the creation of the cross-section dividing plane by angle.

7. The automatic extension method for curved surfaces with varying ratios in a three-dimensional CAD environment according to claim 2, characterized in that, The i-th tangent extension curve and the i-th curvature extension curve are combined to create the i-th variable ratio extension curve according to the surface extension ratio CR, which includes the following steps: Step 51. Extend the curve of the i-th tangent line to include m points evenly distributed at the endpoints, where m is a positive integer and m>2; Step 52. The i-th curvature extension curve contains m points with endpoints evenly distributed; Step 53. Create a loop variable j, which is a positive integer with an initial value of 1, a step size of 1, and a value range of (1, m). Step 54. Connect the j-th point on the i-th tangent extension curve with the j-th point on the i-th curvature extension curve to establish a straight line, and establish the j-th variable ratio control point on the straight line starting from the j-th point on the i-th tangent extension curve according to the surface extension ratio CR. Step 55. Repeat steps 53 to 54 to connect the variable ratio control points in the order of variable j to establish the i-th variable ratio extension curve.

8. The automatic surface extension method with varying ratios in a three-dimensional CAD environment according to claim 7, characterized in that, The method further includes: using the established variable ratio extension curve as the cross-section line and the edge line of the surface to be extended as the guide line to construct a surface, thereby completing the automatic construction of the variable ratio extension surface of the surface to be extended.

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