Smoothing Method Of Class A Surfaces For Auto-Body Based On Boundary And Curvature Of Cloud Points

Smooth and fluent contour is the key factor for automotive products to survive in the fierce market competition, so smoothing technologies of class A surfaces for Auto-body are supposed to be more efficient. Although much theoretical research on surfaces smoothing has been done by domestic and foreign scholars, the practical application on smoothing for Auto-body was still at a low level. Therefore, how to smooth class A surfaces efficiently and high-quality is a difficult problem that smoothing engineers have to face.Aiming at the above problems, research on the smoothing method based on boundary and curvature of cloud points has been presented in the paper. Specific research contents are as follows:(1) An reverse algorithm for control vertex of Bezier surface has been improved through classifying the parameter values of characteristic points that used to construct interpolation surfaces according to whether the parameter values in u, v direction is equal to zero, which improved the stability of reverse algorithm and made it easily programmed.(2) An algorithm of extracting boundary points from the cloud points has been presented in order to overcome the problem that the surface fitted from cloud points directly can not satisfy the border characteristics of the cloud points. In order to increase the efficiency of the boundary points extraction algorithm, the space points have been projected on a plane and the bounding box of the plane points which will be divided into several small grids has been built, then a magnitude algorithm can be used to extract the boundary points from the boundary grid.(3) An algorithm that can make the searched characteristic points distributed evenly according to the curvature of cloud points has been given. Plane mesh intersections have been built and the relation between space cloud points and plane mesh intersections have also been built, then the plane mesh intersections can be moved to adjust the position of characteristic points that used to construct interpolation surfaces. A method that can divide string lengths between characteristic points in each row or column has been used to adjust the position of plane mesh intersections in order to make the characteristic points selected satisfy the curvature feature of the cloud points.(4) An algorithm that used to smooth Class A surfaces for Auto-body based on boundary and curvature of cloud points has been realized in VC++language, and the smoothing module has been integrated into the UG software with the help of Interface Techniques between VC++and UG software, which can improve the automation level for Auto-body Class A surface.Through the examples validating for the smoothing module, conclusions as follows have been drawn:Surfaces smoothed by this smoothing module satisfy the requirements of Auto-body Class A surface for the cloud points with gentle curvature; For cloud points with large curvature changes or transitional surfaces, this module can reconstruct surface easily and conveniently, and save time for later artificial interactive operation and improve the smoothing quality and efficiency for Auto-body Class A surface.