Free-form Surface Matching Technology Research

Free-form surface is widely used in mold, shipbuilding, automobile, aerospaceand other fields, it is known for its complicated surface shape. The difficulty ofmanufacture and testing for freeform surface is far greater than ordinary surface. Ithas now become a research hotspot in the field of modern manufacturing. Currentlythe universal standard or technology for free curved surface allowance analysis andsurface shape accuracy detection has not been made,which affected the promotion offreeform surface to a certain extent. The surface matching technique is the premise ofmachining allowance, profile detection and error evaluation for free-form surface. Thetechnology has important theoretical significance and practical application value topromote the development of free surface manufacturing and testing, and importantapplication in reverse engineering, pattern recognition, computer vision,photogrammetry and other fields at the same time. The further research on the theoryand its engineering application has been made in this paper.The key links of the free-form surface matching technology--the nearest pointcalculation method of free-form surface in different representation is studied.Respectively, studied the nearest point between the point and the discrete point cloud,the nearest point from points to the triangular mesh polyhedron and the nearest pointbetween the point and parametric surface. Based on the nearest point calculationmethod between the point and the discrete point cloud in the surface, the distancefrom points to the triangular mesh polyhedron is calculated. After analyzing on thecalculation method of the nearest point to parametric surfaces, a new nearest pointcalculation method of points to the B-spline surface combining grid method anditerative method is proposed, which is commonly applied to the distance calculationof bicubic B-spline surface.The unified mathematical model is established according to the matchingproblem of the free-form surface. Two kinds of matching problems are respectivelydiscussed around whether the surface is constrained. The unconstrained matching isrealized based on initial matching of Hausdorff distance and the optimization ofmatching for improved iterative nearest point algorithm, which the curvature index is introduced into the matching technology for the first time according to the geometricinvariance of surfaces.The constrained matching is solved by combining the improvedgenetic algorithm. The simulation analysis and experiments verification of surfacematching between surface discrete point cloud and surface discrete point cloud, pointcloud and the triangle mesh polyhedron, point cloud and the B-spline surface areaccomplished.Using the free-form surface related matching technique and theory verified thepoint-cloud split between local overlapping multiple segmentation surface, surfacequality evaluation, auto-alignment and other fields, which shows that the technologyin more extensive field has a certain universality and feasibility, and practicalapplication value in engineering field.With the blade which is a typical free-form surface as the experimental object,the experimental verification is carried out relying on the blade measurementexperimental platform. The matching is accomplished between measurement pointsand the CAD model,and the regional deviation of blade surface is quantitativeaccounted. On the basis of polyhedron method, the machining path is planned, thetrack point allowance is calculated and the corresponding GUI interface is developedwith MATLAB platform.