Key Technologies Research On On-line Inspection System For NURBS Surface Based On IGES

Free-form surface in the fields of aviation, aerospace, shipbuilding, mold, automotive attaches great importance and rapid development. In order to meet the application requirements of the surface, the researchers have in-depth study from shape description, modeling methods, mechanical processing and testing of free-form surface. Free-form surface online detection, base on hardware platform mainly composed of CNC equipment and probe, improve the detection efficiency and reduce testing costs, but the detection precision is comparable with the CMM and other offline detection. NURBS method is the major form of free-form surface in description of industrial products geometry. In this paper, the authors have in-depth study to some key technologies of on-line inspection system for NURBS-surfaces base on IGES. The main contents include four key question.1. Base on the information carrier: IGES, establish the technical route and propose the scheme for on-line inspection system of NURBS surface.2. Development of IGES postprocessor. Base on depth study on IGES structure and analyzing the topology of the entity records, extract information about the visible geometric entities and store information about trimmed NURBS surfaces with a good data structure. The IGES postprocessor is mainly used for successfully extract the information of IGES V5.2/5.3.3. Visualization and Human-computer interaction with OpenGL platform. Complete visualization of trimmed NURBS surfaces. Realize the basic operation of the view, such as rotation, zooming and translation. Complete the pickup point in the viewport, and transform window coordinate(x,y) into object coordinate(x,y.z) of this point on the model. With the help of picking, achieve the editing functions of adaptive planning points to improve the quality of the set of measurement points.4. Radius compensation and path planning of measurement points. By exploring and demonstrating the theory of mathematical description of NURBS surface shape, it’s successful to calculate the normal vector of the NURBS surfaces and complete radius compensation of the adaptive planning point. Design a method named Search Approximation Method, by which it can calculate the normal vector and complete radius compensation of a measurement point only with coordinate(x,y,z) on the NURBS surfaces, and the result is accurate by revising coordinates of measuring point and transfering error. Complete the path planning of measurement points by improved Dijkstra algorithm with thought of linked list, so it improves efficiency of measuring process and the solution process of path planning.