Pattern Recognition of 3D CAD Objects: Towards an Electronic Yellow Pages of Mechanical Parts

Industry estimates show that aggressive reuse of existing inventory could reduce the delivered cost of large, complex manufactured systems by as much as 20%. In most cases these savings are not captured, principally because the current technology to locate reusable designs and inventory, which uses taxonomies and other arti cial indices, is too cumbersome. Furthermore, current systems do not address the design phase where opportunities for reuse rst arise. This paper describes a computer-based technology that will be an important step towards solving this problem. For mechanical parts, the modern design phase starts with computer aided design (CAD) packages. Given a prototype design of a solid object, the design engineer should be able to determine whether the part under consideration is already designed or in manufacture. Our system does this by using physical shape as a direct index to existing designs and manufactured components, eliminating time-consuming and error-prone searches of the taxonomy. Other applications of this technology include identi cation of warehoused parts according to scanned shape and e cient management of 3-dimensional objects in computer animation and virtual reality systems. Our system takes a standard digital representation of a solid object, such as in IGES form, and produces a surface triangular mesh representing the boundary of the object. The surface mesh allows a voxel approximation representation of the solid which is computed by ood lling. Zeroth, rst and second order geometrical moments are used to normalize the orientation of the solid. Then a variety of volumetric invariants are computed and used as features. These features determine a hash function which maps similar shapes to closely related feature vectors. Nearby feature vectors identify a small subset of objects which are compared using symmetric di erencing on a voxel by voxel basis. This voxel symmetric di erence gives a rank ordering of similarity between 3-dimensional shapes in the database and the object under consideration. Using this small subset of like-shaped objects, the design engineer can browse a reasonable subset of parts from the complete database. The described research has signi cant applications in industries which seek to reuse existing designs and inventory thereby reducing manufacturing costs. Applications in aerospace, automobile and machine tool industries are most promising and urgent. We expect that this research will lead to the commercial development of software that will enhance existing CAD and database systems.