VALIDATION OF 3-D CURVED OBJECTS - CAD MODEL AND FABRICATED WORKPIECE

This paper proposes a new method to describe and identify a 3-D curved object for the purpose of validating a fabricated object to the desig n specification. Curved 3-D objects are, in general, difficult to repr esent and identify because they lack distinct properties such as edges , planes, or cylindrical surfaces which are the building blocks in rep resenting objects. In this paper, we propose to use principal axes of a 3-D object to establish a reference for the representation. A method of obtaining an inertia matrix from a 3-D range image is developed. T he unique set of principal axes is obtained from the inertia matrix of an object with an arbitrary 3-D position and orientation, and the obj ect can be described uniquely on these principal axes. On the principa l axes, an object is described by a set of features describing the sha pe of the object such as spine, section size, section orientation, and section contraction. The features are used for comparing two objects for the validation purpose. We also propose a direct measure of simila rity between two objects as a mean-squared difference of radii. As an experiment, two 3-D object models are designed through a CAD package, and fabricated objects are compared with the designed models for valid ation purposes.