Localization of parts with irregular shape for CMM inspection

The part coordinate setup is a necessary and important step in coordinate measuring machine (CMM) inspection. It usually counts on the precise machining of certain datum features for the determination of the part coordinate. In some manufacturing processes, such as die casting, stamping, pressing, injection, etc., precise machining of the datum features is difficult. Dimensional inspection of such parts, therefore, requires a reliable procedure for the determination of the part coordinate beforehand. The purpose of this study is to propose a new algorithm for the part coordinate setup of irregular shapes. The proposed algorithm is composed of a rough positioning and a fine positioning. The rough positioning is applied to bring the part coordinate into the neighborhood of the model coordinate. The fine positioning is then applied to assure that the part coordinate and the model coordinate match each other perfectly. A standard sphere is used for the verification of the proposed method. Several industrial examples are also presented to illustrate the feasibility of the proposed method.