Abstract: The modeling method of fixture location error is proposed. By the analysis of location error transmit route, the workpiece-fixture system is defined as a composition of four elements, i.e. machining feature, process datum, location datum and locators. The fixture location errors are obtained by calculating the relative position variations among the four elements. The position variation relationships among the four elements are represented by link mechanism model. The workpiece-fixture system is composed by the contact pair equivalent mechanisms, tolerance equivalent mechanism and process dimension equivalent mechanism. The rules mapping from contact pairs to equivalent mechanism components are established, the modeling methods of the equivalent mechanisms of tolerance and process dimension are proposed, here, tolerance mechanism reflects the relationships between process datum and location datum, and process dimension mechanism embodies the relationship between process datum and machined surface, and the approaches to using mechanism structure & motion parameters to represent the process information and the inner relationship of workpiece-fixture system are explored. According to the mapping rules mentioned above, the equivalent mechanism model is established automatically, and the automatic solution of location error can be realized by means of the position calculation methods of mechanism.

Key words: Automated modeling, Equivalent mechanism, Location errors, Mapping ruies