Design Rules for Tolerance-Insensitive and Multi-purpose Fixtures

The manufacturing and installation of xtures in a factory can be costly, especially for high-volumeproduction runs. Once xtures are installed, part shape can vary due to: (1) tolerance variations because of inherent im-precision in manufacturing processes, and (2) redesign. Variations of type (1) occur constantly and are usually small; variations of type (2) can be large but occur at few distinct points in the product life cycle. For both cases, it is often desirable to reuse one xture for all variations of part shape. In this paper we address both types of variation in the context of modular xtures. For tolerance variation (1) , we give a method for comparing xtures in terms of how much geometric tolerance they will permit before failing. For design variation (2), we identify design rules that can rapidly check if a proposed part design is consistent with a given previous xture. The idea behind the design rule is that it can be incorporated into the CAD design cycle to rapidly evaluate manufactura-bility in a manner analogous to the geometric design rules so successful in VLSI design. We also present an eecient algorithm to nd multipurpose xtures that can xture multiple distinct parts, using the geometric hashing technique 10, 11].