Design rules for tolerance-insensitive and multi-purpose fixtures

The manufacturing and installation of fixtures in a factory can be costly, especially for high-volume production runs. Once fixtures are installed, part shape can vary due to: (1) tolerance variations because of inherent imprecision 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 fixture for all variations of part shape. In this paper we address both types of variation in the context of modular fixtures. For tolerance variation (1), we give a method for comparing fixtures 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 fixture. The idea behind the design rule is that it can be incorporated into the CAD design cycle to rapidly evaluate manufacturability in a manner analogous to the geometric design rules so successful in VLSI design. We also present an efficient algorithm to find multipurpose fixtures that can fixture multiple distinct parts, using the geometric hashing technique