| Automated fixture analysis and planning are essential for unmanned manufacturing, particularly in small-batch machining and assembly. However, fixturing and fixture planning are among the least solved challenges facing unmanned, flexible manufacturing systems today. This thesis presents automated fixture analysis and planning as a component of a computational system for concurrent product and process design. The system is responsible for determining sets of fixturing arrangements to restrain and locate parts as they are machined. A set of rules and procedures provides the fixture agent with spatial and geometric reasoning capabilities (e.g., checking for accessibility and interference) and for choosing fixtures from a small library. The system also checks whether a fixture arrangement can fully locate and restrain a part by computing whether the set of contacts achieves kinematic form closure and force closure.;To properly handle more complex parts, the fixture agent is designed to be able to reason at different levels of detail, employing fast geometric checks at the most superficial level and more time-consuming force and friction analyses at a deeper level, depending on the completeness of the machining plan. The focus of this thesis is on the approaches used for analyzing fixture kinematics and clamping forces, including the analysis of friction. Since many fixture arrangements rely on friction, the ability to reason about friction is an important component of fixture planning. Limit surfaces in force/moment space are introduced as a convenient formalism to check whether parts will slip and to help in specifying clamping forces.;The final section of this thesis discusses the issues involved in turning a set of analysis programs and rules into an agent that can interact continually with other modules of a concurrent design system. A key aspect of the approach is to maintain a graph of dependencies among fixturing arrangements, machined features and geometric elements so that the effects of minor changes in the part geometry can rapidly be assessed, without computing a new fixture plan from scratch. |
