A framework for assembly sequence planning for computer aided design of mechanical assemblies

Abstract

This thesis presents a framework for interactive assembly sequence panning for mechanical assemblies. Realizing the utility of such a tool that will enable the product engineer to evaluate the assemblability of his designs and generate suitable assembly sequences, many systems have been developed by beseechers all over the world. The input to these system is a model of the assembly and the output is a set of feasible assembly sequences. The system needs a geometric reasoning capacity to aid this process. The research issue is to devise a framework that preserves design rationale and utilizes all the available assembly information to optimize the assembly planning process, reduce the computational complexity associated with extensive geometric reasoning and represent the constraints in the assembly in a manner that is easy to interpret. This thesis contributes to simplification of the assembly sequence planning by developing a framework to represent and input vital information regarding implicit precedence relationships, directionality and base-part assumptions to the planner. This is achieved by generating three graph structures: an Abstract Assembly Graph, a FinalPrecedence Graph and a Diamond Graph. Extensive autistic geometric reasoning required to reason about the feasibility of assembly operation is often expensive and time consuming and is therefore replaced with a user interface. A question-answer session with the designer to reason about the assemblability will also help in incorporating additional information other than geometric feasibility constraints into the planning process. The process of finding constraints in the assembly is further streamlined by taking a hierarchical approach to set up precedence among all the assembly operations needed to generate the complete assembly. Preserving and utilizing the precedence information from one level to the next in a hierarchy drastically reduces the number of queries needed to find out all the precedence relationships in the assembly. Finally, all the constraint information is represented using a Final Precedence Graph. The Final Precedence Graph serves as the input to the generation of all the feasible assembly sequences that are then represented using a Diamond Graph.