Reliability and flexibility-a mutually exclusive problem for robotic assembly?

One problem often encountered when performing assembly using robots is how to deal with variation and uncertainty in the workcell. Either the workcell becomes tightly constrained, thus losing the flexibility of the system, or errors occur, which reduces the reliability of the system. This paper attempts to address this problem using a hybrid architecture. A planning system produces a high-level ordering of the assembly in terms of part motions, which are translated into robot motions by an adaptive run-time execution system. The execution system contains a flexible hierarchy of competent modular units which combine to perform the assembly reliably. The work in this paper attempts to reduce the complexity found in assembly planning and to provide a reactive run-time system which can deal with uncertainty and variation without reference to a computationally expensive global-world model. The background to this work is presented, along with an experimental system designed to test out the ideas. Conclusions about the usefulness of the system are drawn at the end of the paper.