On replanning for assembly tasks using robots in the presence of uncertainties

High-precision assembly tasks cannot be successfully done by robots without taking into account the uncertainties that can cause failure of robot motion. The authors address this problem by planning robot motions at two levels: nominal planning, which assumes no uncertainty, and dynamic replanning, to deal with uncertainties that would cause nominal plans to fail. They introduce a replanning approach based on knowledge of contacts among assembly parts. It consists of patch planning to resolve the case when a commanded robot motion prematurely stops at a contact other than those planned, and motion strategy planning, to regulate robot motions in order to guarantee the eventual success of a task. A task-independent strategy for patch-plan generation based on concepts of contact planes and abstract obstacles is developed. It is also shown how to apply motion strategies so that, under proper design and motion constraints, the replanning can be guaranteed to succeed