Design of modular fault tolerant manipulators

In this paper, we deal with two important issues in relation to modular recon gurable manipulators, namely, the determination of the modular assembly con guration optimally suited to perform a speci c task and the synthesis of fault tolerant systems. We present a numerical approach yielding an assembly con guration that satis es four kinematic task requirements: reachability, joint limits, obstacle avoidance and measure of isotropy. Further, because critical missions may involve high costs if the mission were to fail due to a failure in the manipulator system, we address the property of fault tolerance in more detail. We prove the existence of fault tolerant manipulators and develop an analysis tool to determine the fault tolerant work space. We also derive design templates for spatial fault tolerant manipulators. For general purpose manipulators two redundant degrees-of-freedom are needed for every order of fault tolerance. However, we show that only one degree of redundancy is su cient for task speci c fault tolerance.