Designing a Failure-Tolerant Workspace for Kinematically Redundant Robots

Kinematically redundant manipulators are inherently more robust to locked joint failures than non-redundant manipulators. However, if poorly designed, performance degradation may still occur in the presence of a single locked joint. This paper presents a technique for designing a desired operating workspace for a kinematically redundant manipulator that can be guaranteed after the occurrence of an arbitrary single locked joint failure. The existence of such a workspace, called a failure-tolerant workspace, will be guaranteed by imposing a suitable set of artificial joint limits prior to a failure. Conditions are presented that characterize end-effector locations within the failure-tolerant region. Based on these conditions, an algorithm for computing the failure-tolerant workspace is presented. The algorithm is based upon identifying the boundaries of the failure-tolerant workspace. Examples are presented to illustrate the application of the proposed algorithm to various manipulator design problems.