Fault tolerance for kinematically redundant manipulators: anticipating free-swinging joint failures

Fault tolerance is an important design criterion for robotic systems operating in hazardous or remote environments. This article addresses the issue of tolerating a free-swinging joint failure by focusing on how to best configure a slow-moving manipulator before a failure. Three scalar measures of fault susceptibility are defined using joint torques/forces, accelerations, and swing angles. Minimizing these measures is an approach to achieving fault tolerance, and for this, algorithms to calculate their gradients are also given. The formulas are valid for general n-link manipulators.