Torque redistribution method for fault recovery in redundant serial manipulators

As a robot loses some of its capabilities due to component failure, fault-tolerant controllers isolate the faulty unit and complete the task with minimum performance loss. However, as the robot undergoes a failure and accumulates large errors, controller torque requirements usually increase and may even exceed actuator capacities. This problem can be avoided in redundant serial manipulators if the redundancy of the system is exploited to redistribute the actuator torques. This is accomplished by implementing the controller in the end-effector space. The computed torque method and PID feedback control are used in the controller. When torque demand on an actuator exceeds the allowable limit, that actuator is isolated and the required load is distributed among the remaining actuators. This controller not only avoids the saturation problem, but also allows the robot to eliminate errors and track the original trajectory. Application of the method is demonstrated on a four degree-of-freedom serial manipulator