On path errors of redundant robots in fault tolerant operations for locked joint failures

While a redundant robot is still able to continue the desired task in the presence of locked joint failures, its end-effector error both at the instant of locking joint and in post-failure operations will increase obviously. This work discusses the path error of a redundant robot in fault tolerant operations for locked-joint failures. First, the analytical formula of the optimal joint velocity with minimum jump is derived, and a new fault tolerant algorithm with the minimum jump is proposed. Then, the jump difference between the minimum jump solution and the least-norm velocity solution is mathematically analyzed. Finally numerical simulations and experimental studies are implemented with a planar 3R robot for the two algorithms. Study results indicate that the increase of the path error at the instant of locking joint mainly depends on the joint velocity jump; the increase of the path error in post-failure operations mainly depends on the joint velocity of the reduced robot. The new algorithm proposed in this paper can be used to reduce the path error at the instant of locking joint.