Null Torque based Dynamic Control (NTDC) for Kinematically Redundant Manipulators

This paper presents a new control method for redundant manipulators, named the "Null Torque based Dynamic Control," which can guarantee stability for joint torques. The proposed method resolves the redundancy at the torque level. The command torque induced by the proposed method is composed of the two terms: 1) the minimum-norm torque which locally minimizes torque loadings at the joints and 2) the null torque which is intermittently added to the minimum-norm torque according to a kinematic criterion to globally reduce excessively large torque requirements. In particular, the concept of null torque is based on the property of full row-rank minors for a Jacobian matrix - the aspect which is a function of a manipulator's configuration. The simulation results illustrate that the proposed method is effective for torque optimization when compared with conventional methods.