Hierarchical Control of End-Point Impedance and Joint Impedance for Redundant Manipulators

This paper proposes an impedance control methodfor redundant manipulators, which can control not only the endpointimpedance using one of the conventional impedance controlmethods, but the joint impedance which has no effects on theend-point impedance. First, a sufficient condition for the jointimpedance controller is derived. Then, the optimal controller fora given desired joint impedance is designed using the least squaresmethod. Finally, computer simulations and experiments using aplanar direct-drive robot are performed in order to confirm thevalidity of the proposed method

Multi-Point Impedance Control for Redundant Manipulators

The present paper proposes an impedance controlmethod called the Multi-Point Impedance Control (MPIC) forredundant manipulators. The method can not only control endeffectorimpedance,but also regulate impedances of several pointson the links of the manipulator, which are called virtual endpointimpedances, utilizing arm redundancy. Two approachesfor realizing the MPIC are presented. In the first approach,controlling the end-effector impedance and the virtual end-pointimpedances are considered as the tasks with the same level, andthe joint control law developed in this approach can realize theclosest impedances of the multiple points, including the endeffectorand the virtual end-points to the desired ones in theleast squared sense. On the other hand, in the second approach,controlling the end-effector impedance is considered the mostimportant task, and regulating the impedances of the virtual endpointsis considered as a sub-task. Under the second approach,the desired end-effector impedance can be always realized sincethe joint control torque for the regulation of the virtual end-pointimpedances is designed in such a way that it has no effect on theend-effector motion of the manipulator. Simulation experimentsare performed to confirm the validity and to show the advantagesof the proposed method