Actuator limitations on achievable manipulator impedance

The effects of actuator torque/speed constraints on achievable manipulator mechanical impedance are discussed. Beginning with a simplified dynamic model, a describing function analysis is used to examine the constraints for linear behavior as well as the effective closed-loop impedance resulting from the actuator nonlinear characteristics. It is shown that the closed-loop manipulator impedance is a blend of two extreme impedances, and the degree of nonlinearity in the actuator controls the proportion of these two components in the overall dynamic response. The extension to multiple-degree-of-freedom manipulators is also discussed, revealing behavioral properties similar to the single-degree-of-freedom case. The relevance of this simple analysis to manipulator system preliminary design and feasibility studies is stressed