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An impedance controller for industrial manipulators is presented in this paper. Special attention has been paid to all the aspects that qualify an industrial robot, including decentralized proportional-integral-derivative position control, torsional flexibility, and friction at the joints. A discussion of a single-degree-of-freedom (DOF) case is first presented. The selection of the impedance parameters is based on the behavior in contact and makes reference to a new design parameter, the compliance bandwidth. The single-DOF analysis is then used in the design of the impedance controller for a complete manipulator. A rotational impedance based on a geometrically consistent representation of the orientation is used. Several experimental results obtained on a 6-DOF industrial robot, equipped with a force/torque sensor, are presented. The experiments show the effectiveness of the proposed approach in several conditions, including contact with an extremely stiff surface and noncontact/contact transition.
Ferretti et al. (Tue,) studied this question.