Robust Internal Force-tracking Impedance Control for Coordinated Multi-arm Manipulation - Theory and

Robust internal-force impedance control has been shown to be an effective control strategy for coordinated multiple-arm manipulation. It enforces a relationship between the the velocity of each manipulator and the internal force on the manipulated object and does not require knowledge of the object dynamic model. Each manipulator's nonlin-ear dynamics is compensated by a robust auxiliary controller which is insensitive to robot-model uncertainty and payload variation. For accurate force tracking, exact knowledge of the kinematic models of the manipulators and the object and the transformations between the manipulator base frames is required. Errors in the kinematic models can cause steady-state internal force errors which are proportional to the kinematic error and the desired manipulator stiiness. In this paper , we introduce an internal force-tracking impedance controller which compensates for kinematic uncertainty and regulates the desired internal force error to zero. Conditions for stability visa -vis the controller gains are derived which are independent of the environmental stiiness. Experiments are conducted on a dual-arm system which validate the proposed algorithm.