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Zero-Potential-Energy Motions due to Stiffness in Impedance Control of Robotic Tasks: an Innovative Theory and Experimental Study

This paper presents an analytical methodology and experimental study to identify quantitatively the zero-potential-energy (ZP) motion due to the stiffness matrices in Cartesian impedance control of redundant manipulators. This mode of motion, analogous to the rigid-body mode in classic mechanical systems, shows up as a result of the redundancy of the robot and creates a steady-state deviation from its initial configuration after it reaches equilibrium when subject to a perturbation, because of the principle of least energy for dynamic systems. We determine such ZP motion(s) by utilizing a vibration-based closed-form solution recently developed. We identify and provide experimental validation of the existence of the ZP motions on a 7 DoF Panda robot.