Passive Mass Reduction in Admittance Control

Admittance control has been used in recent years to reproduce a desired dynamic response on non-backdrivable manipulators. One of the topics of research has been to increase the apparent admittance by reducing the virtual mass. However, mass-reduced admittance controllers become unstable when the environment (e.g. the operator) the robot is interacting with has too high impedance. In this paper, a framework is proposed to guarantee passive interaction between robot and human operator, while attempting to increase admittance as much as possible. An additional adaptive feedforward component is proposed, if direct force control is possible, to increase the apparent admittance further. The proposed framework is tested in simulation and has shown to indeed reduce apparent admittance.