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Absolutely stable model-based 2-port force controller for telerobotic applications

Large industrial-like slave robots pose a challenging problem for telerobotic control designers focused on achieving good transparency. The human operator typically feels both the large friction forces and heavy inertial forces inherent to these robots. Force control can be used to attempt and hide these internal forces from the user, but force control is a challenging design problem, especially in situations like telerobotics where it is not clear what the environmental impedance will be at any given moment. This paper introduces a model-based force controller designed to reject the friction in slave robots to improve the overall transparency of the telerobotic system. The primary objective of the force controller is to ensure the closed loop slave 2-port is absolutely stable such that the controller maintains the robustness of the overall telerobot. An analysis is provided that shows that, in order to achieve absolute stability, a local slave-side force controller cannot hide any of the robot’s inertial forces. It is from this result that model-based force control gets its name as it uses a model of the robot’s inertial properties to reject friction forces without attempting to reject inertial forces.