Hyperbolic tangent function based force-position compliant controller for robotic devices

A new type of force-position compliant control is proposed, where hyperbolic tangent function is used to dynamically adjust the gain of the position feedback loop so that to control the contact force safely and according to a given pattern. The proposed compliant controller uses a high gain in the position control loop when the robotic device is in free space motion, and as and when it comes into contact with the environment, the gain of the position loop is lowered according to the roll-off of inverse tangent function. The controller is tunable with only one parametery, and is capable of mimicking a wide range of force control behaviors. In this paper we apply the proposed controller to mimic human compliant motion in gripping and lifting objects. And, we have verified that the human compliant behavior can be satisfactorily realized by the proposed compliant controller.