Naturally-Transitioning Rate-to-Force Control in Free and Constrained Motion

Abstract

The Naturally-Transitioning Rate-to-Force Controller (NTRFC) is presented for teleoperation of manipulators. Our goal is to provide a single controller which handles free motion, constrained motion, and the transition in-between without any artificial changes. In free motion the displacement of the master device (via the human operator’s hand) is proportional to the commanded Cartesian rate of the manipulator. In contact, the displacement of the human operator’s hand is proportional to the wrench (force/moment) exerted on the environment by the manipulator. The transition between free rate motion and applied-wrench contact with the environment requires no changes in control mode or gains and hence is termed natural. Furthermore, in contact, if the master enables force reflection, the wrench of the human operator’s hand exerted on the master is proportional to the wrench exerted on the environment by the manipulator. This article demonstrates the NTRFC concept via a simple 1-dof model and then discusses experimental implementation and results from a Merlin manipulator teleoperated via the force-reflecting PHANToM interface.