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.

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This research focuses on improved control for force-reflecting teleoperation systems in free motion and contact tasks. Specifically, the Naturally Transitioning Rate-to-Force Controller (NTRFC) is implemented in an Air Force experimental force-reflecting teleoperation system to achieve a unified controller with no mode switches from free motion to contact, and to reduce the wrench exerted on the environment by the slave manipulator during remote teleoperation tasks. In an effectiveness evaluation experiment, the experimental hypothesis is validated: the NTRFC with force reflection performs the best amongst four teleoperation control modes with respect to minimal wrench exertion on the environment. A negligible difference was found in total task-completion times amongst the four modes. The NTRFC with force reflection has the potential to improve task performance in remote, hazardous, teleoperation tasks in which minimal exerted wrench is desirable.

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