Friction Compensation for a Force-Feedback Teleoperator with Compliant Transmission

Friction forces in the joints of manipulators of a force-feedback teleoperator apply unwanted resistant forces to the human operator who moves the master manipulator. The resistant forces contribute to operator fatigue and reduce the transparency of the teleoperator in low frequencies. This paper presents a model-based approach to cancel friction in manipulators of a teleoperator with a compliant tendon drive. Friction compensation reduces the resistant forces applied to the operator and improves the transparency, but it can cause oscillations. This is due to displacement lags between the inputs to the friction compensators and actual displacements of friction contact surfaces that can cause overcompensation around zero velocity. We use a low-stiffness Dahl model to prevent over-compensation around zero velocity. It is shown using passivity theory that the low-stiffness friction compensators preserve the passivity of the teleoperator. Experiments performed on a teleoperator confirm the theoretical results