Enhancing Transparency of a Position-Exchange Teleoperator

Dynamic properties of robotic manipulators, including inertia, damping, and friction, limit the transparency of a haptic-feedback teleoperator. In this paper, we develop a position-exchange controller to provide haptic-feedback for a surgical teleoperator. The controller consists of proportional controllers and model-based feedforward terms that cancel the dynamic properties of the manipulators. We show that the teleoperator transmits the impedance of a soft environment to the operator when the gains of the proportional controllers are very high and dynamic terms of the manipulators are canceled. However, the high gains and complete cancellation of the dynamic terms of the manipulators can make the teleoperator unstable. We use IlewellynJs criteria for absolute stability to limit the controller parameters to values that keep the teleoperator stable during interactions with any passive user and environment. Experimental results using a custom version of the da Vinci Surgical System show that 70% of the inertia of the slave manipulators during low-frequency motion and almost all static friction of the manipulators during sliding motion can be canceled