Passivity Issues in Bilateral Teleoperation - a Phase Property

In control design for bilateral telemanipulation there is a trade-off between high transparency and sufficient stability margins. Stability problems can occur when the stiff slave manipulator encounters a stiff environment and large contact forces are fed back to the badly damped master giving oscillative behaviour in the teleoperator. This is the case for the research project presented in this paper where the environment is human bone which has a high stiffness. Adaptive control methods which adds extra damping in the teleoperator control loop when it is needed is a promising concept. This paper presents an idea on how to detect when to engage such an adaptive controller. The idea is based on the fundamental passivity result where passivity is regarded as a phase property and experimental results which show that during certain stiff contacts and oscillative behaviour, the teleoperator controller has a slightly positive net energy as a result of power gain on the master port and power loss on the controller’s slave port. The power loss on the slave port can then be used to engage a future stabilizing control portion.