A Passivity Criterion For Sampled-data Bilateral Teleoperation Systems
In a bilateral teleoperation system, conditions involving open-loop model parameters and controller parameters for ensuring teleoperator passivity are useful as control design guidelines to attain maximum teleoperation transparency (due to passivity/transparency tradeoffs). By teleoperator, we mean the teleoperation system excluding the human operator and the remote environment. The rationale behind considering teleoperator passivity instead of teleoperation system stability is that, unlike the former, the latter is influenced by the dynamics of the human operator and the remote environment, which are typically uncertain, time-varying, and/or nonlinear. In this paper, a condition for the passivity of a teleoperator is found when the teleoperation controllers are implemented in the discrete-time domain. Such a new passivity analysis is necessary because discretization causes energy leaks and does not necessarily preserve passivity. We show that the passivity criterion for the sampled-data teleoperator imposes a lower bound on the robot damping and upper bounds on the control gains and the sampling time. The criterion has been verified through computer simulations as well as experimental tests involving a bilateral teleoperation system consisting of a pair of Phantom Omni robots. In the experiments, a passivity observer was used to estimate the forces and calculate the energy integral. In addition, the teleoperation system was initially and intentionally destabilized by the operator as a way to detect teleoperator non-passivity when force measurements are not available.