Passivation of Force Reflecting Bilateral Teleoperators with Time Varying Delay

This paper addresses the problem of time-varying communication delay in force reflecting bilateral teleoperation. The problem is motivated by the increasing use of the Internet as a communication medium where the time delay varies depending on factors such as congestion, bandwidth, or distance. The well-known scattering formalism introduced in (Anderson and Spong, 1989) preserves passivity of the communication channel for constant transmission delay. We demonstrate how passivity is lost in the case of time-varying transmission delay and show that a suitable time varying gain inserted in the transmission path can recover passivity provided a bound on the rate of change of the delay is known. Preservation of passivity by itself does not guarantee good transient performance and so we also investigate the use of saturation control to improve the tracking. Simulation results are presented showing the performance of the resulting control architecture.