Stability analysis of teleoperation systems under strictly passive and non-passive operator

A bilateral teleoperation system includes a human operator and an environment, which make the system stability analysis complicated due to their unknown, time-varying and nonlinear nature. Unable to have exact models for the human operator and the environment, it is typically assumed that they are passive but otherwise arbitrary. In this paper, through a set of experiments, first we show that a human operator´s relaxed arm is strictly passive while voluntary motions of the human operator´s arm involve non-passive characteristics. Then, we adjust the passivity assumption of the human operator´s arm (by tightening it for an input-strictly-passive arm and relaxing it for a non-passive arm) in order to enable a more precise stability analysis of the teleoperation system. Inspired by Llewellyn´s absolute stability criterion, a powerful stability analysis approach is developed to investigate the stability of a two-port network when it is coupled to an input-strictly-passive or a non-passive termination. Although this new stability criterion is applicable to any two-port network system, we apply it to a position-error-based bilateral teleoperation system as a case study.