Fundamental limits of performance for force reflecting teleoperation

The quality of telepresence provided by a force-reflecting teleoperator is determined,for the most part, by the fidelity of the contact-force information fed back to the operator These fed-back forces, however also directly influence system stability, and in this paper we investigate the relationship between fidelity and stability with a view toward understanding how stability considerations impose fundamental limits on system performance. The key idea of our work is to draw an explicit distinction between the information conveyed by the force signal and the energy inherent in that signal. Using known physiological properties of the operator we argue that there exists a natural partitioning between information and energy wherein information is conveyed at frequencies above roughly 30 Hz, while the energetic interaction between the slave and the environment takes place at frequencies below this. We embody this distinction in a two-channel framework that we claim provides insight into the design of force-reflecting systems. Using a I-DOF model, we study the effect of various system characteristics, notably mass, stiffness, and damping properties, on performance and stability. This model is used to derive expressions for the maximum force-reflection ratio that guarantees stability against pure-stillness environments and to investigate the role of various compensation elements, including local force control around the slave. Finally, a framework is developed for force-reflecting teleoperation that maximizes the force information conveyed to the operator subject to the constraints imposed by stability considerations.