On the use of shunt impedances versus bounded environment passivity for teleoperation systems

This paper analyses and compares two passivity-based approaches that allow to include a-priori knowledge on the dynamic range of the human operator and/or the environment. This can lead to less conservative teleoperation systems compared to systems designed to be purely passive or absolutely stable. The first approach under investigation is a method where the absolute stability is analysed of a teleoperation system augmented with shunt impedances in series and/or parallel with the teleoperation system. It is shown that the traditional interpretation of the use of shunt impedances is not valid and a more accurate description of how to use this method is presented. The second approach under investigation is the bounded environment (operator) method. It is shown that the original idea to restrict the analysis to the so-called worst-case scenarios of a pure mass and a pure stiffness as environment can be too simplistic. Illustrative examples with mass-spring-damper systems fixed to the ground and floating objects as environments are made to demonstrate this in detail. In conclusion, this paper shows that embedding environment knowledge into the controller analysis/design is not straightforward and further research should be dedicated to determine which bounds should be used to obtain practically stable systems for different applications.