Position-Force Domain Passivity of the Human Arm in Telerobotic Systems

In order to guarantee safe human-robot interaction in single-master/single-slave teleoperation systems, passivity-based controllers have traditionally been developed for communication delay compensation in the velocity-force domain (VD) with the assumption of passivity of the human arm. The same controllers can also make the delayed communication channel passive in the position-force domain (PD), which provides a convenient position-drift-free control strategy for more complicated scenarios such as multi-master/single-slave systems. This would, however, only work if the operator's arm also remains passive in the PD. Whether the arm remains passive in the PD is a critical question yet to be answered. In this paper, passivity of the human arm in the PD is investigated through mathematical analysis, experimentation, and statistical user studies involving 12 subjects and 48 trials. It is shown that unlike in the VD, the human operator will not remain passive in the PD for all frequency ranges. This implies the need for appropriate control strategies to make the human operator termination passive in the PD. For future design of suitable controllers, statistical analyses are performed to investigate correlations between the levels of PD passivity of the left and the right arms of the human participants, as well as the levels of passivity of the subjects' arms and their physical characteristics, e.g., weight, height, and body mass index. Possible control strategies through which the passivity of the operator termination can be guaranteed are also discussed.