Position-Force Domain Passivity Of Human Arm In Telerobotics 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 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, 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 position-force domain. Whether the arm remains passive in the position-force domain is a critical question yet to be answered. In this paper, passivity of the human arm in the position-force domain is investigated through mathematical analysis, experimentation and statistical user studies involving 12 subjects and 48 trials. It is shown that unlike in the velocity-force domain, the human operator will not remain passive in the position-force domain for all frequency ranges. This implies the need for appropriate control strategies to make the human operator termination passive in the position-force domain. For future design of suitable controllers, statistical analyses are performed to investigate correlations between the levels of position-force domain 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.