Human-machine admittance and transparency adaptation in passive user interaction with a haptic interface

This paper addresses human adaptation to changes in coupling impedance and force amplitude during passive user induced (PUI) interactions with a haptic interface. PUI interactions are characterized as event-based haptic interactions or haptic recordings that are replayed to the user. In the study, virtual environments are displayed to passive users with variable coupling stiffness and force amplitudes, and transparency bandwidth and human-machine admittance are measured. Results indicate that transparency bandwidth and the human-machine admittance do not change significantly for permutations of force amplitudes and coupling impedances, nor do they vary significantly across users. The reason for this invariance is that, during a PUI interaction, users tend approach a similar displacement profile. As a result, all users will have similar apparent admittance and transparency. The findings give sufficient justification for the use of universal compensators that improve transparency bandwidth, and that can be designed based solely on a priori transparency measurements for a typical user.