Passivity control of a passive haptic device

In this paper, we propose an energy-based stability control of a passive haptic device equipped with passive actuators such as an electric brake. Unstable behavior is observed even in the passive haptic system due to time delay mainly arising from the slow update rate of the virtual environment. The force approximation, one of the major limitations of the passive haptic device, is explained in the passive FME analysis. The ideal force display of passive haptic device is investigated, and it is shown that the passive haptic system frequently obtains the pullback capability due to the force approximation. The indirect force control scheme is proposed in that the change rate of passivity is controlled to simulate the ideal force display. To avoid the increase of the passivity due to the rate controller, which is not correlative to stability, passivity feedback is established. An experiment was conducted with a 2-link passive haptic device equipped with two electric brakes. From the experiment, the proposed control method showed satisfactory performance in displaying a plain virtual wall.