Robust stable control of haptic devices based on transparency maximization

Abstract

The performance of haptic devices is evaluated based on the concept of transparency, while their stability has prevalently been evaluated based on the passivity criterion. Due to the conservativeness of passivity, it appears as an obstacle to improving transparency. In the present paper, passivity is suggested to be replaced by the complementary stability criterion which accounts for the robust stability of the interaction in the presence of uncertain user hand dynamics. In this respect, an algorithm is proposed which guarantees transparency of the haptic device in a stable manner. Assuming that the dynamics of the device is known, a certain compensatory structure is assigned. This special structure guarantees transparency of the device by compensating for the dynamics of the device and its control loop. The design objective is to obtain a stabilizing controller which achieves robust interaction stability in the presence of parametric uncertainties of user hand dynamics and other sources of uncertainties. An iterative method is implemented, in conjunction with the D-K iteration algorithm, to derive controller dynamics. The algorithm is applied to a series elastic actuator-based haptic device. This results in a widened frequency range of transparent impedance emulation. Simulation results confirm enhanced transparency and robust stability.