Dynamics of coupled haptic systems

The sampled-data nature and time delays induce complex dynamic behaviours in haptic systems which makes the stable, high performance force feedback challenging. Physiological factors, such as reflex delay, and the variable impedance of the human operator further complicate the modeling and analysis of these systems. Often the operator is neglected and only the dynamics of the uncoupled haptic device is investigated. When considered, the human model is typically represented by passive impedance elements attached to the device; most studies employ only simple mass-spring-damper representations. The dynamics of coupled systems with multiple degrees-of-freedom device- and human operator models have not been much investigated. In the present paper, we discuss reduced order, parametric dynamic representations for such complex models. We also consider the coupled system, and demonstrate the effect of the human operator on the combined dynamics. Structural flexibility, different grasping conditions, and active human stabilization with reflex delay are considered. The results are validated and illustrated experimentally by using a haptic device based on a five-bar mechanism.