Haptic interface design based on impedances and characteristics of human arm

Abstract

This dissertation presents a new passivity condition for the design of a haptic system which takes into account human arm impedance and proposes an adaptive virtual coupling to improve the performance of the haptic system, when the human arm impedance varies largely. There exists a trade-off between increasing performance and guaranteeing stability in haptic system control. Although it is important to transfer the reflective forces, computed from the virtual environment, to a user as it is in order to increase his or her immersion in the virtual reality, guaranteeing stability of the system has been a top priority in haptic system control research because the haptic system exchanges physical energy with a human operator directly. Since the haptic system includes the human operator, the stability and performance of haptic systems are critically influenced by the human arm impedance. To adequately control these systems, it would be useful to know the mechanical impedance of the human arm. Then, it would be also necessary to develop a stable and optimal control scheme for the haptic system considering the human arm impedance. Human arm impedance is modeled as a second-order mass-damper-spring system. An impedance model is developed to describe the dynamic behavior of a haptic system that includes human arm impedance. We define the Passivity Margin (PM) and it should be always nonnegative to guarantee the passivity of the haptic system. A new passivity condition of the haptic system is derived using an energy-based approach. The proposed passivity condition makes the lower bound of the PM of the haptic system nonnegative at every sampling period. The derived passivity condition shows that the achievable maximum stiffness at each sampling period depends on the local minimum viscosity of the human arm during the sampling period. Human arm impedance during five force regulation tasks at five configurations is estimated in three subjects using the developed impe...