Stable User-Specific Haptic Rendering of the Virtual Wall

Abstract

Abstract Efficient control algorithms are developed to implement stiff virtual walls without chatter. An analysis of the complete coupled system comprising controller, interface device, and user’s finger underlies the design of a wall algorithm, thus each virtual wall is tailored to a specific user impedance. The finger is modeled as a static second order impedance with justification drawn from empirical studies of limb dynamics available in the literature and from observations of the disparity in time scales between contact instability and volitional control. Compensation is incorporated for the destabilizing effects of the zero order hold using either model based prediction or design in the digital domain. The destabilizing effects of asynchronous wall on/off switching times and sampling times are tracked by a special watchdog while deadbeat control is used to periodically eliminate these effects. Extensions are discussed, including on-the-fly system identification of the user impedance.