Stable User-specific Haptic Rendering of the Virtual Wall

E cient control algorithms are developed to implement sti virtual walls without chatter. An analysis of the complete coupled system comprising controller, interface device, and user's nger underlies the design of a wall algorithm, thus each virtual wall is tailored to a speci c user impedance. The nger is modeled as a static second order impedance with justi cation 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 e ects of the zero order hold using either model based prediction or design in the digital domain. The destabilizing e ects of asynchronous wall on/o 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-they system identi cation of the user impedance.