Case Study on Haptic Devices: Human-Induced Instability in Powered Hand Controllers

This article describes the dynamic behavior of a hand controller when it is maneuvered by a human. A general control architecture is developed that guarantees various impedance's on the hand controller. We show that some compliancy either in the hand controller or in the human arm is necessary to achieve stability of the hand controller and the human arm taken as a whole. The actuators' backdrivability, the dynamics of the hand controller mechanisms, and the computer sampling time are discussed as they relate to system stability. A set of experiments that were performed on a prototype hand controller are presented to show the system performance.