A performance index for under-actuated, multi-wire, haptic interfaces

Manipulability measures are well known tools for the analysis of the capability of a mechanical device of performing in the velocity or force domain. They have been firstly introduced for single kinematic chains, assuming them to have full controllability of each joint and considering the kinematics and the statics of the manipulator. Then, significant extensions have been proposed, including the dynamic case, the presence of multiple arms, different motion capabilities of the robotic device(s). Only a few studies have concerned the study of performance indices for devices actuated by wires (or tendons), and, in practice, nobody has considered in this context (wire actuation) the case of defective systems. In this paper, this case is explicitly addressed taking into consideration as applicative example the WireMan, a haptic interface for helping mobility of visually impaired people