CoaxHaptics-3RRR: A Novel Mechanically Overdetermined Haptic Interaction Device Based on a Spherical Parallel Mechanism

This paper presents the CoaxHaptics-3RRR, a novel concept for haptic interaction devices that is based on a 3-RRR spherical parallel mechanism (SPM). The novelty lies in its mechanical overdetermination through a central hollow shaft, which brings two advantages. First, the device can be built with high rigidity with regard to translational degrees of freedom (DoF). Second, it enables a lighter design with less rotational inertia, as the moving links do not need to withstand translational or gravitational forces. In order to fully exploit these advantages, an optimization process has been conducted that simultaneously optimized for workspace, manipulability, inertia, and structural stiffness. The resulting functional demonstrator provides an unlimited workspace around the shaft axis and +/− 55 degrees in the other two rotational DoF, thus covering a large portion of the human wrist’s rotational range. Tests confirm the validity and superiority of the concept over existing devices, making it a promising solution for the category of mechanically overdetermined haptic devices.