Comparative study and experimental verification of singular-free algorithms for a 6 DOF parallel haptic device

Abstract

It is well known that there exist many more singularities in parallel type mechanisms compared to serial type mechanisms. In haptic applications, these singularities deteriorate the force reflecting performance. Furthermore, as opposed to general manipulators, haptic systems cannot avoid the singular point, since they are operated by the user's random motion command. Although many singularity-free algorithms for kinematically redundant manipulators have been proposed, singularity-free algorithms for parallel haptic application have not been extensively discussed. In this paper, various singularity-free algorithms that are appropriate for parallel haptic systems will be discussed. A new 6 degree-of-freedom (DOF) parallel mechanism equipped with four sub-chains is designed and employed as the test device. To cope with the singularity problem, four task-priority algorithms and a redundant actuation algorithm are introduced and compared through simulation. In addition, experiments have been performed to show the effectiveness of those algorithms at the presence of singularity. (c) 2004 Elsevier Ltd. All rights reserved.