A Spatial Six-Dof Parallel Manipulator with Redundant Actuators for Gross and Fine Motions

We presented a spatial parallel manipulator with redundant actuators for gross and fine motions to achieve fine positioning together with gross motion in three dimensional space. Four types of parallel mechanisms with redundancy for such a manipulator were proposed and their infinitesimal displacement characteristics were investigated. Of the four mechanisms, a mechanism was chosen, and a kinematic synthesis was carried out. A prototype parallel manipulator was designed and built based on the synthesis result. A control system to achieve a fine motion together with a gross motion and a procedure to determine desired input of gross and fine motion drive systems for a specified pose of the output link were presented. We showed experimental results of fine positioning achieved by our prototype manipulator. A high ratio greater than 10(6) of total stroke of gross motion to positioning resolution and repeatability was achieved by our prototype manipulator.