GENERIC FEATURES FOR RESOLVING THE REDUNDANCY IN ONE CLASS OF 7-JOINTED ROBOTIC WORKCELLS

The redundancy is resolved for a class of controllably dextrous seven- jointed serially connected robots, and the generic features of the inv erse kinematics for their control are developed. The generic features are the specific motions of the outermost two joints of the wrist and the aggregates of the motions of the rotary joints in each of the rema ining directions. Global-motion properties of spherical mechanisms, wi th R-joints lying in just four and five directions, were utilized to r esolve the redundancy at the position-level in a way to ensure that ev ery robot in the class can produce finite translations and can change the orientation of its tool arbitrarily by at least a full turn at eve ry controllably dextrous fixture-point, all without encountering the m echanical effects of axis-dependence. For those robots with three P-jo ints in the arm, the dexterity of motion is accomplished with all rota ry joints operating at speeds within 2.5 times the speed of the task-r otation. However, there is potential for lowering this globally maximu m speed for most trajectories by optimally positioning the trajectory in a workcell. In this paper, the quantitative evaluation is restricte d to manipulators with 3R spherical wrists having successively orthogo nal axes, the first of which is mounted at right-angles to the adjacen t joint-axis in the arm. The CPU-time for executing each computational step is short enough to be useful for on-line operations.