A comparative study of ideal elbow and dual-elbow robot manipulators

The positional and orientational capabilities of a robot are directly influenced by the joint configuration. The elbow configuration is the most prevalent among existing robot installations. Elbow manipulators are anthropomorphic; the first three axes form the positioning "arm" and the last three form the orienting "wrist". This arrangement maximizes the reachable workspace of the robot for a given total link length. Recently, dual-elbow manipulators emerged as a novel geometry in which the positioning "arm" and the orienting "wrist" are interchanged in the kinematic chain. Dual-elbow robots, maximize the reachable workspace as well, yet they have not received considerable attention in the literature due to the effective marketing of elbow robots and the fascination of roboticists with anthropomorphism. The present work is the first attempt to examine systematically this alternative, nonanthropomorphic, kinematically-optimum articulated robotic geometry. In this paper, it is shown that ideal dual-elbow manipulators share all the basic properties of ideal elbow manipulators and thus should be at least equally appealing. In the companion paper [Mech. Mach. Theory 28, 375-396 (1993)], it is demonstrated that practical dual-elbow robots are superior in terms of reachability and dexterity.