Comparative Study of Serial-Parallel Delta Robots With Full Orientation Capabilities

More than thirty years after the initial concepts, commercial Delta and Delta-like robots serve a niche market for high-speed pick-and-place applications. Expired patents and new fields of application have led to increased research and innovative designs. By functionally extending the original translational Delta robot with additional serial chains, commercial concepts obtain up to three additional rotational degrees-of-freedom. In this context, the paper in hand is concerned with the analyses of serial-parallel Delta robots with full orientation capabilities. Based on efficient kinematic relations, an energy-related dynamic model is derived for four potential extensions. By solving the inverse dynamic problem, the influences of the additional serial chains on the actuation torques of the basic parallel Delta robot are analyzed. Furthermore, the merits of each individual concept are evaluated using torque-related indices (i.e., energy consumption and root mean square torque) and discussed from a design point of view. It is shown that two types of extensions are predestined for industrial application. In these variants, the wrist motors are either attached to the frame or to the distal links.