Design and analysis of the bearingless planetary gearbox

High performance legged and mobile manipulating robotic platforms require light weight actuators with high torque density, efficiency, and accuracy. This paper introduces a new type of high reduction bearingless gearbox which is based on a gearbox with double-row planetary pinion, and can achieve high reduction ratios in a single composite stage. We discuss the practical issues which limit the applicability of the existing double row gearbox, and motivate our innovations. Several advantages of the bearingless gearbox over current approaches in terms of robustness, possible load distribution, manufacturability, and assembly are described. In the concept, all gear components float unconstrained, which is achieved by introducing an additional kinematic constraint that allows planets to be the same, in which case the planet carrier can be substituted with a secondary sun gear. The resulting planetary gearbox can be readily integrated into compact robotic joints. Its few lightweight components can be manufactured with high accuracy with standard machining techniques.