Lightweight, Low-Backlash Robot Wrist With Epicyclic Drive

A unique lightweight wrist with three degrees of rotational freedom has been developed as a prototype of wrists for future anthropomorphic robots that would perform a variety of tasks on Earth and in outer space. The three degrees of freedom (two rolling, one bending) intersect at the center of the wrist. Included in the wrist is a power transmission with an epicyclic ring-gear configuration that enables efficient packaging and provides a wide internal passage through the center of rotation for routing of wires and drive cables. The power transmission combines low-backlash planetary gearing and a triple-input differential with a triple-load-path, cable-driven output stage that generates minimal radial bearing loads and no thrust (that is, axial) bearing loads.