Bi-directionally Efficient, Backdrivable Gearbox with Low Backlash for Robot Actuators

This article presents a design framework for a backdrivable, bi-directionally energy-efficient 3K compound gearbox with a high reduction ratio and low backlash. The 3K compound planetary gearbox is a promising candidate for the robot actuators deployed in physically interacting environments possessing a compact design with a high gear ratio and high back-drivability. However, the existing 3k composite planetary gearbox has a high backlash for use in robot actuators. In this context, the proposed design framework comprises 1) backlash modeling 2) effective inertia of the 3K compound planetary gearbox 3) maximization of the bi-directional efficiency under bounded backlash constraints. We created a prototype to demonstrate the design framework for a low-backlash gearbox with a high reduction ratio (1/96.2) which is both bi-directionally efficient and back-drivable. The angular backlash of the prototype was 7.1 arcminutes. The forward and backward efficiencies of the developed prototype were 87.1 % and 82.5 %, respectively, and the back-driving starting torque was 0.025 Nm.