Compact Gearboxes for Modern Robotics - Tom Verstraten

Talk from the IROS 2021 workshop:
From gears to direct drive: Recent trends and opportunities in actuation
Website: https://www.ram.eemcs.utwente.nl/gear...

Abstract:
High torques and high accuracy are typical design requirements for robots. To meet these requirements, designers usually pair high-speed electrical motors with high-ratio gearboxes. These gearboxes are often the source of high energy losses, non-linear behaviour and lost motion. Moreover, their poor backdrivability reduces their usability in new robotic applications such as collaborative robots, powered prostheses, exoskeletons and legged robots. High-torque motors, which allow to eliminate the gearbox partially (direct drive) or entirely (often termed quasi-direct drive ), are gaining traction as a solution to this problem. There are, however, some novel and lesser-known gearbox concepts with interesting properties which could make traditional designs with high-speed motors and high-ratio reducers more competitive. Novel actuator concepts, too, could open up new ways to improve backdrivability and energy efficiency.

In this talk, I will present the latest research of the Robotic and Multibody Mechanics Research Group (R&MM) of the Vrije Universiteit Brussel on compact gearboxes and innovative actuators of robotics. First, I will discuss the challenging requirements of robots and give an overview of the scaling laws that govern the design of gearboxes and motors. These scaling laws will provide some general insights needed to make a sensible trade-off between high-ratio gearboxes and high-torque motors. Next, I will focus on compound planetary geartrains as a compact and lightweight alternative to traditional gearbox types. After introducing their advantages, I will present our work on novel, compact gearboxes based on the Wolfrom topology. These gearboxes are highly backdrivable, even at large reductions (over 100). Finally, I will introduce the concept of redundant actuation, i.e. using multiple motors to drive a single output, as an alternative to a single high-torque motor.