Introducing compound planetary gears (C-PGTs): A compact way to achieve high gear ratios for wearable robots

Abstract

In the field of wearable robots, high power density and highly efficient actuators are required to handle the high-power motion without becoming heavy and bulky and hence hamper their mobility. Typically, electrical motors are used in combination with high gear ratio gearheads or lever arms in order to achieve the required torques. These gearboxes consist mainly out of several stages of simple Planetary Gear Trains (PGTs). However, this approach leads to big and heavy gearboxes when high torque is needed. An alternative, more compact, design to obtain the required torque increase can be achieved using Compound Planetary Gears (C-PGTs). It is shown that the latter mechanism can obtain gear ratios up to 1:600 while withstanding an output torque of 100 Nm.