Harmonic gears are a type of strain wave gear. There are typically 3 components to this type of drive: a wave generator, a flex spline (inner rotating gear) and a circular spline (outer rotating gear).
The wave generator is elliptical in shape and is covered by a ball bearing. The ball bearing allows independent rotation of the inner flex spine, which is powered by the wave generator. The flex spline's teeth are located on the outside of the gear. The wave generator causes the flex spline to rotate in a elliptical formation, therefore the inner gear requires less teeth than the outer circular spline. The teeth only mesh in two opposite sides of the flex spline at the same time. Click here for more information on how harmonic drives work. What does this mean? Since the flex spline has less teeth, it can rotate slower in the opposite direction of the wave generator, but increase rotational speed for the outer circular gear. This allows for the two gears to have less impact and friction which then reduces wear. It also reduces the size and weight of the drive compared to traditional gears.
You may not be shopping for a harmonic drive itself, but it's good to know what kind of gears are inside the type of robot system you purchase. This helps you understand the maintenance and lubricants required for these particular drives. RobotWorx recommends using RWVG-1 SK1 Tribolube VG-1 synthetic grease for harmonic drives.
For more information, contact RobotWorx today at 740-251-4312.
Additional sources: https://en.wikipedia.org/wiki/Harmonic_drive