Cycloidal Reducer

A reducer that meshes an eccentrically spinning cycloidal disc with a ring of pins for a large speed reduction.

A cycloidal reducer is a mechanical speed-reduction device: the input shaft drives an eccentric shaft that makes a disc, shaped with cycloidal teeth around its edge, “roll” inside a fixed ring of pins; for each full orbit the disc makes around the ring, it only rotates on its own axis by a small amount, producing a large reduction ratio (commonly tens-to-one in a single stage). Because many teeth share the load at once, it's shock-resistant, stiff, and can be built with very little backlash (the play when gears reverse direction). The RV reducer commonly used in the base and shoulder joints of industrial robot arms is exactly this: a planetary-gear stage combined with a cycloidal-drive stage. In humanoid and quadruped robots, it's often compared with harmonic drives and planetary gearboxes — more shock-resistant than a harmonic drive, but heavier and requiring tighter manufacturing tolerances.

ExampleIn the RV reducer used in a six-axis industrial robot's base and upper-arm joints, the second stage is exactly this cycloidal-pin structure.

Also called

Cycloidal Drive, Cycloidal Speed Reducer

Related

Speed Reducer / Gearbox · Rotate Vector (RV) Reducer · Strain Wave Gear (Harmonic Drive) · Planetary Gearbox · Backlash · Gear Ratio

Sources

Cycloidal drive - Wikipedia