Planetary Roller Screw

行星滚柱丝杠Common

A screw drive that uses threaded rollers to turn motor rotation into high-force linear motion.

A planetary roller screw is a mechanism that converts rotary motion into linear motion; it's structurally similar to a ball screw, but instead of balls, a ring of threaded rollers sits between the screw shaft and the nut, each roller spinning on its own axis while also orbiting the shaft, like planets. Swedish engineer Carl Bruno Strandgren produced an early practical design in the 1940s. Because it has many more contact lines than a ball screw of the same size, it carries a much larger load, is stiffer, and lasts longer, but the threads are harder to machine, and it can cost roughly ten times as much as a comparable ball screw — historically it was mainly used in aerospace and machine tools. With the rise of humanoid robots, it has been built into linear actuators to drive high-force joints like the knee, elbow, and ankle, making it a sought-after core component and a target for domestic-substitution efforts in China (replacing imported parts with locally made ones).

ExampleThe linear actuator Tesla showed for Optimus at AI Day 2022 pairs a motor with a planetary roller screw, converting rotation into the push-rod motion that drives the joint.

Also called: Roller Screw
Related: Ball Screw · Inverted Planetary Roller Screw · Linear Actuator (Electric Cylinder) · Screw Lead · Tesla Optimus · Domestic Substitution
Sources: Roller screw - Wikipedia