Inverted Planetary Roller Screw

反向式行星滚柱丝杠Advanced

A planetary roller screw variant with the long thread cut inside the nut, so the rollers travel with the screw shaft.

A planetary roller screw uses a ring of threaded rollers, instead of balls, to transmit force between the screw shaft and the nut, converting rotation into linear motion with higher load capacity and longer life than a ball screw. In the standard configuration, the screw shaft is long and the nut is short, with the nut traveling along the shaft; in the inverted configuration, this is reversed — the long thread is cut into the inside of the nut, and the rollers travel together with the shorter screw shaft along the nut, with output taken from the extending screw shaft. This lets the nut double as the motor's rotor, nesting the motor and the screw together into a very compact linear actuator. Humanoid robots, which need high push force from a small package at joints like the knee, ankle, and elbow, are a natural fit for this approach; Tesla's Optimus linear actuators are reported to use a planetary roller screw. It's difficult to machine, and its domestic manufacture is one focus of the robotics supply chain in China.

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