Ball Screw

A screw and nut with ball bearings packed between their threads, turning rotation into linear motion efficiently.

A ball screw converts a motor's rotary motion into linear motion: rows of steel balls sit in the matching helical grooves of the screw shaft and the nut, rolling and recirculating as the nut travels, which turns the sliding friction of an ordinary lead screw into rolling friction. That gives it high transmission efficiency, high precision, and low wear. It's widely used in CNC machine tools, linear modules, and Cartesian robots. In humanoid robots, ball screws are used to build linear actuators (electric cylinders) that drive joints like the knee or ankle; for heavier loads, a planetary roller screw, which has more contact area, is used instead. Because it's so efficient, a ball screw generally can't self-lock, so a holding brake is needed to keep the load from sliding back when power is cut.

ExampleA CNC machine tool's worktable is driven by a servo motor turning a ball screw, giving it precise linear feed motion.

Related

Planetary Roller Screw · Linear Actuator (Electric Cylinder) · Screw Lead · Trapezoidal Lead Screw & Self-Locking · Holding Brake

Sources

Wikipedia: Ball screw