Ball screws are devices that convert rotational motion into horizontal motion. A rotating shaft with a helical groove moves an nut with internal grooves via ball bearings which circulate between the inner (shaft) and outer (nut) grooves. This motion can be very precisely controlled when the ball screw has been manufactured to a precise tolerance. These mechanisms are used when precise linear positioning is very important. In order to ensure high performance, the ball screw should be protected from anything which might contaminate it and cause increased internal friction.
Ball screws can be over 90% efficient, requiring about a third of the drive power used by standard sliding screws. They are generally made from stainless or hardened steel. Some are used in actuators, laser cutting systems and linear tables.
When specifying ball screws for an application, one must pay attention to desired lifespan, operating environment (temperature changes can cause the shaft to vary in length), required torque, output force, backlash, contamination, end machining and end support. Backlash is the back-and-forth linear motion that occurs without any rotational input to the shaft. Usage of a preloaded nut can minimize backlash.