Ball screw overview
Ball screw is mechanical actuator used for translating rotary motion to linear motion.
Parts of ball screw are screw spindle and a nut integrated with balls and the balls return mechanism, return tubes or return caps.
They look similar to lead screw with threaded rod and nut but function differently.
Where the lead screw thread profile is generally trapezoidal, ball screw threads are more rounded. The ball screw nut also does not mate directly with the ball screw. Instead, the threads cut into the ball nut form circular channels which are filled with a line of small balls. The balls transmit force between the ball screw and the ball nut and are forced along the thread channel to a return channel, where they are delivered back into the thread channel for another trip.
The return path for the recirculating balls can be either internal or external.
Ball screw Applications
- CNC machinery : CNC machine center, CNC lathe, CNC milling machine, CNC EDM, CNC grinder, wire cutting machine, boring machine, etc.
- Precision machine tools : Milling machine, grinder, EDM, tool grinder, gear manufacturing machine, drilling machine, planer, etc.
- Industrial machinery : Printing machine, paper-processing machine, automatic machine, textile machine, drawing machine, special purpose machine,injection molding machine, etc.
- Electronic machinery : Robot measuring instrument, X-Y table, medical equipment, surface mounting device, semi-conductor equipment, factory automation equipment, etc.
- Transport machinery : Material handling equipment, elevated actuator, etc.+
- Aerospace industry : Aircraft flaps, thrust open-close reverser, airport loading equipment, fin actuator, etc.
- Miscellaneous : Antenna leg actuator, valve operator, etc.
Ball screw advantages
- Ball screws have greater efficiency means reduced power requirements
- Ball screws have reduced friction means that limited duty cycles are less common with ball screws, some even being rated for continuous duty.
- Ball screws have low backlash
- Ball screws have higher load ratings, better positional accuracy, and higher efficiencies than similarly sized lead screws.
Ball screw disadvantages
- Expensive to manufacture than lead screws due to the precision machining needed for nut and screw.
- Ball screws might need mechanical brake as they are not self-locking.
- Ball screws are limited in translational speed by how fast the balls can circulate through the nut.
How to select Ball screw or Lead Screw
The design choice between ball screws and lead screws depends on many application parameters.
- Ball screws cost more up front, but in the long run deliver better accuracy and lower maintenance costs.
- The positional accuracy and increased load handling of ball screws may not be required for some applications in such cases, a lead screw may be fine.
- The increased friction of a lead screw might mean that the motor driving it will need to be upsized.
- lower duty cycle of the lead screw might be an issue.
Ball screw types
- Rolled Ball Screws
- Ground Ball Screws
Selection of Hiwin Ball screw series