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Low Cost Automation Tutorial

#108 Mastering Ball Screws : Characteristics of Ball Screws

Category : Linear Motion Components
March 9, 2012

Invention of rollers contributed in dramatically reducing friction resistance when transporting un-suspended objects. Rather than dragging a stone over strewn sand, the stone can be moved with much less force if pulled over rollers. The former is an equivalent of slide linear bearing arrangement and the latter is the roller linear bearing arrangement. Ball screws are mechanical components utilizing this roller linear bearing principle to convert rotary motion into linear motion and vise versa, and have the following characteristics.

Characteristics and benefits of ball screws

(1) Very small rolling friction coefficient. (Friction coefficient = 0.002 ~ 0.004)


  • High energy efficiency obtained due to very small friction losses.
  • Both "rotary to linear" and "linear to rotary" motion conversions are possible.
  • Static friction coefficient and dynamic friction coefficient are very small, virtually no stick-slip occurs.
  • High rigidity and low backlash can be made possible by applying preloads.

(2) Highly reliable product backed by accumulated technologies of rolling bearings.


  • Running life can be approximated by calculations.
  • Quality and stability controlled by JIS Standards.
  • Performance can be maintained by normal maintenance processes such as grease applications.

Characteristics and shortcomings

(a) Precision assembled unit with point contact sliding mechanism.

  • Susceptible to shock loads. (Dents on point contact surface, etc.)
  • Somewhat inferior vibration damping characteristic (Limited by point contact design and number of bearing balls)
  • Foreign object intrusion on bearing rolling surfaces may cause unstable accuracy.
  • Bearing noises and recirculating vibrations become unavoidable as the operational speed inceases.