Motion System Design

On a roll

A new report from the Bearing Specialists Association (BSA) indicates that planetary roller screws are often more effective in converting rotary motion to linear motion. They offer higher static and dynamic capacities, increased rigidity, lower axial clearance, and higher limiting speed. In the planetary configuration, the rollers have a timing gear at both ends. The result is a higher capacity without compromise.

The report indicates that rates of deflection increase a lot less rapidly for higher loads with planetary roller screws than with ballscrews. For example, at 20,000 N, both have a deflection of about 10 µm, but at 60,000 N, ballscrews have a deflection rate of more than 75 µm, while roller screws have only a 20+ µm deflection rate at this same load rating. In fact, at 180,000 N, planetary roller screws only reach about 45 mm deflection.

The planetary roller screws report is one of many commissioned by the BSA's Educational Services Committee. Previous reports have covered topics such as bearing repair, bearing installation fitting, ceramic bearings, wear sleeves and other shaft repair options, vibration analysis, seal selection, and load ratings and bearing life.

To view the report in its entirety, visit

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