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Comparison of planetary roller screw and ball screw

Views:1     Author:Site Editor     Publish Time: 2021-02-19      Origin:Site

■Comparison of movement mechanism and force state 

Rolling element

Circulating motion of rolling body

Force state of rolling element

Centrifugal force of rolling element

Pure rolling ratio

Planetary roller screw

Threaded small roller

The small threaded roller makes planetary motion around the screw axis

The rolling element has a large cross-sectional area and is loaded at any time without cyclic alternating stress.

Planetary mechanism prevents centrifugal force

Very High

Ball screw


Reverse mechanism to achieve circular scrolling

The ball has a small cross-sectional area and is intercepted in turn, generating cyclic alternating stress.

Large centrifugal force will be generated when running at high speed

Higher (sometimes "wedge effect")

Comparison of principle and structure
As shown in the figure on the right: the structure of the planetary roller screw is similar to that of the ball screw, the difference is that the load transmission element of the planetary roller screw is a threaded roller instead of a ball. The advantage is that there are numerous threads to support the load.

The roller in the planetary roller screw design structure is non-circulating, so its rotation speed is twice that of the ball screw. The design of the ball screw is that the balls are circulating, so the balls will collide when rotating at high speed.

Since the lead is a function of the pitch of the planetary roller screw, the lead can be designed as an integer or a decimal. The lead of the ball screw is limited by the diameter of the ball, so the lead will be standard.

Comparison of service life:

Both planetary roller screws and ball screws apply to Hertz's law. From the law of Hertz pressure, we can conclude that the static load of the planetary roller screw is 3 times that of the ball screw, and the life span is 10-15 times that of the ball screw.

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