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Research Papers

Kinematics of Roller Migration in the Planetary Roller Screw Mechanism

[+] Author and Article Information
Matthew H. Jones

Steven A. Velinsky1

Department of Mechanical and Aerospace Engineering,  University of California, Davis, One Shields Avenue, Davis, CA 95616savelinsky@ucdavis.edu

1

Corresponding author.

J. Mech. Des. 134(6), 061006 (Apr 27, 2012) (6 pages) doi:10.1115/1.4006529 History: Received July 21, 2011; Revised March 22, 2012; Published April 27, 2012; Online April 27, 2012

This paper develops a kinematic model to predict the axial migration of the rollers relative to the nut in the planetary roller screw mechanism (PRSM). This axial migration is an undesirable phenomenon that can cause binding and eventually lead to the destruction of the mechanism. It is shown that this migration is due to slip at the nut–roller interface, which is caused by a pitch mismatch between the spur-ring gear and the effective nut– roller helical gear pairs. This pitch circle mismatch can be due to manufacturing errors, deformations of the mechanism due to loading, and uncertainty in the radii of contact between the components. This paper derives the angle through which slip occurs and the subsequent axial migration of the roller. It is shown that this roller migration does not affect the overall lead of the PRSM. In addition, the general orbital mechanics, in-plane slip velocity at the nut–roller interface, and the axial slip velocities at the nut–roller and the screw–roller interfaces are also derived. Finally, an example problem is developed using a range of pitch mismatch values for the given roller screw dimensions, and the axial migration and slip velocities are determined.

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Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Roller screw and the relevant components [20]

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Figure 2

Planetary gear dimensions, pitch circle mismatch exaggerated

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Figure 3

Slip angle definition—Dashed lines are helical and solid lines are spur gear pairs, pitch circle mismatch exaggerated

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Figure 4

Region of pure slip

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Figure 5

Axial displacements and sign convention

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Figure 6

Normalized total axial migration of roller, δRNTotalλ, as a function of pitch mismatch error, ɛ

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Figure 7

Normalized slip velocity, υP on the left axis and υRN on the right axis as a function of pitch mismatch error, ɛ

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