Contact Kinematics in the Roller Screw Mechanism

[+] Author and Article Information
Steven A. Velinsky

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

1Corresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the JOURNAL OF MECHANICAL DESIGN. Manuscript received February 17, 2012; final manuscript received February 25, 2013; published online April 23, 2013. Assoc. Editor: Kwun-Lon Ting.

J. Mech. Des 135(5), 051003 (Apr 23, 2013) (10 pages) Paper No: MD-12-1119; doi: 10.1115/1.4023964 History: Received February 17, 2012; Revised February 25, 2013

This paper investigates the nature of the contact between the load transferring surfaces in the roller screw mechanism, i.e., between the screw and roller threads and between the nut and roller threads. The analysis is applied to both planetary roller screws and recirculating roller screws. Prior work has neglected to take a fundamental approach toward understanding the kinematics of the contact between these components and, as a consequence, detailed analyses of aspects such as contact mechanics, friction, lubrication, and wear are not correctly carried out. Accordingly, in this paper, the principle of conjugate surfaces is used to establish contact at the screw/roller and nut/roller interfaces. The in-plane angles to the contact points are derived and it is shown that for the screw/roller interface, the contact point cannot lie on the bodies' line of centers, as has been the assumption in previous papers. Then, based on the curved profile of the roller thread, the radii of contact on the roller, screw, and nut bodies are also derived. Knowledge of the contact point locations is necessary in order to understand the interaction forces between the key components of the roller screw mechanism. The principal radii of curvature at the contact points and the angle between the principal axes are also derived. Lastly, a brief example is developed showing how the developed theory may be used to design a roller screw for improved stiffness and decreased contact stresses.

Copyright © 2013 by ASME
Topics: Screws , Rollers , Thread
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Fig. 1

Exploded view of relevant roller screw components (www.rollvis.com)

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Fig. 5

Contact normal for the screw surface

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Fig. 4

Frenet frame at the screw contact

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Fig. 3

In-plane contact between the screw and roller (exaggerated for clarity)

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Fig. 7

Cross section of the roller showing the roller profile

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Fig. 2

Cross-sectional cut of contact between the screw (dark gray) and roller (dark gray)

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Fig. 6

In-plane contact between the nut and roller (exaggerated for clarity)

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Fig. 8

Slope of the profile and the contact angle

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Fig. 9

Complete in-plane contact diagram

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Fig. 10

Angle between the axes of the principal radii of curvature at the screw/roller interface

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Fig. 11

Principal radii of curvature versus contact angle

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Fig. 12

Contact pressure and Hertzian deflection versus contact angle

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Fig. 13

Minimum screw contact angle versus roller profile radius




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