Compact, lightweight servo-controllable brakes capable of high torques are being developed for incorporation into robot joints. A brake of this type is based partly on the capstan effect of tension elements, which is described by the well known equation

Th/Tl = eμβ,

where Th is the higher tension at one end and Tl is the lower tension at the other end of a rope, belt, chain, or other tension element that is wrapped around a capstan so as not to slip; β is the total wrap angle in radians; and μ is the coefficient of friction between the capstan and the tension element. For example, a tension-multiplication factor of the order of 106 can be achieved by wrapping several turns of steel wire around a steel capstan. Heretofore, the capstan effect has been exploited in wound-spring clutches that operate in an on-or-off fashion. In a brake of the type under development, a controllable intermediate state of torque is reached through on/off switching at a high frequency.

This work was done by Christopher S. Lovchik of Johnson Space Center, William Townsend and Jeffrey Guertin of Barrett Technology, Inc., and Yoky Matsuoka of Carnegie Mellon University. For further information, contact the JSC Innovation Partnerships Office at (281) 483-3809.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:

Barrett Technology Inc.
625 Mt. Auburn St.
Cambridge, MA 02138

Refer to MSC-23389-1, volume and number of this NASA Tech Briefs issue, and the page number.

Motion Control Technology Magazine

This article first appeared in the August, 2010 issue of Motion Control Technology Magazine.

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