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"Rolabelt" Rotary-To-Linear Motion Device Using Toothed Belt

IP.com Disclosure Number: IPCOM000042174D
Original Publication Date: 1984-May-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Hollis, RL: AUTHOR

Abstract

Linear positioning may be accomplished for a robot manipulator, without slippage and with very low friction loss, by using a flexible toothed belt as a band in a rolamite bearing. A traditional solution to the problem of converting rotary to linear motion has been the rack-and-pinion drive. In rack and pinion drives it is critical to maintain the proper pitch separation between the rack and the pinion. Too much separation leads to backlash; too little separation causes excessive friction and wear. Maintaining the proper separation is a major problem in tool design. The problem may be partially circumvented by maintaining zero separation when the drive is at rest, and by mounting the pinion in such a way that it "rides up" to the proper pitch separation when the drive is in motion.

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"Rolabelt" Rotary-To-Linear Motion Device Using Toothed Belt

Linear positioning may be accomplished for a robot manipulator, without slippage and with very low friction loss, by using a flexible toothed belt as a band in a rolamite bearing. A traditional solution to the problem of converting rotary to linear motion has been the rack-and-pinion drive. In rack and pinion drives it is critical to maintain the proper pitch separation between the rack and the pinion. Too much separation leads to backlash; too little separation causes excessive friction and wear. Maintaining the proper separation is a major problem in tool design. The problem may be partially circumvented by maintaining zero separation when the drive is at rest, and by mounting the pinion in such a way that it "rides up" to the proper pitch separation when the drive is in motion. In such a design, a complicated set of bearings provides constraint of the motion to one degree of freedom in the approximate direction of the rack. A particularly elegant solution to the linear motion problem is the rolamite device described by Sandia in 1969, in which linear motion is achieved with extremely low friction (said to be one tenth that of conventional ball or roller bearings). The physics of rolamite have been investigated extensively, and commercially exploited. The basic rolamite drive uses two rollers captured between parallel guides by means of a taut metal band. Two rollers maintain a fixed relationship with each other and are free to move as a pair between the guides. There is no sliding friction and little rolling friction because of the large contact area between the bands and rollers. All play in the device is taken out by the tension in the band. The rolamite provides a linear motion degree of freedom, whereas the motive force for the degree of freedom is provided external to the rolamite by some other means. Another traditional drive element is the flexible toothed belt, normally used to transmit rotary motion. Toothed belts are widely available in several different pitches and are made of nylon or urethane with steel cable reinforcement. (The cables lie on the pitch line to restrict belt stretch as much as possib...