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Browse Prior Art Database

Very High Resolution Compact Rotary Encoder

IP.com Disclosure Number: IPCOM000045965D
Original Publication Date: 1983-May-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Taylor, RH: AUTHOR

Abstract

A high resolution rotary encoder utilizing a fiber-optic interferometric tape measure wrapped around a shaft is described. The encoder offers good immunity to noise, and can be made very compact.

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Very High Resolution Compact Rotary Encoder

A high resolution rotary encoder utilizing a fiber-optic interferometric tape measure wrapped around a shaft is described. The encoder offers good immunity to noise, and can be made very compact.

Optical incremental encoders are commonly used to determine shaft rotation. These encoders generally have a pattern of slits around the outside of a disk (Fig. l) and employ a light source and photo detector to count the slits as they go by. The resolution of such encoders is essentially limited by the number of slits that can be placed around the perimeter of the encoder while still allowing enough light through for the photodetector. Encoders of reasonably convenient size for use in robots (E l-2") typically are limited to c l0/3/ counts/rev. This number is too small for use with directly driven rotary joints. Increased resolution requires either increasing the size of the encoder or introducing gearing. Neither of these approaches is desirable.

The proposed apparatus is illustrated in Fig. 2. The principal component is a fiber-optic interferometric tape measure (see preceding article) wrapped around the shaft whose angle is to be measured. The mirror end of the fiber is clamped to the shaft, so that the length of fiber in the optical path of the interferometer is proportional to the angular displacement of the shaft, and interference fringes correspond to the slits in a conventional encoder.

The resolution of the encoder is...