Optical displacement transducers

US4388613A · kind A · utility

Assignee

• Smiths Industries Public Limited Company · GB

Inventors

• Derek A. Rush · Gilroy, US
• Roger D. Swadling · Cheltenham, GB

Key dates

• Filing date: Dec 30, 1981
• Grant date: Jun 14, 1983
• Expiry date: Dec 30, 2001

Classification

• Technology area (CPC G): Physics
• CPC primary: G01D5/34723
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

An optical displacement transducer for providing a digital output representative of the displacement of a variable from a datum value comprises a light beam emitter and a light beam receiver disposed on a common optical axis, a digital encoding element comprising an optical grating disposed between the light beam emitter and receiver, the grating extending in a circular path with the grating lines extending substantially radially of the path, means for causing relative rotation between the light beam and the grating about the center of the circular path whereby the light beam as seen by said receiver is in the form of a series of light pulses, a first reference position at a stationary position on the circular path, a second reference position on the circular path and angularly displaced about the center of the circular path from the first reference position whereby a predetermined light pulse count is produced during the relative rotation through the angle between the first and second reference positions, and control means for adjusting the second reference position relatively to the first reference position in response to displacement of the variable whereby to vary the pulse cou…