Browse Prior Art Database

Position Sensing

IP.com Disclosure Number: IPCOM000091994D
Original Publication Date: 1968-Aug-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Rottmann, HR: AUTHOR

Abstract

Prisms 10 and 12 utilize the principle of frustrated total reflection for fine position sensing of device 14 in the X direction. The accuracy of position sensing is in the order of one tenth of the wavelength L of light. Such accuracy is realized by detecting a difference in intensity between reflected light R and transmitted light T.

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Position Sensing

Prisms 10 and 12 utilize the principle of frustrated total reflection for fine position sensing of device 14 in the X direction.

The accuracy of position sensing is in the order of one tenth of the wavelength L of light. Such accuracy is realized by detecting a difference in intensity between reflected light R and transmitted light T.

Prism 10 is permanently attached to a base structure. Prism 12 is attached to device 14. The hypotenuse surfaces are separated by an air film approximately one half the wavelength L in thickness. Light source 16 provides a light beam of wavelength L which is split into reflected portion R and transmitted portion T. R and T are reflected by mirror 18 and mirror 20, respectively, and converge at beam splitter 22. The latter is oriented at an angle A slightly less than 45 degrees so that angle B is not equal to zero. Mirror 24 rotates or oscillates to alternately reflect beam R or beam T through slit 26 onto photocell
30. When all pulses in the pulse train from photocell 30 are of equal amplitude, device 14 is properly positioned. The desired thickness of the air film between prisms 10 and 12 can be varied by changing the wavelength L or by inserting filter 32 in one of beams R or T.

Prisms 10 and 12, utilizing the principle of frustrated total reflection, also provide a light chopper as in drawing 2. Prism 10 is permanently mounted to a base structure. Prism 12 is attached to a piezoelectric vibrator. Transmitted beam...