Browse Prior Art Database

Digital Position Recorder

IP.com Disclosure Number: IPCOM000082700D
Original Publication Date: 1975-Jan-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Koepcke, RW: AUTHOR [+2]

Abstract

A nondestructive method for measuring changes in the shape of a flexible disk, while spinning at high speed, comprises rapidly scanning a light beam synchronized with the motion of the disk to be measured, and measuring the transit time of the beam between the edge of the disk and a fixed edge.

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Digital Position Recorder

A nondestructive method for measuring changes in the shape of a flexible disk, while spinning at high speed, comprises rapidly scanning a light beam synchronized with the motion of the disk to be measured, and measuring the transit time of the beam between the edge of the disk and a fixed edge.

To perform the method, a synchronous motor 12 is used to drive an aluminum turntable 14 that is mounted on the motor shaft by a hub assembly 16, which is arranged to clamp a MYLAR* disk 10. To provide an opaque reference, the outermost periphery is metallized with a thin layer (3000 Angstrom) of chromium. The turntable 14 is formed with a tapered knife edge and is of a diameter less than the inner diameter of the opaque chromium band on the disk. This creates a fixed reference or edge on the turntable 14, and leaves a transparent annulus between the turntable and the chromium band.

A deflector mirror 18 is positioned such that, when caused to oscillate, the focussed beam from a laser 20 is deflected radially along the disk 10 and across the annulus. During the portion of time the beam is traversing the annulus, the light reaches the detector 22 and a gate signal is generated. The mirror 18 oscillates the beam at a constant velocity so that the width of the gate varies according to the radial length of the annulus. * Trademark of E. I. du Pont de Nemours & Co.

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