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Blocked Reflectance Document Sensor

IP.com Disclosure Number: IPCOM000080738D
Original Publication Date: 1974-Feb-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Rohrer, GD: AUTHOR

Abstract

This document sensing system operates on the basis of blocking the reflection of a light beam from the document, unless the document is within a predetermined distance from the reference surface.

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Blocked Reflectance Document Sensor

This document sensing system operates on the basis of blocking the reflection of a light beam from the document, unless the document is within a predetermined distance from the reference surface.

As shown in Fig. 1, the apparatus comprises a light emitter 3 with a suitable lens 5, and a photodetector 7 arranged at suitable angles with respect to a glass plate or reference surface 9, as shown. An opaque baffle 11 having a knife edge is also positioned relative to the reference surface and the photodetector, as illustrated in Fig. 1. The dotted lines in Fig. 1 illustrate the path of the light beam, when the distance D of the document or reflecting surface 13 from the reference surface 9 is less than a predetermined amount. As shown, the beam will be reflected from the reflecting surface 13, and will be detected by the detector 7 since some of it falls on the sensitive surface of the detector.

The detector 7 will provide an output until the distance of the document equals a critical value B as shown in Fig. 2, where the reflected light just grazes the knife edge of the baffle 11.

In Fig. 3 there is shown the situation which results when a document is greater than the proper distance to the reference surface, in this case the distance being indicated as A. Under these conditions, the light beam from emitter 3 will be reflected from surface 13, but instead of striking detector 7, it will be intercepted by the baffle 11 and hence wil...