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Integrating Rod

IP.com Disclosure Number: IPCOM000077823D
Original Publication Date: 1972-Sep-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 3 page(s) / 45K

Publishing Venue

IBM

Related People

Dattilo, AJ: AUTHOR

Abstract

When designing a flying spot scanner it is necessary to collect the light reflected from a document, so that it may be directed onto a detector surface. It is desirable that the collection efficiency of the system be independent of spot position. That is, the amount of light incident on the detector, when the spot is reflected from a white section in the center of the document, should be the same as when the spot is reflected from a white section at the edge of the document. The integrating tube 1 provides a simple means of achieving this result with a compact and inexpensive device.

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Integrating Rod

When designing a flying spot scanner it is necessary to collect the light reflected from a document, so that it may be directed onto a detector surface. It is desirable that the collection efficiency of the system be independent of spot position. That is, the amount of light incident on the detector, when the spot is reflected from a white section in the center of the document, should be the same as when the spot is reflected from a white section at the edge of the document. The integrating tube 1 provides a simple means of achieving this result with a compact and inexpensive device.

Integrating tube 1 uses a combination of diffused reflection and total internal reflection.
1) Diffused Reflection

When a light beam is reflected from a diffused surface, the

surface becomes a Lambertian radiator. A Lambertian

radiator produces an intensity pattern

I(o) = I(o) cos Theta

independent of the direction of the incident beam.

I(o) = Intensity at angle - in watts/steradion

o = Angle measured from the normal to the surface

I(o) = Intensity normal to the surface
2) Total Internal Reflection

Total internal reflection occurs when a light ray encounters

a glass-air boundary at an angle greater than the critical

angle. Total internal reflection can occur only when the

ray is passing from the more dense media into the less dense

media. The critical angle "0" is measured from a normal

to the surface and is determined from the index of

reflection.

sin 0 = 1/n

n = Index of refraction of the more dense media.

The index of refraction of air is assumed as 1.

Integrating tube 1 is made from a bar of cast acrylic. The exterior surface is covered with a diffused reflector 2 (e.g. white bond paper), except for slits 2a and 2b on the top and on the bottom and the end where a photodetector 3 is attached. This establishes air-acrylic interfaces as at 7a and 7b. Document 4 to be scanned is passed under integrating tube 1. Scanning beam 5 is rotated through the sweep angle 6 and is incident on the document through the slits in integrating tube 1.

When beam 5 strikes a white portion of document 4 the diffused light is reflected as rays back into the tube. These reflected rays will fall into one of three categories:
1) A small portion will escape back through the top slit 2a and

be lost.
2) Some of the light...