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DIFFUSE CAVITY ILLUMINATORS FOR NON-PLATEN OR DVT RIS SYSTEMS

IP.com Disclosure Number: IPCOM000024920D
Original Publication Date: 1982-Oct-31
Included in the Prior Art Database: 2004-Apr-04
Document File: 4 page(s) / 145K

Publishing Venue

Xerox Disclosure Journal

Abstract

An optimum geometry for a diffusely reflective cavity illuminator is a generally rectangular configuration shown in the Figure. As shown, a cavity illuminator 10 shown in cross-section, is positioned beneath a platen 12 upon which a document 14 is to be copied. It is assumed the scanning requirements are such that illumination scan strip 16 is smaller than 0.5 inch. A pair of elongated light sources 18, 19 are placed within the cavity. The interior walls of the cavity are coated with a diffuse paint providing a high reflectance value R in the actinic spectral region. A diffuse white paint is frequently used for this purpose. The cavity has a total perimeter P and has a width W extending into the plane of the Figure. Illumination from within the cavity illuminates point Q in the center of the illumination slit through an aperture 20 having a width L The document reflects a bundle of rays, represented by a principal ray ?; which exit the illuminator through a second aperture 22 of width L1 and are projected via a lens 24 onto an imaging plane (not shown).

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Page 1 of 4

DIFFUSE CAVITY ILLUMINATORS FOR NON-PLATEN OR DVT RIS SYSTEMS William L. Lama

Proposed Classification US. Cl. 355/67
Int. Ci. G03b 27/54

d

Volume 7 Number 5 September/October 1982 339

[This page contains 1 picture or other non-text object]

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DIFFUSE CAVITY ILLUMINATORS FOR NON-PLATEN OR DVT RIS SYSTEMS (Cont'd)

An optimum geometry for a diffusely reflective cavity illuminator is a generally rectangular configuration shown in the Figure. As shown, a cavity illuminator 10 shown in cross-section, is positioned beneath a platen 12 upon which a document 14 is to be copied. It is assumed the scanning requirements are such that illumination scan strip 16 is smaller than 0.5 inch. A pair of elongated light sources 18, 19 are placed within the cavity. The interior walls of the cavity are coated with a diffuse paint providing a high reflectance value R in the actinic spectral region. A diffuse white paint is frequently used for this purpose. The cavity has a total perimeter P and has a width W extending into the plane of the Figure. Illumination from within the cavity illuminates point Q in the center of the illumination slit through an aperture 20 having a width L The document reflects a bundle of rays, represented by a principal ray ?; which exit the illuminator through a second aperture 22 of width L1 and are projected via a lens 24 onto an imaging plane (not shown).

An optimum design for illuminator 10 is derived by developing document irradiance equations and examining those parameters which yield the maximum irradiance at point Q. Illuminator 10 can be considered as a three-dimensional space surrounded by a surface which is closed except for aperture 20 (ignoring for a moment aperture 22). The reflectance R is averaged over the actinic spectrum. Sources 18, 19 produce a primary source of radiant flux F within the cavity. A portion of this flux escapes through aperture 20 to illuminate the document in scan strip 16. Assuming that the distribution of light on the illuminator interior is uniform both initially on energization of sources 18, 19 and, after reflection from the illuminator walls, the flux emitted from the aperture, FA, is given by the expression:

      *F FA = 1-R (l-AF) F

where A is the ratio of the aperture area to the cavity surface area.

F

The effective aperture radiance NA is the radiant emittance (flux per unit area) divided by W or

I'

NA - 'KAL2W

(2)

The irradiance H at point Q is

?

    XEROX DISCLOSURE JOURNAL Volume 7 Number 5 September/October 1982

340

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