CA1111009A - Photocopier scanning illumination system - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A photocopier object platen scanning illumination system is disclosed in which a linear light source illuminates an object on the platen by strip scanning the same. A facetted reflector faces the linear lamp from the other side of the exposure strip and directionally reflects light from the lamp onto the exposure strip.

Description

BACKCROUND OF T~E INVENTION
This invention relates to photocopying optical æystems and more particularly to a platen scanning illumination system for a photocopier.
Typically in the prior art to which the present invention relates, one or more linear light sources is disposed for scanning of an object platen. Such scanning lamps sometimes have light apertures to direct light at the desired scan strip, or they may have one or more associated reflectors, such as elliptical reflectors to focus light onto the scan strip. Examples of these two systems are shown respectively in U.S. Patents 3,779,640 to Kidd and 3,982,116 to Sakuma.
It is an object of the present invention to provide a scanning illumina-tion system in a more compact geometry than has been heretofore known.
Another object is to provide a scanning illumination system by which desired object illumination can be achieved with a single light source.
Another object is to provide a scanning illumination system by which a scan strip is illuminated for both sides thereof to prevent object shadows.
SU~ARY OF THE INVENTION
This invention is practiced in one form by a photocopier ob~ect platen scanning illumination system in which a linear light source illuminates an object on the platen by strip scanning the same. A facetted reflector faces the linear lamp from the other side of the exposure strip and directionally reflects light from the lamp onto the exposure strip.
Thus, in accordance with the present teachings, a scanning illumination system is provided for incrementally illuminating an object disposed on an object surface for photocopy. The system includes a linear light source dis-posed adjacent to the Db~ect surface to illuminate an object disposed thereon, the light source directing light to a scan strip of the object surface, A
reflector is provided disposed substantially normal to the object surface and operatively connected to and facing the light source with the light source and the reflector being on opposite sides of the scan strip. The reflector com-,.~

prises a plurality of offset reflective facets forming a "Fresnel" reflector to direct reflected light from the light source to the scan strip of the object surface with means being provided to effect relative scan travel of the object surface and the illumination s~stem whereby the scan strip is illuminated from both sides thereof.
For a better understanding of this invention, reference is made to the following detailed description of an exemplary embodiment, given in connection with the accompanying drawing.

-2a-DRAWING
Figure 1 is a schematic optical diagram of a scanning il-lumination system of the prior art.
Figure 2 is a schematic diagram of an improved scanning il-lumination system according to this invention.
Figure 3 is an enlarged and exaggerated view of the facetted reflector shown in Figure 2.
DESCRIPTION
ReEerring now to Figure 1, a scanning illumination system of the prior art is indicated generally at 2 and includes a platen 4 dis-posed in an object plane, a photoreceptor 6 disposed in an image plane, a projection lens 8 appropriately located between the object and image planes, first and second mirrors 10 and 12 to fold the optical system, and a scanning linear lamp 14 immediately under the platen 4. Platen 4 is mechanically supported on a machine frame of which a vertical member - or side 16 of the machine is shown ~oining the platen 4 at or near its edge.
In operation, lamp 14 scans the underside of platen 4 while simultaneously projection lens 8 scans in the same direction at an appropriate speed depending on system magnification. A composite image of the incrementally scanned object plane is thus laid down on the syn-chronously moving photoreceptor 6.
A benefit to the flush or nearly flush arrangement of the platen 4 with the side 16 is that it facilitates copying of originals in book format. That is, a book can more easily be laid on the platen 4 by opening it to 90 than by flatening it out to 180 on an extended flat platen. The presence of side 16 flush with the edge of the platen 4 has its disadvantage, however, to the extent that there is insufficient space beneath the platen, at its edge, to accommodate a double lamp configuration of the type illustrated by the cited patent 3,779,640.
The present invention remedies tbis.

Referring now to Figure 2, an enlarged schematic of the il-lumination portion of the optical system 2 is represented and includes the present invention. Lamp 14 is a tubular lamp, such as a fluorescent lamp, and includes a reflective coating 16 on the lamp envelope, coating 16 defining an aperture 18 for the transmission of light in the desired direction of the scan strip area of platen 4. Lamp 14 is mounted to a lamp carriage 20 for reciprocating movement relative to the platen 4.
A facetted reflector 22 is positioned generally perpendicular to the surface of platen 4 and facing the light aperture 18 of lamp 14.
Reflector 22 is mounted to the lamp carriage 20 for movement therewith.
Lamp 14 and facetted reflector 22 are on opposite sides of the instanta-neous strip scan area A.
Reflector 22 is a multi-facetted or "Fresnel" reflector, the equivalent of a cylindrical mirror in the sense that a Fresnel lens is the equivalent of an ordinary lens. The several facets 24 of the reflec-tor 22 are configured to direct reflected light in the direction of the scan slit A as indicated by the arrows. In an exemplary embodiment, raflector 22 has 100 facet pairs per inch. Figure 3 is an enlarged view of the facetted configuration of reflector 22. Figure 3 is exaggerated as to relative angles of adjacent facets; it is only illustrative of the facetted reflector.
The reflected and directed illumination from the facetted re-flector 22 nearly doubles the irradiance at the scan slit on the platen 4. Because of this increased irradiance and therefore exposure level, it is now possible to use a smaller exposure slit near the image plane with resulting improvements in resolution and tracking error. Alternatively or additional:ly, it is possible to use a lens of smaller aperture (higher f/#) in the optical system. Another benefit of this illumination system is that objects or documents that are not perfectly planar, such as pasted-up documents, do not cause shadows to be cast which have hereto-fore been reproduced along with desired object information. In other words, illumination from both sides of the scan strip prevents shadows from being cast.
The foregoing description of an embodiment of this invention is given by way of illustration and not of limitation. The concept and scope of the invention are limited only by the following claims and equivalents thereof whlch may occur to others skilled in the art.

Claims

WHAT IS CLAIMED IS:

1. A scanning illumination system for incrementally illumi-nating an object disposed on an object surface for photocopy, including:
a linear light source disposed adjacent to said object surface to illuminate an object disposed thereon, said light source directing light to a scan strip of said object surface;
a reflector disposed substantially normal to said object surface and operatively connected to and facing said light source;
said light source and said reflector being on opposite sides of said scan strip;
said reflector comprising a plurality of offset reflective facets forming a "Fresnel" reflector to direct reflected light from said light source to said scan strip of said object surface;
means to effect relative scan travel of said object surface and said illumination system;
whereby said scan strip is illuminated from both sides there-of.