GB1597569A - Photocopier scanning illumination system - Google Patents

Description

(54) PHOTOCOPIER SCANNING ILLUMINATION SYSTEM (71) We, XEROX CORPORATION of Xerox Square, Rochester, New York, United States of America, a corporation organised under the laws of the State of New York, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state ment This invention relates to photocopying optical systems 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 and 3,982,116.

It is an object of the present invention to provide a scanning illumination system of a more compact form.

According to the invention, there is provided a scanning illumination system for incrementally illuminating an object disposed on an object surface for photocopying, including a linear light source disposed aajacent 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 scan strip relative to a normal through said 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 irrespective of the point along the reflector at which the light is reflected, means to effect relative scan travel of said object surface and said illumination system, whereby said scan strip is illuminated from both sides thereof, relative to a normal through said strip A photocopier illumination scanning system according to the invention will now be described by way of example with reference to the accompany drawings in which: Figure 1 is a schematic optical diagram of a scanning illumination system of the prior art; Figure 2 is a schematic diagram of a novel scanning illumination system; and Figure 3 is an enlarged and exaggerated view of a faceted reflector shown in Figure 2.

Referring now to Figure 1, a scanning illumination system of the prior art is indicated generally at 2 and includes a platen 4 disposed 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 joining 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 synchronously 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 900 than by flatening it out to 1800 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 this.

Referring now to Figure 2, an enlarged schematic of the illumination portion of the optical system 2 is represented. 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 facted 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 faceted reflector 22 are on opposite sides of the instantaneous strip scan area A.

Reflector 22 is a multi-faceted 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 reflector 22 are configured to direct reflected light in the direction of the scan slit A as indicated by the arrows. In an exemplary embodiment, reflector 22 has 100 facet pairs per inch.

Figure 3 is an enlarged view of the faceted configuration of reflector 22. Figure 3 is exaggerated as to relative angles of adjacent facets; it is only illustrative of the faceted reflector.

The reflected and directed illumination from the facted reflector 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 additionally, it is possible to use a lens of smaller aperture (high 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 heretofore been reproduced along with desired object information. In other words, illumination from both sides of the scan strip prevents shadows from being cast.

WHAT WE CLAIM IS: 1. A scanning illumination system for incrementally illuminating an object disposed on an object surface for photocopying, 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 relative to a normal through said 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 irrespective of the point along the reflector at which the light is reflected; means to effect relative scan travel of said object surface and said illumination system; whereby said scan strip is illuminated from both sides thereof relative to a normal through said strip.

2. A scanning illumination system sub- stantially as herein described with reference to Figs. 2 and 3 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (2)

**WARNING** start of CLMS field may overlap end of DESC **. schematic of the illumination portion of the optical system 2 is represented. 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 facted 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 faceted reflector 22 are on opposite sides of the instantaneous strip scan area A. Reflector 22 is a multi-faceted 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 reflector 22 are configured to direct reflected light in the direction of the scan slit A as indicated by the arrows. In an exemplary embodiment, reflector 22 has 100 facet pairs per inch. Figure 3 is an enlarged view of the faceted configuration of reflector 22. Figure 3 is exaggerated as to relative angles of adjacent facets; it is only illustrative of the faceted reflector. The reflected and directed illumination from the facted reflector 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 additionally, it is possible to use a lens of smaller aperture (high 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 heretofore been reproduced along with desired object information. In other words, illumination from both sides of the scan strip prevents shadows from being cast. WHAT WE CLAIM IS:

1. A scanning illumination system for incrementally illuminating an object disposed on an object surface for photocopying, 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 relative to a normal through said 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 irrespective of the point along the reflector at which the light is reflected; means to effect relative scan travel of said object surface and said illumination system; whereby said scan strip is illuminated from both sides thereof relative to a normal through said strip.

2. A scanning illumination system sub- stantially as herein described with reference to Figs. 2 and 3 of the accompanying drawings.