LIGHT COLLECTOR ROD FOR USE WITH A FLYING SPOT SCANNER

Abstract: A light collector (100) for collecting light reflected from a photoconductive surface bearing a developed image and scanned by a flying spot scanner. The collector comprises a rod-like element (102), the central core (104) of which is com­ prised of a relatively rigid transparent material. The core is en­ cased by a cladding material (106) having an index of refraction lower than that of the core. A light diffusing coating (110) is provided on the outer surface of the cladding material, except for a slit-like aperture (108) for receiving light reflected from the photoconductive surface. In an alternative embodiment, the dimension of the light receiving aperture is varied uniformly along the length of the collector, the size of the aperture at the collector center being at a minimum. In a further embodiment, a slit-like axial section of the cladding material opposite the light receiving aperture is removed and replaced by a highly reflecting, light diffusing coating.

Description: Liqht Collector Rod for Use with a Flying Spot Scanner This invention relates to a light collector for use with a flying spot scanner for raster scanning images, said collector being disposable opposite the image to be scanned to collect light reflected from the image. In xerographic systems of the type wherein the toner developed image on the system photoconductive member is scanned by a flying spot beam, the light reflections therefrom are converted to analog image signals representative of the developed image being scanned. One manner of doing so utilizes a light collector disposed adjacent the photoconductive surface to gather or collect the scattered and reflected light emanating from the photoconductive surface. While light collectors may take various forms, a preferred type, because of its small size and relatively low cost, is a transparent rod. However, the light collection efficiency of a rod is so low as to effectively rule out use of this device. Attempts to improve the collection efficiency of ro & ype collectors by applying various reflective or opaque coatings to the exterior thereof has resulted in some improvement. Still, despite modifications and improvements, the collection efficiency of rod-type collectors remains marginal. The present invention is intended to provide a light collector of improved efficiency, and is characterised by a) an elongate transparent, central core; b) a layer of cladding material covering the periphery of said core; c) a layer of light diffusing material covering the outer periphery of said cladding material, except for a slit-like aperture through which light reflected from the image being scanned enters said core, said aperture extending in a direction substantially parallel to the length of said core; and d) a photosensor at at least one end of said collector, said photosensor being operatively coupled to said collector to enable said photosensor to sense light transmitted axially along said core whereby to provide image signals representative of the image being scanned, light reflected from the image being scanned passing through said aperture and through said cladding material and said core to said light diffusing material, said light diffusing material diffusing said light and reflecting said light back into said core, a portion of said diffused light being trapped in said cladding material whereby to form a secondary diffusion, said light travelling by reflection axially along said core and said cladding material to said photosensor. In one embodiment of the invention, the layer of cladding material has a slit-like aperture extending in a direction parallel with the slit-like aperture in the layer of light diffusing material but on the opposite side of the core. A light collector in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic view showing an exemplary apparatus for carrying out multiple function image processing imcorporating the improved light collector of the present invention; Figure 2 is an isometric view showing details of the light collector shown in Figure 1; Figure 3 is a cross-sectional view of the light collector shown in Figure 2; Figure 4 is a side view of an alternative light collector construction providing a variable sized light aperture; Figure 5 is an isometric view of a second alternativelight collector construction wherein a portion of the cladding material is removed and a light diffusing coating substituted therefor; and Figure 6 is an enlarged cross-sectional view of the light collector shown in Figure 5. There is shown herein a multi-mode reproduction apparatus operable selectively in a COPY mode to xerographically make copies of original documents in the manner typical of xerographic copiers or machines, in a WRITE mode to xerographically produce copies from image signals input thereto using a flying spot type scanner, and in a READ mode to read images developed on the machine photoreceptor with the same flying spot scanner to produce image signals representative thereof and thereby convert the image to electronic signals. Referring now particularly to Figures 1 and 2 of the drawings, there is shown an exemplary xerographic type reproduction apparatus 10 incorporating the present invention. Xerographic reproduction apparatus 10 includes a viewing station or platen 12 where document originals 13 to be reproduced or copied are placed. For operation in the COPY mode as will appear more fully herein, a light/lens imaging system 1l is provided, the light/lens system including a light source 15 for illuminating the original 13 at platen 12 and a lens 16 for transmitting image rays reflected from the original 13 to the photoconductive surface 19 of drum 18 at exposure station 21. Charging, developing, transfer, and cleaning stations 20, 22, 26, 32 respectively are disposed about drum 18 in operative relation thereto. Charging station 20 includes a corona charging means 23 for depositing a uniform electrostatic charge on the photoconductive surface 19 of drum 18 in preparation for imaging. A suitable developing mechanism, which may for example comprise a magnetic brush 25, is provided at developing station 22 for developing the latent electrostatic images created on drum 18. At transfer station 26, corona transfer means 27 effects transfer of the developed image to a suitable copy substrate material 28. A suitable drum cleaning device such as a rotating cleaning brush 33 is provided at cleaning station 32 for removing leftover developing materials from the surface 19 of drum 18. Brush 33 may be disposed in an evacuated housing through which leftover developer materials removed from the drum surface by the cleaning brush are exhausted. A suitable erase lamp (not shown) may be provided to discharge residual charges on the photoconduc- tive surface 19 prior to charging by charging means 23. In the example shown, photoconductive surface 19 comprises a uniform layer of photoconductive material such as amorphous selenium on the surface of drum 18. Drum 18 is supported for rotation by suitable bearing means (not shown). A suitable drive motor (not shown) is drivingly coupled to drum 18 and rotates drum 18 in the direction shown by the solid line arrow when processing copies. When operating in the COPY mode, the photoconductive surface 19 of drum 20 is charged to a uniform level by corona charging means 23. Platen 12 and the original document 13 thereon is irradiated by light source 15, the light reflected from document 13 being focused onto the photoconductive surface 19 of drum 18 by lens 16 at exposure station 21. Platen 12 and the document 13 thereon are at the same time moved in synchronism with rotation of the drum 18. The light reflected from the original 13 selectively discharges the charged photoconductive surface in a pattern corresponding to the image that comprises the original document. The latent electrostatic image created on the surface 19 of drum 18 is developed by magnetic brush 25 and transferred to copy substrate material 28 through the action of transfer corona means 27. Following transfer, the photoconductive surface 19 of drum 18 is cleaned by cleaning brush 33 to remove leftover developer material. A suitable fuser or fixing device (not shown) fixes the image transferred to copy substrate material 28 to render the copy permanent. While a drum type photoconductor is illustrated other photoconductor types such as belt, web, etc. may be envisioned. Photoconductive materials other than selenium, as for example, organic may also be contemplated. And while a scan type imaging system is illustrated, other types of imaging systems such as full frame flash, may be contemplated. The photoconductor may be opaque, that is, impervious to light, or wholly or partially transparent. The exemplary drum 18 typically has an aluminum substrate which renders the drum opaque. However, other substrate materials such as glass may be contemplated, which would render drum 18 wholly or partially transparent. One material consists of an aluminized mylar substrate having a layer of selenium dispersed in poly-Nvinyl carbazole with a transparent polymer overcoating containing a charge transport compound such as pyrene. Xerographic reproduction apparatus 10 includes a flying spot scanner 59. Scanner 59 has a suitable flux source of electromagnetic radiation such as laser 60. The collimated beam 61 of monochromatic radiation generated by laser 60 is reflected by mirror 62 to a modulator 65, which for operation in the WRITE mode, modifies the beam 61 in conformance with information contained in image signals input thereto, as will appear. Modulator 65 may comprise any suitable modulator, such as acousto-optic or electro-optic type modulators for imparting the informational content of the image signals input thereto to beam 61. Beam 61 is diffracted by disc deflector 68 of a holographic deflector unit 70. Defleetor 68 comprises a substantially flat disc-like element having a plurality of grating faces or facets 71 forming the outer periphery thereof. Deflector 68 which is preferably glass, is driven by motor 72. Preferably, deflector 68 is disposed so that light beam 61 is incident to the facets 71 thereof at an angle of substantially 450. The diffracted scanning beam 61' output by deflector 68 exits at a complementary angle. The scanning beam 61' output by deflector 68 passes to an imaging lens 75. As shown, lens 75 is located in the optical path between deflector 68 and mirror 77, lens 75 being of a diameter suitable to receive and focus the scanning light beam diffracted by facets 71 of deflector 68 to a selected spot in the focal plane proximate the surface 19 of drum 18, as will appear. The scanning beam 61' from lens 75 is reflected by mirror 77 to read/write control mirror 78, which in turn, reflects the beam to provide selectively image READ beam 63 (shown by solid line in Figure I) or image WRITE beam 64 (shown by dotted line in Figure 1). Image READ beam 63 is reflected by mirror 80 to a location on the surface 19 of drum 18 downstream of developer 22, while image WRITE beam 64 is reflected by mirror 85 to a location on surface 19 upstream of developEr 22. In the case where the photoconductive material is opaque, a portion of the light impinging on the surface 19 of drum 18 is reflected. In the ease where the photoconductive material is transparent, the light is transmitted, depending on the degree of transparency of the photoconducz tive material through the photoconductive material to the drum interior. As will be understood, reflected light is composed of both specular and diffuse reflected light while transmitted light is composed of specular and diffuse transmitted light. The reflected or transmitted light from the photoconductive surface 19 of drum 18 and the developed image thereon is collected in collector 100, and there converted to image signals, as will appear. Read/write control mirror 78 is supported for limited movement between a READ position (shown in solid line in the drawing) and a WRITE position (shown in dotted line in the drawing). A suitable driving mechanism such as solenoid 81 is provided to selectively move the mirror 78 from one position to the other. Return spring means (not shown) may be provided to return mirror 78 to the original position upon deenergization of solenoid 8L OPERATION In the COPY mode, latent electrostatic images are formed on the photoconductive surface 19 of drum 18 through exposure of the document 13 on platen 12 as described heretofore. In the WRITE mode, latent electrostatic images are created on the charged photoconductive surface 19 of drum 18 by means of the flying spot scanner 59 in accordance with image signals input thereto. In this mode, solenoid 81 is energized to move control mirror 78 to the WRITE position (the dotted line position shown in Figure 1). In this position, mirrors 78, 85 cooperate to provide image WRITE beam 64 at a point on the surface 19 of drum 18 upstream of developing station 22. Modulator 65 modulates the light intensity of beam 64 in accordance with the content of the image signals input thereto so that image WRITE beam 64 dissipates the electrostatic charge on the drum surface to create a latent electrostatic image representative of the image signals input thereto as beam 64 scans thereacross. The electrostatic latent image so created is thereafter developed by magnetic brush 25 and transferred to copy substrate material 28 by corona transfer means 27 at transfer station 26. Following transfer, the surface of drum 18 is cleaned by cleaning brush 33 as described. In this mode, and in the image READ mode described below, deflector 68 is continually driven at substantially constant velocity by motor 72. In the WRITE mode, the image signal source is controlled so as to be synchronized with rotation of deflector 68. The rotational rate of xerographic drum 18 which determines the spacing of the scan line, is preferably synchronized to the signal source in order to maintain image linearity. In the image READ mode, where it is desired to read original 13 and convert the content thereof to image signals, solenoid 81 is deenergized to place control mirror 78 in the READ position (the solid line position shown in Figure 1). In this position, mirror 78 cooperates with mirror 80 to provide image READ beam 63 on the surface 19 of drum 18 at a point downstream of developing station 22, beam 63 scanning across the surface of drum 18 and any image developed thereon. In this mode, a latent electrostatic image of the original 13 on platen 12 is created on the surface 19 of drum 18 through exposure of the original 13 and subsequent development by magnetic brush 25 in the manner described heretofore. As the developed image is carried on drum 18 from developing station 22 to transfer station 26, the image is scanned line by line by image READ beam 63. The light is reflected from the photoconductive surface 19 in accordance with the presence or absence of toner on the drum surface, the reflected light being picked upby collector 100 and converted to image signals as will appear hereinafter. As will be understood where the light beam strikes toner, the light is absorbed and no light is reflected. Where the light beam strikes uncovered portions of the photoconductive surface 19 of drum 18, a portion of the light is reflected back by the photoconductive surface to collector 100. The presence or absence of light is sensed by collector 100 which provides an analog image signal representative of the developed image scanned as will appear. Image signals generated by collector 100 may be used to produce additional copies of the original 13, or stored, or transmitted to a distant point, etc.. Following scanning, the developed image on drum 18 may be transferred to substrate material 28 in the manner described heretofore. Alternatively, transfer may be dispensed with and the drum surface cleaned by cleaning brush 33. Referring particularly to Figures 2 and 3, collector 100 comprises a rod-like element 102, the inner or central core 104 of which is comprised of a relatively hard homogeneous transparent material such as glass, plastic, etc.. One suitable material comprises polymethyl methacrylate. To protect the rod 102 against loss in light collecting efficiency due to accumulations of dirt, toner dust, and the like on the rod surface, particularly from toner dust originating from the nearby developing station 22, and to improve collector efficiency, the outer surface of core 104 is covered, i.e. clad, with a suitable cladding material 106 having an index of refraction lower than the index of refraction of core 104. One suitable cladding material 106 comprises a low-index flurocarbon compound. The outer periphery of the cladding material 106, except for a slit-like aperture 108 extending axially along the length of rod 102 is covered with a suitable light diffusing coating or covering 110 which may for example comprise titanium dioxide. A suitable light detector such as a photocell 112 is provided at one end of the rod 102 for sensing light transmitted axially along the collector interior. A suitable specular reflecting surface 114 such as aluminum foil, is provided at the opposite end of collector 100 to reflect light back along the rod interior toward photocell 112. Alternatively, the reflecting surface may comprise a suitable diffusing material. Collector 100 is supported in spaced relation to the photocon- ductive surface 19 by suitable means (not shown), with the slit-like aperture 108 facing the photoconductive surface 19. Preferably, the longitudinal axis of collector 100 is parallel with the axis of rotation of drum 18. Referring particularly to Figure 3 of the drawings, light reflected from the photoconductive surface 19 during scanning of the developed image thereon by beam 63 when operating in the READ mode passes into the interior of collector 100 via the slit-like aperture 108. Light substantially normal to the collector 100 passes through the cladding material 106 and inner core 104 and strikes the light diffusing coating llO which diffuses and reflects the light back toward the collector interior at various angles of incidence, the light returning through the cladding material 106 to the core 104 where the light is reflected back and forth along the core interior in a direction axial of rod 102. Due to the diffusion of the light beyond the critical angle of re-entry into core 104, some light passing through the cladding material 106 is reflected within the bounds of the cladding material, creating secondary diffusion. The diffused light propagates axially along the length of rod 102 and the cladding material 106, the light being reflected by and within both the rod 102 and the cladding material 106. Light reaching the end of collector 100 adjacent photocell ll2 is detected by photocell 1l2. Light transmitted through rod 102 and cladding material 106 and reaching the opposite end of collector 100 is reflected back along the axis of collector rod 102 toward photocell 112 by the reflecting surface 114 to intensify the brightness of the light striking photocell 1l2. Where the reflecting surface 114 is composed of a diffusing material, the light reaching the rod end is diffused back into the rod/cladding material interior. Photocell 112 generates analog image signals in response to the presence or absence of light, the signal level being representative of the intensity of the light striking photocell 112. The resulting signal output of photocell 112 is representative of the developed image on the photoconduetive surface scanned by image READ beam 61. In the embodiment shown in Figure 4, where like numerals refer to like parts, the size of the aperture 108' of the collector 100' thereshown is varied in order to provide a uniformity of response along the length of the collector. In the example shown, the degree of wrap around of the light diffusing coating 110 is at a maximum at some point along the rod length, with the degree of wrap thereafter diminishing as the rod ends 115, 1l6 are approached. In one example, the maximum degree of wrap around of coating 1l0 is adjacent the rod center with minimum degree of wrap around at the rod ends 115, 116. In use, collector 100' is supported adjacent the photoconductive surface 19 of drum 18 in the manner described heretofore with the variable size aperture 108' thereof opposite to and facing photoconductive surface 19. While aperture 108' is shown as being uniformly varied, nonuniform variations may instead be contemplated, for example a stepped aperture. Referring now to the embodiment shown in Figures 5 and 6 of the drawings, where like numerals refer to like parts, the collector thereshown has a slit-like portion 125 of the cladding material 106 diametrically opposite light receiving aperture 108 removed in order to increase the trapping of light within the high transmission modes of the clad rod, and to reduce the trapping of light within the cladding material 106 as in the Figures 23 embodiment Light diffusing coating 1l0' covers the outer periphery of the remaining cladding material 106' as well as the portion 125 of rod 102 where cladding material has been removed to further enhance the efficiency of the collector and to minimize effects of dirt, etc. In the Figures 5and 6 embodiment, light reflected from the photoconductive surface 19 enters rod 102 through aperture 108. Light rays pass directly across the rod 102 and strike the surface of rod 102 covered by diffusing coating 110'. Coating 110' diffuses the light rays back to the interior of the rod 102 where the rays are reflected by cladding material 106', the reflected rays passing axially along rod 102 toward the ends thereof where the light is sensed by photodiode 112 or reflected toward photodiode 112 by a reflecting surface like the reflecting surface 114 of figures 2 and 3. In this embodiment, the diffusing coating Ild serves to diffuse a fraction of the entering light rays at an angle greater than the criticial angle through which cladding material 106 transmits light. As a result, the cladding material 106' reflects rather than transmits the light striking the cladding material to reduce light loss and increase efficiency. While a single photosensor 112 is illustrated at one end of collector 100, it will be understood that photosensors may be provided at both ends of collector 100. In that event, reflecting material 114 would be dispensed with. While collector 100 is disclosed herein in conjunction with apparatus for scanning images developed on a photoconductive surface, it will be understood that the collector of the present invention may be used with other types of scanning systems as for example, where a document original is read by a raster scanner.

Claims: CLAIMS: 1. A light collector for use with a flying spot scanner for raster scanning images, said collector being disposable opposite the image to be scanned to collect light reflected from the image, the collector. being characterised by:a) an elongate, transparent, central core; b) a layer of cladding material covering the periphery of said core; c) a layer of light diffusing material covering the outer periphery of said cladding material, except for a slit-like aperture through which light reflected from the image being scanned enters said core, said aperture extending in a direction substantially parallel to the length of said core; and d) a photosensor at at least one end of said collector, said photosensor being operatively coupled to said collector to enable said photosensor to sense light trasmitted axially along said core whereby to provide image signals representative of the image being scanned, light reflected from the image being scanned passing through said aperture and through said cladding material and said core to said light diffusing material, said light diffusing material diffusing said light and reflecting said light back into said core, a portion of said diffused light being trapped in said cladding material- whereby to form a secondary diffusion, said light travelling by reflection axially along said core and said cladding material to said photosensor. 2. The collector according to claim 1, in which the width of said aperture varies over the length of said core. 3. The collector according to claim 2 in which the width of said aperture varies uniformly over the length of said core from a maximum at the core ends to a minimum adjacent the center of said core. 4. The collector according to claim 1 in which the layer of cladding material has a slit-like aperture extending in a direction parallel with the slit-like aperture in the layer of light diffusing matey vial but on the opposite side of the core. 5. The collector according to any one of claims 1 to 4 in which the refractive index of the cladding material is less than that of the core. 6. The collector according to any one of claims 1 to 5 in which said collector includes a single photosensor at one end thereof, and specular reflecting means at the opposite end of said collector for reflecting light transmitted through said core and said cladding material toward said photo sensor. 7. The collector according to any one of claims 1 to 5 in which said collector includes a single photosensor at one end thereof, and diffuse reflecting means at the opposite end of said collector for diffusing light transmitted through said core and said cladding material back into said core and said cladding material. 8. Xerographic copying apparatus including a flying spot scanner adapted to raster scan images developed on a photoconductive surface, and a light collector disposed adjacent the photo conductive surface to collect light reflected from the photoconductive surface when scanning images developed thereon, the collector being in accordance with any one of claims 1 to 7.

Inventors: BANTON, MARTIN E., SNELLING, CHRISTOPHER
Applicants: XEROX CORPORATION
Application year: 1981
Main classification: H04N1
IPC codes: H04N1