US 3152528 A
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Description (OCR text may contain errors)
Oct. 13, 1964 J. R. PENDRY DOCUMENT CARRIER Filed Sept. 23, 1963 INVENTOR. JAMES R. PENDRY A TTORNEY United States Patent 3,152,528 DOCUMENT CARRIER James R. Pendry, Rochester, N.Y., assignor to Xerox Corporation, Rochester, N.Y., a corporation of New York Fiied Sept. 23, 1963, Ser. No. 310,785 1 Claim. (Cl. 95--1.7)
This invention relates to xerography, and in particular, to a document carrier for use in supporting small, or thin, or irregular shaped documents to be transported through a document reproducing apparatus and for use in reproducing continuous tone and solid area images in a xerographic reproducing apparatus.
More specifically, the invention relates to an improved document carrier for use in a xerographic reproducing apparatus, the document carrier also being suitable for use in comparable types of. device.
In various types of reproducing devices, the document to be reproduced, inserted into the device by an operator, is transported by a suitable conveyor or conveyors and guides through a copying station before being discharged from the reproducing device. In most of these devices, the documents must be of a minimum length or minimum width or both, in order to be properly handled by the document conveying mechanism used in the reproducing apparatus. However, it is often desirous to make reproduction of documents of a length or width less than the minimum size which can be handled by the conveying device of the document reproducing apparatus. In addition, it is often desirous to make reproduction of irregular shaped documents, such as an article cut out of a larger document, or to make a reproduction of a combination of small original documents.
in the process of xerography, for example, as disclosed in either Carlson Patent 2,297,691, issued October 6, 1942, or in Carlson Patent 2,357,809, issued September 12, 1944, a xerographic plate, comprising a layer of photoconductive insulating material on a conductive backing, is given a uniform electric charge over its surface and is then exposed to the subject matter to be reproduced, usually by conventional projection techniques. This exposure discharges the plate areas in. accordance with the radiation intensity which reaches them and thereby creates an electrostatic latent image on or in the plate coating.
Development of the image is effected with developer material or developers which comprise, in general, a mixture of a suitable pigmented or dyed electroscopic powder, hereinafter referred to as toner, and a granular carrier material, which later functions to carry and to generate triboelectric charges on the toner. More exactly, the function of the granular material is to provide the mechanical control to the powder, or to carry the powder to an image surface and, simultaneously, to provide almost complete homogeneity of charge polarity. In the development of the image, the toner powder is brought into surface contact with the coating and is held thereon electrostatically in a pattern corresponding to the electrostatic latent image. Thereafter, the developed xerographic image is usually transferred to a support or transfer material to which it may be fixed by any suitabl means.
Excellent results have been obtained with this process, especially with cascade development using toner-carrier mixtures, in automatic continuous xerographic machines for line work such as letters or lines on a white background and for half-tone images.
Due to the electric field conditions in the region of the electrostatic image, however, large solid areas do not develop uniformly. Xerographic reproductions of such areas delineate their outline only, the centers not being developed or filled in with powder, unless a closelyspaced development electrode is used in the development zone. Cont-inuoustone images suffer in like manner, the tonal rendition being poor unless a development electrode is used. However, with continuous automatic equipment it is not usually feasible to provide a development electrode closely-spaced enough to the xerographic drum surface for the purpose without seriously interfering with the flow of developer and hence slowing down the speed of the machine, and also producing dangerous developer jamming at times.
US. Patent 2,598,732, to Walkup discloses a method of overcoming these difliculties in stationary flat-plate xerographic equipment by exposing the xerographic plate to a screen pattern in addition to the image pattern to be recorded, thereby breaking up the image into a half-tone pattern.
It is therefore the object of this invention to improve document carriers for use in conveying small, or thin, or irregularly shaped documents through the copying station of a document reproducing apparatus.
Another object of this invention is to improve document carriers for use in making a xerographic rendition of a document having variation in tonal value throughout all or part of the area being reproduced.
For a better understanding of the invention as well as other objects and further features thereof, reference is bad to the following detailed description of the inven tion to be read in connection with the accompanying drawings, wherein:
FIG. 1 is a perspective view of a document carrier constructed in accordance with the invention;
FIG. 2 is a perspective view similar to FIG. 1 with an irregular shaped document supported by the document carrier;
FIG. 3 is an enlarged view of a small area of a suitable screen pattern used on the document carrier illustrated in FIG. 1; and
FIG. 4 illustrates schematically a xerographic reproducing apparatus adapted for continuous and automatic operation showing a document carrier and a document to be reproduced supported in the document carrier, about to be transported through the copying station of the xerographic apparatus.
Although the document carrier, constructed in accordance with the invention may be used in any suitable type of reproducing apparatus, the apparatus shown schematically in FIGURE 4, is a xerographic reproducing apparatus of the typpe disclosed in Eichorn et al7 Patent 3,099,943. As shown, the xerographic reproducing ap paratus comprises a xerographic plate including a photoconductive layer or light-receiving surface on a conductive backing and formed in the shape of a drum generally designated by numeral 20, which is journaled in a frame (not shown) to rotate in the direction indicated by the arrow to cause the drum surface sequentially to pass a plurality of xerographic processing stations.
As the drum is rotated, an electrostatic charging unit, such as corona charging device 21 serves to apply a uniform electrostatic charge over the photoconductive layer which is dissipated in part by a radiant image exposure of the original or document to be reproduced, leaving thereon an electrostatic latent image corresponding to g the image of the original document.
Exposure of the charged drum surface to a radiation image is made by a suitable exposure mechanism such as, desirably an optical scanning or projection system, or the like, designed to project a line image onto the surface of the photoconductive xerographic drum from a suitable original.
In the embodiment shown, the optical scanning or projection assembly consists of a copy board in the shape of a drum, hereinafter referred to as copy drum 30, which is adapted to support copy to be reproduced and is arranged to rotate in light projection relation to the moving light-receiving surface of the xerographic drum. Uniform lighting is provided by suitable lamps 31 attached to a slotted light reflector 32 mounted adjacent to copy drum at the copying station of the apparatus.
A slotted light shield 33, adapted to protect the xerographic plate from extraneous light, is positioned adjacent to the surface of the xerographic plate. A slot aperture in the light shield extends transversely to the path of movement of the light-receiving surface of the zerographic drum 20, to permit reflected rays from the copy drum to be directed against a limited transverse area of the light receiving surface of the drum as it passes thereunder.
To enable the optical system to be enclosed within a relatively small cabinet, a folded optical system including an object mirror 34, a lens 35, and an image mirror 36, is used in this particular embodiment of a xerographic reproducing apparatus.
A document fed through document guides 17 to the copy drum is removably secured thereon by a suitable gripper mechanism for movement therewith in timed relation to the movement of the xerographic drum whereby a flowing image of the document is projected onto the xerographic drum. The document is held against the surface of the copy drum until gripped by means of document retaining guides 38. Pressure guides 39 and document guard 4-1 help to retain and guide the trailing edge of the document on the copy drum. After the document is scanned, it is released from the copy drum to be transported out of the machine by the copy drum and document feed-out rollers 4-2 through document feedout guide 43.
In the reproducing device of the type shown in FIG. 4, and in similar types of reproducing devices, the apparatus used for conveying a document through the copying station is only capable of conveying documents of a minimum length and/or Width.
Referring now to the subject matter of the invention and, in particular, to FIGS. 1, 2 and 3, the reference numeral it indicates generally a document carrier con structed in accordance with the invention. The document carrier in is preferably formed of a flexible transparent sheet of cellophane, cellulose acetate or a like material. This member is of a length at least twice as long as the minimum length of a document that can be conveyed by the conveyor system of the reproducing device for which it is intended to use the document carrier. In addition, this member is also of a width at least equal to the minimum width of a document which can be conveyed by the conveyor system of the reproducing device. Preferably though, this member can be made to correspond to the maximum size document conveyable through the reproducing apparatus. Thus if the document carrier is to be used in a reproducing device capable of reproducing a maximum size document of say, for example, 9 inches by 13 inches, the member can be 9 inches wide and 26 inches long, so that when it is folded over, as described hereinafter, the document carrier is suitable for supporting a 9 x 13 document.
On one-half of the sheet, forming the document carrier, there is printed, or otherwise applied, a screen or dot pattern 14- of opaque areas on the transparent sheet. After the application of the screen or dot pattern 14- to one surface of one-half of the sheet, the sheet is folded in half along a line extending transversely across the sheet to form, in effect, a document carrier consisting of tvo sheets 11 and 12 joined together along a common fold line which forms the common fold or leading edge 15 of the document carrier.
One of the sheets thus formed, sheet 1 transparent, while the other sheet, sheet as shown, is 2, as shown,
is provided with a screen or dot pattern of opaque and transparent areas. Preferably, the sheet is folded so that the screen or dot pattern on sheet 12 is directly adiacent to sheet ill. This arrangement is preferred, since it will minimize the casting of a shadow on a document inserted between these sheets when the document is to be scanned through sheet 112. It is also preferred that opposite corners of the trailing edge, or free edges of these members be cut away to facilitate separation of these members for the insertion or removal of documents therebetween.
For reproducing documents containing line copy, a document 16 is inserted between the members ill and 12 with the back of the document in contact with memer 21. With this arrangement the document is scanned through the clear transparent member ll of the document carrier. As shown in FIGS. 1 and 2, one of the members, here shown as member 11, is raised to facilitate inserting or removal of a document into the document carrier.
Referring now to part of the subject matter of the invention, and specifically to the use of the screen or dot pattern of member 12, exposure of the charged drum surface of the xerographic reproducing apparatus, shown in PEG. 4, to a radiation image takes place continually. The exposure time is controlled by the exposure slit in the slotted light shield which spans the photoconductive surface portion of the drum. With the drum rotating at a peripheral speed of, for example, one and one-half inches per second, one and one-half inches of drum surface will pass under any given point of the exposure slit opening every second. Thus if the width of the slit is one-quarter of an inch, any given point of the image will be exposed onto a corresponding point on the drum surface throughout the entire period of time that it takes this point on the drum surface to traverse the one-quarter of an inch opening.
With this arrangement, the charge on the drum can be dissipated in the illuminated areas in accordance with image pattern of the original and the period of exposure, i.e., the charge remains on or in the photoconductive layer of the drum until exposed to the focused image from a document, which then causes a release of charge proportional to the radiation from the copy. Possibly due to the configuration of the electrostatic field above the photoconductive layer, the electrostatic lines of force tend to concentrate at the edges of areas still carrying a charge after exposure.
During development of the latent electrostatic image, the developing material, or toner, is attracted mainly to the areas where the electric fields are the highest and the lines of force most concentrated. This is excellent for developing narrow lines and printed or typed characters, but where large solid areas are present in the original, they are not reproduced on development as solid areas of toner, but rather the toner will deposit heavily along the edges of the areas, and very little or none will deposit in the centers, resulting in an odd-looking copy. With continuous-tone originals similar effects are encountered.
In accordance with the present invention, these problems are overcome in rotating drum-type xerographic machines by the introduction in the exposure system of the machine, of a shadow-casting member comprising an array of opaque lines or opaque dot elements which break up the light into a half-tone pattern. The resulting electrostatic images, after exposure, are therefore subdivided into a half-tone pattern, resulting in a configuration of the electrostatic fields above the photoconductive surface which causes the uniform half-tone development of large solid areas and the rendering of continuous tones as halftones.
Stated in other words, when it is desired to make reproductions of documents having large solid areas present in the document or when it is desired to make reproductions of continuous tone originals, the document is inserted in the document carrier with the back of the document in contact with the clear transparent member 11. With this arrangement the document to be reproduced is scanned through the screen or dot pattern of member 12, that is, the shadow-casting member just described.
Any one of several screen sizes may be used, the finer sizes generally giving the more natural or higher quality results in continuous tone rendition. Thus, while a coarse screen having 50 or 60 dots or lines to the linear inch will be useful for some purposes, such as in the direct production of half-tone images, finer screens, such as those having 100, 200, 300, 400 and even more dots or lines to the inch will give more nearly a continuous tone appearance to the finished reproduction. With the finer screens the screen pattern may be barely perceptible as such in the finished reproduction and the copy will have the appearance of a continuous tone photograph. The contrasty appearance obtained without the use of the screen exposure step is eliminated or greatly reduced and large black areas are rendered with apparently uniform density throughout. Preferably, the member 12 of the document carrier is formed with a 50-50 ratio of clear and opaque areas.
While the invention has been described with reference to the structures disclosed herein, it is confined to the specific details set forth, and this application is intended to cover such modification or changes as may come within the purposes or scope of the following claim.
6 What is claimed is: A document carrier for use in a document reproducing apparatus having a copying station and a conveyor system for transporting documents of a minimum length and/ or width through the copying station, said document carrier being adapted for conveying documents of a length or width shorter than said predetermined minimum length or width through said conveying system,
said document carrier comprising a flexible member of a length at least twice as long as the minimum length of a document conveyable by said conveyor system, and of a width at least as wide as the minimum width of a document conveyable by said conveyor system,
said flexible member having a transverse fold to form two superimposed sheets of approximately equal length, the length of said sheets being at lea-st equal to the minimum length of a document conveyable by the conveyor system,
said fold of said member defining a common leading edge for said sheets to enter into the conveyor system, the trailing edges of said sheets being free for relative movement with respect to each other to permit insertion of a document therebetween,
one of said sheet being transparent, and the other one of said sheets having alternate small transparent areas and small opaque areas, the opaque areas and the spacing between the opaque areas being of equal area to provide a -50 ratio of opaque and transparent areas.
No references cited.