CA1114003A

CA1114003A - Duplex reproduction machine

Info

Publication number: CA1114003A
Application number: CA231,943A
Authority: CA
Inventors: George D. Delvecchio
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1974-08-05
Filing date: 1975-07-21
Publication date: 1981-12-08
Also published as: JPS5570854A; FR2281590A1; NL7509333A; DE2534977C2; BR7504957A; SE7508701L; DE2560246C2; GB1517347A; AU8316775A; BE832115A; IT1040276B; ES440012A1; JPS5139054A; JPS563546B2; FR2281590B1; DE2534977A1

Abstract

ABSTRACT OF THE DISCLOSURE
Method and apparatus for projecting information existing on both sides of a duplex document, using dual scan of a transparent sandwich platen. Duplex copies of the docu-ment may be produced by applying a print of one side of the document to one side of the copy sheet, and then transporting the copy sheet within the apparatus to apply a print of the second side of the document to the reverse side of the copy sheet.

Description

BACKGROUND AND SUMMARY OF I~VENTION
The present invention relates generally to the photocopying of documents, and is illustrated as applied to the copying of documents by electrostatic photography.
More particularly, the present invention is directed to an improvement in the copying of duplex documents, and by the term "duplex documents" is meant a document wherein infor-mation is contained on both sides of the document sheet.
Further, the present invention contemplates the reproduction of duplex documents as duplex copy, wherein both sides of the copy sheet are utilized to reproduce the two sides of the original duplex document.
The electrostatic photocopying process is well known. In one common xerographic form of electrostatic phot~copying, an optical image of a document to be copied is applied to a uniformly charged photoconductive plate or photoreceptor, causing the plate to discharge in those areas which are struck by light. As a result, an electro-static latent image of the document is formed on the photo-receptor plate. This latent image may then be developed to a visible image by the selective attraction of electro-.
scopic toner particles to the charged areas of the latentimage. Usually, the toner particles of the developed image are transferred from the photoreceptor to a receiving copy-sheet so the photoreceptor can be re-used, and the transferred toner particles may then be fused to the copy sheet to form a permanent copy of the document.
Many documents carry information on both sides of the document sheet. To copy both sides of such duplex

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documents in the conventional mode of copier operation, first one side of the document is exposed to the copier so that an optical image of the first side is applied to the photoreceptor, then the document is turned over to ex-pose the secona side to the copier. Typically, each side of the document is reproduced on a separate copy sheet, resulting in two sheets of copy for each single sheet of duplex document.
In accordance with the present invention, a duplex document is placed in a sandwich platen which is : transparent on both sides, and then one side of the document sheet is exposed to the copier through one side of the platen, followed by exposure of the other side of the docu-ment through the other side of the platen. Dual optical paths are pro~ided, so that each side of the document can be exposed to the copier automatically, and without the necessity of turning the document over. In addition, it is contemplated that the copy sheet will be processed through the copier twice, being turned over between the two traverses, so that an image of one side of the docu-ment will be reproduced on one side of the copy sheet, and an image of the other side of the document will be repro-duced on the other side of the copy sheet, to provide a duplex copy of the original duplex document.
The present invention thus provides a system for projecting images of both surfaces of an original duplex object in an object plane to an image plane and includes the means to support the object to be projected in the object plane, first optical means is provided for pro~ecting an image of the first surface at the object plane along a first optical path to the image plane and a second optical means is provided for pr~jecting an image of the second surface of the object along a second optical path to the image plane. Means are provided to orient the im~ge of the first surface to ~ predetermined sense on the

-3-image plane and means to orient the image of the second surfa~eat the predetermined sense on the image plane~ The first and second orientation means providing a resultant 180 change in orientation of the first and second images at the image plane relative to the first and second images at the object plane.
A method is also provided for duplex projection : comprising placing an original duplex object in an object plane.
An image of the first surface of the original is projected along a first path to an image plane and orienting the image between the object and image planes to a predetermined sense on the image plane. An image of the second surface of the original is projected along a second path to the image plane and orienting the image of the second surface between the object plane and the image plane to the predetermined sense on the image plane. The orientations to the predetermined sense provides a xesultant 180 change in orientation of the first and second images at the image plane relative to the first and second images at the object plane.
In another aspect the present invention provides a method of producing duplex copies with first and second images on opposite sides respectively of a copy sheet from a single imaging surface memb~r comprising:
forming first and second transferable developed but unfixed images on the same imaging surface;
transferring the first unfixed transferable image from said imaging surface to one side of said copy sheet;
removing said copy sheet from said imaging surface, and inverting it and returning it to said same imaging surface without fixing said first ~mage thereto;
then transferring said second transferable unfixed image directly to the opposite side of said copy sheet from said ~maging surface;

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then removing said copy sheet from said imaging surface with said first and second unfixed images on opposite sides thereof; and feeding said copy sheet with said unfixed images on opposite sides thereof through a fixing apparatus for fixing both of said first and second images to said opposite sides of said copy sheet. In accordance with one aspect of the invention said first and second images are transferred u~fixed to opposite sides of said copy sheet in immediate sequence, without any intervening copy sheets having images transferred thereto between said images of said first and second images. In another aspect a method is provided wherein said sheet is electrostatically retained on a transport member between said transfer of said first and second images to said opposite sides thereof.
In one embodiment the present invention provides a copying apparatus in which duplex copies are generated with first and second images fixed to opposite sides thereof, utilizing a single imaging surface member on which first and second images are formed from an imaging station and then are transferred directly to opposite sides of the same copy sheet by transferring the first image to one side of the copy sheet and removing the copy sheet from the imaging surface member and turning it over and returning it to the same imaging surface member, then transferring the second image to the opposite sid~
of the copy sheet from that imaging surface member, the improvement comprising a copy sheet transport means for said remo~ing and inverting and returning said copy to said imaging surface member without fixing said first image to said copy sheet and means for transferring said second unfixed image to said second side of said copy sheet while said first image remains unfixed and fixing means for subsequently fixing both of - 4a -B

said unfixed first and second images to said opposite sides ofsaid copy sheet.
Other aspects and advantages of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description of several illustrative specific embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The following detailed description of the invention is given in conjunction with the accompanying drawings, in which like reference characters refer to like or corresponding parts, and wherein: -Fig. 1 is a schematic illustration of a xerographic photocopying machine showing dual optical paths for sequentially exposing the top and bottom sides of an original duplex document;

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Figs 2A and 2G show, in sequence, how a duplex document is sandwiched between a double-sided glass platen, and how one side of the document is exposed as the platen traverses in one direction and the other side of the docu-ment is exposed as the platen traverses in the opposite direction;
Figs. 3A and 3B are perspective views showing how the top and bottom sides of the duplex document are re--spectively projected onto the photoreceptor during the two directions of traversé of the platen;
Fig. 4, on the page containing Fig. 1, shows one mode of recirculating a copy sheet to obtain duplex copy of the duplex document; and Fig. 5, on the page containing Fig. 1, shows the dual optical paths cooperating with two photoreceptors to produce -duplex copy of a duplex document.
DETAILED DESCRIPTIO~ -Fig. 1 schematically illustrates a duplex copying machine embodying the present invention. Within the housing 11, a conventional xerographic electrostatic reproducing apparatus is illustrated, comprising a rotating photo-receptor drum 6 having the various operational stations positioned around its periphery. At station A the photo-conductive surface of the drum 6 is uniformly electro-statically charged by means of a corotron. As the drum rotates, the charged area is moved to station B where it receives an optical exposure of the documen~ to be copied, thereby forming an electrostatic latent image of the docu-ment. At station C this latent image is developed by the selective attraction of electroscopic toner particles to the drum surface in accordance with the latent ima~e pattern.

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Sheets of copy paper are fed from supply 20 along path 12 into contact with the drum 6 at station D, where the toner image on the drum is transferred to the copy sheet, which may be effected with the aid of a transfer corotron. The copy sheet then continues along path 12 to a fusing rolls 13, 14 where the toner image is permanently fixed to the copy sheet; and the copy sheet is then fed to a receivîng bin 15. After toner transfer, the drum surface is cleaned of residual toner particle at station E, as may be accomplished for example by a rotating brush. The photoreceptor drum surface leaving the cleaning station E is ready to be recycled to receive another image.
The duplex photocopying feature of the invention will be best understood by reference to Figs. 2A-2G in conjunàtion with Fig. 1. The document platen utilized in the practice of the invention is formed of two transparent plates 2 and 3, which may be glass or transparent plastic.
These two plates are hinged at 16, and open in the manner , .
shown in Fig. 2A to receive a duplex document sheet 1.
With a document 1 in position and the platen 2, 3 closed, a cycle of operation can be iniated, starting from the position shown in Fig. 2B.
With the upper exposure lamp 4 illuminated, a rack and pinion drive 17, 18 causes the platen to traverse to the right as viewed in Figs. 1 and 2. Simultaneously, drum 6 is rotated clockwise in synchronism with the traverse of the platen. Light from lamp 4 is reflected from the upper surface of document 1, and is then directed by mirror 7 through a focusing lens system 8, and reflected by mirror 9 to the surface of drum 6 at station B. As the platen 2, 3 continues its traverse to the right as depicted in Figs.
2s-2D, a continuous incremental image of the upper surface of document 1 is focused on the surface of rotating drum 6, as is well understood in the art. At the completion of the traverse of the platen 2, 3 to the right, a complete image of the upper surface of document 1 is formed on the drum 6, and on continuing operation of the machine, that image will be developed at station C and then transferred to a copy sheet at station D.
Upon completion of the platen traverse to the right, a limit switch (not shown) is actuated, which turns off upper exposure lamp 4, turns on lower exposure lamp 5, and reverses the rack and pinion drive 17, 18 causing the platen 2, 3 to traverse to the left as viewed in Figs. 1 and 2. Under these circumstances, the lower side of docu-ment 1 is illuminated, and light reflected therefrom is directed by mirror 10 through the focusing lens system 8, and by mirror 9 to the surface of photoreceptor 6 at station B. As the platen 2,3 traverses to the left through the stages illustrated in Figs. 2E-~G, an image of the under side of document 1 is focused on the photo-receptor drum 6, and like the image from the upper surface of document 1, this image is also developed at station C
and transferred to a copy sheet at station D.
Figs. 3A and 3B depict the optical representations of the images obtained from the document sheet 1. Fig. 3A
does this for the upper surface of document 1 moving to the right, using the optical path of mirror 7, lens 8, and mirror g.
As clearly shown from this comparative representation the optical projection system provides a manner of reorienting images present on opposite sides of a duplex original such that they are provided at the image plane, in this case the photo-receptor, in an orientation or sense that may be predetermined.
A particular advantage is the ability to reorient images such that they are provided at the image plane in the same orientation or sense. This feature has particular significance in the reproduction of manuscript and some pictorial representations in duplex form in that it provides a simple manner of reproducing the images of the original in simplex form with the images reading in the same direction or in duplex form with images in the original orientation.
Illumination and exposure of the duplex original may be achieved with well known techniques such as full frame exposure, including flash techniques, as well as scanning. A particular advantage of a scanning technique is illustrated in Figures 3A
and 3B wherein the manuscript material on both sides of the duplex original is scanned in the same sense or in the reading direction from edge to edge providing successive images which are in the same sense or reading direction. The advantage is achieved in manuscript reproduction if the scanning is from edge to edge of the original in the reading direction. With most duplex originals such as pages from a report or the like the intelligence on one side reads from left to right and the intelligence on the other side without reorienting the original and reading from underneath reads from right to left~ Thus a positive scan of the one side of the original parallel to the reading direction and a reverse scan of the opposite side of the original parallel to the reading direction combine to produce images having the same orientation or sense. In contrast, sranning of the original from top to bottom produces a satisfactory image on one side but the reverse scan on the opposite side of the original would provide a distorted image having, for example, an incorrect line sequence corresponding to an order of from bottom to top of the original.
A further advantage of the system is the ability to use common elements in the optical paths for the projections from both surfaces of the duplex original. Thus Figures 3A
and 3B represent this in simple form by using a single reflecting surface to reflect the image from the top of the duplex original and a single reflecting surface to reflect the image from the bottom of the duplex original and thereby obtain comparative images in an image plane which are in a predetermined sense or 180 different in orientation relative to their orientation in the object plane. Thereafter, common optical elements such as lenses and reflectors may be common to the two optical paths if desired.
In the foregoing embodiment of the invention, the duplex original document is copied from both sides as a result of one cycle of scan of the platen 2, 3 utilizing dual optical paths. However, as depicted, the copy is simplex, i.e., each side of the document is reproduced on a separate copy sheet.
It is apparent that by recirculating the copy sheet and turning it over after receiving the image of the first side of the original document, the second side of the document can be reproduced on the second side of the CoFy sheet. Such a mechanism is schematically illustrated in Fig. 4, for making multiple duplex copies of a duplex document. The dual optical scanning paths of Figs. 1 and 2 are utilized for Fig. 4, but are omitted from this figure for simplifications.
As shown in Fig. 4, the photoreceptor drum 6 is divided into three image fields, and the document e~posure is keyed thereto and alternates between the document top side (image A) and the document bottom side (image B).
Copy sheets are fed from sheet feeder 20 to endless belt 31, in synchronism with the document exposure cycle and the positions of the image fields on drum 6. After each sheet receives its first side image from drum 6, it is retained on belt 31 by aid of tacking corotron 19 and recycles back toward the feeder 20 on the lower course of the belt, where it is received on lifter 32, raised thereby to the vacuum conveyor 33 of the sheet feeder, and returned to the upper course of the belt 31. In this process, it will be appreciated that the sheet has been turned over. It is now returned to the drum 6 to receive its second side image, after which it is removed from the conveyor belt 31 and fed by rolls 21 through a toner fuser 22, and thence to the copy receiving bin 15 shown in Fig. 1.
Obviously, the length of conveyor 31 and the operation of sheet feeder 20 must be appropriately related to each other, and synchronized with the cycling rate of the document plagen 2, 3 and the drum 6 to effect proper registration of each copy sheet side with the proper document image and image field on drum 6.
An illustrative timing chart for a copy sheet feed operation of three sheets per cycle of the drum 6 is presented in the following table.

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An alternative manner of producing duplex copies from a duplex document is shown in Fig. 5. Again, the system uses the same dual optical paths as described for Fig. 1 for scanning the duplex original 1 in the sand-wich platen 2,3. In this instance, a semi-transparent mirror 23 reflects the image onto photoreceptor drum 6, as in the preceding embodiments. In addition, the image transmitted by mirror 23 is reflected by mirror 24 to a second photoreceptor drum 25. Each of the drums 6 and 25 is provided with charging, developing, transfer, and cleaning stations, although they are not shown in this figure to simplify the presentation. Thus, with each cycle of traverse of platen 2, 3, latent images of one side and then of the other side of document l are formed on both drums 6 and 25, and these latent images are developed and transferred to receiving sheets. As schematically illustrated, a copy sheet is fed from a sheet feeder to bring one side into image transfer relation with drum 25. When the copy sheet leaves drum 25, it is turned and re-fed with the opposite side in image transfer relation with drum 6. A proper timing relation-ship between sheet feed, rotation of the photoreceptor drums, and the scan traverse of platen 2, 3, produces a duplex copy of the duplex document 1.
For example, upon completion of scan of side A
of the document, a copy sheet from the feeder can reach the image transfer station of drum 25 to pick up image A.
This copy sheet i~ then turned and re-fed to drum 6 as the scan of side B of the document is completed, to pick up the B image from drum 6 at its transfer station. While the first copy sheet is picking up image B from drum 6, a second copy sheet can be picking up image B from drum 25.
As the system continues to cycle, the second copy sheet will be turned and re-fed to drum 6 in time to pick up image A, while a third copy sheet is fed to pick up image A
from drum 25.
Accordingly, it will be appreciated that a copying system is provided for the efficient reproduction of duplex document sheets, wherein both sides of the document are scanned in sequence during one cycle of the document platen.
In addition, the copy sheet can provide a duplex reproduction of the document, either by turning and recirculating the copy sheet, or by utilizing two photoreceptors and feeding the copy sheet to receive from one photoreceptor the image from one size of the document on one side of the copy sheet, and from the other photoreceptor the image from the other side of the document on the other side of the copy sheet.
While the operation of applicant's device has been described for use with a document having printing or image material on both sides of a single document, it should be understood that the term document embraces not only a single sheet of support material having image material on both sides but also two (2) sheets of support material each having images on only one side which are thereafter placed in back-to-back relationship to provide, in effect, a double-sided document.
It is understood that the specific embodiments shown and described are presented only as illustrative of the invention.
Various modifications will be apparent to those skilled in the art, and such modifications as are embraced by the spirit and scope of the appended claims are contemplated as being within the purview of the present invention.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of forming images on first and second sides of a copy sheet comprising the steps of:
forming first and second unfixed images on a photoreceptor;
transferring said first unfixed image from said photoreceptor to a first side of a copy sheet having first and second opposite sides;
inverting said copy sheet and transferring said second unfixed image from said photoreceptor to the second side of said copy sheet before fixing of said first image to said copy sheet; and transporting the copy sheet having said first and second unfixed images away from said photoreceptor to a fixing station.

2. The method of claim 1 including the step of fixing the first and second unfixed images on said copy sheet simultaneously at said fixing station.

3. The method of claim 1 wherein said forming step comprises :
forming first and second images on said photoreceptor;
and developing first and second images with electroscopic particles to form first and second visual unfixed images on said photoreceptor.

4. The method of claims 1 or 2 wherein said forming step includes the copying of both sides of a duplex original document to form said first and second images, so that said copy sheet is a duplex copy of said duplex original document.

5. The method of claim 1 wherein means for transferring said first unfixed image, means for inverting the copy sheet and means for transferring said second unfixed image are positioned closely adjacent to one another along a path taken by said copy sheet in that order and also closely adjacent said photoreceptor so as to minimize the distance between said first and second sequential images formed on said receptor.

6. The method of claim 5 wherein the step of inverting said copy sheet comprises turning and refeeding said copy sheet in a reverse direction of motion.

7. The method of claim 6 wherein the inverting of said copy sheet is effected by a vacuum conveyor.

8. The method of claims 5, 6 or 7 wherein said first and second unfixed images are sequential images of opposite sides of a duplex original document.

9. The method of claims 1, 2 or 3 including delivering each copy sheet to said photoreceptor twice and turning each copy sheet over between the two deliveries to provide a duplex copy .

10. Electrophotographic apparatus for producing duplex copies comprising:
means for forming first and second unfixed images on a photoreceptor;

means for transferring said first unfixed image from said photoreceptor to a first side of a copy sheet having first and second opposite sides;
means for inverting said copy sheet;
means for transferring said second unfixed image from said photoreceptor to the second side of said copy sheet; and means for transporting said copy sheet having said first and second unfixed images away from said photoreceptor to an image fixing station.

11. Electrophotographic apparatus for producing duplex copies comprising:
a photoreceptor means;
image forming means for forming first and second sequential unfixed images on said photo-receptor means;
first transfer means for transferring said first unfixed image from said photoreceptor means to the first side of a copy sheet having first and second opposite sides;
sheet inverting means for inverting said copy sheet having said first unfixed image on the first side thereof before fixing of said first image to said sheet so as to present the second side thereof for transfer of the second unfixed image on said photoreceptor means to said second side of said copy sheet;
second transfer means for transferring said second unfixed image from said photoreceptor means to said second side of said copy sheet; and transport means for transporting said copy sheet having said first and second unfixed images thereon to an image fixing station.

12. The apparatus of claims 10 or 11 including means for fixing said first and second unfixed images on said copy sheet simultaneously at said image fixing station.

13. The apparatus of claim 11 wherein said first transfer means, said sheet inverting means and said second transfer means are positioned closely adjacent to one another along a path taken by said copy in that order and also closely adjacent said photoreceptor means so as to minimize the distance between said first and second sequential images formed on said photoreceptor means.

14. The apparatus of claim 13 wherein said sheet inverting means comprises means for turning and refeeding said copy sheet in a reverse direction of motion.

15. The apparatus of claim 14 wherein said inverting means comprises a vacuum conveyor.

16. The apparatus of claims 10 or 11 wherein said first and second unfixed images are images of opposite sides of a duplex original document.

17. The apparatus of claims 10 or 11 including means for delivering each copy sheet to said photoreceptor means twice and for turning each copy sheet over between the two deliveries to provide a duplex copy.