US 3697170 A
The method of producing a duplex copy by simultaneously placing images of the original subject matter to be reproduced on both sides of a sheet of final support material. A first latent electrostatic image and a second latent electrostatic image containing original input scene information are sequentially formed on a photoconductive plate and developed in the conventional xerographic manner by contacting the charged images with oppositely charged toner particles. The first image is transferred to an image storage member where the polarity of the charged toner particles making up the image is reversed. The first image, carried on the support member, is then brought adjacent to the second image on the photoreceptor surface and a sheet of final support material interposed therebetween. The two oppositely charged images are subjected to an electrostatic force of a polarity and a potential to produce simultaneously a transfer of the images to opposite sides of the final support sheet.
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Description (OCR text may contain errors)
United States Patent Bhagat et al.
[541 AUTOMATIC DUPLEXING APPARATUS  Inventors: Gopal C. Bhag at, Rochester; John M. Randall, Fairport, both of N.Y.
3,5 80,670 5/1971 Bhagat ..355/23 [451 Oct. 10,1972
Primary Examiner-Samuel S. Matthews Assistant Examiner-Richard L. Moses Attorney-James J. Ralabate, Donald F. Daley and Thomas J. Wall  ABSTRACT The method of producing a duplex copy by simultaneously placing images of the original subject matter to be reproduced on both sides of a sheet of final support material. A first latent electrostatic image and a second latent electrostatic image containing original input scene information are sequentially formed on a photoconductive plate and developed in the conventional xerographic manner by contacting the charged images with oppositely charged toner particles. The first image is transferred to an image storage member where the polarity of the charged toner particles making up the image is reversed. The first image, carried on the support member, is then brought adjacent to the second image on the photoreceptor surface and a sheet of final support material interposed therebetween. The two oppositely charged images are subjected to an electrostatic force of a polarity and a potential to produce simultaneously a transfer of the images to opposite sides of the final support sheet.
7 Claims, 1 Drawing Figure Panamanian 10 1912' INVENTORS. GOPAL C. BHAGAT JZHN M. RANDALL BY ATTORNEY AUTOMATIC DUPLEXING APPARATUS This invention relates to transferring powder images to a final support sheet and, in particular to an improved method of transferring simultaneously images to both sides of a sheet of final support material.
More specifically, this invention relates to a duplexing method suitable'for use in the xerographic process wherein a first right or direct reading electrostatic image of the original subject matter to be reproduced is formed and then developed on the surface of a photoconductive member and is transferred for retention to a storage member. A second wrong reading or mirror latent electrostatic image is then formed on the photoconductive surface in a similar manner and is brought into contact with one side of a final support sheet. The first image, retained on the storage medium is brought into contact with the opposite side of the final support sheet and the two images subjected to an electrostatic force capable of transferring the images to the sheet so as to form a duplex reproduction composed of the original subject matter Although not necessarily so limited; the teachings of the present invention are herein disclosed, for illustrative purposes, in conjunction with the xerographic reproducing technique. In the process of xerography, a photosensitive plate comprising a photoconductive layer on a conductive backing is uniformly charged and the charged surface exposed by a light image of the original subject matter to be reproduced. This exposure causes the charge to be selectively dissipated in accordance with the light intensity incident thereon thus creating a latent electrostatic image containing original input scene information. Development of the image is effected by developer materials which generally consist of a mixture of suitable pigmented resin based toners that are supported in a charged state on the surface of relatively coarser carrier beads. During development, the toner particles are brought into surface contact with the electrostatic latent image wherein the charged toner particles are attracted to the more highly charged imaged areas on the plate surface. Thereafter, the developed xerographic image is transferred to a final support sheet, such as paper or the like, to which it is affixed by suitable means to form a permanent record of the original input scene information.
Many techniques are known in the art to accomplish the aforementioned basic procedure of xerography, but generally these prior art methods and devices are limited in application by the fact that only one surface of the support material can be utilized to create a facsimile of the original subject matter. However, duplex reproductions are, in many instances, more desirable simply because of the convenience afforded, particularly when the copies are to be assembled in a book form. A great economy of physical volume of reproduction is thus realized in duplex copying any many problems associated with the handling and storage of copies alleviated.
One attempt in the prior art to produce a duplex copy of an original is disclosed in US. Pat. No. 3,182,212 to Rubin wherein images are xerographically produced on both sides of a final support sheet. Although this system, as disclosed by Rubin, provides satisfactory duplex reproductions, it nevertheless suffers from certain disadvantages which limit the system application. The apparatus is comparatively complex and requires that the images be tackified prior to the duplex transfer operation. The provision of a tackified image calls for the utilization of special vapor chambers capable of acting on both images prior to the images being brought into contact with the final support sheet. This, in turn, requires that each operation be exactly timed in order that both images contact the support sheet in the proper tackified state to accomplish transfer.
It is therefore a primary object of this invention to improve the xerographic reproducing process whereby duplex copies can be conveniently and efficiently produced.
Still another object of this invention is to improve methods for simultaneously transferring powder images to both sides of a single sheet of final support material.
These and other objects of the present invention for simultaneously transferring a first and a second charged powder image from a photoconductive surface to both sides of a sheet of final support material are attained by transferring a first charge powder image to a storage member, reversing the polarity of the first powder image while on the surface of the storage member, bringing the first charged image on the storage member and the second charged image on the surface of the photoconductive surface in close proximity to opposite sides of a sheet of final support material and subjecting the two oppositely charged images in proximity with the support sheet to an electrostatic force capable of transferring simultaneously the images from their respective support member to the opposite sides of the sheet.
For a better understanding of the present invention as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be read in connection with the accompanying drawing of a schematic illustration of an automatic xerographic reproducing device encompassing the teachings of the present invention for simultaneously transferring developed images to both sides of a final support sheet.
Referring now specifically to the FIGURE shown, the apparatus of the present invention for producing duplex reproductions is shown embodied in a drum type automatic xerographic reproducing device. The central element of this machine is a drum 10 which is mounted for rotation in the machine frame on shaft 11 and is driven in a clockwise direction by motor means 12. The drum basically comprises an outer surface having a layer of photoconductive insulating material 13, such as vitreous selenium or any other suitable material, that is placed upon a grounded conductive substrate 14. A uniform electrostatic charge is placed on the photoconductive surface of the drum by means of a conventional corona charging device 15 similar to corona generator disclosed by Vyverberg in U. S. Pat. No. 2,836,725. The uniformly charged surface is then moved past an exposure means, generally referred to as 17, capable of exposing the charge surface to a light image of the original to be reproduced thus forming a latent electrostatic image on the photoconductive surface. The optical system herein utilized is similar to that disclosed in the aforementioned US. patent to Rubin wherein the original to be reproduced is stored on a microfilm input 18. A movable reflecting means 19 is positioned in the optical light path and is arranged to redirect a flowing light image onto the bottom portion of the drum surface. The reflecting means comprises a mirror surface and a roof mirror 21 which, in operation, are alternately interposed into the systems optical light path wherein each successive image presented to the drum surface is optically reversed.
In operation, the optical means exposes the photoconductive surface to an input wherein a first right or direct reading latent electrostatic image is formed thereon. Following the formation of this first right reading image, the image moves past a conventional cascade development device 25 adapted to bring the latent electrostatic image into contact with a two component developer material wherein the charged toner particles are attracted into the imaged areas thus making the latent image visible.
After development, the now visible first direct reading image moves to a transfer station 26 which includes a corotron 27 mounted adjacent to the backside of a belt type storage member 30. The storage member is fabricated of a relatively thin dielectic belt of acetate,
mylar or the like. It is contemplated within the scope of this invention, however, to use other forms and materials for the storage member without departing from the teaching of the present invention. The belt 30 is mounted between rollers 31 and 32 and is driven in the direction indicated by motor means 33 at the same peripheral speed as drum 10. The length of the dielectic belt may be of any convenient size but is preferably one-half the circumference of the photoconductive drum.
Corotron 27, mounted inside the dielectic belt, applies an electrostatic charge to the back of the belt of a polarity and a potential sufficient to electrostatically transfer the first developed image from the drum surface to the outer surface of the belt. For example, if the charged toner particles making up the first developed image are of a negative polarity, the dielectic belt would be sprayed with a positive ion discharge capable of overcoming the forces holding the toner to the drum so that the charged powder is transferred in image configuration to the surface of the belt.
Subsequent to the formation of the first right reading image upon the drum, a second area on the surface thereof is uniformly charged by the charging corotron 15. The second uniformly charged surface of the drum is then moved past exposure means 17 exposing the surface thereof to a flowing light image composed of the additional subject matter to be copied and forms a second wrong reading latent electrostatic image on the drum surface. To produce a wrong reading latent image, roof mirror 21 is interposed into the optical light path in the place of mirror 19. This second wrong reading latent image is moved on the drum surface through the development system and the second image is made visible in a manner similar to that heretofore described in reference to the direct reading image.
The time sequence of charging, exposing and developing of the two oppositely reading images in the present apparatus is controlled in a predetermined timed relation by means of the machine control logic circuitry (not shown). The particular selection of timed sequences of operation depends on many factors such as the locations of various stations around the drum surface, the length and velocity of the image storage member relative to the size of the drum surface to mention a fewiFor convenience of illustration, the area of the surface drum to receive the first right reading images is diametrically opposite to that area on the drum supporting the second wrong reading image. As can be seen, when the first right reading image reaches transfer station 26, preparatory to transfer to the storage belt, the central region of the first image is positioned from the central region of the second or wrong reading image. By selecting the length of a storage belt equal to one-half the circumference of the drum surface, and moving the belt at a speed similar tothat of the drum, the leading edge of the first image transferred to the storage belt will be transported around the belt loop and will arriveonce again at the transfer station at the same time that the leading edge of the second image on the drum arrives. Accordingly, the two images lying respectively on the storage belt andthe drum surface confront each other at the same moment. 7
Prior to being redelivered to the transfer station, the first image on the belt is brought under the influence of an image reversing corotron 35 positioned adjacent to the surface of the belt as illustrated. In operation, the image bearing belt is moved over a grounded backing electrode 36 and is subjected to a corona discharge of sufficient strength to cause the charge on the toner particles to be reversed. For example, assuming the first image transferred to the belt surface is predominately negative, corotron 35 would generate a corona discharge capable of inducing a positive charge in the imaged areas.
A single sheet of final support material 40, such as paper, is forwarded from a supply stack into moving contact with the storage belt by means of cooperating advancing rollers 41 and 42. The movement of the support sheet is timed in relation to the movement of the first image on the storage member wherein the support sheet is positioned directly over the toner image. The final support sheet and the image bearing belt surface are forwarded in synchronous timed relation between a paper tacking corotron 43 and a conductive grounded backing plate 44. A charge is applied by corotron 43 to the support material causing the sheet to be electrostatically tacked into intimate contact with the surface of thestorage member. Although any polarity corona discharge can be herein utilized to tack the sheet to the belt, it is nevertheless preferred that the corotron be of a type capable of producing a charge having a polarity similar to that produced by the image reversing corotron 27.
The sheet of final support material, which is now tacked in contact with the reversing polarity first image, is carried to the transfer zone 26 on the moving belt surface. Here, the back of the belt is once again acted upon by transfer corotron 27, that is, the side away from the support sheet, in a manner similar to that described in reference to the transfer of the first reverse reading image. The nature of the electrostatic charge produced by the corona discharge device 27 is such as to attract the second wrong reading image from the drum surface to the side of the support sheet moved in contact therewith. At the same time, the corona discharge causes the first image to be repelled from the surface of the storage member onto the opposite side of the sheet of final support material. The image bearing sheet of final support material is stripped from the storage member by conventional mechanical stripping means (not shown). The sheet is then forwarded through heat fixing means 45 wherein the images are permanently affixed to the support material to form a permanent record of the original input scene information and the sheet finally transported to a storage bin or the like by means of advancing rolls 46 and 47. Finally, the photoconductor is cleaned by applying a fibrous brush member 50 thereto capable of removing the residual toner left behind after transfer.
It should be apparent that the first developed image stored on a belt creates a right reading toner image on one side of the final support material when transferred thereto in the manner herein described. Similarly, the oppositely reading second image transferred from the drum surface to the opposite side of the support sheet likewise creates a right reading toner image so that a suitable reading duplex copy is reproduced.
in the above disclosure, there has been described an approved method of effectively creating a duplexing reproduction of desired input information. While for the sake of convenience, reference has been made throughout this specification to negatively charge toner particles, it is to be understood that the description of the specific nature of the charges involved is not intended to limit this invention. For instance, it would be possible to utilize a carrier material and a toner material having a different charge relationship as to their triboelectric properties whereby the toner applied to the photoconductor would carry a positive charge. This, of course, would call for a similar change in the relationship of the charges induced by the various corona generating devices utilized. Therefore, all references to positive or negative charges in the specification are considered as defining a relationship and the teachings of the present invention can be practiced as long as the relationships involved are maintained.
While the invention has been described with reference to the structure disclosed herein, it is not confined to the details as set forth and this application is intended to cover such modifications or changes as may come within the scope of the following claims.
What is claimed is:
l. The method of producing toner particle images on opposite sides of a final support member comprising forming a first toner particle image on an image retaining member with toner particles electrostatically charged to a first polarity,
transferring said first image to a storage member by moving the storage and image retaining members past a transfer station where the charged toner particles are electrostatically transferred,
forming a second toner particle image on an image retaining member with toner particles electrostaticallycharged to the first polarity with said second image being optically reversed relative to the first image,
reversing the charge polarity of the particles comprising one image relative to the charge polarity of the particles comprising the other image, and
simultaneously transferring charged particles of said first and second images to opposite sides of a final support member by positioning the image retaining member carrying said second image and the storage member carrying the first image on opposite sides of the final support member and moving said member past a transfer station where the charged particles from both images are electrostatically transferred to opposite sides of said final support member.
2. The method of claim 1 further including the step of fixing said first and second toner particle images to the opposite sides of the transfer member to which they are transferred.
3. The method of claim 1 wherein said first and second images are sequentially formed on a continuous image retaining member including a photoconductive layer, said particles comprising the first and second images have the same charge polarity when the images are formed and wherein said reversing step includes changing the charge polarity of the particles comprising the first image while the first image is on said storage member.
4. The method of claim 3 wherein said storage means includes a continuous dielectric belt member.
5. The method of claim 4 wherein said images are electrostatically transferred to opposite sides of said final support member by steps including depositing electrostatic charge on the dielectric belt surface opposite the belt surface carrying the first image.
6. The method of claim 5 wherein said transfer station includes corona generating means for depositing charge on the side of said dielectric belt opposite the side carrying an image for transferring the first image to the storage member and for transferring the first and second images to the final support member.
7. The method of claim 3 wherein the polarity of said first image on said storage member is reversed by spraying said image with oppositely charged corona.