US3620615A

US3620615A - Sheet stripping apparatus

Info

Publication number: US3620615A
Application number: US789030A
Authority: US
Inventors: Stewart W Volkers
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1968-12-31
Filing date: 1968-12-31
Publication date: 1971-11-16
Anticipated expiration: 1988-11-16
Also published as: CA927472A; GB1290518A; DE1964199A1

Abstract

Apparatus for stripping a copy sheet electrostatically supporting a toner image from an oppositely charged xerographic surface. The apparatus includes an electrically biased roller slightly spaced from the copy sheet in the stripping zone to effect the stripping. Contact between the roller and copy sheet neutralizes the sheet. Alternately, the neutralization may be effected by a corona discharge device.

Description

United States Patent Inventor Stewart W. Volkers Williamson, N.Y.

Appl. No. 789,030

Filed Dec. 31, 1968 Patented Nov. I6. 197i Assignee Xerox Corporation Rochester, NY.

SHEET STRIPPING APPARATUS 6 Claims, 3 Drawing Figs.

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Field of Search. i i t .v

ass/3 003; 15/16 355/3. 13.

[56] References Cited UNITED STATES PATENTS 295L443 9/1960 Byrne 355/11 X 3,3l8,2l2 5/l967 Rubin 355/3 3,332,328 7/l967 Rothv Jr 355/3 Primary Examiner-Samuel S Matthews Assistant Examiner-M. L Gellner Attorneys-Norman F Schrader, James]. Ralabate and Michael J. Colitz. Jr

ABSTRACT: Apparatus for stripping a copy sheet electrostatically supporting a toner image from an oppositely charged xerographic surface. The apparatus includes an electrically biased roller slightly spaced from the copy sheet in the stripping zone to effect the stripping. Contact between the roller and copy sheet neutralizes the sheet. Alternately, the neutralization may be effected by a corona discharge device.

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PATENTEDuuv 1e |97| INVIz'N'IUR. STEWART W. VOLKERS BY M18 26%,

ATTORNEY SHEET STRIPPING APPARATUS This invention relates to xerography and in particular to apparatus for removing copy sheets, with transferred toner images from a xerographic surface.

In the practice of xerography, as described for example in U.S.,Pat. No. 2,297,691, to Chester F. Carlson, a xerographic surface comprising a layer of photoconductive insulating material afi'lxed to a conductive backing is used to support latent electrostatic images. In the usual method of carrying out the process, the xerographic plate is electrostatically charged uniformly over its surface and then exposed to a light pattern of the image being reproduced to thereby discharge the charge in the areas where light strikes the layer. The undischarged areas of the layer thus form an electrostatic charge pattern in conformity with the configuration of the original pattern;

The latent electrostatic image can then be developed by contacting it with a finely divided electrostatically attractable material such as a powder. Thepowder is held. in image areas by the electrostatic charge on the layer. Where the charge is greatest, the greatest amount of material is deposited; and where the charge is least, little or no material is deposited. Thus, a powdered image is produced in conformity with a light image of the copy being reproduced. The powder is subsequently transferred to a sheet of paper or other surface and suitably affixed thereto to form a permanent print.

The electrostatically attractable developing material commonly used in xerography comprises a pigmented resinous powder referred to herein as toner" and a larger granular material called carrier." The carrier is formed of, or coated with, a material removed in the triboelectric series from the toner so that a charge is generated between the powder and the granular carrier upon mutual interaction. Such charge causes the powder to adhere to the carrier. The carrier, besides providing a charge to the toner, permits mechanical control so that the toner can readily be brought into contact with the exposedxerographic surface for the development of the surface. The powder particles are attracted to the electrostatic image from the granular material to produce a visible powdered image on the xerographic surface.

When xerography is practiced on "a cylindrically shaped endless xerographic surface, as for example, a drum described in U.S. Pat. No. 3,062,536 to .l. Rutkus, Jr., et.al.,, the final copy paper is caused to move in synchronous contact withvthe drum during a portion of the rotation of the drum. During this time, a potential opposite from the polarity on the toner is applied to the side of the paper remote from the drum to electrostatically attract the toner image from the drum to the copy paper. A puff of air or other mechanical means may then be employed to separate the image bearing paper from the drum. The toner image is then fused to the paper for the production ofthe final xerographic copy.

During the transfer of the. toner image from the drum .to the paper, the transfer corotron. which is a positive polarity when negatively charged toner is applied; deposits a positive charge on the copy paper. The copy paper, which is an insulator, retains the positive charge while inducing a negative charge in the nondischarged areas of the xerographic drum. This new charge orientation creates an electrostatic bond between the paper and drum.

To separate the paper from the drum, the electrostatic bond therebetween must first be overcome either mechanically or electrostatically. When an air puffer is used to achieve this separation, at relatively high pressure of air must be employed to overcome the attraction of the paper for the drum. However, when high air pressures are employed, there is a tendcncy of such air to agitate the .unfused toner image on the paper and disrupt the image configurationof the toner on the copy sheet. This exhibits itself aspuffer smears on the final copy. This blowing of toner powder may also result .in toner dust problems throughout the functioning elements of the system. Furthermore. when a copy is being separated from the xerographic surface, the high pressure of air may repel the toner-bearing paper against the output conveyor with a tonerjarring force. Another approach is to mechanically wedge the copy sheet from the drum. Mechanical fingers, however, have a tendency to scratch and abrade the xerographic surface.

In another technique for separating a copy sheet from a xerographic surface, as describedin pending application Ser. No. 585,816 filed Oct. ll, 1966 in the name of Norbert H. Kaupp, the charge on the copy sheet is neutralized by a corona discharge while the sheet is on the xerographic surface. With the copy sheet neutralized, it willsimply gravity fall from the drum whereafter it is transported away for fusing. Such a system is generally designed for use in a system where the copy sheet is beneath the xerographicsurface so that gravity may be employed to complete the separation.

The present invention is directed toremoving copy from a xerographic surface by electrostatically'attracting the charged copy sheet from the charged xerographic surface and then discharging the sheet so that it will not be reattracted thereto.

It is, therefore, an object of the instant invention to electrostatically remove image-bearing xerographic copy from a xerographic surface.

It is another object of the invention to remove charged copy sheets from a. xerographic surface by electrostatic attraction and then neutralizethe charge on the sheet to prohibit its reattraction to the surface.

It is another object of the invention to create an electrostatic field adjacent a charged copy sheet to remove it from a xerographic surface.

It is a further object of the invention to eliminate toner smears, toner dust contaminatiomdrum abrasion, and other deleterious effects generally caused by the removal of imagebearing copy from a xerographic surface.

These and other objects of the invention are achieved by electrostatically attracting a toner-image-bearing copy sheet from an oppositely charged xerographic surface to effect the removal of the copy sheet from the surface. When the means providing the electrostatic attractive force is a biased roller, contact between the roller and copy sheet can neutralize the sheet to prohibit its reattractionto the xerographic surface. Alternately, the copy sheet neutralization may be effected by .a corotron.

For a betterunderstanding of the 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 wherein:

FIG. 1 is a schematic showing of a continuous and automatic xerographic reproducing machine utilizing sheet stripping apparatus constructed in accordance with the instant invention;

FIG. 2 is an enlarged perspective. view of the xerographic drum, sheet feed elements and sheet stripping apparatusand FIG. 3 is a schematic showing of sheet stripping apparatus similar to that-of FIGS. 1 and 2 but showing an alternate embodiment .of the invention.

Referring now to the figure, there is in FIGS. 1 and 2 an embodiment of. the subject invention in a suitable environment such as a continuous and automatic xerographic reproducing machine. The machine has a xerographic surface 10 including a photoconductive layer on a conductive backing. The surface is formed in the shape of a drum which is mounted on a shaft journaled in the frame of the machine to rotate in a direction as indicated by the arrow. This movement. causes the drum surface to move sequentially past a plurality of xerographic processing stations.

For the purpose of the present disclosure. the several xerographic processing stations in the path of movement of the drum surface may be described functionally, as follows:

A charging station A, at which a. uniform electrostatic charge is deposited on the photoconductive surface of the xerographic drum;

An exposure station B, at which a light or radiation pattern of a copy to be reproduced is projected onto the drum surface to dissipate the drum charge in the exposed areas thereof thereby forming a latent electrostatic image of the copy to be reproduced;

A development station C, at which the xerographic developing material including toner particles having an electrostatic charge opposite to that of the latent electrostatic image, are cascaded over the drum surface, whereby the toner particles adhere to the latent electrostatic image to form a xerographic powder image in the configuration of the copy being reproduced;

A transfer station D, at which the xerographic powder image is electrostatically transferred from the drum surface to a transfer or support material and then removed from the drum for fusing the image onto the support material; and,

A drum cleaning and discharge station E, at which the drum surface is brushed to remove residual toner particles remaining thereon after image transfer, and at which the drum surface is exposed to a relatively bright light source to effect substantially complete discharge of any residual electrostatic charge remaining thereon.

It is believed that the foregoing description is sufficient for the purposes of this application to show the general operation of the xerographic reproducing apparatus.

As the drum-shaped surface rotates past the development station C, a sheet of a suitable backing material such as paper 12 is brought into contact with the xerographic surface by first sheet feeding mechanisms 14. The xerographic surface 10 may be of any cylindrical endless shape and need not be a right-circular cylinder. The sheet and drum then move at the same linear speed past a transfer corotron 16 which acts to electrostatically draw the toner image from the drum towards the paper. At the same time, however, the electrostatic charge emitted by the transfer corotron electrostatically tacks the paper to the drum. The drum and paper then travel together to suitable mechanisms capable of removing the paper from the drum to thereby allow the toner-bearing paper to be transported away by second sheet feeding mechanisms 18. The second sheet feeding mechanisms transport the tonerbearing paper past a fusing station 26 for the production of the final copy.

Most known machines of this type employ some sort of mechanical mechanisms to strip the image-bearing paper from the xerographic drums. The puffer, which propels a jet of air or other aeriform fluid between the paper and drum, is probably the most common means used for stripping. A description of a puffer may be found in the aforementioned Rutkus et al. patent, which patent also more fully describes the other xerographic processing stations referred to above.

The instant invention requires no puffer or other mechanical stripping mechanisms. In place thereof, a stripping roller 20 is positioned across the xerographic drum slightly downstream from the transfer corotron. The stripping roller is preferably mounted on an axis parallel with that of the xerographic surface adjacent the transfer corotron. The roller is adapted to be rotated in a direction and at a speed concurrent with that of copy sheet material being removed from the drum. It can be driven off any convenient power source including the main serpentine drive of the reproducing machine.

As shown in FIG. 2, the opposite end of the roller may be provided with an insulating collar formed of tape 22 or the like whereby the distance of separation between it and the xerographic drum may be kept constant. The use of the insulator as the separating unit prohibits the flow of charge between the drum and the roller. The distance between the roller and the drum is, for example, about 0.015 inch, slightly greater than the thickness ofa copy sheet to be removed. A nominal paper thickness for these parameters would be about 0.0035 inch. These distances prohibit the contacting of the roller with the copy sheet while it is still on the drum. This has been found desirable, since contact of the copy sheet on the drum by the conductive face of the roller would disturb the charged orientation between the paper, toner and photoconductor and could result in the destroying of the charge relationship holding the toner to the copy sheet and thus disorient the desired toner image. The roller is shown as a conductive member mounted to a suitable source of potential 24. In the instant application, the potential on the roller is about 800 volts negative direct current, a voltage of about equal magnitude but opposite polarity from the charge on the copy sheet. In a practical application, where an original potential of L000 volts was positive was uniformly placed on the photoconductor and the exposure step reduced the charge on the image areas to 800 volts positive and to volts positive in nonimage areas, a transfer corotron having a current to charge the copy sheet positively to 800 volts was found suitable to effect transfer. Under these conditions, a negative direct current voltage of 800 volts was found capable of effecting good electrostatic removal of the copy sheet from the xerographic surface. While the roller is shown as a conductive member, it could readily be made of an insulating material with an electrically conductive surface so long as it was sufficient to support the necessary potential.

As the leading edge of the copy sheet, having a toner image electrostatically adhering thereto, is moved adjacent the stripping roller 20, the fields created therebetween cause the copy sheet to be electrostatically attracted toward the stripping roller away from the photoconductive surface. With a negative 800 volts on the roller 20 and a positive 800 volts on the copy sheet prior to separation, there is a resulting force sufficient to attract the paper from the xerographic surface. With the paper being removed from the drum it then contacts the roller whereupon the contact therebetween neutralizes the charge in the copy sheet. Due to the fact that the roller is rotating in the same direction and at the same linear speed as the copy sheet, the roller assists in transporting the image bearing sheet toward the fuser 26 for creating the permanent copy. The neutralization of the copy sheet by the roller prohibits the reattraction of the copy sheet toward the drum since the charge in the copy sheet is not removed until this neutralization occurs. Prior to this neutralization, reattraction of the sheet to the drum is possible due to the electrical field therebetween. Due to the undesirability of having this reattraction which could have a toner jarring effect, the charge neutralizing roller is positioned adjacent the copy sheet.

The illustrative example of apparatus capable of carrying out the instant invention shows the sheet removing roller beneath the image bearing copy sheets and xerographic surface. In this location, the force of gravity assists in permitting the copy sheet to move toward the roller. It is not, however, necessary that such relationship be retained in order to affect good stripping. The transfer and stripping could adequately be carried out adjacent other segments of the photoconductive surface since the field created between the roller copy sheet can be made sufficient to electrostatically remove he copy sheet from the drum independent of gravity.

In an alternate embodiment of the invention, that disclosed in FIG. 3, an additional corotron 28 is provided beyond the paper removing roller. The purpose of this corotron, which may be connected to an alternating or negative source of potential 30 is to electrostatically neutralize the copy sheet as it is moved away from the xerographic surface toward the sheet attracting roller 20 while advancing toward the fuser 26. This is done as a further safeguard against the reattracting of the copy sheet to xerographic surface before its contact with, and neutralization by, biased roller.

Note is taken that the roller need not, in fact, be a roller and need not, in fact, be rotating. It is sufficient, merely that the field creating member is in proximity to the photoconductive surface and charged copy sheet in the area adjacent where its removal is desired. The use of the roller merely provides a convenient way to neutralize and transport the stripped copy sheet away from the xerographic surface.

While the present invention, as to its objects and advantages, have been described herein has carried out in specific embodiments thereof, it is not desired to be limited thereby; but it is intended to cover the invention broadly within the scope of the appended claims.

What is claimed is:

1. ln apparatus for producing xerographic copy which includes means for electrostatically charging a cylindrically shaped photoconductive surface, means to expose the charged surface to dissipate the charge in a patterned configuration of image and nonimage areas corresponding to the object to be reproduced, means to develop the exposed surface with charged toner particles, means to bring a backing sheet into contact with the photoconductive surface in registration with the developed charge pattern and means to electrostatically transfer the toner particles to the backing sheet, the improvement comprising means to electrostatically attract the backing sheet from the xerographic surface to thereby separate the toner-bearing backing sheet from the xerographic surface.

2. The apparatus as set forth in claim 1 wherein the lastmentioned means includes an electrically biased roller extending across the xerographic surface and spaced therefrom at a distance greater than the thickness of the backing sheet.

3. The apparatus as set forth in claim 2 wherein the roller is mounted for rotation in the direction of movement of the copy sheet and xerographic surface.

4. The apparatus as set forth in claim 3 and further including means to maintain the distance between the xerographic surface and roller surface substantially constant during rotation.

5. The apparatus as set forth in claim 3 wherein the roller is provided with insulating collars around each end thereof to keep the roller properly spaced from the xerographic surface.

6. The apparatus as set forth in claim 1 further including a corona discharge device to remove the charge from the copy sheet as the copy sheet moves away from the xerographic surface.

Claims

1. In apparatus for producing xerographic copy which includes means for electrostatically charging a cylindrically shaped photoconductive surface, means to expose the charged surface to dissipate the charge in a patterned configuration of image and nonimage areas corresponding to the object to be reproduced, means to develop the exposed surface with charged toner particles, means to bring a backing sheet into contact with the photoconductive surface in registration with the developed charge pattern and means to electrostatically transfer the toner particles to the backing sheet, the improvement comprising means to electrostatically attract the backing sheet from the xerographic surface to thereby separate the toner-bearing backing sheet from the xerographic surface.

2. The apparatus as set forth in claim 1 wherein the last-mentioned means includes an electrically biased roller extending across the xerographic surface and spaced therefrom at a distance greater than the thickness of the backing sheet.