Apparatus For Conveying Sheet Material

Abstract

An apparatus for electrostatically tacking sheet material such as paper onto a moving dielectric belt and conveying it to a remote location having a ground plate in contact with the undersurface of the belt, and a tacking corona device over the upper surface of the belt opposite the ground plate and a control device to activate the tacking corona device only when a sheet of paper is between it and the belt. The tacking corona device in combination with the ground plate introduces a current flow through the paper sheet and belt which enhances the electrostatic attraction between the paper and belt. The conveying apparatus has an additional corona-charging device of a polarity opposite that of the tacking corona device which neutralizes any residue charge on the upper surface of the belt after the sheet has been conveyed to the remote location and removed from the belt.

Description

This invention relates to an apparatus for conveying sheet material, and, more particularly, to an apparatus for conveying a sheet by electrostatically tacking the sheet to a moving belt conveyor.

In apparatus which conveys sheet material from one place to another, such as that commonly used to convey paper sheets in reproduction systems, it is desirable to transport the sheet while it is maintained in the substantially flat condition so that one side of the sheet can easily be brought into contact with processing elements. For this purpose, copying systems often utilize conveyors which carry sheets to and through the various process stations in a flattened position. Electrostatic copying systems, such as those which employ transfer xerography, have advantageously used sheet conveyors to transport a sheet of paper from a supply of sheets to the transfer station.

In the process of xerography, an electrostatic plate, commonly in the shape of a rotatable drum and having a layer of photoconductive material over a conductive backing, is given a uniform electrostatic charge over its surface and then exposed to a light pattern conforming to the information to be reproduced. When the light pattern is exposed onto the drum, the charge on the photoconductive layer is dissipated in the light areas thereby forming a latent electrostatic image on the drum surface. The drum is developed with a finely divided, pigmented material such as toner and then the developed image transferred from the drum surface to a sheet of paper at a transfer station.

During the transfer step, successive portions of the toner image are transferred to the sheet from the drum surface as the sheet and drum pass through the transfer station in contact with one another. To carry out the transfer step quickly and efficiently it has been found beneficial to feed the sheet of paper to the transfer station at a speed which is synchronous with the speed of the surface of the drum and in a relatively flattened position so that the sheet and drum effectively make contact only in the transfer station. One type of conveyor used to transport a flat sheet is a moving belt. The sheet is placed on the top of the belt and the friction force between the sheet and belt causes the sheet to be carried along with the belt. As a practical matter, this type of conveyor is limited to transporting sheets on a substantially horizontal plane since there is the hazard that the sheet might slip from the conveying surface otherwise. In many copier systems such a conveyor is not feasible since sheets cannot always be conveyed in a horizontal plane due to space limitations within the machine.

Another type of belt conveyor utilizes mechanical clamps or fasteners to assure that the sheet is conveyed at all times regardless of whether the belt travels in a horizontal plane or not. Although this type of conveyor prevents the sheet from falling off the belt, the clamps may deform or even mutilate the sheet during transport. It is important, particularly in copying systems to deliver sheets to a process station, such as the transfer station, without deformation or mutilation to be certain that the process is carried out without impairment. For this reason, the employment of such fasteners are disadvantageous since they may bend, fold, or even tear the sheet during transport.

The invention disclosed herein conveys a sheet in such a manner that it cannot be deformed or mutilated by the conveying apparatus since there is no need to contact the sheet with mechanical fastening elements. The sheet is securely fastened onto a belt conveyor and can be transported at high speeds in any direction without fear of it slipping off the belt or moving relative to the belt. In addition, the apparatus is compact, has a minimum number of moving parts, and is extremely reliable.

The present invention includes a moving dielectric belt to which a sheet of paper or the like is electrostatically tacked while in a flattened condition. The sheet is tacked to the belt by a corona-charging device while the belt is electrically grounded to cause a current flow through the belt and sheet during tacking. After the sheet being conveyed is removed from the belt, any residue charge on the belt surface is neutralized to assure good electrostatic tacking in succeeding cycles.

Accordingly, it is an object of the present invention to improve conveying apparatus for sheet material.

It is another object of the invention to improve sheet conveyors by electrostatically tacking the sheet to the conveyor.

It is another object of the invention to improve sheet conveyors by providing a conveying apparatus which does not deform or mutilate the sheet during transport.

It is another object of the invention to improve sheet conveyors by providing a conveying apparatus in which the sheet cannot move relative to the conveyor during transport.

It is another object of the invention to improve sheet conveyors by providing a conveying apparatus in which the sheet does not move relative to the conveyor at high rates of acceleration.

It is another object of the invention to improve sheet conveyors by electrostatically tacking the sheet to a grounded dielectric belt and neutralizing any residue electrostatic charge on the belt after the sheet has been removed from it.

SUMMARY

The present invention is a conveyor apparatus which transports a sheet material, such as paper, to a remote location. The sheet is placed on a moving, dielectric, endless belt in a loading station and electrostatically tacked to the belt surface by a first charging means. The electrostatic attraction between the belt and sheet is greatly enhanced due to a grounding means placed on the belt in the loading station which, together with the first charging means, introduces a flow of current through the sheet and belt when the first charging means is activated.

The first charging means is activated by a control mechanism which enables the sheet to be tacked to the belt at an appropriate time in relation to the desired time of delivery of the sheet to the remote location. A second charging means of equal voltage and opposite polarity as the first charging means acts on the belt after a sheet has been removed from the belt to neutralize any residue charge in the belt to prepare the belt for its next cycle through the loading station.

DESCRIPTION OF THE DRAWINGS

For a better understanding 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 used in conjunction with the accompanying drawings:

FIG. 1 is a schematic illustration of the invention;

FIG. 2 is a schematic illustration of the loading station; and

FIG. 3 is a block diagram illustrating the controls device used in the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is an apparatus for transporting sheet material such as paper. Although the invention can be utilized by any system in which sheets are to be conveyed from one place to another, it is described herein as part of a xerographic copier system. Referring to FIG. 1, there is shown a photocopying system with an electrostatic drum 19 which has various stations, A through E, about its periphery. The periphery of the drum contains a layer of photoconductive material overlaying a layer of conductive material. A latent electrostatic image is formed on the drum surface by placing a uniform charge on the drum at station A and then exposing the charged surface of the drum to a light pattern conforming to the information to be reproduced in station B. The light pattern dissipates the charge on the drum in the light areas thereby forming a latent electrostatic image on the drum surface. Station A can include any suitable charging means such as a corona-charging device and station B can include any suitable light-imaging apparatus such as a projector.

After the latent image has been formed on the surface of the drum, it is developed as it passes through station C. The latent image is developed with a finely divided, pigmented material such as toner which can be applied to the drum surface in any suitable technique such as by mixing the toner with suitable carrier material and cascading the mixture across the drum surface. Following the development of the image, the drum passes through transfer station D where a sheet of paper is fed into contact with the drum and the developed image is electrostatically transferred from the drum to the paper by corona transfer device 25. The sheet is fed into contact with the drum by belt conveyor 12 which moves at the same speed that the drum surface is rotating. The speeds are equalized to assure that the toner image is not smeared during the transfer process due to relative motion between the drum and paper. After the toner image has been transferred to the paper, the drum passes through station E where any residual toner is removed from the drum surface in preparation for another cycle. The configuration of the drum and location of the various stations around the periphery enable the system to operate continuously and all of the functions described above are carried out during each cycle of the drum.

The sheet of paper is transported through the transfer station by endless belt 12. The belt is supported and driven by rollers 21 and 22 at a rate of speed which is substantially equal to the speed at which the periphery of drum 19 moves through the transfer station. The sheet 11 is electrostatically tacked to the belt at tacking station 40 and is transported through transfer station D and under fuser 16 to unloading apparatus 60 where it is removed from the belt and stored. As the sheet enters the transfer station it depresses the belt 11 away from drum 19 so that it can pass between the belt and drum. In this manner it is assured that the paper always makes firm contact with the drum during the transfer step.

The belt is made of any suitable flexible dielectric material such as Mylar, a product of E. I. DuPont de Nemours and Company, and the sheet 11 is electrostatically tacked to it in tacking station 40 by a suitable charging means such as tacking corona-charging device 14. In addition to the tacking device 14, station 40 contains a ground plate 13 which electrically grounds the belt in the area of the tacking device 14. It is the combination of the tacking device and ground plate which enables the sheet to be electrostatically tacked to the belt in such a manner that it will not move relative to the belt in spite of large acceleration forces imposed on it by the belt's movement when tacking occurs.

When the tacking device 14 is activated, the sheet between it and the belt is sprayed with an electrical charge. Due to the presence of the ground plate in contact with the belt opposite the tacking device, a current flow is introduced through the sheet and belt as tacking takes place. If the corona device 14 emits a charge of positive polarity, the surface of the sheet adjacent the belt will tend to become positively charged and the surface of the belt adjacent the sheet negatively charged. As a result of this charging phenomenon, the surface of the paper adjacent the belt is electrostatically attracted to the belt. The presence of ground plate on the belt enhances the electrostatic attraction between the paper and belt and thereby prevents movement of the paper relative to the belt throughout the conveying process.

The polarity of the charge placed on the sheet in the loading station depends on the charge placed on the drum 19 at charging station A. If, for example, the drum were charged with a positive polarity, the toner particles would preferably bear a negative charge for good development. In this case, both the transfer and tacking corotrons would be of positive polarity to attract the toner from the drum to the sheet and the sheet to the belt, respectively. If, on the other hand, the charge placed on the drum required a positively charged toner, the tacking and transfer corotrons would have a negative polarity.

Sheets of paper are fed into the tacking station between corona device 14 and the ground plate 13 by feeding apparatus 30. The sheets are fed one at a time from a supply of sheets by and between rollers 31 and 32 by any suitable device (not shown). Rollers 31 and 32 feed the leading edge of the sheet over guide 33 across belt 11 and between corona device 14 and the belt. Rollers 31 and 32 are spaced from the corona device 14 a distance approximately equal to the length of the sheet being fed so that after the trailing edge of the sheet has passed through the rollers, the leading edge of the sheet is positioned just ahead (or to the right) of the corona device 14 where it remains adjacent the moving belt until corona device 14 is activated. There is too little friction between the belt and sheet at this time to enable the belt to carry the sheet towards the transfer station before corona device 14 is activated. This is the case especially since only the leading portion of the sheet is adjacent the belt. However, in order to be certain that the sheet is not carried through the transfer station by the belt before the tacking apparatus is activated, the trailing edge portion of the sheet optionally can be retained on guide 33 by a finger 34 which is biased towards guide 33 (as can best be seen in FIG. 2).

Feed rollers 31 and 32 feed the sheet towards the transfer station until they cease to have driving contact with the sheet. At this time the leading edge of the sheet, which is being supported by moving belt 12, is adjacent corona device 14. In order to maintain positive control over the sheet prior to activation of the corona device 14, finger 34 is lightly biased (not shown) onto the sheet thereby holding the sheet against guide 33. The biasing means on the finger is just sufficient to hold the sheet until the tacking device is activated at which time the sheet is pulled through the finger and guide by the belt. The bias on the finger, in addition, is insufficient to retard the movement of the sheet when the feed rollers feed the leading edge portion of the sheet through the finger and guide. The sheet-feeding apparatus shown in FIGS. 1 and 2 and described above is optional in the conveying apparatus. As an alternative, a sheet can be manually placed on the belt with its leading edge adjacent the corona device 14 and tacked to the belt in the same manner as described above by activating corona device 14. The feeding apparatus 30, however, is a particularly desirable feature in a completely automatic copier system.

Referring to FIG. 1, after the sheet passes through transfer station D, the belt carries it under fuser 16 to unloading station 60. As the belt passes under the fuser the toner image transferred to the sheet is fused into the sheet to make the toner image permanent. At the unloading station the sheet is stripped from the belt by virtue of the natural beam strength of the paper and guided into storage tray 37 by guide 36. The sharp turn that the belt makes around roller 22 enables the sheet to overcome its attraction to the belt by the tendency of the sheet to be unable to follow the path of the belt as it turns.

In addition to the apparatus described above an optional corona device 23 can be employed in the system to enhance the tacking process carried out in the loading station. After the sheet has been unloaded from the belt at station 60 the belt may still retain a residue charge on its surface which does not fully dissipate prior to the belt again passing into the loading station due to the dielectric nature of the belt material. In order to return the belt to a neutral condition, which is desirable for most effective tacking, corona device 23, together with ground plate 24, is employed in neutralizing station 50. Station 50 can be located anywhere adjacent the belt between unloading station 60 and loading station 40 after a sheet is removed from the belt. Corona device 23 sprays a charge over the belt having a polarity opposite to that placed on the sheet by corona device 14 and, preferably, of equal potential. Corona device 23 can be continuously activated by a suitable power source (not shown), or activated only while those portions of the belt that transported a sheet pass through neutralization station 50. By the use of this second corona device a "neutralized" belt is presented to the tacking station at all times.

The voltage potentials used by corona devices 14 and 23 are functions of the type of sheet material to be transported, the type of belt material used, the amount of electrostatic attraction desired between the belt and sheet, the proximity of the corona devices to the sheet, and the speed of the belt. After testing the apparatus with Mylar belt running at 14-24 inches per second and using paper as the sheet material, it was found that effective tacking would occur when the emitting wire of the corona device operated between 4,500 and 6,500 volts and was within 0.5 inch of the sheet. However, the most preferred voltage range for best tacking occurred when 5,000 to 6,000 volts was applied to the corona device wire.

The rotation of drum 19 and the operation of the various stations around the drum can be controlled by any suitable control device. The tacking device 14 is controlled so that it is activated to place a sheet within the transfer station in registration with the toner image on the drum surface and inactivated as the trailing edge of the sheet passes through the loading station. Any suitable way of achieving such control of the tacking corona device can be used. For instance, if the surface of the drum and belt travel at the same speed and if the distance between the tacking device 14 and transfer device 25 is equal to the length of the path the surface of the drum 19 travels between the exposing station B and the transfer corona device, the tacking device can be activated just as the drum begins to be exposed by a signal generated in response to the exposure step beginning. In a similar manner, a signal generated in response to the exposure step being completed can be used to inactivate the tacking corona device. Similar signals can be used to control intermittent operation of the neutralizing corona device 23 if it is desired to neutralize only those portions of the belt to which a sheet has been tacked.

Referring to FIG. 3, any suitable control device, such as a reed coil switch, is fed current from a power supply which drives the tacking corona device. Prior to receiving the electrical signal indicating that the exposing step is about to begin, the switch prevents the tacking corona device from being activated by the power supply. However, once the sensor signal is received by the reed coil control switch, it allows current to flow from the power supply directly to the tacking corona device thereby activating the corona device. A sensor signal can be generated when the exposing step has been completed in order to inactivate the tacking corona device through a similar control switch as the trailing edge of the sheet passes through the tacking station.

In addition to the apparatus outlined above, many other modifications and/or additions to the invention will be readily apparent to those skilled in the art upon reading the disclosure, and these are intended to be encompassed within the spirit of the invention.

Claims

What is claimed is:

1. In a xerographic reproduction apparatus wherein a latent electrostatic image of copy being reproduced is formed on a moving electrostatic drum by placing a uniform electrostatic charge on the drum surface and exposing the surface of the drum to the light image of the copying being reproduced, the latent image on the drum is developed with toner particles bearing a charge of a predetermined polarity, and the toner image is transferred to a sheet of paper or the like at a transfer station, said apparatus having a dielectric endless belt with outer and inner surfaces for supporting the sheet, means to support the belt on its inner surface for movement from a sheet-loading station to a remote location while passing through the transfer station in contact with the electrostatic drum, means to drive the belt at the same speed as the surface of the drum to bring each portion of the belt from the sheet-loading station through the transfer station to the remote location, and means to feed the leading edge of the sheet from the supply of sheet material onto the outer surface of the belt in the loading station, an apparatus for neutralizing any electrostatic charge on the belt and then electrostatically tacking the sheet to the belt comprising:

a. first charging means of a first polarity, the first polarity being opposite the predetermined polarity of the toner particles, located adjacent the outer surface of the belt in the loading station to charge the sheet and belt when the sheet is positioned between the charging means and belt,

b. control means to activate the first charging means only when the sheet is between the first charging means and the belt, the first charging means being activated at a time which is appropriate to bring the toner image on the drum and the sheet in registration with one another at the transfer station,

c. first means to electrically ground the belt in the loading station in contact with the inner surface thereof to enable current to flow from the first charging means through the sheet and belt to the first ground means when the first charging means is activated,

d. means to remove the sheet from the belt at the remote location,

e. second charging means of a second polarity, the second polarity being opposite the first polarity, located adjacent a portion of the outer surface of the belt that is being driven between the means to remove and the loading station to neutralize any residue electrostatic charge of a first polarity on the outer surface of the belt prior to being driven through the loading station,

f. means to activate the second charging means continuously to neutralize any electrostatic charge of the first polarity of the belt before it is driven through the loading station, and

g. second means to electrically ground the belt in contact with the inner surface thereof adjacent the second charging means to enable current to flow from the second charging means through the dielectric belt to the second ground means.