Biased Electrode Transfer Apparatus

Abstract

A roller for pneumatically supporting copy sheets in the transfer station of a xerographic machine. The roller is electrically biased to transfer toner images from a photoreceptive member to copy sheets supported on the roller. Recirculation of the roller may effect the transfer of superimposed images to the backing sheets.

Description

This invention relates to the transfer of toner images from a photoreceptive member to a backing sheet. More particularly, this invention relates to apparatus for pneumatically supporting copy sheet material on a roller which is electrically biased to effect the transfer of the toner images to the support sheets.

In the practice of xerography as described for example in U.S. Pat. No. 2,297,691 to Chester F. Carlson, a xerographic plate comprising a layer of photoconductive insulating material affixed 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 light pattern.

The latent electrostatic image can then be developed by contacting it with a finely divided electrostatically attractable material such as a powder. The powder is held in image areas by the electrostatic charge field on the plate. Where the charge field is greatest, the greatest amount of material is deposited; and where the charge field 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 suitable affixed thereto to form a permanent print.

The electrostatically attractable developing material commonly used in xerography comprises a pigmented resinous powder referred hereto as "toner" and a coarse granular material called "carrier." The carrier is generally coated with a material removed in the triboelectric series from the toner so that a charge is generated between the toner and the 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 exposed xerographic surface for its development.

The powder particles then are attracted to the electrostatic image from the granular material to produce a visible powdered image on the xerographic surface. Electrostatic means may then be employed to transfer the toner image to a final backing sheet to which it is fused for creating a final permanent copy.

In copending application Ser. No. 830,426 filed June 4, 1969 in the name of Michael J. Langdon, apparatus is disclosed for transferring the toner powder images from the photoreceptive member to a backing sheet. As disclosed in that application, an electrically biased transfer roll is employed as an efficient and highly desirable mechanism for effecting such transfer. The backing sheet is mechanically supported on the roll for recirculation. Such an arrangement is particularly useful where it is desired to recirculate the copy sheets so that superimposed toner images may be sequentially transferred to the final backing sheet, as for example, when creating multicolored copies thereon.

The present invention is directed to an improvement over a system of the Langdon type in that it is adapted for greater mechanical control of the copy sheet during the transfer of toner images thereby. In addition, the apparatus of the instant invention provides for good registration of the leading edge of the copy sheet as it is introduced to the roll and for a positive release thereof after the transfer of the toner images during one or more passes.

It is therefore an object of the instant invention to transfer toner images to sheet material.

It is a further object of the instant invention to efficiently support a backing sheet on a drum during the transfer of toner images thereto.

It is a further object of the instant invention to assure good registration of a backing sheet of a transfer roll.

It is a further object of the instant invention to efficiently release, from a transfer roll, copy sheet material supporting toner images.

These and other objects of the instant invention are achieved by a transfer roll adapted to receive and pneumatically support a backing sheet material. The roll is electrically biased to effect the transfer of toner images from a xerographic member in rolling contact therewith, to a copy sheet supported thereon. The roll may also pneumatically repel the leading edge of the sheet therefrom after the transfer of toner images thereto.

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 read in connection with the accompanying drawings wherein:

FIG. 1 is a schematic diagram of an automatic xerographic reproducing machine having a transfer roll, shown in a section view, employing the principles of the instant invention,

FIG. 2 is a perspective view of the transfer roll of FIG. 1 with parts broken away to show internal constructions thereof, and

FIG. 3 is a sectional view of the roll of FIGS. 1 and 2.

Referring now to the figures, there is shown an embodiment of the subject invention in a suitable environment such as an automatic xerographic reproducing machine. The machine has a xerographic member 10 formed of 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 layer 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 on 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 supported in the transfer roll, and

A drum-cleaning 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.

After the drum-shaped surface rotates past the development station C, a suitable backing material 12 such as paper is brought into contact with the transfer roll and xerographic surface 10 by first sheet feeding mechanisms 14. Other insulating backing materials, such as Mylar or the like, may also be used. Beyond the transfer station D, the secondary sheet-feeding mechanism 16 convey the sheet material bearing toner images through the fuser assembly F to deliver permanent copy to exterior of the machine.

Control of the sheet material in the transfer station is effected by a transfer roll having a length preferably substantially equal to the length of the xerographic drum. This length is also substantially equal to the length or width of the copy sheet to be supported thereon depending on the direction in which it is to be moved. If the long edge of a sheet of paper is to be moved into the nip between the transfer roll and xerographic drum, the transfer roll would preferably be 14 inches in length to thereby accommodate sheet material from 81/2 .times.11 to 81/2 .times.14 inches, the most common lengths of sheet material in general copying use. The circumference of the drum would then be slightly larger than the other dimension of the sheet, as for example, slightly larger than 81/2 inches. If sheet material were to be fed in the other direction, the roll would be about 81/2 inches in length and about 14 inches in circumference.

The drum 18 is preferably formed of a stiff cylindrical core 20 of an insulating material, preferably plastic, having holes 22 of a pinhole size therein for the movement of air therethrough. The core is preferably an electrical insulator so that electrical charges on material contacting it will not be conducted thereby. Placed thereon and coextensive therewith is an apertured member, screen 24, constructed of an electrically conductive material adapted to support an electrical bias and pass the field through an exterior or surface layer 26. Layer 26 is constructed of a resilient material capable of passing air therethrough. A preferred material is Chamberlin Grade 5,000, a commercially available material from the Chamberlin Rubber Corporation. This material is a conductive rubber which, due to its conductivity, enhances the toner transferring field and due to its resiliency, will deform to prevent drum abrasion if a carrier granule comes to the area. An insulating material, sufficiently thin to permit the field of screen 24 to pass therethrough could also be employed. Pinholes form the apertures 28 in the layer 26.

The exterior layer 26 overlies the entire cylindrical screen except for one circumferential strip 30 on the edge thereof extending beyond drum 10 so that an electrical bias may be applied thereto by means of a suitable power source, not shown, through an electrical brush 32. This brush is stationary and will be in continual contact with the exterior strip 30 of the screen extending beyond the external layer 26 during all positions of rotation of the transfer roller or drum 18.

The end caps 36 of the drum core 20 are constructed of an imperforate stiff insulating material, preferably plastic, adapted to receive shafts 38 and 40 which are supported on the side frames of the machine. The shafts are each mounted on bearing assemblies 44 so that the drum may rotate relative thereto. A gear 46 mounted on the one end cap for rotation therewith is adapted to cooperate with gear member 58 which is rotated by motor MOT-1 so as to rotate the drum in the direction of the arrow as indicated at a peripheral speed equal to the xerographic drum 10.

Each of the shafts is hollow and is coupled adjacent an exterior end with a source of vacuum, VS-1 and VS-2. The shaft 38 pneumatically coupled with vacuum source VS-1 defines a passage through the first shaft to a central shaft 48 pneumatically coupling the first and second shafts and adapted to be rotated with the rotation of the drum through the bearings 44. Adjacent the central portion of the central rotatable shaft 48 is a pneumatic conduit 50 coupling it with a trough 52 formed of a rigid insulating material, imperforate plastic or the like, so that the application of a negative pressure by vacuum source VS-1 will apply a vacuum through the shaft to provide a vacuum within the area defined by the trough through the apertured rigid cylinder, metal conductive screen and porous conductive exterior surface of the systems. As can be understood, the edges of the trough contacting the core 20 and end caps 36 are pneumatically sealed thereto for supporting the vacuum therein and above the surface of the roller 18. The area on the surface of the roller defined by the trough and its high vacuum is adapted to support the leading edge of sheet material 12 moved into contact therewith.

The vacuum source VS-2 is adapted to be pneumatically coupled to apertures 54 in the rotatable internal shaft whereby the second vacuum, preferably of lesser magnitude than the first, may be established internal of the transfer roll except for the area within the trough. A blocking plate 56 within the central rotatable shaft permits the application of diverse vacuums to these diverse regions within the roll.

As can be seen in FIG. 1, there circumference of the roll is provided with an indent portion 60 adjacent an edge of the roller above the high-vacuum trough. This can function to stop the leading edge of the sheet as it is received from the input transport 14 which will direct the leading edge of the backing sheet in association therewith in timed registration with the rotation of the drum and transfer roll. Stop register fingers 62 are preferably employed in association with the sheet feeding mechanisms, as described for example in U.S. Pat. No. 3,301,126 to Osborne et al. This permits accurate registration of the copy sheet with images on the drum for accurate alignment during transfer. The transfer roll is also rotatable off of the machine timing elements with the sheet feeders and drum drive means. If desired, gripper fingers of the type disclosed in the aforementioned Langdon application and could be employed to further assure gripping and registration of the leading edge in conjunction with the other described mechanisms.

Upon completion of one or more passes of the copy sheet, the leading edge will be moved to an area adjacent the output feed belts 16, whereupon the first vacuum source VS-1 may be reversed providing positive pressure sufficient to pneumatically eject the copy sheet therefrom. A pulse of high pressure has been found to effect a more positive removal of the copy sheet material.

The potential source adapted to apply the electrical bias to the transfer roll may be variable in nature in the manner described in the aforementioned Langdon application whereby successive transfers of toner are desirable. Increases in electrical potential for successive transfers has been found to transfer more efficiently when multiple transfers are to be employed.

In operation, a copy sheet 12 is fed toward the xerographic drum 10 and transfer roller 18. Since then the leading edge of the copy sheet will enter the xerographic development zone at the nip between the xerographic drum and the transfer roll in registration with the leading edge of the developed image on the xerographic surface, the stop register fingers 62 may detain the copy sheets momentarily if its leading edge has arrived at this location prematurely. As the leading edge hits the nip it will contact the indented portion 60 on the surface of the transfer roll.

The vacuum created interior of the transfer roll will hold the copy sheet to the transfer roll such that the surface speed of the copy sheet and transfer roll are the same as the surface speed of the xerographic surface. As the copy sheet moves through the development zone, the electrical bias applied to the screen 24 is such that the electrical field extending through the copy sheet material will create a sufficient field to attract and transfer the charged toner particles from the xerographic surface to the copy sheet.

After the passage of the leading edge of the copy sheet from the transfer station, the pressure from vacuum source VS-1 may be reversed to blow the leading edge of the copy sheet therefrom to the secondary sheet conveying mechanisms 16. In combination with this, the vacuum supplied to the rest of the transfer cylinder through VS-2 may be removed so that the entire copy sheet may be directed to exterior of the xerographic machine by conveyor assembly 16. If plural transfers are to be made to the same copy sheet, the high and low vacuums will remain to retain the copy sheet on the surface of the transfer roll. After the last transfer has been made, the vacuum source VS-2 will be inactivated and the vacuum source VS-1 will be reversed to positively eject the leading edge of the copy sheet to the supplemental conveyor belts 16 for fusing and creation of the permanent copy.

While the instant invention as to its objects and advantages has been described and carried out in a specific embodiment hereof it is not intended to be limited thereby but it is intended to protect the invention broadly within the scope of the appended claims.

Claims

What is claimed is:

1. Apparatus for transferring charged toner to a backing sheet from a member electrostatically supporting the toner powder including,

a rotatable cylinder having a peripheral surface adapted to support and bring the backing sheet into contact with the member bearing the toner powder to be transferred,

vacuum means within said cylinder to retain the backing sheet thereon and

means to apply an electrical bias to the cylinder to effect the electrostatic transfer of the toner from the member to the backing sheet.

2. The apparatus as set forth in claim 1 wherein the surface of said cylinder includes a high-vacuum section to support the leading edge of the backing sheet and a low-vacuum section to support the remainder of the sheet.

3. The apparatus as set forth in claim 1 wherein said cylinder includes an apertured member of an electrically conductive material having a supplemental apertured layer thereover.

4. Apparatus for effecting the transfer of electrostatically charged powder to an insulating backing sheet including,

a cylindrically shaped member formed of an electrically conductive material and having apertures therethrough,

means to create a vacuum internal of said member to thereby pneumatically retain an insulating backing sheet thereon,

means to apply an electrical bias opposite that on the powder to said member sufficient to create a field through an insulating backing sheet supported thereon and

means to rotate said member about its axis whereby an insulating backing sheet supported thereon may contact the toner powder to cause its transfer thereto.

5. The apparatus as set forth in claim 4 and further including means to feed an insulating backing sheet to said cylinder.

6. The apparatus as set forth in claim 5 and further including an indented portion on the surface of said member adapted to be contacted by the leading edge of the insulating backing sheet.

7. Apparatus for transferring charged toner powder to an insulating backing sheet from a cylindrically shaped member electrostatically bearing the toner powder including

a cylinder having a peripheral surface adapted to support and bring the backing sheet into contact with the member bearing the toner powder to be transferred,

means to rotate the member about its axis to continually bring toner powder adjacent said cylinder,

means to rotate said cylinder at a linear speed equal to the linear speed of the member and at a distance therefrom such that when an insulating backing sheet is supported on said cylinder it will contact the toner powder on the member,

means within said cylinder to pneumatically retain the backing sheet thereon and

means to apply an electrical bias to said cylinder to effect the electrostatic transfer of the toner powder from the member to the backing sheet.

8. The apparatus as set forth in claim 8 wherein said cylinder includes a first layer constituting a core and formed of an electrically insulating member, a second layer constituting the exterior surface and formed of a resilient material and a third layer of an electrically conductive material intermediate said first and second layers.

9. The apparatus as set forth in claim 8 wherein said first, second and third layers are all apertured to permit the flow of air therethrough.

10. The apparatus as set forth in claim 9 and further including a first vacuum section within the portion of said cylinder adapted to receive the leading edge of the insulating backing sheet and a second vacuum section within the portion of said cylinder adapted to receive the remainder of the insulating backing sheet.