GB2334950A - Pivoted static discharge brush for sheet printing/stacking device - Google Patents

Abstract

The static discharge brush unit 20, comprising flexible, conductive brush fibers 24, is mounted adjacent to the output 14 of a printer device, such as an electrostatographic printer, to reduce the residual static charge on each sheet. The brush may be pivoted above its centre of gravity allowing it to come to rest in a vertical position, but is deflected away from the vertical by the emerging paper sheet 12.

Description

SHEET STACKING SYSTEM The disclosed system relates to improved sheet stacking from the output of electrostatographic or other printing systems by improved static discharge of the image substrate sheet surface(s). In particular, it is an improvement to the conductive brush type static eliminators used for many years at the sheet exit of such machines.

By way of background, static charges on the paper or plastic image substrates being outputted by a printing system, particularly those from a xerographic or other electrostatographic printer, can cause various stacking problems in the exit stack or in subsequent finishing operations for the sheets, by electrostatic adhesion, etc.. Thus, it has been typical for many years, especially in low and mid-volume machines, to use a passive conductive or semi-conductive static discharge fiber brush system adjacent the sheet exit, and elsewhere. One recent example of electrically conductive fibers is disclosed in US-A-5,689,791. Of particular interest here, some examples of static eliminator brushes for removing static on copy paper in particular, and static conducting brush fiber materials therefor, are disclosed in US-A-4,330,349; US-A-4,553,191; and US-A5,354,607. Accordingly, that known technology need not be re-described herein.

It is particularly difficult to discharge static charges accumulated on the surface(s) of recycled papers (paper made with scrap paper) or plastic transparencies during their printing operations and/or their movement through the printing apparatus. As is well known, the heating of the paper and its image in a fusing device or system, and/or low ambient humidity conditions, can aggravate the static electricity problems, and thus the sheet stacking problems, unless there is adequate static discharge of the printed sheets, preferably at the exit area of the sheets just before they are stacked.

It has been found that static discharge efficiency can be improved, even for "passive" static eliminator brush systems (electrically grounded brushes rather than A.C. voltage corona static eliminator systems) if the sharp tips of these small diameter conductive brushes can be maintained in contact longer with the sheet surface.

It is thought that these sharp (cut off) tips of the fibers may provide better electrical contacts for static discharge and/or create "Paschen fields" for conditions of air breakdown or corona-mode electrostatic discharge which can improve the overall effective discharge, particularly where the static charge level on the sheet is high.

Present passive brush static elimination systems typically employ a fixed brush unit, and the brush fibers thereof are typically highly deflected and bend by the passage thereby of the sheets they are discharging. In the disclosed embodiment, it has been found that a significant improvement can be provided in the static discharge of the sheets by providing a static eliminator brush which is pivotally mounted in such a way as to pivot the brush unit relative to the exiting sheet. It has been found that such an appropriately designed pivotal static eliminator brush system can substantially lengthen the area and time of contact of the conductive fiber tips with the sheet surface, for improved static elimination, particularly of difficult to discharge sheets. Furthermore, it has been found that this system also has the further advantage of increasing the life of the static eliminator brush by reduced fiber bending. By locating the subject pivoting static eliminator brush unit closely adjacent to the exit rolls and providing a low force resistance to the pivoting of the static eliminator brush, the exiting sheet lead edge itself can pivot the static eliminator brush to the desired position. It has been found that, especially with the typical sheet corrugation provided for exiting sheets from printers for increased beam strength of the sheet adjacent the exit, that the sheet itself can provide such sufficient force for pivoting the static eliminator brush even if the exiting sheet is thin and flimsy, and even though the sheet is only engaging the highly flexible thin brush fibers themselves as the sheet exits.

Furthermore, the disclosed embodiment desirably accommodates significant variations in the exit position or angle of the sheet exiting the sheet output. It prevents the brush fibers from taking a permanent bend or "set" by being excessively bent by exiting sheets, as was previously experienced, especially with such variations in the sheet output level. As is well known, copy sheets may have lead edge curl in either the up or down direction of the output, affected by the upstream processing of the sheet such as fuser rolls, imaging materials, and/or humidity changes. Such sheet lead edge curl can affect the vertical position of the exiting lead edge of the sheet, and therefore the point at which the fiber brushes are engaged by the lead edge of the sheet.

The disclosed system can accommodate and compensate for these additional variations in operating conditions of the reproduction apparatus.

A specific feature of the specific embodiment(s) disclosed herein is to provide a sheet printing and stacking apparatus, with a sheet output at which the printed sheets have a static electricity charge thereon which could interfere with sheet stacking, having a static elimination system with a static removal brush unit with flexible conductive brush fibers adjacent said sheet output positioned for engaging the printed sheets adjacent said sheet output and at least partially discharging said static electricity charge on the printed sheets, said flexible conductive brush fibers extending from said static removal brush unit to brush fiber tips; the improvement in said static elimination system wherein said static removal brush unit with said flexible conductive brush fibers is pivotally mounted adjacent to said sheet output with a pivotal mounting system providing pivoting of said entire static removal brush unit by engagement of a sheet outputted from said sheet output with said flexible conductive brush fibers, said static removal brush unit being pivotable by said sheet engagement with said flexible conductive brush fibers sufficiently to reduce flexing of said flexible conductive brush fibers and to substantially increase the engagement of said brush fiber tips thereof with said sheet.

Further specific features disclosed herein, individually or in combination, include those wherein said pivotal mounting system for said static removal brush unit provides said pivotal mounting thereof on a pivot axis above the center of gravity of said static removal brush unit, so that said static removal brush unit is normally maintained by gravity in a substantially vertical position until said engagement by said sheet outputted from said sheet output; and/or wherein said pivot axis of said static removal brush unit is intermediate of said static removal brush unit and above but adjacent to said sheet output; and/or wherein said static removal brush unit is pivotal by said sheet outputted from said sheet output with a force of less than 4 grams.

In reproduction apparatus such as xerographic and other copiers and printers or multifunction machines, it is increasingly important to provide faster yet more reliable automatic handling of the physical image bearing sheets in general. It is desirable to reliably feed and accurately register sheets of a variety and/or mixture of sizes, types, weights, materials, humidity and other conditions. The sheets of a set or print job to be stacked may have come from different paper batches or have variably changed with different age or humidity conditions, different imaging, fusing, etc..

In the description herein the term sheet' or "copy sheet" refers to the usually flimsy physical sheet of paper, plastic, or other suitable physical substrate for images, whether precut or initially web fed. The term conductive as used herein also includes partially conductive or semi-conductive brush fibers also capable of removing static charges from the paper.

A particular embodiment in accordance with this invention will now be described with reference to the accompanying drawings in which: Fig. 1 illustrates an embodiment of the subject sheet stacking assistance system with a pivoting static eliminator brush system in a partial side view of the exit area of an exemplary reproduction apparatus such as an electrostatographic printer - the operation is shown here at the point at which the lead edge of the exiting copy sheet first engages the brush fibers; Fig. 2 shows the embodiment as Fig. 1 in the subsequent operating position at which the exiting copy sheet (in this case a sheet with an upward curl in the lead edge area of the sheet) has pivoted the exemplary pivoting static eliminator brush, as shown by its movement arrow, maintaining improved engagement of the tips of the brush fibers with the exiting sheet surface; Fig. 3 is a top view of the embodiment of Figs. 1 and 2, showing in further detail the exemplary pivoting system for this static eliminator brush unit and also an exemplary flexible ground wire connection of this static eliminator brush unit to the mounting frame; Fig. 4 is the same top view as Fig. 3, showing the Fig. 2 pivoted operating position of the static eliminator brush unit; Fig. 5, labeled "prior art", illustrates a previous fixed (stationary) static eliminator brush system in the same basic operating position of the exiting sheet as for Fig. 1; and Fig. 6, labeled "prior art", shows the same prior fixed brush system as in Fig. 5, but in the copy sheet output operating position corresponding to Fig. 2 of the Figs. 1-4 system herein, illustrating undesirably bent brush fibers.

Referring now to the exemplary embodiment illustrated in Figs. 1 - 4, there is shown here, merely as one example, the output area of a printer 10 or other reproduction apparatus in which printed sheets 12, having a lead edge 12A, exit the sheet output 14 of the machine 10 for stacking in an adjacent stacking tray or compiler tray (not fully shown). The sheet output 14 here comprises output rolls 16 extending across the output path of the sheet, which rolls 16 also desirably also provide corrugation of the sheet for increased beam strength thereof in that area, as is shown in US-A5,280,901.

Figs. 5 and 6 illustrate one example of a prior passive (grounded) electrostatic charge removal system for the exiting sheets, with a fixed brush of such flexible conductive or semi-conductive fibers extending into the sheet exit path from the sheet output 14. As described above, these fibers can be excessively deflected by the exiting sheet, particularly if the lead edge thereof or other parts of the sheet extend upwardly due to curl or misalignment, as shown in Fig. 6. As described above, this can cause the fibers of the brush in this prior art system to excessively bend and deform, as shown in Fig. 6, which can cause damage thereto, such as a permanent "set". Furthermore, as is also shown in Fig. 6, this can cause the brush fibers to engage the sheet on the sides of the bent fibers rather than maintaining engagement of the outer ends or tips of the brush fibers with the sheet surface as the sheet exits for stacking.

Turning now to the subject embodiment, there is illustrated in Figs. 1 through 4 a pivotal static removal system 20 for overcoming the above and other disadvantages of the previous systems. In this embodiment, the static removal system 20 can utilize a modified form of an otherwise conventional static removal brush unit 22. That is, a brush unit 22 comprising a conventional elongated array of small diameter flexible conductive or semi-conductive fibers 24 mounted in a connective base or brush clamp 25 such as a lightweight aluminum channel member. However, in the pivotal static removal system 20 of Figs. 1 - 3, unlike the fixed system shown in Figs. 4 and 5, the brush unit 22 here is pivotally mounted, with a pivot axis 26. The pivot axis 26 is preferably located, as shown, slightly above the center of gravity of the entire brush unit 22 so that the brush unit 22 has a small net gravitational force tending to maintain the brush unit 22, and thus the fibers 24 thereof, normally vertically aligned, except when a sheet 12 is being exited by the sheet output 14, yet a very low resistance force to pivoting from that normal position.

The brush unit 22 is freely pivotable on the pivot axis 26 from a mounting support 28 above the sheet 12 exit path, but closely adjacent to the sheet output 14 provided by the output rolls 16. The pivoting of the brush unit 22 can accommodate wide variations in the height of the body of the sheet, as well as its lead edge, to avoid what was previously a wide fluctuation in the amount of brush fiber deflection with a fixed brush unit, leading to brush "set". The pivot axis 26 is positioned such that, irrespective of even a large upward curl or misalignment of the sheet 12 exiting the output rolls 16, the sheet lead edge 12A and the rest of the sheet will always engage the brush unit 22 below the pivot axis 26 and substantially spaced below the brush clamp 25. One example of such a pivotable mounting system for the brush unit 22 is shown in more detail in the top views of Figs. 3 and 4.

Figs. 3 and 4 also show one example of a freely or highly flexible ground wire 30 connection, which electrically connects between the brush clamp 25 and the mounting support 28 or other grounded frame element of the printer 10, so as to conduct away the static electric charge on the sheet acquired by the fibers 24 of the brush unit 22. The brush fibers can be otherwise grounded, as by contact with end bundles of the fibers outside of the paper path engaging a grounded bracket.

As particularly shown in Fig. 2, as a sheet 12 begins to exit the sheet output 14, the sheet lead edge 12A engages and begins to pivot away the brush unit 22, to reduce the amount of flexing of the fibers 24. The pivotal resistance of the brush unit 22 is empirically set lightly enough, as described above, or otherwise, to allow even a flimsy sheet 12 to pivot the brush unit 22 without excessive flexing of the fibers 24 engaged by that sheet 12. As shown in Fig. 2, this results in the advantages described above, in particular, what has been found to be a highly advantageous improved engagement of the tips 24A of the fibers 24 with the upper surface of the sheet 12, for improved static removal, and, therefore, improved sheet stacking.

It will be appreciated that an additional such pivotal brush unit could also be provided on the lower side of the sheet output path for similar conductive fiber engagement with the fiber tips of the lower side of the sheet 12, if desired. In either case, it will be appreciated that a light spring force could be utilized in lieu of, or in addition to, gravity for control of the initial position and the pivoting force of the brush unit 22, if desired. However, it will be appreciated that in the above-described system, by utilizing a small gravitational force for the pivotal brush unit 22 about the pivot axis 26 intermediate of the brush clamp 25 that the initial resistance to pivoting of the brush unit 22 is very slight, which is desirable, and the resistance to further pivoting increases only slightly with the increase in the angle of pivoting, without requiring any spring system for that purpose.

Claims (5)

1. CLAIMS 1. A sheet printing and stacking apparatus, with a sheet output at which the printed sheets may have a static electrical charge on them having a static elimination system with a static removal brush unit with flexible conductive brush fibers adjacent said sheet output positioned for engaging the printed sheets adjacent said sheet output and at least partially discharging said static electrical charge on the printed sheets, said flexible conductive brush fibers extending from said static removal brush unit to brush fiber tips; wherein said static removal brush unit with said flexible conductive brush fibers is pivotally mounted adjacent to said sheet output with a pivotal mounting system providing pivoting of said entire static removal brush unit by engagement of a sheet output from said sheet output with said flexible conductive brush fibers, said static removal brush unit being pivotable by said sheet engagement with said flexible conductive brush fibers sufficiently to reduce flexing of said flexible conductive brush fibers.
2. 2. A sheet printing and stacking apparatus according to claim 1, wherein said pivotal mounting system for said static removal brush unit provides said pivotal mounting thereof on a pivot axis above the center of gravity of said static removal brush unit, so that said static removal brush unit is normally maintained by gravity in an upright position until said engagement by said sheet output from said sheet output.
3. 3. A sheet printing and stacking apparatus according to claim 2, wherein said pivot axis of said static removal brush unit is intermediate said static removal brush unit and above but adjacent to said sheet output.
4. 4. A sheet printing and stacking apparatus according to any one of the preceding claims, wherein said static removal brush unit is pivotal by said sheet outputted from said sheet output with a force of less than 4 grams.
5. 5. A sheet printing and stacking apparatus substantially as described with reference to Figures 1-4 of the accompanying drawings.