05/279146

12/25/1973

08/09/1972

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Xerox Corporation (Rochester, NY)

399/358

101/425, 118/70, 118/106, 15/1.510, 118/104, 15/256.530

G03G21/00; G03G15/00

355/15 15/1.5,256.53,256.51 118/70,104,106,637 117/17.5

Sheer, Richard M.

What is claimed is

1. In combination with an electrostatographic imaging device including charging means for applying an electrostatic charge to an imaging surface, means having an electrostatographic imaging surface thereon, means for moving said imaging surface relative to said charging means, imaging means for exposing said imaging surface to form an electrostatic latent image thereon, developing means for forming a powder image on said imaging surface with electroscopic toner material, and transfer means for transferring said powder image from said imaging surface to a support surface; cleaning means for cleaning residual toner material from said imaging surface, said cleaning means comprising an endless loop of flexible material having mounted thereon a layer of porous foam material, means for driving said endless loop of flexible material for bringing said layer of porous foam material into sweeping engagement with said imaging surface in a direction transverse to the direction of movement of said imaging surface, backing means mounted in fixed position relative to said flexible material for applying pressure to said flexible material in the area of sweeping engagement of said layer of porous foam material with said imaging surface so that said layer of porous foam material will fill with residual toner material during said sweeping engagement thereby cleaning said imaging surface, and removal means in contact with said layer of porous foam material for removing toner material from said layer of porous foam material.

2. The combination of claim 1 wherein said removal means includes scraping means and means for recycling removed toner material for reuse.

3. The combination of claim 1 wherein said backing means comprises a backing plate for applying pressure to said endless loop of flexible material along an axis skewed with respect to the direction of movement of said endless loop of flexible material.

4. The combination of claim 1 wherein said drive means for said endless loop comprises a drive roller cooperating with an idler roller, said drive roller having a crowned surface for maintaining tracking of said endless loop thereon.

5. The combination of claim 1 wherein said layer of porous foam material is polyurethane.

6. Apparatus for removal of image development material from means having an electrostatographic imaging surface thereon comprising means for moving the imaging surface in a first direction, endless loop cleaning means for cleaning development material from said imaging surface, means for transporting said cleaning means over an area of sweeping engagement with said imaging surface in a second direction of motion transverse to said first direction of motion of said imaging surface, removal means engaging said endless loop cleaning means for removing material therefrom, and backing means mounted in contact with said endless loop cleaning means for applying pressure thereto, in the area of sweeping engagement of said cleaning means with said imaging surface, wherein said backing means comprises a backing plate for applying pressure to said endless loop cleaning means along an axis skewed with respect to said second direction of motion of said endless loop cleaning means.

7. The apparatus of claim 6 wherein said endless loop cleaning means is a continuous belt having a polyurethane foam coating thereon for forming a continuous cleaning nip along said imaging surface for said sweeping engagement.

8. The apparatus of claim 6 wherein said endless loop cleaning means is a continuous belt having a fiber mat coating thereon for forming a continuous nip along said imaging surface for said sweeping engagement.

This invention relates to electrostatographic imaging systems and, more particularly, to an improved apparatus for cleaning electrostatographic imaging surfaces.

The formation and development of images on the surface of recording materials by electrostatographic means is well known. One basic process, as taught in U.S. Pat. No. 2,297,691, by C. F. Carlson involved placing a uniform electrostatic charge on an imaging surface such as a photoconductive insulating layer, exposing the layer to a light-and-shadow image to dissipate the charge on the areas of the layer exposed to the light and developing the resulting electrostatic latent image by depositing on the image a finely-divided electroscopic material referred to in the art as "toner". The toner is normally attracted to those areas of the layer which retain a charge, thereby forming a toner image corresponding to the electrostatic latent image. This toner image may then be transferred to a support surface such as paper, and the transferred image may subsequently be permanently affixed to the support surface. After transfer, the residual toner remaining on the layer is removed by a cleaning operation and the layer may then be employed for another imaging cycle.

As is well known in recent years, the steadily increasing size of various industries has required an enormous increase in the amount of paper work that must be accomplished, maintained, and made available for wide circulation. In present day commercial automatic copiers/reproduction machines, the electrostatographic imaging surface, which may be in the form of a drum or belt, moves at high rates in timed unison relative to a plurality of processing stations. This rapid movement of the electrostatographic imaging surface has required vast amounts of toner to be used during development.

Associated with the increased amounts of toner is the difficulty in removing the residual toner image remaining on the imaging surface after transfer. In the reproduction process of Carlson as described above, the residual image is tightly retained on the photoconductive layer by a phenomenon that is not fully understood but believed to be caused by an electrical charge and Van der Waals forces that prevents complete transfer of the toner to the support surface, particularly in the image area. The residual toner image is normally removed by cleaning devices such as a "brush" type cleaning apparatus or "web" type cleaning apparatus. A typical brush cleaning apparatus is disclosed in U.S. Pat. No. 2,832,977 to L. E. Walkup et al. and in U.S. Pat. No. 2,911,330 to H.E. Clark. The brush-type cleaning means usually comprises one or more rotating brushes which brush toner from the photoconductive surface into a stream of air which is exhausted through a filtering system. A typical web cleaning device which retains toner is disclosed in U. S. Pat. No. 3,186,838 to W. P. Graff, Jr. et al.

While ordinarily capable of cleaning electrostatographic imaging surfaces, conventional cleaning devices have not been entirely satisfactory. Most of the known cleaning devices usually become less efficient as they become contaminated with toner which cannot be removed necessitating frequent replacement of the cleaning device. As a result, valuable time is lost during "down time" while a change is being made. A further problem is that cleaning devices employed in current commercial copier/duplicator machines permanently remove residual toner particles from the system. Since toner is an expensive consumable, permanent removal of the residual toner particles from the system during cleaning is undesirable because it adds to the cost of machine operation. Both the web-type and brush cleaning units normally do not return residual toner particles to be reusable as developer after the cleaning operation due to the collection of lint from the web or brush. Furthermore, the cleaning operation can result in generation of heat resulting in physical and chemical changes in the toner. In addition, an elaborate and noisy vacuum and filtering system is necessary to collect the residual toner particles removed by the brush. Moreover, large amounts of toner particles thrown into the air by the rapidly rotating brush cleaner often drift from the brush cleaning housing and form unwanted deposits on critical machine parts.

While the web type cleaner has some advantages it is difficult to align with the surface of the electrostatographic imaging surface and uneven contact between the web and the surface as well as uneven takeup of the web on a takeup roll is often encountered even with complex alignment apparatus. Another problem with the web type cleaner is that pressure contact between cleaning webs and some imaging surfaces must be kept to a minimum to prevent destruction of the imaging surface.

In U.S. Pat. No. 3,580,673 to F. Y. Yang, there is disclosed another type of cleaning device employing a brush roller contacting the imaging surface and wherein magnetic beads are intermixed with toner particles and subjected to an attractive bias force which aids in dislodging the residual toner image. However, although the use of magnetic beads accomplishes the cleaning function, it is more desirable to effect an efficient cleaning operation without the use of additional particulate material. In U.S. Pat. No. 3,572,923 to D. J. Fisher, opposite biasing is employed to attract particles from a brush roller which contacts the imaging surface to remove residual toner.

Both of the foregoing systems, although improving toner removal by means of electrostatic forces, require a brush roller engaged in frictional contact with the imaging surface.

As reproduction and copying devices become both smaller and more sophisticated, spacing on the imaging surface becomes more critical. It is, therefore, desirable to reduce the spacing occupied by the individual stations along the surface as much as possible. Cleaning devices, such as rotating brushes, contacting webs and the like have heretofore occupied a necessarily large area on the imaging surface as was necessary in order to accomplish their cleaning function effectively. One problem encountered in reducing cleaning spacing is early clogging, a condition resulting from insufficient absorbent or adsorbent action of toners resulting from an insufficient capacity cleaning action, such as too small a brush roller, or the like.

It is, therefore, a primary object of this invention to provide a novel apparatus for cleaning electrostatographic imaging surfaces over a reduced spacing area and which overcomes the above-noted deficiencies.

It is another object of this invention to improve the quality of prints produced by electrostatographic reproduction machines.

It is a further object of this invention to reduce toner consumption in automatic electrostatographic imaging machines.

It is another object of the present invention to provide a cleaning apparatus with reduced spacing requirements that will be less subject to clogging.

It is also an object of this invention to utilize cleaning apparatus and reproduction equipment which does not require extensive alignment or adjustment.

It is another object of this invention to remove residual toner for immediate reuse in an electrostatographic imaging machine.

It is a further object of this invention to provide a simple, inexpensive and reusable apparatus for an electrostatographic imaging machine which is more efficient than existing cleaning devices.

It is still a further object of this invention to prevent powder cloud formation as a result of a toner particle dispersion at the cleaning station of an electrostatographic imaging machine.

It is another object of this invention to reduce noise level of an electrostatographic imaging machine.

The foregoing objects of the present invention are achieved by an endless loop cleaning means in the form of a web or belt and which is composed of a material suitable for removal of marking material from an imaging surface. The endless loop is transported over an area of sweeping engagement with said imaging surface in a direction transverse to the longitudinal dimension of the imaging surface. After engagement, the endless loop is brought into proximity with a removal means for removing marking material from the endless loop. In an alternative form, the endless loop is maintained in sweeping engagement with the imaging surface by means of a backing member which is positioned in a skewed relationship with respect to the endless loop such that a clean segment of the loop is continuously presented for the sweeping engagement.

The foregoing objects and brief description of the present invention as well as other objects and further features thereof will become more apparent from the following more detailed description and appended drawings wherein:

FIG. 1 is a partial schematic and cross-sectional side elevational view of a cleaning apparatus as employed in conjunction with a form of electrostatographic imaging machine;

FIG. 2 is a detail of the cleaning mechanism of FIG. 1;

FIG. 3 is a further detail of the cleaning mechanism of FIG. 1;

FIGS. 4a and 4b illustrate an alternative embodiment of the present invention; and,

FIG. 5 and FIG. 6 each illustrate forms of cleaning material.

For a general understanding of the processing system in which the present invention is incorporated, reference is made to FIGS. 1 and 2 wherein like numerals refer to like components in which the various system components are schematically illustrated. In the electrostatographic system shown, a light image of copy to be reproduced is projected onto the charged surface of an electrostatographic plate to form an electrostatic latent image thereon. Thereafter, the latent image is developed with an oppositely charged electroscopic developing material to form a powder image, corresponding to the latent image, on the plate surface. The powder image can then be electrostatically transferred to a web of suitable transfer material in sheet form to which it may be fused by a fusing device, whereby the powder image is caused permanently to adhere to said transfer sheet material.

In the system disclosed herein, documents to be reproduced are placed at the imaging station, generally designated by reference character 11, which includes a light projecting system, for the purpose of scanning. The illuminated data is projected downwardly by means of a mirror-lens imaging assembly 12 and through a slit aperture assembly 13 and onto the imaging or reproducing surface of an electrostatographic plate in the form of a drum 14.

The electrostatographic drum 14 includes a cylindrical member mounted in suitable bearings in the frame of the machine and is driven in a clockwise direction as viewed in FIG. 1 by a motor at a constant rate that is proportional to the scan rate whereby the peripheral rate of the drum surface is substantially identical to the rate of movement of the reflected light image. The drum surface comprises a layer of photoconductive material on a grounded conductive backing that is sensitized prior to exposure by means of a corona generating device 15. Although the present invention is described herein with respect to use of a photoconductive surface, it is equally applicable to instances wherein an electrostatic latent image is formed on an insulating surface as in electrography.

The exposure of the drum surface of the light image discharges the photoconductive layer in the areas struck by light, whereby there remains on the drum an electrostatic latent image corresponding to the light image projected. As the drum surface continues its movement, the electrostatic latent image passes through a developing station in which there is positioned a developer apparatus including a housing 16 for developing material. A suitable driving means is used to carry the developing material to the upper part of the developer housing where it is cascaded down over a hopper chute onto the electrostatic latent image on the drum.

As the developing material is cascaded over the electrostatographic drum, toner particles are pulled away from the carrier component of the developing material and deposited on the drum to form powder images, while the partially denuded carrier particles pass off the drum into the developer housing sump.

Positioned next and adjacent to the developing station in a clockwise direction is an image transfer station which includes a sheet feeding mechanism adapted to feed sheets successively to the developed image on the drum at the transfer station. This sheet feeding mechanism, generally designated 18, includes a sheet source for a plurality of sheets of a suitable transfer material that is typically sheets of paper or the like, a separating roller adapted to feed the top sheet of the stack to feed belt and rollers 20 which direct the sheet material into contact with the rotating drum at a speed preferably slightly in excess of the rate of travel of the surface of the drum in coordination with the appearance of the developed image at the transfer station. In this manner, the sheet material is introduced between the feed rollers and is thereby brought into contact with the rotating drum at the correct time and position to register with the developed image. To effect proper registration of the sheet transfer material with the feed roller and to direct the sheet transfer material into contact with the drum, guides are positioned on opposite sides of the feed rollers.

The transfer of the powder image from the drum surface to the transer material is effected by means of a corona transfer device 21 that is located at or immediately after the point of contact between the transfer material and the rotating drum. The corona transfer device 21 is substantially similar to the corona discharge device 15 in that it includes an array of one or more corona discharge electrodes that are energized from a suitable high potential source and extend transversely across the drum surface and are substantially enclosed within a shielding member.

In operation, the electrostatic field created by the corona transfer device is effective to tack the transfer material electrostatically to the drum surface, thus causing the transfer material to move synchronously with the drum while in contact therewith. Simultaneously with the tacking action, the electrostatic field is effective to attract a significant portion of the toner particles, forming the powder image, from the drum surface and cause them to adhere electrostatically to the surface of the transfer material.

Immediately subsequent to the image transfer station is positioned a transfer material stipping apparatus or paper pickoff mechanism, generally designated 22, for removing the transfer material from the drum surface. This device includes a plurality of small diameter, multiple outlet conduits 24 of a manifold that is supplied with pressurized aeriform fluid through the outlet conduits into contact with the surface of the drum slightly in advance of the sheet material to strip the leading edge of the sheet material from the drum surface and to direct it onto a horizontal conveyor 23. The sheet material is then carried to a fixing device in the form of a fuser assembly 25, whereby the developed and transferred powder image on the sheet material is permanently fixed thereto.

After fusing, the finished copy is preferably discharged from the apparatus at a suitable point 26 for external collection, in a copy collector positioned at a convenient place for copy removal by the machine operator.

The next and final station in the device is a drum cleaning station having positioned therein a corona precleaning device 27 similar to the corona charging device 15, to impose an electrostatic charge on the drum and residual powder adherent thereto to more readily permit removal of residual or untransferred toner. To aid in effecting removal of the powder a drum cleaning device 28, adapted to remove any powder remaining on the drum surface after transfer, is also provided as is a source of light 29 whereby the photoconductive drum is flooded with light to cause dissipation of any residual electrical charge remaining thereon.

In general, the electrostatic charging of the electrostatographic drum in preparation for the exposure step and the electrostatic charging of the transfer material to effect transfer are accomplished by means of corona generating devices whereby electrostatic charge is applied to the respective surfaces in each instance. Although any one of a number of types of corona generating devices may be used, a corona charging device of the type disclosed in Vyverberg U. S. Pat. No. 2,836,725 is used for both the corona charging device 15, the corona transfer device 21, and the corona precleaning device 27, each of which is secured to suitable frame elements of the apparatus and connected to suitable power sources.

Further details of a reproduction device employing a drum surface is shown in the U. S. Pat. No. 3,301,126 to Osborne et al.

In addition to the rotating drum illustrated, it will be evident from the following description that the present invention may be employed with other forms of reproducing devices, such as the endless loop photoreceptor shown in U. S. Pat. No. 3,432,231 to Gardner. In addition, the present invention may also be used with other forms of development employing marking materials such as inks instead of the electroscopic toner material as described in conjunction with the foregoing embodiments.

Referring now to FIG. 2, the cleaning apparatus 28 employed in conjunction with the present invention is illustrated in greater detail. As shown therein, the drum 14 rotates in the direction indicated by the arrow to form a longitudinal image surface relative to a cleaning mechanism 28. Cleaning mechanism 18 includes an endless cleaning means shown as an endless loop 30 in the form of a web or a belt, having a direction indicated by the arrow 32 such that its travel carries the surface of the loop 30 into sweeping engagement with the surface of the drum 14. The driving of the belt 30 is effected by means of a motor 34 having a shaft 36 driving a pulley 38 which has in turn coupled thereto a belt 40 imparting motion to a pulley 44. The pulley 44 imparts rotary motion to a shaft 46 which is in turn coupled to a driven roller 48. The pulley 44 and roller 48 are fixed to the shaft 46 which is in turn journaled for rotation into the external frame of the machine, not shown, in a well known manner. At the opposite end of the endless loop 30 is a further roller 50 which is driven about a central shaft 52 which may be journaled into the machine housing for free rotation in a well known manner not shown. Tracking of the loop 30 may be maintained with a fair degree of accuracy by means of providing a crown on the surface of the roller 50 as is well known. Tension on the loop may be maintained by spring biasing the rollers 48 and 50, or either of them, away from each other.

The loop 30 is maintained in sweeping engagement with surface of the drum 14 by means of a backing plate 54 illustrated in broken section in FIG. 2. The backing plate 54 may be attached by means of an end plate 56 through the use of screws or bolts or the like to the machine housing illustrated generally as 58. Since the backing plate 54 is a relatively non-resilient member, composed of a suitable material such as metal or stiff plastic or the like, applying pressure to the rear side of the loop 30, the front of the loop 30 provides sweeping engagement with the surface of the drum 14 in a manner sufficient to give the desired nip, width and contact pressure necessary for the cleaning operation.

At the completion of sweeping engagement, the surface of the endless loop 30 containing the marking material comes around the tracking roller 50 to a removal mechanism illustrated generally as 60 which includes a pick-off means 62 which serves to remove the material from the surface of the endless loop 30. The pick-off means 62 may constitute a scraper mechanism such as a doctor blade or the like and is fixed mounted into a frame indicated generally as 64. Particles thus removed from the surface as shown can be channeled as by gravity or the like into a trap portion 68 and thence conveyed by means of an auger mechanism 70 to a removal chute 72 and from there fed back into the developer housing for further use, thus recycling the material. It will be understood that the pick-off means 62 may constitute other types of removal mechanisms, such as a vacuum system, filtering, electrostatic attraction, and the like. An example of such electrostatic removal is illustrated in U. S. Pat. No. 3,572,923 to Severynse et al. Since the small segment of the loop 30 is in the area to be serviced by the pick-off mechanism, a greatly reduced volume of pick-off apparatus is required. Thus, a vacuum system can be greatly reduced in size over that required for a long dimension cleaning device, such as the prior art brush roller. With certain combinations of loop materials the toner material may be sufficiently removed by gravity when the loop flexes around the roller 50.

Referring now to FIG. 3, the backing plate 54 is illustrated with respect to the portion of the loop 30. For purposes of explanation, it is assumed that the backing plate 54 includes a long axis 74 and the loop 30 a long axis 76. The axis 74 describes the longitudinal dimension of the backing plate whereas the axis 76 describes the direction of movement of the loop 30 along its path of sweeping engagement with the drum surface. By mounting the backing plate 54 such that its long axis is at a skewed angle with respect to the long axis of the loop 30, the pressure applied by the backing plate to the loop 30 will serve to insure that a clean segment of the loop 30 is continually urged against the surface of the drum. Ideally, the pressure should be applied uniformly along a line defining a diagonal path with respect to the area of the loop 30 urged against the drum surface. In this manner, the cleaning efficiency of the loop 30 is maintained at a high level.

Referring now to FIGS. 4a and 4b, an alternative embodiment of the present invention is illustrated wherein the backing plate, illustrated in this embodiment as 78 is provided with a diagonal indentation portion 80 which is stamped or otherwise provided along the diagonal dimension thereof. In this embodiment, the long axial dimension of the backing plate is aligned with the long axial dimension of the loop. The diagonal indentation 80, however, forms a line of pressure against the loop 30 material which is designed in this embodiment to be relatively deformable under the pressure provided by the indentation 80 of the backing plate 78. Thus, as the loop 30 progresses along the indentation 80 of the backing plate 78, the deformed area 82 of the loop 30 progresses from the upper portion of the loop 30 down towards its lower portion as the loop 30 traverses the width of the drum 14. In this manner, the efficiency of the cleaning operation is maintained as described in connection with the embodiment shown in FIG. 3.

Referring to FIGS. 5 and 6, materials which may be employed for the endless loop 30 are illustrated. Thus, in FIG. 5 a resilient backing 82 is illustrated with a cleaning material 84 bonded to the surface of the backing 82. In this illustration, the cleaning material 84 consists of an expanded structural material having a porous surface structure, such as a polyurethane foam. Where the marking material is particulate electroscopic toner, the open surface pores of the porous structure 84 will become filled with particles as it traverses the drum. By employing the diagonal backing pressure concept illustrated in FIGS. 3, 4a and 4b, various portions of the porous structure of the foam element 84 will be continually exposed to the surface of the drum, thereby providing the cleaning operation. In FIG. 6, resilient backing 86 has bonded thereto a fiber mat structure 88 which effects the cleaning operation by means of the interference contact of the fibers against the surface of the drum and thereby removing particle materials by a frictional rubbing effect. Typical cleaning materials which can be employable as fibers are acrylic velvets, Orlon, Polypropylene, rayon, acetates, mohair, Arnel, glass, Dynel, Dacron, cotton and other natural and synthetic fibers or filamented materials and mixtures thereof. In addition, in order to further enhance the attraction of the toner to the cleaning fibers, the fibers may be made of or coated with a material having a triboelectric attraction for toner particles. Typical materials having this relationship are described in U.S. Pat. No. 2,168,551 to Walkup, U.S. Pat. No. 2,618,552 to Wise, U.S. Pat. No. 2,638,416 to Walkup and Wise, and U.S. Pat. No. RE25136 to Carlson. Backing materials which may be employable with the present invention are any suitable materials of sufficient strength and resiliency to withstand the continuous deformation about the rollers. Other types of porous web materials may be employed having absorbent features where the marking material is more liquid in nature.

Although the invention has been described with reference to the structures disclosed herein, should not be confined to the details set forth since it is apparent that various modifications can be made. Thus, for example, the endless belt cleaning loops may be adapted to move with a different angular relationship with respect to the surface. Also, additional cleaning stations may be employed at desired locations about the surface to be cleaned.

Other variations and changes will be obvious to those skilled in the art. It will be understood that the examples given in the embodiment shown are done so for purposes of illustration and that the invention may be modified and embodied in various other forms without departing from the scope and spirit of the invention as disclosed herein.