Field of the Invention

The invention relates to a process unit used in laser printers and /or photocopiers. In particular, the invention relates to an improved process unit which permits printing an A3 image plus printer's mark on oversize (larger than A3) paper.

Background of the Invention Process units or kits which are used in laser printers for image forming and printing of printed sheets are well known. Process units generally consist of a photoconductive drum, a magnetic or developer roller, developer agitator augers, a primary charger, a cleaning unit, and an auto-toner control probe. For a detailed description of the internal operation of existing process units, reference is made to U.S Patent 5,153,649 issued to Park and U.S. Patent 5,196,884 issued to Sugiyama et al.

Most existing process units are configured to print on standard United States paper widths, such as 8-1/2 inch by 11 inch letter paper (215.9 mm by 279.4 mm), or 11 inch by 17 inch (279.4 mm by 431.8 mm) ledger paper, or standard A4 paper widths, such as 297 mm by 210 mm paper, and A3 paper widths, such as 297 mm by 420 mm paper. To print on these paper sizes, the process unit is provided with an imageable area that is about as wide as the width of the paper. Thus, for regular format laser

printers which print on only 8-1/2 inch wide paper, the standard imageable area is typically about 200 mm - 205 mm (7.87 inches - 8.07 inches), leaving a peripheral margin of about 1/4 inch where the process unit cannot print. For larger format laser printers, such as those used for commercial printing, the standard imageable area is much wider, typically between about 290 mm - 296 mm (11.41 inches - 11.65 inches).

The excess width of the imageable area for large format process units that is beyond 11 inches allows for the printing of printer's marks, such as crop marks, registration marks and bleeds, around the periphery of the paper size image area of 11 inch by 17 inch paper sizes, for example. Unfortunately, large format process units having this standard imageable and printable area are not able to print in expanded, wider margin formats on oversized paper, such as A3 paper. The A3 paper size is 297 mm by 420 mm. As a result, the standard imageable area for large format process units does not even provide a print area that extends to the very edges of the A3 paper size, let alone provide a print area that could accommodate expanded margin format printing to include printers marks.

One possible solution to this problem is described in U.S. Patent 4,605,299 issued to Mochimaru which discloses a plurality of replaceable image forming cartridges or process kits for use in an electrophotographic copier or printer. In Mochimaru, each process kit is a different physical size and is capable of producing images of a maximum size distinct from each of the other kits. The specific kit that must be loaded into the printer is determined by the desired image size. The use of a number of different kits as disclosed in Mochimaru is not advantageous because it is necessary to manually change the process kits if different image sizes are required for a particular project. In addition, a selection of the different size process kits must always be on hand in order to print a variety of different image sizes. It would be advantageous to have a process unit for a large format laser printer which is configurable to print both standard size and expanded margin format images using the same process unit, particularly

for A3 paper sizes. Additionally, it would be advantageous to have a process unit for a large format laser printer which has an imageable area that could accommodate both standard size and expanded margin format images without having to remove and replace the process unit for each printed output having a different output image size.

Summary of the Invention

In accordance with the first embodiment, an improved process unit for use in a large format electrophotographic imaging device that can accommodate oversize paper for A3 size paper is disclosed. The improved process unit comprises a modified developer roller with substantially no shoulder bushing. In addition, the improved' process unit includes an enlarged developer roller cavity which permits axial re-positioning of the modified developer roller. A shim structure is also disclosed for exerting an axial force on the modified developer roller to axially re-position the modified developer roller. The improved process unit also includes an extended doctor blade to allow charging of an enlarged imageable area on the modified developer roller so that the improved process unit has a printing width at least about 2 mm wider than the printing width of existing process units. Further an extended cleaning blade is disclosed to clean the photoconductive drum across the entire printing width of the enlarged imageable area.

In accordance with the second embodiment, a method of developing latent images at the extreme ends of a photoconductive developer roller of an improved process unit for a large format electrophotographic imaging device that can accommodate oversize paper for A3 size paper is disclosed. The developer roller is modified to have substantially no shoulder bushing. A developer roller cavity is enlarged so as to permit axial re-positioning of the developer roller. A shim mechanism is used to axially re-position the developer roller. A doctor blade is positioned adjacent to the developer roller and a cleaning blade is positioned adjacent to a photoconductive drum at a distance

corresponding to the increase in length of the modified developer roller cavity. In addition, an enlarged imageable area on the developer roller is charged to develop latent images at the extremes of the ends so as to create an enlarged imageable area capable of printing an oversized A3 image. Brief Description of the Drawings

Figure 1 is a fragmentary vertical cross section taken along the longitudinal axis of the developer roller and associated housing and mechanical elements of a current process unit;

Figure 2 is a fragmentary enlarged section thereof showing the housing with the existing roller removed and taken along line 2-2 in Figure 3;

Figure 3 is a fragmentary transverse section showing the housing with the existing roller removed and taken along line 3-3 of Figure 2;

Figure 4 is a fragmentary transverse section showing modifications in phantom lines to the housing of an existing process unit;

Figure 5 is a fragmentary enlarged section showing modifications in phantom lines to the housing of an existing process unit;

Figure 6 is a fragmentary transverse section showing the completed modifications to the housing in the improved process unit; Figure 7 is a fragmentary enlarged section showing completed modifications to the housing of the improved process unit;

Figure 8 is a fragmentary perspective view of a housing in an existing process unit illustrating the adjustment end;

Figure 9 is a fragmentary perspective view of the modified housing and doctor blade reconfiguration at the adjustment end in the improved process unit;

Figure 10 is a fragmentary enlarged view of the selected adjustment plate used at the adjustment end of the housing;

Figure 11 is a fragmentary side elevational view of an existing magnetic developer roller;

Figure 12 is a fragmentary side elevational view of a modified magnetic developer roller used in the improved process unit;

Figure 13 is a fragmentary vertical cross section taken along the longitudinal axis of the magnetic developer roller and associated housing and mechanical elements of the modified magnetic developer roller and housing used in the improved process unit; Figure 14 is a side view of an existing cleaning blade showing modifications in phantom dashed line with proportional dimensions;

Figure 15 is an end view of the cleaning blade shown in Figure 14; Figure 16 is a plan view of the grille of an existing scorotron; Figure 17 is a plan view of the grille of an existing scorotron showing the modifications used in the improved process unit; and

Figure 18 is a schematic diagram contrasting the imageable area size of existing process units with that of a process unit in accordance with the present invention.

Detailed Description of the Invention The invention relates to an improved process unit which may be used in an electrophotographic imaging device, such as a laser printer or a photocopier. The invention also relates to an improved electrophotographic subsystem for use in laser printer or photocopier engines enabling a high ratio of imageable area to overall width of the image formation mechanism, thereby enabling the printing of images greater than A3 size paper. Modifications are made to an existing process unit so that the unit may be used to print both standard size and oversize paper using the same process unit, without requiring any changing of the process unit. Generally, a process unit consists of a photoconductive drum, a magnetic developer roller, developer agitator rollers, a main charger, a cleaner unit, and an auto-toner probe. For this improved process unit, the magnetic developer roller and components related to the developer roller and photoconductive drum have been reconfigured or retrofitted. The modifications to components in the improved process unit will be discussed as compared to an existing process unit.

Components of the currently existing process unit not discussed remain basically unchanged.

Referring to Figure 1, a fragmentary vertical cross section of an existing process unit 10 is shown taken along the longitudinal axis of a magnetic developer roller 12. Developer roller 12 is positioned within a housing 14, and is attached to housing 14 at an adjustment end 16 and at drive end 18 of housing 14. A bracket or doctor blade 20, shown in phantom dashed lines, is positioned adjacent developer roller 12 such that surface 22 of doctor blade 20 is adjacent to, but does not touch, developer roller 12. Doctor blade 20 extends over the image forming area of developer roller 12, and does not cover the entire length of developer roller 12. A cleaning wiper or cleaning blade 24, shown partially in phantom dashed lines, is positioned adjacent to the photoconductive drum (not shown) in the existing process unit 10.

As shown in Figure 1, a shaft 26 extends through developer roller 12, with ends 28, 30 extending from developer roller 12. End 28 at adjustment end 16 of housing 14 extends into a shaft detent 34 on an adjustment plate 32, so that shaft end 28 abuts shaft detent 34. A shoulder bushing 36 end of developer roller 12 abuts housing 14, creating a space 38 between housing 14 and developer roller 12. A threaded insert 40, such as a brass insert, extends through adjustment end 16 of housing 14, having a flange 41 positioned adjacent developer roller 12. A fastening member 42, such as a locking screw or other suitable member, extends through shaft detent 34 into shaft 26 to position and retain developer roller magnet in a fixed orientation. A fastening member 44, such as a locking screw or other suitable member, extends through adjustment plate 32 and into insert 40 to retain the magnet shaft within developer roller in a fixed orientation. Shaft 26 of magnetic developer roller 12 extends through a bearing 46 and a gear 48 at the drive end 18 of housing 14. A bearing cap 50 is positioned against a shoulder 52 of shaft 26 and around bearing 46. Shaft 26 necks down or tapers creating a shoulder 54 and a substantially flat surface 56 on a part of shaft 26 at drive end 18 of housing 14. Gear 48 is positioned on flat surface 56 of shaft 26, abutting shoulder 54 of shaft 26.

Figure 2 is a fragmentary enlarged view showing adjustment end 16 of housing 14 in an existing process unit 10 with developer roller 12 removed. A shaft aperture 60 extends through housing 14 for receiving shaft end 28 of magnetic developer roller 12, which includes magnets. Threaded insert 40 extends through housing 14. Doctor blade 20 extends up to edge 62 of housing 14. Mounting screw 64, shown in phantom, or other suitable attachment means, extends from housing 14 toward where developer roller 12 would be positioned. End surface 66 of housing 14 includes substantially more material than side surface 68 of housing 14. Figure 3 is a fragmentary transverse section view showing the end surface 66 of housing 14 in an existing process unit 10, with developer roller 12 removed. Shaft aperture 60 is positioned in an approximate center of a substantially circular, in cross section, developer roller cavity 70, formed by side surface 68. Insert 40 is positioned within end surface 66 of adjustment end 16 of housing 14. End 72 of doctor blade 20 is adjacent developer roller cavity 70.

Referring to Figure 4 and Figure 5, fragmentary views similar to Figures 2 and 3 are shown, indicating modifications to housing 14 in process unit 10 in dashed lines in order to create an improved process unit 110 in accordance with the present invention. A cutting instrument is used to retrofit housing 14 such that center point 74 of the cutting instrument positioned in developer roller cavity 70 is moved slightly off center of the center point 76 of developer roller cavity 70 of existing housing 14, as shown in Figure 4 and Figure 5. Shaft aperture 60 remains in the same position and is not modified, with the center line 78 of shaft aperture 60 and centerline 79 of the cutting instrument being illustrated in Figure 5. A developer roller cavity 170 is enlarged by the cutting instrument, as shown in phantom in Figure 4, such that developer roller cavity 170 is eccentrically shaped, but is still substantially circular in cross section. A substantial portion of housing material is removed from housing 14 as modified to create a housing 114, as indicated by the cutter profile 80 in phantom lines in Figure 5. As shown in Figures 4 and 6, a

doctor blade 120 is extended in length, with a vertical notch 172 being cut in housing 14 to accommodate the extended doctor blade 20, thereby requiring removal of housing material.

Figure 6 illustrates a modified housing 114 of an improved process unit 110 showing the completed modifications illustrated in Figure 4. The perimeter of a developer roller cavity 170 is enlarged due to the removal of material from housing 114. A threaded insert 140 in developer roller cavity 170 is in the same position as in existing housing 14, but is smaller in size, and does not include flange 41. A shaft aperture 160 is in the same position as in the existing housing 14. A center point 174 of developer roller cavity 170 is somewhat off center due to the slightly eccentric shape of developer roller cavity 170, but the center point 176 of shaft aperture remains in the same position. Developer roll cavity 170 is not concentric with developer roller cavity 70. Doctor blade 120 is extended in length to allow a larger imageable area of developer roller 112 to be charged. Doctor Blade 120 is positioned within and between vertical notch 172.

The modifications to housing 114 in improved process unit 110 are also shown in Figure 7. An end surface 166 and a side surface 168 of housing 114 are reduced in size due to the enlargement of developer roller cavity 170. Developer roller cavity 170 has been enlarged in cross section and also in depth by removal of housing material. Threaded insert 140 is reduced in length and depth, and does not include flange 41, but remains in the same position within housing 114. Shaft aperture 160 remains in the same position within housing 114, but the depth of shaft aperture 160 has been reduced. Doctor blade 120, positioned adjacent modified developer roller 112, is extended in length, and is positioned within vertical notch 172.

Figure 8 is a fragmentary perspective view of adjustment end 16 of existing housing 14 in an existing process unit 10. Developer roller cavity 70 is substantially circular in cross section, and is formed between end surface 66 and side surface 68 of housing 14. Shaft aperture 60 is positioned on end surface 66 of housing 14 to receive shaft 26 of developer

roller magnet. Threaded insert 40, including flange 41, is positioned within end surface 66 of housing 14. Doctor blade 20 is attached to housing 14 with mounting screw 64, or other suitable fastening member. End 82 of doctor bracket 20 fits within notch 72 in housing 14, and does not extend through housing 14. Rather, end 82 of doctor blade 20 rests on housing 14 material within notch 72 formed within housing 14.

Modifications to an adjustment end 116 of housing 114 in improved process unit 110 are shown in Figure 9. Developer roller cavity 170 is enlarged by removal of side surface 168 material, and has more depth due to removal of housing material on end surface 166 of housing 114, such that the cavity space of developer roller cavity 170 is increased in length above a length of the developer roller cavity 70. Having an enlarged developer roller cavity 170 allows for the axial re-positioning of developer roller 112 and also allows the charging of toner /developer in a region typically reserved for bushings and bearings. Developer roller cavity 170 has a space equal to or greater than one half millimeter larger than the external diameter of developer roller 112 to receive ambient toner and developer prior to doctoring of the developer roller 112 by means of doctor blade 20. Developer roller cavity 170 has its greatest volume of ambient toner and developer contained in the region below or next to doctor blade 20. Doctor blade 120 is extended in length such that a surface 184 is positioned within vertical notch 172. Doctor blade 120 is extended in length a distance corresponding to the increase in length of developer roller cavity 170. Doctor blade 120 is attached to housing 114 with a mounting screw 164, or with other suitable fastening member. Threaded insert 140 is positioned within end surface 166 of housing 114, flange 41 of insert 40 has been removed, such that threaded insert 140 is preferably flush with end surface 166 of housing 114.

Figure 10 illustrates adjustment plate 32 which is used in both existing and modified process units 10, 110. Adjustment plate 32 is substantially semi-circular in shape, having a tab 84 at end 86 of adjustment plate 32. Adjustment plate 32 is positioned adjacent

adjustment ends 16, 116 of housings 14, 114, on the outside surface of process units 10, 110. Shafts 26, 126 (only shaft 26 illustrated in Figure 10) of developer rollers 12, 112 include a flat registration surface 88 which is positioned within shaft detent 34. Shaft detent 34 includes incisions 90, 92 and a detent aperture 94. A slot 96 is also positioned on adjustment plate 32 adjacent tab 84. Screw 42, or other suitable fastening member, extends through detent aperture 34 and engages with threaded end of shafts 26, 126, as shown in Figures 1 and 13. Screw 44, or other suitable fastening member, extends through slot 96 in adjustment plate 32, and engages with threaded insert 40, 140, as shown in Figure 1 and Figure 13.

Referring to Figure 11, bushing 98 on an end 100 of existing developer roller 12 is shown. A surface 101 of bushing 98 is substantially planar, except for a shoulder 103 positioned around shaft 26. Shoulder 103 provides space for flange 41 of threaded insert 40. As shown in Figure 12, bushing 198 has been modified in improved process unit 110. An end 200 of bushing 198 includes a slight chamfer 202, and shoulder 103 has been removed. The slight chamfer 202 of bushing 198 provides clearance for potential buildup of the toner /developer mixture used in the improved process unit 110 when developer roller 112 is positioned within housing 114.

Additional modifications to improved process unit 110 are shown in Figure 13. Developer roller 112 is positioned within housing 114. Shaft 126 extends through developer roller 112. Shaft 126 extends through adjustment plate 32 on adjustment end 116 of housing 114, abutting shaft detent 34. Screw 42 extends through adjustment plate 32 into shaft 126, and is tightened, holding shaft 126 in place. A shim 206, such as a plurality of washers or other members, is positioned between adjustment plate 32 and housing 114, adjacent tab 84. Locking screw 44 extends through slot 96, through shim 206, and into insert 140 in housing 114. Shim 206 translates the axis of the multiple magnets contained within developer roller 112, s such that the magnets and developer roller 112 are axially re-positioned and pulled from drive end 118 toward adjustment end 116 of housing 114,

as indicated by arrows 208 in Figure 13, due to the axial force exerted on developer roller 112 by shim 206. An axial force is exerted between housing 114 and shaft 126 of the developer roller 112 magnets toward end 116 within developer roller 112. In addition, detent 34 of plate 32 locks and radially holds the multiple magnets contained within developer roller 112 in proper orientation. Shim 206 also causes adjustment plate 32 to be displaced from end 210 of housing 114, as indicated by arrow 212. Shim 206 also provides planar stabilization of adjustment plate 32 parallel to exterior adjustment end 116 of improved process unit 110. Shifting of developer roller 112 towards adjustment end 116 of housing 114 results in shaft 126 at drive end 118 of housing 114 also shifting toward adjustment end 116. As a result, flat surface 156 of shaft 126 also moves in a direction toward adjustment end 116 of housing 114. A sufficient portion of flat surface 156 of shaft 126 remains for engagement with gear 148. A chamfered bushing 198 on developer roller 112 is positioned adjacent end surface 166 of housing 114, such that an enlarged cavity 214 in developer roller cavity 170 results to provide clearance for potential toner buildup. As seen in Figure 13, doctor blade 120, shown in dashed lines, has been extended in length to cover an additional area of developer roller 112 adjacent adjustment end 116 of housing 114.

In a preferred embodiment of the improved process unit 110, developer roller 112 is moved approximately four (4) mm (0.16 inches) toward adjustment end 116, the magnets within developer roller 112 are displaced by approximately 1.02 mm (0.04 inches) toward adjustment end 116, and doctor blade 120 is lengthened by approximately 9 mm (0.36 inches) at end 200 of developer roller 112 adjacent adjustment end 116. The net result is that the effective image area is increased from approximately 293 - 297 mm to greater than 300 mm.

Referring to Figure 14, cleaning wiper or cleaning blade 24 is also modified in the improved process unit 110 of the invention. Existing photoconductive drum 105 is shown having ends 107, 109, with existing cleaning blade 24 mounted in position using mounting bracket 111, shown

in Figure 15, such that cleaning blade 24 is in contact with drum 105. Cleaning blade 24 comprises a flexible yet durable material, such as silicone rubber or polyurethane. Cleaning blade 24 on drum 105 does not extend the entire length of drum 105, such that a dimension D of drum 105 is unaffected by blade 24. For the improved process unit 110, cleaning blade 124 is extended at each end, as shown at 216 in dashed lines, by approximately dimension D, thereby extending blade 24 substantially the entire length of photoconductive or electrophotographic drum 218, as shown in Figure 14. Cleaning blade 124 is extended in length a distance corresponding to the increase in length of developer roller cavity 170. Modified cleaning blade 124 allows cleaning of the photoconductive drum 218 surface across the entire printing width of the enlarged imageable area, and also cleans in regions that are not imaged. This aids in greatly reducing the incidence of background development, such as noise and dusting, in the margins of the printed page. In a preferred embodiment of improved process unit 110, cleaning blade 124 is extended by approximately eight (8) mm (2.03 inches).

Figure 16 illustrates a scorotron or grid 113 used in conjunction with the main (primary) charging assembly of the existing process unit 10. Scorotron or grid 113 is mounted to the process unit 10 with mounting apertures 115, 117. Grille 119 extends substantially the entire length of grid 113. Figure 17 illustrates the modification made to grid 220. Mounting apertures 221, 223 mount grid 220 to process unit 100. A plurality of perforations 222 are placed on mounting ends 224, 226 of grid 220. It is recognized that perforations 222 may be on one or both mounting ends 224, 226. Perforations 222 allow the charge on drum 218 and the regulation of the charge on drum 218 to image a larger area. The perforations have a larger cross sectional area than is typical of the rest of grid, thereby allowing photoconductive drum 218 to be charged at higher levels than other portions of drum 218, thereby enabling erasure of unwanted images in the margins of printed pages.

Referring to Figure 18, a schematic diagram is shown contrasting the imageable area size of existing process units with that of an improved process in accordance with the present invention. Imageable area 230 represents the imageable are attainable by using an existing electrophotographic imaging device, such as a laser printer or photocopier. Paper width 232 indicates the width of standard A3 paper. Enlarged imageable area 234 shows the enhanced imageable area attainable by using the improved process unit 110 of the present invention. It can be seen that the increase in printing width between imageable area 230 and improved imageable area 234 is at least about 2 mm and can be up to at least 8 mm to 10 mm, preferably 5 mm, larger than the printing width capable by existing process unit 10. Imageable area 234 illustrates the results of a process unit 110 in accordance with the present invention having an expanded imageable area width in excess of 300 mm. In operation, a currently existing process unit 10 is modified by removing a plastic strip of material covering end 100 of developer roller 12 adjacent to adjustment end 16 of housing 14. A cutter is utilized to reconfigure and enlarge developer roller cavity 170, and to increase the depth of developer roller cavity 170, by removing housing material. Doctor blade 120 which extends over developer roller is extended slightly in length. Cleaning blade 124 positioned against photoconductive drum 105 is modified to extend substantially the entire length of drum 218. Developer roller 112 and the magnets within developer roller 112 are shifted axially toward adjustment end 116 of housing 114. As a result of these modifications, a larger imageable area is achieved, such that the printing margin for a sheet of paper may be extended by an approximate 5 mm or more, extending the margin in which images may be printed from the approximate 293 mm range to an extended range beyond 300 mm. Preferably, the printing margin for a sheet of paper may be extended by an approximate 5 mm or more, extending the area in which images may be printed from a width less than 297 mm to an extended width beyond 300 mm. The enlarged imageable area 234 has a printing width at least about 2

mm to 3 mm wider than a printing width of an imageable area 232 corresponding to A3 size paper. The ability to extend the margins and increase the imageable area permits a full bleed, crop marks, and registration marks to be imaged and printed on oversized (larger than A3) paper. The modified process units of the present invention may, therefore, be used to print images on both standard (A3) and oversized paper (larger than A3), such as A3 and A4 paper, without having to remove and replace the process units.

Latent images may be developed at the ends of developer roller 112 proximate adjustment end 116 and drive end 118. Developer roll cavity 170 is not concentric with developer roller cavity 70. By maintaining the original radius in the area in which developer roller 112 is tangent to photoconductive drum 218, the energy of development of the latent image is unaffected. The oversize bore on the developer roller's edge where the toner is charged and prepared for its role in development of the latent image allows an adequate amount of toner /developer to be sufficiently highly charged to permit development even at the very end of developer roller 112 and photoconductive drum 218. Cavity 170 permits developer roller 112 to be positioned adjacent end 116 of electrophotographic drum 218 in a manner enabling developer roller 112 to develop latent images at end 116 of drum 218.