Abstract:
A vacuum transport for a printer or copier guides a sheet through a machine, such as from a photoreceptor toward a fuser. The vacuum transport includes a partially enclosed vacuum chamber having rollers rotatably mounted therein. Portions of the rollers protrude through openings in the top of the chamber. A series of ribs are disposed between the openings. Some of the ribs extend diagonally toward one end of the width of the paper path over the transport.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a vacuum transport for moving sheets, such as paper sheets, within a xerographic printing apparatus, such as a copier or “laser printer.” 
     BACKGROUND OF THE INVENTION 
     Electrostatographic or xerographic printing devices, such as copiers or digital “laser printers,” are well known. In many types of apparatus, a key area from a reliability standpoint is the zone between the charge-retentive member, such as a photoreceptor, and the fuser. The sheet that receives an image from the photoreceptor in a transfer step must be pulled from the photoreceptor (which is typically in the form of a rotating drum or belt) and, as smoothly as possible, directed to a fuser, which typically comprises two rollers forming a nip therebetween. The length of the gap between the photoreceptor and the fuser is crucial when the machine is handling short sheets as the photoreceptor may not ensure continuous drive to deliver the sheet to the fuser, causing a paper jam. If the sheet is caused to jam very close to the fuser, heat from the fuser is liable to create a dangerous situation. Further, because the toner image on the sheet as it passes from the photoreceptor to the fuser is only loosely attached to the sheet, any irregularities in the paper feeding between the photoreceptor and the fuser are likely to cause unacceptable smearing of the image. 
     In many designs of copiers or printers, particularly of the high-speed variety, the preferred device for moving a sheet from the photoreceptor to the fuser is a vacuum transport. A typical design of a vacuum transport is shown in FIG.  4 . As shown in the Figure, the vacuum transport generally indicated as  100  is disposed within a copier or printer between a photoreceptor  102  and the fuser rolls  104 . Vacuum transport  100  itself typically comprises a belt  110  which is entrained about two rollers  112 ,  114 . This belt  110  typically defines a number of small holes therein (not shown). Disposed inside the belt  110  is a vacuum chamber  116 . The vacuum chamber  116  is an actuated by a motor (not shown) and thereby draws air through the holes in belt  110  particularly in the area where a sheet moving in a process direction in is passing over the belt  110 . In this way, vacuum chamber  116  holds a sheet against the outer surface of belt  110 , while belt  110  moves that sheet from photoreceptor  100  toward the nip of fuser rolls  104 . 
     While the vacuum transport of the general design shown in the Figure has long been proven to be effective, it suffers from various impracticalities. For instance, transport  100  tends to be heavy and expensive, and the belt  110  may require replacement over the life of the machine. The large size of the vacuum transport tends to preclude its use in compact printers and copiers. The present invention is directed toward a small, low-cost, yet effective vacuum transport. 
     SUMMARY OF THE INVENTION 
     The present invention is a vacuum transport for conveying a sheet in a process direction within a printing apparatus. A chamber defines an external surface, the external surface defining a full width perpendicular to the process direction. A first plurality of openings is defined in the external surface. A first plurality of ribs protrude from the external surface, the ribs being disposed between pairs of openings of the first plurality of openings, the ribs being oriented along the process direction. An axle is rotatably mounted within the chamber, and a plurality of rollers are disposed on the axle, whereby a portion of each roller protrudes through one of the first plurality of openings, and a gap is defined between a surface of each roller and an edge of the opening. 
    
    
     BRIEF SUMMARY OF THE DRAWINGS 
     FIG. 1 is a perspective view showing, in isolation, a module including the main portions of a vacuum transport according to the present invention; 
     FIG. 2 is a simplified sectional view through line  2 - 2  of the vacuum transport shown in FIG. 1; 
     FIG. 3 is a simplified sectional view through line  3 - 3  of the vacuum transport shown in FIG. 1; and 
     FIG. 4 is a simplified elevational view showing of the function of a vacuum transport of the prior art in the context of an electrostatographic printer. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows, in isolation, a module including the vacuum transport according to a preferred embodiment of the present invention. The module is shown generally as  10 . In a preferred embodiment of the present invention, the module  10  further includes a tray  12  for accommodating a corotron, such as to enable transfer of electrostatic images from a photoreceptor, but this corotron is not immediately germane to the present invention. Disposed next to the tray  12  is vacuum chamber  14 . Chamber  14  communicates with a source of vacuum pressure (not shown) through an opening  16 . Chamber  14  is generally enclosed, and extends a full width of a paper path through which sheets pass through the printing apparatus, such as through a process direction P shown in the Figure. 
     While chamber  14  is a generally enclosed chamber, the main external surface of the chamber  14 , indicated as surface  18 , forms the surface over which sheets passing from a photoreceptor to a fuser slide. As with the basic prior art design of a vacuum transport, it is generally intended that sheets be held against this surface  18  while passing from the photoreceptor to the fuser. 
     FIG. 2 a is a simplified elevational view through the line marked  2 - 2  in FIG. 1, showing a detail of vacuum chamber  14 . As can be seen in FIG. 2, there is partially disposed within vacuum chamber  14  a plurality of rollers, one of which is shown as  20  in FIG. 2, all of which are preferably disposed on a single axle  22 . As can be seen in FIG. 2, a portion of each roller  20  protrudes through an opening  24  defined in the surface  18 . As can be seen in FIG. 1, preferably each of these rollers  20  has defined around the circumference thereof at least one groove. The axle  22  may in turn include a pick up gear, such as shown as  26  in FIG. 1, which in turn would contact a driver gear (not shown) within the machine itself. 
     When a partial vacuum is created within vacuum chamber  14 , such as by applying a vacuum through opening  16 , air will flow between an outer surface of each roller  20  and the edges of the corresponding opening  24 , as well as through any grooves which are defined around the circumference of each roller  20 . This airflow into the vacuum chamber  14  is helpful in causing a sheet, such as indicated as S, in contact with the surface of the rollers  20  to maintain a relatively firm contact with the rollers  20  and also, generally, the surface  18  of the vacuum transport  10 . When a sheet is in such contact with the rollers  20  and the surface  18 , and the rollers  20  are caused to rotate such as via axle  22  and the gear  26 , the sheet will be directed from the photoreceptor to a fuser. 
     In the preferred embodiment of the present invention, the rollers  20  are distributed to be concentrated toward one end of the full width of the paper path formed by surface  18 . As can be seen in the Figure, four rollers  20  are disposed toward one end of the paper path, with only two other rollers, indicated as  21  in FIG. 1, disposed along the rest of the width of the paper path. The purpose of distributing rollers  20 ,  21  in this way is to provide a vacuum transport which is particularly useful in transporting relatively small sheets, such as index cards. Typically, with larger sheet sizes, a leading edge of the sheet will enter the fuser while another trailing portion of the sheet is still attached to the photoreceptor, and in such a case misfeeding or jamming is unlikely. However, small sheets, which do not occupy the full width across the vacuum transport  10 , will have a similarly short dimension along the process direction P, and these small sheets are particularly vulnerable to misfeed between the photoreceptor and fuser. Therefore, particularly in the case of where the design of the printer is “edge-registered,” (i.e., where the sheets regardless of size are urged against one edge of the paper path as opposed to being centered along the paper path), it is desirable to have more openings such as  24  along those portions of the width of the paper path over which the smaller sheets will pass. Indeed, in a preferred embodiment of a printer according to the present invention, the vacuum is applied to vacuum chamber  14  only when it is desired to feed smaller sheets; when feeding larger sheets (that is, sheets which occupy almost the full width across the paper path) no vacuum is applied. 
     Also shown on the surface  18  of vacuum transport  10  in FIG. 1, is a plurality of ribs, or fins, which are oriented along the process direction P over which sheets pass over the vacuum transport  10 . These ribs, generally indicated in FIG. 1 as  30 , are preferably evenly spaced across the full width of the surface  18 , and, where the openings  24  for rollers  20  are concentrated, the ribs are disposed between adjacent pairs of rollers  20 . 
     According to a preferred embodiment of the present invention, the geometry of the ribs is different for those ribs which are disposed adjacent to rollers  20 , as opposed to other ribs, particularly where the rollers  20  are concentrated toward one end of the width of the paper path. FIG. 3 is a partial sectional view through line  3 - 3  shown in FIG.  1 . As can be seen in the Figure, where rollers  20  protrude through openings  24 , the ribs  31  are configured to extend diagonally from the surface  18  generally toward one end of the width of the paper path, as shown by the geometry of ribs  31 , as opposed to the relatively symmetrical geometry of ribs  30  which are disposed along the balance of the width of the paper path. The purpose of this special geometry of ribs  31  is to ensure that the top and/or bottom edge of any sheet cannot coincide with any immediate edge offered by the geometry of rib type  30 . 
     Although the preferred embodiment of the invention is especially useful for transporting sheets within an electrophotographic printing apparatus, such as in the position shown in FIG. 4, the invention as claimed can be useful in other types of printers, such as an ink-jet printer, or within other types of sheet-handling equipment.