Abstract:
An entrance guide for externally fed sheet ( 4 ) to printer ( 1 ) is configured to bow the sheets. In one embodiment guides ( 5   a,    5   aa ) within slot  7  have upper and lower configurations which force sheet into a bow. In one embodiment slot ( 7   a ) is bowed and is sufficiently narrow in height to only accept a bowed sheet. The bowed sheets do not sag against the printer ( 1 ), which aids in sheet registration.

Description:
TECHNICAL FIELD 
   This invention is to feeding sheets in a manner, which causes the sheets to be accurately received in transport mechanism so as to be properly positioned for imaging. Typically the sheets are intended to be manually inserted in the imaging device. 
   BACKGROUND OF THE INVENTION 
   In imaging devices, such as printers, feeding sheets individually from external of the imaging device allows selection of individual sheets having unique characteristics, such as letterhead or preprinted borders, or selected width. It is common to either simply provide a slot leading to the sheet transport mechanism of the device or to provide an external tray on which the sheet is slid across so as to be more reliably positioned in the sheet transport. 
   Reliably positioning the sheet is important because, if the sheet sags against the imaging device structure, the sheet may not feed evenly. When the sheet sags against the device an uneven frictional drag can occur and the sheet enters the sheet feed mechanism turned from the intended position. Accurate registration of the sheet is then lost and not normally recovered, and the final image is turned from the correct position. In extreme cases the sheet jams within the printer. 
   In those devices in which no guide structure is provided, entire reliance is on the careful insertion of the sheet by the operator. Experience indicates that defective insertions will occur fairly frequently, especially with new operators. 
   Those devices that have a guide tray are generally effective in achieving proper insertion of the sheets. However, such guide surfaces necessarily extend from the side of the imaging device during use. To avoid such extension being permanent and thereby always defining a perimeter of the imaging device, the guide trays are generally thin structures, which slide into or out of the imaging device or fold out from the device or otherwise need to be positioned by the operator. Such operator intervention reduces productivity and requires some training of the operator. The tray structures themselves add cost to the imaging device, and, since they are thin and relatively unprotected, they are subject to damage. 
   DISCLOSURE OF THE INVENTION 
   This invention provides a sheet guide at or near the wall of the imaging device that causes the sheet to bend along the direction of insertion and therefore not sag. Operation is intuitive because pertinent structures are at or near the opening into which the operator necessarily must insert the sheet. Guide structures may be at each end of an entrance opening, with the opposing guide structures each having lower surfaces higher than the center of the opening and upper surfaces sloped downward to reach at least somewhat below the upper level of the lower surfaces. A wide variety of alternative structures configured to force the sheet to bend, and it is the bending which provides beam strength so that the sheet does not sag against the image device. One alternative is an entrance slot in the form of an arc with the low point in the center and of limited height so as to only accept a bowed sheet. 
   It is widely understood in the paper feed and imaging art that a bent paper or other such sheet has increased beam strength perpendicular to the line of the bend. Only a single bend is necessary in accordance with this invention, but structures that provide multiple, parallel bends would similarly prevent sag and function in accordance with this invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The details of this invention will be described in connection with the accompanying drawings, in which: 
       FIG. 1  is illustrative of a printer having a manual entry sheet feed in accordance with this invention: 
       FIG. 2  is a partial view from a right perspective of the printer of  FIG. 1  with parts omitted to show the opposing guide structures in relations to the sheet feed mechanism into which a sheet is fed; 
       FIG. 3  illustrates the opposing sheet guides as mounted for lateral movement; 
       FIG. 4  is a front view showing the opposing sheet guides in relation to the entry slot in which they are located; and 
       FIG. 5  is illustrative of an alternative embodiment in which the slot itself is bent. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The printer  1  in  FIG. 1  is shown without details as it is intended to be illustrative since this invention would be operable with virtually any imaging device. The imaging engine of printer  1  (internal and not shown) might be a conventional xerographic system. Printer  1  has an internal paper tray to supply paper from a stack of paper without manual intervention except to refill the tray. The imaged paper or other sheet is exited onto the top surface or tray  3  of printer  1 . A sheet of paper  4  inserted in accordance with this invention is shown, in dotted outline for overall clarity of FIG.  1 . 
   The paper  4  has a bowed configuration along the direction of entry, which is required by the left, and right guide structures,  5   a  and  5   aa  respectively. The center of paper  4  is at or near the bottom of slot  7 , while the configuration of guide structures  5   a  and  5   aa  lift the left and right sides of paper  4  above the bottom of slot  7 . 
   Slot  7  is an opening in the front side  9  of printer  1  which is directly opposite sheet feed mechanism of printer  1 , shown in  FIG. 2  with respect to this embodiment. Stationary upper guide ribs  20  receive paper from slot  7  and direct it against lower guide ribs  22 . The paper  4  is then in the proper position to enter a nip between upper feed rollers  24  and lower feed rollers (not shown). Such sheet feed mechanism is essentially entirely conventional and therefore will not be discussed in further detail.  FIG. 2  also shows the guide structures  5   a  and  5   aa , thereby showing the spacing relationship between the sheet feed mechanisms and the guides structures  5   a  and  5   aa.    
   The guide structures  5   a  and  5   aa  are shown just with their mounting elements in FIG.  3 . The guide structures  5   a  and  5   aa  are mirror images of each other. The ribbed, outer sides  40   a  and  40   aa  respectively are handles for grasping by the operator. Guide structure  5   a  is fixedly mounted to an upper supporting plate  42   a , which has a toothed rack extending toward guide structure  5   aa . Similarly, guide structure  5   aa  if fixedly mounted to upper supporting plate  42   aa , which has a toothed rack extending toward guide structure  5   a . The teeth of structures  5   a  and  5   aa  face each other, and engage mating teeth of wheel  44  (shown only in small part) which depends from drag ring  46 . This combination provides a structure in which the two guide structures  5   a ,  5   aa  can be moved different widths manually, by pushing one or both of the guide structures  5   a ,  5   aa  while remaining centered in slot  7 . Friction from drag ring  46  then holds guide structures  5   a ,  5   aa  in place until they are again manually moved with force to overcome that friction. The guide structures  5   a ,  5   aa  are thereby positioned to receive paper  4  of other sheets of different widths. 
   The front view of  FIG. 4  best illustrates the forcing action of guide structures  5   a  and  5   aa . The bottom surface of each structure  5   a ,  5   aa  is an upward sloping section  50   a ,  50   aa , sections  50   a ,  50   aa  being lower at the front of the printer  1  and higher on the side more internal to printer  1 . The upper surface  52   a ,  52   aa  are downward sloping. Each structure  52   a ,  52   aa  respectively terminates downward at a location as shown, which is below the final height of the sections  50   a ,  50   aa . Depending stationary blocking elements  54  located in near the center of slot  7  terminate at a location substantially equal in height to the final height of the sections  50   a ,  50   aa . Blocking elements  54  are visually apparent and thereby further discourage incorrect insertion of paper  4  by at least appearing to block paper  4  from passing through slot  7  while horizontal. 
   An operator beginning to insert paper in slot  7  necessarily observes that the paper  4  must be bent downward in the middle, as the paper  4  would be blocked in other configurations. This is also a natural way to grasp paper. When the paper  4  is inserted, it is under surfaces  52   a ,  52   b , and, as it is moved by the operator into printer  1 , it encounters upward sloping sections  50   a ,  50   aa , and thereby is forced into a bowed configuration. 
   With paper  4  in such a bowed configuration, it will not sag against the body of printer  1  and therefore will be accurately received by feed rollers  24 . This assures that paper will not drag against the front surface of printer  1  when being fed. Elimination of such drag is a necessary component of ensuing good registration. However, other factors as the media enters, such as the user loading the paper  4  or other sheet perpendicular to the feed rollers  24  and the mechanical accuracy of the feed mechanism of printer  1  or other imaging device as the media enters, are also important to accurate sheet registration. 
   A wide variety of configurations could provide the bowed configuration by which this invention functions. One alternative is shown in FIG.  5 . Slot  7   a  is an open slot leading directly to sheet feed mechanism as is slot  7 . However, slot  7   a  is in the form of a bow and has no guide on each side. Slot  7   a  should be of sufficient height to permit relatively easy insertion, but a disadvantage is that is must be sufficiently narrow in height so as to not allow flat insertion of the paper in slot  7   a.    
   Accordingly, a wide variety of implementations are anticipated, as is intended to be understood with respect to the accompanying claims.