Abstract:
A media transport unit includes an envelope transport structure that utilizes support fingers directly under the envelope. The support fingers are canted toward the center line of the paper path. The envelope flap passes over the support fingers at an angle that prevents the envelope flap from catching a support finger and potentially causing envelope wrinkling or a jam. The support fingers on either side of the area over which the envelope passes are canted away from the center line of the paper path to prevent the edges of full width media from catching the surface of a support finger.

Description:
FIELD OF INVENTION 
     This invention relates generally to imaging of envelopes and, more specifically, to an envelope transport structure that minimizes wrinkling of envelopes during an imaging process. 
     BACKGROUND OF THE INVENTION 
     In electrostatic or electrophotographic image forming apparatus, such as monochrome and color laser printers and photocopiers, it is common to fuse a loose toner image by passing the imaged media through a fusing nip. The fusing nip is typically formed from a first fusing roller urged against a second fusing roller to create a pressurized nip through which the media passes. One or both of the fusing rollers are typically heated to increase the temperature within the nip. 
     In those imaging systems utilizing a fusing nip as described above, wrinkling of envelopes within the fusing nip has been a continuing problem. Previous attempts to reduce envelope wrinkling have involved relieving the pressure on the envelopes at various points in the fusing operation. An example of this approach is found in U.S. Pat. No. 5,268,726 to Oleksa et al. 
     It is also known to utilize individual support ribs or fingers within a paper path to reduce friction between the moving media and the surfaces of the paper path. The support fingers also serve to lessen pre-heating of the media due to heat transfer from the support surfaces of the paper path. Additionally, to prevent any one point on the image from being in extended continuous contact with a single support finger, the fingers may be angled with respect to the direction of travel of the media. This helps to avoid uneven heating of the media and image that can cause print defects and variations in the gloss of the printed image. 
     It is also known to angle the support fingers away from the center line of the paper path to prevent the leading corners of a media sheet from catching the sides of the fingers and pushing the media laterally to either side of the paper path. Should the media be pushed laterally prior to the fusing nip, wrinkling can occur and, in a worst case scenario, a paper jam may be created. An example of utilizing support fingers that are canted away from the center line of the paper path is found in U.S. Pat. No. 5,870,661 entitled APPARATUS AND METHOD FOR CONTROLLING MEDIA TEMPERATURE IN AN IMAGING APPARATUS and assigned to the assignee of the present application. 
     It has been found that support fingers that are canted away from the center line of the paper path have a disadvantage when printing envelopes. When the addressee side of an envelope is printed and the envelope travels along the paper path, the flap of the envelope on the opposite side hangs down at an angle that is canted away from the center line of the paper path, similar to the angle of the canted support fingers. As the envelope travels over the support fingers, the flap may catch the side of a finger and cause the envelope to be pushed laterally to the side or opened while moving through the fuser. This can cause severe wrinkling, print defects, and/or a media jam. 
     The present invention seeks to overcome the disadvantages of previous implementations of canted support fingers by changing the angle of the support fingers directly under the envelope to prevent the envelope flap from catching the side of a support finger. More specifically, the support fingers directly under the envelope in a central area are canted toward the center line of the paper path to allow the envelope flap to pass over the support fingers at an angle oblique to the angle of the support fingers. The support fingers on either side of the area over which the envelope passes are canted away from the center line of the paper path to prevent the corners of full width media from catching the surface of a rib. Accordingly, a reduction in wrinkling of both envelopes and full width media is achieved with a simple, low-cost structure. 
     SUMMARY OF THE INVENTION 
     It is an aspect of the present invention to provide a media transport unit including an envelope transport structure for supporting an envelope traveling along a media path in an imaging apparatus. 
     It is another aspect of the present invention that the media transport unit utilizes a plurality of media supports grouped in a first lateral portion, a second lateral portion, and a center portion between the first and second lateral portions. 
     It is a feature of the present invention that the center portion of media supports are canted toward the center line of the media path to allow an envelope flap to travel over the media supports without being urged laterally by a support. 
     It is another feature of the present invention that the media supports in the first and second lateral portions are canted away from the center line of the media path to prevent the leading corners of a full width media sheet from catching a media support and pushing the media laterally. 
     It is an advantage of the present invention that the envelope transport structure allows the use of individual media supports in the paper path while also preventing media and envelope wrinkling. 
     It is another advantage of the present invention that the envelope transport structure comprises a simple and compact design that utilizes low-cost components. 
     Still other aspects, features, and advantages of the present invention will become apparent to those skilled in this art from the following description, wherein there is shown and described a preferred embodiment of this invention, simply by way of illustration of one of the modes best suited to carry out the invention. As it will be realized, the invention is capable of other different embodiments and its several details are capable of modifications in various, obvious aspects, all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive. And now for a brief description of the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of an electrophotographic printing apparatus showing the media path through the printer. 
     FIG. 2 is a schematic perspective view of a pair of fusing rollers forming a fusing nip and an envelope traveling along the media path and approaching an envelope transport structure upstream from the fusing nip. 
     FIG. 3 is a schematic top view of the envelope transport structure showing the positioning and orientation of the individual media supports and an envelope approaching the supports. 
     FIG. 4 is an enlarged schematic top view of the envelope traveling over the media supports. 
     Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a schematic illustration of the media path  12  in an electrostatic or electrophotographic image forming apparatus  10  that utilizes the envelope transport structure of the present invention. The following description of a preferred embodiment of the invention refers to its use in an electrostatic printing apparatus. It will be appreciated, however, that the apparatus of the present invention may be used with other types of electrostatic imaging apparatus, such as photocopiers, and with other types of imaging apparatus, such as aqueous ink jet printers. Accordingly, the following description will be regarded as merely illustrative of one embodiment of the present invention. 
     With continued reference to FIG. 1 a receiving substrate  11 , such as a sheet of paper or an envelope, is picked from a media tray  14  by a conventional pick roller mechanism (not shown). The receiving substrate  11  travels along the media path  12  and through an imaging station  16  which deposits a toner image on the receiving substrate. An example of an electrostatic imaging station is found in U.S. Pat. No. 5,576,824 (the &#39;824 patent) entitled FIVE CYCLE IMAGE ON IMAGE PRINTING ARCHITECTURE. The &#39;824 patent is hereby incorporated by reference in pertinent part. 
     After passing through the imaging station  16 , the receiving substrate  11  travels over a media transport unit  18  that includes an envelope transport structure, described in more detail below. The media transport unit  18  is positioned in a pre-nip portion of the media path  12  upstream from the fusing nip  20 . The fusing nip  20  is created by urging together fusing rollers  22  and  24 . In the fusing nip  20 , the toner image is permanently affixed to the receiving substrate  11 . After passing through the fusing nip  20 , the receiving substrate is transported out of the printer  10  for retrieval by a user. 
     With reference now to FIGS. 2 and 3, the arrangement and operation of the media transport unit  18  and envelope transport structure  19  of the present invention will now be described in more detail. The media transport unit  18  includes a plurality of media supports for supporting a sheet of media or an envelope as the sheet or envelope approaches the fusing nip  20 . In the preferred embodiment, the media supports comprise elongated, spaced apart support fingers indicated by the even numbered reference numerals  30 - 52 , with each finger including a first end and a second end indicated by a prime and double prime, respectively, of the corresponding reference numeral. For example, finger  30  includes a first end  30 ′ and a second end  30 ″. 
     The support fingers are arranged in a first lateral portion  60  comprising support fingers  30 ,  32 ,  34 , and  36 , and a second lateral portion  62  comprising support fingers  46 ,  48 ,  50 , and  52 . Between the first lateral portion  60  and the second lateral portion  62  is a center portion  64  comprising support fingers  38 ,  40 ,  42 , and  44 . As explained below, the center portion  64  of support fingers corresponds to the envelope transport structure  19 . It will be appreciated that any suitable number of support fingers may be utilized in any of the first lateral, second lateral and center portions. 
     With continued reference to FIG. 3, the media path  12  includes a center line indicated by the dotted line  15 . Sheets of media and envelopes travel in the direction of action arrow A along the media path  12  and are generally centered over the center line  15 . As shown in FIG. 3, the support fingers in the first and second lateral portions  60 ,  62  are canted away from the media path center line  15 . Preferably, each of the support fingers in the first and second lateral portions  60 ,  62  form an angle with the center line  15  of between about 3 degrees and about 45 degrees, and more preferably between about 10 degrees and about 20 degrees. As explained above, this ensures that the edges of a media sheet (not shown) do not contact the side of a support finger, which can urge the media sheet laterally out of alignment as it travels through the fusing nip  20  and potentially cause media wrinkling and/or a media jam. 
     In an important aspect of the present invention, the support fingers  38 - 44  in the center portion  64 /envelope transport structure  19  are each canted toward the media path center line  15 . Preferably, each of the support fingers  38 - 44  form an angle with the center line  15  of between about 3 degrees and about 45 degrees, and more preferably between about 10 degrees and about 20 degrees. With reference now to FIG. 4, as an envelope  28  travels over the envelope transport structure  19  with the envelope flap  29  on the underside of the envelope, the flap rides over the top of the support fingers  38  and  40 . The flap  29  and support finger  38  initially create an acute angle  41  that allows the flap to ride over the top of the support finger. 
     With reference now to FIG. 3, the long edges  31 ,  32  of the envelope  28  travel between the first lateral portion  60  and the center portion  64  of support fingers, and between the second lateral portion  62  and center portion  64  of support fingers, respectively. In the preferred embodiment, the distance between the first end  38 ′ of support finger  38  and the first end  44 ′ of support finger  44  is less than the length of the short edge  35  of the envelope  28 . Additionally, the distance between the first end  36 ′ of support finger  36  and the first end  46 ′ of support finger  46  is greater than the length of the short edge  35  of the envelope  28 . It will be appreciated that standard letter envelopes have a long edge length of between about 9.5 inches (241 mm.) and 9.8 inches (250 mm.), and a short edge length of about 4.0 inches (102 mm). 
     In the preferred embodiment, the support fingers  38  and  40  on a first side of the center line  15  are substantially parallel. Similarly, the support fingers  42  and  44  on the opposite side of the center line  15  are substantially parallel. 
     While the invention has been described above with references to specific embodiments thereof, it is apparent that many changes, modifications and variations in the materials, arrangements of parts and steps can be made without departing from the inventive concept disclosed herein. Accordingly, the spirit and broad scope of the appended claims is intended to embrace the use of these other inks and all other changes, modifications and variations that may occur to one of skill in the art upon a reading of the disclosure. All patent applications and patents cited herein are incorporated by reference in their entirety.