Abstract:
In an apparatus, such as a fuser for xerographic printing, wherein sheets pass through a nip formed by two moving rollers, a substantially enclosed, effectively funnel-shaped path is defined to direct sheets from the nip to a subsequent processing station. When a jam condition occurs in the path, a movable surface defining the path moves to increase a size of the path. The increase in size prevents impaction of subsequent sheets entering the path, and also facilitates manual jam clearance.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to printing apparatus, in particular to clearance of jammed sheets as could be found in the post-fuser path of a xerographic printer or copier.  
         BACKGROUND OF THE INVENTION  
         [0002]    In electrophotographic printers commonly in use today, a charge-retentive member is charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the charge-retentive surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image areas contained within the original document. Subsequently, the electrostatic latent image on the charge-retentive surface is made visible by developing the image with developing powder referred to in the art as toner. Most development systems employ a developer material which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development the toner particles are attracted from the carrier particles by the charge pattern of the image areas on the charge-retentive area to form a powder image on the photoconductive area. This image is subsequently transferred to a support surface, such as copy paper, to which it is permanently affixed by heating or by the application of pressure. Following transfer of the toner image to a support surface, the charge-retentive member is cleaned of any residual toner that may remain thereon in preparation for the next imaging cycle.  
           [0003]    One approach to fixing, or “fusing,” the toner image is applying heat and pressure by passing the print sheet containing the unfused toner images between a pair of opposed roller members at least one of which is internally heated. During this procedure, the temperature of the toner material is elevated to a temperature at which the toner material coalesces and becomes tacky. This heating causes the toner to flow to some extent into the fibers or pores of the sheet. Thereafter, as the toner material cools, solidification of the toner material causes the toner material to become bonded to the sheet.  
           [0004]    After the fusing step, it is common that the resulting output sheet be fed to a subsequent processing station, such as an inverter, collator, stapler, booklet maker, etc. In order to direct a sheet emerging from the fuser rolls to the next processing station, it is common that the volume of space immediately downstream of the fuser in the process direction, which can be called the “post-fuser path” be effectively shaped in a funnel configuration, so that a sheet passing through the post-fuser path is directed toward a fairly narrow opening, such as toward a stapler.  
           [0005]    [0005]FIG. 1 is an elevational view of some basic elements of an electrostatographic printer, illustrating a practical problem addressed by the present invention. Blank sheets are drawn one at a time from a supply stack  100  and conveyed, by known means, through a paper path  102  along a process direction P. At a charge-retentive surface such as on photoreceptor  104 , marking material forming an image is electrostatically transferred to each sheet by one or more corotrons  106  or equivalent devices. Following transfer, the sheet is sent through fuser rolls  108  and  110 . After fusing, the sheet can be sent on for further processing, such as stapling or binding.  
           [0006]    Following the fuser along process direction P, it is typical that the sheets pass through the post-fuser path which is of a general funnel shape, such as formed by surfaces of baffles  10  and  12 , whereby the vertical width of the path decreases to a relatively narrow slot  14 , through which the sheet can be directed to a subsequent processing station.  
           [0007]    As can be seen in the Figure, a problem can occur if the subsequent processing station following slot  14  is unable to accept input of a sheet, such as if the station is malfunctioning. If a sheet S cannot be accepted through slot  14  and is nonetheless pushed forward by the motion of fuser rolls  108 ,  110 , the sheet S will jam and be compacted between surfaces formed by baffles  10  and  12 . The funnel-like surfaces of the baffles  10 ,  12  tend to exacerbate a jamming problem, because the shape causes a very compact accordion-folding of the moving sheet. The post-fuser path will fill up quickly with one or more sheets, and the compaction of sheets is liable to damage the hardware around baffles  10  and  12 .  
           [0008]    The present invention is directed toward avoiding and obviating damage that can be caused in a post-fuser path in a printing apparatus, or indeed any post-roller path in any apparatus which feeds sheet material.  
         DESCRIPTION OF THE PRIOR ART  
         [0009]    U.S. Pat. No. 5,245,395 discloses a fusing apparatus wherein a baffle associated with the stripper fingers on the exit side of the apparatus imparts an arcuate profile on sheets emerging from the apparatus; this tends to prevent longitudinal waves from forming in the sheet.  
           [0010]    U.S. Pat. No. 5,822,668 discloses a fusing apparatus which pivots open on its exit side for jam clearance. Various stripper fingers and plates are mounted on the pivoting exit side of the apparatus.  
         SUMMARY OF THE INVENTION  
         [0011]    According to one aspect of the present invention, there is provided an apparatus useful in moving sheets, comprising a first roller and a second roller, forming a nip therebetween; means defining a substantially enclosed post-roller path downstream of the nip along a process direction toward an output opening; and opening means for increasing a size of the post-roller path.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is an elevational view of elements of an electrostatographic printer in the prior art, illustrating a problem addressed by the present invention.  
         [0013]    [0013]FIG. 2 is an elevational view of a post-fuser path in an electrostatographic printer, showing one embodiment of the present invention.  
         [0014]    [0014]FIG. 3 is an elevational view of a post-fuser path in an electrostatographic printer, showing another embodiment of the present invention.  
         [0015]    [0015]FIG. 4 is an elevational view of a post-fuser path in an electrostatographic printer, showing another embodiment of the present invention. 
     
    
       [0016]    In the various Figures, like numerals indicate functionally analogous elements.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    [0017]FIG. 2 is an elevational view of a post-fuser path in an electrostatographic printer, showing one embodiment of the present invention. At the exit side of the fusing apparatus formed largely by rolls  108  and  110 , surfaces defining the post-fuser path to the output opening, or slot,  14  are defined by what can be called plates or “baffles”  10  and  12 . (Although baffles  10  and  12  are shown as smooth plates in the illustrated embodiments, either of the surfaces converging toward slot  14  can be effectively formed by fingers, ridges, etc., or to some extent by surfaces of neighboring hardware.) As can be seen, in a basic state, the baffles  10  and  12  form a funnel in the vertical direction, wherein the vertical cross-section of the post-fuser path decreases along the process direction. More broadly, the surfaces of baffles  10  and  12  in effect substantially enclose the post-fuser path for purposes of directing sheets from the nip between rolls  108  and  110  to the slot  14 .  
         [0018]    In a typical fuser apparatus, there is further provided one or more stripper fingers such as  16 , which have the purpose of stripping sheets from the image-side (in this case, the lower side) of sheets emerging from the nip between rolls  108  and  110 . Such stripper fingers and their associated mounts (not shown) are likely to be damaged by the impaction of sheets within the post-fuser path.  
         [0019]    According to the FIG. 2 embodiment, the lower baffle  10  is pivotably mounted, such as on hinge  18 , within the body of the printing machine, and thus provides a movable surface defining the post-fuser path. Further, the baffle  10  is held in a basic position by a spring force provided by a spring  20 , which can be a spring of any type, and could include, for example, a counterweight system to provide the spring force. As can be seen by the “down” or “open” position of the baffle indicated as  10 ′, any downward force greater than the spring force of spring  20  will cause the baffle  10  to be pushed downward, and, as shown, increase a size of or in other words “open” the post-fuser path. The downward force would of course be provided by the presence of any sheets stuck in the post-fuser path, or in other words a “jam condition,” such as shown in FIG. 1 above.  
         [0020]    By thus “opening” the post-fuser path, first, more volume is available to avoid further compaction of sheets fed into the post-fuser path; and, second, the crumpled jammed sheets can be relatively easily removed by hand from the post-fuser path. In this embodiment, after the crumpled sheets are removed from the post-fuser path, spring  20  will return baffle  10  to its basic position.  
         [0021]    In the FIG. 2 embodiment, a spring force associated with spring  20  is chosen based on the expected force of sheets being crumpled by jamming within the post-fuser path, which in turn may be affected by, for instance, the speed of sheets being fed through fuser rolls  108 ,  110 .  
         [0022]    [0022]FIG. 3 shows another embodiment of the present invention. Instead of being springably mounted as in the previous embodiment, in FIG. 3 the lower baffle  10  is supported in its basic upward position by a flexible linkage generally indicated as  30 . The linkage  30  is in turn held in place by a trip member indicated as  32 . A portion  34  of trip member  32  extends through an opening  11  in baffle  10  and into the post-fuser path, and is thus positioned to contact a jammed sheet in the post-fuser path. When the post-fuser path fills up with a crumpled sheet during a jam condition, eventually the sheet will push down portion  34 , and, as shown in the Figure, trip member  32  will assume the position shown in phantom as  32 ′. When this occurs, linkage  30  is no longer supported by trip member  32  and will then flex in the direction shown by arrow  36 . When linkage  30  thus flexes, baffle  10  will move downward, in a similar manner as in the FIG. 2 embodiment, and the volume of the post-fuser path will open, as described above, to avoid compaction and provide easy removal of crumpled sheets. After crumpled sheets are removed, baffle  10  can be returned to its basic, upward position, and trip member can be reset to once again support flexible linkage  30 .  
         [0023]    Although FIG. 3 shows one arrangement of hardware to enable a “trip” for opening the volume in the post-fuser path, other mechanical arrangements having substantially the same effect would be apparent to one of skill in the art. Such arrangements may include springs or equivalent elements to enhance performance, either in determining under what conditions baffle  10  should move downwards, and/or to facilitate a reset of baffle  10  to its basic position.  
         [0024]    [0024]FIG. 4 shows another embodiment of the present invention. In this embodiment, the position of lower baffle  10  is directly controlled by an electronic control system, here indicated as  40 . Of course control system  40  can be embodied as a routine within a larger control system governing the entire printing apparatus. In this embodiment, jamming conditions within the post-fuser path can be inferred by monitoring the behavior of sheets passing into the fuser nip between rolls  108  and  110  and exiting through slot  14 . Briefly, a monitor  42  (which may be of any variety used in determining sheet position, such as a mechanical sensor or an optical sensor) monitors the feeding of sheets into the fuser, and if the apparatus is working properly, a sheet detected at monitor  42  should be detected at a monitor  44 , disposed along paper path  102  just after slot  14 , within a predetermined time window thereafter. If a sheet detected by monitor  42  is not matched by a subsequent detection of the sheet by monitor  44 , the condition is consistent with a jam in the post-fuser path. Control system  40 , detecting this condition, then causes baffle  10  to move to a downward position which opens the post-fuser path. The downward movement of baffle  10  can be performed by an electromechanical actuator  46  of any type, such as an electromagnetic plunger or servomotor.  
         [0025]    Although the illustrated embodiments of the present invention are directed toward avoiding and obviating damage that can be caused in a post-fuser path in a printing apparatus, the invention can be applied to any post-roller path in any apparatus which feeds sheet material.