Abstract:
A fuser has a heater housing extending through an endless belt with end caps on the housing adjacent to opposite lateral sides of the belt. The end caps have inner flanges spaced radially outward from a center portion and radially inward from the opposite marginal side edge portions of the belt so as to define clearance therebetween. Protuberances on the inner flanges of the end caps project toward opposite marginal edge portions of the belt and are circumferentially spaced apart to reduce belt skew relative to the end caps by either decreasing the surface area of contact of the inner flanges with the opposite marginal side edge portions of the belt to reduced surface areas of contact of protuberances therewith or decreasing the radial height of the clearance between the inner flanges and opposite side edge portions of the belt to the reduced radial height between the latter and the protuberances.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to image forming machines and, more particularly, to a fuser for an image forming machine with end caps having protuberances strategically placed on an inner flange for reducing belt skew. 
         [0003]    2. Description of the Related Art 
         [0004]    An image forming machine, such as a printer, copier, fax machine, all-in-one device or a multifunctional device, typically includes a heating device, such as a fuser, to fix a developing agent, such as toner, to a media sheet. The fuser typically contains a heater and an endless belt and backup pressure roll that form a nip for the media sheet to pass through. They provide heat and/or pressure to the toner to soften the toner so that it will adhere to the media sheet. The fuser belt defines an inner loop. The heater is positioned within the inner loop and in direct contact with the belt. The heater has a profile generally corresponding to the travel path of the belt to provide an area contact rather than a line contact for more efficient thermal transfer. The heater is in the form of a ceramic heater held in a heater housing positioned within the inner loop and against the belt. The fuser belt is an “idling belt” having no drive rolls within it. The belt is driven by the rotation of the backup pressure roll, through the driving association of the belt with the pressure roll at the nip. 
         [0005]    The location of the belt is controlled by an end cap attached to each end of the heater housing. The end cap has an inner flange that limits the left to right axial movement of the belt. The backup pressure roll rotates which, in turn, rotates the belt and drives the print media through the fuser nip. The end caps do not rotate. 
         [0006]    Sometimes the belt in the fuser skews with respect to the fuser backup pressure roll and the end caps. The belt skew results from differences in friction along the heater. This misalignment allows the belt to infringe on the media path as it enters the fuser nip causing smudging on the printed page that results in unacceptable print quality. Another phenomenon that belt skew affects is the “left to right” movement of the media as it passes through the fuser nip. This is known as “media walk” and is defined as the distance in millimeters the paper moves side to side. Excessive media walk may cause the media to crash into limiting features within the printer&#39;s paper path. 
         [0007]    Thus, there is still a need for an innovation that will reduce skew between the end caps and the belt so as to reduce belt skew with the backup pressure roll. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention meets this need by providing an innovation that strategically places features in the form of protuberances on the inner flange of each of the end caps that reduce the amount of belt skew by reducing the clearance between the inner flange of the end cap and the belt and also reducing the area of surface contact between the inner flange and the belt. 
         [0009]    Accordingly, in an aspect of the present invention, a fuser for an image forming machine includes an endless belt having opposite marginal side edge portions and opposite exterior and interior surfaces on the belt extending between the opposite marginal side edge portions, a heater housing disposed within the endless belt such that the interior surface thereof surrounds the housing lengthwise between opposite ends of the housing, a pair of end caps mounted to opposite ends of the housing adjacent to opposite lateral sides of the belt, each of the end caps having an inner flange spaced radially outward from a center portion of the end cap and radially inward from the opposite marginal side edge portions of the belt so as to define a clearance of a first radial width between the inner flange and the one of the opposite marginal side edge portions of the endless belt, and a plurality of protuberances defined on the inner flange of each of the end caps projecting toward the one of the opposite marginal edge portions of the endless belt and circumferentially spaced apart from each other to reduce belt skew relative to the end caps by enabling at least one of: decreasing the surface area of contact of the inner flange of the end cap with the one of the opposite marginal side edge portion of the endless belt to the reduced surface area of contact of the protuberances with the one of the opposite marginal side edge portions of the belt or decreasing the radial height of clearance between the inner flange and the one of the opposite side edge portions of the belt to the reduced radial height between the one marginal side edge portion of the belt and the protuberances. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: 
           [0011]      FIG. 1  is a schematic end view of an exemplary embodiment of a fuser of an image forming machine with a media sheet having toner thereon traveling through a nip between an endless belt and a backup pressure roll of the fuser. 
           [0012]      FIG. 1A  is an enlarged fragmentary sectional view of an end cap of the fuser as seen along line  1 A- 1 A of  FIG. 1  showing inner and outer flanges of the end cap and a marginal side edge portion of an endless belt of the fuser extending into the clearance between the flanges and containing no feature. 
           [0013]      FIG. 2  is a schematic side elevational view of the belt showing the angle of belt skew at approximately 1°. 
           [0014]      FIG. 3  is an enlarged schematic end view of the belt showing too much contact of the inner flange of the end cap with the belt, resulting in high friction in small local areas of the belt which produces adverse effects on the belt. 
           [0015]      FIG. 4  is a view of the belt similar to that of  FIG. 3  but now showing the inner flange of the end cap having features of the present invention strategically located or place on the inner flange about the clearance between it and the belt. 
           [0016]      FIG. 4A  is a view of the end cap similar to that of  FIG. 1A  now showing a feature or protuberance separately provided on the inner flange and underlying the marginal side edge portion of the endless belt. 
           [0017]      FIG. 4B  is a view similar to that of  FIG. 4A  but now showing a feature or protuberance integrally formed on the inner flange and underlying the marginal side edge portion of the endless belt. 
           [0018]      FIG. 5  is a view of the belt similar to that of  FIG. 2  but now showing the angle of belt skew reduced to approximately 0.1°. 
           [0019]      FIG. 6  is a bar graph of the angle of belt skew with and without features of the present invention. 
           [0020]      FIG. 7  is a bar graph of the amount of media walk per page with and without the features of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numerals refer to like elements throughout the views. 
         [0022]    Referring now to  FIG. 1 , there is illustrated an exemplary embodiment of a fuser, generally designated  10 , of an image forming machine (not shown). The fuser  10  fixes or fuses toner particles  12  defining an image to a media sheet  14 . Toner particles  12  may be monochrome particles or particles of different colors (e.g., cyan, magenta, yellow and/or black particles). The fuser  10  includes an endless belt  16 , a heater  18  and a backup pressure roll  20 . The belt  16  defines an inner loop  22  having a metal tube and, to improve the degree to which the belt conforms to the varying heights of the various piles of toner particles, a compliant rubber layer on the base and a release coating covering the rubber layer to enhance thermal conductivity. More specifically, the belt  16  is typically a Teflon® coated, silicone rubber molded over a flexible metal tube. 
         [0023]    The heater  18  is positioned within the inner loop  22  and in direct contact with the endless belt  16 . The heater  18  has a profile (e.g., flat or curved) generally corresponding to the travel path of the belt  16  to provide an area contact rather than a line contact for more efficient thermal transfer. The heater  18  may be in the form of a ceramic heater component held in a heater housing  24  positioned within the inner loop  22  of and against the belt  16 . The belt  16  is somewhat loosely fit around the heater housing  24 , which is a high-temperature plastic body made of a liquid crystal polymer, in one example about 22% glass and mineral filled but not limited to this combination. 
         [0024]    The backup pressure roll  20  defines a nip  26  with the belt  16  through which the print media sheet  14  travels. The nip  26  has an entrance  26 A and an exit  26 B. The belt  16  is positioned adjacent the toner side  14 A of the sheet  14  as it is transported through the nip  26 , with the pressure roll  20  on the opposite side thereof. As known to those skilled in the art, the backup pressure roll  20  includes a metal core  28 , a compliant layer  30  surrounding the core  28 , and a release layer  32  surrounding the compliant layer  30 . The metal core  28  may be formed from a suitable metal that provides structural rigidity and stores thermal energy, such as extruded aluminum or steel. The compliant layer  30  may be formed from a material providing compliance of pressure roll  20 , and can be in the form of silicone rubber, but may be formed of other resilient materials. Additionally, the release layer  32  may be in the form of a sleeve made from a material providing suitable release properties. 
         [0025]    The endless belt  16  is a so-called “idling belt” having no drive rolls within its inner loop  22 . The belt  16  is driven by the rotation of the backup pressure roll  20  through the driving association of the belt  16  therewith in the nip  26 . The print media sheet  14  is transported to the fuser  10  by a transport belt (not shown), and passes through the nip  26 . During printing, the fuser  10  fixes or fuses the toner particles  12  to the toner side  14 A of the print media sheet  14 . The heater  18  positioned within the inner loop  22  of the endless belt  16  is energized such that the heater  18  provides a desired heat output. Heat is transferred principally via conduction from the heater  18 , through the belt  16 , and to the outer periphery of the backup pressure roll  20 . The outer surface  16 A of the belt  16  is also the surface that transfers heat to toner particles  12 , for fixing or fusing an image on the print media sheet  14 . The print media sheet  14  is transported through the nip  26  between the backup pressure roll  20  and the belt  16 . Heat is transferred from the belt  16  to toner particles  12 , to fix or fuse the image on the sheet  14 , and is additionally transferred to the backside of the sheet  14  from the pressure roll  20 , to assist in the fusing process. The compliant rubber layer of the belt  16  accommodates the varying thickness of toner particles  12  on the print media sheet  14 . 
         [0026]    The fuser  10  also includes end caps  34  (one being shown at the one end of the fuser  10  shown in  FIGS. 1 ,  3  and  4  and fragmentarily shown in  FIGS. 1A and 4A ) attached to opposite ends  24 A of the heater housing  24  and by which means the side-to-side location of the belt  16  is controlled. Each end cap  34  has a substantially circular inner flange  36  that fits inside of the inner loop  22 , the inside diameter, of the belt  16  with an outer surface  36 A of the inner flange  36  to locate the belt  16  up and down and front to back in the fuser  10 . The outer surface  36 A of the inner flange  36  of the end cap  34  is shaped to match the shape or configuration the belt  16  (as viewed from an end as seen in  FIGS. 1 ,  3  and  4 ) wants to take when the belt  16  is pressed up against the heater  18  by the backup pressure roll  20 . The inner flange  36  of the end cap  34  limits the left to right axial movement of the belt  16 . The end cap  34  also has an outer flange  38 . As best seen in  FIGS. 1A and 4A , both inner and outer flanges  36 ,  38  project in the same direction from an end panel  40  of the end cap and a clearance  42  is defined between the inner and outer flanges  36 ,  38  due to their being spaced apart radially from one another. As mentioned above, the endless belt  16  is an idler; it is only rotated due to the pressure and angular forces applied to it by the rotation of the backup pressure roll  20  in driving the print media sheet  14  through the fuser nip  26 . The end caps  34  do not rotate. 
         [0027]    As seen in  FIG. 2 , heretofore it has been noted that the belt  16 , and thus its central axis  44  (see also  FIG. 4 ) in the fuser  10  can skew with respect to the rotational axis  46  of the backup pressure roll  20  and to the end caps  34 . Belt skew is believed to result from differences in friction between the heater  18  and belt  16  along the length of the heater  18 . The angle of the belt skew relative to the axis  46  of the backup roll  20  can be up to approximately 1°. Though this degree of belt skew may seem slight it can have large consequences. This misalignment allows the belt  16  to infringe on the media path as it enters the fuser nip  26  at entrance  26 A causing smudging on the printed sheet  14  that results in unacceptable print quality. Another phenomenon that belt skew affects is the “left to right” movement of the media sheet  14  as it passes through the fuser nip  26 . This is known as “media walk” and is defined as the distance in millimeters the sheet  14  moves side to side. Excessive media walk may cause the media to crash into limiting features within the printer&#39;s paper path. 
         [0028]    When too much of the surface of the inner flange  36  comes in contact with the belt  16 , as depicted in  FIG. 3 , this condition could cause what is termed “Band Brake” effect. This would result in high friction in very small local areas of the belt  16 . In this case two phenomenons could occur. The first is that the increased friction would cause the belt  16  to stop momentarily. This stoppage would result in a print quality defect on the print page. The second would be catastrophic belt failure or destruction due to extremely high torque placed on the belt  16 . This would render the printer inoperative. 
         [0029]    To minimize friction with the inner surface  16 B of the belt  16  a portion of the clearance  42  provided between the inner and outer flanges  36 ,  38  is also between the inner surface  16 B of one of the opposite marginal edge portions  16 C of the belt  16  and the outer surface  36 A of the inner flange  36 , as seen in  FIG. 1A . It should be noted that the clearance  42  between the inner and outer flanges  36 ,  38  of the end cap  34  and the marginal side edge portions  16 C of the metal belt  16  is important to the performance of the fuser  10  when it is a color fuser. The amount of the clearance  42 , side-to-side, is what allows the belt  16  to skew. This clearance  42  allows the belt central axis  44  to not be parallel to the backup roll axis of rotation  46 . The relative angle between these axes  44 ,  46  creates a point load at the contact point of the belt  16  and the end cap  34 . In addition to accelerated wear due to this point load, another failure mode is caused by this point load. This point load can produce a localized buckling of the belt  16  as it contacts the end cap  34 . This buckling usually results in the belt  16  bending over short distances. Since it is localized the buckling fatigues the edge of the belt  16  and can put a crease in the belt  16 . Buckling results in fatigue of the belt  16  which results in cracks in the belt  16  in the axial direction and circumferential direction. These cracks cause failure of the belt  16 . 
         [0030]    The present invention is directed to features provided on the inner flange  36  of the end cap  34  which reduce the amount of belt skew by taking up or reducing portions of the clearance  42  that exists between the opposite marginal side edge portions  16 C of the endless belt  16  and the inner flanges  36  of the end cap  34 . In an exemplary embodiment as seen in  FIGS. 4 and 4A , these features take the form of a plurality of dimples or protuberances  48 A- 48 D formed on the inner flange  36  of the end cap  34  which are circumferentially spaced from one another and project outward along radial lines  50 A- 50 B from a central portion  52  of the end cap  34 . The profile of the number and shapes of protuberances  48 A- 48 D and their circumferential and radial positions when taken together and also their total surface contact areas may be tailored so as to conform to the profile of the path of travel of the endless belt  16  and reduce the radial height of the clearance  42  between the inner flange  36  and the belt  16  and the amount of the surface area of the inner flange  36  to come in contact with the belt  16 . Thus the spacing or distance between the protuberances  48 A- 48 D is important so that the “Band Brake” phenomenon does not occur because of too much frictional contact, as also shown and described in  FIG. 3 . 
         [0031]    In  FIGS. 4A and 4B , there is shown the protuberances  48 A- 48 D provided in alternative designs in the inner flange  36  with respect to how they reduce the radial height of the clearance  42  between the inner flange  36  of the end cap  34  and the inside of the metal belt  16 . These features or protuberances  48 A- 48 D are strategically positioned circumferentially around the inner flange  36  of the end cap  34 , as best seem in  FIG. 4 , where the radius of the belt  16  is closest to the natural radius of the belt  16  under zero loading so that no additional stresses are imposed on the metal belt  16 . Because the clearance portion  42 A is lesser at locations nearer the entrance  26 A to the nip  26  than at locations nearer the exit  26 B from the nip  26 , which in part at least may be due to the fact that the direction of the pulling force exerted on the belt  16  goes from the entrance  26 A toward the exit  26 B of the nip  26 , the radial projection beyond the inner flange  36  of the one of the protuberances  48 A- 48 D, as viewed along radial lines  50 A- 50 D, nearer to the entrance  26 A may be less than the radial projection beyond the inner flange  36  of the one of the protuberances  48 A- 48 D nearer to the exit  26 B. Also, the protuberances  48 A- 48 D going from the entrance  26 A to the exit  26 B may increase in radial height as the height of the clearance  42  between the belt  16  and inner flange  36  increases. In such manner, the profile of the protuberances  48 A- 48 D when taken together are tailored to correspond to the height of the clearance  42  at these locations and to the profile of the path of travel of the endless belt  16 . The protuberances  48 A- 48 D can be features integrally molded, as seen in  FIG. 4B , on the inner flange  36  of the end cap  34  or features separately provided, as seen in  FIG. 4A , on an insert made from plastic or metal material that is attached to the end cap  34 , such as between the end panel  40  and the inner flange  36 . 
         [0032]    To recap, the present invention is directed to features taking the form of dimples, protrusions or bulges, referred to generically as protuberances  48 A- 48 D, on the inner flange  36  of the end cap  34  that control belt skew. Thus, point loads of the belt  16  on the end cap  34 , due to the angle θ t  between the belt  16  and end cap  34  as depicted in  FIGS. 3 and 4 , or run-out of the belt  16  can be compensated for resulting in elimination of belt end flaring and thus damage. These features control the front to back axial motion of the belt  16  and reduce the amount of media sheet walk rate which can cause the media sheets  14  to crash into limiting features within the printer&#39;s paper path. Improved control of belt skew with the implementation of protuberances  48 A- 48 D compared to the situation without them is clearly illustrated in  FIG. 5  and in the bar graph of  FIG. 6  which show that the angle of belt skew is reduced to approximately 0.1° The improved media walk rate is shown in the bar graph of  FIG. 7 . 
         [0033]    The foregoing description of several embodiments of the invention has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be defined by the claims appended hereto.