Abstract:
A fuser has a protuberance extruding lengthwise from the surface of a heater opposite the interior surface of an endless belt and is positioned in transverse relationship to the interior surface of the endless belt. A pressure roller defines a nip with the endless belt wherein the nip has an entrance side and an exit side and wherein the position of the protuberance adjacent to the nip creates pressure upon the endless belt. The print media sheet is driven through the nip in reaction to the pressure applied by the pressure roller to the belt. The position of the protuberance and the pressure created upon the endless belt directs the lubricant from the endless belt surface to the nip.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    None. 
       BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to image forming machines and, more particularly, to a fuser for an image forming machine with a heater having a protuberance strategically placed on the surface of the heater for maintaining adequate lubricity between the belt and the heater. 
         [0004]    2. Description of the Related Art 
         [0005]    An image forming machine, such as a printer, copier, fax machine, all-in-one device or 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. 
         [0006]    The sliding contact between the belt and the heater can cause high friction force. Lubricants such as grease and oil have commonly been used between the belt and the heater in order to reduce this high friction force. 
         [0007]    In the prior art a problem exists in that greases normally have a higher viscosity than oil and can form a thicker film on the belt and heater surface. This higher viscosity can cause higher frictional force and driving torque. Further, the greater film thickness can cause lower fusing capability. As the grease/oil is removed from the fuser nip by the rotating action of the belt against the glass heater surface and the shear created by this action, the lubricity between the belt and the heater becomes increasingly worse. This leads to a higher driving torque, higher belt wear, and sometimes the destruction of the belt. 
         [0008]    Thus, there is still a need for an innovation that will prevent the grease/oil form leaving the fuser nip in order to maintain the lubricity between the belt and the heater. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention meets this need by providing an innovation that strategically places a feature in the form of a protuberance on the outer surface of the heater and perpendicular to the belt such that when the belt moves along the heater surface, the incoming edge of the protuberance scrapes the grease/oil from the belt surface and keeps it in the fuser nip. As a result, the grease/oil moving towards the exits of the belt is pushed back into the fuser nip. 
         [0010]    Accordingly, in an aspect of the present invention, a fuser for an image forming device has an endless belt with lubricant applied to the surface. The endless belt has opposite marginal side edge portions and opposite exterior and interior surfaces on the belt that extend between the opposite marginal side edge portions. Within the endless belt is a heater housing wherein the interior surface of the endless belt surrounds the heater housing lengthwise between opposite ends of the heater housing. A heater is within the heater housing and the heater has a lengthwise surface disposed in heat transfer relationship with the endless belt. A protuberance extrudes lengthwise from the surface of the heater opposite the interior surface of the endless belt and is positioned in transverse relationship to the interior surface of the endless belt. A pressure roller defines a nip with the endless belt wherein the nip has an entrance side and an exit side and wherein the position of the protuberance adjacent to the nip creates pressure upon the endless belt. The print media sheet is driven through the nip in reaction to the pressure applied by the pressure roller to the belt. The position of the protuberance and the pressure created upon the endless belt directs the lubricant from the endless belt surface to the nip. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    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: 
           [0012]      FIG. 1  is a schematic end view of an exemplarily 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. 
           [0013]      FIG. 2  is a schematic top view of the protuberance located on the outer surface of the heater. 
           [0014]      FIG. 3  is an enlarged fragmentary sectional view of the protuberance located on the outer surface of the heater. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    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. 
         [0016]    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 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 fluorpolymer layer (either in the form of a sleeve or a coating, silicone rubber molded over a flexible metal tube or a polyimide seamless tube. 
         [0017]    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 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. 
         [0018]    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. 
         [0019]    The endless belt is a so-called “idling belt” having no drive rolls within its inner loop. The belt 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 of  14  A of the print media sheet. 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 . 
         [0020]    The sliding contact between the endless belt  16  and the heater  18  can cause high friction force. Generally, a lubricant such as grease or oil is applied to the surface of the endless belt  16  to reduce this friction force. Greases normally have a higher viscosity than oil and can form a thicker film on the belt and heater surface. This higher viscosity can cause higher frictional force and driving torque. Further, the greater film thickness can cause lower fusing capability. The grease/oil is removed from the fuser nip by the rotating action of the belt against the glass heater surface. This removal and the shear created by this action, decreases the lubricity between the belt and the heater. This leads to a higher driving torque, higher belt wear, and sometimes the destruction of the belt. In the present invention, the grease/oil moving towards the exits of the endless belt is pushed back into the fuser nip. 
         [0021]    Turning now to  FIG. 2 , which is a top view of the protuberance  3  located on the heater  18  shown in  FIG. 1 , the heater  18  has a protuberance  3  on the outer surface of the heater  18  that substantially overcomes the lubricity problem at the fuser nip. As shown in  FIGS. 1 and 2 , the heater  18  has a protuberance  3  on the outer surface of the heater  18  that is perpendicular to the endless belt  16 . When the endless belt  16  moves along the heater  18  surface, the incoming edge of the protuberance  3  scrapes lubricant such as grease or oil (not shown) from the surface of the endless belt  16  and moves it to the fuser nip  26 . As shown in  FIG. 2 , the leading edge  9  of the protuberance  3  extruding from the outer surface of the heater  18  is perpendicular to the paper moving direction  11  and extends longer than the paper width  7 . The leading edge  9  of protuberance  3  is slightly outside of the nip  26  formed by the backup roller length  20 . Resistive stripes  28  are energized via an AC line voltage in order to generate the heat required to melt the toner to the printed media. 
         [0022]    Turning now to  FIG. 3 , which is an expanded side view of the protuberance  3  located on the outer surface of the heater  18  shown in  FIG. 2 , the leading edge of the protuberance  9  is located at the trailing edge of the fuser nip (not shown), which is at the end of the backup roller (not shown). The leading edge  9  is preferably less than 1 mm in height and preferably between 0.05 and 0.1 mm in width. The protuberance  3  can be created in several forms by those skilled in the art including but not limited to a series of thick film printing sequences to create a bump with a height in the tens to hundreds of microns range or a glass rod attached to the outer surface of the heater  7  covered with one or more thick film printed glass layers. Thermal coefficient of expansion would be considered in the selection of the protuberance  3  material(s). 
         [0023]    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.