Patent Publication Number: US-2019171147-A1

Title: Fuser assembly having nip reduction force for imaging device

Description:
FIELD OF THE INVENTION 
     The present disclosure relates to a fuser assembly in an imaging device. The assembly includes a heated and backup member forming a fusing nip. The disclosure relates further to reducing the force of the nip to minimize wrinkling when imaging media, such as envelopes. 
     BACKGROUND 
     In an electrophotographic (EP) imaging process used in printers, copiers and the like, a photosensitive member, such as a photoconductive drum or belt, is uniformly charged over an outer surface. An electrostatic latent image is formed by selectively discharging the surface and applying toner. The toner is transferred to media and is fixed by applying heat and pressure in a fuser assembly. 
     Fuser assemblies take many forms. They include hot rolls or belts that springs bias against a backup roll to form a fusing nip. The nip exerts a force on media traversing the nip, but the force is often too great when imaging smaller-sized media, such as envelopes, causing wrinkling. To overcome this, manufacturers introduce devices to remove the force of the springs acting on the nip. However, proximity of the rolls and belts, their relative hardness, their deflection, etc., sometimes does not provide sufficient enough relief in the nip force. Conversely, the removal of the spring force sometimes causes components to become so lax that a gap develops at the fusing nip eliminating sufficient force to even advance media through the nip. The inventor recognizes a need to overcome these and other problems. 
     SUMMARY 
     A fuser assembly includes a heated member and backup member forming a fusing nip. A nip loading spring biases into contact the two members. A bellcrank contacts the nip loading spring such that upon opening of an access door of the imaging device, the bellcrank acts on the nip loading spring to reduce a force between the backup member and the heated member but keeping in contact with one another the backup member and the heated member. The bellcrank typifies a wire or other flexible lever. A cam pivots as an access door to the imaging device opens and engages the wire to compress the nip loading spring with a predetermined force during use. The symmetry of the fuser assembly allows duplicate features on proximate and distal ends of the fusing nip. The introduction of a flexible bellcrank provides at least the advantage of keeping the force of the loading spring, albeit a reduced force, acting to keep in contact the heated and backup members. The members typify rolls or belts depending upon selection. The loading spring acts on a shaft of the backup member. The shaft defines the rotational axis of the backup member. Other designs are possible. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a diagrammatic view of an imaging device, including cutaway with exaggerated and simplified view of a fuser assembly; 
         FIG. 2  is a diagrammatic view of a fusing nip; 
         FIGS. 3A-3C  are sequential views of a bellcrank acting on the fusing nip as an access door to the imaging device transitions from a closed, to intermediate, to open position, including a cam acting on the bellcrank; 
         FIGS. 4A and 4B  are diagrammatic views of the fusing nip with forces acting thereon; and 
         FIG. 5  is a diagrammatic view of a representative bellcrank. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     With reference to  FIG. 1 , an electrophotographic imaging device  10  prints images on sheets of media  12 . A controller (C), such as an ASIC(s), circuit(s), microprocessor(s), etc., receives image data from a scanner  13 , computer, laptop, mobile device, etc. and controls hardware to convert it to printed data. The controller has access to a local or remote memory that stores parameters useful to conducting imaging operations. 
     During use, the controller (C) activates one or more laser or light sources (not shown) to selectively discharge areas of a photoconductive (PC) drum  15  to create thereon a latent image of the image data. Toner particles are applied to the latent image to form a toned image  22  on the PC drum  15 . At a transfer nip  25  formed between the PC drum  15  and a transfer roll  30 , for example, the toned image  22  is electrostatically transferred from the PC drum  15  to a media sheet  12  travelling in a process direction PD. The media sheet  12 ′ with toned image  22 ′ enters a fuser assembly  40  through its entrance  45  for application of heat and pressure to fix the toned image to the media sheet  12 ′. Media sheet  12 ′ with fused toner image  22 ″ exits the fuser assembly  40  through its exit  50  and is either deposited into an output media area  55  for collection by a user or enters a duplex media path for transport back to the PC drum  15  for imaging on the reverse side of the media sheet. The fuser assembly is disposed within a housing  70  for configuration as a customer replaceable unit for ease of maintenance. The housing includes a heated member  60  and backup member  65 . 
     As seen in  FIG. 2 , the heated member  60  and the backup member  65  form a fusing nip (N) to provide heat and pressure to fix toner to media. The heated member defines a hot roll, such as a metal core with coating(s) exhibiting good thermal mass, and a heating lamp (L) internal to the core, as is familiar. Alternatively, the heated member defines a polymeric belt with internal heating lamp or ceramic heater and resistive traces, as is also familiar. The backup member  65  typifies a microballoon (e.g., porous foam rubber) or liquid injection molding (LIM) rubber. The backup member  65  connects to a motor  77  via an integral shaft  79  and the motor turns the shaft to rotate the backup member. Rotation of the backup member, in turn, causes rotation of the heated member to convey media through the fusing nip in the process direction. Alternatively, the motor rotates the heated member, which causes rotation of the backup member. A controller C governs the speed of rotation in a feedback relationship with the motor. The controller also regulates the temperature of the heated member in feedback with one or more thermistors  71 . 
     To maintain the pressure of the fusing nip N, a nip loading spring  80  applies upward pressure to the shaft  79  of the backup member  65 . The spring  80  resides at both the proximal end  82  and distal end  84  of the backup member to maintain uniformity of force of the fusing nip throughout an axial length of the backup member during use. A fitting  90  connects to the shaft to allow rotation of the shaft and provide an attachment point for the spring  80  to connect thereto. A bellcrank  100  also attaches to the nip loading spring  80 , preferably at fitting  90 . The bellcrank serves to reduce the force of the fusing nip between the backup member and the heated member when fusing envelopes, for example, but otherwise keeping in contact with one another the two members  60 ,  65  by way of the force from the nip loading spring  80 . 
     As illustrated in the sequential views of  FIGS. 3A-3B , the bellcrank acts on the nip loading spring to compress the nip loading spring upon the opening of an access door  110  of the imaging device. In turn, the force exerted by the spring  80  on the shaft  79  of the backup member  65  becomes reduced, but not eliminated, thereby ensuring contact between the backup member and the heated member. 
     The bellcrank  100 , in the form of a wire, has its terminal end  108  anchored to the housing  70  of the fuser assembly while its other end  112  attaches to a cam arm assembly  120 . The wire remains generally stationary until the cam arm assembly moves with movement of the access door  110  from a closed position ( FIG. 3A ) to an open position ( FIG. 3C ). The wire end  112  forms a bent loop  114  about a cam  125  of the cam arm assembly. In turn, the arm  130  of the cam arm assembly has a protrusion  132  that is guided in slots  140  of the access door  110 . When the door  110  is fully closed, the wire and cam do not contact one another ( FIG. 3A ). Upon movement of the door  110  from its fully closed position to an intermediate position ( FIG. 3B ), the slots  140  rotate in the direction of Action Arrow A 1 . This pulls downward the arm  130  of the cam arm assembly  120  and causes the cam  125  to rotate about its axis  150  in the direction of the movement of the door, e.g., in the direction of action arrow A 2 . In turn, the cam  125  contacts the loop end of the bellcrank  100  at position B and acts to rotate downward the bellcrank  100 , thus compressing from above the nip loading spring  80  at the fitting  90 . With further movement of the access door  110  to its fully open position ( FIG. 3C ), the cam  125  rotates further about its axis  150  in the direction of Action Arrow A 3  thereby exerting even more force on the bellcrank  100 , thus levering further the nip loading spring  80  in the direction of Action Arrow B. 
     As seen by comparing the greatly simplified diagrams of  FIGS. 4A and 4B , the fusing nip N formed between the heated member  60  and  65  changes in force upon activation of the bellcrank  110  upon the opening of the access door. In  FIG. 4A , when the access door is closed, the bellcrank  110  does not force downward the nip loading spring  80  and a first force F 1  is exerted by the spring  80  on the shaft  79  of the backup member  65 . In  FIG. 4B , when the access door is open, the cam arm assembly causes the bellcrank  110  to lever downward with a force F 3  and compress the nip loading spring  80 . In turn, the nip loading spring  80  exerts a second force F 2  less than force F 1  (F 2 &lt;F 1 ) on the shaft  79  of the backup member  65 . This lessens the fusing nip force on media traveling through the fusing nip and also decreases the nip distance of travel from ND 1  in the first instance to ND 2  in the second instance (ND 2 &lt;ND 1 ). Wrinkling is avoided when imaging media, such as envelopes 
     With reference to  FIG. 5 , a representative bellcrank  100  includes a wire, such as music wire, having a diameter in a range from about 1-2 mm. Its working length extends in a range from about 60-70 mm. A distance also extends in a range from about 20-30 mm from the anchored terminal end  108  to a location  111  where the bellcrank acts on top of the nip loading spring. Of course, other flexible levers could serve as a bellcrank meeting the functions described herein. 
     The foregoing illustrates various aspects of the invention. It is not intended to be exhaustive. Rather, it is chosen to provide the best mode of the principles of operation and practical application known to the inventor so one skilled in the art can practice it without undue experimentation. All modifications and variations are contemplated within the scope of the invention as determined by the appended claims. Relatively apparent modifications include combining one or more features of one embodiment with those of another embodiment.