Abstract:
A nip release mechanism for a fuser of a printing device includes a movable component in the printer base frame moved by opening and closing a cover, and a follower component in the fuser which follows movement of the movable component to adjust positions of a fuser pressure roll.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to fusers and electrophotographic printing devices, and, more particularly, to release mechanisms that unload the nip formed by the pressure roll against the hot roll in the fuser. 
   2. Description of the Related Art 
   In the 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 exposing the uniformly charged surface of the photosensitive member. Toner particles are applied to the electrostatic latent image, and thereafter the toner image is transferred to the media intended to receive the final permanent image. The toner image is fixed to the media by the application of heat and pressure in a fuser. 
   A fuser is known to include a heated roll and a pressure roll, each covered with a compliant outer covering. The pressure roll is loaded against the heated roll by means of a spring-loaded bell crank to create a nip region for fusing the toner. 
   As color printers have become smaller in size, to reduce cost and to minimize space requirements in offices, the paper path through the printer has become shorter and shorter. As a result, if a paper jam or other process interruption occurs while a portion of the media is still in the fuser nip, the media is likely trapped in at least one and as many as four transfer nips. In some vertical machine architectures, the PC drum to transfer roll nip is located in the front of the machine. As the door of the machine is opened, the media is caught in nips between rolls moving with the opening cover and the fuser nip. The fuser nip pressure is normally higher than even a combination of several transfer nips. The media is likely pulled out of the transfer nips rapidly as the door is opened, which could cause damage to the PC drums or even cause the PC drums to be pulled off the front door. The PC drum is unloaded when the door is fully opened, but for the first part of the door motion the PC drum is still loaded against the transfer rolls. The paper will tug on the PC drum and slip in the transfer nips, possibly scratching the drums or even pulling them from their located features in the front door. 
   Several attempts are known in the prior art to overcome this problem. Manual levers have been used on the fuser module to relieve the fuser nip load. This requires an additional action by the user, and is not desirable. Further, because the fuser load is high, significant mechanical advantage is required, which results in a large, unsightly fuser nip release lever. Since opening the cover does not automatically release the fuser nip, it is possible that a user could open the cover and attempt to remove a jam without releasing the fuser nip lever potentially causing damage to the machine. 
   It is known also to employ a mechanism whereby opening one cover causes a part in the base machine to push on the fuser bell crank, thus releasing the fuser nip. In designs of this type it is common that the front door cannot be opened unless the cover that releases the fuser nip is opened first. A disadvantage of this design is that the base machine applies considerable load to the fuser module, which makes inserting or removing the fuser module difficult for the user. 
   A further attempted solution has been to provide a mechanism on board the fuser module itself that opens and closes the fuser nip. The actuation of the mechanism is also accomplished internal to the fuser itself. Usually this is achieved through a gear train and cam acting on the spring loaded bell cranks, which could be powered by a separate motor or by reversing the fuser motor. A disadvantage of this design is that the mechanism is expensive and may require a separate motor in the case of printers in which the fuser motor is dedicated to driving the fuser rolls forward and backward in a duplexing arrangement. 
   What is needed in the art is a simple, inexpensive and effective structure to automatically unload the fuser nip and to retain the fuser nip in an unloaded position during servicing. 
   SUMMARY OF THE INVENTION 
   The present invention provides a nip release cam rotated by a link mechanism when the printer cover is opened. The nip release cam moves a nip release cam follower, which rotates the bell crank sufficiently to unload the fuser nip. A locking feature on the cam follower automatically locks onto the fuser frame to hold the pressure roll in an open nip position. Closing the cover reverses the actuation mechanism thereby loading the fuser nip. 
   In one aspect thereof, the present invention provides a printing apparatus with a machine frame and a cover assembly pivotally connected to the machine frame and moveable between closed and opened positions. A fuser assembly is mounted in the machine frame and includes a hot roll, a pressure roll for forming a fuser nip with the hot roll, and loading means applying force to the pressure roll against the hot roll. A nip release mechanism is operable to adjust the loading means between loading and unloading conditions. A linkage assembly interconnects the cover assembly and the nip release mechanism for operating the nip release mechanism by moving the cover assembly between opened and closed positions. 
   In another aspect thereof, the invention provides a fuser nip release mechanism for a printing apparatus having a cover assembly and a fuser module having a hot roll, a pressure roll nip against the hot roll and loading means for moving the pressure roll with respect to the hot roll. The fuser nip release mechanism has an actuating means to engage and disengage the loading means between loaded and non-loaded conditions; and a linkage assembly connecting the actuating means and the cover assembly for moving the actuating means in response to opening and closing the cover assembly. 
   In still another aspect thereof, the invention provides a nip release mechanism for a printing apparatus having a machine frame, a cover assembly rotatably connected to the machine frame and a removable fuser module including a hot roll, a pressure roll and loading means for holding the pressure roll against the hot roll. The nip release mechanism has a movable component in the machine frame connected to the cover to be moved by movement of the cover between opened and closed positions. A follower in the fuser module is engageable with the movable component, the follower being moved by movement of the movable component. A connection between the follower and the loading means moves the loading means in response to movement of the follower. 
   An advantage of the present invention is providing automatic unloading of the fuser nip as a machine cover is opened to facilitate service of the printing device, and automatic nip loading as the cover is closed. 
   Another advantage is providing a simplified structure for loading and unloading the fuser nip not requiring additional motors and gear trains. 
   A further advantage of the present invention is automatically securing the fuser nip in an opened position so long as the fuser is uninstalled, thereby reducing potential roll or roll cover distortion. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a schematic, fragmentary illustration of a printing device having a fuser nip release mechanism in accordance with the present invention, the fuser nip being shown in a loaded condition; 
       FIG. 2  is an enlarged schematic, fragmentary illustration of the fuser nip in the printing device of  FIG. 1 , but illustrating the fuser nip in an open, non-loaded condition; 
       FIG. 3  is a fragmentary, schematic illustration of the printing device and the fuser nip release mechanism of the present invention, with the nip shown in a closed and loaded position; 
       FIG. 4  is a fragmentary, schematic view similar to  FIG. 3  but illustrating the cover in an open position and the fuser nip in an unloaded condition; 
       FIG. 5  is a further enlarged, fragmentary, schematic view of the nip release mechanism shown with the fuser nip in a loaded condition; 
       FIG. 6  is a fragmentary, schematic view similar to  FIG. 5 , but showing the fuser nip release mechanism partly rotated toward the unloaded position; 
       FIG. 7  is a fragmentary, schematic view similar to  FIGS. 5 and 6  but, illustrating the release mechanism in a further rotated condition; 
       FIG. 8  is a fragmentary, schematic view similar to  FIGS. 5–7 , but illustrating the release mechanism in a fully unloaded and locked condition; 
       FIG. 9  is a fragmentary, schematic view similar to  FIGS. 5–8 , but illustrating the release mechanism rotated slightly from the locked and unloaded condition toward the loaded condition; and 
       FIG. 10  is a fragmentary, exploded, perspective view of the release mechanism shown in the previous figures. 
   

   Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings and particularly to  FIG. 1 , there is shown an embodiment of a fuser module  10  in accordance with the present invention, suitable for use in an electrophotographic (E.P.) printing apparatus  12  shown in fragmentary form in  FIGS. 3 and 4 . Apparatus  12  further includes a machine frame  14 , a fragment thereof which is schematically represented in  FIG. 3 . Fuser module  10  is removable from frame  14 , as indicated by the dashed line in  FIG. 3  interconnecting fuser module  10  and machine frame  14 . A cover assembly  16  is pivotally connected to machine frame  14 , and can be rotated between closed ( FIG. 3 ) and opened ( FIG. 4 ) positions. A linkage assembly  20  interconnects cover assembly  16  and components of fuser module  10 , as will be described in further detail hereinafter. Apparatus  12  further includes other components of a print engine, media feed system and the like (not shown) which are well known to those skilled in the art and will not be described in further detail herein. 
   Fuser module  10  includes a hot roll  22  in opposed relationship with a pressure roll  24 . A path is defined between hot roll  22  and pressure roll  24  through which individual pieces of media pass during printing in printing apparatus  12 . A combination of heat and pressure is applied to the media with toner thereon, for fusing and permanently affixing the toner particles to the media. Pressure roll  24  is loaded against hot roll  22  by a loading means such as a bell crank  26  and a spring  28 . The manner in which a bell crank and spring are configured to apply pressure from a pressure roll  24  to a hot roll  22  is well known to those skilled in the art and will not be described in further detail herein, except as related to operation of a fuser nip release mechanism  30  in accordance with the present invention. 
   Fuser nip release mechanism  30  provides an interconnection between cover assembly  16 , via linkage assembly  20 , and bell crank  26 . Fuser nip release mechanism  30  provides an actuating means to engage and disengage the load applied by pressure roll  24  on hot  22 . Release mechanism  30  includes a nip release cam  32  rotatable about a cam axis  34 . Cam axis  34  is defined by a shaft in base machine frame  14 . Linkage assembly  20  includes one or more arms  36  suitably connected by pivots  38  to each other and to cover assembly  16 . An end of linkage assembly  20  is connected to shaft  34 . Two such arms  36  are shown in  FIGS. 3 and 4 , connected pivotally to each other, with one arm  36  connected pivotally to cover assembly  16  and the other arm  36  connected to shaft  34  by keyed connection or the like to rotate together. As shown most clearly in  FIGS. 3 and 4 , movement of cover assembly  16  between a closed ( FIG. 3 ) and an open ( FIG. 4 ) position moves arms  36 , causing rotation of shaft  34  and thereby rotation of release cam  32 . 
   Nip release cam  32  is operatively engaged with a nip release cam follower  40  contained in fuser module  10 . Cam follower  40  is pivotably connected to bell crank  26  so as to be slightly rotatable relative to bell crank  26 . As illustrated in the preferred embodiment shown in the drawings, cam follower  40  includes an extended portion  42  having an enlarged head  44  contained within a slot  46  of bell crank  26 . Cam follower  40  includes a follower surface  48  slidable against cam  32  to be moved by the contoured surface of cam  32 . Bell crank  26  is moved by movement of cam follower  40 , through the connection of head  44  in slot  46 . Movement is enacted by rotation of nip release cam  32 , with the movement of bell crank  26  being guided also in part by a pin  50  from base  42  disposed within a slot  52  of bell crank  26 . 
   Operation of nip release mechanism  30  to unload and load the nip formed between pressure roll  24  and hot roll  22  can be best understood by comparing  FIGS. 3 and 4  showing the loaded and unloaded conditions, and the sequential views of operation shown in  FIGS. 5–9 . Cover assembly  16  is a main access cover to the components of printing apparatus  12 , and is opened when service or repair is required. With cover assembly  16  in the closed position ( FIGS. 3 and 5 ), pressure roll  24  is loaded against hot roll  22  via bell crank  26  and spring  28 . As cover assembly  16  is rotated to the opened position shown in  FIG. 4 , arms  36  are pulled, thereby rotating shaft  34  and nip release cam  32  in a counter clockwise direction, as shown in the drawings. As nip release cam  32  rotates, cam follower  40  pushes bell crank  26  to move pressure roll  24  away from hot roll  22 , thereby opening the nip formed between the two rolls,  22  and  24 . Sequential views of nip release mechanism  30  are shown in  FIGS. 5–9  as cover assembly  16  is moved from a fully closed position ( FIG. 5 ) to a fully opened position ( FIG. 8 ), and back toward the closed position ( FIG. 9 ). 
   When cover assembly  16  is rotated back towards the closed position, the resulting clockwise rotation of shaft  34  and cam  32  allows movement of bell crank  26  under the force from spring  28 , to again load the nip formed between hot roll  22  and pressure roll  24 . Thus, opening cover assembly  16  causes an automatic unloading of the nip formed between hot roll  22  and pressure roll  24 , and closing cover assembly  16  causes automatic loading of the nip formed between hot roll  22  and pressure roll  24 . 
   An additional feature of the present invention is that bell crank  26  is secured automatically in a position whereby the nip formed between hot roll  22  and pressure roll  24  is unloaded and the nip opened when cover assembly  16  is moved to a fully opened position. The shape of cam  32  riding against cam follower  40  moves cam follower  40  to provide opening and closing movement of the fuser nip as described above. Friction between cam  32  and cam follower  40  causes tilting of cam follower  40  relative to bell crank  26 , performing the locking and unlocking function. 
   As most clearly seen in the exploded view of  FIG. 10 , cam follower  40  includes an arm  54  having a lip or catch  56  that cooperatively associates with a locking feature  58  in the way of an edge on a frame member  60  of fuser module  10 . Rotation of cam  32  and the movement of cam follower  40  caused thereby both engages and disengages catch  56  from locking feature  58 . As shown in  FIG. 6 , initial rotation of cam  32  moves arm  54  and catch  56  toward locking feature  58 . A most-prominent lobe  62  on cam  32  moves catch  56  past locking feature  58 . Friction between cam  32  and cam follower  40 , together with the shape of cam  32  when rotated counterclockwise is such as to allow slight angular movement, or tilting, of cam follower  40  relative to bell crank  26 , moving arm  54  toward locking feature  58 . As cam  32  rotates further counterclockwise, moving lobe  62  away from cam follower  40 , bell crank  26  rotates only slightly toward the loading condition. However, catch  56  then engages locking feature  58 , securing bell crank  26  in a fixed position, wherein the nip formed between hot roll  22  and pressure roll  24  is open. As nip release cam  32  rotates still further counter clockwise, nip release cam  32  disengages from follower  40  ( FIG. 8 ), and force load from the fuser nip loading mechanism force is no longer transmitted through release mechanism  30  to the base machine. The fuser nip is open and will stay open even if fuser module  10  is removed from machine frame  14 , which is facilitated in that the force from spring  28  is carried entirely within fuser module  10 . 
   If cover assembly  16  is moved from the fully open position towards the closed position, nip release cam  32  is thereby rotated clockwise, again pushing bell crank  26  to move pressure roll  24  slightly away from hot roll  22 . Movement of cam follower  40  is sufficient to disengage catch  56  from locking feature  58 . Friction between cam  32  and cam follower  40  together with the shape of cam  32  causes slight angular movement, or tilting, of cam follower  40  relative to bell crank  26 , separating catch  56  from locking feature  58 , and allowing catch  56  to slide past locking feature  58 . Thereafter, further clockwise rotation of cam  32  caused by movement of cover assembly  16  toward the closed position allows cam follower  40  and bell crank  26  to move pressure roll  24  toward hot roll  22  ( FIG. 9 ), and thereby eventually closing and again loading the nip between hot roll  22  and pressure roll  24  when cover assembly  16  is fully closed ( FIGS. 3 and 5 ). 
   Actuation of nip release mechanism  30  of the present invention is accomplished by means of opening a machine cover necessary to service or maintain the printing apparatus, with no additional motion or action required from the user. Since cover assembly  16  is relatively large in comparison to the size of fuser module  10 , a significant mechanical advantage can be incorporated therein, to reduce the force required from the user to open the cover and unload the fuser nip. Since the nip release is engaged and disengaged by cover movement, there is reduced risk of user error in either installing a fuser with the nip released or accidentally removing the fuser without releasing the nip pressure. 
   Once the fuser nip is fully opened, it is locked in the open position by features of the fuser module itself. The fuser nip thereby remains open even when the fuser is removed from the machine and totally separated from machine frame  14 . Thus, when removed from the machine, hot roll  22  and pressure roll  24  are separated, and the elastomeric compliant covers thereon will not be distorted from a nip relationship between the rolls. With the roll nip open the creation of compression set or other distortions is reduced. As fuser module  10  is installed, the fuser nip is open and no load is transferred between the fuser module and the machine. An individual installing the fuser module does not have to overcome a large load on the fuser due to the nip release mechanism, which makes installation easier. Further, the nip release mechanism is simple in both design and operation, and is relatively inexpensive to supply and assemble, in that it does not require additional gear trains and motors for actuation. 
   While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.