Abstract:
The invention generally relates to the field of fusing powder toner images on receiver sheets. According to various aspects of the invention, methods and apparatus are provided of cleaning, only during standby, a pressure roller that cooperates with a fuser roller in fusing toner images. The pressure roller is cleaned with a cleaning pad mounted adjacent the pressure roller in an electrographic printer.

Description:
BACKGROUND 
   The invention generally relates to the field of fusing powder toner images on receiver sheets. 
   Fusers for fusing powder toner images on receiver sheets, for examples images formed by an electrographic process, typically include a fuser roller and a pressure roller. In general, the fuser roller is heated, and the pressure roller is not heated. The pressure roller is subject to contamination, for example, from toner and paper residue. Most pressure roller contamination is cleaned by subsequent prints, as they pass through the fusing nip. Some pressure roller contamination however, remains on the pressure roller after a print run is completed. Pressure roller contamination that remains on the pressure roller after a print run can cause image defects, or even jams on subsequent print runs if the contamination is sufficiently severe. 
   It has thus been noted that both image defects and jams occur with a higher frequency just after a machine standby period. Heating of the fuser roller typically continues during standby. In the case of an externally heated fuser, heating of the fuser roller is accomplished through rotating contact with the heater rollers and pressure roller. This rotating contact also heats the pressure roller. Contamination is more easily removed from a hot pressure roller, and tends to be removed in an uncontrolled and incidental manner leading to image defects and jams. 
   A primary source of pressure roller contamination is cold offsetting from the backside of a print onto the pressure roller. Offset increases as run length increases since cold offset tends to increase as temperature is decreased, and pressure rollers are typically unheated during a run. Heating the pressure roller will reduce pressure roller contamination, but is expensive and may cause side effects such as print “bricking” and excessive curl since the prints receive more heat. 
   Since pressure roller contamination accumulates during continuous runs, and is inadvertently removed after standby periods, the higher the ratio of run length to standby, the higher the level of pressure roller contamination. Thus, as print rate and run length increase, the probability of pressure roller contamination also increases. 
   SUMMARY OF THE INVENTION 
   Methods and apparatus are provided of cleaning a pressure roller that cooperates with a fuser roller in fusing toner images, comprising cleaning the pressure roller only during standby with a cleaning pad mounted adjacent the pressure roller in an electrographic printer. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  presents a cross-sectional view of a pressure roller, paper entrance guide, and load arm assembly, with a cleaning pad according to an aspect of the invention. 
       FIG. 2  presents a cross-sectional view of a fuser roller, pressure roller, and an entrance guide with a cleaning pad assembly according to an aspect of the invention, disengaged. 
       FIG. 3  presents a cross-section view of a fuser roller, pressure roller, and an entrance guide with a cleaning pad assembly according to an aspect of the invention, engaged. 
       FIG. 4  presents an enlarged cross-sectional view of a pressure roller and cleaning pad, according to an aspect of the invention. 
       FIG. 5  presents a perspective a paper entry guide having a cleaning pad, according to an aspect of the invention. 
       FIG. 6  presents an enlarged perspective view of a cleaning pad, according to an aspect of the invention. 
   

   DETAILED DESCRIPTION 
   Various aspects of the invention are presented in  FIGS. 1–6 , which are not drawn to any particular scale, and wherein like components in the numerous views are numbered alike. Referring now to  FIG. 1 , a cross sectional view of a portion of a fuser comprising a paper entrance guide  102 , a pressure roller  104 , and a pressure roller load arm  106 . With reference to  FIGS. 2 and 3 , a load is applied to the pressure roller load arm  106  during normal operation of the fuser that forces the pressure roller  104  against a fuser roller  108  with a predetermined force, as is known in the art. The load arm  106  causes the pressure roller  104  to pivot around a pressure roller load arm pivot  116 . The pressure roller  104  is formed from metal, and the fuser roller  108  is formed from a metal core  110  covered by an elastomeric blanket  112 . The paper entrance guide  102  comprises a cleaning pad assembly  114  configured to clean the pressure roller  104 . The paper entrance guide  102  is an existing structure presently used to guide paper into a particular location about the fuser roller  108  so that paper wrinkles and other paper defects are reduced. The cleaning pad assembly  114  could be mounted other places as well. 
   Referring now specifically to  FIG. 2 , a cross-sectional view of the fuser roller  108 , pressure roller  104 , and the entrance guide  102  with the cleaning pad assembly  114  disengaged is presented. According to a preferred embodiment, the entrance guide  102  is configured to pivot around the pressure roller load arm pivot  116 , and the cleaning pad assembly  114  is mounted on the entrance guide  102  and pivots with the entrance guide  102  around the pressure roller load arm pivot  116 . In the embodiment presented, the entrance guide  102  comprises an arm  118 . A solenoid  120  is mounted in a fixed position relative to the entrance guide  102 , and has a plunger  122  in contact with the arm  118 . The entrance guide  102  guides sheets into a nip formed between the pressure roller  104  and the fuser roller  108 . 
   Referring now to  FIG. 3 , a cross-sectional view of the fuser roller  108 , pressure roller  104 , and the entrance guide  102  with the cleaning pad assembly  114  engaged is presented. The cleaning pad assembly  114  preferably has a pliable pad  124  that conforms to the surface of the pressure roller  104 . The structure of the cleaning pad assembly  114  will be discussed in more detail. The cleaning pad assembly  114  is engaged by actuating the solenoid  120 , which extends the plunger  122  against the arm  118 , thereby causing the entrance guide  102  and cleaning pad assembly  114  to rotate around the pressure roller load arm pivot  116 . The solenoid generates a force adequate to clean the contamination off the pressure roller  104  in a fixed amount of time. 
   According to one aspect of the invention, a method of cleaning a pressure roller  104  that cooperates with a fuser roller  108  in fusing toner images is provided, comprising cleaning the pressure roller  104  only during standby with a cleaning pad  124  mounted adjacent the pressure roller  104  in an electrographic printer. As used herein, “standby” means a period of time wherein the electrographic printer is able to print images, but is not printing images, and the fuser roller  108  and pressure roller  104  are engaged with each other and rotating, and the fuser roller  108  is heated in order to maintain it at an elevated temperature suitable for fusing toner images. The load on the pressure roller load arm  106  may be decreased during standby in order to extend life of the fuser roller  108 . Thus the pressure roller may be cleaned while the fuser roller  108  is heated and rotating and the pressure roller  104  is rotating, without passing sheets through the pressure roller  104  and the fuser roller  108 . According to a preferred embodiment, the cleaning is initiated and stopped during this period of time. The cleaning period may be subsequent to an initial period during standby wherein the fuser roller  108  is heated in order to heat the pressure roller  104  so the pressure roller  104  is hotter than at the beginning of the initial period. Alternatively, the cleaning period may be prior to the initial period. 
   Referring now to  FIG. 4 , an enlarged cross sectional view of the cleaning pad assembly  114  and pressure roller  104  is presented. The cleaning pad assembly  114  comprises support  126 . A pad holder  128  is mounted to the support  126  with a gimble pin  130  so that it can rotate about the gimble pin  130 . In this example, the gimble pin  130  comprises a screw and sleeve. The gimble pin  130  acts as a pivot and allows the pad holder  128  to rotate about an axis  132  defined by the gimble pin  130 , thereby allowing the cleaning pad  124  to align itself longitudinally with the surface of the pressure roller  104 . The gimbaling eliminates the need for tight tolerances and distributes the load evenly across the cleaning pad  124 . The cleaning pad  124  is adhesively bonded to a slotted bar  134 , and the pad holder  128  comprises mounting pins  136  that extend into the slotted bar  134 , thereby registering the slotted bar  134  with the pad holder  128 . 
   Referring now to  FIG. 5 , a perspective view of the cleaning pad assembly  114  and paper entrance guide  102  is presented. The cleaning pad assembly  114  comprises a pair of brackets  138  that attach the support  126  to the paper entrance guide  102 , preferably rigidly. Each bracket  138  comprises a pivot hole  117  that receives a corresponding pivot  116 . The support  126  comprises an access hole  131  so the gimble pin  130  may be reached with a tool for detachment. The pad holder  128  comprises one or more gimble pin holes  129  (shown in phantom) that receive the gimble pin  130 . 
   Referring now to  FIG. 6 , an enlarged perspective view of the slotted bar  134  and pad  124  is presented. The slotted bar  134  comprises a slot  135  similar to a keyway. 
   In a certain embodiment, the cleaning pad  124  is a replaceable polyaramide needled felt pad, 0.125 inch thk.×0.25 inch wide×14.75 inch long, bonded to the slotted bar  134 , which is metal. A suitable fiber is Nomex® (E. I. Dupont and de Nemours, &amp; Co.) polyarimide fiber. A suitable polyaramide fiber pad material is available from BMP America, Inc., of Medina, N.Y., as catalogue number CX-18.5-FPES2. The pad, after bonding to the slotted bar  134 , is precompressed at 300° F. for 1 minute with a 25 pound load, and the exposed surface is singed to remove loose fiber ends. The slotted bar  134  is slid lengthwise into the pad holder  128 . 
   The Solenoid exerts a minimum force of 6 lbs. This force is magnified by 3.5 times through the principal of mechanical leverage, thereby providing a minimum of 21 lbs. distributed across a 14.5 inch long cleaning pad  124 . To enable immediate cleaning the pad is engaged for 15 seconds immediately after completion of a job. This is sufficient for cleaning during short standby periods, even though pressure roller  104  is not at an optimum temperature for cleaning because the temperature of the pressure roller tends to decrease while the paper stream is passing between the pressure roller  104  and the fuser roller  108  (note that the pressure roller  104  is heated secondarily by the fuser roller  108  and the paper stream acts like an insulator between the two). The cleaning pad  124  is then disengaged for 245 seconds, which gives the fuser roll  108  time to heat the pressure roller  104  time to heat back to approximately 290° F. The higher temperature has been shown to clean easier than a cooler pressure roller. The temperature of the pressure roller  104  can drop as much as 90° F. during a paper run. After 245 seconds a second 15 second cleaning cycle is initiated wherein the cleaning pad  124  is pressed against the pressure roller  104 . In order to reduce unnecessary, frequent, immediate cleaning cycles, a 1000 sheet minimum run requirement may be implemented before these actuations occur. We also abandon any cleaning cycle, if a new job gets started before the cleaning cycle is done, so as not to impact productivity. Periodically replacing the cleaning pad  124  is desirable. 
   Although the invention has been described and illustrated with reference to specific illustrative embodiments thereof, it is not intended that the invention be limited to those illustrative embodiments. Those skilled in the art will recognize that variations and modifications can be made without departing from the true scope and spirit of the invention as defined by the claims that follow. It is therefore intended to include within the invention all such variations and modifications as fall within the scope of the appended claims and equivalents thereof.