Patent Publication Number: US-7215918-B1

Title: Fuser roller with improved crack resistance

Description:
FIELD 
   This invention relates, generally, to image-forming machines and methods and, more specifically, to the fusing systems in an electrophotographic reproduction machine. 
   BACKGROUND 
   Electrophotographic image-forming machines are used to transfer images onto paper or other medium in both printing and facsimile systems. Generally, a photoconductor is selectively charged and optically exposed to form an electrostatic latent image on the surface. Toner is deposited onto the charged photoconductor surface. The toner has a charge, thus it will adhere to the photoconductor surface in areas corresponding to the electrostatic latent image. The toner image is transferred to the paper or other medium. The toned paper is heated by a fuser roller system for the toner to fuse to the paper. The photoconductor is then refreshed—cleaned to remove any residual toner and charge—to make it ready for another image. The imaged paper is then passed to a document output collection area or tray where the user collects the finished, permanently imaged paper or documents. 
   The fuser rolls used in these image-forming systems are usually driven by a keyed hub that rides in a slot at the end of the fuser roll. The key drives the fuser roll which is made up of an aluminum core and a coating such as Teflon® (a trademark of DuPont); sometimes a small stainless steel limit stop is attached to the slot. When the key drives the fuser roll, it transfers the load to the fuser roll core causing it to rotate. Cracks forming after extended use in the fuser roll have been frequently experienced which eventually reduces the useful fuser roll life and requires replacement. After some investigation, it has been found that this cracking initially occurs in the upper region of the drive slot primarily because of the substantial load transferred to the fuser core slot during rotation and subsequent frequent braking of the fuser roll. 
   This cracking at the fuser roll slot which occurs in all sizes of fuser rolls has become a significant problem and results in frequent fuser roll replacement. It is not uncommon for fuser rolls to be recoated with Teflon® (or other coating) after the initial coating is worn or damaged. Sometimes this coating is replaced on the same fuser roll core two or three times. Extending the useful life of the relatively expensive core has become a high priority since cost effectiveness is always a concern. The load placed on the slot by the drive key with sudden stopping of the rotation plus the sometimes high temperatures used during fusing have accelerated the formation of cracks and deterioration of the core around the slot. Also it has been determined that the relatively small dimensions of the prior art slots in fuser rolls makes the cracks caused by stress more likely to occur. 
   SUMMARY 
   It has now been found that if the drive slot is machined with larger dimensions (or radii) this will help reduce points of stress concentration. Also in an embodiment, replacing the prior art stainless steel limit stop with a stainless steel drive yoke will further reduce these points of stress or load. This yoke transmits the drive load over a larger area and also transmits the braking load over a larger area when the roll is stopped. These improved embodiments will eliminate the cracking and breaking experienced in the existing fuser roll designs, thereby increasing fuser roll life and preventing ultimate damage to the fuser roll drive mechanism. 
   In an embodiment, the prior art slots are increased at least 1½ times their original dimensions. The terms “larger”, “enlarged” or “expanded” slot size means a slot increased at least 1½ times that size of the original standard or currently used fuser roll slots up to a suitable effective size. A specific numerical increase is difficult to define since several varied size of fuser rolls are used; some are about ten (10) inches long and others extend to about 24 inches long. The normal or standard prior art slot, for example, in the fuser rolls that are about 24 inches long are about ⅝ inch long and about 5/16 inch wide. Expanding this slot in several rolls of an embodiment to about 1 inch long and about ⅜ inch wide has significantly reduced the cracking experienced in prior art slots. A key, therefore, is to expand the seat at least about 1½ times its original or standard dimensions in all size fuser rolls to transmit the drive and braking load over a larger area. The upper limit of expansion is any suitable size that effectively reduces or eliminates cracking around the slots. This larger radius or larger dimensions will provide additional stress relief to this slot area of the fuser roll that is prone to cracking and fractures. This increase of at least 1½ the original slot dimensions will distribute the load forces along a wider surface area and will reduce stress points. Also in all embodiments, it is important that the slot be machined so that rounded contours are provided on the closed portion of the slot. As used herein “rounded” portion or end includes inverted U-shaped slots, inverted key hole slots and other forms where the slot end (opposite the slot opening end) is rounded. This will provide stress relief over prior art cornered slots. 
   The larger slot, together with either or both: A. a wraparound yoke and B. at least two lugs on both sides of the slot (as shown in the drawings) significantly reduces cracking of the drive slot of fuser rolls. 
   Another embodiment combines a larger slot with a stainless steel (or other suitable) wraparound drive yoke that contacts both sides of the drive slot. This yoke replaces the current stainless steel limit stop which in the prior art is fitted on one side of the drive slot. This combination of drive yoke with a larger dimension rounded slots will provide excellent stress relief to this vulnerable area of the fuser roll. The yoke in one embodiment will match the contour of the drive slot. 
   In other embodiments where cost is a primary consideration, limit stops or lugs are used on both sides of the expanded larger slot, one to apply the load to the roll for driving and the other to apply the load to the roll for braking. 
   The increased larger slots can be machined to be circular, keyhole shaped or any other suitable shape having a rounded end. Using slots and yokes absent corners is helpful in reducing and eliminating cracks. For example, inverted u-shaped slot and u-shaped yokes alone or in combination will provide excellent resistance to cracking. A u-shaped slot with an attached drive lug has also been found to provide excellent results. Keyhole slots and corresponding keyhole yokes have shown to provide maximum crack protection. This wraparound keyhole shaped yoke with a large radius of a rounded section which follows the substantial contour of a keyhole shaped slot has been shown to be very effective. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a prior art fuser roll having a conventional drive slot. 
       FIG. 2  illustrates an embodiment of the present invention where a larger and expanded slot is used in the fuser roll. 
       FIG. 3A  illustrates an expanded unshaped slot with a wraparound yoke attached to it.  FIG. 3A  shows the machined slot ready to accept the drive yoke.  FIG. 3B  illustrates an enlarged view of the fuser roll slot yoke design of  FIG. 3A .  FIG. 3B  shows the machined slot depicted in  FIG. 3A  with the drive yoke installed. 
       FIG. 4A  illustrates a keyhole slot having outside supporting lugs connected thereto.  FIG. 4A  shows the machined slot ready to accept dual drive lugs.  FIG. 4B  illustrates an enlarged view of the fuser roll slot double lug design of the slot of  FIG. 3A .  FIG. 4B  shows the machined slot depicted in  FIG. 4A  with the dual drive lugs installed. 
       FIG. 5  illustrates the keyhole slot with dual drive lugs embodiment from an inner fuser roll view. 
   

   DETAILED DISCUSSION OF DRAWINGS AND PREFERRED EMBODIMENTS 
   In  FIG. 1  embodiment an existing prior art fuser roll smaller slot  1  is shown with cracks  2  which frequently occur in the prior art slots  1 . A stainless steel limit stop  3  is shown attached to the outside of one side of slot  1  as presently used in existing or current fuser rolls  4 . Cracking generally occurs in the region indicated in the drawing  FIG. 1  sometimes on both sides of slot  1 . These cracks have usually occurred at points of stress concentration caused by the drive load. 
   In  FIG. 2  an embodiment of the present invention is shown whereby the enlarged slot  5  has dimensions substantially enlarged over the smaller prior art slot of  FIG. 1 . Notice the absence of sharp corners in enlarged slot  5  and the larger length  6  and radius of upper keyhole  7  with rounded section  22 . The slot  5  is located at the end of fuser roll  8  which usually has an aluminum core  9  and a Teflon® (or rubber Teflon) coating  10 . This enlarged drive slot  5  has been machined with a longer length  6  and a much larger radius  7  in rounded portion  22  to help reduce stress concentration to this area of the fuser roll  8  that is prone to cracking. On the end of the fuser roll opposite to the location of the driver slot  5  is an idler slot (not shown in drawings). This disclosure is concerned with the driver slot  5  since cracking occurs at this location and rarely at the idler slot location; however, the driver slot contour may also be used in the idler slot, if desirable. 
   In  FIGS. 3A and 3B  an embodiment of an expanded u-shaped slot  11  with a wraparound yoke  12  attached thereto is shown. The reinforcing driver yoke  12  ( FIG. 3B ) that follows the contour of the slot  11  will substantially reduce cracking. In  FIG. 3A , the slot  11  has two holes  23  for attachment of yoke  12  thereto. The yoke  12  transmits the drive load over a larger area and also transmits the braking load over a larger area when the fuser roll  8  is suddenly stopped. This improved drive and braking configuration will eliminate the cracking and breaking experienced in the prior art and existing designs, thus increasing fuser roll  8  life and preventing damage to the fuser roll drive mechanism. In  FIG. 3B , the yoke  12  is attached with screws  13  and  14  to the area surrounding u-shaped slot  5  with an open end  21  and a rounded section  22  and extends inwardly with projections  15  to further strengthen the drive slot  11  which when in contact with a drive key will eliminate the cracking and life reduction of the fuser roll  8 . As earlier noted, both the enlarged slot  5  and the yoke  12  alone or in combination both with a rounded portion  22  ensures an effective anti-cracking embodiment. The yoke  12  may be made from stainless steel or any other suitable material. Generally, core  9  is made from aluminum. 
   In  FIGS. 4A and 4B  an enlarged keyhole shaped slot  5  with a rounded portion  22  is reinforced by lugs  16  and  17  in  FIG. 4B  which are positioned at the upper section surrounding slot  5 . In  FIG. 4A , two holes  24  are shown for attachment of lugs  16  and  17 . This configuration is one of the most economical yet effective embodiments. Here the inverted enlarged keyhole slot  5  is partially surrounded by lugs or holds  16  and  17  and connected thereto by screws  18  and  19 .  FIG. 4  illustrates this embodiment from the outside of fuser roll  8  while  FIG. 5  illustrates this same embodiment from an inner view of fuser roll  8 . Note that screws  18  and  19  extend through the thickness of fuser roll  8 . The drive key fits through the interior  20  of the core of fuser roll  8 . Slot  5  has an open end  21  and a closed end  22 , the open end  21  being located at the farthest end portion of fuser roll  8 . 
   All of the above described embodiments have a drive slot on one driver end of tubular shaped fuser roll  8 , and an idler slot located on the opposite end of fuser roll  8 . The above embodiments are obviously refer only to the drive slots; the idler slots are used to merely hold the fuser roller position. All of the above slots have on one end an open terminal end portion  21  for entrance of a fuser roll drive key and in the opposite end a rounded portion  22 . The fuser roll  8  of the above embodiments is useful in toner fusing systems of any applicable marking system. 
   It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.