Fuser roller with improved crack resistance

This is a fuser roll having a driver slot having a large rounded upper portion to reduce cracking caused by drive load stresses. Around the slot is a reinforcing driver yoke to add additional resistance to cracking. Two reinforcing lugs can be used in place of the driver yoke.

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.

DETAILED DISCUSSION OF DRAWINGS AND PREFERRED EMBODIMENTS

InFIG. 1embodiment an existing prior art fuser roll smaller slot1is shown with cracks2which frequently occur in the prior art slots1. A stainless steel limit stop3is shown attached to the outside of one side of slot1as presently used in existing or current fuser rolls4. Cracking generally occurs in the region indicated in the drawingFIG. 1sometimes on both sides of slot1. These cracks have usually occurred at points of stress concentration caused by the drive load.

InFIG. 2an embodiment of the present invention is shown whereby the enlarged slot5has dimensions substantially enlarged over the smaller prior art slot ofFIG. 1. Notice the absence of sharp corners in enlarged slot5and the larger length6and radius of upper keyhole7with rounded section22. The slot5is located at the end of fuser roll8which usually has an aluminum core9and a Teflon® (or rubber Teflon) coating10. This enlarged drive slot5has been machined with a longer length6and a much larger radius7in rounded portion22to help reduce stress concentration to this area of the fuser roll8that is prone to cracking. On the end of the fuser roll opposite to the location of the driver slot5is an idler slot (not shown in drawings). This disclosure is concerned with the driver slot5since 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.

InFIGS. 3A and 3Ban embodiment of an expanded u-shaped slot11with a wraparound yoke12attached thereto is shown. The reinforcing driver yoke12(FIG. 3B) that follows the contour of the slot11will substantially reduce cracking. InFIG. 3A, the slot11has two holes23for attachment of yoke12thereto. The yoke12transmits the drive load over a larger area and also transmits the braking load over a larger area when the fuser roll8is 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 roll8life and preventing damage to the fuser roll drive mechanism. InFIG. 3B, the yoke12is attached with screws13and14to the area surrounding u-shaped slot5with an open end21and a rounded section22and extends inwardly with projections15to further strengthen the drive slot11which when in contact with a drive key will eliminate the cracking and life reduction of the fuser roll8. As earlier noted, both the enlarged slot5and the yoke12alone or in combination both with a rounded portion22ensures an effective anti-cracking embodiment. The yoke12may be made from stainless steel or any other suitable material. Generally, core9is made from aluminum.

InFIGS. 4A and 4Ban enlarged keyhole shaped slot5with a rounded portion22is reinforced by lugs16and17inFIG. 4Bwhich are positioned at the upper section surrounding slot5. InFIG. 4A, two holes24are shown for attachment of lugs16and17. This configuration is one of the most economical yet effective embodiments. Here the inverted enlarged keyhole slot5is partially surrounded by lugs or holds16and17and connected thereto by screws18and19.FIG. 4illustrates this embodiment from the outside of fuser roll8whileFIG. 5illustrates this same embodiment from an inner view of fuser roll8. Note that screws18and19extend through the thickness of fuser roll8. The drive key fits through the interior20of the core of fuser roll8. Slot5has an open end21and a closed end22, the open end21being located at the farthest end portion of fuser roll8.

All of the above described embodiments have a drive slot on one driver end of tubular shaped fuser roll8, and an idler slot located on the opposite end of fuser roll8. 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 portion21for entrance of a fuser roll drive key and in the opposite end a rounded portion22. The fuser roll8of the above embodiments is useful in toner fusing systems of any applicable marking system.