Patent Application
20090180819
This invention relates to paper handling systems, and more specifically, to stripping mechanisms useful in roll or belt assemblies.
While the present invention can be effectively used in a plurality of paper handling systems that utilize finger stripping elements to remove paper from rolls or belts, it will be described for clarity as used in electrostatic marking systems, such as electrophotography.
Generally, in a commercial electrophotography marking or reproduction apparatus (such as copier/duplicators, printers, multifunctional systems or the like), a latent image charge pattern is formed on a uniformly charged photoconductive or dielectric member. Pigmented marking particles (toner) are attracted to the latent image charge pattern to develop this image on the dielectric member. A receive member, such as paper, is then brought into contact with the dielectric or photoconductive member, and an electric field applied to transfer the marking particle developed image to the receiver member from the dielectric member. After transfer, the receiver member bearing the transferred image is transported away from the dielectric member to a fusion station, and the image is fixed or fused to the receiver member by heat and/or pressure to form a permanent reproduction thereon. The receiving member passes between a pressure roll and a heated fuser roll or element.
An electrographic fuser element generally includes metallic substrates, such as aluminum, an elastomeric cover layer, usually a silicone, and at least one coating over the silicone, generally made of a fluoropolymer, such as Teflon® (a trademark of DuPont).
Sometimes copies made in Xerographic or electrostatic marking systems have defects caused by improper fusing of the marking material or the fuser itself. The incomplete fusing can be the result of many factors, such as defects in the pressure or fuser rolls. Defects in the fuser rolls can be caused by improper compression set properties resulting from extended use or improper coating of the fuser substrates during manufacture. Another cause of defects in the fuser roll is caused by paper stripping fingers that gouge the fuser roll surface.
This invention and its various embodiments are concerned with improving the performance and extending the life of these coated fuser elements, including fuser rolls and other configurations. While for clarity the term “fuser roll structure or member” will be used throughout this disclosure and claims, any suitable fusing configurations are intended to be included, such as rolls, belts, and pressure members.
There is a tendency during the fusing step for the print substrate to remain tacked to the fuser roll after passing through the nip between the fuser roll and the pressure roll despite use of low surface energy materials. If this occurs, the tacked print substrate does not follow the normal substrate path but rather continues in an arcuate path around the fuser roll, which eventually causes a paper jam. This then requires an operator to manually remove the jammed paper before any subsequent imaging cycle can proceed. In an attempt to correct this, it has been common practice to ensure that the print substrate is stripped from the fuser roll downstream of the fuser nip. One approach is the use of a plurality (4-6) of stripper fingers placed in angular spring contact with the surface of the fuser roll in order to strip the print substrate from the fuser roll. This practice often suffers from difficulties with respect to both fuser roll life and print quality. To ensure an acceptable level of stripping, it is frequently necessary to load such a stripper finger against the fuser roll with such a force and at such an attack angle that there is a tendency to peel the silicone rubber surface off the fuser roll, thereby damaging the roll to such an extent that it must be replaced or can no longer effectively function as a fuser roll.
Stripping copies off rubber covered rollers is not easy. The balance between tip load and attach angle is critical to roll and finger wear and failure to strip copies or worse yet, digging into the soft rubber. For years companies have used a steel strip as a finger that deforms under stripped paper load or a rigid plastic design that does not significantly change shape as a function of load. These types of fingers tend to damage the rubber on covered rolls with great ease during jamming or hard stripping situations, rigid fingers are much worse.
Embodiments of the present invention involve the use of steel stripper finger with fuser roll contact skiis positioned such that the applied load during an excessive stripping condition or a jam condition is supported by the skiis against the fuser roll thereby preventing the finger tip from damaging the soft roll surface. The purpose of the metal ski feature (which could be made of other materials) is to lift the stripping tip off the fuser roll when paper loads the finger and deforms the steel supporting beam. The skiis extend below the surface of the finger tip and have a configuration similar to a bent elbow, with the rounded elbow portion enabled to contact the fuser roll surface. The steel provides flexibility to auto adjust to paper loads while the ski shape and position can eliminate roll damage. The critical shape on the roll side of the finger is a smooth rounded shape approximately 6 mm behind the tip that contacts the fuser roll with small deflections of the steel support. The use of the metal as a finger material also reduces the cost of the part due to design simplification and manufacturing approach and reduced wear rate of the finger tip.
This invention provides, as above noted, a fuser stripper finger design that prevents a common problem in Teflon® over Silicone (TOS) rolls. Under hard stripping conditions or during paper jams, paper exerts enough force on stripper fingers to gouge the soft TOS roll rendering it useless. The disclosed design prevents this gouging via tab like ski features that contact the roll during a jam and deflect the sharp tip away from the surface of the roll. An additional hump feature is provided to minimize the width of any stripper finger marks on prints. The finger is made of steel and coated in a release material (possibly Teflon®) rather than the traditional all plastic design.
For years companies have used a steel strip as a finger that deforms under stripped paper load. The stripping of a copy occurs in two stages. First and most challenging is to get the leading edge of the copy off the fuser roll when it is adhered with toner. After the leading edge is stripped, the finger is simply peeling the body of the sheet off the roll, again with toner as the adhesive. The magnitude of the stickiness of the toner is similar to Scotch Tape since a good finger can easily strip it off a cold fuser roll.
To strip the lead edge, the attach angle of the finger (angle from the roll side of the finger to the tangent of the roll at the tip contact point) needs to be about 15 degrees and the load about 25 grams. (These are approximate values and change a little depending on the roll surface and release agent presence). As the paper edge hits the finger tip, it imparts a force to the finger tangent to the roll. The flexible fingers are stiff enough that this loading results in very little shape change and the finger slides between the paper and the roll. The load is trying to increase the curvature of “pre-buckled” column that is fairly short and stiff.
After the lead edge is stripped, the sheet is able to exert a force on the finger that is near radial to the roll or normal to the long axis of the steel strip. Now the loading case is more like a distributed load over a simply supported beam. This radial force comes from the image on both sides of the finger pulling the paper towards the roll while the finger is trying to guide it away from the roll. Or, many times higher loads are exerted on the finger by a jammed sheet or sheets of paper. The effect of the radial load is to increase the tip load and in the case of a flexible finger, reduce the attach angle by causing the simply supported beam to bend more.
As the sheet is stripped, the attach angle is fairly high and the load fairly low, but after the lead edge is stripped, if high stripping forces are present, the tip load will go up but the attach angle goes down in a proportional manner. Reducing attach angle as the load goes up is key to preventing roll gouging and helpful in reducing roll wear. In the case of a jam or other sources of very high load, deformation continues until the ski lifting feature contacts the fuser roll and lifts the tip off the roll so it cannot damage or wear the soft roll surface. As the metal supporting beam deforms the attach angle of the tip reduces about 5 degrees and then the support ski contacts the roll and subsequent deformation of the steel causes the sharp tip to lift off the roll completely. It is then unable to damage the roll surface even as paper loads on the finger get large, such as during a jam. This has been demonstrated on the fuser system to prevent roll damage that is frequent if this feature is not present.
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In the disclosure and claims the listed terms or phrases will have the following meaning: The stripper finger has a flat configuration-means, a flexible bar-like configuration with a thickness of from about 0.05 to 0.2 mm. The skis are located behind said tip-means; the elbow shaped skiis are positioned from 2 to −8 mm behind said tip of the stripper finger; front end or tip or terminal portion means that tip that contacts the paper carrying surface, initially exert pressure-means before the skiis contact the surface.
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.
