Abstract:
A pressure member is provided suitable for use in an image forming system. The pressure member includes a core surrounded by a sleeve. The inner perimeter of the sleeve is large than the outer perimeter of the core to enable the sleeve to be removed and replaced easily when worn out.

Description:
TECHNICAL FIELD 
     The present invention relates generally to printing in image forming systems, and specifically relates to pressure members in such systems. 
     BACKGROUND OF THE INVENTION 
     Conventional image forming systems, such as toner imaging systems, where a latent charge image is developed with a pigmented toner before being transferred to a substrate, such as a sheet of paper, are widespread in the office and home. The latent image is formed on an imaging member with a charge-emitting device, and then developed with the toner. The developed image is ultimately transferred to the substrate to form a printed image. 
     Many technologies exist for forming a latent charge image, including optical image projection onto a charged photoconductive belt or drum, charging a dielectric member with an electrostatic pin array or electron beam, and charge projection from an ionographic print cartridge or from a plasma generator. Once a latent image is formed by any of these methods, the image may be developed with a toner before transferring the image to the substrate. 
     The developed image is transferred from a transfer member to the substrate. In some image forming systems the imaging member is also the transfer member, which transfers the developed image directly onto the substrate. In other image forming systems, the imaging member first transfers the developed image to a distinct transfer member, which then transfers the developed image to the substrate. 
     In general, there are at least three methods of producing the final image on a substrate. In the heating method, the toned image is heated to dry or fix the image on the substrate during the final stage of printing. In the transfusing method, the toned image is simultaneously transferred to and fixed on the substrate in a melted or fused state. By controlling the temperature, the relative tackiness, or the self-adherence of the heated toner, may be made to vary to achieve optimal transfer of the image. Finally, in the transfixing method, the final image may be produced by applying pressure, instead of heat, on either side of the substrate to transfer the image from the transfer member to the substrate. This pressure may be applied with a heavy pressure roll. Other methods of producing the final image on the substrate may include a hybrid of these methods, where, for example, some heat and pressure may be applied to transfer the image. 
     In the aforementioned methods of producing the final image on a substrate, pressure members, such as pressure rolls, can play an important role. The substrate is sandwiched between the transfer member and a pressure member at the transfuse nip. The transfer member applies a force to one side of a substrate while the pressure member applies a force on the opposite side of the substrate, thereby facilitating the transfer of the image from the transfer member to the substrate. The pressure exerted by the pressure member can exceed 2000 lb/in 2  to effectively transfer the image onto the substrate. The pressure member should ideally be able to withstand these high pressures, and be rigid in order to apply this pressure evenly. 
     To withstand the high pressure, and provide rigidity, the pressure member can weigh upwards of 40 lbs., and be composed of a metal or alloy, such as an aluminum alloy or steel. Despite the strength of the constituent materials of the pressure member, however, the surface of the pressure member can be damaged by, for example, wrinkled paper passing through the transfuse nip. This type of damage is more likely when the substrate is a continuous web instead of a cut sheet. When the web mistracks, wrinkles can develop in the paper. These wrinkles can cause permanent deformation of the pressure member due to the high pressure, thus impairing printing quality. 
     SUMMARY OF THE INVENTION 
     To solve the aforementioned problems, a pressure member having a sleeve is provided suitable for use in an image forming system. The pressure member includes a core surrounded by the sleeve. The inner perimeter of the sleeve is larger than the outer perimeter of the core to enable the sleeve to be removed and replaced easily when worn out. Replacing the sleeve, instead of the entire, and much heavier, pressure role facilitates the maintenance of the image forming member, and reduces costs. 
     In particular, a pressure member suitable for use in an image forming system is provided. The member includes a core, and a sleeve removably and replaceably disposed around the core. The core may have an outer perimeter, and the sleeve may have an inner perimeter such that the inner perimeter of the sleeve is larger than the outer perimeter of the core to permit the sleeve to be removed from the core and replaced by a new sleeve. The inner perimeter of the sleeve may be about 2% larger than the outer perimeter of the core. At least one of the core and the sleeve may be formed of a metallic alloy, such as steel and/or aluminum alloy. 
     The core may include a cylinder and the sleeve may include a coaxial cylindrical shell disposed around the cylinder of the core, the inner circumference of the cylindrical shell being larger than the circumference of the cylinder of the core. The core may further include a flange formed at one end thereof to prevent the sleeve from separating from the core at that end. 
     Also provided below, suitable for use in an imaging forming system, is a pressure member including a core having a periphery, and a sleeve disposed about the core in intimate facing contact with only a portion of the periphery of the core, thereby allowing removal of the sleeve from the core. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of an image forming system having a pressure member according to the teachings of the present invention. 
     FIG. 2 is a schematic representation of a pressure member according to the teachings of the present invention. 
     FIG. 3 is a schematic representation of a side view of a pressure member according to the teachings of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A pressure member suitable for use in an image forming system is described herein. Image forming systems include electrophotographic, electrostatic or electrostatographic, ionographic, ink-jet, and other types of image forming or reproducing systems that are adapted to capture and/or store image data associated with a particular object, such as a document. The system of the present invention is intended to be implemented in a variety of environments, such as in any of the foregoing types of image forming systems, and is not limited to the specific systems described below. 
     Referring to FIG. 1, an image forming system  10  is shown including a pressure member  12 . The image forming system  10  includes an imaging center  14  and an imaging and transfer member  16 . The system  10  further includes an image developer station  18  having a magnet roll  20 . 
     The imaging center  14  has a charge-emitting device  15 , such as an electron beam imaging head, for forming a latent image on a dielectric surface of the imaging and transfer member  16 . The latent image may then be developed with toner particles from the magnet roll  20 . The image developer  18  encases the magnet roll  20 , and houses and conditions the toner prior to the application of the toner on the imaging and transfer member  16 . The developed image may then be transferred to a substrate  22 , such as a sheet of paper, at a transfuse nip  24  formed between the imaging and transfer member  16  and the pressure member  12 . 
     The image forming system  10  shown in FIG. 1 is of the type where the imaging member, the device on which the latent image is formed, and the transfer member, the device that directly transfers the developed image to the substrate, are coincident. Thus, the imaging and transfer member  16  functions as both a device to form an image thereon, and as a device to transfer the image onto the substrate  22 . In other embodiments, the imaging member may first transfer the developed image onto a distinct transfer member, before the transfer member transfers the image to the substrate. The distinct transfer member can be a drum, or belt, for example. 
     Referring to FIG. 2, a pressure member  12  consistent with the principles of the present invention is shown. A transfuse nip  24  is formed between the imaging and transfer member  16  and the pressure member  12 . The pressure member  12  includes any device that may be used in an image forming system, which applies pressure to an object to facilitate the task of forming an image on a substrate. For example, the pressure member can be used to apply pressure to the substrate at the transfuse nip, while the transfer member applies an opposing pressure, to facilitate the transfer and/or fusing of the image to the substrate. The pressure member  12  includes a core  26 , and a sleeve  28  removably and replaceably disposed about the core  26 . The core  26  has an outer perimeter  30 , and the sleeve  28  has an inner perimeter  32 . The inner perimeter  32  of the sleeve  28  is larger than the outer perimeter  30  of the core  26 . In one embodiment, the inner perimeter  32  of the sleeve  28  is about 2% larger than the outer perimeter  30  of the core  26 . In one example, a 1.5 inch diameter sleeve was fitted on a core that had a diameter that was 0.03 inches smaller. The core  26 , and the sleeve  28  may include a metallic alloy, such as an aluminum alloy, or steel. 
     In one embodiment of the present invention, the core  26  includes a cylinder  34  and the sleeve  28  includes a coaxial cylindrical shell  36 , resembling a pipe with open ends, disposed around the core  26 . The inner circumference  32  of the cylindrical shell  36  is larger than the circumference  30  of the cylinder  34  of the core  26 . 
     The pressure member  12  helps transfer and fuse the developed image from the imaging and transfer member  16  onto the substrate  22  by applying a force to one side of the substrate  12 , while the member  16  applies a force on the opposite side of the substrate at the transfuse nip  24 . As the substrate passes through the transfuse nip  24 , the simultaneous forces exerted at the nip  24  by the member  16  and the pressure member  12  help to pressure fuse the developed image onto the substrate  22 . 
     Wear and tear on the pressure member  12 , such as deformations on the outer surface of the sleeve  28  caused by wrinkles in the substrate, eventually results in impaired print quality. Instead of replacing the entire pressure member  12 , the pressure member  12  is adapted to allow replacement of just the sleeve  28 . Because the inner circumference  32  of the cylindrical shell  36  of the sleeve  28  is larger than the circumference  30  of the cylinder  34  of the core  26 , it does not require much effort to remove the sleeve  28  from the core  26 , and to replace it with a new sleeve. These features obviate the need to replace the entire pressure member  12 , which can weigh upwards of 40 lbs. There is therefore a savings in both effort and materials, and hence cost, by employing the pressure member of the present invention. 
     Referring to FIG. 3, a side view of a pressure member  12  consistent with the teachings of the present invention is shown. The pressure member  12  includes a core  26  and a sleeve  28  removably and replaceably disposed around the core  26 . The core  26  includes a cylinder  34  and the sleeve  28  includes a coaxial cylindrical shell  36  disposed around the core  26 . The inner circumference  32  of the cylindrical shell  36  is larger than the circumference  30  of the cylinder  34  of the core  26 . The core  26  further includes a flange  38  disposed on a surface of the core to prevent the sleeve  28  from inadvertently, or accidentally separating from the core  26 . 
     In operation, a latent image is formed on the imaging and transfer member  16  by a charge-emitting device included in the imaging center  14 . The latent image is developed on the imaging and transfer member using toner particles from magnet roll  20  included in the image developer  18 . Next, the imaging and transfer member rotates to bring the developed image to the transfuse nip  24  formed between the imaging and transfer member  16  and the pressure member  12 . As the substrate  22  passes through the nip  24 , the imaging and transfer member  16  and the pressure member  12  rotate and exert pressure on the two sides of the substrate  22 . The pressure facilitates the transfer of the developed toner form the imaging and transfer member  16  to the substrate  22 . As can be seen in FIG. 2, when in operation, the sleeve  28  is in intimate contact with the core  26  near the nip and not at other locations. 
     When the pressure member  16  becomes worn, the sleeve  28  alone need be replaced. Because the inner circumference  32  of the cylindrical shell  36  of the sleeve  28  is larger than the circumference  30  of the cylinder  34  of the core  26 , it does not require much effort to remove the sleeve  28  from the core  26 , and to replace it with a new sleeve. 
     It should be understood that although the above description has described the use of pressure rolls in transfuse nips, where some heating may be involved to fuse the image onto the substrate, the use of pressure roles consistent with the principles of the present invention can also be used in transfix nips. In transfix nips, pressure is mainly used to transfer the image to the substrate. 
     Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments and methods described herein. Such equivalents are intended to be encompassed by the scope of the following claims.