Abstract:
A heated fuser roller that includes an elongated roller and a series of heating wires extending axially through the roller. The heating wires are positioned near the surface of the roller. Voltage is applied from a power source to the heating wires through conductive disks mounted on each end of the roller. A conductive wiper, shoe or other suitable contact device slides along each disk to maintain the electrical connection between the disks and the power source as the roller rotates.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation of application Ser. No. 09/082,359 filed on May 20, 1998, U.S. Pat. No. 6,160,983. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to a fuser for use in an electrophotographic printing device and, more particularly, to a heated fuser roller. 
     BACKGROUND OF THE INVENTION 
     In electrophotographic printing devices, toner particles are used to form the desired image on the print medium, which is usually some type of paper. Once the toner is applied to the paper, the paper is advanced along the paper path to a fuser. In many printers, copiers and other electrophotographic printing devices, the fuser includes a heated fusing roller engaged by a mating pressure roller. As the paper passes between the rollers, toner is fused to the paper through a process of heat and pressure. A variety of different techniques have been developed to heat the fusing roller. One of the most common techniques for heating a fusing roller uses a quartz lamp placed inside the roller. The lamp is turned on to heat the fusing roller during printing. So called “instant-on” fusers were developed to reduce warm-up time, eliminate the need for standby power and improve print quality in single page or small print jobs. U.S. Pat. Nos. 5,659,867, 5,087,946, and 4,724,303 describe instant-on type fuser heaters that utilize a thin walled heated fusing roller. In the &#39;867 patent, the heating element is a group of resistive conductors positioned on the surface of a thin walled ceramic tube. The conductors are overlaid with a glassy coating to provide a smooth exterior surface for the ceramic tube. In the &#39;946 patent, the heating element is a conductive fiber filler material added to the plastic composition that forms the wall of the roller. In the &#39;303 patent, the heating element is a resistance heating foil or printed circuit glued to the inside surface of the thin metal wall of the roller. 
     While these “instant-on” fuser heating techniques may be advantageous because the heating element is near the surface of the roller, substantial changes must be made to conventional fuser roller designs to incorporate both techniques. Hence, these techniques cannot be easily incorporated into the more common fuser roller designs. In addition, these techniques are all designed for hard walled fusing rollers, not for pressure rollers in general and not for the compliant pressure rollers used in many modern fusers. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a heated fuser roller that utilizes a series of heating wires in the outer layer of the roller. The invention was developed as a means to effectively heat the pressure roller in heated pressure fusers without requiring any major modifications or changes to the design of the fuser or the fuser rollers. The fuser roller includes an elongated roller and a plurality of heating wires extending axially through the roller. The heating wires are positioned near the surface of the roller. The heating wires may be embedded in the roller as an integrated component or the heating wires may be inserted into holes that extend axially through the rollers. In one preferred version of this embodiment of the invention, a voltage is applied from a power source to the heating wires through conductive disks mounted on each end of the roller. Each heating wire runs axially through the roller between the disks. A conductive wiper, shoe or other suitable contact device slides along each disk to maintain the electrical connection between the disks and the power source as the roller rotates. 
     The invention may also be embodied in a fuser that includes a pressure roller and a fusing roller. The heating wires are used to heat the pressure roller, the fusing roller, or both. In one preferred version of this embodiment, the fuser includes a conventional heated fusing roller and a heated pressure roller that engages the fusing roller during fusing operations. The heating element in the fusing roller is a quartz lamp. The heating element in the pressure roller includes a series of heating wires extending axially through the pressure roller near the surface of the roller. 
     “Heating wire” or “heating wires” as used in this Specification and in the claims refers generally to all types of elongated resistive conductors. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a representational elevation view of a laser printer. 
     FIG. 2 is a front view of a heated fuser in which heating wires form the heating element in the pressure roller. 
     FIG. 3A is a cross section view taken along the line  3 — 3  in FIG. 2 showing heating wires embedded in the outer layer of the roller. 
     FIG. 3B is a cross section view taken along the line  3 — 3  in FIG. 2 showing heating wires extending through holes formed in the outer layer of the roller. 
     FIG. 4 is a perspective exploded end view and partial cut-away view of one version of the pressure roller shown in FIGS. 2 and 3 in which a solid conductive disk is used as the contact between the heating wires and the voltage source. 
     FIG. 5 is an assembled perspective end view of the pressure roller shown in FIG.  4 . 
     FIG. 6 is an assembled perspective end view of another version of the pressure roller of FIGS. 2 and 3 in which a segmented conductive disk is used as the contact between the heating wires and the source of electrical current. 
     FIG. 7 is an assembled perspective end view of a third version of the pressure roller shown in FIGS. 2 and 3 in which a conductive shoe slides along the disks to maintain the electrical connection between the disks and the power source as the roller rotates. 
     FIG. 8 is a schematic view in which the heating wires in the pressure roller are energized through the same voltage source used to energize the heating element in the fusing roller. 
     FIG. 9 is a schematic view in which the heating wires in the pressure roller are energized and controlled independent of the heating element in the fusing roller. 
     FIG. 10 is a cross section view of an alternative embodiment of the invention in which heating wires form the heating element in the fusing roller. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a laser printer, designated by reference number  10 , that incorporates one embodiment of the present invention. In general, and referring to FIG. 1, a computer transmits data representing an image to input port  12  of printer  10 . This data is analyzed in formatter  14 . Formatter  14  consists of a microprocessor and related programmable memory and a page buffer. Formatter  14  formulates and stores an electronic representation of each page to be printed. Once a page has been formatted, it is transmitted to the page buffer. The page buffer breaks the electronic page into a series of lines one dot wide. This line of data is sent to the printer controller  15 . Controller  15 , which also includes a microprocessor and programmable memory, drives laser  16  and controls the drive motor(s), fuser temperature and pressure, and the other print engine components and operating parameters. 
     Each line of data is used to modulate the light beam produced by laser  16 . The light beam is reflected off a multifaceted spinning mirror  18 . As each facet of mirror  18  spins through the light beam, it reflects or “scans” the beam across the side of a photoconductive drum  20 . Photoconductive drum  20  rotates just enough that each successive scan of the light beam is recorded on drum  20  immediately after the previous scan. In this manner, each line of data is recorded on photoconductive drum  20 . Toner is electrostatically transferred from developing roller  28  onto photoconductive drum  20  according to the data previously recorded on the drum. The toner is thereafter transferred from photoconductive drum  20  onto paper  30  as paper  30  passes between drum  20  and transfer roller  32 . Drum  20  is cleaned of excess toner with cleaning blade  36 . Drum  20  may be completely discharged by discharge lamps  38  before a uniform charge is restored to drum  20  by charging roller  26  in preparation for the next toner transfer. 
     Each sheet of paper  30  is advanced to the photoconductive drum  20  by a pick/feed mechanism  42 . Pick/feed mechanism  42  includes motor driven feed roller  44  and registration rollers  56 . A paper stack  48  is positioned in input tray  50  to allow sliding passage of the top sheet of paper  30  into pick/feed area  40  at the urging of feed roller  44 . In operation, as feed roller  44  rotates, the frictionally adherent outer surface  54  of feed roller  44  contacts the upper surface of paper  30  and pulls it into pick/feed area  40 . As the leading edge of paper  30  moves through pick/feed area  40 , it is engaged between the pair of registration rollers  56 . A ramp  58  helps guide paper  30  into registration rollers  56 . Registration rollers  56  advance paper  30  fully into image area  52  until it is engaged between drum  20  and transfer roller  32  where toner is applied to the paper as described above. Once the toner is applied to paper  30 , it is advanced along the paper path to fuser  34 . Fuser  34  includes a heated fusing roller  60  and a heated pressure roller  62 . As the paper passes between the rollers, toner is fused to the paper through a process of heat and pressure. 
     Referring now to FIGS. 2 and 3, the shafts  60   a  and  62   a  of the fuser rollers  60  and  62  are mounted on bearings (not shown) which are biased to press the fuser rollers  60  and  62  against one another. Fusing roller  60  and pressure roller  62  engage to form a nip  64 , which is best seen in FIG.  3 . Toner is fused to paper  30  in nip  64 . One or both rollers are motor driven to advance paper  30  through nip  64 . As shown in FIG. 3, fusing roller  60  is typically constructed with a metal core  66  and an outer layer  68 . Outer layer  68  is often made of a hard “release” material such as Teflon®. Core  66  is hollow. A quartz lamp or other suitable heating element  70  is positioned inside core  66  along the length of fusing roller  60 . Pressure roller  62  is typically constructed with a metal core  72  and a pliable outer layer  74 . Pressure roller  62  may also include a thin Teflon® release layer (not shown). 
     Referring to FIGS. 2-5, a series of heating wires  76  extend axially along the length of pressure roller  62 . Wires  76  are positioned in outer layer  74  of pressure roller  62 . Heating wires  76  may extend straight along the length of pressure roller  62  as shown in the drawings, or heating wires  76  may form a helical wrap around and along roller  62  or any other form of axial extension that may be necessary to achieve the desired heating profile for roller  62 . Heating wires  76  may be embedded in outer layer  74  as an integrated component as shown in FIG. 3A, or heating wires  76  may be inserted into holes  77  formed axially through outer layer  74  of roller  62  as shown in FIG.  3 B. Although wires  76  should be positioned near the surface  78  of pressure roller  62 , the actual depth of wires  66  in outer layer  74  will depend on the composition of outer layer  74 , the size, number and resistivity of wires  76 , the magnitude of the voltage applied to wires  76 , and the desired temperature profile at nip  64 . For example, it is expected that the application of 220 volts to eighteen 20 gage nickel-chromium wires spaced evenly around the pressure roller at a depth of 2.5 mm in an elastomeric outer layer  74  that is 5 mm thick will be sufficient to heat surface  78  to about 150° C. 
     Voltage is applied to wires  76  from a power source  80  through conductive disks  82 . Conductive disks  82  are attached to the ends  84  of pressure roller  62 . Because conductive disks  82  rotate with pressure roller  62 , a pair of wipers  86  are used to provide the sliding electrical contact between conductive disks  82  and power source  80 . In an alternative embodiment shown in FIG. 7, a conductive shoe  88  rides along a groove  90  in disks  82  to provide the sliding electrical contact between disks  82  and power source  80 . Conductive disks  82  may be constructed as a unitary conductive member, as shown in FIGS. 2-5, or as a series of segments  82   a - 82   f  insulated from one another by insulating members  92 , as shown in FIG.  6 . Conductive disks  82  should be constructed as unitary conductive members when it is desirable to energize all the heating wires  76  at the same time. Conductive disks  82  should be constructed as a series of insulated conductive segments when it is desirable to energize individual heating wires  76  or groups of heating wires  76 . Heating wires  76  in pressure roller  62  may be energized through the same voltage source  80  used to energize heating element  70  in fusing roller  60  at the direction of controller  15 , as shown in FIG.  8 . Or, heating wires  76  can be energized and controlled independent of heating element  70  in the fusing roller  60 , as shown in FIG.  9 . 
     Although the invention has been shown and described with reference to a pressure roller in a laser printer fuser, the invention may be embodied in other components and printing devices. For example, heating wires  76  may be used to heat fusing roller  60 , as shown in FIG. 10, alone or in combination with the heated pressure roller described above. Outer layer  68  of fusing roller  60  is somewhat thicker in this embodiment to accommodate heating wires  76 . And, although the outer surface of fusing roller  60  may still receive a coating of Teflon®, it is expected that outer layer  68  will be made of a hard rubber compound. The heated fuser roller of this invention is also suitable for use in all types of laser printers, copiers, facsimile machines and the variety of other electrophotographic printing devices that use a heated roller fuser. Therefore, it is to be understood that the invention may be embodied in other forms and details without departing from the spirit and scope of the invention as defined in the following claims.