Patent Publication Number: US-6661990-B2

Title: Fusing apparatus having a pneumatic member

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to electrostatographic reproduction machines, and more particularly to a fusing apparatus including a pneumatic member for increasing fusing nip width, and fusing dwell time. 
     In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to selectively dissipate the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member. After the electrostatic latent image is recorded on the photoconductive member, the electrostatic latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules either to a donor roller or to an electrostatic latent image on the photoconductive member and form a toner powder image on the photoconductive member. The toner powder image is transferred from the photoconductive member to a copy substrate. The toner powder image is then heated to permanently fuse and affix it to the copy substrate. 
     In order to fix or fuse toner material onto a support member permanently by heat, it is necessary to elevate the temperature of the toner material to a point at which constituents of the toner material coalesce and become tacky. This action causes the toner to flow to some extent onto the fibers or pores of the support members or otherwise upon the surfaces thereof. Thereafter, as the toner material cools, solidification of the toner material occurs causing the toner material to be bonded firmly to the support member. 
     One approach to thermal fusing of toner images onto a supporting substrate has been to pass the substrate with unfused toner images thereon between a pair of opposed roller members at least one of which is internally heated, i.e. a heated fuser roller. During operation of a fusing system of this type, the substrate to which the toner images are electrostatically adhered is moved through a nip formed between the roller members with the toner image contacting the heated fuser roller to thereby effect heating of the toner images within the nip. In a Nip Forming Fuser Roller (NFFR), the heated fuser roller is provided with a layer or layers that are deformable by a harder pressure roller when the two rollers are pressure engaged. The length of the nip determines the dwell time or time that toner particles remain in contact with the surface of the heated fuser roller. 
     Roller fusers work very well for fusing color and monochrome images at low speeds since the required process conditions such as temperature, pressure and dwell time can easily be achieved. When process speeds approach 100 pages per minute (ppm) roller fusing performance starts to falter. At such high speeds, dwell time must remain constant which necessitates an increase in nip width. Increasing nip width can be accomplished most readily by either increasing the fuser roller (FR) rubber thickness and/or the outside diameter of the fuser roller. Each of these solutions reach their limit at about 100 ppm. Specifically, the rubber thickness is limited by the maximum temperature the rubber can withstand and the thermal gradient across the elastomer layer. The fuser roller size becomes a critical issue for reasons of space, weight, cost, and stripping. 
     Thus conventional attempts to produce long fusing nips have tended to increase fuser roller diameter or require use of fusing belts. These approaches have their drawbacks which include increasing the overall size and hence the cost of the fusing apparatus. Additionally, current rubber pressure roller technology is also at its limit as far as increasing nip width by using softer materials. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided a compact long nip fusing apparatus including (a) a frame; (b) a rotatable first member for mounting to the frame; (c) a heat source for heating the rotatable first member; and (d) a rotatable and compressable pneumatic member forming a long fusing nip against the rotatable first member for contacting and fusing a fusible image. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     In the detailed description of the invention presented below, reference is made to the drawings, in which: 
     FIG. 1 is a schematic illustration of an electrostatographic reproduction machine incorporating the fusing apparatus including a pneumatic member in accordance with the present invention; 
     FIG. 2 is a schematic illustration of a first embodiment of the fusing apparatus including a pneumatic member in accordance with the present invention; and 
     FIG. 3 is a schematic illustration of a second embodiment of the fusing apparatus including a pneumatic member in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the present invention will be described in connection with preferred embodiments thereof, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. 
     For a general understanding of the features of the present invention, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to identify identical elements. 
     Referring now to the drawings, where the showings are for the purpose of describing a preferred embodiment of the invention and not for limiting same, and where the various processing stations employed in an electrostatographic reproduction machine as illustrated in FIG. 1, will be described only briefly. 
     As illustrated, an electrostatographic reproduction machine  8 , in which the present invention finds advantageous use, utilizes a charge retentive image bearing member in the form of a photoconductive belt  10  consisting of a photoconductive surface  11  and an electrically conductive, light transmissive substrate. The belt  10  is mounted for movement past a series of electrostatographic process stations including a charging station AA, an exposure station BB, developer station CC, transfer station DD, fusing station EE and cleaning station FE. Belt  10  moves in the direction of arrow  16  to advance successive portions thereof sequentially through the various processing stations disposed about the path of movement thereof. Belt  10  is entrained about a plurality of rollers  18 ,  20  and  22 , the former of which can be used to provide suitable tensioning of the belt  10 . Roller  20  is coupled to a motor  23  by suitable means such as a belt drive. Motor  23  rotates roller  20  to advance belt  10  in the direction of arrow  16 . 
     As can be seen by further reference to FIG. 1, initially successive portions of belt  10  pass through charging station AA. At charging station AA, a corona discharge device such as a scorotron, corotron or dicorotron indicated generally by the reference numeral  24 , charges the belt  10  to a selectively high uniform positive or negative potential. Any suitable control, well known in the art, may be employed for controlling the corona discharge device  24 . 
     Next, the charged portions of the photoconductive surface  11  are advanced through exposure station BB. At exposure station BB, the uniformly charged photoconductive or charge retentive surface  11  is exposed to a laser based input and/or output scanning device  25  which, as controlled by controller or ESS  26 , causes the photoconductive surface  11  to be discharged in accordance with the output from the scanning device  25 . The ESS  26 , for example, is the main multi-tasking processor for operating and controlling all of the other machine subsystems and printing operations, including aspects of the present invention. The scanning device is a three level laser Raster Output Scanner (ROS). The resulting photoconductive surface  11  contains both charged-area images and discharged-area images. 
     At developer station CC, a development system, indicated generally by the reference numeral  30  advances developer materials into contact with electrostatic latent images, and develops the images. The development system  30 , as shown, comprises first and second developer apparatuses  32  and  34 . The developer apparatus  32  comprises a housing containing a pair of magnetic brush rollers  35  and  36 . The rollers  35 ,  36  advance developer material  40  into contact with the photoconductive surface  11  for developing the discharged-area images. The developer material  40 , by way of example, contains negatively charged color toner. Electrical biasing is accomplished via bias power supply  41  electrically connected to developer apparatus  32 . A DC bias is applied to the rollers  35  and  36  via the bias power supply  41 . 
     The developer apparatus  34  comprises a housing containing a pair of magnetic brush rollers  37  and  38 . The rollers  37 ,  38  advance developer material  42  into contact with the photoconductive surface  11  for developing the charged-area images. The developer material  42  by way of example contains positively charged black toner for developing the charged-area images. Appropriate electrical biasing is accomplished via bias power supply  43  electrically connected to developer apparatus  34 . A DC bias is applied to the rollers  37  and  38  via the bias power supply  43 . 
     Because the composite image developed on the photoconductive surface  11  consists of both positive and negative toner, a pre-transfer corona discharge member  56  is provided to condition the toner for effective transfer to a substrate using corona discharge of a desired polarity, either negative or positive. 
     Sheets of substrate or support material  58  are advanced to transfer station DD from a supply tray, not shown. Sheets  58  are fed from the tray by a sheet feeder, also not shown, and advanced to transfer station DD through a corona charging device  60 . After transfer, the sheets  58  continues to move in the direction of arrow  62  towards fusing station EE. 
     Referring now to FIGS. 1-3, fusing station EE includes the fusing apparatus  100  or  101  which comprises a frame  102  a rotatable first member  104  that is heated, for example by a heating device  106  (shown as an internal lamp but as well could be an external heater). The fusing apparatus  100  and  101  also includes a rotatable and compressable pneumatic member  110  in accordance with the present invention. As illustrated, the first member  104  forms a long fusing nip  108  with the rotatable and compressable pneumatic member  110  for fusing toner images carried on a copy sheet or substrate  58 . The heating device  106  is sufficient for elevating temperatures within the fusing nip  108  to a suitable level for fusing toner particles. 
     In a first embodiment of the fusing apparatus  100  of the present invention as shown in FIG. 2, the heated, rotatable first member  104  is arranged as a fusing member. As such, it has a surface  105  that is suitable for contacting and fusing toner images. Accordingly, the rotatable and compressable pneumatic member  110  is therefore arranged in this embodiment as a pressure member for contacting a backside of the copy sheet or substrate  58  within the fusing nip  108 . 
     In a second embodiment of the fusing apparatus  101  of the present invention as shown in FIG. 3, the rotatable and compressable pneumatic member  110  is arranged as the fusing member, and thus has a surface  111  that is suitable for contacting and fusing toner images. In this embodiment, the heated, rotatable first member  104  is arranged as an external heating device forming a heating nip  107  against the pneumatic member  110  for heating the surface  111  of the pneumatic member  110 . Alternatively, the rotatable and compressable pneumatic member  110  can also be heated internally for example by using a controllably heated fluid  117  for pressurizing the pneumatic member  110 . A rotatable second member  112  is provided as a pressure member and is mounted in nip forming pressure engagement with the pneumatic member  110  and forms a long fusing nip  115 , and for contacting a backside of the copy sheet or substrate  58  within the fusing nip  115 . 
     In both embodiments, the rotatable and compressable pneumatic member  110  can for example be comprised of a flexible, pressurized or pressurizeable sleeve or shell  116  that is mounted on a rigid core  118 . The rigid core  118  typically can be made of a metallic material. As illustrated in the second embodiment, the rotatable and compressable pneumatic member  110 , is positioned between a conventional hard pressure roller which is the rotatable second member  112  forming the fusing nip  115 , and an external heat roller which is the rotatable first member  104 . The sleeve or shell  116  can be made of a thermally conductive material such as silicone rubber with a conductive filler for receiving and retaining heat for example from the external heating device  104  or the fluid  117  inside. 
     The rotatable and compressable pneumatic member  110  in a fusing apparatus has many benefits including the long fusing nip  108  and  115  which advantageously results in increased dwell time for images being fused through such a nip. The long nip allows the fusing apparatus to run at a relatively higher speed, and higher copy volume. Additionally, it produces relatively high uniformity in nip pressure from entrance to exit, as well as relatively low strain levels on sleeve material, resulting in a relatively longer life fusing apparatus. In loading the rotatable and compressable pneumatic member  110  within the fusing nip  108  and  115 , external loading means may not be necessary because the rotatable and compressable pneumatic member  110  itself is, and can act as an integrally adjustable pneumatic spring. 
     Thus as shown in FIGS. 1-3, there is illustrated a compact long nip fusing apparatus  100  and  101  in accordance with the present invention. As shown, the compact long nip fusing apparatus  100  and  101  includes a frame  102 ; a rotatable first member  104  for mounting to the frame; a heating device or heat source  106  for heating the rotatable first member  104 ; and a rotatable and compressable pneumatic member  110  forming a long fusing nip  108  and  115  against the rotatable first member  104 . 
     In the first embodiment shown in FIG. 2, the rotatable first member  104  comprises a roller which as heated can be a fuser roller having a surface  105  that is suitable for contacting and fusing toner images. The heat source  106  for example is mounted internally within the rotatable first member or roller  104 , but as is well known, the heat source  106  can also be externally located relative to the rotatable first member or roller  104 . 
     The rotatable and compressable pneumatic member  110  comprises a flexible, hollow sleeve or shell  116  that can be filled and pressurized by means of a pressurized fluid such as air, a gas or a suitable liquid. The volume and pressure of such fluid within the hollow sleeve or shell  116  determines the size and firmness of the rotatable and compressable pneumatic member  110 . As shown, the rotatable and compressable pneumatic member  110  may include a constant pressure control means  120  coupled thereto for maintaining its pressure at a constant level, or the control means  120  may be a variable pressure control means for varying its pressure and fusing nip pressure responsively to the requirements of different types of fusing jobs. 
     In the first embodiment (FIG.  2 ), the rotatable first member  104  and the rotatable and compressable pneumatic member  110  are mounted into pressure contact (by means not shown) within the long fusing nip  108 . The long fusing nip  108  has an arcuate profile  109  that is formed by the rotatable first member  104  compressing the rotatable and compressable pneumatic member  110 . 
     In the second embodiment, the compact long nip fusing apparatus  101  includes the frame  102 , the rotatable and compressable pneumatic member  110 , and the rotatable first member  104  with the heating device  106  therein. As shown, the rotatable first member  104  with the heating device  106  therein forms a heating nip  107  against the rotatable and compressable pneumatic member  110 . This embodiment of the fusing apparatus  101  also includes a rotatable second member  112  that is mounted oppositely from the rotatable first member  104  relative to, and forming a long fusing nip  115  with, the rotatable and compressable pneumatic member  110 . In this second embodiment, the rotatable and compressable pneumatic member  110  is heated externally by the rotatable first member  104  through the heating nip  107 . The externally heated rotatable and compressable pneumatic member  110  serves thus as the fusing member, and thus has a surface  111  that is suitable for contacting and fusing toner images. 
     As also shown, the rotatable and compressable pneumatic member  110  of the second embodiment may include a constant pressure control means  120  coupled thereto for maintaining its pressure at a constant level, or the control means  120  may be a variable pressure control means for varying its pressure and fusing nip pressure responsively to the requirements of different types of fusing jobs. 
     The rotatable and compressable pneumatic member  110  is pressurized using a fluid  117 , such as a gas, air or a liquid. After pressurization, the rotatable and compressable pneumatic member  110  can be permanently sealed to operate at a fixed pressure or its pressure can be variably controlled using an adjustable variable pressure control means  120  as above. 
     As can be seen, there has been provided a compact long nip fusing apparatus including (a) a frame; (b) a rotatable first member for mounting to the frame; (c) a heat source for heating the first rotatable member; and (d) a rotatable and compressable pneumatic member forming a long fusing nip against the first rotatable member for contacting and fusing a fusible image. 
     While this invention has been described in conjunction with a particular embodiment thereof, it shall be evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variations as fall within the spirit and broad scope of the appended claims.