Abstract:
A belt fuser includes a fuser roller and a guide roller rotatably supported in a frame, as well as a floating idler roller and a tension roller. A belt reeved over the fuser, guide, idler, and tension rolls holds the idler roll in place and forms a nip by the reeving of the belt over the fuser roller. The tension roller is connected to a constant force mechanism that applies, through the tension roller, a tension force in the belt and a normal force against the fuser roller throughout the nip. Fusing nip length, dwell time, and thermal efficiency are greatly improved over roller fusers, and the fusing temperature can be significantly reduced as a result. In addition, the belt fuser of embodiments is significantly more compact than previous belt fusers, occupying only slightly more space than a conventional two roll fuser.

Description:
[0001]    This application is based on Provisional Patent Application No. 60/407,214, filed Aug. 29, 2002. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates generally to marking machines in which a fuser assembly or apparatus is used, such as electrostatographic reproduction machines. More particularly, the invention relates to a compact fusing apparatus for use in such a machine for increasing fusing dwell time and fusing thermal efficiency.  
         BACKGROUND AND SUMMARY  
         [0003]    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 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 a latent image on the photoconductive member. The toner attracted to a donor roller is then deposited on a latent electrostatic images on a charge retentive surface which is usually a photoreceptor. The toner powder image is then transferred from the photoconductive member to a copy substrate. The toner particles are heated to permanently affix the powder image to the copy substrate.  
           [0004]    In order to fix or fuse the toner material onto a support member permanently by heat and pressure, 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.  
           [0005]    One approach to thermal fusing of toner material images onto the supporting substrate has been to pass the substrate with the unfused toner images thereon between a pair of opposed roller members at least one of which is internally heated. During operation of a fusing system of this type, the support member to which the toner images are electrostatically adhered is moved through the nip formed between the rollers with the toner image contacting the heated fuser roller to thereby effect heating of the toner images within the nip. In a conventional two roll fuser, one of the rolls is typically provided with a layer or layers that are deformable by a harder opposing roller when the two rollers are pressure engaged. The length of the nip determines the dwell time or time that the toner particles remain in contact with the surface of the heated roller.  
           [0006]    Roller fusers work very well for fusing images at low speeds since the required process conditions such as temperature, pressure, and dwell can easily be achieved. When process speeds approach 100 pages per minute (ppm) roller fusing performance starts to falter. At such higher speeds, dwell must remain constant, which necessitates an increase in nip width. Increasing nip width can be accomplished most readily by either increasing the roller rubber thickness and/or the outside diameter of the rollers. Each of these solutions reach their limit at about 100 ppm. Specifically, the rubber thickness and durometer (softness) are limited by the thermal and physical properties of the material. The roller size becomes a critical issue for reasons of space, weight, cost, and stripping.  
           [0007]    Belt fusers, such as those disclosed in U.S. Pat. Nos. 5,250,998 and 5,465,146, are a type of toner image fixing device in which an endless belt is looped around a heating roller, a conveyance roller, and a pressure roller. The pressure roller presses a sheet having a toner image onto the heating roller with the endless belt intervening between the pressure roller and the heating roller. The fixing temperature for the toner image is controlled on the basis of the temperature of the heating roller detected by a sensor, such as a sensor in the loop of the belt and in contact with the heating roller. A first nip region is formed on a pressing portion located between the heating roller and the fixing roller. A second nip region is formed between the belt and the fixing roller, continuing from the first nip region but without contacting the heating roller. The disclosures of U.S. Pat. Nos. 5,250,998 and 5,465,146 are incorporated by reference.  
           [0008]    Most belt fusers, however, take significantly more space than more conventional roller fusers. Thus, marking machines, such as electrostatographic reproduction machines, incorporating belt fusers must have larger housings, which is undesirable. Therefore, there is a need for more compact belt fusers.  
           [0009]    Embodiments comprise a belt fuser with elongated fusing nip a compact overall size including such a mechanism are disclosed for use in a reproduction machine. The compact long nip width fusing apparatus includes, in embodiments, a rotatable fuser roller about which a fuser belt is reeved to form the fusing nip. The belt fuser also includes a rotatable guide roller and a tension roller about which the belt is reeved. The resulting belt fuser has a longer nip and dwell time than roller fusers, better thermal efficiency and lower fusing temperature than roller fusers, but occupies only slightly more space than a conventional roller fuser. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a schematic illustration of an electrostatographic reproduction machine incorporating the fusing apparatus of embodiments.  
         [0011]    [0011]FIG. 2 is an end view schematic of the fusing apparatus of FIG. 1 in accordance with embodiments  
         [0012]    [0012]FIG. 3 is an end view schematic of a variation of the fusing apparatus of FIG. 1 in accordance with embodiments.  
         [0013]    [0013]FIG. 4 is an end view schematic of a variation of the fusing apparatus of FIG. 1 in accordance with embodiments.  
     
    
     DETAILED DESCRIPTION  
       [0014]    While the present invention will be described in connection with embodiments thereof, the description is not intended to limit the invention to those embodiments. For a general understanding of the features of the present invention, reference is made to the drawings, in which like reference numerals have been used throughout to identify identical elements.  
         [0015]    Referring now to FIG. 1, the various processing stations employed in an electrostatographic reproduction machine are illustrated to provide an example of a marking machine in which embodiments can be employed.  
         [0016]    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 stations CC, transfer station DD, fusing station EE and cleaning station FF. 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 photoreceptor belt  10 . Roller  20  is coupled to 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 .  
         [0017]    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 photoreceptor surface are advanced through exposure station BB. At exposure station BB, the uniformly charged photoreceptor or charge retentive surface  10  is exposed to a laser based input and/or output scanning device  25  which, as controlled by controller or ESS  26 , causes the charge retentive surface to be discharged in accordance with the output from the scanning device. 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 can be, for example, a three level laser Raster Output Scanner (ROS). The photoreceptor then contains both charged-area images and discharged-area images.  
         [0018]    At development station CC, a development system, indicated generally by the reference numeral  30 , advances developer materials into contact with the electrostatic latent images, and develops the image. The development system  30 , as shown, can comprise first and second developer apparatuses  32  and  34 , that can take any suitable form as is known in the art, so long as they advance developer material  40 ,  42  into contact with the photoreceptor for developing the discharged-area images. The developer material  40 , by way of example, can include negatively charged color toner, and the developer material  42  can include, for example, a black toner. Electrical biasing is accomplished via power supply  41 ,  43  electrically connected to developer apparatus  32 ,  34 . A DC bias is applied to the rollers  35 ,  36 ,  37 ,  38  via the power supply  41 ,  43 .  
         [0019]    Because the composite image developed on the photoreceptor 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.  
         [0020]    Sheets of substrate or support material  58 , such as paper, are advanced to transfer station DD from a supply tray, not shown. Sheets 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 sheet continues to move in the direction of arrow  62  towards fusing station EE.  
         [0021]    As illustrated, fusing station EE includes a compact belt fusing apparatus  90  in accordance with embodiments. As illustrated, the fusing apparatus  90  includes a rotatable fuser roller  92 . Fuser roller  92  can be heated, for example, by a heating device  94 . The heating device  94  is shown as an internal lamp, but can also be an external heater directed at the roller  92  or at the belt  10 . Additionally, internal heating devices  94  can be placed in one or more other rollers of the apparatus, as seen in FIG. 3. The heating device  94  elevates the temperatures of the surface  96  of the fuser roller to a suitable toner fusing temperature. The fusing apparatus  90  also includes a rotatable guide roller  98  that aids in formation of the fusing nip  110  and application of pressure thereto in cooperation with the rotatable fuser roller  92 .  
         [0022]    As mentioned above, the compact fusing apparatus  90  increases fusing dwell time and fusing thermal efficiency relative to roller nip dwell time and fusing thermal efficiency as a result of its use of the belt and idler roller configuration. Referring now to FIGS.  2 - 4 , and particularly FIG. 2, the belt fuser includes a tension roller  104  on the exit side  114  of the fusing nip  110 , and a floating idler roller  102  on an entrance side of the fusing nip  112 . The idler and tension rollers  102 ,  104  can comprise an extruded aluminum member or another suitable article of manufacture. As further shown, an endless belt member  106 , a fusing belt, is reeved over the idler roller  102  and over the tension roller  104 , thus forming a deflectable or pinchable closed loop  108  about the rollers  102 ,  104 , as seen in FIGS.  2 - 4 . The fusing belt  106  is also reeved over or impinged by the rotatable fuser roller  92  and the rotatable guide roller  98 . Advantageously, the closed loop when pinched as such forms a long width fusing nip  110  against the rotatable fuser roller  92 . The long fusing nip  110  has increased fusing dwell time and fusing thermal efficiency relative to the same from a conventional roller nip.  
         [0023]    The long width fusing nip  110  includes two comparatively high nip pressure areas, comprising an entrance area  112  into the long width fusing nip, and an exit area  114  thereof. As shown, the first high nip pressure area  112  at the entrance into the long width fusing nip is created by the fuser roller  92  pinching a portion of one leg of the closed loop against the idler roller  102 . Similarly, the second high nip pressure area  114  at the exit thereof is created by the fuser roller  92  pinching a portion of one leg of the closed loop against the tension roller  104 .  
         [0024]    The idler roller  102  preferably is a floating idler roller held in place solely by the closed loop of the belt member  106 . The tension roller  104  is connected to an adjustable force mechanism or tension control mechanism that exerts a force F on the tension roller  104 . The adjustable force mechanism thus allows adjustment of the tension of the fusing belt  106 . The adjustable force mechanism can, for example, take the form of a spring or a linear actuator such as a screw drive or the like.  
         [0025]    To recapitulate, the fusing apparatus  90  utilizes a unique floating idler roller  102  held in position solely by a closed loop of a belt member  106 . The idler roller  102  does not require any conventional radial bearings or positioning mechanisms as a result of the support of the belt  106 . Because there are no bending moments applied to the idler roller  102 , it can be of low cost, small diameter, thin wall, low mass construction. The tension roller  104  can be used to adjust tension in the belt  106  by virtue of the tension control or adjustable force mechanism, typically a mechanical spring but which can also be a linear actuator or the like, to which it is connected. This allows for a simple design that is much more compact, thermally efficient, and lower cost when compared to other belt fusers having a similar long width fusing nip. As pointed out above, the pressure profile of the long width fusing nip  110  of embodiments is also unique in that the highest pressure areas (two of them) can be at the nip entrance area  112 , and at nip exit area  114 .  
         [0026]    Still referring to FIGS.  1 - 4 , the fuser roller  92  preferably is the drive roller and can be mounted in a fixed position in a suitable frame  93  through a pair of end bushings (not shown). The guide roller  98  is fixedly mounted in the frame  93  and the belt tension and consequently the nip pressure are adjusted via the constant force mechanism and tension roller  104  as discussed above. The floating idler roller  102  is held in its position solely by the closed loop  108  of the belt member  106  and does not need conventional radial bearings or positioning mechanisms. Rather, the idler roller  102  only needs some form of thrust bushing (not shown) at each end thereof for locating it laterally.  
         [0027]    In operation, the copy medium  58  with an unfused toner image  89  on the top side as shown, enters the long width fusing nip  110  through the entrance area  112 , and exits the nip  110  through the exit area  114 . The high pressure area nip entrance will advantageously minimize cockle and other deformities on the incoming medium or sheet, and the high pressure area nip exit will act to improve fused image fixing onto the medium or sheet  58 . As can be clearly seen, the toner image is in contact with the heated surface  96  of the fuser roller  92 , and travels a much greater distance in such contact through the nip  110 , as compared for example to travel through the roller nip of a typical two roll fuser. As such, fusing dwell time, at a given travel speed, will be significantly greater through the long width nip  110  as compared to a roller nip.  
         [0028]    In embodiments, the unfused toner image  89  can enter the fusing nip  110  oriented to engage the fuser belt  106 . In such embodiments, the belt surface is the fusing surface and is heated by one or more heating devices  94 . The heating devices  94  can be mounted inside and/or outside any or all of the rollers or belt. Such embodiments also enjoy the significantly improved dwell time and thermal efficiency and other advantages listed above as compared with two roll fusers.  
         [0029]    Advantageously, the fusing apparatus  90  results in a compact belt fusing apparatus having a relatively small heated belt surface area as compared to other belt fusing systems. The compact structure and small heated surface area minimize thermal loss and require less energy for its operation. Fusing tests on similar such compact fusing apparatus were found to result an 84° F. reduction in a required fusing temperature as compared to a baseline or conventional heated and pressure roller fusing apparatus. Additionally, the belt member  106  is relatively short and hence cost relatively less, as does the idler roller.  
         [0030]    As can be seen, embodiments provide a compact long nip width fusing apparatus for use in a marking machine, such as a reproduction machine. While this invention has been described in conjunction with a particular embodiment thereof, unforeseeable alternatives, modifications and variations may arise 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.