Patent Publication Number: US-7587160-B2

Title: Toner repelling stripper finger assembly

Description:
The present invention relates to an electrostatographic reproducing machine and, more particularly, to such a machine including a toner repelling, electrically biased stripper finger assembly. 
   One type of electrostatographic reproducing machine is a xerographic copier or printer. In a typical xerographic copier or printer, a photoreceptor surface, for example that of a drum, is generally arranged to move in an endless path through the various processing stations of the xerographic process. As in most xerographic machines, a light image of an original document is projected or scanned onto a uniformly charged surface of a photoreceptor to form an electrostatic latent image thereon. Thereafter, the latent image is developed with an oppositely charged powdered developing material called toner to form a toner image corresponding to the latent image on the photoreceptor surface. When the photoreceptor surface is reusable, the toner image is then electrostatically transferred to a recording medium, such as paper, and the surface of the photoreceptor is cleaned and prepared to be used once again for the reproduction of a copy of an original. The paper with the powdered toner thereon in image wise configuration is separated from the photoreceptor and moved through a fuser apparatus to permanently fix or fuse the toner image to the paper. 
   One approach to fixing, or “fusing,” the toner image is applying heat and pressure by passing the copy sheet carrying the unfused toner image between a pair of opposed roller members of a fusing apparatus, at least one of the rollers is internally heated. During this procedure, the biasing level and polarity of the toner material is elevated to a biasing level and polarity at that the toner material coalesces and becomes tacky. This heating causes the toner to flow to some extent into the fibers or pores of the sheet. Thereafter, as the toner material cools, solidification of the toner material causes the toner material to become bonded to the sheet. 
   After the fusing step, the sheet carrying the fused image is stripped from the fusing member and then fed to a subsequent processing station, such as an inverter, collator, stapler, or booklet maker. Prior art stripper finger assemblies typically involve solid rigid fingers that either slide away from the fuser surface or include expensive articulating assemblies for attempting to achieve similar results. Examples of fusing apparatus including such prior art stripper finger assemblies are disclosed in the following references. U.S. Pat. No. 4,929,983 issued May 29, 1990 and entitled “Stripper mechanism” discloses a stripper for separating a print substrate from a fusing member in an electrostatographic printing machine has a substantially flat, thin, resiliently flexible finger-like member having a raised dimple-like bump adjacent one end of the finger-like member for contacting the print substrate when stripped from the fusing member, the finger-like member being coated on both sides with a smooth low surface energy film. 
   U.S. Pat. No. 5,160,130 issued Nov. 3, 1992 and entitled “Thin-tip stripper finger for use with a fuser roll in an electrostatographic apparatus” discloses a stripper finger separates a substrate from a fusing member in an electrostatographic reproduction machines. The stripper finger is a member defining an edge in the form of a symmetrical convex arc across the width of the member. The thickness of the member decreases from a chord through the convex arc perpendicular to the axis of symmetry of the arc, to the edge. 
   U.S. Pat. No. 6,785,503 issued Aug. 31, 2004 and entitled “Stripper fingers and roller assembly for a fuser in an electrostatographic reproduction machines” discloses stripper fingers that remove the print sheet from a fuser roll in a fuser for xerographic printing. The stripper finger having a tip for stripping a lead edge of a sheet from the fuser roll. A roller assembly, positioned adjacent to the stripper finger; for engaging the lead edge of a sheet and lifting the sheet from further contact with the tip after the tip of the stripper finger strips the lead edge of the sheet from the fuser roll. The roller assembly is removably mounted by using a snap-on mounting structure. 
   Unfortunately, conventional stripper fingers such as those disclosed herein have a tendency tolerate a build up of toner particles. Thus, toner image reproduction machines with such conventional stripper fingers will tend to suffer from contamination on sheets of copies being produced because such contaminated stripper fingers detrimentally cause undesirable image blotches and marks on the sheets of subsequent copies stripped by such contaminated fingers from the fusing apparatus. 
   In accordance with the present disclosure, there has been provided a toner repelling stripper finger assembly for stripping toner image carrying copy sheets from an outer surface of a moving heated fusing member. The toner repelling stripper finger assembly includes (a) a finger shaft having a first end for attaching to a baffle, and a second distal end; (c) an electrically conductive tip located at the second distal end of the finger shaft for contacting the outer surface of the moving heated fusing member to strip the toner image carrying copy sheets therefrom; and (d) an electrical biasing source connected to the electrically conductive tip for electrically biasing the electrically conductive tip to a desired electrical polarity, thereby repelling and preventing charged toner particles from being attracted and building up on the stripper finger assembly. 

   
       FIG. 1  is a schematic elevational view of an exemplary electrostatographic reproduction machine including a fusing apparatus including the toner repelling stripper finger assembly in accordance with the present disclosure; and 
       FIG. 2  is an enlarged end section schematic of the fusing apparatus of  FIG. 1  showing further details of the toner repelling stripper finger assembly in accordance with the present disclosure. 
   

   Referring first to  FIG. 1 , it schematically illustrates an electrostatographic reproduction machine  8  that generally employs a photoconductive belt  10  mounted on a belt support module  90 . Preferably, the photoconductive belt  10  is made from a photoconductive material coated on a conductive grounding layer that, in turn, is coated on an anti-curl backing layer. Belt  10  moves in the direction of arrow  13  to advance successive portions sequentially through various processing stations disposed about the path of movement thereof. Belt  10  is entrained as a closed loop  11  about stripping roll  14 , drive roll  16 , idler roll  21 , and backer rolls  23 . 
   Initially, a portion of the photoconductive belt surface passes through charging station AA. At charging station AA, a corona-generating device indicated generally by the reference numeral  22  charges the photoconductive belt  10  to a relatively high, substantially uniform potential. 
   As also shown the reproduction machine  8  includes a controller or electronic control subsystem (ESS)  29  that is preferably a self-contained, dedicated minicomputer having a central processor unit (CPU), electronic storage, and a display or user interface (UI). The ESS  29 , with the help of sensors and connections, can read, capture, prepare and process image data and machine status information, as well as selectively control various aspects of such functions, including for example the polarity and level of charge to the toner repelling stripper finger assembly of the present disclosure. 
   Still referring to  FIG. 1 , at an exposure station BB, the controller or electronic subsystem (ESS),  29 , receives the image signals from RIS  28  representing the desired output image and processes these signals to convert them to a continuous tone or gray scale rendition of the image that is transmitted to a modulated output generator, for example the raster output scanner (ROS), indicated generally by reference numeral  30 . The image signals transmitted to ESS  29  may originate from RIS  28  as described above or from a computer, thereby enabling the electrostatographic reproduction machine  8  to serve as a remotely located printer for one or more computers. Alternatively, the printer may serve as a dedicated printer for a high-speed computer. The signals from ESS  29 , corresponding to the continuous tone image desired to be reproduced by the reproduction machine, are transmitted to ROS  30 . 
   ROS  30  includes a laser with rotating polygon mirror blocks. Preferably a nine-facet polygon is used. At exposure station BB, the ROS  30  illuminates the charged portion on the surface of photoconductive belt  10  at a resolution of about 300 or more pixels per inch. The ROS will expose the photoconductive belt  10  to record an electrostatic latent image thereon corresponding to the continuous tone image received from ESS  29 . As an alternative, ROS  30  may employ a linear array of light emitting diodes (LEDs) arranged to illuminate the charged portion of photoconductive belt  10  on a raster-by-raster basis. 
   After the electrostatic latent image has been recorded on photoconductive surface  12 , belt  10  advances the latent image through development stations CC, that include four developer units as shown, containing CMYK color toners charged to a desired polarity, in the form of dry particles. At each developer unit the charged toner particles are appropriately attracted electrostatically to the latent image using commonly known electrostatographic imaging techniques. 
   With continued reference to  FIG. 1 , after the electrostatic latent image is developed, the toner powder image present on belt  10  advances to transfer station DD. A print sheet  48  is advanced to the transfer station DD, by a sheet feeding apparatus  50 . Sheet-feeding apparatus  50  may include a corrugated vacuum feeder (TCVF) assembly  52  for contacting the uppermost sheet of stack  54 ,  55 . TCVF  52  acquires each top sheet  48  and advances it to vertical transport  56 . Vertical transport  56  directs the advancing sheet  48  through feed rolls  120  into registration transport  125 , then into image transfer station DD to receive an image from photoreceptor belt  10  in a timed. Transfer station DD typically includes a corona-generating device  58  that sprays ions of a suitable polarity onto the backside of sheet  48 . This assists in attracting the toner powder image from photoconductive surface  12  to sheet  48 . After transfer, sheet  48  continues to move in the direction of arrow  60  where it is picked up by a pre-fuser transport assembly and forwarded to fusing station FF. 
   Fusing station FF includes the fusing apparatus of the present disclosure that is indicated generally by the reference numeral  70  for fusing and permanently affixing the transferred toner powder image  213  to the copy sheet  48 . Preferably, fusing apparatus  70  includes a heated fuser roller  72  having an outer surface  76 , and a pressure roller  74  that form a fusing nip  75  through which the sheet  48  is passed with the powder image  213  on the copy sheet  48  contacting fuser roller  72 . The pressure roller  74  is loaded against the fuser roller  72  forming the fusing nip  75  for providing the necessary pressure to fix the heated toner powder image  213  to the copy sheet. The fuser roll  72  for example is internally heated by a quartz lamp  71 . The fuser roll outer surface  76  may be cleaned by a roll  77 , and release agent, stored in a reservoir (not shown), may be pumped to a metering roll  79  for application to the surface as shown, after the sheet is stripped from such surface by the toner repelling stripper finger assembly  200  of the present disclosure (to be described in more detail below). 
   After that, the sheet  48  then passes to a gate  88  that either allows the sheet to move directly via output  17  to a finisher or stacker, or deflects the sheet into the duplex path  100 . Specifically, the sheet (when to be directed into the duplex path  100 ), is first passed through a gate  134  into a single sheet inverter  82 . That is, if the second sheet is either a simplex sheet, or a completed duplexed sheet having both side one and side two images formed thereon, the sheet will be conveyed via gate  88  directly to output  17 . However, if the sheet is being duplexed and is then only printed with a side one image, the gate  88  will be positioned to deflect that sheet into the inverter  82  and into the duplex loop path  100 , where that sheet will be inverted and then fed to acceleration nip  102  and belt transports  110 , for recirculation back through transfer station DD and fuser  70  for receiving and permanently fixing the side two image to the backside of that duplex sheet, before it exits via exit path  17 . 
   After the print sheet is separated from photoconductive surface  12  of belt  10 , the residual toner/developer and paper fiber particles still on and may be adhering to photoconductive surface  12  are then removed by a cleaning apparatus  150  at cleaning station EE. 
   Referring now to  FIGS. 1-2 , the fusing apparatus  70  includes the toner repelling stripper finger assembly  200  for stripping toner image carrying copy sheets  48  from an outer surface  76  of the moving heated fusing member or fuser roller  72 . As illustrated, the toner repelling stripper finger assembly  200  includes (a) at least one baffle  202  forming part of a sheet path  204  downstream of the fusing nip  75 ; (b) a finger  210  comprising a finger shaft  212  having a first end  214  for attaching to the at least one baffle  202 , and a second distal end  216  including an electrically conductive finger tip  218  for contacting the outer surface  76  of the moving heated fusing member or fuser roller  72  to strip the toner image carrying copy sheets  48  therefrom; (c) an electrical biasing source  230  having a desired polarity P, N; and (d) an electrically conductive member  220 , such as a spring as shown, that is connected to the tip  218  and to the electrical biasing source  230  for biasing the tip  218  to a desired polarity, and at a desired voltage level, for example, within a range of −300 to −500 volts for negatively charged toner particles within the same range. Although only one finger  210  is illustrated, as is well known, a plural number of such finger  210  would be required and would be arranged spaced apart from one end to the other, longitudinally, of the fuser roller  72 . 
   The finger  210  as a whole may be made of an electrically conductive material, it could be made of a non-conductive material in which case the electrically conductive tip  218  would be formed by coating with a conductive coating  240  such as metallic paint. The biasing source  230  for example comprises a voltage source that as shown is connected, through a control device  242 , by an electrically conductive member  220 , for example an electrically conductive spring. The control device  242  is connected by means  244  to the controller  29  and is capable of being selected to apply positive P or negative N polarity charge to the finger tip  218 , depending on which of the positive and negative polarity is the same as the polarity of the charged toner particles  213  forming the images being fused and stripped. 
   Although only one finger assembly is illustrated, the toner repelling stripper finger assembly  200  will include a plural number of the finger  210  each with a shaft  212  and a corresponding plural number of the electrically conductive tip  218 . Accordingly, each conductive tip  218  will be connected as described to an electrically biasing source  230 . 
   As can be seen, there has been provided a toner repelling stripper finger assembly for stripping toner image carrying copy sheets from an outer surface of a moving heated fusing member. The toner repelling stripper finger assembly includes (a) a finger shaft having a first end for attaching to a baffle, and a second distal end; (c) an electrically conductive tip located at the second distal end of the finger shaft for contacting the outer surface of the moving heated fusing member to strip the toner image carrying copy sheets therefrom; and (d) an electrical biasing source connected to the electrically conductive tip for electrically biasing the electrically conductive tip to a desired electrical polarity, thereby repelling and preventing charged toner particles from being attracted and building up on the stripper finger assembly. 
   The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.