Abstract:
The present invention includes a toner cartridge comprising a developer roller having a cylindrical exterior surface with a tapering ramped channel formed in the surface of at least one end of the developer roller. The tapering channel having a narrow proximal end nearest the at least one end of the developer roller and a wide distal end furthest from the at least one end of the developer roller. The narrow proximal end of the tapering channel extends deeper into the surface of the developer roller than the wide distal end. The tapering ramped channel functions to propel toner or other fluid accumulating against an end seal away from the seal, toward a central portion of the developer roller.

Description:
RELATED APPLICATIONS  
       [0001]    The present application is related to commonly assigned U.S. patent application Ser. No. [Attorney Docket No. 10014849-1] entitled “A SYSTEM FOR AND METHOD OF REDUCING TONER SEAL LEAKAGE BY THE INTRODUCTION OF A STEP GROOVE IN THE DEVELOPER ROLLER” filed concurrently; U.S. patent application Ser. No. [Attorney Docket No. 10013385-1] entitled “SYSTEM FOR AND METHOD OF PREVENTING TONER LEAKAGE PAST DEVELOPER SEALS USING STATIC CHARGE” filed concurrently; U.S. patent application Ser. No. [Attorney Docket No. 10015398-1] entitled “SYSTEM FOR AND METHOD OF REDUCING OR ELIMINATING TONER LEAKAGE WITH A VIBRATING SEAL” filed concurrently; and U.S. patent application Ser. No. [Attorney Docket No. 10015369-1] entitled “SYSTEM FOR AND METHOD OF TONER FLOW CONTROL” filed concurrently the disclosures of which are hereby incorporated herein by reference in their entirety. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention generally relates to electrophotographic printing devices and more specifically to the reduction of toner leakage through seals in these devices.  
         BACKGROUND  
         [0003]    Currently there are several types of technologies used in printing and copying systems. Electrophotographic printing devices such as laser printers and copiers use toner particles to form the desired image on the print medium, which is usually some type of paper. While the toner particles are solid, their small size (on the order of 3-15 microns) results in highly fluid properties. 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.  
           [0004]    [0004]FIG. 7 is a diagram of typical laser printing device  700  employing an ElectroPhotography (EP) process. For monochromatic printing, a single color of toner particles  701  are held in toner supply hopper  702 . Toner particles  701  are typically small plastic (e.g. styrene) particles on the order of 5 microns (10 −6 ) meter in size. Agitator, or stirring blade,  703  is typically made of plastic or mylar and ensures toner particles  701  are uniformly positioned along developer sleeve  704  while inducing a negative charge onto the toner particles in the range of −30 to −40 microcoulomb per gram (μc/g). Developer sleeve  704  rotates in a counterclockwise direction about an internal stationary magnet  705  which acts as a shaft. Toner particles  701  are attracted to the rotating developer sleeve  704  by the magnetic forces of stationary magnet  705 . Doctor blade  706  helps in charging toner particles  701  and metes out a precise and uniform amount of toner particles  701  onto developer sleeve  704  as its outer surface rotates external to toner supply hopper  702 . Developer sealing blade  707  allows excess toner particles  701  affixed to developer sleeve  704  to be returned to toner supply hopper  702  without leakage.  
           [0005]    Primary Charging Roller (PCR)  708  conditions Organic PhotoConductor (OPC) drum  709  using a constant flow of current to produce a blanket of uniform negative charge on the surface of OPC drum  709 . Production of the uniform charge by PCR  708  also has the effect of erasing residual charges left from the previous cycle.  
           [0006]    A major component of the EP process is OPC drum  709 . OPC drum  709  is a thin-walled aluminum cylinder coated with a photoconductive layer. The photoconductive layer may constitute a photodiode that accepts and holds a charge from PRC  708 . Initially, the unexposed surface potential of the OPC is approximately −600 volts. Typically, the photoconductive layer comprises three layers including, from the outermost inward, a Charge Transport Layer (CTL), Charge Generation Layer (CGL), and barrier or oxidizing layer formed on the underlying aluminum substrate. The CTL is a clear layer approximately 20 microns thick, which allows light to pass through to the CGL and controls charge acceptance to the OPC. The CGL is about 0.1 to 1 micron thick and allows the flow of ions. The barrier layer bonds the photoconductive layer to the aluminum substrate  
           [0007]    Laser beam  710  exposes OPC drum  709  one line at a time at the precise locations that will receive toner (paper locations which correspond to the image being printed). OPC drum  709  is discharged from −600V to approximately −100V at points of exposure to laser beam  710 , creating a relatively positively charged latent image on its surface. Transformation of the latent image into a developed image begins when toner particles  701  are magnetically attracted to rotating developer sleeve  704 . Alternatively, if nonmagnetic toner is used, developer sleeve  704  may comprise a foam roller to mechanically capture toner particles  701 . In this case, an open cell foam roller may be included to apply toner to developer sleeve  704 . The still negatively charged toner held by developer sleeve  704  is attracted to the relatively positively charged areas of the surface of OPC drum  709  and “jumps” across a small gap to the positively charged latent image on OPC drum  709  creating a developed image.  
           [0008]    Paper to receive toner from OPC drum  709  is transported along paper path  711  between OPC drum  709  and transfer roller  712 , with the developed image transferred from the surface of OPC drum  709  to the paper. The transfer occurs by action of transfer roller  712  which applies a positive charge to the underside of the paper, attracting the negatively-charged toner particles to move to the paper. Wiper blade  713  cleans the surface of the OPC drum  709  by scraping off the (untransferred or waste) toner into waste hopper  715 , while recovery blade  714  prevents the waste toner from falling back onto the paper. Fusing occurs as the paper, including toner particles, is passed through a nip region between heated roller  716  and pressure roller  717  where the toner is melted and fused (or “bonded”) to the paper. Heated roller  716  and pressure roller  717  are together referred to as the fuser assembly.  
           [0009]    One design consideration with imaging devices such as laser printers and copying systems is to minimize the leakage of toner or toner particles  701  from the supply hopper  702 . As shown in FIG. 8, in its normal position, developer sleeve  704  has a toner supply on one side of seal  801  and the atmosphere on the other side of seal  801 . Seals in this area are incorporated in an attempt to reduce or eliminate toner leakage.  
           [0010]    Leakage sometimes occurs along the roller and at the ends of developer sleeve  704 . Several methodologies have been used to reduce or eliminate such leakage. For example, some printers employ a foam or felt mechanical seal at the ends of developer sleeve  704  as a physical barrier to prevent toner particles from leaking past the end of developer sleeve  704  and out of toner supply hopper  702 . Alternatively, when the toner includes magnetic particles, such as in some black and white printers, magnetic seals may be provided at the ends of developer sleeve  704  to attract and capture toner particles and to create a physical barrier, consisting of the toner particles, to prevent additional particles from leaking.  
           [0011]    [0011]FIG. 8 shows the configuration of developer sleeve  704 , toner particles  701  and seal  801 . As shown, seal  801  is positioned between support  802  and developer sleeve  704 . As developer sleeve  704  rotates, toner particles  701  are forced into junction  803  of seal  801  and developer sleeve  704 . This action causes a buildup of toner and corresponding fluid pressure at junction  803  causing toner particles  701  to leak under, around and through seal  801 .  
           [0012]    Accordingly, a need exists for a system and a method for reducing toner leakage in a toner cartridge.  
         SUMMARY OF THE INVENTION  
         [0013]    The present invention is directed to a system and method which comprises a toner cartridge including a developer roller having a cylindrical exterior surface with one or more peripheral tapering channels formed in the surface at one end of the developer roller. The channel has a narrow proximal end nearest the nearest end of the developer roller and a wide distal end toward the middle of the developer roller. The narrow proximal end of the channel extends deeper into the surface of the developer roller than does the wide distal end. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a frontal view of a left portion of a developer roller according to an embodiment of the present invention including a toner collection channel;  
         [0015]    [0015]FIG. 2 is a cross sectional view of the tapering channel along lines  2 - 2  of FIG. 1;  
         [0016]    [0016]FIG. 3 is a front view of a developer roller incorporating a plurality of toner collection channels on opposing ends of the roller;  
         [0017]    [0017]FIG. 4 is a perspective view of one end of a toner roller having formed therein a plurality of toner collection channels;  
         [0018]    [0018]FIG. 5 is a perspective view of a developer roller according to the invention with toner collection channels formed proximate a roller end seal;  
         [0019]    [0019]FIG. 6 is an exploded perspective view of the structure of FIG. 5;  
         [0020]    [0020]FIG. 7 shows a prior art electrophotographic printing device; and  
         [0021]    [0021]FIG. 8 shows a configuration of a prior art developer roller, seal and support. 
     
    
     DETAILED DESCRIPTION  
       [0022]    [0022]FIG. 1 shows developer roller  101  with an improved tapering channel feature that is designed to reduce the fluid pressure on seal  107  by directing the flow of toner particles  108  away from the junction between developer roller  101  and seal  107 . The fluid pressure resulting from toner buildup near seal  107  is reduced as a result of the relative rotation of developer roller  101  and tapering ramped channel  102  with respect to stationary seal  107 . The geometry and orientation of tapering ramped channel  102  relative to developer roller  101  depends on the rotational speed of developer roller  101  and the size of toner particles  108 . Preferably, the tapering ramped channel feature is machined into the surface of developer sleeve  101  so that the toner is moved, by the geometry of the tapering ramped channel, away from the seal. Multiple tapering ramped channels  102  may be included in developer sleeve  101 . Channels  102  are spaced circumferencely around the diameter so that the toner is continually scooped or paddled away from seal  107  much as performed by an auger. Tapering ramped channels  102  are preferably incorporated on both ends of developer roller  101  to reduce or eliminate toner leakage at both seals.  
         [0023]    Developer sleeve  101  rotates in a direction indicated by arrow  103 . Tapering ramped channel  102  has a narrow section  104  (or proximal end) near to seal  107  and a wider section  105  (wide distal end) toward the longitudinal center of developer sleeve  101 .  
         [0024]    [0024]FIG. 2 shows a cross section of tapering ramped channel  102  along cut line  2 - 2  (FIG. 1) which is generally formed as a tapered wedge or ramp cut into the surface of developer sleeve  101  at an arcuate angle. As can be seen from FIG. 2, narrow proximal end  104  of tapering ramped channel  102  extends deeper into developer sleeve  103  than wide distal end  105  of tapering ramped channel  102 . The narrow, deeper portion  104  of tapering ramped channel  102  ensures toner is pushed or falls into the opening at narrow proximal end  104 . The wider, shallower structure of distal end  105  of tapering ramped channel  102  ensures that the toner particles that are pushed into narrow proximal end  104  are conveyed to wide distal end  105 . This movement of toner particles from narrow proximal end  104  to wide distal end  105  reduces toner-particle pressure on seal  107 .  
         [0025]    Tapering ramped channel  102  is also oriented in developer sleeve  101  so that narrow proximal end  104 , closest to the seal, moves in under any toner buildup first, scooping out the toner and pushing it toward wide distal end  105  and the center of the roller. This orientation, and the shape of the tapering channel ensures toner travels from high pressure to low pressure, or away from seal  107 . Reference arrow  106  indicates the direction of toner flow in FIG. 1.  
         [0026]    As described, the shape of tapering ramped channel  102  that is machined into the surface of developer sleeve  101  transitions from narrow and deep to wide and shallow. In other words, as shown in FIG. 2, narrow proximal end  104  extends deeper into developer sleeve  101  than wide distal end  105 . The orientation encourages toner particles  108  to travel from a high pressure to a low pressure, in other words, away from seal  107 . Toner is being pushed away from seal  107  as developer sleeve  101  rotates in an “auger” type fashion. Thus, as developer sleeve  101  rotates, the tapering ramped channel or channels generate a circular path of toner on developer sleeve  101  at a point away from seal  107 . The tapering ramped channels transport the toner from near the seal back towards the center of the paper where the toner is spread across the roller onto the page by the doctor blade. Typically in a toner cartridge not incorporating the present invention, toner located near the seal never does get developed onto a page because it is the outboard of the page.  
         [0027]    Further details of a roller according to the invention can be seen in FIGS. 3 through 6. In particular, FIG. 3 is a front view of a developer roller  304  incorporating a plurality of toner collection channels or tapering ramped channels  102  on opposing ends of the roller. Tapering ramped channels  102  are formed in the surface of developer roller  304  at an arcuate angle relative to a longitudinal axis of the roller. For example, a projection of a centerline longitudinally bisecting channel  102  onto the longitudinal axis of roller  304  may form an angle of between 30 and 60 degrees and, more preferably, 45 degrees. Typically, for commonly used page-width developer rollers and for fluids such as printer toner, each tapering ramped channel  102  is between 1 and 5 mm long. A deep end of channel  102  proximate seal  107  extends between 0.1 and 1 mm down into the surface of the roller, gradually ramping up to the upper surface of the roller at the end of the distal end of the channel farthest from the seal. The taper is narrowest at the proximal end nearest seal  107 , widening toward the distal end to a final width of between 0.2 and 1 mm, the walls of the channel forming an angle of between 5 and 20 degrees there between. The bottom of the channel may have a rounded portion at the proximal end as shown in FIG. 2 with a radium R of between 2 and 10 mm so as to minimize any tendency for toner particles to get stuck between the sidewalls of the channel. The sidewalls may be straight or include a gradually tapering slope to avoid a sharp transition with the floor of the channel.  
         [0028]    Preferably, a plurality of tapering ramped channels  102  are arranged in annular rings at opposite ends of developer roller  101  immediately adjacent respective seals  107  as shown in FIG. 4. Seals  107  are better seen in FIGS. 5 and 6 as extending around a portion of roller  101  that is exposed to toner contained in toner supply hopper  110 . The number, size, geometry and relative placement of tapering ramped channels  102  may be optimized in view of the specific application including roller geometry, speed of rotation, fluid or particle properties (in this case, toner fluidity, size, etc.), operating temperature, etc. For a conventional developer roller, it is expected that a single annular ring of between 10 and 50 tapering ramped channels would be provided at each end of the roller. However, other configurations may be used including, for example, multiple rings of channels and/or staggered positioning of channels.  
         [0029]    As shown in FIG. 7 as viewed from the left end of the roller, the surface of developer sleeve  704  rotates counterclockwise. Thus, a point on the surface of sleeve  704  would initially be positioned within toner hopper  702  for a portion of time, pass through doctor blade  706 , be exposed to OPC  709 , pass under developer blade  707  and repeat this cycle. When the tapering ramped channel of the current invention is incorporated into the circumference of developer roller  101  (FIG. 1) and located inboard of seal  107 , the tapering channel travels into and out of toner hopper  702 . When tapering ramped channel  102  passes through toner hopper  702 , the action of the channel causes toner to flow away from seal  107 . Toner is also doctored by doctor blade  706  so that when the tapering channel is rotated such that it is on the exterior of the supply of toner it would have a consistent thickness of toner  803  due to doctor blade  706  smoothing the toner, including the toner recovered from against seal  107 , as it goes by doctor blade  706 .