Abstract:
An apparatus and method for dispensing toner in an electrostatographic printer includes an apparatus for transporting powder into a developer station containing at least powder and magnetic carrier including a conveyance housing divided into a mixing space adjacent to a second separate transport space, the second transport space located adjacent to a development roller, a powder conveying device located in the conveyance housing comprising two or more augers and a conveyance controller for controlling the powder conveying device, including the one or more augers, such that the auger preferentially mixes in the first mixing space and transports in the second transport space as the powder conveying device conveys the powder toward the imaging device of a print engine.

Description:
FIELD OF THE INVENTION 
   The invention relates to electrographic printers and apparatus thereof. More specifically, the invention is directed to an apparatus and method for transporting a powder, such as developer to an image device in an electrostatographic printer. 
   BACKGROUND OF THE INVENTION 
   Electrographic printers and copiers utilizing developer comprising toner, carrier, and other components use a developer mixing apparatus and related processes for mixing the developer and toner used during the printing process. The term “electrographic printer,” is intended to encompass electrophotographic printers and copiers that employ dry toner developed on an electrophotographic receiver element, as well as ionographic printers and copiers that do not rely upon an electrophotographic receiver. The electrographic apparatus often incorporates an electromagnetic brush station or similar development station, to develop the toner to a substrate (an imaging/photoconductive member bearing a latent image), after which the applied toner is transferred onto a sheet and fused thereon. 
   As is well known, a toner image may be formed on a photoconductor by the sequential steps of uniformly charging the photoconductor surface in a charging station using a corona charger, exposing the charged photoconductor to a pattern of light in an exposure station to form a latent electrostatic image, and toning the latent electrostatic image in a developer station to form a toner image on the photoconductor surface. The toner image may then be transferred in a transfer station directly to a receiver, e.g., a paper sheet, or it may first be transferred to an intermediate transfer member or ITM and subsequently transferred to the receiver. The toned receiver is then moved to a fusing station where the toner image is fused to the receiver by heat and/or pressure. 
   In electrostatographic copiers and printers, pigmented thermoplastic particles, commonly known as “toner,” are applied to latent electrostatic images to render such images visible. Often, the toner particles are mixed with and carried by somewhat larger particles of magnetic material. During the mixing process, the magnetic carrier particles serve to triboelectrically charge the toner particles to a polarity opposite that of the latent charge image. In use, the development mix is advanced, typically by magnetic forces, from a sump to a position in which it contacts the latent charge image. The relatively strong electrostatic forces associated with the charge image operate to strip the toner from the carrier, causing the toner to remain with the charge image. Thus, it will be appreciated that, as multiple charge images are developed in this manner, toner particles are continuously depleted from the mix and a fresh supply of toner must be dispensed from time-to-time in order to maintain a desired image density. Usually, the fresh toner is supplied from a toner supply bottle mounted upside-down, i.e., with its mouth facing downward, at one end of the image-development apparatus. Under the force of gravity, toner accumulates at the bottle mouth, and a metering device, positioned adjacent the bottle mouth, operates to meter sufficient toner to the developer mix to compensate for the toner lost as a result of image development. Usually, the toner-metering device operates under the control of a toner concentration monitor that continuously senses the ratio of toner to carrier particles in the development mix. 
   It is well known that toner is a powdery substance that exhibits a considerable degree of cohesiveness and, hence, relatively poor flowability. Since the force of gravity alone does not usually suffice in causing toner to flow smoothly from the mouth of an inverted toner bottle, other supplemental techniques have been used to “coax” the toner from the bottle. For example, flow additives, such as silica and the like, have been added to the mix to reduce the troublesome cohesive forces between toner particles. See, e.g., the disclosure of U.S. Pat. No. 5,260,159 in which a “fluidization” agent is added to a developer mix in a development sump to assist the movement of developer therein. While beneficial to a more consistent flow of developer, such substances influence other performance attributes of the development process and their effectiveness is therefore constrained. Automatically operated stirring devices or augers mounted within a horizontally oriented toner container, and thumping or vibrating devices connected to such containers have also been used to urge toner from its rest position towards an outlet or exit port. Such mechanical techniques work well when the toner container is relatively small (e.g., 2 to 5 liters) and the height of the toner column above the exit port is relatively low (e.g., lower than about 15 cm.) so as to avoid gravity-assisted compaction of the toner which further compromises flowability. But, as the size of the toner bottle or container increases, e.g., to accommodate high speed and wide format printing in which toner is consumed at extraordinarily fast rates, the above-noted flow-enhancing techniques have been found to be inadequate. In such high toner-consumption situations, toner sumps of the order of tens of liters are desirable in order to eliminate the need for frequent toner bottle replacements. The weight of the toner in these large volume containers is too great for conventional rappers and vibrators to keep the toner flowing through the outlet, and most of these devices only exacerbate the toner-packing problem. 
   In U.S. Pat. No. 5,570,170, there is disclosed an apparatus for dispensing single-component, electrically conductive magnetic toner particles from a pair of inverted toner bottles mounted above a conventional development station in an electrostatic printing apparatus. A screen positioned at the mouth of each bottle serves to prevent toner flow from the bottle whenever the toner is piled up atop the screen. The toner-dispensing apparatus includes a pair of gas-permeable, but toner-impermeable, tubes that extend upwardly, into each bottle, a distance of about 30-60% of the height of the bottles. On command, pressurized gas is introduced into the tubes. As the gas passes through the tubes and into the toner bottles, it acts to fluidize the toner in the bottle in the vicinity of the bottle&#39;s outlet, thereby enabling the toner to flow smoothly through the screen mesh and into the development station of the printer, as needed. In effect, the screen acts as a gate to prevent toner flow into the development station until the toner above the screen is fluidized. A microprocessor controls the application of pressurized gas to each of the bottles, switching from one bottle to the other as one-bottle empties. By using two bottles, the machine operator can replace an empty bottle without shutting down the machine. 
   Development stations require replenishment of toner into the developer sump to replace toner that is deposited on the photoconductor or receiver. In development stations utilizing carrier, this toner must be mixed uniformly with the carrier. Replenishment has been done at a single location in the developer sump but this has lead to high concentrations of low-charge toner in one area of the sump, which tends to produce a dark streak on the image or receiver, or produces non-uniform areas in an image. 
   The present invention corrects the problem of non-uniform mixing. The apparatus and related methods transport and mix the toner efficiently when needed, maintaining the correct proportions necessary to produce the high quality prints or powder coatings required by consumer demand. The following invention solves the current problems with developer mixing so that the mixer will work in a wide variety of situations and with different types of toners, powders, or particles. 
   SUMMARY OF THE INVENTION 
   The invention is in the field of mixing apparatus and processes for electrographic printers and powder coating systems. More specifically, the invention relates to an apparatus and method for distributed mixing and transport of toner and powders, including toner in powder form as well as powder coatings and similar materials. The apparatus for transporting powder into a developer station containing at least powder and magnetic carrier including a conveyance housing divided into a mixing space adjacent to a second separate transport space, the second transport space located adjacent to a development roller, a powder conveying device located in the conveyance housing comprising two or more augers and a conveyance controller for controlling the powder conveying device, including the one or more augers, such that the auger preferentially mixes in the first mixing space and transports in the second transport space as the powder conveying device conveys the powder toward the imaging device of a print engine. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side elevational view, in cross-section, of a reproduction apparatus magnetic brush developer station according to this invention. 
       FIG. 2  is an end view, partly in cross-section and on an enlarged scale, of the development roller and metering skive of the magnetic brush development station of  FIG. 1 . 
       FIG. 3  is a bottom view, partly in cross-section and on an enlarged scale, of a portion of the development roller and metering skive of  FIG. 2 , particularly showing the magnetic seal according to this invention. 
       FIG. 4  is a view, in perspective, of the mixing augers of the magnetic brush development station of  FIG. 1 . 
       FIG. 5  is a schematic top view of  FIG. 1 . 
       FIG. 6  is a schematic side view a single auger in a asymmetric sump. 
       FIG. 7  is a schematic showing one embodiment of the present invention. 
       FIGS. 8   a  and  8   b  show a schematic of a single channel auger. 
       FIGS. 9   a  and  9   b  shows a schematic of auger rotation. 
       FIG. 10  is a schematic showing another embodiment of the present invention. 
       FIG. 11  is a schematic further showing the embodiment of  FIG. 10 . 
       FIG. 12  shows a graphic representation of the present invention. 
       FIG. 13  shows a graphic representation of the present invention. 
       FIG. 14  shows a graphic representation of the present invention. 
       FIG. 15  shows a graphic representation of the present invention. 
       FIG. 16  shows a variety of optimized examples. 
       FIG. 17  shows an example for different auger orientations. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a reproduction apparatus magnetic brush developer station, according to this invention, (also referred to as a developer station) designated generally by the numeral  10 . The magnetic brush development station  10  includes a development station housing  11 , divided into a feed apparatus  8  and a powder conveyance device  12 . The powder conveyance device  12  is divided into a mixing space  44  adjacent to a transport space  46  (See  FIG. 5 ). The housing forming, in part, a reservoir for developer material. A plurality of augers  28 , having suitable mixing paddles, stir the developer material within the reservoir of the housing  11 . The outside diameter of this auger typically spaced a distance Z from the inner wall of the housing. A development roller  14 , mounted within the development station housing  11 , includes a rotating (counterclockwise in  FIG. 1 ) fourteen-pole core magnet  16  inside a rotating (clockwise in  FIG. 1 ) shell  18 . Of course, the core magnet  16  and the shell can have any other suitable relative rotation. The quantity of developer material delivered from the reservoir portion of the housing  11  to the development zone  20  is controlled by a metering skive  22 , positioned parallel to the longitudinal axis of the development roller  14 , at a location upstream in the direction of shell rotation prior to the development zone. The metering skive  22  extends the length of the development roller  14  (see  FIG. 3 ). The core magnet  16  does not extend the entire length of the development roller, as such, the developer nap on the shell  18  does not extend to the end of the development roller. 
   At each end of the development roller  14 , a single pole permanent ceramic magnet  24  is used (one end shown in  FIGS. 2 and 3 ) as a seal to prevent leakage of developer material from the ends of the development roller. The magnet  24  is selected to provide a magnetic field with a strength in the range of 400 to 1200 gauss, and preferably 900 gauss. One end  24   a  of the magnet  24  is approximately flush with the end of the development roller  14  and extends along the longitudinal axis of the development roller such that an overlap (approximately 10 mm) exists with the roller. The single pole magnet  24  is secured to the underside of the mount for the metering skive  22  by a metal plate and fastener  26  with the active pole of the magnet in close proximity to the developer roller circumference. The metal plate  26  functions to shunt the magnetic field except in the area of the magnet  24  which faces the developer roller  14 . 
   It is apparent that the magnet  24  as described above provides an effective seal preventing developer material from escaping from the ends of the developer roller. Since this seal does not have any moving parts, there is no wear, and there is no mechanical friction which would generate heat and create undesirable developer material flakes. Moreover, there is no seal material which would wear and contaminate the developer material. 
   To further prevent development material from escaping from the development station housing  11 , there is provided an easily serviced assembly for the driveshaft of the augers  28 . A rotatable shaft  50  connected to each auger  28  to move the auger and thus help transporting developer material within the development station housing reservoir. One or more sealing members  48  including a lip seal formed of a material which is able to stretch sufficiently to maintain contact with shaft  50  while the shaft is being rotated by the drive member  38 . This assembly is robust to wear and any heat generation. The two bearings with a spacer in between are used so as to maintain minimum radial movement of the shaft  50 . The shaft includes a feature used for drive rotation and also a yoke to accept the end of the marking particles delivery auger. The shaft is hardened and ground to reduce wear and heat generation at the seal interface. The auger  28  is attached to the shaft  50  removeably with a pin or other attachment device that is captured in either side of the yoke of the shaft feature. The washer and e-rings complete the assembly and hold it together, and can be removed by disassembling any drive mechanism, and then removing the assembly. 
   The development station housing  11  has a membrane-type seal placed over a hole  11   a  in the side wall of the housing. The seal serves the purpose of providing pressure equalization within the housing. The surface area of the seal is selected to provide sufficient pressure equalization efficiency. The seal allows air flow, caused by pressure differential between inside the housing  11  and the exterior thereof, through the membrane without carrying developer material dust out of the housing. The seal is located in such a position as to cause developer material in the housing to continuously be moving across the membrane surface to continuously clean the membrane seal to maintain the efficient operation thereof. 
   It should be noted that, as the reproduction apparatus market has evolved from black and white copiers to process color printers, more development stations needed to be fit into essentially the same amount of machine space. To do this a more compact station was needed that would still adequately mix developer material and hold as large a developer material volume as possible. The increased station capacity was desired to increase the time between developer material replenishment and changes. Also, the larger volume of developer material would allow for higher takeout rates of marking particles while removing a smaller percentage of the available particles. The solution has been to increase the development station housing reservoir “floor” space increase the nominal diameter of the augers. The magnetic brush development station  10 , according to this invention, uses two augers  28  (see  FIG. 1 ), although a different number could be used. The augers are controlled by controller  60  (See  FIG. 4 ). The controller controls the powder conveying device, such that the auger preferentially mixes in the mixing space  44  and transports in the second transport space  46  as the powder is conveyed toward the feed apparatus  8 . The increased reservoir capacity has two main advantages; it increases the time between developer changes, and allows for a longer dwell time of developer material in the reservoir for mixing (this improves material charging and material dispersion which aid in reducing dusting) 
   The magnetic brush development station  10 , according to this invention, provides for replenishing the housing reservoir with a fresh supply of marking particles for the developer material as required, A single point system allows for greater total throughput of material while maintaining a minimal amount of fresh marking particles being added at any one point. This allows the marking particles to be mixed into the developer material much quicker and can subsequently get triboelectrically charged much quicker. This aids in reducing dusting and maintaining a uniform concentration of marking particles throughout the sump. 
   The developer station  10  must have a set spacing of the developer roller  14  to a photoconductor surface  40 . There have been many attempts at different ways to control developer nap thickness on the developer roller  14  as a way to decrease the spacing sensitivity between the developer roller  14  and photoconductor  40 . If the developer nap is too thick developer material can leak away from the ends of the magnetic core of the developer roller resulting in contamination of other areas of the electrophotographic reproduction apparatus, such as the photoconductor  40  and the intermediate transfer roller (blanket cylinder)  42 . If the developer nap is too thin there may not be enough toner present to enable high quality development. To facilitate recharging of the developer material with new marking particles, the magnetic core  16  of the roller  14  is placed eccentrically inside the developer roller shell  18  allowing developer to fall off the shell when it reaches a region of lower magnetic field. This eliminates the need for a skive to remove developer from the roller and the toner flake and agglomerate generation that normally accompanies such design. 
   One embodiment of this invention is the orientation of the elements. The apparatus  10 , according to this embodiment of the invention, has a plurality of auger shafts for the mixing of developer with fresh toner and the transport of the developer to the toning zone for image development. These augers consist of a shaft populated with blades (paddles), roughly semi-circular in shape, that are fixed at some angle with respect to the axial centerline of the shaft. It was suspected that the paddle properties could have a great influence on the movement and mixing efficiency of developer within the sump, and little historical data on the motivation for the current paddle setpoints were found. A series of experiments ensued to reveal the nature of paddle properties to both developer transport and mixing efficiency. This involved understanding the relationship between the relative amount of developer, including controlling the volume of powder to magnetic carrier volume, that is transported parallel to the axis of the auger shaft (Axial) vs. perpendicular to the axis of the auger shaft (Radial). 
   In the asymmetric sump (as defined by non equal heights of the opposing sidewalls) shown in  FIG. 5 , axial flow is maximized when the rotation of the auger is in the direction from the lower wall to the higher wall (see  FIG. 5 . The relationship between a series of factors influence the amount of developer that is pushed (axially to the shaft) and flipped (radially to the shaft) which effects the efficiency of the mixing and transportation of the powder.  FIG. 7  shows a single channel example where the rotation sense of the auger relative to the sump is as shown. When the rotation of the auger relative to the sump changes the effectiveness of both mixing and transporting is effected as shown in  FIG. 8 . 
     FIG. 8  is shows the auger configuration discussed above (equivalent sump size/orientation, center wall height, paddle angle, paddle pitch and auger speed), run against counterclockwise (CCW) and clockwise (CW) rotations. Clockwise rotation Push % (axial to shaft) and Flip % (radial to shaft) developer flow data were obtained from a visual observation of developer distributions after operation. The reason for this effect has to do the mechanism by which developer is moved axially along the wall of the sump. As the paddle rotates, the sidewall of the sump keeps the developer from moving radially under the action of the centrifugal force created by the rotation of the paddle. This then allows the developer to be moved axially along the sump, proportional to the angle the paddle to the auger shaft. Given this, a symmetrical sump, or one that has opposing walls of equal height, would not be sensitive to this effect. Thus, with an asymmetrical sump design, the rotation sense needs to be consistent with that described in the Summary of Invention section in order to establish an axial flow component in a dual auger sump. 
     FIG. 9  shows one example of the auger shaft  50  for the mixing of developer with fresh toner and the transport of the developer to the toning zone for image development. These augers consist of a shaft populated with blades (paddles), roughly semi-circular in shape that when populated on the auger shaft has an equivalent conveyance housing diameter of 10 mm to 75 mm. The paddles are fixed at some angle (for example, 20 to 40 degrees) with respect to the axial centerline of the shaft. It was suspected that the paddle angle could have a great influence on the movement and mixing efficiency of developer within the sump, and little historical data on the motivation for the current paddle angle were found. A series of experiments ensued to reveal the nature of paddle angle to both developer transport and mixing efficiency. This involved understanding the relationship between the relative amounts of developer that is transported parallel to the axis of the auger shaft (Axial) vs. perpendicular to the axis of the auger shaft (Radial) based on a representative 90 angle paddle orientation as shown in  FIG. 10 . 
   The push to flip ratio (P/F) for a single channel auger can be optimized with the following relation:
 
 P/F=− 0.9582+0.085*Sump Radius−0.1309 *X -Over Ratio−0.0057*Blade Angle+0.2832*Blade Pitch−0.0012*Auger Speed+0.0659*Load Ratio, where:
         Sump Radius—Nominal radius of the auger sump, mm   X-Over Ratio—Sump Radius (mm)/Height of centerwall from sump tangent point (min)   Blade Angle—Angle of blade w.r.t. shaft drive axis (deg)   Blade Pitch—Axial Center to Center distance between blade pairs on the auger shaft (in)   Auger Speed—Speed of Auger Shaft (rpm)   Load Ratio−(π*(Sump Radius)^2)mm^2/150 gm, where 150 gm is a experimentally derived nominal single channel developer load       

   Although this relationship holds specifically for an auger configuration where adjacent paddles (paddle pairs) are oriented 90° apart, adjacent paddle tips are in contact, and the auger is nominally spaced 0.5 to 1 mm from the inner wall of the housing, it can be modified or extended to cover other orientation angles and spacings. The relationship between a series of factors and how these factors influence the amount of developer that is pushed (Axially to the shaft) and flipped (radially to the shaft) was then developed. This experiment was structured as a 6 factor Central Composite Design (CCD), face centered, with 9 centerpoint replicates. The strategy was to characterize the flow with a single channel auger (see  FIG. 7 ). The experimental factors for a single channel auger implementation are shown below (see Table 1 below): 
   
     
       
             
           
             
             
             
             
             
           
         
             
               TABLE 1 
             
           
           
             
                 
             
             
               Factors for Single Channel Auger 
             
           
        
         
             
                 
                 
                 
                 
               High 
             
             
                 
               Factor 
               Low Level 
               Mid Level 
               Level 
             
             
                 
                 
             
             
                 
               Sump 
               17.4625 mm 
               20.6375 mm 
               25.4 mm 
             
             
                 
               Radius 
             
             
                 
               X-Over 
               2.5 
               3.7 
               4.9 
             
             
                 
               Angle 
               20° 
               30° 
               40° 
             
             
                 
               Pitch 
               0.3600 in 
               0.5625 in 
               0.7650 in 
             
             
                 
               Speed 
               106 rpm 
               162 rpm 
               218 rpm 
             
             
                 
               Load Ratio 
               5 
               6 
               7 
             
             
                 
                 
             
           
        
       
     
   
   These factors apply to a single channel auger and were developed specifically under the following conditions including preloading the sump with the specified amount of developer (from the experimental array). The motor was then started, along with a timer. The axial container was observed and the timer was stopped when no more developer was observed exiting the axial portion of sump. The contents of the axial container, the radial container and the residual the left in the sump were measured and reconciled against the original sump load. This relationship is shown graphically in  FIG. 12 .  FIG. 12  shows a Contour plot of End % (% of total sump load pushed out axial end of the sump) vs. Paddle Angle and Paddle Pitch (data for 20.64mm Sump Radius, 3.7X-Over, 160rpm, 6Load Ratio). 
   From the information in  FIG. 12 , one can see for this paddle configuration (adjacent paddles @90°), the amount of developer pushed out the end of the channel is maximized when the paddle angle is ≈22°-32°, and the paddle pairs are pitched≈0.500″-0.630″. In this manner, the proper circulation (as defined by the % of developer that circulates on the outer walls of a dual auger sump), can be optimized by this invention. 
   Another important element to a well-mixed and efficient transport apparatus with augers as shown in  FIG. 9  including the shaft populated with blades (paddles), roughly semi-circular in shape, is the angle that the blades are fixed with respect to the axial centerline of the shaft. The paddle angle and/or orientation have a great influence on the movement and mixing efficiency of developer within the sump. This relationship is optimized by a relationship between the relative amount of developer that is transported parallel to the axis of the auger shaft (Axial) vs. perpendicular to the axis of the auger shaft (Radial). The proportion of developer moved axially and radially to the auger axis can be adjusted by changing the angular orientation of adjacent paddles on the auger shaft between 0° and 180° relative to an orientation of adjacent paddles with the paddles represented by the darker lines in  FIG. 11 . 
   The relationship between a series of factors influences the amount of developer that is pushed (Axially to the shaft) and flipped (radially to the shaft). This experiment was structured as a 3 factor Central Composite Design (CCD), face centered, with 2 centerpoint replicates. The strategy was to characterize the flow with a single channel auger (see  FIG. 7 ). The experimental factors consisted of (Table 2) shown below: 
   
     
       
             
           
             
             
             
             
             
           
         
             
               TABLE 2 
             
           
           
             
                 
             
             
               Factors for Single Channel Auger 
             
           
        
         
             
                 
                 
                 
                 
               High 
             
             
                 
               Factor 
               Low Level 
               Mid Level 
               Level 
             
             
                 
                 
             
             
                 
               Sump 
               17.4625 mm 
               20.6375 mm 
               25.4 mm 
             
             
                 
               Radius 
             
             
                 
               Paddle 
               20° 
               30° 
                40° 
             
             
                 
               Angle 
             
             
                 
               Orientation 
                0° 
               90° 
               180° 
             
             
                 
                 
             
           
        
       
     
   
   These factors apply to a single channel auger and were developed specifically under the following conditions including preloading the sump with the specified amount of developer (from the experimental array). The motor was then started, along with a timer. The axial container was observed and the timer was stopped when no more developer was observed exiting the axial portion of the sump. The contents of the axial container, the radial container and the residual left in the sump were measured and reconciled against the original sump load. This relationship is shown below graphically showing a Contour plot of End % (% of total sump load pushed out axial end of the sump) vs. Paddle Angle and Paddle Orientation. From this graph, one can see that the paddle orientation can regulate the amount of developer pushed out the end of the channel, with maximum axial flow exhibited at 180° adjacent paddle orientation and 20° paddle angle. In this manner, the proper circulation (as defined by the % of developer that circulates on the outer walls of a dual auger sump), can be maximized/optimized by this invention as shown in  FIG. 13 . 
   Another important element to a well-mixed and efficient transport apparatus with augers as shown in  FIG. 9  including the shaft populated with blades (paddles), roughly semi-circular in shape, is the angle that the blades are fixed with respect to the axial centerline of the shaft. The paddle angle and/or orientation have a great influence on the movement and mixing efficiency of developer within the sump. This relationship is optimized by optimizing the relationship between the relative amounts of developer that is transported parallel to the axis of the auger shaft (Axial) vs. perpendicular to the axis of the auger shaft (Radial) in addition to the factors discussed above. Mixing efficiency (as defined by the lowest standard deviation of ‘n’ Toner Concentration measurements at different areas of the sump) is maximized by minimizing the ratio of the amount of developer that is transported axially along the sump shaft (Push) to the amount moved radially between the auger shafts (Flip) in a dual auger sump configuration. The factors evaluated and optimized to characterize mixing efficiency w.r.t include the following factors that affect mixing efficiency and developer flip %: 
   
     
       
             
             
           
         
             
                 
             
             
               Factor 
               Description 
             
             
                 
             
           
           
             
               X-Over 
               Ratio of Sump Radius to Centerwall Height 
             
             
               Paddle 
               Angular Orientation of Adjacent Paddles 
             
             
               Orientation 
             
             
               Paddle Angle 
               Angle of the Paddle to Drive Axis of Auger Shaft 
             
             
               Auger Speed 
               Nominal Speed of the Auger Shaft 
             
             
                 
             
           
        
       
     
   
   These factors apply to a multi-channel auger, in particular a dual channel, auger and were developed specifically under the following conditions including loading the sump with an appropriate amount of developer, and running for some period of time to uniformly distribute the developer load within the sump. Toner was added to raise the toner concentration in the sump by a prescribed amount. The sump was then run additionally, to allow for mixing and transport of the toner-replenished developer. A number of toner concentration measurements were made at various mixing times. Results of the toner concentration after these mixing times formed the basis for the assessment of the mixing efficiency are summarized below in the tables and charts comparing effect of certain paddle configuration parameters on both Flip % and effect on mixing efficiency. 
   
     
       
             
           
             
             
             
           
         
             
               TABLE 1 
             
           
           
             
                 
             
             
               Chart comparing effect of certain paddle configuration parameters on 
             
             
               both Flip % and effect on mixing efficiency. 
             
           
        
         
             
                 
               Effect on Developer 
               Effect on Mixing 
             
             
               Factor 
               Flip % 
               Efficiency 
             
             
                 
             
             
               X-Over 
               As Centerwall Height 
               As Centerwall Height 
             
             
                 
               Becomes Lower, Flip % 
               Becomes Lower, Mixing 
             
             
                 
               Increases 
               Efficiency Improves 
             
             
               Paddle 
               Flip % Maximixed at 
               90° Orientation Results in 
             
             
               Orientation 
               40° &gt;= Paddle 
               Better Mixing Efficiency 
             
             
                 
               Orientation &lt;= 120°, 
               than 180° Orientation 
             
             
                 
               Minimum Flip % at 
             
             
                 
               180° 
             
             
               Paddle 
               Flip % increases 
               40° Paddle Angle Mixing 
             
             
               Angle 
               substantially with Paddle 
               Superior than 20°/30° 
             
             
                 
               Angles &gt; 30° 
             
             
               Auger 
               Flip % increases with 
               Mixing efficiency 
             
             
               Speed 
               increasing Auger Speed 
               improves with increasing 
             
             
                 
                 
               Auger Speed 
             
             
                 
             
           
        
       
     
   
     FIG. 14  is a graphical representation of some of the data gathered showing mixing effect of Centerwall height, Paddle Orientation, Paddle Angle and Auger Speed. (Lower Std. Dev. Equates to better mixing efficiency).  FIG. 14  shows a contour of cross % versus sump radius and/or cross over in percentages for an angle of 30 degrees, pitch of 0.5625, speed of 160 and a load of 6. 
     FIG. 15  is a graphical representation of some of the date gathered showing data for Contour Plot of Flip % (Cross %) vs. Paddle Orientation (Orientation). Paddle Angle (Angle) and Sump Radius (Sump). The contour plot of Flip % (Cross %) against Sump Radius and X-Over (Centerwall Height). X-Over has inverse relationship to Centerwall Height, thus X-Over 4.5 has shorter Centerwall Height than X-Over 2.5.  FIG. 15  shows a contour of cross % for orientation angle, sump angle and sump orientation for an angle of 30 degrees and an orientation 90 degrees. 
   The above described along with the summarized relationships between the Flip % and the resulting mixing efficiency as well as those shown in  FIGS. 12-15  allow optimization of the auger in a development station in a variety of situations. Configurations that flip better result in more intimate contact between the opposing streams of the developer, resulting in faster and more efficient mixing of the replenished toner. 
   An example of one optimized arrangement based on this information includes a full sump with a configuration of 90° Paddle Orientation (40° Paddle Angle) against 180° Paddle Orientation (20° Paddle Angle) (Sump Radius=25.4 mm, X-Over=3.7, Auger Speed=500 rpm). The curves clearly show the preference for the 90° Paddle Orientation (40° Paddle Angle) over the 180° Paddle Orientation (20° Paddle Angle) as shown in  FIG. 17 . 
   The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.