Abstract:
An apparatus for applying toner to a photoconductor in an electrophotographic printing apparatus includes a feed auger for feeding developer from a channel to a toning roller. The toning roller transfers toner to a photoconductor. Depleted developer is removed from the toning roller to a return auger channel where it is refreshed with fresh toner. The refreshed developer is combined with the unused developer in the feed auger channel. The combined refreshed developer is transferred to a mixing channel. The mixed developer is transferred to the feed auger channel. An axis of the feed auger is tilted with respect to an axis of the toning roller.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Reference is made to commonly-assigned copending U.S. patent application Ser. No. ______ (Attorney Docket No. 96667US01NAB), filed herewith, entitled ANGLED MAGNETIC AUGER FOR A DEVELOPER STATION, by Rapkin; the disclosure of which is incorporated herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates in general to electrophotographic printing and in particular to an improved agar for a developer station. 
       BACKGROUND OF THE INVENTION 
       [0003]    The three channel development system used in electrophotographic printers has a development roller that moves developer containing toner into proximity with a primary imaging member, usually a photoconductor; and a first channel containing a feed auger, a second channel containing a return auger, a third channel containing a mixing auger. The primary imaging member is used for forming an electrostatic image. The developer used in development systems of this type usually contains magnetic particles and marking particles. The marking particles are removed from the development system to form an image on the primary imaging member. 
         [0004]    The flow of developer through the three channel development system is such that developer is fed from the third channel to a first end of the feed auger in the first channel. As the developer travels longitudinally down the length of the feed auger, a portion of the developer is fed transversely from the feed auger to the development roller to produce a layer of developer on the development roller. The remainder of developer in the first channel continues to travel longitudinally down the length of the feed auger. 
         [0005]    To produce a uniform image, the layer of developer on the development roller should be uniform along its length. The developer that is fed to the development roller moves over the development roller and is not returned to the feed auger but instead drops into the return auger in the second channel. Consequently, the volume of developer in the first channel decreases along the length of the first channel in the direction of developer flow along the first channel. 
         [0006]    Developer moves longitudinally in the same direction in both the first channel and the second channel, from the first end of the augers to the second end, which is at the rear or drive end of the development system. At the rear of the development system, the developer collected by the second channel and the remaining developer in the first channel are both dropped into the third channel. It is also at this point that replenishment marking particles are added to the developer to replace the marking particles that have been applied to the primary imaging member. The developer is moved transversely along the third channel by the mixing auger, toward the first end of the feed auger. The developer that has traveled the length of the third channel is fed to the first end of the feed auger in the first channel, so that the developer is cycled continuously from the first channel to the development roller while the development system is running 
         [0007]    In comparison, one channel or two channel development system designs often have the characteristic that developer that has travelled over the development roller is dropped back into the channel from which it was fed to the development roller. Some of this developer will have had marking particles removed by the image. In other words, the concentration of marking particles in the developer is reduced as the developer is used for image development, returned to the feed auger, and subsequently travels down the feed auger of a one channel or two channel development system. As the toner concentration decreases, the developed mass and image density also decrease undesirably. 
         [0008]    An advantage of the three channel design compared to a one channel or two channel design is that the marking particle concentration is maintained down the length of the first channel. However, the volume of developer in the first channel does not remain constant down its length, usually resulting in more developer on the development roller near the first end of the feed auger, where there is a relatively large volume of developer in the first channel. Near the second end of the feed auger, where there is a relatively small volume of developer, there is usually less developer on the development roller. 
         [0009]    It is advantageous to have a constant mass flow of developer at any point along the entire length of the development roller as well as having a constant marking particle concentration in the developer that is presented to the primary imaging member via the development roller. Specifically, it is advantageous to have a means of maintaining the developer feed to the development roller despite the reduction in developer volume down the length of the first channel. 
       SUMMARY OF THE INVENTION 
       [0010]    Briefly, according to one aspect of the present invention a method of applying toner to a photoconductor in an electrophotographic printing apparatus includes feeding developer from a feed auger channel to a roller; transferring toner from the development roller to a photoconductor; removing depleted developer from the development roller to a return auger channel; refreshing the depleted developer with fresh toner; combining the refreshed developer with unused developer in the feed auger channel; transferring the combined refreshed developer to a mixing channel; transferring the mixed developer to the feed auger channel; and wherein an axis of the development roller is tilted with respect to an axis of the toning roller. 
         [0011]    One embodiment of the invention tips the feed auger relative to the development roller such that the development roller is substantially parallel to the developer level of the feed channel, not parallel to the axis of the feed auger as is typical. The invention and its objects and advantages will become more apparent in the detailed description of the preferred embodiment presented below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a cross-sectional view of an electrophotographic printer. 
           [0013]      FIG. 2  is a transverse cross-sectional view of a development system for an electrophotographic printer according to an embodiment of the invention. 
           [0014]      FIG. 3  is a longitudinal cross-sectional view of a development system for an electrophotographic printer according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    The present invention will be directed in particular to elements forming part of, or in cooperation more directly with the apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. 
         [0016]      FIG. 1  shows an electrophotographic (EP) engine  100  or printer, often referred to as a tandem print engine including EP modules ( 120 A,  120 B,  120 C,  120 D,  120 E, and  120 F), wherein each contains a single primary imaging member (PIM)  115  and a single development system ( 10 A,  10 B,  10 C,  10 D,  10 E, and  10 F) to print on receiver  111 . The EP printer is shown having dimensions of A×B which are around in one example, 52×718 mm or less. Development stations  10 A- 10 D would typically contain marking particles that are typically used in most color prints. For example, marking particles having typical optical densities such that a monolayer coverage (i.e. sufficient application of marking particles such that a microscopic examination would reveal a layer of marking particles covering between 60% and 100% of a primary imaging member would have a transmission density in the primarily absorbed light color, as measured using a device such as an X-Rite Densitometer with Status A filters of between 0.6 and 1.0) of the subtractive primary colors cyan, magenta, yellow, and black would typically be contained in four of these development stations. The additional development systems can be used to print specialty marking particles that are commonly used for many applications, selectively determined by a control element. An individual operating or owning (hereafter referred to as the operator) the EP engine could control the control element and this effectively determines which specialty marking particles would print. 
         [0017]    For example, a full-color image can be made using marking particles that function as ink containing typical cyan, magenta, yellow, and black subtractive primary colorants such as pigment particles or dyes. The marking particles are contained in a development system that develops an electrostatic latent image and is in proximity to a cylindrical primary imaging member or a frame of a primary imaging member in the form of a continuous web. Additional marking particles corresponding to specialty toners or inks are contained in one of a plurality of development systems, any one of which can be brought into proximity with a primary imaging member bearing an electrostatic latent image and convert that electrostatic latent image into a visible image. For example, the electrophotographic engine shown in  FIG. 1  contains six print modules. Four of the modules would each contain a single development system containing marking particles of one of the four subtractive primary colors. The fifth and sixth EP modules  120 E and  120 F are shown with development systems, each containing marking particles having the function of a distinct specialty ink that can convert an electrostatic latent image into a visible image with only that specific specialty ink. 
         [0018]    For example, if clear toner is commonly used as a marking particle by a particular EP engine, the fifth development system  10 E could contain clear toner. Alternatively, other marking particles that would be commonly used throughout a variety of jobs can be contained in the fifth EP module. The sixth EP module  120 F is also capable of selectively printing a specialty marking particle. Images produced with specialty marking particles include transparent, raised print, magnetic image carrier recognition (MICR) magnetic characters, specialty colors and metallic toners as well as other images that are not produced with the basic color marking particles. 
         [0019]    Development systems suitable for use in this invention include dry development systems containing two component developers such as those containing both marking particles and magnetic carrier particles. The development systems used for two component development can have either a rotating magnetic core, a rotating shell around a fixed magnetic core, or a rotating magnetic core and a rotating magnetic shell. It is preferred that the marking particles used in practicing this invention are toner that is a component of dry developer. Marking particles are removed from the development system when images are printed. Replacement marking particles are added to the development systems  10 A- 10 F by replenishment stations  158 , each of which contain the appropriate marking particle. 
         [0020]    In the example shown in  FIG. 1 , after each development system develops the electrostatic latent image on the primary imaging member (PIM)  115 , thereby converting the electrostatic latent image a visible image, each image is transferred, in register, to an intermediate transfer member (ITM)  150 . The ITM can be in the form of a continuous web as shown or can take other forms such as a drum or sheet. It is preferable to use a compliant intermediate transfer member, such as described in the literature, but noncompliant ITMs can also be used. 
         [0021]    The receiver sheets are held in the printer at a paper tray (paper source)  105  and, in the example shown, enter the paper path  180  so as to travel initially in a counterclockwise direction. The paper could also be manually input from the left side of the electrophotographic engine. The printed image is transferred from the ITM to the receiver and the image bearing receiver then passes through a fuser  170  where the image is permanently fixed to the receiver. The image then enters a region where the receiver either enters an inverter  162  or continues to travel counterclockwise. If the receiver enters the inverter, it travels clockwise, stops, and then travels counterclockwise back onto the paper path  180 . This inverts the image, thereby allowing the image to be duplexed. Prior to the inverter is a diverter  152  that can divert the receiver sheet from the inverter and sends it along the paper path in a counterclockwise direction. This allows multiple passes of the receiver on the simplex side, as might be desired if multiple layers of marking particles are used in the image or if special effects such as raised letter printing using large clear toner are to be used. Operation of the diverter to enable a repeat of simplex and duplex printing can be visualized using the paper path  180  shown in  FIG. 1 . 
         [0022]    It should be noted that, if desired, the fuser  170  can be disabled so as to allow a simplex image to pass through the fuser without fusing, if desired. This might be the case if an expanded color balance in simple printing is desired and a first fusing step might compromise color blending during the second pass through the EP engine. Alternatively, a fusing system that merely tacks, rather than fully fuses, an image and is known in the literature can be used if desired such as when multiple simplex images are to be produced. The image can also be sent through a subsystem that imparts a high gloss to the image, as is known in the literature and is described in co-owned U.S. Pat. Nos. 7,212,772; 7,324,240 and 7,468,820 as well as U.S. Publications 2008/159786 and 2008/050667, which are hereby incorporated by reference. 
         [0023]    Referring now to  FIG. 2  and  FIG. 3 , an arrangement of a development roller  11  whose axis is tipped relative to the feed auger  13  axis  32  of development system  10  but substantially parallel to the developer level of the feed channel  12 . In this manner, the feed of developer to the development roller is assisted and remains substantially uniform as the volume of developer in the first channel decreases.  FIG. 2  is a transverse cross-sectional view of a development system  10  for an electrophotographic printer according to an embodiment of the invention. A development roller  11  is adjacent a feed auger  13  in a first channel  12 . The cross-sectional view of  FIG. 2  shows a low volume of developer  14  containing magnetic particles and marking particles  25  (not to scale), with the marking particles represented schematically as a filled-in circle and the magnetic particles as an unfilled circle. Developer is fed from the first channel  12  to the development roller  11 , is moved to proximity with primary imaging member  115 , and drops into second channel  15  with second auger  16 . At the rear of the development system, the developer collected by the second channel  15  and the remaining developer in the first channel  12  are both dropped into the third channel  19 , where at least a third auger  20  moves the developer to the front of the station, where it is fed to the first end of the feed auger  13  in the first channel  12 . 
         [0024]      FIG. 3  is a longitudinal cross-sectional schematic view of a development system for an electrophotographic printer according to an embodiment of the invention that shows a direction of developer flow  18  in the first channel  12  along an axis of the feed auger  32  shown with flight  23  and working face  24 . The decreasing volume of developer in the first channel  12  is indicated by the decreasing length of the arrows  18  in the direction of developer flow. Uniform flow of developer over the development roller  11  is indicated by similar arrows of the same size. Increasing volume of developer in the second channel  15  is indicated by the increasing length of the arrows in the direction of developer flow. The arrows also indicate that developer from the first channel and the second channel is collected in the third channel  19 , where it is mixed and fed to the first channel. 
         [0025]    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 scope of the invention. 
       Parts List  
       [0026]      10  development system 
         [0027]      10 A- 10 F development system 
         [0028]      11  development roller 
         [0029]      12  first channel 
         [0030]      13  feed auger 
         [0031]      14  developer 
         [0032]      15  second channel 
         [0033]      16  second auger 
         [0034]      18  direction of developer flow 
         [0035]      19  third channel 
         [0036]      20  third auger 
         [0037]      23  auger flight 
         [0038]      24  working face of auger 
         [0039]      25  magnetic particles and marking particles 
         [0040]      32  axis of the feed auger 
         [0041]      100  electrophotographic (EP) engine or printer 
         [0042]      105  paper source 
         [0043]      111  receiver 
         [0044]      115  primary imaging member (PIM) 
         [0045]      120 A- 120 F electrophotographic (EP) module 
         [0046]      150  intermediate transfer member (ITM) 
         [0047]      152  diverter 
         [0048]      158  replenishment station 
         [0049]      162  inverter 
         [0050]      170  fuser 
         [0051]      180  paper path