Abstract:
The invention relates generally to development apparatus for mixing and applying developer material to a latent image on an image-bearing member in an electrostatographic reproduction machine, such as a copier or printer. More particularly, this invention relates to a blender of the type for mixing electrostatographic developer comprising a plurality of blender segments mounted on a shaft. A resilient spacer is provided, according to an aspect of the invention, wherein said resilient spacer and said plurality of blender segments are compressed between said pair of stops. Residual looseness due to tolerance stack-up is eliminated.

Description:
[0001]    This application claims the benefit of U.S. Provisional Application No. 60/204,880. 
     
    
     
         [0002]    This invention relates generally to development apparatus for mixing and applying developer material to a latent image on an image-bearing member in an electrostatographic reproduction machine, such as a copier or printer. More particularly, this invention relates to a blender of the type for mixing electrostatographic developer comprising a plurality of blender segments mounted on a shaft.  
           [0003]    Development apparatus, for example a magnetic brush development apparatus, are well known for mixing and applying developer material to a latent electrostatic image on a photoconductor in an electrostatographic reproduction machine such as a copier or printer. Such a development apparatus typically includes an elongate housing which has a sump portion for containing the developer material. A two-component developer material comprises a mixture of carrier particles and toner particles. These particles are usually moved and mixed by a mixing device in the sump portion of the housing for triboelectrically charging the particles. Mixing also promotes uniformity in the concentration of toner particles throughout the sump portion, and in the distribution of developer material within the sump. The mixed and charged developer material can then be fed from the sump portion for development of the latent image on the photoconductor, which is generally a film or drum.  
           [0004]    The quality of such an image development depends, in significant part, on factors such as the level of charge on the toner particles achieved triboelectrically for example, and such as the level and uniformity of the concentration of toner particles in the developer material being applied. As is well known, these factors are mainly determined by the effectiveness of a mixing device used in the sump portion of the development apparatus housing for moving, mixing and charging the developer material particles.  
           [0005]    Certain prior blender assemblies implement a row of blender segments mounted on a shaft. Such assemblies typically exhibit a looseness in the blender segments after assembly due to tolerance stack-up. The segments are able to move small distance relative to the shaft and relative to each other. This movement, although limited, can cause toner flakes in the developer which, in turn, causes objectionable artifacts in the developed image. In addition, the outside diameter of certain blenders is ground during manufacturing to ensure an accurate fit with the developer housing. Looseness in the segments can cause the segments to chatter during the grinding operation.  
         SUMMARY OF THE INVENTION  
         [0006]    According to an aspect of the invention, a blender for mixing electrostatographic developer is provided, comprising a shaft having a pair of stops spaced along a length thereof, a plurality of blender segments of the type for mixing electrostatographic developer, each blender segment having an aperture, the shaft being received within the aperture of each blender segment, and a resilient spacer, wherein the resilient spacer and the plurality of blender segments are compressed between the pair of stops.  
           [0007]    According to a further aspect of the invention, a method of fabricating a blender for mixing electrostatographic developer is provided, comprising disposing a resilient spacer and a plurality of blender segments of the type for mixing electrostatographic developer on a shaft, each blender segment having an aperture, the shaft being received within the aperture of each blender segment, and compressing the resilient spacer and the plurality of blender between a pair of stops on the shaft.  
           [0008]    According to a still further aspect of the invention a blender for mixing electrostatographic developer is provided, comprising a shaft having a pair of stops spaced along a length thereof and a plurality of serrations, one of the stops comprising a snap ring engaging one of the serrations, a plurality of blender segments of the type for mixing electrostatographic developer, each blender segment having an aperture, the shaft being received within the aperture of each blender segment, and at least one belleville washer disposed immediately adjacent one of the stops, wherein the resilient spacer and the plurality of blender segments are compressed between the pair of stops.  
           [0009]    A blender according to the present invention has a plurality of blender segments exhibiting no residual looseness due to tolerance stack-up. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 presents a side view of a blender comprising a plurality of segments according to an aspect of the invention.  
         [0011]    [0011]FIG. 2 presents a side view of a blender segment implemented in the blender of FIG. 1, according to an aspect of the invention.  
         [0012]    [0012]FIG. 3 presents an end view of a blender segment according to an aspect of the invention taken along line  3 - 3  of FIG. 2.  
         [0013]    [0013]FIG. 4 presents a side view of a shaft implemented in the blender of FIG. 1.  
         [0014]    [0014]FIG. 5 presents cross-section view of a shaft taken along line  5 - 5  of FIG. 4.  
         [0015]    [0015]FIG. 6 presents a side view of a blender comprising a plurality of segments according to a further aspect of the invention.  
         [0016]    [0016]FIG. 7 presents side view of a blender segment according to an aspect of the invention.  
         [0017]    [0017]FIG. 8 presents an end view of a blender segment according to an aspect of the invention taken along line  8 - 8  of FIG. 7.  
         [0018]    [0018]FIG. 9 presents a side view of the shaft implemented in the blender of FIG. 6.  
         [0019]    [0019]FIG. 10 presents a cross-sectional view of the shaft taken along line  10 - 10  of FIG. 9.  
         [0020]    [0020]FIG. 11 presents an enlarged exploded view of the blender of FIG. 6 with parts broken away.  
         [0021]    [0021]FIG. 12 presents a plan view of a snap ring implemented in the blender of FIG. 6.  
         [0022]    [0022]FIG. 13 presents a plan view of an e-ring implemented in the blender of FIG. 6.  
         [0023]    [0023]FIG. 14 presents a side cross-sectional view of the blender assembly with tooling for installing the snap ring. 
     
    
     DETAILED DESCRIPTION  
       [0024]    Various aspects of the invention are presented in FIGS.  1 - 14 , which are not drawn to scale, and wherein like components are numbered alike. Referring now specifically to FIGS.  1 - 4 , a blender  10  for mixing electrostatographic developer is presented according to an aspect of the invention comprising a shaft  12  having a pair of stops  14  and  16  spaced along a length L. A plurality of blender segments  18  of the type for mixing electrostatographic developer are provided, each blender segment  18  having an aperture  20 . The shaft  12  is received within the aperture  20  of each blender segment  18 . A resilient spacer  22  is provided, the resilient spacer  22  and the plurality of blender segments  18  being compressed between the pair of stops  14  and  16 .  
         [0025]    According to an aspect of the invention, the resilient spacer  22  provides a greater degree of elastic compression than the blender segments  18  and compensates for variations in the width of the row of blender segments  18  induced by tolerance stack-up. Each blender segment  18  is manufactured to prescribed dimensions, each dimension having a tolerance. Of particular interest here, with reference to FIG. 2, is the width W of each blender segment, and the tolerance dW associated with the width W.  
         [0026]    The tolerance dW may be expressed in numerous ways as an absolute positive or negative value, or as a positive/negative (+/−), in accordance with the particular tolerance system employed. In any event, each blender segment  18  typically includes a small amount of variation in the manufactured width. Such variation is magnified when several blender segments  18  are placed in a row, a phenomena known as “tolerance stack-up.” 
         [0027]    The maximum variation in the total width of the row is the sum of the tolerances dW of each blender segment  18  (and the tolerances of any intermediate structures). Since the blender segments  18  are generally manufactured from a relatively incompressible material such as plastic or metal, the length L between the first and second stops  14  and  16  is set to approximately the greatest possible width of the stack. This ensures that all of the blender segments  18  will fit between the stops  14  and  16 .  
         [0028]    In practice, the actual width of the row of blender segments  18  is usually less than the maximum possible width since the width of each blender segment  18  is usually less than the maximum allowed by the tolerances. If left uncompensated, the individual blender segments  18 , after assembly of the blender  10 , are able to move a small distance relative to the shaft and relative to each other. This residual looseness is undesirable. The resilient spacer  22  solves this problem by maintaining the blender segments  18  under compression over the relatively large variation in total width induced by tolerance stack-up, thus eliminating the residual looseness. The resilient spacer  22  may comprise a coil spring, a belleville washer, or other resilient structure that compensates for tolerance stack-up in the blender segments  28 .  
         [0029]    In a typical installation, the blender  10  is mounted in a developer sump and the shaft  12  is rotationally driven about its longitudinal axis. Examples of development apparatus that may implement a blender according to the present invention are described in U.S. Pat. Nos. 4,634,286; 4,825,244; and 4,887,132. While not limited to any particular toner or developer, the present invention is particularly useful with two-component developer that implements a mixture of toner and carrier. Driving the blender  10  in a two-component developer induces tribocharging of the toner and carrier particles. The phenomena of tribocharging is well known in the electrostatographic arts. The blender segments may be configured in numerous ways, including knives, paddles, scoops, and/or ribbons, without limitation.  
         [0030]    The blender segments  18  are preferably driven by the shaft  12 . As best shown in FIG. 5, the shaft  12  may have a key  13  that mates with the apertures  20  of the blender segments  18 . The key  13  ensures rotation of the blender segments  18  with the shaft  12 , although other geometries that render the shaft  12  and apertures  20  non-circular in cross section may be implemented.  
         [0031]    The blender segments  18  may be formed from any suitable material, including plastics and metals. They may be made by molding, casting, machining from bulk material, or any other suitable manufacturing processes for rendering geometries useful in a developer blender.  
         [0032]    According to a preferred embodiment, the plurality of blender segments  18  are disposed in seriatim with the resilient spacer  22  adjacent one of the pair of stops  14  and  16 , as presented in FIG. 1. In FIG. 1, the resilient spacer  22  is immediately adjacent the stop  14 .  
         [0033]    Referring now to FIGS.  6 - 10 , an embodiment of a blender  100  for mixing electrostatographic developer is presented, according to a further aspect of the invention. Blender  100  comprises a shaft  112  having a pair of stops  114  and  116  spaced along a length L. A plurality of blender segments  118  of the type for mixing electrostatographic developer are provided, each blender segment  118  having an aperture  120 . The shaft  112  is received within the aperture  120  of each the blender segment  118 . Resilient spacers  122  and  124  are provided, the resilient spacers  122  and  124  and the plurality of blender segments  118  being compressed between the pair of stops  114  and  116 . In the embodiment presented in FIG. 6, the resilient spacer  122  is adjacent the stop  114 , and the resilient spacer  124  is adjacent the stop  116 . Wipers  115 , or other structure, may be provided immediately adjacent the stops  114  and  1   16 , as presented in FIG. 6.  
         [0034]    According to a further aspect of the invention, the shaft  112  may comprise a plurality of serrations  126 , and one of the stops  114  comprises a snap ring  128  engaging one of the serrations  126 . The other stop  116  may also comprise a snap ring  132  engaging a mating groove  134  in the shaft  112 .  
         [0035]    According to a preferred embodiment, the blender segments  118  form a ribbon blender, and the resilient spacer  122  comprises a plurality of stacked belleville washers  130 . One or more additional spacers, such as resilient spacer  124 , may also comprise a plurality of stacked belleville washers  130 . The blender segments  118  may form a ribbon blender having a double helix  136  and  138 . Various ribbon blenders that may be implemented in the practice of the present invention are described in U.S. Pat. Nos. 4,634,286; 4,956,675; and 5,146,277.  
         [0036]    The blender segments  118  are of three general configurations; a first configuration  140  wherein helix  136  is outside helix  138 , a second configuration  142  wherein helix  138  is outside  136 , and a transition configuration  144  wherein the helixes  138  and  136  switch relative position. This geometry greatly enhances mixing of the developer, as described by U.S. Pat. No. 4,634,286.  
         [0037]    Referring now specifically to FIGS. 7 and 8, each blender segment  18  comprises a ferrule  119  and an integral rib  121 . Referring again to FIG. 6, the individual ribs  121  are aligned and form a rib that runs along the length of the blender segments  118 .  
         [0038]    Referring again to FIGS.  1 - 4 , a method of fabricating a blender for mixing electrostatographic developer is provided, according to a further aspect of the invention, comprising disposing a resilient spacer  22  and a plurality of blender segments  18  of the type for mixing electrostatographic developer on a shaft  12 , each blender segment  18  having an aperture  20 , the shaft  12  being received within the aperture of each the blender segment  18 , and compressing the resilient spacer  22  and the plurality of blender segments  18  between a pair of stops  114  and  116  on the shaft  112 . The method may further comprise disposing the plurality of blender segments  18  in seriatim with the resilient spacer  22  adjacent one of the pair of stops  114  and  116 .  
         [0039]    Referring again to FIGS.  6 - 10 , one of the stops, stop  114  for example, may comprise a snap ring  128 , and the method may further comprise pressing the snap ring  128  toward another of the stops into engagement with one of the plurality of serrations  126 .  
         [0040]    Referring now to FIG. 11, an enlarged exploded view of blender  100  with portions broken away is presented. Only the left-most blender segment  118  and right-most blender segment of FIG. 6 are presented in FIG. 11 for the sake of clarity. According to a certain embodiment, snap ring  126  is configured as shown in FIG. 12, and snap ring  132  is configured as shown in FIG. 13. Referring again to FIG. 11, blender  100  is fabricated by installing inserting the end of the shaft  112  into the apertures of the belleville washers  130  and the wiper  115 . The snap ring  132  is then installed into a mating groove on the shaft  112 . The blender segments  118  are installed onto the shaft from the opposite end. The belleville washers  130  on that end are then installed, followed by the wiper  115 . The snap ring  128  is then installed on the shaft resting against the wiper  115 . The entire assembly is then placed in a press that forces the snap ring  128  onto the serrations  126 . A press having a load indicator is preferred in order to avoid overloading the assembly. The snap ring  128  may engage any one of the serrations  126 , depending upon the prescribed load.  
         [0041]    Referring now to FIG. 14, a side-cross sectional view of the blender  100  is presented with tooling that may be employed to press snap ring  128  onto the serrations  126 . The end of the shaft  112  proximate the snap ring  132  is placed in a cylindrical end-piece  146 . The other end of the shaft  112  proximate the snap ring  128  is placed in a cylindrical end-piece  148 , and is pressed toward the end-piece  146 . The assembly may be placed in a lathe, for example, and the tail stock may be used to apply the force. The cylindrical end-piece  146  preferably does not contact the snap ring  132 .  
         [0042]    In a certain embodiment, a blender  100  has twenty-one (21) blender segments having a total nominal width of 14.7 inches. Allowable manufactured width, including tolerances, ranges from 14.616 inches to 14.784 inches (a range of 0.168 inches). Four belleville washers are stacked on each end, as shown in FIG. 11, that provide a total deflection of 0.051 inches at a force of 150 lbf. The length of the section having the serrations is 0.180 inches (three serrations at 0.060 inches per serration). The overall range of adjustment is the sum of 0.180 inches for the serrated section plus 0.051 inches for compression of the belleville washers. This provides more than sufficient adjustment for the 0.168 inches worst case variation due to tolerance stack-up.  
         [0043]    Although the invention has been described and illustrated with reference to specific illustrative embodiments thereof, it is not intended that the invention be limited to those illustrative embodiments. Those skilled in the art will recognize that variations and modifications can be made without departing from the true scope and spirit of the invention as defined by the claims that follow. It is therefore intended to include within the invention all such variations and modifications as fall within the scope of the appended claims and equivalents thereof.