Abstract:
A doctor blade may be mounted between a pair of L-shaped brackets. The brackets may include a pair of opposed openings that receive mounting posts which extend outwardly from the printer housing. A pair of threaded fasteners may be used to secure the assembly of brackets and doctor blade to the housing. The L-shaped brackets may include a long end and a shorter end, the longer end supportable on a land provided on the printer housing. The longer end of one of the brackets may overlap the longer end of the other of the brackets so that the doctor blade may flex away from one of the brackets.

Description:
BACKGROUND  
       [0001]     This invention relates generally to electro-photographic printers that use toner to transfer an image to a medium.  
         [0002]     In conventional electrophotographic printing, toner is transferred from a developer roll to a medium. In order to obtain a good transfer of the image, it is desirable that the toner on a developer roll be applied very evenly. Even application of toner may be facilitated by using a doctor blade that controls the thickness of the toner on the developer roll. As the developer roll rotates, the doctor blade doctors the toner applied thereto and provides a relatively uniform toner coating.  
         [0003]     Since the application of the uniform toner coating may be critical to the performance of the printer, there is a continuing need for better doctor blade designs. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]      FIG. 1  is a partial, cross-sectional view of one embodiment of the present invention;  
         [0005]      FIG. 2  is an exploded depiction of a developer frame in accordance with one embodiment of the present invention; and  
         [0006]      FIG. 3  is a schematic depiction of a printer in accordance with one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0007]     Referring to  FIG. 1 , a developer roll  14  rotates in the direction indicated by the arrow A. The developer roll  14  may be coated with a coating of toner (not shown). Biased against the surface of the developer roll  14  is a doctor blade  22 . In one embodiment of the present invention, the doctor blade  22  is a thin, highly resilient metallic sheet that acts as a cantilevered leaf spring. For example, the doctor blade  22  may be made of spring steel in one embodiment of the present invention. The blade  22  may have a curved end  24 . While a checkmark shaped end  24  is shown in  FIG. 1 , other end designs may be utilized as well.  
         [0008]     As the developer roll  14  rotates in the direction indicated by A, uneven toner on the surface of the developer roll impacts the end  24  of the doctor blade  22  and is squeezed into the nip between the end  24  and the roll  14 , providing a uniform thickness toner coating on the output, counterclockwise, or downstream side of the doctor blade  22 .  
         [0009]     The doctor blade  22  may be supported in a spring biased configuration against the surface of the developer roll  14  through the application of a counterclockwise applied force applied by a mounting bracket system. The mounting bracket system may include a front bracket  18  and a rear bracket  16 , as well as a locating post  38  which extends through locating post apertures  36  in the front and rear brackets  16  and  18  and the doctor blade  22 .  
         [0010]     In one embodiment, each of the brackets  18  and  16  may be L-shaped, having parallel opposed surfaces  17  that clamp the doctor blade  22  between themselves. The rear bracket  16  may be arranged so that its longer leg  48   a  rests on lands  44  formed in the developer frame  42 , as shown in  FIG. 2 . The brackets  16  and  18  may be nested so that they lie generally parallel to one another.  
         [0011]     In position within the developer frame  42 , shown in  FIG. 2 , the locating posts  38  protrude completely through the brackets  18  and  16 . In some embodiments, the locating posts  38  may have curved ends  37  ( FIG. 1 ) to facilitate their insertion through the apertures  36  in the brackets  18  and  16 .  
         [0012]     As shown in  FIG. 1 , the rear bracket  16  may be arranged so that the longer leg  48   b  of the front bracket overlaps the longer leg  48   a  of the rear bracket  16 . This overlap allows the doctor blade  22  to flex in a counterclockwise direction away from the portion  48   b  due to the bias applied to the blade by the brackets  16  and  18 .  
         [0013]     Thus, in some embodiments, the brackets  16  and  18  may be substantially more rigid than the relatively resilient doctor blade  22 . As a result, a consistent biasing force may be applied by the brackets  16  and  18  to the doctor blade  22 , biasing the blade  22  against the surface of the developer roll  14 . In one embodiment of the present invention, the doctor blade  22  makes contact with the developer roll  14  between about one and two o&#39;clock, relative to the surface of the developer roll  14  or, taking the vertical diameter through the developer roll  14 , at an angle of about 10 to 35 degrees therefrom.  
         [0014]     Referring to  FIG. 2 , a developer frame  42  may be replaceably inserted within an electrophotographic printer. In other words, it may be replaceably plugged into the printer to replace consumables included in the frame  42 . The developer frame  42  may include an integral toner storage and an integral developer roll  14  in one embodiment.  
         [0015]     The front bracket  18  and the rear bracket  16  may sandwich the doctor blade  22  and bias the blade  22  against a surface of the developer roll  14 . This bias is facilitated by the outwardly protruding locator posts  38  formed at two spaced locations along the length of the developer frame  42 . Thus, the locating posts  38  pass through the apertures  36  in the back bracket  16 , the doctor blade  22  and the rear bracket  18 .  
         [0016]     Once secured in position on the developer frame  42 , the locating posts  38 , near either end of the developer frame  42 , protrude through the front bracket  18  as shown in  FIG. 1 . At this point, screws  34  may be used through two opposed openings  32  in each of the front bracket  18 , doctor blade  22 , and rear bracket  16 . These screws  34  are secured to the developer frame  42  through molded, protruding screw holes  40  and, in one embodiment, may be threaded or threadable.  
         [0017]     Thus, in some embodiments, through the imposition of locating posts  38  and the rigid brackets  16  and  18 , only two screws may be needed to secure the assembly together, facilitating attachment. However, if greater rigidity is desired, additional screws may be used in additional openings  50  in each of the brackets  16  and  18  in doctor blade  22 , securing to intermediate holes  40  (not shown), intermediate between the two mounting pads  44  shown in  FIG. 2 .  
         [0018]     Referring to  FIG. 3 , there is shown one embodiment of an electro-photographic device  60  in which embodiments of the present invention may be applied. Of course the present invention is in no way limited to any specific printer design and may be applicable to a variety of different printer arrangements.  
         [0019]     The device  60  includes laser print heads  62 ,  64 ,  66 , and  68 , a black toner cartridge  70 , a magenta toner cartridge  72 , a cyan toner cartridge  74 , a yellow toner cartridge  26 , photoconductive drums  78 ,  80 ,  82 , and  84 , an intermediate transfer belt  86 , and a controller  87 . In one embodiment, the controller may be a combination of application specific integrated circuits, microprocessors, and firmware suited to the tasks of printing documents.  
         [0020]     Each of the laser print heads  62 ,  64 ,  66 , and  68  projects a respective laser beam  88 ,  90 ,  92 , and  94  off a respective one of the polygonal mirrors  96 ,  98 ,  100 , and  102 . As each of the polygonal mirrors  96 ,  98 ,  100 , and  102  rotates, it scans a respective one of the reflected beams  88 ,  90 ,  92 , and  94  in a scan direction, perpendicular to the plane of  FIG. 3 , across a respective one of the photoconductive drums  78 ,  80 ,  82 , and  84 .  
         [0021]     Each of the photoconductive drums  78 ,  80 ,  82 , and  84  may be negatively charged, for example, to approximately −1000 volts, and is subsequently discharged to a lower level, such as approximately −300 volts, in the areas of the peripheral surface that are impinged by a respective one of the laser beams  88 ,  90 ,  92 , and  94 .  
         [0022]     During each scan of a laser beam across the photoconductive drum, each photoconductive drum  78 ,  80 ,  82 , and  84  is continuously rotated, for example, in a clockwise direction, in a process direction indicated by the arrow  104 . The scanning of the laser beams  88 ,  90 ,  92 , and  94  across the peripheral surface of the photoconductive drums is cyclically repeated, thereby discharging the areas of the peripheral surfaces on which the laser beams impinge.  
         [0023]     The toner in each of the toner cartridges  70 ,  72 ,  74 , and  76  is negatively charged and is transported upon the surface of a developer roll  110  and biased, for example, to approximately −600 volts. Thus, when the toner for the cartridges  70 ,  72 ,  74 , and  76  is brought into contact with the respective one of the photoconductive drums  78 ,  80 ,  82 , and  84 , the toner is attracted to and adheres to the portions of the peripheral surfaces of the drums that have been discharged to the lower voltage, say −300 volts, by the laser beams.  
         [0024]     As the belt  86  rotates in the direction indicated by the arrow  106 , the toner from each of the drums  78 ,  80 ,  82 , and  84  is transferred to the outside surface of the belt  86 . As a print medium, such as paper, travels along the path  108 , the toner is transferred to the surface of the print medium and nip  112 .  
         [0025]     References throughout this specification to “one embodiment” or “an embodiment” mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation encompassed within the present invention. Thus, appearances of the phrase “one embodiment” or “in an embodiment” are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be instituted in other suitable forms other than the particular embodiment illustrated and all such forms may be encompassed within the claims of the present application.  
         [0026]     While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.