Variable length transfer assist blade

#The present invention relates generally to a reprographic printing machine. More specifically, the present invention pertains to an apparatus for assisting the transfer of a developed image from an imaging surface, such as a photoconductive surface or intermediate image transfer surface, to a print sheet, such as paper, by optimizing the contact between the print sheet and the imaging surface. The present invention also pertains to such a transfer assist apparatus including a variable length transfer assist blade that may be adjusted for a plurality of different size print sheets.

#FIG. 1 is a schematic illustration of a typical electrophotographic printing machine 10 that may employ a transfer assist blade according to the present invention (not shown in FIG. 1). The illustrated printing machine 10 includes a conventional photoconductive layer or light sensitive surface 12 on a conductive backing in the form of a photoconductive belt 14. The photoconductive belt 14 is mounted on a plurality of rollers journaled in a machine frame (not shown), in order to rotate the photoconductive belt 14 and cause the photoconductive layer 12 to pass sequentially through a plurality of reprographic process stations A through E.

#The several generally conventional processing stations A through E in the path of movement of the photoconductive layer 12 may be as follows. A charging station A, where the photoconductive layer 12 of the photoconductive belt 14 is uniformly charged. An exposure station B, where a light or radiation pattern of a document to be printed is projected onto the photoconductive layer 12 to expose and discharge select areas of the photoconductive layer 12 to form a latent image thereon. A developing station C, where developer material is applied to the photoconductive layer 12 of the photoconductive belt 14 to generate a toner image on the photoconductive layer 12. A transfer station D, where the toner image is electrostatically transferred from the photoconductive surface to a print sheet 30. Finally, a cleaning station E, where the photoconductive surface is brushed or otherwise cleared of residual toner particles remaining thereon after image transfer.

#The invention will now be described, by way of example, with reference top the following drawings, of which:

#FIG. 1 is a diagrammatic illustration of an exemplary reprographic printing machine;

#FIG. 2 is side plan view of a transfer assist blade and associated actuating mechanism according to an embodiment of the present invention, showing the transfer assist blade in the unengaged position;

#A transfer station D incorporating a transfer assist blade mechanism 40 according to one form of the present invention is illustrated in FIGS. 2 through 4. The illustrated transfer station D includes a corona generating device 42 attached to base plate 44 that is mounted to the machine frame (not shown). The corona generating device 42 (only shown in FIG. 2) charges a print sheet 30 (shown in FIG. 3) to the proper magnitude and polarity, so that the print sheet 30 is tacked to photoconductive belt 14 and moves in unison with photoconductive belt 14 in the direction of arrow S. As the print sheet 30 moves in unison with the photoconductive belt 14, a toner image is electrostatically attracted from the photoconductive belt 14 to the print sheet 30.

#The transfer assist blade mechanism 40 also includes a transfer assist blade 50. As the print sheet 30 moves into a transfer zone between the corona generating device 42 and the photoconductive belt 14, the transfer assist blade 50 is pressed against the print sheet 30 (As shown in FIG. 3). Thus, the transfer assist blade 50 applies a uniform contact pressure to the print sheet 30 as it passes through the transfer station D, for pressing the print sheet 30 into uniform contact with the photoconductive surface 12 of the photoconductive belt 14.

#The transfer assist blade 50 is secured in a blade holder 52 (also see FIG. 6) by wrapping one elongate edge of the transfer assist blade 50 around a retaining rod 54, and securely snapping or sliding the retaining rod 54 into a C-shaped retaining head formed on the blade holder 52 (best seen in FIG. 3). The blade holder 52 is secured between a pair of pivot arms or blade brackets 56, only one of which is visible in FIGS. 2 and 3. The pivot arms 56 are pivotally journaled on a pair of blade axles 58 that are affixed to a portion of the machine frame (not shown). Lower ends of the pivot arms 56 are interconnected by a bar 60 that extends therebetween. A first stepper motor 62 is secured to the base plate 44 or is otherwise secured to the machine frame. A crank arm 64 is secured to the output shaft of the first stepper motor 62. The crank arm 64 is connected to the bar 60 by a link 66. The blade axles 58 are offset to one side of the pivot arms 56 by legs that extend from the pivot arms 56.