Patent Application
20070189814
This invention relates generally to electro-photographic printers that use toner to transfer an image to a medium.
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.
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.
Referring to
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.
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.
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 48a rests on lands 44 formed in the developer frame 42, as shown in
In position within the developer frame 42, shown in
As shown in
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'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.
Referring to
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.
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
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
Referring to
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.
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
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.
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.
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.
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.
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.
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.
