BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevational view of an electrostatographic printing apparatus incorporating a semiconductive magnetic brush development (SCMB) system having two magnetic rolls.
FIG. 2 is a sectional view of a SCMB developer unit having two magnetic rolls.
FIG. 3 is a perspective view of a SCMB developer unit having two magnetic rolls.
FIG. 4 is a sectional view of the trim blade of the present disclosure.
DETAILED DESCRIPTION
FIG. 1 is an elevational view of an electrostatographic printing apparatus 10, such as a printer or copier, having a development subsystem that uses two magnetic rolls for developing toner particles that are carried on semiconductive carrier particles. The machine 10 includes a feeder unit 14, a printing unit 18, and an output unit 20. The feeder unit 14 houses supplies of media sheets and substrates onto which document images are transferred by the printing unit 18. Sheets to which images have been fixed are delivered to the output unit 20 for correlating and/or stacking in trays for pickup.
The printing unit 18 includes an operator console 24 where job tickets may be reviewed and/or modified for print jobs performed by the machine 10. The pages to be printed during a print job may be scanned by the printing machine 10 or received over an electrical communication link. The page images are used to generate bit data that are provided to a raster output scanner (ROS) 30 for forming a latent image on the photoreceptor 28. Photoreceptor 28 continuously travels the circuit depicted in the figure in the direction indicated by the arrow. The development subsystem 34 develops toner on the photoreceptor 28. At the transfer station 38, the toner conforming to the latent image is transferred to the substrate by electric fields generated by the transfer station. The substrate bearing the toner image travels to the fuser station 44 where the toner image is fixed to the substrate. The substrate is then carried to the output unit 20. This description is provided to generally describe the environment in which a double magnetic roll development system for developer having semiconductive carrier particles may be used and is not intended to limit the use of such a development subsystem to this particular printing machine environment.
The overall function of developer unit 100, which is shown in FIG. 2, is to apply marking material, such as toner, onto suitably-charged areas forming a latent image on an image receptor such as the photoreceptor 28, in a manner generally known in the art. The developer unit 100, however, provides a longer development zone while maintaining an adequate supply of developer having semiconductive carrier particles than development systems previously known. In various types of printers, there may be multiple such developer units 100, such as one for each primary color or other purpose.
Among the elements of the developer unit 100, which is shown in FIG. 2, are a housing 120, which functions generally to hold a supply of developer material having semiconductive carrier particles, as well as augers, such as 30, 32, 34, which variously mix and convey the developer material, and magnetic rolls 36, 38, which in this embodiment form magnetic brushes to apply developer material to the photoreceptor 28. Other types of features for development of latent images, such as donor rolls, paddles, scavengeless-development electrodes, commutators, etc., are known in the art and may be used in conjunction with various embodiments pursuant to the claims. In the illustrated embodiment, there is further provided air manifolds 40, 42, attached to vacuum sources (not shown) for removing dirt and excess particles from the transfer zone near photoreceptor 28. As mentioned above, a two-component developer material is comprised of toner and carrier. The carrier particles in a two-component developer are generally not applied to the photoreceptor 28, but rather remain circulating within the housing 12. The augers 30, 32, and 34 are configured and cooperate in a manner described in co-pending U.S. application Ser. No. 11/263,370, which was filed on Oct. 31, 2005, entitled “Xerographic Developer Unit Having Variable Pitch Auger,” and co-pending U.S. application Ser. No. 11/263,371, which was filed on Oct. 31, 2005, entitled “Developer Housing Design With Improved Sump Mass Variation Latitude”, both of which are hereby expressly incorporated herein in their entireties by reference and are commonly assigned to the assignee of this patent application.
FIG. 3 is a perspective view of a portion of developer unit 100. As can be seen in this embodiment, the upper magnetic roll 36 and the lower magnetic roll 38 form a development zone that is approximately as long as the two diameters of the magnetic rolls 36 and 38. As further can be seen, a motor 60 is used with a mechanism, generally indicated with reference numeral 62, to cause rotation of the various augers, magnetic rolls, and any other rotatable members within the developer unit 100 at various relative velocities. There may be provided any number of such motors. The magnetic rolls 36 and 38 are rotated in a direction that is opposite to the direction in which the photoreceptor moves past the developer unit 100. That is, the two magnetic rolls are operated in the against mode for development of toner. In one embodiment of the developer unit 100, the motor 60 and the mechanism 62 cause the magnetic rolls to rotate at a speed in the range of about 1 to about 1.5 times the rotational speed of the photoreceptor 28. This rotational speed is lower than the rotational speed of magnetic rolls in developer systems that rotate in the same direction as the photoreceptor. That is, the magnetic rolls operated in the against mode may be rotated at lower speeds than magnetic rolls operated in the with mode. These slower speeds increase the life of the magnetic rolls over the life of magnetic rolls that are operated in the with mode to develop toner carried on semiconductive carrier particles.
As is well known, magnetic rolls, such as magnetic rolls 36 and 38, are comprised of a rotating sleeve and a stationary core in which magnets are housed. In order to provide a surface that impedes the slippage of carrier particles as the outer sleeve rotates, the outer surface of the rotating sleeve may be sand-blasted or grooved. Previously known SCMB systems used sand-blasted stainless steel rollers, but these rollers have relatively short functional life of approximately 2 million prints or copies. Other known magnetic brush systems that use other types of developers used grooved stainless steel rollers having a depth of approximately 200 to 250 microns. The use of these grooved rollers in a double magnetic roller development subsystem operating in the against mode reduced the trim gap for the development subsystem from approximately .7 mm to approximately .135 mm. The trim gap is the distance between the trim blade and the upper magnetic roll 36. The trim blade assists in the removal of excess developer from the upper magnetic roll 38 before it is carried into the development zone.
A narrow trim gap presents issues with respect to the manufacturing of the developer unit. For one, the tolerances for the components that comprise the trim blade that assists in the removal of carrier particles from the upper magnetic roll are more difficult to meet. More precise manufacturing techniques and higher rejection rates increase the unit manufacturing cost for the trim blade. Additionally, a narrower trim gap requires greater torque from the motor driving the roller and it also increases the aging of the developer.
Now focusing on FIG. 4, trim blade 110 of the present disclosure divides the function of a trim bar into two separate parts: support and cutting edge. In an embodiment of the present disclosure the bottom bar is made of a support with a stainless steel shim screwed on to form the cutting edge.
As illustrated in FIG. 2, trim blade 110 meters toner to a predefined toner bed height on a magnetic roll 36. The trim blade having a support portion 112; and a cutting portion 114, adjacent to the magnetic roll; the support portion is a major portion of the trim bar and a cutting portion is a minor portion of the trim bar 114. The cutting portion 114 is attached to the support portion by fastener 116 ie. screw or other suitable means can be employed such as welding or heat staking (in case of plastic. The cutting portion has a wear factor substantially higher than the support portion. Preferably the support portion is made from aluminum or other suitable materials can be employed such as steel, plastics or other metals. Preferably the cutting portion is made from stainless steel or other suitable materials can be employed such as nickel or carbon composites. Preferably the cutting portion has a thickness between 0.5 mm and 5 mm; the support portion has a thickness between 2 mm and 10 mm and, the cutting portion has a wear factor substantially higher than said support portion. Note that if the support has a longer life than the cutting edge (which is likely), the edge can be replenished by replacing the stainless part only.
In recapitulation, there has been provided a robust trim bar design for use in two component development or donor loading systems. Developer is metered onto the developer roll at the trim position, and the gap between the bar and roll sets the developer supply and thus to a large extent controls developability. Any excessive trim bar wear, due to developer grinding, will alter print quality. Aluminum trim bars wear excessively, particularly when magnetically pigmented toner is used, and stainless steel bars, while more durable are very expensive and difficult to manufacture. The function of the trim bar of the present disclosure is divided into two separate parts: the support and the cutting edge. The support being less critical is made from extruded aluminum. The cutting edge, that controls the roll to trim gap, can be made from a commercially available stainless steel shim and then fastened to the aluminum support. This composite provides a highly durable steel trim edge at much lower cost than a thick steel bar.
Advantageous feature of the present disclosure is that cutting portion and/or support can have magnetic properties depending on the xerographic process employing a ferromagnetic developer material. For example the cutting portion could have non magnetic properties to prevent the developer material from collecting on the edge combined with a support having magnetic properties to magnetically move developer material away from the edge.
The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
Patent Application
20070292167
