Abstract:
A metering blade suspension system utilizes a leaf spring that performs multiple combined functions such as supporting a metering blade assembly, controlling the angle, position and/or load of the blade assembly while allowing the assembly to pivot in a quasi-frictionless motion, locking the blade assembly in place, providing an electrical connection and/or bleeding static charge.

Description:
BACKGROUND OF INVENTION  
       [0001]     1. Field of Invention  
         [0002]     This invention relates to a suspension system for a metering blade.  
         [0003]     2. Description of Related Art  
         [0004]     It is known to utilize intermediate transfer layers in ink printing systems, such as disclosed in U.S. Pat. Nos. 6,068,372 and 6,431,703, to Rousseau et al. These systems utilize an oiling roller that engages the imaging drum and applies a liquid intermediate transfer layer to the imaging drum. The print head ejects drops of ink onto the liquid intermediate transfer layer to form an ink image thereon. A receiving substrate such as paper is then brought into contact with the intermediate transfer layer on the imaging drum and the ink image is transferred to the receiving substrate.  
         [0005]     A part of the solid ink technology printing process includes the drum maintenance unit. One of the drum maintenance unit&#39;s objectives is to apply a metered amount of release agent to the imaging drum prior to the print head imaging process. The metering blade meters the oil applied by the oiling roller into a very thin film that will be sufficient to have the ink preferably stick to the media rather than to the drum.  
       SUMMARY OF THE INVENTION  
       [0006]     It is important that ink printing systems apply a desired amount of liquid onto the intermediate transfer layer. The amount of liquid should be consistent and should not vary over time. Insufficient control over the distribution and thickness of the liquid intermediate transfer layer has negative effects on printed image quality. Non-uniform film distribution or improper film thickness around the imaging drum results in undesirable image artifacts. Those areas of the surface that have more fluid may be visible on the image as low gloss spots or streaks. If the intermediate transfer layer becomes too thin or is absent, ink can adhere to the imaging drum and not be transferred to the receiving substrate. It is also important to remove foreign matter from the surface of the imaging drum. Optimum performance is achieved by controlling the position, angle and load of the blade.  
         [0007]     This invention is directed to a metering blade suspension system that avoids various disadvantages and drawbacks associated with conventional systems. In various exemplary embodiments a leaf spring suspension system is contemplated.  
         [0008]     This invention provides a simpler, more reliable, and easier to assemble design that uses fewer parts.  
         [0009]     This invention separately provides a system for controlling the blade angle, position and load of a metering blade.  
         [0010]     This invention separately provides reduced rotational friction.  
         [0011]     This invention separately provides improved static discharge.  
         [0012]     This invention separately provides a more compact blade suspension system.  
         [0013]     This invention separately contributes to a reduction in size of a drum maintenance unit.  
         [0014]     This invention separately contributes to a reduction in costs of manufacture and maintenance of a drum maintenance unit.  
         [0015]     Various exemplary embodiments of this invention provide a metering blade suspension system comprising a metering blade assembly and at least one leaf spring connected to the assembly. The at least one leaf spring may be a pair of leaf springs. Each of the pair of leaf springs may be substantially identical.  
         [0016]     In various exemplary embodiments of this invention, the metering blade assembly pivots on the at least one leaf spring.  
         [0017]     In various exemplary embodiments of this invention, the at least one leaf spring controls the blade angle, position, and/or load of the metering blade.  
         [0018]     In various exemplary embodiments of this invention, the at least one leaf spring is part of an electrical connection to the blade assembly. Further, in various exemplary embodiments, the at least one leaf spring may serve as a grounding path for bleeding static charge in the metering blade assembly. The at least one leaf spring may be made of an electrically conductive material such as, for example, metal.  
         [0019]     Various exemplary embodiments of this invention provide a drum maintenance unit (DMU) comprising the metering blade assembly. The DMU may be disposed in a removable cassette. The DMU and or the cassette may be a consumable unit.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     Various exemplary embodiments of the systems and methods of this invention are described in detail below, with reference to the attached drawing figures, in which:  
         [0021]      FIG. 1  is a view of a known metering blade, which is part of a suspension system;  
         [0022]      FIG. 2  is a view of an exemplary embodiment of a metering blade suspension system according to this invention;  
         [0023]      FIGS. 3 and 4  are enlarged partial views of the exemplary embodiment of  FIG. 2 ;  
         [0024]      FIG. 5  is an exploded perspective view of a replaceable cassette for an imaging apparatus according to an exemplary embodiment of this invention;  
         [0025]      FIGS. 6 and 7  are cross sectional views of an exemplary embodiment of a drum maintenance unit into which an embodiment of a metering blade suspension system according to this invention is installed; and  
         [0026]      FIG. 8  is a diagrammatic illustration of a blade suspension system engaged with the drum unit and oiling roller with potential electrical charges. 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0027]     This invention may be applied to various metering blade assembly configurations and is not limited to the particular configurations disclosed by the exemplary embodiments. Those skilled in the art will appreciate a metering blade suspension system in accordance with this invention without including all of the particular features disclosed by the exemplary embodiments.  
         [0028]      FIG. 1  illustrates a conventional metering blade suspension system  100 . A metering blade  110  is affixed to an elongated blade mounting bracket  120  that provides both a rigid support and arms  130  for rotation. Two torsion springs apply a load to bias the blade  110  against a drum (not shown). The arms  130  are provided at each end of the mounting bracket  120  and include an aperture  140  to facilitate the attachment of the mounting bracket  120  and to provide an axis of rotation. Typically, the metering blade  110  comprises an elastomeric material. As described above, the metering blade  110  functions to apply a finely metered amount of oil to the transfer drum surface. The blade  110  also functions to capture paper fibers, untransfixed pixels and other debris.  
         [0029]     Problems exist with the conventional metering blade system  100 . For instance, the arms  130  at each end of the blade mount bracket are at risk of being bent during shipping or handling. This can cause misalignment of the metering blade  110  in the system  100 . The conventional system  100  requires multiple steps to assemble and relies on multiple parts to hold the assembly in place. The conventional system  100  requires the attachment of at least two torsion springs  150  and  152  that are mirror images of each other. Tensioning and latching the torsion springs  150  and  152  present significant assembly steps.  
         [0030]      FIG. 2  illustrates a first exemplary embodiment of a metering blade suspension system  200  according to this invention. A metering blade assembly  290  comprises a metering blade  210  affixed to an elongated blade mounting bracket  220 . A leaf spring  230  is attached to each lateral end of the elongated mounting bracket  220 . The leaf spring  230  serves as an arm for rotation of the blade  210  and also flexes to provide a load to the blade  210 . The leaf spring includes cutout portions  260  that contribute to the degree of flex. One end of the leaf spring  230  is attached to the mounting bracket  220  by a crimping means  250 . At the other end opposite to the mounting bracket attachment, the leaf spring  230  includes a tab portion  240  that facilitates attachment of the leaf spring  230  to a drum maintenance unit (not shown). The mounting bracket  220  includes lateral ends  222  and  224 .  
         [0031]     In the first exemplary embodiment, the metering blade  210  and mounting bracket  220  include multiple downwardly directed drip points  270  and  280  from which excess oil and entrained debris drip. These drip points thus facilitate the efficient filtration and reclamation of the oil.  
         [0032]      FIGS. 3 and 4  illustrate enlarged views of the first exemplary embodiment of this invention. In  FIG. 3 , the metering blade  210  may be attached to the mounting bracket  220  by any known or hereafter developed technique, for example by adhesive. One end of the leaf spring  230  is attached to the blade assembly  290 . The exemplary attachment involves crimping an overhanging tab portion  250  of the leaf spring. The tab portion  250  is bent over and around the mounting bracket  220 . The tab portion  250  is crimped sufficiently so that an end  254  of the tab is directed substantially downward. The tab portion  250  includes a tab  252  that presses against the mounting bracket  220 .  
         [0033]     In  FIG. 4 , the leaf spring  230  is shown detached from the blade assembly  290 . The mounting bracket  220  includes a tab  256  and the leaf spring  230  includes a slot  258 . When the leaf spring  230  is attached to the blade assembly  290 , the tab  256  fits into the slot  258 . The attachment is not limited to the crimping method shown in  FIGS. 3 and 4 , however, the attachment should provide sufficient strength to withstand stresses resulting from flexing the leaf springs during use of the metering blade  210 .  
         [0034]      FIG. 5  illustrates an exploded perspective view of a replaceable cassette  510  for an imaging apparatus according to an exemplary embodiment of this invention. Disposed within the replaceable cassette  510  is a static shield  520 , a filter  530 , an oiling roller  540 , a metering blade assembly  290  with leaf springs  230  and a top cover  550 . The static shield  520  includes a tab portion  522 . Details of the replaceable cassette are discussed in copending U.S. Patent Applications Nos. (Attorney Docket Nos. 117420, 117421, 117423 and 117424).  
         [0035]      FIGS. 6 and 7  illustrate an exemplary embodiment of how a metering blade suspension system can be assembled as part of a drum maintenance unit  600 . In the exemplary embodiment shown in  FIG. 6 , the leaf spring  230  is first fastened onto the blade mount  220 . Then, the blade assembly  290  is dropped into a drum maintenance unit cassette  610 . The tab portion  240  of the leaf spring  230  serves as point of attachment for partially locking the assembly  290  in place in the drum maintenance unit  600 . The tab portion  240  slips into a receptacle slot  620  located in the drum maintenance unit  600 , partially locking the assembly  290  in place. Next, each lateral end  222  and  224  of the blade assembly  290  is further locked into position by the cassette  610 , fully locking the assembly  290  in place.  
         [0036]      FIG. 7  illustrates an exemplary embodiment of an assembled drum maintenance unit  600  in operation. During operation, the drum maintenance unit  600  is raised so that the oiling roller  540  contacts the surface of the image drum  710 . The image drum  710  rotates in the direction of the arrow A. In response, the oiling roller is driven to rotate in the direction of arrow B and applies a release agent  720  to the surface of the image drum  710 . The metering blade  210  engages with the  710 , downstream from the oiling roller  540 . The metering blade  210  distributes a uniform thickness of release agent to consistently form an optimal liquid intermediate transfer layer  730  across the surface of the image drum  710 . The oiling roller  540  applies enough release agent to the image drum surface  710  to insure that there is always a sufficient amount of agent available to be metered.  
         [0037]     Optimum performance is achieved by controlling the position, angle and load of the blade  210 . As the blade  210  meters the release agent, the blade is lifted off the drum surface  710  to allow a metered portion of the agent to flow past the blade. By adjusting the contact force of the blade  210  against the image drum surface  710  and the angle of the blade, the desired amount of blade lift is established. In exemplary embodiments of this invention, the leaf spring  230  applies a vertical load to the blade  210  of about 1-2 pounds per each side of the blade. In various exemplary embodiments of this invention, the angle of the blade  210  at the point of contact with the image drum  710  ranges from about 57 to about 67 degrees as measured between the front face of the blade and a tangent to the drum at the point of contact. In exemplary embodiments of this invention, the leaf spring  230  allows the metering blade assembly  290  to pivot in a quasi-frictionless motion.  
         [0038]     In various exemplary embodiments of this invention, the leaf spring  230  comprises an electrical connection. The leaf spring may provide an electrical connection between the metering blade assembly  290  and other parts of the drum maintenance unit for example, by maintaining a point of electrical contact in a relatively stationary area of the spring, such as for example, the tab portion  240 . Thus, in various exemplary embodiments of this invention, the tab portion  240  electrically connects with the tab portion  522  of the static shield  520 .  
         [0039]      FIG. 8  illustrates an exemplary embodiment of this invention, in which the leaf spring  230  comprises a grounding path for bleeding static charge in the metering blade assembly  290 , imaging drum  710  and oiling roller  540 . Normal operation of an imaging drum  710  causes the development of an electrostatic field  810 . Dispersing the static charge can occur through an electrical contact that includes the leaf spring  230 . Thus, in the exemplary embodiment of this invention, the tab portion  240  of the leaf spring  230  and the tab portion  522  of the static shield  520  electrically connect to form a static charge bleeding circuit  820  between the metering blade assembly  290  and a grounding circuit  840 , which is located outside of the drum maintenance unit  600 . In the exemplary embodiment of this invention, the connection between the tab portion  240  and the tab portion  522  occurs at the receptacle slot  620  of the drum maintenance unit  600  (not shown).  
         [0040]     While this invention has been described in conjunction with the exemplary embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent from a review of the foregoing. Accordingly, the exemplary embodiments of the invention, as set forth above, are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention.