Abstract:
A modular printhead is disclosed having the ability to separate, leaving a first collection of predetermined layers relatively permanently affixed to a print engine while a second collection of predetermined layers resides in a relatively disposable component thereof. The modular printhead includes a first printhead component having at least a first electrode and a second electrode. There is additionally a second component of the printhead. The second component can have a third electrode. The first printhead component of the printhead demountably presses against the second component, held in place by at least one fastening mechanism.

Description:
FIELD OF THE INVENTION 
     The invention relates to a printhead suitable for use with image forming systems, and more particularly relates to a modular printhead arrangement. 
     BACKGROUND OF THE INVENTION 
     Different printhead technologies in use today in image forming systems create and reproduce images in different ways. Some of these technologies include a process of charging a dielectric layer on a surface of a drum with an electronic image. A developer then transfers developer material, such as toner particles, to the charged surface. Rollers then press a printing medium, such as a sheet of paper, against the developed toner particles to permanently affix the toner particles to the paper sheet. 
     An alternative arrangement provides a photoconductive member within the imaging device charged to a substantially uniform potential. The light image of a document projects onto the photoconductive member, dissipating the charge on selected areas of the photoconductive member. The dissipation of charge results in an electrostatic image forming on the photoconductive member, which corresponds to a particular image on a document. A similar process develops a toner particle image and transfers it to a paper sheet. 
     One specific type of image forming system is an electrostatographic image system. Such image forming systems typically include at least one image forming device, such as a printhead. A known configuration for a printhead is a three layer structure. A first layer is an electrode layer, a second layer is a dielectric layer, and a third layer is another electrode layer. Electrodes within each of the electrode layers cross with electrodes from the other of the electrode layers, forming intersections, physically separated by the dielectric layer. These electrode intersections form charge generation sites. 
     Current printhead technology has resulted in a combination of layers, in addition to the basic three layers, to form the printhead. Some of the added layers are relatively expensive, causing the cost for the overall printhead to exceed that which is supported by the marketplace. 
     SUMMARY OF THE INVENTION 
     There exists in the art a need for a modular printhead having the ability to separate a first collection of predetermined layers relatively permanently affixed to a print engine from a second collection of predetermined layers residing in a relatively disposable component thereof. 
     A modular printhead, according to one aspect, includes a first printhead component having at least a first electrode, a second electrode. A second component of the printhead can have a third electrode. The first printhead component of the printhead is separable from the second component and couples thereto in a removable and replaceable manner. A fastening mechanism or mounting element can press the components together, holding them in position. 
     The first electrode is an RF-line, or drive, electrode or electrode array, the second electrode is a finger electrode or electrode array, and the third electrode is a screen electrode or electrode array, in more common configurations and according to the teachings of the present invention. The first printhead component further includes a dielectric layer, to electrically insulate the first electrode (RF-line electrode) from the second electrode (finger electrode). A number of different materials can form the dielectric layer, including semi-conductor materials. 
     A spacer layer separates the second electrode and the third electrode in accordance with further aspects of the present invention. Mounting blocks mount the third electrode in place. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The aforementioned features and advantages, and other features and aspects of the present invention, will become better understood with regard to the following description and accompanying drawings, wherein: 
     FIG. 1 is a diagrammatic illustration of an image forming system; 
     FIG. 2 is a diagrammatic illustration of a printhead suitable for use in the image forming system of FIG. 1, according to the teachings of the present invention; and 
     FIG. 3 is a diagrammatic illustration of the printhead of FIG. 2, illustrating the separation of selected components. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention generally relates to a modular printhead mounted within an image forming system. A characteristic of the modular printhead is that there exists at least two components of the printhead structure. A first printhead component contains several layers contributing to the formation of the printhead that share one or more common characteristics. The first printhead component, for example, can contain a layer or layers that are generally less expensive than a second layer or layers found in the second component of the printhead. The second component of the printhead mounts in the print engine and contains components that should not need to be replaced during the life of the image forming system. The first printhead component can include parts that are less costly to replace, and are disposable as necessary. More specifically, when components within the first printhead component of the printhead wear out, a user removes the first printhead component and replaces it with a like component to restore printhead function. This procedure leaves the second component in tact in the print engine of the image forming system. Such an arrangement results in a printhead that is more easily maintained and is relatively less costly to the owner of the image forming system. 
     Referring now in detail to the figures wherein like parts are designated by like reference numerals throughout, FIGS. 1 through 3 illustrate an example embodiment of a modular printhead according to the teachings of the present invention. Although the present invention will be described with reference to the example embodiments illustrated in the figures, it should be understood that the present invention can be embodied in many alternative forms. In addition, any suitable size, shape, or type of elements or materials can be utilized. 
     The image forming system illustrated is shown solely for the purpose of providing a general structure in which the present invention can reside. One skilled in the art will understand that other image forming systems, or charge transfer apparatus can be utilized in combination with different embodiments of the present invention, without departing from the spirit and scope of the invention herein. Image forming systems, for example, can include a collection of different technologies, such as electrophotographic, electrostatic, electrostatographic, ionographic, acoustic, inkjet, and other types of image forming or reproducing systems that are adapted to capture and/or store image data associated with a particular object, such as a document, and reproduce, form, or produce an image. 
     FIG. 1 illustrates an image forming system  10  that can have a drum  12  that mounts for rotation about an axis  14 . The drum  12  incorporates an electrically conductive core  16  coated with a dielectric layer  18 . An alternative structure, known to those of ordinary skill in the art and therefore not shown herein, provides a wide belt supporting the dielectric layer and rotating around several wheel mechanisms. 
     The dielectric layer  18  receives a charged image from a printhead  20 . Electrical connectors  24  connect a controller  22 , which drives the printhead  20  as desired. As the drum  12  rotates in the direction of the arrow shown around the axis  14 , charge generation sites within the printhead  20  generate the charged image and transfer the image to the dielectric layer  18  on the outer surface of the drum  12 . The drum  12  continues to rotate as a hopper  28  feeds toner particles  26  through a feeder  30  to the charged portion of the dielectric layer  18 . The toner particles  26  electrostatically adhere to the charged image on the dielectric layer  18 , developing the charged image into a toner image. The rotating drum  12  then carries the toner image towards a nip formed with a pressure roller  32 . The pressure roller  32  has an outer layer  34  positioned in the path of a receptor, such as a paper sheet  36 . The paper sheet  36  enters between a pair of feed rollers  38 . The pressure in the nip is sufficient to cause the toner particles  26  to transfer to the paper sheet  36 , permanently affixing the toner particles  26  thereto. The paper sheet  36  continues through and exits between a pair of output rollers  40 . After passing through the nip between the drum  12  and the pressure roller  32 , a scraper blade assembly  42  removes any toner particles  26  that may remain on the dielectric layer  18 . A discharge head  44  positioned between the scrapper blade assembly  42  and the printhead  20  removes any residual charge remaining on the dielectric layer  18  surface. The process repeats for the next image. 
     FIG. 2 illustrates a unique printhead  20  configuration according to the teachings of the present invention. The printhead  20  has a series of different layers. There is a backbone  46  at one end, which serves as a base support for the printhead  20 . The backbone  46  can be made of a number of different materials including, e.g., plastics, composites, or other like materials able to structurally support the pressures placed on the printhead  20  during operation. A substrate  48  layer adheres to the backbone  46 . The substrate  48  provides a support structure for the RF-line electrodes  50 . A dielectric layer  52  separates the RF-line, or drive, electrodes  50  from a layer of finger electrodes  54 . The dielectric layer, or dielectric composition, as disclosed herein includes a number of different structures and materials. The dielectric, for example, can be a single layer of a single material, or a plurality of layers of either the same or differing dielectric materials. A plethora of compositions can form the dielectric. Some possible materials include silicon dioxide, aluminum oxide, magnesium oxide, silicon nitride, and boron nitride. 
     As viewed from a point in space generally orthogonal to the plane containing each of the electrode layers, the RF-line electrodes  50  form intersections with the finger electrodes  54 . However, the electrodes  50  and  54  are physically separated, and electrically insulated from each other, by at least one dielectric layer  52  or composition, as viewed from a cross-sectional perspective of the printhead film containing the electrode and dielectric layers. 
     The finger electrodes  54  are adjacent a spacer  56 , which maintains a desired distance between the finger electrodes  54  and a screen electrode layer  58 . A set of mounting blocks  62  mount to the screen electrode  58 , completing the modular printhead  20 . The screen electrode  58  has within it a series of screen holes  60  in alignment or registration with the intersections of the RF-line electrodes  50  and the finger electrodes  54 . 
     The spacer  56  and the screen electrode  58  are not requirements of the modular printhead  20 . In the embodiment illustrated, they do form a substantial portion of the second printhead component  70 . However, the second printhead component  70  can be formed from other layers within the printhead  20  as further discussed below. 
     FIG. 3 illustrates the printhead  20  according to one aspect of the present invention, split into two separable and connectable components  68  and  70 . The backbone portion  46  of the first printhead component  68  supports the substrate layer  48 . The RF-line electrodes  50  mount on the substrate  48  layer. The dielectric layer  52  electrically insulates RF-line electrodes  50  from the finger electrodes  54 . This first group of layers forms the removable and replaceable first printhead component  68 . Between the removable and replaceable first printhead component  68  and the spacer  56  is a gap  66 . This gap  66  represents the splitting point between each of the printhead components  68  and  70 . 
     The spacer  56  of the second printhead component  70  supports the screen electrode  58 , which mounts thereto with the mounting blocks  62 . The screen electrode  58  includes screen holes  60  in registration with the intersections of the RF-line electrodes  50  and the finger electrodes  54 . The spacer  56 , the screen electrode  58 , and the mounting blocks  62  form the second printhead component  70 . 
     The collection of layers that form each of the illustrated components  68  and  70  is not restricted to the embodiment illustrated herein. The printhead  20  can separate at several different locations, depending on the various motivations for utilizing the modular feature, and can contain a different number and type of layers. A significant advantage of the printhead  20  of the invention is the relatively low cost achieved by separating the printhead  20 . The more expensive and longer lasting layers are in the semi-permanent second printhead component  70 , while the less expensive layers are in the removable, replaceable, and disposable first printhead component  68 . A cost efficiency results by placing the less costly layers of the printhead  20  that have shorter life spans or need to be cleaned more often in the removable and replaceable first printhead component  68 . The user must replace only the less costly portion of the printhead  20  in order to achieve an extended printhead life. 
     An electroforming process, as understood by one of ordinary skill in the art and therefore not further discussed herein, can form the thick film that forms the screen electrode  58  in the illustrated embodiment. The electroforming process is a method of achieving the thickness required for spanning between the overall width of the printhead  20 , while concomitantly achieving the required accuracy to place the screen holes  60  in line with the RF-line electrode  50  and finger electrode  54  intersections. If the electroformed thick film were in the disposable component of the printhead  20 , the cost would be prohibitive for the targeted user. However, the second printhead component  70  is semi-permanently fixed in the printing engine and is not typically discarded with the first printhead component  68 . This allows for the use of more expensive, higher quality, longer lasting elements. 
     The spacer  56 , as viewed in FIG. 3, is the next largest contributor to charge output variation. Therefore, control of the thickness of the spacer  56  is a significant factor in the design of printheads. According to aspects of the present invention, the spacer  56  permanently attaches to the engine mounted screen electrode  58 . The spacer  56  can be formed of high precision materials, such as glass, ceramic, and the like. The relative high cost of these materials is justified by semi-permanently mounting the spacer  56 , and hence the second printhead component  70 , in the print engine. This results in a higher quality print output, and therefore a better overall printhead. 
     The foregoing components  68  and  70  can be assembled in a removable and replaceable manner to form the modular printhead  20  of the present invention. For example, a retaining mechanism, such as retaining cams  64 , can rotate to press the first and second printhead components  68  and  70  together in locking fashion (see FIG.  2 ). The retaining cams  64  can rotate in an opposite direction to release the first and second printhead components  68  and  70  (see FIG.  3 ). The modular design of the printhead  20  provides for relatively easy maintenance. A user can remove the first printhead component  68  of the printhead  20  from the second printhead component  70  to gain access to screen holes  60  for maintenance and cleaning. This extends the life of the screen electrode  58 , and maintains good print quality. Further, the rigidity of the thick film screen electrode  58  allows for easy cleaning of the screen electrode  58 . This is not possible with thin film screens utilized in other printhead applications, which are instead replaced. Corona bi-products can also be removed from the finger electrodes  54 , which are exposed when the first printhead component  68  and second printhead component  70  of the modular printhead  20  separate. 
     In addition to the improved access to the screen holes  60  and the finger electrodes  54 , the printhead  20  is relatively less expensive to construct because it has a simpler design. More specifically, in the illustrated printhead  20 , there are no additional layers above the finger electrode  54  layer, which simplifies the manufacturing process. Furthermore, arranging the screen electrode  58  and the spacer  56  within the machine places the more costly elements of the printhead on the more permanent print engine, which is designed to last the life of the image forming system  10 . 
     Numerous modifications and alternative embodiments of the invention will be apparent to those skilled in the art in view of the foregoing description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the best mode for carrying out the invention. Details of the structure may vary substantially without departing from the spirit of the invention, and exclusive use of all modifications that come within the scope of the appended claims is reserved. It is intended that the invention be limited only to the extent required by the appended claims and the applicable rules of law.