Patent Publication Number: US-6904243-B2

Title: Image forming system and method and photoconductor having wear indicator

Description:
FIELD OF THE INVENTION 
     The invention relates to the electrophotographic imaging arts. It finds particular application to an image forming system and photoconductor that includes a wear indicator. It will be appreciated that the present invention will find application in printers, copiers, facsimile machines or other imaging devices that include a photosensitive device for forming images. 
     BACKGROUND OF THE INVENTION 
     In electrophotographic imaging devices, electrostatic latent images are formed on photosensitive devices such as a organic photoconductor drum. These drums may include one or more layers of materials which include at least a surface layer of photosensitive material. The surface layer is selectively charged and discharged to form electrostatic latent images thereon. Toner is then magnetically attracted to the latent image and transfer to a print media. 
     Over time, the photosensitive material, which is relatively thin, will wear through at various areas. As worn areas lose the photosensitive material, the charging characteristics of the drum change which may alter its imaging quality. In prior art drums, worn areas of the drum are not easily identifiable making it difficult to determine the cause of poor image quality or potential defects in the photosensitive layer. 
     The present invention provides a new and useful photoconductor and imaging device that addresses the above problems and others. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment of the present invention, an electrophotographic photoconductor is provided that includes a substrate and a first photoconductive layer disposed on the substrate, the first photoconductive layer having a first color. A second photoconductive layer is disposed over the first photoconductive layer and the second photoconductive layer has a second color distinct from the first color. 
     In accordance with another embodiment of the present invention, a replaceable cartridge for an image forming device is provided. The cartridge includes a toner reservoir for containing toner; a light sensitive device for forming an electrostatic latent image where the light sensitive device includes a surface layer of photosensitive material and an intermediate layer of photosensitive material under the surface layer. The intermediate layer is visually distinct from the surface layer where the intermediate layer indicates worn portions of the surface layer when the intermediate layer is visible. A developer roller applies toner from the toner reservoir to the light sensitive device. 
     One advantage of the present invention is that an early warning mechanism is provided that can alert a user when portions of a photosensitive device becomes worn. 
     Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the illustrated embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings which are incorporated in and constitute a part of the specification, embodiments of the invention are illustrated, which, together with a general description of the invention given above, and the detailed description given below, serve to example the principles of this invention. 
         FIG. 1  is an exemplary simplified system diagram of an imaging device in accordance with one embodiment of the present invention; 
         FIG. 2  is an exemplary replaceable cartridge in accordance with one embodiment of the present invention; and 
         FIG. 3  is an exemplary cross-section of a photoconductor drum in accordance with one embodiment of the present invention. 
         FIG. 4  is a cross-section of an example photoconductor drum having a plurality of layers. 
         FIG. 5  is a cross-section of an example flexible band photoconductor. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENT 
     The following includes definitions of exemplary terms used throughout the disclosure. Both singular and plural forms of all terms fall within each meaning: 
     “Image”, as used herein, includes but is not limited to any form of data representing an image that is to be generated and/or transferred to a print media during a printing process. Image includes any type of printable or printed markings such as characters, text, graphics or any combination of these. 
     “Imaging device”, as used herein, includes but is not limited to electrophotographic printers, laser printers, facsimile machines, copiers, and other types of imaging devices that convert data to visible markings. 
     The present system provides an early warning mechanism to indicate wear on a photosensitive element, such as an organic photoconductor drum. Generally describing the configuration, a photoconductor drum or other type of photosensitive device includes at least two layers of differently colored photosensitive material. As portions of the surface layer wear through, the color of the second layer becomes visible. This identifies worn areas of the surface layer and identifies wear patterns that may assist troubleshooting. The photosensitive element may be embodied in an imaging device, or in a replaceable cartridge as will be described below. 
     Illustrated in  FIG. 1  is a simplified cross sectional view of an exemplary electrophotographic imaging device, such as an electrophotographic printer  10 , in accordance with one embodiment of the present invention. Exemplary components of the printer and its general operation will be discussed with reference to FIG.  1 . The printer includes, for example, a charge roller  15  that charges the surface of a photoconductor, such as an organic photoconductor drum  20 , to a predetermined voltage. The surface of the drum  20  includes a layer of photosensitive material that can be selectively charged and discharged. A laser scanner  25  includes a laser diode (not shown) that emits a laser beam  30  onto the photoconductor drum  20  to selectively discharge its surface. The laser beam is reflected off a multifaceted spinning mirror (not shown) that reflects or “scans” the beam across the surface of the photoconductor drum  20  forming a latent electrostatic image corresponding to the data being printed. The photoconductor drum  20  rotates in a clockwise direction as shown by the arrow  35  such that each successive scan of the laser beam is recorded on the drum  20  after the previous scan. 
     To this end, the electrophotographic imaging device  10  may include a software configured processing device, such as formatter  60  and controller  65 . Alternatively, the electrophotographic printer  10  could use other processing devices such as a microprocessor, discrete logic or other digital state machines. To form a latent electrostatic image, the formatter  60  receives data, including print data (such as, a display list, vector graphics, or raster print data) from an application program running on a computer  70 . The formatter  60  converts the print data into a stream of binary print data that is an electronic representation of each page to be printed, and sends it to the controller  65 . The controller  65  supplies the stream of binary print data to the laser scanner  25  causing the laser diode to pulse in accordance with the data, thus creating the latent electrostatic image on photoconductor drum  20 . In addition, the formatter  60  and controller  65  exchange data necessary for controlling the electrophotographic printing process as known in the art for a particular imaging device. 
     With further reference to  FIG. 1 , after the surface voltage of the drum  20  has been selectively discharged, a developing device, such as a developing roller  40 , transfers toner to the surface of the drum  20 . Toner  45 , for example, is stored in a toner reservoir  50  of a toner print cartridge  55 . The cartridge  55  may be detachable to replace consumed toner, worn parts, or both. Based on a desired configuration the cartridge  55  may include one or more replaceable components ranging from toner to an image forming system including, for example, the charger roller  15 , the drum  20 , the developing roller  40  and other associated parts. Another embodiment of a replaceable cartridge is shown in FIG.  2 . 
     With continued reference to  FIG. 1 , the developing roller  40  is magnetized, for example, by a magnet (not shown) so that it magnetically attracts the toner  45  to the surface of the developing roller. As the developing roller  40  rotates, the toner is electrostatically transferred from the developing roller to the discharged surface areas on the photoconductor drum  20  thus covering the latent electrostatic image with toner particles. 
     A print media  75 , such as paper, envelops, transparencies, etc., is loaded from a media tray  80  by a pickup roller  85  and travels in a printing path in the electrophotographic printer  10 . The print media  75  moves through drive rollers  90  so that the arrival of the leading edge of the print media  75  at a transfer point below the photoconductor drum  20  is synchronized with the rotation of the latent electrostatic image on the drum  20 . There, an image transfer device, such as a transfer roller  95 , charges the print media so that it attracts the toner particles away from the surface of the photoconductor drum  20 . As the drum  20  rotates, the toner adhered to the discharged areas contacts the charged print media  75  and is transferred thereto. 
     The transfer of toner particles from the drum  20  to the surface of the print media  75  is not always complete and some toner particles may remain on the drum  20 . To clean the drum  20 , a cleaning blade  100  may be included to remove non-transferred toner particles as the drum continues to rotate and the toner particles are deposited in a toner waste hopper  105 . The drum may then be completely discharged by discharge lamps (not shown) before a uniform charge is restored to the drum  20  by the charging roller  15  in preparation for the next image generation and toner transfer. 
     As the cleaning blade  100  contacts and cleans the surface of the photoconductor drum  20 , the contact causes frictional wear which, over time, removes portions of the photosensitive surface of the drum  20 . As the thickness of the photosensitive surface decreases, the drum  20  may lose some of its charging characteristics which may affect the quality of printed images. As a warning mechanism, the drum  20  includes a second photosensitive layer under the surface layer that is visibly distinct from the surface layer. When portions of the surface layer wear through, the second layer will be visible which serves as a visual indicator that the photoconductor drum  20  should be replaced. Since the second layer is also photosensitive, the charging characteristics of the drum  20  can be substantially maintained without causing serious defects in print quality, thus, allowing some time for a user to replace the drum  20  individually, or if part of a replaceable cartridge, by replacing the cartridge  55 . The dual photosensitive layers are further discussed with reference to FIG.  3 . 
     Continuing with the printing example, as the print media  75  moves in the printing path past the photoconductor drum  20  and the transfer roller  95 , it enters a post transfer area. There, a conveyer  110  delivers the print media  75  to a fixing device, such as a heated fuser roller  115  and a heated pressure roller  120 , generally referred to herein as a fuser. The rollers are in pressure engagement with each other and form a nip at the contact point. As the media passes between the rollers through the nip, the toner is fused to the media through a process of heat and pressure. One or both rollers are motor driven to advance the media  75  between them. In one embodiment, the fuser is an on-demand fuser and the fuser roller  115  includes, for example, a flexible rotating sleeve that surrounds a carrier which holds a ceramic heating device  117 . The carrier provides structure to the fuser roller so that pressure may be applied against the pressure roller  120 . The flexible sleeve is typically made of polyimide. Alternately, the fuser can be a hard roller constructed with a hollow metal core and an outer layer often made of a hard “release” material such as a Teflon® film. 
     The heating device  117 , such as a ceramic heating strip, is positioned inside the fuser roller  115  and along its length. The heating strip can be silver based with a glass cover to reduce friction with the fuser roller film  115 . Other heating devices may include a quartz lamp, heating wires or other suitable heating element as known in the art. The pressure roller  120  is, for example, constructed with a metal core and a pliable outer layer. The pressure roller may also include a thin Teflon® release layer (not shown). After fusing the toner to the print media, output rollers  125  push the print media into an output tray  130  and printing is complete. 
     With continued reference to  FIG. 1 , the controller  65  also controls a high voltage power supply (not shown) to supply voltages and currents to components used in the electrophotographic processes, such as to the charge roller  15 , the developing roller  40 , the transfer roller  95  and fuser. Furthermore, controller  65  controls a drive motor (not shown) that provides power to a gear train (not shown) and controls various clutches and paper feed rollers that move the print media through the printing path within the electrophotographic printer  10 . It will be appreciated that different imaging devices may have components and control mechanisms different than those shown in the exemplary system of FIG.  1 . One of ordinary skill will appreciate that the present invention will apply to other devices in accordance with their particular configuration and obvious modifications thereto. 
     Illustrated in  FIG. 2  is another embodiment of a replaceable cartridge  200  in accordance with the present invention. The cartridge  200  includes a housing that contains a photoconductive drum  205 , a charge roller  210 , a magnetic developer roller  215 , a toner doctor blade  217  for cleaning the roller  215 , a cleaning blade  220  for cleaning the drum  205 , and a toner waste hopper  225  which operate as described above with reference to FIG.  1 . As will be described in greater detail below, as the photosensitive layer of the drum  205  wears away through repeated use and engagement with the cleaning blade  220 , portions of the drum  205  that are worn will change in color. The color change visually indicates to a user that the drum, or in this embodiment, the cartridge  200  should be replaced. To create the color change, the drum  200  includes at least two photosensitive layers, one being the top surface and the other being under it and having a different color than the top surface. 
     With further reference to  FIG. 2 , when the cartridge  200  is installed into an imaging device, the photoconductor drum  205  will be adjacent to a transfer roller  95  such that print media  75  passes between them and toner on the drum  205  transfers to the print media. Furthermore, the cartridge  200  will be aligned such that a laser window  230  formed through the housing allows a laser  30  to illuminate and discharge the drum  205 . 
     The photoconductive drum  205  also includes a spline gear drive interface (not shown) that engages a gear drive of the imaging device to control rotation of the drum  205 . In this embodiment, the cartridge  200  also includes one or more toner reservoirs  235  that contain toner, and a toner stirring blade  240  that rotates to push toner out of the toner reservoir to deliver the toner to the developer roller  215 . Other components may include a toner recovery blade  245  that reduces waste toner from leaking out of the cartridge and a developer sealing blade  250  also to reduce toner leaks. 
     With reference to  FIG. 3 , one embodiment of a photoconductive drum  300  having a wear indicator mechanism is shown that can be used in the systems of FIG.  1  and/or FIG.  2 . The drum  300  is typically a cylindrical aluminum drum that includes a top surface layer  305  of photosensitive material. An intermediate indicator layer  310  of photosensitive material is disposed under the top layer  305  and acts as a wear indicator that is visually distinguishable when portions of the top layer  305  deteriorate over time. In one embodiment, the top layer  305  and indicator layer  310  have different colors so they are distinguishable by a user. As seen in example,  FIG. 4 , it will be appreciated that additional layers  315  can be added to the drum  300  to obtain desired properties. 
     In one embodiment, the top layer  305  and the indicator layer  310  are formed from the same material so that they have the same properties and charging characteristics except for their color. In this manner, once portions of the top layer  305  wear away, imaging quality will be minimally affected for the time being because the indicator layer  310  will maintain the charging characteristics of the drum  300  in the worn portions. Once the indicator layer  310  is visible, this is an early warning to a user that the cartridge and/or drum should be replaced. 
     By observing the photoconductor drum  300 , color changes caused by excess wear will indicate which areas are effected. This may assist technicians when diagnosing problems with an imaging device. For example, if an imaging device is frequently used to print envelops or otherwise small print media, this can be determined by the color changes on the drum. When printing small media, the drum does not get toner applied over its entire surface and those areas that do not receive toner will show wear much sooner than areas that receive toner. This is because toner acts as a lubricant on the drum. Thus, when the drum gets cleaned by the cleaning blade, the no-toner areas will be subjected to more frictional engagement causing premature deterioration of the photosensitive layer. This situation can be easily determined from the visual indication of the exposed areas of the indicator layer  310 . 
     In another embodiment, the top layer  305  and indicator layer  310  may be formed with different photosensitive materials. For example, in certain applications, one of the layers may be desired to be harder and more resistant to wear than the other layer. 
     Various materials can be used as the photosensitive layers such as selenium, cadmium sulfide, zinc oxide, phthalocyanine, amorphous silicon (hereinafter abbreviated as a-Si), etc. Among these materials, non-single-crystal deposited films containing silicon atoms as the main component, as represented by a-Si, for example amorphous deposited films such as a-Si compensated with hydrogen and/or halogen (for example fluorine or chlorine), may be used to form a photosensitive member having high performance and high durability properties, but with little or no ecological concerns. For example, U.S. Pat. No. 4,265,991 and U.S. Pat. No. 6,365,308 B2 disclose examples of electrophotographic photosensitive members and their compositions, which are incorporated herein by reference. 
     It will be appreciated that the layers  305 ,  310  can be made with the same thickness or different thicknesses. Also, it is contemplated that additional layers may be added to the drum  300  so that the top layer  305  and indicated layer  310  are not necessarily the first and second surface layers. For example, an intermediate layer may be added to the surface of either layer or in between the layers to add a desired property, but which will not significantly affect the charging characteristics of the photosensitive materials. 
     In its simplest embodiment, a method of manufacturing a photoconductive drum includes providing a metallic drum, applying an indicator layer of photosensitive material, and applying a surface layer of photosensitive material where the indicator layer and the surface layer have different distinguishable colors. 
     With reference to  FIG. 5 , in another embodiment, the cylindrical photoconductor drum may be embodied as a flexible band  500  that can be rotated by one or more rollers  505 . In general, the drum or band  500  is a substrate used to support one or more photosensitive layers (e.g. layers  305 ,  310 ). In another embodiment, the wear indicator layer may be formed of a non-photosensitive material having a different color than the photosensitive surface layer. In this configuration, print quality may be affected much sooner as the photosensitive layer diminishes. 
     With the present invention, an early warning mechanism is provided to indicate excess wear of a photoconductor drum. Since the indicator layer is also photosensitive, a user may continue printing operations for a limited time even when the surface layer begins to wear through. 
     While the present invention has been illustrated by the description of embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention, in its broader aspects, is not limited to the specific details, the representative apparatus, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicant&#39;s general inventive concept.