Abstract:
Two thick film charging devices or a common thick film charge device with two separated obverse conductors, sharing a common power supply are used for photoreceptor charge and erase. The thick film charging devices use a set of AC biased electrodes supported on a dielectric material which also support a counter electrode on an opposite side of the dielectric. A DC offset applied to the counter electrodes is used to set photoreceptor charge level. One DC voltage is used for photoreceptor charge and a zero or near zero DC voltage is used to erase residual charge for the photoreceptor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Cross-reference is hereby made to commonly assigned and U.S. application Ser. No. 13/030,220, filed Feb. 18, 2011, now U.S. Pat. 8,478,173,and entitled “Limited Ozone Generator Transfer Device” by Gerald F. Daloia, et al., and U.S. application Ser. No. 13/160,845, filed Jun. 15, 2011 , now U.S. Pat. 8,335,450, and entitled “Method for Externally Heating a Photoreceptor” by Gerald F. Daloia, et al. The disclosures of the heretofore-mentioned applications are incorporated herein by reference in their entirety. 
     BACKGROUND 
     1. Field of the Disclosure 
     The present disclosure relates generally to an electrostatographic printing apparatus, and more particularly, concerns a system and method for charging and erasing the surface of a photoreceptor in such a machine. 
     2. Description of Related Art 
     Typically, in an electrostatographic printing process of printers, a photoconductive or photoreceptor member is charged by a charging device to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoreceptor member is exposed to selectively dissipate the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoreceptor member. After the electrostatic latent image is recorded on the photoreceptor member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules either to a donor roll or to a latent image on the photoreceptor member. The toner attracted to the donor roll is then deposited on latent electrostatic images on a charge retentive surface, which is usually a photoreceptor. The toner powder image is then transferred from the photoreceptor member to a copy substrate. 
     In order to fix or fuse the toner material onto a support member permanently by heat, it is necessary to elevate the temperature of the toner material to a point at which constituents of the toner material coalesce and become tacky. This action causes the toner to flow, to some extent, onto fibers or pores of the support members or otherwise upon surfaces thereof. Thereafter, as the toner materials cool, solidification of the toner materials occurs causing the toner material to be bonded firmly to the support member. 
     Transfer is typically carried out by the creation of a “transfer-detack zone” (often abbreviated to just “transfer zone”) of AC and DC biases where the print sheet is in contact with, or otherwise proximate to, the photoreceptor member. A DC bias applied to the back (i.e., on the face away from the photoreceptor member) of the paper or other substrate in the transfer zone electrostatically transfers the toner from the photoreceptor member to the paper or other substrate presented to the transfer zone. The toner particles are heated to permanently affix the powder image to the copy substrate. Biased transfer rolls are also used to transfer an image from a photoreceptor member to media, for example, the segmented bias roll disclosed in U.S. Pat. No. 3,847,478. 
     An erase device is used to remove any remaining photoreceptor charge in the xerographic process, such as, shown in U.S. Pat. Nos. 4,534,641 and 7,424,250 B2. Known charge/discharge systems utilize different charging devices such as a pin scorotron or dicorotron, and different erase mechanisms such as erase lamps or wires and different AC and DC power supplies. The different components and power supplies required for the charging and erase functions can be quite costly. 
     Thus, there is still a need for a system and method for performing the charge/erase functions at reduced cost. 
     BRIEF SUMMARY 
     In answer to this need, provided hereinafter is a single charge/erase system that employs two thick film charging devices sharing a common power supply for photoreceptor charge and erase. Each thick film charging device uses a set of AC biased electrodes supported on a dielectric material which also supports a counter electrode on the obverse side. A DC offset, applied to the common counter electrode or upper conductor, is used to set the photoreceptor charge level. One DC voltage is used for photoreceptor charge and a zero or near zero DC voltage for photoreceptor erase. The common counter electrodes can be individually biased enabling either a single unified charge device or a pair of devices. 
     The disclosed system may be operated by and controlled by appropriate operation of conventional control systems. It is well known and preferable to program and execute imaging, printing, paper handling, and other control functions and logic with software instructions for conventional or general purpose microprocessors, as taught by numerous prior patents and commercial products. Such programming or software may, of course, vary depending on the particular functions, software type, and microprocessor or other computer system utilized, but will be available to, or readily programmable without undue experimentation from, functional descriptions, such as, those provided herein, and/or prior knowledge of functions which are conventional, together with general knowledge in the software of computer arts. Alternatively, any disclosed control system or method may be implemented partially or fully in hardware, using standard logic circuits or single chip VLSI designs. 
     The term ‘printer’ or ‘reproduction apparatus’ as used herein broadly encompasses various printers, copiers or multifunction machines or systems, xerographic or otherwise, unless otherwise defined in a claim. The term ‘sheet’ herein refers to any flimsy physical sheet or paper, plastic, media, or other useable physical substrate for printing images thereon, whether precut or initially web fed. 
     As to specific components of the subject apparatus or methods, it will be appreciated that, as normally the case, some such components are known per se&#39; in other apparatus or applications, which may be additionally or alternatively used herein, including those from art cited herein. For example, it will be appreciated by respective engineers and others that many of the particular components mountings, component actuations, or component drive systems illustrated herein are merely exemplary, and that the same novel motions and functions can be provided by many other known or readily available alternatives. All cited references, and their references, are incorporated by reference herein where appropriate for teachings of additional or alternative details, features, and/or technical background. What is well known to those skilled in the art need not be described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various of the above-mentioned and further features and advantages will be apparent to those skilled in the art from the specific apparatus and its operation or methods described in the example(s) below, and the claims. Thus, they will be better understood from this description of these specific embodiment(s), including the drawing figures (which are approximately to scale) wherein: 
         FIG. 1A  is a partial, frontal view of an exemplary modular xerographic printer that employs the dual purpose thick film charging/erase device of the present disclosure; 
         FIG. 1B  is a partial, frontal view an exemplary modular xerographic printer that employs a dual purpose thick film charging/erase device in a second embodiment of the present disclosure; 
         FIG. 2A  is perspective view of the dual purpose thick film charging device in accordance with the present disclosure used in the printing apparatus of  FIG. 1 ; 
         FIG. 2B  is perspective view of the dual purpose thick film charging device in accordance with the present disclosure used in the printing apparatus of  FIG. 1B ; 
         FIG. 3  is an electrical schematic for controlling ion production of the electrodes shown in  FIGS. 2A and 2B ; and 
         FIG. 4  is a thick film charging device operational depiction. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     While the disclosure will be described hereinafter in connection with a preferred embodiment thereof, it will be understood that limiting the disclosure to that embodiment is not intended. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the disclosure as defined by the appended claims. 
     For a general understanding of the features of the disclosure, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to identify identical elements. 
     Referring now to  FIG. 1A , an electrographic printing system is shown that includes two thick film charging devices configured to charge a photoreceptor surface and to erase the charge from the photoreceptor surface. 
     In  FIG. 1A , a marking device  100  is shown that includes a photoreceptor  110  which advances through processing stations in the direction of arrow  8 , a cleaning device  120 , a developer  140 , a transfer device  150 , a detack device  160 , a thick film charging device  200 , an exposure device  170  and a controller  180 . Controller  180  controls a charge being applied to the photoreceptor  110  by thick film charging device  200 , then an image-wise pattern of light from exposure device  170  exposes and photo-discharges the photoreceptor  110 . Subsequently, charged toner particles are provided to adhere to the discharged areas of the photoreceptor  110 , then the controller controls the application of a charge, with a sign opposite to the charge applied to the photoreceptor  110 , to the receiving substrate at the transfer device  150  to remove the developed toner while retaining the image-wise pattern, and some additional charge is applied via the detack device  160  to the substrate to facilitate stripping of the substrate from the photoreceptor  110 . Residual toner is then cleaned off the photoreceptor  110  by cleaner  120 . 
     In accordance with the present disclosure, the thick film charging device  200  is used to charge photoreceptor  110  and thick film charging device  300  is used to erase the charge from the photoreceptor as shown in FIGS.  2 A and  3 - 4 . Both thick film charging devices  200  and  300  comprise a ceramic substrate  201  that supports a dielectric layer  202  positioned between two conductive layers  206  and  208 . Conductive layer  206  includes slots  210  and  212  therein while conductor  208  is in the form of two conductive strips with the two conductive strips underlying the slots  210  and  212  of the upper electrode. Corona generation is created within the slots  210  and  212 . Energizing conductive layers  206  and  208  charges the surface of the photoreceptor to a relatively high, substantially uniform potential. 
     The electrical schematic in  FIG. 3  depicts the two thick film charging devices  200  and  300  in a one line operational mode. Each line has one electrode (lower conductor) and all electrodes have a common upper conductor ( FIG. 2A ). The number of electrodes is dependent upon the charging device application and the ceramic substrate&#39;s physical dimensions and the amount of power needed for the application. 
     The charging device&#39;s selected materials allow for the thick film circuit to handle AC voltages as high as 3000 volts pk-pk and DC voltages up to 1100 volts. The ceramic&#39;s rigidity permits the device to be suspended adjacent photoreceptor  110 , while being supported at its ends. 
     Switch S-A controls the AC high voltage delivered to the first thick film charger used as the photoreceptor erase device while switch S-B delivers the AC high voltage to the 2 nd  thick film charger used as the photoreceptor charge device. Operation of the charging device requires the AC voltage to be greater than 1800 volts pk-pk in order to strike corona. The upper conductors are connected to a variable DC voltage supply or to ground. 
     Corona generation occurs when the electrodes are subjected to the AC high voltage. The electrical fields that surround the electrodes cause the air molecules to ionize on the surface of the dielectric between the upper conductor fingers in slots  210  and  212  ( FIG. 2A ). The upper conductor may be further energized to a DC voltage which establishes and controls the charge on photoreceptor surface. The charge device  200  ( FIG. 1A ) generates a plasma field which enables the DC charge to flow from the top conductive layer onto the photoreceptor surface. 
     By applying suitable AC and DC voltages to the conductors of the thick film charge device  200  ( FIG. 2A ), a corona and a voltage potential are produced on the upper conductor and then to the photoreceptor as shown in the single charge/erase system operational depiction in ( FIG. 3 ). Utilizing the same power supply system and applying the AC voltage to the erase device  300  ( FIG. 1A ), while applying zero DC potential on the upper conductor; a corona on the surface of the thick film device will be produced. The erase device exposes the surface of photoreceptor  110  to a zero potential; thereby removing any polarity residual charge from the photoreceptor surface. Both the charge device and erase device can be activated together or separately as the system demands using the same single power supply system. 
     Alternatively, as disclosed in  FIGS. 1B and 2B , a single dual purpose charge/erase thick film device  400  powered by a single power source can be used to both charge and erase photoreceptor surface  110 . Thick film charging device  400 , as shown in  FIG. 1B , includes units  401  and  402  with each unit comprising, as shown in  FIG. 2B , a common ceramic substrate  403  that supports a common dielectric layer  404  positioned between separate upper conductive layers  406  and  407  and lower conductive layer  408 . Conductive layers  406  and  407  include slots  410  through  413  therein while conductor  408  is in the form of conductive strips with the conductive strips underlying the slots  410  through  413  of the upper conductive layers  406  and  407 . Corona generation is created within the slots of upper conductive layers  406  and  407 , respectively. Energizing the conductive layers  408  by applying AC voltages as high as 3000 volts pk-pk and energizing the conductive layer  406  by applying DC voltages up to 1100 volts, charges the surface of the photoreceptor to a relatively high, substantially uniform potential. Then separately and simultaneously energizing conductive layers  408  by applying the same AC voltage and by applying zero volts DC on conductive layer  407  erases the surface of the photoreceptor. A single power source is used to energize both units  401  and  402 . 
     In recapitulation, the single charge-erase system of the present disclosure includes a thick film mechanism composed of dielectric layer and conductive layers ( FIG. 2A ). The charge device can be activated in two configurations. The first applies AC and DC high voltages to the inputs and the device outputs a DC charge that flows to the photoreceptor. The second applies an AC high voltage and a zero DC voltage to the inputs and the device outputs an AC zero potential DC charge which eliminates any residual DC charge on the photoreceptor. Using two thick film charging devices and connecting them to a common power supply results is a single system with one supply and common parts. Alternatively, a single thick film charge device with a separated upper conductor powered by a single power source can be used to both charge and erase a charge retentive surface of a substrate, if desired. 
     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. Unless specifically recited in a claim, steps or components of claims should not be implied or imported from the specification or any other claims as to any particular order, number, position, size, shape, angle, color, or material.