Method and apparatus for lightweight corona device shield mounting

Abstract: A lightweight easily installed shield for a corona generating device. A frame to support the end blocks and provide a structural member for a corona generating device is provided. The shield (158) for the corona generating device is made of a lightweight, thin conductive material such as stainless steel and is formed so as to have a generally bowed out cross section prior to installation in the frame (58). To install the shield (158) in the frame (58) it is squeezed together and inserted in the frame. Once released the resilient bias of the steel causes the shield to be restrained within the frame and can be accurately located and retained by using a locating pin or ridge formed in the frame. The shield described allows easy and accurate assembly of the corona generating device.

Description: This invention relates generally to a corona generating device, and more particularly concerns a method and apparatus for mounting a lightweight, low cost shield on a corona generating device. In printing machines, corona devices perform a variety of other functions in the printing process. For example, corona devices aid the transfer of the developed toner image from a photoconductive member to a transfer member. Likewise, corona devices aid the conditioning of the photoconductive member prior to, during, and after deposition of developer material thereon to improve the quality of the electrophotographic copy produced thereby. Both direct current (DC) and alternating current (AC) type corona devices are used to perform these functions. One form of a corona charging device comprises a corona electrode in the form of an elongated wire connected by way of an insulated cable to a high voltage AC/DC power supply. The corona wire is partially surrounded by a conductive shield. The photoconductive member is spaced from the corona wire on the side opposite the shield. An AC voltage may be applied to the corona wire and at the same time, a DC bias voltage is applied to the shield to regulate ion flow from the corona wire to the photoconductive member being charged. Another form a corona charging device is a dicorotron. The dicorotron comprises a coronode having a conductive wire that is coated with an electrically insulating material. When AC power is applied to the coronode by way of an insulated cable, substantially no net DC current flows in the wire due to the thickness of the insulating material. Thus, when the conductive shield forming a part of the dicorotron and the photoconductive member passing thereunder at the same potential, no current flows to the photoconductive member or the conductive shield. However, when the shield and photoconductive member are at different potentials, for example, when there is a copy sheet attached to the photoconductive member to which toner images have been electrostatically transferred thereto, an electrostatic field is established between the shield and the photoconductive member which causes current to flow from the shield to ground. Still other forms of corona charging devices include pin corotrons and scorotrons. The pin corotron comprises an array of pins integrally formed from a sheet metal member that is connected by a high voltage cable to a high power supply. The sheet metal member is supported between insulated end blocks and mounted within a conductive shield. The photoconductive member to be charged is spaced from the sheet metal member on the opposite side of the shield. The scorotron is similar to the pin corotron, but is additionally provided with a screen or control grid disposed between the coronode and the photoconductive member. The screen is held at a lower potential approximating the charge level to be placed on the photoconductive member. The scorotron provides for more uniform charging and prevents over charging. It is desirable to be able to easily assemble each of the above described devices and to accurately locate the shield member of the corona generating device. It is further desirable to supply a corona shield that is easy to manufacture and of relatively low cost. US-A-4764675 describes a self-tensioning coronode structure. The system utilizes a tensioning system for tensioning the coronode to a frame. In accordance with one aspect of the present invention, there is provided a corona generating device comprising a frame, a pair of end blocks located on opposite ends of said frame, a conductor attached at a first end to one of said pair of end blocks and attached at a second end to said other of said pair of end blocks and a shield, where said shield is biased into engagement with said frame, wherein the beam strength of said shield provides the biasing force to maintain said shield in proper spatial relationship to said frame and said conductor. Pursuant to another aspect of the present invention, there is provided a method of installing and retaining a shield in a corona generating device, comprising compressing a metallic shield member and inserting the shield into an aperture in a frame member and releasing the shield so that the resiliency of the metallic member biases the shield into position and retains the shield within the frame member. Other features of the present invention will become apparent as the following description proceeds and upon reference to the drawings, in which: Figure 1 is a schematic elevational view of a typical electrophotographic printing machine utilizing the corona shield of the present invention; Figure 2 is an exploded perspective view of the xerographic CRU module further illustrating the components thereof; Figures 3 and 4 are schematic end views illustrating the method of installing the corona shield; Figure 5 is a top view of the corona shield; Figure 6 is a side view of the corona shield; Figure 7 is a perspective view of the frame into which the corona shields are installed; and Figure 8 is a perspective view of the corona shields for the Figure 7 frame. Referring to Figure 1 of the drawings, an original document is positioned in a document handler 27 on a raster input scanner (RIS) indicated generally by reference numeral 28. The RIS contains document illumination lamps, optics, a mechanical scanning drive and a charge coupled device (CCD) array. The RIS captures the entire original document and converts it to a series of raster scan lines. This information is transmitted to an electronic subsystem (ESS) which controls a raster output scanner (ROS) described below. Figure 1 schematically illustrates an electrophotographic printing machine which generally employs a photoconductive belt 10. Preferably, the photoconductive belt 10 is made from a photoconductive material coated on a ground layer, which, in turn, is coated on an anti-curl backing layer. Belt 10 moves in the direction of arrow 13 to advance successive portions sequentially through the various processing stations disposed about the path of movement thereof. Belt 10 is entrained about stripping roller 14, tensioning roller 20 and drive roller 16. As roller 16 rotates, it advances belt 10 in the direction of arrow 13. Initially, a portion of the photoconductive surface passes through charging station A. At charging station A, a corona generating device indicated generally by the reference numeral 22 charges the photoconductive belt 10 to a relatively high, substantially uniform potential. At an exposure station, B, a controller or electronic subsystem (ESS) indicated generally by reference numeral 29, receives the image signals representing the desired output image and processes these signals to convert them to a continuous tone or greyscale rendition of the image which is transmitted to a modulated output generator, for example the raster output scanner (ROS), indicated generally by reference numeral 30. Preferably, ESS 29 is a self-contained, dedicated minicomputer. The image signals transmitted to ESS 29 may originate from a RIS as described above or from a computer, thereby enabling the electrophotographic printing machine to serve as a remotely located printer for one or more computers. Alternatively, the printer may serve as a dedicated printer for a highspeed computer. The signals from ESS 29, corresponding to the continuous tone image desired to be reproduced by the printing machine, are transmitted to ROS 30. ROS 30 includes a laser with rotating polygon mirror blocks. The ROS will expose the photoconductive belt to record an electrostatic latent image thereon corresponding to the continuous tone image received from ESS 29. As an alternative, ROS 30 may employ a linear array of light emitting diodes (LEDs) arranged to illuminate the charged portion of photoconductive belt 10 on a raster-by-raster basis. After the electrostatic latent image has been recorded on photoconductive surface 12, belt 10 advances the latent image to a development station, C, where toner, in the form of liquid or dry particles, is electrostatically attracted to the latent image using commonly known techniques. The latent image attracts toner particles from the carrier granules forming a toner powder image thereon. As successive electrostatic latent images are developed, toner particles are depleted from the developer material. A toner particle dispenser, indicated generally by the reference numeral 39, dispenses toner particles into developer housing 40 of developer unit 38. With continued reference to Figure 1, after the electrostatic latent image is developed, the toner powder image present on belt 10 advances to transfer station D. A print sheet 48 is advanced to the transfer station, D, by a sheet feeding apparatus, 50. Preferably, sheet feeding apparatus 50 includes a nudger roll 51 which feeds the uppermost sheet of stack 54 to nip 55 formed by feed roll 52 and retard roll 53. Feed roll 52 rotates to advance the sheet from stack 54 into vertical transport 56. Vertical transport 56 directs the advancing sheet 48 of support material into the registration transport 120 past image transfer station D to receive an image from photoreceptor belt 10 in a timed sequence so that the toner powder image formed thereon contacts the advancing sheet 48 at transfer station D. Transfer station D includes a corona generating device 58 which sprays ions onto the back side of sheet 48. This attracts the toner powder image from photoconductive surface 12 to sheet 48. The sheet is then detacked from the photoreceptor by corona generating device 59 which sprays oppositely charged ions onto the back side of sheet 48 to assist in removing the sheet from the photoreceptor. After transfer, sheet 48 continues to move in the direction of arrow 60 by way of belt transport 62 which advances sheet 48 to fusing station F. Fusing station F includes a fuser assembly indicated generally by the reference numeral 70 which permanently affixes the transferred toner powder image to the copy sheet. Preferably, fuser assembly 70 includes a heated fuser roller 72 and a pressure roller 74 with the powder image on the copy sheet contacting fuser roller 72. The pressure roller is cammed against the fuser roller to provide the necessary pressure to fix the toner powder image to the copy sheet. The fuser roll is internally heated by a quartz lamp (not shown). Release agent, stored in a reservoir (not shown), is pumped to a metering roll (not shown). A trim blade (not shown) trims off the excess release agent. The release agent transfers to a donor roll (not shown) and then to the fuser roll 72. The sheet then passes through fuser 70 where the image is permanently fixed or fused to the sheet. After passing through fuser 70, a gate 80 either allows the sheet to move directly via output 84 to a finisher or stacker, or deflects the sheet into the duplex path 100, specifically, first into single sheet inverter 82 here. That is, if the sheet is either a simplex sheet, or a completed duplex sheet having both side one and side two images formed thereon, the sheet will be conveyed via gate 80 directly to output 84. However, if the sheet is being duplexed and is then only printed with a side one image, the gate 80 will be positioned to deflect that sheet into the inverter 82 and into the duplex loop path 100, where that sheet will be inverted and then fed to acceleration nip 102 and belt transports 110, for recirculation back through transfer station D and fuser 70 for receiving and permanently fixing the side two image to the backside of that duplex sheet, before it exits via exit path 84. After the print sheet is separated from photoconductive surface 12 of belt 10, the residual toner/ developer and paper fiber particles adhering to photoconductive surface 12 are removed therefrom at cleaning station E. Cleaning station E includes a rotatably mounted fibrous brush in contact with photoconductive surface 12 to disturb and remove paper fibers and a cleaning blade to remove the nontransferred toner particles. The blade may be configured in either a wiper or doctor position depending on the application. Subsequent to cleaning, a discharge lamp (not shown) floods photoconductive surface 12 with light to dissipate any residual electrostatic charge remaining thereon prior to the charging thereof for the next successive imaging cycle. The various machine functions are regulated by controller 29. The controller is preferably a programmable microprocessor which controls all of the machine functions hereinbefore described. The controller provides a comparison count of the copy sheets, the number of documents being recirculated, the number of copy sheets selected by the operator, time delays, jam corrections, etc.. The control of all of the exemplary systems heretofore described may be accomplished by conventional control switch inputs from the printing machine consoles selected by the operator. Conventional sheet path sensors or switches may be utilized to keep track of the position of the document and the copy sheets. Turning next to Figure 2, there is illustrated a perspective exploded view of a xerographic customer replaceable unit (CRU). The xerographic CRU module mounts and locates xerographic subsystems in relationship to the photoreceptor module and xerographic subsystem interfaces. Components contained within the xerographic CRU include the transfer/detack corona generating devices 58, 59, the pretransfer paper baffles 204, the photoreceptor cleaner 206, the charge scorotron 22, the erase lamp 210, the photoreceptor(P/R) belt 10, the noise, ozone, heat and dirt (NOHAD) handling manifolds 230 and filter 240, the waste bottle 250, the drawer connector 260, the Customer Replaceable Unit Monitor (CRUM), the automatic cleaner blade engagement/retraction and automatic waste door open/close device (not illustrated). The CRU subsystems are contained within the xerographic housing. The housing consist of three main components which include the front end cap 192, right side housing 194 and left side housing 196. The xerographic housing 190 is a mechanical and electrical link. It establishes critical parameters by mounting and locating subsystems internal and external to the CRU in relationship to the photoreceptor module 300 and other xerographic subsystem interfaces. The housing allows easy reliable install and removal of the xerographic system with out damage or difficulty. Turning next to Figures 3 and 4, there is shown a schematic end view of an example of the lightweight corona shield of the present invention. As illustrated the shield 158, is bowed outward due to the resiliency of the material, in the illustrated case, a light stainless steel, prior to installation in the frame 150. The shield 158 is squeezed together and inserted into the frame 150 by moving it in the direction of arrow 151. Once within the frame 150, the shield 158 is retained due to the tendency to try to return to the bowed position. It is also possible to construct or fabricate the shield member from a conductive plastic material or other lightweight, resilient conductive material. Figures 5 and 6 are top and side views of the actual corona shields 158, 159 (Fig. 2) that are inserted into frame 150 as illustrated in Figure 7. Figure 8 is a perspective view of the shields which also illustrates the ground connections 160, 161 respectively for the shields 158, 159.

Claims: A corona generating device comprising: a frame (150); a pair of end blocks located on opposite ends of said frame; a conductor attached at a first end to one of said pair of end blocks and attached at a second end to said other of said pair of end blocks; and, a shield (158), characterised in that said shield is biased into engagement with said frame, wherein the beam strength of said shield provides the biasing force to maintain said shield in proper spatial relationship to said frame and said conductor. A corona generating device according to claim 1, further comprising a high voltage contact located in one of said pair of end blocks for providing cement to said wire. A corona generating device according to claim 1 or claim 2, wherein said shield further comprises an electrical ground connection (160) integral to said shield. A corona generating device according to any of the preceding claims, wherein said conductor comprises a wire. A corona generating device according to any of claims 1 to 3, wherein said conductor comprises an array of pins integrally formed from a sheet metal member. A method of installing and retaining the shield (158) in a corona generating device according to any of claims 1 to 5 comprising: compressing a conductive shield member (158) and inserting the shield into an aperture in a frame member (150); releasing the shield (158) whereby the resiliency of the metallic member biases the shield into position and retains the shield within the frame member (150).

Inventors: CARYL BRUCE D, DIEHL ELIZABETH D, GROSS ROBERT A, CARYL, BRUCE D., DIEHL, ELIZABETH D., GROSS, ROBERT A.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1998
Main classification: G03G15
IPC codes: G03G15, H01T19