Corona charger wire tensioning mechanism
BACKGROUND OF THE INVENTION 
     The present invention relates in general to charging devices such as utilized in electrostatographic reproduction apparatus or the like, and more particularly to a mechanism for facilitating corona wire replacement and easily and accurately tensioning the corona charger wires. 
     In typical commercial electrostatographic reproduction apparatus (copier/duplicators, printers, or the like), a latent image charge pattern is formed on a uniformly charged dielectric member. Pigmented marking particles are attracted to the latent image charge pattern to develop such image on the dielectric member. A receiver member is then brought into contact with the dielectric member, and an electric field applied to transfer the marking particle developed image to the receiver member from the dielectric member. After transfer, the receiver member bearing the transferred image is transported away from the dielectric member and the image is fixed to the receiver member by heat and/or pressure to form a permanent reproduction thereon. 
     The electrostatic fields for various reproduction apparatus operations are commonly provided by corona charging devices. For example, corona chargers may be used to deposit the uniform charge on the dielectric member prior to light exposure, to implement transfer of a developed image from the dielectric member to a receiver member, or to neutralize charge on the dielectric member subsequent to developed image transfer to facilitate release of the receiver member or residual marking particles from the dielectric member. 
     Corona chargers typically include at least one very thin corona wire, located within a housing shell held at a ground potential. The corona wire is electrically coupled to a high voltage to generate ions or charging current to charge a surface (such as the dielectric member surface) brought into close proximity with the corona wire. The corona wire is tightly suspended between insulating end blocks, supported in the housing shell, such end blocks being connected to a high voltage source for producing the ion generating condition within the corona wire. 
     It is important that the corona wire be maintained at a tension within a particular preselected range. This is necessary because if the tension is too high, the corona wire is easily broken, and if the tension is too low the corona wire will tend to vibrate which will materially effect the ability of the wire to provide for the desired uniform charging of the intended surface. To maintain the desired tension in the corona wire, the typical corona charging device anchors the wire to one end block and connects the other end to the opposite end block through, for example, a coiled spring connector. The spring constant of the spring connector is selected to yield tension in the corona wire within the desired preselected range. 
     It should be well appreciated that the high voltage of the corona wire creates a corrosive environment which adversely effects the wire. That is, the atmosphere surrounding the wire is conducive to the promotion of coating and/or pitting of the wire. Over time, such action on the corona wire will cause the wire, which by its very nature is extremely fragile, to no longer be effective in producing the desired uniform charging of the surface intended to have a charge applied thereto. As such, the corona wire has to be periodically replaced. However, due to the mounting of the corona wire under tension, it has been difficult to readily effect wire replacement. 
     One type of corona charging device which attempts to facilitate corona wire replacement is shown in U.S. Pat. No. 4,764,675 (issued Aug. 16, 1988, in the name of Levy et al). In the corona charging device of this patent, a pivot member mounted on an end block of the device. The pivot member is movable to a first position where the corona wire can be connected to the member while untensioned, and to a second position where the wire is held under a selected tension. However, due to the space constraints with the particular arrangement of this charging device, it is still extremely difficult to attach the corona wire to the pivot member. Thus, because of the fragile nature of the wire, the attempted attachment of the wire to the pivot member may still often cause the wire to break as it is being replaced. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing discussion, this invention is directed to a corona charger wire tensioning mechanism, for a corona charging device for applying a charge to a selected surface within an electrostatographic reproduction apparatus or the like, which facilitates corona wire replacement. The corona charging device comprises at least one corona wire, and a housing. A mechanism, located in the housing, anchors one end of the corona wire and electrically couples an electrical potential source to the corona wire. A tensioning mechanism is removably receivable in the housing in spaced relation to the anchoring mechanism. The tensioning mechanism has an anchor for securing the opposite end of the corona wire thereto, and an arm adapted to engage the housing along a line which forms a pivot axis for the tensioning mechanism. After the corona wire is easily and readily anchored to the tensioning mechanism remotely from the housing, the tensioning mechanism can be received in the housing and pivoted about the pivot axis to a position to apply a preselected tensioning to the corona wire. 
    
    
     The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the detailed description of the preferred embodiment of the invention presented below, reference is made to the accompanying drawings, in which: 
     FIG. 1 is an exploded view, in perspective, of a corona charger and a corona wire tensioning mechanism, according to this invention, for the corona charger, with portions removed or broken away to facilitate viewing; 
     FIG. 2 is front view, in perspective and on an enlarged scale, of the tensioning mechanism according to this invention; 
     FIG. 3 is a side elevational view of the tensioning mechanism of FIG. 2, in cross-section taken along the lines 3--3 of FIG. 2; 
     FIG. 4 is a side elevational view of the tensioning mechanism of FIG. 2, showing the tensioning mechanism in a non-tensioning orientation within the housing shell of the corona charger device of FIG. 1; and 
     FIG. 5 is a side elevational view of the tensioning mechanism of FIG. 2, similar to FIG. 4, but showing the tensioning mechanism in a tensioning orientation within the housing shell of the corona charger device of FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the accompanying drawings, FIG. 1 shows a typical corona charger, designated generally by the numeral 10. The corona charger 10 is utilized, for example, for the general purpose of uniformly charging a surface in well known electrostatographic reproduction apparatus or the like. The corona charger 10 includes a housing shell 12 having a first end portion 12a and a second end portion 12b interconnected by an elongated central portion 12c. The housing shell 12 is formed, for example, from an insulative resin material molded in the desired shape as shown. At least one corona wire 14 (three corona wires are shown in the preferred embodiment) is supported to span the length of the central portion 12c of the housing shell. The central portion 12c is bounded at its ends by walls 16a and 16b. The walls 16a, 16b may be integrally formed with the housing shell 12, or may be separate structures connected to the housing shell in any well known manner. A plurality of V-shaped notches 18 are respectively provided in the walls 16a, 16b for supporting and locating the corona wires 14, whereby the surface to be charged can be brought into accurate spaced association with the corona wires. 
     A mechanism 20 is provided in the first end portion 12a of the housing shell 12 for anchoring one respective end of the corona wires 14, and for electrically coupling a suitable electrical high voltage potential source to the corona wires. The mechanism 20 includes an anchor assembly 22 formed of conductive material, such as {metal} for example. The anchor assembly 22 has a body 24 connected by suitable fasteners 26 to the housing shell 12. The body 24 has a plurality of tabs 28 extending upwardly at an acute angle from the longitudinal edge 24a of the body. The tabs 28 respectively define slots 30 at the ends remote from the body 24. The slots 30 are adapted to respectively receive corona wires 14, which are secured to the tabs 28 by knots or loops formed in the ends of the corona wires. 
     Additionally, the body 24 of the anchor assembly 22 has a tab 32 extending substantially at a right angle away from the longitudinal edge 24b of the body. The tab 32 is connected to an electrical conductor 34 supported so as to extend through an end wall 12d of the housing shell 12. The conductor 34 is adapted to be coupled to a high voltage potential source (not shown), whereby the electrical potential of the source is applied to the corona wires 14 through the electrically conductive path described from the conductor 34, to the body 24 of the anchor assembly 22, and then to the corona wires. 
     In order to facilitate replacement of the corona wires 14 in the corona charger 10 and provide a preselected desired tensioning to the corona wires, a tensioning mechanism 40, according to this invention, is provided. The tensioning mechanism 40, as best shown in FIGS. 2 and 3, includes a substantially L-shaped body 42 having a configuration which defines a step 42a at the junction between the arms 42b and 42c of the body. A plurality of openings 44 are defined in the step 42a extending through the body. Also, the body includes a plurality of features 46 respectively extending from the rear of the step 42a. The features 46 cooperate with the underside surfaces of the step 42a to form a retainer for a shaft 48. 
     The shaft 48 of the tensioning mechanism 40 serves to capture a plurality of springs 50. The springs 50, as shown in the preferred embodiment, are coiled tensioning springs. Of course, other suitable spring-like configurations, such as elastic bands for example, can be used with this invention. One end 50a of the respective springs is connected to the shaft 48. The springs 50 extend from the shaft 48 through the openings 44 in the step 42a of the L-shaped body 42. The opposite end 50b of the respective springs is adapted to have an end of the corona wire 14 attached thereto. The spring constant for the springs 50 is preselected to be of a value to insure that the springs will provide the desired tensioning in the corona wires on assembly. 
     For effecting replacement of the corona wires 14, the replacement wires are respectively secured, in the manner described above, to the tabs 28 of the anchoring assembly 22 located in the first end 12a of the housing shell 12. The tensioning mechanism 40 is then located conveniently relative to the housing shell 12. There, the corona wires 14 are easily and readily secured respectively to the ends 50b of the springs 50 (of course, the corona wires could be secured to the spring ends 50b first, and then secured to the anchoring assembly 22). The convenient location of the tensioning mechanism 40 is selected so that the wires are not under any tension as they are secured to the tensioning mechanism. For example, the tensioning mechanism can be positioned remotely from the end 12b of the housing shell 12 toward the end 12a. Accordingly, undue breakage of the corona wires is substantially prevented. 
     After the corona wires 14 are secured to the springs 50 of the tensioning mechanism 40, the tensioning mechanism is inserted into the end 12b of the housing shell 12 in the position shown in FIG. 4. In this position, it is insured that a minimum tension is applied to the corona wires as they are moved into association with the V-shaped notches 18 for accurate location within the corona charger 10. The tapered lead edge of the arm 42c of the tensioning mechanism 40 engages the wall 16b of the end 12b of the housing shell 12. In this position, the lead edge forms a pivot axis, designated by the letter A in FIGS. 4 and 5, for the tensioning mechanism 40. 
     Arm 42b of the tensioning mechanism 40 is conveniently used as a lever arm to enable the tensioning mechanism to be pivoted to the location shown in FIG. 5. In this position, the springs 50 will apply the desired preselected tension to the corona wires 14 to ensure proper operation of the charger 10 in an electostatographic reproduction apparatus or the like. The tensioning mechanism 40 is conveniently retained in the tension-inducing position by a set screw 52, or other similar device, inserted through the end wall 12e of the housing shell 12 to engage a slot 54 defined in the arm 42b of the tensioning mechanism. Of course, other retaining apparatus are suitable for use with this invention. 
     The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as set forth in the claims.