Abstract:
An apparatus for a corona wire housing comprising a continuous piece of corona wire mounted in a serpentine fashion around multiple pulleys with a single tension spring tensioning the continuous piece of corona wire and fixed terminals supporting the ends of the wire.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Reference is made to commonly assigned, copending U.S. patent application Ser. No. 09/280,119, filed Mar. 26, 1999, entitled A METHOD OF MOUNTING CORONA WIRE INTO A CHARGER HOUSING OF AN ELECTROPHOTOGRAPHIC APPARATUS AND AN APPARATUS FOR MOUNTING CORONA, by Andreas Dickhoff; U.S. patent application Ser. No. 09/280,121, filed Mar. 26, 1999, entitled AN APPARATUS AND METHOD OF ATTACHING CORONA WIRE TO CORONA CHARGER HOUSING, by Andreas Dickhoff; and U.S. patent application Ser. No. 09/280,121, filed Mar. 26, 1999, entitled CORONA WIRE REPLENISHING MECHANISM, by Andreas Dickhoff. 
    
    
     FIELD OF THE INVENTION 
     The invention is in the field of electrophotography. More specifically, it is directed to a corona charger with a serpentine wire strung along a serpentine path and tensioned by a single tensioning mechanism. 
     BACKGROUND OF THE INVENTION 
     A corona charger is used to generate an electrostatic charge on a surface, for example, a sheet of paper, a photoconductor or a transport web. A corona charger typically includes one or more tightly strung corona wires. The two ends of each wire are firmly attached to the corona charger housing, for example, by copper lugs, or by manually twisted loops which are connected to the charger housing. Applying high voltage to these corona wires creates the requisite charge. 
     The corona wires are usually mounted one by one. Mounting and adjusting the tension of each wire independently of other wires is time consuming and relatively expensive. In the mounting process the wire is touched multiple times by tools or by the operator&#39;s hand. The mounting process includes unpacking the wire, mounting one end of each wire into the corona charger, attaching a tensioning spring to the other end of each wire, and mounting this other end of each wire and the tensioning spring into the corona charger housing. 
     U.S. Pat. Nos. 4,112,298, 4,258,258, 5,140,367, 5,181,069, 5,358,165, and 5,424,540 describe a corona charger that utilizes individual wires strung to produce several separate corona wire strings. These patents do not disclose the process of assembling these wires. An OCE charger, implemented in the copier No. 20600, includes a five string corona wire strung in a serpentine manner. The corona wire is mounted on four sleds, each of which is tensioned by a spring. (See FIG. 1.) 
     The tension of each spring has to be properly adjusted. This requires that some or all of these springs be adjusted several times, making it time consuming and relatively expensive to properly tension the corona wire. 
     Furthermore, the usual way of mounting corona wires in a corona charger is difficult and time consuming because these wires are thin and are easily damaged by handling. Even small damage to the wires can cause breakage or non-uniformity in the charge generated. Finally, the wires need to be renewed regularly because of contamination damage. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a corona charger with several strings of wire, all tensioned by a single tensioning mechanism. 
     According to the present invention, an apparatus comprises (i) a continuous piece of corona wire forming a serpentine path; (ii) a fixed terminal securing one end of the wire; (iii) at least one mount around which the wire is mounted so as to support two strings of the wire; and (iv) a fixed terminal securing another end of the wire. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 illustrates a prior art corona charger; 
     FIG. 2 is a schematic view of a spool tool as it is being used to string corona wire in a corona charger housing; 
     FIG. 3 illustrates a corona charger housing and a corona wire provided by the spool tool of FIG. 2; 
     FIG. 4 is a perspective view of a spool tool according to one embodiment of the present invention; 
     FIG. 5 is another perspective view of the spool tool of FIG. 4; 
     FIG. 6 shows orientation of the spool tool of FIGS. 4 and 5 when the corona wire is being strung in a charger; 
     FIG. 7 is a partially cut-out view of the spool tool of FIG. 6 showing the orientation of a wire that is being fed from a spool cylinder into a dispenser pen of the spool tool; 
     FIG. 8 is an enlarged cross sectional view of a portion of the spool tool shown in FIG. 7 without the wire; 
     FIG. 9 is a schematic drawing of an enlarged cross section of the radius pipe; 
     FIG. 10 is an enlarged view of a portion of the spool tool shown in FIG. 8 with the wire that is being fed from a radius pipe; 
     FIG. 11 illustrates the base of the spool tool of FIG. 4; 
     FIG. 12 is a schematic cross section of the spool use in the spool tool of FIG. 4; 
     FIG. 13 illustrates a leg spring utilized in the spool tool of FIG. 4; and 
     FIG. 14 shows a continuous piece of corona wire forming a serpentine path with four parallel wire strings. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     According to one embodiment of the present invention a spool tool  10  contains a corona wire  20 . This spool tool  10  automatically feeds the desired amount of wire for mounting into the corona charger housing  25 , minimizing the direct handling of corona wire. (See FIGS.  2  and  3 ). 
     With reference to FIGS. 4,  5 , and  6  the spool tool  10  includes a spool  30  with a spool cylinder  32  containing wound wire  20  and supported on a spool carrier  31 , and a wire dispenser pen  40  terminating on one end with a radius pipe  50 . The other end of the wire dispenser pen  40  has a flange  54  with a groove  56 . The wire dispenser pen  40  has inner wall  42  forming a long hollow shaft  60  that is circular in cross section. (See FIG. 7.) In this embodiment the circular cross sections of the shaft  60  (near the output end) are of three different diameters d 1 , d 2 , d 3  and d 1 &gt;d 2 , d 3 &gt;d 2 . (See FIG. 8.) A flexible pipe  70  is mounted in the shaft  60 . It is preferred that the portion of the inner wall  42  forming the smallest diameter (d 2 ) keep the flexible pipe  70  in a press fit connection. This is shown in FIGS. 8 and 9. 
     One end of the radius pipe  50  is press fit into one end of the shaft  60  and is adjacent to the flexible pipe  70 . The radius pipe  50  is curved and has a radius of curvature r 1  of 5 mm to 20 mm. When the radius r 1  is smaller than about 5 mm the wire transport through the radius pipe  50  is difficult because the stiffness of the wire creates resistance, making it difficult to bend the wire and to push it through the radius pipe  50 . When the radius r 1  is larger than 20 mm, the radius pipe  50  becomes too large and the spool tool is difficult to handle in the restricted space of a corona charger housing  25 . Furthermore, the radius pipe  50  should be curved to provide an approximately 90° angle between its wire entrance opening  71  and the wire exiting opening  72 . This angle provides a proper direction for the wire exiting the spool tool and makes it easy to string the corona wire across the corona charger housing  25 . If radius r 1  is too small, the wire fed through the radius pipe  50  may be forced to bend sharply, resulting in a damaged wire. Furthermore, the smaller the radius r 1  the higher is the chance that the corona wire  20 , may be deformed permanently, which would cause non-uniformities is the charge created. Ideally the radius r 1  should be not smaller than the spool diameter to avoid any further damage to the wire. If the radius r 1  is too large the radius pipe  50  becomes too long, making it difficult to string the wire inside the corona charger housing  25 . 
     The radius pipe  50  has a tapered entrance opening  71  from which the wire  20  is fed from the spool tool  10 . (See FIG. 9.) The taper is needed so that the wire tip of wire  20  does not jam into the edge of the radius pipe  50 , when a new wire is pushed from the flexible pipe  70  into the radius pipe  50 . The radius pipe  50  also has an exit opening  72 , a central hole  74  connecting the openings  71 ,  72 , and a rounded outer edge  75  (see FIG.  9 ). The corona wire is directly fed from the flexible pipe  70  into the hole  74  of the radius pipe  50 . (See FIGS.  8  and  10 ). It is preferred that the hole  74  be tapered. The tapered hole  74  allows the wire to freely enter the radius pipe  50  and to provide an appropriate amount of tension when the wire exits the radius pipe  50 . The rounded outer edge  75  of the radius pipe  50  protects the wire from bending on the edge. 
     Because the wire  20  is pushed from the wire spool  30  into the radius pipe  50  (for example, when the spool is replaced), the wire  20  should be constrained very tightly all the way from the spool  30  to the entrance opening  71  of the radius pipe  50 , otherwise the wire could kink and jam very easily. However, some flexibility is needed in order to adjust for different spool diameters and positions in the axial directions. The flexible pipe  70  is the most cost effective resolution of these requirements. 
     It is preferred that the flexible pipe  70  be made of helically wound steel wire. In order to accept corona wires with typical diameters of 0.02 mm to 0.1 mm, it is also preferred that the flexible pipe has an inner diameter of about 0.15 to 1.5 mm and preferably 0.5 mm to 1.5 mm. The flexible pipe  70  may also be made from other materials, but steel is preferred because helically wound steel wire is manufactured easily and is inexpensive. 
     The spool tool  10  also comprises a base  80  (see FIG. 11.) The base  80  is mounted to the wire dispensing pen  40 , for example, with a snap in connection feature such as snap plate  82 , which fits inside the groove  56  of the flange  54 . (See FIGS. 4,  5 ,  7 .) Other means of attaching the base to the wire dispenser pen may also be used. 
     The base  80  has holes  83   a  and  83   b . First and second pins  84 ,  86  are mounted on the base  80  through the holes  83   a  and  83   b . The spool carrier  31  has a cylindrical hole  87  and the first pin  84  is inserted therethrough. The spool carrier  31  rotates relative to the first pin  84 . The spool cylinder  32  is supported by the spool carrier  31  and is rotably mounted around the pin  84 . (See FIG. 12.) The second pin  86  supports the lever  90  which holds the pin  92 . (See FIG. 4.) 
     A cylindrical spool driver  94 , preferably made of plastic, and a spool roller  96 , preferably made of a foam material or soft rubber material, are mounted on the pin  92 . Making the cylindrical spool driver  94  of plastic makes it light weight and inexpensive to produce. Making the cylindrical spool driver  94  of a foam material results in a compliant surface with a high friction coefficient that is needed to drive the spool safely and reliably without damaging the wire  20 . A leg spring  97 , shown in FIG. 13, pushes the spool roller  96  via lever  90  and pin  92  against the spool cylinder  32 . The leg spring is located between the lever  90  and the base  80 . 
     To put in a new spool  30  of corona wire  20  into the spool tool  10  the free end of the corona wire is first fed manually into the flexible pipe  70  until the end appears at the exit opening  72  of the radius pipe  50 . Then the lever  90  is lifted from the spool carrier  31  and the wire supply spool  30  is pushed on the spool carrier  31  so that the wire  20  is oriented as shown in FIG.  7 . Then the lever  90  is released so that the spool roller  96  touches the spooled corona wire  20 . Now corona wire  20  is pulled through the flexible pipe  70  and out of the radius pipe  50  (for the length of about 20 cm-30 cm) until untouched corona wire reaches the exit opening  72  of the radius pipe  50 . The wire  20  is now cut at the exit opening  72 . The spool tool  10  is now loaded and is ready for use. 
     The handling of the spool tool  10  is similar to the handling of a ballpoint pen or a pencil (see FIG.  2 ). Only instead of drawing lines on paper, the corona wire is stretched and mounted in a corona charger housing  25  (FIG.  3 ). The main interface of the spool tool  10 , the wire dispenser pen  40 , is held like a ballpoint pen. In order to string a corona wire into a corona charger housing  25  the corona wire  20  is fed 1 cm-2 cm out of the exit opening  72  of the radius pipe  50  by turning the spool driver  94  in a draw direction indicated by an arrow in FIG.  6 . This end  20   a  of the wire  20  is fixed into the corona charger housing  25 . The spool tool  10  is then pulled to the other end of the corona charger housing  25 . The spool driver  94  should not be actively turned in this operation. The resistance of the spool tool at rotation of the spool  10  determines the tension during the stringing operation. On the other end of the corona charger housing  25  the spool tool  10  is moved around the wire mount for the second string of wire (and again for a third, fourth, or fifth string of wire) or, if only one string is needed, the second end of the wire is fixed and cut off. 
     The spool tool  10  accommodates commercially available spools of corona wire. They can be replaced after the wire is used completely or a different type of wire is needed. The wire can be fed out of the radius pipe  50  and mounted into the charger with minimum impact on the wire. The main advantage of this spool tool  10  is the safe and fast mounting of the wire. 
     More specifically, according to the preferred embodiment of the present invention, a method for mounting a corona wire  20  into the corona charger housing  25  comprises the steps of (i) supporting a spool tool  10  including a spool  30  and wire dispenser pen  40 ; (ii) feeding a wire  20  out of the wire dispenser pen  40  and securing an open end  20   a  of the wire to a corona charger housing  25 ; (iii) moving the spool tool  40  to another portion of said corona charger housing  25  while feeding more wire  20  out of the wire dispenser pen  40  and stringing the wire across the corona charger housing  25 . It is preferable that prior to securing the second end of the wire  20  said spool tool  40  is moved around at least one wire mount, such as a pulley roller  123   a ,  123   b  or  123   c , producing at least two strings of corona wire in the corona charger housing  25 . (See FIG. 14) This is described in more detail below. 
     Method of Mounting Corona Wire in a Charger Housing 
     Referring to FIG. 14, a continuous piece of corona wire  20  is mounted along a serpentine path in a corona charger housing  25 . First, one end  20   a  of the corona wire is fixed to a start terminal  122  and the corona wire  20  is strung over one or more pulley rollers  123   a ,  123   b ,  123   c  (in a sequence shown by arrows on wire; see FIG.  14 ). It is preferable, in order to provide a uniform charge, that the corona wire  20  is strung such that strings  1 ,  2 ,  3  and  4  of corona wire  20  are parallel to one another. Then, the second end  20   b  of the corona wire  20  is fixed to end terminal  124 . One of the pulley rollers  123   b  is mounted on a linearly movable sled  125 , tensioned with one tension spring  126 . The other pulley rollers  123   a ,  123   c  are fixed to the corona charger housing  25 . The pulley rollers  123   a ,  123   b ,  123   c  ensure that the tension of the corona wire  20  is essentially the same over the whole length of the corona wire  20 . Thus, only one tension spring  126  is needed to tension two or more strings of a corona wire. The tension spring  126  is secured to the corona charger housing by a mounting pin  127  after the wire  20  is strung to form a serpentine path and after the second end  20   b  is secured into the end terminal  124  of the corona charger housing  25 . The tension spring  126  now pulls the sled from position  1  (Pos.  1 ) to position  2  (Pos.  2 ). The strings  1 ,  2 ,  3  and  4  of wire  20  rest upon two bridges  128   a ,  128   b . These bridges  128   a ,  128   b  apply minimal deflection to both ends of each wire strings  1 ,  2 ,  3 ,  4  and determine the precise position of each wire string. The start terminal  122 , the end terminal  124 , the mounting pin  127  of the tension spring  126 , bridges  128   a ,  128   b  and the shafts on which the pulley rollers  123   a ,  123   c  are mounted are all connected to the corona charger housing  25 . 
     This serpentine path of the corona wire allows a plurality of wire strings  1 ,  2 ,  3 ,  4  to be strung with minimum variation of tension. As stated above, only one tensioning mechanism (for example, the tension spring  126 ) is needed to tension two or more strings of corona wire. For example, FIG. 14 shows four strings of corona wire being tensioned with only one spring. This arrangement of mounting and tensioning corona wires on the corona charger housing  25  reduces the number of individual wires, springs, variability in tolerances, and complexity of handling multiple wires from n (where n is the number of individual wire strings to just one). The tension between individual strings  1 ,  2 ,  3 ,  4  of wire varies only due to variability of friction between the pulley rollers and their shafts, and the friction between the corona wire  20  and bridges  128   a ,  128   b . Because the friction forces are small compared to tension forces, the variation in the tension is small. Since the most difficult part in mounting the corona wire  20  is the affixation of the wire end, this difficulty is reduced from 10 to 2 in a typical five string wire charger (which has 10 ends). Furthermore, in such five-wire chargers, the number of tension springs is reduced from four or five to one. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     PARTS LIST 
       10  spool tool 
       20  corona wire 
       25  corona charger housing 
       30  spool 
       32  spool cylinder 
       40  dispenser pen 
       42  inner wall 
       50  radius pipe 
       54  flange 
       56  groove 
       60  hollow shaft 
       70  flexible pipe 
       71  tapered opening of the radius pipe 
       72  tapered exit opening 
       74  central hole 
       75  rounded outer edge 
       80  base 
       82  snap plate 
       83   a, b  holes 
       84  first pin 
       86  second pin 
       87  cylindrical hole 
       90  lever 
       92  pin 
       94  spool driver 
       96  spool roller 
       97  leg spring 
       122  start terminal 
       123   a, b, c  pulley roller 
       124  end terminal 
       125  moveable sled 
       126  tension spring 
       127  pin 
       128   a, b  bridges