Abstract:
The present invention is in the field of electrographic printers (including copiers). More specifically this invention relates to a corona charging device used to charge the surface of a photoconductor. At least one wire in a corona charger in an electrographic printer is damped by contacting the wire with a damping pad. In one preferred embodiment, the damping pad is a foamed silicone elastomer.

Description:
This application claims the benefit of prior provisional patent application Ser. No. 60/413,805 of the same title and filed on Sep. 26, 2002. 

   BACKGROUND 
   The present invention is in the field of electrographic printers (including copiers). More specifically this invention relates to the corona charging device used to charge the surface of a photoconductor. 
   In electrography, a corona charging device may be employed to charge the surface of a photoconductor. Exemplary devices are disclosed by U.S. Pat. Nos. 5,485,255 and 5,424,540. The charging device may contain one or more small diameter (eg. 0.003 inch diameter) corona wires. It is important that these wires be properly tensioned. Excessive tension can result in wire breakage, whereas insufficient tension can result in wire vibration and subsequent non-uniform charging of the photoconductor, or arcing between the corona wire and adjacent grid. However, even when the wire is tensioned to the maximum, the displacement of the wire due to vibration can be unacceptable. The wire vibration is driven primarily by the corona current and can be linear or circular polarized (even chaotic) at higher current levels. Damping elements can absorb energy and limit vibration to an acceptable level. 
   SUMMARY OF THE INVENTION 
   An apparatus and method for damping at least one corona wire mounted to a charger body in an electrographic printer is provided, according to one aspect of the invention, comprising contacting said at least one corona wire with a damping pad. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  presents a perspective view of a corona wire apparatus and damping pad according to one aspect of the invention. 
       FIG. 2  presents a perspective view of a corona wire apparatus and damping pad according to a further aspect of the invention. 
       FIG. 3  is a side view of the corona wire apparatus and damping pad of  FIG. 2 . 
       FIG. 4  is a top view of the corona wire apparatus and damping pad of  FIG. 2 . 
       FIG. 5  is a top view of a continuous corona wire configuration that may be implemented in the practice of the invention. 
   

   DETAILED DESCRIPTION 
   Various aspects of the invention are presented in  FIGS. 1–5 , which are not drawn to scale, and wherein like components in the numerous views are numbered alike. Referring now to  FIG. 1 , a wire tensioning mechanism  2  for tensioning a corona wire  6  in a charger body  4  is presented, in combination with a corona wire damper  100 , according to one aspect of the invention. The corona wire  6  has an attachment  3  at one end and is fixed to the charger body  4  at the end, for example by a lug. The mechanism  2  also comprises a slide block  30 , and a spring  40 . The charger body  4  may be attached or attachable to an electrographic machine. 
   The corona wire damper  100  comprises a damping pad  102  and a pad holder  104  that holds the damping pad  102 , and is mounted proximate the terminal end of at least one corona wire  6 . The damping pad  102  defining an exposed surface  110  that extends along the at least one corona wire  6  in contact therewith. The damping pad  102  is attachable to the charger body  4  and removable therefrom. According to a preferred embodiment, the damping pad  102  is formed of a cellular foamed elastomer that is square in cross section, and can be rotated to present multiple fresh surfaces to the wires. However, other cross-sections are possible, including triangular, rectangular, round, elliptical, etc., without limitation. The pad may also be moved in a lateral direction relative to the wires to present new surfaces. The density of the foamed elastomer may be on the order of 12 to 28 pounds/cubic foot, with a density on the order 24 pounds/cubic foot being a presently preferred embodiment. 
   The pad material is preferably tolerant of high voltages on the wire (in excess of 18 kv for some applications) and the presence of concentrated levels of ozone and NOx species. A foamed silicone elastomer has been found to be an excellent material, although other elastomers may be used having suitable ozone resistance, NOx resistance, dielectric properties, and temperature resistance, for use proximate a corona wire. The pad holder  104  contains the damping pad  102  and is easily slipped over a feature in the charger body  4 . The holder/pad assembly  102 / 104  may be secured in place by the charger body  4  and the corona wires  6 . 
   In a certain embodiment, the damping pad  102  is a 0.25 inch square by about 2 inches long foamed silicone elastomer, 24 pounds/cubic foot, catalog number HT-820 BISCO Cellular Silicone available from Rogers Corporation of Elk Grove Village, Ill. Manufacturer&#39;s properties of the HT-820 foam are listed on Table 1. The damping pad  102  engages the corona wire  6  (is compressed) 0.030 inch+/−0.030 inch. Thus, mere contact has been found to damp vibrations in the corona wire  6 . 
   
     
       
             
             
             
           
         
             
               TABLE 1 
             
             
                 
             
             
               Property 
               Test Method 
               Performance 
             
             
                 
             
           
           
             
               Compression Force Deflection, psi (kpa) 
               ASTM D-1056 
               14 (97) 
             
             
               @ 25% Deflection 
             
             
               Compression Set @ 70° C. (158° F.) 
               ASTM D-1056 
               &lt;1% 
             
             
               Compression Set @ 100° C. (212° F.) 
               ASTM D-1056 
               &lt;5% 
             
             
               Density, pounds/cubic foot 
               ASTM D-3574 
               24 (384) 
             
             
               (kilograms/cubic meter) 
             
             
               Tensile Strength, psi (kpa) 
               ASTM D-412 
               60 (414) 
             
             
               Elongation, % 
               ASTM D-412 
               65 
             
             
               Water Absorption 
               ASTM D-570 
               0.8% 
             
             
               UV Resistance 
               SAE J-196 
               No Degradation 
             
             
               Ozone Effect Rating 
               ASTM D-1171 
               0 (No Cracks) 
             
             
               Stain Resistance 
               ASTM D-925(A) 
               No Staining 
             
             
               Corrosion Resistance 
               AMS-3568 
               Pass 
             
             
               Flame Resistance 
               UL94 
               HBF (Listed) 
             
             
               Flame Spread Index (Is) 
               ASTM E-162 
               &lt;25 
             
             
               Limiting Oxygen Index (LOI) 
               ASTM D-2863 
               42% 
             
             
               Smoke Density (D x ) @ 4.0 Minutes 
               ASTM E-662 
               &lt;50 
             
             
               Smoke Density (D x ) @ 1.5 Minutes 
               ASTM E-662 
               &lt;20 
             
             
               Toxic Gas Emissions Rating 
               SMP-801 &amp; 
               Pass 
             
             
                 
               BSS 
             
             
               Weight Loss After 168 Hours @ 135° C. 
               ASTM D-573 
               0.8% 
             
             
               Dielectric Constant 
               ASTM D-149 
               1.50 
             
             
               Dielectric Strength (Volts/mil) 
               ASTM D-150 
               93 
             
             
               Dry Arc Resistance (Seconds) 
               ASTM D-495 
               96 
             
             
               Volume Resistivity (Ohm-cm) 
               ASTM D-257 
               10 14   
             
             
               Thermal Conductivity (BTU in./hr/sq. ft./° F.) 
               ASTM C-518 
               0.75 
             
             
               (Wm/° K.) 
                 
               0.11 
             
             
               Hot Flex @ 230° C. 
               ASTM D-573 
               Pass 
             
             
               Low Temperature Embrittlement 
               ASTM D- 
               −67° F. (−55° F.) 
             
             
                 
               746(B) 
             
             
               Recommended Use 
               SAE J-2236 
               −67° F. to 392° F. 
             
             
                 
                 
               (−55° C. to 200° C.) 
             
             
               Recommended Intermittent High 
               Rogers Internal 
               482° F. (250° C.) 
             
             
               Temperature Use 
             
             
                 
             
           
        
       
     
   
   In the embodiment presented, the slide block  30  is slidably mounted to the charger body  4  at an end  7  of the wire, such that the slide block  30  slides parallel to the wire  6 . The slide block  30  has a slot  35  which is wider than the wire  6  but narrower than the attachment  3 , such that when the slide block  30  is mounted on the charger body  4 . The wire end  7  is slidable within slot  35  such that pulling the slide block  30  in the direction away from the wire  6  forces the attachment  3  against the slot  35 , but does not allow the attachment  3  to pass through. The slot  35  is lined up with the wire  6  such that when the wire  6  is in tension, there are no side loads on the attachment  3 . In a preferred embodiment, the attachment  3  is a lug crimped on the wire end  7 . 
   In order to align the wire  6  in a desired direction, the charger body  4  may comprise grooves  8 , and the corona wire  6  lays in a corresponding groove. In such case, the slide block  30  is preferably slightly offset from the groove  8  in order to register the wire  6  against the groove  8 , which inhibits movement of the wire  6 . 
   The spring  40  is mounted between the charger body  4  and the slide block  30  such that the spring  40  exerts a force on the slide block  30  in the opposite direction of the force which the tensioned wire  6  exerts on the slide block  30 . The force of the spring  40  can cause the slide block  30  to slide, and the spring  40  is chosen such that the force exerted on the slide block  30  causes the wire  6  to achieve the desired tension. Thus the spring  40  forces the slide block  30  to pull on the wire  6 . 
   Referring now to  FIGS. 2–4 , a further embodiment is presented, wherein the pad holder  104  comprises a pair of laterally spaced arms  106  configured to engage the charger body  4  by wrapping around a mating portions on the charger body  4 . The pad holder  104  is removable. Each arm may comprise a protuberance  108  that helps register and retain the corresponding arm  106  to the charger body  4 . The charger body  4  may comprise a mating hole or ledge that engages the protuberance  108 . The arms  106  preferably form a integral part with the pad holder  102 , for example, as a one-piece plastic molding, and the protuberance  108  may be shaped as a ridge. 
   The pad holder  104  preferably exhibits environmental resistance similar to the damping pad  102 . The pad holder  104  may formed from the same material as the charger body  4 , for example molded polyphenylene oxide (PPO). In a certain embodiment, the pad holder  104  is formed from Noryl® N190X PPO available from GE Plastics of Pittsfield, Mass. 
   The wire tensioning mechanism  2  may further comprise a wire holder  10  which is mounted to the machine  4 . In this embodiment, the slide block  30  is slidably mounted to the wire holder  10 . A preferred means of slidably mounting the slide block  30  to the wire holder  10  is to use a slide pin  20 , wherein the slide pin  20  is mounted to the wire holder  10 . A slide pin  20  may be mounted directly to the charger body  4 , wherein the slide block  30  is slidably mounted to the charger body  4  on the slide pin  20  (see  FIG. 1 ). 
   When a wire holder  10  is incorporated, the spring  40  may be mounted between the charger body  4  and the slide block  30  or between the wire holder  10  and the slide block  30  (see  FIGS. 2–4 ). The preferred embodiment is to have the spring  40  mounted between the slide block  30  and the wire holder  10 . 
   The slide block  30  may be v-shaped, and the v-shaped slide block  30  comprises a first leg  34  and a second leg  32  (this is best seen in  FIG. 3 ). The first slide block leg  34  is slidably mounted to the charger body  4 , and the second slide block leg  32  is on the same side of the first leg  34  as the wire  6  such that the second leg  32  angles away from the wire  6 . Thus the “v” is laying on one of its sides (first leg  34 ), and the slot  35  is in the other side of the “v” (second leg  32 ). The portion of the slide block  30  with the slot  35  angles away from the wire  6  in order to better keep the wire  6  from slipping out of the slot  35 . 
   The spring  40  may be a compression spring. Although a compression spring is preferred for space constraint reasons, a tension spring will also work. 
   In a typical electrographic machine, multiple corona wires are present. 
   Referring now to  FIG. 5 , rather than have individual wires, a single continuous wire  6  may be used which would be strung in such a way as to create multiple segments. This continuous wire  6  would have a first end  5  and a second end  7 , wherein the first end  5  is secured against movement and the second end  7  has a lug  3  crimped on. The bends in the wire are achieved by wrapping the wire  6  around restraining devices  50 , the second end  7  is wrapped around a final restraining device  51  such that it makes an angle with the rest of the wire  6  of approximately 90°. The second end  7  is then secured by a wire tensioning mechanism of the type described above. Many different types of restraining devices are acceptable; posts, pins, pulleys and grooves are all examples of restraining devices which may be used. However this invention is not limited to these specific examples, any device which acts to restrain the wire such that the wire may be bent into multiple segments may be used. 
   Although the invention has been described and illustrated with reference to specific illustrative embodiments thereof, it is not intended that the invention be limited to those illustrative embodiments. Those skilled in the art will recognize that variations and modifications can be made without departing from the true scope and spirit of the invention as defined by the claims that follow. It is therefore intended to include within the invention all such variations and modifications as fall within the scope of the appended claims and equivalents thereof.