US3887843A

US3887843A - Static eliminator

Info

Publication number: US3887843A
Application number: US468930A
Authority: US
Inventors: Robert Harold Richardson; Edward Richard Vokoun
Original assignee: Harris Intertype Corp
Current assignee: Harris Corp
Priority date: 1974-05-10
Filing date: 1974-05-10
Publication date: 1975-06-03
Anticipated expiration: 1992-06-03

Abstract

An improved static eliminator is provided for neutralizing accumulated electric static charge on a web or sheet material. The static eliminator includes an elongated cable of the type having an inner conductive core surrounded by a dielectric layer with the core being adapted to be connected to a high AC voltage source. A portion of the length of the cable extends longitudinally within an elongated hollow metal housing. An insulator is located within the housing and is constructed so as to mount the cable in place within the housing while minimizing electrical capacitance between the core and the housing.

Description

United States Patent [1 1 Richardson et al. 5] June 3 1975 [5 STATIC ELIMINATOR 3,697,806 10/1972 Herbert, Jr. 317/2 F 3,725,736 4 1973 B' h 317 [75] Inventors: Robert Harold Richardson, ls Op /2 F Melbourne; Edward Richard Vokoun, Melbourne Beach, both of w Mlller Asszstant ExammerHarry E. Moose, Jr.

[73] Assignee: Harris-Intertype Corporation,

Cleveland, Ohio [57] ABSTRACT [22] Filed, Ma 10 1974 An improved static eliminator is provided for neutraly izing accumulated electric static charge on a web or [21] Appl. No.: 468,930 sheet material. The static eliminator includes an elongated cable of the type having an inner conductive core surrounded by a dielectric layer with the core ((1311. sin/25613317505 being adapted to be Connected to a g AC Voltage source- A portion of the length of the cable extends [58] Flew of Search 317/2 2 262 4 longitudinally within an elongated hollow metal hous- References Cited ing. An insulator is located within the housing and is constructed so as to mount the cable in place within UNITED STATES PATENTS the housing while minimizing electrical capacitance 3,120,626 2/1964 Schweriner 317/2 F between the core and the housing 3,137,806 6/1964 Schweriner 317/2 F 3,443,155 12 Claims, 6 Drawing Figures 5/1969 Schweriner 317/2 F STATIC ELIMINATOR This invention relates to the art of static eliminators and, more particularly, to an improved static eliminator construction for removing or neutralizing static electricity accumulated on sheet material, such as paper or cloth when such material is processed so as to be charged with static electricity.

The invention is particularly applicable for use in conjunction with removing or neutralizing static charge on a web or sheet material processed by xerography of electrophotographic printing and will be described with particular reference thereto; although, it is to be appreciated that the invention may be utilized in various applications requiring the removal of static electric charge from material.

A typical static eliminator comprises an elongated cable having an inner conductive core surrounded by a dielectric layer. A plurality of needle-like projections are electrically connected to respectively associated conductive sleeves which are longitudinally spaced apart in close proximity to the cable. The assembly is mounted so as to'be electrically insulated from a metallic housing which is, in turn, connected to electrical ground. A high voltage AC source on the order of 7,000 volts is connected between ground and the inner electrical core. The assembly is positioned such that the needle-like projections extend toward a web or sheet material having an accumulated static charge to be neutralized. The needle points do not make engagement with the web but are slightly spaced therefrom. The high AC voltage applied to the inner core produces an ionized field about the pointed ends of each needlelike projection and has the effect, when placed in the vicinity of a charged web or sheet, to neutralize the static charge accumulated thereon.

In the construction of such static eliminators, it is desirable that leakage current from the inner conductive core to the housing be minimized so as to not detract from the ability of the eliminator to provide an ionized field sufficient to neutralize static charge on a web or the like. The electrical circuit provided by such an eliminator includes capacitance between the inner core and the needles and a resistance from the needles through the web or the like to ground. An effective capacitance is also provided between the conductive core and the metal housing with this effective capacitance being in parallel with the previously mentioned resistance. The greater the effective capacitance, the greater will be the tendency to provide a path for leakage current, and hence, adversely effect the ability of the eliminator to provide an ionized field. Ideally, the conductive core should be suspended in air within the metal housing so as to minimize the dielectric therebetween and hence, minimize the magnitude of the effective capacitance. Obviously, such an idealized condition provides no means to support the cable within the housing.

It is, therefore, a primary object of the present invention to provide an improved static eliminator construction for minimizing the effective capacitance between the conductive core and the surrounding housing so as to thereby minimize leakage current.

It is a still further object of the present invention to provide a static eliminator wherein a conductive core is mounted within a metal housing or shield in such a manner as to minimize the dielectric constant therebetween while still providing support for the core.

In accordance with the invention, an improved static eliminator construction includes an elongated cable having an inner conductive core surrounded by a dielectric layer with the core being adapted to be connected to a high voltage AC source. A plurality of conductive needles are aligned in a spaced apart longitudinal array along the length of the cable with each needle having a sharp projection at one end facing in a direction away from the cable. An electrically conductive hollow housing has a longitudinally extending slot in communicationwith a longitudinally extending channel within the housing. The cable and the needles are mounted within the housing in a manner to minimize the leakage current between the core and the housing. This is accomplished with an insulator member which extends longitudinally within the housing. The insulator member has a body portion and mounting means extending from the body portion for engaging cooperating inner walls of the housing in such a manner to hold the insulator member in place. This insulator member has an inverted U-shaped groove therein and which extends longitudinally of the housing. The cable has a portion of its length received within the groove in such a manner that the cable is spaced from the walls of the housing. The needles extend through the insulator member in a direction toward the longitudinal opening in the housing and conductive means are interposed between the needles in the conductive core so as to provide capacitance therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects and advantages of the invention will become more readily apparent from the following description of the preferred embodiment of the invention as taken in conjunction with the accompanying drawings which are a part hereof and wherein:

FIG. 1 is a perspective view illustrating the static eliminator constructed in accordance with the present invention;

FIG. 2 is a sectional view taken generally along line 22 looking in the direction of the arrows in FIG. 1;

FIG. 3 is a plan view taken generally along line 3-3 looking in the direction of the arrows in FIG. 1;

FIG. 4 is a sectional view, with parts broken away, taken generally along line 4-4 looking in the direction of the arrows in FIG. 1.

FIG. 5 is an enlarged fragmentary view illustrating the manner of installing a spherical ball to the terminated end of the cable; and

FIG. 6 is a schematic illustration of the equivalent circuit of the eliminator structure DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings wherein the showings are for purposes of illustrating a preferred embodiment of the invention only and not for purposes of limiting same, FIG. 1 is a perspective view illustrating a static eliminator SE constructed in accordance with the invention. The static eliminator includes an electrically conductive housing 10, which may be constructed of aluminum, and is generally of rectangular shape in cross section. The housing is somewhat elongated and serves to carry a portion of the length of an insulated cable 12. Cable 12 is conventional in the art and includes an inner electrical core 14 (see FIG. 2) surrounded by a dielectric layer 16 and an outer insulating layer 18, which may be constructed of insulating material such as polyethelene. Housing is provided with a longitudinally extending channel 20 in which there is mounted a longitudinally extending cable retaining member 22, constructed of electrical insulating material. Retaining member 22, in turn, carries a portion of the length of cable 12 as well as a plurality of needlelike projections 30. These projections extend upwardly through member 22 and thence, into a longitudinally extending slot 32 defined in the upper face of housing 10.

The housing 10 is of rectangular cross section and includes walls defining a bottom wall 40 and

upstanding side walls

42 and 44 and which respectively terminate with inwardly extending

flange portions

46 and 48. The

flange portions

46 and 48 terminate so as to define the slotted opening 32 which extends longitudinally of the length of the housing (see FIG. 1).

Walls

40, 42, 44 and

flange portions

46 and 48 are preferably of uniform thickness, as is shown in FIG. 2. The channel 20 defined by the walls is rectangular in cross section and extends throughout the length of the housing and is plugged at opposite ends by rectangular-

shaped insulators

50 and 52. The insulator cable retaining member 22 extends longitudinally within the housing and is interposed between

plugs

50 and 52.

The pointed end 34 of each projection 30 extends to a point just under the upper surfaces of inwardly extending

flanges

46 and 48 of housing 10. These upper surfaces are essentially flat and sheet material 36, having an accumulated static charge, is passed over these flat surfaces so as to be located proximate to the pointed ends of projections 30. The housing 10 is connected to electrical ground and an AC voltage source 38, on the order of 7,000 volts is impressed between ground and the inner core 14. This develops an ionizing field around the point 34 of each projection 30 for purposes of neutralizing the accumulated electric charge on the sheet material as it is passed over the upper surfaces of

flanges

46 and 48.

The cable retaining member 22, as best shown in FIGS. 2 and 4, has a body portion 50 spaced inwardly from the facing surfaces of

walls

40, 42, 44 and

flanges

46 and 48. A pair of upwardly and outwardly facing

leg members

52 and 54 extend from the body portion 50. As will be noted from FIG. 2, the inner surface of flange 46 and wall 42 forms a corner. Leg portion 52 extends to and is configured to conform with the corner so as to fit snugly therewith. Similarly, the inner faces of wall 44 and flange 48 define a corner and leg portion 54 extends to this corner and is configured so as to conform therewith for a snug fit. A pair of leg portions 60 and 62 extend downwardly and outwardly from the body portion 50 and terminates in

non-continuous feet portions

64 and 66. The feet portion 64 on leg portion member makes a sliding but snug fit with the inner corners of the housing.

The retainer member 22 has a cable carrying groove extending longitudinally throughout its length with the groove being located approximately at the center of the body portion 50. Groove 70 is essentially circular in cross section but is of slightly less diameter than cable 12. The retainer member is constructed of material exhibiting some degree of resiliency so that leg portions 60 and 62 may be spread apart somewhat permitting a portion of the length of cable 12 to be snapped into place into the groove 70 by way of longitudinally extending slot 72. Since the groove 70 is normally of smaller diameter of that than the cable, it will tightly hold the cable once the cable is snapped into place. This automatically positions the conductive core 14 of cable 12 at a location corresponding with the geometric center of the housing. The inner walls of groove 70 are painted at longitudinally spaced apart locations with a conductive layer so as to define a plurality of longitudinally spaced apart conductive layers 74 (see FIGS. 2 and 4). Each conductive layer 74 is associated with one of the electrically conductive needles 30. Each needle 30 has a cylindrical base portion 31 which extends through a suitable aperture 76 in the roof portion of retainer member 22. The pointed end of each needle is exposed in the channel area of slot 32 and the cylindrical portion is mounted in the aperture 76 so as to make electrical contact with an associated electrically conductive layer 74. Once the cable 12 has been snapped into place in groove 70, the exposed lower surface (FIG. 2) is painted at spaced apart portions to define conductive layers 75, each of which corresponds with an associated conductive layer 74 to define a circular ring about the cable. Thus, these conductive circular rings define capacitor plates which are spaced along and extend coaxially about the inner conductive core 14.

As shown in FIGS. 4 and 5, cable 12 is terminated within the housing, leaving the conductive core exposed. This conductive core may be formed of stranded wires and the severed end of each wire may define a sharp point providing a source of corona discharge. If this is permitted, it might adversely effect the operation of the static eliminator by reducing the corona field at each needle 30. Also, the corona discharge at the ends of such wire strands would tend to burn away the surrounding insulating material and conceivably provide a bum-out hole through the static eliminator housing. This effect is minimized by employing a corona ball 80 which is mounted flush up against the exposed end of cable 12. Ball 80 may be constructed of electrically conductive material, such as aluminum. The ball carries a projecting pin 82 which extends radially outward therefrom and is secured to the ball, as by a press fit into a radially extending recess 84 or by welding. Preferably, pin 82 is constructed of relatively hard material, such as stainless steel, and is provided with a pointed end 86. On assembly, the pointed end 86 is forced into the cable so as to engage the core 14 until the ball abuts the exposed end of the cable, as is shown in FIG. 4. Thereafter, a portion of the length of the end of the cable, including ball 80, is encapsulated in an encapsulating cap 88, which is preferably constructed of insulating bonding material to resist corona effects.

Reference is now made to FIG. 6 which provides an approximate equivalent circuit of the static eliminator. Here, electrical ground corresponds with the metal housing or shield 10. Capacitor C connected to the AC voltage source 38, is comprised of two plates with one plate corresponding with conductive core 14 and the second plate corresponding with needles 30 in electrical contact with conductive layers 74. Resistance R represents the resistance taken from needles 30 through the air gap thence through the web material 36 to thegrounded housing. In parallel with resistor R there is shown a capacitor C between the voltage source 38 and ground. This represents what may be termed as the stray capacitance between the conductive rings 74 7S and the surrounding metal housing 10. The greater the magnitude of. capacitor C the greater will be the leakage current drawn thereby, leaving less current for the corona discharge needles 30. As the value of capacitance C increases relative to that of capacitance C the leakage current will increase. If the capacitance of capacitor C is great enough, leakage current will be sufficient to effectively eliminate corona discharge from needles 30. Consequently then, the capacitance of capacitor C should be such that it is substantially less than that of capacitor C and the impedance of capacitor C should be substantially greater than that of resistor R In constructing the static eliminator then, an ideal construction would be to have cable 12 suspended in air with no other dielectric medium interposed between the cable and the surrounding metal housing. Obviously, owever, some support is required. The support must be of electrical insulating material to prevent short circuits between the conductive core or the capacitor plates or the needles and the surrounding housing. However, if the channel is totally filled with an insulator block, the dielectric constant will be quite high, resulting in a very large capacitance value of capacitor C In accordance with the present invention, the insulator member 22 has been constructed so as to have longitudinally extending cut away recesses 100, 102 and 104 providing longitudinally extending air pockets between the insulator member and the respectively corresponding

walls

40, 42 and 44. Similarly, the upper portion of insulator member 22 has a longitudinally extending recess 106 extending longitudinally so as to define a somewhat enlarged channel opening for needles 30. These cut away portions defined by

recesses

100, 102, 194, and 106 decrease the dielectric between the conductive paint 74-75 and the metal shield. This decreases the magnitude of capacitor C while, at the same time, provides sufficient' structural strength for the retainer member 22 to provide support for the cable 12 and the needles 30. The leakage current is also minimized by increasing the surface distance by which current might flow from conductive layer 72 (FIG. 2) to the metal housing 10 by orienting the structure such that the distance from the core 14 to wall 40 is greater than that to either

side wall

42 or 44. Also, the cut away portions leaving only spaced feet 64 connected to leg portion 60 or spaced apart feet 66 connected to leg portion 62, the distance from the conductive layer 72 to the housing 10 is effectively increased.

From the foregoing then, it is seen that the static eliminator constructed in accordance with the present invention provides both mechanical and electrical improvements. From a mechanical standpoint, the snap fit of cable 12 into groove and retainer member 22 permits a construction which does not require potting material or the like to hold the cable in place. This,

then, provides for relatively quick assembly. In addition, by minimizing the dielectric between the conductive layer 74-75 and the metal housing 10, the leakage current is minimized to thereby effectively increase the efficiency of the static eliminator.

Although the invention has been described in conjunction with a preferred embodiment, it is to be appreciated that various modifications may be made without departing from the scope of the appended claims.

We claim:

1. A static eliminator comprising an elongated hollow metal housing having walls defining internally facing bottom and side walls and a continuous longitudinally extending slot disposed opposite saidbottom wall for defining a channel opening, an elongated cable having a portion of its length located within and extending longitudinally of said housing, said cable having an inner conductive core surrounded by a dielectric layer with said core adapted to be connected to a high voltage AC source; an array of longitudinally spaced electrically conductive needles, each having a sharp projection at one end facing in a direction away from said cable; said means for mounting said cable and said needles within said housing comprising a longitudinally extending insulator member mounted within said housing, said insulator member having a body portion and mounting means extending from said body portion for engaging said housing to hold said member in place, said member having an inverted U-shaped groove therein extending longitudinally of said housing, said cable having a portion of its length within said housing received in said groove, said needles extending through said member in the direction away from said groove so as to extend beyond said member in a direction toward said slotted opening.

2. A static eliminator, as set forth in claim 1, wherein said insulator member has a plurality of recesses therein between said body portion and said housing to define air pockets and thereby minimize the dielectric constant between said core and said metal housing.

3. A static eliminator, as set forth in claim 2, wherein said plurality of recesses extend longitudinally of said insulator member.

4. A static eliminator, as set forth in claim 3, wherein said housing member has a plurality of longitudinally extending walls, each said recess being located so as to face one of said walls to define a said air pocket therebetween.

5. A static eliminator, as set forth in claim 4, wherein said housing channel is essentially rectangular in cross section and is defined by said walls including a flat bottom wall and upstanding flat first and second side walls, said recesses including first, second and third recesses, respectively, interposed between said body portion and said bottom wall and said first side wall and said second side wall.

6. A static eliminator as set forth in claim 5, wherein said housing includes first and second flange portions which extend inwardly from the upper ends of said first and second sidewalls and terminate so as to define said longitudinally extending slot.

7. A static eliminator as set forth in claim 6, wherein said sidewalls, flange portions and said bottom wall define four inwardly facing longitudinally extending corner areas, said insulator mounting means including four leg portions extending from said body portion with each leg member engaging one of said corners to thereby mount said insulator member within said housmg.

8. A static eliminator as set forth in claim 7, wherein at least two of said leg portions are each configured to conform with its associated corner area so as to provide a snug, longitudinally slideable fit therewith.

9. A static eliminator as set forth in claim 8, wherein each said leg portion extends longitudinally along said insulator member.

10. A static eliminator as set forth in claim 1, wherein said insulator member has a longitudinally extending slot communicating with said groove to permit access for said cable.

11. A static eliminator as set forth in claim 10, including downwardly extending leg portions straddling said access slot, said slot being normally of a width less than the diameter of said cable, said leg portions exhibiting sufficient resiliency that they may be spread apart to increase the width of said access slot so as to receive said cable therethrough for mounting in said groove.

12. A static eliminator comprising an elongated cable having an inner conductive core surrounded by a dielectric layer, said core adapted to be connected to a high voltage AC source; an array of longitudinally ating facing walls of said housing to hold said memberin place, said member having a substantially inverted U-shaped groove therein extending longitudinally of said housing, said U-shaped groove having an exposed opening facing in a direction opposite said longitudinal opening in said housing with the walls of said groove being spaced substantially away from said housing, said cable having a portion of its length received within said U-shaped groove such that said cable is spaced from said housing, said needles extending through said member in a direction toward said longitudinal opening in said housing, and conductive means interposed between said needles and said conductive core so as to provide capacitance therebetween.

Claims

1. A static eliminator comprising an elongated hollow metal housing having walls defining internally facing bottom and side walls and a continuous longitudinally extending slot disposed opposite said bottom wall for defining a channel opening, an elongated cable having a portion of its length located within and extending longitudinally of said housing, said cable having an inner conductive core surrounded by a dielectric layer with said core adapted to be connected to a high voltage AC source; an array of longitudinally spaced electrically conductive needles, each having a sharp projection at one end facing in a direction away from said cable; said means for mounting said cable and said needles within said housing comprising a longitudinally extending insulator member Mounted within said housing, said insulator member having a body portion and mounting means extending from said body portion for engaging said housing to hold said member in place, said member having an inverted U-shaped groove therein extending longitudinally of said housing, said cable having a portion of its length within said housing received in said groove, said needles extending through said member in the direction away from said groove so as to extend beyond said member in a direction toward said slotted opening.

7. A static eliminator as set forth in claim 6, wherein said sidewalls, flange portions and said bottom wall define four inwardly facing longitudinally extending corner areas, said insulator mounting means including four leg portions extending from said body portion with each leg member engaging one of said corners to thereby mount said insulator member within said housing.