US 3585448 A
Description (OCR text may contain errors)
United States Patentlnventor Appl. No.
Filed Patented Assignee SHOCKLESS-TYPE STATIC ELIMINATOR WITH SEMICONDUCTIVE COUPLING Reierences Cited UNITED STATES PATENTS 11/1943 Slayter Primary Examiner- Lee T. i-lix AnorneyStanley Bilker ABSTRACT: A shockless-type static eliminator in which a semiconductive sheath is employed to support and capacitatively couple a plurality of spaced conductive discharge points to a conductive member having an alternating current high voltage connected thereto, The semiconductive sheath acts as 10 Claims, 3 Drawing Figs.
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a high resistance series element between adjacent discharge points but at the same time is sufficiently conductive to function as a condenser plate when insulated from the high voltage conductive member by a suitable dielectric.
PATENTED JUN! 5 I971 I; ATTORNEY SIIOCKLESS-TYPE STATIC ELIMINATOR WITH SEMICONDUCTIVE COUPLING This invention relates to static eliminators, and more par ticularly relates to shockless-type static eliminators in which discharge points are capacitatively coupled to the high voltage conductive member. I
In the past, the discharging points projected from a plurality of longitudinally spaced conductive rings coaxially arranged about an insulated conductive cable to which the alternating current high voltage power was applied. In prior US. Pat. No. 3,120,626 the method employed for fabricating the shockless static eliminators consisted of alternately sliding a plurality of dielectric sleeves and conductive sleeves upon an insulated flexible wire conductor. This was followed by coaxially sliding a rigid dielectric tube about the alternate. sleeves and then pressing conductive needles through the dielectric tube in registration and abutment with only the conductive sleeves. Of course, this procedure required not only the step of slidingthe various sleeves in the proper alternating sequence upon the flexible cable, but also demanded considerable attention to proper alignment so that abutment of a conductive needle .with a conductive sleeve would be assured. In prior US. Pat.
No. 3,037,149, the conductive stripes were painted upon the outside insulative layer of the cable rather than using slidable sleeves. However, the alignment problem still existed, and this problem was even accentuated by a tendency toward piercing the insulation of the cable when the needles were pressed through the dielectric support tube by virtue of the lack of rigidity in painted or coated stripes.
The present invention resides in the use of a single partially conductive or semiconductive tube or sheath which supports a plurality of longitudinally spaced conductive needles about the periphery of the insulated cable to which the high voltage AC power source is connected. The material from which the semiconductive sheath is fabricated may have a resistivity of ohm centimeters as compared to an insulator which would be in excess of 10 ohm centimeters. Also desirable would be to duplicate the maximum shorting current in .the prior shockless-type static eliminators, approximately 7 microamperes which might represent the current discharged across adjacent shunted points or across a single point to ground. lt has been determined that a low current in the range of7 microamperes is not of sufficient level to produce a shock or even annoy personnel accidentally touching the discharge points. On the other hand, the discharge from high voltage power supply rated at 2 to 22 milliamperes could create an appreciable jolt to personnel accidentally touching the discharge pointsof the directly connected high voltage points in a conventional static eliminator.
lt is therefore an object of this invention to provide a means and method for constructing an improved shockless-type static eliminator.
Another object of this invention is to provide a shockless static eliminator in which the use of alternate insulative and conductive sleeves is eliminated.
Yet another object of this invention is to provide a shockless static eliminator in which the usual alignment problems in registering discharge points with conductive rings is avoided.
Yet still another object of this invention is to employ a single semiconductive member for supporting all of the discharge points in spaced capacitative disposition withrespect to a high voltage cable.
A further object of this invention is to provide a shockless static eliminator having a single semiconductive member supporting all of the discharge points and wherein the capacitative coupling and the maximum shorting current are substantially the same as those of prior shockless bars.
Other objects of this invention are to provide an improved device of the character described which is easily and economically produced, which is sturdy in construction and both highly efficient and effective in operation.
- similar reference characters refer to similar parts, there is shown a shockless-type static eliminator comprising a first conductive member in the form of an insulated flexible cable, generally designated as A, a tube of semiconductive material, generally designated as B, coaxially arranged about the cable, a plurality of longitudinally spaced conductive needles or discharge points, generally designated as C, mounted in the tube and projecting radially therefrom, and a casing or housing D shielding the points.
The first conductive member A may be any conventional flexible cable having an internal wire conductor 12 which is preferably stranded copper and sheathed by a polyethylene jacket 14. An external coating 16 of suitable insulation, such as vinyl plastic, provides a protective as well as insulative cover for the jacket 14.
The sheath or tube B, as has been set forth hereinbefore, is composed of a semiconductive material having a resistivity in the range of 10 ohm centimeters. A suitable composition for this purpose has been found to be a phenolic resin base compounded with carbon black or other conductive material to provide a volume resistivity approximating 2000 to 3000 megohms per cubic centimeter. The inside diameter of the tube B is such as to provide a sliding fit with the exterior of the cable cover 16. The thickness'of the tube wall must be sufficient to support the needles C when pressed into holes radially passing through the wallnThe holes are longitudinally spaced on 34 inch centers. After drilling the holes in the tube wall, the needles C, which are of steel construction for combined strength and conductivity, are pressed through the holes so that the base of the points is flush with the inner surface of the tube 8. Alternatively, the holes in the tube B may be blind such thatthey extend radially from the outer diameter to a position short of the inside diameter. This variation (not shown) would space the bases of the needles C from the interior wall of the tube and thereby provide additional insulation between the needles and the wire conductor 12.
The distal end of the cable A is encapsulated in a vinyl cup 18 after being inserted through the semiconductive tube B from the opposite end. The insulative cup or plug 18 is secured within a counterbore at the distal end of the tube B so as to be flush with the end thereof. An outer insulative collar 20 made of a suitable dielectric, such as an acrylic resin, is cemented over the end of the tube B and is retained within the casing D by means of a setscrew 22. The cup 18 and the collar 20 assure insulation of the wire conductor 12 which is coupled to the high voltage power supply E. A second insulative collar 24 isretained within the casing D at the opposite end thereof by setscrew 26. The two collars 20 and 24 together with a medial insulative spacer 28 maintain the tube B in concentric disposition within the shield casing D. ln addition, the needles C extend coaxially within longitudinally spaced apertures 30 extending through the casing wall.
The casing D is made of brass or aluminum to provide strength, structural rigidity and conductivity. The ground side of the high voltage power supply E is connected tothe casing D such that a high'voltage field exists between the inner wire conductor 12 and the casing shield. The power supply E is any suitable alternating current high voltage generator capable of supplying an output of perhaps 5000 to 15,000 volts. The current capacity of such a generator is in the 2 to 22 milliampere range.
By providing a snug fit of the cable A within the semiconductive tube B, maximum capacitative coupling is achieved between the inner tube surface and the wire conductor 12. Because of the partially conductive nature of the ring of material adjacent each needle or discharge point C, a small condenser is defined about the wire conductor. Thus, each of the needles is capacitively coupled to the wire conductor 12. In effect, this coupling consists of a plurality of capacitance slices to define an infinite number of condensers in parallel. However, because there is also an infinite number of resistance slices of semiconductive material in series between the adjacent points, this resistance is additive so as to limit the potential current capability of the discharging capacitances. Therefore, the approximate maximum current which could result from a person shorting adjacent points or shorting a point to the casing D through his body would not exceed 7 microamperes. This current at the voltage specified is below that of the threshold of a person's sensitivity to shock. Hence, the semiconductive capacitive-resistance coupling achieves an efficient neutralizing system which is essentially shockless in character.
Although this invention has been described in considerable detail, such description is intended as being illustrative rather than limiting, since the invention may be variously embodied without departing from the spirit thereof, and the scope of the invention is to be determined as claimed.
What l claim is: v
l. A static neutralizing apparatus comprising a first conductive member, a semiconductive member in adjacently spaced noncontacting disposition with said first conductive member and including a dielectric therebetwcen, a plurality of spaced conductive points projecting outwardly from said semiconductive member, a second conductive member spaced about said points, and means for connecting an alternating current high voltage across said first and second conductive members whereby said points are capacitatively coupled to the first conductive member and wherein the shorting current capability across adjacent points or from points to ground is limited by the series resistance of the semiconductive portion intermediate adjacent discharge points.
2. The apparatus of claim 1 wherein said first conductive member is a wire and said semiconductive member is tubular.
3. The apparatus of claim 1 wherein said semiconductive member has a resistivity in the range of 10' ohm centimeters.
4. The apparatus of claim 1 wherein said dielectric comprises a flexible insulation over said first conductor to define a flexible wire cable.
5. The apparatus of claim 4-wherein said semiconductive member is tubular in configuration and coaxially supported about the flexible wire cable.
6. The apparatus of claim 5 wherein said discharge points are longitudinally spaced along said tubular semiconductive member.
7. The apparatus of claim 6 wherein said discharge points are embedded in said semiconductive member.
8. The apparatus of claim 7 wherein said discharge points constitute needles having bases flush with the interior surface of said tubular semiconductive member.
9. The apparatus of claim 7 wherein said points radially project in a single plane.
10. The apparatus of claim 9 wherein said second conductive member comprises a tubular member having longitudinally spaced apertures coaxially disposed about the respective points.