US2753491A

US2753491A - Electrostatic grounding devices for tables, equipment, and the like

Info

Publication number: US2753491A
Application number: US331457A
Authority: US
Inventors: Walter G Legge
Original assignee: Individual
Current assignee: Individual
Priority date: 1953-01-15
Filing date: 1953-01-15
Publication date: 1956-07-03
Anticipated expiration: 1973-07-03

Description

y 3, 1956 w. G. LEGGE ELECTROSTATIC GROUNDING DEVICES FOR TABLES. EQUIPMENT. AND THE LIKE Filed Jan 15 1953 IN V EN T OR. P16452221? LEGGZ BY jrrafin lm MPW ELECTROSTATIC GROUN DING DEVICES FOR TABLES, EQUIPMENT, AND THE LIKE Walter G. Legge, Brooklyn, N. Y.

Application January 15, 1953, Serial No. 331,457

1 Claim. (Cl. 317--2) This invention relates to grounding devices for conducting electrostatic charges from tables, chairs, benches, mechanical and electrical equipment and the like to the conductive supporting surface or flooring.

An object of the invention is to provide an effective grounding device which will permit of the flow of electrostatic charges from articles of said character to the the supporting surface or flooring and which will prevent the upward flow of a high potential current.

Operating tables, anesthetic equipment in hospitals, and tables, chairs, benches and the like in laboratories and ordnance factories may become charged with static electricity if the legs supporting the same are insulated from the conductive supporting surface by nonconductive casters or non-conductive floor surfacing. Furthermore, such articles are frequently moved about and if not properly grounded may endanger the occupants, or physicians or workmen by the articles coming in contact with a source of high potential current or by the accumulation of static electricity of suflicient intensity to produce a spark so as to ignite combustible gases in the room or inflammable liquids being used in the room. An object of the present invention, therefore, is to provide protection for those in a room where such articles are used or who may occupy the same, by insuring that the articles are satisfactorily grounded at all times when disposed in a stationary position or when being moved from place to place.

Another object of the invention is to provide a device of said character which is adjustable for attachment to articles of different heights and which is weighted for frictional engagement with the supporting or conductive surface to thereby insure proper electrical contact therewith at all times.

With the foregoing and other objects in view, reference is now made to the following specification and accompartying drawings in which the preferred embodiments of the invention are illustrated.

In the drawings:

Fig. l is a perspective view of a table provided with an electrostatic grounding device constructed in accordance with the invention.

Fig. 2 is an enlarged view partially in section and parts broken away of the electrostatic grounding device.

Fig. 3 is a sectional view taken approximately on line 3-3 of Fig. 2.

Fig. 4 is a view similar to Fig. 2 of another modified form of electrostatic rounding device.

Fig. 5 is a sectional view taken approximately on line 5--5 of Fig. 4.

The floorings in hospitals, laboratories, ordnance plants and the like are usually of conductive material so as to form a good ground, or such floorings have conductive bars embedded therein and exposed at the surface, the bars being connected with a water pipe and the like for grounding the flooring. Referring to the drawings by characters of reference, the grounding device indicated generally by the reference character is shown in its United States atent O ice;

application to the grounding of a table such as a hospital operating table T which is supported on a conductive flooring F. The grounding device 10 is made of non-sparking metal such as brass, copper, or other metal which will not emit sparks in the event that a piece of flint or the like should accidentally strike the same.

The grounding device includes a hook 11 adapted to engage the metal frame of the table and which is connected with a metallic grounding member 13 by a flexible conductor 14. The flexible conductor consists of a conductor wire or chain as illustrated and a tensioning member 15 and a resistor 16 which are interposed between sections of the flexible conductor. The combined length of the flexible conductor 14 and the grounding member 13 is greater than the distance from the engagement of the hook 11 with the metal frame of the table to the supporting surface or flooring, whereby the grounding member will be canted when in engagement with the supporting surface. The grounding member 13 may be of solid formation or the same may be of tubular formation and have a filling of lead or other metal to weight the same. The said grounding member is constructed to provide a socket at its lower end in which a metallic ball or sphere 17 is rollably fitted. The ball 17 being weighted by the grounding member provides a positive contact with the supporting surface for grounding the table T and when the table is moved the ball 17 will have rolling contact with the supporting surface for free rolling movement thereover and for providing a positive grounding of the table.

The tensioning member 15 includes inner and outer telescopically associated cylindrical tubes 18 and 19 which are linked with the

conductor sections

20 and 21 respectively and have a coil spring 22 arranged within the innermost tube and secured at its ends to the end walls of the tubes respectively. The spring is in tensioned retracted relation so as to permit of sliding movement of the tubes with reference to each other. The resistor 16 is located adjacent the grounding member 13 and is interposed between the

conductor sections

21 and 25. The resistor permits the passage of electrostatic charges but prevents the upward flow of a high electric current from the grounding member 13.

The coil spring 22 is suflicient to maintain the flexible conductor 14 in taut condition so as to prevent sagging thereof and a positive electrical connection of all the parts forming the flexible conductor. The resistor 16 includes a resistance wire 27 which is connected at its ends with the

conductor sections

21 and 25 and which constitutes a safety fuse having a resistance which will prevent an excessive current flowing therethrough in the event that the grounding member 13 came into contact with a high potential conductor. The resistance 27 may be of 250,000 ohms and may vary from 50,000 to 2,000,000 ohms depending upon the use to be made of the grounding device. The flexible conductor 14 includes a split ring 28 adjacent the hook 11 and one of the links intermediate the hook 111 and the tensioning member 15 is provided with a relatively small hook 29 which is adapted to engage the split ring 28 for shortening the flexible conductor when the article to which it is to be attached is of reduced height.

The grounding device may be as indicated in Figs. 4 and 5 of the drawings, which similarly includes a clamp 30, a grounding member 31, and a flexible conductor 32 interposed between the clamp and the grounding member and connected therewith. The flexible conductor may also include a tensioning member 33 and a resistor 34 similar to the tensioning member 15 and resistor 16 in the previous form of the invention. In this form of the invention, however, the grounding member 31 includes a metallic bar 35 and a base 36, the base being approxi- J mately 6" in diameter or in cross-sectional dimension for engagement with conductive members embedded in composition flooring. The metallic bar may be of solid formation or the same may be of tubular formation and have a filling of lead or other metal to weight the same. The base 36 is made of sheet metal to provide a peripheral flange 37 and an upstanding hollow central portion 38. The metallic bar 35 is connected with the base 36 centrally thereof for free or universal swinging movement of the bar with reference to the base. For this purpose, the bar is provided with a chain 40 which extends downwardly through an opening 41 in the base and is engaged by a pin 42 within the upper portion 38 of the base for retaining the bar and base in assembled relation.

What is claimed is:

In a grounding device for an article of the character described, a flexible conductor affixed at its upper end to said article, a conductive grounding member including a surface engaging member and a weighted metallic body, said surface engaging member having a broad flat bottom face adapted to slideably engage the surface on which the article is supported and said metallic body being connected with the lower end of said flexible conductor, means connecting said surface engaging member and said metallic body for relative movement therebetween and for imposing the weight of said metallic body on said surface engaging member, and said flexible conductor including an insulated resistance for preventing high electrical charges passing beyond said resistance and upwardly of the flexible conductor.

References Cited in the file of this patent UNITED STATES PATENTS 993,447 Hotchkiss May 30, 1911, 2,084,523 Crawford June 22, 1937 2,325,414 McChesney July 27, 1943 2,502,496 Wickman Apr. 4, 1950 2,586,747 Van Atta Feb. 19, 1952 FOREIGN PATENTS 746,925 France June 8, 1933