CONDUCTIVE CASTER

Abstract: A two wheel roller caster (10) for use in supporting movable objects on a floor having a conductive band (56) which has two ends and is mounted between two wheels (16) so as to provide conductive contact between the movable object and the floor. A conductive path (60, 58, 56) connects a stem (14) to the connective band (56).

Description: Conductive Caster This invention relates to a two-wheel roller caster for use in supporting movable objects such as chairs on a floor wherein said caster includes two wheels, an axle connecting said wheels, a curved conductive band having two ends and being mounted between said two wheels for providing conductive contact between said caster and said floor, and a conductive path means connecting said conductive band to said movable object so as to permit said movable object to be electrically grounded to said floor through said conductive band. A device of this kind is described in DE-U-8 315 483.3. Static electricity buildup can be a problem in both office and factory environments. In the office environment, static buildup can occur simply as a result of an occupant using a chair or other equipment. In a factory environment, static buildup can be a problem in certain types of equipment. In particular, the buildup of static electricity can be a problem in environments where computers, computerized equipment, electronic devices, or similar equipment is being either assembled or used. It is, therefore, desirable to ground the object being supported so as to permit continuous discharge of static electricity and, thereby, prevent the buildup of an electrical charge. Continuous discharge is particularly important where the object, be it furniture or equipment, is movably mounted on casters. The roller caster according to DE-U-8 315 483.3 has a conductive band which is cantilevered, i.e., it is secured at one end only to a body supporting the two rollers. Besides, it is positioned completely free between the rollers so that wax, dirt or other film of insulating material can build up on the conductive band and between the rollers. Furthermore, the conductive band is likely to deform and bend over a period of time so that it will no longer contact the floor surface or at least will not contact it with sufficient force to provide a good discharge path. It is the problem of the invention to provide a two-wheel roller caster having anti-static properties and which avoids the buildup of wax, dirt and other debris. At the same time, the caster should have a very stable conductive band which resists deformation as it moves over surfaces. The invention solves this problem by the features of the main claim. Further embodiments are described in the subclaims. The conductive band can be secured at one end to the housing and slidably secured at its other end between the shroud and housing. The conductive band is sized so that it has a somewhat larger radius of curvature then the wheels themselves. The strap, when in place, bulges outwardly somewhat and exerts a pressure against the floor when the caster is in use. In this manner, the conductive band is maintained in substantially continuous sliding contact with the floor when the caster rolls along the floor. The conductive band has a crowned, cross-sectional shape. This shape causes the longitudinal edges of the strap to be raised somewhat with respect to the longitudinal axis of the strap. This configuration permits free movement of the caster in a plurality of directions. The conductive path includes a conductive lead and can also include a resistor for impeding shocks resulting from electrical buildup. The conductive lead can be secured to a stem at an upper end thereof by means of a collar so as to insure adequate conductive contact between the conductive lead and the caster. A lower end of the conductive lead is secured by the housing to the conductive band. The conductive band is so positioned and sized as to maintain substantially continuous sliding contact with the floor when the wheels of the caster are rotated. This sliding motion acts to perform a scraping function which prevents the buildup of wax, film, or other foreign matter which may act as an insulating barrier preventing the discharge of static electrical buildup. The invention will now be described with reference to the accompanying drawings in which: Figure 1 is a perspective view, partially broken away, of a caster according to the invention; Figure 2 is a side sectional view of the caster shown in Figure 1; Figure 3 is a view taken along line 3-3 of Figure 2; Figure 4 is a view taken along line 4-4 of Figure 2; Figure 5 is a perspective view of a conductive strap according to the invention. Figure 6 is a perspective view of a wheel according to the invention; and Figure 7 is a sectional view taken along line 7-7 of Figure 2. Referring now to the drawings and to Figure 1 in particular, there is shown a caster 10 adapted for movably supporting objects such as chairs or tables. The caster 10 comprises a housing 12, a stem 14, and a pair of wheels 16. The housing 12 rotatably supports the wheels 16, and the stem 14 is adapted to support a chair or other furniture item which receives the stem 14 through a socket. Referring now to Figures 1 and 2, the housing 12 has a semi-cylindrical outer shell 18 with a central partition webbing 20 extending diametrically across the shell. A central opening 22 is provided in the webbing 20. A ridge 24, formed by a pair of outwardly directed flanges is formed at a bottom front portion of the webbing 20. A vertical socket 26 is formed at a rear portion of the webbing 20 and extends upwardly through the cylindrical shell 18. A pair of laterally extending retaining pins 28 are positioned at a bottom portion of the webbing 20 and the socket 26. A resilient projection 23 extends downwardly from the webbing 20. A C-shaped portion is formed of a front, lower portion of webbing 20. Each of the wheels 16 comprises an outer rim 32, circular outer wall 34, and a central hub 36. A central opening 38 is formed in the central hub 36, and an annular flange 40 is formed on the inner end of the hub 36. An axle 44 is positioned within the central opening 22 of the housing web 20 and is adapted to fit within the central opening 38 of the wheels 16. The annular flange 40 abuts a boss 30 on the webbing 20 to space the outer rims 32 of the wheels a given distance apart, as illustrated in Figure 1. A retainer 48 has an indentation 50 at one end and a projection 52 at the other end. The indentation 50 snap-fits with retaining pin 28. The projection 52 fits within the C-shaped portion 25 of the housing partition webbing 20. Further, the bottom portion of the retainer 48 has a slot which receives and is retained by the projection 23 of the housing partition webbing 20. When the retainer 48 is snapped into place, as illustrated in Figure 2, it fits between the circular outer wall 34 and the annular flange 40 of the wheel 16 to retain the wheel on the axle 44. The stem 14 fits within the socket 26 and is retained therein through conventional means, such as a snap-ring. The foregoing description has described a conventional two-wheel caster of a type manufactured by Herman Miller, Inc. of Zeeland, Michigan. These casters are further described in U.S. Patent 4,024,601, issued May 24, 1977 and U.S. Patent 4,143,442, issued March 13, 1979. These patents are incorporated herein by reference. According to the invention, an anti-static conductor assembly is provided in the two-wheel caster. The anti-static assembly comprises a conductive band 56, a conductive lead 58, a collar 60, and a shroud 62. Conductive band 56 is formed of a suitable conductive material, such as aluminum, so as to provide sufficient electrical contact between the caster 10 and the floor (not shown). The band is in the form of an elongated strap having two ends 30, 31. As can be seen in Figure 5, the first end 30 has an upwardly extending U-shaped configuration formed by two upwardly extending prongs 64. Conductive band 56 has a aperture 65 extending therethrough below prongs 64. The opposite end 31 comprises a rearwardly extending portion having a pair of inwardly extending flanges 32. A small aperture 66 extends through conductive band 56 near end 30. In use, end 30 slip-fits onto webbing 20 between socket 26 and shell 18. End 31 is secured to housing 12 by means of flanges 32 which snap-fit over ridge 24. The manner in which flanges 32 engage ridge 24 can best be seen in Figure 7. In this manner, conductive band 56 can be easily snap-fit between wheels 16. Conductive band 56 is sized so that it has a radius of curvature when in place which is somewhat larger that the radius of curvature of wheels 16. Thus, in use, conductive band 56 is deformed outwardly somewhat so as to maintain continuous contact against a floor (not shown). The longitudinal edges of conductive strap 56 are curved somewhat upwardly with respect to the longitudinal axis thereof, as shown in Figure 3. In this manner, the longitudinal edges of conductive band 56 do not interfere with the movement of caster 10. In particular, the longitudinal edges do not interfere with changes of direction of movement of the caster 10. As can best be seen in Figures 1 and 2, a conductive lead 58 extends along the outer surface of semi-cylindrical shell 18 between stem 14 and conductive band 56. Conductive lead 58 can comprise a standard piece of conductive electrical wire. Conductive lead 58 can further comprise a resistor 66 having a desired resistance. A lower end of conductive lead 58 extends through aperture 65 in conductive band 56. In this manner, the lower end of conductive lead 58 is secured in intimate conductive contact with conductive band 56. An upper end of conductive lead 58 is secured by twisting, soldering or otherwise secured in intimate conductive contact with a collar 60. Collar 60 is securedly mounted in intimate conductive contact with stem 14 as is herein further described. In use, conductive lead 58 provides a conductive path extending between conductive band 56 and stem 14. Collar 60 comprises a circular metallic collar or cap having an aperture extending therethrough (not shown). Collar 60 is adapted to seat over stem 14 so that stem 14 extends upwardly through the aperture in collar 60. Collar 60 has a downwardly extending portion 68. Downwardly extending portion can have an aperture 69 extending therethrough. Aperture 69 is adapted to receive an upper end of conductive lead 58 therethrough. Conductive lead 58 can then be bent, twisted, soldered, or otherwise secured in intimate conductive contact with downwardly extending portion 68. In use, collar 60, conductive lead 58, and conductive band 56 together form a conductive path permitting the discharge of electrical charge from stem 14 to a floor (not shown). A shroud 62 is also provided. Shroud 62 comprises a hollow, plastic shell having a curved inner, or open, face adapted to seat against the outer surface of semi-cylindrical shell 18 and an outer surface 70 having an aperture at a top portion thereof adapted to receive stem 14. In use, shroud 62 seats over stem 14. Shroud 62 rests against semi-cylindrical shell 18 so that collar 60 and conductive lead 58 are concealed within, and protected by, outer surface 70 of shroud 62. In this manner, shroud 62 acts to prevent dust, foreign matter, or other material from contaminating lead 58 and collar 60. Further, shroud 62 prevents mechanical damage to the conductive path formed by stem 14, collar 60, lead 58 and conductive band 56. Reasonable variations and modifications are possible within the scope of the forgoing disclosure and drawings without departing from the scope of the invention which is defined in the appended claims.

Claims: A two-wheel roller caster (10) for use in supporting movable objects such as chairs on a floor wherein said caster includes two wheels (16), an axle (44) connecting said wheels (16), a curved conductive band (56) having two ends and being mounted between said two wheels (16) for providing conductive contact between said caster (10) and said floor, and a conductive path means (58,66) connecting said conductive band (56) to said movable object so as to permit said movable object to be electrically grounded to said floor through said conductive band (56), characterized by a housing (12) rotatably supporting said wheels (16) and forming an outer shell (18), said conductive band (56) being secured at both ends thereof to said housing (12). A two-wheel roller caster (10) according to claim 1, wherein said conductive band (56) is slidably secured at one of its ends to said housing (12). A two-wheel roller caster (10) according to claim 1 or 2 wherein said conductive band (56) is shaped and sized so as to have a larger radius of curvature than said two wheels (16), so that said conductive band (56) deforms somewhat so as to conform to the shape of said floor thereby exerting continuous pressure against said floor when said caster (10) is in use. A two-wheel roller caster (10) according to claim 1, 2 oder 3 wherein said conductive band (56) is of a crowned cross-sectional shape, so that longitudinal edges of said conductive band (56) permit free movement of said caster (10) in a plurality of directions. A two-wheel roller caster (10) according to anyone of the foregoing claims, wherein said conductive path further comprises: a conductive lead (58); and a resistor means (66) mounted in series in said conductive lead for limiting current flow therethrough. A two-wheel roller caster (10) according to anyone of the foregoing claims and further comprising a shroud means (62) for protecting said conductive path means (58, 66). A two-wheel roller caster (10) according to anyone of the foregoing claims wherein said conductive band (56) is shaped and positioned so as to maintain substantially continuous sliding contact with said floor when said wheels (16) are rotated, so that said sliding motion maintains said conductive band (56) relatively free of foreign debris buildup. A two-wheel roller caster (10) according to claim 6 or 7 wherein said two wheels (16), said housing (12) , and said shroud means (62) substantially conceal said conductive band (56) and said conductive path means (58, 66) from view when said caster (10) is in use.

Inventors: WILCOX, JEFFREY S.
Applicants: HERMAN MILLER, INC.
Application year: 1987
Main classification: B60B33
IPC codes: B60B33, B60R16