CASTORS

Abstract: A castor 10 comprises a body 12, a castor wheel 14 mounted on the body and a stem 16 extending from and rotatable in said body for mounting said castor on a piece of furniture. An outer peripheral portion 36 of the wheel comprises an electrically conductive material and at least the outer surface of the stem 16 is electrically conductive. An electrical connection means 40 is biased into wiping electrical contact with said outer peripheral portion of the wheel and the outer surface of the stem to provide an electrical path therebetween. Thus the castor provides an electrical path to enable any static electric charge to leak from furniture to which it is fitted.

Description: This invention relates to castors, and particularly to castors for use in furniture such as chairs, tables, trollies, beds and cabinets to enable such furniture to be moved. When such furniture is liable to become charged with static electricity, there is the possibility of undesirable sudden discharges occurring from the furniture. An object of the invention is to provide a castor which provides an electrical path to enable any static electric charge to leak from furniture to which it is fitted. Accordingly the invention includes a castor comprising a body, a castor wheel mounted on said body and a stem extending from and rotatable in said body for mounting said castor on a piece of furniture, wherein an outer peripheral portion of the wheel comprises an electrically conductive material, at least the outer surface of the stem is electrically conductive and an electrical connection means is biased into wiping electrical contact with said outer peri­ pheral portion of the wheel and the outer surface of the stem to provide an electrical path therebetween. The wheel of the castor may be formed of plastics material since although plastics material per se are electrically insulative, said outer peripheral portion of the wheel can be formed of a plastics material which is loaded to render it electrically conductive. Preferably said outer peripheral portion extends across the whole axial extent of the wheel at the outer periphery thereof. In an embodiment of the invention, to be described hereinafter, said electrical connection means is biased into wiping contact with said outer peripheral portion at a side face thereof. In this embodiment, said wheel is mounted to one side of the stem, and said electrical connection means is disposed between said wheel and stem. Advantageously, the wheel is mounted on a spindle extending from said body and said electrical connection means comprises a spring member located on said spindle and provided with portions which are oppositely biased into engagement with said stem and said side face. This spring member may be elongate and said portions may be provided on a plurality of longi­ tudinally extending fingers thereof, at least one of which fingers is directed towards said stem, and at least one other of which fingers is directed towards said side face. In such an arrangement the or each finger directed towards said stem may extend through an aperture in said body into engagement with said stem. The above-mentioned embodiment is a twin-wheeled castor with a second wheel mounted to the other side of said stem and a second said electrical connection means is disposed between said second wheel and stem. In order that the invention may be well understood, the embodiment thereof referred to above, which is given by way of example only, will now be described, reference being made to the accompanying drawings in which: Figures 1 to 3 are respectively side, front and top plan views of a twin wheel castor; Figure 4 is a side view of the same twin wheel castor with one wheel removed and the other wheel part broken away; and Figure 5 is a section along the line V-V in Figure 4. Referring first to Figures 1 to 3, the illustrated castor 10 generally comprises a body 12, of a plastics material, for example a polyamide, two plastics castor wheels 14 mounted on the body and a metal stem 16 extending from the rotatable in the body 12 for mounting the castor 10 on a piece of furniture. The body 12 also includes a hood 34 which extends over the wheels. Referring now to Figures 4 and 5, the wheel 14 shown is mounted to one side of the stem 16 and the non-illustrated wheel is mounted to the other side of the stem. The two wheels are rotatably mounted on respective end portions of a spindle 18 which is mounted in a through-bore 20 of a boss 22 of the body 12 so as to extend from the boss on each side thereof. In the illustrated embodiment each wheel is axially retained on its respective spindle end portion by interengaging groove and rib means 24 shown in Figure 2 in relation to the mounting of wheel 14 on spindle end portion 26. The stem 16 is rotatably mounted in a bore 28 of a boss 30 of the body 12 and is axially retained therein by interengaging groove and rib means 32. In order to provide an electrical path to enable leakage of any static electric charge in an item of furniture to which the castor is fitted an outer peripheral portion 36 of the wheel 14 comprises an electrically conductive material and an electrical connection means 38 is biased into wiping electrical contact with the portion 36 and the outer surface of the stem to provide an electrical path therebetween. This electrical path extends to the item of furniture to which the stem is fitted in use. In the illustrated castor the stem is made of an electrically conductive metal, but it will be under­ stood that only the outer surface of the stem need be electrically conductive in order to provide the above-­ mentioned electrical path. In the illustrated embodiment, the wheel 14 is formed of plastics material and the electrically conductive outer peripheral portion 34, which is shown as extending across the whole axial extent of the wheel at the outer periphery thereof, is a plastic material which is loaded to render it electrically conductive. Because of its loading with electrically conductive filler material the strength of the plastics of the portion 34 is reduced. However this is acceptable since this portion 34 comprises only a small proportion of the structure of the wheel and is subjected to compressive forces only in use. The electrical connection means 38 is disposed between the wheel 14 and the stem 16 and comprises a spring member 40 of an electrically conductive metallic material, for example phosphor bronze. This spring member 40 is located on the spindle 18 and is provided with portions 42 and 44 which are oppositely biased into engagement with the stem 16 and a side face 46 of the electrically conductive portion 36 of the wheel 14. As illustrated, the spring member 40 is elongate and the portions 42, 44 are provided on a plurality of longitudinally extending fingers 48,50 of the member which are directed respectively towards the stem 16 and side face 46. As illustrated the member 40 comprises one such finger 48 and two such fingers 50, the latter being disposed one to each side of the former which itself extends through an aperture 52 in the boss 30 into engagement with the stem 16. Of course, other arrangements and numbers of fingers are possible providing the spring member includes one finger directed towards the stem and one other directed towards the side face 46 to provide an electrical connection between the stem and side face. In the illustrated embodiment the wheel not shown in Figures 4 and 5 is of a like construction to the wheel 14 illustrated (although this is not essential) and a second electrical connection means is disposed between this wheel and the stem in like manner to the connection means 38. This second connection means is illustrated in the drawings and designated 38′ with parts thereof corresponding to like parts of connection means 38 indicated by the designations provided with primes.

Claims: 1. A castor comprising a body, a castor wheel mounted on said body and a stem extending from and rotatable in said body for mounting said castor on a piece of furniture, wherein an outer peripheral portion of the wheel comprises an electrically conductive material, at least the outer surface of the stem is electrically conductive and an electrical connection means is biased into wiping electrical contact with said outer peripheral portion of the wheel and the outer surface of the stem to provide an electrical path therebetween. 2. A castor as claimed in claim 1, wherein the said wheel is formed of plastics material, said outer peripheral portion thereof being a plastics material which is loaded to render it electrically conductive. 3. A castor as claimed in claim 1 or 2, wherein said outer peripheral portion extends across the whole axial extent of the wheel at the outer periphery thereof.4. A castor as claimed in claim 1, 2 or 3, wherein said electrical connection means is biased into wiping contact with said outer peripheral portion at a side face thereof. 5. A castor as claimed in claim 4, wherein said wheel is mounted to one side of the stem, and said electrical connection means is disposed between said wheel and stem. 6. A castor as claimed in claim 5, wherein said wheel is mounted on a spindle extending from said body and said electrical connection means comprises a spring member located on said spindle and provided with portions which are oppositely biased into engagement with said stem and said side face. 7. A castor as claimed in claim 6, wherein said spring member is elongate and said portions are provided on a plurality of longitudinally extending fingers thereof, at least one of which fingers is directed towards said stem, and at least one other of which fingers is directed towards said side face. 8. A castor as claimed in claim 7, wherein the or each finger directed towards said stem extends through an aperture in said body into engagement with said stem. 9. A castor as claimed in any one of claims 5 to 8, wherein a second said wheel is mounted to the other side of said stem and a second said electrical connection means is disposed between said second wheel and stem.

Inventors: DANIELS, RAYMOND ROBERT JAMES
Applicants: GUY-RAYMOND ENGINEERING COMPANY LIMITED
Application year: 1988
Main classification: B60B33
IPC codes: B60B33, B60C19, B60B9, B60R16