GB1580231A - Castor - Google Patents

Description

(54) CASTOR (71) We, JACK PHILLIP KEGG, COLIN ALBERT FULLER, GEOFFREY ERIC KEGG, all Australian Nationalities, respectively of 12/104 St. George Crescent, Drummoyne, Sydney, 2047; 25 Awatea Road, St. Ives, Sydney 2075; 40 Boundary Road, Wahroonga, Sydney 2076, all in the State of New South Wales, Commonwealth of Australia, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: The present invention relates to castors, such as may be used on domestic and office furniture, industrial equipment, trolleys and the like.

The majority of castors in present use are of the swivel-wheel type. This type of castor essentially comprises a wheel mounted on a horizontal or substantially horizontal axle which in turn is supported for turning about a substantially vertical swivel axis. Such castors, though highly versatile and efficient if well designed, do have certain inherent drawbacks. One drawback is that the bearings, especially the vertical swivel bearings are subject to non-axial forces which tend to accentuate wear and require heavy duty ball or roller bearings if wear is to be minimised and bearing life to be prolonged. Another problem is the need to provide and maintain adequate lubrication for the bearings.A further problem is that since the swivel (vertical) axis is normally offset in a vertical plane with respect to the horizontal axis, any load sap- ported on the castor will generate a turning moment about the vertical axis and thus an extremely rigid connection must be made between the castor and the article to which it is mounted in order to withstand the resulting side forces.

To offset the aforementioned drawbacks, modern swivel castors are ruggedly built with heavy duty bearings and high quality materials. This however makes such castors relatively expensive to manufacture and replace.

Another drawback inherent in a swivel castor is that it will tend to align itself in the particular direction in which it is moving, so that when it is intended to suddenly shift the article through an angle of, say, 900, the castor will tend to resist this change in direction. Thus, in general, articles mounted on swivel castors are awkward to move around corners.

To overcome the above mentioned drawbacks, a number of so-called "ball castor" designs have previously been proposed. In this context a ball castor is one in which the main rolling element is a ball as contrasted with the wheel of a swivel castor. A ball castor is inherently symmetrical and does not require a vertical swivel axis. Furthermore, the load (i.e. weight of article supported on the castor) acts vertically through the axis of the ball and therefore the castor is not subject to large side forces, unlike the case with a swivel castor in which the load does not act vertically through the axis of the wheel. Thus, in principle, a ball castor is free from a number of drawbacks inherent in a swivel castor.

On the other hand, there are certain difficulties associated uniquely with the design of a ball castor in practice. A main difficulty is that of supporting the ball in a manner to reduce friction as much as possible, but at the same time to maintain the ball in a stable relationship with its support. This problem arises from the fact that the ball must be capable of rotating freely in any direction about a horizontal axis and thus the means for supporting the ball must be capable of doing so with the least possible friction or resistance to the rotation of the ball. Unlike the wheel of a swivel castor, a ball has no axle or bearings and must be supported solely by some member or members in cntat with its surface.

The present invention is concerned with the problem of overcoming these difficulties.

In accordance with the invention there is provided a castor comprising a socket member defined by a base portion and a cup portion extending from the base portion, the base portion being adapted to be affixed to the underside of an article and the cup portion defining a cavity therein, a ball adapted to be received in the cavity in a manner to be freely rotatable in any direction in the cavity, the cup portion having at least three rollers rotatably mounted within the cavity for supporting the ball at respective points of contact intermediate its upper and equaterial regions and spaced about the surface of the ball, the rotational axis of each roller being substantially parallel to the tangent at the point of contact with the surface of the ball and being transverse to the axis of the cavity, and retaining means for maintaining the ball when mounted in the cavity, in its mounted position.

In this description and in the appended claims, the term "roller" means a wheel rotatable on or with an axle.

The invention will be more fully understood from the following description, taken in conjunction with the accompanying drawings, in which: Figure 1 is a section of one form of ball castor, Figure 2 is a partial view, in section, of a form of mounting of the ball castor.

Figure 3 is a bottom plan view of a ball castor in accordance with a preferred embodiment of the invention, Figure 4 is a side elevation of the castor shown in Figure 3, Figure 5 is a vertical section of the castor of Figure 3, and Figure 6 is a section showing a mounting arrangement for the castor.

Referring to the drawings, the castor shown in Figure 1 and 2 does not fall within the scope of the invention claimed herein, but a description thereof is included to assist in understanding the present invention. An article of furniture or a trolley, etc. has a leg diagrammatically shown at 1 to which a castor 2 is fixed by means of a coach screw 3. The castor 2 comprises a spherical solid phenolic resin ball 4 which may be, for example, of two inches diameter. This is trapped in a socket member 5 in the form of an inverted cup made of a plastics material and having a central well 6 in which is located the head of the screw 3.

The cavity of the cup 5 accommodates the major portion of the ball periphery and has an outer circular rim 7, the diameter of which is marginally less than the diameter of the ball. The cup is also provided with small projections 8 around the well 6. The area of contact between the ball and the cup 5 is limited to the inside surface of the rim 7 and the projections 8.

In the arrangement shown in Figure 2, the castor is secured to the leg of an article 9 by a bolt 10 and a nut 11.

In both Figures 1 and 2, the castor has a relatively wide base 12 having a flat surface 13 which engages a flat undersurface of the leg od the article 1 or 9. This provides stabi lity and strength in the castor and is parti cularly desirable where the cup 5 consists wholly of a plastics material such as nylon.

If the base 12 were od narrow cross-section, the castor might break during use, whereas this possibility is substantially avoided when the castor has a wide base.

When the castor is sold, the ball and cup may be provided separately. The leg of furni ture to which the castor is to be fitted may be drilled if necessary to receive the screw 3 or the bolt 10 as the case may be. The castor 5 is then secured to the leg by means of the screw or bolt and the ball 4 force fitted into its captured position as illustrated.

When the castor is in use it will be appreciated that the ball 4 can rotate in any direction so that at all times the weight is transmitted vertically upwards through the fixture connecting the castor to the furniture leg.

Bending moments on this fixture are largely eliminated since the castor is not offset with respect to its axis as in the case of a conventional castor.

Another advantage of the castor is the ease with which the castor can be mounted to the article of furniture and the ease with which it can be replaced.

It will also be noted that the castor has no inherent tendency to align itself in any particular direction, and this greatly contributes to the ease with which furniture fined with the castor can be moved.

The resiliency of the plastics material of the socket member allows the ball to be push fitted into position. Advantageously the material is of the kind which has a self-lubricating property in conjunction with the ball 4, such as nylon, for example. Although the castor of the embodiment described above is a considerable improvement in many respects over swivel type castors, some problems were encountered during the initial design stages, when a practical design for domestic and commercial applicautons was sought. A first problem was that the ball did not roll quite as smoothly in the cavity as one would have liked. Although the material of the socket member 5, which was of nylon and had self lubricating properties when used in conjunction with a phenolic ball 4, friction between the bearing surfaces and the ball was found to be not significant and on a smooth, low friction surface, the ball 4 could stick and consequently slide instead of rolling over that surface as intended. Many attempts have been made initially to overcome this problem but most of those attempts failed to achieve entirely satisfactory results. For example, it was thought that replacing the bearing surfaces defined by the projections 8 with a set of ball rollers in an annular race should result in a substantial reduction in friction and thereby overcome this problem. However this was not found to be the case at all.In fact the ball rollers were found to provide low friction in one mode only of rotation of the ball, namely, about a vertical axis, but this happens to be precisely the mode of rotation which is not required of the ball. The ball has to rotate about any one of an infinite number of horizontal axes and the ball rollers simply do not help to reduce friction for that kind of movement at all. Another very serious problem was found to be caused by ingress of dirt into the castor between the cavity walls and the ball. Such dirt tended to accumulate within the cavity and increase friction and cause sticking of the ball and the dirt would become trapped in the cavity and the ball would periodically have to be removed to clean out the dirt. Another serious drawback was noise, which was found to occur particularly when ball rollers were used as the bearing for the ball.Another, but rather minor disadvantage was the need to provide a countersunk hole to accommodate the head of the bolt. Another problem of using ball rollers instead of the projections 8, is that these are awkward to use because if they are not held in the socket in some way they will fall out when the ball is replaced and this makes replacement somewhat inconvenient. It is also possible that ball bearings or the projections 8 may tend to damage the surface of the ball 4.

These problems, especially the problem of reducing friction to the low level desired have proved difficult to solve because although many attempts have been made to reshape the bearing surfaces, e.g. as defined by the projections 8, or by relocating them, or by replacing them with various different materials, or by replacing them by rotatable balls or rollers, have all been found to give little or no improvement and certainly were unable to provide the results which were sought. It was obvious that if the problem could be solved, while still retaining the basic concept of the ball-mounted castor, it would be necessary to use a completely different method of supporting the ball in the cavity.

Finally, it was found that the problem could be solved in a very simple but elegant manner. More particularly, it was found that the idea of using either stationary bearing surfaces, or ball or roller bearings as previously tried, had to be rejected completely if the ultimate desired results were to be obtained, and the particular solution was found, surprisingly, in the use od rollers for supporting the ball 4, but the rollers had to be mounted on non vertical axes to engage the ball surface somewhere between the uppermost point of that surface within the cavity and the equatorial region of the ball. The rollers, at least three in number, each has its axis preferably horizontal and parallel to the tangent at the point where the rollers engage the surface of the ball.In this context it is assumed that the castor has a vertical axis of symmetry and is intended to roll in a horizontal direction, and terms such as vertical and horizontal are to be construed in this context.

It has also been found possible to solve the problem of dirt becoming trapped within the castor. To a large extent, this problem has already been solved by abandoning the original method for supporting the ball and replacing it with the rollers mentioned above.

Originally, dirt tended to ingress past the projections 8, or equivalent ball bearings, into the central well 6 and, once there, would become trapped and accumulate. When the original design was modified and rollers were used, it was found that dirt no longer accummulated above the ball, because there was ample space for the dirt to move out of the cavity as well as in. In other words, the dirt did not become trapped as previously. However, the problem was still not fully solved because, it was found, the circular rim 7 also had the effect of entrapping dirt within the cavity. It was found that one way of solving this problem was to provide a retaining means defined by spaced lugs, which may be of resilient plastics material, arranged about the periphery of the ball so that a free space is provided between the wall of the cavity, the surface of the ball and the lugs.Although dirt may freely enter the cavity, it is no longer trapped therein and thus the ball is not likely to stick, - There are very few moving parts required, and this is highly advantageous. Apart from the rollers, the only moving part is the ball 4 and this can freely move in any direction.

The socket member does not have to turn and therefore there is no vertical support bearing which is subject to wear. As for the rollers, these may be mounted on pin bearings securely mounted to the body of the socket member and they do not have to withstand any particularly large forces. Thus, such bearings are inherently capable of long life without any particular maintenance. Even if wear does take place, the castor is self adjusting in the sense that the load applied to the castor actually tends to maintain the moving parts in firm contact with each other so that no vibration or "wobbling" is likely to occur. This is an important advantage over conventional castor designs.

Another advantage, not to be overlooked, is the ease with which the ball may be replaced should it, for some reason, become damaged. Since the ball is merely a press fit into the socket cavity it is merely necessary to lever the ball out of the cavity and the use of resilient retaining means, such as the spaced lugs enables this to be done without any difficulty. Alternatively, non resilient means may be used, for example, an annular cap which is applied over the ball after the ball is inserted into the socket. The castor may be made of any suitable material. For example, the socket body may be made of metal, or a plastics material, while the roller surfaces and the lugs (ball retaining means) are preferably made of a low friction, long wearing plastics material. Phenolic resin has been found to be a particularly suitable material for the ball.

A preferred embodiment will now be described with reference to Figures 3-6 of the accompanying drawings.

Wherever possible, similar references are used to those used in Figures 1 and 2 to identify similar parts. Thus, in the preferred embodiment as illustrated in Figures 3-6, the castor comprises a ball 4 mounted in a socket member 5 which is adapted to be fixed to the underside of an article 1. Bearing support for the ball 4 is provided by a set of rollers 15, which may be symmetrically placed about the vertical axis of symmetry of the castor and contact the surface of the ball at a position approximately midway between the top of the ball and the equatorial region thereof. The rollers 15, which are at least three in number, are mounted on pin bearings 16 which are supported in a suitable manner in lugs 17 projecting inwardly of the wall of the cavity containing the ball.In the example illustrated in Figure 3, there are six rollers 15 supported in pairs arranged symmetrically about the vertical axis of the ball.

It has been found that this arrangement provides smoother and quieter operation than does one using only three rollers. The roller surfaces are composed of a relatively hard, low coefficient of friction plastics material.

To retain the ball in the cavity, there are provided six symmetrically placed lugs 18 which project inwardly towards the ball 4 from a lower rim of the socket member, the lugs 18 being of a yieldable resilient plastics material so as to hold the ball in place while permitting the ball to be removed and replaced, if necessary, using a suitable tool for forcing the ball past the lugs. The lugs may be integral with or separately attached to the socket member 5, which may be of, for example, a cast metal or plastics material.

The socket member has a general dome shape and has an aesthetically attractive appearance. A hole through the centre of the base 12 receives a screw 3 for fastening the castor to the underside of an article 1. Advantageously, ribs are cast into the socket member, on the inside thereof, such as ribs 19 formed in the base of the socket member and ribs 20 formed on the cavity wall, so as to provide rigidity combined with low weight and minimum use of material. The castor as a whole has exceptional strength and stability for its weight, especially when compared with conventional castors. As previously mentioned, there are no significant bending moments acting on the castor and thus stabi lity and long life are assured.

Another feature which may be mentioned is that the lugs 18 preferably do not extend below the bottom edge of the annular rim 7a (see Figure 5). If the ball is temporarily removed while the castor is affixed to the article 1 (there is no need to remove the socket member when replacing the ball) the castor can be allowed to rest with its annular rim 7a supported on the horizontal surface without danger of bending or damaging the lugs 18.

Referring now to Figure 6, this shows one method of attaching the castor to an article 1. In this case, the central bore in the base of the castor is aligned with a bore drilled through a bracket at the bottom of the article 1, and a bolt 10 passes through the aligned bores and fixes the castor with the bracket by means of a nut 11 threaded on the bolt.

It will be appreciated that modifications may be made to the embodiment described.

For example, in the embodiment the socket member comprises a frusto conical base portion 12, a cylindrical portion Sa surrounding the ball and an intermediate frusto conical portion 5b, however other shapes as, for example, rounded, hemispherical, polygonal etc.

may be used.

Also, the position and number of the rollers 16 can be varied. By comparison, in the castor shown in Figure 1 the rim 8 has to be relatively close to the top of the ball 4, approximately as shown, for lowest friction but this means that there is a tendency for the ball to jump out of the socket due to forces acting on the ball when rolling on a horizontal surface. However in the preferred embodiment illustrated in Figs. 3-6, the position of the rollers 16 can be made closer to the equatorial region of the ball so as to virtually eliminate any tendency for the ball to jump out as a result of side forces acting on it. At the same time low rolling friction is substantially retained and the operation has been found to be very smooth. The optimum position (as viewed in vertical section) of the rollers appears to be one which is slightly closer to the equator of the ball than to the top of the ball. As viewed in horizontal section (Fig. 3) the rollers may be arranged in pairs (as shown) or may be distributed, for example, equally about the vertical axis of the ball.

The axis of each roller is substantially parallel to the tangent at the point of contact of the roller with respect to the surface of the ball.

Because of its symmetry, the castor descrbed herein eliminates a problem of most conventional castors, namely one concerned with their replacement. Conventional castors are generally left handed or right handed, and thus are sold in pairs. If one castor of a pair has to be replaced it may be necessary to purchase a pair of castors even though one of those is not required. Even if individual (con ventional) castors can be obtained it is still necessary to manufacture left and right handed castors and retailers would have to stock both kinds. This problem does not apply with castors of the present invention which are readily interchangeable.

WHAT WE CLAIM IS:- 1. A castor comprising a socket member defined by a base portion and a cup portion extending from the base portion, the base portion being adapted to be affixed to the underside of an article and the cup portion defining a cavity therein, a ball adapted to be received in the cavity in a manner to be freely rotatable in any direction in the cavity, the cup portion having at least three rollers rotatably mounted within the cavity for sup porting the ball at respective points of contact intermediate its upper and equatorial regions and spaced about the surface of the ball, the rotational axis of each roller being substantially parallel to the tangent at the point of contact with the surface of the ball and being transverse to the axis af the cavity, and retaining means for maintaining the ball, when mounted in the cavity, in its mounted position.

2. A castor as claimed in claim 1 wherein there are six said rollers arranged uniformly in pairs about the axis of the cavity.

3. A castor as claimed in claim 1 wherein there are six said rollers uniformly spaced about the axis of the cavity.

4. A castor as claimed in any one of the preceding claims wherein the rollers are mounted on bearings which in turn are sup ported on inwardly projecting lugs integral with the cavity wall.

5. A castor as claimed in any one of the preceding claims wherein the retaining means is resiliently yieldable to permit the ball to be mounted in or removed from the cavity.

6. A castor as claimed in claim 5 wherein the retaining means is defined by a resiliently yieldable annular outer rim of the cavity, the rim having a diameter which is less than the diameter of the ball.

7. A castor as claimed in claim 5 wherein the retaining means comprises a plurality of resilient, inwardly projecting lugs adjacent an outer rim of the cavity.

8. A castor substantially as herein described with reference to and as illustrated in Figs.

3 to 6 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. ventional) castors can be obtained it is still necessary to manufacture left and right handed castors and retailers would have to stock both kinds. This problem does not apply with castors of the present invention which are readily interchangeable. WHAT WE CLAIM IS:-

1. A castor comprising a socket member defined by a base portion and a cup portion extending from the base portion, the base portion being adapted to be affixed to the underside of an article and the cup portion defining a cavity therein, a ball adapted to be received in the cavity in a manner to be freely rotatable in any direction in the cavity, the cup portion having at least three rollers rotatably mounted within the cavity for sup porting the ball at respective points of contact intermediate its upper and equatorial regions and spaced about the surface of the ball, the rotational axis of each roller being substantially parallel to the tangent at the point of contact with the surface of the ball and being transverse to the axis af the cavity, and retaining means for maintaining the ball, when mounted in the cavity, in its mounted position.

2. A castor as claimed in claim 1 wherein there are six said rollers arranged uniformly in pairs about the axis of the cavity.

3. A castor as claimed in claim 1 wherein there are six said rollers uniformly spaced about the axis of the cavity.

4. A castor as claimed in any one of the preceding claims wherein the rollers are mounted on bearings which in turn are sup ported on inwardly projecting lugs integral with the cavity wall.

5. A castor as claimed in any one of the preceding claims wherein the retaining means is resiliently yieldable to permit the ball to be mounted in or removed from the cavity.

6. A castor as claimed in claim 5 wherein the retaining means is defined by a resiliently yieldable annular outer rim of the cavity, the rim having a diameter which is less than the diameter of the ball.

7. A castor as claimed in claim 5 wherein the retaining means comprises a plurality of resilient, inwardly projecting lugs adjacent an outer rim of the cavity.

8. A castor substantially as herein described with reference to and as illustrated in Figs.

3 to 6 of the accompanying drawings.