GB2524567A

GB2524567A - A coupling assembly for a swivel castor wheel

Info

Publication number: GB2524567A
Application number: GB1405550.3A
Authority: GB
Inventors: James Pollard
Original assignee: Individual
Current assignee: Individual
Priority date: 2014-03-27
Filing date: 2014-03-27
Publication date: 2015-09-30
Also published as: GB201405550D0

Abstract

A coupling assembly for coupling a swivel castor wheel to an object which is to be moved across a surface. In use, an orientation of the swivel castor can be adjusted in order to change a direction of travel of the object across the surface. One disclosed coupling assembly 10 comprises a first coupling component 18 which can be mounted to one of a swivel castor wheel (figure 1, 12) and an object (figure 1, 8), and a second coupling component 20 which can be mounted to the other one of the swivel castor wheel and the object. The coupling components are arranged so that they can rotate relative to one another about a common rotation axis 22, to facilitate adjustment of the orientation of the swivel castor wheel relative to the object. The coupling components are arranged so that, in use, they are biased under the action of gravity towards at least one predetermined rotational orientation relative to one another, to provide a directional bias in the orientation of the swivel castor wheel with respect to the object and so direction of travel of the object across a surface.

Description

A COUPLING ASSEMBLY FOR A SWIVEL CASTOR WHEEL

The present invention relates to a coupling assembly for coupling a swivel castor wheel to an object which is to be moved across a surface. In particular, but not exclusively, the present s invention relates to a coupling assembly for use in coupling a swivel castor wheel to an object such as a trolley, which may be a supermarket trolley, hospital trolley or industrial trolley, a wheeled stretcher, handcart or a wheelchair.

There is a need for trolleys, such as supermarket trolleys, to have a high degree of manoeuvrability and directional stability. This enables an operator of the trolley to easily navigate around obstacles, and to negotiate, for example, the aisles of a supermarket and car parks, without accidental collisions resulting in damage to property or personal injury.

This requirement has been addressed to a certain extent by the provision of swivel castor wheels. For example, conventional supermarket trolley designs may comprise swivel castor wheels primarily at the front two corners of a frame of the trolley, with fixed wheels at the rear, or alternatively with swivel castor wheels at all four corners of the trolley frame.

Despite this, operators are often left frustrated by trolleys which are difficult to steer, requiring additional effort and strength to manoeuvre. It is well known in the art that trolleys become particularly difficult to manoeuvre when filled with heavy loads, andlor when being pushed on a gradient. Even the slightest gradient when encountered by a heavily laden trolley poses a substantial problem. This is because the swivel castor wheels have a tendency to automatically align with the slope of the gradient, with the result that the trolley can easily become uncontrollable. The operator is often required to exert additional force on the trolley in order to maintain a desired direction of movement, and this usually means that the individual must position themselves at a particular angle to push the trolley safely in the desired direction.

With such physical exertion, it is conceivable that there is the risk of personal injury.

Moreover, for individuals who are physically challenged, the task of pushing a heavy trolley may be impossible without assistance. This problem can be exacerbated if the swivel castor wheels are not properly maintained. Additional friction, through wear and tear, can result in the trolley being even harder to safely manoeuvre.

Attempts have been made at addressing the problems associated with the directional stability of swivel castor wheels. For example, International Patent Publication No.WO-2008/OOl 131 of the present applicant discloses a castor wheel assembly of a type suitable for use with trolleys. The castor wheel assembly comprises a swivel castor wheel mounted on a first member which is configured for connection to a trolley frame in such a way that a steering axis of the wheel can be moved between first and second rake angles, without substantially changing the height of the trolley above a surface. The first member can be moved from a zero rake angle configuration to a rearwardly raked configuration, when the trolley is moved in a forward direction. In the zero rake angle configuration of the first member, the castor wheel can freely rotate about the first member, so that the trolley can more easily be steered.

In the rearwardly raked configuration of the first member, rotation of the wheel about the first member is restricted, improving directional stability of the trolley when moving over a surface.

Although the castor wheel assembly disclosed in WO-2008100 1131 goes some way towards addressing the problems with the prior art, there is a desire in the industry to provide a more cost-effective andlor robust solution. Supermarkets, for example, have a high turnover of trolleys due to some being lost or damaged, and so there is demand to produce a low cost solution which is quick and easy to manufacture.

It is amongst the objects of the present invention to obviate or mitigate at least one of the foregoing disadvantages.

According to a first aspect of thc present invention, there is provided a coupling assembly for coupling a swivel castor wheel to an object which is to be moved across a surface, in which an orientation of the swivel castor wheel relative to the object can be adjusted in order to change a direction of travel of the object across the surface, the coupling assembly comprising: a first coupling component which can be mounted to one of the swivel castor wheel and the object; a second coupling component which can be mounted to the other one of the swivel castor wheel and the object, the coupling components arranged so that they can rotate relative to one another about a common rotation axis to facilitate ad] ustment of the orientation of the swivel castor wheel relative to the object; in which the coupling components are arranged so that, in use, they are biased under the action of gravity towards at least one predetermined rotational orientation relative to one another, to provide a directional bias in the orientation of the swivel castor wheel with respect to the object and so direction of travel of the object across the surface.

According to a second aspect of the present invention, there is provided an arrangement of a swivel castor wheel and an object coupled together using a coupling assembly according to the first aspect of the invention.

Arranging the first and second coupling components so that they are biased, under the action is of gravity, towards at least one predetermined rotational orientation may address the problems with known coupling assemblies, such as those between a swivel castor wheel and a trolley. This is because biasing of the coupling components towards the at least one predetermined rotational orientation may have the effect of biasing the swivel castor wheel so that it assumes a particular orientation relative to the object (or vice-versa), or so that movement of one of the swivel castor wheel and the object away from a particular orientation relative to the other is resisted, to thereby assist in movement of the object across the surface.

For example, the coupling components may be biased towards a rotational orientation in which the swivel castor wheel and the object are aligned with a desired direction of travel of the object, to facilitate movement of the object in that direction. This may assist in overcoming external factors which may otherwise hamper movement of the object in the desired direction over the surface, such as external forces encountered when traversing an inclined slope. The coupling assembly may provide a simple, inexpensive assembly for coupling a swivel castor wheel to an object which provides inbuilt directional stability which is useflil to a user, but which does not impede manoeuvrability of the object.

The object may be at least part of: a trolley, which may be a supermarket trolley, hospital trolley or industrial trolley; a wheeled stretcher; a handcart; or a wheelchair.

The axis of rotation of the coupling assembly may be disposed, in use, transverse to the direction of travel of the object over the surface, and may be disposed substantially perpendicular to said direction of travel. The axis of rotation of the coupling assembly may be disposed, in use, transverse to the surface across which the object is to travel, and may be disposed substantially perpendicular to said surface.

The wheel may define a wheel plane disposed, in use, transverse to the surface and which may be disposed substantially perpendicular to the surface. The rotation axis may be disposed in the wheel plane. The rotation axis may be disposed parallel to the wheel plane.

The coupling component which is mounted to the wheel may be mounted so that the wheel and the coupling component rotate in unison about the rotation axis.

The first coupling component may be a male coupling component and the second coupling component may be a female coupling component, and the female coupling component may receive the male coupling component so that the coupling components can rotate relative to one another about the common rotation axis. The male and/or female coupling components may be generally elongate. At least one of the male and female coupling components, in particular the female coupling component, may be substantially tubular, and may comprise an internal wall and an external wall, The coupling assembly may comprise a bearing andlor a lubricant disposed between an external wall of the male coupling component and an internal wall of the female coupling component.

The female coupling component may comprise an open end for receiving the male coupling component, and a closed end opposite the open end. The male coupling component may abut the closed end of the female coupling component when the coupling components are coupled together.

The first and second coupling components may define respective surfaces, which may be abutment surfaces, and the surfaces may be matching andlor complementary in shape so that under the action of gravity and by a reduction in a height of the coupling assembly, the components are automatically biased towards the at least one predetermined rotational orientation. This may serve to energise directional alignment and stability to a swivel castor wheel, achieved by action of gravity alone. The surfaces may be brought into abutment when the coupling components are coupled together, or a spacing element or material may be provided between the surfaces. A bearing, bearing element and/or lubricant may be provided between the surfaces. The surfaces may be disposed generally transverse to the rotation axis.

The surfaces may be adapted for rotation relative to one another, to facilitate relative rotation between the coupling components. The closed end of the female coupling component may define the surface of said component. The surfaces of the male coupling component and the female coupling component may cooperate to define at least one predetermined rotational orientation of the male coupling component and female coupling component relative to one another, to provide the directional bias in the orientation of the swivel castor wheel with respect to the object and so the direction of travel of the object across the surface.

The surfaces may be substantially planar (i.e. flat) and may be inclined relative to the rotation axis. This may serve to bias the coupling components towards the at least one rotational orientation under the action of gravity. This arrangement may provide a single rotational orientation of the coupling components relative to one another, and so directional bias in the orientation of the swivel castor wheel relative to the object.

Part or parts of the surface defined by each coupling component may extend out of a plane which is disposed transverse to, and optionally generally perpendicular to, the rotation axis, The surfaces may fonn cam surfaces. Each cam surface may have at least one lobe or peak.

Each cam surface may have at least one trough. The part of the surface extending out of said plane may form a lobe or peak. A lobe or peak on one of the surfaces may cooperate with a trough on the other surface, to thereby define at least one predetermined rotational orientation of the coupling components. The surfaces may be shaped so as to bias a lobe on one surface towards a trough on the other surface, positioning of the lobe in the trough defining a predetermined rotational oricntation of the coupling components.

There may be a plurality of lobes or peaks spaced around a circumference of the surface of the respective coupling component. There may be a plurality of troughs spaced around a circumference of the surface of the respective coupling component. In this way, a plurality of rotational orientations of the coupling components may be defined (by the positioning of a lobe or peak of one of the surfaces in a trough of the other surface). The number of possible rotational orientations will depend upon the number of lobes or peaks and the corresponding number of troughs. For example, where there are two lobes and two troughs, two possible rotational orientations may be defined. The angular spacing of these rotational orientations will depend upon the angular positions of the lobes/troughs on the surfaces. For example, s two lobes (and corresponding troughs) spaced 1800 apart will provide two possible rotational orientations spaced by that amount. The surfaces may comprise ramp portions extending between a trough and a lobe or peak, which may bias a lobe on one surface towards a trough on the other surface. The ramp portions may facilitate rotation of the surfaces relative to one another. The ramp portions may extend up out of said plane. The ramp portions may be inclined relative to the rotation axis.

One of the surfaces may define a protrusion which extends out of said plane, and the other one of the surfaces may define a recess shaped to receive the protrusion, the protrusion and the recess being shaped to define the predetermined rotational orientation of the coupling components relative to one another. For example, the protrusion and the recess may be generally elliptical in shape, providing two rotational orientations spaced 1800 apart. A centre of the protrusion nay be aligned with/disposed on the rotation axis. The at least one protrusion may have a centre which is spaced laterally from the rotation axis. The at least one protrusion may have a rounded profile.

One of the surfaces may be generally concave and the other abutment surface generally convex.

The surfaces may be load bearing so as to accommodate a portion of the weight of one of the object, directed along the rotation axis. The directional bias provided in the rotational orientation of the swivel castor wheel relative to the object may be overcome by the addition of sufficient rotational force (torque) to one or both of the components, about the rotation axis of the coupling assembly. The extent to which the surfaces are inclined, or to which the at least one lobe/peak or protrusion extends out of said plane, may define the magnitude of directional bias which is provided. The greater the inclination, or distance between the lobe/peak and the trough (i.e. its height), or between the surface of the protrusion and a remainder or main part of the surface, the larger will be the rotational force (torque) required to move rotate the coupling components relative to one another. It will therefore be understood that rotation of the coupling components may cause one of the components to translate relative to the other component, in a direction along the rotation axis.

An inclination of the surfaces, or a distance which the at least one lobe or protrusion extends out of the plane of the abutment surface, may be selected taking account of the portion of the weight of the object borne by the surfaces. The greater the weight, the lesser may be the inclination, or the smaller may be the distance which the at least one lobe/protrusion extends out of the plane of the surface. The magnitude of torque needed to be applied to move the coupling assembly from one predetermined rotational orientation to another may therefore be determined by the magnitude of the load imparted to the surfaces, and the distance which the at least one lobe/protrusion extends beyond the plane of the surface. For example, greater weight or greater extension of the at least one lobe/protrusion beyond the plane results in a greater degree of torque required to move from one predetermined rotational orientation to another. Therefore, more force must be applied to change the directional bias of the swivel castor wheel relative to the object.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of a trolley comprising a coupling assembly according to an embodiment of the present invention, the coupling assembly serving for coupling a wheel of the trolley to a frame of the trolley; Figs. 2A and 2B are enlarged side views of the coupling assembly of Fig. 1, shown during movement of the trolley across a surface in opposed first and second directions, respectively; Figs. 3A and 3B are side views of a coupling assembly in accordance with another embodiment of the present invention, shown during movement of a trolley can'ying the coupling assembly across a surface in opposed first and second directions, respectively; Fig. 4A is an enlarged perspective view of a first, male coupling component and a second, female coupling component of the coupling assemblies of Figs. 2AIB or 3MB; Fig. 4B is an enlarged perspective view of alternative male and female coupling components of the coupling assemblies of Figs. 2k/B or 3AIB; Fig. 5 is an enlarged perspective view of further alternative male and female coupling components of the coupling assemblies of Figs. 2k/B or 3k/B, the female coupling component shown partially cut-away, for illustration purposes; Fig. 5A is a plan view of the male coupling component of Fig. 5; Fig. 6 is an enlarged perspective view of further alternative male and female coupling components of the coupling assemblies of Figs. 2A/B or 3k/B, the female coupling component shown partially cut-away, for illustration purposes; and Fig. 7 is an enlarged perspective view of further alternative male and female coupling components of the coupling assemblies of Figs. 2k/B or 3A!B, the female coupling component shown partially cut-away, and illustrating a bearing located between the male and female components.

Turning firstly to Figure 1, there is shown a perspective view of a trolley, in the fonn of a supermarket trolley 8, comprising a coupling assembly according to an embodiment of the present invention. The coupling assembly is shown in more detail in the enlarged side views of Figures 2A and 2B, and is indicated generally by reference numeral 10. In the illustrated embodiment, the coupling assembly 10 is used to couple a swivel castor wheel 12 to an object, in the form of a frame 14 of the trolley, It will be understood that the coupling assembly 10 of the present invention is not restricted to use with supermarket trolleys, and that the assembly has a use with other forms of trolley, including but not restricted to industrial trolleys used for transporting goods, hospital trolleys or wheeled stretchers used for transporting patients, as well as with wheelchairs and handcarts. Typically, at least the rear wheels of the trolley 8 will be swivel castor wheels 12. Front wheels 13 may be fixed orientation wheels, or swivel castor wheels.

As best shown in Figure 2A and 2B, the coupling assembly 10 generally comprises a first coupling component in the form of a male coupling component 18, and a second coupling component in the form of a female coupling component 20. In the illustrated embodiment, the male coupling component 18 is mounted to the wheel 12 of the trolley 8, and the female coupling component 20 is mounted to the trolley frame 14. However, the male coupling component 18 may equally be mounted on the trolley frame 14 and the female coupling component 20 on the wheel 12. This is illustrated in the alternative coupling assembly lOa shown in Figures 3A and 3B, like components of the coupling assembly lOa with the assembly 10 of Figures 2A/2B sharing the same reference numerals, with the addition of the suffix a'. In this embodiment, a male coupling component 1 8a is shown mounted to the trolley frame 14 and a female coupling component 20a to the wheel 12.

The female coupling component 20 of the assembly 10 receives the male coupling component 18 so that the coupling components can rotate relative to one another, about a common rotation axis 22. This facilitates adjustment of the orientation of the wheel 12 relative to the trolley frame 14, so that the trolley 8 can be steered across a surface 16. The male and female coupling components 18 and 20 are arranged so that, in use, the coupling components are biased under the action of gravity towards at least one predetermined rotational orientation relative to one another, to provide a directional bias in the orientation of the wheel 12 with respect to the trolley frame 14, and consequently in the direction of travel of the trolley frame (and thus the trolley 8) across the surface 16.

Arranging the male and female coupling components 18 and 20 so that they are biased towards at least one predetermined rotational orientation addresses the problems with prior coupling assemblies discussed above. This is because biasing of the coupling components 18 and 20 towards the at least one predetermined rotational orientation has the effect of biasing the wheel 12 so that it assumes a particular orientation relative to the trolley frame 14 (or vice-versa), andlor so that movement of one of the wheel 12 and frame 14 away from a particular orientation rclativc to the other one of the wheel and frame is resisted. This assists movement of the trolley frame 14 (and so the trolley 8) across the surface 16. Furthermore, the coupling assembly 10 provides a simple, inexpensive assembly for coupling the swivel castor wheel 12 to the trolley 8 which provides inbuilt directional stability which is useful to a user, but which does not impede manoeuvrability of the trolley.

By way of example, the coupling components 18 and 20 may be biased towards a rotational orientation in which the wheel 12 and trolley frame 14 are aligned with a desired direction of travel of the trolley frame, to facilitate movement of the frame in that direction. This may assist in overcoming external factors which may otherwise hamper movement of the trolley frame 14 in the desired direction over the surface 16, such as external forces encountered when traversing an inclined slope.

Figure 2A shows the relative rotational orientation of the male and female components 18 and 20 during movement across the surface 16 in a first direction, which may be a forward direction of movement of the trolley 8, as indicated by the arrow X. Figure 2B shows the relative rotational orientation of the male and female components 18 and 20 during movement across the surface 16 in a second, opposite direction, which may be a reverse direction of movement of the trolley 8, as indicated by the arrow Y. The male and female coupling components 18 and 20 are biased towards the rotational positions shown in Figures 2k/B, to provide the required directional bias in the orientation of the wheel 12 relative to the trolley frame 14. Thus in the illustrated embodiment, there are two predetermined rotational orientations of the male and female components 18 and 20 relative to one another, corresponding to forward and reverse directions of movement, X and Y, of the trolley 8.

Whilst the coupling assembly 10 of the illustrated embodiment provides two such rotational orientations, it will be understood that only one, or more than two rotational orientations may be provided.

The coupling assembly 10 will now be described in more detail, with reference also to Figure 4A, which is an enlarged perspective view of the male and female coupling components 18, 20 of the coupling assembly of Figures 2AIB. It will be understood that the illustrated features may also apply to the coupling assembly I Oa of Figures 3A/B, suitably inverted.

The female coupling component 20 typically takes the form of an elongate, hollow tube which has an open end 30, and a closed end 32 opposite the open end. The open end 30 of the female coupling tube 20 receives an end 36 of the male coupling component 18, so that the male coupling component can be mounted within the female tube. Typically, the male coupling component 18 will also be an elongate hollow tube, for reasons of weight/material saving, but it will be understood that the male component need not be hollow and could be substantially solid. The female coupling tube 20 is mounted on the trolley frame 14 in a suitable way, typically by welding. The male coupling tube 18 is mounted on the castor wheel 12, and is typically mounted on a spigot or shaft (not shown) of the wheel. In this way, when the male coupling tube 18 is coupled to the female coupling tube 20, the male tube 18 and wheel 12 can rotate in unison, relative to the female tube 20, so that a rotational orientation of the wheel 12 relative to the trolley frame 14 can be adjusted.

The ends 32, 36 of the coupling components 20, 18 form surfaces 48, 50 which may be abutment surfaces that can abut or engage when the female coupling component 20 is coupled to the male component 18. A bearing, bearing elements and/or lubricant (not shown) may be provided between the surfaces 48 and 50. For example, a plurality of ball bearing elements may be provided, captured between the surfaces 48 and 50. The coupling components 20, 18 are able to rotate relative to one another about the common rotation axis 22, by sliding contact between the abutment surfaces 48 and 50 (or via the bearing/bearing elements, as appropriate). The rotation axis 22 is disposed transverse to, and typically substantially perpendicular to, the direction of travel of the trolley 14 across the surface 16, and indeed relative to the surface itself. In addition, the abutment surfaces 48, 50 are disposed generally transverse and typically substantially perpendicular to the rotation axis 22.

The abutment surfaces 48 and 50 are matching and/or complementary in shape so that, under the action of gravity and by a reduction in a height of the coupling assembly 10, the male and female components 18 and 20 are automatically biased towards the at least one predetennined rotational orientation. This may serve to energise directional alignment and stability to the swivel castor wheel 12, achieved by action of gravity alone.

As can be seen in Figure 4A, the abutment surfaces 48, 50 are shaped so as to complement one another, to facilitate sliding contact between the abutment surfaces, and biasing of the coupling tubes 18 and 20 towards a particular orientation. To this end, the abutment surface 48 of the female coupling tube 20 is shaped so that it defines a cam surface, with two lobes/peaks 54 and two troughs 52 spaced 180° apart around a circumference of the abutment surface 48. The lobes 54 extend out of a plane 55 which is disposed perpendicular to the rotation axis 22, and which intersects with the troughs 52. The abutment surface 48 may be essentially concave, as shown in Figure 4A, or may be essentially convex, as shown in the alternative embodiment of Figure 4B.

The abutment surface 50 of the male coupling tube 18 complements the abutment surface 48, S and so similarly defines a cam surface. The abutment surface 50 has two lobes/peaks 56 which extend out of a plane 57, and two troughs 58, spaced 180° apart around the circumference of the abutment surface 50. The abutment surface 50 is essentially convex, as shown in Figure 4A, but may be essentially concave as shown in the alternative embodiment of Figure 4B.

Upon rotation of the coupling tubes 20, 18 relative to one another about the rotation axis 22, the abutment surfaces 48, 50 co-operate to define two predetermined rotational orientations in which the two lobes 56 of the male coupling tube 18 are located within the two troughs 52 of the female coupling tube 20. Similarly, the two lobes 54 of the female coupling tube 20 are located within the two troughs 58 of the male coupling tube 18. In this way, two predetermined rotational orientations of the coupling tubes 18 and 20 are defined, spaced 180° apart. This has the effect of creating a directional bias in the orientation of the wheel 12 relative to the trolley frame 14, under the action of gravity and through a change in height of the assembly 10, as the wheel 12 and male coupling tube 18 rotate in unison about the rotational axis 22.

Typically, the male and female tubes 18 and 20 will be positioned on the trolley frame 14 and wheel 12 so that the lobes 54, 56 cooperate with the respective troughs 58, 54 to provide an appropriate directional bias in the wheel/frame orientation. For example, the lobes 54 on the abutment surface 48, and the troughs 58 on the abutment surface 50, may be aligned along the forward!reverse directions of travel X-Y of the trolley 8. In addition, the wheel 12 may be mounted to the male tube 18 in such a way that a plane of the wheel 12 is parallel to the direction of travel X-Y, when the lobes 54, 56 and troughs 58, 54 are so oriented.

The cam shape of the abutment surfaces 48 and 50 is such that the lobes 56 are effectively biased towards the troughs 52, and the lobes 54 towards the troughs 58, which has the effect of directionally biasing the wheel 12 so that it is aligned with the direction of travel X or Y (depending on whether travelling forwards or backwards). It will be understood that the biasing effect is achieved as a result of a load of the trolley 8, imparted on the abutment surface 48, and transferred to the surface 50, acting in the direction of the rotation axis 22.

This has the effect of affording directional stability to the trolley 8, particularly when heavily laden and being pushed across a gradient, for example, in a supermarket car park. Transition of the lobes 54, 56 between the respective troughs 58, 52 is facilitated by means of respective inclined ramp portions 55 and 59 on the surfaces 48, 50.

It will be readily understood that there may be more than two lobes and two troughs spaced around the circumference of the abutment surfaces 48, 50. The number of lobes/troughs may define the number of predetermined rotational positions. For example, an arrangement of four lobes and troughs on each surface (not shown) would provide four predetermined rotational orientations, and so four biased positions of the wheel 12 relative to the trolley frame 14.

In a variation on the embodiments of Figures 2MB and 3AIB, an assembly may be provided which comprises an arrangement of a protrusion and a recess which cooperate to define the predetermined rotational orientations, instead of lobes and troughs. Thus turning now to Figure 5, there is shown a perspective view of a coupling assembly lOb in accordance with another embodiment of the invention. Like components of the coupling assembly lOb with the assembly 10 of Figures 2A12B share the same reference numerals, with the addition of the suffix b'.

In this embodiment, a protrusion 62 is provided on an abutment surface 50b of a male coupling tube 1 8b. The protrusion 62 is elliptically shaped, to complement an elliptically shaped recess 60 in an abutment surface 48b of a female coupling component 20b, which receives the protrusion. This is best shown in the plan view of Figure 5A. The protrusion 62 and recess 60 are arranged so that centres of the protrusion 62 and recess 60 are each positioned at the centre of the abutment surfaces 48, 50 and so disposed on rotation axis 22b.

The elliptical shapes of the protrusion 62 and recess 60 are such as to defme two rotational orientations for the male and female tubes 1 8b, 20b which are spaced 1800 apart. The protrusion 62 is also rounded, to facilitate engagement of the protrusion within the recess 60, when the male and female components 1 Sb and 20b are rotated to the appropriate orientation.

It will be understood that the provision of a protrusion and recess of different shape will provide for a different number of rotational orientations. For example, a generally egg-shaped protrusion (in plan view) and recess may provide a single rotational orientation, whilst a generally square shape would provide four rotational orientations. Equally, whilst the protrusion is shown on the male coupling tube, and the recess in the female coupling tube, it will be understood that the protrusion may be provided on the female tube and the recess on the male tube.

Figure 6 shows a coupling assembly lOc, which is essentially a variation on the assembly lOb of Figure 5. Like components of the coupling assembly lOc with the assembly 10 of Figures 2A!2B share the same reference numerals, with the addition of the suffix c'. In this embodiment, a male coupling tube I 8c defines a planar abutment surface 50c, and a female coupling tube 20c defines a complementary planar abutment surface 48c. The surfaces 48c and 50c are inclined relative to a rotation axis 22, and define a single rotational orientation for the coupling components 48c, 50c and so directional bias for the swivel castor wheel 12 relative to the trolley 8 (typically in the forward direction of travel X').

In each of the above described embodiments, the predetermined rotational orientations of one coupling component relative to the other, and hence the directional bias on the direction of travel of the trolley 14, are overcome by the application of sufficient force (torque) to the coupling assembly about its rotational axis. For example, and considering the coupling assembly 10 of Figures 2A1211, moving from the predetermined rotational orientation of Figure 2A to that of Figure 2B involves rotation of the male tube 18 relative to the female tube 20, This requires the application of a rotational force (torque) to the male tube 18, to rotate it about the rotation axis 22. The trailing position of the wheel 12 is such that pulling the trolley 14 backwards at a slight angle to the desired direction of travel Y may impart a torque on the wheel 12, and so the male tube 18, to cause it to rotate towards the next predetermined position. This requires the operator of the trolley 14 to push or pull the trolley in the desired direction with sufficient force to overcome the predetermined rotational orientation of the coupling components 20, 18 relative to one another.

In use, a portion of the weight of the trolley 14 (and of any items carried in the trolley) acts on the coupling assembly 10, as described above. The extent to which the lobes 54, 56 (or protrusions in appropriate embodiments) extend out of the planes 55 and 57, in other words a height' of each lobe/protrusion, may be chosen taking account of the maximum likely load.

For example, a relatively heavy load acting through the abutment surfaces 48, 50 would mean that the lobes 54, 56 (or protrusions) would only be required to extend out of the plane 55, 57 S a relatively small distance, in order to provide sufficient biasing to maintain the tubes 18, 20 in a desired rotational orientation. If, for a given load, the degree of extension of the lobes 54, 56 beyond the planes 55, 57 were made too great, it could be difficult to move from one predetermined rotational orientation to another, as the force (torque) which would need to be applied to the coupling assembly 10 would be too great. Similarly in relation to Fig. 6, an extent of inclination of the surfaces 48c and SOc detennines the torque required to rotate the male and female components 1 8c and 20c relative to one-another.

The coupling assembly 10 may comprise a bearing for reduce friction between the male and female coupling components 18, 20 during rotation, to facilitate movement from one predetermined rotational orientation to another. As discussed above, a bearing, bearing elements and/or lubricant may be provided between the abutment surfaces. Figure 7 shows a plurality of optional ball-type bearing elements 45 positioned between the abutment surfaces 48 and 50. The bearing elements 45 are arrayed across and captured between the surfaces 48 and 50. The bearing elements 45 may be captured by suitably coupling the male and female coupling components 18 and 20 together, to prevent complete separation of the components and so retaining the bearing elements. Figure 7, however, also shows an optional bearing 46 disposed between the internal wall 38 of the female coupling tube 20 and an external surface 44 of the male tube 18. The bearing 46 may be of any suitable type, and so may comprise ball or needle bearing elements (not shown). Although a bearing is shown in Figure 7, it will be appreciated that a friction reducing material, such as an oil-based lubricant, may be used to achieve the same effect. Of course, the lubricant may be provided between the abutment surfaces 48, 50 and/or between the tube surfaces 38, 44.

Various modifications may be made to the foregoing without departing from the spirit or scope of the present invention.

Claims

CLAIMS1. A coupling assembly for coupling a swivel castor wheel to an object which is to be moved across a surface, in which an orientation of the swivel castor wheel relative to the s object can be adjusted in order to change a direction of travel of the object across the surface, the coupling assembly comprising: a first coupling component which can be mounted to one of the swivel castor wheel and the object; a second coupling component which can be mounted to the other one of the swivel castor wheel and the object, the coupling components arranged so that they can rotate relative to one another about a common rotation axis to facilitate adjustment of the orientation of the swivel castor wheel relative to the object; in which the coupling components are arranged so that, in use, they are biased under the action of gravity towards at least one predetermined rotational orientation relative to one another, to provide a directional bias in the orientation of the swivel castor wheel with respect to the object and so direction of travel of the object across the surface.
2. A coupling assembly as claimed in claim 1, in which the coupling components are biased towards a rotational orientation in which the swivel castor wheel and the object are aligned with a desired direction of travel of the object.
3. A coupling assembly as claimed in either of claims 1 or 2, in which the first coupling component is a male coupling component and the second coupling component is a female coupling component, and in which the female coupling component receives the male coupling component so that the coupling components can rotate relative to one another about the common rotation axis.
4. A coupling assembly as claimed in claim 3, in which the female coupling component is substantially tubular comprising an internal wall and an external wall, and in which the coupling assembly comprises a bearing disposed between an external wall of the male coupling component and the internal wall of the female coupling component.
5. A coupling assembly as claimed in any preceding claim, in which the female coupling component comprises an open end for receiving the male coupling component, and a closed end opposite the open end.
6. A coupling assembly as claimed in claim 5, in which the male coupling component abuts the closed end of the female coupling component when the coupling components are coupled together.
7. A coupling assembly as claimed in any preceding claim, in which the first and second coupling components define respective surfaces which are complementary in shape so that, under the action of gravity and by a reduction in a height of the coupling assembly, the components are automatically biased towards the at least one predetermined rotational orientation.
8. A coupling assembly as claimed in claim 7, in which the surfaces are brought into abutment when the coupling components are coupled together.
9. A coupling assembly as claimed in claim 7, in which a spacing element is provided between the surfaces.
10. A coupling assembly as claimed in claim 7, in which a bearing is provided between the surfaces.
11. A coupling assembly as claimed in any one of claims 7 to 10, in which the surfaces are disposed generally transverse to the rotation axis.
12. A coupling assembly as claimed in any one of claims 7 to 11, in which the surfaces are adapted for rotation relative to one another, to facilitate relative rotation between the coupling components.
13. A coupling assembly as claimed in any one of claims 7 to 12, in which the surfaces of the male coupling component and the female coupling component cooperate to define at least one predetermined rotational orientation of the male coupling component and female coupling component relative to one another, to provide the directional bias in the orientation of the swivel castor wheel with respect to the object and so the direction of travel of the object across the surface.
14. A coupling assembly as claimed in any one of claims 7 to 13, in which the surfaces are substantially planar and inclined relative to the rotation axis.
15. A coupling assembly as claimed in any one of claims 7 to 13, in which part of the surface defined by each coupling component extends out of a plane which is disposed transverse to the rotation axis.
16. A coupling assembly as claimed in any one of claims 7 to 13 or 15, in which the surfaces are cam surfaces, each cam surface having at least one peak and at least one trough, a peak on one of the surfaces cooperating with a trough on the other surface to thereby define at least one predetermined rotational orientation of the coupling components.
17. A coupling assembly as claimed in claim 16, in which the surfaces are shaped so as to bias a peak on one surface towards a trough on the other surface, positioning of the peak in the trough defining a predetermined rotational orientation of the coupling components.
18. A coupling assembly as claimed in either of claims 16 or 17, in which there are a plurality of peaks and a plurality of troughs spaced around a circumference of the surface of the respective coupling component, to thereby define a plurality of rotational orientations of the coupling components.
19. A coupling assembly as claimed in any one of claims 16 to 18, in which the surfaces comprise ramp portions extending between a trough and a peak, which bias a peak on one surface towards a trough on the other surface.
20. A coupling assembly as claimed in claim i, in which one of the surfaces defines a protrusion which extends out of said plane, and the other one of the surfaces defines a recess shaped to receive the protrusion, the protrusion and the recess being shaped to define the predetermined rotational orientation of the coupling components relative to one another.
21. A coupling assembly as claimed in claim 20, in which the protrusion and the recess are generally elliptical in shape, providing two rotational orientations spaced 1800 apart.
22. A coupling assembly as claimed in any one of claims 7 to 21, in which the surfaces are load bearing so as to accommodate a portion of the weight of the object, directed along the rotation axis.
23. A coupling assembly as claimed in any preceding claim, in which the axis of rotation of the coupling assembly is disposed, in use, transverse to the surface across which the object is to travel.
24. A coupling assembly as claimed in any preceding claim, in which the wheel defines a wheel plane disposed, in use, transverse to the surface, and in which the rotation axis is disposed in the wheel plane.
25. An anangement of a swivel castor wheel and an object coupled together by a coupling assembly according to any one of claims 1 to 24.
26. An arrangement as claimed in claim 25, in which the object is selected from the group comprising: a supermarket trolley; a hospital trolley; an industrial trolley; a wheeled stretcher; a handcart; and a wheelchair.