This invention relates to locking devices, and in particular, but without limitation, to locking devices suitable for use with omnidirectional castors.

Omnidirectional castors are used in a variety of situations where it is desired manoeuvre loads over the ground, a floor, or other level or gently sloping surface. An omnidirectional castor, is also known as a "single bearing", a "single ball castor", a "ball transfer device", a "near instantaneous directional ball castor" and an "omni turn ball castor". For simplicity and clarity, they will be referred to from this point on as "ball castors".

A ball castor is a device which employs a single ball that is mounted to roll over a floor surface. The ball is held captive in a cage or socket and is thus free to rotate in any direction. The size of the ball can be selected to meet the load requirements of a particular application, and the tolerances between the ball and cage/socket can be selected to meet the friction and play requirements as well. In certain cases, the ball is held in situ by cooperation with one or more secondary balls, or low-friction pins (e.g. of PTFE), which can reduce friction considerably.

Ball castors offer a number of advantages over conventional castors, namely that they do not have an axle-mounted roller that is mounted on a turntable. With a conventional castor, it is necessary to "track" it so that the axle trails behind the pivot point depending on the direction of travel. This enables a ball castor to respond instantly to a change in direction, and thus overcomes the problem of the castors jamming or needing manipulation to re-align them.

A further advantage of ball castors compared with conventional castors is that the point of contact with the floor remains fixed relative to the cage/socket. As such, load platforms fitted with conventional castors can become unbalanced or "wobbly" depending on the "spread" of the castors at any given time, but moreover, the "wheel base" of the load platform varies, in use, which introduces uncertainty, which is undesirable when transporting fragile items, or people, on the load platform. Ball castors overcome this problem because the "wheel base" is fixed, thus enabling, for a given desired minimum, wheel base, a smaller load platform to be used.

On the other hand, it is relatively straightforward to brake and/or lock a conventional castor by providing an over-centred or spring-loaded pawl that can pivot into engagement with the roller.

However, such mechanisms can be difficult to use where the castor has tracked underneath a load platform to which is it is affixed, thereby making the brake pedal inaccessible. This necessarily requires the load platform to be manipulated to expose the brake pedal, and in any event, where more than one lockable castor is used, the action tracking one of the castors to expose its brake pedal, causes another castor's brake pedal to track out of reach. Therefore, where, say, a locking castor is provided on all four corners of a load platform, it can often be impossible to lock all four of them simultaneously, without the addition of, for example, a cable-actuated braking arrangement.

The same is not true, necessarily, for ball castors because the cage/socket remains (in most cases) in a fixed relationship to the load platform. Thus, regardless of the rotation of the ball, the brake pedal(s) can remain exposed at all times. On the other hand, existing braking systems for ball castors need to be individually locked. As independent locking can introduce delays, proper braking protocols (e.g. ensuring that all brakes are applied before abandoning the load platform) are inevitably skipped, in use, which can lead to safety issues arising.

A need therefore exists for an improved and/or an alternative braking system for ball castors, and/or for load platforms fitted with a plurality of ball castors. According to a first aspect of the invention there is provided a locking system for a plurality of ball castors, each ball castor comprising a ball adapted, in use, for rolling on a surface, and being retained by a cage comprising a cage aperture providing direct access to a portion of the surface of the ball, the locking mechanism comprising a substantially rigid engagement means having a first portion adapted to engage, through the cage aperture, the surface of the ball of a first ball castor, and a second portion adapted to engage, through the cage aperture, the surface of the ball of a second ball castor, wherein, in use, manipulation of the engagement means causes the first and second portions to engage with the balls of the respective ball castors to brake them.

Suitably, because the engagement means is substantially rigid, it will attempt, in use, to centre itself between the first and second ball castors, when manipulated into engagement therewith.

Moreover, should a first one of the balls begin to rotate, the point of contact between the engagement means and the first ball will move, causing the point of contact between the engagement means and the second ball to move in unison. The effect of this is that the "loosening" or disengagement of the engagement means with a first one of the ball castor's balls causes it to engage, and/or bear against, more with a second one of the ball castor's balls.

Suitably, the distance between the first and second portions of the engagement means is less than the distance between the first and second ball centres, but greater than the distance between the diameters of the respective balls. Such a configuration ensures that the engagement means cannot seat atop one of the balls (thus reducing its braking efficacy) or to move past its equator (thus preventing it from "missing" the ball).

In a preferred embodiment of the invention, the dimensions of the engagement means are selected such that the distance I between the points of contact with the balls having a radius r, and a centre spacing d is: l > d - 2r -(1)

and

I < d -(2)

Thus: l = d - 2(r cos 0) -(3) Where Θ is in the range >0° and <90°.

Where the criteria of equation 1 above are met, the locking system of the invention will work because the engagement means will always be in contact with two of the balls in an engageable position. However, the invention has been found to work better where: Θ is in the range 15° to 75°, and best where Θ is in the range 30° to 60°.

The locking system is suitably a braking system for a plurality of ball castors.

The substantially rigid engagement means is suitably adapted for movement relative to the ball castors, and is most suitably adapted to float relative thereto. In one embodiment, such a

configuration can be accomplished by providing an engagement means in the form of a board that is loosely retained within a partial surround, and which is supported, for example, by springs or resiliently deformable members, to float within its surround. In an alternative embodiment, the engagement means can comprise a board that is mounted to a support frame via a block of resiliently deformable material, such as a foamed polymer, that enables the board to move relative to the support frame.

The engagement means can be brought into engagement with the balls by a mechanism, such as a lever, wedge or cam. In an embodiment of the invention, the first and second portions of the engagement means are the corners of a board.

The invention has been found to address the problems associated with known constructions or mechanisms and to allow loads to be moved in any direction easily and smoothly and to be securely and easily locked or braked when desired.

It will be appreciated that the system of the invention would be of great utility in extending the use of the ball castors in many of their applications, such as the industrial uses outlined previously or in such products as pieces of furniture in domestic, commercial or, especially, institutional applications. This will apply whether the furniture is a chair, occupied or not, or some other item such as a cabinet.

As such, it will be appreciated that embodiments of the invention may be applied to a variety of load platforms, such as to trolleys, hospital beds, ambulatory chairs etc.

A second aspect of the invention provides an ambulatory chair comprising a support structure, a plurality of ball castors affixed to the support structure, and a locking system for at least two of the ball castors as described herein.

A third aspect of the invention provides a trolley comprising a support structure, a plurality of ball castors affixed to the support structure, and a locking system for at least two of the ball castors as described herein.

A fourth aspect of the invention provides a load transfer device comprising a support structure, a plurality of ball castors affixed to the support structure, and a locking system for at least two of the ball castors as described herein.

A fifth aspect of the invention provides a bed comprising a support structure, a plurality of ball castors affixed to the support structure, and a locking system for at least two of the ball castors as described herein.

The support structure can, in certain embodiments, comprise the framework of a chair or bed, a loading board, the legs of a furniture item, etc.

The invention will be especially helpful when applied to chairs for disabled or elderly people when, fitted to such a chair, it will remove the need to lift a person from a static armchair to a wheelchair to move them from room to room, or from room to bathroom.

A preferred embodiment of the invention shall now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a schematic side view of a ball castor;

Figure 2 is a schematic side view of a locking system in accordance with the invention in an unlocked state;

Figure 3 is a schematic side view of a locking system in accordance with the invention in a locked state;

Figure 4 is a partial plan view from above of the locking system of Figures 2 and 3;

Figure 5 is a perspective view of an ambulatory chair comprising a locking mechanism in accordance with the invention; and

Figure 6 is a perspective view from the side of the ambulatory chair of Figure 5.

In Figure 1, a ball castor 10 comprises a ball 12 adapted to roll over a surface 14, in the illustrated example, a floor surface 14. The ball 12 is held captive by a cage 16 that partially surrounds the ball 12. The cage 16 comprises one or more through apertures 18 through which an upper part of the ball 12 is accessible. The castor 10 is mountable, in use, to a load platform (not shown) via a mounting bracket (not shown) or a pin 20, which engages with a socket (not shown) on the underside of the platform (not shown) to mount the ball castor 10 securely to it. There are some variations on this precise arrangement, but all follow this general pattern.

In Figures 2 to 4, it can be seen that four ball castors 10 are affixed to the corners of a load platform 22, via respective mounting brackets , which have been simplified in the drawings for clarity. Looking from one side of the platform 22, it can be seen that the castors 10 are located on opposite sides of the platform 22 and a rigid engagement plate 26 is mounted to float relative to the platform 22. The edges of the engagement plate 26 are loosely guided by guides 24, as shown in Figures 2 and 3 to inhibit lateral movement thereof. The engagement plate 26 is formed as a generally rectangular plate (in the illustrated embodiment, although it will be appreciated that its shape and dimensions can be adjusted to meet the design requirements of the system) that is suspended on springs 28 to hang loosely below the platform 22. The springs 28 urge the plate 26 upwards out of engagement with the balls 12, thus allowing them to rotate freely within their respective cages 16, thus allowing the platform 22 to be moved at will.

A cam 30 is interposed between the platform 22 and the engagement plate 26 and comprises an off-centre axle 32. Rotation of the cam 30 about the axle 32 causes it to urge the engagement plate 26, against the action of the springs 28, until the corners 34 of the engagement plate 26 engage with the balls 12 of the castors 10.

Notably, the corners of the engagement plate 26 may engage one of the balls only at first, but further rotation of the cam 30 causes the plate 26 to move laterally, following the surface of the ball 10, until an opposite (or adjacent) corner 34 of the plate 26 engages a respective ball 10, as shown in Figure 3. As such, the engagement plate 26 self-centres between two of the balls 12.

As can be seen in Figure 3, if one of the balls 12 is rotated, i.e. if the platform 22 is urges sideward in the drawing, one of the point of contact (the corner) 34 of the engagement plate 26 with one of the balls may move. However, this simply causes, owing to the rigid construction of the engagement plate 26, the opposite corner 34 to engage more tightly with the opposite ball 10, thus applying a greater braking force to the opposite ball 12, thereby resisting the lateral movement of the platform 22. It will be further appreciated that any attempt to move the platform in any direction will cause some of the corners 34 to 'dig in' to their respective balls 12 such that they will lock the balls 12 tighter the more force is applied.

The illustrated configuration urges the locking plate 26 to come into contact with all of the balls 10 simultaneously, thus providing a reliable braking force to each of the castors 10 simultaneously. The brake can be released by rotating the cam 30 to allow the engagement plate 26 to rise out of engagement with the balls 12, thereby permitting free movement of the balls 12 once again.

It will be appreciated that the function of the cam 30, as shown, could equally be performed by a suitably shaped cam, lever or wedge, or any one of a number of suitable and commonly known mechanical devices.

In Figure 4, it can be seen that the engagement plate 26 is retained by a set of four guides 36 that loosely engage with each of the four sides thereof. Figure 4 also shows a generally square arrangement of the device, and employing four ball castors 10 such as may be suitably fitted to a square platform or beneath a chair. In this view it will be seen that the engagement plate 26 has an extension 38 at each corner, each of which bears upon one ball 12. The extension 38 conveniently allows the corners 34 of the engagement plate 26 to extend easily through the through apertures 18 of the castor's cages 16 to engage with the respective balls 12.

The cam 30 in the version shown is rotated by its being fixed on a shaft or axle which can be rotated by suitable means such as for example, a lever, gear drive or hand wheel mounted on or above the platform in a position easily accessible to an operator.

It will be further appreciated in this view that the braking plate 26 can be of any suitable shape, such as a cross or open framework, providing that the extensions 38 are in the positions shown in this view relative to balls 12, and that there is a substantially centrally positioned bearing surface for the cam 30 to contact and bear down upon, and a suitable number of guides 36 are suitably placed to accurately control the movement of plate 26 relative to the balls 12.

The plate 26 and operating eccentric (cam) with its actuating mechanism may be constructed of any suitably stiff material such as steel or aluminium, or engineering plastics, and the elastic members may be provided by any suitable means, for example tension springs above plate 5, compression springs below plate 5, flexible levers or elastic cords.

An embodiment of the invention, as applied to an ambulatory chair 50 is shown in Figures 5 and 6 of the drawings. Here, it can be seen that the load platform 22 is the underside of the frame of the chair 50. The cam (not visible) is actuated by an axle 32 to extends beyond a periphery of the chair 50, and which terminates in a foot pedal 60 that can be operated conveniently by a user. In the embodiment of Figures 5 and 6 it can be seen that the engagement plate 26 can be manufactured from timber and that the braking mechanism is located above floor level above a line extending between the lower edges of the ball castor's cages 16. This helps to avoid collisions with floor undulations.

Figure 7 shows a variation of the embodiment of Figures 2 to 4, whereby the engagement plate 26 is held in situ by a slab of foam 52. The foam slab 52 serves to constrain the movement of the engagement plate 26, thereby obviating the need for the guides 36 shown in Figure 4, whilst at the same time, providing the necessary resilience to lift the engagement plate 26 out of engagement with the balls 12, when the brake is released.

Finally, Figure 8 shows a schematic corresponding to equations 1, 2 and 3, above.