So what exactly are castors?
A support structure for a caster or castors, castors provided with such a support-structure, and a trolley with castors is described. The support structure comprises a first member , a second member that is rotatable with respect to the first member about a pivot axis, and magnetic means that is operable up to a certain torque to restrain movement of the rotatable member from one angular position with respect to the first member. Preferably the magnetic means comprises at least one hair of magnetically co-operable components. Preferably one component of the at least one pair of components is a permanent magnet. In another angular positions without registration of the first and second members free rotation is possible unless and until re-registration occurs.
The present invention relates to a support structure for castors, to casters provided with such a support structure, and to a trolley with castors, especially a manually movable trolley, such as a supermarket trolley, a roll container, or a hospital trolley, but without limitation to same.
The majority of such trolleys, intended for the transport of goods or persons, are normally provided with four castors, each freely rotatable through 360°. In practice, this frequently leads to steering difficulties, either duringrequired straight line movement, or when negotiating a corner or bend.
With a view to providing some steering control it is known to restrain the freedom of rotation of castors by means of a spring loaded pin engaging in a recess, but such control proposals have been subject to minimal adoption.
An aim of the present invention is the provision of an improved support structure for castors, and consequently an improved castor, and an improved trolley with castors.
Accordingly a first aspect of the present invention provides a support structure for castors comprising a first member, a second member that is rotatable with respect to the first member about a pivot axis, and magnetic means that is operable upto a certain torque to restrain movement of the rotatable member from one angular position with respect to the first member.
Conveniently, said one angular position corresponds to a desired registration of the first and second members. In other angular positions the magnetic means may be operable to permit free rotation unless and until re-registration occurs. Additionally or alternatively the magnetic means may be operable to bias the rotatable member into said one angular position when displaced therefrom.
The first and second members may comprise first and second plates. The first and second members may be located in co-axial spaced apart relationship so as to provide mutually facing surfaces. Bearing means may be located between the first andsecond members.
The magnetic means comprises at least one magnet. Preferably the magnetic means comprises at least one permanent magnet. More particularly the magnetic means comprises at least one pair of magnetically co-operable components, which may be theaforesaid first and second members, separate components or at least one separate component. More preferably they are two separate components. When separate components are provided one component of at least one pair of magnetically co-operablecomponents is conveniently mounted with respect to each of said first and second members. More particularly a small air gap between the magnetically co-operable components creates a magnetic flux that provides said restraining effect.
A specific embodiment of the invention provides a support structure for castors, comprising: (i) first and second plates located in co-axial, spaced apart relationship so as to provide mutually facing surfaces, (ii) bearing means located betweenthe plates whereby one plate is rotatable with respect to the other plate, and (iii) one component of at least one pair of co-operable components being mounted on each plate, at least one of which pair of components is a permanent magnet adapted, in oneangular position of the rotary plate with respect to the non-rotary plate, to be brought into registration with a relatively small air gap between adjacent surfaces of the two co-operable components to create a magnetic flux that, up to a certain torquerestrains rotation, and in other angular positions without registration permits free rotation unless and until re-registration occurs.
When the co-operable components are in register, i.e. aligned opposite one another, the magnetic flux restrains rotation of the rotatable member so that, when applied to castors of, for example, a super market trolley, directional stability isachieved assisting steering of the trolley. Also, due to the use of magnetic flux to restrain rotation, there are no contact faces and no parts subject to wear. Clearly, the torque required to exceed the magnetic flux is a factor of the surface area ofthe magnet(s), and the air gap.
A second aspect of the invention provides castors suitable for a manually movable trolley and comprising a support structure according to the first aspect of the invention.
The castor comprises a wheel, roller or other ground engaging rolling element that is mounted rotatably with respect to a support bracket. Conveniently the support bracket constitutes or forms part of the aforesaid second (rotatable) member. Preferably the support bracket is U shaped. Most usually bearing means is provided between the first and second members. Preferably at least one ball or roller bearing is used.
A third aspect of the invention provides a trolley provided with at least one, and preferably four, castors in accordance with the second aspect of the invention.
Most usually the non-rotatable member is attached to a leg of the trolley by a bolt, the head of which engages an outer surface of the rotatable member via a second ball or roller bearing. The trolley may be a super market trolley, a rollcontainer, a patient trolley or any other wheeled conveyance provided with at least one castor for steering purposes. Preferably the trolley is manually movable.
Where provided the aforesaid first and second plates may be circular. Conveniently one of the first and second members, and preferably an upper one of the members, has an annular skirt or rim extending therefrom toward the other one of themembers. More preferably still the skirt shrouds a part of the other member. The skirt preferably encloses the magnetic means.
Where a pair of co-operable components is utilized one component of the pair may be a permanent magnet and the other component of the pair may be a ferro-magnetic element. Alternatively, both components of the pair may be permanent magnets. Thepolarity of the magnets may be such as to rely on attraction or repulsion to achieve the desired registration of the relatively movable members. The permanent magnets may be disc magnets, bar magnets, ring magnets or any other shape of magnet. Anyferro-magnetic element that is used preferably has a shape that is the same as or complimentary to the shape of the permanent magnet or magnets that are used. The ferro-magnetic element is preferably steel. In one embodiment discs are used for themagnetically co-operable components. In another embodiment the magnetically co-operable components are arcuate, and extend over a limited area in the form of a predetermined quadrant, e.g.