Hospital bed castors
This invention relates to castors, for example for builders’ staging and hospital beds. The castor includes an upright spindle on which wheel-carrying plates are mounted, a wheel having an axle extending through openings in the plates, a wheel braking device, cam means for moving the axle along the openings to and from a braking position, said openings being of constant depth so that the axle has substantially no play and the cam means has cam slots so shaped that movement of the cam plates causes braking device to engage the wheel firmly when not loaded, the load being then shared by the axle and the wheel.
Hospital bed castors comprising a wheel carrying device including an upright spindle, wheel carrying plates spaced apart from each other and carried by the lower end of the spindle, a wheelhaving an axle, said axle extending horizontally through horizontally elongated openings in the plates, a wheel braking surface carried by said device between said plates, a pivot having a fixed axis extending through the axle-carrying plates and saidaxis being parallel with the axle to one side thereof, and cam plates pivoted on said pivot, said cam plates having elongated cam slots extending at a substantial angle to the elongated openings, said slots being engaged by the wheel axle and of suchshape as to move the wheel axle along the elongated openings during pivoting of said cam plates, said axle moving from a position where the wheel is spaced from the braking surface to a position where the wheel is engaged by said braking surface, saidopenings being made of constant depth so that the axle has substantially no vertical play, and the cam slots being shaped in such a manner that movement of the cam plates by the user to the brake-on position causes the braking surface and the wheel to beengaged firmly even when not loaded, the said elongated openings stopping short of passing beneath said braking surface whereby the load is shared by the axle and the surface.
Casters as claimed wherein the braking surface is provided by an abutment which is located at such a position that it contacts the wheel in the brake-on position within the arc taken about said axle and extending from 10° to 80° offset from the top of the wheel on the forward side of the castor, the cam plates having a handle which extends below the abutment.
casters as claimed wherein the braking surface is provided by a bar mounted in the plates and located between them.
casters as claimed wherein the braking surface abutment is located at such a position that it serves as a stop engaged by the handle extending from the cam plates.
This invention relates to castors for use on builders’ staging, hospital beds and other devices that require to be wheeled along at times and locked against movement at other times by braking the wheels of the castors.
casters of this kind forms the subject according to which the castor comprises a wheel carrying device including an upright spindle and wheel carrying plates spaced apart from each other andcarried by the lower end of the spindle, a wheel having an axle, said axle extending through openings in the plates, a wheel braking surface carried by said device and cam plates pivoted on the axle carrying plates for moving the wheel axle along theopenings from a position where the wheel is spaced from the braking surface to a position where the top part of the wheel is engaged by said braking surface, said openings in the plates being elongated on a horizontal line and having adjacent endslocated directly below the vertical axis of the spindle where they are enlarged vertically to give the axle a small vertical play; said cam plates having cam slots therein engaged by the axle and being pivoted on the wheel carrying plates at their endsremote from said enlarged ends of said openings at a point substantially horizontally in line with said horizontal openings.
While this castor has been very successful in practice certain difficulties are sometimes experienced. In particular it is necessary to form said openings with a fairly high degree of accuracy. Moreover, when the braking surface deforms thetyre above a certain load the axle seats on the upper surfaces of the openings and any greater load does not increase the braking force. The braking force depends on the load. Substantially no load is taken on the axle but the load is transmittedthrough the wheel to the ground. If the openings are further enlarged vertically to obtain greater braking load, a wedging action occurs which makes it difficult to release the brake.
According to the present invention the openings are made of constant depth so that the axle has substantially no vertical play and the cam slots are shaped in such a manner that movement of the cam plates by the user to the brake-on positioncauses the braking surface to engage the wheel firmly even when not loaded, the load being then shared by the axle and the wheel.
Thus the cam surfaces of the slots press the wheel directly on to the braking surface. By actual tests we have found that the braking effect is practically the same when the castor is under substantially no load as when it is loaded up to fullload e.g. 600 lbs. whereas with the castor of British Patent 882617 the braking is very effective under high load but is too small at substantially no load to be acceptable in certain conditions especially after some wear on the braking surface. Withthe present invention a greater amount of wear of the braking surface can be tolerated. Wear is also less with the present invention because no relative movement accurs between the braking surface and the wheel after they have been engaged whereas withthe castor of British Patent 882617 some such relative movement does occur e.g. when a workman is getting on and off a light weight staging fitted with the castors.
Preferably the braking surface is provided by an abutment which is provided at such a position that it contacts the wheel (i.e. in the brake-on position) within an arc extending from 10° to 80°, offset from the top of the wheel onthe forward side of the castor i.e. the side of the axle remote from the pivot of the cam plates, the cam plates having a handle which extends below the abutment.
The abutment may be formed by turning down the front part of a plate that connects the wheel carrying plates together, or by a separate bar located below that abutment. The separate bar is preferred especially if the wheel carrying plates areformed integrally by pressing a plate into an approximately U-shaped section; the bar then serving to strengthen and stiffen this plate section.
With this construction a greatly increased braking action has been achieved .