GB2181343A - Castor brake mechanism - Google Patents

Abstract

A castor has a tubular mounting member (1) rotatably carrying at its lower end a castor body (2) having a fork portion journalling a wheel (4). A brake pedal (5) pivots on the member (1) about a horizontal axis to move a disc-shaped brake element (40) downwardly against the wheel by means of a cam mechanism (21, 31). The brake pedal (5) is thus positioned independently of the angular position of the body (2). The brake element (40) engages the wheel (4) as a position spaced from the rotational axis of the body (2) so as to hold this against rotation. <IMAGE>

Description

SPECIFICATION Castor brake mechanism The invention relates to a castor incorporating a brake mechanism.

Castors normally comprise a bodyjournalling one or two wheels four rotation about a horizontal axis, the body being capable of swivelling about a vertical axis spaced from the horizontal one. In many applications, the castor m ust be bra ked when requiredandthe castor may then carry a lever or pedal which can be operated to apply and release the brake mechanism. It is an inconvenience of prior art castors of this kind that the control lever or pedal is carried by the rotatable wheel-supporting body ofthe castor, so that its position is not fixed relative to the article offurniture supported by the castor, but depends on the angular position taken up by the castor body.

The invention accordingly provides, in a castor comprising a mounting head which can be fixedly secured to an article to be supported by the castor, and a wheel supporting body rotatable on the mounting head, a brake mechanism operated buy a control memberwhich is movablycarriedonthe mounting head. The brake mechanism can thus be operated by movement ofthe control member regardless ofthe angular position of the castor body on which the castor wheel or wheels arejournalled.

The control member is conveniently pivotably carried by the mounting head, preferably so as to pivot about an axis which is horizontal and thus transverse to the normally substantially vertical axis about which the castor body rotates on the mounting head. The control member can be constituted buy a pedal with two arms extending from the pivot axis and including an angle between their upper surfaces of less than 180O.

The brake mechanism can comprise a brake ele ment movable either to engage the castor wheel or wheels, orto engage the ground surface on which they rest. The brake element can move generally vertically, conveniently along the substantially vertical axis about which the castor body rotates on the mounting head. The mounting head can thus slidingly guide the brake element within it, the lower end ofthe brake element being engageable directly with the wheel or wheels. The brake mechanism can thus be carried solely by the mounting head, without having any portion located on the body.

The mounting headcan beconnectedtoanarticleto be supported by the castor, as by being arranged for reception in a recess in the article, for example, the head can betubularfor reception within a hollow bed leg, but the mounting head can instead comprise a horizontal mounting plate. In any event, the brake mechanism can be located substantially entirely belowthe mounting head connections means and/or substantially entirely below the article.

The brake element can be arranged to prevent swivelling of the body on the mounting head in its locking position. If the brake element moves along the substantially vertical axis on which the body swivels relative to the mounting head, it can be arranged to engage the wheel or wheels at a position spaced from this axis, so as to hold the body against swivelling. The brake element may be formed as a disc, a part of periphery of which can be brought into engagement with rim ofthewheel, regardless ofthe angular position ofthe body. The brake disc periphery can be shaped so as to conform to that of the wheel,to ensure good frictional contact.

The wear of the wheel rim and/orthe brake element due to braking can be accommodated by adjustably journalling the wheel orwheel on the body. The or each wheel can thus bejournalled on a shaft received in eccentric bushings which can be rotated and secured in a position corresponding to a desired spatial relation between the wheel and the brake element.

The invention can thus provide a castor having means for selective application of a brake, which are positioned so as to be accessible independently ofthe position of the castor wheel or wheel. The brake mechanism can be carried solely by the mounting means and can be arranged so as not to substantially increasethe castor height over the height of a similar castor without braking means. Where a brake element is engageable with a castorwheel,convenientadjust- mentto accommodatewearcan be provided.

The invention is further described below, by way of illustration,with reference to the accompanying drawings, in which: Figure lisa rear view of a castor embodying the invention; Figure 2 is a fragmentary view of a cam mechanism included in the castor; Figure 3 is a partial side view of the castor, with parts shown in section; and Figure 4 is a plan view ofthe castor.

The illustrated castor comprises a mounting head 1, by which the castor is secured to an article of furniture which it is to support, and a body 2. The body2 is carried at the lower end of the mounting head for rotation about an axis which is substantially vertical in useandincludesaforkportionjournalling wheel 4 for rotation aboutan axiswhich isa generally horizontal and spaced from the vertical axis. The castor includes an operating or control member5 by movementofwhich the castor can be selectively braked against wheel rotation and swivelling.

The mounting head 1 comprises a tubular member 11, for example of steel, for reception in a recess of the furniture article, for example into the lower end of a hollow metal bed leg 12 of a hospital bed.The member 11 and the leg 12 are non-rotatably secured together by suitable fastener means extending through diamet ricallyopposed aligned apertures l4inthemember and the leg.

At its lowerend,thetubular member 11 externally carries the inner race 15 of a ball bearing and has an internal annularflange 16which guidesforaxial movement therein a cam follower 20 having a head portion 21 from which a stem portion 22 of smaller diameter downwardly extends. The cam follower 20 is urged upwardly by a return spring 24 received between the upper end of the flange 16 and the annular surface beneath the cam follower head portion 21.

The lower end ofthe leg 12 abuts against an external annular step formed buy a lower portion of the tubular member 11 1 of greater external diameter about which is carried a plastics casing 30. Diametrically aligned apertures extend through the plastics casing 29 and the member 11 and journalledtherein areend portion 30 of circular cross-section of a shaft having between the end portions a cam portion 31 of segmental cross-section. The portion 31 is of smaller diameter than the portions 30 and the shaft is retained against axial displacement by reception ofthe head portion 21 between these larger diameter portions.

The shaft is part of the control member 5 and carries at one end, externally ofthe casing 29, a two-armed lever of which the two limbs 32 have an angle of about 105 between them. Thetwo limbs 32 extend radially ofthe shaft and expose flat upper surfaces convenient forfoot operation and which may bear appropriate markings as appears from Figure 4.

In the position shown, the arcuate surface ofthe cam portion 31 engages the cam follower head portion 21 which is accordingly held down againstthe return spring 24. By turning the control member 5 aboutthecam portion axisthrough a bout 754 the flat ofthe cam portion 31 overlies the head portion, allowing the cam follower 20to be moved bythe return spring into an upper position.

The body2 comprises an annular portion 35 which surrounds the lower end ofthetubular member 11 and from the underside of which two spaced walls 36 extend downwardly to form afork in which the wheel 4 is journalled. The portion 35 has an internal groove in which is received the outer race 37 ofthe ball bearing.

The body 2 is advantageously an integrally moulded plastics member, the outer race 37 being secured within it during the moulding operation.

The lower end of the cam follower 20 projects beyond the lower end ofthe member 11 and has non-rotationally secured to it a headed pin 39 on the shank of which is retained a braking element in the form of a disc 40 the lower side ofwhich includes an approximatelyfrusto-conical braking surface which is also curved in radial cross-section to correspond at least approximatelyto the outer periphery ofthe wheel 4, which is preferably constituted by a tyre for example of rubber. The braking surface can be radially ridged to enhance frictional engagement with the tyre.

In the position shown, with the cam follower depressed, the brake disc 40 is engaged with the wheel 4 againstthe force of the return spring 24. This braking engagement is effective regardless ofthe angular position ofthe body 2, and thus ofthe wheel 4, aboutthe vertical swivel axis, because whatever the angular position, a part of the non-rotatable brake disc will be engaged with the wheel. The wheel 4 is brakingly engaged at a position spaced from the swivel axis, so the application of the brake not only opposes rotation ofthe wheel, but also swivelling of the body 2 on the mounting head 1.

When it is desired to release the brake mechanism, the control member 5 is turned, about the axis ofthe cam portion 31, conveniently by the action of the operator'sfooton one ofthe limbs 32 in the anti-clockwise direction from the position shown in Figure2toengagetheflatofthecam portion 31 with the cam follower20. The return spring 24 liftsthe cam follower 20, conveniently by some 1.5 mm., so the brake disc 40 rises clear ofthe wheel which can turn freely, as can the body 2 on the mounting head 1.

To accommodate wear ofthe brake disc 40 and of the wheel tyre, the wheel 4 is adjustably mounted on the side walls 36 ofthe body. As appears from Figures 1 and 3,the side walls 36 have alignedapertures receiving bushes 41 provided with diametrically opposed axially extending ridges 42 receivable in upper and upper lower grooves 44 extending axiaily in the side wall apertures. The bushes 41 can consequently be received in either oftwo positions angularly spaced 180 apart. The wheel 4 is journalled on a metal bush 45 on the shankofa bolt46, held in place buy a nut47, and extending through bores in the bushes41 which are offsetfrom the common axes of the bushes.Consequently, the wheel axis may have an upper or a lower position, depending on the orientation chosen forthe bushes 41 Initially, the wheel axis will be in its lower position, at its furthest spacing from the brake disc40. To adjust for wear, the retaining nut 47 is removed from the bolt 46to enable the two bushes to beturned through 180 , afterwhich the nut is restored and tightened. The wheel axis can be raised thereby by, for example, about 1.5 mm. to accommodate wear. The engagement of the bushes 41 with the bush 45 serves to prevent "cold flow" of the material ofthe side walls 36 when these are formed of plastics material, undertightening of the nut47 on the bolt 46.

As will be evident, the invention can be embodied in a variety of ways otherthan as specifically described and shown.

Claims (18)

1. A castor comprising a castor body carried by a mounting head for rotation about a substantially vertical axis,atleastonecastorwheel journalled on the body for rotation about an axis spaced from the vertical axis, and a brake mechanism operable bya control member located relative to the mounting head independently of the angu lar position of the castor body.

2. A castor as claimed in claim 1 wherein the brake mechanism acts by engagement of a brake element with the at least one castorwheel.

3. A castor as claimed in claim 1 wherein the brake mechanism acts by substantially vertical movement of a brake element.

4. A castor as claimed in claim 3wherein the brake element movement is along the substantially vertical axis.

5. A castor as claimed in claim 3 or 4wherein the brake element is movable downwardly from a release position to a braking position of engagementwith the at least one castor wheel.

6. A castor as claimed in any preceding claim wherein the brake mechanism is operable to oppose rotation ofthe castor body on the mounting head.

7. A castor as claimed in claim 5 wherein the brake element is arranged to brakingly engage the at least onecastorwheel art a position laterally spaced from the substantially vertical axis, so asto present rotation ofthecastorbody on the mounting head

8. A castorasclaimed in claim 5 or7 wherein the brake element has an approximatelyfrustoconical braking surface curved in radial cross-section to correspond at least approximately to the shape of the castorwheel.

9. Acastor as claimed in claim 5,6 or 8 wherein the brake element is carried by a cam follower engageable buy a cam rotatable by the control member.

10. A castor as claimed in claim 8 wherein the cam isjournalled by the mounting head to extend trans verselythereof, the control member comprising a lever external to the mounting head and having two arms extending radially ofthe cam axis.

11. Acastor as claimed in claim 9 10 having a spring biassing the brake element to the brake release position.

12. Acastor as claimed in claim 9,10 or 11 wherein the mounting head comprisesatubularmember slidably guiding the cam followerwithin its-lower end and having a bearding for the castor body around its lower end.

13. Acastoras claimed in any preceding claim wherein the mounting head has meansfor connection thereof to an article to be supported by the castor, the brake mechanism being located substantially entirely below the connection means.

14. A castor as claimed in any preceding claim in which the brake mechanism is located so asto be substantially entirely below an article to which thecastor is connected so asto support the article.

15. A castor as claimed in any preceding claim wherein the mounting head is arranged to be received within a recess in an articleto be supported bythe castor.

16. Acastorasclaimed in any preceding claim having means for accommodating wear ofthe brake elementand/orthe castorwheel.

17. A castor as claimed in claim 15 wherein the castor wheel is journalled in eccentric bushes,the angular position ofwhich is selectively adjustable to alterthe spacing of the wheel axis from the brake element to accommodate wear.

18. A castorsubstantially as herein described with reference to the accompanying drawings.