GB2096254A - Twin-wheeled castor; brakes therefor - Google Patents

Abstract

The wheels 13, 14 are mounted on body 10 and an attachment member 19 for mounting the body on an article is movable relative to body 10 about a generally upright swivelling axis 18 which is offset from rolling axis 12 of wheels 13, 14; a braking element 27 is slidably mounted on the attachment member 19 and is movable along the swivelling axis 18 but is constrained against rotation thereabout relative to the attachment member 19, the element being movable to engage the peripheries of the wheels directly or via a brake shoe 35 to prevent rotation of the wheels and swivelling of the body. As shown, the element 27 can rock slightly about axes perpendicular to swivelling axis 18 - it has teeth engageable with teeth 38 on shoe 35. The element 27 has a flange 42 notched to receive a head 41 to hold the castor wheels in a fore-and-aft direction. To adjust for wear, a spacer 23, which may be one of a plurality, is removed. <IMAGE>

Description

SPECIFICATION Twin-wheeled castor Description of invention This invention relates to a castor comprising a pair of wheels mounted on a part of a castor body which lies between them. The invention is primarily concerned with the provision of a brake in this kind of castor.

There is described in British Specification 1,322,260 a castor having a body on which there is pivotally mounted a brake shoe engageable with the periphery of a castor wheel, the castor further comprising a vertically displaceable plunger for urging the brake shoe against the periphery of the wheel to restrain rotation of the wheel. The plunger is restrained against swivelling relative to an article on which the castor is fitted and engagement of the plunger with the brake shoe thus restrains swivelling of the castor body and wheel. However, the brake arrangement disclosed in this published Specification is not suitable for use in a twin wheeled castor wherein the body lies mainly between the wheels.

In Specification 1,477,142, there is disclosed a twin-wheeled castor wherein the body lies between the wheels and wherein there is provided a brake for restraining rotation of the wheels. This brake does not restrain swivelling of the castor body and wheels relative to an article on which the castor is fitted.

A castor according to the present invention comprises a body, two wheels mounted on a part of the body which lies between them for rotation relative to the body about a rolling axis, an attachment member for use in mounting the body on an article, the attachment member being movable relative to the body about a swivelling axis which is generally upright in use and is off-set from the rolling axis, and a braking element which is mounted on the outside of the attachment member, is constrained against rotation about the swivelling axis relative to the attachment member and is movable relative to the attachment member in directions generally along the swivelling axis into and out of engagement either with the peripheries of the wheels or with a brake shoe engageable with the peripheries of the wheels.

Since the braking element is constrained against rotation relative to the attachment element, engagement of the braking element with the wheels, either directly or via a brake shoe, restrains rotation of the body and wheels about the swivelling axis.

An example of a castor embodying the invention will now be described, with reference to the accompanying drawings wherein: Figure 1 shows an elevation of the castor; and Figure 2 shows a cross-section on the line Il- II of Figure 1.

The castor comprises a body 10 in which there is mounted an axle 11 defining a rolling axis 12 of the castor. A pair of wheels, 13 and 14, are mounted on the axle 11 for rotation relative to the body about the rolling axis and the body is disposed mainly between the wheels. An upper part 1 5 of the body protrudes beyond the peripheries of the wheels and has an upwardly presented face which is substantially horizontal when the castor is in use. There extends through the castor body from this face to a lower face 1 6 of the castor a cylindrical bore 1 7 which defines a swivelling axis 18, the swivelling axis being offset from the rolling axis 12 and being substantially upright when the castor is in use.

The castor further comprises an attachment member 19 for use in mounting the body 10 on an article on which the castor is to be used. The attachment member includes a spindle 20 which extends through the bore 17 and is a sliding fit therein. The body 10 is trapped between opposed abutments on the spindle, namely a washer 21 retained by a nut 22 and a spacer 23 abutting a shoulder 24 on the attachment member. An upper end portion of the attachment member 19 is received within a sleeve 25 which is used to mount the castor on an article, for example on the leg of a bed, in a known manner. In use, the sleeve 25 is rigidly secured to the article and therefore the attachment member 1 9 is restrained against rotation relative to the article.For convenience of assembly, the sleeve 25 is split diametrically, the two halves being secured together adjacent to their upper ends by a bolt 43 and adjacent to their lower ends by an annulus 44 which embraces the sleeve just above a radially outwardly projecting flange thereon. Axial displacement of the sleeve relative to the attachment member 19 is restrained by a radially inwardly projecting flange on the sleeve which engages in an annular groove in the attachment member and is further restrained by screws 26 which are used to secure the castor to a hollow leg (not shown) in which the sleeve 25 is received. The screws pass through aligned apertures in the leg and in the sleeve and engage in threaded bores formed in the attachment member 19.

The castor further comprises an annular braking element 27 which is slidably mounted on an intermediate portion of the attachment member which lies between the shoulder 24 and the sleeve 25. There is a substantial clearance between the radially inner boundary of the braking element and the exterior of the attachment member so that the braking element can slide on the attachment member in a direction along the swivelling axis 1 8 and can also rock slightly relative to the attachment member about axes which are perpendicular to the swivelling axis.

For moving the braking element 27 along the swivelling axis 18, there is provided operating means including a cam 28 mounted in the sleeve 25 for rotation about an axis perpendicular to the swivelling axis 1 8 and connected with an arm 29 by means of which a user can rotate the cam. The arm may be a handle. Alternatively, the arm may be part of system for operating the brakes of a set of castors on an article.

That part of the attachment member 1 9 which lies above the shoulder 24 is hollow. The operating means further comprises a plunger 30 disposed within this part of the attachment member and arranged for transmitting motion from the cam 28 to the braking element 27. The plunger is urged upwardly by a coiled compression spring 31 trapped between a head of the plunger and a step in the bore formed in the attachment member. The head of the plunger is maintained in engagement with the cam 28 by the spring 31. The braking element 27 is connected with the plunger by a pin 32, the length of which is at right angles to the swivelling axis 18 and which extends through aligned bores in the braking element and in the lower end portion of the plunger.

The pin 32 extends through a pair of elongated slots 33 formed in the attachment member 19, the length of each slot being parallel to the swiveiling axis 1 8. The pin is received with sliding clearance in the slots 33 so that the braking element 27 and plunger 30 are constrained against rotation about the swivelling axis. The pin 32 may be a fairly loose fit in the plunger 30 so that the pin can rock slightly with the braking element relative to the plunger.

There is mounted on the body 10 for pivoting about an axis 34 parallel to the rolling axis 12 a brake shoe 35. The axis 34 is spaced from the swivelling axis 1 8 in a direction towards or beyond the rolling axis 12 and typically lies directly above the rolling axis. An end portion of the brake shoe which lies adjacent to the axis 34 is fairly narrow and is clear of the wheels 13 and 14. An opposite end portion of the brake shoe is sufficiently wide to overlap with both of the wheels 13 and 14 and is formed with an aperture through which the attachment member 1 9 extends with clearance.

When the braking element 27 is in the intermediate position shown in Figure 2, it is clear of the brake shoe 35 and the brake shoe rests lightly on the peripheral surfaces of the wheels without significantly impeding the rotation of the wheels. Since the brake shoe is mounted on the body, it does not impede movement of the wheels and body about the swivelling axis 18.

By means of the cam, the braking element 27 can be moved downwardly into engagement with the brake shoe 35 to urge the brake shoe into pressure-engagement with the wheels and thereby restrain rotation of the wheels about the rolling axis 12. The braking element is also adapted, when in its lower position, to restrain rotation of the wheels and body about the swivelling axis 1 8 relative to the attachment member 1 9. On the downwardly presented face of the braking element there is provided an annular array of upwardly facing teeth, some of which project directly towards a smaller number of teeth 38 provided on the upwardly facing surface of the brake shoe at one side of the swivelling axis. These teeth mesh when the braking element is in its lower position.At the side of the swivelling axis 18 remote from the teeth 38, there is provided on the upwardly facing surface of the brake shoe a pad 39 which engages the braking element when the braking element is in its lower position. Thus, downwardly directed force is transmitted to the braking element at two diametrically opposite positions.

Use of the castor over an extended period may result in wear of the castor wheels to an extent such that the pressure contact between the brake shoe 35 and the wheels 13 and 14 which can be established by means of the cam 28 is significantly reduced. In this event, an adjustment can be effected by removing the nut 22, washer 21, body 10 and spacer 23 from the spindle 20 and then replacing the body, nut and washer without the spacer. The effect of this will be to adjust the wheels and brake shoe along the swivelling axis 1 8 slightly closer to the cam. If required, during manufacture of the castor, a plurality of spacers may be provided in place of the single spacer 23 so that a selected number of spacers can be removed to effect a selected degree of adjustment.In addition to and adjacent to the spacers, there may be provided a washer to provide a thrust bearing between the shoulder 24 and the body 10.

The castor further comprises a stop 40 which projects upwardly from the castor body 10 through an opening in the brake shoe 35 at a position between the axis 34 of the brake shoe and the attachment member 19. At its end remote from the body, the stop 40 includes a head 41 which projects from the remainder of the stop in a direction towards the swivelling axis 1 8.

The braking element 27 has a radially outwardly projecting flange 42 which can lie beneath the head 41. There are formed in this flange, at diametrically opposite positions, two notches in which the head 41 can be received with slight clearance. The castor would normally be mounted on a bed or other article with the notches in the flange 42 spaced apart from each other in a direction extending along the bed or other article.

With this arrangement, when the head 41 engages in one of the notches, the castor wheels are constrained to the fore-and-aft direction relative to the bed and the rolling axis 12 is maintained perpendicular to the length of the bed.

It will be appreciated that the head 41 can engage in one of the notches in the flange 42 only when the braking element 27 occupies an upper position (not shown) and when that notch is aligned with the head 41 by rotation of the body 10 relative to the braking element 27 about the swivelling axis 1 8. The braking element 27 is urged towards its upper position by the spring 31 but is prevented by the cam 28 from moving to its upper position during normal use of the castor. To permit the head 41 to engage a notch of the flange 42, it is necessary for the cam to be rotated to an appropriate position which allows the braking element to move upwardly from the intermediate position shown in Figure 2.

Generally, where a set of castors is applied to an article, one only of those castors would be provided with a stop 40. It will be noted that, when the head 41 is engaged in a notch of the flange 42, the wheels 13 and 14 are free to rotate about the rolling axis 12.

Whilst we prefer to interpose between the braking element 27 and the wheels 13 and 14 a brake shoe 35, this brake shoe could be omitted.

The braking element would then be arranged to bear directly on the peripheral surfaces of the wheels and thereby restrain both rotation of the wheels about the rolling axis 12 and swivelling of the body and wheels about the swivelling axis 18.

It will be understood that if swivelling of a twinwheeled castor occurs whilst both of the wheels are engaged with a floor surface, some degree of rotation of one or both wheels about the rolling axis must occur. If the braking element is effective to prevent such rotation about the rolling axis, it will inhibit swivelling about the swivelling axis.

Claims (9)

Claims

1. A castor comprising a body, two wheels mounted on a part of the body which lies between them for rotation relative to the body about a rolling axis, an attachment member for use in mounting the body on an article, the attachment member being movable relative to the body about a swivelling axis which is generally upright in use and is offset from the rolling axis, and a braking element which is mounted on the outside of the attachment member, is constrained against rotation about the swivelling axis relative to the attachment member and is movable relative to the attachment member in directions generally along the swivelling axis into and out of engagement either with the peripheries of the wheels or with a brake shoe engageable with the peripheries of the wheels.

2. A castor according to Claim 1 wherein there is provided a brake shoe which is engageable with the peripheries of the wheels and is constrained against rotation relative to the body about the swivelling axis.

3. A castor according to Claim 2 wherein the braking element is adapted to engage the brake shoe at two positions between which the swivelling axis lies.

4. A castor according to Claim 3 wherein the braking element has at one of said positions teeth engageable with teeth on the brake shoe to restrain rotation of the brake shoe and body relative to the attachment member about the swivelling axis.

5. A castor according to any preceding claim wherein the braking element has limited freedom to rock about axes which are perpendicular to the swivelling axis.

6. A castor according to any preceding claim further comprising a removable spacer which is trapped between opposed surfaces of the body and attachment member which face along the swivelling axis.

7. A castor according to any preceding claim wherein there is associated with the body a stop and wherein the braking element can be moved relative to the attachment member in a direction parallel to the swivelling axis into engagement with the stop in a manner to restrain swivelling of the body and wheels relative to the attachment member about the swivelling axis whilst the wheels are free to rotate about the rolling axis.

8. A castor according to Claim 7 wherein the braking element is urged by a spring towards a position in which it is engageable with the stop in said manner.

9. A castor substantially as herein described with reference to and as illustrated in the accompanying drawings.

1 0. Any novel feature or novel combination of features disclosed herein or in the accompanying drawings.