GB2220560A

GB2220560A - A brake mechanism in a castor

Info

Publication number: GB2220560A
Application number: GB8812054A
Authority: GB
Inventors: John Verhaeg
Original assignee: British Castors Ltd
Current assignee: British Castors Ltd
Priority date: 1988-05-21
Filing date: 1988-05-21
Publication date: 1990-01-17
Anticipated expiration: 2008-05-21
Also published as: GB2220560B; GB8812054D0

Abstract

A castor comprises a body 10, a wheel 11 which is rotatable relative to the body about axis 12, an attachment member 15 connected with the body 10 for swivelling relative thereto about axis 14 and braking means for braking rotation of the wheel and swivelling of the body 10 relative to the attachment member 15, wherein the braking means is carried by the body 10 for swivelling with the body relative to the attachment member and comprises an interfering element 29 which engages the attachment member 15 to brake swivelling of the body 10 relative to the attachment member, a braking element 16 which engages the wheel, 11, to brake rotation thereof, an operating element 23 movable relative to body 10 by a user, means for transmitting force between the operating element 23 and the interfering and braking elements 29, 16, and a latch 26 for latching the interfering and braking elements in braking engagement with the attachment member 15 and wheel 11, respectively, wherein the latch is movable downwardly relative to the body between a blocking position (Fig. 2) in which the latch 26 positively blocks movement of the interfering 29 and braking 16 elements from their braking engagement and a releasing position (Fig. 1) in which the latch 26 does not block said movement. <IMAGE>

Description

Title: "Castor and method of braking and releasing a castor wheel" Description of Invention From one aspect, the present invention relates to a castor comprising a body, a wheel mounted for rotation relative to the body about a rolling axis, an attachment member connected with the body for swivelling relative thereto about a swivel axis which is transverse tó and is offset from the rolling axis and braking means for braking rotation of the wheel and swivelling of the body relative to the attachment member. Such a castor is hereinafter referred to as being a castor of the kind specified.

The invention is concerned primarily with means for maintaining the braking means of a castor of the kind specified in an operative condition. In GB 2,047,364, there is disclosed a castor of the kind specified in which the braking means includes a lever provided with a cam which acts against an abutment fixed with respect to the body of the castor to displace a slide of the braking means against the action of a leaf spring and set the braking means in an operative condition. Friction between the cam and the abutment impedes return of the braking means to an inoperative condition. GB 1,555,926A also discloses, in figure 5, a castor of the kind specified in which reliance is placed upon friction to maintain the braking means in an operative condition.There is also disclosed in this latter specification an alternative braking means having an over-centre toggle mechanism for setting the braking means in the operative condition. This provides somewhat more convenient and reliable retention of the braking means in the operative condition.

A latch for positive retention of braking means of a castor is shown in Figure 4 of GB 1,377,155. By positive retention, we mean that reliance is not placed upon friction or upon the resilient deformation of components under stress, for example in an over-centre toggle mechanism, for retaining the braking mechanism in the operative condition. The latch disclosed in GB 1,377,155 bears on an abutment to positively hold a braking element in an operative position. To release the braking element, the latch is moved out of engagement with the abutment. However, the braking means disclosed in GB 1,377,155 acts only upon the wheel of the castor and does not prevent swivelling of the castor body relative to the attachment member.

Another arrangement for maintaining the braking means of a castor of the kind specified in an operative condition, but which does not achieve positive latching of the braking means, is disclosed in GB I ,052,78O. The castor disclosed in this specification has a lever which can be rocked between operative and inoperative positions. A spring loaded detent is provided for maintaining the lever in the operative position. When the lever is in the operative position, teeth on the lever mesh with teeth on the attachment member to prevent swivelling of the castor body relative to the attachment member and further elements on the lever engage a tyre on the wheel of the castor to prevent turning of the wheel. The teeth which prevent swivelling are pointed teeth, to facilitate movement of the lever into the operative position.If, when the castor is in a braked condition, the castor is subjected to a large force which tends to swivel the wheel and body relative to the attachment member, or the lever is subjected to force in some other way, the spring loading of the detent may be overcome and the castor inadvertently released from the braked condition.

According to the first aspect of the present invention, the braking means of a castor of the kind specified is carried by the body for swivelling with the body relative to the attachment member and comprises an interfering element which is engageable with the attachment member to brake swivelling of the body relative to the attachment member, a braking element which is engageable with the wheel to brake rotation thereof, an operating element movable relative to the body by a user, means for transmitting force between the operating element and the interfering and braking elements and a latch for latching the interfering and braking elements in braking engagement with the attachment member and the wheel respectively, wherein the latch is movable relative to the body in a direction which is a downward direction when the castor is in use on a horizontal floor between a blocking position in which the latch postively blocks movement of the intefering and braking elements relative to the body from their braking engagement with the attachment member and wheels respectively and a releasing position in which the latch does not block such movement.

With a castor in accordance with the first aspect of the invention, there is no substantial risk of the braking means inadvertently becoming ineffective to brake rotation of the wheel and swivelling of the body, for example as a result of inadvertent application of force to the operating element, whilst the latch remains in its blocking position. In order for the interfering and braking elements to be released for movement from their braking engagement with the attachment member and wheel respectively, it is necessary for the latch to be moved from the blocking position. Thus, the braking means of a castor in accordance with the invention maintains the braked condition of the castor more reliably than do the resilient detent, the over-centre mechanism and cam mechanism which are relied on in the known arrangements hereinbefore mentioned.

Movement of the latch in the downward direction from the blocking position to the releasing position can be effected conveniently. In contrast with this, the latch disclosed in GB 1,377,155 is released by an upward pivoting movement, which is less convenient. A further latch for the braking means of a castor is disclosed in GB 2,147,802A, but upward movement of an element by the user is necessary to release the braking means of this arrangement also.

The latch of a castor in accordance with the present invention preferably protrudes above the operating element when the latch is in the blocking position and the braking element is in braking engagement with the wheel. The latch preferably protrudes by a distance exceeding one fifth of the travel of the operating element. Downward movement of the latch relative to the operating element until the latch is substantially flush with the operating element may be necessary, in order to release the operating element.

In the preferred castor, the latch is biased upwardly from its releasing position to its blocking position and has means for entraining the operating element when the latch moves from its releasing position to its blocking position. With this arrangement, the latch will automatically return the operating element to a raised position, once the operating element is unlatched.

According to a second aspect of the invention, there is provided a method of braking and releasing a castor wheel wherein an operating element is moved downwords with or relative to a latch until the operating element is latched by the latch in a lowered position, the downward movement of the operating element is transmitted to a braking element and the braking element engages the wheel to brake rotation thereof and wherein the latch is subsequently moved downwards relative to the operating element, the operating element is released from its lowered position, the operating element moves upwards and the upward movement of the operating element is transmitted to the braking element to move same out of braking engagement with the wheel.

An example of a castor embodying the first aspect of the invention and which is used in a method according to the second aspect of the invention will now be described, with reference to the accompanying drawings, wherein: FIGURE I shows diagrammatically a vertical cross-section through a castor with braking means of the castor in an inoperative condition; FIGURE 2 shows a similar diagrammatic representation of the castor with the braking means in an operative condition; and FIGURE 3 shows a perspective view of a braking element of the castor.

The castor illustrated in the drawings comprises a body 10 having a pair of limbs which are spaced apart and between which there is disposed a wheel I I of the castor. The wheel is connected with the body by means of an axle which passes through respective openings in lower end portions of the limbs of the body and the wheel is rotatable relative to the axle about a rolling axis 12, which is normally horizontal, when the castor is in use on a horizontal floor. The limbs depend from a bridging portion 13 of the body in which there is formed a circular aperture centered on a swivelling axis 14 of the castor.

An annular portion of the castor body which borders the aperture in the bridging portion 13 is trapped between upper and lower portions of an attachment member 15. As shown, boll bearings may be interposed between these portions of the attachment member and the bridging portion of the body so that the body is connected with the attachment member for free rotation relative thereto about the swivelling axis 14. The swivelling axis is offset from the rolling axis 12 and would normally be upright, when the castor is in use on a horizontal floor. The attachment member 15 is adapted, in a manner not illustrated, to be fixed with respect to an article (not shown) to be supported by the castor. Typically, four castors will be provided on a common article.

The castor further comprises braking means which is carried by the body 10 for swivelling with the body relative to the attachment member IS.

The braking means includes a braking element 16 which is disposed in a tapering gap between the wheel II and the underside of the attachment member 15. The braking element has a surface 17 which faces towards the rolling axis 12 and which is adapted to grip the peripheral surface of the wheel II. For example, the surface 17 may include a number of ribs arranged with their lengths at least approximately parallel to the rolling axis.

The braking element 16 is preferably a rigid component; whereas the wheel may have a resiliently deformable tyre. As viewed from the side of the castor body, the braking element 16 has the form of a wedge with an elongated tail 18. The braking element may be of substantially solid form.

However, as shown in Figure 3, the braking element is preferably hollow, in order to reduce the amount of material in the braking element. The wedgeshaped form may be confined to opposite flanges of the braking element, a relatively thin web 19 extending between these flanges and presenting the surface 17 towards the wheel.

The braking means further comprises a lever 20 which is connected with the body 10 for pivoting relative thereto about a pivot axis 21 parallel to but spaced from the rolling axis 12. The pivot axis is preferably spaced from the rolling axis by a distance which does not exceed the radius of the wheel I I.

Thus, the lever 20 preferably comprises opposite flanges, one of which is shown at 22, which lie at opposite sides of the wheel 11 adjacent to respective ones of the limbs of the body 10. Conveniently, the flanges of the lever lie partly between the limbs of the body.

The lever 20 further comprises a bridging portion which extends between the flanges of the lever and which is spaced further from the rolling axis 12 than the radius of the wheel I I. A part of the bridging portion which lies furthest from the pivot axis 21 constitutes an operating element 23 and carries at its underside a housing 24 for an adjustment screw 25. The operating element has a surface which faces generally upwardly, is somewhat wider than the wheel II and has a length which is approximately equal to its width. This upwardly facing surface is readily accessible by a user and is suitable to receive a downwardly directed force exerted by the foot of a user.

The lever 20 also is a rigid component of the castor and is conveniently formed of sheet metal by a pressing and piercing operation. There is in the bridging portion of the lever 20 adjacent to the operating element 23 and lying between that element and the attachment member 15 an opening through which a latch 26 can protrude, in proximity to a free-end of the adjustment screw 25. The latch is a generally "L"-shaped portion of a further component 27 of the castor, which component includes a central portion 28 which is fixed with respect to the bridging portion 13 of the castor body, for example by riveting. An end portion of the component 27 which is remote from the latch 26 constitutes an interfering element 29 and is adapted for cooperation with the attachment member 15 to interfere with swivelling of the body 10 relative to the attachment member.The component 27 of the castor is formed of a resiliently flexible material, for example spring steel, so that the latch 26 and the interfering element 29 can undergo limited movement independently of one another relative to the central portion 28.

The interfering element 29 extends from the central portion 28 of the component 27 beneath the underside of the attachment member 15 and terminates in upwardly projecting teeth 30 which lie at opposite sides of the swivelling axis 14. There is formed on the underside of the attachment member 15 an annular row of teeth 31 spaced from the swivelling axis by substantially the same distance as the teeth 30 are spaced from that axis.

Thus, the attachment member is adapted to receive the teeth 30 between appropriately positioned ones of the teeth 31. To facilitate engagement of the teeth 30 between the teeth 31, the latter teeth are of pointed form. In the unstressed condition of the component 27, the teeth 30 are spaced downwardly from the teeth 31 so that swivelling of the castor body so that there is no interference with swivelling of the castor body and wheel.

There are provided on the tail 18 of the braking element 16 formations 32 which protrude in opposite directions from the tail through respective apertures formed in the flanges of the lever 20 to couple the braking element with the lever at a position spaced upwards from the pivot axis 21. There is freedom for limited pivoting of the tail 18 relative to the lever 20 about an axis parallel to the rolling axis 12 and the, formations 32 may be pivots.

These formations are adapted to transmit between the tail and the lever forces acting in opposite directions tangential to the wheel I I. The axis defined by the formations 32 lies further from the rolling axis 12 than does the axis 21.

The resilient component 27 includes a limb 33 which depends from the central portion 28 into the path of travel of the braking element 16 during rocking of the lever 20. When the braking means is in the inoperative condition and the components are in the position of Figure I, the limb 33 is unstressed. When the operating element 23 is pivoted downwardly to the position of Figure 2, the braking element engages and flexes the limb 33, so that the limb is stressed and exerts a returning force on the braking element.

The pivot formations 32 are spaced apart by a distance exceeding the width of the wheel 1-1 so that these do not interfere with the wheel. The intervening portion of the braking element 16 remains clear of the wheel.

This intervening portion of the braking element has an upwardly projecting lug 34 which, when the components are in the position illustrated in Figure 1, bears against a surface of the body 10 facing away from the swivelling axis 14 so that the lug limits pivoting of the braking element relative to the body in an anti-clockwise direction, as viewed in Figure 1, and so maintains the braking surface 17 clear of the wheel II. When the components are moved to the position of Figure 2, the lug 34 moves away from this surface of the body so that it no longer restricts pivoting of the braking element relative to the body.

An aperture 35 is formed in the latch 26 by punching a tongue 36 into a perpendicular attitude relative to an adjacent part of the latch. The aperture 35 is sufficiently large to receive an end portion of the adjustment screw 25 with clearance and the tongue 36 provides a seat on which the screw bears so that downward pivoting of the lever 20 relative to the latch 26 is prevented, whilst the end portion of the screw occupies the aperture 35. Whilst the end portion of the screw 25 occupies the aperture 35, it couples the lever 20 and the latch 26 together so that substantial movement of one of these components relative to the other is prevented. It will be appreciated that a non-adjustable projection may be substituted for the screw 25, although the.

provision of an adjustable projection is advantageous.

When the braking means is in the inoperative condition illustrated in Figure I, an upwardly facing surface of the latch 26 is substantially flush with the upwardly facing surface of the operating element 23. The operating element lies, however, further from the attachment member 15 than does the latch, so that a user can bear downwardly on the operating element by means of his foot, without bearing directly on the latch. With the castor in the condition of Figure I, the latch 26, interfering element 29 and limb 33 are all substantially unstressed.

In order to establish the operative condition of the braking means, the user exerts downward pressure on the operating element 23 to swing the operating element downwardly about the pivot axis 21. Owing to coupling of the lever 20 and latch 26 together by the projecting screw 25, the tongue 36 is carried downwardly with the operating element and the latch 26 is flexed so that it exerts a returning force on the operating element.

As the operating element 23 is moved downwardly, the screw 25 is withdrawn from the aperture 35 because the pivot axis 21 is spaced a considerable distance below the latch 26. As the screw leaves the aperture, the latch returns to the position of the latch illustrated in Figures I and 2, which is called herein the blocking position. When the latch assumes the blocking position, the free-end of the screw 25 bears against a surface 37 of the latch below the aperture 35, this surface facing along the screw and preferably being at right angles to a longitudinal axis of the screw and parallel to an end face of the screw.

As the operating element 23 moves into the lowered position illustrated in Figure 2, the braking element 16 is drawn to the right, as viewed in Figures I and 2, that is in a direction from the wider part of the gap between the periphery of the wheel and the attachment member 15 towards the narrower part of that gap. The interfering element 29 rests on upwardly facing surfaces of the flanges of the braking element and these surfaces include inclined ramps which are drawn beneath the interfering element to drive the interfering element upwardly in a direction generally along the swivelling axis 14 so that the teeth 30 enter gaps between teeth 31.Concurrently, the braking surface 17 is drawn into engagement with the peripheral surface of the wheel 11. Upward movement of the interfering element 29 is limited by the attachment member 15 so that a considerable force can be exerted on the wheel by the braking element 16. The dimensions of the components are such that the teeth 30 are firmly seated in the valleys between adjacent teeth 31 and the braking surface 17 engages the periphery of the wheel under considerable pressure, before the free-end portion of the adjustment screw 25 leaves the aperture 35 and the latch returns to its blocking position. If one or more components of the castor wears during the service life of the castor compensating adjustment of the screw 25 can be effected to ensure that required pressure is still exerted by the braking surface 17 on the wheel.

Whilst the latch 26 remains in its blocking position, upward movement of the operating element 23 from the position shown in Figure 2 is postively prevented. Upward movement of the operating element can occur only if the adjusting screw 25 penetrates into or through the latch and this is possible only when the screw is aligned with the aperture 35.

It will be noted that, when the operating element is in the lowered position of Figure 2 and the latch is in its blocking position, the latch protrudes upwardly from the operating element by a distance which is equal to the travel of the free-end portion of the adjusting screw 25 during movement of the operating element from the raised position to the lowered position. This distance is in excess of one fifth of the travel of that part of the operating element which is furthest from the pivot axis 21.

If, with the braking means in the operative condition, downward pressure is exerted on the latch 26 to flex the latch until it is substantially flush with the operating element, the aperture 35 is brought into alignment with the screw 25. The latch then no longer blocks upward movement of the operating element 23. The operating element is urged upwardly by the action of the limb 33 on the braking element 16 so that the free-end portion of the screw 25 is urged into the aperture 35. If the latch is then relieved of the downward pressure, it returns to its blocking position. Since the screw 25 is entrained by the latch, the operating element 23 is moved to its raised position and the formations 32 on the braking element are moved towards the swivelling axis 14 to engage the lug 34 with the body 10.Such movement of the braking element allows the interfering element 29 to move downwardly away from the attachment member 15 until the teeth 31 are clear of the path of travel of the teeth 30, during swivelling of the body and wheel relative to the attachment member. The braking surface 17 is moved clear of the periphery of the wheel.

Whilst we prefer to form the interfering element 29, the latch 26 and the limb 33 of a single piece of metal, it will be understood that one or more of these elements may be formed separately and mounted on the body 10.

Furthermore, the interfering element may be integral with the braking element 16. For example, the teeth 30 may be formed on the flanges of the braking element.

In a further modification of the structure illustrated in the accompanying drawings, the braking element 16 and the lever 20 are incorporated in a single component, preferably being formed of a single piece of material. The material used to form this component may be a metal but would more conveniently be a plastics material. In this modified arrangement, the material used to form the member which incorporates the braking element and the lever, the form and the dimensions of this member are selected to provide thot the braking element can undergo limited movement relative to the lever by flexing of the member within the elastic

Claims

CLAIMS: I. A castor comprising a body, a wheel which is rotatable relative to the body about a rolling axis, an attachment member connected with the body for swivelling relative thereto about a swivelling axis which is transverse to and which is offset from the rolling axis and braking means for braking rotation of the wheel and swivelling of the body relative to the attachment member, wherein the braking means is carried by the body for swivelling with the body relative to the attachment member and comprises an interfering element which is engageable with the attachment member to brake swivelling of the body relative to the attachment member, a braking element which is engageable with the wheel to brake rotation thereof, an operating element movable relative to the body by a user, means for transmitting force between the operating element and the interfering and braking elements and a latch for latching the interfering and braking elements in braking engagement with the attachment member and the wheel respectively, wherein the latch is movable relative to the body in a direction which is a downward direction when the castor is in use on a horizontal floor between a blocking position in which the latch positively blocks movement of the interfering and braking elements relative to the body from their braking engagement with the attachment member and the wheel respectively and a releasing position in which the latch does not block said movement.
2. A castor according to Claim I wherein the latch protrudes above the operating element when the latch is in the blocking position and the braking element is in braking engagement with the wheel.
3. A castor according to Claim I wherein the latch protrudes above the operating element by a distance exceeding one fifth of the travel of the operating element when the latch is in the blocking position and the braking element is in braking engagement with the wheel.
4. A castor according to any one of Claims I to 3 wherein the latch is biased upwardly from its releasing position to its blocking position.
5. A castor according to Claim 4 wherein the latch has means for entraining the operating element when the latch moves from its releasing position to its blocking position.
6. A castor according to Claim 5 wherein the latch has an opening, said means for entraining the operating element forms a boundary of the opening and wherein the operating element has a projection which enters the opening when the operating element is released.
7. A castor according to any preceding Claim wherein the operating element is connected with the body for pivoting relative thereto about a pivot axis which is parallel to but is spaced from the rolling axis.
8. A castor according to any one of Claims I to 6 wherein the braking element is connected with the operating element for pivoting relative thereto about an axis which is parallel to but is spaced from the rolling axis.
9. A castor according to Claim 7 wherein the braking element is connected with the operating element for pivoting relative thereto about an axis which is parallel to but is spaced from both the rolling axis and the pivot axis.
10. A castor according to any preceding Claim wherein there is between a peripheral surface of the wheel and a lower face of the attachment member a tapering gap and wherein the braking element lies at least partly in said gap and wherein said means for transmitting force is arranged for moving the braking element along a path which extends transversely of both the swivelling axis and the rolling axis along the gap.
II. A castor according to Claim 10 wherein the interfering element is distinct from the braking element and wherein the braking element engages the interfering element to transmit force thereto from the operating element.
12. A castor according to any preceding Claim wherein the interfering element is integral with the latch.
13. A castor according to any preceding Claim wherein the braking means further comprises a resilient element which is stressed when the braking element and the interfering element are moved into braking engagement with the wheel and the attachment member respsectively.
14. A castor according to Claim 13, as appendant to Claim 12, wherein the resilient element is integral with the latch and the interfering element.
15. A method of braking and releasing a castor wheel wherein an operating element is moved downwardly with or relative to a latch until the operating element is latched by the latch in a lowered position, the downward movement of the operating element is transmitted to a braking element and the braking element engages the wheel to brake rotation thereof and wherein the latch is subsequently moved downwardly relative to the operating element, the operating element is released from its lowered position, the operating element moves upwardly and the upward movement of the operating element is transmitted to the braking element to move same out of braking engagement with the wheel.
16. A method according to Claim 15 wherein after the latch has been moved downwardly to release the operating element, the latch is permitted to move upwardly with the operating element.
17. A method according to Claim 16 wherein the latch is biased to a raised position and raises the operating element when the latch is permitted to move upwardly after release of the operating element.
18. A method according to Claim 17 wherein, prior to latching of the operating element, the latch is initially carried downwardly with the operating element and wherein latching occurs by upward movement of the latch relative to the operating element.
19. A castor having braking means substantially as herein described with reference to the accompanying drawings.
20. Any novel feature or novel combination of features disclosed herein or in the accompanying drawings.