GB2122167A - Safety stop - Google Patents

Abstract

A safety stop, particularly for a vehicle tail lift, has a stop member such as a pawl (7) which is pivotably mounted on a tail lift carriage (2) and is connected to the drive cable (6) for the carriage. A bias mechanism such as a spring (16) normally urges the stop member into braking engagement with a guide column (3) of the tail lift. The stop member pivots away from the column to release the carriage when the requisite traction force is applied through the drive cable. <IMAGE>

Description

SPECIFICATION Safety stop This invention relates to a safety stop for use to prevent undesired relative movement of structures, particularly although not exclusively in the context of a tail lift of the kind (hereinafter referred to as the kind defined) which is provided for use with a road transport vehicle to assist in loading and unloading and which comprises a platform which is mounted so as to be movable upwardly and downwardly on an upright support structure fixed to the vehicle.

Tail lifts of the kind defined find wide application in the road transport industry and may be used regularly with heavy loads. Inevitably therefore there is the possibility of accidents or damage to goods occurring due to undesired movement of the platform for example as a consequence of breakage of the cables conventionally used to lift the platform.

An object of the present invention is to provide means capable of preventing or at least limiting such undesired movement with a relatively simple and inexpensive yet effective and reliable construction.

According to the invention therefore there is provided a safety stop for use with a first structure which can be moved relative to a second structure by application of a traction force to said first structure by a driving mechanism, said safety stop comprising a stop member adapted to be pivotably mounted on said first structure and to be connected to said drive mechanism, and a bias mechanism adapted to urge said member about said pivotal mounting thereof in a direction into engagement with said second structure to break or stop relative movement between the structures, the said application of said traction force to said first structure being arranged to cause said member to pivot in the opposite direction away from said second structure. Preferably the bias mechanism is a spring mechanism.

With this arrangement, in so far as the stop member engages the second structure whenever the traction force is not applied to the first structure, it will be appreciated that the safety stop can provide a fail safe function by stopping or breaking relative movement of the structures in the event of failure of the driving mechanism or associated parts as used in the application of the said traction force. As required, it is also possible for the safety device to be arranged such that it holds or assists in holding the structures in desired attained relative positions for example after deactuation of the driving mechanism. Moreover, having regard to the nature of the stop device this can be constructed simply and inexpensively yet such as to be reliable and effective in operation.

It is visualised that the safety stop of the invention will find particular application in the context of a tail lift of the kind defined wherein said upright support structure thereof defines the said second structure. In this case the arrangement may be such that: said second structure comprises a pair of upright columns fixed to the vehicle on opposite sides of a rear opening thereto, carriages are connected to the platform and mounted respectively on the columns so as to be slidable therealong, said carriages are connected to the driving mechanism via lifting cables, and said stop member of said safety stop is interconnected between one said carriage and a respective said cable. If desired there may be two safety stops one for each carriage.In a preferred embodiment the connection between the stop member and the respective cable is effected via a pivotal mounting and the said spring mechanism acts to urge the stop member to a position at which such pivotal mounting is offset laterally relative to the pivotal mounting of the stop member on the carriage, the application of a traction force via said stop member being arranged to act to move said pivotal mountings into vertical alignment with each other and hence to effect said pivoting of the stop member in the said opposite direction.

The stop member may be directly pivotally mounted on the said first structure or alternatively may be indirectly mounted thereon via a link. In a particularly preferred embodiment the stop member has.opposed stop parts which are arranged for braking or stopping engagement with opposed surfaces of said second structure by jamming against such surfaces. Thus, the stop member may be located within a hollow second structure such as a column as referred to above and the opposed parts thereof may engage opposed inner surfaces thereof. The stop member may be in the form of a pawl having a projecting nosepiece (preferaly sharply tapered) for engagement with the said second structure and, if desired, the said spring mechanism may be arranged to act on this nosepiece. In one embodiment the stop member comprises two plates interconnected in spaced-apart disposition.

The invention will now be described further by way of example only and with reference to the accompanying drawing which is a diagrammatic side view of part of a tail lift incorporating one form of a safety stop in accordance with the invention.

The tail lift is mounted at the rear of a lorry or other road transport vehicle to assist in the loading and unloading of the vehicle through a rear opening thereof.

The tail lift has a pair of vertical columns 1 which are securely fixed to the vehicle at opposite sides of the said rear opening.

Each column is in the form of a channel section member (generally of C-shaped cross-section) and a respective carriage 2 is free to run on wheels along (whilst being held captive within) each column 1. The carriages 2 are connected (in a manner yet to be described) to a driving mechanism (not shown) operable to effect movement of the carriages upwardly and downwardly along the columns between upper and lower limit positions at which a stop or stops on each carriage engages stops on the respective column.

The carriages 2 have brackets at their lower ends (not shown) and respective arms are pivotally mounted on these. The arms support a platform structure which in an operative position thereof extends horizontally outwardly from the columns 1 but which can be pivoted upwardly with the said arms to a stowed position at which the platform structure and arms extend vertically and lie against the columns, a releasable locking mechanism being provided for retaining such structure and arms in this position.

As shown in the drawing, each column 1 has a back wall 3 (facing the vehicie), two mutually parallel side walls 4 extending at right angles to the back wall 3, and lips 5 extending towards each other parallel to the back wall 3 from the inner sides of the front edges of the side walls 3. Most of the respective carriage 2 is contained within the confines of the column walls 3-5 but a part (which carries the aforesaid brackets) projects beyond the column 2 at the front thereof through a gap defined between the lips 5.

The top end of that part of the carriage 2 which is within the confines of the column walls 3, 5 is joined to a lifting cable 6 via a pawl member 7 and a link member 8 all contained within the column 1. The cable 6 extends vertically upwardly along and within the column 1 and is connected to the said driving mechanism which comprises a motordriven winch or other device.

The pawl member 7 comprises two identical shaped plates 9 disposed side by side in slightly spaced-apart disposition. The plates 9 are joined by two pivot pins 10, 11 securely fixed to the plates 9 and extending at right angles thereto. One pivot pin 10 is located adjacent an upper extremity of the plates 9 and an eye member 12 fixed to the end of the cable 6 is mounted on this pin so as to be pivotable axialiy relative thereto. The other pivot pin 11 is located adjacent a lower extremity of the plates 9 and the link member 8 is mounted on this. The said link member 8 comprises a bar having eyes respectively at opposite ends which eyes are mounted respectively on the said lower pin 11 and on a pivot pin 13 fixed to the top end portion of the carriage 2 so as to be rotatable relative thereto.The plates 9 have nosepieces 14 which project at the rear i.e. towards the back wall 3, and which are tapered to hardened tips. The plates also have curved edges 1 5 opposite the nosepieces 14 and adjacent the lips 5.

A spring mechanism 1 6 is mounted on the top end of the carriage 2 beneath the projecting nosepieces 14, such mechanism 1 6 comprising a helical spring 1 7 supported on a fixed spigot 1 8 and acting to press against the nosepiece 14, via the intermediary of a contact member 1 9 such as to tend to rotate the pawl member 7 about the pin 11 (anticlockwise as shown in the drawing) until the tips of the nosepiece 14 engage the inner surface of the backwall 3, the axis of the pin 10 is offset laterally (towards the open front of the column) away from the vertical plane containing the axis of the pin 11, and the curved edges 15 engage the inner surfaces of the lips 5.

In use, with the platform structure in its operative position, such structure can be moved upwardly and downwardly to facilitate loading or unloading of the vehicle by lifting or lowering the carriages 2 as appropriate respectively by applying a controlled traction force thereto by winding up the cables 6 with the driving mechanism and by releasing the cables in controlled manner by unwinding same.

Whenever the cables 6 are in tension (i.e.

whenever they are supporting the weight of the platform structure and any load thereon whether in the lifting or lowering condition) the pawl 7 will be pivoted about the pin 11 (clockwise as shown in the drawing) against the action of the spring mechanism 1 6 to a position at which the axes of the pins 10, 11 (and also the pin 13) are vertically aligned and the nosepieces 14 and edges 15 are spaced respectively from the back wall 3 and the lips of the column 1.

Whenever the tension in either cable 6 falls to zero or a low value as would be the case in the event of breakage thereof, and as might also be the case if the carriages are held in a desired stopping position by means other than the cables, then the or each pertaining pawl 7 is rotated by the spring mechanism 1 6 to the position shown in the drawing in which the tips of the nosepieces 14 and the edges 1 5 respectively engage the back wall 3 and the lips 5 and therefore brake or arrest falling movement of the respective carriage or carriages. The braking or arresting action of the pawl 7 derives from the tight jamming of same between the back wall which is engaged by the sharp, hardened tips, and the lips which are engaged by the opposite curved edges 1 5 of the pawl plates 9. In this way, even in the case where both cables break when the platform structure is supporting a heavy load it is feasible to stop the platform structure within a drop of no more than say 20 mm. The arrangement described can therefore provide an effective and reliable safety function.

It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiment which are described by way of example only.

Thus, for example, in place of the spring mechanism it is possible to use a bias mechanism comprising a counter-weight on a spindle fastened to the pawl 7 and adapted to act in equivalent manner to the spring 17.

Claims (14)

1. A safety stop for use with a first structure which can be moved relative to a second structure by application of a traction force to said first structure by a driving mechanism, said safety stop comprising a stop member adapted to be pivotably mounted on said first structure and to be connected to said drive mechanism, and a bias mechanism adapted to urge said member about said pivotal mounting thereof in a direction into engagement with said second structure to brake or stop relative movement between the structures, the said application of said traction force to said first structure being arranged to cause said member to pivot in the opposite direction away from said second structure.

2. A stop according to claim 1, wherein said bias mechanism comprises a spring mechanism.

3. A stop according to claim 1 or 2, wherein said stop member is pivotally mounted on said first structure via a link.

4. A stop according to any one of claims 1 to 3, wherein said stop member has opposed stop parts which are arranged for braking or stopping engagement with opposed surfaces of said second structure by jamming against such surfaces.

5. A stop according to claim 4, wherein said stop member is located within a hollow second structure and the opposed parts engage opposed inner surfaces thereof.

6. A stop according to any one of claims 1 to 5, wherein said stop member is in the form of a pawl having a projecting nose piece for engagement with the said second structure.

7. A stop according to claim 6, wherein said bias mechanism is arranged to act on said nose piece.

8. A stop according to claim 6 or 7, wherein said nose piece is sharply tapered.

9. A stop according to any one of claims 6 to 8, wherein said pawl comprises two plates interconnected in spaced-apart disposition.

10. A safety stop substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.

11. A vehicle tail lift of the kind defined incorporating at least one safety stop according to any one of claims 1 to 10, wherein said upright support structure defines the said second structure.

12. A vehicle tail lift according to claim 11, wherein said second structure comprises a pair of upright columns fixed to the vehicle on opposite sides of a rear opening thereto, carriages are connected to the platform and mounted respectively on the columns so as to be slidable therealong, said carriages are connected to the driving mechanism via lifting cables, and said stop member of said safety stop is interconnected between one said carriage and a respective said cable.

13. A vehicle tail lift according to claim 12, wherein there are two safety stops one for each carriage.

14. A vehicle tail lift according to claim 12 or 13, wherein the connection between the stop member and the respective cable is effected via a pivotal mounting and the said bias mechanism acts to urge the stop member to a position at which such pivotal mounting is offset laterally relative to the pivotal mounting of the stop member on the carriage, the application of a traction force via said stop member being arranged to act to move said pivotal mountings into vertical alignment with each other and hence to effect said pivoting of the stop member in the said opposite direction.