GB2256414A

GB2256414A - Fall arrest device.

Info

Publication number: GB2256414A
Application number: GB9111150A
Authority: GB
Inventors: Stephen Griffiths
Original assignee: INVETEK PLC
Current assignee: INVETEK PLC
Priority date: 1991-05-23
Filing date: 1991-05-23
Publication date: 1992-12-09
Also published as: GB9111150D0

Abstract

The device comprising a main drum journalled within a housing and carrying a spring biassed lifeline. The housing also includes a sub-shaft (16) carrying a pinion (19), for driving the main drum. The sub-shaft (16) has a threaded end on which is engaged a threaded bushing (28) coupled to a handle (14), the bushing being prevented from winding off the sub-shaft by a spring means (49). Loosely disposed around the sub-shaft (16), between the bushing (48) and a shoulder (24a) and sandwiched between annular friction discs (30, 32) is an annular ratchet wheel (34). Rotation of the handle (14) in one direction causes the bushing (28) to wind onto the threaded part (26) of the sub-shaft so that the ratchet wheel (34) is eventually gripped between the friction discs, to drive the main drum. On the other hand, rotation of the bushing (28) by the handle (14) in the opposite direction initially causes slight winding off of the bush from the threaded pant (26) of the sub-shaft, to release the ratchet wheel (34) followed by rotation of the sub-shaft and hence by the drum. <IMAGE>

Description

DESCRIPTION FALL ARREST DEVICE The present invention relates to fall arrest equipment for protecting operatives working in hazardous locations and is concerned in particular with fall arrest devices of the type wherein a steel or synthetic lifeline is wound on a rotatable drum contained in a hollow metal housing. The lifeline, which in use is attached to an operative, can be withdrawn slowly from the drum and in so doing causes a coil spring in the housing to be wound up. If the tension on the withdrawn lifeline is released, then the spring causes the drum to be rotated so that the lifeline is retracted onto the drum.However, if the speed of withdrawal of the lifeline from the drum exceeds a predetermined rate - as would be the case if the operative had fallen from his working position, then in known arresters of this type the drum is arranged to be brought to a halt so as to prevent the operative from falling further. In some cases, the fall arrest equipment includes a ratchet mechanism on the housing which can be rotated manually by a handle to enable the drum to be turned to wind back the lifeline, and hence the operative secured thereto.

One problem with the latter equipment is that the known ratchet mechanism only enables the lifeline to be retracted back onto the drum in the housing. In some circumstances, it would be desirable not only to be able to wind in the lifeline onto the drum by use of the manual handle but also to be able to allow the lifeline to be paid out from the drum in a controlled manner - for example where an operative who is being raised has to move through a relatively tortuous path, e.g. around scaffolding or out of a pot hole.

It is thus a primary object of the present invention to provide a fall arrest device of the aforegoing type which enables the lifeline to be selectively wound onto or wound off the drum by a manual handle.

According to the present invention there is provided a fall arrest device having a main drum journalled within a housing and carrying a lifeline which can be withdrawn from and returned to the drum against and by a spring, respectively, and further comprising a sub-shaft journalled in the housing and carrying a pinion, rotation of which drives, or can be made to drive, the main drum and hence the lifeline carried thereby, the sub-shaft having a threaded end on which is engaged a correspondingly threaded bushing coupled to a handle, the bushing being prevented from winding off the threaded end of the sub-shaft by a spring means, there being loosely disposed around the sub-shaft, between the bushing and a shoulder on the sub-shaft, or annular ratchet wheel, sandwiched between annular friction discs, the arrangement being such that rotation of the bushing by the handle in one direction causes the bushing initially to wind onto the threaded part of the sub-shaft whereby the bushing is initially displaced towards said shoulder on the sub-shaft so that the ratchet wheel is eventually gripped between the friction discs, further relative displacement of the bush and sub-shaft in that direction thereby being prevented whereby the rotation of the bushing is taken up by the sub-shaft and hence by the drum; and rotation of the bushing by the handle in the opposite direction initially causes slight winding off of the bush from the threaded part of the sub-shaft, sufficient to release the ratchet wheel from the friction discs but limited by said spring means so that additional rotation of the bushing in that direction relative to the sub-shaft is prevented by the spring means and such additional rotation of the bushing by the handle is followed by the sub-shaft and hence by the drum.

The rotation of the bushing in said one direction is arranged to wind in the lifeline onto the drum, the radial wheel engaging a spring loaded pawl on the housing to prevent rotation in the opposite direction during this winding up mode.

Preferably, the sub-shaft is longitudinally displaceable within the housing for engaging and disengaging the pinion on the sub-shaft from its driving connection with the main drum.

Advantageously, the sub-shaft is biassed longitudinally by a coil spring towards its position in which the pinion is in driving engagement with the main drum.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a front perspective view of one embodiment of a fall arrest device fitted with a mechanism in accordance with the invention; and Fig. 2 is a diagrammatic sectional side elevation of the mechanism.

The present invention resides in a mechanism which is incorporated within an otherwise conventional fall arrester and which enables the lifeline 10 to be both wound onto and wound off the usual drum (not shown), contained within the arrester housing 12, by manual rotation of a handle 14 in the appropriate rotational direction.

A conventional fall arrester having the facility for winding the lifeline back onto the drum includes a sub-shaft mounted in the housing parallel to the axis of rotation of the drum. The sub-shaft is keyed to a toothed pinion which in the normal operational state of the arrester lies to one side and clear of a toothed ring carried by the drum. When it is required to place the arrester into a winding mode, the sub-shaft is displaced longitudinally such as to bring the toothed pinion into driving engagement with the toothed ring carried by the drum. One end of the sub-shaft projects from the housing and carries a freely rotatably bush defining a socket for receiving a handle.The bush carries a spring loaded pawl and the sub-shaft carries a toothed pulley which cooperate such that rotation of the bush by the handle in one direction causes the sub-shaft to be rotated in a rotational direction which drives the main drum, via the toothed ring and toothed pinion, so as to rewind the lifeline onto the drum. On the other hand, rotation of the handle in the opposite direction does not transfer any rotation to the sub-shaft by virtue of the one-way action of the spring-loaded pawl and toothed pulley arrangement.

The illustrated embodiment of a mechanism in accordance with the present invention also includes a sub-shaft 16 which is journalled rotatably within the arrester housing 12 and is adapted to be longitudinally displaceable between a first position, in which a toothed pinion 18 keyed to the shaft -16 lies clear of a toothed ring 20 carried by the main drum (not shown), and a second position (see Fig. 2) in which the toothed pinion 18 and toothed ring 20 are in meshing engagement. The shaft 16 is biassed towards the latter position by a spring 17. If the sub-shaft 16 is rotated when in the latter position, such rotation is transferred to the main drum via the meshing pinion 18 and ring 20.

The sub-shaft 16 extends out of the housing 12 via a housing aperture 22. Outboard of the housing aperture 12, there is rigidly fixed to the sub-shaft 16 a disc 24 having a first portion 24a of relatively large diameter and a second portion 24b of smaller diameter. Outboard of the disc 24, the sub-shaft 16 is formed with a coarse left-handed screw thread 26 which extends to the end of this shaft. In screwthreaded engagement with the thread 26 is a correspondingly screw-threaded bush 28 having a main portion 28a of diameter larger than that of the portion 24a of the disc 24 and a minor portion 28b of diameter corresponding to that of the portion 24b of the disc 24. Disposed loosely around the smaller diameter portion 24b of the disc 24 is a first annular braking ring 30 made of a friction (brake) pad material.Disposed loosely on the smaller diameter portion 28b of the bush 28 is a second, identical braking ring 32. Also disposed loosely on the smaller diameter portion 28b of the bush 28 between the annular brake pads 30, 32 is an annular ratchet ring 34 which is engaged by a spring biassed pawl 36, pivotally mounted to the main housing 12 at 38. The handle 14 is connected to a flanged portion 28c of the bush 28 by screws 40. Finally, a locking screw 44 is received within a screw-threaded axial blind bore 42 in the outboard end face of the bush 28 remote from the bush portion 28b, there being disposed between the head of the screw 44 and the adjacent end face 46 of the bush 28 a Belleville washer 48.

The aforegoing mechanism operates as follows.

When the shaft 16 is displaced such as to separate the toothed pinion 18 from the toothed ring 20, then the present mechanism is in its non-operational mode and the arrester works in its conventional manner wherein the lifeline 10 can be withdrawn from and returned to the drum against and by the main spring, respectively.

The operational mode of the mechanism is obtained by bringing about the meshing engagement of the pinion 18 and ring 20 by release of a spring-loaded plunger 21.

If then the lifeline has been paid out by the main drum and it is required to wind it back onto the drum, the handle is turned manually in an anti-clockwise direction, as viewed in the direction A in Fig. 2.

This rotation of the handle 14 firstly causes the bush 28 to be wound onto the threaded part 26 of the shaft 16 as a result of the left-hand thread, whereby to displace the friction ring 32 laterally against the ratchet ring 34, and the ratchet ring laterally against the friction ring 30, until the ratchet ring becomes firmly gripped between the friction rings 30, 32 and thereby located relative to the bush 28 and disc 24. Further anti-clockwise rotation of the handle then causes all of the latter components, and hence the sub-shaft 16, to be rotated such as to drive the main drum, via the pinion 18 and ring 20, in a direction to wind the lifeline back on to the drum. A person suspended by the lifeline is thereby raised as the handle is turned.This rotation also causes the ratchet ring 34 to turn relative to the pawl 36, the pawl 36 being effective to prevent rotation of the drum in the opposite direction under those conditions.

However, should it be desired to lower the person on the lifeline, i.e. to wind the drum in the opposite sense, then the rotation of the handle is simply reversed. The first slight turn of the handle in the clockwise direction causes the bush 28 to wind back slightly along the thread 26 sufficient to release the ratchet ring 34 from the friction rings 30, 32 so that the latter ring 34 remains in its position relative to the pawl 36. However, the bush is prevented from winding off the thread 26 any further by virtue of the Belleville washer and, once this small winding back has taken place, any further clockwise rotation of the handle and bush 28 causes the sub-shaft 16 to be similarly rotated by virtue of the effectively locked interengagement of the threads on the bush 28 with the threaded part 26 of the shaft. Thus, such further clockwise rotation of the handle causes the drum rotation to be reversed to lower the person suspended by the lifeline 10.

Claims

1. A fall arrest device having a main drum journalled within a housing and carrying a lifeline which can be withdrawn from and returned to the drum against and by a spring, respectively, and further comprising a sub-shaft journalled in the housing and carrying a pinion, rotation of which drives, or can be made to drive, the main drum and hence the lifeline carried thereby, the sub-shaft having a threaded end on which is engaged a correspondingly threaded bushing coupled to a handle, the bushing being prevented from winding off the threaded end of the sub-shaft by a spring means, there being loosely disposed around the sub-shaft, between the bushing and a shoulder on the sub-shaft, an annular ratchet wheel, sandwiched between annular friction discs, the arrangement being such that rotation of the bushing by the handle in one direction causes the bushing initially to wind onto the threaded part of the sub-shaft whereby the bushing is initially displaced towards said shoulder on the sub-shaft so that the ratchet wheel is eventually gripped between the friction discs, further relative displacement of the bush and sub-shaft in that direction thereby being prevented whereby the rotation of the bushing is taken up by the sub-shaft and hence by the drum; and rotation of the bushing by the handle in the opposite direction initially causes slight winding off of the bush from the threaded part of the sub-shaft, sufficient to release the ratchet wheel from the friction discs but limited by said spring means so that additional rotation of the bushing in that direction relative to the sub-shaft is prevented by the spring means and such additional rotation of the bushing by the handle is followed by the sub-shaft and hence by the drum.

2. A fall arrest device as claimed in claim 1, wherein the rotation of the bushing in said one direction is arranged to wind in the lifeline onto the drum, the radial wheel engaging a spring loaded pawl on the housing to prevent rotation in the opposite direction during this winding up mode.

3. A fall arrest device as claimed in claim 1 or 2, in which the sub-shaft is longitudinally displaceable within the housing for engaging and disengaging the pinion on the sub-shaft from its driving connection with the main drum.

4. A fall arrest device as claimed in claim 3, in which the sub-shaft is biassed longitudinally by a coil spring towards its position in which the pinion is in driving engagement with the main drum.

5. A fall arrest device substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.