GB2279636A - Indicating use of fall-arrest apparatus - Google Patents

Abstract

A fall-arrest apparatus for protecting workers who are exposed to the risk of a fall from an elevated work site incorporates a drum (1) onto which a safety line (SL) is wound and a drum brake mechanism which becomes automatically applied in the event of an excessive unwinding speed of the safety line. A safety line guide roller (27) is located between the drum (1) and the exit passage (26) through which the safety line leaves the apparatus. In the event of the fall of a worker attached to the safety line the fall-arrest forces on the safety line result in exertion of such pressure of the safety line on the guide roller (27) that the roller spindle snaps and an associated disc (31) become displaced. Such displacement results in exposure to view of a coloured ring (33) which serves as a warning that the apparatus has arrested a fall and must not be re-used until it has been serviced. <IMAGE>

Description

FALL-ARREST APPARATUS This invention relates to fall-arrest apparatus for protecting workers who are exposed to the risk of a fall from an elevated work site.

Various apparatus in this category are known. They basically consist of a safety line drum and a brake mechanism assembled to carrier means which is attachable to a fixture.

The apparatus includes means defining a fixed point of exit of the safety line from the apparatus. A safety line wound onto the drum extends from the apparatus via the said exit point and is attachable to a worker's safety harness. The safety line becomes drawn off from the drum responsive to pulling forces exerted on the safety line in consequence of movement of the worker away from the drum. The drum is self-winding so as automatically to take up any slack which would otherwise develop in the line as the worker moves closer to the drum. The brake mechanism incorporates a clutch which functions automatically to cause application of the brake in the event of excessive unwinding speed of the drum. If the worker attached to the safety line should fall the brake decelerates the drum at a rate which avoids subjection of the worker to highly injurious and possibly fatal arrest forces.

It is desirable for the apparatus to incorporate some form of indicator which is activated in the event of a fall and serves as a visible warning signal that the apparatus has been heavily loaded and should not be used until it has been serviced and certified for re-use.

The warning indicators hitherto proposed are activated by movement of a rotatable brake element forming the driven member of a centrifugal clutch (see for example United Kingdom Patent 1552667 and UK Patent 2192679).

In the apparatus disclosed in United Kingdom Patent 1552667 the rotatable brake element is in screw engagement with a casing of the apparatus and bears against a cooperating brake element formed by a pack of spring discs.

The rotation of the threaded brake element progressively deforms the spring discs with consequent progressive increase in the frictional resistance to such rotation. In the event of a fall, the deformation of the spring discs causes displacement of an indicator button into a position in which it projects externally of the casing and thereby gives the warning signal. The resistance to rotation of the rotatable brake element, imposed by the spring discs, should be such as to prevent any such rotation unless the torque is of a high magnitude such as results from a fall. Otherwise the initial setting of the rotatable brake member may be disturbed by forces exerted on the safety line during normal use of the apparatus.In consequence, if and when a fall occurs, the performance of the brake in terms of the braking force v time profile will be incorrect with consequent risk of serious and possibly fatal injury.

The apparatus disclosed in United Kingdom Patent 2192679 incorporates a brake of constant force type, which is generally more satisfactory. Constant force brakes are used in various fall-arrest apparatus currently in use. The brake comprises driven and fixed brake elements which are held together under a constant force which determines the frictional resistance to rotation of the driven element. In the apparatus disclosed in United Kingdom Patent 2192679, rotary movement of the driven brake element causes accompanying rotary movement of a pointer relative to an indicator dial. The position of the pointer is intended to indicate whether the apparatus has arrested one or more falls since the apparatus was last re-set for use.The pre-set resistance of such constant force brakes is normally such that it can be overcome by forces substantially lower than those reached in the event of a fall. The pre-set resistance may be and usually is such that it can be overcome by manual exertion of a rapid and strong pull on the safety line. In fact, users of fall-arrest apparatus often test the functioning of the brake mechanism by exerting a sharp pull on the safety line to cause engagement of the centrifugal clutch. It has been found that repetitive testing in this way can and sometimes does cause successive increments of rotation of the driven brake element and consequentially leads to misleading activation of the warning indicator.

The present invention provides apparatus having an indicator device which works on a different principle and is without the described disadvantage of the earlier devices.

The present invention provides to a fall-arrest apparatus for protecting workers who are exposed to the risk of a fall from an elevated work site, said apparatus incorporating a safety line drum, a drum braking mechanism which functions automatically to brake the drum in the event of it reaching an excessive unwinding speed such as occurs in the event of the fall of a person attached to the safety line, said drum and braking mechanism being assembled to carrier means which is attachable to a fixture; means defining a fixed point of exit of the safety line from the apparatus; and signalling means which is automatically actuated in the event of the arrest of a fall by the apparatus thereby to signal that fact to anyone inspecting the apparatus; characterised in that between the safety line drum and said exit point there is safety line guide means located so that the subjection of the safety line to increasing tension results in increasing pressure of the safety line against such guide means; the guide means is held in that location by means which allows it to become displaced under such pressure if it reaches a magnitude such as may result from the arrest of the fall of a person attached to the safety line, and said displacement of the guide means actuates said signalling means.

Hand-testing of the braking mechanism of apparatus according to the invention, however many times repeated, is not liable to actuate the signalling means because the tensile forces to which the safety line is subjected when sharp pulls are exerted on it by hand to check that the brake mechanism functions does not approach the tensile force to which the safety line is subjected at the time of a fall-arrest.

The braking mechanism can be designed so that in the event of a fall it decelerates the falling body to a low speed and allows the body then to continue its descent at the controlled reduced rate under its own weight. Alternatively the braking mechanism can be designed so that it decelerates a falling body to zero velocity and then holds the body suspended pending rescue. Braking mechanisms falling in both of these functional categories are known per se.

In the event of the fall of a worker attached to the safety line, while it is important to avoid such abrupt arrest of the fall as would be likely to cause series injury to the worker, for most use situations it is also important that the deceleration is not unnecessarily slow because lengthening of the fall distance itself entails increased risks of injury. Various local standard specifications prescribe maximum fall-arrest loads on the person and maximum fall distances. An example of a said Standard is ANS1 (American National Standards Institution) Z359.1 (1991). In order to comply with various such local standards, it is desirable for apparatus according to this invention to arrest a fall within a distance of about 1 to 3 feet from the moment any slack in the safety line is taken up and the braking of the drum commences.

The arrest of a fall within a short fall distance as above referred to imposes very large tensile force on the safety line irrespective of whether the braking mechanism allows or does not allow descent of the body to continue following the fall arrest. While the magnitude of that tensile force will depend in any given case on the weight of the person attached to the safety line, the force on that line will generally be in excess of 3 KN.

In apparatus according to this invention, the load which has to be applied to the safety line in order to cause signal-actuating displacement of the guide means is preferably in excess of 1.5 KN.

There is a wide variety of ways in which the displaceable guide means can be functionally associated with the signalling means in order to achieve the desired result.

For example the guide means can be arranged so that on its displacement it abuts against a trigger of a spring-loaded signalling member causing the latter to spring into a position it which it gives the necessary warning signal.

Such a signalling member can for example be in the form of a stud which on actuation of the signal springs into a position in which it protrudes through an opening in a casing housing the safety line drum and braking mechanism.

In the presently most favoured way of carrying out the present invention, the displaceable safety line guide is in the form of a roller which is rotatable with or around a spindle which is constituted so that it will snap under the force imposed upon it in the event of a fall arrest; and the snapping of the spindle causes actuation of the warning signal. Preferably the spindle is associated with a warning signal mask which when the spindle snaps becomes displaced so that the warning signal is exposed to view. The warning signal can for example be constituted by an area of colour, preferably red, which can be seen through a window of a casing of the apparatus when the mask is displaced.

The safety line of apparatus according to the invention can for example be a cable, rope or webbing.

An apparatus according to the invention, selected by way of example, will now be described with reference to the accompanying drawings, in which: Fig. 1 is an elevation of the apparatus; Fig. 2 is a section on line A-A in Fig. 1; and Fig. 3 is a view in elevation showing parts of the drum braking mechanism.

The illustrated apparatus comprises a drum 1 on which a safety line SL is wound. The free end (not shown) of the safety line it carries hook means for attachment to a worker's safety harness. The drum has an axial bearing bush 2 which is rotatable around a shaft 3. The shaft 3 is supported by a main bearing 4 which rotatably supports a brake component 5. Brake component 5 is itself rotatably supported by a spine plate 6. The component 5 has on one side an annular rib 7 which makes an accurate running fit in an aperture in the spine plate. The spine plate is shaped to provide a handle 8 by which it can be suspended from a fixture. A peripheral radial flange 9 of the brake component 5 overlaps a marginal portion of the spine plate 6 surrounding its aperture into which the rib 6 of the brake component 5 intrudes. A clamping ring 10 is secured to the spine plate by bolts 11.Friction discs 12 and 13 are interposed between the spine plate and the flange 9 of the brake component and between that flange and the clamping ring 10. The clamping pressure exerted by the bolts 11 determines the resistance of the brake component 5 to rotation relative to the clamping ring and the spine plate.

The brake component 5 is formed with a series of raked teeth 14 around the inner periphery of its annular rib 7.

The safety line drum 1 carries pawls 15,16. These pawls are pivotally mounted on pins 17,18 secured to the drum. The pawls are biased into inoperative position by springs 19,20 and remain inoperative during normal use of the apparatus.

Should an excessive unwinding speed of the drum occur due to the fall of a person attached to the safety line, centrifugal forces cause the pawls to pivot against the resistance of springs 19,20 into positions in which nose portions of the pawls engage with teeth 14 on the brake component 5, so causing that brake component to rotate with the drum. The aforementioned frictional resistance to rotation of this brake component has a braking effect on the drum, causing it to decelerate to rest.

The safety line drum 1 houses a spring return spring 21 which biases the drum in the winding direction. The drum is therefore self-winding. Pay-out of safety line from the drum takes place under pulling forces exerted on the safety line, against the resistance imposed by the spring 21. The spring therefore automatically takes up any slack in the safety line.

The safety line drum and brake mechanism are enclosed by a casing 22 formed in two parts which are secured together, with the interposition of sealing gaskets 23, by bolts such as 24 which secure the opposed casing parts to the spine plate 5. One part of the casing affords support to an end of the drum shaft 3.

In an opening at the bottom of the casing 22 there is a fixed guide member 25 which defines a fixed exit opening 26 for the safety line SL from the apparatus.

In the illustrated apparatus the characterising features of the present invention are embodied in the manner which will now be described.

Between the safety line drum 1 and the fixed guide member 25 there is a safety line guide roller 27. As appears from Fig. 3, this roller is so placed that it deflects the safety line from a straight line path from the drum to the bottom exit 26. In consequence any pulling force on the safety line causes the safety line to exert some lateral pressure against the roller. In normal use of the apparatus such lateral force is small. The pressure increases with increase in the pulling force on the safety line while the drum brake is applied.

The roller 27 is supported by a spindle 28. A main part 29 of this spindle is integral with the roller. One end portion of that main part of the spindle is supported in the spine plate 6. In the other end of that spindle part there is an axial socket. A signal masking disc 31 is located in an opening located in the casing 22 in register with the roller 27. This masking disk has a spigot 32 which fits into that socket and itself forms part of the roller spindle.

Behind the masking disk 31 there is a coloured disc 33.

The spindle 28 is capable of supporting the roller 27 against displacement under the lateral forces which are exerted against it as a result of loading of the safety line SL up to about 2 KN. The roller 27 is therefore not liable to be displaced by any lateral forces exerted on it during normal use of the apparatus or even by lateral forces caused by hand-testing the braking mechanism, i.e. by manually jerking the safety line downwardly from the suspended casing to check that the brake mechanism functions. However, in the event of the fall of a worker attached to the safety line the load on the safety line will considerably exceed 2 KN and will cause the spigot 32 to snap. In consequence of this breakage of the spindle 28, the masking disk 31 will fall out of the casing recess in which it is located, so exposing the coloured disc 33.The exposure of this disc to view constitutes a warning signal making it immediately apparent to anyone inspecting the apparatus that it has been heavily loaded and requires careful examination and recertification before being again put to use.

The guide roller 27 and masking disc and their associated spindle parts can very suitably be plastics mouldings, e.g. of Nylon.

The guide roller 27 assists proper reeling of the safety line SL onto the drum.

The masking disk 31 can be connected to a loop of material which extends externally of the casing 22 and through which the safety line SL passes at a position below the point at which it passes out of such casing. In this case, when the masking disk falls out of the casing recess it will not fall free from the apparatus. It will remain captive to the safety line by the loop. The latter will slide down the safety line to the hook means by which the line is attached to the worker's safety harness. The disk will remain there after the rescue operation as a further indication that the apparatus has effected a fall-arrest.

Claims (7)

1. A fall-arrest apparatus for protecting workers who are exposed to the risk of a fall from an elevated work site, said apparatus incorporating: a safety line drum; a drum braking mechanism which functions automatically to brake the drum in the event of it reaching an excessive unwinding speed such as occurs in the event of the fall of a person attached to the safety line, said drum and braking mechanism being assembled to carrier means which is attachable to a fixture; means defining a fixed point of exit of the safety line from the apparatus; and signalling means which is automatically actuated in the event of the arrest of a fall by the apparatus thereby to signal that fact to anyone inspecting the apparatus; characterised in that between the safety line drum and said exit point there is safety line guide means located so that the subjection of the safety line to increasing tension results in increasing pressure of the safety line against such guide means; the guide means is held in that location by means which allows it to become displaced under such pressure if it reaches a magnitude such as may result from the arrest of the fall of a person attached to the safety line, and said displacement of the guide means actuates said signalling means.

2. Apparatus according to claim 1, wherein the braking mechanism comprises a driven braking element which is held under constant pressure against a fixed braking element.

3. Apparatus according to claim 1 or 2, wherein the load which has to be applied to the safety line to cause signal-actuating displacement of the guide means is in excess of 1.5 KN.

4. Apparatus according to any preceding claim, wherein the displaceable safety line guide is in the form of a roller which is rotatable with or around a spindle which is constituted so that it snaps under force imposed upon it in the event of a fall arrest; and the snapping of the spindle causes actuation of the warning signal.

5. Apparatus according to claim 4, wherein said spindle is associated with a warning signal mask which when the spindle snaps becomes displaced so that the warning signal is exposed to view.

6. Apparatus according to claim 5, wherein said mask has an integral spigot which constitutes part of the guide roller spindle and the force imposed on the roller in the event of a fall arrest snaps the said spigot.

7. Apparatus according to claim 4 or 5, wherein the warning signal is constituted by an area of colour, preferably red, which can be seen through a window of a casing of the apparatus when the mask is displaced.