WO2009047470A1

WO2009047470A1 - Rotary drum and safety line system

Info

Publication number: WO2009047470A1
Application number: PCT/GB2007/003908
Authority: WO
Inventors: Karl Jones; Owain Jones
Original assignee: Latchways Plc
Priority date: 2007-10-12
Filing date: 2007-10-12
Publication date: 2009-04-16

Abstract

A safety line system includes a rotary drum and a safety line for winding on the drum. The line passes through an opening in the circumferential wall of the drum to be secured internally of the drum. A capture arrangement (typically one or more bolts) is provided to capture the line internally of the drum. The arrangement is particularly suited for use in fall arrest systems. Such systems may include a biased re-spooling mechanism to act on the drum to rewind the line following feeding out of the line and a speed sensitive clutch mechanism connected to the drum and arranged to respond to rotation of the drum in a direction tending to unwind the safety line from the drum and above a predetermined speed, by locking the drum against further rotation. The capture arrangement is accessible from externally of the drum, in order to permit reconfiguration between a capture configuration and a release configuration.

Description

Rotary Drum and Safety Line System

The present invention relates to a rotary drum and safety line system, in particular for retaining a safety line for a fall arrest system.

Fall arrest systems are used to prevent personnel working at a height from suffering injury or death due to falls. Fall arrest systems are often referred to as height safety systems or fall prevention systems. Such apparatus generally comprises an anchor member and a rotatable drum on which is wound a safety line, and although the claimed arrangement may be used in various other kinds of apparatus, the invention will be described with particular reference in connection with fall arrest apparatus.

The anchor member is connected to a high point on a fixed structure and a safety line which is wound onto the drum is attached to a body harness with which a worker is equipped. The safety line is released from the drum as required by the worker to carry out his tasks. The feed out of the line is generally relatively small in order that there is a limited risk in the event of a fall by the worker. The apparatus generally further comprises a re-spooler mechanism in order to rewind the line, for ease of use. Brake mechanisms are generally provided to prevent release of the safety line in the event of a fall by the worker. This is achieved by the use a speed sensitive clutch device that acts to lock rotation of the drum once a pre-determined feed out speed has been reached. This is achieved through locking the drum. However, sudden locking of the drum may cause injury to the worker and as such an energy absorber is provided to absorb the kinetic energy of a falling user, so slowing and then arresting their fall.

An improved arrangement has now been devised.

According to a first aspect, the present invention provides a safety line system comprising a rotary drum and a safety line for winding on the drum, the line passing through an opening in the circumferential wall of the drum to be secured internally of the drum, a capture arrangement being provided to capture the line internally of the drum. Beneficially, the capture arrangement is realeasable to enable the line to be captured by, and released from, the drum. The capture arrangement preferably comprises a detent arranged to capture the line. The line preferably includes a stop portion (such as a termination head, boss or similar) and the detent preferably abuts or engages against the stop portion.

The stop portion (boss or head) may include a stop shoulder and the detent is positioned, in situ, adjacent the stop shoulder of the stop portion.

It is preferred that the detent is releasable to enable the line to be captured and released from the drum.

In one embodiment, one or more bolts arranged to be received in a respective bore such that the shaft of the respective bolt acts as the detent. Beneficially, a pair of bolts is provided the shafts of the respective bolts passing on opposed sides of the line and acting as detents to prevent release of the line.

It is beneficial that the capture arrangement is accessible from externally of the drum, in order to permit reconfiguration between a capture configuration and a release configuration from externally of the drum. This enables detachment and re-attachment of line without the need to disturb or dismantle certain other components of the system. In one embodiment the capture arrangement is accessible at a side of the drum transverse to the rotational axis of the drum.

Beneficially, a side of the drum transverse to the rotational axis of the drum, is provided with a viewing aperture permitting the position of the line to be viewed internally of the drum.

hi certain embodiments the system includes a biased re-spooling mechanism arranged to act on the drum to rewind the line following feeding out of the line. In certain embodiments the system includes a speed sensitive clutch mechanism connected to the drum. Preferably the speed sensitive clutch mechanism is arranged to respond to rotation of the drum in a direction tending to unwind the safety line from the drum and above a predetermined speed, by locking the drum against further rotation.

In certain embodiments the system includes an energy absorber adapted to respond to an applied load on the safety line, by deploying and absorbing energy. The energy absorber may comprise an elongate plastically deformable element.

The system may include attachment means for attaching the system to a support structure.

In a certain embodiments the system may include one or both of: a biased re-spooling mechanism arranged to act on the drum to rewind the line following feeding out of the line; and

a speed sensitive clutch mechanism connected to the drum and arranged to respond to rotation of the drum in a direction tending to unwind the safety line from the drum and above a predetermined speed, by locking the drum against further rotation;

wherein the capture arrangement comprises a detent arranged to capture the line, the detent being releasable and deployed from externally of the drum and one or both of the clutch mechanism and the re-spooling mechanism.

According to a further aspect, the invention may be viewed as a method of attaching a safety line to a rotatable winding drum, particularly for a fall arrest system, wherein the line passes through an opening in the circumferential wall of the drum, and a capture arrangement is provided to capture the line internally of the drum, the capture arrangement being accessed from externally of the drum, in order to reconfigure the capture arrangement between a capture configuration in which the line is secured and a release configuration in which the line can be retracted from, or inserted into the drum.

The present invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure Ia- Id is a schematic perspective view of an apparatus according to an exemplary embodiment of the present invention wherein the sequence of retaining the safety line in the apparatus is represented through sequential views, wherein a portion of the cover has been removed in order to show how the line is retained by the system.

Figure 2 is a schematic representation of the side view of the safety line and retaining mechanism in isolation according to an exemplary embodiment of the present invention.

Figure 3 is a schematic side view of the drum and components connected thereto according to an exemplary embodiment of the present invention.

Figure 4a and b are schematic side views of a clutch mechanism according to an aspect of an exemplary embodiment of the present invention.

Referring to Figures Ia - e, there is a fall arrest system according to an exemplary embodiment of the present invention. The apparatus generally comprises a drum 2 mounted for rotation within a frame 8. The drum 2 is arranged to enable a safety line 4 to be wound on the drum 2. In a functioning embodiment, the arrangement further comprises a re-spooling mechanism 6 (not visible with respect to Figure 1), a speed-sensitive clutch 10 and an energy absorber 12 mounted with respect to the frame 8. The energy absorber 12 comprises an attachment point 14 for attachment in the chosen location to a support structure (not shown). The relative mounted positions of the re-spooling mechanism 6 and speed-sensitive clutch 10 are shown schematically with respect to Figure 3 which shows a side view of the longitudinal length of the drum mounted to the frame 8. The fall arrest system comprises a length of safety line 4 wound on the drum 2. The drum 2 is connected to the re-spooling mechanism 6 which maintains a re-spooling force acting on the drum 2 tending to rewind any deployed length of safety line 4 onto the drum 2. Typically the re-spooling mechanism comprises a clock spring type device. The drum 2 may also be connected through the speed-sensitive clutch 10 to the energy absorber 12. However in the embodiment indicated in the figures the energy absorber is mounted to the frame, with the attachment point 14 acting as the attachment point for the apparatus to be mounted to a structure.

In use, a user is attached to the free end of the safety line 4 by personal safety equipment, such as a safety harness. During normal movement of the user, the safety line 4 is wound out from the drum 2 to follow the movement of the user and any excess safety line 4 is wound back onto the drum 2 by the re-spooling mechanism 6. The speed-sensitive clutch 10 is set not to respond to the slow rotation of the drum encountered during this normal movement of the user.

If the user falls, the safety line 4 is unwound rapidly from the drum 2 resulting in rapid acceleration of rotation of the drum 2. When the speed of rotation of the drum 2 reaches the response speed of the speed-sensitive clutch 10, the clutch 10 engages the drum 2 causing an activation force to be applied to the energy absorber 12. The load of the falling user is then applied to the energy absorber 12 as a couple and the energy absorber 12 responds by deploying and absorbing energy until the fall is arrested. Various types of energy absorber 12 are envisaged and known in the art.

In a preferred embodiment of the present invention, the speed-sensitive clutch 10 is a rocking pawl type. A schematic representation of such a pawl type may be found in Figures 4a and 4b in an engaged and unengaged configuration respectively. The rocking pawl device has a ratchet mechanism in the form of an outwardly facing ratchet wheel 16 attached to the rotating component 18 and a pawl 20 arranged to contact the ratchet wheel 16. The pawl 20 is able to pivot between a first unengaged position shown in Figure 4a in which the pawl 20 is not engaged with the ratchet wheel 16 so that the component 18 is able to rotate freely, and a second engaged position shown in Figure 2b where the pawl 20 is engaged with the ratchet wheel 16 preventing rotation of the component 18 relative to the frame 8. The pawl 20 is biased by resilient means 22 towards the first unengaged position. As the component 8 rotates and the ratchet wheel 16 rotates relative to the pawl 20, each tooth of the ratchet wheel 16 in turn strikes a first end of the pawl 20 and pushes it outwardly away from the ratchet wheel 16 so that the pawl 20 pivots towards the engaged position. The pawl 20 is resiliently biased towards the first unengaged position, and as a result this outward pushing of the pawl 20 by the ratchet wheel teeth results in an oscillating movement of the pawl 20 from the unengaged position towards the engaged position and back towards the unengaged position. As the speed of rotation of the component 18 and the ratchet wheel 16 increases the amplitude of the oscillation of the pawl 20 increases until the amplitude of the oscillation is large enough to bring the pawl 20 into the engaged position. The pawl 20 then engages with the ratchet wheel 16 and rotation of the component 18 relative to the pawl 20 and frame 8 is prevented.

In the arrangement shown, the pawl 20 is not biased when in the engaged state wherein contact between the teeth of the ratchet wheel 16 and pawl 20 is achieved. This is because of the problem of bounce caused by the fact that when this type of engagement system is used in a fall arrest system and a fall arrest occurs, there is a stretching or tensioning of the safety line followed by a momentary reduction in tension to zero as the arrested person bounces at the end of the safety line. During this momentary reduction in tension, the automatic rewinding mechanism causes the drum to rotate slightly in a rewinding direction, releasing the pawl 20 from engagement with the ratchet teeth and thereby causing the pawl 20 to be moved to the unengaged position and releasing the drum and allowing the person to start falling again. Ensuring that the pawl 20 is not biased when in the engaged configuration therefore prevents release of the pawl 20 from the teeth of the ratchet when the force is removed.

Referring now to Figure 3, the circumferential wall of the drum body 2 onto which the safety line 4 is wound comprises a cross-section of generally increasing diameter from one edge to the opposing edge. This aids in winding of the safety line onto the drum 2. The drum body comprises a deepening groove 24 therein into which the safety line 4 seats. The groove 24 leads to an aperture 30 extending through the circumferential wall of the drum. The safety line 4 has a termination head stop portion 26 of greater diameter relative to the diameter of the safety line 4. The head stop portion 26 has a shoulder portion 28 at the point of connection to the narrower length of line 4. The head_. stop portion 26 is dimensioned to be inserted into, and retracted out of the drum 2 passing through aperture 30 in the circumferential wall of the drum body and be secured internally of the drum. The safety line 4 seats in the channel 24 as the line is wound onto the drum.

As indicated with respect to Figures la-c, the head stop 26 and line 4 is inserted into the body of the drum 2 passing through the aperture 30, until the head stop 26 abuts the inner wall of the drum and seats therein. Referring to Figures Id and Ie, in a preferred embodiment, a pair of detent capture bolts 34 are arranged to be inserted through outer wheel 36, the frame 8, components of the speed-sensitive clutch 10, and the re-spooling mechanism 6 and received in receiving apertures 41 , 42 in the drum body. Because the ratchet wheel of the clutch, components of the re-spooling mechanism, drum and outer wheel 36 are rotatably mounted to one another, ease of access for insertion and removal of the detent capture bolts 34 is provided. When inserted, the detent capture bolts 34 extend past the line 4 adjacent the lower shoulder portion 28 of the head stop portion 26, thereby capturing the head stop 26 and preventing tension in the line from pulling the line back out of the interior of the drum. When tension is applied to the line 4, and with the capture bolts in place, the bolts abut in contact against the shoulder portion 28 of the head stop portion 26 thereby preventing release of the head 26 from internally of the body of the drum 2. It will be appreciated that in such an embodiment, in order to remove and reattach a respective line 4, access to the detent capture bolts 34 can be made from the side of the apparatus without disassembly of certain significant components such as the re- spooling mechanism or the clutch mechanism. This is extremely beneficial as, if a fall has occurred, then it is often necessary to replace the safety line 4. Additionally, safety lines 4 can only be used for a predetermined time period and as such replacement is necessary on a regular basis.

Replacement may simply be made by removing the detent capture bolts 34 using standard tooling such as an Allen Key, withdrawing the safety line from the body of the drum 2, inserting a new safety line head 26 first into the drum body via aperture 30 and reinserting the detent capture bolts 34 once the head stop portion 26 is located beyond the apertures 41 42 for receiving the detent capture bolts 34. Replacement of the safety line 4 is therefore quick and effective, reducing the chance of accidental release of the safety line from the drum. In the locked configuration, a person assembling the device can also ensure that the safety line 4 is safely secured as further apertures are provided in the outer rotating member 36, enabling visible confirmation to be made that the head 26 is safely secured. As a result of the configuration of the head stop portion and the capture arrangement (i.e. detent bolts 34 and bores 41 42) it is not possible to insert and tighten the detent bolts 34 without the head stop portion being completely inserted into its home position. The wheel 36 and other components may have an axial aperture permitting the interior of the drum to be viewed. This aids in confirming that the head stop portion has been fully inserted into the drum 2.

It will be appreciated that other embodiments of the present invention are envisaged, in which other means of captively securing the head stop 26 (and thus the safety line within the drum body 2) is envisaged. For example a single threaded member could be utilised providing release of the head stop 26 from the drum body is prevented. Thus, a single component could be utilised to secure against the shoulder portion 28. Additionally or alternatively a retractable component having a part annular collar or ring could engage about the line 4 to abut the shoulder 28. A further alternative embodiment that is envisaged is, for example, the head may comprise one or more threaded apertures therethrough for receipt of a securing member such as a retaining pin.

Referring now to the energy absorber 12, in a preferred embodiment of the fall arrest system, the energy absorber 12 has a structure comprising a housing 40 and an attachment point 14. The energy absorber 12 is arranged to locate within a frame 42 of the device such that the attachment point slots through an aperture located in the upper surface of the frame 42 and further comprises attachment point 44 for secure location of the housing within the frame 42. A length of material 46 is a strip material that is wound into a spiral 48 and bent at the centre thereof to be fixed between at least two pins (not shown). This prevents the length of material 46 being separated from the housing 40. The opposing end may be attached in situ as required for use. The spiral winding enables a long length of material to be stored within a relatively short linear space. When the energy absorber 12 is required to absorb energy, an increasing tension force is applied to the attachment point 14 until the applied force becomes sufficiently high to pull material 46 around pins (not shown) such that the absorber extends to absorb energy. Alternative types of energy absorbers may additionally or alternatively be utilised. In the simplest form, the safety line 4 can act as an energy absorber through its material properties. However, additional energy absorbers are preferred and may be located on the axis of rotation of the drum 2. The present invention is not limited in this regard.

A preferred embodiment of the present invention has been described, however, it will be appreciated by a person skilled in the art that alternative types of energy absorber 12 might be utilised and additionally alternative configurations of drum, clutch and re-spooling mechanism may be envisaged. A specific clutch 10 has been described above, however, it will be appreciated by a person skilled in the art that a number of alternatives may be utilised, including for example a centrifugal clutch type. It will therefore be appreciated by a person skilled in the art that variations and modifications may be made to the present invention without departing from the scope of the appended claims.

Claims

Claims:

1. A safety line system comprising a rotary drum and a safety line for winding on the drum, the line passing through an opening in the circumferential wall of the drum to extend internally of the drum, a capture arrangement being provided to capture the line internally of the drum.

2. A system according to any preceding claim, wherein the capture arrangement is realeasable to enable the line to be captured by, and released from, the drum.

3. A system according to claim 1 or claim 2, wherein the capture arrangement comprises a detent arranged to capture the line.

4. A system according to claim 2, wherein the line includes a stop portion and the detent engages against the stop portion.

5. A system according to claim 4, wherein the stop portion includes a stop shoulder and the detent is positioned, in situ, adjacent the shoulder of the stop portion.

6. A system according to claim 4 or claim 5, wherein the detent is releasable to enable the line to be captured and released from the drum.

7. A system according to any preceding claim wherein one or more bolts arranged to be received in a respective bore such that the shaft of the respective bolt acts as the detent.

8. A system according to claim 7, wherein a pair of bolts are provided the shafts of the respective bolts passing on opposed sides of the line and acting as detents to prevent release of the line.

9. A system according to any preceding claim, wherein the capture arrangement is accessible from externally of the drum, in order to permit reconfiguration between a capture configuration and a release configuration.

10. A system according to any preceding claim, wherein the capture arrangement is accessible at a side of the drum transverse to the rotational axis of the drum.

11. A system according to any preceding claim, wherein a side of the drum transverse to the rotational axis of the drum, is provided with a viewing aperture permitting the position of the line to be viewed internally of the drum.

12. A system according to any preceding claim including a biased re-spooling mechanism arranged to act on the drum to rewind the line following feeding out of the line.

13. A system according to any preceding claim including a speed sensitive clutch mechanism connected to the drum.

14. A system according to claim 13, wherein the speed sensitive clutch mechanism is arranged to respond to rotation of the drum in a direction tending to unwind the safety line from the drum and above a predetermined speed, by locking the drum against further rotation.

15. A system according to any preceding claim, including an energy absorber adapted to respond to an applied load on the safety line, by deploying and absorbing energy.

16. A system according to claim 15, wherein the energy absorber comprises an elongate plastically deformable element.

17. A system according to any preceding claim comprising an attachment means for attaching the system to a support structure.

18. A system according to any preceding claim, including one or both of: a biased re-spooling mechanism arranged to act on the drum to rewind the line following feeding out of the line; and

19. A fall arrest system including a safety line system according to any preceding claim.

20. A rotary drum for a safety line system, the drum including a circumferential wall for winding on of the line and an opening in the circumferential wall permitting the line to pass into the drum to be secured internally of the drum, a capture arrangement being provided to capture the line internally of the drum.

21. A safety line system including a drum according to claim 20.

22. A method of attaching a safety line to a rotatable winding drum, particularly for a fall arrest system, wherein the line passes through an opening in the circumferential wall of the drum, and a capture arrangement is provided to capture the line internally of the drum, the capture arrangement being accessed from externally of the drum, in order to reconfigure the capture arrangement between a capture configuration in which the line is secured and a release configuration in which the line can be retracted from, or inserted into the drum.

23. A method according to claim 22, carried out using a system according to any of claims 1 to 21.