Abstract:
A safety device for use in a fall arrest system, has a safety line drum mounted for rotation and a speed responsive engagement mechanism responsive to the speed of rotation of the drum, which is activated above a predetermined rotational speed of the drum to deploy an energy absorber. A rotational transmission member (which may be in the form of a shaft) is coupled, via the speed responsive engagement mechanism, when activated, to rotate with the drum. The energy absorber is deployed in response to operation of the rotational transmission member. The speed responsive engagement mechanism may be mounted intermediate the drum and the energy absorber for ease of replacement.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field 
         [0002]    The present invention relates to a fall arrest system safety device and in particular to a device including a drum upon which a safety line is used including an energy absorber arrangement to absorb the energy of a fall arrest event. 
         [0003]    2. State of the Art 
         [0004]    Fall arrest systems are used to prevent personnel working at height from suffering injury as a result of falling. Fall arrest systems are often referred to as height safety systems or fall prevention systems. Frequently such systems include a so called safety block arranged to be suspended overhead from an anchor structure. Such arrangements typically include a drum upon which a safety line is wound; a speed responsive mechanism arranged to inhibit the drum rotation above a predetermined rotational speed and an energy absorber device arranged to be activated if a load above a predetermined threshold is deployed when the speed responsive mechanism is deployed. The energy absorber devices are typically either friction brake devices or plastically deformable metallic strip arrangements that are plastically deformed during deployment in order to absorb energy. 
       SUMMARY OF THE INVENTION 
       [0005]    An improved arrangement has now been devised. 
         [0006]    According to a first aspect, the present invention provides a safety device for use in a fall arrest system, the safety device comprising: 
         [0007]    an energy absorber arrangement; 
         [0008]    a safety line drum mounted for rotation; 
         [0009]    a speed responsive engagement mechanism responsive to the speed of rotation of the drum, which is activated, above a predetermined rotational speed of the drum; 
         [0010]    a rotational transmission member, which transmission member is coupled, via the speed responsive engagement mechanism, when activated, to rotate with the drum; the energy absorber arrangement being activated in response to operation of the rotational transmission member. 
         [0011]    The transmission member is typically a shaft which is coupled so as to rotate in unison with the drum only when the speed responsive engagement mechanism is engaged. Accordingly it is preferred that the transmission member comprises a shaft and preferably that the drum is arranged in a first movement regime to rotate independently of and about the shaft; and in a second movement regime to rotate in unison with the shaft. 
         [0012]    The drum is preferably mounted on the shaft and provided with bearings permitting the drum to rotate independently about the shaft in the first movement regime. 
         [0013]    The speed responsive engagement mechanism is preferably positioned intermediate the drum and the energy absorber arrangement. In this way the energy absorber is mounted outboard the speed responsive engagement mechanism. This enables the energy absorber to be removed and replaced without dismantling of the speed responsive engagement mechanism. 
         [0014]    Consequently, according to a further aspect, the invention provides a safety device comprising: 
         [0015]    a support shaft; 
         [0016]    an energy absorber arrangement mounted on the shaft; 
         [0017]    a safety line drum mounted for rotation; 
         [0018]    a speed responsive engagement mechanism responsive to the speed of rotation of the drum and at least a portion of which is carried by the shaft and, which is activated, above a predetermined rotational speed of the drum in order to couple rotation of the drum to the energy absorber arrangement; 
         [0019]    wherein the speed responsive engagement mechanism arrangement is mounted intermediate the drum and the energy absorber arrangement. 
         [0020]    In either embodiment it is preferred that the transmission member comprises a shaft and the shaft has a portion arranged to cooperate with the energy absorber to deploy or operate the energy absorber. 
         [0021]    It is preferred that the respective portion of the shaft engages with a drive member comprising the energy absorber arrangement. 
         [0022]    Beneficially the transmission member comprises a shaft and the energy absorber arrangement is arranged to be fitted about the end of the shaft. 
         [0023]    In a preferred embodiment the energy absorber arrangement comprises: 
         [0024]    a coiler member; 
         [0025]    an elongate element of a plastically deformable material; and 
         [0026]    a deformer structure; 
         [0027]    the elongate element having a first end attached to the coiler member and a second free end remote from the first end; the elongate element extending past the deformer structure at apposition intermediate the first and second ends; relative rotation of the coiler member and deformer structure causing the elongate element to be drawn past the deformer structure, plastically deforming the elongate element and winding the elongate element coil form about the coiler member. 
         [0028]    In such an embodiment, it is preferred that the elongate element is stored in coil form prior to drawing through the deformer structure. Beneficially, the coiler member comprises an inner member arranged for relative rotation with respect to an outer member; the outer member comprising the deformer structure. 
         [0029]    In an alternative embodiment, the energy absorber arrangement may comprise a friction disc brake arrangement. 
         [0030]    Beneficially, the transmission member comprises a shaft and the shaft extends through from the interior of a housing via a dividing wall in the housing; the housing containing the drum and the speed responsive engagement mechanism, wherein the energy absorber arrangement is mounted onto the shaft externally of the housing separated from the drum and speed responsive engagement mechanism by means of the dividing wall. 
         [0031]    As a result of such a construction the drum and the speed responsive engagement mechanism (and the re-spooler mechanism, where present) can be held in a sealed environment which does not need to be disturbed in order to maintain or replace the energy absorber arrangement which lies outside the housing. 
         [0032]    Accordingly, a further aspect of the invention provides a safety device for use in a fall arrest system, the safety device comprising: 
         [0033]    an energy absorber arrangement; 
         [0034]    a safety line drum mounted for rotation; 
         [0035]    a speed responsive engagement mechanism responsive to the speed of rotation of the drum, which is activated, above a predetermined rotational speed of the drum; 
         [0036]    a housing containing the drum and the speed responsive engagement mechanism; 
         [0037]    a transmission member comprising a shaft capable of rotating with the drum and which extends through from the interior of a housing via a dividing wall in the housing 
         [0038]    wherein the energy absorber arrangement is mounted onto the shaft externally of the housing separated from the drum and speed responsive engagement mechanism by means of the dividing wall. 
         [0039]    Beneficially, the housing is sealed from the environment externally of the housing, a seal being provided for the shaft and the dividing wall. 
         [0040]    It is preferred that an enclosure or housing for the energy absorber is provided, this being secured with respect to the housing containing the drum and the speed responsive engagement mechanism. 
         [0041]    In a preferred embodiment the speed responsive engagement mechanism comprises a ratchet and pawl mechanism. Beneficially, the ratchet comprises a ratchet disc and there is relative rotation between the ratchet disc and the pawls. In a preferred embodiment the pawls are carried to rotate with the drum. 
         [0042]    As mentioned earlier it is preferred that the device further comprises a rewinding (or re-spooling) mechanism arranged to rotate the drum to rewind the safety line onto the drum in the absence of sufficient tension in the safety line to pay out the line. 
         [0043]    The invention will now be further described by way of example only and with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0044]      FIG. 1  is a schematic sectional view of a first embodiment of a fall arrest system safety device in accordance with the invention; 
           [0045]      FIG. 2  is an exploded perspective view of the device of  FIG. 1 ; 
           [0046]      FIG. 3  is a schematic view of a preferred embodiment of the energy absorber arrangement in accordance with the invention; 
           [0047]      FIG. 4  is a schematic sectional view of a second embodiment of a fall arrest system safety device in accordance with the invention; 
           [0048]      FIG. 5  is an exploded perspective view of the device of  FIG. 4 ; 
           [0049]      FIG. 6  is a perspective view of the embodiment of  FIGS. 4 and 5 ; 
           [0050]      FIG. 7  is a schematic sectional view of an embodiment similar to the embodiment of  FIG. 1  with a recoil brake arrangement. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0051]    Referring to the drawings, and initially to  FIG. 1 , there is shown a safety device  1  in accordance with the invention having a main housing  2  within which is mounted a shaft  5  and a rotary drum  3  mounted to be able to rotate about the shaft by means of bearings  4 . The device includes an attachment eye  43  for suspension from an anchor structure as is known for prior art safety block devices. A safety line wound on the drum passes out of the device via an exit portion  44 . 
         [0052]    A reduced diameter proximal end  6  of the shaft  5  is held in a tail bearing  7  in the side of the main housing  2 . 
         [0053]    Within the main housing  2  adjacent and connected to the rotary drum  3  is a rewinding or re-spooling mechanism  8 . When a length of safety line is played out from the drum (causing rotation of the drum  3 ) the rewinding mechanism applies a small torque to the drum  3  causing it to contra-rotate in a direction which tends to rewind the safety line back onto the drum. One preferred type of rewinding mechanism is a coiled spring of the clockspring type. Many suitable rewinding mechanisms are known in the art and will therefore not be described in detail herein. The rewinding mechanism is provided with a shaft bearing  18   
         [0054]    Also coupled to the drum at its other side is a speed responsive engagement arrangement comprising a pawl  10  and ratchet  11  arrangement. The pawl and ratchet arrangement may for example be of a type as described in WO2008/007119. The pawls  10  are mounted for rotation with the drum  3  by means of a pivoting boss  27  that is received in a respective boss recess  12 ,  13  provided in the drum  3  and a facing plate  14  which is fixed to the rotary drum  3  by means of securing bolts  15 . The ratchet plate  11  is secured for rotation with the shaft  5 . At speeds of rotation of the drum below a predetermined rate the safety line is able to pay out from the drum unabated. In this regime, the pawls  10  rotate with the drum  3  and do not engage the ratchet  11  teeth formations. The ratchet  11  remains fixed to the shaft  5  and the shaft  5  and ratchet  11  do note rotate with the drum  3 . 
         [0055]    The main housing  2  is closed by an end plate  16  which is bolted to the main housing  2  by means of bolts  17 . The distal end  21  of the shaft  5  extends through a bush  29  secured in an axial aperture in the end plate  16 . The bush  29  permits rotation of the shaft  5  with respect to the end plate  16  and main housing  2 . The distal end of the shaft  5  is D shaped in section, having a flat  28  that provides a keying engagement connection with a connecting coiler member of an energy absorber as will be described. A shaft seal  19  seals the shaft  5 . This arrangement ensures that the interior of the main housing  2  is sealed from the exterior environment of the device, even though the shaft extends through the end plate  16  which acts as a dividing wall. 
         [0056]    An energy absorber housing  20  is bolted to the main housing  2  and contains an energy absorber cartridge  22  containing an energy absorber strip  23 . The energy absorber strip  23  is loaded into the cartridge  22  in un-deployed form. When deployed during a fall arrest event the energy absorber strip is deployed to a deformed state in order to absorb the energy of a fall. This will be described in greater detail herein. 
         [0057]    A preferred embodiment of energy absorber is shown in  FIG. 3 . The energy absorber cartridge  22  comprises a coiler member  35  and a circular annular deformer ring  33  arranged concentrically about the coiler member  35  and having an inner surface  33   a  and an outer surface  33   b . The coiler member  35  has a central aperture  32  which is D shaped in section in order to engage with the D shaped sectioned distal end  21  of the shaft  5 . In this way the shaft  5  and coiler member  35  are keyed to be coupled to drivingly rotationally engage when the absorber cartridge is loaded in position. 
         [0058]    The energy absorber strip  23  is arranged to absorb energy in response to relative rotational movement of the shaft  5  and coupled coiler member  35  with respect to the deformer ring  33 . In the illustrated embodiment the energy absorber is arranged to absorb energy in response to anti-clockwise rotation of the shaft ends  21  relative to the deformer ring  33 . 
         [0059]    The energy absorber strip comprises a stainless steel strip  23  having a constant thickness and width along its entire length. In operation, the energy absorber absorbs energy by plastic deformation of the stainless steel strip  23 . 
         [0060]    The coiler member  35  is provided with a key aperture  32  (in the form of D shaped aperture) for keying and driving engagement with the end  21  of shaft  5 . The coiler member  35  is mounted on the shaft end  21  so that the coiler member  35  rotates with the shaft end  21  relative to the deformer ring  33 . An annular space  38  is defined between the coiler member  35  and the inner surface  33   a  of the deformer ring  33 . The ring  33  has a deformer slot  33   c  passing through the ring  33  and oriented tangentially to the inner surface  33   a  of the ring  33 . The slot  33   c  is slightly wider than the thickness of the strip  34 . The slot  33   c  has a flat clockwise face  33   d  and a parallel flat anticlockwise face  33   e , and the anticlockwise face  33   e  of the slot  33  is tangential to the inner surface  33   a  of the ring  33 . The slot  33   c  has a curved entry surface  33   f  where the clockwise surface  33   d  of the slot  33   c  contacts the outer surface  33   b  of the ring  33  and a curved exit surface  33   g  where the clockwise surface  33   d  of the slot  33   c  contacts the inner surface  33   a  of the ring  33 . The curved entry surface  33   f  and the curved exit surface  33   g  are separated by the flat clockwise face  33   d.    
         [0061]    The strip  23  has a first end  23   a  secured to the coiler  35  and a free end  23   b . The strip  23  passes through the slot  33   c , and rest of the strip, ending in the free end  23   b , is coiled around the outer surface  33   b  of the deformer ring  33 . An upstanding outer circular wall  36  is provided for the absorber cartridge concentrically about the deformer ring  33  so that an annular strip storage channel  37  is formed between the outer surface  33   b  of the ring  33  and the wall  36 . The wall  36  and the deformer ring  33  stand upwardly from a backplate of the absorber cartridge  22 . The absorber cartridge  22  is secured by means of bolts to the end plate  16  of the main housing and provides protection against environmental effects such as weathering or dust. 
         [0062]    In a fall arrest event the safety line pays out from the drum  3  at a higher speed than in normal ‘safe’ pay out situations. Upon the drum  3  rotational speed reaching a predetermined threshold, the ratchet  11  causes the pawl  10  to kick out to a degree such that the pivotally mounted pawls  10  pivot about their pivot bosses  27  beyond a tipping point and become orientated to an engagement position in which the pawl  10  engages with the teeth of the ratchet  11 . This is described in detail in WO2008/007119 but in the arrangement described in that document the pawls are fixed with respect to the safety line drum and the ratchet rotates with the safety line drum which is the reverse of the situation described herein. In the teeth engaged position, the drum  3  is effectively coupled to the shaft  5  by means of the pawl  10  engagement with the ratchet  11 . Further rotation of the drum  3  therefore causes coupled rotation of the shaft  5  (and the drum  3 ) in the same direction. Also, the end  21  of the shaft  5  is drivingly coupled to the coiler member  35 , which is therefore caused to rotate relative to the deformer ring  33 . This relative rotation will wind the stainless steel strip  23  around the coiler member  35  and pull the stainless steel strip  23 , coiled in the annular strip storage channel  37 , through the deformer slot  33   c  into the annular space  38 . As the strip  23  passes through the slot  33   c  the strip  23  is plastically deformed and so absorbs energy. 
         [0063]    If the energy absorber remained subject to an applied couple greater than the predetermined deployment couple the entire length of the strip  23  would pass through the slot  33   c  and when the free end  23   b  of the strip  23  passed through the slot  33   c  the shaft  5  (and coiler member  35 ) would be released to rotate freely relative to the ring  33  without any energy being absorbed. In order to prevent this, the annular space  38  defined between the coiler  35  and the inner surface  33   a  of the ring  33  is arranged to be too small to contain the full length of the strip  23  when the strip  23  is wound around the coiler  35 . Thus, the total amount of energy absorbed by the energy absorber is controlled by the size of the annular space  38  and length of the strip  23  which can fit into the annular space  38 . 
         [0064]    The energy absorber cartridge  22  is loaded with a stainless steel absorber strip  23  in the un-deployed condition, with the end of the strip being connected to the coiler member  35 . The absorber cartridge is then fitted into the absorber casing  21 , and the casing  21  fitted with the cartridge  22  is then bolted to the end plate  16  connected to the main housing. In so doing, the D shaped aperture  32  of the coiler member  35  is matched up to receive in arrangement the D shaped sectioned distal end  21  of the shaft  5 . In this way the shaft  5  and the coiler member  35  are keyed to be coupled to drivingly rotationally engage when the absorber cartridge is loaded in position. The absorber holds the shaft  5  against rotation up to application of a predetermined torque or couple after which the shaft  5  is able to rotate with respect to the tail bearing  7  until the strip  23  is deployed to its maximum extent. 
         [0065]    As a result, following deployment of the energy absorber as a result of a fall arrest event, the energy absorber can be easily replaced by means of removing the absorber casing  21 , removing the spent cartridge  22 , replacing the cartridge by fitting a replacement cartridge and re-securing in position the absorber casing  21 . All of this can be achieved without disturbing any other working components of the device which remain sealed off in the main housing  2  closed by the face plate  16  acting as a dividing wall through which the shaft end  21  extends. 
         [0066]    In the embodiment of  FIGS. 1 to 3 , the shaft  5  is held from rotation by the positioning of the energy absorber in place. The shaft  5  is therefore able to rotate until the absorber is positioned in place. This permits the re-spooling spring mechanism  8  to be tensioned by rotation of the shaft  5 , before the shaft is fixed by fitting the absorber cartridge  22  in position. Following a fall event and deployment of the energy absorber, it is necessary to replace the absorber. When the energy absorber is removed for replacement, there is nothing to prevent the shaft  5  from rotating under the influence of the re-spooling spring mechanism  8  which unwinds (becomes de-energised). This means that it is necessary to re-energise the re-spooling spring mechanism  8 , each time the energy absorber is replaced. This adds a degree of complexity to changing over to replace a spent absorber cartridge. 
         [0067]    In the embodiment of  FIG. 7 , the proximal end  6  of the shaft  5  is extended through the bearing  18  and provided with a threaded end  6   a . A threaded nut  70  is fastened to the threaded end  6   a  of the shaft  5 . Before replacing the cartridge  22  following a deployment event, the nut  70  is tightened against the outer casing  2  to secure the shaft  5  relative to the casing  2 . This allows the absorber/cartridge to be replaced without unwinding/de-energising of the re-spooler spring mechanism  8 . The nut  70  is positioned in a recess  71  provided in an enlarged boss  72  of the casing, and a sealing cap  74  is provided. This prevents exposure of the arrangement which could lead to corrosion in hostile environmental conditions. The clamping of the shaft  5  using the nut  70  does not hinder deployment of the energy absorber  23  during a fall event. The thread on the shaft end  6   a  and the nut  70  is arranged to be in a rotational sense that as the shaft rotates during a deployment event (causing the absorber coil  23  to be pulled through the absorber casing) the nut  70  unscrews on the threaded shaft end  6   a . This ensures that the absorber performance is not interrupted or interfered with. 
         [0068]    In an alternative embodiment shown in  FIGS. 4 to 6 , the concept of the present invention is realised using an alternative embodiment of energy absorber. In this arrangement the components of the device are identical to those of the first described embodiment having regard to all items enclosed within the housing  2  and face plate  16 . In this embodiment however the energy absorber cartridge  22  and coil stored energy absorber strip arrangement  23  is replaced with an alternative-form energy absorber comprising a friction brake arrangement  51 . 
         [0069]    The friction brake arrangement  51  comprises a first annular friction disc  52  secured to the outer surface of the end plate  16  and through which the distal end  21  of shaft  5  extends. In this arrangement the distal end  21  of shaft  5  has an external thread for engaging with a threaded bore of tightening nut  53 . It will be appreciated that the disc  52  being fixed with respect to the end plate  16  cannot rotate with the shaft end  21 . Two further annular friction brake discs  54   55  are mounted over the end of the shaft and a frustoconical compression energiser spring  56  is mounted between a keyed drive disc  57  and the brake disc  55 . The drive disc  55  includes a flat sided key slot  58  for fitting over the D shaped distal end  21  of shaft  5 , for engagement with the shaft, such that rotation of the shaft  5  causes rotation of the drive disc  57 . The threaded nut  53  is tightened onto the threaded end  21  of shaft  5  up to a predetermined torque. This causes the drive disc  57  to compress the spring  56  against the disc  55  in order to energise the brake arrangement. In operation, as in the previous embodiment, in the event of a fall arrest event the safety line pays out from the drum  3  at a higher speed than in normal ‘safe’ pay out situations. Upon the drum  3  rotational speed reaching a predetermined threshold, the ratchet  11  causes the pawl  10  to kick out to a degree such that the pivotally mounted pawls  10  pivot about their pivot bosses  27  beyond a tipping point and become orientated to an engagement position in which the pawl  10  engages with the teeth of the ratchet  11 . In the teeth engaged position, the drum  3  is effectively coupled to the shaft  5  by means of the pawl  10  engagement with the ratchet  11 . Further rotation of the drum  3  therefore causes coupled rotation of the shaft  5  (and the drum  3 ) in the same direction. Also, the end  21  of the shaft  5  is drivingly coupled to the drive disc  57  and rotation of the drive disc causes rotation of the brake discs  52 ,  54 ,  55  relative to one another in a friction brake action. This absorbs energy during the fall arrest event. 
         [0070]    The brake disc arrangement  51  can be sealed from the environment in a similar manner to the sealing of the coil energy absorber of the first embodiment, by means of a housing similar to housing  20  bolted (or otherwise secured) to the main housing  2  or the face plate  16 . In common with the first described embodiment, following a fall arrest event and usage of the friction brake arrangement  5  to absorb the energy of the fall, the fiction brake components can be conveniently and easily accessed in order to replace the components and re-tighten the arrangement to the required torque. It is important to ensure that the tightening torque is at the predetermined level in order to ensure hat the correct energy absorption occurs during the fall arrest event.