Patent Publication Number: US-8991556-B2

Title: Fall arrest block

Description:
This invention relates to a fall arrest block for use by a workman working above the ground. The block will be connected to a secure fixed point, and a lifeline wound on the block is connected to a harness worn by the workman, with the lifeline winding up and unwinding under spring control whilst the workman moves around, but locking up and providing a soft landing if the workman falls. 
     In this specification, the term “lifeline” or “lifeline medium” is used to denote the connecting line between the block and the workman, and which is wound onto a drum within the fall arrest block. 
     Some fall arrest blocks use wire rope as the lifeline, others use webbing and still others use a fibre rope. The choice of lifeline is individual to the user and the environment. For example, wire lifelines are not used in areas where the production of a spark is to be avoided but are preferred over webbing lines where there is a risk of chafe. The lifelines are wound on a drum in the block, and conventional blocks use a different design of drum, depending on the nature of the lifeline. 
     According to the present invention, there is provided a drum for use in a fall arrest block, the drum comprising a core and flanges on either side of the core, wherein the core and one of the flanges are formed as a plastics moulding, and the core has separate anchorage points for more than one type of lifeline. 
     The drum preferably has anchorage points for wire rope and for webbing. 
     The drum can be a skeletal plastics moulding, and the outer periphery of the drum can be discontinuous, with the circumference on which the lifeline is wound being formed by annularly spaced regions around a pitch circle. The core and said one of the flanges are preferably formed as a single plastics moulding. 
     The other of the flanges can be in the form of a disc, and the core and the other flange may have interengaging formations which prevent relative rotation between the flange and the core. 
     A spring is preferably provided to rewind the lifeline onto the drum, the core and said one of the flanges being famed as a single plastics moulding and the moulding incorporating a housing for the spring on the side of said one of the flanges which faces away from the core. 
     The invention also provides a brake unit for use in a fall arrest block, the unit comprising a first part which is adapted to be secured to a chassis of the block, a second part which can be locked to the drum when a fall is to be arrested, and friction surfaces within the unit which allow rotation between the first and second parts against the friction generated by the friction surfaces, characterised in that the brake unit is a sealed unit. 
     The brake unit is preferably in the form of a disc, with the first part forming the centre of the disc and the second part in the form of an annulus lying generally around the edge of the first part. The first part can be in the form of two spaced plates connected by axially extending studs by which the first part can be secured to the chassis. The second part can be a ring, with an inwardly directed annular flange which lies between the two spaced plates and with an outwardly directed periphery carrying teeth which can be engaged by a pawl to lock the second part to a drum on which a lifeline is wound. 
     Friction linings can be provided between the plates and the inwardly directed flange, on both sides of the flange. The linings can be in the form of annuli. 
     O-rings can be provided to seal between the first and second parts. The O-rings can be fitted between the circumferential outer edges of the spaced discs, and opposing flanges on the second part. 
     The invention also extends to a fall arrest block incorporating a brake unit as set forth above, to a fall arrest block incorporating a drum as set firth above, and to a fall arrest block incorporating both a drum as set forth above and a brake unit as set forth above. 
    
    
     
       The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is an external perspective view of a fall arrest block in accordance with the invention; 
         FIG. 2  shows the block of  FIG. 1  with one cover removed, to show the internal components; 
         FIG. 3  shows the block in an exploded view; 
         FIG. 4  is a perspective view of the lifeline drum, separated from the other components of the block; 
         FIG. 5  is a plan view of the drum of  FIG. 4 ; 
         FIGS. 5   a  and  5   b  show how two different lifelines can be terminated for use with the drum of  FIGS. 4 and 5 ; 
         FIG. 6  is a side view of the drum of  FIGS. 4 and 5 ; 
         FIG. 7  is a perspective, rear view of the drum; 
         FIG. 8  shows a brake assembly forming part of the fall arrest block; and 
         FIG. 9  is a cross-section through the brake assembly of  FIG. 8 . 
     
    
    
       FIG. 1  shows the external housing of a fall arrest block which is contained within a housing made up from two plastics moulded cover sections  10 ,  12 . The cover sections have slots  14  through which a carrying handle can be threaded, and a recess  16  through which a metal hanger plate  18  extends. The block will be attached to a fixed structure by means of a link passing through the hole in the plate  18 , and the plastics housing halves  10 ,  12  will carry no load. 
     In use, a lifeline will extend out of the housing through an opening  20 , and the two halves of the housing will be secured together by screws passing through apertures  22 . 
       FIG. 2  shows the internal components of the block, with one of the housing cover sections  12  removed. Within the housing there is a chassis formed by two hanger plates  18 . One of those plates has been removed in  FIG. 2  so that the other components can be seen. Between the two hanger plates (both plates are visible in  FIG. 3 ) there is a brake unit generally designated  24  and a lifeline drum generally designated  26 . It will be seen from  FIG. 2  that the brake unit  24  has en outer ring  28  with a series of teeth and that two pawls  30  are mounted on the drum  26 . Under normal operation the brake unit will be held stationary as the unit is secured to the right hand hanger plate  18  by three threaded studs  29  passing through holes  31  in the plate, and the pawls  30  will remain outside the pitch circle of the teeth  28 . The drum  26  on which the pawls  30  are mounted can then rotate freely, against the action of a spring behind the drum. Thus the lifeline (which is not shown in the figures) can be pulled off from the block resulting in rotation of the drum  26 , and can be rewound onto the block through the action of the spring (which will be described later). However if there should be a sudden rapid pull on the lifeline if a workman falls, the drum  26  will rotate fast and this will cause the pawls  30  to pivot about their axes and to engage with the teeth  28 . The pawls  30  are provided with weighted ends  36  so that centrifugal force will cause the weighted end to fly outwards and the opposite end of the pawl to engage with the teeth. At this point the drum  26  is locked to the outer rim of the brake unit. The brake unit can however still rotate, but this time against the braking force generated by the brake unit  24  which will absorb energy and thus allow the workman&#39;s fall to be arrested. 
       FIG. 2  also shows the screws  38  which secure the two halves of the cover together. 
     Turning now to  FIGS. 4 and 5 , the main part of the drum  26  is a plastics moulding with a flange  40  and a core generally designated  42 . The core  42  is not a solid body, but is skeletal in nature. A lifeline indicated schematically at  44  ( FIG. 5 ) will be wound around the drum. In  FIG. 5  only one turn of lifeline is shown, but it will be understood that in fact there will be multiple turns of lifeline around the drum. The lifeline stretches between contact points indicated at  46 . Within the skeletal core are two lifeline anchorage points  48  and  50 . The anchorage point  48  is for use with a fibre rope or webbing lifeline. To anchor a webbing lifeline, the and of the webbing  44   a  would be doubled back on itself as shown in  FIG. 5   a  and stitched at  52  to leave an eye  54  at the end. This end of the webbing will then be inserted into the recess  48 , and a metal pin placed inside the eye  54 . The diameter of the metal pin and of the eye  54 , together with the thickness of the webbing will be sufficient to lock the webbing in the recess  48 . 
     A similar technique can be used if the lifeline is of braided fibre rope, when an eye splice can be formed in the end of the rope and a pin inserted in the same way as just described. 
     If the lifeline instead is a wire cable  44   b , then this will be secured in the drum at  50 , and to secure the cable the end of the cable will be provided with a swaged on terminal  56  ( FIG. 5   b ) which will fit within the rectangular recess at  50 , with the cable  44   b  suiting the anchorage point  50  through the passage  58 . 
     The other openings in the skeletal core (some of which indicated at  60 ) are designed to reduce the overall weight of the core, whilst ensuring that the core remains rotationally balanced. 
     The drum  26  is completed by a second flange  62  ( FIG. 3 ) which is secured to the core  42  through screws through the plate  62  into threaded inserts  64  in the drum  40 . The core  42  has upstanding lips  66  (see  FIG. 6 ) which engage in corresponding recesses in the plate  62 . 
     On the back of the flange  40  an integrally moulded cup  68  houses a clock spring  70 . This spring  70  will wind the lifeline back onto the drum  40 , when there is no load on the lifeline, but will allow lifeline to be drawn off by a steady pull. 
     The brake drum shown in  FIGS. 8 and 9  is provided as a sealed unit. Correct and fault free operation of the brake is critical to the operation of the block, and thus the brake needs to be reconditioned from time to time. When the braking function needs to be reconditioned, the unit shown in  FIGS. 8 and 9  can simply be removed and replaced with a new unit, to avoid having to service this part. As the correct functioning of the brake is critical to the operation of the block, it is highly desirable for this to be in the form of a sealed unit. 
     The central brake plate  80  is held fast to the hanger plate  18  through studs  29  which pass through the brake plate and the brake stud plate  84  ( FIG. 9 ) so that these two plates rotate together. 
     The pawl ring  28  has an inwardly extending flange  86 , and two friction rings or brake pads  88  sit between the flange  86  and the plates  80 ,  84 . Thus, the pawl ring  28  can rotate relative to the (fixed) plates  80 ,  84  against the friction generated between the plates and the flange by the brake pads  88 . The friction generated will depend on the clamping force by which the plates  80  and  84  are clamped together, and this force can be preset by tightening the nuts  85  on the studs  29 . To seal the unit, O-ring seals  90  are provided between the outer edges of the plates  80 ,  84  and the pawl ring  28 . 
     When the fall arrest block is serviced, and in any case after a fall has been arrested, the brake unit  24  will be replaced with a pre-assembled, pre-tested unit. 
     As a result of the skeletal nature of the drum  26 , considerable weight savings can be made. The ability to attach different types of lifeline to a single drum configuration reduces stocking costs, and distributors of fall arrest blocks need only keep one type of block in stock, which can be would with whatever lifeline medium is requested by the end user.