Patent Publication Number: US-2017361137-A1

Title: Self-braking pulley

Description:
The present invention relates to a self-braking pulley. 
     It is well known for individuals working or operating at height to use a tether to secure themselves to a suitable support to arrest their fall should they unexpectedly fall or otherwise need to escape from their position. The tether is typically secured to the individuals harness and as such, while the tether may arrest their fall, there can be a significant jolt upon the individual as the tether becomes taught. Moreover, once the individual has come to a rest and is held suspended from the tether it is necessary to lower the individual to avoid any trauma from prolonged suspension, particularly if the individual is unconscious and held in an inverted orientation. 
     We have now devised a self-braking pulley, which provides for a controlled extraction of a tether therefrom and thus a controlled descent of an individual coupled to the tether. 
     In accordance with the present invention there is provided a self-braking pulley for controlling a rate of extraction of a tether coupled with the pulley, the pulley comprising: 
     a pulley housing; 
     a spool for receiving a tether, the spool being configured to rotate about a first axis, relative to the pulley housing; 
     a piston assembly comprising a chamber having a first and second chamber portion which are rotationally locked to the housing, a fluid disposed within the chamber, and a piston which is arranged to move within the chamber along a second axis between the first and second chamber portions, the piston assembly further comprising at least one bore formed within the piston for fluidly coupling the first and second chamber portions, 
     the pulley further comprising means for coupling rotational motion of the spool with reciprocating motion of the piston back and forth between the chamber portions, to cause the fluid to transfer between the chamber portions via the at least one bore as the spool rotates. 
     The movement of the piston between the first and second the chamber portions is restricted by the fluid pressure within the chamber portions. In order to relieve the pressure within the chamber portion into which the piston is moving, so that the piston can continue to move toward that chamber portion, the fluid is required to pass along the at least one bore into the other chamber portion. The rate of transfer of fluid and thus the ease with which the pressure can be redistributed, and thus the ease with which the piston can move, is dependent upon the number of bores and a cross-sectional area of the bores, in addition to the viscosity of the fluid. The piston assembly thus serves to brake the rotation of the spool owing to the means for coupling rotational motion of the spool with reciprocating motion of the piston. 
     In an embodiment, the first axis and the second axis are collinear. 
     In an embodiment, the means for coupling the rotational movement of the spool with reciprocating motion of the piston comprises at least one follower member which is coupled to the spool, and which extends within an annular channel disposed in an outer surface of the piston, such that as the spool rotates, the follower member is arranged to move along the channel. Preferably, the means for coupling comprises at least two and more preferably three follower members. In an embodiment, the follower members extend radially inwardly of the spool and are equidistantly spaced around the spool. 
     In an embodiment, the or each follower member comprises a shaft which is coupled at a proximal end thereof to the spool and which comprises a roller disposed at a distal end for facilitating the passage of the respective follower member within the channel. 
     In an embodiment, the channel comprises a continuous channel which extends circumferentially around the piston, namely a channel which comprises no definitive start or end and where a start and end of the channel coincide. The channel preferably further extends back and forth along the rotational axis, in extending around the rotational axis. The channel preferably follows a harmonically varying path around the piston. 
     In an embodiment, the spool is arranged to rotate within a bearing arrangement within the housing. 
     In an embodiment, the piston comprises a first portion and a second portion which separately extend into the first and second chamber portions respectively, in moving back and forth along the second axis. Preferably, the channel extends intermediate the first and second piston portions. In an embodiment, the piston further comprises a first and second seal which extends around the first and second portions respectively, for sealing the first and second piston portions within the first and second chamber portions, respectively. 
     In an embodiment, the piston comprises at least two bores which extend through the piston. The at least two bores preferably extend along a linear path through the piston. In an embodiment, the at least two bores extend substantially parallel to each other, and preferably parallel to the second axis. 
     In an embodiment, the piston assembly further comprises at least one connecting rod which couples the first and second chamber portions. The connecting rod extends through a guide bore formed within the piston, such that the piston is arranged to slide upon the connecting rod in moving back and forth between the first and second chamber portions. In an embodiment, the piston assembly comprises at least two connecting rods which extend through a respective guide bore formed within the piston. Preferably, the at least two connecting rods are substantially parallel. The guide rod(s) preferably minimise any rotational motion of the piston about the second axis and restrict the piston to substantially linear motion along the second axis. 
     In an embodiment, the first and second chamber portions are rotationally locked to the housing via at least a first protuberance and at least a second protuberance, respectively, formed on an outer wall of the respective chamber portion. Preferably, the protuberances extend within a complimentary shaped recess formed within the housing. 
     Whilst the invention has been described above, it extends to any inventive combination of features set out above or in the following description. Although illustrative embodiments of the invention are described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to these precise embodiments. 
     Furthermore, it is contemplated that a particular feature described either individually or as part of an embodiment can be combined with other individually described features, or parts of other embodiments, even if the other features and embodiments make no mention of the particular feature. Thus, the invention extends to such specific combinations not already described. 
    
    
     
       The invention may be performed in various ways, and, by way of example only, embodiments thereof will now be described, reference being made to the accompanying drawings in which: 
         FIG. 1  is a perspective view of a self-braking pulley according to an embodiment of the present invention; 
         FIG. 2  is a view of the pulley illustrated in  FIG. 1 , with a front casing removed; 
         FIG. 3  is a perspective view of the pulley illustrated in  FIG. 1 , with the housing removed; 
         FIG. 4  is an exploded view of the piston assembly; 
         FIG. 5  is an assembled view of the piston assembly illustrated in  FIG. 4 , with the follower members positioned in situ within the channel; 
         FIG. 6  is a sectional view through the piston assembly of  FIG. 3 , taken across line A-A, with the bearing elements removed; 
         FIG. 7  is an exploded view of the pulley illustrated in  FIG. 1  with the piston assembly removed; 
     
    
    
     Referring to  FIGS. 1 and 2  of the drawings, there is illustrated a self braking pulley  100  according to an embodiment of the present invention for controlling a rate of extraction of a tether (not shown) coupled to the pulley  100  for controlling a rate of descent for example, of an individual (not shown) coupled to the tether. The pulley  100  comprises a pulley housing  110  having a front and rear casing  110   a,    110   b,  which may be formed of a rigid plastics or metal alloy, for example. The housing  110  comprises a cylindrical body  111  region orientated such that a longitudinal axis of the body  111  extends substantially horizontally in use. The housing further comprises a handle  112  formed integrally with the body  111 , at an upper region thereof, which may also be used for coupling with a karabiner (not shown) or similar for securing the pulley  100  to an anchor position, and a base  113  integrally formed at an underside of the body  111 . The front and rear casing  110   a,    110   b  separately comprise a front and rear portion of the handle  112   a,    112   b,  body  111   a,    111   b  and base  113   a,    113   b,  and are coupled together by a plurality of fasteners  114  which are arranged to separately extend through aligned apertures  115  formed in the front and rear casing  110   a,    110   b.    
     The pulley  100  further comprises a spool  120  and a piston assembly  130  disposed within the body  111  of the housing  110 . The spool  120  is arranged to rotate about a first axis which is substantially collinear with a longitudinal axis of the body  111 , and is arranged to receive a tether (not shown), such as a rope (not shown) or webbing (not shown), which may be wound upon the spool  120 . A free end of the tether may be rigidly coupled to the spool  120 , while the other free end of the tether is arranged to extend out from the housing  110  via an aperture  116  disposed at an underside of the base  113 . Alternatively, a tether may be arranged to pass into the housing  110  via the aperture  116 , pass around spool  120  and pass out from the housing via the aperture  116 . In this respect, the tether may be simply looped around the spool  120 , for example. The aperture further comprises a plurality of spacer rods  117  which extend across the aperture  116  and upon which may be disposed rollers  118  which are free to rotate upon the spacer rods for providing a snag free passage of the tether into and out from the pulley housing  110 . 
     Referring to  FIGS. 2 and 3  of the drawings, the spool  120  comprises a ring shape having a circumferentially extending recess  121  formed in an outer curved surface thereof, for receiving the tether (not shown). The recess  121  is disposed between opposing annular flanges  122  which are separately receivable in a respective annular bearing element  123   a,    123   b.  The bearing elements  123   a,    123   b  separately extend along an interior curved surface of the front and rear body portions  111   a,    111   b  of the respective casing  110   a,    110   b,  and are coupled thereto, such that the spool  120  can freely rotate within the body  111 , but is restricted from moving along the first axis. 
     Referring to  FIGS. 3 and 4  of the drawings, the piston assembly  130  is disposed radially inwardly of the spool  120  and comprises a chamber  131  having a longitudinal or second axis which is coincident with the first axis. The chamber  131  comprises a first and second chamber portion  132 ,  133 , each comprising a cylindrical outer wall  132   a,    133   a  and an end wall  132   b,    133   b  which closes one end of the respective chamber portion  132 ,  133 . The chamber portions  132 ,  133  are orientated such that the open end of each chamber portion  132 ,  133  face each other, but are separated from each other along the second axis by a predefined spacing. 
     The piston assembly  130  further comprises a piston  134  having a substantially cylindrically shaped body  135  which is closed at opposite ends thereof via a respective end wall  136 , and which is arranged to move in sliding relation within the chamber  131 . In particular, the piston  134  comprises a first piston portion  137  and a second piston portion  138  which are arranged to separately extend in sliding relation within the first and second chamber portions  132 ,  133 , respectively. The first and second portions  137 ,  138  of the piston  134  separately comprise a circumferentially extending seal  139 , such as one or more O-rings, for sealing the outer surface of the body  135  of the first and second piston portions  137 ,  138  with the inner surface of the cylindrical wall  132   a,    133   a  of the respective chamber portion  132 ,  133 . 
     The piston  134  and first and second chamber portions  137 ,  138  are coupled together by at least one connecting rod  140 . In the illustrated embodiments, the piston assembly comprises three connecting rods  140  which orientated substantially parallel to each other and the second axis, and which are arranged in a substantially trigonal arrangement. The connecting rods  140  extend through a respective guide bore  141  formed within the piston  134 , and the chamber portions  132 ,  133  are coupled to the rods by passing a fastener  142  through an aperture  143  formed within the end walls  132   b,    133   b  of the chamber portions  132 ,  133 , to couple with an internally threaded portion  140   a  at the distal ends of the connecting rods  140 . The fasteners  142  are sealed within the apertures  143  via respective seal  142   a.  The piston  134  is arranged to slide in sealing relation, upon the connecting rods  140  via one or more seals  144 , such as O-rings, located in an annular recess  145  formed upon the connecting rods  140 . The piston  134  is thus limited to substantially linear motion back and forth within the chamber  131 , between the chamber portions  132 ,  133 , and the trigonal configuration of the connecting rods  140  further minimises any rotation of the piston  134  within the chamber portions  132 ,  133 . 
     The first and second chamber portions  132 ,  133  separately extend to either side of the spool  120 , along the first axis, as illustrated in  FIGS. 5 and 6  of the drawings. An outer surface of the cylindrical wall  132   a,    133   a  of the chamber portions  132 ,  133  separately comprise at least one protuberance  146  which extend radially out from the cylindrical wall  132   a,    133   a  and locate within a complimentary shaped recess  147  (as illustrated in  FIG. 7  of the drawings) formed within an inner side of the body  111  of the housing  110 . In this respect, the first and second chamber portions  132 ,  133  and thus the piston assembly  130  is rotationally locked to the housing  110 , to minimise any rotational movement of the assembly  130  within the housing  110 . 
     The pulley  100  further comprises means for coupling and converting the rotation of the spool  120  with reciprocating motion of the piston  134  back and forth within the chamber portions  132 ,  133 . In the illustrated embodiment, the means comprises three follower members  150  coupled with the spool  120 , which are arranged to locate within an annular channel  160  formed in the piston  134 . The follower members  150  extend in the plane of the spool  120  and extend into the channel  160  via the spacing between the chamber portions  132 ,  133 . The follower members  150  separately comprise an elongate shaft  151  which is arranged to snap-locate for example, within a respective aperture  152  formed within the spool  120  and which is disposed at a base of the recess  121 . The shaft  151  is inserted through the aperture  152  along a radially inward direction of the spool  120 , and is prevented from passing completely through the aperture  152  via an oversize shaft head  153 . A distal end of the shaft  151  is coupled with a roller  154  or similar for facilitating the passage of the follower member within the annular channel  160  and for centralising the shaft  151  of each member  150  within the channel  160 . The follower members  150  are angularly separated equidistantly around the inner periphery of the spool  120 , and in the illustrated embodiment comprising three follower members  150 , the members  150  are thus angularly separated by substantially 120°. 
     The channel  160  extends around an outer periphery of the piston  134  and is disposed intermediate the first and second piston portions  137 ,  138 . The channel  160  comprises a continuous channel, having no definitive start or end. The channel  160  extends back and forth along the piston  134 , along the first axis, in extending around the axis and comprises a substantially harmonically varying profile. The number of harmonic periods, namely the number of repetition periods of the channel profile in extending back and forth along the first axis, either side of the plane of the spool  120 , is configured to comprise one less than the number of follower members  150 . This ensures that each follower member  150  experiences the same channel profile at the same time. Accordingly, as the spool  120  rotates about the first axis, the follower members  150  are arranged to rotate with the spool  120 . 
     Referring also to  FIG. 7  of the drawings, the movement of the follower members  150  imparts a reciprocating motion of the piston  134  back and forth along the second axis (which in the illustrated embodiment is collinear with the first axis) as the follower members  150  move along the channel  160 , owing to the harmonically varying profile of the annular channel  160 . The piston assembly  130  further comprises a fluid (not shown), such as an oil or similar, disposed within the first and second chamber portions  132 ,  133  and the piston  134  further comprises a plurality of bores  170  which extend through the piston body  135 . The plurality of bores  170  extend substantially parallel to each other and the second axis, and communicatively couple the chamber portions  132 ,  133 , such that the fluid can transfer between the chamber portions  132 ,  133  via the plurality of bores  170 . 
     As the spool  120  rotates within the bearing elements  123   a,    123   b,  the piston  134  is arranged to move along the connecting rods  140  toward the first chamber portion  132 , for example. During this motion, the end wall  136  of the piston portion  132  will compress the oil disposed between the end wall  136  and the end wall  132   b  of the first chamber portion  132 . This compression will cause the fluid to transfer into the second chamber portion  133  via the plurality of bores  170  within the piston body  135 . The speed with which the fluid can pass into the second chamber portion  133  and thus the speed with which the piston  134  can continue to move into the first chamber portion  132  is dependent on the number of bores  170 , a cross-sectional area of the bores  170  and the viscosity of the fluid. Similarly, the speed with which the fluid can pass into the first chamber portion  132  and thus the speed with which the piston  134  can continue to move into the second chamber portion  133  on the return stroke, is dependent on the number of bores  170 , a cross-sectional area of the bores  170  and the viscosity of the fluid. The piston assembly  130  and fluid thus impart a braking force upon the spool  120 , since the reciprocating movement of the piston  134  is coupled to the rotational movement of the spool  120  via the follower members  150  and the piston channel  160 . Accordingly, the rate of extraction of a tether (not shown) from the spool  120 , and thus a rate of descent of an individual (not shown) from an elevated position, can be suitably controlled by designing a piston  134  with the required number of bores  170 , having the required cross-sectional area, in conjunction with the required viscosity of the fluid. 
     The fluid is arranged to mechanically dampen the motion of the piston  134  and thus in turn, the rotation of the spool  120  by transferring the fluid back and forth between the chamber potions  132 ,  133 . The forced passage of the fluid through the bores  170  is found to generate heat, but this heat is quickly dissipated owing to the thermal conductance of the housing  110 . 
     From the foregoing, it is evident that the self-braking pulley  100  provides an effective means of controlling a rate of rotation of a pulley spool  120 .