Patent Document

CROSS-REFERENCE TO RELATED APPLICATION AND PRIORITY CLAIM 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 15/093,317 filed on Apr. 7, 2016, which is based on and claims priority to U.S. Provisional Patent Application No. 62/144,260 filed on Apr. 7, 2015, which is incorporated herein by reference in its entirety for all purposes. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to the field of rope access and rescue. More particularly, the present invention relates to a descender that is typically attached to an operator&#39;s harness to allow controlled descent down a fixed rope. Descenders may be used in other applications that require holding and controlled release of a rope under load. 
       BACKGROUND 
       [0003]    Descenders are widely used in the field of rope access and rescue for controlling the descent of people or equipment suspended by rope. Descenders are commonly used by operators to descend down a rope that is affixed overhead. Descenders may also be attached to an anchor position to allow an operator to control the descent of one or more people or gear from a remote location. Typically, descenders are comprised of elements that clamp or pinch the rope and are self-energized by load applied to the rope in one direction through the device. Controlled release is typically achieved by actuation of a lever which alleviates the clamping force holding the rope, allowing controlled release of rope through the device. Under certain circumstances it is necessary to pull rope through the descender, thereby reversing the direction of travel. In these cases the descender serves as a turning point for the rope and a means of progress capture. 
         [0004]    Descenders commonly incorporate a “panic” safety feature such that if the means of release is inadvertently actuated too far, the descender will cease the release of rope, preventing an uncontrolled freefall of the suspended persons or equipment. 
         [0005]    Descenders that are currently available have some recognized limitations. Compact descenders of the type that would be worn on a harness do not excel at handling the greater loads involved with a two person descent, as is common in a rescue situation. The maximum working load specification of commonly available descenders does not accommodate requirements of two person rescue, or requires additional hardware to configure the device for high loads. The effort required to initiate release at higher loads is difficult, and controllability is diminished. At these higher loads, descenders commonly have the undesirable effect of flattening the rope or milking the rope sheath due to the aggressive localized pinching employed to grip the rope. Additionally, compromises made to make the device perform well over a wide range of loads contribute to poor performance at low loads. For example, a user may find difficulty initiating descent of a light weight load due to high friction in the device, or may find that the release is initiated at a handle position very near the point of panic relock, making operation frustrating. 
         [0006]    As such, there is a need for a compact descender capable of managing a large range of loads while maintaining easy and controlled release. 
       SUMMARY 
       [0007]    A descender for controlling descent of a load along a rope includes a chassis and an opening plate pivotably attached to the chassis. A generally circular sheave having a groove around its circumference is attached to one end of a pivot arm. The other end of the pivot arm is pivotably attached to the chassis. A shoe is attached to the chassis and is positioned such that when the opening plate is in an open position, the rope may be installed by feeding the rope around a significant portion of the circumference of the sheave, and past the shoe. When the opening plate is in a closed position, a path for a rope is formed through the descender such that the rope slides against the shoe, and is selectively forced into the groove on the sheave. The second end of the pivot arm is biased toward the shoe so that when the rope is in tension, the sheave is rotated toward the shoe, trapping the rope there between. 
         [0008]    A handle is attached to the chassis and engaged with the pivot arm such that movement of the handle controls the amount of force biasing the pivot arm against the shoe, which allows a user to selectively reduce the force between them. By reducing the force between the sheave and the shoe, the tension of the rope is able to overcome frictional force holding the descender in place, thus allowing the descender to move along the rope. 
         [0009]    An attachment hole is provided that passes through the chassis and the opening plate such that when the opening plate is in the closed position, an operator can lock the descender in the closed position by inserting any suitable attachment means through the attachment hole, including but not limited to a carabiner. 
         [0010]    It will be understood by those skilled in the art that one or more aspects of this invention can meet certain objectives, while one or more other aspects can lead to certain other objectives. Other objects, features, benefits and advantages of the present invention will be apparent in this summary and descriptions of the disclosed embodiment, and will be readily apparent to those skilled in the art. Such objects, features, benefits and advantages will be apparent from the above as taken in conjunction with the accompanying figures and all reasonable inferences to be drawn therefrom. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a perspective view of one embodiment of a descender in accordance with the invention, showing a rope installed as would be seen by an operator in use; 
           [0012]      FIG. 2  is another perspective view of the descender of  FIG. 1 , with a swing plate open; 
           [0013]      FIG. 3  is another perspective view of the descender of  FIG. 1 , showing the descender from the opposite direction as  FIG. 1 ; 
           [0014]      FIG. 4  is another perspective view of the descender of  FIG. 1 , showing a release mechanism cover removed to reveal internal components of the descender; 
           [0015]      FIG. 5  is an exploded perspective view of the descender of  FIG. 1 , with release mechanism cover  14  removed; 
           [0016]      FIG. 6  is a perspective view of one embodiment of a handle subassembly in accordance with the invention showing one handle member removed; 
           [0017]      FIG. 7  is a perspective view of an alternative embodiment of a descender in accordance with the invention; 
           [0018]      FIG. 8  is a perspective view of an additional alternative embodiment of a descender in accordance with the invention having an alternative cam release mechanism and showing a rope installed as it would be seen by an operator in use; 
           [0019]      FIG. 9  is another perspective view of the descender of  FIG. 8  showing the opposite side of the descender; 
           [0020]      FIG. 10  is a perspective view of the descender of  FIG. 9  with a portion of a handle removed to reveal internal components; 
           [0021]      FIG. 11  is another perspective view of the descender of  FIG. 9  with the rope removed and the handle in a stowed position; 
           [0022]      FIG. 12  is a perspective view of a handle for the descender of  FIG. 8  showing the internal components of the handle; 
           [0023]      FIG. 13  is a perspective view of a chassis for the descender of  FIG. 8 ; 
           [0024]      FIG. 14  is a partially exploded perspective view of the descender of  FIG. 8 ; 
           [0025]      FIG. 15  is a perspective view of the descender of  FIG. 8  shown in an open position; 
           [0026]      FIG. 16  is another perspective view of the descender of  FIG. 8  shown in an open position and further demonstrating how the descender can be rigged; 
           [0027]      FIG. 17  is a perspective view of the descender of  FIG. 8  showing the descender in an open position; 
           [0028]      FIG. 18  is a section view of the descender of  FIG. 8  taken generally along the line  18 - 18  in  FIG. 17 ; 
           [0029]      FIG. 19  is a side view of the descender of  FIG. 8 ; 
           [0030]      FIG. 20  is a section view of the descender of  FIG. 8  taken generally along the line  20 - 20  in  FIG. 19 ; 
           [0031]      FIG. 21  is a perspective view of one embodiment of a descender in accordance with the invention showing the front of the descender; 
           [0032]      FIG. 22  is another perspective view of the descender of  FIG. 21  showing the descender in an open position; and 
           [0033]      FIG. 23  is another perspective view of the descender of  FIG. 21  showing the back of the descender. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    As shown in  FIG. 1 , the present invention is a descender  1  having a chassis  10 , which together with swing plate  12  contain rope  28 . Rope  28  is reeved such that a load to be managed pulls in direction A. Swing plate  12  is pivotably attached to chassis  10 , which allows a user to rig the descender  1 . Hole  10   a  provides a means of attachment, typically accomplished with a carabiner, but any other suitable attachment may alternatively be used. Hole  10   a  passes through the swing plate  12  and the chassis  10  so that when descender  1  is in use and a carabiner or other attachment means is in use, the swing plate  12  cannot open. Handle member  30  is pivotally mounted to chassis  10 . An operator can control the release of rope  28  by rotating handle member  30  in direction D. 
         [0035]      FIG. 2  shows descender  1  with swing plate  12  pivoted to an open position, which is only made possible if there is no attachment means passing through hole  10   a . Sheave  22  has an acutely V-shaped groove  22   a  about its circumference that enhances the frictional interface between rope  28  and sheave  22  as tension is applied to rope  28 . Sheave  22  is rotatably mounted to pivot arm  20  and has a one-way ratchet which only allows rotation in one direction. In the embodiment shown in  FIG. 2 , the ratchet allows rotation in direction B. In this embodiment, one-way rotation of sheave  22  is achieved by a pawl that engages teeth integrally formed in sheave  22 . Of course, any suitable ratchet or backstopping clutch that only allows rotation of sheave  22  in direction B relative to pivot arm  20  may be used without departing from the invention. The one-way rotation of sheave  22  enables the descender  1  to act as an efficient pulley if ascent is required because free movement of sheave  22  in direction B means that the frictional forces between sheave  22  and rope  28  need not be overcome. 
         [0036]    As shown in  FIG. 2  a user may install rope  28  by inserting the rope into the chassis  10  at guide  16  and wrapping the rope around sheave  22 , and exiting the chassis at shoe  18 . Pivot arm  20  constrains motion of the sheave  22  such that the resultant force of the rope on the sheave clamps the rope between the sheave and shoe  18 . Alternative mechanical means of constraining motion of sheave may be also employed without departing from the invention. Guide  16  and shoe  18  may alternatively be rotating rollers, but shown here are fixed deflection locations having low friction surfaces to keep the descender compact and to minimize cost. 
         [0037]    As shown in  FIG. 3 , release mechanism cover  14  is attached to chassis  10  on the opposite side of swing plate  12  and provides pivot locations for components within the descender  1 .  FIG. 4  shows descender  1  with release mechanism cover  14  removed. Bellcrank  40 , is attached to chassis  10  and pivots about axis E. Bellcrank opening  40   a  engages pivot arm boss  20   b,  which is integrally formed in the chassis  10 . Bellcrank spring  42  biases bellcrank  40  in direction F, maintaining contact between bellcrank opening  40   a  and pivot arm boss  20   b.  As such, motion is transmitted from sheave  22  through pivot arm  20  to bellcrank  40  allowing rope  28  to freely travel through the descender at no load. Handle member  30  pivots about axis G and is rotatably attached to selector link  32 . 
         [0038]    As can be seen in  FIG. 5 , handle spring  44  engages chassis  10  and handle member  30 . Handle spring  44  biases handle member  30  and selector link  32  in rotational direction H about axis G. Selector link  32  engages handle member  30  via selector link pin  32   b,  which may move from a notch  30   a  to slot  30   b.  As can be seen in  FIG. 6 , selector link spring  38  engages selector link lobe  32   c,  and serves to both bias selector link pin  32   b  into the notch  30   a  and bias selector link  32  to rotate in direction I and against stop pin  34 . 
         [0039]    Referring back to  FIGS. 1 and 2 , when descender  1  is in use, a carabiner links through hole  10   a  to attach the descender to an operator&#39;s harness or any other suitable anchor point. As tension is applied to rope  28  in direction A, the aforementioned ratchet mechanism causes sheave  22  to resist rotation in the direction opposite of direction B. The resulting moment causes sheave  22  and pivot arm  20  to rotate in direction C about axis J, thereby clamping rope  28  between shoe  18  and sheave  22 . As such, rope  28  is forced into groove  22   a  of sheave  22  by shoe  18 , initiating holding forces and further driving rope  28  into the groove. Frictional forces between rope  28  and sheave  22  are great enough to resist motion of the rope in direction A. These relationships describe the self-energizing braking action that occurs as tension exists in rope  28  in direction A. 
         [0040]    Controlled release of rope  28  is initiated by the operator pulling handle members  30 , pivoting said handle members in direction D as shown in  FIG. 4 . As handle members  30  rotate in direction D, so too does selector link  32  until one of notches  32   a  engages boss  40   b  of bellcrank  40 , thereby rotating pivot arm  20  and sheave  22  in rotational direction opposite of direction C, thereby reducing the force on rope  28  between sheave  22  and shoe  18 . Reduced force on rope  28  between sheave  22  and shoe  18  reduces the total frictional force applied to rope  28  by the descender, thereby allowing rope  28  to slip past the sheave. Regulation of the rate of slipping of rope  28  is achieved by the operator input to the handle, thereby regulating the clamping force on rope  28  between sheave  22  and shoe  18 . A large mechanical advantage is achieved via the leverage of handle members  30  to selector link  32 , and from bellcrank  40  to pivot arm  20 , which yields a high degree of control of descent with minimal operator effort applied to handle members  30 . 
         [0041]    When holding rope  28  under load, certain conditions will affect the resting angular position of pivot arm  20  about axis F. Variations in rope diameter will affect the distance between sheave  22  and shoe  18 . Likewise, different rope constructions may have different rates of compressibility, which will affect the distance between sheave  22  and shoe  18 . Additionally, different magnitudes of load applied to the descender via the rope will result in different amounts of compression of the rope, which will affect the distance between sheave  22  and shoe  18 . These variables introduce the reality of different angular positions of pivot arm  20  and sheave  22  about axis F for the same holding (no motion) condition. It follows that bellcrank  40  will also reside in different angular positions about axis E when holding the rope based on the same variables of rope diameter, construction, and tension. It also follows that, when in the state of holding the rope, boss  40   b  of bellcrank  40  may reside in different positions based on the variables of rope diameter, construction, and tension. As such, when the operator initiates release by rotating handle members  30  with selector link  32  in direction D, selector link  32  will engage the most appropriate of notches  32   a  with boss  40   b  according to the position of bellcrank  40 . The interaction between notches  32   a  and boss  40   b  provides the benefit of automatically adjusting the effective length of selector link  32  to the variables of rope diameter, construction, and tension. This feature ensures that the operator will experience similar handle member  30  positions during the act of releasing the rope  28 , regardless of rope diameter, construction, and tension. 
         [0042]    If an operator inadvertently actuates handle members  30  too far in direction D, travel of selector link  32  between the circular paths of selector link pin  32   b  and boss  40   b  will reach a position where selector link  32  will contact panic trigger pin  36 . Continuation of handle motion in direction D past this position will cause selector link pin  32   b  to become dislodged from a notch  30   a  in handle members  30 , and selector link pin will overcome selector link spring  38 , traveling into slot  30   b  in handle members  30 . The result is that handle members  30  are unable to drive selector link  32 , so bellcrank  40  counter rotates on axis F resuming the clamping force on rope  28  between sheave  22  and shoe  18 , allowing sheave  22  to resume holding of rope  28 . Release of handle member  30  by the operator will enable handle spring  44  to rotate handle members  30  in direction H to the starting position of the handle, and allows selector link spring  38  to return selector link pin  32   b  to a notch  30   a,  thereby resetting the handle mechanism and making it again ready to initiate release. 
         [0043]    In an alternative embodiment of a descender  2  in accordance with the invention shown in  FIG. 7 , a sheave  52  is rotatably mounted to a chassis  50 , with guide  54  and shoe roller  56  mounted on a first link  58  which constrains motion but allows the guide and the shoe roller to translate relative to the chassis and sheave. In the embodiment shown, sheave  52  may only rotate in direction R. Guide  54  is mounted to first link  58 , which pivots about axis N. Guide  54  is linked to shoe roller  56  via second link  60 . Shoe roller  56  is mounted to third link  62  and pivots about axis O. As tension is applied to rope  28  in direction Q, guide  54  is forced in direction R about axis N, forcing shoe roller  56  against rope  28 , which forces the rope into a groove in sheave  52 , initiating holding forces and further driving rope  28  into groove of sheave  52 . Frictional forces between rope  28  and sheave  52  are great enough to resist motion of rope  28  in direction Q. These relationships describe the self-energizing braking action that occurs as tension exists in rope  28  in direction Q. Handle  64  rotates about axis P and operates in conjunction with selector link  66  in a manner comparable to handle members  30  and selector link  32  in the preferred embodiment. 
         [0044]    An alternative embodiment of a descender  3  in accordance with the invention is shown in  FIGS. 8-20  and includes a chassis  410 , which together with opening plate  412 , contains rope  28 . Rope  28  is reeved such that the load to be managed pulls in direction S. Hole  410   a  provides a means of attachment, typically accomplished with a carabiner although any suitable means of attachment may also be used. Handle  430  is pivotally mounted to chassis  410 , and control of the rope through the descender is achieved by an operator rotating the handle in direction T. 
         [0045]    The means of gripping the rope in this embodiment is substantially similar to the device shown in  FIG. 1  and described above. The rope  28  is captured between sheave  422  and rollers  454  and  456 . Although rollers  454  and  456  are shown, any suitable bearing surface may be used without departing from the invention. As shown in  FIG. 14 , pivot arm  420  supports sheave  422  and is rotatably attached to chassis  410  such that the pivot arm can move about axis U. Applying tension to rope  28  in direction S results in translation of sheave  422  toward roller  456 , which forces rope  28  into a groove  422   a  of sheave  422 . As the tension on rope  28  increases, so does the force moving sheave  422  toward roller  456 . As with the device shown in  FIG. 1 , frictional forces between rope  28  and sheave  422  are great enough to resist motion of rope  28  in direction S. 
         [0046]    As shown in  FIGS. 10-13 , a pivot arm roller  424  is attached to pivot arm  420  and extends into opening  428 . A cam  90  is rotatably attached to the chassis  410  and can rotate about boss  426 . Cam spring  91  forces cam  90  in direction T relative to chassis  410 , initiating and maintaining contact between cam surface  90   a  and pivot arm roller  424 . Handle  430  contains handle pawl  80  which is rotatably mounted to the handle about axis W. Handle pawl spring  81  engages with handle pawl  80  and biases it in direction X about axis W. Handle pawl  80  includes handle pawl teeth  80   a  and handle pawl tail  80   b . Boss  432  protrudes from handle  430  and serves to limit angular rotation of handle  430  when assembled. 
         [0047]      FIG. 13  shows a control ring  434  and control ring aperture  436  of chassis  410 . As seen in  FIG. 10 , handle  430  pivots about boss  426  of chassis  410 . Handle pawl  80  engages control ring  434  to control which positions of handle  430  will allow handle pawl teeth  80   a  to mesh with cam teeth  90   b.    FIG. 11  shows handle  430  in a stowed position, i.e. positioning handle  430  such that handle pawl tail  80   b  contacts control ring  434 , which causes handle pawl  80  to rotate, thereby providing clearance between handle pawl teeth  80   a  and cam  90 .  FIG. 10  shows handle  430  in an operable position, i.e. positioning handle  430  in an angular position such that handle pawl tail  80   b  is positioned in aperture  436 , handle pawl spring  81  causes handle pawl  80  to rotate in direction X about axis W, thereby making handle pawl teeth  80   a  available to engage cam  90 . 
         [0048]    Handle  430  may be rotated in direction T from the stowed position shown in  FIG. 11  to the operable position shown in  FIG. 10 . As previously explained, aperture  436  of chassis  410  enables handle pawl teeth  80   a  to engage with cam teeth  90   a . Meshing handle pawl teeth  80   a  with cam teeth  90   b  links the motion of handle  430  and cam  90  while handle pawl tail  80   b  of handle pawl  80  is positioned in control ring aperture  436 . From the handle operable position, controlled release of rope  28  is achieved by the operator pulling handle  430  in direction T, which rotates cam  90  in the same direction. Contact between cam  90  and pivot arm  420  via cam surface  90   a  and pivot arm roller  424  causes pivot arm  420  and sheave  422  to rotate about axis U, thereby reducing the force on rope  28  between sheave  422  and roller  456 . Reducing the force applied to rope  28  between sheave  422  and roller  456  reduces the total frictional force between the rope and the descender  3 , allowing rope  28  to slip past the sheave  422 . 
         [0049]    Cam  90  will also reside in different angular positions depending on the angle of pivot arm roller  424  in relation to cam surface  90   a.  The plurality of cam teeth  90   b  allows the descender  3  to adapt to variations in rope diameter, construction, and tension in the same way that the multiple notches of the selector link does in the first embodiment described above. This release mechanism allows the handle  430  to rotate much further than previous descenders, making it possible to create a “stowed” position where the handle is out of the way when not needed for release. 
         [0050]    Using cam  90  to achieve the mechanical advantage required for controlled release of rope  28  allows the mechanical advantage to be easily tuned and optimized for the magnitude of force applied to the rope—the highest loads typically equate to the furthest rotation of the cam, and the corresponding area of the cam surface can be made more gradual to provide greater mechanical advantage. The teeth of the handle pawl and cam allow for much finer resolution of the adaptive release, which maximizes the release travel better than what was possible with the selector link of the first embodiment. Another advantage of this design is that it is very easy to incorporate the panic locking function. By controlling the size and location of the aperture  436 , the handle can be disconnected from the cam if the handle is swung too far because handle pawl tail  80   b  will come in contact with control ring  434 , rotating handle pawl  80  and disengaging handle pawl teeth  80   a  from cam teeth  90   b.    
         [0051]    As shown in  FIGS. 15-20 , opening plate  412  is hinged about the ends of roller pins  70  such that opening plate  412  opens relative to chassis  410 . In the embodiment shown, rollers  454  and  456  are attached to opening plate  412 . Roller pins  70  include spherical heads  72  (see  FIG. 18 ) that engage sockets  440  shown in  FIG. 13 . Other means of articulation including but not limited to pinned joints may alternatively be used without departing from the invention. With opening plate  412  fully opened, the space between chassis  410 , opening plate  412 , and rollers  454  and  456  is large enough to enable a bight of rope to be inserted and guided about sheave  422  as shown in  FIG. 16 . This simplified approach to rigging greatly reduces the likelihood of an operator incorrectly rigging the descender  3  and causing an unsafe condition. The carabiner used to attach the descender through hole  410   a  maintains closure of the plates when the unit is under load. Additional latches and/or magnets may be also be used to enhance the security of closure. 
         [0052]    Turning now to  FIGS. 21-23 , another embodiment of a descender  500  in accordance with the invention is shown. Descender  500  is similar in many ways to the previously described embodiments, except descender  500  only includes one roller or shoe, rather than two. Using only one roller or shoe is made possible by positioning roller  516  with respect to holes  506 ,  506   a  such that a sufficient portion of rope  28  engages sheave  510  without the need to guide the rope onto the sheave as it enters descender  500 . In the embodiment shown, descender  500  has a chassis  502  and a swing plate  504 , which together enclose rope  28 . Swing plate  504  is pivotably attached to chassis  502 , which allows a user to rig the descender  500 . Holes  506 ,  506   a  provide a means of attachment, typically accomplished with a carabiner, but any other suitable attachment may alternatively be used. In the embodiment shown, hole  506  passes through the swing plate  504  and hole  506   a  passes through the chassis  502  so that when descender  500  is in use, the two holes are substantially aligned and a carabiner or other attachment means is in use inserted through the holes, and swing plate  504  is prevented from opening. Handle member  508  is pivotally mounted to chassis  502  such that an operator can control the release of rope  28  by rotating handle member  508  in direction D. Rotating handle member  508  in direction D causes sheave  510  to rotate away from roller  516 , which allows the rope to pass through the descender  500 . 
         [0053]      FIG. 22  shows descender  500  with swing plate  504  pivoted to an open position, which is only made possible if there is no attachment means passing through holes  506 ,  506   a.  Sheave  510  has an acutely V-shaped groove  512  about its circumference that enhances the frictional interface between rope  28  and sheave  510  as tension is applied to the rope. Sheave  510  is rotatably mounted to pivot arm  514  and has a one-way ratchet which allows rotation only in one direction. In the embodiment shown in  FIGS. 21-24 , the ratchet allows rotation in direction B. In this embodiment, one-way rotation of sheave  510  is achieved by a pawl that engages teeth integrally formed in sheave  510 . Of course, any suitable ratchet or backstopping clutch that allows rotation of sheave  510  only in direction B relative to pivot arm  514  may be used without departing from the invention. The one-way rotation of sheave  510  enables the descender  500  to act as an efficient pulley if ascent is required because free movement of sheave  510  in direction B means that the frictional forces between the sheave and rope  28  need not be overcome. 
         [0054]    As further shown in  FIG. 22 , a user may install rope  28  by inserting the rope into the chassis  500 , wrapping the rope around sheave  510 , and exiting the chassis at roller  516 . Pivot arm  514  constrains motion of the sheave  510  such that the resultant force of the rope on the sheave clamps the rope between the sheave and roller  516 . Roller  516  may alternatively be a fixed shoe having a low friction surface without departing from the invention. 
         [0055]    When descender  500  is in use, a carabiner links through holes  506 ,  506   a  to attach the descender to an operator&#39;s harness or any other suitable anchor point. As tension is applied to rope  28  in direction A, the aforementioned ratchet mechanism causes sheave  510  to resist rotation in the direction opposite of direction B. The resulting moment causes sheave  510  and pivot arm  514  to rotate in direction C about axis J, thereby clamping rope  28  between roller  516  and sheave  510 . As such, rope  28  is forced into groove  518  of sheave  510  by roller  516 , initiating holding forces and further driving rope  28  into the groove. Frictional forces between rope  28  and sheave  510  are great enough to resist motion of the rope in direction A. These relationships describe the self-energizing braking action that occurs as tension exists in rope  28  in direction A. Controlled release of rope  28  is initiated by the operator pulling handle member  508 , pivoting the handle member in direction D as shown in  FIG. 21 . 
         [0056]    When holding rope  28  under load, certain conditions will affect the resting angular position of pivot arm  20  about axis J. Variations in rope diameter will affect the distance between sheave  510  and roller  516 . Likewise, different rope constructions may have different rates of compressibility, which will affect the distance between sheave  510  and roller  516 . Additionally, different magnitudes of load applied to descender  500  via rope  28  will result in different amounts of compression of the rope, which will affect the distance between sheave  510  and roller  516 . These variables introduce the reality of different angular positions of pivot arm  514  and sheave  510  about axis J for the same holding (no motion) condition. Finally, descender  500  includes a release mechanism that is identical to the one described above in relation to descender  3  and as shown in  FIGS. 10-13 , although any suitable release mechanism could be used without departing from the invention. 
         [0057]    Although the invention has been herein described in what is perceived to be the most practical and preferred embodiments, it is to be understood that the invention is not intended to be limited to the specific embodiments set forth above. Rather, it is recognized that modifications may be made by one of skill in the art of the invention without departing from the spirit or intent of the invention and, therefore, the invention is to be taken as including all reasonable equivalents to the subject matter of the appended claims and the description of the invention herein.

Technology Category: 1