Abstract:
A device for facilitating a controlled descent of a body, the device comprising a rotatable reel around which at least a portion of a cable is wound, a first end of the cable secured to the reel and a second end or the cable free; a friction drum mounted coaxially around the reel, the cable, upon leaving the reel wound at least partially around the drum; a carrier on which the reel and the drum are mounted; wherein the reel is provided with braking means for braking rotational motion of the reel and for balancing descending speed or the body.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a self-braking safety apparatus adapted to permit the rapid descent of persons on the outside of buildings or the like in cases of emergency. More particularly it relates to a device and method for.  
       BACKGROUND OF THE INVENTION  
       [0002]     It is at times necessary to evacuate upper floors in buildings or other high-elevations without having access to normal routes of egress. The cause is usually a fire on a lower floor that prevents persons on upper floors from passing through the lower floor and get down to safety.  
         [0003]     While fire is the most common case there are many others such as events that render the building structure in danger of imminent collapse, such as earthquakes or other events that result in an extensive damage.  
         [0004]     A related result of terrorism and of skyscraper fire tragedies is a change in the public&#39;s perception of high building safety. A dependable, portable safe device for rapid escape in the event of danger is in great demand if the public is to continue to accept the increasing risk associated with these structures.  
         [0005]     There is therefore a need for a means for rapid, controlled descent of a person on the outside of a building. Such a device can also be used in similar circumstances requiring rapid, safe descent from high places, such as cliffs, bridges, ships, or helicopters.  
         [0006]     A number of prior art devices have been proposed such a winches, rappelling devices, and parachute shock absorbers. The devices suffer from various disadvantages, such as damage incurred from inadequate dissipation of heat generated from friction during descent; reliance on batteries, oil, or other materials with limited shelf life and/or heavy weight; complex mechanisms that are costly to manufacture, maintain, and use; and fixed-point installation, which renders them useless if the emergency condition prevents people from reaching the device installation point.  
         [0007]     For example, in U.S. Pat. No. 4,729,454 (Barelli et al.), there was disclosed a self-braking apparatus provided for cases of emergency in which a rapid descent of persons threatened by fire or danger is required on the outside of buildings or the like. The apparatus can be secured to a fixed point from which the descent is to be made and comprises a rotor on which a rope is wound which is mounted coaxially and inwardly of a drum. A heat-resistant handle and a brake, which can be actuated by the user are secured to the drum by brackets. The rotor is provided with a plurality of radial holes each containing a spring urging a brake pad outwardly against the inner surface of the drum. The brake, which can be actuated by the user, is formed by a pair of levers pivotally connected to each other and acting with one of their ends on rods having an inclined plane in turn acting on brake pads urged against the lateral surface of the drum by the rods. When the hand brake is released, the rotation of the rotor and centrifugal force generated thereby exert braking action against the inner surface of the drum to produce a constant speed of descent of about 2.5 m/sec.  
         [0008]     In US 2001/0023793 (Okamura) there was disclosed an escape device for escaping from a building or other high area in an emergency comprises a worm gear mechanism driven by an electric motor and operatively coupled to a reel having a length of high tension line wound around it, arranged within a casing, and a belt connected to the casing for supporting a person&#39;s body. The worm gear mechanism rotates the reel, feeding out the line, and thereby lowering the user to a safe location below.  
         [0009]     The present apparatus is portable, is inexpensive to mass manufacture, is lightweight, dissipates heat efficiently and safety, requires no maintenance, can be used without special training by almost any person, and can even be used to lower an unconscious person to safety.  
         [0010]     Other objects and advantages of the present invention will become apparent after reading the present specification and reviewing the accompanying drawings.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0011]     There is thus provided, in accordance with some preferred embodiments of the present invention, a device for facilitating a controlled descent of a body, the device comprising:  
         [0012]     a rotatable reel around which at least a portion of a cable is wound, a first end of the cable secured to the reel and a second end of the cable free;  
         [0013]     a friction drum mounted coaxially around the reel, the cable, upon leaving the reel wound at least partially around the drum;  
         [0014]     a carrier on which the reel and the drum are mounted;  
         [0015]     wherein the reel is provided with braking means for braking rotational motion of the reel and for balancing descending speed of the body.  
         [0016]     Furthermore, in accordance with some preferred embodiments of the present invention, the carrier is provided with a harness, for harnessing the device to the body.  
         [0017]     Furthermore, in accordance with some preferred embodiments of the present invention, the carrier is provided with a fixator for fixing the device to an anchorage position.  
         [0018]     Furthermore, in accordance with some preferred embodiments of the present invention, the braking means comprises at least two braking arms, each pivotally connected to the reel, operable by a centrifugal force when the reel is rotated, thus exerting friction force between the arm and the drum.  
         [0019]     Furthermore, in accordance with some preferred embodiments of the present invention, the braking arms comprise, each an arm pivotally connected at a first end to the reel and provided with a mass at a second end.  
         [0020]     Furthermore, in accordance with some preferred embodiments of the present invention, each braking arm is provided with a braking pad.  
         [0021]     Furthermore, in accordance with some preferred embodiments of the present invention, the braking pad is located between the first end and the second end of the arm, facing the drum.  
         [0022]     Furthermore, in accordance with some preferred embodiments of the present invention, the braking means comprises at least one dynamo, for producing electric current driven through resistance, the resistance serving for braking the reel, transferring rotational energy of the reel into heat.  
         [0023]     Furthermore, in accordance with some preferred embodiments of the present invention, the braking means comprises hydraulic means.  
         [0024]     Furthermore, in accordance with some preferred embodiments of the present invention, the hydraulic means comprises a hydraulic pump.  
         [0025]     Furthermore, in accordance with some preferred embodiments of the present invention, the device is further provided with additional friction exerting elements for exerting friction on the cable as the body descends.  
         [0026]     Furthermore, in accordance with some preferred embodiments of the present invention, the additional friction exerting elements comprise drums.  
         [0027]     Furthermore, in accordance with some preferred embodiments of the present invention, the carrier is enclosed in a casing.  
         [0028]     Furthermore, in accordance with some preferred embodiments of the present invention, the dimensions of which fit an office shelf.  
         [0029]     Furthermore, in accordance with some preferred embodiments of the present invention, the device is further provided with a recoil mechanism for retracting loose cable and recoiling the cable on the reel.  
         [0030]     Furthermore, in accordance with some preferred embodiments of the present invention, the recoil mechanism comprises springs.  
         [0031]     Furthermore, in accordance with some preferred embodiments of the present invention, the device further comprises initial tension limiter, for preventing sudden impact on the body as it starts descending.  
         [0032]     Furthermore, in accordance with some preferred embodiments of the present invention, the device further comprises a fixed cable outlet, for securing a single outlet on the carrier for the cable.  
         [0033]     Furthermore, in accordance with some preferred embodiments of the present invention, there is provided a method for facilitating a controlled descent of a body, the method comprising:  
         [0034]     providing a rotatable reel around which at least a portion of a cable is wound, a first end of the cable secured to the reel and a second end of the cable free;  
         [0035]     providing a friction drum mounted coaxially around the reel, the cable, upon leaving the reel wound at least partially around the drum;  
         [0036]     providing a carrier on which the reel and the drum are mounted;  
         [0037]     wherein the reel is provided with braking means for braking rotational motion of the reel and for balancing descending speed of the body;  
         [0038]     attaching the carrier to the body and securing the free end of the cable to an anchorage position;  
         [0039]     allowing the body to descend.  
         [0040]     Furthermore, in accordance with some preferred embodiments of the present invention, there is provided a method for facilitating a controlled descent of a body, the method comprising:  
         [0041]     providing a rotatable reel around which at least a portion of a cable is wound, a first end of the cable secured to the reel and a second end of the cable free;  
         [0042]     providing a friction drum mounted coaxially around the reel, the cable, upon leaving the reel wound at least partially around the drum;  
         [0043]     providing a carrier on which the reel and the drum are mounted;  
         [0044]     wherein the reel is provided with braking means for braking rotational motion of the reel and for balancing descending speed of the body;  
         [0045]     attaching the carrier to an anchorage position and securing the free end of the cable to the body;  
         [0046]     allowing the body to descend. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0047]     The invention is described herein, by way of example only, with reference to the accompanying Figures, in which like components are designated by like reference numerals.  
         [0048]      FIG. 1  is an isometric view of a portable apparatus for controlled descent in accordance with a preferred embodiment of the present invention.  
         [0049]      FIG. 2  is a front view of static and dynamic energy transfer mechanisms in accordance with a preferred embodiment of the present invention.  
         [0050]      FIG. 3  is a front view detail of components of a dynamic energy transfer mechanism in accordance with a preferred embodiment of the present invention.  
         [0051]      FIG. 4  is a sectional side view of a preferred embodiment of the present invention.  
         [0052]      FIG. 5  is an isometric drawing of a preferred embodiment of the present invention, in a casing.  
         [0053]      FIG. 6  is a front view detail of an outlet through which the cable leaves the apparatus in accordance with a preferred embodiment of the present invention.  
         [0054]      FIG. 7  is a rotated isometric view of a portable apparatus for rapid controlled descent in accordance with another preferred embodiment of the present invention.  
         [0055]      FIG. 8  is a top view of the alternative embodiment of  FIG. 7 .  
         [0056]      FIG. 9  is sectional view of the embodiment shown in  FIG. 8 , along section line C-C.  
         [0057]      FIG. 10A  is an exemplary installation of an apparatus for rapid controlled descent in accordance with yet another preferred embodiment of the present invention.  
         [0058]      FIG. 10B  is an enlargement of detail D in  FIG. 10A .  
         [0059]      FIG. 11  is an isometric view of an apparatus for rapid controlled descent with the dynamic mechanism implemented as a dynamo in accordance with yet another preferred embodiment of the present invention.  
         [0060]      FIG. 12  is an isometric view of an apparatus for rapid controlled descent with the dynamic mechanism implemented as a hydraulic pump in accordance with yet another preferred embodiment of the present invention.  
         [0061]      FIG. 13  is a view of the apparatus of  FIG. 12  with a gear housing cover installed.  
         [0062]      FIG. 14  is a diagram of the factors involved in an energy transfer calculation for a dynamic braking mechanism in exemplary apparatus for rapid controlled descent in accordance with a preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0063]     The present invention provides a portable apparatus for controlled descent of a person (or other body of mass) from a height by means of a cable wound onto a reel of the apparatus. According to a preferred embodiment of the present invention, the user straps on the apparatus, attaches the free end of the cable to a solid fixed point, and lowers himself out of a window or other egress point from which he or she can descend to a lower point. The most common anticipated use for the apparatus is for escaping from high building floors down the outside of the building.  
         [0064]     The controlled descent is effected automatically by two energy transfer mechanisms that convert the energy of the falling person into heat and dissipate that heat: a static mechanism based on friction of the cable on a drum takes up most of the descent energy and a dynamic mechanism based on friction exerting arms, that are coupled to the reel on which the cable is wound, and interact with the drum, affected by centrifugal forces, thus balancing the speed of descent.  
         [0065]     The dynamic mechanism applies a centrifugal brake to a drum, preferably the internal surface of the cable drum. The greater the tension on the cable, the faster the spin of the dynamic mechanism and consequently the greater the centrifugal force and consequently the greater the braking effect.  
         [0066]     While a centrifugal brake is a preferred embodiment of the dynamic mechanism for energy transfer of the present invention, one skilled in the art, understanding the principles of the present invention will be able to employ alternative embodiments of this mechanism (some of which are also described hereinafter), such as but not limited to: a set of gears, a hydraulic rotor, a dynamo, or a viscous motor. All such alternative embodiments of the dynamic mechanism as are apparent to one skilled in the art are anticipated, and incorporated, by the present invention.  
         [0067]     With reference to  FIG. 1 , the components of a portable apparatus for rapid controlled descent in accordance with a preferred embodiment of the present invention are now described.  
         [0068]     Cable  1  is characterized by having a distal free end for attachment to a fixed point in the building, the point characterized by being able to support the weight of the body and the apparatus during descent. The fixed point can be a dedicated component, such as a ring anchored to the building structure for this purpose or it can be a non-dedicated component, for example the wall between two adjacent windows where the cable is looped around the wall and then hooked onto itself.  
         [0069]     Cable  1  preferably has at its distal end an attachment means  25  for attaching to the fixed point through tension limiter  12 . An example of an attaching means is a hook or ring.  
         [0070]     Cable  1  feeds through cable outlet  14  and external wheel  3  to friction drum  2 . Cable  1  is wound around friction drum  2  at least one of a plurality of windings (typically more than one winding, but even partial winding—for example only a sector of the drum—may suffice).  
         [0071]     Cable  1  is characterized by having adequate tension strength to maintain its structural integrity when tension is applied to it during descent and by having a high coefficient of heat conduction for dissipating much of the heat generated by friction between cable  1  and friction drum  2  during descent into the surrounding air as it plays out behind the descending person.  
         [0072]     Friction drum  2  is characterized by having adequate structural strength to maintain its structural integrity when tension is applied to it during descent and by having a low coefficient of heat conduction, thereby causing most of the heat generated by friction between cable  1  and friction drum  2  during descent to be conducted into cable  1  for dissipation.  
         [0073]     From friction drum  2 , cable  1  passes over internal wheel  5  to cable winding reel  4 , where the cable is initially wound up and attached to cable winding reel  4  at the cable&#39;s proximal end.  
         [0074]     Cable  1  and friction drum  2  comprise the main static energy transfer mechanism of the present apparatus. By “static energy transfer” is meant energy transfer without the aid of moving parts other than the cable itself, as opposed to “dynamic energy transfer”, which relates to energy transfer through moving parts in addition to the cable. The dynamic apparatus is now described.  
         [0075]     To cable winding reel  4  is attached an end of at least one of a plurality of pivotal arms  6 B. Arm  6 B is attached at its other end to mass element  7 , which is turned by cable winding reel  4  as the reel spins to unwind cable  1  during descent. Centrifugal force causes brake pad  8  attached to arm  6 B against the internal surface of a friction ring  9 , which is preferably friction drum  2 . Arm  6 B may be pivotally attached directly to reel  4  or alternatively (as shown in this Figure) it may be pivotally attached to extension arm  6 A coupled to the reel.  
         [0076]     The entire apparatus as described here starting from outlet  14  is mounted on base carrier  10  to which is also preferably connected a harness, such as straps  11 , which are used to strap the user to the other side of base carrier  10 . Preferably straps  11  comprise a standard rappelling harness for unskilled users with a low connective center of gravity such that an unconscious user will remain in a heads-up position during descent. Optional hip straps  11   b  (see  FIG. 4 ) may be also provided for better engagement of the apparatus to the person using it. The drum may be an integral part of the carrier base, in some preferred embodiments of the invention.  
         [0077]     Optional initial tension limiter  12  takes up initial excess tension by running cable  26 —in the embodiment shown in this figure this is a separate cable, through holes  13  in the initial tension limiter  12 . Initial excess tension can occur if the user drops in an uncontrolled manner from his building egress point and/or if the user plays out a length of cable before starting his descent. Cable clamps  28  may be used.  
         [0078]     With reference to  FIG. 2 , there is now summarized the division of tensions produced on cable  1  by the descent of the apparatus and its user (passenger). Cable  1  enters the apparatus under high tension T 1  produced by the force of gravity on the mass of the apparatus and its user. Cable  1  passes through cable outlet  14  and external wheel  3  to friction drum  2 . Cable  1  is wound around friction drum  2  at least one of a plurality of windings (typically more than one winding, but even partial winding—for example only a sector of the drum—may suffice), which convert via friction a significant portion of tension T 1  to heat that is dissipated by the unwinding cable  1 . After friction drum  2  (location indicated with number  1   a  in figure), cable  1  is under reduced tension T 2  and passes through internal wheel  5  to cable winding reel  4 . Details A and B of  FIG. 2  are referred to later in this disclosure, with references to  FIGS. 6 and 3 , respectively.  
         [0079]     The relationship between T 1  and T 2  derives from the friction of cable  1  on friction drum  2  according to the formula: 
 
 T 1= T 2* e ˆ( M *Alfa)   (equation 1) 
        where T 1  is the tension on the cable outside the apparatus (before friction drum  2 ), T 2  is the tension on the cable inside the apparatus (after friction drum  2 ), M is the static coefficient of friction between cable  1  and friction drum  2 , and Alfa is the winding angle in radians of cable  1  on friction drum  2 .        
 
         [0081]      FIG. 3  is an enlargement of detail B of  FIG. 2 , illustrating mass element  7  that applies, due to centrifugal force (Fr) a frictional force (Ff) via brake pad  8  against the internal surface of friction ring  9 , which can be the internal surface of drum  2 .  
         [0082]      FIG. 4  is a sectional side view of a preferred embodiment of the present invention. Cable  1  is shown wound around friction drum  2  and cable winding reel  4 . Friction ring  9 , which receives braking friction from brake pad  8  of arm  6 B, is illustrated as a separate component from friction drum  2  although the two components can be combined, with the outer surface of friction drum  2  receiving friction from cable  1  and the inner service receiving braking friction from arm  6 B.  
         [0083]      FIG. 5  is an isometric drawing of a preferred embodiment of the present invention with a casing. Insulation element  21  insulates the user from the heat generated by active system components mounted on base  10  and also improves the comfort of the user when he is wearing the apparatus. Cover  10   b  is used to close and protect the unit, housed in casing  10   c  when in storage.  
         [0084]      FIG. 6  is an enlargement of detail A of  FIG. 2 , illustrating cable  1  running through cable outlet  14  and external wheel  3  to friction drum  2 .  
         [0085]      FIG. 7  is a rotated isometric view of a portable apparatus for rapid controlled descent in accordance with an alternative preferred embodiment of the present invention.  
         [0086]     In this embodiment, cable  1  feeds through cable outlet  14  and then around at least one of a plurality (preferably four) of external friction exerting drums  30 . The increased number of external friction exerting drums  30  translates into increased static frictional energy transfer from cable motion to heat. An optional recoil mechanism  34  (see explanation hereinafter) may be provided. Additional friction exerting elements, such as plate  32 , with a curved edge, for guiding cable  1  across the element, may also be provided. Note that on one or more friction exerting drums the cable may be wound more than one winding. The tension on cable  1  is reduced over the friction exerting drums and is therefore lower where it reaches the reel (the portion of the cable indicated by  1   b ).  
         [0087]      FIG. 8  is a top view of the alternative embodiment of  FIG. 7 .  
         [0088]      FIG. 9  is a cross sectional view across section line C-C of the embodiment shown in  FIG. 8 . An optional recoil mechanism  34  is provided, for recoiling the cable after it is unwound in the process of descent. Here the recoil mechanism comprises a spiral spring  42 , coupled to rotor  46 , and enforced with force-enforcing spring  44 , whose force is determined by locking screw  40 . Rotor  46  rotates about stator  48 , in between which friction pad  47  is preferably provided.  
         [0089]      FIG. 10A  is an exemplary installation of a portable apparatus for rapid controlled descent installed in a room in accordance with an embodiment of the present invention.  FIG. 10B  is an enlargement of detail D in  FIG. 10A . In this embodiment, the apparatus  100  is permanently installed in wall rack  104  (here provided with screw holes  106  for securing the rack to the wall by screws, but other securing means may be used too) on wall  102 . The user wears a rappelling harness and connects it to cable attachment means. The user then lowers himself from a point of egress to the outside of the building. The apparatus comprises dynamic and static mechanisms for controlling the descent as have been described earlier.  
         [0090]     The operation of a portable apparatus for rapid controlled descent in accordance with a preferred embodiment of the present invention is now described in detail.  
         [0091]     The primary concept is to convert the potential energy of the descending user and apparatus to heat energy.  
         [0092]     A person wearing the apparatus has the following potential energy: 
 
 Ep=m*g*h    (Equation 2) 
        where:     m=person&#39;s weight     g=accelerative force of gravity on a free object at the Earth&#39;s surface     h=height of the person        
 
         [0097]     When a user descends with the apparatus, the apparatus performs two operations:  
         [0098]     Operation 1: Cable  1  rubs against friction drum  2 , thereby releasing energy. The coefficient of heat conduction of friction drum  2  is low and that of the cable is high, therefore the cable warms up from the friction and unwinds above the descending user where it cools off safely in the air, away from the user and the apparatus, while the friction drum does not heat up to a point that could damage the apparatus or injure the user.  
         [0099]     Operation 2: Cable winding drum  4  spins as the cable unwinds, thereby spinning with it the mass elements  7  attached to it. Brake pads  8  create a dynamic centrifugal frictional force on friction ring  9  (preferably internal surface of friction drum  2 ), thereby dynamically maintaining the system in a state of balance where the user descends steadily at a predetermined velocity.  
         [0100]     As mentioned earlier in this disclosure, the dynamic braking of operation 2 can equally be implemented by other mechanisms producing similar results, such as viscous friction of the brake pads in a fluid or of gears in oil.  
         [0101]     An exemplary alternative embodiment of the present invention, where the dynamic mechanism is implemented as a dynamo, is shown in  FIG. 11 . In this embodiment, winding gear  120  is connected to dynamo  124  by belt  122 . Current generated by dynamo  124  passes through wires  128  to resistor  126 . Resistance or resistor  126  slows dynamo  124 , thereby slowing winding gear  120 .  
         [0102]     Another exemplary alternative embodiment of the present invention, where the dynamic mechanism is implemented as a hydraulic pump, is shown in  FIG. 12 . In this embodiment, gear housing  130  houses braking gear  132 , which is coaxially connected to cable winding reel  4 , and second gear  134 . Braking gear  132  is turned by cable winding reel  4  and turns second gear  134 . Oil from oil reservoir  138  flows through pipe  136  to gear housing  130  where it is pumped by the turning gears out the other side of gear housing  130  into the remaining portion of pipe  136 , through reducer  140  back to oil reservoir  138 . Reducer  140 , which can be on either side of gear housing  130 , slows the flow of oil, thereby slowing braking gear  132  and by translation, cable winding reel  4 .  
         [0103]      FIG. 13  is a view of the alternative embodiment of  FIG. 12  with gear housing cover  142  installed.  
         [0104]     In addition an alternative embodiment of the present invention can be built without the static mechanism of operation 1, however the static mechanism enables the dynamic mechanism to be built more simply and at lower cost.  
         [0105]     The following data is given for exemplary purpose only and serves to illustrate the design principles of the present invention. 
        Calculations (refer to  FIG. 14 ): 
            Weight of person and apparatus: m=100 [kg]    Acceleration of gravity: g=9.8 [m/secˆ2]    Initial height (distance to descend): h=100 [m]    Potential energy: Ep=mgh=98000 [3]    Coefficient of friction between cable and friction drum: M=0.15     Number of windings of cable around friction drum: 2.5=15.4 [rad]=Alfa [winding angle]    Difference of tensions: T 1 =T 2 *eˆ(M*Alfa) 
 
 T 2 =T 1/ e ˆ( M *Alfa)=100/ e ˆ(0.15*15.4)=10 [kg]
   
            Therefore: 
            T 1 =100 [kg]=tension on cable due to weight of man and apparatus     T 2 =10 [kg]=tension on cable after it passes through static mechanism (operation 1) and before dynamic mechanism (operation 2)    
               
 
         [0117]     The static mechanism of operation 1 diffused 90% of the energy, most of it as heating of the cable playing out above the apparatus. The internal tension (T 2 ) on the cable remains a constant 10% of the external tension (T 1 ) due to the friction between cable and drum. 
        Calculation of internal forces ( FIG. 1214 ): 
            Internal tension on cable: T 2 =10 [kg]    Radius of friction ring: Rf=0.13 [m]    Radius of center of gravity of brake arm: Rc=0.08 [m]    Distance to braking operation from brake hinge: A=0.015 [m]    Distance to brake arm center of gravity from brake hinge: B=0.06 [m]    Centrifugal force of brake arm: FR [N]    Reactive force at the braking point between the braking arm and the friction ring: Ff [N]    The linear velocity of the center gravity of the braking arm is described by Vc=W*Rc    
            Where: ANGULAR Velocity of winding drum rotation: W [rad/sec]
            LINEAR velocity of center of mass of brake arm: Vc [m/sec]    Mass of brake arm: G=0.4 [kg]   
            Braking power of brake arm: 
 
 Fr*W=G*Vcˆ 2/ Rc=G*Wˆ 2* Rc  
    Balance of moments around the brake arm hinge: 
 
 Fr*B=Ff*A  
 
 Ff =( G*Wˆ 2)*( Rc*B )/ A,  (neglecting  Fs ) 
    Assuming frictional force between brake arm and friction ring with friction coefficient: Nf=0.25     then: 
 
 Fs=Nf*Ff =( G*Wˆ 2)*( Rc*B )* Nf/Od  
    Calculate the balance of moments around the center of the ring assuming there are two brake arms, then: 
            Diameter of winding drum with cable fully wound up: RD 1 =0.06[m]    Diameter of winding drum with cable wound out: RD 2 =0.02[m] 
             T   ⁢           ⁢   2   *   RD     =       F   ⁢           ⁢   S   *   R   ⁢           ⁢   f     =     G   *     W   ^   2           )     *   Rc   *   B   *   N   ⁢           ⁢   f   *   Rf   ⁢     /     ⁢   A       
             W   =       ⁢     SQRT   ⁡     (     T   ⁢           ⁢   2   *   RD   *               A   /   2     /   G     /   Rc     /   B     /   Nf     /   Rf       )                   =       ⁢     SQRT   ⁡     (     100   *   RD   *               0.015   /   2     /   0.4     /   0.08     /   0.06     /   0.25     /   0.13       )                   =       ⁢     SQRT   ⁡     (     120192   *   RD     )                 
               W   ⁡     (     RD   =   0.06     )       =       ⁢     SQRT   ⁡     (     120192   *   0.06     )                   =       ⁢       85   ⁡     [     rad   ⁢     /     ⁢   sec     ]       =     13.5   ⁡     [   rps   ]                     =       ⁢     810   ⁡     [   rpm   ]                 
               W   ⁡     (     RD   =   0.02     )       =       ⁢     SQRT   ⁡     (     120192   *   0.02     )                   =       ⁢       49   ⁡     [     rad   ⁢     /     ⁢   sec     ]       =     7.8   ⁡     [   rps   ]                       =       ⁢     468   ⁡     [   rpm   ]         ⁣             
   
            The dynamic mechanism (operation 2) balances itself. The more the rotational velocity increases, the more the braking force of the mechanism increases because the braking force is based on centrifugal force that increases to the fourth power of an increase in the rotational velocity. At the same time, the cable winding drum empties out, making it easier for the mechanism to brake the cable winding drum because the moment goes down in direct proportion to the diameter of the wound cable.        
 
         [0138]     In other words, it can be expected that a person at a higher point in his descent, when more cable is still on the winding drum, would fall faster than at a lower point when there is less cable on the winding drum.  
         [0139]     It should be noted that the apparatus of the present invention has special appeal stemming form the fact that it needs no special fittings or installation and the end user may decide for himself if he wants to get such an apparatus, regardless the conditions of his home or workplace. He can chose where to store the apparatus and it is his choice what would be the location and timing of his personal evacuation.  
         [0140]     It should be clear that the description of the embodiments and attached Figures set forth in this specification serves only for a better understanding of the invention, without limiting its scope as covered by the following Claims.  
         [0141]     It should also be clear that a person skilled in the art, after reading the present specification could make adjustments or amendments to the attached Figures and above described embodiments that would still be covered by the following Claims.