Patent Publication Number: US-2021170208-A1

Title: Polarized deceleration brake for self retracting device

Description:
TECHNICAL FIELD 
     Various embodiments relate generally to personal protective equipment (PPEs) and more specifically to safety lanyards and self-retracting devices (SRDs). 
     BACKGROUND 
     Worldwide, individuals make a living performing in a myriad of jobs. Many jobs include various hazards from minor cuts and abrasions to more serious hazards such as loss of life. In some examples, highway construction workers may be exposed to adjacent flows of automobile traffic. Welders may be exposed to intense light that may cause eye damage. Construction workers may be exposed to falling objects. In some examples, trash and recycling collectors may be exposed to abrasive, sharp or corrosive waste. 
     Personal protection equipment (PPEs) may be worn by workers in hazardous environments. PPEs may protect workers from the harmful effects of various hazards. For example, highway construction workers may wear brightly colored vests to become highly visible to motorists. Welders may strap on a face-shield with protective light filtering lenses to filter out the effects of damaging light from welding arcs. In the construction industry, workers may wear various headgear, such as hardhats, to protect against falling objects. Construction workers on scaffolding or roofs may be tethered to safety lanyards to prevent or to minimize the effects of an accidental fall. In some instances, the lanyards may be implemented in various types of self-retracting devices (SRDs). 
     SUMMARY 
     Apparatus and associated methods relate to a directionally polarized deceleration module (PDM) including a shuttle fixedly coupled to a spring-biased spool rotatably coupled to a module housing, a dynamic braking member (DBM) and the shuttle configured to travel inside a channel anchored to the module housing. In an illustrative example, a tether may be anchored on a proximal end to the spool. In some examples, as the tether is retracted, the DBM may be pushed by an angled distal-end of the shuttle. The DBM may be forced between the angled distal-end of the shuttle and an inner channel wall, for example, providing motional resistance to the tether. In some examples, as the tether is extracted, the DBM may be pushed substantially normal to a proximal-end of the shuttle, providing minimal motional resistance to the tether. Various PDMs may decelerate safety lanyards in one direction to substantially avoid tangling and/or damage. 
     Various embodiments may achieve one or more advantages. For example, some embodiments may substantially avoid or eliminate tangling of lanyards within various self-retracting devices (SRDs). Some embodiments may substantially avoid or eliminate damage to SRDs due to impacts of distal ends of lanyards colliding with SRD enclosures. Some examples of a PDM implemented on an SRD may substantially avoid or eliminate whiplash of an SRD cord as it is retracted into the SRD. Various embodiments may provide a polarized deceleration, slowing the longitudinal motion of a lanyard in a retraction direction only. 
     The details of various embodiments are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts an exemplary self-retracting device (SRD) providing fall protection to a construction worker on a roof, the SRD providing control of a lanyard filament speed. 
         FIG. 2A  depicts a plan view of an exemplary SRD in a tether retraction mode, being decelerated by a brake pad puck in an impinging frictional engagement between a ram-trolley and a track wall. 
         FIG. 2B  depicts a plan view of an exemplary SRD in a tether extraction mode, being decelerated by a brake pad puck in minimal frictional engagement between a ram-trolley and a track wall. 
         FIG. 3A  depicts a perspective exploded view of an exemplary SRD, illustrating a shuttle coupled to a spring-biased drum. 
         FIG. 3B  depicts a cross-sectional view of an exemplary SRD, illustrating a shuttle coupled to a spring-biased drum. 
         FIG. 4  depicts a perspective view of an exemplary shuttle and brake disk located and guided by a channel ring, the brake disk frictionally engaged with an inner wall of the channel ring. 
         FIG. 5  depicts a perspective view of an exemplary shuttle and brake disk located and guided by a channel ring, the brake disk frictionally engaged with an outer wall of the channel ring. 
         FIGS. 6A, 6B, 6C, 6D, 6E and 6F  depict plan views of exemplary shuttle embodiments. 
         FIGS. 7A, 7B, 7C, 7D, 7E and 7F  depict plan views of exemplary DBM embodiments. 
         FIGS. 8A and 8B  depict plan views of exemplary shuttle embodiments centering a DBM to minimize friction against a channel ring. 
         FIG. 9  depicts a plan view of an exemplary shuttle and DBM embodiment, both the shuttle and the DBM providing friction against a channel ring. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     To aid understanding, this document is organized as follows. First, an exemplary use case depicting a polarized deceleration module (PDM) is briefly introduced with reference to  FIG. 1 . Second, with reference to  FIGS. 2A and 2B , the discussion turns to exemplary embodiments that illustrate the operation of PDMs. Specifically,  FIG. 2A  illustrates resistive movement in a retraction mode, and  FIG. 2B  illustrates free movement in an extraction mode. Next, with reference to  FIGS. 3A and 3B , exemplary PDMs are presented applied to self-retraction devices (SRDs). Next, with reference to  FIG. 4  and  FIG. 5 , the discussion turns to exemplary frictional locations. Next,  FIGS. 6A-6F  present various exemplary surface shapes implemented on various exemplary shuttles. Next,  FIGS. 7A-7F  present exemplary dynamic braking members (DBMs) with various shapes. Next, with reference to  FIGS. 8A and 8B , further discussion of exemplary extraction ends of a shuttle are presented to explain frictional reduction techniques. Finally, with reference to  FIG. 9 , an exemplary embodiment that produces frictional engagement with both inner and outer walls of a shuttle track is presented. 
       FIG. 1  depicts an exemplary self-retracting device (SRD) providing fall protection to a construction worker on a roof, the SRD providing control of a lanyard filament retraction speed. An SRD safety deployment scenario  100  includes an SRD  105 . The SRD  105  includes a channel ring  110  fixedly coupled to an SRD housing  115 . A rotating drum  120  is rotatably coupled to the SRD housing  115 . A shuttle  125  is fixedly coupled to the rotating drum  120 . The shuttle  125  translates within the channel ring  110 . A dynamic braking member (DBM)  130  is advanced by the shuttle  125  within the channel ring  110 . The shuttle  125  includes an inclined surface  135 . As the DBM  130  is advanced by the inclined surface  135  of the shuttle  125 , the DBM  130  is forced into an impinging frictional engagement between an inner surface of an outer wall of the channel ring  110  and the shuttle  125 . The impinging frictional engagement may advantageously slow the retraction speed of a lanyard filament. In various examples, slowing the retraction speed may advantageously mitigate tangling of various lanyard filaments, and may mitigate damage to various SRD housings. The inclined surface  135  may guide the DBM  130  into a frictional retraction impingement with an inside surface of a circular channel, such as the channel ring  110 , when a cylindrical drum, such as rotating drum  120 , is in a retraction mode. 
     A lanyard filament  140  is mechanically coupled on one end to the rotating drum  120 . The SRD  105  is configured to manage the lanyard filament  140  by spooling the lanyard filament  140  onto the rotating drum  120  in the retraction mode and by unspooling the lanyard filament  140  off from the rotating drum  120  in an extraction mode. In an illustrative example, the rotating drum  120  is spring biased to reel in any length of lanyard filament  140  that may be extracted from the SRD  105 . In the depicted example, a worker  145  is coupled to the lanyard filament  140 . The lanyard filament  140  is held taut since the rotating drum  120  is spring biased in a retraction direction. 
     In an illustrative example, when the worker  145  completes his tasks on the roof, he releases the lanyard filament  140  from a safety vest  150 . The worker  145  releases the lanyard filament  140  without restraint. As the lanyard filament  140  self-retracts into the SRD  105 , the shuttle  125  begins to travel around the channel ring  110  in response to rotation of the spring biased rotating drum  120 . Since the lanyard filament  140  is unrestrained, the spring biased rotating drum  120  and the shuttle  125  may freely rotate in a retraction direction. The shuttle  125  comes in contact with the DBM  130  at a point in its travel around the channel ring  110 . Due to the inclined surface  135  of the shuttle  125 , the DBM  130  is forced into an impinging frictional engagement between an inner surface of an outer wall of the channel ring  110  and the shuttle  125 . The impinging frictional engagement opposes the translation of the shuttle  125  within the channel ring  110 . The translation of the shuttle  125  slows down in response to the impinging frictional engagement. The shuttle  125  slows the rotating drum  120 , which slows the retraction speed of the lanyard filament  140 . Slower speeds of the lanyard filament  140  may advantageously reduce tangling of the lanyard filament  140  within the rotating drum  120 . 
     The lanyard filament  140  is fixedly coupled to a filament termination  155  on a distal end. Slower speeds of the lanyard filament  140  may advantageously mitigate damaging impacts of the filament termination  155  against the SRD housing  115 . 
     In various exemplary deployments, the SRD  105  may be mechanically coupled overhead. For example, the SRD  105  may be coupled to a rotational boom anchor. The rotational boom anchor may advantageously provide the user a larger protected work area than the SRD  105  alone. In some examples, the SRD  105  may be mechanically coupled overhead to various scaffolding or may be mechanically coupled to various extending members of a crane. 
       FIG. 2A  depicts a plan view of an exemplary SRD in a tether retraction mode, being decelerated by a brake pad puck in an impinging frictional engagement between a ram-trolley and a track wall. An SRD  205  in a retraction mode  200 A includes an enclosure  210 . The enclosure  210  is rotatably coupled to a take-up reel  215 . The take-up reel  215  is fixedly coupled to a proximal end of a tether  220 . In the depicted example, the tether  220  is wound around the take-up reel  215 . A tether termination handle  225  is fixedly coupled to a distal end of the tether  220 . The take-up reel  215  is spring biased in a retraction direction. In the depicted example, the take-up reel  215  is rotating in a counterclockwise direction  230  illustrating the tether  220  being actively retracted  235 . 
     The enclosure  210  is fixedly coupled to a circular track  240 . The circular track  240  is in confined engagement with a ram-trolley  245 . The ram-trolley  245  is fixedly coupled to the take-up reel  215 . The ram-trolley  245  is configured with a ramp surface at a retraction end  250 , and with a surface parallel to a radius of the circular track  240  at an extraction end  255 . The circular track  240  includes an inner wall  260  and an outer wall  265 . The inner wall  260  and the outer wall  265  constrain a brake pad puck  270 . The brake pad puck  270  is free to move between the confines of the inner wall  260  and the outer wall  265 . 
     In operation, as the tether  220  is retracted into the SRD  205 , the ram-trolley  245 , being coupled to the take-up reel  215 , travels in a retraction direction (e.g., the counterclockwise direction  230  with reference to  FIG. 2A ). The ramp surface at the retraction end  250  of the ram-trolley  245  translates the brake pad puck  270  toward the outer wall  265 . The motion of the ram-trolley  245  in combination with the ramp surface forces the brake pad puck  270  into a frictional engagement between the ram-trolley  245  and the outer wall  265 . In some examples, the ramp surface may be inverted from the depicted example, forcing the brake pad puck  270  into a frictional engagement between the ram-trolley  245  and the inner wall  260 . The retraction end  250  may guide a DBM, such as brake pad puck  270 , into a frictional retraction impingement with an inside surface of a circular channel, such as the outer wall  265  of the circular track  240 , when a cylindrical drum, such as the take-up reel  215 , is in the retraction mode. 
       FIG. 2B  depicts a plan view of an exemplary SRD in a tether extraction mode, being decelerated by a brake pad puck in minimal frictional engagement between a ram-trolley and a track wall. In the depicted example, an SRD  205  is in an extraction mode  200 B. The take-up reel  215  is rotating in a clockwise direction  275  illustrating the tether  220  being actively extracted  280 . 
     In operation, as the tether  220  is extracted out of the SRD  205 , the ram-trolley  245 , being coupled to the take-up reel  215 , travels in an extraction direction (e.g., a clockwise direction  275  with reference to  FIG. 2B ). The surface parallel to a radius of the circular track  240  at an extraction end  255  of the ram-trolley  245  translates the brake pad puck  270  along the circular track  240  without impingement. The take-up reel  215  is free to move in the extraction direction without the braking force present in the retraction direction. Various SRD embodiments may advantageously provide a directionally polarized deceleration force, provide substantially free lanyard extraction and provide an advantageous deceleration during retraction. 
       FIG. 3A  depicts a perspective exploded view of an exemplary SRD, illustrating a shuttle coupled to a spring-biased drum. An SRD  300 A includes a rear enclosure  305 . The rear enclosure  305  is rotatably coupled to a drum  310 . The drum  310  is fixedly coupled to a tether  315  on a proximal end. The tether  315  is fixedly coupled to a handle  320  on a distal end. The drum  310  is captured between the rear enclosure  305  and a front enclosure  325 . A circular track  330  is fixedly coupled to the front enclosure  325 . A dynamic braking member (DBM)  335  is captured within a recessed channel of the circular track  330 . A shuttle bracket  340  is fixedly coupled to the drum  310 . The shuttle bracket  340  is fixedly coupled to a shuttle  345 . The shuttle  345  is confined within the recessed channel of the circular track  330 . 
     In operation, the DBM  335  is free to move within the recessed channel of the circular track  330 . The shuttle  345  moves within the recessed channel the circular track  330  in response to the rotation of the drum  310 . Accordingly, as the drum  310  rotates, the shuttle  345  may push the DBM  335  through the recessed channel of the circular track  330 . 
     The circular track  330  includes an inner wall  350  and an outer wall  355 . The shuttle  345  is configured on an inclined end  360  to force the DBM  335  into an inner track surface of the inner wall  350 . The inclined end  360  is configured to bind the DBM  335  between the inner track surface of the inner wall  350  and the inclined end  360 . The inclined end  360  may guide the DBM  335  into a frictional retraction impingement with an inside surface of a circular channel, such as the circular track  330 , when a cylindrical drum, such as the drum  310 , is in a retraction mode. 
     The binding action may provide an opposing force to the translation of the shuttle  345 . The opposing force may slow the rotational speed of the drum  310 . The slower rotational speed of the drum  310  may slow the retraction of the tether  315 . Slower retraction speeds of the tether  315  may advantageously reduce damaging impacts of the handle  320  colliding with the rear enclosure  305  and/or the front enclosure  325 . The shuttle  345  is configured on a second end to translate the DBM  335  between, and parallel to, the inner wall  350  and the outer wall  355  without binding. 
       FIG. 3B  depicts a cross-sectional view of an exemplary SRD, illustrating a shuttle coupled to a spring-biased drum. In the depicted example, an SRD  300 B includes a track  365 . The track  365  is fixedly coupled to the inside of a housing cover  370 A. The housing cover  370 A is fixedly coupled to a housing back-shell  370 B. The housing cover  370 A and the housing back-shell  370 B are rotatably coupled to an axle  375 A. The axle  375 A is rotatably coupled to a drum  375 B. The drum  375 B is fixedly coupled to a shuttle bracket  375 C. The shuttle bracket  375 C is coupled to a shuttle  380 . The shuttle  380  is housed in, and translates within, the confines of the track  365  in response to the rotation of the drum  375 B. As the drum  375 B rotates, a filament  385  is reeled or unreeled from the drum  375 B. 
       FIG. 4  depicts a perspective view of an exemplary shuttle and brake disk located and guided by a channel ring, the brake disk frictionally engaged with an inner wall of the channel ring. An inner wall brake configuration  400  includes a channel ring  405 . The channel ring  405  is unitary and formed of an inner wall  410 , a floor  415  and an outer wall  420 . A shuttle  425  is captured between and translationally guided by the inner wall  410 , the floor  415  and the outer wall  420 . A brake disk  430  is captured between and translationally guided by the inner wall  410 , the floor  415  and the outer wall  420 . The shuttle  425  includes an inclined plane surface  435 . In the depicted example, when the shuttle  425  translates counterclockwise, the brake disk  430  is forced toward the inner wall  410  by the inclined plane surface  435 . In various examples, the brake disk  430  may be in frictional engagement with the shuttle  425  and the inner wall  410 . The inclined plane surface  435  may guide a DBM, such as the brake disk  430 , into a frictional retraction impingement with an inside surface of a circular channel, such as the channel ring  405 , when a cylindrical drum is in a retraction mode. 
       FIG. 5  depicts a perspective view of an exemplary shuttle and brake disk located and guided by a channel ring, the brake disk frictionally engaged with an outer wall of the channel ring. A shuttle  440  includes an inclined plane surface  445 . In the depicted example, when the shuttle  440  translates counterclockwise, the brake disk  430  is forced toward the outer wall  420  by the inclined plane surface  445 . In various examples, the brake disk  430  may be in frictional engagement with the shuttle  440  and the outer wall  420 . The inclined plane surface  445  may guide a DBM, such as brake disk  430 , into a frictional retraction impingement with an inside surface of a circular channel, such as the channel ring  405 , when a cylindrical drum is in a retraction mode. 
     As depicted in  FIG. 5  the shuttle  440  bake disk  430  may be replicated and distributed about the channel ring  405 . In each instance the shuttles  440  may be mechanically coupled to a rotating drum, such as the rotating drum  310  ( FIG. 3A ). Multiple instances of the shuttle  440  along with multiple instances of the brake disk  430  may advantageously increase a braking force. In some examples, multiple instances of the shuttle  440  along with multiple instances of the brake disk  430  may advantageously provide design redundancy. 
       FIGS. 6A, 6B, 6C, 6D, and 6E  depict plan views of various shuttle embodiments. Each embodiment includes a distal surface on a retracting end and a proximal surface on an extending end. The retracting end is the leading edge during a lanyard retraction process (e.g.,  FIG. 2A ). The extending end is the leading edge during an extension process (e.g.,  FIG. 2B ). 
     In some embodiments, the distal surface may be linear, for example, incorporating a linear ramp or wedge. In some implementations, the distal surface may be, for example, hyperbolic or reverse hyperbolic, implementing a scooped or reverse scoop shape. 
       FIG. 6A  depicts a shuttle component  600 A including an outward facing concave incline feature  605  on a distal surface. The outward facing concave incline feature  605  may include an incipient angle  610  forming a leading point. The incipient angle  610  may generate an impinging force against a dynamic braking member, providing a braking function. The outward facing nature of the outward facing concave incline feature  605  may force the dynamic braking member toward an outer wall of a raceway, which may advantageously increase braking force. 
       FIG. 6B  depicts a shuttle component  600 B including an inward facing concave incline feature  615  on a distal surface and a triangular point feature  620  on a proximal surface. The inward facing nature of the inward facing concave incline feature  615  may force a dynamic braking member toward an inner wall of a raceway, which may decrease force, advantageously decreasing the sensitivity of an angle on the inward facing concave incline feature  615  contacting the dynamic braking member. Decreasing sensitivity may loosen manufacturing tolerances of the part. The triangular point feature  620  on the proximal surface may further minimize friction between the dynamic braking member and the shuttle component  600 B, in an extraction mode. The friction may be minimized by minimizing the contact area between the triangular point feature  620  and the dynamic braking member. 
       FIG. 6C  depicts a shuttle component  600 C with a first incline feature  625  on a distal surface and a second incline feature  630  on a proximal surface. The first incline feature  625  may be configured to slow the retraction speed, and the second incline feature  630  may be configured to slow the extraction speed. Slowing the extraction speed may advantageously slow down a rapid fall of a tethered individual. Accordingly, various SRDs may be simultaneously customized for limiting maximum retraction and extraction speeds. 
       FIG. 6D  a shuttle component  600 D including an outward facing convex incline feature  635  on a distal surface. The outward facing convex incline feature  635  may include an incipient angle  640  forming a blunt leading end. The incipient angle  640  may substantially reduce or minimize frictional engagement against a dynamic braking member, providing a substantially reduced or minimized braking force. The minimal braking force may reduce wear on the dynamic braking member, which may advantageously increase a working life of the dynamic braking member. The outward facing nature of the outward facing convex incline feature  635  may force the dynamic braking member toward an outer wall of a raceway. 
       FIG. 6E  depicts a shuttle component  600 E including an inward facing convex incline feature  645  on a distal surface. The inward facing nature of the inward facing convex incline feature  645  may force a dynamic braking member toward an inner wall of a raceway. 
       FIG. 6F  depicts a shuttle component  600 F including an adjustable incline feature  650 . The adjustable incline feature  650  is hingedly coupled to the shuttle component  600 F. When a selected incline is configured, a set screw  655  may be tightened to hold the incline in place. In some embodiments, the adjustable incline feature  650  may be user accessible. The inclined features  605 ,  615 ,  625 ,  635 ,  645 ,  650  may guide a DBM into a frictional retraction impingement with an inside surface of a circular channel when a cylindrical drum is in a retraction mode. 
       FIGS. 7A, 7B, 7C, 7D, 7E and 7F  depict plan views of various DBM embodiments. Some embodiments may include iron. Iron may advantageously provide wear resistance. Some embodiments may include copper. Copper may be advantageously combined with other metals to provide more softness creating a more friction for a given force. Some embodiments may include ceramic, which may provide an advantageous compromise between durability and loss of friction. In various implementations, the DBM may include rubber. Rubber may provide very high friction for a given force application. Some embodiments may include various synthetic material (e.g., polymers, synthetic rubber, cellulose fibers). Various synthetic materials may provide high friction for a given force application. 
       FIG. 7A  depicts a DBM component  700 A. The DBM component  700 A is puck shaped.  FIG. 7B  depicts a DBM component  700 B. The DBM component  700 B is a central slice of a sphere.  FIG. 7C  depicts a DBM component  700 C. The DBM component  700 C is spherical.  FIG. 7D  depicts a DBM component  700 D. The DBM component  700 D is rectangular.  FIG. 7E  depicts a DBM component  700 E. The DBM component  700 E is trapezoidal. 
       FIG. 7F  depicts a DBM component  700 F. The DBM component  700 F exists as two separate parts. On one end is a V-shaped throat  705 . The two separate parts meet on a horizontal surface with respect to the example depiction, intersecting with the center of the V-shaped throat. The DBM component  700 F may be used, for example, in combination with the shuttle  600 B ( FIG. 6B ). In operation, the triangular point feature  620  ( FIG. 2 ) may be forced into the V-shaped throat and may produce braking forces on both the inner and outer walls of a raceway. The wear of the DBM component  700 F may be even, and the DBM component may advantageously continue to be effective as its surfaces wear down. 
       FIGS. 8A and 8B  depict plan views of exemplary shuttle embodiments centering a DBM to minimize friction against a channel ring. With reference to  FIG. 8A , an extension end  805  of a shuttle  810  is concave. The concave shape of the extension end  805  holds a DBM  815  away from both an inner and outer wall of a channel ring, such as channel ring  405  ( FIG. 4 ). With reference to  FIG. 8B , an extension end  820  of a shuttle  825  is V-shaped. The V-shape of the extension end  820  holds a DBM  830  away from both an inner and outer wall of a channel ring, such as channel ring  405  ( FIG. 4 ). 
       FIG. 9  depicts a plan view of an exemplary shuttle and DBM embodiment, both the shuttle and the DBM providing friction against a channel ring. In the depicted example  900 , a shuttle  905  in a retraction mode  910  translates counterclockwise. During translation, the shuttle  905  moves a DBM  915 . The DBM  915  and the shuttle  905  include complementary ramps which face each other. When in motion, the shuttle  905  and the DBM  915  are forced in opposite directions along a path radius. In the depicted example, the shuttle  905  is forced toward an inner wall of a channel ring, such as channel ring  405  ( FIG. 4 ). The DBM  915  is forced toward an outer wall of the channel ring. The shuttle  905  includes radial coupling slots  920 . The slotted shape of the coupling slots  920  may allow the shuttle  905  to move radially with respect to the channel ring while being translated around the channel ring. 
     Although various embodiments have been described with reference to the figures, other embodiments are possible. For example, a deceleration system may be configured with a railway channel combined with an SRD housing. A drive block may be combined with a drum and may rotate with the drum. A friction pin may translate through the railway. 
     When an SRD cable retracts, the drum may rotate simultaneously with the drive block. The drive block may push the friction pin on the railway. The drum and the cable retraction may slow down in response to a friction force from this deceleration system. When the SRD cable is extracted from the SRD, the deceleration system may not slow down the cable extraction speed. 
     In an exemplary aspect, a polarized deceleration apparatus may be implemented in a self-retracting device (SRD) in personal protection applications. The apparatus may include a cylindrical drum rotatably coupled to a housing. The drum may be rotatable about a longitudinal axis so as to unspool a tether in an extraction mode and to spool the tether in a retraction mode. The apparatus may include a circular channel fixedly coupled to the housing and in a plane orthogonal to the longitudinal axis. The apparatus may include a shuttle mechanically coupled to rotate in response to the cylindrical drum, the shuttle configured to translate within the circular channel. The apparatus may include a dynamic braking member (DBM) configured to translate within the circular channel. The shuttle may include a retraction face configured to guide the DBM into a frictional retraction impingement with an inside surface of the circular channel when the cylindrical drum is in the retraction mode. The shuttle may include an extraction face configured to guide the DBM around the circular channel when the cylindrical drum is in an extraction mode. 
     The extraction face of the shuttle may be substantially parallel with a radius of the circular channel. The retraction face of the shuttle may include a substantially linear slope. In some examples, the retraction face of the shuttle may be concave. In various examples, the retraction face of the shuttle may be convex. In some embodiments, the retraction face of the shuttle may be hyperbolic. In some examples, the retraction face of the shuttle may be piecewise linear. In various examples, the retraction face of the shuttle may be complementary to at least one face of the DBM. The DBM may be substantially cylindrical. In operation, a frictional extraction force associated with the extraction mode may be less than a frictional retraction force associated with the retraction mode. 
     A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. For example, advantageous results may be achieved if the steps of the disclosed techniques were performed in a different sequence, or if components of the disclosed systems were combined in a different manner, or if the components were supplemented with other components. Accordingly, other implementations are within the scope of the following claims.