Abstract:
A controlled descent device for use in industrial or recreational settings for controlled descent of a user from an upper level to a lower level. The device comprises principally a steel housing, an internal spring-loaded drum on which a webbing line is wound, and an attachment to a harness worn by a user. A centrifugal brake mechanism which acts upon the drum to limit the rate of descent includes a manufactured one-way bearing. The line constituent provides increased shock absorbing capabilities and is field replaceable.

Description:
This application claims the benefit of Provisional Application No. 60/216,110, filed Jul. 6, 2000. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to a controlled descent device intended for use in industrial or recreational settings. More particularly, in industrial settings, the present invention is used for emergency rescue or evacuation of personnel from a height by lowering them to safety at a controlled rate. In recreational settings, such as artificial rock climbing walls, it serves as a hands free belay device which lowers a climber to the ground at a controlled rate. 
     BACKGROUND OF THE INVENTION 
     Controlled descent devices of various types have been in use in general industry as a component in rescue and evacuation systems on buildings, bridges, towers, derricks, ladders, roofs and tanks and in a variety of settings including manufacturing, construction, oilfield, refinery and maintenance. An example of one such device is currently manufactured by Rose Manufacturing under the product name Dynescape® descender. 
     As shown in FIGS. 1-3, the Dynescape® descender is a controlled descent device  100  that consists principally of a steel housing  101  with an installation bracket  120 , an internal spring-loaded drum  103  on which a wire line  102  is wound, and a snaphook  105  on the line for attachment to a full body harness (not shown) worn by the user. Attached to the housing  101  is a centrifugal brake mechanism  107  which acts upon the drum  103  to limit the rate of descent. The wire line  102  passes around a pulley  123  and through a nozzle  104  before exiting the housing  101 . 
     During forced line extraction, line  102  which is wrapped around the drum  103  produces a moment, causing the drum  103  to rotate on its axle  108 . During line retraction, a constant force spring  106  biased in the direction of retraction acts on the drum  103  causing it to rotate in the direction that feeds line onto the drum  103 . A bull gear  109  rigidly fixed to the drum  103  rotates with the drum  103 . The bull gear  109  is meshed with a pinion gear  110 . The axis of rotation of the pinion gear  110  is aligned with the centrifugal brake mechanism  107 . The pinion gear  110  is linked to a pinion shaft  111  and is coupled in such a manner that when rotation is in the direction produced during line extraction, the two rotate together. During line retraction, the pinion shaft  111  and pinion gear  110  remain uncoupled, such that the pinion gear  110  spins freely on the pinion shaft  111 , and the pinion shaft  111  remains stationary. Through this interaction of the pinion gear  110  and pinion shaft  111 , the centrifugal brake mechanism is only engaged to rotate during line extraction. 
     The pinion shaft  111  is supported by two roller bearings  112 , and is rigidly linked to a brake hub  113 . Three dowel pin spokes  114  protrude axially from the hub, and engage with three brake shoes  115 . The brake shoes  115  are formed of arc shaped steel masses with a brake liner material  121  bonded to their outer surfaces. The end of each spoke  114  is situated within a bore  122  centered in the brake shoes  115 . The bore  122  is oversized with respect to the spoke diameter, providing a loose fit that permits both axial and rotational degrees of freedom of the brake shoe  115  within the confines of the brake housing  116 . The three brake shoes  115  are contained in a brake housing  116  with a cylindrical interior  117 . During braking, this cylindrical surface  117  mates with the curved brake shoe liner material  121 . During line extraction, the pinion gear  110 , pinion shaft  111 , hub  113 , spokes  114  and brake shoes  115  all rotate in unison within the housing. As the brake shoes  115  rotate with sufficient angular velocity, they are forced outward, along the axis of the spokes  114 , towards the brake housing  116 , due to centripetal acceleration. The centripetal acceleration acting on the brake shoe  115  forces the brake shoe  115  against the housing cylindrical surface  117 , producing friction that resists line extraction. The friction force is increased by the camming action of the brake shoes  115 . Because the bore  122  in the brake shoe is oversized with respect to the spoke  114 , the shoe  115  will tilt when in sliding contact with the brake housing  116 . This tilting cams the leading end of the shoe braking surface towards the housing  116 , increasing the braking friction force. 
     As mentioned previously, the mechanism linking the pinion shaft  111  to the pinion gear  110  permits relative rotation between these two components in one direction only. The pinion shaft  111  has a rectangular slot (see FIG. 3) cut perpendicular to its axis. This slot contains a double ended sliding key  118 . The key interacts with an internal cam profile  119  cut into the shoulder of the pinion gear. The cam profile  119  is a one-way ratchet shape with three high points, three low points, and three steps. This shape produces forced engagement of the sliding key  118  against the ratchet step when rotation of the pinion is in the direction of line extraction. The high point of the profile pushes one end of the sliding key  118 , such that the opposite end is forced into the low point and against the ratchet step on the opposite side of the cam profile. During line retraction, a relief angle on the key  118  and cam profile  119  allow the key  118  to flutter back and forth in the slot without engaging against the step of the cam profile  119 . The pinion gear  110  is thereby free to rotate about the pinion shaft  111  during line retraction, keeping the brake mechanism uncoupled from the drum  103 . During line extraction, the pinion gear  110  remains rotationally fixed to the pinion shaft  111 , keeping the brake mechanism engaged to rotate as the drum  103  rotates. 
     As the Dynescape® descender is intended for emergency use it typically is not subject to prolonged use. During prolonged use, components of the Dynescape® descender may need to be replaced due to increased wear. The sliding key  118  may become worn by the cam profile during prolonged use. The sliding key  118  may also become bent or deformed when subject to impact loading. Impact loading can occur in recreational applications when a climber attempts to jump for a hold that is out of reach, and free-falls on the line. Such prolonged use or abuse will eventually lead to compromised performance of the braking mechanism, which may engage during both line retraction and extraction. 
     A need exists, therefore, for a more robust design that will withstand repeated use and impact loading and whose components are not susceptible to wear during prolonged use. 
     Another feature of the Dynescape® device is that the line  102  is a wire rope. Over prolonged use this wire rope line  102  is prone to bird-caging (unraveling or kinking). Bird-caging is felt to be a result of the line material and the manner in which the line is layered onto the drum. Because the line is not stacked in consecutive layers and can cross itself, it can bind with itself and rub against itself as it is reeled on and off the drum during line retraction and extraction. Additionally, because the wire line  102  is a stiff member it is not capable of absorbing considerable energy in the event that a user free-falls on a slack line. 
     Another need exists, therefore, to develop a line that is not prone to bird-caging and which is capable of serving as a shock absorber during a user fall. An additional need exists for a field-replaceable line which allows a worn or deteriorated line to be replaced by a new line without having to return the device to the factory. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a controlled descent device for use in industrial or recreational settings for lowering a user to the ground at a controlled rate. 
     Like the Dynescape® descender device, the controlled descent device of the present invention includes a steel housing containing a line wound on a spring loaded drum. The line feeds out of the housing through a nozzle. A snap hook or carabiner on the free end of the line is used to attach to a full-body harness worn by the user. A constant force retraction spring acts on the drum to retract the line into the housing as the user ascends or when the line is released. A centrifugal brake mechanism engages the drum to produce a resisting force when the line is extracted. This brake mechanism slows a user&#39;s descent rate by paying out extracted line at a controlled rate. 
     The braking mechanism of the present invention is similar in function to that of the Dynescape® device, however, the pinion, pinion shaft, and brake hub have each been modified. The pinion gear, slider key, and pinion shaft have been replaced by a single pinion gear with shaft. The brake hub is no longer rigidly linked to the shaft. Instead the hub is supported on the shaft by a one-way roller bearing. The one-way roller bearing connecting the shaft to the hub permits engagement of the brake mechanism only during cable extraction. During retraction, the pinion with shaft will rotate freely, while the hub, spokes and brake shoes remain stationary. The pinion with shaft and one way roller bearing are not as susceptible to wear during prolonged use. 
     The line of the present invention is preferably constructed from a flat webbed material such as nylon which is wrapped onto the drum in consecutive layers. Other suitable materials include polyester or any webbing with similar elastic properties having a minimum 20% elongation at break. The use of webbing in this configuration has several advantages over wire line. Because nylon webbing or the like will stretch under load, the webbing serves as a shock absorber in the event that a climber free-falls on a slack line. The manner in which the webbing is wrapped onto the drum in consecutive layers also serves as a shock absorbing mechanism. During free-fall arrest, tension on the line pulls the wraps of the webbing tighter around the drum. Friction between consecutive layers of webbing absorbs the energy of a fall. In this manner, the webbing on the drum acts as an efficient shock absorber when the line is fully paid out or when the line is fully retracted. When fully paid out, the stretch of the extracted line under load absorbs the energy of a fall. When fully retracted, the wraps of webbing about the drum absorbs the energy of a fall. 
     Because the webbed line of the present invention is susceptible to abrasion and wear, the present invention may preferably incorporate a linkage that allows a worn or deteriorated line to be detached, and a new line be reattached in the field by the user. This avoids having to return the device to the factory to have the line replaced. 
     Thus, it may be seen that an improved controlled descent device is provided whose braking components are less prone to wear, and whose line provides increased shock absorbing capabilities and is field replaceable. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     An illustrative and presently preferred embodiment of the invention is shown in the accompanying drawings in which: 
     FIG. 1 is front view, partially in section of the prior art Dynescape® descender; 
     FIG. 2 is cross-sectional view through line C—C of FIG. 1; 
     FIG. 3 is a partial cross-sectional view through line B—B of FIG. 2; 
     FIG. 4 is a front view shown partially in section of the present invention; 
     FIG. 5 is a cross-sectional view through line C—C of FIG. 4; 
     FIG. 6 is a cross-sectional view through line D—D of FIG. 5 showing a sprag type one-way bearing; 
     FIG. 7 is a cross-sectional view through line D—D of FIG. 5 showing a roller ramp type one-way bearing; 
     FIG. 8 is a front view of the present invention showing the preferred embodiment of the field replaceable feature; 
     FIG. 9 is a front view of the present invention showing a second embodiment of the field replaceable feature; and 
     FIG. 10 is a front view of the present invention showing a third embodiment of the field replaceable feature. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The controlled descent device  10  of the present invention shown in FIGS. 4-10 comprises a steel housing  1  containing a line  23  having a carabiner  5  or the like on one end wound on a drum  24 . A constant force retraction spring  6  provides a force on the drum  24  to retract the line  23  into the housing  1 . A centrifugal brake mechanism  7  like the braking mechanism of the Dynescape® descender is attached to the housing and engages the drum to produce a resisting force when the line is extracted. The preferred embodiment of the braking mechanism  7  includes a brake hub  13 , three spokes  14 , brake shoes  15  and brake housing  16  similar in form and function to the Dynescape® descender. A pinion gear with shaft  29  is supported on the brake housing  16  by two roller bearings  12 . The brake hub  13  is supported on the shaft by a one-way roller bear  21  and an additional bearing  12   a.    
     This one-way bearing  21  may be one of several types of manufactured mechanisms such as those commercially available from Morse and Formsprag®, that produce a rotational motion in one direction and a fixed motion in the opposite direction such as back stopping, clutch or indexing bearings, roller-ramp type bearings or sprag clutches and sprag clutch/roller bearing combinations. Specifically, the one-way bearing permits rotation of its inner raceway relative to its outer raceway in one direction. When rotated in the opposite direction, the two raceways remain fixed with respect to one another, rotating in unison. 
     The sprag type bearing  35  illustrated in FIG. 6 contains a series of spring loaded sprags  36  that reside between, and are in contact with the inner  37  and outer  38  bearing raceways. When rotation of the outer raceway  38 , relative to the inner raceway  37 , is in one direction, these sprags  36  cam, locking the inner raceway  37  to the outer raceway  38 . When rotation is in the opposite direction, the sprags  36  uncam, permitting the inner raceway  37  to rotate relative to the outer raceway  38 . Sprag type bearings  35  frequently have a set of rollers  42  situated next to the sprags as shown in FIG.  5 . These rollers provide concentricity and produce smooth rolling motion between the raceways. 
     The roller-ramp type bearing  40  illustrated in FIG. 7 contains an array of balls or rollers  41  that reside between, and are in contact with the inner  37  and outer  38  raceways. The surface of the inner raceway  37  is ramped  39 , such that the balls or rollers  41  roll up the ramps  39  during rotation in one direction, and down the ramps  39  in the opposite direction. As the balls or rollers  41  roll up the ramps, they wedge between the inner  37  and outer  38  raceway, preventing relative rotation of the inner  37  and outer  38  raceways. As the balls or rollers rolls down the ramps  39 , they unwedge and provide clearance for the outer raceway  37  to roll relative to the inner raceway  37 , like a standard roller bearing. The one-way roller bearing  21  connecting the shaft  29  to the hub  13  permits engagement of the brake mechanism only during line extraction. During line retraction, the pinion with shaft  29  will rotate freely, while the hub  13 , spokes  14  and brake shoes  15  remain stationary. 
     The line  23  of the present invention is formed from flat webbing, preferably of nylon material. The drum  24  on which the line  23  is wrapped has side walls spaced slightly wider than the webbing width, such that when line  23  is wrapped on the drum  24  the line  23  will stack in consecutive layers. The line  23  passes through a nozzle  25  as it leaves the housing  1 . The nozzle opening is dimensioned slightly larger than the webbing cross-section. This shape is designed to direct the webbing onto the drum  24  in consecutive layers. The webbing also passes across a cylindrical roller  26  between the nozzle  25  and drum  24 . The roller  26  helps redirect the webbing  23  and lay it flat on the drum  24 . 
     The line  23  of the present invention may also be field replaceable as shown in FIGS. 8-10. The field replaceable line comprises an internal portion of line  27  that is permanently attached to the drum, and a distal portion of line  28  that extracts from the housing and is replaceable. The ends of each portion are joined by a linkage. The ends of the webbing are sewn in loops  29 . In the preferred embodiment shown in FIG. 8, the loops  29  each contain a steel cylinder  30 , oriented with their diameters supporting the webbing. A bolt  31  passes through a hole formed in the top of each loop  29  and through each cylinder. The linkage, including the two cylinders  30 , has a width identical to the width of the webbing. The shape of the linkage facilitates it fitting inside the drum, and laying flat and neatly on the drum beneath the other layers of webbing. To replace the line, a user removes the nozzle  25 , and extracts all of the line from the housing until the linkage is external to the housing. The user then disconnects the replaceable portion of line by removing the bolt  31  connecting the cylinders. A new nozzle  25 , line  23 , cylinders  30  and bolt  31  is then connected, replacing the worn components. The line  23  is then returned to the housing and the new nozzle  25  is re-attached. 
     It is contemplated that any means of joining two portions of webbing that are attached using loops that contain hardware joined by a screw, bolt or other means or two loops attached using a screw lock link could be substituted for the above-described arrangement. Alternate linkage mechanisms are illustrated in FIGS. 9 and 10. In a second alternate embodiment illustrated in FIG. 9, a steel plate  32  is threaded through each loop  29 . At least one screw  33  and preferably two screws pass through the loops  29  and plates  33  to anchor the two portions of webbing together. FIG. 10 depicts a third alternate embodiment in which a screw lock link  34  is threaded through loops  29 . 
     If not otherwise stated herein, it may be assumed that all components and/or processes described heretofore may, if appropriate, be considered to be interchangeable with similar components and/or processes disclosed elsewhere in the specification, unless an indication is made to the contrary. 
     It should be appreciated that the apparatus and methods of the present invention may be configured and conducted as appropriate for the application. The embodiments described above are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is defined by the following claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.