You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
FIELD OF THE INVENTION  
       [0001]     This invention relates to collapsible structural members or beams and more particularly to collapsible structural members which use substantially identical modules to form beam which are rigid in three dimensions.  
       BACKGROUND OF THE INVENTION  
       [0002]     Various collapsible members have been used to form beams for collapsible structures such as temporary buildings and tents and also for work arms to position working tools in awkward locations. The collapsible structural members typically employ cables as tensioning members to bring separate segments or modules together to form a rigid structure. Such prior art structures usually rely on the cable itself to provide rigidity to the member or to separate pins or fasteners which must be installed to obtain rigidity and must be removed to permit collapse of the structure. Usually collapsible structural members require multiple parts and also require substantial time to form a structure and to collapse that structure.  
         [0003]     There is a need for a collapsible structural member which is simple to erect and to collapse and uses a minimum number of parts. It appears also that there is a need for a collapsible structural member which uses a tensioning member to bring the parts together but which locks them in a position so that they are not reliant on the tensioning member for rigidity or strength.  
         [0004]     An object of the invention is to provide a collapsible structural member which is simple and eliminates the need for many removable parts.  
         [0005]     Another object of the invention is to provide a collapsible structure member where a tensioning member is used to bring components, segments or modules of the structure together and into a position in which the components lock together frictionally and are maintained in the locked position without undue loading required on the tensioning member.  
         [0006]     A further object of the invention is to provide a collapsible beam structure which uses frictional locking principles similar to that used in Morse tapers for locking tapered drill bits and complementary tapered rotatable chucks to provide frictional locking between the drill and the chuck to transmit rotational torque.  
         [0007]     Still another object of the invention is to provide a collapsible beam structure having the ability of locking adjacent modules relative to each other using complementary spherical locking surfaces to provide a frictional lock required to hold the modules in a rigid position relative to each other whether the modules are aligned axially or at an angle to each and independently of the cable or tensioning member.  
       SUMMARY OF THE INVENTION  
       [0008]     The objects of the invention are attained by a collapsible structural member utilizing a plurality of substantially identical adjacent modules with each of the modules including an elongated body with a pair of oppositely facing walls forming a head at one end and a skirt forming a socket at the other end to receive the head of an adjacent module. Each of the heads forms a pair of outwardly facing spherical concave locking surfaces facing away from each other and the skirts of each of the modules form concave complementary spherical locking surfaces facing each other. A passage is formed within the modules to extend longitudinally from the head and through the skirt to receive a tensioning member in the form of a cable. Upon application of the tension to the cable at the skirt of an end module of a number of modules on the cable to bring the pair of convex spherical locking surface of the head portions of each module into frictional locking engagement with a pair of concave locking surfaces of an adjacent one of the modules to form a lock between the adjacent modules of all of the modules. Stops are formed on each module to determine the angular relation of the modules so that the collapsible beam can be curved or straight and to form a rigid but collapsible structural member. The cable is used to maintain the position of the modules and upon release permits the cable to be collapsed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a perspective view of a single module used to form a collapsible structural member.  
         [0010]      FIG. 2  is a front elevation of one of the modules;  
         [0011]      FIG. 3  is a side elevation of one of the modules;  
         [0012]      FIG. 4  is a top view of the modules seen in the preceding figures;  
         [0013]      FIG. 5  is a bottom view of the modules seen in  FIGS. 1-3 ;  
         [0014]      FIG. 6  shows two adjacent modules in an aligned position just prior to locking;  
         [0015]      FIG. 7  shows three adjacent modules in their locked position;  
         [0016]      FIG. 8  is a cross sectional view of the modules seen in  FIG. 7  showing the position of the tensioning cable within the modules;  
         [0017]      FIG. 9  is a cross sectional view taken on line  9 - 9  in  FIG. 7 ;  
         [0018]      FIG. 10  is a modified version of the module of the collapsible structural member embodying the invention shown in  FIG. 2 ;  
         [0019]      FIG. 11  is a view similar to  FIG. 4  showing another modification of the module with the head portion of the module rotated slightly relative to the skirt portion for the purpose of changing the direction of curves in a collapsible structural member;  
         [0020]      FIG. 12  is a view similar to  FIG. 3  showing a modified module with the head displaced relative to the skirt to form three-dimensional curved beam;  
         [0021]      FIG. 13  is a diagrammatic showing of a plurality modules of  FIGS. 1 through 8  showing a collapsible structural member curved in a coil or in three dimensions; and  
         [0022]      FIG. 14  is a diagrammatic view of a collapsible structural member forming an arch to support a swimming pool cover.  
     
    
     DESCRIPTION OF THE INVENTION  
       [0023]     The present invention utilizes a concept of spherical frictional locking surfaces.  
         [0024]     A common example of a frictional locking surface is the conical form found in the Morse taper invented by Steven A. Morse about 1864 and still in wide commercial use in drill presses and lathes. In such a locking arrangement the conical end of a shaft of a tool or drill bit has an included angle at the apex of about seven degrees (7°) or less. When the tool is inserted in a chuck having a complementary conical socket with the same included angle, friction alone maintains the tool in the socket. A small axial force applied to the tool to bring the tapered locking surfaces into engagement with each other is sufficient to frictionally lock the shank of the tool in torque transmitting relationship to the socket. A similar axial force in the opposite direction is applied to disconnect the tapered locking surfaces from each other.  
         [0025]     The locking surfaces employed in the present invention uses opposed complementary spherical locking surfaces to form a frictional locking angle of about seven degrees (7°) or less. The spherical surfaces are used to accommodate angled positions of modules relative to each other.  
         [0026]     A collapsible beam  10  of the present invention is made up of a plurality of modules or beads  12 . The modules  12  are substantially identical to each other when the beam  10  is to be straight and vary only slightly from each other if any portion of the beam is to be curved. The modules required for straight beams or those curved in a single plane will be discussed first.  
         [0027]     Each module  12  of the plurality of modules forming a collapsible beam  10  has a generally flat and elongated body portion  14  with a head  16  at one end and a skirt  18  at the other end forming a receiving socket  20  for the head  16  of an adjacent module  12 .  
         [0028]     Each module  12  is generally flat with front and back walls  22  which are identical to each other but facing in opposite directions from an imaginary longitudinal plane indicated at  24  in  FIGS. 3 and 4 . Also, the modules  12  have opposite side walls  26  which face away from each other and are identical in shape. The side walls  26  are spaced equally to opposite sides of another imaginary plane  28  intersecting the first mentioned imaginary plane  24  at a right angle as seen in  FIGS. 2 and 4 . All of the opposed wall surfaces  22  and  26  are symmetrical to a longitudinal axis  30  formed at the intersection of planes  24  and  28  as seen in  FIG. 4 . The longitudinal axis  30  is coaxial with a passage  32  as best seen in  FIGS. 2 and 3 . The position of the imaginary planes  24  and  28  as well as the longitudinal axis  30  are also indicated in  FIGS. 4 .  
         [0029]     The side walls  26  of the head  16  are portions of the circumference of a circle with the center of radius  33  being located at the point  34  as seen in  FIG. 2  with the diameter of the circular walls being slightly less than an opening  36  formed in end wall  37  as an entrance to socket  20  in skirt  18  as seen in  FIG. 5 .  
         [0030]     Front and back walls  22  of head  16  have identical convex surfaces  38  which are formed by opposed segments of a sphere having a radius  39  centered at point  40  in  FIG. 9  and extending to the opposite side of longitudinal plane  24  and disposed in a transverse plane  42  that passes through the center  34  of the radius for circular side walls  26  of head  16  as seen also in  FIG. 2 . As seen in  FIG. 9 , the two convex segments  38  of the sphere face in opposite directions and are relatively closely spaced to each other to form a relatively thin and flat head  16 .  
         [0031]     By making the radius approximately the length of the illustrated modules as illustrated in the drawings, the appropriate seven-degree (7°) or less included angle for frictional locking will be obtained. In the present case, if the overall length of the module is about three inches, the radius  39  could be approximately three inches and centered at  40  as seen in  FIG. 9  to form one of the convex spherical frictional locking surfaces. The opposed convex spherical locking surfaces  38  forming the head  16  can be visualized by considering diametrically opposed equal segments of the sphere brought close together as seen in  FIG. 9  for each of the modules.  
         [0032]     The sockets  20  in the skirts  18  of each of the modulesl 2  are provided with a pair of concave spherical locking surfaces  46  which face each other and are complementary to the spherical convex locking surfaces  38  on the head  16  of an adjacent module.  
         [0033]     The concave locking surface  46  in socket  20  are generated with a radius  45  substantially equal to radius  42  used to form the complementary spherical locking surface  38  with the convex shape. Referring to  FIG. 9  and to the lower one of the modules  12 , transverse plane  42  coincides with the end wall  37  of the skirt  18 . The convex-concave matching frictional locking surfaces with the spherical shape are found to approximate the under seven-degree (7°) taper angle of Morse tapers common with conical connections. Also, the spherical frictional locking surfaces  38  and  46  are desirable to form curved collapsible beams since the taper locking surfaces are effective when adjacent modules  12  have their longitudinal axes  30  aligned or at an angle to each other. As seen in  FIG. 2  the circular sides  49  of socket  20  defining the opposite edges of the concave locking surfaces  46  are defined by radius extending from point  37 A at the intersection of longitudinal axis  30  and end wall  37  of skirt  18 . Radius  37 A is substantially equal to radius  37 . The circular, concave side walls  49  of the socket  20  are complementary to the convex circular side walls  26  of the heads of adjacent modules.  
         [0034]     The passages  32  formed longitudinally of each module  12  serve to receive a cable or tensioning member  48  in which the modules or beads  12  are strung as best seen in  FIG. 8 . The cable  48  serves to maintain the modules  12  aligned with each other when the beam  10  is in its collapsed condition. When tension is applied to the cable  48 , which can be to either end of a collapsible structural member  10  and as shown in  FIG. 8  is anchored to the head  16  at a point indicated at  51 . Upon tightening the cable  48  at its opposite end, the head portions  16  are brought into locking engagement in the sockets  20  in adjacent modules of all of the modules on the cable  48  to form a rigid beam as will be described. It will be noted that the axial opening  32  is much wider than required for a single cable  48 . This is provided to accommodate additional cables to activate or apply tension to portions of a collapsible beam or to branch beam portions (not shown).  
         [0035]     The plurality of adjacent modules  12  in a collapsible beam  10  are maintained in line with each other by the cable or other tensioning member  48  extending in axial passage  32  in each of the modules  12  as best seen in FIG.  8 . The cable has been omitted in most of the other figures to simplify the drawings. The passages  32  and the cable  48  are so arranged that the modules  12  are in substantial alignment with each other in the collapsed condition of the structural members  10  with a portion of the head  16  in the socket  20  of an adjacent module as illustrated by the two modules in  FIG. 6 . With cable  48  anchored to a first module, the application of tension to the cable  48  at another module  12  tends to bring adjacent modules  12  together to bring the convex locking surfaces  38  on the head  16  of each module  12  into locking engagement with the complementary and concave locking surfaces in the socket  20  in the adjacent module. The tension can be applied to the cable by a winch  56  shown diagrammatically in  FIGS. 13 and 14  and operated either manually or by power. Thereafter, the loading of the cable  48  is such that only enough tension must be maintained to prevent the modules from changing position relative to each other. The strength or rigidity of the beam  10  is not dependent solely on the tension in the cable  48  which needs to be only high enough to maintain the adjacent modules in position relative to each other.  
         [0036]     The straight or angled position of adjacent modules  12  in their interlocked relation is determined by a pair of stop elements  50  formed on each of the front and back walls  22  of the head  16  of each of the modules  12  as seen in  FIGS. 2 and 3 . The pairs of stop elements  50  are coaxial to each other as seen in  FIGS. 3 and 4  and are disposed equally from opposite sides of plane  28  that intersects the longitudinal axis  30  and longitudinal plane  24  at a right angle. The stop elements  50  on front and back walls  22  of the modules are aligned with each other and are spaced equally from the longitudinal axis  30  of each head portion. Also, all four of the stop elements  50  can be regarded as disposed in the same plane  42  that also passes through radius center  40  for spherical locking surfaces  38  as seen in  FIG. 9 .  
         [0037]     The four stop elements  50  are adapted to engage four stop recesses or notches  52  formed in the end wall  37  of the skirt  18  of an adjacent module  12 . The end walls  37  on skirts  18  coincide with the transverse plane  42  so that as seen in  FIGS. 6 and 7  the stop elements  50  are engaged with the stop recess  52  and the top two adjacent modules  12  in  FIGS. 7 and 8  are aligned with each other in a straight line. If the modules or beads  12  are to be at an angle with each other, the stop elements  50  are repositioned by moving them in an arc about radius center  34  out of reference plane  42  in  FIG. 2 . By way of example, if the adjacent modules are to be at a fifteen-degree (15°) angle to each other, the stop elements  50  are moved from their original transverse position in  FIG. 2  through an arc of fifteen degrees (15°) to the transverse plane  42  about the center  34  midway of stop elements  50  as illustrated also in  FIG. 6  for the bottom module  12 . The axially aligned stop elements  50  at each side of head  16  are moved equally in opposite directions in an arc of fifteen degrees (15°) about radius center  34  from the original transverse position.  
         [0038]     In the preferred embodiment of the invention shown in  FIGS. 1 through 9  maximum angle of adjacent modules is approximately twenty-two and one half degrees (22½°) to insure efficient operation of the cable or tension member  46 .  
         [0039]     The modules for any given size are molded of plastic material and the only differences between modules for straight beams and for curved beams is the position of the stop elements  50 . To create a collapsible structural member  10  only a few different modules are required namely those for straight beam portions and those for curved beam portions. Even here the inventory is simplified because modules for angled connection form an angle either to the left or to the right by simply turning the module one hundred eighty degrees (180°) about its longitudinal axis  26 .  
         [0040]     Thus far the modules  12  had been described as substantially identical except for the positioning of stop elements  50  to make curves in the collapsible structural member  10 . However, in  FIG. 10  the module  12 A has been elongated by changing the distance between the head  16  and the socket  20  in skirt portion  18  which remain identical to the head  16  and socket  20  of the prior modules. Only the body member  14  has been changed by elongation as indicated by the bracket at  53  in  FIG. 10  to space the head  16  at some greater selected distance from the socket  20  in skirt  18 . In all other respects the module  12  remains the same except for the possible positions of stop elements  50 .  
         [0041]     A further modification can be made to the modules  12  in the event a collapsible structural beam is to be curved in more than a single plane, that is a three-dimensional curve or for example such as that that would occur in a spiral on helix as illustrated diagrammatically in  FIG. 13 . In that case, a module  12 B can be formed as a unitary module by rotating the head  16  relative to the skirt  18  and socket  20  about the longitudinal axis  30  of the module as seen in  FIG. 11 . The angle of head  16  can be up to a full ninety degrees (90°) relative to skirt  18 , if desired, since it would not affect the operation of the tensioning member or cable  48 .  
         [0042]     Still another variation of modules  12  can be made by bending the head  16  relative to skirt  18  out of the longitudinal plane  24  as seen in  FIG. 12  to form module  12 C. This variation of the module can also be used to form three-dimensional curved beams such as a helix shown diagrammatically in  FIG. 13 . The tensioning members  48  should be in a path that avoids kinking of the cable and for that reason the angle of displacement of the head  16  relative to the skirt  18  should not exceed about fifteen degrees (15°).  
         [0043]     In all of the modifications of the basic module  12  seen in  FIGS. 10, 11  and  12  the head  16  and socket  20  in skirt portions  18  remain unchanged. Only the body portion  14  between the head  16  and skirt  18  change by either stretching, as shown for module  12 A in  FIG. 10 , by twisting, as shown for module  12 B in  FIG. 11 , or by bending for module  12 C, as seen in  FIG. 12 . In all of the modifications, the head and socket  20  in skirt  18  operate as in the first embodiment. Also, the stops  50  and recesses  52  operate in the same way for all versions of the modules.  
         [0044]     A three-dimension beam  60  is shown in  FIG. 13  in a form of a spiral. The beam  60  would require not only the basic module  12  but a few of the modules  12 B or  12 C.  
         [0045]     A two dimensional beam  64  is illustrated in  FIG. 14  and is made up and curved in a single plane using the basic modules  12  and elongated modules  12 A to form the support beam  64  for a flexible cover  66  for a swimming pool  68 . In such a cover arrangement to curved beam or beams  64  could be collapsed to permit the beams to be rolled up in the cover  66  to uncover the pool  68 .  
         [0046]     A collapsible beam structure has been providing a variety of straight or curved structural members of various sizes utilizing a basic module to be molded of plastic material. The basic module  12  is used to form straight beam structures and is modified slightly by repositioning stop elements  50 , which determine the angular position of adjacent modules relative to each other. The basic module  12  is further modified to twist the head  16  relative to the head receiving socket  20  as in module  1   2 B or to bend the head portion  16  relative to the socket portion  20  relative to the longitudinal transverse plane  28  of the modules  12  or to elongate the module as in module  12 A by separating the head  16  and socket  20  and stretching the skirt portion  18  of the module  12  with a greater distance than the basic module  12 . By selecting and arranging the basic module  12  and modified modules  12 A,  12 B and  12 C, regular and irregular configurations of structural beams can be constructed using only a few different modified modules to accomplish the end result.  
         [0047]     The beam structure of the present invention are rigid not only in a single plane or three planes but are rigid radially relative to the central axis of all of the modules. The structural strength comes from the frictional locking surfaces and the tensioning cable is required only to maintain the position of the modules.

Summary:
A collapsible structural member has been provided in which substantially identical modules made up of metal or plastic are threaded on a tensioning member such as a cable and are movable relative to each other in the collapsed condition of the beam and are brought together into a condition where adjacent modules are locked together to form a rigid construction when the beam is in its erected operating condition. The beam is changed from its erected condition to its collapsed condition by relaxing the tensioning member or cable.