Patent Abstract:
A portable telescopic mast assembly with positive retraction for raising and lowering an associated device includes an outer body and a plurality of mast sections slideably engaged with the outer body. A lifting cable is disposed between the plurality of mast sections. The lifting cable operatively connects the plurality of mast sections so as to urge one or more of the mast sections towards an extended position. The lifting cable includes a first end and a second end, the first end being secured to an inner most mast section of the plurality of mast sections. A retraction cable is disposed at least partially inside the outer body. The retraction cable includes a first end and a second end, the first end being secured to the inner most mast section. A winch is secured to the outer body. The winch includes a first output and a second output, the second end of the lifting cable operatively connected to the first output and the second end of the retraction cable operatively connected to the second output.

Full Description:
BACKGROUND 
       [0001]    The present exemplary embodiment relates to extendable masts. It finds particular application in conjunction with portable masts that are intended to be rapidly deployed and or removed while in the field, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications. 
         [0002]    Various field mast designs are known in the art. Generally, a field mast is a transportable rapidly deployable support column having a height adjust system for raising or lowering an associated device. The associated device can include a communication, audio/video, and or lighting system or any other device whose function or performance is dependent on height or line of sight operation. Typical applications of such masts include both military and civilian settings where a mast must be erected quickly, quietly and or manually. 
         [0003]    However, the prior art field mast assemblies are deficient in a number of ways. First, it is a typical and recurring problem that in the process of removing or collapsing the prior art field masts, the individual mast sections will bind and prevent the mast assembly from being placed into its fully collapsed state. The binding of the mast sections can occur from a variety of reasons, for example, debris trapped between the telescopic mast sections, high wind loads that create a bending moment in the mast sections, or simply lack of proper maintenance and or lubrication of the mast assembly. 
         [0004]    In addition, the prior art masts include an open design winch assembly for raising or lowering the individual mast sections. Particularly in sandy or dry dusty regions, an open design winch assembly is prone to accelerated wear-out. This is due to debris or other aggregate materials accumulating on various internal operating components of the winch assembly, such as the bearings, drums, gears, ratchet assemblies, etc. Moreover, open winch designs create pinch hazards for the operators. 
         [0005]    Furthermore, the prior art masts often include a winch assembly that is not easily detached from the mast assembly. In these cases, a fixed or permanent winch increases the transport weight and creates a bulky protrusion that inhibits the portability and efficient storage of the mast assembly. 
         [0006]    Further still, the prior art mast assemblies include a fixed input-to-output reduction ratio for driving the winch. In these cases, either valuable time is lost in a system with excessive reduction or increased fatigue is experienced in a system with inadequate speed reduction. 
         [0007]    Accordingly, it has been considered desirable to develop a new and improved field mast system which would overcome the foregoing difficulties and others while providing better and more advantageous overall results. 
       BRIEF DESCRIPTION 
       [0008]    According to one aspect of the present invention, a portable telescopic mast assembly with positive retraction for raising and lowering an associated device is provided. The mast assembly includes an outer body and a plurality of mast sections slideably engaged with the outer body. A lifting cable is disposed between the plurality of mast sections. The lifting cable operatively connects the plurality of mast sections so as to urge one or more of the mast sections towards an extended position. The lifting cable includes a first end and a second end, the first end being secured to an inner most mast section of the plurality of mast sections. A retraction cable is disposed at least partially inside the outer body. The retraction cable includes a first end and a second end, the first end being secured to the inner most mast section. A winch is secured to the outer body. The winch includes a first output and a second output, the second end of the lifting cable operatively connected to the first output and the second end of the retraction cable operatively connected to the second output. 
         [0009]    According to another aspect of the present invention, an extendable strap driven mast assembly for raising and lowering an associated device is provided. The mast assembly includes an outer hollow body. A plurality of nested mast sections of consecutively smaller transverse dimension are disposed at least partially inside the outer body when the mast sections are in a collapsed state. Each of the mast sections is slideably engaged with respect to the other. A lifting strap is disposed in a serpentine configuration between the plurality of mast sections and operatively connects the plurality of mast sections so as to urge one or more of the mast sections towards an extended state. The lifting strap includes a first end and a second end, the first end being secured to an inner most mast section of the plurality of mast sections. A retracting cable is disposed partially inside the outer body. The cable includes a first end and a second end, the first end being secured to the inner most mast section so as to urge the mast sections into the collapsed state. A winch is secured to the outer body. The winch includes a first spool and a second spool. The second end of the lifting strap is operatively connected to the first spool and the second end of the retraction cable is operatively connected to the second spool. Wherein the first spool is adapted to withdraw the lifting strap and the second spool is adapted to release the retracting cord when the winch is driven in a first direction. And, wherein the first spool is adapted to release the lifting strap and the second spool is adapted to withdraw the retracting cord when the winch is driven in a second direction. 
         [0010]    According to yet another aspect of the present invention, a portable telescopic strap driven mast assembly having an outer body with a plurality of mast sections slideably engaged with the outer body is provided. The mast assembly includes a lifting strap disposed between the plurality of mast sections. The lifting strap is operatively connected to the plurality of mast sections so as to urge one or more of the mast sections towards an extended position. The lifting strap includes a first end and a second end, the first end being secured to an inner most mast section of the plurality of mast sections. A retraction cable is disposed at least partially inside the outer body. The retraction cable includes a first end and a second end, the first end being secured to the inner most mast section. A winch is selectively engaged to the outer body. The winch includes a housing and a transmission. The transmission includes an input, a first output and a second output. The transmission selectively couples the input to the first output and the second output. The first output selectively engages the second end of the lifting strap and the second output selectively engages the second end of the retraction cable. 
         [0011]    Still other aspects of the invention will become apparent from a reading and understanding of the detailed description of the preferred embodiments hereinbelow. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The present invention may take physical form in certain parts and arrangements of parts, preferred embodiments of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part of the invention. 
           [0013]      FIG. 1  is a perspective view of a first embodiment of a telescopic strap driven field mast, according to the present invention. 
           [0014]      FIG. 1A  is a schematic representation of a partial cross sectional view of the field mast of  FIG. 1 , illustrating the pathway of a lifting strap and a plurality of nested mast sections. 
           [0015]      FIG. 2  is an enlarged detail view of a set of upper collar assemblies each for receiving a respective one of a plurality of mast sections of the field mast of  FIG. 1 . 
           [0016]      FIG. 3  is an enlarged detail view of one of the upper collar assemblies of  FIG. 2 . 
           [0017]      FIG. 4  is an enlarged detail view of a set of lower collar assemblies or base rings each for receiving a respective one of a plurality of mast sections of the field mast of  FIG. 1 . 
           [0018]      FIG. 5  is an enlarged detail view of one of the lower collar assemblies of  FIG. 4  illustrating a mast lock and a plurality of locking post members. 
           [0019]      FIG. 6  is an enlarged detail view of the mast lock of  FIG. 5 . 
           [0020]      FIG. 7  is a perspective view of a first side of a winch assembly of the field mast of  FIG. 1  illustrating a sealed transmission housing, a lifting strap drum, and a retraction cable drum. 
           [0021]      FIG. 8  is a perspective view of a second side of the winch assembly of  FIG. 7 , illustrating a carrying handle and an auxiliary input. 
           [0022]      FIG. 9  is a perspective view of a transmission of the winch assembly of  FIG. 7 . 
           [0023]      FIG. 10  is a perspective view of the transmission of the winch assembly, partially broken away, illustrating a ratchet assembly and a retraction cable belt drive. 
           [0024]      FIG. 11  is a perspective view of an intermediate drive shaft of the transmission of  FIG. 7  illustrating a one-way clutch and a ratcheting hub. 
           [0025]      FIG. 12  is an illustrative view of various embodiments of a non-flanged strap roller capable of being used in a strap driven mast, according to the present invention. 
           [0026]      FIG. 13  is an illustrative view of various embodiments of a flanged strap roller capable of being used in a strap driven mast, according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    With reference to  FIG. 1 , a first embodiment of a telescopic field mast  100  is shown. Generally, the field mast  100  includes an outer body  102 , a plurality of nested mast sections  104 , a winch assembly  106  and a base  108 . The plurality of mast sections  104  may include any number of sections necessary to achieve the height required for a given application. In the present embodiment, a field mast  100  is shown having a total of six (6) mast sections  104   a - 104   f  (not including the outer body  102 ). The first or inner most mast section  104   a  is typically adapted to carry a particular pay load or associated device (e.g., an antenna, a satellite dish, a vision system, a guidance or positioning system, etc). 
         [0028]    With reference to  FIGS. 1 and 1A , the inner most or first mast section  104   a  is nested within the second mast section  104   b . Similarly, the second mast section  104   b  is nested within the third mast section  104   c  which in turn is nested within the fourth mast section  104   d  and so on. Lastly, the sixth mast section  104   f  is nested within the outer body  102 . It should be noted that the mast sections  104  are telescopic in nature with each having a consecutively smaller transverse dimension than the other. In addition, each of the mast sections are slidably engaged with respect to the other such that when each of the individual mast sections  104  is urged into an extended state, the net length of the mast  100  is many times the length of any one of the mast sections  104 . 
         [0029]    With continued reference to  FIGS. 1 and 1A , the upper and lower portions of each mast section receives an upper and a lower collar assembly  110 ,  112 . A lifting strap  113  or other cable is sequentially threaded through the respective upper and lower collar assemblies of each of the mast sections in a serpentine fashion. The strap can be substantially flat and fabricated from a high strength low stretch braided nylon or other resilient yet pliable material. Generally, the strap follows a convoluted pathway between and among the mast sections. Beginning from the winch assembly, the strap can pass through the outer body  102 , and travel upward to a fixed upper collar assembly  110   g  ( FIG. 2 ). The strap may then travel downward between the outer body  102  and the sixth mast section  104   f  to a lower collar assembly  112   f  ( FIG. 4 ). The strap can then be redirected upward to an upper collar assembly  110   f  ( FIG. 2 ) of the sixth mast section  104   f  and from there return downward to a lower collar assembly  112   e  ( FIG. 4 ) of the fifth mast section  104   e . The strap can continue this “zig-zag” or serpentine pattern until terminating at the upper portion of the inner most mast section  104   a . When tension is applied to the portion of the strap external to the outer body  102 , the mast sections ( 104   a - 104   f ) are then urged toward an erect or extended state. 
         [0030]    With reference to  FIG. 2 , an enlarged detailed view of the upper collar assemblies  110  is shown. In particular, the first mast section receives a first upper collar assembly  110   a , the second mast section receives a second upper collar assembly  110   b , the third mast section receives a third upper collar assembly  110   c  and the fourth mast section receives a fourth upper collar assembly  110   d . Similarly, as described previously, the fifth mast section receives the fifth upper collar assembly  110   e , the sixth mast section receives the sixth upper collar assembly  110   f , and the outer body section  102  ( FIG. 1 ) receives the stationary or fixed upper collar assembly  110   g . As shown in  FIG. 2 , the individual upper collar assemblies  110   a - 110   g  are illustrated in their most compact state, with one being in a stacked configuration with respect to the other. It should be noted that with exception to the first upper collar  110   a , the remaining upper collar assemblies  110   b - 110   g  are substantially identical in structure varying primarily only in size or diameter. 
         [0031]    With reference to  FIG. 3 , the second upper collar assembly  110   b  is shown in greater detail. Generally, the collar assembly  110   b  includes a collar body  110   b   1 , a primary roller  110   b   2 , a secondary or guide roller  110   b   3 , a support or guy plate  110   b   4  and one or more device cable guides  110   b   5 . The primary roller  110   b   2  is generally responsible for redirecting the lifting strap and for carrying the majority of the tension load created in the lifting strap. In addition, a roller surface of each primary roller of each collar assembly may include a convex or curved profile to facilitate the alignment of the strap as it passes over the roller and through the collar body. If the strap is not properly aligned or centered as it passes over the rollers of the collar assemblies, the strap may interfere with the collar bodies leading to fraying and or premature failure of the strap. On the other hand, the secondary or guide roller  110   b   3  is subject to lower loads and is generally used to offset the lifting strap in a transverse direction so as to prevent the lifting strap from directly contacting the collar body or rubbing against the mast sections. In addition, the second upper collar assemblies may include a bearing surface (not shown) along an inner wall surface of the assemblies for slideably engaging an outer wall surface of each of the respective inner mast sections. 
         [0032]    With continued reference to  FIG. 3 , a lower portion of the collar body  110   b   1  is configured to be secured to its respective mast section, which in this example is the second mast section  104   b  ( FIG. 1 ). The collar body  110   b   1  can be secured to the mast section via a plurality of threaded fasteners which engage threaded apertures  110   b   6  as well as the underlying mast section. Because of the thin wall and/or light construction of the individual mast sections, the tips of the threaded fasteners which engage the threaded apertures  110   b   6  include smooth or unthreaded shoulders. The shoulders are adapted to engage the walls of the mast section without compressing or contorting the geometry of the mast section. The guide plate  110   b   4  may be provided for receiving a stabilizing guy wire for stabilizing the mast either during or after the mast erection process. The guide plate  110   b   4  may be fabricated from a flat piece of material having bent ears or tabs with various apertures for receiving the stabilizing guy wires. 
         [0033]    Now with reference to  FIG. 4 , an enlarged view of the base rings or lower collar assemblies  112  is shown. In particular, the first mast section receives a lower collar assembly  112   a , the second mast section receives a lower collar assembly  112   b , the third mast section receives a third lower collar assembly  112   c  and the fourth mast section receives a fourth lower collar assembly  112   d . Similarly, as described previously, the fifth mast section receives the fifth lower collar assembly  112   e , the sixth mast section receives the sixth lower collar assembly  112   f  and the outer body receives a first or convex shaped base portion  112   g . As with the upper collar assemblies described above, each of the mast sections receive a lower collar assembly  112  and the majority of the lower collars are substantially identical in structure varying only in overall size or geometry (with exception of the first lower collar  112   a ). It should be noted the convex shaped base portion  112   g  permits the mast to be received into a base  108  having a recessed or concave portion. The concave/convex design of the base portion of the mast allows the mast to be erected in a desired orientation (e.g. a plumb or vertical orientation) even if the ground or support surface is not orthogonal with respect to the mast. 
         [0034]    With reference to  FIG. 5 , the second lower collar assembly  112   b  is shown in greater detail. It should be noted that the second lower collar assembly  112   b  is representative of the remaining lower collar assemblies  112   c - 112   f . The collar assembly  112   b  includes a collar body  112   b   1 , a primary roller  112   b   2 , and a secondary or guide roller  112   b   3 . It should also be noted that the rollers of the lower collar assemblies are similar in structure and serve a similar purpose as the rollers of the upper collar assemblies. In addition, the second lower collar assembly  112   b  includes a bearing surface  112   b   4  for slideably engaging an inner wall surface of the overlying mast section. The second lower collar assembly  112   b  further includes one or more locks  112   b   5  and a plurality of locking posts  112   b   6  having a supporting surface  112   b   7 . Furthermore, the second mast section  104   b  ( FIG. 1 ) is received onto a flange surface  112   b   8  of the collar body  112   b   1  and is attached in a similar manner as discussed with respect to the upper collar assemblies  110  ( FIG. 2 ). 
         [0035]    In general, the locks of the lower collar assemblies engage the locking posts of the lower collar assembly just ahead of or above the instant lower collar assembly. By way of example and with respect to the second lower collar assembly  112   b  shown in  FIG. 5 , the lock  112   b   5  operates to secure the locking post of the first collar assembly  112   a  ( FIG. 4 ). Similarly, the lock of the third lower collar  112   c  ( FIG. 4 ) engages the locking post  112   b   6  of the second lower collar assembly  112   b  and so on. An advantage of this design is that it prevents the mast sections from being erected simultaneously or in an out of sequence fashion. In the field, it is generally preferred to raise the largest diameter sections first since they offer greater stiffness and stability while supporting the smaller diameter mast sections ahead of it. 
         [0036]    For example, the sixth mast section  104   f  ( FIG. 1 ) is the largest diameter mast section of the instant embodiment. Since the sixth mast section does not lock to the outer body, the sixth mast section will extend out of the outer body carrying with it all of the remaining mast sections as tension is applied to the lifting strap. As the sixth mast section reaches its fully extended state, a lock trip  103  ( FIG. 1 ) near the upper portion of the outer body  102  ( FIG. 1 ) causes the lock of the sixth lower collar assembly  112   f  ( FIG. 4 ) to be disengaged thus releasing the locking posts of the fifth lower collar assembly  112   e . With the locking posts of the fifth lower collar assembly  112   e  ( FIG. 4 ) released, the fifth mast section can then be raised or extended into place. At this point the winching process may be temporarily halted so that the support or guide plate of the sixth collar assembly  110   f  ( FIG. 2 ) can be secured. This process of unlocking and stabilizing can then be repeated with respect to the fifth, fourth, third, second and first mast sections or until an adequate amount of extension or elevation is obtained. 
         [0037]    Now with reference to  FIG. 6 , an enlarged detail of the lock of the second collar assembly  112   b  is shown. It should be noted that the lock  122   b   5  is representative of the remaining locks on the remaining lower collar assemblies  112   c - 122   f  ( FIG. 4 ). The lock assembly  112   b   5  includes a lock housing  112   b   9  for pivotally securing a rocker  112   b   10 , as well as a locking member  112   b   11 . The rocker  112   b   10  and the locking member  112   b   11  operate in an over-center type configuration such that the locking member  112   b   11  is securely in a latched or unlatched state depending on the relatively sensitive movement of the rocker  112   b   10 . Furthermore, a set of threaded fasteners  112   b   12  may be used to secure the lock housing  112   b   9  to the respective lower collar assembly  112  or, as in this case, to the second lower collar assembly  112   b  ( FIG. 5 ). In addition, multiple lock assemblies may be disposed about the circumference of the lower collar bodies to better balance the loads on the locks and the individual mast sections. 
         [0038]    With reference to  FIG. 7 , the winch assembly  106  is shown in greater detail. The winch assembly  106  generally includes a transmission or winch assembly housing  113 , and a set of winch or crank handles  114  for driving a transmission  116  ( FIG. 9 ). The winch assembly further includes a first or main winch drum or spool  118 , a tensioning assembly  120 , and a second or positive retraction drum or spool  122 . A first attachment point or mounting sleeve  124  and a second attachment point  126  are also provided for quickly and selectively mounting the winch assembly  106  to the outer body  102  ( FIG. 1 ). In addition, a carrying handle  128  can be integrated as part of the winch assembly  106  for ease of handling when the winch assembly  106  is detached from the outer body. 
         [0039]    As shown in  FIG. 7 , the transmission  116  of the winch assembly  106  includes a first or high speed input  130  as well as a second or low speed input  132 . The crank handles  114  may be relocated from the first input  130  to the second input  132  as needed, depending on the overall weight of the mast to be lifted and/or the associated payload or device to be carried by the mast. As the crank handles  114  are rotated, the transmission  116  provides a geared mechanical advantage to the main drum or lifting spool  118  such that the lifting strap is drawn towards the drum or spool  118  against the tensioning assembly  120  and wrapped or rolled onto the drum or spool  118 . Simultaneously, when the drum or spool  118  is taking-up or gathering the lifting strap, the retraction drum or spool  122  is rotating in a direction that releases or feeds out a retraction cord or cable. The retraction cord or cable includes a first and second end. The first end of the retraction cord can be attached to the inner most mast section and the second end can engage the retraction drum  122 . Thus, as the lifting strap is drawn towards or into the main drum  118 , the mast sections begin to move in an upward or outward direction, the retraction drum  122  unwinds, and the retraction cable is drawn into the outer body. 
         [0040]    Now with reference to  FIG. 8 , a second side of the winch assembly  106  is shown. The gear or transmission housing  113  can be comprised of two halves, a first half  113   a  and a second half  113   b . Furthermore, the gearing assembly or transmission  116  can be fully enclosed, and thus sealed from dirt, debris, liquids, or other foreign matter, etc. that could damage the gear train, bearings, and/or other elements of the transmission. It should be noted that, in addition to the first and second inputs of the transmission described previously, the transmission  116  may include a third input  134  for use with an external or auxiliary torque source. For example, a chuck portion of a cordless drill may be adapted to engage and drive the input  134 . In addition, the input  134  may include a hexagonal or other irregular surface feature so as to ensure positive contact or drive between the auxiliary torque source and the input  134 . 
         [0041]    Now with reference to  FIG. 9-11 , the transmission  116  of the winch assembly  106  is shown in greater detail. Generally, the transmission  116  includes a first driving gear  136  associated with the first speed or input  130  ( FIG. 7 ), a second driving gear  138  associated with the second speed or input  132  ( FIG. 7 ) and a third driving gear  140  associated with the third speed or auxiliary torque source  134  ( FIG. 8 ). The first, second, and third driving gear  136 ,  138 ,  140  can rotate a first driven gear  142  that in turn rotates an intermediate drive shaft  144 . 
         [0042]    With particular reference to  FIG. 11 , when the first driven gear  142  rotates in the lifting direction, the intermediate drive shaft  144  rotates, which in turn rotates a fourth driving gear  146 . The fourth driving gear  146  then rotates the primary or main output gear  148  and the main drum or spool  118  ( FIG. 10 ). In addition, the intermediate drive shaft  144  includes a ratcheting hub  150  that prevents the fourth driving gear  146 , the main output gear  148 , and the main drum or spool from unwinding during the lifting or winching process. It should be noted that a plurality of bearings  156  serve to support the shaft  144  with the transmission and housing of the winch assembly. 
         [0043]    With reference to  FIGS. 10 and 11 , when the first driven gear  142  rotates in the retraction direction, a one way clutch  152  selectively disengages the first driven gear  142  from the ratcheting hub  150  while continuing to allow the first driven gear  142  to rotate a driving retraction pulley  154 . The driving pulley  154  then drives a retraction drive belt  158 . Whether the drive belt  158  can rotate a driven retraction pulley  160  and corresponding retraction drum  122  depends on the coupling/decoupling position of the tensioning assembly  120 . The tensioning assembly  120  includes a reaction arm  162  having an idler roller  164  for tensioning and de-tensioning the belt drive  158  according to the amount of tension in the strap or lifting belt. 
         [0044]    When the lifting belt has a significant amount of stress applied to it, the tensioning assembly  120  reacts against the force of an embedded spring  166  such that the driven pulley  160  is decoupled from the input side of the transmission  116 . As such, the retraction cord is permitted to unwind at a rate that is commensurate with the overall distance traveled by the mast sections. When no tension is present on the lifting strap, the spring  166  reacts against the reaction arm  162  to provide tension against the drive belt  158  so as to couple or provide relative positive traction between the driving pulley  154  and the driven pulley  160 . Thus, a user can retract the mast sections by driving the crank handles in reverse, de-tensioning the lifting strap, coupling the retraction belt to the retraction drum, and withdrawing the retraction cord or cable from the outer body of the mast. 
         [0045]    With reference to  FIGS. 12 and 13 , a variety of roller geometries are illustrated for use with the strap driven mast of the present invention. In particular,  FIG. 12  illustrates a variety of flangeless roller geometries. A first embodiment of a flangeless roller  200 A includes a generally cylindrical surface geometry  210   a . A second embodiment of a flangeless roller  200 B includes a surface geometry similar to that of the first roller  200 A, except that the ends include a chamfer  210   b . A third and fourth embodiment of a flangeless roller  200 C,  200 D includes a generally convex surface geometry  210   c ,  210   d . By contrast, a fifth embodiment of a flangeless roller  200 E includes a generally concave surface geometry  210   e.    
         [0046]    With reference to  FIG. 13 , a variety of flanged roller geometries are illustrated. A first embodiment of a flanged roller  300 A is shown having a generally cylindrical surface  310   a  as well as an undercut  312   a  near the ends of the roller and adjacent to a flanged portion  314   a . A second embodiment of a flanged roller  300 B is shown that is similar to the first embodiment of the flanged roller  300 A in that it includes a generally cylindrical surface  310   b  as well as a pair of flanged end portions  314   b , however, no undercut is provided. Lastly, a third and a fourth embodiment of a flanged roller  300 C,  300 D is illustrated having a generally concave surface geometry  310   c ,  310   d  and a transition region or fillet  312   c ,  312   d  between the strap engaging surface and the flange. 
         [0047]    The various embodiments of roller geometries  200 A- 200 E,  300 A- 300 D may be used in various combinations to optimize the self-centering characteristics of the rollers while minimizing any interference between the lifting strap or cable and the structures of the mast assembly surrounding the strap or cable. Furthermore, depending on the elastic properties of the strap or cable and the overall stress or loads expected to be carried by the strap certain ones of the above disclosed geometries may be more suitable than the others for a given application. In addition, the curvilinear profile or geometry of the roller surface can be modified so as to optimally and evenly distribute the stress through a cross section of the strap, thus, maximizing the longevity of the lifting strap. 
         [0048]    Generally, the convex roller geometry provides for optimum tracking and compensates for production variations (such as twist or other misalignment in the tubes or mast sections). On the other hand, the concave roller geometry can be useful in guiding the strap into and out of the tubes or mast sections while allowing the concave rollers to be mounted in close proximity to the tubes. This can occur since the “concavity” of the concave rollers can be matched to the outer diameter of the tubes. Finally, the straight roller geometry generally provides the most uniform loading across the strap and serves as a good intermediate geometry next to a concave or convex roller. The lips, undercuts, and chamfers on the edges of the rollers further aid in tracking the strap on the roller by interrupting the surface onto which the strap would otherwise begin to track off center. In other words, the strap is most likely to travel off center on a uniform (straight), continuous surface. As such, these features provide an interruption to prevent the strap from moving too far off center or to one side of the respective roller. 
         [0049]    Lastly, the strap driven mast assembly of present invention can be operated or used in any number of ways. In general, the associated device to be elevated can be attached (if not already secured to the mast assembly) to the inner most or first mast section  104   a . The base  108  ( FIG. 1 ) of the mast system is then secured to the ground or other associated support surface where the mast is to be erected. Once the base is installed, the convex end portion  112   g  of outer body  102  is then located in the recess portion of the base  108 . The outer body  102  is then raised and temporarily held in the desired orientation. Typically a vertical or plumb orientation is chosen since side loading of the mast sections is minimized. At this point, the outer body is stabilized by attaching three or more guy wires to the support or guide plate of the fixed upper collar assembly  110   g  ( FIG. 2 ). Next, the winch assembly  106  can be attached to the outer body via the first and second attachment points  124 ,  126  ( FIG. 7 ). 
         [0050]    Once the winch assembly is attached, the ends of the lifting strap and retraction cable are attached to the lifting drum and to the retraction drum, respectively. The crank handles may then be attached to the first or second speed inputs on the winch assembly. Alternately, an external or auxiliary torque device (e.g. an electric motor) may be attached to the third or auxiliary input. Rotating the first, second, or third inputs in the lifting direction, causes the main or lifting drum to wind or withdraw the lifting strap. As tension is created, the sixth mast section  104   f  will rise carrying with it the remaining mast sections  104   a - 104   e . In the meantime, the retraction drum remains decoupled so long as there is some degree of tension in the lifting strap. As such, the retraction cable is released or drawn into the outer body as the mast sections are raised. Once the sixth mast section is raised to its maximum height or fully extended position, trip  103  causes the lock assembly of the sixth lower collar assembly  112   f  ( FIG. 4 ) to disengage and release the fifth mast section  112   e . The process of raising, releasing, and stabilizing mast sections continues in a similar manner for the remaining mast sections or until the desired height is reached. 
         [0051]    When the mast is to be lowered, the crank handles are simply operated in an opposite or retraction direction. As described previously, this causes a lesser amount of tension on the lifting strap and a coupling of the retraction drum  122 . If the mast sections begin to bind slightly, the retraction drum begins to pull on the retraction cable or cord, urging the inner most mast section (as well as the remaining mast sections) into a collapsed state. As the mast sections are lowered, the stabilizing guy wires, if any, are removed. Once all of the mast sections have reached their fully retracted or collapsed state, the associated payload or device, the winch assembly, and the initial stabilizing guy wires can all be removed. The mast is then lowered to the ground, the base detached from the associated support surface, and the mast is prepped for transportation. 
         [0052]    The exemplary embodiment has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Technology Classification (CPC): 4