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CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority from U.S. Provisional Patent Application Ser. No. 61/989,568, filed May 7, 2014, the contents of which are incorporated in this disclosure by reference in their entirety. 
     
    
     BACKGROUND 
       [0002]    This invention relates to telescoping masts for radio antennas, flood lights and the like. In another respect the invention pertains to portable telescoping masts that are specially adapted for quick and reliable operation under extreme environmental conditions. In yet another respect the invention relates to such portable masts, which can be extended, used, and retracted with improved convenience and safety. 
         [0003]    Telescoping masts have been widely employed for radio antennas, lights and a variety of other fixtures. Such masts have been operated by a variety of mechanism, including winches, hydraulic systems and the like. More recently, telescoping masts have been devised which use an axial screw mechanism for raising and lowering the mast sections. For example, an axial screw operated mast is disclosed in U.S. Pat. No. 4,062,156. Another example is disclosed in U.S. Pat. No. 8,413,390, assigned to the same assignee as the present application. 
         [0004]    When telescoping masts are used under extreme environmental conditions and particularly in military or other portable operations, it is highly desirable that the masts be ruggedly constructed and be extremely fast, reliable, and safe to operate. In such portable masts, especially those extended and retracted using axial screw mechanisms such as masts constructed in accordance with U.S. Pat. No. 8,413,390, it is particularly important that the sections are capable of being reliably extended and retracted without twisting or binding so that the mast can be extended to the full desired height and the possibility of accidents and injuries due to one or more of the mast sections failing to extend or retract properly is minimized. 
         [0005]    Therefore, there is a need for a new extruded mast system and method for manufacturing such a system that overcomes the disadvantages of the prior art. 
       SUMMARY 
       [0006]    According to one illustrative embodiment of the invention, an extruded mast section for a telescoping tower includes a plurality of spaced apart axially aligned internal screw bosses running the length of the mast section. 
     
    
     
       DRAWINGS 
         [0007]    These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
           [0008]      FIG. 1  is an isometric diagram showing a mast system including a plurality of nested extruded mast sections according to the present invention with a section with a top mast section extended. 
           [0009]      FIG. 2  is an isometric diagram showing a mast system including a plurality of nested extruded mast sections according to the present invention with all sections retracted. 
           [0010]      FIG. 3  is an end view of a mast tube section showing a typical arrangement and profile of the internal screw bosses of an extruded mast section according to an exemplary embodiment of the present invention. 
           [0011]      FIG. 4  is an exploded view of an upper portion of a mast tube section and support flange or collar in accordance with an exemplary embodiment of the present invention. 
           [0012]      FIG. 5  is a cross-sectional view of four nested mast tubes in an exemplary embodiment of the present invention showing the internal screw bosses acting as keys and support collars providing keyways along which the screw bosses travel. 
           [0013]      FIG. 6  is a perspective view of four nested mast tubes in an exemplary embodiment of the present invention showing the internal screw bosses acting as keys and support collars providing keyways along which the screw bosses travel. 
           [0014]      FIG. 7  is a diagram showing an illustrative motor control apparatus in accordance with the present invention. 
           [0015]      FIG. 8  is a flow diagram showing an illustrative method for employing a protected mode of operation. 
           [0016]      FIG. 9  is a cross-sectional view of a gearbox in its locked condition. 
           [0017]      FIG. 10  is a cross-sectional view of a gearbox in its unlocked condition. 
           [0018]      FIG. 11  is an isometric view of the gearbox with the lock housing removed for clarity. 
       
    
    
     DESCRIPTION 
       [0019]    Referring first to  FIG. 1 , in accordance with one embodiment of the present invention, an internally keyed extruded mast system  10  is depicted and includes a mast bottom section  12  mounted on base  14 . The bottom section  12  of internally keyed extruded mast system  10  is shown retracted.  FIG. 2  shows internally keyed extruded mast system  10  in a partially extended position where top section  16  extends from mast bottom section  12 . 
         [0020]    Motor drive unit  18 , for extending and retracting the mast sections, is mounted on base  12 . One exemplary mechanism for extending and retracting the mast sections is disclosed in U.S. Pat. No. 8,413,390, which is incorporated by reference herein in its entirety. The nested mast sections may be raised using a driving screw arrangement as disclosed, for example, in U.S. Pat. No. 8,413,390. 
         [0021]    Referring now to  FIG. 3 , a top view of an illustrative mast section  20  is shown. As previously noted, mast section  20  may be circular or polygonal in cross section. Polygonal shapes may increase the strength of the mast section  20  with respect to bending moment force as is known in the art. The illustrative embodiment of  FIG. 3  shows the mast  20  formed as an octadecagon (18-sided polygon). Persons of ordinary skill in the art will recognize that masts formed as polygons having other numbers of sides, or other shapes such as circular or oval shapes may be employed in the present invention. 
         [0022]    According to one embodiment of the invention, the mast sections can be manufactured from aluminum by an extrusion process. In other embodiments of the invention, the mast sections or from composite materials by a suitable method such as, but not limited to, a pultrusion process. 
         [0023]    According to one aspect of the present invention each mast section utilized in the internally keyed extruded mast system  10  of the present invention includes internal screw bosses  22  that are preferably evenly spaced around the circumference of the mast section  20  that run the full length of the tube section. For purposes of illustration, an illustrative mast section  20  is depicted in  FIG. 3  and includes three internal screw bosses  22 . Each screw boss is integral to the internal wall of each tube section and defines a pilot hole  24  that also runs the length of the tube. The arrangement shown in  FIG. 3  allows the mast sections to be formed by an extrusion process. 
         [0024]    The design benefit of the internal screw bosses  22  is at least three-fold. For a mast of this nature, it may be desirable or necessary to affix a support collar (one of which is shown at reference numeral  26  in  FIG. 4 ) at both ends of each telescoping mast section. This support collar may be a wear ring, a flange, or some other structure. The screw bosses  22  can be internally threaded to allow mounting of any necessary collar, flange, or other structure at either end of the mast section  20 . 
         [0025]    Utilization of the screw bosses in this way reduces the amount of time required to manufacture each tube section. Rather than having to make radial penetrations in the tube and then utilizing some form of captive fastener or threaded insert, internal threads are easily created in pilot holes  24  using a standard tap. Internal threads are shown at dashed lines around pilot holes  24  in  FIG. 3 . Preferably, a minimum of three screw bosses  22  are used in each mast section as shown in  FIG. 3 . 
         [0026]      FIG. 4  is an exploded view showing an illustrative embodiment including six screw bosses  22  in mast section  20 . Screws  28  are used to fasten the support collar  26  to both the top and bottom ends of the mast section  20 . The arrangement of the screw bosses  22  around the internal wall of the tube provide a ribbed structure that functions to improve the strength of the mast section  20 , especially in resisting stresses induced on the mast section by an applied bending moment. The placement of the screw bosses  22  ensures that at least two or more screw bosses  22  are located at some distance away from the neutral axis when a moment is being applied to the masts section  20 . Placing additional material further away from the neutral axis, in the form of the screw bosses  22 , improves the area moment of inertia of the mast section  20  allowing it to better mitigate stress that is applied to it during an applied bending moment. 
         [0027]    An additional benefit to the design of the internal screw bosses  22  is that they act as multiple keys to prevent the relative rotation of one tube to the next. This is shown in  FIG. 5  and  FIG. 6 .  FIG. 5  is a cross sectional view of an illustrative embodiment of the internally keyed extruded mast system  10  of the present invention and shows four nested mast sections  20   a ,  20   b ,  20   c , and  20   d . Bottom support collars  26   a ,  26   b ,  26   c , and  26   d  are shown in  FIG. 5 .  FIG. 6  is a perspective view showing the bottom end of an illustrative embodiment of the internally keyed extruded mast system  10  of the present invention and also shows four nested mast sections  20   a ,  20   b ,  20   c , and  20   d . The support collar for the base section  20   a  has been removed to enable the interaction of the support collars  26   b ,  26   c , and  26   d  and the screw bosses in tower sections  20   b ,  20   c , and  20   d  to be more easily seen. 
         [0028]    The support collars  26   a ,  26   b ,  26   c , and  26   d  are provided with external keyways  30  that engage the internal screw bosses of the mast section immediately nested within the mast section  20 . As the threaded spindle rotates, the mast section that has its nut engaged with the threaded spindle needs to resist this rotating force. The internal screw bosses accomplish this by allowing the section that is being acted on by the spindle to be keyed to the next outermost section by way of the screw bosses  22  in engagement with the keyways  30 . Three such keyways  28  are shown in support collar  26  of  FIG. 4 . 
         [0029]    In  FIG. 5  and  FIG. 6 , each of mast sections  20   b ,  20   c , and  20   d  is shown with its support collar  26   b ,  26   c , and  26   d . The screw bosses  22  of each of mast sections  20   a ,  20   b ,  20   c , and  20   d  is nested in keyways  30  of the one of the support collars attached to the mast section nested immediately inside of it. In the illustrative embodiment of  FIG. 5  and  FIG. 6 , mast sections  20   a  and  20   b  each have six screw bosses  22  nested in six corresponding keyways of support collars  26   a  and  26   b . Mast sections  20   c  and  20   d  each have three screw bosses and the screw bosses of mast section  20   c  are nested within the keyways  30  of support collar  26   d  attached to mast section  20   d.    
         [0030]    As shown in  FIG. 5  and  FIG. 6 , this keying effect continues until it reaches the outermost (or base) mast section  20   a , which is rigidly fastened to some external attachment point. The keying arrangement prevents any of the mast sections  20   b ,  20   c , and  20   d  from rotating relative to any other mast section or to the external attachment point. 
         [0031]    Referring now to  FIG. 7 , a block a diagram shows an illustrative motor control apparatus  40  in accordance with another aspect of the present invention. Motor  42  is controlled by motor controller  44 . Numerous motor controller configurations that can be used in conjunction with the present invention are well known in the art and the particular details of motor controller  44  are not within the scope of the present disclosure. Motor controller  44  receives data from tower height sensor  46  to control the speed and activation of motor  42 . Sensors such as microswitches, hall effect sensors and the like, or rotation counters etc. may be used to perform the function of tower height sensor  46 . Tower height sensor  46  sends a signal to motor controller  44  when the tower is close to fully extended or retracted, or when the tower has reached or is close to a predetermined height. Motor controller  44  responds by either turning off the motor  44  or by first slowing the speed of motor  44  and then turning it off as desired for any particular application. 
         [0032]      FIG. 8  is a flow diagram showing an illustrative method  50  for employing a protected mode of operation. A system for performing the method can easily be implemented using a microcontroller or other controller. Protected modes of operation are useful in numerous situations. For example, protected modes of operation are particularly useful in situations where the tower is deployed in remote locations. 
         [0033]    As may be seen from  FIG. 8 , the method begins at reference numeral  52 . At reference numeral  54  the method enters a loop to interrogate whether a maintenance operation is due to be performed on the tower installation. Such maintenance operations may be prescheduled at designated time intervals that can be pre-programmed into the system. The need for a maintenance operation may also be determined from operating parameters of the system such as motor current or temperature, bearing temperature or other suitable indicators based on the nature of the installation. Such maintenance conditions will readily suggest themselves to persons of ordinary skill in the art. Software implementation of such a loop is a routine programming task. As will be appreciated by persons of ordinary skill in the art, other alarm or flag conditions may be used determine the need for maintenance. 
         [0034]    At reference numeral  56 , the system enters a protected operating mode. When in protected operating mode, the motor controller operates the motor at a lower speed. Other operational restrictions, such as the maxim height to which the tower can be extended, can also be implemented during protected operating mode. Optionally, at reference numeral  58 , the system operator can be notified that the system has placed itself into protected operating mode. This can be done via either hardwired communication channel or wirelessly, as is well know in the art. 
         [0035]    As illustrated at reference numeral  60 , the system will remain in protected operating mode until it is cleared at reference numeral  62 . This is usually accomplished on site by a technician who accesses the system controller and clears the protected mode status after performing whatever maintenance has been deemed necessary. After the system has exited protected operating mode, the method returns to reference numeral  52  where maintenance status is again polled or looped, starting the maintenance protection procedure over again. 
         [0036]    According to one aspect of the present invention, the mast system utilizes a gearbox designed to accept a variety of external power sources in order to extend and retract the mast. These sources include, but are not limited to, human power, power from a hand-held drill, power from a portable motor or other such devices. 
         [0037]    In order to prevent inadvertent movement of the mast it may be necessary to install a brake somewhere between the input shaft and the threaded spindle. In accordance with one embodiment of the present invention, as may be seen in  FIGS. 9 and 10 , a lock is placed directly on the input shaft to create a simple and cost-effective solution for locking the mast at any desired height and preventing unintended extension or retraction. 
         [0038]    Referring now to  FIG. 9 , gearbox  70  includes worm gear  72  mounted on worm gear shaft  74 . The worm gear  72  rotates a helical gear (not shown) in a conventional manner to extend and retract the tower sections. A first end  76  of shaft  74  includes some feature (for example a hex cross section cavity shown at reference numeral  78 ) that allows attachment of a tool for rotating the shaft  74  to raise and lower the mast. A non-rotatable locking plate  80  keyed to the gearbox  70  is designed to closely fit over this feature on the input shaft to prevent it from rotating. The locking plate  80  is biased in a locked position by a spring  82  applying a force to bias the locking plate in a locked position against the end wall  84  of the gearbox. In this position, shaft  74  cannot rotate because the locking plate  80  is engaged over the feature  78  on the end  76  of the shaft  74 . 
         [0039]    As shown in  FIG. 10 , when extension or retraction of the mast is desired, a tool  86 , such as a hex socket is inserted into the housing and engaged on the feature  78  of the end  76  of shaft  74 . The tool is urged inward against the locking plate  80 , compressing spring  82  and moving the locking plate  68  until it is no longer engaged with the feature input shaft and is disposed around a reduced-diameter portion  88  of shaft  74 . At this point, the shaft  74  is able to rotate to cause the mast to either extend or retract. 
         [0040]      FIG. 11  shows the portion of the gearbox  60  housing worm gear  62 , with a portion of the housing removed for clarity, showing an exemplary hex end  78  of shaft  74  as well as locking plate  80  having keys  90  biased by spring  82 . Persons of ordinary skill in the art will appreciate that the other portion  92  of the gearbox houses the helical gear (not shown) that engages worm gear  72 . 
         [0041]    Although the present invention has been discussed in considerable detail with reference to certain preferred embodiments, other embodiments are possible. Therefore, the scope of the appended claims should not be limited to the description of preferred embodiments contained in this disclosure.

Summary:
An extruded mast section for a telescoping tower includes a hollow extrusion having an exterior surface and an interior surface, and a plurality of spaced apart axially aligned internal screw bosses running the length of the mast section. A telescoping tower assembly includes a first extruded mast section having an exterior surface and an interior surface and a plurality of spaced apart axially aligned internal screw bosses running the length of the first mast section along the interior surface. A second extruded mast section disposed within the first mast section has a plurality of spaced apart axially aligned internal screw bosses running the length of the second mast section along the interior surface. Support collars are disposed at the top and bottom ends of the second mast section each having keyways disposed around its outer perimeter and aligned with a different one of the screw bosses of the first extruded mast section.