Abstract:
A rigid support bearing for a rotating shaft has bearings arranged concentrically around the shaft instead of spaced axially and is used in a screw drive telescoping mast assembly. An axial drive screw is centrally located in the mast assembly for extending and retracting the tubular sections. A lower bearing assembly supports the drive screw and uses the concentric bearing arrangement to reduce the nested height of the mast.

Description:
CLAIM OF PRIORITY 
     This application claims priority to provisional Application No. 60/660,805, filed on Mar. 11, 2005, which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to rigid supports for rotating shafts. More particularly, it relates to the application of a rigid support to one end of an axial drive screw in a screw drive telescoping mast. 
     The present invention is applicable to a screw-driven telescoping mast and will be described with particular reference thereto; however, the invention has much broader applications and may be used in various other applications where a rigid bearing assembly for a rotating shaft is required. 
     Two important criteria for a telescoping mast are the “nested” or fully retracted height and the “extended” or fully extended height. The nested height is the height of the mast when fully retracted. For a given extended height many factors can affect the nested height. These may include the number of tubes in the mast, the amount of overlap between tubes when extended and the details of the end features (such as collars and bottom structures) on each tube. For screw driven masts an additional factor affecting the mast nested height is the amount of height required for a support for supporting the axial drive screw. It is preferable to minimize the nested height. A smaller nested height helps facilitate integrating the mast in shelters and vehicles where clearance is a concern. Thus, it is preferable to provide a drive screw support which minimizes the nested height of the mast. 
     Existing rigid supports for rotating shafts use two bearings which are axially spaced along the length of the shaft. This spacing results in a height of the support typically three (3) times the diameter of the shaft or more. Thus, in screw drive mast applications where the screw is has a one (1) inch diameter, the spacing of the axial support would be about three (3) inches. When the thickness of the bearings and the necessary support structures are included, an overall height for the rigid bearing assembly of five (5) or more inches can result. This height proves excessive for many screw drive telescoping mast applications. Thus, this excessive height is a deficiency that the present invention addresses and overcomes. 
     Some existing screw driven telescoping masts attempt to minimize the vertical space required of the axial screw support bearings by using a single bearing instead of the preferred rigid bearing assembly. This arrangement provides inadequate support to the screw, allowing the screw to wobble during operation, potentially causing damage to the mast. This single bearing scheme is also only workable at all at a slow speed, which is inconvenient for any user and potentially critical for the emergency or military user. Thus, there is a need for a mast telescopic system which overcomes the above-mentioned defects and others while providing more advantageous overall results. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a rigid bearing support for a rotating shaft. In a particular application, the invention relates to a rigid support for a centrally located, axial drive screw for a telescoping mast assembly. The invention can further be used in any situation requiring a rigid bearing support for a rotating shaft. 
     The primary aspect of the present invention is to provide a rigid bearing support for a rotating shaft via a pair of bearings that are arranged concentric to one another. 
     In accordance with another aspect of the invention, a rigid bearing support has a bearing assembly base; a first bearing assembly positioned on the base; and, a second bearing assembly positioned radially outwardly of the first bearing assembly on the bearing assembly base wherein the first and second bearing assemblies are concentric to each other. 
     In accordance with another aspect of the invention, a telescoping mast assembly has at least two elongate tubular sections, wherein a second elongate tubular section is telescopically received by a first elongate tubular section. An axial drive screw is centrally located in the mast assembly for extending and retracting the second elongate tubular section. A lower support assembly supports a lower portion of the drive screw. The lower support assembly has two bearing assemblies arranged concentrically about the axial drive screw. 
     In accordance with yet another aspect of the invention, a method of supporting a drive screw for a mast assembly includes: providing a first bearing assembly which receives a lower end of a drive screw through a central portion thereof; providing a hug nut adjacent the first bearing assembly and surrounding the lower portion of the drive screw; and providing a second bearing assembly positioned radially outward of the first bearing assembly and concentric with the first bearing assembly. 
     The screw drive mast of the present invention can be used for communications and surveillance applications that require rapid, automatic development and maximum reliability with high antenna pointing accuracy. The mast has self-locking sections and positive mechanical drive for extension and retraction. 
     A primary aspect of the present invention is to provide a rigid bearing support for a telescoping assembly shaft that reduces the overall height of the support. 
     A still further aspect of the invention is to provide a rigid bearing support which reduces the axial space required for the rigid support bearing assembly for the axial drive screw in a screw drive mast. 
     A still further aspect of the invention is to provide a rigid bearing support which results in a significant reduction in the nested height of the mast. 
     Another aspect of the present invention is to provide a support for the drive screw of the mast to minimize wobble of the screw. 
     Yet another aspect of the present invention is provide a telescoping mast assembly which obviates the problems and limitations of the prior art devices. 
     Yet another aspect of the present invention is to provide low height rigid bearing support for a drive screw used in any application, not necessarily limited to an axial location or to a telescoping mast assembly. 
     A final aspect of the present invention is to provide a lower height rigid bearing support for a rotating shaft used in any application, in particular where there are axial space constraints. 
     These and other aspects and advantages will become apparent from the following description taken together with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may take form in certain components, structures, and steps, the preferred embodiments of which will be illustrated in the accompanying drawings. 
         FIG. 1  is a side sectional view illustrating an existing rigid bearing support with bearings axially separated from each other. 
         FIG. 2  is a side elevational view of a telescoping mast assembly in a fully retracted position in accordance with a preferred embodiment of the present invention; 
         FIG. 3  is a side-elevational view of the telescoping mast of  FIG. 1  in a fully extended position; 
         FIG. 4  is an enlarged sectional view taken along line  4 - 4  of  FIG. 3  of the telescoping mast assembly illustrating a mast support bearing assembly with a rigid bearing support having concentric bearings in accordance with the preferred embodiment of the present invention; 
         FIG. 5  is a further enlarged sectional view illustrating a rigid bearing support in accordance with the present invention; and, 
         FIG. 6  is a top plan sectional view taken along line  6 - 6  of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 1 , an existing rigid bearing assembly  10  surrounding a rotating shaft  12  is illustrated. The rotating shaft is shown to be the axial drive screw of a screw drive telescoping mast assembly, but is not limited to same. The bearing assembly allows the shaft to freely rotate. Bearings  14  and  16  are positioned axially along the length of the shaft to provide lateral support to the rotating shaft. The axial spacing of the bearings provides a resistant moment to prevent the shaft from tipping. Vertical support in a downward direction is provided by a lower shoulder  18  of the shaft transmitting force through a washer  20 , an inner race  22  of upper bearing  16 , a spacer  24 , an inner race  26  of the lower bearing  14 , ball bearings  28  of the lower bearing, and an outer race  30  of lower bearing  14  onto the upper surface  33  of base  32 . Vertical support in an upward direction is provided by the shaft lifting up on a locking nut or “hug nut”  34  threaded onto the bottom of the shaft. Force is transmitted through the hug nut to the inner race of the lower bearing, the ball bearing of the lower bearing, the outer race of the lower bearing onto a shoulder  36  of a bearing assembly housing  38 . The bearing assembly housing is attached to base  32  via retaining screws  40 . 
     A rigid bearing support should adequately perform the following functions: allow the shaft to rotate, provide lateral support for the shaft, provide resistant moment to shaft tipping, and provide axial support in upward and downward directions. Most existing rigid bearing support assemblies perform these functions, but a deficiency of these supports is that they extend along the axis of the rotating shaft which is a disadvantage in some applications such as a screw drive telescoping mast. The present invention performs all of the necessary functions of a rigid bearing support while overcoming the above-mentioned deficiency. 
     Referring now to the drawings wherein the showings are for the purpose of illustrating preferred embodiments of the invention only, and not for the purpose of limiting same, referring to  FIG. 5 , in accordance with the preferred embodiment of the present invention, a drive shaft portion  119  with a threaded end  121  is rigidly and permanently attached to a screw base  120 . The screw base extends from the shaft to an outer bearing  122 . The inside diameter of the outer bearing is significantly larger than the shaft diameter, in contradistinction to existing bearing assemblies. The screw base has a concave void  124  which allows space for an inner bearing  126  and a middle bearing ring  128 . The inner bearing slides freely onto the end of the shaft  119  and is retained at the lower end by a prevailing torque locking nut or “hug” nut  130  threaded onto the end of the shaft and at the upper end and sides by the middle bearing ring  128 . The middle bearing ring is attached to a bearing assembly base  132  by retaining screws  134  or any suitable fasteners. The shaft is able to rotate since it is connected to the base  132  by retaining screws  134  or any suitable fasteners. The shaft is able to rotate since it is connected to the base  132  exclusively through the ball bearings  122 ,  126 . The shaft is supported laterally via the bearings  122 ,  126 . The shaft is supported laterally via the bearings  122 ,  126  pushing against shoulders  140 ,  142  on the base  132  and the middle bearing ring  128 , respectively. 
     The bearing assembly provides a resistant moment to shaft tipping as follows. When the shaft attempts to tip, it pushes down via the screw base  120  onto one side of outer bearing  122 . This force is transmitted via an inner race  144  to ball bearings  146  and finally onto a floor  148  of the bearing assembly base  132 . Simultaneously the shaft lifts up at its center portion via the hug nut  130  threaded on the end of the shaft  119  pressing on the inner ring  150  of the inner bearing  126  then through ball bearings  152 , outer ring  154  to middle ring  128  and finally the bearing assembly base with attachment screws  134 . The combination of pressing down on one side of a large outer bearing with the lifting up at the center of the shaft that generates the resistant moment to shaft tilting. 
     The bearing assembly also provides axial support in opposite upward and downward directions. In the downward direction, force is transmitted through the screw base  120  to the outer race  156  of the outer bearing  122  through the ball bearings  146  through the inner race  144  and onto the floor  148  of the bearing assembly base  132 . In the upward direction, force is transmitted through the hug nut  130  threaded onto the end of the shaft to the inner race  150  of the inner bearing  126  through the ball bearings  152  through the outer race  154  and onto the roof  158  of the middle ring  128 . The middle ring is attached to the bearing assembly base  132  with attachment screws  134 . 
     Thus, the invention fulfills all functions of a rigid bearing assembly, but since its bearings are concentric rather than axially separated a noticeable height savings is achieved. In some embodiments such as a screw drive telescoping mast, this height savings is a distinct advantage. 
     Referring now to  FIG. 2 , a mast assembly is shown which uses the rigid bearing support of  FIG. 5 . An antenna A is used with a mast assembly B and an associated gear drive unit C. A telescoping mast assembly  50  is typically used in conjunction with a vehicle or ground surface D. The telescoping mast assembly  50  typically includes a plurality of interconnected mast sections  52 ,  54 ,  56 ,  58 ,  60 ,  62 ,  64 ,  66  and  68  as shown in  FIG. 2 . Although nine interconnected mast sections are illustrated, it is within the scope of the present invention to incorporate any number as desired. Typically, the mast extends vertically in a range from about 20 feet to about 150 feet. However, it is within the terms of the invention to lengthen or shorten the range as required. As illustrated in  FIGS. 2 and 3 , the outermost mast section is stationary and is immovably affixed to a movable support structure such as a vehicle or ground surface D. The innermost mast section  68  is attached to any desired operating equipment  70 , such as an antenna, which is supported by the mast assembly  50 . 
     As further illustrated in  FIG. 3 , each of the interconnected mast sections are cylindrical tubes having outwardly extending cylindrical collars  73 ,  75 ,  77 ,  79 ,  81 ,  83 ,  85 ,  87  which have a slighter larger diameter than the external diameter of the tubes  52 - 66 , respectively, in a longitudinal direction. The cylindrical collars can provide a bearing surface between the cylindrical tubes. The collars are substantially parallel to each other. 
     Typically, the individual mast sections are manufactured from high strength, heat treated anodized aluminum alloy tubes and collars. It is also within the terms of the present invention to form the tubes of other materials such as carbon fiber-epoxy composite structures which are advantageous because of their light weight relative to their high strength. Moreover, these materials can easily be shaped into cross-sections, other than circular, as desired. 
     The mast is shown fully extended in  FIG. 3 . As is well known in the art, tube sections latch or lock onto adjacent tube sections until the mast is fully extended. Tube section  52  remains stationary. During retraction of the mast, latch plates are uncoupled from latch bodies and the tubes are unlocked from each other and lowered. As can be seen from  FIG. 3 , there is some overlap between adjacent tubes when they are fully extended. That is, the latches and latch receiving members are typically positioned about half way along the longitudinal axis of each tube section so that a portion of each tube extends into a portion of an adjacent tube and has some overlap with the adjacent tube. 
     Referring now to  FIG. 4 , inner tube section  54   a  of tube  54  is secured to outermost tube section  52   a  of tube  52  and partially extends into tube  52 . A threaded nut  90  is in threaded engagement with threaded portion  91  of drive screw  92 . From a top view of the mast, the screw is rotated clockwise (see arrow  93 ) to raise the nut and the corresponding tube section. The nut is housed within a central raised portion  94  of plate  95 . The plate  95  is attached to one end of tube  54 . The nut  90  is captured via a retaining ring  96  and a washer  97 . Further, a grooved pin  98  which engages a portion of the nut also engages a set screw  99  to maintain its position. Springs  101  can be positioned above and below the pin to provide further biasing of the pin in an engaging position. 
     One example of a driving mechanism for the mast assembly is shown in  FIG. 6 . A sprocket and chain drive is illustrated, but a gear drive or belt assembly could also be used without departing from the scope of the invention. A motor  100  is provided adjacent to the mast assembly. The motor assembly includes a sprocket  102  which is connected via chain  104  to sprocket  106  mounted rigidly and concentrically to the drive screw  92 . Sprocket  106  has a plurality of sprocket teeth  108  which engage the chain  104 . 
     The drive system further includes a manual drive sprocket  112  for manually driving the mast sections if the motor assembly does not properly function. A manual crank arm (not shown) is vertically placed in a socket  114  of the manual drive. The crank arm is then rotated to raise or lower the mast. 
     This chain drive system includes a plurality of teeth  113  for manually driving the mast sections if the motor assembly does not properly function. 
     Other drive systems can be used, including, but not limited to, a belt drive in which a belt replaces the chain, a spur gear drive in which a driving spur gear engages a driven gear rigidly attached to drive screw, likewise a worm gear drive, and perhaps a bevel gear drive. 
     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.