Abstract:
There is provided a rotary positioning apparatus including a driven element and a driving element, each of which has a curved outer surface. A cable connects the driven element to the driving element. The cable is wound a plurality of times about a portion of the outer surfaces of the driving element and the driven element for applying rotational forces from the driving element to the driven element. The outer surface of at least one of the driving element or the driven element having a plurality of V-shaped grooves therein. Portions of the cable are wedged in portions of the grooves thereby substantially reducing slippage of the cable.

Description:
RELATIONSHIP TO PRIOR APPLICATION 
       [0001]    This is a U.S. non-provisional application relating to and claiming the benefit of U.S. Provisional Patent Application Ser. No. 61/192,405, filed Sep. 17, 2008. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates to a positioning apparatus and in particular to a positioning apparatus in which a driving element is rotatably connected to a driven element by a cable for positioning the driven element. For various apparatus such as parabolic reflectors for satellite antennas there is a need to position such apparatus very precisely. Mechanical positioning systems have been provided which utilize a driving element which is connected to an electric motor through a gearing system or through a mechanical linkage such as a belt. A driven element which is directly connected to the apparatus which needs to be precisely positioned, such as a satellite antenna, is also provided. Normally, the driving element is connected to the driven element by cables. Such cable systems are described in U.S. Pat. Nos. 5,105,672 and 4,351,197, both issued to Carson. While the apparatii disclosed in the Carson patents provide a certain degree of precise positioning, there is a need for more stiffness and capacity for many applications, in particular for satellite antenna applications. 
       BRIEF SUMMARY OF THE INVENTION 
       [0003]    In accordance with one form of this invention, there is provided a positioning apparatus having a driven element and a driving element. The driven element includes a drum having an outer surface. The drum is adapted to rotate. The driving element also has an outer surface. At least one cable connects the driving element to the drum. The outer surface of at least one of the driving element or the driven element has a plurality of grooves therein. The grooves have two opposing side walls, a bottom, and an open top. The side walls slope inwardly from the open top to the bottom. A portion of the cable is received in the grooves and is wedged between the side walls. 
         [0004]    In accordance with another form of this invention, there is provided a rotary positioning apparatus including a driven element and a driving element each of which having a curved outer surface. At least one cable connects the driven element to the driving element. A portion of the cable is wound a plurality of times about a portion of the outer surfaces of the driving element and the driven element for applying rotational forces from the driving element to the driven element. The outer surface of at least one of the driving element or the driven element has a plurality of radial grooves therein. The radial grooves are somewhat V-shaped. Portions of the cable are wedged in portions of the grooves thereby substantially reducing slippage of the cable. 
         [0005]    In the preferred embodiment, the outer surfaces of both the driving element and the driven element have the grooves. Also, in the preferred embodiment the wedging of the cable in the grooves causes an increase in the contact forces between the cable and the driving and/or driven element(s) thus increasing friction and reducing the likelihood that the cable will slip. Portions of the cable may become deformed or, flattened where the cable contacts the side walls of the grooves, due to this increased pressure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a front perspective view of a satellite antenna including the parabolic reflector which requires precise positioning and utilizes driving elements and driven elements in accordance with this invention. 
           [0007]      FIG. 2  is a rear elevational view of a portion of  FIG. 1  which shows a pair of driving elements and a pair of corresponding driven elements. 
           [0008]      FIG. 3  is a plan view showing a driving element and driven element in accordance with one embodiment of the invention. 
           [0009]      FIG. 4  is a side elevational view of a portion of  FIG. 3 . 
           [0010]      FIG. 5  is a simplified top view of the apparatus of  FIG. 4 . 
           [0011]      FIG. 6  is a side elevational view of the driven element of  FIG. 5  in simplified form. 
           [0012]      FIG. 7  is a detailed sectional view of a portion of  FIG. 6  taken through section line  7 - 7 . 
           [0013]      FIG. 8  is a cross-section of the cable, taken through section lines  8 - 8  of  FIG. 4 , which illustrates its round shape before it is inserted into a groove. 
           [0014]      FIG. 9  is a sectional view of  FIG. 4  taken through section line  9 - 9  and shows the deformed cable of  FIG. 7  having been removed from the groove. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0015]    Referring now more particularly to  FIG. 1 , there is provided a satellite antenna system  10  including parabolic reflector  12  and transponder element  14  which is extended away from the surface of parabolic reflector  12 . The satellite antenna system  10  includes a pair of driven elements, 16  and  18 , which are used to precisely position parabolic reflector  12 . The driving elements, which will be discussed below, are not visible from the front side of the antenna system of  FIG. 1 . The antenna system  10  also includes a base  21  for stabilizing the system on the ground. 
         [0016]      FIG. 2  shows a portion of the rear of the satellite system of  FIG. 1 . Driven element  16  is connected to driving element  20  by a plurality of cables  22  or multiple loops of a single cable. Driven element  16  includes a drum  24  having an outer surface  26 . Driving element  20  also includes an outer surface  28 . Driven element  18  and its corresponding drive element are identical to driven element  16  and driving element  20 . The remaining description with respect to the driven element and driving element will therefore only be in reference to driven element  16  and driving element  20 . 
         [0017]    Portions of cable  22  are received in V-shaped grooves in the outer surface  26  of drum  24  and the outer surface  28  of driving element  20 . As used herein, the term “V-shaped” means both in the shape of a V having a somewhat of a point at its apex, as well as a V shape with a bottom wall rather than a point at its apex which, in the preferred embodiment of this invention, is somewhat rounded to form a concave shape which is illustrated in  FIG. 7 . 
         [0018]    Driving element  20  may be connected to a drive shaft  30  as illustrated in  FIG. 2 , or drive wheel  32  as illustrated in  FIG. 3 . 
         [0019]    Referring now more particularly to  FIG. 3 , the outer surface  26  of drum  24 , which forms a portion of driven element  16 , includes a plurality of V-shaped grooves  34 . In addition, the outer surface  28  of driving element  20  also includes a plurality of V-shaped grooves  36 . It is preferred that the V-shaped grooves  36  on the outer surface of the driving element are somewhat at an angle, i.e. similar to the threads on a screw. 
         [0020]    In the embodiment of  FIG. 3 , driving element  20  is coupled to pulley  32 . Drive belt  38  connects pulley  32  to pulley  40 , which in turn is connected to electric motor  42 . 
         [0021]      FIG. 4  shows cable  22  looped about drum  24  of driven element  16  and looped about driving element  20 . Preferably cable  22  is made of steel. 
         [0022]    Referring now more particularly to  FIG. 5 , portion  44  of cable  22  is shown wedged in V groove  34  of driven element  16 . In addition, portions  46  of cable  24  are shown wedged in groove  34  of driving element  20 . The wedging of portion  44  of cable  22  in V groove  34  of driven element  16  is also illustrated in  FIG. 6 . 
         [0023]    Referring now more particularly to  FIG. 8 , there is shown a cross-section of cable  22  before the cable is mounted on the driven and driving elements. In the preferred embodiment, cable  22  is round before it is installed on driven element  16  and driving element  20 . 
         [0024]    Referring now more particularly to  FIG. 7 , there is a more detailed view of a portion of the driven element  16  of  FIG. 6 . Portion  44  of cable  22  is shown wedged in V groove  34  which is in the outer surface  26  of drum  24  which forms a part of the driven element  16 . V groove  34  includes opposing side walls  48  and  50  as well as bottom wall  52 . The top of the groove  34  is open to receive cable  22 . Side walls  48  and  50  project inwardly from the outer surface  26  to the bottom wall  52  so as to form the angle E between the side walls  48  and  50 . Preferably the angle θ is between 32° and 40°. The opening  54  in groove  34 , or major width, is greater than the diameter of cable  22  as illustrated in  FIG. 8 . However, part of the way into the groove, the distance between side walls  48  and  50  becomes less than the diameter of cable  22 . The distance between side walls  48  and  50  at the bottom wall  52 , or minor width, is substantially less than the diameter of cable  22 . Thus cable  22  should not contact bottom wall  52 . Since cable  22  is forced into groove  34  under substantial load, cable  22  becomes wedged between side walls  48  and  50 . This wedging results in higher contact forces and higher pressure between the cable  22  and the drum  24  and/or the driving element  20  which reduces the likelihood that the cable  22  will slip thus increasing the positioning precision for the reflector  12 . Portions of cable  22  may deform as illustrated by flattened portions  56  and  58  of cable  22 . Flattening of cable  22  is illustrated both in  FIG. 7  and  FIG. 9 . 
         [0025]    The wedging of cable  22  within groove  34  also increases the friction between the walls  48  and  50  of groove  34  and cable  22 . Thus, the contact forces are increased thereby enhancing the traction capacity of the interface between the cable and the groove. This in turn will improve the stiffness of the system by substantially eliminating the slipping between the cable and the driven element and, in addition, substantially reduces stretching of the cable. The angle θ between the walls  48  and  50  of the groove  34  should be such that the cable  22  will be wedged between the walls  48  and  50 , and the cable does not contact bottom wall  52 . Normal forces are increased as the cable wedges into each groove. 
         [0026]    Stiffness of the system referred to is measured in general by the amount of load the cable can carry before it begins to slip. Initial tests show an increasing stiffness at higher torques in the V groove system described above over a non-grooved or flattened system such as the one described in U.S. Pat. No. 5,105,672 or a wide grooved system such as the one described in U.S. Pat. No. 4,351,197. Also, because of the improved friction between the cable and V grooves constructed as set forth above, a fewer number of wraps or loops, particularly about the driving element, are required. By reducing the slippage of the cable, positioning of the driven element and thus the entire satellite apparatus system which is attached to the driven element such as the satellite antenna reflector, is made more precise. While the V grooves have been specifically discussed in reference to the driven element  16 , preferably the identical V grooves are used in the driving element  18 , and thus the detailed description of such V groove in the driving element need not be repeated. 
         [0027]    While the invention has been described in terms of the above embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the appended claims.