Antenna with motorized positioner
BACKGROUND AND SUMMARY OF THE INVENTION 
     This invention relates to an antenna having a motorized positioner connected thereto, whereby with operation of the positioner, the antenna is caused to shift on its mounting. More particularly, and as described herein, the invention concerns a positioner for moving a dish which receives signals from orbiting satellites, whereby the dish and its feed horn may be moved from a position aimed at one satellite, to pick up or acquire another satellite. While the invention is described in connection with such positioning of a signal-receiving dish, it is appreciated that features of the invention may have other applicability. 
     A so-called TVRO (television receiving only) dish is employed to receive signals from orbiting satellites in geosynchronous orbit over the equator of the earth. These satellites are approximately 23,000 miles in outer space, and are in orbit, but appear to remain stationary because of the rotation of the earth. With a so-called polar mount for the dish, i.e., a mount whereby the dish may be swung about an axis aligned in azimuth and elevation with the rotational axis of the earth, the dish may be swung about this pivot axis to change the satellite to which the dish is directed. 
     So-called linear actuators have been employed to move a TVRO dish. These are relatively inexpensive, and because of the geometry involved in the installation of a linear actuator, any play or looseness in the parts of the actuator does not introduce significant problems with respect to accuracy of positioning and dish movement caused by external factors such as wind buffeting. A disadvantage of a linear actuator is that such can produce controlled movement of a dish over an arc which is limited to about 140° , meaning that a linear actuator may not produce movement of a dish from horizon to horizon. A gear-drive type of actuator may be employed to move a dish from horizon to horizon, but because of the geometry involved in such a system, any play or looseness in the parts of the gear drive results in inconsistency in the accuracy of adjustment and renders the dish controlled thereby sensitive to displacement under the action of buffeting winds. To overcome this problem, gear-drive units may be manufactured with tightly meshed gears manufactured under close tolerances, but this type of unit generally requires a more powerful motor to produce adjusting movement, and with any wear occurring in the parts, looseness is introduced with attendant inaccuracy and instability. 
     In general terms, an object of this invention is to provide an improved power-operated antenna positioner, which may be utilized to move an antenna such as a dish from horizon to horizon, without looseness or play in the parts introducing the problems above described. 
     More specifically, an object of the invention is to provide such a positioner which utilizes a gear drive to position the antenna or dish, more specifically, a worm wheel and meshing worm gear, and a construction which eliminates undesirable looseness or play. Following the invention, mass produced worm wheels and worm gears may be employed in the gear drive, with sufficient clearance provided for smooth and quiet running of the gears and the motor driving the gears, any clearance in effect being taken up in such a manner as to eliminate play or slop and attendant problems heretofore encountered. 
     In a specific and preferred embodiment of the invention, a gear-drive unit is employed to produce adjustable movement in the dish or antenna, which includes a worm wheel secured to a shaft, the axis of the shaft providing the pivot axis for movement in the dish and the shaft being secured to bracket structures supporting the antenna. The shaft is turned or rotated through a worm gear and motor assembly, both supported on a rocker plate or rocker, which is pivotable about an axis extending transversely of the axis of the worm wheel shaft, in a direction causing the worm gear to move toward the worm wheel and into snug engagement with the worm wheel. The assembly is biased in this direction through biasing means, such as a spring interposed between the assembly and framework such as a casing which may be provided for enclosing the drive parts of the gear-drive unit. With the teeth of the worm wheel and the helical drive of the worm gear having a slight taper, and with the organization described, the gear and wheel are always in snug engagement without undue loading of the motor which powers the unit and without conditions producing wear in the parts. The gear drive of the unit is self-adjusting, with the elimination of slop or looseness, even after repeated cycling of the dish or antenna across the sky. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and advantages are obtained by the invention, which is described hereinbelow in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a perspective view illustrating a TVRO dish and a mounting which supports the dish, which includes a stand and a motorized gear-drive unit as contemplated by the invention; 
     FIG. 2 is a view, on a somewhat larger scale, and also in perspective, but looking upwardly from the underside of the mounting for the dish, and more particularly at that portion of the mounting which includes the motorized gear-drive unit; 
     FIG. 3 is a perspective view, on a somewhat larger than FIG. 2, but looking downwardly and at an angle at the motorized gear-drive unit which is part of the mounting for the dish; 
     FIG. 4 is a cross-sectional view taken along the line 4--4 and on a larger scale, of the gear-drive unit; 
     FIG. 5 is a view taken generally along the line 5-5 in FIG. 4; and 
     FIG. 6 is a view taken generally along the line 6-6 in FIG. 4. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, and first of all, more particularly to FIGS. 1-3, shown at generally at 10 is a TVRO dish assembly which includes a parabolic reflector shown at 12 and in front of the reflector, a feed horn 14. The dish assembly is supported in a position, normally above the ground, by mounting structure which includes a ring 16 appropriately secured to the back side of reflector 12, ring 16 being secured to horn 14 through rods 18 having ends joined to the ring through angle pieces 20. The mounting for the dish assembly further includes bracket structure indicated generally at 22 supporting the ring on a gear-drive unit or motorized positioner, indicated generally at 24. The gear-drive unit is mounted on a channel-shaped bracket 26. Bracket 26 in turn is mounted on the upper end of an upstanding post 28. 
     As will hereinafter be described in greater detail, bracket structure 22 connects the dish assembly to an adjustor shaft extending from the top and bottom of a casing 32 which houses the gear-drive unit, the adjustor shaft being rotatable about an axis indicated in FIGS. 1 and 2 at 34. In shifting the dish assembly from one satellite to another, the dish assembly is swung about axis 34. 
     The dish assembly is supported in what is referred to herein as a polar mount, in that the support for the dish assembly is adjusted in azimuth and elevation to place axis 34 in parallel alignment with the rotational axis of the earth. In this connection, it will be noted that casing 32 of the gear-drive unit is supported on bracket 26 by a fastener 36 which supports the forward part of the casing, and a fastener 38 which supports a rear portion of the casing. A series of ports 40 are provided in the sides of bracket 26. By loosening fastener 36 and removing fastener 38, the casing may be swung about the axis of fastener 36 to produce a course adjustment in the elevation of the casing, i.e., the angle of the casing relative to the ground, with fastener 38 placed through an appropriate port to secure the casing in its adjusted position. Fine adjustment in the elevation of the casing is permitted by reason of fastener 36 extending through a slot (not shown) in bracket 26 permitting incremental shifting of the position of the forward part of the casing. Azimuthal adjustment in the mounting for the dish assembly is permitted as by providing a means indicated generally and schematically at 42 for turning post 28 about its axis. 
     Considering now in more details of the gear-drive unit or positioner 24, and referring now also to FIGS. 4, 5 and 6, casing 32 is hollow and includes an upper wall 44, a perimeter wall 46 bounding the casing between its upper and lower sides, and a removable lower wall 48 forming the bottom side of the casing and suitably secured in place to perimeter wall 46. 
     The adjustor shaft earlier referred to is shown at 30. Such extends through the casing and has an upper end projecting beyond the upper wall and lower end projecting downwardly beyond lower wall 48 of the casing. Encircling the shaft and disposed within the casing, and suitably fixed to the shaft, is a worm wheel 50 with worm wheel teeth 52 extending about the perimeter thereof. The teeth have a slight taper in a direction extending radially of the worm wheel. The worm wheel is suitably rotatably supported within the casing, as by bearing 54 and bosses 56, 58. By reason of its securement to the worm wheel, the adjustor shaft may also be thought of as a worm wheel shaft in the gear-drive unit. 
     Shown at 60 is a shallow channel-shaped piece which is secured by fasteners 62 to the underside of upper wall 44 in the casing. This provides a mounting for a rocker plate or rocker element 64, which mounts a worm gear 66 and a DC electric motor 68, with the helical drive gear 70 of the worm gear engaging teeth 52 of the worm wheel. 
     More specifically, secured as by fasteners 72 to the rocker element is a pivot shaft 74 having counter-bores 76 at opposite ends thereof bottomed by conical surfaces. Seated in these counter-bores are the tapered ends of bolts 78 secured in an adjusted position by nuts 80. The organization enables accurate positioning of the pivot shaft with the shaft being pivotable about an axis extending transversely of the worm wheel shaft at a location parallel to and laterally spaced from the axis of the worm gear. 
     The worm gear is mounted on a worm gear shaft 82 suitably journaled as by bearings 84 in depending portions 86 of the rocker element. Secured to an end of the worm gear shaft is a spur gear 88. 
     Interposed between channel-shaped piece 60 and the rocker element is a biasing means, more specifically, a coil spring 90. The rocker element, by reason of its pivotal mounting, constitutes a support for the worm gear mounted for movement in a defined path within the casing, more specifically, arcuate movement about the axis of pivot shaft 74. The spring biases the rocker element 64 in a clockwise direction in FIG. 4, such movement urging the helical drive gear of the worm gear toward and into snug engagement with the teeth of the worm wheel. The helical drive gear of the worm gear has a tapered cross-section, and with such pivotal movement and by reason of the tapered profile of the teeth on the worm wheel, the spring operates to produce snug engagement of the helical drive gear and worm wheel teeth devoid of any looseness or play between these parts. 
     Electric motor 68 is supported on the rocker element to one side of the worm gear. Its output shaft 92 has mounted thereon a spur gear 94 with teeth meshing with the teeth of spur gear 88. Thus, a nonslip driving connection is established between the output shaft of the motor and the worm gear. 
     Mounted on the extreme end of the output shaft of the motor is a magnet 96, and mounted adjacent this magnet and supported on the rocker element is a reed switch 98. The reed switch, through opening and closing as induced by the magnet, with rotation of the magnet, maintains an electronic count of the rotations which have occurred in the motor output shaft, this being related to the rotations occurring in the worm gear. With suitable electronic means connected to the reed switch, means is provided permitting controlled actuation of the DC motor to produce rotation of the worm gear to the extent necessary to move the dish assembly from a position aimed at one satellite to a position aimed at another selected satellite. 
     The dish assembly is supported on the protruding ends of actuator or worm wheel shaft 30. More specifically, and referring also to FIG. 3, the upper end of the worm wheel shaft has secured thereto an arrow-shaped element 100 which is pivoted through turning of the worm wheel shaft. Bracket plate 102 of bracket structure 22 is secured by fasteners 104 to element 100. Bracket structure 22 further includes a strut 106 on the underside of the antenna joined to a tubular element 108 which encompasses and is secured to the lower end of the worm wheel shaft. 
     Generally describing the operation of the apparatus described, to produce movement of the dish assembly whereby it is shifted to be directed toward a new satellite, DC motor 68 is energized to rotate spur gear 94 and with it spur gear 88 secured to the worm gear. Rotation of the worm gear produces turning of the worm wheel and pivotal movement of the dish assembly about axis 34. Movement continues until the electronic control for the motor commands the motor to stop, stopping occurring when the dish assembly reaches a position directed toward the new satellite. 
     With the biasing means described, any looseness or play in the internal parts of the casing is taken up, with the helical drive gear of the worm gear always snugly engaging the teeth of the worm wheel. There is no need to use precisely machine gear parts. The dish assembly is firmly supported from buffeting by the wind. Positioning of the dish assembly is accurate and this accuracy is maintained after repeated cycling of the parts. 
     While an embodiment of the invention has been described herein in detail, variations and modifications are possible without departing from the invention.