Abstract:
An apparatus for rotating structures such as large antennas which incorporates a motor for controlling rapid rotation of the structure through a ring gear and a screw jack which is selectively coupled to the ring gear for controlling a slower more exacting rotation of the structure about a common axis.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This device is directed to devices for rotatably adjusting such structures as antennas used in satellite communications. 
     It is known that antennas for communication with satellites must be able to scan a demi-sphere centered on the vertical axis of a fixed pedestal. To that end, it is necessary to combine movement along two planes, the first in azimuth, or in a horizontal plane, the second in elevation, i.e. in a vertical plane. 
     For average structures, namely those with a diameter less than or equal to 13 meters, the movement in elevation is obtained by a jack which allows the antenna to pivot through about 90°, while the movement in azimuth is obtained by two gear motors on the shafts of which are fixed pinions which mesh with a fixed ring gear whose diameter is about 1.5 meter. The gear motors, which are normally adjustable, are disposed symetrically and are secured to the assembly rotating with the antenna. The gear motors allow rapid movements (homing mode to change aiming) and slow movements (tracking mode). 
     When antennas are employed whose diameter is greater than or equal to 16 meters, the movement in elevation is still obtained by a jack as for the average structures, but the movement in azumith, made by two gear motors, requires a ring gear of large diameter (about 4 meters) in order to maintain structural rigidity taking into account the increase in mass. This is both expensive and cumbersome, with the result that the solution adopted consists in a configuration with mean clearance allowing displacements by bounds of 60° with an overlap of 30°. 
     This configuration with mean clearance is hardly more satisfactory than that using a large-diameter ring gear. 
     SUMMARY OF THE INVENTION 
     The improvements forming the subject matter of the present invention overcomes the aforementioned drawbacks and allow a device to be produced which ensures a displacement in azimuth with large clearance continuously, i.e. of the order of 340°, with a ring gear of reduced diameter. 
     According to the invention, in order to effect the rapid movements of the structure, a gear motor is used whose pinion meshes with the ring gear, while, for slow movements, the gear motor is at rest, while the displacement of the structure through a relatively small angle (more or less 18°) is effected by means of a jack acting on the ring gear by way of a carriage provided with a disengageable positive coupling system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, given by way of example, will enable the invention, the characteristics that it presents and the advantages that it is capable of procuring, to be more readily understood. 
     FIG. 1 is a view in elevation of a structure to which the improvements according to the invention are applied. 
     FIG. 2 is a section taken along II--II (FIG. 1). 
     FIG. 3 is a view in direction F (FIG. 2) of the carriage bearing the positive coupling system. 
     FIG. 4 is a section along IV--IV (FIG. 3) illustrating the positive coupling system in position engaged with the ring gear. 
     FIG. 5 is a view similar to that of FIG. 4, but illustrating the positive coupling system in its disengaged position. 
     FIG. 6 is a section along VI--VI (FIG. 3) in the positive coupled position. 
     FIG. 7 is a view similar to that of FIG. 6, but showing the positive coupling system in disengaged position. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a parabolic antenna 1 with a diameter larger than 16 meters and which is mounted to rotate with respect to a fixed pedestal 2. Antenna 1 is mounted on a base 1a. It may pivot with respect to its base 1a by means of a screw jack 3 and an assembly 4 simulating a pivot axis 4a. The pedestal includes a fixed ring gear 5 while the base 1a of the antenna is provided, on the one hand, with a reversible gear motor 6 on the driven shaft of which is fixed a pinion 7 (FIG. 2) meshing with the ring gear 5. The base 1a also includes a screw jack 8 of which the end of the piston 8a in a form of a screw is associated with a carriage 9 which carries a positive coupling system 10. As illustrated in FIG. 2, the cylinder of jack 8 is articulated about a vertical pin carried by the lug 4a which is secured to base 1a of the antenna 1. 
     FIG. 3 illustrates the carriage 9 which comprises, on its upper and lower faces, a ball joint 11 associated with the corresponding branch of a fork 8b which is integral with the free end of the piston 8a. 
     Carriage 9 comprises a body 12 made in the form of a thick plate which is mounted to slide with respect to two tie-rods 13 illustrated in FIGS. 4 and 5. One of the ends of each tie-rod 13 is provided with a shoe 14 abutting against the inner face of two collars 5a, 5b which are upstanding above and below the periphery of the ring gear 5, on either side of its teeth 5c. 
     Each tie-rod 13 passes through a lining 15 fixed within the body 12 and includes a head 13a. Between the head 13a at its opposite end and a washer 16 in abutment against 12 are placed elastic washers 17, with the result that body 12 is urged in the direction of arrow F1, so that a tooth 12a made in the center of body 12 is positively fitted in the teeth 5c of the ring gear 5. 
     Each head 13a is disposed in a cylinder 18 fixed to the lining 15 and which is supplied with fluid under pressure through a pipe 19, with the result that, when fluid enters this pipe, the chamber 20, constituted between the bottom of the cylinder 18 and the head 13a which bears peripheral O-rings, is placed under pressure for a purpose which will be explained in greater detail hereinbelow. 
     The presence is observed of a guiding system 21 fixed on body 12 and extending into a slot in each shoe 14 to guide the shoe and to block their rotation. 
     Body 12 is further provided with four rods 22 which pass right through it (FIGS. 6 and 7). One of the ends of each rod 22 is provided with a fixed stop 23, while its opposite end carries a pad 24 which overlaps each collar 5a, 5b of ring gear 5. Each pad is composed of two independent elements of which one, 24a, which is fixed to the relevant end of rod 22, is in abutment against the inner face of the corresponding collar 5a, 5b, while the other element 24b of the pad is mounted to slide freely on rod 22. This second element 24b is in contact with the horizontal face of the corresponding collar and with the collars external face by way of a hoop 25. Contact between element 24b and collar 5b is obtained with the aid of an elastic abutment. Body 12 includes around each rod 22 a chamber 26 in which is placed a compression spring 27 which abuts against the bottom of the chamber and the element 24b. 
     Functioning follows from the foregoing explanations. 
     When fluid is sent into pipe 19 (FIG. 5) under a pressure sufficient to overcome the force developed by the elastic washers 17, the force is cancelled, with the result that the springs 27 cause body 12 to move in the direction of arrow F2 (FIGS. 5 and 7) until it comes to rest against the four stops 23. This displacement of body 12 disengages tooth 12a from tooth 5c in which it was previously locked. 
     This position is adopted when the gear motor 6 must change the angular orientation of antenna 1. 
     On the contrary, for a slow, so-called tracking displacement, the pressure is cut in pipes 19 with the result that locking of the tooth and of the ring gear is effected by action of elastic washers 17. In this way, operation of jack 8 brings about a slow rotation of the antenna in one direction or in the other, depending on whether screw 8a rotates in one direction or in the opposite one. 
     It is observed that elements 24a of pads 24 are, like shoes 14, guided by angle irons 28. 
     It must, moreover, be understood that the foregoing description has been given only by way of example and that it in no way limits the domain of the invention which would not be exceeded by replacing the details of execution described by any other equivalents.