Abstract:
The central part of the nut of a gimbal mounting system for rotating a microwave antenna and the like is given a movement of elevation about the second axis (5) when the corresponding motor (II) is started-up and a circular movement about the first axis (3) orthogonal with the second axis when the corresponding motor (I) alone is started up, said circular movement automatically producing a movement of elevation about the second axis.

Description:
This invention relates to a device for rotating an element about two orthogonal axes of rotation, more particularly applied to the orientation of a radar antenna and a radar antenna orientated by such a device. 
     In order to orient particularly heavy systems or to increase the orientation speed, it is necessary to make use of increasingly powerful drive mechanisms and to minimize the weight of moving parts. 
     In known types of orientation devices, each axis of rotation has its own motor-drive mechanism for actuating a platform which carries the following rotation axis and its motor. Since certain mechanisms are placed on movable portions, the use of motor-drive mechanisms which are more powerful and therefore heavier has the effect of slowing-down these movements. 
     SUMMARY OF THE INVENTION 
     The aim of the present invention is to overcome the disadvantages mentioned in the foregoing. 
     An object of the present invention is a device for orienting an element about two orthogonal axes in which the motor-drive mechanisms are installed on stationary portions. 
     Another object of the invention is an orientation device where a large useful volume is made available by virtue of the displacement of the motor-drive mechanisms to a stationary portion. 
     The device, according to the present invention, for rotating an element about a first axis and a second axis which is orthogonal to the first one and carried by it, including a stationary part and a movable part, a first and a second motor-drive mechanism, placed in the stationary part, for controlling through a first and a second gearing means the rotating movement about said first and second axes respectively, the rotation movement about the second axis is actuated by the corresponding second motor-drive mechanism or together with the rotation movement about the first axis by the corresponding first motor-drive mechanism through a third gearing means. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features of the invention will be more apparent to those skilled in the art upon consideration of the accompanying drawings, wherein: 
     FIG. 1 is a view in perspective showing an orientation device according to the prior art; 
     FIG. 2 is a view in perspective showing the orientation device according to the invention; 
     FIG. 3 is a sectional side view of the device shown in FIG. 2. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The perspective view of FIG. 1 illustrates a device according to the prior art for orienting a radar antenna. In this device, the motor 31 drives a pinion (not shown in the figure) which engages with the toothed portion 33 of a member 34. Said member 34 is adapted to carry a motor 32 and a gear-wheel 35 which is disposed in meshing engagement with a pinion 36 driven by the motor 32. The apex of a V-shaped member 37 is fixed on the external diameter of said gear-wheel 35. The two arms of said V-shaped member are each pivotally attached to one end of a rod designated respectively by the reference numerals 40 and 41. The other end of each rod is pivotally attached to a point of the surface of the antenna 42 to be oriented. Said antenna is also maintained at its center by means of a member 38 which is capable of pivotal motion with respect to the member 34 about the pivot 39. 
     The two motors 31 and 32 therefore serve to orient the antenna 42 by displacing this latter in pivotal motion with respect to two axes 43 and 44 respectively, that is, with respect to the axis 43 by pivotal displacement of the member 34 about the pivot 39 and with respect to the axis 44 by pivotal displacement of the member 37 and therefore of the gear-wheel 35. However, the circular displacement of the antenna about the axis 43 is slowed-down by the inertia of the weight of the motor 32. 
     The present invention makes it possible to overcome the drawback just mentioned. 
     The device according to the invention as shown in perspective in the general view of FIG. 2 comprises a stationary portion having the shape of an elongated C, the two arms 1, 2 of which constitute the first supporting member of the gimbel mounting system, and a movable portion 4a, 4b 8 forming the central junction assembly designated as the gimbal nut, the longitudinal axis 5 of which constitutes one of the two orientation axes. Said gimbel nut is composed of a cylindrical element 4a, 4b and of a coaxial external structure 8, from which the element 4a, 4b is decoupled and within which said element is capable of pivotal displacement about the common longitudinal axis 5. The structure 8 is in turn capable of pivoting about the first axis 3 at right angles to the second axis 5 between the arms 1 and 2 of the stationary portion. 
     FIG. 3 is a sectional side view of FIG. 2 after the structure 8 has been displaced in pivotal motion about the axis 3 through an angle of 90°. 
     The arm 1 of the stationary portion houses the motor-drive mechanism I which controls the so-called circular motion of the system to be oriented. Said mechanism is coupled to a transmission shaft 6 which is placed within the interior of the arm 1 and rotatable within this latter by making use of bearing means 20. The opposite end of the transmission shaft 6 produces action on a bevel coupling formed by a pinion 17 mounted at the end of the shaft 6 and a gear-wheel 18 having an axis 3 at right angles to the axis of the pinion 17 and of the shaft 6. Said gear-wheel 18 is placed within the interior of the arm 1 and is coupled with the structure 8 through the wall of the arm 1 by means of the cylindrical member 21 which forms one of the points of pivotal attachment of the structure 8 to the stationary portion. Rotation of said cylindrical member 21 is effected by making use of bearing means 10 provided in the wall of the arm 1 through which said cylindrical member passes. A cylindrical portion is placed within the interior of the structure 8 and is formed by two separate and distinct hollow elements 4a and 4b of cylindrical shape located on each side of the axis 3. These two elements 4a and 4b have an axis 5 which is common with the external structure 8 and are decoupled from this latter by means 9. 
     The arm 2 of the C-shaped stationary portion houses the motor-drive mechanism II which controls the so-called movement of elevation of the system to be oriented. This mechanism is connected to a transmission shaft 7 placed within the interior of the arm 2 and decoupled from this latter by means 20. The opposite end of the shaft 7 produces action on a bevel coupling housed within the arm 2 and formed by a pinion 13 mounted at the end of the shaft 7 and by a gear-wheel 14 having an axis 3. By means of a cylindrical member 19 having an axis 3, the first bevel coupling drives a second bevel coupling placed within the interior of the structure 8 and comprising a gear-wheel 15 having an axis 3 and disposed in meshing engagement with a gear-wheel 16 having an axis 5 and placed at the periphery of the cylindrical element 4a. The cylindrical transition member 19 passes through the wall of the arm 2 and is decoupled from this latter by means 11. 
     The system to be oriented (not shown in the drawings) is fixed at A, B and A&#39;, B&#39; on the cylindrical elements 4a and 4b respectively, externally of the structure 8, and constitutes the second supporting member of the gimbal mounting system. 
     If current is supplied to the motor-drive mechanism II alone, only the so-called movement of elevation about the axis 5 is initiated. 
     In fact, the gear-wheel 14 and the gear-wheel 15 which are coupled together by means of the cylindrical member 19 are driven in rotation from the motor II by means of the shaft 7 fitted with the pinion 13. The gear-wheel 15 engages with the gear-wheel 16 and causes the element 4a to rotate about the axis 5. The system which is attached to said element 4a also pivots about said axis and is accompanied by a movement of rotation of the element 4b in synchronism. The elements 4a and 4b are rotatable relative to the structure 8, however, and said structure remains motionless. No movement in azimuth therefore takes place. 
     On the other hand, if current is supplied to the motor-drive mechanism I alone, there takes place both a circular movement about the axis 3 and a movement of elevation about the axis 5 at the same time. 
     By means of the shaft 6 fitted with the pinion 17, the motor I in fact has the effect of driving the gear-wheel 18 in rotation about the axis 3 and consequently causing rotational motion both of the structure 8 to which said gear-wheel is attached and of the elements 4a and 4b which are placed within the interior of the structure, and therefore of the system to be oriented. This is the circular movement about the axis 3. By virtue of the bearing means 11 aforementioned, however, the structure 8 is rotatable relative to the cylindrical member 19, with the result that said member and therefore the gear-wheel 15 which is attached to this latter are accordingly motionless since the motor-drive mechanism II is not supplied with current. Since the element 4a and therefore the gear-wheel 16 rotate about the axis 3, taking into account the circular movement of the structure 8, the gear-wheel 16 must undergo a displacement along the gear-wheel 15 having an axis 3 with which it is in contact, thus producing a movement of rotation of the element 4a about the axis 5 and consequently a movement of rotation of the system to be oriented as well as a movement of rotation of the element 4b. This is the movement of elevation about the axis 5. 
     Means such as rate gyros or annular digital coders placed between stationary portion and movable portion serve to determine and to measure the circular movements and movements of elevation, thus making it possible to control the driving mechanisms in consequence. 
     The movement of elevation can be cancelled when the circular-motion drive mechanism I is supplied with current. In fact, it is only necessary to ensure that the gear-wheel 15 is driven by means of the motor-drive mechanism II at the same time and by the same angular quantity as the gear-wheel 18 in order to neutralize the relative motion of the two gear-wheels 16 and 15. 
     In a preferential embodiment, the drive mechanisms can be reduction-gear motor units. 
     The decoupling means 9, 10, 11, 12, 20 may consist, for example, of ball-bearings. 
     The device according to the invention can be used in particular for orientating a radar antenna. 
     It is in fact necessary to provide for the possibility of rapid orientation about two axes. When making use of an orientation device of the prior art, the drive mechanisms placed within the movable portions occupy a volume which could be used to greater advantage for housing microwave rotating joints. By reason of the lack of available space for rotating joints, the microwave receiver is placed in this case as close as possible to the antenna. As a general rule, the receiver is therefore mounted against the back of the antenna and is subjected to very strong vibrations. Furthermore, it produces additional inertia during antenna movements and the motors mounted on movable portions impose limitations on the diagrams of angular displacement of antennas. 
     By means of the orientation device according to the present invention, the drive mechanisms which are installed on stationary portions permit antenna displacements of substantial amplitude. Furthermore, they free the volume which is located at the center of the gimbel mounting system and which can thus accommodate rotating joints. The microwave receiver can accordingly be displaced to the stationary portion in which the vibrational environment is less severe. 
     The applications of this device are not limited to the example mentioned in the foregoing but extend to all cases of two orthogonal movements such that one movement is carried by the other, in which the drive mechanisms should preferably be located in the stationary portion of the device.