Apparatus for stabilizing underwater devices
BACKGROUND OF THE INVENTION 
     The present invention relates to a stabilizing apparatus provided on a self-propelled underwater device connected to its base by a cable, which apparatus is intended to prevent the cable from applying to the device stray forces due to hydrodynamic thrust on the cable. 
     The technical field with which the invention is concerned is that of the construction of self-propelled underwater devices, manned or otherwise, connected to their control base (surface craft, submarine, fixed underwater structure or shore installation) by a cable, known as a leash, which supplies energy to the device and/or is used to transmit signals between the device and said control base. 
     Movements of the device and of the water currents apply hydrodynamic thrust to the connecting cable which transmits the thrust to the device in the form of drag or torque, and this complicates the piloting of the device. 
     These parasitic forces are at present dealt with by equipping the device with guide propellers which are started up to correct the direction of travel of the device. This method calls for the use of costly supplementary guiding equipment and does not enable the hydrodynamic forces to be completely offset. Thus the paths of travel are irregular. 
     The object of the present invention is to eliminate automatically all the parasitic forces transmitted to the device through the connecting cable. 
     SUMMARY OF THE INVENTION 
     This object is achieved by means of an apparatus which comprises an auxiliary propeller located to the rear of the device in a support to which is secured the connecting cable and which is connected to the device by a universal joint; the apparatus also includes means for measuring the forces which the universal joint applies to the device to automatically act on the propeller so as to offset these forces. 
     The auxiliary propeller preferably consists of two screws rotating in opposite directions to each other and applying zero axial torque by differential counter-balancing. In a preferred arrangement it is disposed along the diameter of a first ring which pivots within a second concentric ring; the latter is mounted to rotate about one of its diameters on two diametrically opposed pivots which turn in a mounting in the form of a doublepronged fork formed by the rear end of the device. The two pivots are preferably located in a plane slightly offset from the plane of the rings. 
     The means for measuring the forces applied by the universal joint to the device preferably consist of strain gauges placed on the bearing surfaces of the journals of the pivots for rotating the universal joint in said mounting. 
     The screws are preferably variable-pitch screws, and the pitch is automatically varied so that the sum of the signals supplied by the strain gauges remains zero. 
     The invention results in a novel product constituted by a self-driven underwater device equipped with a connecting cable, which device is not subjected to any force or to any torque through the connecting cable. 
     The cable is in fact secured to a support which, because of the presence of the universal joint, is free to take up any position about two axes which are at right angles to each other and which are initially at right angles to the longitudinal axis of the device. The hydrodynamic forces on the cable, which would be converted into torque about these two axes, cause rotation of the auxiliary propeller and of its support in relation to the device, and are not transmitted to the device. 
     The strain gauges placed on the bearing surfaces of the journals of the pivots of the universal joint detect the occurrence of any force at this locality. The signals produced in these strain gauges are used in a regulating chain of known type to act automatically on the propeller either for causing the pitch of the screws to be varied if the screws are of the variable-pitch type, or for causing their speed of rotation to be varied in the direction for offsetting the sum of the signals and therefore the forces transmitted to the device by the universal joint. 
     The piloting of the device, either from within if the device is manned, or from a distance, becomes considerably easier, and in particular, it becomes possible to keep the device on a regular course. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a general perspective view of a device equipped with an apparatus in accordance with the invention; 
     FIG. 2 is an exploded view of the apparatus of the invention; 
     FIG. 3 is a plan view of the apparatus of the invention; 
     FIG. 4 is a rear view taken along line IV--IV in FIG. 3; and 
     FIG. 5 is a longitudinal section taken along line V--V in FIG. 3. 
    
    
     DESCRIPTION OF A PREFERRED EMBODIMENT 
     FIG. 1 shows an underwater device 1 equipped with a cable 2 connecting it to its control base. The device 1 is self-propelled. The cable 2 is used, for example, for supplying electrical energy or for passing signals between the control base and the device. Because of the speed of displacement of the device and of water currents, the cable 2 is subjected to hydrodynamic thrust which is normally transmitted to the device, thus altering its course. 
     According to the invention, the device 1 is equipped with an apparatus 3 intended to prevent the cable 2 from applying force or torque to the device 1. The longitudinal axis oy of the device and two axes ox and oz at right angles thereto are shown in FIG. 1. 
     The apparatus 3 consists of a variable-direction auxiliary propeller 4 shown with a system of connected coordinates ΩXYZ. Like the propellers of torpedoes, this propeller is formed, for example, by two screws turning in opposite directions and driven through a differential or by a motor having two rotors turning in opposite directions. The propeller 4 is connected to the device 1 by a universal joint, the two pivotal axes of which are the axis XX 1 , at right angles to the plane zoy, and the axis ZZ 1  contained in the plane zoy. 
     The propeller 4 is mounted at the rear of the device 1 in a support 5 formed by two concentric rings pivoting relative to each other about the axis ΩZ at right angles to the plane of the two rings and located in the plane yoz. The outer ring is mounted to pivot about the axis ΩX by means of two diametrically opposed pivots 6 which turn in a mounting 7. 
     FIGS. 2-5 show the detailed construction of the invention. In particular, the apparatus for mounting propeller 4 comprises an outer equatorial ring 5a having two diametrically opposed pivots 6a and 6b which turn in bearings 8a and 8b carried by the two arms 7a and 7b of a fork formed by the rear end of the device 1. The equatorial ring 5a forms the outer race of a ballbearing unit 9, the inner race of which is formed by the ring 5b. A central tube 10 is disposed on a diameter of the ring 5b. Tube 10 acts as a shaft for the two screws 4a and 4b which rotate in opposite directions and which are driven by a motor reduction gear system (not illustrated). 
     The apparatus is completed by a housing formed by an upper shell 11a and a lower shell 11b secured to the inner ring 5b by upper and lower rings 12 and 13, respectively. The arrangement formed by the housing, the propeller and the inner ring 5b thus pivot in unison about the axis ZZ 1  relative to the outer ring 5a which pivots about the axis XX 1  in relation to the body of the device. 
     FIG. 2 shows strain gauges 14a, 14b and 14c placed on each of the bearings 8a and 8b and arranged in three directions, ox, oy and oz, respectively, which are at right angles to each other. These gauges provide electrical signals porportional to the forces transmitted to the device by the bearings. The outputs of the strain gauges are coupled to appropriate circuits for deriving a control signal based on a comparison of predetermined strain gauge output combinations. 
     FIG. 3 is a rear view of the device 1. This view shows the mounting 7 formed by the two arms 7a and 7b and supporting the bearings 8a and 8b. The pivots 6a and 6b solidly connected to the outer equatorial ring 5a are mounted to pivot in bearings 8a and 8b. This Figure also shows the inner equatorial ring 5b supporting the hollow shaft 10. The connecting cable 2, equipped with floats 2a, is secured at 15 to one end of the shaft 10. The electrical conductors extend into the interior of the device either by way of a flexible portion, which does not interfere with rotation, or by way of a rotary contact. FIG. 3 also shows the two screws 4a and 4b of the propeller which rotate in opposite directions and are driven by motor reduction gears 16a and 16b interconnected by a differential gear 16c. The assembly consisting of the screws and the drive units is enclosed in the housing 11 which has two extensions 17a and 17b enclosing the ends of the shaft 10. 
     The arm 7b carries a servo-motor 18 which drives the pivot 6b. This servo-motor is automatically controlled by a signal provided by a torque pick-up which measures the torque along the axis XX 1  transmitted by the support 5a to the body of the device. The signal acts on the servo-motor 18 to cause the movable assembly to turn about the axis XX 1  in the direction for offsetting the torque. For example, the signal which controls the servo-motor 18 is equal to the difference between the signals provided by the two strain gauges 14a placed on the bearings 8a and 8b. This servo-motor 18 may be dispensed with, since in practice the hydrodynamic thrust of the cable on the movable assembly causes the latter to turn about the axis XX 1  in the direction for offsetting the torque along said axis. 
     The apparatus may comprise a second servo-motor for causing the equatorial ring 5b to turn automatically in the ring 5a and controlled in a similar manner to that of the first servo-motor 18. This second servo-motor is not shown in the drawings and, like the first servo-motor 18, it can be dispensed with, since the forces applied by the cable are sufficient to cause this turning movement. FIG. 4 shows the rings 5a and 5b in an inclined position following a turning movement about the axis XX 1 . 
     FIG. 5 shows, in section, the outer equatorial ring 5a and the inner equatorial ring 5b forming the two races of a ball-bearing unit. The outer ring 5a is mounted to pivot in the bearings 8a and 8b carried by the two arms 7a and 7b of the mounting at the rear of the device. The pivots 6a and 6b are located at the end of two arms which are angled downwardly so that they are located at a level slightly lower than that of the top of the equatorial ring 5b, and so that the central tube 10 and the cable 2 are able to turn freely over the entire periphery. 
     FIG. 5 also shows the screws 4a and 4b which rotate in opposite directions and the drive units 16a and 16b, together with the differential gear 16c through which they are powered. The screws are, for example, variable-pitch screws and the mechanisms 19a and 19b for changing the pitch are shown diagrammatically. 
     These mechanisms are automatically controlled by signals provided by pick-ups, for example, by the sum of the signals provided by the strain gauges 14a, 14b and 14c placed on the support surfaces of the bearings 8a and 8b. The automatic action on the pitch-changing mechanisms is so selected that the thrust of the propeller acts in the direction for offsetting the sum of the signals provided by the strain gauges, said action therefore offsetting the pull of the cable on the device. 
     To balance the movable assembly, a counterweight 20 is secured to the housing 11b. 
     It is, of course, possible, within the scope of the invention, to replace various of the elements forming the arrangements that have been described by elements having a similar function and well known to the person skilled in the art.