Abstract:
The position, velocity or acceleration of a weapon in traverse and/or elevation is maintained constant at its value just prior to firing of the weapon, for a short period including the firing, thereby minimizing operator errors in aiming caused by smoke and vibration.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a device for aiming of a weapon, for instance an anti-aircraft gun, at a moving target which is to be fired upon, comprising a sight arranged in connection with the weapon, in which an operator can observe the target, and at least one aiming system with the aid of which the operator can aim the weapon at the target observed. 
     When firing upon a moving target with a weapon of the kind described above, an operator keeps the line of sight of the sight constantly aimed at the moving target, at the same time as he guides the weapon so that the firing direction of the weapon moves in conformity with the line of sight. With a system in which the sight is mounted on the weapon which can be aimed, the aiming of the line of sight of the sight at the target usually takes place by aiming of the weapon itself. When the operator during the aiming is located on the gun mounting, problems arise due to the fact that the operator is annoyed by smoke and shaking when the firing commences, so that he no longer can perform his task with accuracy. Tests have shown that only the first few rounds in a salvo can be expected to take effect, while the subsequent rounds in the salvo will have such a great miss distance that no effect can be expected. Attempts have been made to solve this problem through the introduction of feed-back control according to which it is determined in a computer how the sight on the gun should be aimed to continue to track a target which moves along a rectilinear path. However, such equipment is complicated and costly. Moreover, it requires, inter alia, a knowledge of the range to the target, which otherwise is not needed in certain cases with less complicated fire control sights. 
     SUMMARY OF THE INVENTION 
     The purpose of the present invention is to achieve a device of the kind mentioned above at a low cost, and which makes it possible to fire comparatively long salvos at a moving target, with good effect. The invention is mainly characterized in that the aiming system comprises means which at the firing of the weapon are arranged to carry out a switching in the aiming system so that the angular position of the weapon or one or a plurality of its position derivatives are kept constant during the time the firing is taking place. 
     If the device comprises an aiming system for aiming the weapon in traverse, for instance, the acceleration in traverse, the velocity in traverse, or the angular position in traverse can be kept constant during the time the firing is taking place. If the device comprises an aiming system for aiming the weapon in elevation, the velocity in elevation or the angular position in elevation can be kept constant during the time the firing is taking place. 
    
    
     Brief Description of the Drawings 
     In the following, the invention will be described in more detail with reference to the accompanying drawings, in which 
     FIG. 1 shows schematically the invention in connection with an anti-aircraft gun; 
     FIG. 2 shows the design of the traversing system of a device according to the invention; 
     FIG. 3 shows the design of the elevating system; 
     and FIG. 4 shows an alternative design of the traversing system of the device. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The anti-aircraft gun illustrated as an example and only schematically in FIG. 1 comprises a barrel 1 which in a conventional way is supported so that it can be elevated on an upper mounting 2. The upper mounting 2 can be traversed with the aid of a servomotor 3 which engages in the gear ring 4. A part of the upper mounting 2 has been cut away to show the positioning of the servomotor 3 and the gear ring 4. Elevation of the gun takes place with the aid of a servomotor 5 placed on the upper mounting 2 in position to engage a gear arc 6 on the elevating mass 7. 
     The anti-aircraft gun also comprises a sight 8, which is mounted on the elevating mass 7. The sight is only shown schematically in the drawing, as its configuration has no significance, in principle, for the invention. The sight can comprise, for instance, a conventional optical sight, a radar sight or a laser sight. The only essential thing is that the gun operator can continuously judge the position of the line of sight of the sight in relation to a target observed with the sight. A gun operator sitting on a seat 9, placed on the side of the gun on the upper mounting 2, with the aid of an aiming lever 10 can actuate the two servomotors 3 and 5 so that the gun is elevated and traversed. Thus, he tracks the target, with an appropriate angle of aim-off and tangent elevation, with the aid of the sight 8. 
     FIG. 2 shows an example of how the traversing system can be designed with a device according to the invention. The figure shows the servomotor 3 which engages in the gear ring 4 for traversing of the upper mounting of the gun. A tachometer generator 11 is connected to the servomotor 3, and which in a conventional way generates an electric signal proportional to the angular velocity in traverse of the barrel 1 and therewith the direction of fire. The servomotor is controlled by an amplifier 12 which is connected with feed-back to the tachometer generator 11 via a summation means 13 which in turn is fed from an integrator 14. On the input of the integrator a so-called sample and hold circuit, consisting of a capacitor 15 and a relay 16 is connected. Traversing takes place with the aid of the aiming lever 10, which is connected with the sample and hold circuit via a control filter 17. The control filter comprises an electric circuit which is designed in such a way that its transmission function has such properties that the gun operates task is made as easy as possible. An example of an appropriate design of the control filter for tracking rapid aerial targets is ##EQU1## in which s designates the Laplace operator and A, B and C are constants, with values, for instance, of A=1 Sec.; B=0.25 Sec. 2  and C=0.05 Sec. The relay 16 is connected to a firing circuit 18, which emits a signal when the gun is fired, and the relay then breaks the circuit at the switching means 19 in the control circuit. 
     FIG. 3 shows an example of the design of the elevating system with a device according to the invention. The servomotor 5 coacts with the gear arc 6 on the elevating mass 7 of the gun. As in the case of the servomotor 3 for traversing, a tachometer generator 20 is connected to the servomotor 5, and which generates an electric signal proportional to the angular velocity in elevation of the barrel 1 and therewith the direction of fire. The servomotor 5 is controlled by an amplifier 21, which is connected with feed-back to the tachometer generator 20 via a summation means 22. On the input of the summation means a sample and hold circuit, consisting of a capacitor 23 and a relay 24, is connected. The gun operator elevates the gun with the aid of the aiming lever 10, which is connected with the sample and hold circuit via a control filter 25. The control filter comprises an electric circuit which, for instance, has the transmission function ##EQU2## in which s is the Laplace operator and D and C are constants with values, for instance of D=0.5 Sec. and C=0.05 Sec. The relay 24 is connected to the firing circuit 18, which emits a signal when the gun is fired, and the relay then breaks the circuit at the switching means 26 in the control circuit. 
     The device described above functions in the following way. The gun operator aims the gun with the aid of the aiming lever 10 and tracks the target with the sight 8. It is assumed that the sight 8 is arranged in an appropriate, known way for calculating or estimating the angle of aim-off and the tangent elevation. The firing takes place with the aid of the firing device 18, which at the same time influences the relays 16 and 24 in the sample and hold circuits, so that the aiming lever 10 is disconnected from the two control systems. The gun then continues to move with a constant acceleration in traverse and constant velocity in elevation. Calculations have shown that it is then possible to maintain accurate tracking of the target and therewith firing with good effect during approximately 2 Secs. when rapid targets moving with a speed of a magnitude of 300 m/Sec. and at a range of 1000-2000 meters, are involved, and during a longer time when slower targets or targets at a longer range are involved. 
     The device described above can be modified in various ways without deviating from the concept of the invention. An example of a different design of the control system for the control in traverse is shown in FIG. 4. The system from the summation means 13 to the gun is identical to the system according to FIG. 2, and has therefore not been shown in FIG. 4. However, the system between the aiming lever 10 and the summation means 13 has been modified in such a way that a further summation means 27 has been connected to the input of the summation means 13. The summation means 27 forms the sum of the output signal from an integrator 28 and the input signal to this integrator multiplied by a constant E. Analagously with the control system according to FIG. 2, a sample and hold circuit, consisting of a capacitor 29 and a relay 30 is connected to the input of the integrator 28. The aiming lever 10 is connected to this sample and hold circuit via a control filter 31, with the transmission function ##EQU3## in which s is the Laplace operator and the constants E, A and C have, for instance, the values E=1 Sec.; A=0.5 Sec. and C=0.05 Sec. 
     The above-mentioned control filter dimensions are examples only, and the most appropriate design is influenced by the other properties of the system, such as the magnification of the sight, the properties of the aiming lever, the band width of the servo systems for control in elevation and traverse etc. 
     The design indicated of the system is optimized for combatting rapid aerial targets. When combatting slow targets, for instance helicopters and ground targets, it can be advisable to eliminate the integrators 14 and 28, and the traversing system will then have properties similar to those of the elevating system described in FIG. 3. It is also conceivable to replace the tachometer generator 11 in FIG. 2 and/or 20 in FIG. 3 with an angle transmitter, for instance a potentiometer, and then, when firing, the traversing and/or elevating position, respectively, may be kept constant. 
     In cases when the weapon is installed on a moving base, for instance on a ship or a land vehicle, the angular position of the weapon is to be kept constant in relation to a space-fixed co-ordinate system, and the tachometer generators 11 and 20 should then be replaced by speed gyros which are installed on the elevating mass or the traversing parts of the weapon.