Patent GB-639041-A (GB)
Title: Improvements in and relating to computing gun sights
IPC: F41G5/00
Filed: 1944-05-18
Abstract: 639,041. Gun-sight predictors. SPERRY GYROSCOPE CO., Inc. May 18, 1944, No. 9626. Convention date, Sept. 12, 1942. [Class 92 (ii)] Relates to predictors of the type in which the sight is carried by or moved in synchronism with the gun or gun platform. According to the invention means in addition to those for obtaining the prediction 'lead Angle, are provided for counteracting during the initial tracking period the reverse component movement which is given to the sight when the sighting line is moved up to the target, and for correcting during the following period of continued steady tracking the initial error caused by the previous counteraction. Fig. 1 shows schematically the arrangement of the guns 11 and sight 13 on a platform 12, the sight being moved in azimuth with respect to the platform by a servo 42, and the platform being rotated in azimuth about a fixed toothed ring 17 by a servo 14, all such movements being controlled by a manual control member 18. In one construction the movement of the handle 18 produces a voltage across terminals 21, Fig. 2, the voltage corresponding in sense and magnitude to the sense and magnitude of such movement, in the manner described in Specification 631,517. A resistance 22 connected across the terminals is in series with a resistance 23 and connections are made as shown to an amplifier 24 whose output drives the servo 14, thus rotating the turret. Servo 14 also drives a shaft 32 connected to a generator 29 of such type that its output voltage is proportional to the speed of shaft 32 and hence proportional to the speed of rotation of platform 12. This voltage is impressed on resistance 23 in series with a condenser 33. Assuming constant angular velocity of the platform, the constant voltage generated by generator 29 will charge the condenser 33, and as this is charging, the voltage across resistance 23 decreases. The voltage across resistance 22 must therefore be made to decrease accordingly to provide the constant input to amplifier 24, and thus it follows that control 18' must be gradually returned to its neutral position. The voltage across the generator, corresponding to angular speed of platform 12 and therefore of the target, is also applied to a potentiometer 34 whose arm 36 is moved by control 37 in accordance with the range or time of flight. The resultant voltage drop from one terminal of the potentiometer to the arm is therefore proportional to the prediction angle, and accordingly this is impressed via a further potentiometer 38 upon an amplifier 41 actuating the servo 42 for the sight 13. Servo 42 also drives the cam 44 of potentiometer 38 until the latter balances the prediction voltage. A condenser 46 and resistance 47, the values of which are so chosen that the voltage derived across 47 corresponds to the rate of change of the control signal, are arranged in the circuit as shown. By this means any movement of control 18, say, to enable the sight to catch up with the target should it be lagging, applies an immediate additional voltage to amplifier 41, thus moving the sight. This additional voltage subsequently dies out while the target is being tracked and the correct lead angle between target and sight is then restored. In a modification, Fig. 5 (not shown), the sight servo 42, which imparts only the lead angle to the sight, drives a further generator whose output voltage, proportional to the rate of change of lead angle, is arranged in series with resistance 23. By this means the gun orientation is advanced by an amount corresponding to the change in the lead angle, leaving the, sight orientation unaffected by changes in the position of control 18. In another construction, Fig. 3, the pinion 16 on the platform which engages the fixed ring 17 to rotate the guns in azimuth, is driven by the cylinder 56 of a variable-speed device 52 at a speed proportional to the displacement of control 18 which displaces the ball carriage 51. Thus the displacement of the rod 50 connecting the control 18 with the ball carriage is proportional to the angular speed of the target in azimuth, and such movement is conveyed by levers 68, 71, and 72 to the sight 13 to move the sight initially in the direction of movement of the target. Rod 50 also moves lever 76 whose pivot 77 is adjusted by control 98 in accordance with range or time of flight. Link 78 connected to lever 76 thus moves in proportion to the prediction angle, and such movement is conveyed to a ball carriage 86 whose disc 90 is driven by the same constant speed motor 54 as that for the disc of carriage 51. The driven cylinder 88 of carriage 86 drives a shaft 91 which carries a screw-thread whose nut 94 carries the pivot of one of its links interposed between link 78 and carriage 86, and by this means the carriage is restored to its neutral position. A further screw 93 on shaft 91 is fitted with a nut 95 carrying a pivot on link 68 and the latter, now pivoting on a pin 70 of rod 50, is moved to swing the sight in the reverse direction to its correct prediction angle with the guns. Cylinder 88 through gearing 89 and other shafts and gearing leading to a torque amplifier connected to gear 16, also serves to move the platform 12 whereby the orientation of the sight is unaffected by changes in the prediction angle. In another modification employing a similar system of levers and ball carriages, Fig. 4 (not shown), the telescopic sight 13 is replaced by mirrors which are tilted to displace the image of a reticle. In this construction the range control 98 in addition to displacing the pivot 77 of lever 76, also serves to vary the speed of the driving- disc 90 whereby the settling time for ball carriage 86 and therefore of the sight, varies with different ranges. Means are also provided for ensuring that the correct prediction correction in azimuth is obtained for varying angles in elevation and for applying the correct superelevation correction. Fig. 4 shows the mechanism as applied both to the elevation and azimuth prediction corrections for the sight.