Patent GB-697390-A (GB)
Title: Improvements relating to gun-directing systems and apparatus
IPC: F41G5/08
Filed: 1944-04-19
Abstract: 697,390. Gun-fire control systems. SPERR GYROSCOPE CO., Inc. April 19, 1944 [April 19, 1943]. No. 7292/44. Class 92(ii) Also in Group XXXVI] Relates to a system for directing a gun to hit a moving target of the type in which a sighting device and rangefinder provide primary control quantities measuring the azimuth and elevation angles of the slant range to the target, which quantities together with prediction and ballistic corrections provided by associated mechanisms are applied to a transmitter system for controlling the gun. According to the invention such a system is provided with means for differentiating the first or the first and second derivative of a spherical co-ordinate, for multiplying the values of the co-ordinate and of its derivatives with factors proportionate to the respective powers of the time of flight for combining the so obtained products and for computing thus the corrected co-ordinate according to Taylor's Theorem. General circuit. As shown schematically in Fig. 1, an automatic radio sighting system 1, as described in Specification 621,485 is employed in conjunction with an automatic range circuit 4 as described in Specification 582,492, [Group XXXVI], these devices serving to produce rotations of shafts 2, 3 6, proportional to present azimuth position A 0 , present elevation E o , and present slant range D 0  of the target. The ultimate function of the apparatus is to produce rotations of the shafts 8, 9, 10, proportional respectively to the required angle of train A.T. quadrant elevation Q.E. and time of flight tp. these shafts being connected to transmitters 31. 31', 31", which convey the data to the gun battery. The apparatus also includes a predicting circuit 13, ballistic correcting mechanism 16 and a difference indicator 25, the mechanism 16 having set into it by graduated scale arrangements 20 - - - 23 data corresponding to muzzle velocity, percentage change in air density from standard, wind velocity, and wind direction respectively, and by shafts 17, 18, 19, data corresponding to A.T., O.E. and tp respectively. Such data, by the use of differentiating, multiplying and adding devices illustrated in Figs. 3, 7 and 8 respectively are combined in accordance with certain empirical formulae to give the reauired correcting output signals on leads 24, 24<SP>1</SP>, 24" corresponding to azimuth correction #, elevation correction # 5 , and slant range correction p. These are fed to the indicator 25. The predicting circuit also includes a plurality of the devices illustrated in Figs. 3, 7 and 8 these being so arranged and combined that the prediction correction signals @ A, AE. and #D fed to indicator 25 by their output leads 15, 15<SP>1</SP>, 15" are produced in accordance with Taylor's theorem as previously stated. Fig. 2 not shown, indicates the method by which A A may be obtained. In operation, considering azimuth prediction cnly, the shaft 2 actuates a permanent magnet generator 11 which accordingly produces in its output lead 12 a signal proportional to the first time derivative A 0  of the present azimuth A 0 . This signal is fed to circuit 13 to which tp data is also fed by shaft 14. Circuit 13. by means of its calculating devices. thereupon calculates the correction #A according to the formula:- and supplies #A to indicator 25, which also receives ballistic correction # from 16. The indicator 25 makes a comparison of the input data (AA + 5) with data (AT.-A 0 ) imparted by a shaft 28, and should any difference exist produces a voltage in its output lead 30 to drive a servo 26. This servo drives shafts 8, 29, according to the angle of train AT, the shaft 8 leading to transmitter 31 and shaft 29 leading to a subtracting differential 27 to produce the data (A.T. - A 0 ) in shaft 28. When voltage in lead 30 is zero the gun is correctly trained in azimuth. Similar mechanism is provided for obtaining Q.E. and tp, the tp mechanism including a fuze converter and corrector 34. Multiplying unit. For multiplying or for obtaining functions of an independent variable, or for a combination of these two purposes, a potentiometer 95, Fig. 7, is employed having an arm 98 on a shaft 96 which is shown rotated through a distance x. The voltage signal Vi applied to the terminals 96, 97. may be constant or variable. and the resistance between the grounded terminal 97 and arm 98 may be directly proportionate to x or to a function 'F(x) of x. According to the input voltage and the form of resistance employed, the output signal on conductor 100 connected to arm 98. is proportional to x. F(x), x. Vi or F(x), Vi. The conductor 100 leads to a follower circuit, details of which are given in Fig. 6 (not shown), the function of which is to use the signal without drawing current therefrom. Adding unit. In this unit. Fig. 8, the two input voltage signals V and V2 to be added algebraically are applied one to each of the grids of two electrodes 104, 105. The cathodes of these are arranged in circuit, as shown, with resistances 113 - - - 115 and variable resistances 118, 119, and the plates in circuit with a battery 106 and resistances 107, 108, 109. The screen grids of both tetrodes are connected to the positive terminal of a battery the negative temrinal of which is connected to parts 117, 120, as shown. With both input signals at zero the variable resistances 108. 118 and 119 are adjusted so that points 110, 117 and 120 are at zero potential. By this arrangement the potential at point 110 is proportional in magnitude to the algabraic sum (V1 + V2) of the two input signals but of opposite polaritv. This signal is reversed in a circuit 111, details of which are given in Fig. 6 (not shown), to produce the required algebraic sum (V1 + V2) in output lead 112. More than two tetrodes may be combined in a similar manner when it is desired to find the algerbraic sum of more than two signals. Differentiating and smoothing unit. As shown in Fig. 3, the voltage on an input lead 40 corresponds to the first derivative A o  of present azimuth position A 0 . Lead 40 is connected to a condenser 56 arranged in series with a resistance 57. and it follows that the charging current flowing through the condenser is proportional to the rate of change of the voltage in lead 40, that is proportional to the second derivative A 0 . This signal A 0  is fed to the grid of a valve 58, the cathode of which is grounded through resistance 59 and circuit 60. 61, and the plate of which is arranged as shown in circuit with a battery 62 and variable resistance 63. Circuit 60, 61 smooth out any of the irregularities caused for instance by backlash in the gearing in other parts of the apparatus, and accordingly a smoothed A 0  signal appears in the output lead 43. Specification 418,670 also is referred to.