Patent GB-1115866-A (GB)
Title: Improvements in computing fire control systems
IPC: F41G5/00
Filed: 1965-06-23
Abstract: 1,115,866. Fire control computation; digital calculating. BREVETS AERO-MECANIQUES S.A. 23 June, 1965 [26 June, 1964; 18 June, 1964], No. 26489/65. Headings G4A and G4G. General.-An automatic LAA gun (Fig. 1, nob shown) is rotatable about a horizontal axis YY and a vertical axis ZZ by the gunner through electrohydraulic mechanism powered by an I.C. engine and dynamo; and a sight assembly comprising a tracking telescope, a laser transmitter of red or infra red coherent light, and a reflected light receiver 19 associated with a target range computer, and an orientation control handle are mounted on a column to be rotatable about other horizontal inclined axes yy, zz. The laser comprises a parallelopipedal ruby crystal (Fig. 2, not shown) with reflecting rear face and partially transparent front face surrounded by a helical flash tube pulsed by a feed unit at regular time intervals from a control unit, and the laser beam is collimated optically and obturated by a shutter responsive to the control unit determining the instants of transmission. A reflected beam from the target is concentrated by mirrors through a diaphragm and filter to a photomultiplier, whose output is amplified and applied to a computer unit determining the range d of the target in digital form for a prediction computer also receiving bearing g and elevation a angles of the target derived from the column displaced about axes zz, yy by the gunner in accordance with sighted target movements. The prediction computer responsive to the control unit determines the bearing and elevation of the gun about axes ZZ, YY necessary for a projectile to impinge on the target, and controls the electro-hydraulic mechanism accordingly. Theory. In Fig. 3, the following parameters are shown TA the rectilinear path of the target C the gun position c the barrel axis A the present target position F the future target position at impact of projectile CX a reference line in the horizontal plane of C a the projection of A on horizontal plane of C K a the projection of A on reference line CX X a Y a } the cartesian coordinates of A Za g the bearing of A s the elevation of A d the range AC f the projection of F on horizontal plane of C K f the projection of F on reference line CX X f Y f } the cartesian coordinates of F Z f    g f  the bearing of F = bearing G of gun firing to hit target at F S f  the elevation of F d f  the range of future target F h the angle of vertical deflection of gun S the angle of gun with horizontal plane = S f  + h T a  the projection of TA on the horizontal plane d c  the displacement of gun position from target path V x  the cartesian components of target speed V between positions A and F, V y  measured positively when retreating from gun and negative when advanc- V z  ing on it T the time of flight of projectile G c  the calculated bearing and S c  elevation of the gun Ge the actual bearing and S e  elevation of the gun. 2. 3. 4. 5. 6. 7. 8. In calculation of the required angles G c , S c , A 1 , A 2 , A 3  &c. are the successive positions of A at successive instants 0, dt, 2dt &c., of range measurement, d 1 , d 2 , d 3  &c. are the successive ranges CA 1 , CA 2 , CA 3  &c. at 0, dt, 2dt, 3dt &c. g 1 , g 2 , g 3  &c. are the values of g for A 1'  A 2 , A 3  &c. obtained by sampling the continuous measurement of g. S 1 , S 2 , S 3  &c. are the values of S for A 1 , A 2 , A 3  &c. obtained by sampling the continuous measurement of S. It is shown that if x, y, z are the cartesian coordinates of A 2  at time dt and that after a known time of flight T from A 2  the successive values of X f , Y f , Z f  being obtained by increasing the indices of d, s, g by two units per successive value. The laser and computer unit delivers range values of d 1 , d 2 , d 3  &c. at times 0, dt, 2dt &o., and the coders produce after sampling, the parameters cos s 1 , cos s 2  cos s 3  etc.; sin s 1 , sin s 2 , sin s 3  etc.; cos g 1 , cos g 2' cos g 3 etc.; sin g 1 , sin g 2 , ain g 3 &c., from which T is determined as a function of d f , the range of future point F, by reference to a repetitive non-iterative algorithm of the firing tables. It is shown that wherein h is obtained from the firing tables as a function of (d f )<SP>2</SP> (equation 6). Determination of T It is shown that where Tb is an approximate value of T and d x  is the component along CX of the distance d n  travelled by the target during determination of Tb, starting from an estimated value of T 0  of T; and values d 1  s 1 , g 1 , d 2 , s 2 , g 2 , at which approximate values of X f , Y f , Z f  and (d f )<SP>2</SP> are determined by equations 12, 13, 14, and 6. An approximate calculated time T s  corresponding to (d f )<SP>2</SP> is obtainable from the firing tables as a function of To, d, s, g and for predetermined average initial conditions of target speed and path T s  = f(T 0 , d) and corresponding curves P 1 , P 2 , P 3 , P, (Fig. 9) give T s  as f(T 0 ) for differing values of d. BS denotes T s  = T 0  = correct value of Tb at the intersection of BS with curve T s  = f(T 0 ), for the future range d f  which is necessarily varying. d Initially, To has approximate value -, n where n is e.g. 1000 and d 1  is e.g. 3000, and T 0  intervals P 3  at H having ordinate T s0 , which intersects BS at G 1  having abscissa T s0 . After time interval 2dt, range is d 3  corresponding to curve P 2  so that intercept GH is 2dt. If T s0  is taken as an approximation to T, the new value T s1  of T s2  is the ordinate of the intersection E of the abscissa T s0  with curve P 2  containing G. T s0  and T s  are not identical and do not represent Tb correctly, which is given by the abscissa and ordinate of the intersection K of BS with curve P 2  containing G. It is shown mathematically that 16. from dt known initially To assumed d 2 /1000 known after time dt T s0  calculable after time 2dt T s1  calculable after time 4dt. A correction factor dT is added to Tb to allow for target movement during the time of calculation 2dt of Tb. The travel of the target d n  (and cartesian components dx, dy, dz) during time 2dt from A as a function of speed V, range d, and minimum distance d c  from its path to the gun C, are calculable, and dT is obtainable as a function of d n , v, d. Fig. 10 shows curves Q 1  to Q 6  showing variations of dT with d for values of v and d C , assuming 2dt =0À1 sec., according to the equation 17. and with small error for a typical equipment 18. when d n  = #(dx<SP>2</SP>) + (dy<SP>2</SP>) + (d z 2) 19. and d x  = d 2  cos s 2  cos g 2 - d 1  cos s 1  cos g 1  20. dy = d 2  cos s 2  sin g 2  - d 1  cos s 1  sin g 1  21. d z  = d 2  sin s 2  - d 1  sin s 1  22. so that T = Tb + dT 23. the constants depending on ballistic factors. Control arrangements Laser rangefinder 16, computer unit 53, and coder units 56, 57, 58, 59 (Fig. 4) produce signals representing d, cos g, sin g, cos s, sin s, which are stored in memories 64, and are delivered through control unit 63 to computer unit 62 together with signals representing tan h and time of flight T as functions of d<SP>2</SP>, from generators 60, 61. Output signals representing the required values of tan G c , tan S c  the bearing and elevation of the gun, are compared at 88, 89 with signals representing actual values tan G e , tan S e  from coders 66, 67 coupled to the gun barrel 31. The error signals are converted to analogue signals m, n at 90, 91, amplified at 94, 95 and applied to electrohydraulic valves 68, 69 regulating hydraulic pumps 70, 71 driven from the I.C. engine power source 27, 28 which control the rotation of hydraulic motors 80, 81 geared to the bearing and elevation trains of the gun and coupled to the coders 66, 67 (Fig. 5, not shown). Analogue extrapolation circuits (Fig. 11, not shown) comprising RC differentiating circuits 100, 101 in series with normally closed gates 102, 103 are connected from the output to secondary inputs of amplifiers 94, 95; further normally open gates (not shown) being provided in the outputs of 90, 91. When the target is visually obscured the gates may be respectively opened and closed by the gunner through control unit 63, and signals dm/dt, dn/dt are derived by the differentiators and fed back to maintain traverse of the gun barrel in accordance with the preceding displacement, so that the target is followed. Computation In a complete prediction cycle of the future point F of the target, V is determined from two successive sets of values of d, g and s over a time interval dt, while a single determination of S e  and G e  is sufficient, so that two successive values of d, cos g, sin g, cos s, sin s and single values of tan G e , tan Se from coders 57 to 59, 66 and 67 are stored per cycle in twelve memories J 1  to J 12  (Fig. 6) storing after two measurements (time dt), four measurements (time 3dt), six measurements (time 5dt) the following signals: and the cycles of switching U 1 , U 2 , V 1 , V 2 , V 3 , V 4 , V 5 , over successive time intervals dt are tabulated in Fig. 7 (not shown). At time 0, the range computer 53 and the sighting device coders 56 to 59 supply the series of variables #l while coders 66, 67 supply variables #G and #S. Switch U 1  in its LH position connects coder 67 to V, while switch U 2  in its RH position connects V 1  to V 3 . During period 0 to dt, V 1  connects its six inputs successively to its single output, and by operation of V 1 , V 3  intermediate memories I 1 , I 2 , I 3 , I 4 , I 5 , I 6  receive the series of variables #l, #S. At time dt, U 1  changes over to its RH position and substitutes #G for #S while U  2  changes over to its LH position to connect the output of V 1  to V 2'  During period dt to 2dt, V 2  connects its six inputs successively to its single output, and by operation of V 1 , V 2  intermediate memories I 7 , Is, I 9 , I 10 , I 11 , I 12  receive the series of variables #2, #G. In memory unit 111 (Fig. 6) coders 56, 57, 5