Patent GB-606795-A (GB)
Title: Improvements in target-tracking apparatus and in computing apparatus for the control of gun-fire
IPC: F41G3/06
Filed: 1944-05-01
Abstract: 606,795. Gun-sighting apparatus. SPERRY GYROSCOPE CO., Inc. May 1, 1944, No. 8200. Convention date, April 30, 1943. [Class 92 (ii)] A tracking system for tracking a remote, relatively moving object or target, such as an aerial target against which gun-fire is to be directed, i.e. for maintaining the line of sight on to a target, has a rotatably-mounted tracking element (5) whose angular movements produce angular movements of the line of aim and which is arranged to be rotated by a variable-speed servomotor whose speed and direction of motion are controlled in part by a quantity that is a function of, and is derived from, the output displacements produced by the variable-speed motor. Spacial diagram and formulµ.-In Fig. 2 the target 1 is moving at a constant velocity V along a straight line 3 and is at a distance S from a point 4 which is that point on line 3 nearest to the tracking unit 2. The distance from 2 to 4 is designated Ro, and 6 is the angle between the lines subtended at the tracking unit between the target and the point 4. The letter t indicating time, the Specification shows that the following formulµ apply: Tracking apparatus.-The target is tracked by a telescope 5, Fig. 1, which rotates about azimuth axis 6, such rotational movements serving to rotate shafts 24, 23 leading to a computer 20 by an amount corresponding to 6. The computer, details of which are shown in Fig. 3, produces a rotation of a shaft 19 by an amount corresponding to cos<SP>2</SP> #, thereby through the medium of shaft 21 and rack and pinion mechanism 22, positioning a ball carriage 18 of a variable-speed device 12 driven by a constantspeed motor 13. The driven cylinder 11 of device 12 drives, the disc 10 of a second variablespeed device 9, the ball carriage of which is positioned by a handle 16 and the driven cylinder 8 of which is geared to the sighting device to rotate it about axis 6 at a speed proportional to the speed of the discs of the devices 9, 12 and to the displacements, of their respective ball carriages from the central positions. In operation, with the cylinder 11 rotating at any arbitrary speed, the operator adjusts handle 16 to make the sighting device track the target at the correct angular speed. The consequential movements of shafts 24, 23 introduce the target position data into the computer 20, with the result that its output shaft 19, positioned according to cos<SP>2</SP>   #, will reposition ball carriage 18, thus changing the speed of cylinder 11. Further adjustments of handle 16 are therefore necessary until, when ball carriage 15 has been finally positioned, the computer by continually varying the speed of cylinder 11 via ball carriage 18 ensures that the sighting device automatically follows the target, the ball carriages 15, 18 under such conditions having displacements corresponding respectively to the constant V/Ro and the variable cos<SP>2</SP>. # in accordance with equation (1). Computer.-The computer obtains tan # by finding d#/dt and d<SP>2</SP>#/dt<SP>2</SP> and combining them in accordance with equation (2), and then converts tan # to cos<SP>2</SP> # by means of a cam 58, Fig. 3. As the computer thus only employs the time rate of change of the angular position of the target, it follows that any zero reference line may be used in place of the line joining 2 and 4, Fig. 2, for tracking purposes. As shown in Fig. 3, the computer includes permanent magnet generators 31 and 48, potentiometers 34, 44, 50 having their contact arms 36, 46, 53 mounted on shafts 33, 49 as shown, amplifiers 39, 51, as described in U.S.A. Specification 1,664,455 each adapted to produce across its output leads an alternating voltage of amplitude and phase corresponding to the magnitude and polarity of the input direct voltage and twophase motors 38, 52, each having one phase winding energized by constant alternating current sources and the other winding by the output leads of the amplifiers 39, 51. The generators 31, 48 are each designed, for instance by providing them with pawl-and-ratchet mechanism, Fig. 4 (not shown), so that its shaft will always have the same direction of rotation irrespective of the direction of their input shafts. In operation, rotation of shaft 23 giving # data produces a voltage across leads 32, 321 corresponding to d#/dt. Lead 32<SP>1</SP> is connected to potentiometer 34, whose arm 36 is also moved in accordance with d#/dt as later explained, and the voltage across lead 32<SP>1</SP> and the lead 37 connected to arm 36 is placed in series opposition with the voltage across leads 32, 321. Amplifier 39 and motor will therefore come into operation if these two voltages differ, and as the motor serves to drive the shaft 33 carrying arm 36 it follows that arm 36 will be constantly positioned so that its setting is proportional to d#/dt. The second potentiometer, preferably having a much higher resistance than 34, is energized from a voltage proportional to d#/dt by connecting it to leads 37, 32<SP>1</SP> and as its arm 46 moves with shaft 33 through an angle proportional to d#/dt the voltage across leads 45, 45<SP>1</SP> is proportional to (d#/dt)<SP>2</SP>. This voltage is applied to potentiometer 50, the arm 53 has connected to it a lead 54 whereby the voltage across leads 54, 45<SP>1</SP> is proportional to α (d#/dt)<SP>2</SP> , where a is the angular position of shaft 49 carrying arm 53. This voltage is placed in series opposition with a voltage proportional to d<SP>2</SP>#/dt<SP>2</SP> supplied by generator 48, whose input shaft 43 is positioned in accordance with d#/dt and the resultant voltage is applied to amplifier 51 which actuates motor 52. Shaft 49 therefore continues to rotate until α(d#/dt)<SP>2</SP> =d<SP>2</SP>#/dt<SP>2</SP>, whereby according to equation (2) α= - 2 tan #. Such motion of the shaft actuates cam 58 and rack and pinion device so designed as to rotate shaft 19 through an angle proportional to cos<SP>2</SP> #. Prediction lead angle.-The prediction lead angle is given by the formula # L =V/v cos #, where v is the average projectile velocity. The target velocity is set into the mechanism by a knob 65, Fig. 1, which rotates a cam 63 translated by rack-and-pinion device 74 on shaft 21. The cam is so designed that its follower rotates shaft 69 in accordance with the required V/v cos #, it being assumed that v is constant for a given station. The lead angle # L  given by shaft 69 is then added to target position angle # given by shaft 7, in a differential 72 whose output shaft 73 is moved in accordance with the correct aiming angle for the gun. Shaft 73 may lead directly to the guns or to electric transmitters.