Patent GB-711894-A (GB)
Title: Apparatus for instruction or training in navigation
Inventor: CUTLER ALBERT ERNEST
IPC: G09B9/24
Filed: 1952-10-27
Abstract: 711,894. Electric analogue computing system. COMMUNICATIONS PATENTS, Ltd. Oct. 27, 1952, No. 26946/52. Class 37. [Also in Group XXXVIII] Navigation training apparatus for tracing the simulated movement of a craft travelling with a fixed compass heading on a conical projection chart wherein the meridians are radial lines from a fixed point, and the latitudes are arcs of concentric circles with this point as centre, comprises means for computing the rectangular components of velocity required to make the recording pen trace the equivalent path on the chart so that a fixed heading course is recorded by a curved line cutting all the meridians at a constant angle. In an alternative apparatus the displacement of the pen by co-ordinated rectangular movements is controlled in accordance with the mathematical relationship between the polar co-ordinates of the craft and its velocity 'and bearing. Velocity translation. Movement of the recorder pen 12 (Fig. 2) over the conical projection chart 1O is produced by combined vertical movement along a lead-screw 13 produced by rotation of a motor 14, and horizontal movement along a lead-screw 18 produced by rotation of a motor 20. If the perpendicular components of the instantaneous velocity of the craft are V N-S  and V E-W  when the pen 12 is on a meridian making an angle a with the vertical meridian, the corresponding perpendicular components of velocity to be given to the pen via the lead-screws 13, 18 are (V N-S  cos a - V E-W  sin a) vertically, and (V N _ S  sin a + V E-W  cos a) horizontally. These components are computed in the circuit of Fig. 2. Vertical lead screw 13 is coupled to the slider 23 of a potentiometer 24 connected in series with ganged potentiometers 25, 26 and having an A.C. voltage across the potentiometers so that the voltage at the slider 23 represents the vertical distance of the pen 12 from the pole of the conical chart. Similarly, horizontal lead screw 18 is coupled to the slider 27 of a potentiometer 28 connected in series with ganged potentiometers 29, 30 and having an A.C. voltage across the potentiometers so that the voltage at slider 27 represents the horizontal distance of the pen 12 from the vertical meridian. The voltages at sliders 23, 27 are amplified and fed to coils 33, 34 of a sine-cosine resolver having rotor winding 35, the rotor signal being amplified at 36 to energise a motor 37 coupled to the rotor 35 which is thus rotated through the angle a to be perpendicular to the direction of the resultant field due to coils 33, 34. The motor 37 also drives two contoured drum-type potentiometers 40, 43 each having two brushes 41, 42 and 44, 45 spaced 90 degrees apart, the windings being shaped so that when an A.C. voltage is fed across two diametrically opposite points, the output signals from the brushes are proportional to the sine and cosine of the angle of rotation from a reference position, the brushes 41, 42 of potentiometer 40 lagging by 90 degrees with respect to the brushes 44, 45 of potentiometer 43. The A.C. voltage fed to potentiometer 43 represents the E-W ground speed (V  E-W ) of the craft, and the voltage fed to potentiometer 40 represents the N-S ground speed (V N-S) . Motor 14, driving the vertical lead-screw 13, is fed with the signals from brush 42 (V N-S  cos a) and brush 44 (-V E-   W  sin a), and motor 20, driving the horizontal lead-screw 18, is fed with the signals from brush 41 (V N-S  sin a) and brush 45 (V E-W  cos a). Thus the movement of the pen 12 will be consistent with the fixed compass course. Displacement translation. In the alternative method of producing the required movement of the pen by rectangular lead-screws, the rectangular co-ordinates of the position of the pen after time t relative to an origin (R 0 , a 0 ) and having one axis parallel to the vertical meridian, are given by x = R sin a, y = Ro-R cos a, where (R, a) are the polar co-ordinates of the pen relative to the pole of the chart and the vertical meridian at time t. Also, if the velocity of the craft at time t is V and heading angle b, then dR/dt = V cos b, and da/dt = V sin b/R. The apparatus for solving these equations is shown in Fig. 4. The rotor winding 71 of a sine-cosine resolver is connected by a selsyn system to a rotor coil 63 which is mechanically coupled to a heading indicator, and rotor 7<SP>I</SP> is supplied with an A.C. voltage proportional to the ground speed V of the simulation' craft. The signals induced in stator coils 73, 74 are therefore V cos b and V sin b respectively. The former signal, which is equal to dR/dt, feeds a motor 76 via amplifier 75, and the total rotation with an initial setting corresponding to R 0 , is equal to R. The motor  7 6 drives two drum-type potentiometers 80, 81 the former having a winding such that the output is proportional to the reciprocal of the rotation, i.e. I/R, and being fed with V sin b volts from stator winding 74, so that the output is V sin b/R, i.e. da/dt. This is integrated by motor 8 3  producing a rotation corresponding to a on two further potentiometers 8 5 ; 86 whose windings produce outputs proportional to sin a and cos a respectively. Potentiometer 86 is fed with R volts from potentiometer 81, thereby producing a signal representing R sin a, which equals x and energizes a motor 88 driving the horizontal lead-screw 91, whilst potentiometer 8 5  produces an R cos a signal which is deducted from a preset value representing R 0  set up on a potentiometer 99 to energize motor 94, driving the vertical lead-screw 97. The pen 98 is initially set up at the point (R 0 , a 0 ). In a modification to deal with varying scales on the chart depending on the value of R, the law of the windings of potentiometers 80, 81 are such as to produce the correct output signals for each value of R. To eliminate hunting of the motors, each motor also drives a generator which supplies a velocity feedback signal to the amplifier energizing that motor. Specification 711,294 is referred to.