Patent GB-611030-A (GB)
Title: Improvements in or relating to automatic control systems
IPC: G05D1/08
Filed: 1945-01-08
Abstract: 611,030. Automatic control systems. SMITH & SONS (ENGLAND), Ltd., S., and MEREDITH, F. W. Jan. 8, 1945, No. 687.. [Class 38 (iv)] . [Also in Group XX] The desired angular relationship about a given horizontal axis of two bodies mounted on a moving craft is maintained by relatively rotating the bodies until the deviation relatively to the body of pendulums or other pivoted members mounted on the bodies for motion about the said axis is the same. One body may be the pitch gimbal of a gyro vertical and the other a compass carrying platform, each pendulum being associated with an induction pick-off to generate a signal proportional to the sine of the angle of deviation of the pendulum from the vertical about the pitch axis, the resultant of these two signals monitoring the compass platform about the pitch axis. Fig. 1 shows the invention incorporated in an automatic control system for aircraft. The shafts 2 and 3 are stabilized in pitch and roll respectively by the gyro vertical 1. A pitch detector 5, e.g. a potentiometer or induction pick-off, has one part fixed to the shaft 2 and the other part, i.e. the pitch datum, on a shaft 4, and feeds from a constant voltage 400- cycle/sec. A.C. source to a channel 6 a voltage 6 proportional to the deviation in pitch from the pitch datum. Similarly, a bank detector 8 comprises a part fixed to the shaft 3 and a part, i.e. the bank datum, on a shaft 7 feeds to a channel 9 a voltage # proportional to the deviation in roll from the bank datum. Devia-  tion about the yaw axis is detected by a directional gyro 10 controlled by an earth inductor compass 61 and mounted on a turntable 11 which in turn is mounted on a shaft 7 so as to roll therewith. A signal voltage # proportional to the deviation in yaw from the datum set by the table 11 is fed to the channel 12. The positions of the pitch, bank and yaw datums determine the attitude of the craft which is maintained by the automatic control system. Any desired pitch datum and yaw datum can be set up at any desired rate by a miniature control column in a pilot's control panel 13, which includes a switch 14 for cutting out the automatic control. The bank datum is set automatically to give the correct bank for the prescribed rate of yaw. Fore-and-aft tilting of the miniature control column feeds a voltage, proportional to the angle of tilt and in phase or anti-phase with the supply according as the column is tilted forwards or backwards, via channel 15 and amplifier 16 to one phase of a two-phase hysteresis motor 17 (of the type described in Specifications 576,248 and 576,249), the other phase being fed with 400-cycle quadrature voltage of constant amplitude. The motor 17 rotates the shaft 4 through gear-box 18, drives the transmitter 19 providing a distant indication on the dial 20 of the position of the pitch datum, and drives a hysteresis generator 21 (of the type described in Specification 576,351). The latter generates a voltage proportional to the speed of the motor 17 and this is fed to the amplifier 16 in opposition to the voltage from the channel 15 so that the motor 17 runs and the pitch datum is adjusted at a speed proportional to the forward or backward tilt of the control column. The datum may be fixed at any desired position, as shown by the indicator 20, by restoring the-column to its central position. Tilting of the column to the right or left feeds a voltage via channel 24 and amplifier 25 to a motor 27 driving the turntable 11 and similarly controls the setting of the yaw datum, a distant indication of which is given at 13. The bank datum on shaft 7 is automatically moved to the correct position by a motor 43 which is fed via the amplifier 42 and channel 41 from the bank computer 32 with a voltage proportional to the air speed and the ordered rate of yaw. A banking unit 44 comprising a tangent potentiometer applies through channel 45 to oppose the voltage in the channel 41 a voltage proportional to the tangent of the angle through which the shaft 7 has been rotated. The shaft 7 is then moved to the correct datum position, an indication of which is given on the attitude indicator 20 through transmitter 48 and receiver 49. Damping is effected by a generator 46 feeding a voltage proportional to speed through channel 47 to the amplifier 42. The signals #, #, # in the channels 6, 9 and 12 are used to operate servomotors controlling the elevators, ailerons and rudder respectively. The servo unit for operating the rudder comprises a hysteresis motor-generator 58, an amplifier 59 and a differentiating unit 60. The voltage # is fed direct to the amplifier 59 through channel 64 and is also fed to the differentiating unit 60 where it is modulated from the 400-cycle supply to give a direct current which is differentiated by an inductance, the differentiated signal being remodulated with the supply and fed to the amplifier 59 through the channel 65. The output of the amplifier 59 is fed to one phase of the motor 58 which operates the rudder through suitable gearing and also drives the generator so that a voltage proportional to speed is fed back to the amplifier. The rudder is thus driven at a speed proportional to rate and angle of yaw. The servomotors for controlling the ailerons and elevators are similar except that in the latter case an additional proportional to the differential of the square of the rate of yaw is fed from the back computer 32 through channel 69 to the amplifier to provide a pitch correction when the aircraft goes into a banked turn. When the switch is .operated to effect manual control, the signals #, #, # are disconnected from the servo units and applied to the amplifier 16, 42, 25 respectively in place of the signals from the miniature control column and bank computer 32. The three datums are thus set to the actual attitude adopted by the aircraft at any instant and the automatic control may be cut in during any attitude of flight and will continue to fly the aircraft in that attitude. The indicators 20 and 31 will show the actual attitude of flight during manual control. The gyro vertical is erected in pitch by a hysteresis motor 53 controlled through amplifier 52 in accordance with the relative displacement between a pitch pendulum 50 and the shaft 2. A hysteresis motor 57 for applying precessional forces to erect the gyro 1 in roll is controlled through an amplifier 6 in accordance with the sum of signals proportional to (1) deviation relatively to the aircraft of a bank pendulum 54 pivoted about the roll axis; (2) the tangent of the actual angle of bank derived from the channel 45 and (3) the correct angle of bank derived from the channel 41. Signals (2) and (3) cancel each other except when the gyro precesses in roll from the true vertical. To compensate for the effect of changes of air speed on the pitch pendulum 50 a voltage proportional to the differential of the air speed, obtained from the generator 34 driven by the air mileage unit 35 and a differentiating unit in the bank computer 32, is fed to the amplifier 52 and motor 53. To correct for the effects of transient sideslips, a voltage proportional to the differential of the output of the bank pendulum 54 is fed to the amplifier 56 and motor 57. Other modifications are described in the Group XX abridgment. Specifications 611,020 and 611,029 also are referred to.