Patent GB-627974-A (GB)
Title: Automatically controlled electric steering equipment for vessels or aircraft
IPC: G05D1/02
Filed: 1946-03-07
Abstract: 627,974. Automatic control system for steering-gear. AUTOMATISK ROR-KONTROL AKTIESELSKAB. March 7, 1946, No. 7208. Convention date, Feb. 12, 1942. [Class 38 (iv)] [Also in Group XL (b)] In electric automatic ship or aircraft steering gear, deviation from a preset course causes a steering signal to be photo-electrically derived from the indications of a control compass, differentiated, combined with the differential signal, and applied to a balanced electric circuit controlling rudder operation, the movements of the rudder varying an element of the balanced circuit to oppose the effect of the steering signal and to rebalance the system when the rudder has been given a deflection appropriate to restore the course of the vessel. An illuminated black compass card has a crescent-shaped white field 2 reflecting light on a pair of photo-cells 5, 6 mounted on the compass and rotatable about its axis to set the course. When the vessel is on course, the crescent is symmetrically disposed with regard to the photo-cells which then pass equal currents. Deviations from course swing the compass card from its normal position, causing unbalanced illumination of the photo-cells so that unbalance voltages are applied to the grids of normally balanced D.C. amplifier valves 24, 29 in accordance with the deviation, together with differential voltage components produced in adjustable differentiating circuits 12, 18, 19 and 15, 20, 21. The anode currents flow in a balanced network comprising variable resistances 47, 52, potentiometers 48, 53, variable resistances 49, 54, and potentiometers 50, 51 having a common tap 55 movable in response to the rudder deflection. The anode currents of valves 24, 29 (the total current of which is limited by a common cathode resistance), develop voltages which are applied to the grids of normally balanced D.C. amplifier valves 70, 82 through secondaryadjustable differentiating circuits comprising resistances 61, 66, 63, 67 and condensers 64, 65, and the anode currents of the latter valves flow through variable resistances 85, 86 and normally shunted inductances 87, 88 to the operating coils 89, 90 of relays having double contacts 93, 94, 97, 98, the total valve current being again limited by a common cathode resistance 75, variable to adjust the backlash of the apparatus. Deviation from course causes the photo-cells to be unequally illuminated, and unbalanced voltages proportional to the deviation are applied, together with their differentials, to the grids of the first pair of valves to develop combined unbalance voltages in the balanced network, which after further differentiation unbalance the anode currents of the second pair of valves, which operate one or other of the relays to start a rudder motor (not shown) to correct the course deviation and deflect the common tapping 55 of potentiometers 50, 51, until balance is again restored and the relay is de-energized. Relay operation shunts the appropriate relay coil with a variable resistance 95 or 99 to equalize the operate and release relay currents, which may be adjusted by varying resistances 85, 86, 95 and 99. At the same time the shunt across the appropriate inductance 87 or 88 is removed, and the consequent voltage surge ionizes neon lamp 91 or 92 which limits the voltage across the relay coil to protect it against over-magnetization. Sensitivity and balance may be adjusted by resistances 48, 49, 53, 54 while the response characteristic is variable by adjusting the law of potentiometers 50, 51. The valve and photo-cell electrode voltages are derived from a series of potentiometers across a stabilized power supply which may comprise a vibrator. For manual steering, the grids of valves 24, 29 are shorted to earth by relays 34, and rudder movement is controlled by varying the resistances 47, 52. Multiple relays or grid-controlled rectifiers may be used to control the rudder motor operating-speed in accordance with the magnitude of the unbalance signal, and the output valve anode currents may operate a differential measuring instrument arranged when deviated to unbalance the illumination of a further pair of photo-cells. A single photo-cell co-operating with an assymmetrical light field on the compass card may control the steering through a single-ended amplifier and the field may be other than crescent shaped. The system may respond to alternating signals produced by pulsating photo-cell illumination, and may be rebalanced by a differentially variable condenser. The Specification as open to inspection under Sect. 91 differs in detail from that described above, particularly in that a low-pass filter is inserted between the photo-cells and the first amplifying stage, the differentiating and rebalancing circuits are differently arranged, two further stages of amplification are introduced, and the relay neon lamps and-series inductances are eliminated. This subject-matter does not appear in the Specification as accepted.