Patent GB-1150029-A (GB)
Title: Improvements in or relating to vehicle guidance systems and vehicles therefor
Inventor: BROOKE DAVID WILLIAM INGHAM
IPC: G05D1/02
Filed: 1967-02-22
Abstract: 1,150,029. Automatic steering control. INTERNATIONAL HARVESTER CO. OF GREAT BRITAIN Ltd. Feb. 22, 1968 [Feb. 22, 1967], No.8355/67. Heading G3R. [Also in Division H4] The invention provides a system for guiding a vehicle, e.g. for agricultural purposes, by means of an energized cable preferably buried in the ground, wherein the guide cables are arranged as two sets of parallel wires A 1 , A 2  &c., and B 1 , B 2  &c. Fig. 1, the wires A being energized at a frequency f1 different from that f2 of wires B. The vehicle is provided with programme means enabling a predetermined route to be set up, e.g. the dotted line D, by selecting appropriate turning points. A sensing head 1, Fig. 2, is carried by the vehicle and includes a circuit 2 comprising a pair of coils 4a, 4b which are disposed on either side of the centre line of the vehicle and may be tuned to either of the frequencies f1, f2 by relay-operated switch 6 and capacitors 5a, 5b. The coils are connected in opposition so that the voltage across the selected capacitor 5a, 5b will be zero when the coils are symmetrically disposed above the guide wire. Otherwise the voltage has a magnitude and phase representing the amount and direction of the displacement. A further circuit 3 including a coil 7 tuned by a capacitor 8a or 8b as selected by switch 9 linked to switch 6, provides a reference voltage of fixed phase. The outputs of circuits 2, 3 are supplied via amplifiers 10, 11, Fig. 3, to a phase detector 12 whose output is supplied via a relay contact 14 to a differential amplifier 15 controlling a valve 16 in the power-assisted steering system of the vehicle. The valve 16 directs hydraulic fluid from a pump 17 to the left or right side of a steering ram 18 to move the wheels 19 accordingly. The sensing head 1 is mounted ahead of the wheels, the mounting being linked to the steering so that the error signal is reduced more quickly. In operation, the number of crossings of wire B before the turn away from wire A 1  is set into a counter and when the count-down reaches zero relay-controlled circuits contacts 14, 21 are operated for a right hand turn. For a left hand turn contacts 14, 21, 22 would be operated. A potentiometer 23 supplies a voltage dependent on the angle through which wheels 19 have been turned (zero when the wheels are straight ahead) to the amplifier 15 together with an input V 1  which causes the steering mechanism to operate until the voltage from potentiometer 23 equals V 1 . At this time the programme device switches over contacts 6, 9 so that the sensing head is responsive to f2. A null detector 25 detects when the sensing head passes over wire B 1  and causes contacts 14, 21, and 22 if operated, to change over, and the vehicle comes under the control of guide wire B 1 . A level detector 24 shows whether the signal f2 received becomes sufficient for satisfactory control within a predetermined time and if not causes the vehicle to stop and an alarm to be given. Potentiometer 23 may be replaced by a rate of turn detector.