Patent GB-992790-A (GB)
Title: Improvements relating to vehicles
Inventor: FINN-KELCEY PETER GERARD
IPC: G05D1/02
Filed: 1960-06-23
Abstract: 992,790. Leadergear systems. ELECTRICAL RESEARCH ASSOCIATION. June 19, 1961 [June 23, 1960], No. 22022/60. Heading H4U. In a vehicle having a steering mechanism under the control of a sensing head which picks up signals emitted from a conducting wire to cause the vehicle automatically and successively to follow a number of different paths defined by the wire, the head has a number of laterally spaced positions corresponding to the paths, and the vehicle has arrangements for changing the lateral position from which the control of the steering is exercised, in response to a given signal. A tractor used with a plough has five pick-up heads mounted on and equally spaced along a boom in front of the tractor wheels, each head comprising two separate coils spaced at about a foot part. Only one head, chosen by switching arrangements to be described, is used at any one time to steer the tractor and this it does by receiving in its two halves radiation emitted from a wire buried in the ground. If the two halves are symmetrically disposed with respect to the wire electrical signals of equal strength are induced in the two coils and these are arranged to ensure that no current flows through solenoids which when operated actuate a piston in an hydraulic system controlling the steering gear (Fig. 2, not shown). If, however, the two halves are not symmetrically disposed, the steering gear is operated to turn the tractor to its proper path. The wire 43 which emits the signals (which may be at a frequency of, say, lkc./s.) is embedded in the ground of the field to be ploughed at a depth of about 18 inches in a series of loops A, B, C &c. (see Fig. 5) and energized from a source 50. A further wire 51 is embedded at a depth of some 22 inches around the perimeter of the field and is energized from a 4 kc./s. source 55 and this signal controls the raising and lowering of the plough at each side of the field (see below). The tractor is required to start from a point 60, make five circuits of the loop A, using a different head for guidance each time so that five different stretches are ploughed, then five circuits of the loop B in a similar way and so on until a point 70 is reached. The switching to the correct head for a particular circuit is controlled by a counting head 75 mounted on the boom close to the head 1. To start the operation, the tractor moves along the wire 44 under the control of the head 3. Each time the tractor crosses a loop wire the head 75 receives a signal, which is amplified in an amplifier 105 (Fig. 7) and used to actuate a counting uniselector U2. At the fourth signal the uniselector U2 closes a circuit which actuates a uniselector U1, whose closed contacts are changed so that the tractor comes under the control of the head 1. This head turns the tractor to line up on the loop wire A (see Fig. 6) but further contacts now closed on the uniselector U1 bring into operation a delay circuit 152 which is arranged to again actuate the uniselector U1 to transfer control to the head 2, and so on until the tractor moves under the control of the head 5, and ploughs the circuit A in the appropriate position. The control circuitry from the uniselector contacts U1A and U1B includes amplifiers 80, 81; contacts 82, 83 normally in the position shown and coils 85 and 87. These cause an armature 90 to be actuated, energizing either solenoid 33 or 34 to control the steering device 25. The uniselectors are arranged so that after 5 circuits of the loop A the tractor will proceed to the loop B and then to the loop C. After five circuits of C however, it is necessary for the tractor to pass over six wires before starting a circuit of the loop D. Provision for this is made by the uniselector U3 which is allowed to move through its first three positions by a link in the uniselector U2 operated after each 5 circuits of the track. In these three positions, the uniselector U3 allows U2 to operate by means of links between the contacts S11 and S12. When it moves to its fourth position, however, after the fifth circuit of loop C the uniselector U2 is rendered inactive, but the uniselector U3, by means of its connections between the contacts S9 and S10 comes under the control of the head 75 and is advanced once each time the head crosses a wire. After three such crossings the system as a whole is returned to its original condition and the head crosses three more such wires before the uniselector U2 brings the steering pick-up heads into action and the first circuit of the circuit D is commenced. The raising and lowering of the plough at the sides of the field is actuated by means of the head 102, which when it receives a signal from the wire 51 causes relays to be energized which control the motor used to bring about the raising or lowering of the plough. Provision, described in detail and operating similarly, may also be made in the system to steer the tractor round obstacles which may occur in the field, and raise the plough. Alternatively the tractor may be automatically stopped when it reaches an obstacle, or for any reason leaves its proper course with relation to the wire. An alternative embodiment is described wherein only one steering control head is used, but which can be moved along the boom by apparatus controlled by the switching gear to the position required for each circuit. The control signals on the leader wires may be in the form of short pulses of alternating current, to reduce power consumption, or the wires may be energized in separate sections when required.