Patent GB-1055592-A (GB)
Title: Improvements relating to vehicle navigational systems
Inventor: THOMASON ROY
IPC: G05D1/02
Filed: 1962-07-06
Abstract: 1,055,592. Radio vehicle position control. RIPPER ROBOTS Ltd. July 8, 1963 [July 6, 1962], No. 26049/62. Heading H4D. The movement of a vehicle within a designated area is controlled by means of a system comprising two base transmitters positioned on either side of the area and radiating phase comparison signals to define in the space between the transmitters at least one line along which the phase difference between the signals is constant at a predetermined value, means being provided to vary the phase of one of the comparison signals to vary the position of the line, and receiving means on the vehicle responsive to the phase difference between the received signals to provide an indication of the vehicle's position relative to the line, whereby information is provided on the vehicle enabling the movement of the vehicle to be controlled relative to the varying position of the line. The information may be fed to an automatic control system whereby the vehicle position can be remotely controlled, or the information may be made available to a human pilot directing the vehicle in the form of a phase difference indication on a centre zero phase difference meter wherein the pilot directs the vehicle to maintain a zero phase difference indication. In one embodiment, Fig. 1, a first base transmitter 1, transmits a signal of frequency F1 whilst the second transmitter 2, transmits a signal of a harmonically related frequency F2. The signal from transmitter 1 is received at the site of transmitter 2, by a receiver 3, and is passed via a phase shifter 4 to control the phase of the signal transmitted by transmitter 2. The phase shift introduced by the phase shifter 4 is controlled by a signal from a phase detector 6, which produces a control signal in dependence on a positional demand signal on line 7. The positional demand signal thus controls the phase of the control signal fed to transmitter 2, which in turn controls the phase of the F2 signal and the spatial position of the equiphase difference line. The F2 signal may also be modulated by means 8 to convey manoeuvre demand signals to the vehicle. The phase shifter 4, may comprise,- Fig. 12 (not shown), two phase shift networks 65 and 67, introducing phase shifts of + 45 degrees and- 45 degrees respectively in the signal from receiver 3, to produce two signals in quadrature. These two signals are fed via variable gain amplifiers 66 and 68 to vector addition circuit 69. The summation output of the vector addition circuit 69 has a phase relative to that of the signal from receiver 3 depending on the relative amplitudes of the two added signals. The gain of amplifiers 66 and 68 is therefore controlled by signals from phase detector 6, such that the required phase shift is produced. The vehicle equipment comprises receivers 10 and 11 respectively receiving the signals at frequencies F1 and F2. The two received signals are converted to signals of equal frequency by frequency changers 12 and 13, for phase comparison in detector 14. The output of the detector may, as stated, be used in remote control system or to provide a visual indication for a pilot. The signal from frequency changer 13 is also passed to a demodulator 15 to extract the manoeuvre demands. In an alternative embodiment, Fig. 2 (not shown), the two transmitters may transmit carriers of different frequencies, transmitter 1 being modulated by a first phase comparison signal, and transmitter 2 being modulated by a signal of the same frequency as the first comparison signal but phase shifted relative thereto. The vehicle equipment comprises two demodulators at the outputs of the two receivers. Fig. 3 (not shown) illustrates the use of the invention in the control of a crop spraying aircraft C over a rectangular field wherein the frequency of the phase comparison signal is such that many lines of zero phase difference are produced over the field between the two transmitters 1 and 2, as shown. The aircraft is directed along a first zero phase difference line FG, until it receives a command signal to stop or hover at point G at the edge of the field. The phase comparison signal from one of the stations now undergoes a 360-degree phase change, thus causing the aircraft to move in the directions GH to maintain the zero phase difference relationship. The aircraft now travels back over the field along path HE, I, the distance EF being equal to half the wavelength of the phase comparison signal. Where the frequency of the phase comparison signal is such that only one zero phase difference line can be placed within the area of the field, the shift along path GH can be accomplished by a small phase shift of one of the transmitted signals. If it is required to keep the aircraft aligned along one of the equi-phase difference paths, two receiving aerials 35 and 36, Fig. 8 (not shown), may be provided on the aircraft, one at its head (36), one at its tail (35). The outputs from the two phase detectors 40 and 41 are compared in comparator 42, which will give a zero output when the aircraft is correctly aligned along the path. The individual outputs of the phase detectors may be used to determine which equi-phase difference path the aircraft is aligned along. In another embodiment, Fig. 5 (not shown) the transmitters 1 and 2 transmit alternately, and only one aerial and receiver is used on the aircraft for both transmissions. Reception of the first transmission causes a signal to be transmitted from the aircraft to the second transmitter to cause it to transmit in turn. The phase detector, having two inputs switched in synchronism with the reception of the two transmissions, has a long enough time constant for the discontinuous effect of the received signals to be negligible. If a point is to be defined on the path of the aircraft, three base transmitters may be used to provide two lines of equi-phase difference, intersecting at the desired point. The two lines may be provided by switching in suitable control voltages to the transmitter phase shifters. When it is desired that the aircraft follow nearly straight paths, the transmitters 1 and 2, Fig. 10, may be positioned at one side of the field and the control voltage on positional demand signals to the transmitter phase shifters may vary in an inverse hyperbolic manner such that the aircraft exactly follows the straight path 50 to 52, Fig. 10 (not shown), or the control voltage may be stepped or it may be exponential from a resistance capacitor circuit. whereby the aircraft follows the path 50 to 54. When it is desired to know when the aircraft has reached the end of one path the beam from an energy source such as infra-red, light, sound or radio waves to a suitable detector may be interrupted by the aircraft, or a beam from source of energy on the aircraft may fall on detector.