Patent GB-1410774-A (GB)
Title: Method and device for the transmission of control commands via radio links
IPC: G05D1/00
Filed: 1972-09-18
Abstract: 1410774 Control of D.C. motors WITEFI ANSTALT 18 Sept 1972 [17 Sept 1971] 43198/72 Heading H2J [Also in Division H4] In a remote control system, e.g. for controlling a vehicle, the control commands are transmitted as pairs of different frequencies pulse modulating a radio-frequency carrier, the command signals being grouped into mutually exclusive pairs (e.g. forward and reverse or left turn and right turn) and the pulses of each frequency pair being width-modulated in complementary manner, the greater pulse width of a pair denoting the command and the pulse width ratio denoting the analogue value. Transmitter.-The R.F. carrier is generated at HFS, Fig. 1, and supplied via driver TSt and amplifier SVr to the aerial. A multivibrator MVo provides time intervals ZT, Fig. 2, for the transmission of pairs of commands and triggers a bi-stable FF which in one position controls monostables MV1, MV2, and in the other, monostables MV3, MV4. The pulse durations at the outputs of the monostable pairs are controlled in complementary manner, Fig. 2, as required, by variable resistors R1, R2 respectively. In their stable states, the monostables connect in via switches S1 to S4 respectively, the low frequency generators TonS1 to TonS4, the generators corresponding to a pair being connected successively. The sequence of each pair of frequencies is changed at each transmitting time interval to provide balanced demodulation at the receiver. The outputs of generators TonS1 to TonS4 modulate the RF carrier via amplifier MVr. A plurality of different RF carriers may be modulated in similar manner. Receiver.-The signals are received by a conventional superheterodyne receiver and after demodulation at DM, Fig. 3, are supplied to filters F1 to F4. The filter pairs F1, F2 and F3, F4 are coupled to discriminators DK1, DK2 respectively, Fig. 4 (not shown), which each derive a control signal of a polarity which identifies the command and an amplitude defining the value. These signals, via amplifiers Vr1, Vr2 control motors M1, M2 respectively. Motor control circuits.-As described the two control signals RS1, RS2, Fig. 5, control the driving motor M1 and steering motor M2 respectively. Motor M1 can be connected to either + 6 V or -6V supply via switching transistor T16 or T17 respectively under the control of transistors T13, T14, T15 and differential amplifier T11, T12. Signal RS1 provides the input for amplifier T11, T12 the polarity of the output signal determining which transistor T16 or T17 is switched and hence the direction of motion, and the amplitude the degree of drive of these transistors and hence the r.p.m. In the initial position with equal pulse durations of the two signals of the pair the motor is at rest. The signal RS2 is compared at D with the voltage derived from a potentiometer RG which is driven by the motor M2 and may be positive or negative in accordance with the position of the motor. The output of the comparator switches one or other of transistors T18, T19 to adjust the motor in the appropriate direction according to the polarity of the output, the amplitude of the output determining the speed of rotation. When the two inputs to the comparator become equal the motor is stopped.