Patent GB-1220626-A (GB)
Title: Despin control system
Inventor: MEARS CARLETON MARCHAND JR
IPC: H01Q1/18
Filed: 1968-07-09
Abstract: 1,220,626. Automatic attitude control. HUGHES AIRCRAFT CO. July 9, 1968 [July 31, 1967], No.32766/68. Heading G3R. A moving body e. g. a satellite, comprises a rotor mounted on a platform which is maintained in a desired angular position despite reaction forces imparted thereto from the rotor by a control system which consists of means mounted on the platform and rotor for generating a master index pulse for each complete revolution of the rotor relative to the platform, means mounted on the rotor for generating a leading edge pulse when the rotor is oriented with one boundary of a region, the centre of which is the desired angular position, and a trailing edge pulse when the rotor is aligned with the other boundary, and means responsive to the time of occurrence of the master index pulse relative to the leading and trailing edge pulses for generating a deviation error signal which is fed to means for returning the platform towards its desired position. A bolometer carried by the rotor senses the boundaries of the earth and the leading and trailing edge pulses are fed from earth sensor 20 to sensor processing circuit 32 which is also fed with a master index pulse from a magnetic pulse generator 26, 28 on the platform and rotor. The output is fed through shaping circuit 36 and summing circuit 38 to motor control circuit 40 which controls an electric motor 22 or fluid jets 22 to return platform 12 to its desired position. The sensor processing circuit 32 (Fig. 5) comprises a flip-flop 43 which is set by a leading edge impulse from earth sensor 20 to enable an integrator 44 to commence integrating the output of a one shot circuit 41. The waveform of the integrator is positive going until the arrival of a master index pulse from pulse source 26, 28 whereupon it becomes negative going. The integrator 44 is turned off by the trailing edge pulse which resets flip-flop 43 and the final output of the integrator is applied to a summing circuit 46 which compares it with a desired level provided by a bias circuit 48. The output of the circuit 46 is applied to a gate 50 which is enabled by resetting of flip-flop 43. The signal from gate 50 is the deviation error signal. A shaft angle encoder 34 and counter and logic circuits 42 are optionally provided to provide a deviation rate error signal which is combined with the error signal in summing circuit 38. The shaft angle encoder comprises a voltage controlled oscillator which generates a predetermined number of pulses for each revolution of the rotor. The encoder includes a counter which is reset to zero by successive leading edge pulses from the earth sensor. If the counter completes its count coincidentally with the arrival of a leading edge pulse the oscillator frequency is unaltered. Should the completion of the count occur before or after the next leading edge pulse the voltage control circuit of the oscillator is energized to raise or lower the oscillator frequency. The output of the oscillator is fed through a frequency divider to a further counter which automatically resets when full in response to further pulses from the divider. The counter has a capacity of 1024 and is provided with three outputs, one corresponding to a count of 1020 which generates a resetting pulse, one to 1023 and one to 1024. If the count output 1023, corresponds to the occurrence of a master reference pulse an AND gate is enabled which sets off a flip-flop which enables a further AND gate to apply a correcting bias voltage to the motor control circuit. If the master index pulse occurs after the 1024 count, the 1024 output which includes a one-shot delay circuit, applies a pulse coincidentally with master index pulse to apply a correcting voltage to the motor controller through similar circuitry to that described for the 1023 output.