GB999919A - Servo control system and apparatus therefor - Google Patents

Abstract

999,919. Change-speed control. FLIGHT REFUELLING Ltd. June 12, 1964 [June 23, 1963], No. 15997/63. Heading F2D. [Also in Division G3] A variable-speed gear servocontrol system includes servo means operatively coupled to the gear, means for producing electric signals indicative of any difference between a predetermined and the actual value of a parameter of the system, e.g. output speed or gear ratio, and electronic control means responsive to the signals for effecting control of the servo unit and of the gear. In the arrangement shown for controlling the output speed of a gear unit 1 speed-proportional signals derived from the output shaft 4 by a tachometer and reference signals from a source 9, such as a potentiometer, are fed to a differential amplifier 8. The amplified error signals are fed to pulse generators 11, 12 connected to the servo unit 13 which regulates the setting of a ratio control shaft 14 for the gear unit 1. A control loop 16 between the servo unit 13 and the amplifier 8 prevents hunting. If the speed of the gear input shaft 3 is substantially constant control signals may be taken from the regulator shaft 14 to control the ratio of the gear unit 1, Fig. 2 (not shown). Circuit details.-The amplifier 8 preferably includes a pair of PNP transistors in long-tailed pair connection, the tail of the pair using a further transistor with large emitter resistance and with the base clamped to a Zener diode. The pulse generators 11, 12 operate individually according to the sense of the error signal and each includes a PNP transistor with the base connected to the collector of one of the amplifier transistors and the amplified current is used to positively charge a capacitor connected to the emitter electrode of a unijunction transistor. Servo unit 13 is preferably a motor of the D.C. shunt wound commutator type with an integral worm gear for operating regulating shaft 14, the armature being supplied through a pair of parallel-connected silicon controlled rectifiers arranged in opposition and the conducting angle of which is varied to increase stability. Control loop 16 is a derivative feedback loop in which a smoothed portion of the servomotor armature voltage is fed back to the emitters of the amplifier to oppose the applied error voltage, the correction speed decreasing with the error signal to minimize overrun and hunting.