GB1208479A - Improvements in or relating to electronic synchronizing systems - Google Patents

Abstract

1,208,479. Automatic speed control. MAGNAVOX CO. Aug. 1, 1968 [Aug. 17, 1967], No. 36706/68. Heading G3R. In a system for synchronizing the drive motors of facsimile transmission equipment, the receiver drive motor is retroactively controlled until the phase error is reduced below a predetermined value and is thereafter driven by a constant frequency source. The motors are synchronous types and each drives a pulse generator whose output is indicative of the speed and position of the motor. The two pulse outputs are compared in a logic circuit 14 and a control signal generated in the form of a train of pulses whose width is a measure of the phase difference between the drive motors. This control signal is used to gate a counter 34 so that the counter is reset to zero at the beginning of each control pulse and then counts from a clock 32 for the duration of the control pulse. The value on the counter is read by a converter 35 which generates both a speed up and a slow down signal, each dependent upon the phase difference. The appropriate one of these is selected by a series of gates 36-39 and applied to a voltage controlled oscillator 17 feeding the receiver motor. When synchronism is achieved the control pulses disappear and a two stage counter 43 is enabled to begin counting pulses from the receiver pulse generator. When three consecutive control pulses have not appeared a selector 19 switches the motor supply from the voltage controlled oscillator 17 to a fixed frequency oscillator. In an alternative arrangement Fig. 6 (not shown), the control pulses are applied with other pulses from a crystal oscillator to an integrator the output of which controls the frequency of a voltage controlled oscillator feeding the receiver motor. When the control pulses diappear the voltage controlled oscillator continues to run, but in phase synchronism with the crystal oscillator so that no irregularity due to switching is introduced. A short while after synchronism is achieved or after a longer time even if synchronism is not achieved the control signal generator is blocked and thereafter the motor runs only under the control of the crystal oscillator.