Phase lock control system with trajectory correction

Abstract

A phase lock system for locking the output pulses of a motor driven tachometer in phase with reference pulses that recur at a prescribed reference frequency. A phase/frequency detector operates in a frequency mode when there is a frequency difference between the output pulses and the reference pulses so as to generate an error signal indicative of the frequency difference and a saturating amplifier coupled between the phase/frequency detector and the tachometer motor responds to the error signal to provide maximum drive power to the motor so as to vary the tachometer and drive the output pulse frequency toward the reference pulse frequency at a maximum rate. When frequency equality is achieved, the phase/frequency detector operates in a phase mode in which the phase error between the output pulses and the reference pulses is measured at a time when the system is still in saturation because of its high gain. A phase error rate signal is derived from another phase detector responsive to the phase error to produce a counter torque pulse having a duration related to the phase error rate. Such counter torque pulse is applied momentarily to override the effect of the phase error signal so as to drive the saturating amplifier briefly into saturation in the opposite direction as phase lock is approached whereby the motor is slowed as it approaches phase lock in order to assure phase lock without oscillation upon entry into the linear region of the amplifier.