System for detecting mechanical movement

A system for detecting mechanical movement of a body under detection comprising:

• a synchro generator having multiple-phase primary windings and a secondary winding, either of the primary windings or the secondary winding capable of being coupled to said body,
• an exciting circuit for providing multiple-phase, sinusoidal exciting voltages to said primary windings,
• said secondary winding inducing a sinusoidal signal when said primary windings are excited,
• a reference signal generator for providing a first set of two-phase, reference sinusoidal signals of a predetermined frequency,
• a phase-shifting circuit receiving the signal induced in said secondary winding and producing a phase-shifted signal having a phase 90.degree. different from the induced signal,
• a phase comparator for comparing the first set of the two-phase reference sinusoidal signals and a second set of two-phase signals consisting of the induced signal and the phase-shifted signal and producing a phase difference signal indicative of the phase difference between the two sets of signals,
• first means responsive to the phase difference signal for producing pulses at a frequency corresponding to the phase difference,
• a frequency-divider counting said pulses and producing a first digital signal indicative of the count value at each moment,
• said exciting circuit being responsive to the first digital signal from the frequency-divider for determining the instantaneous values of the exciting voltages at each moment,
• said synchro generator, said reference signal generator, said phase-shifting circuit, said phase comparator, said frequency-divider and said exciting circuit forming a phase-locked-loop controlling the induced voltage so as to be in phase with the reference signals, and
• second means responsive to the phase-locked-loop for producing a second digital signal relating to the movement of said body under detection.