Method and apparatus for controlling the rotational speed and phase of synchronous motors

Apparatus for controlling the rotational speed and phase of a synchronous motor having a rotor with at least one pair of poles and a stator with at least one field coil, to which acceleration driving or braking driving pulses are applied, comprising:

• a sensor coil, having an output, coupled with the stator capable of being influenced by the rotor and for providing sensor signals of a frequency proportional to the rpm of the rotor;
• comparator means, having an output, connected to said output of said sensor coil for converting said sensor signals into rectangular sensor pulses;
• a pulse generator, having an output, for generating control pulses of constant frequency and width;
• and
• a phase comparator means, having an output, and including means for generating driving pulses at said output, connected to the field coil, said driving pulses being synchronized with said sensor pulses, said phase comparator means being connected to said output of said comparator means and said output of said pulse generator, for comparing said sensor pulses with said control pulses as to phase and pulse width, wherein if a positive phase shift (poles lagging) results, accelerating driving pulses are generated of a time duration in proportion to that phase shift, if a negative phase shift (poles leading) results, braking driving pulses are generated of a time duration in proportion to that phase shift.