The step motor which has been used in the digital servomechanism is the so-called exciting phase control type step motor, in which the stator windings are excited in sequence on the arrival of each input pulse, attracting the rotor.
However, in this paper, the rotating magnetic field type step motor is newly suggested. In this new step motor, both the stator and the rotor possess rotating magnetic field which rotates in the same direction with the same angular velocity. By the digital control of the phase of this rotating magnetic field, a universal motor possessing the wound rotor and stator is driven as a step motor with the following advantages.
(1) When one input pulse arrives, the rotating angle of the rotor that corresponds to this input pulse can be controlled by the simple electric circuit, and therefore this angle can easily be varied in a wide range.
(2) The heat loss at the time of light-load, compared with the conventional step motor, is extremely small. Especially, at standstill and no load (when output torque is zero), the electric current in the step motor is the exciting current only, so the heat loss of this motor is negligible.
(3) By the use of a universal wound-rotor induction motor, a high power step motor can easily be obtained.
In this paper, the principles of the new step motor and the control circuit are discussed. By using the control circuit, the resolver replacing the low power wound-rotor type induction motor was driven as a step motor. The results of this experiment were successful.