In this paper, the author, deriving new characteristic equations of 2-phase servo-motor consisting of five simultaneous differential-integral equations, gave the relations of reference current i_R(t), control current i_C(t), rotor current distribution i(t, φ), torque T(t) and angular displacement of rotor θ(t).
By solving these equations for the cases when the servo-motor is driven by several types of power sources under the condition that the rotor is stationarily revolving with a constant speed, various characteristics such as the effect of circuit constants on rotor torque, the condition under which a single-phase running does not occur, etc. are studied.
Especially it is emphasized that, in the torque-speed curves, the time-varying torque having a frequency twice as large as the source voltage frequency exists at non-zero speed, and therefore, when the servo-motor is rotating by its own torque, the rotor intrinsically has speed variation whose magnitude will be affected by the rotor inertia.