SPEED DETECTOR USING RESOLVER

PURPOSE:To realize a speed control in a wide range and a position control of high accuracy in an electric motor by setting an excitation frequency of a resolver in its excitation power supply circuit to a high value in a speed control condition and to a low value in a position control condition. CONSTITUTION:In accordance with a speed control operation mode set by an operator, a speed control condition signal 1 is input to a control unit 3 of an electric motor 7. Thus the control unit 3 outputs an excitation frequency instruction signal 4 of excitation frequency fe, determined from a maximum rotary speed, to an excitation power supply circuit 5 of a resolver 8. While in accordance with a position control operation mode set by the operator, the electric motor 7 is decelerated obtaining a low speed thereafter the speed control condition signal 1 is released, and a position control condition signal 2 is input. In this way, the control unit 3 outputs an excitation frequency instruction signal 4 of excitation frequency fe lower than that in the before said speed control condition determined from resolving power of a rotary speed.