In the previous article we mainly introduced the composition of the CNC milling machine spindle motor, today we come to explore the operating principle of the spindle motor and frequency control mode.
CNC milling machine three-phase AC induction motor operating principle is shown in the figure.
Three-phase AC asynchronous motor stator winding into the three-phase AC generated after the rotating magnetic field, the speed no known as the synchronous speed. no = 60f/p, p for the stator winding pole pairs, f for the stator winding power supply frequency, change f to change no. The rotating magnetic field cuts the guide bar in the rotor core and generates an induced current in the guide bar. In this way, the rotor bar with induced current interacts with the rotating magnetic field to generate electromagnetic torque, and the rotor rotates with the rotating magnetic field at the rotational speed nM under the action of the electromagnetic torque. Because the motor running state when the rotor speed can only be less than the synchronous speed, so called asynchronous motor; and because the rotor bar in the current from the rotating magnetic induction, it is also known as induction motor. When the power frequency f decreases, the rotating magnetic field speed no decreases, but because of the rotor mechanical inertia, the rotor speed nM instantly remain unchanged, at this time, the rotor speed is greater than the rotating magnetic field speed, the motor is in the power brake state, the motor winding flows out.
2. Frequency control
Changing the power frequency of the milling machine spindle motor can realize the speed regulation of the motor. Three-phase AC induction motor frequency conversion speed is usually U/f and vector control. In order to meet the requirements of the three-phase AC asynchronous motor stator winding electromagnetic frequency requirements, in the rated frequency (50Hz) below the frequency control, change the frequency f at the same time also change the stator voltage U, and keep the voltage / frequency is not change. In this speed range, the maximum electromagnetic torque remains constant and constant torque is achieved. Rated frequency above the frequency control, the stator winding voltage U to maintain the rated voltage (380V) unchanged. In this speed range, the electromagnetic torque decreases with the frequency rise, and the electromagnetic power unchanged, to achieve constant power speed, as shown.
The above is a brief introduction about the CNC milling machine spindle motor operation principle and frequency control mode.