Stepper motor moves by rotating a fixed angle (called stepping angle) step by step. It doesn’t have accumulative error. Control way is open loop. Stepping motor is run via a stepper motor driver. The driver transforms the pulse signal from the CNC router machine controller into angular displacement of the stepper motor. Or we can say, driver makes stepping motor rotate one stepping angle when it received one pulse from the CNC controller.  So the speed of stepper motor is proportional to the frequency of the pulse signal. Therefore, the motor speed can be controlled accurately via controlling the frequency of the pulse signal; the motor can be precisely positioned via controlling the quantity of the pulse signal.
   

Servo motor rotor is a permanent magnet. Three phase electricity U/V/W (controlled by servo pack) formed electric magnetic field. The rotor turns under the action of magnetic field. Encoder feeds back signal to drive pack and drive pack adjust the angle of rotor according to the compare result of target value and feedback value. So AC servo motor is a closed-loop system. The system will know how many pulses are sent to the servo motor, and how many pulses are received from the encoder, so that the motor rotation can be precisely controlled to achieve accurate positioning. The positioning accuracy is 0.001mm.

                                                                                                  Original article from Jinan EagleTec CNC Machinery Co.,Ltd.

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