The difference between AC servo motor and brushless DC servo motor in function: AC servo is better, because it is sine wave control, and the torque ripple is small. DC servo is trapezoidal wave. But DC servo is simple and cheap.
When the servo motor receives one pulse, it will rotate the corresponding angle of one pulse to realize the displacement. Because the servo motor itself has the function of sending out pulses, the servo motor will send out the corresponding number of pulses for each rotation angle.
In this way, the pulse received by the servo motor forms a echo, or closed loop. the system will know how many pulses are sent to the servo motor and how many pulses are received at the same time. It can accurately control the rotation of the motor, so as to achieve accurate positioning, which can reach 0.001mm.