Five phase and ten beat stepper motor is used on stepping wire cutting machine. The rotation angle is controlled by controlling the number of pulses, and the step angle is generally 0.36 °. Therefore, the pulse (0.001mm) sent out by the CNC system corresponds to a step angle, so it needs to be completed through the reducer gearbox. The open-loop control is adopted in the stepping wire cutting machine, but there is no feedback signal. The motor does not know the specific position it has reached, and the position accuracy is not high enough. At the same time, there is no overload capacity, the motor force is not enough will block the rotation, so when the speed is too high, there will be overshoot phenomenon, easy to cut scrap workpiece.
AC servo motor is used in servo wire cutting machine, and its precision control is guaranteed by rotary encoder. The accuracy of the 17 bit encoder is 0.0027 ° and the driver pulse equivalent is 360 ° / 131072 = 9.89 seconds (each received 217 = 131072 pulses, the motor rotates one circle), which is also controlled by the number of pulses. Each rotation angle of the servo motor will send out a corresponding number of pulses. At the same time, the driver will also receive the feedback signal, which is compared with the pulse received by the servo motor. In this way, the system will know how many pulses are sent to the servo motor and how many pulses are received, it can be very accurate control motor rotation, so as to achieve accurate positioning, can reach 0.001mm. The control performance is more reliable and the precision is higher than that of step and closed-loop step.
