The drive unit for medium-speed wire EDM consists of two parts: the drive unit and the motor. Therefore, the selection of the drive unit mainly depends on the selection of the drive unit, because the motor is a common component, and the performance difference only exists between different manufacturers and different models.
Stepper motors can be mainly classified into three categories: reactive stepper motors, hybrid (also known as permanent magnet reactive) stepper motors, and servo motors. Reactive stepper motors have no rotor windings; stepping is achieved by the reactive torque generated by the energized stator windings. Hybrid stepper motors use permanent magnets in their rotors; stepping is achieved by the electromagnetic torque generated by both the energized and permanent magnets. Stepper motors are controlled by pulses; changing the energizing sequence changes the motor's rotation direction, and changing the pulse frequency changes the motor's speed. Stepper motors have a certain step pitch accuracy and no cumulative error. However, stepper motors have low efficiency, limited load-driving capacity, limited pulse equivalent, and a narrow speed range. Currently, stepper motors are available in two-phase, three-phase, and five-phase configurations, with five-phase stepper motors being the most commonly used. While stepper motors held a large market share in the past, they are gradually being replaced by servo motors.
Currently, the most commonly used servo motors are AC servo motors. An optical encoder is mounted on the motor shaft end, which detects the rotor angle for frequency conversion control. Servo motors can operate smoothly from the lowest to the highest speed with minimal torque fluctuation. Servo motors have a long overload capacity, low rotational inertia, and high stall torque. They also have a very low starting frequency, allowing them to quickly accelerate from the lowest speed to the rated speed.
