1. Different operating performance

The control of the stepper motor is open-loop control. If the starting frequency is too high or the load is too large, it is easy to lose steps or stall. When the speed is too high, it is easy to cause overshoot. Therefore, in order to ensure its control accuracy, it should be handled properly. Ascending and decelerating problems. The AC servo drive system is closed-loop control, the drive can directly sample the feedback signal of the motor encoder, and the position loop and speed loop are formed internally. more reliable.

2. Different overload capacity

Stepper motors generally do not have overload capability. AC servo motors have strong overload capacity. Take the Panasonic AC servo system as an example, it has speed overload and torque overload capabilities. Its maximum torque is three times the rated torque, which can be used to overcome the inertial moment of inertial load at the moment of starting. Because the stepping motor does not have such overload capacity, in order to overcome this inertia moment, it is often necessary to select a motor with a larger torque, and the machine does not need such a large torque during normal operation, so the torque appears. wasteful phenomenon.

3. Different control precision

The step angle of the two-phase hybrid stepping motor is generally 3.6° and 1.8°, and the step angle of the five-phase hybrid stepping motor is generally 0.72° and 0.36°. There are also some high-performance stepper motors with smaller step angles. For example, a stepping motor produced by Stone Company for slow wire-feeding machine tools has a step angle of 0.09°; a three-phase hybrid stepping motor produced by BERGER LAHR in Germany has a step angle that can pass through The DIP switch is set to 1.8°, 0.9°, 0.72°, 0.36°, 0.18°, 0.09°, 0.072°, 0.036°, which is compatible with the step angle of two-phase and five-phase hybrid stepping motors.

4. The performance of the speed response module slide is different

It takes 200 to 400 milliseconds for a stepping motor to accelerate from a standstill to a working speed (usually several hundred revolutions per minute). The acceleration performance of the AC servo system is good. Taking the Panasonic MSMA 400W AC servo motor as an example, it only takes a few milliseconds to accelerate from standstill to its rated speed of 3000RPM, which can be used for control occasions requiring rapid start and stop.

5. Different low frequency characteristics

The stepper motor is prone to low frequency vibration at low speed. The vibration frequency is related to the load condition and the performance of the drive, and it is generally considered that the vibration frequency is half of the no-load take-off frequency of the motor. This low-frequency vibration phenomenon determined by the working principle of the stepping motor is very detrimental to the normal operation of the machine. When the stepper motor works at low speed, damping technology should generally be used in the module slide application mode to overcome the low frequency vibration phenomenon, such as adding a damper to the motor, or using subdivision technology on the driver.

The AC servo motor runs very smoothly and does not vibrate even at low speeds. The AC servo system of the module slide table has the function of resonance suppression, which can cover the lack of rigidity of the machine, and the system has a frequency analysis function (FFT), which can detect the resonance point of the machine and facilitate the system adjustment.

6. Different moment-frequency characteristics

The output torque of the stepping motor decreases with the increase of the speed, and will drop sharply at a higher speed, so its high working speed is generally 300-600RPM. The AC servo motor has a constant torque output, that is, within its rated speed (generally 2000RPM or 3000RPM), it can output the rated torque, and above the rated speed, it is a constant power output.

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