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1. Different running performance
The control of stepper motor is open-loop control. If the starting frequency is too high or the load is too large, it may cause step loss or stalling. When the speed is too high, it may cause overshoot. Therefore, to ensure its control accuracy, it should be handled properly. Speed issues. The AC servo drive system is closed-loop control. The driver can directly sample the feedback signal of the motor encoder. The position loop and speed loop are formed internally. The module slide table generally does not experience step loss or overshoot of the stepper motor. Control performance More reliable.
2. Different overload capacity
Stepper motors generally do not have overload capability. AC servo motor has strong overload capacity. Take Panasonic AC servo system as an example, it has speed overload and torque overload capabilities. Its large torque is three times the rated torque, which can be used to overcome the inertia moment of the inertia load at the moment of starting. Because stepping motors do not have such an overload capability, in order to overcome such inertia moments during selection, a motor with a larger torque is often required, and the machine does not need such a large torque during normal operation, and a torque appears. Waste.
3. Different control accuracy
The step angles of two-phase hybrid stepping motors are generally 3.6 ° and 1.8 °, and the step angles of five-phase hybrid stepping motors are generally 0.72 ° and 0.36 °. There are also some high-performance stepper motors with smaller step angles. For example, a stepping motor for slow-walking machine tools produced by Stone Co., Ltd. has a step angle of 0.09 °; the three-phase hybrid stepper motor produced by BERGER LAHR can pass the step angle The DIP switches are set to 1.8 °, 0.9 °, 0.72 °, 0.36 °, 0.18 °, 0.09 °, 0.072 °, 0.036 °, and are compatible with the step angles of two-phase and five-phase hybrid stepping motors.
4. Speed response module slide table performance is different
It takes 200 to 400 milliseconds for a stepper motor to accelerate from standstill to a working speed (generally several hundred revolutions per minute). The AC servo system has better acceleration performance. Taking Panasonic's MSMA 400W AC servo motor as an example, it only takes a few milliseconds to accelerate from standstill to its rated speed of 3000 RPM, which can be used for control occasions that require rapid start-stop.
5. Different low frequency characteristics
Stepping motors are prone to low frequency vibration at low speeds. The vibration frequency is related to the load and the performance of the driver. Generally, the vibration frequency is considered to be half of the motor's no-load take-off frequency. This low-frequency vibration phenomenon, which is determined by the working principle of the stepper motor, is very unfavorable to the normal operation of the machine. When the stepper motor works at low speed, the module sliding table application mode should generally use damping technology 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 module sliding table is equipped with an AC servo system with a resonance suppression function, 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 system adjustment.
6.Different torque frequency characteristics
The output torque of a stepping motor decreases with the increase of the speed, and it will decrease sharply at a higher speed, so its high working speed is generally 300 ~ 600RPM. The AC servo motor has constant torque output, that is, it can output rated torque within its rated speed (generally 2000RPM or 3000RPM), and constant power output above the rated speed.