Different control precision.

The step angle of the two-phase hybrid stepping motor is generally 1.8°, 0.9°, and the step angle of the five-phase hybrid stepping motor is generally 0.72°, 0.36°. There are also some high-performance stepper motors with smaller step distances after subdivision. Compatible with step angle of two-phase hybrid stepper motors.

The rotary encoder at the rear end of the motor shaft ensures the control accuracy of the AC servo motor. For a motor with a standard 2000-line encoder, the pulse equivalent is 360°/8000=0.045° due to the quadruple frequency technology used by the driver. For a motor with a 17-bit encoder, the motor rotates one revolution every time the driver receives 131072 pulses, that is, the pulse equivalent is 360°/131072=0.0027466°, which is 1/655 of the stepper motor pulse equivalent of 1.8°.

The low frequency characteristics are different.

Low-speed stepper motors are prone to low-frequency vibration. The vibration frequency is related to the load and driving performance, and it is generally considered that the vibration frequency is half of the no-load take-off frequency of the motor. The low frequency vibration phenomenon determined by the working principle of the stepper motor is very detrimental to the normal operation of the machine. When the stepper motor works at low speed, damping technology is generally used to overcome the phenomenon of low frequency vibration, such as adding a damper to the motor, or using subdivision technology on the driver. AC servo motors do not vibrate even at low speeds. The AC servo system has the function of resonance suppression, which can cover the lack of mechanical rigidity. The system has the function of frequency analysis (FFT), which can detect the mechanical resonance point, which is convenient for system adjustment.

The torque frequency characteristics are different.

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

The overload capacity is different.

Stepper motors generally do not have overload capability. The AC servo motor has strong overload capacity. Its maximum torque is two to three times the rated torque, which can be used to overcome the inertial torque of inertial loads at the moment of startup. Since the stepper motor does not have such overload capability, in order to overcome this inertia torque, 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 there is a waste of torque.

different operational 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 or block the rotation. If the speed is too high when stopped, it is easy to overshoot. Therefore, in order to ensure its control accuracy, the lifting problem should be dealt with. The AC servo drive system is controlled by closed loop. The driver can directly sample the feedback signal of the motor encoder, and internally form a position loop and a speed loop. Generally speaking, the stepper motor will not lose step or overshoot, and the control performance is more reliable.

Different speed response performance.

It takes 200-400 milliseconds for a stepper motor to accelerate from a standstill to a working speed (usually several hundred revolutions per minute). The AC servo system has good acceleration performance and can be used in control occasions that require quick start and stop.