Stepper motor is an open-loop control element stepper motor that converts electrical pulse signals into angular displacement or linear displacement. In the case of non-overloading, the speed and stop position of the motor only depend on the frequency and number of pulses of the pulse signal. , and is not affected by the load change, when the stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle in the set direction, called "step angle", its rotation is fixed The angle is run step by step. The angular displacement can be controlled by controlling the number of pulses, so as to achieve the purpose of accurate positioning. At the same time, the speed and acceleration of the motor rotation can be controlled by controlling the pulse frequency, so as to achieve the purpose of high speed.

Servo motor, also known as executive motor, is used as an executive element in an automatic control system to convert the received electrical signal into angular displacement or angular velocity output on the motor shaft. The rotor inside the servo motor is a permanent magnet. The U/V/W three-phase electricity controlled by the driver forms an electromagnetic field. The rotor rotates under the action of this magnetic field. At the same time, the encoder that comes with the motor feeds back the signal to the driver. Values are compared, and the angle of rotation of the rotor is adjusted. The accuracy of the servo motor is determined by the accuracy (number of lines) of the encoder, that is to say, the servo motor itself has the function of sending out pulses. Every time it rotates an angle, it will send out a corresponding number of pulses, so that the pulses of the servo drive and the encoder of the servo motor are formed. It echoes, so it is closed-loop control, and the stepper motor is open-loop control.

The difference between stepper motor and servo motor is: 1. The control precision is different. The more phases and beats of the stepper motor, the higher the accuracy. The servo motor takes the block from the built-in encoder. The more scales of the encoder, the higher the accuracy. 2. Different control methods; one is open-loop control and the other is closed-loop control. 3. The low frequency characteristics are different; the stepper motor is prone to low frequency vibration at low speed. When it works at low speed, damping technology or subdivision technology is generally used to overcome the low frequency vibration phenomenon. The servo motor runs very smoothly, even at low speed. Vibration will occur. The AC servo system has the function of resonance suppression, which can cover the lack of rigidity of the machine, and has a frequency analysis function (FFT) inside the system, which can detect the resonance point of the machine and facilitate the system adjustment. 4. The torque-frequency characteristics are different; the output torque of the stepper motor will decrease with the increase of the speed, and the AC servo motor is a constant torque output. 5. The overload capacity is different; the stepper motor generally does not have the overload capacity, while the AC motor has a strong overload capacity. 6. The operating performance is different; 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. The AC servo drive system is closed-loop. Control, the driver can directly sample the feedback signal of the motor encoder, and form a position loop and a speed loop internally. Generally, the phenomenon of step loss or overshoot of the stepping motor will not occur, and the control performance is more reliable. 7. The speed response performance is different; it takes hundreds of milliseconds for the stepper motor to accelerate from standstill to the working speed, while the acceleration performance of the AC servo system is better, generally only a few milliseconds, which can be used for control occasions requiring rapid start and stop.

To sum up, AC servo systems are superior to stepper motors in many performance aspects, but the price ratio is not the same.