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Difference between stepper motor and servo motors
- Dec 02, 2017 -

Stepper motor is the electrical pulse signal into angular displacement or linear displacement of the open-loop control element stepper motor parts in the case of non-overload, the motor speed, stop the position depends only on the pulse signal frequency and the number of pulses , Regardless of load changes. When the stepper driver receives a pulse signal, it drives the stepping motor to rotate in a fixed direction by a fixed angle, called "step angle". Its rotation is based on a fixed The point of view of the step by step operation. You can control the number of pulses to control the amount of angular displacement, so as to achieve the purpose of accurate positioning, at the same time by controlling the pulse frequency to control the motor speed and acceleration of rotation, so as to achieve high-speed purpose.

    Servo motor, also known as the implementation of the motor, in the automatic control system, as the implementation of components, the received electrical signal into the motor shaft angular displacement or angular velocity output. The rotor inside the servo motor is a permanent magnet. The U / V / W three-phase power controlled by the driver forms an electromagnetic field. The rotor rotates under the action of the magnetic field. At the same time, the feedback signal from the motor comes from the encoder to the driver. The values are compared to adjust the angle of rotation of the rotor. The accuracy of the servo motor depends on the accuracy of the encoder (number of lines). That is to say, the servo motor has the function of sending a pulse. Each rotation of an angle causes a corresponding number of pulses to be generated. Thus, the pulse of the servo driver and the servo motor encoder Echo, so it is closed-loop control, stepper motor is open-loop control.

    The difference between stepper motor and servo motor is:

1, different control accuracy. Stepper motor phase and the more the number of shots, the higher its accuracy, take the block servo motor comes with the encoder, the more the encoder scale, the higher the accuracy.

2, different control methods; one is open-loop control, one is closed-loop control.

3, low-frequency characteristics are different; stepping motor prone to low-frequency vibration at low speeds, when it works at low speed damping technology or subdivision generally used to overcome the phenomenon of low-frequency vibration, servo motor operation is very smooth, even at low speed Will appear vibration phenomenon. AC servo system with resonance suppression function can cover the lack of mechanical rigidity, and the system has a frequency analysis function (FFT), can detect the mechanical resonance point to facilitate system adjustment.

4, different frequency characteristics; stepper motor output torque will increase with the speed down, AC servo motor output for the constant torque,

5, different overload capacity; stepper motor generally does not have overload capacity, while the AC motor has a strong overload capacity. 6, different operating performance; stepper motor control for the open-loop control, the starting frequency is too high or too large load easily lost or blocked stall phenomenon, excessive speed prone to overshoot overshoot, AC servo drive system for the closed-loop Control, the driver can directly sample the motor encoder feedback signal, the internal structure of the position loop and speed loop, generally do not appear stepping motor lost or overshoot phenomenon, the control performance is more reliable.

7, the speed response performance is different; stepper motor speed from rest to work speed needs hundreds of milliseconds, and AC servo system acceleration performance is good, usually only a few milliseconds, can be used for quick start and stop control occasions.

    In summary, the AC servo system in many performance advantages over the stepper motor, but the price is not the same.

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