What is the difference between a servo motor and a stepper motor?

Stepper motors, like servo motors, are equipped with a mechanism that controls the angle of rotation by receiving external signals. They can perform operations such as device positioning, but have the following differences.

1. Control method

The servo motor detects the rotation position through the encoder (rotation detector) and feeds back the information detected by the encoder to the controller to control the position.

Therefore, it can achieve high-precision stop, even if it is stopped during rotation, it can return to the original position if the position is deviated.

On the other hand, the rotation angle of the stepping motor is proportional to the number of pulses, and the driver controls the position by receiving this pulse signal from the controller.

Therefore, in fact, it does not need a mechanism to detect the position, and it cannot identify the deviation of the position. Therefore, loss of synchronization may occur due to unexpected load fluctuations (a state where the indicated rotation angle is not synchronized with the motor rotation).

①Servo motor
Program→controller (pulse signal)→drive (current conversion)→motor→encoder (encoder signal)→drive (action information)→controller
②Stepper motor
Program→controller (pulse signal)→drive (current conversion)→motor

2. Torque/speed

The servo motor can generate stable torque in both low-speed area and high-speed area, so high-speed operation can be realized. Stepper motors can only generate higher torque in the low-speed area, and reduce the torque in the high-speed area, so they are not suitable for high-speed rotation.

3. Cost

Servo motors need to use expensive rotary encoders and servo control devices (servo drives), which cost more than stepper motors.

4. Speed up performance

It takes 200 to 400 milliseconds for a stepping motor to accelerate from a standstill to a working speed (generally several hundred revolutions per minute). The acceleration performance of the AC servo system is better. It only takes a few milliseconds to accelerate from a standstill to its rated speed of 3000RPM, which can be used in control situations requiring fast start and stop.