The main difference between stepper motors and servo motors

Various motors are needed in many fields, including the well-known stepper motors and servo motors. However, for many users, they do not understand the main differences between these two motors, so they always do not know how to choose. So, what are the main differences between stepper motors and servo motors?

Basic structure

▲Stepper motor structure diagram

▲Servo motor structure diagram

The differences are briefly described below:

1. Working Principle

There are great differences in the principles of these two motors. The stepper motor is an open-loop control element that converts electrical pulse signals into angular displacement or linear displacement. Check out the working principle of the stepper motor.

The servo mainly relies on pulses for positioning. The servo motor itself has the function of sending pulses, so every time the servo motor rotates one angle, it will send out a corresponding number of pulses. This forms an echo with the pulses received by the servo motor, or a closed loop. In this way, the system will know clearly how many pulses have been sent and how many pulses have been received, thereby being able to accurately control the rotation of the motor and achieve precise positioning.

2. Control accuracy

The accuracy of a stepper motor is generally achieved through precise control of the step angle. The step angle has a variety of different subdivisions to achieve precise control.

The control accuracy of the servo motor is guaranteed by the rotary encoder at the rear end of the motor shaft. Generally, the control accuracy of the servo motor is higher than that of the stepper motor.

3. Speed ​​and overload capacity

When stepper motors are running at low speed, they are prone to low-frequency vibration. Therefore, when stepper motors are working at low speed, damping technology is usually required to overcome the low-frequency vibration phenomenon, such as adding a damper to the motor or using subdivision technology on the driver, etc., while servo motors do not have this phenomenon. Its closed-loop control characteristics determine that it maintains excellent performance at high speeds. The torque-frequency characteristics of the two are different. Generally, the rated speed of servo motors is greater than that of stepper motors.

The output torque of a stepper motor decreases as the speed increases, while the servo motor outputs a constant torque. Therefore, stepper motors generally have no overload capacity, while AC servo motors have a stronger overload capacity.

4. Operational performance

Stepper motors are usually open-loop controlled. If the starting frequency is too high or the load is too large, they may lose steps or stall. Therefore, you need to handle the speed problem or add encoder closed-loop control when using them. Check what is a closed-loop stepper motor. Servo motors use closed-loop control, which is easier to control and does not cause loss of steps.

5. Cost

Stepper motors have advantages in terms of cost performance. To achieve the same function, the price of a servo motor is higher than that of a stepper motor of the same power. The advantages of servo motors, such as high response, high speed and high precision, determine the high price of the product, which is inevitable.

In summary, stepper motors and servo motors have great differences in terms of working principle, control accuracy, overload capacity, operating performance and cost. However, each has its own advantages. If users want to make a choice between them, they need to combine their actual needs and application scenarios.