High control accuracy of AC servo motor or stepping motor

In the field of industrial automation control, the utilization rate of AC servo motor and stepper motor is about the same. The two motors have great similarities in control methods, but in practical applications, there are still great differences in control accuracy between them. For enterprises, is it AC servo motor or stepping motor? Is it AC servo motor with high control accuracy or stepping motor? Together with the small editor of CIIC Electric to understand this problem.

As we all know, the internal rotor of AC servo motor is a permanent magnet. Its working principle is that the rotor rotates under the action of electromagnetic field. At the same time, the encoder of the servo motor will feed back the received signal to the driver. The driver will then compare the feedback value with the target value to adjust the rotation angle of the rotor. The working principle of the stepping motor is to convert the electric pulse signal into the corresponding angular displacement or linear displacement. Every time a pulse signal is input, the rotor will rotate an angle or move forward one step. The output angular displacement or linear displacement is proportional to the number of pulses input, and the speed is proportional to the pulse frequency.

After understanding the working principle of AC servo motor and stepping motor, let's look at the difference in control accuracy between them.

The control accuracy of the AC servo motor is guaranteed by the rotary encoder at the rear end of the motor shaft. Take the AC servo motor of CIIC Electric as an example. For the motor with standard 2500 line encoder, the driver uses quadruple frequency technology, so the pulse equivalent is 360 °/10000=0.036 °, which meets the requirements of high-precision control. The motor rotor is specially processed to improve the response speed. It can support 17 bit/23 bit (131072 line/8388608 line) * * value encoder, which greatly improves the positioning accuracy and low-speed operation accuracy. For the motor with 17 bit encoder, the driver will rotate once every 217=131072 pulses received by the motor, so the pulse equivalent is 360 °/131072=9.89 seconds.

The step angle of two-phase hybrid stepping motor is generally 1.8 ° and 3.6 °, and that of five phase hybrid stepping motor is generally 0.72 ° and 0.36 °. There are also some high-performance stepping motors with smaller step angle after subdivision, reaching 0.09 °. The specific control accuracy is related to this step angle. The smaller the step angle, the higher the control accuracy. It is compatible with the step angle of two-phase and five phase hybrid stepping motors.

From the above information, the pulse equivalent value of the AC servo motor is equivalent to 1/655 of the pulse equivalent value of the stepping motor with a step angle of 1.8 °. It can be seen that there is really a big difference between the two in terms of control accuracy. The control accuracy of the AC servo motor is more precise, which also makes a significant difference between the two in the application field. The AC servo motor is suitable for industries with higher requirements for control accuracy. If the requirements are not high, the stepping motor can be used as the executive motor. If the requirements for the motor are high, it is recommended to choose the AC servo motor. In the design process of the control system, it is necessary to comprehensively consider the control requirements, cost and other factors, and select the appropriate control motor.