As the core executive component of industrial automation, AC servo motors integrate electromagnetic theory and precision control technology to form a complete system from electromagnetic field generation to closed-loop feedback.

Electromagnetic field generation and torque control

The stator of the AC servo motor adopts a three-phase winding structure, which generates a rotating magnetic field when three-phase AC power is applied. The rotor is divided into permanent magnet synchronous type and induction asynchronous type: the rotor of a permanent magnet synchronous motor is embedded with high-performance permanent magnets such as neodymium iron boron, and the rotating magnetic field interacts with the magnetic field of the permanent magnet, directly driving the rotor to rotate synchronously through the principle of magnetic polarity attraction; The rotor of an induction asynchronous motor is a squirrel cage structure, and the rotating magnetic field cuts the rotor conductor to generate induced current, which in turn forms electromagnetic torque. Vector control technology decomposes stator current into excitation component (controlling magnetic field strength) and torque component (controlling output torque), and achieves decoupling control of magnetic field and torque by independently adjusting the two components, enabling the motor to maintain constant torque output over a wide speed range.

Closed loop feedback and dynamic correction

The motor shaft end is integrated with a high-precision encoder (such as a 24 bit absolute encoder), which monitors the rotor position and speed in real time and feeds back the signal to the driver. The driver adopts PID control algorithm to dynamically adjust the phase, amplitude, and frequency of the three-phase current by comparing the deviation between the target command and the actual feedback value. For example, when the load increases and the speed decreases, the system automatically increases the torque component current to compensate for the load change and ensure stable speed. This closed-loop mechanism of "detection comparison correction" enables the motor to have millisecond level response capability and position accuracy up to arcseconds.

Key technologies in control practice

Field Oriented Control (FOC) converts three-phase currents into DC components in the rotor coordinate system through coordinate transformation, simplifying control logic; The automatic gain adjustment function optimizes control parameters in real-time based on load characteristics to avoid overshoot or oscillation; The thermal protection module monitors the winding temperature through temperature sensors and automatically reduces the frequency or stops the machine. In the joint drive of industrial robots, the use of AC servo motors combined with electronic gears can achieve multi axis synchronous motion and meet high-precision trajectory tracking requirements.