As a core driving component in modern industrial automation, AC servo motors have become critical parts of high-end equipment such as CNC machine tools, robots, and precision instruments due to their high precision, rapid response, and stable operation. Their technological development and practical application reflect distinct characteristics of the era. This article provides a systematic explanation from three dimensions: working principle, classification of speed control methods, and technical features.
An AC servo motor is essentially an AC motor employing closed-loop control, and its operational mechanism is based on the law of electromagnetic induction. After three-phase AC power is supplied to the stator windings, a rotating magnetic field is generated, which drives the permanent magnet rotor to rotate synchronously. Compared to ordinary motors, its unique feature lies in the built-in high-precision encoder (resolution up to 23-bit), which can feed back rotor position information to the control system in real-time, forming a three-loop control structure for position, speed, and current. This closed-loop mechanism enables its dynamic response time to be shortened to the millisecond level, with positioning accuracy reaching ±1 pulse equivalent.
In terms of structural types, they are mainly divided into synchronous and asynchronous types. The synchronous type uses rare-earth permanent magnet materials (such as neodymium iron boron) for the rotor, featuring high power density and efficiency exceeding 90%. The asynchronous type generates torque through electromagnetic induction, making it more suitable for high-power applications. Modern servo motors commonly adopt a modular design, integrating the motor body, drive, and encoder into one unit. For example, the Yaskawa Σ-7 series products are 40% smaller in size compared to the previous generation while increasing output torque by 15%.
This technology decouples three-phase current into excitation and torque components through coordinate transformation, achieving control characteristics similar to DC motors. When using Field-Oriented Control (FOC) algorithms, speed fluctuations can be controlled within ±0.01%. For instance, Mitsubishi Electric's MR-J5 series drives achieve a current loop refresh cycle of 150 μs via a 32-bit DSP processor, making them particularly suitable for industrial robot scenarios requiring rapid acceleration and deceleration.
Pioneered by ABB, DTC technology eliminates the coordinate transformation step, directly controlling flux linkage and torque. Its advantage lies in a dynamic response speed 30% faster than vector control, but torque ripple exists at low speeds. The latest generation ACS880 drive uses an adaptive observer algorithm, reducing low-speed torque fluctuation to ±1.5% of the rated value.
Modern speed control systems widely integrate intelligent algorithms such as fuzzy PID and neural networks. For example, the Fanuc 30i-B system can automatically optimize control parameters to adapt to different load inertias through its self-learning function. Experimental data shows this adaptive control can shorten positioning time by 20% and reduce energy consumption by 8%.
(1) Overload Capacity: Typically can reach 3 times the rated torque (for several seconds). Such as SM80 AC Servo Motors.
(2) Speed Control Range: Can reach 1:5000 in vector control mode. For example, the Delta ASDA-A3 series maintains smooth operation even at 0.1 rpm.
(3) Repeat Positioning Accuracy: Can reach ±0.01 mm when using an absolute encoder.
Permanent magnet synchronous servo motors maintain efficiency above 85% even at 25% rated load, saving 15%-20% more energy compared to induction motors. The SM servo motors series drives are equipped with energy consumption monitoring functions, allowing real-time display of energy-saving effects.
Supports industrial bus protocols like EtherCAT and PROFINET, with transmission delays less than 1 μs. The Beckhoff AX5000 series drive further integrates PLC functions, reducing peripheral components by 30%.
In the semiconductor equipment field, linear servo motors combined with linear scales enable nanometer-level positioning. In textile machinery, the common DC bus technology improves the utilization of regenerative energy in multi-motor systems by 40%. Notably, the Electric Power Steering (EPS) systems in new energy vehicles now commonly use brushless servo motors, reducing the failure rate by 90% compared to traditional hydraulic systems.
With the application of SiC power devices and edge computing technology, a new generation of servo systems is developing towards higher frequency (switching frequency reaching 100 kHz) and networking. For instance, the Bosch Rexroth CtrlX AUTOMATION platform compresses the control cycle to 62.5 μs, providing a more flexible solution for Industry 4.0. In the future, the deep integration of digital twin technology with servo control will further push the performance boundaries of intelligent manufacturing systems.
