Abstract: This article first introduces the historical process of how modern AC servo systems emerged from the large family of motor control systems, and then presents the current development status of AC servo systems from both technical and market perspectives. It focuses on comparing domestic and international markets, technologies, products, and manufacturer competitive strategies, aiming to provide a panoramic view for those interested in the growth of China's AC servo industry. Overview 1. Historical Perspective on Motor Development The invention of the battery by Volta in 1800 marked the beginning of electricity. The birth and development of the electric motor can be divided into several stages. From 1820 until the end of the 19th century, the discovery of electromagnetic phenomena and related laws led to the creation of the prototype of the AC motor and the establishment of its industrial applications. From the beginning of the 20th century until the 1970s, the electric motor experienced growth and maturity. Various types of motors, such as brushed DC motors, induction motors, synchronous motors, and stepper motors, were successively developed. The introduction of semiconductor drive technology and electronic control concepts brought about the practical application of frequency conversion drives. From the 1970s to the late 20th century, the rapid development of computing technology created opportunities for the development of high-performance drives. With continuous advancements in design, evaluation, measurement, control, power semiconductors, bearings, magnetic materials, insulating materials, and manufacturing technologies, electric motors underwent a series of transformations, including lightweighting, miniaturization, high efficiency, high torque output, low noise and vibration, high reliability, and low cost. Correspondingly, drive and control devices became more intelligent and programmable. Entering the 21st century, in the information age characterized by multimedia and the internet, electric motors and drive devices continue to play a supporting role, developing towards resource conservation, environmental friendliness, and high-efficiency energy-saving operation. The permanent magnet brushless DC motor is a new type of motor that emerged with the development of permanent magnet material technology, semiconductor technology, and control technology. Brushless DC motors originated in the 1950s and began to be used in aerospace and military equipment in the 1960s. After the 1980s, lower-priced neodymium iron boron permanent magnets appeared, and research and development gradually expanded to industrial, civilian equipment, and consumer electronics industries. Essentially, a brushless DC motor is an AC permanent magnet synchronous motor that operates using electronic commutation based on rotor position feedback. Compared to brushed DC motors, it has a series of advantages and has experienced rapid development in recent years, continuously replacing DC motors and asynchronous motors in many fields. Since the 1990s, permanent magnet motors have evolved towards higher power, higher functionality, and miniaturization, resulting in models with single-unit capacities exceeding 1000KW, maximum speeds exceeding 300,000rpm, minimum speeds below 0.01rpm, and minimum dimensions of only 0.8x1.2mm. In fact, both permanent magnet brushless DC motors and the permanent magnet AC servo motors discussed in this article belong to the category of AC permanent magnet synchronous motors. Based on the back electromotive force waveform and the drive current waveform, permanent magnet synchronous motors can be divided into square wave driven and sine wave driven types. The former is what we commonly refer to as a brushless DC motor, while the latter is also known as a permanent magnet synchronous AC servo motor, mainly used in servo control applications. So, what does servo mean? How are the basic performance characteristics of servo control measured? 2. Introduction, Basic Performance, and Control Methods of AC Servo Systems Servo, derived from the English word "servo," refers to a system that follows external commands to perform desired movements, including position, speed, and torque. The development of servo systems has progressed from hydraulic and pneumatic to electrical systems. Electrical servo systems include servo motors, feedback devices, and controllers. In the 1960s, DC motors were initially the primary actuators. However, after the 1970s, the cost-effectiveness of AC servo motors improved, gradually replacing DC motors as the dominant actuators in servo systems. The controller's function is to perform closed-loop control of the servo system, including torque, speed, and position. The servo driver we commonly refer to already includes the basic functions of a controller and a power amplification section. Although open-loop servo systems directly driven by power stepper motors were widely used in the so-called economical CNC field in the 1990s, they were quickly replaced by AC servos. In the 21st century, AC servo systems have become increasingly mature, and the market has experienced rapid diversification, with numerous domestic and international brands entering the market. Currently, AC servo technology has become one of the supporting technologies for industrial automation. In AC servo systems, motors are categorized into permanent magnet synchronous AC servo motors (PMSM) and induction asynchronous AC servo motors (IM). PMSMs, with their excellent low-speed performance, ability to achieve high-speed control with field weakening, wide speed range, and high dynamic characteristics and efficiency, have become the mainstream choice for servo systems. While asynchronous servo motors are robust, simple to manufacture, and inexpensive, they lag behind in characteristics and efficiency, and are only valued in high-power applications. This article will focus on PMSM AC servo systems. The performance indicators of AC servo systems can be measured by factors such as speed range, positioning accuracy, speed stability, dynamic response, and operational stability. Low-end servo systems have a speed range of 1:1000 or higher, typical systems range from 1:5000 to 1:10000, and high-performance systems can reach 1:100000 or higher. Positioning accuracy generally needs to reach ±1 pulse. Speed ​​stability, especially at low speeds (e.g., with a given 1 rpm), is typically within ±0.1 rpm, and high-performance systems can reach within ±0.01 rpm. Regarding dynamic response, the commonly measured metric is the system's highest response frequency; given a sinusoidal speed command at the highest frequency, the system's output speed waveform should have a phase lag of no more than 90 degrees or an amplitude of no less than 50%. Imported Mitsubishi MR-J3 series servo motors have a response frequency as high as 900Hz, while the frequency of mainstream domestic products is between 200 and 500Hz. Operational stability mainly refers to the system's ability to maintain stable operation and ensure certain performance indicators under conditions of voltage fluctuations, load fluctuations, changes in motor parameters, changes in the output characteristics of the host controller, electromagnetic interference, and other special operating conditions. In this regard, domestically produced products, including some Taiwanese products, lag significantly behind world-class levels. Regarding control strategies, voltage-frequency control methods based on the steady-state mathematical model of the motor and open-loop flux trajectory control methods struggle to achieve good servo characteristics. Currently, the widely used method is vector control based on the dynamic decoupling mathematical model of the permanent magnet motor, which is the core control method of modern servo systems. Although theories such as feedback linearization control, sliding mode variable structure control, and adaptive control have been proposed to further improve control characteristics and stability, as well as fuzzy control and neural network control methods that do not rely on mathematical models, most of these methods are applied in addition to vector control. Furthermore, high-performance servo control relies on high-precision rotor position feedback. There has been a long-standing desire to eliminate this step, leading to the development of sensorless control technology. To date, in commercially available products, sensorless control technology can only achieve a speed ratio of approximately 1:100, suitable for some low-end servo control applications where position and speed accuracy requirements are not high, such as the servo control of sewing machines that simply pursue rapid start-stop and braking. The high-performance development of this technology still has a long way to go. 3. The Development History of AC Servo Technology in China China began tracking and developing AC servo technology in the 1970s, with major research efforts concentrated in universities and research institutions, primarily focusing on military and aerospace applications, without considering cost factors. Major research institutions included the Beijing Machine Tool Research Institute, the Xi'an Micro-Motor Research Institute, and the Shenyang Institute of Automation, Chinese Academy of Sciences. After the 1980s, it began to enter the industrial sector. Until 2000, domestically produced servos remained in a state of small-batch production, high prices, and narrow application scope, with technical levels and reliability failing to meet industrial needs. After 2000, with China becoming the world's factory and the rapid development of its manufacturing industry, the market space for AC servos expanded significantly, and several domestic companies began launching their own branded AC servo products. Currently, major domestic servo brands or manufacturers include Senchuang (Holysys Motor), Huazhong CNC, Guangzhou CNC, Nanjing Estun, and Lanzhou Electric Machinery Plant. Among them, Huazhong CNC and Guangzhou CNC mainly focus on the CNC machine tool field. Technical Status 1. Current Level of Domestic and International AC Servo Products The related technologies of AC servo systems have continuously evolved with user needs. The continuous evolution of related technologies such as electric motors, drives, sensing, and control has led to a wide variety of configurations. For electric motors, various types can be used, including disc motors, coreless motors, linear motors, and external rotor motors. Drives can employ various power electronic components. Sensing and feedback devices can be encoders, resolvers, Hall effect sensors, or even sensorless technology of varying precision and performance. Control technology has progressed from using microcontrollers to high-performance DSPs and various programmable modules, as well as the practical application of modern control theory. The SPS/IPC/Drives exhibition held in Nuremberg, Germany in November 2005 showcased the latest developments in electric drives, motion control, and related software worldwide. AC servo products were particularly noteworthy, representing the current international level. This section only excerpts a few points, and correspondingly compares and explains the R&D trends of domestic manufacturers. B&R Industrial Automation's AcoposMulti drive system features a modular, scalable architecture. Each axis module can provide control of 1 to 2 servo axes and integrates a 24VDC auxiliary power module, providing a DC bus link for the drive, controller, and peripherals, offering open-circuit, short-circuit, and overload protection. Other features include a modular design cooled by air, oil, or water, and an energy regeneration system to ensure environmental safety. Domestically, we have not yet seen any manufacturers adopting similar modular designs and incorporating machine safety concepts into their products. Elmo showcased a range of servo drives and controllers, including the latest Whistle miniature digital servo drive. These matchbox-sized drives, measuring only 5 x 4.6 x 1.5 cm, deliver 0.5 kW of continuous power (or 1 kW of peak power), making them the highest power density and most intelligent servo drives on the market today. Correspondingly, only Hollysys Electric Co., Ltd. in China has launched a similar intelligent digital servo controller—the Hummingbird series. This driver accepts 24V~48VDC input, can provide 250W continuous power and 500W peak power, and measures 10x8x2cm. Its power density is lower than Whistle's. However, it integrates a high-performance 32-bit RISC chip, providing RS232 and 485 serial communication control functions and 32 motion commands, including advanced circular interpolation commands, and uses a 14-bit absolute magnetic encoder. A brushless servo motor with a 16-bit absolute encoder and a drive module with CAN communication are expected to be launched in 2007. Emerson Control Techniques showcased Unidrive and other AC and DC drive products. Unidrive covers a power range from 0.55 to 675 kW, and can drive asynchronous motors, permanent magnet synchronous servo motors, and brushless DC motors by changing different control software. The Varmeca series integrates variable speed motors and variable speed drives (VSDs) with rated output power ranging from 0.25 to 11 kW, available in both closed-loop vector and distributed (Proxdrive) versions. Notably, the VSD system (ATEX) is suitable for operation in potentially explosive gases. The FLSD drive, with a rated output power ranging from 0.55 to 400 kW, is claimed to operate in Group IIB or Group IIC Class 1, Category 2 gases. In contrast, domestic servo drive manufacturers primarily offer products with power ranges below 10 kW, and no commercially available products with special protection ratings are available. This gap between domestic and international manufacturers is significant and represents a future direction for differentiated competition among domestic servo drive manufacturers. Rockwell Automation showcased its PowerFlex drive technology. The PowerFlex roadmap indicates that the "Common Industrial Protocol (CIP) Motion Application Protocol," expected to emerge in 2006-07, will allow for seamless synchronization of multi-axis servo and frequency converter drives operating within the same system. Regarding industrial protocols suitable for motion control, we also see Beckhoff's EtherCAT, B&R's PowerLink, SynqNet developed by MEI under Danaher, Siemens' ProfiNet, and the renowned Sercos, which has evolved to SercosIII. These communication protocols all provide possibilities for multi-axis real-time synchronous control and have been integrated into some high-end servo drives. In China, even mid-to-low-end buses like CAN have not become standard configurations for servo drives, and commercially available drives using high-performance real-time fieldbuses have not yet appeared. This is partly because the basic performance of our servos has not yet reached the corresponding level, and partly because the market has not yet developed to this extent. Encouragingly, we have seen some organizations conduct beneficial R&D practices, absorbing advanced foreign technologies on the one hand, and attempting to launch their own bus standards on the other. Hollysys Motors expects to integrate a variety of optional communication modules in its next-generation servo products, including CAN, USB, Fireware, and Sercos, as well as CANsmc (a bus for multi-axis synchronous motion control) jointly developed by Hollysys Motors and Beihang University. Modules based on Bluetooth wireless communication are also under development. Some institutions, such as the Shenyang Advanced CNC R&D Center of the Chinese Academy of Sciences, have also developed their own motion control bus protocols. Schneider Electric's Lexium 05 servo controller, exhibited at the event, has the same form factor as a VFD inverter and is targeted at low-cost applications. In fact, leveraging the mass production capabilities of inverters to launch low-end servos has become a competitive tactic for some manufacturers. The Berger Lahr brand, under the company, was prominently featured at their booth. Their Intelligent Integrated Motor and Controller (Icla) products are available in three motor versions: stepper motors, AC servo motors, and three-phase brushless DC motors. Icla (an acronym for "integrated, closed-loop, actuator") integrates the motor, position control, power electronics, and feedback into a compact unit. This integrated design approach is also evident in companies like Animatics in the US, and AMK in Germany also has similar products. These are true mechatronic products, presenting designers with a series of engineering challenges, including electromagnetic compatibility, thermal control, component miniaturization, and special structural designs. Domestically, no manufacturers have launched products with independent intellectual property rights. Baumuller offers high-performance servo motors with integrated planetary gear drives, boasting efficiency up to 98% and very low noise; their direct-drive high-torque servo motors can output 13500Nm within a 100-300rpm range. Domestically, Hollysys Electric offers similar products with integrated planetary gear reducers in its Dolphin series of low-voltage brushless servo motors, and Shenzhen Stepper also claims to offer Stepper servo motors with reducers. In the direct-drive torque motor market, Chengdu Precision Motor Factory can provide customized motor components, but customers need to add feedback devices and third-party drivers. Yaskawa Electric Europe (YEE) showcased its popular general-purpose Sigma II servo motor. Other developments by YEE include explosion-proof AC servo motors with rated power of 0.5-5 kW that comply with ATEX standards, currently under development. Another development by Yaskawa is a high-power servo motor with an output power of up to 500 kW. The commercialization of this project is expected to be completed in 2007. From this, we can see the trend of major international manufacturers moving towards specialized and large-scale servo systems. 2. Technological Development Direction Modern AC servo systems have undergone a transformation from analog to digital. Digital control loops are now ubiquitous, such as commutation, current, speed, and position control. The use of new power semiconductor devices, high-performance DSPs plus FPGAs, and dedicated servo modules (such as the dedicated servo control engine launched by IR) is also commonplace. International manufacturers upgrade their servo products every 5 years, new power devices or modules are updated every 2-2.5 years, and new software algorithms are constantly evolving; in short, product lifecycles are getting shorter and shorter. Summarizing the technical and product roadmaps of domestic and foreign servo manufacturers, combined with changes in market demand, we can see the following latest development trends: i. Increased Efficiency Although work in this area has been underway for some time, it still needs further strengthening. This mainly includes improving the efficiency of the motor itself, such as improving the performance of permanent magnet materials and better magnet mounting structure design, as well as increasing the efficiency of the drive system, including optimizing the inverter drive circuit, optimizing acceleration and deceleration motion, regenerative braking and energy feedback, and better cooling methods. ii. Direct Drive Direct drive includes turntable servo drives using disc motors and linear servo drives using linear motors. By eliminating intermediate transmission errors, high speed and high positioning accuracy are achieved. The ability of linear motors to easily change shape allows for the miniaturization and weight reduction of various devices using linear mechanisms. iii. High Speed, High Precision, and High Performance Using higher precision encoders (millions of pulses per revolution), higher sampling accuracy and data bit depth, faster DSPs, high-performance rotary and linear motors without cogging effects, and applying various modern control strategies such as adaptive and artificial intelligence, the performance of servo systems is continuously improved. iv. Integration and Integration Vertical integration of motors, feedback, control, drive, and communication has become a development direction for current low-power servo systems. Sometimes we call motors that integrate drive and communication "smart motors," and sometimes we call drivers that integrate motion control and communication "intelligent servo drivers." The integration of motor, drive, and control makes the three more tightly integrated from design and manufacturing to operation and maintenance. However, this approach faces greater technical challenges (such as reliability) and challenges related to engineers' usage habits, making it difficult to become mainstream and remaining a small, distinctive segment in the overall servo market. v. Generalization General-purpose drivers are equipped with a large number of parameters and rich menu functions, allowing users to easily set them to five operating modes without changing the hardware configuration: V/F control, sensorless open-loop vector control, closed-loop flux vector control, permanent magnet brushless AC servo motor control, and regenerative unit. Suitable for various applications, they can drive different types of motors, such as asynchronous motors, permanent magnet synchronous motors, brushless DC motors, and stepper motors. They can also adapt to different sensor types, even those without position sensors. A semi-closed-loop control system can be constructed using the feedback configured in the motor itself, or a high-precision fully closed-loop control system can be constructed through an interface with external position, speed, or torque sensors. vi. Intelligentization Modern AC servo drives all possess parameter memory, fault self-diagnosis, and analysis functions. Most imported drives have load inertia measurement and automatic gain adjustment functions; some can automatically identify motor parameters and automatically measure encoder zero position, while others can automatically suppress vibration. Combining electronic gears, electronic cams, synchronous tracking, interpolation motion, and other control functions with the drive provides a better experience for servo users. vii. Networking and Modularization Integrating fieldbus, industrial Ethernet, and even wireless network technologies into servo drives has become common practice for European and American manufacturers. A key direction in the development of modern industrial LANs and a focal point of competition among various bus standards is how to adapt to the real-time, reliable, and synchronous requirements of high-performance motion control for data transmission. With the increasing domestic demand for large-scale distributed control devices and the successful development of high-end CNC systems, the development of networked digital servos has become an urgent priority. Modularization refers not only to the combination of servo drive modules, power supply modules, regenerative braking modules, and communication modules, but also to the modularity and reusability of the servo drive's internal software and hardware. viii. From Fault Diagnosis to Predictive Maintenance With the continuous development of machine safety standards, traditional fault diagnosis and protection technologies (identifying the cause and taking measures to prevent the escalation of problems when they occur) are outdated. The latest products incorporate predictive maintenance technology, allowing people to understand the dynamic trends of important technical parameters in a timely manner via the Internet and take preventative measures. For example, monitoring current increases, assessing peak currents during load changes, monitoring temperature sensors when the casing or core temperature rises, and being vigilant for any distortions in the current waveform. ix. Specialization and Diversification While general-purpose servo product lines exist in the market, servo systems specifically designed and manufactured for particular applications are ubiquitous. The emergence of motors utilizing different properties of magnetic materials, different shapes, different surface bonding structures (SPM), and embedded permanent magnet (IPM) rotor structures, along with the use of segmented core structure technology in Japan, has enabled high-efficiency, high-volume, and automated production of permanent magnet brushless servo motors, prompting research from domestic manufacturers. x. Miniaturization and Enlargement Both permanent magnet brushless servo motors and stepper motors are actively developing towards smaller sizes, such as 20, 28, and 35mm outer diameters; simultaneously, larger power and larger models are also being developed, with 500KW permanent magnet servo motors already appearing. This reflects a trend towards polarization. xi. Other Trends Heat suppression, noise reduction, and cleaning technologies, etc.