With the development of information, communication, and automation technologies, a wide variety of automatic control devices have gradually entered people's daily lives. Network communication technology not only provides convenient communication methods but also offers simple and reliable communication channels for various electronic devices. Utilizing new network communication technologies and powerful digital signal processor (DSP) chips, various smart information appliances with basic intelligence can be developed, such as robots that help with cleaning and electronic pets for entertainment. The core component of these devices, which integrate mechanics, electronics, communication, control, and information technology, is the network servo controller. Servo technology has been widely applied in our daily lives, such as servo control of optical disc drive heads, wing control of remote-controlled aircraft, autofocus control of digital cameras, network video surveillance systems with image tracking capabilities, and autonomous driving in automobiles. Servo systems cover a wide range of applications and are highly interdisciplinary. Servo systems—a key technology in mechatronics— are defined as "servomechanism systems," which refer to systems that achieve position, speed, or acceleration control of a mechanical system through closed-loop control. A servo system typically consists of several parts, including the controlled object (plant), actuator, and controller. The controlled object refers to the object being controlled, such as a robotic arm or a mechanical work platform. The actuator's function is primarily to provide power to the controlled object, which may be pneumatic, hydraulic, or electric. If hydraulic drive is used, it is generally called a hydraulic servo system. Currently, most servo systems use electric drive. The actuator includes a motor and a power amplifier. The motor specifically designed for servo systems is called a servo motor, and it usually contains a position feedback device, such as an optical encoder or a resolver. Currently, the servo motors mainly used in industry include DC servo motors, permanent magnet AC servo motors, and induction AC servo motors, with permanent magnet AC servo motors being the most prevalent. The controller's function is to provide closed-loop control for the entire servo system, such as torque control, speed control, and position control. Currently, industrial servo drives typically include a controller and a power amplifier. Figure 1 shows the composition of a traditional servo mechanism system. The servo driver mainly includes a power amplifier and a servo controller. The servo controller typically includes a speed controller and a torque controller. The motor usually provides analog speed feedback signals. The control interface uses ±10V analog signals. Through analog commands from the external loop, the motor speed or torque can be directly controlled. Using this type of servo driver, a position controller is usually required to complete position control. Figure 2 shows a modern servo mechanism system structure diagram, where the servo driver includes a servo controller and a power amplifier, and the servo motor provides high-resolution photoelectric encoder feedback signals. Multi-axis Motion Control System Precision servo systems are widely used in multi-axis motion control systems, such as industrial robots, CNC machine tools, electronic component assembly systems, PCB automatic insertion machines, etc. Figure 3 shows a block diagram of a motion control platform. The position control of the work object can be achieved by moving the platform. There are two ways to detect the platform position: one is through the photoelectric encoder installed on the servo motor itself. Because this indirectly feeds back the position of the work object, and then achieves position control through closed-loop control, it is also called indirect position control. Another approach is to directly mount position sensing components on the platform, such as optical rulers or laser position detectors, to directly feedback the position of the work object. Position control is then achieved through closed-loop control, a method known as direct position control. A multi-axis motion control system consists of a high-order motion controller and a low-order servo driver. The motion controller is responsible for decoding motion control commands, the relative motion between the various position control axes, acceleration/deceleration contour control, etc., with its main focus being reducing the path error of the overall system motion control. The servo driver is responsible for the position control of the servo motors, with its main focus being reducing the following error of the servo axes. Figure 4 shows a simplified control block diagram of a dual-axis motion control system. Under normal circumstances, the dynamic response characteristics of the X-axis and Y-axis will differ significantly, causing significant errors in high-speed contour control. Therefore, a motion controller must be designed to address this issue from a holistic perspective. Network Distributed Servo Systems With the advancement of network communication technology, servo systems employing real-time network communication technology have also developed. Figure 5 shows a network-controlled distributed servo system developed using SERCOS real-time network communication technology. Currently, there are various distributed motion control systems using different communication protocols, such as SERCOS, Real-Time Ethernet, and Real-Time CAN bus. Applying high-speed network technology to distributed servo systems has many advantages, such as more flexible system applications and better system integration and control effects. Ethernet-based Motion Control Networking Technology In early 2003, when the third-generation SERCOS and PROFInet working groups proposed solutions for future motion control networking technology, they recommended using Ethernet as the basis for servo drive networking, significantly improving the performance of servo drive systems. Both working groups claimed that for high-performance motion control applications, standard Ethernet technology can serve as the physical layer for the next generation—and as a compatible protocol for high-performance motion control applications. At the 2003 Hannover Messe, PROFIBUS International (http://www.profibus.com/) announced that it had begun developing a high-performance real-time solution for high-dynamic motion control applications based on PROFInet 3.0 IRT. This solution uses standard Ethernet media, compatible protocols, and ASICs (Application-Specific Integrated Circuits) that can be embedded in switches and protocols, thus ensuring real-time performance and determinism. Also at the 2003 Hannover Messe, SERCOS announced that it had begun developing the next-generation SERCOS (NGS) protocol to further improve the SERCOS interface standard, introducing industrial Ethernet technology. Ethernet Applications in Motion Control The biggest advantages of Ethernet in motion control are low hardware and cabling investment costs, and its status as a de facto standard, offering benefits in training, flexibility, and familiarity. Ethernet is a standard network in the business sector, widely used on almost every company's PCs. In the manufacturing sector, Ethernet adoption is also growing, with many companies establishing maintenance and support infrastructure to effectively configure and manage these networks. The biggest obstacle to the application of Ethernet in motion control is overcoming its inherent limitations in real-time performance, the additional hardware costs required to ensure determinism, the limitations of star network topologies, and the question of whether specific implementations can provide interoperability. FireWire (IEEE-1394), as the foundation of motion control networking protocols, has established the IEEE-1394 standard, with built-in deterministic FireWire standard chipsets supporting real-time applications. The third-generation SERCOS standard was developed by different working groups comprising member companies of the SERCOS organization. Its development plan was announced to the industry at the 2003 SPS/IPC/DRIVES exhibition in Germany, and the SERCOS organization subsequently focused on chip-level technology development. After thorough market research, SERCOS member companies believed that integrating Ethernet and SERCOS timing mechanisms would result in a robust, durable, and cost-effective motion control networking technology. The third-generation SERCOS extends the existing SERCOS standard using Ethernet technology. All nodes (controllers, drivers, and I/O) are connected either to a traditional ring topology or a bus topology. A dedicated, conflict-free real-time channel is used for hard real-time communication, while an additional IP channel can be configured in parallel with the real-time channel. Both channels use the standard Ethernet framework, and a dedicated controller chip handles the switching between real-time and IP channel traffic, ensuring hard synchronization of all connected nodes. The third-generation technology retains all proven SERCOS mechanisms, such as established protocols, hardware synchronization, and unique motion control protocol conventions. Key enhancements include the additional IP channel for transmitting asynchronous data (maintenance, diagnostics, etc.) and the possibility of direct communication (cross-communication) between network nodes. An additional improvement is the definition of a redundancy mechanism, which can be implemented when a ring topology is used. For example, if a cable breaks, this redundancy mechanism provides alternative paths for communication, thus restoring communication functionality "disruptlessly." SERCOS Performance Using the efficient SERCOS protocol combined with high-bandwidth Fast Ethernet, the SERCOS working group claims that the performance of motion control networks will be remarkable, with an expected performance supporting up to 150 drives on a single network at an update rate of 500μs (depending on the data volume per drive and the size of the configured IP channels). This performance improvement facilitates multi-axis drive schemes with centralized signal processing (16 drives at an update rate of 62.5μs). The SERCOS organization also claims that third-generation SERCOS will be a low-cost yet highly efficient new technology, requiring only an ASIC chip, an Ethernet connector, and cabling. Hard real-time performance is achieved without the need for any additional Ethernet components such as bridges, routers, or switches (which would significantly increase costs), all of which makes third-generation SERCOS attractive even for "low-cost devices." SERCOS will continue to support fiber optic cabling, allowing interference-sensitive controllers controlling drive operation to be unaffected by electromagnetic interference generated by motors. For motion control, the next-generation SERCOS network will use CAT5-level cable as the physical medium, with the rest of the network using hybrid Ethernet technology, but with a certain number of SERCOS ring topologies and other configuration attributes on top of this Ethernet medium. The new SERCOS architecture will offer a different model, rather than simply addressing the issue through bandwidth. Leveraging the advantages of time services, it can achieve better performance and higher reliability on a time-synchronized network than on ultra-high-speed networks. Servo System Synergy Integration Technology Servo systems inherently possess synergy technology. Servo system design must integrate multiple key technologies, such as automatic control, motion control, digital control, motor control, power electronics, microprocessor hardware and software design, etc. Servo system design engineers must integrate multiple different technologies according to the application requirements of the system. This system integration characteristic will be more clearly presented as "real-time multi-tasking flexible control technology" with the advancement of microelectronics technology. The integration process of a servo system is shown in Figure 6. Servo System Hierarchical Control Structure Servo systems generally include multiple control loops, such as current loops, speed loops, and position loops. These loops have different dynamic responses (bandwidths) and different functions. Therefore, based on these characteristics, different loops can be layered in the hardware and software design. Following the principles of systems engineering, a reasonable hardware structure and corresponding control strategy can be selected to achieve a high performance/price ratio for the entire system. The layered control structure of a servo system is shown in Figure 7, the closed-loop multi-loop control structure of a servo system is shown in Figure 8, and the schematic diagram of the layered control interface of a modern servo system is shown in Figure 9. [ALIGN=CENTER] [/ALIGN] Servo mechanism theory originated during World War II. In order to develop radar tracking systems with automatic control functions, the U.S. Department of Defense commissioned MIT to develop closed-loop control technology for mechanical systems. This development laid the foundation for later servo mechanism theory. The development of microprocessors has not only driven the development of the information industry but also indirectly driven the development of servo drive technology. The system structure of a general-purpose servo driver and the block diagram of a typical closed-loop control system are shown in Figures 10 and 11, respectively. [ALIGN=CENTER] [/ALIGN] Multi-loop Control Structure Practical servo systems typically employ a closed-loop multi-loop control structure, as shown in Figures 12-15. This control structure inherently possesses decoupling control effects, allowing for layered control of position, speed, and acceleration required within a servo system. [ALIGN=CENTER] [/ALIGN] Development of Digital Servo Control Technology With the development of high-performance microprocessors and digital signal processors, digital servo control technology has become the mainstream of industrial servo systems. The evolution of digital motor control technology is shown in Figure 16. The Development of DSP Digital Servo Control Technology: A DSP can be considered a microprocessor with powerful computing capabilities. Wherever a microprocessor can be used, and where faster computing power is required, a DSP can be considered. However, it is worth noting that single-chip microcontrollers are widely used in industrial control, primarily due to their complete I/O interface, which is not typically found in DSPs. However, in recent years, single-chip DSP controllers specifically designed for servo motor control have been developed, such as Texas Instruments' TMS320F24xx and TMS320F2812. These controllers not only boast powerful computing performance and the I/O interface required for motor control, but are also quite inexpensive, directly driving the development of DSP-based digital motor control technology. A DSP-based servo system solution is shown in Figure 17. In industrial control applications, such as robot control, disk drive and optical drive control, and servo control, the main focus of using DSPs to implement digital controllers is their rapid computing power. Due to the rapid computing power of DSPs, adaptive servo systems can be implemented. Using DSPs to implement digital control systems requiring complex calculations to meet the demands of high-performance control systems will become a future development trend. Key technologies include: • Single-chip DSP-based digital servo control technology; • Real-time network communication technology applied to digital motion control systems; • Adaptive servo control technology; • Development of programmable digital servo control ICs. Computer-Aided Servo System Design Because servo system design involves the integration of multiple different technologies, its design process is more complex. Utilizing computer-aided design and real-time online control simulation has become an important method in modern servo system design. Figure 18 shows a computer-aided design scheme for a servo motor drive system. Key technologies include: • Systematic design methods and implementation techniques combining DSP with MATLAB/SIMULINK; • Real-time online control simulation; • Development of computer-aided servo system design tools. Some Practical Issues in Servo System Design The design of a modern servo system encompasses mechanical design, motor control, power electronics, servo control, motion control, programming, network communication protocols, noise suppression, and practical applications. Its core technology lies in integrating microelectronics and power electronics to achieve servo control. Some important practical design considerations should include the following aspects: • Interface circuit design for high-resolution photoelectric encoders; • How to calculate rotational speed from incremental feedback signals; • Bandwidth requirements of the servo system; • Limitations on servo system bandwidth caused by power amplifier voltage and current outputs; • Whether the digital servo system uses fixed-point or floating-point arithmetic; • Selection of the control loop sampling frequency; • Sampling method of current feedback signals and resolution requirements of the ADC converter. Conclusion Anything that moves requires control. Electric drive will remain the primary driving method in the future. With the development of microelectromechanical systems (MEMS), power electronics, and network communication technologies, various forms of micromotors will be connected via wired, wireless, and power line network communication technologies. Servo technology will further integrate microelectronics and power electronics to present flexible control. The development of servo technology will also move towards single-chip control, intelligent control, and network connectivity. The future market demand for intelligent electronic pets and home robots will further promote the development of servo technology. Intelligent servo control chips with network interfaces are a worthwhile area for research and development.