With the increasing maturity of fieldbus technology, the United States, Japan, and Europe have successively developed industrial automation control systems that integrate fieldbus technology, 100Mbps Ethernet technology, PLC technology, visual human-machine interface technology, and global production management technology. Companies such as Jetter AG (Germany) with JetWeb, KEB with KEBmotion, Lence with Lence, Triomotion with Trio (UK), and Elmo with Massetro (Israel) have emerged. Ethernet is part of the controller and serves as the system bus connecting intelligent control modules; there is no distinction between internal and external data communication, and the network is the controller. The Ethernet system bus is the fieldbus, which can be connected to each independent control module. To adapt to the development of new fieldbus technologies, many universities have successively offered the course "Modern AC Servo Control" (Note: the textbook has been published by Tsinghua University Press) in electrical engineering, electronics, mechatronics, and other majors. However, the number of experimental equipment and devices配套 with this course is still very limited, which is undoubtedly a significant deficiency for students learning advanced automatic control technology. To address this issue, the author's research institute has developed an "Ethernet-based AC Servo Experimental System." Students can build network experiments using CAN bus and Ethernet to complete a series of fieldbus-based control experiments, such as remote data acquisition, remote motor control and detection. Experimental System Composition and Working Principle In the research of open servo CNC, the United States, Germany, Japan, and Europe are technologically leading. Domestic servo research started relatively late. In collaboration with Tianjin Luosheng Group, the author used the Israeli ELMO servo system to build a networked open servo control system for teaching, based on Ethernet and CAN bus. The advantages of this design are: it solves the urgent need for experimental courses in the university course "Modern AC Servo Control," enhancing students' perceptual understanding, improving their hands-on skills, and increasing their learning interest; it changes students' past concept of field control, broadening their horizons; it is not only suitable for experimental research in production internships and course design for mechatronics, electronics, and electrical automation majors in universities, but can also serve as an open experimental platform for undergraduate and graduate students in electrical engineering, laying a necessary foundation for their understanding and mastery of modern AC speed regulation and servo systems, and can be directly applied to industrial production applications such as digital engraving, packaging machinery, and mold production. It constitutes a remote control servo control system. Through microcomputer programming, it can perform multi-degree-of-freedom and multi-machine coordinated control, realize servo characteristics such as high speed, high progress and low vibration, and can also be used in fields such as robot control and flexible manufacturing. It can realize remote control, maintenance, diagnosis, etc., and save operating costs. The teaching AC servo system architecture based on Ethernet and CAN bus [1] is shown in Figure 1. The control system consists of a host computer (1), a multi-axis motion controller (2), an AC servo driver (3) and an AC servo motor (4). Its feature is that the multi-axis motion controller (2) is connected to the host computer (1) through Ethernet or LAN, the AC servo drivers (3) are connected to each other and the AC servo drivers are connected to the multi-axis motion controller (2) through the CAN bus, and the output of the AC servo driver (3) is connected to the AC servo motor (4). [align=center] Figure 1 Servo experimental equipment system based on Ethernet[/align] System working principle The host computer (1) obtains support for the Ethernet bus by plugging in a network communication adapter card (100m) that supports the TCP/IP protocol, and is responsible for monitoring and managing the operation and working status of the entire system. After the host computer (1) completes the task planning, it sends instruction information to the multi-axis controller (2) via Ethernet according to the TCP/IP protocol. After the controller interprets the instruction, it converts the TCP/IP protocol into the CAN 2.0b network protocol through the transparent gateway [2] and sends control commands to the AC servo drive (3) through the CAN bus. After the CAN node interprets the instruction, it converts it into digital pulse signals to control the AC servo motor (4). Since hub technology is integrated into each controller, internal communication can be separated from external communication by allocating address space. The integration of hub technology and underlying protocols ensures the determinism and compatibility of Ethernet and eliminates communication collision problems. The whole process or system is regarded as a logical unit, or even an independent controller. There is no need to consider the concept of each layer of the network, but only one layer is formed, which removes the bottleneck effect of the CPU. All data only needs to be expressed once in the network, and the network plays the role of a real server. The interpolation scheme adopts two-stage coarse and fine interpolation. The host computer performs coarse interpolation and calculates the displacement of each axis in each interpolation cycle according to the requirements of feed speed and acceleration and deceleration. The displacement is converted into pulse number and sent to the multi-axis controller. Each multi-axis controller can coordinate and control up to 109 servo motors. Of course, the servo driver can also be directly controlled by the CAN bus, but the programming is more complicated. In position servo control, this system adopts the PIP (proportional-integral-proportional) control algorithm instead of the traditional PID control [3]. PIP control was originally proposed by Young et al. [4][5]. Due to the length of this paper, it will not be analyzed in detail. Experimental Design The AC servo experimental system based on Ethernet has been successfully built in the Institute of Motion Control of Nanjing University of Technology. The system has stable performance and reliable quality. It can be widely used in industrial production applications such as digital engraving, packaging machinery, and mold production. It is more suitable for experimental research in production internships and course design courses for students (graduates) majoring in mechatronics, electronics, and electrical automation in colleges and universities. And developed a series of experiments such as CAN bus basic experiment, remote control experiment, AC servo control experiment, CNC interpolation, motion trajectory design, etc. The developed experiments are divided into three levels: basic experiment, extended experiment, and innovative experiment. The following is a system teaching experiment design of this experimental system through a remote control motor system experiment. Basic Experiment The basic experiment requires students to understand the principle and process of the experiment and be able to independently complete the verification experiment required in the experimental guide. Students complete the experiment according to the requirements and steps of the experimental guide (such as control algorithm, observation of various curve trajectory interpolation process, multi-motor synchronous control and linkage parameter adjustment, guidance on regulator parameter setting, motion system performance test, etc.) to achieve verification, and at the same time further understand the principle and process of the experiment. This system uses the position servo control system of the Israeli company Elmo, and its driver integrates the motor-specific chip DSP56F805 developed by Motorola. Figure 2 is a block diagram of the experimental system for controlling a three-phase permanent magnet synchronous motor using DSP56F805[7][8][9]. This system can realize closed-loop control of motor speed. The motor position detection employs a "back EMF zero-crossing detection method." The zero-crossing signal is read from the input monitoring register (IMR) of the DSP56F805 quadrature decoding module, and the switching of the PWM output channel masking operation is achieved by the corresponding MSK bit written into the PWM channel control register (PMCCR) of the PWM module. The PWM module is set to independent mode with an output frequency of 16kHz. The program can run either in the DSP56F805's internal flash or in the external RAM on the EVM board, which can be achieved by selecting the target during program compilation. The parallel port in the system is used for downloading the program's target code. Thus, the motor's start/stop and speed regulation control can be performed manually or via computer access control. Extended Experiments The extended experiments build upon the basic experiments to master the software's workflow and familiarize students with the functionalities required to complete this experiment. The experimental object is a multi-motor coordinated control system. Each motor is controlled by a DSP56F805 chip, thus forming an intelligent node with the DSP controller as the core and the purpose of controlling the motor. Then, the intelligent nodes are connected by the CAN bus, and finally a remote control system is formed by Ethernet. The control system consists of a computer (PC), a computer-based Ethernet information management terminal (NIC), an embedded transparent gateway (multi-axis controller), an AC servo motor, and an AC servo driver with DSP [6]. Students master the process of the experimental software and become familiar with the function of completing this experiment through the lecture of the experimental instructor. They read the software code in the software compilation environment and realize the interpretation of control commands by running the function run(). Students develop curve control programs in VC++ for the experiments listed in the experimental guide and realize the function run(). Then, based on the proficiency of TCP/IP and CAN protocols, they develop the communication control interface API and develop a small control software interface in MFC, loading various curve controls that need to be developed. For example, students can use their local computer (assuming IP: 10.0.0.23) to perform experiments such as remotely controlling a servo motor with CAN controller ID=004 to rotate clockwise a specified number of revolutions, and controlling servo motors ID=001 and ID=002 to work together to draw repeating circles. Students must first find the control commands for controlling the servo motors in the experiment manual, then obtain the control commands according to the experiment requirements, send the control commands according to the experimental steps, and finally verify the correctness of the experiment on the computer terminal with IP address 10.0.0.28. Innovative Experiments Innovative experiments are developed based on the previous two experiments to fully explore the potential of the experiments and cultivate students' innovative abilities. Students are required to improve the experimental software by modifying the program code to address its shortcomings. For higher-level research, students can develop various CNC machining components, improve the deficiencies of the Nanjing University of Technology fieldbus control software, or improve the software problems they discover during operation. For example, if the software lacks CNC G-code, students can try to implement new functions based on their knowledge of the remote control code for servo motors. This part of the experiment is relatively difficult. Students can form a team of many people and complete it under the guidance of the experimental teacher. As a course design for students, the experimental device has reserved a lot of expansion interfaces for subsequent development. For example, many important equipment/occasion now need to be monitored by video. In the past, the method was to send the analog signal from NTSC/PAL to the central monitoring room. 100 monitoring points need to be connected to 100 coaxial cables [6]. If it is necessary to reflect the status of the equipment on site in the management network of the enterprise, the host computer is connected to the enterprise network, and the video image is transmitted on the Internet through the video card digitization and video server. To view the operating status of the equipment remotely, it is also necessary to go to the enterprise network through the Internet and then to the I/O server of the control system that is closely connected to the field controller to get the data. Now, the Taiwan Shangshang Company has launched a fully digital camera based on TCP/IP. Since students have already implemented TCP/IP control in their own software, they only need to add the corresponding controls in their own software. They can directly control the camera through the Internet/Intranet or feed back the real-time video image and process data to the system. The feedback data is used to control the Nut teaching bus servo system through the Internet/Intranet for the purpose of video remote control. [img=562,307]http://www.ca800.com/uploadfile/maga/servo2006-5/tcz2.jpg[/img] Figure 2. DSP-based motor speed control system. Conclusion The experimental control system combining Ethernet, CAN bus, and DSP proposed in this paper represents a valuable new exploration for the networked research and application of AC servo systems. Ethernet can easily form a remote control network via TCP/IP, while the CAN bus can well meet the high requirements of the control system for real-time response. Furthermore, the use of the CAN bus also gives the system excellent scalability. The NUT bus servo system can perform multi-degree-of-freedom coordinated control, achieving high speed (3000 r/min), high precision (16384 p/r), and low vibration servo characteristics. This technology represents the latest speed control and servo drive control in the 21st century and can be applied to fields such as robot control and flexible manufacturing. The developed student experimental system can provide an open experimental platform for undergraduate and graduate students in electrical engineering, laying a necessary foundation for their understanding and mastery of modern AC speed control and servo systems. This system combines small size, high performance, and ease of use. Its design fully considers students' characteristics, offering good openness and allowing them to design their own algorithms according to teaching requirements. It emphasizes students' thinking and hands-on abilities, deepening their understanding of theory. Simultaneously, it considers the needs of teachers, creating conditions for their research and development. The successful development of this system will undoubtedly play a significant role in the field of motion control in the 21st century.