This paper elucidates the meaning of motion controllers, introduces their development status from several aspects such as types, control methods, and development trends, makes a comprehensive comparison, and presents typical applications in AC servo systems. 1 Introduction A motion control system is an electrical drive control system composed of an electric motor as the controlled object, a controller as the core, and power electronics and power conversion devices as actuators, guided by control theory. From a basic structural perspective, the hardware of a typical modern motion control system mainly consists of a host computer, a motion controller, a power drive device, an electric motor, sensor feedback detection devices, and the controlled object, as shown in Figure 1. The electric motor and its power drive device, as actuators, mainly provide power to the controlled object. Motors specifically designed for servo systems are called servo motors, which usually contain position feedback devices, such as photoelectric encoders. A motion controller is a control device with a central logic control unit as the core, sensors as signal sensing elements, and motors or power devices and actuators as the controlled objects. Its function is to provide closed-loop control for the entire servo system, such as position control, speed control, and torque control. 2 Classification of Motion Controllers Currently, motion controllers on the market are classified in different ways according to different methods. 2.1 Classification by Controlled Object Based on the different controlled objects in the application, motion controllers can be classified into stepper motor motion controllers, servo motor motion controllers, and motion controllers that can control both stepper motors and AC servo motors. 2.2 Classification by Structure (1) Computer Standard Bus-Based Motion Controllers Bus-based motion controllers utilize computer hardware and operating systems, combined with user-developed motion control applications, and possess high-speed data processing capabilities. The main bus types include ISA, PCI, VME, RS232, and USB interfaces. These motion controllers mostly use DSP or microcomputer chips as CPUs, enabling them to perform motion planning, high-speed real-time interpolation, servo filtering control and servo drive, and standardized universal interface functions between external I/O. They also provide powerful motion control software libraries: C language motion function libraries, Windows DLL dynamic link libraries, etc., allowing users to develop application software on DOS or Windows platforms according to different needs, forming various control systems. For example, the PMAC multi-axis motion controller from Dehatau in the United States uses Motorola's high-performance digital signal processor DSP5600X as its CPU, which can control up to 8 axes simultaneously and complete various functions together with various types of host, amplifier, motor and sensor. Similar products include the TRIO motion control card from Award in the United Kingdom, the GT series motion controller products from Googol Technology (Shenzhen) Co., Ltd., and the NI series motion controllers from NI in the United States. From the user's perspective, the differences between these PC-based motion controllers are mainly in the hardware interface (types and performance of input/output signals) and the software interface (functions of the motion control function library). (2) Soft-type open motion controllers provide users with great flexibility. Its motion control software is all installed in the computer, while the hardware part is only a standardized universal interface between the computer and the servo drive and external L/O, just like the various brands of sound cards, CD-ROMs and corresponding drivers can be installed in the computer. With the support of Windows platform and other operating systems, users can use the open motion control kernel to develop the required control functions and construct various types of high-performance motion control systems, thus providing users with more choices and flexibility. [IMG=Figure 1 Typical Motion Control System Composition]/uploadpic/THESIS/2007/11/2007111313585775289D.jpg[/IMG] Figure 1 Typical Motion Control System Composition (3) Embedded Motion Controller This type of motion controller is a product that embeds a computer into the motion controller, and it can operate independently. The communication between the motion controller and the computer is still based on the computer bus, which is essentially a variant of the motion controller based on the bus structure. In use, field network communication interfaces such as industrial Ethernet, RS485, SERCOS, and Profibus are used to connect to the upper-level computer or control panel. Embedded motion controllers can also be configured with floppy disks and hard disks, and can even be remotely diagnosed via the Internet, such as the Smart Controller from ADEPT in the United States, and the GU embedded motion control platform series products from Googol Technology. 2.3 Classification by Controlled Variable and Motion Control Method The control forms of motion controller application scenarios are: (1) Point-to-point motion control. That is, only the endpoint position is required, and it is not related to the intermediate process of the motion, i.e., the motion trajectory. The corresponding motion controller requires a fast positioning speed and adopts different acceleration and deceleration control strategies in the acceleration and deceleration phases of the motion. In order to enable the system to accelerate to the set speed quickly during acceleration, the system gain and acceleration are often increased. In the final phase of deceleration, an S-curve deceleration control strategy is adopted. In order to prevent vibration after the system is in place, the system gain is appropriately reduced after the system is in place. Therefore, point-to-point motion controllers often have the ability to have online variable control parameters and variable acceleration and deceleration curves. (2) Continuous trajectory motion control, also known as contour control, is mainly used in the motion contour control of traditional CNC systems and cutting systems. The corresponding motion controller needs to solve the problem of how to ensure the contour accuracy of the system machining and the constant tangential speed of the tool when moving along the contour under high-speed motion. For machining small line segments, there is a multi-segment program preprocessing function. (3) Synchronous motion control refers to the motion coordination control between multiple axes. It can be that multiple axes are synchronized throughout the entire motion process or that there is speed synchronization in a local part of the motion process. It is mainly used in the control of systems that require electronic gearbox and electronic cam functions. Industrial applications include dyeing, printing, papermaking, steel rolling, and synchronous shearing. The corresponding motion controllers often employ adaptive feedforward control algorithms. This involves automatically adjusting the amplitude and phase of the control variable to ensure that a control action with the same amplitude but opposite phase to the disturbance is applied at the input, thus suppressing periodic disturbances and guaranteeing synchronous control of the system. 3. Application Examples of Motion Controllers 3.1 Hardware Structure of an Open Motion Control System [IMG=Figure 2 Two-Axis Motion Control System Structure Diagram]/uploadpic/THESIS/2007/11/2007111314032480905C.jpg[/IMG] Figure 2 Two-Axis Motion Control System Structure Diagram [IMG=Figure 3 Two-Axis System Software Module]/uploadpic/THESIS/2007/11/2007111314053216575J.jpg[/IMG] Figure 3 Two-Axis System Software Module As shown in Figure 2, the entire system is based on a "PC + motion controller" core, using the NI N17340 series motion controller N17342, Telemecanique drivers, and AC servo motors to form an open hardware structure. In this servo control system, the dedicated CPU on the controller and the PC CPU form a master-slave dual-CPU control mode. The PC is responsible for managing the human-computer interface and real-time monitoring of the control system, including keyboard and mouse management, system status display, control command transmission, and monitoring of external I/O signals. The motion controller is equipped with a rich and powerful motion function library for user use to complete motor motion planning. The system adopts analog output position control. In Figure 2, the magnitude of the analog signal controls the motor speed, and the positive or negative sign controls the motor's forward and reverse rotation, achieving two-axis position control. The X-axis and r-axis origin and limit detection are achieved through a set of mechanical devices. The origin detection switch serves as the zero point position for each axis, and the limit detection switches ensure the working stroke limits of each axis. These status signals are sent to the motion control card's status register and read by the CPU at any time, achieving I/O status signal detection. In terms of hardware, the opto-isolation measures on the motion controller isolate interference from external devices to the internal digital system and effectively prevent damage to the computer system from external emergencies such as overvoltage and overcurrent, greatly improving the system's control accuracy and reliability. 3.2 Software Development of the Motion Control System The motion controller is also equipped with a motion function library, which provides many motion functions for single-axis and multi-axis stepper or servo control, such as single-axis motion, multi-axis independent motion, multi-axis interpolation motion, and multi-axis synchronous motion. The control system based on the N17342 motion controller can be used to develop user applications using LabVIEW, VB, VC, and other languages. Since LabVIEW itself is an NI product, it is the most supported and convenient tool for development. As a graphical programming language, like other high-level languages, it provides various loops and structures, replacing the functions of other languages ​​in the form of Virtual Instrument VI. NI specifically provides VI-NI-Motion for motion control, which users can easily call using graphical programs written in LabVIEW technology. It also facilitates the design of user-friendly human-machine interfaces, enabling human-machine interaction and management. The system's program structure modules are shown in Figure 3. In addition to the main motion control program, it also includes initialization, real-time data interaction with the PC, system protection, and status monitoring. 4. Current Status and Trends in Motion Controller Development Motion controllers adopt an open architecture, are easy to use, feature-rich, and highly reliable. Using the PCI bus, no jumper settings are required on the card; all resources are automatically configured, and all input and output signals are opto-isolated, improving the controller's reliability and anti-interference capabilities. On the software side, a rich motion control function library is provided to meet different application requirements. Users only need to develop a human-machine interface according to the control system requirements and call the instruction functions in the motion function library to develop a multi-axis motion control system that meets the requirements and is cost-effective. Motion controllers have evolved from those based on single-chip microcomputers or microprocessors and those based on ASICs as the core processor, to open motion controllers based on PC buses and using DSPs and FPGAs as core processors. Meanwhile, the organic integration of motion control technology and network technology is a new research and development direction, which can better realize the synchronous control of multiple motors and communication between controllers. Under the control architecture of general controllers and drivers, there are disadvantages such as numerous wiring, poor synchronization characteristics, and non-fully digital nature, and it is difficult for external controllers to read and adjust servo parameters in real time. With the development and application of Ethernet technology, network communication solutions can be used to solve problems in traditional motion control architectures. For example, in serial motion control networks, communication protocols such as IEEE-1394 and SER-COS-II are widely used, and their hardware transmission media are mainly RS-485, fiber optic, FireWire, and Ethernet. 5 Conclusion Motion controllers have been applied in numerous fields, especially in AC servo and multi-axis control systems. They can fully utilize computer resources, conveniently helping users to achieve motion trajectory planning, complete predetermined motion, and high-precision servo control. Motion control technology will continue to combine with AC servo drive technology, linear motor drive technology, etc., promoting the continuous improvement of mechatronics technology in China. (Proceedings of the 2nd Servo and Motion Control Forum, Proceedings of the 3rd Servo and Motion Control Forum)