Abstract This paper discusses the composition of a servo system and the design concepts and methods of the CU and DU. Servo control systems are increasingly widely used in industrial sectors. Their main task is to control the position of various functional components quickly, accurately, stably, and reliably, ensuring that the electric axes of the functional components are always aligned with the target to complete various tasks. Keywords CU DU PDU 1 System Composition The task of a servo control system is to adopt various control strategies to quickly, accurately, stably, and reliably control the position of the target, ensuring that the mechanical axes of the functional component mounts move according to control commands, or that the electric axes of the functional components are always aligned with the target to complete various tasks, and ensuring that the functional component system operates safely, reliably, and stably for a long time. The servo control unit mainly consists of a control unit (CU), a drive unit (DU), an axis angle encoder (PDu), an error demodulator, safety protection logic, and actuators, measuring elements, and control and protection elements installed on the functional component mounts. The functional component control unit (CU) is the control center of the servo system. It performs various controls on the movement of the functional components and calculates and implements various control strategies in real time, ultimately achieving precise positioning of the functional components. The Control Unit (CU) is based on an industrial control computer, integrating control, monitoring, calculation, and fault monitoring. It provides safe and reliable operation of functional components and utilizes flexible, fully digital equipment. The CU offers advanced control algorithms and measures to achieve closed-loop position control of each axis, PID controllers, data acquisition and transmission, communication with the host computer, and system parameter setting and storage. The CU performs real-time inspections of key operating points, such as power supply voltage, state switching, and safety switches, and takes timely corrective action. The Drive Unit (DU) consists of a power amplifier, loop control, drive motor, and safety control unit. It adopts mature current loop and speed loop structures, and the control principles and equipment configurations for orientation and depression branches are basically similar. Besides receiving commands from the functional component control units, the Drive Unit (DU) has independent control functions, facilitating use and maintenance. The tracking error demodulator outputs an error voltage, which the CU uses to perform loop correction calculations and sends a speed signal to control the motor's rotation, driving the functional components to rotate in the direction of reducing the error, thus completing the task. The shaft angle encoder converts the analog signal output from the angle sensor's rotary transformer into a digital signal and provides it to the CU. Various safety protection devices and components are installed on the functional component base, indicating various functional states and providing necessary protection for personal and equipment safety. Therefore, the drive unit is equipped with limit switches and locking linkage protection functions. 2. Drive Unit (DU) The starting point for the drive unit design is to ensure the equipment can operate reliably for a long time while meeting technical specifications. Therefore, reliability design is a key consideration in the drive unit design. Considering the technical requirements, reliability requirements, maintainability requirements of the servo control system, and our technical advantages in thyristor power amplifiers, the core component of the functional component drive unit, the power amplifier, adopts a single-phase full-wave inverse parallel thyristor power amplifier with circulating current. The biggest advantages of using a single-phase full-wave inverse parallel SCR power amplifier with circulating current are simple circuitry, mature technology, strong engineering inheritance, high reliability, and good maintainability. The azimuth and elevation branches both adopt a single DC motor drive and mechanical backlash elimination scheme. Each motor has its own independent speed loop, current loop, voltage loop, and power amplifier. The drive unit also includes control and protection logic circuits. 2.1 Drive Unit Loops The drive unit, in principle, is a dual closed-loop speed control system with both current and speed. The current loop is primarily designed to overcome the dead zone and nonlinearity of torque control, maintain controllable current, prevent overcurrent, improve the motor's dynamic characteristics, and provide a wider frequency control target for the speed loop. It also forms the basis for torque distribution and backlash elimination. The speed loop is mainly designed to improve resistance to load disturbances and grid disturbances, overcome the nonlinear characteristics of the load and motor, expand the speed range, improve low-speed stability, and provide a good control target for the position loop. Both the current and speed regulators use parallel PID controllers. The current loop uses a first-order zero-steady-state-error design, and the speed loop uses a second-order zero-steady-state-error design. 2.2 Control and Protection Logic To ensure the safe and reliable operation of functional components, safety protection switches are installed in the functional component housing, such as: handle interlock, pitch axis pre-limit and final limit switches, and high-voltage and audible/visual alarms. Motors and power amplifiers are equipped with overvoltage absorption, surge voltage absorption, phase sequence and phase loss protection, overload protection, current limiting, automatic air switches, and fuses. 3 Control Unit (CU) From the system principle block diagram, it is easy to see that the CU's main tasks are communication, monitoring, and real-time calculation. 3.1 Main Functions of CU Switching operating modes, status display, real-time data recording and post-processing printing, functional component axis angle encoding and display, receiving commands from the host computer, and receiving operator input. Functional component safety protection. 3.2 CU Hardware The functional component control unit (CU) is based on an industrial control computer system, integrating control, monitoring, and calculation to achieve safe and reliable control of functional components. The CU mainly consists of an industrial control computer (including various templates), a monitor, a keyboard, a mouse, etc. • Communication card: used for communication with the host computer. • A/D card: analog input board, used to receive incoming level signals and error voltage signals. • D/A card: 2-channel analog output board, used to send speed command signals to the DU. • I/O card: opto-isolated and relay-isolated I/O board, used to implement the interface for control signals and status signals with the DU, as well as various digital information. • Encoding card: a self-developed angle encoder board conforming to the ISA bus. The shaft angle encoder uses a multi-stage resolver as the angle measuring element and an RDC-based conversion circuit. The shaft angle encoder is made into a board structure, designed according to the ISA bus, and can be directly plugged into a PC industrial control chassis. It features high precision, easy development, and stable and reliable performance. [b]4 CU Software 4.1 Overall Software Description[/b] Software is the soul and nerve of the equipment. Its main task is to direct and coordinate the hardware to complete the corresponding functions. From a macro perspective, software functions mainly include communication, control, calculation, monitoring, data acquisition, and display functions. The system software operates fully automatically. The real-time control part runs in the background and is invisible to the user; what the user sees is the human-machine interface. The real-time control software first initializes the system, including port initialization, data initialization, and variable initialization. Only after initialization is complete does it begin responding to external events and timed events. 4.2 Software Module Hierarchy Following the principles outlined above, in the software system design, software modules are divided into four main layers, from bottom to top: The hardware control layer provides access to hardware resources such as ports, interrupts, and communication ports. All hardware access must be through the hardware control layer. For the same hardware, only one external module can access it at a time. External modules must apply for access rights from the hardware control layer module; only the module with control rights can perform hardware operations. The hardware control layer module provides services to the device control layer module. The device control layer module uses virtual functional components to track various devices in the subsystem, such as drive mechanisms, encoders, and position loops. It encapsulates the interface protocols and operations for each device, and collects the device status. The device control layer provides the connection status, operating status, and action execution status of the devices upwards, and communicates with the actual devices in the hardware system downwards through the hardware control layer. The human-machine interface layer realizes human-machine interaction work such as displaying monitoring data and receiving operation commands. The human-machine interface requests data and status of the devices from the virtual devices in the device control layer, and requests the system's working status data from the management module in the application management layer, and displays this data. 5 Real-time control implementation function The CU part of the program needs to be executed in a timed loop, such as data sampling, automatic tracking, digital guidance, etc., which has high real-time requirements. Therefore, a hardware timer is needed to periodically generate interrupt signals to provide accurate timing. The real-time control program module runs as the interrupt service routine of the timer interrupt. The real-time control part of the CU needs to complete the following tasks: acquisition and control of the motion status of functional components, acquisition and control of the working status of drive units, angle encoding, data acquisition, processing and control protection logic of various working modes, and communication with the host computer. The human-machine interface (HMI) of the CU mainly performs the following tasks: • Displaying system operating status and fault information; controlling operator commands; inputting parameters for various operating modes; and system settings. References: 1. Li Xuegan. Computer System Architecture. Xi'an University of Electronic Science and Technology. 2. Advantech Manual. Taiwan Advantech. 3. User Manual. AD Company. Author Biography: Yang Guangnan, graduated from Xi'an University of Electronic Science and Technology, has been engaged in research on computer control technology and received the second prize of the Science and Technology Progress Award from the former Ministry of Electronics Industry. Servo System Design: PDF