0 Introduction
Antenna servo systems, while ensuring precise pointing of ground station antennas to relay satellites, also require high stability, high reliability, and long lifespan, making them one of the most complex and indispensable electronic devices in satellite ground stations. With the rapid development of power electronics, control theory, computer technology, and continuous improvement in motor manufacturing processes, servo systems have evolved from hydraulic to electric. As the scale of satellite ground station construction expands, many ground stations now possess multiple large antennas instead of just one. For these ground stations, with the central control room as a reference point, the distribution of antennas and their servo systems typically exhibits a star topology. Given the trend towards integrated ground station equipment monitoring systems, remote centralized monitoring of each antenna servo system is imperative. Typically, the communication protocols of different antenna servo systems are incompatible, making the design of parallel monitoring software for multiple antenna servo systems quite complex. Therefore, the centralized monitoring of multiple antenna servo systems of various models has become essential for the design and implementation of integrated centralized monitoring systems for ground station electronic equipment.
1 Basic knowledge of antenna servo As early as 1934, the term "servo mechanism" had already appeared. With the continuous development of automatic control theory, the theory and practice of servo system, a branch of automatic control, have gradually matured and have been widely used since the 1950s. [1] The application of servo technology in satellite communication earth station subsystem has formed antenna servo technology. Early DC servo systems were mostly composed of thyristor DC speed control drive cabinet and ACU with industrial control computer as the core. There is also a trend of AC in general servo systems. The main reason is that AC servo motors overcome the various disadvantages of brushes, commutators and other mechanical components in DC servo motors. In particular, the overload characteristics and low inertia of AC servo motors further demonstrate the superiority of AC servo systems. 1.1 The main functions and performance indicators of the antenna servo system are as follows: (1) Main functional indicators 1. Azimuth and elevation axis motor drive control and braking control; 2. Azimuth and elevation axis position detection and antenna control in multiple modes; 3. Can store multiple satellite positions; 4. Three-level limit protection: soft limit, switch pre-limit and final limit; 5. Elevation collection lock control; 6. Fault display, alarm and recording. The parameters of the satellite observed by the earth station antenna are determined by the position of the earth station antenna and the position of the geostationary satellite. The position of the geostationary satellite is represented by the longitude of its sub-satellite point, and the position of the earth station antenna is represented by the geographical longitude and geographical latitude of the location. Based on the longitude and latitude of the earth station antenna location and the longitude of the satellite, the azimuth angle (AZ) and elevation angle (EL) of the antenna aligned with the satellite can be calculated, and the antenna can be adjusted using AZ and EL to align with the corresponding satellite. Let the latitude of the earth station be . . (North latitude is positive, South latitude is negative), longitude is (East longitude is positive, West longitude is negative), satellite longitude is (East longitude is positive, West longitude is negative), azimuth is zero with due north and positive with clockwise direction. Using the geometric relationship between the geostationary satellite and the earth station, the calculation formulas for the azimuth angle Az and elevation angle EL of the earth station antenna pointing at the satellite can be easily derived from geometry and spherical trigonometry [2]. When the earth station antenna is located in the Northern Hemisphere, the calculation formulas for its azimuth angle and elevation angle pointing at the satellite are 1-1 and 1-2: Rs represents the Earth radius (6378km), and H represents the altitude of the geostationary satellite above the Earth surface (35786km). When the earth station antenna is located in the Southern Hemisphere, the azimuth angle AZ of the antenna pointing at the satellite is calculated as follows: AZ is the azimuth angle of the antenna pointing at the satellite when the earth station antenna is located in the Northern Hemisphere. 1.2 Composition and Principle of Antenna Servo System An antenna servo system is a device that performs antenna driving, position detection, and various control functions. The antenna servo system, the drive motor on the antenna, the position sensor and limit device, and the tracking signal loop equipment together constitute an antenna servo tracking system. It can generally be divided into the following five parts: power supply, system control, azimuth drive, pitch drive, and human-machine interface. An antenna servo system generally includes three control loops: a signal control loop, a position control loop, and a speed control loop. A block diagram of an antenna servo system is shown in Figure 1.Figure 1. Block diagram of antenna servo control system
When the antenna is operating in tracking mode, all control loops function normally, and the ultimately controlled variable is the antenna's received signal. When the antenna is operating in various position control modes, the signal control loop is open-loop, while the position control loop and speed control loop are active, and the ultimately controlled variables are azimuth and elevation. 2. Working principle of centralized monitoring of antenna servo The centralized monitoring system of antenna servo generally consists of multiple sets (up to 8 sets) of antenna servo systems, centralized monitoring equipment of antenna servo and monitoring host computer of ground station. The composition diagram of the centralized monitoring system of antenna servo is shown in Figure 2. The centralized monitoring equipment of antenna servo is compatible with the communication protocols of various types of servo equipment such as dual motor gap elimination, AC speed regulation, AC and DC speed regulation, simple antenna controller, feed polarization controller, etc., and monitors up to eight sets of antenna servo systems in real time through RS485 serial port. [3] Figure 2 Composition diagram of centralized monitoring system of antenna servo The centralized monitoring equipment of antenna servo has two main functions: remote real-time monitoring of multiple types and multiple sets of antenna servo systems, and responding to the monitoring operation of the monitoring host computer of ground station. The monitoring host computer of ground station implements remote desktop control of the equipment through TCP/IP protocol and with the help of third-party software, thereby realizing the function of monitoring each antenna servo system through the equipment. 3 Hardware composition of centralized monitoring of antenna servo The centralized monitoring equipment of antenna servo mainly consists of centralized monitoring software of antenna servo, industrial control computer, RS485 communication card and other parts. Both the industrial control computer and the RS485 communication card are purchased externally. In ground stations with fiber optic communication networks, or between several ground stations, RS485/optical conversion modules can be used to significantly extend the serial communication distance, while simultaneously solving problems related to electromagnetic interference, ground loop interference, lightning strikes, and surges. This greatly improves the reliability, security, and confidentiality of data communication. (See Figure 3.)Figure 3. Deployment diagram of centralized monitoring of antenna servo after RS485/optical conversion module
3.1 Characteristics of LabVIEW ITRI Language
The main features of the LabVIEW language are as follows [4]: (1) It provides a rich library of functions for data acquisition, analysis and storage; (2) It provides traditional program debugging methods, such as setting breakpoints and single-step execution, and provides unique execution tools to make the program run in an animated manner, which is conducive to designers and developers observing the details of program operation, thereby improving the efficiency of program debugging and development; (3) The 32-bit compiler compiles and generates a 32-bit compiler to ensure the high-speed execution of user data acquisition and test measurement schemes; (4) It integrates interface functions of various instrument communication bus standards such as PCI, GPIB, PXI, VXI, RS232/485, USB, etc., which makes it convenient for developers to use different bus standard interface devices and instruments; (5) It provides a large number of mechanisms for linking with external code or software, such as DLL (Dynamic Link Library), DDE (Shared Library), AetiveX, etc.; (6) It has powerful Internet functions, supports common network protocols, and facilitates the development of network remote measurement and control instruments; (7) It uses the ApplicationBuilder software package to generate executable applications and independent installers that are independent of the source code environment. 3.2 Development steps of virtual instrument program LabVIEW program is called virtual instrument program, abbreviated as VI. A basic VI consists of three parts: front panel, block diagram program and icon/connection port. [3] The development steps of a virtual instrument program are as follows: (1) Design window in front panel (2) Place nodes and block diagram in flowchart editing window. (3) Data flow programming (4) Run verification (5) Program debugging (6) Data observation (7) Name and save 4 Specific function implementation Considering the configuration item distribution of antenna servo centralized monitoring software, antenna servo centralized monitoring software adopts a three-layer software programming structure 19 for development, as shown in Figure 4. The software hierarchy diagram is shown in Figure 4. The three-layer structure is as follows from top to bottom: MainLevel1 (top layer), TestLevel1 (functional layer) and DriverLevel (driver layer). The driver layer contains the lower-level functions such as communication and control between the program and all hardware or other application software. In the functional layer, it is how to connect the functions of each driver layer to realize a continuous and meaningful process to complete a certain function. The biggest advantage of a three-tier software architecture is that it maximizes the reusability of program code. [5] 4.1 Polling Algorithm The polling algorithm embodies a management approach for equipment. This software developed a concurrent polling algorithm to meet the software requirements for parallel monitoring of the servo system; and a serial polling algorithm to meet the software requirements for controlling the selected servo system. Parallel monitoring utilizes the fact that there is no inherent data or resource connection between the serial ports of a multi-serial-port communication card, possessing the decomposability of tasks and data, allowing for task parallelism and data parallelism programming modes. Figure 5 shows the source code for forming the concurrent polling queue and the serial polling queue.Figure 5. Concurrent query queue vs. serial query queue
4.2 Human-Computer Interaction Interface
The antenna servo centralized monitoring software accurately judges the opening or blocking of various remote control functions in real time based on various alarm information, so as to avoid the situation where the user performs control operations through the human-machine interface of the antenna servo centralized monitoring equipment but the servo system does not execute the control failure. The main requirements of the user interface are: to use a parallel window interface to display the status of 8 antenna servo systems and to use a pop-up window to display the status of a single antenna servo system. Specifically, it can be divided into the following parts: (1) The main interface displays the status of the eight antenna servo systems; through this interface, users can select the antenna to control and terminate the program.
(2) The antenna position control interface realizes functions such as preset position, satellite calculation, and satellite preset; 5. The research results verify the prototype of the antenna servo centralized monitoring equipment. The equipment is applicable to satellite ground stations where the antenna servo equipment is hundreds of meters, several kilometers or even further away from the central computer room, or where there are many antenna servo equipment, or both of the above situations exist. Currently, six of this type of antenna servo centralized monitoring equipment have been put into actual use in various satellite ground stations. The characteristics of the antenna servo centralized monitoring equipment are: (1) Complete functions: The equipment realizes remote centralized monitoring and control of eight sets of antenna servo equipment, comprehensively monitors the operation information of each servo system in real time, and provides multiple control modes such as preset position, manual speed control, storage and preset satellite, automatic tracking, automatic search, and polarization control. In addition, there are auxiliary functions such as alarm logs and operation logs. (2) Good compatibility: The device is compatible with the communication protocols of current mainstream antenna servo systems such as dual-motor backlash elimination, AC/DC speed regulation, AC speed regulation, simple antenna controller, and feed polarization controller, realizing centralized monitoring and control of multiple servo systems. (3) According to user feedback, the human-machine interface is user-friendly. 6 Summary This paper, through the research on centralized monitoring and control technology of antenna servo and the practice of software engineering methods and processes, has successfully solved the problem of incompatible communication protocols of multiple antenna servo devices and the design of software for parallel centralized monitoring and control of multiple sets of antenna servo devices, accumulating knowledge and experience for future ground station equipment system monitoring projects. About the author: Wang Naixu (1986-), Master's student, whose main research areas are intelligent control and pattern recognition. Email: [email protected] Tel: 13070899172 Address: No. 53 Zhengzhou Road, Sifang District, Qingdao City, Shandong Province Postcode: 266042
