# The Evolution and Development Trends of LNG Loading and Unloading Arms
## 3 Development of Land-Used LNG Loading and Unloading Arms
### Land-Used Loading Arm Actuation and Its Intelligence and Automation  
Due to differences in working environments and application requirements between marine loading and unloading arms and land-used loading and unloading arms, there are significant disparities in their intelligent development directions. Marine loading and unloading arms need to operate on swaying tankers, so their intelligent development focuses more on the precise positioning and docking of flange ports, as well as the remote monitoring and control of the loading and unloading arms. Land-used loading and unloading arms mostly operate in relatively stable environments, and their intelligent development should focus on improving the convenience, safety, and loading and unloading efficiency of the loading arm operations. For example, in unmanned tank truck loading and unloading operations, integrating functions such as quantitative loading controllers, license plate recognition systems [62; 63], reservation systems, and skid-mounted systems [64] to achieve real-time monitoring throughout the process can greatly enhance loading and unloading efficiency and safety. The automatic LNG loading process is shown in Figure 13.  
There are mainly two ways for the land-based loading arms to dock with the loading and unloading ports: manual dragging docking and mechanically driven automatic docking. The comparison between the two methods in terms of operation efficiency, docking precision, safety performance, cost, and environmental adaptability is shown in the following Table 1.  
Figure 13: The automatic LNG loading process. To improve loading efficiency, optimize the tank truck filling process, and enhance the intelligence and automation of tank truck filling, an intelligent management and control system for LNG tank trucks is of great importance. CNOOC Gas and Power Group Co., Ltd. [65] proposed an intelligent filling system for LNG tank trucks (the case is depicted in Figure 14), which includes a tank truck loading skid, a quick-connection interface with the tank truck, an upgrade of tank truck instruments, and a tank truck vehicle management process control system. This system enables remote monitoring and management of the tank truck filling situation through a PC. The loading skid is equipped with its own PLC control system, which uses GPRS [66] technology to interact with the computer, allowing one person to control the operations of multiple loading skids. Although this research has made the tank truck filling process more intelligent, there are still some issues in terms of automation. For example, the movement of the loading arm still requires manual dragging. Although the structure of the loading arm has been optimized to make the outer arm lighter, the operation mode still relies on manual intervention, and the full-automation docking of the loading arm cannot be achieved. The automated docking technology for LNG loading arms aims to achieve rapid, safe, and unmanned operations between tank trucks and storage tanks or refueling stations, representing a critical development direction for LNG land transportation and refueling systems. The objectives of this technology include fully unmanned operations, adaptability to various complex environments, precise docking with the flange interface of tank trucks within a \(\pm\)1 mm accuracy range, and emergency disconnection with valve closure within 0.5 s in case of contingencies. The key to realizing automated docking for loading arms lies in trajectory planning [67] and image processing [68].