## 3 Development of a Software for LNG Cargo Welding Automation Using Mobile Robots  
### Fundamental Functions of the Developed Software  
The developed software distinguishes itself from existing offline programming commercial software, such as [14; 15], by its compatibility with mobile manipulators and its ability to handle large workspaces, including intricate tasks that involve both movement and welding operations. The software comprises two primary components: one that processes spatial information related to the LNG cargo window, and the other that generates robot movements based on identified topology information. The overall architecture of the software is depicted in Figure 4. There are two methods for determining the spatial information of the LNG cargo window: extracting topology information between membranes that form the window from CAD files, or receiving input in the form of a self-generated Topology Description File (TDF). If the input is in the form of CAD, the topology generator simultaneously generates TDF files and internal memory space using the extracted topology information. These inputs are illustrated in Figure 4a,b. Figure 5 illustrates the topology of the LNG cargo window. The composition of the LNG cargo window comprises membranes, the topology of which is determined by specifying the names of the membranes located above, below, to the left, and to the right of each membrane. The Topology Definition File (TDF) lists the topology information of all membranes constituting the LNG cargo window, where the topology information of each membrane is expressed by the unique membrane names surrounding it in all directions. The first field of topology information, the membrane name, represents the unique name of the membrane, while the second field, the membrane type, indicates the type of membrane. The LNG cargo window has been created by combining various types of membranes. It is mandatory to adhere to certain guidelines when extracting topology information from CAD files, particularly in the case of a multilayered LNG cargo window, wherein a solitary layer must be assembled and the entire LNG cargo window assembly must be depicted as a collection of assemblies demarcated by layers. Each layer comprises a horizontal enumeration of the membrane component parts that make up that layer. In this context, the names of membrane components must be unique. In the program developed, the membranes were identified by their names without an additional identifier. For example, the names of the membranes are utilized to represent the relative arrangement of the membranes in TDF. It is imperative to comprehend the spatial information of the LNG cargo window before generating robot movements for membrane-joining. Although the robot has general autonomous driving capabilities, the mixed-use function of layer-by-layer maps due to inter-floor movement has not been implemented. However, separate maps have been developed for each destination floor, allowing users to input the current floor and enable autonomous driving on that floor. For welding tasks, the robot must identify the weldable area from its current position. This function is unnecessary for typical stationary robots, but is crucial for robot welding while moving through vast spaces. The weldable area includes not only spatial coordinates, but also the recognition of the membranes included in that area. The robot engages in laser welding considering the quality of the welding, and the target seam must be welded in a single operation. In an LNG cargo window composed of membranes, the welding target seam is ultimately one of the four directions of the membrane edge. Therefore, the membrane completely belonging to the manipulator's operational area of the mobile robot is defined as the Membrane Of Interest (MOI), as represented by (e) in Figure 4. In reality, MOI includes approximately one to three membranes from a single membrane, considering the size of the membranes and support load of the elevator and scaffold in the LNG cargo window space.