## 3 Model Establishment
### The Method of Modelling Process  
In this study, DES technology is employed to model the complex product assembly workshop, as it effectively simulates complex dynamic systems under multiple resource constraints. The production process in such workshops involves multi-stage assembly of large components, requiring a high degree of coordination between resources and logistics scheduling. DES enables detailed modeling of tasks, resources, logistics flows, and event sequences, accurately reproducing workshop operations and offering reliable support for developing and evaluating optimization strategies. The overall process of the complex product assembly workshop production model, based on DES, is illustrated in Figure 4. During model construction, the system first initializes the processing status of each workpiece and machine, as well as the standby positions of all AGVs, ensuring that all resources are in their designated states before the simulation begins. Once initialization is complete, the production tasks commence. If all tasks are finished, the process ends; otherwise, the system continues executing production tasks and checks for material shortages. If materials are available, the assembly tasks proceed. Upon completing an assembly task, if transportation is not required, the system advances to the next task. If transportation is needed, the system issues a transport instruction and assigns an available AGV. If materials are lacking, the system dispatches a replenishment request to an idle AGV to complete the delivery. The overall process of the AGV transport task is as follows. First, an idle AGV receives a transport request from the system and prepares to execute the task. Before the task begins, the system verifies whether the AGV meets the necessary transport conditions. If deemed suitable, the AGV is selected based on task priority, workstation status, and the condition of the workpiece. Once assigned, the AGV proceeds to the designated location for pickup. After collecting the cargo, it transports the items to the specified destination, completing the transport operation. The AGV then returns to its standby position and awaits the next transport instruction. Figure 3: AGV roadmap in the aerospace product production workshop. The pseudocodes for the AGV cargo transfer process and the production control process are respectively Algorithm 1 and Algorithm 2. ```
1. If transhipment request is true then
2. If AGV is idle then
3. Perform transhipment tasks
4. If transport conditions are met then
5. Select AGV according to the selection strategy
6. AGV runs to the pickup position
7. AGV pickup
8. AGV runs to the sending position
9. Send AGV to the standby position
10. Else
11. // Handle the case where transport conditions are not met
12. End if
13. Else
14. // Handle the case where no AGV is idle
15. End if
16. Else
17. // No action needed if no transhipment request
18. End if
19. End

Figure 4: Production process modelling method based on DES. ### Application of Simulation Software

This study employs Plant Simulation software to model and optimize the AGV scheduling problem. To evaluate the effectiveness of the proposed method, comparisons were conducted with other widely used simulation tools, including FlexSim [32], Arena Simulation [33], and AnyLogic [34]. These tools were applied to simulate the same scheduling scenario, and their performance was evaluated based on production efficiency, workstation utilization, and transportation time. Experimental results indicate that Plant Simulation significantly reduces total transportation time in multi-AGV collaborative scheduling and complex task scenarios, while also exhibiting strong stability under high-load conditions. By comparing key performance indicators before and after optimization, the proposed method enhances process efficiency, reduces idle time, and improves both workstation utilization and AGV scheduling performance. These improvements highlight the method's practical applicability in complex assembly workshop environments.