## 5 System Feasibility Verification  
To verify the success rate and efficiency of manufacturing, the experiments with physical units and virtual systems are conducted, respectively. In the experiment of the robot manufacturing unit, the trajectory planning algorithm is applied to the prototype mainly through the test of manufacturing accuracy and time. By tracking the manufacturing process, the operation of the whole production line and the state of the robot can be known. The experimental physical prototype of the two-arm cooperation robot is shown in Figure 25.  
To verify the synchronization relationship between the virtual and the physical system, the physical manufacturing unit is connected to the virtual system. The initial state of the system is adjusted to match the physical operation unit, and the state of the robot is judged by observing the operation process of the physical unit. Data from the physical unit manufacturing process are sent to the virtual system to complete the precise manufacturing of the virtual system, which can monitor the status of the system in real time. At the same time, by observing the trajectory of robots in multi-robot cooperative CBFMS, we can judge whether the two-arm cooperation robots are assembled according to the optimal trajectory, which is of great significance to the practical research of dual-robot-arm cooperation. The experimental software environment is Microsoft Visual Studio 2019 and Unity3D 5.5.2f1 development platform, and the hardware environment is Intel (R) Core (TM) i7-11800H @ 2.3 GHz processor and NVIDIA GeForce RTX3060 display adapter. The multi-robot cooperative CBFMS includes the parts, carriers, robot system, goods shelves, boxes, rails, etc. The robot system is composed of a six-axis robot arm, a four-axis robot arm, a parallel robot, a mobile robot, end clamping jaws, and industrial control system. The composition of the DT system and the information of each production unit are displayed through data interaction, which is convenient for customers to observe the productivity and operation status of the equipment. The CB flexible manufacturing DT system is shown in Figure 26.  
Figure 26: Main interface of DT system of multi-robot cooperative CBFMS. Figure 25: Two-arm cooperation robot physical prototype. Through a visual display of DT system data, the whole state of the production line can be clearly seen in the main interface. The DT system of the multi-robot collaborative CBFMS built for a 3D engine in the middle can visually display the dynamic effect of each manufacturing unit. The other parts visually display the relevant operating parameters generated by system manufacturing in the form of data diagrams, including the production status, production data, time cost, equipment energy consumption, and fault status. The lower part is the buttons of each unit of the system. Each unit system is switched by clicking the button on the main interface. After entering, the production status of each unit is viewed, including the total cost of path length, time, manufacturing accuracy, etc. The different units are shown separately in Figure 27.  
Serious consequences will occur if the fault cannot be found in time. The DT system's visual service is used for fault display. When the real physical production line encounters problems, it will send a signal to the DT system. When the DT system receives the fault signal, the corresponding fault unit will brighten, which is convenient for operators to find the fault in time. The DT system highlighted when a unit fails is shown in Figure 28.  
When a unit in the system fails, the unit in question lights up a red light, and the whole system stops working. When entering the work interface of the unit, the data of the whole system turn red and stop updating, which facilitates the operator finding the fault. To verify the validity of the design scheme in this paper, the multi-robot cooperative CBFMS is compared with the traditional CBs manufacturing scheme through a digital visual service system.