## 5 Testing and Verification of the Virtual Commissioning Model
Modern assembly systems are typically controlled by PLCs, which are currently the most widely used and suitable solution for industrial automation. PLC sequential control operates using a symbolic table of input and output signals and follows a scanning cycle, effectively emulating the behaviour of parallel circuits that respond in real time. When the program is executed in the PLC, it continuously performs the scanning cycle, ensuring real-time processing of input signals, logic execution, and output updates, which are crucial for the efficient and reliable operation of automated systems. PLC control communicates with the virtual model exclusively through a communication protocol using input and output symbols. While input symbols receive electrical signals from devices, output symbols are used to send commands to actuators and other system components, ensuring proper interaction between the PLC and the simulated system. The digital twin model of the assembly system was tested and verified using a virtual commissioning tool, where signals were mapped through the integration of Tecnomatix  
Figure 23: The virtual commissioning project of the assembly system was implemented using an SiL approach, where the digital twin model and the simulated control system operated simultaneously on separate monitors. One monitor displayed the simulation model representing the digital twin, while the second monitor ran the control program, allowing real-time testing and verification. This setup enabled direct interaction between the control logic and the simulated system, ensuring accurate evaluation of system behaviour and response within the virtual commissioning environment. Figure 22: Created virtual model of the automated assembly system in Process Simulate. The system is shown with its components, including the control sequence editor for operation management and sequence visualization. Process Simulate 14.0.1 and Siemens TIA Portal V14. This setup was also chosen to enable model control via an HMI panel, developed in SIMATIC WinCC V14. Signals generated from the logical behaviour models were exported from Tecnomatix Process Simulate 14.0.1 and imported as symbols into the PLC tag table. Figure 24 presents an overview of the symbol table, where variable names, data types, IEC format addresses, PLC connection methods, and comments are defined. In Figure 25, the PLC control program in LAD is displayed in online mode, monitoring the real-time status of the system. Figure 24: Overview of the symbol table in Process Simulate, displaying variable names, data types, IEC format addresses, PLC connection methods, and comments, facilitating efficient signal mapping and integration between the virtual model and external control systems; the red colour indicates both true and false states, depending on the context, as seen online. Figure 25: Testing and verification of the PLC control program on the digital twin model of the assembly system. The virtual model of the assembly system was designed to support multiple communication protocols, enabling PLC control program testing and verification of created programs and sequences during testing. The PLC control program was developed in Siemens TIA Portal V14, while the virtual assembly system was controlled through commands displayed on the HMI panel, ensuring real-time interaction and functional validation of the automation process.