## 1 Introduction
### Analysis of Virtual-Physical Integration in Various Stages  
The levels of intelligence and virtual-physical integration have progressively increased across the four development stages described above. Figure 1 illustrates the system characteristics, integrated technological concepts, and human-machine collaboration methods exhibited at each stage, revealing the connotations of virtual-physical integration at each stage. The system characteristics exhibited at each stage, categorized by the degree of intelligence, are as follows:  
1. Offline Simulation and Display: During the Integrated Systems and Enhanced Functions stage, this system characteristic was mainly achieved through 3D modeling and virtual reality technologies. For example, using CFD (Computational Fluid Dynamics) offline modeling technology, it is possible to effectively monitor the state of smart factories and provide operational guidance [23]. By the stage of Intelligent and Collaborative Robots, with the development of augmented reality (AR) and digital twin technologies, virtual information can be superimposed on the actual physical environment, allowing operators to intuitively see the equipment status and operational guidance in the real environment, thereby improving operational efficiency and accuracy. 2. Immersive Training and Simulation: Initially, this system characteristic was achieved through virtual reality (VR) technology. With the help of head-mounted devices and controllers, operators could enter a fully simulated industrial environment to perform equipment operation and maintenance training. VR training has significant advantages in improving operator skills and proficiency [24]. Similarly, AR, digital twins, parallel systems, and cyber-physical systems (CPS) technologies can also realize this system characteristic, endowing it with new connotations. 3. Real-time Simulation and Monitoring: This system characteristic is realized through AR technology, which allows real-time monitoring of equipment operational status. Operators can test and optimize equipment behavior in a virtual environment, where the simulation environment can reflect the  
Figure 1: Industrial metaverse evolution: virtual–physical trajectory diagram. reactions of real equipment in real time, achieving efficient virtual-physical integration. In CPS factory modeling and simulation, real-time monitoring and feedback are used to optimize production processes [25]. 4. Production Process Simulation and Validation:  
This system characteristic combines the advantages of virtual simulation and actual operations, using digital twin technology to simulate and validate production processes. Operators perform operations in a virtual environment to ensure the optimization of production processes and the effectiveness of actual operations. The application of digital twin technology in multi-robot systems enhances production line optimization and operational efficiency [26]. 5. Reverse Control:  
This system characteristic is achieved through the combination of real-time data feedback and advanced algorithms, enabling reverse control of equipment. Behaviors and adjustments learned in the virtual environment can be directly applied to actual operations, enhancing adaptive and efficient operations. Real-time monitoring servers allow for real-time data feedback and reverse control of equipment, improving the system's adaptability and efficiency [27]. 6. Human-Machine Integration and Collaboration Platform:  
This system characteristic creates an immersive, fully virtual workspace where operators and team members can interact in real time with colleagues around the globe. The virtual collaboration and innovation platform allows for work and learning in an environment without geographical and physical limitations, realizing global collaborative innovation in the industrial metaverse. In industrial environments, intuitive adaptive control technologies that enhance human-machine interaction can significantly improve team collaboration efficiency and innovation capabilities [28].