## 3 OPC UA-Based VR/AR Collaboration Model
### VR/AR Collaboration Model  
Figure 1 depicts the main components of the VR/AR collaboration model using CPS by dividing the VR/AR layer, Visualization layer, and CPS layer.  
The CPS Layer is the central source data store of this system and serves as middleware. The standard of OPC UA, an international standard technology for smart factories used for Digital Twin technology in factories, was applied here. OPC UA is not just a protocol, but it standardizes all the authentication, exchange, storage, alarms, and distribution required for data exchange. The CPS service has a real-time memory structure called Address Space, which serves the machine's information modeling and attribute values in real time. In this system, real-time data generated by a simulator or an actual machine is delivered to a VR/AR rendering service. It also exchanges data with standard specifications on all existing systems that require data interworking and exchange. In big data analysis, all information data generated in this cooperative design is stored and used to generate big data. The simulation, which is characteristic of this service, calculates real-time data, such as the actual machine operating based on the physical engine, stores and analyzes it, and lastly returns the analysis results to the simulator to improve the accuracy and virtuality of the simulation. Further, by visualizing and serving all data, participating designers provide services that enhance design capabilities through visualized data analysis. Moreover, by providing a management module, it offers systematic services such as all of the user management, security management, authentication management, access management, and history management services necessary to service this 3D collaboration design system.  
The visualization layer optimizes 3D modeling to convert models extracted from 3D design files into VR/AR, converts them into stream images from virtual rendering servers, and simultaneously transmits simulator values to VR/AR in real-time interworking with CPS. It synchronizes the time and data of simultaneous multi-access users; detects the location, control, and event occurrence of design participants; and communicates in both directions with the VR/AR rendering server in real time to service the video stream without delay. Further, the voices of participating designers are synchronized in real time through VOIP.  
The VR/AR Layer based on 3D design modeling and physical engine is used for product development, and the contents necessary for product inspection are developed and applied to deliver inspection results to CPS systems. The CPS system delivers it to the existing system required for existing inspection and quality. Based on the 3D design modeling and physical engine used for product development, it provides contents and  
Figure 1: VR/AR collaboration model construction process.  
services that allow customers to perform maintenance and defect repair through an AR service that allows them to watch video transmitted through AR goggles and Live Cam.  
Figure 2 shows the system configuration diagram. It is a structure in which several engines and servers such as real-time rendering and big data analysis engines are combined with existing CPS servers and VR/AR collaboration servers. Digital Twin is not essential for untact manufacturing VR/AR collaborative AI systems, but the most effective configuration is to build real-time Digital Twins for factory machines and robots. In the OPC UA-based CPS server and VR/AR collaboration system, the real-time data of a Digital Twin is an important system for data analysis and prediction. Collaborators and fielders are connected to each other with videos through communication, and the fielders' images are shared with collaborators. If a Digital Twin is used, VR models and CPS data are overlaid over real-time images with an AR function.