# A Method for Building a Mixed-Reality Digital Twin of a Roadheader Monitoring System
###### Abstract  
The working environment of the coal mine boom-type roadheader is harsh with large blind areas and numerous safety hazards for operators. Traditional on-site or remote control methods do not meet the requirements for intelligent tunneling. This paper proposes a digital twin monitoring system of an EBZ-type roadheader based on mixed reality (MR). First, the system integrates a five-dimensional digital twin model to establish the boom-type roadheader digital twin monitoring system. Second, the Unity3D software (v2020.3.25f1c1) and the MR Holdens (v22621.1133 produced by Microsoft) are used to build a digital twin human-machine interaction platform, achieving bidirectional mapping and driving of cutting operation data. Third, a twin data exchange program is designed by employing the Winform framework and the C/S communication architecture, making use of the socket communication protocol to transmit and store the cutting model data within the system. Finally, a physical prototype of the boom-type roadheader is built, and a validation experiment of the monitoring system's digital twin is conducted. The experimental results show that the average transmission error of the cutting model data of the twin monitoring system is below 0.757%, and the execution accuracy error is below 3.7%. This system can achieve bidirectional real-time mapping and control between the twins, which provides a new monitoring method for actual underground roadheader operations. It effectively eliminates the operator's blind areas and improves the intelligence level of roadheader monitoring. Beyond mining, this methodology can be extended to the monitoring and control of other mining equipment, predictive maintenance in manufacturing, and infrastructure management in smart cities. a 2 tools [3]. The coal mine roadheader is an exceptionally dangerous equipment because when it operates, the rock is crushed under pressure. When coal and rock burst suddenly, a large quantity of gas (mainly methane) is released. In the air mixture after ejection, the concentration of methane can reach 100%, which might cause significant casualties [4]. Realizing the visual remote monitoring of the roadheader and keeping the roadheader operators away from the harsh environment can effectively improve the working conditions of underground personnel, guarantee the personal safety of workers, and improve work efficiency, all of which hold great significance for achieving the intelligent unmanned mining of deep coal mines [5; 6; 7]. However, the realization of the remote monitoring of roadheaders still encounters numerous problems. Factors such as low underground illumination, high dust concentration, water mist generated during cutting operations, and electromagnetic interference lead to poor imaging quality, restricting the application of traditional video monitoring technologies. Another instance is that the positioning technology of the roadheader is not yet mature and reliable. The positioning error of inertial navigation technology accumulates over time, and visual positioning is also challenging to apply due to the interference of the roadway environment [8]. The digital twin, as a novel type of digital technology for system modeling, monitoring, and analysis, can be an effective solution to the challenges mentioned above [9]. It is an organic combination of several technologies, including physical sensing technology, data processing and analysis technology, simulation technology, and computer technology, etc. [10; 11]. The digital twin emphasizes the two-way interaction and mapping of information between the physical world and the digital space [12], that is, the twinning of data. A digital twin system comprises two twins: the physical entity and the digital model.