# A Method for Building a Mixed-Reality Digital Twin of a Roadheader Monitoring System
## 4 Laboratory Experiment of the Roadheader Digital Twin Monitoring System
### Accuracy Validation of the Digital Twin  
The movement positions of the cutting arm, shovel plate, rear support, and slewing platform can all be represented by the mechanism angles. During the cutting operation, the angles of the up and down swinging of the cutting arm and the left and right rotation of the slewing platform are monitored. This monitoring can be used to evaluate the accuracy of the virtual twin of the monitoring system. Assuming that the angle values of the cutting arm and the slewing platform in the initial state are both 90\({}^{\circ}\), the angle values of the two components are collected every 0.5 s, and the curve graphs are plotted with time as the abscissa and the angle values as the ordinate, as shown in Figures 17 and 18. Figure 21: Transmission error of slewing platform angle. Figure 19: Transmission error of cutting arm angle. Figure 20: Measurement error of cutting arm angle. Based on the above data, the following conclusions are summarized:  
1. Timeliness of virtual mapping. The operating information of the roadheader test prototype model can be quickly transmitted to the digital model to achieve the action synchronization of the two. The delay time difference scatter plot is shown in Figure 23. After measurement and calculation, the average delay is 60 ms, and the timeliness is good. 2. Accuracy of virtual-real interaction. The angle values of the mechanism motion positions between the roadheader test prototype and the digital model are highly consistent. The maximum transmission errors of the cutting arm and the slewing platform are 3.756% and 5.000%, respectively, and the average transmission errors are 0.288% and 0.757%, respectively. There are mainly two reasons for the generation of transmission errors: Firstly, field loss occurs during the process of data format conversion and splitting, resulting in a deterioration in the accuracy. Secondly, the program cannot process data in a timely manner during the measurement process, resulting in data delay, thereby causing deviations in the observed data. 3. Reliability of virtual-real interaction. The measurement errors generated during the action execution process of the roadheader test prototype model are relatively large, with the maximum values being 15.028% and 19.725%, respectively, and the average values being 3.695% and 1.306%, respectively. Although the maximum values are large, the average values are both lower than 3.700%, so they basically meet the accuracy requirements. There are the following three reasons for the generation of the measurement errors: Firstly, errors arise due to the insufficient accuracy of the actuator of the test prototype and the existence of a large rotation dead zone. At the same time, there is accuracy loss in the process of the digital signal to electrical signal conversion and pulse signal length calculation, inevitably leading to observation errors. Secondly, there are a few moments with large delays during the signal transmission and execution process, which leads to the action delay of the actuator and thus causes large deviations. Finally, problems such as the accuracy of the sensor and the jitter of the servo motor will further expand the error. In conclusion, through the analysis of the test results, the following conclusions can be drawn: The architecture of the roadheader digital twin monitoring system can complete the \"bidirectional mapping and bidirectional transmission\" of the roadheader cutting data between the physical entity and the virtual entity with a high accuracy and fast speed, thereby achieving bidirectional control of the behaviors and synchronization of the actions of the multi-dimensional attribute physical entity and the twin virtual entity. At the same time, supported by the mixed-reality technology, the roadheader driver can understand the working status of the roadheader during the cutting operation  
Figure 22: Measurement error of slewing platform angle. more quickly and stereoscopically, improving the accuracy of monitoring and the efficiency of the cutting work.