# Research on the Positioning Method of Steel Belt Anchor Holes Applied in Coal Mine Underground
## 3 Coil Self-Inductance Simulation Analysis  
ANSYS Electronics Desktop 2021 R1 software [25] is a user-friendly tool with powerful functions and a precise structure for 2D/3D electromagnetic finite element analysis. It calculates various electromagnetic fields, including static electric, static magnetic, time-varying electric, time-varying magnetic, eddy current, transient, and temperature fields. The simulation analysis is conducted on the sensor coil of the inductive sensor with the ANSYS Electronics Desktop software. The purpose of the analysis is to explore how the vertical distance between the inductive sensor and the steel belt affects the detection results.  
A portion of the steel belt is selected for analysis in the construction of the steel belt simulation model. The selected section is a steel cuboid with a length of 270 mm, a width of 230 mm, and a thickness of 3 mm. The anchor holes have a diameter of 35 mm. The sensor's coil is made of copper and consists of five turns with an inner diameter of 20 mm  
Figure 4: Sketch of sensor movement patterns.  
and an outer diameter of 40 mm. The solution domain coincides with the coil boundary and is specified as a vacuum. The simulation model is shown in Figure 5.  
To analyze the impact of the distance between the inductive sensor and the steel belt on anchor hole identification, the vertical distance between the coil and the steel belt is set at 10 mm, 15 mm, 20 mm, 25 mm, and 30 mm. The simulated self-inductance of the coil is then recorded as it moves horizontally toward the edge of the steel belt at different positions, as displayed in Figure 6.  
The simulation results indicate that when the coil is close to the steel belt, a valley value of the self-inductance is observed when the center of the coil aligns exactly with the center of the anchor hole, namely when the distance is 38 mm, which accurately reflects the location of the anchor hole. As the distance between the coil and the steel belt increases, changes in the coil's self-inductance become less significant, which cannot accurately indicate the position of the anchor hole. To verify the above simulation results, the voltage of the inductive sensor at different lateral positions are measured at different coil-to-belt distances, as shown in Figure 7. The experiment considers the need to maintain a safe distance between the inductive sensor and the steel belt. It is suggested that when the inductive sensor detects a reduction in the steel plate area, the self-inductance inside the coil decreases, resulting in an increase in the output voltage of the inductive sensor. The results shown in Figure 7 are consistent with the simulation data in Figure 6. The optimal anchor hole detection effect occurs when the coil is at a ver  
Figure 5: Simulation model.  
Figure 6: Relationship between the coil’s horizontal displacement and its self-inductance at different distances from the steel belt.  
from the steel belt and the detection effect gradually worsens when the distance becomes 20-25 mm. Therefore, due to the influence of the inductive sensor structure, the appropriate distance between the coil and the steel belt for detection with the inductive sensor should be 15-20 mm.