# Performance Evaluation of Track Curvature Sensor for
## 2 Development of the Track Curvature Sensor
### Curvature Sensor Prototype  
A curvature sensor was designed based on the curvature measurement method discussed in the previous section and a prototype was manufactured. Figure 10 shows the shape and structure of the curvature sensor. Figure 11 is the installation position of the curvature sensor installed in a running direction between the vehicle car body and bogies. One set of curvature sensors is installed in the front bogie and the rear bogie, respectively, and a total of two sets are installed per vehicle.  
The curvature sensor has a rectangular cylinder shape structure equipped with a non-contact laser sensor to measure the relative displacement that occurs between the vehicle car body and the bogie when a railway vehicle runs. It was designed to protect the non-contact displacement sensor installed inside the curvature sensor from external alien substances when installed in a railway vehicle. The outer cylinder and the inner cylinder  
Figure 11: Installation position of the curvature sensor.  
Figure 10: Structure of the curvature sensor.  
are structured to be guided and moved by an LM guide installed therein. A wrinkled rubber cover is mounted between the inner tube and the LM guide part to prevent wear and the inflow of external alien substances. In addition, ball joints are mounted on both ends of the curvature sensor to minimize rotational resistance caused by the roll, pitch and yaw movement of the vehicle when installed in the vehicle. Table 2 shows the specifications of the curvature sensor and Figure 12 represents the shape of the manufactured curvature sensor prototype.  
A functional test was performed to confirm the curvature measurement function according to the relative displacement stroke of the manufactured curvature sensor prototype. As shown in Figure 13, the test was performed by setting a stroke according to the curve radius in the curvature sensor and recording the result of the curve radius measured at that time. At this time, one-half of the distance between the center of the front bogie and the rear bogie (\(L\)), and lateral spacing between the curvature sensor and the bogie center (\(x\)), which have a fixed value according to the curve radius calculation formula, were input as 6.9 m for \(L\) and 1050 mm for \(x\). In addition, in the functional test, the curve radius test condition was set from R75 to R1000, which is the curve radius measurement range of the curvature sensor.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Item** & **Specifications** \\ \hline curve-sensing range & R75 to R1000 \\ stroke & 500 \(\pm\) 120 mm \\ laser sensor resolution & 0.1 mm \\ sensor supply power & +18 to +30 V \\ sensor output & 0 to +10 V \\ ball joint rotation angle & \(\pm\)10\({}^{\circ}\) \\ temperature environment & \(-\)25 \({}^{\circ}\)C to +40 \({}^{\circ}\)C \\ \hline \hline \end{tabular}
\end{table}
Table 2: Specifications of the curvature sensor.  
Figure 12: Curvature sensor prototype.  
Table 3 shows the functional test results for the curvature sensor prototype. The error was confirmed to be between \(-1.26\%\) and \(1.36\%\) and it is expected that the manufactured curvature sensor prototype will show good curvature measurement performance.