# Research on Temperature Compensation Method in Crankshaft Online Measurement System
## 4 Experiment
### Validation of Temperature Compensation  
In order to verify the feasibility of the temperature compensation of the crankshaft measuring machine proposed in this paper, the laboratory crankshaft measuring instrument RD-QZ-201890 was used for experimental testing. The experimental platform is shown in Figure 11.  
An experiment was carried out according to the temperature compensation method mentioned in Section 3. To improve the accuracy of the measurement system, 20 repeated measurements at 4 different temperatures were performed on the crankshaft measuring machine. The main purpose is to get temperature compensation value of calibration part and workpiece to be measured. The materials used for the crankshaft and calibration part are all 45# steel, and the thermal expansion coefficient is 11.59 \(\times\) 10\({}^{-6}\)/\({}^{\circ}\)C. The error \(\Delta\) can be obtained according to Formula (6). In this way, the compensated part diameter can be obtained. The same workpiece was repeatedly measured at different temperatures, and it was found that the radius of the same workpiece showed a large range of dimensional changes. Take the crankshaft main journal J1 as an example. Part of the measurement results are shown in Table 2. The measured radius before temperature compensation is shown in Figure 12. And the measured radius after temperature compensation is shown in Figure 13. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Algorithm** & **BP** & **PSO-BP** & **IDA-BP** \\ \hline MSE & 398.5531 & 118.954 & 83.6031 \\ RMSE & 19.9638 & 10.9066 & 9.1435 \\ Residual error/mV & 3.2468 & 1.3944 & 0.6930 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of the three models. Figure 11: Crankshaft measuring machine. Before temperature compensation, it can be found that the radius value of the main journal J1 measured at different temperatures is different. Obviously, affected by temperature, the error range of the measured value with the same workpiece is relatively large at different temperatures. When the ambient temperature is 17.4 \({}^{\circ}\)C, the measured value of crankshaft main journal J1 radius is smallest, which is 49.9744 mm. When ambient temperature is 28.1 \({}^{\circ}\)C, the measured value of crankshaft main journal J1 radius is biggest, which is the maximum value 49.9900 mm. The error range is 0.0156 mm. After temperature compensation, measured radius value range is 49.9972 mm-50 mm. The error range is significantly reduced, that is 0.0028 mm. The measurement fluctuation is relatively small, and it is closer to the radius value of the main journal J1. On this measuring machine, the crankshaft main journal and connecting rod journal are measured at the same time. So this temperature compensation method is applicable to all main journals and connecting rod journals of the crankshaft. The deviation values before and after temperature compensation are shown in Figure 14. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Temperature** & **17.4 \({}^{\circ}\)C** & **19.8 \({}^{\circ}\)C** & **23.7 \({}^{\circ}\)C** & **28.1 \({}^{\circ}\)C** \\ \hline
1 & 49.9750 & 49.9782 & 49.9846 & 49.9895 \\
2 & 49.9763 & 49.9776 & 49.9851 & 49.9898 \\
3 & 49.9762 & 49.9777 & 49.9848 & 49.9897 \\
4 & 49.9751 & 49.9779 & 49.9854 & 49.9898 \\
5 & 49.9761 & 49.9781 & 49.9845 & 49.9897 \\
6 & 49.9758 & 49.9783 & 49.9855 & 49.9897 \\
7 & 49.9766 & 49.9781 & 49.9852 & 49.9896 \\
8 & 49.9760 & 49.9779 & 49.9855 & 49.9895 \\
9 & 49.9763 & 49.9782 & 49.9847 & 49.9895 \\
10 & 49.9761 & 49.9780 & 49.9849 & 49.9894 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Part measurement data of main journal J1 at different temperatures /mm. Figure 12: Measured radius before temperature compensation. In Figure 14, the polyline with ''*' is the measurement value at different temperatures before temperature compensation, and the polyline with 'o' is the measurement result after temperature compensation.