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Calibration of force sensor

Calibration of force sensor mounted in tire tread block under rolling contact condition


This study investigates a sensor calibration method for accurately measuring the three-axis contact forces of a single tread block using sensor-equipped tires. Two calibration methods were examined: a static method based on forces generated by applying three-axis displacements, and a dynamic method using rolling contact. Significant errors were observed in the static method when road surface sensors were used as reference values during tire rotation. In contrast, the dynamic method showed minimal speed dependency but was influenced by the slip angle and inflation pressure. 

It was confirmed that the accurate reproduction of three-axis contact forces from tire sensors is possible if calibration coefficients corresponding to the slip angle and inflation pressure are available. Several methods have been proposed previously to measure the contact force of the entire tire by attaching sensors inside the tire; however, the method proposed in this study can measure the triaxial load acting on a single tread block, which is particularly useful for designing the tread pattern in the contact patch and is unique from previous studies. Considering the conditions commonly used in general tire tests, it will be necessary in the future to establish calibration coefficients that consider the slip angle, tire inflation pressure, and speed; in addition, the validity of linear interpolation should be examined.

In this study, a sensing tire was developed by attaching a three-axis force sensor to the belt area of a tire, thereby enabling the measurement of the contact forces on a tread block. The sensor was calibrated to ensure accurate measurements of the sensing tire. Calibration methods can be broadly classified into two types: static and dynamic. When the load of the calibration road under tire rotation was used as the true value, significant errors occurred when using the static calibration method. In contrast, the dynamic calibration method showed minimal influence from speed variations. 
However, changes in the slip angle and inflation pressure were influenced, with the impact of the slip angle being particularly significant. A calibration matrix was created based on the slip angle and inflation pressure, and it was confirmed qualitatively and quantitatively that the contact force could be accurately reproduced by the tire sensors. The ability to perform calibrations with varying slip angles is a major novelty of this study. In addition, it was demonstrated that the stick-slip phenomenon occurring within the tread block could be measured.
Future challenges include expanding the range of calibration conditions. It is necessary to verify whether interpolation is possible when changing variables, such as the vertical load, slip angle, tire inflation pressure, and speed. Furthermore, because the tread block was not positioned at the center of the tire width, the deformation of the tread block was not symmetrical when the slip angle changed in both directions. Therefore, calibration is required when the sign of the slip angle changes.

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