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The angle of attack (AOA) α refers to the yaw angle of the wheelset relative to the track (Figure 1) resulting from the wheelset inability almost never to perfectly align with the track tangent during curve negotiation. The phenomenon is the most pronounced in case of the leading wheelset and in the sharp curves. Considering its importance for estimation of the railway vehicles curving performances, this paper presents the development of laser based system for AOA measurements installed on the track, with emphasis on the factors influencing uncertainty of the whole measurement process depending on the selected measuring principle and laser device quality. Other similar systems using possible measuring principles [1–4] presented by other authors were also analysed. Common to all systems, whether installed on the tracks or on the vehicles, is that they use different sensors and transducers for detecting the wheel position relative to rail. Angle between the reference wheel line and the reference rail line in the horizontal plane determines wheel to rail angle of attack. Any horizontal line on outer or inner part of the wheel vertical plane surface can be used as the reference wheel line. Any longitudinal generatrix of the rail can be adopted as the reference rail line. Due to the guiding principle of the rail vehicles, AOA has the highest values in curves. As a result increased lateral guiding forces and wear of the wheel and rail appear. Consequently, derailment of the railway vehicle may occur. Therefore the AOA measurements in sharp curves are in the focus of the performed research. The measurements can be done in two general ways: with a measurement system installed on a vehicle (vehicle based), or placed on the track (wayside or track based). Vehicle based systems are more complex because the different time dependent relative movements between vehicle parts and rail should be measured and then processed. Their advantage is that AOA of one wheel can be recorded along the track, i.e. on different track configurations (primarily different curve radii). On the other hand, wayside systems, usually installed in sharp curves, provide data about AOA of all wheels of one train, passing over the equipped track section. This paper presents wayside system for AOA measurements using one laser device.

Uncertainty of the wheel-rail angle of attack measurements using laser based wayside system