Dynamic structured-light measurement for wheel diameter based on the cycloid constraint.

Wheel diameter is a significant parameter related to the safety and comfort level of trains. The traditional circle fitting method can be sensitive to noise because of the small distribution of contact points. This paper proposes a structured-light measurement based on the cycloid constraint to obtain a wide distribution of contact points. The wheel is measured twice while running. The cycloid is used to integrate all the contact points to one circle. Simulations are implemented to analyze the possible errors, and the results are compared with the traditional method, which shows the method is more precise and has good stability against 3D reconstruction noise and out-of-roundness. The physical experiment also shows that the result is precise and robust.