Standard-wheel-based field calibration method for railway wheelset diameter online measuring system

Laser displacement sensor (LDS)-based online measuring of the wheel diameter has been widely adopted in engineering for advantages such as noncontact, high efficiency, and high precision. For almost all these online measuring systems, calibration is certainly needed in order to obtain the extrinsic parameters of sensors. A field-based easy-to-operate, economical, and efficient calibration method is proposed for an LDS-based wheel diameter online measuring system. Only one standard wheelset is used to build the 3D calibration target that is also the measurement target of the system. The extrinsic parameters for each LDS are obtained through minimizing the residual summation of squares. A multistart framework combining the generation of certain numbers of uniformly distributed starting points and a nonlinear programming solver is adopted to solve the minimizing function to obtain the global optimizer. Factors include the number of standard wheelset placement and sensor noises that will result in calibration error are analyzed. Field experiments are carried out, and the correctness of the calibration method is verified through comparisons with manual caliper-measuring results.