Analysis of the Measurement Error of Coupler Knuckle Special Measuring Machine

The coupler is a connecting device in railway vehicles, used for passing the traction and the impact. The dimension error of the traction platform and impact platform in coupler knuckle is the main factor that affects the smooth connection and safety performance. Use coordinate measuring technology to detect the coupler knuckle, obtaining the dimension of every surface efficiently and accurately. However, the traction platform and the impact platform are eccentric arcs relative to the measuring datum, with non-complete large radius short arcs. So with little collection scale, there're many factors that affect the measurement accuracy. This paper takes a research on the influence of the measurement error of the traction platform and impact platform by coupler knuckle special measuring machine, including location error, sampling method and data processing method. Firstly, based on the character of knuckle and fixture, eliminate the fit tolerance between locating pin and knuckle pinhole by the radius compensation method. And then, analyze the uncertainty of the three-point-circle algorithm and the multi-point-circle algorithm, choosing a reasonable sampling method. At last, with center-fixed method, eliminate the eccentric error of traction and impact platform relative to measurement datum. The research results above provide the theoretical basis for improving the measurement accuracy of the traction platform and the impact platform.