A model based method for centering double ball bar test results preventing fictitious ovalization effects

The telescoping magnetic double ball bar (DBB) is widely used to assess the motion and link errors of machine tools through circular tests. Despite a careful setup, some slight eccentricity of the balls relative to the circular trajectory often remains. Removing the eccentricity from the DBB results is essential due to its effects on the estimated trajectory. However, if the centering is not performed with great care, a fictitious ovalization effect may appear in the processed data. The source of the fictitious ovalization is discussed in this paper and a method is proposed to quantify the eccentricity and adequately process the data so that the fictitious ovalization is avoided. The results obtained by applying the proposed method both in simulation and in practice demonstrate its effectiveness.