Measurement Method of Geometric Accuracy of Five-axis Controlled Machining Centres (Measurement by a Master Ball and a Displacement Sensor)

Abstract

Ball bar instruments are often used for the measurement of the trajectories of the circular interpolation motion of NC machine tools. This paper describes a new method which is an alternative method of the ball bar. The proposed method consists of a master steel ball and a linear variable differential transformer (LVDT). The method was applied to the measurement of the geometric deviations inherent to five-axis machining centers with a tilting rotary table. The master ball is mounted on the main spindle through a tool holder and the displacement detector is also set on the rotary table. In order to identify the geometric deviations circular arc trajectories which are measured under different four kinds of simultaneous three-axis motion are needed. Especially, the eccentricities of the trajectories obtained by the proposed method have important meanings. For this reason, the eccentricities were calculated from the measured trajectories of a quarter circle as well as a full circle by the least square method. The measurements of the deviations were actually carried out on a five-axis machining center and then the deviations were identified. The proposed method is compatible to the ball bar system from the view point of the measurement accuracy.