Abstract: Aiming at the problem that the contact points on ruby ball will lead to different pre-travel errors under different stylus orientations, leading to low calibration accuracy and efficiency, a feasible graph construction method for optimizing stylus orientation is proposed. Firstly, the interference-free stylus orientations at each to-be-measured point are calculated according to the bounding box algorithm. Then, the relationship between the touch positions on the ruby ball and the rotating axis of machine tool is established by using the kinematics chain of machine tool, and then the feasible graph of the rotary angle of the machine tool turntable is constructed. In order to improve the detection accuracy, the stylus orientation is optimized based on the principle of reducing the changes of the ruby ball contact positions and the direction of the machine tool rotary axis, so as to meet the conditions of interference-free and minimum ruby ball contact positions. Finally, the centrifugal impeller exemplifies that this method can not only ensure the least number of the touch positions and greatly shorten the calibration time but also reduce the introduced error of the machine tool and improve the measurement accuracy. The experimental results show that the method has good repeatability and feasibility.

Key words: on-machine measurement, pre-travel error, feasible graph, stylus orientation, five-axis machine tool