Rapid method to determine accuracy and repeatability of positioning of numerically controlled axes

Machine tool testing and accuracy analysis is an important task in evaluation of machine's capability. Currently quasi-static, time consuming techniques are proposed by standards. This paper proposes a new method for evaluation of accuracy and repeatability of machine tool positioning under dynamic conditions - on the fly. In this method, displacements are captured by a laser interferometer during continuous motion of the analyzed axis. The method is capable of analyzing accuracy and repeatability of axis positioning without synchronization of the laser interferometer with the machine position transducer. Transformation of time domain measurements into nominal position domain is performed using a novel curve fitting approach. The drawback of performing the tests during machine motion is the potential contribution of the measuring system vibration to the registered signal. In this paper permissible ranges of vibration frequency for lens commonly used in optical metrology systems for axis positioning of computer numerically controlled machine tools were experimentally determined. Application of the proposed method on a typical computer numerically controlled lathe, lathe for non-circular turning and milling machine is undertaken. Results of the tests carried out at various feed rates are compared to quasi-static results.