A new method and device for motion accuracy measurement of NC machine tools. Part 1: principle and equipment

This paper describes in two parts a new method and device for measuring motion accuracy of numerical control (NC) machine tools. In the first part, the measurement principle and the characteristics of the prototype device are proposed. The device consists of a double-bar linkage with two rotary encoders. The working range of the device is disc-shaped with a radius of almost the double the link length, except a small area around the centre of the disc and an outer area both around the change points of the linkage at the centre and the circumference of the disc. Because the method has high resolution for any measuring point within the working range, it can be applied to measure most items of motion accuracy of NC machine tools. The method is particularly suitable to measure the trajectory accuracy of circular motions. The device has a compact structure and its installation on a machine tool to be measured is simple and quick. The experimental results show that the prototype device has very good response to small displacement and good repeatability with high precision to the measurement of circular motion trajectories. The influence of measurement noise is hardly observed in the experimental results.