Radial Error Motion Measurements at Nanometer-level Precision Using Angle Encoder with Different Four-scanning-heads Arrangements

Four-scanning-heads error separation method under optimal arrangement has proven useful for measuring the radial error motion of axis of rotation. This technique is based upon the fact that angles read by scanning heads are mainly affected by both the graduation error of the angle encoder’s scale and the spindle radial error motion. This paper presents a further validation of this method on a high-accuracy air-bearing rotary stage equipped with an angle encoder with six scanning heads. Experiments are performed to measure the radial error motion by three different four-scanning-heads arrangement schemes. The results show a nanometer-level repeatability of the measured error motion. Moreover, the error motion values obtained by these three arrangement schemes agree very well, which further confirm the effectiveness of the method. This technique is well suited for error motion measurement of rotary tables with angle encoder as the angle measuring device, since it needs no additional artifact compared with the conventional methods.