A precision length measuring system for a variety of linear artefacts

To calibrate precision length standards and length measuring transducers, the Korea Research Institute of Standards and Science (KRISS) has built a new linear measuring machine. The main requirement on the machine is to achieve sufficient flexibility to be able to calibrate a variety of standards such as step gauges, long-range linear transducers, industrial line scales and end bars with high accuracy. This system is not designed for calibrating primary standards such as a gauge block or a primary standard line scale. which are usually measured by specially designed precise interferometers. The main parts of the system are a precision stage and a laser interferometer. For smooth motion and precise positioning, we have built double stages, which consist of a global stage with an air bearing and a micro-stage with a flexure structure. Furthermore. two tilting stages are used for compensating for the pitch motion and the yaw motion of the global stage. Two double-pass plane mirror interferometers based on the heterodyne technique measure the displacement of the stage. The Abbe offset error is minimized by two interferometers with double-pass arrangements and two servo-controlled tilting stages. The measuring range of the system is 2500 mm and the expanded uncertainty for 1000 mm end bar calibration is 0.8 mum at the 95% confidence level.