Straightness/coaxiality measurement system with transverse Zeeman dual-frequency laser

The characterization of straightness/coaxiality is a fundamental geometric tolerance in modern mechanical industries. Straightness measurement over a long range is difficult to implement due to atmospheric disturbance. A novel straightness/coaxiality measurement system that combines a transverse Zeeman dual-frequency laser with a pair of Wollaston prisms is presented in this paper. Orthogonally linearly polarized light from the laser output is divided into two beams by a Wollaston prism, which simultaneously acts as a sensor to measure the straightness of a guideway. The two beams become parallel to each other when they pass through the other Wollaston prism and then are reflected by a rectangular reflector. The measuring signals are processed by means of a phase measurement method with a resolution of 0.1°, which corresponds to 1 µm in straightness measurement. The system meets the principle of self-adaptation so that it is capable of overcoming disturbances in the air. It also has the advantages of compact structure, long-range measurement and good stability. Possible errors of the system are analysed theoretically. A calibration experiment of the straightness measurement over a range of 16 m demonstrated high accuracy with a stability of 3.6 µm.