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Interferometer for pitch and yaw measurement using LC-screen and four ball lenses

The positioning accuracy of machine-tool tables used for translatory movement and coordinate measuring machine carriages requires improvement. Transmission and blocking of light can be realized by combining a transmissive liquid crystal and a polarizing plate. In this study, this technique was applied to a laser interferometer to realize selective multi-degree-of-freedom motion measurement using one measurement system. A ball lens was adopted as a reflecting mirror, and the rotational-movement amount was measured using a photodetector. In addition, rotational movement with two degrees of freedom was selectively measured using one interferometer, through transmission and blocking of light. It was found that the pitch and yaw rotational movement can be selectively measured using the difference between displacements of the axial directions of two ball lenses for the movement of the goniometer stage with 0.0032° resolution and the rotational stage with 0.004° resolution, respectively, and that the influence of the crosstalk of yaw and pitch is slight when the pitch and yaw rotational movements are simultaneously applied to the stage. Therefore, there is scope for this technique to be used to improve multi-degree-of-freedom motion measurements.