Analysis of squareness measurement using a laser interferometer system

Squareness measurements of the driving axes of a machine tool are very important in order to evaluate the performance of the machine. A laser interferometer measurement is one of the most reliable ways to measure squareness. However, a squareness measurement using a laser interferometer system with an optical square causes restrictions in the straightness interferometer setup, which results in the occurrence of Abbe's offset. The Abbe's offset combined with angular errors during the motion of an axis causes Abbe's error. In addition, difficulty in the optical square setup causes restrictions on other optics and limitations of the measurable range. We present mathematical approaches that can be used to eliminate Abbe's error and to estimate squareness over the full range by using the best fit of straightness data measured without an optical square. Experiments for squareness measurements of a threeaxis machine tool are conducted. The proposed techniques are used for squareness evaluation with the elimination of Abbe's error and also for squareness estimation for the full travel range.