Machine error components of 1-axis translational moving stage have 6 error components; positional error, vertical and horizontal straightness error, and 3-rotational errors such as rolling, pitching, yawing. In general, a commercial laser interferometer is restricted to 1-degree-of-freedom error component measurement in one setting.
This paper presents a method that is possible for a simultaneous and real-time measurement of 5-degree-of-freedom of the translational moving stage except positional error using combined two Twyman-Green interferometers. This method uses a null-balance technique in which two plane mirrors are used as target mirrors to generate an interferometric fringe pattern utilizing the optical principles of Twyman-Green interferometry. Fringe is detected by 2D photodiode array at high speed. Errors are then independently suppressed by activation of piezoelectric actuators by real-time feedback control while the machine axis is moving. Experimental results demonstrate that a machine axis can be controlled with movement errors about 10 nm in displacement, 0.18 arcsec in angle by adopting the real-time correction method.
