First and second order periodic error measurement for non-constant velocity motions

This paper describes a digital algorithm that can be applied in real time to measure and compensate first and second order periodic error in heterodyne displacement measuring interferometers. Comparisons are made between the new algorithm and the traditional frequency domain measurement approach, where the error signal is Fourier transformed into the frequency domain to identify periodic error magnitudes. Experimental results are provided for both constant velocity and non-constant velocity conditions.