Amplitude and mean value force control for fatigue testing machines operating at low frequency

This paper addresses the design, implementation and experimental evaluation of a recently proposed force control scheme for fatigue testing machines. The phase shift between the desired force signal and the applied force to the specimen is irrelevant for keeping the force within the fatigue testing requirements considered here. Thus, the proposed approach relies only on an appropriate amplitude and mean value tracking control, disregarding the phase. An estimator for the amplitude and mean value of the output force signal is proposed based on a demodulation technique. Global exponential stability of the complete error system with respect to a small residual set is guaranteed via averaging analysis, for the plant operating at low frequencies. Experimental results and numerical simulations performed at the Non-destructive, Corrosion and Welding Laboratory (LNDC/COPPE/UFRJ) illustrate the remarkable behavior of the proposed scheme, considering real fatigue testing machines.