Ｍ系列を用いた空気圧疲労試験機周波数特性の解析

Abstract

Low-damping and low-robustness characteristics of pneumatic servo systems are sometimes troublesome for the ordinary control systems, but if the pneumatic system is applied to a fatigue tester, and worked near the resonant frequency, then a quick and energy-saving fatigue test can be implemented. For this purpose, it is necessary to know the frequency characteristics of the fatigue tester with a test object. However, because of its strong nonlinearity, the conventional sinusoidal input analysis method is too time-consuming.This paper proposes a new method, which adopts the advantage of both M-sequence and sinusoidal signals. With this method, a quick and precise frequency characteristics analysis can be achieved. First, the time response of the system to M-sequence input is calculated, then through the FFT analysis of both the input and output signals, the system frequency characteristics can be obtained. Then, coordinated by the sinusoidal input calculation at some special frequencies, the optimal test frequency can be determined. At the frequency for the same amplitude under the same load, the air consumption of the tester for one cycle would be kept to a minimum. Comparisons have been made between the experiment and simulation for six pieces of test object samples. The results show that the optimal frequencies predicted by the simulation agree well with experimental ones. Finally, the load influence on the optimal test frequency is illustrated.In the paper, comparisons have been also made between the frequency characteristics obtained with sinusoidal and M-sequence inputs for different signal amplitudes. Also the influence of Coulomb friction on the characteristics is discussed.