Lee C., Jwo H.

The platform with vibration isolation suspension is frequently used in the high precision machinery. When the component mounted on the platform generates periodic oscillation due to parametric excitation, e.g. rotation of an eccentric mass, the induced vibration of the platform, especially near the resonance, could undermine the functionality of the platform. The dynamic characteristics of a platform supported with four SMA suspension springs were investigated in this study. The SMA spring undergoes phase transformation reversibly from martensite to austenite as the temperature is raised. In the meanwhile, the elastic modulus of the austenite phase is different from that of martensite. Therefore, by controlling the temperature of the suspension SMA springs, the resonance frequency of the platform can be tuned. The spring constants of the helical spring both in longitudinal and transverse deformation were derived by employing Castigliano¡¦s theorem. The derived spring constants were justified by the finite element analysis of ANSYS. Consequently, the spring constant measurements both from static and vibration setups were used in the theoretical equations to infer the elastic modulus of the SMA at different temperatures. Finally, the dynamic equations of the platform with SMA spring suspension were formulated. The dynamic tuning capability of the platform was demonstrated both theoretically and experimentally. It was found that both the resonance frequencies for in-plane and out-of-plane vibration modes of the platform could be tuned within 20% of variation as the temperature of the springs was changed between 25C and 90C.