Active Vibration Absorbers in Machine Tools Using Shape Memory Alloys

Conventional "tuned" vibration absorbers reduce the vibrations of machine tools at resonant conditions only. These vibration absorbers are ineffective during other operating conditions. In this paper, the emphasis is placed on providing the vibration absorber with active control capabilities in order to absorb the vibrations in all operating frequencies. The shape memory alloy (SMA), which has a unique behavior of changing its elastic modulus up to three times as the alloy undergoes a phase transformation from martensite to austenite. This unique behavior of the SMA is used to "tune" the vibration absorber actively according to the different operating frequencies of machine tool structure. The shape memory alloy is used as the variable-stiffness spring in vibration absorber. The stiffness of the spring, which is made by shape memory alloy, is tuned using shape memory effect, which is thermally induced or magnetically induced by a controller kit. According to the operating speed, the stiffness of the SMA spring is dynamically changed so that the natural frequency of vibration absorber is tuned to the forcing frequency (operating speed) of machine tools. A controller designed to act according to the level of vibration that the machine tool produces, varies the stiffness actively. ANSYS results are used to analyze the developed active vibration absorber system and it is concluded that the active vibration absorber suppresses the vibration of machine tool structure actively.