Impact damper systems are used to reduce the vibration of a lightly damped resonant primary system. The impact damper consists of an impactor and a container. The container is attached to the mass part of the primary system. The container mainly consists of two walls, and the impactor is placed inside the container. And since the impactor is free to move in the container, the impactor collides with the walls. When the impactor collides, some of the vibration energy of the primary system is momentarily converted to kinetic energy of the impactor. That is, impact damper system is damper which utilizes this energy conversion by impact phenomenon. We compared the damping characteristics in an impact damper system between a translating impactor and a rotating impactor and found that the rotating impactor is superior to the translating impactor. Then, with the aim of improving the damping characteristics of the rotating impactor, we proposed that an eccentric mass be added to the rotating impactor and confirmed that the damping effect improves because of the eccentric mass. Next, we calculated the mechanical energy of a vibration system having an impact damper and investigated the mechanism behind this improvement in damping characteristics due to the eccentric mass. In particular, we classified the impacts that occur between the impactor and wall into three types and examined the change in energy of the primary vibration system immediately after such impacts. In this way, we clarified the mechanism behind improved damping effect due to the addition of an eccentric mass.
We made a test apparatus which consists of a cantilevered beam onto which a primary mass with an impact damper was attached to the free end of the beam. We measured the acceleration time history of the primary mass when the frequency of the foundation excitation was swept up under the constant magnitude of the acceleration of the foundation while changing the clearance between the impactor and the wall of the primary system. The experimental tests indicate that the acceleration level decreases at resonance when the number of the impactor increases. We also created a simulation program to calculate the vibration response of the impact damper, and verified that the calculation result was in accordance with the experimental one. Furthermore, we calculated mechanical energy of the vibration system to explain the mechanism of damping in the case of multi-impactor.
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