In order to reduce the vibration of the system excited by the external force, the dynamic absorder is generally used. When the exciting frequency is fixed, the un-damped dynamic absorber whose the natural frequency equales to the exciting frequency is used. In this case, the amplitude of the system is reduced to zero only at that frequency. On the other hand, when the exciting frequency changes with the time over the wide frequency range, the damped dynamic absorber is used. Then the vibrating system is kept on the optimum damping condition by ajusting well the coefficients of viscus damping. The result not satisfactory compared with the former one.
If the natural frequency of the dynamic absorber can be changed in wide range and if the natural frequency can be controlled so that it can follow to the exciting frequency which is changing with the time, it is expected that the amplitude of the system reduced to zero.
Magnetic dynamic absorber is composed of two side magnets and a movable magnet (absorber mass) and its natural frequency can be changed by adjustingly the length of the distance between side magnets and the magnitude of their magnetic force.
In this paper, it is analized that the natural frequency of the magnetic dynamic absorber depends on the distance between side magnts and their magnetic coefficient. Next when the exciting frequency of the system is changed with the time, the device whose the natural frequency is controlled so that the frequency follows to the exciting one well is made and the experiment is done. The result shows that the amplitude of the system could be sufficiently reduced to less value here than in the optimum damping condition.