Abstract
In this study we propose a design procedure of a three degree of freedom vibration isolator supported with four air suspensions with slit restrictions and reservoir tanks. Since an arbitrary oscillating mode of the foundation of the three degree of freedom vibration isolator corresponds to a rotating motion around its instantaneous center axis, the oscillating mode can be describe by using a distance from a center of mass of the supported mass to its instantaneous center axis and an attitude angle of it. We use a design concept of minimizing standard deviation of amplitude against external disturbance random vibrations of foundation. To minimize standard deviation of amplitude of the supported mass, the optimum damping ratio which minimize the standard deviation of amplitude of the supported mass under the condition of rotating oscillating has to be chosen when the natural frequency of the parallel mode is lower than that of the rotating mode. In this case, the optimum damping ratio for the rotating mode of higher mode should be chosen. Although a structure of the proposed vibration isolator is more simple than that of a conventional vibration isolator with air suspensions and viscous dampers, the amplitude of the optimized proposed vibration isolator is larger only 5% than that of the optimized conventional vibration isolator in case of the volume ratio of air suspensions of the proposed vibration isolator is 0.9. From this fact, it can be said that the proposed vibration isolator is useful.
