For manufacturing equipment of VLSI chips, etc., it is desirable to have isolation floors which are effective for not only ambient micro-vibration but also weak earthquakes and even strong earthquakes. Though the isolation floor mentioned in the 1st report could meet such requirements, its applicability was limited because its structure needed a height of 1.8 m or so, Which was too heigh for wide application. A new device for vertical isolation was developed to make the isolation floor having a lower heigh. The device integrated a coil spring and viscous dampers for micro-vibration and for earthquakes. By using the device for vertical isolation, the isolation floor with a heigh of 0.6 m was achieved. For horizontal isolation, the floor used multi-stage rubber bearings and viscous shear dampers which were already used in the former structure. Seismic excitation tests and micro-vibration tests were carried out for a test model on which a equipment model was mounted. The tests verified that the newly developed isolation floor performed satisfactorily for implementation.
