1. Field of the Invention
The present invention relates generally to a foot structure for an apparatus, and more particularly to an earthquake-resistant foot structure suitable for an electronic apparatus.
2. Description of the Related Art
When installing an electronic apparatus such as a computer in a building construction, it is important to take measures against an earthquake, so as to minimize falling of the apparatus and damage to the inside of the apparatus due to seismic vibrations. In conventional measures against an earthquake, a foot structure used in installing the apparatus in the building construction has had emphasis placed on increasing a mechanical strength thereof. Recently, however, attention is being given to a vibration isolating technique intended to reduce damage by efficiently converting vibration energy into another form of energy such as energy of movement.
FIG. 1A shows a conventional foot structure used in installing an apparatus 2 on a floor surface 4. The foot structure shown in FIG. 1A includes a bolt member 6 and a slide cup 8. The bolt member has a first end 6A and a second end 6B. The first end 6A is fixed to the apparatus 2. The slide cup 8 has at its upper portion a recess 8A for slidably supporting the second end 6B of the bolt member 6 and has at its lower portion a lower surface 8B slidable on the floor surface 4. When relatively small seismic vibrations are given to this foot structure, the bolt member 6 horizontally moves within the recess 8A of the slide cup 8, so that energy of the seismic vibrations is converted into energy of movement (or frictional heat), thus exerting a vibration isolating effect.
When large seismic vibrations are imparted to this earthquake-resistant foot structure, and the floor surface 4 is displaced in the direction of an arrow A as shown in FIG. 1B, not only the bolt member 6 moves within the recess 8A of the slide cup 8, but also the slide cup 8 itself horizontally slides on the floor surface 4, thereby obtaining a great vibration isolating effect by relative movement of the bolt member 6 and the slide cup 8 and relative movement of the slide cup 8 and the floor surface 4.
Further, another foot structure has been proposed (Japanese Patent Laid-open No. 5-99273). In this foot structure, the recess 8A of the slide cup 8 has a spherical surface, and the second end 6B of the bolt member 6 also has a spherical surface whose radius of curvature is smaller than that of the spherical surface of the recess 8A, thereby easily restoring the relative positional relation between the bolt member 6 and the slide cup 8 to an original state when seismic vibrations stop.
The conventional foot structure does not have a function of limiting the range of displacement of the apparatus relative to the floor surface. Accordingly, in the case that an earthquake having a large magnitude beyond expectation occurs for a long period of time, the apparatus moves, thus causing a collision between the apparatus and another apparatus or with a wall of the building construction. As a result, each apparatus or the building construction is damaged. Further, in the case that a man is present between the apparatus and the wall, a survival space for the man is lost.
Further, the conventional foot structure does not have a vertical vibration isolating effect to the apparatus. Accordingly, when the apparatus receives vertical seismic vibrations, the bolt member may come out of the recess of the slide cup, so that the original performance of the slide cup cannot be exhibited.
Further, in the case that the floor surface, which is generally expected to be horizontal and flat is in fact uneven or inclined, there is a possibility of the bolt member escaping from the slide cup in the conventional foot structure so that the expected vertical vibration isolating effect cannot be exerted.