Isolator for seismic activity

An isolator for seismic activity including an upper level for supporting an object to be protected, an intermediate level, and a lower level for attachment to the floor or other structure. An interconnection is provided between the upper and intermediate levels to permit relative movement between the levels along a first axis, and a similar interconnetion is provided between the intermediate and lower levels to permit relative between along a second axis perpendicular to the first axis. Each of the interconnections includes one or more bars mounted on one of the levels and defining guide faces oblique to the axis of movement, and a lever pivotally mounted on the other of the levels with a roller for engaging the guide faces, with a spring biasing the roller toward the guide faces. The interconnection also includes tracks and bearings riding on the tracks to provide the interface movement between the levels.

BACKGROUND OF THE INVENTION 
This invention relates to protection from shock and vibration, and in 
particular, to apparatus for protection of objects from damage resulting 
from seismic activity such as earthquakes. The invention is of particular 
significance to the protection of large art objects and antiquities of 
museum quality. 
A variety of configurations have been utilized in the past for protection 
from damage due to earthquake. In one approach the structure is designed 
to be exceedingly strong so that the structure and its support, such as a 
single object or entire building, moves with the earth movement without 
damage. Another approach has been to support the object on some type of 
apparatus so that the object remains essentially fixed while the earth 
moves, with the object ultimately being restored to its original 
relationship with the earth. Structures of this nature are shown in U.S. 
Pat. Nos. 4,496,130; 4,596,373; and 4,801,122; and in Italian patent 
639,666. A variation utilizing cables and springs for controlling motion 
is shown in U.S. Pat. Nos. 4,371,143; 4,402,483; 4,565,039; 4,577,826; 
4,617,769; and 4,662,133. 
While these prior designs have been satisfactory for some situations, 
problems are encountered in other arrangements and installations, and it 
is an object of the present invention to provide a new and improved 
isolator construction. 
In the case of art objects and antiquities many times they are inherently 
weak or have been weakened over time and often are unstable. 
One of the advantages of the isolator of the present invention is the 
ability to tune the return mechanism so that the natural frequency of the 
system can be adjusted for each particular object or circumstance. Long 
period motions may be attenuated by the very large displacement capacity 
and in addition, vertical accelerations may be controlled with the rigid 
locking to eliminate chatter. Other advantages include a lower profile and 
very little maintenance required. 
SUMMARY OF THE INVENTION 
An isolator for seismic activity including a plurality of levels with 
interengaging means providing for relative movement between levels. In the 
preferred embodiment, three levels are utilized to provide movement 
between the upper and lower levels along two perpendicular axes. The 
interengaging means between levels includes a lever pivotally mounted on 
one of the levels with a roller member for engaging one or more guide 
faces carried on the other level, with the guide faces oblique to the axis 
of motion. A spring provides a bias force urging the roller against the 
guide face with this engagement providing a restoring force which tends to 
maintain one level in a centered position relative to the other level. 
Bearings carried on one level ride on tracks carried on the other level, 
with the bearing-track engagement providing the load carrying capability 
and with the roller-guide face engagement providing the centering and 
restoration forces. 
Other objects, advantages, features, and results will more fully appear in 
the course of the following description.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1, a statue 11 is mounted on a base 12 which in turn is supported 
on an isolator covered by a shroud 13, with the isolator resting on a 
floor 14. A typical statue is greater than life size and may weigh in 
excess of 1,000 pounds. Toppling of such an item as a result of accident 
or seismic activity or otherwise, usually results in severe damage to the 
item, and the isolator of present invention is designed to substantially 
eliminate the possibility of toppling. Also, the isolator can be used for 
objects as small as 20 pounds. The isolator provides for movement of the 
floor relative to the statue along a first axis 15 and along a second axis 
16, with the axes being perpendicular to each other so that the isolator 
functions for relative movement in all directions. 
The isolator is shown in detail in FIGS. 2-7 and includes an upper plate 
20, an intermediate plate 21, and a lower plate 22. Three rails or tracks 
24 are attached to the lower plate 22 by screws 25, and two tracks 24 are 
attached to the plate 21 by screws. Bearings 26 are attached to the 
intermediate plate 21 by screws 27 and similar bearings are attached to 
the upper plate 20 by screws, typically with two bearings for each track. 
The tracks and bearings may be conventional in design and one suitable 
source is THK Co., Ltd. LM Guide HSR Type bearings which provide for equal 
load capacities in four directions, as shown in FIG. 8. In the 
construction of FIGS. 8 and 9, the bearings 26 ride on the tracks 24 on 
balls 28 carried in retainers 29 and riding in grooves 30 in the tracks. 
Details of the particular tracks and bearings are shown in U.S. Pat. No. 
4,253,709. 
The interengagement of the bearings and tracks provide for movement of the 
upper plate relative to the intermediate plate along the axis 16 and for 
movement of the intermediate plate relative to the lower plate along the 
axis 15. While the presently preferred track and bearing configuration is 
illustrated, it will be understood that other combinations may be utilized 
to provide the relative movement of the plates. 
A centering and restoring mechanism between the upper plate 20 and the 
intermediate plate 21 is shown in FIG. 5. A lever 35 is pivotally mounted 
at one end on a bracket 36 of the upper plate 20. A roller 37 is carried 
on the lever 35 adjacent the other end, with a tension spring 38 connected 
between an arm 39 of the lever 35 and an arm 40 of the upper plate 20. 
A guide bar 43 is pivotally mounted at one end on the intermediate plate 21 
by a pin 44. The angular position of the guide bar relative to the 
intermediate plate is controlled by another pin 45 carried at the other 
end of the guide bar, which pin can be positioned in any one of a series 
of holes 46 disposed in an arc on the intermediate plate 21. The guide bar 
43 has a guide face 47 disposed at an oblique angle to the axis 15, and 
the spring 38 urges the roller 37 into contact with the guide face. In the 
preferred embodiment the guide face 47 is straight, but other shapes can 
be used as desired. 
Movement of the upper plate 20 in the direction of the arrow 49 causes the 
roller 37 to move to the left along the guide face of the guide bar 43 and 
extend the spring 38. The spring tends to resist this movement and, when 
the force causing the movement terminates, the spring causes the roller to 
move in the opposite direction indicated by the arrow 50 to return the 
system to the position of FIG. 5. A force producing a movement of the 
upper plate 20 in the opposite direction as indicated by the arrow 50, 
causes the roller to move along the oblique face of the guide bar 48, 
again extending the spring 38. When the force producing the plate movement 
terminates, the spring moves the upper plate in the opposite direction to 
restore the mechanism to the position of FIG. 5. 
In the preferred embodiment, two such centering and restoring mechanisms 
are utilized, one at the lower side as previously discussed in FIG. 5, and 
a similar one at the upper side as shown in FIG. 5. In an alternative and 
simpler embodiment, only one such centering and restoring mechanism may be 
utilized. In other alternative embodiments, only one guide bar may be used 
on each side, and the two guide bars may be produced in a single piece, 
and the angles of the guide faces may be fixed rather than being 
adjustable. 
A similar configuration may be utilized between the intermediate plate 21 
and the lower plate 22, as shown in FIG. 7, with lever 35', roller 37', 
spring 38', and guide bars 43', 48'. In an alternative configuration, one 
or more compression springs 53 may be utilized in place of the tension 
springs 38, 38'. In the embodiment illustrated, two compression springs 53 
are positioned between a bracket 54 carried on the lower plate 22 and a 
similar bracket 55 carried on the lever 35'. 
Snubbers may be utilized at the extremes of motion of the plates. Referring 
to FIG. 2, spring snubbers 56 are mounted on the intermediate plate 21 for 
engaging the upper plate 20 at each end of the travel of the upper plate 
relative to the intermediate plate. Similarly, elastomer snubbers 57 are 
carried on the lower plate 22 for engaging the intermediate plate 21 at 
the extremes of relative movement. More than one set of tracks in the same 
direction may be used to obtain increased displacement while resulting in 
a smaller package.