Base isolation table in consideration of long-period ground motion

Abstract

To provide a base isolation table manufactured using an easily-manufacturable X-direction and Y-direction motion mechanism, having an excellent base isolation effect, capable of suppressing a resonance due to a long-period ground motion, and having a lower height.SOLUTION: A X-direction motion mechanism includes: a X-direction base-isolation mechanism having two X-direction guide rails held on a bottom plate in parallel with both ends being held by fixing walls, two motion plates that travel by being coupled at front and rear on the two guide rails, and a coil spring and an oil dumper attached between one of the motion plates and one of the fixing walls; and a X-direction resonance suppressing mechanism having two linear bearing shafts fixed between the two motion plates in parallel with the guide rails, two movable parts that travel smoothly on each of the linear bearing shafts, and two gradually-hardening spring-dumper device attached between the movable parts and the two holding walls on the bottom plate. A Y-direction motion mechanism having a configuration equivalent to the X-direction motion mechanism is fixed on the X-direction motion mechanism, and a table plate is fixed thereon.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a horizontal seismic isolation table device (hereinafter simply referred to as a seismic isolation table) that can prevent equipment and devices placed on the table top from falling over or being damaged not only when subjected to normal short-period seismic motion but also when subjected to long-period seismic motion. [Background technology]

[0002] Various types of seismic isolation tables are used to protect precision equipment, computers, artwork, Buddhist altar fittings, etc. from falling over or being damaged by earthquakes. These seismic isolation tables generally consist of a table top, a spring to return the table top to its original position after the earthquake has ended, and a damper to reduce the vibration of the table top by converting it into heat.

[0003] When equipment is mounted on a table supported by springs, it becomes a system with one degree of freedom in the direction of the seismic waves. Its natural period Tn (seconds) is given by k (N / m) for the spring constant of the supporting spring, m (kg) for the total mass of the table and mounted equipment, and ignoring damping: Tn = 2π(m / k) 1 / 2 is given by:

[0004] Earthquakes such as the Great Hanshin-Awaji Earthquake (January 1995), the Great East Japan Earthquake (March 2011), and the Kumamoto Earthquake (April 2016), which caused many deaths and extensive damage, were earthquake motions dominated by short-period components with periods of about 0.2 to 1 second. From here on, we will refer to such fast earthquake motions with a predominance of short-period components as "normal earthquake motions."

[0005] Most seismic isolation table systems (referring to seismic isolation tables equipped with equipment) are primarily designed for normal earthquake motions, and are designed so that the natural period of the equipment mounted on them is 2 to 4 seconds.

[0006] Seismic isolation table systems designed with a natural period of 2 to 4 seconds are effective against normal earthquake motion, and are said to reduce the maximum acceleration of earthquake motion to about 1 / 5 to 1 / 10.

[0007] However, when earthquake motion containing a slow dominant component with a period of 2 seconds or more (hereafter referred to as long-period earthquake motion) hits this seismic isolation table system, and the dominant component of the earthquake motion and the natural period of the seismic isolation table system nearly match, the seismic isolation table system will resonate and vibrate significantly beyond the allowable displacement range.

[0008] Long-period ground motion has been observed to occur during several major earthquakes in the past. For example, during the Great East Japan Earthquake, long-period ground motion reached Osaka, about 800 km from the epicenter, and it was reported that the Sakishima Government Building (55 stories) resonated with the ground, causing it to shake violently sideways.

[0009] In addition, if a massive earthquake were to occur along the Nankai Trough, it is predicted that long-period seismic motion would occur in the three major metropolitan areas of Tokyo, Nagoya, and Osaka.

[0010] The following two methods can be considered to prevent a seismic isolation table system designed to have a high seismic isolation effect against normal earthquake motion from resonating due to long-period earthquake motion.

[0011] (Method of suppressing resonance by changing the natural period of the seismic isolation table system) When the natural period of the seismic isolation table system and the period of the dominant component of the long-period earthquake motion nearly coincide, resonance occurs, so when resonance occurs and the seismic isolation table system vibrates strongly, the resonance can be stopped by greatly increasing the spring constant of the support springs of the seismic isolation table, thereby greatly increasing the natural period. In other words, the support springs should be made to exhibit gradually hardening characteristics beyond a certain displacement.

[0012] (Method of suppressing resonance by increasing damping force) Another method for suppressing resonance of the seismic isolation table system caused by long-period earthquake motion is to increase the damping force of the damper when the seismic isolation table system is displaced significantly. If the damping force is increased, the large kinetic energy of the seismic isolation table system is converted into heat, and the vibration is suppressed.

[0013] If the support springs are not used in the seismic isolation table, it is possible to realize a seismic isolation table system that does not shake significantly against both normal and long-period earthquake motions. However, without the support springs, the load on the table will not return to its original position after the earthquake ends, so this type of seismic isolation table will not be considered here.

[0014] The following Patent Documents 1 and 2 disclose known seismic isolation tables that take into account both the seismic isolation effect when the seismic isolation table system is subjected to normal seismic motion and the resonance suppression effect when subjected to long-period seismic motion. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] JP 2011-47514 A [Patent Document 2] JP 2017-48910 A

[0016] The seismic isolation table described in Patent Document 1 mentioned above is constructed by stacking and fastening a linear table of the same structure, which is supported by a coil spring and a friction damper and can move in the X direction, on top of which is a linear table which has the same structure but can move in the perpendicular Y direction. Any object placed on the Y direction table plate can be moved to any position within the horizontal plane without any rotational movement. In addition, as a countermeasure against resonance of the seismic isolation table system due to long-period seismic motion, a mechanism is provided that increases the spring force and damping force when the relative displacement of the table plate becomes large.

[0017] The seismic isolation table described in the above Patent Document 2 is a linear table that can move in the X and Y directions, with a table plate attached to one guide shaft in each direction, and multiple freebears attached to both the left and right sides of the table plate to act as auxiliary wheels to prevent the table plate from rotating around the guide shaft. This allows the seismic isolation table to have the same movement function within a horizontal plane as a commercially available linear table. In addition, as a countermeasure against resonance of the seismic isolation table system due to long-period seismic motion, a mechanism is provided that increases the spring force and damping force when the relative displacement of the table plate becomes large. Summary of the Invention [Problem to be solved by the invention]

[0018] The linear table used in the seismic isolation table described in Patent Document 1 above requires two precisely machined linear guide shafts arranged strictly parallel to allow the moving part (linear bearings) to move smoothly on them, which has the disadvantages of being difficult to manufacture and install, and expensive to manufacture. In addition, the hardened friction damper used in the above-mentioned Patent Document 1 has a drawback in that it is not easy to manufacture since it uses a precisely machined shaft having a central parallel portion and tapered portions on both sides.

[0019] On the other hand, the seismic isolation table described in Patent Document 2 has the advantage of being easy to manufacture and install because it uses one guide shaft, but has the disadvantage of being tall and having a large number of parts because it uses many free bearings and many vertical friction dampers. Furthermore, the seismic isolation table in Patent Document 2 uses a spring system with gradually hardening spring characteristics or broken-line increasing spring characteristics from zero displacement as a countermeasure against resonance of the seismic isolation table system due to long-period earthquake motion, which are not ideal spring characteristics. Ideal spring characteristics (restoring force characteristics) are those that have linear spring characteristics in the seismic isolation range, and have gradually hardening spring characteristics in the range where the seismic isolation table system resonates due to long-period earthquake motion and experiences large relative displacement.

[0020] (Objective of the Invention) The present invention aims to propose a low-profile XY-direction movement mechanism (simple linear table mechanism) that is easy to manufacture and install, and that provides a high seismic isolation effect against normal earthquake motion, while also providing a seismic isolation table that can suppress resonance of the seismic isolation table system caused by long-period earthquake motion by using ideal non-linear spring characteristics and increasing damping force characteristics. [Means for solving the problem]

[0021] In order to realize a seismic isolation table that is easy to manufacture, inexpensive, and low in height, the X- and Y-directional movement mechanisms of this table use two guide rails, each made of a metal plate several centimeters wide and a plastic plate with a low friction coefficient attached to it. This X-directional movement mechanism consists of two guide rails installed parallel to each other along the X-direction on the bottom plate, and two moving plates that are processed to slide on these guide rails and are connected at the front and rear. This seismic isolation table is made by stacking and fixing a Y-directional movement mechanism, which has the same structure and can move in the orthogonal Y direction, on top of the X-directional movement mechanism, which can move in the X-direction, and then attaching a table plate on top of that. Any load placed on the table plate can be moved to any position in the horizontal plane without any rotational movement.

[0022] In order to provide a high seismic isolation effect against normal earthquake motion and to prevent resonance of the seismic isolation table system due to long-period earthquake motion, this invention uses an ideal spring system that has linear spring characteristics in which the restoring force is proportional to the relative displacement up to a certain relative displacement s, and beyond s, has gradually hardening spring characteristics in which the spring constant increases with the relative displacement.

[0023] In order to obtain a high seismic isolation effect against normal earthquake motion and an effect of suppressing resonance of the seismic isolation table system caused by long-period earthquake motion, this invention uses an incremental damper system in which the damping force is small up to a certain relative displacement s and increases when the displacement exceeds s. These dampers are used horizontally, so the back of the seismic isolation table can be made low. Effect of the Invention

[0024] The X- and Y-direction movement mechanism used in the seismic isolation table of the present invention uses two guide rails and a moving plate that slides on them, and even if some rattle occurs between the guide rails and the moving plate, it does not significantly affect the seismic isolation effect and the resonance suppression effect. This X- and Y-direction movement mechanism is easy and inexpensive to manufacture, and can realize a low-profile seismic isolation table. In addition, this seismic isolation table has linear spring characteristics and linear damping force characteristics up to a certain relative displacement, and at the time of large relative displacement when the seismic isolation table system resonates, it has gradually hardening spring characteristics and increasing damping force characteristics, so it can obtain a high seismic isolation effect and resonance suppression effect. [Brief description of the drawings]

[0025] [Figure 1] 1 shows a perspective view of an X-direction and Y-direction movement mechanism. [Diagram 2] FIG. 2 shows a front cross-sectional view of the seismic isolation table system of the present invention. [Diagram 3] FIG. 2 is a schematic front view of a spring-damper device used in the present invention (schematic cross-sectional view of an oil damper container). [Figure 4] FIG. 1 shows a schematic front view (schematic cross-sectional view of the damper container) of an additional spring-damper device A for imparting gradually stiffening spring-increasing damping characteristics to the seismic isolation table system during large displacement. [Diagram 5] FIG. 1 shows a schematic front view (schematic cross-sectional view of the damper container) of an additional spring-damper device B for providing gradually stiffening spring-increasing damping characteristics during large displacement of the seismic isolation table system. [Figure 6] The diagram showing the position of the XY movement mechanism when stationary is shown. [Figure 7] An explanatory diagram of the operation of the XY movement mechanism in a large displacement state is shown. [Figure 8] The spring characteristics in the X and Y directions of the seismic isolation table system used in the present invention are shown below. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] (First embodiment) A seismic isolation table according to a first embodiment of the present invention will be described below with reference to FIGS. 1 to 4 and 6 to 8. FIG.

[0027] 1 shows a perspective view of an X-direction movement mechanism in the first and second embodiments. The Y-direction movement mechanism has exactly the same structure as the X-direction movement mechanism.

[0028] Figure 2 shows a front cross-sectional view of the seismic isolation table of the present invention. This seismic isolation table is constructed by stacking and fixing a Y-direction movement mechanism on top of an X-direction movement mechanism, and then fixing a table plate on top of that. An object placed on the table plate can be moved to any position in the horizontal plane without rotational motion.

[0029] The X-direction movement mechanism shown in Figures 1 and 2 is composed of a base plate 1, two guide rails 2a, 2b, 3a, 3b placed parallel to each other in the X-direction, guide rail fixed walls 4a, 4b, two movable plates 5a, 5b connected by connecting members 6a, 6b and sliding on the guide rails, a spring-damper device 7 that applies a linear spring force (a spring force proportional to the displacement) and a linear damping force (a damping force proportional to the speed) in response to the relative displacement of the movable plates, and an additional spring force-damping force generating mechanism for applying additional spring force and damping force when the movable plates are greatly displaced. The Y-direction movement mechanism has exactly the same structure as the X-direction movement mechanism, but differs in that it moves the moving plates 5a and 5b in the Y direction (a direction that is 90 degrees different from the X direction).

[0030] As shown in FIG. 3, the spring-damper device 7 is an oil damper 70 filled with oil 71, to which a cylindrical coil spring 73 wound at equal intervals is attached. When the movable plates 5a and 5b are displaced relative to the bottom plate 1 by u, the resistance force F is F = ku + c (du / dt) Here, k is the spring constant of the coil spring, and c is the viscous damping coefficient of the oil damper.

[0031] The additional spring force-damping force generating mechanism includes two linear bearing shafts 10a, 10b fixedly mounted between two movable plates 5a, 5b, movable parts 11a, 11b that can move smoothly on the linear bearing shafts, and additional spring-damper devices A 8a, 8b attached between these movable parts and retaining walls 12a, 12b.

[0032] The additional spring-damper devices A 8a, 8b used in the first embodiment are configured by attaching a variable pitch coil spring 83 to the outside of a piston rod 82 of an oil damper 80 filled with oil 81, as shown in Fig. 4. The variable pitch coil spring 83 is a coil spring wound so that both ends of the coil are densely wound and gradually become sparser towards the center, and exhibits gradually hardening spring characteristics in which the restoring force on the compression side increases in spring constant with displacement.

[0033] Fig. 6 shows the state of the spring when the X-direction moving mechanism is stationary, and Fig. 7 shows the deformation state of the spring when the relative displacement u of the moving plates 5a, 5b exceeds s (the deformation state of the damper is omitted). From Fig. 6 and Fig. 7, it can be seen that in the range where the relative displacement u is smaller than s, only the spring force and damping force of the spring-damper device 7 is generated, but when u exceeds s, the spring force and damping force of the additional spring-damper devices A 8a, 8b are also added. The same is true for the Y direction.

[0034] Figure 8 shows the restoring force characteristics of the X-direction movement mechanism. As can be seen from Figure 8, the seismic isolation table system of the present invention can be designed so as not to resonate with normal earthquake motion, making it possible to obtain a high seismic isolation effect. Furthermore, when it resonates due to long-period earthquake motion, even if the displacement becomes large, the spring constant increases immediately and the natural period changes, so it can be assumed that it will escape from the resonance range and subside. Furthermore, at the time of resonance, the damping force of the additional oil damper is also added, which helps to suppress resonance.

[0035] Second embodiment Next, a second embodiment will be described with reference to FIG.

[0036] The second embodiment differs from the first embodiment in the additional spring-damper device. The additional spring-damper devices B 9a and 9b used in the second embodiment have a structure in which a variable pitch coil spring 93 is attached to the outside of a friction damper 90 using a friction piece and a friction plate 91, as shown in Fig. 5. As a result, when the seismic isolation table system resonates, the gradually hardening spring (variable pitch coil spring) acts to change the natural period and an additional damping force (friction force) is generated, thereby suppressing the resonance. [Industrial Applicability]

[0037] The present invention can provide a low-profile seismic isolation table that is easy to manufacture, and in addition, can be expected to provide the same seismic isolation effect as conventional seismic isolation tables, and can also suppress resonance of the seismic isolation table system caused by long-period seismic motion, so it has the potential to be widely used as an earthquake countermeasure for precision instruments, art and craft items, Buddhist altar implements, etc. [Explanation of symbols]

[0038] 100, 200...X-direction and Y-direction movement mechanism 1...Bottom plate 2a, 2b: Guide rail base material 3a, 3b Guide rail sliding material 4a, 4b Guide rail fixing wall 5a, 5b...Moving board 6a, 6b...Moving plate connection material 7. Spring-damper device 8a, 8b: Additional spring-damper device A 9a, 9b: Additional spring-damper device B 10a, 10b... Linear bearing shaft 11a, 11b...Movable parts 12a, 12b: Additional spring-damper device retaining wall 13. Table top 14. Onboard Equipment

Claims

1. In addition to the X-direction seismic isolation mechanism, which is composed of two X-direction guide rails on a flat bottom plate, both ends of which are held in parallel by fixed walls, two movable plates which are joined together and run on the two X-direction guide rails in the front-rear direction, and a cylindrical coil spring and an oil damper attached between one of the movable plates and one of the fixed walls, an X-direction moving mechanism provided with an X-direction resonance suppressing mechanism, the X-direction resonance suppressing mechanism being composed of two linear bearing shafts fixed in parallel to the guide rail between the two moving plates, two moving parts running smoothly on each linear bearing shaft, and two gradually hardening spring-oil damper devices attached between the moving parts and the two holding walls on the bottom plate; This seismic isolation table is characterized in that a Y-direction movement mechanism, which has the same structure as the X-direction movement mechanism but is rotated 90 degrees for use, is fixed on top of the X-direction movement mechanism, and a table plate is fixedly installed on top of the Y-direction movement mechanism.

2. The seismic isolation table according to claim 1, A seismic isolation table characterized in that the oil damper of the gradually hardening spring-oil damper device is replaced with a friction damper.

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