A.The foundation can absorb the energy of the reaction force in the vibration test and achieve vibration isolation from the ground.
According to Newton’s first law, the action force and reaction force are equal. When vibration occurs, the electromagnetic excitation force pushes the dynamic load of the vibration table upward (moving coil + table + fixture + specimen) to achieve vibration, and at the same time, it also excites downward. The static load mass of the vibration table (table body + platform + foundation) causes it to “vibrate”.
Since there is an air spring for vibration isolation between the electric vibration table body and the bracket (or vibration table base) located on the ground, the resonance frequency fn of the mass-spring system composed of the air spring and its load is about 3~5Hz. The test frequency fs of the shaking table is higher than 3 times the resonance frequency fn of the table body, that is (fs≥3fn). The air spring will play a very good vibration damping effect. The vibration of the shaking table will not cause obvious vibration interference to the ground, so the vibration When the platform is applied in the frequency range above 5~10Hz, it is not necessary to use a large foundation for vibration isolation. It can be directly located on the flat cement floor to avoid consuming a lot of resources and energy. Therefore, for electric vibration tables, the “vibration isolation” function of the foundation is mainly used to perform effectively during low-frequency vibrations.

B. The foundation is used to improve the low-frequency performance of the electric vibrating table.
When the electric vibration table works in the low frequency band, the resonance of the table body and its isolation air spring will bring a lot of inconvenience to the low-frequency vibration test. The fundamental way to solve this problem is to build a foundation with a large inertial mass, then lock the air spring for vibration isolation so that it does not play the role of vibration isolation, and rely on the large foundation to absorb the energy of the reaction force.
In order for the large inertial mass foundation to achieve the above functions, the construction of the foundation must meet the following requirements:

1,The ratio of the inertial mass of the foundation (kg) to the maximum thrust of the vibration table (kgf) reaches 8:1.

2, When the electric vibration table operates below the resonance frequency of the table body 3~5Hz, the maximum acceleration of the vibration is limited by the maximum vibration displacement, and the acceleration value will not be higher than (1/100) the maximum peak acceleration of the vibration table. If the vibration table The ratio of the inertial mass of the foundation to the maximum excitation force of the vibration table is 10:1, then the highest possible vibration magnitude of the vibration table body is (1/1000) of the maximum peak acceleration of the vibration table. Therefore, a large-tonnage If the foundation is firmly connected to the vibration table body, it can be considered that the vibration table body is in a relatively “stationary” state during the low-frequency vibration test. The problems in the ultra-low-frequency sinusoidal vibration test mentioned above will not occur. This is the fundamental reason why electric vibration tables used in low-frequency or ultra-low-frequency bands must build large inertial mass foundations.

3,The body of the vibration table and the large-tonnage foundation must be firmly connected as a whole.
If the ratio of the inertial mass of the foundation to the maximum excitation force of the vibration table is 10:1, even if the vibration table reaches the maximum thrust during the vibration test (this condition rarely occurs), for example, the maximum thrust of the 50t vibration table (50ⅹ103kgf ) The maximum acceleration value that excites a 500t (50ⅹ104kg) inertial mass foundation is only 0.1g. The vibration generated by a foundation of this magnitude on the ground will not cause significant vibration interference to other equipment and facilities (such as house foundations) adjacent to the vibration table. or destructive effect.