Numerical Estimation of Precision Equipment Vibration Isolation System

This work is devoted to the numerical estimation of the effectiveness of high-precision lithography scanner foundation and its vibration isolation system when it is installed in a reconstructed building. The manufacturer requires that the scanner's foundation has to be isolated from both the background vibrations and from the vibration sources that occurs inside the considered building. Based on manufacturer specifications of the foundation, its dynamic stiffness and power spectral density of the basement surface vibration accelerations in the frequency range 1 - 100 Hz have to be within specified limits. In the course of this work, we performed field measurements of the vibration levels of the construction site, as well as at the bottom of the excavation. The results of the measurements revealed the presence of non-stationary random vibration sources at frequencies from 7 up to 150 Hz. The problem of assigning the appropriate thicknesses of elastic and damping elements of the vibration isolation system is that at the time of designing the system, there was no information available about the levels of dynamic influence from the installed in the building vibrating equipment. To ensure utilization of the company's process technology, there was planned to install inside the building powerful ventilation systems, air conditioning, feeding and batching system of liquid nitrogen and other chemicals, etc. In order to meet the requirement of the foundation dynamic stiffness special reinforcing technology was applied, and to meet the vibration requirements - an increase in the mass of the concrete block due to under-foundation structure with gravel mixture filling was considered. To evaluate the effectiveness of the designed vibration isolation system, an analysis of vibration propagation from vibrating equipment through the supporting structures of the building and the ground layers to the scanner's foundation was performed using finite element package MSC Patran/Nastran. The results of non-stationary dynamic analysis of vibration propagation allowed us to estimate the amplitudes of foundation oscillations and to adjust the parameters of the vibration isolating materials both in the scanner's foundation, and at the sources of vibration.