Modeling and analysis of a two-stage tri-linear pendulum ultra-low frequency horizontal vibration isolator with experimental investigations.

Abstract

In engineering practice, the external horizontal oscillations always influence the working performance of precise instruments, advanced manufacture equipment, and gravitational wave detection. In order to ensure the normal operation of these instruments, it is necessary to attenuate these vibrations adequately. The pendulum mechanism horizontal vibration isolator is an efficient method. Hence, this paper presents a type of two-stage tri-linear pendulum horizontal vibration isolator (TPHVI). The first-stage TPHVI is connected in series with the second-stage one. The dynamic equations of the two-stage TPHVI are subsequently established so that the vibration isolation performance of the two-stage TPHVI is acquired. The analysis result of the natural frequency of the two-stage TPHVI reveals that it can obtain a low frequency vibration isolation performance when the first-stage TPHVI swings in a small value. As a case study, an experimental rig is constructed. The measured transmissibility keeps in good agreement with the calculated one. The natural frequency of the second-stage TPHVI is 0.25Hz. The initial vibration isolation frequency is 0.3Hz. When the external frequency is 0.8Hz, the transmissibility of the second-stage TPHVI reaches -20 dB. Meanwhile, when the external frequency is 3Hz, the transmissibility of the second-stage TPHVI is -40 dB. These measured data demonstrate that the proposed two-stage TPHVI can realize low frequency vibration isolation horizontally, which will have broad application prospects in the field of ultra-precision in engineering practice.