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 0.25 Hz. The initial vibration isolation frequency is 0.3 Hz. When the external frequency is 0.8 Hz, the transmissibility of the second-stage TPHVI reaches -20 dB. Meanwhile, when the external frequency is 3 Hz, 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.
ABSTRACT
The vibration isolator is a key part of many ultra-precision machines and measuring apparatus. Magnetic suspension vibration isolators (MSVIs) will have excellent application prospects in these instruments to restrain external oscillations. So this paper firstly proposes a new basic configuration of MSVI. Then, in order to study the mechanical characteristics of the MSVI, an analytical expression of the magnetic force is established. The effectiveness of which is demonstrated by the experiment and finite element analysis (FEA). The stiffness of the MSVI is obtained by the derivative of the established analytical magnetic force. Both the axial magnetic force and stiffness appear strong nonlinearity when the inner ring moves at both ends of the fixed outer ring. While the inner ring travels in the middle of the fixed outer one, the axial magnetic force and stiffness indicate approximate linearity with enough bearing capacity. Furthermore, parametric analysis, based on the created magnetic force and stiffness, is performed. The analytical results show that the axial magnetic stiffness may achieve a zero or even negative stiffness value in this range at some size dimensions. The MSVI appears to have a negative stiffness characteristic. More importantly, if a linear and nonlinear positive stiffness spring is combined with the MSVI, it can increase the load capacity of the MSVI. As an example study, the vibration isolation performance of the MSVI is analyzed. The vibration isolation calculation and experiment with the zero stiffness MSVI will be the further focus of the paper.
