A three-axis modular horizontal vibration isolation system with adjustable stiffness: Design, analysis and experimental validation

Abstract

In this study, a modular vibration isolator design is introduced in which the horizontal stiffness of the system can be adjusted in three axes (translational stiffness in the horizontal x and y axes and torsional stiffness about the vertical z-axis) by changing the compressive forces on the leg modules, which are composed of elastic stepped columns and a string. A novel multi-string tensioning mechanism is developed to change the axial compressive forces on all the elastic stepped columns simultaneously, which in turn vary the translational and torsional stiffness of the system. Consequently, the translational and torsional natural frequencies of the system can be tuned to a targeted value by increasing/decreasing the tension forces in the strings for light/heavy payloads. With the use of multiple leg modules in the isolator, the torsional natural frequency can be kept close to the translational natural frequencies at any value of the tension forces in the strings even if the payload masses vary over a wide range. To investigate the relationship between the tension forces and natural frequencies, a leg module is produced. Analytical and finite element models of the leg module are formed, and the results of these models are found to be in good agreement with the experimental results. It is shown that the translational and torsional natural frequencies of the isolator with multiple leg modules can be adjusted to 0.5 Hz and 0.6 Hz, respectively, keeping the lower limits of the isolation bandwidth in the translational and torsional axes less than 1 Hz. Moreover, the upper limit of the isolation bandwidths can be kept above 135 Hz. Therefore, the proposed isolation system has a very wide isolation bandwidth at low frequencies.