Vibration Isolation in Six Degrees of Freedom Using Combined Passive and Active Isolation Technique

Low-frequency vibration isolation in all six degrees of freedom has been a requirement in many space and other applications. The traditional linear vibration isolators are not suitable for low-frequency isolation. A nonlinear vibration isolator with the characteristics of high static and low dynamic stiffness (HSLDS) conceived by the idea of negative stiffness using magnetic spring is employed for the purpose of low-frequency isolation. To realize the six dof isolation, a Stewart isolator with its struts designed based on the quasi zero stiffness (QZS) concept is used. The effect of struts deformation on the movement of the upper plate is known by performing kinematic analysis in the cubic configuration arrangement of the Stewart platform. Equations of motion are derived using Lagrange’s equation, and simplifications are done to reduce the computational effort. By performing the Numerical simulation, the transmissibility plots are developed and compared with the traditional system and the merits are highlighted. An active control is included to increase the isolation region and decrease the resonant amplitude which are limited by the parameter of the negative stiffness and making the system hybrid. Active control is achieved by using constant and integral force feedback. In active control, the constant force feedback decreases natural frequencies and the integral part will induce damping and decreases the resonant amplitude. The results from active control are compared with passive one giving a better isolation region and decreasing the resonant amplitude.