Active horizontal suspension system using negative stiffness control

Realizing an active horizontal suspension system using negative stiffness for attenuating the effect of direct disturbance to the isolation table is presented in this paper. The inclination of the suspension system causes dislocation of the suspended table. The vibration isolation characteristics of the proposed active system controlled by negative stiffness controller are investigated on horizontal and inclined surface in this study. Negative stiffness is accomplished between the isolation table and the middle mass and positive stiffness is accomplished between the middle mass and the base. The transfer function approach is used to design the controllers. The infinite stiffness and the corresponding zero compliance to the isolation table against direct static disturbance is achieved by series combination of the negative stiffness and positive stiffness of equal magnitude. Both the isolation table and the middle mass are driven by voice coil motors (VCMs) according to the relative displacements of the table and mass which are measured with eddy current gap sensors. The control method for realizing negative stiffness as well as infinite stiffness to the isolation table with VCM is presented analytically. The validity of this technique is confirmed experimentally and theoretically. The results show that the active system with proposed control method can suppress direct static and dynamics disturbances associated with horizontal translation.