Control of a hybrid active-passive vibration isolation system

Precision vibration control is a major issue in nanotechnology. In particular, nano-precision measurement systems such as Atomic force microscopes (AFM) and Scanning probe microscopes (SPM) are sensitive to ground vibrations. The amplitude of a ground vibration is typically sub-micrometer and ground vibrations adversely affect both the precision and accuracy of these measuring equipment. Consequently, hybrid active-passive vibration isolation systems are typically used as they reduce ground vibrations. This paper presents a hybrid vibration isolation system composed of four spiral metal springs for passive isolation and eight voice coil motors for active isolation. H-infinite and Proportional–integral–derivative (PID) controllers are applied to its 6-DOF vibration control system using six velocity sensors to measure system vibrations. The transmissibility of the presented hybrid isolation system is in the range -10 to -48 dB at its passive resonance frequency and is at least -4 dB better than hybrid isolation systems employing acceleration sensors. The results of various tests conducted to verify the control performance of the developed system with a separately developed shaker indicate that it can serve as a bench-top device for precision measurement machines.