Active vibration isolation of a large stroke scanning probe microscope by using discrete sliding mode control

Active vibration isolation is gaining increased attention in the ultra high precision applications to effectively treat the unavoidable ground vibration. The use of active vibration isolation is now being explored for the Molecular Measuring Machine (M3) at the National Institute of Standards and Technology to improve its imaging resolution. The M3 system uses a Mallock suspension to establish a non-rotation constraint to the stage motion. The vibration isolation system has to work within the Mallock geometry. The system is also a six-input-six-output system; therefore, a clever design is needed to maximize the controller performance while limiting it to within the stability range. The control algorithm adopted uses discrete sliding mode control, taking advantage of its easy computer implementation and its robust high performance properties. The experimental results show that the controller is effective over the operating frequency band and is superior to the conventional lead-lag type controller.