A low cost, DC-coupled active vibration isolation system

Abstract

In this thesis, I designed and implemented an isolation system that interfaces with traditional air mounts for improved force disturbance rejection relative to passive optical tables.Force disturbance rejection and position alignment are two major functional requirements of vibration isolation systems. With conventional passive isolation systems, a tradeoff exists between improving force disturbance rejection maintaining ground vibration isolation. Commercial active isolators address such a tradeoff through the use of inertial sensors, but the AC-coupled nature of the sensors leads to an inconvenient low frequency response. By referencing a payload stiffly to a softly suspended proof mass, both of the aforementioned functional requirements can be resolved while maintaining ground disturbance isolation performance. Philips Applied Technologies originally developed the concept, named Advanced Isolation ModuleS (AIMS).The AIMS system uses a relative displacement measurement between a payload which is to be isolated from vibrations and a proof mass as feedback. The displacement sensor allows the inertial measurement to be DC-coupled. The objective of this research is to find a relatively low-cost approach for the AIMS concept.A 1-DOF active vibration isolation system based on closed loop control utilizing the DC-coupled inertial measurement as feedback was retrofitted onto an optical table. The coil of a commercial geophone was used as the proof mass, as the geophone provides a relatively inexpensive, low frequency suspension. Error budgeting was performed on the system to estimate and improve payload acceleration noise levels. The results yielded a system bandwidth of 30 Hz and a total system acceleration la value of approximately 1 mm/s².