Low frequency control strategy for seismic attenuation in inertial platforms and mechanical suspensions

This paper describes a new application of the monolithic folded pendulum configured as seismometer (no force feed-back) and used as sensor in the control of inertial platforms and suspensions, like, for example, those used in interferometric detectors of gravitational waves, where a residual horizontal motion better than 10 −15 m /√ Hz in the band 0.01 ÷ 100 Hz is a requirement. The experimental results, obtained in the band 0.01 ÷ 10 Hz , demonstrate that this sensor has enough dynamics and sensitivity to introduce no limitations to the state-of-the-art control systems. Moreover, its full scalability allows an easy integration and positioning also on the different stages of multistage mechanical suspensions (seismic attenuators) and inertial platforms. This new application demonstrates not only the feasibility of the proposed new control strategy in the low frequency region, but, and it is very relevant, that it is now possible the implementation of very effective control systems with a large reduction of control electronics, replaced by less noisy optical and mechanical devices, with the further advantage of rendering the whole system surely less sensitive to environmental noises. The results of this study, although preliminary and obtained with sensors not optimized for the specific application, are presented and discussed in this paper, in connection with some of the possible applications (platforms and mechanical structure control and stabilization, building controls, etc.) and the planned further developments and improvements.