The Feedforward Control Research Of A Tabletop Active Vibration Isolation System Based On LMS Algorithm

As we keep improving the precision in the area ofprecision measurement, ultra-precision machining, manufacturing of integrated circuits,the tiny vibration will be able to affect the working environment which can lead to many unexpected errors. In order to meet the demand of isolating vibration from the ground forhigh precision manufacture and measurement equipment, high precision vibration isolation system must have a wider bandwidth, the higher vibration isolation efficiency and more degrees of freedom.In order to meet the demand of vibration isolation,the vibration isolation technology has gradually developed many branches which includethe passive vibration isolation technology, the active vibration isolation technology that uses actuator to generate compensating force attenuation and the combination of the active and passive vibration isolation technology which has a wider bandwidth.This paper takes the table-type vibration isolation system as the research object which is hybrid vibration isolation contains the active and passive isolating system.This thesis focuses on the research on the feed-forward control method.First of all, the analysis has been done to the characteristics of vibration isolation system which has complicated nonlinear characteristics so that the dynamics model is difficult to meet the requirements of the design of the feed-forward controller.in the accuracy and the forms. The adaptive filter algorithm which is not based on the accurate mathematical model can be appliedin the active vibration isolation system of feed-forward control so that it can avoid establishing the exact dynamics model and also can be adapted to the change of controlled parameter. Adaptive filtering algorithm is suitable for stationary and no stationary random signal detection and estimation which can be divided into update the coefficients of the filter and the filter output process. Thanks to the least mean square(LMS) algorithm which has the characteristics of iterative optimization to update the coefficients of the filter so that the adaptive control process can be completed. Considering that thesecondary path has effects on the control signal and the reference signal instantaneous energy becomes larger shortly in the practical application, we decided to use x-LMS filter normalization(x-NLMS) algorithm.In order to obtain a more accurate model of the secondary path, a two-stepped identification scheme has been proposed which is first using the frequency domain identification method to obtain the transfer function model of sub channel, then compensatingfor the secondary path model to obtain more accurate model of sub channels for the use of design the controller of feed-forward control. In this paper we also carried on a single channel simulation and experimentfor the feed-forward controller design and the secondary path compensation, the experimental results demonstrate the validity of the secondary path compensation.Because the table-type active vibration isolation system is a vibration isolation system which contains a multi degree of freedom, the multiple-locations controlling systemis needed to acquire a better result, we used the multi-channel method of centralized feed-forward controland carried a contrast experiment aiming at shortcoming of decentralized feed-forward control, the experiment proved that the multi-channelmethod hasa more excellentrate of decay than the dispersion feed-forward control The experimental results show thatthe feed-forward control method which is studied in this paper can effectively improve the performance of isolating vibration in the frequency bands that we gave.