Research On Design And Switch Control Of Hybrid Active/Semi-active Vibration Isolator

Along with the development of micro-nano fabrication and precision measurement in recent years, the adverse effect of environment vibrations, which are induced by multiple sources and of micro-amplitude and wide range bandwidth, on machining accuracy and measuring sensitivity is more obvious. Passive isolator amplifies lowfrequency vibrations and has a poor adaptability while the semi-active one is unable to attenuate low-frequency vibrations. The active one with high power consumption becomes unstable easily when subjected to high-frequency vibrations. To protect the high-tech equipment from wide-bandwidth micro vibrations, a hybrid isolator featuring both piezoelectric stack actuator(PSA) and magnetorheological elastomer(MRE) is proposed in this work, and the methods of theoretical analysis, numerical simulation and experimental verification are applied to design and test the isolator and synthesis the controllers of the isolation system. The major research works completed in this paper is listed in the following:(1) The mechanical structure and magnetic circuit of the piezostack/MRE hybrid isolator are devised based on Kirchoff’s magnetic law and finite element analysis(FEA) software ANSYS. The dynamic characteristics of the piezostack and MRE isolator under different loadings and excitations are explored respectively and parameter identification for the isolator’s dynamic model is undertaken based on experimental results.(2) The half precision platform’s modal frequencies and shapes are obtained by the FEA method and verified by experimental test. The active PID controller, fuzzy controller and self-tuning fuzzy controller are designed respectively to attenuate variable harmonic vibrations of the flexible beam. The performances of different controllers are investigated and acceleration responses of the controlled beam to single-frequency and multifrequency vibrations are evaluated, which indicates that the designed self-tuning fuzzy controller is independent on the system’s complex accurate model and adaptive for varied excitations.(3) For the quarter precision platform system, a new semi-active control law for the MRE isolator is derived. Considering the nonlinearity of the MRE isolator and excitation uncertainty of an isolation system, the semi-active fuzzy controller and self-tuning fuzzy controller are formulated for the first time, which are evaluated and compared with conventional ON-OFF controller through numerical simulations and experiments. The obtained results show that the proposed self-tuning fuzzy controller, which is independent of the system’s complex model, could maintain consistent performance under varying excitations and thus adaptive.(4) The dynamic model of the quarter precision platform with a hybrid isolator is established, and the switch condition between active working mode, semi-active mode and passive mode is obtained based on testing and simulation results. The fuzzy switch controller for the hybrid isolation system is then proposed, and the responses of the isolated load to complex excitations are simulated in the MATLAB/Simulink software, which indicates that the proposed fuzzy switch system could attenuate wide-bandwidth micro vibrations effectively.