Optimal Design And Performance Study Of The Hybrid Magneto-rheological Vibration Isolator

Precision measuring and micro-manufacturing load platforms play an important role in the field of national defense research and civil industry,while complicated and harsh broadband micro-amplitude vibration will seriously affect the measuring or machining accuracy of precision instruments and equipments,so that it stringently conforms to allowable vibration standards and brings forward urgent requirements to the vibration suppression technique.The traditional passive isolator has a limited effect on the attenuation of broadband vibration due to its fixed structure parameters and performance.Moreover,the active actuator still involves technical pain points such as large energy consumption and poor control stability.In recent years,featuring a combination of instantaneous,continuous,and reversible magnetic-control mechanical characteristics and a supplemented semi-active control strategy,vibration isolators based on magneto-rheological(MR)technology have provided a novel solution to the broadband vibration isolation challenge of precision load platforms.However,as of now,most MR isolators are restricted to a single material or component structure,and it is difficult to achieve the combination control of variable stiffness and variable damping(VSVD),which limits the semi-active vibration isolation system to broadening control bandwidth and attenuating responsive peak.In view of the foregoing,in order to approach the dynamic characteristics of “large stiffness and damping at low frequency,low stiffness and damping at high frequency” in the ideal vibration isolation system,this study proposed and designed a hybrid magnetorheological elastomer-fluid(MRE-F)isolator.This hybrid MRE-F isolator merges the variable stiffness technique of magneto-rheological elastomers(MRE)with the variable damping technique of magnetorheological fluids(MRF).A systematic research on key scientific issues was carried out from the aspects of its working mechanism and theoretical design,structural parameters and performance optimization,magnetic-control mechanical performance evaluation and semi-active real-time control.The specific research contents and results of this thesis are summarized as follows:(1)The VSVD mechanism and performance analysis model of the hybrid MRE-F isolator.The proposed structure of hybrid MRE-F vibration isolator is composed of MRE variable stiffness unit(MRE-VSU)and MRF variable damping unit(MRF-VDU)in parallel,which avoids the interaction of working magnetic circuit and realizes the independent VSVD control.In order to give full play to the MR effects of MRE and MRF materials,the analytical model of working magnetic circuit was used to evaluate the magnetic flux densities of MRE layer and MRF gap.The distribution of magnetic flux density inside the isolator is obtained accurately through the electromagnetic finite element simulation,thus the effectiveness and rationality of two magnetic circuit layouts are verified.Taking structural geometric parameters and material mechanical properties as design variables,mechanical calculation models of the vertical static stiffness of MRE-VSU and the output damping force of MRF-VDU are established on the base of cylinder-shaped MRE-in-shear structure and plate-flow/shear model of MRF,respectively.Then,analytical models of power consumption and electromagnetic response performance are derivated,which provides the basis for the optimal design of the hybrid isolator.(2)Structural parameters and performance optimizing design of the hybrid MRE-F isolator.In order to deal with multi-parameter and multi-objective(magnetic-control stiffness and damping,power consumption and response time)optimization problems of the hybrid isolator,using full factorial design of experiments(Do E)method,the factorial analysis of structural geometric parameters for MRE-VSU and MRF-VDU is carried out to select key design variables.According to the design requirements of MRE-VSU and MRF-VDU,the corresponding multi-objective optimization models are established,and the optimal design scheme with more reasonable structural parameters and more balanced performance indicators is achieved based on the Pareto optimal theory and NSGA-? optimization algorithm.In order to realize the automation of optimization process and iterative calculation,by integrating the electromagnetic finite element module and performance calculation models into the optimization workflow of mode FRONTIER,a multi-objective co-simulation platform based on the NSGA-?algorithm is built,by which the effectiveness of the optimization method is verified.(3)Experimental study on mechanical characteristics of the hybrid MRE-F isolator.In order to analyze the magnetic-control stiffness and damping of the hybrid isolator,the test scheme for mechanical properties is developed according its working modes,and the evaluation standard of magnetic-control mechanical performance is established.Using the MTS hydraulic servo test system,the experimental study and analysis are carried out by taking several influencing factors into account,such as excitation current,excitation frequency and peak displacement.The experimental results reveal as follows.In VS mode,the effective stiffness increases with the increase of the excitation current applied to MRE-VSU and decreases with the increase of the peak displacement,and is less affected by the excitation frequency.In VD mode,the equivalent viscous damping coefficient increases with the increase of the excitation current applied to MRF-VDU,but decreases with the increase of the excitation frequency and peak displacement.(4)Research on VSVD modeling and control of the hybrid MRE-F isolation system.Considering the problems of multiple factors and complicated analysis in the conventional VSVD modeling,the equivalent dynamics model of the hybrid isolation system is established by the dimensionless method,and its analytical and numerical solution of the amplitude-frequency response are obtained by the harmonic balance method and the Runge-Kutta method,respectively.According to the different VSVD control modes,the sweeping frequency vibration experimental study on the acceleration transmissibility are conducted to obtained the effective operating frequency band,which verified the resonant frequency shift characteristic of VS mode and the resonance peak attenuation characteristic of VD mode.To validate the control effectiveness of the hybrid MRE-F isolation system,a semi-active ON-OFF controller is designed,and the d SPACE hardware-in-the-loop(HIL)is built,which is employed to the comparative study of passive control,VS control and VSVD control.The results show that VSVD control not only broadens the vibration suppression range of passive resonance,but also achieves greater vibration attenuation in the broadband resonance region.In this paper,researchs on the hybrid MRE-F vibration isolation structure and system provides a new idea for solving the problem of broadband micro-amplitude vibration isolation using magnetorheological VSVD technology,which has important theoretical guiding significance and practical reference value.