Application Research Of Sliding Mode Variable Structure Control In The Floating Raft Active Vibration Isolation System

In the ship,the mechanical vibration is mainly the line-spectrum vibration,especially the low frequency one,which is caused by such reciprocating,rotary,fluid power devices and mechanical equipments.Taking control of such vibration is one of the main approaches to improve the ship concealment and fighting force.Since active vibration control technology can overcome the defects of traditional passive vibration isolation technology that has low frequency vibration isolation effect,it is then widely studied.The majority of motive power machines within the ship are the rotaries,most of whose vibration signals are periodic under the circumstance of certain rotative velocity,including the fundamental frequency relating to the speed and its harmonic components,which appear as the form of discrete linear spectrum in the autopower spectrum.While in the practical work,working speed of motive power machines fluctuates in a certain range,which also leads to the fluctuation of vibration signal frequency.Therefore,the mechanical noise of ship carries the characteristics of pseudo periodicity and fluctuating frequency components,which require the active vibration control methods restraining such noise to possess good robustness.Sliding mode variable structure control has strong robustness to system parameter perturbation and external disturbance.In addition,this control algorithm possesses advantages of mathematical model without the need of precision,and simple physical implementation.So this paper uses two vibration motors as vibration source of the active floating raft vibration isolation system and perceives the two as the research object,doing the research to sliding mode variable structure control methods,thus providing a reliable way for active vibration control of ship vibration and noise reduction.The main contents of this paper include: the building of control channel model of active floating raft vibration isolation system,design of sliding mode variable structure controller to restrain disturbance of frequency fluctuation and sliding mode variable structure control experiments of active floating raft vibration isolation system.The experiment of system identification is designed and completed,two-input and two-output discrete transfer function model is gotten through calling system identification toolbox,then the degree of fitting of the model in the time domain and frequency domain is tested,and both two fitting degrees are more than 85%.Based on gained active floating raft vibration isolation system control channel transfer function,the transfer function model is transformed into state space model,and then the appropriate sliding mode variable structure control strategy is selected to design the controller and describe via S function.The simulation model of active floating raft vibration isolation system variable structure control restraining single frequency external disturbance,narrowband disturbance,and dual-frequency external disturbance is constructed by using the simulation tool MATLAB/Simulink.And the simulation results show that the maximum amplitude of error signal is decreased by more than 50% before and after control.The Experimental device of active floating raft vibration isolation system is established,and single frequency,dual frequency,narrowband disturbance control experiments are done on active floating raft vibration isolation system by using simulation design controller.The control experiment has achieved obvious damping effect,and the error signal RMS(Root Mean Square)value decreased more than 50% before and after control.The experimental results are consistent with simulation results.