Type-2 Fuzzy Sliding Mode Control For Linear Motor Suspension Platform System

The linear motor suspension platform system of the two degrees of freedom(2-DOF)is researched in this thesis.In suspension platform,considering the required independent control in two 2-DOF directions and the requirements of strong robustness and high precision,there exists no assurance for traditional control strategy to keep the performance of the system.Sliding mode control with decoupling function is proposed in this thesis according to characteristics of nonlinear control in SMC.Combined with interval type-2 fuzzy logic system(IT2-FLS)and fractional calculus,the control strategy is studied for nonlinear coupling among variables of suspension system and the uncertainty disturbance,the main contents of this thesis are as follows:On the basis of analysis on the mathematical model of the suspension platform system,the sliding mode controller is presented to advance robustness of the system according to the effects of uncertain factors,existed in the operating suspension system,such as load disturbance and parameter variation.Based on the self decoupling characteristics of SMC,the input and output of dual-input and dual-output suspension system can be decoupled without separate decoupling controller.The suspension system is divided into two single-input single-output(SISO)subsystems,and the sliding mode surface of which is derived respectively.Taking advantage of the principle of hierarchical control,the state of the two subsystems can be converged to the corresponding sliding surface according to Lyapunov theory,accordingly,high-precision positioning in the direction of 2-DOF is achieved subsequently.What’s more,the sliding mode control switching term is replaced by an interval type-2 fuzzy logic controller to retard the system degradation caused by chattering.The simulation results illustrate that the decouple between input and output is achieved in the proposed decoupling interval type-2 fuzzy sliding mode controller,besides,the interval type-2 fuzzy logic system performs better than typical type-1 fuzzy logic system in dealing with uncertain problem.The proposed control strategy realizes suppression function on the parameters variation and the disturbance caused by the sudden load,ensures strong robustness of the system,and weakens the chattering phenomenon effectively.Considering the fractional calculus features softening signal,the interval type-2 fuzzy fractional order sliding mode controller is proposed,which could further improve the performances of the system.Meanwhile,the fractional sliding surface and fractional reaching law are designed in the process of decoupling in system.And the product of the gain and the discontinuous symbolic function in the sliding mode control switching term is replaced by an interval type-2 fuzzy logic controller subsequently.Consequently,the simulation results demonstrate that the proposed interval type-2 fuzzy fractional order sliding mode control owns better performance than the interval type-2 fuzzy integral order sliding mode,furthermore,the system features strong robustness to the variation of load and parameters.