Fractional Order Modeling And Second Order Sliding-mode Control Of IPMC Actuators Based On Hysteresis Characteristics

IPMC(Ionic Metal Polymer Composites),as a new intelligent composite material,attracts a lot of attention of scholars due to its electro-actuation,that is,when driven by an applied electric field,it will produce bending deformation,which can be quickly restored to the initial state after the electric field is removed.IPMC has the following advantages:low drive voltage(1V～5V),fast response speed,large actuator deformation,light weight,good flexibility,various shapes can be tailored according to the demand,and better performance in water environment.Therefore,it is more used as an actuator at present,and it has a broad application prospect in bionics,biomedicine and microelectromechanical fields.However,the disadvantages of IPMC actuator include complex response mechanism,sensitive to changes of material parameters,short life in the air,and strong nonlinearity,especially hysteresis characteristic,which seriously affects the control accuracy.In view of this problem,the main work of IPMC actuator in water environment is as follows:(1)The existing preparation methods of IPMC actuator electrode are summarized.IPMC actuator with platinum electrode is prepared by the combination of main electroless plating and secondary electroless plating.Then the electric drive performance of the platinum-electrode IPMC actuator is tested,and the hysteresis characteristics of the IPMC actuator are analyzed and summarized.(2)In view of the hysteresis characteristics of IPMC actuator,a fourth-order autoregressive controlled transfer function model is used to model the displacement response of the tip of the electric drive of IPMC actuator,and the phase lag which can represent the hysteresis phenomenon is described by using the delay link.The system identification toolbox in Matlab proves that the delay link can effectively compensate the hysteresis nonlinearity,and the model built with this is closer to the actual IPMC actuator.(3)The experimental data are converted from time domain to frequency domain.The integer order model and fractional order model of IPMC actuator are identified by Sanko identification algorithm based on frequency domain.Then the frequency response graph shows that the transfer function model based on fractional order has a higher fitting degree with the experimental data and better modeling effect.Then the artificial bee colony algorithm is used to optimize the parameters in the Sanko identification algorithm so as to further optimize the model.(4)The second order sliding-mode control algorithm based on fractional order is designed and its feasibility is verified.Then,in Matlab,the fractional order transfer function model established above is simulated by using this control algorithm and the fractional order PIλDμcontrol algorithm which commonly used in fractional order system.The comparison shows that the proposed control algorithm can control the IPMC actuator model better.The influence of the structural parameters of the control algorithm on the system performance is analyzed.(5)Based on the DSP system,the experimental platform for the IPMC actuator control is set up and then the actual control over the IPMC actuator is realized.The result shows that the control effect of the second order sliding-mode control algorithm based on fractional order is better and more accurate than that of the fractional order PIλDμ control.