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Ionic polymer metal composite (IPMC) actuator is a group of electro-active polymer (EAP) which bends in response to a relatively low electrical voltage because of the motion of cations in the polymer network. IPMC has a wide range of applications in robotics, biomedical devices and artificial muscles. The modeling of the IPMC actuator is a multi-physics task as it involves the electricity, chemistry, dynamics and control fields. Due to its complexity and nonlinearity, IPMC modeling is difficult in terms of mathematics and its behavior is still not fully agreed upon by researchers. This paper presents a novel discrete-time model with state-dependent parameters (SDP) for identification of the nonlinear response of an IPMC actuator. A single-input single-output nonlinear identification algorithm is formulated and demonstrated for an IPMC actuator that exhibit both soft and hard nonlinearities. The nonlinear characteristics of the identified system are represented with coefficients which are a function of the input and output states. Following the SDP algorithm, the model is identified from input–output data to represent the model parameters as functions of past inputs and outputs. The proposed modeling approach is validated using an existing model and show exact representation of the non-linear behavior of the IPMC actuator

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In this research, the dynamic behavior and nonlinear vibration of a clamped-clamped initially curved microbeam under electrostatic step actuation is investigated. The initially curved microbeams under transverse loading may exhibit two different stable states and this is the basis of the emergence of bi-stable micro electro mechanical systems (MEMS). The equation of motion is derived based on energy method and Hamiltonian principle, and re-written in non-dimensional form by using appropriate non-dimensional parameters. The resultant equation of motion in non-dimensional form is discretized and converts to a system of nonlinear ordinary differential equations by using a reduced order model based on the Galerkin procedure. Runge-kutta method of order four is employed to solve the resulting system of nonlinear ordinary differential equations. COMSOL Multiphysics software is used for finite element simulation. Then, the effect of various parameters including voltage parameter, damping, initial midpoint elevation and gap length is investigated. It is concluded that the critical voltage of pull-in is decreased by increasing of the initial midpoint elevation. Also The results depict that by increasing of the damping parameter, the possibility of transition between two stable stats is eliminated.