Ionic polymer-metal composites (IPMCs) are soft materials that can generate large deformation under a low voltage. IPMCs have many potential applications in biomedical, robotic and micro/nano manipulation systems. In this paper, we first present a distributed, nonlinear circuit model for IPMC, which incorporates the nonlinear capacitance, the nonlinear DC resistance, and the effect of surface resistance. The bending displacement is proportional to the total stored charge in IPMC. After

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... ing the model in the length direction, we obtain a multiplesegment model which can be represented in the state space for nonlinear control design. The model is validated using experimental data, and we show that a one-segment model can predict the current and displacement response reasonably well. A model-based nonlinear controller is proposed for IPMC actuators, where feedback linearization is applied. Simulation results show that model-based nonlinear controller delivers better performance than a traditional PI controller in terms of the tracking error, control effort, and robustness to sensing noises.