Ionic polymer–metal composite (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 electricity, chemistry, dynamics and control. Due to its complexity and its nonlinearity, IPMC modeling is difficult and its behavior is still not fully agreed upon by researchers. In this paper, a dynamic model of a cantilever IPMC actuator based on a distributed RC electrical circuit is developed. The RC transmission line theory is used to derive the simple analytical impedance and actuation model of an IPMC actuator. This method permits us to identify the current and voltage as functions of polymer length and frequency. First, an infinite-dimensional impedance model is developed and then replaced with a simple second-order electro-mechanical model using the Golubev method. The proposed modeling approach is validated using existing experimental data.

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The effect of clamping pressure on the actuation performance of ionic polymer-metal composite (IPMC) actuators is newly investigated by carefully considering changes of mechanical stiffness and electrical resistance due to the interfacial contacts between the IPMC and clamping devices. During the clamping process, the soft ionic exchangeable polymer membrane will be squeezed along the thickness direction in the clamping area, resulting in a change of the mechanical stiffness of the cantilevered IPMCs. Also, the electrical contact resistance between two electrodes of the IPMC and the clamping device will be greatly changed according to the change of clamping pressures. Present experimental results show that clamping pressures between the IPMC and the clamping device will strongly affect the actuation performance of the IPMC actuators. An exact electro-mechanical model is developed to fully describe dynamics of the IPMC actuators by considering structural damping, hydrodynamic loading and electro-mechanical force. This study shows that there exists an optimal clamping pressure to obtain the largest bending deformation of the IPMC actuator because of a trade-off between mechanical stiffness and electrical contact resistance.

Nowadays, ionic polymer metal composite actuators are widely used in many fields such as biometric, biomedical, and micro-manipulator devices. Although extensive research exists on control of the ionic polymer metal composite actuators, not much research has been done on robust control considering the nonlinear dynamics of the ionic polymer metal composite. In this study, for the first time, a closed-loop robust controller based on quantitative feedback theory is designed to overcome the actuation performance degradation of the ionic polymer metal composite actuators. First, an analytical electromechanical model is developed to fully describe dynamics of the flexible ionic polymer metal composite actuator. The model is based on the Euler–Bernoulli beam theory and includes structural damping to model viscoelastic behavior of the ionic polymer metal composite actuator. Considering the highly nonlinear and uncertain dynamics of the ionic polymer metal composite actuator, a feedback controller based on quantitative feedback theory is designed to suppress the arbitrary external disturbances and consistently track desired input. Results indicate that the robust quantitative feedback theory control techniques can significantly improve the ionic polymer metal composite performance against nonlinearity and parametric uncertainties.