Conjugated polymer actuators and sensors: Modeling, control, and applications

Conjugated polymers are soft actuation and sensing materials with promising applications in biomedical devices and micromanipulation systems. However, their sophisticated electro-chemo-mechanical dynamics and nonlinear behaviors present significant challenges in such applications. This dissertation is focused on using systems and control tools to address these challenges. In particular, a systems perspective is taken to model the dynamic and nonlinear behavior of conjugated polymer actuators and sensors, an adaptive control scheme is developed to handle model uncertainties, and a conjugated polymer actuated-micropurnp is explored both as an interesting application and a, platform for validating and extending proposed models. Experimental results on trilayer polypyrrole (PPy) actuators and sensors are presented throughout the dissertation to support the modeling and control studies.On the modeling aspect, a linear, partial differential equation (PDE) is first used to capture the ion transport dynamics in actuation and sensing. With proper boundary conditions, the PDE is solved to derive an infinite-dimensional transfer function model that is geometrically scalable and amenable to model reduction. Nonlinear behaviors, in both electrical and mechanical domains, are also modeled. In particular, on the electrochemical side, a reduction-oxidation (redox) level-dependent impedance model is obtained by applying perturbation analysis to a nonlinear PDE. On the mechanical side, a nonlinear elasticity theory-based framework is proposed to capture the mechanics involved in large deformation. The framework has not only been effective in modeling a bending actuator, but also motivated the study of a novel, torsional actuator that is based on a fiber-directed PPy tube.On the control aspect, a robust adaptive control scheme is proposed to tackle the time-varying behavior of conjugated polymer actuators. Based on a reduced, linear model, a self-tuning regulator with parameter projection is designed and implemented. The robust adaptive control scheme has shown in experiments its superiority to traditional PID control schemes and a fixed model-following scheme.Finally, the application of conjugated polymer actuators to micropumps is explored. A conjugated polymer-actuated diaphragm micropump is designed and fabricated. In contrast to a typical design of clamping an actuation membrane at all edges, a novel, petal-shaped diaphragm design is proposed to alleviate the effect of edge constraints. Transfer function models from the actuation voltage to the diaphragm curvature and to the flow rate are obtained and verified experimentally. A flow rate of 1260 microL/min is achieved for the new diaphragm design, which represents a significant improvement over the traditional design.