A mathematical model to describe bending mechanics of polypyrrole (PPy) actuators

In order to make use of conducting polymer actuators such as PPy actuators suitable for many cutting edge applications, and more importantly to provide enhanced degrees of understanding and predictability in quantifying their performance, it is needed to establish a valid mathematical model of such actuators. With this in mind, the aim of this study is to establish and experimentally validate a lumped-parameter model of strip-type PPy actuators for use in improving their displacement and force outputs. With reference to their operation principle, we draw an analogy between the thermal strain and the real strain in the PPy actuators due to the volume change to set up the mathematical model, which is a coupled structural/thermal model. The Finite Element Method (FEM) is used to solve the model. The rate of propagation of the ion migration into the PPy layers is mimicked with a temperature distribution model. Theoretical and experimental results demonstrate that the model is practical and effective enough in predicting the bending angle and bending moment outputs of the PPy actuators quite well for a range of input voltages. We claim that it is a fruitless task to include the influence of their mechanical, electrical and chemical parameters in an analytical model describing their input/output behaviour.