A stiffness enhancement methodology for artificial muscles

Electroactive conducting polymer actuators have been proposed as alternative to conventional actuators due to their extraordinary properties. This paper reports on a stiffness enhancement methodology for cantilever type conducting polymer actuators based on a suitably designed contact surface with which the actuators are in contact during operation. Finite element analysis and modeling are used to quantify the effect of the contact surface on the effective stiffness of a tri-layer cantilevered beam, which represents one-end free, the other end fixed polypyrrole (PPy) conducting polymer actuator under a uniformly distributed load. After demonstrating the feasibility of the stiffness enhancement concept, experiments were conducted to determine the stiffness of bending-type conducting polymer actuators in contact with a range (20-40 mm in radius) of circular contact surfaces. The simulation and experimental results demonstrate that the stiffness of the actuators can be varied in a nonlinear fashion using a suitably profiled contact surface. The larger is the radius of the contact surface, the higher is the stiffness of the polymer actuators.