Design of an Innovative Cylindrical Spring with a Negative Stiffness

Interest in the dielectric electroactive polymer is growing in the medical field because of the large similarity with the biological muscles. With the objective to create an artificial pump based on DEAP, this paper presents the concept of an innovative spring with a negative stiffness and radial displacement. It was demonstrated that coupling a spring with such characteristic and the DEAP allows to improve the performance of DEAP actuators. The final design is close to a stent with monostable beams instead of current bistable one. The complete spring is composed of several modules which include one beam and one rigid support. The radial displacement is induced by the tangential compression of each beams and the equations of deformations demonstrates that the radial displacement is increased if the number of modules is higher than 6. In the design procedure, relevant choices have allowed to reduce computation time of the FE simulation. The different equations are validated through FEM results and less than 1.5% of error is obtained. The proposed spring is finally coupled with a tubular dielectric electroactive polymer membrane in order to create a cylindrical actuator. The radial displacement is around 3 mm. The result has been validated through FEM and an error of 6.8% is obtained.