Characterization of a radial cylindrical spring using an electromechanical test bench

The Center for Artificial Muscles of EPFL in Neuchâtel focuses his research on designing a less invasive cardiac assist device based on a dielectric elastomer actuator. The idea is to place a ring around the aorta and activate it to help failing heart pumping. To enhance the performances of the actuator, in terms of both force and displacement, a cylindrical negative stiffness spring has been designed and manufactured; the latter being combined with the dielectric elastomer actuator. The aim of this paper is to propose an innovative set-up to validate the theoretical characteristic of this particular spring. This is performed by means of an electromechanical test bench that allows to radially compress the spring and measure the resulting characteristic. The test bench is composed of 16 fingers that are responsible for radially compressing the spring. A force sensor is integrated in one finger and a laser position sensor is used to measure the deformation. A user interface is built on LabVIEW in order to perform the measurement process. A first experiment is carried out with a planar negative stiffness module in order to validate the concept of the test bench with a simple sample. In the second part of the experiment, the cylindrical spring is tested. In both experiments, the negative slope in the force displacement characteristic is observed.