Dynamically reconfigurable DEAs incorporating shape memory polymer fibers

We present variable stiffness dielectric elastomer actuators (DEAs), combining a single DEA actuator with embedded shape memory polymer (SMP) fibers, which can be electrically addressed to locally reduce the stiffness by a factor of 100. The device accommodates two SMP fiber sets oriented perpendicularly on both sides of a DEA, which enables a selective deformation in two different directions. During electrostatic actuation, one of the SMP fiber sets is softened by Joule heating, whereas the unaddressed fiber set remains stiff and determines the actuation direction, principally along the direction of the soft fibers. Using SMPs as a latching mechanism allows holding a given actuated position without any power, which leads to much longer lifetime in static (DC) conditions. The DEA is made of a prestretched acrylic elastomer (VHB, 3M) sandwiched between carbon-loaded polydimethylsiloxane electrodes providing an active area of 20 mm x 20 mm. The SMP fibers are electrically isolated from the DEA electrodes using 40 mu m thick acrylic elastomer films. Each SMP fiber is 100 mu m thick, 750 mu m wide and is on a 6 mm pitch. The ratio of locked strains in the direction of the heated and the unheated fibers is measured to be 1.80 for a square DEA. This ratio is increased up to 8 with a cross-shape DEA using only two variable width fibers, one aligned vertically and the other horizontally.