We report electrically shielded capacitive stretchable force sensors, that simultaneously measure normal and shear strains, even near electric sparks. The device consists of an outer conductive stretchable shielding layer (carbon-loaded silicone) and a central silicone layer with embedded air channels and three liquid metal electrodes. We report sub-mN force resolution in both normal and shear directions, can measure forces larger than 10 N, and operate reliably after repeated loading to 20 N load. Performance is unaffected by nearby high DC and AC electric fields, allowing use in a wide range of robotic sensing applications.
We develop and validate an analytical model in order to achieve large actuation deformation and high load-bearing capacity in a multistable dielectric elastomer actuator (DEA). We integrate patterned shape memory polymers (SMPs) and stretchable heaters with a 30 mm x 30 mm DEA to locally soften different SMP regions by 250 times during the actuation, allowing multiple a wide range of actuated shapes, and latching of those shapes. The model allows optimizing SMP thicknesses and other design parameters to offer the best trade-off between the actuation and the load-bearing.
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 μm thick acrylic elastomer films. Each SMP fiber is 100 μm thick, 750 μm 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.
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