Large, uni-directional actuation in dielectric elastomers achieved by fiber stiffening

Abstract

Cylindrical actuators are made with dielectric elastomer sheets stiffened with fibers in the hoop direction. When a voltage is applied through the thickness of the sheets, large actuation strains are achievable in the axial direction, with or without pre-straining and mechanical loading. For example, actuation strains of 35.8% for a cylinder with a prestrain of 40%, and 28.6% for a cylinder without pre-strain have been achieved without any optimization. Furthermore, the actuation strain is independent of the aspect ratio of the cylinder, so that both large strains and large displacements are readily actuated by using long cylinders.

Dielectric Elastomer Based “Grippers” for Soft Robotics

“…One of these is to construct a cylindrical actuator consisting of an elastomer sleeve attached to a series of stiff rings. [15] The rings constrain the expansion of the elastomer parallel to the rings and convert it to an increased stretch in the perpendicular direction, along the axis of the cylinder to produce an axial actuator. Equivalently, a stiff strip or fiber attached to the elastomer prevents the elastomer expanding along the strip and since the volume of the elastomer sheet cannot change with applied voltage, the elastomer stretches in a direction perpendicular to the strips instead [16] .…”

The thickness and stretch dependence of the electrical breakdown strength of an acrylic dielectric elastomer

“…This absence of deformation is not the case for soft elastomers and indeed their change in thickness with an applied voltage has been exploited to create electric field-induced actuators. [11][12][13][14][15][16][17][18][19][20][21][22] Very large actuation strains can be achieved using soft elastomer dielectrics but they must first be biaxially stretched. It is now understood that pre-straining is necessary to forestall an electromechanical instability mode associated with dielectric thinning identified by Stark and Garton.…”

Highly deformable actuators made of dielectric elastomers clamped by rigid rings

“…5-7. A recent design where the hoop direction is constrained by stiff thin fibers might be an optional choice. 36 We also note that in our current calculations, loss of tension at the boundary (Figs. 3 and 4) precedes electrical breakdown, when we assume the dielectric breakdown strength to be 200MV/m.…”