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Among the electronic polymers EAPs especially the dielectric elastomers are functional materials that have promising
potential as muscle-like actuators due to their inherent compliancy and good overall performance. The combination of
huge active deformations, high energy densities, good efficiencies and fast response is unique to dielectric elastomers.
Furthermore, they are lightweight, have a simple structure and can be easily tailored to various applications.
Up to now most scientific research work has been focused on the planar expanding actuation mode due to the fact that
the commercially available acrylic material VHB 4910 (3M) can easily be processed to planar actuators and has
demonstrated very high actuation performance when pre-strained. Many different actuator designs have been developed
and tested which expands in plane when voltage is applied and shrinks back as soon as the applied charges are removed
from the electrodes.
Obviously the contractive operation mode at activation is required for a wide range of application. Due to the principle of
operation of soft DE EAP, mainly two directions to performed work against external loads are possible. Beside of the
commonly used expanding actuation in planar direction the contractile actuation in thickness direction of the DE film
represents a very promising option in the multilayer configuration. First approaches have been presented by the folded
actuator design and by the multilayer tactile display device.
In this study a novel approach for active structures driven by soft dielectric EAP is presented, which can perform
contractive displacements at external tensile load. The device is composed of an array of equal segments, where the
dielectric films are arranged in a pile-up configuration. In order to maintain satisfying structural integrity when external
tension load is applied special attention was paid to the compliant electrode design which takes a central importance
concerning the force transmission capability between each layer of the actuator. Due to the stack configuration of the
actuator the commonly used and pre-strained acrylic film was replaced by the stress-free IPN modified acrylic film in
order to eliminate the need for external pre-strain-supporting structures.
Introductorily, the specific problems on conventional expanding actuators are discussed and the aims for contractive
tension force actuators are specified. Then some structural design parameters are addressed in order to achieve a high
rate of yield and reliable working principle. In the main part of the study the manufacturing process of the actuators and
some measurement results and experiences are discussed in detail.
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