Dielectric elastomers are a subclass of electronic EAPs able to produce large deformations (and thus mechanical work)
when an external electric field is applied. While the intrinsic compliance of this kind of polymeric actuators have been
always addressed as major benefit with respect to traditional electromagnetic motors, unable to fully capture the
capabilities and mechanical properties of biological muscles, their polymeric nature poses peculiar challenges in
controlling a system which is subject to nonlinearities, hysteresis and viscous creep behavior. In this paper we explore
the controllability properties of a simple rotational joint driven by two dielectric elastomer actuators arranged in an
antagonistic configuration. A number of sensors are used to obtain information about the state of controlled system: the
angular position of the joint is measured by an angular encoder, custom-designed tension sensors are used to monitor the
tension of the two driving tendons and linear encoders provide accurate measurements of the displacements generated by
the two actuators. Using this feedback information, a control algorithm has been implemented on a microcontroller unit
in order to independently activate the two actuators, allowing a closed loop control of both the angular position of the
joint (position control) and the tensions of its tendons (force control). A description of the developed control strategy and
its performances under different load conditions are discussed in this paper.
One problem related to the actuation principle of macroscopic dielectric elastomer actuators is the high voltage required,
typically in the Kilovolt range, that imposes particular care in the insulation of the whole actuator from the surrounding
environment. This high actuation voltage, however, can be drastically reduced if a thin film of dielectric elastomer is
used. Despite this, the manufacture of a macroscopic stack-like actuator, starting from thin films of dielectric elastomer
can present many manufacture difficulties, like the handling and the assembly of the films, the power distribution to
hundreds or thousands of layers, the presence of defects in one single layer that can cause the complete failure of the
whole actuator. In this paper, a fast, semi-automatic process is proposed for the manufacture of modular units of
dielectric elastomer, each of them consisting of many layers of rolled thin dielectric film. All the manufactured units are
independent and take their power from a lateral, compliant supply rail that contacts the sides the electroded layers. This
design is very suitable for industrial production: each module can be independently tested and then assembled in a
complete macroscopic actuator composed by an unlimited number of these modules. The simple assembly methodology
and the semi-automatic manufacture process described in this paper allows the fabrication of multilayer stacked devices,
that can be used both as contractile or expanding actuators.
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