  Roboticists have been seeking to address this situation in recent years
through the use of soft robots. Unfortunately, identifying appropriate models
for the complete analysis and investigation of soft robots for design and
control purposes can be problematic. This paper seeks to address this challenge
by proposing two complementary modeling techniques for a particular type of
soft robotic actuator known as a Fiber-Reinforced Elastomeric Enclosure (FREE).
We propose that researchers can leverage multiple models to fill gaps in the
understanding of the behavior of soft robots. We present and evaluate both a
dynamic, lumped-parameter model and a finite element model to extend
understanding of the practicability of FREEs in soft robotic applications. The
results with the lumped-parameter model demonstrate that it predicts the actual
rotational motion of a FREE with at most 4% error when a closed-loop controller
is embedded in the system. Additionally, finite element analysis was used to
study FREE design parameters as well as the workspace achieved with a module
comprised of multiple FREEs. Our finite element results indicate that
variations in the material properties of the elastic enclosure of a FREE are
more significant than variations in fiber properties. Finally, finite element
results show that a 30-degree difference in winding angle dramatically alters
the shape of the workspace generated by four FREEs assembled into a module.
Concludingly, comments are made about the relative advantages and limitations
of lumped-parameter and finite element models of FREEs and FREE modules in
providing useful insights into their behavior.
