  The characteristic ``in-plane" bending associated with soft robots'
deformation make them preferred over rigid robots in sophisticated manipulation
and movement tasks. Executing such motion strategies to precision in soft
deformable robots and structures is however fraught with modeling and control
challenges given their infinite degrees-of-freedom. Imposing \textit{piecewise
constant strains} (PCS) across (discretized) Cosserat microsolids on the
continuum material however, their dynamics become amenable to tractable
mathematical analysis. While this PCS model handles the characteristic
difficult-to-model ``in-plane" bending well, its Lagrangian properties are not
exploited for control in literature neither is there a rigorous study on the
dynamic performance of multisection deformable materials for ``in-plane"
bending that guarantees steady-state convergence. In this sentiment, we first
establish the PCS model's structural Lagrangian properties. Second, we exploit
these for control on various strain goal states. Third, we benchmark our
hypotheses against an Octopus-inspired robot arm under different constant tip
loads. These induce non-constant ``in-plane" deformation and we regulate strain
states throughout the continuum in these configurations. Our numerical results
establish convergence to desired equilibrium throughout the continuum in all of
our tests. Within the bounds here set, we conjecture that our methods can find
wide adoption in the control of cable- and fluid-driven multisection soft
robotic arms; and may be extensible to the (learning-based) control of
deformable agents employed in simulated, mixed, or augmented reality.
