Multiparameter actuation of a neutrally-stable shell: a flexible gear-less motor

TL;DR

This paper presents the design and experimental validation of a neutrally stable shell actuated by multiparameter piezoelectric control, enabling shape manipulation akin to a gear-less motor through controlled precession of curvature.

Contribution

It introduces a novel multiparameter piezoelectric actuation method for a neutrally stable shell, demonstrating shape control and motion without traditional gears.

Findings

Successful fabrication and testing of a prototype shell

Effective control of shape and orientation via piezoelectric actuators

Demonstration of a shape precession motion similar to a gear-less motor

Abstract

We have designed and tested experimentally a morphing structure consisting of a neutrally stable thin cylindrical shell driven by a multiparameter piezoelectric actuation. The shell is obtained by plastically deforming an initially flat copper disk, so as to induce large isotropic and almost uniform inelastic curvatures. Following the plastic deformation, in a perfectly isotropic system, the shell is theoretically neutrally stable, owning a continuous manifold of stable cylindrical shapes corresponding to the rotation of the axis of maximal curvature. Small imperfections render the actual structure bistable, giving preferred orientations. A three-parameter piezoelectric actuation, exerted through micro-fiber-composite actuators, allows us to add a small perturbation to the plastic inelastic curvature and to control the direction of maximal curvature. This actuation law is designed through a geometrical analogy based on a fully non-linear inextensible uniform-curvature shell model. We report on the fabrication, identification, and experimental testing of a prototype and demonstrate the effectiveness of the piezoelectric actuators in controlling its shape. The resulting motion is an apparent rotation of the shell, controlled by the voltages as in a "gear-less motor", which is, in reality, a precession of the axis of principal curvature.