Over-Actuation in Soft Robots: Towards Active Variable Stiffness & Viscoelasticity

Abstract

Continuum soft robots (cSR) represent a particular class of the highest compliant deformable robots made of elastomers, typically driven by embedded pneumatic chambers. While their structural compliance is appealing for many tasks, most existing research on variable stiffness at a constant generalized position relies on empirical evidence rather than a formal method that enhances the properties of cSR. Consequently, few sound advances have been reported regarding closed-loop (control-based) variable stiffness and furthermore for variable viscoelasticity for tracking in cSR, nor have they fully exploited the ease with which soft robots incorporate additional actuation inputs. In this extended abstract, the control of the fundamental behavioral structural viscoelasticity is addressed through commanding redundancy of actuation during motion. To this end, m pneumatic chambers are introduced into the cSR such that n chambers are used for motion tracking, while the remaining r=m-n are available to allocate variations of stiffness in regulation tasks, and of viscoelasticity in tracking tasks.