Over-Actuation in Soft Robots: Towards Active Variable Stiffness & Viscoelasticity
Carlos Ernesto Vazquez-Garcia, Ernesto OlguÃn DÃaz, Vicente Parra-Vega
AI summary
Problem
Existing variable stiffness methods for continuum soft robots rely on empirical evidence or non-homogeneous designs, lacking formal closed-loop control approaches that exploit redundant actuation for simultaneous tracking and viscoelasticity modulation.
Approach
The authors use an over-actuated pneumatic soft robot model and inject a forward active viscoelasticity term into an integral sliding mode controller, using redundant chambers to independently regulate motion and tune structural tension.
Key results
- Model-free integral sliding mode controller guarantees local exponential tracking with variable viscoelasticity
- Redundant pneumatic chambers successfully decouple motion tracking from active stiffness and viscosity modulation
- Simulations demonstrate real-time adaptation of internal pneumatic pressure to track trajectories under disturbances
- Introduction of Pneumatic Field Tension quantifies internal stress from concurrent tracking and modulation inputs
Why it matters
Enables soft robots to dynamically tune their mechanical properties in real-time for robust performance in unstructured environments without complex modeling.
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 q ∈Rn 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, r ∈Rm, m > n redundant 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.