Stiffness Change for Reconfiguration of Inflated Beam Robots

TL;DR

This paper demonstrates how variable stiffness control, via embedded positive pressure layer jamming, enables reconfiguration and increased workspace in inflated beam soft robots, overcoming actuation limitations and buckling issues.

Contribution

It introduces a novel stiffness change method using embedded layer jamming for inflated beam robots, allowing active shape control with fewer actuators and compatibility with robot growth.

Findings

Stiffness change enables selective joint activation.

Variable stiffness increases robot workspace.

Method is compatible with robot growth and eversion.

Abstract

Active control of the shape of soft robots is challenging. Despite having an infinite number of passive degrees of freedom (DOFs), soft robots typically only have a few actively controllable DOFs, limited by the number of degrees of actuation (DOAs). The complexity of actuators restricts the number of DOAs that can be incorporated into soft robots. Active shape control is further complicated by the buckling of soft robots under compressive forces; this is particularly challenging for compliant continuum robots due to their long aspect ratios. In this work, we show how variable stiffness can enable shape control of soft robots by addressing these challenges. Dynamically changing the stiffness of sections along a compliant continuum robot can selectively "activate" discrete joints. By changing which joints are activated, the output of a single actuator can be reconfigured to actively control many different joints, thus decoupling the number of controllable DOFs from the number of DOAs. We demonstrate embedded positive pressure layer jamming as a simple method for stiffness change in inflated beam robots, its compatibility with growing robots, and its use as an "activating" technology. We experimentally characterize the stiffness change in a growing inflated beam robot and present finite element models which serve as guides for robot design and fabrication. We fabricate a multi-segment everting inflated beam robot and demonstrate how stiffness change is compatible with growth through tip eversion, enables an increase in workspace, and achieves new actuation patterns not possible without stiffening.