Expanding the Design Space for Electrically-Driven Soft Robots through Handed Shearing Auxetics

TL;DR

This paper introduces a new design approach for electrically-driven soft robots using Handed Shearing Auxetics, significantly expanding their force and stiffness capabilities through optimized structural parameters.

Contribution

It demonstrates how adjusting auxetic trajectory points and cell count in HSAs enhances actuation range, force, and stiffness, addressing previous limitations.

Findings

Force range expanded from 5N to 150N

Stiffness range increased from 2 N/mm to 89 N/mm

Viscoelastic effects limit force over time

Abstract

Handed Shearing Auxetics (HSA) are a promising structure for making electrically driven robots with distributed compliance that convert a motors rotation and torque into extension and force. We overcame past limitations on the range of actuation, blocked force, and stiffness by focusing on two key design parameters: the point of an HSA's auxetic trajectory that is energetically preferred, and the number of cells along the HSAs length. Modeling the HSA as a programmable spring, we characterize the effect of both on blocked force, minimum energy length, spring constant, angle range and holding torque. We also examined the effect viscoelasticity has on actuation forces over time. By varying the auxetic trajectory point, we were able to make actuators that can push, pull, or do both. We expanded the range of forces possible from 5N to 150N, and the range of stiffness from 2 N/mm to 89 N/mm. For a fixed point on the auxetic trajectory, we found decreasing length can improve force output, at the expense of needing higher torques, and having a shorter throw. We also found that the viscoelastic effects can limit the amount of force a 3D printed HSA can apply over time.