Reconfigurable Auxetic Devices (RADs) for Robotic Surface Manipulation

TL;DR

The paper tackles the challenge of creating adaptive robotic surfaces that conform to varying geometries by introducing Reconfigurable Auxetic Devices (RADs), a lattice of rotating-square auxetic cells connected by controlled backlash and actuated with embedded servos. A simple ReLU-like intercell coupling model ties joint angles to local dilation, enabling regionally tunable Poisson's ratios and 2D surface conformity. The authors demonstrate fabrication of PLA RAD lattices, develop a 3D software model for backlash-driven morphing, and validate the approach experimentally with 3D surface scans and optical tracking, achieving close agreement (within ~12%) to predictions. This work offers a scalable, compliant method to produce conformable robotic surfaces, with potential applications in soft robotics and custom tooling, and outlines pathways to more complex convex geometries and multifunctional materials.

Abstract

Robotic surfaces traditionally use materials with a positive Poisson's ratio to push and pull on a manipulation interface. Auxetic materials with a negative Poisson's ratio may expand in multiple directions when stretched and enable conformable interfaces. Here we demonstrate reconfigurable auxetic lattices for robotic surface manipulation. Our approach enables shape control through reconfigurable locking or embedded servos that underactuate an auxetic lattice structure. Variable expansion of local lattice areas is enabled by backlash between unit cells. Demonstrations of variable surface conformity are presented with characterization metrics. Experimental results are validated against a simplified model of the system, which uses an activation function to model intercell coupling with backlash. Reconfigurable auxetic structures are shown to achieve manipulation via variable surface contraction and expansion. This structure maintains compliance with backlash in contrast with previous work on auxetics, opening new opportunities in adaptive robotic structures for surface manipulation tasks.

Figures (9)

• Figure 1: (A) Using a lattice of semi-rigid auxetic cells with significant backlash between joints, we achieve structures with reconfigurability through dilation factor ($\alpha(x,y)$) variation. (B) Unit cells are rotating square auxetic mechanisms. (C) By adding actuators with position feedback, we create a robot that can manipulate an object on a surface.
• Figure 2: (A) A simplified diagram of a chain of RADs unit cells. (B) Relationship between normalized backlash, cell size, and the distance of intercell coupling ('die-off').
• Figure 3: (A) Cartoon of key terms in simplified cell coupling model. (B) The range of intercell coupling (die-off distance), is a function of cell geometry when backlash is included.
• Figure 4: (A) Curvature of three auxetic linkages varying in accordance with different arm length and normalized backlash. (B) The points shown align with model results.
• Figure 5: (Left) A RADs lattice with 11x8 layout and mechanical locks conforming to a NACA 0018 airfoil profile. (Right) The same lattice with alternative locks conforming to the NACA 2408 profile.