Directional Stiffness Control Through Geometric Patterning and Localized Heating of Field’s Metal Lattice Embedded in Silicone

Emily Allen,John Swensen

doi:10.3390/act7040080

Abstract

This research explores a new realm of soft robotic materials where the stiffness magnitude, directionality, and spatial resolution may be precisely controlled. These materials mimic biological systems where localized muscle contractions and adjustment of tissue stiffness enables meticulous, intelligent movement. Here we propose the use of a low-melting-point (LMP) metal lattice structure as a rigid frame using localized heating to allow compliance about selectable axes along the lattice. The resulting shape of the lattice is modeled using product of exponentials kinematics to describe the serial chain of tunably compliant axes; this model is found to match the behavior of the physical test piece consisting of a Field’s metal (FM) lattice encased in silicone rubber. This concept could enable highly maneuverable robotic structures with significantly improved dexterity.

Highlights

Soft robotics and compliant robotic mechanisms have become increasingly popular over the last few years as their soft, compliant nature makes them safe for interaction with humans and ideal for applications that require adaptability, such as in squeezing through tight spaces or grasping objects [1,2,3]
A simple Field’s metal (FM) lattice encased in a silicone matrix with six heating elements proved capable of bending along nine different axes with the axes of compliance selected/controlled by the heating of localized segments
Whereas previous studies on multi-stiffness materials have investigated controllability of overall material stiffness, this work presents an initial step toward a new realm of stiffness variability where the directionality of the stiffness is controlled in addition to its magnitude

Summary

Introduction

Soft robotics and compliant robotic mechanisms have become increasingly popular over the last few years as their soft, compliant nature makes them safe for interaction with humans and ideal for applications that require adaptability, such as in squeezing through tight spaces or grasping objects [1,2,3]. Many soft robotic actuators are fabricated using elastomeric materials activated by pneumatic chambers that deform the elastomer when pressurized [6,7,8,9,10]. Fiber reinforcements and high pressure within the pneumatic chambers enable these hands and grippers to exert substantial forces [3,11,12]. Other soft actuators are fabricated with thin electrode coatings on both sides of an elastomer that cause deformation of the elastomer when a high voltage is applied across the electrodes [9]. These methods involve patterned deposition of ink to induce localized heating/shrinkage under infrared irradiation or spatially controlled swelling of a medium within a polymer matrix [13,14]

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