Dynamically Tunable Friction via Subsurface Stiffness Modulation

Abstract

Currently soft robots primarily rely on pneumatics and geometrical asymmetry to achieve locomotion, which limits their working range, versatility, and other untethered functionalities. In this paper, we introduce a novel approach to achieve locomotion for soft robots through dynamically tunable friction to address these challenges, which is achieved by subsurface stiffness modulation (SSM) of a stimuli-responsive component within composite structures. To demonstrate this, we design and fabricate an elastomeric pad made of polydimethylsiloxane (PDMS), which is embedded with a spiral channel filled with a low melting point alloy (LMPA). Once the LMPA strip is melted upon Joule heating, the compliance of the composite structure increases and the friction between the composite surface and the opposing surface increases. A series of experiments and finite element analysis (FEA) have been performed to characterize the frictional behavior of these composite pads and elucidate the underlying physics dominating the tunable friction. We also demonstrate that when these composite structures are properly integrated into soft crawling robots inspired by inchworms and earthworms, the differences in friction of the two ends of these robots through SSM can potentially be used to generate translational locomotion for untethered crawling robots.

Stiffness Variable Polymer for Soft Actuators with Sharp Stiffness Switch and Fast Response

“…After decades of development, there have been many strategies proposed to achieve variable stiffness, including granular materials or laminar jamming structures, , fluid–polymer composites, , magnetorheological materials, − electrorheological materials, , shape memory polymers, − shape memory alloys, , liquid crystal elastomers, − and low-melting-point alloys, − which are desired in many technological fields such as soft robotics, − medical devices, aerospace, , automotive industry, , and wearable electronics . However, most of these stimulus methods require bulky equipment that adds considerable design complexity, weight, and cost to engineered systems, , which limit their application.…”

Robust Bicontinuous Elastomer–Metal Foam Composites with Highly Tunable Stiffness

“…[ 6,23,24 ] For example, smart composites with tunable stiffness have enabled novel design of smart adhesives with dynamically tunable dry adhesion, [ 6 ] which can be used as compliant grippers for pick‐and‐place manufacturing and transfer printing of semiconductors, [ 23 ] as well as locomotion mechanisms for climbing robots. [ 24 ]…”

“…[6,23,24] For example, smart composites with tunable stiffness have enabled novel design of smart adhesives with dynamically tunable dry adhesion, [6] which can be used as compliant grippers for pick-and-place manufacturing and transfer printing of semiconductors, [23] as well as locomotion mechanisms for climbing robots. [24] Existing approaches to tunable stiffness can be roughly grouped into two categories: changing shape/geometry and altering material properties. [15] The second category typically involves using active materials such as piezoelectric materials, and adaptive (semiactive) materials such as shape memory polymers and shape memory alloys, which have low energy requirements for activation.…”

“…[18][19][20][21][22][23] Dynamically tunable reversible stiffness enables robots to actively change their shapes and elastic deformations to adapt to complex environments and realize their functionalities. [6,23,24] For example, smart composites with tunable stiffness have enabled novel design of smart adhesives with dynamically tunable dry adhesion, [6] which can be used as compliant grippers for pick-and-place manufacturing and transfer printing of semiconductors, [23] as well as locomotion mechanisms for climbing robots. [24] Existing approaches to tunable stiffness can be roughly grouped into two categories: changing shape/geometry and altering material properties.…”

Effect of Filler Aspect Ratio on Stiffness and Conductivity in Phase‐Changing Particulate Composites

“…Materials and structures that can reversibly switch their stiffness between "rigid" and "soft" in response to external stimuli are required in many emerging applications in soft robotics, [1][2][3][4] medical devices, [5] the automotive industry, [6,7] and wearable electronics. [8] Specifically in soft robotics, these materials can be used as artificial muscles or stiffness-tunable tendons and ligaments.…”