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.
Highlights
The field of soft robotics has been growing rapidly and opening up possibility of achieving new maneuvers and locomotion approaches that cannot otherwise be accomplished by conventional hard robots (Laschi et al, 2016)
We explore a novel approach to dynamically tunable friction through subsurface stiffness modulation (SSM) (Figure 1), inspired by recent work on dynamically tunable adhesion through SSM for robotic manipulation (Tatari et al, 2018)
These plots show that the coefficients of friction (CoF) in the activated state are in general higher than their values in the non-activated case, despite the fact that the enhancement ratio varies in each sample
Summary
The field of soft robotics has been growing rapidly and opening up possibility of achieving new maneuvers and locomotion approaches that cannot otherwise be accomplished by conventional hard robots (Laschi et al, 2016). Many of these soft robots are inspired by biological creatures and processes. Untethered soft robots can potentially match the abilities of these biological creatures. Many studies focused on mimicking these shortening/lengthening maneuvers to achieve robotic locomotion (Trimmer et al, 2006; Umedachi et al, 2013). Trimmer et al developed a caterpillar robot using shape memory alloy (SMA) springs and elastomers, which is able to deform and crumple
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