KnitSkin: Machine-Knitted Scaled Skin for Locomotion
Jin-Hee (Heather) Kim, Shreyas Patil, Sarina Matson, Melissa Conroy, Cindy Hsin-Liu Kao
ACM Human Factors in Computing Systems (CHI) 2022 PDF I DOI
Introduction
KnitSkin is a machine-knit sleeve that can traverse cylindrical terrains with diverse properties. KnitSkin takes inspiration from nature, configuring stepped arrays of knitted scales that exhibit anisotropic friction. This anisotropic friction, which is prevalent in the locomotion of limbless organisms such as snakes or earthworms, is coupled with soft pneumatic actuators that extend and retract. These knit scales enable effective directional locomotion on cylindrical surfaces with varying slopes, textures, and curvatures.
Knit scales exhibiting anisotropic friction
The geometries and materials of knit scales can be fine-tuned, dominating the overall differential friction thus the distance KnitSkin can travel in a single actuation. In the paper, we characterize the parameters of knit scales and their resulting anisotropic behaviors. In evaluating the locomotion, we examine the variables associated with the surface and actuator characteristics. KnitSkin envisions exciting applications of soft wearable robots.
10x playback. KnitSkin crawling an inclined surface. Pictured is a close-up of KnitSkin’s knitted scales, which is bio-inspired from the scales of snakeskin (top right is a closeup of rattlesnake skin). In the knit substrate, when monofilament is drawn laterally, it forms a downward arch. The collection of arches is configured on an elastic knit substrate to mimic the mechanical property of snake scales.
Knit structure to form a scaled substrate. The notation indicates that five needles are skipped to form a scale. (a) Illustrates when the scales consist of nylon monofilament. The stiffness of the monofilament induces the curve as the ground layer draws in. In contrast, scales in (b) show negligible curves due to the lack of stiffness in the yarn. The scales are straightened up, causing no “stepped” texture. (c) depicts the change in tension as the substrate is released from the needles post-knitting. The draw-in of knit loops induces the lateral curve of the scales.
During the contraction of the interface, the sliding end now sticks to the surface and lets the other end retract. This movement alternates as the interface repeats extension and contraction, giving directionality to the motion.
