Cavatappi artificial muscles from drawing, twisting, and coiling polymer tubes

Abstract

Compliant, biomimetic actuation technologies that are both efficient and powerful are necessary for robotic systems that may one day interact, augment, and potentially integrate with humans. To this end, we introduce a fluid-driven muscle-like actuator fabricated from inexpensive polymer tubes. The actuation results from a specific processing of the tubes. First, the tubes are drawn, which enhances the anisotropy in their microstructure. Then, the tubes are twisted, and these twisted tubes can be used as a torsional actuator. Last, the twisted tubes are helically coiled into linear actuators. We call these linear actuators cavatappi artificial muscles based on their resemblance to the Italian pasta. After drawing and twisting, hydraulic or pneumatic pressure applied inside the tube results in localized untwisting of the helical microstructure. This untwisting manifests as a contraction of the helical pitch for the coiled configuration. Given the hydraulic or pneumatic activation source, these devices have the potential to substantially outperform similar thermally activated actuation technologies regarding actuation bandwidth, efficiency, modeling and controllability, and practical implementation. In this work, we show that cavatappi contracts more than 50% of its initial length and exhibits mechanical contractile efficiencies near 45%. We also demonstrate that cavatappi artificial muscles can exhibit a maximum specific work and power of 0.38 kilojoules per kilogram and 1.42 kilowatts per kilogram, respectively. Continued development of this technology will likely lead to even higher performance in the future.

Fast Large‐Stroke Sheath‐Driven Electrothermal Artificial Muscles with High Power Densities

“…Artificial muscles that convert external energy to mechanical energy are of great interest because of their potential applications in devices like exoskeletons, prostheses, and bionic robots. Many functional materials have been used as artificial muscles, such as shape memory polymers, [1,2] shape memory alloys, [3] dielectric elastomers, [4][5][6][7][8] polymer fibers, [9][10][11] ionic polymer metal composites, [12,13] graphene-based fibers, [14][15][16] and carbon nanotubes (CNTs). [17][18][19][20][21] CNT yarns are especially promising candidates due to their high strokes, electrical conductivity, thermal conductivity, and mechanical strength.…”

Bistable and Multistable Actuators for Soft Robots: Structures, Materials, and Functionalities

“…Thanks to the capability of pre‐storing energy before actuation, TAMs deliver much higher work capacity and output force compared with most existing actuation approaches. [ 172,173 ] Specifically, TAMs can have 50 times larger work capacity than the biological skeletal muscles and can deliver force output more than 1000 times of their own weight when composed of carbon nanotubes, SMPs, fishing lines and PVC tubes. [ 172,174–176 ] In addition, their output force and the work capacity can be greatly enhanced by tailoring the component or the structure of the precursor fiber of the muscle, such as adding the graphene oxide (GO) platelets inside to the precursor fiber [ 175 ] or designing a tough sheath on its surface, [ 177 ] which could potentially advance the fields of humanoid robots, prosthetic limbs, microfluidic devices, and soft robotics.…”

“…Thanks to the capability of pre-storing energy before actuation, TAMs deliver much higher work capacity and output force compared with most existing actuation approaches. [172,173] Specifically, TAMs can have 50 times larger work capacity than the biological skeletal muscles and can deliver force output more than 1000 times of their own weight when composed of carbon nanotubes, SMPs, fishing lines and PVC tubes. [172,[174][175][176] In addition, their output force and the work capacity can be greatly enhanced by tailoring the component or the structure of the precursor fiber of the muscle, such as adding the graphene oxide (GO) platelets inside to the precursor fiber [175] or designing a tough sheath on its surface, [177] which could…”

Miniature coiled artificial muscle for wireless soft medical devices

“…At the centimeter and larger length scales, coiled artificial muscles have been promising actuators that can be fabricated by continuously twisting polymer fibers into a coiled shape (13,14). Recent works have proposed that the coiled muscles can have higher work capacity and larger output force than several popular actuation approaches (15,16). Specifically, the coiled muscles can have 50 times larger work capacity than the biological skeletal muscles and can deliver force output more than 1000 times of their own weight when composed of carbon nanotubes, shape memory polymers, and fishing lines (16)(17)(18).…”