High-curvature, high-force, vine robot for inspection

Abstract

Robot performance has advanced considerably both in and out of the factory, however in tightly constrained, unknown environments such as inside a jet engine or the human heart, current robots are less adept. In such cases where a borescope or endoscope can't reach, disassembly or surgery are costly. One promising inspection device inspired by plant growth are "vine robots" that can navigate cluttered environments by extending from their tip. Yet, these vine robots are currently limited in their ability to simultaneously steer into tight curvatures and apply substantial forces to the environment. Here, we propose a plant-inspired method of steering by asymmetrically lengthening one side of the vine robot to enable high curvature and large force application. Our key development is the introduction of an extremely anisotropic, composite, wrinkled film with elastic moduli 400x different in orthogonal directions. The film is used as the vine robot body, oriented such that it can stretch over 120% axially, but only 3% circumferentially. With the addition of controlled layer jamming, this film enables a steering method inspired by plants in which the circumference of the robot is inextensible, but the sides can stretch to allow turns. This steering method and body pressure do not work against each other, allowing the robot to exhibit higher forces and tighter curvatures than previous vine robot architectures. This work advances the abilities of vine robots--and robots more generally--to not only access tightly constrained environments, but perform useful work once accessed.

Figures (10)

• Figure 1: Like a plant, the vine robot grows and bends by asymmetrically extending one side of its body. The keys to this design are an anisotropic skin that allows the robot to extend axially, and layer jamming locking bodies along its inside that prevent one side from extending to create bends. For scale, robot is 32 mm in diameter.
• Figure 2: The robot bends by letting its uniaxially-wrinkled composite film stretch while one side of the robot is locked by a layer jamming locking body compressed by the internal body pressure of the robot.
• Figure 3: Model geometry (a) and forces (b).
• Figure 4: Fabrication of the robot. (a, b) The TPU bladder is pre-stretched by an LDPE tube. (c) Dyneema composite fabric as attached to the TPU. (d) The LDPE tube is deflated and removed, leaving a wrinkled robot body. (e) The locking body is assembled of two sets of alternating strips of plastic and placed inside a TPU tube. (f) The locking bodies are attached to the inside of the robot body.
• Figure 5: Stress-strain curves of the anisotropic material in the longitudinal and transverse direction. (a, b) Longitudinal corresponds to the direction with presence of wrinkles and transverse direction is its orthogonal direction that lacks wrinkles. (c) Data showing that pre-stretch in the fabrication increased the ability of the anisotropic material to stretch in the longitudinal direction.