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Meshworm: A robot made of a single Artificial Muscle

Meshworm is the prototype proof of concept for a new type of artificial muscle, based on an in-depth study of the movement patterns of the common earthworm, and shows how it is possible to create a 'soft' robot or prosthetic that is basically a single muscle and very little else.

Meshworm can be stomped on, slammed down onto with a hammer, and the robot will just straighten itself out and crawl away. It is not indestructible, but it is very hard to stop.

The whole concept is based around peristalsis; a type of symmetrical constriction and relaxation of muscles and muscle groups to allow the ground to flow around the object, or allow objects inside a flexing tube, to be dragged along by it. In nature, earthworms use the former example to crawl along the ground, and human digestive tracts use the latter, to move material through the intestines, even against gravity.

Quite a few creatures use peristalsis is one form or another: like humans, all mammals use it as part of the digestive process, and smaller creatures such as slugs, snails, and sea cucumbers use it as their sole form of self-propulsion. Given this level of success, it was a natural candidate for artificial muscle research.

Engineers from three universities working in partnership created Meshworm. MIT, Harvard University and Seoul National University all pitched in to create different aspects of the deceptively complex robot.

As the name itself implies, the core of Meshworm is a mesh of muscle, made out of a mesh of shape-memory alloy wire, crafted from a mix of nickel and titanium. This alloy's shape changing properties are triggered by heat, so the hotter it gets, the tighter the alloy contracts. What generates heat through metal? Why, an electrical charge of course!

The researchers wound additional wire loops around a mesh tube made of this alloy, and insulated the two from one another. This created a segmented body not unlike that of an earthworm. By running a tiny current into each segment in a controlled process, the robot constricts one part of its body whilst another relaxes. The constricting part grips the ground firmly, whilst the relaxing part moves ahead, to grip the ground when it contracts. By repeating this pattern many times along Meshworm's length, the robot slowly crawls forward, across almost any surface.

This is also the secret of its strength. No matter how you pound the body, the shape alloy will always return to its normal configuration when current is next applied – and this is the job of the mesh tube in the centre. No matter how the segments constrict, or how hard the hammer comes down, so long as current can still flow, the mesh cage will always return it to its original shape.


Soft autonomous robot inches along like an earthworm

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