Origami-Inspired Artificial Pneumatic Muscles

Right now, there are two main types of continuum robots

• Vertebrate (backbone), like the one depicted above, generally use cables (tendons) that are shortened and lengthened

• Invertebrate (no backbone), like the one depicted to the right, generally use Pneumatic Artificial Muscles (PAMs)

  • The most common PAM is the McKibben muscle, which is able to compress by 20-30%

  • An improved PAM muscle involving a long polyethylene tube with rubber o-rings constricting flow, was able to compress a maximum of 40%

The idea was to implement a compliant TPU folding mechanism that acts as the "vertebrae" by being stable when extended but compressible by folding onto itself

 The model on the right was a prototype of the linkages between segments and was used to determine if this approach was viable

• It was learned that if printed flat, the links would be able to hinge, but there was no bias on which direction, which would make it difficult to make the origami muscle fold in a specific way

• It was found that by prefolding the hinges and heating it up, it is possible to force a bias in the way that the part folds

The origami-inspired Kresling Spring was chosen to prototype because of its lateral stability and high compressibility

• The first Kresling spring prototype was moderately successful, but it was stiff and too short.

• Compressible from 30mm to 17mm (43% compressibility) 

An alternate design (created by Christopher Lim) involved one flat, foldable sheet. I prototyped this method, but it struggled with compressing in a biased way under vacuum, so I did not continue with this design.