Team Reinvented 300-Year-Old Piston Design for a Plethora of Applications

A team of roboticists at Harvard's Wyss Institute for Biologically Inspired Engineering, the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), and Massachusetts Institute of Technology (MIT) has developed a new way to design pistons that replaces their conventional rigid elements with a mechanism using compressible structures inside a membrane made of soft materials. They published the study in Advanced Functional Materials.

The Wyss Institute Founding Core Faculty member and co-corresponding author Wood, Ph.D., said that Fabricated with structures incorporating soft, flexible materials, these "tension pistons" are a fundamentally new approach to piston architectures that open vast design space. They could be dropped into machines, replacing conventional pistons, providing improved energy efficiency. Importantly, this concept also enables a range of new geometries and functional variations that may empower engineers to invent new machines and devices and to miniaturize existing ones.

Wood was the leader of the research together with Daniela Rus, Ph.D., Professor and Director of MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL) and Shuguang Li, Ph.D., a Professor Fellow mentored by Wood and Rus.

The concept of the tension piston builds on the researchers' 'fluid-driven origami-inspired artificial muscles' (FOAMs) that use such materials to give soft robots more power and motion control while maintaining their flexible architectures.

FOAMS are made of a folded structure that is embedded within a fluid in a flexible and hermetically sealed skin. Changing the fluid pressure triggers the origami-like structure to unfold or collapse along a pre-configured geometrical path which induces a shape-shift in the entire FOAM, allowing it to grasp or release objects or to perform other kinds of work.

According to Li, in principle, they explored the use of FOAMs as pistons within a rigid chamber. They can separate fluid compartment that exhibits the functionality of a piston by using a flexible membrane bonded to a compressible skeletal structure inside and connecting it to one of the two fluid ports.

The team revealed that a rise in driving pressure in the second fluid reservoir surrounding the membrane in the chamber increases the tension forces in the membrane material that are directly transmitted to the bonded skeletal structure. Compression of the skeleton is coupled to a mechanical movement outside the piston by physically connecting the skeleton with an actuating element that reaches out of the chamber.

Li explained further that by configuring the compressible skeletons with different geometries such as a series of discrete discs, as hinged skeletons, or as spring skeletons, the output forces and motions become highly tunable.

The team can even incorporate more than one tension piston into a single chamber, or go a step further and also fabricate the surrounding chamber with a flexible material like an air-tight nylon fabric.