300 years old piston reinvented with soft and flexible materials

Since their invention in the late 1700s, when the British-born British physicist Denis Papin, the inventor of the pressure cooker, proposed the principle of the piston, the pistons were used to exploit the fluids power to work in many machines and devices.

Conventional pistons consist of a rigid chamber and an inner piston, which can slide along the inner wall of the chamber while maintaining a perfect seal. As a result, the piston divides two spaces filled with two fluids and connected to two external fluid sources. If the fluids have different pressures, the piston will slide in the direction where the pressure is the lowest and can simultaneously cause the movement of a shaft or other device to perform physical work. This principle has been used to design many machines, including various piston engines, hydraulic lifts and cranes such as those used on construction sites, as well as power tools.

However, conventional pistons suffer from several drawbacks: the high friction between the moving piston and the chamber wall can cause gasket rupture, leakage and gradual or sudden malfunctions. In addition, especially in the lower pressure spectrum, energy efficiency and response speed are often limited.

At present, a team of robot scientists from the Harvard Wyss Institute for Biologically Inspired Engineers, Harvard School of Engineering and Applied Sciences John A. Paulson (SEAS) and the Massachusetts Institute of Technology (MIT) has developed a new way to design conventional rigid element pistons with a mechanism using compressible structures inside a membrane made of soft materials.

The resulting "tension pistons" generate more than three times the force of comparable conventional pistons, eliminate much of the friction and, at low pressure, are up to 40% more energy efficient. The study is published in Advanced functional materials.

"These" tension pistons "made with structures incorporating soft and flexible materials represent a fundamentally new approach to piston architecture, opening up a vast design space that could be dropped into machines, replacing pistons. conventional, thus improving energy efficiency, "said Wyss Institute Wood, Ph.D., founding faculty member and corresponding author, is also professor of engineering and applied science Charles River at SEAS and co-director of the Bioinspired Soft Robotics Initiative of the Wyss Institute. "This concept also allows engineers to invent new machines and devices and miniaturize existing ones."

Wood led the study with Daniela Rus, Ph.D., professor and director of the MIT Computer Science and Artificial Intelligence Laboratory (CSAIL) and Shuguang Li, Ph.D., postdoctoral fellow directed by Wood and Rus.

The tension piston concept is based on the team's "origami-inspired artificial muscles" (FOAM), which use flexible materials to give virtual robots more power and control of movement while maintaining their flexible architectures. The FOAMS consist of a folded structure that is embedded in a fluid in a supple and hermetically sealed skin. Changing the fluid pressure triggers the deployment or collapse of the origami-like structure along a preconfigured geometric path, causing a shape change in the overall foam, allowing it to to enter or release objects or perform other types of work.

"In principle, we have explored the use of FOAM as pistons in a rigid chamber," said Li. "Using a flexible membrane linked to a compressible skeletal structure inside and connecting it at one of the two fluid ports, we can create a separate fluid compartment that has the functionality of a piston. "

Researchers have shown that an increase 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 linked skeletal structure. By physically connecting the skeleton to an actuating element that leaves the chamber, the compression of the skeleton is coupled to a mechanical movement on the outside of the piston.

"Better pistons could fundamentally transform the way we design and use many types of systems, from shock absorbers to car engines, to bulldozers and mining equipment," says Rus, Andrew (1956) and Erna. Viterbi, professor of electrical engineering and computer science at MIT. "We believe that such an approach could help engineers design different ways to make their creations stronger and more energy efficient."

The team tested their piston against a conventional piston during a crushing task and showed that it broke objects such as wood pencils at much lower inlet pressures (pressures generated in the fluid compartment surrounding the skin). At the same inlet pressures, particularly in the lower pressure range, the tension pistons have developed output forces that are more than three times higher and have an energy efficiency of up to 40% by exploiting the fluid-induced tension. in their flexible skin materials.

"By configuring compressible skeletons with very different geometries, such as a series of discrete disks, articulated skeletons or spring-loaded skeletons, the forces and outward motions become highly adjustable," Li said. can even incorporate more than one tension piston into a single chamber, or go even further and build the surrounding chamber with a flexible material, such as an air-tight nylon fabric. "