ASME IAM3D Challenge Case Study: 3D-Printed Granular Jamming Hand

By Joshua Olesker/ASME Public Information

Maggie Serra presents the Granular Jamming Hand entry at the IAM3D Challenge

On a chilly November day at the 2014 IAM3D Challenge finals, team after team of young male engineering students rose to describe their projects. But in the end, the IAM3D judges awarded Maggie Serra of the Stevens Institute of Technology the title for Best Presentation.

Serra and all those she bested from around the world were in Montreal for a competition which calls on mechanical and multi-disciplinary engineering undergraduates to re-imagine existing products or create new ones. Entrants use Additive Manufacturing technologies to improve on old solutions to industrial, manufacturing, and humanitarian challenges using advanced manufacturing techniques to minimize energy consumption and improve efficiency.

Demonstration of how the thumb meets the middle finger

To answer this challenge, Serra and the Stevens team she represented created an open-source, easy-to-produce hand/upper arm prosthetic. In her winning Montreal presentation, she explained their particular challenge:  

“There are two types of hand and arm prostheses,” Serra said. “Passive, body-control types, and then the active, myoelectric kind. The passive kind has poor dexterity; it’s just a hook and cable.” More, she said, “It’s ugly. People tend to stop wearing them – they attract negative attention.”

But so-called “active,” myoeletric prostheses are heavy and expensive and, according to Serra, cost upwards of $11,000. And out of an estimated 10 million of amputees worldwide, she said, only half ever have access to any prosthetic of either kind.

Serra’s team wanted to design a new kind of prosthesis that could be readily available to anyone, anywhere.

Finger Design

They began with a thorough study of anthropometry – finger lengths, forearm ratios, the mechanics of the human hand and knowledge of how human beings really use their hands in everyday life. “It turns out we really mostly use our first three fingers and our palm,” said Serra. “Granular jamming was perfect for palm and grip stabilization.”

The granular jamming technique they used allows the hand they designed to grip small objects: a quantity of grainy material (coffee grounds work well) are massed in a soft container, for instance a balloon. At normal atmospheric pressure, the grounds-filled balloon will be soft and its filling can move within it much as liquid flows. Remove the air from that filled balloon, however, and the grains will “jam.” The balloon will become rigid and firmly retain the shape it was in at the moment the air was removed.

This technique allowed the team to engineer a firm grip for their hand on objects of many sizes and shapes.

“Granular jamming works, but it needs a lot of surface contact,” Serra said. “That’s why it’s on the palm and not on every finger.”

IAM3D audience members examine the Granular Jamming Hand as Serra looks on

The overall challenge of creating a working hand/arm prosthesis limited what the Stevens device could finally make it do, however. For example, Serra can’t recommend it for use with heavy weights.

“But it can give you back your quality of life,” Serra pointed out. “So you can eat on your own, drink on your own, open doors, and not have to struggle.”

To return a higher quality of life to as many people as possible, hand mechanics weren’t all they sought to redesign.

“We needed a brand new distribution model,” said Serra. “[A better prosthesis] needs to be manufacturable by anyone with minimal training. It needs to be mobilized to the source of the need, and it needs to be less expensive than traditional designs or we’re not going to be helping anyone. The solution is 3D Printing.”

She pointed out that production of prosthetic devices has till now required specialized manufacturing equipment, skilled machinists, as well as dedicated power and space for the shop. The Stevens Granular Jamming Hand required none of these. “All you need here a $2000 3D printer that you just carry with you, enough electricity to run it, and a computer,” said Serra.

In a post-competition interview, Serra spoke about the opportunity to turn her engineering skills to the benefit of underserved humanity.

“You're replacing an entire machine shop with a single, $2000 desktop machine you can take pretty much anywhere. That means that a humanitarian worker can just find somebody who needs a prosthetic arm, measure them for an arm, and then just print one up and give it to them. 3D printing gives us the ability to take something that has only been available to small groups of people and make it available to everybody.”