Students develop prosthetic hand

| August 5, 2010

The young women in Sweet Briar College’s Wyllie Engineering Program have no illusions about the difficulty of the task they have chosen. They intend to produce a prosthetic hand that looks and performs like the real thing — for less than a thousand dollars.

If the students and their faculty advisor, Scott Pierce, are successful, amputees in poor countries may no longer have to choose between a cosmetic hand that hides their injury or a functional mechanical device, which exposes them to stigma. Today, the price of a prosthetic that achieves both is $11,000 to $17,000.

The hand will need to be reliable in harsh conditions and easy to fix if something does break. To meet all of these criteria is a lot to ask from an undergraduate engineering program, though Sweet Briar’s is not the first to try. Others have found some success by scaling back their objectives.

But Sarah Lightbody said she and her teammates are aiming for nothing less than a fully articulated, natural-looking hand. Moreover, it will perform normal tasks such as turning a knob or lifting a drink the size of a Big Gulp.

“Another prosthetic hand that looks weird isn’t filling the niche,” said Lightbody, a junior engineering major who is designing the thumb for Sweet Briar’s prototype for her Honors Summer Research project. “We have the attitude that we can do it, we just need to put our heads together and think about it.”

Lightbody acknowledges the end may be years away, but that’s OK. Pierce, too, is taking the long view. A mechanical engineer by training, his industrial expertise in precision positioning led him to research interests in biomechanics and robotics.

Last year he and MaryAnne Haslow-Hall, then a rising junior, were looking for a project for her Honors Summer Research. At the time, the pair had just been involved in an award-winning class project to design tools that aid disabled workers at a light manufacturing plant in Lynchburg, Va.

“We both really enjoyed the feeling we got out of helping these people and decided we wanted to help others in some way,” Haslow-Hall recalled in an e-mail.

They settled on the hand after discussing alternatives and doing initial research, including investigating the Open Prosthetics Project. Sweet Briar researchers both use and contribute to the website, where innovators in prosthesis development freely share their designs and collaborate with funders and prosthesis users.

Shoulders, arms and hands are complex and present different technological hurdles than lower limb prostheses, Pierce noted when he announced the project in the summer of 2009. The hand’s complexity means that a truly functional, lifelike replacement is available only to the wealthy or well-insured.

“We can’t push the state-of-the-art technology, but maybe we can use existing technology to help more people,” Pierce said.

It’s a goal that fits neatly with the philosophy of Sweet Briar’s engineering program, which is one of two in the country at all-women’s colleges to offer the degree. Solving problems in a global context is a point of emphasis. And the universal truth that engineers apply technology to design a better world is what attracts most Sweet Briar women to the program.

With Pierce advising her, Haslow-Hall used her eight-week summer scholarship to review existing research and design the first phase of the hand, the index finger. Her work continued through independent study during the 2009-2010 academic year.

This summer, Lightbody and Lauren Perhala, an engineering and math double major also entering her junior year, were awarded HSRP scholarships to work with Pierce. While Lightbody is using computer modeling to design the thumb, Perhala is learning how to program a microcontroller that is part of a key element of the prosthesis design — myoelectrics.

The microcontroller will receive electrical impulses — myoelectric signals — from the user’s brain, interpret them, and output signals that tell the fingers and thumb what to do. An actuator receives the signal and powers a cable running through each digit, causing them to flex and move.

In the case of the thumb, an additional gear motor will provide rotational movement to Lightbody’s “base lever” design. The idea is to match as closely as possible the dexterity of the human hand, allowing for the three most-used grasping positions, the pinch, the power grip and the tripod.

Haslow-Hall calculated the force and torque necessary to simulate the action of the hand and found an actuator to meet the specifications. She built her finger prototype from carbon fiber tubing and aluminum joints — all materials that are low-cost and available in the countries where the prosthetics will be used.

Over the summer, Lightbody completed a computer model of the hand and began building and testing her thumb prototype. She also plans to continue the project through independent study, including working with Perhala on the myoelectrics.

The students know they’ll be graduated by the time a real person is fitted with the hand. But they measure success by the goals they set for themselves, Haslow-Hall said.

“I did way beyond what I had hoped for,” she said. “I came up with an idea, designed it on paper and 3-D [computer] models. Then I spent four months building a single finger. But the end of those four months was the happiest moment for me after a year’s worth of work. I finally got to see my finished design take shape in the world.”

Category: Engineering Science