The Wire @ WPI Online
VOLUME 11, NO. 2     SEPTEMBER 1997

More motions possible with prototype prosthesis

Today there is no such thing as a fully motorized, user-actuated shoulder prosthesis. But tomorrow there may well be--thanks to the ingenuity of three recent WPI graduates.

For their Major Qualifying Project, Colleen Fox '97, an electrical engineering major from Fairbanks, Alaska, Nicole Robert '97, an engineering physics major from Webster, Mass., and Jason Wening '97, a mathematical sciences major from Jefferson City, Mo., set for themselves an especially challenging goal-the development of a prototype electronic control unit that will allow an amputee to simultaneously execute motions in more than one joint of a motorized prosthesis.

Each student brought to the project his or her special area of expertise. In addition, Wening, a double leg amputee, provided insights that only the physically challenged can offer. "Our project began a process we hope will result in the development of a shoulder prosthesis that will give the amputee the tools necessary to be self sufficient," he says.

During the first phase of the project, the students (who utilized a combination of analog and digital devices), established the design parameters for the control unit by modeling the forces involved in moving a prosthetic arm. They learned how long it takes for the arm to accelerate, the torque changes required to retain constant angular velocity, the predictability of starting/stopping accuracy, and the possibility of overshooting.

"During the second phase, we built the electronic control unit," says Fox. "We used a motion algorithm based on the models from Phase 1 to transform input signals into output signals that drive the motors of the prosthesis."

The group used three motors to model the motion of the prosthesis: two to control shoulder flexibility and one to control elbow flexibility. "We used a double arm-driven pendulum to simulate two joints and a single arm-driven pendulum to simulate one joint of the prosthesis," explains Robert.

As an added challenge, the students had to consider the fact that the motors put out a certain torque in order to move the arm in specific patterns. They ultimately designed a motion control system to include a low-power device that is compact in size and weight-one that has the ability to change the limb's velocity or to stop it at any time in any location.

The students emphasize that their project is just a first step in the development of a motorized prosthesis. Their recommendations for the future include developing more sophisticated motion algorithms, and creating lightweight motor and battery systems.

On its own, the "Simultaneous Motion Control for Upper Extremity Prosthesis" project is a winner; it recently received Provost's MQP Awards from both the Electrical and Computer Engineering Department and the Physics Department.

The MQP advisors were ECE Professor Fred Looft, physics Professor Van Bluemel, and mathematical sciences Professor Paul Davis. The project sponsor was Liberty Mutual Insurance Research Group, where Ted Clancy '83 serves as the principal MQP contact for WPI.

Members of this MQP team speak in one voice about the future of their particular project: "We hope our efforts will enable the physically challenged to enjoy a better quality of life."

--Ruth Trask

Photo caption: Prosthesis MQP Team members Nicole Robert '97, Jason Wenning '97, and Colleen Fox '97 pose for a shot during Project Presentation Day (April 1997).

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Last modified: Thu Oct 2 16:31:46 EDT 1997