R E S E A RC H
By Stephen Filmanowicz
POWERING UP HOPE FOR BETTER-PERFORMING PROSTHETICS
Dr. Phil Voglewede was just months into his first faculty appointment in the early days of the Iraq War when he and a colleague first wondered whether engineers had a role to play in improving prosthetics for the war’s many amputees. Now, as an assistant professor of mechanical engineering at Marquette, Voglewede is on his way to answering that question, leading a federally funded interdisciplinary research team in creating a promising motorized prosthetic ankle and foot. From its earliest phases, Voglewede’s project has revealed the promise and challenges involved in pursuing natural human motion through engineering. Then, as now, the most common prostheses — passive devices that fix the foot and ankle at a 90-degree angle — offered minimal range of motion and limited thrust (springing back to form after flexing slightly under the user’s weight). They have the benefit, however, of being lightweight and affordable.
Photos by Dan Johnson
We’re dealing with something that can be directly applicable to people’s lives.
13 // Research Features
Early discoveries revealed that mechanisms familiar to any engineer could, at least in theory, contribute positively to prosthetic performance. A standard four-bar linkage like those found in classroom door closers closely matched the interplay of foot and ankle. A torsion spring could help supply thrust for walking. A motor could provide the extra lift required for inclines or stairs.
As these basic components became part of the team’s concept design, each added bulk and weight, however — dealbreakers if not managed carefully. “You’re only dealing with so much real estate ... and so much weight and so much power you can put on there,” explains Voglewede. “Then you have all the constraints of the practical. ...Will this work in the rain? Those are tremendous constraints that you don’t typically get in robotic applications.” Voglewede and his team have come a long way from a working model that tested well in terms of force and motion but tipped the scales at 10 pounds and was scaled more for Bigfoot than a human. After retooling made possible by a $390,000 grant from the National Institutes of Health in 2009, its replacement is appropriately human-scaled and weighs about 5 pounds. It also has a backpack power source and sensors that cue the release of force. Due soon for testing on amputees, the device is a focal point of a growing collaborative team at Marquette and the Medical College of Wisconsin. Included in that group is Marquette mechanical engineering professor Dr. Joseph Schimmels, a specialist in spring design, who is working on potential breakthrough ideas that could yield the power of a motorized ankle using only springs that harness and redirect energy generated as part of the walking process (including the heel strike). “It’s not like we’re doing nanotechnology,” concludes Voglewede, “but this is to me just as exciting because we’re dealing with something that can be directly applicable to people’s lives and so fundamental to engineering, something within very strict constraints. To me, that’s the beauty of engineering, working within the constraints.”