New robotics prostheses make movement more natural, energy efficient

A CSL alum is helping transform prostheses from “fancy sticks” into biomedical robots that more accurately mimic power-generating human legs – and even help restore muscle function.

Robert D. Gregg

Robert D. Gregg recently was honored for his work on lower-limb prosthetic control systems with a 2012 Career Award at the Scientific Interface given by the Burroughs Wellcome Fund, a private foundation dedicated to advancing the biomedical sciences. Gregg, who graduated from Illinois in 2010 with a Ph.D. in electrical and computer engineering, is an Engineering into Medicine Fellow working with Dr. Jonathon Sensinger, Dr. Levi Hargrove and Dr. Todd Kuiken at the Center for Bionic Medicine of the Rehabilitation Institute of Chicago and Northwestern University.

“The vast majority of prosthetic legs today do not replace the power-generating capabilities of muscles in biological legs,” said Gregg, who noted that amputees use up to three times more energy than able-bodied people. “Our primary goal is to make prosthetic legs very safe but also reduce the energy that the subject would use.”

In the past, merging robotics with leg prostheses wasn’t technologically feasible. Motors and batteries were too large and heavy, while sensors weren’t sophisticated enough. But recent advancements in hardware have opened up new possibilities.

Still, challenges remain – particularly in the area of control. Humans are dynamic systems that are difficult to model. While it is possible to measure a robot’s limbs and joint angles with fair accuracy, says Gregg, “We can’t just detach a person’s limbs to figure masses and inertia.”

In addition, engineers have struggled to replicate humans’ volatile behavior. People can transition from a walk to a run to a full stop in minimal time, while prosthetic legs lack that ability. Gregg is working on these problems using tools that apply dynamic and control theory in uncertainty. He uses sensors that measure forces, such as those that determine a person’s gait, to help mitigate some of the uncertainty.

Assisted by a team of researchers at the Rehabilitation Institute of Chicago and Northwestern University, he has developed an instrumented foot that will help measure forces. Gregg’s focus has been on improving the sensory capabilities of an experimental prosthetic leg developed at Vanderbilt University, allowing more natural, energy-efficient movement. The team will test the prototype on human subjects in the near future.

In many ways, Gregg’s work at CSL helped lay the theoretical foundation for his present research. Under advisor Mark Spong, now engineering dean at the University of Texas at Dallas, Gregg developed a new way of controlling robots to mimic human walking. He won the ACC Hugo Schuck Award in 2010 for his contributions to the field.

Personal experiences also have shaped his work. In his last year of graduate school at Illinois, Gregg’s father was diagnosed with heart failure. As his father waited for a transplant, Gregg talked with many doctors who were starting to use surgical robots for a variety of minimally invasive procedures.

“It showed me how research in the field I was in really could be helpful to patients,” Gregg said.

He believes control will continue to play an even greater role in biomedical advances in the future. He plans to continue pursuing breakthroughs when he joins the faculty of the University of Texas at Dallas in 2013.

“I’ve seen some really cool work on an artificial pancreas that involves a closed-loop system to deliver insulin to impact sugar levels in the blood,” he said. “These are dynamical systems that are using control theory to regulate factors on an individual basis.”