SciTech

Novel hardware systems developed to improve prosthesis

By Jonathan Calvello  |  Dec 6, 2015
Steve Collins, an associate professor in Carnegie Mellon’s Department of Mechanical Engineering, and Hartmut Geyer, an assistant professor in Carnegie Mellon’s Robotics Institute, are developing hardware systems called universal device emulators, capable of quickly testing variations in prostheses design, which will allow researchers to understand how to improve prosthetic limbs and hopefully lead to improved designs and prescription. (credit: Courtesy of Steve Collins) Steve Collins, an associate professor in Carnegie Mellon’s Department of Mechanical Engineering, and Hartmut Geyer, an assistant professor in Carnegie Mellon’s Robotics Institute, are developing hardware systems called universal device emulators, capable of quickly testing variations in prostheses design, which will allow researchers to understand how to improve prosthetic limbs and hopefully lead to improved designs and prescription. (credit: Courtesy of Steve Collins) Credit: Courtesy of Steve Collins Credit: Courtesy of Steve Collins

In the United States alone, there are over one million amputees, people who suffer from some sort of limb loss. One of the most difficult things about making life better for these amputees is developing robust, effective prosthesis technology that can supplant the role of regular human limbs. The intricate locomotion and modalities of muscle movement are complex, and these obstacles pose difficulties for scientists in developing prosthesis equipment.

In effort to abate these difficulties, Steve Collins, an associate professor in Carnegie Mellon’s Department of Mechanical Engineering, and Hartmut Geyer, an assistant professor in Carnegie Mellon’s Robotics Institute, along with a team of researchers, are working to develop innovative prosthesis technology that better addresses current issues facing leg prostheses, such as maintaining balance and the energy cost of walking.

The team’s new technology centers around modeling the reflexes that control walking via computer simulations, implementing those neuromuscular reflexes into prosthetic legs, and studying how well the prostheses mimic the reflexes. Although these reflexes are very intricate, we are all familiar with them. For example, during a doctor’s visit, when the doctor taps your kneecap, the local reflexes in your leg muscles produce the observed jerking motion.

Understanding these reflexes can lead to solutions for some of the problems amputees have when using prosthesis. For example, balance is currently one of the major issues with leg prostheses. Human limbs’ reflexes can respond to imbalances in terrain. This allows them to adapt their gait while walking to maintain balance. While current prostheses attempt to mimic these reflexes, they lack the technology to properly replicate natural leg motion.

Geyer and Collins are trying to gain a better understanding of what local reflexes in the leg control balance and how to implement those reflexes into prostheses.

“Our work is motivated by the idea that if we understand how humans control their limbs, we can use those principles to control robotic limbs,” Geyer said.

So far, their models have been able to respond to disturbances at the beginning and the end of the prosthesis’s leg-swing. Although these results are promising, Geyer recognizes that there is more to be done, as the model still has issues with leg-swing disturbances.

To supplement this work, Collins is developing prosthetic knee simulator systems, which he calls universal device emulators. These systems are designed to be able to test the output performance of prosthetic limbs based on variations in prosthesis design. The aim in designing these systems is to allow scientists to test variations on what they think are effective prostheses models, and then run experiments to determine the success of the model.

The systems are also designed to be flexible, so that scientists can quickly and easily tweak parts of the prosthesis and observe how these tweaks affect output. By developing these hardware systems, Collins hopes to deliver better conclusions about what prostheses need, and thus how to better design them.

One of the outcomes Collins hopes to see with these emulators is their application as clinical tools to improve the prescription of prostheses to amputees. Much like optometrists prescribe glasses based on a series of vision tests, Collins believes the same can be done for amputees using these systems “by quickly changing the behavior of the robotic device, thereby quickly optimiz[ing] the prosthesis for each individual patient.”

Additionally, Collins hopes to use these systems to continue studying and optimizing prostheses so that eventually they can outperform their able-bodied counterparts. The group strives to develop technologies that can supersede current limitations on prosthetic limbs, and it has already experienced some success in this endeavor: “Earlier this year, we developed an exoskeleton that reduces the cost of walking,” Collins said.

Although the focus of these technologies is to develop better prostheses, another goal of Collins and Geyer’s research is implementing the technology into human augmentation. Once the team has developed effective prosthetic models and finalized the universal device emulators, they will hopefully turn to using these technologies to improve physical performance for people without any amputations.

The boundaries of such applications, which could theoretically range from improving military personnel to enhancing athletic activity, provide ample space for imaginative, novel applications.