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A smoother expertise for robotic prosthetic leg customers is the goal of a College of Michigan undertaking that has obtained renewed assist from the Nationwide Institutes of Well being. The R01 grant of $3 million can even allow the implementation of the researchers’ improved management program on a commercially accessible robotic prosthetic leg.
Sit to face, stand to stroll, up and down stairs and inclines — the human physique shifts amongst these actions nearly thoughtlessly. However these transitions are onerous for robots, and robotic prosthetic legs have the extra problem of not being hooked into the human consumer’s central nervous system to remain synchronized with their physique.
Engaged on the issue since 2013, principal investigator Robert Gregg, an affiliate professor of robotics, noticed early success controlling the place of the knee and ankle joints via a mannequin that repeatedly represents all phases of the gait cycle. Beforehand, robotic prosthetic legs used separate controllers for every stage within the gait cycle just like the heel strike, push-off and swing. Consequently, the management parameters for every mannequin and guidelines for switching from one mannequin to a different needed to be optimized for every affected person.
“Each particular person has completely different parameters as a result of each particular person walks otherwise. And that resulted in very, very cumbersome medical deployment,” Gregg stated.
Utilizing the movement of the thigh to foretell joint place with a steady mannequin turned out to be a reasonably great way of making a pure gait. With the preliminary R01 grant in 2018, Gregg’s staff prolonged the strolling management mannequin to cowl different necessary eventualities: inclines, stairs, sit-to-stand, and stand-to-walk. Research individuals may do all of those actions with extra typical biomechanics utilizing the robotic leg than they may with passive prosthetics. Nonetheless, pinning the management algorithm to joint angles results in a extra inflexible expertise when making an attempt to vary actions.
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“The robotic has very robust motors, and so, should you’re controlling the place and it’s one way or the other incompatible with the setting, it will possibly really feel very inflexible and jarring,” he stated, which might imply ache for amputees the place the limb meets the socket.
So Gregg’s staff is now controlling joint place not directly — mimicking biomechanical impedance as a substitute — utilizing their steady modeling framework. With an impedance strategy, there’s an equilibrium place, and the forces are set to softly pull the joint again into that place if it’s disturbed. This offers some wiggle room.
Gregg compares it to the suspension on a automotive. “You’ve got the spring, after which you might have a shock-absorbing mechanism. You wish to hit the pothole and have sufficient bounce to melt the jolt, however you don’t wish to oscillate endlessly.”
This could allow the leg to supply the identical capability to seamlessly transfer from one exercise to a different whereas additionally offering a cushier experience.
The programming of the leg is predicated on biomechanical measurements of individuals with two organic legs, to duplicate the movement that the hips and again developed for. Customers of passive prosthetic legs typically expertise ache within the hips, again, and natural knee because of the method they should compensate for the useless weight of the prosthetic leg.
To learn the way the leg ought to behave throughout actions, Gregg united with collaborator Elliott Rouse, who research the mechanical properties of wholesome human gait.
College of Michigan college students demo a robotic prosthetic designed by Robert Gregg’s Locomotor Management Programs Laboratory. | Credit score: Brenda Ahearn, Michigan Engineering
“We acquire the measurements for figuring out the biomechanical properties of the leg utilizing an exoskeleton,” stated Rouse, affiliate professor of robotics and mechanical engineering, and co-investigator on the undertaking. “The exoskeleton principally offers no help however sometimes applies a fast perturbation that displaces the limb. From these measurements, we will decide the mechanical impedance, together with properties like stiffness, viscosity, and inertia.”
The management applications will first be examined on the robotic leg that Gregg’s staff constructed in-house, with motors to energy each the ankle and knee. Then, to see if the brand new algorithms are prepared to start out serving to folks now, the staff will check them on Ossür’s Energy Knee prosthetic leg. Along with measuring the biomechanics of examine individuals as they stroll with the prosthetic legs, the staff will gather formal suggestions to quantify will increase in consolation and reductions in ache.
The Energy Knee has a springy, passive ankle with a smaller vary of movement, however it’s also lighter than the lab leg—and most significantly, it’s serving to folks stroll now. Gregg’s staff is assured that they’ll modify their management mannequin to work on it, maybe bettering on the fashions Ossür is at the moment working.
Editor’s Observe: This text was reprinted from the College of Michigan.