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A smoother expertise for robotic prosthetic leg customers is the goal of a College of Michigan challenge that has obtained renewed help 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 obtainable robotic prosthetic leg.
Sit to face, stand to stroll, up and down stairs and inclines — the human physique shifts amongst these actions virtually thoughtlessly. However these transitions are onerous for robots, and robotic prosthetic legs have the extra problem of not being hooked into the human person’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 by means of 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. Because of this, 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 totally different parameters as a result of each particular person walks in a different way. And that resulted in very, very cumbersome scientific deployment,” Gregg mentioned.
Utilizing the movement of the thigh to foretell joint place with a steady mannequin turned out to be a fairly great way of making a pure gait. With the preliminary R01 grant in 2018, Gregg’s workforce prolonged the strolling management mannequin to cowl different vital situations: inclines, stairs, sit-to-stand, and stand-to-walk. Examine 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 attempting to vary actions.
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“The robotic has very sturdy motors, and so, if you happen to’re controlling the place and it’s in some way incompatible with the surroundings, it might really feel very inflexible and jarring,” he mentioned, which might imply ache for amputees the place the limb meets the socket.
So Gregg’s workforce is now taking a look at controlling joint place not directly — mimicking biomechanical impedance as a substitute — utilizing their steady modeling framework. With an impedance method, 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 automobile. “You may have the spring, after which you will 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 eternally.”
This could allow the leg to supply the identical means to seamlessly transfer from one exercise to a different whereas additionally offering a cushier experience.
The programming of the leg relies 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 usually expertise ache within the hips, again, and natural knee because of the manner they should compensate for the useless weight of the prosthetic leg.
To find out how 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 Methods Laboratory. | Credit score: Brenda Ahearn, Michigan Engineering
“We get hold of the measurements for figuring out the biomechanical properties of the leg utilizing an exoskeleton,” mentioned Rouse, affiliate professor of robotics and mechanical engineering, and co-investigator on the challenge. “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 packages will first be examined on the robotic leg that Gregg’s workforce constructed in-house, with motors to energy each the ankle and knee. Then, to see if the brand new algorithms are prepared to begin serving to individuals now, the workforce will take a look at them on Ossür’s Energy Knee prosthetic leg. Along with measuring the biomechanics of research individuals as they stroll with the prosthetic legs, the workforce 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 additionally it is lighter than the lab leg—and most significantly, it’s serving to individuals stroll now. Gregg’s workforce is assured that they’ll modify their management mannequin to work on it, maybe enhancing on the fashions Ossür is presently operating.
Editor’s Be aware: This text was reprinted from the College of Michigan.
