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Researchers at the Massachusetts Institute of Technology have developed a mechanical ankle robot that can help the recovery of stroke patients who have difficulty walking.
The robot, known as Anklebot, is designed to train and strengthen a patient's lower-extremity muscles. It senses a person’s ankle strength and adjusts its force accordingly as part of a rehabilitation programme.
Therapists can use the robot in daily physiotherapy sessions where patients are seated in a chair and the robot is fitted to the ankle. Initially, the robot does most of the work, moving the patient’s ankle back and forth and side to side, loosening up the muscles. But it senses when patients start to move their ankles on their own, and adapts by offering less assistance.
Neville Hogan, the Sun Jae professor of mechanical engineering at MIT, said that the ankle is not a simple joint. “Imagine you have a collection of pebbles, and you wrap a whole bunch of elastic bands around them. That’s pretty much a description of what the ankle is,” he said.
Hogan's robot is different from other robotic therapies, which aim to train the muscles to walk and are designed to do most of the work for the patient. These designs are sometimes said not to be successful, as they impose motion, leaving little room for patients to move on their own, Hogan explains.
He adds: “What we’re trying to do with machines in therapy is equivalent to helping the patients, and weaning them off the dependence on the machine. It’s a little bit like coaching.”
Experiments with healthy volunteers used the robot to measure the stiffness of the ankle in various directions. The researchers mounted the robot to a knee brace and it connected to a custom-designed shoe. As a patient moves his or her ankle, the robot moves the foot along a programmed trajectory. Electrodes record the angular displacement and torque in specific muscles, which researchers use to calculate the ankle’s stiffness.