Engineering news
Both walking and running have in common an extension of the hip joint, which begins when the foot comes into contact with the ground, and requires considerable energy as it plays a key role in forward motion.
Now, researchers at Harvard University have developed a portable exosuit that can assist with hip extension during both walking and running. It’s lightweight, and made of textile components worn at the waist and thighs, and a system of actuators controlled by an algorithm that can detect the transition from walking to running.
The suit, development of which was funded by DARPA - the research arm of the US military, is designed to be simpler and more lightweight than previous multi-joint exosuits. A cable actuation system applies a tensile force between the waist belt and thigh wraps to generate an external extension torque at the hip joint, working in concert with the gluteal muscles of the wearer.
The suit weighs 5kg, but more than 90% of its weight is located close to the body’s centre of mass. "This approach to concentrating the weight, combined with the flexible apparel interface minimises the energetic burden and movement restriction to the wearer," said co-first-author Jinsoo Kim. "This is important for walking, but even more so for running as the limbs move back and forth much faster."
Research published today in the journal Science describes test of the system on a treadmill, which found that those wearing the reduced their metabolic rates of walking by 9.3% and of running by 4% compared to when not wearing it. "We were excited to see that the device also performed well during uphill walking, at different running speeds and during overground testing outside, which showed the versatility of the system," says Conor Walsh, who led the study. “While the metabolic reductions we found are modest, our study demonstrates that it is possible to have a portable wearable robot assist more than just a single activity, helping to pave the way for these systems to become ubiquitous in our lives.”
One of the biggest challenges was distinguishing between walking and running and enabling the suit to adjust its actuation profiles accordingly. Researchers measured it by tracking the movement of the wearer’s centre of mass, which moves up and down during each stride.
“We took advantage of these biomechanical insights to develop our biologically inspired gait classification algorithm that can robustly and reliably detect a transition from one gait to the other by monitoring the acceleration of an individual's centre of mass with sensors that are attached to the body," says co-corresponding author Philippe Malcolm, Assistant Professor at University of Nebraska Omaha. "Once a gait transition is detected, the exosuit automatically adjusts the timing of its actuation profile to assist the other gait, as we demonstrated by its ability to reduce metabolic oxygen consumption in wearers.”
Future work will be focussed on optimising the technology, reducing weight, improving ease of use and personalising it for individual needs. “It is very satisfying to see how far our approach has come," said Walsh, "and we are excited to continue to apply it to a range of applications, including assisting those with gait impairments, industry workers at risk of injury performing physically strenuous tasks, or recreational weekend warriors.”