Development of exoskeletons
When to push the walking?
Exoskeletons have not yet entered widely into our lives, but they are already beginning to be used little by little in the armed forces, during loading and unloading operations, in rehabilitation centers. However, up to a full "power armor", up to a "servobrony" protecting and supporting the entire body, like a space marine in the fictional Warhammer 40,000 universe or some computer game characters Encased, we are still far away. Many modern models of exoskeletons are limited to supporting, for example, only the legs, only the arms, only the spine. Moreover, this support is often passive, simply helping to redistribute the unloading through the body.
One of the most important problems standing in the way of the development of the exoskeleton industry is nutrition: in order to store enough energy for any long operation of a "decent" full exoskeleton, which would make it relatively easy to handle heavy loads, today batteries of such size and such mass would be needed that if you hang them on the exoskeleton itself, it will become useless. For understanding: the famous robot dog Spot weighs 47.6 kg, of which 4.2 kg is the mass of the battery, while the payload that the robot is capable of carrying is only 14 kg, and its maximum operating time is a miserable 90 minutes. And this is the operating time without a payload! With less load. But there is no living person inside the robot, that is, on the one hand, it is not necessary to support it, on the other hand, a person has his own skeleton and muscles, and if you combine their passive support, which helps to redistribute the load, with selective active support only when necessary, this will reduce the size of the wearable battery. In addition to saving energy, such selective support has another plus: an active impact on the musculoskeletal system of a person at times when it is not necessary, and also not with the force that is needed, and in the wrong direction, will rather interfere, even if its purpose is to help.
Of course, the developers of exoskeletons understand all this perfectly well, but the question is: at what exact moments of what actions does our body need support? And here everything is not so simple. For example, a recent study of external walking assistance, an article about which was published in March in Science Robotics (Antonellis et al., Metabolically efficient walking assistance using optimized timed forces at the waist), showed not the most intuitively expected results.
Researchers from the American National Institutes of Health (NIH) and the University of Nebraska at Omaha (University of Nebraska at Omaha) have built an installation from a treadmill, a robotic rope capable of pulling a person walking along the track forward by a wide belt at the waist, and many sensors. The purpose of the study was to figure out at what points it is best to provide external assistance to the walking person in order to minimize the metabolic costs of his body. And — suddenly — it turned out that the best effect is achieved when exposed in the very middle of the double support interval.
Video from the UNO Research press release Discovers A Surprising Way to Make Walking Easier – VM.
"When we walk, there is a short gap between steps when one leg stops moving forward while the other is preparing to accelerate to take the next step. Our study shows that this short window, when both feet are on the ground, is the best time to apply force to help walking most effectively," explained Dr. Phillippe Malcolm, one of the authors of the study.
It is curious that the results of the study contradict the helping strategies inspired by "common sense". After all, it seems logical to help the leg at the moment when it pushes the body forward. The authors call such strategies bioinspired, i.e. based on direct everyday observation of nature.
"Although bioinspired movement assistance may provide certain benefits, our study shows that this strategy is not necessarily the best for reducing metabolic costs or energy expended," says Prokopios Antonellis (Prokopios Antonellis), the first author of the study. "This discovery confirms the need to pay more attention to the results of biomechanical testing, rather than trying to predict optimal strategies by simply observing nature."
So that it doesn't seem to you that everything is too simple, we note that in a walking situation, it's not just about pulling a walking person forward at moments when both of his feet touch the ground. Firstly, it is important to calculate the impact time very accurately, and secondly, the force curve is important, that is, how the pulling drive accelerates and slows down. And this is only walking and only one way of external influence. To create a perfectly balanced active exoskeleton, it is necessary to explore a huge variety of possible movements in this way. Moreover, it should be borne in mind that not always the strategy of external assistance to our body should proceed from the task of reducing metabolic costs. This can be a decrease in the compression force acting on the spine, and an increase in the "load capacity", and ensuring comfortable movement without feeling "glues" — the moments of turning on and off the servos. A lot more research is needed to ensure all this.
The results of the mentioned study can be applied not only in the development of exoskeletons, but also in rehabilitation robotics — for example, to facilitate the training of patients who are learning to walk again after various immobilizing injuries, operations and diseases.
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