At the University of Michigan, a groundbreaking set of knee exoskeletons has been developed using commercially available knee braces and drone motors. These innovative exoskeletons have been proven to effectively combat fatigue during lifting and carrying tasks. Notably, they assist users in maintaining proper lifting posture even when fatigued, which is crucial for preventing on-the-job injuries.
“Rather than directly bracing the back and giving up on proper lifting form, we strengthen the legs to maintain it,” said Robert Gregg, U-M professor of robotics and corresponding author of the study in Science Robotics. “This differs from what’s more commonly done in industry.”
In industries where workers frequently engage in lifting, such as construction and manufacturing, the use of back braces and exoskeletons is becoming increasingly common. However, traditional back support devices are often cumbersome and restrict natural movement, while back exoskeletons are limited in their functionality and can be inconvenient to use during tasks that involve more than just lifting.
A team from Michigan has developed knee exoskeletons that target the quadriceps muscles, providing a less intrusive and more effective solution for protecting workers from back injuries. During testing with a 20 lb kettlebell, participants performed various lifting and carrying tasks, including navigating inclines and stairs.
The results were impressive: the exoskeletons not only helped participants maintain better posture when fatigued but also enabled them to lift at almost the same speed as when they were not fatigued, in stark contrast to a significant decrease in lifting speed without the exoskeletons.
These findings highlight the potential of knee exoskeletons in revolutionizing workplace safety and efficiency, making a compelling case for their widespread adoption in industries where lifting is a regular part of the job.
“This is especially important when a worker has to keep up with a conveyor belt. Usually, when a worker is fatigued, they’ll keep up with that rate but with a compromised posture. They’ll bend their back more, and that’s when injuries are most likely,” said Nikhil Divekar, a postdoctoral research fellow in robotics at U-M and first author of the study.
The feedback from participants was overwhelmingly positive. They expressed high levels of satisfaction, particularly when walking on level ground. The exoskeleton’s design minimizes the assistance needed from the quadriceps during this task, providing just the right amount of support.
The remarkable wearability of the exoskeleton can be attributed to its advanced motors and gearing system, allowing users to move their knees naturally. Additionally, the software accurately anticipates the user’s needs by analyzing various measurements such as knee joint angle, thigh and lower leg orientations, and force detected by a sensor in the user’s shoe.
Through rapid and precise measurements taken 150 times per second from both legs, the exoskeleton seamlessly adapts to the user’s movements, providing optimal assistance for various activities.
This innovative approach sets itself apart from traditional exo controllers by adapting to a wide range of tasks rather than following predetermined patterns for a limited set of actions. According to Gregg, the creator, many exo controllers struggle with task switching and may take a full second to discern the user’s intentions.
For instance, when your exo is programmed to climb stairs, but you want to descend, it can lead to complications. The new controller, however, combines a physics model with machine learning to prevent unexpected movements, ensuring seamless adaptation to the user’s behavior.
The initial cost of the lab prototypes is approximately $4,000 per pair. However, Gregg envisions that mass production could bring the price down to around $2,000 per pair.
During the study, which involved ten participants (five women and five men), each individual performed various tasks on two separate days: one when feeling fresh and the other when fatigued. Fatigue was induced by a series of squat lifts with a kettlebell until they required a lengthy break between repetitions. All participants were experienced in proper squat lifting techniques.
Journal reference:
- Nikhil V. Divekar, Gray C. Thomas, Avani R. Yerva, Hannah B. Frame, Robert D. Gregg. A versatile knee exoskeleton mitigates quadriceps fatigue in lifting, lowering, and carrying tasks. Science Robotics, 2024; DOI: 10.1126/scirobotics.adr8282