Almost one-third of work-related injuries result from workers lifting heavy items. This is a huge number of injuries that impact both employees and employers alike, and perhaps the most unfortunate thing about it is that it is entirely preventable. By using proper lifting techniques, or getting help from assistive devices when needed, these types of injuries can be prevented. To reduce the health and economic burdens associated with these injuries, better preventative measures are sorely needed.
At the forefront of emerging technology in this area is the robotic exoskeleton. These systems are strapped to the body to provide a boost to the wearer during physical labor. This extra assistance can make short work of a heavy lift, preventing injuries that might otherwise result from heavy or repetitive lifting. However, exoskeletons have not yet entered mainstream use. They tend to be limited in their capabilities, only providing very specific assistance which is not useful in all scenarios — and which may even make non-target tasks more difficult.
The wearable robot requires only one motor (📷: D. Lee et al.)
One of the biggest issues with existing lifting exoskeletons is that they only have a single degree of freedom, allowing for just a single path of motion during assistance. A team led by researchers at Yonsei University recognized that this is severely limiting in real-world use cases and wanted to do something to remedy the problem. However, adding additional actuators to realize additional degrees of freedom adds both weight and additional energy consumption (i.e., more batteries) to an exoskeleton. And since these devices are worn, the additional weight itself is a constant burden on users.
So to address these issues, the researchers built what they call the Wearable Robot (WeaRo). It provides multi-degree-of-freedom assistance to the lumbar and arm muscles while maintaining a lightweight, wearable structure. A key innovation in WeaRo is the use of an Adjustable Twisted String Actuator (ATSA) and a Two-Stage Transmission Mechanism (2TM), which work together to enable efficient force transmission for multi-degree of freedom movements using a single electric motor. The ATSA operates by twisting strings to contract and generate force, and its adjustability allows it to meet the varying force and motion requirements of different body parts, such as the lumbar and arms, without the need for additional actuators. This reduces the system’s overall complexity, weight, and cost.
The 2TM further enhances the functionality of the system by distributing the actuator’s force to different joints. The first stage transmits force from the motor to the lumbar and arms, while the second stage fine-tunes the distribution to ensure optimal assistance for each targeted muscle group. This dual-stage approach allows WeaRo to provide precise support for multi-degree of freedom movements, such as lifting objects using lumbar muscles and carrying them using arm muscles.
An overview of the system’s operating principles (📷: D. Lee et al.)
WeaRo’s fabric-based design contributes to its lightweight structure, weighing in at just 5.2 kg, including the batteries. The use of soft, flexible materials ensures that the wearable conforms to the user’s body, enhancing comfort and wearability. Additionally, the system avoids restricting the user’s natural motion, enabling transparent operation during both normal daily activities and manual labor.
Experimental results show that WeaRo reduces muscle strain in the lumbar, biceps, and triceps by 18.2 percent, 29.1 percent, and 27 percent, respectively, while maintaining user mobility. Its lightweight, fabric-based design, weighing just 5.2 kg including batteries, ensures high rates of user acceptance.
Looking to the future, the team intends to work to make their system more durable for real-world use. The string-based mechanism may not wear well without lubrication or other measures that help in dealing with friction. Furthermore, the researchers hope to integrate artificial intelligence algorithms into WeaRo so that it can predict when, and how much, assistance is needed by the wearer.
