Prolonged work in fixed postures often fatigues muscles and causes musculoskeletal disorders because muscles do not handle sustained contractions well, even at low intensity. Gravity exerts maximum torque on the shoulder and elbow when the upper and lower arms extend forward horizontally, as in repetitive tasks like drilling.
Exoskeletons for Musculoskeletal Relief
Despite increasing automation, work-related musculoskeletal disorders remain common in overhead and forward-reaching tasks, posing a global occupational health challenge. Exoskeletons have emerged as wearable robotic devices that assist users by enhancing or supporting physical capabilities, often helping with heavy lifting or repetitive movements in industrial settings.
There are two main types of exoskeletons: passive and active. Upper-limb passive exoskeletons can reduce muscle fatigue and injury risk by counteracting arm weight, gravitational forces, and the load of handheld tools. These compact, lightweight devices use elastic components like springs to provide support torque. However, they assist only during arm elevation, and during lowering, they create resistance that can strain muscles and joints.
Active exoskeletons provide adjustable torque, position, and speed, but their bulky structures and heavy, high-capacity batteries limit comfort and portability.
To overcome these issues, this study presents a backpack-style exoskeleton that improves user comfort and minimizes interference with natural movements. The system incorporates three pneumatic-driven variable-stiffness components: a bending actuator, a tensile actuator, and a teeth-engagement clutch.
Portable Semi-Active Exoskeleton Design and Function
Building on these designs, researchers developed a portable semi-active upper-limb exoskeleton to support sustained overhead and forward-reaching postures. The device uses a portable pneumatic system (vacuum pump) and weighs 3.35 kg. In its flexible mode, it allows natural movement with minimal resistance, while in its rigid mode, it limits joint motion and provides support for maintaining posture.
The feasibility of integrating the proposed variable-stiffness units into exoskeleton design was confirmed through performance evaluations involving 12 participants performing four common assembly postures, both with and without the device. Compared to working without the exoskeleton, its use resulted in an average reduction in muscle activation of 42.3 ± 2.4% across all postures, highlighting its potential for ergonomic support. Additionally, the bending variable-stiffness actuator achieved a stiffness of 50.98 Nm/rad and an 87.9-fold variation ratio at a relatively low vacuum pressure of 40 kPa.
These findings suggest strong potential for the exoskeleton to provide long-term assistance in fixed overhead and forward-reaching tasks.
Read the original article on: IEEE Xplore
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