A lightweight and minimal exoskeleton for reducing grip fatigue and increasing endurance during heavy object carrying

Background

The field of wearable assistive technology has seen significant growth, particularly in applications aimed at reducing musculoskeletal strain during manual handling tasks. In scenarios such as disaster relief, medical evacuation, and industrial labor, workers are often required to carry heavy objects for extended periods, leading to rapid accumulation of grip fatigue and increased risk of injury. Traditional ergonomic interventions, such as padded gloves or load-distributing harnesses, primarily focus on redistributing weight to larger muscle groups like the back or shoulders. However, these solutions often fall short in addressing the specific issue of grip fatigue, which remains a limiting factor for endurance and safety during prolonged carrying tasks. As a result, there is a pressing need for assistive devices that not only alleviate fingertip and forearm strain but also remain unobtrusive, allowing users to maintain dexterity for other tasks.

Current approaches to grip assistance present several limitations that hinder their effectiveness in real-world, multi-task environments. Passive wearables and weightlifting hooks can offload some load from the fingers, but they are typically bulky, always engaged, and interfere with fine motor tasks once the carrying phase is over. More advanced exoskeletons and supernumerary robotic limbs have been explored, but these often target low-force assistance or balance rather than providing substantial grip support for heavy loads. Additionally, many existing devices lack the ability to quickly engage or disengage the assistive function, making them impractical for situations that require frequent transitions between carrying and dexterous manipulation. Ergonomic discomfort, excessive distal weight, and high power consumption further limit the adoption of these solutions, underscoring the need for a new approach that combines effective load transfer, user comfort, and operational flexibility.

Technology

CASET is a wearable assistive device engineered to reduce grip fatigue during heavy object carrying by transferring the load from the user’s fingers to their wrists. The system features a back-mounted linear actuator that tensions Bowden cables, which are routed to two wrist-mounted hooks. When activated, the actuator pulls on the cables, causing the hooks to curl into a rigid C-shape using trapezoidal linkages, securely gripping the object and offloading the force from the fingers. When disengaged, the hooks uncurl and become flexible, allowing for unobtrusive wear and preserving hand dexterity for other tasks. The device is lightweight, with only 154 grams worn on each wrist, and operates with high efficiency, consuming just 0.12 W while holding a load. CASET is designed for rapid engagement and disengagement, making it suitable for scenarios where users need both grip assistance and freedom of movement, such as in disaster relief or medical evacuation.

What differentiates CASET is its hybrid approach that combines the benefits of supernumerary digits and powered exoskeletons while addressing the limitations of traditional grip aids. Unlike passive devices that merely offload weight to the back or shoulders and remain obtrusive, CASET actively curls and uncurls its hooks, enabling on-demand assistance without hindering dexterity when not in use. Its non-backdrivable actuator ensures low power consumption and secure load holding, while the Bowden cable transmission allows the bulk of the device’s weight to be carried on the back rather than the wrists. Experimental validation demonstrated a 56% reduction in grip fatigue and a 320% increase in carry time, with excellent usability scores from participants. This combination of effective load transfer, unobtrusive design, rapid activation, and user comfort positions CASET as a significant advancement in assistive grip technology, particularly for tasks requiring prolonged load holding and frequent transitions between assisted and unassisted hand use.

Benefits

• Significantly reduces grip fatigue by transferring load from fingers to wrist, decreasing muscle activation by 56%
• Increases carry time endurance by 320%, enabling longer static holding of heavy objects
• Low power consumption (~0.12 W while holding) allows extended use with minimal energy requirements
• Lightweight design (1.81 kg total, 154 g on each wrist) minimizes wearer burden and preserves dexterity
• Quick engagement and disengagement of wrist-mounted hooks enable unobtrusive wear during multi-tasking
• Excellent usability with high user satisfaction scores, facilitating adoption in real-world scenarios
• Custom actuation mechanism provides reliable, rigid grip support mimicking weightlifting hooks with active control
• Potential for ergonomic improvements to reduce wrist discomfort and improve blood flow during use

Applications

• Disaster relief litter carrying
• Medical evacuation stretcher transport
• Industrial heavy object handling
• Warehouse manual load carrying
• Construction material transport assistance

Additional info

This wearable assistive device, CASET, reduces grip fatigue by offloading force from fingers to wrists. It features a back-mounted linear actuator, Bowden cables, and wrist-mounted hooks. The actuator tensions cables, curling the hooks into a rigid C-shape via trapezoidal linkages to grasp objects. This mechanism transfers load, consuming minimal power (0.12 W) while holding. Hooks uncurl for unobtrusive wear.

Auburn is looking for a devleopment and commercialization partner. Auburn can bring to such a partnership a collaborative team experienced with engineering, prototype building, and testing for data from live subjects. Partnerships on SBIR/STTR awards is possible.