A Chain-Based Cable-Driven Upper-Limb Exoskeleton: Design, Mechanical Analysis and Development

Exoskeletons have garnered significant attention in recent years, particularly in rehabilitation and assistive technology, due to their potential to aid people with motor disabilities in their recovery process and activities of daily living (ADLs). However, current upper-limb exoskeletons in the market would have issues such as user discomfort and inconvenience, and high costs for individual customers. This paper introduces a new chain-based cable-driven upper-limb exoskeleton that is lightweight, cost-effective, and comfortable for the wearer in various movements. It focuses explicitly on three degrees of freedom (DOFs) actuated by foldable chain mechanisms: flexion-extension and abduction-adduction for the shoulder joint and flexion-extension for the elbow joint. The exoskeleton's structure is fabricated using lightweight and printable materials, such as Thermoplastic Polyurethane (TPU), Polyethylene Terephthalate Glycol (PETG), and carbon fiber. A compact control system consisting of high-torque DC motors, microcontroller, and cable-driven mechanism was meticulously selected to optimize the device size. Moreover, stress analysis and topology optimization simulations are conducted to minimize weight and ensure the exoskeleton's functionality while maintaining a safety factor of 2. This prototype has a total weight of 15 lbs. Experimental studies were performed to evaluate the exoskeleton's range of motion for shoulder abduction-adduction and elbow extension with up to 33 Nm torque. Overall, this new chain-based upper-limb exoskeleton exhibits promise as an affordable and comfortable rehabilitation tool for individuals with upper limb impairments.