Low-resistance, high-force, and large-ROM fabric-based soft elbow exosuits with adaptive mechanism and composite bellows

Due to the lightweight and compliance, fabric-based pneumatic exosuits are promising in the assistance and rehabilitation of elbow impairments. However, existing elbow exosuits generally suffer from remarkable mechanical resistance on the flexion of the elbow, thus limiting the output force, range of motion (ROM), and comfortability. To address these challenges, we develop a fabric-based soft elbow exosuit with an adaptive mechanism and composite bellows in this work. With the elbow kinesiology considered, the adaptive mechanism is fabricated by sewing the interface of the exosuit into spring-like triangle pleats, following the profile of the elbow to elongate or contract when the elbow flexes or extends. The composite bellows are implemented by further sealing a single blade of bellows into two branches to enhance the output force. Based on these structural features, we characterize the mechanical performance of different soft elbow exosuits: exosuit with normal bellows-NB, exosuit with adaptive mechanism and normal bellows-AMNB, exosuit with adaptive mechanism and composite bellows-AMCB. Experimental results demonstrate that by comparing with NB, the mechanical resistance of AMNB and AMCB decreases by 80.6% and 78.6%, respectively; on the other hand, the output torque of AMNB and AMCB increases to 120.3% and 207.0%, respectively, at 50 kPa when the joint angle is 120°. By wearing these exosuits on a wooden arm model (1.25 kg), we further verify that AMCB can cover a full ROM of 0°–130° at the elbow with 500 g weight. Finally, the application on a health volunteer with AMCB shows that when the volunteer flexes the elbow to lift a weight of 500 g, the sEMG activity of the biceps and triceps is markedly reduced.