Foldable Pouch Motor for Wearable Upper Limb Assistance and Rehabilitation

Abstract

Restoring shoulder function is critical for upper-limb rehabilitation, yet achieving lightweight, comfortable, and sufficiently powerful wearable assistance remains a major challenge. This work presents a soft shoulder-assist exosuit driven by a zig-zag Foldable Pouch Motor (FPM), a multi-fold rotary pneumatic actuator designed to enhance torque generation while accommodating the large range of motion required for shoulder movement. By introducing additional inner folds, the proposed FPM improves kinematic redundancy, delays geometric flattening, and promotes torque retention over a wider angular range, while its centerline-anchored configuration preserves spatial compliance for wearable integration. A quasi-static analytical model is established to predict the actuatorś torque-angle-pressure behavior and support design interpretation. The FPM is fabricated using scalable heat-sealing of TPU-coated fabric, enabling lightweight integration into a textile-based exosuit. Benchtop characterization confirms that the actuator delivers up to 12.79 Nm at $90^{\circ }$ shoulder abduction, meeting the torque demand for passive arm elevation. On-body experiments with eight healthy participants show that the exosuit preserves over 90% of native shoulder ROM in most tested motions, indicating good mechanical transparency, while surface electromyographic (sEMG) measurements reveal significant reductions of up to 40.1% in anterior-deltoid activation during a controlled abduction task. During assistance, sEMG and IMU signals are fused to identify motion phases and trigger phase-dependent pneumatic support. These results demonstrate that the proposed system provides effective shoulder assistance in a lightweight and compliant wearable format, and represents a promising candidate for daily assistive and rehabilitation applications. This paper was recommended for publication by Associate Editor Haoyong Yu and Editor Tamim Asfour upon evaluation of the reviewers’ comments.