Bidirectional Support for Individual Finger Joints in Soft Rehabilitation Gloves: Integration of Foldable Pouch Actuators with Modular Elastomeric Actuators

In recent years, a proliferation of soft actuators tailored for hand rehabilitation has been observed. In particular, modular soft actuators have garnered particular interest due to their capacity for individual customization and joint-specific support, a feature often lacking in whole-finger soft actuators. Despite these advancements, a significant limitation persists: the majority of these actuators facilitate only finger flexion, neglecting the equally vital extension movements required for comprehensive hand rehabilitation. Traditional approaches to achieving multi-degree-of-freedom or bidirectional motion have relied on the integration of multiple chambers within soft actuators. However, this strategy has proven impractical for modular soft actuators, primarily due to spatial constraints within the finger joint. To address this challenge, we introduce a foldable pouch actuator (FPA). Designed as a flat, foldable structure composed of a single sheet, the FPA expands solely upon pressurization, generating the requisite force for finger extension. Notably, the FPA seamlessly integrates with existing modular soft actuators without compromising their structural integrity or functional capabilities, thereby enabling bidirectional support for individual joints. Evaluations using a synthetic finger model achieved a joint flexion torque of 0.17 Nm and estimated an overall extension torque of 0.12 Nm. These advancements were accomplished without compromising the traditional flexion functionality, adding individual joint extension support to the existing capabilities. This study constitutes a substantive leap forward in the utilization of soft actuators for clinical hand rehabilitation applications.