Design, manufacturing, and testing of a novel omnidirectional soft sleeve actuator

Soft actuators have become central to modern robotics due to their inherent flexibility, enabling safer and more adaptable interactions. Within this domain, omnidirectional actuators are particularly valuable because they enable multidirectional motion suitable for complex robotic tasks and human-robot interaction. However, existing omnidirectional actuators are often bulky and exhibit high design complexity, which limits wearability and often requires high operating pressures. This study presents a novel sleeve-type soft omnidirectional actuator (OSSA), a compact, self-contained sleeve that achieves independent linear extension and contraction and multidirectional bending through differential pressurization of a folded bellows architecture, which lowers the required pressure to 130 kPa and enhances wearability and system integration. To enable reliable fabrication at scale, a manufacturing framework for indirect extrusion 3D printing in thermoplastic polyurethane was developed and validated, mitigating common challenges in flexible printing, including nozzle clogging and loss of airtightness. OSSA achieved 60 N blocked axial force, 81 mm linear displacement, 25 mm contraction, and 18 N bending force at angles up to 45° under low pressure operation. A parametric analysis revealed key relationships between design geometry and material behavior, providing a framework for actuator optimization. These results advance the development of high-performance omnidirectional soft actuators for applications such as wearable robotics.