Bio-Inspired Rigid-Soft Hybrid Origami Actuator with Controllable Versatile Motion and Variable Stiffness

Conventional soft pneumatic actuators (SPAs) are made of soft materials that facilitate safe interaction and adaptabil- ity. In positioning and loading tasks, however, SPAs demonstrate limited performance. In this article, we extend the current designs of SPAs upon integrating a tendon-driven parallel mechanism into a pneumatic origami chamber, inspired by the performances and structures of vertebrates. The inner rigid/outer soft actuator exploits the advantages of both, parallel mechanisms to achieve precise, versatile motion, and SPAs, to form a compliant, modular structure. With the antagonistic actuation of tendons-pulling and air-pushing, the actuator can exhibit multimode motion, tunable stiffness, and load-carrying maneuvers. Kinematic and quasi-static models are developed to predict the behavior and to control the actuator. Using readily accessible materials and fabrication meth- ods, a prototype was built, on which validation experiments were conducted. The results prove the effectiveness of the model, and demonstratethemotionandstiffnesscharacteristicsoftheactuator. The design strategy and comprehensive guidelines should expand the capabilities of soft robots for wider applications, and facilitate the development of robots with rigid-soft hybrid structures.