Design, Modeling, and Bionic Applications of a Rigid-soft Integrated Soft Actuator

Fiber-reinforced soft actuators are particularly promising candidates in the field of soft robotics. To minimize circumferential expansion, the cross-sectional shapes of the fiber-reinforced soft actuators are generally designed as circles, squares, and semicircles. The specific requirement for the cross-sectional shape limits their further development. Therefore, we propose a novel rigid-soft integrated soft actuator that primarily consists of soft inflatable chambers and rigid frames. For comparison, the change in the cross-sectional shape of fiber-reinforced soft actuators under pressurization is investigated in theory. Then, a predictive model for the behavior of the rigid-soft integrated soft actuators is established by using the virtual work principles and integrating the Yeoh model, and it is also verified through experiments and finite element simulations. The results show that rigid frames can provide geometric constraints, minimize circumferential expansion, and ensure that noncircular cross-sectional shapes remain unchanged during inflation. Furthermore, the potential applications of the proposed rigid-soft integrated design are demonstrated with two examples: a flexible gripper and a biomimetic fishtail. The proposed soft actuators, which combine hyper-elastic materials with the properties of geometric constraints, expand the design scope of the soft pneumatic actuators and exploit more possibilities for practical application.