Development of a Joint-like Pneumatic Actuator Applied to Soft Frog-inspired Swimming Robot

In order to realize the miniaturization of the frog-inspired swimming robot and enhance its environmental adaptability, a joint-like pneumatic soft actuator is proposed by combining the superior characteristics of the soft material and the swimming mode of the frog, which can achieve more compact and lighter limb structure, while satisfying the kinematics and mechanical properties during swimming of the soft frog-inspired robot. Based on the Yeoh constitutive model and the virtual work principle, the deformation analysis model of the actuator is established with the geometric parameters of the joint-like pneumatic soft actuator. Furthermore, the output recovery torque of the actuator is maximized at a certain bending angle in the case that the overall size of the actuator is constrained, and the specific structural parameters of the actuator are determined. The joint-like pneumatic soft actuator is fabricated by 3D printing, molding and other processing methods. Through the comparative analysis, the winding form and winding density of the fiber-line are determined to suppress the radial protrusion effect of the actuator. Finally, the experimental test and analysis show that the actuator with a mass of about 7.5 g can perform a morphological change from the 180° bending state to the straightening state, and can match different load torques within a certain range by adjusting the filling air pressure at a certain bending angle. Thus, the feasibility of the joint-like pneumatic soft actuator designed for the soft frog-inspired swimming robot is verified.