Abstract
Underwater robots are useful for exploring valuable resources and marine life. Traditional underwater robots use screw propellers, which may be harmful to marine life. In contrast, robots that incorporate the swimming principles, morphologies, and softness of aquatic animals are expected to be more adaptable to the surrounding environment. Rajiform is one of the swimming forms observed in nature, which swims by generating the traveling waves on flat large pectoral fins. From an anatomical point of view, Rajiform fins consist of cartilage structures encapsulated in soft tissue, thereby realizing anisotropic stiffness. We hypothesized that such anisotropy is responsible for the generation of traveling waves that enable a highly efficient swimming. We validate our hypothesis through the development of a stingray robot made of silicone-based cartilages and soft tissue. For comparison, we fabricate a robot without cartilages, as well as the one combining soft tissue and cartilage materials. The fabricated robots are tested to clarify their stiffness and swimming performance. The results show that inclusion of cartilage structure in the robot fins increases the swimming efficiency. It is suggested that arrangement and distribution of soft and hard areas inside the body structure is a key factor to realize high-performance soft underwater robots.
Highlights
Underwater robots are useful for exploring valuable resources and marine life
The plane morphology of Rajiform swimmer is expected to be suitable for moving around the seafloor, which would enable efficient exploration of mineral resources and marine life
Four types of specimens were prepared as shown in Fig. 3a: “Flat cartilaginous” specimen with soft tissue and cartilages, “Sharp cartilaginous” specimen with soft tissue and cartilages which has relatively narrow width and large thickness, “Homogeneous soft” specimen consisting of soft tissue only, and “Homogeneous rigid” specimen consisting of randomly arranged cartilage materials in the soft tissue
Summary
Underwater robots are useful for exploring valuable resources and marine life. Traditional underwater robots use screw propellers, which may be harmful to marine life. From an anatomical point of view, Rajiform fins consist of cartilage structures encapsulated in soft tissue, thereby realizing anisotropic stiffness. We hypothesized that such anisotropy is responsible for the generation of traveling waves that enable a highly efficient swimming. The results show that inclusion of cartilage structure in the robot fins increases the swimming efficiency. Cartilage structures are radially distributed across the fins, resulting in anisotropic nature of their stiffness Anisotropy of the fins realized by the cartilage structure can increase the swimming efficiency even though the overall stiffness of the robots remains the same
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