Applying coupled nonlinear oscillators to imitate swimming modes of cow-nosed rays

Cow-nosed rays can perform diversified swimming modes including linear cruise, pitching, yawing, and gliding. This paper focuses on the realization of these swimming modes. Furthermore, the role of tail fins are taken into account. The phase oscillators with controlled amplitudes have been adopted to build a new central pattern generator (CPG) network that includes six pectoral fin ray oscillators and two tail fin ray oscillators. Meanwhile the coupling connections are analyzed. The swimming modes of asymmetric oscillations in time, asymmetric oscillations in spatial, yawing based on the amplitudes, turning on the spot, and pitching based on tail fins are achieved. The simulations and experiments demonstrated that the CPGs are effective for controlling multi-fin actuated robotic fish to imitate the swimming modes of cow-nose rays and enable the robotic fish to achieve more complex movements by controlling the coordination of the pectoral fins and the tail fins.