Adaptive fault-tolerant depth control for a bionic robotic dolphin with stuck oscillating joints

The bionic robotic dolphin often employs a multi-joint dorsoventral mechanism to achieve dolphin-like undulatory propulsion, ensuring excellent maneuverability. However, the motors of the oscillating joints in this mechanism are susceptible to sticking faults, posing a challenge for the robotic dolphin to maintain its intended swimming depth, leading to undesired ascent or descent. To address this issue, we propose an adaptive fault-tolerant depth control method fora bionic robotic dolphin experiencing oscillating joint faults. First, the mechatronic design and dynamic model of a four-joint robotic dolphin are introduced. Thereafter, the swimming behaviors of the robotic dolphin with struck oscillating joints are analyzed. Based on this, an adaptive fault-tolerant depth controller is designed to minimize the reference tracking errors by updating dynamic model parameters in real time. Extension experiments are conducted to validate the effectiveness of the proposed fault-tolerant control method. The results demonstrate that this controller enables the robotic dolphin to successfully achieve and maintain the target depth, even in the presence of stuck oscillating joints. These findings confirm the robustness and practicality of the fault-tolerant depth control approach for the bionic robotic dolphins, thereby ensuring their safety in complex ocean conditions.