Opportunity
Underwater robots require high maneuverability and energy efficiency to perform tasks in complex, unstructured aquatic environments. Biomimetic approaches, particularly body-and-caudal-fin (BCF) propulsion, are popular due to their natural, low-noise interaction with marine life. However, existing robotic swimmers face significant limitations. Discrete body designs suffer from large friction losses, leading to low propulsion efficiency. While soft, continuous body designs using materials like ionic polymer-metal composites (IPMCs) or dielectric elastomers address some issues, they often produce relatively weak thrust. This makes precise control for high agility and maneuverability difficult, especially in dynamic water flows. A critical gap exists in achieving both strong, amplified thrust and dexterous, accurate controllability. Although elastic instability in bistable structures can provide force amplification and rapid morphing through snap-through phenomena, existing soft robots utilizing such mechanisms lack precise control over the nonlinear dynamics, resulting in poor maneuverability and hindering practical deployment.
Technology
This patent presents a robotic fish featuring a novel, controlled bistable elastic propulsion system. The core innovation is a compliant fishtail mechanism that combines an elastic spine and a lightweight parallel linkage mechanism actuated by two servo motors. The parallel linkage mechanism actively and precisely controls the endpoint trajectory of the elastic spine. This design enables tunable bistability, allowing the tail to switch flexibly between two distinct motion modes: a smooth-swinging monostable mode and a rapid, impulsive bistable mode that harnesses elastic snap-through. The system's kinematics are derived from inverse kinematics of the parallel linkage, allowing predefined tail-beat trajectories (defined by parameters like amplitude, frequency, and offset) to be accurately executed. By controlling the servo motors according to these trajectories, the passive rotational joint connecting the linkage to the spine dictates the motion of the attached compliant caudal fin. This integration provides exceptional controllability over the tail's nonlinear dynamics, enabling high thrust amplification from the bistable snap-through while maintaining precise, programmable motion for agile swimming and turning.
Advantages
- Achieves superior swimming speed and thrust force amplification by effectively harnessing controllable elastic snap-through in the bistable mode.
- Enables high energy efficiency across a wide speed range through flexible switching between monostable (efficient at lower speeds) and bistable (effective at higher speeds) propulsion modes.
- Provides outstanding maneuverability, including fast turning rates and small turning radii, due to precise trajectory control of the continuous, fish-like tail morphology.
- Offers tunable system performance through adjustable stiffness of the elastic spine and caudal fin, allowing optimization for different operational requirements.
- Features a self-contained, compact robotic system suitable for practical underwater applications.
- Generates low noise and natural interference with the aquatic environment, ideal for marine observation.
Applications
- Autonomous underwater vehicles (AUVs) for oceanographic research, environmental monitoring, and seabed mapping.
- Biomimetic robotic platforms for close-up, non-invasive observation and interaction with marine life.
- Inspection and maintenance of underwater infrastructure such as pipelines, cables, and offshore platforms.
- Search and rescue operations in aquatic environments.
- Educational and research tools in robotics, biomimetics, and fluid dynamics.
