Variable Stiffness Structures in Biomimetic Robotic Fish: A Review of Mechanisms, Applications, and Challenges

Area of Science:

• Biomimetics
• Robotics
• Fluid Dynamics

Background:

• Biological fish adapt swimming using dynamic body stiffness, a capability lacking in most robotic fish.
• Existing robotic fish often use fixed-stiffness designs, limiting their adaptability and performance.

Purpose of the Study:

• To comprehensively review variable stiffness structures and their applications in biomimetic robotic fish.
• To classify and analyze different variable stiffness mechanisms for robotic fish.

Main Methods:

• Systematic classification of variable stiffness technologies into four categories: smart material-driven, bio-inspired, fluid-driven, and hybrid-driven.
• Comparative analysis of state-of-the-art robotic fish prototypes based on key performance metrics.
• Critical assessment of advantages and limitations of each variable stiffness category.

Main Results:

• Variable stiffness mechanisms offer significant potential to enhance robotic fish hydrodynamic performance.
• Smart material-driven, bio-inspired, fluid-driven, and hybrid-driven mechanisms represent distinct approaches to achieving variable stiffness.
• Prototypes were evaluated on dimensions, swimming speed, maneuverability, and efficiency (Strouhal number).

Conclusions:

• Variable stiffness technology is crucial for advancing robotic fish capabilities, enabling better adaptation to fluid environments.
• Addressing current research challenges and exploring prospective directions will facilitate practical engineering applications of advanced robotic fish.
• The review highlights the transformative potential of variable stiffness in robotic fish design and deployment.