A Swimming Rigid-Soft Coupled Robot Using Tensegrity Principle With Adjustable Bistable Characteristics

Robotic fish can enhance swimming performance through bistability, enabling rapid response and increased force. Existing bistable robotic fish are typically classified as either purely soft or purely rigid, which may constrain their performance. This paper introduces the rigid-soft coupled tensegrity robotic fish. The potential energy parameters, such as the energy barrier, are modified by adjusting the preload of the tension elements. An intermittent gear transmission scheme is proposed to accommodate the bistable state snapping. Experiments with the robotic fish were conducted to measure potential energy, swing speed, swimming performance, and thrust. The experimental results showed that the robotic fish's maximum swimming speed, minimum cost of transport, and maximum thrust were 1.1 BL/s, 10.5 J/kg/m, and 8.77 N, respectively. These metrics rank above the medium level compared to existing bistable robotic fish. Adjusting the energy barrier increases the average angular velocities of the robotic fish's step response and continuous swing by 88.8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\rm o}/\rm {s}$</tex-math></inline-formula> s and 503 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\rm o}/\rm {s}$</tex-math></inline-formula>, respectively. Moreover, the maximum thrust increased by 97.2%, and the average thrust increased by 1400%. These findings underscore the potential of mechanisms for adjusting bistable characteristics to improve the swimming performance of robotic fish, providing valuable insights for designing future generations of robotic fish.