Bistable Robotic Fish Propulsion for Thrust and Maneuverability
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Solution Overview
Problem
Existing robotic swimmers face challenges in achieving high maneuverability and energy efficiency due to limitations in propulsion system design and control, particularly in dynamic underwater environments, with soft robots lacking dexterous and accurate controllability of bi-stable nonlinear dynamics.
Innovation Solution
A robotic fish with a compliant propulsion system incorporating an elastic spine and a parallel linkage mechanism, utilizing a passive rotational joint and servo motors to control a bistable mode, enabling precise control of the caudal fin for efficient and agile swimming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If soft materials are used to achieve continuous compliant fish bodies, then the friction loss is reduced and propulsion efficiency is improved, but the thrust produced is relatively weak and controllability is poor
Solution Approach 1:
The patent employs bistable elastic structures that can switch between two stable states, enabling the robotic fish to generate strong thrust forces through rapid shape transitions. This parameter change approach transforms the continuous compliant body into a system with discrete stable states, resolving the contradiction between compliance and force generation capability
Solution Approach 2:
The patent introduces active control mechanisms that dynamically adjust the shape and configuration of the compliant body during swimming. By making the system dynamically adaptable, the robotic fish can optimize its morphology for different swimming conditions, achieving both low friction loss and high thrust when needed
2Loss of energy
If soft materials are used to achieve continuous compliant fish bodies, then the friction loss is reduced and propulsion efficiency is improved, but the maneuverability and agility are limited
Solution Approach 1:
The bistable elastic structures enable rapid transitions between different body configurations, allowing the robotic fish to achieve high maneuverability through quick shape changes. This resolves the contradiction by providing both the compliance needed for efficient swimming and the rapid actuation capability for agile maneuvers
Solution Approach 2:
The patent utilizes periodic oscillation of the caudal fin driven by the compliant body to generate propulsion. The rhythmic motion pattern enables efficient propulsion while the ability to modulate the oscillation frequency and amplitude provides maneuverability control
3Force
If elastic instability of bistable structures is utilized for snap-through motion, then force amplification and rapid morphing are achieved, but dexterous and accurate controllability is lacking
Solution Approach 1:
The patent incorporates feedback control mechanisms that sense the state of the bistable structures and adjust actuation inputs accordingly. This feedback loop enables precise control of the snap-through transitions, resolving the contradiction between force amplification and controllability by actively managing the nonlinear dynamics
Solution Approach 2:
The system pre-loads the elastic structures to specific configurations before triggering snap-through transitions. By preparing the system in advance with appropriate pre-stress and positioning, the patent achieves both strong force amplification during transition and precise control over when and how the transition occurs
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system provides exceptional controllability and tunable bi-stability, enhancing propulsion efficiency and maneuverability, allowing for accurate control of swimming trajectories and forces.
Implementation Method 1
Elastic instability of bistable or multi-stable structures can induce an interesting bi-stable snap-through phenomenon i.e., quickly storing and releasing strain energy
Implementation Method 2
A first end of the first link is adapted to pivot by a first servo motor. A first end of the second link is adapted to pivot by a second servo motor
Data Source
AI summary
A device for providing propulsion in water that includes an elongated elastic member, a parallel linkage mechanism with a first link and a second link, and a propelling member connected to a free end of the elongated elastic member. A first end of the first link is fixedly located relative to a fixed end of the elongated elastic member and adapted to pivot by a first servo motor. A first end of the second link is fixedly located relative to the fixed end of the elongated elastic member and adapted to pivot by a second servo motor. A second end of the first link and a second end of the second link are pivotally connected to each other, as well as to the free end of the elongated elastic member, to form a passive rotational joint. A high-efficiency fishtail designed through nonlinear bi-stable mechanism can be provided.