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Biomimetic robots borrow their senses and structure from animals, such as insects, fishes, and human. Development of underwater vehicles is one of the areas where biomimetic robots can potentially perform better than conventional robots. In this paper, an undulating fin mechanism has been developed and used as the propulsion system of fish in various fin types. The layout and workspace of the modular fin segments are considered and analyzed. The relationship of the individual fin segment and phase angles with the overall fin trajectory is also discussed. A gymnotiform knifefish robot, as an example, has been developed to demonstrate the design methodology and prototype performance. The maneuvering and the buoyancy control can be achieved by the integration of a buoyancy tank with the undulating fin. Experiments were conducted in the laboratory tank and the variation of velocity with respect to several swimming parameters was analyzed. Field trials have also been conducted in an outdoor pool to demonstrate the swimming capability of the knifefish robot and its buoyancy performance in 4 m deep water.

In this paper, mathematical model, control law design, different locomotion patterns, and locomotion planning are presented for an Anguilliform robotic fish. The robotic fish, consisted of links and joints, are driven by torques applied to the joints. Considering kinematic constraints, Lagrangian formulation is used to obtain the mathematical model of the robotic fish. The model reveals the relation between motion of the fish and external forces. Computed torque control method is first applied, which can provide satisfactory tracking performance for reference joint angles. To deal with parameter uncertainties, sliding model control is adopted. Three locomotion patterns — forward locomotion, backward locomotion, and turning locomotion — are realized by assigning appropriate reference angles to the joints, and the three locomotions are verified by experiments and simulations. A new form of central pattern generator (CPG) model is presented, which consists of three-dimensional coupled Andronov–Hopf oscillators, artificial neural network, and outer amplitude modulator. By using this CPG model, swimming pattern of a real Anguilliform fish is successfully applied to the robotic fish in an experiment.

The recent explosion of interest in sub sea research and industries has led to a demand for efficient versatile submarine robots to perform interaction and survey tasks. Whilst most of these robots employ conventional propeller or thruster based locomotion, there has been a growing interest in the development of biologically inspired robotic swimmers (or robotic fish). In a hope to gain some of the manoeuvrability and efficiency advantages characteristic of their biological counterparts.

Early robotic fish achieved their gait, by directly controlling the relative angel between each vertebrae, using multiple active actuators.

Following observations that many biological locomotory gaits, utilize spring dynamics to create efficient oscillatory motion with minimal active input, there has been a recent trend towards the development of under-actuated robotics utilizing dynamics to achieve harmonic locomotory gaits, examples can be found in McGeer’s passive dynamic walkers, or MIT’s compliant swimming devices.

For a harmonic dynamic system, the path is dependent on the total energy in the system. By controlling the total energy in the system the gait can be controlled by varying a single degree of freedom.

This paper aims to explore the potential for energy based control to produce an effective propulsive gait.