Modelling and parametric study of modular undulating fin rays for fish robots

Biomimetic robots borrow their senses and structure from animals, such as insects, fish and birds. Development of underwater vehicles is one of the areas where biomimetic robots can potentially perform better than conventional robots. In this paper, the biomimetic design and the workspace study of undulating fin propulsion mechanisms are considered and discussed. We are interested in fish with long and/or wide undulating body/fin – especially those of anguilliform, amiiform, rajiform, and gymnotiform. Two major mechanism layouts developed to mimetic fin undulations of real fish are compared and discussed. Various kinematics expressions of fin waves are presented and the model’s limitation is also discussed. For a parametric study, the geometry of a single fin segment of the assembled fin mechanisms and the fin wave generated are first developed. Next, the fin workspace of the single fin segment is derived based on a defined area ratio. By virtue of the obtained fin dimensions, a gymnotiform robot, Nanyang knifefish (NKF-II), has been designed and constructed. With the fin-ray linkages with sliders connecting in series, the fish robot is able to generate arbitrary undulating waveforms. The robot’s maneuvering and its depth control have also been achieved by the integration of a buoyancy tank with the undulating fin mechanisms. Initial pool testing has been conducted to demonstrate the basic performance of the fish robot underwater.