Biomimetic motion planning of an undulating robotic fish fin

This paper presents a locomotion control implementation of a robotic system mimicking the undulating fins of fish. To mimic the actual flexible fin of a real fish, we created a ribbon fin type actuation device with a series of connecting linkages and attached it to the robotic fish. By virtue of a specially designed strip with a slider, each link is able to turn and slide with respect to the adjacent link. The driving linkages are used to form a mechanical fin consisting of several fin segments, which are able to produce undulations, similar to those produced by actual fins. By virtue of the modular and reconfigurable fin mechanisms, two robotic fish with different fin layouts have been designed and constructed: The first prototype is a robotic stingray, swimming by undulations of a pair of lateral fins; the second is a robotic knifefish, swimming by undulations of a long anal fin. The locomotion scheme and mechatronics implementation of the robotic stingray are presented and discussed with a parametric study of the slider's workspace and joint trajectory. Some experimental observations of the robotic knifefish are also shown and discussed. The results demonstrate that the designed fin mechanisms are able to undulate sections of pectoral and anal fins, with different amplitudes and phases, along the length of the fin in the direction of motion. This may lead to further developments that better mimic the fin locomotion capability of real fish.