Motion control for an underwater robotic fish with two undulating long-fins

Abstract

Motion control for one kind of underwater robotic fish is presented in this paper. Here our robotic fish prototype has two long-fins installed symmetrically on its both sides. And one long-fin is made up by springiness membrane covered on ten ray-fins. Ten servo-motors are used to control the motions of the ten ray-fins on one side. Due to the special structure of the prototype, swimming motion modes can be broken into four basic motion modes: marching mode, receding mode, rotating mode and side-swaying mode. Aiming at the four motion modes, this paper presents relevant control method separately. Our controller is based on FPGA. Through reading signal data stored in the memory of control chip, servo-motors may oscillate the ray-fins at scheduled way. Therefore, different frequency and different phase difference of adjacent ray-fins may bend the long-fin formed by membrane into relevant waveform. Because the membrane is soft and elastic, hydrodynamic forces produced by expelled water may drive fish body into swimming motions. Using different control methods, hydrodynamic force provide fish body with many motion modes, including the four basic motion modes. In addition, one motion modes switch system is designed based on Mega128. Through producing different voltage level combination, robotic fish may switch its motion mode by the transferred one in swimming. The experiments show our method for motion control is valid.