Development of Middle-Level Controller of Biomimetic Swimming and Walking Robot for Seabed Investigation

This paper describes the control of multiple fins for basic modes of an underwater fin-type robot. The developed robot can swim along a given path and walk on the seabed with its six fins for precise seabed investigation. The middle-level controller for swimming, walking, and mode transition is needed for the robot to move with better thrust efficiency and to recognize the environment stably. First, the fin oscillation method was chosen to be a sinusoidal motion by comparing the average thrust of one fin. For more stable swimming movement, the fin forces and torques by fin grouping methods were analyzed. To maintain the posture of the robot during walking, we formulated the minimum delay length between each stride. Also, the strategy of mode transition, such as ascending and descending, was determined by simulating the fin thrust and the robot motion. Sea trials were conducted to achieve the data of robot motion using proposed methods. The results showed that swimming and ascending motions appeared close to those predicted through simulation.