A simplified model based disturbance rejection control for highly accurate positioning of an underwater robot

In this paper, we proposed a disturbance rejection control method to improve the position keeping accuracy of an underwater robot. Not like a ground robot, the controlling of a floating body is a critical requirement to acquire high quality sensor data from, for examples, a gyro, an underwater optical camera, and an imaging sonar. The proposed controller consists of a model-based robust compensator called RIC(robust internal-loop compensator) in an internal-loop, and a conventional PID controller and a null motion controller in an external-loop, where the model we used in the RIC was designed by experimental data of a regulation motion. The proposed scheme was experimentally verified by an observation class ROV, iTurtle which has been developed by the Korea Research Institute of Ships and Ocean Engineering (KRISO) for underwater structure inspection. Results show much improvement in rejecting disturbances for position keeping.