Aaron M. Hanai

Development of an underwater robot, ODIN-III

During the last decade, the first autonomous underwater robot of the Autonomous Systems Laboratory of the University of Hawaii, ODIN (Omni-Directional Intelligent Navigator) built in 1991 has produced a lot of valuable results in development and control methods [(S.K. Choi et al., July 1994), (Choi, S.K. et al., March 1995), (S.K. Choi et al., April 1996), (Yang, K.C. et al., September 1999), (J. Yuh et al., 2000)]. Recently, ODIN was born again in the 3rd generation with unique features under recent technologies such as abundant system resources owing to a PC104+, new vehicle system software architectures with an object-oriented concept and its implementation, a graphical user interface and an independent algorithm module using a dynamic linking library (DLL) based on the Windows operating system. These give us an ideal environment for developing various algorithms which are needed for developing an advanced underwater robotic vehicle. This paper describes details of the development of ODIN-III and presents initial experimental results for fine motion control.

Experimental validation of model-based thruster fault detection for underwater vehicles

This paper describes a model-based thruster fault detection scheme for an autonomous underwater vehicle. For a vehicle equipped with servo motor based marine thrusters, the velocity and current feedback from the motor controllers can be used to derive two independent thrust approximations. The difference between the two models reveals the presence of fault conditions, and quantifies the error of the output thrust relative to the desired reference. The method is proven effective through experimental validation.

Experimental study on fine motion control of underwater robots

This paper considers thruster dead zones and saturation limits, which are nonlinear elements that complicate fine motion control of underwater robots. If the vehicle is configured with redundant thrusters, the respective dead zones and their surrounding nonlinear regions could be avoided by implementing a null motion solution for the command input of the vehicle. This solution is derived from the vehicles geometry and is realized before the application of the motion control algorithm. The result is an improvement in system performance exclusive of the implemented controller type. The approach is illustrated through simulation and experiment with an underwater robot, ODIN.

Experimental analysis and implementation of redundant thrusters for underwater robots

This paper identifies the key issues in the empirical implementation of redundant marine thrusters for two different autonomous underwater vehicles of different designs, so as to maximize the effectiveness for fine motion control. A crucial factor in the development of a precision control scheme is the thorough understanding of the system geometry. Other critical elements include the contribution of the thruster amplifier gains to the steady state response of the thrusters, and the influence of the power source on system performance. These findings are proven through experimental analysis and verification.

A new approach to a laser ranger for underwater robots

This paper describes the development of a laser-based ranging device, as part of a sensor work package that is to be integrated into an autonomous underwater vehicle. The objective of the laser ranging component includes robust operation in turbid ocean environments from 1 to 10 meters with a balance of accuracy and speed. A calibration technique that utilizes a spline interpolation is employed as an accurate, yet simple alternative to conventional triangulation methods. The resulting configuration is capable of range detection within 2% absolute error, at a 10 Hz refresh rate, out to 4 meters in turbid ocean conditions, and to greater than 10 meters in air. The maximum underwater range of the system is currently limited by the existing hardware, whereas the software is ready for any future system upgrades.