Norimitsu Sakagami

Neuro-fuzzy control of underwater vehicle-manipulator systems

Abstract This paper presents an intelligent controller for underwater vehicle-manipulator systems (UVMS) based on the neuro-fuzzy approach. The controller is composed of fuzzy PD control with membership function tuning by linguistic hedge. A neural network compensator approximates the dynamics of the UVMS in decentralized form. The new controller has the advantages of simplicity of implementation due to decentralized design, precision, and robustness to payload variations and hydrodynamic disturbances. It has significantly low energy consumption compared to both the conventional PD and conventional fuzzy control methods. The effectiveness of the proposed controller is illustrated by results of simulations for a six degrees of freedom autonomous underwater vehicle with a three degrees of freedom on-board manipulator.

Analysis on dynamics of underwater robot manipulators based on iterative learning control and time-scale transformation

A new method to analyze the dynamics of underwater robot manipulators is proposed in this paper. In the proposed method, hydrodynamic terms such as added mass, drag and buoyancy in dynamics of underwater robots are obtained by iterative learning control and time-scale transformation. The advantage of the proposed method is not to use parameter estimation of the dynamics. In this paper, we explain that the proposed method can be applied to hardware design, motion control and motion planning of underwater robots. Moreover, the experimental results using a 1-DOF and a 3-DOF manipulator demonstrate the effectiveness of the proposed method.

Development of a human-sized ROV with dual-arm

In this paper, we describe the development of a human-sized remotely operated vehicle (ROV) with dual-arm. The developed ROV was designed to perform biological researches, geological researches and archaeological explorations in Lake Biwa, the biggest lake in Japan. This ROV has two distinguishing characteristics: one is a dual-manipulator system and the other is an attitude control system. The size of the manipulators is related to the size of a human arm so that the ROV can do work that human divers usually do using the arms. The attitude control system is capable of keeping the vehicle in a horizontal plane, and purposely changing the vehicle attitude angle. Additionally, we developed a new master-slave controller system for this ROV. Some fundamental experiments in a diving pool were performed in order to test the capabilities of the developed ROV. After those experiments, a field trial was conducted in Lake Biwa and the ROV carried out some works at a depth of about 10–20 meters.

An attitude control system for underwater vehicle-manipulator systems

As described in this paper, we propose an attitude control system for underwater vehicle/manipulator systems (UVMSs) based on control of the position of the center of buoyancy with respect to the center of gravity. Control of the center of buoyancy is accomplished using movable float blocks. The attitude control system is useful to control the pitch angle of UVMSs to enhance their performance and to improve their efficiency of underwater operations. A UVMS that has two 5-degree-of-freedom (DOF) manipulators was developed to verify the effectiveness of the proposed attitude control system. This paper presents a numerical study and some experimental results obtained using the UVMS with the attitude control system. We experimentally confirmed that the proposed system can change the pitch angle of the vehicle between −120 and +105 deg. In another experiment, attitude-maintenance control was conducted. Results show that the proposed system can maintain the vehicles horizontal attitude during motion of the manipulators.

Robust nonlinear controller for underwater vehicle-manipulator systems

In this paper, a robust nonlinear controller is proposed for trajectory tracking of underwater vehicle-manipulator systems (UVMS). The controller is non-adaptive and of sliding mode type, and is designed based on the decentralized form of the dynamics of UVMS. It has the advantages of simplicity, robustness, precise performance, and ease of implementation. In order to demonstrate the effectiveness of the controller, several simulations using a five degrees of freedom UVMS are conducted. The results show that the proposed controller provides high performance of trajectory tracking in the presence of uncertainties about the dynamics and hydrodynamic disturbances

A neuro-fuzzy controller for underwater robot manipulators

Autonomous underwater vehicles are increasingly replacing the prevalent remotely operated vehicle-manipulator systems. Most current generation AUVs are not fitted with manipulators and hence are mainly limited to underwater surveying and surveillance tasks because of the difficulty in the coordinated control of the resulting underwater vehicle-manipulator systems. While several researchers have proposed various techniques for control of AUVs, there is still much research to be done on the precise control of underwater manipulators. This paper presents an intelligent control method for underwater manipulators based on the neuro-fuzzy approach. The controller is composed of fuzzy PD control with feedback gain tuning by linguistic rules. A neural network compensator approximates the dynamics of the multiple degrees of freedom manipulator in decentralized form. The proposed controller has advantages of simplicity of implementation due to decentralized design, precision, and robustness to payload variations and hydrodynamic disturbances. It has lower energy consumption compared to the conventional PD control method. The effectiveness of the proposed controller is illustrated by experimental results for a three degrees of freedom underwater manipulator.

Time optimal control for underwater Robot manipulators based on iterative learning control and time-scale transformation

For underwater robot manipulators, this paper presents a new time optimal control method without parameter estimation. The proposed method is based on iterative learning control and time-scale transformation. With this method, it is not necessary to estimate any physical parameters in order to form an input torque pattern that realizes a minimum time motion. Therefore, this method is very practical for control of the underwater robot manipulators with very complicated dynamics expressed by a lot of parameters including hydrodynamic parameters such as added-mass and drag coefficients. To realize time optimal control, we consider a class of motions whose spatial paths are fixed, but whose time trajectories (speed patterns) are changed. By using time-scale transformation, the feedforward input pattern is formed from the basic torque patterns obtained through iterative learning control. In this paper, we theoretically derive the time optical control method based on iterative learning control and time-scale transformation. The effectiveness of our proposed method is verified by several experiments and the results are presented.

Development of an Underwater Robotic Inspection System using Mechanical Contact

This paper reports the development of a robotic inspection system using a mechanical contact mechanism that enhances the positioning stability of a small and lightweight underwater robot to take clear images of underwater targets and to work with manipulators for inspections under external disturbances. As described in this paper, first we perform a two-dimensional numerical analysis based on force and moment acting on an underwater robot with a contact mechanism. Second, we experimentally investigate the friction coefficients of several soft and high friction materials for the contact points of a prototype contact mechanism to enhance the positioning stability of the robot. Based on the results of numerical analysis and the experimental investigation, we design and develop a prototype contact mechanism for an underwater robot. Moreover, we experimentally test the stability of the underwater robot with the contact mechanism in a test tank. Finally, a ship hull inspection is conducted as a field test in a port using the robot with the developed contact mechanism. The experimentally obtained results indicate that the proposed contact mechanism is a useful tool for underwater visual inspections and manipulator tasks of a small and lightweight underwater robot.

Fabrication of a fish-like underwater robot with flexible plastic film body

A portable underwater robot that has a high pressure resistance is required for easy observations in wide area. In this manuscript, we discuss the fabrication and design of a fish-like underwater robot that the outer body is composed by a flexible thin plastic film. Force generated by the differential pressure between inside and outside of the robot is zero due to the flexibility. Therefore, the plastic film of the robot does not ideally break under high pressurized environment. The entire body of the robot is fabricated by a vacuum packaging machine. We call this fabrication robot packaging. The design guide of our fish-like robot depends on the density of insulating fluid containing within the body. Even the fluid is lighter or heavier than water, we can construct the fish-like robot that is at neutral buoyancy Graphical Abstract

Autonomous Spilled Oil and Gas Tracking Buoy System and Application to Marine Disaster Prevention System: Part 1

This paper describes the ongoing project on autonomous spilled oil and gas tracking buoy system and application to marine disaster prevention system for 5 years since FY2011. Objectives of this project are as (1)autonomous tracking and monitoring of spilled plumes of oil and gas from subsea production facilities by an underwater buoy robot, (2)autonomous tracking of spilled oil on the sea surface and transmission of useful data to a land station through satellites in real time by multiple floating buoy robots, (3)improvement of the accuracy of simulations for predicting diffusion and drifting of spilled oil and gas by incorporating the real-time data from these robots. To realize (1) and (2) objectives, we have developed an autonomous underwater robot named SOTAB-I, and an autonomous surface vehicle named SOTAB-II. To realize (3) objective, Data fusion methods in the simulation models incorporating real time measured data not only from a SOTAB-I for gas and oil blowouts, but also from multiple SOTAB-IIs for spilled oil drifting on sea surface were developed.