Underwater Manipulator Research Articles

Integrate and Optimized Design of a Hydraulic Underwater Manipulator

Underwater manipulator as efficient tools plays important roles in ocean exploitation. Because of its specificity for underwater operations, the structure of an underwater manipulator should be designed compactly with light weight and small size. Structure of a 7-function underwater manipulator is designed here. Except forearm rotation and wrist rotation which use hydraulic motors, other functions are driven by hydraulic cylinders, whose parameters are determined by force analysis and limit positions. The hydraulic pipelines from the elbow joint to the end are passed through the forearm, and the hydraulic cylinder of the jaw is integrated into the wrist motor. Built-in pipelines are achieved in the designed structure and the whole weight and volume are greatly reduced by integrated and optimized design.

Workspace control system of underwater tele-operated manipulators on an ROV

This paper presents a control technique for structured undersea tasks that require a high degree of precision. The overall efficiency of tele-operated underwater manipulation is improved by reducing the burden on the human operator. A new workspace-control system composed of a computer and input devices in workspace was developed to support the operator. The computer transforms the desired velocity of end-effector in workspaces to desired joint angles by solving the inverse kinematics of the slave manipulators. The desired joint angles are transferred to the slave controller through RS-485 serial communication, and be followed by the slave manipulator. The developed master system provides advantages in conducting structured tasks(coring, drilling, underwater connector mating, etc.) that require precise control of the end-effector’s motion and attitude. The existing master system, however, is more useful for unstructured tasks than newly developed master system. By combining the two master systems, the work efficiency of the underwater tele-operated manipulator system was improved. This paper presents the development of the workspace-control system and a working strategy to alleviate operator’s burden in underwater works. Experimental results are presented to evaluate the effectiveness of the proposed method using underwater manipulators mounted on the KORDI deep-sea ROV Hemire.

Underwater Target Localization

This contribution focuses on the problem, intrinsic to autonomous underwater manipulation, of medium-range target localization for guiding the vehicle toward the target area. Based on the use of the dual-frequency identification sonar (DIDSON) sonar, the goal is to acquire the Earth-referenced Cartesian coordinates of a known target, with the necessary accuracy required for positioning the vehicle, so that the target falls within the manipulator workspace.

Swimmer simulation using robot manipulator dynamics under steady water

To help swimmers improve, we have developed a computational swimming model using underwater manipulator dynamics. We formulate the equations of the underwater manipulator dynamics using the fluid drag, which is proportional to the square of the velocity. We construct a swimming model consisting of several links based on these equations. The distance traveled by the optimal swimming motion is derived using the model. The input parameters are the joint torques. The arm and leg positions in the model are determined from the joint torques. The force transmitted from the water to the manipulator is defined to be the action force, and the force transmitted from the manipulator to the water is defined to be the reaction force. This reaction force is defined to be the propulsion force. By combining the propulsion force generated by the arms and legs and the frictional drag with respect to the body we can calculate the distance traveled. To optimize the propulsion, which depends on the swimmer’s motion, a variational approach using the Lagrange function is applied. We can use the model to simulate 2D pseudo-backstroke motion. Our model has a lower cost than other techniques in the literature, because it does not require computational fluid dynamics (CFD). The swimmer velocity calculated by our model agrees quite closely with the results in the literature. The model qualitatively captures the movement of an actual swimmer.

Propulsive Velocity Optimization of 3-Joint Fish Robot Using Genetic-Hill Climbing Algorithm

Underwater robot is a new research field which is emerging quickly in recent years. Previous researches in this field focus on Remotely Operated Vehicles (ROVs), Autonomous Underwater Vehicles (AUVs), underwater manipulators, etc. Fish robot, which is a new type of underwater biomimetic robot, has attracted great attention because of its silence in moving and energy efficiency compared to conventional propeller-oriented propulsive mechanism. However, most of researches on fish robots have been carried out via empirical or experimental approaches, not based on dynamic optimality. In this paper, we proposed an analytical optimization approach which can guarantee the maximum propulsive velocity of fish robot in the given parametric conditions. First, a dynamic model of 3-joint (4 links) carangiform fish robot is derived, using which the influences of parameters of input torque functions, such as amplitude, frequency and phase difference, on its velocity are investigated by simulation. Second, the maximum velocity of the fish robot is optimized by combining Genetic Algorithm (GA) and Hill Climbing Algorithm (HCA). GA is used to generate the initial optimal parameters of the input functions of the system. Then, the parameters are optimized again by HCA to ensure that the final set of parameters is the “near” global optimization. Finally, both simulations and primitive experiments are carried out to prove the feasibility of the proposed method.

Underwater autonomous manipulation for intervention missions AUVs

Many underwater intervention tasks are today performed using manned submersibles or remotely operated vehicles in teleoperation mode. Autonomous underwater vehicles are mostly employed in survey applications. In fact, the low bandwidth and significant time delay inherent in acoustic subsea communications represent a considerable obstacle to remotely operate a manipulation system, making it impossible for remote controllers to react to problems in a timely manner. Nevertheless, vehicles with no physical link and with no human occupants permit intervention in dangerous areas, such as in deep ocean, under ice, in missions to retrieve hazardous objects, or in classified areas. The key element in underwater intervention performed with autonomous vehicles is autonomous manipulation. This is a challenging technology milestone, which refers to the capability of a robot system that performs intervention tasks requiring physical contacts with unstructured environments without continuous human supervision. Today, only few AUVs are equipped with manipulators. SAUVIM (Semi Autonomous Underwater Vehicle for Intervention Mission, University of Hawaii) is one of the first underwater vehicle capable of autonomous manipulation. This paper presents the solutions chosen within the development of the system in order to address the problems intrinsic to autonomous underwater manipulation. In the proposed approach, the most noticeable aspect is the increase in the level of information transferred between the system and the human supervisor. We describe one of the first trials of autonomous intervention performed by SAUVIM in the oceanic environment. To the best knowledge of the authors, no sea trials in underwater autonomous manipulation have been presented in the literature. The presented operation is an underwater recovery mission, which consists in a sequence of autonomous tasks finalized to search for the target and to securely hook a cable to it in order to bring the target to the surface.

マニピュレータを搭載した水中ロボットの開発

We have been developing an autonomous underwater vehicle (AUV) with a manipulator aiming at underwater operations using AUVs.At first, we describe an underwater manipulator which is designed based on motion control simulation and the modular concept. From the results of simulation, the specifications of the manipulator such as maximum torque and velocity are decided.As the waterproof mechanism of the manipulator, we introduced the magnet coupling structure to transfer motor torque from inside motor to outside gear. And the modular concept is introduced to realize reliability and good maintenance. Each link of manipulator has the same structure and includes a motor and a motor driver inside. Multi degree of freedom manipulator can be realized by combining same link modules. The modular concept is introduced into the AUV design, such that a functional device can be plugged into a matherboard to be less-wiring. Finally, the experimental results using an AUV with a manipulator are discussed.

Control of an underwater manipulator mounted for an AUV considering dynamic manipulability

In this paper, kinematics, dynamics and trajectory routing algorithm of a 2-link underwater manipulator of an AUV (Autonomous Underwater Vehicle) “Twin-Burger” are discussed considering the dynamic manipulability and the interaction between the manipulator and the AUV. As the control system, the RAC (Resolved Acceleration Control) method is introduced. In order to evaluate the efficiency of the proposed method, the numerical simulation is carried out including the effect of hydrodynamic forces. Also, an underwater manipulator is designed using a CAD/CAM system and realized by the waterproof mechanism based on magnet coupling.

1P1-E26 マニピュレータを搭載したAUVの開発 : 第一報 : 水中用マニピュレータの開発と制御

In this paper, we discuss a manipulator for underwater robots. The Waterproof-Mechanism was one of most important componets for developing underwater mechanisms. And an underwater manipulator is designed using a CAD/CAM system and realized by the waterproof mechanism based on magnet coupling. Finally, we develop underwater manpulator and equip Autonomous Underwater Vehicle (AUV) with it.

USING ARTICULATED BODY ALGORITHM WITHIN SLIDING-MODE CONTROL TO COMPENSATE DYNAMIC COUPLING IN UNDERWATER-MANIPULATOR SYSTEMS

A control scheme is presented for compensating dynamic coupling between an underwater robotic vehicle (URV) and a manipulator. During task execution the torques commanded at the manipulator joints lead to reactions at the junction point of the manipulator and vehicle. These reactions disturb the vehicle position and orientation and are the source of the vehicle-manipulator coupling. In many underwater robotic vehicle-manipulator (URVM) applications, the URV serves as a base while the manipulator performs a required task. Therefore, it is necessary to hold the URV as stationary as possible. In the current work, Slotine’s sliding mode control approach is used to compensate the dynamic effect of the underwater manipulator on the URV. The articulated body (AB) algorithm is used both for the time-domain simulation of the system and for the dynamic equations within the model-based sliding-mode controller. The AB algorithm is preferred for the time-domain system simulation, as it provides a computationally efficient simulation scheme. Finally, a three DOF manipulator mounted on a URV is considered, and results of time-domain numerical simulations of the proposed control scheme are presented.

수중로봇팔의 동역학 모델링과 동적 조작도 해석

This paper describes dynamic manipulability analysis of robotic arms moving in viscous fluid. The manipulability is a functionality of manipulator system in a given configuration under the limits of joint ability with respect to the task required to be performed. To investigate the manipulability of underwater robotic arms, a modeling and analysis method is presented. The dynamic equation of motion of underwater manipulator is derived based on the Lagrange-Euler equation considering with the hydrodynamic forces caused by added mass, buoyancy and hydraulic drag. The hydrodynamic drag term in the equation is established as analytical form using Denavit-Hartenberg (D-H) link coordination of manipulator. Two analytical approaches based oil manipulability ellipsoid are presented to visualize the manipulability of robotic arm moving in viscous fluid. The one is scaled ellipsoid which transforms the boundary of joint torque to acceleration boundary of end-effector by normalizing the torques in joint space, while the other is shifted ellipsoid which depicts total acceleration boundary of end-effector by shifting the ellipsoid as much as gravity and velocity dependent forces in work space. An analysis example of 2-link manipulator with proposed analysis scheme is presented to validate the method.

A hierarchical real-time control architecture for a semi-autonomous underwater vehicle

This paper describes a real-time control architecture for Dual Use Semi-Autonomous Underwater Vehicle (DUSAUV), which has been developed at Korea Research Institute of Ships and Ocean Engineering (KRISO) for being a test-bed of development of underwater navigation and manipulator technologies. DUSAUV has three built-in computers, seven thrusters for six DOF motion control, one 4-function electric manipulator, one ballasting motor, built-in power source, and various sensors. A supervisor control system with GUI and a multi-purpose joystick is mounted on the surface vessel and communicates with vehicle through a fiber optic link. Furthermore, QNX, one of real-time operating system, is ported on the built-in control and navigation computers for real-time control purpose, while Microsoft OS product is ported in the supervisor computer for GUI programming convenience. A hierarchical control architecture, which consists of application layer, real-time layer and physical layer, has been developed for efficient control system of above complex underwater robotic system. The experimental results with implementation of the layered control architecture for various motion control of DUSAUV in an ocean engineering basin of KRISO is also presented.

The optimum dimensioning of an underwater manipulator for weld inspection

The optimum dimensioning of an underwater inspection manipulator is discussed in this paper. The inspection of a weld seam using an alternating current field measurement (ACFM) probe was identified as a five-dimensional Cartesian task. Due to the forward positioning of the required workspace, this manipulator requires two additional axes to locate its base with respect to the weld seam. This leads to a seven-axis manipulator, comprising a two-axis launching stage and a five-axis dexterous inspection stage. The optimization of the architecture of the latter five-axis inspection manipulator is the subject of this paper. In optimizing the architecture, various postures of the manipulator during the inspection process were considered, which thus allows identification of the limiting values of the joint angles for maximum dexterity. The optimum link lengths to ensure the highest dexterity were then determined from the results of the analysis. It is shown that the weld seam diameter and the manipulator condition number can be used as the deciding parameters for determining the relative link lengths of the five-axis inspection stage of the manipulator.

The optimum dimensioning of an underwater manipulator for weld inspection

The optimum dimensioning of an underwater inspection manipulator is discussed in this paper. The inspection of a weld seam using an alternating current field measurement (ACFM) probe was identified as a five-dimensional Cartesian task. Due to the forward positioning of the required workspace, this manipulator requires two additional axes to locate its base with respect to the weld seam. This leads to a seven-axis manipulator, comprising a two-axis launching stage and a five-axis dexterous inspection stage. The optimization of the architecture of the latter five-axis inspection manipulator is the subject of this paper. In optimizing the architecture, various postures of the manipulator during the inspection process were considered, which thus allows identification of the limiting values of the joint angles for maximum dexterity. The optimum link lengths to ensure the highest dexterity were then determined from the results of the analysis. It is shown that the weld seam diameter and the manipulator condition number can be used as the deciding parameters for determining the relative link lengths of the five-axis inspection stage of the manipulator.

Kinematic Design and Analysis of a 7 Degree-of-Freedom Dual-Stage Inspection Manipulator for Dexterous Subsea Applications

This paper describes the design of a 7 degree-of-freedom (d.o.f) manipulator for underwater inspection applications. The functional requirements of an underwater manipulator for subsea inspection are discussed and the desired performance requirements identified. The inspection process of a weld joint using a manipulator is described and the desirable attributes of a 5 d.o.f manipulator for the inspection process established. A novel kinematic structure, for Underwater Robotic Vehicle (URV) operation, having a 2 d.o.f launching stages and a 5 d.o.f inspection stage is proposed for the manipulator. This configuration increases the dexterity, without compromising on the total reach of the manipulator. The kinematic structure of the 7 d.o.f, 2 stage, manipulator is presented. A hybrid power actuation is proposed for the manipulator to exploit the benefits of both hydraulic as well as electric actuators. Kinematic analysis of the manipulator is presented. The link dimensions of the inspection stage manipulator is done on the basis of kinematic performance indices of the manipulator. The novel kinematic structure and the hybrid power actuation strategy results in a power efficient, dexterous manipulator for underwater applications.

水中ロボットの現状と課題 水中マニピュレータの動作計画

In this paper, a motion planning method for underwater manipulator is considered. Generally, there are some obstacles such as rock, submarine ridges and so on in the work area of underwater manipulators. The manipulators have to work carefully with avoiding these obstacles. Therefore, the aim of this paper is to propose a method that generates the secure moving path of the tip of the manipulator and the manipulator's posture that avoid obstacles in the work area. The work area considered this paper is divided into some cubes. The position of the obstacles is defined as the position of the cube. The path of the tip of the manipulator is also derived as the set of positions of the cubes. In order to generate the path, we use the Genetic Algorithm (GA) that gives quasi-optimal path. On the other hand, the posture of the manipulator is derived by inverse kinematics after generating the path of the tip of the manipulator. Since the manipulator considered this paper is for underwater robots, the effect of the drag force is also considered when the posture of the manipulator is decided. Our proposed motion planning method that combines the path and the posture plan-ning is repeated every sampling time. The effectiveness of our method is shown by several experiments using a 7 degree-of-freedom manipulator.

THE MOTION PLANNING FOR UNDERWATER MANIPULATORS DEPEND ON GENETIC ALGORITHM

An approach for the motion planning of an underwater manipulator is described in this paper. This approach is composed of the path planning of the tip of the manipulator and the posture planning of the manipulator. In order to execute each planning, two kinds of Genetic Algorithm is used in this approach. One is used to generate the suitable path. The other is used to generate candidates for secure manipulator's postures. And one secure manipulator's posture is decided from among generated candidates, by an evaluation considering the drag force.

Experiments on a floating underwater robot with a two-link manipulator

This article concerns experiments with a free-floating underwater robot with a two-dimensional, horizontal planar, two-link manipulator. Some dynamic models of underwater manipulators have been proposed, but only a few experiments have been carried out. Here, we derive a dynamic model for a free-floating underwater robot with a two-link manipulator, including the hydrodynamic forces, and validate the effectiveness of the model by simulation and experiment. We also show an experimental result using a resolved acceleration control method. These experimental results show the effectiveness the model and the control method.

A unified force control approach to autonomous underwater manipulation

A unified force control scheme for an autonomous underwater robotic system is proposed in this paper. This robotic system is composed of a six degree-of-freedom autonomous underwater vehicle (AUV) and a robotic arm that is mounted on the AUV. A unified force control approach, which combines impedance control with hybrid position/force control by means of fuzzy switching to perform autonomous underwater manipulation, is presented in this paper. This controller requires a dynamic model of the underwater vehicle-manipulator system. However, it does not require any model of the environment and therefore will have the potential to be useful in underwater tasks where the environment is generally unknown. The proposed approach combines the advantages of impedance control with hybrid control so that both smooth contact transition and force trajectory tracking can be achieved. In the absence of any functional autonomous underwater vehicle-manipulator system that can be used to verify the proposed controller, extensive computer simulations are performed and the results are presented in the paper.

Disturbance observer-based robust control for underwater robotic systems with passive joints

Underwater exploration requires mobility and manipulation. Underwater robotic vehicles (URV) have been employed for mobility, and robot manipulators attached to the underwater vehicle (i.e. rover) perform the manipulation. Usually, the manipulation mode takes place when the rover is stationary. The URV is then modeled as a passive joint and joints of the manipulator are modeled as active joints. URV motions are determined by inherent dynamic couplings between active and passive joints. Furthermore, the control problem becomes complex since there are many hydrodynamic terms as well as intrinsic model uncertainties to be considered. Tocope with these difficulties, we propose a disturbance observer-based robust control algorithm for underwater manipulators with passive joints. The proposed control algorithm is able to treat an underactuated system as a pseudo-active system in which passive joints are eliminated. Also, to realize a robust control method, a non-linear feedback disturbance observer is applied to each active joint. A four-jointed underwater robotic system with one passive joint is considered as an illustrative example. Through simulation, it is shown that the proposed control algorithm has good position tracking performance even in the presence of several external disturbances and model uncertainties.