Jin-Yeong Park

A new concept and technologies of multi-legged underwater robot for high tidal current environment

In this paper, we present a new concept of multi-legged seabed robot for high tidal current environment. The robot moves on seabed by walking with 4 or 6 legs which is different moving mechanism from the existing underwater thrust system such as screw or Caterpillar. The main concept to endure the high current is utilization of hydrodynamic forces acting on the body and legs. The advantage of this concept is that the robot is able to have high stability in positioning as well as that the robot is less disturbs the seabed environment than other thrust system. In order to optimize the configuration of the leg with respect to tidal current, an optimization problem is formulated. And a simplified model of hydrostatic and hydrodynamic forces acting on the legs is presented. Presented model can be used for optimization of body and leg configurations, and for drag-optimal path planning of legs. Because the shape of leg is a main factor to the hydro dynamic forces, a design of slender leg is also presented in this paper.

Experiment on Underwater Docking of an Autonomous Underwater Vehicle `ISiMI' using Optical Terminal Guidance

An AUV (Autonomous Underwater Vehicle) being able to dock without surfacing to a launcher or an underwater station can give us long-time duration. It is important for the AUV to be guided to the dock safely. This paper introduces a test bed platform AUV named ISiMI and her optical terminal guidance system. ISiMI uses the optical terminal guidance system for underwater docking. The guidance system consists of a hardware part and a software part. One CCD camera and a frame grabber constitute the hardware part. An image process and a final approach algorithm based on visual servo control are the software part. A dock center which is a final approach target position of ISiMI is estimated by the image process and a reference yaw and pitch are generated by the final approach algorithm. We developed, also, an auxiliary controller to reinforce the final approach algorithm. This additional controller is necessary because there is an area where ISiMI cannot see the target lights near the dock. This makes the performance of docking better. Underwater docking experiments were conducted and the results are included in this paper.

Modified linear terminal guidance for docking and a time-varying ocean current observer

Unidirectional docking of a torpedo-type underactuated AUV (Autonomous Underwater Vehicle) has been developed. In this paper, guidance scheme considering drift caused by ocean currents will be investigated. To compensate drift, we design an ocean current observer. The observer is based on kinematic equations of the AUV. We also suggest a guidance scheme based on linear terminal guidance using the observer. The LTG (Linear Terminal Guidance) is in the framework of optimal control but there is no compensation against external disturbances. The conventional linear terminal guidance is modified to be adapted to unidirectional docking compensating the effect of ocean currents. Simulation results are also included.

An In-situ Correction Method of Position Error for an Autonomous Underwater Vehicle Surveying the Sea Floor †

Abstract This paper presents an in-situ correction method to compensate for the position error of an autonomous under-water vehicle (AUV) near the sea floor. AUVs generally have an inertial navigation system assisted with auxiliary navigational sensors. Since the inertial navigation system shows drift in position without the bottom reflection of a Doppler velocity log, external acoustic positioning systems, such as an ultra short baseline (USBL), are needed to set the position without surfacing the AUV. The main concept of the correction method is as follows: when the AUV arrives near the sea floor, the vehicle moves around horizontally in a circular mode, while the USBL tran-sceiver installed on a surface vessel measures the AUVs position. After acquiring one data set, a least-square curve fitting method is adopted to find the center of the AUVs circular motion, which is transferred to the AUV via an acoustic telemetry modem (ATM). The proposed method is robust for the outlier of USBL, and it is inde-pendent of the time delay for the data transfer of the USBL position with the ATM. The proposed method also reduces the intrinsic position error of the USBL, and is applicable to the in-situ calibration as well as the initializa-tion of the AUVs’ position. Monte Carlo simulation was conducted to verify the effectiveness of the method.

Underwater docking approach of an under-actuated AUV in the presence of constant ocean current

Abstract Underwater docking of an AUV (Autonomous Underwater Vehicle) provides a means of data transmit and battery recharge to extend the endurance capability of the vehicle. In this paper, we consider a torpedo-shaped under-***actuated vehicle and a funnel-shaped unidirectional docking station. The problem is that the desired heading to approach to the docking station compensating the effect of ocean current is different from the desired heading to be aligned to the direction of the dock entrance. We propose final approaching and guidance scheme in the terminal phase of underwater docking considering the effect of ocean current. A conventional PID controller for path following and a bang-bang controller for the final alignment are adopted. Switching criterion between two controllers is proposed. Simulation was carried out to validate the proposed scheme and results are included.

Development of Test-Bed AUV 'ISiMI' and Underwater Experiments on Free Running and Vision Guided Docking

In this chapter, development of a test-bed AUV is described. Free running test and vision guided docking are also presented. Autonomous underwater vehicles (AUVs) have become a main tool for surveying below the sea in scientific, military, and commercial applications because of the significant improvement in their performance. Despite the considerable improvement in AUV performance, however, AUV technologies are still attractive to scientists and engineers as a challenging field. For example, multiple AUVs and underwater docking are recent challenging issues in the field of AUV technologies (Edwards et al., 2004; Fiorelli et al., 2004; Stokey et al., 2001; Singh et al., 2001). To successfully implement these new technologies in the field, a number of sub-functions have to be tested and verified in advance. They could be control, navigation and communication functions as well as basic functions for AUVs, including an emergency architecture for survival. Since it would be very expensive and time consuming to conduct all these tests at sea, researchers and engineers engaged in the operation and development of underwater vehicles need easier test schemes and faster feedback of results in an environment similar to that of the sea. Underwater docking of an AUV to a launcher without surfacing allows the AUV have longer and more frequent investigations. Data uploading, mission downloading and recharge of batteries are essential duties of docking systems. Many research institutes have developed docking systems for AUVs. An ElectroMagnetic homing (EM) system was proposed as one of them (Feezor et al., 1997). A magnetic field generated by coils on the dock was used in that system. An AUV sensed this magnetic field and was guided to the dock. The range of the EM system was limited to 25-30m. An optical terminal guidance system was also introduced (Cowen et al., 1997). That system was simple but highly effective. The optical docking system provided targeting accuracy on the order of 1 cm under real-world conditions, even in turbid bay water. Autonomous docking demonstrations using an ultra-short baseline (USBL) acoustic homing array were shown in (Allen et al., 2006). The acoustic system was capable of acquiring a dock-mounted transponder at ranges of 3,000m or more. O pe n A cc es s D at ab as e w w w .in te ch w eb .o rg

Measurement of hydrodynamic forces and moment acting on Crabster, CR200 using model tests

Crabster CR200 is a remotely operated vehicle which has six artificial and articulated legs driven by BLDC motors. It is supposed to walk on the sea floor. As a result, the robot has a very complicated appearance and hydrodynamic forces and moment acting on the robot experience a variety of changes according to configurable legs and body postural position. This paper describes the experiments to estimate lift force, drag force and pitching moment acting on CR200 using a 1/4 length ratio scaled model. A 6-axis Force/Torque sensor was adopted and installed in the middle of inner space of the model to measure the forces and moment. The experiments were conducted in a circulating water channel whose width and depth are 3.5m and 3.0m, respectively. To define hydrodynamic characteristics effected by the floor, the authors approached in two ways. The first is that CR200 was assumed to stand on the ground. The other is when the robot is placed in the middle of stream of water flow.

Multi-legged ROV Crabster and an acoustic camera for survey of underwater cultural heritages

In west coast of Korea peninsula, there are some offshore sites where ancient sunken shipwrecks have been discovered. These ships are supposed to carry an amount of artifacts what show lifestyle and culture of the day. In these areas, however, because of fast ocean currents and low visibility, underwater survey and excavation by divers are strictly restricted. Especially, optical cameras and humans visual inspection become defective. To overcome these conditions, use of unmanned underwater vehicles such like a ROV(Remotely Operated Vehicle) which is equipped with acoustic imaging devices has been raised. This paper describes preliminary performance experiments for survey of underwater cultural heritages using a ROV whose name is Crabster driven by six artificial legs with a high-resolution acoustic camera in sea. The Crabster uses the six articulated legs actuated by BLDC motors as its thrusters. Therefore, it moves on the sea floor without disturbances by propellers which are widely used as thrusters of any other general ROVs. In addition, The robot is expected to minimize shadow areas of acoustic imaging sensors by controlling its body posture precisely using the legs. In this paper, we introduce operations of Crabster and the acoustic imaging devices when we conducted from April to May in 2015. Using acoustic imaging devices, we could find dispersed potteries and iron caldrons. Mosaicked image to show surround of the robot is also included.

Multi-beam Echo Sounder Operations for ROV Hemire - Exploration of Mariana Hydrothermal Vent Site and Post-Processing

This paper presents the operations of a multi-beam echo sounder (MBES) installed on the deep-sea remotely operated vehicle (ROV) Hemire. Hemire explored hydrothermal vents in the Forecast volcano located near the Mariana Trench in March of in 2006. During these explorations, we acquired profiling points on the routes of the vehicle using the MBES. Information on the position, depth, and attitude of the ROV are essential to obtain higher accuracy for the profiling quality. However, the MBES installed on Hemire does not have its own position and depth sensors. Although it has attitude sensors for roll, pitch, and heading, the specifications of these sensors were not clear. Therefore, we had to merge the high-performance sensor data for the motion and position obtained from Hemire into the profiling data of the MBES. Then, we could properly convert the profiling points with respect to the Earth-fixed coordinates. This paper describes the integration of the MBES with Hemire, as well as the coordinate conversion between them. Bathymetric maps near the summit of the Forecast volcano were successfully collected through these processes. A comparison between the bathymetric maps from the MBES and those from the Onnuri Research Vessel, the mother ship of the ROV Hemire for these explorations, is also presented. Received 4 July 2016, revised 8 February 2017, accepted 10 February 2017 Corresponding author Jin-Yeong Park: +82-42-866-3835, jinyeong96@kriso.re.kr c 2017, The Korean Society of Ocean Engineers This is an open access article distributed under the terms of the creative commons attribution non-commercial license (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Navigation System for a Deep-sea ROV Fusing USBL, DVL, and Heading Measurements

This paper presents an integrated navigation system that combines ultra-short baseline (USBL), Doppler velocity log (DVL), and heading measurements for a deep-sea remotely operated vehicle, Hemire. A navigation model is introduced based on the kinematic relation of the position and velocity. The system states are predicted using the navigation model and corrected with the USBL, DVL, and heading measurements using the Kalman filter. The performance of the navigation system was confirmed through re-navigation simulations with the measured data at the Southern Mariana Arc submarine volcanoes. Based on the characteristics of the measurements, the design process for the parameters of the system modeling error covariance, measurement error covariance, and initial error covariance are presented. This paper reviews the influence of the outliers and blackout of the USBL and DVL measurements, and proposes an outlier rejection algorithm that is robust to USBL blackout. The effectiveness of the method is demonstrated with re-navigation for the data that includes USBL blackouts. Received 3 May 2017, revised 16 May 2017, accepted 28 July 2017 Corresponding author Pan-Mook Lee: +82-42-866-3810, pmlee@kriso.re.kr c 2017, The Korean Society of Ocean Engineers This is an open access article distributed under the terms of the creative commons attribution non-commercial license (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.