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Distance Measurement System using A Stereo Camera and Radial Pattern Target for Automatic Berthing Control
Abstract
In this paper, we propose a distance measurement system for automatic berthing control using a stereo camera mounted on a rotation control device, and a radial pattern target. Automatically controlling the position and attitude of a ship aims to prevent maritime accidents due to human error. Our goal is to measure the relative distance between a ship and an onshore or offshore target for berthing. Therefore, the distance should be continuously measured while tracking a fixed point on a target. To this end, we developed a stereo camerabased distance measurement system that satisfied these requirements. This paper describes the structure and principle of the measurement system. We validate the distance error for target incline due to the relative position and attitude between a camera and a target in miniature scale. In addition, the findings of an experiment in an outdoor environment demonstrate that the proposed measurement system has accuracy within 1 m at a range of 20-100 m which is the acceptable accuracy for automatic berthing.
... The first system was described by [10] where a distance measurement system includes stereo camera and radial pattern. To find out the distance from ship to berth and distance from ship to one target on wharf line, two cameras will be controlled to capture the target on same point in their lens. ...
In the studies on an berthing control of ship, an artificial neural network (ANN) model is commonly employed as the main controller to control the rudder and the propeller. The existing ANN controllers that use the parameters consisting of the ship position and the ship heading as inputs cannot be applied to control automatically the ship into berth in different ports. To deal with this problem, the parameters, such as relative bearing and distance from ship to berth calculated by radar can be used as inputs for the controller. However, the calculation of these factors is not accurate because some errors arise on using radar for berthing process. This leads to the lack of confidence in ship berthing system using the parameters determined by radar. In this research, the neural network based-automatic berthing system is developed for ship by using the parameters which are measured by distance measurement system. By this proposed system, the ship is brought automatically into berth in different ports without retraining the neural network. In addition, this system guarantees that the parameters used for inputs of the neural network is measured exactly and continually. To validate the proposed algorithm, numerical simulations are carried out to two imaginary ports and a real port, and result showed the good performance of the proposed system for automatic ship berthing.
... The first system was described by [10] where a distance measurement system includes stereo camera and radial pattern. To find out the distance from ship to berth and distance from ship to one target on wharf line, two cameras will be controlled to capture the target on same point in their lens. ...
In the studies on an berthing control of ship, an artificial neural network (ANN) model is
commonly employed as the main controller to control the rudder and the propeller. The existing
ANN controllers that use the parameters consisting of the ship position and the ship heading
as inputs cannot be applied to control automatically the ship into berth in different ports. To
deal with this problem, the parameters, such as relative bearing and distance from ship to
berth calculated by radar can be used as inputs for the controller. However, the calculation
of these factors is not accurate because some errors arise on using radar for berthing process.
This leads to the lack of confidence in ship berthing system using the parameters determined
by radar. In this research, the neural network based-automatic berthing system is developed
for ship by using the parameters which are measured by distance measurement system. By
this proposed system, the ship is brought automatically into berth in different ports without
retraining the neural network. In addition, this system guarantees that the parameters used for
inputs of the neural network is measured exactly and continually. To validate the proposed
algorithm, numerical simulations are carried out to two imaginary ports and a real port, and
result showed the good performance of the proposed system for automatic ship berthing.
... The authors have been proposed vision-based system for relative position and heading measurement [6]. However, this system also needs the installation of specific landmarks for measuring the distance between a vessel and a target [7][8][9]. ...
This paper presents a technique for quickly and accurately measuring the position and heading of a vessel for relative vessel positioning at close distances to a target. To this end, we propose a measurement system that consists of camera units and landmarks. This system calculates the position and heading based on the distance and angle between the camera units on the vessel’s side and landmarks on the target’s side. Cameras with a high frame rate, wide sensing range, and excellent angular resolution are employed as sensors for measuring the position and heading, rather than GPS, radar, or lasers. A pattern-matching method based on the intensity gradient is developed in order to provide the proposed system with a fast response time. Correction methods for the distance measured by the camera unit and installation errors are also proposed to improve the accuracy of the measurement. We evaluated the accuracy of the proposed system using several positional relations between the camera units and landmarks. We demonstrate that the proposed system can accurately measure the position and heading of a vessel, despite the vessel’s roll and pitch motion as a result of waves.
... The authors have been proposed vision-based system for relative position and heading measurement [6]. However, this system also needs the installation of specific landmarks for measuring the distance between a vessel and a target [7][8][9]. ...
Themeasurement of relative vessel positioning is important to prevent the risk of vessel collision or the deterioration of working efficiency. This study presents a vision-based system for measuring the relative position and heading between a vessel and a target object without the installation of transponders, reflectors, or markers. Such a markerless measurement system, which is not restricted by the presence or the absence of transponders, is a method of expanding feasible conditions for relative vessel positioning. The proposed system consists of multiple camera units that can measure the distance and direction between an initially designated point on a target object while keep track of the designated point. To evaluate the measurement performance for the proposed system, the authors conducted measurements by using a prototype system in water. The results demonstrated that the system can keep track of the designated points and accurately measure the position and heading of a vessel relative to a target object, despite the vessel's roll motion.
... Because the hydrodynamic coefficients change a lot when the ship moves from open sea into harbor, a number of authors have sought to develop intelligent control strategies independent of the dynamic model. These include fuzzy 4,5) and artificial neural network [6][7][8][9] control theory, etc 10,11) . The other studies for ship berthing use optimal [12][13][14][15] and adaptive control theory 16) . ...
Everyday about 90% of cargos are delivered by ships, and thousands of vessels enter and depart the international container harbors such as Shanghai, Singapore, Hong Kong, Busan, Rotterdam, etc. Maneuvering at harbor is known as the most sophisticated and difficult procedure, because the effectiveness of actuators during low speed berthing is reduced. In this paper, a new berthing method is discussed. Tugboats are combined with damper systems to ensure safe berthing. A mathematical model describing the interaction between unactuated ship, tugboats and damper systems is presented. An optimal controller is designed to maneuver the ship without oscillation and overshoot. MCL (Marine Cybernetics Lab) model ship is used to evaluate the efficiency of the proposed approach through MatLab simulation.
Research on motion control systems for marine surface vessels has generated a vast academic literature and many industrial applications since the early 20th century. The recent focus on autonomous ships has sparked intensive research and innovation activities of dock-to-dock operations, including the final docking phase. Specifically, automated docking involves systems that enable vessels to dock safely, independently, and energy-efficiently at designated locations with a specific heading. Challenges include managing large sideslip angles, static and dynamic obstacles, and navigation in complex port geometries. Despite its complexity, the docking problem has received less attention compared to dynamic positioning or course-keeping systems. This paper therefore provides a thorough overview of the research on automated docking for marine surface vessels, from 1980 to June 2023. The paper introduces the Docking Characteristic Index (DCI) as a metric to identify the scope and approach of systems addressing various docking challenges, not as an evaluation of their overall quality. Using the calculated DCI-Scores, we discuss some of the works in more detail. The survey reveals a rising trend in publications and an increasing emphasis on experimental verification. Despite advancements, current methodologies exhibit trade-offs and limitations, particularly in handling dynamic obstacles, robustness against external forces, and situational awareness. The paper identifies the need for more comprehensive and integrated solutions to these challenges. As the demand for fully autonomous operations grows, the results suggest that future research should focus on developing holistic and robust docking strategies, that are verified experimentally, to achieve safe, efficient, and effective automated docking systems.
This paper describes a distance measurement system with high accuracy that utilizes a stereo-based camera and a pan-tilt unit for automatically maintaining the positional relationship between a vessel and a target on the side of a facility at a close range. The measurement system offers an advantage in that it can measure the distance to a target while tracking it. In order to improve the ability to control the position of a vessel between it and a target while maintaining the distance especially at a close range, the accuracy of the measurement system has to be improved. The accuracy of the distance measured by our system is increased with revisions of the conclusively generated data of distance measurement. We verified the accuracy of our system from an experiment, which generated results that had an accuracy of 30 mm for distances in the range between 2-8 m.
High speed and efficiency are highly important factors in handling cargo at ports. The ability to handle cargo at high speed
strongly depends on the anti-sway system employed. However, it is not easy to realize a high-performance anti-sway control
system due to a number of problems. High-speed operation of container cranes is continuously required for crane operators
who work as cargo handlers at ports. Undesirable motion can lower the work efficiency due to the prolonged strain to which
operators are subjected. To overcome this problem, we propose an anti-sway system with an image sensor for container cranes.
In this system, the image sensor is used for measuring the motion of the spreader, and the measured data are fed back to the
controller in real time. The applied image processing technique is a kind of robust template matching method referred to as
vector code correlation (VCC), which was devised in order to consider real environmental conditions. The anti-sway system
proposed in this paper is a mass damper type system in which a movable mass is installed on the spreader. The actuator acting
on the movable mass applies inertial force to the spreader, which results in suppressing undesirable sway motion. The system
is simple and can be easily applied to any crane system. In this regard, the useful features and the performance of the proposed
anti-sway system are experimentally verified.
This paper discusses the general concept of an automatic berthing system. The research considered the automatic berthing
of a large merchant ship. A global positioning system (GPS)-based system, which provides the necessary information on position,
velocity, attitude (roll, pitch, and heading), angular velocity, and time, was the principal sensor used. Field tests were
conducted on board a hydrographic sounding ship to assess the quality of information obtained from a GPS-based system. The
data were processed using the software with which the algorithms developed in this research were implemented. This paper also
discusses various aspects concerning a real-time GPS-based system in relation to an automatic berthing system, such as integration
of sensors, mathematical models, port infrastructure, and training of crews.
Speedy operation efficiency is constantly required of the container crane operators who work for cargo handling in the port. They are experts in suppressing the sway motion which is generated in the process of the handling. This undesirable motion may deteriorate the operation efficiency due to strained nerves of the operator. Therefore, an anti-sway controller has been required on practical job-site. To accomplish an adequate anti-sway control, sensors are also required to be able to measure the position of a crane spreader moving on. In this paper, we propose a position measurement system with an image sensor. The image sensor detects two devised landmarks attached to the upside surface of a spreader to measure the displacement and height to one. The image processing technique used for the sensor is a kind of robust template matching method, named vector code correlation (VCC), devised to consider the conditions of real environments. We employ the simple mechanism, so that the system can be easily applicable to existing container cranes. The details and performance of the measurement system are introduced together with the experimental results performed with the pilot system. We will also show that the system has the sufficient efficiency and accuracy for the use on practical job-site.
Recently, anti-sway systems for container crane spreaders have played an important role in efficiently handling cargo at terminals. A camera-based measurement system for the anti-sway systems, which consists of two reference marks on the upper surface of the spreader and a camera mounted on the crane's trolley, has been developed. However, the quality of the reference marks in images taken in bad weather such as mist, fog, and rain is degraded, and consequently, the measurement accuracy also deteriorates. To preserve measurement accuracy in bad weather, a rapid method for image restoration is needed. We propose a method that restores the quality of reference marks in images by modeling the degradation of the light intensity. The two constants in the model are estimated from the variances and averages of the intensities in two reference mark images extracted from two images taken at different heights of the spreader. The height of the spreader, as measured by the system, is also fed back into the restoration. The measurement accuracy attained by the method under simulated bad weather conditions is compared with the accuracy achieved in normal conditions. It is found that measurement accuracy is preserved, with only small errors of up to 1.39 mm under a swaying motion. The processing time of the method is 0.83 ms on average, which does not affect the measurement period of the system.
Accident database review of human-element concerns: what do the results mean for classification?
- C C Baker
- D B Macafferty
- C C Baker
- D B Macafferty