OCEANS 2013 MTS/IEEE Bergen: The Challenges of the Northern Dimension, 2013
ABSTRACT Different Terrain Based Navigation systems for underwater vehicles have already been pre... more ABSTRACT Different Terrain Based Navigation systems for underwater vehicles have already been presented, with experimentally validated results and consistent performance. However, these results are mostly based on the use of both high accuracy inertial navigation systems and high quality sonars. This article presents a study on Particle Filter algorithms that cope with peculiarities of Terrain Based Navigation for sensor limited systems. The focus is on the influence on several parameters, namely the process noise, the measurement noise and the number of the particles, and how these can improve the obtained results. Based on the results obtained by simulation, we present some conclusions relevant for the design of future implementation of the algorithms.
This paper presents the development and the experimental validation of a centralized coordination... more This paper presents the development and the experimental validation of a centralized coordination control scheme that is robust to communication constraints and individual tracking errors for a team of possibly heterogeneous marine vehicles. By assuming the existence of a lower level target tracking control layer, a centralized potential-field-based coordination scheme is proposed to drive a team of robots along a path that does not necessarily need to be defined a priori. Furthermore, the formation is allowed to hold its position (the vehicles hold their positions with regard to a static virtual leader), which is particularly appreciated in several marine applications. As it is important to guarantee stability and mission completion in adverse environments with limited communications, the centralized control scheme for coordination is constructed in a way that makes it robust to tracking errors and intermittent communication links. The study and developments presented in this paper are complemented with field experiments in which vehicles have coordinated their operation to keep in formation over a dynamic path and static points. This work considers two types of communication technologies. Firstly, standard high rate radio communications are used to drive the formation and, secondly, acoustic communications are employed to assess the performance and the robustness of the proposed approach to degraded and highly variable conditions.
The problem of homing a mobile robot to a given reference location under unknown relative and abs... more The problem of homing a mobile robot to a given reference location under unknown relative and absolute positions is addressed in this paper. This problem is easy to solve when all the position and kinematic variables are known or are observable, but remains a challenge when only range is measured. Its complexity further increases when variable and unknown drifts are added to the motion, which is typical for marine vehicles. Based on the range measurements, it is possible to drive the robot arbitrarily close to the reference. This paper presents a complete solution and demonstrates the validity of the approach based on the Lyapunov theory. The use of models, which are often affected by uncertainties and/or unmodeled terms, is intended to be minimal and only some constraints are imposed on the speed of the robot. We derive a control law that makes the robot converge asymptotically to the reference and prove its stability theoretically. Nevertheless, as it is well know, practical limitations on the actuation can weaken some properties of convergence, namely when the system dynamics require increasing actuation along the approach trajectory. We will demonstrate that the robot reaches a positively invariant set around the reference whose upper bound is determined. Finally, we conclude our work by presenting simulation and experimental data and by demonstrating the validity and the robustness of the method.
In this paper, we discuss the design aspects and the development of the MARES AUV, a 1.5m long ve... more In this paper, we discuss the design aspects and the development of the MARES AUV, a 1.5m long vehicle, weighting 32kg, designed and built at the University of Porto, Portugal. This vehicle is highly maneuverable, with the ability to move in the vertical plane, controlling pitch and vertical velocity; forward velocity can also be determined, anywhere between 0 and 2 m/s. MARES can easily integrate any new payload within reason, finding applications in a wide range of areas, such as pollution monitoring, scientific data collection, sonar mapping, underwater video or mine countermeasures.
The thermocline is a vertical transition layer in the water column with a strong impact on marine... more The thermocline is a vertical transition layer in the water column with a strong impact on marine biology, since it affects phytoplankton concentration and, hence, primary production. AUVs can play an important role in understanding this relationship, by sampling the relevant data, usually describing yo-yo patterns spanning the whole water column. In this paper we describe a reactive behavior implemented onboard a small sized AUV, to adapt depth in real time in order to maintain the vehicle in the vicinity of the thermocline and therefore increasing efficiency in the sampling process. Preliminary field tests show that the method is simple, robust and effective.
Autonomous Underwater Vehicles (AUVs) are routinely being used to provide the scientific communit... more Autonomous Underwater Vehicles (AUVs) are routinely being used to provide the scientific community with detailed ocean data at very reasonable costs. In typical operations, AUVs are programmed to follow pre-defined geo-referenced trajectories, while collecting the relevant information about the underwater environment, with a clear separation between navigation and payload sensors. Under the adaptive sampling paradigm, the AUVs are able to interpret some of the payload data in order to change the sampling pattern and concentrate measurements in the regions of interest. In this paper, we describe an implementation of such paradigm, in which a small sized AUV is able to process CTD data, in real time, and change depth in order to maintain tracking of the thermocline region. We demonstrate the developed algorithms with data from field experiments in a dam reservoir, which show a very good performance, even in very shallow waters with hardly detectable features. The implementation ensures the safety of the AUV, by resuming to standard yo-yo patterns if the thermocline is not detected.
Challenges and Paradigms in Applied Robust Control, 2011
Control theory has been applied to several domains where practical considerations are relevant. R... more Control theory has been applied to several domains where practical considerations are relevant. Robotics is a notable example of this. In most cases, mobile robotic systems are governed such that their behavior obeys to a defined motion. However, during their ...
In this paper, we present an approach to control an autonomous underwater vehicle in the vertical... more In this paper, we present an approach to control an autonomous underwater vehicle in the vertical and the horizontal planes while pitching down or up (θ = ±π/2). Such a capability is explored in MARES, a small-sized, torpedo-shaped hovering AUV with four degrees of freedom. Despite the fact that roll angle is not controllable, we find a guidance law that makes the vehicle reach any point in the horizontal plane while maintaining the vehicle in the vertical position.
2013 IEEE International Underwater Technology Symposium, UT 2013, 2013
In opposition to the surface, no common solution is available for localization of active objects ... more In opposition to the surface, no common solution is available for localization of active objects underwater. Typical solutions use acoustics as a means to implicitly measure ranges or angles and consequently determine the position of a transmitter. If the receivers are synchronized among themselves, the position of the transmitter can be estimated based on the time-of-arrivals (TOA). The confidence on the estimate varies with respect to the relative positions of the receivers and the transmitter. In this paper, we present recent developments for optimal 3D positioning of TOA sensors based on the a metric that uses the Fisher information matrix. We give the necessary conditions to obtain the best possible estimate. To our best knowledge, no analytical solution has been yet presented for this problem. We complete and validate our study with a simulation of optimal positioning of four TOA sensors.
2013 IEEE International Underwater Technology Symposium, UT 2013, 2013
The design of an Autonomous Underwater Vehicle (AUV) is governed by a complex tradeoff between mi... more The design of an Autonomous Underwater Vehicle (AUV) is governed by a complex tradeoff between mission performance and required payload sensors, and taking into account possible constraints in fabrication, assembly and operational logistics. On a commercial level, the technology is relatively mature, with several companies offering off-the-shelf AUV solutions in a wide range of sizes and performance levels, for a wide variety of operational scenarios. However, to ensure proper performance in specific applications, such broad-range systems require factory customization, with the consequent impact in time and cost. This paper describes a program for the development of underwater vehicles based on modular building blocks. In this case, modularity encompasses both physical parts and also software and control systems. These modules can be rearranged, replaced or individually redesigned to yield a great variety of AUV configurations in a relatively short time. The paper describes the development of MARES, a small hovering AUV, and also TriMARES, a custom 3-body hybrid AUV/ROV, built from the same modules in little over 6 months.
This paper addresses the development of a new generation of lightweight intelligent buoys. These ... more This paper addresses the development of a new generation of lightweight intelligent buoys. These buoys are used to support underwater acoustic positioning systems, but were also designed to be elements of portable coastal observatories for short term deployments. We will present the main features of a buoy prototype including the physical structure, the computational system and algorithms developed to support operations. The paper also shows how to take advantage of this new tool to implement different navigation algorithms for AUVs.
Journal of Automation and Control Engineering, 2013
A new and fast methodology is discussed as a solution to pinpointing the location of a robot, in ... more A new and fast methodology is discussed as a solution to pinpointing the location of a robot, in a robust way, without environment preparation, even in dynamic scenarios. This solution does not require a high computational power. The methodology is a threedimensional map based approach, which uses the 3D map of the surrounding environment and data acquired by a tilting Laser Range Finder (LRF), to pinpoint the robot pose. Experimental results about the accuracy of the proposed method are presented in this paper. Index Terms-robot localisation, 3D matching, EKF-SLAM, laser range finder
2009 35th Annual Conference of IEEE Industrial Electronics, 2009
This paper describes the interaction between the kinematic model of the AUV MARES and the measure... more This paper describes the interaction between the kinematic model of the AUV MARES and the measurement or observation of the environment through images obtained with the Sonar use. Three types of sonar are discussed in this paper, they are forward-look, side scan and multibeam, but the sonar used to develop this work was the side scan sonar. The type of observations and characteristics of the environment provided by the sonar are described here. The method which connects the sensory part of the vehicle with the observations of the sonar, was the Kalman filter (EKF). In this paper, we present two simulations of filters for two different characteristics. Both filters estimate the characteristics of the natural landmarks, creating a environment map, but both of them consider different states of the vehicle. Results of the simulation are obtained. The features that are considered are an underwater pipe on the floor and a wall. It also generated a control for the vehicle that provides the capacity to move along the feature/landmark from a reference distance.
OCEANS 2013 MTS/IEEE Bergen: The Challenges of the Northern Dimension, 2013
ABSTRACT Different Terrain Based Navigation systems for underwater vehicles have already been pre... more ABSTRACT Different Terrain Based Navigation systems for underwater vehicles have already been presented, with experimentally validated results and consistent performance. However, these results are mostly based on the use of both high accuracy inertial navigation systems and high quality sonars. This article presents a study on Particle Filter algorithms that cope with peculiarities of Terrain Based Navigation for sensor limited systems. The focus is on the influence on several parameters, namely the process noise, the measurement noise and the number of the particles, and how these can improve the obtained results. Based on the results obtained by simulation, we present some conclusions relevant for the design of future implementation of the algorithms.
This paper presents the development and the experimental validation of a centralized coordination... more This paper presents the development and the experimental validation of a centralized coordination control scheme that is robust to communication constraints and individual tracking errors for a team of possibly heterogeneous marine vehicles. By assuming the existence of a lower level target tracking control layer, a centralized potential-field-based coordination scheme is proposed to drive a team of robots along a path that does not necessarily need to be defined a priori. Furthermore, the formation is allowed to hold its position (the vehicles hold their positions with regard to a static virtual leader), which is particularly appreciated in several marine applications. As it is important to guarantee stability and mission completion in adverse environments with limited communications, the centralized control scheme for coordination is constructed in a way that makes it robust to tracking errors and intermittent communication links. The study and developments presented in this paper are complemented with field experiments in which vehicles have coordinated their operation to keep in formation over a dynamic path and static points. This work considers two types of communication technologies. Firstly, standard high rate radio communications are used to drive the formation and, secondly, acoustic communications are employed to assess the performance and the robustness of the proposed approach to degraded and highly variable conditions.
The problem of homing a mobile robot to a given reference location under unknown relative and abs... more The problem of homing a mobile robot to a given reference location under unknown relative and absolute positions is addressed in this paper. This problem is easy to solve when all the position and kinematic variables are known or are observable, but remains a challenge when only range is measured. Its complexity further increases when variable and unknown drifts are added to the motion, which is typical for marine vehicles. Based on the range measurements, it is possible to drive the robot arbitrarily close to the reference. This paper presents a complete solution and demonstrates the validity of the approach based on the Lyapunov theory. The use of models, which are often affected by uncertainties and/or unmodeled terms, is intended to be minimal and only some constraints are imposed on the speed of the robot. We derive a control law that makes the robot converge asymptotically to the reference and prove its stability theoretically. Nevertheless, as it is well know, practical limitations on the actuation can weaken some properties of convergence, namely when the system dynamics require increasing actuation along the approach trajectory. We will demonstrate that the robot reaches a positively invariant set around the reference whose upper bound is determined. Finally, we conclude our work by presenting simulation and experimental data and by demonstrating the validity and the robustness of the method.
In this paper, we discuss the design aspects and the development of the MARES AUV, a 1.5m long ve... more In this paper, we discuss the design aspects and the development of the MARES AUV, a 1.5m long vehicle, weighting 32kg, designed and built at the University of Porto, Portugal. This vehicle is highly maneuverable, with the ability to move in the vertical plane, controlling pitch and vertical velocity; forward velocity can also be determined, anywhere between 0 and 2 m/s. MARES can easily integrate any new payload within reason, finding applications in a wide range of areas, such as pollution monitoring, scientific data collection, sonar mapping, underwater video or mine countermeasures.
The thermocline is a vertical transition layer in the water column with a strong impact on marine... more The thermocline is a vertical transition layer in the water column with a strong impact on marine biology, since it affects phytoplankton concentration and, hence, primary production. AUVs can play an important role in understanding this relationship, by sampling the relevant data, usually describing yo-yo patterns spanning the whole water column. In this paper we describe a reactive behavior implemented onboard a small sized AUV, to adapt depth in real time in order to maintain the vehicle in the vicinity of the thermocline and therefore increasing efficiency in the sampling process. Preliminary field tests show that the method is simple, robust and effective.
Autonomous Underwater Vehicles (AUVs) are routinely being used to provide the scientific communit... more Autonomous Underwater Vehicles (AUVs) are routinely being used to provide the scientific community with detailed ocean data at very reasonable costs. In typical operations, AUVs are programmed to follow pre-defined geo-referenced trajectories, while collecting the relevant information about the underwater environment, with a clear separation between navigation and payload sensors. Under the adaptive sampling paradigm, the AUVs are able to interpret some of the payload data in order to change the sampling pattern and concentrate measurements in the regions of interest. In this paper, we describe an implementation of such paradigm, in which a small sized AUV is able to process CTD data, in real time, and change depth in order to maintain tracking of the thermocline region. We demonstrate the developed algorithms with data from field experiments in a dam reservoir, which show a very good performance, even in very shallow waters with hardly detectable features. The implementation ensures the safety of the AUV, by resuming to standard yo-yo patterns if the thermocline is not detected.
Challenges and Paradigms in Applied Robust Control, 2011
Control theory has been applied to several domains where practical considerations are relevant. R... more Control theory has been applied to several domains where practical considerations are relevant. Robotics is a notable example of this. In most cases, mobile robotic systems are governed such that their behavior obeys to a defined motion. However, during their ...
In this paper, we present an approach to control an autonomous underwater vehicle in the vertical... more In this paper, we present an approach to control an autonomous underwater vehicle in the vertical and the horizontal planes while pitching down or up (θ = ±π/2). Such a capability is explored in MARES, a small-sized, torpedo-shaped hovering AUV with four degrees of freedom. Despite the fact that roll angle is not controllable, we find a guidance law that makes the vehicle reach any point in the horizontal plane while maintaining the vehicle in the vertical position.
2013 IEEE International Underwater Technology Symposium, UT 2013, 2013
In opposition to the surface, no common solution is available for localization of active objects ... more In opposition to the surface, no common solution is available for localization of active objects underwater. Typical solutions use acoustics as a means to implicitly measure ranges or angles and consequently determine the position of a transmitter. If the receivers are synchronized among themselves, the position of the transmitter can be estimated based on the time-of-arrivals (TOA). The confidence on the estimate varies with respect to the relative positions of the receivers and the transmitter. In this paper, we present recent developments for optimal 3D positioning of TOA sensors based on the a metric that uses the Fisher information matrix. We give the necessary conditions to obtain the best possible estimate. To our best knowledge, no analytical solution has been yet presented for this problem. We complete and validate our study with a simulation of optimal positioning of four TOA sensors.
2013 IEEE International Underwater Technology Symposium, UT 2013, 2013
The design of an Autonomous Underwater Vehicle (AUV) is governed by a complex tradeoff between mi... more The design of an Autonomous Underwater Vehicle (AUV) is governed by a complex tradeoff between mission performance and required payload sensors, and taking into account possible constraints in fabrication, assembly and operational logistics. On a commercial level, the technology is relatively mature, with several companies offering off-the-shelf AUV solutions in a wide range of sizes and performance levels, for a wide variety of operational scenarios. However, to ensure proper performance in specific applications, such broad-range systems require factory customization, with the consequent impact in time and cost. This paper describes a program for the development of underwater vehicles based on modular building blocks. In this case, modularity encompasses both physical parts and also software and control systems. These modules can be rearranged, replaced or individually redesigned to yield a great variety of AUV configurations in a relatively short time. The paper describes the development of MARES, a small hovering AUV, and also TriMARES, a custom 3-body hybrid AUV/ROV, built from the same modules in little over 6 months.
This paper addresses the development of a new generation of lightweight intelligent buoys. These ... more This paper addresses the development of a new generation of lightweight intelligent buoys. These buoys are used to support underwater acoustic positioning systems, but were also designed to be elements of portable coastal observatories for short term deployments. We will present the main features of a buoy prototype including the physical structure, the computational system and algorithms developed to support operations. The paper also shows how to take advantage of this new tool to implement different navigation algorithms for AUVs.
Journal of Automation and Control Engineering, 2013
A new and fast methodology is discussed as a solution to pinpointing the location of a robot, in ... more A new and fast methodology is discussed as a solution to pinpointing the location of a robot, in a robust way, without environment preparation, even in dynamic scenarios. This solution does not require a high computational power. The methodology is a threedimensional map based approach, which uses the 3D map of the surrounding environment and data acquired by a tilting Laser Range Finder (LRF), to pinpoint the robot pose. Experimental results about the accuracy of the proposed method are presented in this paper. Index Terms-robot localisation, 3D matching, EKF-SLAM, laser range finder
2009 35th Annual Conference of IEEE Industrial Electronics, 2009
This paper describes the interaction between the kinematic model of the AUV MARES and the measure... more This paper describes the interaction between the kinematic model of the AUV MARES and the measurement or observation of the environment through images obtained with the Sonar use. Three types of sonar are discussed in this paper, they are forward-look, side scan and multibeam, but the sonar used to develop this work was the side scan sonar. The type of observations and characteristics of the environment provided by the sonar are described here. The method which connects the sensory part of the vehicle with the observations of the sonar, was the Kalman filter (EKF). In this paper, we present two simulations of filters for two different characteristics. Both filters estimate the characteristics of the natural landmarks, creating a environment map, but both of them consider different states of the vehicle. Results of the simulation are obtained. The features that are considered are an underwater pipe on the floor and a wall. It also generated a control for the vehicle that provides the capacity to move along the feature/landmark from a reference distance.
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Papers by Anibal Matos