CRAS

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http://localhost:4000/handle/123456789/39
This performs research and development activities in autonomous robotic systems, mobile robotics and multi-robot mobile systems for inspection, monitoring and mapping, with applications in security, energy, environment, aquaculture, oceanography, marine biology, resource extraction, among other sectors. These activities are supported by research in perception, navigation, control, localization, coordination, and automatic data acquisition and processing.

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Browsing CRAS by Author "5155"
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    ALARS - Automated Launch And Recovery System for AUVs
    ( 2018) Nuno Cruz ; Carlos Filipe Gonçalves ; Almeida,RM ; Vitor Hugo Pinto ; 6852 ; 6920 ; 5155
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    Altitude control of an underwater vehicle based on computer vision
    ( 2019) Nuno Cruz ; Rodrigues,PM ; Pinto,AM ; 5155
    It is common the use of the sonar technology in order acquire and posteriorly control the distance of an underwater vehicle towards an obstacle. Although this solution simplifies the problem and is effective in most cases, it might carry some disadvantages in certain underwater vehicles or conditions. In this work it is presented a system capable of controlling the altitude of an underwater vehicle using computer vision. The sensor capable of computing the distance is composed of a CCD camera and 2 green pointer lasers. Regarding the control of the vehicle, the solution used was based on the switching of two controllers, a velocity controller (based on a PI controller), and a position controller (based on a PD controller). The vehicle chosen to test the developed system was a profiler, which main task is the vertical navigation. The mathematical model was obtained and used in order to validate the controllers designed using the Simulink toolbox from Matlab. It was used a Kalman filter in order to have a better estimation of the state variables (altitude, depth, and velocity). The tests relative to the sensor developed responsible for the acquisition of the altitude showed an average relative error equal to 1 % in the range from 0 to 2.5 m. The UWsim underwater simulation environment was used in order to validate the integration of the system and its performance. © 2018 IEEE.
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    Autonomous Tracking of a Horizontal Boundary
    ( 2014) Nuno Cruz ; Aníbal Matos ; 5155 ; 5158
    The ability to employ autonomous vehicles to find and track the boundary between two different water masses can increase the efficiency in waterborne data collection, by concentrating measurements in the most relevant regions and capturing detailed spacial and temporal variations. In this paper we provide a guidance mechanism to enable an autonomous vehicle to find and track the steepest gradient of a scalar field in the horizontal plane. The main innovation in our approach is the mechanism to adapt the orientation of the crossings to the local curvature of the boundary, so that the vehicle can keep tracking the gradient regardless of its horizontal orientation. As an example, we show how the algorithms can be used to find and track the boundary of a dredged navigation channel, using only altimeter measurements.
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    Cooperative deep water seafloor mapping with heterogeneous robotic platforms
    ( 2017) Pinto,A ; Dias,A ; Melo,J ; Alfredo Martins ; Abreu,N ; Almeida,J ; Almeida,R ; José Carlos Alves ; Carlos Filipe Gonçalves ; Ferreira,H ; Ferreira,B ; Nuno Cruz ; Silva,E ; Aníbal Matos ; Hugo Miguel Silva ; Eduardo Silva ; Vitor Hugo Pinto ; 5570 ; 258 ; 5155 ; 5158 ; 5429 ; 5473 ; 6852 ; 6920
    This paper describes the PISCES system, an integrated approach for fully autonomous mapping of large areas of the ocean in deep waters. A deep water AUV will use an acoustic navigation system to compute is position with bounded error. The range limitation will be overcome by a moving baseline scheme, with the acoustic sources installed in robotic surface vessels with previously combined trajectories. In order to save power, all systems will have synchronized clocks and implement the One Way Travel Time scheme. The mapping system will be a combination of an off-the-shelf MBES with a new long range bathymetry system, with a source on a moving surface vessel and the receivers on board the AUV. The system is being prepared to participate in round one of the XPRIZE challenge. © 2017 Marine Technology Society.
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    DART - A portable deep water hovering AUV
    ( 2017) Aníbal Matos ; Bruno Miguel Ferreira ; Almeida,RM ; Nuno Cruz ; 5158 ; 5238 ; 5155
    Autonomous Underwater Vehicles are remarkable machines that revolutionized the collection of data at sea. There are many examples of highly operational man-portable vehicles for shallow waters, but there was no similar solution for deep water operations. This paper describes the development of a portable, modular, hovering AUV for deep water operations. The vehicle has little over 50kg, 2.4m of length, and a depth rating of 4000m. The first version of the vehicle has been assembled, it has gone through the initial tests in water tanks, and it is being prepared for the first operations at sea. © 2017 Marine Technology Society.
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    Development of a Dynamic Model for Twin Hull ASVs
    ( 2018) André Filipe Coelho ; Bruno Miguel Ferreira ; Vitor Hugo Pinto ; Nuno Cruz ; 7259 ; 6852 ; 5238 ; 5155 ; 6599
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    Development of an autonomous underwater profiler for coastal areas
    ( 2017) Nuno Cruz ; Monteiro,JM ; 5155
    One of the most common ways of collecting ocean data is to deploy sensors from the surface, allowing to understand the variation of water properties with depth. Autonomous vertical profilers are robotic vehicles that replace human operators in this task. They form a particular class of autonomous underwater vehicles that move predominantly along the vertical axis, typically with reduced control on the horizontal axis. This paper describes a propeller driven autonomous underwater profiler, optimized for shallow waters. The vehicle has no fins or other control surfaces, and uses four independent thrusters to provide both vertical and horizontal motion, including hovering in the water column. The paper describes the main subsystems, including the hardware implementation, the software structure, and the motion controllers, with experimental data from the first trials. © 2017 Marine Technology Society.
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    Development of an Electrohydraulic Variable Buoyancy System
    ( 2019) Carneiro,JF ; Pinto,JB ; Nuno Cruz ; de Almeida,FG ; 5155
    The growing needs in exploring ocean resources have been pushing the length and complexity of autonomous underwater vehicle (AUV) missions, leading to more stringent energy requirements. A promising approach to reduce the energy consumption of AUVs is to use variable buoyancy systems (VBSs) as a replacement or complement to thruster action, since VBSs only require energy consumption during limited periods of time to control the vehicle's floatation. This paper presents the development of an electrohydraulic VBS to be included in an existing AUV for shallow depths of up to 100 m. The device's preliminary mechanical design is presented, and a mathematical model of the device's power consumption is developed, based on data provided by the manufacturer. Taking a standard mission profile as an example, a comparison between the energy consumed using thrusters and the designed VBS is presented and compared.
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    Guidance of an Autonomous Surface Vehicle for Underwater Navigation Aid
    ( 2018) Nuno Cruz ; Sousa,JP ; Bruno Miguel Ferreira ; 5238 ; 5155
    Unmanned Underwater Vehicles (UUVs), such as Autonomous Underwater Vehicles (AUVs) and Remotely Operated Vehicles (ROVs) are versatile tools, suitable for many activities in different fields, and have seen an increase in usage, making them an area of interest in the study of robotics. The performance of any underwater vehicle in any given task is deeply affected by the precision of its localization system. The main challenge in underwater localization is the significant attenuation of any Radio Frequency (RF) signal underwater, which prevents the use of many common location methods such as the Global Positioning System (GPS). Many methods have been studied for the localization of UUVs, including the use of acoustic beacons. One of these methods is the use of a single moving beacon to obtain acoustic ranges, as opposed to a stationary single beacon, which restricts the UUV's trajectory or multiple beacons, involving more hardware, complicating missions' logistics and increasing costs. In this paper, a guidance algorithm based on the Fisher Information Matrix is proposed for an Autonomous Surface Vehicle to serve as a beacon vehicle and aid in the navigation of a UUV. The approach performances are assessed by means of simulations of the complete system under realistic conditions. © 2018 IEEE.
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    Optimizing the Power Budget of Hovering AUVs
    ( 2019) Nuno Cruz ; 5155
    The maximum mission duration and range of an Autonomous Underwater Vehicle are governed by the amount of energy carried on board and the way it is spent during the mission. While an increase in battery capacity and a decrease in electronics demand yield a direct increase in vehicle range, the impact of velocity variation is not so obvious. With slower velocities, most of the energy will be spent in electronics, not in motion, while for faster velocities a lot of energy will be needed to balance drag. Flying-type AUVs have a minimum velocity for the control surfaces to be effective, reducing the range of values for optimization. Hovering type AUVs, on the other hand, are typically slower moving platforms, able to travel at arbitrarily slow velocities. This paper addresses the analysis of the power consumption of hovering type AUVs, providing guidelines and analytical expressions to compute the optimal velocity when the vehicle travels in a single direction, and also when the trajectory is a combination of horizontal and vertical motion. © 2019 IEEE.
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    Pushing for Higher Autonomy and Cooperative Behaviors in Maritime Robotics
    ( 2019) Curtin,TB ; Nuno Cruz ; Djapic,V ; Potter,JR ; Kirkwood,WJ ; 5155