Eugenio Fortaleza

Development of a stereo vision measurement architecture for an underwater robot

Underwater robotics tasks are considered very critical, mainly because of the hazardous environment. The embedded systems for this kind of robots should be robust and fault-tolerant. This paper describes the development of a system for embedded stereo vision in real-time, using a hardware/software co-design approach. The system is capable to detect an object and measure the distance between the object and the cameras. The platform uses two CMOS cameras, a development board with a low-cost FPGA, and a display for visualizing images. Each camera provides a pixel-clock, which are used to synchronize the processing architectures inside the FPGA. For each camera a hardware architecture has been implemented for detecting objects, using a background subtraction algorithm. Whenever an object is detected, its center of mass is calculated in both images, using another hardware architecture to do that. The coordinates of the object center in each image are sent to a soft-processor, which computes the disparity and determines the distance from the object to the cameras. A calibration procedure gives to the soft-processor the capability of computing both disparities and distances. The synthesis tool used (Altera Quartus II) estimates that the system consumes 115.25mW and achieves a throughput of 26.56 frames per second (800×480 pixels). These synthesis and the operation results have shown that the implemented system is useful to real-time distance measurements achieving a good precision and an adequate throughput, being suitable for real-time critical operation.

An Investigation About the Trajectory Control During the Subsea Equipment Installation Using Cable

Nowadays, several seafloor equipments have been developed and deployed in order to enhance the production of petroleum and natural gas from reservoirs in deep and ultra-deep waters. Thus the installation and maintenance of such seafloor equipments shall be an issue.The most important seafloor equipment during the production phase is the “Wet Christmas-Tree” (X-tree), which is a set of valves that controls the pressure at well bottom. This equipment is installed by a Mobile Offshore Drilling Unit (MODU) after the drilling and completion are finished. Recently, beside the X-mas, a variety of subsea pumps, usually called as Subsea Booster System, have been deployed in the development of new reservoirs in deep-water. At the beginning, such subsea pumps and even other seafloor equipments had been installed by a MODU. But the high-cost of the MODUs is one of the main concerns about the installation and maintenance of the subsea equipments. One alternative to reduce the installation cost is to use cable system installed on a service boat instead the completion riser of a MODU.This paper presents an initial investigation for the installation of a seafloor equipment using cable. The dynamic model will be featured; the dynamic analysis will be carried out using an in house developed simulation program in time-domain. Discussion about the trajectory and control of the equipment to be installed is also included.Copyright

Semi-Active Hydropneumatic Heave Compensator

A hydropneumatic heave compensation system and a semi-active control are proposed according to the requirements drilling offshore of 6 km deep. The goal of this semi-active control is to maintain an acceptable performance of the system when the drill string mass changes, which also changes the performance of the hydropneumatic system. The control action is executed just by a servo valve, which modifies the system damping to optimize the compensator performance. This servo valve is the only moving part of the control system and therefore, this system is more robust regarding mechanical/ electrical failures and it has low consumption energy. The results show a satisfactory frequency response of semi-active control when the drill string mass is changed.Copyright

Analysis of Phenomenological Models of Vortex Induced Vibrations

The objective of this article is to identify a model able to represent the first harmonic behavior of a rigid cylinder undergoing VIV in the most different cases of a rigid cylinder supported by a spring/damper system. This analysis of the first harmonic behavior is made considering three different non-dimensional variables: the damping coefficient, the reduced velocity and the mass ratio. The challenge is to define a model that represents the changes on the lock-in zone considering the different combination of damping coefficient and mass ratio thus able to represent the different real systems. Two new phenomenological models using the Van der Pol oscillator are studied. They follow the framework of the phenomenological model proposed by Facchinetti et al.Copyright

Trajectory tracking for a quadrotor system: A flatness-based nonlinear predictive control approach

This paper proposes a flatness-based nonlinear predictive control strategy to solve the trajectory tracking problem for an underactuated quadrotor system model. It is shown that the present nonlinear model can be transformed to a controllable linear system on Brunovskys canonical form by using the differential flatness theory. Thus, a model predictive controller (MPC) is designed for the linear equivalent system to carry out trajectory tracking tasks. Since certain variables of the corresponding transformed system can not be measured directly, a state estimation is performed by a derivative-free Kalman filtering approach. The efficiency of the proposed control scheme is demonstrated through numerical simulations.

An efficient data fusion architecture for infrared and ultrasonic sensors, using FPGA

This paper shows the hardware implementation of a sensor fusion technique applied to both an ultrasonic and an infrared sensors, for estimating the distance, using an FPGA. Sensor fusion is a natural application of stochastic filtering area (such as Kalman filters), being applied extensively in different areas such as mobile robotics, signal processing, bioengineering, among others. This technique permits to combine the information provided by the sensors, improving the estimate of the measured variable, as well as its uncertainity. The sensors have previously been characterized using the same acquisition system that was used for the sensor fusion, and the fitting curves have been calculated for them. Finally, synthesis and simulation results demonstrate that the architecture implemented in the FPGA is suitable for calculating the estimate and uncertainity of the overall fusion process.

Modelamiento matemático y control de un helicóptero de cuatro motores

This paper shows the mathematical modeling of a four-engine helicopter (Quadri-motor), the system is modeled by Euler Lagrange equations. The flight control is designed using the planning and tracking of trajectories, the mean objective is to get an easy stabilizing control to operate this equipment in various applications such astaking pictures of places with difficult aces to human being, control verification is done by studying a planned entry exposed to a disturbance and a Gaussian measure error, it is studied the effects of the controller over the output variance and expected value. We also present a comparison between experimental and theoretical data to validate the applied theory.

Motion Planning and Tracking for Marine Vessels

Trajectory tracking is an issue of vital practical importance for manoeuvreing of marine vessels and dynamic position system in many offshore oil field operations. In this work, a flatness based approach is proposed on the tracking control design to define open loop trajectories for a simplified model of the underactuated Hovercraft. The flat outputs are given by using the inverse of the controllability matrix, which allows the design of control law to ensure a global stabilization of the trajectory’s tracking error. Numerical simulations are presented to demonstrate the performance of the tracking controller from arbitrary initial conditions and in the presence of external sinusoidal perturbations. The reference trajectory was chosen with respect to the Earth-fixed frame.Copyright

Passive and semi-active heave compensator: Project design methodology and control strategies

Heave compensator is a system that mitigates transmission of heave movement from vessels to the equipment in the vessel. In drilling industry, a heave compensator enables drilling in offshore environments. Heave compensator attenuates movement transmitted from the vessel to the drill string and drill bit ensuring security and efficiency of the offshore drilling process. Common types of heave compensators are passive, active and semi-active compensators. This article presents 4 main points. First, a bulk modulus analysis obtains a simple condition to determine if the bulk modulus can be neglected in the design of hydropneumatic passive heave compensator. Second, the methodology to design passive heave compensators with the desired frequency response. Third, four control methodologies for semi-active heave compensator are tested and compared numerically. Lastly, we show experimental results obtained from a prototype with the methodology developed to design passive heave compensator.

Control of underactuated AUVs: A flatness-based approach

The problem of tracking a desired trajectory for a nonlinear underactuated autonomous underwater vehicles (AUVs) model with only three actuators is addressed. This paper proposes to compute offline open loop trajectories exploiting the liouvillian character of the nonlinear model. A flatness-based control approach is applied in the system linearized around the planned trajectories, which allows to obtain an incremental feedback controller to ensure a stabilization of the trajectorys tracking error. In order to validate the proposed tracking control, simulation results are presented and discussed.