221 research outputs found
Reducing actuator switchings for motion control of autonomous underwater vehicles
No full textA priority when designing control strategies for autonomous underwater vehicles is to emphasize their cost of implementation on a real vehicle. Indeed, the major issue is that due to the vehicles' design and actuation modes usually under consideration for underwater platforms, the number of actuator switchings must be kept to a small value to ensure feasibility and precision. This constraint is typically not satisfied by optimal trajectories, for instance. Our goal is to provide a trajectory which preserves with great accuracy some of the properties of a desired trajectory that reduces the implementation cost. We first introduce the theoretical framework and illustrate our algorithm on two AUV applications. In both cases, we can achieve similar localization results in the same fixed time with respect to the reference trajectory, but with significantly fewer actuator switchings
Reconstruction of tubular structures from 2.5D point clouds: A mesophotic gorgonian coral case study
No full textA method for the surface reconstruction of 3D tubular branched structures characterized by low informative point clouds (i.e., 2.5D) is proposed. These specific clouds can arise when using photogrammetry techniques on complex subjects in challenging scanning environments (e.g., underwater gorgonian coral at mesophotic depths). The core idea behind the proposed Sphere Skeleton Approach (SSA) is to approximate the assumed tubular shapes via merged spheres having variable radii and centered in the points of the medial skeleton. To assess the generality and robustness of the proposed SSA, additional experiments have been conducted on 2.5D point clouds that were synthetically generated from 3D model benchmarks. Hausdorff distances between the target and the reconstructed 3D models are used to quantitatively compare the SSA performances to a classical meshing algorithm. Early results highlight the capability to outperform existing approaches in reconstructing objects from 2.5D clouds.
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Geometric control for autonomous underwater vehicles: Overcoming a thruster failure
No full textThe goal of this paper is to show how geometric control theory can be used to design efficient trajectories for an autonomous underwater vehicle descending into a basin, as well as performing its recovery after experiencing an actuator failure. The underwater vehicle is modeled as a forced affine connection control system, and the control strategies are developed through the use of integral curves of rank one and kinematic reductions. Such a method is particularly efficient in case of actuator failure and it provides a constructive way to design trajectories for the new under-actuated system. A typical scenario of basin descent is presented, control signals are computed to realize the desired trajectories and some simulations are provided
Minimum fuel round trip from a Earth-Moon Halo orbit to Asteroid 2006 RH
No full textInternational audienceThe goal of this paper is to design a spacecraft round trip transfer from a parking orbit to Asteroid 2006\;RH, during its capture time by Earth's gravity, while maximizing the final mass or equivalently minimizing the delta-v. The parking orbit is chosen as a Halo orbit around the Earth-Moon libration point. The round-trip transfer is composed of three portions: a rendezvous transfer departing from the parking orbit to reach 2006\;RH, a lock-in portion with the spacecraft following the asteroid orbit, and finally a return transfer to . An indirect method based on the maximum principle is used for our numerical calculations. To partially address the issue of local minima, we restrict the control strategy to reflect an actuation corresponding to up to three constant thrust arcs during each portion of the transfer. The model considered here is the circular restricted four-body problem (CR4BP) with the Sun considered as a perturbation of the Earth-Moon circular restricted three body problem. A shooting method is applied to solve numerically this problem, and the rendezvous point to and departure point from \RH\ are optimized using a time discretization of the trajectory of \RH
Optimization problems for controlled mechanical systems : bridging the gap between theory and application
No full textMechanical control systems have become a part of our everyday life. Systems such as automobiles, robot manipulators, mobile robots, satellites, buildings with active vibration controllers and air conditioning systems, make life easier and safer, as well as help us explore the world we live in and exploit it’s available resources. In this chapter, we examine a specific example of a mechanical control system; the Autonomous Underwater Vehicle (AUV). Our contribution to the advancement of AUV research is in the area of guidance and control. We present innovative techniques to design and implement control strategies that consider the optimization of time and/or energy consumption.\ud
Recent advances in robotics, control theory, portable energy sources and automation increase our ability to create more intelligent robots, and allows us to conduct more explorations by use of autonomous vehicles. This facilitates access to higher risk areas, longer time underwater, and more efficient exploration as compared to human occupied vehicles. The use of underwater vehicles is expanding in every area of ocean science. Such vehicles are used by oceanographers, archaeologists, geologists, ocean engineers, and many others. These vehicles are designed to be agile, versatile and robust, and thus, their usage has gone from novelty to necessity for any ocean expedition.\u
Design and implementation of time efficient trajectories for an underwater vehicle
No full textThis paper discusses control strategies adapted for practical implementation and efficient motion of underwater vehicles. These trajectories are piecewise constant thrust arcs with few actuator switchings. We provide the numerical algorithm which computes the time efficient trajectories parameterized by the switching times. We discuss both the theoretical analysis and experimental implementation results
Geometric Path Planning for a Lego AUV
No full textFor the last thirty years or so, differential geometry and control theory have merged and grown together to produce extraordinary results. When applied to mechanical systems, one sees a system waiting to be exploited for its inherent geometric properties. In this paper, we present the equations of motion for a submerged rigid body from a geometric point of view and use tools from differential geometry to provide solutions to the motion planning problem for an autonomous underwater vehicle. Specifically, the geometry allows us to deduce permissible motions for a vehicle that is underactuated purely from the available degrees of freedom. The geometric equations of motion are then used to path plan for a cost-effective Lego vehicle through simulations and actual implementation as providing a proof of concept
Autonomous underwater vehicles: development and implementation of time and energy efficient trajectories
No full textAutonomous underwater vehicles (AUVs) are increasingly used, both in military and civilian applications. These vehicles are limited mainly by the intelligence we give them and the life of their batteries. Research is active to extend vehicle autonomy in both aspects. Our intent is to give the vehicle the ability to adapt its behavior under different mission scenarios (emergency maneuvers versus long duration monitoring). This involves a search for optimal trajectories minimizing time, energy or a combination of both.\ud
Despite some success stories in AUV control, optimal control is still a very underdeveloped area. Adaptive control research has contributed to cost minimization problems, but vehicle design has been the driving force for advancement in optimal control research. We look to advance the development of optimal control theory by expanding the motions along which AUVs travel. Traditionally, AUVs have taken the role of performing the long data gathering mission in the open ocean with little to no interaction with their surroundings, MacIver et al. (2004). The AUV is used to find the shipwreck, and the remotely operated vehicle (ROV) handles the exploration up close. AUV mission profiles of this sort are best suited through the use of a torpedo shaped AUV, Bertram and Alvarez (2006), since straight lines and minimal (0 deg - 30 deg) angular displacements are all that are necessary to perform the transects and grid lines for these applications. However, the torpedo shape AUV lacks the ability to perform low-speed maneuvers in cluttered environments, such as autonomous exploration close to the seabed and around obstacles, MacIver et al. (2004). Thus, we consider an agile vehicle capable of movement in six degrees of freedom without any preference of direction
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