Pedro Encarnação

3D path following for autonomous underwater vehicle

A new methodology is proposed for the design of path following systems for autonomous underwater vehicles. Global convergence to reference paths is achieved with a nonlinear control strategy that takes explicitly into account the dynamics of the vehicle. Formal convergence proofs are indicated. Simulation results with the model of a prototype autonomous underwater vehicle are presented to illustrate the performance of the path following system derived.

Combined trajectory tracking and path following: an application to the coordinated control of autonomous marine craft

The paper presents a solution to the problem of combined trajectory tracking and path following system design for autonomous marine craft. This problem is motivated by the practical need to develop control systems for marine craft that can yield good trajectory tracking performance while keeping some of the desired properties normally associated with path following. The solution described builds on and extends previous work by Hindman and Hauser (1992) on so-called maneuver modified trajectory tracking. An application is made to the problem of designing a control system for the coordinated operation of an autonomous surface craft (ASC) and an autonomous underwater vehicle (AUV). Simulations with nonlinear models of an underactuated marine craft and a fully actuated underwater vehicle illustrate the performance of the control system derived.

Path Following for Autonomous Marine Craft

Abstract A new methodology is proposed for the design of path following systems for autonomous marine craft in the presence of constant but unknown currents. Convergence to reference paths is achieved with a nonlinear control strategy that takes explicitly into account the dynamics of the vehicle as well as those of a current estimator. Formal convergence proofs are indicated. Simulation results with the model of a prototype marine craft are presented to illustrate the performance of the path following system derived.

Path Following for Marine Vehicles in the Presence of Unknown Currents 1

Abstract A new methodology is proposed for the design of path following systems for autonomous marine vehicles in the presence of constant but unknown currents. Convergence to reference paths is achieved with a nonlinear control strategy that takes explicitly into account the dynamics of the vehicle as well as those of a current estimator. Formal convergence proofs are indicated. Simulation results with the model of a prototype marine craft are presented to illustrate the performance of the path following system derived.

Robots: Assistive technologies for play, learning and cognitive development

Robots have been widely used in rehabilitation. Among the various applications, robots have been developed to assist children with motor disabilities in play and academic activities. Several studies have shown the efficacy of these robot ic tools, not only for allowing children to actively participate in th e activities, with direct impact on the development of their cognitive, social, and linguistic skills, but also as a means to assess c hildrens understanding of cognitive concepts, when stand ard tests cannot be used due to physical or language limitations. In this paper the use of robots for assistive play is reviewed from the perspectives of rehabilitation engineering and robot desi gn, aiming at defining a set of desirable characteristics for such robots. Commercially available robots are then surveyed in comparison to the defined characteristics to evaluate to what extent they can be used as assistive robots for play, learning and cognitive development.

Robot Skills and Cognitive Performance of Preschool Children

Several studies have demonstrated the potential of robots as assistive tools for play activities. Through the use of ro bots, children with motor impairments may be able to manipulate objects and engage in play activities as their typically devel oping peers, thus having the same opportunities to learn cognitive, social, motor and linguistic skills. Robot use can also pr ovide a proxy measure of disabled childrens cognitive abilities by comp aring their performance with that of typically developing children. This paper reports a study with eighteen typically developing children aged three, four and five years to assess at which a ges the cognitive concepts of causality, negation, binary logic, a nd sequencing are demonstrated during Lego robot use.

Obstacle Avoidance for Unmanned Aerial Vehicles

This work is framed within the PITVANT project and aims to contribute to the development of obstacle avoidance techniques for unmanned aerial vehicles (UAVs). The paper describes the design, implementation and experimental evaluation of a potential field obstacle avoidance algorithm based on the fluid mechanics panel methods. Obstacles and the UAV goal position are modeled by harmonic functions thus avoiding the presence of local minima. Adaptations are made to apply the method to the automatic control of a fixed wing aircraft, relying only on a local map of the environment that is updated with information from sensors onboard the aircraft. Hardware-In-Loop simulations show the good performance of the proposed algorithm in the envisioned mission scenarios for the PITVANT vehicles.

Ground Target Tracking Control System for Unmanned Aerial Vehicles

The work here presented contributes to the development of ground target tracking control systems for fixed wing unmanned aerial vehicles (UAVs). The control laws are derived at the kinematic level, relying on a commercial inner loop controller onboard that accepts commands in indicated air speed and bank, and appropriately sets the control surface deflections and thrust in order to follow those references in the presence of unknown wind. Position and velocity of the target on the ground is assumed to be known. The algorithm proposed derives from a path following control law that enables the UAV to converge to a circumference centered at the target and moving with it, thus keeping the UAV in the vicinity of the target even if the target moves at a velocity lower than the UAV stall speed. If the target speed is close to the UAV speed, the control law behaves similar to a controller that tracks a particular point on the circumference centered at the target position. Real flight tests results show the good performance of the control scheme presented.

The role of assisted manipulation in cognitive development

Objective: Motor experience plays a central role in cognitive development. Assistive technologies can thus provide augmentative manipulation for children with motor disabilities. This paper explores the use of robots to this end. Method: A revision of studies conducted with typically‐developing children and children with disabilities regarding the use of robots is presented. This revision provides a description of the cognitive skills required and revealed by the child when using a robot. Opportunities for participation and exploration were identified and further research is discussed. Results: Robots provide insight into the cognitive skills of children with motor disabilities. Robots also provide means for independent exploration and participation in learning and play activities. Integration of augmentative manipulation and communication increases interest and participation of children with disabilities. Conclusion: Children with disabilities can use augmentative manipulation systems to independently explore and interact with their environment. Children can use robots as tools providing them with opportunities to reveal and further develop their cognitive skills. Alternative access methods can increase access for children with severe motor disabilities.

Moving Path Following for Unmanned Aerial Vehicles With Applications to Single and Multiple Target Tracking Problems

This paper introduces the moving path following (MPF) problem, in which a vehicle is required to converge to and follow a desired geometric moving path, without a specific temporal specification, thus generalizing the classical path following that only applies to stationary paths. Possible tasks that can be formulated as an MPF problem include tracking terrain/air vehicles and gas clouds monitoring, where the velocity of the target vehicle or cloud specifies the motion of the desired path. We derive an error space for MPF for the general case of time-varying paths in a two-dimensional space and subsequently an application is described for the problem of tracking single and multiple targets on the ground using an unmanned aerial vehicle (UAV) flying at constant altitude. To this end, a Lyapunov-based MPF control law and a path-generation algorithm are proposed together with convergence and performance metric results. Real-world flight tests results that took place in Ota Air Base, Portugal, with the ANTEX-X02 UAV demonstrate the effectiveness of the proposed method.