Luís M. M. Custódio

Production planning and scheduling using a fuzzy decision system

In this paper short-range planning and scheduling problems are addressed using a nonclassical approach supported by fuzzy theory. The proposed methodology uses a hierarchical structure which includes three decision levels (higher, middle, lower), each responsible for a different production problem with a different time scale. The methodology approaches the tasks associated with each level using a heuristic formulation and solves the short-range planning and scheduling problems with a nonstationary policy. The higher decision level determines safety stock levels used to compensate for future resource failures. At the middle level, loading rates are computed. This is accomplished through a fuzzy controller that tends to minimize the error between the cumulative production and the cumulative demand while keeping the work in process below acceptable values. Finally, the lower level controls the flow of parts among the resources, using a modified version of the Yagers fuzzy decision method. This method has the ability to use several criteria to generate a decision. Simulation results reveal that the proposed system exhibits good performance, in terms of a high production percentage and a low WIP, under resource failures and demand variations. >

Artificial Intelligence and Systems Theory: Applied to Cooperative Robots

This paper describes an approach to the design of a population of cooperative robots based on concepts borrowed from Systems Theory and Artificial Intelligence. The research has been developed under the SocRob project, carried out by the Intelligent Systems Laboratory at the Institute for Systems and Robotics - Instituto Superior Técnico (ISR/IST) in Lisbon. The acronym of the project stands both for “Society of Robots” and “Soccer Robots”, the case study where we are testing our population of robots. Designing soccer robots is a very challenging problem, where the robots must act not only to shoot a ball towards the goal, but also to detect and avoid static (walls, stopped robots) and dynamic (moving robots) obstacles. Furthermore, they must cooperate to defeat an opposing team. Our past and current research in soccer robotics includes cooperative sensor fusion for world modeling, object recognition and tracking, robot navigation, multi-robot distributed task planning and coordination, including cooperative reinforcement learning in cooperative and adversarial environments, and behavior-based architectures for real time task execution of cooperating robot teams.

A Modified Potential Fields Method for Robot Navigation Applied to Dribbling in Robotic Soccer

This paper describes a modified potential fields method for robot navigation, especially suited for unicycle-type non-holonomic mobile robots. The potential field is modified so as to enhance the relevance of obstacles in the direction of the robot motion. The relative weight assigned to front and side obstacles can be modified by the adjustment of one physically interpretable parameter. The resulting angular speed and linear acceleration of the robot can be expressed as functions of the linear speed, distance and relative orientation to the obstacles. For soccer robots, moving to a desired posture with and without the ball are relevant issues. To enable a soccer robot to dribble a ball, i.e., to move while avoiding obstacles and pushing the ball without losing it, under severe restrictions to ball holding capabilities, a further constraint among the angular speed, linear speed and linear acceleration is introduced. This dribbling behavior has been used successfully in the robots of the RoboCup Middle-Size League ISocRob team.

A Functional Architecture for a Team of Fully Autonomous Cooperative Robots

A three-level functional architecture for a team of mobile robots is described in detail, including the definition of the role assigned to each level, the main concepts involved, and the corresponding implementation for each individual robot. The architecture is oriented towards teams of fully autonomous cooperative robots, able to carry out different types of cooperative tasks. Complexity is reduced by the decomposition of team strategies into individual behaviors, which in turn are composed of primitive tasks. Relationships among robots of the team are modeled upon the joint intentions framework. An application to Robotic Soccer and some of its preliminary results are presented.

RoboCup 2004 Competitions and Symposium: A Small Kick for Robots, a Giant Score for Science

RoboCup is an international initiative with the main goals of fostering research and education in artificial intelligence and robotics, as well as of promoting science and technology to world citizens. The idea behind RoboCup is to provide a standard problem for which a wide range of technologies can be integrated and examined, as well as being used for project-oriented education, and to organize annual events open to the general public, at which different solutions to the problem are compared. The eighth annual RoboCup -- RoboCup 2004 -- was held in Lisbon, Portugal, from 27 June to 5 July. In this article, a general description of RoboCup 2004 is presented, including summaries concerning teams, participants, distribution into leagues, main research advances, as well as detailed descriptions for each league.

Supervision of fuzzy controllers using genetic algorithms

The fast growth of fuzzy control applications in industry, together with the need of getting increasingly efficient control systems, has been the motivation for the development of approaches to the supervision of fuzzy controllers. Some novel approaches to this problem encompass the application of artificial intelligence techniques, such as the utilization of neural networks and genetic algorithms. In this article an approach based on the genetic algorithms (GAs) technique is proposed, allowing the simultaneous determination of: (i) the set of fuzzy rules, (ii) the shape of membership functions, and (iii) the universes of discourse for the linguistic variables. To illustrate the application of the suggested approach, two systems were selected: an inverted pendulum and a manufacturing system.

ISocRob - Intelligent Society of Robots

The SocRob project was born as a challenge for multidisciplinary research on broad and generic approaches for the design of a cooperative robot society, involving Control, Robotics and Artificial Intelligence researchers. In this paper the basic aspects of last year implementation as well as the improvements made meanwhile are briefly recalled and presented. Naturally, a special emphasis is given here to the novel solutions proposed for this year implementation, the results obtained and the expected future developments.

Fuzzy modelling: a rule based approach

System modelling is an important subject in engineering both from a research point of view and from a practical perspective models have an important role in several intelligent systems and, as it is observed from the research developed in the last years, fuzzy logic is relevant to this topic. This is mainly due to the expressiveness of fuzzy logic that permits the treatment of some kinds of uncertainty largely present in real systems. Also, the if-then rule mechanism is easy to manipulate and, in a certain extent, domain independent. A modelling procedure must produce good models in an effective way. This is the main concern of this paper.

Contingency planning for automated vehicles

Automated driving is a safety critical process, which requires complex decision making. In order to validate driving decisions, it is possible to maintain at all times a contingency maneuver, which transfers the vehicle to a safe standstill, if other decision making processes fail. In this paper we present a motion planner, which computes contingency maneuvers for an automated vehicle in a 0.1[s] time frame. A discrete set of motion primitives is assembled in a heuristic best-first search. In order to speed up the search, an obstacle sensitive heuristic is applied, which maintains properties of bounded sub-optimality and completeness. A run-time comparison with and without the obstacle sensitive heuristic is presented on two exemplary collision avoidance scenarios.

RoboCup 2004 overview

RoboCup is an international initiative with the main goals of fostering research and education in Artificial Intelligence and Robotics, as well as of promoting Science and Technology to world citizens. The idea is to provide a standard problem where a wide range of technologies can be integrated and examined, as well as being used for project-oriented education, and to organize annual events open to the general public, where different solutions to the problem are compared.