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- Arquitecturas dos sistemas de informaçãoPublication . Rodrigues, Luis SilvaArquitecturas dos sistemas de informação
- Chaotic Phenomena and Fractional-Order Dynamics in the Trajectory Control of Redundant ManipulatorsPublication . Duarte, Fernando B. M.; Tenreiro Machado, J. A.Redundant manipulators have some advantages when compared with classicalarms because they allow the trajectory optimization, both on the freespace and on the presence of obstacles, and the resolution ofsingularities. For this type of arms the proposed kinematic controlalgorithms adopt generalized inverse matrices but, in general, thecorresponding trajectory planning schemes show important limitations.Motivated by these problems this paper studies the chaos revealed by thepseudoinverse-based trajectory planning algorithms, using the theory offractional calculus.
- Active Replication: Towards a Truly SRAM-based FPGA On-Line Concurrent TestingPublication . Gericota, Manuel G.; Alves, Gustavo R.; Silva, Miguel L.; Ferreira, J. M. MartinsThe reusing of the same hardware resources to implement speed-critical algorithms, without interrupting system operation, is one of the main reasons for the increasing use of reconfigurable computing platforms, employing complex SRAM-based FPGAs. However, new semiconductor manufacturing technologies increase the probability of lifetime operation failures, requiring new on-line testing / fault-tolerance methods able to improve the dependability of the systems where they are included. The Active Replication technique presented in this paper consists of a set of procedures that enables the implementation of a truly non-intrusive structural on-line concurrent testing approach, detecting and avoiding permanent faults and correcting errors due to transient faults. In relation to a previous technique proposed by the authors as part of the DRAFT FPGA concurrent test methodology, the Active Replication technique extends the range of circuits that can be replicated, by introducing a novel method with very low silicon overhead.
- Fractional-order describing function of systems with backlashPublication . Barbosa, Ramiro; Tenreiro Machado, J. A.This paper analyses the dynamical properties of systems with backlash and impact phenomena based on the describing function method. It is shown that this type of nonlinearity can be analysed in the perspective of the fractional calculus theory.
- Commande d'ordre fractionnaire position/force d'un manipulateur mécaniquePublication . Tenreiro Machado, J. A.; Barbosa, Ramiro; Ferreira, N. M.Cet article étudie l'implementation d'algorithmes d'ordres fractionnaires pour la commande hybride position/force de robots manipulateurs. Les performances du système snt analysées en termes de temps de réponse et de robustesse. Une comparaison avec une stratégie de commande basée sur des algorithmes de type PID est également effectuée. Par ailleurs, des phénomènes non linéaires issus de joints tels que les frottements, les jeux de transmission dynamiques et la flexibilité non linéaires sont étudiés.
- Power analysis of multi-legged systemsPublication . Silva, Manuel; Tenreiro Machado, J. A.; Lopes, António M.This paper studies periodic gaits of multi-legged robot locomotion systems based on dynamic models. The purpose is to determine the system performance during walking and the best set of locomotion variables that minimizes the optimization indices. For that objective the precribed motion of the robot is completely characterized in terms of several locomotion variables such, gait, duty factor, body height, step length, stroke pitch, foot clearance, leg links length, foot-hip offset, body and legs mass and cycle time. In this perspective, we formulate four performance measures of the walking robot namely, the foot locomobility index, the mean absolute power, the mean power dispersion and the mean power lost in the joint actuators per walking distance. A set of model-based experiments reveals the influence of the locomotion variables in the proposed indices.
- A new contribution for solving dynamic scheduling problems using genetic algorithmsPublication . Madureira, Ana Maria; Ramos, Carlos; Silva, Sílvio do CarmoScheduling is an important element of manufacturing systems because it allows to improve the system performance and serves as an overall plan on which system activities are based. The main purpose of this paper isto explore the use of evolutionary computation techniques for solving real world optimisation problems. These classes of problems have additional difficulties for the traditional optimisation techniques. This paper presents a simple and general framework based on Genetic Algorithms to solve dynamic Job-Shop scheduling problems. A new generation of initial individual and population is proposed. The proposed framework adapts the resolution of the deterministic problem to the non-deterministic one in which changes may occur continually. This takes into account dynamic occurrences in a manufacturing system and adapts the current population.
- A new contribution for solving dynamic scheduling problems using a Tabu searchPublication . Madureira, Ana Maria; Ramos, Carlos; Silva, Sívio do CarmoMany real-world optimisation problems are eventually dynamic. New jobs are to be added to the schedule, the quality of the raw material may be changing, new orders have to be included into the problem etc. In such cases, when the problem changes over the course of the optimisation, the purpose of the optimisation algorithm changes from finding an optimal solution to being able to continuously track the movement of the optimum through time. This paper starts by presenting a new scheduling method based on Tabu Search for the resolution of the dynamic Job-Shop Scheduling Problem, which considers job release times, job due dates and different assembly levels (parallel operations). This framework is based on a decomposition of the Job-Shop Scheduling Problem into a series of deterministic Single Machine Scheduling Problem (SMSP) and on a Tabu Search Algorithm, which solves each SMSP whose solutions are, then, integrated. An inter-machine activity coordination mechanism is described. Finally, the used approach adapts the resolution of the deterministic problem to the non-deterministic one in which changes may occur continually. This takes into account dynamic occurrences in a manufacturing system and adapts the current neighbourhood to a new regenerated neighbourhood.