Browsing by Issue Date, starting with "2002-07"
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- Arquitecturas dos sistemas de informaçãoPublication . Rodrigues, Luis SilvaArquitecturas dos sistemas de informação
- 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.
- 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.
- 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.