Browsing by Issue Date, starting with "2002-05"
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- AR2T: Implementing a Truly SRAM-based FPGA On-Line Concurrent TestingPublication . Gericota, Manuel G.; Alves, Gustavo R.; Silva, Miguel L.; Ferreira, J. M. MartinsThe new partial and dynamic reconfigurable features offered by new generations of SRAM-based FPGAs may be used to improve the dependability of reconfigurable hardware platforms through the implementation of on-line concurrent testing / fault-tolerance mechanisms. However, such mechanisms call for the development of new test strategies that do not interfere with the current system functionality. The AR2T (Active Replication and Release for Testing) technique is 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. The experimental results presented prove the effectiveness of these solutions. In relation to a previous technique proposed by the authors as part of the DRAFT FPGA concurrent test methodology, AR2T extends the range of circuits that can be replicated, by introducing a small replication aid block.
- Performance 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. For that objective the prescribed motion of the robot is completely characterized in terms of several locomotion variables such as gait, duty factor, body height, step lenght, stroke pitch, foot clearance, legs link lengths, foot-hip offset, body and legs mass and cycle time. In this perspective, we formulate four performance measures of the walking robot namely, the locomobility of the foot, 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.
- Pseudoinverse trajectory control of redundant manipulators: A fractional calculus perspectivePublication . Duarte, Fernando B. M.; Tenreiro Machado, J. A.Redundant manipulators have some advantages when compared with classical arms because they allow the trajectory optimization, both on the free space and on the presence of obstacles, and the resolution of singularities. For this type of arms the proposed kinematic control algorithms adopt generalized inverse matrices but, in general, the corresponding trajectory planning schemes show important limitations. Motivated by these problems this paper studies the chaos revealed by pseudoinverse-based trajectory planning algorithms, using the theory of fractional calculus.
- An evolutionary optimization for robotic manipulatorsPublication . Pires, E. J. Solteiro; Tenreiro Machado, J. A.; Oliveira, P. B. de MouraThis work proposes a real time algorithm to generate a trajectory for a 2-link planar robotic manipulator. The objective is to minimize the space/time ripple and the energy requirements or the time duration in the robot trajectories. The proposed method uses an off-line genetic algorithm to calculate every possible trajectory between all cells of the workspace grid. The resultant trajectories are saved in several trees. Then any trajectory resquested is constructed, in real time, from these trees. The article presents the results for several experiments.
- Fractional describing function analysis of systems with backlash and impact phenomenaPublication . 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 analyzed in the perspective of the fractional calculus theory. The fractional-order dynamics is illustrated using the Nyquist plot and the results are compared with those of standard models.
- Application of fractional calculus in the control of mechanical systemsPublication . Tenreiro Machado, J. A.; Barbosa, Ramiro; Duarte, Fernando B. M.; Ferreira, Nuno M. F.The Fractional Calculus (FC) goes back to the begining of the theory of differential calculus. Nevertheless, the application of FC just emerged in the last two decades, due to the progress in the area of chaos that revelead subtle relationships with the FC concepts. In the field of dynamical systems theory some work has been carried out but the proposed models and algorithms are still in a preliminary stage of establishment. Having these ideas in mind, the paper discusses a FC perspective in the study of the dynamics and control of mechanical systems.
- Gait efficiency of walking robotsPublication . 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. For that objective the prescribed motion of the robot is completely characterized in terms of several locomotion variables such as gait, duty factor, body height, step length, stroke pitch, foot clearance, legs link lengths, foot-hip offset, body and legs mass and cycle time. In this perspective, we formulate three performance measures of the walking robot namely, the mean absolute power, the mean power lost in the joint actuators and the mean force of the interface body-legs per walking distance. A set of model-based experiments reveals the influence of the locomotion variables in the proposed indices.