Loading...
320 results
Search Results
Now showing 1 - 10 of 320
- 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.
- Combining genetic and particle swarm algorithms for the design of combinational circuitsPublication . Reis, Cecília; Tenreiro Machado, J. A.Evolutionary computation (EC) is a growing research field of Artificial Intelligence (AI) and is divided in two main areas: the Evolutionary Algorithms (EA) and the Swarm Intelligence (SI). This paper presents an algorithm that combines an EA algorithm - the Genetic Algorithm (GA) with a SI algorithm - the Particle Swarm Optimization Algorithm (PSO). The new algorithm is applied to the synthesis of combinational logic circuits. With this combination is possible to take advantage of the best features of each particular algorithm.
- Analysis of Systems with Backlash and Impacts through the Describing FunctionPublication . Barbosa, Ramiro S.; Machado, J. A. TenreiroThis paper analyses the dynamical properties of systems with backlash and impact phenomena based on the describing function method. The dynamics is illustrated using the Nyquist and Bode plots and the results are compared with those of standard models.
- On the Sensor Classification Scheme of Robotic ManipulatorsPublication . Lima, Miguel; Machado, J. A. Tenreiro; Crisóstomo, Manuel; Ferrolho, AntónioThis paper analyzes the signals captured during impacts and vibrations of a mechanical manipulator. The Fourier Transform of eighteen different signals are calculated and approximated by trendlines based on a power law formula. A sensor classification scheme based on the frequency spectrum behavior is presented.
- Describing function of systems with nonlinear frictionPublication . Duarte, Fernando B. M.; Tenreiro Machado, J. A.This paper studies the describing function (DF) of systems composed of a mass subjected to nonlinear friction. The friction force is decomposed in three components namely, the viscous, the Coulomb and the static forces. The system dynamics is analyzed in the DF perspective and the reliability of the DF method is evaluated through the signal harmonic content.
- Fractional order calculus on the estimation of short-circuit impedance of power transformersPublication . Albert, W. Malpica; Silva, J. Fernando; Tenreiro Machado, J. A.; Barros, M. T. CorreiaThis paper reports investigation on the use of fractional order calculus to analytically estimate the inlfuence of skin and proximity effects in the short circuit impedance of power transformers. The aim is to better characterize the medium frequency range behavior of leakage inductances of power transformer models, which include terms to represent the magnetic field diffusion process in the windigns. Comparisons between calculated and measured values are shown and discussed.
- Robotic Manipulator Synthesis using a Hierarchical Multi-objective Genetic AlgorithmPublication . Pires, E. J. Solteiro; Tenreiro Machado, J. A.; Oliveira, P. B. de MouraRobotic manipulator synthesis considering the simultaneous optimization of several design objectives is a NP-hard problem. This paper proposes a hierarchical multi-objective genetic algorithm to generate a robot structure and the required manipulating trajectories. The aim is to minimize the trajectory space ripple, the initial and final binary torques, while optimizing the mechanical structure. Simulations results are presented from solving a structure synthesis problem which considers the optimization of three simultaneous objectives.
- Manipulator trajectory planning using a MOEAPublication . Pires, E. J. Solteiro; Oliveira, P. B. Moura; Machado, J. A. TenreiroGenerating manipulator trajectories considering multiple objectives and obstacle avoidance is a non-trivial optimization problem. In this paper a multi-objective genetic algorithm based technique is proposed to address this problem. Multiple criteria are optimized considering up to five simultaneous objectives. Simulation results are presented for robots with two and three degrees of freedom, considering two and five objectives optimization. A subsequent analysis of the spread and solutions distribution along the converged non-dominated Pareto front is carried out, in terms of the achieved diversity.
- Which differintegration?Publication . Ortigueira, M. D.; Machado, J. A. Tenreiro; Costa, J. S.Despite the great advances in the theory and applications of fractional calculus, some topics remain unclear, making a systematic use difficult. In this paper, the fractional differintegration definition problem is studied from a systems point of view. Both local (Grunwald-Letnikov) and global (convolutional) definitions are considered. It is shown that the Cauchy formulation should be adopted since it is coherent with usual practice in signal processing and control applications.
- Single-Objective Front Optimization: Application to RF Circuit DesignPublication . Pires, E. J. Solteiro; Mendes, Luís; Oliveira, P. B. de Moura; Tenreiro Machado, J. A.; Ferreira, N. M. Fonseca; Vaz, João; Rosário, MariaThis paper proposes a new algorithm which promotes well distributed non-dominated fronts in the parameters space when a single- objective function is optimized. This algorithm is based on ǫ-dominance concept and maxmin sorting scheme. Besides that, the paper also presents the results of the algorithm when it is used in the automated synthesis of optimum performance CMOS radiofrequency and microwave binary-weighted differential switched capacitor arrays (RFDSCAs). The genetic synthesis tool optimizes a fitness function which is based on the performance parameter of the RFDSCAs. To validate the proposed design methodology, a CMOS RFDSCA is synthesized, using a 0.25 μm BiCMOS technology.