Browsing by Issue Date, starting with "2004-08-30"
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- Considerations about the choice of a differintegratorPublication . Ortigueira, Manuel D.; Machado, J. A. Tenreiro; Costa, J. Sá daDespite the great advances in the theory and applications of fractional calculus, some topics remain unclear making difficult its use in a systematic way. This paper studies the fractional differintegration definition problem from a systems point of view. Both local (Grunwald-Letnikov) and global (convoluntional) definitions are considered. It is shown that the Cauchy formulation must be adopted since it is coherent with usual practice in signal processing and control applications...
- Population size and processing time in a genetic algorithmPublication . Reis, Cecília; Tenreiro Machado, J. A.; Cunha, J. BoaventuraThis paper presents several experiments with a genetic algorithm (GA) for designing combinational logic circuits. The study addresses the population size and the processing time for achieving a solution in order to establish a compromise between the two parametrs. Furthermore, it is also investigated the use of different gate sets for designing the circuits namely RISC and CISC like gate sets.
- Fractional-order position/force robot controlPublication . Ferreira, N. M. Fonseca; Machado, J. A. Tenreiro; Cunha, J. BoaventuraThis paper presents the implementation of fractional-order algorithms both for hybrid and cascade position/force control of robotic manipulators. The system performance and robustness is analyzed in the time frequency domains. The effects joint backlash and flexibility are also investigated.
- Dynamics of the fractional-order Van der Pol oscillatorPublication . Barbosa, Ramiro S.; Machado, J. A. Tenreiro; Ferreira, Isabel M.; Tar, József K.In this paper we propose a modified version of the classical unforced Van der Pol oscillator that occurs when introducing a fractional-order time derivative in the state space equations that describes its dynamics. The resulting fractional-order Van der Pol oscillator is analyzed in the time and frequency domains, for several values of order's fractional derivative and, consequentlly, of the total system order. It is shown that the system can exhibit different output behavior depending on the total system order. Several numerical simulations and performances indices illustrate the fractional dynamics.
- Fractional order adaptive active vibration damping designed on the basis of simple kinematic considerationsPublication . Tar, József K.; Rudas, Imre J.; Bitó, János F.; Machado, J. A. TenreiroIn this paper a simple nonlinear, adaptive control using fractional order derivatives is applied for damping the vibration of a car forced during passing along a bumpy road. Its key idea is the partial replacement of the integer order derivatives in a traditional PD controller with a time-shift invariant, causal approximation of Caputo's fractional derivative that behaves like a Green function. Since its physical essence is rather frequency filtering than providing integer order derivatives in limit cases, the approximation applied numerically is quite convenient. In htis way simple kinematic design of the desired damping becomes possible. The adaptive part of the controller guarantees the realization of this kinematic design without making it necessary for the system to be controlled or to design a sophisticated linear "CRONE" controller that has to take the responsability for the unknown dynamics of the system. The applicability of the approach is illustrated via simulations for a paradigm that is a rough model of a car. It was found that both adaptivity and the use of fractional order derivatives in the control are essential parts of the success of the method.
- Gait selection for quadruped and hexapod walking systemsPublication . Silva, Manuel F.; Machado, J. A. Tenreiro; Lopes, António M.; Tar, József K.This paper studies periodic gaits of quadruped and hexapod locomotion systems. The purpose is to determine the best set of gait and locomotion variables for different robot velocities based on the system dynamics during walking. In this perspective, several performance measures are formulated and a set of experiments that reveal the influence of the gait and locomotion variables upon those proposed indices are performed.