Browsing by Issue Date, starting with "2004-07-19"
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- Least-squares design of digital fractional-order operatorsPublication . Barbosa, Ramiro; Tenreiro Machado, J. A.; Ferreira, Isabel M.In this paper we develop a method for obtaining digital rational approximations to fractional-order operators of type s^y, where y e R. The proposed method is based on the least-squares (LS) minimization between the impulse response of the fractional Euler/Tustin operators and the digital rational-fraction approximation. We make a comparison with other approaches and the results reveal that the LS method gives superior approximations. The effectiveness of the method is demonstrated both in the time and frequency domains through an illustrative example.
- 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.
- Fractional-order position/force robot controlPublication . Ferreira, N. M. Fonseca; Tenreiro Machado, J. A.; Galhano, Alexandra; Cunha, J. BoaventuraIn this paper it is studied the implementation of fractional-order algorithms in position/force control of two cooperating robotic manipulaotrs. The performance and system robustness are analyzed in the time and frequency domains. The effect of backlash and flexibility at the robot joints is also investigated.
- Hexapod control through a fractional algorithmPublication . Silva, Manuel F.; Machado, J. A. Tenreiro; Lopes, António M.This paper studies the performance of a Fractional Order controller in a hexapod robot with joint leg actuators having saturation. For that objective the robot percribed motion is characterized in terms of several locomotion variables. Moreover, two indices measure the walking performance based on the mean absolute density of energy per travelled distance and on the hip trajectory erros. A set of experiments reveals the influence of the different controller tuning upon the proposed indices and on the feet trajectory tracking.