The technology associated with active magnetic bearings has been widely used in the last years and can be considered as being one of the most promising solutions for several applications in rotating machinery. Lubricants are not necessary, and high rotation speeds are reached without any relevant heating. Active magnetic bearings are classified as mechatronic systems because they are composed of mechanical and electronic parts that are controlled by using dedicated software. In this context, the present work is devoted to the design of robust controllers applied to supercritical rotors supported by active magnetic bearings. For this aim, numerical and experimental tests were carried out. Different from previous studies reported in the literature, the present contribution proposes a novel design procedure to robustify the neuro-fuzzy controller of a rotor supported by active magnetic bearings based on optimal robust design. This optimal design procedure tunes the robust neuro-fuzzy controller taking into account the optimal balance between vibration attenuation performance and robustness, that is the increase in vibration attenuation implies the reduction in the robustness. The first stage of the controller synthesis is dedicated to the specification of all design requirements. Then, the adaptative neuro-fuzzy controller was obtained, starting from the determination of the plant dominant poles and finally performing the model-based analysis of the system stability and performance. Finally, the vibration control performance and robustness are optimally balanced by using a robust optimization procedure. The behavior of the controller was evaluated by investigating the unbalance response of the rotating system. The obtained results demonstrated the effectiveness of the conveyed approach.
The present contribution proposes an active vibration control technique devoted to shafts with cracks aiming to minimize their propagation. The existence of a crack in rotating shafts can be characterized by 2 X and 3 X super-harmonic amplitudes in the vibration responses of the rotor, which can increase as the crack propagates along the shaft’s cross-section. A proportional-integral-derivative control technique is applied to suppress the 2 X and 3 X vibration amplitudes of a cracked shaft, which is performed by using a bandpass filter applied to the vibration responses of the rotor. Numerical and experimental results are obtained through both a representative finite element model of a horizontal rotor and its corresponding test-rig. In this case, electromagnetic actuators are used to apply the control effort to the rotor. The Mayes model is applied for simulating the breathing behavior of the transverse crack. The linear fracture mechanics theory is considered to correlate the crack depth with the corresponding additional rotor flexibility. Both numerical and experimental results demonstrate the possibility of reducing the effects of a transverse crack through active control on the dynamic behavior of a rotating machine. Moreover, it is shown that the proposed control law is capable of controlling the crack effects with the rotor operating in different rotation speeds.
O presente trabalho é dedicado à síntese de controladores utilizados em rotores supercríticos suportados por mancais magnéticos. Em primeiro lugar, construiu-se um modelo numérico/computacional em ambiente MATLAB ® /Simulink com base nas especificações fornecidas pelo fabricante da bancada. Dai, em conjunto com o processo de validação experimental correspondente, resultou um modelo representativo do comportamento dinâmico do sistema físico real. O passo seguinte foi o projeto de 3 controladores para o sistema, a saber, o PID baseado nas características fornecidas pelo fabricante, o PID adaptativo que tem por premissa a atualização da sua referência e o PID Fuzzy, que proporciona o ajuste dos ganhos do controlador. Todos foram avaliados a partir de suas funções de transferência em malha fechada e sob o ponto de vista da sua reposta ao desbalanceamento, sendo esta conduzida de acordo com as diretrizes da norma API 684 e classificada com base nos critérios definidos na norma ISO 14839-2. Com base nestes resultados, foi possível analisar as dificuldades de projeto dos controladores e criar, então, o controlador Neuro Fuzzy Robusto, que teve por objetivo considerar as incertezas presentes no sistema e que não foram consideradas nos controladores anteriores. O novo controlador proposto foi avaliado utilizando os mesmos critérios aplicados aos três primeiros controladores. Com base nos resultados obtidos, é possível afirmar que a principal contribuição deste trabalho é caracterizada pela sistematização da utilização de um controlador Neuro Fuzzy ótimo-robusto para o estudo e projeto de rotores supercríticos suportados por mancais magnéticos.
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