Rotating machinery usually works under conditions of variable speed. The vibration signals extracted from such equipment contain more fault information than those operating in steady-state conditions, therefore harmonic component extraction on this occasion becomes a hot issue. However, some harmonics still cannot be extracted effectively by traditional signal processing methods, i.e. how to separate the components that are too close to each other in the time–frequency plane, and how to separate the cross-coupled components around a critical speed during rotor startup or shut down. To solve these problems, a new method is developed based on improved variational mode decomposition (VMD) by generalized demodulation technology (GDT) and a zero-phase shift filter (ZPSF) in this paper. After obtaining the instantaneous frequency of the main dominant component, GDT and the ZPSF are used as preprocessing methods to enhance the signal-to-noise ratio (SNR) and to extract separable components, and the wide-band component is improved in the form of a tractable narrowband. Finally, VMD is used to enhance the SNR of the separable components and reduce the coupling effect between the crossed components. Compared with conventional methods, the stimulation signal and the experimental signal analysis obtained from the rotor kit show that this hybrid approach is able to effectively compromise the speed fluctuation and thus extract all the useful vibration components from the rotor system during startup; therefore, it can effectively be applied to fault diagnosis.
A novel fractional PIa control strategy for frequency response directly and continuously, which makes it pneumatic position servo system is presented in order to solve its possible to design more robust control system. However, strong non-linearity and low natural frequency problem. To FOC was not widely applied in control engineering mainly demonstrate their better control characteristics, the fractional due to most researchers' unfamiliar idea of fractional calculus order control experiments under various conditions, which and limited computational power, which leads to few physical include step position signal, sine position signal with different applications existed in the past. Microprocessors with frequency and amplitude, variety load etc, are carried out along owerful computation abili and digital realizations for FOC with a detailed comparative analysis with traditional control. p p ty gThe results show the effectiveness of the proposed scheme and become available now, which made it possible to adopt verify their fine control performance for pneumatic position fractional order control strategies to solve traditional control servo system with the nonlinearity and parameter uncertainty. questions. The last application researches in many complex objects, such as flexible robot [16], satellite attitude I. INTRODUCTION control[13], spacecraft attitude control[17], hydraulic In last decade, pneumatic servo systems are increasingly actuator[18] and so on, have attracted much attention andused and studied in a great deal of industrial applications showed that FOC possesses fine robust performance and can because of a number of advantages over other servo systems control the low damping system. To solve strong in point of high power weight and power volume ratios, high non-linearity and low natural frequency problem of speed, low cost and simple operational mechanism. However, pneumatic systems, fractional order control strategy is the dynamic characteristics are complex and highly nonlinear investigated in this work. due to compressibility of air, external disturbances such as This paper is organized as follows. Section II presents the friction and payload and pressure supply variations[ 1-2]. The dynamic model of pneumatic systems. Section III introduces compressibility of air results in very low stiffness leading to the fractional order control and their digital realizations. low natural frequency, and low damping system makes it Section IV presents experimental design. The results and difficult to be controlled. Especially, precise control of discussions are carried out in section V. Some conclusions pneumatic position servo system is more difficult in the are drawn in section VI. presence of uncertainties and nonlinearities. In order to overcome those difficulties, many researchers have II. SYSTEM MODEL extensively studied the application of different control methods in pneumatic servo systems [3][4][5][6][7][8][9][10]. The research Thsceaidagmofpuatcipleensrv meffors mainly foeu icused wo sstpems of10 contro...
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