Application of integrated PCA and FIS approach to the selection of current and vibration signal features in mechanical fault classification of induction motor

The detection as well as analysis of faults in Induction Motor (IM) is prominent in the industrial process in recent decades, since it has been a demanding issue in industries to confirm the safe and reliable operations of IM. Though the electrical faults, mechanical faults and environmental faults cause damages in IM, as per Electric Power Research Institute (EPRI) statistical studies, the faults due to (i) rotor mass unbalance and (ii) rotor shaft bending substantially contribute 8-9% of the total motor fault. This present research work focuses on the issue of detecting and analysing the faults by studying the current and vibration data obtained from the three-phase squirrel cage IM under healthy and faulty conditions using the experimental workbench. It also depicts the development of a fault detection model for IM which comprises the integrated approach of Principal Component Analysis (PCA) and Fuzzy Interference System (FIS) and two level decision fuzzy measures. Besides, fuzzy integral data fusion technique has been used in this work for the improvement of diagnosing accuracy. The data acquired from the workbench system are first investigated through the PCA to extricate the appropriate features that provide the major information of collected data without reducing its dimensions. The projected data space using the principal components is non-deterministic for further synthesis process of fault classification. Hence, to classify the faults in IM, the obtained feature vectors from PCA are fed into FIS as an input and the classification performance is compared finally. The work experiment has been carried out under the healthy and different faulty conditions of motor and the proposed integrated approach is executed by using MATLAB.

Predicting unbalance asymmetric rotor vibration behavior based on sensitivity analysis and using Response Surface Methodology method considering parallel misalignment

Mass unbalance, shaft misalignment, rotor asymmetry, and force due to rotor weight are the main causes of vibrations in rotary machines especially when the shaft is not symmetric. Although extensive researches have been carried out to determine the effect of each on the increase of vibration levels far, there has been no clear study on the simultaneous existence of all these parameters and their interactions. In this research, the model is a rotor composed of a rigid disk and a flexible asymmetric shaft. The general equations of motion are first derived by considering the effect of high order large deformation in bending. The equations are discretized using the Rayleigh–Ritz method. The obtained equations are nonlinear coupled differential equations that are solved using the numerical method. Sensitivity analysis has been utilized to identify the percentage of the contribution of each parameter to the increase of vibration. Then a DOE-based Response Surface Methodology (RSM) is applied to present a model to predict the vibration behavior of the system with good accuracy. Genetic algorithm is also used to optimize the effective parameters and to verify the results. A 3D model of the asymmetric rotor is carried out in experimental studies to attain more precise responses. The research shows that rotor asymmetry alone and also its combination with gravitational force has much more effects on the vibration amplitude. These effects are observed at frequencies both once and twice the rotational speed in spectral data, in comparison with other factors. The mass unbalance also plays a significant role in frequency equal to the rotational speed. In the end, the achieved results are validated with experimental simulations.

Studi Prediksi Analitik Posisi Bantalan (Journal Bearing) Pada Turbin Gas

AbstrakBantalan menyediakan antarmuka utama antara bagian-bagian mesin yang bergerak dan tidak bergerak. Bantalan memberikan sebagian besar kekakuan dan redaman untuk struktur yang bergerak. Dapat dimengerti bahwa gaya dinamis yang dikembangkan pada bagian yang bergerak ditransmisikan ke bagian stasioner melalui bantalan penyangga utama ini. Gaya tersebut dapat berupa beban radial statis karena berat rotor, atau mungkin gaya dinamis karena mekanisme seperti ketidakseimbangan massa. Dalam kedua kasus tersebut, bantalan radial harus membawa beban yang diterapkan, atau mesin akan mengalami kegagalan. Dalam kebanyakan kasus, secara teknis sulit (jika bukan tidak mungkin) untuk secara langsung memeriksa validitas atau akurasi dari koefisien bantalan yang dihitung. Namun, setiap perhitungan harus diakhiri dengan keseimbangan gaya, ditambah keseimbangan posisi jurnal dalam jarak bebas bantalan. Karena jurnal dalam bantalan film-oli dapat diukur secara langsung dengan proximity probes, logis untuk melakukan pemeriksaan prediksi analitik versus data mesin yang sebenarnya. Proximity probe sensorik dipasang pada ± 450 dari garis tengah vertikal sebenarnya. Pada bantalan ujung saluran masuk turbin # 1, probe dipasang di atas poros. Sebaliknya, di exhaust # 2 bantalan, probe terletak di bawah poros. Untuk penelitian pada kasus ini dilakukan pada empat turbin gas poros tunggal yang beroperasi antara 5.000 dan 5.350 RPM. Unit ini memiliki daya 40.000 HP, dan digunakan untuk menggerakkan kompresor sentrifugal bertekanan tinggi melalui satu kotak roda gigi heliks. Dapat dimengerti bahwa jika posisi eksentrisitas yang dihitung benar, maka parameter yang dihitung lainnya juga mewakili karakteristik bantalan. Kata kunci: journal bearing, turbin gas, proximity probe, posisi eksentrisitas. Abstract Bearings provide the primary interface between the moving and the stationary parts of a machine. Although the seal and the process fluids (or magnetic fields) coexist, the bearings provide the majority of the stiffness and damping for the moving assembly. It is understandable that dynamic forces developed on the moving part are transmitted to the stationary part across these main support bearings. The forces may be the static radial loads due to the rotor weight, or they may be dynamic forces due to mechanisms such as mass unbalance. In either case, the radial bearings must carry the applied loads, or the machine will fail. In most cases, it is technically difficult (if not impossible) to directly check the validity or accuracy of the computed bearing coefficients. However, each calculation must conclude with a force balance, plus a position balance of the journal within the bearing clearance. For this case history, consider a group of four single shaft gas turbines that operate between 5,000 and 5,350 RPM. These units are rated at 40,000 HP, and they are used to drive high pressure centrifugal compressors through a single helical gear box. The shaft sensing proximity probes are mounted at ±450 from the true vertical centerline. At turbine inlet end#1 bearing, the probes are mounted above the shaft. Conversely, at the exhaust end #2 bearing, the probes are located below the shaft. Since journal within an oil film bearing can be measured directly with proximity probes, it is logical perform a check of the analytical prediction versus actual machine data. It is reasonable to believe that if the calculated eccentricity position is correct, than the other computed parameters are also representative of the bearing characteristics. Keywords: journal bearing, gas turbine, proximity probes, eccentricity position.

Vibration Mechanism and Compensation Strategy of Magnetic Suspension Rotor System under Unbalanced Magnetic Pull

The existing imbalance compensation strategies for magnetic suspension motors mainly focus on the mass unbalance force, ignoring the effects of the unbalanced magnet pull (UMP). This paper studied the vibration mechanism and compensation strategy of magnetic suspended permanent magnet synchronous motor (PMSM) under the influence of UMP. Firstly, an analytical model of the flux density was established based on equivalent magnetic circuit method, then the analytical expressions of UMP was deduced by Maxwell stress tensor method. Furthermore, an unbalanced compensation method based on hypothetical reference frame (HRF) transformation was proposed. The stability of the closed-loop system with compensation was analyzed based on the complex-coefficients theory. The proposed model and compensation strategy were verified by the simulations and experiments. The results indicate that the proposed compensation strategy can achieve effective suppression of the magnetic rotor vibration.

Nonlinear Vibration Mechanism of the Marine Rotating Machinery with Airbag Isolation Device under Heaving Motion

In this paper, we put an investigation into the nonlinear vibration mechanism of the marine rotating machinery with an airbag isolation device under heaving motion. First, we consider the effects of mass unbalance and heaving motion and propose a mathematical model of the marine rotating mechanical system with airbag vibration isolation. Then, the multiple-scale method is conducted to analyze the nonlinear dynamic characteristics of the mechanical system; the frequency-response curves are mainly studied under different parameters, such as the heave excitation, rotor speed, and damping; and the numerical method is also introduced to analyze its dynamic behaviors, such as the steady-state response and its corresponding phase diagram, Poincaré section. The dynamic stability of the system is investigated based on the bifurcations and the largest Lyapunov exponent about rotor speed and heaving frequency. The obtained results indicate complex nonlinear characteristics of the system compared to the system without heaving excitation, which can help us fully understand the dynamic characteristics and parametric optimization as well as structural design of the marine mechanical isolation system.

Dynamics of on-board rotors on finite-length journal bearings subject to multi-axial and multi-frequency excitations: numerical and experimental investigations

On-board rotating machinery subject to multi-axial excitations is encountered in a wide variety of high-technology applications. Such excitations combined with mass unbalance forces play a considerable role in their integrity because they can cause parametric instability and rotor–stator interactions. Consequently, predicting the rotordynamics of such machines is crucial to avoid triggering undesirable phenomena or at least limiting their impacts. In this context, the present paper proposes an experimental validation of a numerical model of a rotor-shaft-hydrodynamic bearings system mounted on a moving base. The model is based on a finite element approach with Timoshenko beam elements having six degrees of freedom (DOF) per node to account for the bending, torsion and axial motions. Classical 2D rectangular finite elements are also employed to obtain the pressure field acting inside the hydrodynamic bearing. The finite element formulation is based on a variational inequality approach leading to the Reynolds boundary conditions. The experimental validation of the model is carried out with a rotor test rig, designed, built, instrumented and mounted on a 6-DOF hydraulic shaker. The rotor’s dynamic behavior in bending, torsion and axial motions is assessed with base motions consisting of mono- and multi-axial translations and rotations with harmonic, random and chirp sine profiles. The comparison of the predicted and measured results achieved in terms of shaft orbits, full spectrums, transient history responses and power spectral densities is very satisfactory, permitting the experimental validation of the model proposed.

A Review on Self-Recovery Regulation (SR) Technique for Unbalance Vibration of High-End Equipment

The high-end equipment represented by high-end machine tools and aero-engines is the core component of the national intelligent manufacturing plan, and the mass unbalance is the main reason for its excessive vibration, that seriously impacts the operation efficiency and running life of the equipment. In order to change the traditional way that the fault of equipment can only be repaired by human, the self-recovery mechanism of human and animal are given to the equipment in this paper, which forms the self-recovery regulation (SR) system for unbalance vibration of high-end equipment. The system can online generate the self-recovery force to restrain the unbalance vibration of the equipment in operation, which is an important direction for the development of the equipment to the advanced intelligent stage. Based on the basic principles of SR technique, the typical engineering application cases of this technique in the field of aeroengine and high-end machine tools are introduced, and four related studies promoting the development of this technique are summarized and analyzed in turn. It includes feature extraction, imbalance location, regulation method and balancing actuator. Self-recovery Regulation (SR) Technique is an important way to realize intelligent manufacturing and intelligent maintenance. Relevant research can lay a technical foundation for the development of high-end equipment with self-health function.