Instantaneous Angular Acceleration Research Articles

Torsional and lateral vibration analysis of wind turbine generator bearing outer ring fault considering unbalanced magnetic pull

Rolling bearings play a critical role in wind turbine generators, operating continuously in an electromagnetic excitation environment. Their fault vibration characteristics are affected by unbalanced magnetic pull (UMP), which has received little attention in previous studies. Moreover, torsional vibration can provide advantages in bearing fault diagnosis, since it has a good signal-to-noise ratio (SNR) and it can be easily measured by the encoder. However, torsional vibration is rarely considered in the existing model of wind turbine generator. Accordingly, this paper proposes a dynamic model with 8 degrees of freedom to analyze the bearing outer ring fault characteristics of wind turbine generator under the influence of UMP, while also taking into account the torsional vibration in the model. The validity of the model is verified through experiments conducted on a test rig. The results displays modulation of the ball pass frequency outer (BPFO) harmonics with both UMP frequency and rotation frequency in lateral vibration, and this phenomenon can also be observed in instantaneous angular speed (IAS) and instantaneous angular acceleration (IAA) signals that represent torsional vibration. Besides, the lateral vibration spectrum reveals two distinct resonance bands, and simulation analysis suggested that the rotor and bearings give rise to low-frequency and high-frequency resonance, respectively. This study provides a reference for bearing faults diagnosis in wind turbine generator.

Generalized Gini indices–enhanced sparsity decomposition for rotating machinery health assessment using a rotary encoder

ABSTRACT Rotary encoder signal has been attracting considerable attention for health estimation of the rotating elements, since its advantages in lower testing costs and sensitive to torsional stiffness loss caused by incipient faults. However, the practical encoder signal often keeps low signal-to-noise ratio due to its instantaneous angular acceleration conventional method, which brings new challenges for the commonly used feature extraction methods. Sparse decomposition is an efficient method for fault impact features extracting of rotating machinery. However, limited by the quality of initial dictionary and the learning efficiency of K-SVD algorithm, commonly used sparse decomposition is susceptible to the signal noise, especially when unsuitable initial atoms are applied. To overcome this problem, a simple but effective framework term Generalized Gini indices-enhanced sparsity decomposition is established in this paper for practical encoder signal analysis. Firstly, the de-trended and frequency domain weighting methods are used for instantaneous angular acceleration estimation. After that, a Generalized Gini indices guided tunable Q-factor wavelet filter is introduced for the atom selection. Then, the shift-invariant K-SVD method is introduced for dictionary updating and sparse coefficients calculation. Through the analysis of simulation and experiment, the transient characteristics of the gear can be extracted well which provides an alternative methodology for incipient fault detection of rotating machinery.

Influence of Pitting Failure on Dynamic Performance of Herringbone Gear Transmission System Considering Friction Coefficient

Background: Gearboxes are used in many industrial fields. Due to uncontrollable external factors and inevitable fatigue damage, gearboxes are likely to fail. It has become a major research trend to collect dynamic signals of gearboxes and develop effective fault diagnosis methods for gearboxes. Objective: The purpose of this paper is to study the dynamic characteristics of herringbone gear transmission (HGT) under different friction coefficients and pitting faults. Methods: A virtual prototype model of the system with different friction coefficients and pitting faults was established jointly with KISSsoft, SolidWorks, and ADAMS. The contact stiffness, penetration coefficient, damping, and other factors were considered in the model. The contact force and angular acceleration signals of the Driven gear are collected and analyzed by simulation. Results: The increase of friction coefficient results in the increase of contact force and instantaneous angular acceleration. The modulation side frequency band on both sides of the frequency becomes dense, and the side frequency band in the frequency domain of angular acceleration becomes sparse. When pitting failure exists, all dynamic signals show fault characteristics. Conclusion: This work provided a theoretical basis for fault diagnosis and gear dynamics research, Due to many nonlinear factors, the fault diagnosis of the HGT system is relatively difficult. The research results can quickly diagnose the fault of the HGT system, which makes up for the shortcomings in the study of the fault diagnosis of the HGT system.

Analysis of changes in the angular velocity of the crankshaft of the marine engine for diagnosing the wear and location the failure of the fuel injection system

Abstract The combustion process can be simply described as periodic explosions in a cylinder with its frequency dependent on the number of cylinders and the rotational speed of the shaft. In practice, uniformity of combustion parameters in every cylinder is almost impossible. Due to this fact, instantaneous angular acceleration does not remain the same at the ends of the crankshaft. These observations formed the basis for the investigation of the instantaneous angular speed of the crankshaft ends. To investigate the influence of the failure behavior of the fuel systems during a shaft's rotational movement, a series of experiments were planned. For the simulations, a medium-speed marine engine driving electro generator was selected. The failure simulation was based on the installation of clogged spray holes, draining of part of fuel dose from high-pressure pump and decreasing of injection pressure by a lower tension of the injector spring. The results of measurement were processed and analyzed through a comparison of the fast Fourier transform spectra. As a general conclusion, a difference between general harmonics order of magnitudes was detected.

A Novel Moment of Inertia Identification Strategy for Permanent Magnet Motor System Based on Integral Chain Differentiator and Kalman Filter

In a motor control system, the parameters tuning of speed and position controller depend on the value of the moment of inertia. A new moment of inertia identification scheme for permanent magnet motor system was proposed in this paper. This is an extension of the existing acceleration deceleration methods, which solves the large moment of inertia identification error caused by variable angular acceleration, large calculation error of inertia torque, and large measurement noise in the acceleration process. Based on the fact that the angular acceleration is not constant and the sampling signal is noisy, the integral chain differentiator was used to calculate the instantaneous angular acceleration at any time and suppress the sampling signal noise at the same time. The error function with instantaneous angular acceleration and inertia torque as parameters was designed to estimate the moment of inertia. In order to calculate the inertia torque accurately, viscous friction torque was considered in the calculation of inertia torque, and Kalman filter was used to estimate the total load torque to solve the problem of under rank of motor motion equation. Simulation and experimental results showed that the proposed method could effectively identify the moment of inertia in both noisy and noiseless environments.

Spectral Analysis of Output Voltages and Currents as a Criterion for Technical Diagnostics of Synchronous Generators of Ship Diesel Engine

Abstract Diesel generator sets (DGU) are very widely used in autonomous power supply systems. An example is marine power plants, diesel locomotives with electric power transmission, uninterruptible power supply units, etc. The power of ship DGUs reaches 2–6 or more MW in one unit. The number of units on ships can be different, but, as a rule, at least two. In this paper, we propose a method of monitoring the dynamic electromechanical system “diesel synchronous generator”. The method aims at using a synchronous generator machine as a multifunctional accurate and sensitive sensor for diagnostic parameters of the electromechanical system. The proposed method of technical diagnostics is based on continuous monitoring of non-uniformity of diesel torque, fluctuations in the instantaneous angular velocity and instantaneous angular acceleration of the diesel crankshaft. These data are the results of a spectral analysis of stator currents and voltages of a synchronous generator.

Servo axis incipient degradation assessment of CNC machine tools using the built-in encoder

Servo axis system has been widely applied in the high-precision CNC machine tools. Its performance degradation may lead to the degradation of whole machine and ultimately result to the accuracy degradation of parts manufacturing. Thus, health assessment of the servo axis is very essential, especially for those in-service CNC machine tools. However, restricted by the complexity of servo axis structure, weak signal of incipient degradation, and limited sensors’ installation space, traditional degradation evaluation methods, such as the vibration based scheme, are very difficult to be applied in real service environment directly. In this paper, a new methodology is established for servo axis incipient degradation assessment by reusing the position fluctuation information captured by built-in encoder. Firstly, to highlight the torsional behavior of the servo axis components, the instantaneous angular acceleration (IAA) is estimated by using the position fluctuation information with frequency domain weighting (FDW) method. After that, the wavelet packet transform (WPT) is employed for decomposition of these nonstationary IAA signals. Finally, a Gini index (GI)–guided denoising scheme is established for incipient degradation feature reconstruction. The effectiveness of the proposed method is investigated by simulations; thereafter, it is applied for the X-axis assessment of an in-service high-precision vertical machining center. All the results illustrate that the proposed method is sensitive to incipient degradation of the rotating components and offers an alternative solution for health assessment of servo axis.

An encoder information-based anomaly detection method for planetary gearbox diagnosis

To keep the reliability of the planetary gearbox, anomaly detection has been widely investigated for its health monitoring. To this end, a novel approach is presented in this paper to extract fault features based on the merits of built-in encoder signals. Considering that collected encoder data is accumulated in angular positions, instantaneous angular acceleration (IAA) is firstly calculated to highlight the characteristic components. And then time synchronization average (TSA) is applied on an estimated multi-period for denoising, which improves the robustness of the TSA to the feature attenuation effect caused by the round-off error of the basic period. In this paper, we explore the distinguishing properties of regular components and the fault anomaly to impose different restraints on them, which is embodied as a periodicity-enhanced model of robust principle analysis. And objective features are further separated by solving this optimization model. The validation analysis of the proposed framework is applied on both the simulation and experimental cases. The results show that the proposed method is of good performance to deal with encoder signals from the planetary gearbox for fault diagnosis.

A Novel Permanent Magnetic Angular Acceleration Sensor.

Angular acceleration is an important parameter for status monitoring and fault diagnosis of rotary machinery. Therefore, we developed a novel permanent magnetic angular acceleration sensor, which is without rotation angle limitations and could directly measure the instantaneous angular acceleration of the rotating system. The sensor rotor only needs to be coaxially connected with the rotating system, which enables convenient sensor installation. For the cup structure of the sensor rotor, it has a relatively small rotational inertia. Due to the unique mechanical structure of the sensor, the output signal of the sensor can be directed without a slip ring, which avoids signal weakening effect. In this paper, the operating principle of the sensor is described, and simulated using finite element method. The sensitivity of the sensor is calibrated by torsional pendulum and angle sensor, yielding an experimental result of about 0.88 mV/(rad·s−2). Finally, the angular acceleration of the actual rotating system has been tested, using both a single-phase asynchronous motor and a step motor. Experimental result confirms the operating principle of the sensor and indicates that the sensor has good practicability.

A looming-sensitive pathway responds to changes in the trajectory of object motion

Two identified locust neurons, the lobula giant movement detector (LGMD) and its postsynaptic partner, the descending contralateral movement detector (DCMD), constitute one motion-sensitive pathway in the visual system that responds preferentially to objects that approach on a direct collision course and are implicated in collision-avoidance behavior. Previously described responses to the approach of paired objects and approaches at different time intervals (Guest BB, Gray JR. J Neurophysiol 95: 1428-1441, 2006) suggest that this pathway may also be affected by more complicated movements in the locust's visual environment. To test this possibility we presented stationary locusts with disks traveling along combinations of colliding (looming), noncolliding (translatory), and near-miss trajectories. Distinctly different responses to different trajectories and trajectory changes demonstrate that DCMD responds to complex aspects of local visual motion. DCMD peak firing rates associated with the time of collision remained relatively invariant after a trajectory change from translation to looming. Translatory motion initiated in the frontal visual field generated a larger peak firing rate relative to object motion initiated in the posterior visual field, and the peak varied with simulated distance from the eye. Transition from translation to looming produced a transient decrease in the firing rate, whereas transition away from looming produced a transient increase. The change in firing rate at the time of transition was strongly correlated with unique expansion parameters described by the instantaneous angular acceleration of the leading edge and subtense angle of the disk. However, response time remained invariant. While these results may reflect low spatial resolution of the compound eye, they also suggest that this motion-sensitive pathway may be capable of monitoring dynamic expansion properties of objects that change the trajectory of motion.

A data processing method for determining instantaneous angular speed and acceleration of crankshaft in an aircraft engine–propeller system using a magnetic encoder

This paper presents a method for determining the instantaneous angular speed and instantaneous angular acceleration of the crankshaft in a reciprocating engine and propeller dynamical system from electrical pulse signals generated by a magnetic encoder. The method is based on accurate determination of the measured global mean angular speed and precise values of times when leading edges of individual magnetic teeth pass through the magnetic sensor. Under a steady-state operating condition, a discrete deviation time vs. shaft rotational angle series of uniform interval is obtained and used for accurate determination of the crankshaft speed and acceleration. The proposed method for identifying sub- and super-harmonic oscillations in the instantaneous angular speeds and accelerations is new and efficient. Experiments were carried out on a three-cylinder four-stroke Saito 450R model aircraft engine and a Solo propeller in connection with a 64-teeth Admotec KL2202 magnetic encoder and an HS-4 data acquisition system. Comparisons with an independent data processing scheme indicate that the proposed method yields noise-free instantaneous angular speeds and is superior to the finite difference based methods commonly used in the literature.