Showing papers on "Bearing (mechanical) published in 2008"

Switchable rotation drive device

Abstract: A switchable rotation drive device has a switching mechanism wherein a first connecting sleeve that always rotates integrally with a motor hollow rotor, and a second connecting sleeve that always rotates integrally with a planetary carrier of a planetary gear reduction mechanism are connected via a bearing in a relatively rotatable state, and the first connecting sleeve is formed with a sun gear. By sliding the switching mechanism, the output shaft can be switched between high-speed rotation and low-speed rotation. In comparison to a case in which the entirety of the planetary gear reduction mechanism is made to slide, the sliding region may be smaller, and the required space needed to allow sliding may also be smaller. Therefore, it is advantageous to reduce the size of the device and make it more compact.

Models for Bearing Damage Detection in Induction Motors Using Stator Current Monitoring

Abstract: This paper describes a new analytical model for the influence of rolling-element bearing faults on induction motor stator current. Bearing problems are one major cause for drive failures. Their detection is possible by vibration monitoring of characteristic bearing frequencies. As it is possible to detect other machine faults by monitoring the stator current, a great interest exists in applying the same method for bearing fault detection. After a presentation of the existing fault model, a new detailed approach is proposed. It is based on the following two effects of a bearing fault: 1. the introduction of a particular radial rotor movement and 2. load torque variations caused by the bearing fault. The theoretical study results in new expressions for the stator current frequency content. Experimental tests with artificial and realistic bearing damage were conducted by measuring vibration, torque, and stator current. The obtained results by spectral analysis of the measured quantities validate the proposed theoretical approach.

Knee joint prosthesis system and method for implantation

Abstract: A prosthesis system for replacing a knee joint between a femur and a tibia can include a femoral component (16), a tibial component (18), a bearing (20), a first yoke (22), and a first key (182). The femoral component can include a first condylar portion (26), a second condylar portion (28), a first sidewall (40) extending superiorly from the first condylar portion, a second sidewall (42) extending superiorly from the second condylar portion where the first and second sidewalls collectively comprise a first hinge portion (44). The tibial component can have a bone engaging inferior surface (56) and a bearing engaging superior surface (58). The bearing can have an inferior surface (96) that engages the bearing engaging surface and a superior femoral engaging surface (90,92). The bearing can define an opening (94). The first yoke can have an inferior portion (122), a superior portion (120) and a yoke keyway (126) extending through the therethrough.

Diagnosis of Bearing Faults of Induction Machines by Vibration or Current Signals: A Critical Comparison

Abstract: Early diagnosis of faults in induction machines is an extensively investigated field, for cost and maintenance savings. Mechanical imbalances and bearing faults account for a large majority of faults in a machine, especially for small-medium size machines. Therefore their diagnosis is an intensively investigated field or research. Recently many research activities were focused on the diagnosis of bearing faults by current signal. Stator current components are generated at predictable frequencies related to the electrical supply and mechanical frequencies of bearing faults. However their detection is not always reliable, since the amplitude of fault signatures in the current signal is very low. This paper compares the bearing fault detection capability obtained with vibration and current signals. To this aim a testbed is realized that allows to test vibration and current signal on a machine with healthy or faulty bearings. Signal processing techniques for both cases are reviewed and compared in order to show which procedure is best suited to the different type of bearing faults. The paper contribution is the use of a simple and effective signal processing technique for both current and vibration signals, and a theoretical analysis of the physical link between faults and current components including torque ripple effects. As expected because of the different nature of vibration and current, bearing fault diagnosis is effective only for those fault whose mechanical frequency rate is quite low. Experiments are reported that confirm the proposed approach.

Fault diagnosis of low speed bearing based on relevance vector machine and support vector machine

Abstract: This study concerns with fault diagnosis of low speed bearing using multi-class relevance vector machine (RVM) and support vector machine (SVM). A low speed test rig was developed to simulate various types of bearing defects associated with shaft speeds as low as 10rpm under several loading conditions. The data was acquired from the low speed bearing test rig using acoustic emission (AE) and accelerometer sensors under a constant load with different speeds. The aim of this study is to address the problem of detecting an incipient bearing fault and to find reliable methods for low speed machine fault diagnosis. In this paper, two methods of multi-class classification techniques for fault diagnosis through RVM and SVM are presented and the effectiveness of using AE and vibration signals due to low impact rate for low speed diagnosis. In the present study, component analysis was performed initially to extract the features and to reduce the dimensionality of original data features. The classification for fault diagnosis was also conducted using original data feature and without feature extraction. The result shows that multi-class RVM produces promising results and has the potential for use in fault diagnosis of low speed machine.

Bearing Fault Detection Via Stator Current Noise Cancellation and Statistical Control

Abstract: This paper proposes a new approach to detect in situ bearing faults via stator current monitoring. For in situ bearing faults, the characteristic bearing fault frequencies may not exist, particularly at an early stage. In addition, the bearing fault signatures are usually subtle compared to the dominant components in the sampled stator current. Therefore, in this paper, a noise cancellation technique is used to suppress those dominant components that are not related to a potential bearing fault. The remaining components, i.e., the noise-cancelled stator current, are then closely related to the health condition of the bearing. Furthermore, it is observed that under the presence of a bearing fault, the noise-cancelled stator current displays a significant amount of degrees of uncontrolled variation in its magnitude. The uncontrolled variation is detected by observing the samples falling outside the three-sigma limits on Shewhart's control charts. Therefore, it is possible to detect in situ bearing faults by detecting the variation in magnitude of the noise-cancelled stator current, as verified by online experiments performed in this paper.

Porous metal cup with cobalt bearing surface

Abstract: An acetabular cup assembly (10) can include a cup portion and a bearing. The cup portion can include a porous metal outer layer having a first thickness and a solid titanium inner layer having a second thickness. A mating feature can be formed between the cup portion and the bearing. The bearing can be adapted to be selectively secured to the titanium inner layer. In one example, the bearing is formed of cobalt.

Testing and modeling of square carbon fiber‐reinforced elastomeric seismic isolators

Abstract: Steel-reinforced elastomeric isolators (SREIs), as an effective seismic isolation device, are the most common isolators in use. However, SREIs are typically heavy and expensive and, as a result, application of these devices is often limited to large and expensive structures. A reduction in the cost and weight of elastomeric isolators would permit a significant increase in their application to many ordinary residential and commercial buildings. Fiber-reinforced elastomeric isolators (FREIs) are a new type of elastomeric bearing that employs fiber as the reinforcement material rather than steel. FREIs have several advantages over traditional SREIs including superior damping properties, lower manufacturing cost, light weight, and the possibility of being produced in long rectangular strips with individual isolators cut to the required size. This paper presents a brief literature review on experiments with FREIs, and reports on an experimental study conducted on carbon FREIs from which the mechanical properties of the bearings, including displacement characteristics and damping values are evaluated. A brief description of an analytical approach to model the cyclic response of the bearings is another component of this paper. As a special application, the bearings considered in this study were not bonded to the test platens. For bearings having suitable aspect ratio values, this particular type of application resulted in a stable rollover deformation, which reduced the horizontal stiffness and increased the efficiency of the bearing as a seismic isolator device. Test results suggest that for many high seismic risk regions worldwide, the application considered in this study can be viable for the base isolation of ordinary low-rise buildings. Copyright © 2007 John Wiley & Sons, Ltd.

Whirl and whip instabilities in rotor-bearing system considering a nonlinear force model

Abstract: Linear models and synchronous response are generally adequate to describe and analyze rotors supported by hydrodynamic bearings. Hence, stiffness and damping coefficients can provide a good model for a wide range of situations. However, in some cases, this approach does not suffice to describe the dynamic behavior of the rotor-bearing system. Moreover, unstable motion occurs due to precessional orbits in the rotor-bearing system. This instability is called “oil whirl” or “oil whip”. The oil whirl phenomenon occurs when the journal bearings are lightly loaded and the shaft is whirling at a frequency close to one-half of rotor angular speed. When the angular speed of the rotor reaches approximately twice the natural frequency (first critical speed), the oil whip phenomenon occurs and remains even if the rotor angular speed increases. Its frequency and vibration mode correspond to the first critical speed. The main purpose of this paper is to validate a complete nonlinear solution to simulate the fluid-induced instability during run-up and run-down. A flexible rotor with a central disk under unbalanced excitation is modeled. A nonlinear hydrodynamic model is considered for short bearing and laminar flow. The effects of unbalance, journal-bearing parameters and rotor arrangement (vertical or horizontal) on the instability threshold are verified. The model simulations are compared with measurements at a real vertical power plant and a horizontal test rig.

Modeling Triple Friction Pendulum Bearings for Response-History Analysis

Abstract: There are currently no applicable hysteresis rules or nonlinear elements available in structural analysis software that can be used to exactly model triple Friction Pendulum bearings for response-history analysis. Series models composed of existing nonlinear elements are proposed since they can be immediately implemented in currently available analysis software. However, the behavior of the triple Friction Pendulum bearing is not exactly that of a series arrangement of single concave Friction Pendulum bearings—though it is similar. This paper describes how to modify the input parameters of the series model in order to precisely retrace the true force-displacement behavior exhibited by this device. Recommendations are made for modeling in SAP2000 and are illustrated through analysis of a simple seismically isolated structure. The results are confirmed by (a) verifying the force-displacement behavior through comparison with experimental data and (b) verifying the analysis through comparison to the ...

Computational fluid dynamics analysis of a journal bearing with surface texturing

Abstract: An analysis of a lubricated conformal contact is carried out to study the effect of surface texture on bearing friction and load carrying capacity using computational fluid dynamics The work focus

Fault diagnosis of rolling element bearing using time-domain features and neural networks

Abstract: Rolling element bearings are critical mechanical components in rotating machinery Fault detection and diagnosis in the early stages of damage is necessary to prevent their malfunctioning and failure during operation Vibration monitoring is the most widely used and cost-effective monitoring technique to detect, locate and distinguish faults in rolling element bearings This paper presents an algorithm using feed forward neural network for automated diagnosis of localized faults in rolling element bearings Normal negative log-likelihood value and kurtosis value extracted from time-domain vibration signals are used as input features for the neural network Trained neural networks are able to classify different states of the bearing with 100% accuracy The proposed procedure requires only a few input features, resulting in simple preprocessing and faster training Effectiveness of the proposed method is illustrated using the bearing vibration data obtained experimentally

Induction Motor Bearing Failure Detection and Diagnosis: Park and Concordia Transform Approaches Comparative Study

Abstract: This paper deals with the problem of bearing failure detection and diagnosis in induction motors. Indeed, bearing deterioration is now the main cause of induction motor rotor failures. In this context, two fault detection and diagnosis techniques, namely the Park transform approach and the Concordia transform, are briefly presented and compared. Experimental tests, on a 0.75 kW two-pole induction motor with artificial bearing damage, outline the main features of the aforementioned approaches for small- and medium-size induction motors bearing failure detection and/or diagnosis.

Fault diagnostics of roller bearing using kernel based neighborhood score multi-class support vector machine

Abstract: Roller bearing is one of the most widely used rotary elements in a rotary machine. The roller bearing's nature of vibration reveals its condition and the features that show the nature are to be extracted through some indirect means. Statistical parameters like kurtosis, standard deviation, maximum value, etc. form a set of features, which are widely used in fault diagnostics. Finding out good features that discriminate the different fault conditions of the bearing is often a problem. Selection of good features is an important phase in pattern recognition and requires detailed domain knowledge. This paper addresses the feature selection process using decision tree and uses kernel based neighborhood score multi-class support vector machine (MSVM) for classification. The vibration signal from a piezoelectric transducer is captured for the following conditions: good bearing, bearing with inner race fault, bearing with outer race fault, and inner and outer race faults. The statistical features are extracted therefrom and classified successfully using MSVM. The results of MSVM are compared with and binary support vector machine (SVM).

Magnetic Bearing Configurations: Theoretical and Experimental Studies

Abstract: A radial magnetic bearing, consisting of two permanent magnets, is an attractive choice because of its zero wear, negligible friction, and low cost, but it suffers from low load capacity, low radial stiffness, lack of damping, and high axial instability. To enhance the radial load and radial stiffness, and reduce the axial thrust, we have made a theoretical and experimental study of various radial configurations, including hydrodynamic lubrication to improve dynamic performance of the magnetic bearing. We developed an experimental setup to investigate the performance of bearing configurations under different operating conditions. The motion of a rotating shaft is mapped by two displacement sensors with a data acquisition system and personal computer. The first critical speed of each configuration is determined experimentally and verified through frequency analysis. We present a polar plot of displacement data.

3D Simplified Finite Elements Analysis of Load and Contact Angle in a Slewing Ball Bearing

Abstract: Bolted bearing connections are one of the most important connections in some industrial structures, and manufacturers are always looking for a quick calculation model for a safe design. In this context, all the analytical and numerical models reduce the global study to the study of the most critical sector. Therefore, the main inputs for these models are the maximal equivalent contact load and the corresponding contact angle. Thus, a load distribution calculation model that takes all the important parameters, such as the stiffness of the supporting structure and the variation in the contact angle, into consideration is needed. This paper presents a 3D finite element (FE) simplified analysis of load distribution and contact angle variation in a slewing ball bearing. The key element of this methodology, which is based on the Hertz theory, is modeling the rolling elements under compression by nonlinear traction springs between the centers of curvature of the raceways. The contact zones are modeled by rigid shells to avoid numerical singularities. Each raceway curvature center is coupled to the corresponding contact zone by rigid shells. The main contribution of this method is not only the evaluation of the contact loads with a relatively reduced calculation time but also the variation in the contact angle from the deformed coordinates of the curvature centers. Results are presented for several loading cases: axial loading, turnover moment, and a combined loading of axial force and turnover moment. The influence of the most important parameters such as the contact angle, the stiffness of the bearings, and the supporting structure is discussed. Finally, a preliminary experimental validation is conducted on a standard ball bearing. The results presented in this paper seem encouraging. The FE study shows an important influence of several parameters and a good correlation with experimental results. Consequently, this model can be extended to other types of slewing bearings such as roller bearings. Moreover, it can be implemented in complex industrial structures such as cranes and lifting devices to determine the corresponding load distributions and contact angles and, consequently, the most critical sector.

Bearing Signature Analysis as a Medium for Fault Detection: A Review

Abstract: Rolling element bearings find widespread domestic and industrial application. Defects in bearing unless detected in time may lead to malfunctioning of the machinery. Different methods are used for detection and diagnosis of the bearing defects. This paper is intended as a tutorial overview of bearing vibration signature analysis as a medium for fault detection. An explanation for the causes for the defects is discussed. Vibration measurement in both time domain and frequency domain is presented. Recent trends in research on the detection of the defects in bearings have been included.

Scaling Effects of Inverter-Induced Bearing Currents in AC Machines

Abstract: In this survey paper, we show by straightforward mathematical scaling considerations that small inverter-fed ac motors of up to typical 20 kW at 1500/min are likely to suffer from discharge (electric discharge machining) bearing currents, whereas larger motors are likely to be subjected to high-frequency (HF) circulating bearing currents. When comparing motors that operate at the same voltage level, the resulting bearing-current density is high for very small and very large motors. Smaller values occur in between these two extremes with medium size motors in the range of 10-100 kW. Therefore, electric bearing insulation is useful for larger motors to interrupt the HF circulating bearing-current path, whereas small motors need rotor shielding, common-mode voltage filters, or hybrid bearings.

Sensor-equipped bearing for wheel

Abstract: A sensor-equipped wheel support bearing assembly capable of accurately detecting load acting on the vehicle wheel by reducing concentration of strain on a cutout portion corner area of a strain generating member in a sensor unit is provided. The wheel support bearing assembly having rolling elements interposed between rolling surfaces in outer and inner members, includes at least one sensor unit provided in a stationary member, which is one of the outer and inner members. The sensor unit includes a strain generating member, having two or more contact fixing segments secured to the stationary member in contact therewith, and a sensor fitted to the strain generating member for detecting a strain in the strain generating member. The strain generating member has a cutout portion between the contact fixing segments, and corner area of such cutout portion is of an arcuately sectioned shape.

Machine Fault Signature Analysis

Abstract: The objective of this paper is to present recent developments in the field of machine fault signature analysis with particular regard to vibration analysis. The different types of faults that can be identified from the vibration signature analysis are, for example, gear fault, rolling contact bearing fault, journal bearing fault, flexible coupling faults, and electrical machine fault. It is not the intention of the authors to attempt to provide a detailed coverage of all the faults while detailed consideration is given to the subject of the rolling element bearing fault signature analysis.

Compliant hybrid gas journal bearing using integral wire mesh dampers

Abstract: A compliant hybrid gas journal bearing includes compliant hybrid bearing pads having a hydrostatic recess and a capillary restrictor for providing a flow of pressurized gas to the bearing The bearing also includes an inner rim adjacent the bearing pads, an outer rim and a damper bridge between the inner and outer rims The damper bridge has an axial length that is less than an axial length of the bearing pads and the outer rim to form a damper cavity on each side of the damper bridge An integral wire mesh damper is situated within the damper cavity on each side of the damper bridge Integral centering springs are located between the inner and outer rims to provide radial and rotational compliance to the bearing pads The oil-free bearing design addresses the low damping and low load capacity characteristics that are inherent in present day compliant air foil bearing designs, while retaining the compliance to changes in rotor geometry