Showing papers on "Bearing (mechanical) published in 2000"

Neural-network-based motor rolling bearing fault diagnosis

Abstract: Motor systems are very important in modern society. They convert almost 60% of the electricity produced in the US into other forms of energy to provide power to other equipment. In the performance of all motor systems, bearings play an important role. Many problems arising in motor operations are linked to bearing faults. In many cases, the accuracy of the instruments and devices used to monitor and control the motor system is highly dependent on the dynamic performance of the motor bearings. Thus, fault diagnosis of a motor system is inseparably related to the diagnosis of the bearing assembly. In this paper, bearing vibration frequency features are discussed for motor bearing fault diagnosis. This paper then presents an approach for motor rolling bearing fault diagnosis using neural networks and time/frequency-domain bearing vibration analysis. Vibration simulation is used to assist in the design of various motor rolling bearing fault diagnosis strategies. Both simulation and real-world testing results obtained indicate that neural networks can be effective agents in the diagnosis of various motor bearing faults through the measurement and interpretation of motor bearing vibration signatures.

Intervertebral disc prosthesis and method

Abstract: The present invention is directed to intervertebral prosthetic devices and methods. The intervertebral prosthetic devices and methods of the invention provides a variable instantaneous axis of rotation. In general, the disclosed devices include two bearing surfaces, a first bearing surface being curved and a second bearing surface being planar. In some embodiments, the curved bearing surface provides at least three degrees of rotational freedom and the planar bearing surface provides at least two degrees of translational freedom and one degree of rotational freedom. Several embodiments with varying degrees of rotational or translational freedom are disclosed.

Ac generator for vehicle

Abstract: In An AC generator for a vehicle in which a bearing is inserted into a bearing box formed in a bracket and the bearing is fixed and retained by a retainer, the retainer has a cylindrical shape and a threaded portion is formed on the cylindrical section thereof, a threaded portion is formed on the bearing box, and the threaded portion of the retainer is directly screwed to the threaded portion of the bearing box in order to fix and retain the bearing, so that the gap between the outer circumference surface of the bearing box or the outer circumference surface of the retainer and the opposing side of a cooling fan is made uniform.

Toroidal type continuously variable transmission

Abstract: A continuously variable transmission including discs made of heat-resisting bearing steel, and rollers made of ceramics. The heat-resisting bearing steel contains 0.8-1.5 wt % of C, 0.5-2.0 wt % of Si, 0.3-2.0 wt % of Mn, 1.3-1.98 wt % of Cr, and 0.3-1.0 wt % of Mo, (Si+Mo) being 1.0 wt % or more. Because the rollers are made of ceramics superior in heat resistance, the toroidal type continuously variable transmission, even if used under high load and high rotational speed, is free from occurrence of sticking between discs and rollers and damage of the raceway surfaces.

Floating bearing knee joint prosthesis with a fixed tibial post

Abstract: This invention relates to a floating bearing knee joint prosthesis (146) having a fixed tibial post used for replacing the articulating knee portion of a femur and a tibia. The floating bearing knee joint prosthesis (146) includes a femoral component (152), a tibial component (154), a guide post (206) and a bearing member (156). The femoral component (152) includes an engagement member (176), a first femoral bearing surface (162) and a second femoral bearing surface (164). The tibial component (154) includes a tibial bearing surface (196). The guide post (206) extends from the tibial component (154) and is operable to be engaged by the engagement member (176) of the femoral component (152). The bearing member (156) includes a first bearing surface (200) that articulates with the first femoral bearing surface (162), a second bearing surface (202) that articulates with the first femoral bearing surface (164) and a third bearing surface (198) that articulates with the tibial bearing surface (196). The bearing member (156) further includes a posterior lip extension (284) that substantially inhibits the bearing member (156) from dislocating upon flexion of the knee prosthesis (146).

Rotating Machinery Vibration: From Analysis to Troubleshooting

Abstract: Part I: Primer on Rotor Vibration Vibration Concepts and Methods One-Degree-of-Freedom Model Multi-DOF Models Modes, Excitation, and Stability of Multi-DOF Models Lateral Rotor Vibration Analysis Models Simple Linear Models Formulations for RDA Software Insights into Linear LRVs Nonlinear Effects in Rotor Dynamical Systems Torsional Rotor Vibration Analysis Models Rotor-Based Spinning Reference Frames Single Uncoupled Rotor Coupled Rotors Semidefinite Systems Part II: Rotor Dynamic Analyses RDA Code for Lateral Rotor Vibration Analyses Unbalance Steady-State Response Computations Instability Self-Excited-Vibration Threshold Computations Additional Sample Problems Bearing and Seal Rotor Dynamics Liquid-Lubricated Fluid-Film Journal Bearings Experiments to Measure Dynamic Coefficients Annular Seals Rolling Contact Bearings Squeeze-Film Dampers Magnetic Bearings Compliance Surface Foil Gas Bearings Turbo-Machinery Impeller and Blade Effects Centrifugal Pumps Centrifugal Compressors High-Pressure Steam Turbines and Gas Turbines Axial Flow Compressors Part III Monitoring and Diagnostics Rotor Vibration Measurement and Acquisition Introduction to Monitoring and Diagnostics Measured Vibration Signals and Associated Sensors Vibration Data Acquisition Signal Conditioning Vibration Severity Guidelines Casing and Bearing Cap Vibration Displacement Guidelines Standards, Guidelines, and Acceptance Criteria Shaft Displacement Criteria Signal Analysis and Identification of Vibration Causes Vibration Trending and Baselines FFT Spectrum Rotor Orbit Trajectories Bode, Polar, and Spectrum Cascade Plots Wavelet Analysis Tools Chaos Analysis Tools Symptoms and Identification of Vibration Causes Part IV Trouble-Shooting Case Studies Forced Vibration and Critical Speed Case Studies HP Steam Turbine Passage through First Critical Speed HP-IP Turbine Second Critical Speed through Power Cycling Boiler Feed Pumps: Critical Speeds at Operating Speed Nuclear Feed Water Pump Cyclic Thermal Rotor Bow Power Plant Boiler Circulating Pumps Nuclear Plant Cooling Tower Circulating Pump Resonance Generator Exciter Collector Shaft Critical Speeds Self-Excited Rotor Vibration Case Studies Swirl Brakes Cure Steam Whirl in a 1300 MW Unit Bearing Unloaded by Nozzle Forces Allows Steam Whirl Misalignment Causes Oil Whip/Steam Whirl "Duet" Additional Rotor Vibration Cases and Topics Vertical Rotor Machines Vector Turning from Synchronously Modulated Rubs Air Preheater Drive Structural Resonances Aircraft Auxiliary Power Unit Commutator Vibration-Caused Uneven Wear Impact Tests for Vibration Problem Diagnoses Bearing Looseness Effects Tilting-Pad versus Fixed-Surface Journal Bearings Base-Motion Excitations from Earthquake and Shock Parametric Excitation: Nonaxisymmetric Shaft Stiffness Rotor Balancing Index

Bearing induced vibration in precision high speed routing spindles

Abstract: This paper presents a detailed model of bearing vibration, including the effect of contact spring non-linearity in balls-to-raceways' contacts. The model incorporates the effect of surface waviness of rolling elements and off-sized balls upon the dynamic internal radial clearance of the bearing. The vibration forces and moments generated are formulated and the significant principal and secondary side-band contributions are highlighted. This model is employed successfully in the recognition of complex real-time vibration spectra of a precision routing spindle, obtained by accurate non-contact sensors.

Performance and Durability of High Temperature Foil Air Bearings for Oil-Free Turbomachinery

Abstract: The performance and durability of advanced, high temperature foil air bearings are evaluated under a wide range (10 to 50 kPa) of loads at temperatures from 25° to 650 °C. The bearings are made from uncoated nickel based superalloy foils. The foil surface experiences sliding contact with the shaft during initial start/stop operation. To reduce friction and wear, the solid lubricant coating, PS304, is applied to the shaft by plasma spraying. PS304 is a NiCr based Cr2O3 coating with silver and barium fluoride/calcium fluoride solid lubricant additions. The results show that the bearings provide lives well in excess of 30,000 cycles under all of the conditions tested. Several bearings exhibited lives in excess of 100,000 cycles. Wear is a linear function of the bearing load. The excellent performance measured in this study suggests that these bearings and the PS304 coating are well suited for advanced high temperature, oil-free turbomachinery applications. Presented at the 55th Annual Meeting Nashville, Tenn...

Experimental and Numerical Investigations on the Influence of Tooth Friction in Spur and Helical Gear Dynamics

Abstract: A model based upon a finite element procedure is introduced for analyzing the influence of tooth friction on spur and helical gear dynamics. The equations of motion are solved by combining a time-step integration method with several iterative algorithms aimed at satisfying normal and tangential contact conditions. Comparisons between simulated and measured quasi-static bearing forces are satisfactory and largely validate the theoretical developments. Results also reveal the potentially significant contribution of tooth friction to gear vibration and noise. Simulations are then extended to high speeds and the interest of considering both transmission error and tooth friction excitations to achieve silent gears is discussed.

Static and Dynamic Tooth Loading in Spur and Helical Geared Systems-Experiments and Model Validation

Abstract: The primary objective of this study is to validate a specific finite element code aimed at simulating dynamic tooth loading in geared rotor systems. Experiments have been conducted on a high-precision single stage spur and helical gear reducer with flexible shafts mounted on hydrostatic or hydrodynamic bearings. The numerical model is based on classical elements (shaft, lumped stiffnesses,...) and on a gear element which accounts for non-linear time-varying mesh stiffness, gear errors and tooth shape modifications. External and parametric excitations are derived from the instantaneous contact conditions between the mating flanks by using an iterative contact algorithm inserted in a time-step integration scheme. First, experimental and numerical results at low speeds are compared and confirmed that the proposed tooth mesh interface model is valid. Comparisons were then extended to dynamic fillet stresses on both spur and helical gears between 50-6000 rpm on pinion shaft. Despite a localized problem in the case of spur gears with one particular bearing arrangement, the broad agreement between the experimental and numerical response curves demonstrated that the model is representative of the dynamic behavior of geared systems.

Analysis of Gas Lubricated Foil Thrust Bearings Using Coupled Finite Element and Finite Difference Methods

Abstract: Load performance of gas lubricated, compliant surface foil thrust bearings has an interlocking relationship with the compliance of the bearing and hydrodynamics of convergent wedge surface. Compliance of the bearing consists of supporting spring elements (elastic foundation) and a smooth elastic top foil. In this paper, a class of gas lubricated foil thrust bearings has been investigated analytically utilizing a novel approach which combines Finite Difference (FD) and Finite Element (FE) methods. Solution of the governing hydrodynamic equations dealing with compressible fluid is coupled with the structural resiliency of the foil bearing surfaces. FD method is utilized for hydrodynamic analysis while FE is used to model structural resiliency. Influence coefficients were generated to address the elasticity effects of combined top foil and elastic foundation on the hydrodynamics of thrust bearing, and were used to expedite the numerical solution. Within 2 to 3 iterations the convergence criterion was reached. The overall program logic proved to be an efficient technique to deal with the complex structural compliance of various foil bearing. Case study has been conducted and sample solutions are provided. Unlike prior analytical investigations, the essential effect of the top foil on the performance of the bearing has been elucidated.

Gas bearings for use with vacuum chambers and their application in lithographic projection apparatus

Abstract: A bearing for use in a vacuum chamber comprises a gas bearing discharging pressurised gas into a gap between two members to maintain a predetermined separation between those members. To avoid the gas forming the gas bearing being an unacceptable leak into the vacuum chamber, a vacuum pump is provided between the vacuum chamber and the gas bearing.

Calculation of the Stiffness Matrix of Angular Contact Ball Bearings by Using the Analytical Approach

Abstract: The stiffness matrix of angular contact ball bearings is calculated by using the analytical approach in which the summation of ball-race loads is replaced by an integration. The matrix connected to the conventional model in two degrees of freedom is first presented. A practical application of this formulation is illustrated through the common problem of sizing a two bearings-shaft arrangement. Variations of displacements, axial forces, and bearing fatigue life related to preload are shown to be easily obtained. Then, the matrix connected to the model in five degrees of freedom is given. This may be coupled with finite elements which are generally used to model the shaft or the housing.

Unbalanced force calculation in switched-reluctance machines

Abstract: This paper presents a detailed analytical model for computing the radial magnetic forces that arise in switched reluctance machines (SRM's). The model is general and includes iron saturation, displacements of the rotor from its center location, and arbitrary angular rotor positions. The force between an individual stator pole and its corresponding rotor pole is calculated. The model is used to calculate the unbalanced magnetic forces on the SRM rotor, due to the rotor being displaced from its center location, by calculating the difference in the radial magnetic forces on opposite stator poles. The calculation of the unbalanced magnetic rotor forces requires an especially accurate model for the radial magnetic forces since the unbalanced forces are the difference between the two large radial forces on opposite sides of the rotor. The side pull created by the unbalanced forces will stress the bearings of the motor. The detailed analytical model presented here will simplify the bearing system design and will be especially useful if less stiff magnetic bearings are being employed. Finite-element analysis is used to validate the detailed analytical model. This same model for calculating the radial magnetic forces can be used as the input to a calculation of stator yoke ovulation due to radial magnetic forces and of the resulting acoustical noise production.

Bearing failure of composite bolted joints with non-uniform bolt-to-washer clearance

Abstract: This paper investigates the effect of the relative positions of the bolt and the washer on bearing failure behavior of bolted composite joints with various lateral constraints. Two extreme diametral fit positions, with a positive or negative bolt hole-to-washer clearance, were considered. Experimental results show that the relative location can affect the initial failure loads but not the ultimate failure loads. The measured failure loads were also used to validate an existing analytical model.

Surface roughness effect on the dynamic stiffness and damping characteristics of compensated hydrostatic thrust bearings

Abstract: On the basis of Christensen's stochastic model of rough surfaces, this study theoretically analyzes the effect of surface roughness on the dynamic stiffness and damping characteristics of compensated hydrostatic circular step thrust bearings. Both the stochastic Reynolds equation with rotational inertia effect and the recess flow continuity equation with recess volume fluid compressibility effect are derived to take into account the presence of roughness on the bearing surfaces. Using a small perturbation method, the dynamic coefficients of bearings are evaluated. According to the results, the mean stiffness and damping behaviours are significantly affected by the roughness pattern and the height of roughness. The effect of circumferential roughness provides an increase in the mean bearing stiffness and damping characteristics as compared to the smooth-bearing case. However, these trends are reversed for the bearing having radial roughness structure. An illustration of a design example is also included for industrial practice.

Optimization of radial active magnetic bearings using the finite element technique and the differential evolution algorithm

Abstract: An optimization of radial active magnetic bearings is presented in the paper. The radial bearing is numerically optimized, using differential evolution-a stochastic direct search algorithm. The nonlinear solution of the magnetic vector potential is determined, using the 2D finite element method. The force is calculated by Maxwell's stress tensor method. The parameters of the optimized and nonoptimized bearing are compared. The force, the current gain, and the position stiffness are given as functions of the control current and rotor displacement.

A theoretical model to predict the vibration response of rolling bearings in a rotor bearing system to distributed defects under radial load

Abstract: A theoretical model to predict the vibration response of rolling element bearing in a rotor bearing system to distributed defects under radial load has been developed. The rotor bearing system has been considered as a three degrees of freedom model. The distributed defects considered are, the waviness of outer and inner races, and off size rolling element. The model predicts discrete spectrum with specific frequency components for each order of waviness. For outer race waviness, the spectrum has components at outer race defect frequency and its harmonics. In the case of inner race waviness, the waviness orders equal to number of rolling elements and its multiples give rise to spectral components at inner race defect frequency and its multiples. Other orders of waviness generate sidebands at multiples of shaft frequency about these peaks. The model predicts the amplitudes of the spectral components due to outer race waviness to be much higher as compared to those due to inner race waviness. In the case of an off-size rolling element, the model predicts discrete spectra having significant components at multiples of cage frequency.

Double wall bearing cone

Abstract: A double wall bearing cone closes an opening between a bearing housing and an exhaust frame in a gas turbine. The bearing cone includes a conical forward plate having an inner diameter and an outer diameter and a conical aft plate nested with and spaced from the conical forward plate. A hub connects the inner diameters of the forward plate and the aft plate. The hub preferably includes holes therein that serve to meter air flow between the forward plate and the aft plate. The double wall bearing cone defines a cooling circuit that reduces wear between a third stage turbine wheel in a gas turbine and the rotor aft shaft.

Combination Radial-Axial Magnetic Bearing

Abstract: The design and application of a patented active actuator design that combines the radial and axial actuator into one combination radial-axial actuator is presented. The theory of operation of the actuator is defined and magnetic finite element analysis modeling shown verifying operation. Its mechanical construction is then presented to show how this actuator configuration is successfully integrated into a mechanical system. Applications up to 60,000 rpm are then presented, with a detailed presentation of a 42,000 rpm energy storage flywheel currently under test at the University of Texas Center for Electromechanics. INTRODUCTION Conventional active magnetic bearing systems, whether electromagnet bias or permanent magnet bias, typically utilize three actuators for a 5-axis system (shown in Figure 1). This would be in the form of two radial actuators, each supporting and controlling two radial axes, and a thrust actuator supporting and controlling a single axial axis. Each actuator axis functions independently to provide forces in its defined axis for stable support and control of the levitated rotor. FIGURE 1. Three Bearing, Five Axis System The elimination of one actuator can simplify the system, reduce overall system size, possibly improve rotor dynamics and simplify control, and inherently reduce cost. A five axis, two bearing system is shown in Figure 2. These benefits have been realized to some extent with conical active radial bearings utilized to provide axial centering. However, this type of system presents manufacturing, control and integration challenges, in addition to issues with the long distance between the two radial bearings providing the axial control. What is needed for most applications is a full five active axis system to meet the load capacity and control requirements in all five axes adequately. FIGURE 2. Two Bearing, Five Axis System The combination bearing presented in Figure 3 reduces the total actuators required for a five axis active system from three to two, with one active actuator supporting and controlling three axes. This combination actuator configuration offers high radial and axial load capacities typically required for all active magnetic bearing systems. The simple construction and the elimination of a separate thrust actuator minimizes the space necessary to integrate the design and also minimizes rotor diameter, making it well suited for high-speed applications. FIGURE 3. Three Dimensional View of Combination Bearing MAGNETIC DESIGN This novel bearing design is constructed in a homopolar configuration such that the bias field is one polarity on all the radial poles, and the opposite polarity on the axial poles (i.e. the bias field enters the rotor through the radial air gaps and exits the rotor through the axial air gaps). This eliminates field polarity changes in the radial air gap to minimize rotor losses [1,2]. The design utilizes a permanent magnet or electromagnet to provide both radial and axial bias fields. The permanent magnet provides the linear negative stiffness benefit as present in the radial homopolar magnetic bearing [3]. Control coils for each radial axis and the axial axis act independently to modulate forces in each of the independent axes. The control field boosts the bias field in the direction of added force, and bucks the bias in the opposite pole. This difference in opposite pole fields provides the net force in the direction desired. The combination radial/thrust bearing utilizes a single radially polarized permanent-magnet ring to energize the radial and axial magnetic air gaps. The packaging of the control coils and ferromagnetic pole pieces results in virtually all of the volume being utilized functionally, leaving very little unused space within the confines of the bearing module. This highly efficient use of volume results in maximum spatial, magnetic, and electrical efficiencies. Figure 4 identifies the primary components of the bearing. Pole

The Evaluation of a Modified Chrome Oxide Based High Temperature Solid Lubricant Coating for Foil Gas Bearings

Abstract: This paper describes the friction and wear performance of PS304, a modified chrome oxide based coating, for foil gas bearings. PS304 contains 60 wt% NiCr binder, 20 wt% Cr2O3 hardener, and 10 wt% each Ag, and BaF2/CaF2 lubricants. For evaluation, the coating is plasma spray deposited onto test journals which are slid against a superalloy partial arc foil bearing. The test load was 10 KPa (1.5 psi) and the bearings were run under start/stop cyclic conditions. The data show good wear performance of the bearing, especially at temperatures above 25 deg. C. Bearing friction was moderate (micron approx. or equal to 0.4) over the entire temperature range. Based upon the results obtained, the PS304 coating has promise for high temperature, oil-free turbomachinery applications.

Granular packings and fault zones

Abstract: The failure of a two-dimensional packing of elastic grains is analyzed using a numerical model. The packing fails through formation of shear bands or faults. During failure there is a separation of the system into two grain-packing states. In a shear band, local ``rotating bearings'' are spontaneously formed. The bearing state is favored in a shear band because it has a low stiffness against shearing. The ``seismic activity'' distribution in the packing has the same characteristics as that of the earthquake distribution in tectonic faults. The directions of the principal stresses in a bearing are reminiscent of those found at the San Andreas Fault.

Oil-Free Turbocharger Demonstration Paves Way to Gas Turbine Engine Applications

Abstract: An oil-free, 150 Hp turbocharger was successfully operated to 100% speed (95,000 rpm), with turbine inlet temperatures to 650°C on a turbocharger gas test stand. Development of this high speed turbomachine included bearing and lubricant component development tests, rotor-bearing dynamic simulator qualification and gas stand tests of the assembled turbocharger. Self acting, compliant foil hydrodynamic air bearings capable of sustained operation at 650°C and maximum loads to 750 N were used in conjunction with a newly designed shaft and system center housing. Gas stand and simulator test results revealed stable bearing temperatures, low rotor vibrations, good shock tolerance and the ability of the rotor bearing system to sustain overspeed conditions to 121,500 rpm. Bearing component development tests demonstrated 100,000 start stop cycles at 650°C with a newly developed solid film lubricant coating. In a separate demonstration of a 100 mm compliant foil bearing, loads approaching 4,500 N were supported by a compliant foil bearing. This combination of component and integrated rotor-bearing system technology demonstrations addresses many of the issues associated with application of compliant foil bearings to gas turbine engines.Copyright © 2000 by ASME