Showing papers on "Bearing (mechanical) published in 1994"

Motor bearing damage detection using stator current monitoring

Abstract: This paper addresses the application of motor current spectral analysis for the detection of rolling-element bearing damage in induction machines. Vibration monitoring of mechanical bearing frequencies is currently used to detect the presence of a fault condition. Since these mechanical vibrations are associated with variations in the physical air gap of the machine, the air gap flux density is modulated and stator currents are generated at predictable frequencies related to the electrical supply and vibrational frequencies. This paper takes the initial step of investigating the efficacy of current monitoring for bearing fault detection by correlating the relationship between vibration and current frequencies caused by incipient bearing failures. The bearing failure modes are reviewed and the characteristic bearing frequencies associated with the physical construction of the bearings are defined. The effects on the stator current spectrum are described and the related frequencies determined. This is an important result in the formulation of a fault detection scheme that monitors the stator currents. Experimental results which show the vibration and current spectra of an induction machine with different bearing faults are used to verify the relationship between the vibrational and current frequencies. The test results clearly illustrate that the stator current signature can be used to identify the presence of a bearing fault. >

Advancements in the Performance of Aerodynamic Foil Journal Bearings: High Speed and Load Capability

Abstract: An advanced-design, aerodynamic, air-lubricated foil journal bearing achieved a landmark speed of 2200 cps (132,000 rpm) and a major breakthrough in load performance of 673.5 kPa (97.7 psi). At 20°C (68°F) room temperature, normal ambient pressure, 995 cps (59,700 rpm) rotor speed, and with bearing projected pad area of 1081 mm2 (1.675 in2 ), the bearing demonstrated a load capacity of 727.8 N (163.6 lb). The bearing also exhibited low heat generation, with about 40°C (104°F) average side leakage temperature rise. For this demonstration, a highspeed spindle utilizing a pair of 35-mm (1.375-in.) bearings and supporting a test rotor with a mass of 1.545 kg (weighing 3.41 lb) and overall length of 211 mm (8.3 in.) was successfully taken to the limiting speed of the test apparatus. This speed was set by the maximum sound velocity (Mach 1) in the spindle’s turbine wheel. The rotor/bearing speed of 4.62 × 106 DN is beyond the capability of any advanced oil-lubricated ball bearings or conventional gas-lubricated bearings. The net result is a highly stable bearing at high operating speed. This paper presents the development of this air-lubricated foil journal bearing, the operational procedures used during testing, test results (dynamic analyses), and load performance characteristics.

A Review of Rolling Element Bearing Vibration 'Detection, Diagnosis and Prognosis',

Abstract: : Rolling element bearings are among the most common components to be found in industrial rotating machinery. They are found in industries from agriculture to aerospace, in equipment as diverse as paper mill rollers to the Space Shuttle Main Engine Turbomachinery. There has been much written on the subject of bearing vibration monitoring over the last twenty five years. This report attempts to summarize the underlying science of rolling element bearings across these diverse applications from the point of view of machine condition monitoring using vibration analysis. The key factors which are addressed in this report include the underlying science of bearing vibration, bearing kinematics and dynamics, bearing life, vibration measurement, signal processing techniques and prognosis of bearing failure. (jg)

Dynamically stable magnetic suspension/bearing system

Abstract: A magnetic bearing system contains magnetic subsystems which act together to support a rotating element in a state of dynamic equilibrium. However, owing to the limitations imposed by Earnshaw's Theorem, the magnetic bearing systems to be described do not possess a stable equilibrium at zero rotational speed. Therefore, mechanical stabilizers are provided, in each case, to hold the suspended system in equilibrium until its speed has exceeded a low critical speed where dynamic effects take over, permitting the achievement of a stable equilibrium for the rotating object. A state of stable equilibrium is achieved above a critical speed by use of a collection of passive elements using permanent magnets to provide their magnetomotive excitation. The magnetic forces exerted by these elements, when taken together, levitate the rotating object in equilibrium against external forces, such as the force of gravity or forces arising from accelerations. At the same time, this equilibrium is made stable against displacements of the rotating object from its equilibrium position by using combinations of elements that possess force derivatives of such magnitudes and signs that they can satisfy the conditions required for a rotating body to be stably supported by a magnetic bearing system over a finite range of those displacements.

Thrust bearing for use in downhole drilling systems

Abstract: A thrust bearing for use in downhole drilling systems employing fluid motors having a stator retaining ring and a rotor retaining ring. These rings have a plurality of bearing inserts. The bearing insert surfaces of the rotor contact the bearing surfaces of the stator. The studs which make up the bearing surface have a threaded bolt secured thereto. The threaded bolt extends through a plurality of threaded holes in each of the retaining rings. The studs and bolt may be removed or inserted by use of a simple hand tool, such as an Allen wrench.

A Test Apparatus and Facility to Identify the Rotordynamic Coefficients of High-Speed Hydrostatic Bearings

Abstract: A facility and apparatus are described which determine stiffness, damping, and added-mass rotordynamic coefficients plus steady-state operating characteristics of high speed hydrostatic journal bearings. The apparatus has a current top speed of 29,800 rpm with a bearing diameter of 7.62 cm (3 in.). Purified warm water, 55 C (130 F), is used as a test fluid to achieve elevated Reynolds numbers during operation. The test-fluid pump yields a bearing maximum inlet pressure of 6.9 Mpa (1000 psi). Static load on the bearing is independently controlled and measured. Orthogonally mounted external shakers are used to excite the test stator in the direction of, and perpendicular to, the static load. The apparatus can independently calculate all rotordynamic coefficients at a given operating condition.

Hydrostatic and active control movable pad bearing

Abstract: A one piece hydrodynamic bearing which can include hydrostatic support features. The pads are supported on a single thin web for pivoting on a support structure which can include one or more beam-like members. The bearings may have hydrostatic and active control attributes and is very attractive in cryogenic applications where it is very difficult to prevent leakage in conventional hydrostatic tilt pad bearings. The hydrostatic feed through the post eliminates this problem completely and prevents the fretting at the pivots common with conventional tilt pad bearings. A cavity provided under a pad support membrane can be used as an active control device. The pressure can cause the bearing set or assembly clearance to be reduced thus providing better damping and centering capability. The preload in the pad can be actively controlled in this manner. The pad has a limiting device to prevent a negative pre-load condition from occurring. This active control of bearing clearance can allow bearings to operate at large spreads in temperatures.

Strut assembly with integral bearing and spring seat

Abstract: A quarter car vehicle suspension including a wheel, a bearing having an axis of rotation, the piston rod axis aligned at an acute angle with respect to a spring axis of a coil spring of the suspension, and a spring seat integral with the bearing, wherein the bearing is located between the spring seat and the vehicle body, and wherein the axis or rotation of the bearing is substantially aligned with a spring axis and at an acute angle to the piston rod axis.

Advanced Methods For Repeatable Runout Compensation

Abstract: This paper presents and compares experimental results from two types of periodic disturbance compensation methods. The repeatable runout (RRO) cancellation techniques studied in this paper are adaptive feedforward cancellation (AFC) and repetitive control. Two modifications (phase advance and a feedthrough term) to the basic AFC structure are also stud- ied experimentally. Of the AFC methods, the feedthrough tech- nique is superior, but the repetitive controller provides better RRO rejection. Overall it is found that the removal of repeatable runout improved the tracking precision by as much as 53%. I. INTRODUCTION Periodic disturbances are inherent in any rotating machin- ery. In disk data storage technology, the periodic disturbances appear in the error of the position of the head following a data track. This repeatable runout in the position of the head with respect to the track center can be a considerable source of tracking error. In an operating disk system, some control effort is usually expended to compensate for at least the largest of these periodic disturbances. Generally, the frequencies of the geriodic disturbances are integer multiples of the frequency of "ion of the disk drive. The sources of repeatable runout can be an eccentricity of the track, an offset of the track center with respect to the spindle center, bearing geometry and wear, and motor geometry. This pager considers advanced methods of repeatable runout (RRO) compensation. These methods learn the true shape of the track to be followed on-line. A simple adaptive method is described in this paper, and modifications and struc- changes to this basic algorithm are discussed. In addition, a repetitive control method is presented and compared to the adaptive methods. The primary goal of this paper is to present experimental results for these different methods of repeatable mnout compensation. These results are compared, and the effectiveness of each method and modification is discussed. 11. REPEATABLE RUNOUT COMPENSATION ALGORITHMS

Horizontal-axis wind power plant multi-pole sync generator

Abstract: The multiple pole synchronous generator is for gear-free horizontal axis wind power systems. The generator acts as the inner or outer rotor and includes a stator (8) and a rotor (11). The stator (8) and rotor (11) are connected to each other by a fly bearing (15). The bearing (15) assists the rotary movement of the rotor and also picks up externally applied forces and moments. Preferably the generator (1) includes, as integral components, a cooler (12), a seal (5), a brake system (6), a clamp box (7), signal transmission interfaces and bearing lubrication.

Structural damping of self-acting compliant foil journal bearings

Abstract: This paper describes an experimental investigation into the dynamic characteristics of corrugated foil (bump foil) strips used in compliant surface foil journal bearings and dampers. An the experimental method described herein, a test facility with a journal supported by a compliant foil journal bearing was built. The nonrotating journal was driven by two shakers which were used to simulate dynamic forces acting on bump foil strips. The dynamic structural stiffness and equivalent viscous damping coefficients are calculated based on the experimental meaurements for a wide range of operating conditions. The results are compared to the analytical predictions obtained by a theoretical model developed earlier

A State-Space Model for Monitoring Thermally Induced Preload in Anti-Friction Spindle Bearings of High-Speed Machine Tools

Abstract: Catastrophic and premature bearing failure caused by excessive thermally induced bearing preload is a major design problem for spindle bearings of highspeed machine tools. Due to a lack of a low cost and easy to maintain on-line preload measuring technique, the traditional solution is to limit the maximum spindle speed and the initial bearing preload. This solution is incompatible with the need to increase machining productivity, which requires increasing the spindle speed, and to increase product qualily (surface finish, dimensional accuracy), which requires increasing (or at least not decreasing) the preload to keep the spindle system stiff. This paper proposes a dynamic mathematical model of the spindle system, which can be used as part of a model-based monitoring system for estimating the spindle bearing preload

Structural stiffness and Coulomb damping in compliant foil journal bearings: Theoretical considerations

Abstract: Compliant foil bearings operate on either gas or liquid, which makes them very attractive for use in extreme environments such as in high-temperature aircraft turbine engines and cryogenic turbopumps. However, a lack of analytical models to predict the dynamic characteristics of foil bearings forces the bearing designer to rely on prototype testing, which is time-consuming and expensive. In this paper, the authors present a theoretical model to predict the structural stiffness and damping coefficients of the bump foil strip in a journal bearing or damper. Stiffness is calculated based on the perturbation of the journal center with respect to its static equilibrium position. The equivalent viscous damping coefficients are determined based on the area of a closed hysteresis loop of the journal center motion. The authors found, theoretically, that the energy dissipated from this loop was mostly contributed by the frictional motion between contact surfaces. In addition, the source and mechanism of the nonline...

Stability and Bifurcation of Unbalanced Response of a Squeeze Film Damped Flexible Rotor

Abstract: The stability and bifurcation of the unbalance response of a squeeze film damper-mounted flexible rotor are investigated based on the assumption of an incompressible lubricant together with the short bearing approximation and the “π” film cavitation model. The unbalanced rotor response is determined by the trigonometric collocation method and the stability of these solutions is then investigated using the Floquet transition matrix method. Numerical examples are given for both concentric and eccentric damper operations. Jump phenomenon, subharmonic, and quasi-periodic vibrations are predicted for a range of bearing and unbalance parameters. The predicted jump phenomenon, subharmonic and quasi-periodic vibrations are further examined by using a numerical integration scheme to predict damper trajectories, calculate Poincare maps and power spectra. It is concluded that the introduction of unpressurized squeeze film dampers may promote undesirable nonsynchronous vibrations.

Analysis of Aerodynamic Journal Bearings With Small Number of Herringbone Grooves by Finite Element Method

Abstract: A numerical study of gas herringbone grooved journal bearings is presented for small number of grooves. The compressible Reynolds equation is solved by use of the Finite Element Method. The nonlinearity of the discretized equations is treated with the Newton-Raphson procedure. A comparison of the results for a smooth bearing with previously published results is made and the domain of validity of the Narrow Groove Theory is analyzed. Load capacity, attitude angle, and stiffness coefficients are given for various configurations: groove angle and thickness of grooves, bearing number, and that for both smooth and grooved member rotating.

Chaos in the unbalance response of journal bearings

Abstract: The behaviour of non-linear systems often yield unexpected phenomena which are extremely sensitive to initial conditions. The hydrodynamic journal bearing is a common machine element which is strongly nonlinear for large excursions within the clearance space. A simple model of a rigid journal, supported hydrodynamically using a short bearing theory is shown to behave chaotically when the rotating unbalance force exceeds the gravitational load. At these values of the force ratio the time history of the response is very sensitive to initial conditions and a spectral analysis demonstrates a significant broadening from the expected peak at the rotational frequency. A once per revolution sampling of the time history (Poincare plot) revealed an apparent aperiodic pattern. An estimate of the fractal dimension using the Grasberger-Procaccia algorithm resulted in a lower bound of 2.15, a typical result for low dimensional systems with significant dissipative action. The required levels of unbalance are only an order of magnitude greater than acceptable levels for rotating machinery and thus could be achieved with in-service erosion or minor damage. The subsequent non-synchronous response could result in fatigue and potential shaft failure.

Wheel bearing hub with deformed bead

Abstract: A wheel bearing unit for example for use in a motor vehicle, including an antifriction bearing clamped on the hub. The hub includes a bore which defines a tubular hub part that prior to deformation extends past the axially outer end of the inner ring of the bearing. The tubular hub part is deformed radially outward around the radially inner, axially outer edge of the inner ring to clamp the inner ring and the bearing to the hub. Features of the inner ring and hub for enabling such clamping are disclosed including the hub material hardness, the hub having a tubular part of a particular wall thickness and a length protruding beyond the axial end of the bearing, the radius of the edge of the inner ring about which the bead is formed, the thickness of the bead and its angle of inclination both with reference to the end of the inner ring and to the interior bore, and the depth of the bore.

Multi mode shower head

Abstract: A cartridge (2) secured for angular movement on the handset head (10) has a valve-like cooperation with openings (12) in the head (10) for water flow via passageways (20, 21, 22) in the cartridge (2) to showering outlets (30, 31, 32) on appropriate rotational setting of the cartridge (2). Cleaning pins (7) rotatable with the cartridge (2) and co-axially movable relative to it are operated by a cam track (8, 81) to penetrate fine spray outlets (32) to clean them of scale. The cam co-action of the pin ring followers (71) with the track (8) causes the pins (7) to remain inoperative during the showering modes but the pins (7) are operated for penetration by further turning of the cartridge (2) i.e. independently of the showering modes. The followers (71) are spring urged against the track (8) such as by resilient blades (75) bearing against the taper periphery (27) of the cartridge (2). Clearance pin penetration of the outlets (32) permits water flow to wash away scale and minimize back pressure. Angular movement of the cartridge (2) is limited by stops (83, 84) and showering settings are located by cam track recesses (82).

Syringe for the controlled discharge of viscous materials

Abstract: A syringe having a bearing divided at least once in the axial direction of a threaded rod into bearing parts The bearing parts are held at a distance from one another and at a distance from the threaded rod by at least one expanding part The bearing parts, on their surfaces facing the threaded rod, have surfaces which can be brought by external pressure into engagement with the threaded rod against the resistance of the bearing parts

Structural stiffness and Coulomb damping in compliant foil journal bearings : parametric studies

Abstract: This paper presents the results of the second part of the investigation on structural stiffness and Coulomb damping in compliant foil journal bearings. In the first part, a theoretical model was developed to calculate equivalent viscous damping coefficients and structural stiffness of a bump foil strip in a journal bearing or damper. A computer program was also developed to compute the eccentricity and attitude angle of the journal static equilibrium position as well as the deflections, displacements, reacting forces, and equivalent friction coefficient of each bump on the strip. This model and program enabled further parametric studies to be conducted in the second part of the investigation, the results of which are the subject of this paper. The design parameters studied were static eccentricity (bearing load), pad angle (load angle), sliding friction coefficients, and perturbation amplitude (dynamic load). In addition, more effective methods of achieving both Coulomb damping and optimum structural stif...

Image forming apparatus having weighting material in image bearing member and process cartridge usable with same

Abstract: An image forming apparatus includes a rotatable image bearing member including an image bearing layer and a base member for supporting the image bearing layer; a charging member contactable to the image bearing member for electrically charging the image bearing member; a voltage applying device for applying an oscillating voltage to the charging member; a weighting material inside the base member; and an elastic material between the base member and the weighting material. The elastic material has a hardness not more than 70 degrees (JIS-A), a thickness of 1-5 mm and an outer diameter larger by 40-400 microns than an inner diameter of the base member before it is press-fitted into the base member.

Strut assembly with bearing axis alignment

Abstract: A quarter car vehicle suspension including a wheel, a bearing having an axis of rotation, a quarter car steer axis about which the wheel steers, a strut with a piston rod and a piston rod axis, the piston rod axis aligned at an acute angle with respect to the quarter car steer axis, and a spring seat, wherein the bearing is mounted between the spring seat and the vehicle body, and wherein the axis or rotation of the bearing is substantially aligned with the quarter car steer axis and at an acute angle to the piston rod axis.

Disk drive pivot nonlinearity modeling. I. Frequency domain

Abstract: This paper describes studies done at HP Labs on the actuator pivot bearing nonlinearity of a small disk drive. The nonlinear frictional behavior of the pivot bearing varies with actuator position, from drive to drive, and with time and temperature. This nonlinear behavior has made the traditional linear disk drive models inadequate. The paper shows how the swept-sine/describing function method was used to develop a nonlinear model of the pivot. This model departs from the classical friction models, but does a good job of matching laboratory frequency domain measurements.

Prosthetic knee tibial component constructed of synthetic polymeric material

Abstract: A tibial component for use in a prosthetic knee implant is constructed of a one-piece unitary member of synthetic polymeric material including a bearing portion having bearing surfaces for accepting the load imposed by the femoral component of the prosthetic knee implant and a keel projecting axially downwardly from the bearing portion and having flanges extending from a generally centrally located post outwardly at an angle to one another to be placed beneath the bearing surfaces of the bearing portion for reinforcing the bearing portion against the load imposed by the femoral component during service, while providing strength as well as rigidity and added stability for providing a relatively inexpensive alternative to metallic tibial components in recipients where the levels of performance offered by the higher cost metallic tibial components are not required.

Magnetic bearing apparatus

Abstract: A magnetic bearing apparatus comprises a pair of radial magnetic bearings arranged on both sides in the axial direction of an axial magnetic bearing. A pair of first touchdown bearings are arranged at both ends of a spindle. Annular slide bearings are mounted as second touchdown bearings for receiving the spindle on inner peripheral parts of electromagnets in the axial magnetic bearing. The radial internal clearance between the slide bearing and the spindle is larger than the radial internal clearance between the first touchdown bearings and the spindle and is smaller than the radial internal clearance between the radial magnetic bearings and the spindle. Even if a central part of the spindle is deflected at the time of emergency stop, both the first touchdown bearings and the slide bearings receive the spindle, so that the load on the first touchdown bearings can be reduced.

Damping for passive magnetic bearings

Abstract: The apparatus includes a resilient mounting for the damping of magnetic bearings. This mount may include a resilient material placed between the magnetic stator and the fixed structure to damp vibrations of the stator induced by variations in the position of the shaft and rotor of the bearing. Alternatively, the resilient material may be placed between successive concentric magnetic rings of the stator. The resilient material is typically an elastomer or a woven metal material with both stiffness and damping properties. The mounting also may consist of separate spring and damping elements. The spring elements can include thin rods or bars which provide both alignment and stiffness. The damping element may consist of a resilient material or a device to provide damping through viscous or mechanical friction configurations.

Rotary actuator vibration damper

Abstract: A bearing assembly supports an actuator arm for rotation about an axis in a disc drive. The bearing assembly includes a shaft generally defining the axis. A plurality of bearings are disposed about the shaft. A sleeve is coupled to the bearings for rotation about the shaft, and a damper is coupled to the sleeve. The damper damps rotary actuator vibrations.

Influence of High Rotational Speeds on Heat Transfer and Oil Film Thickness in Aero-Engine Bearing Chambers

Abstract: Increasing the thermal loading of bearing chambers in modern aero-engines requires advanced techniques for the determination of heat transfer characteristics. In the present study, film thickness and heat transfer measurements have been carried out for the complex two-phase oil/air flow in bearing chambers. In order to ensure real engine conditions, a new test facility has been built up, designed for rotational speeds up to n = 16,000 rpm and maximum flow temperatures of Tmax = 473 K. Sealing air and lubrication oil flow can be varied nearly in the whole range of aero-engine applications. Special interest is directed toward the development of an ultrasonic oil film thickness measuring technique, which can be used without any reaction on the flow inside the chamber. The determination of local heat transfer at the bearing chamber housing is based on a well-known temperature gradient method using surface temperature measurements and a finite element code to determine temperature distributions within the bearing chamber housing. The influence of high rotational speed on the local heat transfer and the oil film thickness is discussed.