Showing papers on "Bearing (mechanical) published in 1995"

Effect of PWM inverters on AC motor bearing currents and shaft voltages

Abstract: This paper investigates AC induction motor shaft voltage problems, current flow through motor bearings and electric discharge current problems within bearings when operated under both pure sinewave and pulse width modulated (PWM) inverter sources. Experience suggests that PWM voltage sources with steep wavefronts especially increase the magnitude of the above electrical problems, leading to motor bearing material erosion and early mechanical failure. Previous literature suggests that shaft voltage-bearing current problems under 60 Hz sinewave operation are predominantly electromagnetically induced. It is proposed that under PWM operation these same problems are now predominantly an electrostatic phenomenon. A system model to describe this phenomenon is characterized and developed. Construction and test of a new electrostatic shielded induction motor (ESIM) verifies this model and is also a possible solution to the bearing current problem under PWM operation. >

Modeling of motor bearing currents in PWM inverter drives

Abstract: Pulse-width modulated (PWM) inverters have recently been found to be a major cause of motor bearing failures in inverter-fed motor drive systems. Specifically, all inverters generate common-mode voltages relative to the earth ground. These voltages provide coupling or bearing currents through motor parasitic capacitances to the rotor iron which flow via the bearings to the grounded stator case. In this paper, a model of bearing currents caused by PWM inverters is proposed. The model is based on transmission line theory which uses an equivalent lumped parameter /spl pi/-network to describe the parasitic coupling phenomenon. The model parameters are then identified by matching the calculated model outputs with those of experimental measurement. The validation of the method is demonstrated by the fact that the model can reproduce a variety of experimental results obtained on a test motor. An application of this method also gives a motor grounding current model. As the conducted electromagnetic interference (EMI) in motor drive systems is related to the grounding currents, the grounding current model can be used for the analysis of conducted EMI in motor-drive systems.

Bearing currents and their relationship to PWM drives

Abstract: This paper examines AC motor shaft voltages and the resulting bearing currents when operated under pulse width modulation (PWM) voltage source inverters. The paper reviews the mechanical and electrical characteristics of the bearings and motor in relation to shaft voltages and bearing currents. A brief review of previous work is addressed including the system model and experimental results. The theory of electric discharge machining (EDM) is presented including component calculations of the system elements. The effect of system elements on shaft voltages and bearing currents are evaluated experimentally and the results compared to theory. A design calculation is proposed that provides the relative potential for EDM. Finally, the paper presents quantitative results on one solution to the shaft voltage and bearing current problem.

Low rotational drag in high-temperature superconducting bearings

Abstract: Bearings consisting of permanent magnets stably levitated over high-temperature superconductors exhibit low rotational drag and have the potential to enable high-efficiency flywheel energy storage. The coefficient of friction /spl mu/ for such storage systems is derived as a function of bearing parameters and is shown to be an appropriate figure of merit to describe bearing losses. Analysis shows that values of /spl mu/ >

Wave journal bearing with compressible lubricant--Part 1: The wave bearing concept and a comparison to the plain circular bearing

Abstract: To improve hydrodynamic journal bearing steady-state and dynamic performance, a new bearing concept, the wave journal bearing, was developed at the author's lab. This concept features a waved inner bearing diameter. Compared to other alternative bearing geometries used to improve bearing performance such as spiral or herring-bone grooves, steps, etc., the wave bearing's design is relatively simple and allows the shaft to rotate in either direction. A three-wave bearing operating with a compressible lubricant, i.e., gas is analyzed using a numerical code. Its performance is compared to a plain (truly) circular bearing over a broad range of bearing working parameters, e.g., bearing numbers from 0.01 to 100.

Slide positioning and holding device

Abstract: A slide positioning and holding device includes a base, a number of first bearing members defining a bearing surface for slidably engaging a first edge of the slide, at least one second bearing member for slidably engaging a second edge of the slide generally perpendicular to the first edge, and first and second arms for contact with third and fourth edges, respectively, of the slide to urge the first and second edges of the slide into contact with the bearing members.

EHD Analysis, Including Structural Inertia Effects and a Mass-Conserving Cavitation Model

Abstract: The dynamic behavior of two elastic connecting-rod bearings is studied. The Newton-Raphson method and 8-node isoparametric elements for the lubrication analysis are used. For the structural analysis, 3-D elasticity assumptions are made and 20 nodes isoparametric elements are used. Inertia forces due to the kinematics of the structure are incorporated with the effects of the hydrodynamic pressures in the elastic deformations of the bearing. Comparisons with Goenka‘s results are presented for the General Motors connecting-rod bearing. A mass-conserving model used in conjunction with Murty‘s algorithm is presented for the transient evolution of the cavitation area. This model is applied for the EHD study of a Renault connecting-rod bearing.

Nonlinear control of a rigid rotor magnetic bearing system: modeling and simulation with full state feedback

Abstract: Control strategies for magnetic bearings often focus on linear optimal control techniques. While these methods afford many advantages, the literature is conspicuously sparse with regard to attempts at nonlinear control. Here, we treat the equations of motion of a rigid, horizontal rotor magnetic bearing system. Through feedback linearization and sliding mode control techniques, we formulate a nonlinear control law which maintains the shaft centered in the bearings. This system is then simulated to demonstrate disturbance rejection properties and its robustness to parameter uncertainty and unmodelled dynamics. >

Precise bearings only geolocation in systems with large measurements bias errors

Abstract: Bearing rate of change, or equivalently bearing differences, are used to estimate emitter geolocation, in contrast to using such rates or differences to estimate only range. In using the bearing differences, it is not necessary to maintain the same relative bearing to compensate for DOA dependent errors. Nor does the invention require a precise fully resolved and calibrated interferometer to generate DF measurements. Furthermore, it can be used with currently implemented amplitude DF systems that employ no phase interferometry at all. By making minimal changes, these systems will produce accurate geolocation. The invention will also work with any system that can be modified to produce an accurate bearing rate-of-change. Therefore, it can be used with time-difference-of-arrival (TDOA) systems also. If bearing measurements are also produced by such systems, the magnitude of the bias on that bearing measurement is not important. The effect of angle bias errors in performing bearings-only geolocation are greatly reduced or eliminated. Bias and random components of the measurement error are separated, an estimation of bias error in azimuth or AOA measurements can also be generated. Bearings differences are uniquely associated with curves, e.g. circles, on which the emitter must lie. A plurality of circles are generated to unamibiguously determine emitter geolocation. Multiple platforms may be used to generate the bearing differences. It is also possible to utilize existing bearings-only emitter location software by generating psuedo bearings. The new pseudo bearing measurements use bearing differences, rather than AOA. Geolocation is thus derived strictly from bearing differences, thus eliminating the effects of bias error.

Piezoelectric film transducer sytem for bearings

Abstract: An in-use rolling element bearing monitoring system which uses a piezoelectric film transducer on either a bearing, bearing support structure, or on a separate washer in close proximity to a bearing for monitoring bearing performance. One embodiment provides a bearing monitoring system for detecting and predicting bearing failure. Another embodiment provides a system configured for detecting rotational speed of a rolling element bearing. Each embodiment of the invention entails maintaining a piezoelectric film transducer in contiguous pressure wave responsive communication with a bearing for detecting bearing performance, and provides the system in a compact configuration for in-use operation on a variety of machinery and vehicle components heretofore previously not compatible.

A Transient Thermohydrodynamic Analysis Including Mass Conserving Cavitation for Dynamically Loaded Journal Bearings

Abstract: A comprehensive transient thermohydrodynamic analysis for dynamically loaded journal bearings such as engine crankshaft bearings has been developed. A key element in this analysis is consideration of different time scales for the oil film, journal and bushing. Another important element of this analysis is consideration of moving grids in the oil film. Mass conserving cavitation is included via the Elrod cavitation algorithm. Th 3-D energy equation is solved without any simplification in the oil film or the bushing. The journal is treated as a lumped thermal element. We found that the time scales for thermal transients in the oil film are of the same order as the period of the dynamic loading (one engine cycle for a crankshaft bearing); consequently, thermal transients in the oil film were considered. However, the time scales for thermal transients in the journal and bushing are several orders of magnitude greater than those for the oil film. Consequently, these elements were treated as if they were in quasi-steady state over one loading cycle. Results from this analysis are presented for an engine crankshaft main bearing under sinusoidal loading. Oil film temperatures are found to vary considerably over time and space

The dynamics of molecular bearings

Abstract: Various types of molecular bearings have recently been proposed in the growing nanotechnology literature. Using novel molecular dynamics methods, we have simulated several model graphite bearings. The bearings varied in size from inner shafts of between 4 and 16 A in diameter, up to 120 A in length, and outer cylinders of between 10 and 23 A in diameter, up to 40 A in length. The turning shaft was either instantaneously started or torqued up to the desired rotational speeds. Frictional properties were size-, temperature- and velocity-dependent. The presence of more than one bearing vibrational mode in some simulations created beats that could possibly adversely affect bearing performance; placing a stretching tension on the bearing suppressed one of the modes and therefore the beats. These and future studies will help evaluate the performance, wear and load-bearing properties of fundamental components of nanomachines such as bearings.

Hydrodynamic bearing with controlled lubricant pressure distribution

Abstract: A rotating-shaft hydrodynamic bearing assembly adapted for use in a rotating disk data store. The bearing assembly combines a plurality of spaced-apart radial journal bearings with a two-faced axial thrust plate to provide stiffness against runout at high rotational velocities. Fluid pressure is controlled on both sides of every fluid dement by bounding all radial fluid bearing layers and the dual thrust bearing layers with circumferential undercuts coupled to ambient pressure through a plurality of fluid-filled passages in the rotating shaft. Outward-biased surface-relief patterns are disposed in both axial thrust bearing layers to increase hydrostatic pressure and prevent cavitation in the non-bearing thrust-plate peripheral layer. The fluid bearing layers are disposed in a continuous pressure-controlled fluid film sealed at both ends by surface tension, thereby eliminating sources of air-bubble entrapment. Control of air-bubble entrapment and cavitation eliminates both as sources of surface-tension seal leakage and blowout.

Square and Rectangular Hollow Sections under Transverse End-Bearing Force

Abstract: This paper describes tests on a range of cold-formed square and rectangular hollow section members subject of end-bearing force. The concentrated force was applied by means of a bearing plate, which acted across the full flange width of the section. The parameters varied in the tests included (1) the bearing length; (2) the slenderness of the member; and (3) the shape of the section [rectangular hollow sections (RHS) or square hollow sections (SHS)]. The results are compared with existing American Australian, Canadian, and European design formulas. The results are also compared with the formulas given by the writers, which were based on tests of SHS and RHS sections under interior bearing force. A design model is proposed for SHS and RHS sections under end-bearing force. The reliability analysis method is used to calibrate the existing and proposed design formulas.

On the Adjusting of the Dynamic Coefficients of Tilting-Pad Journal Bearings

Abstract: This paper gives a theoretical and experimental contribution to the problem of active modification of the dynamic coefficients of tilting-pad journal bearings, aiming to increase the damping and stability of rotating systems. The theoretical studies for the calculation of the bearing coefficients are based on the fluid dynamics, specifically on the Reynolds equation, on the dynamics of multibody systems and on some concepts of the hydraulics. The experiments are carried out by means of a test rig specially designed for this investigation. The four pads of such a bearing are mounted on four flexible hydraulic chambers which are connected to a proportional valve. The chamber pressures are changed by means of the proportional valve, resulting in a displacement of the pads and a modification of the bearing gap. By changing the gap, one can adjust the dynamic coefficients of the bearing. With help of an experimental procedure for identifying the bearing coefficients, theoretical and experimental results are co...

Classification and synthesis of permanent magnet bearing configurations

Abstract: Quite a number of configurations allow to get passive permanent magnet thrust or radial bearings. However, most of existing devices are based on the same two or three structures. In many cases, a different geometrical structure keeping the same magnetic and mechanical characteristics would allow a simpler and cheaper realisation. We present here a synthesis of passive bearings allowing original structures.

An experimental study of elastomeric bridge bearings with design recommendations

Abstract: Recent AASHTO specifications have placed a number of restrictions on the use of elastomeric bridge bearings. Elastomeric bearings with tapers built in to accommodate span end elevation differences were disallowed by the most current specifications even though no previous research into elastomeric bearing performance has included tests on tapered pads. The purpose of this study was to analyze elastomeric bearing performance on the basis of elastomer hardness, shape factor, reinforcing shim orientation, degree of taper and compressive stress level with the goal of developing a simple design procedure which standardizes as many of those parameters as possible. Particular emphasis was placed on comparing the behavior of flat and tapered bearings. Experimentation included shear, compressive, and rotational stiffness tests, shear and compression fatigue loading, long-term compressive loading, and tests to determine compressive stress limits. In many cases, bearings were intentionally loaded non-uniformly to define safe limits for bearing/girder slope mismatches. Research showed that tapered elastomeric bearings performed equally as well as flat bearings and that manufacturing tapered bearings with steel shims oriented parallel to one another offers several benefits over spacing shims radially. Additionally, bearings made from elastomers with lower hardness ratings displayed several advantages over those made from harder elastomers, particularly rotation capacity far in excess of the current AASHTO limitation. More highly reinforced bearings performed better in compression fatigue and creep tests and easily accommodated compressive stresses in excess of 6.9 MPa (1000 psi). Mismatches between the slope of the girder and the bearing taper had little effect on performance. Also, a field and laboratory investigation was performed into bearing slip and anchorage by friction. Bearings that had slipped while in service were subjected to comparable conditions in a laboratory test apparatus to study their behavior. Research showed that secretion of antiozonant waxes to the bearings' surfaces caused a dramatic lowering of the bearing's friction coefficient and resulted in slipping. Several tests were performed that established friction coefficients for natural rubber against a variety of steel and concrete surfaces. A standard design for Texas bearings is recommended. Recommended changes to the current AASHTO specification are presented.

Roller cone bit with positive and negative offset and smooth running configuration

Abstract: An earth-boring bit has a bit body and at least a pair of cantilevered bearing shafts depending downwardly and inwardly therefrom. A first cutter is mounted for rotation on one of the bearing shafts and has a region of contact with the sidewall of the borehole. A second cutter is mounted for rotation on another of the bearing shafts and has a region of contact with the sidewall of the borehole that is non-opposite that of the first cutter. Stabilization is provided by a stabilizer pad carried on the bit body and arranged to be opposite the contact regions of the first and second cutters.

System Considerations Favoring Rotary Artificial Hearts with Blood‐Immersed Bearings

Abstract: Hydrodynamic blood pumps provide such advantages as not requiring an air vent or compliance chamber as well as a great reduction in mechanical complexity with the potential for very long durability. The detailed design of their bearings is emerging as the single most important determinant of long-term success. Three categories of bearings include remote force, such as magnetic suspension; blood-isolated, which require a shaft seal; and blood-immersed using either mechanical or hydrodynamic support. Blood-immersed bearings permit maximum simplification and miniaturization of the entire system, require no flush fluid, and require no electronics as with magnetic suspension. The Jarvik 2000* heart represents an example of their potential. The intraventricular titanium pump (25 mm diameter, 25 cc, 85 g), uses blood flow through the motor air gap with blood-immersed bearings. The longest in vitro bearing durability test is ongoing at 20,000,000,000 revolutions with minimal wear (3 years at 15,000 rpm). In vivo results include 5-month calf survival, no thromboembolism, plasma Hb 2–5 mg%, and power under 10 W. Key Words: Artificial hearts— Blood-immersed bearings—Rotary blood pumps—Axial flow pumps—Left-ventricular assist devices.

Clamshell pipe lathe having improved bearing arrangement

Abstract: A clamshell machining lathe for cutting and finishing pipes in industrial settings comprises a split-ring assembly, including a clamping ring that is positioned about the pipe, and journaled to the clamping ring is a rotatable gear ring that supports a tool block carrying a cutting tool. The improvement resides in the bearing arrangement used to journal the gear ring to the stationary clamping ring. One face of the gear ring includes an annular groove whose side walls define a bearing race. The race is dimensioned to receive a plurality of roller bearings therein, the roller bearings being affixed to a planar surface of the clamping gear in a circumferential arrangement so as to fit into the bearing race when the gear ring is coupled to the clamping ring. The arrangement can support greater loads without canting, thus reducing wear on the moving parts.

Linear motion bearing

Abstract: A linear motion bearing assembly is provided having a rail assembly with a flexible base portion (46) and a bearing carriage assembly (22) with flexibly depending legs (32) configured for longitudinal movement along the rail assembly on rolling elements (25). A plurality of load bearing inserts (40, 54) are positioned on the rail assembly and/or carriage assembly and define load bearing tracks with rolling elements (25) therebetween. The flexible rail and carriage assemblies permit optimization of the contact angle between the load bearing inserts and the rolling elements when the linear motion bearing assembly is under load.

Low friction in mixed‐mu superconducting bearings

Abstract: Individual magnetic steel rotors were levitated by combining the attractive force between permanent magnets and the steel with the repulsive force between high‐temperature superconductors and the steel The free spindown of several rotors was observed, and the effective coefficient of friction for the bearing was calculated as a function of geometry Low‐speed coefficients of <10−8 were observed, and the velocity dependence of MnZn ferrite rotors suggest that coefficients of <10−6 are attainable at bearing rim velocities of 100 m/s

Analysis of a model to forecast thermal deformation of ball screw feed drive systems

Abstract: In machine tools with semi-closed loop numerical control, the thermal deformation of the ball screw directly produces the position error of the feed drive system. In this work the method of multiple regression is used to analyze the thermal deformation of a ball screw feed drive system. Key points of thermal source (front bearing, nut and back bearing) were selected as independent variables of the analysis model. The test results show that this method can well predict the thermal deformation of the ball screw during variation of the speed of rotation.

A Generalized Computational Fluid Dynamics Approach for Journal Bearing Performance Prediction

Abstract: The use of computational fluid dynamics (CFD) techniques enables performance predictions of bearing designs to be made when the usual operating assumptions of the Reynolds equation Jail to hold. Th...

Plain bearing assembly

Abstract: A plain bearing assembly including an inner bearing, outer bearing, and at least one intermediate bearing. The inner bearing has an annular inner bearing surface. The intermediate bearing includes a ring bearing having an annular inner and outer surface. The intermediate bearing also includes bushes rotatably mounted about the inner bearing and rotatable with respect to the bearing ring and outer bearing. The bushes provide a bearing surface adjacent to the annular inner bearing surface of the bearing ring and providing a bearing surface adjacent to the annular outer bearing surface of the bearing ring.

An Experimental Investigation into Bearing-Induced Spindle Vibration

Abstract: This paper describes experiments carried out to investigate the frequency response of a grinding machine tool spindle supported by preloaded angular‐contact ball bearings. The experimental apparatus includes a loading device to simulate grinding head radial loads. The frequency spectra obtained show bands of frequencies associated with the ball passage frequency. The spectra also include bounce and rocking vibration modes of the assembly, where the supporting bearings act as non‐linear springs. Good correlation of the dominant frequencies was obtained with the results of the theoretical models published elsewhere.