Showing papers on "Bearing (mechanical) published in 1996"

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.

Load bearing spinal joint implant

Abstract: An implant is provided which has an upper member which pivots and is locked to a lower member and engages adjacent vertebrae and have surfaces which are ceramic and will allow bone growth into such surfaces and thus bonding with the adjacent vertebra. The opposing and bearing surfaces of the upper and lower member are coated with ceramic zirconium for long wear. Since the upper and lower members are captured, the implant device herein cannot be forced out of place by spinal tension. Particularly for the lower spinal vertebrae, the option of securing the upper and lower members with screws is facilitated. A vertebral replacement system using components in common with the implant is used to make a spaced connection between two pivoting points and is used to replace badly damaged vertebrae where the load bearing portion of the vertebra will be insufficient to allow normal support. It is expected that the implant and vertebral replacement will have several sizes corresponding to the spinal cross sectional shape being bonded to, and that exact dimensioning will be obtained through tomographic scans to enable rapid final sculpting of a highly customized implant.

Source of induction motor bearing currents caused by PWM inverters

Abstract: The recent increase of bearing damage in induction machines driven by transistorized inverters has spurred activity on possible causes related to PWM inverters. This paper looks into a typical power conversion system from this perspective. It identifies the existence of the common mode voltages produced in all types of converters. A hypothesis is then proposed to explain the bearing current problem. In particular, it is shown that in an inverter-motor system the common mode voltages generated by a PWM inverter, which are attributed to PWM switching harmonics, couple through parasitic capacitances from stator windings to the rotor body and then returns through the motor bearings to the commonly grounded stator case as a closed loop circuit. The hypothesis is verified by experimental measurement of common mode coupling currents and true bearing currents in a specially modified induction motor. Solutions are then provided to suppress the bearing currents.

Expandable prosthesis for spinal fusion

Abstract: A spine stabilizing prosthesis has first and second hollow, cylindrical bearing members interconnected by a hollow, cylindrical jacking screw adjustable to expand the prosthesis within a cavity to bridge respective opposite axial ends of the bearing members into pressure engagement with opposing vertebral faces. Walls of the bearing members are perforated by a plurality of bone fragment admitting apertures and forming a bone fragment receptacle so that bone can grow and fuse completely through said bearing members when the prosthesis is installed in the cavity. Respective axial ends of the bearing members are formed with rings of vertebrae engaging teeth having ramp surfaces permitting sliding engagement when rotated in one direction and biting into the facing surfaces when rotated in the opposite direction resisting rotation to permit further expansion apart of the bearing members by rotation of the jacking screw.

The importance of multidirectional motion on the wear of polyethylene.

Abstract: The development of a new hip simulator for the study of bearing materials used in total hip replacements has led to several findings which add important new information to the understanding of wear process of ultra-high molecular weight polyethylene, the most commonly used bearing material today for total joint replacements. Using this hip simulator which is capable of applying the physiological motion pathways occurring during gait to total hip components which are held in the correct anatomical position under the complex loading conditions of the hip in gait, the authors have shown that physiological motion pathways produce very different wear rates and morphology of the wear surface than unidirectional reciprocating pathways. Scanning electron microscopy studies show striking differences in the morphology of the wear surfaces of the polyethylene depending upon the relative motions of the components. Wear rates, surface morphology and particle debris generation consistent with clinical and retrieved studies are achieved when physiological conditions are simulated.

Experience with the Metasul total hip bearing system.

Abstract: The author and Sulzer Medical Technology Ltd, Switzerland, have developed a new generation of metal on metal bearing total hip joints. The design is different than the McKee type prostheses in that the cobalt chrome alloy heads and cups (Metasul) are of the highest precision with controlled loose fitting. These allow low friction and low wear of approximately 5 micrometers per year. It is anticipated that debris related late loosening will be avoided by the use of this design. Approximately 30,000 Metasul hearings have been produced. The first 110 Weber metal on metal hip implants have been analyzed. No adverse effects from the wear of the new metal on metal components have been noted in this series.

Rotating blowout preventer

Abstract: A rotating blowout preventor having at least two rotating stripper rubber seals which provide a continuous seal about a kelly or drilling string having drilling string components of varying diameter. A stationary housing is designed to support a bearing assembly and a clamp cooperates with the housing to secure the bearing assembly in the housing. Chilled water and/or antifreeze may be circulated through the top inner barrel seal of the bearing assembly and lubricant is pumped into the top seal for lubricating the seals and bearings that facilitate rotation of the stripper rubber seals, kelly and drilling string with respect to the stationary housing and pressurize the inner barrel seals and bearings to at least partially offset well pressure.

System electrical parameters and their effects on bearing currents

Abstract: This paper examines AC motor shaft voltages and resulting bearing currents when operated under pulse width modulation (PWM) voltage source inverters. The paper reviews the electrical characteristics of bearings and motors that cause shaft voltages and bearing currents. A brief review of previous work is presented, including a system model for electrical analysis of bearing currents. Relying on the work of a companion paper, the propensity for electric discharge machining (EDM) is determined by a design equation that is a function of system components. Pertinent machine parameters and their formulae are presented and values calculated for machines from 5 to 1000 hp. The effects of system elements on shaft voltages and bearing currents are evaluated experimentally and the results compared to theory. Finally, the paper presents quantitative results for one solution to the shaft voltage and bearing current problem.

Soldering with resilient contacts

Abstract: A method of making a solder connection. An element bearing a solder mass is forcibly engaged with another element bearing a resilient metallic contact so that the contact wipes the surface of the solder mass and so that the contact is deformed and bears against the wiped surface. While the contact is in its deformed condition, the contact and solder mass are brought to an elevated bonding temperature sufficient to soften the solder, so that the contact penetrates into the solder mass under the influence of its own resilience. The contact bonds with the pure solder inside the solder mass, so that the effective bonding can be achieved even without flux.

Implantable electric axial-flow blood pump with blood-cooled bearing

Abstract: An axial-flow blood pump (10) has a rotor (20) suspended in ball-and-cup bearings (38, 34) which are blood-cooled but not actively blood-lubricated. The ball-and-cup structures are made of highly heat-conductive material and are in heat-transferring contact with heat-conductive stator blades (30) that serve as heat sinks for the bearings. The ball-and-cup structures are radially much smaller than the stator blades. The ball-to-cup interface has so small a gap that the ball-to-cup structures present an essentially continuous surface to the blood flow.

Response of steel bridge bearings to reversed cyclic loading

Abstract: This study investigates the seismic performance of low and high type steel bridge bearing specimens. Experimental apparatus was developed to allow large cyclic horizontal loads and displacements to be applied to bearing specimens while keeping gravity loads constant. Simple seismic retrofit strategies are proposed and investigated experimentally to increase seismic performance. To increase the resistance in the longitudinal direction of the high type rocker bearings, retrofitting consisted of welding steel wedges to the masonry plate. It is shown that retrofitting the existing high type steel bridge bearings provides sufficient strength and displacement capability to withstand substantial ground shaking. The weak link thus becomes the anchor bolts and/or the reinforced concrete pedestal. Results demonstrate the importance of considering the flexibility of the concrete pedestal-anchor bolt system.

Mobile bearing total joint replacement

Abstract: A prosthetic component is provided for a condylar joint. The prosthetic component includes a platform having a bearing surface and a pair of side walls. The side walls include a pair of concave surfaces which face one another and define arcs of the same right circular cylinder. The prosthetic component also includes a plastic bearing having a bearing surface slidably engaged with the bearing surface of the platform. The bearing also includes thrust surfaces defining arcs of two right circular cylinders having radii less than the radius of the side wall surfaces of the platform. The thrust surfaces are spaced from one another to permit only limited sliding movement of the bearing in medial to lateral directions, but greater sliding movement in anterior to posterior directions.

Bearing Failure of Bolted Composite Joints. Part II: Model and Verification:

Abstract: An investigation was performed to study the bearing failure and response of a mechanically fastened laminated composite joint. The experimental work of the study was presented in Part I, and this paper summarizes the analytical work.An accumulative damage model based on the damage mechanisms observed from the experimental study was developed to simulate the bearing failure in the laminated composite joints. The model consists of two parts: damage prediction and constitutive modeling. Damage accumulation criteria by modifying Hashin criteria were proposed to predict the mode and extent of bearing damage as a function of the stress state, and the relationships between material properties and bearing damage were established based on failure mechanisms.A nonlinear finite element analysis based on the model was developed. Data obtained from this study and existing literature were used to validate the model. Overall, the predictions agreed with the data very well.

Positioner with long travel in two dimensions

Abstract: A precision positioning system is provided which provides long travel in two of the linear dimensions, while using non-contact bearings for both a first subassembly which provides long travel in one of the linear dimension and a second subassembly which provides long travel in the second linear dimension. The first or upper subassembly is preferably a magnetic subassembly which, in addition to providing long travel, also compensates or positions in three rotary dimensions and in the third linear dimension. The second subassembly is preferably either an air bearing or magnetic subassembly and is normally used only to provide long travel. Angled surfaces may be provided for magnetic bearings and capacitive or other gap sensing probes may be mounted to the stage and ground flush with the bearing actuators to provide more precise gap measurements.

On the Generalization of Thermohydrodynamic Analyses for Journal Bearings

Abstract: The results of extensive amount of thermohydrodynamic simulations are presented in the form ofdesign charts for journal bearings. These charts enable one to evaluate the maximum temperature and an effective bearing temperature. Numerous examples are presented that show the applicability of these charts in predicting bearing performance parameters.

Stabilized prosthetic knee

Abstract: A semi-constrained prosthetic knee (10) for surgical replacement of a dysfunctional knee includes a tibial platform (22), a movable bearing element (16), and a femoral component (12). The femoral and tibial components are typically constructed of a cobalt/chromium alloy and each includes an extension for securing the component to the bone. The femoral component includes a polycentric convex bearing which slidably engages a movable bearing, typically constructed of high molecular weight polyethylene. The superior surface of the bearing element is designed to congruently slidably engage the inferior surface of the bearing portion of the femoral component throughout the flexion/extension range of the knee. The inferior surface of the femoral component is generally convex with two or more offset portions of varying radii of curvature matching complementary superior surfaces of the bearing element. The superior surface of the tibial platform is generally flat and includes at least one protrusion for controlling the movement of the bearing element.

Blood pump bearing system

Abstract: Methods and apparatus are provided for a blood pump bearing system within a pump housing to support long-term high-speed rotation of a rotor with an impeller blade having a plurality of individual magnets disposed thereon to provide a small radial air gap between the magnets and a stator of less than 0.025 inches. The bearing system may be mounted within a flow straightener, diffuser, or other pump element to support the shaft of a pump rotor. The bearing system includes a zirconia shaft having a radiused end. The radiused end has a first radius selected to be about three times greater than the radius of the zirconia shaft. The radiused end of the zirconia shaft engages a flat sapphire endstone. Due to the relative hardness of these materials a flat is quickly produced during break-in on the zirconia radiused end of precisely the size necessary to support thrust loads whereupon wear substantially ceases. Due to the selection of the first radius, the change in shaft end-play during pump break-in is limited to a total desired end-play of less than about 0.010 inches. Radial loads are supported by an olive hole ring jewel that makes near line contact around the circumference of the shaft to support high speed rotation with little friction. The width of olive hole ring jewel is small to allow heat to conduct through to thereby prevent heat build-up in the bearing. A void defined by the bearing elements may fill with blood that then coagulates within the void. The coagulated blood is then conformed to the shape of the bearing surfaces.

System for producing a knee-joint endoprosthesis

Abstract: System to produce a knee-joint endoprosthesis with joint elements (10) are constructed to be attached to the lower end of the femur, and have a convexly curved joint bearing surface. Bearing elements (12) are constructed to be attached to the upper end of the tibia (11). A meniscus (14) is movably disposed between each femoral joint element (10) and tibial bearing element (12) and are provided on its upper and lower sides with sliding surfaces complementary in shape to the associated joint bearing surface of the femoral joint element (10) and the associated bearing surface of the tibial bearing element (12), respectively. The peripheral or sagittally outer boundary (16) of the sliding surfaces (15) of the menisci (14) that face the femoral joint elements (10) is higher than their central or sagittally inner boundary. The system is designed for modular, universally compatible supplementation to form a total knee prosthesis, revision prosthesis or femoropatellar joint prosthesis.

Effect of Roughness on the Behavior of Squeeze Film in a Spherical Bearing

Abstract: The behavior of a hydrodynamic squeeze film between a non-rotating spherical surface and a hemispherical bearing under a steady load is analyzed. It is assumed that the bearing surface as well as the surface of the approaching sphere have a longitudinal random roughness which is distributed throughout the surfaces. The stochastic film thickness characterizing the roughness is assumed to be symmetric and its mean value is equal to zero. The modified Reynolds equation is solved and the expressions for pressure, load-carrying capacity and the response lime are obtained. The results are presented graphically. It is observed that the performance of the bearing is adversely affected by the composite roughness of the surfaces.

The effects of PWM voltage source inverters on the mechanical performance of rolling bearings

Abstract: Modern power inverters provide the industrial control industry with significant advantages. Faster switching devices have increased drive performance, but with some recently discovered disadvantages. One disadvantage, rotor shaft voltage and resulting bearing current, has become an industry concern. The oil film in a bearing acts as a capacitor and provides a charging mechanism for rotor shaft voltage buildup. Electrical breakdown of the film can damage the bearing. The paper examines the mechanical and electrical characteristics of the bearing and converts them into models. The mechanical model for the bearing contact area establishes an allowable bearing current density, which is used to estimate the effect of electrical life of a mechanical bearing. The electrical model for the bearing provides a significant advancement to aid bearing design and in the analysis of electrically induced bearing damage. Finally, the paper presents quantitative results on one solution to the shaft voltage and bearing current problem.

Yoke apparatus for rack and pinion

Abstract: A yoke apparatus 34 is useful with a steering system having a pinion gear 20 and a longitudinally movable rack 24 engaged with the pinion gear 20. The yoke apparatus 34 comprises a bearing disc 36 received in the aperture 32, and a pair of biasing members 40 and 38 disposed in parallel with one another, each biasing the bearing disc 36 against the rack 24. This in turn biases the rack 24 against the pinion gear 20. The biasing members 40 and 38 have different spring constants and different compliances. Preferably, one of the biasing members 40 and 38 is a compression spring member 40 while the other is an elastomeric O-ring member 38, or other elastomeric member having a highly non-linear compliance. The yoke apparatus 34 also preferably comprises a plug 42 adjustably received in the aperture 32 which applies an axial load to the pair of biasing members 40 and 38. The bearing disc 36 is preferably barrel-shaped and includes a short circumferential outer surface 54 having a diameter formed for sliding engagement with a smooth portion 33 of the aperture 32, about which the bearing disc 36 can pivot in response to an applied lateral shock. The yoke apparatus 34 is of compact design and may be substituted in a conventional rack-and-pinion steering gear to substantially eliminate shock and rattle, and significantly improve its smoothness of operation. The support provided to the bearing disc 36 permits proper alignment and improved lubrication of its support surfaces 52 so that the rack 24 moves smoothly in either direction with minimal hysteresis due to Coulomb friction.

Hand power tool

Abstract: A hand power tool formed as a hand-guided angular grinder has a tool, and an electric-motor drive for the tool, a housing accommodating the drive and carrying a central bearing pin, a handle composed of two semi-shells, rotatably arranged on the bearing pin, overlapping an end side of the motor housing and having a switch strip, an electrical switch actuated by the switch strip and connected with the drive, and a fixing device for fixing the handle in at least two different positions in a relative rotation to the motor housing and having a manual actuating member arranged on the handle, each of the handle shells being provided with a bearing semi-shell formed on the handle shell and rotatably arranged on the bearing pin, the bearing pin being provided at an end side with a blind hole, and a sleeve is inserted in the blind hole, provided with a radial flange overlapping concentric ends of the bearing pin and the bearing semi-shells, and having a snapping hook located at an end which is remote from the flange and arrested in radial recesses in the bearing pin.

Starvation and Reflow in a Grease-Lubricated Elastohydrodynamic Contact

Abstract: The lubrication mechanisms of a grease in a rolling-element bearing has been studied through the measurement of film thickness in a rolling point contact. To simulate bearing conditions the contact runs under fully starved conditions; there is no attempt to maintain bulk flow of the grease into the inlet using an external supply. In consequence the film thickness drops off rapidly as the contact progressively starves. After a few minutes rolling (at constant speed) an equilibrium film thickness is attained which has two components: a residual film (hR) comprised of degraded grease thickener and a hydrodynamic component (hEHD) due to the liquid phase from the grease. The hydrodynamic contribution represents a balance between lubricant lost from the contact and replenishment from the grease close to the track. The ability of the grease to replenish the rolling track has been inferred from measurements of lubricant reflow around the static contact. These results are discussed in light of current starvation a...

Transient Response Technique Applied to Active Magnetic Bearing Machinery During Rotor Drop

Abstract: The active magnetic bearing (AMB) is a relatively new technology which has many advantages compared with conventional bearing design. In an AMB system. the rolling-element back-up bearings are indispensable to protect the magnetic bearing rotor and stator, and other stationary seals along the rotor shqft. In this paper, a theoretical formulation is proposed and solved numerically to examine the transient response of the flexible rotor, from the time just previous to when the AMB shuts down and including the rotor drop onto the back-up bearing. The backward whirl of the rotor, which may lead to the destructive damage of the machinery, has been analytically predicted at very light support damping and very high support damping. Also, the vibration due to the nonlinearity of the contact point geometry has been included in the analysis. The influence of the support damping on the displacement of the disk and also the contact force between the journal and the inner-race of the back-up bearing have been computed for various rotor system parameters. By comparing these results with the optimum support damping for the simple flexible rotor model, it is shown that this support damping optimization can be applicable for specifying the required optimum range of support damping for the back-up bearings of AMB systems.

Hydrodynamic fluid film bearing

Abstract: A hydrodynamic fluid film bearing has a stationary retaining member (12) having a cylindrical opening (14) to receive for rotation therein a rotatable shaft (16). The inner surface (20) of the opening (14) is lined by a generally cylindrical-shaped foil assembly (18) comprised of a plurality of foil sub-assemblies (24) each comprised of spring foils (26), contact foils (30) and, optionally, inner foils (32). Each foil sub-assembly (24) subtends a rotational segment, less than all, of the inner surface (20), e.g., from about 45 degrees to 120 degrees of rotation. The spring foils (26) and contact foils (30) are affixed to the retaining member (12) in such a way that sliding travel of the spring foils (26) along the inner surface (20) is in the opposite rotational direction of sliding travel of the contact foils (30) along the inner surface (20). The foil sub-assemblies (24) may be affixed to the retaining member (12) by means of keyways (22a-22e) within which the foil sub-assemblies (24) are mounted.