Passive Bearings Research Articles

Bearings only single-sensor target tracking using Gaussian mixtures

This paper presents a new approach for single sensor tracking using passive bearings only measurements. Gaussian mixture measurement presentation, together with a track splitting algorithm, allow space-time integration of the target position uncertainty with a simple algorithm. The bearings-only measurements are incorporated into track as they arrive using a dynamic bank of linear Kalman filters. While this approach is applicable to the case with the target detection, data association and multitarget issues, this paper concentrates on the target trajectory estimation using associated measurements. A simulation study demonstrates the benefits of this approach.

A Passive Magnetically and Hydrodynamically Suspended Rotary Blood Pump

A combined hydrodynamic-magnetic bearing allows the design of rotary blood pumps that are not encumbered with mechanical bearings and magnets requiring sensors or electrical power. However, such pumps have so far needed very small and accurately manufactured gaps between rotor and housing to assure effective hydromagnetic bearing behavior. In order to use this concept in disposable pump heads, a design that allows larger rotor-housing gaps, and thus larger manufacturing tolerances, is needed. A pump with passive magnetic bearings and a gap between rotor and housing in the range of 0.5 mm was designed. Numerical simulations were performed to optimize the rotor geometry at low levels of shear stress. An experimental test stand was used to find a range of speeds and gap settings that resulted in low levels of vibration and useful pressure-flow relationships. Three different rotor geometries were tested using a viscosity-adjusted test fluid. Blood damage tests were conducted within the desirable range of speeds and gap settings. In this study stable pump performance was demonstrated at total gap widths between 0.3 and 0.7 mm at flows of 0-10 L/min, with afterloads up to 230 mm Hg. Best performance was achieved with rotors sliding on a fluid pillow between the rotor and the outer housing at a gap distance of 50 to 250 microm. The inner gap distance, between the rotor and the inner housing, could be as great as 500 microm. Hemolysis tests on the prototype within the chosen operating range showed lower values (NIH = 0.0029 +/- 0.0012 g/100 L) than the Biomedicus BP-80 pump (NIH = 0.0033 +/- 0.0011 g/100 L). In conclusion, it is possible to build rotary blood pumps with passive hydromagnetic bearings that have large gaps between their rotors and housings. Rotor behavior is sensitive to the position of the permanent magnetic drive unit. To minimize vibration and blood damage, the fluid gaps and the rotational speed have to be adjusted according to the desired operating point of the pump. Further study is needed to optimize the magnetic drive unit and to ascertain its ability to withstand inertial loads imposed by sudden movements and external shock.

Magnetic Design for the PediaFlow Ventricular Assist Device

This article describes a design process for a new pediatric ventricular assist device, the PediaFlow. The pump is embodied in a magnetically levitated turbodynamic design that was developed explicitly based on the requirements for chronic support of infants and small children. The procedure entailed the consideration of multiple pump topologies, from which an axial mixed-flow configuration was chosen for further development. The magnetic design includes permanent-magnet (PM) passive bearings for radial support of the rotor, an actively controlled thrust actuator for axial support, and a brushless direct current (DC) motor for rotation. These components are closely coupled both geometrically and magnetically, and were therefore optimized in parallel, using electromagnetic, rotordynamic models and fluid models, and in consideration of hydrodynamic requirements. Multiple design objectives were considered, including efficiency, size, and margin between critical speeds to operating speed. The former depends upon the radial and yaw stiffnesses of the PM bearings. Analytical expressions for the stiffnesses were derived and verified through finite element analysis (FEA). A toroidally wound motor was designed for high efficiency and minimal additional negative radial stiffness. The design process relies heavily on optimization at the component level and system level. The results of this preliminary design optimization yielded a pump design with an overall stability margin of 15%, based on a pressure rise of 100 mm Hg at 0.5 lpm running at 16,000 rpm.

Bearings only multi-sensor maneuvering target tracking

This paper presents a solution to target trajectory estimation when multiple asynchronous passive bearings only sensors with uncertain positions are employed. Asynchronous target position triangulation is achieved. Gaussian mixture measurement presentation, together with a track splitting algorithm allows space/time integration of the target position uncertainty with a simple algorithm. Gaussian mixture measurement presentation incorporates sensor position uncertainty, as well as the spatial uncertainty brought by bearings only measurement. Each sensor detects the target emissions independently, and the measurements are incorporated into track as they arrive. Measurements by arbitrary number of sensors can be incorporated, provided that the triangulation observability criterion is satisfied. The approach is verified by a single target, two sensors, two-dimensional surveillance simulation experiment.

Numerical and In Vitro Investigations of Pressure Rise in a New Hydrodynamic Blood Bearing

The reliability and simplicity of rotor bearing are vital to the success of long-term implantation of rotary blood pumps. This article describes both numerical and in vitro studies of the pressure rise in a 5-cm-diameter spiral groove bearing. Results show that the simplified analytical model overpredicts the pressure rise across the bearing while the results from a more comprehensive three-dimensional computational fluid dynamics (CFD) model agree well with the measurements. The discrepancy between the analytical model and the measurements is attributed to the exclusion of the fluid inertia effects in the analytical model. In addition, the assumption of linear pressure variations at the entrance of the groove and the ridge may have oversimplified the analysis. CFD results show that the pressure variation at the entrance of the groove and ridge is nonlinear. A correction factor taking into consideration the fluid inertia effect has been incorporated, and the modified analytical results agreed well with the measurement as well as that of the more comprehensive CFD model. The pressure generated is sufficient to lift the rotor, and this design provides the designer an alternative design for passive bearing.

Gyro-effect Stabilizes Unstable Permanent Maglev Centrifugal Pump

According to Earnshaw's Theorem (1839), the passive maglev cannot achieve stable equilibrium and thus an extra coil is needed to make the rotor electrically levitated in a heart pump. The author had developed a permanent maglev centrifugal pump utilizing only passive magnetic bearings, to keep the advantages but to avoid the disadvantages of the electric maglev pumps. The equilibrium stability was achieved by use of so-called "gyro-effect": a rotating body with certain high speed can maintain its rotation stably. This pump consisted of a rotor (driven magnets and an impeller), and a stator with motor coil and pump housing. Two passive magnetic bearings between rotor and stator were devised to counteract the attractive force between the motor coil iron core and the rotor driven magnets. Bench testing with saline demonstrated a levitated rotor under preconditions of higher than 3,250 rpm rotation and more than 1 l/min pumping flow. Rotor levitation was demonstrated by 4 Hall sensors on the stator, with evidence of reduced maximal eccentric distance from 0.15 mm to 0.07 mm. The maximal rotor vibration amplitude was 0.06 mm in a gap of 0.15 mm between rotor and stator. It concluded that Gyro-effect can help passive maglev bearings to achieve stabilization of permanent maglev pump; and that high flow rate indicates good hydraulic property of the pump, which helps also the stability of passive maglev pump.

Design and Implementation of a Fault-Tolerant Magnetic Bearing System for Turbo-Molecular Vacuum Pump

One of the obstacles for a magnetic bearing for use in a wide range of industrial applications is the failure modes associated with magnetic bearings, which are not expected for conventional passive bearings. These failure modes include electric power outage, power amplifier faults, position sensor faults, and the malfunction of controllers. Fault tolerant magnetic bearing systems have been proposed so that the system can operate in spite of some faults in the system. In this paper, we describe the design and implementation of a fault tolerant magnetic bearing system for a turbo-molecular vacuum pump. The system can cope with actuator/amplifier faults, as well as faults in position sensors, which are the two major fault modes in a magnetic bearing system.

Measurement of the Rotor Motion and Corresponding Hemolysis of a Centrifugal Blood Pump With a Magnetic and Hydrodynamic Hybrid Bearing

This study proposed a centrifugal blood pump with a novel magnetic and hydrodynamic hybrid passive bearing, which consisted of a plain journal bearing for radial stability and a permanent magnetic bearing for axial and tilting stability. We measured the radial motion of the bearing and performed hemolysis tests for the different radial clearance sizes. In the results, it appeared that the radial motion had two modes: the stable center mode, in which the radius of the radial motion rapidly converged to less than 20 microm; and the unstable circle mode, in which the rotor suspension linearly increased with the rotation speed. It also appeared that the pumps with the radial clearance of 80 microm caused more hemolysis than with the smaller clearance sizes in the circle mode. The circle mode was avoidable by the higher rotation or the asymmetric pump structure, but the mechanism of hemolysis in this mode was still unclear.

Bearings-only target localization using total least squares

A total least-squares (TLS) algorithm is developed for two-dimensional location estimation of a stationary target by using only passive bearing measurements of the target. This problem has been studied extensively for several decades and has applications in electronic warfare, surveillance, passive sonar, interference location and suppression, and so forth. The nonlinear nature of the estimation problem poses a number of challenges related to complexity, convergence and estimation bias. After a critical review of the least-squares (LS) algorithms, a TLS estimation algorithm is developed based on the method of orthogonal vectors with the advantage of simplicity and reduced bias in the presence of bearing noise and observer position errors. A constrained TLS (CTLS) algorithm is also developed to improve the estimation accuracy, especially in the case of large measurement errors. Numerical examples are provided to compare the performance of the TLS and CTLS algorithms with the LS target localization algorithms, viz. the maximum likelihood estimator, Stansfield estimator and the method of orthogonal vectors.

Analytical model of interaction between hexagonal wire mesh and silty sand backfill

The interaction behavior between hexagonal wire mesh and silty sand backfill can be evaluated from pullout tests. The pullout resistance of the hexagonal wire mesh reinforcement consists of two components, namely friction resistance and passive bearing resistance. The friction resistance – relative displacement relationship of a hexagonal wire mesh can be simulated by a linear elastic – perfectly plastic model. The passive bearing resistance of an individual bearing member can be modelled by a hyperbolic function. The friction resistances for galvanized and PVC-coated hexagonal wire mesh were 25 and 21%, respectively, of the total pullout resistance. A new analytical model for predicting the pullout resistance of hexagonal wire mesh reinforcement has been proposed. The proposed solution can estimate the maximum pullout force at different reinforcement levels from observed horizontal movement of a hexagonal wire mesh reinforcement.Key words: hexagonal wire mesh, necking phenomena, bearing resistance, analytical model, pullout box, bearing resistance.

Diamagnetic suspension system for small rotors

A novel frictionless motor-bearing combination, featuring a passive five degrees of freedom (DOF) suspension system is presented in this paper. In conventional frictionless systems, levitation is achieved by means of feedback controlled electromagnetics or electrostatics (active bearings), permanent magnets in combination with displacement (passive bearings) or by superconductive repulsion of permanent magnets. Earnshaw's theorem discards the possibility of passive static magnetic levitation, but by taking advantage of the diamagnetic effect, a passive magnetic system can be stabilized. In the proposed system, all the degrees of freedom of a disc-shaped magnetic rotor, except its rotation around the main axis, are stabilized using the diamagnetic properties of materials such as bismuth and graphite. As the weight of the rotor is compensated with a permanent magnet, the proposed system can make use of the weak diamagnetic repelling forces, presenting the only known principle for 'real' levitation (no energy input) at room temperature. The presented approach leads to very compact energy-saving solutions. The principle of diamagnetic levitation is well known and understood. The presented experimental work adds radial stiffness to the classic three degrees of freedom suspension and powers the rotor using an induction motor. The realized motor is hardly bigger than one cubic centimeter and turns with up to 800 rpm. This paper intends to draw attention to this uncommon method of levitation and to show that it could be used to design micro-mechatronical actuators.

A design methodology for permanent magnet microbearings

A 2D analytical calculation method for permanent magnet bearings is proposed and used with a novel computer-aided constrained-design methodology. This methodology uses symbolic computation and automatic programming to generate the optimization software, based on an analytical model of the device. The methodology, implemented in experimental software, Pascosma, is applied to miniaturize passive bearings using bonded and thin-film magnets.

Classification and synthesis of permanent magnet bearing configurations

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.

A novel magnetic suspension cum linear actuator system for satellite cryo coolers

Stirling cycle cryogenic coolers have been widely used for device cooling in satellites. Various types of magnetic bearings and linear actuators find application in such systems. The most widely used configurations have two-axis-radially-active suspension stations placed at either end of a reciprocating shaft in the compression and expansion sections. Separate or integral linear motors are provided in each section for axial shaft movement. It may be noted that such configurations are rather complicated and less reliable because of the presence of numerous electro-mechanical components, sensors and electronic servo channels. In this paper, a simple and reliable scheme is suggested which axially stabilizes and linearly perturbs the piston so that the need of a separate motor for axial actuation can be totally dispensed with. The piston is radially supported by passive repulsive bearings. In the axial direction, a servo actuator 'balances' the piston and also actuates it bi-directionally. Implementation of this 'bearing cum motor theme', reduces the number of electromechanical and electronic components required to operate the system and hence minimizes the chances of system failure. Apart from this, the system's power consumption is reduced and efficiency is improved as electrical heating losses caused by quiescent-operating currents are removed and electromagnetic losses on the moving parts are minimized. The necessary system parameters have been derived using finite element analysis techniques. Finally, the proposed design is validated by computer-aided system simulation. >

Study of permanent magnet arrangements for superconducting passive bearings

Magnetic bearings are one of the more interesting applications for high temperature superconducting materials. Different structures of permanent magnets and superconductor are studied assuming a total Meissner effect. The use of alternated poles highly increases axial forces and stiffnesses. Consequences of real superconducting material behavior are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An efficient method of passive emitter location

The problem of locating a stationary emitter from passive bearing and frequency measurements taken by a moving and autonomously operating sensor along its trajectory is considered. The estimation procedure based on bearings only is quite different from that based on frequency measurements. From the Cramer-Rao (CR) analysis of the single-measurement case, the characteristic features of each method become transparent and an intuitive understanding of both methods is provided. One of the major results is that the orientation of the error ellipses of the bearings method (BM) and frequency method (FM) differ significantly. From this a considerable integration gain in accuracy results, when processing the combined set of bearing and frequency measurements. The results of the theoretical CR analysis are verified in a numerical simulation based on the maximum-likelihood (ML) estimation. The simulations demonstrate that a combined method is definitely superior to BM and FM with respect to the bias and the size of the error ellipses.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Erfahrungen mit der Versorgung der frischen Kreuzbandruptur bei Sportlern

Since 1984 we have done over the top repair of the acutely torn anterior cruciate ligament combined with augmentation by McIntosh lateral-substitution over the top procedure with iliotibial band in view of frequent instabilities following simple reconstruction. After treatment by continuous passive motion and early weight bearing is possible. The results at review were good. This method is recommended to avoid the risk of rerupture.

Passive axial stabilization of a magnetic radial bearing by superconductors

Contactless bearings for high-speed operation can be constructed using passive magnet systems which inherently need a second active bearing for their stabilization. Completely passive bearings only can be obtained using diamagnetic materials. The axial stabilization of magnetic radial bearings using a permanent magnet/superconductor system is considered. Using finite-element calculations, it is shown that axial forces of up to 3000 N and stiffnesses of up to 400 N/mm can be achieved; good diamagnetic behavior ( mu /sub r/ >

A Passive Magnetic-Thrust Bearing for Energy-Storage Flywheels

Flywheels for the storage and subsequent release of energy in general involve the suspension of rather large masses rotating at speeds limited by the strength of the flywheel material. Since drag torque on the flywheel represents an undesirable energy drain during storage, windage can be eliminated by operation in a vacuum, leaving bearing drag as a significant item. Using a vertical shaft configuration, a passive repulsion-type permanent-magnet thrust bearing is virtually frictionless while small, low-loss, oil-lubricated pintle bearings maintain the shaft radially. This paper discusses the analytical design of the passive magnetic-thrust bearing, including its nonrotating damper. Reliability of the system is high since no servo-control system is required. Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE Lubrication Conference in San Francisco, California, August 18–21, 1980.

Passive magnetic bearings with permanent magnets

The various geometrical dispositions which allow to realize passive magnetic bearings with permanent magnets, have been Known for several decades. Devices running by attraction were the first to be built. When new magnets, which can be used in repulsion appeared on the market (SmCo 5 ), new types of passive magnetic bearings, running by repulsion, started to be made. Up to now, to our knowledge, most of the devices realized have been made with radially magnetized rings. We proved that for identically shaped bearings, strengths and stiffnesses were exactly the same in both magnetic configurations : radial and axial magnetization. The proof is only based on the rigidity of the magnetization. These results are still true for axial or radial passive bearings, and can also be used for devices in attraction. Ring shaped magnets with radial magnetization are usually made of several sectors stuck together. Axial magnetization is much easier to manufacture because large sized rings are already industrially provided.