Linear Magnetic Bearing Research Articles

Force Characteristic Analysis of a Linear Magnetic Bearing With Rhombus Magnet Array for Magnetic Levitation Positioning System

Magnetic levitation positioning systems (MLPSs) are of great interest in high-precision applications in vacuum. In this paper, a linear magnetic bearing with rhombus magnet array (RMA-LMB) for MLPS is proposed. With the RMA, the proposed RMA-LMB possesses advantages of excellent force uniformity, high force density, and good manufacturability. First, the basic structure and operating principle of the proposed RMA-LMB are presented. Second, the expressions of magnetic field, static force and torque, and dynamic force and torque are obtained by an equivalent current model. Third, the 3-D finite-element analysis (3-D FEA) is employed to investigate the RMA-LMB, and the magnetic field distribution, the static force and torque, as well as the dynamic force and torque are analyzed. Finally, a prototype is constructed, and experiments show a good agreement with the FEA results.

Control of Active Magnetic Bearings in Turbomolecular Pumps for Rotors with Low Resonance Frequencies of the Blade Wheel

Rotors with high gyroscopic effects and low resonance frequencies caused by the blade wheel (blade frequencies) can lead to stabilization problems in the application field of turbomolecular pumps. If such a rotor is stabilized by active magnetic bearings, the control structure could be destabilized by the splitting up of the rigid body eigen-frequencies caused by the gyroscopic effect. The control structure of the magnetic bearings can also destabilize the eigen-modes caused by the blade wheel, if the gain of the control structure is too high in the range of the eigen-frequencies of the blade wheel. To deal with the problem of the gyroscopic effect, a decoupling and compensation method was developed based on the inverse dynamics of the rigid body rotor. The gain of the control structure in the range of the blade frequencies is decreased using a Kalman filter. To increase the damping of the system, the predicted states of the linear magnetic bearing model using a Kalman filter are applied instead of the sampled values of the sensors directly. For the decoupled structure, PID controllers are used for stabilization. The functionality of the control structure is verified by a measurement of the current and position signal using the Kalman states and the sensor values. The robustness and performance in the frequency range are verified using the sensitivity and compliance function.

Impact of Cryogenics and Superconducting Components for HTS Magnetic Levitation Devices

Practical REBCO bulk superconductor-based components and devices as rotational and linear magnetic bearings are well understood. A high-stiffness high temperature superconductor (HTS) magnetic bearing with 0.1 mm low-hysteresis is demonstrated for narrow-gap operation. Linear magnetic bearings up to 10-ton load have been successfully implemented in linear Maglev trains under real outside conditions. The REBCO bulk-based magnetic levitated (Maglev) trains are proposed for urban and low-speed transport concepts. On the contrary, high-mobile, lightweight, and flexible HTS bulk components are developed under the extreme and safe conditions of manned spaceflight for astronomy and space application. YBCO bulk proton irradiation tests for space application are presented. In the International Space Station (ISS), the interaction of the earth magnetic field with a perfect fast-moving diamagnet within a project called Magvector/MFX is measured and investigated. We compare an anticipated model with space experiments performed in the last two years in the ISS. The paper will summarize recent progress in this field, and present how cryogenic and HTS component design can positively impact levitation and screening performance. Properties of cryogenic systems and devices of mobile applications in their complexity and required robustness will be compared to stationary HTS systems, and the effect of different cooling options has to been considered.

Optimization of the Superconducting Linear Magnetic Bearing of a Maglev Vehicle

Considering the need for cost/performance prediction and optimization of superconducting maglev vehicles, we develop and validate here a 3D finite element model to simulate superconducting linear magnetic bearings. Then we reduce the 3D model to a 2D model in order to decrease the computing time. This allows us to perform in a reasonable time a stochastic optimization considering the superconductor properties and the vehicle operation. We look for the permanent magnet guideway geometry that minimizes the cost and maximizes the lateral force during a displacement sequence, with a constraint on the minimum levitation force. The displacement sequence reproduces a regular maglev vehicle operation with both vertical and lateral movements. For the sake of comparison, our reference is the SupraTrans prototype bearing. The results of the optimization suggest that the bearing cost could be substantially reduced, while keeping the same performances as the initial design. Alternatively, the performances could be significantly improved for the same original cost.

A High-Precision Dual-Servo Stage Using Halbach Linear Active Magnetic Bearings

In this paper, a high-precision dual-servo stage with a magnetically levitated fine stage is described. For magnetic levitation, a Halbach linear active magnetic bearing (HLAMB) is used. The HLAMB has two functions: gravity compensation and actively control of vertical motion. To implement these functions, the HLAMB utilizes permanent magnet arrays and Lorentz coils. The fine stage has positioning capabilities with 6 DOF due to four HLAMBs and four voice coil motors (VCM). The HLAMBs control out-of-plane motions, and the VCM control in-plane motions. The fine stage achieves high-precision position feedback using laser interferometers and capacitive sensors. The coarse stage has an H-type structure that can carry the fine stage 300 mm by 300 mm along the x - and y-axes. Positioning and scanning performances are verified by the experimental results. It has ±10 and ±15 nm in-position stability in the x- and y-axes, respectively. At the scan with 10 mm/s constant velocity, ±1 nm mean tracking error and 4.7 nm jitter were obtained.

Tests on a Superconductor Linear Magnetic Bearing of a Full-Scale MagLev Vehicle

A full-scale MagLev vehicle prototype has been developed by the team of the Laboratory for Applied Superconductivity from the Federal University of Rio de Janeiro. This vehicle is named MagLev-Cobra (cobra means snake in Portuguese), because it is composed by several modules and its motion in curves resembles the movement of a snake. The suspension technology proposed for this vehicle is the levitation of bulk superconductors above a rail made with Nd-Fe-B magnets and steel. The main advantages of the MagLev-Cobra vehicle are low energy consumption, negligible noise emission, curvature radius of 45 meters and capability to ascend ramps of 15%. These properties allow the vehicle to be perfectly adjusted to big cities layout and to be constructed along roads and rivers. One of the most important parts of this project is the superconductor linear magnetic bearing (SLMB) development for the MagLev. In this work, some new results of the SLMB are presented. Measurements of the vertical levitation force of the SLMB and the effect of the flux creep on this force are presented. Also, some tests were made to investigate the influence of the load variation on the levitation force and the SLMB levitation gap. Finally, some tests were made to measure the levitation force and torque in the cryostat for an angular displacement between it and the magnetic guideway. These tests simulate the vehicle operation in real conditions.

Rolling Motion Control of a Levitated Mover in a Permanent-Magnet-Type Bearingless Linear Motor

A bearingless linear motor(BLLM) has no support elements such as a linear guide or additional linear magnetic bearing. Instead, it levitates a mover by controlling magnetic forces generated between the mover and stators as well as moves it. Its structure is very similar to a both-sided linear motor which is symmetrically combined of a common mover and two stators with permanent magnet arrays. Also the principle for movement is not quite different from that of conventional linear motors. But, to levitate the mover, the amplitudes of phase currents provided to both-side coils are controlled, based on the air gap between mover and stator. In this system, since the coils are divided into two groups in the movement direction and perform the levitation control separately, pitching motion of the mover can be controlled. And lateral translation and yawing motion are stable if the stable levitation were achieved. However, the rolling motion still needs to be stabilized by an additional control. Thus, this paper suggests a method to stabilize the rolling motion by using a pair of small electromagnetic actuators. It includes the actuator design method which is so as not to affect the BLLM performance, and the derivation of the equation of motion for controller design. Some experimental test results show that the rolling motion can be successfully controlled during levitation.

A new magnetic bearing using Halbach magnet arrays for a magnetic levitation stage

Next-generation lithography requires a high precision stage, which is compatible with a high vacuum condition. A magnetic levitation stage with six degrees-of-freedom is considered state-of-the-art technology for a high vacuum condition. The noncontact characteristic of magnetic levitation enables high precision positioning as well as no particle generation. To position the stage against gravity, z-directional electromagnetic levitation mechanisms are widely used. However, if electromagnetic actuators for levitation are used, heat is inevitably generated, which deforms the structures and degrades accuracy of the stage. Thus, a gravity compensator is required. In this paper, we propose a new magnetic bearing using Halbach magnet arrays for a magnetic levitation stage. The novel Halbach magnetic bearing exerts a force four times larger than a conventional magnetic bearing with the same volume. We also discuss the complementary characteristics of the two magnetic bearings. By modifying the height of the center magnet in a Halbach magnetic bearing, a performance compromise between levitating force density and force uniformity is obtained. The Halbach linear active magnetic bearing can be a good solution for magnetic levitation stages because of its large and uniform levitation force.

Positioning performance and straightness error compensation of the magnetic levitation stage supported by the linear magnetic bearing

This paper reports high-precision motion control at the target position and the offline compensation of the straightness error occurring during the motion of the magnetically levitated stage supported by the linear magnetic bearing. The linear magnetic bearing is composed of electromagnets and sensors in the same module to enable easy maintenance and to reduce the machining error, and the conventional linear quadratic Gaussian control is adopted for the motion control of the stage. The test results show that the stage can compensate the straightness error precisely, so that it is expected that this stage can be applied to high-precision linear motion applications.

201 非接触クリーンロボットのリニアアームの浮上制御 : 磁気軸受のバイアス電流制御による安定走行

This paper describes a new levitation control method of linear magnetic bearings for a linear arm in clean robot without any mechanical contact. The linear arm consists of a slender beam like a ladder and carries a silicon wafer on a tip. It is levitated by linear magnetic bearings and is driven by a linear stepping motor without any mechanical contact. A new control method for the linear active magnetic bearing is applied for its levitation, in which the bias current of each magnet is changed according to the distance between the center of the bearing and the center of gravity of the arm. The experiments have been carried out on the levitation control while the arm is moved by the linear stepping motor. The experiment shows that the arm is levitated and moves smoothly without any mechanical contact.

Linear Magnetic Bearing and Levitation System for Machine Tools

Magnetic bearings work without abrasion, (static) friction and attrition while providing the highest possible travel velocity and acceleration. Consequently magnetic bearings could be ideal guideways for high-speed machine tools. This paper describes a new linear magnetic bearing system suitable for machine tools. Within this contribution the development of a test bench with a linear synchronous direct drive and a magnetic bearing and levitation system is presented. The conjunction of electrical, electronic and mechanical components as parts of a mechatronical system is shown. In addition, measurements of the stiffness are presented to demonstrate the feasibility of the approach.

Linear Drive Systems and their Related Technologies. Development of Magnetically Suspended Linear Pulse Motor for Contactless Direct Drive in Vacuum Chamber Robot.

In the semiconductor manufacturing industries, the demand for semiconductor wafer processes in an ultra-high vacuum chamber is increasing in connection with development of more highly integrated circuits. This may impose severer restrictions on wafer transfer robot with regard to contamination of the vacuum environment. In the severest case, a robot mechanism without use of lubricant, generation of dust particle and release of gases will be necessary. One of advantage methods for realizing such mechanism is to drive robot arm directly without mechanical contact by means of magnetic suspention techniques. For example, it is considered to employ a linear motor and magnetic bearings which are hermetically enclosed in a box-like casing.In this paper, a magnetically suspended linear pulse motor (LPM) is proposed as contactless direct drive mechanism of vacuum chamber robot. Here the major problem is a marked lowering of thrust caused by a broad air gap which must be arranged between stator teeth and mover ones in consideration of the wall thickness of the motor casing. So the LPM is designed to be composed of a pair of flat-type stators and a ladder-like robot arm corresponding to the floating mover so that it can be compensated for the resultant decrease of the ratio of thrust to mover mass. The validity of this approach is examined by the static thrust measurements for a tested LPM, and confirmed through the experiments on the robot arm transfer with a magnetic suspention system.

Magnetic Bearing Stage for Photolithography

This paper describes a linear magnetic bearing stage which controls a suspended object in six degrees of freedom. The intended application is for X-Y wafer positioning in photolithography stages. Magnetic bearings offer superior performance and resolution over existing mechanical X-Y stages. An advanced prototype magnetic bearing stage that improves the ideas verified in the existing stage has been designed and is currently under construction. The paper will also present the advanced stage design methodology used and the reasons for the decisions made.

宇宙用スターリング冷却機の開発

For earth observations and for astronomical observations in space, there is a need to extend observation periods and improve detector performance. Development of mechanical cryocoolers with longer lifetimes and improved cooling capacity is anticipated. The free piston-type Stirling cryocooler, which applies 1) the Stirling cycle for refrigeration, 2) linear motors for driving, 3) magnetic bearings for support systems, and 4) fine gaps for clearance seals, is the most suitable design for a mechanical cryocooler utilized in a space environment. Development of this type of cryocooler began in 1987 with Bread Board Model 1. Its major components, the linear motors and magnetic bearings, were studied in order to identify the technical problems. In the present model, Bread Board Model 2, design criteria which enhance operating life, compactness, and light weight are being studied. The thrust force of moving magnet-type oscillatory linear motors satisfies the required specifications. Radial vibration amplitudes were reduced to less than 25μm with the use of PID control for magnetic bearing control. Further, the total amplitude of axial vibration was decreased to only 17μm when a dynamic damper was utilized to reduce cryocooler vibration. A cooldown time of about 17min, to a surface temperature of 70K, and an ultimate surface temperature of about 50K were achieved. The cooling power at a temperature of 70K is 2W, which is not sufficient compared with the design specification of 5W. It is supposed that stroke shortage in a piston is the primary reason for this. It was also confirmed that the stroke of a piston can be significantly increased by decreasing the clearance between the piston and the cylinder, as well as by decreasing the passage resistance of a connecting section. Further investigation of cooling power improvement to satisfy the design specifications and durability tests are planned on Bread Board Model 2, which is redesigned and now being manufactured based on the forementioned results.

Magnetic repulsion bearings for turbine engines

A six-month feasibility study has shown that magnetic repulsion bearings (MRB) possess the load capacity and stiffness required by future high-performance turbine engines. The fundamentals of MRBs are presented, and the method of analysis used to determine bearing feasibility is described. It involved a magnetic finite-element analysis on a linear magnetic bearing, the results of which were applied to a radial geometry. >

An integrated magnetic actuator and sensor for use in linear or rotary magnetic bearings

An integrated magnetic bearing actuator and sensor was realized using a specially designed ferrite pole piece. Eight of these pole pieces have been used in a magnetic bearing system to suspend a 37 mm diameter shaft in a close tolerance bore (50 μm diametral clearance). The sensors measure radial position with a resolution better than 0.25 μm and negligible temperature drift; while each actuator provides a controllable force in the range of 0 - 10 N. A servo loop accurately controls the radial position of the shaft within the bore to prevent any mechanical contact, virtually eliminating friction and wear. This radial control system exhibits a bandwidth greater than 200 Hz and yields a static stiffness of 24 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> N/m (140,000 lbs/in).