Magnetic Bearing Research Articles

Polarization Modulator Unit Harness Thermal Design for the Mid- and High-Frequency Telescopes of the LiteBIRD Space Mission

Polarization modulator units (PMUs) represent a critical and powerful component in CMB polarization experiments to suppress the 1/f noise component and mitigate systematic uncertainties induced by detector gain drifts and beam asymmetries. The LiteBIRD mission (expected launch in the late 2020 s) will be equipped with 3 PMUs, one for each of the 3 telescopes, and aims at detecting the primordial gravitational waves with a sensitivity of delta r<0.001. Each PMU is based on a continuously rotating transmissive half-wave plate held by a superconducting magnetic bearing in the 5 K environment. To achieve and monitor the rotation a number of subsystems is needed: clamp and release system and motor coils for the rotation; optical encoder, capacitive, Hall and temperature sensors to monitor its dynamic stability. In this contribution, we present a preliminary thermal design of the harness configuration for the PMUs of the mid- and high- frequency telescopes. The design is based on both the stringent system constraint for the total thermal budget available for the PMUs (lesssim 4 mW at 5 K) and on the requirements for different subsystem: coils currents (up to 10 mA), optical fibers for encoder readout, 25 MHz bias signal for temperature and levitation monitors.

Unbalance Vibration Suppression of Maglev High-Speed Motor Based on the Least-Mean-Square

The harmonic response caused by unbalanced excitation vibration for the high-speed rotating machinery will reduce the control accuracy and stability of the maglev high-speed motor, and limit the increase of its speed. When the active magnetic bearing is used to solve the unbalanced vibration, it will increase additional electromagnetic force and energy consumption, sometimes leading to the saturation of the power amplifier, and will transfer to the bearing foundation, causing the foundation to vibrate. In this paper, we analyzed periodic unbalance excitation force and the principle of rotor unbalanced vibration suppression, and the unbalance vibration model of the maglev rotor is derived. The Least-Mean-Square (LMS) algorithm is introduced into the PID control, an unbalance vibration control strategy based on real-time filtering compensation of rotor displacement signal is proposed, the vibration is eliminated by filtering the synchronous frequency and harmonic signal of the input of the PID control. The experimental results show that the proposed method can improve the maglev rotor’s rotation accuracy, reduce the magnetic bearing’s maximum control current, and decrease the vibration of the supporting foundation.

Fuzzy logic control of five-DOF active magnetic bearing system based on sliding mode concept

In rotor dynamics, the deviation of the shaft is a common phenomenon. The main reasons for the deviation are non-linear attractive forces, harmonic disturbances, system parameter variations, etc. Active magnetic bearings (AMBs) are used to support the rotor inside the air gap in rotating machines, thus avoiding wear and tear and possible breakdowns. This paper proposes a fuzzy sliding mode-inspired control (FSMIC) technique for the five-degrees-of-freedom (DOF) AMB system in the presence of system uncertainties and measurement noises. The fuzzy logic is used to estimate the auxiliary control input of the sliding mode control (SMC) to attenuate the chattering. The variable gains are designed with the help of superintended fuzzy logic to bring more flexibility to the controller performance. The stability analysis is presented with the help of the Lyapunov function candidate. The simulation studies for the AMB system under distinct types of control techniques, i.e., PID, SMC, and FSMIC, illustrate the effectiveness of the proposed control strategy.

Identification of the dynamic force and moment characteristics of annular gaps using linear independent rotor whirling motions

Nowadays, most studies on the dynamic properties of annular gaps focus only on the force characteristics due to translational motions, while the tilt and moment coefficients are less well studied. Therefore, there is hardly any reliable experimental data for the additional coefficients that can be used for validation purpose. To improve this, a test rig first presented by Kuhr (2022); Kuhr et al. (2022a) is used to experimentally determine the dynamic force and moment characteristics of three annuli of different lengths. By using active magnetic bearings, the rotor is excited with user-defined frequencies and the rotor position and the forces and moments induced by the flow field in the annulus are measured. To obtain accurate and reliable experimental data, extensive preliminary studies are carried out to determine the known characteristics of the test rig rotor and the added mass and inertia imposed by the test rig. Subsequently, an elaborate uncertainty quantification is carried out to quantify the measurement uncertainties. The experimental results, i.e. the 48 rotordynamic coefficients, are compared to a calculation method by Kuhr (2022); Kuhr et al. (2022b). It is shown that the presented experimental data agree well with the calculation method, especially for the additional rotordynamic tilt and moment coefficients. Furthermore, it is shown that the annulus length significantly influences the coefficients of the first sub-matrix. A dependence of the additional coefficients on the length is recognisable, but less pronounced. Even for the shortest investigated annulus, i.e. L≔L̃/R̃=1, the stiffness coefficients due to the forces from the angular motion of the rotor are of the same order of magnitude as the stiffness coefficients due to the forces from the translational motion. This supports recent results by Kuhr (2022); Kuhr et al. (2022b), indicating that the additional coefficients become relevant much earlier than assumed throughout the literature, cf. Childs (1993).

Magnetic field analytical calculation method for radial unite of a combined magnetic bearing

AbstractCombined magnetic bearing with radial and axial unites is an important supporting element for high speed and high energy density motor. Accurate calculation of the magnetic field is a key to design and optimise a Combined Radial and Axial Magnetic Bearing (CRAMB). This study focuses on magnetic field analytical calculation method for radial Unite of CRAMB. The analytical calculation model of magnetic field is based on subdomain method. The Laplace's equations in the air‐gap subdomain are solved by the variable separation method. The magnetic field of magnetic bearing with large diameter rotor is analysed and calculated in Cartesian coordinate system. Considering the influence of curvature the magnetic field distribution of magnetic bearing with small diameter rotor is deduced and calculated analytically in polar coordinate system. The effectiveness of the analytical method is verified by finite element and experimental results.

Modeling and mu-synthesis control of a flexible rotor stabilized by active magnetic bearings including current free control

Designing a controller for a magnetically stabilized rotor that experiences non negligible gyroscopic moments requires careful attention on the rotordynamic behavior, the design of the position and current free control as well as the actuator and sensor characteristics. Most of the controller design procedures for magnetic bearings separate the synthesis of the current free controller and the position controller using different methods. This article connects the synthesis of the current free controller and the position controller in the μ-framework. Therefore, the modeling of the rotor, the position controller design and the design of the current free control of a flexible rotor stabilized by active magnetic bearings is described. The rotor is modeled by using the finite element method. Afterwards, the flexible system is reduced to get an appropriate model size for the control design. For the optimization of the controller parameters the μ-synthesis method is applied. However, compared to the general μ-synthesis method in this article an a priori fixed control structure is utilized. This control structure splits up the tilting subsystem to a control path for the nutation mode and one for the precession mode. Thus, the proposed controller has the advantage of a low system order and that the parameter variant nature of the plant is already considered in the control structure. Additionally, the synthesis of the current free controller is added to the μ-framework. Hence, the current free controller is optimized for a plant with defined uncertainties using necessary constraints of the closed loop systems. Finally, the stabilization of the system using the proposed control method is experimentally validated on a turbomolecular pump with a magnetically levitated rotor.

Angular Rate Measurement Method of Magnetically Suspended Control and Sensing Gyroscope Using Component-Level Rotation Modulation

Magnetically suspended control and sensing gyroscope (MSCSG) is a novel concept gyroscope with attitude control and attitude measurement. In order to eliminate constant drift error and improve the angular rate measurement accuracy of MSCSG, a high-precision angular rate measurement method based on component-level rotation modulation (CLRM) is proposed in this article. First, the structure of MSCSG, the Lorentz force magnetic bearing (LFMB), and the angular rate measurement principle of MSCSG are analyzed. Second, the basic principle of rotational modulation is introduced. Third, based on the principle of CLRM angle measurement, the high-precision measurement of angular rate based on MSCSG is realized by taking the derivative of the angle and sliding smoothing. After CLRM processing, the angular rate measurement error of MSCSG is quantified and the installation error is analyzed and compensated. Finally, the error compensation of CRLM and installation error compensation effect is verified by simulation. The feasibility of the proposed method is verified by experiments. The method of CLRM can reduce the MSCSG drift error by two orders of magnitude. The method proposed in this article can be used as a reference for MSCSG attitude measurement and attitude control integration.

Structure and Application of Flywheel Energy Storage-A Simple Perspective

Flywheel energy storage is a new sustainable development technology, which has the advantages of high energy storage density, fast charging and discharging speed, long service life and so on. It breaks through the constraints of traditional chemical fuel cells and stores energy in a physical way. This paper discusses the structure and composition of flywheel energy storage, introduces three kinds of common and practical high-speed motors for flywheel, and three kinds of powerful flywheel magnetic levitation bearings. The development of flywheel energy storage in different industries and the reuse of resources in different situations are introduced. The application of flywheel energy storage technology to achieve energy saving and emission reduction production has a broad market application prospect.

General-purpose controller for multiple types of magnetic bearing rotor systems

With the increasingly widespread application of magnetic bearings (MBs) in high-speed motors, turbomachinery, and machine tools, the development of magnetic bearing controllers (MBCs) is becoming increasingly significant. Conventional MBCs are designed specifically for a particular type of MB and have poor generality. Given this, an MBC with a digital signal processor (TMS320F28377S) as the core is developed. Meanwhile, a generality calculation method for the circuit module is proposed. The displacement conditioning circuit designed in this paper can match most MB displacement sensors, and the generality is improved to 91.66%. The designed power amplifier can realize the switching of two-level and three-level pulse width modulation (PWM). It can also realize the switching of unidirectional and bidirectional power amplifier control. Therefore, it can apply to most MB rotor systems, and the generality is improved to 66.67%. In addition, the proposed dual closed-loop control strategy based on linear active disturbance rejection control (LADRC) makes the system’s anti-interference capability, robustness and self-adaptive capability enhanced, further improving the generality of the controller. Simulation and experimental results show that the MBC is highly general and has good dynamic performance, and the electrical control system of the MB is optimized.

Suppression of lateral vibration in a shafting system via an auxiliary active magnetic bearing with position control

The bearings in a shafting system are important paths for the lateral vibration of the shaft to transmit to the hull structure and induce underwater sound. An auxiliary active magnetic bearing for suppressing the lateral vibration at the stern support of a shafting system is investigated. The active magnetic bearing situated close to the stern bearing generates electromagnetic forces to support the shaft, which decreases the contact stiffness as well as the friction between the shaft and the stern bearing and accordingly reduces the stern support acceleration. A dynamic model is established using the Timoshenko beam theory and Hamilton’s principle and the performance of the active magnetic bearing in vibration suppression of the shafting system is evaluated with position control. An experimental system is also built to verify the effectiveness of the active magnetic bearing. Numerical and experimental results have shown that the active magnetic bearing is able to suppress the stern support acceleration responses after the shaft is suspended by the active magnetic bearing. Moreover, the orbit of the shaft center is controlled as well.

Radial Displacement Detection Using Sensing Coils Weakly Coupled With Magnetic Bearing

This article presents a novel displacement detection method with sensing coils weakly coupled with a conventional eight-pole active magnetic bearing. To improve integration, the sensing coils are completely wound on the magnetic poles of the active magnetic bearing. The proposed method is different from others since each sensing coil is wound around two teeth of an active magnetic bearing, reducing the mutual inductance coefficient between sensing and excitation coils. Thus, the influence of excitation coils on displacement detection can be reduced. A core multiplexing and frequency discrimination method is proposed to detect displacements along <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${x}$ </tex-math></inline-formula> - and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${y}$ </tex-math></inline-formula> -directions, simultaneously. Experiment results show that sensitivity along the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${x}$ </tex-math></inline-formula> - and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${y}$ </tex-math></inline-formula> -axes are 8.98 and 5.61 mV/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> , respectively, showing the feasibility of displacement detection without being affected by displacement variation of the orthogonal axis. Finally, the displacement detected by sensing coils is used for close loop control in an active magnetic bearing system at 2500 rpm, validating the feasibility of sensing coils in active magnetic bearing control.

News From Japan

Dr. H. K. Onnes discovered the zero electric resistance or superconductivity (SC) in mercury (Hg) in 1911, and Dr. J. G. Bednorz and Dr. K. A. Müller discovered high-temperature SC (HTSC) in ceramics in 1986. Although a long time has passed since the discovery of various SC phenomena and materials, their industrial use is still limited. Among various SC phenomena, applications using the generation of a strong magnetic field have been used relatively widely. This column, “News from Japan,” has reported the development of HTSC coil windings for a power transformer [1], HTSC magnetic resonance imaging used in medical diagnosis [2], and flywheel energy storage using HTSC magnetic bearings [3], as typical Japanese examples of HTSC applications.

Design, optimization and test of RHMB considering dynamic characteristics

The coil inductance, stiffness and losses of the magnetic bearing (MB) have great influence on the dynamic performance for the magnetically suspended control moment gyro (MSCMG) application. Based on the equivalent magnetic circuits considering flux leakage effects, a design, optimization and test method is proposed to enhance the dynamic response ability for the radial hybrid MB (RHMB). The optimization design objectives including bearing force, stiffness, coil current, mass, inductance and loss estimation are discussed under the multiple constraints. Compared with the original design, the dynamic characteristics including frequency responses of current and rotor displacements for the RHMB-rotor system are significantly improved after optimization. A prototype of MSCMG is fabricated to verify the dynamic response characteristic of the RHMB.

Discrete Dynamics of Balls in Cageless Ball Bearings

Cageless ball bearings are often preferred as a back-up bearing for active magnetic bearings to support a falling rotor, but the contact between the balls of the cageless ball bearing may lead to the deterioration of the bearing performance and affect the dynamic stability of the rotor system. Thus, we studied the discrete dynamics of cageless ball bearings. First, a model is proposed to change the groove curvature center of the local outer raceway to control the ball velocity to achieve dispersion. Combined with the spatial geometry theory, the mathematical model of the discrete raceway is established, the collision between the balls is considered as an abruptly added constraint, and the non-smooth dynamics equation of the cageless ball bearing with a local discrete raceway is established. Then, the fourth-order Adams prediction correction algorithm is used to numerically solve the dynamic discretization of the ball, and the structural parameters of the discrete raceway are preferably selected, according to the phase diagram of the ball and the change in the angular spacing. The results show that the structure of the discrete raceway has a strong influence on the discrete dynamics of the ball.

Optimized multi-layer radial permanent magnet bearing with an eddy current damping systems

This research work proposes the conventional and novel eddy current damping systems (CECDS & NECDS) for an optimized multi-layer radial permanent magnet bearing, which is axially magnetized. Firstly, the design and optimization of a bearing are carried out by adopting the general procedure for maximum radial force and stiffness by selecting stator outer diameter, radial air gap, and length as parameters. The maximum radial force and stiffness concerning an optimized structure are also calculated using semi-analytical equations, and force results are validated with three-dimensional (3D) finite element analysis results. Then, the analysis of both damping systems is carried out for damping forces and coefficients using 3D electromagnetic transient analysis in ANSYS. The proposed dampers provide adequate damping to the bearing structure, and conductor plate thickness significantly affects the damping characteristics. The NECDS could be used to replace the conventional type as it eliminates the effect of reduced radial air gap on the performance of the bearing.

Dynamic and Thermal Investigations of the Forward Dry-Friction Whirl/Whip of a Vertical Rotor-AMB System during Touchdowns

When an active magnetic bearing (AMB) rotor drops, it impacts the touchdown bearing (TDB) and produces friction on its surface. The vertical AMB rotor has no stable support in the radial direction, and the rotor exhibits a violent whirl motion in the gap of the TDB. In this study, a complete dynamic and thermal model of the AMB-rotor-TDB system was established, and the complete drop process was simulated. When the rotor dropped, it obtained stable support after several bounces on the thrust surface of the TDB inner ring in the axial direction. In the radial direction, the rotor entered whirl motion after the initial collisions. There is a natural whirl frequency so that the drop forward whirl is divided into the dry-friction whirl and whip states. The contact force and heat generation of the TDB were monitored in the simulation and had different performancs in the two states. Both the initial collisions and the stabilized whirl motions were studied to evaluate the reliability of the TDB. Finally, a series of drop tests were performed, and the experimental results were in good agreement with the simulation.

Analysis and measurement of the shape of spinning balloons

The development of superconducting magnetic bearings as the twisting element in ring spinning renews the study of the dynamic model of the ring spinning process. In this paper, the variational equation describing the steady motion of the yarn is developed using Hamilton’s principle, the balloon shape is represented by the Bezier polynomial, the undetermined coefficient is solved by Galerkin method, and the semi-analytical solution of the steady-state balloon shape is obtained. Digital images of the balloon yarn are collected by binocular cameras and a stroboscope, and the balloon curve is reconstructed by stereo vision technology. The calculated balloon curve is in good agreement with the measured balloon curve. The balloon shapes and the radial forces acting on the permanent magnetic ring at different radii of the wind-point on the bobbin are investigated by the semi-analytical model when the spindle is spinning at different speeds. The solution procedures developed can be used to explore the vibration and stability of the system, consisting of the magnetic stiffness, permanent magnetic ring, and balloon yarn in the superconducting magnetic bearing twisting mechanism.

Milling Chatter Mitigation with Projection-Based Robust Adaptive Controller and Active Magnetic Bearing

Milling Chatter Mitigation with Projection-Based Robust Adaptive Controller and Active Magnetic Bearing

Analysis and testing of the natural frequencies of the ring-spinning balloon

The development of superconducting magnetic bearings as the twisting element in ring spinning renews the study of the dynamic model of the ring-spinning process. In this paper, the variational equations governing yarn in the balloon are developed using Hamilton’s principle. The balloon curves are represented by the Bezier function, and the semi-analytical steady-state balloon is obtained by the Galerkin method. The linearized equation of motion is completed by elimination of the nonlinear displacement terms and cancellation of the steady-state terms. The displacement field of the balloon yarn about the steady state is expressed by the Bezier polynomial, and the natural frequencies of the balloon yarn are calculated by the Galerkin method. The semi-analytical solution of the steady-state balloon and the natural frequencies of the balloon yarn are in good agreement with those in the experimental measurement. The influences of rotational speed, balloon height, and yarn count on the natural frequencies of the balloon yarn are investigated. For a realistic parameter set, the possible resonances caused by the change of balloon height, which is due to the up-and-down movement of the ring rail, are discussed in more detail.

An Active Magnetic Bearing With Controllable Permanent-Magnet Bias Field

Permanent-magnet (PM) biased magnetic bearings use a magnet to produce the bias field rather than applying a bias current, thereby eliminating the associated electrical power losses and heat generation. In the existing PM-biased magnetic bearings, the PM materials NdFeB or SmCo are generally employed due to their superior properties. However, these PMs should be pre-magnetized, and the generated bias magnetic field cannot be adjusted, limiting the flexibility of the magnetic bearings. This article proposes a new type of PM-biased magnetic bearing that uses a low-coercivity AlNiCo magnet and equips a magnetization coil to magnetize the magnet <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> . As a result, the magnet can be post-magnetized to make the assembly process of the machines easier without the disturbance of magnetic force, and the bias field generated by the magnet can be actively controlled to improve the rotor iron losses and force characteristics of the magnetic bearing. Experiments on a prototype successfully verify the advantages of the presented magnetic bearing.