Back Yoke Research Articles

Study on Thrust Improvement and Ripple Suppression of HTS Linear Switched Reluctance Motor with Coreless HTS Excitation Windings

This paper describes a linear switched reluctance motor (LSRM) in which HTS tapes are used for coreless excitation windings in order to reduce the thrust ripple and normal force. This LSRM consists of a mover with saliency structure, coreless HTS coils and a stator back yoke. In this paper, we first describe the operating principle of the HTS-LSRM. Next, we calculate performances of the HTS-LSRM using 3-D FEM analysis. The effects of the motor structure on the thrust characteristic and normal force characteristics are clarified from the numerical results. Furthermore, we investigate the motor structure for thrust improvement, thrust ripple and normal force reduction.

Double Pancake Exciting Coils with Back Yoke for Magnetics Field Generator to Medical Treatment

Double Pancake Exciting Coils with Back Yoke for Magnetics Field Generator to Medical Treatment

磁気シートで構成したバックヨーク付医療用磁界発生装置の研究

磁気シートで構成したバックヨーク付医療用磁界発生装置の研究

Vector Magnetic Properties and 2-D Magnetostriction of Various Electrical Steel Sheets Under Rotating Flux Condition

In electrical equipment, such as transformers and motors, rotating magnetic fluxes occur at T-joint parts and back yoke parts. It is therefore necessary to understand the magnetic properties and magnetostrictions under several rotating flux conditions. This paper presents measured vector magnetic properties including 2-D magnetostriction of a nonoriented electrical steel sheet (including a 6.5%SiFe sheet), a grain-oriented electrical steel sheet, and a permendur sheet under rotating flux conditions. The relationship among the magnetic flux density vector, the magnetic field strength vector, and the 2-D magnetostriction is clarified in comparison of the various electrical steel sheets. Furthermore, from the measurement results, suitable materials are suggested for equipment.

Source and Reduction of Uneven Magnetization of the Permanent Magnet of a HDD Spindle Motor

Uneven magnetization of a permanent magnet (PM) generates cogging torque with slot harmonics and an unbalanced magnetic force, which are the major sources of vibration and noise in a hard disk drive (HDD) spindle motor. We investigated several potential sources of uneven magnetization of a ring-shaped PM magnetized in a capacitor-discharge impulse magnetizer by transient finite element analysis. We verified our simulation model by comparing the simulated surface magnetic flux density along the ring-shaped PM with the measured flux density. Our research findings demonstrate that positioning error of the coil of the magnetizing yoke is the dominant source of uneven magnetization. High magnetic field intensity in the magnetization moment due to high magnetizing voltage or the presence of a back yoke decreases the uneven magnetization of the PM by compensating for the coil-positioning error.

Dynamic Analysis Method for Electromagnetic Artificial Muscle Actuator under PID Control

We have been studying an interior permanent magnet linear actuator for an artificial muscle. This actuator mainly consists of a mover and stator. The mover is composed of permanent magnets, magnetic cores and a non-magnetic shaft. The stator is composed of 3-phase coils and a back yoke. In this paper, the dynamic analysis method under PID control is proposed employing the 3-D finite element method (3-D FEM) to compute the dynamic response and current response when the positioning control is active. As a conclusion, computed results show good agreement with measured ones of a prototype.

Performance Analysis of Brushless DC Motor According to Polar Magnetizing Characteristic of Ferrite Bonded Permanent Magnet

Abstract - The magnetization directions of a polar magnetized ferrite‐bonded magnet are analyzed by finite element method (FEM). The influence of the width of SmCo magnets for magnetic field generation is investigated. The surface flux densities of the polar anisotropic magnets are analyzed and compared according to the pole number and thickness of the magnets. And the electromotive force (EMF) values of brushless DC motors with the magnets are investigated. The validity of the analysis method is verified by comparing the analyzed results with measured ones.Key Words : Brushless DC motor, Polar anisotropic, Ferrite bonded magnet, Magnetic field, Electromotive force. *펠로우회원 : 동국대 공대 전자전기공학부 교수․공박E-mail : baekuniv@dongguk.edu 접수일자 : 2010년 10월 15일 최종완료 : 2010년 nylon,11월 17일 1. INTRODUCTION Ferrite-bonded magnets are widely used in small brushless DC motors for many applications such as fan and pump motor. As a magnet material, ferrite material is frequently used for low torque applications[1]. Ferrite magnets are classified into isotropic and anisotropic material as their material characteristics, and classified into sintered and bonded magnets according to the manufacturing methods. Bonded magnets are made by injection molding process of mixed ferrite powder with binder such as nylon. At this procedure, appropriate magnetic field is applied in order to determine the anisotropic directions[2]. In many cases, ferrite-bonded magnets (frequently names as plastic magnets) are made with polar anisotropy for brushless DC motor applications, and the magnets do not need ferromagnetic back yoke. It reduces manufacturing cost and inertia of the rotating part. The characteristics of the polar anisotropic plastic magnets are different from parallel or radially directed magnets[3]. In this paper, the magnetization directions of a polar anisotropic plastic magnet are analyzed by finite element method (FEM). The influence of the width of SmCo magnets for magnetic field generation is investigated. And, the surface flux densities of the polar anisotropic magnets are analyzed and compared according to the pole number and thickness of the magnets. The electromotive force (EMF) values of brushless DC motors with the magnets are investigated. The validity of the analysis method is verified by comparing the analyzed results with measured ones.

Simulation results of a hexahedron-octahedron based spherical stepping motor

The simulation results of a novel stepping motor based on a pair of a regular hexahedron and a regular octahedron (call “6-8 spherical stepping motor” afterward) are presented. The 3D electromagnet and motion coupled simulation program “Magnet 6” is used for the simulation. As the conditions of simulation, the excitation current and frequency is 1 A and 5.3 Hz, respectively. Three phase sinusoidal excitation currents are applied to two pairs of three coils of the stator individually at 120 deg intervals. The simulation results show that the rotor rotates along the rotating magnetic field and the output torque is 0.04 Nm. The simulation results prove the correctness of the 6–8 spherical motor driving method. The developed 6–8 spherical stepping motor is air-core type without back yoke for avoiding the cogging torque. When using iron core with back yoke, the proposed motor will be a high-torque spherical motor. The 6–8 spherical stepping motor was tested and the experimental results were compared with the simulation results. Then, the simulation program was used for optimum design of the 6–8 spherical stepping motor.

Development of Flux Concentrated type Self-Bearing Motor

Self-bearing motor has combined function of AC motor and magnetic bearing. Usually levitation force is produced by Maxwell force while the motor torque is produced by Lorentz force. The authors have proposed Lorentz type self-bearing motor where strong magnetic flux is the key technology for good characteristics. In this paper three types of rotors are designed and compared: a flux concentrated PM rotor, Halbach rotors with iron back yoke and aluminum back yoke. The high density flat coils are designed and used for the stator. The experimental setup is fabricated and tested. The results obtained are compared and discussed in details.

Ferrite cores as back yoke for enhancing hall sensor sensitivity in caliper tool for pipeline inspection

PurposeThe purpose of this paper is to describe how to improve magnetic pick up sensor for detection of weak magnetic field. A magnetic marker detection system, built using hall sensors is improved by providing ferrite cores as back yoke to obtain benchmarked performance with reduced number of hall sensors in an equipment for pipeline inspection called caliper tool.Design/methodology/approachThe paper opts for an exploratory study by making various configurations of sensors possible under given constraints, analyzing results of each one of them and correcting the configuration.FindingsInstead of using highly sensitive hall sensors, one can increase the sensitivity of sensor by putting simple ferrite core as back yoke in order to detect weak magnetic field.Originality/valueThis paper fulfils the need of detection of weak magnetic field by changing field direction and maximizing field component in direction of sensitive axis of magnetic sensor.

Development of a Lorentz-Force-Type Slotless Self-Bearing Motor

Magnetic bearing motors have advantages such as no friction loss, no abrasion, and lubrication-free operation. However, they are not widely used due to their high cost and large size. In order to solve these problems, a self-bearing motor having a simple structure with distributed windings is proposed. The rotor consists of a permanent magnet and an iron yoke, which rotates in a body. The stator consists of a six-phase distributed winding and is installed between the permanent magnet and the back yoke of the rotor. A Lorentz force, generated by interaction between stator current and permanent magnet field, is used to control the rotation speed and radial position of the rotor. In this study, the rotating torque and bearing force are analyzed theoretically, and methods for their control are discussed. A simple experiment confirms that the proposed self-bearing motor can be realized.

A new method of magnetic shielding: Combination of flux repulsion and backing up magnetic pathways

The guiding principle of the magnetic shield is to redirect magnetic fluxes so that they do not enter an area of interest. There are two ways to do this: the one way is to provide magnetic fluxes with good pathways and the other way is to use repulsive forces acting on the magnetic flux. In this paper, a new method of magnetic shielding combining the above two is proposed. A circulating current and a thin magnetic plate working as a back yoke are the key components. Repulsive forces that act on the magnetic fluxes originating from a noise source are present only on one side of a thin back yoke. By enclosing an area to be shielded with several of those, one can make a magnetic shield in which thin magnetic plates are not necessarily connected. Several numerical examples as well as experimental results are given to demonstrate this idea.

Magnetic Bearing Sets for a Flywheel System

This paper presents a magnetic bearing set developed to work in a flywheel energy storage system. The bearing set is composed of a permanent magnetic bearing (PMB) and a superconducting magnetic bearing (SMB). A new configuration of a PMB having Nd-Fe-B magnet rings and a back yoke is proposed and compared with an existing one. Finite element method (FEM) simulations were used to design two different PMB configurations. Measurement results of axial and radial forces were carried out in zero field cooling (ZFC) and field cooling (FC) processes in two SMB topologies. These measured force results are presented and discussed in order to discover which configuration is more promising for the proposed application.

Effect of design variables on irreversible magnet demagnetization in brushless dc motor

The large demagnetizing currents in brushless dc (BLdc) motor are generated by the short-circuited stator windings and the fault of a drive circuit. So, irreversible magnet demagnetization occurs due to the external demagnetizing field by these currents. In this paper, we deal with the effect of design variables on irreversible magnet demagnetization in BLdc motor through the modeling approach using a two-dimensional finite-element method (2D FEM). The nonlinear analysis of a permanent magnet is added to 2D FEM to consider irreversible demagnetization. As a result, it is shown that magnet thickness, teeth surface width, and rotor back yoke thickness are the most important geometrical dimensions of BLdc motor in terms of irreversible magnet demagnetization.

Development of the caliper system for a geometry pig based on magnetic field analysis

This paper introduces the development of the caliper system for a geometry PIG (Pipeline Inspection Gauge). The objective of the caliper system is to detect and measure dents, wrinkles, and ovalities affect the pipe structural integrity. The developed caliper system consists of a finger arm, an anisotropic permanent magnet, a back yoke, pins, pinholes and a linear hall effect sensor. The angle displacement of the finger arm is measured by the change of the magnetic field in sensing module. Therefore the sensitivity of the caliper system mainly depends on the magnitude of the magnetic field inside the sensing module. In this research, the ring shaped anisotropic permanent magnet and linear hall effect sensors were used to produce and measure the magnetic field. The structure of the permanent magnet, the back yoke and pinhole positions were optimized that the magnitude of the magnetic field range between a high of 0.1020 Tesla and a low of zero by using three dimensional nonlinear finite element methods. A simulator was fabricated to prove the effectiveness of the developed caliper system and the computational scheme using the finite element method. The experimental results show that the developed caliper system is quite efficient for the geometry PIG with good performance.

Improvement of the sensor system in magnetic flux leakage-type nondestructive testing (NDT)

In magnetic flux leakage (MFL)-type nondestructive testing (NDT) system, the sensitivity of MFL sensor depends on the change of the magnetic field, not just on the magnitude of the field. In this paper, the leakage parameter was defined to determine the operating point in saturation curves, and an optimum design method to determine the size of the magnet to maximize the MFL signals in NDT is described. For detecting the small depth defect, we also developed the back yoke sensor system. The sensitivity of the optimum sensor system is increased up to 200%. The computed MFL signals in the optimally designed system are verified by measurement using Hall sensors mounted on the six-legged PIG in an 8-in test pipe with defects. The rhombic defects could be successfully measured and identified from the weak defect signals.

134 回転損失のきわめて少ない磁気軸受(磁気浮上・磁気軸受の制御II)(OS 磁気浮上・磁気軸受の制御)

A Lorentz force type magnetic bearing is introduced in this paper. It is intended for the magnetic bearing to reduce the rotating loss drastically. The rotor is composed of a ring type permanent magnet and back yoke which produce a constant magnetic flux in the gap. The stator is composed of four concentrated coils which are installed in the airgap. The bearing force is produced by the stator coil current in the constant gap flux. A simple experimental setup is made to confirm the operation principle of the proposed magnetic bearing.

Sputtered sandwich heads for high-density digital video recording

A sandwich type of head for application in high-frequency and high-density digital video systems is described. Amorphous CoNbZr films laminated with an Al/sub 2/O/sub 3/ insulator layer are used as core material. The influence of rotating and static field annealing on the domain structure and on the permeability is discussed. In order to achieve a sufficiently high efficiency, a polycrystalline ferrite back yoke is applied. Sandwich heads with several ceramic materials in the contact plane are evaluated. The performance of the heads is investigated on the basis of a signal-to-noise criterion, defined specially for the digital video application. A sandwich head made with 2 mu m*5 mu m amorphous CoNbZr, laminated with 0.1 mu m Al/sub 2/O/sub 3/, between glass-ceramic substrates fulfils the requirement on MP tape. >

THE EFFECT OF USING SOLID IRON IN THE SECONDARY OF LINEAR INDUCTION MACHINES

ABSTRACT This paper intends to give an experimental contribution to the comparison between the performances of single-sided linear induction motors having either a solid or a laminated back iron secondary. This study has been performed with a Gramme wound arc shaped primary, associated with two different secondaries. In spite of small differences between the main characteristics of the two secondary parts, a comparison has been possible through a theoretical model, Our results show that, in this case, the use of a solid secondary back iron reduces the maximum thrust of the motor for a given current, but increases slightly its maximum efficiency. So, although the use of such a solid back yoke reduces the cost of the motor, it is not obvious to know whether or not this is offset by the alteration of its performances.