• 한국소음진동공학회논문집
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• 제12권1호
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• pp.73-81
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• 2002

This paper introduces a four-Pole Lorentz force type self-bearing motor in which a new winding configuration is proposed to enable the sing1e winding to function both as a synchronous PM motor and as a magnetic bearing. The Lorentz force type has some good points such as the linearity of control force, freedom from flux saturation, and high efficiency, unlike conventional self-bearing motors using a reluctance force. And also, compared with the previously proposed eight-pole type, this four-pole self-bearing motor is more profitable for high rotational speed. In this paper, mathematical expressions of torque and radial force in the proposed self-bearing motor are derived to show that they can be separately controlled regardless of rotational speed and time. For verification of the theory, a prototype is made, where a ring-shape outer rotor is actively controlled in two radial directions while the other motions are passively stable supposing the radial stability. Through some experiments. it is shown that the proposed scheme can provide high capability and feasibility for a small high-speed self-bearing motor.

• Design & Manufacturing
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• 제6권2호
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• pp.48-53
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• 2012

In previous study, it showed that the MAP was greatly effective polishing process for magnesium plate. But it had lower efficiency than magnetic materials such as SM45C. It was very difficult to cut non-magnetic materials using the MAP process because the process was fundamentally possible by help of a magnetic force. This study aimed to verify analytically formation of the magnetic field in a case of the non-magnetic materials especially focused on magnesium plate. So, In this study, the magnetic density flux was predicted using simulation program. As a result, the magnetic density flux was lower at the center of pole on inductor than outside. It had same result on the experimental verification. And magnetic force was lower according to increase of working gap. So, to improve the magnetic force, permanent magnet was installed under the workpiece. In that case, the magnetic density flux not only at center but also at outside of pole was increased. Therefore, the efficiency of magnetic abrasive polishing was also increased. A design of experimental method was adopted for assessment of parameters' effect on the MAP results of magnesium plate for improving the magnetic force.

• 한국금형공학회:학술대회논문집
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• 한국금형공학회 2008년도 하계 학술대회
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• pp.45-50
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• 2008

In previous study, it showed that the MAP was greatly effective polishing process for magnesium plate. But it had lower efficiency than magnetic materials such as SM45C. It was very difficult to cut non-magnetic materials using the MAP process because the process was fundamentally possible by help of a magnetic force. This study aimed to verify analytically formation of the magnetic field in a case of the non-magnetic materials especially focused on magnesium plate. So, In this study, the magnetic density flux was predicted using simulation program. As a result, the magnetic density flux was lower at the center of pole on inductor than outside. It had same result on the experimental verification. And magnetic force was lower according to increase of working gap. So, to improve the magnetic force, permanent magnet was installed under the workpiece. In that case, the magnetic density flux not only at center but also at outside of pole was increased. Therefore, the efficiency of magnetic abrasive polishing was also increased. A design of experimental method was adopted for assessment of parameters' effect on the MAP results of magnesium plate for improving the magnetic force.

• Journal of Magnetics
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• 제5권2호
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• pp.55-58
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• 2000

Local magnetic properties and magnetization distributions on the air-bearing surface of a thin-film magnetic head have been studied by using scanning magneto-optical Kerr microscopy. The examined head was a merged MR read/inductive writing head with a write gap equal to 0.3 $\mu m$. Sizes of top and bottom pole-tips on the air-bearing surface of the writing head were equal to $3\mu m\times3\mu m$ and $3\mu m\times30\mu m$, respectively, The measured magnetic characteristics on the head air-bearing surface were found to be very sensitive to the head design. In particular, magnetization distributions were discovered to have asymmetrical shape. Maximum magnitudes of the magnetization were located near the shorten pole-tip. So, it was experimentally proved that more magnetic flux emanates just from this part of the air-bearing head surface.

• 전기학회논문지
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• 제64권6호
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• pp.872-877
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• 2015

The Permanent Magnet (PM) machine used at speed control using field-weakening control method. But the field-weakening current, which reduces the field flux for high speeds, causes significant copper and core losses. Therefore, this paper deals with the PM performance evaluations in a pole changing memory motor (PCMM). The PCMM can change the number of magnetic poles and produce two types of torque. When the motor operates with eight poles, it produces a magnetic torque at low rotational speeds. When the motor changes to four poles, it produces both magnetic torque and reluctance torque at high speeds. The paper explain the principle and basic characteristics of the motor by using a finite element method magnetic-field analysis, which consists of a PM magnetized by a pulse d-axis current of the armature winding. The results of our experiment show that the proposed motor reduces core loss by 10% and 55% under no-load and load conditions, and doubles the speed range of the motor.

• Journal of Electrical Engineering and Technology
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• 제10권3호
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• pp.1025-1034
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• 2015

This paper presented an improved analytical method for calculating the open-circuit magnetic field in the surface-mounted permanent magnet machines accounting for slots and eccentric magnet pole. Magnetic field produced by radial and parallel permanent magnet is equivalent to that produced by surface current according to equivalent surface-current method of permanent magnet. The model is divided into two types of subdomains. The field solution of each subdomain is obtained by applying the interface and boundary conditions. The magnet field produced by equivalent surface current is superposed according to superposition principle of vector potential. The investigation shows harmonic contents of radial flux density can be reduced a lot by changing eccentric distance of eccentric magnet poles compared with conventional surface-mounted permanent-magnet machines with concentric magnet poles. The FE(finite element) results confirm the validity of the analytical results with the proposed model.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집 Vol.14 No.1
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• pp.284-287
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• 2001

Multi-pole anisotropic Sr-ferrite sintered magnets has been studied by powder injection molding under applied magnetic field. The orientation of anisotropic Sr-ferrite powders higher than 80% during injection molding is achieved at the following conditions; apparent viscosity lower then 2500 poise in 1000 $sec^{-1}$ shear rate and applied magnetic field higher then 4 kOe. For the high fluidity and strength of injection molded compact, and the effective binder removal without defects during solvent extraction and thermal debinding, the optimum multi-binder composition is paraffin wax(PW)/carnauba wax(CW)/HDPE = 50/25/25 wt%. The rate of binder removal is proportional to the mean particle size of Sr-ferrite powders whereas it is inversely proportional to the content of Sr-ferrite powders and the sample thickness. The high magnetic properties of Sr-ferrite sintered magnets are; 3.8 kG of remanent flux density, 3.4 kOe of intrinsic coercivity, and 1.2 kG of surface flux density (l-mm-thick) in the direction of applied magnetic field.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집
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• pp.284-287
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• 2001

Multi-pole anisotropic Sr-fertile sintered magnets has been studied by powder injection molding under applied magnetic field. The orientation of anisotropic Sr-ferrite powders higher than 80% during injection molding is achieved at the following conditions; apparent viscosity lower then 2500 poise in 1000 sec$\^$-1/ shear rate and applied magnetic field higher then 4 kOe. For the high fluidity and strength of injection molded compact, and the effective binder removal without defects during solvent extraction and thermal debinding, the optimum multi-binder composition is paraffin wax(PW)/carnauba wax(CW)/HDPE = 50/25/25 wt%. The rate of binder removal is proportional to the mean particle size of Sr-ferrite powders whereas it is inversely proportional to the content of Sr-ferrite powders and the sample thickness. The high magnetic properties of Sr-ferrite sintered magnets are; 3.8 kG of remanent flux density, 3.4 kOe of intrinsic coercivity, and 1.2 kG of surface flux density (1-mm-thick) in the direction of applied magnetic field.

• 한국철도학회논문집
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• 제15권3호
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• pp.237-243
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• 2012

3차원 유한요소법을 이용하여 엔드코일 효과를 고려한 SRM의 자계해석을 수행하였다. 고정자 극 형상에 따른 자계특성의 비교를 통하여 제안된 형상에서 자계특성이 향상됨을 확인하였다. 해석한 자계특성을 적용하여 철도부하에 대한 PI 제어기와 슬라이딩모드 제어기의 속도제어를 수행하였다. 속도 제어 시뮬레이션은 Matlab-Simulink를 사용하여 구현되었으며 부하 가변 조건에서 슬라이딩모드 제어기가 PI 제어기에 비해 더 우수한 과도응답 및 정상상태응답을 나타냄을 확인하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.834-839
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• 2007

This paper investigates the distortion of magnetic field of a brushless DC (BLDC) motor due to deformed rubber magnet. Global or local deformation of rubber magnet in the BLDC motor is mathematically modeled by using the Fourier series. Distorted magnetic field is calculated by using the finite element method, and unbalanced magnetic force are calculated by using the Maxwell stress tensor. The first harmonic deformation in the global deformation of rubber magnet generates the first harmonic driving frequency of the unbalanced magnetic force, and the rest harmonic deformations of rubber magnet except the harmonic deformation with multiple of common divisor of pole and slot introduces the driving frequencies with multiple of slot number ${\pm}1$ to the unbalanced magnetic force. However, the harmonic deformation with multiple of common divisor of pole and slot does not generate unbalanced magnetic force due to the rotational symmetry. When the rubber magnet is locally deformed, the unbalanced magnetic force has the first harmonic driving frequency and the driving frequencies with multiples of slot number ${\pm}1$.