• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.920-922
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• 2002

This paper investigates the cogging torque reduction in a brushless DC(BLDC) motor having an inner-rotor with surface-mounted segment-type permanent magnets. The kind of magnets for the BLDC motor could have different waveforms of magnetization such as square, trapezoidal and sinusoidal form. This paper discusses the effect of the unsymmetrical magnetization distribution in the segment-type permanent magnet, which is able to obtain through a segment structure that the number of poles per segments is 2 ($N_p/N_s$), on the cogging torque and EMF waveform. Where the existing magnetizer fixture for the square-type magnetization is used to magnetize the magnets in two segment structures of $N_p/N_s$ = 1 and 2. The effectiveness of the proposed designs had been confirmed by comparing cogging torque, and EMF waveform between conventional and new models which are analyzed by Finite Element Method (FEM).

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.250.1-250.1
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• 2014

A multicusp ion source has been used widely in negative hydrogen cyclotrons mainly for radioisotope productions. The ion source is designed to have cusp geometries of magnetic field inside plasma chamber, where ions are confining and their mean lifetimes increase. The magnetic confinement produced a number of permanent magnetic poles helps to increase beam currents and reduce the emittance. Therefore optimizing the number of magnets confining more ions and increasing their mean lifetime in plasma has to be investigated in order to improve the performance of the ion source. In this work a numerical simulation of the magnetic flux density from a number of permanent magnets is carried to optimize the cusp geometries producing the highest plasma density, which is clearly indicated along the full-line cusp geometry. The effect of magnetic fields and a number of poles on the plasma structure are investigated by a computing tool. The electron confinement effect becomes stronger and the density increases with increasing the number of poles. On the contrary, the escape of electrons from the loss cone becomes more frequent as the pole number increases [1]. To understand above observation the electron and ion's trajectories along with different cusp geometries are simulated. The simulation has been shown that the optimized numbers of magnets can improve the ion density and uniformity.

• Proceedings of the Korean Magnestics Society Conference
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• 2013.12a
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• pp.89-89
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• 2013

Rare earth (RE) - transition metal based high energy density magnets are of immense significance in various engineering applications. $Nd_2Fe_{14}B$ magnets possess the highest energy product and are widely used in whole industries. Simultaneously, composite alloys that are cheap, cost effective and strong commercially available have drawn great attention, because rare-earth metals are costly, less abundant and strategic shortage. We designed rare-earth free alloys and fabrication process and developed novel route to prepare $Nd_2Fe_{14}B$ powders by wet process employing spray drying and reduction-diffusion (R-D) without the use of high purity metals as raw material. MnAl-base permanent magnetic powders are potentially important material for rare-earth free magnets. We have prepared the nano-sized MnAl powders by plasma arc discharge and micron-sized MnAl powders by gas atomization. They showed good magnetic property, compared with that from conventional processes. $Nd_2Fe_{14}B$ powders with high coercivity of more than 10 kOe were successfully synthesized by adjusting R-D step, followed by precise washing system. It is considered that this process can be applied for the recycling of RE-elements extracted from ewaste including motors.

• Journal of Magnetics
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• v.4 no.2
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• pp.52-54
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• 1999

Injection molding is one of the methods to prepare dielectromagnets-permanent magnets made from hard magnetic powder (or from mixture of powders) bonded by dielectric materials. Magnetic properties of dielectromagnets are worse than those of sintered magnets made from the same hard magnetic powders, but this type of the permanent magnet has many advantages. One of them is simpler technology-easier in comparison to the technology of sintered magnets. The injection molded dielectromagnets do not need any final treatment. This technology permits to control magnetic, thermal and mechanical properties of dielectromagnets. The main chracteristics of dielectormagnets are magnetic properties, however mechanical properties have serious influence onto a range of their applications. The main factors shaping mechanical properties have serious influence onto a range of their applications. The main factors shaping mechanical properties of dielectromagnets are the kind and quantity of resin and the technology. The purpose of this investigateion was to find the correlation between infection conditions and the mechanical properties of dielectromagnets. Influence of two parameters of injection, temperature and pressure on mechanical and magnetic properties of dielectromagnets were not significantly changed. Increasing of pressure of injection also does not influence on mechanical properties of analysed samples, however increasing of temperature of injection significantly improved both compression and bending strength.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.8
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• pp.873-878
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• 2012

Putting a conductive rod between rotating axial electrodynamic wheels composed of repetitive permanent magnets, three-axial magnetic forces generate on the conductive rod. It is possible to levitate and transfer the rod on space with the forces. However, the forces vary in direction and magnitude for a position of the rod between the electrodynamic wheels. Thus, the position influences the stability of the rod also. To guarantee the stability of a levitated object, the force acting on the object should have negative stiffness like a spring. So, we analyze the stable operating range of the conductive rod levitated by the axial wheels with the commercial finite element tool in this paper. Specially, as the pole number and the radial width of permanent magnets has much influence on the generated force and thereby the stable region, their sensitivities are analyzed also. The analytic result is compared with experimental result.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.12 s.117
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• pp.1201-1207
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• 2006

This paper introduces a step motor with a passively levitated rotor which comprises a homopolar step motor and a passive magnetic bearing. Compared with conventional self-bearing motors which are mostly based on the active magnetic bearing technology, the proposed motor has a very simple structure and operating principle. For the levitation, it works just like passive magnetic bearings which use the repulsive force between permanent magnets. Halbach array is used to increase the bearing stiffness. On the other hand, its rotation principle is just the same with that of conventional motors. In this paper, we introduce the design scheme to avoid the flux interference possibly produced by electromagnets and permanent magnets, and show some results of FEM analysis to predict the performance of the proposed motor.

• Journal of Magnetics
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• v.1 no.2
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• pp.94-100
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• 1996

A hysteresis loop tracer using a pulsed high magnetic field of 113.4 kOe, which is suitable for rare earth based permanent magnets, is constructed. The high pulsed magnetic field is generated by discharging a large capacitance charge (5 mF) with a voltage of 600 V into an air solenoid with the inner diameter of 14 mm, outer diameter of 36 mm and the lingth of 34 mm. A computer simulation method is used for the construction of an electromagnet to optimize the many parameters such as the discharge current, generated pulsed magnetic field intensity, thermal dissipation, capacitance, charged voltage, period of damping oscillation and solenoid geometry. By using the hysteresis loop tracer constructed in this work, we are able to measure hystersis loops of several rare earth based permanent magnets with large values of the remanent magnetization, coercvity and energy product.

• Journal of Magnetics
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• v.5 no.2
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• pp.59-64
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• 2000

A drum type of high gradient magnetic separator was designed and optimized by computer simulations. The magnetic separator consists of high performance rare earth $(Nd_2Fe_14B)$ permanent magnets and magnetic yokes of extremely low carbon steel interconnecting the permanent magnets. Magnetic circuits of the separator were simulated for the aim of the least cost, highest magnetic strength and most efficient function by using specialized S/W (Vector Field Program) employing the Finite Element Method. The magnetic flux density was provided to be strong enough to collect the invisible fine metal particles from the surface of hot rolled steel plate with the efficiency of almost 95%.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.3 s.96
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• pp.334-340
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• 2005

A disk-type 3-DOF actuator which has new principle and very simple structure is proposed. Also it utilizes the relation of bias and control fluxes produced by permanent magnets and coils, respectively, like other conventional electromagnetic actuators, but its main feature is that both the coils and permanent magnets are fixed in the stator, which makes it easy to design the shape of moving part. Operating principle is that a moving disk is driven by reaction force of Lorentz force acting on the fixed equivalent coil. Simple analytic approach and FEM analysis are performed to determine the design parameters so as to increase the driving force and distance. And some experimental results show the feasibility of the proposed actuator.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.990-995
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• 2008

During the ship's construction process, most high place workings have been carried out by human power, like welding, grinding and so on. Because of the ability to relieve human beings from these, the need of developing a hull-plate moving robot has been rising. This paper describes a hull-plate moving robot, using magnet modules as the adhesive method. Magnet modules maintain the magnetic force between hull-plate and magnets constantly. So that allows the robot to perform movements on the curved plate without the loss of adhesive force. The robot consists of driving motors, control system and magnet modules. The performance of the robot is verified on the curved plate.