• The Journal of Advanced Prosthodontics
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• v.8 no.1
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• pp.9-15
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• 2016

PURPOSE. Although magnetic attachment is used frequently for overdenture, it is reported that attractive force can be decreased by abrasion and corrosion. The purpose of this study was to establish the clinical basis about considerations and long term prognosis of overdenture using magnetic attachments by investigating the change in attractive force of magnetic attachment applied to the patients. MATERIALS AND METHODS. Among the patients treated with overdenture using magnetic attachments in Dankook University Dental Hospital, attractive force records of 61 magnetic attachments of 20 subjects who re-visited from July 2013 to June 2014 were analyzed. Dental magnet tester (Aichi Micro Intelligent Co., Aichi, Japan) was used for measurement. The magnetic attachments used in this study were Magfit IP-B Flat, Magfit DX400, Magfit DX600 and Magfit DX800 (Aichi Steel Co., Aichi, Japan) filled with Neodymium (NdFeB), a rare-earth magnet. RESULTS. Reduction ratio of attractive force had no significant correlation with conditional variables to which attachments were applied, and was higher when the maintenance period was longer (P<.05, r=.361). Reduction ratio of attractive force was significantly higher in the subject group in which attachments were used over 9 years than within 9 years (P<.05). Furthermore, 16.39% of total magnetic attachments showed detachment of keeper or assembly. CONCLUSION. Attractive force of magnetic attachment is maintained regardless of conditional variables and reduction ratio increased as the maintenance period became longer. Further study on adhesive material, attachment method and design improvement to prevent detachment of magnetic attachment is needed.

• Journal of Power System Engineering
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• v.16 no.3
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• pp.64-68
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• 2012

Because the magnetic bearing supports levitating body without contact, wear, noise and vibration are very small comparing with mechanical bearings, it is very useful to high revolution machinery. In general, the magnetic attractive force function that is proportional to square of control current(x), and inversely proportional to square of an air gap(i) has been widely used. This paper proposed the new magnetic attractive force function that is proportional to cube of the control current, and inversely proportional to square of the air gap. The function was optimized to minimize the cost function that is the percentage of deviation about the change of a proportional constant(k), using the experimental data, ie, control currents and air gaps.

• 제어로봇시스템학회:학술대회논문집
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• 1992.10b
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• pp.355-359
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• 1992

This paper presents a procedure to design a real time control system for a magnetic levitation system based on the state space approach by adopting a control method compensating attractive force according to load variation of maglev vehicle. Also the paper has realized a robust control algorithm for the change of self-inductance parameters and the disturbance such as the change of mass of Maglev vehicles. The theoretical results are applied to the gap control problems of an attractive-type-magnetic levitation system and the effectiveness is proved by the implementation of digital control using 16 bits microcomputer.

• Tribology and Lubricants
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• v.11 no.1
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• pp.20-26
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• 1995

Most magnetic bearings are based on the attractive force between the magnets and ferrous materials. One of the disadvantages of such attractive type magnetic bearings is the instability so that an active control device is necessary to operate bearing successfully. In this study a repulsive type magnetic bearing is analyzed which uses eddy current as a force source. The load capacities are analyzed for the various gap sizes, the rotor velocities and the frequencies of current supplied to electromagnet. Analytic Results show that as the gap size decreases, the levitation and drag forces increase, while the number of poles increasqs, the drag force decreases in the higher linear velocity region. Experimental results show that as the gap size decreases the levitation and the drag force increase, and as the velocity of rotor increases, the drag is larger than the levitation force up to certain velocity. But after that, the levitation is larger than the drag force. As the frequency of the current increases the levitation and drag decreases while the thickness of rotor gets thicker the forces decrease because of increase in eddy current loss.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.349-350
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• 2009

Superconducting magnetic bearing and rotating system were developed by utilizing the high magnetization YBaCuO superconductor. The pellets prepared by quasi-melt process had a high magnetic levitation force and a high magnetic attractive force. The shaft also could be moves its position and orientation of the rotating axis freely. Is is essential to enhance the materials properties and to improve the system design for the application of the system to industrial purpose.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.11
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• pp.75-80
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• 2000

Recently, there are a great many research for magnetic levitation system. In case electromagnet is operated as the actuator of control system, first of all, we must analysis about an electromagnet. Important parameters of this system are inductance(L) and resistance(R) which are induced from the coil of electromagnet. And attractive force equation is also important. If the load of this system is large, phase delay is caused by self-inductance effect. Because this delay effect cause stability of whole magnetic evitation system to grow worse, a measures to diminish time constant must have been taken. And the linearized attractive force equation which is used at small range of the operating point is compensated to use at larger range, thus the experiment of magnetic levitation system will get a better result.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.1866-1870
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• 2008

In this paper, electric braking performances of linear induction motor(LIM) designed for propelling the MAGLEV are presented. Regenerative braking is carried out from 110km/h to 20km/h, and plugging which converts the direction of travelling magnetic field is carried out in the low speed region below 20km/h. It is important to reduce attractive force which can affect the magnetic levitation load during regenerative braking or plugging operation mode. So in this paper the braking performances are analyzed by finite element method. As a result, braking force, attractive force, phase current, voltage to frequency patterns and its magnetic fields of braking LIM are presented.

• Journal of Magnetics
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• v.22 no.1
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• pp.155-161
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• 2017

This paper presents a new nonmechanical rehabilitation system driven by magnetic force. Typically, finger rehabilitation mechanisms are complex mechanical systems. The proposed method allows wireless operation, a simple configuration, and easy installation on the hand for active actuation by magnetic force. The system consists of a driving coil, driving magnets (M1), and auxiliary magnets (M2 and M3), respectively, at the finger, palm, and the center of coil. The magnets and the driving coil produce three magnetic forces for an active motions of the finger. During active actuations, magnetic attractive forces between M1 and M2 or between M1 and M3 enhance the flexion/extension motions. The proposed system simply improves the extension motion of the finger using a magnetic system. In this system, the maximum force and angular variation of the extension motion were 0.438 N and $49^{\circ}$, respectively. We analyzed the magnetic interaction in the system and verified finger's active actuation.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.10
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• pp.165-171
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• 1998

An axial electromagnetic levitation system using attractive force is a highly nonlinear system due to the nonlinearity of materials, variable air gap and flux density. To control the levitating system with large air gap, a conventional PID control based on the linear model is not satisfactory to obtain the desired performance and the position tracking control of the sinusoidal motion by simulation results. Thus, sliding mode control(SMC) based on the input-output linearization is suggested and evaluated by simulation and experimental approaches. Usefulness of the SMC to this system is conformed experimentally. If the expected variation of added mass can be included in the gain conditions and the model, the position control performance of the electromagnetic levitation system with large air gap will be improved with robustness.

• Journal of Electrical Engineering and Technology
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• v.10 no.4
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• pp.1667-1673
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• 2015

The vibration and noise caused by the dynamic interaction between electromagnetic suspension and the linear synchronous motor stator beneath a flexible guideway remain problems in designing attractive Maglev trains. One possible method to reduce the sources of vibration is to minimize the detent force in the linear synchronous motor that creates variations in both lift force and thrust. This paper proposes lowering detent force by using separated core instead of single united core. The magnet is designed to adapt to the deflected guideway at a speed of 550km/h. This study will analyze the electromagnetic field and control performance, and how they relate to lift forces and dynamic responses.