• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.7
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• pp.1156-1165
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• 1997

Complex modal testing is employed for the in-situ parameter identification of a four-axis active magnetic bearing system while the system is in operation. In the test, magnetic bearings are used as exciters as well as actuators for feedback control. The experimental results show that the directional frequency response function, which is properly defined in the complex domain, is a powerful tool for identification of bearing as well as modal parameters. It is also shown that the position and current stiffnesses can be accurately estimated using the relations between the measured forces, displacements, and currents.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1083-1086
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• 2003

Recently, the study on bearingless motors which integrate both motor and magnetic bearing function in one stator is very active, as many machines have high rotational speed, high precision, smaller size and lighter weight. In this paper, we propose a novel rotary actuator including function of axial bearing using Lorentz force as a preceding research for development of a bearingless motor. As using Lorentz force, this type has some merits such as the linearity of control force, freedom from flux saturation and high efficiency unlike conventional rotary actuators using a reluctance force. This type is cotrolled independently in levitation and rotational directions respectively. It shows by mathematical expression of levitation force and torque in the proposed rotary actuator. And also, the levitation force is generated by magnetic interaction between the magnetic materials and the rotational torque is generated by Lorentz force. Finally. for verification of this proposed system, a prototype is made and some experiments will be performed in the near future.

• Journal of Mechanical Science and Technology
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• v.17 no.5
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• pp.708-717
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• 2003

With the development of precision manufacturing technologies, the importance of precision positioning devices is increasing. Conventional actuators, dual stage or mechanically contacting type, have limitation in coping with performance demands. As a possible solution, magnetic suspension technology was studied. Such a contact-free system has advantages in terms of high accuracy, low production cost and easy adaptability to high precision manufacturing processes. This paper deals with magnetically suspended multi-degrees of freedom actuator which can realize large linear motion. In this paper, the operating principle is explained with the magnetic force analysis, and the equations of motion are derived. Experimental results of the implemented system are also given.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.7 s.172
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• pp.102-111
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• 2005

In this paper, we address a position control for a parallel stage, which is levitated and driven by electric magnetic force. This consists of a levitating object (called platen) with 4 permanent magnetic linear synchronous motors in parallel. Each motor generates vertical force for suspension against gravity and propulsion force horizontally as well. This stage can generate six degrees of freedom motion by the vertical and horizontal force. A dynamic equation of the stage system is derived based on Newton-Euler method and it's special Jacobian matrix describing a relation between the limited velocity and Cartesian velocity is done. There are proposed two control methods for positioning which are Cartesian space controller and Actuator space controller. The control performance of the Cartesian space controller is better than the Actuator space controller in task space trajectory while the Actuator space controller is simpler than the Cartesian space controller in controller realization.

• Advances in materials Research
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• v.11 no.4
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• pp.331-349
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• 2022

In the present work, we proposed an analytical study on buckling behavior of a sandwich plate with polymeric core integrated with piezo-electro-magnetic layers such as BaTiO3 and CoFe2O4 reinforced by graphene platelets (GPLs). The Halpin-Tsai micromechanics model is used to describe the properties of the polymeric core. The governing equations of equilibrium are obtained from first-order shear deformation theory (FSDT) and the Navier's method is employed to solve the equations. The results show the effect of different parameters such as thickness, length, weight fraction of GPLs, and also effect of electric and magnetic field on critical buckling load. The result of this study can be obtained in the aerospace industry and also in the design of sensors and actuators.

• International Journal of Aeronautical and Space Sciences
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• v.8 no.2
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• pp.17-27
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• 2007

Minimum-time attitude maneuvers of three-axis stabilized spacecraft are presented to study the feasibility of using three magnetic torquers perform large angle maneuvers. Previous applications of magnetic torquers have been limited to spin-stabilized satellites or supplemental actuators of three axis stabilized satellites because of the capability of magnetic torquers to produce torques about a specific axes. The minimum-time attitude maneuver problem is solved by applying a parameter optimization method for orbital cases to verify that the magnetic torque system can perform as required. Direct collocation and a nonlinear programming method with a constraining method by Simpson's rule are used to convert the minimum-time maneuver problems into parameter optimization problems. An appropriate number of nodes is presented to find a bang-bang type solution to the minimum-time problem. Some modifications in the boundary conditions of final attitude are made to solve the problem more robustly and efficiently. The numerical studies illustrate that the presented method can provide a capable and robust attitude reorientation by using only magnetic torquers. However, the required maneuver times are relatively longer than when thrusters or wheels are used. Performance of the system in the presence of errors in the magnetometer as well as the geomagnetic field model still good.

• Journal of the Korean Ceramic Society
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• v.39 no.9
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• pp.813-817
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• 2002

Magnetoelectric(ME) laminate composites of $Pb(Mg_{1/3}Nb_{2/3})O_3-PbTiO_3 (PMN-PT)$ and Terfenol-D were prepared by sandwiching single crystals of PMN-PT between Terfenol-D disks. The magnetoelectric voltage coefficient (dE/dH) of the composite was determined to be 10.30 V/cm${\cdot}$Oe, at 1 kHz and under a dc magnetic bias of 0.4 T. The value of dE/dH is ∼80 times higher than either that of naturally occurring magnetoelectrics or artificially-grown magnetoelectric composites. This superior magnetoelectric voltage coefficient is attributed to the high piezoelectric voltage constant as well as the high elastic compliance of PMN-PT single crystal and the large magnetostrictive response of Terfenol-D.

• Tribology and Lubricants
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• v.10 no.2
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• pp.43-50
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• 1994

The hydrodynamic bearing is accepted in many rotating systems because it has a large load carrying capacity. But the anisotropic pressure distribution of the bearing can arise the unstable vibration phenomenon over a certain speed. The magnetic bearing is an active element so that the unstable phenomenon of the hydrodynamic bearing, which is induced by the anisotropic support pressure of the oil film, can be controlled if the control algorithm and the controller gains are chosen appropriately. In this study, we investigate the stabilization method of the hydrodynamic bearing system composing the hybrid bearing which is the single unit of hydrodynamic bearing and magnetic bearing. The load carrying conditions of the hybrid bearing is modelled by the sum of the stiffness and damping coefficients of the hydrodynamic and the magnetic bearings in each direction. The dynamics of the rotor is analyzed by the Finite Element Method and the stability limit is determined by the eigenvalues of the hybrid bearings and shaft system. The eigenvalue study of the system shows that the stability limit of the hybrid bearing is increased compared to that of the hydrodynamic bearing. A Small increment of the stiffness and damping coefficient of the hybrid bearings by the magnetic actuators can increase the stability limit of the system. In this paper we tried to show the design references of the hybrid bearings by using the nondimensional bearing parameters. The analysis results show the possibilities of the stability limit increment of the hydrodynamic bearing system by combining the magnetic bearing.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.323-326
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• 2001

NI$_2$MnGa-based ferromagnetic shape memory alloys (FSMA) are hoped to be used as robust actuators with high performance and power density, as a replacement of other actuation materials such as thermo-mechanical SMAs and mechanical-electric piezoelectrics. Recently, we have observed significant shape changes under magnetic field application when single- and poly-crystalline forms are used. In the present study, two mechanisms have been proposed to predict the magnetic field-induced shape change as a function of external magnetic field at temperatures below Mr and above Ar. In the case of the field-induced shape change at temperature below M$_{f}$, paired martensite variants are assumed to form by application of magnetic field. The direction of magnetization in martensites formed in austenite matrix is assumed to be parallel to the applied magnetic field in the case of shape change by application at temperature above Af. Various energies has been considered in the shape change under two mechanisms.s.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07a
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• pp.114-116
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• 2004

적층형 piezoelectric ceramic actuators를 제작하여 신뢰성을 평가하였다. 소자의 신뢰성 측정을 위하여 3kV/mm, 5kV/mm, 7kV/mm의 정류된 교류전압을 인가하였으며, 실험중 온도와 습도를 일정하게 유지하기 위하여 항온항습조안에서 실험을 실시하였다. 각 실험의 경우에 16개의 소자를 동시에 평가하였으며, 평균파괴시간을 Weibull 통계방식을 이용하여 계산하였으며, Arrhenius model, Power law model을 이용하여 사용 조건하에서 예상수명을 예측하였다.