• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2009년도 춘계학술대회 논문집
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• pp.735-736
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• 2009

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.963-967
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• 2007

Flywheel energy storage systems (FESS) have advantages over other types of energy storage methods due to their infinite charge/discharge cycles and environmental friendliness. The system has two radial bearings and one hybrid-thrust bearing. Thrust hybrid-type bearing use permanent magnet to relieve gravity load. The radial bearings were designed to provide sufficient force slew rate considering the unbalance disturbance at the operating speeds. In this paper, we will derive dynamic model of hybrid-type bearing using permanent magnet for thrust bearing and present simulation and stability of the model.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.987-992
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• 2000

In a high speed spindle system, it is very important to monitor the operation of the spindle to prevent catastrophic damage to the system. Widely used sensors for monitoring are eddy-current and capacitive types. These sensors provide high accuracy of monitoring, but their steep prices lead to expensive high speed spindle systems. The main goal of our research is to develop technology for producing high speed spindle system utilizing magnetic bearings. As active magnetic bearings require position sensors for feedback control, a noncontact position sensor is being developed as a part of this main goal. Once developed, it will contribute to affordable high speed spindle system. This paper describes the selection process of the sensor types and the design of the driving circuit. We also report the experimental results that characterize the static and dynamic performances of the inductive sensor.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2009년도 추계학술대회 논문집
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• pp.258-263
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• 2009

This paper describes an analysis of the stability and performance of a large-capacity flywheel energy storage system (FESS) supported by active magnetic bearings. We designed and manufactured the system that can store up to 5kWh of usable energy at the maximum speed of 18,000 rpm. In order to analyze the stability of the systems accurately, we derived a rigid body rotor model, flexible rotor model using finite-element method, and a reduced-order model using modal truncation. The rotor model is combined with those of active magnetic bearings, amplifiers, and position sensors, resulting in a system simulation model. This simulation model is validated against experimental measurements. The stability of the system is checked from the pole locations of the closed-loop transfer functions. We also investigated the sensitivity function to quantify the robustness of the systems to the disturbances such as mass imbalance and sensor noises.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.290-293
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• 2008

This paper proposes a criterion to select the modes for modal truncated model of flexible rotor only supported by active magnetic bearings. The proposed approach relies on the concepts of minimum control input and output energy assuming that the system is subjected to transient disturbances. Accurate large order model for the levitated rotor is taken by finite element analysis and transformed to the modal equation. By proposed methodology, which modal states should be retained in the truncated model are investigated over the whole operational speed range by the calculation. Finally, the effectiveness is verified by checking the model error between original model and reduced model.

• 대한기계학회논문집A
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• 제37권4호
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• pp.511-519
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• 2013

능동 자기베어링의 바이어스 선형화 방법은 자기베어링의 동역학적 성능과 선형성을 확보하지만, 바이어스 전류에 의한 상시 소모전력이 발생하여 시스템의 효율이 저하된다. 반면, 스위칭 제어기는 바이어스 전류를 사용하지 않아 베어링의 소비 전력을 최소화할 수 있다. 본 논문에서는 능동 자기베어링 시스템에 적용되는 스위칭 제어기와 동기 노치필터를 포함하는 비례-미분 제어기의 성능을 비교하였다. 공정하고 객관적인 비교를 위해 기준제어기인 동기 노치필터 제어기를 합리적으로 설계하고, 스위칭 제어기가 기준제어기와 동일한 동역학 특성을 갖도록 하였다. 회전축의 굽힘 유연모드 및 센서와 증폭기의 특성을 포함하는 시스템의 동역학 모델을 수립하고 성능 비교 지표를 수립하였다. 불평형 질량에 응답 측면에서 제어기를 비교하여, 저속 영역에서 스위칭 제어기가 기준제어기 대비 10 배 이상 동손을 저감할 수 있으나, 회전축의 굽힘 유연모드와 일치하는 회전 속도 근방에서는 스위칭 제어기가 유효하지 않음을 확인하였다.

• 한국정밀공학회지
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• 제30권12호
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• pp.1321-1325
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• 2013

In this paper, we proposed an air bearing stage with active magnetic preloads in vertical directions compensating motion errors and attenuating vibrations to improve dynamic characteristics. This preloaded design gives simpler configuration of the stage, and active control of preload can be used for compensating motion errors by feedforward method. To improve dynamic characteristics, vibration of the table is monitored by an accelerometer, and controlled by a DSP based digital controller with integrator and band pass filters for suppressing roll and pitch vibration modes. The modes were evaluated by measuring frequency response functions, and compared with compensated responses. This showed effective results for suppressing poorly damped regenerative vibration of air bearings.

• 한국소음진동공학회논문집
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• 제16권12호
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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.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2002년도 추계학술대회 논문집
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• pp.440-445
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• 2002

The characteristic equation for regenerative chatter loop including a delay element replaced by a rational function is presented by a linear differential-difference equation, accounting for the dynamics of the AMB controllers, the uncut chip thickness equation and the cutting process as well as the rigid spindle dynamics itself. The chatter stability analysis of a rigid milling spindle suspended by 5-axes active magnetic bearings(AMBs) is also performed to investigate the influences of the damping and stiffness coefficients of AMBs on the chatter free cutting conditions, as they are allowed to vary within the stable region formed by the AMB control gains. Several cutting tests varying the derivative gains of the AMB were performed to investigate the regenerative chatter vibrations, and it was concluded that the theoretical analysis results are in good consistency with the test results.

• 대한전기학회논문지:시스템및제어부문D
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• 제52권7호
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• pp.393-400
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• 2003

In this paper we deal with the virtually zero power control for the rigid rotor with radial suspension by the permanent magnetic bearing and axial suspension by electromagnetic bearing. The purpose of the virtually zero power control is to reduce the power consumption of the electromagnetic bearings. The axial active force is expressed by the normal second order equation which has only one degree-of-freedom. The virtually zero power control structure has two schemes. One is the coil control current integrator which is used to make the convergence of the control current to a range which is very close to zero. By using the current integrator the DC component which is included in the control current is eliminated, thus the control current converges to a range which is close to zero. The other is normal PD control loop which is used to make the rotor reach to stable equilibrium point and to maintain air gap so that the axial force produced by radial permanent magnet always balances the total weight of the rotor and its load. First we show a simple mathematical plant model and the virtually zero power (VZP) control blocks. Second, we investigate the theoretical feasibility and the stability of the proposed virtually zero Power control levitation system with PD feedback loop by using linear control theory Finally we show the effectiveness of the proposed control method to reduce the power consumption by simulations.