• 한국소음진동공학회논문집
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• 제13권7호
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• pp.508-516
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• 2003

The dynamic characteristics of an ell-lubricated, short squeeze film damper (SFD) with a central feeding groove are derived based on a theoretical analysis considering the effect of a groove, and identified experimentally using an Active Magnetic Bearing (AMB) system as an exciter. In order to get the theoretical solution, the fluid film forces of the grooved SFD are analytically derived so that the dynamic coefficients of the SFD can be expressed in terms of its design parameters. For the experimental validation of the analysis, a test rig using an AMB as an exciter is proposed. As an exciter. the AMB represents a mechatronic device to levitate and position the test Journal without any mechanical contact, to generate relative motions of the Journal inside the tested SFD and to measure the generated displacements during experiments with fairly high accuracy. Using this test rig, experiments are extensively conducted with various values of clearance, which Is one of the most important design parameters. in order to investigate its effect on the dynamic characteristics and the performance of the SFD. Damping and Inertia coefficients of the SFD that are experimentally Identified are compared with the analytical results to demonstrate the effectiveness of the applied analysis. It Is also shown that the AMB is an ideal device for tests of SFDs.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1998년도 추계학술대회
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• pp.245-246
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• 1998

AMB(Active Magnetic Bearing) systems are popularly used in various areas. In biomedical engineering applications it is a key part of magnetically suspended rotary blood pumps. The special advantage of AMBs is that they enable the rotor to revolve with no physical contact and provide rotary blood pumps with better performances such as low hemolysis level. Fundamentally, AMB systems consist of three parts, proximity sensors for distance detection, microprocessor for control algorithm and power amplifiers for actuating electromagnets. We have developed an inductive type proximity sensor with satisfactory characteristics that can be used in AMB systems. Frequency response was flat at least up to 10 kHz and sensitivity, resolution$(>5{\mu}m)$ and sensing range(<5mm) of the sensor could be adjustable for various purposes. The characteristics of the completed model showed to have satisfactory behaviors compared with the commercially available ones that already appeared to have reliable behaviors in AMB systems.

• 전자공학회논문지 IE
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• 제48권1호
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• pp.1-6
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• 2011

본 연구에서는 스테이터 구조에 의한 마그네틱 베어링의 전자장해석을 수행하였으며 AMB 시스템의 설계 기준을 얻기 위하여 3가지 방식의 구조에서 전기적 특성을 구하였다. FEM 기법을 이용하여 AMB의 3가지 방식을 시뮬레이션한 결과, 1, 2, 그리고 3번 방식은 N극에서 S극으로 많은 자속선 벡터가 이동하는 것으로 나타났으며, 이 자속선들은 로타로 전달되고 있다. 이 선들은 로타가 회전하는 것을 도와주고 있다. 따라서, 이러한 전기적 특성 자료는 마그네틱 베어링 설계자료로 이용되고, 설계 기준을 만드는데 도움이 될 것이다.

• Investigative Magnetic Resonance Imaging
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• 제20권2호
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• pp.95-104
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• 2016

Purpose: To evaluate the knee joint after double-bundle anterior cruciate ligament (ACL) reconstruction with three-dimensional (3D) isotropic magnetic resonance (MR) image, and to directly compare the ACL graft findings on 3D MR with the clinical results. Materials and Methods: From January 2009 to December 2014, we retrospectively reviewed MRIs of 39 patients who had reconstructed ACL with double bundle technique. The subjects were examined using 3D isotropic proton-density sequence and routine two-dimensional (2D) sequence on 3.0T scanner. The MR images were qualitatively evaluated for the intraarticular curvature, graft tear, bony impingement, intraosseous tunnel cyst, and synovitis of anteromedial and posterolateral bundles (AMB, PLB). In addition anterior tibial translation, PCL angle, PCL ratio were quantitatively measured. KT arthrometric values were reviewed for anterior tibial translation as positive or negative. The second look arthroscopy results including tear and laxity were reviewed. Results: Significant correlations were found between an AMB tear on 3D-isotropic proton density MR images and arthroscopic proven AMB tear or laxity (P < 0.05). Also, a significant correlation was observed between increased PCL ratio on 3D isotropic MRI and the arthroscopic findings such as tear, laxities of grafts (P < 0.05). KT arthrometric results were found to be significantly correlated with AMB tears (P < 0.05) and tibial tunnel cysts (P < 0.05). Conclusion: An AMB tear on 3D-isotropic MRI was correlated with arthroscopic results qualitatively and quantitatively. 3D isotropic MRI findings can aid the evaluation of ACL grafts after double bundle reconstruction.

• 한국축산식품학회지
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• 제32권4호
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• pp.448-457
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• 2012

The predictive ability for off-flavor development and quality change of ground beef was evaluated using a microbial time temperature indicator (TTI). Quality indices such as off-flavor detection (OFD) time, color, pH, volatile basic nitrogen (VBN), aerobic mesophilic bacteria (AMB) counts, and lactic acid bacteria (LAB) counts were measured during storage at 5, 10, 15, and $25^{\circ}C$, respectively. Arrhenius activation energies (Ea) were estimated for temperature dependence. The Ea values for TTI response (changes in titratable acidity (TA)), VBN, AMB counts, LAB counts, and freshness, which is defined based on OFD time for quality indices of ground beef, were 106.22 kJ/mol, 58.98 kJ/mol, 110.35 kJ/mol, 116.65 kJ/mol, and 92.73 kJ/mol, respectively. The Ea of microbial TTI was found to be closer to those of the AMB counts, LAB counts, and freshness. Therefore, AMB counts, LAB counts, and freshness could be predicted accurately by the microbial TTI response due to their Ea similarity. The microbial TTI exhibited consistent relationships between its TA change and corresponding quality indices, such as AMB counts, LAB counts, and freshness, regardless of storage temperature. Conclusively, the results established that the developed microbial TTI can be used in intelligent packaging technology for representing some selected quality indices of ground beef.

• 한국지능시스템학회:학술대회논문집
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• 한국퍼지및지능시스템학회 1998년도 The Third Asian Fuzzy Systems Symposium
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• pp.337-342
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• 1998

A new fuzzy control algorithm for the control of active magnetic bearing (AMB) systems is proposed in this paper. It combines PDC design of Joh et al. [8][9] and Namdani-gype control rules using fuzzy singletons to handle the nonlinear characteristics of AMB systems efficiently. They are named fine mode control and rough mode control , respectively. The rough mode control yields the fastest response for large deviation of the rotor and the fine mode control fives desired transient response for small deviation of the rotor. The proposed algorithm is applied a AMB systems to verify the performance of the method, The comparison of the proposed method to a linear controller using a linearized model about the equilibrium point and PDC algorithm in [7] show the superiority of the proposed algorithm.

• 대한기계학회논문집A
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• 제29권12권
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• pp.1561-1566
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• 2005

In this paper, a new compact active magnetic bearing(AMB) is proposed in which radial and axial bearings are integrated in one bearing unit. It consists of four U-shaped cores circumferentially connected by yokes and two-layer coils for radial and axial controls. For the radial control action, it has the same principle as conventional homopolar AMBs, while for the axial control, it uses the Lorentz force generated by the interaction of the bias flux for radial control and the axial control flux. The proposed structure makes it easy to design a compact AMB because it has no disk for axial control. This paper introduces the proposed structure, principle, and design process based on the magnetic flux analysis. By using a control algorithm with feedforward action to compensate the coupled flux effect, the feasibility of the proposed AMB is experimentally verified.

• 한국분무공학회지
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• 제19권4호
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• pp.211-215
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• 2014

The main purpose of this study is to provide basic information of droplet soot generation of decane fuel. To achieve this, this paper presents the experimental results on the decane droplet combustion conducted under various ambient pressure($P_{amb}$), and oxygen concentration($O_2$) conditions. At the same time, the experimental study was conducted in terms of soot volume fraction($f_v$) and its maximum value. Also, visualization of single fuel droplet was conducted by high resolution CCD camera and ambient pressure($P_{amb}$) and oxygen concentration($O_2$) was changed by control system. It was revealed that higher ambient pressure($P_{amb}$), and oxygen concentration($O_2$) enhanced the soot generation and improved the maximum soot volume fraction( $f_v$).

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집B
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• pp.682-687
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• 2001

The cone-type AMB system consists of only 4 couples of magnets, and it can be smaller and lighter than radial-type AMB system. In this paper, the equations of motion on the cone-type AMB system are derived first, and the digital PID controllers are designed for its vibration control. The controllers are designed based on the decoupled equations of motion, and the performance of the designed controller is evaluated through its real system experiment. The results of the experiment show good performance of the controllers.

• 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.