• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.407-412
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• 2004

본 연구에서는 PMN-PT bimorph actuator를 이용하여 초소형 광디스크 드라이브용 광픽업 구동기를 제작하였다. 최근에 휴대용 기기에서의 고용량 정보 저장기기에 대한 필요성이 대두됨에 따라 착탈식이 가능한 수 기가급 초소형 광디스크 드라이브가 개발중에 있다. PMN-PT는 약 1.5kV/cm 이하의 전기장에서는 PZT같은 압전 소자와 마찬가지로 입력 전압에 대한 변형률이 선형성을 나타내는데, 사용된 PMN-PT는 PZT의 약 3배 가까운 압전 상수값을 나타내었다. 보 끝단에 외부 힘이 작용할 때 PMN-PT bimorph 구동기가 낼 수 있는 수직 방향의 힘과 변위에 대해서 일반적인 적층 형태로 이론적인 해석을 수행 하였다. 그리고 이 bimorph로 구동될 Cymbal 형태의 변위 확대 기구의 변위에 대한 이론적인 모델을 제시하고, 이를 이용하여 2개의 bimorph로 2축을 동시에 구동하는 픽업 구동기를 제작하였다. 3개의 제작된 prototype으로 실험을 수행하여 예상 변위량과 잘 일치함을 보였다. 또한, 상용 해석 프로그램인 Matlab과 Ansys를 이용하여 Cymbal 확대 기구의 여러 파라미터에 따른 구동 성능의 민감도를 확인해 보았다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.1
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• pp.41-51
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• 2018

Downwash from helicopter rotor blades and external winds from various maneuvering make an unguided rocket change its trajectory and range. For the prediction of the trajectory and range, it is essential to consider the downwash effect. In this study, an algorithm was developed to calculate 6-Degree-Of-Freedom(6 DOF) forces and moments exerting on the rocket, and total flight trajectory of a 2.75-inch unguided rocket in a helicopter downwash flow field. Using Actuator Disk Model(ADM) analysis result, the algorithm could analyze the entire trajectory in various initial launch condition such as launch angle, launch velocity, and external wind. The algorithm that considered the interference between a fuselage and external winds could predict the trajectory change more precisely than inflow model analysis. Using the developed algorithm, the attitude and trajectory change mechanism by the downwash effect were investigated analyzing the effective angle of attack change and characteristics of pitching stability of the unguided rocket. Also, the trajectory and range changes were analyzed by considering the downwash effect with external winds. As a result, it was concluded that the key factors of the rocket range change were downwash area and magnitude which effect on the rocket, and the secondary factors were the dynamic pressure of the rocket and the interference between a fuselage and external winds. In tailwind case which was much influential on the range characteristics than other wind cases, the range of the rocket rose as increasing the tailwind velocity. However, there was a limit that the range of the rocket did not increase more than the specific tailwind velocity.

• Proceedings of the KIEE Conference
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• 1999.11c
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• pp.652-654
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• 1999

This paper presents approaches to the control of the DVD(Digital Video Disk) system using DSP(Digital Signal Processor) in order to improve the precision and robustness. To improve the performance of the Pick-Up servo actuator of the digital video drive, the tracking and focusing servo control algorithms is applied to this system. Simulation results show the performance of the robust control algorithm applied the pick-up servo system comparing to the linear controller.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.53 no.10
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• pp.671-677
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• 2004

This paper presents the design of a now controller for the read/write head of a hard disk drive. The general controller for seeking is the time-optimal control. However if we use only the time optimal control law, this could be vulnerable to chattering effect. To solve this problem, we propose a modified controller design algorithm in this paper. The proposed controller consists of bang-bang control for seeking and sliding-mode control for tracking. Moreover, to test the robustness and stability of control system, a bounded disturbance is selected to maximize a severity index. Simulation results show the superiority of the proposed controller through comparison with time optimal VSC(variable structure control).

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.413-418
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• 2004

Recently, the development of mobile devices demands information storage systems to use micro drive devices. 1-inch micro drive hard disk uses the load/unload(L/UL) technology to increase area recording density and reduce power consumption. Because micro drive has light actuator, effects of the flexible cable that is ignored in 3.5-inch hard disk drive is important to load/unload performances. In this paper, effects of flexible cable on load/unload performances are studied.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.159-159
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• 2009

Existence of physical moving parts (ex. check valve) produces several problems (mechanical abrasion, deterioration of reliability, limited temperature performances etc.) in driving pumps. To overcome such problems, we proposed a valveless piezoelectric micro-pump which has new type volume transferring mechanism. The proposed micro-pump has a double faced disk type vibrator that can generate peristaltic motion formed by traveling wave in each surface of a disk. This type of micro-pump is able to apply to a fluid supply system that provides two different kinds of fluid simultaneously. In this paper, we propose a simple and novel design of piezoelectric micro-pump that is peristaltically by piezoelectric actuators and allows the removal of the need for valves of other physically moving parts. The finite elements analysis on the proposed pump model was carried out to verify its operation principle using the commercial analysis software.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.8
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• pp.1545-1551
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• 2002

The optical storage device has recently experienced significant improvement, especially for the aspects of high capacity and fast transfer rate. However, it is necessary to study a new shape of air bearing surface for the rotary type actuator because the optical storage device has the lower access time than that of HDD (Hard Disk Drives). In this study, we proposed the air bearing shape by using SA (Simulated Annealing) algorithm which is very effective to achieve the global optimum instead of many local optimums. The objective of optimization is to minimize the deviation in flying height from a target value 100nm. In addition, the pitch and roll angle should be maintained within the operation limits.

• Tribology and Lubricants
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• v.20 no.6
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• pp.322-329
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• 2004

Recently, a load/unload(L/UL) system is adopted to the hard disk drive(HDD) due to its advantages such as lower power consumption, larger data zone, simpler fabrication of disk due to no bumped parking zone, and rarer contact between slider and media. An analysis of the transient motion for the slider is very important to design an air bearing surface(ABS) of the slider to secure the stable performance of the system. During the L/UL process, however, there are several issues occurred such as contact or collision between slider and media. Sometimes this will cause the system failure. In this study, the dynamics of a pico slider during the loading process are investigated through numerical simulation using FEM analysis and experiment. Ramp profile and angular velocity of the swing arm actuator are very important parameters for the design of L/UL system to avoid collision between slider and disk.

• 한국전산유체공학회:학술대회논문집
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• 1999.11a
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• pp.167-173
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• 1999

An Euler-based CFD tool has been developed for the performance evaluation of a thrust reverser mounted on a high bypass ratio turbofan engine. The computational domain surrounded by the ground and non-reflection boundary includes the whole nacelle configuration with a deployed thrust reverser. The numerical algorithm is based on the modified Godunovs scheme to allow the second order accuracy in both space and time. The grid system is generated by using eleven multi-blocks, of which the total cell number is 148,400. The thrust reverser is modeled as if it locates at the nacelle simply in all circumferential direction. The existence of a fan and an OGV(Outlet Guide Vane) is simulated by adopting the actuator disk concept, in which predetermined radial distributions of stagnation pressure ratio and adiabatic efficiency coefficient are used for the rotor type disk, and stagnation pressure losses and flow outlet angles for the stator type disk. All boundary conditions including the fan and OGV simulation are treated by Riemann solver. The developed solver is applied to a turbofan engine with a bypass ratio of about 5.7 and the diameter of the fan cowl of 83 inch. The computational results show that the Euler-based inviscid method is very useful and economical to evaluate the performance of thrust reversers.

• International Journal of Precision Engineering and Manufacturing
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• v.9 no.4
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• pp.22-25
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• 2008

The dynamic response of the head arm assembly (HAA) of a hard disk drive to an impact load was obtained from a 3D non-linear finite element model using ANSYS/LS-DYNA and from experiments using a modified levitation mass method (LMM). In the finite element model, the impact load was created by modeling the mass as a rigid body and making it collide with the HAA. The velocity, displacement, acceleration, and inertial force of the mass were then obtained from the time history data of the finite element analysis. In the LMM, a mass that was levitated with an aerostatic linear bearing, and hence encountered negligible friction, was made to collide with the actuator arm, resulting in a dynamic bending test for the arm. During the collision, the Doppler frequency shift of the laser beam reflected from the mass was accurately measured with an optical interferometer. The velocity, displacement, acceleration, and inertial force of the mass were accurately calculated from the measured time-varying Doppler frequency shift. A good correlation between the experimental data and FEA results was observed. The FEA was also used to investigate the dynamic response of the HAA to impact by different masses.