• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2001.05a
• /
• pp.496-503
• /
• 2001

The suspension of the optical pickup actuator is damped by the presence of silicone rubber damper bond at its termination. In spite of the presence of it, the actuator still exhibits a strong mechanical resonance which affects its settling time and vibrational characteristics. This resonance can cause errors in reading information from the disk, particularly in high speed CD-ROM and DVD-ROM drives. Ferrofluids are stable colloidal suspensions of sub-micron sized magnetic particles in a carrier liquid. In the actuator design, ferrofluid is applied to the surface of the magnets until the quantity is sufficient to maintain intimate contact with the bobbin/carrier assembly. The fluid is retained in the magnetic field and its viscosity provides the desired mechanical damping to the moving assembly, improving the actuators settling time and vibrational characteristics. Access time is also improved, particularly on warped or eccentric discs.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2002.05a
• /
• pp.67-70
• /
• 2002

This paper presents the property of the Squeeze Film Damper (SFD) using Magneto-Rheological fluid (MR fluid). The damping property of a SFD for a flexible rotor system varied according to vibration mode. MR fluid is known as a functional fluid with controllable apparent viscosity of the fluid by applied magnetic field strength. When the MR fluid is applied in the SFD, the SFD using MR fluid can effectively reduce vibrations of the flexible rotor in a wide range of rotating speed by control of the applied magnetic field strength. To investigate in detail the SFD using MR fluid, the SFD to support one mass was constructed and its performance was experimentally investigated in the present study. The damping property of the SFD using MR fluid has viscous damping by Newtonian fluid, but not Coulomb friction by Bingham fluid. Therefore, The system damped by the SFD can be considered as a linear system.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.13 no.7
• /
• pp.508-516
• /
• 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.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2001.05a
• /
• pp.323-327
• /
• 2001

Electrorheological(ER) and magnetorheological(MR) fluids have a unique ability to increase the dynamic yield stress of the fluid substantially when electric or magnetic field is applied. Controllable fluids such as ER and MR fluids have received considerable attention as several components of engineering devices. One of them is a smart impact damper using ER/MR fluids. Impact damper system can be used in the joint mechanism of railroad vehicle, protection equipment of elevator's drop, and launch equipment of aircraft. This paper presents the results of an analytical study of the performance of a smart impact damper to suppress vibration during impact excitation. The damping capabilities of MR impact damper for variable applied current are analyzed using Bingham model under sudden impact load.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2003.05a
• /
• pp.510-513
• /
• 2003

The paper represents the stability of a rotor system with the squeeze film damper (SFD) using an electromagnet. The electromagnet is installed in the inner damper of the SFD. The proposed SFD has basically property of a conventional SFD and variable damping property according to variation of the applied electric current. Therefore, when the applied current controlled, the whirling vibration of the rotor system can be effectively reduced in a wide operational speed range. In the present work, the performance of the SFD was experimentally investigated according to changing the magnetic field strength. When the applied current increased, the whirling amplitude greatly reduced and the damping ratio also increased.

• Proceedings of the KIEE Conference
• /
• 1999.07g
• /
• pp.3289-3291
• /
• 1999

The vibration and impact hinders the movement of micro dynamic system. The controllable micro damper is a solution for this problem. In this paper, the controllable micro damper for MR(Magneto - Rheological) Fluid is designed and fabricated using bulk micromachining process and organic bonding technique. The damping constant of micro MR damper changes according to input magnetic field. The response of the micro MR damper is measured and the experimental results are compared.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.13 no.6
• /
• pp.484-489
• /
• 2003

The paper represents stability of a rotor system with the squeeze film damper (SFD) using an electromagnet. The electromagnet is installed in the inner damper of the SFD. The proposed SFD has basically the property of a conventional SFD and variable damping property according to variation of the applied electric current. Therefore, when the applied current Is controlled, the whirling vibration of the rotor system can be effectively reduced in a wide operational speed range. In the present work, the performance of the SFD was experimentally investigated according to changing the magnetic field strength. As the applied current increased, damping ratios increased, while whirling amplitudes greatly reduced.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2005.06a
• /
• pp.313-317
• /
• 2005

Precision motor dynamometer is requiring for nano positioning control performance recently. Particularly, linear motor is using rapidly and the dynamometer needs is increasing. In this study, a precision control dynamometer is designed using MR (Magnetic Rheological) damper. The ultra precision motor system including the driver and controller is tested using the MR damper dynamometer. This dynamometer is able to measure torque for rotary motor or traction force with linear positioning accuracy for linear motor system.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1995.10a
• /
• pp.769-772
• /
• 1995

Most turbo machines, which operate at high speeds, such as gas turbines, jet engines, pumps, and compressors are prone to perrturbing vibrations. The best vibration control method for rotors is to eliminate destabilizing factors. Careful balancing application of "more stable" oil-lubricated bearing, such as tilting pad bearings or use of anti-swirl devices in seals, are examplse of passive vibration control methods. the use of magnetic bearing is an active control method. An obvious advantage of active control is that it provides damping (or modifies system stiffness or other parameters) only when there is a need for that, i.e., in emergency states, while not affecting the rotor normal operational conditions. Moreover, active control methods provide exact position control through on-line control. In this study, a magnetic actuator, digital contrliier using DSP, and bipolar operational power supply/amplifiers were developed to show the effectiveness of reducing robot vibration. Also the curve fitting procedure to obtain the transfer function of frequency dependent component was developed. Results presented in this dissertation will provide a well-defined technical parameters in designing magnetic damper system.er system.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
• /
• 1999.02a
• /
• pp.81-84
• /
• 1999

The purpose of this paper is to find the magnetic field distribution inside the motor in order to find out if the high-Tc superconducting tapes operate stably in actual motor operation. With this gola, magnetic field distribution in a detailed model of the actual motor was analyzed through F.E.M. (Finite Element Method). As a result, it has been proved that the high-Tc superconducting tapes can withstand 4 A of current with stability. 4 A was the amount of current needed to achieve 600 A ·turns which is required by the previous simulation aimed at developing this motor. Also, it has been observed that the flux damper reduces armature reactance during the motor operation and during load changes, helping the stable motor operation. But, it was observed that the flux damper generates loss by means of leakage flux and this decreases the output of the motor by about 5%.