• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.1170-1175
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• 2003

Recently, the disturbance caused by an optical disk vibration and the external vibration/shock are more serious problem in an optical disk drives (ODD) as an ODD become small size and rotation speed increases. The conventional controller cannot cope with the mentioned problems properly when the disturbance and vibration are larger than some range. Therefore, we propose a new control scheme using a disturbance observer (DOB) and it can control the aforementioned problems. The designed the controller is applied to a commercial ODD in focusing direction, then its validity is proved by experimental method. By rising the disturbance observer theory, the focusing performance is conspicuously improved in the presence of sinusoidal vibrations or a shock disturbance. This algorithm also applies to a tracking structure also, because focusing structure is very similar to it.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.706-711
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• 2001

A dynamic vibration absorber(DVA) is developed to reduce the excessive focusing vibration of an optical disc drive(ODD) originated from the resonance of an wobble disc. We design the material properties of the DVA by FEM model such as Young's modules, damping coefficient, shapes and dimensions, analyze its dynamic characteristics and provide its design guide line for suppressing the vibration of an optical disc drive. To examine the performance. of the DVA, the vibration of the wobble disc and the feeding system is measured by using a laser vibrometer and the noise level is checked by using microphone. The result shows that the proposed DVA reduces the vibration and. the noise in an optical disc drive.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.792-798
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• 2012

This study shows the vibration characteristics of an actuator with six wire-suspensions, used in optical pickups of optical disc drives (ODDs). In this paper, the vibration characteristics of this beam structure is induced mathematically. To obtain vibration modes of focusing direction, the vibration analysis is achieved in lateral and longitudinal directions of the structure. The accuracy of induced vibration characteristics is proved by comparing mode frequencies with a finite element analysis. Finally, it is shown that mode shapes can be modified by changing design parameters in mathematical expressions.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.234-238
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• 2003

Ultra small optical drive or PCMCIA type needs a focusing actuator because or applying Blue Laser and enhancing compatibility according to disk physical specification. Based on this need, this paper presents a novel focusing actuator adapted for ultra small optical drive of PCMCIA type. The focusing actuator using Lorenz force generated consists of coil, magnets and plate springs of pivoting. The design issues of the focusing actuator are the flexibility to focus direction, the rigidity to track direction and the higher natural mode of the moving part. For settling these Issues, this paper present mechanical design, computer simulations and test results of the realized focusing actuator. Finally, suitability and usefulness of the focusing actuator was demonstrated by the comparison of simulations and test results in a view of the possibility adapted for ultra small optical drive.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.506-509
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• 2006

Shaped Sound Focusing is defined as the generation of acoustically bright shape in space using multiple sources. The acoustically bright shape is a spatially focused region with relatively high acoustic potential energy level. In view of the energy transfer, acoustical focusing is essential because acoustic energy is very small to use other type of energy. Practically, focused sound shape control not a point is meaningful because there are so many needs to enlarge the focal region especially in clinical uses and others. If focused sound shape can be controlled, it offers various kinds of solutions for clinical uses and others because a regional focusing is essentially needed to reduce a treatment time and enhance the performance of transducers. For making the shaped-sound field, control variables, such as a number of sources, excitation frequency, source positioning, etc., should be taken according to geometrical sound shape. To verify these relations between them, wavenumber domain matching method is suggested because wavenumber spectrum can provide the information of control variables of sources. In this paper, the procedures of shaped sound focusing using wavenumber domain matching and relations between control variables and geometrical sound shape are covered in case of an acoustical ring.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.127-133
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• 2002

After the vibration source is searched in optical disk drive as an information storage device broadly used the influence of it against FES(Focusing Error Signal) which is a kind of positioning error of pick up from the circuit is carefully examined. For that Purpose, partial coherence function method is applied on a simple multi-degree of freedom model made for the theoretical verification and it is practically introduced in optical disk drive for analyzing the effect of vibration source. Finally, partial coherence output spectrum is attentively observed in order to know which vibration source is a great influence on FES.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1014-1017
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• 2007

Sound focusing technologies has been studied for various purposes from early 1990s. As a result, these technologies make us possible to apply in many uses. For example, we can treat tumors using focused ultrasonic waves without surgical knife and communicate in the ocean using time reversal array. Also applications for personal audio system become issues. Recently, as technologies are developing, in some applications, needs for regional focusing become increasing because previously suggested focusing methods, such as phase conjugation, time reversal and inverse filtering, were all about a point focusing. Therefore, studies on regional focusing method are essentially needed. Regional focusing method was firstly mentioned by Choi and Kim in 2002: acoustic contrast control. However, in regional focusing, physical interpretations between control variables and results are still not easy because of its complexity. In this regard, we tried to understand the relations between control variables and results in wavenumber domain and suggested a solution method for regional focusing: wavenumber spectrum matching. We also showed how to make spatially focused sound shape using the suggested method from the simplest case: line focusing.

• Proceedings of the KSRS Conference
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• 2005.10a
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• pp.601-603
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• 2005

Refocusing methods are used to compensate optical performance degradation of high resolution satellite camera during on-orbit operation. Due to mechanical vibration during launch and thermal vacuum environment of space where camera is exposed, the alignment of optical system may have error. The focusing error is dominant of misalignment and caused by the de-space error of secondary mirror of catoptric camera, which is most sensitive to vibration and space environment. The high resolution camera of SPOT, Pleiades and KOMPSAT2 have refocusing device to adjust focusing during orbital operation while QuickBird of US does not use on orbit refocusing method. For the Korsch type optical configuration which is preferred for large aperture space remote sensing camera, secondary mirror and folding mirror are available as refocusing element.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.04a
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• pp.722-725
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• 2014

The spatial focusing of time reversal Lamb waves on a plate has attracted considerable attention for identifying the location of an input source. This study investigates the spatial focusing performance on a plate with respect to the number of piezoelectric (PZT) sensors for varying locations of input sources. In particular, a small number of PZT sensors produce spatial focusing through the virtual sensor effect due to reflection of Lamb waves at plate edges. The spatial focusing performance with respect to the number of PZT sensors is quantified in terms of signal to noise ratio through numerical simulation and its implication is discussed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.537-540
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• 2005

Shaped Sound Focusing is defined as the generation of acoustically bright zone with a certain shape in space using multiple sources. The acoustically bright zone is a spatially focused region with relatively high acoustic potential energy level. In view of the energy transfer, acoustic focusing using multiple sources is essential because acoustic energy is very small to use other type of energy. It can be done by taking optimization techniques which can be acoustic brigtness control and acoustic contrast control. But it has not been frequently concerned about several cases, so the case of hollow cylinder shaped sound focusing is adapted and there wi11 be arguments about available control variables and spatially controllable region in this case.