Hyuck-Dong Kwon

Aspherical Solid Immersion Lens of Integrated Optical Head for Near-Field Recording.

New solid immersion lenses (SILs) have been studied for a high-density optical storage system by the near-field process that can overcome the far-field diffraction limit. We have proposed the aspherical SILs, named elliptic SIL (ESIL) and Cartesian SIL (CSIL) according to geometrical optics. The SILs have a high numerical aperture (NA), for instance, the NAs of the ESIL and the CSIL are over 1, with a refractive index of 1.56 of the disc cover layer. The SILs that include the function of the objective lens are able to read/write the signals inside the disc substrate. The optical heads employing an internal recording method are expected to be utilized in an unsealed environment. Experimental results of the application of an ESIL are presented. The replicated ESIL (RESIL) has been proposed to solve critical issues such as the problems of the thickness error of the SILs or the disc substrate. These problems need to be solved for the commercialization of the near field recording (NFR) technology.

Modeling, vibration, and stability of elastically tailored composite thin-walled beams carrying a spinning tip rotor

The problems of the mathematical modeling, eigenvibration, and stability of cantilevered thin-walled beams carrying a spinning rotor at its tip are investigated. The structure modeled as a thin-walled beam encompasses nonclassical features such as anisotropy, transverse shear, and secondary warping, and in this context, a special ply-angle configuration inducing a structural coupling between flapping-lagging-transverse shear is implemented. The implications of combined gyroscopic effects and conservative force upon the free vibration and stability of this structural system are revealed and a number of pertinent conclusions are outlined. Among others, it is shown that the judicious implementation of the tailoring technique can yield dramatic enhancements of both the vibrational and stability behavior of the system.

Elliptic solid immersion lens for NFR; compensation for disk thickness variation and disk tilt

In the last decade of optical data storage development, near-field recording (NFR) technology has been suggested for achieving higher areal density. However, there remain several serious and practical issues. The major defects in NFR due to the use of a solid immersion lens (SIL) are dust and thermal problems compared to orthodox optical storage technologies. The existing SIL is delicate in an unsealed environment due to heat, dust, contamination etc. CISD released a new SIL concept called elliptic solid immersion lens (ESIL) at the last ISOM (T.S. Song et al, ISOM01 p. 130, 2001). The new ESIL is capable of resolving some critical problems that are possibly caused by the existing SIL which records on the disk surface; in addition, the ESIL does not require an objective lens and with its simple structure, it has achieved improvements in mechanical tolerances of the alignment process and in pickup actuator dynamics. Although the ESIL possesses the potential to reduce present restrictions from the conventional SIL, it is necessary to establish a focusing servo system against variation in thickness of the cover layer. Also, a gap maintenance and tilt compensation system using an optical sensor and PZT was proposed in this paper.

Gap maintenance system using near-field optics and piezoelectric materials for near-field recording

In this paper, our aim is to develop a system that can not only maintain stable gap distance under 100nm but also compensate the tilting between a pick-up head and disk surface for near-field recording (NFR), which is known as a key technology for a next generation optical storage. Applying total internal reflection (TIR) to the air gap measurement, we design an optical sensor to measure the gap distances at three points. Stack and bimorph piezoelectric actuators are utilized for high precision control with nanometer resolution. To understand dynamic characteristics of the system, an analytical method for boundary coupled beam model is performed and verified by comparison with the results of the finite element method (FEM).

Vibration and stability control of robotic manipulator systems consisting of a thin-walled beam and a spinning tip rotor

Vibration and stability feedback control of a robotic manipulator modeled as a cantilevered thin-walled beam carrying a spinning rotor at its tip is investigated. The control is achieved via incorporation of adaptive capabilities that are provided by a system of piezoactuators, bonded or embedded into the host structure. Based on converse piezoelectric effect, the piezoactuators produce a localized strain field in response to an applied voltage, and as a result, an adaptive change of vibrational and stability response characteristics is obtained. A feedback control law relating the piezoelectrically induced bending moments at the beam tip with the appropriately selected kinematical response quantities is used, and the beneficial effects of this control methodology upon the closed-loop eigenvibration characteristics and stability boundaries are highlighted. The cantilevered structure modeled as a thin-walled beam, and built from a composite material, encompasses non-classical features, such as anisotropy, transverse shear, and secondary warping, and in this context, a special ply-angle configuration inducing a structural coupling between flapping-lagging and transverse shear is implemented. It is also shown that the directionality property of the material of the host structure used in conjunction with piezoelectric strain actuation capability, yields a dramatic enhancement of both the vibrational and stability behavior of the considered structural system.

Smart robotic manipulator systems consisting of a thin-walled beam and a spinning tip rotor: vibration and stability control

Vibration and stability feedback control of a robotic manipulator modeled as a cantilevered thin-walled beam carrying a spinning rotor at its tip are investigated. The control is achieved via incorporation of adaptive capabilities that are provided by a system of piezoactuators bonded or embedded into the master structure. Based on converse piezoelectric effect, the piezoactuators produce a localized strain field in response to an applied voltage, and as a result, an adaptive change of vibrational and stability response characteristics is obtained. A feedback control law relating the piezoelectrically induced bending moments at the beam tip with the kinematical response quantities appropriately selected is used, and the beneficial effects of this control methodology upon the closed-loop eigenvibration characteristics and stability boundaries are highlighted. The cantilevered structure modeled as a thin-walled beam, and built-up from a composite material, encompasses on-classical features, such as anisotropy, transverse shear and secondary warping, and in this context a special ply-angle configuration inducing a structural coupling between flapping-lagging transverse shear is implemented. It is also shown that the directionality property of the material of the host structure used in conjunction with piezoelectric strain actuation capability, yields a dramatic enhancement of both the vibrational and stability behavior of the considered structural system.

Dynamics of Thin-Walled Composite Aircraft Wings Carrying External Stores

In this paper, the free vibration and dynamic response to external time-dependent loads of aircraft wings modeled as thin-walled anisotropic composite beams and carrying eccentrically located heavy stores are analyzed. In this context, bending-twist coupling induced by both the eccentric heavy stores distributed along the wing span and chord, and by the anisotropy of the wing material, that is essential when dealing with aircraft wing problems was included . In addition to the anisotropy of constituent materials, also transverse shear and warping restraint effects have been incorporated. The governing equations of the wing-store system and the related boundary conditions are derived via application of Hamiltons Principle. To solve the eigenvalue/boundary problems, the Extended Galerkin Method (EGM) is applied. Numerical simulations highlighting the implications of external stores coupled with the implementation of the structural tailoring technique on eigenfrequency and dynamic response to external time-dependent loads are supplied, and pertinent conclusions are outlined. Nomenclature ij a = 1-D global stiffness coefficients i b = mass terms L = wing semi-span i Z ,ηi = the i-th mass location along the wing span and its dimensionless (≡ Zi/L) counterpart i m , i m = mass of the i-th store and its dimensionless (≡ mi/mw) counterpart θ = ply angle i r , i r = the offset between the centroid of the i-th store and the central line of the clean wing, and its dimensionless (≡ ri/L) counterpart