Soo-Hun Lee

Survey on Roller-type Nanoimprint Lithography (RNIL) Process

Nanoimprint lithography has been demonstrated as a high-throughput, high-resolution and low-cost manufacturing method on nano scale pattering since it was first proposed by Dr. S.Y. Chou in 1995. In this article we presented a general literature review on the roller-type nanoimprint tithography (RNIT), a continuous nanoimprint lithography process. Several kinds of typical Roller-type Nanoimprint Lithography process have been briefly introduced and some examples are also introduced to gain a clear general view and perceive.

A study on active balancing for rotating machinery using influence coefficient method

Unbalance-induced vibration of rotating machineries is an essential factor in lowering the efficiency and performance of a rotating system. Particularly, the severe resonant vibration of a rotor while passing critical speeds has harmful effect on the rotor system. To minimize this vibration effect, this paper shows the active balancing approach using the active balancing device of an electromagnetic type and the balancing control program with a gain scheduling control for real spindle system. The designed active balancing device features a simple structure, fast response, accurate control, and non-contact driving in order to resolve major problems of existing balancing system. In addition, the balancing control method using influence coefficient matrix of a reference model as the gain matrix is proved to be effective in balancing by experiments even though rotating systems characteristics are changed suddenly. The stability of reference influence coefficient is verified by frequency response functions. The active balancing experiment for spindle system with our balancing device and program is well performed during operation, and then controlled unbalance responses are also below the vibration limit at all rotating speed ranges including critical speeds.

Design of voice coil motor dynamic focusing unit for a laser scanner

Laser scanning systems have been used for material processing tasks such as welding, cutting, marking, and drilling. However, applications have been limited by the small range of motion and slow speed of the focusing unit, which carries the focusing optics. To overcome these limitations, a dynamic focusing system with a long travel range and high speed is needed. In this study, a dynamic focusing unit for a laser scanning system with a voice coil motor (VCM) mechanism is proposed to enable fast speed and a wide focusing range. The VCM has finer precision and higher speed than conventional step motors and a longer travel range than earlier lead zirconium titanate actuators. The system has a hollow configuration to provide a laser beam path. This also makes it compact and transmission-free and gives it low inertia. The VCMs magnetics are modeled using a permeance model. Its design parameters are determined by optimization using the Broyden-Fletcher-Goldfarb-Shanno method and a sequential quadratic programming algorithm. After the VCM is designed, the dynamic focusing unit is fabricated and assembled. The permeance model is verified by a magnetic finite element method simulation tool, Maxwell 2D and 3D, and by measurement data from a gauss meter. The performance is verified experimentally. The results show a resolution of 0.2 μm and travel range of 16 mm. These are better than those of conventional focusing systems; therefore, this focusing unit can be applied to laser scanning systems for good machining capability.

Dynamic characteristics of a flywheel energy storage system using superconducting magnetic bearings

The high-temperature superconducting magnetic bearing flywheel energy storage system (SMB-FESS) is proposed as an efficient energy storage system. It is important to identify the dynamic behaviour and the characteristics of the SMB-FESS. First, a new method for identifying SMB characteristics has been suggested. The suggested modelling method is verified by comparing the experimental and analytical frequency response functions. In this study, the analyses of critical speed and unbalance response are performed using the analytical model. The experimental test has been carried out to verify the result of simulation. A good agreement has been observed between the experiment and the simulation result.

Design and verification of a novel hollow vibrating module for laser machining.

If a vibration module is added on laser machining system, the quality of surface finish and aspect ratio on metals can be significantly enhanced. In this study, a single mobility model of vibrating laser along the path of laser beam was put forward. In order to realize the desired unidirectional motion, a resonance type vibration module with optical lens was designed and manufactured. This cylindrical module was composed of curved-beam flexure elements. The cylindrical coordinate system was established to describe the relationship of a curved-beam flexure elements motion and deformation. In addition, the stiffness matrix of the curved-beam element was obtained. Finite element method and dynamical modeling were provided to analyze the resonance frequency and the displacement of the motion. The feasibility of the design was demonstrated with the help of experiments on frequency response. Experimental results show good agreement with theoretical analysis and simulation predictions.

Design of Compact 6-DOF Precision Aligner for Micro-Assembly

This work will develop a 6 Degrees Of Freedom (DOF) precision aligner with a small size and a high resolution for the assembly of the micro-scale parts used in mobile electronics. The arrangement of actuators in the aligner is symmetrical, based on kinematic design. A VCM (Voice Coil Motor) actuator that is small and reliable will be applied to this aligner system. This paper presents the combination of two modules to form the mechanism for the 6-DOF precision aligner. The first is a stage that can control XY θZ motion, while the second can control Z motion, i.e. Z tilt motion. According to its specifications, it is expected to satisfy precision requirements. Several tests will be carried out to confirm the specifications with PID control.Copyright

Precision XY Positioning Stage With Coupled Flexures and Piezo Actuators for Avoiding Parasitic Tilt Error

In the field of scanning probe microscopes (SPMs), a precision positioning stage has become an important component as the requirement of the SPMs has been extended from high resolution to high accuracy. The stages used in SPMs plays a role of transferring a specimen or a probe in multiple directions. The stage should satisfy the requirements for small parasitic motion and compactness. Therefore a coupled flexure leaf spring is used as a guide mechanism at recently developed multi-directional nano positioning stage with piezo actuator. Using the coupled flexure leaf spring mechanism, a compact and symmetric stage can be embodied. However, in this case, there are some problems caused by assembly process of piezo actuators. The first is that piezo actuator can be broken because of bending force when another axis is working. Commercially stack type piezo actuators are composed some ceramic materials, so they are brittle. This problem causes the durability weakening of ultra precision positioning stage. The second is unnecessary parasitic tilt error. When an actuator of one axis is acting, the other non-acting actuator works as constraint force. As a consequence, the accuracy of each axis gets lower and the control to compensate parasitic motion becomes difficult. In this research, we will propose a precision positioning stage with coupled flexures and piezo actuator to withstand bending force and avoid a parasitic tilt error. This research includes performance analysis and parametric design of the stage. The stage is designed for motion of two degree of freedom using a flexure leaf spring. Design optimization based on a finite element method (FEM) is also covered in this study. Simulation results show that the optimally designed stage decreases a tilt error less than 25% compared to the stage without concerning the bending and constraint.© 2009 ASME