Dae-Gab Gweon

Optimal design of a flexure hinge based XYθ wafer stage

Abstract Optimal design o1 a XYφ micromotion stage is presented. The stage consists of a monolithic flexure hinge mechanism with three piezoelectric actuators. This paper describes the procedures of selecting parameters for the optimal design. In particular, it presents a mathematical formulation of the optimization problem. Based on the solution of the optimiiation problem, the final design of the stage is also presented. Experimental results indicate that the design procedure is effective, and the designated stage has the total range of 41.5 μm mid 47.8 μm along the X- and Y-axes, respectively, and the maximum yaw motion range of 322.8 aresec (1.565 mrad).

New open-loop actuating method of piezoelectric actuators for removing hysteresis and creep

Many researchers have studied the actuation of piezoelectric actuators using a model of the hysteresis of piezoelectric transducer(PZT). However, these hysteresis modeling methods to remove the nonlinearity in PZT did not include the consideration of PZT’s creep effect which is a very important factor in many open-loop application of piezoelectric actuator. In order to compensate for the creep effect of PZT as well as the hysteresis of displacement, the notion of “voltage creep” is proposed in this article. And, with the notion, a new actuation method of piezoelectric actuators for removing the hysteresis and creep will be proposed and the actuation result will be presented.

Quantitative Analysis of Methyl Parathion Pesticides in a Polydimethylsiloxane Microfluidic Channel Using Confocal Surface-Enhanced Raman Spectroscopy

A fast and ultra-sensitive trace analysis of methyl parathion pesticides in a polydimethylsiloxane (PDMS) microfluidic channel was investigated using confocal surface-enhanced Raman spectroscopy (SERS). A three-dimensional PDMS-based passive micromixer was fabricated for this purpose. This PDMS micromixer showed a high mixing efficiency because a strong chaotic advection was developed by the simultaneous vertical and transverse dispersion of the confluent streams. The confocal SERS signal was measured after methyl parathion pesticides were effectively adsorbed onto silver nanoparticles while flowing along the upper and lower alligator-teeth-shaped PDMS channel. A quantitative analysis of the methyl parathion pesticides was performed based on the measured peak height at 1246 cm−1. Our method has a detection limit of 0.1 ppm. This value satisfies the requirement recommended by the Collaborative International Pesticides Analytical Council (CIPAC) for the determination of methyl parathion in pesticide formulations. This study demonstrates the feasibility of using confocal SERS for the highly sensitive detection of methyl parathion pesticides in a PDMS microfluidic channel.

Creep characteristics of piezoelectric actuators

A major limitation of piezoelectric translator (PZT) actuators is their lack of accuracy originated from the hysteresis and creep. Nevertheless the creep phenomenon is an important factor in many applications of PZT actuators, but it has been investigated less frequently in comparison with the displacement hysteresis. In this article, we present a basic creep model with some parameters that have hysteresis properties which make it possible to predict an open loop response of PZT actuators based on these properties.

Robotic assembly: a synthesizing overview

Robotic assembly systems offer tremendous promise for the flexible assembly automation but present a variety of complex research issues due to the positioning inaccuracy of the manipulator, dimensional variation of mating parts and their physical interactions. This paper provides an up-to-date survey of researches in robotic assembly with emphasis on parts mating technology. Depending upon the mating strategy, presently available methods of performing precision assembly operations are classified and their advantages and limitations are discussed from the view points of the system complexity, adaptability and reliability. The performance variables such as the mating speed, positioning error absorbing capability and applicability are compared in some details for various assembly methods.

A High-Precision Dual-Servo Stage Using Halbach Linear Active Magnetic Bearings

In this paper, a high-precision dual-servo stage with a magnetically levitated fine stage is described. For magnetic levitation, a Halbach linear active magnetic bearing (HLAMB) is used. The HLAMB has two functions: gravity compensation and actively control of vertical motion. To implement these functions, the HLAMB utilizes permanent magnet arrays and Lorentz coils. The fine stage has positioning capabilities with 6 DOF due to four HLAMBs and four voice coil motors (VCM). The HLAMBs control out-of-plane motions, and the VCM control in-plane motions. The fine stage achieves high-precision position feedback using laser interferometers and capacitive sensors. The coarse stage has an H-type structure that can carry the fine stage 300 mm by 300 mm along the x - and y-axes. Positioning and scanning performances are verified by the experimental results. It has ±10 and ±15 nm in-position stability in the x- and y-axes, respectively. At the scan with 10 mm/s constant velocity, ±1 nm mean tracking error and 4.7 nm jitter were obtained.

Error analysis of a flexure hinge mechanism induced by machining imperfection

Abstract Modeling of manufacturing tolerances for machining of a monolithic flexure hinge mechanism is presented. This modeling uses a computer-based method to generate the equations of motion for the mechanism and to predict the induced motion errors for various types of machining imperfections. This paper describes the modeling and the quantitative analysis of the motion errors using a well-known simple compound linear spring as an example. Based on the simulation results of the example problem, effects of the machining imperfection types on motion errors are generalized. The simulation demonstrates that the imperfection of the center position and the size of a machined hole provide an in-plane motion error X, Y, θ z . In addition, the machining error in the perpendicularity of the hole with respect to the plate also provides an out-of-plane parasitic error Z, θ y , θ y .

Compact soft x-ray transmission microscopy with sub-50 nm spatial resolution

In this paper, the development of compact transmission soft x-ray microscopy (XM) with sub-50 nm spatial resolution for biomedical applications is described. The compact transmission soft x-ray microscope operates at lambda = 2.88 nm (430 eV) and is based on a tabletop regenerative x-ray source in combination with a tandem ellipsoidal condenser mirror for sample illumination, an objective micro zone plate and a thinned back-illuminated charge coupled device to record an x-ray image. The new, compact x-ray microscope system requires the fabrication of proper x-ray optical devices in order to obtain high-quality images. For an application-oriented microscope, the alignment procedure is fully automated via computer control through a graphic user interface. In imaging studies using our compact XM system, a gold mesh image was obtained with 45 nm resolution at x580 magnification and 1 min exposure. Images of a biological sample (Coscinodiscus oculoides) were recorded.

A new 3-DOF Z-tilts micropositioning system using electromagnetic actuators and air bearings

Abstract A new 3-DOF Z-tilts (z, pitch, and roll motion) micropositioning system has been developed. It uses electromagnetic actuators and air bearings. An electromagnetic actuator produces an attraction force between the air bearing and the base plate. An air bearing has the role of suspension and guidance, with a clearance of several tens of micrometers in the z-direction. Therefore, this system has design features of guiding 3-DOF XYθ motion without limiting the plane motion and playing the role of a z-directional position actuator. With the control of current, the equilibrium position between magnetic attraction force and air bearing thrust force can be controlled with inherently infinite resolutions. The theoretical background of an electromagnetic actuator is explained. Then, an air bearing is analyzed in the point of z-directional positioning mechanism. The air bearing can be modeled as a second-order system with parameter variation—stiffness and damping vary with respect to the z-directional displacement. Therefore, a simple robust control algorithm is applied to improve the control performance. With the aid of robust control, this system provides 25 nm positioning resolution over the total range of 40 μm along the z-direction and, accordingly, 0.29 μrad resolution over the total range of 460 μrad in pitch and roll motion.

Optimal design of a flexure hinge-based XYZ atomic force microscopy scanner for minimizing Abbe errors

To establish of standard technique of nanolength measurement in a two-dimensional plane, a new (AFM) system has been designed. In this system, measurement uncertainty is dominantly affected by the Abbe error of the XYZ scanning stage. No linear stage is perfectly straight; in other words, every scanning stage is subject to tilting, pitch, and yaw motion. In this article, an AFM system with minimum offset of XYZ sensing is designed. And, the XYZ scanning stage is designed to minimize the rotation angle because Abbe errors occur through the multiply of offset and rotation angle. For XY stage, optimal design is performed to minimize the rotation angle by maximizing the stiffness ratio of motion direction to the parasitic motion direction of each stage. For the Z stage, the optimal design of maximizing the first-resonant frequency is performed. When the resonant frequency increases, the scan speed is improved, thereby reducing errors caused by sensor drift. This article describes the procedures of selecting p...