Moon G. Lee

Robust Design and Performance Verification of an In-Plane XYθ Micropositioning Stage

This paper describes the robust design, fabrication, and performances verification of a novel ultraprecision XYθ micropositioning stage with piezoelectric actuator and flexure mechanism. The main goal of the proposed novel design is to combine a translational motion part and rotational motion part as a decoupled serial kinematics on a same plane. Proposed compound cymbal mechanisms of the translational motion part have functions of motion amplifier as well as motion guide. And Scott-Russell linkage mechanism is applied to the rotational motion part. In this research, Taguchi Design of Experiments is used for robust design with flexure notch hinge fabrication errors as noise factors. Target specifications of the design are sufficient range and bandwidth of motion. The proposed XYθ stage has a translational motion range of 58.0 μm and rotational motion range of 1.05 mrad, and a closed-loop resolution of ±2.5 nm, ±2.5 nm, and ±0.25 μrad in X-, Y-, and θ-directional motion, respectively. The proposed XYθ micropositioning stage has a novelty with in-plane and decoupled kinematic design, compared with many previously developed stages based on planar parallel kinematics.

A new magnetic bearing using Halbach magnet arrays for a magnetic levitation stage

Next-generation lithography requires a high precision stage, which is compatible with a high vacuum condition. A magnetic levitation stage with six degrees-of-freedom is considered state-of-the-art technology for a high vacuum condition. The noncontact characteristic of magnetic levitation enables high precision positioning as well as no particle generation. To position the stage against gravity, z-directional electromagnetic levitation mechanisms are widely used. However, if electromagnetic actuators for levitation are used, heat is inevitably generated, which deforms the structures and degrades accuracy of the stage. Thus, a gravity compensator is required. In this paper, we propose a new magnetic bearing using Halbach magnet arrays for a magnetic levitation stage. The novel Halbach magnetic bearing exerts a force four times larger than a conventional magnetic bearing with the same volume. We also discuss the complementary characteristics of the two magnetic bearings. By modifying the height of the center magnet in a Halbach magnetic bearing, a performance compromise between levitating force density and force uniformity is obtained. The Halbach linear active magnetic bearing can be a good solution for magnetic levitation stages because of its large and uniform levitation force.

Development of compact high precision linear piezoelectric stepping positioner with nanometer accuracy and large travel range

Many application areas such as semiconductor manufacture, precision optics alignment, and microbiological cell manipulation require ultraprecision positioning systems with a high positioning resolution and large motion range. This article describes the development of a compact high precision linear piezoelectric stepping positioner for precision alignment of optical elements. The positioner is designed to have a compact and symmetric structure, high positioning resolution, large motion range, high force density, adequate dynamic range, and power-off hold. The positioner is fabricated according to these specifications and performance evaluation tests are carried out. A resolution of 10 nm, speed of 1 mms, push force of 25 N, and stiffness of 10.4 N/microm are attained while maintaining a compact size of 32x42x60 mm(3). The required power consumption is 52.33 W. The test results confirm that the developed positioner could be successfully applied to the precision alignment of optical elements.

A novel stylus profiler without nonlinearity and parasitic motion for FPD inspection system

There are increasing needs to inspect micro-pattern of flat panel display (FPD) device such as PDP and LCD. The inspection system should be able to measure over large size mother glass with high productivity and accuracy. Stylus profilers are adopted as an inspection system. To scan over large and heavy FPD device specimen, a “tip-scanning” head for stylus profiler is required. A simple method to realize a tip-scanning system is to miniaturize the whole scanning unit. In this study, a novel stylus profiler is proposed as a tip-scanning stylus profiler. The novel stylus profiler has leaf spring instead of conventional lever and pivot. To measure position of stylus an optical senor is used. Linear variable differential transformer is applied to feed-back scanning stage displacement. The stage is actuated by a voice coil motor (VCM). Target performances of the stylus profiler head are in the stroke over 20 μm with high accuracy. Specifications of xy-scanning stage are over 250 μm×250 μm and high bandwidth over 20 Hz. The magnetic and elastic characteristics of the mechanism are designed based on finite element (FE) analysis. After fabrication of the head and stage, they are integrated. Current amplifier and feedback controller are also developed. The performance of the stylus profiler is also validated by inspecting standard sample.

Multisegmented Magnet Array on Voice Coil Motor in Rotating Data Storage Devices

The swing-arm-type voice coil motor (VCM) is widely used as an actuator in rotating data storage devices. Recently, it has been found that to achieve a faster data transfer rate and a higher data storage areal density, a high performance actuator is required. Moreover, a small form factor has become desirable for portable devices. In this paper, a novel magnetic circuit of VCM with multisegmented magnet array (MSMA) is proposed. Both the magnetic circuits of the conventional VCM and the MSMA VCM are optimized using the 3D finite element method. Sample magnetic circuits are fabricated with optimally designed parameters and a comparative analysis is carried out. The performances of magnetic circuits are evaluated and the experimental results prove the effectiveness of the proposed magnet array.

Note: Design of a novel ultraprecision in-plane XYθ positioning stage.

This paper presents the design, fabrication, and experimental results of a novel ultraprecision in-plane XYθ positioning stage with kinematic decoupling between translational motion and rotational motion components. Two translational motions are guided by four cymbal mechanisms that have both motion guide and motion amplifier. Four leaf springs guide a rotational motion amplified by a Scott-Russell linkage mechanism. The proposed stage has advantages such as an in-plane symmetrical configuration as well as ease of design and control by serial kinematics. The experimental results demonstrate that the stage has a translational full motion range of 58 μm and a rotational full motion range of 1.05 mrad. The crosstalk experimental results show good agreement with the theoretical prediction of the decoupling between translational motion and rotational motion.

A Comparative Analysis of Voice Coil Motors with Multisegmented and Conventional Magnet Arrays for Rotating Data Storage Devices

The recent trend towards higher density and the faster transfer rate in portable rotating data storage devices requires their track-following system to be controlled with high speed and downsized. Usually, a voice coil motor is used in the system as an actuator. In this paper a novel voice coil motor with a multisegmented magnet array is proposed for making the actuating force higher and the size smaller.

Failure Diagnosis System for a Ball-Screw by Using Vibration Signals

Recently, in order to reduce high maintenance costs and to increase operating ratio in manufacturing systems, condition-based maintenance (CBM) has been developed. CBM is carried out with indicators, which show equipment’s faults and performance deterioration. In this study, indicator signal acquisition and condition monitoring are applied to a ball-screw-driven stage. Although ball-screw is a typical linearly reciprocating part and is widely used in industry, it has not gained attention to be diagnosed compared to rotating parts such as motor, pump, and bearing. First, the vibration-based monitoring method, which uses vibration signal to monitor the condition of a machine, is proposed. Second, Wavelet transform is used to analyze the defect signals in time-frequency domain. Finally, the failure diagnosis system is developed using the analysis, and then its performance is evaluated. Using the system, we estimated the severity of failure and detect the defect position. The low defect frequency (≈58.7 Hz) is spread all over the time in the Wavelet-filtered signal with low frequency range. Its amplitude reflects the progress of defect. The defect position was found in the signal with high frequency range (768~1,536 Hz). It was detected from the interval between abrupt changes of signal.

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.

Development of compact high precision two degree of freedom XY piezoelectric stepping positioner

In this article, a linear piezoelectric stepping positioner developed by Kang et al. [Rev. Sci. Instrum. 78, 075112 (2007)] is extended to have a two degree of freedom XY linear motion and it is experimentally evaluated. A resolution less than 10 nm, a speed of over 0.5 mm/s, push forces of 17.9 and 19.5, and stiffnesses of 6.54 and 5.90 N/microm are attained while maintaining a compact size of 96x96x39 mm3 and the required power consumption of 102.74 W.