Jaehwa Jeong

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 a Novel Spherical Actuator With Two Degrees of Freedom

This paper describes the design and implementation of a novel spherical actuator that can generate two tilt-motion degrees of freedom. Voice coil motors were adopted as actuators in a spherical actuator to utilize their simple driving principle and constant torque coefficient characteristic. The sensing and guiding mechanism was built inside the proposed spherical actuator and enabled compactness and ease of connection to other application systems. The actuator was designed using a design optimization framework to obtain high torque. A prototype actuator was manufactured with optimally designed parameters, and its performance was evaluated.

A novel damping scheduling scheme for proximate time optimal servomechanisms in hard disk drives

The proximate time-optimal servomechanism (PTOS) is widely used in hard disk drives because of its simplicity and good performance. There have been many studies to improve PTOSs, though they are complex or need a time-consuming tuning process. Here, we propose a novel damping scheduling PTOS (DSPTOS) for hard disk drives. The proposed algorithm keeps the closed-loop damping coefficient at a predetermined value. Compared to the original PTOS, smaller damping in deceleration will boost the rising speed, and larger damping in the settling phase reduces the overshoot and residual vibrations. Moreover, the DSPTOS maintains the simplicity of the PTOS by introducing just a predetermined damping coefficient. We applied the proposed DSPTOS algorithm to a voice coil motor in a hard disk drive. Through simulations and real-time experiments, we verified the effectiveness of the DSPTOS. In particular, with respect to long stroke seeks, the DSPTOS performs better than the PTOS.

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.

Modified Damping Scheduling Proximate Time Optimal Servomechanism for Improvements in Short Strokes in Hard Disk Drives

Proximate time-optimal servomechanism (PTOS) has been widely used as a point-to-point motion control algorithm in many control systems, especially in hard disk drives, because of its simplicity and good performance. A great deal of research for improving PTOS has been reported; however, most of it is complex or needs a time-consuming tuning process. Damping scheduling PTOS (DSPTOS), which maintained the simplicity of PTOS and showed faster settling in long strokes by scheduling a closed-loop damping coefficient, was proposed previously. In this paper, we propose a modified DSPTOS which can schedule a closed-loop damping coefficient not only in long strokes, but also in short strokes. The proposed algorithm improves seek and settling performances significantly in short strokes. The effectiveness of the proposed algorithm is verified through simulations and real-time experiments. Consequently, we achieved over a 25% settling time improvement for a short stroke (10 tracks).

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.

Halbach Magnetic Circuit for Voice Coil Motor in Hard Disk Drives

Rotary-type voice coil motors are widely used as actuators in hard disk drives. The recent trend toward higher density and smaller form factors in data storage devices requires performance improvement of the voice coil motor. In this study, we introduce a Halbach magnet array to the voice coil motor in order to increase the force generation. The Halbach magnetic circuit outperforms the conventional magnetic circuit due to the confined magnetic flux. To investigate the performance of the Halbach magnetic circuit, we analyze air gap flux density with the various shapes and thickness of the magnets using 3-dimensional finite element analysis. Consequently the optimum shape of the Halbach magnetic circuit is proposed. Simulations and experimental results proved effectiveness of the proposed magnet array in the voice coil motor for a commercial hard disk drive.

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.

Design of a four-degree-of-freedom nano positioner utilizing electromagnetic actuators and flexure mechanisms

Positioning devices are widely used in industrial applications. High precision is a key performance of the positioner and recently high precision positioners for advanced applications are required to satisfy other performances such as larger motion range, nanometer level precision, and multiple degree-of-freedom (DOF) motion within compact size. We propose a new 4-DOF high-precision positioner employing voice coil motors and flexure guides. Millimeter motion range and nano level resolution were achieved simultaneously, utilizing the frictionless characteristic of the voice coil motors and the flexures. The mathematical model describing static and dynamic behaviors of the positioner was developed and the design parameters were optimized to achieve the best performances. The proposed positioner was manufactured with the size of 180 × 180 × 30.7 mm(3) which was very compact. The experiment of feedback control showed the motion range more than 1.80 × 1.80 mm(2) in-plane and 0.3 mm vertically and the minimum resolution of 10 nm in-plane and 14 nm vertically.