Dahoon Ahn

Development of a Nanoprecision 3-DOF Vertical Positioning System With a Flexure Hinge

This paper describes the conceptual design of an ultraprecision 3-DOF (Z, Ox, Oy) vertical positioning system with nanometer precision. The vertical out-of-plane positioning system can be used for various nanoalignment applications, such as optical instrument alignment. The proposed vertical positioning system is driven by three piezoelectric (PZT) actuators and is guided by three rotationally symmetric hinges. Because the displacement generated by a PZT actuator is very small, the proposed system also includes an amplification hinge mechanism. Because the relationships between the variables of the hinge parameters and system performance levels are complicated, an optimization procedure to obtain optimal design parameters, which maximize the system bandwidth, is developed. Based on the solution to the optimization problem, the design of a vertical positioning system and finite-element-method simulation results are presented. Finally, the stage is manufactured and tested for verification. The stroke of the translational movement is 190 mm, and the stroke of the rotational movement is 0.5 mrad, whereas their in-position stability levels are ±2 nm and ±20 nrad and resolutions are 5 nm and 80 nrad, respectively. The settling time is less than 45 ms.

Development of a novel 3-degrees of freedom flexure based positioning system

Flexure mechanisms have been widely used for nanometer positioning systems. This article presents a novel conceptual design of an ultra-precision 3-degrees of freedom (XYθ(Z)) positioning system with nanometer precision. The main purpose of this novel stage design is for the application of measurement equipment, in particular biological specimens. The stage was designed as a hollow type and with a compact size for the inverted microscope. This stage includes piezoelectric transducer actuators, double compound amplification mechanisms, moving plate, and capacitor sensors. The double compound amplification mechanism was designed using a mathematical model and analyzed by the finite element method. Since the relationship between the variables of the hinge parameters and system performances are complicated, an optimization procedure was used to obtain the optimal design parameters, which maximized the system bandwidth. Based on the solution of the optimization problem, the design of the stage and FEM simulation results are presented. Finally, the stage was manufactured and tested.

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.

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.

Design and Control of a 6-DOF Active Vibration Isolation System Using a Halbach Magnet Array

Active vibration isolation systems (AVIS) reduce the vibrations transmitted to ultraprecision mechanical systems by providing managed stiffness and damping. Many types of AVIS are used in various fields. In nanoprecision measuring instrument fields, such as atomic force microscopy and scanning probe microscopy, the requirement for isolation of ground vibrations has always been of great interest to researchers. Bench-top-type six-degree-of-freedom (6-DOF) AVIS have been widely used in ultraprecision measuring applications. This paper describes the design, modeling, optimization, and validation of a new 6-DOF AVIS. The unique feature of the proposed system is its voice coil motor actuator that uses a Halbach magnet array to produce a high force constant. The results obtained using the proposed AVIS show that it can serve as a bench-top device for precision measuring machines.

Development and optimization of a novel 3-DOF precision flexure stage

This article presents a novel concept design and optimal design of an ultra-precision XYθz flexure and PZT stage with nanometer accuracy. The stage consists of a regular triangle monolithic flexure mechanism with three piezoelectric actuators, and the stage uses a parallel mechanism. Since the relationship between the variables of the hinge parameters and system performances are complicated, it is very difficult to set design variables manually. Therefore, optimal design is used. Using the optimal design results, a FEM simulation was performed. The stage was designed to simultaneously attain ±50um in the X and Y directions and ±0.025° in the yaw direction, and have a first resonant frequency of 207 Hz in the yaw direction The main purpose of this novel stage is to design appropriate measurement equipment; for biological specimens in particular, the stage was designed as a hollow type and with a compact size (330 mm × 330 mm × 50 mm).

Design of a Rectangular-Type Voice Coil Actuator for Frame Vibration Compensation

Precision motion stages used in the manufacturing process of flat-panel displays have inevitably low settling performance due to their huge mass and bulky structures. In order to improve the settling performance, several methods of frame vibration compensation have been developed so far. These methods are used to cancel the vibration by imposing a counter force or modifying the resonance mode of the frame of the stage. To compensate the frame vibration, high force actuators are required. In this paper, a mighty voice coil actuator is proposed to generate the counter force against the frame vibration. The proposed voice coil actuator has an axis-symmetric rectangular structure to achieve a large force with simple and low cost fabrication. Also, the voice coil actuator allows radial clearance up to ± 4 mm. Using an optimized design process and a magnetic circuit model, the power consumption is minimized while the required force is obtained. With a power of 322 W, the VCA has been designed to have a maximum force of 574 N with a force constant of 164 N/A. Experimental results verified the force constant of the fabricated voice coil actuator is well matched with the designed value.