Showing papers by "Chien-Hung Liu published in 2008"

Sliding-mode control of a three-degrees-of-freedom nanopositioner

Abstract: This paper presents the sliding-mode control of a three-degrees-of-freedom nanopositioner (Z, θx, θy). This nanopositioner is actuated by piezoelectric actuators. Capacitive gap sensors are used for position feedback. In order to design the feedback controller, the open-loop characteristics of this nanopositioner are investigated. Based on the results of the investigation, each pair of piezoelectric actuators and corresponding gap sensors is treated as an independent system and modeled as a first-order linear model coupled with hysteresis. When the model is identified and the hysteresis nonlinearity is linearized, a linear system model with uncertainty is used to design the controller. When designing the controller, the sliding-mode disturbance (uncertainty) estimation and compensation scheme is used. The structure of the proposed controller is similar to that of a proportional integral derivative controller. Thus, it can be easily implemented. Experimental results show that 3-nm tracking resolution can be obtained. Copyright © 2008 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society

Application of the astigmatic method to the thickness measurement of glass substrates

Abstract: We developed a high accuracy thickness measurement system for glass substrates based on the optical design of the astigmatic method. The astigmatic optical system includes a laser diode, a cylindrical lens, a convex lens, and a quadrant detector. This method measures the astigmatic focusing error signal induced from the measured glass placed in the astigmatic optical system. The astigmatic focusing error signal is converted into the thickness of the glass substrate. The proposed glass thickness measurement system is verified by using a coordinate measuring machine (CMM). The accuracy of the proposed system is 0.2 μm, with a standard deviation of 0.7 μm within the thickness measuring range of 1.2 mm.

A novel 5DOF thin coplanar nanometer-scale stage

Abstract: To minimize the size of a stage with more DOF motion, this paper concentrates on the design, manufacturing process and control of a 5DOF thin coplanar nanometer-scale stage with high accuracy and multiple DOF motion. This paper uses the features of a flexible structure to develop a 200 mm × 200 mm × 35 mm thin coplanar nanometer-scale stage with 5DOF that allows the increase or decrease of axis action in accordance with various needs. The flexible structure of the thin coplanar nanometer-scale stage includes a cylindrical flexible body and an arc flexible body. The thin coplanar nanometer-scale stage allows for three-translational and two-rotational motions and is provided with eight piezoelectric actuators—one on the X -axis, another on the Y -axis, and the others on the Z -axis. The displacement characteristics of the output member of the stage were measured with the built-in capacitive sensors. It also used an analysis and identification controller design method for piezoelectric actuated systems. From the results, it can be seen that the performance of this controller is good and 10 nm controlling error of the step input can be obtained. The controlling error of the rotational angle is about 0.004 arcsec.

Nanoscratch behavior of multi-layered films using molecular dynamics

Abstract: Molecular dynamics simulations are performed to study the plastic deformation, stress and chip formation of scratched multi-layered films. The results showed that stick–slip and work-hardening behaviors were observed during the scratching process. There was a pile-up of amorphous disordered debris atoms and shear rupture ahead of the probe and a clear side-flow on the lateral sides of the probe when the probe moved forward. Both the plastic energy and the adhesion increased with an increase in the scratching depth. The glide band of the interface was on the {111}〈110〉 slip system with a maximum width of the glide band of about 1 nm. The strain energy stored in the deformed structure caused a higher stress region in the material in front of the tool edge, with a maximum stress of about 10 GPa. In addition, the mechanical response and thermal softness phenomenon are discussed.

Static/dynamic multi-function measuring device for linear unit

Abstract: A static/dynamic multi-function measuring device for linear unit, includes a foundation, a multi-direction sliding unit having eddy current detector, a linear motor, a linear unit with a sensing element and an optical measuring unit; the static/dynamic multi-function measuring device uses the linear motor to drive the multi-direction sliding unit with low friction to provide a non-contact measurement of a parallel alignment of the linear unit, a linear accuracy measurement of the linear unit, and a vibration measurement of the linear unit to detect the parallel alignment of the linear unit and the linear accuracy of a slide rail and so on, the static/dynamic multi-function measuring device also measures errors of the linear unit and a slide block moving in the vibrating and the rolling direction.

Means for measuring a working machine's structural deviation from five reference axes

Abstract: Means for measuring a working machine's structural deviation from five reference axes includes a main sensing body bonded with a main axis of the working machine (or controlled to revolve), and a lighting unit set around the main sensing body to circle about the main sensing body with a fixed radius (or the lighting unit radiates a light on the main sensing body from that radial distance and circles along with the main sensing body) such that as soon as the main sensing body has detected an optical signal, it is converted to an error signal informing of the working machine's structural deviation in two or three dimensional displacement.