Kuo-Ming Chang

Squeeze film damping effect on a MEMS torsion mirror

In this paper we discuss the dynamical characteristics of a torsion mirror in microelectromechanical systems. The squeeze film is modeled using the so-called modified molecular gas film lubrication (MMGL) equation with the coupling effects of surface roughness and gas rarefaction. The MMGL equation is linearized and then a simple mapping method is utilized to obtain the analytical solution of the transformed two-dimensional diffusion equation. From the numerical analyses, it is shown that the surface roughness parameter (Peklenik number), the gas rarefaction parameter (inverse Knudsen number) and squeeze film damping frequencies significantly affect the dynamic characteristics (spring and damping coefficients) of the torsion mirror.

Formation and Morphology of Zn2Ti3O8 Powders Using Hydrothermal Process without Dispersant Agent or Mineralizer

Synthesis of Zn2Ti3O8 powders for attenuating UVA using TiCl4, Zn(NO3)2·6H2O and NH4OH as precursor materials by hydrothermal process has been investigated. The X-ray diffractometry (XRD) results show the phases of ZnO, anatase TiO2 and Zn2Ti3O8 coexisted when the zinc titanate powders were calcined at 600 °C for 1 h. When calcined at 900 °C for 1 h, the XRD results reveal the existence of ZnO, Zn2TiO4, rutile TiO2 and ZnTiO3. Scanning electron microscope (SEM) observations show extensive large agglomeration in the samples. Transmission electron microscope (TEM) and electron diffraction (ED) examination results indicate that ZnTiO3 crystallites formed with a size of about 5 nm on the matrix of plate-like ZnO when calcined at 700 °C for 1 h. The calcination samples have acceptable absorbance at a wavelength of 400 nm, indicating that the zinc titanate precursor powders calcined at 700 °C for 1 h can be used as an UVA-attenuating agent.

Adaptive Neural Network Control for Piezoelectric Hysteresis Compensation in A Positioning System

Piezoelectric (PZT) actuators are popularly applied as actuators in micro-positioning systems due to its characteristic of infinitely small displacement resolution. Piezoelectricity material has nonlinear hysteresis phenomena. Owing to its nonlinear hysteresis effect, the tracking control accuracy of the precision positioning system is difficultly achieved. Hence, it is desirable to take hysteresis effect into consideration for improving the control performance. In this paper, a trajectory tracking controllers composed of adaptive neural network and PI controller is presented for a nano-positioner driven by a piezoactuator to realize the control performance that the displacement of a nano-positioner driven by a piezo-actuator can follow accurately the reference input signal and the transient response of the system can be improved. In this paper, some computer simulations are made to show that the system output can track the reference input exactly and the system transient response can be improved

Lubrication of journal bearings: influence of stress jump condition at the porous-media/fluid film interface

In this study, the microstructure of bearing surface is modeled as a thin porous film press-fitted on an impermeable surface. On the basis of the Brinkman-extended Darcy model with stress jump condition at the porous-media/fluid film interface, the effects of viscous shear stress and stress jump on the performance of finite journal bearings are examined. The Elrod algorithm as well as the successive over-relaxation method is utilized to solve the modified Reynolds equation and determine the accurate cavitation region. The results show that the increase in stress jump parameter (β) provides a decrease in the load capacity, an increase in the attitude angle, and an increase in the coefficient of friction.

Model reference adaptive control for a precision positioning system

Piezoelectric actuators having the characteristics of infinitely small displacement resolution are popularly applied as actuators in precision-positioning systems. Due to their nonlinear hysteresis effects, the tracking control accuracy of the precision positioning system is difficultly achieved. Hence, it is desirable to take hysteresis effect into consideration for improving the trajectory tracking performance. In this paper, a model reference adaptive control scheme based on hyperstability theory is developed for a moving stage system driven by a PZT actuator. It is worth emphasizing that the controller can be constructed without a nonlinear hysteresis dynamic equation to compensate the hysteresis effect. Through experimental examinations, the tracking performance was obtained as precision as ten nanometer order. The effectiveness of the proposed adaptive control scheme was validated.

A modified robust adaptive control with dead zone for nonlinear plants with bounded disturbance

In this paper, basing on Lyapunov stability theory, a typical adaptive control system with dead zone is firstly proposed for a class of nonlinear plants with bounded disturbance. It is shown that a larger state tracking error norm is given when a conservative dead zone value is set to achieve a stable adaptive control scheme for the plant subjected to a bounded disturbance. To solve this problem, a modified adaptive control with dead zone scheme is proposed. The proposed adaptive control scheme is proved to be stable and the state tracking error norm can be reduced. Finally, the performance of the modified robust adaptive control with dead zone is shown by some simulation results.

Adaptive control for uncertain systems with sector-like bounded nonlinear inputs

In this paper, a general approach to the synthesis of model reference adaptive control systems is proposed for uncertain time -delay systems with the so-called sector-like bounded nonlinear inputs via hyperstability theory. In the presence of system parameter variations and external disturbances, it can be ensured that the system output can track the reference model output asymptotically. Finally, some computer simulations are given to illustrate the performance of the proposed adaptive control scheme.

Model reference adaptive control for uncertain systems with sector-like bounded nonlinear inputs

In this paper, a model reference adaptive controller design based on hyperstability theory is considered for the uncertain nonlinear system with the so-called sector-like bounded nonlinear inputs, which is subjected to the norm-bounded system parameter variation, unmodelling error, and external disturbance uncertainties. In the proposed adaptive control scheme, the asymptotical tracking objective of system output for the desired output can be achieved and the bounded conditions of all the signals in the controlled system can be ensured. Finally, some computer simulation results are given to illustrate the performance of the proposed adaptive control system.

Real-time scheduling for elevator group systems

The traditional assignment approaches for elevator group systems, which are simple and rough, are only fit for low-rise buildings. Hence, they are not suitable in the high-rise buildings with complex traffic requests. In this article, a so-called Score Index Assignment (SIA) approach is proposed to design the real-time scheduling for elevator group systems. Simulation results are given to show that the SIA approach can improve the total service performance of the elevator group system subjected to uncertainties. The SIA approach can fit in any different traffic request conditions by tuning the control (assignment) parameters in the so-called total service evaluation index function of elevator.

A Lubrication Theory for Anisotropic Slips and Flow Rheology

abstract A lubrication theory, considering the coupled effects of anisotropic slip on both the solid–liquid interface and non-Newtonian power law lubricant, is proposed to enhance surface treatment and oil additives. A modified Reynolds equation as well as Poiseuille and Couette flow rate correctors are then derived by applying the rheology model and Navier slip boundary conditions with orthogonal principal slip lengths ( , ). Hence, the different slenderness ratios that lead to different performance of journal bearings are used to highlight the coupling effects of anisotropic slips and flow rheology. Contours of constant load ratios are plotted and then the parameters in flow rheology and boundary slip can be located while designing functional surfaces in journal bearings.