Wei-Hua Chieng

Modeling of piezoelectric actuator for compensation and controller design

This work proposes a novel method for describing the hysteretic non-linearity of a piezoelectric actuator. The hysteresis behavior of piezoelectric actuators, including the minor loop trajectory and the residual displacement near zero input, are modeled by a set of hysteresis operators, including a gain and an input-dependent lag, as well as the parameter scheduling method. A hysteresis model, using the identified parameters, and containing only the dominant hysteresis operator, is presented herein. Based upon a simplified hysteresis model, tracking is controlled to reduce the non-linear effects in the characteristics of the piezoelectric actuator. A proportional-integral (PI) controller, with inverse model feed-forward, suppresses the tracking error to within ±1% full span range (FSR) of the actuator, noticeably improving the tracking performance of the piezoelectric actuator.

Adaptive control optimization in end milling using neural networks

Abstract In this paper, we propose an architecture with two different kinds of neural networks for on-line determination of optimal cutting conditions. A back-propagation network with three inputs and four outputs is used to model the cutting process. A second network, which parallelizes the augmented Lagrange multiplier algorithm, determines the corresponding optimal cutting parameters by maximizing the material removal rate according to appropriate operating constraints. Due to its parallelism, this architecture can greatly reduce processing time and make real-time control possible. Numerical simulations and a series of experiments are conducted on end milling to confirm the feasibility of this architecture.

Precision alignment of mask etching with respect to crystal orientation

For most micro-mechanical devices, a high precision alignment of mask pattern to crystal orientation is preferred. Such alignment even becomes critical for devices that simultaneously require a smooth sidewall and minimal undercut. In this article, we present an innovative pre-etching pattern to determine the crystal orientation on [100] silicon wafers. This pattern etched on the wafer allows us to determine the crystal orientation within an accuracy of . Such a pre-etching pattern can be used as a valuable reference for all subsequent mask patterns.

ANALYSIS OF MINIMUM CLAMPING FORCE

Abstract Our objective is to determine the minimum clamping force that keep the workpiece stable during the metal cutting process. In analyzing the stability of the workpiece, one usually proves that no instant center of motion can occur on the clamping plane. However, previous search algorithms for the instant center of motion either lack theoretical sufficiency or computational efficiency. This paper presents a new method derived from the correlation between cutting force and clamping moment. This method increases the search efficiency by pruning inadequate search directions. In addition, examples are provided to illustrate minimum clamping force analysis under different fixturing conditions.

Modeling and Analysis of the Intermediate Shaft Between Two Universal Joints

Unlike a single universal joint, in which the output shaft rotates with a fluctuating speed depending on the misalignment angle, a double universal joint is used to connect two offset shafts. If a double universal joint is correctly arranged, with equal joint angles in perfect alignment, the output shaft rotates in a synchronous motion with uniform speed. However, in practice, the intermediate shaft of a double universal joint system suffers from bending moments induced by joint friction and velocity fluctuation induced by the joint angles. These factors distort the linear relationship between the input and output shafts. In this paper, the effects of joint angles and joint friction on the steady-state responses of a double universal joint system are examined. The mass matrix, damping matrix, stiffness matrix, and nonconservative force of a universal joint are derived analytically for finite element modeling. The formulation introduced generates an elementary matrix suitable for the analysis of complex rotor-bearing systems that include double universal joints.

Measuring virtual experience in a three-dimensional virtual reality interactive simulator environment: a structural equation modeling approach

With the rapid development of the VR market, virtual experience has increasingly been the object of study in recent years. A growing number of studies have reported the positive effect that virtual experience can have on a user’s mood and loyalty. However, few studies have investigated the influence of the mechanism of virtual experience on users’ mood and loyalty. To compensate for this research gap, this study aims to evaluate consumers’ virtual experience by examining the flow state in a virtual environment. A total of 368 valid questionnaires were collected, and a structural equation modeling approach was employed in the data analysis. The study reveals that forming flow involves many factors: the intrinsic characteristics of the mediated environment, the consumer’s assumptions and perceptions prior to entering the flow state, the stage at which the customer enters the flow state, and the consequences of the flow experience.

Estimating Speed Using a Side-Looking Single-Radar Vehicle Detector

This paper presents a side-looking single-beam microwave vehicle detector (VD) system for estimation of per-vehicle speed and length. The proposed VD system is equipped with a 2-D range Doppler frequency-modulated continuous-wave (FMCW) radar using a squint angle. The associated Fourier processor uses an inverse synthetic aperture radar (ISAR) algorithm to extract range and speed data for each vehicle using a single-beam FMCW radar. The simulation and experimental results show accurate estimations of vehicle speed and length. The measurement errors of speed and length were approximately ±4 km/h and ±1 m, respectively. The proposed method has excellent detection capability for small moving targets, such as bikes and pedestrians, at speeds down to 5 km/h. A commercial 10.6-GHz radar with signal processing modifications was used in the experiments.

Method for finding multiple roots of polynomials

Conventional numerical methods for finding multiple roots of polynomials are inaccurate. The accuracy is unsatisfactory because the derivatives of the polynomial in the intermediate steps of the associated root-finding procedures are eliminated. Engineering applications require that this problem be solved. This work presents an easy-to-implement method that theoretically completely resolves the multiple-root issue. The proposed method adopts the Euclidean algorithm to obtain the greatest common divisor (GCD) of a polynomial and its fast derivative. The GCD may be approximate because of computational inaccuracy. The multiple roots are then deflated into simple ones and then determined by conventional root-finding methods. The multiplicities of the roots are accordingly calculated. A detailed derivation and test examples are provided to demonstrate the efficiency of this method.

Gallium nitride electrical characteristics extraction and uniformity sorting

This study examined the output electrical characteristics--current-voltage (I-V) output, threshold voltage, and parasitic capacitance--of novel gallium nitride (GaN) power transistors. Experimental measurements revealed that both enhanced - and depletion-mode GaN field-effect transistors (FETs) containing different components of identical specifications yielded varied turn-off impedance; hence, the FET quality was inconsistent. Establishing standardized electrical measurements can provide necessary information for designers, and measuring transistor electrical characteristics establishes its equivalent-circuit model for circuit simulations. Moreover, high power output requires multiple parallel power transistors, and sorting the difference between similar electrical characteristics is critical in a power system. An isolated gate driver detection method is proposed for sorting the uniformity from the option of the turn-off characteristic. In addition, an equivalent-circuit model for GaN FETs is established on the basis of the measured electrical characteristics and verified experimentally.

Estimation of single-tone signal frequency with special reference to a frequency-modulated continuous wave system

Estimating the frequency of a single-tone signal is a common problem in radar applications, such as frequency-modulated continuous wave radar. This study presents a frequency estimation algorithm called the gradient search method using the derivative of discrete Fourier transform on the received signal samples. The analytical boundaries of the proposed method for different signal-to-noise ratios under the two conditions, with the rectangular window and with the Hann window, are derived. This study also compares the most appropriate algorithms available in the literature, including chirp-Z transform and other advanced methods. Simulation and experimental results show that the proposed algorithm provides superior performance to previous methods.