Browsing by Author "Liu, TS"

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A gap capacitance method for slider flying height measurement in near-field optical disk drives
(2004-12-01)
Chen, JW
;
Liu, TS
;
機械工程學系
;
Department of Mechanical Engineering
In order to overcome the diffraction limit of conventional optical disk drives, and substantially increase data storage capacity and density, near-field optical disk drives remain to be realized. The slider of a flying pickup head in a near-field optical disk drive has to fly at a stable spacing above the disk surface. To sense the slider flying height, a gap capacitance method is developed in this study to measure capacitance variation between the pickup head and disk surface. The capacitance varying with the flying height is modulated by a Colpitts oscillator. Subsequent demodulation accounts for height variation of the flying pickup head. Measurement results of this method are verified by using a laser Doppler interferometer. (C) 2004 Elsevier Ltd. All rights reserved.
A Petri net approach to early failure detection and isolation for preventive maintenance
(1998-09-01)
Yang, SK
;
Liu, TS
;
機械工程學系
;
Department of Mechanical Engineering
To improve preventive maintenance, this study uses a hybrid Petri net modelling method coupled with parameter trend and fault tree analysis to perform early failure detection and isolation. A Petri net arrangement is proposed that facilitates alarm, early failure detection, fault isolation, event count, system state description and automatic shutdown or regulation. These functions are very useful for health monitoring and preventive maintenance of a system. A fault diagnosis system for district heating and cooling facilities is employed as an example to demonstrate the proposed method. (C) 1998 John Wiley Br Sons, Ltd.
A repetitive learning method based on sliding mode for robot control
(2000-03-01)
Liu, TS
;
Lee, WS
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機械工程學系
;
Department of Mechanical Engineering
In order to make a robot precisely track desired periodic trajectories, this work proposes a sliding mode based repetitive learning control method, which incorporates characteristics of sliding mode control into repetitive learning control. The learning algorithm not only utilizes shape functions to approximate influence functions in integral transforms, but also estimates inverse dynamics functions based on integral transforms. It learns at each sampling instant the desired input joint torques without prior knowledge of the robot dynamics. To carry out sliding mode control, a reaching law method is employed, which is robust against model uncertainties and external disturbances. Experiments are performed to validate the proposed method.
A similarity method for miniature mobile robots
(1998-03-01)
Liu, TS
;
Lee, JY
;
機械工程學系
;
Department of Mechanical Engineering
Taking advantage of a piezoelectric material to fabricate miniature mobile robots, this study presents a similarity method, fabrication process, and walking experiment method. A curved piezoelectric material is first analyzed for vibration behavior in order to provide a basis for deriving model laws. Since the behavior of miniature mobile robots is nor amenable to modeling, the similarity method is carried out to obtain model laws. A prototype for the miniature robot is further scaled down in different geometric sizes to conduct walking experiments. Experimental results that are primarily concerned with walking speeds comparison among robots of different sizes serve to verify model laws.
A sliding-mode approach to fuzzy control design
(1996-03-01)
Wu, JC
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Liu, TS
;
交大名義發表
;
機械工程學系
;
National Chiao Tung University
This study develops a method for fuzzy control design with sliding modes in which robustness is inherent, Fuzzy control is formulated to become a class of variable structure system (VSS) control, Sliding modes are used to determine best values for parameters in fuzzy control rules, thereby robustness in fuzzy control can be improved. A switching manifold is prescribed and the phase trajectory is demanded to satisfy both the reaching condition and the sliding condition for sliding modes, Both computer simulations and experiments are carried out for an apparatus which can to some extent represent cornering motion of a motorcycle on which a rider leans to maintain stability, Experimental results demonstrate that the proposed method outperforms both proportional integral derivative (PID) control and neural-network-based fuzzy control.
A wavelet network control method for disk drives
(2006-01-01)
Chang, CM
;
Liu, TS
;
機械工程學系
;
Department of Mechanical Engineering
This paper proposes a wavelet network control method to online learn and cancel repetitive errors in disk drives. In contrast to Fourier transforms, wavelet transforms can provide detailed local information of signals. Based on the wavelet transform, wavelets can approximate any finite energy function. This paper proposes wavelet networks to approximate periodic functions. Accordingly, a wavelet network controller is developed to eliminate repetitive error caused by repetitive disturbance. Experiments for flying height control of a disk drive system are implemented to demonstrate the present method in comparison with another method using Fourier series based network control.
Airflow velocity effects on air bearing with grooved disk surface in near-field optical disk drives
(2006-05-01)
Wang, HC
;
Liu, TS
;
機械工程學系
;
Department of Mechanical Engineering
By means of an air bearing, the pickup head slider of a near-field optical disk drive flies above data tracks on a rotating disk surface to achieve a stable flying height. The influence of airflow velocities of the air bearing on lift force deserves investigation, as the airflow velocity varies during track seeking or disk speed variation. In this study, a direct simulation Monte Carlo method is used to investigate three-dimensional nanoscale gas film lubrication at the air bearing between a slider and a rotating disk. This study aims to investigate air bearing behavior at different airflow velocities. Computational results show that faster flow generates larger pressure and lift force. Lower flying height reduces force variation caused by different velocities. This study also proposes a method for maintaining the flying height within the near-field range. (C) 2006 American Institute of Physics.
Analysis of Sun et al.'s linkability attack on some proxy blind signature schemes
(2006-02-01)
Wu, LC
;
Yeh, YS
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Liu, TS
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資訊工程學系
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Department of Computer Science
The proxy blind signature scheme allows the designated proxy signer using the proxy secret key to generate a blind signature on behalf of the original signer. Tan et al. presented the DLP-based and ECDLP based blind signature schemes. Awasthi and Lal proposed a improved DLP-based scheme later. Recently, Sun et al. presented linkability attack on Tan et al.'s and Awasthi-Lal's proxy blind signature schemes respectively. In this paper, we show that Sun et al.'s attack is failed and these schemes are still satisfy the unlinkability property. (C) 2005 Elsevier Inc. All rights reserved.
Application of discrete wavelet transform to repetitive control
(2002)
Chang, CM
;
Liu, TS
;
機械工程學系
;
Department of Mechanical Engineering
This study aims to apply the discrete wavelet transform to reduce the memory size of a repetitive controller. The repetitive error signal is decomposed. Only the highest-level approximation coefficients in a tree-structured wavelet transform have to be saved and hence the error signal is compressed. The compressed error signal is in turn reconstructed to compensate the control system. Simulation results are presented to demonstrate effectiveness of the proposed method.
Decoupling control of pickup head motion in near-field optical disk drives
(2002)
Liu, TS
;
Liu, PC
;
機械工程學系
;
Department of Mechanical Engineering
For the flying pickup head in near-field optical disk drives, this study attaches a piezoelectric bender to the pickup head and develops a single-input multi-output control method to deal with the bender motion in both bending deflection and longitudinal displacement.
Design a linear motor absorber
(2006-04-15)
Chang, CS
;
Liu, TS
;
Lin, SK
;
機械工程學系
;
電控工程研究所
This paper raises a valid method to design a linear motor which serves as active dynamic vibration absorber to reduce disk drives vibration at multiple speeds. A better linear motor performance, such as lower consumption energy and higher electrical efficiency, can be achieved by tuning the diameter of a winding coil, the thickness of the magnet, and the winding spaces in a linear motor absorber. (C) 2006 American Institute of Physics.
Design of adaptive dynamic absorber to reduce optical disk drive vibration at multiple rotating speeds
(2006-02-01)
Chang, CS
;
Liu, TS
;
機械工程學系
;
Department of Mechanical Engineering
In this study, we design a dynamic absorber to reduce optical disk drive vibration at multiple rotating speeds using an enlarged bandwidth control at targeted rotating speeds. In addition to the basic absorber as a passive device, a voice coil motor serves to actively control vibration. Combining passive and active devices leads to far greater stability and robustness. The proposed dynamic absorber has been validated in simulations and experiments.
Dynamic analysis of a spur gear by the dynamic stiffness method
(2000-07-06)
Huang, KJ
;
Liu, TS
;
機械工程學系
;
Department of Mechanical Engineering
This study treats a spur gear tooth as a variable cross-section Timoshenko beam to construct a dynamic model, being able to obtain transient response for spur gears of involute profiles. The dynamic responses of a single tooth and a gear pair are investigated. Firstly, polynomials are used to represent the gear blank and the tooth profile. The dynamic stiffness matrix and natural frequencies of the gear are in turn calculated. The forced response of a tooth subject to a shaft-driven transmission torque is calculated by performing modal analysis. This study takes into account time-varying stiffness and mass matrices and the gear meshing forces at moving meshing points. The forced response at arbitrary points in a gear tooth can be obtained. Calculation results of fillet stresses and strains are compared with those in the literature to verify the proposed method. (C) 2000 Academic Press.
Dynamic analysis of rotating beams with nonuniform cross sections using the dynamic stiffness method
(2001-10-01)
Huang, KJ
;
Liu, TS
;
機械工程學系
;
Department of Mechanical Engineering
This study develops dynamic analysis based on the dynamic stiffness method for a rotating beam of nonuniform cross-section. To deal with nonuniform beams, coefficients related to material and geometric properties in the equation of motion are expressed in a polynomial form. A dynamic stiffness matrix is accordingly formulated in terms of power series. The dynamic response of the rotating beam is calculated by performing modal analysis. It is demonstrated that the present method provides an alternative to the finite element method in dealing with nonuniform rotating beams.
Failure analysis for an airbag inflator by Petri nets
(1997-05-01)
Yang, SK
;
Liu, TS
;
機械工程學系
;
Department of Mechanical Engineering
Petri nets are useful for modelling a variety of asynchronous and concurrent systems, such as automated manufacturing, computer fault tolerant systems, and communication networks. This study employs an airbag inflater system as an example to demonstrate a Petri net approach to failure analysis. This paper uses Petri nets to study minimum cut sets finding, marking transfer, and dynamic behaviour of system failure. For Petri net models incorporating sensors, fault detection and higher-level fault avoidance is dealt with. Compared with fault trees that present only static logic relations between events, Petri nets indeed offer more capabilities in the scope of failure analysis. (C) 1997 by John Wiley & Sons, Ltd.
Frequency-shaped sliding mode control for flying height of pickup head in near-field optical disk drives
(2005-02-01)
Wu, WC
;
Liu, TS
;
機械工程學系
;
Department of Mechanical Engineering
To achieve stable flying height of a pickup head in near-field optical disk drives, this study investigates a discrete sliding mode control with a frequency-shaped sliding surface. A compensator is introduced in a sliding mode using a frequency-shaped performance index with linear quadratic optimal and sliding mode control. As an actuator, a piezoelectric bender is used in this study to complement an air bearing at the head/disk interface. Experiments are carried out to demonstrate that the proposed controller performs better in flying height control than an optimal sliding mode controller. Accordingly, the controller can achieve stable flying height control in the presence of certain frequency vibration of optical disks.
Fuzzy control stabilization with applications to motorcycle control
(1996-12-01)
Wu, JC
;
Liu, TS
;
機械工程學系
;
Department of Mechanical Engineering
This study develops fuzzy control that is designed with sliding modes to achieve stability of the fuzzy controller. Fuzzy control is formulated in the form of variable structure system (VSS) control, In contrast to previous works in which Lyapunov functions are used to examine the stability, the current study investigates the stability of fuzzy control from the view-points of differential geometric methods and the sliding mode theory. Best values for parameters in fuzzy control rules are determined with the aid of sliding modes. In order to improve control performance, a tuning algorithm is executed to adjust parameters for dealing with uncertainties and disturbances, Both computer simulations and experiments with regard to an inverted pendulum hinged to a rotating disk are carried out to validate the proposed method, This apparatus can to some extent represent cornering motion of a motorcycle on which a rider leans to maintain stability, Effects of rider's leaning angle on both stability and handling control are examined according to Bode plots.
Fuzzy control stabilization with applications to motorcycle control
(1996-12-01)
Wu, JC
;
Liu, TS
;
交大名義發表
;
機械工程學系
;
National Chiao Tung University
This study develops fuzzy control that is designed with sliding modes to achieve stability of the fuzzy controller. Fuzzy control is formulated in the form of variable structure system (VSS) control, In contrast to previous works in which Lyapunov functions are used to examine the stability, the current study investigates the stability of fuzzy control from the view-points of differential geometric methods and the sliding mode theory. Best values for parameters in fuzzy control rules are determined with the aid of sliding modes. In order to improve control performance, a tuning algorithm is executed to adjust parameters for dealing with uncertainties and disturbances, Both computer simulations and experiments with regard to an inverted pendulum hinged to a rotating disk are carried out to validate the proposed method, This apparatus can to some extent represent cornering motion of a motorcycle on which a rider leans to maintain stability, Effects of rider's leaning angle on both stability and handling control are examined according to Bode plots.
Fuzzy reliability using a discrete stress-strength interference model
(1996-03-01)
Wang, JD
;
Liu, TS
;
交大名義發表
;
機械工程學系
;
National Chiao Tung University
This paper uses a fuzzy line-segment method to calculate the fuzzy unreliability of a system when only discrete-interval probabilities of stress & strength inside an interference region are available. The discrete-interval probabilities are treated as fuzzy numbers. A stress-strength interference model and extended operations of fuzzy numbers are used to calculate the fuzzy unreliability, Probability density functions are approximated by piecewise fuzzy line-segments that are expressed by linear fuzzy polynomials; the centroid of the membership function for the fuzzy unreliability is treated as the point estimate of unreliability, This method requires less computer time than previous methods in the literature, and is useful since it does not require information on distribution types of stress & strength, Numerical examples demonstrate the method.
H-infinity repetitive control for pickup head flying height in near-field optical disk drives
(2005-02-01)
Chen, JW
;
Liu, TS
;
機械工程學系
;
Department of Mechanical Engineering
The slider of a flying pickup head in a near-field optical disk drive has to fly at a stable height above the disk surface. An air bearing force between the slider and optical disk is affected by disk rotation speed and deformation, which represent low-frequency periodic disturbance to the slider. The repetitive control is adopted in this study to eliminate the periodic disturbance. H. control inherited with robust properties can deal with model uncertainty and disturbances. Therefore, to solve model uncertainty and disturbance, this study designs a repetitive controller cascaded by an H-infinity controller. The proposed controller is validated by experimental results.