T.S. Liu

A sliding-mode approach to fuzzy control design

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.

The application of Petri nets to failure analysis

Abstract Unlike the technique of fault tree analysis that has been widely applied to system failure analysis in reliability engineering, this study presents a Petri net approach to failure analysis. It is essentially a graphical method for describing relations between conditions and events. The use of Petri nets in failure analysis enables to replace logic gate functions in fault trees, efficiently obtain minimal cut sets, and absorb models. It is demonstrated that for failure analysis Petri nets are more efficient than fault trees. In addition, this study devises an alternative; namely, a trapezoidal graph method in order to account for failure scenarios. Examples validate this novel method in dealing with failure analysis.

State estimation for predictive maintenance using Kalman filter

Abstract Failure can be prevented in time by preventive maintenance (PM) so as to promote reliability only if failures can be early predicted. This article presents a failure prediction method for PM by state estimation using the Kalman filter on a DC motor. An exponential attenuator is placed at the output end of the motor model to simulate aging failures by monitoring one of the state variables, i.e. rotating speed of the motor. Failure times are generated by Monte Carlo simulation and predicted by the Kalman filter. One-step-ahead and two-step-ahead predictions are conducted. Resultant prediction errors are sufficiently small in both predictions.

Transparent electrodes based on conducting polymers for display applications

The materials science and engineering related to the fabrication of conducting polymer thin films and the progress in the development of devices integrated with organic transparent electrodes based on conducting polymers for display applications are reviewed. Transparent electrodes are essential components for many display modules. With the evolution of display technologies, conducting polymers are recently emerging as important alternative materials for the fabrication of transparent electrodes. Conducting polymers offer some advantages, such as light weight, low cost, mechanical flexibility and excellent compatibility with plastic substrates for the development of next-generation display technologies and, in particular, are expected to play an important role in the development of flexible display technologies.

A PETRI NET APPROACH TO EARLY FAILURE DETECTION AND ISOLATION FOR PREVENTIVE MAINTENANCE

SUMMARY 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. ©1998 John Wiley & Sons, Ltd.

Failure analysis for an airbag inflator by petri nets

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 inflator 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.

H/sub /spl infin// repetitive control for pickup head flying height in near-field optical disk drives

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/sub /spl infin// 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/sub /spl infin// controller. The proposed controller is validated by experimental results.

Automatic Control System for Thermal Comfort Based on Predicted Mean Vote and Energy Saving

For human-centered automation, this study presents a wireless sensor network using predicted mean vote (PMV) as a thermal comfort index around occupants in buildings. The network automatically controls air conditioning by means of changing temperature settings in air conditioners. Interior devices of air conditioners thus do not have to be replaced. An adaptive neurofuzzy inference system and a particle swarm algorithm are adopted for solving a nonlinear multivariable inverse PMV model so as to determine thermal comfort temperatures. In solving inverse PMV models, the particle swarm algorithm is more accurate than ANFIS according to computational results. Based on the comfort temperature, this study utilizes feedforward-feedback control and digital self-tuning control, respectively, to satisfy thermal comfort. The control methods are validated by experimental results. Compared with conventional fixed temperature settings, the present control methods effectively maintain the PMV value within the range of ± 0.5 and energy is saved more than 30% in this study.

Fuzzy control stabilization with applications to motorcycle control

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 viewpoints 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 riders leaning angle on both stability and handling control are examined according to Bode plots.

Dynamic analysis of flexible linkages with lubricated joints

Abstract The dynamic behavior of flexible linkages with lubricated revolute joints is investigated, with consideration of elastic deformation, bearing clearances and hydrodynamic lubrication. An inertial frame based approach to elastic linkage dynamics yields equations of motion in a form amenable to finite element formulations. Non-linear stiffness and damping characteristics are used to obtain impact forces at revolute joints. Pressure caused by hydrodynamic lubrication is calculated by using a finite difference method. Illustrative examples are shown to compare vibratory behaviors of idealized, clearanced, squeeze film lubricated and hydrodynamically lubricated flexible linkages.