Chen Youping

Hydrogen gas sensor based on palladium and yttrium alloy ultrathin film.

Compared with the other hydrogen sensors, optical fiber hydrogen sensors based on thin films exhibits inherent safety, small volume, immunity to electromagnetic interference, and distributed remote sensing capability, but slower response characteristics. To improve response and recovery rate of the sensors, a novel reflection-type optical fiber hydrogen gas sensor with a 10 nm palladium and yttrium alloy thin film is fabricated. The alloy thin film shows a good hydrogen sensing property for hydrogen-containing atmosphere and a complete restorability for dry air at room temperature. The variation in response value of the sensor linearly increases with increased natural logarithm of hydrogen concentration (ln[H(2)]). The shortest response time and recovery response time to 4% hydrogen are 6 and 8 s, respectively. The hydrogen sensors based on Pd(0.91)Y(0.09) alloy ultrathin film have potential applications in hydrogen detection and measurement.

Compensation Scheme of Position Angle Errors of Permanent-Magnet Linear Motors

The position angle is very important in the current control of permanent-magnet linear motors (PMLMs), and its error affects the control precision of currents. However, the position angle is often not accurately detected because of faults in motor making, pulse loss of linear encoders, and so on. In order to precisely control the currents of PMLMs, a compensation scheme of position angle errors is proposed based on the mathematical relation between position angle errors and currents. In the scheme, a position angle error compensator is designed to compensate the position angles detected by linear encoders. Furthermore, a filter and a class of iteration learning algorithm are proposed to avoid the errors produced by detected phase currents and phase voltages. Simulation results show that position angle errors of PMLMs are fully compensated. Using the designed position angle error compensator, currents can be controlled in a more precise manner.

Fuzzy-immune PID control for AMB systems

In order to improve the dynamic performance of active magnetic bearing systems with highly nonlinear and naturally unstable dynamics, a new nonlinear fuzzy-immune proportional-integral-derivative (PID) controller is proposed by combining the immune feedback law with linear PID control. This controller consists of a PID controller and a basic immune proportional controller in cascaded connection, the nonlinear function of the immune proportional controller is realized by using fuzzy reasoning. Simulation results demonstrate that the active magnetic bearing system with the proposed controller has better dynamic performance and disturbance rejection ability than using the linear PID controller.

Robust Optimization and Simulation of Production/inventory System with Stochastic Demand

In this paper a multi-stage multi-item production/inventory system with limited production capacity in stochastic demand environment is considered. We proposed a robust optimization model to deal with the uncertain market demands that are denoted as a number of discrete scenarios with known probabilities. An effective genetic algorithm is designed. The result of a simulation example shows that robust optimization is possible. By choice of proper programming weight omega, we can meet the stochastic demand with little error and very little cost.

The maintenance economy and economic life of structures

Abstract Up to now, fatigue life analysis has been essentially based on the safety and/or the functional requirements of structures. To prevent structures with slow-growing cracks from suffering fatigue failure, a maintenance proramme is usually needed in modern fatigue design methods. In this paper, a quantitative criterion to evaluate the maintenance economy of structures in service is proposed, and it is found that there is an economic repair period for the service time of structures. The definition of the economic life of structures is then discussed on the basis of maintenance economy. Finally, the formulae for the above analysis and a simple example are given.