Hybrid robust fault detection and isolation of satellite reaction wheel actuators

In this paper,a combined robust fault detection and isolation scheme is studied for satellite system subject to actuator faults,external disturbances,and parametric uncertainties.The proposed methodology incorporates a residual generation module,including a bank of filters,into an intelligent residual evaluation module.First,residual filters are designed based on an improved nonlinear differential algebraic approach so that they are not affected by external disturbances.The residual evaluation module is developed based on the suggested series and parallel forms.Further,a new ensemble classification scheme defined as blended learning integrates heterogeneous classifiers to enhance the performance.A wide range of simulations is carried out in a high-fidelity satellite simulator subject to the constant and time-varying actuator faults in the presence of disturbances,manoeuvres,uncertainties,and noises.The obtained results demonstrate the effectiveness of the proposed robust fault detection and isolation method compared to the traditional nonlinear differential algebraic approach.

THE PARALLEL CONFOCAL DETECTING SYSTEM USING OPTICAL FIBER PLATE

Objective Focusing on the problem such as slow scanning speed, complex system design and low light efficiency, a new parallel confocal 3D profile detecting method based on optical fiber technology, which realizes whole-field confocal detecting, is proposed. Methods The optical fiber plate generates an 2D point light source array, which splits one light beam into N2 subbeams and act the role of pinholes as point source and point detecting to filter the stray light and reflect light. By introducing the construction and working principle of the multi-beam 3D detecting system, the feasibility is investigated. Results Experiment result indicates that the optical fiber technology is applicable in parallel confocal detecting. Conclusion The equipment needn't mechanical rotation. The measuring parameters that influence the detecting can easily be adapted to satisfy different requirments of measurement. Compared with the conventional confocal method, the parallel confocal detecting system using optical fiber plate is simple in the mechanism, the measuring field is larger and the speed is faster.

Design of a novel correlative reflection electron microscope for in-situ real-time chemical analysis

A novel instrument that integrates reflection high energy electron diffraction(RHEED),electron energy loss spectroscopy(EELS),and imaging is designed and simulated.Since it can correlate the structural,elemental,and spatial information of the same surface region via the simultaneously acquired patterns of RHEED,EELS,and energy-filtered electron microscopy,it is named correlative reflection electron microscopy(c-REM).Our simulation demonstrates that the spatial resolution of this c-REM is lower than 50 nm,which meets the requirements for in-situ monitoring the structural and chemical evolution of surface in advanced material.

Dependent Randomization in Parallel Binary Decision Fusion

We consider a parallel decentralized detection system employing a bank of local detectors(LDs)to access a commonly-observed phenomenon.The system makes a binary decision about the phenomenon,accepting one of two hypotheses(H_(0)("absent")or H_(1)("present")).The kth LD uses a local decision rule to compress its local observations yk into a binary local decision uk;uk=0 if the kth LD accepts H_(0)and uk=1 if it accepts H_(1).The kth LD sends its decision uk over a noiseless dedicated channel to a Data Fusion Center(DFC).The DFC combines the local decisions it receives from n LDs(u_(1),u_(2),...,u_(n))into a single binary global decision u_(0)(u_(0)=0 for accepting H_(0)or u_(0)=1 for accepting H_(1)).If each LD uses a single deterministic local decision rule(calculating uk from the local observations yk)and the DFC uses a single deterministic global decision rule(calculating u_(0)from the n local decisions),the team receiver operating characteristic(ROC)curve is in general non-concave.The system's performance under a Neyman-Pearson criterion may then be suboptimal in the sense that a mixed strategy may yield a higher probability of detection when the probability of false alarm is constrained not to exceed a certain value,α>0.Specifically,a"dependent randomization"detection scheme can be applied in certain circumstances to improve the system's performance by making the ROC curve concave.This scheme requires a coordinated and synchronized action between the DFC and the LDs.In this study,we specify when dependent randomization is needed,and discuss the proper response of the detection system if synchronization between the LDs and the DFC is temporarily lost.

ERROR ANALYSIS OF 3D DETECTING SYSTEM BASED ON WHOLE-FIELD PARALLEL CONFOCAL MICROSCOPE

Compared with the traditional scanning confocal microscopy, the effect of various factors on characteristic in multi-beam parallel confocal system is discussed, the error factors in multi-beam parallel confocal system are analyzed. The factors influencing the characteristics of the multi-beam parallel confocal system are discussed. The construction and working principle of the non-scanning 3D detecting system is introduced, and some experiment results prove the effect of various factors on the detecting system.