Key Engineering Materials Vols. 419-420

Abstract: A new hybrid-control structure for the compensation of the volume-delay negative effect in the mixed-gas pressure control is designed. The volume-delay mechanism is discussed. A Smith predictor is used in the primary loop of a cascade control system where the secondary loop has a negligible delay while the primary loop has a significant and variant delay. To deal with the sensitivity of Smith predictor to modeling error, the gas pipe model for the Smith predictor can be updated by measuring the gas pressure and choosing the model characteristics through a lookup table. The results show that the proposed control structure brings together the best merits of a cascade control and the Smith predictor structure, and it can provide a better performance than the traditional cascade control.

Abstract: The effectiveness of separation and identification of mechanical signals vibrations is crucial to successful fault diagnosis in the condition monitoring and diagnosis of complex machines.Aeroengine vibration signals always include many complicated components, blind source separation (BSS) provides a efficient way to separate the independent component.In order to get the most effective algorithm of vibration signal separation,experiment has been done to acquire plenty of multi-mixed rotor vibration signals,three sets of vibration data generated from aeroengine rotating shafts were separated from the synthetic vibration signal. The results prove that blind source separation is effective and can be applied for vibration signal processing and fault diagnosis of aeroengine.

Abstract: Order tracking is an important method to analyze the response characteristics of rotating machinery for fault diagnosis and condition monitoring in rotating machinery. Order tracking method overcomes the shortcomings of traditional resampling and FFT method. A new use based on the order tracking analysis is proposed in this paper, the computed order tracking method is applied to analyse the dynamic vibration signals during aeroengine start-stop process.In the aeroengine test, the fault characteristic of rotating shafts is related to the rotating speed,vibration will be more complicated and diversified with the increasing speed during run-up process, and has characteristics of periodicity and multiple frequency. It is of vital critical to extract characteristic information from exterior measurement vibration signal and get interior fault information. Applying the order tracking in the analysis of aeroengine signals shows that it can extract the fault characteristics and realize the state monitoring.

Abstract: In order to manufacture geometrically complex or hard material parts, a new kind of multi-axis electro-discharge machining (EDM) computer numerical control (CNC) system, which is based on RT-Linux platform, was presented. Dual-kernel structure of System is adopted: Linux and RT-Linux are used to realize Time-sharing tasks and Real-time tasks separately. The system is divided macroscopically into two parts: Real-time part and Time-sharing part, microcosmically into three modules: Real-time Control Module, Drive Module and CNC User Module. Through the communications among them, three modules construct the whole system. Rimed Turbine Blisk was experimentalized to validate the performance of the system. The process and the results implied that the system is Real-time, stable and reliable.

Abstract: . The purpose of this paper is to study the application of electrochemical machining (ECM) technology for the fabrication of micro structures. The stray current corrosion, i.e. machining localization is a critical obstacle to micro fabrication for ECM. To machine micro structures by electrochemical machining ultra short voltage pulse is used. The effects of electrochemical machining parameters such as voltage, pulse duration, pulse frequency, and electrolyte composition on the machining accuracy were studied. In experiments, a micro hole was machined on stainless steel with cylindrical and square electrodes to investigate these effects.

Abstract: This paper presents a method for bearing health condition identification based on improved multiscale entropy (IMSE) and support vector machines (SVMs). IMSE refers to the calculation of improved sample entropies, i.e., fuzzy sample entropies (FSampEn) across a sequence of time scales, which takes into account not only the nonlinearity but also the interactions and coupling between mechanical components, thus providing much more information regarding machine health condition compared to traditional single scale-based entropy. On the other hand, in engineering practice, the amount of fault samples is often limited, which thus decrease the performance of traditional classifiers like artificial neural networks (ANNs). Currently popular SVMs provide a favorable solution to small sample-sized problems. In this study, IMSE and SVMs were employed as fault feature extractor and classifier, respectively. The experimental results verify that the proposed method has potential applications in bearing health condition identification.

Abstract: Based on a self-developed pulse power supply, effects of working fluid to machining efficiency and relative wear of electrode are studied. tangent-hole machining experiments are designed and carried out. Tangent holes with 0.75mm and 0.56mm diameters on some nozzles are obtained.

Abstract: Sacttering of SH-wave of combined deffectiveness which included single circular cavity and double linear cracks in elastic medium was investigated in detail. Analytic solution of this problem was obtained by Green’s Function method and idea of crack-division at actual position of crack at two times. There were two key steps of this method. First step was to employ a special Green’s Function which was a fundamental solution of displacement field for an elastic space with a cavity in it subjected to out-of-plane harmonic line source force at any point at first. The sceond step was crack-division which was artificially to produce a crack by apllying opposite shear stress caused by incident SH-wave. Distribution of dynamic stress concentration factor (DSCF) at edge of cavity was studied by numerical analysis. Distribution Curves of DSCF of three models were plotted by numerical method in polar coordinate system. Three models were one circular cavity and without crack, one circular cavity and single crack and single circular cavity double cracks. The results were compared and discussed in different incident angle of SH-wave.Conclusion was that the interaction among SH-wave, single cavity and double crack was obvious. Dynamic stress concentration factor varied with angle and distance between cavity and crack.

Abstract: This paper discusses the structure of wheel mobile robot, dynamics model and control model are developed. The method is tested by computer simulation, which is used to control the wheel mobile robot to follow straightaway and circle path, and numerical results show good result.

Abstract: In this paper, the modern theory of milling and the optimization technique are applied to the establishment of the mathematical model of face milling to obtain the optimum face milling parameters, in which the highest productivity is the optimizing objective，and many constraints are taking into consideration．The optimization is programmed based on the complex form method and castigatory function method．And a optimization system is established, the system which is composed of optimizing calculation module, special milling parameters database and man-machine interface．And it is programmed by adopting Visual Basic．The NC milling example is optimized，the validity and practicability of optimizing mathematic model is proved，and the base of the optimization of the NC machining process is established．