Research On Key Technology Of Fault Diagnosis For Pumping Hydraulic System Of Concrete Pump Truck

Concrete pump truck has the advantages of flexibility, high efficiency and good pouring quality, so it plays an important role in infrastructure construction and national economic development. But faults often happen because of poor working conditions and laggard maintenance. As the key part of concrete pump truck, pumping hydraulic system is a highly nonlinear system. There is much interference between the various circuits. The principal elements failure mode, failure mechanism is complex and diverse. It is difficult to extract fault features and identify fault mode. So Conventional signal processing and fault diagnosis methods are invalid on the fault diagnosis of pumping hydraulic system.The work in this thesis was supported by the National "863" Plan essential project of China "Construction Machinery Remote Maintenances and Monitoring System"(2008AA0428). Aiming at the safety issues for the construction of concrete pump truck, around the critical components and systems which are easily lead to failure in pumping hydraulic system, using theoretical studies, simulation modeling, experimental analysis and prototyping as research tools, this thesis study the research on key technology of fault diagnosis for pumping hydraulic system, such as fault inference mechanism, fault feature extraction and fault pattern recognition. The main contents are as follows:1.The statistical analysis of the common failure of the pumping hydraulic system was done. The simulation model of the pumping hydraulic system was established and used to analyze the dynamic characteristics. The dynamic characteristics was also studied by experimental analysis. The fault diagnosis strategy was formulated at last.2.According to the characteristics of complicated structure as well as fuzzy failure probabilities, mechanism and degree of the hydraulic system of concrete pump truck, a fault diagnosis method of hydraulic system based on T-S fuzzy fault tree analysis is proposed. This method describes failure probability of hydraulic components and system with fuzzy numbers, describes connection between events using T-S fuzzy gate, describes failure degree with fuzzy numbers. Applications of this method in fault diagnosis of hydraulic system are introduced in combination with an example of failure analysis of hydraulic system.3.In fault diagnosis of hydraulic pump, the failure mechanism is complex and the fault characteristic is weak, so a fault diagnosis approach based on Hilbert-Huang transform(HHT) and envelope spectrum is proposed. According to the method, the vibration signal is decomposed into some intrinsic mode function (IMF) using Empirical Mode Decomposition(EMD) at first. Then the first IMF is envelope analyzed and the envelope spectrum is obtained which include the main fault information. Finally, the working conditions and fault types of the pump is determined by the analysis of the envelope spectrum.4.An intelligent diagnostic method based on HHT and PSO-SVM is proposed. According to the method, the vibration signal is processed by HHT at first. Then the IMF number, center frequency and energy of previous IMF components together constitute the fault feature vectors. At last these eigenvectors are input into PSO-SVM and the working conditions and fault types of the hydraulic pump is determined.5.A new characteristic sensitivity concept of classification definition and a new feature extraction method of CD-PCA is proposed. According to the method, time domain parameters, frequency domain parameters and other parameters are extracted at first. Then the sensitive characteristic parameters are selected by classification definition. At last,PCA is used to extract principal components of the sensitive characteristic parameters as the final feature parameters. The method can effectively select the sensitive features and eliminate the correlation between them.It is proved effective in fault diagnosis for leakage of hydraulic cylinder.6. Applying the aforementioned methods and theory into practice, a fault diagnosis prototype system was development and it meet the application requirements.