Leakage-Diagnosis System With Wavelet Analysis For Composite Hydraulic Press

Composite material with resin is an important part of the field of new materials,and is also an indispensable basic material for the development of modern industry,national defense,and science and technology.The performance of the molding equipments directly determines the product quality.In recent years,the development of automotive lightening is increasingly rapid,and"plastic-steel"has made great progress.This has imposed higher performance requirements on hydraulic presses that are in the position of core equipment for molding,and the performance reliability indexs of the hydraulic system are also increasingly demanding.In this paper,the new fault diagnosis method based on wavelet analysis is carried out around the problem of leakage that restricts the performance improvement of hydraulic system in composite hydraulic press.The details are as follows:(1)Base on composite material molding process and features of electro-hydraulic equipments,the process parameters and equipment failure characteristics that affect the high quality molding of composite materials are analyzed.Combining the working principle of composite molding,the operation laws of electrical and hydraulic systems for high-quality molded composite presses are analyzed.After decomposition the failure mode of the hydraulic system that affects the molding accuracy,a fault tree model of the press hydraulic system is built.(2)To improve the quality of leveling cylinder hydraulic system of composite material,a mathematical model is established and its leakage characteristics are analyzed.A mathematical model of the leveling cylinder during the forming process is built based on the leakage characteristics.The type of leakage and the reasons are analyzed,and the leakage characteristics and laws during the process of pressing and forming are studied.The pressure signal response characteristics when the leakage occurred in the leveling cylinder are studied and it provides analysis data for the study of fault characteristics of press leakage based on wavelet analysis.(3)A method of wavelet analysis,which is sensitive to the leakage characteristics for the hydraulic cylinder of the press,is proposed to analyze the pressure signal components of the leveling cylinder.After studying the time-frequency characteristics of wavelet transforms,the characteristics of the local spectrum analysis of the wavelet pressure signal in the leveling cylinder are analyzed.The denoising effect of wavelet threshold denoising and traditional filtering denoising methods are compared.By using thresholds and its processing techniques,the wavelet denoising model parameters are optimized.Based on the analyses of the characteristics for wavelet transform in detecting pressure abrupt signal and different frequency segmented signals,the sensitivity of wavelet transform feature parameters to leakage of press leveling cylinder is studied.Therefore,the resulting wavelet coefficients will be used to improve the detection accuracy of leveling cylinder leakage.(4)In order to verify the reliability of the proposed detection and diagnosis method,the paper build a hydraulic cylinder leakage test experimental station,data real-time acquisition and its analysis system.Jointed Lab VIEW and Matlab,a wavelet analysis and detection station for hydraulic cylinder pressure signals on the simultaneous occurrence of leaks inside and outside the leveling cylinder is builded.By extracting key characteristic sensitive pressure signals when hydraulic cylinders leak and using the proposed wavelet coefficient sensitive feature analysis method for identifying leveling leakage faults the reliability of wavelet transform monitoring and diagnosis of fault signals is verified.This paper focuses on the core part of the hydraulic system in composite press,and an online data monitoring fault diagnosis method based on wavelet analysis is proposed.According to the molding process characteristics of composite material press,the fault feature is extracted from leakage of hydraulic cylinder.Wavelet analysis of fault pressure signal can realize the identification and leakage degree diagnosis of small leakage fault of hydraulic cylinder.The method can realize monitoring and diagnosis of hydraulic cylinder leakage only by collecting the two chamber pressure signals of the hydraulic cylinder,and has the advantages of no need to change the original hydraulic system(i.e.lossless).It provides a new method with high accuracy and short diagnosis time for the failure analysis of the hydraulic press.