Research On Leakage Characteristics Of Leveling Cylinder Of Composite Hydraulic Press Based On Lifting Scheme Wavelet

Due to its excellent mechanical properties and physicochemical properties,composite materials have become important materials in the fields of new energy vehicles,and they have been widely used in many fields.Ensuring the high reliability of the leveling cylinder of composite hydraulic press and restraining the unavoidable strong eccentric load in the process of moulding with dynamic leveling are the keys to the high quality moulding of composite materials.This paper proposes a leakage diagnosis method with the lifting scheme wavelet,which provides a new idea for the study of the leakage characteristics of leveling cylinder.The main research contents are as follows:Firstly,the principle of composite molding pressing is analyzed,and the operating mechanism and failure mechanism of the electromechanical hydraulic system of composite hydraulic press are studied.Based on the structure of the composite hydraulic press and the molding pressing technology of composite,the operating principle of the press are analyzed.Combined with the characteristics of electromechanical and hydraulic system,the key factors affecting the molding quality of composite are analyzed.On this basis,the fault feature of the composite hydraulic press and the leakage mechanism of the leveling cylinder are studied.These provide a basis for subsequent modeling.Secondly,the mathematical model of leakage fault and the single cylinder hydraulic circuit model of leveling system are established,and the dynamic characteristic of the system sensitive to leakage is analyzed.Based on the leakage feature of leveling cylinder,a mathematical model describing its leakage characteristics is established.The leakage model of valve controlled leveling cylinder is deduced and the system response characteristic under the leakage fault is analyzed.The single cylinder hydraulic circuit model of leveling system is established and the response regularity of relevant parameters under the leakage fault of leveling cylinder is analyzed.Then,based on the lifting scheme wavelet,the research method of leveling cylinder leakage characteristics is proposed.Considering the unsteady pressure signal of the leveling cylinder,the characteristics of signal singularity detection which is based on the lifting scheme are analyzed.On this basis,the lifting scheme wavelet is used to analyze the time-frequency of the pressure signal,and the local spectrum feature and the main leakage sensitive characteristic parameters of the signal are obtained.The variance of the characteristic quantity is taken as the sensitivity criterion to obtain optimal characteristic quantity of leakage diagnosis.The lifting scheme wavelet threshold for signal denoising was studied,and the signal preprocessing effect of each threshold scheme was compared to further improve the accuracy of leveling cylinder leakage detection.Finally,the validity of hydraulic cylinder leakage diagnosis method based on lifting scheme wavelet is verified by experiments.The hydraulic cylinder leakage characteristic analysis experiment platform is established,and the hydraulic cylinder position control system and pressure data monitoring system are designed.The pressure signal of the hydraulic cylinder is collected and the threshold noise reduction pretreatment is carried out.The independent sensitive characteristic quantity for internal and external leakage is obtained by using the lifting scheme wavelet analysis method.The identification of internal and external leakage state of the hydraulic cylinder and the distinction of leakage degree are realized.Compared with the traditional wavelet method,the effectiveness and sensitivity of the lifting scheme wavelet method are verified.The innovation of this paper is to propose a new method to research the leakage characteristics of leveling cylinder based on the lifting scheme wavelet.This method uses the existing pressure signal to obtain the fault characteristic quantity which is sensitive to the leakage.Without changing the original hydraulic system,it can realize the identification of the internal and external leakage of the hydraulic cylinder and the distinction the leakage degree,and it has the advantage of good adaptability.This provides a new method for fault diagnosis of dynamic leveling system of composite hydraulic press.