Study On Processing Error Tracing Based On Empirical Mode Decomposition

The21st century is "The Century of Quality"’, with the deepening of enterprise competition, the quality is becoming more and more important.Machining precision is the base of mechanical product quality. Under the influence of various error sources, there might be machining errors on the parts. When the machining process is abnormal, only a little time will be spent in dealing with the abnormal factors, more than80percent time will be spent in finding them. The traditional error tracing methods based on statistical theory needs plenty of sample data, so it’s difficult to be applied to the mainstream way of multi-varieties and small batch production mode. In order to overcome the deficiency of the traditional methods, the processing error tracing method based on Empirical Mode Decomposition (EMD) is proposed in this paper. In order to put forward reasonable and accurate adjustment measures, the error sources from the machine tools must be traced. The main research content includes three aspects:(1) The EMD theory is researched and applied to the machining error signal processing. Analyzed the reason of endpoint effect and proposed the method of combining Extreme Point Symmetry Continuation method and Gray Error Separation method to suppress the endpoint effect. The program of EMD and Endpoint Effect suppressing method is developed with MATLAB. The Endpoint Effect suppressing method proposed in this paper is proved to be effective by decomposing simulation signal.(2) The form error is gotten by the decomposition of the work piece machining error with EMD, and then the error sources are traced by the characteristics of the form error. The Hilbert spectrum is applied to the processing error diagnosis. The Hilbert spectral characteristics of spindle imbalance and other faults, slide way imbalance, transmission chain errors are analyzed by analyzing the frequency characteristic of spindle, slide way and transmission chain. And then the machining error of work piece is traced by EMD method.(3) After a research on the stiffness of bearing and shaft, the paper proposed a simple method to calculate the deformation of the spindle under cutting force, so the spindle model is established. Then the slide way model is established on the basis of carrying out stress analysis for slide way. When the concentrated high energy appears in the high frequency part of Hilbert spectrum, the main error source is cutting force. The paper proposed a method to trace the error caused by cutting force based on EMD and machine tool model. Then a simulation signal is used to simulate the error tracing process, and the method is proved to be effective by correlation analysis. In the end, the spindle model is corrected by EMD method, so that the deformation caused by static force can be calculated correctly.