Research Of Random Pulse Excitation With Cutting Using On Operational Modal Analysis Of CNC Machine

Heavy and large CNC machine tools are core equipments of leading enterprises inmanufacturing industry. As domestic technology of manufacturing developing, abreakthrough has been made on processing performance of the CNC machine tools.However, compared with the foreign ones, processing performance still did not reachthe international leading level, because of poor dynamic characteristics.Experimental modal analysis method(EMA) is an effective way to studydynamically characteristics of the heavy and large CNC machine tools. But traditionalexcitation (hammer impact&vibration exciter) is limited by large masses of parts andcomplex structures. That made the practice of studying dynamically characteristics ofCNC machine tools hampered. In response to that problem, a new excitation waspresented for machine tools, which satisfied the requirement of excitation in theoperational modal analysis(OMA). The specific contents showed as follows:Firstly, random pulse mode of excitation, which was easy to practice in cuttingprocess and satisfied the excitation assumptions of OMA, was studied. The effect tothe frequency band and energy of excitation of parameters of random pulse mode wereanalysed through a statistic.Secondly, the practical forms of acting that excitation in milling and turning weredesigned. To performance that excitation in milling, a process of milling narrowworkpiece tooth with a one tooth tool in random spindle speed is put forward. For thepractice of that excitation in turning, a process of turning a face with narrow workpiecetooth in random distribution is presented. The effect of parameters of two processeswere analysed with the one of random pulse mode.Then, the computation of modal scaling factor was showed. It was introduced thathow to compute natural frequencies, damping ratioes and mode shape vectors with thepoly-reference least squares complex frequency domain method(p-LSCF) in OMA.The calculation of modal scaling factor was deduced with the former result and thepower spectral density estimates of random pulse cutting forces. Finally, a modalparameter validation method is put forward based on operational deflectionshapes(ODS).Lastly, effectiveness was proved through experiment. The excitation of randompulse cutting practice on a CNC milling machine. Through the analysis of the cutting force measured, comparison of response signal and preliminary modal parameteridentification results, the excitation was proved to be effective. Also, The excitation ofrandom pulse cutting was practiced on a heavy CNC turning machine, and it wassuccessful to identify the modal parameter of it.Totally, random pulse excitation with cutting rely on special cutting process. itcan act to heavy CNC machine tools.which satisfied the requirement of excitation inOMA in particular frequency band, and energy of excitation.