| Heavy duty NC machine tools are the core equipments in the leading manufacturing enterprises. Because of the particularity in the field of employment, these equipments were prohibited from being exported to China by foreign governments. With many years' effort, enterprises have made a great breakthrough in manufacutring of high-end heavy NC machine tools, and the technical level has also been greatly enhanced. However, compared with foreign similar products, the anti-vibration and load capacity of these machine tools were poor, which seriously affected the machining performance. Poor dynamic characteristics of machine tools is the main factor of affecting the machining performance of machine tools.Because of the complex structure of CNC machine tools and the huge self-weight of heavy duty CNC machine tools, and constrained by modeling accuracy of current theoretical research methods, a practical dynamic model of machine tools can not be established. At the same time, restricted by the exciting method, experimental modal analysis(EMA) can not be applied in the dynamic analysis of heavy duty CNC machine tools. Thus, a novel experimental modal analysis method for machine tool, based on the movement exciting method, was presented in this thesis. In this paper, the fundamental principle of movement exciting method was studied, the key factors of affecting the excitating result were analysed, the principle of parameter'selection and laws'design was proposed, and the measuring point distribution, modal parameter identification method based on the response signal and pseudo-modal identification were studied. The main research contents are summarized as follows:1. Based on the inertial exciting caused by the movement change of CNC machine tools, combined with the controllability and control parameters'modification of CNC machine tools, a new movement exciting method relying on its own movement was proposed. Its fundamental principle and implementation procedure were also presented.2. On condition of the CNC machine tools'movement, the movement mode based on the change between acceleration and deceleration was designed. Through the experimental research of acceleration and deceleration process, the regulation and control law of movement parameters to the acceleration and deceleration process was determined. By characteristic parameters analysis of the machine's vibration response signal, the effectiveness of the designed movement exciting method was proved.3. According to excitation energy and frequency brand, the influence of excitation mode, movement parameters and feed shaft on the exciting effect was studied, and the design principle of effective movement exciting method oriented to the excitation effect was also put forward.4. Based on the FEA result of modal analysis, the sensitive area to vibration response of the whole structure was predicted. By using multi-point excitation in different subareas method, the optimized configuration of the location and quantity of measuring point on the whole structure was studied, so as to reflect the vibration response information of the structure effectively, accurately and comprehensively5. Combined with random decrement technique(RTD) and ITD method, aiming at the possible existing pseudo-mode problem during movement exciting process, the pseudo-mode identification method was studied based on the two criteria of experience damping ratio and modal stability principle. By this method, the modal parameter identification of NC machine tools based on the response signal of movement exciting method was realized.6. Experimental verification and parameter identification were done on the XHK5140 CNC tools. By comparing the testing result with EMA result, the effectiveness of the proposed method was proved. This method can identify the first 3 modal parameters within low frequency which seriously impact the machining quality and efficiency of CNC machine tools. |
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