Papers by Keyword: Modal Test

Abstract: Dynamic characteristics of numerical control (NC) machine tools, such as natural frequency and vibration property, directly affect machining efficiency and finished surface quality. In general, low-order natural frequencies of critical components have significant influences on machine tool’s performances. The headstock is the most important component of the machine tool. The reliability, cutting stability, and machining accuracy of a machining center largely depend on the structure and dynamic characteristics of the headstock. First, in order to obtain the natural frequencies and vibration characteristics of the headstock of a vertical machining center, modal test and vibration test in free running and cutting conditions were carried out by means of the dynamic signal collection and analysis system. According to the modal test, the first six natural frequencies of the headstock were obtained, which can not only guide the working speed, but also act as the reference of structural optimization aiming at frequency-shift. Secondly, by means of the vibration test, the vibration characteristics of the headstock were obtained and the main vibration sources were found out. Finally the corresponding vibration reduction plans were proposed in this paper. That provides the reference for improving the performance of the overall unit.

Abstract: In order to conduct dynamics simulation analysis on an airborne electronic equipment, total mass equivalent method is used to simplify the finite element model of electronic building brick. Considering this method’s disadvantage that it does not take into account the effect which the components have on stiffness of the printed circuit board(PCB), the modal test technique is carried out to recify the model and generate the equivalent stiffness of the substrate. Then the modal analysis and random vibration analysis are performed on the complete machine, calculating more accurate dynamics simulation results which provide a reliable qualitative basis for improving the vibration-proof design of the equipment.

Abstract: The optimal placement of actuators is studied with the combination of numerical calculation and modal test methods. The results indicate that the optimal excitation position is close to the maximum displacement of a cantilever beam, but the conclusion is not the same as a simply supported beam. The calculation results are consistent with the experimental results, which show that the approach in the present study is correct, and can be popularized.

Abstract: A new kind of combined finite element named three-dimensional virtual laminated element and its deduce process is introduced. The new finite element was proved to be convenient, accurate and efficient in the calculation of bridge structures by a modal test and corresponding numerical example. Then some research and discussion were done, which show that with small modal construction scale being comparative with beam element, the static and dynamic spatial behavior of complicated structures can be simulated precisely. Furthermore, it is sensitive to structural damages, and more damage information can be obtained than corresponding spatial beam element, which means it is highly promising in the application of structural damage detection.

Abstract: The vibration modals and harmonic responses of the dual ball screw-driven feed system in Z direction are analyzed by the software ANSYS. In this paper, the equivalence of characteristics of fixed and rolling joints is emphasized, while the influence of joint faces on the dual ball screw-driven feed system is analyzed. In addition, the FEM results of spindle and spindle box connecting the feed system are compared with the modal testing value. The results show that the relative errors between corresponding order natural frequency and the test results are within 10%, which verified the accuracy of the modeling method, and the influence of combination on the analysis of the ball screw feed system can't be ignored. Depending on the above, weaknesses of dual ball screw-driven feed structure is found out, which provides the basis for structural optimization.

Abstract: The dynamic characteristics of machine tool directly affect machining accuracy of the final parts. Taking the self-developed HRG ultra-precision polishing CNC machine tool as the research object, the simplified finite element model is established with the finite element analysis software to do the dynamic analysis and the natural frequency is detected as the index of the dynamic performances. Based on the comparative analysis of the natural frequency and vibration modes, the gantry and the supporting frame are recognized as structural weaknesses of the machine tool, and then the modal test is done to verify simulation results. Eventually the structural weaknesses are optimized effectively. The 1st order nature frequency of the optimized gantry and the optimized supporting frame is increased 75.5% and 80.8% respectively so that they have better dynamic performances, resulting in offering higher workpiece quality and process stability.

Abstract: The DGZX - 1425 high-speed milling motorized spindle which is made and designed independently by Hao Zhi electrical and mechanical company in Guangzhou China is made as the research object, the method of establishing numerical simulation model for the spindle units dynamic performances is established, and the design of the spindles structure has been verified reasonable. Modal analysis of the spindle has been completed in ANSYS Workbench to get the first six natural frequencies and mode shapes. Harmonic analysis of the spindle is also completed to obtain the dynamic stiffness at the highest speed. Modal test and vibration test of the assembled spindle are also processed, which have verified the accuracy of the finite element method. The paper has provided a theoretical basis for the motorized spindles design, structural optimization and the improvement of the dynamic performances.

Abstract: In order to obtain the first 4 natural frequencies and vibration modals of ZJ70D drilling rig base. The experimental modal of the base is measured under the environment of uTekMa modal test system. Testing result shows it is identical to actual vibration condition. Comparing to the power frequency of engine, reducer, etc, it is found their working frequencies and frequency multiplications approach the drilling rig base natural frequencies, which are the main reason of drilling rig base vibration.

Abstract: Based on environmental stochastic excitation, a large scale modal test was conducted at an important section of Shanghai Metro Line 1. According to the collected time response data, the natural frequencies of the soft soil-tunnel system were obtained by means of theoretical and experimental analysis, which can provide calculation parameters for further relevant dynamic analysis.

Abstract: The research on the combination of the characteristics becomes extremely important to the success of machine tool design. This paper mainly studies the dynamic and static characteristic parameters of heavy machine tool guide-way joint. And put forward a practical machine tool combining surface analysis method according to the experimental verification. It is presented that small linear guide as a scale model based on similarity theory. And make a research on the static and dynamic characteristics of small guide joint and the conclusion extended to heavy machine set of faces. And the conclusion is extended to the heavy machine set of faces. The results can be used as reference data about structure and design of the machine tool due to the similarity principle and error range.