Dynamic Analysis And Optimization On The Upper Transmission Shaft Of H947 Computerized Embroidery Machine’s Single Head

With the development of social economy and the progress of human civilization,embroidery products have been widely used in our daily lives.The large demands for embroidery products has been driven the rapid progress of embroidery industry.However,how to efficiently produce high quality embroidery products is still challenging.The computerized embroidery machines usually suffer from broken needles,broken threads,noises and vibration in the manufacturing process,and with the increase of rotational speed more and more serious.Motivated by this observation,in this thesis we conduct an in-depth study on analyzing the upper transmission shaft(the drive shaft system of the machine head)of the embroidery machines.In this study,a H947 computerized embroidery machine is utilized as an example.The major work of this thesis is as below.1.First,a summary on the current status of embroidery machine vibration analysis and research was carried out.A dynamics analysis on the drive shaft system of the embroidery machine head was proposed,based on the characteristic of the embroidery machine as rotating machinery.By way of transference matrix,dynamics analysis on the upper transmission shaft of the H947 computerized embroidery machine was conducted and it was found out that the first-order natural frequency of it is 18.99 Hz,namely the lateral vibration critical speed is 1139 rpm.2.With the help of the SolidWorks,a 3D entity model of the H947 computerized embroidery machine single head was constructed.Then,the 3D model of the upper transmission shaft of the machine head was simplified,and imported into ANSYS Workbench.Afterwards,the finite element model in the Mechanical module was built,and finite element modal analysis was conducted.The results show that: the first order natural frequency in free modal is 19.860 Hz,and the first order natural frequency in constrained modal is 21.103 Hz.Since the principal first-order vibration mode is tangential vibration,the constraints has a little influence on vibration mode.The main vibration modes of the two modals are quite similar.Comparison of each order natural frequencies and main vibration modes shows the following observations: constrains can alter the structural natural frequencies,and the main vibration mode of constrained modal is formed by adding constrains on the main vibration mode of the free modal.Finite element modal analysis and transference matrix analysis on the upper transmission shaft of the embroidery machines demonstrate similar results.As such,the two analysis approaches verified each other.Our analysis provides reference for avoiding the resonance region of an embroidery machine,and cast new lights on the intrinsic relationship between parametric method and discrete method.3.Shafting modal experiments on the embroidery machine was conducted incorporating AVANT MI-7008 data collection and analysis machine and experimental modal analysis software termed Modal Genius,which further verifies the finite element modal analysis and transference matrix analysis approaches.Towards analyzing the effect of the upper transmission shaft to the vibration of the entire machine,we tested the vibration acceleration of the key points under rotation speeds 800rpm~1300rpm.We have the following observations on the experimental results.The vibration acceleration along the Z-axis direction is significantly higher than that along other directions.Vibration acceleration at the needle bar frame is much higher than that at the body frame.The vibration acceleration increases abnormally starting from 1250 rpm.The reasons for these observations are that the axis rotation brings much vibration long the Z axis of the frame;needle bar hits the needle bar frame which leads to the high vibration acceleration at the needle bar frame;and abnormal vibration acceleration increase dues to local resonance.According to the tests comparison of the four key points,we are able to provide the best operating speed of the H947 computerized embroidery machine.4.Following the requirements of the manufacturer of the H947 computerized embroidery machines,Dynamics optimization was conducted on the H947 computerized embroidery machines in production under the goal of least alteration costs.Towards this aim,we adopted a scheme of moving the components integrally,set the distance L between the ferrule of high-speed presser foot and the right side of the main shaft as the design variable,and chose the maximum first-order natural frequencies of the upper transmission shaft under free mode and constrained mode as the objective functions to perform the optimization.The optimization results demonstrate that when L=140mm,(1)the first-order natural frequency under free mode increases from the original 19.860 Hz to 28.295 Hz,namely the first-order natural frequency has increased by 42.47%,and(2)the first-order natural frequency under constrained mode increases from the original 21.103 Hz to 22.866 Hz,namely the first-order natural frequency has increased by 8.4%,.As such,our optimization can avoid the drive sensitive bandwidth 16Hz~22Hz of the H947 computerized embroidery machine,and can significantly benefit the embroidery machines in terms of guaranteed normal operation.