Study On Vibration And Noise Reduction Of Industrial Sewing Machines

The industrial sewing machines are the major production equipments of clothing industry,and their working conditions determine the quality and efficiency of garment sewing to a large extent.With the development of science and technology, the high-speed is becoming the obvious increasing trend of modern industrial sewing machines.As the same as other machinery,the moving components will abrade sharply,following with the escalating high-speed of sewing machine.And the resulting failure or design flaw will cause vibration impact and noise pollution.At present,China has become the major manufacturer of sewing machines,and the total output of sewing machines accounts for more than 70%in the world.The problem about vibration and noise is a major bottleneck of industrial sewing machines for further development in our country.If the problem has not been resolved,the high-speed will be subject to some restrictions.Therefore,the study on vibration and noise reduction of industrial sewing machines will become more necessary.The industrial sewing machine has a large number of mechanisms and complex components,each of which is related closely to the overall performance of the sewing machine.Firstly,the mechanism transmission systems are introduced briefly in overlock machine JK788-4-13H and lockstitch sewing machine JK-8700 in this paper.Secondly,in the current experimental conditions,vibration and noise are tested and analyzed to identify the main vibration source,so as to provide a basis for further analysis of appropriate parts and structure improvement.According to the signal analysis results of vibration and noise,we can see that the main influencing factors are the mainshaft(or called crankshaft) in overlock machine and the upper-shaft's mechanism in lockstitch sewing machine.The problem of vibration and noise in JK788-4-13H mainly dues to excessive residual imbalance of the crankshaft.An effective balance method of overlock machine's crankshaft is presented in this paper.The Pro/ENGINEER is used to build a 3-D modular of crankshaft,then the balance of the modular is calculated and analyzed with this software technology.The crank-arms need to redesign the unbalance mass in multi-plane for balance correction.Thus the result can meet the balance precision of overlock machine's crankshaft,which achieves the purpose of reducing vibration and noise.After re-correction and redesign,the crankshaft's residual unbalance value decreases from 368g·mm to 30g·mm,up to 91.8%in decline,and the effect is obvious in vibration and noise reduction.The main influencing position in JK-8700 is the upper-shaft,and the factor is the total inertial force being too large in the upper-shaft's mechanism,resulting in the imbalance of body vibration.Through the kinematics and dynamics analysis of the needle bar and thread taking-up mechanism,we derived the track expressions of components' mass centers and the total mass center,and we got the expressions of mechanism inertial force and inertia moment.Then the software Pro/ENGINEER is used to set up the parts for assembly modeling and to analyze dynamic simulation. According to the balance theory analysis of the needle bar mechanism and the thread taking-up mechanism,without changing the original mechanism trajectory,and considering the space restrictions of actual moving location,we redesign the structure of some parts.To some degree,the total inertial force is reducing,so as to achieve the purpose of reducing vibration and noise.After improvement,the values of total inertial force and its root mean square were reduced by over 25%,and the vibration situation of the needle bar and thread taking-up mechanism has improved obviously.So,the vibration and noise have reduced in lockstitch sewing machine JK-8700 in a certain extent.The software Pro/ENGINEER is adopted to build the solid models for casings of JK788-4-13H and JK-8700.Then the Pro/MECHANICA is used to set up the casings' finite element models,which are analyzed and calculated by ANSYS.So, we can get the natural frequency of each rank and their corresponding vibration modes of casings.Thus we consider the issue to avoid resonance in order to reducing the noise of industrial sewing machines.Finally,a summary is made to the research work,and some ideas are put forward on the further research.