| In considering the potential drawbacks of low efficiency,high impact and friction,etc,inherent in traditional mechanical mode of needle-selection,a new type of magnetic levitation drive theory has been proposed by our research group to serve as a substitute.By utilizing "Electrical mode" rather than "Mechanical mode",needles can be driven directly under new magnetic-drive mechanism,which raised both the knitting efficiency and performance metrics for knitting machinery.Based on the theory we've presented,a hybrid structure made of normal winding coils and magnet is explored by our group.However,according to what we obtained from previous study,it reveals that mere cylindrical coil is unable to provide enough magnetic force needed to drive the needles along their working heights,nor can it help significantly for the stable suspension of working needles,due to the magnetic field intensity it induced decreased rapidly as the suspension gap enlarges.Our group has therefore put forward a new type of magnetic levitation drive mode with double coils of hyperbolic style as the drive segment,which is supposed to achieve larger-gap suspension and higher thrust.In this thesis,the electro-magnetic theoretical model has been studied,also investigated were the impacts of bending yarn tension,magnetic forces and magnetic coupling on the motion stability of needles,as follows.(1)Based on theoretical mechanics,the impacts that the variation of yarn tension during its communicate with needle has on moving needle have been investigated.Combined with theoretical modeling and ANSYS simulation,and with experimental data,yarn behavior has been predicted,and the theoretical model has been validated.(2)The central magnetic drive segment of the system has been studied.In order that the drive can provide a permanent and stable magnetic force for suspended needle,a mathematical model of the magnetic field induced by alien coil structure has been derived as well as a model for computing the magnetic force exerted on needle.The results gained from ANSYS simulation validate that co-axially arranged double hyperbolic coils with 2mm axial distance are able to complete the work of needle selection-they can levitate the object of 2.6g(an accumulative mass of a needle and a permanent magnet)and provide a comparatively stable magnetic suspension force for needle with 5% force deviation along the needle's working heights.(3)Magnetic-Force coupling between adjacent needles has been investigated within the system.Based on ANSYS magnetic-field simulation,the real-time coupling interaction between adjacent needle cylinders has been observed on each time step.After numerous attempts by revising the structural parameters of the cylinder,several simulation results are obtained,which can be utilized for future optimization of single needle cylinder.(4)Finally,the analytical results obtained from theoretical calculation and numerical simulation have been applied to make a real magnetic levitation prototype.Through real-time record of needle motion,the motion status of needles are also obtained.The experimental results indicate that this new type of magnetic drive mode satisfies the knitting process requirements of 5inch machine prototype containing 288 needles,with magnetic force deviation no more than 9.7%.In conclusion,by comparing the analytical results gained previously with subsequently experimental data,,the feasibility of this magnetic-levitation drive application on jacquard circular knitting machine has been validated. |
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