| The driving mode of knitting needle is the key to improve the efficiency of circular knitting machine.The needle selection and driving process of the existing knitting circular machine are realized by the needle selection device and the triangle CAM mechanism.Due to the limitations of mechanical structure,material properties,device principle and other factors,this driving mode has become the bottleneck of further speed-up of circular knitting machine.To solve this problem,this paper combines the knitting principle and magnetic levitation technology to propose a new model of magnetic levitation direct drive knitting needle.The basic principle is that the knitting needle(which is connected to the permanent magnet as a whole)and the electromagnetic coil are combined to form a magnetic suspension hybrid system.The coil generates a controllable magnetic field when energized,and the permanent magnet ACTS on the knitting needle to drive the needle to complete the corresponding work position.For the magnetic levitation system,the combination of the hybrid drive model and the drive coil structure determine its performance.The high-performance drive model and structure can be obtained by establishing its mathematical model and performing finite element simulation analysis.In addition,multiple physical fields such as electromagnetic field and temperature field exist in the working process of single drive coil and its array,and the coupling effect makes the needle movement unstable.The finite element numerical simulation can be used to analyze the coupling and propose a decoupling method.so as to improve the system stability.Therefore,the main research contents of this paper can be summarized as follows:Under the requirement of sufficient driving force,in order to reduce the size of the driving coil and realize the compact array of the knitting needle,the finite element simulation analysis method was used to analyze the spatial magnetic field distribution of the finite length solenoid.The analysis results show that the magnetic field induction intensity was the maximum within the symmetrical range of 3 radius of the coil,and the attenuation was fast at the adjacent ends.Based on this,a suspension symmetrical hybrid driving model of the needle moving inside the driving coil is proposed.Compared with the traditional end ejection model,this model has a larger driving force and the radial size is reduced by one time.At the same time,in order to meet the requirements of the smooth movement of the knitting needle,according to the electromagnetic field theory,the mathematical model of the force of the knitting needle and the driving structure is established.By solving the mathematical relationship through Matlab integral function,a two-stage curved driving coil structure is obtained.Through simulation and experiment,it is found that the driving force of the structure is more stable than that of the cylinder.According to the designed driving model,the knitting mechanism,feeding mechanism,pulling and crimping mechanism and control structure of the magnetic suspension direct drive circular knitting machine were designed,and a 5-inch,32-needle and 2-way direct drive circular knitting machine with active synchronous feeding was established.According to the theories of electromagnetic field and temperature field,Ansoft Maxwell and Ansys Workbench finite element simulation platform were respectively used to analyze the magnetic field,temperature field and coupling process of the designed single drive coil and its array.Study found: double curved shape drive coil axial magnetic field intensity in knitting needle motion segment is larger,and uniform distribution,comply with the design requirements.But as a result of single drive coil external magnetic field exists divergence distribution state,so the array coupling between the magnetic field,which in turn reduce the knitting movement stability.Based on the principle of magnetic circuit,after using ferromagnetics shell material for shielding,can significantly reduce its interference degree,thus improve the movement stability knitting needle system.The temperature field increases from the primary to the secondary coil,and the temperature in the secondary coil area is the highest,while the heat flux at the heat conduction junction surface is the largest.Therefore,heat dissipation can be focused on this area to reduce the steady-state temperature of the system.At the same time,using the method of loose coupling,the magneto-thermal coupling process of single drive coil and its array was analyzed in Maxwell 3D and Steady-State Thermal module.The analysis shows that the coupling effect is weak when the single drive coil is excited by a constant current and the frequency is low,but when the frequency is fast,the coupling effect should be fully considered.For the array system,the magnetic-thermal coupling effect is obvious even the excitation change is small,which can make the array system temperature rise is about 7.5 ?.Therefore,its coupling effect should be fully considered in thermal design to dissipate heat sufficiently in the whole drive array system.Through the online knitting experiment,the knitting effects under different conditions of excitation voltage and frequency were compared respectively.It was found that when the excitation voltage was insufficient due to fluctuation,the driving force would be reduced,which would lead to incomplete knitting trajectory,and knitting errors would occur.When the excitation frequency is too high or too low,it will lead to the knitting needle track and yarn track stagger and knitting error.Therefore,for a knitting system,there is an optimal compromised excitation size and frequency,but it can be improved by improving the system response performance. |
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