Study On Forced Vibration Characteristics Of Underwear Knitting Needles

The knitting needle is the core executive component in the knitting mechanism of the underwear machine.The knitting process rotates with the needle cylinder and makes a forced lifting movement along the arc of the cam track.The vibration characteristics of the knitting needles during the knitting process are very important to the normal knitting of the underwear machine,but at this stage,there is a lack of corresponding research results on the vibration characteristics of the knitting needles during the knitting process.It is impossible to determine whether there is vibration in the knitting process of the knitting needle,nor to determine the frequency,amplitude and other parameters of the needle vibration,and it is impossible to improve the stability of the knitting needle from the perspective of vibration through corresponding means.In view of the above problems,this article has carried out research on the forced vibration characteristics of the knitting needles of underwear machine.Combining the characteristics of the slender needle size and thin wall of the underwear machine,the Euler-Bernoulli beam theory and finite element simulation software are used to analyze the modal characteristics of the needle in the free state.n the free state of the knitting needle obtained by the simulation,the first three-order vibration shapes are consistent with the theoretical ones.The corresponding first three-order simulation frequencies are 383.1 Hz,1019.0 Hz,and 1962.0 Hz,respectively,and the relative deviation from the theoretical calculation does not exceed 3.04%.According to the dynamic characteristics of the knitting process of knitting needles,the kinetic equation is established,and the relationship between the support reaction force and the cam inclination,friction,needle quality,knitting oil viscosity resistance,and horizontal acceleration of the needle cylinder is obtained.The elastic coefficient of the knitting needle itself needs to be considered in the transition process of the contact cam.The dynamic simulation model of the knitting needle knitting process was established by ANSYS finite element analysis software.The results showed that the vibration amplitude can be reduced by appropriately increasing the friction between the knitting needle and the inner wall of the needle groove.The longitudinal vibration response model of the knitting needle under the excitation of the cam foundation is established.The theoretical results show that there is a deviation between the knitting needle longitudinal displacement response curve and the displacement input curve,but the deviation range is not large,and the maximum deviation is 1.57%.Taking the tuck cam as an example,the longitudinal vibration response equations of the knitting needles in the upper resting and rising phases are obtained.From the response equations,we can see that the knitting needles vibrate during the upper resting and rising phases.By appropriately increasing the stiffness of the knitting needle and cam,the longitudinal vibration characteristics of the knitting needle can be improved.The Euler-Bernoulli beam theory and ANSYS finite element analysis software are used to analyze the lateral vibration characteristics of the needles with different extension lengths.Taking the RFSM20 underwear machine as an example,the maximum excitation frequency in the knitting process of the knitting needle is much smaller than the first-order natural frequency of the knitting needle,and there will be no resonance in the knitting process.Establish the lateral vibration model of the knitting needles with axial movement,and obtain the lateral vibration curve of the knitting needles during the knitting process.The finite element simulation model of the knitting needle is established based on the transient dynamics,and the simulation and theoretical calculation results are basically consistent.By appropriately changing the triangular inclination value,Adjust the transverse vibration characteristics of the knitting needle during the process of knocking-over and tucking of the knitting needle,It can reduce the lateral offset value when the knitting needle reaches the position of knocking-over,tuck,etc.Based on the impedance analyzer,the first three-order natural frequency test value under the free state of the needle is obtained.The value is basically consistent with the theoretical calculation result,and the maximum deviation is 4.7%.A high-speed camera was used to capture the transverse vibration frequency of the needle knitting process.Compared with the frequency calculated by the theory,the relative deviation of the test result did not exceed 7.64%,and the relative deviation of the frequency calculated by the simulation did not exceed 5.45%.The curves of displacement,speed and acceleration in the knitting process of the knitting needles are drawn.The experimental results show that there is a small vibration during the forced lifting and lowering of the knitting needles,which proves the accuracy of the theory and simulation model from the experimental point of view.The article carried out theoretical modeling and finite element simulation analysis on the vibration characteristics and dynamic characteristics of the knitting needles in the free state and during the knitting process,and designed an experimental platform for verification.The research results show that there is indeed vibration during the knitting process of the needles,By appropriately increasing the friction,reducing the needle slot gap,improving the stiffness of the knitting mechanism,and adjusting the cam inclination angle,the vibration characteristics during the knitting process of the knitting needles can be improved,and the stability of the underwear knitting process can be improved.