| The variable lead screw transmission mechanism is widely used in aviation and military industry,textile equipments,extraction equipments and medical equipments.With the trend of high speed,high precision of automation equipments,higher requirements on screw transmission mechanism are put forward.The special type of lead screw can be produced with the development of domestic NC machining technology.Viewing of the fact that the upscale rapier loom with variable lead screw weft insertion mechanism can’t yet be fully independent manufacturing and in order to promote the use and development of variable lead screw transmission mechanism in all areas,the variable lead screw weft insertion mechanism was taken as the research carrier in this paper.Kinematics analysis of it was carried out through theoretical analysis and virtual prototype test.Furthermore,a comprehensive analysis of the influence of clearance and flexibility was carried out in ideal rigid body model,rigid-flexibility model.The main work and results are summarized as follows:1)The general kinematics model of lead screw weft insertion mechanism was established.The inadequacy of the constant lead screw was analyzed by the gained output characteristic curve through MATLAB,pointing the necessity of introducing variable lead screw.A systematic design method for rapier displacement characteristic curve was presented based on the transformed trapezoidal acceleration curve.According to the actual working condition of weft insertion and the overall consideration of the peak acceleration,the peak velocity and the velocity of the critical point in weft transition area,the optimal parameters were selected.The weft insertion mechanism with the optimal parameters confirms a excellent weft insertion function.2)The axial displacement function about the rotation angle for the variable lead screw was obtained based on the curve fitting toolbox in MATLAB,and then got the parameter equation of helical curve in space.In order to facilitate the manufacturing of variable lead screw,the plane unfolded curve of helical curve in space was carried out on reverse decomposition and reconstruction based on the concept of Free Curve Reverse Subdivision Engineering.Finally,the original helical curve can be approximately equivalent replaced with several equal pitch helical lines.Under the given approximation accuracy,the reconstructed helical line does a good equivalent substitution to the original curve,greatly reducing the cost of manufacture and making process more easier.3)In order to improve the stability and accuracy of weft insertion mechanism,the influence of flexible component and clearance should be taken into consideration.The rigid-flexible model of lead screw weft insertion mechanism was built through ADAMS combined with ANSYS.Dynamics simulation was carried out by ADAMS.Considering the hinge clearance,the influence on the output characteristic curve of rapier was respectively analyzed for the rigid system and rigid-flexible system.A considerable Proportion of noise signal was discovered in the simulation data,in order to eliminate the influence of the noise signal,the abnormal value was identified by upper and lower quartiles and replaced by median.A new curve was obtained by the deviation value between the de-noised acceleration curve and the one in rigid system.This curve does a high frequency wave in a fixed interval,presenting a similar characteristic of periodic acoustic signal.The result shows that: the hinge clearance is the major factor to the stability and accuracy of rapier movement;the collision impact tends to be cyclical by the comprehensive effect of clearance and flexible component. |
