摘要
纬编针织机编织系统在运行过程中导针片和织针与三角发生的冲击和碰撞现象，会引起导针片和织针的位移曲线偏离理论轨迹，影响编织效果。大量的冲击和碰撞还引起导针片和织针磨损，甚至疲劳断裂，极大的降低了系统的稳定性和工作效率。随着现代纬编针织机械朝着高速、高性能的方向发展，对其编织系统进行建模和动力特性分析，以及对其控制策略进行研究具有重要的理论价值和工程指导意义。
论文首先概述了圆型针织机的织针与三角间冲击特性的理论分析和实验检测相结合的国内外研究现状和进展。以横机和无缝内衣机为例分析了纬编针织机的工作原理，得出纬编针织机的三角与织针在编织过程中的冲击和振动问题是纬编针织机研究的核心内容。
提出了成圈、集圈、移圈工艺的理论模型，给出了织针运动的理论曲线。以单自由度系统从动件与几何封闭的凸轮机构模型为编织系统的动力学模型，研究了织针和导针片与三角之间的受力、碰撞、冲击等问题，并给出动力学方程。
分析了在运动过程中导针针踵与三角凸轮轮槽工作表面发生的横越冲击问题。得出横越冲击速度与加速度变号点的跃度的立方根成正比；碰撞速度与凸轮轮槽间隙的大小成正比关系。建立了织针、导针片、三角的动力学模型，运用有限元软件进行瞬态动力学仿真。
以高速成像测速实验的方法进行实验研究，使用高速摄像仪得到织针在成圈方向上的位移图像，通过图像处理得到位移、速度、加速度等实验数据，最终通过MATLAB软件进行数据处理，并得到织针针钩在成圈方向上的位移、速度、加速度、跃度等运动特征曲线。分析实验结果可知，织针与三角的冲击在初始点和最大升程点存在大量振动。
随着纬编针织机智能化水平的不断提高，控制策略的研究已成为高性能针织机研究的核心内容。考虑到纬编针织机的织针与三角凸轮的动力学特性，提出实时针位置跟踪算法，并运用前瞻控制理论，提出一种机器变速运转的最佳控制方法。控制策略的提出进一步弥补了由于机械加工、安装等引起的动力学响应无法达到理论设计要求的缺陷。核心控制算法对纬编针织机的稳定性和可靠性将起决定性的作用。
论文对纬编编织工艺理论分析、三角凸轮轨迹优化、导针片和织针的受力分析、编织系统动力学特性分析，以及纬编针织机核心控制算法的研究等方面具有一定的参考价值。
There are quantities of contacts and impacts between knitting needle or guide needle andcam, especially when weft-knitting machine is running at high speed. It leads to knitting needle’sdisplacement departure comparing with its theory track, and it makes system instabilityinefficient as well as fatigue fracture due to the abrasion of knitting needle and guide needle. Withthe development of weft-knitting machine towards high-speed and high-performance, it isbecoming increasingly important to analyze the modeling and dynamic of knitting mechanismssystem and control strategy.
The domestic and international research actualities of circular weft-knitting machine’sdynamic characteristics between knitting needle and cam have been summarized; the theoreticalanalysis and experimental testing of impact properties have been discussed. Weft-knittingmachines, such as the knitting system mechanism of the flat knitting machine, glove machine,circular knitting machine, seamless underwear machine and hosiery machine, have beenanalyzed. The impact and contact of the triangle, knitting needle and guide needle is the core ofthe weft-knitting machine.The theory models of looping, tuck and loop transfer technology, as well as the theoreticaldisplacement curve of the knitting needle movement theory displacement, have been proposed.As one follower and form-closed cam mechanisms for weft knitting machine knitting systemtheory model with a single degree of freedom system; focus on the force, contacts and impactsbetween knitting needle or guide needle and cams. The kinematic equations and dynamicequations of the system model have been proposed, and then solve the equations with the Fourierseries method and mode superposition method.
Across impact has been analyzed between guide needle-butt and working surface of thetriangular cam wheel groove. Impact velocity increases with the increase of the cam wheelgroove gap. The velocity of traversed impact and acceleration change point is proportional to thecube root of the jerk. Dynamic models of knitting needle, guide needle, needle bed and camshave been proposed. Transient dynamics simulation result is in accord with the theoretical curvein the trend using finite element software.
On the basis of experimental study, the displacement photographs of needle in the directionof knit have been obtained. Experimental results, displacement, velocity, acceleration, etc, havebeen processed by the image processing software. Finally, the displacement, velocity,acceleration and jerk movement characteristic curve in the knitting direction of the needles hookshave been obtained by the MATLAB software. The analysis of experimental results, the impactof the needles and the cam repeatedly occur at the initial point and the point of maximum lift. The model has been improved validity by comparative analysis of the motion characteristics ofthe key points.
With the continuous improvement of the weft knitting machine intelligence level, the controlstrategy has become the core topic of the high performance knitting machines. Taking intoaccount the dynamic characteristics of the weft knitting machine needles and triangular cam, theproposed location of the real-time needle tracking algorithm and look-ahead control theory havebeen proposed. The control strategy compensate for the theoretical design requirements cannotbe achieved due to the dynamic response caused by mechanical processing, installation and other defects. The core control algorithms will play a decisive role in the stability and reliability of theweft knitting machine.
The study has a certain reference value on the weft knitting machine weaving theoreticalanalysis, cam trajectory optimization and stress analysis of the guide needle and knitting needles,weaving system dynamics analysis and the core of the weft knitting machine control algorithm.
引文
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