关键词: 恒张力, 输纱器, 无刷直流电动机, 磁场定向控制, 自抗扰控制, 圆纬机

Abstract:

Objective Yarn tension is a critical parameter in the textile process, and its fluctuation directly affects the fabric quality. Aiming at the problems existing in the yarn feeding mode of circular knitting machines, such as large fluctuation of yarn tension, unadjustable yarn tension and feeding speed, a new yarn feeding control system based on active disturbance rejection control is proposed.

Method Through the mathematical modeling of yarn tension, its formation mechanism and influencing factors were clarified. Based on this, a series of design schemes were proposed, such as the control strategy of feeding with constant tension, the main hardware structure of the system, and the closed-loop control algorithm of yarn tension. The system used PID controller to control the speed loop of the brushless direct-current (DC) motor in the inner closed loop and and active disturbance rejection controller to control the tension loop of yarn in the outer closed loop. Both of them constituted the inner and outer double closed loop control system of constant tension yarn feeding on circular knitting machine. Among them, active disturbance rejection control technology was adopted to obtain real-time yarn dynamic index, and to combine each yarn dynamic index through a nonlinear combination method to obtain the corrected reference speed of the brushless DC motor. The reference speed was finally applied to the brushless DC motor through the field oriented control technology. It was adopted to adjust the yarn feeding speed and ensure that the yarn tension is maintained near the set value.

Results The yarn feeding test showed that the system achieved better results in controlling yarn tension fluctuation and overshoot. Taking the first group of experiments as an example, the yarn tension overshoot decreased by 50% and 54%, respectively, and the standard deviation of tension fluctuation decreased by 15% and 25%, respectively. The second group of experiments also reflected this rule, and it also showed that the fluctuation of yarn tension increased significantly with the increase of yarn feeding speed. When the target yarn tension increased by 52% instantaneously, the actual yarn tension reached the target yarn tension without obvious overshoot within 70ms. At the same time, the tension showed good real-time and following performance during continuous changes. In case of sudden change of yarn feeding speed, the yarn feeder reacted quickly to ensure that the yarn tension was still maintained close to the set value, and the yarn tension overshoot during the speed change process was controlled within 20%. In addition, the feeder also demionstrated good performance of constant tension control for elastic and non-elastic yarn. The test results suggested the suitability for the constant tension yarn feeding control system to be used for feeding yarns with small tension fluctuation and readjustable yarn feeding speed and yarn tension, which meets the process requirements for the circular knitting under different working conditions.

Conclusion The new constant tension yarn feeding control system plays an important role in improving the intelligence of circular knitting machine, reducing the surface defects of fabrics, improving the elastic evenness of fabrics, and reducing the yarn breaking rate. The yarn feeder has the characteristics of programmability and wide range of yarn applications. It can also be conveniently applied to automatic winding machine, hosiery machine, seamless underwear machine and other textile equipments. Considering the large fluctuation of yarn tension under high-speed feeding conditions, a series of optimizations should be made in future research for the wire storage disk of the yarn feeder for yarns with small diameter and weak strength, such as the winding path, the number of winding turns, and the roughness of the contact surface of the wire storage disk.

Key words: constant tension, yarn feeder, brushless direct-current motor, field oriented control, active disturbance rejection, circular knitting machine control