Constant Tension Yarn Feeding Control System Of Weft Knitting Machine Based On Vector Control

Yarn tension is a critical parameter in the textile process,its fluctuation directly affects the fabric quality.The traditional negative and positive yarn feeders have problems such as large fluctuation of yarn tension,yarn tension and yarn speed can not be arbitrarily adjusted.Therefore,this paper deeply analyzes the mechanism and influencing factors of yarn tension,and proposes a yarn feeding control system which can feed constant tension yarn for circular knitting machine.Firstly,through the mathematical modeling of yarn tension,its formation mechanism and influencing factors are clarified.Based on this,a constant tension yarn feeding control strategy is proposed.The system uses PID controller to control the speed loop of the yarn feeding motor in the inner closed loop and Active Disturbance Rejection controller to control the tension loop of yarn in the outer closed loop.Both of them constitute the inner and outer double closed loop control system of constant tension yarn feeding on circular knitting machine.Among them,the Active Disturbance Rejection Control technology is used to obtain real-time yarn dynamic index,and combine each yarn dynamic index through a nonlinear combination method to obtain the corrected reference speed of the yarn feeding motor.The reference speed is finally applied to the yarn feeding motor through the Field Oriented Control technology.It is used to adjust the yarn feeding speed and ensure that the yarn tension is maintained near the set value.Secondly,the hardware and software design scheme of the constant tension yarn feeding system was determined.At the hardware level,with ARM processor as the core,the yarn tension signal sampling circuit and the full bridge drive circuit for the yarn feeding motor were designed.Based on the structural characteristics of the circular knitting machine,a CAN communication bus was designed to support communication between the main controller of the circular weft machine and each yarn feeder;At the software level,a constant tension yarn feeding internal and external dual closed-loop control system was designed.The inner loop uses PID controller to achieve closed-loop control of yarn feeding motor speed,while the outer loop uses the Auto Disturbance Rejection Controller to achieve closed-loop control of yarn tension.In order to reduce the effect of torque pulsation on the yarn tension,the Field Oriented Controller was designed to achieve stable driving of the yarn feeding motor.According to the actual project requirements,the CAN bus communication instruction format has been customized and corresponding encoding and decoding programs have been designed.Finally,an experimental platform was built to test the tension control performance of the yarn feeding system under various working conditions.From the test results,it can be seen that the constant tension yarn feeding control system can be used for circular knitting machine to feed yarn with small tension fluctuation,both the feeding speed and yarn tension can be adjusted arbitrarily.It also has achieved better results in controlling yarn tension fluctuation and overshoot,which can meet the process needs of circular knitting machine under different working conditions.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.Considering the large fluctuation of yarn tension under high-speed feeding conditions,optimizations should be made for the wire storage disk of the yarn feeder for yarn with small diameter and weak tensile resistance,such as the winding path,the number of winding turns,the roughness of the contact surface of the wire storage disk,etc.