Abstract:

Objective Due to the friction between spandex yarn and guide nozzle and the variation of knit loop feeding length in knitting production process, the conveying tension of spandex yarn is uneven, often resulting in fabric horizontal strips, uneven elasticity, and even yarn breakage, wire turning and other phenomena. At present, the use of dynamic constant tension method for the transport control of spandex yarns is a new trend. In this paper, the friction mechanism and spandex conveying process characteristics are analyzed in depth, and a constant tension spandex conveying control scheme based on the double closed-loop method of speed and tension is proposed.
Method Based on the analysis of spandex conveying related processes, spandex tension model and hybrid stepper motor mathematical model were constructed with the proposed tension fuzzy PID control strategy. Simulink simulation and Recurdyn/Colink electromechanical joint simulation as carried out, and the implementation of constant tension spandex yarn transmission algorithm was elaborated.
Results The single-phase excitation transfer function of the two-phase hybrid stepper motor was calculated from the relevant parameters of the stepper motor, the syringe speed was set to 558.292 r/min, and the preset tension value was calculated according to the difference between the syringe speed and the spandex yarn conveyor. Setting the step signal input as 0.32 and a unit step disturbance at the 10th second to obtain the tension control step response curve(Fig. 12), it was found that spandex tension control using fuzzy PID had better performance, faster response time, and stronger anti-interference ability. In this paper, 30.8 tex spandex bare filament was used as the conveying object, the basic parameters were obtained by consulting the relevant reference manuals and literature, and the simulation parameters were set and the simulation was run. The overall tension fluctuation of spandex yarn using constant tension conveying control was small, and the vibration of spandex yarn was significantly suppressed during simulation, and the spandex yarn without constant tension conveying control (only let the spandex yarn conveyor follow the movement of the syringe barrel at a certain rotational ratio) showed large tension fluctuations as a whole, and the vibration of spandex yarn was obvious during simulation. Through the analysis, it can be seen that the spandex yarn controlled by the constant tension spandex conveying control in this paper was more stable, and the yarn vibration was suppressed to a certain extent, which has better performance. In order to further verify the reliability of the simulation and the feasibility of this scheme, an experimental platform was built for verification, as shown in Fig. 14 where the tension fluctuation of the control force without constant tension transmission was large and cannot be restored to the preset tension when encountering external disturbances (change of friction, touch of the adjustment master's hand). Using constant tension conveying control, the spandex tension basically fluctuates around 3 g, and can return to the preset tension in a short time when encountering external disturbances. Through experimental verification analysis, the reliability of the simulation and the feasibility of this scheme were proved.
Conclusion The tension control device has been installed on the RFSM20 seamless underwear machine of a manufacturer, and after several debugging, the spandex conveying control system operates correctly, and the spandex elastic fabric can be knitted normally. The woven spandex elastic fabric has excellent elasticity and the elasticity of each part is basically the same, and the cloth surface is flat and meets the elastic fabric standard. Experiments verify the adaptability and superiority of the control strategy, and the dynamic constant tension spandex transport control scheme has engineering application value.

Key words: electromechanical co-simulation, constant tension, fuzzy control, spandex conveying