Investigating the unwinding behavior of technical yarns and development of a new sensor system for the braiding process

A new cost-efficient sensor module for the detection of thread tension anomalies in braiding machines was developed. The sensor module is mainly attached to the body of the braiding machine and works by contactlessly detecting the positions of the levers of the yarn tensioning units of the bobbin carriers through magnets and stationary Hall effect sensors as the bobbins pass by. This way, time-discrete estimations of the tension of the moving braiding yarns can be calculated. The sensor module was validated by investigating the unwinding behavior of several kinds of technical yarns from bobbins on a stationary test stand which simulates the unwinding process during braiding. Flawless reference measurements revealed that the signals from the Hall probe are in good agreement with precise yarn tension measurements obtained simultaneously from a deflection roller based yarn tension measurement device. Further measurements with purposefully provoked unwinding-related irregularities showed that braiding defects are foreshadowed by prominent variations in yarn tension which the Hall effect sensors are able to detect. Finally, experiments with the sensors installed into a running braiding machine were conducted. In this near-production environment, the sensor module was capable of identifying irregularities soon enough before major braiding defects evolved. (paper)