Development of a novel type of online monitoring 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 (bobbin carrier independent) and works by contactlessly detecting the position of the lever of the yarn tensioning mechanism 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 in a braiding machine can be calculated. Validation experiments of the module on a stationary test stand which simulates the unwinding process during braiding were conducted. 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. For carbon fibre yarns, the sensor module detected an unusual rise in yarn tension at least by the time 510 mm of yarn remained to be unwound from the bobbin until the final yarn breakage occurred. Thus, the sensor module is capable of identifying irregularities soon enough before major braiding defects evolve. However, the lead times were significantly shorter when investigating polyester yarns. If a high detection reliability is required for this kind of material, the number of sensors needs to be increased or additional sensor modules have to be put in place.