There are several sensors and their light sources evenly distributed within the width of fabric. When
fabric runs through the sensors and bulbs of light source, each weft shall affect The brightness of the ray detected by The sensor. The receiver on the sensor can receive the alternative dark and bright signals, which shall be collected by the defector. After comparing and analysing, The angle of weft can be calculated and sent to The computer for treatment. The computer can judge The amount of bias and bowed weft from several sensors and drive the straightening actuator of'bias and bowed wefts immediately thus to straighten them automatically.