The most important part of the automatic weft straightener is that which detects weft distortion.

It is said that the performance of the distortion detector is equal to the performance of the automatic weft straightener.

As mentioned before, there are many fabrics having complex textures such as twill, satin, 3-D weave and Double Raschel.

To detect the weft distortion of many kinds of fabric is the biggest point in weft straightening.

The way to find weft distortion, is to position several detectors over the fabric width at appropriate intervals to detect skewed parts and bowed parts of weft distortion.

There are 2 kinds of detection, one is transmission detection that is to detect light transmission from the opposite side of the fabric and the other one is to detect the reflected light of a floodlight projector from the same side.

Since transmission detection is not affected by the condition of the fabric surface, such detection is a more precise and stable way than reflection.

For fabric that does not allow light through, such as blackout curtains, reflection detection is effective.

There are 2 kinds of detection mechanism in weft detectors, slit detection and moire detection.

Slit detection is effective for simple weaves such as plain weave however detection by the slit method is impossible for complex woven structures such as twill or satin for such fabrics the higher performance moire method makes detection possible.

(1) Weft detector.

Simple explanations of the slit detection system and the moire detection system that is a unique development of Seiren Electronics are as follows:

(A) Slit detection system

Utilizes angled slits to detect weft distortion.
With the newest technology, there is zooming slit detection that optically adapts itself to accommodate any fabric density or thickness of yarn.
With this zooming slit detector, detection is possible for high density woven fabric or fabric which does not easily show moire. (Fig-6)

Fig-6 Slit detector.

(B) Moire detector.

This is a system to detect weft distortion by utilization of the moire effect through a densimeter.

In the case of twill or satin, it is possible that weft straightening would be mistakenly triggered because the signal would be read not as a satin weave signal but a weft distortion signal.

To prevent this mal detection, it is necessary to consider fabric density.

With this moire detector, by specifying weft yarn density, it is possible to detect signals of only weft yarns. (Fig-7)

Fig-7 Moire detector.

(2) Floodlight projector.

As light sources, there are 2 kinds, one is by LED and the other is by reflector bulb. As mentioned before, detection by light transmission is more precise and stable than reflection but those high-density fabrics or 3D wovens, which it is difficult for light to pass through need more light to have precise and stable detection.

Also, a moire detector needs a wider range and much more light than is required for a slit detector.

Today, small size but very bright LEDs have been developed, but the light amount is still 1/5 of a reflector bulb, and detection performance is limited. Furthermore, in the case of LEDs, general distribution of the amount of light is not even, so, fabric construction becomes complex, unevenness makes for defects in detection.

Accordingly, Seiren Electronics, placing more importance on detection performance rather than the longevity of the lamp, is using a reflector bulb.