Optical foreign matter detection in the fiber flow
In the late 1980ies in luxury garments contamination with plastic and coloured fiber in cotton products caused huge claims by consumers. Japanese buyers of luxury underwear complained when a black "hair-looking" fiber showed up in the fabric. One single black fiber caused, for example, a $ 100,00 claim. You can well imagine what damage caused a black piece of fabric that went to the gin. In America, this was never a hot topic as cotton was grown professionally in large field and automatically picked.In other countries, there is still hand-picking and farmers charge crops year by year, depending on where they see most profit.
When they use fertilizer, they often distribute the fertilizer from the back of a pick-up truck and the bags are lost in the field. When the cotton has grown in later years, these bags (out of synthetic) are then harvested together with the cotton. Another source for contamination is people and automobiles that travel through the cotton fields and leave waste. Plastic - when it is in a cotton fabric that is ironed - melts.
In the non-woven area we supplied scanners to customers that use viscose because this sometimes is stuck in the dryer and overheated and turns yellow. Also in some medical applications the scanner is used to avoid any visible contamination. These applications also use a line scanner on the final product. Usually one wants to detect and eject everything that is not white. We once had a customer where we had to eliminate everything that was not black. He delivered fibers for non-woven products for ladies.
In 1999, the Japanese company Tatsumi introduced the first contamination scanner ejector. In this machine an "aquarium" was filled with fibers. Then cameras took a picture and when foreign matter was detected, the whole content of the aquarium was sent into a box by a flap. This machine cost more than 500.000,00 D-Mark, needed an electronic specialist and was not very effective. Only a few machines were built, and Tatsumi is no longer serving this market.
In 1992 a friend who owned a spinning mill asked me to make a machine. This first machine, "OPTiSCAN", built the market. It was working continuously, was simple and introduced sectional ejection.
That means following the optic sensors there is an array of nozzles and only in the section where foreign matter is detected by the sensors, valves open and blow the foreign matter of of the goof fiber stream. e, By now, all scanner detections work by this principle. The improvements have been mainly in the camera sensors. A further step was the recognition of Perspex films. These fibers can cause the same melting problem and cannot be detected by normal cameras. They are nowadays detected by an additional module that uses the polarization effect or by systems that claim detection by higher frequencies.
What can be detected is determined by the opening of the fibers, the density in the observation area, the illumination and the resolution of the cameras.
Normally, pieces of 1 x 1 inch can be detected with a reliability of about 80 %.
Smaller pieces require more opening and more cameras.