Optimizing Yarn Quality
A combination of different modular systems can provide optimal solutions for foreign matter detection in ginning and spinning operations.
Textile World Asia Special Report
M
odern manufacturing processes must produce right-first-time. This is of the highest
importance in fiber opening and preparation. In spinning, second-quality or contaminated yarns must
be avoided. One obstacle for top-quality yarn is the increasing amount of foreign matter and
particles. This article, based on experience and information of Germany-based machinery
manufacturer Trützschler GmbH & Co. KG, presents a modular approach to solving the problem of
foreign matter in ginning and spinning.
The nature and extent of foreign matter contamination are strongly dependent on the origin of the cotton. US and Australian cotton, which are 100-percent machine-picked, do not have significant problems with foreign matter. Cotton from Turkey contains many red ribbon-shaped contaminants. In China, mills are battling threads from bleached cotton as well as white fluorescent polypropylene (PP) ribbons. Cotton from Central Asia is contaminated with white, non-transparent packaging residues. These are just a few examples.
Battle Of The Systems
A number of foreign matter separators, each operating on different detection principles, are available on the market. In addition to different kinds of sensors, material presentation to the sensors and the method of illumination are approached differently. Each system is distinguished by a combination of these three characteristics.
Sensors
Photo sensors are relatively cheap sensors that are arranged in-line and detect differences in brightness in the passing flow of fibrous tufts.
Ultrasonic sensors, also arranged in-line, detect foreign parts with solid, sound-reflecting surfaces but cannot detect foreign fibers, threads and strings.
Color sensors, or 1-CCD (charged couple device) cameras, are line-scan cameras with a single CCD chip. These systems are used in office scanners. Sensitivity depends on the resolution of these cameras and the scanning width. Because these cameras work with three adjacent scan lines - red, green and blue - with a certain offset, the color recognition of moving objects is limited and results in a so-called color noise effect.
Much more effective, although more expensive, are 3-CCD cameras. Today, such systems are used in TV cameras. The three basic colors - red, green and blue - are separated by a prism and simultaneously directed onto three CCD chips. This system is also called a true-color system. Thanks to this simultaneous process, the variable speed of objects in the material flow no longer has a negative effect. Currently, 3-CCD cameras represent the high-end approach to foreign matter detection.
Illumination
Another important factor in determining object detectability is the type of illumination. Cameras, as well as the human eye, can only detect objects that distinguish themselves in color, contrast, structure or luster from cotton tufts. For this reason, the type of illumination applied in foreign matter separators plays an essential role. Today's standard is illumination units with fluorescent tubes operating in reflected light mode.
Ultraviolet (UV) light sources make white and other colorless foreign objects with stronger UV reflection clearly visible. The phenomenon is called fluorescence. Such objects may include pieces of polyester (PET), PP, or even bleached cotton treated with optical brighteners. With polarized reflected light and the corresponding camera filters, differences in surface luster of foreign objects can be detected. The system reaches its limits with dull objects.
Polarized transmitted light is the ideal system for detecting transparent and semi-transparent objects, such as polyethylene (PE) foil or PP fabric from bale packaging. The presence of these particles often results in the dreaded foreign fiber claim.
Material Presentation
The presentation of the fibrous material to the sensors also affects the performance of foreign matter separators. Almost all systems on the market monitor the tuft flow in a rectangular chute. One major disadvantage is the undefined velocity of cotton tufts and foreign objects. Since it is not constant, the downstream separation nozzles must be activated for a longer period of time. This inevitably results in an increasing loss of good fibers. However, one advantage that should not be underestimated is the gentle treatment of cotton fibers, which are not mechanically stressed. Systems that feature detection on or close to the surface of a rotating needle roll have three very important advantages: First is the accurately defined material velocity and, hence, the minimal loss of good fibers during removal. Second, accurately detecting the position of foreign objects is advantageous, as there are no problems due to differences in illumination intensity depending on chute depth, as is the case with chute-based systems. The third advantage lies in the high degree of material opening and the associated excellent exposure of the foreign objects. Figure 1 shows a schematic comparison of these different systems.
Figure 1: The application range of different foreign matter systems is a function of object size and optical properties.
Solution: Modular Systems
This close examination of the different sensors, illumination systems and methods of material presentations clearly shows there is no single ideal system. However, by using systems precisely adapted to the actual requirements, one can come very close to this ideal. An optimum solution consists of an intelligent combination of different systems. Trützschler has developed three modules that, individually or in combination, are integrated in different machines.
The Colour Module features high-resolution 3-CCD cameras and can be applied in conjunction with a chute as well as a rotating cylinder. In the latter case, even white, non-transparent PP objects can be detected. The high resolution of the cameras also ensures reliable detection of tiny threads and ribbon-shaped objects. The PP Module reliably detects transparent and semi-transparent objects in transmitted light mode. Here, the patent-pending polarized light method is applied. The module is said to be ideal if cotton is contaminated with PE foil or packaging residue from PP fabric. The Trützschler UV Module complements the other two systems if the cotton is contaminated with fluorescent objects from bleached cotton threads, PP or PET.
Figure 2 shows a comparison of the different modules, with four scenarios. The combination of these three modules with the cylinder and/or chute system led to the development of a new range of foreign matter separators.
Figure 2: Comparison of Trützschler's foreign matter detection modules: Each of the four pictures shows the same foreign objects and a cotton tuft in the center. By applying different sensors and illumination systems, the different objects can be detected.
Different Modules
For Different Requirements
Four solutions, each designed for specific applications, are available. The right decision depends on the particular requirements. The most important decision criteria are:
• nature and extent of foreign matter contamination;
• plant configuration;
• dust removal required;
• required detection and separation efficiency;
• investment costs;
• operating costs; and
• waste handling.
The foreign matter separator must fit into the plant concept. An optimal cleaning line is more than just individual units put together. Consequently, foreign matter separation must become an integral part of the cleaning line concept in a cotton gin or a spinning mill.
October/November/December 2009
The nature and extent of foreign matter contamination are strongly dependent on the origin of the cotton. US and Australian cotton, which are 100-percent machine-picked, do not have significant problems with foreign matter. Cotton from Turkey contains many red ribbon-shaped contaminants. In China, mills are battling threads from bleached cotton as well as white fluorescent polypropylene (PP) ribbons. Cotton from Central Asia is contaminated with white, non-transparent packaging residues. These are just a few examples.
Battle Of The Systems
A number of foreign matter separators, each operating on different detection principles, are available on the market. In addition to different kinds of sensors, material presentation to the sensors and the method of illumination are approached differently. Each system is distinguished by a combination of these three characteristics.
Sensors
Photo sensors are relatively cheap sensors that are arranged in-line and detect differences in brightness in the passing flow of fibrous tufts.
Ultrasonic sensors, also arranged in-line, detect foreign parts with solid, sound-reflecting surfaces but cannot detect foreign fibers, threads and strings.
Color sensors, or 1-CCD (charged couple device) cameras, are line-scan cameras with a single CCD chip. These systems are used in office scanners. Sensitivity depends on the resolution of these cameras and the scanning width. Because these cameras work with three adjacent scan lines - red, green and blue - with a certain offset, the color recognition of moving objects is limited and results in a so-called color noise effect.
Much more effective, although more expensive, are 3-CCD cameras. Today, such systems are used in TV cameras. The three basic colors - red, green and blue - are separated by a prism and simultaneously directed onto three CCD chips. This system is also called a true-color system. Thanks to this simultaneous process, the variable speed of objects in the material flow no longer has a negative effect. Currently, 3-CCD cameras represent the high-end approach to foreign matter detection.
Illumination
Another important factor in determining object detectability is the type of illumination. Cameras, as well as the human eye, can only detect objects that distinguish themselves in color, contrast, structure or luster from cotton tufts. For this reason, the type of illumination applied in foreign matter separators plays an essential role. Today's standard is illumination units with fluorescent tubes operating in reflected light mode.
Ultraviolet (UV) light sources make white and other colorless foreign objects with stronger UV reflection clearly visible. The phenomenon is called fluorescence. Such objects may include pieces of polyester (PET), PP, or even bleached cotton treated with optical brighteners. With polarized reflected light and the corresponding camera filters, differences in surface luster of foreign objects can be detected. The system reaches its limits with dull objects.
Polarized transmitted light is the ideal system for detecting transparent and semi-transparent objects, such as polyethylene (PE) foil or PP fabric from bale packaging. The presence of these particles often results in the dreaded foreign fiber claim.
Material Presentation
The presentation of the fibrous material to the sensors also affects the performance of foreign matter separators. Almost all systems on the market monitor the tuft flow in a rectangular chute. One major disadvantage is the undefined velocity of cotton tufts and foreign objects. Since it is not constant, the downstream separation nozzles must be activated for a longer period of time. This inevitably results in an increasing loss of good fibers. However, one advantage that should not be underestimated is the gentle treatment of cotton fibers, which are not mechanically stressed. Systems that feature detection on or close to the surface of a rotating needle roll have three very important advantages: First is the accurately defined material velocity and, hence, the minimal loss of good fibers during removal. Second, accurately detecting the position of foreign objects is advantageous, as there are no problems due to differences in illumination intensity depending on chute depth, as is the case with chute-based systems. The third advantage lies in the high degree of material opening and the associated excellent exposure of the foreign objects. Figure 1 shows a schematic comparison of these different systems.
Figure 1: The application range of different foreign matter systems is a function of object size and optical properties.
Solution: Modular Systems
This close examination of the different sensors, illumination systems and methods of material presentations clearly shows there is no single ideal system. However, by using systems precisely adapted to the actual requirements, one can come very close to this ideal. An optimum solution consists of an intelligent combination of different systems. Trützschler has developed three modules that, individually or in combination, are integrated in different machines.
The Colour Module features high-resolution 3-CCD cameras and can be applied in conjunction with a chute as well as a rotating cylinder. In the latter case, even white, non-transparent PP objects can be detected. The high resolution of the cameras also ensures reliable detection of tiny threads and ribbon-shaped objects. The PP Module reliably detects transparent and semi-transparent objects in transmitted light mode. Here, the patent-pending polarized light method is applied. The module is said to be ideal if cotton is contaminated with PE foil or packaging residue from PP fabric. The Trützschler UV Module complements the other two systems if the cotton is contaminated with fluorescent objects from bleached cotton threads, PP or PET.
Figure 2 shows a comparison of the different modules, with four scenarios. The combination of these three modules with the cylinder and/or chute system led to the development of a new range of foreign matter separators.
Figure 2: Comparison of Trützschler's foreign matter detection modules: Each of the four pictures shows the same foreign objects and a cotton tuft in the center. By applying different sensors and illumination systems, the different objects can be detected.
Different Modules
For Different Requirements
Four solutions, each designed for specific applications, are available. The right decision depends on the particular requirements. The most important decision criteria are:
• nature and extent of foreign matter contamination;
• plant configuration;
• dust removal required;
• required detection and separation efficiency;
• investment costs;
• operating costs; and
• waste handling.
The foreign matter separator must fit into the plant concept. An optimal cleaning line is more than just individual units put together. Consequently, foreign matter separation must become an integral part of the cleaning line concept in a cotton gin or a spinning mill.
October/November/December 2009
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优化纱线质量
现代制造加工业强调生产的一次性成功。这对纤维开松和前处理也是最重要的。在纺纱中，次级品或含杂质的纱线必须避免。生产优质纱线的一个障碍就是不断出现的杂质及颗粒。根
据德国纺机制造商特吕茨勒公司提供的经验和信息，本文提出了利用模块化的方式解决轧棉和纺纱过程中出现的杂质的难题。
根据棉花产地的不同，所含的杂质污染的成分和程度也不一样。美国和澳大利亚棉是纯机械摘棉，没有非常严重的杂质问题。土耳其棉主要含有红色的带状污染物。而在中国，工
厂疲于从漂白的棉花中挑出线或是荧光的聚丙烯丝带。中亚地区的棉主要含白色的不透明的包装残留物。以上只是一部分例子。
图1：不同杂质系统的应用范围是物质大小和视觉特征的一项功能。
各种系统之争
市场上有很多杂质除尘器，每一种都依据不同的检测方式运行。除了有不同种类的传感器外，原料呈现到传感器的方式以及照明方式也不一样。每一种系统都是这三类方式的不同组合而成。
传感器
光电传感器是相对比较便宜的传感器，它排成一列，可以检测到所通过的纤维状簇丛的不同明暗度。
超声波传感器也是排成一列，可以通过声音表面反射稳定的检测出杂质，但它发现不了异纤维及线带等。
色彩传感器，或叫1-CCD（电荷耦合器）摄像头，是通过一个单独的CCD芯片进行线性扫描的摄像头。这种系统也应用在办公室的扫描仪上。它的敏感度是基于这些摄像头的分辨率和扫描的幅度。由 于这些摄像头通过三条相邻的扫描线，红、绿、蓝，以某种确定的偏移量进行工作，移动物体的色彩分辨率是有限的，这就导致一个被称为色彩噪音的效果。而更有效的、也更昂贵的是3-CCD摄像头。今天，这 种系统被用于电视摄像机。三原色——红、绿、蓝——通过棱柱被隔开，同时被3个CCD芯片所检测到。这种系统也被称为真彩色系统。由于在同时进行，在原料流通中物质的不同速度不再是一种负面影响。目前，3 -CCD摄像头代表着最高端的杂质检测技术。
照明
决定目标可检测性的另一个重要因素是照明的类别。摄像头，也包括人类的眼睛，只能通过物质本身的色彩、对比度、形状和光泽度与棉簇丛的不同把它们区分出来。基于这种原因，应 用在杂质除尘器上的照明类别就起到一个重要作用。今天的标准是带荧光管的照明组件以反射光方式运行。
紫外线（UV）光源让白色和其它无色杂质有更强的紫外线反射。这一现象被称为荧光现象。这些物质可能包括涤纶（PET）、PP碎片，甚至是经过增白剂加工过的漂白棉。通过偏光反射光和对应的摄像头，杂 质表面光泽的不同可以被检测出来。但这一系统遇到晦暗的物质也有局限性。
偏光投射光是检测透明和半透明物质的理想系统，比如聚乙烯（PE）箔或来自包装材料的PP织物。这些颗粒的存在经常导致让人讨厌的杂质问题。
图2：特吕茨勒的杂质检测模块的对比：四张图片每一张显示了同一种杂质和在中心的棉簇。通过应用不同的传感器和照明系统，不同的物质能够被检测出来。
原料的呈现
纤维状原料呈现到传感器的方式也会影响杂质除尘器的效果。几乎市场上所有系统都是在一个矩形槽内监控簇丛的流通。一个主要的不利因素就是棉簇和杂质不确定的速度。由于它不是始终如一的，下 游的分离喷嘴必须经过更长时间才能激活。这一点不可避免的导致了不断增长的好纤维的损失。然而，有一个不容忽视的优势是对棉纤维温和的处理，它们没有受到机械挤压。表面有旋转针辊的检测系统有三大优势：首 先是精确的原料速度，由此最大限度的避免了在去除过程中好纤维的损失。第二，精确检测到杂质的位置很有好处，对于建立在斜槽系统的系统就不存在由于斜槽深度不同而亮度不一致带来的麻烦。第 三个优势在于原料开松率高，以及相应的极大的暴露出杂质来。图1显示了这些不同系统的对比。
解决方案：模块化系统
对于不同传感器、照明系统和原料呈现方式的封闭测试清楚的显示了没有一个单独的系统是理想的。然而，通过精确使用符合实际需求的系统，人们可以非常接近理想化状态。一 种优化的解决方案包含了不同系统的智能组合。特吕茨勒开发了三种传感器，有单独的，也有组合型的，集成到不同的机器里。
色彩模块带有高分辨率的3-CCD摄像头，能够与斜槽以及旋转滚筒结合应用。后者，即使白色的非透明PP物质也能被检测出来。高分辨率的摄像头也能确保可靠检测出细小线头和带状物质。P P模块能够通过投射光方式可靠的检测出透明和半透明的物质。补充一点，这种偏光方法正在申请专利。这种模块据说是检测被PE箔或PP织物的包装材料污染的棉纤维的最佳方式。特 吕茨勒UV模块是对其它两种系统的补充，如果棉是被漂白棉线、PP或PET等荧光物质污染的话。
图2显示了四种情况下不同模块的对比。这三种模块与斜槽或滚筒系统结合的结果是开发出一系列新的杂质除尘器。
针对不同需求的不同模块
目前有四种解决方案，每一种针对特别应用设计。正确的选择是根据特殊的要求决定。最重要的决策标准是：
• 杂质污染物的成分和程度；
• 工厂的结构；
• 要求去除尘埃；
• 确定的检测和除尘效率；
• 投资成本；
• 运行成本；
• 以及废料的处理。
杂质除尘器必须适合工厂的理念。最佳的清洁生产线不仅仅是把不同的组件放在一起。因此，杂质除尘器必须成为轧棉或纺纱厂清洁线上的一个集成部分。