Flexible Automation in Textile Manufacturing
In most sectors of textile manufacturing, automation is one major key to quality improvement and cost competitiveness. Early modernisation and technical developments in textiles concentrated on the automation of individual machines and their processes. Here, all process and machine variables were identified and placed under the surveillance of monitors or microprocessors. The machine and operating parameters of acceptable change were studied and programmed to control the quality and reproducibility of materials being produced.
The next step involved the inter-linking of sequential machinery processes. Progress has been made in connecting operations such as yarn spinning systems, but considerable technical improvements are required to achieve fully automated textile mill operations. Table 1 depicts the history of technological evolution in the textile industry.
A look at the 1990s gives evidence of where it is going. Throughout the 1990s, Computer Integrated Manufacturing (CIM) and Flexible Manufacturing Systems (FMS) has been the dominant production philosophies of the textile and clothing industries, both in developing and in developed countries. The ultimate goal seems to be the fully automated textile mill. On the whole, the industry has moved from the era of computer applications in textile operations to the era of computer integrated textile manufacturing.
The main objectives of Computer Integrated Manufacturing (CIM) are first to provide accessible information for every sector of a plant for the efficient management of the various stages of production, second, to provide facilities for planning and control at strategic points, available for the directors, managers and supervisors to make decisions and third to have compatible sophisticated high technology systems - particularly software - so that computers can talk to one another within the network, and modules can be linked with other modules, accepting additional work stations as the business grows.
(1) FIBER MANUFACTURING:
A major direction for evolutionary change in extrusion technology is the continuing integration of extrusion with downstream processes. Today, it is possible to find commercial examples for spin-draw-wind, spin-drawwarp and spin-draw-textile processes. These technologies place a different emphasis on material handling requirements; robotic technologies for package doffing and transport are increasingly available and yet because of the linking of processes, need be placed only at critical points in the overall process.
The emphasis on flexible manufacturing, even in the fiber industry, has led to the development by some fiber producers of robotic techniques for the rapid change and replacement of spin packs and spinnerettes. In these examples, robots are called upon to do what humans cannot do - change hot parts before they have cooled.
Automated inspection of yarn packages for broken ends, poor package building, and improper tensions and misidentified packages is a goal being pursued by a number of fiber producers.
The history of the man-made fiber industry has emphasized process control more than any other segment of the textile operation. Increasing emphasis on product uniformity and adherence to quality standards continues to require fiber diameter monitoring, temperature and tension control, and monitoring of the solution properties of the polymer. These requirements are especially critical in micro-denier fiber extrusion, a process that produces fibers and eventually fabrics of truly different properties.
(2) YARN MANUFACTURING:
Computer Integrated Manufacturing Systems are available that monitor and/or control practically all yarn production processes from opening and blending to spinning, winding and twisting as shown in Fig.1. Applications include inventory control, order tracking, maintenance control, budgeting, mill management and many others. Most companies now offer advanced controls on opening, blending, carding and other fiber preparation equipment, which are compatible with CIM. Ring spinning machines with individual spindle drives are available and these offer great flexibility and will readily fit into the CIM concept. Sliver weights can be controlled and the levels changed by on-machine electronics that can readily be connected to a computer network.
On-line quality control in carding and drawing can perform spectral analysis and determine the cause of problems based on the frequency analysis of the defects. Yarn spinning is now so automated that a large spinning mill can be operated by a very small number of people since automatic end piecing and automatic doffing is performed by robotic mechanisms.
One of the world's most advanced examples of CIM applied to a spinning mill is Kondobo-Murata CIM mill at Horigane in Japan. The nucleus of Horigane plant is Murata's Link Coner Spinning/winding link system, while their 'Sky-Rev' automated inter-process transportation system operates between the post-carding sliver and ribbon-lapping and combing and again takes over to provide the automated transport link between combing and drawing.
(3) FABRIC MANUFACTURING:
Weaving and knitting machine builders have been leading the way in utilizing computer technology in textile manufacturing for many years with their use of CAD, bidirectional communication and artificial intelligence. With the availability of electronic dobby and jacquard heads, automatic pick finding, and needle selection etc. these machines are the most easily integrated into computer networks of any production machines. Bi-directional communication systems can be used to control many functions on a weaving machine. As Fig.2 shows a CAD system can be used to develop the fabric to be produced and the design can then be transmitted over the network to the production machines to produce the desired fabric. Now, the design instructions can even be sent by modem from one country to a weaving machine located anywhere else in the world. A weaving machine capable of receiving and responding to instructions in this way can therefore be operated in a developing country while the designs it is weaving are originated and controlled, long-distance from a developed country. These technologies can greatly reduce the time needed to produce a fabric and give true meaning to the term 'quick response'. Weaving also is the area where artificial intelligence is progressing the fastest with developments such as expert systems to assist in troubleshooting looms.
In the 1990s, due to remarkable progress in computer technology, the application in sizing machines has increased to a greater extent such as multi-point thermo sensors for energy saving, automatic control of squeezing pressure, size pick-up detectors, multi-functional counters etc. Sizing machine control systems provide a tool for management to insure that all warps are sized identically under standard operating conditions. These monitoring and control capabilities can be included in a computer network of a weaving mill as shown in Fig.3.
For years knitting machine manufacturers have been making excellent use of electronics to provide machines that are more automatic and versatile and many refinements of these advances have been made. These automatic machines are already 'islands of automation' that can be incorporated into a CIM network.
Automated weaving plants are on the drawing boards. None is yet in operation but should be a reality within a few years. The six production steps winding, warping, sizing, weaving inspection and packing include 16 points of automation. Of these, 12 deal with materials handling or transport. Only four applications deal with automating the machine operations themselves. This includes automated process control on the slasher and the weaving functions of (1) Automatic Pick Repair (2) Automated Warp breakage Locator and (3) Computerised Machine control. Manual assistance is still required for beam replacement and repair of warp breaks.
(4) TEXTILE DYEING:
The automatic control of dyeing machines dates well back into the 1960s, and each succeeding year has shown miniaturization and enhancement in the management of information on a timelier basis. The automation started with the introduction of a system that controlled a set temperature by switching heaters on or off. A short time later these were replaced by systems that controlled the dyeing cycle according to a time/temperature sequence. The processes of dye and auxiliary chemical addition as well as loading and unloading of textile materials were also automated to result in automated dye-house management. A monitor displays scheduling for any machine and allows the operator to arrange the next lot. Batch weighing updates inventory each minute and give inventory of each dye by bulk and container. Any errors later in the process can be traced to a particular container if it should become necessary.
Now, the jiggers have been fully computerized with total control over process. In the pad-batch dyeing system, the most outstanding development is special dye dispensing system, on-line color monitoring and dye pickup control.
The knowledge-based methods are becoming increasingly significant in the field of dyeing process automation. Essentially Neural Network and Fuzzy Logic are frequently being used. The Glen Raven's new automated dye-house near Burlington, N.C. is among the most robotized plants in U.S. textile industry. In the plant automated system directs the entire manufacturing process from dyeing to loading and unloading yarns. It knows what color and how much dye to add, when to mix it and when and where to route the yarn for the next step in the dye process. The system creates a highly effective and extremely efficient facility. Also, in India, a State-of-the-Art Indigo Dyeing Plant can be remotely operated and diagnosed for any maintenance across the globe.
(5) ON-LINE QUALITY CONTROL:
An important factor in the success of automated textile mill is on-line quality measuring, monitoring and controlling. More and more instrument companies have devices to perform these tasks while they were applied externally when introduced several years ago, today they are being incorporated internally.
The importance of on-line monitoring and quality control cannot be over emphasized. With the high rates of production now achievable, any off standard condition can produce large quantities of second grade material. This can represent non-recoverable value added production costs as well as the loss of full priced, first grade products. Should the off standard material remain in the production line, further deterioration in product quality such as, foreign-matter, broken filaments, slubs or unevenness can be expected in down-stream processing. Additionally, machine stoppages can occur. It is essential to incorporate on-line quality detectors that can measure quality on a continuing basis, adjust machine settings within prescribed tolerances to maintain nominal quality parameters, or stop production if automatic corrections cannot be made.
Recent advances in imaging technology have resulted in inexpensive, high quality image acquisition and advances in computer technology allow image processing to be performed quickly and cheaply. This has given rise not only to a number of developments for laboratory quality testing equipments for fibers, yarns and fabrics but also to developments of on-line equipments for continuous monitoring of quality in textiles such as Fiber Contamination Eliminator, Intelligent Yarn Grader and Automatic Fabric Inspection.
The Above article is an extract from ITCTI (Information Technology Centre for Textile Industry) Monograph. And published under authorization from ATIRA.
· PB Jhala & RM Sankar