FOURIER ANALYSIS

8 Automated Systems Techniques for On-Line Quality and Production Control in the Manufacture of Textiles Stantcho N. Djiev Technical University of Sofia Luben I. Pavlov Technical University of Sofia 8.1 Introduction 8.2 Automation of Basic Textile Processes Automation of Spinning · Automated Systems in Weaving · Automated Systems in Finishing 8.3 Distributed Systems for On-Line Quality and Production Control in Textiles Basic Concepts for On-line Control in Textiles · Approaches to Building Cost Effective Real-Time Control Systems in Textiles · Software Realization · Integrating Control and Manufacturing Systems in Textiles 8.4 Summary 8.1 Introduction Textile manufacturing involves a variety of sequential and parallel processes of continuous and discrete nature. Each requires precise, on-line control of preset technological parameters such as speed, pressure, temperature, humidity, and irregularity. On the manufacturing sites, these processes take place within separate machines or production lines where a relatively large number of operating personnel and workers are engaged. The intensities of the material flows: raw materials (fibers, yarn, and sliver), dyes, chemicals, ready production, etc., are substantially high, and this leads to heavy transport operations, inevitably involving costly hand labor. The raw materials processed in textile possess poor physical and mechanical properties concerning tensile strength, homogeneity, and others. This causes frequent stops in the technological process due to thread breaks, engorgement, winding of the material around rollers, etc.As a result, labor-consuming and monot-onous hand services are required for the proper operation of each textile machine. Statistics show that due to higher productivity and new technologies, the total number of machines at an average textile factory has decreased more than twice in recent decades [Baumgarter et al., 1989]. Nevertheless, the problem for replacing hand labor in textile manufacturing still remains a challenge in all aspects of process automation. © 2001 by CRC Press LLC Textile materials usually undergo many technological passages, leading to greater energy consumption and large amounts of expensive wastes, some of which may be recycled within the same process. Taking into account the above mentioned characteristics of the textile production as a whole, the following approaches for application of automated systems techniques in the field can be outlined. · Creation of new processing technologies and development of new generations of highly automated textile machines. · Application of highly efficient controlling and regulating microprocessor-based devices, integrated in to distributed control systems. This would ensure reliability of information and allow the implementation of standard industrial fault-tolerant information services. · Usage of industrial robots and manipulators for automation of the basic and supplementary operations, resulting in increased productivity and lower production costs. · Automation of transport operations for reducing the amount of hand work and process stops which often occur when sequential processes are badly synchronized. The optimization of machine speeds and loading is an important source for higher efficiency throughout textile manufacturing. · Development and implementation of new concepts and informational and control strategies, so that the highly automated and computerized CAD, CAM, CAP, and CAQ sub-systems can be totally integrated, forming a Computer Integrated Manufacturing (CIM) or a Computer Aided Industry (CAI) system. The resulting systems are not just a mixture of sub-structures, but process internal informational homogeneity, common software tools, databases, and other features. Usually, these systems are developed using systematic approach techniques. The CIM and CAI super systems and the level of their internal integration should be considered on the basis of the specific, and often contradictory, requirements of textile manufacturing. The development of automated systems in textiles, as a whole, can be summarized in the following four stages: The first stage is characterized by partial automation of separate machines or operations using conventional controlling devices. Such examples are the pick finders and cop changers in the weaving machines, local controllers of temperature, speed, pressure, etc. At this stage, a large percentage of handwork is still used. The second stage involves usage of automated systems for direct (most often digital) control of the technological process. This stage requires a greater reliability level of the equipment due to the centralized structure and remote mode of operation and data processing of these systems. Hand-labor is reduced by means of manipulators, robots, and automated machines. The automated control subsystems collect information from various objects and pass it to a central control unit while retaining control over the following. · Continuous control of local process parameters. · Timing registration and basic statistics for machines stops, idle periods, malfunctioning, etc. · The local systems produce alarm signals, or even stop machines for the operators if their abnormal operation affects the quality beyond preset limits or when dangerous situations occur. · Some indirect qualitative and quantitative indices are calculated or derived: materials and energy consumption, quality parameters of the ready production, actual or expected (extrapolated) amounts of wastes, etc. As a result, the central control unit produces and sends information in the form of data sheets, protocols, and recommendations to the operating personnel. This information is also stored and retrieved later for off-line decision support when optimizing and planning the material flows, machines loading, etc. The third stage is characterized by implementation of direct numerical control of many or all tech-nological variables using dedicated and totally distributed control systems. The term distributed here does not represent only the spatial dispersion of the control equipment, but rather, the fully autonomous © 2001 by CRC Press LLC mode of action of each controlling/measuring node while it is still connected with other devices through the industrial network. Local control units for data acquisition, processing, and retrieval, combined with intelligent field sensors, substantially increase the reliability of the automated system as a whole. The latter is usually built on a hierarchical principle, incorporating within itself several independently working layers. Nearly fully automated production lines are implemented at this stage using high production volume machines running at variable speeds, so that a total synchronization is achieved throughout. Computerized subsystems like CAD, CAQ, CAP, and others are implemented at this stage to different extents. There exists here some integration among them, using local area networks (LANs) and wide area networks (WANs). As a whole, the production facilities, although highly automated, do not yet exhibit substantial integration. The fourth stage involves the integration of the production in computer-integrated manufacturing (CIM) or computer-aided industry (CAI) systems. Due to the specific features of textiles and the dynamic changes in the stock and labor markets, this stage still remains a challenge for future development and will be discussed later in this chapter. 8.2 Automation of Basic Textile Processes Automation of Spinning Bale-Opening and Feeding Lines In the preparatory departments of the textile mills take place actions for bale-opening and feeding of the card machines. The transportation and unpacking of the incoming bales, e.g., cotton bales and ready laps involved much hand labor in the recent past. As an alternative, an automated cotton bale-opening machine is shown in Figure 8.1. It comprises two main assemblies: a motionless channel (see 10 in figure) for the cotton transportation and a moving unit (4) for taking off the material. This unit is mounted on the frame, (13) FIGURE 8.1 Automated bale-opening machine. © 2001 by CRC Press LLC which slides down the railway alongside the transportation channel. The cotton bales are placed on both sides of the channel. Approximately 200 bales with different sorts of cotton of variable height can be processed simultaneously. The take-off unit (4) is programmed in accordance with the type of the selected mixture. It takes off parts of the material by means of the discs (1), actuated by the AC motor (2). The depth of penetration into the bale is controlled by the rods (3). The pressing force of the unit (4) is controlled according to the readings of a pneumatic sensor. The signal is forwarded to a microprocessor controller (usually a general-purpose PLC) which commands a pneumatic cylinder (5) to change the elevation of the unit (4). The material then goes into pneumo-channels (8,9) and the transportation channel (10). The subsequent machines are fed through the channel (12) by means of a transporting ventilator.A magnetic catcher placed inside the channel (12)prevents the penetration of metallic bodies into the feeding system. The take-off unit (4) moves along the railway at a speed of 0.1–2.0 m/s, driven by the AC motor (7). It can make turns of 180 degrees at the end of the railway and then process the bales on the opposite side. The frame (13) and the bearing (14) accomplish this, while the position is fixed by the lever (15). The productivity of these machines approximates 2000 kg/h, and they usually feed up to two production lines simultaneously, each of them processing a different kind of textile material mixture. Automation of Cards Figure 8.2 shows a block diagram of an automated system for control of the linear density of the outgoing sliver from a textile card machine. The linear density [g/km] is measured in the packing funnel (2). The sensor signal is processed in the controller module (3/14), which governs the variable-speed drive (4) by changing the speed of the feeding roller (5); thus, long waves of irregularity (over 30 meters in length) are controlled. The regulator also operates the variable-speed system (6), which drives the output drafting coupled rollers (7) of the single-zone drafter (8). Long-term variances of the sliver linear density are suppressed by the first control loop. The winding mechanism (9) rotates at constant speed and provides preset productivity of the card. Automation of Drawing Frames The growing intensification of contemporary textile production resulted in the development of high-speed drawing frames for processing the textile slivers after the cards. The output speeds of the drawing frames often reach 8–15 m/s. This, together with the high demands for product quality, brings to life new techniques for development, and implementation of automatic control systems for on-line quality and production FIGURE 8.2 Card with automatic control of the output sliver linear density (closed-loop control system). © 2001 by CRC Press LLC FIGURE 8.3 FIGURE 8.4 Drawing frame with open-loop automatic control of the sliver linear density. Drawing frame with closed-loop automatic control of the sliver linear density. control. The processes here possess relatively high dynamics, and the overall response times, in general, are within several milliseconds.One of the principles used in that field is illustrated in Figure 8.3.An electrical signal is formed at the output of the transducer (1) under the action of the sensing rollers. This signal is proportional, to some extent, to the linear density of the cotton slivers passing through. The transducer is usually an inductive type with moving short-circuit winding. A high-frequency generator powers it to ensure greater sensibility. The sensor output signal is detected, to the balance emitter repeater, (2) and conformed to the input resistance of the memory device (3). The balance circuit (2) secures minimal influence of the ambient temperature and power voltage on the level of the sensor signal. The memory device holds the signal for the time required by the sliver to reach the drafting zone (9). Both the sensor signal and the speed feedback signal drive the phase pulse block (4) from the tacho-generator. (5) The thyristor drive system varies the speed of the DC motor (M) and thus, the drafting rate of the rollers (9). The electro-magnetic clutch (6) is used to couple the rollers (9) to the basic kinematics of the machine at startup. A time relay (7) is used to power the clutch, thus disconnecting the rollers and switching to variable speed. In this way, speed differences throughout the transition processes of starting and stopping the machine are avoided. Figure 8.4 shows an example of a closed-loop control system on a textile drawing frame. The sliver linear density is measured in the packing funnel using an active pneumatic sensor or alike. The signal is transformed and conditioned by the circuit (2) and compared to the setpoint value Uref. The latter is controlled manually via the potentiometer (3). The error (DU) is processed by the regulator (5) according © 2001 by CRC Press LLC ... - tailieumienphi.vn