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Advanced extrusion control technology.

Manufacturers of extruded products face many challenges in today's competitive and high-tech world. Customers and end users have significantly increased their expectations and demands for quality response and service. The performance requirements of the products continue to expand while costs must continually be reduced. At the same time, labor force skill level and motivation generally are declining, facilities are aging and competition is getting tougher.

Fortunately, technology can provide the means to meet today's challenges and excel in the modern world market environment. New extrusion machinery is capable of higher productivity and quality and modern methods help to solve many problems. The greatest advances in new technology, however, that can offer solutions and maximize competitive advantage for manufacturers are in the area of computers, electronics and controls technologies.

All extrusion lines have basic control needs for temperature speed, pressure, measurement, etc. Primitive lines have separate control devices for each element and depend on the operator for line coordination. He establishes all settings and makes all the interactive decisions based on his observations and by using his training, experience and skill. A talented operator can make a good product on extremely primitive equipment, reacting to many conditions and events, but his breed is becoming extremely rare. Todays' world-class quality standards make demands beyond his capabilities and in effect make obsolete this approach to manufacturing.

Current technology uses two principle approaches to improving quality, productivity and consistency. The first is to establish uniformity in the process by eliminating variations in the equipment by using higher precision drive motor controllers, better temperature controllers and other types of controls that improve stability and accuracy. The second is through the use of closed loop feed back controls such as a laser diameter gage to control line speed. These approaches help the operator to keep the process under control, but still depend on his skill for set-up and direction. In addition to these equipment improvement approaches, most modern manufacturers have improved quality and productivity through the use of statistical process control methods. Primarily through the utilization of control charts, operators monitor and evaluate the process so that they can recognize conditions that lead to problems and take corrective action before quality is lost.

The latest state of the art control systems for the modern extrusion line go far beyond these concepts and use the power of modern technology to provide the plant manager. not just the operator the tools and controls necessary to insure maximum productivity, quality and reliability. This is accomplished through features that provide control, simplify operation, insure repeatability and manage information control. Control is provided in an integrated system that allows ease of connecting, cascading and changing interactive loops among the various devices in the line, as well as providing the highest performance available for each. Operation is simplified by using the power and flexibility of graphical operator interfaces with touch screen technology. Repeatability is insured by total system set point recipe storage and retrieval. Information management and processing, recognized as one of the most powerful tools towards quality and productivity improvement, is provided through data acquisition and storage of all pertinent parameters and conditions, which allows for trending graphs, SPC analysis and reports, both on and off line in real time or historically. By utilizing these latest advances in control technologies, astute manufacturers can successfully compete in today's demanding markets.

Modern control systems are commonly based on three different types of hardware. The first, the most popular and with the longest development history is the programmable logic controller, or PLC. These first appeared several decades ago as replacements for relay logic systems and featured "ladder logic" programming. Analog, digital, computer and specialized modulus along with more powerful programming languages have since been developed, allowing PLCs to evolve into highly capable controllers that are used in all industries to control all manner of processes. They are the most popular, most powerful and most flexible of available controller types. They have been specifically designed for high reliability in industrial environment, ease of maintenance and for flexibility of connectivity to equipment and other computers.

Major manufacturers of PLCs, such as Texas Instruments, Allen Bradley, GE, Seimens, Modicon and many others offer extensive support, training and service for their products throughout the world. Many third party engineering and service organizations also offer application and programming services.

The second common type of system is based on personal computer hardware, usually IBM compatible PCs. These have evolved primarily from the lab-test-bench and prototyping environments where ease of programming in basic engineering languages was the main consideration. A large variety of input/output boards and systems have been developed by an assortment of vendors offering a wide range of capability.

Many software vendors have developed control programs with concentration on data acquisition and screen display, such as Factory Link, Fix, Genesis, Wonderware, Lab Tech Notebook and many others. They offer more screen display and data handling features than PLCs. but suffer in control response and slower scan rates and do not have the durability or service support in hardware, making them questionable for industrial applications.

The third type of controls commonly found in the extrusion industry are proprietary systems. All components are manufactured by the system supplier and operate only on proprietary software. This type of system is very popular in the injection molding industry, where much more similarity exists between the various processes and installations than in extrusion. Systems that are designed specifically for extrusion and available and offer experience and required features, but they usually lack the extensive customer support offered by the major PLC manufacturers fall short on operator interface options and because of the large investment required, often lag the industry somewhat in technology.

The ideal control system is a combination of all these types, incorporating the best from each. Machine control is executed in a PLC in order to take advantage of the excellent response, reliability, service and flexibility. Specialized modules are used for special functions like parison control, temperature sensing and high resolution applications.

The PLC program can easily be changed to accommodate changes in equipment or process. The operator interface and data acquisition functions are managed by a PC based system linked to the PLC. This provides all the advantages of a PCs graphical screen display and it's data handling features.

Properly designed high resolution graphical touch screens greatly reduce training time and simplify operation of complex extrusion lines. Information can be displayed in the most clear logical manner to operators, either digitally or graphically. Data can be collected and analyzed using SPC techniques or in raw trends graphs for on-line and historical process evaluation. PCs can readily be networked to central systems or a supervisor's desktop for management tasks. Software written specifically for the extrusion industry completes the system.

Davis Standard's EPIC II control system is an excellent example of the latest in the application of controls technology and illustrates all of these advanced benefits. It is a result of over 10 years of evolution and revolution in the computerized control world, incorporating both in house and industry wide developments.

The system reflects the philosophy of an "open system" in that it is based on standard industrial components, a PLC for machine control and an IBM compatible computer for operator interface. This allows for changes in hardware or software to accommodate technology changes or customer requirements, provides maximum connectability to networks or other systems and allows a myriad of options including the ability to change the operator interface software from the EPIC II proprietary program to user configurable programs such as Factory Link, Genesis, Fix, Wonderware, or others.

The operator interface and data acquisition software offers all of the features necessary for the modern extrusion system including menus, custom graphics, reports, recipes, data logging and trending and full SPC capabilities. The graphic screens starts with a custom line overview which is a pictorial of the actual extrusion line. With just a touch to any screen area or line component, the screen "zooms" to that device, giving the operator all the control features necessary. Touching a barrel zone on an extruder screen, for instance, pops up a keypad on which the new temperature set point is entered.

Trending screens show historical data in line graphs for problems analysis and cause-and-effect investigation. SPC screens show X and R charts and display calculated Cpk values. Operating "buttons" for any device or action are drawn on screen as well as menu and feature selection buttons. The concept of touch screen graphics has proven over time and many installations to provide the simplest, most straight forward operating interface available. The system has a built-in interface for simple conncetivity to a standard ethernet PC network. Data files are stored in standard format for off-line PC software programs such as Lotus 123 or any of the many SPC packages available.

Each system is custom configured for it's specific application with full support for customers to help change configurations and to upgrade new features and revisions. Customers who have special needs or desire the independence of a user configureable program can optionally use software such as Factory Link, Fix or one of the others as part of the system.

The prudent manufacturer of extruded products must enlist the aid of the latest in control technologies in order to compete in today's difficult world market. Operator skill levels must be a major consideration and information manipulation and management is essential. In this fast-paced area of computers and electronics, it is vital that a system is "open", upgradable, flexible and supported by competent and dedicated suppliers.
COPYRIGHT 1992 Lippincott & Peto, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1992, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Author:Kramer, William A.
Publication:Rubber World
Date:Jul 1, 1992
Words:1595
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