Structured development of a generic workstation controller

Abstract

Developing Computer Integrated Manufacturing controllers is a complicated design activity. It requires mastery of the formidable complexity of manufacturing environments as wellas of the hardware and software components required to build the controllers. We discuss system engineering techniques that can be applied to structure this complexity into manageable design phases.The starting point is a conceptual design of a factory wide Cl M system, which describes, in manufacturing terminology, the tasks, information requirements, and performance requirements of a suite of Cl M controllers. Formal, structured techniques are then available for translating the conceptual description of controllers to their detailed requirement specifications, design and computer based implementation. We demonstrate the translation techniques by reviewing the development of a particular Cl M component, a workstation controller, currently in industrial use. IntroductionMany commercially available factory controllers for CIM provide computer solutions for industrial automation: general purpose computer systems which have been tailored for the factory environment with real-time operating systems, graphics support, and a large number of I/O ports (Allen-Bradley 1987,Society of Manufacturing Engineers 1988). While such platforms are useful ingredients of a CIM system, they do not relieve the user of the burden of developing complex manufacturing control solutions. Developing such CIM applications is difficult, since it requires a rare combination of skills: mastery of the formidable complexity of manufacturing, as well as system engineering.We participated in a company-wide programme to develop a suite of CIM controllers. Unlike the computer solutions mentioned above, these controllers provide manufacturing control solutions: applications software to control a transport system, control a warehouse, schedule operations, etc. The programming effort required by the user to tailor these controllers for specific factories is minimal. The controllers have other advantages as well. For example, user interactions with the controllers use manufacturing terminology rather than computer terminology. Furthermore, the CIM controllers are generic, and hence applicable to a wide variety of situations, including the handling of new products. Finally, the controllers can easily be integrated into a factory-wide CIM system responsible for a variety of control tasks such as machine control, machine maintenance, and scheduling, because they can exchange information according to specified protocols.