The DIRECT activity (DIstributed Real-time ConTrol) aims at simplifying the construction of distributed real-time control applications by using object-oriented principles and tools. A control application is designed as a collection of real-time objects dis

Reinhold Kroeger

Fachhochschule Wiesbaden, Fachbereich Informatik

Kurt-Schumacher-Ring 18, D-65197 Wiesbaden, Germany

email: kroeger@informatik.fh-wiesbaden.d400.de

DIRECT: A Basis for

Distributed Real-time Control Applications1

The DIRECT activity (DIstributed Real-time ConTrol) aims at simplifying the construction of distributed real-time control applications by using object-oriented principles and tools. A control application is designed as a collection of real-time objects distributed over the nodes of a system. The objects are invoking each others operations. Interface definitions of object types are formally described using a standard interface definition language. Existing conventional subsystem implementations can be integrated and appear from the outside as a set of objects. Our testbed is an automated laboratory for analyzing environmental samples (WICIL, WIesbaden Computer Integrated Laboratory). The subsystems are connected via a two-level network based on CAN and Ethernet. The object-oriented layer is realized on top of a real-time operating system kernel. This paper provides an overview of the system design, the implementation approach, and reports the status of work.

1.Introduction

Distributed system structures for automation and control systems have become popular during the last years. Decentralized structures are considered as an alternative even in areas like control of a single machine spanning multiple aggregates. "Intelligent" sensors and actuators can be built cost-effectively based on cheap and powerful microcontrollers (e.g. SAB80C166, MIPS R3100) and low-level field busses (e.g. CAN). Open architectures which ensure interoperability between components of different suppliers and offer interfaces to non-real-time higher-level environments for production planning, monitoring, and quality control are a must already. For complex applications, it will not suffice to reuse traditional centralized system structures combined with remote I/O over a fieldbus. A new generation of open control systems is needed, based on a cooperation-oriented paradigm.

1Proc. 1. Int. CAN Conference, Mainz, 13.-14. September 1994, CAN in Automation, 1994

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