Modern factory facilities are characterized by highly flexible manufacturing cells and highly dynamic processes, where clusters of fixed or moving sensors and actuators have to be controlled in a limited space under stringent real-time and reliability constraints. In such demanding industrial environments, wireless systems can also be beneficial by improving flexibility, cutting cables, and enabling solutions, which are cumbersome or even not possible to realize with wireline systems, especially in controlling moving or rotating parts. In this paper, we present a conceptual study of a wireless real-time system dedicated for remote sensor/actuator control in production automation. System development is based on user requirements, which were extracted from customer interviews and a market research. Low level measurements of frequency-and space-selective wireless channels in a factory-like environment were carried out. System design aspects, i.e., network topology, multiple access schemes, and radio technologies, will be thoroughly reviewed. The performance of a first prototype implementation will be discussed with emphasis on timing behavior and power consumption, as sensors and actuators of the wireless system are intended to operate without power lines or batteries.Index Terms-Factory automation systems, multipath radio propagation, real-time communications, wireless sensor/actuator network.
The AS-Interface (AS-i) is a simple and costeffective network solution connecting simple I/O devices to the upper fieldbus levels. A fully loaded AS-iVersion I network with one master and 31 slaves has a maximum response time of 5 ms per I/O. The AS-Interface has been chosen as reference system for the development of a wireless fieldbus gateway, which will be presented in this paper. Standard modules have been employed to achieve a price-competitive solution. A high reliability level with wireless system can only be achieved if radio wave propagation characteristics and coexistence to other radio services are taken into account. Especially wireless local area network (WLAN) technologies already installed in the field can affect proper sensor/actuator network operation. Therefore bit and frame error probabilities in the presence of WLAN systems also have been investigated.
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