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Bernhard Wiesgickl: Actuator-Sensor Interface Reduces Connection Costs

A so-called Actuator-Sensor Interface (AS-i) is used to control and monitor all the components of a conveyor system, ensuring that it never comes to a halt. Standardized worldwide according to IEC 62026-2, this piece of communications technology connects, via one cable, all the sensors and drives that are required for smooth operation. It is to be found in the production lines of automobile plants, in the baggage conveyors at airports, in the conveyor belts of steel plants, in logistics centers, and even machine tools. As a rule, AS-i is only installed once. If, however, all possibility of system failure needs to be avoided, a second, connection is required. "Two cables with the same high technical specifications? Is that really necessary?" thought Bernhard Wiesgickl, a 50-year-old development engineer, from Siemens Automation and Drives in Amberg. Wiesgickl has been working on the actuator-sensor interface for the last 15 years. During this time, he has been responsible for 28 innovations in this field.

It was during an innovation workshop that Wiesgickl first realized that it would be possible to redesign the second interface in a much simpler way. "Actually, the original aim of the workshop was to develop a wireless system for the complete bus communications, but in the end we were forced to admit that current technology just isn't up to the job," he says. The problem was that wireless connections between the master, i.e. the main control unit, and slaves, i.e. the modules that are controlled, would have been too slow. Only cable can provide the fast response times required.

However, reflecting on these facts, Wiesgickl suddenly realized that the second channel, which has exactly the same capacity as the main one, is completely oversized. In his experience, it is rare that a malfunction hits the whole system or does so for a sustained period of time; instead, it usually affects just a few of the elements to be controlled, i.e. the slaves. In Wiesgickl's new system, the second communications channel remains inactive during normal operation. It only goes into action if the master receives no response from the slave. But here, too, it transmits much less data than the main channel. In such a situation, communication is limited to the information - the so-called message - that has failed to arrive at the slave component. At the same time, this message is retransmitted via the main channel, which is, of course, still fully available. In the event that the main channel fails completely, it is possible to continue an emergency operation via the second channel in order either to run the whole system down to a defined state of malfunction or to continue operation until the main channel has been repaired. Wiesgickl's innovation has therefore significantly reduced the reaction time requirements and the capacity of the second channel.

In other words, it enables the creation of systems with high availability at a reduced cost. Given the lower requirements regarding transmission capacity, the second channel between the master and slaves is now able to utilize a wireless connection. This option, which was formerly impossible, is cheaper than using cable. In the increasingly competitive market for industrial communications systems, this basic invention creates new innovation possibilities for the well established actuator-sensor interface, thus ensuring a further 15 years of successful AS-i applications at the heart of automation technology.