| Muting and Personnel Protection |
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Sophisticated sensors - combined with a diverse range of redundant safety technology |
- can differentiate without contact between movements of persons and production-relevant goods.
Applications with safety technology must be reliable in order to guarantee safe operation. This for example, includes the self-monitoring function. This means that a system has a safe and redundant design by multiple use of components. The ultimate in such systems is used in the field of personnel protection.
The effort involved should be demonstrated on the example of a safety lightscreen which initiates the shutdown of the dangerous machine when persons are detected who are too close to the vicinity of the danger area.
The hardware and firmware of the control unit is subject to a very rigorous “failure mode and effect analysis” (FMEA) test, in order to ensure that a dangerous state cannot occur due to the failure of an individual system component. This is only possible when two processors of different designs with different firmware versions mutually test each other on a cyclic basis.
Accordingly, a random failure of the same type of component due to the same fault is thus eliminated. Systems of this type also provide very good diagnostics features resulting from their capability to perform self tests. This can on the one hand result in the output of the error code, which is in turn described at a suitable location, e.g. in the operating manual or on the actual device.
On the other hand the visualisation is performed via the connection to a PC. The controlled blanking out of the safety function appears to oppose this rigorous concept, it is however particularly useful with special tasks, e.g. with the transport of manufactured parts in a processing cell.
It is important to ensure that the objects being transported through the lightscreen can on the one hand be differentiated from persons, and on the other hand to ensure that it is still not possible for persons to enter the danger zone.
Muting for the safety check
Exactly this trick is possible using the muting function, i.e. the controlled suppression of the safety switching output when manufactured parts pass through the endangered and secured area of a machine. For this purpose the switching output of the safety device is uniquely combined with further input factors which prevent the machine from stopping, even though a stop command has been issued...
The author:
Dipl.-Phys. Ing. Markus Bregulla
is product specialist for photoelectric and ultrasonic sensors
within the product management team of
Hans Turck GmbH & Co., Mülheim a.d. Ruhr.
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