openSAFETY: what's in it for you?
14 June 2011
openSAFETY is a response to the long-awaited goal of uniformity and interoperability across all systems. It comes in the wake of that other holy grail: safety signal transfer via the fieldbus, a welcome alternative to traditional hard-wired installation, even though 'safety over the bus' - until now, at least - has remained largely network dependent. Les Hunt reports
Transferring safety related data via an industrial Ethernet network eliminates the majority of the cabling that would normally be installed to route individual safety status signals back to the supervisory control system, removing a notorious source of errors. And for safety systems that use direct communication without a detour via the controller, the machine safety status notification and system response is executed so much faster, which in turn increases productivity.
Given this, it easy to see why all leading manufacturers of control and automation technology advocate ‘safety over industrial Ethernet’, but there is a catch, according to B&R’s Stefan Schönegger. That is, with very few exceptions, all of these systems can only be operated together with the control hardware or field network system from the respective manufacturer. This may be down to technical reasons, but more often than not, it is purely market forces at play.
This is less than convenient for machine manufacturers because they aren‘t always able to choose the hardware they want to use in their products, but instead must often follow their customers‘ demands. This highlights the only real advantage of hard-wired systems; namely, installed once, certified once, the solution remains the same regardless of the controller that is being used.
The ‘black channel’
According to Schönegger, a network-based safety system doesn‘t offer the level of independence sought by machine builders, and this frequently offsets its clear advantages. One of the key aims of the openSAFETY development was not to compromise this autonomy of the safety system from the system bus. The solution was found in the ‘black channel principle’, which facilitates safety data transfer that is independent of the transport protocol being used, thus enabling secure transfer of this data over any fieldbus. This benefits machine manufacturer and device manufacturer alike as both enjoy a shorter time-to-market thanks to the fact that they only have to go through development and certification once.
Georg Plasberg, a member of the management team at SICK AG, says that in many other electronic applications, interoperability of different systems has practically become a requirement. “Although we will continue to integrate the full range of proprietary solutions in our products, I believe that only those who can overcome network limitations using open communication standards will have long-term success in industrial applications,” says Dr Plasberg. “Of course, we strive for this level of openness beyond the specification level and right up to the interface level of the engineering systems."
Trumpf Maschinen’s Alfred Hutterer says the lack of interoperability between different systems is not only expensive, it also extends the time-to-market and prevents a reasonable second-source policy at the purchasing end. Quoted recently in the pages of an Austrian trade journal, Dr Hutterer believes the different schools of thought evangelising their individual technologies make it difficult for manufacturers of field devices to develop hardware that is compatible with the different networks.
Machine manufacturers like Trumpf are now benefiting from the standardised openSAFETY purchasing portfolio because they can now use alternative suppliers when necessary. No minor factor, says Schönegger, since the ready availability of product always plays an important role in making sales and ensuring continued customer satisfaction. Moreover, with openSAFETY, service technicians only need to be trained on one technology.
End-users benefit as well
In addition to the cost advantages that device manufacturers are able to pass on to the machine builders, production companies and machine owners can also benefit directly from openSAFETY. The uniform nature and universal application possibilities also reduce expenditure on technician training courses and the costs for procuring replacement parts.
And thanks to openSAFETY‘s independence from the system bus, users are able to equip entire groups of different machines, robots and handling equipment with one shared safety system, opening up opportunities for streamlining productivity, that would barely have been possible in the past using conventional technologies.
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