Safe Line Automation
openSAFETY meets OPC UA
Up until now, it has been virtually impossible to implement safety technology when automating highly modular and flexible machine lines. B&R aims to change that by combining OPC UA and openSAFETY to form Safe Line Automation – providing fully automated safety communication for modular production lines.
Self-organizing safety networks will make it possible to add or remove entire machines or individual components from the machine network without having to reprogram the safety application. It would even be conceivable to create a self-validating line.
To make that possible – while continuing to meet all the requirements for safety and security – B&R draws on the particular advantages of OPC UA and openSAFETY.
How it works
When a new piece of equipment – an entire machine, individual part or even a robot – is added to the machine network, OPC UA security mechanisms begin by establishing a secure connection.
The new device then searches for other servers that offer safety functions using the OPC UA discovery service and server capability identifiers, which allow servers on the network to be filtered according to desired criteria. In the next step, OPC UA browsing services identify which functions each server offers and which attributes support Safe Line Automation.
In this way, any OPC UA server is able to obtain a complete map of the network without requiring a single line of code to be written. This completes the first phase of Safe Line Automation – the discovery phase.
Next comes the validation phase, where Safe Line Automation checks whether the new component is already known, or if it matches a previously validated safety configuration. If so, there is nothing else for the machine operator to do at this point.
If significant differences are identified, the user is prompted – via standardized elements in the HMI application – to check the new configuration and confirm that it is correct. To organize these elements practically, both the prompts and the corresponding UI elements are categorized according to the type of work being performed: commissioning, modification or servicing. This input is saved, so the new Safe Line Automation configuration will be recognized automatically in the future.
The process is very similar to the checks that are generally performed when a machine is started up. It includes a test of whether the response times and cycle times are fast enough to ensure reliable execution of the respective safety functions. In the Safe Line Automation phase model, these steps are referred to as the plausibility phase.
How does openSAFETY communicate via OPC UA?
The open source safety protocol openSAFETY can use any fieldbus or Industrial Ethernet network as its transport medium. The black channel principle allows safety-relevant data to be exchanged without allowing it to be influenced by the transport protocol.
openSAFETY exchanges process data – in the form of Safety Process Data Objects – using the OPC UA publish-subscribe model. As a result, openSAFETY nodes can communicate with each other directly and achieve extremely fast response times. During the plausibility check, on the other hand, data is queried using Safety Service Data Objects. These make use of OPC UA method calling to avoid unnecessary traffic on the networks and OPC UA servers.