Not many years ago, safety systems were standalone networks.
It was common practice to make sure the safety network was physically separate from the network that controlled the plant. Many machines had their own safety tools that were completely separate from networks altogether. This made for an inefficient patchwork of differing systems running through the plant, but that has completely changed in just a few short years. Now the unthinkable is the rule: Safety lives on the same Ethernet network as the control system. And even while machine safety is now networked, individual devices contain their own safety intelligence and can shut down a dangerous problem faster than devices that have to check in with central control.
The result of these changes is that safety is now more efficient, more flexible, less expensive, and safer.
To simplify the development of complex machines, Bosch Rexroth is integrating safety technology into the Sercos automation
network, ensuring safe communication from the control unit to the drive without any additional wiring.
Safety on Ethernet
One of the precautions that allow safety to live on the control network is the division between safety and control called the black channel. "You can have a safe network on a standard network. The thing we use is the black channel principle," Zachary Stank, safety specialist at Phoenix Contact, told Design News. "The safety is on the same network as control, but it can't be touched by anything."
Before the shift to Ethernet networks, the idea of running safety and control on the same network was considered reckless. The two functions were incompatible. This incompatibility is still the case. The difference now is that Ethernet allows clear separation between control and safety even though they're on the same wire. "People were afraid of
safety on control networks, but they're well protected," Stank told us. "Running safety on the same network as control ended up an improvement on safety."
Because control and safety are on the same network, the overall network system is much simpler. For one thing, you no longer have two sets of wires snaking through the plant. "Digital safety systems simplify safety. Now you can send commands that are safety certified,Ē Joey Stubbs, North American representative for EtherCat Technology Group and safety specialist for Beckhoff Automation, told Design News. "You can tell a machine like a robotic actuator that it can only go so far. So a person can work side-by-side with the machine without any danger."
The combination of control and safety on the same network also makes it easier for operators to see everything that's going on in the plant. They don't have to jump from one system to another. That makes the process of identifying problems much easier. "We're trying to have all the parameters on one network to make it easier to troubleshoot the safety system," Joaquin Ocampo, product manager at Bosch Rexroth, told us. "Safe motion is also on the system. We promote it as safety for humans, safety for machines, and more uptime for the machines."
Paradoxically, having one networked system for control and safety lets operators split off chunks of the system for easier management. The modular approach to managing the plant comes with a number of benefits. For one, when a safety breech occurs, you can shut down just the portion of the plant that is experiencing trouble rather than shutting down the whole plant. Second, the modular approach makes for greater flexibility. "A lot of companies are looking at modular manufacturing. That allows them to move from one product to another with a minimal amount of change," John D'Silva, safety technology manager at Siemens, told Design News. "Networked safety gives them that flexibility. It supports high speeds, faster changeovers, and reduced downtime." D'Silva also noted that plants are shifting safety to wireless systems. "Companies are moving to wireless networks with safety included. The wireless safety is now as secure as hardwired safety."