Machine Safety Automation Requires Planned Strategy

Business and plant managers actively seek a well-thought-out, intelligent safety strategy that not only protects humans, machines and the environment—but also supports increased productivity, improved machine efficiency and increased uptime, believes Sal Spada, research director for discrete automation at ARC Advisory Group Inc. (www.arcweb.com), Dedham, Mass.

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For robotics, for example, “an ‘inside out’ approach using robotic programmable safety systems (RPSSs) may well provide the key to this strategy.”

Calling the new generation of safety solutions “more effective in preventing accidents, less costly to implement, easier to adapt and more reliable than existing hard-wired systems,” Spada explains that robotics suppliers base these innovations on the concept of “work-envelope limitations.” These are, he says, “more akin to a ‘designed-in’ safety approach, than an ‘add-on’ safety approach.” Facilitating the shift in safeguarding implementations are RPSSs certified according to the European Committee for Standardization’s standard EN 954-1—“Safety of machinery, Safety-related parts of control systems”—Category 4 risk assessment levels.

But the standards landscape changes continuously. One most important change is the pending replacement of EN 945-1 by the International Organization for Standardization’s (ISO) 13849-1, which has the same title as the EN standard, suggests Tim Roback, marketing manager, safety systems, for automation vendor Rockwell Automation Inc. (www.rockwellautomation.com), Milwaukee. The basic difference is that “the EN standard is more prescriptive. It would talk about number of channels, number of faults to be tolerated to get a category rating and the like. But with the ISO standard, it is probabilistic, meaning it’s quantitative.” Though the European Commission is currently considering requests to extend the deadline for 13849 compliance beyond the originally scheduled Dec. 29, 2009 date, Rockwell is encouraging machine builders to adopt the standard as early as possible to gain competitive advantage.

ISO 13849 is “a big leap for end-users, from one level of safety sophistication to a higher level,” Roback asserts. “It will drive more commonality.” That’s important because, with the EN standard, “you could apply parts of it and get widely varying implementations.” And that means that end-users could see failures that would or would not be accounted for. But with the ISO standard, original equipment manufacturers and end-users will have to calculate the probability of failure, he notes.

Meet global standards

Another recent advance in workplace practices also expands protection of personnel.  “The trend is to use vision-based safeguarding to remove physical barriers from the application,” states Eric H. Hollister, a product sales engineer with Pilz Automation Safety L.P. (www.pilz.us), Canton, Mich., a safety equipment provider. “This allows the user to safely interact with the machine/application without first moving—that is, opening, sliding or closing—physical guards.”

The vision safeguarding allows end-users to interact with the machine without completely shutting down the application, Hollister explains. The result: shorter cycle times, higher throughput and potentially a smaller footprint for the whole application—all waste-and-cost reducers. “Optical and vision-based safeguarding also offer a more cost-effective solution for reconfiguring safety based on model changes, work-area changes, new machinery and the like,” he adds. 
 
Migrating control from field programmable logic controllers (PLCs) to personal computer (PC)-based control is yet another current cost-effective strategy. “The PC-based system gives access to higher-level languages and the safety system,” says Tim Parmer, safety products specialist at vendor Siemens Energy & Automation Inc. (www.sea.siemens.com), Alpharetta, Ga.

Some machine solutions can be drive-centric and PLC-centric that work together, Parmer explains. That allows end-users to potentially make decisions on “dozens of inputs and give commands to several drives.” This functionality, he suggests, “is a place no one has been before. The drives participate—and they’re getting clearer information from the PLC. That gives better choices of what safe state to be in.” That should be the goal of every safety system, shouldn’t it?

C. Kenna Amos, ckamosjr@earthlink.net, is an Automation World Contributing Editor.

ARC Advisory Group Inc.
www.arcweb.com

Rockwell Automation Inc.
www.rockwellautomation.com

Pilz Automation Safety L.P.
www.pilz.us

Siemens Energy & Automation Inc.
www.sea.siemens.com

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