By Jason Christopher, Field Editor
THE INTEGRATION of enhanced safety systems by system integrators and machine builders is accelerating at an unprecedented pace—and with good reason. It’s estimated that $7.2 billion per year is lost in compensation payments for workplace injuries in the industrial sector alone.
And this figure is just the direct cost of workplace injuries, such as medical and insurance administration fees, and represents only 29% of the total expense associated with these injuries. The other 71% involves lost revenue and fringe benefits. The total amount lost by U.S. firms from avoidable injuries reaches a staggering $32 billion annually.
At the same time, machine control professionals are always under pressure to create designs that meet tighter budget requirements, while still providing better performance than ever before, especially in the domain of safe operation. Though these two forces might seem mutually exclusive, engineers and manufacturers now are capable of making their systems safer for all parties involved. This is largely possible because they’re using programmable safety systems in place of traditional, hardwired, relay-based solutions.
Just What They Needed
“We thoroughly evaluated a variety of safety approaches for our latest tandem-line installation, and, hands down, the best choice was a safety PLC system,” says Joe Quigg, corporate controls engineering manager for International Automation in Windsor, Ontario, Canada. “Start-up time, engineering time, material costs, and space considerations all pointed to the use of this technology. We could not have achieved the functionality we needed with a traditional hardwired system. The safety PLC was our only real option.”
This is one of those few, genuine paradigm shifts for many of us. The hard-and-fast rule of safety systems always has been that anything related to the safety system—even remotely—had to be hardwired with absolutely no exceptions. However, when today’s advantages are weighed against today’s disadvantages, perhaps we’ll be willing to reconsider what we’re comfortable implementing. Further, when the finance department catches wind of these advantages, they’ll help persuade you, too.
“More of the standard automation technology we have today will be adapted to also become safe automation,” believes Tina Hull, applications engineer with Pilz Automation Safety. Hull adds this means using programmable safety systems for controlling safety systems on industrial and skid-mounted machines. “Some designers will have to adjust their comfort zone. There usually is some resistance to change, but people find it easier to accept and use technology when it proves its robustness, and demonstrates its effectiveness in saving lives.”
“The newest versions of safety networks integrate the safety and control system as one common unit. There is no need for a separate safety bus or safety PLC.”
The PLC revolutionized industrial automation when it first emerged, but it wasn’t adapted for safety applications until recently. The failure of solid-state devices is difficult to anticipate without some very sophisticated self-monitoring capabilities, and this had presented problems for using them in safety systems. Also, revision control and different authorization levels for safety software edits weren’t traditionally advanced enough to provide the security that safety applications require.
In 2002, however, a revised edition of National Fire Protection Association (NFPA) 79 standard was published. NFPA 79 is one of the most prominent standards covering industrial machinery safety in the U.S. This revision was the first for the standard since 1997. Just think of how much automation changed in those five years. The revision included a few key changes that helped push implementation of programmable safety systems. [See the sidebar below, “NFPA Revisions,” which includes the new standard’s key elements.]
Other machine builders taking advantage of safety PLC technology include Vince Gunkle, electrical engineering team leader for Heller Machine Tools, Troy, Mich. “With the latest drive and safety PLC technologies, we can bring safer, more functional machine tools to our customers without increasing costs,” says Gunkle. “We can help our customers safely manipulate the machine without the risk of it running away. In the past, the drive speed would need to be monitored by external systems, and it was very difficult to do. Now, it’s all done right in the CNC.”
Omron Electronics in Schaumburg, Ill., also is onboard with programmable safety systems. “Network safety revolutionizes the way safety is done,” says Gil Guajardo, Omron’s safety product marketing manager. “Unless the safety application is small-scale or trivial, system integrators, machine builders, and end users strongly consider network safety solutions, and most often conclude that a network safety device is the optimal safety solution.”
Similarly, fieldbuses and the whole concept of digital networking long ago modernized machine control design. It’s now rare to see anyone using “home-run” wiring to integrate a piece of equipment. The cost of a networked system is less than point-to-point, and it provides more diagnostic tools for easier installation and faster troubleshooting in the event of a failure.