Machine safety components are the fastest spreading of discrete-manufacturing automation. Why? Workplace injuries cost U.S. businesses more than $171 billion a year, there's continued demand for industrial machinery, and safety offsets declines in skilled labor pools. Also, according to a recent study by the ARC Advisory Group, Dedham, Mass., now intelligent safety is less of a cost burden and more of an advantage.
“Control-reliable safeguarding components — servos, fluid power, and PLCs — are on the rise,” says research director Sal Spada. Their ever-improving electronics, software, and fieldbus networks are enabling some replacement of traditional safety relay modules.
The current standards
The proliferation of safety capabilities is matched by that of standards. One classic is IEC/EN61508. Its safety integrity levels (SILs) indicate how much a system reduces risk of machine or human injury. SIL4 provides the most protection; SIL1, the least. EN62061 is a newer, daughter standard of IEC61508 that addresses specifics on electronic and electrical machinery parts — particularly useful for programmable systems.
BS EN954-1 is a straightforward standard, predecessor to the relatively new ISO 13849-1. Designers can choose to adhere to either EN954-1 or ISO 13849-1 until November 2009. Similar to the SIL scale, EN954-1 classifies systems as Category B (for Basic), 1, 2, 3, and 4 — the last of which indicates highest protection. Quantitative ISO 13849-1 covers integration, safety-related parts of controls systems (SRP/CS) and mechanical and fluid power system safety as well.
Making a robot work cell safer
SureFire LLC of Fountain Valley, Calif. manufactures premium flashlights for military, law enforcement, and consumer use. Recently, the company wanted to automate their flashlight assembly. Each robot work cell includes e-stops, light curtains, and safety gate switches to protect operators. “I was looking for a programmable device to not only monitor processes, but to replace multiple safety relays,” says Daniel Fischer, SureFire's vice president of assembly operations. “This would make the equipment easier to configure and would also require less wiring in the control box.”
Fischer selected a PNOZmulti modular safety system (from Pilz Automation Safety, LP, Canton, Mich.) that consists of a base unit — which in turn includes a chip card that communicates with safety devices, while also sending signals out for annunciation of the safety system status. “In every machine we build, there's less wiring and hardware, which translates into cost savings,” Fischer says.