| March 11, 2012
Integrating Pneumatics into Safety Circuits
Rodney Law finds it surprising just how many people have ignored pneumatic power in the past when they designed their safety systems.
“It’s a big part of the energy stored in a piece of equipment,” says the manager of the controls engineering department at Farason Corp. (www.farason.com), a builder of flexible automation in Coatesville, Pa.
Law has been noticing a change in attitude recently, however. More manufacturers have been asking Farason to include pneumatics, as well as electric and hydraulic actuation, in their safety circuits. He attributes the change to two trends. First is the continuing harmonization of European and American safety standards, a process that has brought greater attention to safety in pneumatic actuation.
The other trend is the electronics being embedded into the latest generation of safety valves, such as the MS6-SV from Festo Corp. (www.festo.com/us) of Hauppauge, N.Y. “Besides the typical mechanical redundancy inside the valve, we also have electronic sensors that monitor the spool position,” says Frank Latino, product manager at Festo. The electronics enhance control over the valve, and also perform self-diagnostics.
Farason is using the valves on the assembly machines that it builds for the cosmetic industry. These machines grab an empty compact from a pallet, open it, glue a pan of makeup into the well, place a brush or applicator in it, close the assembly, and place a label on the bottom. “Most of the machinery that we build now has at least one robot in it,” says Law. “Often times, air cylinders and pneumatic slide mechanisms interact with the robot.
“We’re able to wire the electronics in the valve back to our safety PLC,” Law continues. “Even on small machines where we’re not using a safety PLC, we still have the option of hardwiring the valve into a typical safety relay.” So, when an operator requests entrance into the machine, the Festo valve releases any remaining air pressure in the system to atmosphere. Not only can the PLC check the status of the valve, but an LED flashes an error code for the operator to read.
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