JON SEVERN

Stay safe, even under pressure

Having 'done some time' as a machine designer, I know only too well the hazards presented by pneumatics; even when the actuators are small and look relatively harmless, they can still bite! So, as I have watched the market for safety related components grow and evolve as machine builders have taken on board the requirements for compliance with the Machinery Directive, it has always surprised me how little has been announced by the pneumatics suppliers.

If you look at the developments on the electrical side, there are now numerous safety relay manufacturers, and some of them can offer literally dozens of alternatives. Variable speed drives and robot controllers are now being developed with built-in safety functionality, and let's not forget the programmable safety systems that have been around for a few years now. Then there are safety fieldbuses: machine builders and systems integrators are reaching the point where they are spoilt for choice.

But what about the pneumatics? I wouldn't like to guess a percentage, but I bet that 'most' production machinery uses pneumatics alongside electrical equipment, yet there seems to be so little on offer apart from dump valves (which do not eliminate all of the pneumatic hazards all of the time). A quick search of the internet did throw up a few safety-orientated pneumatic products; for example, Allen-Bradley's Guardmaster range includes pneumatic limit valves (similar in appearance to electrical limit switches), rope-operated emergency stop valves and trapped-key interlocks. Norgren does well with a complete catalogue devoted to "Products for Safe Pneumatic Systems" and, as was suggested above, most pneumatics companies offer dump valves. I happen to know that SMC has some safety related products, and other suppliers may also have extensive ranges - but they don't make it easy to find them.

There is, however, one safety related pneumatic system that I think is worth of highlighting. ASi has proved to be one of the most popular fieldbuses for certain types of application, and it is reasonable to assume that AsiSafe (sorry, AS-Interface Safety at Work) will do quite well too. Hoerbiger-Origa has therefore taken the logical step of creating a second generation of its ASi-ready intelligent actuators, to be known as Interact II. Interact is a concept whereby an actuator, position sensors, flow controllers, cushioning, control valve and ASi bus interface are rolled into one, and Interact II benefits from a bus interface that is AsiSafe-compatible.

Both VDMA standard rodded cylinders and Origa System Plus rodless cylinders are available, as well as compact pneumatic modules that enable the concept to be extended to other types of conventional actuator.

Fail-safe pneumatics is not a new idea; air-operated braking systems are used worldwide on lorries and trains. Hoerbiger-Origa and the other suppliers mentioned above clearly believe that there is a market for safety related pneumatic products and systems, and there is certainly something attractive about an intelligent pneumatic actuator that can be hooked up to a fieldbus that handles both control and safety related data. Compressed air needs to be treated with respect; it's good to see technology being used to tame the power source that is sometimes mistakenly viewed as being inherently safe.

Finally, a plea! This column was partly researched on the web, which is probably how I would work if I were still designing machines. Locating the pneumatics companies' web sites is easy enough, but finding what you want from there can be challenging. I was infuriated to see how few of the large companies (with, presumably, fat budgets to pay web designers huge sums to create whizzy sites with clever graphics), fail to include a 'search' facility. For those that had, I could simply type 'safety' and hit 'go'. Easy. For the others, design engineers must surely struggle to find what they want quickly. So this is a plea, not a whinge, aimed at all technically-orientated companies with a web presence: always include a search facility! After all, if your site is not user-friendly, customers can easily surf to your competitors' sites to see if they are faster to navigate.