IT Jan 2008 - Industrial Technology Magazine

QIndustrial Technology asks
the important
uestions...
feedback@itmagazine.uk.com
Does effective machine safety have
to mean sacrificing machine efficiency?
recycling. Indeed, this last point is brought out in a number of standards
Terry Hayward of Schmersal has the answer
under the heading of safety life cycle such as BS EN 61508, BS EN
62061 and of course, the latest BS EN 13849.
Recently Schmersal has been running a series of seminars
There need not be a conflict of interest between operator safety and
explaining the implications and application of the new standard machine efficiency. What is needed is an acceptance that the latest safety
BS EN ISO 13849:2006. I introduced the programme, rather systems can, by accommodating many different machine operating modes,
controversially you may think, by saying: “If you think
comply with legislation whilst contributing to the machine’s efficiency.
machinery safety is simply about complying with the latest legalisation,
This is reinforced by a recent study in the HSE document, ‘Out of
then I think you are wrong.”
Control’, which states that accidents generally happen in a machine’s nonautomatic
Whilst this point of view may indeed be controversial I believe it needs
mode rather than its automatic mode – for example during
to be aired. So many people build the machine first and then say “OK, setting up, fault finding, maintenance and modification. Whilst not directly
let’s make it safe”, which often means doing the minimum required to covered by legislation, emerging standards do require machine
meet current legislation. The machine is in effect ‘retrofitted’ with fairly manufacturers to consider all anticipated operating modes when preparing
basic relays and guard interlocks, in what has become common practice a safety specification.
for safeguarding the operator.
This will ensure that when adjustments or changes need to be made,
The fact that the machine will almost certainly under perform, fall well engineers can disable certain parts of the machine and allow the rest of it
short of its production targets and may never realise its true manufacturing to operate safely whilst still protecting those operating it. This new concept
potential, is offered up on the altar of machine safety as the sacrifice of functional safety is being driven by the introduction of many innovative
needed to make the machine safe! And the unfortunate end user may have safety devices, and requires a change in the mindset of designers and
bought a machine that complies with the latest legislation but is of little or safety officers alike.
no use to the production manager because it constantly trips out, can’t be To get the most from a machine requires both disciplines to look
easily maintained, can only be used in automatic mode, and can’t even beyond meeting legislation at the lowest cost and concentrate instead on
provide feedback to explain why?
designing a safety system that takes account of the different modes of
The situation isn’t helped by the fact that, in a typical plant the safety machine operation and their effect on production efficiency.
officer’s role is to protect operators from the machine to the levels
A simple analogy is the way electronic diagnostics have evolved in the
stipulated in the appropriate standard, often with no reference to the automotive industry. Today’s cars can tell you if a tyre’s pressure is low, or
machine’s efficiency or to maximising the plant’s output. So does the if a light has blown, but it doesn’t stop the car. An even better example is
modern manufacturing plant need a new breed of safety officers who can the air suspension fitted to some luxury cars and 4x4s. If a fault is
make a positive contribution on machine output? Perhaps, but it also detected, the car’s management system displays a warning light to alert
needs a new breed of engineers with their minds open to an alternative the driver but it doesn’t stop the car. The driver is allowed to continue to
approach to machine safety.
the nearest dealer at a reduced speed of up to 50mph.
At the risk of being branded a ‘safety hippy’ for using the two words in So ask yourself, do you really want to buy a machine that stops
the same sentence, the ALTERNATIVE is a more HOLISTIC approach because it isn’t designed to provide prior warning of a guard door switch
where safety is addressed at every stage of machine design and
that is misaligned or about to fail? Surely it’s more efficient for the
implemented for every phase of operation including installation,
machine to warn you of the failure and allow you to make the repair in
commissioning and maintenance – and even its eventual dismantling and complete safety without interrupting production. Similarly, if a cross-wire
“
fault is detected in a traditional safety relay the machine instantly shuts
down, even though there is no immediate danger to the operator. Contrast
Specified correctly, machinery safety
that with ‘smart thinking’ functional safety, which signals the machine that
systems will increase the efficiency of it will be allowed to run till the end of the shift (safety bodies agree that
up to six hours is acceptable), when maintenance can fix the problem
automated processes and be capable of before the next production cycle begins.
Pulse-echo and non-contact devices are examples of technologies that
protecting both man and machine.
enable functional safety. They also provide much improved machine
However, if the only consideration is to diagnostics, which make an invaluable contribution to machine efficiency.
So, to sum up, it is possible using the new generation of safety devices
conform to legislation, manufacturers
to achieve effective machine safety without sacrificing machine efficiency.
will have missed the point and their
”
Terry Hayward is managing director of Schmersal, and will be
customers an important opportunity.
contributing his thoughts on machinery safety throughout the year.
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INDUSTRIAL TECHNOLOGY • January 2008