Is an ‘old friend’ compromising your workers’ safety?

For more than half a century, safety mats have been the ever-present
‘old faithful’ of virtually every industrial environment – a universal standard
form of safety protection for workers.

But, as technology costs have plummeted and factory safety
control systems have become more complex, the choice of replacing a safety mat
with a safety laser scanner has become an affordable option. Not only is a laser scanner justifiable in
terms of cost, it may offer additional benefits.

In many small works and machine shops up and down the land,
workers are protected from hazardous processes such as stamping, cutting and
pressing with the simple safety mat. You
stand on it and the machine stops. From garages to packaging firms, finishers
to printers this simple, old friend is taken for granted.

Simple? Yes. Dependable? Hopefully. Safe? Maybe. Good value?
Now very debatable – especially if you measure value in terms of employee
safety. In fact, a laser scanner may
cost less than two mats. Changing to
laser technology could have additional benefits too, be easy to use and ensure
compliance with the latest machine safety directives.

Stepping on it

Typically, safety mats operate using an open switch which
responds to compression via a transducer that sends a signal to a controller
connected to the machine being guarded. Pressure on the mat completes a circuit
which stops the machine safely and may also trigger an alarm.

One of the biggest issues with safety mats is that they stop
working properly because people repeatedly step on them – after all, that’s
what they’re designed to do. The
compressive resilience of the mat changes with age and use, becoming inherently
less safe. Worn or old mats may not
compress enough except under ever increasing loads and the insulating materials
degrade causing false alarms.

The reliability of the mat can be damaged by heavy items
such as forklifts, trolleys, loaded pallets, and stillages. Punctures can allow fluids such as hydraulic
oils or chemicals to compromise safety.

All this leads to downtime, frequent replacement and growing
uncertainty of the risks involved. The
latest machine safety directives concentrate on speed of response of a safety
device compared with the distance moved by an operative. If the mat response is
uncertain can you be sure the machine will stop quickly enough to prevent a
moving limb from getting into the danger zone?

Time of flight measurement

With nearly 20 years of successful use already under its
belt, the safety laser scanner is a small, all-in-one device, with very precise
and easily programmable operation.

The principle of operation is simple, comprising a pulsed
laser beam that reflects if it meets an object and the reflection is registered
by a receiver. The difference in time between emitting and receiving the
reflected signal is measured by the software in the scanner. Pulses are emitted
and received at the rate of 100 – 200 per second depending on model, so
detection of movement is very rapid.

If the time of the reflected pulse is shorter than a set
level, i.e. the object is too close, a command signal goes to the machine
controller to issue an alarm, or shut it down. Time-of-flight measurement is used in millions
of laser devices all around the world.

An internal rotating mirror deflects the pulsed laser beam
so that a fan-shaped scan is made of the surrounding area. So, not only is the safe distance set, the
field of coverage can be set as a segment of a sphere – up to 270° around – and
also from the ground upwards.

Safety laser scanners can define protective and warning
fields, also referred to as zones or areas. These zones are freely programmable
and can be changed easily by authorised personnel. By having warning fields machine down time
can be reduced significantly, because an approaching person can be warned by an
audible or visible alarm before the machine needs to be stopped.

Fail safe

Laser safety scanners are reliable and durable. They will not wear out with use in the same
way as a mat would do and, as a non-contact technology mounted above the ground,
they are less likely to be damaged. A
laser scanner is a fail-safe device not subject to gradual deterioration; it
either works or doesn’t.

If a mat fails because of physical contact, a machine will
likely have to be shut down, depending on a company’s internal processes and
procedures regarding safeguarding. This shut down will remain in effect until
the safety mat is replaced by one in stock or another is shipped and
mounted. This process takes time and
disrupts production, in addition to incurring capital costs. Laser safety
scanners are not subject to this risk.

Because safety mats are not “one-size fits all” a range of
mat sizes need to be carried in stock for different machines and floor plans to
avoid extended downtime. If a new machine configuration is introduced, the
previous mat may not fit the safety area and could even need to be
custom-fitted.

Replacing a mat is likely to mean replacing the controller
too and this could result in compatibility problems.

With a safety laser scanner, the scanning field can be
configured to whatever is required. Static obstructions like walls or pillars
can be swiftly taught-in and the same scanner is easy to reconfigure whenever a
change is made.

If the device is damaged, it is frequently only the scanner
head that needs changing; a simple plug-in replacement. The safety settings are retained in the system
plug memory and are automatically downloaded to the new scanning head.

Few exceptions

Are there some times when lasers are still not the best choice?
Some. Although the safety laser scanner is designed for reliable operation in
challenging environments where there is extreme dirt or heavy moisture. Leaking
oil, grease or dust can cause the laser scanners to trip in some circumstances.

However, manufacturers like Sick are constantly improving
the technology to make laser scanners highly reliable even in the most
challenging environments. They can be
IP67/69 protected and can be programmed with advanced algorithms to compensate
to a large degree for particles, spray and even snow, although response times
will be degraded.

As laser safety scanning technology becomes accessible and
universal, the argument for change gets ever stronger. There may a few
applications where a simple step-on mat is a better choice, but this is likely
to be only in extreme conditions where a safety mat will still need frequent
replacement.

Perhaps it is time to consider making the change? If you are still unsure, manufacturers like
Sick have vast experience in design, development and application of laser
sensing and machinery safety technologies.
A call to expert advisers can help to answer any questions.