Tackling a pressing safety issue

A collaborative development project between two UK-based companies has resulted in a safer working environment for operators of a hand-fed platen press

With the HSE about to
commence on-site inspections
of hand-fed platen presses,
users of this high-risk machinery need to
ensure that their presses meet the
required safety standards. By working
closely together, two companies have
developed a novel, high integrity safety
solution for a hand-fed platen press,
which uses an array of light beam
sensors and a modular safety control
and monitoring system.

In November 2009, machinery safety
specialist Pilz Automation Technology
and SCA Display UK, a manufacturer of
Point-of-Display (POD) products for
retail customers, began working together
to improve the safety of a hand-fed platen
press at SCA Display’s production plant
in Shenstone.

Part of SCA, SCA Display’s Shenstone
plant employs around 80 staff and
manufactures a wide variety of point-ofsale
and POD products, mostly custom
designed products made from cardboard.

The factory uses a wide range of
machinery, including digital and
silkscreen printers, die cutters, folding &
gluing machines and platen presses. Most
of the die cutting uses semi-automatic
presses, but one of the presses is hand-fed,
which is used for short runs and one-off
customer specials.

Ian Clews, facilities manager at
Shenstone, has been working with platen
presses for more than 30 years and SCA
are members of the Confederation of
Paper Industries, where machinery safety
is high on the agenda. “Quite frankly, the
use of these machines has been a concern
for many years, particularly in the dwell
mode. With two fatalities in the UK in
recent years, users of these machines need
to review their safety systems.”
“A typical hand fed platen press closes
with a tremendous force, often with the
operator’s body in close proximity. This
means that operator safety is extremely
critical. At Shenstone we have a continual
improvement policy which instigated
further upgrades to our platen press to
ensure that additional operator safety
measures.”

Safety alerts and inspections
Ian Clews is not alone in his views on the
need to improve the safety of hand-fed
platen presses. In the UK, the HSE has
recently issued safety alerts to users of
hand-fed platen presses. It is estimated
that in the UK alone, there are between
1,000 and 2,000 such presses that require
safety upgrades, mostly operated by
companies in the printing and packaging
industries. Most of the high-risk
machines fall into the 1.4m to 2m-width
range.

The HSE is currently considering
issuing alerts to users in order to raise
awareness of the potential dangers of
whole body access between the platens of
these machines when operating in the
‘dwell’ mode. The alerts are in response to
two fatalities since 2008 in the UK, where
operators were crushed between the
platens as they intervened during normal
production. In both cases, the hand-fed
machine was being used in the dwell
mode and the power to the platen was not
isolated before the intervention occurred
and so the safety devices fitted to the
machine did not prevent the platens
closing on the operator.

“During the setting process, waste
removal, replacement of lay stops or misfeed
retrieval, even with the most safety
conscious operators may try to beat the
dwell and climb onto the platen press bed
or lean into the machine. Whilst between
the fixed and moving platen beds the
operator is not detected by any of the
usual safety systems,” explains Ian Clews.

According to the HSE, the latest handfed
platen presses are much larger than
their predecessors and many users now
use the machine’s dwell mode to either
give them more production flexibility or
to speed up the machine’s output, as this
mode can often double the speed of
operation. On most hand-fed platen
presses, climbing onto the platen from the
normal operating position in front of the
machine can be done without operating
the safe edge that is normally fitted to the
leading edge of the lower platen. This
means that if a safe system of work is not
followed, including isolating the machine,
the platen may then continue to cycle if it
is being used in the dwell mode and the
protective devices will not automatically
be triggered.

Further investigation by the HSE has
showed that standards of guarding and
working practices on many existing, larger
hand-fed platen presses need to be
improved significantly. HSE has
announced that it will commence on-site
inspections of hand-fed platen presses in
October 2010.

In his presentation to a group of
machinery safety suppliers at the HSE’s
Birmingham offices on 12th July 2010,
Tim Small, HM Principal Inspector at the
HSE, stated: “The HSE deems hand-fed
platen presses as high risk machines.

Enforcement action will be taken against
any UK firms that aren’t taking
appropriate action to meet these new
safety expectations.”

Employee safety-driven approach
In November 2009, SCA Display decided
to improve the safety of its hand-fed
platen press at Shenstone to better protect
employees. Ian Clews contacted Pilz
Automation Technology to discuss
possible safety solutions. “By this time, I
had already devised several concepts for
upgrading the safety of the platen press,
but needed to talk to a machinery safety
specialist supplier such as Pilz about how
the solution could be realised from a
technological viewpoint. I also wanted the
solution to be modular, enabling a best
option for employee protection rather
than a cost option. It was critical that we
worked with a supplier that had in-depth
knowledge of current machinery safety
legislation and standards, but with the
ability to then apply that knowledge to
developing the most appropriate safety
system for our machine,” says Ian Clews.

Chris Sloan (area sales engineer) and
Stewart Robinson (consultant engineer) at
Pilz Automation Technology have worked
closely with Ian Clews on the platen press
project since early 2010. Chris Sloan says:
“Initially we visited Shenstone to assess
and analyse the platen press and to
discuss safety issues and potential
solutions. SCA wanted a working solution
based on a modular safety platform that
would include all the necessary hardware
and software, tailored to suit the
machine.”
Stewart Robinson adds: “One of Ian
Clews’ favoured concepts was to use an
array of light beam sensors that would
monitor the side and platens in order to
detect any violation of the machine’s
danger zone whilst the press was closing.

As far as we are aware, the solution we’ve
developed is the only one of its kind in
the UK, where light beam sensors are
being used to monitor the area directly
above the moving platen.”
The overall safety solution is based on
Pilz’s PNOZmulti modular safety system.

PNOZmulti is multifunctional, freely
configurable and is ideal for monitoring
safety functions such as Emergency-Stop,
safety gates and light barriers, as well as
performing standard control functions.

Rather than hard wiring, safety circuits
can be generated on a PC using
PNOZmulti’s intuitive configuration
software. This configuration can then be
stored on a memory card and
downloaded to the PNOZmulti base unit.

The solution incorporates a
PNOZmulti base unit, with input and
output expansion modules to control all
aspects of machine safety and control.

“We wrote a functional specification for
the press, then engineered a solution
based on these functional safety
requirements. We supplied all the
hardware, including the light beam array
and safety controller, as well as writing all
the software code for the application,”
states Stewart Robinson.

The hand-fed platen press at Shenstone
is fitted with a number of general purpose
safety devices such as trip bars,
interlocked guards, right and left hand
emergency stops, safety mat, front safe
edge, lumbar bar, safety gate key switch,
left and right side light curtain. All these
devices have the same functional safety
requirements, which are to prevent all
hazardous movement by ensuring that the
clutch safety valve is de-energised and that
the main motor is stopped, and to
prevent unintended restart. The target
safety integrity level for each General
Safety Function is SIL 3 (EN 62061),
equivalent to PLe according to EN ISO
13849-1.

SCA’s safety solution
The machine now uses an array of
PSENop4S light beams supplied by Pilz.

As Ian Clews explains: “We did have a few
teething problems based around
alignment of the sensors, but this was
down to the original machine mountings,
which were not robust enough to provide
a solid foundation for the light beam
sensors. We quickly resolved this issue by
developing more robust bearing
mountings, which enable the sensors to
be adjusted more easily. We also
developed an infra-red sighting device
that simplifies the alignment of the
sensors.”
The light beam array now detects a
violation of the danger zone whilst the
press is closing. This is achieved by
sequentially muting the laser beams as the
press closes. If any beam is broken before
it has been muted, the press clutch safety
valve is de-energised immediately
bringing the hazardous movement to a
stop. Once the final beam has been
broken (press closed) the beams remain
muted until the press cam switch has
operated, signalling that the press is at the
‘home’ position. The muting points are
derived from the simulation of press
position carried out within the
PNOZmulti control system. The
application also includes checking that the
press cam switch operates correctly in
each press cycle.